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Metal-organic materials :

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Title:
Metal-organic materials : from design principles to practical applications
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Book
Language:
English
Creator:
Alkordi, Mohamed
Publisher:
University of South Florida
Place of Publication:
Tampa, Fla
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Subjects

Subjects / Keywords:
Self-ssembly
Coordination polymers
Supermolecular building blocks
Catalysis
Hydrogen storage
Metal−organic cubes
Dissertations, Academic -- Chemistry -- Doctoral -- USF   ( lcsh )
Genre:
non-fiction   ( marcgt )

Notes

Abstract:
ABSTRACT: The works presented herein outline rational design approaches towards construction of solid state materials with great potentials to answer some of current demanding applications. Specifically, the materials targeted are metal−organic materials with desirable structural features and functional properties. Metal−organic materials are constructed from organic linker molecules and metal ions under relatively mild solvothermal reaction conditions that preserve the structural features of the relatively simple building blocks. Therefore, it is feasible to conceive a retrospective pathway of the reaction and thus deconstruct the desirable structures into simple, chemically-relevant, building blocks in an approach known as the molecular building block approach. Due to the large number of reaction variables, e.g. concentration, stoichiometry of reactants, nature of solvents, counterions, temperature, etc., it is very significant for advancements in the field to employ a systematic investigation strategy to asses and better understand the relevant roles played by the various reaction conditions towards construction of the targeted materials. The modular nature of metal−organic materials allows for tuning their properties to meet a specific application through careful design of the molecular precursors, i.e. information encoding at the molecular level. Research in this area is highly interdisciplinary where synthetic organic chemistry, in silico modeling, and various analytical techniques merge together to afford better understanding of the basic science involved and eventually to result in enhanced control over the properties of targeted materials.
Thesis:
Dissertation (Ph.D.)--University of South Florida, 2010.
Bibliography:
Includes bibliographical references.
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Mode of access: World Wide Web.
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Statement of Responsibility:
by Mohamed Alkordi.
General Note:
Title from PDF of title page.
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Document formatted into pages; contains X pages.
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Includes vita.

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ABSTRACT: The works presented herein outline rational design approaches towards construction of solid state materials with great potentials to answer some of current demanding applications. Specifically, the materials targeted are metal−organic materials with desirable structural features and functional properties. Metal−organic materials are constructed from organic linker molecules and metal ions under relatively mild solvothermal reaction conditions that preserve the structural features of the relatively simple building blocks. Therefore, it is feasible to conceive a retrospective pathway of the reaction and thus deconstruct the desirable structures into simple, chemically-relevant, building blocks in an approach known as the molecular building block approach. Due to the large number of reaction variables, e.g. concentration, stoichiometry of reactants, nature of solvents, counterions, temperature, etc., it is very significant for advancements in the field to employ a systematic investigation strategy to asses and better understand the relevant roles played by the various reaction conditions towards construction of the targeted materials. The modular nature of metal−organic materials allows for tuning their properties to meet a specific application through careful design of the molecular precursors, i.e. information encoding at the molecular level. Research in this area is highly interdisciplinary where synthetic organic chemistry, in silico modeling, and various analytical techniques merge together to afford better understanding of the basic science involved and eventually to result in enhanced control over the properties of targeted materials.
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Metal–Organic Materials: From Design Pr inciples to Practical Applications by Mohamed H. Alkordi A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Chemistry College of Arts and Sciences University of South Florida Co-Major Professor: Mohamed Eddaoudi, Ph.D. Co-Major Professor: Ra ndy W. Larsen, Ph.D. Michael J. Zaworotko, Ph.D. Roman Manetsch, Ph.D. Edwin Rivera, Ph.D. Date of Approval: March 19, 2010 Keywords: Self-assembly, coordination pol ymers, supermolecular building blocks, catalysis, hydrogen storage, metal organic cubes Copyright 2010, Mohamed H. Alkordi

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Dedication For Dr. Mohamed Mostafa ElBaradei.

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Acknowledgments First and foremost, I would like to express my sincere appreciation to my advisor, Dr. Mohamed Eddaoudi, for his guidance and sup port throughout the enti re course of this work. He always encouraged me to explor e through different avenues of science and provided unlimited financial support and valuable scientific advice th roughout this entire project. Working with Dr. Eddaoudi was a gr eat chance for me to learn, to become a better chemist, and to sharpen my lab and writing skills. He provided a very healthy working environment and was always a big brother to me. I would also like to thank my Co-major professor, Dr. Randy W. Larsen, for all the valuable discussions we had through the years of my research and the wonderfull class he taught me. It was always an enj oyable and instructive experience to discuss science with him. I trully appreciate the w ealthness of information he provided on all the subjects we discussed. Thanks is due also to Dr. Michae l Zaworotko, for all the support and encouragement he provided in all of our co-p rojects, for his very helpful insights and his enthusiasm towards new ideas and for the inst ructive class I had with him. His various expertise brought another whole dimension to my works. Working with Dr. Edwin Rivera was certain ly a great learning experience full of exploration and fruitful results I trully appreciate the long hours he spent teaching me

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different aspects of NMR spectroscopy which, to say the least, introduced me to new areas and techniques that helped me in my pr ojects and certainly will continue to benefit from in the future. Dr. Rivera was a close friend to me who I consulted frequently on personal and professional matters. I can’t express enough my gratitue to Dr. Roman Manetsch who welcomed me in his lab to conduct part of my research and who always had his office door open for me whenever I needed his help. Thanks also due to Dr. Victor Kravts ov, Dr. Lukasz Wojtas, and Dr. Gregory McManus, for their valuable help with X-ra y crystallography. Fina lly, I would like to thank Dr. Abdessadek Lachgar for serving as the chair person on my committee and for refferring me to Dr. Eddaoudi’s research group, a very well appreciated advise that I will be forever indebted for.

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i Table of Contents List of Tables ................................................................................................................ ..... iv List of Figure................................................................................................................. .......v List of Schemes ............................................................................................................... xvii Abstract ...................................................................................................................... .... xviii Chapter 1: Introduction ....................................................................................................... 1 1.1 Supramolecular Chemistry .................................................................................1 1.1.1 Supermolecules ............................................................................................ 1 1.1.2 Molecular Recognition: Functi onal and Shape Complimentarity ................ 3 1.1.3 Cooperative Molecular Recognition Processes ............................................ 8 1.1.4 Self-Assembly in Supramolecular Chemistry .............................................. 9 1.1.5 Templates in Self-Assembly Processes ...................................................... 10 1.1.6 Rational Design Strategies in Self-Assembled Supermolecules ................ 11 1.2 Coordination Polymers ....................................................................................12 1.2.1 Metal Organic Frameworks ...................................................................... 14 1.2.2 Historical Perspective ................................................................................ 16 1.2.3 Coordination Polymers Uti lizing Polytopic, Nitrogen-Donor Ligands ....................................................................................................... 25 1.2.4 Coordination Polymers Utilizing Polytopic, Carboxylate-Based Ligands ....................................................................................................... 29 1.2.5 Coordination Ppolymers Utiliz ing Polytopic, Heterofunctional Ligands: The Single-Metal-Ion MBB Approach ....................................... 36 1.3 Practical Applications of Functional Metal Organic Materials ......................39 1.3.1 Porosity in Microporous Coordination Polymers ...................................... 44 1.4 Analytical Techniques in Chemistr y of Metal–Organic Materials ..................49 1.4.1 Crystals and X -ray Diffraction. .................................................................. 49 1.4.2 Isothermal Titration Calorimetry (ITC) ..................................................... 54 1.4.3 Mass Spect rometry ..................................................................................... 58 1.4.4 Solution Nuclear Magnetic R esonance (NMR) Spectroscopy ................... 61

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ii 1.5 References ........................................................................................................63 Chapter 2: Imidazole-bBased Ligand-Directed Self-assembly ......................................... 76 2.1 Introduction ......................................................................................................76 2.1.1 Ligand Molecules for Zeolite-like MOFs (ZMOFs) .................................. 77 2.1.2 Geometry and Rigidity ............................................................................... 78 2.1.3 Imidazole Ring in Coordination Polymers ................................................. 79 2.2 Results and Discussion ....................................................................................81 2.2.1 Imidazole-Based Organic Linkers.............................................................. 81 2.2.2 Pyrimidine-Based organic linkers .............................................................. 98 2.3 Experimental ..................................................................................................104 2.4 Conclusion .....................................................................................................117 2.5 References ......................................................................................................119 Chapter 3: Metal Organic Cubes (MOCs) ..................................................................... 121 3.1 Zeolite-like Metal–Organic Fr ameworks (ZMOFs) Based on the Directed Assembly of Finite Metal–Organic Cubes (MOCs) .........121 3.1.1 Introduction .............................................................................................. 121 3.1.2 Results and Discussion ............................................................................. 126 3.1.3 Experimental ............................................................................................ 140 3.1.4 Conclusion ............................................................................................... 144 3.2 Insight Into the Self-assembly of MOCs .......................................................145 3.2.1 Introduction .............................................................................................. 145 3.2.2 Results and Discussion ............................................................................. 148 3.2.3 Experimental ............................................................................................ 190 3.2.4 Conclusion ............................................................................................... 195 3.2.5 References ................................................................................................ 196 Chapter 4: Molecular Squares fo r Hydrogen Storage Materials ..................................... 204 4.1 Introduction ....................................................................................................204 4.2 Results and Discussion ..................................................................................208 4.3 Experimental ..................................................................................................224 4.4 Conclusion .....................................................................................................225 4.5 References ......................................................................................................226 Chapter 5: Zeolitelike Metal organic Frameworks (ZMOFs) as Solid Matrices for Metalloporphyrin-Based Heterocatalysis...................................................... 229 5.1 Introduction ....................................................................................................229

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iii 5.2 Results and Discussion ..................................................................................239 5.3 Experimental ..................................................................................................247 5.4 Conclusion .....................................................................................................249 5.5 References ......................................................................................................250 Chapter 6: Unexplored potenti al Applications of Metal Organic Materials in Photochemical Hydrogen Generation. .......................................................... 254 6.1 Harvesting Solar Energy ................................................................................254 6.2 Homogenous Systems for Water Photolysis ..................................................255 6.3 Dye-Sensitized Solar Cells (DSSCs) .............................................................257 6.4 Polymer-Based Solar Cells ............................................................................259 6.5 Potential Applications of Metal Organic Materials in Photochemical Hydrogen Generation ......................................................................261 6.6 References ......................................................................................................279 Appendices .................................................................................................................... .. 286 Appendix A. Crystallographic data. .....................................................................287 Appendix B. Powder X-Ray Di ffraction Patterns (XRPDs) ................................313 Appendix C. Selected TGA traces: ......................................................................317 Appendix D. Selected NMR spectra for compounds H-L1, 3.9S, and the reaction mixture of H-L1 and CoCl2 in aqueous medium. .............320 About the Author ................................................................................................... End Page

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iv List of Tables Table 3.2.1. Crystallographic data for 3.9 3.12 and 3.9(a-d) 151 Table 3.2.2 Crystallographic data for 3.9e and 3.9f 155 Table 3.2.3. Summary of the e xperimental conditions for 3.9 3.12 and 3.9(a-e) 155 Table 3.2.4. 1H and 13C NMR peak assignments for HL1 in DMSO-d6 and 3.9S in D2O, reported in ppm. a = axial, e = equatorial thp ring protons. 170 Table 3.2.6. Experimental spin lattice relaxation times ( T1 ) for 1H signals (in the 7-24 ppm chemical shift range) of the paramagnetic reaction mixture, the corresponding cobalt-to-proton (rCo-H) distances relative to the reference distance of 5.324 for the proton at = 8.68 ppm, and the rCo-H distances obtained from th e geometrically-optimized model of [Co2( L1 )(H2O)8]3+ fragment. 176 Table 4.1: Selected targets se t by the DOE for On-board H2 storage systems2: 205 Table 5.1. Summary of cyclohexane oxida tion reactions usin g metalloporphyrins encapsulated in solid matrices. 245

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v List of Figures Figure 1.1. Intermolecular hydrogen interact ions showing shape (A and B) and shape and functionality (C) complimentarity in the molecular recognition process. 5 Figure 1.2. Molecular recognition of guanidinium cation by 1,3-xylylene-27crown-8.6c 6 Figure 1.3. Crystal structure of T state haemoglobin with oxygen bound at all four haems (depicted in ball-and-stick model for clarity).14b 9 Figure 1.4. Histogram highlighting the num ber of publications containing the terms “Coordination polymer” (red) and “Metal organic framework” (green) as topics in publications (source: ISI Web of Knowledge, 01/03/2010, refined to include only publications in chemistry, materials science, physics, and pol ymer science subject areas). 16 Figure 1.5. (Top) an example of the Werner complex, Ni(NCS)2(4methylpyridine)4,38 (below) crystal packing showing inclusion of benzene rings guest molecules (highlighted). Ni(magenta), C(gray), N(blue), S(yellow), H(white). 18 Figure 1.6. Crystal structure for one of Hofmann-type clathrates44 (top) single 2D periodic layer outlining the square planar Ni(CN)4 and the octahedral Fe(CN)4(NH3)2 (below) disordered benzene guest molecules (highlighted in orange) are enclathr ated by the 2D layers. Fe (red), Ni (magenta), C (gray), N (blue). 19 Figure 1.7. Examples of organic linkers util ized in early examples of coordination polymers. 22 Figure 1.8. Hoskins and Robson’s first repor t of a 3D coordina tion polymer based on diamond-like net with the form ula Cu[C(C6H4CN)4]BF4, the tetraflouroborate counterions we re highly disordered and not localized through the X-ray crystal structure. 47 23 Figure 1.9. Crystal structure of the non-in terpenetrating [CuZn(CN)4](NMe4) 48 24 Figure 1.10. Examples of Ndonor polytopic linkers. 25 Figure 1.11. [Cu(pyrimidine)2]BF4 fram ework58c with the counterions highlighted. Cu (orange), C (g ray), H (white), N (blue). 26

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vi Figure 1.12. (Left) crystal stru cture of the framework attained from HMTA as an axial bridging ligand to Cu(II) propionate clusters, (right) part of the structure showing the bridging through HMTA (hydrogen atoms omitted for clarity).58e Cu (orange), C (gray), H (white), N (blue), O (red). 27 Figure 1.13. (Left) crystal st ructure of the framewor k obtained by Long et al 59 based on the tetrazolate linker and Mn. (Right) Schematic representation of the cube-like Mn4(4-Cl)(tetrazolate)8 building blocks interconnected through tritopic phenyl rings. Disordered solvent molecules and solvated Mn ions are omitted for clarity. Mn (magenta), Cl (green), C (gray), O (red), H (white) and N (blue). 28 Figure 1.14. (Left) the polyt opic, anionic, N-donor orga nic linker utilized by Long et.al coordinate Mn ions to forge the tetranuclear Mn4(4Cl)(tetrazolate)8 build ing block. The points of extension of this building block (highlighted) could be regarded as a cube-like cluster (right) that upon bridging through triangular linker (the benzene ring in the organic ligand) affords the structure shown in Figure 1.13. Mn (magenta), Cl (green), C (gray), O (red), H (white) and N (blue). 28 Figure 1.15. Different coordinati on modes of carboxylate ions. 29 Figure 1.16. Metal-carboxylate clusters commonly encountered and utilized as MBBs. Left is the actual cluster a nd to the right is the conceptual secondary building unit (SBU ) depiction (a) binuclear tetracarboxylate paddle wheel M2 (RCO2)4, (b) basic chromium acetate trimer M3O(RCO2)6(H2O)3 and (c) basic zinc acetate, M4O(RCO2)6, R represents the or ganic linker, the points of extensions are highlighted in yell ow. Metal ion (green), C (gray), N (blue), and O (red). 30 Figure 1.17. Three polytopic carboxylic acid ligands utilized in construction of MOFs with exceptional structural stability upon guest removal and desirable gas sorption properties. 31 Figure 1.18. Crystal structure of MOF-5,78 guest solvent molecules omitted for clarity. The yellow sphere represents a sphere of radius 7.1 that can fit inside the regular cubic cages of the framework without touching the van der Waals radii of the closest H atoms. Zn (green), C (gray), O (red), H (white). 32 Figure 1.19. The ditopic carboxylic acids util ized to generate (a) IRMOF-1, (b) IRMOF-2, (c) IRMOF-3, (d) IR MOF-4, (e) IRMOF-5,(f) IRMOF-

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vii 6,(g) IRMOF-7, (h) IRMOF-8, (i ) IRMOF-10, (j) IRMOF-12, (k) IRMOF-14, (l).IRMOF-16.79a 33 Figure 1.20. Crystal structure of the so c-MOF. The yellow spheres represent spheres that can fit inside the cages present in the framework without touching the van der Waals radii of the closest atoms of the framework. Two intersecting types of channels exist in the structure, hydrophilic (blue rods) and hydrophobic (red rods). Solvent molecules and nitrate counterions omitted for clarity, In (green), C (gray), O (red), N (blue). 82 34 Figure 1.21. The crystal structure of HKUST-1 MOF showing the interconnectivity of the paddlewh eel-like Cu2(RCO2)4 to the tritopic, triangular 1,3,5-benzenetri carboxylate linkers. Guest solvent molecules omitted for clarity, the two yellow spheres are those that can fit inside the two distinctiv e cages inside the MOF without touching the van der Waals radii of closest atoms. Cu (orange), C (gray), O (red), H (white). 83 35 Figure 1.22. Examples of heterofunctiona l bis-bidentate organic linkers. 37 Figure 1.23. (Left to right) a dodecahedrally-coordinated metal ion MO4N4, the complex of the metal ion coordi nated to four heterofunctional chelating ligands, and the resultan t tetrahedral MBB considering Natoms as the points of extension to the immediate neighbor MBBs. 38 Figure 1.24. (From left to right) the cr ystal structure of rho-ZMOF, the coordination of In(III) ions by four chelating linkers, simplified coordination sphere around In(III), and the resulted tetrahedral singlemetal-ion MBB. In (green), C (gray), O (red), N (blue), hydrogen atoms and solvent molecules omitted for clarity. Yellow sphere represents a sphere with radius c.a. 18 that can fit inside the cages without touching the van der Waals radii of closest atoms. 88 38 Figure 1.25. (Left to right) an octahedrally-coo rdinated metal ion in fac-MO3N3 configuration, the complex of the metal ion coordinated to three heterofunctional chelating ligands, and the resultant tri-connected MBB considering N-atoms as the points of extension to the immediate neighbor MBBs. 39 Figure 1.26. (From left to right) the crysta l structure of MOC-1, the coordination of Ni(II) ions by three chelating linkers, simplified coordination sphere around Ni(II), and the result ed tri-connected single-metal-ion MBB. Ni (green), C (gray), O (red), N (blue), H (white). 89 39

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viii Figure 1.27. The H2 saturation uptake as wt % measured at 77K and 1 atm, and the corresponding Qst values for selected MOFs. MOF-5,97,98 InPmDC sod-ZMOF,99 Cd-PmDC sod-ZMOF, 99 rht-MOF,100 MOF177, 96aMIL-10196a, 98, HKUST-1 MOF,96a,93 and soc-MOF.82 41 Figure 1.28. Crystal structure of the evacuated MOF-5.105 Zn (magenta), C (gray), O (red), H (white). 46 Figure 1.29. Types of physisorption isotherms 48 Figure 1.30. The left panel schematically depicts the instrumental setup of a power compensation calorimeter. Both cells are completely filled, the reference cell with pure solvent, th e sample cell with a solution of one of the host–guest partners (e.g. the host). On addition of microliter aliquots of the guest solution de livered from the computer-driven syringe a heat effect occurs that is counter-regulated by the cell feedback current to maintain T at zero. The right pa nel illustrates the data output consisting in a number of heat pulses that decrease in magnitude following the progressive saturation of the host binding site by the incremental addition of the guest species.112 Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission. 57 Figure 1.31. (Top) schematic equilibria for internal (Kint) and external (Kext) NEt4+ guest binding with 1. The symbol denotes encapsulation. (Bottom) ITC data for the addition of a 90 mM solution of NEt4+ into a 1 mM solution of 1. Inset: total he at vs equiv of NEt4+. Reprinted with permission from 121. Copyright 2010 American Chemical Society. 58 Figure 1.34. Self-assembly of two cuboctahe dron supermolecules. Reprinted with permission from 130. Copyright 1999 American Chemical Society. 63 Figure 2.1. (a) Oxide ion bridging tetrah edrally-coordinated Si(IV) ions in zeolites, (b) pyridine molecule, a nd (c) imidazolate ion bridging two tetrahedrally-coordinated metal ions in MOFs with zeolite-like topologies. O (red), Si (y ellow), N (blue), C (gray), metal ion (green), H (white). 77 Figure 2.2. (Top) infinite chains of Hg(II )-imidazolate3 nitrate, (bottom left) infinite square layers of Ni(II ) imidazolate,4 and (bottom right) infinite network of Zn(II)-imidazolate.5 Hg (orange), Ni (magenta), Zn (green), C (gray), N (blue), O (red), H (white), encapsulated solvent molecules in the Zn(II)-imidazolate omitted for clarity. 80

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ix Figure 2.1. 1H-Imidazole-4,5-dicarboxylic acid (middle) and the two major products attained through utilization in solvothermal reactions with In(III) ions, the metal-organic cube (left) and one of the zeolitic frameworks, the rho-ZMOF (right). In (green), N (blue), O (red), C (gray), H (white). 81 Figure 2.2. The first pathway explored for synthesis of 1H-2-chloroand 1H-2bromo-imidazole-4,5-dicarboxylic acid. 82 Figure 2.3. Crystal structure of 2-diazo-2H-imidazole4,5-dicarbonitrile, (2.1). 83 Figure 2.4. Crystal structure of 2-bromo-1H-imidazole -4,5-dicarbonitrile (2.2a), left, and 2-bromo-5-cyano-3H-imi dazole-4-carboxylic acid (2.2b), right. Br (brown), N (blue), O (red), C (gray), H (white). 84 Figure 2.5. (Left) the 4-ring SBU in RHOzeolite and that in rho-ZMOF (H•••H distances of 4.19 and 4.93 ). Si(yello w), In(green), O(red), N(blue), C(gray), H(white). 85 Figure 2.6. Crystal structures of (a) 1,4-dimethoxy-2,3-dinitro-benzene, (b) 4,7dimethoxy-1H-benzoimidazole, and (c) 1H-benzoimidazole-4,7-diol hydrogen bromide monohydrate (2.3c). Br (brown), N (blue), O (red), C (gray), H (white). 86 Figure 2.7. 1H-Imidazole-4-carbaldehyde, (2.4) 87 Figure 2.8. Crystal structure of (2.5) showing one molecula r square (left) and the ABA packing in the molecular solid (right). Mn (magenta), N (blue), O (red), C (gray), H (white). 88 Figure 2.9.Crystal structure of 2,2'-(1 H-imidazole-4,5-diyl)di(1,4,5,6-tetrahydro pyrimidin-5-ol), (2.8). Imidazole and amidine N–H hydrogen atoms are geometrically disorderd be tween two positions with equal occupancy. C (gray), N (blue), O (red), H (white). 91 Figure 2.10. Crystal structure of 1H,3'H-[ 5,5']bibenzoimidazole, (2.10). C (gray), N (blue), O (red), H (white). 93 Figure 2.11. Crystal structure of (2.12), th e site occupancy factor for imidazole hydrogen is (0.5) resulting in m ono-deprotonated ligand with acidic hydrogen equally displaced between two neighboring complexes due to strong intermolecular hydrogen bo nd interactions.Mn (magenta), Cl (green), C (gray), N (blue), O (red), H (white). 95 Figure 2.12. (Left) zigzag-chains in the crystal structure of (2.13). (Right) fragment of the crystal structure magnified to visualize the coordination of Mn(II) by two ligands, one is axial, mono-dentate imidazolate. Mn (magenta), C (gray), N (blue), O (red), H (white). 96

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x Figure 2.13. (a) Crystal structure of (2.15) (b) backbone of the complex where terminal carbonyl ligands and hydrogen atoms omitted for clarity, one of the two pyramid-like structures is represented as a green pyramid, (c) coordination around centr al Mn(II) ion that coul d be visualized as (d) square planar, 4-connected node. Mn(magenta), C (gray), N (blue), O (red), H (white). 97 Figure 2.14. Coordination modes of tetrazol ates to transition metal ions and the corresponding number of entries in the CSD database (May 2009 update, number of bonded atoms to non-coordinated nitrogen atoms was fixed at 2 when performing the search). 99 Figure 2.15. (Top) Crystal structure of (2.17) showing the Kagome`-lattice and (below) side view of three layers held together through – stacking and C–H••• interactions (pink lines) between pyrimidine rings. Disordered solvent molecules occu pying the 1D hexagonal chanells omitted for clarity. Cu (orange), C (gray), N (blue), H (white). 100 Figure 2.16. Crystal structure of (2.18). Cd( buff), C (gray), N(blue), H (white). 101 Figure 2.17. Crystal structure of (2.20). Ni (f aint blue), Cl (green), N (deep blue), O (red), C (gray), H (white). 103 Figure 3.1. (Middle) single-metal-ion-b ased MBBs (tri-connected nodes and linear spacers) faci litate the assembly of a MO C, which is utilized as 8-connected SBB to generate ZMOF s. Zeolitic nets with AST (top left) and LTA (top right) are cons tructed based on relations with regular (8-connected)-based nets (b ottom). The reo net (bottom right) corresponds to zeolite LTA (middle right) and flu (bottom left) to zeolite AST (middle left) when the 8-connected nodes are augmented, or replaced by cubes. 125 Figure 3.2. (a) Single-crystal structure of AST-ZMOF, (3.1) (yellow sphere represents vdw sphere of a diameter ~ 15 that can fit into the ASTcage without touching vdw surfaces of the framework) with (b) zeolite AST-like network topology. (c) In (3.1), the MOC-based SBBs are linked via simultaneous edge-to-edge connection through coordinated metal ions and vert ex-to-vertex c onnectivity through charge-assisted H-bonded guanidini um ions. (d) In AST-ZMOFs, (3.1) and (3.2), six MOCs (red tile ) are connected to generate the AST-cage (blue tile). 127 Figure 3.3. Bond distance histogram for N HO interactions in guanidiniumcarboxylate complexes, CSD version 5.30 (November 2008). 128

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xi Figure 3.4. Crystal structure of (3.1) showing assembly of six MOCs, simultaneous apex-to-apex H-bonding interactions with guanidinium (top) and edge-to-edge connections through coordinated Zn2+ ions (bottom), generates the AST-cage. Yellow sphere represents the sphere that can fit inside ASTcage without touching van der Waals radii of atoms making up the fr amework. O (red), N (blue), Zn (green), C (grey). 129 Figure 3.5. (a) Supramolecular tetrah edral assembly of MOCs through coordinated Zn ions (green) and H-bonding to guanidinium cations (only 3 MOCs shown for clarit y), (b) tetrahedrally-arranged guanidinium cations, (c) edge-c onnection between MOCs through octahedrally-coordinated metal cations, (d) guanidinium-ImDC interactions through charge-ass isted H-bonds to the carboxylates groups on the vertices of four MOCs in (3.1) (N HO distance of 1.978 2.204). O (red), N (blue), Zn (gr een), C (grey), H (white). 130 Figure 3.6. (Top) crystal stru cture of (3.2) showing MOCs connectivity through coordinated potassium ions. Yellow s phere represents the sphere that can fit inside AST-cage without touching van der Waals radii of atoms making up the framework, (botto m) fragment of (3.2) showing ImDC simultaneously coordinated to Zn2+ and K+ ions. O (red), N (blue), Zn (green), C (grey), K (purple). 132 Figure 3.7. (a) Single-crystal structure of lta-ZMOF, (3.3) (yellow sphere represents vdw sphere) with (b) zeolite LTA-like network topology. (c) In (3.3), twelve MOCs are conn ected through a series of sodium ions to generate (d) an -cage (green tile) that can accommodate a sphere with diameter of ~32 , and six MOCs (red tile) assemble a cage (yellow tile) that can fit a s phere of ~8.5 in diameter. 134 Figure 3.8. MOCs are connected thr ough hydrogen-bonding water molecules and sodium atoms (top), yielding an -cage (bottom left) and a -cage (bottom right), which co mprise the lta-ZMOF. 135 Figure 3.9. (Top) the MOC in compound (3.4), showing simultaneous coordination of the doubly deprotona ted ligand molecules (HImDCA) to Cd (buff) and K (violet). The presence of hydrogen atoms midway between carboxylate ions is due to intramolecular H-bonds. The figure shows 24 K+ ions coordinated to the MOC but it should be noticed that each K+ ion is shari ng coordination to adjacent 3 MOCs (bottom, disordered coordinated water molecules omitted for clarity), thus net number of K+ ions that belong to a MOC is 8. 136

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xii Figure 3.10. Crystal structure of (3.8) showing the In-based MOC, one dimethylammonium cation, and one H-bonded guanidinium ion. 138 Figure 3.11. Crystal structure of the meta l–organic cube (MOC) in 3.9, chloride counterions omitted for clarity. C (g ray), N (blue), H (white), Co (deep red). 149 Figure 3.12. (Left) crystal packing of the MOCs in 3.9 and (right ) total of four MOCs in the unit cell are highlighted and can be described as fourfold interpenetrated arrangement of primitive cells. 150 Figure 3.13. Crystal packing of the MOCs in 3.9a. 152 Figure 3.14. Crystal structure of the meta l–organic cube (MOC) in 3.9b. C (gray), S (yellow), O (red) N (blue), H (white), Co (deep red). 153 Figure 3.15. Crystal packing of the MOCs in 3.9b. 153 Figure 3.16. Crystal structure of 3.9c the MOC is shown surrounded by [CoCl4]2and chloride ions. C (gra y), Co (red), N (blue), H (white), Cl (green), solvent molecules omitted for clarity. 154 Figure 3.17. Crystal packing of the MOCs in 3.9c. 155 Figure 3.18. Crystal packing of the MOCs in 3.9d. 156 Figure 3.19. Crystal packing of the MOCs in 3.9e. 157 Figure 3.20. Crystal packing of the MOCs in 3.9f. 158 Figure 3.21. Crystal structure of 3.10, the MOC is shown, disordered nitrate counterions omitted for clarity. C (g ray), In (green), N (blue), H (white). 159 Figure 3.24. Crystal structure of 3.12, mol ecular chains of [Cd(L1)(NO3)]n, C (gray), Cd (buff), N (blue), H (white), O (red). DMF solvent molecules omitted for clarity. 162 Figure 3.25. Schematic representation of the MOC and its major fragments observed in the MALDI TOF mass spectra of 3.9. 163 Figure 3.26. Molecular ion in the MALDI-TOF MS for 3.9. 164 Figure 3.27. 1H NMR spectrum of H-L1 in D2O acquired at 298 K with inserts of magnified (a) quintet at 1.97 ppm and (b) triplet at 3.5 ppm. = Solvent peak, x = DSS peaks, used as internal standard. 166 Figure3.28. 1H NMR spectrum (top) and 13C NMR spectrum (below) of 3.9S in D2O, spectra acquired at 298 K, proton spectrum referenced to the DSS singlet at 0 ppm as internal standard. = Solv ent peak, x = DMF peaks. 169

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xiii Figure 3.29. (Top) 1H NMR spectrum of the reaction mixture of CoCl2 (0.1 mmol) and H-L1 (0.15 mmol) in 1 mL D2O after mixing at 298K, (below) the 4 24 ppm region of the spectrum magnified. = HDO solvent peak used as internal reference at 4.76 ppm. 173 Figure 3.30. The B3LYP/LANL2DZ geomet rically-optimized model for the [Co2(L1)(H2O)8]3+ fragment. 175 Figure 3.32. UV vis absorption spectra for the reaction mixture of H-L1 (6.25 mM) and CoCl2 (4.15 mM) in aqueous solution, 296 K under aerobic conditions. Spectra accumulated at 30 minutes intervals. 179 Figure 3.33. (a) Changes in A493 and so lution pH for the spectrophotometric titration of CoCl2 (2.5 mM) with in creasing concentration of H-L1 (0.5~6.0 mM) in 20 m L aqueous so lution. (b) Changes in A493 and pH for the titration mixture after addition of 2 equi v (in terms of HL1 added) NaOCH3. Absorption measurements acquired after standing at r.t. for 24 h, meas urements conducted at 296 K. 181 Figure 3.34. Crystal structure of 3.11, NiII mo lecular square. C (gray), Ni (light blue), N (blue), O (red), H (white). DMF solvent molecules omitted for clarity. 185 Figure 3.35. Crystal structure of 3.12, mol ecular chains of [Cd(L1)(NO3)]n, C (gray), Cd (buff), N (blue), H (white), O (red). DMF solvent molecules omitted for clarity. 185 Figure 3.36. 1H NMR spectra of 3.9s in D2 O at various solution pH (top) and temperature (bottom) range. 189 Figure 4.1. MP2/6-31G* optimized model mo lecular square showing the most favorable orientation of a H2 mo lecule interacting simultaneously with the four benzene rings a nd the binding energy dependence on H2-benzene ring separa tion distance, R. 208 Figure 4.2. Crystal structure of 4.1. Pb (deep gray), C (gray), S (yellow), O (red), H (white), DMF solvent molecu les occupying th e square-like channels omitted for clarity. 211 Figure 4.3. Fragment of the crystal stru cture of 4.1 showing the significant dimensions of the square-like st ructure, disordered DMF solvent molecules inside the square channels are omitted for clarity. 212 Figure 4.4 (Top) FT-IR spectrum of the as -synthesized 4.1 and (down) the FT-IR spectrum for the solvent-exchanged 4.1 indicating solvent displacement of guest DMF molecules present in the as-synthesized compound. 213

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xiv Figure 4.5. H2 sorption isotherms for the solvent-exchanged 4.1. 214 Figure 4.6. Isosteric heat of adsorption for the solvent-exchanged 4.1 compound. 215 Figure 4.7. N2 sorption isotherm for 4.1 conducted at 77 K. 215 Figure 4.8. X-ray powder diffraction patte rns for 4.1, before (red) and after (black) solvent exchange in acetonitrile. 216 Figure 4.9. Crystal structure of 4.2,Cd (bu ff), C (gray), O (red), H (white), F (cyan). Solvent molecules omitted for clarity. 217 Figure 4.10. H2 sorption isotherms for solv ent-exchanged 4.2 w ith the two knees in the two isothe rms circled. 218 Figure 4.11. Isosteric heat of adsorp tion for the solvent-exchanged 4.2. 218 Figure 4.12. (Top) crystal stru cture of 4.3, showing only one of the 2D squaregrid layers and (below) view along the z-axis showi ng packing of two immediate neighbor layers (highlig hted). Cd (green), N (blue), C (gray), H (white). 220 Figure 4.13. (Top) crystal struct ure of 4.4, showing the squa re-like channels filled with disordered DMF solvent molecules and (below) the discrete molecular square with significan t dimensions shown, DMF solvent molecules omitted for clarity. Cu (orange), S (yellow), C (gray), O (red), N (blue), H (hydrogen). 221 Figure 4.14. (Top) crystal st ructure of 4.5, showing th e square-like channels partially blocked by phenyl rings prot ruding inside the channels from neighboring molecular squares. The square-like channels are filled with disordered DMF solvent molecules, omitted for clarity. (Below) selected significant dimensions of the molecular square. Cu (orange), S (yellow), C (gray), O (red) N (blue), H (white). 223 Figure 5.1. MFI zeolite utilized in purification of p-xylene. 230 Figure 5.2. Crystal structure of the AC O zeolite (left) and its corresponding topology (right) showing connectivity of tetrahedral atoms that could be constructed from periodic double 4-ring (D4R) as the zerodimensional periodic buildi ng unit (PerBU), in bold. 231 Figure 5.3. Crystal structures (top left to right) of the sod, rho, and usf-ZMOFs and (bottom) the corresponding SOD, RHO, and RHO zeolitic topologies. Color scheme: Indium (green), carbon (grey), oxygen (red), nitrogen (blue), hydrogen (white). 234 Figure 5.4. The In(ImDC)4 MBB present in ZMOFs could be visualized as tetrahedral connected node inte rconnected through bis-bidentate angular ImDC linker. 235

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xv Figure 5.5. crystal structure of rho-ZM OF (left), hydrogen atoms omitted for clarity, and schematic presentati on of [H2TMPyP]4+ porphyrin ring enclosed in rho-ZMOF -cage (right, drawn to scale). 240 Figure 5.6. Experimental powder X-ray diffr action patterns for rho-ZMOF and the intended porphyrin-impregnated rho-ZMOF, confirming the construction and phase purity of the as-synthesized compound. 241 Figure 5.7. Diffuse-reflectance, solid-state UV-vis spectra of H2RTMPyP and its various metallation products. 242 Figure 5.8. Cyclohexane catalytic oxidat ion using (6.1a) as a catalyst at 65 C. Yield % based on TBHP, one equi valent consumed per alcohol produced and two equivalents consumed per ketone produced. 244 Figure 6.1. Light absorption by [Ru(bpy)3] 2+ producing singlet excited state which relaxes to the relatively l ong-lived triplet excited state. Standard redox potentials for the different processes are shown. 256 Figure 6.2. Schematic presentation of the major components in DSSCs. 258 Figure 6.3. Polymer-based Solar cells: (a ) energy diagram with exciton in polymer phase, (b) bi-layer hetero junction, (c) bulk hetero junction and (d) ordered hetero junction. 260 Figure 6.4. Ru-cobaloxime multip le-sensitizer catalytic core assemblies of the P2A-type 264 Figure 6.5. Covalently modified analog of P2A Ru-cobaloxime multiple-sensitizer catalytic core. 265 Figure 6.6. (Left) binuclear Ru complex re ported by Lehn et.al, and (right) the proposed complex utilizing bidentate ligands. 266 Figure 6.7. The proposed P4A complexe s utilizing Ru-bridging through tetradentate ditopic ligand (left) H-bonded cobaloxime and (right) covalently modified analogue. 267 Figure 6.8. [Ru(4,4'-dicarboxy-2,2'-bipyridyl )3]2+ complex as photoactive, 6connected SBB for constructing extended MOF. 271 Figure 6.9. Projected structure of a MO F based on the [1,10]Phenanthroline-5,6dione dioxime (phendioxime) ligand bridging Ru-photosensitizer to cobaloxime redox catalyst. 273 Figure 6.10. Schematic diagram of target ed phosphonate-surface modified TiO2 where photoactive cationic MOF coul d be anchored on the anionic surface. 275

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xvi Figure 6.11. Schematic diagram of the pr oposed tandem photosensitized solar cell with conducting polymer deposited on the surface of photoactive MOF. 276 Figure 6.12. Left: 2,3,5,6-Tetra-pyridin-2-y l-pyrazine (tppz) ligand used by Flores-Torres et al and the gas phase molecular orbitals energy diagrams calculated using B3LYP/ Lanl2DZ for various oligomers obtained. 278 Figure B8. XRPD pattern for 3.9. 316 Figure C1. TGA for compound 3.1 showing a steady decrease in weight percent from 30oC to 80oC is due to a loss of acetonitrile and water molecules followed by a loss of DMF molecules up to 180oC. Degradation of the framework is evident at 300oC. 317 Figure C2. TGA for compound 3.2 showing th at at temperatures below 95oC, a loss of water molecules is observe d. Degradation of the framework begins at 310oC. 318 Figure D1.1H NMR spectrum of H-L1 in DMSO-d6. 320 Figure D2. 1H-1H gCOSY spectrum for 3.9S in D2O. Peak at 2.9 ppm assigned for residual DMF solvent from the reaction mixture. 321 Figure D3. 1H-13C gHSQC spectrum for 3.9S in D2O. 322 Figure D4. (Above) 13C NMR spectrum of 3.9S in D2O. Peaks at 39.21 and 43.65 ppm indicate different chemical shifts for C(4`) and C(6`) carbon atoms of thp rings, respectiv ely, due to chelation of L1 to cobalt ions. (Below) DEPT 135 spectrum of 3.9S in D2O. 323 Figure D5. The 1H NMR spectrum for the reaction mixture. 324 Figure D6. The 13C NMR spectrum for the reaction mixture. 324 Figure D7. The 1H-1H gCOSY NMR spectrum for the reaction mixture. 325 Figure D8. 1H-1H NOESY NMR spectrum for the reaction mixture. 326 Figure D9. 1H-13C gHSQC NMR spectrum for the reaction mixture. 327 Figure D10. The 1H-1H TOCSY NMR spectrum for the reaction mixture. 328 Figure D11. 1H 2D-DOSY spectrum for 1S, 1.2 mM in D2O at 298 K. 329

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xvii List of Schemes Scheme 2.1. Synthesis of 2-diazo-2 H -imidazole-4,5-dicarbonitrile, (2.1). 106 Scheme 2.2. Synthesis of 2-Bromo-1 H -imidazole-4,5-dicarbonitrile (2.2a) and 2bromo-1 H -imidazole-4,5-dicarboxylic acid, (2.2b). 107 Scheme 2.3. Synthesis of 1 H -benzimidazole-4,7-diol hydrogen bromide, (2.3c). 109 Scheme 2.4. Synthesis of 4,5,4'',5''-tetrahydro-1 H ,1' H ,1'' H [2,4';5',2'']terimidazole, (2.6). 110 Scheme 2.5. Synthesis of 2,2'-(1 H -imidazole-4,5-diyl)di-1,4,5,6tetrahydropyrimidine, (2.7). 111 Scheme 2.6. Synthesis of 2,2'-(1 H -imidazole-4,5-diyl)di(1,4,5,6tetrahydropyrimidin-5-ol), (2.8). 112 Scheme 2.7. Synthesis of 2-(3 H -Imidazol-4-yl)-1,4,5,6-tetr ahydro-pyrimidine, (2.9). 113 Scheme 2.8. Synthesis of 1 H ,3' H -[5,5']bibenzoimidazole, (2.10). 113 Scheme 2.9. Synthesis of N,N'-bis-(1 H -imidazol-4-ylmethylene)-propane-1,3diamine, (2.11). 114 Scheme 2.10. Synthesis of N,N' -bis-(1 H -imidazol-2-ylmethylene)-ethane-1,2diamine, (2.14). 115 Scheme 2.11. Synthesis of 2-(1 H -tetrazol-5-yl)-pyrimidine, (2.16). 116 Scheme 2.12. Synthesis of N-Hydroxy-pyrimidine-2-carboxamidine, (2.19). 117 Scheme 3.1 Numbering and prototropic tautomerization in H-L1 165 Scheme 3.2. Synthesis of H-L1. 192 Scheme 6.1. Underlying princi ple for the photosensitized el ectrolytic reduction of H+, the cycle depicted based on one photoactive center. 262 Scheme 6.2. The reaction steps for prep aration of the [Ru(phendioxime)(bpy)]n+. 264 Scheme 6.3. Synthetic pathway for tpphz ligand. 269 Scheme 6.4. Synthetic pathway for dibenz o[1,4]dioxine-bridged phenanthroline. 269 Scheme 6.5. Synthesis of [Ru(phenedioxime)3]2+. 273

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xviii Metal–Organic Materials: From Design Principles to Practical Applications Mohamed H. Alkordi ABSTRACT The works presented herein outline rational design approaches towards construction of solid state materials with gr eat potentials to answ er some of current demanding applications. Specifically, the materials targeted are metal organic materials with desirable structural features and functional pr operties. Metal organic materials are constructed from organic linker molecule s and metal ions under relatively mild solvothermal reaction conditions that preserve the structural features of the relatively simple building blocks. Therefore, it is feas ible to conceive a retrospective pathway of the reaction and thus deconstr uct the desirable structures into simple, chemicallyrelevant, building blocks in an approach known as the molecular building block approach. Due to the large number of reacti on variables, e.g. concen tration, stoichiometry of reactants, nature of solvents, counterions, temperature, etc., it is very significant for advancements in the field to employ a systematic investigation strategy to asses and better understand the relevant roles played by the various reaction conditions towards construction of the targeted materials. The modular nature of metal organic materials allows for tuning their properties to meet a specific applicati on through careful design of the molecular precursors, i.e.

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xix information encoding at the molecular le vel. Research in this area is highly interdisciplinary where s ynthetic organic chemistry, in silico modeling, and various analytical techniques merge together to a fford better understanding of the basic science involved and eventually to result in enhanced control over the prop erties of targeted materials.

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1 Chapter 1: Introduction 1.1 Supramolecular Chemistry Supramolecular chemistry, defined as “chemistry beyond the molecule” 1 or as defined by J. -M. Lehn “chemistry of mol ecular assemblies and of the intermolecular bond’’ 2, is the field of science concerned with chemical, physical, and biological characteristics of molecular ensembles, co mmonly known as supermolecules, constructed via self-assembly processes. Supermolecule s, the term used in 1937 by K.L. Wolf (bermolekle) to describe hydr ogen-bonded dimers of acetic acid 3, are relatively complex chemical entities formed through noncovalent intermolecular interactions between relatively simple chemical species. Su ch interactions are bi nding, as molecules do not act if they are not bound according to Paul Ehrlich “Corpora non agunt nisi fixata”, 4 and highly specific as to allow design a nd control over the resulted structure. Over the past few decades, the field received increasing attention of chemists as their view of molecular properties ch anged gradually from being in trinsic to the molecules to being expressed in presence of other molecu les, or in certain environments, due to noncovalent molecular interactions. 1.1.1 Supermolecules Supermolecules to molecules and intermol ecular bonds are as molecules to atoms and covalent bonds. 2 Supermolecules can be described as being chemical entities of

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2 higher complexity formed through spontaneous, reversible association of two or more chemical species utilizing the intermolecular, noncovalent, interactions. Due to the nature of noncovalent bonding interacti ons involved in construction of supermolecules, selfcorrection emerges as an intrin sic characteristic of supermol ecules. That is to say, the noncovalent nature of chemical bonds in supe rmolecules, thus being reversible, allows for self-correction to result in therm odynamically-controlled product as the major product, which most frequently is the most symmetric product among a pool of potential products.5c Deliberately constructed and functio nalized supermolecules can exhibit a variety of chemical and physical properties 5a like recognition of a substrate among a collection of species, 6 or molecular cataly sis through reaction of catalytic sites with reversibly-bound substrate. The utilization of supermolecu les in catalysis as abiotic enzyme models continues to receive wide scientific interest due to various attributes of supermolecules as hosts capable of selective substrate binding. Of particular importance are the following attributes, enumerated by Jean-Marie Lehn in 1979, 5a of supermolecules that impart close similarity to their biotic catalysts counterparts: (a) Selective host-substrate binding due to specific, complimentary host-substrate intermolecular interactions that are, in a large number of examples, amenable to deliberate modification and thus design. (b) Fast and selective reaction of the bound substr ate, i.e. accelerated reaction rate for bound relative to unbound substrate. (c) Regeneration of the reactive site after accomplishment of th e catalytic transformation, affected due to the noncovalent nature of substrate-host interaction and the altered

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3 nature of the end product as compared to the substrate, resulting in weaker interactions with the supermolecular catalyst. (d) High turnover of the catalyst due to stability of the s upermolecule under the reaction conditions employed. 1.1.2 Molecular Recognition: Function al and Shape Complimentarity Noncovalent intermolecular interactions ra nge from relatively weak attractive van der Walls interactions, moderate to strong hydrogen bond interactions, to strong dipoledipole, ionic, or coor dination interactions. Dispersive fo rces are attractive forces between molecular entities (or between groups within th e same molecular entity) other than those due to bond formation or to the electrostatic in teraction of ions or of ionic groups with one another or with neutral molecules.5b The term includes: dipole–dipole, dipoleinduced dipole and London (instantaneous induced dipole-induced dipole) forces. The term is sometimes used loosely to in dicate nonspecific attractive or repulsive intermolecular forces.7 The novel family of cyclic polyether mol ecules developed by Charles J. Pedersen, commonly known as crown ethers, was show n to exhibit selective binding, i.e. recognition, of alkali metal ions (Li+, Na+, K+, Rb+, and Cs+) where selectivity is imparted by the ring size of the macrocyclic polyether molecule to match the size of the alkali metal ion to be selectively bonded.8 While the early works of Pederson underlin ed the very beginnings of artificial host molecules capable of substrate recogni tion, as simple as it was, a single monoatomic spherical ion, Jean-Marie Lehn and Donald J. Cram subsequently developed increasingly sophisticated host molecules, utilizing synthetic or ganic chemistry, to

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4 construct macromolecules properly designed as hosts for selective binding of a wide variety of relatively larger (anionic, neutral, or cationi c), with more sophisticated recognition sites, substrates.9 To achieve this goal, carefu lly designed host molecules that provide the suitable complimentary molecu lar recognition sites were devised. In recognition of their achievements in this, then and now, rapidl y growing field of science, Pedersen, Lehn and Cram, equally shared the Nobel Prize of Chemistry in 1987 “for their development and use of molecules with structure-specific interactions of high selectivity”. Dispersive interactions are non-directional and thus present greater challenges for their utilization into successf ul design strategies under ca refully controlled synthetic conditions towards construction of host materi als capable of selective substrate binding. In contrast, the hydrogen bond interactions 10 are directional, Figur e 1.1, and essential in a variety of systems, those ranging from most complicated and highly functional biological structures capable of self-replicati on and/or substrat e recognition, best exemplified by the crucial role played by hydrogen bonds in formation and stabilization of double strand DNA and by those in the activ e site of an enzyme, to those being increasingly utilized in man-made supermolecules. Discoveries and advances in artificial supermolecules that rely heavily on intermolecular hydrogen bonding interactions to derive the self-assembly of the molecular components into a supermolecule we re made possible mainly due to careful consideration (both experimentally and con ceptually) of the natu re of hydrogen bond

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5 Figure 1.1. Intermolecular hydrogen interactions s howing shape (A and B) and shape and functionality (C) complimentarity in the molecular recognition process. interactions. First, experiments to construct supermolecules from hydrogen-bonded molecular subunits were conducted in noncompetitive solvents where the hydrogen bonds can become quite strong. This is demons trated in the very early examples of hydrogen bonded “tennis ball” described by Rebek et al 11 in which two glycouril-based molecules self-assemble through multiple hydrogen bonding interactions in dichloromethane as the solvent to create a hos t molecule with the “tennis ball” shape. The authors reported disrupti on of the hydrogen bonded construct upon dissolution in dimethylsulfoxide, a significan t example that clearly dem onstrates the importance of eliminating solvent competition for the hydrogen bond donor/acceptor sites in the molecular precursors to successfully self-assemble, constructing the intended supermolecule. Second, and equally important reason for development in the area of hydrogen-bonded supermolecules is the directionality of th e hydrogen bond. This feature of hydrogen bond interactions permits the desi gn of highly specific interaction sites

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6 Figure 1.2. Molecular recognition of guanidini um cation by 1,3-xylylene-27-crown-8.6c within the molecular precursors of the targeted supermolecule permitting their spontaneous selfassembly under appropriate reaction conditions. Moreover, information can be encoded at the molecular level in th e constructed supermolecule, preor postsynthetically, in the form of fragment s that posses shape and/or functional complimentarity towards a specific substrat e, Figure 1.2. Hydrogen bond interactions can span the range of strong hydrogen bonds with binding energies in the range of 60–120 kJ mol-1 (heteroatom–heteroatom distances between 2.2 and 2.5A ), moderate hydrogen bonds (15–60 kJ mol-1, distances of 2.5–3.2 A ), and weak hydrogen bonds with binding energies below ca. 15 kJ mol-1 and long donor–acceptor distances of up to 4A .5b Among the noncovalent intermolecular inte ractions are the coordination bond interactions. This kind of molecular interacti on exhibits stronger bi nding energies than those found in hydrogen bonding interactions and, in general, are highly directional with well-defined geometries around th e coordinated metal ion. Ther efore, it appeared that construction of supermolecules as hosts for recognition of substrate molecules utilizing

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7 the coordination bond carries the potential fo r success. Indeed, this was demonstrated independently by Fujita and Stang,12 where cage-like supermolecules, commonly known as coordination capsules, were deliberately designed and successfully constructed from pyridine-like N-donor organi c linkers, paneling the surf ace of regularly-shaped polyhedra, and the cis -chelated Pd(II) ions as the vert ices. Coordination capsules offer several advantages compared to their hydroge n bonded “tennis ball” counterparts as hosts for molecular recognitio n of guest molecules. Such advant ages are intimately related to the nature of coordination bonds compared to hydrogen bond interactions. Due to the more thermodynamically favorable metal ionligand interactions in a large number of solvents as compared to energy of solvation for the metal ion, in general, chemists were given amble space to utilize a variety of solv ents and, accordingly, experiment with wide range of metal ion salts and ligand molecule s. In addition, coordi nation capsules are amenable for modular synthesis, i.e. the ligand molecules could be expanded and/or functionalized (with non-coordina ting functionality), the meta l ion could be substituted with a different metal ion that exhibits sim ilar coordination geometry, or altogether both the ligand molecule and the metal ion could be substituted by other linker and metal ions maintaining the same overall topology of the c onstruct. It is due to those advantages of working with coordination capsule that a rapi d growth of the field has been encountered since the last decade.13

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8 1.1.3 Cooperative Molecular Recognition Processes Cooperativity describes the influence of binding a substrate at one of the host’s binding sites on the second binding step occurri ng at another binding site of the same host. Cooperativity can be positive, where binding strength of the second guest is increased by the first one and the sum of bot h binding energies is more than twice the binding energy of the first substrate. Binding co operativity can also be negative, if the first binding process attenuates the binding a ffinity of the host to a second substrate. Many examples for cooperativity are known fr om biochemistry, best represented by successive binding of four oxygen molecules by a single haemoglobin molecule, Figure 1.3.14 Upon binding the first oxygen molecule by one of the haem groups, conformational changes are induced in the protein’s tertia ry structure which also affects the other subunits in a fashion that facilitates c onsecutive binding of oxygen molecules. This example demonstrates the need for a mechanism that can relay the effect of the first binding event to the second one in cooperati ve recognition processes. This aspect (cooperativity in molecular recognition) is of interest to our studies due to the abundance of polytopic linkers utilized in construction of metal organic materials. Although, to date, no studies were conducte d, to the best of our knowle dge, that probe the effect played by binding cooperativity in construction of metal organic materials, it could be a major factor in faci litating the self-assem bly processes underlini ng the construction of metal organic materials and thus is merit of extensive experimental and theoretical investigations.

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9 Figure 1.3. Crystal structure of T state haemogl obin with oxygen bound at all four haems (depicted in ball-and-stick model for clarity).14b 1.1.4 Self-Assembly in Supramolecular Chemistry In supramolecular chemistry, self-assembly 15 is an efficient synthetic strategy to access supermolecules with higher complexity and, by default, functionality. In contrast to tedious multistep covalent syntheses amenable to retrosynthetic approach, selfassembly involves spontaneous, one-pot, associ ation of simple building blocks through noncovalent interactions programmed with a ppropriate information in the form of functional groups capable of mo lecular recognition held at specific relative geometry. This type of chemical synthesis allows access to relatively large, sophisticated assemblies that would be otherwise extremely difficult to attain through stepwise organic synthesis. However, one particular attribute of self-a ssembled supermolecules is the high symmetry

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10 of the supermolecules assembled from identic al repeating units (monomers) due to the very characteristic nature of such asse mblies being thermodynamically controlled products formed under equilibrium conditi ons. While such symmetry might bear interesting functional and st ructural characteristics, dissymmetric macromolecules prepared by conventional organic synthesis c ontinue to hold unique position in medicinal chemistry, polymer chemistry, food products, as well as other areas of interest. Therefore, self-assembly and step-wise organic synt hesis techniques caould be rearded as complementary techniques where advancemen ts in both areas hold great promise to enhance scientists’ control over matter, at the molecular level, aiming to produce novel molecules and materials for demanding applications. 1.1.5 Templates in Self-Assembly Processes In chemistry, the term template bears very close analogy to the simple common perception of a template in industrial applica tions; to serve as an essential part in an assembly process defining the shape of the e nd product though not an in tegral part of the end product and thus could easily be re moved after the assembly process is accomplished. In this sense, a chemical templa te organizes the reactants in a chemical reaction, through noncovalent supermolecular in teractions, permitting control over the end product. However, it is almost impossible to give a concise definition of the term ‘‘template’’ as it spans numerous different branches of chemistry 16. Templates span the whole range from biochemistry, best repres ented by the complex biological structures specialized in DNA replication, 17 to the formation of stru ctured inorganic materials 18 to

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11 the templated synthesis of macrocycles 19 to the preparation of supermolecular catalysts.20 Despite the apparent differences in the prev ious fields of stu dy and, accordingly, the working definitions of a template within, a shared common criteria of a template is its ability to (i) organize reactant species in a pre-determined configuration essential for the formation of a desired product, i.e. the desi red product is inaccessibl e in absence of the template, (ii) the template controls reactivity and/or produces form which requires that (ii) the template binds through reversible, nonc ovalent, interactions to the reactants. Instantly, molecular recognition appears as a necessary prerequisite for templated syntheses, where the binding sites of the re action partners to the template must be complementary in order to establish a successf ul “template effect”. The very nature of this template effect requires molecular de sign and recognition, in a pre-designed fashion, in a step that can fairly be described as information encoding at the molecular level. 1.1.6 Rational Design Strategies in Self-Assembled Supermolecules To arrive at pre-designed artificial supermolecule from self-assembled molecular precursors (building blocks), several requireme nts must be met. Those include the free mobility of the building blocks allowing them to fall into global or local minima on the energetic landscape through optim ized interactions, a require ment that is fulfilled for solvated species due to Brownian motion. In addition, the individual components must be encoded with the appropriate information at the molecular level in the form of binding sites capable of sel ective substrate bindig through complimentary intermolecular interactions and held at correct relative disposition. Since mutual recognition between

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12 reactants requires specificity in binding inte ractions, self-assembly is largely dependent on formulation of well pre-organized build ing blocks. Finally, the bonds between different components must be reversible under the experimental conditions employed. This latter requirement insures that the final construct is generated as thermodynamically controlled product under equilibriu m conditions. This aspect is especially important as kinetically controlled processes do not have the potential for error correction and thus usually lead to ill-defined (amorphous) product, mixture of products, or the kinetically controlled product that is in most cases exhibits lower symmetry compared to the thermodynamically controlled product. 132 The reversibility of self-assembly processes imparts dynamic equilibrium characteristics to the formed constructs, making such supermolecular assemblies prone to excha nge reactions involving their fragments (building blocks).133 1.2 Coordination Polymers Oxford dictionary defines a polymer as “a compound whose formula is an exact multiple of that of another compound, being composed of the same elements in the same proportions”. The more recent definition refe rs to a polymer as a compound with a molecular structure in which a (usually large) number of similar polyatomic units are bonded together. Polymers can be classified according to the nature of polymerization reactions into two types, namely addition and condensation polymers. In addition polymers, the molecular formula of the monomer is identical with that of the structural unit. The polymerization st ep does not generate nor require molecules

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13 other than the monomers. Examples in organi c polymers are numerous and perhaps best demonstrated by the widely employed polystyrene polymer. In condensation polymers the molecular formula of the monomer differs from that of the structural unit through elimination of small molecule, water most commonly, as a side product of the polymerization step. Examples are polyesters and polyamides resulting from condensation polymerization of or ganic acids and alcohols in the first, and acids and amines, in the latter. From the definition of a polymer above, one can draw a clear relation between a widely known class of material compos ed of well-defined repeating units upon association of transition meta ls and functional organic mo lecules through heteroatommetal ion coordination bonds. In this sense, such material is properly labeled as coordination polymer, to express the nature of bonding interactions involved in the polymer synthesis and to dis tinguish this class from wide ly recognized organic polymers that is commonly referred to as “polymers” The use of proper terminology is crucial to avoid misconceptions regarding the materials properties, artificial restrictions and exclusions of intimately-related compounds, and failure to correlate with closely related phenomena. In fact, close inspection of the starting materials and e nd products in coordination polymers, assuming unknown reaction mechanis m, reveals a common trend of loosing metal-coordinated solvent molecules upon fo rmation of each coordination bond. Based solely on this observation, coor dination polymers can further be regarded as condensation polymers. Moreover, this classi fication is still valid for a la rge number of charge-neutral

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14 coordination polymers of metal cations coordina ted to anionic organic functionality in the organic linker, where elimination of another small molecule (e.g. HNO3, HCl, NaNO3, NaCl, etc.) other than the solvent molecu le accompanies each polymerization step. In his introduction of the term coordi nation polymers in 1964, J. C. Bailar 21 draw the resemblance between the then widely known organic polymers and polymeric coordination complexes on basis not so di fferent from the ones mentioned above. 1.2.1 Metal Organic Frameworks Metal organic frameworks (MOFs), a cla ss of coordination polymers, have emerged as novel class of solid state material s with hybrid chemical composition of metal ions, or clusters, and organic molecules bear ing a wide array of f unctional groups capable of metal coordination and/or ch elation. Several attributes of such materials have captured the interest of scientists from different aren a due to the wide poten tial applications in current demanding technologies. The attributes of interest are intrinsic to both the chemical composition and spatial arrangement (order on the molecular and, further, atomic scale) of the metal organic materials. In order to construct a highly ordered solid state materials, a plethora of design principles and experimental tec hniques were devised. Although this kind of constructs might shar e some similarity to previously known silicates, sol-gel, zeolites, and mesoporous material, one distin ct feature of metal organic material is the relatively mild reaction condi tions employed in the synthesis, permitting maintained integrity of well defined building blocks that are generated in situ from molecular or ionic precursors, and thus allo wing enhanced control a nd predictability of

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15 the composition and topology of the final cons truct. Of particular interest, regarding structural properties of metal organic materials, are the ability to generate permanently porous solids that possess high surface ar ea and structural stab ility against guest exchange. Also, the crystallin e nature of such materials permits unequivocal structural characterization through diffrac tion techniques, widely empl oyed are X-ray and neutron diffraction, an essential element for successful structure-function relationship studies. In addition, the available metal ion sites, in va rious examples a coordi natevley-unsaturated metal ion, present reaction sites for desirabl e catalytic transformations and/or guestsubstrate interactions. The organic moiety it self provides the capability to enhanced surface area as well as providing functional sites for guest inte ractions, a property proven useful in gas or liquid sorpti on and/or molecular sensing. As a direct result of the a bove characteristics of metal organic materials, those materials are currently employed in em erging technologies that include gas storage/separation, selective guest sens ing, enhanced heterogeneous catalysis, magnetism, and non-linear optics.22-35 The wide scientific interest in metal organic materials, alternatively known as coordinati on polymers, is reflect ed in the exponential growth in number of publicati ons in the area, Figure 1.4.

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16 Figure 1.4. Histogram highlighting the number of publications containing the terms Coordination polymer (red) and Metal organic framework (green) as topics in publications (source: ISI Web of Knowledge, 01/03/2010, refined to include only publications in chemistry, materials science, physics, and polymer sc ience subject areas). In synthesis of MOFs, a wide array of metal ions, with special interest are transition metal ions that can adopt a variety of well-defined coordination geometries, are generally employed. The versatile analogues of organic linkers, commercially available or synthetically accessible, of the organic linker utilized in a prototypal MOF enables material scientist to choose judicially a su itable linker to either expand or decorate a prototypal MOF in conjunction wi th an appropriate metal ion that exhibit specific activity for applications pertinen t to catalysis, gas sorp tion, guest sensing, etc. 1.2.2 Historical Perspective It was due to the pioneering studies of Alfred Werner, Nobel laureate of 1913, that chemists have first realized the type geometry, and isomerism in octahedrallycoordinated transition metal ions. In th e family of compounds known as Werner

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17 clathrates, solid-state host-gue st composites in which an octahedral metal complex of the formula MA4X2, the complex serve as a clathratin g agent toward appropriately sized organic guests. In a classical Werner clathrate, M is a diva lent metal ion, A is a neutral amine donor ligand (usually a pyridine deri vative), and X is an anionic ligand (NCS-, CN-, NCO-, Cl-, Br-, I-,NO3 -). This family of compounds are based on N-donor ligands (neutral pyridines), Figure 1.5.

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18 Figure 1.5. (Top) an example of the Werner complex, Ni(NCS)2(4-methylpyridine)4,38 (below) crystal packing s howing inclusion of benzene rings guest molecules (highlighted). Ni(magenta), C(gray ), N(blue), S(yellow), H(white).

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19 While Werner complexes are based on disc rete coordination molecular species, another type of coordination compounds with a distinctive extension into 2D layers through utilization of bridging bidentate liga nds were developed a nd first reported by K. A. Hofmann the first reported compound was Ni(NH3)2Ni(CN)42(C6H6) by Hofmann in 1897.39 Figure 1.6. Crystal structure for one of Hofmann-type clathrates44 (top) single 2D periodic layer outlining the square planar Ni(CN)4 and the octahedral Fe(CN)4(NH3)2 (below) disordered benzene guest molecules (h ighlighted in orange ) are enclathrated by the 2D layers. Fe (red), Ni (m agenta), C (gray), N (blue).

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20 Those compounds also exhibit inclusion pr operties of proper size guest molecules and were through works of Iwamoto and co workers that a various derivatives of Hoffman-clathrate were obtained. Those deriva tives maintain the parent Hofmann-type compound topology of 2D sheets although includ ing a second octahedrally-coordinated metal ion other than the octahedral Ni (ca pped with two axial ammonia molecules) or altogether substituting both Ni ions by two di fferent metal ions, one with square-planar and the other with octahedral coordinati on sphere. The general formula of such compounds can be represented as M(NH3)2M'(CN)42G, where M is Mn, Fe, Co, Ni, Cu, or Zn, M' is Ni, Pd, or Pt, and G (guest molecule) is pyrrole, thiophene, benzene, or aniline.40-43 The Hofmann compounds clearly demonstr ate the transition from discrete molecular specie, Werner compounds, into 2D layers of coordination polymers simply through utilization of bridging bidentate liga nds. It is due to th e presence of capping monodentate ammonia molecules coordinated to the trans -MA4B2 octahedral metal ions, where A represents the bidentate cyanide li gand and B represents the capping ammonia, that the former layers were not interconnected into infinite, 3D construct. Thus it seemed logical that replacement of the monodentat e ammonia by a bidentate ligand molecule could provide the route to c onstruction of 3D networks. In fact, the early developed Prussian bl ue, octahedral mixed-valance iron metal ions bridged by cyanide with the general formula Fe4[Fe(CN)6]3xH2O, its first single crystal X-ray diffraction characterization was conducted by Ludi and co-workers,45 best demonstrate this idea and is considered to be the first 3D coordination polymer. 46

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21 Earliest examples of struct urally-investigated coordina tion polymers dates back to 1936, where Keggin and Miles reported the stru cture of Prussian Blue and related compounds,36 and Griffth in 1943, who reported the cr ystal structure of silver oxalate.37 While coordination polymers were known for a relatively long time in chemistry literature, the seminal contributions by Robson et al in 1989, 47-49 can be considered to mark the beginning of a rapidly evolving area of research in materials science, namely MOFs or more generally metal organic materials (MOMs). Robson’s early successful node-and-spacer approach for design and synthe sis of coordination polymers laid the foundation for advancements in the field thr ough early identification of key concepts, especially retrospective structure-based design approach for construction of novel materials based on previously known topologi es of naturally-occurring minerals, identifying the simplest repeating buildi ng unit (molecular building block), observation and control of framework inte rpenetration, and roles of temp lates in determining the end structure. Those early reports clearly demonstrated the feasibility of targeting 3D coordination polymers sharing the same underl ying connectivity (topology) of naturally occurring minerals. Moreover, in cont rary to common per ception then, Robson demonstrated that through simply reacting po lytopic organic linkers and transition metal ions, under appropriate conditions, resulted in crystalline solids instead of what was then expected to result in tangled bird’s nest-lik e structures that are di fficult to characterize. This observation holds a significant place in ad vancement of the field and it stems from reversibility of coordination bonds, where structurally ill-de fined product would be able to dis-assemble and re-assemble again into well-defined crystall ine material, under the reaction conditions employed in syntheses of coordination polymers. The crystalline

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22 nature of coordination polymers attained under carefully adju sted experimental conditions allows for unequivocal structur e determination through X-ray or neutron diffraction techniques, permitting investigati on of structure-function relationship and, equally or more important, design of target ed material. The reversible nature of coordination bonds ensures formation of well-de fined polymer and thus results in highly ordered crystalline material. This is in c ontrast to organic polymers, where covalent bonds are not reversible under the polymerization conditions, usually encountered as noncrystalline material due to the lack of re-organizati on steps during polymerization. For historical perspective, it is important to mention that numerous examples of coordination polymers based on relatively si mple organic linkers can be found in the literature prior to Robson’s reports. Ex amples include oxalate, thiooxamido, 4-Amino3,5,6-trichloropicolinate, dithio -oxalate, 2,3-Pyrazinedicar boxylate, l-tartrate, 2,2'Bipyrimidine, N-tosyl-a-alaninat e, and dithio-oxalate, Figure 1.7. N O HO Cl Cl C lNH2 H2N NH2S S thiooxamide O OH O HO oxalic acid 4-Amino-3,5,6-trichloro picolinic acid N N O HO O OH Pyrazine-2,3dicarboxylic acid OH OH O HO O OH l-tartaric acid N NN N 2,2'-Bipyrimidine H N O HOS O O N-tosyl-a-alanic acid HO OH S S Di t hiooxali c a c id Figure 1.7. Examples of organic linkers utilized in early examples of coordination polymers.

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23 However, the first coordinati on polymers reported by Robson et al demonstrated the feasibility of designing crystalline material s containing solvent-filled cavities with relatively large dimensions yet with essentia lly similar topology of inorganic salts or minerals. 50-57 The first example reported by Robson et al is a diamond-like network based on coordination of tetrahedrally disposed tetr a nitriles from the organic linker 4,4`,4``,4```tetracyanotetraphenylmethane and the tetrahedral Cu(I) metal ions. Although this diamond-like network resembles the topology of diamond, interconnected tetrahedral carbon atoms, but on a much bigge r size scale and even lower ma terial density solely due to the expansion of the linear linker connecti ng tetrahedra, from a si ngle covalent bond in the first to a benzonitrile mol ecule in the la tter, Figure 1.8. Figure 1.8. Hoskins and Robson’s first report of a 3D coordination polymer based on diamond-like net with the formula Cu[C(C6H4CN)4]BF4, the tetraflouroborate counterions were highly di sordered and not localized through the X-ray crystal structure.47

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24 In the follow-up publication, Robson addressed the problem of selfinterpenetration observed when one framew ork grows inside a nd threads through the voids and windows of another identical one. Th is phenomena decreases the available free space inside the targeted MOF a nd Robson was able to direct the synthesis of a particular MOF system that is prone to self-inter penetration to obtain a non-interpenetrated framework through careful design of a re latively bulky counter ion (tetramethyl ammonium) residing in alternating diamond-lik e cages of the overall anionic framework [CuZn(CN)2]-. This framework has the same diamond-like framework topology characteristic of the neutral and interpenetra ted networks existed nearly half a century before Robson’s works, the Zn(CN)2 and Cd(CN)2 coordination polymers, but yet quite different in that interpenetra tion was avoided by first replacing half of the tetrahedrallycoordinated Zn(II) or Cd(II) ions by the tetrah edrally coordinated Cu(I) ion, rendering the framework anionic and in turn required pres ence of counterions. By selecting counterions with appropriate size that prec lude interpenetration of one framework into another, the authors were successful in their endeavor, Figure 1.9. Figure 1.9. Crystal structure of the n on-interpenetrating [CuZn(CN)4](NMe4) 48

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25 1.2.3 Coordination Polymers Utilizing Polytopic, Nitrogen-Donor Ligands In the first reports by Robson et.al, th e authors identified the node-and-spacer approach as a conceptual principle to constr uct coordination polymers In this approach, the metal ion serves as the node, with a we ll-defined coordination sphere acting as a tetrahedral or octahedral node that, upon coordination by an N-donor polytopic organic ligand, the spacer, affords the targeted constr uct. This approach based on molecular, Ndonor ligands towards construction of coor dination polymers have met with great success, demonstrated by numerous exampl es in literature u tilizing pyrazine,58a 4,4`bipyridine, 58b pyrimidine,58c triazine, 58d hexamethylenetetramine (HMTA) 58eand other similar linkers, Figures 1.10 and Figures 1.11-12, for examples of such frameworks. N N pyrazine N N N 1,3,5-triazine N N 4,4`-bipyridine N N N N he x ameth y lenetetramine N N pyrimidine Figure 1.10. Examples of N-donor polytopic linkers.

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26 Figure 1.11. [Cu(pyrimidine)2]BF4 framework58c with the counterions highlighted. Cu (orange), C (gray), H (white), N (blue). However, due to the nature of overall construct being cationic, presence of counterions as guests or solvated inclusions inside the voids of the framework or in close proximity to the metal organic polyhedra, in case of discrete supramolecular coordination entities presents two major challe nges. The first is due to consumption of certain volume inside the voids of the MOF t hus limiting or precludi ng full utilization of available space for applications pertinent to inclusion or adsorption of guest molecules by the MOF. The second is experimentally dete cted phenomenon of instability of the MOF upon removal of solvent molecules simultaneously enclathrated inside the voids of the MOF, either from the mother liquor or from a subsequent solvent exchange process. While the origin

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27 Figure 1.12. (Left) crystal structure of the framew ork attained from HMTA as an axial bridging ligand to Cu(II) propiona te clusters, (right) part of the structure showing the bridging through HMTA (hydrogen atoms omitted for clarity).58e Cu (orange), C (gray), H (white), N (blue), O (red). of this phenomenon is not yet fully inve stigated, it seems r easonable to assume competitive coordination to the metal ions by de solvated counterions, as a direct result of solvent removal, due to the stronger favorable electrostatic interac tion compared to the coordination bonds from the char ge-neutral, N-donor ligand. In fact, MOFs based on anionic N-donor ligands have been synthesized and successfully overcome those two challenges. A representative example is the tetrazolatebased MOF reported by Long et.al., from a so lvothermal reaction of Mn and 5,5',5''benzene-1,3,5-triyltris(1 H -tetrazole)59,60, Figure 1.13. Due to the anionic nature of tetrazolate ions, the attaine d, overall anionic, framework wa s experimentally proven to maintain its structural in tegrity upon desolvation. Theref ore, MOFs based on N-donor, especially anionic, polytopic ligands are expected to demons trate desirable properties to meet specific applications pe rtinent to their structural stability upon desolvation.

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28 Figure 1.13. (Left) crystal structure of the framework obtained by Long et al 59 based on the tetrazolate linker and Mn. (Right) Sche matic representation of the cube-like Mn4(4Cl)(tetrazolate)8 building blocks interconnected through tri-topic phenyl rings. Disordered solvent molecules and solvated Mn ions are omitted for clarity. Mn (magenta), Cl (green), C (gray), O (red), H (white) and N (blue). Figure 1.14. (Left) the polytopic, anionic, N-don or organic linker utilized by Long et.al coordinate Mn ions to forge the tetranuclear Mn4(4-Cl)(tetrazolate)8 building block. The points of extension of this building block (hig hlighted) could be rega rded as a cube-like cluster (right) that upon bridging through tr iangular linker (the benzene ring in the organic ligand) affords the structure shown in Figure 1.13. Mn (magenta), Cl (green), C (gray), O (red), H (white) and N (blue).

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29 1.2.4 Coordination Polymers Utilizing Po lytopic, Carboxylate-Based Ligands As described in section 1.2.3, due to the hurdles encountered in post-synthetic modification and/or activation of coordina tion polymers constructed from neutral Ndonor organic ligands, the focus of material sc ientists in the area ha s shifted towards the anionic carboxylate-based ligands as an attractive alternative to construct robust materials that are stable upon desolvation and/or guest removal. Moreover, due to the anionic nature of carboxylate ligands, a wide variety of positively, neutral, or negatively charged frameworks could be accessed depending on th e ligand-to-metal ion ratio in the overall formulation and, of course, depending on the oxidation state of the metal ions employed. In addition, due to the various coordinati on modes of carboxylate ions, Figure 1.15, it was anticipated that a plethora of compounds could be assembled from the same starting materials depending upon the react ion conditions that potentia lly could be controlled to direct the desirable coordinati on mode of carboxylate ions. One additional feature of carboxylate-base d linkers is the tendency to obtain metal-carboxylate clusters under prop er reaction conditions, generated in situ yet opening the door for utilization of such cluste rs as highly connected building blocks in construction of solid state materials not acce ssible from single-metal-ion building blocks, examples of frequently encountered metal carboxylate clusters ar e shown in Figure 1.16. O O M M Mode A O O M M M Modes A` and A`` A A` A`` O O M M Modes B and B` B B` O O M Mode C C Figure 1.15. Different coordination modes of carboxylate ions.

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30 Figure 1.16. Metal-carboxylate cl usters commonly encountered and utilized as MBBs. Left is the actual cluster and to the right is the conceptual sec ondary building unit (SBU) depiction (a) binuclear tetracarboxylate paddle wheel M2(RCO2)4, (b) basic chromium acetate trimerM3O(RCO2)6(H2O)3 and (c) basic zinc acetate, M4O(RCO2)6, R represents the organic linker, the points of extensions ar e highlighted in yellow. Metal ion (green), C (gray), N (blue), and O (red). The points of extension of the above de picted metal-carboxylate clusters (the clusters being regarded as MBBs accessible in situ under appropriate reaction conditions) define a conceptual well-defined and spatially ordered entities that can be regarded as secondary building units, (SBUs). Based on th e geometry of the MBBs depicted above, the paddlewheel-like metal-carboxylate cluster, frequently encountered in Cu carboxylate complexes, is equivalent to a square-like SBU, the metal-carboxylate trimer MBB found in chromium acetate and analogous species is eq uivalent to a trigonal prismatic SBU, and

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31 the metal-carboxylate tetra-nuclear MBB, f ound in basic zinc acetate clusters, is equivalent to a regular octahedral SBU. Nu merous examples of design strategies and MOFs construction techniques that have utiliz ed such SBUs in conjunction to polytopic carboxylate linkers are found in current literature.61-77 The wide array of either commercially-a vailable or synthe tically-accessible polytopic carboxylic acids provides a seemingly endless supply for materials scientist to design and construct a variety of carboxylate-based solid state materials. Three particular carboxylic acid ligands that have been utilized in current literature to construct three different classes of MOFs that exhibit stru ctural stability upon desolvation along with desirable gas sorption propertie s are depicted in Figure 1.17. O HO O OH O OH O OH O OH O OH O OH N N O O H HO O 5,5'-( E )-diazene-1,2-diyldibenzene1,3-dicarboxylic acid Benzene-1,3,5t ric a rbox y lic a ci d Terephthalic acid Figure 1.17. Three polytopic carboxylic acid ligands utilized in construction of MOFs with exceptional structural stability upon guest removal and desirable gas sorption properties.

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32 The simple, yet elegant, synthesis accomplished by Yaghi et al in 1999, 78 starting from zinc nitrates and terephthalic acid re sulted in a MOF (comm only known as MOF-5) that exhibit the basic zinc acetate MBB, Figure 1.18. The structure could simply be described in terms of octahedral SBUs inte rconnected through the linear organic linker (benzene ring) to result in primitive cubic ( pcu ) topology. Apart from this example representing the successful implementati on of the SBU design strategy to approach highly symmetric and crystalline construct, th e physical properties of the structure are remarkable due to its maintained structural integrity upon desolvation and, accordingly, the ability to utilize the porous nature of the construct towa rds gas sorption applications. This example kindled the interest of scie ntific community in carboxylate-based MOFs and, to date, still a subject of intense e xperimental and theoretical investigations. Figure 1.18. Crystal structure of MOF-5,78 guest solvent molecules omitted for clarity. The yellow sphere represents a sphere of radius 7.1 that can fit in side the regular cubic cages of the framework without touching the va n der Waals radii of the closest H atoms. Zn (green), C (gray), O (red), H (white).

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33 The generality and robustness of this approach was fully exploited through utilization of various anal ogues of terephthalic acid, al l maintaining the relative disposition of the carboxylate functionality but with either enlarged or substituted aromatic ring system. The resulted compounds share the same underlying topology of the prototypal MOF-5 but with far more enhance sorption properties and/or surface area as a direct result of functionalizing or expanding the organic linkers.79-81 The family of reported compounds is termed isoreticular metal organic frameworks (IRMOFs), see Figure 1.19 for examples of derivatives of terephthalic acid utilized. O HO O OH O HO O OH O HO O OH O HO O OH Br H2N O HO HO O O HO O OH O HO O OH O HO O OH O HO O O H O O O HO O OH O O O HO O OH OH O H O O (a) (b)(c) (d) (e)(f) (g) (h) (i) (j) (k) (l) Figure 1.19. The ditopic carboxylic acids utilized to generate (a) IRMOF-1, (b) IRMOF2, (c) IRMOF-3, (d) IRMOF-4, (e) IRMOF-5,( f) IRMOF-6,(g) IRMOF-7, (h) IRMOF-8, (i) IRMOF-10, (j) IRMOF-12, (k ) IRMOF-14, (l).IRMOF-16.79a

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34 The framework constructed from reaction of the tetra-topic carboxylic acid linker, 5,5'-(E)-diazene-1,2-diyldibenzene-1 ,3-dicarboxylic acid, and In(NO3)3 resulted in a MOF with square-octahedral ( soc ) topology containing the basic chromium acetate-like [In3O(CO2)6(H2O)3] clusters regarded as trigonal prismatic SBUs. 82 This framework exhibits interesting hydrogen sorption prope rties due to the highl y localized charges around the indium-carboxylate clusters. This stru cture demonstrates both the ability to access and further to utilize the trigonal prismatic SBU from tri-nuclear metalcarboxylate cluster similar to the basic chromi um acetate cluster towa rds construction of MOFs. Two distinct types of chanells exist in the socMOF, represented in Figure 1.20. Figure 1.20. Crystal structure of the soc -MOF. The yellow spheres represent spheres that can fit inside the cages presen t in the framework without to uching the van der Waals radii of the closest atoms of the framework. Two intersecting types of channels exist in the structure, hydrophilic (blue rods) and hydr ophobic (red rods). Solvent molecules and nitrate counterions omitted for clarity, In (green), C (gray), O (red), N (blue). 82

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35 One noticeable example of a MOF constr ucted from a polytopic carboxylic acid and the binuclear metal-carboxyl ate paddlewheel-like cluste r MBB, equivalent to a square planar SBU, is the one commonly referred to as HKUST-1 MOF with the general formula [Cu3(TMA)2(H2O)3]n, where TMA denotes trimesic acid (1,3,5benzenetricarboxylic acid), Figure 1.21.83 The MBB is defined by four carboxylate ions coordinating two Cu(II) ions in a paddlewheel-lik e structure with four points of extension defining a square-planar SBU. The authors reported the capability of exchanging the axial water molecules coordinated to the Cu(II) paddlewheel, postsynthetically, with pyridine molecules, opening the door for furthe r investigations towa rds the viability of small molecules preferential sorption and/or catalysis on coordi natively-unsaturated metal centers. Figure 1.21. The crystal structure of HKUST-1 MOF showing the interconnectivity of the paddlewheel-like Cu2(RCO2)4 to the tri-topic, triangul ar 1,3,5-benzenetricarboxylate linkers. Guest solvent molecules omitted for clarity, the two yellow spheres are those that can fit inside the two distin ctive cages inside the MOF without touching the van der Waals radii of closest at oms. Cu (orange), C (gray), O (red), H (white). 83

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36 1.2.5 Coordination Ppolymers Utilizing Poly topic, Heterofunctional Ligands: The Single-Metal-Ion MBB Approach While the two approaches based on utiliz ation of polytopic Nbased or carboxylic acid-based organic linkers contin ue to offer a large diversity of solid state materials with desirable physical and chemical propert ies, our group, among others, imparked on exploration of the feas ibility of constructing novel materi als from heterofunctional, those bearing more than one kind of coordinating hete ro atoms with special interest in Nand O-donor ligands. This approach is based on two key ideas; the firs t is to implement rigidity and directionality at the MBB through chelation of the metal ion by a chelating ligand. As chelate metal-ion complexes have much higher stability compared to complexes of monodentate ligands, the well-do cumented chelate effect, it was then anticipated that MOFs constructed from such MBB would express superior chemical and physical stability as compared to their counterpart constructed from mono-dentate complexes. The second idea is concerned with th e directionality impart ed to the chelated MBB, and towards this goal we opted to uti lize ditopic bis-bident ate linkers containing both aromatic nitrogen atoms and carboxylic acid groups. It was expected that due to the more pronounced directionality of a meta l-nitrogen coordination bond and the more flexible nature of a carboxylate-metal ion coordination bonds that the N atoms of the linker would direct the in terconnectivity of the M BB while carboxylate at the -position to the nitrogen would establis h the 5-member ring chelate wi th the coordinated metal ion. In contrast to the polytopic carboxylatebased linkers (where multinuclear metalcarboxylate MBB could be attained), our appro ach utilizes single-metal-ion MBB as a direct result of the chelating na ture of the ligands utilized. 84-87 Several examples of

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37 heterofunctional, bis-bidentate ligand molecules that have be en successfully utilized in construction of functional solid state materi als according to the single-metal-ion MBB approach are shown in Figure 1.22. N NH OH O OH O NN O OH O HO NN O OH OH O Pyrazine-2,3dicarboxylic acid 1H-Imidazole-4,5d i ca r b o x y l i c ac i d Pyrimidine-4,6dicarboxylic acid Figure 1.22. Examples of heterofunctional bis-bidentate organic linkers. Two distinctive examples demonstrating the viability of this approach towards construction of novel functional materials will be described herein. The first example demonstrate the ability to utilize the dodecah edrally-coordinated In(III) metal ion that upon coordination to the bis-bi dentate chelating imidazolate -4,5-dicarboxylate forges a zeolite-like MOF (ZMOF) with rho topology. 88 In this example, th e chelation of In(III) ion by four imidazole-based linkers generates, in situ a single-metal-ion MBB that extends to four neighboring MBBs through the organic linker, Figure 1.23. The two nitrogen atoms of the linker (disposed at an angle ~145 comparable to that provided by the O2ion in zeolites) along with the tetrah edral MBB (considering N-atoms as the points of extension) represent the right geom etric conditions to construct a zeolite-like material but with far more expanded voids and windows due to the replacement of an atomic linker (O2ion in zeolites) with a molecu lar one (imidazolate ring) in rhoZMOF, Figure 1.24.

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38 Figure 1.23. (Left to right) a dodecahedral ly-coordinated metal ion MO4N4, the complex of the metal ion coordinated to four heterof unctional chelating liga nds, and the resultant tetrahedral MBB considering N-atoms as the points of extension to the immediate neighbor MBBs. Figure 1.24. (From left to right) the crystal structure of rhoZMOF, the coordination of In(III) ions by four chelating linkers, simplified coordination sphere around In(III), and the resulted tetrahedral single-metal-ion MBB. In (green), C (gray), O (red), N (blue), hydrogen atoms and solvent molecules omitted for clarity. Yellow sphere represents a sphere with radius c.a. 18 that can fit inside the cages without touching the van der Waals radii of closest atoms. 88 The second example of interest is th e construction of a cube-like metal organic polyhedra (MOP) utilizing 1 H -imidazoledicarboxylic acid and Ni(II) metal ions.89 Due to the favorable fac -NiO3N3 hetero-coordination sphere, chelation of Ni(II) ions by three bis-bidentate linkers resulted in a single-meta l-ion MBB that could be visualized as a three-connected node, Figure 1.25. Upon ex tension of such MBB, generated in situ to three neighboring MBB directed by the N-atoms of the linker (acting as a linear spacer) a cube-like MOP was constructed, Figure 1.26.

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39 Figure 1.25. (Left to right) an octahedrally-coordinated metal ion in fac -MO3N3 configuration, the complex of the metal ion coordinated to three heterofunctional chelating ligands, and the resultant tri-conne cted MBB considering N-atoms as the points of extension to the immediate neighbor MBBs. Figure 1.26. (From left to right) the crystal st ructure of MOC-1, the coordination of Ni(II) ions by three chelati ng linkers, simplified coordinati on sphere around Ni(II), and the resulted tri-connected singl e-metal-ion MBB. Ni (green), C (gray), O (red), N (blue), H (white). 89 1.3 Practical Applications of Functional Metal Organic Materials As function of a material is intimately re lated to its structure at the atomic and molecular level, this is still a valid statement when considering the chemical and physical properties of novel solid state materials. Due to the permanent porosity in various examples of existing MOFs, i.e. structur al integrity upon guest removal from the framework, probed through reversib le gas sorption isotherms of the material in concern,

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40 such MOFs possess the potential to be utilized in a variety of applications pertinent to this particular structural as pect, permanent porosity. In th is regard, the material is considered a host for physisorption applic ations of gases, where MOFs have demonstrated superior performance for carbon dioxide90 and molecular hydrogen91 physisorption. The search for novel materials to meet the DOE goals 92 as hydrogen storage materials for mobile applications enco mpasses a very diverse array of solid state materials, among which MOFs represent potential targets 93 where continuous advancement in the field is expected to offer promising results. In a typical experimental setup for assessment of the capacity of a MOF for hydrogen storage two hydrogen physisorption isotherms ar e conducted on the guest-fr ee MOF at two different temperatures (typically the boiling points of liquid N2 and liquid Ar under one atmospheric pressure, 77K and 87K, respectivel y). Although one isotherm is sufficient to demonstrate the hydrogen storage capacity of a MOF under reported experimental conditions, at least two isotherms conducted at two different temperatures are required to estimate the energy of interaction of mol ecular hydrogen with a MOF by calculation of isosteric heats of adsorption using ei ther the Clausius–Clapeyron equation 94 Experimentally, the isosteric heat of adsorption is determined by numerical analysis of two hydrogen isothe rms performed at different te mperatures (typically 77 and 87 K). The isotherm data are then processed (e ither via curve-fitting or interpolation) and the isosteric heat of adsorption, Qst, is determined over a range of densities ( n ) through a finite-difference approximation to the Clausius-Clapeyron equation: Qst = k T2 ( )n

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41 or by a virial-type expression95 to fit hydrogen sorption is otherms data at the two temperatures. Increasingly more common are hydrogen adsorption studies at higher pressures (up to 100 bar)93 and higher temperatures (up to 298K).96 Some of the top values attained for selected MOFs are demonstrated in Figure 1.27. Figure 1.27. The H2 saturation uptake as wt% measured at 77K and 1 atm, and the corresponding Qst values for selected MOFs. MOF-5,97,98 In-PmDC sodZMOF,99 CdPmDC sodZMOF, 99 rht -MOF,100 MOF-177, 96aMIL-10196a, 98, HKUST-1 MOF,96a,93 and soc -MOF.82 In addition to applications in gas sorpti on and/or separation due to the regular and homogenously distributed cages and window s of MOFs, encapsulation of functional guest molecules inside the voids of the fr amework have emerged as an interesting property that can open doors for utilization of MOFs as platforms of applications tailored

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42 to a specific kind of chemical or physical proc ess that is characterist ic of the encapsulated guest molecule. Our group has utilized the la rge pores of the anionic rhoZMOF (zeolite-like metal organic framework) to exchange encap sulated dimethylammonium counterions (present in the as-synthesized MOF) w ith cationic acridine orange flourophore for sensing applications.88 The framework posses -cages similar to those in RHOzeolite but with far enlarged dimension (diameter of c.a. 18.2 ) along with 8-member ring windows (with c.a. 9 diameter) that allow access of acridine orange molecules to the extra-large cavities, forging a ZMOF impregna ted with a functional organic molecule that could potentially be used as sensor. After ion-exchange of dimethylammonium with the cationic acridine orange molecules, the favor able electrostatic interactions with the framework preclude leaching of acridine guests from the cages of the rhoZMOF. The extra-large dimensions allow further diffusi on of gaseous molecules or other neutral small molecules chosen due to established acridine-guest interactions and thus the impregnated framework acts as a solid support in the sensing process. Examples of such neutral small molecules include methyl xanthenes or DNA nucleoside bases. We have also explored th e potential of encapsulating metalloporphyrins inside the -cages of rhoZMOF generating a catalytically active heterogeneous catalyst, which will be the focus of chapter 5. The earliest investigation of catalytic activity of MOFs was conducted by Fujita et al for the square-grid, 2D Cd(4,4-bpy)2(NO3)2 MOF.134The authors investigated catalytic activity of the framework to wards cyanosilylation of alde hydes and demonstrated sizeand shape-selectivity for the catalytic activity of the MOF towards different substrates.

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43 In general, MOFs exhibit coordinatively-sat urated metal ion site s, as nodes in the framework, where in frequently encountered ex amples some of the coordination sites are occupied by small solvent molecules. Th is carries the opportunity to forge a coordinatively-unsaturated metal ion sites if the solvent molecules could be removed, post synthetically, while maintaining the overa ll structural integrity of the MOF. Such coordinatively-unsaturated metal ion sites c ould prove useful in Lewis acid catalytic transformation. One example is found in the works of Kasel et al where axiallycoordinated water molecules to the Cu-pa ddlewheel moieties of HKUST-1 MOF were removed and the coordinatively-unsaturated Cu(II) metal ion sites catalyzed the cyanosilylation of benzaldehyde or acetone.135 In an alternative strategy to generate catalytically-active, coordinativelyunsaturated, metal ion sites post synthetically in a MOF, a coordi natively-unsaturated metal ions complexed by salen-type molecules c ould be utilized as struts in syntheses of MOFs.136, 137 While salen complexes are known to exhibit catalytic activity towards certain chemical transformation in homogenous catalysis, integrating such species into a MOF provides the means for their utili zation in heterogeneous catalysis. Hupp et al. utilized a two-fold interpenetrate d MOF with square-grid sheets made of 4,4-biphenyldicarboxylate-Zn padd lewheels pillared by (salen)Mn species.138 The pillars in this MOF are (1,2-cyclohexanediaminoN N -bis(3tert -butyl-5-(4pyridyl)salicylidene)MnIIICl 139, 140 a modified analogue of Katsuki–Jacobsen epoxidation catalysts, 141, 142 specifically decorated by pyridine moieties to enable their incorporation as axial ligands to the Zn-paddlewheel clus ters. The forged MOF demonstrated catalytic olefin epoxidation and further revealed that the heterogeneous nature of the catalyst

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44 substantially increased its activity. It was also demonstrated th at the catalytic MOF possess size-selectivity towards substrates and was ascribed to the catalytic process taking place mainly inside the voids of the MOF. The available voids inside microporous MOFs stimulated the interest of researchers to explore their po tentials of encapsulating metal or metal oxide nanoparticles that could subsequently prove useful in heterogeneous catalytic transformations 143 Kholdeeva et al 144 have demonstrated the succes sful electrosta tically-driven encapsulation of Coand Ti-modified Keggin clusters inside the MIL-101 145 cavities, catalyzing oxidation of -pinene to the corr esponding alcohol and ke tone using hydrogen peroxide or molecular oxygen as the oxidant 1.3.1 Porosity in Microporous Coordination Polymers Porosity of a material is defined by IU PAC as “A concept related to texture, referring to the pore space in a material” 101 Microporous materials are porous materials with pore width not exceeding about 2.0 nm, mesopor ous materials are characterized by pore widths in the range of 2 50 nm, and macroporous materials with pore width exceeding 50 nm 102. Permanent porosity of a microporous coordination polymer was first reported by Eddaoudi et al in 1998.103 Yaghi and coworkers were first to report MOF-5, a permanently porous coordination polymer, or metal organic framework (MOF), with pcu topology based on linear terephth alate linkers and octahedrallyconnected basic zinc acetate clusters. 104 The structural stability of the framework upon guest removal was demonstrated both through gas sorption studies and single crystal X-

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45 ray diffraction. Rapidly following their first report, the authors followed up with several publications reporting design prin ciples and practical applicat ions of the novel class of microporous MOFs. Those first reports kindled the scientific inte rest in the newly devised materials that hold great potentials in various applica tions ranging from gas storage and separation, enhanced heter ogeneous catalysis, drug delivery, and CO2 sequestration. Permanent porosity of coordination polyme rs can be demonstrated through gas sorption techniques previously established for zeolites and porous car bon materials. After proper activation of the solid adsorbate, most commonly th rough solvent exchange with readily removable solvent, low boiling point and affinity to the framework, placement under dynamic vacuum at relati vely moderate temperatures ensures removal of guest molecules. Surface area, pore size distribution, total adsorbent uptake, and isosteric heat of adsorption can be determined from measur ements of the gas isotherms. Prior to the determination of an adsorption isotherm it is necessary to ensure proper activation of the material. This is accomplished by outgassi ng, i.e. exposure of the surface to a high vacuum, usually around room temperature or at elevated temperature mild enough not to cause thermal decomposition of the fram ework, Figure 1.28. To obtain reproducible isotherms, it is necessary to control the out gassing conditions which include temperature program and outgassing time (depending on the na ture of the adsorbate and efficiency of guest removal by the adsorption system). Alte rnatively, flushing the adsorbate with the adsorptive followed by heating under dynamic vacuum might prove useful in certain cases.

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46 Figure 1.28. Crystal structure of the evacuated MOF-5.105 Zn (magenta), C (gray), O (red), H (white). According to IUPAC recommendation fo r practices in using gas sorption techniques to assess permanent porosity of an adsorbent, the outgassing temperature may be conveniently selected to li e within the range over which the thermal gravimetric curve obtained in vacuo exhibits a minimum slope However, in common practice, thermo gravimetric analyses (TGA) are conducted under atmospheric pressu re and thus it is widely accepted to adjust the outgassing temp erature to the onset of the platue in TGA curve. The majority of physisorption isotherms fall into the six types shown in Figure 1.29. The reversible Type I isotherm is charact erized by a concave be havior with respect to the P/P axis, where P is the pressure of adsorbate at any given point and P is the saturation pressure of the adsorbate at the bath temperature where the experiment is

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47 conducted, approaching a limiting value as P/P = 1. Type I isotherms are characteristic of microporous solids where the external surf ace areas are negligible compared to the surface areas inside the micr opores of the material (e.g. activated carbons, molecular sieve zeolites, certain porous oxides, and a wide variet y of microporous MOFs), the limiting uptake being governed by the accessi ble micropore volume rather than by the internal surface area. The reversible type II isotherm is the normal form of isotherm obtained with a non-porous or macroporous adsorbent, refl ecting unrestricted monolayer-multilayer adsorption. Point B in the graph indicates the beginning of the almost linear middle section of the isotherm, is often taken to i ndicate the stage at which monolayer coverage is complete and multilayer adsorption about to begin. The reversible type III isotherm is convex with respect to the P/P axis over its entire range and therefore doe s not exhibit the point B obs erved in type II isotherm. Isotherms of this type are uncommon, but th ere are a number of systems (e .g. nitrogen on polyethylene) which give isotherms with gr adual curvature and an indistinct Point B indicating adsorbate-adsorbate interactions pl aying an important role in the total uptake of the material. The distinct features of type IV isotherm appear in two regions of the isotherm. A characteristic hysteresis loop is observed at relatively high P/P, associated with capillary condensation taking place in mesopores, a nd a limiting uptake near the end of the isotherm. The initial part of the type IV isotherm is attributed to monolayer-multilayer adsorption since it follows the same path as the corresponding pa rt of a type II

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F i s a i n i s w F i g ure 1.29. s otherm obt a non-porous n dustrial ad s The T s otherm at r e w eak, and is e Types of p h a ined with t h form. This t s orbents. T ype V isoth e latively lo w e ncountere d h ysisorption h e given ads o t ype of isot h erm is unco m w P/P range d in certain p 48 isotherm s o rptive on t h h erms is cha r m mon; whe r where the a orous adsor b h e same sur f r acteristic o f r e it exhibit s a dsorbent-a d b ents. f ace area of t f many mes o s similar be h d sorbate int e t he adsorbe n o porous h avior to typ e e ractions are n t in e III

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49 The Type VI isotherm is distinguished by multiple sharp steps that depend on the system and the temperature where the measur ement is conducted, reflecting a stepwise multilayer adsorption on a uniform non-porous surface. The step-height represents the monolayer capacity for each adsorbed layer and, in the simplest case, remains nearly constant for two or three adsorbed laye rs. Isotherms obtained for argon or krypton on graphitized carbon blacks conducted at liquid ni trogen temperature exhibit this type of isotherms.106 1.4 Analytical Techniques in Chemis try of Metal–Organic Materials 1.4.1 Crystals and X-ray Diffraction. The Oxford dictionary defines a crystal as “A form in which the molecules of many simple elements and their natural compounds regularly aggregate by the operation of molecular affinity: it has a definite internal structure, with the external form of a solid enclosed by a number of symmetrically arr anged plane faces, and varying in simplicity from a cube to much more complex geometrical bodies ”. The “ definite internal structure ” of a crystal was not accessible until the nineteenth century when modern X-ray crys tallography unraveled th e underlying atomic and molecular structure of single crystals. Th e discovery of X-ray (where X stands for unknown type of radiation, the term origin ally used by W. C. Rntgen in 1895) 107 led Max von Laue to his discovery of X-ray diffrac tion by crystals, for which he received the Nobel Prize in Physics for the year 1914. Hi s idea was that the short wavelength of electromagnetic radiation, pr ovided by X-rays (now known to be in the range of 0.62099

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50 to 1.93998 , angstrom = 1x10-10 m), 108 would cause some kind of diffraction or interference phenomena in such a medium wh ere the wavelength of X-rays is on the order of magnitude of the diffracting elements and that a crystal would provide such a medium. He then successfully demonstrat ed the phenomenon of X-ray diffraction by crystals and published his work in 1912 on th e X-ray diffraction by zinc sulfide crystal. Three years later, Sir William Henry Bra gg and his son, Lawrence Bragg, shared the Noble prize in physics for 1915 "for their services in the analys is of crystal structure by means of X-rays". As Lawrence Bragg hims elf describes von Laue’s contribution: “ When we consider the advances in our knowledge of the structure of matter which have been made by means of the von Laue effect, th is discovery must surely be regarded as occupying a unique position in the history of science ” it is clear that X-ray diffraction, even in its earliest days, contributed, and still, valuable information towards the advancement of science in so many different aspects. When Laue first examined the diffraction pa ttern of zinc sulfide, he noticed that out of a large number of expected diffraction directions, only a certa in number of these appeared on the photographic plate he used to record the effect Laue suggested that this observation could be explained du e to presence of certain wavelengths in the X-ray beam which properly meet the conditions for diffr action. However, Lawrence Bragg elaborated on this finding where he correctly considered that the elements of diffraction in the zinc sulfide crystal (zinc and sulf ur atoms) do not contribute equally to the diffraction of Xrays. In doing so, he directly, and correctly, linked th e observed diffraction directions with the atomic composition and arrangement in the crystal

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51 Bragg’s treatment of the X-ray diffraction phenomenon originated from his consideration of the crystal st ructure to be an arrangement of points (diffracting elements) in parallel and equidistant planes. Upon en counter by X-rays, each diffracting element scatters a wavelet of the incident radiation and as the diffracting elements are arranged in planes the scattered wavelets combine in a reflected wave front, not any different from Huygens’s principle for constructive inte rference. The Bragg’s relation between wavelengths ( ) and the glancing angle ( ) of scattered radiati on is then given by: n = 2 d sin( ) where d is the interplanar distance, n is an integer, and 2 d sin( ) is the path difference between two wave fronts undergoi ng constructive interference. While this does not yet explain why cer tain reflections we re absent from photographs of von Laue’s experiment, Bragg made the assumption that zinc sulfide crystal was in fact face-centered cubic and not a simple cubic lattice. Bragg’s analysis that “ When the planes of such a lattice are arr anged in the order of those most densely packed with atoms, and so most effective for re flection, this order is rather different to that for a simple cubic lattice ” could perhaps be explained more when we consider the reciprocal space treatment of Bragg’s diffraction. Bragg’s diffraction occurs on the atomic crystal lattice, conserving the wave energy and thus is called elastic scattering, where the reflected kf and incident ki wave numbers are equal and just th e direction changes by a reciprocal lattice vector Q = kf ki with the relation to the lattice spacing Q = 2 / d The wave number is related to

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52 wavelength through the relation: k = 2 / The Bragg’s law of di ffraction could thus be re-written as: Q = 4 sin( ) / In Bragg’s own words “By assigning a face-centered cubic structure to zinc blend, it seemed possible to explai n satisfactorily the von Laue photograph as due to the diffraction of white radiation w ith a maximum intensity in a ce rtain part of the spectrum. I made a further test of two simple cubi c crystals, sodium chloride and potassium chloride. While the von Laue photographs obtai ned with sodium chloride indicated a face-centered lattice, those obt ained with potassium chloride were of a simpler nature, and were such as one would expect from an arrangement of points at the corners of cubes. Since it seemed probable that these two crystals had a similar structure, I was led to conjecture that the atoms were arranged in a manner where every corner of the cube is occupied by an atom, whereas the atoms of one kind considered alone are arranged on a face-centered lattice. In potassi um chloride the atoms are so nearly equal in their weight that they act as equivalent diffracting centers and the structure may be regarded as a simple cubic one”109 X-ray Diffraction and Determination of Absolu te Configuration: In many cases chiral octahedral metal complexes ar e encountered, best represente d by tris(chelates). For such complexes the X-ray diffraction patterns of the two enantiomers are identical, precluding determination of absolute configuration. Ho wever, absolute configuration of a single isomer can be determined through anomalous dispersion of X-rays employing Bijvoet statistical analysis, first in troduced by J. M. Bijvoet in 1951 to solve the problem of

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53 determining absolute configuration of noncentrosymetric crystals utilizing X-ray diffraction technique 110 The recent approach to the problem, described by H. D. Flack, is commonly utilized in current lit erature and is the current offi cial method to determine the absolute configuration of chiral mol ecules through X-ray diffraction technique.111. In Flack’s approach, a parameter known as the Flack parameter, calculated during crystal structure refinement on all data, is calc ulated based on the following equation: Where x is the Flack parameter, I is the square of the scaled observed structure factor and F is the calculated structure factor. As the atomic scattering factors cont ain imaginary parts, and due to the anomalous X-ray dispersion effect, the Frie del pairs do not have exactly the same amplitudes (i.e., the scattering intensity | F ( hkl ) | 2 from crystal plane (h k l) is not equal to | F ( h k l )|2), thus allowing utilizat ion of the above equation to determine Flack’s parameter, x As x being calculated for all data, where 1 x 0, the absolute configuration of non-centrosymetric structure could be determined. If the value of x is near 0, with a small standard uncertainty, the absolute stru cture given by the stru cture refinement is likely correct, and if the value is near 1, then the inverted structure, described by F ( h k l ), is more likely correct. If the value is near 0.5, the crystal may be racemic or twinned. As the technique depends heavily on difference between structure factors of opposite planes, i.e. anomalous dispersion phe nomena, presence of heavy atoms in the structure, that exhibit appreciable anomal ous dispersion phenomena in their atomic scattering factors, is highly desirable to utilize this technique effectively.

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54 Alternative to Bijvoet analysis and Flack’s approach, to our field of metal organic materials, if the ligand molecule in a coordination complex contains a chiral center of known absolute configura tion the absolute configuration around the coordinated metal atom in the complex could unequivocally be determined through routine X-ray diffraction. Of the two possibl e enantiomeric structures obtained from direct method solution, the one with correct c onfiguration at the chir al center is to be chosen to represent the true absolute c onfiguration of the co mplex as a whole. 1.4.2 Isothermal Titration Calorimetry (ITC) Isothermal titration calorimetry (ITC) is a thermodynamic technique that directly measures the heat released or absorbed dur ing bond formation or cleavage, respectively, and thus could be utilized to probe binding pr ocess. To our interest, this technique is applicable to probe bindi ng processes in host-guest co mplexation, self–assembly, ionpairing, and solvophobic aggregation of supermolecules. As a binding process will involve bonds cleavage (in reactants ) and formation (in products), heat is either gene rated or absorbed throughout this process, and it is through a single ITC experiment that several para meters of a binding process could be simultaneously determined. Those include reaction stoichiometr y (n), association constant (K), as well as changes in enthalpy ( H) and entropy ( S) upon binding. In the case of self–assembly of superm olecules, by default is a spontaneous process under ambient conditions, generati on of more ordered forms from smaller disordered building blocks might misleadingly imply an overall decrease in the system’s

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55 entropy. However, close inspection of the reac tion systems, where the vast majority is conducted in solution, reveals that overall incr ease in entropy is imparted to the system, as a whole, due to desolvation of the build ing blocks, liberating even larger number of small solvent molecules as compared to the number of building blocks, with more degrees of freedom. In convex supermolecule s, especially those enclosing spherical voids, a total decrease in surf ace area of the supermolecule, compared to the sum of surface areas of its building bl ocks, results in decreased number of surrounding solvent molecules as compared to the total number of solvent molecules solvating corresponding molecular building blocks. Therefore, it is rational to assume an overall increase in entropy of the system in constructing self–asse mbled supermolecules. In the case of self– assembled metal–organic supermolecules, the stronger affinity of organic linkers, as compared to solvent molecules, towards coordinating metal ions result in negative enthalpy change, hence the ove rall process is exothermic. In a typical ITC experiment, portions of a know concentration so lution of a titrant (one of the reacting species, e.g. ligand or guest species) is titrated from a microliter syringe into a solution of known concentration of its binding species (m etal ion, or a host supermolecule, etc.). Upon inje cting aliquots of several microliters from the titration syringe, the association of the bi nding partners produces a neat heat change that raises (or lowers) the temperature in the sample cell rela tive to a reference cell. The deflection of temperature is counteracted by a feedback re gulator that adjusts the electrical power going into a heater in the titration cell to ma intain identical temperatures in both cells. The change in the respective feedback cu rrent is the primary signal observed and corresponds to a heat pulse (h eat production or consumption over time). Integration with

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56 respect to time gives the en ergy that was released (or ab sorbed) upon injecting the known amount of the titrant into the sa mple cell. If a series of injections is made, the compound in the cell is progressively converted to the supermolecular complex leading to diminishing heat effects as the association approaches completion. As the system reaches saturation, the heat signal diminishes until on ly heats of dilution are observed. A binding curve is then obtained from a plot of the h eats from each injection against the ratio of titrand to titrate in the cell. The binding curve is analyzed with the appropriate binding model to determine K, n, H and S. For an exothermic process, the ITC pl ot expresses downward directed pulses indicating the diminution of th e feedback current necessary to keep a zero temperature difference to the reference cell, as the temperature difference is compensated by the heat released from the exothermic process. The integration of the heat pulses when plotted versus the nominal molar ratio of the injected titrant over titrand furnishes a titration curve that exhibits a character istic sigmoidal shape. Specializ ed software calculations are automated in modern calorimeters that utili ze nonlinear curve fitting algorithms to find the most probable parameters describing the association process w ith regard to the specifications of the instrument. Although this technique is widely employed in supramolecular host–guest chemistry,113-120 it has only been utilized recently, by Raymond et al to probe the thermodynamics of gues t binding of a highly charged metal– organic polyhedron as a supermol ecular host in aqueous solution.121 The authors utilized ITC to probe the bind ing process of NEt4 + to a negatively charged metal–organic tetrahedron of composition [Ga4L6]12obtained through selfasse mbly of four Ga (III) metal ions and six tetradeprotonated ligand ions.

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57 Figure 1.30. The left panel schematically depicts the instrumental setup of a power compensation calorimeter. Both cells are comp letely filled, the reference cell with pure solvent, the sample cell with a solution of one of the host –guest partners (e.g. the host). On addition of microliter aliquots of the guest solution delivered from the computerdriven syringe a heat effect occurs that is counter-regulated by the cell feedback current to maintain T at zero. The right panel illustrates the data out put consisting in a number of heat pulses that decrease in magnitude follo wing the progressive sa turation of the host binding site by the incremental addition of the guest species.112 Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission. In their ITC study, the overall 12charges on the supermolecule were counterbalanced by potassium ions and an aqueous solution of NEt4Cl salt was used as th e titrant, a source of NEt4 + ions. The authors reported an intere sting different thermodynamics for NEt4 + binding by the anionic supermolecules. One of the NEt4 + ions is encapsulated inside the void of the supermolecular te trahedron, substituting encapsulated solvent molecules and thus is entropically-driven process, while another 11 NEt4 + ions binds to the surface of the anionic supermolecule, replacing potassium ions, in an enthalpy-driven process to neutralize the negative charges of the supermolecule, Figure 1.31.

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58 Figure 1.31. (Top) schematic equilibria for internal ( Kint) and external ( Kext) NEt4 + guest binding with 1 The symbol denotes encapsulati on. (Bottom) ITC data for the addition of a 90 mM solution of NEt4 + into a 1 mM solution of 1 Inset: total heat vs equiv of NEt4 +. Reprinted with permission from 121. Copyright 2010 American Chemical Society. 1.4.3 Mass Spectrometry The two commonly employed structural characterization te chniques of self– assembled metal–organic supermolecules, wher e organic linkers and metal ions are held together through reversible coordination bonds, are NMR spectroscopy and single crystal X-ray diffraction. However, some limitations occur to those techniques as in some examples the metal–organic supermolecule s contain paramagnetic metal ions where NMR spectroscopy can provide only limited structural information, and in other

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59 examples it is difficult to grow single crys tals of the supermolecules with sufficient quality for structural de termination through X-ray cr ystallography. The latter is commonly encountered especially for fairly large supermolecules where the decreased solubility of the supermolecular construct re sults in rapid precipitation from the reaction solution precluding proper crystallization. Th erefore, mass spectrometry emerges as a substituent or a complimentary technique to the aforementioned ones for structural determination of metal –organic supermolecules. One aspect of mass spectrometry that is pot entially to limit its application towards structural characterization of metal–organic supermolecules and thus requires careful consideration is intrinsic to the nature of ionization process. Seve ral ionization techniques exist for mass spectrometry that range from hard ionization techniques like electron impact (EI), to relatively hard fast atom bombardment (FAB), relatively soft chemical ionization (CI) and elec trospray ionization (ESI), to the soft matrix-assisted laser desorption ionization (MALDI), and the most recently introduced coldspray ionization (CSI) technique. Due to the nature of re latively weak intermolecular interactions (coordination bonds) that sustain the st ructural integrity of metal–organic supermolecules, a suitable soft ionizati on source is required in order to avoid considerable molecular ion fragmentation and thus for detection of the molecular ion in the mass analyzer. 122-125 Yamaguchi and co-workers126 were first to develop the CSI technique, Figure 1.32, which demo nstrated superior efficiency as compared to other commercially available ionization sources to wards generation of molecular ions of metal–organic supermolecules. This ionizati on source, while still not widely employed,

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60 holds the potential to enable routine util ization of mass spectrometry technique in structural characteriza tion of metal–organic su permolecules, Figure 1.33. Figure 1.32 Schematic diagram of the coldspray ion source (CSI) by Yamaguchi et al Reprinted from 126 Copyright (2000), with pe rmission from Elsevier. Figure 1.33. Spectral comparison of compound 1a between (A) CSI and (B) ESI. Reprinted from 126 Copyright (2000), with permission from Elsevier.

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61 1.4.4 Solution Nuclear Magnetic Resonance (NMR) Spectroscopy Nuclear magnetic resonance spectroscopy is a valuable and widely utilized technique for structural characterization of solid, liquid, and solution samples. Our focus is directed towards structural characteriz ation of supermolecules, in general, and metal organic polyhedra, in particular, in solutions, utilizing NMR spectroscopy. Certain characteristics of interest when utilizing solution NMR spectroscopy for structural characterization of supermolecules include changes in chemical shifts, internuclear spin couplings for certain signals, and changes in dimensions of the dissolved species, due to comp lexation or aggregation. Changes in chemical shifts or signal splitting patterns could convey great d eal of information about the nature of species present in solution and thus facilitate structural determination of the dissolved supermolecules. On another end, changes in molecular dimensions, best reflected in measurable changes in diffusion coefficients, could be utilized to probe the progress of the supermolecular assembly process as the reaction reaches equilibrium towards product(s) formation. The hybrid composition of metal organic polyhedra provides both the opportunity and the challenge for structural characterization in solution utilizing NMR spectroscopy. It is due to me tal ion coordination that measurable changes in chemical shifts of the organic linker, re lative to its uncoordinated stat e, could be utilized to signify complexation to the metal ion and in certain cases adequate information sufficient for structural characterization by this technique is obtained.127 However, in cases where the coordinated metal ion is a paramagnetic sp ecies, rapid spin-lattice relaxation induces

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62 considerable peak broadening that render s any reliable structural characterization difficult, if unattainable. However, this very same effect could be utilized to indicate binding of the linker molecules to the paramagnetic metal ion species.128 Another solution NMR technique that coul d probe the size of the supermolecular construct relies on measurements of diffu sion coefficient utilizing magnetic field gradients can be used to indirectly labe l the position of spin s through their Larmor frequency. Cohen et al 129 have reviewed the underl ying principles for diffusion measurement by NMR spectroscopy and its recent utilization in the field of supramolecular chemistry. Stang and coworkers 130 utilized pulsed gradient spin-echo (PGSE) NMR technique 131to measure the self-diffusion co efficient of several of their self-assembled metal organic polyhedra. In one example, the measured diffusion coefficient, of (1.80.05 exp-6 cm2 s-1 and 1.32 0.06 exp-6 cm2 s-1) at 25 C for compounds 6 and 7, respectively, in Figure 1.34 allowed the authors to calculate hydrodynamic diameters of 5.2 nm and 7.5 nm for the self-assembled metal-organic cuboctahedra.130

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63 Figure 1.34. Self-assembly of two cuboctahedron supermolecules. Reprinted with permission from 130. Copyright 1999 Ameri can Chemical Society. 1.5 References 1. Lehn, J.-M. Angew. Chem. Int. Ed. 1988 27 89-112. 2. Lehn, J.-M. Pure Appl. Chem. 1979 51 979-997. 3. Wolf, K. L.; Frahm, H.; Harms, H. Z. Phys. Chem. (B) 1937 36 237. 4. Ehrlich, P. Studies on Immunity ; Wiley: New York, 1906 5. (a) Lehn, J.-M. Pure. Appl. Chem 1979 979-997. (b) Schalley, C. A. Analytical Methods in Supramolecular Chemistry (Ed.); WILEY-VCH Verlag GmbH & Co.: Weinheim, 2007 (c) Hasenknopf, B.; Lehn, J. -M.; Boumediene, N.; Leize, E.; Van Dorsselaer, A. Angew. Chem. Int. Ed. 1998 37 3265-3268. 6. (a) Hosseini, M. W.; Lehn, J.-M.; Du ff, S. R.; Gu, K.; Mertes, M. P. J. Org. Chem. 1987 52 1662-1666. (b) Aarts, Veronika M. L. J.; Van Staveren, Catherina J.; Grootenhuis, Peter D. J. ; Van Eerden, Johan; Kruise, Laminus; Harkema, Sybolt; Reinhoudt, David N. J. Am. Chem. Soc. 1986 108 5035-5036. (c) Uiterwijk, Jos W. H. M.; Van Stav eren, Catherina J.; Reinhoudt, David N.; Den Hertog, Herman J., Jr.; Kruise, Laminus; Harkema, Sybolt. J. Org. Chem 1986 51 1575-1587. 7. Muller, P. Pure. Appl. Chem. 1994 66 1077. 8. (a) Pedersen, C. J. J. Am. Chem. Soc. 1967, 89 2495-2496. (b) Pedersen, C.J. J. Am. Chem. Soc. 1967 89 7017-7036. 9. (a) Cram, D. J.; Kaneda, T.; Helgeson, R. C.; Lein, G. M. J. Am. Chem. Soc. 1979 101 6752-6754. (b) Trueblood, K. N.; K nobler, C. B.; Maverick, E.; Helgeson, R. C.; Brown, S. B.; Cram, D. J. J. Am. Chem. Soc. 1981 103 5594-

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73 116. Corbellini, F.; van Leeuwen, F. W. B.; Bejleveld, H.; Hooiman, H.; Spek, A. L.; Verboom, W.; Crego-Calama, M.; Reinhoudt, D. N. New J.Chem. 2005 29 243-248. 117. Schmidtchen, F. P. In “Calorimetry: An indispensible tool in the design of molecular hosts; in: Macrocyclic Chemistry, Current Tr ends and Future Perspectives”. (Gloe, K. Ed.), Springer Dordrecht, 2005 pp. 291-302. 118. Schmidtchen, F. P. Chem. Eur. J 2002 8 3522-3529. 119. Cooper, A., Nutley, M., MacLean, E. J., Cameron, K., Fielding, L., Mestres, J., Palin, R. Org. Biomolec. Chem. 2005 3 1863-1871. 120. Schmidtchen, F. P. In: Analytical Me thods in Supramolecular Chemistry”. (Schalley, C. Ed.), WILEY-VCH Verl ag GmbH & Co. KGaA, Weinheim, 2007 pp. 55-78. 121. Sgarlata, C.; Mugridge, J.; Pluth, M.; Tiedemann, B.; Zito, V.; Arena, G.; Raymond, K. J. Am. Chem. Soc. 2010, 132 1005-1009. 122. Fenn, J. B.; Mann, M.; Meng, K.; Wong, S. F.; Whitehouse, C. M. Science 1989 246 64–71. 123. Kebarle, P.; Tang, L. Anal. Chem. 1993 65 972A–986A. 124. Yamaguchi, K.; Sakamoto, S.; Tsuruta, H.; Imamoto, T. Chem. Commun. 1998 2123. 125. Bruins, A. P. J. Chromatogr., A. 1998 794 345–357. 126. Sakamoto, S.; Fujita, M.; Kim, K.; Yamaguchi, K. Tetrahedron 2000 56 955– 964. 127. Fujita, M.; Fujita, N.; Ogura, K.; Yamaguchi, K. Nature 1999 400 52-55. 128. Larsen, R. W.; McManus, G. J.; Perry IV, J. J; Rivera-Otero, E.; Zaworotko, M. J. Inorg. Chem. 2007 46 5904-5910.

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74 129. Cohen, Y; Avram, L; Frish, L. Angew. Chem. Int. Ed. 2005 44 520 – 554. 130. Olenyuk, K.; Levin, M. D.; Whiteford, J. A.; Shield, J. E.; Stang, P. J. J. Am. Chem. Soc. 1999, 121, 10434-10435. 131. (a) Stejskal, E. O.; Tanner, J. E. J Chem Phys. 1965 42 288. (b) Tanner, J. E. J. Chem. Phys. 1970 52 2523. 132. Hasenknopf, B.; Lehn, J-M.; Boumediene, N. ; Leize, E.;Van Dorsselaer, A. Angew. Chem. Int. Ed. 1998, 37 3265-3268. 133. Zheng, Y-R.; Stang, P. J. J. Am. Chem. Soc. 2009 131 3487–3489 134. Fujita, M.; Kwon, Y. J.; Washizu, S.; Ogura,K. J. Am. Chem. Soc. 1994 116 1151–1152. 135. Schlichte, K.; Kratzke, T.; Kaskel, S. Microporous Mesoporous Mater. 2004 73 81–88. 136. Kitagawa, S.-i. Noro and T. Nakamura, Chem. Commun. 2006, 701–707 137. Kitaura, R.; Onoyama, G.; Sakamot, H.; Matsuda, R.; Noro, S.-i.; Kitagawa, S. Angew. Chem., Int. Ed. 2004, 43 2684–2687. 138. Cho, S. H.; Ma, B.; Nguyen, S. T.; Hupp, J. T.; Albrecht-Schmitt, T. E. Chem. Commun. 2006 2563–2565 139. Morris, G. A.; Nguyen, S. T. Tetrahedron Lett. 2001 42 2093–2096. 140. Morris, G. A.; Nguyen, S. T.; Hupp, J. T. J. Mol. Catal. A: Chem. 2001 174 15– 20. 141. Katsuki, T. Coord. Chem. Rev. 1995, 140 189–214 142. Palucki, M.; Finney, N. S. ; Pospisil, P. J.; Guler, M. L.; Ishida, T.; Jacobsen, E. N. J. Am. Chem. Soc. 1998 120 948–954.

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75 143. (a) Sabo,M.; Henschel, A.; Frode, H.; Klemm, E.; Kaskel, S. J. Mater. Chem. 2007 17 3827–3832. (b) Hermes, S.; Schrter, M. -K.; Schmid, R.; Khodeir, L.; Muhler, M.; Tissler, A.; Fische r, R. W.; Fischer, R. A. Angew. Chem., Int. Ed. 2005 44 6237–6241. (c) Schrder,F.; Esken, D.; C okoja, M; Berg, M. W. E. v. d.; Lebedev, O. I.; Tendeloo, G. V.; Walaszek, B.; Buntkowsky, G.; Limbach, H.H.; Chaudret, B.; Fischer, R. A. J. Am. Chem. Soc. 2008 130 6119–6130. (d) Mller, M.; Hermes, S. ; Khler, K. ; Ber g, M. W. E. v. d.; Muhler, M.; Fischer, R. A. Chem. Mater. 2008 20 4576–4587. 144. Maksimchuk, N. V.; Timofeeva, M. N.; Melgunov, M. S.; Shmakov, A. N.; Chesalov, Y. A. ; Dybtsev, D. N.; Fedin, V. P.; Kholdeeva, O. A. J. Catal. 2008 257 315–323. 145. Frey,G.; Mellot-Draznieks, C.; Serre, C. ; Millange, F.; Dutour, J.; Surbl, S.; Margiolaki, I. Science 2005 309 2040–2042.

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76 Chapter 2: Imidazole-bBased Ligand-Directed Self-assembly 2.1 Introduction As described in chapter 1, roles played by the organic linker in construction of pre-designed MOFs are crucial towards di ctating the overall topology and imparting chemical and physical stability to the target ed construct. To this end, considerable emphasis is directed towards designing and synthesizing ligands that will serve the aforementioned goals. Two essential elements need to be equally considered in designing appropriate organic linkers. The first is concerned with the spatial relative disposition of the coordination sites provided by the organi c linker, where simple classification of ligand molecules into linear, angular, planar triangular, or other regu lar shaped polygon is visualized by considering the relative posit ions of the coordination sites provided by the ligand. The second, equally important, factor to consider is the chemical nature of the linker; the type and num ber of hetero atoms capable of coordination and/or chelation of metal ions, ionization state on the ionized li gand. As it is described in the previous chapter, organic linkers that fall into the broad families of pyridines, azoles, and carboxylic acids are most suited for constr uction of MOFs, each family of compounds with its own potentials towards accessible topolog ies, structural stab ility, overall charge of the MOF, etc.

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77 2.1.1 Ligand Molecules for Zeolite-like MOFs (ZMOFs) Our interest in this chapter is devote d to organic linkers that can mimic the bridging angle provided by O2in zeolites. In principle, s ubstituting the atomic oxide ion by a molecular linker can poten tially allow for construction of MOFs with zeolitic topologies (i.e. zeolite-like MOFs referred to as ZMOFs), very desirable materials due to the expanded cages and channels in the target ed construct compare to those present in their inorganic counterparts. This particular structural featur e of ZMOFs stems as a direct result of expanding the scale of the linker from an atomic ( oxide ion) to molecular level (organic linker), a strategy known as edge -expansion, Figure 2.1. Turning back to the second part of the targeted ZMOF, the meta l ion, it appeared more feasible, at least synthetically, to adopt the single-metal-ion MBB approach where the coordination number and geometry around single metal i on centers are fairly predictable. The combination of the above requirements set for construction of single-metal-ion based MOFs with zeolitic topologies resulted in identification of the key elements to be provided by the organic linker. Those are, a di-topic linker with a bridging angle of ~145, with readily ionisable functional groups to form an anionic linker with some (a) (b) (c) Figure 2.1. (a) Oxide ion bridging tetr ahedrally-coordinated Si(IV ) ions in zeolites, (b) pyridine molecule, and (c) imidazolate ion br idging two tetrahedrally-coordinated metal ions in MOFs with zeolite-like topologies. O (red), Si (yellow), N (blue), C (gray), metal ion (green), H (white).

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78 degree of control over the ch arge on the ionized linker to compensate for the cationic nature of the metal ions to construct neut ral or anionic ZMOFs. Also, preferably a chelating ligand is to be utili zed to impart rigidity, physical a nd chemical stability and, in turn, permanent porosity to the ZMOF. 2.1.2 Geometry and Rigidity Per the discussion above, targeti ng ZMOFs through single-metal-ion MBB approach requires a specific type of organic linker capable of bridging two coordinated metal ions at ~145 angle and preferably w ith chelating ability to impart structural rigidity. Imidazole or pyrimidine-like molecules can fulfill the linker requirements necessary to accomplish this goal. In those molecules, the nitrogen atoms, as donors in coordination bonds, will direct the connectivity of the MBBs. With special interest are molecules that have imidazole ring as the core structure and functionalized at the position, relative to nitrogen, by ionisable and/or coordinating functiona lity that serve the role needed by a negatively-charged species to mimic the charge on oxide ions in zeolites and/or to result in robust structures due to chelation effect. Our group has successfully utilized 1 H -imidazole-4,5-dicarboxylic acid as th e organic linker to construct three ZMOFs, namely sod, rho, and usf -ZMOFs (discussed more in details in chapter 5). The focus in this chapter is to synthesize organi c molecules that are derivatives of imidazole bearing various functional groups at the -position, relative to imidazole nitrogen(s), aiming to construct novel ZMOFs in anal ogy to the approach utilized with 1 H -imidazole4,5-dicarboxylic acid.

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79 2.1.3 Imidazole Ring in Coordination Polymers A characteristic feature of imidazole ring that upon coordination to a metal ion by the pyridine-type, sp2-hybridized nitrogen the pKa of the other, SP3-hybridized nitrogen is decreased considerably, allowing deprot onation of the metal-coordinated imidazole ring at relatively moderate solution pH (val ues differ depending on the type and valency of coordinated metal ion).1 Therefore, coordination pol ymers from bridging di-topic imidazolate could be attained at moderate s ynthetic conditions; with particular interest are solvothermal syntheses, commonly encount ered in synthesis of MOFs. Accordingly, it is frequently described in current literature that solutions of metal ions and imidazole, under specific solvent and te mperature conditions, react to result in a variety of coordination polymers with, 1D (infinite chains ), 2D (infinite layers), and 3D (extended networks) structures, depending on the synt hesis conditions, Figur e 2.2. These conditions include, stoichiometry of reactants, nature of solvent(s), metal ion(s), temperature, pH, and/or presence of templating species In one particular example, the rhoZMOF,2 it was necessary to employ a 2:1 ratio of the 1 H -imidazoledicarboxylic acid to In(NO3)3, in a mixture of N,N`-dimethylformamid e and acetonitrile as solvents and to heat the reaction mixture at 115C for 24 h to construct the desired product. This example demonstrates the complexity of the reaction conditions that need to be carefully addressed and thus emphasizing that simply designing the appropria te organic linker is the first but not the only step towards a successful synthesis.

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80 Figure 2.2. (Top) infinite chains of Hg(II)-imidazolate3 nitrate, (bottom left) infinite square layers of Ni(II) imidazolate,4 and (bottom right) infinite network of Zn(II)imidazolate.5 Hg (orange), Ni (magenta), Zn (green), C (gray), N (blue), O (red), H (white), encapsulated solvent molecules in the Zn(II)-imidazolate omitted for clarity.

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81 2.2 Results and Discussion 2.2.1 Imidazole-Based Organic Linkers 2-diazo-2H -imidazole-4,5-dicarbonitrile, (2.1). The 1 H -imidazole-4,5dicarboxylic acid is an efficient linker utiliz ed successfully in our group to construct zeolite-like metal organic frameworks (ZMOFs) but with common encounters of formation of the metal organic cubes (MOCs), Figur e 1.2. One route to favor construction of ZMOFs over the MOCs was thought to be achievable through functionalization of the position-2 on the imidazole ring of 1 H -imidazole-4,5dicarboxylic acid with relati vely bulky group compared to hydrogen atom, thus introducing steric hind rance that would prevent formation of the MOCs and, in turn, provide better chances to attain targeted ZMOFs, Figure 2.2. Additionally, functionalized versions of the prototypal 1 H -imidazole-4,5-dicarboxylic acid linker can prove useful in construction of isoreticular ZMOFs with di fferent functional groups pointing inside the large cavities and windows of the framework a nd could potentially impa rt other chemical Figure 2.1. 1 H -Imidazole-4,5-dicarboxylic acid (middle) and the two major products attained through utilization in solvothermal r eactions with In(III) ions, the metal-organic cube (left) and one of the zeolitic frameworks, the rhoZMOF (right). In (green), N (blue), O (red), C (gray), H (white).

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82 NNH NH2 N N NNH Cl N N NNH Br N N NNH B r OH HO O O N NH OH HO O O NNH Cl OH HO O O Figure 2.2. The first pathway explored for synthesis of 1 H -2-chloroand 1 H -2-bromoimidazole-4,5-dicarboxylic acid. and/or physical properties inaccessible through the prototypal, non-functionalized linker.The isolated product (2.1) Figure 2.3, resulted from deprotonation of the intermediate diazonium salt of 2-aminoimidazole-4,5-dicarbonitrile employed in a Sandmeyer synthesis of aromatic halides. Th e first step in Sandmayer reaction requires formation of diazonium salt as an interm ediate through diazotization reaction which subsequently is reacted with CuCl or CuBr to forge the aromatic halide. The acid used in this synthesis (HBF4), tetrafluoro hydrogen borate, util ized due to the weak nucleophilic nature of the tetrafluoro borat es counterions to stabilize the intermediate diazonium salt for the subsequent radiacal-nucleophilic subs titution in Sandmayer reaction apparently induced deprotonation of the imidazole ring to result in the charge-neutral compound (2.1) This compound was found to be extremel y sensitive to heat and shock and presented hazarads for explosion so the shift was made to othe mineral acids instead of HBF4. Trials with HCl acid were successful in attaining the targeted 2-bromo-imidazole4,5-dicarbonitrile but with great difficulty in purifying the end product from Cu(I/II) salts. Due to the observed product of the diazotization reaction ( 2.1 ), the focus was

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83 shifted towards an alternative procedure to attain 1 H -2-bromoimidazole-4,5dicarbonitrile and will be presented in compound ( 2.2a ). Figure 2.3. Crystal structur e of 2-diazo-2 H -imidazole-4,5-dicarbonitrile, (2.1 ). 2-Bromo-1 H -imidazole-4,5-dicarbonitrile, (2.2). As mentioned previously for compound (2.1) the intended functionalization of the imidazole ring of 1 H -imidazole-4,5dicarboxylic acid at the 2-posit ion through replacement of hy drogen by a different atom or functional group (e.g., Cl, Br, NO2) is expected to impart functionality of the to-beconstructed ZMOFs, either isos tructural with previously obta ined ones or altogether with novel zeolitic topologies. In addi tion, due to steric hindrance formation of the frequently encountered metal-organic cube could be avoided, an element of design that would result in enhanced control over the desired product. Initial attempts in our group to probe the viability of this approach included experimenting with 2-chloro-1 H -imidazole, 2-bromo1H-imidazole, and 2-nitro-1 H -imidazole as the organic li nker providing the appropriate bridging angle of (~145) with Zn(II) ions as the tetrahedrally-coordi nated metal ion were

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84 successful in construction three isostructural ZMOFs with sodtopology, the crystal structures of those material s were also published by Yaghi et al 8, where their group is focused more on zeolitic materials based on imidazole linkers. Those three frameworks gave us a strong indication that applyi ng the same design principle towards 1 H imidazole-4,5-dicarboxylic acid could potential ly allow access to our targeted ZMOFs. Despite several experimental tr ials with 2-bromo-5-cyano-3 H -imidazole-4-carboxamide (2.2a) as the linker and In(III) metal ions as the dodecahedrally-coordinated nodes, such trials always resulted in clear solutions w ith no crystalline materials. Two factors might account for such observations. First is that a di-carboxylic acid versi on of this linker is required as starting material for a successful synthesis. However, it has been frequently observed in the works of our group Figure 2.4. Crystal structur e of 2-bromo-1 H -imidazole-4,5-dicarbonitrile (2.2a) left, and 2-bromo-5-cyano-3 H -imidazole-4-carboxylic acid (2.2b) right. Br (brown), N (blue), O (red), C (gray), H (white). that nitrile functionalitie s are readily hydrolyzed, in situ along the react ion progress to forge the carboxylic acid functionality. 9Alternatively, steric hindrance as a result of steric interactions between bromide atoms from f our different ligand molecules might prevent formation of the four member ring construc ted from four metal ions bridged through ditopic linkers in a square-like arrangement, a commonly observed structural feature in a

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85 large number of zeolites and commonly referred to as 4-rings sec ondary building units (SBUs), Figure 2.5. While this effect might prevent formation of ZMOFs containing the 4-ring SBUs, it could potentially result in formation of ZMOFs with novel topologies characterized by absence of the 4-ring SBUs The question remains to be answered through more experimental investigations that will span a wide range of reaction temperatures, solvents and, with specia l interest, structur e directing agents. Figure 2.5. (Left) the 4-ring SBU in RHO -zeolite and that in rho -ZMOF (H•••H distances of 4.19 and 4.93 ). Si(yellow), In(gr een), O(red), N(blue), C(gray), H(white). 1 H -benzimidazole-4,7-diol hydrogen bromide, (2.3c). Synthesis of 1 H benzoimidazole-4,7-diol was pursued due to the expected coordination mode of imidazole coupled to a possible chelation by the phenolic oxygen atoms. The phenolic hydroxyl groups in 1 H -benzoimidazole-4,7-dio l are anticipated to undergo in situ deprotonation under mild reaction conditions. Deprotonation of such hydroxyl groups can provide coordination sites towards metal i ons, analogous to those present in numerous examples involving phenolate-based linkers in the Cambridge Structur al Database (CSD). This molecule bears good structural and functional similarity to 1 H -imidazole-4,5dicarboxylic acid in terms of the core imidazole ring and presence of ionizable hetero

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86 (a) (b) (c) Figure 2.6. Crystal structures of (a) 1,4-di methoxy-2,3-dinitro-benzene, (b) 4,7dimethoxy-1 H -benzoimidazole, and (c) 1 H -benzoimidazole-4,7-diol hydrogen bromide monohydrate (2.3c) Br (brown), N (blue), O (red), C (gray), H (white). atom capable of metal chelation at the -positions of the imidazo le linker. Moreover, the chemical similarity to hydroquinone might c ontribute to impart similar redox properties. The efforts continue trying to obtain crystalline materi als with this linker although numerous trials under widely different expe rimental conditions were not met with success in isolating crystalline product where in most majority of the cases clear solutions were obtained. To the best of our knowledge, th is particular ligand is still unexplored in any published works, as a linker in c onstruction of coordination polymers.

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87 1 H -Imidazole-4-carbaldehyde, (2.4). The rationale behind utilization of this molecule is to acess ZMOFs based on octahedr ally-coordinated metal ions due to their ubiquity in transition metal complexes. In order to construct ZMOFs based on octahedrally-coordinated metal ions, where the metal ion serves the role of tetrahedral node considering its connectivity to the immediate neighbours through bridging ligands, two of the coordination site s around the metal ions should be satisfied with capping ligands. It is the role of the aldehyde functionality at onl y one side of the imidazole ring in (2.4) to provide this requirement, Figure 2.7 demonstrates this design principle. HNN O Figure 2.7. 1 H -Imidazole-4-carbaldehyde, (2.4) Imidazolato-4-carboxaldehyde-Mn(I) molecular square, (2.5). This tetranuclear complex with organic linker that retains the core imidazole ring while functionalized in the 4(5)-position by carboxa ldehyde as a hetero-nucleous coordination bond donor demonstrates perfectly the design pr inciple sought in major parts of this chapter. As intended for octahedrally-coordina ted metal ions, to act as tetrahedral (or 4connected nodes) while simultaneously sati sfying coordination number of 6, through utilizing an imidazole derivative that provides chelation site on one side of the molecule and an aromatic, mono-dentate, N-atom on the other side of the ligand. This type of organic linkers is expected to construct novel solid state materials with zeolitic topologies provided that the perfect combination of de sign principles and e xperimental conditions

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88 are met. In the structure of (2.5) molecu lar squares, which represent a frequently encountered secondary building units in zeoli tic topologies, are constructed. Although the capping carbonyl ligands prevent fu rther extension of the metal organic complex into extended framework, one of the basic building units targeted in construction of ZMOFs, namely the 4-member ring, is obtained. Figure 2.8. Crystal structure of (2.5) showing one molecular squa re (left) and the ABA packing in the molecular solid (right). Mn (magenta), N (blue), O (red), C (gray), H (white). 4,5,4'',5''-Tetrahydro-1 H ,1' H ,1'' H -[2,4';5',2'']terimidazole, (2.6). Compound (2.6) is designed to afford a chem ically-modified analogue of 1 H -imidazole-4,5-dicarboxylic acid, where chelation of metal ions occurs due to presence of nitrogen (in this compound) instead of oxygen atoms in 1 H -imidazole-4,5-dicarboxylic ac id. Although, re taining the core imidazole ring, this compound does not ha ve additional acidic protons capable of facile deprotonation as the imidazoline functi onality has a basic nature instead of the acidic nature of carboxylic acid functionality. Th erefore, the expected overall charge of the to-be-constructed ZMOF will be cationic as the most commonly employed metal ions are multi-valent (mostly in I or II oxidation stat es). This characteristic of this compound,

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89 and closely related ones, will require caref ul design of the reaction conditions, in particular working with metal salts of weakly coordinating counterions, to avoid competitive coordination to the metal ion cen ters. Moreover, to construct ZMOFs based on the single-metal-ion MBB approach, utiliz ing this linker, dodecahedrally-coordinated metal ions are required. N NH N NH N NH 4,5,4'',5''-Tetrahydro-1 H ,1' H ,1'' H -[2,4';5',2'']terimidazole (2.6) 2,2'-(1 H -imidazole-4,5-diyl)di-1,4,5,6-te trahydropyrimidine, (2.7). Compound (2.7) was constructed to meet the same desi gn principles behind the synthesis of (2.6), however with 6-member ring imidazolines inst ead of 5-member ring ones. The expansion of the imidazoline ring size was sought for tw o particular reasons, to increase the biteangle and to impart more hydr ophobic nature to the linker. Those two requirements result as a direct consequence of increasing the ring size of the imidazoline through addition of one methylene group. Indeed, where several trials to construct a MOF with (2.6) were not met with success, utilization of compound (2.7) as the organic linker resulted in several metal organic materials (1D chains, 2D molecula r squares, and 0D MOCs) that will be discussed in greater details in chapter 3.

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90 N NH NH N N HN 2,2'-(1 H -imidazole-4,5-diyl)di-1,4,5, 6-tetrahydropyrimidine (2.7) 2,2'-(1 H -imidazole-4,5-diyl)di(1,4,5,6-tetrah ydropyrimidin-5-ol), (2.8). Compound (2.8) is a functionalized derivative of compound (2.7) with pendant secondary alcohol functional group. Due to the su ccessful attempts to construct metal organic materials with compound (2.7) it was desirable to explore the potential of constructing functionalized isostructural materials thr ough functionalization of the organic linker. However, several attempts to construc t coordination polymers utilizing compound (2.8) were not met with success. One possible expl anation is the chemical interference from the hydroxyl group with the, all-nitrog en, coordination bond donor atoms in (2.8) Throughout all the experimental attempts with this linker, no crysta lline materials were obtained, where either a clear solution or am orphous precipitate re sults under a wide variety of experimental conditions that i nvolve nature of metal ions, counterions, solvents, and reaction temperatures. This exam ple indicates the delicate balance that has to be maintained when designing orga nic linkers seeking desirable products.

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91 Figure 2.9. Crystal structure of 2,2'-(1 H -imidazole-4,5-diyl)di(1,4,5,6-tetrahydro pyrimidin-5-ol), (2.8) Imidazole and amidine N–H hydrogen atoms are geometrically disorderd between two positions with equal occupancy. C (gray), N (blue), O (red), H (white). 2-(3 H -Imidazol-4-yl)-1,4,5,6-tetrahydro-pyrimidine, (2.9). The experimental findings from investigat ions utilizing compound (2.7) were the driving forces behind the design and synthesis of compound (2.9) As it was apparent from trials with (2.7) that complexes of octahedrally-coordinated metal ions (especially metal ions chelated by three ditopic bis-bidentate linkers) are readily accessible, and the requirement of four ligand molecules around single metal ion to construct ZMOFs, compound (2.9) was designed to meet those criteria. Compound (2.9) retains the core imidazole ring and the ability to chelate metal ions but only on one side of the molecule. In the conceptual design, coordination of octahedrally-c oordinated metal ions in the M-L2L`2 (L = chelating ligand and L` = monodentate ligand) configur ation can potentially l ead to successful construction of ZMOFs based on octahedral si ngle-metal-ion approach. However, several attempts to isolate crystalline material with this linker were not successful where in most of the cases clear solutions were obtained. However, these observations might indicate formation of solvated mono or poly-nuclear complexes that were not driven towards formation of polymerized product. Further expe rimentation with this linker is certainly

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92 merit the effort and it is equally important to probe the nature of species present in the resulted clear solutions, most probably ut ilizing solution NMR spectroscopy will provide some answers and insights that would be helpful to guide future experiments. N NH HN N 2-(3 H -Imidazol-4-yl)-1,4,5,6-te trahydro-pyrimidine (2.9) 1 H ,3' H -[5,5']Bibenzoimidazole, (2.10). In compound (2.10) two benzoimidazole rings are covalently linked to provide unexplored area of covalentlylinked imidazole rings with some rotation flexib ility in the linker. In this molecule we target ZMOFs from tetrahedrally-coordinated metal ions, in contrast to dodecahedrallyor octahedrally-coordinated metal ions in the above sections. While it is established that zeolitic MOFs can be constr ucted from benzoimidazole and tetrahedrally-coordinated metal ions 8, to the best of our knowledge no previous attempts were directed to exploring the potential of covalently linked benzoimid azole. Several experimental attempts to isolate crystalline material utilizing this nove l linker were not met w ith success and only amorphous solid precipitates were obtained. Al though it is quite possibl e that appropriate experimental conditions were not met in or der to construct crystalline coordination polymers utilizing this molecule, it is probabl e that the geometric disposition of the two imidazole rings in this molecule is not suit able for construction of targeted coordination polymers.

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93 Figure 2.10. Crystal structure of 1 H ,3' H -[5,5']bibenzoimidazole, (2.10) C (gray), N (blue), O (red), H (white). N,N' -Bis-(1 H -imidazol-4-ylmethylene)-p ropane-1,3-diamine, (2.11). The primary design principle behind compound (2.11) was to synthesize an imidazole based linker that contains on e heteroatom (nitrogen in this case) at the -position to one of the imidazole rings nitrogen. This is primarily due to our efforts to access ZMOFs from octahedrally-coordinated metal i ons using the single-metal-ion MBB (chapter 1), where it is obvious that four ditopic, bis-bide ntate imidazole linkers will only support dodecahedrally-coordinated metal ions and thus it is not highly possible to utilize the vast number of octahedrally-coordinated metal ions as MBBs utilizing such ligand molecules. Therefore, an imidazole-based linker that cont ains only one chelation site was targeted, as four of such molecule can coordinate to a metal ion where two molecules provide chelation (thus satisfying four coordination sites) and another two molecule coordinate as mono-dentate imidazole (providing the additiona l two coordination sites) to satisfy the octahedral coordination number around the metal ion and maintain the specific bridging angle between two MBBs provided by the imid azole ring. Additionally, the alkyl bridge linking two such linkers was introduced to control the geometry (and size) of the coordination pocket around the metal ion. This is a desirable characteristic in this

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94 molecule as the length and natu re of the bridge could easily be tuned to adapt to different coordination radii of different metal ions. As to the stability of th e imine bonds in this type of molecules against hydrolysis unde r the solvothermal conditions employed frequently in our syntheses of MOFs, it is commonly accepted 1b that metal chelation helps to stabilize the imine bond and additi onally we were able to isolate metal complexes with this ligand, further proving th e feasibility of this approach (compounds 2.12 and 2.13 ). N N H N N N N H N,N' -Bis-(1 H -imidazol-4-ylmethylene)-propane-1,3-diamine (2.11) N,N' -Bis-(1 H -imidazolyl-4-ylmethylene)-p ropane-1,3-diamine manganese chloride, (2.12). The discrete, mono-nuclear complex of Mn(II) in (2.12) demonstrates a 5-coordinated Mn ion in squa re-pyramidal geometry with the Mn ion out-of-plane with respect to the organic linker. This comple x represents the delicate balance to be maintained between the geometry of the linke r and the coordination ra dii of the metal ion to be chelated by the linker. Due to th e relatively longer coor dination bond length of N Mn(II) (~2.24) compared to that of N Mn(III) (~1.96), (CSD 5.30 edition updated in May 2009), it is suggested that the out-of-plane movement of coordinated Mn(II) ions in this example is a result of the oxidation stat e of the metal ion. This configuration is not

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95 suitable for construction of intended ZMOFs through coordination of the metal ion to three ligand molecules; two of which are monodentate N-donor im idazolates occupying the two apical positions of the coordina ted metal ion. The next example, compound (2.13) further demonstrates and supports this conclusion. Figure 2.11. Crystal structure of (2.12) the site occupancy fact or for imidazole hydrogen is (0.5) resulting in mono-deprotonated lig and with acidic hydrogen equally displaced between two neighboring complexes due to strong intermolecular hydrogen bond interactions.Mn (magenta), Cl (green), C (gray), N (blue), O (red), H (white). CatenaN,N' -Bis-(1 H -imidazolyl-4-ylmethylene)-propane-1,3-diamine manganese (ii) nitrate, (2.13). Under similar reaction conditions of those employed for compound (2.12) with the only difference is the w eak nucleophilic na ture of nitrate counterion utilized in (2.13) the discrete mono-nuclear complex (2.12) was able to extend into 1D zigzag chain through coordination of the mono-dentate, imidazolate part of a neighboring complex. The mono-dentate imidazolate in this case replaces the capping chloride ion in compound (2.12) apparently due to the weaker nucleophilic nitrate counterion present in the reaction mixture of (2.13) However, the structure was not able to extend into a network most probabl y due to the out-of-plane placement of the Mn(II) ions preventing further coordination to a second mono-d entate, imidazolate part.

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F t h i s ( 2 m c h p r b a d m t w 2 o t h l i F i g ure 2.12. h e crystal st r s axial, mon o N,N' 2 .14) shares m odification h oose to pla r imarily to p e involved i n d dition, the l m atch the re q w o chelated .15) demon s ctahedrallyh is family o f i nker. (Left) zigza g r ucture mag n o -dentate i m Bis-(1 H -im i similar desi as to where ce the imin e p rovide mor e n coo r dinati o l ength and c q uirements o metal ions. T s trates the a b coordinated f linkers to a g -chains in t n ified to vis u m idazolate. M i dazol-2y l m gn approac h the metal c h e nitrogen at o e flexibility o n to a met a c hemical nat u o f different m T he coordi n b ility of imi d metal ions w a ttain better u 96 t he crystal s t u alize the c o M n (magent a m eth y lene)h to compou n h elation site s o m on posit i as to which a l ion as a m o u re of the b r m etal ions, m n ation compl d azole core r w hile also p r u nderstandi n t ructure of ( 2 o ordination o a ), C (gray), N ethane-1,2n d (2.12) w i s are oriente d i on 2of the of the two i m o no-dentate r idging alky l m ost signific a ex attained w r ing to depr o r esenting th e n g and contr o 2 .13) (Righ t o f Mn(II) by N (blue), O diamine, (2 i th slightly d d In compo u imidazole r m idazole ni t or as a chel a l chain can a a ntly the sp a w ith this lin k o tonates in s i e need for f u o l over the f t ) fragment o two ligand s (red), H (w h .14). Comp o d ifferent u nd (2.14) w r ing. This is t rogen atom s a ting atom. I a lso be tune d a cing betwe e k er (compo u i tu to bridg e u rther studie s f lexibility o f o f s one h ite). o und w e s will I n d to e n u nd e two s on f the

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o n u c o M c o m s e c o F c a s t t h N (C10 H ctahedrallyu clear com p o mplex con t M n(II) ion, r e o ordinated i n m onodentate e venth Mn( I o nfiguratio n (a) F i g ure 2.13 a rbonyl liga n t ructures is r h at could be N (blue), O ( r H 10N6)8MnI I coordinated p lex could b e t ains eight m e sulting in a n n a Mn-(C O ligand) and I I) ion is oct a n and occupi e (c)(a) Crystal s n ds and hy d r epresented a visualized a r ed), H (whi I [MnI(CO)3 ] Mn ions co u e visualized m ono-deprot o n overall ne u O )3LL` confi g occupy the a hedrally co e s the share d s tructure of ( d rogen atom s a s a green p y a s (d) square te). 97 ] 3, (2.15). I n u ld be readi l as two trigu o nated liga n u tral charge g uration (w h six terminal ordinated t o d apex betw e (b) (d ) ( 2.15) (b) b a s omitted fo r y ramid, (c) c planar, 4-c o n compoun d l y distinguis lar bipyram i n d molecule s of the com p h ere L = che apexes of t h o six nitroge n e en the two p ) a ckbone of t r clarity, on e c oordinatio n o nnected no d d 2.15, two t y hed. The di s i ds sharing a s six Mn(I) i p lex. Six M n lating ligan d h e two pyra m n atoms in M p yramids, F t he complex e of the two p n around cen t d e. Mn(mag y pes of s crete multi a n apex. Th e i ons and on e n (I) ions are d L` = m ids. The M n-L2L`2 igure 2.13. where term i p yrami d -lik e t ral Mn(II) i enta), C (gr a e e i nal e on a y),

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98 2.2.2 Pyrimidine-Based organic linkers 2-(1 H -Tetrazol-5-yl)-py rimidine, (2.16). Due to the successful attempts in isolating ZMOFs with SODand RHOzeolite 7 topologies in our group utilizing pyrimidine-2-carboxylic acid and the divalent Cd(II) metal ions, it appeared that replacement of carboxylic acid functionality by a tetrazole could potentially result in either isostructural, but functionalized, ZM OFs or altogether novel ones. Therefore, synthesis of compound (2.16) was sought and accomplishe d. Despite that several experiments with this linker did not resu lt in ZMOFs, two interesting coordination polymers were attained util izing this linker, compounds (2.17) and (2.18) In designing this molecule, the pyrimidine nitrogen atoms were sought to provide the proper bridging angle (~145) between two chelated metal ions and thus is a valid target for a linker to forge ZMOFs. The tetrazole ring is capable of in situ deprotonation, under relatively mild reaction conditions, to re sult in an anionic linker and thus either neutral or positively charged ZMOF could be constructed, depending on the oxidation state of the metal ions used. N N NH N N N 2-(1 H -Tetrazol-5-yl)-pyrimidine (2.16)

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99 {(C5H3N6)2Cu}n, Catena-((2-5-(2-Pyrimidyl)tetrazolatoN,N',N'',N''',N'''', N''''' )-copper(ii)), (2.17). While the designed ligand 2-(1 H -Tetrazol-5-yl)-pyrimidine (2.16) was initially sought as an analogue of pyrimidine-2-carboxylic acid that was successfully utilized in our gr oup to construct ZMOFs, it was anticipated that presence of tetrazole ring in this linker might lead to novel materials due to different coordination modes of tetrazolate than those of carboxylat e. While the structure below was completely unpredicted, mainly due to lack of ac cumulative knowledge about the coordination modes of tetrazolates to transition metal i ons, Figure 2.14. In the crystal structure of (2.17) the Kagome` lattice is obtained from 4connected nodes (octahedrally-coordinated Cu(II) ions from two cis -bidentate ligand molecules and two axial monodentate ligand molecules) and a ~120 bent linker (the angl e between two coordinated nitrogen atoms of the tetrazolate ring). While it is to be anticipat ed to arrive at a Ka gome`-like lattice from square-planar nodes and angular linkers, 10, 11the obtained structure was completely unpredicted due to the reason we mentioned above. N NN N N NN N N NN N N NN N 31 entries 70 entries 54 entries33 entries M M M M M M M MN NN N 23 entries M M Figure 2.14 Coordination modes of tetrazolates to transition metal ions and the corresponding number of entries in the CS D database (May 2009 update, number of bonded atoms to non-coordinated nitrogen at oms was fixed at 2 when performing the search).

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100 Figure 2.15 (Top) Crystal structure of (2.17) showing the Kagome`-lattice and (below) side view of three laye rs held together through – stacking and C–H••• interactions (pink lines) between pyrimidine rings. Diso rdered solvent molecules occupying the 1D hexagonal chanells omitted for clarity. Cu (o range), C (gray), N (blue), H (white).

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{ ( c a o a ( 4 t h ( ~ C t h m o i n c o F ( C5H3N6)2C a dmium(ii) ) f ligand (2. 1 metal ion f r 4 ,4)-square g h at the orga n ~ 145) one. C d(II) ion an d h e coordinat i m ode of coo r f coordinati o In co n n -depth exp e o nstruction o F i g ure 2.16. d}n, Caten a ) (2.18). C o 1 6) that was r om four dit o g rid 12 inste a n ic linker is s This appear s d /or placem e i ng nitroge n r dination of t o n complex e n clusion, lig a e rimental in v o f novel co o Crystal stru c a -((2-5-(2P o mpound (2. 1 intended to s o pic, bisb i d ad of a ZM O s erving the r s to be a res u e nt of the C d n atoms of t h t he ligands m e s with the d a nd (2.16) r e v estigations o rdination p o c ture of (2.1 101 Py rimid y l)t e 1 8) represe n s atisfy the d d entate linke r O F. Close in s r ole of a lin e u lt of altern a d (II) ion in a h e pyrimidin e m olecules i n d itopic, bisb e presents an to fully ide n o lymers, in g 8) Cd(buff ) e trazolatoN n ts the desig n d odecahedra l r However, s pection of t h e ar linker in s a ting orient a a geometric a e and tetraz o n this structu r b identate 2,2 interesting l n tify its char a g eneral, and ) C (gray), N N ,N',N'',N'' n principle b l -coordinati o the structur e h e crystal st r s tead of the i a tions of the a lly-relaxed p o late rings. I r e is closely `b ipyrimid i l inker that i s a cteristic an ZMOFs, in N (blue), H ( w ,N'''', N'''' b ehind synt h o n mode aro u e obtained i s r ucture reve i ntended be n linker arou n p osition bet w n effect, the related to t h i ne. s merit of m o d potentials particular. w hite). )h esis u nd s the als n t n d the w een h ose o re in

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102 N -Hydroxy-pyrimidine-2-c arboxamidine, (2.19). Compound (2.19) retains the core pyrimidine ring that is required to direct the connectivity of coordinated metal ions to result in ZMOFs, in analogous way to pyrimidine-2-carboxylic acid and 2-(1 H Tetrazol-5-yl)-pyrimidine. However, compound (2.19) contains a primary amine and a hydroxylamine functionality that were not prev iously explored in our group towards construction of coordination complexes. Theref ore, it represents an interesting molecule to explore the potentials for such functional groups toward s construction of coordination polymers, in general, and ZMOFs, in particular. However, among the several experimental attempts conducted utilizing this linker, the single crystalline product isolated was compound (2.20) a discrete, mono-nuclear, species of octahedrallycoordinated Ni(II) ion. N N HN N H OH N -Hydroxy-pyrimidine-2-carboxamidine Bis-(N-hydroxy-pyrimidine-2-carboxamidin e) nickel(ii) di chloride, (2.20). Compound (2.20) is a discrete, mono-nuclear complex of ligand (2.19) acting as a charge-neutral chelating agent where only one side of the pyrimidine ring is involved in coordination bonding to the Ni(II) ion. While based on ligand (2.19) that retains the core pyrimidine ring, required to dir ect the connectivity of coordina ted metal ions to result in

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Z c o m i n a t c o i o F ( r o t h m a g h y Z MOFs, in a n o ordination m oieties in t h n terest to ex p t tempts con d o mpound (2 o n. Further e F i g ure 2.17. r ed), C (gra y f this novel l h at retain th e m ight be wit h g ents based y droxylami n n alogous w a modes and i h is linker ar e p lore the po t d ucted utiliz .20) a discr e xperimenta l Crystal stru c y ), H (white ) l inker with s e hydroxyla m h great pote n on halopho s n e could pot a y to pyrimi d i onization st a e unexplore d t entials of t h ing this lin k ete, mono-n u l investigati o c ture of (2. 2 ) s pecial inter e m ine functi o n tial in sequ e s phonates (e entially bin d 103 d ine-2-carb o a te of the h y d in the wor k h is linker. H o k er, the singl e u clear, spec i o ns are requ i 2 0) Ni (fain t e st in constr u o nality in ac c e stering and .g. Sarin, S o d the nerve a o xylic acid a n y droxylamin k s of our gro o wever, am o e crystallin e i es of octah e i red to furth e t blue), Cl ( g u ction of po c essible voi d further dea c o man, Cyclo s a gent throug h n d compou n e and prima r up. Therefo r o ng the seve r e product iso e drally-coor d e r elaborate g reen), N (d e rous coordi n d s to guest m c tivating se v s arin, etc.) a h chemical r n d (2.16), th e r y amine r e, it was of r al experim e lated was d inated Ni(I on the pote n e ep blue), O n ation poly m m olecules as v eral of the n a s the acidic r eactions e e ntal I) n tials m ers this n erve

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104 displacing the halide ion. Th is idea is the working pr inciple behind Pralidoxime 13 and it might be anticipated that a metal-coordi nated hydroxylamine moiety becomes more effective in sequestering such organophos phonates due to enhanced acidity of the hydroxylamine functionality. 2.3 Experimental Unless otherwise noted, all compounds disc ussed in the following chapters were synthesized and characterized by Mohamed H. Alkordi in Prof. Mohamed Eddaoudi’s group, Department of Chemistry at the Univer sity of South Florid a according to the following: All chemicals were used as received fr om Fisher Scientific, Sigma-Aldrich, TCI America, or other commercial sources and used without further purification. Single-crystal X-ray diffraction (SCD) da ta were collected on a Bruker SMARTAPEX CCD diffractometerusing with MoK ( = 0.71073 ) or CuK ( = 1.5418 ) radiation source operated at ( 50 kV, 40 mA) for Mo source a nd at (40 kV, 30 mA) for the Cu source. The frames were integrated with SAINT software package 16 with a narrow frame algorithm. The structure was solved using direct methods and refined by fullmatrix least-squares on| F |2. All crystallographi c calculations were conducted with the SHELXTL 5.1 program package,17 Crystallographic tables ar e included in Appendix A. X-ray Powder Diffraction (XRPD) measur ements were carried on a Bruker AXS D8-Advance operated at (50kV, 40mA) for CuK ( = 1.5418 ), with a variable scan

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105 speed. Calculated XRPD patterns were pr oduced using PowderCell 2.4 software 18 and/or Materials Studio MS Modeling version 4.0.19 XRPD patterns are included in Appendix B. The graphical structural analysis wa s performed using Ma terials Studio MS Modeling version 4.0.19 Thermogravimetric analyses (TGA) were performed under N2 and recorded on a Perkin Elmer STA 6000 ther mogravimetric analyzer. TGA profiles are included in Appendix C. Atomic Absorption experiments were conducted on a Varian Spectra AA 100 instrument. Volumetric gas sorption studies were performed on a Quantachrome Autosorb-1 instrument. FT-IR (operated under attenuated total reflec tance mode) spectra were acquired on Thermo Nicolet Avatar 360 FTIR Spectrometer. The MALDI TOF MS spectrum was recorded on a Bruker Daltonics Autoflex III TOF/TOF mass spectrometer using -cyanohydroxy-cinnamic acid as the matrix. Solution UV–vis absorption spectra were collected on a PerkinElmer Lambda900 spectrophotometer, with an attachment fo r solid samples and gaseous atmosphere. All 1H and 13C NMR spectra were acquired on Varian VXR (299.94 MHz for 1H, 75.55 MHz for 13C), UnityINOVA 400 (399.78 MHz for 1H, 100.54 MHz for 13C) equipped with variable temperat ure controller, or UnityINOVA 500 (499.76 MHz for 1H, 125.68 MHz for 13C) spectrometers. The 1H chemical shifts are reported relative to that of TMS and referenced to either the internal HDO signal at 4.76 ppm, the singlet peak of 3(trimethylsilyl)-1-propanesulfonic acid sodium salt (DSS) at 0 ppm, or DMSO-d6 signal at 2.5 ppm, as indicated for each spectrum. All instruments are housed by USF

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106 Interdisciplinary NMR Facility (USFINM RF) at the Department of Chemist ry at the University of South Florida. All spectra were processed by ACD Labs 11.0 package.20 Synthesis of: 2-Diazo-1 H -imidazole-4,5-dicarbonitrile, (2.1). In 20 mL of HBF4 (40% in H2O) at 0C was dissolve 2-amino-1 H -imidazole-4,5-dicarbonitrile (10 mmol), stirred and to this mixture was slowly added a solution of NaNO2 (11 mmol) in 5 mL H2O at 2~5C. After complete addition, the mixture was brought to boil then let to stand at room temperature to result in colo rless crystals. The product was then isolated and air dried (1.12 g, yield = 77.2%). Caution, the solid is chock and heat sensitive; care must be taken in working with nitrite and diazonium salts! N H N NH2 N N NaNO2HBF4N N N N N N 2-Amino-1 H -imidazole4,5-dicarbonitrile 2-Diazo-2 H -imidazole4,5-dicarbonitrile Scheme 2.1. Synthesis of 2-diazo-2 H -imidazole-4,5-dicarbonitrile, (2.1) Synthesis of: 2-Bromo-1 H -imidazole-4,5-dicarbonitrile, (2.2a). To a suspension of 1 H -imidazole-4,5-dicarbonitrile (1.18 g, 10 mmol) in 10 mL D.I. was added NaOH (0.88 g, 22 mmol) and the mixture was stirred at room temperature. To this mixture, Br2 (0.52 mL, 10 mmol) was added drop wise. The mixture was stirred at room temperature for 1h then acidified to pH = 1.8 by few drops of H2SO4, an immediate white precipitate form which was then filtered and washed with D.I. The obtained solid was re-crystallized

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107 from ethanol to give 2-bromo-1 H -imidazole-4,5-dicarbonitrile monohydrate (2.09 g, 9.72 mmol, 97.2 %). NNH N N Br2/ H2O NaOH N NH N N Br 2-Bromo-1 H -imidazole4,5-dicarbonitrile N NH N N Br H2SO4(aq.) reflux 12 hr N NH OH N Br O 2-Bromo-5-cyano-3 H -imidazole4-carboxylic acid amide Scheme 2.2. Synthesis of 2-Bromo-1 H -imidazole-4,5-dicarbonitrile (2.2a) and 2-bromo1 H -imidazole-4,5-dicarboxylic acid, (2.2b) A suspension of 2-bromo-1 H -imidazole-4,5-dicarboni trile monohydrate (1.27 g, 5.9 mmol) in 5 mL D.I. and H2SO4 (36.8 N, 1 mL) was held at reflux for 12 h, then cooled down to room temperature to obtain white precipitate which was subsequently filtered and washed with cold D.I. to obtain 2-bromo-5-cyano-3 H -imidazole-4-carboxylic acid (1 g, 4.65 mmol, 78.8 %). The solid wa s re-crystallized from methanol and characterized through single crystal X-ray diffraction. Synthesis of: 1 H -benzimidazole-4,7-diol hydrogen bromide, (2.3c). In a round bottom flask, finely grinded powder of 1,4-Dimethoxybenzene (6.12 g, 44.3 mmol) was introduced, in portions, to ice-cooled HNO3 (20 mL, 15.8 N) then stirred at room temperature for 1 h followed by heating at 90 C for 1 h. The mixture was allowed to cool

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108 down to room temperature then poured on 100 mL ice to result in bright yellow precipitate. The yellow precipitate was filtered and washed with D.I. then air dried to yield 9.03 g, 89.4% of the di-nitro product (2.3a) The yellow solid was then introduced into a round bottom flask cont aining 150 mL of HCl (10.2 N), with vigorous stirring, a mass of 29.6 g of Sn was introduced into th e reaction mixture, in portions, after which stirring was maintained at 90C for 4 h, the white precipitate was filtered, washed with D.I. and cold acetone then dissolved in D.I. The solution was made basic by addition of NaOH and intense purple color appeared, the product was extracted in chloroform and the golden-yellow organic la yer was dried over Mg(SO4) and instantaneously combined with [1,3,5]-triazine (1.62 g, 20 mmol) and held at reflux for 72 h. The resulted white precipitate was filtered and air-dried to obtain 2.75 g (15.4 mmol, yield = 34.8 % based on p -dimethoxybenzene) of the 4,7-dimethoxy-1 H -benzoimidazole (2.3b) The product was re-crystallized from hot ethanol with few drops of N,N`-dimethylformamide. To 0.546 g (3.06 mmol) of 4,7-dimethoxy-1 H -benzimidazole was added 10 mL of HBr (48%) and the mixture was held at reflux for 2 h then cooled to room temperature to obtain the off-white crystalline material 1 H -benzimidazole-4,7-diol hydrogen bromide (2.3c) 0.535 g (2.33 mmol, yield = 76%). The synthesis is based on a modified previously published procedure.15

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109 NH3 NH3 O O 3,6-Dimethoxy-benzene1,2-diamine.2HCl O O 1.Stir, 00C, 1h 2.Stir, RT, 1h 3.Stir, 900C, 1h O O O2N O2N O O O2N O2N conc. HCl Sn (7 equiv.) 900C NaOH (aq.) NH2 NH2 O O Extract in DCM NH2 NH2 O O NN N DCM reflux 36 h O O N H N 4,7-Dimethoxy1H benzoimidazole [1,3,5]Triazine 2Cl 1,4-Dimethoxy-2,3dinitro-benzene+ NH3 NH3 O O 2Cl O O N H N 4,7-Dimethoxy1H benzoi m idazole HBr OH OH N H H N 1 H -Benzoimidazole-4,7-diol HBr Br 1,4-Dimethoxy-benzeneHNO3 Scheme 2.3. Synthesis of 1 H -benzimidazole-4,7-diol hydrogen bromide, (2.3c)

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110 Synthesis of imidazolato-4-carboxald ehyde-Mn(I) molecular square, (2.5). A stock solution of 1 H -imidazole-4-carboxaldehyde (10 mmo l) in 10 mL of ethanol was prepared. To a 0.5 mL of Mn(CO)5Br solution freshly prepared in acetonitrile (0.1 mM) was added 0.1 mL of the ligand solution, 0.05 mmol of triethylamine, 1mL of DMF and the mixture was heated at 60 C for 4 h to re sult in few pyramid-like crystals formulated as [Mn(Im)(CO)3]4 utilizing single crystal X-ray diffraction. Synthesis of: 4,5,4'',5''-Tetrahydro-1 H ,1' H ,1'' H -[2,4';5',2'']terimidazole, (2.6). 1 H -imidazole-4,5-dicarbonitrile (10 mmol) and excess of ethane-1,2-diamine in presence of sulfur (10 mmol) were held at reflux for 1 h followed by vacuum drying and suspension in water then filtration to afford white powder in excellent yield (9.2 mmol, 92%). 1H NMR (D2O, 400MHz): = 7.99 (s, 1H), 3.92 (s, 8H). NNH N N H2N NH2 Sulfur (cat.) reflux, 1hr + N NH N HN N HN 4,5,4'',5''-Tetrahydro-1 H ,1' H ,1'' H [2,4';5',2'']terimidazole Ethane-1,2-diamine 1 H -Imidazole4,5-dicarbonitrile Scheme 2.4. Synthesis of 4,5,4 '',5''-tetrahydro-1 H ,1' H ,1'' H -[2,4';5',2'']terimidazole, (2.6)

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111 Synthesis of: 2,2'-(1 H -imidazole-4,5-diyl)di-1,4,5,6-tetrahydropyrimidine, (2.7). 1 H -imidazole-4,5-dicarbonitrile (10 mmol) and excess of propane-1,3-diamine in presence of sulfur (10 mmol) held at reflux for 1 h followed by vacuum drying and suspension in water then filtration to afford white powder in excellent yield (9.2 mmol, 92%) and high purity as determined from solution 1H NMR (D2O, 400MHz): = 7.47 (s, 1H), 3.5 (t, J = 5.7 Hz, 8H), 1.97 (quin, J = 5.7 Hz, 4H). N NH N N H2N Sulfur (cat.) reflux, 1hr + N NH N HN N HN 1 H -Imidazole4,5-dicarbonitrile NH2 Propane-1,3diamine 2,2'-(1H-imidazole-4,5-diyl) di-1,4,5,6-tetrahydropyrimidine Scheme 2.5 Synthesis of 2,2'-(1 H -imidazole-4,5-diyl)di-1,4 ,5,6-tetrahydropyrimidine, (2.7) Synthesis of: 2,2'-(1 H -imidazole-4,5-diyl)di(1,4,5,6-tetrahydropyrimidin-5ol), (2.8). In a round bottom flask, a 0.59 g (5 mmol) of 1 H -imidazole-4,5-dicarbonitrile and 0.16 g (5mmol) of sulfur were combin ed. To this mixture was added 0.77 g (20 mmol) of 1,3-diamino-propan-2ol and the mixture was held at reflux for 1h, the excess 1,3-diamino-propan-2-ol was allowed to evapor ate then the precipitate was washed with D.I., filtered and air-dried to obtain 1.2 g (4.55 mmol, yield = 91%) of the 2,2'-(1 H imidazole-4,5-diyl)di(1,4,5,6tetrahydropyrimidin-5-ol). 1H NMR (D2O, 300MHz): = 7.34 (s, 1 H), 4.21 (quin, J =3.2 Hz, 2 H), 3.27 3.54 ppm (m, 8 H). The product was recrystallized from 0.1M solution in DMF to obt ain colorless crystals for single crystal Xray diffraction study.

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112 N NH N N H2N Sulfur (cat.) reflux, 1hr + N NH N HN N HN 1 H -Imidazole4,5-dicarbonitrile NH2 OH 1,3-Diaminopropan-2-ol HO OH 2, 2'-(1 H -imidazole-4,5-diyl) di(1,4,5,6-tetrahydropyrimidin-5-ol) Scheme 2.6. Synthesis of 2,2'-(1 H -imidazole-4,5-diyl)di(1,4 ,5,6-tetrahydropyrimidin-5ol), (2.8) Synthesis of: 2-(3 H -Imidazol-4-yl)-1,4,5,6-tetrahyd ro-pyrimidine, (2.9). To a mixture of 1 H -Imidazole-4(5)-carbaldehyde (10 mmol) and hydroxylamine hydrochloride (10 mmol) in methanol was added sodium methoxide (10 mmol). The mixture was held at reflux for 1 h followed y addition of 10 mL of Acetic acid anhydride. The reflux was continued for an additional 1 h then the volatiles were removed under reduced pressure. The resulted solid was held at reflux for 1 h in excess of 1,3propanediamine in presence of sulfur (5 mmol). The excess 1,3-propanediamine was evaporated and the white solid is suspended in water, filtered, and dried to obtain 7 in high purity (3.5 mmol, 35% yield). 1H NMR (D2O, 300MHz): = 7.80 (s, 2 H), 3.47 (t, J =5.8 Hz, 4 H), 2.00 ppm (quin, J =5.5 Hz, 2 H).

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113 N NH CHO NH2OH NNH N H OH Ac2O N NH N N NH N H2N NH2 S reflux NNH N HN 2-(3 H -Imidazol-4-yl)-1,4,5,6tetrahydro-pyrimidine Scheme 2.7. Synthesis of 2-(3 H -Imidazol-4-yl)-1,4,5,6-tetr ahydro-pyrimidine, (2.9) Synthesis of: 1 H ,3' H -[5,5']Bibenzoimidazole, (2.10). Reaction of biphenyl3,4,3`,4`-tetramine (6 mmol) and [1,3,5]-triazin e (5 mmol) in 1 mL of DMF at 115C for 4 h resulted in light pink solid. The solid wa s filtered and washed with DCM then dried to obtain the 1 H ,3' H -[5,5']bibenzoimidazole as crysta lline solid (3.65 mmol, 61 % yield). The crystalline material was suitable for single crystal X-ray di ffraction studies. The synthesis could also be accomplished according to a previously published procedure 14. H2N H2N NH2 NH2 N N N N H N N NH + DMF 1150C / 4hr [1,3,5]Triazine Biphenyl-3,4,3',4'-tetraamine 1 H ,3' H -[5,5']Bibenzoimidazolyl Scheme 2.8. Synthesis of 1 H ,3' H -[5,5']bibenzoimidazole, (2.10) Synthesis of: N,N'-Bis-(1 H -imidazol-4-ylmethylene )-propane-1,3-diamine, (2.11). Reaction of 1 H -imidazole-4-carbaldehyde (10 mm ol) and propane-1,3-diamine (5 mmol) in 20 mL CH3OH at reflux for 3 hr resulted in clear yellow solution. The solvent was evaporated and the resulted yellow solid is collected to yield the product

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114 quantitatively. 13C NMR (DMSO-d6 101 MHz): = 152.5, 137.1, 58.1, 31.9 ppm. 1H NMR (DMSO-d6 400MHz): = 8.21 (s, 2 H), 7.70 (s, 2 H), 7.40 (br. s., 2 H), 3.54 (t, J =6.7 Hz, 4 H), 1.89 ppm (quin, J =6.8 Hz, 2 H). N HN O H2N NH2 + N NH N HN N N Propane-1,3-diamine 1H-Imidazole4-carbaldehyde CH3OH reflux, 1 hr N,N'-Bis-(1H-imidazol-4-ylmethylene)propane-1,3-diamine Scheme 2.9. Synthesis of N,N'-bis-(1 H -imidazol-4-ylmethylene)-propane-1,3-diamine, (2.11) Synthesis of: Chloro-( N,N' -bis(4-imidazolylmethylidene)-1,3trimethylenediamine)-manganese(ii), (2.12). A mixture of MnCl2 (0.1 mmol) and N,N' bis-(1 H -imidazol-4-ylmethylene)-propane-1,3-diam ine, (0.1 mmol) in 1 mL of DMF was brought to 115C for 12 h to re sult in pale yellow block crys tals, (0.07 mmol, 70 % yield) characterized through single cr ystal X-ray cr ystallography. Synthesis of: CatenaN,N' -Bis-(1 H -imidazolyl-4-ylmethylene)-propane-1,3diamine manganese(ii ) nitrate, (2.13). A mixture of Mn(NO3)2x (H2O), (0.1 mmol) and N,N' -bis-(1 H -imidazol-4-ylmethylene)-propane-1,3-diamine, (0.1 mmol) in 1 mL of DMF was brought to 85C for 12 h to result in pale yellow block crystals, (0.086 mmol, 86 % yield) characterized through si ngle crystal X-ray crystallography.

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115 Synthesis of: N,N'-bis-(1 H -imidazol-2-ylmethylene)-ethane-1,2-diamine, (2.14). To a solution of 1 H -imidazole-2-carboxaldehyde ( 10 mmol) in ethanol (20 mL) was added ethane-1,2-diamine (5 mmol) and th e mixture was maintained at 60 C for 1 h to result in faint yellow soluti on used without further purificat ion in subsequent reactions. N NH O H2N NH2 N N H N N N H N EtOH 60 C N N '-Bis-(1 H -imidazol-2-ylmethylene)ethane-1,2-diamine 1 H -Imidazole-2carbaldehyde Ethane-1,2-diamine Scheme 2.10. Synthesis of N,N' -bis-(1 H -imidazol-2-ylmethylene)-ethane-1,2-diamine, (2.14) Synthesis of: (C10H10N6)8MnII[MnI(CO)3]3, (2.15). Reaction of N,N' -bis-(1 H imidazol-2-ylmethylene)-ethane-1,2 -diamine (0.1 mmol) and Mn(CO)5Br (0.1 mmol) in a solvent mixture of acetonitrile and N,N`-dimethylformamide (1 mL each) at 105 C for 12 h resulted in few colorless polyhedral cr ystals characterized through single crystal Xray diffraction. Synthesis of: 2-(1 H -Tetrazol-5-yl)-pyrimidine, (2.16). An aqueous solution of pyrimidine-3-carbonitrile (10 mmol), sodium azide (12 mmol), and ZnBr2 (10 mmol) was held at reflux for 4 h followed by acidificat ion with HCl and the aqueous solution was extracted with EtOAc several times. Th e organic layer was dried over Mg(SO4), filtered and evaporated under reduced pressure to result in 2-(1 H -tetrazol-5-yl)-pyrimidine (4.18 mmol, 41.8 % yield).

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116 NN N 1. NaN3, ZnBr2 (cat.), H2O 2. HCl EtOAc P y rimidine-2-carbonitrile NN N NN NH 2-(1 H -Tetrazol-5-yl)-pyrimidine Scheme 2.11. Synthesis of 2-(1 H -tetrazol-5-yl)-pyrimidine, (2.16) Synthesis of: catena-((2-5-(2-Pyrimidyl)tetrazolatoN,N',N'',N''',N'''',N''''' )copper(ii)), {(C5H3N6)2Cu}n, (2.17). In 25 mL scintillation vial, a mixture of CuCl2 (0.05 mmol) and 2-(1 H -tetrazol-5-yl)-pyrimidine ( 0.1 mmol) in 2 mL of N,N`dimethylformamide was held at 85C for 24 h, after which few hexagonal plate-like blue crystals were isolated and characterized through single crysta l X-ray diffraction. Synthesis of: catena-((2-5-(2-Pyrimidyl)tetrazolatoN,N',N'',N''',N'''',N''''' )cadmium(ii)), {(C5H3N6)2Cd}n, (2.18). In 25 mL scintillation vial, a mixture of Cd(NO3)2 (0.2 mmol) and 2-(1 H -tetrazol-5-yl)-pyrimidine (0 .2 mmol) in 2 mL of N,N`dimethylformamide was held at 85C for 20 mi nutes, after which cubic colorless crystals were isolated in quantitative yield and characterized through single crystal X-ray diffraction. Synthesis of: N -Hydroxy-pyrimidine-2carboxamidine, (2.19). An ethanolic solution, 10 mL, of pyrimidine-3-carbonitr ile (10 mmol), hydroxylamine hydrochloride (11 mmol), and sodium ethoxide (11 mmol) were held at reflux for 12 h. A white

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117 precipitate was filtered and the filtrate was concentrated under reduced pressure followed by recrystallization from hot aqueous solution to result in faint yellow solid (7.2 mmol, 72% yield). 13C NMR (DMSO-d6, 100.535 MHz): = 123.5, 124.4, 151.7, 156.1, 158.4, 158.6 ppm. NN N Pyrimidine-2carbonitrile H2NOH.HCl Pyridine, reflux NN N NH2 HO N -Hydroxy-pyrimidine2-carboxamidine Scheme 2.12. Synthesis of N-Hydroxy-pyr imidine-2-carboxamidine, (2.19) Synthesis of: Bis-( N -hydroxy-pyrimidine-2-car boxamidine) nickel(ii) dichloride, (2.20). In 25 mL scintillation vial, a mixture of NiCl2 (0.1 mmol) and N hydroxy-pyrimidine-2-carboxamidine (0.2 mmol) in 2 mL of N,N `-dimethylformamide was held at 85C for 12 h, after which green-b lue crystals were isolated in nearly quantitative yield and characterized through single crystal X-ray diffraction. 2.4 Conclusion The works presented in this chapter represent our attempts to design and synthesize organic functional molecules with anticipated potentials to act as proper linkers in construction of novel, pre-designed metal organic materials with Zeolitic

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118 topologies, namely ZMOFs. The nature of the wo rk is mostly exploratory with regards to the chemical properties, coordination modes, ionization states, among other factors of the novel linkers constructed. Despite the fact that geometric design principles were implemented into the syntheses accomplishe d, the modest success in construction of targeted crystalline solid materials with zeolitic topologies em phasizes the equally important factors to consider and contro l during the MOF synthesis, those are the experimental setup ranging from nature of metal ion, counterion, solvent, temperature, stoichiometry, concentration, reaction time, pr esence of structure-directing agent, among others. Although, this combination of reac tion conditions variables might imply an endless number of combinatorial trials, good chemi cal intuition still have much to offer in tackling such situations. One particular factor that deserves furthe r experimental investig ation is the nature of solvent. In all of the trial conducted, a solvent system that contains oxygen donor molecules was employed. Examples of solvents utilized are H2O, N,N` -dimethyl formamide, N,N` -diethylformamide and dimethylsulfoxide. Additional trials are highly recommended in a solvent system that doe s not have oxygen donor molecules; examples include acetonitrile, chlorobenzene, toluene, tr iethylamine and pyridine. This is to avoid competitive coordination by oxygen donor solvent molecules to the metal ions and thus affording better chances fo r metal ion coordination to the nitrogen donor ligands molecules described in this chapter. Equally of interest would be the incorporation of structure directing agents and templates in to the reaction mixtures, most frequently utilized are ammonium salts, that would dir ect the self-assembly of the molecular and ionic precursors to result in the targeted ZMOFs.

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119 2.5 References 1. (a) Brodsky, N. R.; Nguyen, N. M.; Rowan, N. S.; Storm, C. B.; Butcher, R. J.; Sinn, E. Inorg. Chem. 1984 23 891-897. (b) Grimmett, M. R. In Advances in Imidazole Chemistry; A.R. Katritzky and A.J. Boulton, Ed.; Advances in Heterocyclic Chemistry; Academic Press: 1981 ; Vol. 27, pp 241-326. 2. Liu, Y.; Kravstov, V.; Larsen, R.; Eddaoudi, M. Chem. Commun 2006 14 14881490. 3. Masciocchi, N.; Ardizzoia, G.A.; Brenna, S. F.; Galli, C. S.; Maspero, A.; Sironi, A. Chem.Commun. 2003 16 2018-2019. 4. N.Masciocchi, F.Castelli, P.M.Fors ter, M.M.Tafoya, A.K.Cheetham. Inorg.Chem. 2003 42 6147. 5. Kyo Sung Park, Zheng Ni, A.P.Cote, Jae Yong Choi, Rudan Huang, F.J.UribeRomo, Hee K.Chae, M.O'Keeffe, O.M.Yaghi, Proc. Nat .Acad. Sci.USA 2006 103 10186. 6. Franz, G. AAPS PharmSci 2001 ; 3 (2), 1-13. 7. Sava, D. F.; Kravtsov, V. C.; Nouar, F.; Wojtas, L.; Eubank, J. F.; Eddaoudi, M. J. Am. Chem. Soc. 2008 130 3768-3770. 8. (a) Park, K. S.; Ni, Z.; Ct, A. P.; Choi, J. Y.; Huang, R.; Uribe-Romo, F. J.; Chae, H. K.; O’Keeffe, M.; Yaghi, O. M. Proc. Nat. Acad. Sci.USA 2006 103 1018610191. (b) Banerjee, R.; Phan, A.; Wang, B.; Knobler, C.; Furukawa, H.; O'Keeffe, M.; Yaghi, O. M. Science 2008 319 939-943. 9. Sava, D. F.; Kravtsov, V. C.; Eckert, J.; Eubank, J. F.; Nouar, F.; Eddaoudi, M. J. Am. Chem. Soc. 2009 131 10394-10396.

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120 10. Moulton, B.; Lu, J.; Hajndl, R.; Hariharan, S.; Zaworotko, M. J. Angew. Chem. Int. Ed. 2002 41 2821-2824. 11. Atwood, J. L. Nat Mater 2002 1 91-92. 12. Wells, A. Three-dimensional Nets and Polyhedra; John Wiley & Sons: Hoboken, 1977 13. Medical Management of Chem ical Casualties Handbook; Third Edition (June 2000). Aberdeen Proving Ground, MD, pp 118-126. 14. Boydston, A. J.; Williams, K. A.; Bielawski, C. W. J. Am. Chem. Soc 2005 127 12496-12497. 15. Weinberger, L.; Day, A. R. J. Org. Chem 1959 24 1451-1455. 16. Saint Plus, v. 6.01, Bruker Analytical X-ray, Madison, WI, 1999. 17. Sheldrick, G. M. SHELXTL, v. 5.10; Bruker Analytical X-ray, Madison, WI, 1997. 18. Powder Cell for Windows, Version 2.4 (p rogrammed by W. Kraus and G. Nolze, BAM Berlin, 2000). 19. Accelrys MS Modeling 4.0, 2005, Accelrys Software Inc. 20. ACD Labs 11.00 software package, 2007, A dvanced Chemistry Development, Inc.

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121 Chapter 3: Metal Organic Cubes (MOCs) 3.1 Zeolite-like Metal–Organic Frameworks (ZMOFs) Based on the Directed Assembly of Finite Metal –Organic Cubes (MOCs) 3.1.1 Introduction The ability to control coordination nu mber, and geometry, around metal ions, regarded as nodes, through association to polyt opic ligand molecules, regarded as linkers, affords construction of pre-de signed finite and rigid metal organic polyhedra (MOPs).1 MOPs possess several characteristic attribut es, especially important is presence of peripheral functionalities that can further be employed, as coordinating or chelating species towards metal ions or as hydr ogen bond donors/acceptors in conjunction with other hydrogen bond acceptor/donor species, pe rmitting extension of the discrete MOP into an extended framework. This strate gy calls for utilizat ion of MOPs as supermolecular building blocks (SBBs)2 in construction of metal–organic frameworks (MOFs), a strategy we, among others, have impl emented to enhance our control over the targeted framework in a direct consequen ce of information encoding at the molecular level, represented by the well-de fined geometric attributes of the SBB. In this approach, the SBB, a supermolecular chemical species that has the ability to extend through covalent or noncovalent inte ractions is constructed, in situ from simpler units, the molecular building blocks (MBB). In general, the points of extension of the MBB define

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122 a geometric building unit that is equivalent to augmenting a node in an infinite 1 D, 2D or 3D network, with special focus on discre te MOPs, and thus becomes a means of designing and generating metal organic material. Being c onstructed from molecular building blocks, the MOP can further be utili zed as supermolecular building block (SBB) representing the next level of complex ity in designing and constructing novel metal organic materials based on the SBB approac h. The points of extension of the SBB, i.e. available sites for coordination to metal ions and/or hydrogen bond interactions, define a geometric building unit that become s a means of designing and construction of metal organic material with a larger relative scale and a higher de gree of connectivity than that obtained through the MBB approach. Programming the SBB with a hierarchy of appropriate information to promote the synthesis of targeted structures, while simu ltaneously avoiding other easily attainable nets,3 represents a significant adva ncement in framework design.4 Of special interest in crystal chemistry are edge-transitive nets sin ce they are simple networks composed from only one kind of edge.5 Therefore, we opted to utili ze the pre-designed finite metal– organic cube (MOC)6, Figure 1.26, reported previously by our group, as a rigid and directional SBB for the directed assembly and deliberate construction of extended MOFs based on edge transitive nets th at, simultaneously, exhibit zeolitelike topologies. Zeolitelike frameworks, based on tetrahedral nodes, are of scientific and industrial interest due to the myriad potential applications associated w ith their unique structur es and intrinsic pore systems.7 However, the scope of applications is restricted by the synthetic difficulty to construct zeolitelike frameworks with extra-large cavi ties/windows and/or periodic intraframework organic functionality.8

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123 Therefore, it has been the focus of our group, among others, to develop new synthetic pathways and design st rategies to assemble zeolitelike metal–organic frameworks (ZMOFs) to tackle these challe nges, where the unique features of MOFs ranging from facile tuneability, to the ability to tailor the pore size, to the ability to induce intraand/or extra-framework functionality, are combined with the distinctive confined space, ion exchange ability, and, especiall y, the forbidden interpenetration of zeolite structures. While through the single-metal-ion MBB approach, recently implemented by our group, non-default zeolite-like metal organic frameworks (ZMOFs) can be targeted using hetero-chelation to gene rate rigid and directional si ngle-metal-ion-based molecular building blocks (MBBs), the SBB approach towards construction of such materials remains largely unexplored. The MBB appr oach was met with great success in construction of zeolite-like materials where it is possible to avoid default nets (most commonly encountered nets from association of building blocks in absence of proper information encoded at the molecular level of the building blocks) based on assembly of tetrahedral nodes and linear flexible linkers best illustrated by cubic diamond which is the default topology for the assembly of simp le tetrahedral buildi ng units (TBUs) and flexible ditopic linkers,9 but the utilization of rigid and directional TBUs (induced through hetero-chelation) al ong with ligands having the commensurate coordination angle (~144) for zeolite nets enabled us to direct, and furt her control, the assembly of MBBs, generated in situ into non-default ZMOFs. A particular subset of zeolite nets exhibit a common secondary building unit (SBU) composed of eight te trahedra bridged through oxi de ions in a cube-like

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124 arrangement, commonly referred to as a double 4-ring (D4R). Such an SBU is capable to extend into infinite network through coordina tion of the SBU’s vertices to eight oxide ions.11The analogy of this SBU to the MOC suggest s that MOCs could be used as SBBs to target zeolite nets based on D4Rs. Ou r approach encompasses using MOCs as 8connected building blocks, which can be rega rded as D4Rs to construct ZMOFs. This approach could alternatively be visualiz ed as augmenting the nodes of related 8connected edge-transitive nets, i.e. substituti ng an 8-connected node by the vertex figure, a cube in this case. The D4Rs can be connected through linea r linkers to construct nets based on zeolites LTA or ACO or through 4-coordinate nodes to result in AST or ASV -like topologies. The aforementioned zeolites ( ACO AST ASV and LTA ) are especially interesting to reticular chemistry as their ne ts correspond to the augmentation of the edgetransitive nets bcu flu scu and reo respectively, where the D4Rs serve as the cube-like vertex figures.5 Specifically, bcu and reo are both semi-regular 8-connected nets, and scu and flu are edge-transitive (4,8)-connected nets. Based on the above discussion, zeolitic nets that can be inte rpreted as augmented edge-transitive (8connected)-based nets were targeted and successfully constructed, Figure 3.1. As previously described by our group, a metal–organic molecular cube can be assembled through hetero-chelation of octa hedral single-metal ions by ditopic bisbidentate linkers in a fac -MN3O3 manner. The molecular cube itself consists of eight vertices occupied by tri-connected n odes bridged through twelve 4,5-imidazole dicarboxylate (HnImDC, n = 0–1) linkers. By expa nding the coordination of such

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125 vertices, interconnected tetrahed ra similar to the D4R units in zeolites can be attained. The MOCs possess peripheral car boxylate oxygen atoms that can potentially coordinate additional metal ions and/or participat e in hydrogen bonding to construct extended structures, specifically ZMOFs. Figure 3.1 (Middle) single-metal-ion-based MBBs (tri-connected nodes and linear spacers) facilitate the assembly of a MOC, which is utili zed as 8-connected SBB to generate ZMOFs. Zeolitic nets with AST (top left) and LTA (top right) are constructed based on relations with regular (8-c onnected)-based nets (bottom). The reo net (bottom right) corresponds to zeolite LTA (middle right) and flu (bottom left) to zeolite AST (middle left) when the 8-connected node s are augmented, or replaced by cubes.

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126 3.1.2 Results and Discussion Reaction of 4,5-imidazoledicarboxylic acid (H3ImDC) and Zn(NO3)2 6H2O in a N,N` -dimethylformamide (DMF)/ H2O mixture in presence of excess zinc and guanidinium cations yield colo rless polyhedral crystals c ontaining the expected anionic zinc-based MOCs, (3.1) The presence of excess zinc and guanidinium ions permits the linkage of the MOCs thr ough the oxygen atoms of HnImDC to form extended zeolitelike frameworks having AST topology, Figure 3.2. The as-synthesized compound is formulated as {[Zn8 (ImDC)8 (HImDC)4] Zn4 (DMF)8 (H2O)4 (guanidinium)8} (3.1 ), using single-crystal X–ray diffraction. In (3.1) the anionic MOCs, formulated as [Zn8 (ImDC)8 (HImDC)4]16-, are composed of twelve ligands, f our doubly deprotonated and eight triply deprotonated ligands coordinating eight Zn2+ ions, generating an overall 16 charged MOC. In an attempt to direct the assembly of such highly functional anionic MOCs through H-bonding interactions, guanidinium nitrate was employed as a structure directing agent. The guanidinium ion provi des suitable molecular recognition sites in conjuncture to carboxylate ions, acting as H-bond donor in a charge-assisted hydrogen bond interaction, Figure 3.3. In the crystal structure of (3.1) each guanidinium ion is simultaneously hydrogen bonded to three MOCs through the carboxylat e ions present on the vertices of the MOCs. Four guanidini um ions, arranged on the surfaces of a supramolecular tetrahedron, act as a tetrahedra l node linking the vertices of four MOCs through multiple charge-assisted hydrogen bonds. Such arrangement could be visualized as four MOCs tetrahedrally-connect ed through vertices, analogous to AST zeolite.

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127 a) b) c) d) Figure 3.2. (a) Single-crystal structure of AST-ZMOF, (3.1) (yellow sphere represents vdw sphere of a diameter ~ 15 that can fit into the AST-cage without touching vdw surfaces of the framework) with (b) zeolite AST-like network topology. (c) In (3.1) the MOC-based SBBs are linked via simulta neous edge-to-edge connection through coordinated metal ions and vertex-to-vert ex connectivity thro ugh charge-assisted Hbonded guanidinium ions. (d) In AST -ZMOFs, ( 3.1) and (3.2) six MOCs (red tile) are connected to generate the AST-cage (blue tile).

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128 Figure 3.3. Bond distance histogram for N HO interactions in guanidiniumcarboxylate complexes, CSD version 5.30 (November 2008). Moreover, due to presence of external ca rboxylate functionalities, metal ions, in this case excess of Zn2+ added to the reaction mixture, could be employed as nodes to afford coordination linkage of the MOCs through edges. In the crystal structure of (3.1) Figure 3.4, each anionic molecular cube is concurrently connected through its edges and vertices to zinc and guanidinium ions, respectively, and further extends to twelve adjacent MOCs. Each edge-connection occurs through a Zn2+ ion octahedrally coordinated by four carboxylate oxygen atoms (Zn–O distance of 2.07 ), from two ImDC ligands of two MOCs, and two disordered DMF solvent molecules as axial ligands. The twelve edge-connections through Zn2+ ions can be visualized as edge-to-edge connections between the cubes. Intermolecular vertex

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129 Figure 3.4. Crystal structure of (3.1) showing assembly of si x MOCs, simultaneous apexto-apex H-bonding interactions with guanidi nium (top) and edge-t o-edge connections through coordinated Zn2+ ions (bottom), generates the AST -cage. Yellow sphere represents the sphere that can fit inside AST -cage without touching van der Waals radii of atoms making up the framework. O (red) N (blue), Zn (green), C (grey).

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130 a) b) c) d) Figure 3.5. (a) Supramolecular tetrahedral assemb ly of MOCs through coordinated Zn ions (green) and H-bonding to guanidinium catio ns (only 3 MOCs shown for clarity), (b) tetrahedrally-arranged guanidinium cations (c) edge-connection between MOCs through octahedrally-coordinated me tal cations, (d) guanidinium-ImDC interactions through charge-assisted H-bonds to the carboxylates groups on the vertices of four MOCs in (3.1) (N HO distance of 1.978 2.204). O (red), N (blue), Zn (g reen), C (grey), H (white).

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131 connections occur through ch arge-assisted hydrogen bonds between four guanidinium ions, paneling a supramolecular tetrahedr on, and carboxylate oxygen atoms (N HO distances 1.978 2.204 ), Figure 3.5. These H-bonds play a decisive structure-directing role and can be regarded as a tetrahedral node linking four cubes through vertices producing the zeolitic AST topology. In a separate attempt to direct the lin kage between the anionic MOCs bearing carboxylate functionalities, oxophilic metal ions, especially with interest are alkali and alkaline earth metal ions, were considered as potential target to include in the initial reaction mixture to act as li nkers of the MOCs. The choice of oxophilic metal ions was based on the rationale of minimal interferen ce with the construction of the MOC due to weak competition of those ions towards coordi nation to nitrogen atom s of the ligand, thus permitting their utilization in the initial reaction mixture with Zn2+, Cd2+, Mn2+, Co2+, or In3+ ions that exhibit favorable octahedral hetero-coordination fac -MN3O3 sphere, essential for construction of the targeted MO C. From the several different metal ions attempted, only K+ and Cs+ ions afforded crystalline materials suitable for structural analysis. Reaction of (H3ImDC) and Zn(NO3)2 6H2O in a DMF/H2O mixture in presence of potassium chloride yield colorless pol yhedral crystals formulated as {[Zn8(HImDC)12] (DMF)5 K8 (H2O)12}, (3.2) From the X-ray structural analysis, it is evident that the ligands molecules in the MOC are doubly deprotonated, and c oordinating eight Zn2+ ions resulting in an overall 8 charged MOC. The charge balance is attained through coordination of eight K+ ions by the carboxylate functiona lities at the vertices of the MOC.

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F c o c a f r ( r c o F ( t K F i g ure 3.6. ( T o ordinated p a ge without r agment of ( r ed), N ( b lu e In the o ordinate to igure 3.6. E a t wo per cub e K + ions linki n T op) crystal p otassium io touching v a 3 .2) showin g e ), Zn (gree n crystal stru c the oxygen a ch K + ion i e K O bon d n g four cub e structure o f ns. Yellow s a n der Waals g ImDC si m n ), C (grey), c ture of (3. 2 atoms on th s coordinat e d distance o f e s through t h 132 f (3.2) show i s phere repre radii of ato m m ultaneously K (purple). 2 ) Figure 3. 6 e vertices o f e d by six ox y f 2.72~2.8 2 h eir vertices i ng MOCs c o sents the sp h m s making u coordinate d 6 four tetra h f four tetrah e y gen atoms o 2 ). A tetra h are visualiz e o nnectivity t h ere that ca n u p the fram e d to Zn2+ an d h edrallyarr a e drally-arra n o n the vertic h edral ar r an g e d as a tetra h t hrough n fit inside A e work, ( b ott o d K + ions. O a nged K + io n n ged MOCs, es of three c g ement of f o h edral node A ST om ) n s c ubes o ur

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133 linking four MOCs, in a similar manner to that played by guanidinium ions in (3.1) and thus the overall structural topology of (3.2) could be regarded as AST -like ZMOF. We describe the connectivity through these K+ clusters as tetrah edral nodes linking four cubes through the vertices. Th e resulting topology can be represented by the zeolite AST or the flu net, if the SBB is viewed as an 8-coordinate node. The same strategy as detailed above also was applied to Cd2+, Co2+, Mn2+, and In3+ to result in similar extended frameworks ( 3.4 3.8 described later), demonstrating a versatile and readily accessible approach toward construction of ZMOFs based on a variety of octahedrally-coor dinated metal ions. In both (3.1) and (3.2) six MOCs assemble to create the AST -cage in which spheres with diameters ca. 15 and 12 , respectively, can fit without touching the van der Waal s radii of the framework (excluding solvent). The following LTA -ZMOF of the formula {[Cd8 (HImDC)8 (ImDC)4] (H2Pip)2 Na8 (EtOH) (H2O)41} (Pip = Piperazine, EtOH = Ethanol) was prepared solely by Jaccylin A. Brant and will be presented here due to th e close relevancy to the approach described earlier. Reaction of Cd(NO3)2 4H2O and H3ImDC in the presence of Na+ ions results in compound (3.3) formulated as {[Cd8 (HImDC)8 (ImDC)4] (H2Pip)2 Na8 (EtOH) (H2O)41} (Pip = Piperazine, EtOH = Ethanol). In the crystal structure of (3.3) Figure 3.7a, each MOC is linked to eight other cubes through lin ear vertex-to-vertex connections. Half are connected through hydrogen bonded water molecu les and the other four vertices are connected through a series of four sodium atoms, Figure 3.7 b. The framework consists

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134 of two types of cages, namely an -cage encapsulated by 12 cubes and an elliptical cage enclosed by 6 cubes. The largest sphere that can fit into these cages without touching the van der Waals surface of the framework is ~32 for the -cage and ~8.5 for the -cage, Figure 3.8. Figure 3.7. (a) Single-crystal structure of lta -ZMOF, (3.3) (yellow sphere represents vdw sphere) with (b) zeolite LTAlike network topology. (c) In (3.3) twelve MOCs are connected through a series of sodi um ions to generate (d) an -cage (green tile) that can accommodate a sphere with diameter of ~32 and six MOCs (red tile) assemble a cage (yellow tile) that can fit a sphere of ~8.5 in diameter. d) c) b) a)

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135 Figure 3.8. MOCs are connected through hydrogenbonding water molecules and sodium atoms (top), yielding an -cage (bottom left) and a -cage (bottom right), which comprise the ltaZMOF. Topologically, the framework can be viewed as an LTA like network or an augmented version of reo when the hydrogen-bonded and sodium -bridged vertex-vertex connections are considered. However, the structure can be interpreted as nbo if only connections through sodium ions are considered.

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136 Figure 3.9. (Top) the MOC in compound (3.4) showing simultaneou s coordination of the doubly deprotonated ligand molecules (HImDC A) to Cd (buff) and K (violet). The presence of hydrogen atoms midway between carboxylate ions is due to intramolecular H-bonds. The figure shows 24 K+ ions coordinated to the MOC but it should be noticed that each K+ ion is sharing coordination to adj acent 3 MOCs (bottom, disordered coordinated water molecules omitted for clarity), thus net number of K+ ions that belong to a MOC is 8. Compound (3.4) was obtained through simila r reaction conditions of (3.2) but substituting Zn2+ by Cd2+ ions, Figure 3.9. In the crystal structure of (3.4) the MOCs are

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137 connected through coordination of the outer carboxylate f unctionalities to K+ ions. In a similar manner to compound (3.2) four, tetrahedrally arranged, K+ ions link four MOCs through their vertices resulting in the AST topology of (3.4) Each K+ ion is coordinated to three bi-dentate car boxylate functionalities (O K distances 2.699 2.946) and additional disordered water molecules (O K distances 1.766 3.203). Substituting K+ ion in (3.4) by Cs+ ions in (3.5) under essentially the same reaction conditions, resulted in a ZMOF with AST topology where the MOCs are connected through carbo xylate-coordinated Cs+ ions. Four, tetrahedrally arranged Cs+ ions, link four cubes through a tetrahedral nod e, where the overall connectivity can be represented by the underlying zeolitic AST topology. Each Cs+ ion is geometrically disordered over three, closely-disp laced, positions. Coordination of each Cs+ ion to three bi-dentate carboxylat e functionalities (O Cs distances 2.871 3.292 ) and additional disordered water and DMF solvent molecules (DMF, O Cs distance 3.359 , H2O, O K distances 3.359 3.996 ). The observed disorder of Cs+ ions could be attributed to its larger size as compared to the K+ ion, present in (3.4) Compound (3.7) was prepared in a similar procedure to (3.1) through substituting Co2+ ions for Zn2+. Compound (3.7) contains two distinguisha ble kinds of coordination spheres around Co2+ ions. The Co2+ ions present in the MOC exhibit the intended fac MN3O3 coordination sphere, while those on the exterior of the MOC exhibit trans -MO6 through coordination to four carboxylate oxygen atoms (O Co distance 2.063), and two oxygen atoms from two axial DMF ligands (O Co distance 2.095). The MOCs in (3.7) are simultaneously connected th rough edges (coordinated Co2+ ions) and vertices (charge-assisted H-bonded guanidinium ions)

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138 Compound (3.8), Figure 3.10, represents an attemp t to obtain an isostructural compound to (3.1) however upon substituting Zn2+ by In3+ ions, an interesting observation was made. The MOCs in (3.8) are connected through guanidinium ions but no edge connections through bridging In3+ ions were detected. Although the intended Inbased MOCs were obtained and interconnect ed through guanidinium ions in close similarity to (3.1) it appears that absence of edge connections through In3+ ions might be attributed to the overall 12 charge of the MOC in (3.8) twelve triply deprotonated ligands and eight In3+ ions. The charge balance is atta ined through eight guanidinium ions and four dimethylammonium cations, presumably from solvothermal Figure 3.10. Crystal structure of (3.8) showing the In-based MOC, one dimethylammonium cation, and one H-bonded guanidinium ion.

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139 decomposition of DMF solvent molecules. This observation might point towards the relative importance of the guanidinium ion as a structure directing agent (SDA) in construction of the intended ZMOF. Per the definition of a SDA, being involved in molecular recognition to the re actants and thus imparts orde r, guanidinium ions seem very suited to be regarded as SDA in the synthesis of the above ZMOFs. However, in synthesis of zeolites, the clos ely related and widely employed role of “template” refers mostly to a guest molecule, usually cationic ammonium species, that direct the assembly of reactants into a specific topology that is not accessible in absen ce of that specific template, might not apply to our case. This is mainly due to that for an ionic or molecular species to be considered as a true templa te in a reaction, it shoul d be able to undergo facile removal of the construct, most commonly through solvent or ion exchange processes. This very aspect of a template is widely encountered in zeolite chemistry and in ZMOFs constructed through the single-me tal-ion MBB approach. However, in the ast ZMOFs presented herein, the guanidinium i ons represent an integral part of the framework that sustains its integrity and st ructural stability. Moreover, we were not successful in our attempts to, post-synthetical ly, exchange guanidinium ions by a variety of ammonium ions or alkali metal ions. This indicates that it is more appropriate to consider guanidinium ions as S DAs while the question, in compounds (3.1) (3.6) and (3.7) of whether or not guanidini um ions are necessary to obtain those compounds. As in those compounds the extra metal ions provide the edge-linkage be tween the MOCs, the importance of vertex linkage through guani dinium was of concern. Therefore, we conducted the same experiments for compounds (3.1) (3.6) and (3.7) but in absence of guanidinium ions and were not successful in isolating any crystalline or solid product,

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140 where the reaction mixture remains as clea r solution. This observation led us to the conclusion that guanidinium ions are acting as true SDAs, i.e. in absence of such species the MOCs, formed in situ and remained as dissolved species were not able to arrange in a manner appropriate for the e dge-linkage to establish. 3.1.3 Experimental All materials and methods are described in chapter 2, unless otherwise noted. All the ZMOFs reported herein are based on the 1 H -4,5-imidazoledicarboxylic acid (H3ImDC) ligand. Diand tri-deprotonated liga nd molecules in the crystal structures reported are abbreviated HImDC and ImDC, re spectively. All metal salts, solvents, and the organic ligand, H3ImDC, were purchased from Aldrich Chemicals and used as received without further purif ication. All values for yield% reported are based on the amounts of transition metal used. All compounds were prepared by the author except compound (3.3) prepared by Jacilynn A. Brant, and compound (3.6) prepared by Amy J. Cairns. Those compounds were included to th e close relation to th e approach described earlier and to demonstrate the versatility of this approach towards construction of ZMOFs based on the directed assembly of MOCs as SBBs. Synthesis of (3.1). H3ImDC (0.2 mmol), Zn(NO3)2 6H2O (0.2 mmol), N,N`dimethylformamide, DMF, (1 mL), H2O (1 mL) and guanidinium nitrate (0.2 mmol) were mixed in a 25 mL scintillation vial. The reaction mixture was then heated to 115C for 12 h and left to naturally cool down to room temperature. The resulted colorless polyhedral crystals were collected, wash ed with methanol and let to air-dry (0.018g, 28.8% yield).

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141 The as-synthesized material is formulated as C92H128N56O60Zn12 and is insoluble in water and common organic solvents. FT-IR (4000–600 cm-1): 1654 (vs), 1557 (m), 1547 (m), 1471 (s), 1397 (s), 1359 (w), 1255 (m), 1110 (m ), 867 (w), 837 (w), 818 (m), 798(w), 669 (vs). Synthesis of (3.2). H3ImDC (0.2 mmol), Zn(NO3)2 6H2O (0.2 mmol), DMF (1 mL), H2O (1 mL) and potassium chloride (0.2 mmol) were mixed in a capped 25 mL scintillation vial. The reaction mixture was then heated to 115C for 12 h and left to cool down naturally to room temperature. The resu lted colorless polyhedral crystals were collected, washed with methanol and le t to air-dry (0.026g, 31.8% yield). The assynthesized crystalline mate rial is formulated as C75H83N29O65Zn8K8 and is insoluble in water and common organic solvents. FT-IR (4000–600 cm-1): 1664 (m), 1558 (w), 1486 (vs), 1413 (w), 1354 (w), 1303 (m), 1253 (m), 1116 (w), 784 (m), 661 (vs). Synthesis of (3.3). H3ImDC (0.087 mmol, 13.6 mg), Cd(NO3)2 4H2O (0.0435 mmol, 13.4 mg), N,N’-diethylformamide (1 mL), ethanol (0.25 mL), piperazine (0.1 mL, 0.58 M in DMF), sodium hydroxide (0.1 mL, 0. 174 M in ethanol), and 2,4-pentanedione (0.1 mL, 0.174 M in ethanol) were added to a 25 mL scintillation vial, which was then sealed, heated to 85 C and cooled to room temperature at a rate of 1 C/min to produce colorless, hexagonal prism-like crystals formulated as C70H132N28O90Cd8Na8 (0.0137 g, 64.7% yield). FT-IR (4000–600 cm-1): 1650.25 (w), 1622.59 (w), 1548.82 (s), 1484.49 (vs), 1437.5 (s), 1379.16 (s), 1298.34 (m), 1253.75 (m), 1217.09 (w), 1110.98 (m), 997.18 (w), 975.02 (w), 846.39 (w), 786.95 (s), 667.49 (vs), 655.87 (vs), 613.00 (s)

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142 Synthesis of (3.4). H3ImDC (0.2 mmol), Cd(NO3)2 4H2O (0.2 mmol), DMF (1 mL), H2O (1 mL) and potassium chloride (0.2 mm ol) were mixed in a scintillation vial (23 mL). The reaction mixture was then heated to 115C for 12 hours and left to cool down naturally to room temperature. Few colo rless polyhedral crystals were collected for characterization by single-cry stal X-ray diffraction. The as-synthesized material is formulated as C240H96N96O274K32Cd32, which insoluble in water and common organic solvents. Synthesis of (3.5). H3ImDC (0.2 mmol), Cd(NO3)2 4H2O (0.2 mmol), DMF (1 mL), H2O (1 mL) and cesium chloride (0.5 mmol) were mixed in a 25 mL scintillation vial. The reaction mixture was then heated to 115C for 12 hours and left to cool down naturally to room temperature. Few colorless polyhedral crystals we re collected, washed with methanol and let to ai r-dry (0.017g, 16% yield). The as-synthesized material is formulated as C288H192N112O240Cd32Cs32 and is insoluble in common organic solvents. FT-IR (4000–600 cm-1): 1657 (m), 1542 (w), 1483 (s), 1378 (m), 1334 (vs), 11304 (s), 1255 (w), 1112 (m), 832 (s), 786 (w), 661 (m). Synthesis of (3.6). H3ImDC (0.2 mmol), Mn(NO3)2 4H2O (0.2 mmol), DMF (1 mL), acetonitrile (1 mL) and guanidinium n itrate (0.2 mmol) were mixed in a 25 mL scintillation vial. The reaction mixture was then heated to 115C for 12 hours during which colorless polyhedral crystals were obtained, formulated as C358H240N230O244Mn49. The crystals were collected, washed with methanol and let to air-dry (0.0136g, 22.7% yield). The as-synthesized material is inso luble in water and common organic solvents.

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143 FT-IR (4000–600 cm-1): 1653 (s), 1541 (w), 1473 (w), 1380 (vs), 1352 (s), 1245 (m), 1103 (m), 833 (m), 668 (s). Synthesis of (3.7). H3ImDC (0.2 mmol), Co(NO3)2 4H2O (0.3 mmol), DMF (1 mL), and guanidinium nitrate (0.2 mmol) were mixed in a 25 mL scintillation vial. The reaction mixture was then heated to 115C for 12 hours during which pink polyhedral crystals were obtained. The crys tals were collected, washed w ith methanol and let to airdry (0.053 g, 61% yield). The as-synthes ized material is formulated as C358H240N221O245Co50 and is insoluble in water a nd common organic solvents. FT-IR (4000–600 cm-1): 1652.1 (s), 1544.3 (s), 1465.8 (vs), 1393.5 (s), 1252.6 (m), 1104.3 (s), 865.9 (w), 796.5 (w), 669.6 (vs), 625.5(m). Synthesis of (3.8). H3ImDC (0.2 mmol), In(NO3)2 4H2O (0.3 mmol), DMF (1 mL), and guanidinium nitrate (0.2 mmol) were mixed in a 25 mL scintillation vial. The reaction mixture was then heated to 115C for 12 hours during which few colorless polyhedral crystals were isolat ed and subsequently used for single-crystal X-ray analysis. The as-synthesized material is formulated as C272H288N192O337In32 using single-crystal Xray data. X-ray Crystallography. All single-crystal X-ray di ffraction studies reported were conducted on a Bruker-AXS SMART APEX/CCD diffractometer using MoK radiation ( = 0.7107 ) operated at 2000 W power (50 kV, 40 mA). The X-ray intensities were measured at 100(2) K. The frames were integrated with SAINT 13 software package with a narrow frame algorith m. The structure was solved using direct methods and refined by full-matrix least-squares on F 2. All crystallographic

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144 calculations were conducted with the SHELXTL 5.1 program package. 14 All nonhydrogen atoms, except for disord ered solvent molecules, we re refined anisotropically, and hydrogen atoms were placed in geometrically calculated positions and included in the refinement process. Additional details are presented in the corresponding tables. 3.1.4 Conclusion Herein, we demonstrate that the utilization of MOPs as SBBs represents an interesting approach towards rational design a nd synthesis of nanostr uctures, specifically ZMOFs. MOCs, the MOPs of significance, bears structural similiarity to the D4Rs peroiodic building blocks encountered in certa in zeolites and hence offer the potential to target and construct zeolite-like metal-orga nic frameworks sharing the same topology to their inorganic counterparts. The aforem entioned SBBs contain a hierarchy of information regarding the evol ution of single-metal ions, wi th anticipated coordination geometries, deemed as rigid and directional ve rtices, via heterochelation, into MOPs that can be used as defined high-connected buildi ng blocks to yield zeolitic frameworks. This approach carries promising potentials to util ize other MOPs as highly-connected SBBs in construction of specific networks where the SBB serves as the vertex figure of the desired net.

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145 3.2 Insight Into the Self-assembly of MOCs 3.2.1 Introduction Metal–organic materials (MOMs) represen t a family of func tional solid state materials with great potentials to answer a number of current demanding applications such as gas separation and storage, drug deli very, catalysis, small molecules sensing, ion exchange, and CO2 sequestration .15 Such attributes are pertinent to the intrinsic characteristics of MOMs includ ing crystallinity, rigidity, and, in many cases, porosity.16 The crystalline nature of MOMs facilitate s unambiguous structural characterization, permitting better understanding of underlying structure function relationship and subsequently enhanced contro l over the targeted properties.17 It is through identification of the underlying fundamental structural entities in MOMs, widely known as the molecular building blocks (MBBs), that rati onal design strategies for construction of functional MOMs were conceived, and further successfully implemented.18 The MBB appro ach for construction of MOMs encompasses the in situ preparation of rigid and directional MBBs through self -assembly of judiciously designed molecular precursors encoded with appropriate information, compli mentary molecular recognition sites held at specific spatial orientation, under well defined reaction conditions. Due to the relatively mild reaction conditions employed in sol vothermal syntheses of MOMs, the built in rigidity, functionality, and dire ctionality of MBBs are main tained throughout the reaction pathway, facilitating reliable prediction of the underlying topologies in targeted constructs. Hence, geometrical design princi ples for construction of MOMs based on the MBB approach were identified and further su ccessfully implemented into rational design

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146 strategies towards construc tion of several functional MOMs.19 From the above, it is evident that judicial choice of pre-program med MBBs, as well as careful design of the reaction conditions necessary to afford such MBBs, in situ are two inseparable elements of design in any rational strategy for constr uction of functional MOMs. However, despite the wide interest in developing new stra tegies to construct MOMs with specific topologies and/or functionalities utili zing a wide variety of chemically accessible MBBs, systematic investigations aiming to probe th e various effects associated with the wide range of reaction variables on the nature of isolated product(s) are still lacking.20 Valuable information obtained through such systematic investigations could provide useful insight into the crucial roles associat ed with various reacti on variables facilitating both the in situ preparation of targeted MBBs and, s ubsequently, their self-assembly into targeted structures. Accordingly; better unde rstanding of the complexity involved in solvothermal reaction systems could be uti lized to enhance our design strategies for construction of functional MOMs .21d Metal–organic polyhedra (MOPs), a subset of MOMs, are finite supermolecular assemblies with various functionalities, tailorable voids, and fairly predictable geometries.21 Pertinent to their ability to enclos e a confined space, MOPs have been utilized as “nano-reactors” f acilitating specific chemical transformations of encapsulated guest molecules.22 In addition, MOPs with peripheral functionalities can further be employed as supermolecular building blocks (S BBs) with built-in structural information, decorating and expanding the vertices of ta rgeted 3D nets, towa rds construction of metal organic frameworks (MOFs). This approach has been developed and successfully implemented by our group, among others, allo wing access to non-default, n-connected (n

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147 8) nets with enhanced c ontrol over the resulted topology.23 Among the readily accessible MOPs is the imidazolate-based me tal–organic cube (MOC), reported by us, 24and recently employed by our group as an 8-connected SBB forging novel zeolitelike metal organic frameworks (ZMOFs). The MOC, constructed through single-metal-ion MBB approach, represents a relatively simple system suited for the intended systematic study and thus is the focus of our investigations herein. Solvothermal reaction of 2,2'-(1 H -imidazole-4,5-diyl)d i-1,4,5,6-tetrahydropyrimidine, HL1 and CoCl26H2O, under the reported conditi ons, resulted in discrete, cationic, CoIII-based MOCs, 3.9 This system represents a good study case to probe the relative effects associated with the various reaction c onditions on the self-assembly and/or crystallization process of MOCs due to (i) available crystal structure of 3.9 (ii) solubility of 3.9 in water and a variety of polar solvents to yield solvated MOCs, 3.9S ,where structural integrity of the dissolved cubes is maintained in aqueous solution, (iii) the profound and well-documented effects of paramagnetic high-spin CoII ions on the chemical environments, especially protons of coordinated ligand molecules, thus allowing utilization of solution NMR spectrosc opy techniques to pr obe the nature of solvated species formed immediately after mixing, (iv) the presence of multiple protons in L1 that proved useful in structural ch aracterization through solution NMR studies conducted herein, and (v) presence of charact eristic absorption bands in the optical spectrum range for the CoL1 coordination complex(es), permitting solution characterization through UV–vis spectroscopy. In addition, a relatively slow aerobic redox transformation of c oordinated paramagnetic CoII, in reactants, into diamagnetic CoIII, in products, permits accurate contrast of reaction products from reactants.

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148 3.2.2 Results and Discussion Analysis of X-ray Crystal Structures. In the crystal struct ures described below, each mono-deprotonated L1 molecule coordinates to the metal ions in a bis-bidentate fashion and can be considered as a li near linker bridging two metal ions. In L1 two of the four 1,4,5,6-tetrahyd ro-pyrimidin-2-yl ( thp ) nitrogen atoms are pyridine-type (N3`) while the other two are pyrrole-t ype atoms (N1`). Coordination to metal ions occurs only through the N3` atoms of the thp rings, leaving the N1` at oms available as hydrogen bond donors towards halides, nitrates, sulfates, or tetraflouroborates c ounterions present in compounds 3.9-3.12 and 3.9(a-f) Single Crystal X-ray Structure Analysis of 3.9. In the crystal structure of 3.9 Figure 3.11, discrete MOCs cr ystallize in the cubic Pa -3 space group and are held together through a networ k of multiple weak C H Cl hydrogen bonds. In 3.9 the Co N bond distances of 1.911 1.949 ( thp ), and 1.890 1.906 (imidazolate) are in good agreement with bond distan ces found in similar CoIII complexes as determined from analysis of Cambridge Structural Database (CSD, April 2009). The pyrrole-type nitrogen atoms of the thp rings reside on the external surfa ces of the MOCs and are involved in hydrogen bond interactions to chloride ions. Residual elect ron density in the Fourier difference map near N1` atoms were assigne d to hydrogen atoms, further supporting the proposed crystallographic model of mono deprotonated, imidazolate based ligand molecules. Each MOC bears a total of twel ve positive charges where charge balance is attained by twelve chloride counterions, renderi ng it freely soluble in water, DMF, and

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149 Figure 3.11. Crystal structure of the me tal–organic cube (MOC) in 3.9 chloride counterions omitted for clarity. C (gray), N (blue), H (white), Co (deep red). several alcohols. Six of the chloride ions decorate the faces of a MOC, where each chloride ion is hydrogen bonded to three of the four nitrogen atoms on one face of the MOC (N1` Cl distances of 3.096 3.185 ). In addition, each of these chloride ions is hydrogen bonded to two hydrogen atoms (H Cl distances of 2.697 2.739 , normalized data) on two C5` atoms of a neighboring cube.

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150 Figure 3.12. (Left) crystal packing of the MOCs in 3.9 and (right) total of four MOCs in the unit cell are highlighted and can be descri bed as fourfold interpenetrated arrangement of primitive cells The asymmetric unit in 3.9 contains a total of four MOCs adopting a primitive cubic packing due to different orientations of each set of the MOCs, Figure 3.12. One chloride ion occupies the cavity inside the MOC and the additional five chloride ions, geometrically disordered over six positions, reside near the edges of the MOC, hydrogen bonded to one N1` atom (N1` Cl distance of 3.241 ) while simultaneously hydrogen bonded to two hydroge n atoms on the surface of a neighboring MOC (C H Cl distances of 2.697 2.788 , normalized data). On each of the six faces of a MOC in 3.9 two parallel imidazolate rings are separated by a centroid-to-centroid distance of 5.507 . This distance was f ound to be dependent on the nature of counterions present in the crysta l structure, and could be attri buted to variation in the size of counterion, as well as, to the number a nd strength of hydrogen bond interactions to N1` atoms of thp rings. In the crystal structure of 3.9 geometrical disorder between two sites for the methylene carbon atoms C5` in the thp rings is observed.

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151 Table 3.2.1. Crystallographic data for 3.93.12 and 3.9(a-d) Compound 3.9 310 3.11 3.12 Formula C132 H180N72O4Co8Cl12 C132H126N84O40In8 C56H88N32Ni4 C14H22N8O4Cd Fwt, Z 3729.96, 4 4442.39, 3 1700.42, 4 478.80, 4 Crystal system cubic trigonal orthorhombic monoclinic Space group P a-3 R -3 P bca P 21/n a b c, 25.1026(13) 25.1026(13) 25.1026(13) 90 90 90 28.1055(4) 28.1055(4) 19.1669(6) 90 90 120 17377(6) 17522(6) 24.717(8) 90 90 90 12.909(2) 12.0710(19) 12.950(2) 90 115.858(2) 90 Wavelength, 0.71073 1.54178 0.71073 0.71073 T, K 100(2) 100(2) 100(2) 100(2) Final R indices, [I>2 (I)] R1 = 0.0493, wR2 = 0.1350 R1 = 0.058, wR2 = 0.1352 R1 = 0.0660, wR2 = 0.1459 R1 = 0.0401, wR2 = 0.1005 GOF on F2 1.026 1.025 1.070 1.051 Compound 3.9a 3.9b 3.9c 3.9d Formula C132H156N72O18Co8Br12 C135H149N73O56S6Co8 C138H156N72O8S3Co10Cl16 C132H158N84O57Co8 Fwt, Z 4469.65, 2 4362.07, 2 4207.23, 2 4304.86, 2 Crystal system monoclinic monoclinic monoclinic monoclinic Space group P 21/n P 21/n C 2/ m P 21/n a b c, 17.758(5) 19.380(3) 24.772(6) 90 90.257(16) 90 203067(9) 18.7195(8) 249104(10) 90 931820(10) 90 28550(2) 225268(19) 19.4189(16) 90 131.977(3) 90 20.1771(5) 19.4260(5) 22.8118(6) 90 90 90 Wavelength, 1.54178 1.54178 1.54178 1.54178 T, K 293(2) 100(2) 293(2) 100(2) Final R indices [I>2 (I)] R1 = 0.0825, wR2 = 0.261 R1 = 0.0826, wR2 = 0.198 R1 = 0.0851, wR2 = 0.1985 R1 = 0.0546, wR2 = 0.1076 GOF on F2 0.975 1.017 0.777 0.836 Single Crystal X-ray Structure Analysis of 3.9a. In the crystal structure of 3.9a, the cationic charges of CoIII MOCs are balanced by a total of twelve bromide counterions and crystallize in the monoclinic P 21/n space group. Six bromide counterions decorate the faces of a MOC where hydrogen bond intera ctions between bromide ions and the pyrrole-type nitrogen atoms are present (N1` Br distances of 3.0 3.394 ), in a similar manner observed in 3.9. One bromide ion occupies the cavity inside the MOC and the additional 5 bromide ions are highly disordered through the st ructure. Geometric disorder to the aliphatic carbon atoms C5` of coordinated ligand mol ecules is present. The CoN bond distances, 1.916 1.986 ( thp ) and 1.841 1.907 (imidazolate), closely matches those observed in 3.9. On each of the six faces of a MO C, two parallel imidazolate rings are separated by centroid-to -centroid distances of 5.627 5.697

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152 Figure 3.13. Crystal packing of the MOCs in 3.9 a Single Crystal X-ray Structure Analysis of 3.9b. MOCs in 3.9b crystallize in the monoclinic, P 21/ n space group where each face of a MOC is decorated by sulfate counterion H-bonded to N1` atoms of thp rings, Figure 3.14, 3.14. Each sulfate counterion is hydrogen bonded through tw o oxygen atoms to four N1` (N1` O–S distances of 2.824 3.057 ). Such multiple interactions between each sulfate ion and the N1` atoms appear to cause a noticeable decr ease in the centroid-to-centroid distance (5.375 5.408 ) between the two parallel imidazola te rings on each of the six faces of the cube, shorter than those observed in 3.9 and 3.9a for chloride (5.505 ) and bromide (5.627 5.697 ) counterions, respectively. The Co–N bond distances of 1.917 1.994 ( thp ), and 1.89 1.895 (imidazolate), closely matches those observed in 3.9 and 3.9a

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153 Figure 3.14. Crystal structure of the me tal–organic cube (MOC) in 3.9 b C (gray), S (yellow), O (red) N (blue), H (white), Co (deep red). Figure 3.15. Crystal packing of the MOCs in 3.9 b

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154 Single Crystal X-ray Structure Analysis of 3.9c. In 3.9c discrete CoIII-MOCs crystallize in the monoclinic C2/m space group. The twelve positive charged on each MOC are counterbalanced by two [CoCl4]2species and eight Clions. The [CoCl4]2ions are involved in weak hydrogen bond in teractions to the adjacent MOC (C H Cl distances of 2.608 2.935, normalized data), Figures 3.16 and 3.17. Several of the chloride counterions are H-bonded to the faces of the MOC (N Cl distances of 3.21 3.615 ). In the MOC, Co–N bond distances of 1.945 1.953 ( thp ) and 1.88 1.901 (imidazolate) are in close agreem ent with those observed in compounds 3.9 and 3.9(a-b) On each of the six faces of a MOC, two parallel imidazolate rings are separated by centroid-tocentroid distances of 5.569 5.58 . Figure 3.16. Crystal structure of 3.9c the MOC is shown surrounded by [CoCl4]2and chloride ions. C (gray), Co (red), N (blue), H (white), Cl (green), solvent molecules omitted for clarity.

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155 Figure 3.17. Crystal packing of the MOCs in 3.9c Table 3.2.2 Crystallographic data for 3.9e and 3.9f Table 3.2.3. Summary of the experimental conditions for 3.9 3.12 and 3.9 (a-e) Compound 3.9 3.9a 3.9b 3.9c 3.9d 3.9e 3.9f 3.10 3.11 3.12 Metal ion Co3+ Co3+ Co3+ Co3+ Co3+ Co3+ Co3+ In3+ Ni2+ Cd2+ Counterion Cl Br (SO4) 2 [CoCl4] (NO3) (BF4) Cl (NO3) (NO3) (NO3) Solvent H2O/ DMF H2O/ DMF H2O/ DMF H2O/DMSO H2O/DEF H2O/ DMF H2O/ HMP A DEF/Et OH DMF DMF H-L1 equiv 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1 1 Temperature 115C 115C 115C 115C r.t. 115C 115C 85C 85C 85C 1e 1f Formula C138H178N74O16B12Co8F48 C132H168N72O40Co8Cl12 Fwt, Z 4646.7, 4 4300.22, 4 Crystal system monoclinic monoclinic Space group C 2/ c C 2/ c a b c, 31.693(3) 20.047(4) 32.309(6) 90 109.50(3) 90 33.008(8) 19.253(5) 32.654(7) 90 116.116(5) 90 Wavelength, 1.54180 1.54180 T, K 100(2) 100(2) Final R indices [I>2 (I)] 0.0789, wR2 = 0.1715 0.0714, wR2 = 0.1662 GOF on F2 0.947 1.022

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156 Single Crystal X-ray Structure Analysis of 3.9d. The cationic MOCs in 3.9d crystallize in the P 21/ n space group, Figure 3.18, where the cationic charges are balanced by twelve disordered and/or hydrated nitrat e counterions. One nitr ate ion occupies the cavity inside the MOC and is hydrogen bonded to the C2 hydrogen atoms of the imidazolate rings, (CO distances of 2.268 2.901 ). The remaining nitrates ions are hydrogen bonded to the N1` atoms of the liga nd molecules, decorating the faces (NO distances of 2.903 3.067 ) and the edges (NO distances of 2.894 2.981 ) of the MOC. In the crystal structure of 3.9d the MOCs are held t ogether through bridging, hydrogen bonded, nitrate counterions. In the MOC, Co–N bond distances of 1.932 1.95 ( thp ) and 1.899 1.921 (imidazolate) are in close ag reement with those observed in compounds 3.9 and 3.9(a-c) On each of the six faces of a MOC, two parallel imidazolate rings are separated by centroid -to-centroid distances of 5.623 5.69 . Figure 3.18. Crystal packing of the MOCs in 3.9 d

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157 Single Crystal X-ray Structure Analysis of 3.9e. The cationic MOCs in 3.9e crystallize in the C 2/ c space group, Figure 3.19, where the cationic charges are balanced by twelve (BF4)counterions. One disordered (BF4) ion occupies the cavity inside the MOC while the remaining disordered (BF4) ions are hydrogen bonded to the N1` atoms of the ligand molecules, deco rating the faces and edges of the MOC. In the crystal structure of 3.9e the MOCs are held together through bridging, hydrogen bonded, (BF4) counterions. In the MOC, Co–N bond distances of 1.937 1.940 ( thp ) and 1.896 1.918 (imidazolate) are in close agreem ent with those observed in compounds 3.9 and 3.9(ad) In 3.9e each MOC cocrystallize with two DMF solvent molecules hydrogen bonded to two faces of the MOC, (NO distances of 2.806 2.849 ). On each of the six faces of a MOC, two parallel imidazolate rings are separated by centroid-to -centroid distance of 5.631 5.672. Figure 3.19. Crystal packing of the MOCs in 3.9 e.

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158 Single Crystal X-ray Structure Analysis of 3.9f. The cationic MOCs in 3.9f crystallize in the C 2/ c space group, Figure 3.20, where the cationic charges are balanced by twelve chloride counterions. One chloride ion occupies the cavity inside the MOC. The remaining chloride ions are hydrogen bonded to the N1` atoms of the ligand molecules, decorating the f aces (NCl distances of 3.139 3.231 ) and the edges (NCl distances of 2.888 3.141 ) of the MOC. In the crystal structure of 3.9f the MOCs are held together through bridging, hydrogen bonde d, water molecules. In the MOC, Co–N bond distances of 1.937 1.956 ( thp ) and 1.895 1.909 (imidazolate) are in close agreement with those observed in compounds 3.9 and 3.9(a-e) On each of the six faces of a MOC, two parallel imidazolate rings ar e separated by centroid-t o-centroid distances of 5.641 5.661 . Figure 3.20. Crystal packing of the MOCs in 3.9 f.

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159 Single Crystal X-ray Structure Analysis of 3.10. The cationic InIII-MOCs in 3.10 crystallize in the R -3 space group, Figures 3.213.22, the cationic charges are balanced by twelve nitrate counterions. One n itrate ion occupies the cavity inside the MOC. Six nitrates ions are hydrogen bonded to the N1` atoms of th e ligand molecules on the faces of the MOC (NO distances of 2.706 3.032 ). In the crystal structure of 3.10 the MOCs are held together through bridgi ng, hydrogen bonded, water molecules. In the MOC, In–N bond distances of 2.176 2.25 ( thp ) and 2.203 2.223 (imidazolate). On each of the six faces of a MOC, two parallel imidazolate rings are separated by centroidto-centroid distances of 6.465 . Figure 3.21. Crystal structure of 3.10 the MOC is shown, disordered nitrate counterions omitted for clarity. C (gray), In (green), N (blue), H (white).

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160 Figure 3.22. Crystal packing of the MOCs in 3.10. Single Crystal X-ray Structure Analysis of 3.11. In the crystal structure of 3.11 discrete molecular squares crys tallize in the orthorhombic P bca space group, Figure 3.23, and constructed from octahedrally coordinated Ni ions in cis -MN4O2 configuration and bridged through four mono-deprotonated L1 molecules. In the molecular square, each Ni (II) ion is coordinated to nitrat e ion in bidentate fashion resul ting in overall charge neutral molecular squares. Each molecular squa re cocrystallize with two DMF solvent molecules. The four ligand molecules in the molecular squares are hydrogen bonded through N1` atoms of the ligand molecules to four DMF molecules (NO distances of 2.897 2.99 ). Intramolecular Hbonds between the two thp rings of the molecular square are detected (N HN distances of 2.123 2.631 , normalized data). In the molecular squares, Ni–N bond distances of 2.033 2.073 ( thp ) and2.023 2.045 (imidazolate).

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161 Figure 3.23. Crystal packing of the metal organic squares in 3.11. Single Crystal X-ray Structure Analysis of 3.12. The infinite molecular chains in 3.12 result from associati on of the linear linker, L1 and the octahedrally coordinated Cd ions in distorted octahedral cis -MN4O2 geometry, Figure 3.24. Each ligand in the molecular chains is H-bonded to one DMF so lvent molecule and to a nitrate ion of adjacent chain. Furthermore, intramolecular H-bonds exist between the sp3-type N1` atoms of the coordinated ligand molecules (N HN distances of 2.249 2.588 , normalized data). The ligand molecules ar e mono-deprotonated resulting in overall charge neutral molecular chains. In 3.12 Cd–N bond distances of 2.231 2.269 ( thp ) and 2.311 2.374 (imidazolate) are observed.

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162 Figure 3.24. Crystal structure of 3.12 molecular chains of [Cd( L1 )(NO3)]n, C (gray), Cd (buff), N (blue), H (white), O (red). DM F solvent molecules omitted for clarity. MALDI TOF MS Experiments. While the calculated molecular weight of the MOC, including chloride counterions, is 3672.815 amu, the MALDITOF mass spectrum of 3.9 exhibits a molecular ion peak of si ngly-charged species with wide isotope distribution and a maximu m relative intensity at m/z = 3238.353 (calcd 3238.008) assigned to [Co8(C11N6H14)12]+, along with several other molecular fragments at m / z = 1966.323 (calcd 1966.632) [Co5(C11N6H16)2(C11N6H14)5(H2O)3]+, 1677.198 (calcd 1677.449) [Co5(C11N6H16)(C11N6H14)5]+, 1444.994 (calcd 1445.305) [Co5(C11N6H14)5]+, 1157.737 (calcd 1157.250) [Co4 (C11N6H14)4]+, 811.339 (calcd 811.266) [Co2(C11N6H14) (C11N6H15)2]+, and 522.164 (calcd 522.204) [Co2(C11N6H15)2]+, Figure 3.25. The observed molecular ion peak was assigned to a single ionization of the MOC after dissociation of twelve HCl molecules. Wh ile observation of such fragments of the MOC could be explained as products of mol ecular ion fragmentation, the possibility of establishing equilibra between the MOC and its fragments, in solution during sample

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163 preparation, prior to subjecting the sample to ionization canno t be ruled out based solely on the MALDI TOF MS results. In another experiment, MALDI TOF MS spectrum was acquired for the sample subjected to soluti on NMR spectroscopy, direc tly after mixing of HL1 (0.15 mmol) and CoCl26(H2O) (0.1 mmol) in 1 mL aqueous solution at room temperature, in order to characterize the sp ecies present in the reaction mixture. The obtained spectrum was very similar to th at obtained for dissolved crystals of 3.9 with the exception of the molecular ion peak for the MOC. This could simply be due to different sample treatment where it is known that MOPs are generally unstabl e for detection under common MS techniques.16 However; this observation str ongly suggests formation of the MOC, or at least several large fragments of the MOC, simply upon reactants mixing in aqueous solution at ambient conditions. Figure 3.25 Schematic representation of the MOC and its major fragments observed in the MALDI TOF mass spectra of 3.9

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164 Figure 3.26 Molecular ion in the MALDI-TOF MS for 3.9 Nuclear Magnetic Resonance Experiments. The ligand molecule, HL1 is a symmetrically di-substituted imidazole deri vative bearing amidine functional groups and methylene hydrogen atoms in the two thp rings. Therefore, the char acteristic features of such functionalities are e xpected to be observed in the NMR spectra of HL1 For imidazole, even at high pH aqueous solution, rapid prototropic taut omerization involving the ring’s nitrogen atoms N1(3) results in an observed average chemical environment for the C4(5) atoms.17 Amidine functional groups, in ge neral, are also known to undergo

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165 rapid prototropic tautomerization 31which if present in aqueous solution of HL1 is expected to result in an observed average chemical shift for the C4`(6`) atoms of the thp rings. In addition to prototr opic tautomerization, protonation of the basic nitrogen atoms of amidine and imidazole, especially in aque ous solution, is expected to form amidinium and imidazolium ions, respectively, stabi lized by charge delocalization through resonance. Therefore, it is expected that either protonation or rapid tautomerization involving the basic nitrogen functionalities present in H -L1 or a combination thereof, in aqueous solution, will result in observed averag e chemical shifts for C4(5) of imidazole and the C4`(6`) of thp rings, Scheme 3.1. Scheme 3.1 Numbering and prototropi c tautomerization in HL1 Indeed, the ligand molecules, in either D2O or DMSO-d6 solution, exhibit a simple 1H NMR pattern (DMSO-d6, 399.78 MHz): = 7.15 (s, 1 H), 3.35 (t, J = 5.65 Hz, 8 H), 1.75 ppm (quin, J = 5.70 Hz, 4 H), 13C NMR (DMSO-d6, 100.54 MHz): = 153.46, 144.41, 132.59, 39.67, 20.16 ppm. The 13C NMR spectrum of H -L1 in DMSO-d6 clearly indicates chemical shift equiva lence for C4`(6`) atoms of the thp rings ( = 39.67 ppm) as well as the C4(5) atoms of the imidazole ring ( = 132.59 ppm). The simple pattern for the DMSO-d6 1H NMR spectrum of H -L1 indicates absence of geminal

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166 Figure 3.27 1H NMR spectrum of HL1 in D2O acquired at 298 K with inserts of magnified (a) quintet at 1.97 ppm and (b) tr iplet at 3.5 ppm. = Solvent peak, x = DSS peaks, used as internal standard. coupling between homotopic methylene protons which could be ascribed to symmetry introduced to the thp ring, mirror plane through C2 ` and C5`, due to a fast tautomerization and/or protonation of the basi c amidine nitrogen atoms, vide supra. The D2O 1H NMR spectrum, pD = 11.2, of H -L1 (D2O, 399.78 MHz): = 7.47 (s, 1 H), 3.5 (t, J = 5.7 Hz, 8 H), 1.97 ppm (quin, J = 5.8 Hz, 4 H) referenced to the signal of DSS at 0 ppm, Figure 3.27, exhibits an identical pattern to that acquired in DMSO-d6 but with noticeable small shifts toward higher frequencie s which could be ascribed to formation of the conjugate acid(s) through proton ation in aqueous solution of HL1 as expected for (b) (a)

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167 such basic functionalities. Formation of the MOC in 1 presumably proceeds through coordination of CoII ion by the pyridine-type nitrogen of imidazole, f acilitating deprotonation of the pyrrole-type nitrogen18 and thus permitting subsequent coordination to a second CoII ion. Chelation of the two cobalt cations occurs through coordination to the pyridine-type nitrogen atoms (N3`) of the thp rings in L1 Subsequent redox process invo lving molecular oxygen as the oxidant results in formation of the CoIII MOCs. The chemically-balanced equation for the overall reaction is described in eq. 3.1. 8 CoCl2+ 12 H -L1 + 2 O2 [Co8L112]Cl12+ 4 HCl+ 4 H2O (3.1) The observation of CoII/III redox process, under the aerobic synthesis conditions of 3.9 appears to be facilitate d through deprot onation of H -L1 and thus indicates a protoncoupled electron transfer reaction. In related CoII-imidazole complexes, where no deprotonation of the imidazole ring occurred, aerobic oxidation of CoII ions was not detected,19 clearly indicating tuneabil ity of the redox potentials for the coordinated metal center through control of the ligand-field strength. Several examples of stable CoIIimidazole complexes can be enc ountered in literature where CoII/III transformation were observed in octahedral Co-N6 complexes containing the imidazolate ligands33a, 34 Upon coordination to Co ions, the symmetry of thp ring is expected to be reduced, compared to free ligand in solution, due to forbidde n tautomerization and/or protonation. The decreased mobility of C–N double bonds in cobalt-coordinated thp rings facilitates isolation of one tautomer of the amidine functional group, characterized through single crystal X-ray diffraction analysis of 3.9 Coordination of L1 in bis-bidentate fashion, to

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168 two cobalt ions results in a spin-spin splitti ng pattern, characteristic of diasteriotopic protons, in the 1H NMR spectrum for diamagnetic products of the reaction mixture. Observation of diasteriotopic me thylene protons in coordinated L1 molecules can be explained by introducing chiral centers (CoIII-N6 tris-chelates) 35 in the complex(es) formed, and thus gives a st rong indication for the formation of the MOC, or its corresponding molecular fragments, in so lution. Furthermore, due to simultaneous coordination of imidazolate ring to two c obalt ions, chemical shift equivalence for imidazolate C4(5) atoms is expected. Indeed, dissolving crystals of 3.9 in D2O (referred to as 3.9S ), at r.t. resulted in 1H NMR spectrum, Figure 4, where the expected diasteriotopic proton spin-spin splitting patterns are observed. The 1H NMR spectrum of 3.9S reveals seven distinct chemical shifts with all the six methylen e protons being diasteriotopic, 1H NMR (D2O, 399.78 MHz): = 6.09 (s, 1H), 3.45 3.56 (m, 2 H), 3.36 3.44 (m, 2H), 3.20 3.31 (m, 2H), 2.80 2.84 (m, 2H), 2.05 2.18 (m, 2H), 1.61 1.75 ppm (m, 2H),Figure 3.28 and Table 3.2.4. In agreement with the proposed assignment for the proton peaks in the 1H NMR spectrum of 3.9S to represent bis-bident ate, cobalt-coordinated L1 molecules, the 13C NMR spectrum (D2O, 100.54 MHz): = 155.7, 143.6, 135.9, 43.7, 39.2, 21.4 ppm, indicates chemical shift equivalence of imidazolate C4(5) atoms (143.6 ppm) and nondegenerate C4` (43.7 ppm) and C6` (39.2 ppm) of the thp rings. Furthermore, as no proton signals were detected in the paramagnetic region of the sp ectrum, it is concluded that aqueous solution of 3.9 contains the diamagnetic, low-spin CoIII complex(es), in agreement with the crystallographic model of CoIII MOCs in 3.9 .Therefore, it is evident that both 1H and 13C NMR spectra of 3.9S indicate presence of L1 molecules coordinated to CoIII ions in a bis-bidentate fashion with suppressed

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169 Figure3.28 1H NMR spectrum (top) and 13C NMR spectrum (below) of 3.9S in D2O, spectra acquired at 298 K, proton spectrum referen ced to the DSS singlet at 0 ppm as internal standard. = Solv ent peak, x = DMF peaks.

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170 Nucleus HL1 3.9S 1H 13C 1H 13C H(2)Im / C2 Im 7.15 (s, 1 H) 144.41 6.09 (s, 1H) 143.6 H6`(a*) thp / C6` thp 3.35 (t, J = 5.65 Hz, 2H) 39.67 3.36 3.44 (m, 2H) 39.2 H6`(e*) thp / C6` thp 3.35 (t, J = 5.65 Hz, 2H) 39.67 3.45 -3.56 (m, 2 H) 39.2 H5`(a) thp / C5` thp 1.75 (quin, J = 5.70 Hz, 2H) 20.16 1.61 1.75 (m, 2H) 21.4 H5`(e) thp / C5` thp 1.75 (quin, J = 5.70 Hz,2H) 20.16 2.05 2.18 (m, 2H) 21.4 H4`(a) thp / C4` thp 3.35 (t, J = 5.65 Hz, 2H) 39.67 2.80 2.84 (m, 2H) 43.7 H4`(e) thp / C4` thp 3.35 (t, J = 5.65 Hz, 2H) 39.67 3.20 3.31 (m, 2H) 43.7 Table 3.2.5. 1H and 13C NMR peak assignments for HL1 in DMSO-d6 and 3.9S in D2O, reported in ppm. a = axial, e = equatorial thp ring protons. prototropic tautomerization of amidine functi onalities. In addition, th e relative integrals of 1H signals strongly indicate pr esence of mono-dispersed sp ecies which we assigned as the dissolved MOCs. The absence of other detectable proton signa ls that could be assigned to either partiall y or uncoordinated ligand mol ecules, strongly suggests formation of 3.9S with maintained integrity of MO Cs in aqueous solution where it is evident that dissociation of 3.9S would result in libration of free ligand molecules and hydrated cobalt ions. Furthermore, addition of excess CoII ions to the D2O solution of 3.9S did not result in any obs erved isotropically-shifted 1H signals, expected upon coordination of L1 to the paramagnetic CoII ions, confirming the stability of 3.9S towards metal ion-exchange in aqueous solution, where L1 molecules remain coordinated to CoIII ions. From the above, it is concluded that dissolution of 3.9 in D2O at r.t., results in formation of solvated MOCs 3.9S with no detectable dissoci ation products. Distortionless enhancement through polarization transfer (DEPT), 1H-1H correlation (gCOSY), and 1H-13C heteronuclear single quantum correlation (gHSQC) NMR experiments for 3.9S further support the chemical shifts and sp in systems assignments, Figures D2-D4 in appendix D. The majority of 1H and 13C NMR signals of 3.9S are shifted toward higher chemical shift values relative to those of HL1 indicating metal ion chelation by the

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171 ligand molecules. However, the 13C NMR signal of the imidazolate C2 atom appears at lower frequency in 3.9S compared to HL1 ( = 0.987 ppm), most probably due to an increase in electron density caused by deprot onation of acidic imid azole proton prior to second Co coordination. To further probe the nature of solvated species, the hydrodynamic radius of the molecular assembly was calculated from m easurement of the diffusion coefficient obtained through 1H 2D DOSY NMR experiment. The NM R diffusion measurements were performed using a 1.2 mM D2O solution of 3.9 on a Varian Inova-500MHz spectrometer equipped with 5 mm Performa II pulsed-field gradie nt probe where the sample was held at 298 0.1 K using a vari able temperature c ontrol unit. For the determination of self-diffusion coefficients, the calibrated 1H 90 pulse of 8 s was used and the sample temperature was equilibrate d at 298 0.1 K (calibrated with neat methanol sample) for at least 10 min prio r to acquisition. The number of accumulation times was fixed at 256 preceded by 4 dummy scans in all measurements. The 1H 2D DOSY spectra were recorded using the convection corrected bipolar pulse pairs stimulated echo pulse sequence (Dbppste_cc) implemented in the Varian Vnmrj software package, Figure D11 (appendix D). The natural logarithm of the ratio of signal integrals, A and A0, in the presence and absence of the pulsed-field gradient, respectively, is proportional to the square, G2, of the gradient magnit ude according to eq. 3.2 ln( A/A0) = D 2( /3) 2G2 (3.2) where is the magnetogyric ratio of 1H, is the interval between the two gradient pulses, and is the gradient pulse width. 36

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172 Constant values of 4 and 100 ms were used for and respectively. The gradient magnitude, g, was calibrated with a known value of D = 18.5 x 10-10 m2 s-1 for heavy water at 298 K .37 In the measurement, a set of 15 diffe rent values of g was employed and the average value of D = 1.73 0.01 x 10-10 m2 s-1 was obtained for the 1H peaks of 3.9S Through the spherical approximation in Einstein-Stokes equation, D = K T / (6 r), where D is the diffusion coefficient measured, T is the absolute temperature, K is Boltzmann constant, and (1.1 x 10-3 kg m-1 s-1 for D2O at 298K) is the solution viscosity, the extracted hydrodynamic radius, r = 11.5 is in close agreement with the radius, ca. 9.25 of the MOC in the crystal structure of 3.9 The larger hydrodynamic radius measured could be accounted for by presence of firs t solvation shell aro und the solvated MOC. To explore the nature of species present in the initial reaction mixture, shortly after mixing, 1H NMR spectrum of a freshly prepared solution of CoCl26H2O (0.0237 g, 0.1 mmol) and HL1 (0.0348 g, 0.15 mmol) in 1 mL of D2O under anaerobic conditions was acquired. The spectrum obtained exhibits a well-resolved pattern of isotropically shifted proton signals, due to coordinati on of ligand molecule s to paramagnetic CoII ions, Figure 3.29. A line-broadening fact or of 10 Hz was introduced to the spectra containing isotropically shifted proton signals via exponential multiplicati on prior to Fourier transformation to enhance the signal-to-noise ratio, 1H NMR (D2O, 399.78 MHz): = 51.3 (br. s., 1H), 23.546 (br. s., 1H), 21.969 (br. s., 1H), 17.105 (br. s., 1H), 13.452 (br. s., 1H), 12.763 (br. s., 1H), 10.608 (br. s., 1H), 10.168 (br. s., 1H), 9.319 (br. s., 1H), 8.68 (br. s., 1H), 7.652 (br. s., 1H), 14.4 (br. s., 1H), 20.7 ppm (br. s., 1H). The 1H NMR spectrum of the reaction mixture revealed 13 different chemical shifts characteristic of both contact and spin-delocaliza tion effects of paramagnetic CoII ions to the 1H signals of

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173 Figure 3.29 (Top) 1H NMR spectrum of the reaction mixture of CoCl2 (0.1 mmol) and HL1 (0.15 mmol) in 1 mL D2O after mixing at 298K, (below) the 4 24 ppm region of the spectrum magnified. = HDO solvent peak used as internal reference at 4.76 ppm.

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174 CoII-coordinated ligand molecules. As the ligan d molecule possess two chelation sites, coordination to one site was considered as a possible explanation for the observed pattern in the 1H NMR spectrum of the anaerobic reaction mixture. This is to be expected, especially in aqueous solution due to co mpetitive protonation of the basic amidine functionality. However, no changes were de tected to the spectrum upon addition of NaOCH3 (0.15 mmol) as a base, suggesting th at the observed spectrum corresponds to bis-bidentate, mono-deprotonated L1 molecules bridging two CoII ions. Interestingly, the number of observed prot on signals matches th e total number of non solvent-exchangeable proton nuclei presen t in the ligand molecule. This observation suggests that each proton is chem ically distinguishable in the CoII complex(es) obtained. One possible model to explain this fi nding assumes non-equivalent chemical environments for the two thp rings through non planar conf ormation of the two rings, with respect to the central imidazole ring. This molecular conformation results in different ring proximity to the coordinated CoII ions. Indeed, the geometrically-optimized model of the simple fragment [Co2( L1 )(H2O)8]3+, Figure 3.30, indicates presence of an intra-molecular hydrogen bond inte raction between N3` atoms of thp rings. This interaction, also detected in the crystal structure of 3.9, along with unfavorable steric interaction for coplanar thp rings conformation, appear to induce out-of-plane displacement of the two rings re sulting in slight, but detectab le, differences in proximity of the rings’ proton nuclei to the coordinated CoII ions. It is obvious that such effect can cause noticeable differences in the chemical shifts and spin lattice relaxation times of the, otherwise, structurally-similar thp protons. Because the paramagnetic contribution to

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175 Figure 3.30 The B3LYP/LANL2DZ geometrically-optimized model for the [Co2( L1 )(H2O)8]3+ fragment. Figure 3.31. Cobalt-to-proton, rCo-H, distances obtained through T1 measurements, referenced to the signal at 8.68 ppm ( T1 = 0.071 s, rCo-H = 5.324 as extracted from the geometrically-optimized model)

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176 Table 3.2.6 Experimental spin lattice relaxation times ( T1 ) for 1H signals (in the 7-24 ppm chemical shift range) of the para magnetic reaction mixture, the corresponding cobalt-to-proton (rCo-H) distances relative to the refe rence distance of 5.324 for the proton at = 8.68 ppm, and the rCo-H distances obtained from th e geometrically-optimized model of [Co2( L1 )(H2O)8]3+ fragment. Chemical Shift (ppm) T1 (s) rCo-H (experimental) rCo-H (model) 7.652 0.1051 5.683 5.953 8.68 0.07104 5.324 5.324 9.319 0.1226 5.831 5.89 10.168 0.0859 5.495 5.345 10.608 0.0854 5.490 5.452 12.763 0.02174 4.370 4.506 13.452 0.0455 4.943 5.285 17.105 0.024 4.443 4.742 21.969 0.0047 3.386 3.499 23.546 0.01029 3.858 3.692 the nuclear spin lattice relaxation time ( T1) in paramagnetic metal complexes is dependent on the sixth power of the metal nucleus distance, rM-H, a large error in the T1 measurement (e.g., ~50%) would only result in a small error in di stance (i.e., <10%). Moreover, relative distances can be easily obtained with re spect to a reference nucleus employing the relation rM H = [( T1/ T1(ref))1/6 rM H(ref)], where T1 and T1(ref) are the experimental spin lattice relaxation times for the nucleus of interest and a reference nucleus, respectively. 38 P roton spin lattice relaxation times for the majority of isotropically shifted proton signals were determined using the inversion recovery technique (D1 180 90 FID) with 15 different values, Table 3.2.5. The signal at 8.69 ppm ( T1 = 0.071 s) was assigned to the equa torial proton on C6` atom in thp ring furthest from CoII, and employed as the reference nucleus. The rCo-H distances obtained

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177 from experimental T1 measurements correlate well with those from the model, Figure 3.31, further supporting the argument for forma tion of bis-bidentate, mono-deprotonated L1 molecules, bridging two CoII ions upon reactants mixing. Over a period of 12 h under aerobic condi tions and at r.t., gradual decrease in paramagnetic proton integrals with concomitant appearance of severa l proton signals in the diamagnetic region of the spectrum indicates a CoII/III transformation due to aerobic oxidation of coordinated CoII ions. Throughout the aerobic ox idation process we did not detect any changes in the number nor chemical shifts of the isotropically shifted proton signals, suggesting maintained geometry of the initial complex(es) while undergoing transformation into diamagneti c products. Under anaerobic co nditions, the characteristic spectrum of paramagnetic CoII-complex(es) is maintained with no detectable changes, confirming the identity of th e oxidant as molecular oxygen. Moreover, the observed diamagnetic signa ls obtained upon aer obic oxidation of the reaction mixture, in absence of the base, correlate well to the spectrum of 3.9S solvated MOCs, with a noticeable presence of free ligand molecules, as indicated by the characteristic 1H signals for uncoordinated ligand molecules. The presence of uncoordinated ligand molecules is attribut ed to competitive protonation in aqueous solution (pH = 5.76), establishing an equilibr ium between Co-coordinated and protonated [H2-L1]+ species, eq. 3.3. The spectrum obtained for the aerobic react ion mixture, upon addition of the NaOCH3 base, closely matches that of 3.9S with no detectable signals of free ligand molecules, indicati ng quantitative formation of the MOCs in aqueous solution upon reactants mixing at correct stoichiometry and at r.t. H -L1 + H2O [H2-L1 ]+ + OH(3.3)

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178 Solution UV vis Spectroscopy. The freshly prepared aqueous solution of CoCl2 and HL1 exhibits a characteristic absorption ba nd in the visible 400~600 nm range ( 480 = 175 M-1 cm-1). Upon standing at r.t. under aerobic conditions, a gradua l red-shift with an increase in molar extinction coefficient ( 493 = 205 M-1 cm-1) is observed, Figure 3.32.This observation is ascribed to a CoII/III aerobic oxidation process, as confirmed by the 1H NMR study, vide supra. The presence of isosbestic points at 475 and 575 nm in the absorption bands indicates absence of in termediates of the paramagnetic complex(es) undergoing aerobic oxidation. The same changes to the absorption spectr a can be affected on a shorter time scale by incubation of th e reaction mixture unde r 1atm of molecular oxygen. Moreover, it was possible to detect ch anges in the absorp tion spectra of the mixture upon stepwise addition of HL1 to aqueous solution of Co ions. Spectrophotometric titration, CoCl2 (2.5 mM) and HL1 (0 to 6 mM in 0.5 mM portions), was conducted and followed through measurements of A493 after each addition of HL1 Figure 3.33a. Incubation of the reacti on mixture after each addition of HL1 at r.t. for 24 h was necessary to insure comp lete oxidation of coordinated CoII ions. Simultaneous measurements of solution pH clearly indica te suppressed protonation of added ligand due to preferential coordination to Co ions. Fu rthermore, the noticeab le pH drop, dependent on time and concentration of added ligand, strongly suggests de protonation of ligand molecules (generating imidazolate form) due to coordination to Co ions. The observed linear behavior of A493 upon titration with HL1 (up to 2 equiv) along with the observed plateau (beyond 2 equiv) accompanied by an abrupt increase in solution pH could be rationalized by one of two arguments. First, this might indicate presence of complexes maintaining the 2:1 stoichiometry of ligand to Co, as well as the conj ugate acid forms of

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179 Figure 3.32. UV vis absorption spectra for the reaction mixture of HL1 (6.25 mM) and CoCl2 (4.15 mM) in aqueous solution, 296 K under aerobic conditions. Spectra accumulated at 30 minutes intervals. the excess ligand molecules. Alternatively, this behavior could be expl ained as a result of formation of MOCs maintaining the 1.5:1 stoichiometry of ligand to Co, where a fraction of HL1 molecules introduced into solution are not available for metal chelation due to competitive protonation, and thus the plat ue onset should be corrected for HL1 equivalents available for metal chelation through careful control of the solution pH. Accordingly, we repeated the above m easurements in presence of the NaOCH3 base, introduced to the solution as proton s cavenger following each addition of HL1 Figure 3.33b. Indeed, the onset of the A493 platue is shifted to lower HL1 mole equivalents, 1.6 ligand equiv for 2 equiv of NaOCH3 added, supporting the argume nt for formation of the

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180 MOCs in solution upon reactants mixing in correct stoichiometry simply through adjusting the solution pH to suppress comp etitive protonation of th e ligand molecules. The above argument is further supported by solution NMR spectroscopy conducted on a mixture of HL1 (0.15 mmol), CoCl2 (0.1 mmol), and NaOCH3 (0.15 mmol) in D2O, 1 mL, under aerobic conditions where the observed 1H NMR spectrum correlate well with that of 3.9S with no residual peaks of free ligand molecules.

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181 Figure 3.33. (a) Changes in A493 and solution pH for the sp ectrophotometric titration of CoCl2 (2.5 mM) with increasing concentration of HL1 (0.5~6.0 mM) in 20 m L aqueous solution. (b) Changes in A493 and pH for the titration mixture after addition of 2 equiv (in terms of HL1 added) NaOCH3. Absorption measurements acqui red after standing at r.t. for 24 h, measurements conducted at 296 K. (a) (b)

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182 Solvent, Temperature, and Counterion Effects. Due to the relatively weak intermolecular interactions between MOCs in 3.9 different packing patterns of the MOCs are expected upon varyi ng the crystallization conditio ns, provided the ability of MOCs to assemble under different reaction c onditions. We first consider the effects of different counterions on the self-assembly and/or packing patterns of the cationic MOCs. Interestingly, introducing NH4Cl, as a source of chloride ions, into the reaction mixture of HL1 and either Co(SO4) or Co(NO3)2, under the same reaction conditions of 3.9 facilitates isolation of crys talline material characterized through single crystal X-ray diffraction to be identical to 3.9 Reaction of HL1 and CoBr2, under essentially the same reaction conditions for 3.9 resulted in red polyhedral crystals formulated as [Co8(C11N6H15)12]Br12(H2O)x, 3.9a MOCs in 3.9a crystallize in the monoclinic P 21/ n space group, adopting a different packing arrangement than 3.9 Reaction of Co(SO4) and HL1 under solvothermal conditions of 3.9 resulted in crystalline material, 3.9b In 3.9b MOCs crystallize in different packing compared to 3.9 where the twelve positive charges on the MOC are balanced by six (SO4)2 counterions. Reaction of Co(BF4)2 and HL1 under solvothermal conditions of 3.9 resulted in crystalline material, 3.9e In 3.9e MOCs crystallize in different packing compared to 3.9 where the cationic charges on the MOC are balanced by twelve (BF4) counterions. Attempts to isolate crystalline materials containing MOCs starting from Co(NO3)2 under the same reaction conditions of 3.9 were not successful. However, the D2O/DMF-d6 solution 1H NMR spectrum obtained for the mixture of Co(NO3)2 and HL1 was identical to that obtained for CoCl2 and HL1 mixture, indicating presence of the same so lvated cationic species independent on the nature of counterions presen t in the reaction mixture. Mo reover, this observation points

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183 towards an important role of counterions in inducing crystallization of the MOCs, through a network of H-bonds, under the reported solvothermal conditions. Therefore, it is concluded that solution self-assembly of MOCs can be readily achieved from different cobalt salts, namely Cl, Br, (NO3), (SO4)2 and (BF4), due to stronger affinity of the bis-bidentate, chelating L1 molecules to Co ions. It is al so demonstrated that nature of counterions play a major role in facilitating crystallizati on of MOCs and, furthermore, directing the packing patterns of MOCs through a network of weak intermolecular Hbond interactions. The roles and effects of solvents in solvothermal syntheses of MOMs are numerous which include merely serving as so lubilizing agents, acti ng as weak bases for ligand(s) deprotonation, templating the s caffold by balancing the charges on the framework or limiting the cavity size, acting as buffers, serving the role of oxidants or reductants,…etc. In solvothermal synthesi s of MOMs, the choi ce of proper solvent system for in situ generation of pre-programmed MBBs a nd to further facilitate the selfassembly process represents an ongoing challe nge that, in most cases still subjected to trial and error. However, examples of design strategies where such concepts of solvent effect(s) were successfully implemented can be encountered in several previous works. In the original solvothermal synthesis of 3.9 a solvent system of water and DMF (50:50) was necessary to afford crystalline ma terial. As hydrothermal reaction of CoCl2 and HL1 did not result in isolation of crystalline ma terial, it became evident that presence of DMF (a weak base, aprotic, polar solven t with relatively high boiling point, ca. 153C) was necessary to indu ce crystallization of 3.9

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184 In an attempt to probe the relative importanc e of its several char acteristics as a cosolvent, DMF was substituted with N,N`-die thylformamide (DEF) and dimethylsulfoxide (DMSO), in two different trials, as co -solvents in the reaction mixture of 3.9 providing solvent systems with differe nt range of boiling points basicity, hydrophobicity, and ability to act as hydrogen bond acceptors. A solv ent mixture of water and DMSO (polar, aprotic, solvent with high boiling point, ca. 189C) under essentially the same conditions for solvothermal synthesis of 3.9 resulted in brown rectangular crystals, 3.9c where the cationic MOCs cocrystallize with [CoCl4]2species. A mixture of Co(NO3)2(H2O)6 (0.1 mmol) and HL1 (0.15 mmol) in water/ DEF, 1 mL eac h, was prepared and let to stand at r.t. for 7 days (solution volume was re duced to 1 mL due to water loss through evaporation) to yield red polyhedral crystals, 3.9d In 3.9d MOCs crystallize in the P 21/n space group surrounded by H-bonded nitrate coun terions. In comparison to the same reaction carried out in DMF/H2O solvent system, where no crystallization was observed, it is reasonable to assume lowe r solubility of MOCs with ni trates as counterions in the DEF/H2O solvent system, facilitating crystallization of the discrete MOCs. Careful inspection of the above reaction conditions that led to isolation of crystalline material revealed a common tendency of MOCs to crys tallize from polar aprotic solvents upon loss of water molecules. Therefore, it is s uggested that crystallization of MOCs is affected upon decreased solubility of counterions (chloride, br omide, nitrate, etc) in the aprotic solvents that exhibit poor

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185 Figure 3.34. Crystal structure of 3.11 NiII molecular square. C (gra y), Ni (light blue), N (blue), O (red), H (white). DMF solvent molecules omitted for clarity. Figure 3.35. Crystal structure of 3.12 molecular chains of [Cd( L1 )(NO3)]n, C (gray), Cd (buff), N (blue), H (white), O (red). DM F solvent molecules omitted for clarity. solubilizing power for anionic species. To furt her test this hypothesis, reaction conditions of 3.9 were modified to substitute HMPA fo r DMF as a co-solvent Interestingly, the same observation is recorded wh ere crystalline material was isolated, only after loss of

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186 water molecules (through evaporation), in 3.9f This observation points towards a crucial role of the aprotic polar co-solvents used, that is upon loss of water molecules under the solvothermal conditions used crystallizati on of MOCs is induced through decreased solubility of the anionic counterions presen t in the reaction medium Combined with the experimental findings in the solution NMR and UV-vis spectr oscopy sections, where it is evident that MOCs undergo self-assembly in aqueous medium at room temperature in absence of a co-solvent, it is suggested that presence of polar aprotic solvent with a boiling point higher than that of H2O is necessary to induce cr ystallization of the MOCs through decreased solubility of counterions though not essential for solution selfassembly of MOCs. Metal Ions Effect(s). Attempts were made to probe reactivity of different metal ions, other than Co under similar reaction conditions of 3.9 towards construction of MOCs. Solvothermal reaction of In(NO3)36H2O and HL1 in a mixture of DEF and ethanol resulted in formation of the corresponding cationic In-based MOCs, 3.10 As reaction of In(NO3)3 and HL1 in DMF resulted in immediate precipitation of microcrystalline product unsuitable for single crystal X-ray diffraction characterization, the synthesis conditions of 3.10 were modified accordingly to allow for moderate crystal growth rate to isolat e single crystals of 2 with sufficient quality for X-ray diffraction characterization. The similar ity in oxidation state for InIII and CoIII appears to facilitate construction of the isostruc tural cationic MOCs. This ar gument is supported by the observed products in solvotherm al reactions of either NiII or CdII with HL1 Solvothermal reaction of Ni(NO3)24H2O with equimolar amount of HL1 in DMF

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187 resulted in molecular squares, 3.11 where each of the four NiII ions is octahedrallycoordinated to two lig and molecules in bis-bidentate fashion and a nitrate ion as a capping bidentate ligand, Figure 3.34. All attempts to construct MOCs through reaction of NiII ions and 1.5 equiv of HL1 were unsuccessful due to formation of amorphous precipitate. While Ni coordination by (NO3)ions in 3 results in charge neutral molecular squares, such coordinati on precludes further coordination of Ni ions to L1 and, accordingly, appears to prevent transfor mation of molecular squares into MOCs. Furthermore, solvothermal reaction of Cd(NO3)24H2O and HL1 in DMF resulted in molecular chains, 3.12 where the Cd-N4O2 coordination sphere exhibits a distorted octahedral geometry, Figure 3.35. Similar to the case of Ni molecular squares, the coordination of Cd in 3.12 to (NO3)ions appears to prevent is olation of targeted (Cd-N6) MOCs. Analysis of the CSD (May 2009) re vealed that only ~4.8% and ~5.7% of octahedral Ni-N6 and Cd-N6 complexes, respectively, were isolated in presence of NO3 ions. Reaction of HL1 and either NiCl2 or CdCl2 did not result in crystalline materials, under similar reaction conditions of 3.9 Apart from the preferred hetero-coordination spheres observed for octahedral Ni and Cd complexes in presen ce of nitrate ions, the fact that these two ions are in th e +2 oxidation state might contri bute to the feasibility of constructing their respective MOCs. The MOCs based on M2+ ions are cationic bearing 4+ charges and thus might be difficult to crystallize in abse nce of appropriate counterions contributing properly to the cr ystallization process. In c onclusion, oxidation state, and ultimately the overall charge and symmetry of the MOC, the preferred coordination sphere for a metal ion, and nature of count erions are equally im portant elements to consider in rational design stra tegies for construction of MOCs.

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188 Structural stability of MOCs. The MOCs in 3.9 demonstrate structural stability in aqueous solution under a wide range of so lution pH and temperature. Aqueous solution of 3.9 was prepared in D2O and the stability of the solvated MOCs, 3.9S in the solution temperature range (298 333 K) and pH (2.03 8.07) is demonstrated through 1H NMR spectroscopy. The characteristic 1H NMR pattern for 3.9S is maintained throughout the solution temperature and pH ranges reported herein; indicating maintained structural integrity of the dissolved MOCs, Figure 3.36. Moreover, no detectable decomposition of the solvated MOCs, 3.9S was detected in aqueous solution kept for one year at r.t., as confirmed by both 1H and 2D DOSY NMR spectroscopy.

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189 Figure 3.36. 1H NMR spectra of 3.9s in D2O at various solution pH (top) and temperature (bottom) range.

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190 3.2.3 Experimental Nuclear Magnetic Resonance measurements. All 1H and 13C NMR spectra were acquired on Varian VXR (299.94 MHz for 1H, 75.55 MHz for 13C), UnityINOVA 400 (399.78 MHz for 1H, 100.54 MHz for 13C) equipped with variable temperature controller, or UnityINOVA 500 (499.76 MHz for 1H, 125.68 MHz for 13C) spectrometers. The 1H chemical shifts are reported relative to that of TMS and referenced to either the internal HDO signal at 4.76 ppm, the singlet peak of 3-(trimethylsilyl)-1-propanesulfonic acid sodium salt (DSS) at 0 ppm, or DMSO-d6 signal at 2.5 ppm, as indicated for each spectrum. Appendix D contains some of th e NMR spectra conducted for section 3.2 of chapter 3. Variable temperature measurements were conducted on a sample of 3.9 dissolved in D2O and held at the specific temperature for 10 min prior to spectrum acquisition. Solution 1H NMR measurements at variable pH were conducted at 296 K on a mixture prepared by mixing CoCl2 (1 mmol, 0.66 M) and L1 .(1.5 mmol, 0.1 M) in 15 mL of D2O (resulted pH = 6.63), stirred unde r aerobic conditions at 296 K for 1 h prior to pH adjustments. The pH is adjusted through in cremental additions of either NaOD or D2SO4, as required, and the apparent solution pH values are repo rted. Measurements are made with Mettler Toledo EL02 pH meter calibrated with aqueou s buffer solutions at 296 K. Spectrophotometric titration. The entire range of titr ation was conducted on a total of 15 (25 mL) scintillation vials each contains a 20 mL solution of CoCl2 (2.5 mM, 0.05 mmol). To each vial was added L1 in 0.01 mmol increments and the pH was measured after certain intervals as descri bed in the discussion. The mixtures were

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191 incubated at 296K for 24 h under aerobic c onditions before conduc ting the absorbance measurements at 493 nm. Single-Crystal X-ray Diffraction. The X-ray diffraction data were collected using Bruker-AXS SMART-APEX CCD di ffractometer equipped with Mo K radiation source ( = 0.71073 ) or SMART-APEX CCDII di ffractometer equipped with Cu K ( = 1.54178 ) radiation source, as indicate d. Indexing was performed using SMART v5.625. 25 Frames were integrated with SaintPlus 6.28A 26 software package. Absorption correction was performed by multi-scan method implemented in SADABS.27 The crystal structures were solved using SHELXS-97 and refined using SH ELXL-97 contained in SHELXTL v6.10 and WinGX v1. 70.01 programs packages. 28 All non-disordered nonhydrogen atoms were refined with anisotro pic displacement parameters. All H-atoms bonded to carbon atoms were placed in geom etrically optimized positions and refined with an isotropic displacement parameter fixed at 1.2 times U q of the carbon atoms to which they are attached. N bonded protons were located via Fourier difference map inspection and refined isotropi cally with thermal parameters based upon the N atoms to which they are bonded. Crystallographic da ta are included in Tables 1 and 2. Other Physical Measurements. Powder X-ray diffracti on (XRPD) data were collected using Cu K radiation ( = 1.5406) on a Bruker AXS D8 Advance diffractometer. The MALDI TOF MS spectrum was recorded on a Bruker Daltonics Autoflex III TOF/TOF mass spectrometer using -cyanohydroxy-cinnamic acid as the matrix. Solution UV–vis absorption spectra we re collected on a PerkinElmer Lambda900 spectrophotometer, with an attachment fo r solid samples and gaseous atmosphere.

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192 Computer Modeling. The computer model presented in Figure 3.29 is the work of Dr. Jonathan Belof from Dr. Brian Space laboratory in the department of chemistry, university of south Florida. The hydrated fragment [Co2( L1 )(H2O)8]3+, with a net charge of +3 and multiplicity of 7, was geometry optimized using the quantum chemistry code Gaussian 03.39 The minimized energy was calculated via Density Functional Theory (DFT) using the B3LYP hybrid ex change-correla tion functional. 40 The unrestricted calculation employed the LANL2DZ basis set wi th an ECP applied to the cobalt atoms.41 Synthetic Procedures. All reagents were commercia l grade used without further purification. The organic ligand molecule, HL1 is prepared according to a modified procedure reported previously for similar compounds. 29 2,2'-(1 H -imidazole-4,5-diyl)di-1,4,5,6 -tetrahydro-pyrimidine, HL1. 1 H imidazole-4,5-dicarbonitrile (10 mmol) and exce ss of 1,3-diaminopropane in presence of Scheme 3.2. Synthesis of HL1 sulfur (10 mmol) refluxed for 1 h followed by vacuum drying and suspension in water then filtration and drying at 80C to afford HL1 formulated as C11H16N6, in good yield (9.2 mmol, 92%) and high purity as determined from solution 1H NMR (D2O, 400MHz): = 7.47 (s, 1H), 3.5 (t, J = 5.8Hz, 8H), 1.97 (quin, J = 5.7 Hz, 4H), Scheme 1.

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193 [Co8(C11N6H15)12]Cl12 (H2O)4, 3.9. In a capped 25 mL scin tillation vial, reaction of HL1 (0.15 mmol) and CoCl26H2O (0.1 mmol) in a mixture of N,N`dimethylformamide (DMF) and water, 1 mL each, at 115C for 12 h resulted in red polyhedral crystals formulated as [Co8(C11N6H15)12]Cl12(H2O)4 ( 0.04 g, 85% yield based on CoCl2) using single-crystal X-ray diffraction. [Co8(C11N6H15)12]Br12(H2O)7, 3.9a. In a capped 25 mL scin tillation vial, reaction of HL1 (0.15 mmol) and CoBr26H2O (0.1 mmol) in a mixture of DMF and water, 1 mL each, at 115C for 12 h resulted in re d polyhedral crystals formulated as [Co8(C11N6H15)12]Br12(H2O)7 ( 0.044 g, 80% yield based on CoBr2) using single-crystal X-ray diffraction. [Co8(C11N6H15)12](SO4)6(DMF)0.5(H2O)32, 3.9 b. In a capped 25 mL vial, reaction of HL1 (0.15 mmol) and Co(SO4)6H2O (0.1 mmol) in a mixture of DMF and water, 1 mL each, at 115C for 12 h resulted in re d polyhedral crysta ls formulated as [Co8(C11N6H15)12](SO4)6 (DMF)0.5(H2O)32, ( 0.03 g, 55% yield based on Co(SO4)) using single-crystal X-ray diffraction. [Co8(C11N6H15)12][CoCl4]2Cl8(H2O)21, 3.9c. In a capped 25 mL scintillation vial, reaction of HL1 (0.15 mmol) and CoCl26H2O (0.1 mmol) in a mixture of dimethylsulfoxide (DMSO) and water, 1 mL each, at 115C for 12 h resulted in brown rectangular crystals formulated as [Co8(C11N6H15)12][CoCl4]2Cl8(H2O)21 using single crystal X-ray diffraction, Figure 10. [Co8(C11N6H15)12](NO3)12(H2O)22, 3.9d. In an open 25 mL scintillation vial, reaction of HL1 ( 0.15 mmol) and Co(NO3)26H2O (0.1 mmol) in a mixture of N,N`-

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194 diethylformamide (DEF) and water, 1 mL each, kept at room temperature (r.t.) for 7 days after which solution volume was reduced to 1 mL through evaporation, resulted in red polyhedral crystals formulated as [Co8(C11N6H15)12](NO3)12(H2O)22 ( 0.04 g, 74% yield based on Co(NO3)2) using single crystal X-ray diffraction [Co8(C11N6H15)12](BF4)12(DMF)2(H2O)12, 3.9e. In a capped 25 mL scintillation vial, reaction of HL1 (0.15 mmol) and Co(BF4)26H2O (0.1 mmol) in a mixture of N,N`dimethylformamide (DMF) and water, 1 mL each, at115C for 12 h resulted in red polyhedral crystals formulated as [Co8(C11N6H15)12](BF4)12(DMF)(H2O)13 using singlecrystal X-ray diffraction. [Co8(C11N6H15)12]Cl12(H2O)40, 3.9f. In a capped 25 mL scintillation vial, reaction of HL1 (0.15 mmol) and CoCl26H2O (0.1 mmol) in a mixture of hexamethyl phosphoramide (HMPA) and water, 1 mL each, at115C for 12 h resulted in red polyhedral crystals formulated as [Co8(C11N6H15)12]Cl12(H2O)40 using single-crystal Xray diffraction. [In8(C11N6H15)12](NO3)12(H2O)4, 3.10. In a capped 25 mL scintillation vial, reaction of HL1 (0.15 mmol) and In(NO3)36H2O (0.1 mmol) in DEF (5 mL) and ethanol (2 mL) at 85C for 12 h, resulted in colo rless polyhedral crystals formulated as [In8(C11N6H15)12](NO3)12(H2O)4 using single using single crystal X-ray diffraction. [Ni4(C11N6H15)4](NO3)4(DMF)2, 3.11. In a capped 25 mL scintillation vial, reaction of HL1 (0.1 mmol) and Ni(NO3)26H2O (0.1 mmol) in 1 mL of DMF at 85C for 12 h, resulted in green polyhedral crystals formulated as [Ni4(C11N6H15)4] (NO3)4(DMF)2 using single crystal X-ray diffraction Figure 3.33.

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195 [Cd(C11N6H15)(NO3)]n, 3.12. In a capped 25 mL scintill ation vial, r eaction of HL1 (0.1 mmol) and Cd(NO3)24H2O (0.1 mmol) in 1 mL of DMF at 85C for 12 h, resulted in colorless polyhedral crystals formulated as [Cd(C11N6H15)(NO3)]n using single crystal X-ray diffraction Figure 3.34. 3.2.4 Conclusion The solution self-assembly of MO Cs, from pre-programmed MBBs, is characterized utilizing NMR spectroscopy, UV vis absorption spect roscopy, solution potentiometry, as well as MALDI TOF mass spectrometry. Furthermore, aqueous dissolution of the isolated crystalline material results in solvated MOCs which demonstrate structural stability under a wide range of solution temperature and pH. In this study, a systematic investigation is conducted to probe th e roles and effects associated with the wide range of reaction variables (nature of metal ions, counterions, solvent systems, solution pH, and temperature) on the nature of observed products. It is demonstrated that self-assembly of MOCs from a wide variety of CoII salts proceeds readily in aqueous solution simply upon reacta nts mixing. The reaction could be driven to completion by inhibition of competitive prot onation of the ligand molecules through careful adjustment of the solution pH. Howe ver, crystallization of MOCs can only be affected in presence of polar aprotic co-sol vent with elevated boiling point (DMF, DEF, DMSO, and HMPA) after considerable loss of water molecules through evaporation. The observations strongly suggest an important rule associated with the nature of counterions, inducing crystallization of cationic MOCs through intermolecular hydrogen bond interactions and further c ontrolling the pack ing patterns of MOCs, although does not interfere with the solution self-assembly processes. The methodology adopted herein

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196 could potentially be applied to a variety of other MOPs to gain better understanding of the self-assembly processes of MOPs under solvothermal conditions. Such understanding could potentially result into enhanced design strategies for constr uction of MOPs with desirable physical and chemical properties. 3.2.5 References 1. (a) Eddaoudi, M.; Kim, J.; Wachter, J. B.; Chae, H. K.; O'Keeffe, M.;Yaghi, O. M. J. Am. Chem. Soc. 2001 123 4368-4369. (b) Kitagawa, S.; Kitaura, R.; Noro, S. I. Angew. Chem. Int. Ed 2004 43 2334-2375. (c) Moulton, B.; Lu, J.; Mondal, A.; Zaworotko, M. Chem. Commun. 2001 863-864. (d) Yaghi, O. M.; O'Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. Nature 2003 423 705-714. (e) Stein, A.; Keller, S. W.; Mallouk, T. E. Science 1993 259 1558-1564. (f) Brant, J. A.; Liu, Y.; Sava, D. F.; Beauchamp, D.; Eddaoudi, M. J. Mol. Struct. 2006 796 160-164. (g) Bell, Z. R.; Harding, L. P.; Ward, M. D. Chem. Commun. 2003 24322433. (h) Hong, M.; Zhao, Y.; Su, W.; Cao, R.; Fujita, M.; Zhou, Z.; Chan, A. S. C. J. Am. Chem. Soc. 2000 122 4819-4820. (i) Liu, Y.; Kravtsov, V. C.; Beauchamp, D. A.; Eubank, J. F.; Eddaoudi, M. J. Am. Chem. Soc. 2005 127 7266-7267. 2. (a) Cairns, A. J.; Perman, J. A.; Wojtas, L.; Kravtsov, V. Ch.; Alkordi, M. H.; Eddaoudi, M.; Zaworotko, M. J. J. Am. Chem. Soc. 2008 130 1560-1561. (b) Nouar, F.; Eubank, J. F; Bousquet, T; Wojtas, L; Zaworotko, M. J.; Eddaoudi, M. J. Am. Chem. Soc. 2008 130 1833-1835.

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200 Moulton, B.; Rather, B.; Shahgaldian, P.; Zaworotko, M. J. Chem. Commun. 2001 22 2380-2381. (c) Tranchemontagne, D. J.; Ni, Z.; O'Keeffe, M.; Yaghi, O. M. Angew. Chem. Int. Ed. 2008 47 5136-5147. (d) Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002 35, 972-983. (e) Fujita, M.; Tominaga, M.; Hori, A.; Therrien, B. Acc. Chem. Res. 2005 38, 369-378. (f) Caulder, D. L.; Raymond, K. N. Acc. Chem. Res. 1999 32, 975-982. 22. (a) Fujita, M.; Umemoto, K.; Yoshizawa, M.; Fujita, N.; Kusukawa, T.; Biradha, K. Chem. Commun. 2001 6 509-518. (b) Nakabayashi, K.; Ozaki, Y.; Kawano, M.; Fujita, M. Angew. Chem., Int. Ed. 2008 47 2046-2048. (c) Umemoto, K.; Yamaguchi, K.; Fujita, M. J. Am. Chem. Soc. 2000 122 7150-7151. (d) Fujita, M.; Aoyagi, M.; Ibukuro, F.; Ogura, K.; Yamaguchi, K. J. Am. Chem. Soc. 1998 120 611-612. (e) Umemoto, K.; Tsukui, H.; Kusukawa, T.; Biradha, K.; Fujita, M. Angew. Chem. Int. Ed. 2001 40 2620-2622. 23. (a) Nouar, F.; Eubank, J. F.; Bousquet, T.; Wojtas, L.; Zaworotko, M. J.; Eddaoudi, M. J. Am. Chem. Soc. 2008 130 1833-1835. (b) Cairns, A. J.; Perman, J. A.; Wojtas, L.; Kravtsov, V. C.; Alkordi, M. H.; Eddaoudi, M.; Zaworotko, M. J. J. Am. Chem. Soc. 2008 130 1560-1561. 24. Liu, Y.; Kravtsov, V.; Walsh, R. D.; P oddar, P.; Srikanth, H.; Eddaoudi, M. Chem. Commun. 2004 24 2806-2807. 25. Bruker-AXS (2001). SMART-V5.625. Data Collection Software. Madison, Wisconsin, USA. 26. Bruker-AXS (2001). SAINT-V6.28A. Da ta Reduction Software. Madison, Wisconsin, USA.

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204 Chapter 5: Molecular Squares fo r Hydrogen Storage Materials 4.1 Introduction Molecular hydrogen represents a material wi th high chemical energetic density (142 MJ / kg, as compared to gasoline with 47 MJ / kg) 1 and thus attractive as an alternative fuel to fossil fuel. The realization of hydrogen economy will be dependent upon technological achievements that will provide economically-v iable sources of hydrogen, transportation means, storage containers, and fuel cells.1 Our focus is directed to a specific class of solid state materials (namely MOFs) as a potential hydrogen storage materials. While hydrogen could be stored under high pressure or th rough liquefaction at cr yogenic conditions, the two techniques are currently un-suitable for application in daily automotive transportation.1 Hence, the interest of wide scientif ic, social, and governmental sectors is directed towards novel technologies that can provide the tools to overcome this challenge. Table 4.1 below represents select ed targets set by the DOE for efficient onboard hydrogen storage systems.2 As described in earlier chapters, metal–or ganic frameworks (MOFs), as functional solid state materials, continue to receive tremendous scientific in terest due to their potential applications in current dema nding technologies like hydrogen storage, gas separation, carbon dioxide seque stration, enhanced catalysis and drug delivery. Such applications are pertinent to the fundamental attributes of MOFs including dual

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205 Table 4.1 : Selected targets set by the DOE for on-board H2 storage systems2: Storage parameter Units 2007 2010 2015 System Gravimetric Capacity: Usable, specific-energy from H2 (net useful energy/max system mass) a kWh/kg (kg H2/kg system) 1.5 (0.045) 2 (0.06) 3 (0.09) System Volumetric Capacity: Usable energy density from H2 (net useful energy/max system volume) kWh/L (kg H2/L system) 1.2 (0.036) 1.5 (0.045) 2.7 (0.81) Storage system cost b (& fuel cost) $/kWh net ($/kg H2) $/gge at pump 6 (200) --4 (133) 2-3 2 (67) 2-3 Durability/Operability Operating ambient temperature d Min/max delivery temperature Cycle life (1/4 tank to full)e Cycle life variation f Min delivery pressure from tank; FC=fuel cell, I=ICE Max delivery pressure from tank g C C Cycles % of mean (min) at % confidence Atm (abs) -20/50 (sun) -30/85 500 N/A 8FC/10ICE 100 -30/50 (sun) -40/85 1000 90/90 4FC/35ICE 100 -40/60(sun) -40/85 1500 99/90 3FC/35ICE 100 a. Generally, the full mass (including hydrogen) is used, for sy stems that gain weight, the hi ghest mass during discharge is u sed. b. 2003 US$; total cost includes any component replace ment if needed over 15 years or 150,000 mile life. c. 2001 US$; includes off-board costs such as liquefaction, co mpression, regeneration, etc.; 2015 target based on H2 production cost of $2 to $3/gasoline gallon equivalent unt axed, independent of production pathway. d. Stated ambient temperature plus full so lar load. No allowable performance degrada tion from -20C to 40C. Allowable degradat ion outside this limit is TBD. e. Equivalent to 100,000; 200,000; and 300,000 mi les respectively (current gasoline tank spec). f. All targets must be achieved at end-of-life. g. In the near term, the forecourt shou ld be capable of delivering 10,000 psi compressed hydrogen, liquid hydrogen, or chilled hydrogen (77 K) at 5,000 psi. In the long te rm, it is anticipated that delivery pressu res will be reduced to between 50 and 150 atm for solid state storage systems, based on todays knowledge of sodium alanates. composition, high crystallinity, and open struct ures. In particular, porous MOFs have been widely investigated for hydrogen storage,3-8 demonstrating reversible physisorption interactions, within available void space, amenable to a high degree of tuneability associated with the highly modular nature of MOFs. While the potentials for a wide variety of solid state materials capable either of reversible physisorption, like carbon structures, 9 or chemisorption, like metal hydrides, 10 are being currently investigated, the focus of this chapter is directed towards a novel approach proposed by us to enhance the hydrogen storage charac teristics in MOFs. Theoretical studies indicate that hydrogen interactions with metal complexes, clusters, or ions, as the inorga nic part of the framework, are mo stly electrostatic in nature

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206 and could play major roles in determining the H2 uptake characteristics of a particular MOF due to their relatively significant contribution to the overall H2 binding affinities (Qst) and hence are the subject of consid erable theoretical and experimental investigations. 11-13 Although weaker, favorable van der Waals interactions between H2 and the organic linkers in MOFs, best represente d by benzene ring derivatives, have been theoretically investigated 13, 14 and experimentally documented 15 through inelastic neutron scattering experiments. Recent studies demonstrate that such interactions could, in principle, be enhanced through chemi cal modifications to the organic linkers, providing a potential strategy for a material designer to enhance H2 sorption characteristics of MOFs. Nevertheless, no st udies exist, to the best of our knowledge, addressing the possibility of improving H2 binding affinity to the walls of MOFs through simultaneous favorable dispersive inte ractions, acting additively, between H2 molecules and multiple aromatic rings placed at optimal in teraction distance(s) and within a specific geometry. Therefore, we opted to explore this appr oach which could potentially prove useful as a viable target to consider, among others in rational design st rategies for future hydrogen storage materials. Com putational studies by Head-Gordon et al Goddard et al and others, 15 for the H2 binding affinities to benzene and various substituted benzene rings reveal moderate binding a ffinities, mostly due to favorab le dispersive interactions, in the range of 3.34~4.29 kJ/mol. Although belo w an estimated target of 21~32 kJ/mol, for efficient H2 storage materials at ambient conditi ons (-20 C and pressure range 100~1 bar, 14 or 15~20kJ/mol, (room temperature at pressure up to 30 bar) 16 it is not yet clear if

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207 such interactions could be additive and hen ce lead to enhanced favorable interactions between a H2 molecule and multiple aromatic rings in tailored frameworks. We envision a molecular square construc ted of four benzene rings interacting simultaneously with a single H2 molecule, resides in the center of the square, as a potential model for a material with enhanced H2 binding affinity. In this model, the H2 molecule is treated as a rigid ro tor at uniform separation distance, R between its center of mass and the centroids of surrounding benzen e rings. It is obvious that, due to high dependence of dispersive interactions on R decreases as 1/ R6, any expected enhancement in H2 binding affinity due to simultaneous disp ersive interactions within the optimized molecular square geometry will be extremely sensitive to geometric deformations. Although this places a challenge on experimentally achievable structures, with such strict configurations, it pr ovides motivation for further theoretical and experimental investigations which could eventually result in porous crystalline materials with desirable H2 uptake. In this study, we attempt to address this point both via computational modeling of a hypothetical molecular square construct, gui ded by the previous efforts in computing the ideal intermolecular distance(s) and orientation(s) for a single H2 molecule interacting with a benzene ring, and the experimental investigations of two relevant MOFs containing molecular squares with acces sible voids towards hydrogen uptake.

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208 4.2 Results and Discussion To investigate the dimensions of a channel, reminiscent of those in the synthesized structures, that optimize dispersive interac tions, a model system amenable to study via computation was chosen. Perturbative ab initio electronic structure methods were chosen because long range dispersive interactions are not captured well by conventional density functional methods or by Hartree-Fock calculations.24 Thus, to account explicitly for electron correlation, s econd order Mlle r-Plesset perturbation theory25 (MP2) or resolutionof-the-identity Mller-Plesset19 (RI-MP2) was used in all the calculations conducted herein. Figure 4.1. MP2/6-31G* optimized model molecular square showing the most favorable orientation of a H2 molecule interacting simultaneously with the four benzene rings and the binding energy dependence on H2-benzene ring separation distance, R

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209 Dunning basis sets were selected be cause by construction they allow the estimation of the energy of a system in the limit of an infinitely large basis set – the socalled complete basis set (CBS) limit.23 Although it has been observed that CBS extrapolations including the doubl e-zeta basis set is not optimal 23, quadruple-zeta calculations were too time consuming and unnecessary for an physically meaningful estimation using a model system. A two-point extrapolation was performed using the double-zeta (cc-pVDZ) and triple -zeta (cc-pVTZ) basis sets.20, 21 Double-zeta, triple-zeta and CBS energies are sh own in Figure 4.1 for the model system shown. The simple model system was constructed to capture the essential interactions and includes benzene rings as building blocks. Initially, an individual benzene ring was geometrically-optimized at the MP2/6-31G* level of theory to attain a reference geometry from which the model system was constructed. Four benzene rings were arranged in a square geometry, such that th e configuration roughly mi mics a channel or a box in a microporous material occupied by a H2 molecule with its center-of-mass coincident with that of the square. For si mplicity, the square geometry was maintained while the dimensions were varied from 3.0 to 4.5 in increments of 0.05 , measured from center-of-mass of the s quare to center-of-mass of a be nzene ring. For each step, one hydrogen molecule was positioned in the center-of-mass of the square and optimized at the MP2/6-31G* level while the square was held fixed. Using this optimized geometry, binding energies were computed using resolution-of-the-ide ntity MP2 with Dunning's ccpVDZ and cc-pVTZ basis sets with th eir corresponding RI-fitting basis sets.22 All binding energies were counter-poi se corrected and extrapolated to the complete basis set limit. All computations were performed on the TeraGrid27 using NWChem.17,18

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210 The calculations revealed dispersive interacti ons between the aromatic walls of the model box and the H2 molecule reaching a maximum binding energy of 13.8 kJ mol-1 at R =3.05 , reinforcing the role dispersion can play in highly constraining sorption environments. Considering the configuration of the hydrogen molecule relative to the four benzene rings, the calculated energy reveals an additive behavior of aromatic ring-H2 interactions as compared to H2 molecule interacting with one arom atic ring. These results suggest an approach to maximizing H2 binding enthalpy in MOF’s could involve maximizing dispersive interactions through a similar conf inement. While distinct quantities, it is reasonable to compare experimentally measured average isosteric heats of adsorption and calculated binding energies.26 Compound 4.1 crystallizes in the triclinic P -1 space group with square-like channels running through a -axis occupied by disordered DMF solvent molecules. The distinctive shape of the ditopic organic linker ( -SO2angle of 104) facilitates construction of infinite 1D chains of molecular squares, running along the c -axis. In the crystal structure of 4.1 Figure 4.2, coordination of Pb(II) ions by carboxylates in bridging bi-dentate mode results in infinite chains of Pb(CO2)2 running along the a -axis, holding adjacent 1D molecular chains in approp riate configuration to allow formation of solvent-occupied channels in the as-synthesi zed crystalline solid. The resulted geometry of square-like channels lined by di-substituted benzene rings with moderate interplanar distances (8.78~9.16 , centr oid-to-centroid), Figure 4.3, immediately caught our attention to possible projected effect(s) on the H2 interactions with the aromatic walls of the framework. Although the interpla nar distances and dihedral angles observed in this structure are not optimal for inducing multiple interactions of a single H2 molecule with

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211 surrounding aromatic rings, the observed H2 uptake characteristics of this framework are remarkable, especially in term s of the observed shapes for H2 sorption isotherms and the isosteric heat of adsorption. This experiment al observation stimula ted our interest in investigating further the poten tial to obtain isostructura l compounds based on the same organic linker (4,4`-sulfonyldibenzoic ac id) and its structurally analogue 4,4'(hexafluoroisopropyliden e)bis(benzoic acid) F3CCF3O OH O OH S OO O OH O OH 4,4'-sulfonyldibenzoic acid 4,4'-(Hexafluoroisopropylidene) bis(benzoic acid) Figure 4.2 Crystal structure of 4.1. Pb (deep gray), C (gray), S (yellow), O (red), H (white), DMF solvent molecules occupying the square-like channels omitted for clarity.

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212 Figure 4.3. Fragment of the crystal structure of 4.1 showing the significant dimensions of the square-like structure, diso rdered DMF solvent molecules inside the square channels are omitted for clarity. The as-synthesized crystalline material is washed several times with acetonitrile, in which it is soaked for 20 days at ro om temperature to exchange entrapped DMF solvent molecules, generating the solven t-exchanged framework. The FT-IR spectrum obtained for the solvent exchanged framework indicates full solvent exchange, as evident from absence of the characteristic absorption band for the DMF solvent ( C=O = 1674 cm1), Figure 4.4. The solvent-exchanged sample is then placed under dynamic vacuum at room temperature for 8 h before conducti ng the various gas sorption measurements reported herein. The H2 sorption isotherms, Figure 4.5, e xhibit rapid saturation at early dosing stages which could be attrib uted to uniform distribution of H2 binding sites, most probably on the surfaces of aromatic rings lining the square-like channels.

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213 Figure 4.4 (Top) FT-IR spectrum of the as-synthesized 4.1 and (down) the FT-IR spectrum for the solvent-exchanged 4.1 indicating solvent displacement of guest DMF molecules present in the as-synthesized compound.

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214 Figure 4.5. H2 sorption isotherms for the solvent-exchanged 4.1 The plot of isosteric heat of ad sorption vs. uptake (in wt %) for H2 inside 4.1 reveals an interesting behavior, Figure 4.6, as it traces an almost horizontal line (~ 9 kJ / mol) over most of the H2 sorption range and falls quickly to ~ 1 kJ / mol after sorption of ~0.4 wt %. Interestingly, sorption of ~0.4 wt % of H2 corresponds to sorption of two H2 molecules per cage made of two ligand mol ecules coordinating two Pb(II) ions. This could be attributed to rapid satura tion of homogenously distributed H2 interaction sites (presumably the aromatic rings) with apprec iable interaction energy (~9 kJ / mol). For more accurate determination of Qst in 4.1, additional H2 sorption isotherm (s) are required, and most desirably at higher cell bath temperat ures, this is due to the closely displaced values for early loading points in the 77 K a nd 87 K isotherms, almost coincide at very low loadings. The closely displaced point s of the two isotherms might introduce a relatively significant error in calculated Qst, where it is anticipated that at least one

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215 additional isotherm at higher te mperature might reveal higher Qst for compound 4.1. Nitrogen isotherm, Figure 4.7, wa s also obtained for compound 4.1 from which the calculated surface area util izing BET method is (203.1 m2 / g) and the total pore volume is (0.089 cc / g). Figure 4.6. Isosteric heat of adsorption for the solvent-exchanged 4.1 compound. Figure 4.7. N2 sorption isotherm for 4.1 conducted at 77 K.

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216 Figure 4.8 X-ray powder diffr action patterns for 4.1, before (red) and after (black) solvent exchange in acetonitrile. Compound 4.2 crystallizes in the orthorhombic Pccn space group with square-like channels running through b-axis occupied by disordered DMF solvent molecules, Figure 4.9. In the crystal structure of 4.2, infinite rod-shaped metal carboxylate secondary building units (SBU) are present. Two distinct types of coordination spheres around Cd(II) ions are observed. Four bidentate ligand molecules coordinate a Cd(II) i on in a trigonal prismatic configuration. The second Cd(II) ion is octahedrally coordinated to adjacent four ligand molecules and two DMF mol ecules as axial ligands.

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217 Figure 4.9 Crystal structure of 4.2 ,Cd (buff), C (gray), O (red), H (white), F (cyan). Solvent molecules omitted for clarity. The as-synthesized crystalline material is washed several times with acetonitrile, in which it is soaked for 30 days at room temperature to exchange DMF guest molecules, generating the solvent-exchanged framework. The solvent-exchanged sample is then placed under dynamic vacuum at room temperature for 19 h before conducting the various gas sorption measurements reported herein. The H2 sorption isotherms, Figure 4.10, exhibit a distinct shape marked by relativel y steeper rise in th e early dosing stages followed by a knee, in the range of 0.3 0.4 wt % of adsorbed H2, corresponding to two H2 molecules per cavity enclosed by four ligand molecules. This behavior is observed for both of the isotherms conducted at 77 K and 87 K, and could be explained in terms of an activation barrier for adsorbed H2 molecules that is overcome after occupation of the square-like channels by two H2 molecules. The isosteric he at of adsorption, Figure 4.11, obtained for 4.2 revealed a near-linear behavior ar ound 7~6 kJ / mol, an indication of a homogenously distributed adsorption sites, mo st probably the aromatic walls of the MOF.

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218 Figure 4.10. H2 sorption isotherms fo r solvent-exchanged 4.2 with the two knees in the two isotherms circled Figure 4.11. Isosteric heat of adsorption for the solvent-exchanged 4.2.

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219 The crystal structure of compound 4.3 shows a 2D layers of perfect square grid lined by neutral pyrimidine ri ngs and anionic tetrazolates at perfectly disposed orientations and channel dime nsion very close to that predicted by theoretical calculations to be optimum for maximized dispersive interactions with H2. Therefore, compound 4.3 represents a very inte resting study case to test our postulate and our theoretical investig ations. However, crys tal packing of the 2D sheets in a repeating ABCD fashion where the square voids in each sheet is inaccessible to guest molecules due to interdigitation by the two sheets immediately above and below each sheet. We currently have no means to direct the packing of the square-g rid sheets but our efforts continues towards seeking a suitable template or reaction conditions that could result in properly disposed layers as to create square channels running through one of the unit cell axes.

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220 Figure 4.12. (Top) crystal structure of 4.3 showing only one of the 2D square-grid layers and (below) view along the zaxis showing packing of tw o immediate neighbor layers (highlighted). Cd (green), N (blue), C (gray), H (white).

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221 Figure 4.13. (Top) crystal structure of 4.4 showing the square-like channels filled with disordered DMF solvent molecules and (bel ow) the discrete molecular square with significant dimensions shown, DMF solvent mol ecules omitted for clarity. Cu (orange), S (yellow), C (gray), O (red), N (blue), H (hydrogen). Compound 4.4 contains discrete molecula r squares of two 4,4`-sulfonyl (dibenzoate) ligand molecules coordinati ng two, [1,10]Phenanthroline-chelated Cu(II)

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222 ions. Molecular (or more appropriately supr amolecular) packing appears to be governed by favorable stacking (interplanar distance of 3.38 ). Although this system appeared to offer a chance to further test a nd optimize our design principles for tailored materials aimed towards hydrogen storage appl ications, presence of enclathrated DMF molecules inside each of the molecular square s in the as-synthesized material necessitates solvent-exchange to afford a material that could readily undergo so lvent removal through evacuation to afford the targeted material for gas sorption studies. Unfortunately, the material is found to be soluble in most of the common low-boiling point solvents used for solvent exchange and thus precluded fu rther studies. However, one noticeable observation is that the same ma terial could be re-generated if DMF is used as a cosolvent and the solution is heated to boil off the low-boiling point solvent. Trying to overcome the lim itation encountered in compound 4.4 we decided to utilize a slightly different chelating agent, the 4,7-diphenylphenath roline, in designing compound 4.5 Figure 4.14. The goal was to impart more rigidity to the construct through extended stacking interactions that might cause stability of the stacked molecular squares towards dissolution into the solv ent-exchange media. Although this goal was successfully attained, the addi tional phenyl rings from one molecular square protruded into the square-like cavity of an adjacent molecular square, rendering them unsuitable for gas sorption studies. The above two examples ( 4.4 and 4.5 ) perfectly represent the current, commonly encountered findings in our field. While geometric design principles could be, to a satisfactory de gree, included in th e initial stage of the reaction through utilization of properly functiona lized linkers in conj ugation with metal ions that retain a good degree of geometric similarity to previously known com pounds, the number of

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223 other variables present in the reaction mixt ure might render it difficult to anticipate or conceptually conceive the st ructure and properties of the targeted end product in a manner that could be interpreted as “ ab initio design”. Figure 4.14. (Top) crystal structure of 4.5 showing the square-lik e channels partially blocked by phenyl rings protru ding inside the channels from neighboring molecular squares. The square-like channels are fille d with disordered DMF solvent molecules, omitted for clarity. (Below) selected significan t dimensions of the molecular square. Cu (orange), S (yellow), C (gray), O (red), N (blue), H (white).

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224 4.3 Experimental Theoretical modeling. The molecular square model presented in Figure 4.1 and the calculations related are the works of Ab raham Stern and Dr. Jonathan Belof from Dr. Brian Space laboratory at the chemistry de partment, university of south Florida. Synthesis of 4.1 In a capped 25 mL scintillation vial, a mixture of Pb(NO3)2 (0.1 mmol) and 4,4'-sulfonyldibenzoic acid (0.1 mmol) in a DMF and H2O, 1 mL each, was prepared and heated at 85C for 12 h resul ting in colorless rect angular crystals of 4.1 formulated as [Pb(C14SO6H8)(H2O)]2(DMF) using single crysta l X–ray diffraction study. Solvent exchange of 4.1 : Crystals of the as-synthesized compound were washed several times by acetonitrile, and then soaked in acetonitrile at room temperature for at least 30 days to afford the solvent-exchanged framework. Synthesis of 4.2: In a capped 25 mL scintillati on vial, a mixture of Cd(NO3)2 (0.1 mmol) and 4,4'-(hexafluoroisopropylidene)bis(b enzoic acid) acid (0.1 mmol) in a DMF and H2O, 1 mL each, was prepared and heated at 85C for 12 h resulting in colorless rectangular crystals of 4.2 formulated as [Cd2(C17H8F6O4)2(DMF)2]n using single crystal X–ray diffraction study. Solvent exchange of 4.2 : Crystals of the as-synthesized compound were washed several times by dichloromethane, and then soaked in dichloromethane at room temperature for at least 20 days to afford the solvent-exchanged framework. Synthesis of 4.3: In a capped 25 mL scintillation vial a mixture of Cd(NO3)2 (0.05 mmol) and 2-(1 H -tetrazol-5-yl)-pyrimidin e (0.1 mmol) in 1 mL

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225 of N,N'-dimethylformamide (DMF) was h eated at 85C for 1 h to result in colorless cubic crystals. Synthesis of 4.4: In a capped 25 mL scintillation vial a mixture of CuCl2, [1,10]phenanthroline, and 4,4'-sul fonyldibenzoic acid, (0.05 mmol each) in 0.5 mL of N,N'-dimethylformamide (DMF) and 0.5 mL of H2O was heated at 85C for 12 h to result in green-blue prismatic crystalline material. Synthesis of 4.5: In a capped 25 mL scintillation vial a mixture of CuCl2, 4,7-diphenyl-[1,10]phenanthroline, and 4,4'-sulfonyldibenzoic acid, (0.2 mmol each) in 1 mL of N,N'-dimethylform amide (DMF) was heated at 85C for 12 h to result in green-blue prismatic crystalline material. 4.4 Conclusion The theoretical calculations and experime ntal findings in this chapter strongly suggest that certain geomet rical design of the windows lined by aromatic rings in microporous MOFs is a suitable target in our quest to enha nce hydrogen storage properties of MOFs. The theore tical model constructed herein points towards the viability of this approach to attain enhanced isosteric heats of adsorption solely due to multiple dispersive interactions of molecular hydrogen to specifica lly tailored window geometry. Furthermore, the experimental structures pr esented indicate that such materials are synthetically accessible, while the challe nge remains as to generate microporous materials with tailored windows controlli ng access of molecular hydrogen to their

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226 relativle large pore systems, in an attempt to forge hydrogen storage materials with both high isosteric heat of adsorpti on and gravimetric hydrogen uptake. Overall, we present a novel approach with the potential to enhance H2 binding affinity in microporous MOFs. This approach is merit for further experimental and theoretical investigations to assess the extent of additive dispersive interactions in enhancing the H2 binding affinity in hydrogen storage ma terials, in general, and MOFs, in particular. 4.5 References 1. Schlapbach, L.; Zuttel, A. Nature 2001 414 353. 2. http://www1.eere.energy.gov/hydrogenandf uelcells/pdfs/freedomcar_targets_expl anations.pdf 3. Rowsell, J. L. C.; Yaghi, O. M. Angew. Chem. Int. Ed. 2005 44 4670-4679. 4. Collins, D. J.; Zhou, H.-C. J. Mater. Chem. 2007 17 3154-3160. 5. Lin, X.; Jia, J.; Hubberstey, P.; Schroder, M.; Champness, N. R. Cryst. Eng. Comm. 2007 9 438-448. 6. Hirscher, M.; Panella, B. Scr. Mater 2007 56 809-812. 7. Dinc M.; Long, J. R. Angew. Chem. Int. Ed. 2008 47 6766-6779. 8. Murray, L.J.; Dinc M. and. Long J. R. Chem. Soc. Rev. 2009 38 1294–1314. 9. Panella, B.; Hirscher, M.; Roth, S. Carbon 2005 43, 2209-2214. 10. Sakintuna, B.; Lamari-Darkrim, F.; Hirscher, M. Int. J. Hydrogen. Energy. 2007 32 1121-1140.

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227 11. Dren, T.; Bae, Youn-Sang; Snurr, Randall Q. Chem. Soc. Rev. 2009 38 12371247. 12. Han, S. S.; Mendoza-Cortes, J. L.; Goddard, W. A., III. Chem. Soc. Rev. 2009 38 1460-1476. 13. Lochan, R. C.; Head-Gordon, M. Phys. Chem. Chem. Phys. 2006 8 1357–1370. 14. O. Hu¨ ber, A. Glo¨ ss, M. Fichtner and W. Klopper, J. Phys. Chem. A 2004 108 3019. 15. Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Voda k, D. T.; Kim, J.; O'Keeffe, M.; Yaghi, O. M. Science 2003 300 1127-1129. 16. Bhatia, S. K.; Myers, A. L. Langmuir 2006 22 1688-1700. 17. E. J. Bylaska, W. A. de Jong, N. Govi nd, K. Kowalski, T. P. Straatsma, M. Valiev, D. Wang, E. Apra, T. L. Windus, J. Hammond, P. Nichols, S. Hirata, M. T. Hackler, Y. Zhao, P.-D. Fan, R. J. Ha rrison, M. Dupuis, D. M. A. Smith, J. Nieplocha, V. Tipparaju, M. Krishnan, Q. Wu, T. Van Voorhis, A. A. Auer, M. Nooijen, E. Brown, G. Cisneros, G. I. Fa nn, H. Fruchtl, J. Garza, K. Hirao, R. Kendall, J. A. Nichols, K. Tsemekhman, K. Wolinski, J. Anche ll, D. Bernholdt, P. Borowski, T. Clark, D. Clerc, H. Dachse l, M. Deegan, K. Dyall, D. Elwood, E. Glendening, M. Gutowski, A. Hess, J. Ja ffe, B. Johnson, J. Ju, R. Kobayashi, R. Kutteh, Z. Lin, R. Littlefield, X. Long, B. Meng, T. Nakajima, S. Niu, L. Pollack, M. Rosing, G. Sandrone, M. Stave, H. Ta ylor, G. Thomas, J. van Lenthe, A. Wong, and Z. Zhang, "NWChem, A Computational Chemistry Package for Parallel Computers, Version 5.1" (2007) Pacific Northwest National Laboratory, Richland, Washington 99352-0999, USA.

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228 18. "High Performance Computational Chem istry: An Overview of NWChem a Distributed Parallel App lication," Kendall, R.A.; Apra, E.; Bernholdt, D.E.; Bylaska, E.J.; Dupuis, M.; Fann, G.I.; Harrison, R.J.; Ju, J.; Nichols, J.A.; Nieplocha, J.; Straatsma, T.P.; Windus, T.L.; Wong, A.T.; Computer Phys. Comm 2000 128 260-283. 19. Weigend, F.; Haser, M.; Patzelt, H.; Ahrichs, R. Chem. Phys. Lett. 1998 294 143-152. 20. Dunning Jr., T. H. J. Chem. Phys 1989 90 1007-1023. 21. Kendall, R. A.; Dunning Jr., T. H.; Harris, R. J. J. Chem. Phys 1992 96 67966806. 22. Weigend, F.; Kohn, A.; Hattig, C. J. Chem. Phys 2002 116 3175-3183. 23. Halkier, A; Helgaker, T.; Jorgensen, P.; Klopper, W.; Koch, H.; Olsen, J.; Wilson, A. K. Chem. Phys. Lett 1998 286 243-252. 24. Kristyan, S.; Pulay, P. Chem. Phys. Lett 1994 229 175-180. 25. Moller, C.; Plesset, M. S. Phys. Rev 1934 46 618. 26. Belof, J. L.; Stern, A. C.; Eddaoudi, M.; Space, B. J. Am. Chem. Soc 2007 129, 15202–15210. 27. Catlett, C. et al "TeraGrid: Analysis of Organi zation, System Architecture, and Middleware Enabling New Types of Appli cations," HPC and Grids in Action, Ed. Lucio Grandinetti, IOS Press 'Advances in Parallel Computing' series, Amsterdam, 2007.

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229 Chapter 5: Zeolitelike Metal organic Frameworks (ZMOFs) as Solid Matrices for Metalloporphyrin-Based Heterocatalysis. 5.1 Introduction Zeolites are purely inorganic microporous aluminosilicates or aluminophosphates materials that occur naturally as minerals or have been synthetically prepared. The anionic charges of aluminosilicates are balanced by guest cations, e.g. Na+, K+, Ca2+, and Mg2+. Connectivity of tetr ahedrally coordinated atoms (T) through bidentate angular (ca. 145) oxygen is key to afford the non-interpen etrating porous structures of zeolites. Zeolitic structures demonstrat e wide variety of regular cage s, channels and windows as a result of the unique connec tivity of tetrahedra l nodes through an angular linker. Such very aspects of zeolites have enable d their utilization in various industrial applications, e.g. heterogeneous catalysis, ion exchange (ca tion exchange from aqueous solution, particularly useful in water softening) separation of mixtures in petrochemical industry, and gas storage.1-14 Due to the ability to exchange guest cations with others upon contact in solution, zeolites beds are widely employed as water softeners. Mo reover, ability of Zeolites to confine molecule s in their micropores induces changes in the structure and reactivity of guest molecules. One prominent example of industrial ap plication of zeolites is encountered in petrochemical industry for catalytic cracking of crude oil. The hydrogen-exchanged zeolites act as powerful solid-state Lewis acids, facilitating acidcatalyzed reactions of confined guest mol ecules such as isomerization, alkylation and

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230 cracking of hydrocarbons. Conf inement of guest molecules in such highly charged chemical environment drastically alters their reactivity and hence provides an amenable pathway to otherwise difficult or costly chemical transformations.15 The regular windows and channels in zeoli tes with specific dimensions are the basis for their shape-selective properties and accordingly their utilization in purification of gas mixtures or mixtures of branch ed and linear hydrocarbons. The ability to preferentially adsorb certain molecules a nd simultaneously excluding others led to the introduction of the term “molecular sieves” for zeolites and their applications in separation techniques based on th eir size-exclusion properties. Purification of p -xylene by MFI zeolite,16 Figure 5.1, demonstrates the ability of zeolites to separate mixtures based on the molecular size, and hence shape, as certain types of molecules will diffuse through the re gular channels and wi ndows of the zeolite, separated from other more steric or branched molecules. Figure 5.1. MFI zeolite utilized in purification of p -xylene.

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c a p i n t e t r 6 z e t h F ( r d The s y a 170 zeoli t eriodicity, o n variant per i The P e trahedrally r anslation, r o -rings (D6 R e olites is th e 3, which co u h at rely fra m F i g ure 5.2. C r ight) showi n ouble 4-rin g y stematic cl a t es,17 relies o f such fram e i odic buildi n P erBUs are b coordinated o tation. Per B R s), and cage e framewor k u ld be used a m ework dens i C rystal struc t n g connecti v g (D4R) as t h a ssification o n the cryst a e works to g e n g units (Per B b uilt from s m atoms by a p B Us include s, Figure 5. 2 k density, de f a s a measur e i ty to the t ure of the A v ity of tetra h h e zero-dim e 231 of the relati v a lline nature e nerate spec i B Us) m aller units c p plying sim p chains, tub e 2 for an exa m f ined as the n e to compar e A CO zeolite h edral atom s e nsional per i v ely large n u and hence t i fic 0-, 1-, o r c omposed o f p le operatio n e s, layers, d o m ple. Anoth e n umber of t e e between d i (left) and it s s that could b i odic buildi n u mber of ex i t hree dimen s r 2-dimensi o f a limited n u n (s) to the s m o uble 4-ring s e r structural e trahedral a t i fferent zeol i s correspon d b e construct e n g unit (Per B i sting zeolit e s ional o nal structur a u mber of m aller unit, e s (D4Rs), d o characteris t t oms per 10 0 i tes in a ma n d ing topolog y e d from peri B U), in bold e s, a lly e .g. o uble t ic of 0 0 n ner y odic

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232 openness of the framework. This measure is es pecially significant in comparing openness of MOFs with zeolitic topologies to inorganic zeolites. The larger dimensions of zeolitic MOFs will naturally result in fewer tetrahed ral nodes per specific volume compared to zeolites, and hence lower framework densitie s are expected, and indeed observed, for zeolitic MOFs. One particular aspect of synthetic zeolites is the ability to obtain a variety of different topologies through modification of the synthesis conditions. Most prominently, incorporation of structure di recting agents (SDAs) facilita tes isolation of particular zeolite and even can result in novel ones. Due to the anionic nature of aluminosilicates, synthetic pathways that employ cationic SDAs like alkyl ammonium sa lts that can direct the assembly of the building units and/or lim it the size of cages or windows of the zeolite have met with great success in isolat ion of numerous synthetic zeolites. However, targeting novel zeolites with larg er cages for applications pertinent to encapsulation of relatively large functional molecules faces limitations imposed by the observed tendency to obtain zeolites with one -dimensional pore systems, i.e. channels, instead of expanded cage dimensions. This lim itation restricts practical applications of inorganic zeolites as host matrices to relatively small-size functional molecules. Therefore, our group, among others, has opted to explore alternative routes to construct novel materials with zeolitelike topologies and characte ristics, namely anionic crystalline materials that exhibit forbidden interpenetration, guest-e xchange capabilities, and good thermal and chemical st ability. Turning to reticular chemistry, it appeared that two particular strategies, namely edge-expansion and vertex decoration, 18 could be implemented as design principles to c onstruct such zeolite-like materials.

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233 Employing edge-expansion strategy to desi gn and construct zeolite-like materials with anionic nature and extra-large cages co mpared to zeolites relies on substituting the bridging angular oxygen atom with a larger molecular linker. The imidazole ring emerged as a potential molecular species able to serve as di-topic, angular linker when coordinated to two metal ions. To impart rigi dity and chemical stability to the intended construct, we opted to utilize the di-substituted imidazole ring, specifically 1 H -imidazole4,5-dicarboxylic acid (H3ImDC),21 that when coordinated to metal ions will afford the proper bridging angle through its nitrogen atoms while, simultaneously, acting as chelating ligand through metal ion coordina tion to carboxylate groups This bi-functional characteristic of the bridging, expanded e dge, implemented in the design stage is complemented by the proper choice of In3+ ion as the tetrahedral node. As In3+ ions can accommodate dodecahedron hetero-coordination s phere afforded by four bis-bidentate (HImDC) ligands, the ability to construct an ionic zeolite-like mate rials with zeolitic topologies and extra large cages due to the expanded edges seemed feasible. Indeed, solvothermal reactions of In(NO3)3xH2O and H3ImDC afforded zeolite-like metal organic frameworks that demonstrate th e targeted structural and chemical properties. Moreover, analogous to the co mmonly encountered roles of SDAs in syntheses of zeolites, our group has demonstr ated the ability to direct the resulted topology through incorporation of different SD As in the initial reaction mixture. This approach marked the hybridiza tion of two types of materials known previously in solid state ch emistry, zeolites and metal organic frameworks, and hence the term zeolite-like metal organic frameworks (ZMOFs) was introduced to designate materials with hybrid chemical compositi on and zeolitic topologies, Figure 5.3. To

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234 facilitate visualization and pr esentation of the design princi ples employed in construction of ZMOFs, the corresponding cr ystal structures could be d econstructed into relatively simple, chemically-conceivable, building units from which the entire framework could be generated through symmetry operations, known as the molecular building block (MBB). Figure 5.3. Crystal structures (top left to right) of the sod rho and usf -ZMOFs and (bottom) the corresponding SOD, RHO, a nd RHO zeolitic topologies. Color scheme: Indium (green), carbon (grey), oxygen (red) nitrogen (blue), hydrogen (white).

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235 Figure 5.4. The In(ImDC)4 MBB present in ZMOFs could be visualized as tetrahedral connected node interconnect ed through bis-bidentate angular ImDC linker. The MBB present in ZMOFs is the In(HnImDC)4, n = 0, 1, a dodecahedrallycoordinated In3+ ions interconnected th rough the bis-bidentate HnImDC linker, figure 6.4. The single-metal-ion MBB approach towards construction of ZMOFs, first implemented by our group, encompasses utilization of imid azole ring as an expanded linker having the appropriate coordination angle dictated by the two nitrogen atoms, comparable to that provided by single oxygen atom in zeolites Figure 5.4, and hence permitted access to zeolitic topologies but with extended edges and, consequen tly, larger cages and channels. The carboxylate functionalities present on the imidazole ring se rved to impart structural rigidity and chemical stability to the constructed materials due to the well-known chelate effect in metal ion complexes. Moreover, due to the anionic nature of the carboxylate ions, an overall negatively charged ZMOFs could be attained where the principle of utilizing a variety of cationic SDAs, applied to zeolites to induce a variety of zeolitic topologies, could be implemented. This was su ccessfully demonstrated experimentally by isolating three different ZMOFs constructe d from essentially the same MBB but in presence of different SDAs. Namely, the nitrate salts of doubly protonated 1,3,4,6,7,8hexahydro-2 H -pyrimido[1,2-a]pyrimidine (HPP), imidazole (Him), and 1,2-

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236 diaminocyclohexane (DACy), were utilized as SDAs in synthesis of rho, sod, and usfZMOFs, respectively.21 As described above, ZMOFs represent a fam ily of functional solid state materials that share structural, compositional, and functional aspects of inorganic zeolites and the hybrid metal organic frameworks (MOFs). The growi ng scientific and industrial interest in MOFs could be linked to their unique at tributes, crystalline open structures with periodic dual composition amenable to bottom-up assembly of judiciously designed molecular building blocks into a desire d framework expanding and/or decorating a specific blueprint network topology.19 These features of MOFs, open functional MOFs with modular compositions and tailorable pores amenable to bottom-up assembly from rationally selected MBBs, offer great potential for those materials to address some key applications such as hydrogen storage, car bon dioxide sequestration, enhanced catalysis, smart sensors, and drug delivery.20 Despite the relatively large number of MOFs in current literature with accessible voids stable against guest exchange, the id ea of being able to fine-tune an existing structure through post-syntheti c modification or by incorpor ation of functional guest molecules during the synthesis is especially appealing. This is due to the wide potential applications for a porous functional material that is amenable to post-synthetic modifications or ones that demonstrate targ eted functionality due to encapsulated, yet accessible, functional molecules, to generate ma de-to-order materials. In this approach a MOF can be regarded as a platform suitable fo r a variety of desired applications merely through cost, atom, and time-efficient modifications.

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237 Toward this effort, we developed a ne w approach for utilization of ZMOFs, constructed through the assembly of rigid and directional single-metal-ion-based molecular building blocks (MBBs), as tunable platforms for applications in gas storage and porphyrin-based heterocatalysis. As described earlier, ZMOFs are topologically analogous to inorganic zeolites and, similarly, are anionic and chemically stable in aqueous media mainly due to the presence of chelated In3+, a characteristic rarely observed in common MOFs. Additionally, ZM OFs possess extra-large cavities, which offer great potential for their exploration in applications pertinent to larger molecules. Stimulated by such desirable characteristics of ZMOFs, we opted to explore the potential to finely tune their chemical characterist ic through incorporati on of functional guest molecules, namely the cationic 5,10,15,20-te trakis(1-methyl-4pyridinio)porphyrin, [H2TMPyP]4+, that could be encapsulated inside the large cages of rhoZMOF utilizing the ship-in-a-bottle process. In this process, the anionic framework of rhoZMOF would self-assemble from its precursors, MBBs, en capsulating the cationic porphyrin, added as solution to the initial reaction mixture, to result in a functional solid construct with essentially the same topology as RHO zeolite bu t with encapsulated porphyrin molecules in the extra-large -cages of rhoZMOF. The choice of porphyrins as guest molecule s, in this study, originates from the synthetic applications acce ssible through anchoring and is olating catalyt ically-active metalloporphyrins, prohibiting their self-dimer ization and oxidative degradation, and in turn enhancing their catalytic properties. Moreover, an isolated metalloporphyrin encapsulated in well-defined chemical envi ronment might provide a synthetic model for

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238 active sites in various enzymes utilizing metalloporphyrins, of which cytochromes are the most prominent examples. The utilization of metalloporphyrins in catalytic oxidation, e.g. hydroxylation and epoxidation of hydrocarbons 22 represents a wide scale synt hetic application and hence is a viable target for developments. Of special concern are limitations in many homogeneous metalloporphyrin-based catalysts represented by limited lifetime and/or activity due to formation of bridged oxide metalloporphyrin dimers, preventing substrate access to the catalytic si te, and oxidative self-degradation. 23 Therefore, strategies were devised to immobilize metall oporphyrins in solid matrices to address such limitations of homogenously catalyzed systems.24 In this approach, the metalloporphyrin molecule can be isolated, and in essence its catalytic site protecte d, through anchoring to a solid substrate. Examples of such substr ates include modified mixed oxide surfaces25 and porous inorganic solids (i.e. zeolites X and Y, 26 mesoporous silicates, 27 silica surfaces 28 ), which have been investigated as solid-state matrices to immobilize metalloporphyrins. However, these systems also are faced with limitations, including aggregation of the catalyst molecules, limite d catalyst loadings re sulting in potential nonperiodic distribution, and/or leaching of th e catalyst due to cleavage of the catalystsubstrate linkage under the catal ytic reaction conditions used. Therefore, it appears that cer tain attributes are required for a suitable host matrix to overcome the above challenges that in clude: (i) larg e cavities, suitable for the encapsulation, and in effect isolation, of one guest porphyrin molecule per cavity with proper window size not to allow catalyst le aching while allowing diffusion of reactants and products, (ii) mild synthesis conditions of the matrix to avoid degradation of the

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239 guest porphyrin, (iii) presence of framew ork-porphyrin interactions, in our case electrostatic interactions, i nducing and further directing th e assembly of the framework around the porphyrin, permitting the one-step fra mework construction and encapsulation of the free-base porphyrin, (iv) maintain ed framework integrity upon post-synthesis metallation of the encapsulated porphyrin, (v) low affinity fo r the oxidation products to the framework, thus allowing for their diffu sion into the bulk solution and ease of separation, through simple filt ration, of the heterogeneous catalyst from the reaction mixture. 5.2 Results and Discussion Considering the aforementioned criteria for an efficient solid matrix to encapsulate metalloporphyrins, our rhoZMOF (topologically analogous to zeolite RHO ) offers great potential to answ er such criteria and serves to simultaneously merge the realms of MOFs and zeolites with the catalyt ic properties of porphyrins to forge a unique tunable catalyst platform. The la rge voids inside its periodic -cages and their anionic nature suggest the ability for encapsulation of cationic porphyrins. Mo reover, stability of rhoZMOF in different methanolic solutions of metal nitrate salts enabled us to metallate the encapsulated free-base porphyrin with a vari ety of metal ions, forging a versatile precatalyst (the H2RTMPyP, free-base porphyrin in rhoZMOF) that, post-synthetically, can be utilized to prepare a variety of encap sulated metalloporphyrins (M-RTMPyP, M = Cu, Co, Zn, Ni, Mn) for applications in different catalytic reactions requiring different metal ions in the porphyrin ring.

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240 Indeed, reactions of In(NO3)3x H2O and 4,5-imidazoledicarboxylic acid (H3ImDC) in a mixture of N,N`-dimethyl formamide (DMF) and acetonitrile (CH3CN) in presence of 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra( p -toluenesulfonate) ([H2TMPyP] [ p-tosyl]4) have yielded dark red cubic-like crystals, H2RTMPyP, suggesting the presence of the porphyrin, Figure 5.5. The crystals, insoluble in water and comm on organic solvents, were washed with DMF and methanol several times, until no re sidual porphyrin was detected in the solution, as evident from the UV-vis spect rum. The powder X-ray diffraction (PXRD) pattern of the as-syn thesized compound matches that of our previously published colorless rhoZMOF,3 Figure 5.6, confirming the c onstruction of the intended Figure 5.5 crystal structure of rhoZMOF (left), hydrogen atoms omitted for clarity, and schematic presentation of [H2TMPyP]4+ porphyrin ring enclosed in rhoZMOF -cage (right, drawn to scale).

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241 Figure 5.6 Experimental powder X-ray diffraction patterns for rhoZMOF and the intended porphyrin-impregnated rhoZMOF, confirming the construction and phase purity of the as-synthesized compound. crystalline framework; the structure is furthe r supported by single-crystal studies, which confirm identical crystallographic parameters to rhoZMOF (cubic, Im-3m, a = 31.0622(7) ). The framework structur e is based on 8-coordinate In3+ ions N-, O-heterochelated by four separate HImDC ligands (InN4(CO2)4 MBB) to give InN4 TBUs. The assembly of the 4-connected TBUs results in the generation of truncated cuboctahedra (the -cage is enclosed by 48 InN4 TBUs), which link together through double eightmember rings (D8R) to form the rhoZMOF. The framework unit cell (volume 8 times larger than conventi onal inorganic zeolite RHO ) is formulated as ([In48(HImDC)96]48-), where the negatively charged framework is balanced by cationic guest molecules. The presence of [H2TMPyP]4+ inside rhoZMOF was confirmed by solid-state UV-vis studies of the fully washed crystalline solid, H2RTMPyP, where the spectrum shows the characteristic five absorption ba nds associated with the free-base porphyrin

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242 ( max = 434, 522, 556, 593, 648 nm), Figure 5.7. Accordingly, the porphyrin was not metallated by In3+ present in the assembly conditions. It should be noted that the inclusion of the porphyrin inside the cages of rhoZMOF could not be verified by singlecrystal XRD due to the lower symmetry of the porphyrin molecules, C1, compared to the cubic Im-3m symmetry of the framework, i.e. not enough constraints can be exerted on the multiple possible orientations of the porphyrin molecule inside the cages, believed to be necessary to induce long-range order inside rhoZMOF. Figure 5.7. Diffuse-reflectance, solid-s tate UV-vis spectra of H2RTMPyP and its various metallation products. Incubation of H2RTMPyP in an aqueous solution of Na+ ions showed no release of the porphyrin, as indicated by UV-vis studies of the solution. In contrast, smaller cationic molecules, such as acridines, can be reversibly immobilized (through

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243 electrostatic interactions) inside rhoZMOF cavities through ionic exchange due to their smaller dimensions, ca. less than 1 nm.3 Dissolving H2RTMPyP in strongly acidic aqueous solution allows release of the porphyrin into solution, which permits the estimation of the loaded amount of [H2TMPyP]4+ to be 2.5 wt. %, controllable via variable concentration of free-base porphyrin during synthesis of H2RTMPyP.12 These findings prove the encapsulation of the fr ee-base porphyrin, and support the absence of porphyrin leaching, mainly due to the relativ ely smaller size of the window openings to the -cages, i.e. D8Rs. In addition, similar in situ encapsulation conditions to the aforementioned cationic porphyrin did not perm it the encapsulation of neutral nor anionic porphyrins nor phthalocyanines inside rhoZMOF, supporting the importance of electrostatic interactions between the cationic porphyrin and the anionic framework during the simultaneous self-assemb ly and encapsulation processes. Potential metallation of the free-base porphyrin H2RTMPyP will allow for its utilization and exploration as a platform for metalloporphyrin-based catalysis. Indeed, we have successfully metallated the encapsulat ed free-base porphyrin, post-synthesis, by exposing H2RTMPyP to various solutions of transition metal ions. Metallation of H2RTMPyP by various metal ions was accomplished via incubation in a 0.1M methanol solution of the corresponding metal nitrate at room temperature for up to 24 hours. The crystals were subsequently washed with H2O and methanol several times, and air-dried at 40C. The expected metallation was confirmed by UV-vis studies as indicated by the redshifted Soret-bands and collapse of the Q-bands multiplets upon metallation, Figure 5.7. Crystals of H2RTMPyP yield M-RTMPyP, (6.2-6.5) after metallation, where M = Mn, Cu, Zn, or Co ions.

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o c a a t c h p r 2 4 F b c o a m t o o To as s f Mn-RTM P a talyst for c y t 65C in th e h lorobenze n r ogress was 4 hours, bas F i g ure 5.8. C ased on TB H o nsumed pe r m ount of o x o cyclohexa n f 23.5 (catal s ess catalyti c P yP. Specifi c y clohexane o e presence o n e as an inte r monitored b ed on the C yclohexane H P, one equ i r ketone pro x idant prese n n ol/cyclohe x yst loading o c activity, h y c ally, the cr y o xidation. U f tert b utyl h r nal standar d b y analyzin g catalytic o x i valent cons u duced. n t in the initi x anone) of 9 o f 3.8%) w e 244 y drocarbon o y stalline sol i U nder neat c o h ydroperoxi d d and MnR g aliquots of x idation usi n u med per al c al reaction m 1.5% and a c e re observed o xidation w a i d Mn-RTM P o nditions, th d e (TBHP) a R TMPyP as t the bulk sol n g (6.1a) as a c ohol produ c m ixture, a to c orrespondi n Figure 5.8, a s performe d P yP was ex p e oxidation w a s the oxida n he catalyst; ution using G a catalyst at c ed and two tal yield (fr o n g turn ove r noticeably h d in the pres p lored as a w as perfor m n t, the reaction G C-FID. A f 65C. Yield equivalent s o m cyclohe x r number (T O h igher yield ence m ed f ter % s x ane O N)

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245 compared to other systems of supported metalloporphyrins (zeolites or mesoporous silicates), table 5.1. The reaction products were formed in almost stoichiometric amounts. The yield % was calculated assuming a 2:1 TB HP to cyclohexane molar ratio, necessary to produce cyclohexanone through oxidation of the intermediate cyclohexanol. The weakly polar hydrocarbon products shoul d have low affinity for the highly polar rho-ZMOF framework and thus readily diffuse into the solution. Cyclohexanol and cyclohexanone were the only observed products, identified through their retention times Table 5.1. Summary of cyclohexa ne oxidation reactions using metalloporphyrins encapsulated in solid matrices. (a) TON = (moles of cyclohexanol+ 2X mole s of cyclohexanone)/moles of catalyst; (b) based on moles of oxidant; (c) moles of catalyst/moles of oxidant; (d) P = tris(4N -methyl-pyridyl)-mono(pentafluorophenyl) por phyrin; (e) PhIO = iodosobenzene; (f) TMPyP = 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin; (g) va lues reported depend on the diffe rent catalyst systems used i n reference 3; (h) TBHP = tert -butylhydroperoxide. 1. Skrobot, F. C.; Rosa, I.; Marque s, A.; Martins, P.; Rocha, J.; Valente, A.; Iamamoto, Y. J. Mol. Cat A. 2005 237, 86-92. 2. Rosa, I.; Manso, C.; Serra, O.; Iamamoto, Y. J. Mol. Cat. A 2000 160, 199-208. 3. Moreira, M. S. M.; Martins, P. R.; Curi R. B.; Nascimento, O. R.; Iamamoto, Y. J. Mol. Cat. A: Chem. 2005, 233 73-81. Reference Catalyst Solvent Cyclohexane Temperature, Time Oxidant TONa Yieldb Loadingc 1 Fe(III)-Pd encapsulated in zeolite Y Used 025 mol catalyst (1 porphyrin ring per 40 available supercages) Dichloroethane 146 mmole rt, 6 hours PhIOe 5 mol 76 38% 5% 2 Fe(III)-TMPyPf encapsulated in zeolite X Used 0055 mol catalyst (1g solid = 11 mol catalyst) Dichloroethane 266 mmole rt, 75 hours PhIO 1 mol 10 60% 55% 3 Fe(III)-TMPyP supported on silica surface and matrices Used 025 mol catalyst Dichloroethane 200 L rt, not reported PhIO 25 mol 2~20g 2~20% 1% This work Mn-TMPyP encapsulated in rho -ZMOF Used 29 mol catalyst (30 mg solid = 1 mol catalyst) Cyclohexane neat 65C, 24 hours TBHPh 77 mol 24 915% 38%

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246 compared to authentic samples, suggesting th at the investigated oxidation reaction is selective towards the formation of this alc ohol and ketone under the conditions employed (i.e. no further oxidation pr oducts were detected). The solid matrix Mn-RTMPyP readily can be separated from the product solution by simple filtration, a feature unique to he terogeneous solid-immob ilized catalysts that allows for studies of recyclability of the catalyst/platform. Indeed, Mn-RTMPyP is recyclable under the reaction conditions up to at least the 11th cycle (the reported results in this study), as Mn-RTMPyP retains its crystallinity, reactivity and selectivity throughout this number of cycles. Each cycle was run for 24 hours, and then MnRTMPyP was isolated, washed with methanol, a nd dried at 40C. No leaching of the encapsulated metalloporphyrin was observed as evident from the UV-vis spectrum of the product solution. In fact, catalytic activity was observed only when crystals of MnRTMPyP were present in the reaction mixture. No catalytic activity was observed for the control reactions: 1) in th e absence of porphyrin and rho -ZMOF, 2) in the presence of only the rho -ZMOF (no porphyrin), 3) in the presence of Mn2+-exchanged rho -ZMOF (no porphyrin), and 4) in the presence of H2RTMPyP (free-base porphyrin in rho ZMOF). These results confirm that the observed catalytic behavior is unique to MnRTMPyP, rho -ZMOF impregnated with Mn-metallated porphyrin.

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247 5.3 Experimental Synthesis of the free-base porphyrin encapsulated in rho-ZMOF, [H2TMPyP]-rhoZMOF, (6.1): All chemicals were Aldrich reagent grade and used as received, unless otherwise noted. In a 20 ml vial, a mixture of In(NO3)3 x H2O (0.015 g, 0.0435 mmol), 4,5-H3ImDC (0.014 g, 0.087 mmol), DMF (1 ml), CH3CN (1 mL), and 0.1ml of 8 mM methanol solution of [H2TMPyP][ p -tosyl]4, were mixed; the vial was sealed and heated to 85C for 12 h, then to 105 C for 24 h with a heating rate of 1.5C/min, and then cooled down to room temperature with a cooling rate of 1C/min. Dark red crystals of (6.1) [H2TMPyP]4+ encapsulated inside rho -ZMOF, were then collected, washed with DMF, and then washed with metha nol several times, until no resi dual amount of porphyrin was present in the washing solution, as eviden t from the UV-vis spectrum of the washing solution. In an attempt to maximize porphyrin loading into rho -ZMOF, 1.198 mmole of 4,5-H3ImDC, 0.5 mmol of In(NO3)3 x H2O, 30 mol of [H2TMPyP][ p -tosyl]4, DMF, and ethanol (3 ml each) were mixed in a 25 mL sc intillation vial. The vial was then heated using the same procedure for the synthesis of (6.1) The resultant crystals, (6.2) were washed several times with methanol until no residual porphyrin was present. 10.8 mg of (6.2) were dissolved in 25ml conc. HNO3, from which 1 ml was diluted to the volume of 10 ml using D.I. water. Using atomic abso rption to determine concentration of In3+ ions and UV-vis for porphyrin ( 438 = 1.9 x 105 M-1 cm-1), an estimate of 67% loading of porphyrin into the -cages (each made of 24 In3+ ions) was possible. Further increase of

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248 the free-base porphyrin concentration in th e reaction mixture precludes formation of crystalline material. Synthesis of the metallated porphyrin encapsulated in rho-ZMOF, [MTMPyP]-rho-ZMOF, M = Zn, Cu, Co, Mn, Ni: The general procedure to metallate the free-base porphyrin encapsulated inside rhoZMOF is accomplished through immersion of the [H2TMPyP]rhoZMOF crystals in 0.1M methanol solution of the corresponding metal nitrate at room temp erature for 24 hours until metallation was commenced as probed by the characteristic UV-vis spectra of the metallated porphyrin. The crystals were subsequently washed with H2O and methanol several times, and airdried at 40C. The expected metallation was confirmed by UV-vis spectroscopy as indicated by the red-shifted Soret-bands and collapse of the Q-bands multiplets upon metallation. Catalytic oxidation reaction conditions: 77 mol of tert -butylhydroperoxide (TBHP), dried over MgSO4, 100 mol chlorobenzene as internal standard, 10 ml cyclohexane, and 88 mg of the MnTMPyPrhoZMOF catalyst (equivalent to 2.9 mol of Mn-TMPyP) were mixed, under aerobic conditi ons, in a 25 mL round-bottom flask fitted with a silicone septum. The reaction mixture wa s then held at 65C in an isothermallystated bath for the required amount of time, as determined by analyzing aliquots of the mixture over time using a gas-chromatogram c oupled to a flame ionization detector (GCFID).

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249 GC-FID specifications: A Shimadzu GC-201 was used, using N2 carrier gas and equipped with a 30 m, 0.1 mm i.d. Agillnet capillary column DB-5. The injection port was kept at 220C, and the detector port at 320C. Oven program: 73C for 25 minutes, heating rate of 20C/min, fi nal temperature of 250C for 5 minutes. The column flow was kept at 0.1 ml/min, split = 50. Retention time s: TBHP (3 min), cyclohexane (4.5 min), chlorobenzene (14.6 min), cyclohexanol ( 16.9 min), and cyclohexanone (17.8 min). The sample injected volume was 1 L. 5.4 Conclusion Here we have demonstrated the utilization of (In-HImDC)-based rho -ZMOF as a host for large catalytically active molecules, specifically metalloporphyrins, and its effect on the enhancement of catalytic activity. In or der to produce a versatile platform (i.e. can be tailored to meet specific applications), we encapsulated the free-base porphyrin, which was readily metallated, post-synt hesis, by various transition me tal ions to produce a wide range of encapsulated metalloporphyrins. This work has the potential to be exte nded to explore further utilization of rhoZMOF encapsulated metalloporphyrins, towa rds other catalytic transformations like cyclopropanation and epoxidation of alkenes. In addition, pote ntial modifications to the encapsulated porphyrin to induce stereosel ectivity, enhance regioselectivity and/or reactivity are of considerable interest for future investigations.

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250 5.5 References 1. R.F. Gould, Editor, ACS Monograph 101, Am Chem. Soc., Washington, DC (1971). 2. D.W. Breck, New York: Wiley-Interscience, 1974 3. A. Corma, NATO ASI Ser. Ser. C. 1992 352 373-436. 4. R. Le Van Mao, N.T. Vu, S. Xiao, A. Ramsaran. J. Mater. Chem 1994 4 11431147. 5. R. Le Van Mao, Can. Pat. Appl. CA 2125314, 1995 6. G. Hourdin, A.Germain, C. Moreau, F. Fajula, Catal. Lett. 2000 69 241-244. 7. R.P. Claridge, N.L. Lancaster, R.W. Millar, R.B. Moodie, J.P.B. Sandall, J. Chem. Soc. Perkin. Trans. 2. 2001 2 197-200. 8. I.E. Maxwell and W.H.J. Stork, Stud. Surf. Sci. Catal 2001 137 747-819. 9. M. E. Davis. Nature, 2002 417 813-821. 10. S.M. Kuznicki, V.A. Bell, T.W. Langner, J.S. Curran, U.S.Pat. Appl. U.S. 20020074293, 2002 11. S.M. Kuznicki, T.W. Langner, J.S. Curran, V.A. Bell, U.S.Pat. Appl. U.S. 20020077245, 2002 12. X. Yang. Gongye Cuihua. 2003 11 19-24. 13. K. Hagiwara. Appl. Catal. A. 2003 245 N4-N5. 14. R. Glaeser and J. Weitkamp. Springer Ser. Chem. Phys. 2004 75 161-212. 15. Dyer, Alan (1988). An Introduction to Zeo lite Molecular Sieves John Wiley & Sons 16. Sakai, H.; Tomita, T.; Takahashi, T. Separation and Purifi cation Technology 2001 25 297-306

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251 17. Atlas of Zeolite Framework Types, 5th edition, Ch. Baerlocher, W.M. Meier & D.H. Olson, Amsterdam: Elsevier (2001) and http://www.iza-structure.org/databases/ 18. O'Keeffe, M.; Eddaoudi, M.; Li, H.; Reineke, T.; Yaghi, O. M. Journal of Solid State Chemistry, 2000 152 3-20. 19. (a) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O'Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001 34 319-330. (b) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, O. M. Science 2002 295 469-472. (c) Frey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F. Acc. Chem. Res. 2005 38 217-225. (d) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001 101 1629-1658. (e) Kitagawa, S.; Kitaura, R.; Noro, S.-I. Angew. Chem. Int. Ed 2004 43 23342375. 20. (a) Rowsell, J. L. C; Yaghi, O. M. J. Am. Chem. Soc. 2006 128 1304-1315. (b) Dinca, M.; Han, W. S.; Liu, Y.; Dail ly, A.; Brown, C. M; Long, J. R. Angew. Chem. Int. Ed. 2007 46 1419-1422. (c) Mulfort, K. L; Hupp, J. T. J. Am. Chem. Soc. 2007 129 9604-9605. (d) Liu, Y.; Eubank, J. F.; Cairns, A. J.; Eckert, J.; Kravtsov, V. Ch.; Luebke, R; Eddaoudi, M. Angew. Chem. Int. Ed. 2007 46 3278-3283. (e) Hayashi, H.; Cote, A. P.; Furukawa, H.; O'Keeffe, M; Yaghi, O. M. Nat. Mater. 2007 6 501-506. (f) Llewellyn, P. L.; Bourrell y, S.; Serre, C.; Vimont, A.; Daturi, M.; Hamon, L.; DeWeireld, G.; Chang, J. ; Hong, D. ; Hwang, Y. K.; Jhung, S. H.; Frey, G. Langmuir 2008 24 7245-7250 (g) Banerjee, R.; Phan, A.; Wang, B.; Knobler, C.; Furukawa, H.; O'Keeffe, M.; Yaghi, O. M. Science 2008 319 939-943. (h) Cho, So-Hye; Gadzikwa, T.; Afshari, M.; Nguyen, SonBinh T.; Hupp, T. J. Eur.

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252 Jour. Inorg. Chem. 2007 4863-4867. (i) Horcajada, P.; Serre, C.; Vallet-Reg, M.; Sebban, M.; Taulelle, F.; Frey, G. Angew. Chem. Int. Ed. 2006 45 5974-5978. 21. (a) Liu, Y.; Kravstov, V.; Larsen, R.; Eddaoudi, M. Chem. Commun 2006 14881490. (b) Liu, Y.; Kravstov, V.; Eddaoudi, M. Angew. Chem. Int. Ed. 2008 47 84468449. 22. (a) Sheldon, R. A.; Kochi, J. K. Metal-Catalyzed Oxidations of Organic Compounds ; Academic Press: New York, 1981. (b) Metalloporphyrins in Catalytic Oxidations ; Sheldon, R. A., Ed.; Marcel Dekker: New York, 1994. (c) Collman, J. P.; Zhang, X.; Lee, V. J.; Uffelman, E. S.; Brauman, J. I. Science 1993 261 1404-1411. (d) Comprehensive Supramolecular Chemistry ; Suslick, K. S., Ed.; Pergamon: Oxford, 1996; Vol. 5 (Supramolecular Reactivity a nd Transport: Bioinorganic Systems). (e) Meunier, B. In Metalloporphyrin Catalyzed Oxidations ; F. Montanari, L. Casella, Eds.; Kluwer: Dordrecht, 1994; pp 1-48. 23. Guo, C.; Song, J.; Chen, X.; Jiang, G. J. Mol. Catal. A. 2000 157 31-40. 24. (a) Sacco, H.C.; Iamamoto, Y.; Lindsay Smith, J.R. J. Chem. Soc., Perkin Trans. 2001 2 181-190. (b) F.S. Vinhado, C.M.C. Prado-Manso, H.C. Sacco, Y. Iamamoto, J. Mol. Catal. A. 2001 174 279-288. (c) Deniaud, D; Spyroullias, G. A; Bartoli, J. F.; Battioni, P.; Mansuy, D. ; Pinel, C.; Odobel, F.; Bujoli, B. New. J. Chem. 1998 22 901-905. (d) Li, Z; Xia, C. G.; Zhang, X. M. J. Mol. Catal. A 2002 185 47-56. 25. Cardoso, S. W.; Francisco, M. P.; Landers, R.; Gushikem, Y. Electrochim. Acta 2005 50 4378-4384.

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253 26. (a) Khan, T. A.; Hriljac, J. A. Inor. Chim. Acta 1999 294 179-182. (b) Rosa, I. L. V.; Manso, C. M. C. P.; Serra, O. A.; Iamamoto, Y. J. Mol. Cat. A. 2000 160 199208. (c) Skrobot, F. C.; Rosa, I. L. V.; Marques, A. P. A.; Martins, P. R.; Rocha, J.; Valente, A. A.; Iamamoto, Y. J. Mol. Cat. A. 2005 237 86-92. 27. (a)Xu, W.; Guo, H.; Akins, D. L. J. Phys. Chem. B. 2001 105 1543-1546. (b) Nur, H.; Hamid, H.; Endud, S.; Hamdan, H.; Ramli, Z. Mat. Chem. Phys. 2006 96 337342. 28. Moreira, M. S. M.; Martins, P. R.; Curi, R. B.; Nascimento, O. R.; Iamamoto, Y. J. Mol. Cat. A. 2005 233 73-81.

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254 Chapter 6: Unexplored Pote ntial Applications of Metal Organic Materials in Photochemical Hydrogen Generation. Metal organic materials,1 as functional solid state mate rials continue to receive scientific interest due to their myriad applic ations associated with the hybrid composition nature, modular architecture, and rational design approaches mappe d for a wide number of sub families of such compounds. One partic ular application is uncharted yet could prove very rewarding, that is in photoche mical hydrogen generation. The combination of already established systems, mostly molecular, in photochemical hydrogen generation technology and the relatively new area of metal organic materials can pave the road for novel technologies capable of catalytic activity in photochemical hydrogen generation with far enhanced efficacy, a necessary st ep for commercial deployment of such clean energy resource. Such potentials and proposed future investigations are highlighted herein. 6.1 Harvesting Solar Energy The three major conceptual designs for cost-efficient solar energy converters are homogenous light-driven catalytic systems for water splitting, 2,3 dye-sensitized solar cells (DSSCs),4 and polymer-based solar cells.5 While the first system converts solar energy directly into chemical energy stored in molecular hydrogen, the latter two systems generate electric power that could subsequently be uti lized directly for various applications or indirectly by conversion into hydrogen through electrolysis processes.

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255 Each type of the aforementioned solar syst ems utilizes photoactive materials for photonto-electron conversion through either photoactive metal co mplexes or purely organic molecules. Polymer-based solar cells are th e least expensive; however, DSSCs are the most promising solar cells demonstrating high er efficiencies than polymer-based cells. Charge collector anode, regeneration redox s huttle, and a counter electrode are common parts in DSSCs. Differences in the nature of the photoactive materi al, redox shuttle, and photoanode play major roles in determining the cost, efficiency and lifetime of the various DSSCs thus constructed. Consequent ly, attempts were made to enhance the characteristics of those elements thro ugh careful design and manipulation, on the molecular level, aiming to attain optimal performance and energy production cost for commercial deployment of the solar technology.6, 7 6.2 Homogenous Systems for Water Photolysis The Gibbs free energy change for the overa ll water photolysis reaction (eq. 6.1) is 237.2 kJ mol 1. Thus, the reaction is non-spontaneous and requires an input of energy that corresponds to 1.23 eV per electron wh ich could be supplie d by a photon with a wavelength of < 1008 nm. Hence the photolysis of water can be theoretically and thermodynamically met by a photon from the visible region of th e solar spectrum. Unfortunately, only in this regards, water doe s not absorb in the visible region of the solar spectrum, where the most intensity of sola r energy is, and thus th e need of a catalyst that can efficiently absorb visible radia tion and convert the photoenergy into usable electric energy arises. In homogenous photolysis systems, a photosensitizer molecule absorbs photons with energies larger th an the HOMO-LUMO energy gap generating an electron-hole pair. Separati on of the photo-generated elec tron-hole pairs (excitons)

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256 followed by redox reactions at a catalytic site are accomplished on the molecular level. In contrary to heterogonous systems employing se miconductors as the photoactive material, homogenous photolysis systems eliminate the need for an external circuit and integrated photoanode, thus decreasing the voltage pena lty from overpotentials developed in semiconductor solar cells. However, increasin g efficiency and chemical stability of homogenous systems remains a challenge. 2e+ 2H2O 2OH+ H2 -0.41 V 2h+ + H2O 2H+ + 1/2 O2 -0.82 V Equation 6.1. Redox potentials for water at pH = 7 and 25C **[Ru(bpy)3]2+ *[Ru(bpy)3]2+ [Ru(bpy)3]2+h v` Luminesense Radiationless Decay [Ru(bpy)3]+[Ru(bpy)3]3+-1.28 V +1.26 V -0.86 V +0.84 V h v Figure 6.1. Light absorption by [Ru(bpy)3]2+ producing singlet excited state which relaxes to the relatively long-liv ed triplet excited state. St andard redox potentials for the different processes are shown. Separation of the electronhole pair followed by elect ron transfer (ET) from photosensitizer (P) to the ac ceptor (A) catalyst, due to electrochemical potential difference between the photoactive and cataly tic centers, is follo wed by oxidation of water by holes and reduction of protons by electrons. Regeneration of the oxidized

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257 photoactive center could also be attained by a sacrificial chemical agent, as electron donor, to complete the cataly tic cycle. Among the widely employed and by far the most efficient photoactive species in DSSCs and catalytically-active homogenous systems are ruthenium tris -diimine complexes, represented here by [Ru(bpy)3]n+, bpy = 2,2`bipyridine, Figure 6.1. Such dyes exhibit several favorable at tributes as photochemically active species that include (1 ) suitable MLCT band gap energy, allowing absorption in visible region of solar spectrum, (2) relatively long-lived triplet excited state, (3) efficient charge separation, (4) chemical stability, and (5) enhanced redox properties of the photoinduced excited state. Phot o-induced MLCT in [Ru(bpy)3]2+ generates the singlet excited state **[Ru(bpy)3]2+ that relaxes through intersystem cr ossing to the relatively long-lived triplet excited state ( = 0.6 s at 25C), *[Ru(bpy)3]2+.8 The triplet excited state exhibits enhanced electrochemical property, being better redox species than [Ru(bpy)3]2+ by 2.12 V, thus could subsequently undergo an ET pro cess (oxidative quenching) or relaxation to ground state through luminescence. Cataly tically-active centers, in particular cobaloximes, acting as electron acceptors when in proximity of *[Ru(bpy)3]2+, facilitate water reduction. The widely accepted mechan ism for cobaloxime-catalyzed hydrogen generation involves first reduction to Co(I) followed by protonation generating Co(III)hydride that undergoes protonation pr oducing hydrogen and Co(III) species.9 6.3 Dye-Sensitized Solar Cells (DSSCs) Since the original conception of the fi rst DSSC by Grtzel and coworkers in 1991,10 the efficiency of such light-har vesting assemblies has improved while maintaining essentially the same configuration of the original design,6 Figure 6.2. The three major photo-related components of a DS SC, undergone extensive investigation and

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258 optimization, are the dye, redox shuttle, and photoanode.7 In DSSCs, a photoactive material with relatively modera te HOMO-LUMO energy gap, e.g. Ru(bpy)3 ~1.6 eV, is used as photosensitizer. Upon excitation of th e dye due to absorption of solar energy in visible spectrum, an electron-hole pair (excito n) is generated. If th e dye molecules are in good conjugation with n-type semiconductor el ectrode, electron tr ansfer (injection) occurs from the dye molecules to the conduc tion band of semiconductor, leaving behind a localized hole on the phot o-oxidized dye molecule. h S0/S+S*inj C.B.TiO2 Ox Red eVCathode Electrolyte Dye Anode Figure 6.2 Schematic presentation of th e major components in DSSCs. Electron collection by the photoanode, e.g. TiO2, allows for current buildup utilized through external load and thus producing useful electrical work. Electrons re-enter the cell from the cathode which is in contact with an electrolyte solution containing a redox couple, e.g. I-/I3 -, acting as an electron relay to re generate the photo-oxidized dye and thus restoring the cycle. The current advances in technologies for fabrication of photoanodes based on sintered TiO2 nanoparticle film (NP) resulted in enhanced

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259 efficiency of DSSCs. This is mainly due to enhanced internal surface area of the NP film allowing for higher dye loading. Photoanode roughness factor, describe d as the ratio of actual to projected surface, exceeding 1000 is necessary for good li ght harvesting with ruthenium sensitizers. While such sintered TiO2 photoanodes exhibit good performance in current DSSCs, highest va lidated efficiency of 11.1% 11, disadvantages including relatively low surface area,12, 13 limited materials generality,14 tedious particle synthesis, and the use of liquid el ectrolyte unfavorable fo r field applications,15require further modifications for better performance in future generations of DSSCs.16 6.4 Polymer-Based Solar Cells Conductive organic polymers that coul d be regarded as photo-doped organic semiconductors emerged as materials capable of harvesting solar en ergy with economic advantages due to the relatively modera te conditions and less energy-consuming processes involved in fabrication.17 Several low-cost tec hniques for deposition of conductive polymers such as screen printing, doctor blading, inkjet printing and spray deposition are possible due to the solubility of such polymers in several suitable solvents. In addition, polymer-based cells provide aesth etic aspects for integration into modern architecture, and more important is their polymer nature permitting applications in portable appliances and disposable cells. The transitions in conjugated polymers are with strong absorption (extinction coefficients ~105 cm-1) allowing for efficient light harvesting by thin layers of active material s and could be tuned through molecular design to maximize light harvesting efficiency in the optical spectrum.

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F p h j u l o t r a s p h ( 0 m e x c h d ( B p F igure 6.3. P h ase, (b) biu nction. In po l o w electron r ansparent c o s electrodes h oto-genera t 0 .1~1.4 eV m obility (10 x citons in c h emical pot evice archi t B HJ) mode l olyme r b as e P olyme r b as e layer hetero j l ymer solar c affinity an d o nductor, e. The two m t ed electro n c.f. melliel e -7~10-3 cm 2 c onductive ential drop ectures wer l Figure 6. e d cells still b e d Solar cel l j unction, (c ) c ells, Figur e d acceptor w g. fluorinat e m ajor limita t n -hole pairs e ctron volt s 2 /V.s).18 T o polymers, t is sufficien t e devised w 3. Althoug h b elow 6%.5260 l s: (a) energ y ) bulk heter o e 6.3, two d i w ith high el e e d tin oxide t ions of the s that relax s in inorga n o overcome t he exciton t to effect s w here the m h cost effic i y diagram w o junction a n i fferent con d e ctron affin i (FTO), an d s e polymer m to exciton s n ic semicon d the relativ has to di f eparation o f m ost efficien t i ent, the s o w ith exciton i n d (d) order e d ucting poly m i ty, are san d d reflecting m m aterials is s with hig h d uctors), an d ely high b i f fuse to an f charges. T t is the bul k o lar to elect i n polymer e d hetero m ers, dono r d wiched bet m etallic thi n the formati o h binding e n d limited c h i nding-ener g interface w T herefore, s e k hetero ju n ric efficien c r with ween n foil, o n of n ergy h arge g y of w here e veral n ction c y of

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261 6.5 Potential Applications of Metal Organic Materials in Photochemical Hydrogen Generation Discrete supramolecular heteronuclear complexes: multiple-sensitizer cobaloxime catalytic core assemblies (PnA): Co[Ru(bpy)2(phendioxime)]2. The catalytic activity of a cobaloxime system containing Cr(II) ions, as sacrificial regene ration agent, in acidic solution for hydrogen production was first reported by Connolly and Espenson. 19 Electrocatalytic hydrogen production by cobaloximes was reported by Peters et al where structural modifications of cobaloximes resulted in more favorable Co(II/I) redox potential.20, 21 In a recent study by Artero and co-workers, the catalytic act ivity of photosensitized cobaloximes for hydrogen production was first demonstrated.22 In this system, heterodinuclear Ru(diimine)3-cobaloxime photocatalysts were able to accomplish photochemical production of hydrogen. The area of photosen sitized cobaloxime remains largely unexplored and thus we propose the design of novel family of multiple sensitized cobaloximes. In this section, the design principle of P2A-type assemblies, two photosensitizer (P) molecules simultaneously coordinated to one charge-acceptor catalytic center (A), relies on the stoich iometry of photoelectrons necessary to accomplish catalytic water splitting. As evid ent from eq. 6.1, two moles of electrons are required for production of one mole of hydr ogen, and four for each mole of oxygen produced. For PA systems, the catalyst is requi red to stabilize the various intermediates resulted from single ET, as reactants proceed to products, while the next P regeneration cycle commences. Therefore, increasing the number of P molecule s around the catalytic

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c e i n u t a c c o m p H e q e x p h m Sc y m R 5 e nter is exp n termediate s t ilize coba l c commodat e o ordination m echanism o ossibility fo r H owever, bo t q 6.2-6.7. x pected to e h otosensitiz m odification cheme 6.1. U y cle depicte d In ad d m odularity o f R u ions for O ,6-dioxime ected to en h s and/or th e l oxime as t e d around of counte r o f hydroge n r one of tw o t h pathways Therefore, e nhance the ed hydrog e of the phot o U nderlying d based on o d ition to co n f coordinati o O s or Re in t ( phendioxi m h ance the c a e necessary t he catalyti the Co c e r ions and/ o n generati o o pathways, h utilize the t increasing t overall T O e n generati o sensitizer m principle fo r o ne photoac t n trolling the o n complex e t he propose d m e) represe n 262 a talytic effi c P regenera t c center w e nter, leavi n o r substrate s o n catalyze d h omolytic a n t wo one-ele c t he efficien c O N of the c a ng cobalo x m oiety.23 r the photos e t ive center. number of e s allows f o d supramol e n t an ideal c c iency by r e t ion freque n w here two o n g two a x s The cur r d by cobal o n d heterolyt i c tron redox c y of thes e a talyst. Maj o x ime syste m e nsitized el e P molecule s o r investigat i e cular asse m c andidate fo r e ducing eith e n cy. Our in o xime mol e x ial positio n r ent under s o ximes poi i c, or a com b Co(III/II)C e first two o r enhance m m s were r e ctrolytic re d s around th e i ng the effe c m blies. [1.10 ] r this study e r the num b itial syste m e cules coul n s availabl e s tanding fo r nts toward s b ination of b C o(II/I) proc e ET proces s m ents of T O r eported d u d uction of H + e catalytic c e c t of substi t ] -phenanthr o 24 Phendi o b er of m will d be e for r the s the b oth.9 e sses, s es is O N in u e to + the e nter, t uting o lineo xime

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263 molecule is a bis-bidentate ligand ideally su ited as a bridging li nker to construct Ruphendioxime-Co systems. Careful manipulati on of the reactions conditions will allow Electron Transfer: Co(III) + eCo(II) (6.2) Co(II) +eCo(I) (6.3) Hydride Formation: Co(I) + HA Co(III)-H + A(6.4) Heterolytic pathway: Co(III)-H + HA Co(III) + H2 + A(6.5) Co(III) + Co(I) 2Co(II) (6.6) Homolytic pathway: Co(III)-H + Co(III)-H 2Co(II) + H2 (6.7) Equations 6.2-6.7 : Electrocatalytic hydrogen production by cobaloximes. control over the resultant dimensionality of the intended supramolecular complexes, scheme 2. In scheme 6.2, the use of [Ru(bpy)2]n+ in combination with the phendioxime precursor, 1,10-phenethroline-5,6-dione, is e xpected to result in [Ru(phendione)(bpy)2]n+ which could easily be transformed into the corresponding dioxime under mild reaction

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264 conditions. 24The obtained dioxime will subsequen tly be reacted with Co(II) salts in compatible solvents (e.g. H2O, EtOH, MeOH, or DMF), to obtain the targeted P2A supramolecular complex, Figure 6.4. N N H2SO4/ HNO3Cat. NaBr 100 CN N O O [Ru(bpy)2]Cl2EtOH refluxN N O O Ru(bpy)2 N N O O Ru(bpy)2 H2NOH EtOH refluxN N N N Ru(bpy)2 OH OH Scheme 6.2. The reaction steps for prepara tion of the [Ru(phendioxime)(bpy)]n+. N N N N N N N N O O Ru Co N N N N N N N N O O Ru H H a. Figure 6.4. Ru-cobaloxime multiple-sensitizer ca talytic core assemblies of the P2A-type Co[Ru(bpy)2(phendioxime) (BF2)]2. This covalently modified cobaloxime is expected to demonstrate higher chemical st ability over a wide ra nge of solution pH.20, 25 Due to the nature of B-O bonds, being stronge r than charge assisted H-bonds, covalently modified cobaloximes demonstrate higher ch emical stability and thus longer lifetime

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265 compared to their H-bonded prototypes. Co[Ru(bpy)2(phendioxime)(BF2)]2, Figure 6.5, is expected to be accessible from the corre sponding H-bonded structure through treatment with BF3.Et2O.22 This stage of the proposal involves performance optimization of the Rucobaloxime P2A systems. Further modification of the organic moiety of the supramolecular complex through substitution by electron-withdrawing functionalities will be attempted. Examples include nitrate and halide substituted bpy molecules, where previous studies showed enhanced electro chemical properties, less negative redox potential of the Co(II/I) couple, for re latively electron-deficient oximes. N N N N N N N N O Ru Co N N N N N N N N O O Ru B B F F F F O b. Figure 6.5. Covalently modified analog of P2A Ru-cobaloxime multiple-sensitizer catalytic core. Pentranuclear P4A Systems. Ru-cobaloxime cluster based on 4,6-bis([2,2`]bipyrid-6-yl-5-carbaldehyde oxime)pyr imidine as ditopic hexadentate ligand simultaneously coordinated to two tpy-capped Ru centers, tpy = [2,2';6',2'']terpyridine will be targeted. Pyrimidine and tpy are both good and donors and good acceptors, thus able to stabilize the low and high oxida tion states of coordi nated metal ions. In

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266 coordination to Ru ions, these ligands provide kinetically and thermodynamically stable complexes suitable for various electro and photochemical processes. The aforementioned supramolecular complex has been investigated by Lehn et.al ,26 with various substituents on C2 of the pyrimidine ring, however, no re ports of the interactions between the photoactive species and electron a cceptor cobaloxime exist. NN N N N N Ru Ru N N N N N N NN N N N N Ru Ru N N N N N N Figure 6.6. (Left) binuclear Ru complex reported by Lehn et.al and (right) the proposed complex utilizing bidentate ligands. The binuclear Ru-complex exhibits inte resting spectroscopic and electrochemical properties owing to both metal-metal and metal-ligand interactions. The two ruthenium centers, bridged by pyrimidine ring, exhibit me tal-metal interactions affecting both Rupyrimidine and Ru-tpy MLCT bands as well as the redox potentials of the metal centers. The UV-vis spectra of the binuclear complexes reported by Lehn et.al demonstrate the additive behavior of the ligand-centered (LC) transitions along with a red-shift in the MLCT compared to mononuclear complex. The red-shift in MLCT band for tpy (501 to 646 nm) was ascribed to stabilization of the orbitals of the bridging tpy ligand due to second coordination of th e cationic ruthenium ion. Intere stingly, a new MLCT band in the binuclear complex appears at 610 nm whic h accounts for splitting and lowering of the tpy orbitals. These findings are in agreemen t with observed electrochemical results showing reduction of the bridging ligand at lower negative potentials. Two one-electron

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267 oxidation processes (RuII/RuIII, centered at +1.5V vs SCE with E = 0.16 V) were observed and indicate metal-metal interactions in the binuclear complex. However, the binuclear Ru complexes with tridentate pol ypyridinyl ligands, in contrast to their bidentate counterparts, exhi bit poor luminescence most likely due to disordered octahedral geometry of coordinated meta l ions. We propose utilization of 4,6-bis(2Pyridyl)pyrimidine as tetradentate ditopic bridging ligand while substituting tpy by 2,2`bipyridine for construction of the pentanuclear P4A systems below, Figure 6.7. As described above the synthesis of covalently modified cobaloxime will be attempted trying to enhance the lifetime of the catalyst thr ough better chemical stability in aqueous medium. NN N N N N N N O O N N N N N N N N HO OH Co H2O OH2 Ru RuRu Ru N N N N N N N N N N N N NN N N N N N N O O N N N N N N N N O O Co H2O OH2 Ru RuRu Ru N N N N N N N N N N N N B B F F F F Figure 6.7. The proposed P4A complexes utilizing Ru-bridging through tetradentate ditopic ligand (left) H-bonded cobaloxime and (right) c ovalently modified analogue.

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268 Two and three-dimensional Ru metal organic materials: In this design, extended MOMs having the pote ntial to act as solid-state photosensitizers for heterogeneous photoelectrochemical reactions are targeted. The frameworks of interest are extended coordination polymers where Ru-d iimine complexes serve as integral parts of the construct. Through molecular design of judiciously functionalized diimine-type ligands, it is possible to obtain extended Ru-based frameworks with predefined geometries and accessible voids. Several possibl e diimine-type ligands suitable for this approach include the ditopic tetra-dentate diimines and th e 4,4'-dicarboxy-2,2'-bipyridyl ligands. Post-synthetic modi fication of the resulted extended frameworks through diffusion of molecular complexes, e.g. cobal oximes or Pd complexes acting as catalysts for reductive hydrogen production, from aqueous solution into the voids of targeted MOMs could potentially result in the targeted photochemically active materials. Moreover, upon absorption of solar energy, excitation of Ru-dye complex followed by ET to the redox catalyst initiates the photoche mical water splitting. Sacrificial electron donor species, e.g. triethanolamine, could be employed for regeneration of the photooxidized Ru-complex. Organic ligands suitable for construction of Ru-based hexagonal 2D layers or the 3D (10,3)a networks are ditopic tetra-dentate diimine ligands. The use of ditopic tridentate tetra2-pyridyl-1,4-pyrazine (tppz) ha s provided oligomeric linear structures of highly conj ugated Ru complexes showin g interesting spectroscopic properties. An example of the targ eted ligands is the tetrapyrido[3,2a :2`,3`c :3``,2``h :2```,3```j ]phenazine (tpphz), scheme 6.3. While t pphz has been utilized to construct binuclear Ru and Os complexes,27 capped with terminal bpy ligands, there is no

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269 precedence for an extended MOF of Ru or Os constructed from this ditopic tetradentate ligand. N N H2SO4/ HNO3Cat. NaBr 100 CN N O O H2NOH EtOH reflux N N N N HO OH 10% Pd/C H4N2, EtOH refluxN N H2N H2N N N H2N H2N N N O O EtOH refluxN N N N N N Scheme 6.3. Synthetic pathway for tpphz ligand. Extended Ru complexes based on dito pic bi-dentate dibenzo[1,4]dioxine bridging ligands: Extending the organic linker thr ough chemical modification of the bridging unit is a viable rout e for construction of isostructu ral frameworks with enhanced porosity. The extended linker, described in scheme 6.3,28 upon coordination to Ru ions is expected to yield isostructu ral complexes to [Ru(tpphz)3]n but with enhanced porosity thus permitting diffusion of larger catalytic complexes into the voids of the framework. Moreover, the different nature of heteroatom s in this linker will pe rmit investigation of the ligand’s electronic confi guration effects on the overall spectroscopic properties of attained Ru polymer and thus provide insi ght into potential path ways for performance enhancement. O O O2N O2N NO2 NO2 O O H2N H2N NH2 NH2 O O H2N H2N NH2 NH2 N N O O O O N N N N N N N N HCl Sn EtOH reslux Scheme 6.4 Synthetic pathway for dibenzo[1,4] dioxine-bridged phenanthroline.

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270 Binodal mixed ligand-mixed metal MOMs: In these systems, another aspect of molecular design principles will be impl emented towards utili zation of Ru MOMs. Molecular complexes, of the Ru(bpy)3 type, will be utilized as a rigid and directional molecular building block (MBB) with well de fined geometry and coordination sites to construct extended MOMs. An example of th e proposed MBB is the hexacarboxylic acid [Ru(4,4'-dicarboxy-2,2'-bipyridyl)3], regarded as the primar y octahedral node which upon coordination to metal ions (e.g., Zn, Co, Cu …etc.), as secondary nodes, is expected to result in extended binodal MOFs, Figure 6.8. In this design, the primary node acts as both photosensitizer and 6-co nnected node, in conj uncture to secondary coordination nodes, to construct photoactive porous solids. By judicious choice of the reaction conditions (solvents, structure-directing agents, counterions, transition metal ions, etc.) extended porous MOFs could be obtained. Due to th e highly directional na ture of the SBB, attainable topologies, dependent on the secondary node geometry, of the MOFs could be enumerated. Porosity of the constructed frameworks will allow for diffusion of water, redox catalysts, and sacr ificial agents for photos ensitizer regeneration. In this stage of the proposed work, identification of the ideal co mbination of redox catalyst and regenerating agents will be attempted. Moreover, covale nt modification to pr oduce extended linkers similar to the 4,4'-dicarboxy-2,2' -bipyridyl ligand will be at tempted. Extending the size of the linker is one of the robust and well-doc umented molecular design concepts that provided isostructural MOFs with enhanced porosity.

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271 Figure 6.8. [Ru(4,4'-dicarboxy-2,2'-bipyridyl)3]2+ complex as photoactive, 6-connected SBB for constructing extended MOF. Integrated photosensitizer-redox catalyst MOMs: A combination of the multiple-photosensitizer approach developed in earlier sections with enhanced chemical stability of extended MOFs, is proposed. U tilization of specifica lly designed ditopic tetradentate organic linker, [1,10]phenanth roline-5,6-dione dioxime (phendioxime), to construct photochemically-active MOFs is described. Coordination of [1,10]phenanthroline to Ru provides an anal ogue to the discrete photosensitizer Ru(bpy)3, however, functionalization of the phenanth roline ligand to incorporate oxime groups enables the extension of Ru-diimine core into periodic structures. The choice of oxime functionality is justified based on the know n electrochemical activity of cobaloximes towards hydrogen generation. Moreover, th e electron delocalization throughout the targeted Ru-phendioxime-Co system suggest s enhanced ET reactions between the Rudiimine excited state(s) and Co catalyst center. Therefore, the proposed framework combines the unique attributes of MOFs, in ge neral, the photoactivity of Ru-diimine, and

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272 the redox activity of cobaloximes in one integr ated solid-state material. Such system will be of tremendous interest to probe the change s of the various desira ble attributes of its molecular components once assembled into peri odic structures. As applicable to all the Ru-diimine sensitized systems, sacrificial electron donors will be incorporated into the system through simple diffusion. Once constructed, the hybrid MOF will be screened against various available sa crificial electron donor reagents to op timize its overall activity. In this system, photoexcitation of [RuII(Phendioxime)3] generates the **[RuII(Phendioxime)3] singlet excited-state which rela xes to the triplet excited-state through intersystem crossing. ET from *[RuII(Phendioxime)3] to the cobaloxime generates the highly nucleophilic Co(I)-c obaloxime that undergoes protonation generating Co(III)-hydride intermediate. The arrangement of two photosensitizers around one cobaloxime center provides the advantage of multiple sensitizers. The two-step ligand synthesis, scheme 6.2, reported by Bodige and Macdonnell24 starts from [1,10]phenanthroline through oxidation to th e [1,10]-phenanthroline-5,6-dione. This dione intermediate could be transformed into the dioxime under relatively mild conditions, a key step to this part of the proposal. The ability to transform N,Ncoordinated phendione into the correspond ing oxime provide a pathway to avoid competitive coordination of Ru to the oxime functionality, by introducing the oxime functionality to the pre-assembled Ru(phendione)3. Isolation of the Ru(phendioxime)3 complex followed by reaction with Co(II) salts in basic medium is expected to construct the targeted framework.

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273 N N H2SO4/ HNO3Cat. NaBr 100 C N N O O RuCl3EtOH reflux N N O O N N O O N N O O Ru H2NOH EtOH reflux N N N N N N N N N N N N Ru OH HO OH OH O H HO Scheme 6.5. Synthesis of [Ru(phenedioxime)3]2+. Figure 6.9. Projected structure of a MOF base d on the [1,10]Phenanthroline-5,6-dione dioxime (phendioxime) ligand bridging Ru-photos ensitizer to cobaloxime redox catalyst. Photo-active metal-organ ic materials on TiO2 functionalized surfaces: An alternative approach to currently utilized TiO2 nanoparticle films in DSCCs to enhance surface dye loading with minimal processing and at lower fabrication costs could potentially be attained thr ough incorporation of Photo-activ e metal-organic materials on TiO2 functionalized surfaces. This approach encompasses functionalization of the crystalline TiO2 surface with bi-functiona l organophosphonate molecules,29, 30 followed by charge-assisted growth of layered ruthenium-tris -diimine complexes. The Ru complexes of interest should be capable to self-assemble from a solution of molecular precursors into cationic 2D sheets where favor able electrostatic interactions with the

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274 TiO2-phosphonate modified surface will catalyze and further anchor the first layer of deposited Ru-complexes. Furthermore, multiple layers of the Ru-complexes could be deposited, in a controllable fashion, th rough manipulating the reaction conditions including concentration of molecular precursors in the or iginal solution, reaction time, temperature and solvent type. One ideal orga nic linker suitable for generating 2D Rubased coordination polymer is the 2,2`-bipyrimidine molecule. The default structure expected from assembly of octahedrally-coor dinated Ru ions, as tri-connected node, and 2,2`-bipyrimidine, as linear linker, is the hexagonal (hon eycomb) 2D layers, known also as the (6,3)-connected net. (6,3)-networks are characterized by hexagonal 1D channel, where self interpenetration is likely to oc cur. Moreover, it should be noted that supramolecular assembly of tri-connected nodes could result is the 3D (10,3)a-network, a chiral network characterized by presence of four-fold helices with same handedness, amenable also for interpenetration. While this approach allows for higher loading of the photoactive dye on the TiO2 surface, more important, it is expected to enhance the efficiency of DSCCs, preventing unfavorab le injected-electron interception by the electrolyte. Electron interception by the re dox shuttle electrolyte in today’s DSCCs occurs as the electrol yte encounters the TiO2 surface. Therefore, coating the TiO2 surface with the MOF is expected to provide a physic al insulation from the redox electrolyte and thus have the potential to forge DSSCs with enhanced efficiency.

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275 TiO2PO-O O-PO-O-O PO-O O-PO-O-O PO-O O-PO-O-O + ++ + ++ + MOF Figure 6.10. Schematic diagram of targeted phosphonate-surface modified TiO2 where photoactive cationic MOF could be anchored on the anionic surface. Solid-State MOF-Sensitized Bi-Photoelectrode DSSC: In this design, a tandem solar cell is constructed from photoanode n-type semiconductor and a photocathode ptype semiconductor to maximize the cell poten tial through light ha rvesting in broader range of the solar spectrum. Although various de signs for tandem cells already exist, our approach differs in that the photosensitizer is a multi-layer or 3D Ru-based metal organic complexes anchored to chemically-modi fied photoanode surface described in the previous section. Moreover, this proposed cell architect ure allows for potential substitution of the commonly us ed redox shuttle electrolyte I-/I3 in DSSCs by conductive organic polymer deposited in-between the metal organic film and the photocathode. The polymer-MOF contact could be maximized th rough controllable diffu sion of the polymer chains inside the voids of the MOF. Ca reful manipulation of the polymer coating, polymer chains diffusion only through outer fe w layers of the MOF, could establish

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276 h S0/S+S*inj C.B.TiO2 Cathode Conducting polymer Dye Anode ee-h+ C.B. h V e-eFigure 6.11. Schematic diagram of the proposed tandem photosensitized solar cell with conducting polymer deposited on th e surface of photoactive MOF. satisfactory charge conduction from phot ocathode to the MOF, for rapid dye regeneration, while avoiding a short circuit c onfiguration. Ruthenium Coordination Polymers as Low Band Gap Photo-Doped Semiconductors: Given the enormous interest in Ru-diimine complexes as photosensitizers,8, 31-36, 36 a surprisingly very few studies have been co nducted on their extended coordination polymers.27, 33, 37-39 The type of coordination polymers targeted here is polynuclear complexes with organi c diimine-type ligands capable of providing conjugated systems where interactions between electronic states of the metallo complexes are allowed. Conjugated metallo polymers of this type will provide ex perimental raw data for further theoretical works and could result in fabrication of conducting or semiconducting coordination polymers with potential applications in solar cells,

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277 substituting or further enhancing the photo properties of inorganic semiconductor electrodes. Furthermore, the virtually endl ess possible permutati ons of functionalized ligands and the large number of attainable MOF topologies provide an ample space for manipulating the energetics of such materials through control over the degree of conjugation and, by default, charge delocaliz ation and band shape. The organic ligands, variants of bpy, could be fine ly tuned to obtain larger or smaller degree of charge delocalization between the metallo complexes. Different attainable topologies, dependent on the ligand shape and synthesis conditions, are e xpected to result in different degrees of conjugation and thus different spectroscopi c and electrochemical properties of the coordination polymers. Preliminary investiga tions of Ru coordina tion molecular wires, Ru oligomers up to 4 units, demonstrat e tunable HOMO-LUMO energy gap, Figure 6.12, and further suggest the ability of attaining semiconductor or metallic properties through a transition from quantized molecular electr onic states to a ba nd-like continuum of electronic states upon further increase of the monomer units of the coordination polymer.38 Therefore, synthesis of novel Ru coordi nation polymers is with interest, both to advance basic science as well as to provide novel materials with potential applications in solar cells and photo-activ e conducting polymers. It is worth mentioning that Ru diimine complexes have the advantage of efficient charge separation of the photoinduced excitons, in contrast to conducting organic polymers

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F T B w m m i n w p t h c o i n c a e n F igure 6.12. T orres et al a B 3LYP/Lanl 2 w here lower m ain carrier s m aterial in s o n lower pho t w ith higher olymers co u In a r e h e possibilit y o mplexes i n n obtaining a rriers. M o n ergy, abso r Left: 2,3,5, 6 a nd the gas p 2 DZ for var i efficiency o s in the ma t o lar cell co n t o harvestin charge se p u ld provide f e cent study b y of electro n n to TiO2 co n sub-picose c o re interesti n r bed photo n N N 6 -Tetra-pyri d p hase molec u i ous oligom e o f charge s e t erial and t h n structs. De c g efficienc y p aration ef f f urther insig h b y Meyer e t n injection f r n duction ba n c ond electr o n gly, the qu a n energy, a n N N N N 278 d in-2-yl-pyr a u lar orbitals e rs obtained e paration li m h us poses a c reased thic k y and thus i t f iciency. In h t in how to t a l conduc t r om FrankC n d was dem o o n injectio n a ntum yield n d was ratio n a zine (tppz) energy diag r m its the eff e a limit on t h k ness of the t is desirabl e this regar d tackle this l t ed on Ru-d i C ondon state s o nstrated.40 n from non of this proc n alized bas e ligand use d r ams calcul a e ctive diffus i h e thicknes s photo-activ e e to for m ul a d Ru-diim i imitation. i imine phot o s of photoe x The author s thermalize d ess increas e e d on large r d by Floresa ted using i on length o s of photoa e material r e a te new mat e i ne coordi n o -sensitized T x cited Ru-di i s were succ e d electrons e d with exci t r overlap in t o f the a ctive e sults e rials n ation T iO2, i mine e ssful hott ation t egral

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279 between the TiO2 acceptor states and those of the photoe xcited sensitizer, scheme 2. Such observations stimulate our quest for hi ghly conjugated Ru-diimine polymers where stabilized LUMO energy leve ls, lying below CB of TiO2, is first expected to preclude ET from the photo-excited sensitizers. Howeve r, the possibility of ET from Frank-Condon states, i.e. non-thermalized excited states of the photosensitizer, ju stifies the attempt. Moreover, establishing a bandlike superposition of ground and excited st ates in Rudiimine polymers provides efficient solar ener gy utilization through harvesting in a wider range of the so lar spectrum. 6.6 References 1. (a) Rowsell, J. L. C; Yaghi, O. M. J. Am. Chem. Soc. 2006 128 1304-1315. (b) Dinca, M.; Han, W. S.; Liu, Y.; Da illy, A.; Brown, C. M; Long, J. R. Angew. Chem. Int. Ed. 2007 46 1419-1422. (c) Mulfort, K. L; Hupp, J. T. J. Am. Chem. Soc. 2007 129 9604-9605. (d) Liu, Y.; Eubank, J. F.; Cairns, A. J.; Eckert, J.; Kravtsov, V. Ch.; Luebke, R; Eddaoudi, M. Angew. Chem. Int. Ed. 2007 46 3278-3283. (e) Hayashi, H.; Cote, A. P.; Furukawa, H.; O'Keeffe, M; Yaghi, O. M. Nat. Mater. 2007 6 501506. (f) Llewellyn, P. L.; Bourrelly, S.; Se rre, C.; Vimont, A.; Daturi, M.; Hamon, L.; DeWeireld, G.; Chang, J. ; Hong, D. ; Hwang, Y. K.; Jhung, S. H.; Frey, G. Langmuir 2008 24 7245-7250 (g) Banerjee, R.; Phan, A.; Wang, B.; Knobler, C.; Furukawa, H.; O'Keeffe, M.; Yaghi, O. M. Science 2008 319 939-943. (h) Cho, SoHye; Gadzikwa, T.; Afshari, M.; Nguyen, SonBinh T.; Hupp, T. J. Eur. Jour. Inorg. Chem. 2007 4863-4867. (i) Horcajada, P.; Serre, C.; Vallet-Reg, M.; Sebban, M.; Taulelle, F.; Frey, G. Angew. Chem. Int. Ed. 2006 45 5974-5978. (j) Banerjee, R.;

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280 Phan, A.; Wang, B.; Knobler, C.; Furuka wa, H.; O'Keeffe, M.; Yaghi, O. M. Science 2008 319 939-943. 2. (a) Artero, V.; Fontecave, M. Some Genera l Principles for Designing Electrocatalysts with Hydrogenase Activity. Coordination Chemistry Reviews 2005 249 1518-1535. (b) Bak, T.; Nowotny, J.; Rekas, M.; Sorrell, C. C. Photo-Electrochemical Hydrogen Generation from Water using Solar Energy. Materials-Related Aspects. International Journal of Hydrogen Energy, 2002 27 991-1022. 3. Vincenzo Balzani, Alberto Credi,Margher ita Venturi, Photochemical Conversion of Solar Energy. ChemSusChem. 2008 1 26-58. 4. Gratzel, M. Photoelectrochemical Cells. Nature 2001 414 338. 5. Mayer, A. C.; Scully, S. R.; Hardin, B. E. ; Rowell, M. W.; McGehee, M. D. PolymerBased Solar Cells. Materials Today 2007 10 28-33. 6. Jun-Ho Yum, Peter Chen, Michael Grt zel, Mohammad K. Nazeeruddin, Recent Developments in Solid-State Dye-Sensitized Solar Cells. ChemSusChem 2008 1 699-707. 7. Hamann, T. W.; Jensen, R. A.; Martinson, A. B. F.; Ryswyk, H. V.; Hupp, J. T. Advancing Beyond Current Generati on Dye-Sensitized Solar Cells. Energy & Environmental Science 2008 1 66-78. 8. Balzani, V.; Bergamini, G.; Marchioni, F. ; Ceroni, P. Ru(II)-Bipyridine Complexes in Supramolecular Systems, Devices and Machines. Coordination Chemistry Reviews, 2006 250 1254-1266.

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281 9. Razavet, M.; Artero, V.; Fontecave, M. Proton Electroreduction Catalyzed by Cobaloximes: Functional Models for Hydrogenases. Inorg. Chem. 2005 44 47864795. 10. O'Regan, B.; Gratzel, M. A Low-Cost, High-Efficiency Solar Cell Based on DyeSensitized Colloidal TiO2 Films. Nature 1991 353 737-740. 11. Chiba, Y.; Islam, A.; Watanabe, Y.; Komiya R.; Koide, N.; Han, L. Dye-Sensitized Solar Cells with Conversion Efficiency of 11.1%. Jpn. J. Appl. Phys. 45 L638. 12. Papageorgiou, N.; Barbe, C.; Gratzel, M. Morphology and Adsorbate Dependence of Ionic Transport in Dye Sensiti zed Mesoporous TiO2 Films. The Journal of Physical Chemistry B 1998 102 4156-4164. 13. Papageorgiou, N.; Grtzel, M.; Infelta, P. P. On the Relevance of Mass Transport in Thin Layer Nanocrystalline Photoelectrochemical Solar Cells. Solar Energy Materials and Solar Cells 1996 44 405-438. 14. He, J.; Lindstrom, H.; Hagfeldt, A.; Lindqui st, S. Dye-Sensitized Nanostructured pType Nickel Oxide Film as a Photocathode for a Solar Cell. The Journal of Physical Chemistry B 1999 103 8940-8943. 15. Bai, Y.; Cao, Y.; Zhang, J.; Wang, M.; Li, R.; Wang, P.; Zakeeruddin, S. M.; Gratzel, M. High-Performance Dye-Sensitized Solar Cells Based on Solvent-Free Electrolytes Produced from Eutectic Melts. Nat Mater 2008 7 626-630. 16. McFarland, E. W.; Tang, J. A Photovolta ic Device Structure Based on Internal Electron Emission. Nature 2003 421 616-618. 17. Gunes, S.; Neugebauer, H.; Sariciftci, N. S. Conjugated Polymer-Based Organic Solar Cells. Chem. Rev. 2007 107 1324-1338.

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282 18. Hill, I. G.; Kahn, A.; Soos, Z. G.; Pascal, J.,R.A. Charge-Separation Energy in Films of -Conjugated Organic Molecules. Chemical Physics Letters 2000 327 181-188. 19. Connolly, P.; Espenson, J. H. Cobalt-Cata lyzed Evolution of Molecular Hydrogen. Inorg. Chem. 1986 25 2684-2688. 20. Hu, X.; Brunschwig, B. S.; Peters, J. C. Electrocatalytic Hydrogen Evolution at Low Overpotentials by Cobalt Macrocyclic Gl yoxime and Tetraimine Complexes. J. Am. Chem. Soc. 2007 129 8988-8998. 21. Hu, X.; Cossairt, B. M.; Brunschwig, B. S.; Lewi s, N. S.; Peters, J. C. Electrocatalytic Hydrogen Evolution by Cobalt Difl uoroboryl-Diglyoximate Complexes. Chemical Communications 2005 4723-4725. 22. Aziz Fihri, Vincent Artero, Mathieu Razav et, Carole Baffert, Winfried Leibl,Marc Fontecave, Cobaloxime-Based Photocatal ytic Devices for Hydrogen Production13. Angewandte Chemie International Edition 2008 47 564-567. 23. Fihri, A.; Artero, V.; Pereira, A.; Fontecave, M. Efficient H2-Producing Photocatalytic Systems Based on Cyclomet alated Iridiumand TricarbonylrheniumDiimine Photosensitizers and Cobaloxime Catalysts. Dalton Transactions 2008 5567-5569. 24. Bodige, S.; MacDonnell, F. M. Synthesi s of Free and Ruthenium Coordinated 5,6Diamino-1,10-Phenanthroline. Tetrahedron Letters, 1997 38 8159-8160. 25. Schrauzer, G. N.; Windgassen, R. J. Al kylcobaloximes and their Relation to Alkylcobalamins. J. Am. Chem. Soc. 1966 88 3738-3743.

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283 26. Garry S. Hanan, Claudia R. Arana, Jean -Marie Lehn, Gerhard Baum,Dieter Fenske, Coordination Arrays: Synthesis and Ch aracterisation of Rack-Type Dinuclear Complexes. Chemistry A European Journal 1996 2 1292-1302. 27. Bolger, J.; Gourdon, A.; Ishow, E.; Launay, J. Mononuclear and Binuclear Tetrapyrido[3,2-a:2‘,3‘-c:3‘‘,2‘‘-h:2‘‘‘ ,3‘‘‘-j]Phenazine (Tpphz) Ruthenium and Osmium Complexes. Inorg. Chem. 1996 35 2937-2944. 28. Kelly Chichak, Ulrich Jacquemard,Neil R.Branda, The Construction of (Salophen)Ruthenium(II) Assemblies using Axial Coordination. European Journal of Inorganic Chemistry 2002 2002 357-368. 29. Biemmi, E.; Scherb, C.; Bein, T. Oriented Growth of the Metal Organic Framework Cu3(BTC)2(H2O)3.xH2O Tunable with Func tionalized Self-Assembled Monolayers. J. Am. Chem. Soc. 2007 129 8054-8055. 30. Hermes, S.; Schroder, F.; Chelmowski, R. ; Woll, C.; Fischer, R. A. Selective Nucleation and Growth of Metal Organic Open Framework Thin Films on Patterned COOH/CF3-Terminated Self-Assembled Monolayers on Au(111). J. Am. Chem. Soc. 2005 127 13744-13745. 31. Bach, U.; Lupo, D. Solid-State Dye-Sensit ized Mesoporous TiO... Solar Cells with High Photon-to-Electron Conversion.. Nature 1998 395 583. 32. Abrahamsson, M.; Ja ger, M.; Kumar, R. J.; O sterman, T.; Persson, P.; Becker, H.; Johansson, O.; Hammarstro m, L. Bistridentate Ruthenium(II)Polypyridyl-Type Complexes with Microsecond 3MLCT Stat e Lifetimes: Sensitizers for Rod-Like Molecular Arrays. J. Am. Chem. Soc. 2008

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284 33. Susana Encinas, Lucia Flamigni, Frances co Barigelletti, Edwin C. Constable, Catherine E. Housecroft, Em ma R. Schofield, Egbert Fi ggemeier, Dieter Fenske, Markus Neuburger, Johannes G. Vos,Marg areta Zehnder, Electronic Energy Transfer and Collection in Luminescent Molecu lar Rods Containing Ruthenium(II) and Osmium(II) 2,2`:6`,2`-Terpyridine Complexes Linked by Thiophene-2,5-Diyl Spacers. Chemistry A European Journal 2002 8 137-150. 34. Credi, A.; Venturi, M. Molecular Machines Operated by Light. Central European Journal of Chemistry 2008 6 325-339. 35. Chambron, J.; Collin, J.; Dalbavie, J.; Dietri ch-Buchecker, C. O.; Heitz, V.; Odobel, F.; Solladi, N.; Sauvage, J. Rotaxane s and Other Transition Metal-Assembled Porphyrin Arrays for Long-Range Photoinduced Charge Separation. Coordination Chemistry Reviews, 1998 178-180 1299-1312. 36. Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.; von Zelewsky, A. Ru(II) Polypyridine Complexes: Photophysics, Photochemistry, Eletrochemistry, and Chemiluminescence. Coordination Chemistry Reviews 1988 84 85-277. 37. Constable, E. C. Expanded ligands—An Assembly Principle for Supramolecular Chemistry. Coordination Chemistry Reviews 2008 252 842-855. 38. Flores-Torres, S.; Hutchison, G. R.; Soltzberg, L. J.; Abruna, H. D. Ruthenium Molecular Wires with Conjugated Bridgi ng Ligands: Onset of Band Formation in Linear Inorganic Conj ugated Oligomers. J. Am. Chem. Soc. 2006 128 1513-1522. 39. Fantacci, S.; De Angelis, F.; Wang, J.; Bernhard, S.; Selloni, A. A Combined Computational and Experiment al Study of Polynuclear Ru TPPZ Complexes: Insight

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285 into the Electronic and Optical Pr operties of Coordination Polymers. J. Am. Chem. Soc. 2004 126 9715-9723. 40. Hoertz, P. G.; Staniszewski, A.; Marton, A.; Higgins, G. T. ; Incarvito, C. D.; Rheingold, A. L.; Meyer, G. J. Toward Exceeding the Shockley Queisser Limit: Photoinduced Interfacial Charge Transfer Processes that Store Energy in Excess of the Equilibrated Excited State. J. Am. Chem. Soc. 2006 128 8234-8245.

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286 Appendices

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287 Appendix A. Crystallographic data. Crystal data and structure refinement for 2.1 Identification code 2.1 Empirical formula C5 H N6 Formula weight 145.12 Temperature 100(2) K Wavelength 0.71073 Crystal system Trigonal Space group P3(2)21 Unit cell dimensions a = 8.0422(10) , = 90. b = 8.0422(10) , = 90. c = 16.675(4) , = 120. Volume 934.0(3) 3 Z 6 Density (calculated) 1.548 Mg/m 3 Absorption coefficient 0.113 mm -1 F(000) 438 Crystal size 0.10 x 0.10 x 0.10 mm 3 Theta range for data coll ection 2.92 to 28.26. Index ranges -9<=h<=10, -10<=k<=8, -17<=l<=22 Reflections collected 5713 Independent reflections 1482 [R(int) = 0.0354] Completeness to theta = 28.26 97.2 % Absorption correction None Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 1482 / 0 / 100 Goodness-of-fit on F 2 1.029 Final R indices [I>2sigma(I)] R1 = 0.0360, wR2 = 0.0809 R indices (all data) R1 = 0.0437, wR2 = 0.0841 Largest diff. peak and hole 0.234 and -0.167 e. -3

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288 Crystal data and structure refinement for 2.2a and 2.2b Identification code 2.2a 2.2b Empirical formula C5 H5 Br N4 O2 C6 H6 Br N3 O3 Formula weight 233.04 248.05 Temperature 100(2) K 100(2) K Wavelength 1.54178 1.54178 Crystal system Monoclinic Monoclinic Space group Cc P2(1)/c Unit cell dimensions a = 9.522(5) , = 90.000(5) b = 8.643(5) , = 105.391(5) c = 10.628(5) , = 90.000(5) a = 6.1177(2) , = 90. b = 16.4011(4) , = 99.2150(10) c = 8.9706(2) , = 90 Volume 843.3(8) 3 888.47(4) 3 Z 4 4 Density (calculated) 1.836 Mg/m3 1.854 Mg/m3 Absorption coefficient 4.840 mm-1 6.201 mm-1 F(000) 456 488 Theta range for data collection 3.24 to 24.77. 5.39 to 65.07. Index ranges -11<=h<=11, -10<=k<=10, 12<=l<=12 -7<=h<=7, -19<=k<=19, 10<=l<=10 Reflections collected 3568 7189 Independent reflections 728 [R(int) = 0.0214] 1481 [R(int) = 0.0244] Absorption correction None None Data / restraints / parameters 728 / 0 / 61 1481 / 0 / 128 Goodness-of-fit on F2 1.288 1.078 Final R indices [I>2sigma(I)] R1 = 0.0247, wR2 = 0.0625 R1 = 0.0241, wR2 = 0.0591 R indices (all data) R1 = 0.0249, wR2 = 0.0626 R1 = 0.0260, wR2 = 0.0600 Largest diff. peak and hole 0.365and -0.410 e.-3 0.648 and -0.256 e.-3

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289 Crystal data and structure refinement for 2.3a Identification code 2.3a Empirical formula C9 H10 N2 O2 Formula weight 178.19 Temperature 100(2) K Wavelength 0.71073 A Crystal system Triclinic Space group P-1 Unit cell dimensions a = 7.854(7) , = 85.877(12). b = 8.376(7) , = 90 c = 16.958(17) , = 62.04. Volume 982.1(15) 3 Z 4 Density (calculated) 1205 Mg/m3 Absorption coefficient 0.087 mm-1 F(000) 376 Theta range for data collection 1.20 to 28.16 deg Index ranges -7<=h<=9, -7<=k<=6, -16<=l<=21 Reflections collected 3131 / 2958 [R(int) = 0.6495] Completeness to theta = 28.16 61.2 % Absorption correction None Refinement method Full-matrix least-squares on F2 Goodness-of-fit on F 2 0.770 Final R indices [I>2sigma(I)] R1 = 0.0800, wR2 = 0.2048 R indices (all data) R1 = 0.1727, wR2 = 0.2950 Largest diff. peak and hole 0.401 and -0.617 e.A-3

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290 Crystal data and structure refinement for 2.3b Identification code 2.3b Empirical formula C9 H10 N2 O2 Formula weight 178.19 Temperature 293(2) K Wavelength 0.71073 Crystal system Orthorhombic Space group P2(1)2(1)2(1) Unit cell dimensions a = 9.907(18) , = 90. b = 12.90(2) , = 90. c = 13.54(2) , = 90. Volume 1731(6) 3 Z 8 Density (calculated) 1.368 Mg/m3 Absorption coefficient 0.099 mm-1 F(000) 752 Crystal size 0.20 x 0.10 x 0.10 mm3 Theta range for data coll ection 2.18 to 28.09. Index ranges -13<=h<=7, -16<=k<=16, -14<=l<=17 Reflections collected 9633 Independent reflections 3819 [R(int) = 0.2260] Completeness to theta = 28.09 93.2 % Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3819 / 0 / 240 Goodness-of-fit on F2 0.819 Final R indices [I>2sigma(I)] R1 = 0.0818, wR2 = 0.1667 R indices (all data) R1 = 0.1830, wR2 = 0.1910 Largest diff. peak and hole 0.256 and -0.447 e.-3

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291 Crystal data and structure refinement for 2.3c Identification code 2.3c Empirical formula C7 H9 Br N2 O3 Formula weight 249.07 Temperature 293(2) K Wavelength 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a = 6.8690(15) , = 85.585(4) b = 10.869(2) , = 79.920(4) c = 12.772(3) , = 72.191(4) Volume 893.6(3) 3 Z 4 Density (calculated) 1.851 Mg/m3 Absorption coefficient 4.576 mm-1 F(000) 496 Theta range for data collection 1.62 to 28.27. Index ranges -7<=h<=8, -13<=k<=14, -15<=l<=16 Reflections collected 5381 Independent reflections 3882 [R(int) = 0.0253] Completeness to theta = 28.27 87.5 % Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3882 / 0 / 271 Goodness-of-fit on F 2 1.095 Final R indices [I>2sigma(I)] R1 = 0.0438, wR2 = 0.1086 R indices (all data) R1 = 0.0493, wR2 = 0.1117 Largest diff. peak and hole 1.040 and -0.607 e.-3

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292 Crystal data and structure refinement for 2.5 Identification code 2.5 Empirical formula C28 H12 Mn4 N8 O16 Formula weight 936.22 Temperature 100(2) K Wavelength 0.71073 Crystal system Tetragonal Space group I-4 Unit cell dimensions a = 12.045(2) = 90. b = 12.045(2) = 90. c = 11.285(5) = 90. Volume 1637.3(8) 3 Z 2 Density (calculated) 1.899 Mg/m3 Absorption coefficient 1.599 mm-1 F(000) 928 Crystal size 0.05 x 0.05 x 0.05 mm3 Theta range for data collection 2.39 to 28.25. Index ranges -15<=h<=15, -10<=k<=15, -14<=l<=12 Reflections collected 4963 Independent reflections 1901 [R(int) = 0.0875] Completeness to theta = 28.25 96.7 % Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 1901 / 0 / 139 Goodness-of-fit on F 2 1.046 Final R indices [I>2sigma(I)] R1 = 0.0764, wR2 = 0.1305 R indices (all data) R1 = 0.1079, wR2 = 0.1424 Largest diff. peak and hole 0.689 and -0.428 e.-3

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293 Crystal data and structure refinement for 2.8 Identification code 2.8 Empirical formula C14 H24 N7 O3 Formula weight 338.40 Temperature 100(2) K Wavelength 0.71073 Crystal system Monoclinic Space group Cc Unit cell dimensions a = 11.616(3) , = 90. b = 16.143(5) , = 112.954(5). c = 9.476(3) = 90. Volume 1636.2(8) 3 Z 4 Density (calculated) 1.374 Mg/m 3 Absorption coefficient 0.100 mm -1 F(000) 724 Crystal size 0.05 x 0.05 x 0.02 mm 3 Theta range for data coll ection 2.52 to 24.71. Index ranges -13<=h<=10, -18<=k<=18, -4<=l<=11 Reflections collected 3413 Independent reflections 1655 [R(int) = 0.0385] Completeness to theta = 24.71 99.3 % Absorption correction None Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 1655 / 7 / 281 Goodness-of-fit on F 2 1.083 Final R indices [I>2sigma(I)] R1 = 0.0436, wR2 = 0.1041 R indices (all data) R1 = 0.0479, wR2 = 0.1068 Largest diff. peak and hole 0.257 and -0.191 e. -3

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294 Crystal data and structure refinement for 2.10 Identification code 2.10 Empirical formula C14 H10 N2 O2 Formula weight 238.24 Temperature 100(2) K Wavelength 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a = 7.157(14) , = 67.61(8). b = 13.24(4) , = 88.52(16). c = 14.60(3) , = 85.48(12). Volume 1275(5) 3 Z 4 Density (calculated) 1.408 Mg/m 3 Absorption coefficient 0.085 mm -1 F(000) 558 Crystal size 0.10 x 0.10 x 0.05 mm 3 Theta range for data coll ection 2.64 to 24.71. Index ranges -3<=h<=8, -9<=k<=10, -17<=l<=14 Reflections collected 2749 Independent reflections 2749 [R(int) = 0.0000] Completeness to theta = 24.71 63.2 % Absorption correction None Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 2749 / 0 / 208 Goodness-of-fit on F 2 0.939 Final R indices [I>2sigma(I)] R1 = 0.1030, wR2 = 0.198 R indices (all data) R1 = 0.1968, wR2 = 0.2404 Largest diff. peak and hole 1.268 and -0.484 e. -3

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295 Crystal data and structure refinement for 2.12 Identification code 2.12 Empirical formula C11 H13 Cl Mn N6 Formula weight 319.66 Temperature 100(2) K Wavelength 0.71073 Crystal system Orthorhombic Space group Pnma Unit cell dimensions a = 11.660(2) , = 90. b = 15.465(3) , = 90. c = 7.2472(14) , = 90. Volume 1306.7(4) 3 Z 4 Density (calculated) 1.630 Mg/m3 Absorption coefficient 1.209 mm-1 F(000) 656 Crystal size 0.05 x 0.05 x 0.05 mm3 Theta range for data coll ection 2.63 to 28.21. Index ranges -14<=h<=15, -18<=k<=19, -9<=l<=8 Independent reflections 1612 [R(int) = 0.0431] Completeness to theta = 28.21 96.2 % Absorption correction None Refinement method Full-matrix least-squares on F2 Goodness-of-fit on F2 1.04 Final R indices [I>2sigma(I)] R1 = 0.0338, wR2 = 0.0765 R indices (all data) R1 = 0.0419, wR2 = 0.0799 Largest diff. peak and hole 0.414 and -0.282 e.-3

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296 Crystal data and structure refinement for 2.13 Identification code 2.13 Empirical formula C11 H11 N7 O3 Mn Formula weight 344.03 Temperature 100(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P 21/c Unit cell dimensions a = 9.440(2) , = 90. b = 9.247(2) , = 92.492(4). c = 16.904(4) , = 90. Volume 1474.2(5) 3 Z 4 Density (calculated) 1.545 Mg/m3 Absorption coefficient 2.929 mm-1 F(000) 658 Crystal size 0.2 x 0.2 x 0.1 mm3 Theta range for data coll ection 2.16 to 28.31. Index ranges -11<=h<=12, -6<=k<=12, -21<=l<=19 Reflections collected 8616 Independent reflections 3400 [R(int) = 0.0355] Completeness to theta = 28.31 92.5 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3400 / 0 / 227 Goodness-of-fit on F2 0.975 Final R indices [I>2sigma(I)] R1 = 0.0374, wR2 = 0.0885 R indices (all data) R1 = 0.0506, wR2 = 0.0950 Largest diff. peak and hole 0.438 and -0.245 e.-3

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297 Crystal data and structure refinement for 2.15 Identification code 2.15 Empirical formula C58 H40 Mn7 N24 O18 Formula weight 1745.72 Temperature 100(2) K Wavelength 0.71073 Crystal system Orthorhombic Space group Pbca Unit cell dimensions a = 19.247(4) , = 90. b = 16.051(3) , = 90. c = 20.945(4) , = 90. Volume 6471(2) 3 Z 4 Density (calculated) 1.792 Mg/m 3 Absorption coefficient 1.415 mm -1 F(000) 3500 Crystal size 0.1 x 0.1 x 0.05 mm 3 Theta range for data collection 1.92 to 28.35. Index ranges -25<=h<=18, -20<=k<=19, -18<=l<=27 Reflections collected 37034 Independent reflections 7620 [R(int) = 0.2366] Completeness to theta = 28.35 94.3 % Absorption correction None Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 7620 / 0 / 484 Goodness-of-fit on F 2 0.987 Final R indices [I>2sigma(I)] R1 = 0.1084, wR2 = 0.2171 R indices (all data) R1 = 0.2393, wR2 = 0.2701 Largest diff. peak and hole 1.154 and -0.716 e. -3

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298 Crystal data and structure refinement for 2.18 Identification code 2.18 Empirical formula C10 H6 Cd N12 Formula weight 406.68 Temperature 100(2) K Wavelength 0.71073 Crystal system Tetragonal Space group I4(1)/amd Unit cell dimensions a = 6.457(12) , = 90. b = 6.457(12) , = 90. c = 32.69(7) , = 90. Volume 1363(5) 3 Z 4 Density (calculated) 1.982 Mg/m3 Absorption coefficient 1.624 mm-1 F(000) 792 Crystal size 0.10 x 0.10 x 0.10 mm3 Theta range for data coll ection 2.49 to 28.25. Index ranges -8<=h<=7, 0<=k<=8, -33<=l<=19 Reflections collected 1408 Independent reflections 407 [R(int) = 0.0426] Completeness to theta = 28.25 80.9 % Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 407 / 0 / 44 Goodness-of-fit on F2 1.121 Final R indices [I>2sigma(I)] R1 = 0.0238, wR2 = 0.0552 R indices (all data) R1 = 0.0258, wR2 = 0.0559 Largest diff. peak and hole 0.684 and -0.378 e.-3

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299 Crystal data and structure refinement for 2.20 Identification code 2.20 Empirical formula C10 H12 Cl2 N8 Ni O2 Formula weight 405.89 Temperature 100(2) K Wavelength 0.71073 Crystal system Monoclinic Space group C2/c Unit cell dimensions a = 18.210(4) , = 90. b = 7.6245(18) , = 122.680(4). c = 12.608(3) , = 90. Volume 1473.4(6) 3 Z 4 Density (calculated) 1.830 Mg/m3 Absorption coefficient 1.702 mm-1 F(000) 824 Crystal size 0.20 x 0.20 x 0.10 mm3 Theta range for data coll ection 2.66 to 28.24. Index ranges -18<=h<=24, -9<=k<=10, -16<=l<=16 Reflections collected 4265 Independent reflections 1689 [R(int) = 0.0325] Completeness to theta = 28.24 92.4 % Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 1689 / 0 / 129 Goodness-of-fit on F2 1.038 Final R indices [I>2sigma(I)] R1 = 0.0347, wR2 = 0.0850 R indices (all data) R1 = 0.0413, wR2 = 0.0876 Largest diff. peak and hole 0.785 and -0.319 e.-3

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300 Crystal data and structure refinement for 3.1 Identification code 3.1 Empirical formula C92H128N56O60Zn12 Formula weight 3763.12 Temperature 100(2) K Wavelength 0.71073 Crystal system, space group Cubic, Fm-3 Unit cell dimensions a = 25.976(5) , = 90 b = 25.976(5) , = 90 c = 25.976(5) , = 90 Volume 17527(5) ^3 Z, Calculated density 4, 1.475 Mg/m^3 F(000) 7272 Crystal size 0.10 x 0.10 x 0.10 mm Theta range for data collection 1.36 to 22.46 deg. Limiting indices -14<=h<=21, -20<=k<=17, 1<=l<=27 Reflections collected / unique 3419 / 1036 [R(int) = 0.0487] Completeness to theta = 22.46 97.8 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.8486 and 0.8486 Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 1025 / 1 / 128 Goodness-of-fit on F^2 1.211 Final R indices [I>2sigma(I)] R1 = 0.0776, wR2 = 0.1840 R indices (all data) R1 = 0.0908, wR2 = 0.1917 Largest diff. peak and hole 0.652 and -1.343 e.^-3

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301 Crystal data and structure refinement for 3.2 Identification code 3.2 Empirical formula C75H83N29O65Zn8K8 Formula weight 3266.59 Temperature 100(2) K Wavelength 0.71073 Crystal system, space group Cubic, Fm-3 Unit cell dimensions a = 23.1553(15) , = 90 b= 23.1553(15) , = 90 c = 23.1553(15) , = 90 Volume 12415.1(14) ^3 Z, Calculated density 4, 1.722 Mg/m^3 Absorption coefficient 1.893 mm^-1 F(000) 6137 Crystal size 0.10 x 0.10 x 0.10 mm Theta range for data collection 2.49 to 21.93 deg. Limiting indices -24<=h<=24, -24<=k<=15, 24<=l<=24 Reflections collected / unique 11935 / 693 [R(int) = 0.0392] Completeness to theta = 21.93 99.0 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.8333 and 0.8333 Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 693 / 2 / 85 Goodness-of-fit on F^2 1.141 Final R indices [I>2sigma(I)] R1 = 0.0795, wR2 = 0.2277 R indices (all data) R1 = 0.0869, wR2 = 0.2351 Largest diff. peak and hole 0.610 and -0.408 e.^-3

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302 Crystal data and structure refinement for 3.3 Identification code 3.3 Empirical formula C70H132N28O90Cd8Na8 Formula weight 3889.16 Temperature 100(2) K Wavelength 0.71073 Crystal system Trigonal Space group R-3m Unit cell dimensions a = 40.637(5) = 90. b = 40.637(5) = 90. c = 39.063(7) = 120. Volume 55865(13) 3 Z 9 Density (calculated) 1.010 Mg/m3 Absorption coefficient 0.751 mm-1 F(000) 16561 Crystal size 0.10 x 0.10 x 0.10 mm3 Theta range for data coll ection 1.74 to 20.05. Index ranges -39<=h<=36, -37<=k<=37, -11<=l<=37 Reflections collected 27467 Independent reflections 5997 [R(int) = 0.0955] Completeness to theta = 20.05 97.1 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.9287 and 0.9287 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 5997 / 0 / 495 Goodness-of-fit on F2 1.101 Final R indices [I>2sigma(I)] R1 = 0.0983, wR2 = 0.2308 R indices (all data) R1 = 0.1238, wR2 = 0.2463 Largest diff. peak and hole 0.766 and -0.621 e.-3

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303 Crystal data and structure refinement for 3.4. Identification code 3.4 Empirical formula C60 H45 Cd8 K8 N24 O69 Formula weight 3409.28 Temperature 100(2) K Wavelength 0.71073 Crystal system Cubic Space group Fm-3 Unit cell dimensions a = 23.7179(19) , = 90. b = 23.7179(19) , = 90. c = 23.7179(19) , = 90. Volume 13342.2(19) 3 Z 4 Density (calculated) 1.687 Mg/m3 Absorption coefficient 1.596 mm-1 F(000) 6545 Crystal size 0.10 x 0.10 x 0.10 mm3 Theta range for data coll ection 2.43 to 21.91. Index ranges -8<=h<=24, -23<=k<=23, -24<=l<=24 Reflections collected 9432 Independent reflections 730 [R(int) = 0.0485] Completeness to theta = 21.91 96.7 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.8567 and 0.8567 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 730 / 0 / 74 Goodness-of-fit on F2 1.155 Final R indices [I>2sigma(I)] R1 = 0.0880, wR2 = 0.2242 R indices (all data) R1 = 0.0964, wR2 = 0.2298 Largest diff. peak and hole 0.530 and -0.438 e.-3

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304 Crystal data and structure refinement for 3.5 Identification code 3.5 Empirical formula C72 H80 Cd8 Cs8 N28 O60 Formula weight 4260.84 Temperature 100(2) K Wavelength 0.71073 Crystal system Cubic Space group Fm-3 Unit cell dimensions a = 24.593(2) , = 90. b = 24.593(2) , = 90. c = 24.593(2) , = 90. Volume 14874(2) 3 Z 4 Density (calculated) 1.888 Mg/m3 Absorption coefficient 3.137 mm-1 F(000) 7920 Crystal size 0.10 x 0.10 x 0.10 mm3 Theta range for data coll ection 1.66 to 23.21. Index ranges -17<=h<=27, -25<=k<=27, -27<=l<=27 Reflections collected 16459 Independent reflections 951 [R(int) = 0.0433] Completeness to theta = 23.21 97.4 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.7444 and 0.7444 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 951 / 6 / 84 Goodness-of-fit on F2 1.072 Final R indices [I>2sigma(I)] R1 = 0.0794, wR2 = 0.2001 R indices (all data) R1 = 0.0891, wR2 = 0.2091 Largest diff. peak and hole 0.978 and -0.707 e.-3

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305 Crystal data and structure refinement for 3.6. Identification code 3.6 Empirical formula C86 H120 Mn12 N56 O60 Formula weight 3664.56 Temperature 100(2) K Wavelength 0.71073 Crystal system Cubic Space group Fm-3 Unit cell dimensions a = 26.291(6) , = 90. b = 26.291(6) , = 90. c = 26.291(6) , = 90. Volume 18172(7) 3 Z 4 Density (calculated) 1.313 Mg/m3 Absorption coefficient 0.888 mm-1 F(000) 6999 Crystal size 0.1 x 0.1 x 0.1 mm3 Theta range for data coll ection 2.19 to 20.43. Index ranges -25<=h<=6 -21<=k<=13, -3<=l<=25 Reflections collected 3669 Independent reflections 817 [R(int) = 0.0410] Completeness to theta = 20.43 98.0 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.9165 and 0.9165 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 816 / 4 / 103 Goodness-of-fit on F2 1.245 Final R indices [I>2sigma(I)] R1 = 0.0841, wR2 = 0.2320 R indices (all data) R1 = 0.0952, wR2 = 0.2416 Largest diff. peak and hole 0.339 and -0.464 e.-3

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306 Crystal data and structure refinement for 3.7 Identification code 3.7 Empirical formula C92 H117 Co12 N56 O57 Formula weight 3681.48 Temperature 100(2) K Wavelength 0.71073 Crystal system Cubic Space group Fm-3 Unit cell dimensions a = 25.928(3) = 90. b = 25.928(3) = 90. c = 25.928(3) = 90. Volume 17431(4) 3 Z 4 Density (calculated) 1.382 Mg/m3 Absorption coefficient 1.245 mm-1 F(000) 7127 Crystal size 0.10 x 0.10 x 0.10 mm3 Theta range for data coll ection 2.22 to 21.95. Index ranges -27<=h<=27, -27<=k<=26, -27<=l<=23 Reflections collected 16713 Independent reflections 974 [R(int) = 0.1058] Completeness to theta = 21.95 99.8 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.8856 and 0.8856 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 974 / 0 / 107 Goodness-of-fit on F2 1.099 Final R indices [I>2sigma(I)] R1 = 0.0671, wR2 = 0.1849 R indices (all data) R1 = 0.0815, wR2 = 0.1949 Largest diff. peak and hole 0.714 and -0.814 e.-3

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307 Crystal data and structure refinement for 3.8 Identification code 3.8 Empirical formula C76 H138 In8 N52 O71 Formula weight 3827.14 Temperature 100(2) K Wavelength 0.71073 Crystal system Cubic Space group Fm-3 Unit cell dimensions a = 26.123(4) = 90. b = 26.123(4) = 90. c = 26.123(4) = 90. Volume 17826(4) 3 Z 4 Density (calculated) 1.409 Mg/m3 Absorption coefficient 1.106 mm-1 F(000) 7475 Crystal size 0.10 x 0.10 x 0.10 mm3 Theta range for data coll ection 2.21 to 21.96. Index ranges -27<=h<=8, -24<=k<=27, -21<=l<=27 Reflections collected 7400 Independent reflections 1005 [R(int) = 0.0601] Completeness to theta = 21.96 99.8 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.8969 and 0.8969 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 1005 / 0 / 95 Goodness-of-fit on F2 1.110 Final R indices [I>2sigma(I)] R1 = 0.0602, wR2 = 0.1789 R indices (all data) R1 = 0.0781, wR2 = 0.1940 Largest diff. peak and hole 1.091 and -0.375 e.-3

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308 Table 4.1. Crystal data and structure refinement for 4.1 Identification code 4.1 Empirical formula C15.5 H10 N0.5 O7.5 Pb S Formula weight 562.49 Temperature 100(2) K Wavelength 1.54178 Crystal system triclinic Space group P -1 Unit cell dimensions a = 6.6068(3) , = 66.910(3). b = 11.3025(6) , = 78.207(2). c = 12.4360(7) , = 81.511(2). Volume 833.86(7) 3 Z 2 Density (calculated) 2.240 Mg/m 3 Absorption coefficient 21.235 mm -1 F(000) 529 Crystal size 0.10 x 0.10 x 0.05 mm 3 Theta range for data collection 3.92 to 70.55. Index ranges -7<=h<=8, -13<=k<=13, -15<=l<=15 Reflections collected 8385 Independent reflections 2730 [R(int) = 0.0278] Completeness to theta = 70.5585.7 % Max. and min. transmission 0.4165 and 0.2253 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 2730 / 2 / 256 Goodness-of-fit on F 2 1.138 Final R indices [I>2sigma(I)] R1 = 0.0243, wR2 = 0.0579 R indices (all data) R1 = 0.0269, wR2 = 0.0589

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309 Table 4.2. Crystal data and structure refinement for 4.2 Identification code 4.2 Empirical formula C80 H60 Cd4 F24 N4 O20 Formula weight 2302.92 Temperature 293(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P ccn Unit cell dimensions a = 27.497(8) , = 90. b = 7.402(2) , = 90. c = 24.091(7) , = 90. Volume 4904(2) A3 Z 2 Density (calculated) 1.646 Mg/m3 Absorption coefficient 0.971 mm-1 F(000) 2396 Crystal size 0.2 x 0.2 x0.05 Theta range for data collection 1.85 to 25.23 Index ranges -29<=h<=31, -8<=k<=8, -27<=l<=28 Reflections collected 9824 Independent reflections 4305 Completeness to theta = 25.23 92.8 % Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4164 / 0 / 317 Goodness-of-fit on F2 1.094 Final R indices [I>2sigma(I)] R1 = 0.0747, wR2 = 0.1745 R indices (all data) R1 = 0.0977, wR2 = 0.1844

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310 Table 4.3. Crystal data and structure refinement for 4.3 Identification code 4.3 Empirical formula C20 H12 Cd2 N24 Formula weight 813.34 Temperature 100(2) K Wavelength 0.71073 Crystal system Tetragonal Space group I 4(1)/amd Unit cell dimensions a = 6.457(12) , = 90. b = 6.457(12) , = 90. c = 32.69(7) , = 90. Volume 1363(5) 3 Z 2 Density (calculated) 1.982 Mg/m 3 Absorption coefficient 1.624 mm -1 F(000) 792 Crystal size 0.10 x 0.10 x 0.10 mm 3 Theta range for data collection 2.49 to 28.25. Index ranges -8<=h<=7, 0<=k<=8, -33<=l<=19 Reflections collected 1408 Independent reflections 407 [R(int) = 0.0426] Completeness to theta = 28.2580.9 % Max. and min. transmission none Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 407 / 0 / 44 Goodness-of-fit on F 2 1.121 Final R indices [I>2sigma(I)] R1 = 0.0238, wR2 = 0.0552 R indices (all data) R1 = 0.0258, wR2 = 0.0559 Largest diff. peak and hole 0.684 and -0.378 e. -3

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311 Table 4.4. Crystal data and structure refinement for 4.4 Identification code 4.4 Empirical formula C54 H32 Cu2 N6 O17 S2 Formula weight 1228.06 Temperature 293(2) K Wavelength 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a = 6.9333(15) , = 83.109(4). b = 11.794(3) , = 85.299(4). c = 16.909(4) , = 73.817(4). Volume 1316.6(5) 3 Z 1 Density (calculated) 1.549 Mg/m 3 Absorption coefficient 0.967 mm -1 F(000) 624 Crystal size 0.20 x 0.20 x 0.20 mm 3 Theta range for data collection 2.28 to 28.24. Index ranges -9<=h<=8, -15<=k<=15, -6<=l<=22 Reflections collected 6591 Independent reflections 5280 [R(int) = 0.0262] Completeness to theta = 28.24 81.0 % Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 5280 / 0 / 358 Goodness-of-fit on F 2 1.004 Final R indices [I>2sigma(I)] R1 = 0.0561, wR2 = 0.1462 R indices (all data) R1 = 0.0755, wR2 = 0.1586 Largest diff. peak and hole 0.755 and -0.469 e. -3

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312 Table 4.1. Crystal data and structure refinement for 4.5 Identification code 4.5 Empirical formula C82 H62 Cu2 N6 O17 S2 Formula weight 1594.58 Temperature 293(2) K Wavelength 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a = 9.223(13) , = 66.01(3). b = 13.878(19) , = 86.43(3). c = 15.48(2) , = 84.63(3). Volume 1802(4) 3 Z 1 Density (calculated) 1.469 Mg/m 3 Absorption coefficient 0.726 mm -1 F(000) 822 Crystal size 0.40 x 0.20 x 0.10 mm 3 Theta range for data collection 1.44 to 24.71. Index ranges -10<=h<=2, -15<=k<=16, -15<=l<=14 Reflections collected 4575 Independent reflections 4421 [R(int) = 0.1294] Completeness to theta = 24.71 72.0 % Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4421 / 0 / 490 Goodness-of-fit on F 2 1.110 Final R indices [I>2sigma(I)] R1 = 0.1041, wR2 = 0.2708 R indices (all data) R1 = 0.1333, wR2 = 0.3174 Largest diff. peak and hole 0.929 and -1.614 e. -3

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313 Appendix B. Powder X-Ray Diffrac tion Patterns (XRPDs) Figure B1 XRPD pattern for 3.1. Figure B2 XRPD pattern for 3.2.

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314 Figure B3 XRPD pattern for 3.3. Figure B4 XRPD pattern for 3.4.

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315 Figure B5 XRPD pattern for 3.6. Figure B6 XRPD pattern for 3.7.

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316 Figure B7 XRPD pattern for 3.8. Figure B8. XRPD pattern for 3.9.

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317 Appendix C Selected TGA traces: Figure C1. TGA for compound 3.1 showing a steady decrease in weight percent from 30oC to 80oC is due to a loss of acetonitrile and water molecules followed by a loss of DMF molecules up to 180oC. Degradation of the framework is evident at 300oC.

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318 Figure C2. TGA for compound 3.2 showing that at temperatures below 95oC, a loss of water molecules is observed. Degrada tion of the framework begins at 310oC.

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319 Figure C3. TGA for compound 3.6 indicating loss of acetonitrile molecules is observed below 85oC, followed by a loss of DMF molecules up to 180oC. Degradation of the framework begins at approximately 200oC.

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320 Appendix D Selected NMR spectra for compounds H-L1, 3.9S, and the reaction mixture of H-L1 and CoCl2 in aqueous medium. Figure D1.1H NMR spectrum of H -L1 in DMSO-d6.

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321 Figure D2. 1H-1H gCOSY spectrum for 3.9S in D2O. Peak at 2.9 ppm assigned for residual DMF solvent from the reaction mixture.

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322 Figure D3. 1H-13C gHSQC spectrum for 3.9S in D2O.

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323 Figure D4. (Above) 13C NMR spectrum of 3.9S in D2O. Peaks at 39.21 and 43.65 ppm indicate different chemical shifts for C(4`) and C(6`) carbon atoms of thp rings, respectively, due to chelation of L1 to cobalt ions. (Below) DEPT 135 spectrum of 3.9S in D2O.

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324 The spectra below (Figures D5-D10) are for the reaction mixture of CoCl2 (0.1 mmol), HL1 (0.15 mmol), and NaOCH3 (0.15 mmol) in 1 mL D2O under aerobic conditions after standing at r.t. for 24 h. Figure D5 The 1H NMR spectrum for the reaction mixture. Figure D6 The 13C NMR spectrum for the reaction mixture.

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325 Figure D7 The 1H-1H gCOSY NMR spectrum for the reaction mixture.

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326 Figure D8 1H-1H NOESY NMR spectrum for the reaction mixture.

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327 Figure D9. 1H-13C gHSQC NMR spectrum for the reaction mixture.

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328 Figure D10 The 1H-1H TOCSY NMR spectrum for the reaction mixture.

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329 Figure D11 1H 2D-DOSY spectrum for 1S 1.2 mM in D2O at 298 K.

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About the Author Mohamed H. Alkordi received his Bachelor’s degree in Chemistry and Physics from the Alexandria University, Egypt in 2005. In summer 2001, Mohamed joined Professor John D. Roberts’ group at California Institute of T echnology as an undergraduate research fellow where he worked on conformational analysis of small organic molecules utilizing solution NMR spectroscopy. In summer 2005, Mohamed entered the Ph. D program at the University of South Florida and joined Dr. Mohamed Eddaoudi’s r esearch group. While in the Ph.D. program he served as the first author and co-authored sever al scientific publications. Mohamed has presented his research at scientific meetings of the American Chemical Society and Florida Inorganic and Materials Symposium.