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Supramolecular metal-organic and organic materials
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Rather, Elisabeth
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supramolecular chemistry
crystal engineering
calixarene
metal-organic network
porosity
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ABSTRACT: The rational design of functional solids based upon the development of strategies for controlling intermolecular interactions and structural arrangement of simple molecular building units, represents a salient feature in the context of supramolecular chemistry and crystal engineering. Consideration of chemical functionality, geometrical capability and knowledge of the interplay between two or more sets of supramolecular interactions specific of preselected chemical components will facilitate further extension of crystal engineering towards the construction of supramolecular materials possessing valuable properties. Calixarenes represent excellent building blocks for the design of solid-state architectures, in particular calix-4-arenes crystallize easily and the introduction of a wide range of director functions is relatively simple. For example, amphiphilic and pseudo-amphiphilic calixarenes may be synthesized by selective functionalization at either face of the skeleton and a second functionality may then be introduced at the opposite face. Careful examination of the crystal packing of a series of calix-4-arene derivatives systematically modified with various alkyl chain lengths at the lower rim and selected functional groups at the upper rim will be considered in the broader perspective of crystal engineering strategies and development of novel materials. Metal-organic networks are typically based upon the cross-linking of transition metal-based nodes by "spacer" organic ligands. Since there is an inherent control over the chemical nature of the components of such metal-organic structures, it is possible to design infinite architectures that possess well-defined topologies and contain cavities suitable for incorporation of guest molecules. Investigation of metal-organic networks based upon rigid ligands possessing two types of coordination sites (nicotinate and dinicotinate) and conformationally labile ligands possessing saturated fragments (glutarate and adipate) will be addressed in the context of topological approaches to the design of multi-dimensional networks with particular emphasis upon their resulting properties.
Thesis:
Thesis (Ph.D.)--University of South Florida, 2004.
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by Elisabeth Rather.
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Includes vita.
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Document formatted into pages; contains 190 pages.

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ABSTRACT: The rational design of functional solids based upon the development of strategies for controlling intermolecular interactions and structural arrangement of simple molecular building units, represents a salient feature in the context of supramolecular chemistry and crystal engineering. Consideration of chemical functionality, geometrical capability and knowledge of the interplay between two or more sets of supramolecular interactions specific of preselected chemical components will facilitate further extension of crystal engineering towards the construction of supramolecular materials possessing valuable properties. Calixarenes represent excellent building blocks for the design of solid-state architectures, in particular calix-4-arenes crystallize easily and the introduction of a wide range of director functions is relatively simple. For example, amphiphilic and pseudo-amphiphilic calixarenes may be synthesized by selective functionalization at either face of the skeleton and a second functionality may then be introduced at the opposite face. Careful examination of the crystal packing of a series of calix-4-arene derivatives systematically modified with various alkyl chain lengths at the lower rim and selected functional groups at the upper rim will be considered in the broader perspective of crystal engineering strategies and development of novel materials. Metal-organic networks are typically based upon the cross-linking of transition metal-based nodes by "spacer" organic ligands. Since there is an inherent control over the chemical nature of the components of such metal-organic structures, it is possible to design infinite architectures that possess well-defined topologies and contain cavities suitable for incorporation of guest molecules. Investigation of metal-organic networks based upon rigid ligands possessing two types of coordination sites (nicotinate and dinicotinate) and conformationally labile ligands possessing saturated fragments (glutarate and adipate) will be addressed in the context of topological approaches to the design of multi-dimensional networks with particular emphasis upon their resulting properties.
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Supramolecular Metal Organic and Organic Materials by Elisabeth Rather 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 Major Professor: Michael J. Zaworotko, Ph.D Julie P. Harmon, Ph.D Gregory R. Baker, Ph.D Anthony W. Coleman, Ph.D Date of Approval: M arch 26 2004 Keywords: Supramolecular chemistry, crystal engineering, calixarene, metal organic network, porosity Copyright 2004, Elisabeth Rather

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Dedication To my mother and my father.

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Acknowledgements I wish to express my sincere appreciation, first and foremost, to my advisor Dr. Michael Zaworotko for his guidance and suggestions throughout the course of this work. In addition, I would like to thank Dr. Anthony Coleman and his students, in particular Dr. Patrick Sha h galdian and Dr. Eric da Silva, for their collaboration to the work on calixarene compounds. Abuzar Kabi r is gratefully acknowledged for his help with the GC experiments. Finally, I would like to thank Dr. Julie Harmon and Dr. Gregory Baker, members of my supervisory committee, Dr. Victor Kravtsov and Dr. Dwight A. Sweigart, visiting professors at USF; Ashle y Mullen, Patrick Healey, Joanna Bis, Jen Medlar Dr. Jarka Miksovska and Dr. Vasan Kuduva for their helpful comments and encouragements. I would like to extend my deep appreciation to all that has helped in this research. My sincerest wish is that everyon es hard work and collaboration goes on to help m ankind. Thank you again for your support!

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i Table of Contents List of Tables vii List of Figures viii Abstract xv Chapter 1 Introduction 1 1.1. Persp ectives 1 1.1.1. Solid State Chemistry 1 1.1.2. The Cambridge Structural Database, CSD 3 1.2. Supramolecular Chemistry 4 1.2.1. Scope and Co ntext 4 1.2.2. Supramolecular Interactions 6 1.2.3. Crystal Engineering 7 1.3. Supramolecular Organic Materials 9 1.3.1. Scope and Context 9 1.3.2. Properties 10 1.4. Supramolecular Metal Organic Materials 12 1.4.1. Scope and Context 12 1.4.2. Properties 14

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ii 1.5. Supramolecular Materials: Tunable Properties towards Useful Applications 15 Chapter 2 Supramolecular Organic Materials based upon pseudo amphiphilic calixarenes 18 2.1. Introduction 18 2.2. Calixarenes Crystal Packing: a Database Review 20 2.2.1. Scope and Limitations 20 2.2.2. Crystal packing of amphiphilic calixarenes 23 2.2.3. Crystal packing of pseudo amphiphilic calixarenes 25 2.3. Experimental 34 2.3.1. Syntheses 34 2.3.2. X ray Crystallography 34 2.4. R esults and Discussion 39 2.4.1. Influence upon the crystal packing through variation at the lower rim 39 2.4.2. Influence upon the crystal packing through variation at the upper rim 48 2.5. Conclusions 55 Chapter 3 Metal Organic Networks based upon organic ligands containing two types of functionality: Supramolecular isomerism and Functionalization 57 3.1. Introd uction 57

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iii 3.1.1. Metal Organic Networks based upon pyridinecarboxylate ligands 57 3.1.2. Network topologies 59 3.2. Zn and Cu Chromophores: a Database Study 61 3.3. Experimental 67 3.3.1. Materials and Methods 67 3.3.2. Syntheses 68 3.3.3. Guest sorption studies 69 3.3.4. X ray Crystallography 70 3.4. Results and Discussion 72 3.4.1. Supramolecular isomers of [Zn(nicotinate) 2 ] n 72 3.4.2. Additional Functionality: Structures of [Cu(nicotinate) 2 ] n and [Cu(dinicotinate) 2 ] n 81 3.5. Conclusions 85 Chapter 4 Metal Organic Networks based upon conformationally labile organic ligands: Porosity and Flexibility 87 4.1 Introduction 87 4.1.1. Metal Organic Networks based upon dimetal cluster nodes 87 4.1.2. Conformational lability of the organic linker 88 4.2. Porous metal organic net works 97 4.2.1. Context 97

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iv 4.2.2. Classification of porous supramolecular metal organic networks 99 4.2.3. Properties and applications 102 4.3. Experimental 103 4.3.1. Materials and Methods 103 4.3.2. Syntheses 103 4.3.3. Guest sorption studies 105 4.3.4. X ray Crystallography 106 4.4. Results and Discussion 109 4.4.1. 1D structures 109 4.4.2. 2D structures 112 4.4.3. 3D structures 114 4.5. Conclusions 121 Chapter 5 Conclusion and Future Directions 123 5.1. Summary 123 5.2. Supramolecular Materials 125 5.3. Future Directi ons 126 References 128 Appendices 150 Appendix A. AFM studies for compound 10 151

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v Appendix B. Histogram showing the distribution of Cu O distances among the structures found in the CSD search o f the chromophores of mononuclear Cu 4 5 and 6 coordinate containing two functionalities N donor and carboxylate 152 Appendix C 1. Experimental data for compound 13 153 Appendix C 2. Experimental data for compound 14 154 Appendix C 3. Experimental da ta for compound 15 155 Appendix C 4. Experimental data for compound 16 156 Appendix C 5. Experimental data for compound 17 158 Appendix C 6. Experimental data for compound 18 159 Appendix C 7. Experimental data for compound 19 160 Appendix C 8. Experi mental data for compound 20 161 Appendix C 9. Experimental data for compound 21 162 Appendix C 10. Experimental data for compound 22 166 Appendix C 11. Experimental data for compound 23 170 About the Author End Page

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vi List of Tables Table 1.1. Typical supramolecular interactions and their characteristics 7 Table 2.1. Structural analysis of the crystal packing observed in calix 4 arenes 32 Table 2.2. Structural a nalysis of relevant crystal packing observed in para tBu calix 4 arenes 33 Table 2.3. Crystallographic data for compounds 1 5 and 9 12 37 Table 2.4. Ring inclination angles and corresponding distanc es between opposite aryl groups in the crystal structures of compounds 1 5 and 9 40 Table 2.5. Ring inclination angles and corresponding distances between opposite aryl groups in the crystal structures of compounds 3 and 10 12 49 Table 3.1. Crystallographic data for compounds 13 17 71 Table 4.1. Conformational analysis of crystal structures containing the glutarate fragment and metals conducted using the CSD 92 Table 4.2. Conformational analysis of crystal structures containing the adipate fragment and metals conducted using the CSD 94 Table 4.3. Classification of porous supramolecular metal organic networks accordi ng to their behavior upon guest desorption/readsorption 101 Table 4.4. Crystallographic data for compounds 18 23 107

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vii List of Figures Figure 1.1. Representation of a calix 4 arene molecule in the cone conformation showing the sites at the upper and lower rims that can sustain functional substitution 10 Figure 1.2. Self assembly of two calixarenes providing host capsule for small guest mol ecules 11 Figure 1.3. Space filling representation of the supramolecular arrangement of calixarene complexes of resorcinarenes and para sulfonatocalixarenes generating large host compounds 12 Figure 1.4. Crystal structure of the supramolecular arrangement in bilayers of amphiphilic para tert butyl calix 4 arenes 12 Figure 1.5. Schematic representation of the 2D square grid and 3D diamondoid (hexagonal and cubic) networks that can be generated by linking transition metal nodes by linear bifunctional spacers ligands 14 Figure 1.6. Crystal structures of the 2D [Ni(4,4 bipyridine) 2 (NO 3 ) 2 ] n and 3D [Cu(4,4 bipyridine) 2 ] n metal organic networks, org anic and anionic guests are omitted for clarity 14

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viii Figure 1.7. The convergence of experimental sciences towards the field of nanosciences (adapted from the review Pour la Science 290, 2001, p.134) 16 Figure 2.1. Representation of the pseudo amphiphilic calix 4 arene building block possessing alkyl substituents at the lower rim and variable functionalities at the upper rim 20 Figure 2.2. Cone (a), partial cone (b), 1,2 alternate (c) and 1,3 alternate conformations adopted by calix 4 arenes 22 Figure 2.3. Dominant crystal packing observed for calix 4 arene (a) and p tert butyl calix 4 arene (b) 24 Figure 2.4. Tubu lar self assembly of para sulfonato calix 4 arenes, hydrogen atoms, metal ions and organic ligands are omitted for clarity 25 Figure 2.5. Main crystal packing motifs observed for pseudo amphiphilic calix 4 arene derivatives tha t can self assemble in bilayer (a), herringbone of dimers (b) and column (c) modes 26 Figure 2.6. Main crystal packing motifs observed for pseudo amphiphilic para tert butyl calix 4 arene derivatives that can self assemble in b ilayer (a), capsule (b) and herringbone (c) modes 29 Figure 2.7. Representation of the flattened cone conformation observed in para bromo calix 4 arenes and designation of the distances and angles used to describe their geometr y 40 Figure 2.8. Representation of the crystal packing of compounds 1 and 2 down [001] (a) and view of one layer (b) and their superimposition (c) down [010] 41

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ix Figure 2.9. Detailed view of the inte ractions Br Br between the columns of two adjacent layers observed in compound 1 42 Figure 2.10. Representation of the helical motif sustained by compound 3 and detailed view of the hexamer of calixarenes forming the helix, alk yl chains are omitted for clarity 43 Figure 2.11. Representation of the crystal packing of compounds 4 and 5 down [001], hydrogen atoms of the alkyl chains are omitted for clarity 44 Figure 2.12. Re presentation of the non equivalent layers in compounds 4 and 5 and their superimposition down [100] 44 Figure 2.13. Representation of the molecular structure of para Br tetra O dodecyl calix 4 arene in compound 9 47 Figure 2.14. Representation of the crystal packing of compound 9 down [001] (a) and [010] (b) 47 Figure 2.15. Representation of the flattened cone conformation observed in O hexyl calix 4 arenes derivatives a nd designation of the distances and angles used to describe their geometry 49 Figure 2.16. Representation of the crystal packing of compound 10 down [001] (a) and down [010] (b), hydrogen atoms of the alkyl chains are omitted f or clarity 51 Figure 2.17. Detailed view of the Br Br interactions in compound 10a (a) and 10b (b) 51 Figure 2.18. Representation of the crystal packing of compound 11 down [010] (a), hydrogen atoms of the alkyl chains are omitted for clarity, and detailed view of the head to head aromatic stacking interactions (b) 52

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x Figure 2.19. Representation of the crystal packing of compound 12 down [010] (a) and [100] (b) 53 Figure 3.1. Representation of the ligands nicotinic acid (a) and dinicotinic acid (b) 58 Figure 3.2. Network topologies of the 2D square grid, 4 4 (a), 3D diamondoid, 6 6 (b), NbO, 6 4 .8 2 (c), CdSO 4 6 5 .8 (d) and PtS 4 2 .8 4 (e) 60 Figure 3.3. A tetrahedral node projected down the 2 fold axis affording a pseudo square planar geometry (a), a projection of an angular spacer (b), a projection of a four connected circuit from tetrahedral nodes and angular spacers (c) 61 Figure 3.4. Crystal structure of the square grid [Zn(nicotinate) 2 ] n A 62 Figure 3.5. Representation of the two c oordination geometries resulting from coordination of tetrahedral mononuclear Zn(II) with the two different functionalities N donor and monodentate (a) or bidentate (b) carboxylate 63 Figure 3.6. Histogram showing the distribution of Zn O distances among the structures containi ng the mononuclear Zn in coordination with two functionalities N donor and carboxylate 64 Figure 3.7. Representation of the chromophores of mononuclear Cu(II) containing the two functionalities N donor and carboxylate: 4 coordi nate trans square planar (a), cis square planar (b), tetrahedral (c), 5 coordinate square pyramidal (d) and 6 coordinate octahedral (e) 66 Figure 3.8. Histogram showing the distribution of Cu O distances among the structures co ntaining the chromophore mononuclear Cu in coordination with two functionalities N donor and carboxylate 66

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xi Figure 3.9. Representation of the trans configuration adopted by the Cu(II) chromophore (a) in the structure of [Cu(iso nicotinate) 2 ] n (b) 67 Figure 3.10. Crystal structure of the 3D network [Zn(nicotinate) 2 ] n guest molecules are omitted for clarity (a). Schematic representations of the connectivity of the Zn centers for the network of 13 (b). 73 Figure 3.11. Connectivity of 2 tetrahedral and 2 square planar nodes to form the 4 2 .8 4 network of PtS (a) and connectivity of 4 square planar nodes to form 13 (b) and projections of the two networks down [100]. 73 Figure 3.12. X ray powder diffraction pattern calculated from the single crystal structures of A (a), 13 (b), 14 (c) and 15 (d) 74 Figure 3.13. X ray powder diffraction patterns of the products of the reactio n Zn(NO 3 ) 2 + Nicotinate in different conditions: (a) first product of the reaction in PhNO 2 (b) MeOH only, (c) PhH, (c) PhCl, (d) o and p Ph(CH 3 ) 2 (e) p H 2 NPhNO 2 and (f) PhOCH 3 75 Figure 3.14. Crystal structure of the 2D squ are grid in 14 and 15 (a) and the vertical stacking between parallel infinite layers showing the intercalation of naphthalene (b) and nitrobenzene (c) molecules. 76 Figure 3.15. The relationship between 13 15 and A. Reagents an d conditions : (i) PhCH 3 or PhNO 2 in MeOH, diffusion; (ii) C 10 H 8 or PhNO 2 in MeOH, slow diffusion; (iii) MeOH or PhH or PhCl or o p Ph(CH 3 ) 2 or p H 2 NPhNO 2 or PhOCH 3 in MeOH, precipitation; (iv) and (v) 220 250C, 1 hour. 77

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xii F igure 3.16. X ray powder diffraction patterns of 13 (a) fresh sample, (b) sample heated to 250C and (c) calculated from the single crystal structure without guest. 78 Figure 3.17. X ray powder diffraction patterns of 14 (a) fr esh sample, (b) sample heated to 220C and (c) calculated from the single crystal structure without guest 79 Figure 3.18. X ray powder diffraction patterns of 15 (a) fresh sample, (b) sample heated to 250C and (c) calculated f rom the single crystal structure without guest. 80 Figure 3.19. Crystal structure of the 2D square grid in 16 (a) and vertical stacking between parallel infinite layers down [100] (b) and [001] (c) 82 Figure 3.20. Representation of the chromophore mononuclear 5 connected in compound 17 83 Figure 3.21. View of the 2D square grid network within the crystal structure of 17, guest molecules are omitted for clarity 84 Figure 3.22. Crystal structure of the 3D network [Cu(dinicotinate) 2 ] n guest molecules are omitted for clarity (a). Schematic representations of the connectivity of the Cu centers for the network of 17 (b). 85 Figure 4.1. Top (a) and side (b) views of the dimetal tetracarboxylate chromophore and schematic representation of the 2D square grid (c) and 3D octahedral (d) networks that can be generated through use of appropriate linear linkers. 88

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xiii Figure 4.2. Representation of the glutarate (a), adipate (b), benzene 1,3 dicarboxylate (c) and benzene 1,4 dicarboxylate anions (d). 90 Figure 4.3. The three possible conformations of glutarate alkyl chains and the corresponding projections down the Csp 3 Csp 3 bonds with the range of torsion angles observed in the structures deposited in the CSD. 91 Figure 4.4. The five observed conformations of adipate alkyl chains and the correspond ing projections down the Csp 3 Csp 3 bonds with the range of torsion angles observed in the structures deposited in the CSD. 93 Figure 4.5. The three possible conformations of glutarate alkyl chains and the possible geometries of the glutarate anti gauche anions around a bimetallic building unit leading to distinct 1D and 2D topologies. 95 Figure 4.6. Sponge like behavior of the metal organic bilayer structure Ni 2 L 3 (BTC) 4 upon desolvatation and variati on of the corresponding torsion angles of the flexible parts. 99 Figure 4.7. Detailed view of the 1D double chain of [Cu 2 (glutarate) 2 (DMF) 2 ] n formed by compound 18 down [001], (a) and [100] (b) 110 Figure 4.8. Crystal packing of the 1D nets of compound 18 down [001] (a) and [100] (b) 110 Figure 4.9. Detailed view of the 1D double chain of [Cu 2 (adipate) 2 (pyridine) 2 ] n formed by compound 19 down [100] (a) and [001] (b) 111 Figure 4.10. Crystal packing of the 1D nets of 19 down [100] (a) and [110] (b), hydrogen atoms are omitted for clarity 111

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xiv Figure 4.11. Crystal structure of [Cu 3 (adipate) 3 (H 2 O) 2 (C 6 H 11 OH)] n (a) showin g the 1D double chain of [Cu(adipate)(C 6 H 11 OH)] n (b) and the 2D sheets of [Cu 2 (adipate) 2 (H 2 O) 2 ] n (c), hydrogen atoms are omitted for clarity 112 Figure 4.12. Detailed view of the [Cu 2 (glutarate) 2 ] n sheets down [001] (a), crysta l structure of the 2D net of 20 down [010] (b) and [100] (c) 113 Figure 4.13. Detailed view of the [Cu 2 (glutarate) 2 ] n sheets down [100] in 21 (a), crystal structure of the 3D net of 21a down [001] (b) and corresponding space fi lling representation (d) and view of a channel of water molecules in 21a (c) 115 Figure 4.14. FT IR spectra of compound 21b let in atmosphere for 55min (from t = 0, top, to t = 55min, bottom) 116 Fi gure 4.15. TGA traces of the rehydration of 21b crystals (a) and 21b powder (b) under ambient atmosphere 117 Figure 4.16. Crystal structure of the 3D net of 22a down [001] (a) and corresponding space filling representation wher e the guest water molecules are omitted (b) 118 Figure 4.17. FT IR spectra of compound 22a let in atmosphere for 45min (from t = 0, top, to t = 45min, bottom) 119 Figure 4.18. Detailed view of the [ Cu 2 (adipate) 2 ] n sheets down [100] in 23 (a), crystal structure of the 3D net of 23 down [001] (b) and corresponding space filling representation where the guest water molecules are omitted (c) 120

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xv Supramolecular Metal Org anic and Organic Materials Elisabeth Rather ABSTRACT The rational design of functional solids based upon the development of strategies for controlling intermolecular interactions and structural arrangement of simple molecular building units, represents a salient feature in the context of supramolecular chemistry and crystal engineering. Consideration of chemical functionality, geometrical capability and knowledge of the interplay between two or more sets of supramolecular interactions specific of preselect ed chemical components will facilitate further extension of crystal engineering towards the construction of supramolecular materials possessing valuable properties. Calixarenes represent excellent building blocks for the design of solid state architectures in particular calix 4 arenes crystallize easily and the introduction of a wide range of director functions is relatively simple. For example, amphiphilic and pseudo amphiphilic calixarenes may be synthesized by selective functionalization at either face of the skeleton and a second functionality may then be introduced at the opposite face. Careful examination of the crystal packing of a series of calix 4 arene derivatives systematically modified with various alkyl chain lengths at the lower rim and select ed

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xvi functional groups at the upper rim will be considered in the broader perspective of crystal engineering strategies and development of novel materials. Metal organic networks are typically based upon the cross linking of transition metal based nodes by spacer organic ligands. Since there is an inherent control over the chemical nature of the components of such metal organic structures, it is possible to design infinite architectures that possess well defined topologies and contain cavities suitable for incorporation of guest molecules. Investigation of metal organic networks based upon rigid ligands possessing two types of coordination sites (nicotinate and dinicotinate) and conformationally labile ligands possessing saturated fragments (glutarate and ad ipate) will be addressed in the context of topological approaches to the design of multi dimensional networks with particular emphasis upon their resulting properties.

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1 Chapter 1 Introduction 1.1. Perspectives 1.1.1. Solid State Chemistry Order from Chaos K. Eric Drexler The organization that takes place when, from a saturated solution, randomly moving molecules crystallize into an ordered pattern, involves a complex array of interactions that assemble these molecular entities into crystalline architecture s. If the properties of such assemblies are inherently dependant upon the molecular composition of the solid material, they are also affected by the crystal structure and symmetry of the arrangement adopted by the components upon crystal growth. This featu re ha d been discovered long before the first X ray experiments when Abb Hay 1 ob served that the cleavage, the property of a crystal to come apart between specific planes, is directly linked to the nature and arrangement of the building blocks in the crystal. Hays Law of Rational Indices, the building block law, has led to the essent ial concept that the knowledge of the symmetry of a crystal prefigures the knowledge of the symmetry of its properties. 2 The discovery of the X ray in 1895 by W.C. Rntgen and the following

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2 discovery of X ray diffraction by Max von Laue in 1912 and its subsequent application by W.H. and W.L. Bragg to the determination of the crystal structure of mineral and inorganic substances have provided the means to unequivocally characterize the solid state. 3 The structural determination of crystalline substances h as also been of importance for further investigation of the solid state and its properties. In antithetic instances, the highly orderly arrangement of the ionic constituents of inorganic solids results from strong forces, while weaker interactions are invo lved in the cohesion of crystals purely composed of organic molecules. In the context of natural or synthetic molecular compounds, crystal structure determination has primarily focused upon the identification of the molecular entities themselves; however, further analysis of the crystal packing, arrangement of these molecules within the crystalline lattice, has rapidly afforded precise data on the intermolecular interactions holding them within the regular three dimensional architectures in which they cryst allize. Specific investigations on crystal nucleation processes, controlled growth and morphology during crystallization towards the generation of materials possessing properties related to the crystal properties constitute an important branch of modern so lid state chemistry. 4 18 These approaches, generally inspired from the knowledge acquired from natural or biomineral solid sta te systems with the purpose of generating the corresponding properties in synthetic materials, have exemplified how a thorough understanding of the crystallization process may lead to the ability to prepare a variety of products with desirable properties. On the other hand, a separate field has been developed based upon principles delineated by major advances in crystallography and structural

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3 determination, which have provided enhanced insight into how molecules interact and assemble within the solid state, with the goal to design materials directly at the molecular level. 19 25 In summary, the generation of synthetic solid state materials, which can afford unique optical, mechanical, magnetic or electronic properties or possess various polymorphs, represents an important aspect towards a wide variety of applications in materi al or pharmaceutical sciences. Owing to technological advances in both software and hardware, the characterization of these novel materials via crystallographic methods has become relatively straightforward and can afford the means to specifically study th e arrangement of the molecular constituents and to understand how these building blocks are held together within the solid state. 1.1.2. The Cambridge Structural Database, CSD The investigation of the solid state towards the generation of novel materials w ith useful properties can highly benefit from preceding examination of general and reliable trends developed by correlated relevant structures. In this perspective, the Cambridge Structural Database, CSD, 26 constitutes a powerful database possessing exploitable information such as crystal symmetry, atomic coordinates, molecular geometry, interatomic distances and angles, concerning the crystal structures reported in the li terature of over 290,000 organic, inorganic, organometallic, coordination and bioorganic compounds, which have been characterized via X ray or neutron diffraction (ConQuest Version 1.5 CCDC 2002). Accordingly, valuable information can be easily obtained from statistical analysis of the wide range of available data. 27 In the context of the study of 3D arrangement of molecules within the solid state and how molecular

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4 components are held together through intermolecular interactions, early re ports from Pauling 28 and Bondi 29 based upon such statistical type of study, albeit they corresponded to the limited range of structural data available at that time, yet have provided results concerning the van der Waals distances that are still widel y used. Later in the 1980s and 1990s, structural studies by means of statistical analysis using the CSD with respect to intermolecular interactions sustaining the crystal lattice underlying the molecular arrangement in organic solids have been performed by Desiraju 30 32 and Etter 33 and have afforded significant advances in the field of solid state chemistry and crystal design. 1.2. Supramolecular Chemistry 1.2.1. Scope and Cont ext Supramolecular chemistry is the chemistry of the intermolecular bond, covering the structures and function of the entities formed by the association of two or more chemical species. Jean Marie Lehn Supramolecular chemistry 34,35 defined by Lehn as chemistry beyond the molecule , is based on intermolecular interactions between molecules that form more complex organized assemblies. 23 The concepts delineated by this recent field of research have been initiated by the comprehensive work on inclusion compounds clathrates, 36 39 cyclophanes, 40 crown ethers 41 and cryptands 42 devoted to the generation of synthetic receptors, hosts which can be seen as the artificial counterparts of the binding sites in biomolecules. Indeed, Nature has afforded a wide range of complex and sophisticated examples of self assemblies based upon non covalent intermolecular interactions. In a sense, self organization constitutes the basis of most biological assemblies. Double

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5 stranded DNA p erfectly exemplifies this concept since this highly complex system is based upon hydrogen bonding between the two sets of nucleic bases of the complementary helices. 43,44 Countless further examples have also substantiated the importance of intermolecular interactions to sustain various biological systems: from protein folding governed by strong hydrogen bonds 45 to a range of other non covalent interactions including the amphiphilic self assemblies of membranes sustained by the hydrophobic effect upon the polymeric region of phospholipids. 46 These bioch emical processes occurring at the molecular level have largely inspired chemists to create novel artificial systems, 5,47 54 which offer opportunities to impact areas as diverse as material sciences, physics and pharmaceuticals. Such approaches have consisted in using and applying the knowledge acquired from specific natural systems with the purpose of generating the corresponding properti es in novel synthetic materials 55 and they have already lead to important innovations. 56,57 In the context of supramolecular interactions, the underlying concept of molecular recognition between functional groups interacting via non covalent interactions is particularly relevant towards the idea of exploiting encoded molecules that assemble in a defined manner in the same vein as the coupling of matching biological entities provides specific response in living systems. In this regard, Linus Pauling has early foreseen the importance of complementariness between the functional groups of molecular entities, which, by assembling via weak interactions such as hydrogen bonds, generate specific function as disclosed in his volume The Nature of the Chemical Bond:

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6 Although the hydrogen bond is not strong it has great significance in determining the properties of substances. Because of its small bond energy and the small activation energy involved in its formation and rupture, the hydrogen bond is especially suited to play a part in reactions occurring at normal temperatures. It has been recognized that hydrogen bonds restrain protein molecules to their native configurations, and I believe that as the methods of structural chemistry are fur ther applied to physiological problems it will be found that the significance of the hydrogen bond for physiology is greater than that of any other single structural feature. Linus Pauling That molecular recognition between complementary functions is cruc ial in the phenomenon of specific organization between molecules has been further conceptualized within the field of supramolecular chemistry and has revealed to possess great opportunities for new generation s of chemists. 1.2.2. Supramolecular Interactions A tho rough knowledge of the array of non covalent interactions that sustain supramolecular assemblies is critical in order to acquire an understanding of the essential mechanisms that govern the self organization of molecular entities. In this respect, the sign ificance of studying structural patterns via the use of extensive databases has already been mentioned. Judicious exploitation of this information can, in turn, afford the means to develop strategies for controlling the self assembly of molecular component s that possess preselected functional groups, which can engage in specific supramolecular interactions: coordination bonds, dipole dipole interactions, hydrogen bonding, p p stacking or van der Waals interactions. Table 1.1 presents a non exhaustive compara tive overview of these different types of non covalent interactions.

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7 Table1.1. Typical supramolecular interactions and their characteristics Interaction type Energy (kJ/mol) Approximative distance range () Examples Coordination bond M L (with M = tran sition metal, L = electron donor organic ligand) 50 200 d(M O,N) = 1.7 3.5 Variable, dependant on transition metal and donor element Coordination polymers cis platin Dipole Dipole 5 50 Variable Acetone Nitro derivatives Hydrogen bond AH D (with A = acceptor, D = donor) 4 120 d(AD) = 2.2 4.0 Carboxylic acid dimer Nucleic bases p p stacking < 50 d(face to face) = 2.8 3.5 d(edge to face) = 2.9 3.8 Graphite Nucleic bases stacking van der Waals < 5 ca. sum of van der Waal radii Inclusion compou nds Saturated alkyl chains Based upon the knowledge of the interplay between potential interactions in addition to the consideration of accurately selected functional groups within either a single molecular component or multiple complementary molecules, the supramolecular approach represents a method of choice to generate a novel class of functional materials. 1.2.3. Crystal Engineering In the context of solid state chemistry, supramolecular science provides a successful approach to the self assembly of simple m olecular building blocks preselected for their complementary geometrical and binding capabilities and can directly lead to a wide variety of crystalline structures sustained by intermolecular interactions. In effect, crystal has been described as the supe rmolecule par excellence , 24 25 since its formation results from the cohesive arrangement of its constituents via more or less strong forces between these building units. Application of the principles delineated by supramolecular chemistry and molecula r recognition has resulted in the rational design of crystalline architectures sustained by intermolecular interactions between complementary molecular

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8 components. Accordingly, the field of crystal engineering, 19,58 which involves prediction and control of the architecture within crystalline structures, has recently emerged. 5 9 62 The corresp onding strategies are potentially important for designing materials with specific features and chemists have only recently applied the concepts of supramolecular synthesis and crystal engineering to generate new classes of organic solids and coordination p olymers with a remarkable degree of success in terms of design. 63 66 In addition, the modular aspect of these supramolecular assemblies provides a range of opportunities for the variation of the elemental components that can be judiciousl y selected for their potential applications. 67 In summary, the rational design of organic solids and coordination compounds from building units that allow the introduction of specific functionalities may offer valuable information concerning the int erplay between the range of potential interactions and the relative degree of control within the resulting supramolecular architectures. Systematic investigation towards determining the factors that might favor the generation of such self assemblies is of high interest for further development of functionalized supramolecular materials. In this respect, the work presented herein concerns the development of novel supramolecular organic and metal organic materials based upon organic macrocycles and coordinatio n networks respectively. This study will provide design strategies that apply to both types of systems and an understanding of the essential mechanisms that control the generation of crystalline structures of these classes of compounds. Applications of the se principles will delineate our approach towards the construction of organic architectures and metal organic networks possessing valuable

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9 properties. 1.3. Supramolecular Organic Materials 1.3.1. Scope and Context Aiming to the construction of a class of crysta lline compounds based upon organic building units that enable the incorporation of variable of functionalities towards a systematic evaluation of the factors controlling the formation of crystal structures, calixarene molecules constitute a particularly su itable starting material. Calixarenes are macrocycles resulting from the condensation, in basic conditions, of para substituted phenol molecules and formaldehyde. 68 In particular, calix 4 arenes consist in four phenolic moieties bridged in a macrocycli c system by four methylene groups connecting the adjacent positions of the phenol groups. They generally adopt a cone shaped conformation, where all aryl are syn to one another. Such characteristic has actually originated the term calixarene for their re semblance to the Greek vase calix crater . 69 Calix 4 arene derivatives crystallize easily and their selective functionalization is relative ly simple so they represent excellent building blocks for the generation of supramolecular solid state architectures. 70 Figure 1.1 shows the potential for modularity of calix 4 arenes that may be selectively functionalized at the para positions of eac h aryl moiety, the upper rim of the cone, while a second functional group may also be appended to the hydroxylate sites at the lower rim of calix 4 arene molecules. Over a thousand of crystal structures containing calixarene molecules have been deposited i n the CSD to date. For the most part, they involve calix 4 arenes derivatives

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10 illustrating their general aptitude to crystallize. In this context, the systematic study of the arrangement adopted by this type of molecules within the solid state with respect to specified variables, substituents, conformation, etc., has been largely overlooked in the relevant literature; nonetheless such structural analyses 71,72 can provide valuable information concerning the supramolecular interactions that control the self assembly of t hese systems in order to develop an understanding of the factors inherent in such supramolecular control, with the goal of ultimately affording the means to generate materials with required properties for practical applications. Figure 1.1. Representatio n of a calix 4 arene molecule in the cone conformation showing the sites at the upper and lower rims that can sustain functional substitution 1.3.2. Properties The characteristic cone conformation that can be adopted by calixarene derivatives qualifies them as me mbers of a major group of macrocyclic host compounds in supramolecular chemistry. In this regard, their complexation with respect to a range of ions and small organic molecules has been widely studied. 68,73 77 In particular, studies on the inclusion capability of calixarenes, initiated by J. Rebek and V. Bhmer, have revealed that appropriately functionalized calixarenes derivatives, when in presence of guest molecules, c an self assemble to form dimeric units, host capsules, suitable for the

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11 inclusion of these small organic molecules, 76,78 80 Figure 1.2. It should be noted that rational chemical modification of calixarene building units has subsequentl y led to the generation of much larger supramolecular hosts corresponding to the self assembly of multiple calixarene derivatives based upon numerous intermolecular interactions, 47,81,82 Figure 1.3. Another aspect of calixarenes is that they can inherently act as amphiphilic species. In effect, they possess both hydrophobic and hydrophilic groups at the opposite calixarene rims so they are usually sui table for the formation of bilayer arrangements involving head to head and tail to tail interactions. 75,83 For example, many bilayer structures have been reported for para tert butyl calix 4 arenes, in which the presence of hydrophilic phenolic rim and hydrophobic core and upper rim has resulted in the antiparallel alignm ent of adjacent calixarene molecules, 84 87 Figure 1.4. Figure 1.2. Self assembly of two calixarenes providing host capsule for small guest molecules

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12 Figure 1.3. Space filling representation of the s upramolecular arrangement of calixarene complexes of resorcinarenes and para sulfonatocalixarenes generating large host compounds Figure 1.4. Crystal structure of the supramolecular arrangement in bilayers of amphiphilic para tert butyl calix 4 arenes 1. 4. Supramolecular Metal Organic Materials 1.4.1. Scope and Context Metal organic networks or coordination polymers are organic inorganic hybrid infinite structures based upon coordination bonds between a transition metal and the heteroatom of an organic mo lecule called ligand or spacer. Coordination bonds involve the donation of electron density from the donor atom of a ligand to a metal ion. 88 Considering the large variety of possible organic ligands and coordination geometries of transition metals that can afford a wide range of metal organic compounds, an

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13 understanding of how complemen tary shapes of molecular building units can be exploited and the selection of appropriate nodes (metal coordination geometries) and spacers enable the specific synthesis of predictable networks. The first examples of the rational design of supramolecular a rchitectures based upon the coordination between nodes and multi functional organic ligands ha ve afforded coordination polymers with predictable network architectures in the early 1990s. 60,66 Such an approach has lead to the rapid development of controlled metal organic network composition and topology, inspired in part by the concepts delineated in crystal engineering. Prototypical examples of infinite networks based upon the linkage between 4 connected nodes and linear bifunctional linkers are shown in Figure 1.5. 2D square grid and 3D diamondoid topologies directly res ult from square planar and tetrahedral node geometries. The corresponding structures have been generated from commonly available building blocks transition metal ions Co(II), Ni(II), Cu(II) or Zn(II) and 4,4 bipyridine and a variety of guest molecules, 89 92 Figure 1.6. In the context of the description of metal organic networks in terms of the corresponding topologies, it is important to note that both networks possess the same stoichiometry node: linker (1:2) so the corresponding architectures or superstructures exemplify the phenomenon of structural supramolecular isomerism, highly relevant for crystal engineering. 93 In this regard, the importance to develop an understanding of the factors inherent in the supramolecular control of network topologies is evident. Accordingly, the systematic study of recurrent motifs adopted by relevant chromophores, coordination metal geometries and environment configurations, and specific organic

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14 ligands by means of cri tical analysis of a broad range of known structures constitutes an asset towards the design of new metal organic structures with desirable properties. Figure 1.5. Schematic representation of the 2D square grid and 3D diamondoid (hexagonal and cubic) netw orks that can be generated by linking transition metal nodes by linear bifunctional spacers ligands Figure 1.6. Crystal structures of the 2D [Ni(4,4 bipyridine) 2 (NO 3 ) 2 ] n and 3D [Cu(4,4 bipyridine) 2 ] n metal organic networks, organic and anionic guests a re omitted for clarity 1.4.2. Properties The modular nature of crystal engineered metal organic networks, which can be generated from a diverse array of complementary building units, 67,94 96 coupled with the structural diversity represented by the range of supramolecular isomers that can be generated from each s et of molecular components, 93,97 are of particular interest in the context of fine tuning the chemical or physical properties.

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15 Furthermore, the presence of channels or cavities, which are controllable in size by the variation in length of the organic spacer, within the supramolecular structures can afford porous materials. In th is context, rigid linkers have been widely exploited in the design of network topologies corresponding to such anticipated property. Indeed, if one were to just focus upon linear N,N donor spacers, there already exist numerous examples of 2D 66,90 92,97 113 and 3D infinite networks, 89,113 120 many of which have no precedent in minerals. In particular, metal organic square grids possess cav ities that are suitable for interpenetration 90 92,110 113 or enclathration 66,98 103 of a range of guest molecules. In a sense, they have structural features that compare to both clays and zeolites since they are inherently lamellar 109,121 and they can also be porous. 94,103,113 In 3D networks, the presence of large pores may lead to the phenomenon of interpenetrati on, 122,123 which can be overcome via the use of bulky linkers 124 or the presence of guest molecules or ions 60 in order to fill the cavities. On the other hand, recent results have demonstrated that interpenetrated structures can also be porous. 125,126 1.5. Supramolecular Materials: Tunable Properties towards Useful Applications There is current ly intense r esearch in the nanosciences, which merge the basic experimental sciences towards the controlled manipulation of molecules in order to build nanostructured materials, as illustrated in Figure 1.7. In this context, supramolecular chemistry provides a straigh tforward method to generate a wide variety of functional nanoscale structures. 127

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16 Figure 1.7. The convergence of experimental sciences towards the field of nanosciences (adapted from the review Pour la Science 290, 2001, p.134) In addition to their inherent inclusion capability, qualifying them as potential nanoscale containers, 128 the variety of properties of functionalized calixarenes coupled with their low cost and non toxicity may allow their exploitation through mult idisciplary areas of research as catalysts, extractants, semi conductors materials, switchable systems for data storage and sensors or bioactive compounds. 73,128 136 In particular, the ability of amphiphilic systems based upon c alixarene derivatives to self assemble in a reminiscent manner as phospholipids in biological membranes makes them an attractive target towards the construction of a wide range of materials such as sensors, 137 microporous membranes 138,139 or bio active molecules carriers. 140,141 Nanoporous supramolecular metal organic materials present var ious potential applications as adsorbents, sensors, catalysts or in separation and ion exchange. 96,142 145 They constitute an alternative to zeolites that is of inte rest for its simplicity in generation and functionalization. One can also find interesting advantages of these materials, which can possess intrinsic properties due to the presence of metal ions allowing the

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17 incorporation of additional properties such as l uminescence, redox behavior or magnetism. In summary, the application of supramolecular synthesis and crystal engineering strategies towards the generation of metal organic and organic materials in the context of a multidisciplinary approach can afford th e goods: not only smart crystalline materials with useful properties chosen by the crystal engineer and implanted into the molecular building blocks. 146

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18 Chapter 2 Supramolecular Organic Materials based upon pseudo amphiphilic calixarenes 2.1. Introduc tion With a view to the rapid growth of both the biological 73,135,136,147 and material science 73,82,130,137,148 150 applications of calixarenes, recent advances have resulted in the development of simple routes to generate derivatives suitable for coupling to macromolecules such as DNA 151 and proteins 152 155 or for assembly at interfaces towards the production of calixarene thin films. 149,156,157 In this context, amphiphilic cal ixarenes, bearing both hydrophobic and hydrophilic groups at the opposite calixarene rims, have been shown to be suitable for the formation of self assembled mono and multi layers at the surface of solid supports. 158,159 These films can be generated from calixarene derivatives through a variety of techniques. 160 164 Such materials consist in multi dimensional supramolecular assemblies and hence their properties may vary from these of individual molecules in solution. In this regard, the study of the spatial arrangement adopted by selected amphiphilic calixa renes within the solid state is clearly relevant. Amphiphilic molecules or surfactants are well known for their essential roles in biological membranes or detergents. They are commonly defined as molecules possessing both hydrophilic polar functions and li pophilic moieties. Depending on their

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19 molecular geometry, they are capable of self organization into different phases such as bilayers, corresponding to lamellar systems, or colloidal systems including micelles and inverse micelles. 165 Extending the li mits of the definition of the nature of the polar head group, this study will be based upon the so called pseudo amphiphilic calix 4 arenes in which various alkyl groups are coupled to the phenolic oxygen atoms, introducing van der Waals interactions at one face, while different functionalities, not necessarily hydrophilic, are present at the upper rim of the calixarenes, thereby affecting the intermolecular interactions occurring at this face, Figure 2.1. In this context, the rational design of organic s olids based upon the principles of self assembly via hydrogen bonding, stacking interactions, hydrophobic interactions and electrostatics represents a salient aspect of crystal engineering. Considering the modular aspect of calixarene molecular building bl ocks, there are many opportunities for variation of the functional elements that can be judiciously selected for their potential in terms of intermolecular interactions. Examples of these interactions include face to face and edge to face aromatic stacking in para H systems, van der Waals repulsions due to the steric effects of bulky groups such as tert butyl and induced dipole dipole forces in bromo substituted calixarene systems. Knowledge of the interplay between two or more sets of interactions will fac ilitate further extension of crystal engineering. In this respect, systematic investigation of the structural features and general trends concerning the spatial arrangement of calixarene derivatives with respect to the specifics of the molecular components may reveal important towards rational application of principles delineated by supramolecular chemistry and crystal engineering to the design of novel supramolecular

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20 architectures. Figure 2.1. Representation of the pseudo amphiphilic calix 4 arene buildi ng block possessing alkyl substituents at the lower rim and variable functionalities at the upper rim 2.2. Calixarenes Crystal Packing: a Database Review 2.2.1. Scope and Limitations Calixarenes have been widely studied in solid state chemistry: at this t ime, more than 850 structures involving calix 4 arene derivatives have been deposited in the CSD. The examination of these crystal structures, which exclude resorcinarenes, homocalixarenes and other pyrole calixarenes, with regard to the spatial arrangemen t of calix 4 arenes within the solid state has afforded relevant information concerning the factors that can influence the crystal packing. Thiacalixarenes were included in this review since they revealed to adopt comparable trends as these of calixarene m olecules. It should also be noted that this study was purely based upon crystalline architectures and excluded dynamic properties related to solution phenomena. There exist several potential variables that can affect the supramolecular organization of cali xarenes building units. In

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21 particular, chemical composition, shape, position of the functional groups and presence of guest or template molecules may be specifically screened. Considering the substantial amount of data, a primary classification based upon the chemical composition has revealed proportionate division between molecular and metal organic structures. In effect, 53% of the data consisted in purely organic compounds, while the remaining 47% corresponded to metal alkaline or mixte coordination c ompounds. The metal organic structures were generally coordinated through the phenolic oxygen atoms at the lower rim, which may also be bridged or capped by one metal ion, or via specific substituents at the para position such as sulfonate groups that allo w coordination chemistry at these sites. The strong propensity of calix 4 arenes to adopt a cone or flattened cone conformation in the solid state is effectively exhibited in 75% of the crystal structures. The other possible conformations are partial cone (6.5%), 1,2 alternate (2.5%) and 1,3 alternate (16%). Figure 2.2 illustrates the four common conformations observed in calix 4 arene macrocycles. The proportion between the different conformations is consistent in both classes of organic and metal organic structures. Another important trait resulting from the exploitation of these raw data concerns the repartition according to the substituents that have been used to functionalize the upper rim of calix 4 arene molecules. Interestingly, the structures of par a tert butyl calix 4 arenes derivatives markedly outnumber all other derivatives for 60% of the whole data set. This feature can be explained by the relative simplicity and high yield resulting from the condensation of para tert butylphenol and formaldehyd e in basic conditions with respect to the use of other para substituted phenols. 68,166 The other

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22 main derivatives that have been studied are para hydrogen and para sulfonato calix 4 arenes in relative proportions of 16% and 6% respectively. However, the wide diversity of substituents found to functionalize the lower rim, which can also be partially substituted, did not allow delineating specific trends. Fin ally, the presence of additional guest or solvent molecules as part of the crystal structure corresponded to ca. 65% of the cases. A detailed classification of the structures and packing adopted by calix 4 arene derivatives deposited in the CSD can be foun d in the electronic supplementary data. Tables 2.1 and 2.2 represent simplified categorization corresponding to the most relevant structural motifs discussed throughout this review. Figure 2.2. Cone (a), partial cone (b), 1,2 a lternate (c) and 1,3 alternate conformations adopted by calix 4 arenes In the context of this study, the available data concerning the molecular structures of calixarenes in the cone conformation that possess four hydrophobic para substituents, hydrogen an d tert butyl, have been analyzed with respect to the influence of the lower rim functionality, which can induce, inter alia hydrophilicity or hydrophobicity, over the spatial arrangement of these molecules in the solid state. It should be noted that the g uest specifics have been accounted as a secondary variable. a b c d

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23 2.2.2. Crystal packing of amphiphilic calixarenes The model molecule of non substituted calix 4 arene has only resulted in 19 crystal structures essentially differing by the solvent incorporated in the crystalline architecture. In effect, in the vast majority of the cases, with small solvent hydrophilic and hydrophilic molecules, these simple building blocks have afforded a cyclic trimeric arrangement sustained by p p edge to face aromatic intera ctions between the mutually partially included calixarene rings, Figure 2.3a. The spatial arrangement of these trimeric subunits in hexagonal close packing is sustained by van der Waals interactions and generates two types of channels. Further study of the crystal packing and inclusion properties of these subunits has recently been reported by Atwoods group. 167 In the presence of larger guest molecules capable of hydrogen bonding, calix 4 arenes self assemble in tetrameric subunits result ing from guest inclusion. For calix 4 arenes possessing bulky substituents tert butyl at the upper rim, the prevailing crystal packing consists into the formation of bilayer structures, 84 87 whether the included hydrophobic gue st is a small solvent molecule, e.g. CH 3 CN, or a larger organic molecule, e.g. tetradecane. As illustrated in Figure 2.3b, these bilayers are generated from the antiparallel alignment of adjacent calixarene molecules that divide the space in two distinct r egions: a hydrophilic layer composed of the hydroxyl groups of the lower rims orientated towards the same direction and a hydrophobic layer formed by the aromatic rings and tert butyl substituants of the calixarenes including the organic guest molecules. 148 In only few exceptions, for 4 out of 23 structures, a different crystal packing was observed. The absence of included solvent has resulted in the mutual

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24 inclusion of two tert butyl substituents forming dimeric units of para tert but yl calix 4 arenes. On the other hand, the presence of highly sterically hindered guest molecules has resulted in the self assembly of tetramer units similarly to the case of non substituted calix 4 arenes. Figure 2.3. Dominant crystal packing observed for calix 4 arenes (a) and para tert butyl calix 4 arenes (b) Of special interest in the context of this review, the class of bipolar amphiphilic molecules, para sulfonato calix 4 arenes, in which the presence of two hydrophilic r ims separated by a hydrophobic core, has been specifically studied in terms of spatial arrangement that is adopted by the macrocycles in the solid state in a recent review by Atwood and Raston. 75 One consequence of their chemical compositi on is a strong propensity to form bilayer structures involving head to head and tail to tail interactions. Such bilayers can incorporate hydrophilic guests and the overall arrangement is generally controlled by strong interactions, hydrogen bonds or coordi nation, involving the sulfonate groups, the guest molecules and the phenolic groups. In this regard, many reports have described the inclusion of various guests 83,168 170 including small biomolecules 171 174 and their effects upon the bilayer motif. Para sulfonato calix 4 arenes have also been shown a b

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25 to induce three other significant types of crystal packing: capsules that can incorporate hydrophobic molecules such as crown ether 175 177 and azacrown; 178 or spheres and tubules, Figure 2.4, nanostructures resulting from the controlled self assembly of three components calixarene, metal ion and organic ligand in specific stoichiometries. 82 Figure 2.4. Tubular self assembly of para sulfonato calix 4 arenes, hydrogen atoms, metal ions and organic ligands are omitted for clarity 2.2.3. Crystal pac king of pseudo amphiphilic calixarenes Examination of the crystal structures of calix 4 arenes and para tert butyl calix 4 arenes that possess various functionalities at the lower rim has allowed delineating some general trends concerning the factors that govern the crystal packing of this class of macrocycles. First considering the calix 4 arenes with hydrogen atoms at the para positions, three cases can be distinguished according to the degree of substitution at the opposite rim. When the lower rim is tet ra substituted by organic moieties that are not bridging or capping this face, the calix 4 arenes primarily adopt a bilayer motif, in which a rigid region results from the head to head arrangement of anti parallel calixarene aromatic cores pointing towar ds each other and a soft region consists in the self assembly of the

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26 various substituents that can interact via hydrogen bonding, aromatic stacking or van der Waals forces between the included functionalities, Figure 2.5a. When the lower rim is di substi tuted at the two opposite phenolic positions, the almost exclusive tendency of the calixarenes is to form head to head dimers held together by face to face p p stacking. In absence of additional components capable of influencing the self assembly within th e crystal lattice, 179 these dimeric subunits may then arrange in a herringbone type organization, which affords high three dimensional packing efficiency, Figure 2.5b. Figure 2.5. Main crystal packing moti fs observed for pseudo amphiphilic calix 4 arene derivatives that can self assemble in bilayer (a), herringbone of dimers (b) and column (c) modes a b c

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27 When the lower rim is tri substituted or possesses four substituents capping this face, calixarenes form colu mnar type crystal packing via partial inclusion of the non symmetrical substituent or the capped face within the upper rim of a calixarene situated below. These columns of consecutive included calixarenes generally alternate with respect to their direction ality to afford efficient three dimensional packing. It should be noted that this motif only occurs in absence of included guest molecule, Figure 2.5c. Secondly, the study of the spatial arrangement adopted by para tert butyl calix 4 arene derivatives has revealed similar trends with differences attributable to the introduction of a supplementary variable as the presence of bulky substituents at the upper rim. When the phenolic substituents induce a degree of asymmetry within the molecular structure of para tert butyl calix 4 arenes, for example mono substitution or tetra substitution of the lower rim by three equivalent moieties and an additional distinct group, the columnar type motif described above is obtained. In the remaining majority of the cases, the specifics of the substituents in terms of shape and functionality constitute the triggers of the crystalline arrangement. From a general perspective, three major situations can be distinguished. In the case of large substituents that possess functional gr oups susceptible to afford supramolecular interactions with each other such as hydrogen bonds or aromatic stacking, the bilayer type crystal packing described above prevails, Figure 2.6a. The presence or absence of guest/solvent molecules does not essentia lly affect the overall supramolecular arrangement. In fact, such small additional components, when non included in the macrocycles, usually lie between the bilayers; whereas guest inclusion may increase the width of the aromatic layer. When the lower

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28 rim i s functionalized with small groups, the presence of included guest molecules within the cavities of the calixarenes generates the formation of capsules. The spatial organization of these capsules can be described as an anti bilayer situation where rigid and soft parts regularly alternate in order to optimize the packing efficiency, Figure 2.6b. Finally, the presence of bulky groups at the lower position of the molecules of para tert butyl calix 4 arene induces a different packing mode that is principally governed by van der Waals repulsion of the two sterically hindered faces of the macrocycles. The oblique orientation of adjacent molecules generates a herringbone pattern as illustrated in Figure 2.6c, which offers the closest and most compact crystal pack ing for these characteristic shapes. Interestingly, this type of motif is recurrent throughout the structures of all calix 4 arene derivatives. Notable instances are constituted by dimeric units, in particular tail to tail sub assemblies generated from str ong interactions such as coordination or hydrogen bonds between the lower faces of two calix 4 arenes. These dimers present symmetrical hindered opposite faces formed by both upper rims and hence self assemble in a similar manner as a single building unit that contain two opposite bulky faces.

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29 Figure 2.6. Main crystal packing motifs observed for pseudo amphiphilic para tert butyl calix 4 arene derivatives that can self assemble in bilayer (a), capsule (b) and herringbone (c) mod es In the context of the crystallographic study of pseudo amphiphilic building units possessing lipophilic substituents, only a small number of calixarenes bearing exclusively alkyl chains at the lower rim have been synthesized and investigated by X ray cr ystallography. 180 183 The corresponding crystalline arrangements are essentially governed by the substituent particulars, nitro groups or large multi aromatic components, a b c

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30 used to functionalize the upper rim. In the case of amphiphilic calixarenes possessing long alkyl chains, para octanoyl calixarene constitutes a rare and recent example in which the crystal packing is sustained by van der Waals interactions between alkyl chains and by the presence of a hydrophilic layer between two la yers of calixarenes. 184 This behavior in the solid state is very similar to those observed for amphiphilic molecules in liquid crystal phase and typical phospholipids in lyoptropic phase. 185 Finally, with regard towards the study of specific modification of the upper rim of pseudo amphiphilic compounds by halog en groups and the influence of the resulting induced dipole over the supramolecular organization, for example in the case of brominated calixarenes, the extremely scarce number of these types of functionalized macrocycles 180,1 86 189 has not allowed the extraction of any particular trend or preferential behavior of suc h type of halogenated calix 4 arene s In summary, some general trends have been delineated concerning the different variables that may affect the supramolecular organization of amphiphilic and pseudo amphiphilic classes of calix 4 arenes. In the context of this review, several points deserve to be emphasized. First, the extremely large spectrum of functionalities found to modify the lower rim of calix 4 arene derivatives has limited this study from a thorough examination of the systematic variation of the p otential supramolecular interactions that can be incorporated to this face. Second, the influence of specifically designed substituents for their strong tendency to generate well known supramolecular patterns such as the chiral motif resulting from assembl y of calix 4 arene possessing melamine substituents and barbituric acid derivatives 190 has been considered as special cases in the

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31 context of this study since these instances are not representative of the crystal packing of calixarene mole cules. Finally, the scarcity of crystal structures containing calixarenes possessing more or less long alkyl chains represents an interesting opportunity towards the rational study of such class of pseudo amphiphilic synthetic compounds through systematic variation of the hydrophobic part. Moreover, further examination of the effect of the modification of the upper rim by bromine substituents and their comparison with other frequent derivatives may reveal of interest towards the generation of supramolecular organic materials based upon the control over the structural motifs resulting from more than one type of intermolecular interactions. Careful examination of the crystal structures of a series of calix 4 arene derivatives systematically modified at the low er rim with various alkyl chain lengths, and successively systematic modification of the upper rim by three types of functional groups, hydrogen, tert butyl and bromine, which can induce the corresponding sets of weak interactions, aromatic stacking, van d er Waals and halogen or induced dipole forces, sustaining the crystal packing, will be discussed in the broader perspective of crystal engineering strategies and development of novel materials.

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32 Table 2.1. Structural analysis of the crystal packing observed in calix 4 arenes Lower Rim Substituents CSD Refcode Space Group Structural Motif HUVBEF P 3 WUVKAZ P 3 PEZBIF P63 BALHOM P63/m DACMAV P63/m PEZBEB P63/m PEZWIA P63/m WUVKED P63/m WUVKON P63/m WUVKUT P63/m WUVLAA P63/m WUVLEE P63/m WUVLII P63/m WUVLOO P63/m Trimers NUNJUB P 1 HAZJAT P4/nnc Tetramers 4 OH DACLUO Pnma Bilayers QEKMIC P21/c Bilayers 1OH+3OR WIWLOD P21/c Columns KEVYAL P21/c Columns TIWHEM P21/c PAWT OW R 3 RUWGOF P21/n LASDEO P1121/n NEMTUU P 1 WOHJEI P21/a YAKGIA P 1 Dimers 2OH+2OR (Opposite Rings) VIRXAF P21/n Herringbone GODWEB P21/c Bilayers NUVMEW P 1 Dimers 2OH+2OR (Opposite rings bridged) NUVMIA P21/a Columns JOYHEK P21/a WILNOU P 1 RADSAQ P21/n NEDDUV C2/c Bilayers HILVAZ C2/c Columns 4 OR HUBMEW P 1 Herringbone LINLID P2/c Columns 4 OR (Adjacent rings bridged) NEMMUN C2/c Bilayers 4 OR (Opposite rings bridged) TADCOQ P21/c Dimers 4 OR (All rings capped) HEMHUC P 1 Columns

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33 Table 2.2 Structural analysis of relevant crystal packing observed in para tBu calix 4 arenes Lower Rim Substituents CSD Refcode Space Group Structural Motif BHPMYC P4/n BOCZUO P4/n CUPWAL P4/n GOKPEB P4/n GOKQUS P4/n LODNOH P4/n NA PCIQ P4/n NILCEQ P4/n NILCIU P4/n NILCOA P4/n VEGPIG P4/n ZAHMOK P4/n NILCAM P4/n QIGBAJ P 1 BHPMYC01 P112/a 4 OH NAPCEM Pc21n Bilayers FAQDUW P21/n 3OH+1OR LOMGUP P 1 Columns KEVXIS P21/n SUYXIT P 1 QIKTEJ P 1 Capsules KEQYEK P212121 Columns IBOKAL P 1 2OH+2OR (Opposite Rings) BOWFOI P 1 Bilayers WESGIK P21/a Bilayer/Herringbone Hybrid WEHJEY P 1 ABOYAR C2/c QIFHOC P 1 NECWAT C2/c 1OH+3OR ZOJWEA Pnma Bilayers PAMTIG P21/n RADRUJ P21/n JEGQO B P21/a Bilayers DAKSEN P 1 GIYTOX P 1 Capsules KEQYAG P21 4 OR JOYHAG P21/c Herringbone NICDOS P 1 3OR+1OR' KOCQIC Pbca Columns

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34 2.3. Experimental 2.3.1. Syntheses Two series of pseudo amphiphilic calixarenes were synthesized. A first set of bromo substi tuted calix 4 arenes at the para position through systematic variation of the chain length of the four alkylated phenolic oxygen atoms of the lower rim resulted in the following compounds: para Br tetra O alkyl calix 4 arene, with alkyl = butyl, 1 ; pentyl, 2 ; hexyl, 3 ; heptyl, 4 ; octyl, 5 ; nonyl, 6 ; decyl, 7 ; undecyl, 8 ; dodecyl, 9 The second series of calixarenes resulted from variation of the substituent at the upper rim while all phenolic oxygen atoms were alkylated by hexyl groups: ( para H) 2 ( para Br) 2 tetra O hexyl calix 4 arene, 10 ; para H tetra O hexyl calix 4 arene, 11 and para t Bu tetra O hexyl calix 4 arene, 12 Syntheses were achieved using appropriately modified procedures of syntheses described in the literature. 191,192 Recrystallization of all compounds was achieved at room temperature via slow diffusion in mixtures of organic solvents selected for their ability t owards solubilization of calixarene derivatives. 2.3.2. X ray Crystallography Single crystals suitable for x ray crystallographic analysis were selected following examination under a microscope. Single crystal x ray diffraction data for compounds 1 5 and 9 12 and all subsequent compounds described along this dissertation, were collected on a Bruker SMART APEX diffractometer using Mo ?a radiation ( ? = 0.7107 ). Lorentz and polarization corrections were applied and diffracted data for bromo derivatives and all metal organic compounds presented further in this work were also corrected for

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35 absorption using the SADABS v.2.02 area detecto r absorption correction program (Siemens Industrial Automation, Inc., 1996). The structures were solved by direct methods and Fourier techniques. Structure solution and refinement were based on | F | 2 Unless specified, all non hydrogen atoms were refined anisotropically and hydrogen atoms of the C H groups were placed in geometrically calculated positions and refined with temperature factors 1.2 times those of their bonded atoms. All crystallographic calculations were conducted with the SHELXTL 6.10 progra m package (Bruker AXS Inc., 2001). Table 2.3 reveals crystallographic data and structure refinement parameters of the compounds presented in this chapter. Full crystallographic data can be found in the electronic supplementary data. Compound 10 was obser ved to present two different crystalline phases at 200K and at room temperature corresponding to the structures of 10a and 10b respectively. In crystal structures of 1 2 4 5 11 and 12 several carbon atoms of the alkyl chains were disordered around 2 fo ld positions and each corresponding group of atoms was refined with two equally occupied sets of coordinates. In crystal structures of 3 and 10a the carbon atoms of several alkyl chains of the calixarene molecules in the asymmetric unit occupied several ge neral positions and were refined with fixed site occupation factors (s.o.f.) for occupancies of 0.5 (0.6 and 0.4 for 4 atoms of 3 ) for each carbon. All non hydrogen atoms were refined with anisotropic displacement parameters except for several carbon atoms of the alkyl chains in compound 3 5 and 10a which were observed to exhibit high thermal motion. The H atoms of the C H groups were fixed in calculated positions except for the H atoms of the disordered aliphatic chains in compounds 3 4 5

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36 and 10a The relatively high values for the residual electronic density in 5 and 10a were due to the non attribution of these hydrogen atoms. Structure of 3 was badly disordered and presented very low proportion of significant diffraction intensities at higher Bragg an gle so a shortage of high angle data with significant intensity was used to determine a valid solution. The crystal of compound 10a was a racemic twin as highlighted by the value of the Flack parameter (0.47). Although the structure was recollected for di fferent crystals and resolved several times; in every case, a comparable Flack parameter was obtained, such results are indicative of the natural tendency of this particular compound with respect to crystal growth. Recrystallization of compounds 6 7 and 8 afforded needle shaped microcrystals. Due to the poor quality of these crystals, diffraction of 6 8 was very weak and it was not possible to obtain acceptable structure solutions. However it was possible to determine their unit cells as means of compariso n with the series studied herein. Furthermore, data set collected for 6 and 8 provided the possibility to elucidate the main elements of the crystal packing of these compounds, which was found to be analogous to that of 4 and 5

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37 Table 2.3. Crystallographi c data for compounds 1 5 and 9 12 Compound 1 2 3 4 5 Chemical formula C 44 H 52 Br 4 O 4 C 48 H 60 Br 4 O 4 C 52 H 68 Br 4 O 4 C 56 H 76 Br 4 O 4 C 60 H 84 Br 4 O 4 Formula weight 964.50 1020.60 1076.70 1132.81 1188.91 Temperature, K 200(2) 200(2) 200(2) 200(2) 100(2) Crystal system Tri clinic Triclinic Triclinic Monoclinic Monoclinic Space group P 1 P 1 P 1 P2/c P2/c a, 12.2468(12) 13.0107(8) 18.018(4) 28.095(5) 27.628(2) b, 19.0095(19) 18.5940(12) 21.980(4) 16.485(3) 17.4376(15) c, 19.0772(19) 19.8009(12) 23.168(5) 18.384(4) 1 8.4703(16) a, deg 102.245(2) 101.3780(10) 113.40(3) 90 90 deg 91.880(2) 91.8250(10) 95.32(3) 98.359(4) 96.874(2) g deg 93.842(2) 94.3990(10) 109.24(3) 90 90 V, 3 4325.4(7) 4676.9(5) 7681(3) 8424(3) 8834.3(13) Z 4 4 6 6 6 r calcd g.cm 3 1.481 1.4 49 1.397 1.340 1.341 mm 1 3.761 3.483 3.185 2.907 2.776 F(000) 1952 2080 3312 3504 3696 Crystal size, mm 0.30x0.15x0.10 0.30x0.20x0.10 0.20x0.05x0.01 0.10x0.01x0.01 0.30x0.15x0.05 q range for data collection, deg 1.09 to 25.06 1.57 to 24.71 0.99 to 21.87 1.24 to 24.71 1.17 to 26.37 Limiting indices 14<=h<=14 22<=k<=22 22<=l<=22 14<=h<=15 21<=k<=20 23<=l<=22 17<=h<=18 11<=k<=21 22<=l<=21 32<=h<=33 19<=k<=18 21<=l<=17 31<=h<=34 12<=k<=21 22<=l<=23 Reflections collected 31517 24047 1480 7 40470 49331 Unique reflections 15178 15772 13120 14361 18071 R(int) 0.0335 0.0334 0.0252 0.1116 0.0826 Completeness to q % 98.9 98.9 70.8 100 99.9 Absorption correction SADABS SADABS SADABS SADABS SADABS Max. and min. transmission 1.000 and 0.825 1.000 and 0.639 1.000 and 0.795 1.000 and 0.714 1.000 and 0.618 Data / restraints / parameters 15178 / 0 / 1032 15772 / 0 / 1037 13120 / 0 / 1633 14361 / 78 / 918 18070 / 37 / 943 Goodness of fit on F 2 1.021 0.992 1.056 0.962 1.002 Final R indices [I>2sigma(I)] R1 = 0.0433, wR2 = 0.1024 R1 = 0.0479, wR2 = 0.1060 R1 = 0.0567, wR2 = 0.1360 R1 = 0.0631, wR2 = 0.1240 R1 = 0.0716, wR2 = 0.1850 R indices (all data) R1 = 0.0723, wR2 = 0.1202 R1 = 0.0809, wR2 = 0.1209 R1 = 0.1012, wR2 = 0.1666 R1 = 0.1517, wR2 = 0.1601 R1 = 0.1573, wR2 = 0.2280 Largest diff. peak and hole, e. 3 0.730 and 0.631 0.922 and 0.745 0.507 and 0.344 0.7 17 and 0.589 1.004 and 0.708

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38 Table 2.3. (continued) Compound 9 10a 10b 11 12 Chemical formula C 79 H 122 Br 4 O 5 C 52 H 70 Br 2 O 4 C 52 H 70 Br 2 O 4 C 52 H 72 O 4 C 68 H 104 O 4 Formula weight 1471.41 918.90 918.90 761.10 985.51 Temperature, K 200(2) 200(2) 298(2) 200(2) 200(2 ) Crystal system Monoclinic Monoclinic Monoclinic Orthorhombic Monoclinic Space group P2(1)/c P2(1) P2(1)/c Pbca P2(1)/n a, a = 23.725(3) 21.973(3) 19.049(2) 19.3314(15) 19.5064(12) b, b = 15.6770(17) 16.135(2) 16.623(2) 19.2886(15) 16.9184(10) c, c = 21.102(2) 27.137(4) 16.059(2) 50.653(4) 38.139(2) a, deg 90 90 90 90 90 deg 103.075(2) 99.472(2) 97.898(3) 90 92.6920(10) g deg 90 90 90 90 90 V, 3 7645.3(15) 9490(2) 5036.9(11) 18887(3) 12572.5(13) Z 4 8 4 16 8 r calcd g.cm 3 1.278 1.286 1.212 1.071 1.041 mm 1 2.153 1.751 1.650 0.065 0.062 F(000) 3104 3872 1936 6656 4352 Crystal size, mm 0.50x0.10x0.05 0.30x0.10x0.02 0.20x0.10x0.05 0.60x0.30x0.10 0.30x0.25x0.05 q range for data collection, deg 1.63 to 27.10 0.94 to 25.11 1.63 to 24 .71 1.54 to 24.04 1.07 to 26.43 Limiting indices 30<=h<=30 20<=k<=12 25<=l<=27 26<=h<=15 19<=k<=19 32<=l<=32 15<=h<=22 19<=k<=19 18<=l<=18 22<=h<=22 22<=k<=21 44<=l<=58 24<=h<=24 18<=k<=21 47<=l<=39 Reflections collected 45337 50439 24921 86022 71190 Unique reflections 16842 33327 8588 14864 25748 R(int) 0.0884 0.0721 0.1125 0.0734 0.1179 Completeness to q % 99.9 99.2 99.9 99.8 99.4 Absorption correction SADABS SADABS SADABS None None Max. and min. transmission 1.000 and 0.676 1.000 and 0.735 1.000 and 0.903 N/A N/A Data / restraints / parameters 16842 / 0 / 799 33327 / 161 / 1914 8588 / 57 / 477 14864 / 0 / 1027 25748 / 3 / 1347 Goodness of fit on F 2 0.940 1.022 0.859 1.023 0.955 Final R indices [I>2sigma(I)] R1 = 0.0557, wR2 = 0.1094 R1 = 0.1085, wR2 = 0.2585 R1 = 0.0700, wR2 = 0.1676 R1 = 0.0810, wR2 = 0.1819 R1 = 0.0823, wR2 = 0.1725 R indices ( all data) R1 = 0.1354, wR2 = 0.1360 R1 = 0.2061, wR2 = 0.3248 R1 = 0.2578, wR2 = 0.2498 R1 = 0.1385, wR2 = 0.2129 R1 = 0.2208, wR2 = 0.2287 Absolute structure parameter N/A 0.466(16) N/A N/A N/A Largest diff. peak and hole, e. 3 0.778 and 0.589 1.580 a nd 1.240 0.369 and 0.253 0.361 and 0.194 0.513 and 0.399

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39 2.4. Results and Discussion 2.4.1. Influence upon the crystal packing through variation at the lower rim The first part of this study consists in the systematic evaluation of the effect of the substitution by increasing length chains of alkyl groups, C n H 2n+1 (n = 4 12), at the lower rim on the crystal structures of a series of pseudo amphiphilic tetrabrominated calix 4 arenes. Careful examination of the crystal structures with particular attenti on to the overall arrangement of the calixarene molecules reveals a clear tendency towards to formation of bilayer type packing while the chain length increases. In all compounds, the macrocycles exhibit a C 2 symmetrical, flattened cone, conformation. The distortions in the orientation of the aryl units corresponding to the symmetry reduction with respect to the four fold symmetry of the ideal cone conformation are attributed to repulsive van der Waals contacts between adjacent O alkyl groups at the lower r im of the calixarene molecules. 180,193 The ring inclination a ngles and corresponding distances between opposite aryl groups are presented in Figure 2.7 and Table 2.4. These values are consistent with the corresponding values of flattened conformations observed para H tetra O alkyl calix 4 arene derivatives, when the alkyl chain possesses more than 3 carbon atoms. 180 It should be noted that the relatively high inclination of the two opposite closest rims in tetrabrominated calixarene derivatives is also favorized by halogen halogen interactions, with d( BrBr) in a range of 3.85 to 3.95 and corresponding angles ?(C BrBr) = 89.5 96.9 and 97.3 103.5 for compounds 1 5

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40 Figure 2.7. Representation of the flattened cone conformation observed in para bromo calix 4 arenes and designation of the distanc es and angles used to describe their geometry Table 2.4. Ring inclination angles and corresponding distances between opposite aryl groups in the crystal structures of compounds 1 5 and 9 The structures of 1 and 2 p resent analogous crystal packing where the calixarene organization within the solid state affords higher packing efficiency relative to the other compounds presented herein as illustrated by the corresponding densities, Table 2.3. Figure 2.8 shows that 1 a nd 2 form two types of layers repeating down [010]. Each layer consists in the arrangement of calixarene molecules in the typical herringbone pattern presented above. Within the layers, one of the alkyl chains of each calixarene pointing in the same direct ion is partially included in the adjacent macrocycle thus forming columns, Compound Angle 1 () Angle 2 () Angle 3 () Angle 4 () Distance 1 ( ) Distance 2 () 1 60.7 52.7 9.78 8.00 10.0 4.43 2 63.1 50.3 9.04 7.15 10.1 4.45 3 61.6 52.7 14.7 5.47 10.1 4.32 4 54.6 48.9 11.4 6.55 9.85 4.36 5 56.5 50.5 11.9 5.97 9.83 4.41 9 65.1 40.6 6.63 4.3 9.89 4.70

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41 Figure 2.9. Every two columns in the same layer possess opposite orientations related by inversion center and, in 1 they interact with adjacent layers via bromine bromine interacti ons with d(BrBr) = 3.92 Figure 2.9. Considering this type of halogen halogen supramolecular interactions, Desiraju and Parthasarathy have demonstrated their attractive nature in the solid state. 194 These interactions are direction al and present two favorable geometries, when the angles formed by C 1 X 1 X 2 C 2 are noted ? 1 (C 1 X 1 X 2 ) and ? 2 (X 1 X 2 C 2 ), the two preferred geometries of halogen halogen contacts correspond to ? 1 = ? 2 (Type I) and ? 1 =180, ? 2 =90 (Type II). 195 In compound 1 both angles are equal, ?(C BrBr) = 69.6, since they ar e related by an inversion center situated between the two bromine atoms. The distance between the two bromine atoms is slightly higher than the sum of van der Waals radii (3.70 ) 29,196 allowing the interaction between two layers of calixarenes across the interlayer plane. In compound 2 the presence of an additional methylene in th e included aliphatic chain precludes further halogen interactions and adjacent layers essentially self assemble via van der Waals interactions affording similar packing efficiency as in 1 Figure 2.8. Representation of the crystal packing of compounds 1 and 2 down [001] (a) and view of one layer (b) and their superimposition (c) down [010]

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42 Figure 2.9. Detailed view of the interactions Br Br between the columns of two adjacent layers observed in compound 1 When the lower rim is substituted by hexyl chain s, the situation differs entirely. The calixarene molecules in compound 3 assemble in a helical motif. Each helix results from hexameric motifs of calixarenes that are sustained by strong, directional bromine bromine interactions and aromatic edge to face stacking interactions. Figure 2.10. shows the resulting helical packing motif. In the crystal structure of 3 bromine atoms of two adjacent calixarenes point towards the inside of the helix and interact with distances d(BrBr) of 3.57 and 3.76 shorter than the sum of van der Waals radii of bromine atoms, 29,196 with corresponding angles ?(C Br d Br a ) = 88.12 and 88.85 and ?(C Br a Br d ) = 138.00 and 158.14, where Br d is the donor and Br a the acceptor bromine. Halogen interactions of this type have recently been used in the perspective of crystal engineering 195,197 but the formation of such helical architecture by self organization of cali xarene molecules has yet only been reported in the case of the presence of substituents selected for their hydrogen bonding capabilities 198 and related tubular assemblies obtained through metal induced self assemly of sulfonato calixarene s. 75,82 It is should also be noted that few O alkylated cali xarenes 199,200 and resorcinarenes 201 derivatives have been reported to exhibit helical arrangements but in all cases the alkyl

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43 c hains pointed towards the axis of the helix. Figure 2.10. Representation of the helical motif sustained by compound 3 and detailed view of the hexamer of calixarenes forming the helix, alkyl chains are omitted for clarity In the case of alkyl chains con taining more than 6 carbon atoms functionalizing the lower rim, pseudo amphiphilic calixarenes adopt a different type of crystalline arrangement. In particular, compounds 4 and 5 engage in a pseudo bilayer motif, Figure 2.11. Their structures are sustained by head to head and edge to face p p stacking interactions, with distances in a range of 3.40 to 3.70 and tail to tail van der Waals interactions between the alkyl chains. The crystal packing of these compounds can be described as the superimposition o f three non equivalent layers parallel to [100], which pack on top of each other and spatially generate two distinct regions, aromatic and aliphatic, Figure 2.12. In two of the three layers, calixarene molecules adopt a similar herringbone pattern as that observed in compounds 1 and 2 Every two herringbone type layers possess opposite orientations. In the third layer, the pseudo amphiphilic molecules exhibit an ordered bilayer motif where the alkyl chains are interdigitated within the

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44 aliphatic region. Eve ry three layer repeats to result in a pseudo bilayer packing type, where the widths of the aromatic region are 7.63 and 8.00 and those of the aliphatic region are 8.86 and 9.43 for 4 and 5 respectively. Figure 2.11. Representation of the crystal pack ing of compounds 4 and 5 down [001], hydrogen atoms of the alkyl chains are omitted for clarity Figure 2.12. Representation of the non equivalent layers in compounds 4 and 5 and their superimposition down [100]

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45 In compounds 1 5 most alkyl chains were o bserved to possess partial structural disorder. Such patterns are common for the presence of conformationally flexible moieties. The weak diffraction intensities observed for the crystals of calixarenes 6 8, which possess longer alkyl substituents at the l ower rim, are most likely due to the higher disorder affecting these structures. Compound 9 crystallizes in P 2 1 / c and presents no disorder. In the calixarene molecule of the asymmetric unit, the brominated rings present dissimilar inclinations with respect to the vertical C 2 axis of the calixarene, Table 2.4. The significant difference between the proclivities of the two unparallel rings is due to the orientation and conformation of alkyl chains. In effect, one of the four alkyl chain presents a gauche con formation of the first carbon atoms linked to the phenolic oxygen with a torsion angle of 62.3 for O C 1 C 2 C 3 and results in the projection of the corresponding aliphatic chains toward the direction of the C 2 axis of the calixarene, this projection causes a decrease in the inclination ( 4.3) of the aryl unit bearing the alkyl chain, which presents the gauche conformation, while the adjacent aromatic ring exhibits a higher proclivity with respect to the axis of the calixarene. The alkyl chains are not para llel but present a slight curvature with respect to the C 2 axis of the macrocycle, Figure 2.13. Figure 2.14 shows the spatial arrangement of 9 which forms well ordered bilayers, in which the alkyl chains are tilted in one direction, down [010] of ca. 19.1 with regard to the axis perpendicular to the bilayer. This compares to the values of 45 found in the series of amphiphilic para acyl calixarene s 184 and the typical tilt angle of 28 for the aliphatic chains in phospholipids. 202

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46 In the crystal structure of 9 the alkyl chains are deeply interdigitated, Figure 2.14, the width of the aromatic layer is ca. 4.00 when the length of the alkyl chain is ca. 14.5 (such values are those of the distances perpendicular to the bilayer axis). The positions of the alkyl chains are very well defined due to the tight van der Waals interactions between the chains with shortest distances between the hydrogen atoms of alkyl chains of two calixarenes in a range of 2.32 2.50 The overall length of each alkyl chain in 9 is d(OC) = 15.1 (between the phenolic oxygen and the corresponding carbon of the terminal methyl) while the overall bilayer thickness is 18.5 The curvature of the chains leads to a flattened oblique struc ture down [010]. It should be noted that such a result is comparable to the crystal structure of the amphiphilic crown ether, N,N didodecyldiaza 18crown 6, reported in the work of Gokel, 203 where the C 12 chains presented similar interdig itation generating a very compact bilayer motif. The bilayer structure of compound 9 is also sustained by head to head interactions between calixarene molecules. These interactions are stabilized by bromine bromine interactions with d(Br d Br a ) = 3.90 a nd corresponding angles ?(C Br d Br a ) = 91.6 and ?(C Br a Br d ) = 139. These Type II halogen halogen contacts allow the interaction between calixarenes, which adopt a non parallel orientation of the flattened cones, across the interlayer plane. Finally non included mole cules of acetone solvent, which do not participate in the overall crystal packing, were found within the voids of the aromatic layer.

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47 Figure 2.13. Representation of the molecular structure of para Br tetra O dodecyl calix 4 arene in compound 9 Figure 2.14. Representation of the crystal packing of compound 9 down [001] (a) and [010] (b) In summary, general trends can be delineated from this study where increasing the length of the aliphatic part of a series of pseudo amphiphilic calix 4 arenes has resul ted in the evolution of their self assembly from herringbone type layers for 1 and 2 to a highly ordered bilayer system in 9 with intermediates that corresponded to a hybrid between the two motifs, observed in the pseudo bilayer systems sustained by the st ructures of compounds 4 and 5 These results have demonstrated that rational

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48 modification of the building units can afford the possibility of controlling the crystalline architecture and may be important towards the design of supramolecular materials based upon such pseudo amphiphilic molecules. Of particular interest, the helical assembly based upon hexameric units of calixarenes that resembles a macrocycle, generated in the structure of 3 constitutes a very novel and interesting structure, transition bet ween the bilayer 83 and the tubular 82 types of structures previously described as relevant motifs adopted by typical amphiphilic calix 4 arene molecules. 2.4.2. Influence upon the crystal packing through variation at the upp er rim The second part of this study consists in examining the systematic variation of upper rim functionalities in the particular case of calix 4 arenes substituted by O hexyl chains at the lower rim. The crystal structures resulting from selective functi onalization at the para positions with 2Br + 2H, 4H, 4 t Bu have to be associated with the structure of compound 3 in the perspective of evaluating the effect of such directing agents upon the self assembly of these molecules. Treating the molecular level of these systems, Figure 2.15 and Table 2.5 show that the four calixarene derivatives adopt the expected flattened cone conformation due to the O hexyl tetrasubstitution at the lower rim. However, the presence of large, polarizable, electronegative substitue nts at the upper rim additionally affects the usual C 2 symmetry as illustrated by compounds 3 and 10 possessing bromine substituents, which induce higher inclination of the two farthest opposite rims.

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49 Figure 2.15. Representation of the flattened cone con formation observed in O hexyl calix 4 arenes derivatives and designation of the distances and angles used to describe their geometry Table 2.5. Ring inclination angles and corresponding distances between opposite aryl groups in the crystal structures of co mpounds 3 and 10 12 In th e case of introduction of two bromine substituents at the opposite upper rims in compound 10 the presence of functionalities inducing electrostatic interactions results in a strongly organized bilayer arrangement of the calixarenes molecules governed by h alogen halogen interactions between dibrominated calixarenes in association with hydrophobic interactions between the alkyl chains, Figure 2.16. Interestingly, two phases of the structure of the dibrominated derivative were observed at 73C (LT), 10a and at 25C (RT), 10b They exhibit similar crystal packing sustained by head to head aromatic and Br Br interactions and tail to tail van der Waals Compound Angle 1 () Angle 2 () Angle 3 () Angle 4 () Distance 1 () Distance 2 () 3 61.6 52.7 14.7 5.47 10.1 4.32 10 54.6 53.7 7.85 2.85 9.90 4.82 11 48.5 41.6 2.01 0.62 9.44 5.35 12 48.7 43.3 4.84 0.53 9.53 5.24

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50 interactions with a slightly more ordered situation in the structure collected at room temperature. The head t o head interactions are stabilized by edge to face aromatic interactions with d(CAr) = 3.77 to 3.83 (LT) and 3.80 to 3.85 (RT) and by bromine bromine interactions, d(BrBr) = 3.89 (LT) to 4.11(RT) ?(C BrBr) = 77.2 and 151 (LT) and 80.2 and 149 (RT), Figure 2.17. These values diverge from the Type II situation classified by Desiraju and Parthasarathy and the distance between the two bromine atoms is slightly higher than the sum of van der Waals radii. The bromine bromine interactions between opposite rims in compound 10b are equivalent since they are related by inversion. The non parallel orientation of the calixarene molecules is essentially governed by edge to face p p stacking b etween adjacent calixarene molecules positioned at the same side of the bilayer with distances ranging from 3.76 to 3.81 In the bilayer structure of 10 the alkyl chains are not interdigitated, the widths of the aromatic layers are 6.90 (LT) and 7.86 (RT), the lengths of the alkyl layers are 13.1 (LT) and 11.2 (RT), these values are those of the distances perpendicular to the bilayer axis. Along the y axis, the dimensions between calixarenes expand by 0.36 from 25C to 73C. The expansions/con tractions in the dimensions of the crystalline assembly are reversible through several heating/cooling cycles. The two crystalline phases are not liquid crystals under the true definition of a liquid crystal since there is not enough disorder; however, the y correspond to a non standard type of matter that may be classified as a type of crystalline liquid crystal where the chains form a fluid domain and the calixarene rims the rigid part.

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51 Figure 2.16. Representation of the crystal packing of compound 10 do wn [001] (a) and down [010] (b), hydrogen atoms of the alkyl chains are omitted for clarity Figure 2.17. Detailed view of the Br Br interactions in compound 10a (a) and 10b (b)

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52 In the para H system, 11 Figure 2.18, the overall supramolecular arrangeme nt is sustained by face to face, d(CC) = 3.65 and edge to face, d(CC) = 3.93 to 3.99 aromatic stacking interactions between the upper rims of two opposite calixarene cones that are twisted of ca. 90 with each other and between the rings of adj acent molecules that are slightly slipped in the z direction of 4.64 This molecular organization results in the formation of a rippled bilayer system that is additionally stabilized by weak van der Waals interactions within the layers of non interdigita ted alkyl chains with distances between the hydrogen atom centers in a range of 2.55 to 3.45 In the rippled bilayer system of 11 the widths of the undulated aromatic and aliphatic layers are ca. 9.98 and ca. 11.1 respectively. Figure 2.18. Repres entation of the crystal packing of compound 11 down [010] (a), hydrogen atoms of the alkyl chains are omitted for clarity, and detailed view of the head to head aromatic stacking interactions (b)

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53 The presence of bulky groups such as tert butyl in compound 12 disrupts the common head to head/tail to tail spatial arrangement sustained by the model compound para H O hexyl calix 4 arene, 11 Figure 2.19 illustrates how the steric constraints induced by the additional bulky groups t Bu in association with the hyd rophobic interactions between the different alkyl groups result in a disordered layered packing motif where the aromatic stacking interactions are now impossible and substituted by weak van der Waals interactions between the methyl of the bulky groups and the alkyl chains with interatomic distances HH in a range of 2.28 to 2.71 Figure 2.19. Representation of the crystal packing of compound 12 down [010] (a) and [100] (b)

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54 The three dimensional arrangement of 12 can be described as the superimpositio n of two non equivalent layers that repeat along the x direction. In each layer the calixarenes adopt alternate arrangements based upon the herringbone motif due to steric hindrance and van der Waals repulsion between the bulky substituents tert butyl and a bilayer type assembly caused by the partial pseudo amphiphilic effect of the alkyl chains, Figure 2.19b. Such crystal packing constitutes a hybrid situation between the herringbone and bilayer types resulting from the presence of two opposing directing s ubstituents at the upper and lower rims of the calixarenes. The structures generated by the four pseudo amphiphilic calixarene derivatives 3 10, 11 and 12 are controlled by the synergy between intermolecular forces at the upper rim, the varying strength o f the van der Waals forces between the pendant alkyl chains and the steric constraints induced by these alkyl chains. When one of these factors dominates, simple packing motifs occur F or example with long chain substituents and only weak aromatic interact ions at the upper rim ( e.g. p H tetra substitution) a rippled bilayer system is favored. When there is a balance between the forces, more or less simple motifs predominate: steric effect of the t Bu groups and halogen halogen interactions between dibrominat ed calixarenes in association with the hydrophobic interactions between the alkyl chains afford a disrupted bilayer and a strongly organized bilayer, respectively. However in situations where there is imbalance between the controlling forces ( i.e bromine bromine interactions along with an increase of the molecular dipole moment) complex packing motifs are observed. In this particular case, the resulting helical packing motif of the corresponding tetrabromo substituted molecules

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55 is sustained by highly orien tated Br Br interactions between 6 calixarenes. 2.5. Conclusions Structural study of the 12 compounds presented herein has demonstrated that it is possible to control the formation of specific structural motifs, for instance the bilayer type crystal packin g, through the use of appropriately modified pseudo amphiphilic calix 4 arene with respect to the chain length at the lower rim and the functionality at the para positions. Such an understanding of the principles controlling the self assembly of calixarene s in the solid state might lead to the rational design of new classes of materials. Selective functionalization and exploitation of interactions in calixarene systems should develop and expand their applications in a variety of domains such as physics (op tics, electronics), material science (sensors, surfaces), catalysis or biomimetics. Of particular note, the auto organizing properties of compounds 9 and 10 resulting from the cooperative combination of oriented brominated head groups and the presence of alkyl chains of selective lengths capable of forming a tightly packed hydrophobic layer in 9 or a softer expandable aliphatic region in 10 may lead to broader perspectives towards the rational design of tunable supramolecular amphiphilic or pseudo amphiph ilic systems possessing the ability to self assemble at interfaces. Incorporation of a variety of functional groups selected for their intrinsic properties (polarity, magnetism, etc.) or variation of the size of the macrocycle (calix 6, calix 8 arenes) may allow this class of supramolecular materials to be widely applicable. One can also find potential advantages resulting from the logical progression observed in the crystalline organizations that are adjustable through a limited set of

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56 supramolecular param eters. Specifically, the transition between the helical motif of compound 3 and the pseudo bilayer or bilayer organizations of 4 and 10 resulting from little molecular variation of the building units represents a significant outcome that is particularly re levant to supramolecular and crystal engineering strategies. Expansion of this study to a wider range of conditions during crystallization or to the use of closely related calixarene derivatives may enable switching between such structural motifs and affor d supramolecular diversity in systems that could be comparable, to some extent, to the polymorphic phases of amphiphilic biomolecules.

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57 Chapter 3 Metal Organic Networks based upon organic ligands containing two types of functionality: Supramolecular i somerism and Functionalization 3.1. Introduction 3.1.1. Metal Organic Networks based upon pyridinecarboxylate ligands Supramolecular chemistry provides a successful approach to the self assembly of simple molecular building units preselected for their compleme ntary geometrical and binding capabilities. 23 In particular, the rational design of supramolecular architectures based upon metal coordination geometries and multifunctional organic ligands has led to a variety of coordination polymers with predictable net work architectures. 60,66,204 207 An important outcome of this approach is represented by the structural diversity in metal organic networks that can o ccur through the existence of phenomena such as interpenetration 122,123 or supramolecular isomerism 93,208 and it is thereby possible to generate a wide range of structures from even simple ligands and known chromophores. In such a context, m pyridinecarboxylates represent readily available ligands that have already been shown to be capable of generating coordination polymer networks that exhibit properties such as polarity, 209 212 poros ity 213 216 or magnetism. 217 221

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58 Typical m pyridinecarboxylate s are angular ligands resulting from deprotonatio n of pyridine 3 carboxylic acid ( nicotinic acid ) or pyridine 3,5 dicarboxylic ac id ( dinicotinic acid ) Figure 3.1, and contain concomitantly anionic carboxylate and neutral N donor functionalities. These ligands can be seen as hybrid molecules that possess the coordination capability of both functionalities. Specifically metal organic networks can be strategically constructed using such unsymmetrical difunctional ligands via a thorough understanding of the topological features of the numerous structures resulting from the use of linkers containing one type of coordination site, e.g. 4, 4 bipyridine 66,89 92,99 101,222 or benzene dicarboxylate, 95,206,223 237 with respect to chemical composition and propensity of the chromophore coordination geometry. However, considering the intrinsic asymmetry present in m py ridinecarboxylate ligands, there is a range of opportunities for the variation of the network connectivity pattern and therefore a higher degree of structural diversity is expected. Another outcome of the use of such ligands is the expectation that the res ulting infinite networks may provide novel materials possessing zeolitic or clay like features related to the 3D 213 215,238,239 or 2D 209,211,240 242 host guest compounds that can be generated from metal organic self assembly in presence of guest molecules in addition to the po tential properties such as chirality 209,243 due to the use of unsymmet rical ligands. Figure 3.1. Representation of the ligands nicotinic acid (a) and dinicotinic acid (b)

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59 3.1.2. Network topologies Prior reports have already shown that the use of a ligand possessing two different functional groups as simple as nicotinate has allowed the construction of non centrosymmetric structures with optical properties. 210 212,244 Most of these networks can easily be described as 2D clay like type networks, square or rhombus grids, or 3D zeolite type networks, diamondoid or pillared sh eets; however, certain results have shown that the introduction of a supplementary function generates more complex metal organic networks. 214 In this regard, consideration of the network topology represents a convenient tool for the compar ison of multi dimensional structures where the metal centers constitute the nodes of the network and the organic ligands their connecting links. A metal organic network can thus be defined by its circuit notation n p = n 1 .n 2 n p where n p represents the seri es of n gons meeting at each node, all node being equivalent. 245 For example, a 2D square grid is a 4.4.4.4 = 4 4 network since one node defines 4 circuits going through 4 adjacent nodes to join itself in a circuit; in a similar manner, a 3D diamondoid structure can be described as a 6 6 network. For more complex 3D nets, there may be more than one type of circuit starting out from one node, the corresponding circuit notation used is n p m q in which p n gons and q m gons meet at each node. For example, the topologies of well known lattices of inorganic materials such as NbO, 88 CdSO 4 246 or PtS 245 can be simplified by the representation of the connectivity of their nodes corresponding to the center of each element or ionic species. These three networks are all based upon 4 connected nodes and their circuit notations are 6 4 .8 2 6 5 .8 and 4 2 .8 4 respectively, Figure 3.2. It is interesting to note that the five network topologies presented

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60 herein possess the same stoichiometry 1 :2 of node with respect to the links that connect them. Figure 3.2. Network topologies of the 2D square grid, 4 4 (a), 3D diamondoid, 6 6 (b), NbO, 6 4 .8 2 (c), CdSO 4 6 5 .8 (d) and PtS 4 2 .8 4 (e) The knowledge of network topology of complex metal organic netw orks is relevant not only in the perspective of describing and comparing coordination polymers but also towards the prediction of structures and supramolecular isomers that can be generated from molecular building units thus reduced to their geometrical co unterparts. However, if the organic difunctional ligand is easily simplified, particular attention should be devoted to the coordination geometry that can be adopted by the node metal center, which constitutes the critical variable towards generation of sp ecific topologies.

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61 3.2. Zn and Cu Coordination Nodes : a Database Study Zn(II) c enters generally exhibit tetrahedral coordination 88 and, as revealed by Figure 3.3, can in appropriate circumstances serve as pseudo square planar nodes. Therefore, coordination of an angular bifunctional ligand, e.g. nicotinate, to a tetrahedral Zn(II) io n can result in a 4 4 (square grid) network, Figure 3.3c. Indeed, [Zn(nicotinate) 2 ], A exhibits such toplogy, 209,211 Figure 3.4. However, as seen above, there are other possible topologies that are based solely upon square planar nodes: the 3D networks NbO (6 4 .8 2 ) 88 and CdSO 4 (6 5 .8). 246 It sh ould also be noted that PtS exhibits (4 2 .8 4 ) 245 topology but it is sustained by both square planar and tetrahedral nodes in a 1:1 ratio. In this regard, a hydrogen bonded network 247 and a metal organic network 248 solely based upon a square planar geometry of the nodes with 4 2 .8 4 topology have been recently reported. Figure 3.3. A tetrahedral node projected down the 2 fold axis affording a pseudo square planar geometry (a), a projection of an angular spacer (b), a projection of a four connected circuit from tetrahedral nodes and angular spacers (c)

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62 Figure 3.4. Crystal structure of the square grid [Zn(nicotinate) 2 ] n A Clearly the specifics in terms of topological features and coordination propensity represent imp ortant elements towards the rationalization of the diversity of coordination network structures that can result from a given set of molecular components. Accordingly, a structural analysis of the geometrical preferences determined from a survey of the stru ctures reported in the literature that contain the metal centers considered in this study may reveal of interest towards developing an understanding of the factors affecting supramolecular control. The coordination of Zn(II) with two different functionali ties N donor and carboxylate has generated two types of 4 connected nodes, in which the carboxylate function can adopt monodentate or bidentate coordination to metal center, Figure 3.5. A survey of the CSD revealed that out of 45 non equivalent nodes conta ining the mononuclear Zn center coordinated to two nitrogen donor and two oxygen carboxylate, 14 exhibit the bidentate coordination mode of the carboxylate moieties and 31 the monodentate mode. In all coordination compounds, the Zn N distances range betwee n

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63 1.90 and 2.22 with an average of 2.06 (standard deviation s = 0.04). For the Zn O distances, Figure 3.6 illustrates the two types of coordination modes. The distances corresponding to the bidentate carboxylate moities range between 2.01 and 2.43 wi th an average of 2.19 ( s = 0.12); while the distances between Zn and bonded oxygen in the monodentate mode vary between 1.84 and 2.03 (average 1.96 s = 0.03). For the non bonded oxygen, in the monodentate coordination mode, values of d(Zn O) above 3 .5 have been proven to be outliers (with 90% confidence that those values can be rejected based on Q testing) so the corresponding distances Zn O effectively limit to the range 2.6 3.0 for 80% of confidence level, s = 0.125. It should be noted that onl y 17 structures are polymeric, most of them afford the diamondoid topology based upon tetrahedral nodes. 249 However the infinite networks generated from the connectivity of pseudo square planar nodes of Zn(II) present the typical cis coo rdination of the N donor and carboxylate function around the metal center, 209 Figure 3.4. Figure 3.5. Representation of the two coordination geometries resulting from coordination of tetrahedral mononuclear Zn(II) with the two different functionalities N donor and monodentate (a) or bidentate (b) carboxylate

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64 0 5 10 15 20 25 30 35 40 1.7-1.8 1.90-1.95 2.0-2.1 2.2-2.3 2.4.2.5 2.6-2.7 2.8-2.9 3.0-3.1 3.2-3.3 3.4-3.5 d(Zn-O)/ Hits Figure 3.6. Histogram showing the distribution of Zn O distances among the structures containing the mononuclear Zn in coordination with two functionalities N donor and carboxylate A similar study of Cu(II) chromophores shows that their coordination capabilities are more versatile since they can exhibit square planar, tetrahedral, square pyramidal or octahedral coordination, 88 Figure 3.7. The coordination of a mononuclear Cu(II) with two different functionalities N donor and carboxylate has hitherto generated 277 non equivalent chromophores: 99 chromophores contain a 4 coordinate metal center, 92 are 5 coordinate and 86 are 6 coordinate. In all coordination compounds, the Cu N distances range between 1.92 and 2.40 with an average of 2.03 (standard deviation s = 0.07). The distribution of Cu O distances is shown in Figure 3.8. The narrow region corresponding to distances inferior than 2.30 represents the coordination metal oxygen, while the broad repartition of d(Cu O) above 2.30 may be divided in two distinc t regions corresponding to different geometries adopted by the carboxylate group around the metal center. The shortest distances corresponding to the bonded oxygen of the carboxylate moieties in a tetrahedral geometry and these positioned in the equatorial plane of the transition metal range between 1.88 and 2.24 with an average of 1.97 ( s

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65 = 0.05). For the secondary oxygen, the separate study of 4 5 and 6 coordinate reveals interesting trends. In effect, the non coordinated oxygen atoms of 4 coordina te chromophore present a higher occurrence in the range 2.55 to 2.80 (average at 2.78 ), these of 5 coordinate Cu were in higher proportion between 3.00 and 3.30 (average at 3.06 ). The 6 coordinate tetrahedral or octahedral chromophores present both maxima. Careful analysis of the other parameters of the different structural types reveals that the difference does not only correspond to the difference in binding of the two oxygen of each carboxylate group, there is more monodentate character in the ca rboxylate of 5 and 6 coordinate chromophores and more bidentate character in the carboxylate of 4 coordinate and tetrahedral chromophores; the Cu O distances are also representative, to some extent, of the position of the oxygen with respect to the octahe dral or square pyramidal coordination sphere of the metal center so the statistic data illustrates as well the common axial elongation along the fourfold axis of the octahedron observed in Cu(II) +2 coordinated chromophores. 88 It should be noted that the relative orientation of the two types of ligands around the metal node is relati vely homogeneous between cis and trans configurations ( ca. 35% and 65% respectively). However, examination of the 49 infinite network structures provides significant insight concerning these tendencies. The coordination of polyfunctional ligands generally favorizes the trans configuration of square planar nodes as exemplified by the 2D square grid of [Cu(isonicotinate) 2 ] n represented in Figure 3.9 unless one type of coordinating group acts as chelating agent resulting in the alternative cis configuration.

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66 Figure 3.7. Representation of the chromophores of mononuclear Cu(II) containing the two functionalities N donor and carboxylate: 4 coordinate trans square planar (a), cis square planar (b), tetrahedral (c), 5 coordinate square pyramidal (d) and 6 coordin ate octahedral (e) 0 50 100 150 200 250 300 350 1.8 1.95 2.1 2.25 2.4 2.55 2.7 2.85 3 3.15 3.3 3.45 d(Cu-O)/ Hits Figure 3.8. Histogram showing the distribution of Cu O distances among the structures containing the chromophore mononuclear Cu in coordination with two functionalities N donor and carboxylate

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67 Figure 3.9. R epresentation of the trans configuration adopted by the Cu(II) chromophore (a) in the structure of [Cu(isonicotinate) 2 ] n (b) (unpublished results) 3.3. Experimental 3.3.1. Materials and Methods Each synthesis was conducted using materials as received from chemical sources ( Sigma Aldrich or Fischer Scientific ); solvent methanol was purified and dried according to standard methods. 250 IR spectra were recorded on a Nicolet Avatar 320 FT IR spectrometer. Thermogravimetric analysis was performed under nitrogen at a scan speed of 4C/min on a TA Instrument TGA 2950 Hi Res. XRPD data were rec orded on a Rigaku RU15 diffractometer at 30kV, 15mA for Cu Ka (? = 1.5418 ), with a scan speed of 2/min and a step size of 0.02 in 2? at room temperature. The crystals of all compounds were shown to be representative of the bulk by comparison of the XRPD patterns of the fresh samples with the corresponding patt erns calculated from the crystal structures. The simulated XRPD patterns were produced using Materials Studio program package (Accelrys, Inc., 2002) and Powder Cell for Windows Version 2.3 (programmed by W. Kraus and G. Nolze, BAM Berlin, 1999). FT IR spectra, TGA

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68 traces and XRPD patterns of all compounds are presented in appendices C1 C5. 3.3.2. Syntheses Synthesis of {[Zn(nicotinate) 2 ]CH 3 OHH 2 O} n 13 251 A methanolic solution of Zn(NO 3 )H 2 O (0.149 g, 0.500 mmol) was carefully layered onto a methanolic solution of nicotinic acid (0.123 g, 1.00 mmol), pyridine (0.079 g, 1.00 mmol) and toluene (3.00 ml, 28.0 mmol) under ambiant conditions. The solution was left undisturbed for 48h and colorless crystals of 13 (0.112 g, 0.303 mmol, 60.5 %) for med at the interlayer boundary in addition to a white precipitate (0.060 g, 0.193 mmol, 38.7 %) that was characterized by x ray powder diffraction to be the square grid {[Zn(nicotinate) 2 ]} n synthesized by W.B. Lin in 1998. 209 Synthesis of {[ Zn(nicotinate) 2 ]C 10 H 8 } n 14 251 Compound 14 was prepared in a similar manner as 13 with naphthalene, (640 mg, 5.00 mmol) instead of toluene dissolved in the solution of nicotinic acid and pyridine. After 1 month colorless crystals of 14 (0 .015 g, 0.034 mmol, 6.9 %) were collected from the mother liquor by physical separation. Synthesis of {[Zn(nicotinate) 2 ]C 6 H 5 NO 2 } n 15 251 Compound 15 was prepared in a similar manner as 13 with nitrobenzene, (3.00 ml, 29.0 mmol), instead of toluene dissolved in the solution of nicotinic acid and pyridine. After 9 months, colorless crystals of 15 (0.119 g, 0.214 mmol, 42.8 %) were collected from the mother liquor by physical separation.

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69 Synthesis of {[Cu(nicotinate) 2 (CH 3 OH) 2 } n 16 A solutio n of nicotinic acid (0.123 g, 1.00 mmol) dissolved in 10 ml methanol was layered onto a solution of Cu(NO 3 ) 2 .5H 2 O (0.116 g, 0.50 mmol) dissolved in 10 ml methanol. Dark blue crystals of 16 (0.128 g, 0.344 mmol, 68.8%) formed at the interlayer boundary af ter 1 day. Synthesis of {[Cu(dinicotinate) 2 CH 3 OHH 2 O} n 17 A methanolic solution of 3,5 pyridinedicarboxylic acid (dinicotinic acid) (0.167 mg, 1 mmol) was layered onto a solution of Cu(NO 3 ) 2 .5H 2 O (0.116 mg, 0.5 mmol) in 10 ml methanol. Light blue cry stals of 17 (0.160 g, 0.364 mmol, 72.8%) formed at the interlayer boundary after 1 day. 3.3.3. Guest sorption studies Crystals of 13 17 were observed to lose their single crystallinity in days to weeks when removed from the mother liquor. High resolution thermogr avimetric analysis on a fresh sample of 13 revealed a weight loss of ca. 16.5% between 100C and 250C, which is consistent with the removal of solvent molecules (calculated loss of 18% for 2 molecules of H 2 O and 1 molecule of MeOH). Compounds 14 and 15 we re observed to desorb or partially desorb their guest molecules in similar range of temperatures. FT IR and TGA analysis showed that the solvent molecules in the two compounds 16 and 17 were readily desorbed upon exposure to atmosphere. Thermogravimetric a nalysis of 16 revealed a weight loss of 8.6% between 60 and 120C, which is consistent with the removal of one coordinated methanol molecules (calculated loss of 8.6% for one solvent

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70 molecule). A TGA measurement effected on a sample of 16 let under ambient atmosphere for ca. one hour showed no weight loss in this range of temperature. The infra red spectra of 17 shows the absence of bands characteristic of solvent molecules. 3.3.4. X ray Crystallography In crystal structures of 13 17 all non hydrogen ato ms were refined with anisotropic displacement parameters except for the atoms of solvent in 13 and 17 The H atoms of the C H groups were fixed in calculated positions except for the carbon atom of methanol solvent in 13 and 17 The two molecules of solven t in the asymmetric unit of 13 were disordered, the water molecule was refined with fixed site occupation factors (s.o.f). values of 0.5 for each oxygen atom, the methanol molecule was 2 fold disordered and refined over two equally occupied positions of th e O atoms. In the asymmetric unit of 16 one methanol molecule was found to be coordinated to Cu ion, its OH hydrogen atom was located via difference Fourier map inspection and refined with riding coordinates and isotropic thermal parameters based upon the corresponding O atoms [ U (H) = 1.2 U eq (O)]. In 17 the carbon and oxygen atoms of the solvent methanol were disordered over several general positions and refined with fixed s.o.f. for occupancies of 0.5 for each carbon and 0.25 for each oxygen; the water m olecules in the asymmetric unit of 17 were disordered and refined with fixed s.o.f. values of 0.5 for each oxygen atom. Full crystallographic data can be found in the electronic supplementary data. Crystal data and structure refinement parameters of compou nds 13 17 are presented in Table 3.1.

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71 Table 3.1. Crystallographic data for compounds 13 17 Compound 13 14 15 16 17 Chemical formula C 13 H 16 N 2 O 7 Zn C 22 H 16 N 2 O 4 Zn C 24 H 18 N 4 O 8 Zn C 14 H 16 CuN 2 O 6 C 15 H 8 CuN 2 O 10 Formula weight 370.09 437.74 555.79 371.83 439.77 Temper ature, K 200(2) 200(2) 200(2) 200(2) 100(2) Crystal system Tetragonal Monoclinic Monoclinic Monoclinic Monoclinic Space group I 42d C2/c C2/c P2(1)/c P2(1)/c a, 21.351(3) 10.899(2) 11.922(3) 7.075(3) 12.3438(12) b, 21.351(3) 11.292(2) 9.990(2) 7.70 5(3) 10.5840(10) c, 6.9183(15) 15.358(3) 20.107(5) 14.248(6) 14.9068(14) a, deg 90 90 90 90 90 deg 90 100.47(3) 93.708(4) 99.714(8) 94.856(2) g deg 90 90 90 90 90 V, 3 3153.9(10) 1858.6(7) 2389.9(9) 765.5(6) 1940.5(3) Z 8 4 4 2 4 r calcd g.cm 3 1.559 1.564 1.545 1.613 1.505 mm 1 1.593 1.354 1.086 1.459 1.179 F(00 0) 1492 896 1136 382 884 Crystal size, mm 0.2x0.2x0.15 0.2x0.15x0.1 0.2x0.2x0.15 0.50x0.20x0.05 0.10x0.05x0.05 q range for data collection, deg 1.91 to 28.25 2.62 to 28.26 2.03 to 25.00 2.90 to 27.11 1.66 to 27.50 Limiting indices 8<=h<=27 25<=k<=12 8<=l<=8 13<=h<=5 15<=k<=14 9<=l<=20 14<=h<=11 11<=k<=8 23<=l<=23 9<=h<=8 8<=k<=9 16<=l<=18 15<=h<=16 13<=k<=13 16<=l<=19 Reflections collected 4472 2739 5878 4399 13095 Unique reflections 1767 1692 2099 1679 4377 R(int) 0.0442 0.0294 0.0552 0.0550 0.0800 Completeness to q 91.9 73.2 99.9 99.4 98.3 Absorption correction SADABS SADABS SADABS SADABS SADABS Max. and min. transmission 1.000 and 0.777 1.000 and 0.777 1.000 and 0.808 1.000 and 0.805 1.000 and 0.867 Data / restraints / parameters 1767 / 0 / 125 1692 / 0 / 132 2 099 / 0 / 168 1679 / 0 / 107 4377 / 0 / 259 Goodness of fit on F 2 1.152 0.883 1.035 1.019 1.022 Final R indices [I>2sigma(I)] R1 = 0.0449, wR2 = 0.1112 R1 = 0.0427, wR2 = 0.0838 R1 = 0.0463, wR2 = 0.0896 R1 = 0.0461, wR2 = 0.0998 R1 = 0.0589, wR2 = 0.156 6 R indices (all data) R1 = 0.0541, wR2 = 0.1134 R1 = 0.0574, wR2 = 0.0872 R1 = 0.0696, wR2 = 0.0977 R1 = 0.0700, wR2 = 0.1099 R1 = 0.0883, wR2 = 0.1799 Absolute structure parameter 0.10(3) N/A N/A N/A N/A Largest diff. peak and hole, e. 3 0.538 and 0 .329 0.551 and 0.349 0.371 and 0.280 0.414 and 0.335 0.945 and 0.978

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72 3.4. Results and Discussion 3.4.1. Supramolecular isomers of [Zn(nicotinate) 2 ] n Self assembly of Zn(NO 3 ) 2 with nicotinate under mild conditions has afforded several products includi ng a novel 3D network that has a connectivity based solely upon square planar nodes defined by the circuit symbol 4 2 .8 4 {[Zn(nicotinate) 2 ]MeOHH 2 O} n 13 and two new forms of the 2D network [Zn(nicotinate) 2 ] n 209 A presented above, {[Zn( nicotinate) 2 ]naphthalene} n 14 and {[Zn(nicotinate) 2 ] nitrobenzene} n 15, both of which exhibit the same 4 4 topology as A The crystal structure of 13 is illustrated in Figure 3.10a. The metal coordination is the same as that in the square grid [Zn(ni cotinate) 2 ] n A represented in Figure 3.4. However, when one examines the connectivity of the Zn centers, adjacent square planar nodes are twisted at an angle of ca. 25, resulting in a 3D network, Figure 3.10b, instead of a 2D square grid. The circuit symb ol of this network is 4 2 .8 4 PtS 245 is defined by the same circuit symbol; however, the two nets are fundamentally different and the projections down [100] are non superimposable, Figure 3.11. The nodes are eclipsed along the z axis with a vertical di stance between two Zn atoms of 6.92 and there are edge to face interactions between the pyridyl rings of nicotinate ligands with a shortest distance d(C C) = 3.8 13 possesses cavities of effective dimensions 4.35 X 4.35 that form infinite channels p arallel to the z axis, Figure 3.10, left. These channels contain columns of disordered solvent molecules. The density of 13 is 1.56 g.cm 3 (1.30 g.cm 3 without solvent).

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73 Figure 3.10. Crystal structure of the 3D network [Zn(nicotinate) 2 ] n guest molecule s are omitted for clarity (a). Schematic representations of the connectivity of the Zn centers for the network of 13 (b). Figure 3.11. Connectivity of 2 tetrahedral and 2 square planar nodes to form the 4 2 .8 4 network of PtS (a) and connectivity of 4 squa re planar nodes to form 13 (b) and projections of the two networks down [100]. In order to systematically determine the effect of templates on the formation of A or 13 the same reaction was conducted in the presence of several aromatic guests: benzene, ni trobenzene, naphthalene, chlorobenzene, o and p xylenes, p nitroaniline and anisole, as well as in the absence of template. Analysis of simulated and freshly collected XRPD patterns, presented in Figures 3.12 3.13, indicated that most reactions resulted i n the formation of A whereas nitrobenzene affords 13 or 15 and naphthalene affords 14

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74 Figure 3.12. X ray powder diffraction pattern calculated from the single crystal structures of A (a), 13 (b), 14 (c) and 15 (d)

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75 Figure 3.13. X ray powder diffractio n patterns of the products of the reaction Zn(NO 3 ) 2 + Nicotinate in different conditions: (a) first product of the reaction in PhNO 2 (b) MeOH only, (c) PhH, (c) PhCl, (d) o and p Ph(CH 3 ) 2 (e) p H 2 NPhNO 2 and (f) PhOCH 3 14 and 15 contain 2D square grid n etworks (4 4 ), Figure 3.14a. 14 crystallizes in the centrosymmetric space group C 2/ c the parallel infinite layers of square grids are eclipsed and the d(Zn Zn) separations are 7.68 resulting in the formation of parallel channels perpendicular to the pla nes of the square grids. Each cavity has effective dimensions of 4.45 X 4.45 and is filled by one molecule of naphthalene that interacts

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76 with the aromatic rings of the surrounding nicotinate ligands by face to face p p stacking with distances between th e centroids in a range of 3.4 to 3.7 The density of 14 is 1.56 g.cm 3 (1.10 g.cm 3 without guest). 15 contains a larger amount of guest (density without guest = 0.86 g.cm 1 ) and exhibits much larger interlayer separations than either A or 14 (d(Zn Zn) = 10.05 ), Figure 3.14. It should be noted in A adjacent grids are staggered whereas in 14 and 15 they are almost eclipsed. Figure 3.14. Crystal structure of the 2D square grid in 14 and 15 (a) and the vertical stacking between parallel infinite layers showing the intercalation of naphthalene (b) and nitrobenzene (c) molecules. Crystals 13 14 and 15 are sustained by the same node Only a subtle difference of the conditions during crystallization influences which phase is generated. A summary of the rela tionships between the structural supramolecular isomers is shown in Figure 3.15. The characterization of components, achieved by powder diffraction and thermogravimetric analysis, reveals that heating above 220 C results in conversion of 13 14 and 15 to A Figures 3.16 3.18 represent the comparison between simulated and freshly collected powder patterns of the three compounds presented herein, the expected

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77 structures that would result from their guest desorption without structural change and the correspond ing samples obtained after thermal treatment, the later presenting identical patterns as that of the 2D [Zn(nicotinate) 2 ] n shown in Figure 3.12a. A was formed via hydrothermal conditions and it should therefore be unsurprising that it appears to be the the rmodynamically favored product. Figure 3.15. The relationship between 13 15 and A. Reagents and conditions : (i) PhCH 3 or PhNO 2 in MeOH, diffusion; (ii) C 10 H 8 or PhNO 2 in MeOH, slow diffusion; (iii) MeOH or PhH or PhCl or o p Ph(CH 3 ) 2 or p H 2 NPhNO 2 or PhOCH 3 in MeOH, precipitation; (iv) and (v) 220 250C, 1 hour.

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78 Figure 3.16. X ray powder diffraction patterns of 13 (a) fresh sample, (b) sample heated to 250C and (c) calculated from the single crystal structure without guest.

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79 Figure 3.17. X ray powd er diffraction patterns of 14 (a) fresh sample, (b) sample heated to 220C and (c) calculated from the single crystal structure without guest

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80 Figure 3.18. X ray powder diffraction patterns of 15 (a) fresh sample, (b) sample heated to 250C and (c) calcul ated from the single crystal structure without guest.

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81 3.4.2. Additional Functionality: Structures of [Cu(nicotinate) 2 ] n and [Cu(dinicotinate) 2 ] n The reaction of Cu(NO 3 ) 2 .5H 2 O and nicotinate in methanol has afforded the novel 2D rhombus grid network 4 4 [Cu(nicot inate) 2 (MeOH) 2 ] n 16 The use of the organic ligand dinicotinate that contain an additional functional group carboxylic acid has led to the formation of a related 3D network, 17 extended version of the 2D 4 4 network by pillaring via coordination of the ne utral oxygen donor of the additional functionality. The crystal structure of compound 16 consists of a 2D rhombus grid network. Each Cu center is coordinated to two pyridyl groups and two monodentate carboxylate moieties of four nicotinate ligands in a tra ns configuration. The Cu center is further coordinated to the oxygen atoms of two methanol molecules in the axial positions of the octahedral coordination geometry, Figure 3.19a. The axial Cu O(methanol) distances of 2.65 are significantly longer than th e distances Cu O(nicotinate) and Cu N(nicotinate) of 1.97 and 2.00 respectively due to the axial elongation along the fourfold axis of the octahedral environment of Cu(II) chromophore. The non bonded oxygen atoms of the carboxylate groups are at a distan ce d(Cu O non bonded ) = 3.15 These values are consistent with the corresponding standards presented above for this chromophore. The rhombus shaped cavities deviate from regular square geometry by angles of 56.8 and 123. Along the x axis, the parallel r hombus grids are eclipsed and the d(Cu Cu) separations are 7.07 generating parallel channels perpendicular to the planes of the grids, Figure 3.19.

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82 Figure 3.19. Crystal structure of the 2D square grid in 16 (a) and vertical stacking between parallel infinite layers down [100] (b) and [001] (c) Each cavity has effective dimensions of 4.70 X 4.70 and is filled by two molecules of coordinated solvent methanol. The hydroxyl group of each coordinated methanol interacts via hydr ogen bonding with the non bonded oxygen atoms of the monodentate carboxylate of the nicotinate ligands (d(O HO = 2.67 ). The density of 16 is 1.61 g.cm 3 (1.33 g.cm 3 without coordinated solvent). Compound 17 crystallizes in the monoclinic space group P 2 1 / c The asymmetric unit of 17 contains one Cu center and two dinicotinate ligands. Figure 3.20 shows the Cu(II) chromophore in 17 The metal adopts a square pyramidal coordination geometry with two pyridyl groups (d(Cu N) = 2.00 ) and two monodentate c arboxylate moieties (d(Cu O bonded ) = 1.95 d(Cu O non bonded ) = 2.97 and 3.22 ) in a trans configuration in the equatorial positions and one of the oxygen of the additional carboxylic group of the

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83 dinicotinate ligand is coordinated onto the axial positi on (d(Cu O) = 2.35 ). The non deprotonated carboxylic group concomitantly interacts via hydrogen bonding between the hydroxyl proton and the carboxyl group of an adjacent square grid with d(O HO) = 2.53 Figure 3.20 illustrates the environment of the Cu(II) center in compound 17 The overall network of 17 can be described as 2D distorted square grids, represented in Figure 3.21, that are pillared by the additional carboxylic functions hence resulting in a 3D network that possesses a topology related t o the a polonium net, Figure 3.22. 17 possesses cavities of effective dimensions 3.67 X 3.67 that form infinite channels perpendicular to [101]. These channels contain columns of disordered solvent molecules. The density of 17 is 1.50 g.cm 3 (1.35 g.cm 3 without solvent). Figure 3.20. Representation of the chromophore mononuclear 5 connected in compound 17

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84 Figure 3.21. View of the 2D square grid network within the crystal structure of 17, guest molecules are omitted for clarity Compounds 16 and 17 co ntain 2D 4 4 networks. The presence of an additional functionality carboxylic acid in the ligand used to generate 17 does not disrupt the topology of the 2D net but only slightly affects the conformation of the grids from a rombus grid to a distorted squar e grid. The fact that the additional carboxylic is not deprotonated is not surprising considering the necessity of conservation of charge, effectively the Cu(II) chromophore considered in this study can only be coordinated to two carboxylate groups. As a s ideline, it is interesting to mention that a possible supramolecular isomer of compound 17 based upon 2D nets purely hydrogen bonded via the complementary carboxylic functions is possible although the synthesis conditions have ruled it out since the streng th of coordination bond and the efficiency of the overall crystal packing predictably favorize the formation of the 3D net 17 Finally these results exemplify the modular nature of supramolecular metal organic networks, which can be rationally functionaliz ed through variation of the building units without critical change upon the primitive network topology.

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85 Figure 3.22. Crystal structure of the 3D network [Cu(dinicotinate) 2 ], guest molecules are omitted for clarity (a). Schematic representations of the co nnectivity of the Cu centers for the network of 17 (b). 3.5. Conclusions In summary, the five compounds presented herein illustrate structural diversity and modularity of supramolecular metal organic networks. There are three salient features of 13 17 tha t deserve note. First, a novel 4 2 .8 4 network based upon a single 4 coordinated node has been generated and it can be rationalized on the basis of the connectivity and the geometry of the molecular building blocks. The ability of guests to intercalate in th e square grid form of [Zn(nicotinate) 2 ] is perhaps unsurprising 64,97 but to our knowledge such a wide range of separations has not yet been seen in laminated coordination polymers. This study

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86 further confirms how supramolecular isomerism can afford superstructural diversity from even the most simple chemical building blocks. Seco nd, the presence of an additional functionality that can hydrogen bond and even coordinate to the node metal center does not appear to prevent or even strongly influence the topology of the primitive 2D coordination network. Finally, these five new example s of rationalization of networks topology based upon geometry and connectivity of organic and inorganic building blocks suggest that topological approaches to the design of hybrid solids could represent an opportunity of broad relevance towards the constru ction of novel functional supramolecular materials.

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87 Chapter 4 Metal Organic Networks based upon conformationally labile organic ligands: Porosity and Flexibility 4.1. Introduction 4.1.1. Metal Organic Networks based upon dimetal cluster nodes Crystal engineering o f metal organic networks via self assembly of metal ions and multifunctional ligands has attracted considerable attention because of the structural diversity present in such compounds which in turn facilitates systematic evaluation of structure property re lationships. 93,94,144,145 In this context, bimetallic building units constitute an ubiquitous class of nodes in coordination chemistry, 95,206 in particular dimetal tetracarboxylate chromophores possess a well known geometry and coordination capabilities that make them ideal building blocks for the design via self assembly of metal organic coordination polyme rs. Figure 4.1 shows a representation of the chromophore resulting from the complexation of Cu(II) with carboxylate ligands and how it can serve, in appropriate circumstances, as square planar or octahedral node. Therefore, coordination of a bifunctional d icarboxylate ligand to Cu(II) can afford infinite metal organic networks with predictable topology. For example, self assembly of a square planar node with a linear linker has afforded the square grid Cu 2 (benzene 1,4

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88 dicarboxylate) 2 252 such a 2D network can also be pillared via the use of N,N donor ligands generating an octahedral network. 253,254 Figure 4.1 shows a schematic representation of metal organic square grids and octahedral networks generated from square planar and octahedral me tal nodes, they represent prototypical infinite networks and they inherently possess cavities that are suitable for interpenetration or enclathration of a range of organic guest molecules. 66,90 92,97 103,105,110 116,119,122,236,255 In a sense, they have structural features that compare to both clays and zeolites since they can be lamellar or porous. In this perspective, t he use of building blocks specifically chosen for their functionality has been shown to gene rate metal organic networks that exhibit properties such as luminescence, 256 porosity 114,119,236 or magnetism. 125 Figure 4.1. Top (a) and side (b) views of the dimetal tetracarboxylate chromophore and schematic representation of the 2D square grid (c) and 3D octahedral (d) networks that can be generated through use of approp riate linear linkers. 4.1.2. Conformational lability of the organic linker The rational design of supramolecular metal organic networks based upon preselected rigid building blocks has afforded an increasing number of novel compounds

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89 since the early 1990s. 60,66 In this respect, the use of flexible linkers or spacers has yet to be fully developed. In effect, according to a comparative CSD survey, the number of structures reported that contain transition metals in coordination with N or O donor ligands that possess only rigid aromatic groups represents ca. 10 times the number of corresponding metal organic compounds that contain at least two flexible methylene groups (16661 hits for the former search vs. 1756 hits for the latter). Rigid ligands have been shown to be capable of generating multiple supramolecular isomers for a given set of molecular components and a range of reaction conditions. 251 However, use of flexible ligands should in principle offer a greater degree of structural diversity and there has been interest in such ligands for magnetic 257 259 or porous 260 262 materials. While most interest in the literature of coordination polymers containing saturated fragments has focused on introduction of flexibility via alkyl substituents within other wise rigid ligands, 208,235,260,263 269 the use of long bifunctional alkyl chains has generated several coordination networks that present either interpenetration 270 or amphiphilic like behavior 271,272 due to the expected all anti conformation of the aliphatic parts. However there has been very little work designed to show how systemat ic variation of the elemental constituents or the crystallization conditions can direct such flexible ligands to adopt specific conformations. 208,266,269,273 In this regard, the generation of flexible architectures with variable shapes and sizes should represent great potenti al for useful developments in supramolecular chemistry, since the resulting structures may expand the concept of supramolecular isomerism to its conformational counterpart and provide a route to the generation of a novel class of nanostructures possessing atypical

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90 properties towards practical applications. The research presented herein intends to demonstrate how the utilization of bifunctional ligands possessing small aliphatic chains that are related to well known rigid linkers can provide the basis for a farther in depth understanding of the factors that control conformational flexibility/isomerism towards the generation of novel functional metal organic networks. The acquired knowledge will allow the strategic extension of this research to the development of highly tunable hybrid materials. The glutarate anion is a readily available bifunctional ligand which is effectively a flexible variant of benzene 1,3 dicarboxylate, a ligand which can sustain discrete 225,274 an d infinite 230,275 structures with nanoscale features. In a similar vein, the ligand adipate can be seen as a flexible variant of benzene 1,4 dicarboxylate, Figure 4.2. Figure 4.2. Representation of the glutarate (a), adip ate (b), benzene 1,3 dicarboxylate (c) and benzene 1,4 dicarboxylate anions (d). As revealed by Figure 4.3, glutarate anions possess a three carbon aliphatic backbone and there exist three likely conformations: anti anti anti gauche and gauche gauche

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91 F igure 4.3. The three possible conformations of glutarate alkyl chains and the corresponding projections down the Csp 3 Csp 3 bonds with the range of torsion angles observed in the structures deposited in the CSD. A survey of the Cambridge Structural Database revealed that the anti anti and anti gauche conformations tend to be favoured in coordination compounds. A conformational analysis of crystal structures containing the glutarate fragment and metals was conducted using the CSD and revealed that out of 31 n on equivalent glutarate ligands, 13 exhibit the anti anti mode, 13 the anti gauche mode and 5 the gauche gauche conformation, Table 4.1. It should be noted that the orientation of the carboxylate moieties with respect to the backbone is fairly variable alt hough the observed trends are in favor of the staggered conformation for the anti gauche mode versus the eclipsed conformation for the anti anti mode.

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92 Table 4.1. Conformational analysis of crystal structures containing the glutarate fragment and metals co nducted using the CSD. Torsion Angles () CSD Refcode C1 C4 C2 C5 O1 C3 O5 C3 Conformation MIYMOW 65 75 17.5 43.5 ZADJUJ 69 70 32 82.5 MEZSALa 69 69 4.5 4.5 XATNIPa 69.5 69.5 4 4 TODNAB 70 77 20 7 Gauche Gauche QANKOF 43 180 95 35 VIRYUQ 46 172 66.5 85.4 GLUECU 59 170 77.6 31.5 QIVHAE 62 165 6 77 MASXINa 62 180 23 70.5 ACBRUA 65 178 26.5 87.5 GLTECU 68 177 19.5 27 SIFWEJ 68 177 43.5 54 SUJXEA 68 178 21.5 48 HOTGOM 71 170 0.8 75 QIWKEM 71 179 8 49 TODNEF 74 172 6 .5 49.5 QANKIZ disordered 60 66 150 163 3 9 30 77 Gauche Anti OCENUF 166 179 51 34.5 MASXINb 169 174 17 21 XEDCUE 169 176 88 88 QIVGUX 172 172 7 7 TEGMIB 172 173 10 15.5 VIRZAX 173 173 34.5 95 CDGLTR 173 175 4.8 0.35 XODFUR 174 174 34 85 M IYMUC 175 176 0.5 32 FUMCUL 177 180 3.2 0.3 HOTHAZ 179 179 11 8 XATNIPb 179 179 10 10 MEZSALb 180 180 10 10 Anti Anti BOMXOQ structure unavailable Figure 4.4 shows the five conformations anti anti anti anti anti gauche anti gauche anti anti gauche ga uche and gauche anti gauche observed for the four methylene of the ligand adipate.

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93 Figure 4.4. The five observed conformations of adipate alkyl chains and the corresponding projections down the Csp 3 Csp 3 bonds with the range of torsion angles observed i n the structures deposited in the CSD. The corresponding survey of the CSD revealed that the anti anti anti and gauche anti gauche conformations are favoured in coordination compounds: out of 35 non equivalent adipate ligands, 12 exhibit the anti anti anti mode and 12 the gauche anti gauche conformation, Table 4.2. Such a study has also revealed the extreme scarcity of extended structures based upon dimetal tetracarboxylate chromophores, 276 which are of considerable interest to strategical ly prepare metal organic compounds by self assembly. 95,206,223 232 Our strategy towards the rational design of specific structures based upon the coordination between bimetallic building units and flexible spacers was inspired by the analogy between the fl exible bifunctional ligands glutarate and adipate and the rigid benzene 1,3 and 1,4 dicarboxylate anions. In this respect, it is possible to delineate important trends regarding the influence of the conformation adopted by the aliphatic chain of the dianio n associated with the geometry of the node upon the topology of the resulting networks.

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94 Table 4.2. Conformational analysis of crystal structures containing the adipate fragment and metals conducted using the CSD. Torsion Angles () CSD RefCode C1 C4 C2 C5 C3 C6 O1 C3 O6 C4 Conformation NIPHAV 60 65 175 58 12 Gauche Gauche Anti ECIVUH 60 180 60 55 57.5 WIPQER 63 180 63 41 41 TODNIJ 69 180 69 45 45 ZEMZUM 80 180 80 10 10 MITHUSa 68 179 69 38 50 MIYNAJa 56 180 56 60 61 MIYNAJ b 59 173 59 84 82 MIYNENa 59 180 59 57 59 MIYNENb 55 175 55 79 79 MIYNIRa 57 180 57 58 61 MIYNIRb 55 176 55 75 75 IBODOS 85 180 75 66 39 Gauche Anti Gauche OCENOZ 47 151 169 38 5 ADIECU 60 170 170 55 3.5 FOQLOM 60 180 180 64 7 NOVHAH 60 180 180 90 20 JOSNAGa 62 175 180 55 47 POSBAA 65 180 170 62 3 MITHUSb 68 176 170 32 25 IGIDOR 69 176 178 50 14 WOSDAJ 70 180 180 25 5 Gauche Anti Anti MITHUSc 179 75 180 86 80 Anti Gauche Anti LOTDON 170 180 180 8.5 80 QOPLAI 175 180 175 20 20 HU TYOK 177 180 177 17 17 ADIQNI 180 180 180 55 55 JOSNAGb 180 180 180 67.5 67.5 QOPLEM 180 180 180 20 20 QOPLIQ 180 180 180 1.5 4 TUDHOP 180 180 180 1.5 5.5 WAVCAX 180 180 180 7.5 90 WEGJUN 180 180 180 5 5 WIPQAN 180 180 180 55 55 WOSDEN 18 0 180 180 60 60 Anti Anti Anti Considering the case of a dimetal tetracarboxylate chromophore as 4 connected node, complexation with the flexible link glutarate, in a given conformation anti anti is

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95 expected to generate similar topologies as those obtained with benze ne 1,3 dicarboxylate. 225,230 232 When the glutarate anion adopts the anti gauche mode, it can be schematically seen as a curved spacer and, afford 4 possible geometries around the bimetallic unit, Figure 4.5: all glutarate ligands in trans with each other, adopting a C 2 symmetry with respect to the metal metal axis, are expected to generate a 1D, double chain, topology; all glutarate ligands in syn with each other, adopting a C 4 symmetry with respect to the metal metal axis, are expected to generate a 2D, distorted square grid, topology; an alternate coordination modes around the dimetal cluster in syn s yn trans trans or syn trans syn trans should lead to geometrical constraints and force the dicopper tetraglutarate to extend its topology to a more complex 3D network. Figure 4.5. The three possible conformations of glutarate alkyl chains and the pos sible geometries of the glutarate anti gauche anions around a bimetallic building unit leading to distinct 1D and 2D topologies. In the case of glutarate anion adopting the gauche gauche mode, coordination with a transition metal node may undergo high geom etrical constraints and result in

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96 unpredictable structures based upon atypical coordination as exemplified by the 2D polynuclear structure of silver(I)glutarate. 277 On the other hand the conformational constraints of the carbon back bone may be overcome by the variation of the torsion angle of the carboxylate groups with respect to the corresponding methylene groups and generate a curved linker that would afford similar topologies as those expected from the anti gauche mode. The adip ate anion possesses a supplementary degree of freedom in addition to a wide range of possible conformations of the carboxylate functions with respect with the carbon backbone. The resulting metal organic networks may reveal difficult to specifically predic t; however, Figure 4.4 has shown that adipate may simply be seen either as a linear or as a curved ligand, and would therefore generate the corresponding topologies (2D square grid or distorted grid and 1D double chain) in appropriate circumstances. In th is context the coordination of glutarate and adipate anions with bimetallic building units has been systematically evaluated by variation of the neutral axial ligand and the reaction conditions. We have thus prepared a series of coordination polymers based upon these flexible ligands and have observed that the generation of dicopper tetraglutarate and tetraadipate chromophores has lead to the preferential conformations anti gauche and anti gauche gauche with the topologies of the products obtained being in fluenced by the coordination geometry. Since this work has been instigated with an eye towards the generation of supramolecular porous materials, it is important to address some of the significant developments concerning this area.

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97 4.2. Porous metal organi c networks 4.2.1. Context Since the discovery by Hofmann in 1897 of the first cyanide inclusion compound Ni(CN) 2 NH 3 C 6 H 6 36 which was only st ructurally characterized about fifty years later 38,39 ; a large number of sup ramolecular metal organic networks suitable for enclathration of a range of organic guest molecules has been subsequently generated and investigated in terms of network topology and host guest interactions. In this context, metal organic networks structure s exemplify predictability since their network structures can be controlled by the preselection of an appropriate node (metal coordination geometry) and spacer (organic ligand). 88,122,278,279 However their intrinsic properties such as thermal stab ility or porosity have been, to some extent, overlooked. 143 Recent inte nsive research in the field of metal organic networks has resulted in an increasing number of novel porous compounds that possess characteristics unattainable in zeolite chemistry. 95,96,114,125,144,145,236,237,275,280 284 In order to delineate a strategy towards predicting the self organization of molecular building units into 1D, 2D or 3D networks that would possess a sufficient degree of ro bustness to sustain guest free cavity, an in depth study of the relationship between the specifics of such structures, strength and dimensionality of the network connections or potential for interpenetration, and their thermal and dynamic properties is of profound importance. Generally, most stable networks upon guest removal are 3D coordination networks, but 2D, 1D and even 0D topologies have also been reported to enable non covalent interactions via hydrogen bonds, aromatic stacking or van der Waals

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98 force s and generate relatively thermally stable porous networks. 64,285 288 The investigation of the stability of porous materials upon guest removal requires the use of experimental techniques that will provide structural information in addition to visual examination, gravimetric and thermal data of the apohost formed after d esorption of the guest molecules. In this context, X ray powder and single crystal diffraction represent the most appropriate tools for such studies. In effect, the diffraction pattern is representative of the crystalline structure of a given metal organic network and can serve to identify the substance and hence to determine the structural integrity of the network after desorption and/or readsorption of its guest molecules. In this regard, the broadening of diffraction pattern constitutes a common feature observed upon guest removal due to the degradation of the long range order that usually corresponds to the presence of crystalline imperfections within the apohost structure. In such cases, the network may be retained and, when reimmersed in a solution or in contact with a gas containing guest molecules, the initial pattern is restored, although the qualification of the material as porous may be inadequate since the possibility of recrystallization remains. The guest molecules can, in some instances, be dir ectly exchanged without prior removal of the original guest species, but without information concerning the retention of structural features that indicate the conservation of the apohost topology; the corresponding supramolecular networks cannot yet be des ignated as porous materials. Finally, there have been recent examples of flexible structures based upon hydrogen bonds or containing conformationally labile components that undergo reversible structural change upon their transition from host guest to apoho st. 260,289 Their single or micro crystallinity was maintained dem onstrating

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99 their propriety of adjustability in response to external change. This so called sponge like behavior within the solid state may be a valuable feature for a new class of flexible porous materials. Figure 4.6 shows a significant example of such porous 2D metal organic bilayer. Figure 4.6. Sponge like behavior of the metal organic bilayer structure Ni 2 L 3 (BTC) 4 260 upon desolvatation and variation of the corresponding torsion angles of the flexible parts. 4.2.2. Classification of p orous supramolecular metal organic networks Considering the numerous examples of porous supramolecular metal organic networks that have been reported to date and the diversity in terms concerning the description of their sorption properties, their classifi cation according to the stability and dynamic of these materials with respect to their response to guest desorption resulting in different types of micro or nano porosity properties is valuable. 284 In effect, it is important to distinguish non porous structures that collapse upon guest removal from porous ones, which sustain empty cavities. However, it became evident from significant recent examples that such an organization can also be refined in order to take into account the fundamental changes that are associated with the host guest/apohost transition. Along with the latest technological advances that render possible the determination of larger and more complex structures, it is now possible to obtain a precise knowledge of the structura l evolution of porous networks. For example, the

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100 structural elucidation of apohost networks via single crystal or powder diffraction has evidenced the variation of structural parameters resulting from guest desorption. In this context, a classification of porous supramolecular metal organic networks that retain single crystallinity upon guest removal can reveal distinct features that are associated with the structures according to the preservation of chemical or structural integrity during the desorption pr ocess, Table 4.3. In a broader perspective, it should be noted that usual techniques utilized to characterize the porosity of metal organic networks reported in the literature are sufficient. Nevertheless, in specific cases such as these presented in Table 4.3, when the structures present some degree of flexibility that generates more or less critical changes in the apohost network, an extensive study of these structural or chemical modifications may be of interest for potential applications (e.g. size/shap e/function selectivity of the empty cavities for adsorbents or sensing devices, presence of active sites on uncoordinated metal centers for catalysis). As a sideline, the retention of single crystallinity after physical or chemical alteration of such poro us compounds may be important for certain type of device applications.

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101 Table 4.3. Classification of porous supramolecular metal organic networks according to their behavior upon guest desorption/readsorption L 1 = 4,4 bis(4 pyridyl)biphenyl, L 2 = 2,4 (1,4 phenylene)bispyridine, L 3 = 1,1,1 trifluoro 5,5 dimethyl 5 methoxyacetylacetone, L 4 = bis(3 aminopropyl)methylamine, L 5 = C 26 H 52 N 10 bismacrocycle, L 6 = 2,4,6 tris(4 pyridil)triazine, Dim Network Formula Guest Description of change s associated with host guest/apohost transition Ref. 1D Ladder Ni 2 (4,4' bipy) 3 (NO 3 ) 4 MeOH Lattice parameter b reduced by 0.53(9)% upon desorption (120C) Reversibility Function selective readsorption 290 2D Bil ayer Ni 2 (4,4' bipy) 3 (NO 3 ) 4 EtOH Less than 2.3% changes in cell dimensions upon desorption (100C) Reversibility 291 3D Spiral net Cu(Isonicotinate) 2 H 2 O Less than 0.2 % changes in cell dimensions upon desorption (140C) Reversibility Expension (up to 8% vol) upon readsorption of propanol Size selective readsorption 238 3D Distorted diamondoid net Co 2 (H 2 O)(Nicotinate) 4 EtOH+ H 2 O Less than 0.2% changes in cell dimensions upon desorption (vacuum) Reversibility No selectivity observed for readsorption capability 215 3D Cubic net Zn 4 O(1,4 BDC) 3 DMF+ PhCl Less than 0.9% changes in cell dimensions upon desorption (300C) Reversibility 292 3D Octahedral net Cu(4,4' bipy) 2 (SiF 6 ) H 2 O Identical cell parameters of partially desolvated crystals Reversibility 113,119 2D Square grid NiL 1 2 (NO 3 ) 2 o xylene Less than 0.5% changes in cell dimensions upon desorption (150C under vacuum) No study on reversibility 103 3D Pillared rhombus grids Cu(Isonicotinate) 2 EtOH Partial desorption at room temperature (sof 0.53 for EtOH molecules) No study on reversibility 218 No Structral Change 3D Helical arra y Cd 2 L 2 2 (NO 3 ) 4 Free L 2 Less than 3.0% changes in cell dimensions upon desorption (reflux in toluene solubilizing free L 2 ) No study on reversibility 293 0D Packing forming hexagonal channels [CuL 3 2 ]*2/3(CH 2 Cl 2 ) H 2 O S pace group changes from Cmc 2 1 to R 3 upon desorption (vacuum) Reversibility 294 0D Packing via H bonds forming channels [Co(H 2 O) 6 ]H 2 (TC TTF) H 2 O Space group changes from P 1 to P 112/ m upon desorption Reversibility Size/Function s elective readsorption 289 1D 3D assembly of chains via H bonds Cu 2 L 4 2 Ni(CN) 4 (ClO4) 2 H 2 O Space group changes from P 2 1 / m to P 2 1 / c upon desorption (100C) Reversibility Size/Function selective readsorption 295 2D Bilayer Ni 2 L 5 3 (BTC) 4 Pyr+ H 2 O Space group changes from P 1 to P 1 upon desorption (75C) Reversibility 260 2D Rhombus grid 2 fold inter penetration Fe 2 (4,4 azpy) 4 (NCS) 4 EtOH Space group changes from C 2/ c to Ibam upon desorption (102C) Reversibility Spin crossover switched upon transition 125 3D (10,3) b net 2 fold interpenetration (ZnI 2 ) 3 L 6 2 PhNO 2 Space group cha nges from C 2/ c to P 1 upon desorption (170C) Reversibility 296 Sructural Change 0D Assembly of complexes in chains ( tBu Salcam)MnCl CH 2 Cl 2 Lattice parameter b reduced from 49 to 15 upon desorption (with drastic conformational changes) No study on reve rsibility 297 Chemical Change 3D PtS net (decorated) Cu 2 (ATC) H 2 O Space group changes from C 2 /c to P 4 2 / mmc upon removal of coord. and uncoord. water Reversibility Increased antiferromagnetic coupling upon desorption 298

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102 4.2.3. Properties a nd applications Although porous metal organic networks do not compare to zeolite materials in terms of robustness or thermal stability, their inherent modularity allows specific functionalization to provide desirable properties. In effect, the presence of metal centers affords the potential for a variety of redox, acid base or magnetic properties; the use of asymmetric organic ligands can generate chirality or non linear optical properties within the resulting supramolecular networks. The overall topology m ay be fine tuned in terms of size and shape of the cavities and create specific host guest interactions. As a result, these materials present various potential applications as adsorbents, 299 sensors, 300 catalysts 66 or in separation 301 and ion exchange. 113 Among the porous coordination com pounds mentioned above, few examples are known of structures that contain a flexible component, comparatively to their rigid counter parts, because such a lack of rigidity leads to a higher degree of difficulty in terms of designing such materials. However the rational utilization of non rigid building units based upon the strategic principles presented above can provide a range of supramolecular metal organic networks and extend their potential applications to the development of highly tunable hybrid mate rials that will possess properties related to the characteristics of their molecular components such as the possible ability of adaptation of such materials to their surrounding chemical environment.

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103 4.3. Experimental 4.3.1. Materials and Methods General methods, instruments and software suites have been described in Chapter 3, Section 3.3.1. FT IR spectra of all compounds are presented in appendices C6 C11. The crystals of all compounds were shown to be representative of the bulk by comparison of the x ray powder diffraction pattern of fresh samples with the corresponding pattern calculated from the crystal structures. All XRPD patterns can be found in appendices C6 C11. Thermogravimetric analysis was performed in air for readsorption monitoring on TA Instruments TGA 2950 Hi Res. For guest readsorption experiments, the solvents used were HPLC grade (H 2 O = 0.009%) and the concentration changes were measured on a Shimadzu GC 17A gas chromatograph with flame ionization detector (GC FID) using toluene as the internal s tandard. The data were fitted to the equation previously published by K. S. Min and M. P. Suh. 301 4.3.2. Syntheses Synthesis of { [Cu 2 (glutarate) 2 (dimethylformamide) 2 ] } n 18 A solutio n of Cu(NO 3 ) 2 .5H 2 O (0.233 g, 1.00 mmol), glutaric acid (0.264 g, 2.00 mmol) and dimethylformamide (4.72 g, 64.6 mmol) dissolved in 15 ml methanol was stirred briefly before heating to ca. 80 C for 2 hours. The clear blue solution was left undisturbed at room temperature. Green blue crystals of 18 ( 0.230 g, 0.431 mmol, 86.2%), suitable for X ray studies, appeared after 2 weeks.

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104 Synthesis of { [Cu 2 (adipate) 2 (pyridine) 2 ] } n 19 According to an an alogous method as the synthesis of 18, the reaction of Cu(NO 3 ) 2 .5H 2 O (0.233 g, 1.00 mmol), adipic acid (0.292 g, 2.00 mmol), pyridine (0.316 g, 3.99 mmol) in 20 ml methanol gave green crystals of 19 (0.138 g, 0.241 mmol, 48.2%) after 48h. Synthesis of { [ Cu 2 (glutarate) 2 (pyridine) 2 ] } n 20 In a solution of Cu(NO 3 ) 2 .5H 2 O (0.233 g, 1.00 mmol), glutaric acid (0.264 g, 2.00 mmol) and pyridine (0.158 g, 2.00 mmol) dissolved in 30 ml methanol, green crystals of 20 ( 0.268 g, 0.491 mmol, 98.2%), suitable for X ray studies, appeared after 24h. Synthesis of {[Cu 2 (glutarate) 2 (4,4 bipyridine)]H 2 O]} n 21 302 Compound 21 forms via reaction of Cu(NO 3 ) 2 .5H 2 O (1.165 g, 5.009 mmol), glutaric acid (1.982 g, 15.00 mmol) and 4,4 bipyridine, bipy, (0.390 g, 2.50 mmol) in water. The initial product formed, as characterized by x ray powder diffraction of the light blue powder obtained during the synthesis of 21 was found to be isostructural with ML 1.5 ladder 269 compound. The initial product w as converted to green crystals of 21 by heating the reaction mixtures at ca. 80C for several hours. Yield of 1.392g (2.353 mmol, 93.95%) was obtained; excess glutaric acid was recycled by filtration of the supernatant solution and recrystallization. Synth esis of { [Cu 2 (glutarate) 2 (1,2 bis(4 pyridyl)ethane)]H 2 O] } n 22 302 Green crystals of 22 were obtained in a similar manner as those of compound 21

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105 with 1,2 bis(4 pyridyl)ethane, bipyethane, (0.460 g, 2.52 mmol) instead of bipy with a yiel d of 1.615g (2.479 mmol, 98.98%). The initial product formed, as characterized by single crystal unit cell determination of the dark blue crystals obtained during the synthesis of 22 (Monoclinic, C2/c a = 25.21, b = 9.19, c = 19.75 = 94.98 deg, volume = 4548 3 ) and x ray powder diffraction, was found to be isostructural with ML 1.5 bilayer 208 compound. Synthesi s of { [Cu 2 (adipate) 2 (1,2 bis(4 pyridyl)ethane)]H 2 OCH 3 OH] } n 23 A solution of adipic acid ( 0.146 g, 1.00 mmol), NaOH (0.0800 g, 2.00 mmol), bipyethane (0.0921 g, 0.500 mmol) in 25 ml methanol was carefully layered onto a solution of Cu(NO 3 ) 2 .5H 2 O (0.2 33 g, 1.00 mmol) in 10 ml water. An initial product formed, as a blue powder, was characterized by x ray powder diffraction to be isostructural with ML 1.5 bilayer 208 compound and was converted to green crystals of 23 after one week. Yield of 0.180 g (0.260 mmol, 51.9%) was obtained. 4.3.3. Guest sorption studies Crystals of 18 23 were observed to retain their single crystallinity when r emoved from the mother liquor. Thermogravimetric analysis of 21a revealed that it is stable up to 300C with loss of ca. 8.5% mass between 60 and 120C, consistent with desorption of water molecules (calculated 9%). Interestingly, when heated at 150C for 3 days, crystals of 21a were observed to remain crystalline and the crystal structure of the apohost, 21b confirmed that removal of guest molecules does not influence the 3D network. IR, thermal analysis and GC experiments were used to confirm that 21b ca n readsorb water

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106 molecules under various conditions to generate 21c The 3 compounds 21a 21b and 21c have been characterized by X ray single crystallography. 22a was observed to desorb its guest water molecules following exposure to the atmosphere for ca. 1 hour. The resulting apohost 22b retained single crystallinity and was observed to adsorb water molecules via immersion in water. The resulting crystals, 22c, were confirmed to be isostructural to 22a 4.3.4. X ray Crystallography In the crystal structures of 18 23 all non hydrogen atoms were refined with anisotropic displacement parameters except for the oxygen atoms of solvent in 22c The H atoms of the C H groups were fixed in calculated positions except for the carbon atom of methanol solvent in 23 The 2 molecules of solvents water and methanol in 23 were observed to exhibit high thermal motion. The two molecules of water in the asymmetric unit of 21a lie at general and special positions, thereby affording the reported 1:3 stoichiometry. The water molecule s of 21c were disordered over several positions and were refined with fixed site occupation factors (s.o.f.). In 22 the oxygen atoms of the solvent were disordered over several general positions (8 for 22a 5 for 22b and 9 for 22c ) and refined with fixed s.o.f. for total of occupancies of 2.5, 1 and 2.5 respectively. These correspond to 1:5, 1:2 and 1:5 stoichiometries since the tetracarboxylate moities lie around special positions. Full crystallographic data can be found in the electronic supplementary da ta. Crystal data and structure refinement parameters of compound 18 23 are presented in Table 4.4.

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107 Table 4.4. Crystallographic data for compounds 18 23 Compound 18 19 20 21a 21b 21c Chemical formula C 16 H 26 Cu 2 N 2 O 10 C 22 H 26 Cu 2 N 2 O 8 C 20 H 22 Cu 2 N 2 O 8 C 20 H 26 Cu 2 N 2 O 11 C 20 H 20 Cu 2 N 2 O 8 C 20 H 20 Cu 2 N 2 O 11 Formula weight 533.47 573.53 545.48 597.51 543.46 591.46 Temperature, K 293(2) 293(2) 100(2) 100(2) 100(2) 100(2) Crystal system Monoclinic Triclinic Orthorhombic Monoclinic Monoclinic Monoclinic Space group P2(1)/c P 1 Pbca C2/c C2/c C2/c a, 9.0201(12) 8.1820(19) 13.1322(12) 21.191(2) 21.011(2) 21.351(2) b, 7.8902(10) 8.6312(19) 8.4963(8) 13.1900(13) 13.0520(14) 13.1381(13) c, 14.9020(19) 9.245(2) 18.8964(18) 8.5212(9) 8.5284(9) 8.5699(9) a, deg 90 107.860(4) 90 90 90 90 deg 106.012(2) 106.494(4) 90 100.314(2) 100.679(2) 101.007(2) g deg 90 100.433(4) 90 90 90 90 V, 3 1019.4(2) 569.5(2) 2108.4(3) 2343.3(4) 2298.3(4) 2359.8(4) Z 2 1 4 4 4 4 r calcd g.cm 3 1.738 1.672 1.718 1.694 1. 571 1.665 mm 1 2.143 1.919 2.069 1.878 1.897 1.864 F(000) 548 294 1112 1224 1104 1200 Crystal size, mm 0.08x 0.07x0.02 0.02x0.02x0.02 0.07x0.05x0.02 0.08x0.08x0.08 0.08x0.08x0.08 0.08x0.08x0.08 q range for data collection, deg 2.35 to 25.02 2.48 to 25.03 2.16 to 28.32 1.83 to 27.48 1.85 to 27.14 1.83 to 27.12 Limiting indices 10<=h<=10 9<=k<=8 17<=l<=14 9<=h<=5 10<=k<=10 10<=l<=10 15<=h<=17 11<=k<=11 24<=l<=19 19<=h<=27 17<=k<=14 11<=l<=10 26<=h<=21 15<=k<=16 10<=l<=10 27<=h<=27 9<= k<=16 10<=l<=10 Reflections collected 5225 3027 12708 7149 7048 6920 Unique reflections 1798 1987 2549 2670 2532 2582 R(int) 0.0492 0.0649 0.0623 0.0322 0.0387 0.0304 Completeness to q % 99.9 98.4 97.0 99.4 99.6 99.3 Absorption correction SADABS SADABS SADABS SADABS SADABS SADABS Max. and min. transmission 1.000 and 0.820 1.000 and 0.777 1.000 and 0.848 1.000 and 0.843 1.000 and 0.861 1.000 and 0.806 Data / restraints / parameters 1798 / 0 / 138 1987 / 0 / 154 2549 / 0 / 145 2670 / 4 / 159 2532 / 0 / 147 2582 / 0 / 182 Goodness of fit on F 2 1.055 1.023 1.063 1.046 1.038 1.094 Final R indices [I>2sigma(I)] R1 = 0.0349, wR2 = 0.0866 R1 = 0.0642, wR2 = 0.1220 R1 = 0.0452, wR2 = 0.088 5 R1 = 0.0376, wR2 = 0.0921 R1 = 0.0342, wR2 = 0.0859 R1 = 0.0380, wR2 = 0.1071 R indices (all data) R1 = 0.0397, wR2 = 0.0892 R1 = 0.0941, wR2 = 0.1357 R1 = 0.0632, wR2 = 0.0956 R1 = 0.0452, wR2 = 0.0963 R1 = 0.0431, wR2 = 0.0904 R1 = 0.0465, wR2 = 0.111 2 Largest diff. peak and hole, e. 3 0.420 and 0.345 0.826 and 0.631 0.471 and 0.510 0.946 and 0.575 0.533 and 0.416 0.628 and 0.328

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108 Table 4.4. (continued) Compound 22a 22b 22c 23 Chemical formula C 22 H 24 Cu 2 N 2 O 13 C 22 H 24 Cu 2 N 2 O 10 C 22 H 24 Cu 2 N 2 O 13 C 26 H 28 Cu 2 N 2 O 12 Formula weight 651.51 603.51 651.51 687.58 Temperature, K 100(2) 100(2) 100(2) 100(2) Crystal system Monoclinic Monoclinic Monoclinic Monoclinic Space group C2/c C2/c C2/c C2/c a, 24.238(2) 24.047(8) 23.911(3) 24.808(6) b, 13.0527(13) 11.784(4) 11.8685(15) 12.827(3) c, 8.6313(8) 9.059(3) 9.2063(12) 9.031(2) a, deg 90 90 90 90 deg 91.473(2) 91.044(6) 90.350(2) 93.368(5) g deg 90 90 90 90 V, 3 2729.8(5) 2566.4(14) 2612.5(6) 2868.7(12) Z 4 4 4 4 r calcd g.cm 3 1.585 1.562 1.6 56 1.592 mm 1 1.625 1.713 1.698 1.549 F(000) 1328 1232 1328 1408 Crystal size, mm 0.15x0.07x0.05 0.10x0.02x0.02 0.07x0.05x0.02 0.07x0.05x0.05 q range for data collection, deg 1.68 to 27.48 1.69 to 25.07 1.70 to 24.99 1.64 to 25.00 Limiting indices 30<=h<=30 16<=k<=11 10<=l<=11 28<=h<=28 13<=k<=13 10<=l<=9 28<=h<=28 14<=k<=13 10<=l<=9 28<=h<=29 4<=k<=15 9<=l<=8 Reflections collected 8295 6194 6627 3378 Unique reflections 3082 2257 2292 2145 R(int) 0.0286 0.0949 0.0479 0.0413 Completen ess to q % 98.4 98.8 99.4 84.5 Absorption correction SADABS SADABS SADABS SADABS Max. and min. transmission 1.000 and 0.858 1.000 and 0.473 1.000 and 0.815 1.000 and 0.751 Data / restraints / parameters 3082 / 0 / 222 2257 / 0 / 186 2292 / 0 / 187 2145 / 0 / 190 Goodness of fit on F 2 1.049 1.083 1.022 1.037 Final R indices [I>2sigma(I)] R1 = 0.0410, wR2 = 0.0941 R1 = 0.0741, wR2 = 0.1487 R1 = 0.0402, wR2 = 0.0885 R1 = 0.0630, wR2 = 0.1553 R indices (all data) R1 = 0.0484, wR2 = 0.0972 R1 = 0.1139, wR2 = 0.1 618 R1 = 0.0558, wR2 = 0.0948 R1 = 0.0920, wR2 = 0.1740 Largest diff. peak and hole, e. 3 0.594 and 0.417 0.873 and 0.725 0.525 and 0.476 0.899 and 0.524

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109 4.4. Results and Discussion 4.4.1. 1D structures The structure of compound 18 is based on dimetal tet racarboxylates building units bridged by two pairs of glutarate ligands, where the four flexible linkers adopt a syn configuration with each other around the bimetallic node, forming an arrangement in double chains of [Cu 2 (glutarate) 2 ] n along the y axis, F igure 4.7. The center of each dicopper tetracarboxylate chromophore lies on an inversion center, which generates two crystallographically equivalent Cu 2+ ions separated by 2.61 that are additionally coordinated at their axial positions to the oxygen atom s of two DMF solvent molecules. The individual double chains align in layers parallel to [001] sustained by weak hydrogen bonds between the methyl groups of the DMF ligands of one 1D array and the coordinated oxygen atoms of the glutarate ligands of the ad jacent double chains (d(CO) = 3.67 ), Figure 4.8a. The layers are aligned antiparallel with respect to the orientation of the axial ligand DMF and each layer is slipped with respect to the layer beneath along the y direction by b /2 = 3.95 Figure 4.8 b. In the z direction the 3D packing is facilitated by weak interactions between the methylene groups of the glutarate ligands and the oxygen of the coordinated carboxylate moieties of adjacent double chains via hydrogen bonds with (d(CO) = 3.65 to 3.67 ). The glutarate ligands adopt the anti gauche mode with torsion angles of 175 and 57 and the orientation of the carboxylate moieties with respect to the backbone generates dihedral angles of ca. 43 and 37.

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110 Figure 4.7. Detailed view of the 1D doub le chain of [Cu 2 (glutarate) 2 (DMF) 2 ] n formed by compound 18 down [001], (a) and [100] (b) Figure 4.8. Crystal packing of the 1D nets of compound 18 down [001] (a) and [100] (b) Compound 19 crystallizes in the space group P 1 and forms a similar 1D topol ogy as described in compound 18 with pyridine molecules instead of DMF as the axial ligands of the dicopper tetraadipate chromophore, Figure 4.9. The 2D systems of adjacent double chains parallel to [001] allow p p face to face interactions between the pyridine ligands of adjacent layers (d(CC) = 3.31 to 3.53 ), all layers are parallel and present the same orientation relative to the pyridine ligands. Figure 4.10 shows a representation of the crystal packing of the structure of 19 parallel to [001] and [110]. In 19 the conformation of the adipate ligands corresponds to the anti gauche gauche mode with

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111 torsion angles of 170, 67 and 65 and the orientation of the carboxylate moieties with respect to the backbo ne generates dihedral angles of ca. 36 and 31, Figure 4.9. Interestingly, a related 1D network based upon dicopper tetraadipate, where cyclohexanol molecules act as the axial ligands has been reported in a structure that contains analogous double chains stacking between 2D sheets based upon the same metal organic building blocks, Figure 4.11. In the double chain of [Cu(adipate)(C 6 H 11 OH)] n the dihedral angles adopted by the adipate ligand in the anti anti gauche mode are 176, 170 and 68 (Table 4.2, CSD code MITHUS). 276 Figure 4.9. Detailed view of the 1D double chain of Cu 2 (adipate) 2 (pyridine) 2 formed by compound 19 down [100] (a) and [001] (b) Figure 4.10. Crystal packing of the 1D nets of 19 down [100] (a) and [110] (b), hydrogen atoms are omitted for clarity The two novel compounds 18 and 19 based upon a 4 connected node and flexible

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112 links glutarate and adipate, in constrained conformations anti gauche anti anti gauche and anti gauche gauche have afforded the 1D, double chain, topology resulting from the C 2? symmetry of the angled ligands with respect to the dimetal axis. In the alternative case of all flexible linkers adopting a C 4? symmetry around the bimetallic node, the 2D topology is expected, Figure 4.5. Figure 4.11. Cry stal structure of [Cu 3 (adipate) 3 (H 2 O) 2 (C 6 H 11 OH)] n 276 (a) showing the 1D double chain of [Cu(adipate)(C 6 H 11 OH)] n (b) and the 2D sheets of [Cu 2 (adipate) 2 (H 2 O) 2 ] n (c), hydrogen atoms are omitted for clarity 4.4.2. 2D structures Compound 20 consis ts of corrugated sheets of metal glutarate moieties parallel to [001], Figure 4.12a. The glutarate backbone possesses an anti gauche conformational mode with torsion angles of 174 and 56 and a relative orientation of the carboxylate moieties with respect to the backbone of ca. 42 and 35, Figure 4.12a. The axial pyridine ligands of a same 2D sheet interact via p p face to face stacking (d(CC) = 3.53 to 3.58 ) while there is no evidence of strong interaction between two adjacent 2D networks.

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113 The 3D arrangement results from the piling of antiparallel sheets where pyridine molecules are filling of the voids ge nerated by adjacent corrugated sheets, Figure 4.12b c. The topology of the 2D network in the structure of 20 can be described as a distorted rhombus grid, or 4 4 network, comparable to the 2D metal organic network [Cu 2 (adipate) 2 (H 2 O) 2 ] n represented in Figur e 4.11c. Attempts to incorporate various guest molecules during crystallization of 20 were unsuccessful (benzene, toluene, nitrobenzene and anisole) and resulted in the formation of 20 Attempts to adsorb these guests by direct contact with 20 were also un successful. X ray single crystal unit cell determination, FT IR spectra and X ray powder diffraction patterns of the product obtained were identical to these of compound 20 Figure 4.12. Detailed view of the [Cu 2 (glutarate) 2 ] n sheets down [001] (a), cry stal structure of the 2D net of 20 down [010] (b) and [100] (c) The structure directing agents to the formation of a 1D double chain versus a 2D network based upon the same chromophore dicopper tetraadipate have been interpreted as resulting from the biph asic solvothermal synthesis leading to the generation of the double chain in the organic phase of cyclohexanol whereas the 2D sheets are present in the aqueous phase. 276 We have herein obtained analogous 1D and 2D structures from

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114 glutar ate ligand in organic conditions. The formation of the double chain over the 2D network appears to be mainly dependant upon the temperature at which the reaction takes place. These results illustrate how subtle differences of the conditions (temperature, s olvent, pH) during crystallization influence which topology is generated. 4.4.3. 3D structures As mentioned above, the use of glutarate and adipate anions in coordination to bimetallic building units is capable, in appropriate circumstances, of sustaining 2D sh eets. We report herein how such 2D networks can be rationally extended by pillaring via the use of bifunctional N,N donor ligands to generate the modular 3D nets {[Cu 2 (L 1 ) 2 L 2 ]G} n L 1 = glutarate, L 2 = 4,4 bipyridine (bipy), 21 (G = 3H 2 O, 21a G = 0, 21b G = 3H 2 O, 21c ), L 1 = glutarate, L 2 = 1,2 bis(4 pyridyl)ethane (bipyethane), 22 (G = 5H 2 O, 22a G = 2H 2 O, 22b G = 5H 2 O, 22c ) and L 1 = adipate, L 2 = 1,2 bis(4 pyridyl)ethane (bipyethane), G = 1H 2 OCH 3 OH, 23 21a consists of corrugated sheets of metal glu tarate moieties parallel to [100], Figure 4.13a, that are pillared via axial coordination of canted bipy ligands, Figure 4.13b. The resulting 3D network contains channels with effective dimensions of ca. 2.9 X 4.0 occupied by two crystallographically i ndependent water molecules that form hydrogen bonded chains (d(OO) = 2.81 and 2.97 ) which interact with the methylene groups of the glutarate ligands (d(CO) = 3.66 3.88 ), Figure 4.13c. A similar 1D polymer of ordered water molecules was observed in a 3D hydrogen bonded ionic network that contains channels with the requisite size and environment. However, this structure does not survive desorption of the guest water molecules. 303 The glutarate ligands adopt the

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115 anti gauche mod e with torsion angles of 175 and 57 and the orientation of the carboxylate moiety with respect to the backbone generates dihedral angles of ca. 43 and 37, Figure 4.13a. The bridging bipy ligands connect the sheets in a criss cross pattern that facilita tes p p face to face interactions (d(CC) = 3.38 to 3.58 ). Such a criss crossed network possesses a topology related to the a polonium net, a topology that has also been generated via M(CN) 2 sheets linked by pyrazine ligands. 304 Figure 4.13. Detailed view of the [Cu 2 (glutarate) 2 ] n sheets down [100] in 21 (a), crystal structure of the 3D net of 21a down [001] (b) and corresponding space filling representation (d) and view of a channel of water molecules in 21a (c) Thermogravimetric analysis of 21a revealed that it is stable up to 300C with loss of ca. 8.5% mass between 60 and 120C, consistent with desorption of water molecules (calculated 9%). Interestingly, when heated at 150C for 3 days, crystals of 21a were a c b d

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116 observed to remain crystalline and the crystal structure of the apohost, 21b confirmed that removal of guest molecules does not influence the 3D network. IR and thermal analysis were used to confirm that 21b can adsorb water molecules under various conditions, Figures 4.14 and 4.15. For example, under an atmosphere of ca. 60% water vapour, a powdered sample of 21b adsorbs water and reaches saturation after ca. 1 hour whereas single crystals of 21b take ca. 15 hours to reach saturation. The X ray cry stal structure of such a sample, 21c revealed it to be crystallographically identical to 21a Attempts to incorporate other guest molecules during crystallization of 21 were unsuccessful (methanol, hexanes, mixtures of water: methanol (1:1, 1:5 and 1:10), benzene, nitrobenzene or anisole) and resulted in the formation of 21a Attempts to adsorb other guests by direct contact with 21b were also unsuccessful (gas chromatographic experiments and infrared spectra indicated that methanol, ethanol, acetonitrile or n hexane are not adsorbed under anhydrous conditions). Figure 4.14. FT IR spectra of compound 21b let in atmosphere for 55min (from t = 0, top, to t = 55min, bottom)

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1 17 Figure 4.15. TGA traces of the rehydration of 21b crystals (a) and 21b powder (b ) under ambient atmosphere The crystal structure of 22 is similar to that of 21 with differences due to the presence of the additional ethylene moieties, Figure 4.16. 22a contains channels with effective dimensions of ca. 3.5 X 4.4 occupied by 2.5 inde pendent water molecules. The glutarate backbone possesses an anti gauche conformation with torsion angles of 173 and 60 and a relative orientation of the carboxylate moieties with respect to the

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118 backbone of ca. 39 and 33. The bipyethane ligands are can ted and criss cross between the dicopper tetraglutarate sheets. They engage in edge to face aromatic stacking interactions (d(CC) = 3.54 to 4.11 ) reinforced by CH 2 CH 2 interactions (d(CC) = 3.76 ) and CH p interactions (d(CC) = 3.85 to 3.89 ). 22a was observed to desorb its guest water molecules following exposure to the atmosphere for less than 1 hour. Figure 4.17 shows the FT IR spectra of the same sample of 22a let in atmosphere for 45 min and the regular decrease in intensity of the br oad band centered at 3500 cm 1 corresponding to the vibration of O H bonds from the water guest molecules. The resulting apohost 22b retained single crystallinity and was observed to adsorb water molecules via immersion in water. The resulting crystals, 2 2c, were confirmed to be isostructural to 22a The slightly larger channels in 2 2a would therefore appear to result in lower affinity for water molecules when compared to 2 1a which readily adsorbs from gas as well as liquid contact. Figure 4.16. Crystal structure of the 3D net of 22a down [001] (a) and corresponding space filling representation where the guest water molecules are omitted (b) a b

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119 Figure 4.17. FT IR spectra of compound 22a let in atmosphere for 45min (from t = 0, t op, to t = 45min, bottom) The crystal structure of 23 is similar to that of 22 with differences due to the presence of the additional methylene moiety in the adipate ligand, Figure 4.18. 23 contains channels with effective dimensions of ca. 3.1 X 4.3 o ccupied by disordered guest water and methanol molecules. The adipate backbone possesses an anti gauche gauche conformation with torsion angles of 170, 57 and 53 and a relative orientation of the carboxylate moieties with respect to the backbone of ca. 69 and 16. The bipyethane ligands are canted and criss cross between the dicopper tetraadipate sheets. They engage in edge to face aromatic stacking interactions (d(CC) = 3.84 to 4.29 ) reinforced by CH 2 CH 2 interactions (d(CC) = 3.91 ) and CH p interactions (d(CC) = 3.98 to 4.02 ). 23 was observed to readily desorb its guest molecules following exposure to the atmosphere for ca. 10 min. The apohost was observed to retain crystallinity but the quality of the resulting crystals was not suf ficient to obtain an acceptable structure solution. The slight decrease in the dimensions of the channels in 23 as compared with

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120 those of 22 is due to the presence of additional methylene groups of conformationally constrained adipate ligands, which, in return, render the cavities less hydrophilic than 21 and 22 As a sideline, it should be mentioned that our attempt to prepare crystals of the corresponding network of [Cu 2 (adipate) 2 ] n pillared by 4,4 bipyridine ligands was unsuccessful. This is predictab le since the shortening of aromatic linkers would generate destabilizing interactions between the adipate fragments contained in the channels and the 4,4 bipyridine that criss cross the dicopper tetraadipate sheets. Figure 4.18. Detailed view of the [Cu 2 (adipate) 2 ] n sheets down [100] in 23 (a), crystal structure of the 3D net of 23 down [001] (b) and corresponding space filling representation where the guest water molecules are omitted (c) The five compounds studied herein are representative of a relative ly new class of metal organic networks based upon the two conformationally flexible ligands glutarate and adipate. They have formed the two types of networks 1D double chains and 2D grids that can be rationalized on the basis of the conformation adopted by the organic linkers and the connectivity and geometry of the molecular building units. The 1D, double chain, topology resulted from axial coordination of neutral O donor DMF ligand in 18 or N donor pyridine ligand in 19 The formation of corrugated sheets [Cu 2 (glutarate) 2 ] n in the a b c

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121 2D 4 4 network of 20 when pyridine molecules act as the two axial ligands has successfully generated extended modular 3D a Po nets upon the utilization of the neutral difunctional axial N coordinated ligand, the pillars being 4,4 bipyridine, 21 and 1,2 bis(4 pyridyl)ethane, 22 and 23 4.5. Conclusions In conclusion, it should be emphasized that compound 21 represents a novel porous network that was generated in water and acts as a highly selective adsorbent for water molecules. T hat 21 retains single crystallinity might be attributed to the stability of the 2D sheets and the ability of the cross linking ligands to engage in stacking interactions. Compounds 2 1 and 2 2 are new members of a relatively small group of molecular material s that reversibly desorb guest molecules with retention of single crystallinity. 113,125,215,236,238,260,289 291,294 296 In the context of porosity, it has been suggested that the generation of porous m aterials that retain crystallinity during reversible desorption and exhibit high selectivity towards guest molecules might be relevant as adsorbents for separations and sensing devices. 305 These results further confirm how the rational u se of flexible linkers has allowed the generation of predicted crystal structures. Such investigations have provided design strategies that apply to systems containing an inherently high degree of flexibility and an understanding of the essential mechanism s that control the geometrical adaptability typical of this class of compounds. Applications of these principles may lead to the construction of metal organic networks possessing important novel properties directly connected to the conformational flexibili ty of the building units.

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122 In this regard, it is interesting to speculate that a further use of flexible linkers may be rationally used to construct materials that possess sufficient flexibility to allow for geometrical and/or functional recognition. An esp ecially intriguing and exciting aspect of such protocol would consist in the possibility to combine flexibility and porosity within supramolecular metal organic networks, which may potentially lead to cooperative substrate binding. In other words, the netw orks may function as living or smart hosts in a manner reminiscent of biological systems.

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123 Chapter 5 Conclusion and Future Directions 5.1. Summary The generation and systematic study in terms of structures and properties of the metal organic and organ ic systems presented in this dissertation have led to the development of strategies for understanding and controlling intermolecular interactions within the solid state. In particular, this research has contributed to the rationalization of self assembly o f a selection of calixarenes and metal organic networks on the basis of supramolecular approaches towards the organization of individual molecular building units into desirable crystalline architectures. From the structural investigation of the novel supra molecular systems described throughout this thesis, three salient features deserve to be emphasized: Structural control over the crystal packing of pseudo amphiphilic calixarenes is possible, given the use of appropriate functionalization of the building u nits owing to the knowledge of the relative effects resulting from the combination of two or more sets of supramolecular interactions. In effect, it has been established that well organized bilayer structures can be generated from subtle exploitation of th e balance between halogen and van der Waals interactions

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124 introduced at the opposite faces of calixarene building units. New insights concerning structural diversity in supramolecular systems have resulted from the generation of three novel metal organic ne tworks based upon coordination between simple components that can afford different topologies according to their connectivity and geometry. S elf assembly of Zn(II), 4 connected node, and nicotinate, ligand possessing N donor and carboxylate functions, has afforded a 3D 4 2 4 and two 2D 4 4 networks, structural supramolecular isomers interconnected through subtle variation of crystallization conditions. Such results especially emphasize that the composition of a material is not the only parameter to be consid ered prior to the generation of infinite networks since rational topological approaches are critical towards their construction. The use of organic ligands that contain conformationally labile fragments, glutarate and adipate, in metal organic networks bas ed upon the ubiquitous chromophore dicoppertetracarboxylate, has been investigated towards the generation of porous materials. In this context, the novel porous network [Cu 2 (glutarate) 2 (4,4 bipyridine)] n has been shown to retain single crystallinity upon reversible guest desorption and to act as a highly selective adsorbent for water molecules. In summary, this work has contributed to the rational design of metal organic and organic systems that are applicable to the construction of a broader range of sup ramolecular materials.

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125 5.2. Supramolecular Materials Metal organic networks and organic assemblies presented herein represent prototypical examples pertaining to two areas of supramolecular chemistry that are differentiable by the type of intermolecular intera ctions involved. General approaches have been delineated from the structural investigation of individual building units and their modulation to afford functional sites or geometries that are suitable for specific organization between molecules within the s olid state. In this regard, preselection of complementary nodes linkers, metal centers and organic ligands, that can self assemble into predictable topologies has successfully afforded novel supramolecular materials possessing interesting properties. On th e other hand, judicious functionalization of a single type of component possessing typical morphology, as exemplified by the cone shaped calixarene molecules, has generated organic building units that possess adequate geometries and functions to self assem ble into predictable structures. In both cases, preselection of molecular building units, consisting of one or more components that possess molecular recognition potential, represents the key factor to control the resulting supramolecular architectures. In the current intense research in the field of nanosciences towards the controlled manipulation of molecules in order to build nanostructured materials, the use of supramolecular concepts providing enhanced insight into and control of how molecules interact and assemble, exemplified by the two types of supramolecular systems presented herein, represents a successful approach to design materials directly at the molecular level.

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126 5.3. Future Directions Considering the inherent modu larity of systems based upon molecular building units that can be systematically modified and adjusted, application of the supramolecular approach for the design of new materials can be applied to the construction of an even wider range of supramolecular s ystems. The modular nature of crystal engineered metal organic networks, which can be generated from a diverse array of complementary building units and their structural diversity, represented by the range of supramolecular isomers that can be generated f rom each set of molecular components are of particular interest in the context of fine tuning the chemical or physical properties. Investigation towards the variation of the metal centers may result in additional properties integrated to the networks and c ould offer materials possessing catalytical or optical properties. Further investigation towards functionalization of the organic ligands, in an extension to the parallel study of metal organic structures based upon nicotinate and dinicotinate ligands, may be of interest towards the generation of networks containing specific functions as reactive or binding sites at well defined and controllable positions within the network topology. Further use of aliphatic linkers possessing various chain lengths and fun ctionalities should be fully developed. The goal in this regard would be the generation of flexible architectures with variable shapes and sizes, and should represent great potential for supramolecular chemistry. Another outcome from the use of this type o f ligand is the expectation that the resulting structures may expand the concept of supramolecular isomerism to its conformational counterpart and provide a route to the

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127 generation of a novel class of nanostructures possessing useful properties directely r elated to the conformational lability of the organic building units. Finally, in the current context of multi disciplinary research, it should be interesting to expand the study of pseudo amphiphilic calixarenes to other derivatives that would incorporate specific functionalities towards the generation of materials possessing additional properties. Such materials could offer opportunities to impact areas as diverse as material and surface sciences or physics. In addition, further study of inclusion properti es of self assembled bilayers generated from calixarenes may reveal significant with a view towards biomimetics since these artificial and controllable systems could possess similar properties as those of biological membranes. As a last note, it should be emphasized that technological advances in both software and hardware have rendered possible the determination of large complex structures. However, related methods for structural determination of micro and nano crystalline materials may represent inestima ble advantages with respect to the characterization of special classes of supramolecular materials, e.g. large structures possessing broad flexible regions inclined to induce high disorder, and the study of some of their properties, in a similar perspectiv e as porosity can be characterized via single crystal structural determination.

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150 Appe ndices

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151 Appendix A. AFM studies for compound 10. Non contact mode AFM images of compound 10 on glass after annealing for 24 hours at 37 C and 25 C (and corresponding zoom) representative of the variation in self organization of this compound at different temperatures Drying Temperatures 37 C 25C

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152 Appendix B. Histogram showing the distribution of Cu O distances among the structures found in the CSD search of the chromophores of mononuclear Cu 4 5 and 6 coordinate containing t wo functionalities N donor and carboxylate Cu 4-coordinate 0 20 40 60 80 100 120 140 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 d(Cu-O)/ Hits Cu 5-coordinate 0 20 40 60 80 100 120 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 d(Cu-O)/ Hits Cu 6-coordinate 0 10 20 30 40 50 60 70 80 90 100 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 d(Cu-O)/ Hits

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153 Appendix C 1. Experimental data for compound 13 FT IR spectrum, TGA trace and X ray powder diffraction patterns of fresh samp le and calculated from the single crystal structure

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154 Appendix C 2. Experimental data for compound 14 FT IR spectrum, TGA trace and X ray powder diffraction patterns of fresh sample and calculated from the single crystal structure

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155 Append ix C 3. Experimental data for compound 15 FT IR spectrum, TGA trace and X ray powder diffraction patterns of fresh sample and calculated from the single crystal structure

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156 Appendix C 4. Experimental data for compound 16 FT IR spectrum and TGA trace s (after several minutes and one hour of exposure to atmosphere)

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157 Appendix C 4. (continued) X ray powder diffraction patterns of fresh sample and calculated from the single crystal structure

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158 Appendix C 5. Experimental data for compound 17 F T IR spectrum and X ray powder diffraction patterns of fresh sample and calculated from the single crystal structure

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159 Appendix C 6. Experimental data for compound 18 FT IR spectrum and X ray powder diffraction patterns of fresh sample and calculated from the single crystal structure

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160 Appendix C 7. Experimental data for compound 19 FT IR spectrum and X ray powder diffraction patterns of fresh sample and calculated from the single crystal structure

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161 Appendix C 8. Experim ental data for compound 20 FT IR spectrum and X ray powder diffraction patterns of fresh sample and calculated from the single crystal structure

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162 Appendix C 9. Experimental data for compound 21 FT IR spectra of compounds 21a 21b and 21b let in Me OH (HPLC grade H2O = 0.009%) for 1 night

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163 Appendix C 9. (continued) TGA traces of 21a and 21b let in atmosphere for <1hour

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164 Appendix C 9. (continued) X ray powder diffraction patterns of fresh sample and calculated from the single crysta l structure for compounds 21a (left) and 21b (right) and inclusion of apohost solid 21b with various guests from GC experiments Guest G Guest (mol) included per unit formula of 1b MeOH 5.00.10 9 EtOH 3.94.10 7 CH 3 CN 6.70.10 7 n hexane 1.21.10 8

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165 Appendix C 9. (continued) X ray powder diffraction patterns of the blue powder formed during the synthesis of 21a and simulation from the structure of [Co(4,4 bipyridine) 1.5 (NO 3 ) 2 ] n (CSD code REJVUX) 5 10 15 20 25 30 35 170 85 0 PowderCell 2.2 REJVUXEtOH 9.22 9.93 11.72 15.19 16.40 16.84 17.06 17.58 17.78 18.51 19.74 19.93 20.53 21.94 22.92 23.45 23.57 23.76 23.99 24.81 25.09 25.40 26.20 26.81 27.15 27.28 27.91 29.14 29.77 30.00 30.09 30.23 30.66 31.16 31.45 31.97 32.44 32.90 33.46 34.06 34.52 35.60 35.96 36.38 36.87 37.39 37.85

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166 Appendix C 10. Experimental data fo r compound 22 FT IR spectra of compounds 22a 22b and 22c

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167 Appendix C 10. (continued) TGA traces of 22a 22b and 22c

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168 Appendix C 10. (continued) X ray powder diffraction patterns of fresh sample and calculated from the single crystal struct ure 5 10 15 20 25 30 35 213 107 0 PowderCell 2.2 er352 7.29 7.69 12.74 12.88 12.89 13.56 14.61 15.41 16.31 16.66 18.43 19.52 19.98 20.57 21.67 22.32 22.68 23.13 23.20 24.10 24.59 25.01 25.30 25.92 26.62 27.31 28.15 28.84 29.24 29.61 30.10 30.69 31.39 31.96 32.57 32.95 33.46 33.97 34.43 34.89 35.31 35.83 36.54 36.89 37.05 37.36

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169 5 10 15 20 25 30 35 40 125 63 0 PowderCell 2.2 NAMSEZ 6.90 8.88 10.51 10.67 11.27 11.55 11.82 13.53 13.84 14.37 14.71 15.36 16.32 16.72 17.24 17.49 18.43 19.81 20.39 20.82 21.04 21.15 21.42 21.72 22.08 22.64 23.06 23.22 23.77 24.33 25.01 25.13 25.43 26.03 26.28 26.34 26.46 26.84 27.58 28.13 28.68 29.27 30.09 30.35 30.67 31.20 31.45 31.88 32.36 32.85 33.36 34.25 34.89 35.15 35.76 36.46 37.07 37.32 37.50 37.94 38.24 38.82 39.34 Appendix C 10. (continued) X ray powder diffraction patterns of blue crystals formed during the synthesis of 22 and simulation from the structure of bilayer [Co(4,4 bipyridine) 1.5 (NO 3 ) 2 ] n (CSD code NAMSEZ)

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170 Appendix C 11. Experi mental data for compound 23 FT IR spectrum and X ray powder diffraction patterns of fresh sample and calculated from the single crystal structure

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About the Author Elisabeth Rather received a DEA degree in organic chemistry from Universit Claude Bernard, Lyon I, in France in 1999, where she worked on the synthesis of a series of macrocycles via olefin metathesis. In 2000, Elisabeth entered the Ph.D. program at the University of South Florida and joined Dr. Michael J. Zaworotkos research group. While in the Ph.D. program, she was honored with a Chemistry Outstanding Teaching Award in 2001 and the Shembekar Scholarship Award in 2002. She has also coauthored eight publications in chemical journals and made several paper presentations at regi onal and national scientific meetings of the American Chemical Society and the American Crystallographic Association.