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Hierarchical complexity in metal-organic materials

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Title:
Hierarchical complexity in metal-organic materials from layers to polyhedra to supermolecular building blocks
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English
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Perry, John Jackson
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University of South Florida
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Crystal engineering
Coordination polymer
MOF
Topology
Crystal chemistry
Supramolecular chemistry
Dissertations, Academic -- Chemistry -- Doctoral -- USF   ( lcsh )
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non-fiction   ( marcgt )

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Summary:
ABSTRACT: The design and synthesis of novel functional materials with fine-tunable physical and chemical properties has been an aspiration of materials scientists since at least Feynman's famous speech "There's Plenty of Room at the Bottom" which has fittingly been credited with ushering in the nanotechnology era. Crystal engineering, as the solid-state manifestation of supramolecular chemistry, is well positioned to make substantial contributions to this worthwhile endeavor. Within the realm of crystal engineering resides the subdiscipline of metal-organic materials (MOMs) which pertains most simplistically to the coordination bond and includes such objects as coordination polymers, metal-organic frameworks (MOFs), and discrete architectures, each of which share the common aspect that they are designed to be modular in nature.While metal-organic materials have been studied for quite some time, only recently have they enjoyed an explosion in significance and popularity, with much of this increased attention being attributed to two realizations; that this inherent modularity ultimately results in an almost overwhealming degree of diversity and subsequently, that this diversity can give rise to effective control of the properties of functional materials. At long last the goal of attaining fine-tunablity may be within our grasp. In addition to high levels of diversity, MOMs are also characterized by a broad range of complexity, both in their overall structures and in the nature of their constituents. From the simplest molecular polygons to extended 3-periodic frameworks of unprecedented topologies, MOMs have the capacity to adopt an array of structural complexities. Moreover, there has been a recent trend of increasing complexity of the very building blocks that construct the framework.It is the aim of the research presented in this dissertation to survey these two principle aspects of MOMs, diversity and complexity, by focusing upon the use of polycarboxylates and first row transition metals to synthesize several series of closely related materials imbued with varied levels of complexity. Through the use of single crystal X-ray diffraction and the charcterization of the materials' properties, the structure-function relationship has been probed. Finally, novel design strategies incorporating supermolecular building blocks for the creation of a new generation of MOMs has been addressed.
Thesis:
Dissertation (Ph.D.)--University of South Florida, 2009.
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Includes bibliographical references.
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by John Jackson Perry.
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Document formatted into pages; contains 301 pages.
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Includes vita.

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Hierarchical Complexity in Metal-Organic Materials: From Layers to Polyhedra to Supermolecular Building Blocks by John Jackson Perry IV 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. Mohamed Eddaoudi, Ph.D. Brian Space, Ph.D. Stephen J. Loeb, Ph.D. Date of Approval: November 7, 2009 Keywords: crystal engineering, coordinati on polymer, MOF, topology, crystal chemistry, supramolecular chemistry Copyright 2009 John J. Perry IV

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Dedication To my family for their enthusiasm, support and encouragement… …and to Miranda for everything

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Acknowledgments First and foremost, I would like to take this opportunity to express my sincerest and immense appreciation towards my Ph.D. advisor Dr. Michael J. Zaworotko for his guidance and support throughout my doctoral researc h. I am eternally grateful for his allowing me to join his research group and providing me with the opportunity to pursue my studies in this fascinating and stimulating field of research. Additionally, many thanks and accolades are due to the remaining members of my dissertation examination committee Dr. Mohamed Eddaoudi, Dr Brian Space, and Dr. Stephen J. Loeb for their guidance and helpful sugge stions pertaining to the work presented herein. I would esp ecially like to thank Dr. Gre gory McColm for graciously agreeing to act as chairperson for the ex amination committee and taking the time to review the dissertation in its entirety. I would be remiss not to thank the nume rous students and post-doctoral fellows both past and present in th e research groups of Dr. Zaworotko and Dr. Eddaoudi (Especially my closest companions; Mira nda Cheney, Greg McManus, Zhenqiang Wang, and Jason Perman, without whom this would not have been possible) as well as all members of SMMARTT, for all of their support and stimulat ing scientific collaboration. Finally, I would especially like to acknow ledge and thank Dr. Randy Larsen for his countless hours of discussion, mentori ng, and guidance through the years.

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i Table of Contents List of Tables ix List of Figures x Abstract xvi Chapter 1 – Introduction 1 1.1 Preamble 1 1.1.1 Crystals and Crystallochemistry 2 1.1.2 Solid State Chemistry 5 1.1.3 Nanoscience 6 1.2 Supramolecular Chemistry 7 1.2.1 History and Nature 7 1.2.2 Noncovalent Interactions 8 1.2.3 Supramolecular Isomerism 10 1.3 Crystal Engineering 12 1.3.1 History and Scope 12

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ii 1.3.2 Cambridge Structural Database 14 1.3.3 Crystal Engineering vs. Crystal St ructure Prediction 17 1.4 Metal-Organic Materials 18 1.4.1 History and Relevance 19 1.4.2 Design Principles 23 1.4.2.1 Node and Spacer Approach 24 1.4.2.2 Secondary Building Units 26 1.4.2.3 Molecular Paneling 29 1.4.3 Topological Analysis 31 1.4.3.1 Wells’ Notation 32 1.4.3.2 Schlfli symbols 34 1.4.3.3 Vertex symbols 37 1.4.3.4 RCSR and net enumeration 40 1.4.4 Properties and Applications of Metal-Organic Materials 41 Chapter 2 – Two-Periodic Layered Structures 48 2.1 Introduction 48

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iii 2.1.1 Clay Mimics 48 2.1.2 Common Topologies 49 2.2 Kagom Lattice (3.6.3.6) 50 2.2.1 Spin Frustration and Magnetism 51 2.2.2 Structural Analysis 52 2.2.2.1 5-benzyloxy-1,3-bdc Kagom Lattices 52 2.2.2.2 5-hexyloxy-1,3-bdc Kagom Lattice 57 2.2.3 Experimental 59 2.2.3.1 Synthesis 59 2.2.3.2 X-ray Crystallography 67 2.2.3.3 Powder X-ray Diffraction 68 2.2.3.4 FT-IR Spectroscopy 69 2.2.3.5 Thermal Gravimetric Analysis 70 2.3 Square Lattice (4.4) 70 2.3.1 Structural Analysis 71 2.3.2 Experimental 74 2.3.2.1 Synthesis 74

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iv 2.3.2.2 X-ray Crystallography 80 2.3.2.3 Powder X-ray Diffraction 81 2.3.2.4 FT-IR Spectroscopy 81 2.3.2.5 Thermal Gravimetric Analysis 82 2.4 Conclusion 82 Chapter 3 – Three-Periodic Frameworks from Pillaring 2-Periodic Layers 84 3.1 Introduction 84 3.1.1 3-Periodic Structures and Their Most Important Property 84 3.1.2 Pillaring as a Design Strategy 85 3.2 Camphoric Acid Square Lattices with Dipyridyl Based Pillars 88 3.2.1 Camphoric Acid Square Lattices 90 3.2.2 Dipyridyl Type Pillars 91 3.2.3 Structural Analysis 92 3.2.3.1 Layer Arrangements 92 3.2.3.2 Lack of Entanglements in Camphoric Based Structures 94 3.2.3.3 Controllable Pore Size and Predictable

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v Surface Areas 94 3.2.4 Applications and Properties 95 3.2.4.1 Gas Sorption 95 3.2.4.2 Dichroism in Metal-Organic Materials 100 3.2.5 Experimental 101 3.2.5.1 Synthesis 101 3.2.5.2 X-ray Crystallography 113 3.2.5.3 Powder X-ray Diffraction 114 3.2.5.4 FT-IR Spectroscopy 115 3.2.5.5 Thermal Gravimetric Analysis 115 3.3 Conclusion 116 Chapter 4 – From Metal-Organic Polyhedra to Supermolecular Building Blocks 118 4.1 Introduction 118 4.1.1 Discrete Supramolecular Polygons 119 4.1.2 Polyhedra 120 4.1.2.1 Platonic Solids 121

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vi 4.1.2.2 Archimedean Solids 122 4.1.2.3 Faceted Polyhedra 123 4.1.3 Metal-Organic Polyhedra 125 4.2 Alkoxy Nanoball – Dodecyloxy Cu(II) Nanoball 125 4.2.1 Structural Analysis 126 4.2.2 Properties 133 4.2.2.1 Solubility 134 4.2.3 Experimental 135 4.2.3.1 Synthesis 135 4.2.3.2 X-ray Crystallography 137 4.2.3.3 Powder X-ray Diffraction 138 4.2.3.4 FT-IR Spectroscopy 139 4.2.3.5 Thermal Gravimetric Analysis 141 4.3 Aryloxy Nanoballs – Benzyloxy and Naphthyloxy Cu(II) Nanoballs 142 4.3.1 Structural Analysis 143 4.3.2 Properties 158

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vii 4.3.3 Experimental 162 4.3.3.1 Synthesis 162 4.3.3.2 X-ray Crystallography 164 4.3.3.3 Powder X-ray Diffraction 165 4.3.3.4 FT-IR Spectroscopy 167 4.3.3.5 Thermal Gravimetric Analysis 168 4.4 Supermolecular Building Blocks 170 4.4.1 Introduction 170 4.4.1.1 A Matter of Scale 171 4.4.1.2 Rare and Unprecedented Node Connectivities 171 4.4.1.3 Out of Increased Complexity, Increased Control 173 4.4.1.4 Inherent Structural Diversity 174 4.4.2 Structural Analysis 174 4.4.3. Properties 184 4.4.4 Experimental 187 4.4.4.1 Synthesis 187 4.4.4.2 X-ray Crystallography 190

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viii 4.4.4.3 Powder X-ray Diffraction 192 4.4.4.4 FT-IR Spectroscopy 194 4.4.4.5 Thermal Gravimetric Analysis 196 4.5 Conclusion 197 Chapter 5 – Conclusions a nd Future Directions 200 5.1 Summary and Conclusions 200 5.2 Future Directions 202 References 205 Appendices 234 Appendix A. 1H NMR spectra for synthesized ligands 235 Appendix B. FT-IR spectrum for synthesized ligands; FT-IR spectra, PXRD patterns, and Thermal Gravimetric Analysis for synthesized compounds 240 Appendix C. Crystal data and struct ure refinement for select compounds 277 About the Author End Page

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ix List of Tables Table 1.1 Common noncovale nt interactions 10 Table 1.2 Comparison of the coordina tion sequence (CS) and topological density (TD10) for diamond and Lonsdaleite nets 40 Table 4.1 Coordination sequences and TD10 for the four unique nodes found in compound [33] 186

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x List of Figures Figure 1.1 Photograph of snow crystals. 2 Figure 1.2 Schematic illustrating the con cept of supramolecular isomerism. 11 Figure 1.3 Exponential growth of the Cambri dge Structural Database since 1970. 16 Figure 1.4 The universe of me tal-organic materials. 20 Figure 1.5 Number of results for the search query “coordination polymer” (top) and “metal-organic framew orks” (bottom) from ISI’s Web of Science database, broken down by country. 23 Figure 1.6 The node and spacer approach to metal-organic materials. 26 Figure 1.7 Examples of commonly ob served Secondary Building Units used in metal-organic materials. 28 Figure 1.8. Common mol ecular panels. 30 Figure 1.9 Schematic depicting the design principle of molecular paneling. 31 Figure 1.10 Schematic depicting the only thr ee regular plane nets; (3,6) triangle tiling, (4,4) square grin d and (6,3) honeycomb. 33

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xi Figure 1.11 Schematic illustrating the concepts of cycles, rings, and short-cuts. 36 Figure 1.12 Schematic illustrating the concept of kth-topological neighbors. 39 Figure 2.1 Schematic depicting the only three regular plane nets; (3,6) triangle tiling, (4,4) square grind, and (6,3) honeycomb. 50 Figure 2.2 Semi-regular plane tilings. 51 Figure 2.3 Basket weaving depi cting a Kagom lattice. 51 Figure 2.4 A cartoon illustrating the concept of spin frustration. 52 Figure 2.5 5-benzyloxy-1,3-benzenedicarboxylic acid, L1 53 Figure 2.6 Cartoon illustrating the Kagom lattice ( left ) and the metal-organic Kagome lattice as seen in compounds [1] and [2] ( right ). 54 Figure 2.7 Illustration of Sextuplet Phenyl Embrace as seen in compound [1] 55 Figure 2.8 Illustration of the face-to-face stacking interactions in compounds [5] and [6] 57 Figure 2.9 5-hexyloxy-1,3-be nzenedicarboxylic acid, L3 57 Figure 2.10 Stick representation of compound [7]. 59 Figure 2.11 5-(2-naphthylmethoxy)-1,3-benzenedicarboxylic acid, L2 62 Figure 2.12 4.82 fes -like topology. 71 Figure 2.13 Dimetaltetracarboxylate sec ondary building unit observed in

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xii compounds [8]-[13]. 72 Figure 2.14 Illustration of i ndividual layer of compounds [8]-[13]. 73 Figure 2.15 Interdigitation between la yers as observed in compounds [8]-[13]. 74 Figure 3.1 Illustration of the dimetal tetr acarboxylate square paddlewheel SBU. 86 Figure 3.2 Cartoon illustrating the three pos sible pillaring design strategies; axial-to-axial, ligand-to-l igand, and ligand-to-axial 87 Figure 3.3 Chemical Sketch of (1R,3S)-(+)-1,2,2-trimethylcyclop entane-1,3-dicarboxylic acid 88 Figure 3.4 Illustration of a single layer from a pillared camphoric structure 90 Figure 3.5 Dipyridyl type pillars. 92 Figure 3.6 Cartoon illustrating the anti-para llel stacking of layers observed in compounds [16]-[18] 93 Figure 3.7 Left : N2 Isotherm (77K) for compounds [14] (red) and [17 ] (blue) 98 Figure 3.8 Plot of Isosteric Heats of Ad sorption (kJ/mol) vs. volume (cc/g) 99 Figure 3.9 Illustration of the rela tive pore sizes in compounds [17] (left) and [14] (right) 99 Figure 3.10 Digital photograph depicti ng the observed Dichroism in

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xiii compound [18] 101 Figure 3.11 Digital photographs of compounds [16] (left) and [17] (right). 114 Figure 4.1 The Platonic solids. 121 Figure 4.2 The Archimedian solids. 123 Figure 4.3 Faceted Polyhedra generated via vertex linking of regular polygons 124 Figure 4.4 5-dodecyloxy-1,3benzenedicarboxylic acid, L4 126 Figure 4.5 Schematic depicting stick view of the dodecyloxy nanoball. 127 Figure 4.6 Cartoon illustrating the self-i nclusion of two dodecyloxy groups (blue chains) into the center of each nanoball. 129 Figure 4.7 Cartoon illustrating the interactions between nearest neighbor nanoballs in compound [30] 130 Figure 4.8 Scheme isllustration the dist orted supramolecular tetrahedron (with some angles shown) gene rated by the four nearest neighbors of a central (red sphere) dodecyloxy nanoball. 132 Figure 4.9 Digital photograph depict ing single crysta ls of compound [30]. 138 Figure 4.10 Schematic illustrating a stick view of the benzyloxy nanoball, compound [31] 144 Figure 4.11 Body centered cubic close packing of benzyloxy nanoballs. 146

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xiv Figure 4.12 Illustration of the close a pproach of four benzyloxy pendant arms, two each from two separate benzyloxy nanoballs. 148 Figure 4.13 Illustration of the four CH••• interactions (blue) between next nearest neighbors in compound [31] 149 Figure 4.14 Schematic illustrating a s tick view of the naphthylmethoxy nanoball, compound [32] 151 Figure 4.15 The close packing of naphthylmethoxy nanoballs observed in compound [32]. 153 Figure 4.16 Stick represen tation of face-to-face stacking interactions (purple) observed between ne xt nearest neighbors in the crystal packing of naphthylmethoxy nanoballs [32]. 155 Figure 4.17 Stick representation depicting the two types of weak noncovalent interactions between neares t neighbors in the crystal packing of naphthylmethoxy nanoballs [32]. 156 Figure 4.18 Illustration of the quadr uple phenyl embrace of concerted edge-to-face CH••• interactions as seen in the crystal structure of compound [32] 157

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xv Figure 4.19 Digital photographs depict ing single crystals of compound [31] 164 Figure 4.20 Digital photographs depict ing single crystals of compound [32] 165 Figure 4.21 Schematic of a small rhombihexahedron depicting the peripheral nature of the func tional groups (black balls) when the 1,3-BDC moiety is derivatized in the 5th-position. 175 Figure 4.22 Cartoon illustrating the vari ous rotational symmetry elements of the small rhombihexahedron ( Oh). 177 Figure 4.23 Three possible connectivities for the small rhombihexahedron SBB. 178 Figure 4.24 1,3-bis(5-methoxy-1,3-ben zenedicarboxylic acid)benzene, L5 178 Figure 4.25 Stick representation illust rating the cross-linking observed in the Cu linked-nanoballs, compound [33]. 180 Figure 4.26 Cage sharing view of the cross-linked nanoballs structure. 182 Figure 4.27 Stick representation illustra ting the cross-linking observed in the Zn linked nanoballs, compound [34]. 185 Figure 4.28 Digital photographs depict ing single crystals of compound [33] 191 Figure 4.29 Digital photograph depic ting a single crystal of compound [34] 192

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xvi Hierarchical Complexity in Metal-Organic Materials: From Layers to Polyhedra to Supermolecular Building Blocks John J. Perry IV ABSTRACT The design and synthesis of novel functiona l materials with fine-tunable physical and chemical properties has been an aspirati on of materials scientists since at least Feynman’s famous speech “ There’s Plenty of Room at the Bottom ” which has fittingly been credited with ushering in the nanotechnology era. Crysta l engineering, as the solidstate manifestation of supramolecular chemis try, is well positioned to make substantial contributions to this worthwhile endeavor. W ithin the realm of crys tal engineering resides the subdiscipline of metal-organic materials (MOMs) which pertains most simplistically to the coordination bond and includes such objects as coordination polymers, metalorganic frameworks (MOFs), and discrete ar chitectures, each of which share the common aspect that they are designed to be modular in nature. While metal-organic materials have been studied for quite some time, only recently have they enjoyed an explosion in significance and popularity, with much of this in creased attention being attributed to two realizations; that this inhere nt modularity ultimately results in an almost overwhealming degree of diversity and subsequently, that this diversity can give rise to effective control of the properties of functional materials. At long last the goal of a ttaining fine-tunablity may be within our grasp.

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xvii In addition to high levels of diversit y, MOMs are also characterized by a broad range of complexity, both in thei r overall structures and in the nature of their constituents. From the simplest molecular polygons to extended 3-periodic frameworks of unprecedented topologies, MOMs have the capac ity to adopt an array of structural complexities. Moreover, there has been a recent trend of increasing complexity of the very building blocks that constr uct the framework. It is the aim of the research presented in this dissertation to survey these two principle aspects of MOMs, diversity and complexity, by focusing upon the use of polycar boxylates and first row transition metals to synthesize several series of closely rela ted materials imbued with varied levels of complexity. Through the use of single crystal X-ray diffraction and th e charcterization of the materials’ properties, the structure-func tion relationship has b een probed. Finally, novel design strategies incor porating supermolecular building blocks for the creation of a new generation of MOMs has been addressed.

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1 Chapter 1 Introduction 1.1 Preamble “…What could we do with layered structures with just the right la yers? What would the properties of materials be if we could really arrange the atoms the way we want them? They would be very interesting to investigate th eoretically. I can't s ee exactly what would happen, but I can hardly doubt that when we have some contro l of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of diff erent things that we can do.” Richard P. Feynman1 December 29th, 1959 Caltech The modern synthetic chemist aspires to fathom the underlying principles, the governing dynamics of the natural world, precisely so that they may be able to intelligently design and subsequently synthe size novel materials incorporated with specific desired properties. The dream and long-term objective of these chemists and scientists of other related disciplines, is to wrest control over the dominion of matter, so that they might reshape and remold it with an eye toward dictating what the exact properties of those materials will be. It is be lieved that once we have gained sufficient ability to determine, on the atomic level, the structure of matter we will concomitantly inherent the ability to influen ce the properties of materials an d in turn vastly expand those things we can achieve.

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2 1.1.1 Crystals and Crystallochemistry “The thin snow now driving from the north and lodging on my coat consists of those beautiful star crystals,…How full of the crea tive genius is the air in which these are generated! I should hardly admire more if th e real stars fell and lodged on my coat…The same law that shapes the earth-star shapes the snow-star. As surely as the petals of a flower are fixed, each of th ese countless snow-stars come s whirling to earth, pronouncing thus, with emphasis, the number six. Order, (cosmos). Henry David Thoreau4 The inherent symmetry and immense beau ty that crystals exhibit has probably contributed to their being compelling objections of interest and desire since they were first discovered as naturally o ccurring gem stones or when man first took a closer look at snowflakes (Fig. 1.1).5, 6 Modern western science traditionally establishes the advent of scientific inquiry regarding crystals to be the works of Johannes Kepler (December 27th, 1571 – November 15th, 1630) or more specifically his treatise A New Year’s Gift, or On the six-cornered Snowflake.7 However, it is clear that goi ng back at least to the second century B.C. that the ancient Chinese were already well aware of the six-sidedness of these crystals.7 Figure 1.1 Photographs of snow crystals.

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3 Crystals, or a crystalline solid, is a material whose constituents in the form of atoms, molecules, or ions are arranged in an orderly pe riodic array which extends in three spatial directions. The term crystal is derived from the ancient Greek ( krustallos ) which literally meant ice or clear-ice. This stemmed from the fact that they believed crystals (namely rock crystal or quartz) to be a form of hardened water. In fact they used this term to convey meaning for anything that congealed by freezing, not simply for the chemical structure we know of today as water. The majority of matter in the natural world adopts a cr ystalline form upon solidifyi ng. The study of crystals and their internal structures was greatly aide d by the discovery of X-rays, a form of electromagnetic radiation w ith extremely small wavelengt h, by W.C. Rntgen in 1895. While predominately used in the medical sc iences for imaging inside the human body, Xrays have also been critical to the analysis of crystal stru ctures. The modern science of crystals, or crystallography8 was essentially established no t long after the discovery of this new form of electromagnetic radi ation, when in 1912 Max von Laue (1879-1960) suggested to Walter Friedrich and Paul Knipping, a resear ch assistant and a doctoral candidate at the University of Mnich resp ectively, that they attempt to pass X-rays through a crystal of copper sulfate and colle ct the pattern of spots that occur on a photographic plate. This was successful, and from a separate diffraction experiment involving zinc blende, von Laue was able to demonstrate that th e observed pattern of spots could only be caused by the diffrac tion of very short waves by a regular arrangement of atoms or molecules in the cr ystal. Not long thereafte r the Braggs, William H. Bragg and his son William Lawrence Br agg, extended this diffraction method to

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4 analyze the arrangement of atoms in common crystalline materials.9, 10 Since that time crystallography has steadily grown and fl ourished in its capacity to address the underlying atomic structure of crystalline materi als. Over time better X-ray sources were created resulting in better di ffraction of X-rays, but the ba sic photographic plate remained largely unchanged. Still the field made c ountless improvements and grand discoveries; the structure of some large proteins and the double helix nature of DNA being just a few. With the invention of the computer and the CCD detector however, the field has exploded and progressed to such a degree th at X-ray diffraction data acquisition and structure solution for small organic molecules is rather routine. In fact the larger companies which supply X-ray diffractometers and structure soluti on software already sell fully automatic, black-box lab bench X -ray diffractometers which can collect and analyze a sample entirely on its own. While th is has not been perfected, and may never be for more convoluted crystal structures, the pr ogress from just 50 years ago is astounding. Generally the importance of the crystallin e nature of some materials lies in the very fact that they are crystals; that they are construct of a peri odic array of their own constituents instills unto them the capacity to diffract X-rays. This ability to cause the diffraction of X-rays then give s rise to the happy happenstance that we can utilize such an observable (and recordable) phenomenon to discer n the structure of that material on the molecular level. With crystallography, we are ab le to view the structure of crystals down to atomic resolution, so that understanding the structure-property relationship in materials is greatly facilitated.

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5 1.1.2 Solid State Chemistry As the name suggests, solid state chemistr y is the study of matter which exists in the solid state under some set of conditions (temperature, pressure) in which the observations are conducted. More pointedl y, solid state chemistry comprises the synthesis, structural determination, charac terization, and investigation of the ensuing properties of both crystalline and amorphous materials. Traditionally, solid state chemistry has been very clos ely aligned with crystalline materials and crystallography, mainly due to the aspect that crystalline substances are often amenable to solid-state structure elucidation at a pr ecision level suitable for ev aluating structure-property relationships. Additionally, there are many proper ties of crystalline solids that arise solely due to the fact they exist as crystals, and indeed the extent to which some of these phenomena are observed (or are absent) can depe nd critically on the qua lity of the crystal in question. It is not impractic al, however, to also address the solid state chemistry of amorphous materials, which with no l ong range order can be somewhat more complicated when attempting to decipher exac t structural features. What makes solid state chemistry so attractive and essential is th e obvious realization that the vast majority of materials with prac tical importance in our current technological so ciety are solids at ambient conditions. This includes both amorphous (plastics, polymers, glasses, etc.) and crystalline examples of matter which have b een harnessed by mankind to fashion devices with useful applications; superconductors, in sulators, catalysts, magnets, optics, lasers, and ion conductors (batteries and fuel cells ) are just a small sampling of the types of valuable technologies that ha ve been developed with the aid of solid state chemistry.

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6 1.1.3 Nanoscience Just as the vast majority of the research that will be presented in this dissertation can be classified as belonging to the investig ation of solid state crystalline materials, so too can it aptly be described as a foray in to the broad field of nanoscience. Nanoscience pertains to the investigation of materials within a limited size scale, and the unique (and sometimes peculiar) phenomena and propert ies associated with those limitations. Nanoscience or nanotechnology11 entails materials that are within the scale range of between one and one hundred nanometers, where a nanometer (nm) is one billionth of a meter (10-9). A common analogy to the size comparis on between a nanometer and that of a meter is the size of a marble to that of th e Earth. Nanoscience in general has been an extremely popular and fast-growing field the last half of the 20th century, mainly due to the fact that it represents th e convergence of the major branch es of the natural sciences; physics, chemistry, and biology. While the la rgest impetus for the development of nanoscience and nanotechnology has been the goal of miniaturizat ion, perhaps more intriguing are the additional applications which hold the potential to revolutionize practically every aspect of our daily lives from medicine to electronics to energy production.

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7 1.2 Supramolecular Chemistry “ Supramolecular chemistry is a highly interd isciplinary field of science covering the chemical, physical, and biological features of the chemical species of greater complexity than molecules themselves…It’ s roots extend into organic chemistry and the synthetic procedures for molecular construction, into coordination chemis try and the metal ionligand complexes, into physical chemistry and the experimental and theoretical studies of interactions, into biochemistry and the biologic al processes that all start with substrate binding and recognition, into materials science and the mechanical properties of solids. A major feature is the range of perspectives offered by the cross-fertilization of supramolecular chemical research due to it s location at the intersection of chemistry, biology, and physics.” Jean-Marie Lehn12 1.2.1 History and Nature Supramolecular chemistry13-15, or as defined by Lehn12 as chemistry beyond the molecule, is the study of weak noncovalent inte ractions which arise between two or more separate molecular entities. The foundation of supramolecular chemistry lies squarely in the synthetic chemist’s desire to achieve the level of complexity and functionality displayed by nature itself. Foremost, supr amolecular chemistry in the context of both nature and the laboratory deals with the c oncept of molecular r ecognition. Molecular recognition is responsible for the existence of all complex chemical systems, not least of which is life itself. The manner in which two complimentary strands of DNA intertwine to form its characteristic double helix is a classic (and beautiful!) example. The way higher order (tertiary) struct ures of proteins can cons istently and spontaneously regenerate from their primary st ructures is another. While th is supramolecular chemistry developed by nature has existed for millennia, our ability to mimic nature and construct

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8 interesting supramolecular systems of our ow n is relatively infantile. It has only been since perhaps the turn of the last century that we have even thought of matter on terms that could be considered reconcilable w ith supramolecular chemistry. The works of Ehrlich16 (receptors and bi nding) and Fischer17 (lock and key molecular recognition) were seminal to the development of the this field. 1.2.2 Noncovalent Interactions In dealing with the chemistry of molecu les, the nature of the chemical bond is paramount. Seventy years ago, in his seminal and still influential masterpiece, Pauling18 put forth the collective ideas of the time re garding what exactly a chemical bond might be as well as to delineate their importan ce in governing the obs erved properties of molecules. It is of the utmost importance that the synthetic chemist has some grasp of the nature of these interactions, if one wishes to manipulate them for the sake of molecular synthesis. Simply put, molecular synthesi s is the breaking of these bonds followed by controlled rearrangemen t of atoms concluded only by the reformation of new, strong interactions that define the molecules. Analogous to the manipulation of covalent intramolecular bonds in the endeavor of mol ecular synthesis, is the need to understand and manipulate the noncovalent intermolecular interactions (supramolecular synthesis) responsible for the association of molecules in supramolecular assemblies. While Pauling classified three categories of chemical interaction which he grouped into three bond types (electrostatic, covalent, and metallic) and focused heavily on covalent intramolecular bonds, he also addressed the idea of a hydrogen bond, which inspired much of the

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9 groundbreaking chemical research that would lay the foundati on for the development of the field of supramolecular chemistry. The hydrogen bond is easily the most importa nt of all the noncovalent interactions found in supramolecular assemblies as it provid es a robust and perhaps more importantly directional interaction that can be harnessed for the ra tional synthesis of complex supramolecular architectures. It is however, onl y one of many different interactions to be classified as noncovalent (Table 1.1). Gene rally, noncovalent interactions run the gamut from being attractive to being repulsive in nature, and can range in strength from extremely weak to rivaling a weaker covalent bond. While any one noncovalent interaction may be rather weak, the key to supramolecular chemistry lies in the principle that it is extremely rare to observe a single interaction in a species. Rather the formation of a supramolecular entity is the result of the concerted interplay of many noncovalent interactions simultaneously.

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10 1.2.3 Supramolecular Isomerism A phenomenon of molecular chemistry that is closely paralleled in supramolecular chemistry is the concept of isomerism. In molecular species the ability of a compound (or element in the case of a llotropes; diamond, graphite, fullerenes, and carbon nanotubes) to exist in multiple forms is a commonly identified occurrence. On the molecular level, structural isomerism (sometim es referred to as constitutional isomerism) is the existence of more than one compound with the sa me molecular formula. In the context of supramolecular assemblies, and in particular polymeri c network structures (e.g. metal-organic materials), the concept of supramolecular isomerism is extremely salient. Zaworotko has defined supramolecular isomerism as the existence of more than Table 1.1 Common noncovalent interactions. Interaction Type Energy (kJ/mol) Examples Ion – Ion 100 350 Na+ Cl; complex ions; organic ions Ion – Dipole coordinate covalent bond M – L (M = transition metal; L = Lewis base) 50 200 Coordination complex; coordination polymer; Crown ethers binding metal cations Dipole – Dipole 5 – 50 Solid – state organic carbonyls Hydrogen Bond D-HA 4 – 120 DNA double helix; Secondary/Tertiary protein structures – Stacking face-to-face and CH 0 – 50 Graphite; DNA double helix; Benzene herringbone pattern van der Waals London dispersion exchange-repulsion < 5 Noble gases; Inclusion compounds

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11 one type of superstructure for the same molecular components or building blocks.19, 20 That is to say, two or more architectures constructed from identical metal ions and ligands, but arranged in uni que manners (Fig. 1.2). In observing the possibility of isomerism at the supramolecular level, and interpreting it in relation to isomerism at the molecular level, Zaworotko also identified several forms of supramolecular isomerism; when the same components lead to distinct architectures for the superstructure (structural), when the use of flexible ligands results in networks that can be consid ered topological equivalent while the ligands adopt unique orientations (conformational), when the supe rstructure has the ability to exist in Figure 1.2 Schematic illustrating the concept of supramolecular isomerism. Several distinct su p ramolecular architectures are p ossible from the same molecular com p onents.

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12 interpenetrated (interwoven) or non-interpenet rated forms, or interpenetrated to varying degrees and types of interpen etration (catenane), or finally when two superstructures composed of the same components are cons tructed into enantiomorphic frameworks which are chiral (optical). Supramolecular isomerism represents both a blessing and a curse from the vantage point of controlling su pramolecular structures. With an assortment of possible structures for the same buildi ng blocks, it may be difficult to elicit the overriding factors that dictate final structure, hampering our ability to control, on the supramolecular level, the architectures of the materials we make. Conversely, the susceptibility of these assemblies to the phenomenon of supramolecular isomerism will inherently lend itself to a dramatic amplifica tion of the diversity in what may be possible for us to synthesize. 1.3 Crystal Engineering “…crystal engineering, which is defined as the understanding of intermolecular interactions in the contex t of crystal packing and in th e utilisation [sic] of such understanding in the design of new solids with desired physical and chemical properties…The almost perfect alignment of molecules in an or ganic crystal results usually in highly predictabl e physical and chemical propert ies which in turn justify efforts at crystal engineering.” Gautam R. Desiraju21 1.3.1 History and Scope Crystal engineering21-24 is the rational unde rstanding of the in fluence noncovalent interactions have on the crysta l packing of molecules in th e crystalline state, and the attempt to parlay that understanding into a high level of control over the solid-state

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13 structure of materials. If we are to realize Feynman’s dream of being able to exquisitely control the arrangement of atoms (or molecules) at the most precise of levels then we must have a comprehensive understanding of all the factors which influence the materials’ structure. It is only when we have complete control over the structure of matter, that we will be fully able to dictat e the properties of those materials. As it is described here, it is clear that crystal engineering can be view ed as simply the solid-state manifestation of supramolecular chemistry a nd that many of the principles remain the same. The term crystal engineering was first used by Pepinsky25 in terms of crystallography, but perhaps the first use of th e term in a manner that is on par with its use today was by Schmidt, who used crystal engineering in relation to topochemical reactions. In the 1970’s, Schmidt22 was studying the photochemical dimerization of olefins (such as cinnamic acids), and came to th e realization that the nature of the crystal structure, in terms of crystal packing, was essential to the materials ability to react in the solid state. Whether a molecule was imbued with the functionality necessary for the reaction to take place is not th e only criteria for the reaction to proceed in the solid state; of equal importance is how the molecules are arranged with respect to one another in the crystal. In light of this u nderstanding, Schmidt proposed a new way of thinking about the crystal in which he aimed to be able to control the arrangement of molecules in the crystal structure so as to control their supr amolecular reactivity and termed this endeavor crystal engineering.

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14 In the later part of the 20th century Desiraju21, 26-42 and Etter43-52 were largely responsible for extending the field of crystal engineering. Desiraju extensively studied the presence and influence of weaker nonc ovalent interactions, such as CH••• and CH•••X interactions, in the crystal structures of small organic molecules. Etter was largely responsible for investigati ng the weaker noncovalent inte ractions observed in the crystallization of two or more different molecules into a single crystal and laid the foundations for the growing field of cocr ystallization, before her untimely death. 1.3.2 Cambridge Structural Database In parallel with the increasingly more powerful X-ray diffraction detectors and computer software used to process diffrac tion data and subseque ntly solve crystal structures has been the advent of another t ool which has quickly become indispensible to the modern crystal engineer. The early adopti on of databases designed to store, and more importantly, easily retrieve the crystallogr aphic data of a larg e number of crystal structures has been paramount to the success and rapid growth of this fledgling field. These databases provide the capability for the crystal engineer to su rvey a large segment of the known crystal structure population in a relatively short amount of time where ultimately they can contribute to the ability of recognizing pa tterns and discerning trends. The ability to recognize and then be able to exploit these patterns in the design of new crystal structures is essential to the goals and modus operandi of crystal engineering. Today there are several unique databa ses which are maintained and updated periodically with newly publis hed crystal structures. The Inorganic Crystal Structure

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15 Database (ICSD)53 is composed of nearly 120,000 purel y inorganic structures which have been peer-reviewed, including ove r 1,400 crystal structures of the elements. The Protein Data Bank (PDB)54 is a world-wide consortium of published 3D crystal structures of proteins and includes polypeptides and polysacch arides composed of at least 24 residues. The Nucleic Acid Database (NDB)55 is a repository of 3D structural information pertaining to nucleic acids. Th ere are even databases devoted to structures which have been elucidated solely from powder diffracti on data, such as the one maintained by the International Centre fo r Diffraction Data (ICDD).56 However, the standard bearer for the field of crystal engineer ing is easily the CSD. The Cambridge Structural Database (CSD)57 is the world’s preeminent repository for small molecules (i.e. excluding large biom olecules) containing or ganic carbon atoms. This would include the types of molecules wh ich fall into the classifications of small organic molecules, coordination com pounds (metal-organic materials), and organometallic compounds. Additionally, the st ructures contained in the CSD were determined from a variety of methods incl uding single crystal X -ray diffraction, powder X-ray diffraction, and neutron scattering. The CSD also retains other pertinent data related to the crystal structure (atomic coordi nates, angles, bond dist ances, etc.) such as chemical information, crystallographic information (spacegroup, X-ray experimental conditions, R-factor), and even bibliographi c information detailing where the crystal structure was originally publis hed, all which can be useful to the crystal engineer. To date the CSD contains nearly half a million crystal structures and is fully retrospective to 1923. Furthermore, in c onfluence with the adoption of X-ray

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16 crystallography for routine structural analysis and identification in the chemical sciences, the CSD has enjoyed exponential growth rate s over the last four decades (Figure 1.3).58 From the graph we can see clearly that the av erage number of crystal structures published has increased drastically over the years; the 1970’s (~ 2,400), the 1980’s (~ 6,300), the 1990’s (~ 13,400), the 2000’s (~ 28,400). What cannot be easily established however, from this graph is the nature of the materials whose crysta l structures were determined. A closer examination reveals that while the majority of the crystal structures added to the CSD in the 1970’s and 1980’s were small organic molecules, recently there has been a trend of predominately “inorgan ic” MOMs and organometallics. Out of the 494,228 structures deposited in the CSD, only just over 200,000 (~ 42 %) are considered purely organic. This dominance of the CS D by inorganic compounds, while a relatively Figure 1.3 Exponential growth of the Cambridge Structural Database since 1970.

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17 recent event, is also exposed by the fact that the peer-reviewed journal with the highest number of structures co ntributed to the CSD is Inorganic Chemistry The wide utilization of the CSD by those working with crystal st ructures has also been facilitated by the adoption of a standardized data format, th e Crystallographic Information File or CIF59, which is designed to be both computer a nd human readable and easily transferred electronically between individuals. The CIF format is supported by the International Union for Crystallography (IUCr)60, and is the standard data f ile used by the majority of peer-reviewed journals whic h publish crystal structures.61 1.3.3 Crystal Engineering vs. Crystal Structure Prediction Briefly, I believe it is important to clarify the seemingly mundane albeit critical difference between the conceptual ideas of crystal engineering (i.e. the design of crystalline solids) and that of crystal structure prediction19, 62-70. Crystal structure prediction is the more precise exer cise of the two, and entails the ab initio determination of the precise crystallographic data (inc luding space group, cell pa rameters, etc.) and exact packing details to be obser ved in a particular crystal structure. To achieve this there must be a high level of unde rstanding regarding the molecu lar recognition features of small molecule compounds and in turn an understanding of how these molecular recognition events will influence crystallograp hic symmetry operations (leading to space group determination). While great strides have been made in the area of crystal structure prediction, in general we are st ill unable to fully achieve th is endeavor. Currently, much work centers on the concept of analyzing a molecule and attempting to optimize how it close packs. This involves computer simu lations and energy minimization, and can be

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18 very useful in some simple instances. Howeve r, when dealing with flexible of relatively convoluted molecules thes e methods often fail. Crystal engineering on the other hand, is concerned with the supramolecular synthesis of solid-state structures. It aims to achieve reliable control over network structures and network prediction. The endeavor of crystal engineering is to generate a design and then implement that design, fo r the (supramolecular) synthesis of novel materials, and to do so with high fidelit y. There has been some consternation among researchers over the use of the term crystal engineering, as so me feel that what it defines does not truly represent engineering in the fu llest meaning of the word. However, these individuals are applying their own interpretation of what so me definition should mean to a concept that has already clea rly been defined. To then decr y that the subject matter does not hold up to what your expectations of it are, while it clearly accomplishes the goals delineated by its originators is I believe, somewhat fatuous. 1.4 Metal-Organic Materials “…’Tis but thy name that is my enemy. T hou art thyself, though not a Montague. What’s Montague? It is nor hand, nor f oot, nor arm, nor face. O, be some other name belonging to a man. What’s in a name? That which we ca ll a rose by any other word would smell as sweet…” William Shakespeare, Romeo and Juliet, (Act II, Scene ii)71 Metal-organic materials, or MOMs (Fig. 1.4), is an idiom adopted to represent a very broad and encompassing class of materials comprised of metal moieties and organic

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19 molecules which act as ligands. The name was chosen to be as general as possible, specifically because it is mean t to include a rather large population of known and as of yet unknown compounds under a single definitio n. In these materials, the organic molecule is connected to the metal ion via coordinate covalent bonds, and thus MOMs are squarely within the re alm of coordination chemistry. MOMs are exemplified by a diverse collection of compounds that can be either discrete or polymeric in nature. Currently, there is some cons ternation among active research ers in the field (and some outside observers) over the nomenclature us ed to describe th e structures being investigated. In the case of polymeric or pe riodic structures, names such as coordination polymers (CPs), metal-organic framewor ks (MOFs), porous coordination polymers (PCPs), and hybrid inorganic-orga nic materials have all been used to describe compounds which are essentially identical. When discussing discrete stru ctures, such names as metalorganic polyhedra (polygons), molecular ca psules, nanoballs, and molecular polyhedra (polygons) among several others have been us ed. The utilization of so many different terms to describe compounds that are so closely related has, at times, introduced confusion and ambiguity into the research field. 1.4.1 History and Relevance Whereas compounds which c ould accurately be descri bed as belonging to metalorganic materials have existed for several decades72-85 going back to Alfred Werner (1866-1919) and the establishment of coordina tion chemistry, it has on ly been since the early 1990’s that MOMs have garnered broa d attention from the scientific community.

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20 This renewed and increased interest may be due to several factors, chief among which would be that they are prototypal for a divers e range of materials that are amenable to the design strategies of crystal engineering. Additionally, MOMs are inherently modular in nature, they can be synthesized in “onepot reactions” through self-assembly making them facile to prepare, and quite often they are very aesthetically pleasing adding to their interest. Typically, MOMs are crystalline compounds, making the analysis of structureproperty relationships feasible for these material s. It is the very fact that MOMs represent a diverse class of crystalline compounds that are capable of being crystal engineered to fine-tune their structural feat ures and in turn investigate the effect on observed properties that make MOMs such attractive targets for materials chemists. Figure 1.4 The universe of metal-organic materials.

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21 In the early 1990’s the resurgence of metal-organic materi als (coordination polymers) was made possible by the influential works of R. Robson86-98, M. Fujita99-104, and S. Kitagawa105-113 among others114-126. These researchers utilized the so-called “node and spacer” approach to gene rate coordination polymers via the coordination of linear ditopic organic molecules to transition metal cations. The ma terials that they produced could be discrete (0-periodic molecular cage s), 1-periodic (chain s, ladders, etc.), 2periodic (layers or bilayers), or 3-periodic (i.e. diamondoid, Pr ussian blue, etc.) networks. One common thread among the work of these re searchers was that they all utilized single transition metal ions as the nodes and multi-topi c pyridyl type ligands in the construction of their frameworks. They judiciously select ed transition metals that adopted square planar, tetrahedral or octahe dral coordination geometries and paired them with linear bridging ligands to generate the extended structure. Early on it was apparent that these materials were to have interesting properti es that could be exploited for numerous potential applications, especi ally such properties as magnetism and porosity. It was a direct goal of these early researchers to devel op materials with the capacity to enclathrate small organic molecules, whether for chem ical sensing, separations (size and shape exclusion), or storage applica tions. However, a particularly daunting drawback to these early MOMs was the observation that gene rally speaking, materials constructed from single transition metal ions and bridging multi-topic pyridyl-type ligands were insufficiently stable to the removal of solvent and guest molecules in vacuo sometimes resulting in the collapse of the overall stru cture. This reality hampered the progress of

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22 these materials’ potential appl ications and directly contribut ed to the development of a new strategy for the fabricati on of metal-organic materials. A second generation of MOMs19, 63, 127-140 was ushered in upon the adoption of multiple metal clusters as the nodes of frameworks by Yaghi and co-workers. These multiple metal clusters were still predominately based on transition metals, but now involved ligands (i.e. carboxylic acids) capable of bridging th e metal ions together into stable complexes. In fact, these new node s were based on well known discrete metalorganic complexes (i.e. copper acetate, Basi c zinc acetate, etc.) where the original monocarboxylic acid is replaced with a ligand containing multiple carboxylic acids and capable of bridging the separate nodes. With the use of multiple metal clusters, the robustness of the structures was enhanced ul timately resulting in materials that were capable of being evacuated in vacuo which in turn contributed to their ability to be successfully probed for potential application. The realization that discrete and extended crystalline compounds were now obtainable, bo th as designer materials and robust in nature led directly to an explosion is rese arch activity and a bevy of research groups interested in the various applications of thes e materials. As a powerful visual illustration of this rapid growth, Figure s 1.5 depicts the number of results obtained when the query “coordination polymers” and “metal-organic frameworks” was entered and searched in the ISI Web of Science database.141

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23 1.4.2 Design Principles Perhaps the most imperative aspect of metal-organic materials is the perception that they can be designed from first pr inciples. While absolute control over the exact crystal structure may remain elusive, we do currently possess the ability to direct the Figure 1.5 Number of results for the search query “coordination polymers” ( top ) and “metal-organic frameworks” ( bottom) from ISI’s Web of Science database, broken down by country.

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24 general structural motif of a great many MOMs of interest Thus, it is often possible to dictate the structural details (topology, cavity si ze, pore shape, pore dimensions, etc.) of a particular material, by taking advantage of the modular nature of these materials. Once a blueprint has been established for the gene ration of a particular framework structure (topology), it is often possible to then amend the reaction conditions so as to incorporate new, different components (metal ions; or ganic ligands) that result in the same framework structure, albeit with augm ented dimensions or functionality. As the field of metal-organic material s progressed, several reliable methods of designing these materials emerged. The most obvious, unifying theme which connects these separate design strategies is the fact th at they are all geometrical in nature. As we shall unveil in the following sections, each st rategy involves the in terpretation of the frameworks as being constructed from smalle r geometrical shapes. The generation of new materials then becomes an exercise in is olating chemical moieties that can adopt particular geometrical shapes and determining how best to co mbine these structures into the overall frameworks. 1.4.2.1 Node and Spacer Approach The foundations for all that would follow, in regards to designing metal-organic materials, lie with the seminal works of A. F. Wells142-149, who introduced a simple and practical interpretation of peri odic inorganic crystal structur es. In Wells’ interpretation, individual metal ions were trea ted as nodes which were connected via linear spacers that represented bonding. An essential caveat of this “node and sp acer” (Fig. 1.6) approach to

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25 the interpretation of inorganic crystal structures is that th e resultant network topology is contingent on the geometry and coordinati on environment of the nodes alone, while the spacer unit is simply a linear bridge between adjacent nodes. Therefore, if one wished to target a diamondoid topology, it would be prudent to adopt a node that conforms to a tetrahedral geometry. Similarly, if one sought a square grid structure, then they should adopt a square planar node. Wells’ node and spacer approach can imme diately be used in the design and interpretation of metal-organic materials. As with purely inorganic compounds, the metal moiety of the MOM is treated as the node, wh ile in lieu of the bond the organic moiety (ligand) is regarded as the sp acer. By utilizing transition metals with easily controllable coordination geometries and rigid rod-like bridging ligands (i.e. 4,4 -dipyridyl), it became feasible to design and fashion a host of ma terials with unique topologies. This method demonstrated for the first time the effec tiveness of breaking an extended periodic structure down into unique nodes and determ ining how those nodes ar e connected, for the design of novel materials. Previous to th is point, the node and spacer approach was merely a method of interpreting a structure which had already exis ted, but now the same principles could be applied to the construction of new motif s. The adoption of the “node and spacer approach” leads dire ctly to the reemergence of coordination polymers, now as compelling targets for crystal engineers.

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26 1.4.2.2. Secondary Building Units Whereas the first incarnation of the “node and spacer” approach toward the design and synthesis of metal-organic materials dea lt almost exclusively with single transition metal ions as the so-called nodes, another design strategy emerge d not long thereafter which focused upon the utilization of relatively larger scale, multiple metal clusters as the structural building unit in both discrete a nd extended MOMs. In this design strategy, known discrete complexes composed of multiple metal centers bridged by appropriate ligands (typically carboxylates) were id entified and classified based upon their geometrical characteristics. In this method, the terminating monocarboxylates which hold the metal clusters together are seen as possibl e points of extension, where two or more of these clusters could possibly be linked if bridged by the appropri ate polycarboxylate. Figure 1.6 The node and spacer approach to metal-organic materials. Nodes of various coordination geometries (red) can be combined with linear spacers (b lue) to generate a range of topologically distinct networks. Top: Left & Center Angular 2-connected nodes can lead to 1periodic helices and chains. Right Hexagonal diamond (Lonsd alite) constructed from tetrahedral nodes. Bottom: Left Octahedral nodes generate Prussian Blue analogues. Center Cubic diamond constructed from tetrahedral nodes. Right 2-periodic square grid layers can be accommodated b y ado p tin g s q uare p lanar nodes.

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27 Essentially, this design strategy allows the cr ystal engineer to scour the literature for examples of known molecular complexes that adopt particular geom etrical patterns and then contemplate connecting these geometrical shapes together into networks by replacing the original monocarboxylates with a suitable polycarboxylate. Yaghi and coworkers were the first to describe this new strategy and named the new clusters secondary building units (SBUs)150-153 (Fig. 1.7) borrowing the term from the study of zeolites154-156. The implementation of the SBU design strategy has been important to the maturation of the field for several reasons. Th e most apparent contra st with the node and spacer approach is one of scale. While the node and spacer method does not explicitly demand single metal ions (and we shall see that tenets of this methodology are still responsible for the interpretation of structures composed of SBUs, as the SBU is simply treated as the node), in practice those who adopted the node and spacer approach early on in the development of MOMs typically ut ilized single metal ion nodes in their frameworks. With the inclusion of multiple metal clusters as the nodes upon which the frameworks are based, it was necessarily goi ng to result in nodes which are relatively larger in size than their single metal ion count erparts. In the case of a single transition metal ion, the size of the node is only the atom ic radius of the metal in question, whereas in the situation of a multiple metal cluster bridged by multiple carboxylates the size of the node can easily approach one or more nanometers (tens of ngstrms). When incorporating multiple metal nodes which are inhe rently larger, it follows that the scale of the framework itself (dimensions of channels volume of cavities, etc.) will also be augmented.

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28 In addition to the necessary increase in scale, the implementation of SBUs can also contribute to an increase in the robus tness of a framework. One common observation made about the use of SBUs in lieu of singl e metal ions was the relative increase in thermal stability. When Yaghi and co-workers began to investigate the use of SBUs in the generation of MOMs, they also discovered that the use of these rigid building blocks could often preclude framework collapse, increasing the likelihood that a framework could be made to undergo loss of guest and solvent molecules in vacuo which in turn increases the probability that the materials could be activated (as-synthesized occupants evacuated from within the framework cavities) due to the enhanced ri gidity demonstrated by these MOMs. Figure 1.7 Examples of commonly observed Secondary Building Units (SBUs) used in metalorganic materials. a.) Cupric acetate exists as a dimetal tetracarboxylate square paddlewheel cluster with formula [M2(O2CR)4L2] (M = transition metal, L = axial ligand) which can be viewed as a square. Basic Chromium(III) acetate, a 3-oxo trimetallic hexacarboxylate with molecular formula [M3O(O2CR)6] can be interpreted as either a triangle (b) or as a triangular prism (d). Basic Zinc acetate, which can be interpreted as a octahedron is a 4-oxo tetrametallic hexacarboxylate cluster with molecular formula [M4O(O2CR)6].

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29 Finally, in some instances, the use of secondary building units can have the added benefit of superior structural control. In many instances, th e geometry of a particular SBU can be either extremely hard to isolat e with a single metal ion because it prefers a small number of other more common coordina tion geometries, or virtually impossible to achieve as is the case for SBUs that adopt higher coordination numbers. By adopting SBUs the crystal engineer is able to ach ieve some geometries that entail high coordination numbers as well as un ique geometries that are just not feasible in the case of single transition metals. This pr ovides SBUs with a distinct advantage in that they can sometimes lead to framework structures that would previously be unattainable. Perhaps more importantly however, the method of secondary building units not only makes additional types of structures possible, it also demonstrates how to obtain those structures in a rational manner. 1.4.2.3 Molecular Paneling Another design strategy, especially for the gene ration of 0-periodic disc rete architectures, is based upon metal-directed self-assembly of so-called mo lecular panels. This design strategy is related to that of SBUs, in th at it aims to rationall y control the network structure which is obtained by taking advantage of the built in coordination geometry of the metal atoms. But whereas the principles of the secondary building unit strategy teach us to isolate known multiple metal clusters of specific geometry and then determine the most reliable methods of li nking those structures together using linear connectors, the

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30 design strategy of molecular paneling104, 157-164 involves single transition metal ions (with predictable or controllable coor dination geometry) as bridges by planar exo-multidentate organic molecules (i.e. mol ecular panels, Fig. 1.8). Typically the metal ions are chosen to be as reliable and facile to prepare as possible, removing much doubt over the possibl e outcome of the reaction. In many cases the Pd(II) ion, with its ub iquitous square planar ge ometry, is adopted in the cis -protected form, which thereby guarantees a nearly pe rfect 90 orientation fo r the coordination of the molecular panels. The angle here is impor tant because it represents a “turn” with respect to the orientation of subsequent molecular panels within a series. This “turn” is what is required to generate a convex hull seen in discrete molecular structures (Fig. 1.9). One salient feature to point out regarding mol ecular paneling is the realization that when linking planar multidentate ligands via coordination to metal ions (vertex-sharing as Figure 1.8 Common molecular panels.

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31 opposed to edge-sharing) the structure will i nherently be divided into regions of open windows and closed faces (the molecular panels themselves) so that any discrete structure fabricated based upon this strategy will have small openings possibly permitting access to the hollow interior of the structure. 1.4.3 Topological Analysis Metal-organic materials represent an extremely diverse co llection of possible compounds with an equally diverse assortment of potential structures. Additionally, as was seen in the previous section, they can be designed using any one of a number of strategies based principally upon geometrical concepts. Regardless of the design strategy employed, the underlying structure of the resultant MOM could span a truly immense range of possibilities, from simple 1-period ic chains to 3-periodic extended frameworks so complicated that they can only be dec onstructed with the aid of computers and powerful graphic software. Therefore, so me systematic method of analyzing the structures obtained will be needed so that we may be able to catalogue our results. And Figure 1.9 Schematic depicting the design principle of molecular paneling. Here a particular molecular panel in the shape of a tr iangle (2,4,6-tris(4-pyri dyl)-1,3,5-triazine) is combined with the approprtiate metal moiety to generate octahedral M6L4 cages. To generate this descrete strucutre, a “turn” of ~90 is needed and so the use of cis -protected Pd(II) is a judicous choice.

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32 just as we have seen that there is more th an one way to design a MOM, we will find that there are indeed multiple methods of analyzing the structures that are produced. However what they all do hold in common is that are all, to some extent, based on the ideas of mathematical topology. Loosely this means th at we are concerned merely with the connectivity of the nodes (in a topological sense, not necessar ily a chemical one), and are not interested in the geometrical aspects of the framework (i.e. lengths, angles, etc.). 1.4.3.1 Wells’ Notation Perhaps the simplest method of analyzing metal-organic materials topologically is a system that was first described by A.F. Wells.142-148 Wells, who had already deconstructed crystal structures into nodes and spacers which are then connected into a network (or net), found it rather easy to de scribe these structur es from a topological standpoint. In particular, We lls looked to identify polygons that were generated by the linking of the nodes and spacers. He then in troduced terminology to represent both the types of polygons and their numbers, which were incident to each node or vertex. By type of polygon he simply meant the number of sides ( n -gon) and did not restrict them to be regular (same length edges, identical angles). In Wells’ notation149 we write ( n p ) where n is the number of sides in the n -gon and p is the number of these n -gons intersecting at the same node. The three regular plane nets, shown in Figure 1.10, are a nice place to start in understand ing Wells’ notation.

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33 If we evaluate the effectiveness of an an alysis method by its ability to distinguish between two closely related albeit unique nets the notation created by Wells is rather straightforward and works perfectly well for si mple structures, especially those that are constructed from only a singl e type of node (uninodal).165 It should be mentioned that Wells’ methodology does not explicitly require the net to be uninodal, and in fact the notation is equipped to deal with binodal166, 167 nets quite easily using either the form ( ) or ( but if we then extend the scenario to three or more unique vertices the notation becomes very convoluted. When we begi n to delve into nets that are a bit more complex than the plane nets the method can quick ly become entirely ineffective. It turns out that there are often many examples of topologically unique nets that can obey the same simple ( n p ) notation, making another method of topological analysis, capable of discerning between these nets necessary. (3,6) (4,4) (6,3) Figure 1.10 Schematic depicting the only three regular plane nets; (3,6) triangle tiling, (4,4) square grid, and (6,3) honeycomb.

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34 1.4.3.2 Schlfli symbols Another method of topological analysis used for crystal structures in general (and MOMs in particular) is the idea of Schlfli symbols To explain how these symbols are derived, we will first need to be acquainte d with some basic terminology borrowed from mathematical graph theory.168, 169 The first convention that should be stressed is the use of the term n -periodic in lieu of the somewhat more common, but nonetheless incorrect n dimensional. Individuals often use the terms 1-dimensional (1D), 2-dimensional (2D), or 3-dimensional (3D) to describe the number of directions a structur e or network repeats. However this usage is incorrect for at leas t two reasons; in dea ling with real world objects such as molecules and atoms it is obvi ous that the materials we are describing are in fact all 3D, but more preci sely (and mathematically) it is incorrect because the word n dimensional defines another meaning alt ogether. In the world of graph theory n dimensional implies that the graph has an embedding (can be drawn) in three dimensional space. As it happens, all graphs are capable of being em bedded in three dimensions and are therefore 3-dimensional. Be tter is the use of the term n -periodic in trying to describe the number of independent directions in which a particular net has translational symmetry. A graph is a set of vertices (nodes) labeled i, j, ... and edges (spacer) which are simply line segments joining exactly two vertices ( i j ). It is possible to have more than one edge defined between the same two ver tices, as well as the case where there is a special type of edge between the same vertex ( i,i ) called a loop, but when a graph contains only one edge between any tw o vertices and no loops we call it a simple graph.

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35 Next we can talk of a path or chain as a sequence of vertices ( x1, x2, …, xn) linked by edges ( x1, x2), ( x2, x3), …, ( xn-1, xn). A circuit sometimes referred to as a cycle, is a closed path where the first and last vertices of the chain are identical, while a ring is a special circuit in which there are no shortcuts (F ig. 1.11). Finally, a graph is said to be connected if there exists at least one path between any two vertices. In crysta l chemistry, and for the purposes of this dissertation, the term net shall indicate a periodic connected simple graph.168 When deconstructing a crystal structur e we can assign individual atoms as vertices and the bonds between them as edge s. In more complicated circumstances we may wish to define a cluster of atoms as a single node and some ot her abstract notion as the edge linking the vertices together. Once the vertices and edges have been well defined, it is then possible to assign to each unique (unrelated by symmetry) vertex a socalled Schlfli symbol. To achieve this we analyze the net for the presence of the shortest cycles as opposed to the n -gons identified for the Wells’ notation. Since we are discussing cycles, we are limiting ourselves to closed paths that begin and end with the vertex in question. For a vert ex that is connected to n other edges ( n -connected in the parlance of chemistry, but not mathematics!) there will be n ( n -1)/2 different angles formed by the incident edges. It is precisely these angles where a possible cycle will be located and thus this is also the num ber of cycles one can expect for each n -connected vertex.

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36 In a 3-periodic connected graph there can be infinite number of cycles for a given vertex, and it is for this reason that we iden tify only the shortest such cycles for a given angle and ignore the remai nder. This Schlfli symbol170, sometimes referred to as a point symbol, takes the form Aa.Bb.Cc.[…].N n and is composed of the numbers A< B< C, …,
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37 three cycles to be generated from the co rresponding edges, and indeed we do observe these three cycles. In order of shortest cycle we observe one 4-gon, one 6-gon, and one 7gon making the correct Schlfli symbol for this vertex 41.61.71, where 1 + 1 + 1 = 3 = total number of shortest cycl es for the vertex. Typically we omit a superscript of one, thus making the symbol 4.6.7 for vertex 1. The Schlfli symbol represents a marked improvement over that of Wells’ notation, since it is equipped to deal with the common occurrence of more than one type of cycle ( n -gon) meeting at a vert ex. It is however, not without some drawbacks. There still exist so me nets, which while they contain the same types and numbers of shortest cycles, remain topologically distinct. In these situations, Schlfli symbols fail to distinguish between the two nets. 1.4.3.3 Vertex symbols A topological method closely related to Schlfli symbols, but which has been modified to better distinguish between nets that might have the same types and numbers of shortest cycles for a given vertex (and he nce the same Schlfli symbol) is one that is based upon identifying the shortest rings occurring in the structure. This method, based solely upon the use of shortest rings, results in what is called a vertex symbol for each unique vertex. Vertex symbols are currently the favored me thod of topological analysis for metal-organic materials. In this notation, we write Aa•Bb•Cc•[…]•Nn where A, B, C, …, N represent the length of the shortest rings and a, b, c, …, n represent the total number of those sized rings fo r that vertex. It is important to point out that the total number of coefficients (large numbers spaced by bullets) is always equal to the number of angles for an n -connected vertex so that for a 3connected vertex the symbol would

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38 resemble Aa•Bb•Cc while for a 4-connected vertex we would expect Aa•Bb•Cc Dd•Ee•Ff. This notation is equally valid for higher coordination numbers but is somewhat less frequently used. In the case of 5-connected or 6-connected vertices we would have a symbol with 10 or 15 elements respectively, whereas with a 12-connected vertex (which is by no means unheard of) the vertex symbol would have 66 elements, much too many to be of any practical use to write out by hand. There are also examples of topologically independent nets which are represented by identical vertex symbols for each of their unique vertices, but this is decidedly less common than that of the Schlfli symbol. In these circumstances we can go to another common method of topological analysis to dist inguish between two closely related nets. For each unique vertex in a net we can de termine its coordination sequence (CS) and topological density (TD10). The coordination sequence of a vertex is simply a sequence or listing of the kth topological neighbors {n1, n2, n3, …, nk}of a particular vertex. The kth neighbor of a vertex is any other vertex wher e the shortest path between the two vertices is of length k (Fig. 1.12). The topological density is simply the sum of the first k neighbors of a particular vertex, and while there is no set rule, we typically look at the first ten neighbors to sufficiently distinguish two vertices. A nice example showing how coordination sequences and topological density can help resolve the differences in two closely related nets is the case of diamond and Lonsdale ite. Lonsdaleite is the hexagonal form of diamond173, which has only been observed naturally in meteorites that have fallen to earth.

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39 The high temperatures and pressures invol ved in a meteorite’s descent from the heavens causes graphite in the meteor to tr ansform into diamond, albeit retaining the graphite’s hexagonal crystal lattice. Both diamond (cubic diamond) and Lonsdaleite (hexagonal diamond) have the vertex symbol 62•62•62•62•62•62 for their one unique vertex. However, as illustrated in Table 1.2, their coordination sequences (CS) and topological densities (TD10) are distinct. Unfortunately, there is no guarantee that two unique nets will not have identical coordinati on sequences, merely the fact that if their coordination sequence is different it must imply the two nets are indeed themselves different. A prominent example of two different nets which have the same CS would be the nets which underlie the structures of the two zeolites RHO and LTA Figure 1.12 Schematic illustrating the concept of kth-topological neighbors. The central vertex (blue) is directly adjacent to its first (nearest) neighbors (col ored yellow) which have a shortest path length of 1 unit i.e. k = 1. The second neighbors (colored green) to the central vertex are those who have a shortest path length of exactly k = 2, and are themselves the first neighbors to a first neighbor of the central vertex. We note that the topological density decreases from left to right: TD2 = 18, 12, and 9 res p ectivel y

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40 Table 1.2 Comparison of the coordination sequence (CS) and topological density (TD10) for diamond and Lonsdaleite nets. k 1 2 3 4 5 6 7 8 9 10 TD10 diamond 4 12 24 42 64 92 124 162 204 252 981 lonsdaleite 4 12 25 44 67 96 130 170 214 264 1027 Difference 0 0 1 2 3 4 6 8 10 12 46 1.4.3.4 RCSR and net enumeration More recently, a universal system of nomenclature w ith which to identify and classify nets has been proposed and widely adopted. In this system each unique net is provided with an independent three letter sym bol which is always presented in bold font and is modeled after the symbol names given to the various zeolite topologies. While the zeolite symbols were comprised of three cap ital letters in bold, the Reticular Chemistry Structure Resource (RCSR)174 symbols are always comprised of lower case letters. In fact all but two of the zeolite codes have been adopted in the RCSR system, where capitalization is replaced with the identical albeit lowercase letters. In addition to the standard three lowercase bold letters, there is also the possibility of a net requiring an extension to its RCSR symbol name. These ex tensions allow closely related, but still topologically different nets to be given a name showing their relation. Some common extensions that can be ame nded to an RCSR symbol are; –a for an augmented net where the vertices of the original net are replaced with a cluster of vertices the shape of the original coordination figure of the vertex, –b for the binary (binodal) version of a net that was originally uninodal, –c for when a net undergoes catenation (interpenetration), –d for the dual of a particular net (when a net is se lf-dual the original nets symbol and the one

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41 extended with a –d are both correct), and –e which is used to signify the so called edge net obtained by replacing each edge with a ne w vertex and then linking the new vertices to form a net. Along with the universal symbols which can be used to “name” a particular topological net, a se archable database has been de veloped that can be used to investigate nets and their relationshi ps to one another. The RCSR Database175 currently has over 1600 identified nets and includes such information as the space group (i.e. symmetry), unit cell parameters, vertices locations, and the natural tiling for the net, as well as exportable files which can be used to investigate the tiling in 3dt a superb graphical program developed by Olaf Delgado-Friedrichs.176 1.4.4 Properties and Applications of Metal-Organic Materials Metal-organic materials are clearly an intriguing class of compounds that very often represent entirely new forms of matter. They can be intelligently designed based upon first principles to include specific mo lecular components and to adopt particular topologies or superstructures, typically w ith high fidelity. Metal-organic materials are usually crystalline in nature, and are theref ore amenable to preci se structure solution. Additionally, MOMs can of ten be imbued with extraordinary levels of intrinsic symmetry and stunning beauty. All of these features ma ke metal-organic materi als attractive targets for solid state chemists, but even taken together they still fail to adequately explain the explosive growth the field has witnessed in the past two decades (Figs. 1.5 and 1.6). Perhaps the most significant aspect of metal-organic materials remaining, and the apparent motivation for this observed escalation in scientific interest, pertains to these materials physical and chemical properties.

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42 The properties of metal-organic materials, and the ensuing potential applications, are both numerous and varied. It is the very nature of th ese hybrid materials, being composed of both metal ions and organic molecules, which make their observable properties so potentially diverse. Both the metal and the organic moiety can separately contribute to the materials observed propertie s, or in special circumstance, they can combine to result in the desired effect. On top of the fact that they c ontain metals, with all of the intriguing prospects th at arise upon introducing those metals’ properties into the final material, many MOMs are also extended frameworks with cavities whose shapes and dimensions can be tailored by the crysta l engineer. Indeed, many MOMs, especially those constructed using SBUs, have been demonstrated to be permanently porous153, 177184, indicating that they are amenable to the removal of guest and or solvent molecules from within their cavities. W ith the ability to generate customized cavities and channels within a crystalline material with an extende d framework structure, the crystal engineer can now contemplate the prospect of encap sulating new molecules in these chambers. Both the presence of metal ions, and to a lesser extent the incorporation of specific functional organic ligands, and the existence of made to order cavities provide for the majority of the propertie s sought after in MOMs. Perhaps the single most sought after prope rty of metal-organic materials is the sorption of gases153, 179, 180, 185, 186 in general and that of molecular hydrogen gas184, 185, 187198 in particular. The storage of molecular hyd rogen holds great potential for its use as a clean renewable energy source as a direct fuel or for its use in fuel cells. The U.S. Department of Energy (DOE) has established se veral guidelines such as sufficient weight

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43 percent (2010: 2 kWh/kg, 6 wt %; 2015: 3 kWh/kg 9 wt %), percent volume (2010: 1.5 kWh/L; 2015: 3 kWh/L), and cost (2010: $4/kW h; 2015: $2/kWh) as well as other factors such as rate of re fueling/release of H2 and appropriate levels of safety in an attempt to direct research efforts in the area of hydrogen storage.199 In terms of money (grants, centers of excellence, etc.), time, and effort (i.e. the number of di fferent research groups tackling the same challenge simultaneously), hy drogen storage is by far the most invested potential application concerning metal-organic materials, and justly so, because if any material, be it a MOM or ot herwise, should be demonstr ated to sufficiently and efficiently demonstrate the outlined goa ls prescribed by the DOE it will truly revolutionize the world. In terms of the presence of metal ions perhaps the most obvious property which might be instilled into a MO M would be molecular magnetism.108, 200-209 By introducing metal ions which are magnetically active, it should be possi ble under the correct conditions to synthesize mate rials that are themselves magnetically active, potentially leading to solid state magnets with fine-tuna ble magnetic responses. It is not sufficient however to merely include the so-called magne tic moment carriers, be they paramagnetic metal ions or open-shelled organic molecules which will act as ligands. Magnetism, as a cooperative phenomenon, requires an exchange between these magnetic moments, thus magnetism requires the moment carriers to be brought within proximity to one another, a feat which can be often be achie ved in metal-organic materials.200 To date the majority of magnetic MOMs have been synthesized utilizin g paramagnetic first-row transition metals such as V, Cr, Co, Mn, Fe, Ni, and Cu. Additi onally, it may also be possible to introduce

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44 magnetic centers as the guests that occ upy the open cavities of a MOM while the framework itself is essentially non-magnetic. Another interesting potential application concerning the magnetic properties of a particul ar MOM would be the ability to fashion a sensor based upon fluctuations in magnetic response that might be induced by the presence of various guest molecules. In addition to magnetism, metal ions can also impart into the framework centers of catalytic activity210-221. Interestingly, one of the very fi rst applications proposed for the crystalline metal-organic materials was their use as heterogeneous catalysts90, which was quickly demonstrated in the cas e of cyanosilyation of aldehydes.100 More so than simply the presence of catalytically active open me tal sites where the catalytic process might take place, MOMs also hold the capacity to be useful catalysts through several other methods. First, the catalytic site might be in corporated into the st rut of the framework via a metalloligand. It is also po ssible to encapsulate into the open cavities of extended MOMs either molecular species or larger cluste rs which act as the catalytic sites, as was eloquently demonstrated by Eddaoudi and co-workers222 when they encapsulated a metalloporphyrin into the la rge cavity generated in one of their Zeol ite-like Metalorganic frameworks (ZMOFs). Finally, in a small number of cases213, 215, 223 porous MOMs have also been shown to act as cat alysts without the ai d of metal centers. Rosseinsky and co-workers223 have demonstrated a situation in which an amino acid can be judiciously situated in a MOM such that it’s carboxylic acid can remain uncoordinated and be selectively protonated with the use of HCl. This carboxylic acid is then able to act as a Brnsted acidic catalyst. The idea to ta ke advantage of MOMs as new heterogeneous

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45 catalysts was a lucid extension of the relations hip they hold with zeol ites, another class of solid state porous materials. Early on it wa s apparent that MOMs were analogous to the structures of zeolites, so that it was only reas onable to speculate that one of zeolites’ most prolific characteristics and a pplications, namely catalysis, might also be an enticing prospect for metal-organic materials. Another example of a property seen in MOMs which can be related to the presence of particular metals, at least in some instances, is the phenomena pertaining to several forms of emissivity (fluorescence, phosph orescence, and scintillation), broadly entitled as luminescence.131, 133, 224-233 In addition to metal-based emission however, there is also the possibility of the luminescen ce originating from ligand-localized emission, metal-to-ligand charge transfer (MLCT), lig and-to-metal charge transfer (LMCT), or emission from guest molecules adsorbed into the cavities of extended MOMs. Luminescence properties in metal-organic materi als are interesting both as an avenue of basic science directed towa rds understanding MOMs in general as well as the latent application of monitoring the modulation of observable luminescence phenomena in relationship to the uptake or release of specific guest molecules, i.e. sensing via luminescence. As opposed to the influence of the meta l component in the de termination of the observed physical properties of metal-organic ma terials, the nature of the organic spacer, both in its own functionality and in the way it dictates the dimensions and shape of the cavities and channels of extended MOMs, can also have a significant effect on observable properties. Indeed some properties can be achieved regardless and unmitigated by the

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46 nature of the metal ion present. For example the principle of size or shape exclusion is currently an attractive target for the manuf acture of MOMs with the ability to separate and purify small molecule orga nics (solvents and gases).100, 110, 226, 234-238 Currently, one very active area of research related to size selectivity is the goal of CO2 sequestration to slow (or start to reverse) the deleterious eff ects that this and other green house gases are having on the environment. These abilities may also lead to novel materials with the potential to be efficient decont aminates (i.e. water or soil remediation; nerve, chocking, or biological agent sequestration) which can be used to clean up hazards caused by mankind. Non-linear optical behavior (NLO) is a nother phenomenon which can be seen in appropriately engineered metal-organic materials.239-245 NLO pertains to the behavior of electromagnetic radiation (light ) in the presence of material whose dielectric polarization responds nonlinearly to the electric field, otherwise cal led non-linear media. NLO properties cover a range of phenomena, but the most common involve the concepts of frequency mixing. Common forms of fre quency mixing include Second Harmonic Generation (SHG, frequency doubling), in whic h the light’s wavelength is reduced by half, Third Harmonic Generation (THG) where th e wavelength is a th ird of the original, Sum Frequency Generation (SFG), where two light of two different frequencies are combined to form light with a frequenc y equal to the sum, Difference Frequency Generation (DFG), among many others.241 A critical requirement for the observation of NLO properties in MOMs is that the material crystallizes into a noncentrosymmetric spacegroup. It also helps to insure that th ere are efficient electron donor and electron

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47 acceptor moieties linked via a conjugated bridge, as well as adopting metal chromophores which will largely allow light to pass through the material without being adsorbed (i.e. high transmission rate), because what good is a noncentrosymmetric material with nice potential for NLO properties if it cannot efficiently transmit the light that is passed through the material. Generically, metal-organic materials ar e becoming increasingly plausible as functional assets for useful applic ations within industrial settings.127, 238, 246-251 Another intriguing challenge for the field of metal-or ganics rests with the desire to fabricate MOMs into thin films252-257, as opposed to bulk crystalline powders, mainly due to the fact that before many of these materials can be fashioned into any type of practical device, they must first be rendered into func tional thin film coatings which can interface with the electrical components. As more MOMs are designed and synthesized to exhibit specific physical and chemical properties, and as those properties are successfully translated from the bench-top to the market place, the impetus will only continue to grow. Undeniably we have only just begun a ne w golden age of metal-organic materials; increasingly our ability to impart explicit de sirable properties into engineered crystalline mater is equally matched by our ability to subsequently fabricat e useful devices.

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48 Chapter 2 Two-Periodic Layered Structures 2.1 Introduction In terms of their complexity 2-periodic metal-organic materials are inherently more intricate than that of a discrete 0-periodic polygon or a 1-periodic st ructure in the form a chain, ladder, or helix. By definiti on a 1-periodic structur e propagates in only a single spatial directi on. Topologically, the 1-perioidc st ructures are all reducible to chains, in which each node is 2-connected. Th erefore the only variation afforded to these materials is based upon geometry; the angles and conformations of how the next building unit is oriented with respect the one before it is the only possible variable. However, in the case of the 2-periodic struct ures, while the variation in geometry is still a viable option, now several possible inte rconnections of nodes (i.e. the shapes they make in linking together) can also have a profound infl uence on the structure which is generated and in turn affect the prop erties of the material. 2.1.1 Clay Mimics Commonly, 2-periodic archit ectures are referred to co lloquially as layered or lamellar structures. This is because inevitably their topologies are described by planar

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49 networks; the simple connected graphs wh ich represent their connectivity can be embedded in These materials closely resemb le naturally occurring clay-like materials, which also exist as individual la yers closely stacked one upon another to build up the bulk material. Graphite is another part icularly relevant material which is an example of a layered structure. The properties of 2-periodic layered mate rials can often mimic the action of clays. One notable property exhibited by clay-like compounds is their ability to expand; the ability for the layers to move apart for th e intercalation of guest s. This makes clays excellent natural filters capable of removing ions and small molecules from water sources as they pass through the clay material, ensu ring their purification. We can thank clays and related materials for the part they play in f iltering and purifying water as it seeps into the ground and is passed ultimately to the water aquifer. Many researchers working with 2periodic structures early in their development looked to the classical properties of clays as good targets for applications which could be applied to these types of metal-organic materials. 2.1.2 Common Topologies The simplest 2-periodic topologies are those which are constructed from only one type of node and one type of polygon. When the sing le type of polygon is also regular, the resultant tiling (covering) of the plane is also call ed a regular tiling. These can often be referred to as platonic tilings, in a manner an alogous to the concept of platonic solids.

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50 There are exactly three regular tilings for a plane: the (3,6) triangular lattice composed of 6-connected nodes, the (4,4) square lattice co mposed of 4-connected nodes, and the (6,3) honeycomb lattice composed of 3-connected nodes (Fig. 2.1). The next step up in complexity for 2-peri odic topologies would be the situation in which there is still only a singl e type of node (vertex transiti ve), but now more than one type of convex polygon is formed at the inters ection of vertices. Th is type of tiling is deemed to be semi-regular (Archimedean) and th ere are exactly eight of them (Fig 2.2). 2.2 Kagom Lattices (3.6.3.6) One of the more interesting 2-periodic t opologies is that of the so-called Kagom lattice. This lattice is constr ucted from a single type of 4-c onnected node so as to generate a net with (3.6.3.6) topology. This means that it contains both triangular (two) and hexagonal (two) polygons meeting at each node in an alternating fashion. The name of this lattice comes from the Japanese word for a common type of bamboo basket weaving (Fig. 2.3). (3,6) (4,4) (6,3) Figure 2.1 Schematic depicting the only three regular plane nets; (3,6) triangle tiling, (4,4) square grid, and (6,3) honeycomb.

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51 2.2.1 Spin Frustration and Magnetism One of the principle reasons for so much interest in the Kagom lattice is the concept of spin frustration and its implicat ions for magnetism. Spin frustration occurs when a topology is situated in such a manner so that if spin moments are positioned at the vertices of the lattice they are unable to can cel each other out thr ough opposite alignment. Figure 2.3 Basket weaving depicting a Kagom lattice. Figure 2.2 Semi-regular plane tilings. Top (left to right): (34.6), (33.42), (32.4.3.4). Middle (left to right): (3.4.6.4), (3.6.3.6), ( 4.82 ) B ottom ( le f t to ri g ht ) : ( 3.122 ), ( 4.6.12 )

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52 As an example take a simple equilateral tria ngle (Fig 2.4). If you we re to begin placing spin moments at the vertices so that th ey could only adopt one of two possible orientations (up or down), you c ould effectively balance out th e charge of the first spin moment with that of the second. However when, you attempt to place the third spin moment, it becomes impossible to orient this spin so as to leave no net spin for the system. Thus spin frustration inherently l eads to interesting magnetic properties. The Kagom lattice130, 258-273 is one such lattice which exhibits spin frustration, and so is a very important 2-periodic topology for metalorganic materials and solid state materials chemists in general. 2.2.2 Structural Analysis 2.2.2.1 5-benzyloxy-1,3-bdc Kagom Lattices The first Kagom lattice that I synthesized was achieved with a functionalized version of a 1,3-benzenedicarboxylic acid (1,3-bdc), in which the 5th position was substituted with a benzyl ether group L1 (Fig. 2.5). In actuality, this ligand was Figure 2.4 A cartoon illustrating the concept of spin frustration.

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53 synthesized in an attempt to control the supramolecular isomerism observed by Zaworotko and co-workers272 when working with 1,3-bdc and Cu2+. It was observed that when attempting th e synthesis of metal-organic Kagom lattices from these components via room temperature slow diffusion/layering reactions, that multiple compounds were often obtained. Ca reful analysis of the possible structures afforded by the combination of dimetal tetracarboxylate square paddlewheel SBUs through an angle of 120 (aptly provided by th e use of the 1,3-bdc moiety) revealed that several of the structures could be distinguished by the location of where the 5th position of the 1,3-bdc ligand was locate d. In the case of the two 2-pe riodic isomers (square grids and Kagom), the 5th position of the ligand was oriented into the characteristic cavity of the respective networks; the relatively small square cavity seen in the square grid compounds, and the somewhat larger, albeit st ill restrictive hexagona l cavity observed in the Kagom structure. The ligand L1, was synthesized because it was believed to be too bulky for inclusion into either cavity and that steric hindr ance might help prevent the formation of either of these topologies, leav ing only 3-periodic stru ctures or preferably, the 0-periodic nanoball. These assumptions were incorrect, and the hexagonal cavity of Figure 2.5 5-benzyloxy-1,3 benzenedicarboxylic acid, L1.

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54 the Kagom lattice, or more aptly the hexagonal channels formed by the eclipsed stacking of subsequent Kagom layers were more than adequate to accommodate these pendent arms (Fig 2.6). In compounds [1] and [2], the Cu2+ and Zn2+ analogues generate nearly identical structures dictated by the nature of the 5-benz yloxy ligands. Both structures crystallize in the trigonal space group P-3, w ith nearly identical cell pa rameters (Appendix C-1 and C2). The 5-benzyloxy groups thread into th e hexagonal channels alternating up or down around the hexagonal ring in the orientati on they point. These benzyloxy groups thread deep into the center of the cavity, as ev ery first and third layer each contributing 3 benzyloxy groups, interact through six concerted CH••• interactions in a so-called sextuplet phenyl embrace (Fig. 2.7). The distance range observed for these CH••• interactions were measured to be within the range of 5.186 to 5.194 as measured from the centroid of one phenyl ring to the centroid of an adjacent ring. Figure 2.6 Cartoon illustrating the Kagom lattice ( left ) and the metal-organic Kagom lattice as seen in compounds [1] and [2] ( right ).

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55 The distance of interlayer separation betw een adjacent layers in these structures was observed to be ~9.63 in the case of Cu2+ and ~9.53 in the case of Zn2+, both corresponding to the length of the unit cell along the c -axis. Interestingly, the observed distance of interlayer separa tion for these two compounds is shorter than was observed in the case of the parent metal-organic Kagom lattice first reported by Zaworotko et.al.272 This is a strong indication that the existen ce of the sextuplet phenyl embrace has brought the layers closer together than would otherw ise be observed, indicat ing that the repeating pattern of these strong supramolecular motifs has aided the stability of these compounds. The bowl shaped triangular windows, as measure from the closest point of contact at the base of the bowl was observed to be 6.172 (not accounting for van der Waal radii) along the sides of triangle drawn from the carbon atom of one 1,3-bdc ligand to an adjacent one. Within this triangular bowl shap ed cavity resides disordered solvent, most likely MeOH. The diameter of the hexagonal cavity corresponds to the lengths of the aand baxes ~18.40 in the Cu2+ version and 18.48 in that of the Zn2+. Figure 2.7 Illustration of Sextuplet Phenyl Embrace as seen in compound [1].

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56 If the pyridine axial ligand is replaced w ith another pyridyl type base for the synthesis, other versions of the Kagom la ttice will be produced. The choice of the axial ligand (based upon its size) direc tly controls the length of the interlayer separation seen in these structures. In the case of the isoquino line, a base with an extra benzene ring on the end, the separation is farthest at ~12 . If an axial ligand is chosen which is in between the size of pyridine and isoquinoline, as is the case for 4-methoxypyrid ine, the interlayer separation is also intermedia te (~10.4 ). The Kagom skeleton however remains largely unchanged. What is affected however, in th e case of the benzyloxy derivatives is the sextuplet phenyl embrace. For this supramolecular motif to occur, the phenyl rings must be within the correct proximity of each othe r. In the case of both the 4-methoxypyridine and the isoquinoline, the presence of these en larged bases pushes the layers further apart due to steric hindrance and thus the phenyl ri ngs do not come within the required distance for the interactions to take place. Therefore in these structures [3-6] (Appendix C-3 – C6) the SPE does not occur. In the case of the 4-methoxypyridine base the interlayer separation is such that the benzyloxy groups cannot interact with any other free groups. In these structures the phe nyl rings are free to twist in the hexagonal channel and are disordered slightly in the crystal structure. In the case of the isoquinoline however th e layers are pushed apart to such an extent that the benzyl ethe r groups are able to interact with the isoquinoline groups attached to adjacent layers th rough predominately face-to-face stacking interactions (Fig. 2.8).

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57 2.2.2.2 5-hexyloxy-1,3-bdc Kagom Lattice Another derivative of the Kagom lat tice which was synthesized was the 5hexyloxy derivative. This structure was ge nerated though the self assembly of Zn2+ ions together with 5-hexyloxy-1, 3-benzenedicarboxylic acid, L3 (Fig. 2.8). {[Zn2(5-hexyloxy-1,3-benzenedicarboxylate2)(4-picoline)2]3}n, compound [7] crystallized with nearly identical cell parameters as other Zn2+ versions of the Kagom lattice; this compound crystallized in the Trigonal P-3 space group with unit cell dimensions of a = b = 18.9529(6) , c = 10.7825 (7) , V = 3354.3(3) 3, and Z = 3. As Figure 2.9 5-hexyloxy-1,3-benzened icarboxcylic acid, L3 Figure 2.8 Illustration of the face-to-face stacking interactions observed in compounds [5] and [6].

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58 with the other examples of Kagom lattice, especially the Zn2+ versions which all adopt slightly larger unit cells when comparing the same 1,3-bdc and ax ial ligands due to a slightly larger SBU, this vers ion of Kagom contains the ba sic skeleton of the lattice in which hexagons and triangles meet at a co mmon vertex. As was the case for the other Kagom lattices, the dimensions of those cav ities are based upon the dimensions of the unit cell; the shortest distance in the bowl shaped triangular cavity is measured from the bottom of the metallocalix-[ 3]-arene from carbon to carbon on opposite bdc groups. At the bottom of the bowl these all point toward s each making this the bottleneck for the cavity and the dimension was measured to be 6.346 on each side of an equilateral triangle before taking into account van der W aals radii, which reduces the cavity further to ~4.0 , just big enough for small organic solvent molecules to occupy. Indeed, located within the triangular cavity but between layers are disordered o -dichlorobenzene molecules. Located with the larger hexagona l cavities are disorder alcohol solvent molecules. The hexagonal cavity dimensions correspond to the unit cell length in the a and b -axes (where the cavity lies) and was meas ured to be 18.953 , form center of the Zn-Zn internuclear axis of one SBU to anothe r. The interlayer separation (Fig. 2.9) for this compound again corresponds to the caxis length and is therefore ~10.78 (it adopts this distance in good agreement with the length of the axia l pillar as was seen in the benzyloxy Kagom lattices). The large hexagon al channels are filled with the hexyloxy pendant chains threading up and down the ch annel in a manner analogous to the benzyl ether moieties. The presence of these alkyl chai ns greatly alters the chemical nature of

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59 these channels. It is of littl e surprise that the only good qua lity crystal for this ligand came from the use of 4-picoline, given th e nature of the alkoxy pendant chains. 2.2.3 Experimental 2.2.3.1 Synthesis All reagents, unless described otherwise, were purchased from either SigmaAldrich or Fischer Scientific and used as received without further purification. Bulk solvents such as methanol, ethanol, acetone, and dichloromethane were first distilled and stored over drying media (4 molecu lar sieves) before their use. 5-Benzyloxy-1,3-benzenedicarboxylic acid, L1 (Fig. 2.5), was synthesized from commercially available dimethyl-5-hydr oxy-1,3-benzenedicarboxylate and benzyl bromide via established procedures fo r the arylation of phenols.274, 275 In a typical reaction dimethyl-5-hydroxy-1,3-benzen edicarboxylate (5.00 g, 0.0238 mol) and Figure 2.10 Stick representation of {[Zn2(5-hexyloxy-1,3-benzenedicarboxylate2)(4-picoline)2]3}n compound [7]. a.) a view down the c -axis illustrating the presence of the hexyloxy side chains protruding into the center of the hexagonal cavity. b.) A scheme dipicting the interlayer separation and packing of subsequent layers in compound [7].

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60 potassium carbonate (K2CO3, 9.88 g, 0.0715 mol, 3 equivale nts) were weighed out separately and dried on a vacuum pump for approximately three hours. A 3-neck round bottom flask was sealed with rubber septa and the air purged with N2 for 15 minutes prior to the start of the reaction. Upon drying the diester and K2CO3 were added to the 3-neck round bottom flask equipped with two rubber se pta and a cold-water condenser situated in a hot oil bath held at 80 C along w ith approximately 100 mL of dry acetone. The solution was allowed to reflux for 30 minut es before benzyl bromide (6.78 mL, 0.0571 mol, 1.5 equivalents) was added via syringe through a rubber septum. The reaction was allowed to reflux for approximately 12 hours be fore monitoring the extent of completion through TLC. After the reaction was determined to be complete the solution was cooled to room temperature, filtered through Celite, and the acetone solvent removed by heating under vacuum (Rotavap) leaving behind a dark yell ow oil which solidified upon cooling. This solid was dissolved in ~100 mL dichlorometh ane (DCM), transferred to a separatory funnel, washed three times with D. I. H2O, and dried over anhydrous Na2SO4. The DCM solvent was removed via rotavap and the solid recrystall ized from hot ethanol. The ester product crystals were collected via filtration and dried, upon whic h they were added to a NaOH solution (20% by volume, 3 equivalents to the ester) and allowed to stir with a magnetic stir bar on a hot plate until fully dissolved. The conversion from ester to carboxylate was monitored via TLC and upon completion was worked up with HCl (10 % by volume) added dropwise until the soluti on was acidic by pH paper. The precipitate was filtered, washed with D.I. H2O, and allowed to dry at which time 4.102 g (63.31 %

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61 yield) of white solid was obtai ned. The spectroscopic data for L1 (Appendix A-1, B-1) were consistent with previously reported data for this compound.276 All NMR spectra were analyzed using SpinWorks 3.1.211 1H NMR (250 MHz, Acetoned6, ): 5.3(s, 2H, -O-CH2-), 7.4(m, 3 H, -ArH), 7.6(d, J = 7.4 Hz, 2H, -ArH), 7.9(d, J = 1.44 Hz, 2H, -ArH), 8.3(t, J = 1.4 Hz, 1H, -ArH), 11.2(br, 2H, -COOH); mp 263-266 C (lit. 163-166 C). 5-(2-Naphthylmethoxy)-1,3-benzenedicarboxylic acid, L2 (Fig. 2.10), was synthesized form commercially available 2 -(Bromomethyl)-naphthale ne and dimethyl-5hydroxy-1,3-benzenedicarboxylate via established procedures for the arylation of phenols.274, 275 In a typical reaction dimethyl-5 -hydroxy-1,3-benzenedicarboxylate (5.00 g, 0.0238 mol) and potassium carbonate (K2CO3, 9.88 g, 0.0715 mol, 3 equivalents) were weighed out separately and dried on a vacuum pump for approximately three hours. A 3neck round bottom flask was sealed with rubber septa and the air purged with N2 for 15 minutes prior to the start of the reaction. Upon drying, the diester and K2CO3 were added to the 3-neck round bottom flask along with approximately 100 mL of dry acetone. The flask was equipped with two rubber septa and a cold-water condenser and situated in a hot oil bath held at 80 C. The solution was allowed to reflux for 30 minutes before 2(Bromomethyl)-naphthalene (5.79 g, 0.0262 mol, 1.1 equivalents) was dissolved in approximately 20 mL of dry acetone and adde d to the reaction mixture. The reaction was allowed to reflux for approximately 12 hours be fore monitoring the extent of completion through TLC.

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62 When the reaction was determined to be complete the solution was cooled to room temperature, filtered through Celite, and the acetone solvent removed by heating under vacuum (Rotavap) leaving behind a dark yellow oil which solidified upon cooling. This solid was dissolved in ~ 100 mL dichloromethane (DCM), transferred to a separatory funnel, washed three times with D. I. H2O, and dried over anhydrous Na2SO4. The DCM solvent was removed via rotavap and the solid recrystall ized from hot ethanol. The ester product crystals were collected via filtration and dried, upon whic h they were added to a NaOH solution (20% by volume, 3 equivalents to the ester) and allowed to stir with a magnetic stir bar on a hot plate until fully dissolved. The conversion from ester to carboxylate was monitored via TLC and upon completion was worked up with HCl (10 % by volume) added dropwise until the soluti on was acidic by pH paper. The precipitate was filtered, washed with D.I. H2O, and allowed to dry at which time 4.313 g (56.2 % yield) of white solid was obtai ned. The spectroscopic data for L2 is given in Appendix A2 and B-2. 5-(2-naphthylmethoxy)-1,3-benzenedi carboxylic acid was not observed to be present in SciFinder Scholar as either a product or a reactant. Figure 2.11 5-(2-naphthylmethoxy)-1,3-benzenedicarboxylic acid, L2.

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63 1H NMR (250 MHz, DMSOd6, ): 5.4(s, 2H, -O-CH2-), 7.6(m, 4 H, -ArH), 7.8(d, 2H, ArH), 7.98(m, 3H, -ArH), 8.0(s, 1H, -ArH), 8.1(t, J = 1.3 Hz, 1H, -ArH), 13.3(br, 2H, COOH); mp 254-260 C 5-Hexyloxy-1,3-benzenedicarboxylic acid, L3 (Fig. 2.8), was synthesized from commercially available dimethyl-5-hydroxy1,3-benzenedicarboxylate and 1-iodohexane via established procedures for the alkylation of phenols.277-279 In a typical reaction dimethyl-5-hydroxy-1,3-benzenedicarboxyl ate (5.00 g, 0.0238 mol) and potassium carbonate (K2CO3, 9.88 g, 0.0715 mol, 3 equivalents) we re weighed out separately and dried on a vacuum pump for approximately three hours. A 3-neck round bottom flask was sealed with rubber septa a nd the air purged with N2 for 15 minutes prior to the start of the reaction. Upon drying, the diester and K2CO3 along with approximately 100 mL of dry acetone were added to the 3-neck round bo ttom flask which was equipped with two rubber septa and a cold-water condenser situat ed in a hot oil bath held at 80 C. The solution was allowed to reflux for 30 minut es before 1-iodohexane (10.5 mL, 0.0714 mol, 3 equivalents) was added via syringe through a rubber sept um. The reaction was allowed to reflux for approximately 12 hours before m onitoring the extent of completion through TLC. When the reaction was determined to be complete the solution was cooled to room temperature, filtered through Celite, and the acetone solvent removed by heating under vacuum (Rotavap) leaving behind a dark yellow oil which solidified upon cooling. This solid was dissolved in ~ 100 mL dichloromethane (DCM), transferred to a separatory funnel, washed three times with D. I. H2O, and dried over anhydrous Na2SO4. The DCM

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64 solvent was removed via rotavap and the solid recrystall ized from hot ethanol. The ester product crystals were collected via filtration and dried, upon whic h they were added to a NaOH solution (20% by volume, 3 equivalents to the ester) and allowed to stir with a magnetic stir bar on a hot plate until fully dissolved. The conversion from ester to carboxylate was monitored via TLC and upon completion was worked up with HCl (10 % by volume) added dropwise until the soluti on was acidic by pH paper. The precipitate was filtered, washed with D.I. H2O, and allowed to dry at which time 3.428 g (54.09 % yield) of white solid was obtai ned. The spectroscopic data for L3 (Appendix A-3, B-3) were consistent with previously reported data for this compound.280 1H NMR (250 MHz, DMSOd6, ): 0.9(t, J = 6.3 Hz, 3H, -CH3), 1.2(m, 6 H, -CH2-), 1.7(m, 2H, -CH2-), 4.1(t, J = 6.4 Hz, 2H, -O-CH2-), 7.6(s, 2H, -ArH), 8.1(t, J = 1.4 Hz, 1H, -ArH), 13.3(br, 2H, -COOH).; mp 233-236 C (lit. 240 C). {[Cu2(5-benzyloxy-1,3-benzenedicarboxylate)2(pyridine)2]3}n [ 1 ] was synthesized under ambient conditions via a slow diffusion/ layering method. In a typical synthesis, 5-benzyloxy-1,3benzenedicarboxylic acid ( L1 ) (84.1 mg, 0.310 mmol) is dissolved in 10 mL of methanol (M eOH) and combined with 2 mL of odichlorobenzene and pyridine (0.08 mL, 1.00 mmol, 3.2 equivalents). Layered on top of this mixture was a solution of Cu(NO3)2 2.5H2O (69.7 mg, 0.299 mmol) dissolved in 7 mL MeOH, using a pure MeOH “blank” as a middle layer between the two solutions. The layered reaction was left undisturbed on the lab bench to al low for slow diffusion, and after two weeks green hexagonal plates suitable for single crys tal X-ray diffraction we re collected (96 mg, 77.77 % yield with respect to Cu).

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65 {[Zn2(5-benzyloxy-1,3-benzenedicarboxylate)2(pyridine)2]3}n [ 2 ] was synthesized under ambient conditions via a slow diffusion/ layering method. In a typical synthesis, 5-benzyloxy-1,3benzenedicarboxylic acid ( L1 ) (81.5 mg, 0.299 mmol) is dissolved in 10 mL of methanol (M eOH) and combined with 2 mL of odichlorobenzene and pyridine (0.08 mL, 1.00 mmol, 3.3 equivalents). Layered on top of this mixture was a solution of Zn(NO3)2 6H2O (89.1 mg, 0.300 mmol) dissolved in 7 mL MeOH, using a pure MeOH “blank” as a middle layer between the two solutions. The layered reaction was left undisturbed on the lab bench to al low for slow diffusion, and after two weeks colorless hexagonal shaped rods suitable fo r single crystal X-ray diffraction were collected (107 mg, 86 % yiel d with respect to Zn). {[Cu2(5-benzyloxy-1,3-benzenedicarboxylate)2(4-methoxypyridine)2]3}n [ 3 ] was synthesized under ambient conditions via a slow diffusion/ layering method. In a typical synthesis, 5-benzyloxy-1,3benzenedicarboxylic acid ( L1 ) (83.2 mg, 0.306 mmol) is dissolved in 10 mL of methanol (M eOH) and combined with 2 mL of odichlorobenzene and 4-methoxypyridine (0.10 mL, 1.00 mmol, 3.3 equivalents) Layered on top of this mixture was a solution of Cu(NO3)2 2.5H2O (69.7 mg, 0.299 mmol) dissolved in 7 mL MeOH, using a pure MeOH “blank” as a mi ddle layer between th e two solutions. The layered reaction was left undisturbed on the lab bench to allow for slow diffusion, and after two weeks green hexagonal plates suitable for single crystal X-ray diffraction were collected (65 mg, 43.2% yiel d with respect to Cu). {[Zn2(5-benzyloxy-1,3-benzenedicarboxylate)2(4-methoxypyridine)2]3}n [ 4 ] was synthesized under ambient conditions via a slow diffusion/ layering method. In a typical

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66 synthesis, 5-benzyloxy-1,3benzenedicarboxylic acid ( L1 ) (80.2 mg, 0.295 mmol) is dissolved in 10 mL of methanol (M eOH) and combined with 2 mL of odichlorobenzene and 4-methoxypyridine (0.10 mL, 1.00 mmol, 3.4 equivalents) Layered on top of this mixture was a solution of Zn(NO3)2 6H2O (90.1 mg, 0.303 mmol) dissolved in 7 mL MeOH, using a pure MeOH “blank” as a mi ddle layer between th e two solutions. The layered reaction was left undisturbed on the lab bench to allow for slow diffusion, and after two weeks colorless blocks suitable for single crystal X-ray diffraction were collected (115mg, 87.75 % yiel d with respect to Zn). {[Cu2(5-benzyloxy-1,3-benzenedicarboxylate)2(isoquinoline)2]3}n [ 5 ] was synthesized under ambient conditions via a slow diffusion/ layering method. In a typical synthesis, 5-benzyloxy-1,3benzenedicarboxylic acid ( L1 ) (88 mg, 0.323 mmol) is dissolved in 10 mL of methanol (M eOH) and combined with 2 mL of odichlorobenzene and isoquinoline (0.12 mL, 1.00 mmol, 3.1 equivale nts). Layered on top of this mixture was a solution of Cu(NO3)2 2.5H2O (67.8 mg, 0.292 mmol) disso lved in 7 mL MeOH, using a pure MeOH “blank” as a middle laye r between the two solutions. The layered reaction was left undisturbed on the lab bench to allow for slow diffusion, and after two weeks green hexagonal plates suitable for si ngle crystal X-ray diffraction were collected (76 mg, 82 % yield with respect to Cu). {[Zn2(5-benzyloxy-1,3-benzenedicarboxylate)2(isoquinoline)2]3}n [ 6 ] was synthesized under ambient conditions via a slow diffusion/ layering method. In a typical synthesis, 5-benzyloxy-1,3benzenedicarboxylic acid ( L1 ) (84.1 mg, 0.310 mmol) is dissolved in 10 mL of methanol (M eOH) and combined with 2 mL of odichlorobenzene

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67 and isoquinoline (0.12 mL, 1.00 mmol, 3.2 equivale nts). Layered on top of this mixture was a solution of Zn(NO3)2 6 H2O (69.7 mg, 0.299 mmol) disso lved in 7 mL MeOH, using a pure MeOH “blank” as a middle laye r between the two solutions. The layered reaction was left undisturbed on the lab bench to allow for slow diffusion, and after two weeks green hexagonal plates suitable for si ngle crystal X-ray diffraction were collected (90 mg, 65 % yield with respect to Zn). {[Zn2(5-hexyloxy-1,3-benzenedicarboxylate)2(4-picoline)2]3}n [ 7 ] was synthesized under ambient conditions via a slow diffusion/ layering method. In a typical synthesis, 5-hexyloxy-1,3-be nzenedicarboxylic acid ( L3 ) (81.3 mg, 0.305 mmol) is dissolved in 10 mL of methanol (M eOH) and combined with 2 mL of odichlorobenzene and 4-picoline (0.10 mL, 1.00 mmol, 3.3 equivale nts). Layered on top of this mixture was a solution of Zn(NO3)2 6H2O (90.1 mg, 0.303 mmol) dissolved in 7 mL MeOH, using a pure MeOH “blank” as a middle layer between the two solutions. The layered reaction was left undisturbed on the lab bench to al low for slow diffusion, and after two weeks colorless hexagonal shaped rods suitable fo r single crystal X-ray diffraction were collected (<10 mg, ~5 % yiel d with respect to Zn). 2.2.3.2 X-ray Crystallography Single crystals suitable for X-ray cr ystallographic analysis for compounds [1] – [7] were selected following examination unde r a microscope. Intensity data were collected on a Bruker-AXS SMART APEX /CCD diffractometer using Mo k\ radiation ( = 0.7107 ).281 The data were corrected for Lore ntz and polarization effects and for

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68 absorption using the SADABS program (SAINT).282 The structures were solved using direct methods and refined by fu ll-matrix least-squares on |F|2 (SHELXTL).283 Additional electron density, located in the void cavity sp ace, assumed to be disordered solvent, was unable to be adequately refined was removed using the SQUEEZE/PLATON program.284-286 Select crystallographic da ta is presented in tabular form in Appendix C-1 – C-7. 2.2.3.3 Powder X-ray Diffraction Powder samples suitable for powder X -ray diffraction, FT-IR spectroscopy, and Thermal Gravimetric Analysis were obtai ned by removing a large amount of single crystals from the reaction scintillation vial by using a glass Pasteur pipette and depositing these crystal (along with mother liquor) in a small concave agar mortar. Excess solvent was removed via pipette, and surface solvent was removed by wicking action with a Kim-Wipe. Upon wick drying, the crystals were tr ansferred to a small piece of filter paper which was subsequently folded over and they were dried further and slightly crushed with gently pressure. The resulti ng dry powder (~30 mg) was then immediately applied to a PXRD sample puck prepared with a small amount of vacuum grease to fixate the powder sample, and the PXRD experiment performed without delay. All of the Kagom lattice compounds were analyzed for their bulk purity via PXRD, except for compound [7] The synthesis of this compound, through slow/diffusion, layering methods, resulted in only a small amount of single crystals on the sides of the vials along w ith a large amount of powdery precipitate that settled along

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69 the base of the vial. PXRD analysis of the pow dery precipitate indicated that the material was amorphous. It was extremely difficult to is olate sufficient quantities of the material in a pure enough state to obtain a serviceable PXRD pattern. 2.2.3.4 FT-IR Spectroscopy All compounds, including synthesi zed ligands, were characterized via infrared spectroscopy using a Nicolet Avatar 320 Four ier-Transform Infrared Spectrometer (FTIR). Before each sample was analyzed, a background spectrum was obtained for purposes of zeroing out ambient noise in the form of the laboratory atmosphere. Each sample was measured in the range from 4000 cm-1 to 500 cm-1 wavenumbers (wavelength of 2500 nm to 20000 nm respectively) and scanned 64 times. Results were recorded in % transmittance and the spectrum analyzed using the EZ OMNIC (V.5.1b, copyright 1992199 Nicolet Instruments Corporation) computer software suite. A typical sample was a analyzed as a neat, dry solid (~10 mg) obtained via either vacuum filtration and air drying or gently drying with laboratory grade filter paper. The FT-IR spectrum (Appendix B-1) fo r 5-benzyloxy-1,3-benzenedicarboxylic acid L1, illustrates the same br oad featureless hump originating around 3300 cm-1 and bleeding into ~3000 cm-1 which is typical of carboxy lic acids involved in hydrogen bonding, which is to be expected in solid state samples such how the ligand was analyzed. The spectrum as contains a sharp strong band at 1685.95 cm-1 indicative of the carbonyl stretch of an aromatic carboxylic acid. There also exists a moderately strong and

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70 sharp band at 1030.20 cm-1 which I believe to be due to the presence of the ether functional group where the benzyl moiety attaches to the isophthalic ring. The FT-IR spectrum (Appendix B-2) for 5-(2-naphthylmethoxy)-1,3benzenedicarboxylic acid, L2, illustrates the same broad featureless hump originating around 3300 cm-1 and bleeding into ~3000 cm-1 which is typical of carboxylic acids involved in hydrogen bonding, and would be expected in solid state samples such how the ligand was analyzed. This spectrum also contains the moderate peak at around 1030 wavenumbers (1027.32 cm-1) believed to be the ether gr oup. The carbonyl stretch for this ligand was observed at 1688.84 cm-1 within the range for aromatic carboxylic acids (16851710 cm-1).287, 288 2.2.3.5 Thermal Gravimetric Analysis Thermal Gravimetric Analysis for compounds [1] – [7] was performed on a PerkinElmer STA 6000 Simultaneous Thermal An alyzer. Data acquisi tion and analysis was performed with the assistance of the Py ris Series suite of software. Roughly 10-20 mg of dry powder was placed in a sample cr ucible and heated a t a rate of 10 C/min. form a temperature of 30 C up to 700 C under a N2 atmosphere. 2.3 Square Lattice (4.4) Another 2-periodic structure that is so mewhat more common place is that of the (4,4) square grid lattice. This is the ubi quitous checkerboard patte rn seen just about everywhere. The checkerboard orientation is on ly the most symmetric representation of

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71 this topology; in fact a brickwall or herringbon e pattern is also topol ogically a (4,4) net, but with a different geometry around the node. 2.3.1 Structural Analysis Layering reactions uti lizing 5-benzyloxy-1,3-bdc, L1 and the transition metals, Zn(II), Co(II), and Cd(II), with a terminal pyridyl axial base ( pyridine; 4-picoline) afforded a series of closely relate d 2-periodic structures ( compounds [8] – [13] Appendix C-8 – C-13) which can be interpreted in two ways. In the first interpretation they can be simplified into (4,4) square grid networks, while in the second they more closely resemble the 4.82 fes-like topology (Fig 2.11). Each of these structures was obtained via self-assembly during a slow/diffusion reaction and subsequently remade via solvothermal reaction conditions. The use of solvothermal conditions generally increased th e yield of the reaction, but made smaller Figure 2.12 4.82 feslike topology.

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72 crystals. The diffraction quality of the crystals as made by the two processes were basically equivalent. In each of these structures, the 5-benzyloxy-1,3-bdc L1 was reacted with one of Zn2+ Co2+ or Cd2+. In contrast to the Kagom la ttice structures presented in the previous section, these materials are not sustained by the dimetal tetracarboxylate square paddlewheel SBU, but rather a different dimetal tetracarboxylate SBU (Fig 2.12) which has been seen for many different tran sition metals in the context of extended structures. This SBU can be interpreted as a square as well, although it is highly distorted when compared to that of the paddlewheel SBU. Upon formation of this SBU with the se lected bridging ligand, a series of 2periodic sheets was observed. These sheet can be interpreted as (4,4 ) square grids if you simplify this SBU to a single 4-connected point at the center of the SBU. This simplification is a valid way of interpreting this structure. In a second interpretation, the carbon atoms of the four carboxylat es are treated as the points of extension and connected into a geometrical figure (a rectangle) which represents the points of extension observed in the MOM. When this is done, these recta ngles (or distorted squa res) are then linked Figure 2.13 Dimetaltetracarboxylate secondary building unit observed in compounds [8] – [13].

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73 through their vertices to generate a 2-periodic structure with a 4.82 feslike topology. It is important to note that the 4.82 topology is also just the sql-a topology, which is when the vertex of a network is replaced with a vertex figure that has the same connectivity. Thus we simply replace the 4-connected single node with a 4-connected square (rectangle). The individual layers of these compounds stack on top of one another, but are slipped in an ABAB manner. The presence of the 5benzyloxy groups, which thread through the rectangular cavity of the layers (Fig. 2.13), as well as the presence of the pyridine (or 4picoline) groups, causes the layers to undergo in terdigitation with one another (Fig 2.14). Upon this interdigitation, the phenyl rings fr om the ligand of one layer interact through edge-to-face CH••• interactions (measured carbon-to-centroid; ranges 3.564 to 4.196 ). Figure 2.14 Illustration of individual layers of compounds [8] – [13].

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74 2.3.2 Experimental 2.3.2.1 Synthesis All reagents, unless described otherwise, were purchased from either SigmaAldrich or Fischer Scientific and used as re ceived without further purification. Methanol (MeOH) was first distilled and stored over drying media (4 molecular sieves) before being used. [Zn(5-benzyloxy-1,3-benzenedicarboxylate)(pyridine)2]n [ 8 ], was initially synthesized via slow diffusion/layering under ambient conditions. In a typical reaction, 5benzyloxy-1,3-benzenedicarboxylic acid ( L1 ) (86.05 mg, 0.316 mmol ) was dissolved in 10 mL MeOH while separately Zn(NO3)2 6H2O (89.0 mg, 0.299 mmol) was dissolved in 7 mL MeOH. Pyridine was then added to the L1 /MeOH solution (0.08 mL, 1.00 mmol) along with 2 mL of nitrobenzene. The methanolic solution of Zn(NO3)2 was subsequently layered over the methanolic solution contai ning the ligand, pyridine, and nitrobenzene Figure 2.15 Interdigitation between layers as observed in compounds [8] – [13].

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75 using a 5 mL “blank” MeOH middle layer. Th e reaction vessels were capped and left undisturbed to allow for slow diffusion. After se veral weeks, large co lorless blocks of [ 8 ] were obtained (45 m g, 30.48% yield). The synthesis of [ 8 ] was also attempted via a solvothermal process. In this reaction, equimolar quantities of Zn(NO3)2 and L1 (0.300 mmol) were dissolved in 1 mL and 2 mL of N,N -Dimethylformamide (DMF) respect ively. Pyridine (0.08 mL, 1.00 mmol) was added to the L1 /DMF solution along with 1 mL of ethanol. The two solutions were combined in a 20 mL scintillation vial sealed with aluminum foil, capped and heated in a sand bath. The oven was ramped up from room temperature to 85 C at a rate of 1.5 C per minute, held constant for 12 hours and then cooled at a rate of 1.0 C back to room temperature. Solvothermal reactions for [ 8 ] resulted in noticeably improved single crystal quality (colorle ss rhombohedral plates) as well as increased yield over that obtained via slow diffusion (100 mg, 67.5 % yield). The cobaltous analog, [Co(5-benzyl oxy-1,3-benzenedicarboxylate)(pyridine)2]n [ 9 ], was initially synthesized via slow diffusion/layering under ambient conditions. In a typical reaction, 5-benzyloxy-1,3benzenedicarboxylic acid ( L1 ) (82 mg, 0.301 mmol) was dissolved in 10 mL MeOH while separately Co(NO3)2 6H2O (87.1 mg, 0.299 mmol) was dissolved in 7 mL MeOH. Pyridine was then added to the L1 /MeOH solution (0.08 mL, 1.00 mmol) along with 2 mL of nitrobenz ene. The methanolic solution of Co(NO3)2 was subsequently layered over the methanol ic solution containing the ligand, pyridine, and nitrobenzene using a 5 mL “blank” MeOH middle layer. The reaction vessels were

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76 capped and left undisturbed to allow for slow diffusion. After several weeks, large blocks light pink to red in color of [ 9 ] were obtained (33 mg, 22.65 % yield). The synthesis of [ 9 ] was also attempted via a solvothermal process. In this reaction, equimolar quantities of Co(NO3)2 and L1 (0.300 mmol) were dissolved in 1 mL and 2 mL of N,N -Dimethylformamide (DMF) respect ively. Pyridine (0.08 mL, 1.00 mmol) was added to the L1 /DMF solution along with 1 mL of methanol. The two solutions were combined in a 20 mL scintillat ion vial, sealed with aluminum foil, capped and heated in a sand bath. The oven was ramped up from room temperature to 85 C at a rate of 1.5 C per minute, held constant for 12 hours and then cooled at a rate of 1.0 C back to room temperature. Solvothermal reactions for [ 9 ] also resulted in marked improvement in single crystal quality (deep red rhombohedral plates) as well as enlarged yield with respect to that obtained via slow diffusion (120 mg, 82.35 % yield). The cadmium analog, [Cd(5-benzyloxy1,3-benzenedicarboxylate)(pyridine)2]n [ 10 ], was initially synthesized via slow diffusion/layering under ambient conditions. In a typical reaction, 5-benzyloxy-1,3benzenedicarboxylic acid ( L1 ) (86 mg, 0.316 mmol) was dissolved in 10 mL MeOH while separately Cd(NO3)2 6H2O (91.6 mg, 0.296 mmol) was dissolved in 7 mL MeOH. Pyridine was then added to the L1 /MeOH solution (0.08 mL, 1.00 mmol) along with 2 mL of nitrobenz ene. The methanolic solution of Cd(NO3)2 was subsequently layered over the methanol ic solution containing the ligand, pyridine, and nitrobenzene using a 5 mL “blank” MeOH middle layer. The reaction vessels were capped and left undisturbed to allow for sl ow diffusion. After several weeks, large colorless blocks of [ 10 ] were obtained (47 mg, 29.36 % yield).

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77 The synthesis of [ 10 ] was also attempted via a solvothermal pr ocess. In this reaction, equimolar quantities of Cd(NO3)2 and L1 (0.300 mmol) were dissolved in 1 mL and 2 mL of N,N -Dimethylformamide (DMF) respect ively. Pyridine (0.08 mL, 1.00 mmol) was added to the L1 /DMF solution along with 1 mL of odichlorobenzene. The two solutions were combined in a 20 mL scin tillation vial, sealed with aluminum foil, capped and heated in a sand bath. The oven wa s ramped up from room temperature to 85 C at a rate of 1.5 C per minute, held consta nt for 12 hours and then cooled at a rate of 1.0 C back to room temperature. Solvothermal reactions for [ 10 ] also resulted in marked improvement in single crystal quality (col orless rhombohedral plat es) as well as better yield with respect to that obtained via slow diffusion (120 mg, 82.35 % yield). [Zn(5-benzyloxy-1,3-benzen edicarboxylate)(4-picoline)2]n [ 11 ], was initially synthesized via slow diffusion/layering under ambient c onditions. In a typical reaction, 5benzyloxy-1,3-benzenedicarboxylic acid ( L1 ) (88 mg, 0.323 mmol) was dissolved in 10 mL MeOH while separately Zn(NO3)2 6H2O (93.0 mg, 0.313 mmol) was dissolved in 7 mL MeOH. 4-picoline was added to the L1 /MeOH solution (0.10 mL, 1.00 mmol) along with 2 mL of nitrobenzene. Th e methanolic solution of Zn(NO3)2 was subsequently layered over the methanolic solution contai ning the ligand, 4-picoline, and nitrobenzene using a 5 mL “blank” MeOH middle layer. Th e reaction vessels were capped and left undisturbed to allow for slow diffusion. After several weeks, large colorless blocks of [ 11 ] were obtained (41 mg, 30.05% yield). The synthesis of [ 11 ] was also attempted via a solvothermal pr ocess. In this reaction, equimolar quantities of Zn(NO3)2 and L1 (0.300 mmol) were dissolved in 1 mL

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78 and 2 mL of N,N -Dimethylformamide (DMF) respect ively. 4-picoline (0.10 mL, 1.00 mmol) was added to the L1 /DMF solution along with 1 mL of ethanol. The two solutions were combined in a 20 mL scintillation vial sealed with aluminum foil, capped and heated in a sand bath. The oven was ramped up from room temperature to 85 C at a rate of 1.5 C per minute, held constant for 12 hours and then cooled at a rate of 1.0 C back to room temperature. Solvothermal reactions for [ 11 ] resulted in noticeably improved single crystal quality (colorle ss rhombohedral plates) as well as increased yield over that obtained via slow diffusion (105mg, 68.5 % yield). [Co(5-benzyloxy-1,3-benzen edicarboxylate)(4-picoline)2]n [ 12 ], was initially synthesized via slow diffusion/layering under ambient c onditions. In a typical reaction, 5benzyloxy-1,3-benzenedicarboxylic acid ( L1 ) (86 mg, 0.316 mmol) was dissolved in 10 mL MeOH while separately Co(NO3)2 6H2O (85.1 mg, 0.286 mmol) was dissolved in 7 mL MeOH. The L1 /MeOH solution was combined w ith 4-picoline (0.10 mL, 1.00 mmol) and 2 mL of nitrobenzene. The Co(NO3)2 methanolic solution was subsequently layered over the methanolic solution containing 4-pico line, the ligand, and nitrobenzene using a 5 mL “blank” MeOH middle layer. The reaction vessel was capped and left undisturbed to facilitate slow diffusion. After several weeks, large blocks light pink to red in color of [ 12 ] were obtained (43 mg, 22.25 % yield). The synthesis of [ 12 ] was also attempted via a solvothermal pr ocess. In this reaction, equimolar quantities of Co(NO3)2 and L1 (0.300 mmol) were dissolved in 1 mL and 2 mL of N,N -Dimethylformamide (DMF) respect ively. 4-picoline (0.10 mL, 1.00 mmol) and 1 mL of methanol was added to the L1 /DMF solution. The two solutions were

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79 combined in a 20 mL scintillation vial, sealed with aluminum foil, capped and heated in a sand bath. The oven was ramped up from room te mperature to 85 C at a rate of 1.5 C per minute, held constant for 12 hours and then cooled at a rate of 1.0 C back to room temperature. Solvothermal reactions for [ 12 ] also resulted in marked improvement in single crystal quality (deep red rhombohedral plates) as well as enlarged yield with respect to that obtained via slow diffusion (120 mg, 82.35 % yield). The cadmium analog, [Cd(5-benzyloxy-1,3benzenedicarboxyl ate)(4-picoline)2]n [ 13 ], was initially synthesized via slow diffusion/layering under ambient conditions. In a typical reaction, 5-benzyloxy-1,3benzenedicarboxylic acid ( L1 ) (86 mg, 0.316 mmol) was dissolved in 10 mL MeOH while separately Cd(NO3)2 6H2O (93.6 mg, 0.306 mmol) was dissolved in 7 mL MeOH. 4-picoline was then added to the L1 /MeOH solution (0.10 mL, 1.00 mmol) along with 2 mL of nitrobenz ene. The methanolic solution of Cd(NO3)2 was subsequently layered over the methanol ic solution containing the ligand, pyridine, and nitrobenzene using a 5 mL “blank” MeOH middle layer. The reaction vessels were capped and left undisturbed to allow for sl ow diffusion. After several weeks, large colorless blocks of [ 13 ] were obtained (49 mg, 29.6 % yield). The synthesis of [ 13 ] was also attempted via a solvothermal pr ocess. In this reaction, equimolar quantities of Cd(NO3)2 and L1 (0.300 mmol) were dissolved in 1 mL and 2 mL of N,N -Dimethylformamide (DMF) respect ively. 4-picoline (0.10 mL, 1.00 mmol) was added to the L1 /DMF solution along with 1 mL of odichlorobenzene. The two solutions were combined in a 20 mL scin tillation vial, sealed with aluminum foil, capped and heated in a sand bath. The oven wa s ramped up from room temperature to 85

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80 C at a rate of 1.5 C per minute, held consta nt for 12 hours and then cooled at a rate of 1.0 C back to room temperature. Solvothermal reactions for [ 13 ] also resulted in marked improvement in single crystal quality (col orless rhombohedral plat es) as well as better yield with respect to that obtained via slow diffusion (128 mg, 84.35 % yield). 2.3.2.2 X-ray Crystallography Single crystals of compounds [8]-[10] and [13] suitable for X-ray crystallographic analysis were selected following examinati on under a microscope. Intensity data were collected on a Bruker-AXS SMART APEX /CCD diffractometer using Cu k\ radiation ( = 1.54178 ).281 The data were corrected for Lore ntz and polarization effects and for absorption using the SADABS program (SAINT).282 The structures were solved using direct methods and refined by fu ll-matrix least-squares on |F|2 (SHELXTL).283 Select crystallographic data is pres ented in tabular form in A ppendices C-8, C-9, C-10 and C13. Single crystals of compounds [11] and [12] suitable for X-ray crystallographic analysis were selected following examinati on under a microscope. Intensity data were collected on a Bruker-AXS SMART APEX /CCD diffractometer using Mo k\ radiation ( = 0.7107 ).281 The data were corrected for Lore ntz and polarization effects and for absorption using the SADABS program (SAINT).282 The structures were solved using direct methods and refined by fu ll-matrix least-squares on |F|2 (SHELXTL).283 Select crystallographic data is presented in tabular form in Appendices C-11 and C-12.

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81 2.3.2.3 Powder X-ray Diffraction Powder samples suitable for powder X -ray diffraction, FT-IR spectroscopy, and Thermal Gravimetric Analysis were obtai ned by removing a large amount of single crystals from the reaction scintillation vial by using a glass Pasteur pipette and depositing these crystal (along with mother liquor) in a small concave agar mortar. Excess solvent was removed via pipette, and surface solvent was removed by wicking action with a Kim-Wipe. Upon wick drying, the crystals were tr ansferred to a small piece of filter paper which was subsequently folded over and they were dried further and slightly crushed with gently pressure. The resulti ng dry powder (~30 mg) was then immediately applied to a PXRD sample puck prepared with a small amount of vacuum grease to fixate the powder sample, and the PXRD experiment performed without delay. 2.3.2.4 FT-IR Spectroscopy All compounds, including synthesi zed ligands, were characterized via infrared spectroscopy using a Nicolet Avatar 320 Four ier-Transform Infrared Spectrometer (FTIR). Before each sample was analyzed, a background spectrum was obtained for purposes of zeroing out ambient noise in the form of the laboratory atmosphere. Each sample was measured in the range from 4000 cm-1 to 500 cm-1 wavenumbers (wavelength of 2500 nm to 20000 nm respectively) and scanned 64 times. Results were recorded in % transmittance and the spectrum analyzed using the EZ OMNIC (V.5.1b, copyright 1992199 Nicolet Instruments Corporation) computer software suite. A typical sample was a

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82 analyzed as a neat, dry solid (~10 mg) obtained via either vacuum filtration and air drying or gently drying with laboratory grade filter paper. 2.3.2.5 Thermal Gravimetric Analysis Thermal Gravimetric Analysis for compounds [8] – [13] was performed on a PerkinElmer STA 6000 Simultaneous Thermal An alyzer. Data acquisi tion and analysis was performed with the assistance of the Py ris Series suite of software. Roughly 10-20 mg of dry powder was placed in a sample cr ucible and heated a t a rate of 10 C/min. form a temperature of 30 C up to 700 C under a N2 atmosphere. 2.4 Conclusion In summary, this chapter has outlined several examples of novel, 2-periodic crystalline materials. These materials can be divided into two classifications based upon their topology; namely a platform of (4.82) feslike structures as exemplified by the series of [M(5-benzyloxy-1,3-benzen edicarbocylate)(pyridine)2]n (M = Zn2+, Cd2+, Co2+) compounds, and a platform of (3.6.3.6) Kagom lattice ( kgmlike) structures exemplified by the series of compounds with formula unit {[M2(5-benzyloxy-1,3benzenedicarboxylate)2(pyridine)2]3}n (M = Cu2+, Zn2+). These platforms, while only two examples, are indicative of the levels of complexity observed in metal-organic materials. That 2-periodic layered structur es exhibit built in geometrical attributes (i.e. pore shape, pore dimensions, etc.) is a firs t rate indicator that they ha ve inherent complexity not enjoyed by 1-perioic structures. Additionally, th at individual layers in layered 2-periodic materials have the capacity to interact with adjacent layers adds to their interesting

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83 supramolecular chemistry. Through the Kagom platform of material s, the ability to control packing distances has been demonstr ated in a systematic manner. Additionally, control over this packing dist ance can have related effect s on other aspects of these materials supramolecular chemistry.

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84 Chapter 3 Three-Periodic Frameworks from Pillaring Two-Periodic Layers 3.1 Introduction Advancing from 2-periodic to 3-periodic metal-organic materials, it is to be expected that we shall, in general, observe increased complexity in those architectures which are available to us. Analogous to th e extension from 1-periodic to 2-period structures, so too will the step up into 3periodicity result in a higher degree of complexity. As was seen in the 2-periodic structures, where higher order lead to an increase in possibilities for what the node c ould accomplish, we observe the same trends in 3-periodic structures only now within more spatial directions. Geometries can still be distorted, and nodes can still be symmetrically unique, but the shear potential in the number of ways this can occur, in compar ison to what can be obs erved in 2-periodic structures is truly st aggering. This is one reason why, for practicality sake, we often limit our discussion of possible 3-peri odic structures to only those that seem to be chemically feasible (i.e. uninodal, binodal, edge-transitive, networks). 3.1.1 3-Periodic Structures and Th eir Most Important Property The most obvious trait of common 3-period ic when compared to that of their 2periodic and 1-periodic counterparts is their ability to enclose space. More complicated 0-

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85 periodic structures which adopt shapes remi niscent of polyhedra can also enclose space, making them, in my opinion more complicated than simple 2-periodic structures. These structures will be addressed in the next chapter. If a material has the capacity to enclose space, it also has the ability to entrap other smaller chemical entities. Naturally occurring zeolites, built from various cages sharing f aces or bridged by rings, are prime example of this. Much of the interest in the materials arises from their ability to enclose objects within their framework. Metal-organic materials, primarily being modeled after zeolites, aim to harness this same ability ; to enclose space and exhibit porosity .177, 178, 183, 184 3.1.2 Pillaring as a Design Strategy While the majority of 3-periodic metalorganic materials are constructed by the direct self-assembly of judiciously sele cted building blocks predisposed towards generating such expansive structures (or even incapable of forming lower order structures), it is possible to obtain 3-periodic structur es from components that are relatively less controllable. In some instances this is achieved by happenstance, where the components are combined and the conditions implemented such that 3-periodic structures arise serendipitously. Often, building blocks have the capacity to arrange in several different manners, adding to the latent divers ity for these materials, but frequently to the detriment of the crystal engi neer’s control and predictability. In many instances, the answer is simply to conduct copious amounts of crystal engineering experiments, where one hopes to discern the princi ples controlling the formati on of certain topologies with particular components. This however is not always a palatable solution, and so new design strategies which allow the crystal engineer access to 3-periodic topologies for

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86 metal-organic materials constructed from rela tively promiscuous components that might otherwise be difficult to control are exceedingly welcome. One such possible design strategy is to isolate 2-periodic layered structures which are amenable to augmen tation through the addition of an additional component. In this strategy, the SBU that comprises the metal-organic material must either have an open coordination site to accommodate the addition of a new ligand, or in its original state it should have labile axial groups that are easily replaced with stronger binding ditopic ligands. Based upon the use of the square paddlewheel SBU (Fig 3.1), there are at least three possible design stra tegies for the pillari ng of two dimensional topologies into three dimensional frameworks ; axial-to-axial, ligand-to-axial, and ligandto-ligand (Fig. 3.2). Figure 3.1 Illustration of the dimetal tetracarboxylate square paddlewheel SBU.

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87 Each of the design strategies is based upon the location in the network where the pillaring will takes place. In the axial-to-axial strategy, the pillar is an additional chemical moiety, bifunctional in nature and capable of coordinating in the axial position of the SBU (blue atoms in Fig. 3.1). Using the axia l-to-axial method, the individual layers should be layered directly above one another in an eclipsed fashion where the SBU’s are collimated. The ligand-to-axial method, while not a pillar in the traditional sense, involves incorporating a judici ously designed organic ligand which is capable of forming the desired SBU (i.e. a dicarboxylate) and th en contains another separate functional group, usually of a different t ype (i.e. pyridyl moiety) capabl e of coordinating in the axial position of another SBU. This method elim inates the requirement for the additional chemical constituent as the single organic ligand provides for both the bridging between SBUs in the 2D layers as well as the segmen t needed to pillar those layers into the 3periodic framework. Adopting this motif will necessarily force subsequent layers to be slipped with respect to one another. The final method, lig and-to-ligand, involves an Figure 3.2 Cartoon illustrating the three possible pillaring design strategies; axial-to-axial, ligand-to-ligand, and ligand-to-axial

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88 appropriate organic ligand which can simulta neously link two SBUs into the desired 2periodic topology while also connecting two di fferent layers through an organic bridge. 3.2 Camphoric Acid Square Lattices with Dipyridyl Based Pillars For the purposes of this chapter a single dicarboxylic acid, namely (1R, 3S)-(+)1,2,2-trimethyl cyclopentane1,3-dicarboxylic acid (camphoric acid, Fig. 3.3) was employed in combination with several first row transition metal cations (Zn2+, Co2+, and Ni2+) and an assortment of roughly linear di pyridyl organic molecules (pillars) to investigate this diacid’s ability to generate a series of closely related crystalline materials based upon the design principle of pillaring, wh ich could subsequently be investigated further in relation to their physical and chem ical properties and pot ential applications. This dicarboxylic acid is at tractive for several reasons. First and foremost in the synthesis of practical functional metal-organic materials is the general principal that the starting materials should be readily available (i.e. not too difficult to synthesize in high yield and hi gh purity), cheap, and relatively non-toxic to either the user or the environment in general (even “useful” materials that kill the user or overtly poison of the environment will be subjec t to regulation or banishment). As a store Figure 3.3 Chemical Sketch of (1R, 3S)-(+)-1,2,2trimethylcyclopentane-1,3-dicarboxylic acid.

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89 bought chemical which is also widely used in pharmaceuticals where humans can consume large amounts without harmful reperc ussions, camphoric acid satisfies each of these requirements. It may be argued that th e first two points are somewhat flexible in that an appropriately useful ma terial especially suited and ca pable of fulfilling some dire need of society will lead to improvements on bo th fronts. That is to say, if a particular object is the only one of its kind to achieve some necessary endeavor, then the ability to obtain the materials required to make that obj ect will be of keen interest. In such cases, new ways of making difficult lig ands might be explored as well as other means to bring down overall costs. One could say that if the need is vital enough and the material uniquely suited, then the rest is a matter of engineering and persistence. The last point, dealing with the toxicity of the material happe ns to be a little s tickier, and the current political and social environment does not appe ar likely to become more lax anytime soon. Camphoric acid289-298 is also an intriguing ligand because it is chiral which in itself can sometimes lead to interesting physical properties exhi bited in MOMs. If integrated into a robust porous framework, th e presence of camphoric acids’ two chiral centers may influence the observable propert ies of the MOM. Additionally, as will be seen in the section to follow when camphoric acid is incorpor ated into layered sheets, the nature of the angle subtended between carboxyl ate groups and their relative orientation, together with the ligands relative size, combin es to result in a unique and characteristic bow-tie motif. This bow-tie motif will prove to be more useful than simply a unique orientation, and as we shall see it affords the crystal engineer an increased level of structural control.

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90 3.2.1 Camphoric Acid Square Lattices The unique geometry of the individual layers (Fig 3.4) seen in a pillared camphoric structure belies the fact that this layer, at its roots is simply a (4,4) square grid topology. Just as the commonly observe d brick wall pattern and a chess board (uncolored) are topologically equi valent, but with different local geometries, so too is this layer related to both of those patterns. However the bow-tie geometry of this material makes it interesting from the standpoint of c ontrolling interpenetra tion and the generation of pores/channels. The length of the longest portion of the bowtie, as measured from carbon atoms on opposite camphorate ligands was observed to be 11.8 . At the closest approach, the width of the bow tie is only 4.099 in length, and when accounting for van der Waal radii this is reduced to ~1.7 . Carefu l observation shows that no material, except Figure 3.4 Illustration of a single layer from a pillared camphoric structure. Note the distorted bow-tie geomtey for this (4,4) square grid.

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91 perhaps H2 molecules can pass through this “opening” All of the pillared camphoric acid structures have this layer as a repeating unit. 3.2.2 Dipyridyl Type Pillars For the purpose of pillaring camphorate square grid layers into extended 3periodic frameworks, it was d ecided that bifunctional organi c molecules which contained pyridyl moieties (N-donor ligands) on either end would be employed. This is because of the relatively high probability of success that these molecules afford. One the one hand, 2-periodic layered structures composed of the camphoric diacid with several different transition metals, built from dimetal tetra carboxylate square paddlewheel SBUs, and generating a (4, 4) MOF-2 t opology had already been known.297 In these structures, the terminal axial ligand coordinating to the meta l ions was typically either a monopyridyl type ligand (pyridine, picoline, methoxypyr idine, etc.) or a solvent molecule. Additionally, the square paddlewh eel SBU is renowned for its ability to be pillared with dipyridyl type linkages along its metal-metal ax is. The preeminent dipyridyl type pillar is the one that lends its name to the category, 4,4 dipyridyl (also 4,4 -bipyridyl; bipy). This molecule is perfectly linear with respect to the orientation of how the two nitrogen atoms coordinate to metal ions, but the rings themselves do have th e capacity to rotate freely around this same axis. Other pillars closely re lated to bipy modify the length between the two coordinating nitrogen atoms, introduce a dditional functionality into the rings, or achieve both simultaneously. The pillars selected for this study (Fig. 3.5) were chosen to cover a range of dimensions as well as to in corporate some diversity in functionality. All of the pillars were available for purchase form commercial sources and used as is, save

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92 for N,N -di(4-pyridyl)-1,4,5,8-na phthalenetetracarboxydiimide299 (BIP-PY), which was synthesized by another researcher in the lab. 3.2.3 Structural Analysis 3.2.3.1 Layer Arrangements When an extended 3-periodic structure is said to be the result of pillaring other 2periodic layers, it may sometimes be of benefit to retain some of the structural identifiers of the individual layers. If this were not th e case, then the choice of the layer would not be of any consequence. If the goal is to pr eserve a particularly shaped pore and extend this into a channel, then c ontrol over how individual laye rs align through the pillaring Figure 3.5 Dipyridyl type pillars. Left (bottom to top): pyrazine ( pyz ), 4,4 dipyridyl ( bipy ), 1,2-Bis(4-pyridyl)ethane ( bipy ethane ), 1,2-Bis(4pyridyl)ethylene ( bipy ethylene ). Right (bottom to top): N,N -di(4-pyridyl)1,4,5,8-naphtha lenetetracarboxydiimide, ( BIPA-PY ), meso, -di(4pyridyl)glycol ( bipy glycol ).

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93 process will be needed. In the case of undistorted square grids and similar structures this alignment is of no importance; rather all a lignments are equivalent. However, in some cases, as with camphoric acid, the individual la yer is so oriented so as to produce very unique local geometry around the nodes. In these cases, how subsequent layers align could have very important consequences. As an example take an individual layer of the pillared camphoric structures. There are defini tive directions in this distorted brick wall structure. When the layers begin to stack, tw o possibilities arise; either the layers stack perfectly eclipsed in an AAA fashion, or they stack in an anti-parallel ABAB fashion as depicted in Figure 3.6. If there was a desire to retain the unique geometry of the individual layer and extend this into a column running parallel to the pillar axis, it would be necessary to ensure that the anti-paralle l packing does not occur. Specifically in the case of camphoric acid, it turns out that the alignment is not that important after all, as the tight bow-tie confirmation already precludes channel development. Figure 3.6 Cartoon illustrating the anti-parallel stacking of layers observed in compounds [16] – [18]. The two layers (red and blue) are not equivalent. Notice the orientation of the bow-ties in the two layers in the figure to the right.

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94 3.2.3.2 Lack of Entanglements in Camphoric Based Structures The unique bow-tie geometry of the (4,4) square grid layer structure seen in the pillared camphoric structures has at least one important implicati on for the overall solidstate structure. Typically, MO F-2 type layers which are th en pillared into extended 3periodic frameworks, have the potential to undergo interpenetration. The nature of the topology and the dimension of the cavities, are often amenable to a second (or third, or more, etc.) network interweaving with the first. The concept of interpenetrating is sometimes seen as a negative aspect of some frameworks as it can take up space or block access to channels. It is also sometimes diffic ult to control whether a framework exists in an interpenetrated form or not. This often ma kes interpenetration the anathema of crystal engineers who aim to control every as pect of a materials synthesis. In the case of the camphoric structur es, the tight bow-tie arrangement of the individual layers precludes the possibility of interpenetrating t hough these sheets. This implies that a greater control over the possibl e assembly of these materials can be had by the synthetic chemist. It also means that wh en using this ligand in a pillaring motif, one needs not worry about the possibility of interpenetration occurri ng and thus, designed structures can be obtained with a higher degree of certainty. 3.2.3.3 Controllable Pore Size and Predictable Surface Areas As the potential for interpenetration is of no concern, and the ligand has been judiciously selected so that it effectively precludes the possibility of any channels or columns existing along the direction of the pill ar, we have generate d a synthetic system

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95 in which the individual layers are essentia lly sheets or walls with no holes for small molecules or gases to pass th rough. Additionally, these sheets are situated on struts (i.e. the pillar) which we control, both in terms of functionality and in terms of metrics. Therefore we have devised a reliably contro llable system of a closed surface where we can practically dial in the distance between walls This is typically no t an easy feat. Thus the small channel formed perpendicular to th e pillar axis, and regulat ed by the length and girth of the pillars we choose, is the only determining factor controlling th e pore size for this material. This is truly an example of e xquisite control of the st ructure of a material. By dialing in the length of the pillar, we al so can predictably adjust the distance between the walls, and therefore control the expected surface area for this platform of materials. 3.2.4 Applications and Properties 3.2.4.1 Gas sorption Once synthesized, the crystalline materi als were treated th rough a number of protocols in an attempt to “activate” them prior to gas sorption measurements. By “activate”, we mean to replace otherwise higher boiling solvent molecules and guests present in the crystal structure with relati vely low boiling solvent molecules, in an attempt to facilitate the complete rem oval of all guest and solvent molecules upon vacuum evacuation. The presence of any higher boiling solvent molecules, such as N,N dimethylformamide which is present in the reaction solution, may mitigate the materials ability to uptake the sorbent gas being investigated. In a typical activation process the reaction solution in the vial containing th e crystalline samples of aryloxy nanoballs was

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96 removed via Pasture pipette and the crystals washed with neat reaction solvent, in this case DMF. The washing process is prescribed to remove any unreacted starting materials such as ligand or metal ions which may still be present in the mother liquor and possibly coat the sample crystals. The crystals were allowed to sit in the fresh DMF for approximately 15 minutes before the pro cess was repeated, the DMF removed and replaced with a fresh aliquot. The sample wa s washed three times with fresh DMF. After the third washing, the DMF solvent was rem oved and a second, typically a low boiling solvent was introduced. Again the crystals we re allowed to sit immersed in the new solvent, however now the sample was left undisturbed for ~12 hours. After ample time immersed in the exchange solvent, so chosen that is may diffuse into the material while any other solvent guest present will subsequently diffuse out of the material into the bulk exchange solvent, the process is repeated. T ypically the samples were exchanged at least three times before the sorption experiments commenced. Upon activation each of the synthesized pillared camphoric acid structure (compounds [14] – [29] ) was investigated for its sorpti on abilities. With early success from the [Ni(camphorate)( bipy )0.5] n, compound [17], it looked promising that our strategy of designing a material with predictable and exquisitely controllable pore sizes and scalable surface areas would provide a unique se ries of materials with which to test the hypothesis that small pore sizes lead to incr eased isosteric heats of adsorption at low temperatures and pressures. Much of the evidence collated so far in the community seem to validate this assumption, however few syst ematic studies exist to definitively set the record straight; comparisons of materials that are somewhat closely related albeit still

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97 different have had to suffice. The camphoric system was supposed to provide a truly systematic series of compounds that were in timately controllable down to their single pore/channel size and the functionality of their surfaces. Unfortunately the vast majority of th ese structures never made it past the activation stage, failing to exhibit any significant levels of porosity, despite dogged attempts to activate them through myriad protoc ols. The quirky aspect is that the majority display high levels of thermal stabi lity as demonstrated by TGA analysis. [Ni(camphorate)( bipy )0.5]n, compound [17] was the first pillared camphorate structure studied in our lab to demonstrate high levels of porosity. Following an activation protocol as outlined above, using any number of solvents (acetone, CHCl3, MeCN, MeOH, EtOH, and DCM, among others) this crystalline material was su itable evacuated upon exposure to a vacuum pump for ~14 hours, that the mate rial demonstrated the ability to absorb a significant amount of N2 gas when analyzed on the QuantumChrome Instruments NOVA 2000. Five point B.E.T. (Brunauer-Emmett-Teller)300 calculations used for estimating the accessible surface area of a porous soli d, predicted a surf ace area roughly 1450-1500 m2/g after exchange with each of these solv ents, with dichloromethane performing the best. Further analysis was conducted using a QuantumChrome Instruments Autosorb-1, on which isotherms for the sorption of molecular hydrogen (77K and 87K) (Fig. 3.7, green and black respectively) and nitrogen (77K) (Fig. 3.7, red) were collected. The collection of this data revealed an estimated surf ace area of 1450 m2/g in good agreement with the observed value from the NOVA 2000 instrument. All isotherms were observed to be type I (Langmuir isotherms) which is indicative of mi croporous materials.

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98 Hydrogen storage isotherms conducted at 77K showed a maximum uptake of 1.6 wt % H2 at P/P0 = 1.0 (with P0 set at 760 torr). Use of the two different temperature isotherms facilitated calculation of the heats of adsorption (Qst) for this material, which was observed to be ~5.8 kJ/mol at low loading drop ping to a slightly lower value of ~5.3 kJ at 100% loading (Figure 3.8, red) Calculations (using a probe size of 1.8 ) suggest that this material has a pore volume of 0.591 cc/g while the data from the Autosorb-1 experiments suggests a pore volume of 0.588 cc/g in very good agreement. A second structure, [Ni(camphorate)( pyrazine)0.5]n, compound [14], was also show to be highly porous, and fortuitously allowed us at least one compound to compare with. All of this material’s isotherms and Heats of adsorption plot are gi ven in the above figures for easy reference. As expected, with a smaller pore si ze (Fig 3.9) (4.6 x 4.2 for pyrazine versus 8.8 x 4.4 for bipy ), the pyrazine compound demonstrated a markedly higher Qst (~7.3 Figure 3.7 Left: N2 Isotherm (77K) for compounds [14] (red) and [17] (blue) H2 isotherms (77K and 87K) for compounds [14] (red) and [17] (blue)

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99 kJ/mol vs. ~5.8 kJ/mol). Here the calculat ed pore volume was 0.29 cc/g, while the value obtained from data collected on the Autoso rb-1 indicated a pore volume of 0.28 cc/g. Additionally, a third sample, [Co(camphorate)( pyrazine )0.5]n, compound [15] was also shown be porous with similar results to that of the camphorate analogue. Figure 3.9 Illustration of the relative pore sizes in compounds [17] ( left ) and [14] ( right ). Figure 3.8 Plot of Isosteric Heats of Adsorption (kJ/mol) vs. volume (cc/g).

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100 3.2.4.2 Dichroism in Metal-Organic Materials One very peculiar aspe ct of [Co(camphorate)( bipy )0.5]n compound [18], was that upon completion of the solvothermal reaction th ere appeared to be crystal of two very different colors in the same vial (Fig 3.10). The existence of both deep red and deep blue square plate crystals in the reaction vial was not immediately a reason of concern (interest maybe), as many times in the synthesis of metal-organic materials there is a real possibility for the reaction to generate more than structure. Additionally, the different possible crystal structures of ten produce very distinct cr ystal morphologies and colors. Cobalt is also known to adopt both colors in various coordination environments, so it was not as if the colors were outlandish. Upon mounting a sing le crystal on the goniometer head of the single crystal X-ray diffraction in strument, and rotating th e crystal to ensure the incidence of X-rays would be uniform, it was observed that cr ystals appeared to change color from red to blue, as the cr ystal swept through an angle of 90. Further observation under a digital optical microsc ope equipped with a rudimentary light polarizer, revealed that indeed the color of the light transmitted by these crystals was dependent upon the polarization of the incident light. This variable transmittance of light by a crystal based upon the polarization of the light as it hits the crystal is a very common phenomenon in gem stones and other naturally occurring crystals in rock. The term for such a property is pleochroism (for many colo rs) or dichroism in the case when only two colors are observed. Pleochroism is an impor tant aspect of geology because it can aid in the identification of trace substances in rock sample s, based upon how polarized light behaves. Dichroism is seldom if ever menti oned in the case of metal-organic materials

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101 however, and indeed a literature search for examples in MOMs was unsuccessful. Essentially, the existence of this optical phenomenon for these particular crystals indicates that they absorb light differently al ong unique directions in th e crystal as light is transmitted through the sample. Further investigation of this phenomenon using specular reflectance with Dr. Ronald Musselman is ongo ing, but at this time a detailed account for the observed selective adsorption of polarized light is lacking. 3.2.5 Experimental 3.2.5.1 Synthesis All reagents, unless described otherwise, were purchased from either SigmaAldrich or Fischer Scientific and used as received without further purification. Bulk solvents such as methanol, ethanol, acetone, and dichloromethane were first distilled and stored over drying media (4 molecu lar sieves) before their use. Figure 3.10 Digital photograph depicting the observed Dichroism in compound [18]. The sample remained unaltered as the polarization of the light was changed by 90 between capturing the two images.

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102 [Ni2(camphorate)2(pyrazine)0.5]n, [14] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scinti llation vial. In a typical reaction, pyrazine (0.1 mmol, 8.0 mg), 2,6-lutidine (0.4 mmol, 46.44 L), and (1R, 3S)-(+)-1,2,2-trimethyl cyclopentane-1,3-dicarboxylic acid (camphor ic acid, Fig. 3.3) (0.2 mmol, 40.05 mg) were combined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids were fully dissolv ed. To this solutio n, 1 mL of dimethyl sulfoxide (DMSO) was added and the solution agitated for several seconds. Separately, Ni(NO3)2•6H2O (0.2 mmol, 58.2 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ pyrazine /2,6-lutidne/DMSO solution. The vial was sealed with store bought kitchen alumin um foil, capped tightly and placed in a sand bath for transfer to a programmable oven. Th e heat profile was as follows: the reaction temperature was raised from 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hour s. The temperature was then slowly cooled back down to 30 C at a rate of 1.0 C pe r minute. Upon removal from the oven a large amount of green square-plate crystals suitabl e for single crystal X-ray diffraction were observed to have formed (67 mg, 50.56% yield). [Co2(camphorate)2(pyrazine)0.5]n, [15] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, pyrazine (0.1 mmol, 8.0 mg), 2,6-lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were combined t ogether with exactly 2 mL of N,N dimethylformamide (DMF) and manually agitate d until both solids were fully dissolved. To this solution, 1 mL of methanol (Me OH) was added and the solution agitated for

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103 several seconds. Separately, Co(NO3)2•6H2O (0.2 mmol, 58.2 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ pyrazine /2,6lutidne/MeOH solution. The vial was sealed with store bought kitchen aluminum foil, capped tightly and placed in a sand bath for transfer to a programmable oven. The heat profile was as follows: the reaction temperatur e was raised from 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours. The temperature was then slowly cooled back dow n to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a large amount of pink square-plate cr ystals suitable for single crystal X-ray diffracti on were observed to have fo rmed (89 mg, 72.3% yield). [Zn2(camphorate)2(4,4 -dipyridyl)0.5]n, [16] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy (0.1 mmol, 15.62 mg), 2,6-lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were combined t ogether with exactly 2 mL of N,N dimethylformamide (DMF) and manually agitate d until both solids were fully dissolved. To this solution, 1 mL of methanol (Me OH) was added and the solution agitated for several seconds. Separately, Zn(NO3)2•6H2O (0.2 mmol, 59.5 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ bipy /2,6lutidne/MeOH solution. The vial was sealed with store bought kitchen aluminum foil, capped tightly and placed in a sand bath for transfer to a programmable oven. The heat profile was as follows: the reaction temperatur e was raised from 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours. The temperature was then slowly cooled back dow n to 30 C at a rate of 1.0 C per minute.

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104 Upon removal from the oven a large amount of co lorless square-plate crystals suitable for single crystal X-ray diffracti on were observed to have fo rmed (55 mg, 41.7% yield). Ni2(camphorate)2(4,4 -dipyridyl)0.5]n, [17] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy (0.1 mmol, 15.62 mg), 2,6-lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were combined t ogether with exactly 2 mL of N,N dimethylformamide (DMF) and manually agitate d until both solids were fully dissolved. To this solution, 1 mL of ethanol (EtOH) wa s added and the solution agitated for several seconds. Separately, Ni(NO3)2•6H2O (0.201 mmol, 58.45 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ bipy /2,6-lutidne/ EtOH solution. The vial was sealed with store bought kitchen aluminum foil, capped tightly and placed in a sand bath for transfer to a programmable oven. The heat profile was as follows: the reaction temperature was raised fr om 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours. The temperature was then slowly cooled back down to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a large amount of green square-p late crystals suitabl e for single crystal Xray diffraction were observed to ha ve formed (45 mg, 38.2% yield). Co2(camphorate)2(4,4 -dipyridyl)0.5]n, [18] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy (0.1 mmol, 15.62 mg), 2,6-lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were combined t ogether with exactly 2 mL of N,N dimethylformamide (DMF) and manually agitate d until both solids were fully dissolved.

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105 To this solution, 1 mL of ethanol (EtOH) wa s added and the solution agitated for several seconds. Separately, Co(NO3)2•6H2O (0.199 mmol, 57.91 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ bipy /2,6-lutidne/ EtOH solution. The vial was sealed with store bought kitchen aluminum foil, capped tightly and placed in a sand bath for transfer to a programmable oven. The heat profile was as follows: the reaction temperature was raised fr om 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours. The temperature was then slowly cooled back down to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a large amount of what appeared to be purple square-pla te crystals suitable for single crystal X-ray diffraction were obser ved to have formed (63 mg, 51.9% yield). Zn2(camphorate)2(1,2-Bis(4-pyridyl)ethane)0.5]n, [19] was synthesized via a onepot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy ethane (0.098 mmol, 18.06 mg), 2,6lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were combined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids were fully dissolved. To this solution, 1 mL of meth anol (MeOH) was added and the solution agitated for several seco nds. Separately, Zn(NO3)2•6H2O (0.2 mmol, 59.5 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ bipy ethane /2,6-lutidne/MeOH solution. The vial wa s sealed with st ore bought kitchen aluminum foil, capped tightly and placed in a sand bath for transf er to a programmable oven. The heat profile was as follows: the reac tion temperature was ra ised from 30 C to 115 C at a rate of 1.5 C per minute upon whic h time it was held at that temperature for

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106 24 hours. The temperature was then slowly cool ed back down to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a large amount of colorless square-plate crystals suitable for single crystal X-ra y diffraction were observed to have formed (55 mg, 41.7% yield). Ni2(camphorate)2(1,2-Bis(4-pyridyl)ethane)0.5]n, [20] was synthesized via a onepot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy ethane (0.1 mmol, 18.42 mg), 2,6lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were combined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids were fully dissolved. To this solution, 1 mL of meth anol (MeOH) was added and the solution agitated for several seco nds. Separately, Ni(NO3)2•6H2O (0.201 mmol, 58.45 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ bipy ethane /2,6-lutidne/MeOH solution. The vial wa s sealed with st ore bought kitchen aluminum foil, capped tightly and placed in a sand bath for transf er to a programmable oven. The heat profile was as follows: the reac tion temperature was ra ised from 30 C to 115 C at a rate of 1.5 C per minute upon whic h time it was held at that temperature for 24 hours. The temperature was then slowly cool ed back down to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a larg e amount of green square-plate crystals suitable for single crystal X-ra y diffraction were observed to have formed (45 mg, 38.2% yield). Co2(camphorate)2(1,2-Bis(4-pyridyl)ethane)0.5]n, [21] was synthesized via a onepot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical

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107 reaction, bipy ethane (0.1 mmol, 18.40 mg), 2,6lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were combined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids were fully dissolved. To this solution, 1 mL of meth anol (MeOH) was added and the solution agitated for several seco nds. Separately, Co(NO3)2•6H2O (0.199 mmol, 57.91 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ bipy ethane /2,6-lutidne/MeOH solution. The vial wa s sealed with st ore bought kitchen aluminum foil, capped tightly and placed in a sand bath for transf er to a programmable oven. The heat profile was as follows: the reac tion temperature was ra ised from 30 C to 115 C at a rate of 1.5 C per minute upon whic h time it was held at that temperature for 24 hours. The temperature was then slowly cool ed back down to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a larg e amount of what appeared to be purple square-plate crystals suitable for single cr ystal X-ray diffraction were observed to have formed (74 mg, 71% yield). [Zn2(camphorate)2(1,2-Bis(4-pyridyl)ethylene)0.5]n, [22] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy ethylene (0.1 mmol, 15.62 mg), 2,6lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were co mbined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids were fully dissolved. To this solution, 1 mL of meth anol (MeOH) was added and the solution agitated for several seco nds. Separately, Zn(NO3)2•6H2O (0.2 mmol, 59.5 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/

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108 bipy ethylene /2,6-lutidne/MeOH solution. The vial was sealed with store bought kitchen aluminum foil, capped tightly and placed in a sand bath for transf er to a programmable oven. The heat profile was as follows: the reac tion temperature was ra ised from 30 C to 115 C at a rate of 1.5 C per minute upon whic h time it was held at that temperature for 24 hours. The temperature was then slowly cool ed back down to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a large amount of colorless square-plate crystals suitable for single crystal X-ra y diffraction were observed to have formed (79 mg, 59.3% yield). Ni2(camphorate)2(1,2-Bis(4-pyridyl)ethylene)0.5]n, [23] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy ethylene (0.1 mmol, 15.62 mg), 2,6lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were co mbined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids were fully dissolved. To this solution, 1 mL of ethanol (EtOH) was added and the solution agitated for several seconds. Separately, Ni(NO3)2•6H2O (0.201 mmol, 58.45 mg) was dissolved in exactly 1 mL of DMF, and upon di ssolution, was added to the camphorate/ bipy ethylene /2,6-lutidne/ EtOH solution. The vial was sealed with store bought kitchen aluminum foil, capped tightly and placed in a sand bath for transf er to a programmable oven. The heat profile was as follows: the reac tion temperature was ra ised from 30 C to 115 C at a rate of 1.5 C per minute upon whic h time it was held at that temperature for 24 hours. The temperature was then slowly cool ed back down to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a larg e amount of green square-plate crystals

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109 suitable for single crystal X-ra y diffraction were observed to have formed (57 mg, 48.2% yield). Co2(camphorate)2(1,2-Bis(4-pyridyl)ethylene)0.5]n, [24] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy ethylene (0.1 mmol, 18.40 mg), 2,6lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were co mbined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids were fully dissolved. To this solution, 1 mL of meth anol (MeOH) was added and the solution agitated for several seco nds. Separately, Co(NO3)2•6H2O (0.199 mmol, 57.91 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ bipy ethylene /2,6-lutidne/MeOH solution. The vial was sealed with store bought kitchen aluminum foil, capped tightly and placed in a sand bath for transf er to a programmable oven. The heat profile was as follows: the reac tion temperature was ra ised from 30 C to 115 C at a rate of 1.5 C per minute upon whic h time it was held at that temperature for 24 hours. The temperature was then slowly cool ed back down to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a larg e amount of what appeared to be purple square-plate crystals suitable for single cr ystal X-ray diffraction were observed to have formed (74 mg, 71% yield). Zn2(camphorate)2(meso, -Bis(4-pyridyl)glycol)0.5]n, [25] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy glycol (0.098 mmol, 21.19 mg), 2,6lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were co mbined together with exactly 2 mL of

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110 N,N -dimethylformamide (DMF) and manually agitated until both solids were fully dissolved. To this solution, 1 mL of meth anol (MeOH) was added and the solution agitated for several seco nds. Separately, Zn(NO3)2•6H2O (0.2 mmol, 59.5 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ bipy glycol /2,6-lutidne/MeOH solution. The vial was sealed w ith store bought kitchen aluminum foil, capped tightly and placed in a sand bath for transf er to a programmable oven. The heat profile was as follows: the reac tion temperature was ra ised from 30 C to 115 C at a rate of 1.5 C per minute upon whic h time it was held at that temperature for 24 hours. The temperature was then slowly cool ed back down to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a large amount of colorless square-plate crystals suitable for single crystal X-ra y diffraction were observed to have formed (34 mg, 20.7% yield). Ni2(camphorate)2(meso, -Bis(4-pyridyl)glycol)0.5]n, [26] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy glycol (0.105 mmol, 22.71 mg), 2,6lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were co mbined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids were fully dissolved. To this solution, 1 mL of ethanol (EtOH) was added and the solution agitated for several seconds. Separately, Ni(NO3)2•6H2O (0.201 mmol, 58.45 mg) was dissolved in exactly 1 mL of DMF, and upon di ssolution, was added to the camphorate/ bipy glycol /2,6-lutidne/ EtOH solution. The vi al was sealed with store b ought kitchen aluminum foil, capped tightly and placed in a sand bath for transfer to a programmable oven. The heat

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111 profile was as follows: the reaction temperatur e was raised from 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours. The temperature was then slowly cooled back dow n to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a large amount of green square-plate crystals were observed to have formed (63 mg, 40.1 % yield). Co2(camphorate)2(meso, -Bis(4-pyridyl)glycol)0.5]n, [27] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vial. In a typical reaction, bipy glycol (0.1 mmol, 21.62 mg), 2,6-lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were co mbined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids were fully dissolved. To this solution, 1 mL of meth anol (MeOH) was added and the solution agitated for several seco nds. Separately, Co(NO3)2•6H2O (0.199 mmol, 57.91 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ bipy glycol /2,6-lutidne/MeOH solution. The vial was sealed w ith store bought kitchen aluminum foil, capped tightly and placed in a sand bath for transf er to a programmable oven. The heat profile was as follows: the reac tion temperature was ra ised from 30 C to 115 C at a rate of 1.5 C per minute upon whic h time it was held at that temperature for 24 hours. The temperature was then slowly cool ed back down to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a larg e amount of what appeared to be pink square-plate crystals were observed to have formed (103 mg, 77% yield). Ni2(camphorate)2(BIPA-Py)0.5]n, [28] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vi al. In a typical reaction, BIPA-PY

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112 (0.11 mmol, 46.24 mg), 2,6-lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were combined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids we re fully dissolved. To this solution, 1 mL of dimethyl sulfoxide (DMSO) was a dded and the solution agitated for several seconds. Separately, Ni(NO3)2•6H2O (0.201 mmol, 58.45 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ BIPA-PY /2,6-lutidne/ DMSO solution. The vial was sealed with store bought kitchen aluminum foil, capped tightly and placed in a sand bath for transf er to a programmable oven. The heat profile was as follows: the reaction temp erature was raised from 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours. The temperature was then slowly cooled back dow n to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a large amount of dirty olive green squa re-plate crystals suitable were observed to have formed (53 mg, 20.1% yield). Co2(camphorate)2(BIPA-Py)0.5]n, [29] was synthesized via a one-pot solvothermal reaction conducted in a 20 mL scintillation reaction vi al. In a typical reaction, BIPA-PY (0.099 mmol, 41.62 mg), 2,6-lutidine (0.4 mmol, 46.44 L), and camphoric acid (0.2 mmol, 40.05 mg) were combined together with exactly 2 mL of N,N -dimethylformamide (DMF) and manually agitated until both solids we re fully dissolved. To this solution, 1 mL of dimethyl sulfoxide (DMSO) was a dded and the solution agitated for several seconds. Separately, Co(NO3)2•6H2O (0.199 mmol, 57.91 mg) was dissolved in exactly 1 mL of DMF, and upon dissolution, was added to the camphorate/ BIPA-PY /2,6-lutidne/ DMSO solution. The vial was sealed with store bought kitchen aluminum foil, capped

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113 tightly and placed in a sand bath for transf er to a programmable oven. The heat profile was as follows: the reaction temp erature was raised from 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours. The temperature was then slowly cooled back dow n to 30 C at a rate of 1.0 C per minute. Upon removal from the oven a large amount of d eep purple square-plate crystals suitable for single crystal X-ray diffraction were obser ved to have formed (110 mg, 63% yield). 3.2.5.2 X-ray Crystallography Single crystals of compounds [15[, [16], and [29] suitable for X-ray crystallographic analysis were selected following examination under a microscope. Intensity data were collected on a Bruke r-AXS SMART APEX/CCD diffractometer using Cu k\ radiation ( = 1.54178 ).281 The data were corrected for Lorentz and polarization effects and for absorptio n using the SADABS program (SAINT).282 The structures were solved using direct methods and refined by full-matrix least-squares on |F|2 (SHELXTL).283 Additional electron density, lo cated in the void cavity space, assumed to be disordered solvent, was una ble to be adequately refined was removed using the SQUEEZE/PLATON program.284-286 Select crystallographic data is presented in tabular form in Appendix C-14, C-15, and C-16 respectively.

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114 3.2.5.3 Powder X-ray Diffraction Powder samples suitable for powder X-ra y diffraction, FT-IR spectroscopy, and Thermal Gravimetric Analysis were obtain ed by removing a large amount of single crystals from the reaction scintillation vial by using a glass Pasteur pipette and depositing these crystal (along with mother liquor) in a small concave agar mortar. Excess solvent was removed via pipette, and surface solvent was removed by wicking action with a Kim-Wipe. Upon wick drying, the crystals were transferred to a small piece of filter paper which was subsequently folded over and they were dried further and slightly crushed with gently pressure. The resulti ng dry powder (~30 mg) was then immediately applied to a PXRD sample puck prepared with a small amount of vacuum grease to fixate the powder sample, and the PXRD experiment performed without delay. All pillared camphoric acid compounds were analyzed via powder X-ray diffraction. The samples were analyz ed on a Bruker AXS D8 Discover X-ray diffractometer, equipped with GADDS™ (General Area Diffraction Detection System) and a Bruker AXS HI-STAR area detect or. The X-ray source was Cu ( = 1.54178 ) run Figure 3.11 Digital photographs of compounds [16] ( left ) and [17] ( right ).

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115 on a generator operating at 40 kV and 40 mA The data was collected within the 2 range of 3 – 40, in continuous scan mode using a step-size of 0.02 per st ep and a rate of 2.5 per minute. (Appendices B-19 – B34) 3.2.5.4 FT-IR Spectroscopy All compounds [14] – [29] were characterized via infrared spectroscopy using a Nicolet Avatar 320 Fourier-Transform Infr ared Spectrometer (FT-IR). Before each sample was analyzed, a background spectrum was obtained for purposes of zeroing out ambient noise in the form of the laboratory atmosphere. Each sample was measured in the range from 4000 cm-1 to 500 cm-1 wavenumbers (wavelen gth of 2500 nm to 20000 nm respectively) and scanned 64 times. Results were recorded in % transmittance and the spectrum analyzed using the EZ OMNIC (V.5.1b, copyright 1992-199 Nicolet Instruments Corporation) computer software su ite. A typical sample was analyzed as a neat, dry solid (~10 mg) obtained via either vacuum filtration and air drying or gently drying with laboratory grade filter paper. (Appendices B-19 – B34) 3.2.5.5 Thermal Gravimetric Analysis Thermal Gravimetric Analysis for compounds [14] – [29] was performed on a PerkinElmer STA 6000 Simultaneous Thermal An alyzer. Data acquisi tion and analysis was performed with the assistance of the Py ris Series suite of software. Roughly 10-20 mg of dry powder was placed in a sample cr ucible and heated at a rate of 10 C/min. form a temperature of 30 C up to 700 C under N2 gas flow.

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116 Notably the majority of the pillared camphorate MOMs exhibited exceptional thermal stability. Upon a small amount of weight loss attributed to ei ther loss of mother liquor remnant on the surface of the crystals or small amounts of guest solvent trapped in the cavities being evacuated, typically all of the camphorat e compounds showed a nearly flat spectrum indicating no addition al weight loss until well past 200 C 3.3 Conclusion A series of closely related compounds a ll based upon the prin ciple of pillaring a MOF-2 like layer constructed from the diacid (1R, 3S)-(+)-1,2,2-trimethyl cyclopentane1,3-dicarboxylic acid, camphoric acid, into an extended 3-periodic metal-organic material have been described. A large number of r eactions were conducted in synthesizing Zn2+, Ni2+, and Co2+ versions of the pillared structure for a number of pillars. Single crystal Xray crystallography of the thin plates which resulted from the solvothermal reactions were often plagued with multiple problems; First many of the thin plate crystals suffered from stacking of multiple plates and resulted in twinning. Additionally, many of the crystal samples appeared to lose solvent upon sitt ing out on the bench perhaps affecting the crystals diffracting ability. Fi nally, and probably most fundame ntally, the nature of the system provided for much consternation. Ev en in previously published accounts of related camphoric acid pillared MOFs, the described crystallography was suspect. The existence of the chiral centers within th e ligand, and the bow-tie conformation of the individual layers, do not mesh well with the four-fold symm etry preferred by the square paddlewheel SBU. As such the crystallogra pher found it difficult to correctly assign the appropriate space group and for many of the di ffraction collection experiments this lead

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117 to data which was not able to be fully re fined. However, generally unit cells obtained matched the expected dimensions and all other physical characterization methods indicated that many of the unsuccessful co mpounds were isostructural to compounds which were fully refined. Each of the compounds synthesize in the chapter were also analyzed for their porosity through gas sorption measuremen ts. Only three of the compounds ( [14], [15], and [17] ) demonstrated an appreciable extent of gas uptake at low temperatures and low loadings. A fourth sample has been imp roved through the activation technique of supercritical CO2 drying, but has still not been completely successful.

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118 Chapter 4 From Metal-Organic Polyhedra to Supermolecular Building Blocks 4.1 Introduction Until now this dissertation has focused upon structures which repeat periodically in two (2-periodic, Chapter 2) or three (3-p eriodic, Chapter 3) mutually perpendicular spatial dimensions. For this chapter, the disc ussion will shift (momentarily) to structures which are not periodic along any one direction, and are therefore referred to by the term discrete or 0-periodic. As we shall see ma ny beautiful structures are attainable when dealing with discrete objects. However, more than simply being aesthetically pleasing, many discrete structures also have intriguing proper ties not seen in extended structures. This chapter aims to outline several exampl es of novel discrete metal-organic material nanostructures which adopt polyhedral forms. Additionally, the synthesis, characterization, and some pr operties of these discrete metal-organic polyhedra are discussed. Finally, a new design strategy for the generation of extended metal-organic materials, whereby nanoscale metal-orga nic polyhedra are employed as nodes is described.

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119 4.1.1 Discrete Supramolecular Polygons As a central theme of this dissertation, the inherent complexity of the materials in question is always of key concern. While disc rete structures are, by their very nature finite, at first blush they may seem to be the least complex of all the possible architectures observed in metal-organic ma terials. In the case of molecular and supramolecular polygons this is cert ainly true. However in the case of some polyhedra, it will become evident that this ge neralization is often unwarranted. Supramolecular polygons301-305 are discrete structures, often approaching or well established within the nanoscale, which are t ypically fabricated in solution and can often be crystallized into a solid state form. They can be generated through either hydrogen bonding or other weak noncovalent intera ctions, or they might be sustained via the coordinate-covalent coordination bond. Early on in the popularization of what might today be called metal-organic materials, many researchers in the field focused upon the synthesis and characterization of discrete s upramolecular polygons, often in the form of molecular squares. These squares were typically constructed by utilizing 4,4 -dipyridyl molecules together with square pl anar transition metal ions (Cd2+ and Pd2+ were two common examples). Soon other polygons were ta rget as well increasing the library of known compounds and their properties and augm enting synthetic methods at the crystal engineer’s disposal. The design principles which were successfully employed for the isolation of these supramolecular polygons la id the foundations for the development of more complicated supramolecular polyhedra which would soon follow.

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120 4.1.2 Polyhedra Polyhedra are discrete (0-p eriodic) geometric constructs composed of flat faces and straight line segments. The faces are them selves polygons, formed by a circuit of line segments (edges), and the faces of the pol yhedron are parts of larger planes. The polyhedron is generated by the in tersection of these planes al ong the edges so that only two planes meet at an edge; every edge of a particular polygon (face) belongs to exactly one other polygon.306 If all of the vertices of a polyhedron are identical with respect to symmetry (i.e. if there exists an isometry ma pping a vertex into any other vertex) we say that the polyhedron is uniform (vertex-transitive). For the purpos es of this dissertation we will deal only with uniform polyhedra. A comm on way of classifying a polyhedron is to describe its vertex figure which is the structure which re mains if a single node is lopped off. These vertex figures can often be convolut ed, so the use of short hand notation called vertex configuration is often used. The vertex configur ation is a list of the sequence of polygons located around a vertex, and is written as a series of numbers. In the case of uniform polyhedra, where there is only a single type of vertex, the vertex configuration can completely define and distinguish between different polyhedra. In the situation in which a polyhedron is a single closed surface and when none of the boundary planes which make up the faces penetr ate the interior of the polyhedron, we say in that the polyhedron is convex In contrast, a non-convex polyhedron (i.e. star polyhedra) will contain faces which intersect with other f aces and are inherently more complicated structures. The polyhedra most people are familia r with (and the majority of the type to be discussed in the remainder of this ch apter) are classified as convex polyhedra.

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121 4.1.2.1 Platonic Solids The simplest and most widely reco gnized of all polyhedra are those five polyhedra which are commonly referred to as the Platonic Solids —the tetrahedron (33), hexahedron (cube, 43), octahedron (34), dodecahedron (53), and icosahedron (35)—which are all constructed from a single type of regular polygon meeting at identical vertices and sharing identical edges. By use of the term regular it is implied that the polygon is constructed of equal angles (equiangular) and equal e dge lengths (equilateral). Analogously, the Platonic Solids (Fig. 4.1) are themselves regular, meaning that in addition to each of its polygonal faces being regular, all of the vertices (vertex-transitive), edges (edge-transitive), and faces (iso hedral) are identical respectively. As is obvious from the above figure, the Platonic Solids are highly symmetric objects, all of which belong to one of the high symmetry groups; tetr ahedral, octahedral, or icosahedral. Though they have been known for millennia going back at least until the time of the Greeks, these objects are still of immense interest to modern day mathematicians and materials scientists. I ndeed just this year, researchers have Figure 4.1 The Platonic solids. From left to right: tetrahedron, cube (hexahedron), octahedron, dodecahedron, and icosahedron.2, 3

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122 discovered new dense packings307 of these and related object s, which have important influences on the sciences of liqui d, glassy, and crystalline materials. 4.1.2.2 Archimedean Solids When the restriction requir ing that all polygons meeting at a vertex be of the same type is relaxed, the situation arises where two more types of regul ar polygon meet at identical vertices and share edges. In this case the polyhedra are semi-regular, and are commonly referred to as being Archimedean Solids. There are 13 Archimedean Solids : truncated tetrahedron (6.6.3), cuboctahe dron (4.3.4.3), truncated octahedron (4.6.6), truncated cube (8.8.3), rhombicuboctahedron (4.4.3.4), truncated c uboctahedron (8.4.6), snub cube (4.3.3.3.3), Icosidodecahedron ( 5.3.5.3), truncated icosahedron (5.6.6), truncated dodecahedron (10.10.3), rhombi cosidodecahedron (5.4.3.4), truncated icosidodecahedron (10.4.6), snub dodecahedr on (5.3.3.3.3) (Fig. 4.2). The existence of the Archimedean Solids and indeed much more complicat ed polyhedra is a salient reason for a reluctance to claim that discrete structur es, by their very nature of being 0-periodic are less complex than 1-periodic and surely 2-periodic architectures. The very existence of semi-regular polyhedra is much more topologically co mplex than that of any 1periodic structure and ca n be just as complex if not more so than 2-periodic examples. In chapter 2 it was revealed that th ere were just 8 semi-regular ( Archimedean ) plane tilings, while now we see there are 13 semi-regular polyhedra indicating increased diversity. Additionally, each of the plane tilings is intim ately related to a pa rticular polyhedron and can be interpreted as being a projection of the polyhedron onto the plane, making the 2periodic tilings subjective to th at of the 0-periodic polyhedra.

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123 4.1.2.3 Faceted Polyhedra Another class of polyhedra which will be very pertinent to our discussion of metal-organic polyhedr a are the so-called faceted polyhedra These polyhedra result from the linking of regular polygons at identical vertices (making them uniform polyhedra ), but do not involve the edge-sharing betw een polygons as was seen in both the Platonic and Archimedean Solids. By virtue of the polygons meeting at vertices in a manner such that they do not share edges, these non-convex polyhedra in herently contain both closed faces (polygons) and open windows to their hollow interior. There are exactly nine uniform non-convex polyhedra generated via the vertex-sharing of regular convex polygons and they can be composed of either a single type of polygon ( regular ) or more Figure 4.2. The Archimedean Solids. From left to right; Top: truncated tetrahedron, cuboctahedron, truncat ed octahedron, truncated cube, and rhombicuboctahedron. Middle: truncated cuboctahedron, snub cube, icosidodecahedron, and truncated dodecahedron. Bottom: truncated icosahedron, rhombicosidodecahedron, truncated icosidododecahedron, and snub dodecahedron.2, 3

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124 than one type of polygon ( semi-regular ): tetrahemihexahedron (4.4/3.4.3), small icosidhemidodecahedron (10.3/2.10.3), octahemioctahedron (6.3/2.6.3), cubohemioctahedron (6.4/3.6.4), small rhombihexahedron (4.8.4/3.8), small rhombidodecahedron (10.4.10/9.4/3), small dodecahemidodecahedron (10.5/4.10.5), small cubicuboctahedron (8.3/2.8.4), and small dodecaicosidodecahedron (10.3/2.10.5) (Fig. 4.3). Figure 4.3 Faceted Polyhedra generated via vertex linking of regular polygons. From left to right; First Row: tetrahemihexahedron, small icosidhemidodecahedron, and octahemioctahedron. Second Row: cubohemioctahedron, small rhombihexahedron, and small rhombidodecahedron. Third Row: small dodecahemidod ecahedron, small cubicuboctahedron, and sm all dodecicosidodecahedron.2, 3

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125 4.1.3 Metal-Organic Polyhedra Many of the Platonic and Archimedean Solids are potential target for crystal engineers when designin g metal-organic polyhedra308-311. MOPs are attractive as they exemplify discrete nanoscale architecturest that will often exhibit unique physical properties in relation to other extended MOMs (i.e. solubility) To date there have been many examples of MOPs which can interpreted as have structures analogous to simple Platonic and more complicated Archimedean solids. Such MOPs as tetrahedra312-319, cubes313, 320-322, octahedra317, 323, cuboctahedron, small rhombihexahedra324-332, truncated tetrahedra333, and truncated octahedra334 have all been synthe sized and characterized. Many more examples of more complicated pol yhedra have also been investigated. 4.2 Alkoxy Nanoball – Dodecyloxy Cu(II) Nanoball The first derivative form of 1,3-ben zenedicarboxylic (1,3-bdc) acid that was focused upon for the synthesis of a novel functionalized nanoba ll was that of a dodecyloxy pendant group substituted in th e 5-position of the dicarboxylic acid. This ligand, 5-dodecyloxy-1,3-be nzenedicarboxylic acid, L4 (Fig. 4.4), was synthesized in an attempt to discern ways of contro lling the supramolecular isomerism19, 20 observed in the system involving square paddlewheel SBUs and 1,3-bdc. Adopting l ong alkyl chains in the 5th position of the bdc moiety was expected to preclude the possible synthesis of the so-called square grid or Kago m lattice 2-periodic layered networks and instead only facilitate the formation of the 0-periodic discrete nanoball isomer. Indeed, the synthesis of a cupric alkyloxy nanoball constructed from L4 and copper (II) nitrate was achieved,

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126 while extensive attempts to isolate any of the other isomers using this ligand were unsuccessful. 4.2.1 Structural Analysis The reaction of L4 with copper (II) nitr ate under appropriate c onditions gives rise to the self-assembly of 0-period ic alkoxy nanoballs of the form Cu2(5-dodecyloxy-1,3benzenedicarboxylate)2(MeOH)x(H2O)2-x]12, [30] where the nanoball is functionalized with 24 dodecyloxy pendant groups decora ting the periphery (Fig. 4.5). These dodecyloxy nanoballs crystallize in the chiral space group P41212 with cell parameters of a = b = 38.559(2) , c = 54.503(6) , = = = 90, V = 81,035 (11) 3. Before the synthesis of this novel deriva tive nanoball could be verifi ed and the results published, another research team active in the field reported the s ynthesis and deposition onto a graphite surface of a nearly identical compound.335 The synthesis of [30] was conducted utilizing a non-coordinating base so that in the case of th is nanoball derivative, the 24 axial ligands consist of some combination of methanol or water solvent molecules. Figure 4.4 5-dodecyloxy-1,3-benzenedicarboxylic acid, L4.

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127 The addition of dodecyloxy pendant groups to the outer surf ace of the nanoball greatly augments the overall size of these na noparticles, while the inner skeleton of the nanoball remains roughly indisti nguishable from that of a ny other example, except for small variations in the inner/outer diameter or slight changes in the angle between SBUs (i.e. some nanoballs are slightly less spherical than others). The largest outer diameter for the skeleton of the dodecyloxy nanoball, when not taking into account the alkyl chains, was observed to be 24.744 (2.47 nm) as measured from carbon-to-carbon in the 5th position of opposite 1,3-bdc moieties. The shortest inner diameter for the skeleton nanoball was observed to be 15.964 (~1.6 nm) as measured from inner copper atom to inner copper atom, thus ignoring the pres ence of any axially bound solvent molecules within the cavity of the nanoball (i.e. as would be expected if fully desolvated of axially ligands). This leads to an inner and outer volume of approximately 2.13 nm3 and 7.93 Figure 4.5 Schematic depicting stick view of the dodecyloxy nanoball. In this figure hydrogen atoms have been deleted for clarity (Atom color code: carbon = grey; oxygen = red; copper = salmon).

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128 nm3 respectively, well within the ranges esti mated for other nanoball derivatives. When the dodecyloxy chains are taken into consider ation however, a maximal outer diameter of just over 50 (5.0 nm) is observed resulti ng in an outer volume of nearly 69.5 nm3. As will be evident momentarily, this volume is simply an idealization of the volume if the dodecyloxy chains are treated as rigid groups protruding from the nanoball and precluding any other objects from closer appr oach; in fact the nanoballs close pack well within this hypot hetical distance. As might be expected the dodecyloxy pe ndant groups extending outward from the surface of these nanoballs demonstrate a high degree of flexibility. However, what was not expected was the intriguing way these na noballs pack in their solid-state crystal structure. While it is understandable that th e relatively long alkyl chains of one nanoball should in principle be able to intertwine and co-mingle with the alkyl chains of neighboring nanoballs, especially via van der Waal interactions when several nanoballs are forced into a close approach in the crys talline state, it was somewhat astonishing to observe that these long alkyl chains have the ability to thread through the open windows and into the empty interior of its nearest adjacent neighbors. Additionally, the flexibility of the alkoxy pendant groups is such that the long chains ar e capable of enduring extreme distortions in their conformation making feas ible the observed self-inclusion of these alkyl chains through the open wi ndows of its own nanoball. In fact at least two of the dodecyloxy pendant groups of each nanoball self -include and penetrate into the hollow interior of the nanoball core which they are covalently attached to, entering through two separate open square windows (Fig. 4.6).

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129 In addition to the two self-included chai ns, the center of each nanoball also plays host to at least two other dodecyloxy ch ains, one each donated from two different adjacent nanoballs and entering through separa te open triangular windows, bringing the total number of included alkyl groups up to f our (Fig. 4.7 top). Besides accepting four dodecyloxy chains (two from itself and one each from two nearest neighbors), each nanoball also donates one chain each into tw o adjacent nanoballs different that those which donated chains to itself (Fig. 4.7 bottom). Figure 4.6 Cartoon illustrating the self-inclusion of two dodecyloxy groups (blue chai ns) into the center of each nanoball. The green colored chains are those that will include into two different adjacent nanoball neighbors. All hydrogen atoms have been deleted for clarity.

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130 This generates a motif in which a central nanoball accepts chains from two unique adjacent nanoballs while simultaneously dona ting separate chains to two unique neighboring nanoballs. Therefore it is entirely reasonable to interpret any one of these nanoballs as being a type of 4-connected supr amolecular node since it interacts with four nearest neighbors strictly thorough noncovale nt interactions. More precisely this supramolecular node adopts the geometry of a distorted tetrahedron which in turn results in the dodecyloxy nanoballs packing into a distorted supramolecular diamondoid network. Interestingly, this supramolecu lar diamondoid network packing of dodecyloxy nanoballs was also observed and described in th e previous report of the related structure, Figure 4.7 Cartoon illustrating the interactions between nearest neighbor nanoballs in compound [ 30]. Top: Two nearest neighbors donate a single dodecyloxy chain (green) each into the hollow interior of the same nanoball. Bottom: The central nanoball donates two dodecyloxy chains (green) into two nearest neighbors different from those which donate to it.

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131 albeit in that structure no threading of the alkyl chains into the open windows of the nanoballs was apparent. In the first instan ce it was observed that these chains, while adopting variable confirmations, either prot ruded away from its own nanoball core or became entangled with the chain of a nei ghboring nanoball. As to the reason behind the discrepancy in packing motifs realized in th ese two solid state structures, we can only presume that it arises due to the nature of the crystallization processes and/or to the effect of axial ligands present. In the previously published exam ple, the powdery precipitate that was collected from the di rect mixing of the cupric and L4 ligand N,N dimethylformamide solutions was recrystalli zed from a hexane/octanol mixture. This solvent system is decidedly more nonpolar than that which was used to obtain the single crystals of [30] in which the powder precipitate was dissolved in tetrahydrofuran while neat acetonitrile was layered over this solution and the two solvents were allowed to slowly diffuse into one another. The increase d polarity of the crystallizing solvents is perhaps a driving force for the threading of dodecyloxy pendant chains into the hollow interior of the alkoxy nanoballs. Except for the mechanism of how the individual dodecyloxy nanoballs interact when packing ( via the threading of alkoxy chains th rough open windows in my structure versus the lack of penetration in the previously published ex ample), the dimensions of the distorted supramolecular tetr ahedron and subsequent diam ondoid networks of the two structures are nearly identical. In the case of the distorted supramol ecular tetrahedron, the observed angles generated by linking the cente r of the central dodecyloxy nanoball to the centers of each of its nearest neighbo rs range from 98.571 in the case of the

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132 Nanoballacceptor-Nanoballcenter-Nanoballacceptor, 108.506 (x2) and 109.209 (x2) for Nanoballdonor-Nanoballcenter-Nanoballacceptor, and 120.596 for the case of NanoballdonorNanoballcenter-Nanoballdonor (Fig 4.8). The center-to-cente r distance between the central dodecyloxy nanoball and that of each of its f our adjacent nearest neighbors was measured to be 23.755 (as opposed to 23.935 in the previous structure) a nd combined with the observed angles between neighbors, gene rated individual edge lengths (measured centroid-to-centroid) for the distorted supram olecular tetrahedron were measured to be 36.011 , 38.559 (x2), 38.729 (x2), and 41.268 (previously observed to be 33.571 and 41.568 ). Figure 4.8 Scheme illustrating the distorted supramolecular tetrahedron (with some angles shown) generated by the four nearest neighbors of a central (red sphere) dodecyloxy nanoball. The green spheres represent those nanoballs donating alkyl chains into the central nanoball, while the blue spheres represent those nanoballs acce p tin g chains from the central nanoball.

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133 4.2.2 Properties With the addition of long alkyl chai ns in the dodecyloxy derivative of the nanoball, we expect the potential to observ e drastically altered properties for these discrete metal-organic materials in comparis on with either the pare nt nanoball structure or those derivatives already characterize d. Indeed a significant property of these nanostructures, namely their ability to inter act in the solid-state through chain threading as described in the previous section, is in f act quite distinct from that observed for other derivatives of nanoballs. This ability to interact via threading is a direct consequence of the both the flexible nature of the dodecyloxy group as we ll as their unique chemical nature (non-polarity). In addition to how th e dodecyloxy nanoballs interact within the solid-state, the presence of these long alkyl chains should have significant influence upon their solution properties, especially in dicta ting the nature of solvents they might be soluble in. Briefly, I would also like to take a mo ment to mention a property of these materials which lead to an intriguing app lication already describe d by another research group. The fact that these materials possess openings in the form of open square and triangular windows leading into their hollow in terior cavities has al ready been discussed. As such the potential for encapsulation of functional molecular species for various applications is of great interest. However, in addition to the ability to encapsulate larger guests that might otherwise not be able to depart from within the interior (Ship-in-abottle), these hollow spheres with small windows should be able to allow smaller moieties (especially ions) to easily ingress a nd egress from their center. With this in

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134 mind, Kim and co-workers336 have demonstrated the ability to imbed cupric dodecyloxy nanoballs into synthetic membrane bilayers thanks in large pa rt to the presence of the long nonpolar alkyl chains. The dodecyloxy nan oballs then bridge the membrane such that select ions can travel through the nanoball to transverse the membrane, thus utilizing the nanoballs as a form of synthetic ion channel. 4.2.2.1 Solubility Whereas the original nanoball was desc ribed to be solubl e in common polar organic solvents most notably alcohols (methanol, ethanol, etc.), the dodecyloxy derivative is soluble in a range of solvents decidedly more nonpolar. Qualitative solubility experiments were conducted using the turquoise powdery precipitate formed via the direct mixing of Cu(NO3)2 and L4 ligand solutions, upon vac uum filtration and air drying of the solid. A small sample of th e dry powder (~10-20 mg) was placed into a clean, labeled test tube, and to this ~ 1 mL of neat solven t was added. With the aid of manual as well as mechanical (Maxi-Mix) agitation, dissolution of the solid was attempted. If upon agitation for several minutes, the solid was still not dissolved (as evidenced by possible color change; noticeable loss of solid), the use of a hot water bath (steaming, yet not boiling ~85-90 C) was implem ented and the test tube allowed to sit for several minutes before reobserving. Through following this protocol it was determined that the dodecyloxy nanoball is readily soluble in chloroform, dichloromethane, toluene, carbon tetrachloride, 1,4-dioxa ne, tetrahydrofuran, ethyl acetate, benzene, nitrobenzene, and hot N,N -dimethylformamide. They were determined to be insoluble in dimethyl sulfoxide, metha nol, ethanol, acetonitrile, and neat hexane, as

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135 well as instable in neat D.I. H2O (collapse of nanoball structure was taken with the concomitant loss of characteristic blue co lor and the emergence of a milky white precipitate which is presumab ly insoluble free ligand). 4.2.3 Experimental 4.2.3.1 Synthesis All reagents, unless described otherwise, were purchased from either SigmaAldrich or Fischer Scientific and used as received without further purification. Bulk solvents such as methanol, ethanol, acetone, and dichloromethane were first distilled and stored over drying media (4 mol ecular sieves) before their use. 5-Dodecyloxy-1,3-benzenedicarboxylic acid, L4 (Fig. 4.4), was synthesized from commercially available dimethyl-5 -hydroxy-1,3-benzenedicarboxylate and 1bromododecane via established procedures fo r the alkylation of phenols.277, 337 In a typical reaction dimethyl-5 -hydroxy-1,3-benzenedicarboxy lic acid (5.00 g, 0.0238 mol) and potassium carbonate (K2CO3, 9.88 g, 0.0715 mol, 3 equivalents) were weighed out separately and dried on a vacuum pump for approximately three hours. A 3-neck round bottom flask was sealed with rubber septa and the air purged with N2 for 15 minutes prior to the start of the reaction. Upon drying the diester and K2CO3 were dissolved together in approximately 75 mL of dry acetone and added to the 3-neck round bottom flask equipped with two rubber septa and a cold-water condenser situated in a hot oil bath held at 80 C. The solution was allowed to reflux for 30 minutes before 1-bromododecane (17.2 mL, 0.0715 mol; 3 equivalents) was added via syringe through a rubber septum.

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136 The reaction was allowed to reflux for approximately 12 hours before monitoring the extent of comple tion through TLC. Upon completion the solution was cooled to room temperature, filtered through Celite, and the solvent removed by heating under vacuum (Rotavap) leaving behind a dark yellow oil which solidified upon coo ling. This solid was dissolved in ~100 mL dichloromethane (DCM), transf erred to a separato ry funnel, washed three times with D. I. H2O, and dried over anhydrous Na2SO4. The DCM solvent was removed via rotavap and the solid recrystallized from hot ethanol. The ester product crysta ls were collected via filtration and dried, upon which they were added to a NaOH solution (20% by volume, 3 equivalents to the ester) and allowed to stir with a magnetic stir bar on a hot plate until fully dissolved. The conversion from ester to carboxylate was monitored via TLC and upon completion was worked up with HCl (10 % by volume) added drop-wise until the solution was acidic by pH paper. The precipitate was filtered, washed with D.I. H2O, and allowed to dry at which time 5.015 g (60.1 % yield) of white solid was obtained. The spectroscopic data for L4 (Appendix A-4, B-4) were consiste nt with previously reported data for this compound.338 1H NMR (250 MHz, DMSOd6, ): 0.9(t, J = 6.3 Hz, 3H, -CH3), 1.2(m, 18 H, -CH2-), 1.7(m, 2H, -CH2-), 4.1(t, J = 6.4 Hz, 2H, -O-CH2-), 7.6(s, 2H, -ArH), 8.1(s, 1H, -ArH), 13.3(br, 2H, -COOH); mp 166-168 C (lit. 163-166 C).

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137 Cu(II) dodecyloxy nanoballs [30], were synthesized via a reflux reaction conducted in a round bottom flask using methanol as the solvent. In a typical reaction, Cu(NO3)2•2.5 H2O (699 mg, 3.01 mmol) was dissolved in 10 mL of methanol and subsequently added to a refluxing solution of 5-dodecyloxy-1,3-ben zenedicarboxylic acid ( L4 ) (1.078 g, 3.076 mmol) dissolved in 50 mL of methanol. To this solution 2,6-lutidine (1.08 mL, 9.27 mmol) was added and the mixtur e was allowed to continue refluxing for one hour. Upon cooling, the solution and precipitate were separated via vacuum filtration and the filtrand was allowed to air dry overnig ht in the fume hood resulting in 1.027 g of a turquoise-blue microcrystalline powder be ing collected for an overall yield of 82%. 4.2.3.2 X-ray Crystallography Crystals suitable for single crystal X-ray diffraction were grown through the process of recrystallizat ion from a mixed solvent system. The turquoise-blue microcrystalline powder was first dissolved in tetrahydrofuran resulting in a concentrated deep blue solution. Acetonitrile was then carefully layered over this nano ball solution using a small volume of pure THF as a blank middle layer. The crystallization vessel was left to sit on the lab bench at room temperatur e and the solvents allowed to slowly diffuse into one another over the period of a couple week s resulting in the formation of dark blue prisms of [30] (Fig. 4.9).

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138 Single crystals suitable for X-ray crys tallographic analysis were selected following examination under a microscope. Inte nsity data were collected on a BrukerAXS SMART APEX/CCD diffractometer using Mo k\ radiation ( = 0.7107 ).281 The data were corrected for Lorentz and polari zation effects and for absorption using the SADABS program (SAINT).282 The structures were solved using direct methods and refined by full-matrix least-squares on |F|2 (SHELXTL).283 Additional electron density, located in the void cavity space, assumed to be disordered solvent, was unable to be adequately refined was removed using the SQUEEZE/PLATON program.284-286 Select crystallographic data is presented in tabular form in Appendix C-17. 4.2.3.3 Powder X-ray Diffraction Powder samples of [30] suitable for powder X-ray diffraction, FT-IR spectroscopy, and Thermal Gravimetric Anal ysis were obtained by removing a large amount of single crystals from the reaction scinti llation vial by using a glass Pasteur pipette and depositing these cr ystal (along with mother liquo r) in a small concave agar Figure 4.9 Digital photograph depicting single crystals of compound [30]

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139 mortar. Excess solvent was removed via pipette, and surface solvent was removed by wicking action with a Kim-Wipe. Upon wick drying, the crysta ls were transferred to a small piece of filter paper which was subseque ntly folded over and they were dried further and slightly crushed with gently pr essure. The resulting dry powder (~30 mg) was then immediately applied to a PXRD samp le puck prepared with a small amount of vacuum grease to fixate the powder samp le, and the PXRD experiment performed without delay. The Cu(II) dodecyloxy nanoballs, compound [30], was characterized for bulk composition purity via PXRD. The samples were analyzed on a Bruker AXS D8 Discover X-ray diffractomet er, equipped with GADDS™ (General Area Diffraction Detection System) and a Bruker AXS HI-STAR area detector. The X-ray source was Cu ( = 1.54178 ) run on a generator operating at 40 kV and 40 mA. The data was collected within the 2 range of 3 – 40, in continuous scan mode using a step-size of 0.02 per step and a rate of 2.5 per minute. (Appendix B-35) 4.2.3.4 FT-IR Spectroscopy All compounds, including synthesi zed ligands, were characterized via infrared spectroscopy using a Nicolet Avatar 320 Four ier-Transform Infrared Spectrometer (FTIR). Before each sample was analyzed, a background spectrum was obtained for purposes of zeroing out ambient noise in the form of the laboratory atmosphere. Each sample was measured in the range from 4000 cm-1 to 500 cm-1 wavenumbers (wavelength of 2500 nm to 20000 nm respectively) and scanned 64 times. Results were recorded in %

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140 transmittance and the spectrum analyzed using the EZ OMNIC (V.5.1b, copyright 1992199 Nicolet Instruments Corporation) computer software suite. A typical sample was a analyzed as a neat, dry solid (~10 mg) obtained via either vacuum filtration and air drying or gently drying with laboratory grade filter paper. 5-dodecyloxy-1,3-benzenedicarboxylic acid, L4 : IR (dry powder) max (cm-1): 3535 m (-OH, free carboxylic acid), 3451 w (OH, free carboxylic acid), 3122 br (-OH, carboxylic acid Hydrogen bonded), 2922 m s h. (-CH, aliphatic), 2847 m sh. (-CH, aliphatic), 1707 s sh. (C=O carboxylic acid), 1677 m s h. (C=O, carboxylic acid). (Appendix B-4) [Cu2(5-dodecyloxy-1,3-benzenedicarboxylate)2(MeOH)x(H2O)2-x]12 [30] : IR (dry powder) max (cm-1): 3402 v br (-OH, alcohol solvent) 2922 m sh. (-CH, aliphatic), 2852 m sh. (-CH, aliphatic), 1635 m sh. (COO-, carboxylate), 1587 m sh. (C=O, carboxylate), 1378 v sh. (COO-, carboxylate). The most notable cha nges between the IR spectrum for the ligand L4 and compound [ 30 ] is the disappearance of the OH stretch due to the carboxylic acid that was centered around 3122 cm-1 and bleed into the 3000 cm-1 region as well as the two sharp peaks at 3535 cm-1 and 3451 cm-1 which arose from free acids. There are two moderately inte nse and sharp peaks at 2922.81 cm-1 and 2852.29 cm-1 which remained from the ligand IR spectrum and are due to the large presence of –CH2 and –CH3 groups. Additionally, we notice drastic shifts in frequency for the C=O stretches which is expected upon coordina tion of the carboxylate. (Appendix B-35)

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141 4.2.3.5 Thermal Gravimetric Analysis Thermal gravimetric analysis (Appendi x B-35) for Cu(II) dodecyloxy nanoballs, [Cu2(5-dodecyloxy-1,3-benzenedicarboxylate)2(MeOH)x(H2O)2-x]12, [30] was conducted on a T.A. Instruments 2950 TGA operating in the High Resolution Dynamic mode. The program was run from 30 C up to 1000 C and was performed under a flow of N2 gas. The resulting data was graphed as a function of weight percent (wt. %) versus change in temperature. Upon acquisition the data was evaluated using T.A. Instruments Thermal Advantage suite of analyzing software. Initial weight loss of 7.6 % from ~30C to 50 C was observed and interpreted to be loss of mother liquor s till present on the crystalline sample. A small amount of additional weight loss (5.67 %) was observed over a large temperature range of ~50 C to 220 C and thought to be low bo iling interstitial guest molecu les in the crystal lattice. The first major weight loss results in a mode rately sharp weight loss seen form about 220C until approximately 300 C which may be do the first loss of coordinated solvent molecules or possibly trapped solvent molecu les being removed over a large temperature range. This represents ~18% of the sample and most likely was due to the various types of solvent molecules (MeOH, H2O, etc.). The largest weight loss of ~35 % was observed to occur in the temperature range of 310 C unit 380 C. After 380 C, the sample decomposed with a final weight loss of 15.5%.

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142 4.3 Aryloxy Nanoballs – Benzyloxy a nd Naphthyloxy Cu(II) Nanoballs As already outlined in the introduction (4.1.3) and clearly demonstrated by the previous section of this dissertation descri bing the dodecyloxy derivative, the nanoball is more than an aesthetically pleasing structure of mundane interest. It represents a platform of many different possible compounds which can be fabricated using an identical synthesis strategy. In principle one can alter the metal ion holding th e structure together or functionalize the brid ging ligand and thus alte r the nature of the outer surface of the nanoball and in turn influence it s physical and chemical prope rties. But what alterations should be made and which properties should be targeted for influence may not always be clear. However, in the case of the nanoba ll derivatives, a survey of those types of functionalization which already exist may pr ove fruitful. This exercise led to the realization that no derivative of the nanoball s existed with aryl groups positioned around the periphery of the sphere. Aromatic groups such as phenyls and naphthyls could prove interesting additions to the nanoball for several reasons. They should increase the nanoballs solubility in arom atic hydrocarbon solvents, whil e also providing external functional groups known to undergo reli able noncovalent interactions ( ••• stacking and CH••• interactions) in both solution and the solid state. This may make a properly derivatized nanoball amenable to crystal engineering and allo w further investigation into how these supermolecules interact with one another through self-assembly. Finally, simple aryl groups such as phenyl and naphthyl rings are good starting points for the incorporation of fluorescent ac tive groups on the exterior of the nanoball as they are relatively facile to synthesis. Their adopti on could provide useful insights into the

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143 methodology necessary for the future integratio n of more interesting fluorescent active groups for many potential applications. 4.3.1 Structural Analysis As is the case with all nanoballs compound [31], [Cu2(5-benzyloxy-1,3benzenedicarboxylate)2(DMF)x(H2O)2-x]12, or the benzyloxy nanoball, is constructed from the vertex sharing of 12 mo lecular squares linked together via 24 bridging ligands. These molecular squares are fashioned fr om dimetal tetracarb oxylate subunits and therefore each nanoball is composed of exactly 24 transition metals. The benzyloxy nanoball was synthesized from c opper (II) nitrate and ligand L1 through self-assembly, so that there are 24 copper ions as we ll as 24 5-benzyloxy-1,3benzenedicarboxylates. Each of the benzyloxy groups is located at the 5th position of the dica rboxylate which is oriented outward away from th e surface of the nanoball (Fig. 4.10). This nanoball was synthesized in the pr esence of the non-coordinating base 2,6lutidine and as such the axial position of the SBU is occupied with a variable amount of solvent molecules or water. Single-crystal X-ray diffraction was unable to completely refine the identity of all axial ligands wher e electron density was located, but disordered solvent molecules (DMF) or water is expected. The benzyloxy nanoballs [31], selfassemble and crystallize in the tetragonal space group P4/mnc with cell parameters a = b = 27.974 (5) , c = 39.321 (5) , = = = 90, and a cell volume of 30770 (9) 3 with Z =2.

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144 The inner core of the benzyloxy nanoball, as would be expected when using a 1,3bdc derivative, is essentially identical to that of most other derivatives including the parent version. The shortest inner diameter, as measured from one inner copper atom to the opposite inner copper atom is 15.833 (1. 58 nm) meaning the interior volume of this nanoball is approximately 2.08 nm3. This distance was taken as the inner diameter for two salient reasons; the variab le presence of unidentified inner axial ligands makes it difficult to involve these molecules in the calc ulation, and secondly th e labile nature of these axial ligands gives rise to their potenti al removal from the structure and subsequent increase of the inner core volume. Thus it was decided to measure the volume of the hollow interior while disregarding the presen ce of these axially bound solvent molecules. The longest outer diameter of the nan oball skeleton as measured from the 5th position Figure 4.10 Schematic illustrating a stick view of the benzyloxy nanoball, compound [31] (grey = carbon, red = oxygen, green = copper; hydrogen atoms have been deleted for clarity).

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145 carbons on opposite 1,3-bdc rings was measured to be 24.040 (2.4 nm), while the longest measured diameter for this nanoball including the benzyloxy groups was measured to be 36.732 (3.67 nm), resu lting in outer volumes of ~ 7.24nm3 and 25.9 nm3 respectively. As can be expected from a tetragonal space group, the benz yloxy nanoballs pack in a body-centered cubic (bcc) arrangemen t (Fig. 4.11) where each nanoball can be viewed as being placed at the center of a cube (though somewhat distorted along the caxis to make it tetragonal) and having eight nearest neighbors positioned at the corners of said cube. The centroid-to-centroid distan ce between the central benzyloxy nanoball and its nearest neighbors residing at the corner s of the cube was measured to be 27.889 (~2.79 nm). As the nanoballs are positioned around the elongated cube which also represents the unit cell, it follows that the centroid-to-c entroid distance between two adjacent nanoballs which are both nearest neighbors to the same central nanoball can be only one of two dimensions; eith er they rest in the same ab plane and have a distance of 27.974 (length of aaxis) or they are adjacent along the c -axis in which they are separated by a distance of 39.321 (length of c -axis). The central benzyloxy nanoball also has six second nearest nei ghbors oriented at the six faces of the cube and located at the slightly longer distance of 27.974 , because if viewed carefully, it becomes obvious that these neighborly nanoballs can act as th e corners to some other central nanoball and a simple redefining of the unit cell.

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146 The most obvious first impression when the packing of the be nzyloxy nanoballs is viewed is that while the re latively long pendant groups su rround the sphere do indeed protrude to a significant degree, the nanoballs themselves still mana ge to pack tightly together in one of the most efficient pack ing schemes known for spheres (an observation reminiscent of the dodecyloxy nanoballs). Th is is achieved because while the pendant groups may be long, they are also, relatively speaking, thin. Therefore they have the ability to slip past one another when one na noball approaches another as is required for the formation of a crystal. In addition to being able to slide beyond pendant chains from other nanoballs and allowing the shells of the nanoballs to ap proach rather closely, the benzyloxy groups are also able to interact with benzyloxy groups from other nanoballs through weak noncovalent interactions such as ••• stacking and CH••• interactions. In Figure 4.11 Body centered cubic close packing of benzyloxy nanoballs. The figure of the right depicts the eight nearest neighbor s (green) of the central (blue) nanoball in question. In this view the c -axis is vertical in the page so that the four neighbors above (or below) lie in the ab -plane.

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147 particular, every nanoball interacts with each of its eight nearest neighbors through four benzyloxy side chains with two such chains originating from each nanoball respectively. The phenyl ring at the end of each group thread s past another pendant arm which arises from a neighboring nanoball, in an anti-para llel fashion and this phenyl group is located within the proximity of the benzene ring th at constitutes the isophthalic portion of the second glancing ligand (Fig. 4.12). The phenyl group is situated there in such a manner so as there is likely to be favorable noncovalent interactions between the two moieties. The phenyl ring from one ligand is oriented in a faceto-face motif (albeit slightly slipped) with the isophthalic benzene ring of another ligand and the centroi d-to-centroid distance for this face-to-face arrangement was observed to be 3.960 , within the expected range for a weak ••• stacking interaction. Additionally, the phenyl ri ng is positioned in a manner so that it is very likely also interacting with a second ligand’s isophthalic acid be nzene ring, this time through two edge-to-face CH••• interactions. The centroid-to-carbon distances for the two rings here are 3.728 and 3.797 respectiv ely, placing them both well within the distance range normally observed for these t ypes of weak noncovalent interactions.18, 21, 24, 30, 339, 340 The fact that there may be two different CH••• interactions with this second ligand is due to the positioni ng of the phenyl ring from the original pendant arm. The edge of the phenyl ring is nearly centered ove r the face of the isophthalic benzene ring, so that both of the nearest hydrogen atoms on th e phenyl ring may be interacting with the isophthalic group’s -cloud.

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148 There are two face-to-face ••• stacking and four edge-to-face CH••• interactions, for a total of six weak noncovalent interaction between every two nearest neighbors. Since each benzyloxy nanoball has eight nearest neighbor s that indicates 48 total interactions. We have already mentioned that each na noball, in addition to the eight nearest neighbors, also comes within close contact to six additional second nearest neighbors. Upon close examination it appears that there are interacting pendant arms between these neighbors as well. Each next nearest neighbor supplies two protruding pendant arms each towards these interactions, which are observed to be CH••• interactions. Since these nearest neighbors are not as close to one another as was the case for the nearest Figure 4.12 Illustration of the close approach of four benzyloxy pendant arms, two each from two separate benzyloxy nanoballs. The face-to-face ••• stacking is shown in purple, while the two edge-to-face CH••• interactions are colored blue and pink respectively. Notice there are a total of two ••• stacking and four CH••• interactions for a total of 6weak noncovalent interactions between every two nearest neighbors (grey = carbon, red = oxygen, green = copper; hydrog en atoms have been deleted for clarity).

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149 neighbors, it turns out that th e pendant arms are not able to extend completely to the isophthalic benzene rings of the partner liga nds. Instead what is observed is that the phenyl ring from one ligand is posit ioned in the proximity of the CH2 directly adjacent the oxygen atom attached to the 5th position of the isophthalic benzene ring, while that isophthalic benzene ligand’s phenyl gr oup resides adjacent to the –O-CH2 of the first ligand (Fig. 4.13). The measured centroid-tocarbon distance for thes e interactions was observed to be 3.8 , also within expected distance ranges for these interactions. This makes for two interactions betw een a pair of ligands with two pairs of ligands for a total of four interactions between any two next nearest neighbors. Since there are six next nearest neighbors, each benzyloxy nanoball is involved with an additional 24 weak noncovalent interactions bri nging the total number of inter actions for any given nanoball including all of its cl osest neighbors to 72. Figure 4.13 Illustration of the four CH••• interactions (blue) between next nearest neighbors in compound [31] All hydrogen atoms have been deleted for clarity (grey = carbon, red = oxygen, green = copper; hydrogen atoms have been deleted for clarity).

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150 Compound [32], [Cu2(5-(2-naphthylmethoxy)-1,3-benzenedicarboxylate)2(py)0.66(DMF)(H2O)0.33]12, is a discrete func tionalized nanoball constructed from the vertex sharing of 12 molecular squares linked together via 24 bridging ligands. The Cu(II) naphthylmethoxy nanoball [32], or naphthylmethoxy nanoball, is the result of self-assembly of 24 Cu2+ ions together with 24 5-(2naphthylmethoxy)-1,3-bdc ligands ( L2 ) in the presence of pyridine, a known coordinating base. It is theref ore unsurprising that at least some of the axial ligands on this nanoball are indeed pyridine moieties. Py ridine is not the only axial ligand however, and in fact there are at least four disordered N,N -dimethylformamide (DMF) together with eight well refined pyridine molecules in the 12 axial positi ons located around the outside of the nanoball. Ther e were no observed pyridine moieties on any of the axial position located within the hollow interior of the naphthylmethoxy nanoball. Instead there are eight well defined DMF solvent molecules c oordinating as ligands to the interior axial position of the SBU. The remaining four ax ial ligands were not clearly identified by single crystal X-ray diffraction a nd are believed to be some form of disordered solvent molecules, most likely water. The 24 na phthylmethoxy pendant chains decorating the 5th position of the basal isophthalic acid benzene ring are all situated on the periphery of the nanoball and extend outward away fr om the nanoball core (Fig. 4.14).

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151 Discrete naphthylmethoxy nanoballs [32] crystallize in the tetragonal space group I4/m with unit cell parameters a = b = 27.645 (20) , c = 39.9159 (60) , = = = 90, V = 30524.7 (60) 3, and Z = 2. The inner core skeleton of the naphthylmethoxy nanoball is essentially identical to that of most other nanoba ll derivatives including that of the parent version. This is due to the fact that each deco rated version of the nanoball is still based upon the base isophtha lic acid bridging ligand. The shortest inner diameter, as measured from one inner copper atom to the opposite inner copper atom is 15.859 (1.59 nm) meaning the interior volume of this nanoball is approximately 2.10 nm3. It was decided to measure the volume of the hollow interior while disregarding the presence of axially bound solvent molecule s, to better represent the potential volume that might be obtained if all labile axial ligands could be removed from this compound. The longest Figure 4.14 Schematic illustrating a stick view of the naphthylmethoxy nanoball, compound [32] All hydrogen atoms have been deleted for clarity (Atom color code: carbon = g re y ; ox yg en = red; co pp er = g reen )

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152 outer diameter for this nanoball skeleton as measured from the 5th position carbons on opposite 1,3-bdc rings was measured to be 24.546 (2.45 nm), while the longest measured diameter including the napht hylmethoxy groups was measured to be 41.097 (4.11 nm), resulting in outer volumes of ~ 7.7 nm3 and 36.34 nm3 respectively. In a manner which is analogous to that of the benzyloxy nanoball [31], the crystal structure of the naphthylmethoxy nanoball [32], reveals a unit cell with a central nanoball surrounded by eight others centered on the corners of the unit cell (Fig.4.15). The centroid-to-centroid distance between the cen tral naphthylmethoxy nanoball and that of one of these corners was measured to be 27.941 , slightly longer than what was observed in the case of the benzyloxy na noball. As the eight nanoballs surrounding the central nanoball are centered on the corners of the unit cell, the centroid-to-centroid distances measured between these nanoballs correspond to the unit cell dimensions of 27.654 along the a and b -axes, and 39.915 along the c -axis. In the naphthylmethoxy nanoballs, it was observed that the ne ighboring nanoballs which reside in the ab plane where relatively closer together, while th e distance between thos e nanoballs situated above and below that central nanoball were pushed farther apart in comparison to the benzyloxy nanoballs. This elonga tion of the un it cell along the c -axis with concomitant shrinking along the a and b -axes, allows for the central nanoballs of the adjacent unit cells to approach closer than was observed in the benzyloxy structure.

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153 In compound [32] we see that the six nanoballs wh ich constituent the centers of the six face-adjacent unit cells, were observe d to be at a distance of 27.654 (the a, baxes lengths of the unit cell), but also point out that this distance was shorter than the observed distance from the central nanoball to the corner nanoballs. This means that the nearest neighbors in the naphthylmethoxy na noball structure are the six nanoballs which are located at the centers of the surrou nding unit cells and not the eight nanoballs positioned at the corners of the central nanoball’ s own unit cell. This is the reverse of the situation observed in the benzyloxy nanoballs, where the nearest neighbors were the eight corners while the six nanoballs centering adja cent cells were the next nearest neighbors. Figure 4.15 The close packing of naphthylmethoxy nanoballs observed in compound [32]. Notice the eight neig hbors centered on the corners of the unit cell mimic a bcc close packing, but in fact these are the next nearest neighbors as the six nanoballs centering the adjacent unit cells are closer to the central (red) nanoball.

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154 When analyzing the interactions between the central nanoball and its eight next nearest neighbors positioned at the corners of the unit cell, the same type of weak noncovalent interactions as was seen in the benzyloxy nanoballs are present. The naphthylmethoxy pendant arms from neighbori ng nanoballs have the same capacity to thread past one another and in teract through edge-to-face CH••• and face-to-face stacking interactions. Each naphthylmethoxy nanoball contributes a single pendant arm for a total of two. The pendant arm aris ing from one nanoball then interacts via a face-toface stacking interaction with the isophtha lic acid benzene ri ng of the adjacent nanoball. The orientation of the naphthyl groups with respect to each other is rather slipped, which can be common in the observation of stacking. The rings are so slipped however, that the carbon atom at the en d of one ring is effectively situated over the center of the -cloud of the other ring and vice versa The two distances as measured from these carbons to the corresponding centr oid of the adjacent ring were measured to be 3.369 and 3.474 , respectively. The centroi d-to-centroid distance for this complex, which is how stacking interactions are typically measured21, 30, was observed to be 3.743 , still well within the norm for this t ype of weak noncovalent interaction (Fig. 4.16).

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155 As each pendant arm of a naphthylmethoxy nanoball is involved in a single faceto-face stacking interaction, and there are two such interactions between every set of next nearest neighbors, each nanoball undergoes 16 face-to-face stacking interactions. In the benzyloxy nanoball, these ligands were situ ated so that as one ligand approached a nanoball for the stacking inter action, the ligand being approached reciprocated and provided its benzyl group to an interaction with the or iginal nanoball, doubling the number of these interactions observed. In the case of the naphthylmethoxy nanoballs, the ligand which is donated to the next nearest neighbor is not matched by a pendant arm returning to the original na noball. Instead this ligand’s pe ndant arm meanders in space making no observable close appro aches to other naphthyl rings. Figure 4.16 Stick representation of face-to-face stacking interactions (purple) observed between next nearest neighbors in the crystal packing of naphthylmethoxy nanoballs [32]. (grey = carbon, red = oxygen, green = copper; hydrogen atoms have been deleted for clarity).

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156 Analysis of the interactions between a central nanoball and its six nearest neighbors, which themselves are the center of adjacent unit cells, reveals that the same types of edge-to-face CH••• and face-to-face stacking interactions as was witnessed in the benzyloxy nanoballs are again present (Fig. 4.17). Here two pendant arms each from two nearest neighboring nanoballs (for a total of four ligands) are involved in a total of four edge-to-face CH••• interactions. The distance for these interactions, as measured from the centroid of the closest ring in th e naphthylmethoxy group to the carbon atom of the corresponding naphthylmethoxy group, wa s observed to be 3.582 . As every nanoball interacts with each of its six nearest neighbors thr ough these four CH••• interactions, there are a tota l of 24 interactions with re lation to a single nanoball. Figure 4.17 Stick representation depicting the two types of weak noncovalent interactions between nearest neighbors in the crystal packing of naphthylmethoxy nanoballs [32]. Left: Zoomed out view of the interaction between two adjacent nanoballs illustrates the four CH••• (green) and four stacking (purple) interactions. Right: A zoomed in view facilitates observation of the described interactions (grey = carbon, red = oxygen, green = copper; hydrogen atoms have been deleted for clarity).

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157 Interestingly, the interactions of this type are in close proximity to the interactions between neighboring nanoballs so that a concerted quadruple phenyl embrace (QPE) is generated between four nanoballs adjacent in the ab -plane (Fig. 4.18). This QPE motif is a well known supramolecular structure, a nd in the crystal structure of the naphthylmethoxy nanoballs, these QPE are locate d within the well of another nanoball’s metallocalixarene along the c -axis. It is within this square metallocalixarene cavity that the rings forming the QPE also stacking with the ligands of the nanoball forming the calyx. Additionally, each naphthylmethoxy nanoball do nates two more pendant arms for a total of four ligands, which th en interact through face-to-face stacking. This motif is reminiscent of the benzyloxy nanoball structure in that for every pair of pendant arms Figure 4.18 Illustration of the quadruple phenyl embrace of concerted edge-to-face CH••• interactions as seen in the crystal structure of compound [32].

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158 there are two stacking interactions, instead of the single interaction seen between next nearest neighbors described above. Since each pair of ligands involves two such interactions and there are two pairs of liga nds, there are a total of four edge-to-face CH••• interactions between every two nearest neighbors and therefore every nanoball is involved with 24 such interactions. Take n collectively this means there are 48 interactions between a nanoball and its si x nearest neighbors and an additional 16 interactions between the same nanoball and its eight next nearest neighbors for a total of 64 weak noncovalent interactions associat ed with every naphthylmethoxy nanoball. While there are a slightly lower total number of interactions observed in the naphthylmethoxy structure as compared with that of the benzyloxy nanoball structure (64 versus 72), it should also be noted that the observed distance for th e interactions were shorter comparatively, than in the benzyloxy st ructure. A shorter distance between groups in noncovalent interactions implies a stronger interaction, something that is also borne out by the observation that while the penda nt arm in the naphthylmethoxy nanoball is somewhat larger than its benzyloxy count erpart, the naphthylmethoxy nanoballs make a closer approach to one another than that which was observed in benzyloxy derivative. 4.3.2 Properties As with all derivatives of the nanoball, both aryloxy versions described in the previous section are constructed via the vertex linking of mo lecular squares (square paddlewheel SBUs) to generate a discrete arch itecture that contains both open and closed “windows”. With a hollow interior that a pproaches a volume of approximately 1 nm3, and small pores making this space accessibl e, the potential to encapsulate small

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159 molecules (especially gases such as CO2, H2, etc.) is present. As such, experiments were undertaken in an attempt to analyze these ma terials porosity. Crystalline samples of each aryloxy nanoball were obtained following the de tailed synthesis descri bed in a section to follow below. Once synthesized, the crystall ine materials were tr eated through a number of protocols in an attempt to “activate” them prior to gas sorption measurements. By “activate”, we mean to replace otherwise higher boiling solvent molecules and guests present in the crystal structure with relati vely low boiling solvent molecules, in an attempt to facilitate the complete rem oval of all guest and solvent molecules upon vacuum evacuation. The presence of any higher boiling solvent molecules, such as N,N dimethylformamide which is present in the reaction solution, may mitigate the materials ability to uptake the sorbent gas being investigated. In a typical activation the reaction solution in the vial containi ng the crystalline samples of aryloxy nanoballs was removed via Pasture pipette and the crystals washed with neat reaction solvent, in this case DMF. The washing process is prescribed to rem ove any unreacted starting materials such as ligand or metal ions which may still be presen t in the mother liquor and possibly coat the sample crystals. The crystals were allowed to sit in the fresh DMF for approximately 15 minutes before the process was repeated, th e DMF removed and replaced with a fresh aliquot. The sample was washed three times with fresh DMF. After the third washing, the DMF solvent was removed and a second, typi cally a low boiling solvent was introduced. Again the crystals were allowed to sit imme rsed in the new solvent, however now the sample was left undisturbed for ~12 hours. Af ter ample time immersed in the exchange solvent, so chosen so that is may diffuse in to the material while any other solvent guest

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160 present will subsequently diffuse out of the ma terial into the bulk exchange solvent, the process is repeated. Typically the samples were exchanged at least three times before the sorption experiments commenced. In the cas e of both aryloxy nanoballs attempts to activate the crystalline material with se veral exchange solven ts was undertaken; chloroform, ethanol, methanol, dichlorometh ane, carbon tetrachloride, and acetonitrile were all used in trying to activate the samp les. Additionally, the two crystalline materials were investigated when prepared by washi ng with DMF alone and no exchange solvent was employed (as synthesized). After activation protocols were preformed, the sample was exposed to N2 gas under reduced pressure in an attempt to measur e the capacity of the ma terial to adsorb the gas. The amount of N2 adsorbed by the materials can potentially be used in several theoretical models for the prediction of that materials’ accessible surface area. Unfortunately, in the case of both aryl oxy nanoballs the measured five-point N2 B.E.T. surface area never amounted to more than ~40 m2/g for any of the outlined activation procedures. Whether a failure to activate the materials properly, or simply the case that these materials, being discrete and capabl e of small rearrangeme nts on the molecular scale, are generally not porous in nature could not be determined at this time. In addition to attempts to measure thes e materials porosity with respect to gas sorbents, their solubility in common laborat ory solvents was also of interest. Other derivatives of the nanoball have been shown to be soluble in several solvents, facilitating the investigation of their solution properties. One deri vative nanoball, the hydroxylated version, has been shown to be soluble in pre-polymer monomers, so that upon polymer

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161 formation the nanoballs are inco rporated into the polymer ma terial through persistent interactions and can alter the chemical and physical properties when compared with the neat polymer.341, 342 This could play a role in leading to potential application of made to order nanocomposites. Additiona lly, the hydroxylated nanoballs have been investigated for their solution photophysical proper ties through Fluorescence and UV/VIS spectroscopy. The aryloxy nanoball s were targeted in part pr ecisely because the presence of naphthyl and benzyl rings on the ligands should provide for interesting fluorescent markers. Therefore knowledge of which solven ts these discrete compounds are soluble in could greatly benefit the deve lopment of their properties. Qualitative solubility experiments we re conducted using a powder sample obtained via vacuum filtration and air drying of the solid. A small sample of the dry powder (~10-20 mg) was placed into a clean, labele d test tube, and to this ~ 1 mL of neat solvent was added. With the aid of manual as well as mechanical (Maxi-Mix) agitation, dissolution was attempted. If upon agitation fo r several minutes, the solid was still undissolved, the use of a hot water bath (steaming, yet not boiling ~85-90 C) was implemented and the test tube allowed to sit for several minutes before reobserving. Numerous laboratory solvents covering a range of propert ies such as polar versus nonpolar and protic versus aprotic, were used in these qualitative so lubility experiments including such common solvents as metha nol, ethanol, chloroform, dichloromethane, acetonitrile, carbon tetrachlorid e, hexanes, isopropanol, DMF, DMSO, ethyl acetate, benzene, nitrobenzene, o -dichlorobenzene, chlorobenzene, acetone, toluene, tetrahydrofuran, 1,4-dioxane, and cyclohe xane among others. Ne ither aryloxy nanoball

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162 was observed to be soluble in any of thes e solvents even tho ugh they are discrete compounds and solubility in at least some solv ents was expected. The lack of solubility has impeded the ability to incorporate these na noballs in polymers as well as the study of their solution photophysics. It is believed that the large number of individually weak albeit concerted noncovalent interac tions in the form of face-to-face stacking and CH••• interactions plays a significant role in the insolubility of the discrete molecular architectures. The aryloxy nanoball s were also exposed to neat D.I H2O were it was determined that they are instable and likely collapse. This was evidenced by the observed disappearance of the characteristic blue color as well as the appearance of white milky precipitate which was presumed to be the insoluble (in water) dicarboxylate ligand. 4.3.3 Experimental 4.3.3.1 Synthesis All reagents, unless described otherwise, were purchased from either SigmaAldrich or Fischer Scientific and used as received without further purification. The synthesis procedures for the two ligands 5-benzyloxy-1,3-benzenedicarboxylic acid ( L1 ) and 5-(2-naphthylmethoxy)-1,3-be nzenedicarboxylic acid ( L2 ) were reported in a previous section (2.2.3.1). [Cu2(5-benzyloxy-1,3-benzenedicarboxylate)2(DMF)x(H2O)2-x]12 [31] was synthesized from a solvotherm al reaction involving Cu(NO3)22.5H2O (46.9 mg, 0.201 mmol) and L1 (54.7 mg, 0.201 mmol) together with 2,6-lutidine as a non-coordinating base (72 L, 0.599 mmol) in a molar ratio of one ligand to one metals to three 2,6-

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163 lutidine molecules. All components, in addition to 3 mL of N, N -Dimethylformamide and 2 mL of nitrobenzene, were added to a 20 mL scintillation vial which was sealed with aluminum foil and capped tightly. The vi al was then placed in a sand bath and heated in a programmable oven. The heat prof ile was as follows: the reaction temperature was raised from 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours. The temperature was then slowly lowered back to 30 C at a rate of 1 C per minute. U pon removal from the oven a large amount of prismatic green-blue crystals [31] suitable for single crys tal X-ray diffraction were observed to have formed (85 mg, 60.1% yield). [Cu2(5-(2-naphthylmethoxy)-1,3-benzenedicarboxylate)2(py)0.66(DMF)(H2O)0.33]12, [32] was synthesized from a solvothermal reaction involving Cu(NO3)22.5H2O (46.8 mg, 0.201 mmol) and L2 (66.1 mg, 0.205 mmol) together with pyridine as a coordinating base (48.5 L, 0.601 mmol) in a molar ratio of one ligand to one metals to three pyr idine molecules. All components, in addition to 3 mL of N, N -Dimethylformamide and 2 mL of tetrahydrofuran, were added to a 20 mL scintillation vial which was sealed with aluminum foil and capped tightly. The vial was then placed in a sand bath and heated in a programmable oven. The heat profile was as follows: the reaction temperature was raised from 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours. The temperature was then slowly lowered back to 30 C at a rate of 1 C per minute. Upon removal from the oven a large amount of pr ismatic green-blue crystals [32] suitable for single crystal X-ray diffraction were observed to have formed (67 mg, 73.4% yield).

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164 4.3.3.2 X-ray Crystallography Single crystals of compound [31] suitable for X-ray crys tallographic analysis (Fig. 4.19) were selected following examinati on under a microscope. Intensity data were collected on a Bruker-AXS SMART APEX /CCD diffractometer using Cu k\ radiation ( = 1.54178 ).281 The data were corrected for Lore ntz and polarization effects and for absorption using the SADABS program (SAINT).282 The structures were solved using direct methods and refined by fu ll-matrix least-squares on |F|2 (SHELXTL).283 Additional electron density, located in the void cavity sp ace, assumed to be disordered solvent, was unable to be adequately refined was removed using the SQUEEZE/PLATON program.284-286 The phenyl rings of the benzyloxy pendant arm were constrained during refinement. All atoms were refined isotropi cally except for the Cu atoms which were refines anisotropically. Crysta l provided quality diffraction (at frame times utilized) for lower angles only leading to lower resolution (1.2 ). Sele ct crystallographic data is presented in tabular form in Appendix C-18. Figure 4.19 Digital photographs depicting single crystals of compound [31]

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165 Single crystals of compound [32] (Fig. 4.20) suitable for X-ray crystallographic analysis were selected following examinati on under a microscope. Intensity data were collected on a Bruker-AXS SMART APEX /CCD diffractometer using Mo k\ radiation ( = 0.7107 ).281 The data were corrected for Lore ntz and polarization effects and for absorption using the SADABS program (SAINT).282 The structures were solved using direct methods and refined by fu ll-matrix least-squares on |F|2 (SHELXTL).283 Additional electron density, located in the void cavity sp ace, assumed to be disordered solvent, was unable to be adequately refined was removed using the SQUEEZE/PLATON program.284-286 Select crystallographic data is presented in tabular form in Appendix C19. 4.3.3.3 Powder X-ray Diffraction Powder samples suitable for powder X -ray diffraction, FT-IR spectroscopy, and Thermal Gravimetric Analysis were obtai ned by removing a large amount of single crystals from the reaction scintillation vial by using a glass Pasteur pipette and depositing these crystal (along with mother liquor) in a small concave agar mortar. Excess solvent Figure 4.20 Digital photographs depicting single crystals of compound [32]

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166 was removed via pipette, and surface solvent was removed by wicking action with a Kim-Wipe. Upon wick drying, the crystals were tr ansferred to a small piece of filter paper which was subsequently folded over and they were dried further and slightly crushed with gently pressure. The resulti ng dry powder (~30 mg) was then immediately applied to a PXRD sample puck prepared with a small amount of vacuum grease to fixate the powder sample, and the PXRD experiment performed without delay. A sample of Cu(II) benzyloxy nanoballs, compound [31], was characterized for bulk composition purity via PXRD. The samples were analyzed on a Bruker AXS D8 Discover X-ray diffractomet er, equipped with GADDS™ (General Area Diffraction Detection System) and a Bruker AXS HI-STAR area detector. The X-ray source was Cu ( = 1.54178 ) run on a generator operating at 50 kV and 40 mA. The data was collected within the 2 range of 3 – 40, in continuous scan mode using a step-size of 0.02 per step and a rate of 2 seconds per step. (Appendix B-36) A sample of Cu(II) naphthylmethoxy nanoballs, compound [32], was characterized for bulk composition purity via PXRD. The samples were analyzed on a Bruker AXS D8 Discover X-ray di ffractometer, equipped with GADDS™ (General Area Diffraction Detection System) and a Bruke r AXS HI-STAR area detector. The X-ray source was Cu ( = 1.54178 ) run on a generator opera ting at 50 kV and 40 mA. The data was collected within the 2 range of 3 – 40, in continuous scan mode using a stepsize of 0.02 per step and a rate of 2 seconds per step. (Appendix B-37)

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167 4.3.3.4 FT-IR Spectroscopy All compounds, including synthesi zed ligands, were characterized via infrared spectroscopy using a Nicolet Avatar 320 Four ier-Transform Infrared Spectrometer (FTIR). Before each sample was analyzed, a background spectrum was obtained for purposes of zeroing out ambient noise in the form of the laboratory atmosphere. Each sample was measured in the range from 4000 cm-1 to 500 cm-1 wavenumbers (wavelength of 2500 nm to 20000 nm respectively) and scanned 64 times. Results were recorded in % transmittance and the spectrum analyzed using the EZ OMNIC (V.5.1b, copyright 1992199 Nicolet Instruments Corporation) computer software suite. A typical sample was a analyzed as a neat, dry solid (~10 mg) obtained via either vacuum filtration and air drying or gently drying with laboratory grade filter paper. [Cu2(5-benzyloxy-1,3-benzenedicarboxylate)2(DMF)x(H2O)2-x]12, [31] : IR (dry powder) max (cm-1): 1662 med. sh., 1627 m sh. ( carboxylate), 1586 m sh. (C=O, carboxylate), 1378 v sh. (COO-, carboxylate), 1028 vs sh (e ther). The most notable changes between the IR spectrum for the ligand L1 and compound [ 31 ] is the disappearance of the OH stretch due to the carboxylic acid that was centered around 3122 cm-1 and bleed into the 3000 cm-1 region as well as the two sharp peaks at 3535 cm-1 and 3451 cm-1 which arose from free acids. Shifts in frequency for the C=O stretches were observed which is expected upon coordinati on of the carboxylate. (Appendix B-36) [Cu2(5-(2-naphthylmethoxy)-1,3-benzenedicarboxylate)2(py)0.66(DMF)(H2O)0.33]12, [32] : IR (dry powder) max (cm-1): 1664 med.

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168 sh., 1629 m sh. (carboxylate), 1586 m s h. (C=O, carboxylate), 1376 v sh. (COO-, carboxylate), 1038 vs sh (ether). The most not able changes between the IR spectrum for the ligand L2 and compound [ 32 ] is the disappearance of the OH stretch due to the carboxylic acid that was centered around 3122 cm-1 and bleed into the 3000 cm-1 region as well as the two sharp peaks at 3535 cm-1 and 3451 cm-1 which arose from free acids. Shifts in frequency for the C=O stretches were observed which is expected upon coordination of the carbo xylate. (Appendix B-37) 4.3.3.5 Thermal Gravimetric Analysis Thermal Gravimetric Analysis for [Cu2(5-(benzyloxy)-1,3benzenedicarboxylate)2(py)0.66(DMF)(H2O)0.33]12 compound [ 31 ] was performed on a PerkinElmer STA 6000 Simultaneous Thermal An alyzer. Data acquisi tion and analysis was performed with the assistance of the Py ris Series suite of software. Roughly 10-20 mg of dry powder was placed in a sample cr ucible and heated at a rate of 10 C/min. form a temperature of 30 C up to 700 C. The results of the TGA experiment (Appe ndix B-36) was a featureless curve with numerous broad weight losses taking place in extended temperature ranges. This is probably due to the loss of several different “types” of solvent molecules which are guests in the crystal structure, from H2O and DMF moieties located between nanoballs, those present in the cavities of the nanoballs themselves, and finally those bound to the nanoball as axially coordinated ligands. Add itional difficulties in assigning the exact identity of the solvent mol ecules responsible for weight loss upon leaving the sample

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169 arises from the imprecise nature of the crys tal structure. Some unrefined solvent in the form of electron density was observed in the crys tal structure, as well as the fact the exact number of each type of solvent ligand coor dinated to a particular nanoball is unknown. Thermal Gravimetric Analysis for [Cu2(5-(2-naphthylmethoxy)-1,3benzenedicarboxylate)2(py)0.66(DMF)(H2O)0.33]12, compound [ 32 ], the Cu(II) naphthylmethoxy nanoball was performed on a PerkinElmer STA 6000 Simultaneous Thermal Analyzer. Data acquis ition and analysis was performe d with the assistance of the Pyris Series suite of software. Roughly 10-20 mg of dry powder was placed in a porcelain sample crucible and heated at a ra te of 10 C/min. from a temperature of 30 C up to 700 C. The result of the TGA experiment (Appe ndix B-37) was a featureless curve with numerous broad weight losses taken place of extended temperature ranges. This is probably due to the loss of several different “types” of solvent molecules which are guests in the crystal structure, from H2O and DMF moieties located between nanoballs, those present in the cavities of the nanoballs themselves, and finally those bound to the nanoball as axially coordinated ligands. Add itional difficulties in assigning the exact identity of the solvent mol ecules responsible for weight loss upon leaving the sample arises from the imprecise nature of the crys tal structure. Some unrefined solvent in the form of electron density was observed in the crys tal structure, as well as the fact the exact number of each type of solvent ligand coor dinated to a particular nanoball is unknown.

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170 4.4 Supermolecular Building Blocks 4.4.1 Introduction The evolution from the use of single metal ion nodes to the adoption of multiple metal, ligand-bridged clusters or seconda ry building units (SBUs) as nodes was a watershed moment in the development of meta l-organic materials. The importance of the addition of SBUs to the crystal engineer’s t oolbox is centered on thei r ability to augment the numbers and types of materials that can be made. Clearly the use of scaled-up nodes that are composed of several metal and bridging atoms (typically oxygen from carboxylates) as opposed to a single metal ion will result in a metal-organic material (MOM) which is itself scaled up by comparis on. However, more than simply a method of increasing the dimensions of the resultant mate rial, the use of SBUs as a design principle could help guide the synthetic chemist toward previously elusive network topologies. The real accomplishment of SBUs as a design strategy was its ability to lead the field forward in terms of the types of unprecedented material s which could be made and in illustrating how those materials could be achieved. The final section of this chapter ai ms to introduce a new extension to the hierarchy that has come before it. In a manne r analogous to the change from metal ions to SBUs, a new design strategy based upon the impl ementation of metal-organic polyhedra, themselves composed of SBUs (which in tu rn are themselves constructed from metal ions), as new supermolecular building blocks (SBBs)343-345 to perform as the nodes in the design of extended metal-organic materials. Ju st as the move from a single metal ion to

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171 an SBU provided new insights into MOMs, so too will the adoption of the SBB design strategy lead to an increase in the amount of materials which can be fabricated as well as a better understanding of how to get there. 4.4.1.1 A Matter of Scale As was the case for the implementation of SBUs, the first noticeable advantage for the adoption of metal-organic polyhedra as supermolecular buildi ng blocks is that they are inherently larger than their SBU counterparts. Simila r to the jump in scale from a single metal ion (one atom) to a structure co mposed of several atoms in a cluster, the SBBs of this design strategy are themselves constructed from several smaller SBUs. This guarantees that the scale of the final material to be fabricated will also be enhanced. If you begin to build with bigger blocks, you insu re that your structure will be grandiose. Additionally, the SBB nodes are typically ho llow and contain small windows providing small molecules or ions access to their interi or. With the incorporation of SBBs into MOMs, even in the presence of interpen etration, the hollow nodes themselves will preclude interpenetration remaining open, and th us cavities with controllable dimensions and functionality can be incorporated into a framework with high fidelity. The inclusion of some SBBs, with their relatively sma ll windows, is also an astute method of controllably incorporatin g these small pores into a desired framework. 4.4.1.2 Rare and Unprecedented Node Connectivities In the case of single transition metal i ons, the geometry and connectivity of the node depends upon the identity of the metal us ed. In some instances the metal ion can

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172 adopt only a single, reliable coordination geometry, thus limiting what the shape and connectivity of the node will be, or worse stil l precluding the use of that metal for the fabrication of certain frameworks. With ot her metals a limited number of different coordination geometries are pos sible so that precise contro l over reaction conditions may be warranted for the ability to control wh ich chromophore is generated and therefore which MOM is produced. Even in the case of transition metal ions, which are celebrated for their ability to adopt several different geometries, the total possible number of geometries and coordination connectivities are limited to a handful (i.e. square planar, octahedral, tetrahedral etc.). Nodes with higher coordination numbers or unique geometries are therefore unattainable. With the use of SBBs it is possible to design nodes which have coordination numbers unheard of with either single meta l ions or SBUs. As specifically designed metal-organic polyhedra, SBBs represent nodes that can easily have coordination numbers that are higher than those possibl e for SBUs alone. If the vertices of the polyhedron are taken to be th e points of extension, much as the carboxylates of most SBUs were, then the number of vertices for a polyhedron may also represent the connectivity of that SBB node. In this case nodes with very high connectivity should, in principle, be possible as there are many exam ples of metal-organic polyhedra which have 8, 12, 20, 24, or even more vertices. Additiona lly, it may be possible to adopt certain SBBs not for the incidence of extra coordination sites, but rather due to the controlled geometry of the existing coordination sites. As a quick example, both an octahedron (common in octahedral transition metals and SBUs alike) and a trigonal prism have six

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173 vertices which can be used as points of extension making them six-connected to a chemist. However the geometry of how th e vertices are positioned around the central point of the object are clearly very different. As such the in corporation of one of these nodes in perspective to the other will lead to different topologies. In fact the existence of different topologies within the same connectiv ity class arises not onl y from the different possible orientations of some building block with that connectivity, but also from the existence of more than one type of geometry for that connectivity. This is why square planar and tetrahedral nodes, while both 4-connected, ofte n lead to very different topologies. If a particular fram ework topology required a uniq ue geometrical shape, the use of SBBs may facilitate form ation of a structure which adopts the necessary geometry. 4.4.1.3 Out of Increased Complexity, Increased Control While at first glance the metal-organic polyhedra, imbued with their large number of vertices and unique geometries, appear to be more complex buildi ng units than that of the typical SBU (and they are), this does not ne cessarily indicate that the incorporation of these SBBs into extended frameworks will also be more difficult. In fact thanks to the highly symmetric nature of most MOPs, th eir incorporation in to MOMs may actually help limit the possible outcomes of the constr uction process. That is to say certain high coordination number, highly symmetric S BBs may only have a few highly selective framework topologies which it can make (d efault structures). Once a framework topology has been identified as being particularly pred isposed toward formation with the use of a particular SBB, that SBB can be designed in su ch a way so as to incorporate features of the MOP the SBB is based on into the new extended MOMs. That is to say that control

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174 over pore sizes (windows of the MOP), the presence of functional groups inside the hollow interior of the SBB, and other aspect s intrinsic to the metal-organic polyhedra can controllably be instilled into the MOM, a feat that can sometimes be difficult with the use building blocks lower in the hierarchy. 4.4.1.4 Inherent Structural Diversity Finally, as was the case at each level of co mplexity in the building blocks used to construct metal-organic materials, the use of SBBs will also provide an increased level of structural diversity. Just as the same meta l-organic polyhedron can often be made from different metal ions and di fferent (functionaliz ed) ligands, so t oo can the SBB. Identification of a particularly attractive network, sustained by SBBs should be just as amenable to variation in the metals and lig ands used as other MOMs. Moreover, SBBs will be able to generate known common topologies (i.e. diamondoid, bcu pcu etc.) albeit with dimensions, and structural characteris tics not possible with single metal ions and SBUs. This leads to a much greater diversity in the amount of materials which will be possible to synthesis and in what we can do with them. 4.4.2 Structural Analysis The nanoball346-353 ( small rhombihexahedron ) as a platform of diverse nanostructures, represents one of the most widely studied131, 336, 341, 354-357 metal-organic polyhedra. Its facile synthesis achieved via modular self-assembly together with its nearly spherical geometry, make the nanoball a particul arly attractive target for the investigation of metal-organic polyhedra properties. Th e presence of 12 square paddlewheel SBUs

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175 with their outer axial positions availa ble for coordination, along with 24 1,3benzenedicarboxylate moieties with their 5th positions amenable toward pre-synthesis of covalent extensions, all of which are poin ting outward from the surface and situated around the periphery of the nanoball (Fig. 4. 21), also makes them attractive candidates for use a supermolecular building block (SBB) nodes in extended frameworks. Indeed the nanoball has already been inco rporated into extended MOMs in the form of 1-periodic chains and 3-periodic bcu -like networks, alt hough serendipitously, through coordination bonds.349 At first glance, the use of the nanoball’s 24 vertices, which is the 5th position of the 1,3-benze ndicarboxylate moiety, as the points of extension for new MOMs seems daunting. It is hard to see the possibility of a periodic network Figure 4.21 Schematic of a small rhombihexahedron depicting the peripheral nature of the functional groups (black balls) when the 1,3-BDC moiety is derivatized in the 5th-position. Atoms are color coded as follows: carbon (grey), oxygen (red), hydrogen (white), nitrogen (blue), sulfur (yello w), transition metal (salmon).

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176 being constructed from a node with so many point s. In fact only rece ntly did a research team that works on the enumeration of networ ks that are feasible for the synthesis of MOMs, publish an account of a (3,24) net ( rht ) constructed from rhombicuboctahedra (which shares the edge skeleton and thus the arrangement of vertices with the nanoball).358 What may be key however, is the idea that you need not use the nanoballs as solely 24 connected nodes; it is also feasible to use multiple connections between the same two nodes to generate a network. In this case the number of extensions will be reduced by the number of cross-links betw een two nodes (granting that all the nodes share the same number of cross-links). Ther efore if each node is doubly connected to its nearest neighbors, the nanoball would be redu ced to being a twel ve-connected node; if triply connected, then the node would be expected to be 8-connected. To envision how this might be possible, one need only look at the symmetries of the nanoball itself (Fig. 4.22). Careful observation of the nanoball reve als that it has three-fold rotational symmetry axes passing through each of the eight triangular windows (for a total of four axes). As was just mentioned, if the node were to be triply connected to other nodes we would expect it to be eight connected. Thus the symmetry of the na noball itself dictates how this connectivity might occur; if the three cross-links were symmetrically oriented around the triangular windows, of which there are precisely eight, both the conditions of the cross-linking and connectivity would be satisfied with the additional benefit that these cross-links would automatically be situated in the most symmetrical manner possible.

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177 In a similar vein the symmetry elements of the nanoball also dictate how the MOP will behave as two distinct 6-connected nodes (Fig 4.23). The existence of the three fourfold rotational axes passing through the six ope n square windows indi cates that four-fold cross-linking centered on these windows, should be symmetrically favored. Another 6connected node is possible, which at first ma y be difficult to see, but if one of the twofold rotation axes passing through two opposite closed faces (SBUs), in conjunction with the appropriate four open square windows, are used as the po ints of cross-linking, then a node with clearly different symmetry than the first example of a 6-connected node would exist. The two different 6-connected nodes, wh ile very similar (they result from a simple reorientation of the nanoball), would ultimatel y crystallize in different space groups due to the symmetry involved. Figure 4.22 Cartoon illustrating the various rotational symmetry elements of the small rhombihexahedron ( Oh). Purple = 2-fold, Light Blue = 3-fold, yellow = 4-fold.

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178 In an attempt to implement this newfound design strategy for the cross-linking of small rhombihexahedra a tetracarboxylic acid composed of two 1,3-benzenedicarboxylic acid moieties tethered together via a dimethoxy-benzene group was synthesized (Fig. 4.24). The two 1,3-bdc moieties were bridged at their respective 5th positions, so that upon generation of the nanoball on at the diaci d would facilitate concomitant crosslinking to another nanoball. Figure 4.24 1,3-bis(5-methoxy-1,3-benzenedicarboxylic acid)benzene, L5 Figure 4.23 Three possible connectivities for the small rhombihexahedron SBB. Left: Triple cross-linking centered on the eight triangular windows (purple, one not shown) will result in an 8-connected bcu -like network. Center: Quadruple crosslinking through the six open square windows (red) results a six-connected SBB with Oh symmetry. Right: Quadruple cross-linking throug h four closed faces (SBUs, blue) and two open square windows (plum) will result in a different 6-connected SBB with local D4 h symmetry. While both six-connected nodes should generate a pcu-i -like network, the symmetry and space groups of the networks will be different.

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179 Reactions carri ed out using Cu2+ and L5 resulted in the formation of quadruply cross-linked nanoballs, compound [33] which exists as a 2-fold interpenetrated pcu-i like network. Here pcu-i is the RCSR term for an augmented pcu network where the vertex is a rhombicuboctahedron (nanoball), and is face sharing with cubes. The compound crystallized in the tetragona l spacegroup I422, with a = b = 28.885(4) , c = 28.305(6) , V = 23616(7) 3 with Z = 2. The nanoball nodes cross-link via the dimethoxy benzene tethers to 6 adjacent nanoballs positioned ar ound the central nanoball in manner so as to generate D4 h symmetry. The cross-linking occurs through four square faces (the SBUs) along the abplane (Fig. 4.25). The presence of SBUs along these axes, prevents any type of channel running through the nanoball and aligned with th ese axes. The four bridging ligands generate a pseudo-cylinder cavity, as they are bowed outward from the crosslinking axis rather than strai ght. This was made possible by the flexible nature of the ligand L5 In fact the flexible nature of the lig and may also contribute to the tetragonal spacegroup of the crystal structure, as the c onformations of the ligands are different along the aaxis (and baxis) and that of the caxis. Along both the a and b -axes the ligands adopt a syn -conformation while along the caxis they adopt an anticonformation (Fig. 4.25). The dimensions of the cylinders (for med by bridging ligands) directed along the abplane was measured to be 7.24 long (as measure Cu to Cu form the two capping SBU faces) with a diameter of 10.54 (as m easure centroid-to-centroid of the bridging benzene moieties).

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180 The axial sites of the SBUs in these cav ities contain unrefined solvent molecules as ligands, probably MeOH or water, fili ng up the majority of this void. Along the caxis, the cylinder is formed by the anticonformation ligands and was observed to have a length of 5.86 and a diameter of 17.88 . In this cylinder the length is diminished as Figure 4.25 Stick representation illustrating the cross-linking observed in the Cu linkednanoballs, compound [33]. Top: A view of the ab -plane depicts the large square cavities formed by quadruple cross-linking of nanoballs. As this structure involves 2-fold interpenetration, this large cavity is filled with a nanoball node from the second framework (not shown). Middle: cross-linking as observed along the aand baxes. Note here the syn -conformation adopted by the bridging portion of the ligand and how the SBUs which are present in the cylinder along both the aand baxes are perfectly collimated. Bottom: cross-linking as observed along the caxis. Note here the anticonformation adopted by the bridging portion of the ligand and the lack of SBUs, allowing for a persistent channel directed along the caxis. (grey = carbon, red = oxygen, salmon = copper, yellow = sulfur; hydrogen atoms have been deleted for clarity).

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181 the ligands bow out more pronouncedly. Along this axis, there is no SBU capping the cylinder, as the ligands are centered on an open square window. Thus along this c -axis there is a con tinuous cylinder. Within the abplane, the nanoball SBB nodes cro ss-link to form a cavity with impressive dimensions. As measured from opposing benzene moieties of the bridging ligands (centroid-to-centroid), the cavity was observed to be ~ 18.3 or 1.8 nm in length. This square cavity has a diagona l length of ~ 2.5 nm. Measured along the caxis, the cavity is 13.56 tall, making for a recta ngular cavity with dimensions ~ 1.8 x 1.8 x 1.4 nm. However, this large void is preci sely where a nanoball SBB node from the second interpenetrating framework resides. Topologically, the structur e generates an augmented pcu-i like network which can be decomposed into four symmetrically uniqu e nodes. Further analys is of the structure revealed the coordination sequence record ed in Table 4.1. Review of O’Keeffe’s indispensable text170, also indicates that this structure is very closel y related to an infinite polyhedron formed from rhombicuboctahedra and cubes, and given by the notation 3.44. This infinite polyhedron seem to be more clos ely related to the poten tial octahedral node isomer, however, as the cubes are all positioned in what would essentially be the six open square windows. Yet another way of interpreting this structure is that it is a zeolite-like metal-organic framework. Zeolites are an important and expansive class of inorganic compounds which are microporous aluminosilicates They are useful for a wide array of industrial applications, most notably in detergents and wa ter softeners (ion exchange). Zeolites are generically 3-period ic structures that can be c onceptually seen as different

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182 types of cages joining together to generate the architecture. This analogy is apt as the cross-linked nanoball structure can also be viewed as being the result of several types of cages face-sharing. In the case of the cro ss-linked nanoballs, the nanoball SBB node is one type of cage which is then connected to other SBB nanoball nodes through a separate cage, this time in the form of a rectangular box (Fig. 4.26). The four ligands responsible for the quadruple cross-linking between nanoballs form the edges of this rectangular box. A third cage is represented by the void space which is generated when a single nanoballs SBB node is connected to its six neighbors to generate a framework. Since the nanoball SBB in this structure is six-connected, it can loosely be interprete d to be similar in structure to the ubiquities sodalite cage found in zeolites, making the cross-linked nanoball structure closely related to Zeolite A ( LTA ) which is constructed from sodalite cages bridged by face-sharing with cubes in an octahedral arrangement. Figure 4.26 Cage sharing view of the cross-linked nanoballs structure. Here the purple cubes are the cages generated by the bridging ligands.

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183 Table 4.1 Coordination sequences and TD10 for the four unique nodes found in compound [33]. k 1 2 3 4 5 6 7 8 9 10 TD10 Node 1 4 9 20 37 64 88 124 161 214 236 957 Node 2 4 10 24 36 60 86 120 168 208 244 960 Node 3 4 9 20 40 68 92 116 184 216 232 981 Node 4 4 11 22 40 60 91 126 164 210 264 992 Reactions carried out using Zn2+ and L5 also resulted in the formation of quadruple cross-linked nanoballs which ar e 2-fold interpenetrated. The compound crystallized in the tetrag onal spacegroup I4/m, with a = b = 30.144(7) , c = 27.944(11) , V = 25391(13) 3 with Z = 2. The structures of [33] and [34] are nearly identical, except for small variations in the conformati ons of their ligands and relative dimensions of some of the cavities. The Zn version of the linked nanoballs has the same coordination sequence and TD10 values that were observed for the Cu analogue. Additionally, the connectivity and orientation of the respective nanoball SBBs is identical; the crosslinking observed in the abplane occurs via the 4 square faces due to the SBU, while the cross-linking witnessed along the caxis centers on two square open windows. The dimensions of the cylindrical SBB connect ors are also roughly similar; along the aand baxes, the cylinder measures 14.76 ( carbon-to-carbon of opposing carbon atoms on the bridging benzene ring) by 8.033 as meas ured from Zn-to-Zn. One very obvious difference between the Zn analogue and that of the copper version is the presence of pyridine ligands bound in the axial position of some of the SBUs. Inside of the nanoball

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184 SBBs there are eight DMF and four pyridin e axial ligands with all of the pyridine molecules being positioned either along the a or b -axis. The presence of pyridine molecules within the cylindric al cavities situated along the ab -plane (Fig. 4.27), causes the linear orientation of SBUs as seen in compound [33], to be somewhat distorted and greatly reduces any possible free volume there, albeit removal of the pyridine molecules may be feasible. The pyridine molecules seem to be involved in weak CH••• interactions (3.461 measure centroid to centroid) due to a slipped face stacking arrangement. Along the c -axis the dimensions of the brid ging cylinder were observed to be 16.092 x 11.63 , when measured from oxygen atoms bridging metal ions in the SBUs. Here the ligands are severely disordered over at least two positions; however the persistent channel along the c -axis is reminiscent of that observed in the Cu analogue. The dimensions of the large rectangular ca vity are similar as well; 17.019 long with a diameter of ~ 27 . The length of this box along the c -axis is somewhat shorter at 12.782 . 4.4.3 Properties One of the more intriguing facets of th ese linked nanoball structures, is the fact that in addition to the immens e size of the cavities generated, the small pores inherent to the nanoball SBB node persist as well. The de sign strategy of SBBs has allowed for the controlled incorporati on of nanoscale cavities with predet ermined pores shapes and sizes into an extended periodic structure that simulta neously generates vast cavities. This could

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185 potentially be very valuable to the goal of effectively adsorbing and storing molecular hydrogen. A current belief by many experts working towards the use of metal-organic materials for the storage of H2, is that large surface areas (i.e. big, accessible cavities free of occlusions) should be beneficial to storing large amounts of hydrogen (i.e. high % Figure 4.27 Stick representation illustrating the cross-linking observed in the Zn linked nanoballs, compound [34]. Top: A view of the ab -plane depicts the large square cavities. This structure also involves 2-fold interpenetration occluding the large cavity with a nanoball node from the second framework (not shown). Middle: crosslinking as observed along the aand baxes. Note here the presence of the SBUs which have axially coordinated pyridine molecules inside the cylinders. Bottom: cross-linking as observed along the caxis. Note here the lack of SBUs allowing for a persistent channel directed along the caxis. (grey = carbon, red = oxygen, blue = nitrogen, salmon = copper, yellow = sulfur; hydrogen atoms have been deleted for clarity).

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186 volume) especially at high pressures, whereas the inclusion of sm all pore sizes will be beneficial to increasing the strength of the interaction between the framework and H2 (i.e. higher Qst, isosteric heats of adsorption).187-190 Therefore, attempts to incorporate both large surface areas and small pore sizes into a MOM are seen as particularly salient. Indeed that is exactly what can be achieved through the use of th e SBB design strategy, and thus explains a sudden explosion in the number of research groups publishing materials based upon this strategy. As for compounds [33] and [34] both exhibit 2-fold interpenetration which effectively occupies the en tire ~ 1.8 x 1.8 x 1.4 nm cavity. The fact that the SBB nodes themselves are immune to interpenetration assists in the formation of persistent channels directed along the c -axis only. Therefore the ability of these materials to adsorb small guest molecules in the form of gases (N2, H2) was of particular interest. As such experiments were conducted in an attemp t to activate the crystalline materials via solvent guest exchange with low bo iling solvents. Upon solvent guest exchange, the samples were exposed to nitrogen gas at 77 K a nd low pressures and the volumetric uptake recorded. Using this data 5 point B.E.T. surface areas were calculated to estimate the materials’ potential accessi ble surface area. Unfortunate ly, neither material ever demonstrated a B.E.T. surface area greater than ~ 50 m2/g making their porosity questionable. Whether the lack of porosity wa s due to the presence of solvent or guest molecules inside the nanoball SBBs which c ould not be evacuated and thus occluded the potential free volume, or if it’s a factor of the material not surviving the evacuation process and either partially or totally collapsing, could not be determined. Powder X-ray

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187 diffraction patterns obtained after sorption analys is seem to indicate that the material had not completely collapsed. However, this is not conclusive, as the PXRD was not conducted under identical conditions to the sorption experiment (low temperature and pressure) and does not speak to the possibility of surface damage to the microcrystals in which the entrance to extended channels are effectively sealed off while overall the channels persist. In this case the PXRD ma y not be indicative of a material’s channels being unattainable. As a point of interest, another resear ch group, following our strategy and adopting a ligand nearly identical to L5 was able to synthesis a related structure ( pcu -like from quadruply linked nanoballs) albeit without the observed interp enetration. This is because the ligand was slightly shorter in length, reducing the dimensions of the cavity and precluding the presence of a second interp enetrating nanoball network. Consequently, this material has shown one of the highest Qst values for any know metal-organic material, thus validating the design strategy.359 4.4.4 Experimental 4.4.4.1 Synthesis All reagents, unless described otherwise, were purchased from either SigmaAldrich or Fischer Scientific and used as received without further purification. Bulk solvents such as methanol, ethanol, acetone, and dichloromethane were first distilled and stored over drying media (4 molecu lar sieves) before their use.

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188 1,3-Bis(5-methoxy-1,3-benzenedicarboxylic acid)benzene, L5 (Fig. 4.24) was synthesized from commercially available dimethyl-5-hydroxy-1,3-benzenedicarboxylate and -Dibromomxylene via established procedures.360 In a typical reaction the dimethyl-5-hydroxy-1,3-benzenedicarboxylate (3.185 g, 0.0152 mol, 2 equivalents with respect to xylene) and K2CO3 (5.97 g, 0.0432 mmol, 3 equivalent s to ester) were weighed out separately and dried on a vacuum pump fo r three hours prior to use. After drying, the two solids were placed in a 3-neck round bo ttom flask which was purged of air using N2 for ~15 minutes prior to the start of the reaction. Upon the addition of the two solids ~100 mL of dry acetone was added and the mixture s tirred utilizing a stir ba r and hot plate. The round bottom flask was placed in a hot oil bath which was held at a temperature of 80 C. Separately, the dibromoxlye ne (2.00 g, 0.0076 mmol) was diss olved in 20 mL of dry acetone, and then added to the refluxing mixtur e. The solution was allowed to reflux for ~24 hours and the reaction was monitored via TLC. Upon completion of the reaction, the solution was allowed to cool to room temp erature and then filtered through Celite. The solvent was then removed with heat under vacuum, to leave behind a dark yellow oil which solidified upon cooling in the refrigerat or (10 C). The solid that remained was then dissolved in ~100 mL dichloro methane, washed three times with D.I. H2O, and dried over anhydrous Na2SO4. Once more the solvent (DCM) was removed with heat under a vacuum, the resulting oil solidified, and the solid was finally recrystallized from hot ethanol. Upon recrystallizat ion very fine colorless needles where collected via vacuum filtration and allowed to air dry in the hood.

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189 The crystalline ester product was then dissolved in a methanol/ H2O solution of NaOH (20% by volume, 6 equivalents to th e ester). Upon full dissolution the solution was allowed to stir for ~12 more hours, af ter which the completion of the saponification was verified via TLC. The final product was obtained by precipitating the carboxylic acid out of solution by the dropwise addition of HCl solution (10% by volume) until a pH < 2 for the solution was obtained as determined by pH paper. The resultant white solid was washed several times with D.I. H2O, vacuum filtered and then dried in a vacuum oven at 60 C. 1,3-bis(5-methoxy-1,3-ben zenedicarboxylic acid)benzene ( L5 ) was collected (2.15g, 85.8%) as a pure white powdery solid with spectroscopic data that was consistent to those previously reported (Appendix A-5, B-5).360 1H NMR (250 MHz, DMSOd6, ): 5.3(s, 4H, -O-CH2-), 7.5(d, J = 0.9 Hz, 3 H, -ArH), 7.6(s, 1H, -ArH), 7.8(d, J = 1.39 Hz, 4H, -ArH), 8.1(t, J = 1.38 Hz, 2H, -ArH), 13.4(br, 4H, -COOH); mp 279-281 C (lit 230-246 C). In a typical reaction [Cu24( L5 )12(H2O)16(DMF)8]n [ 33 ], was synthesized from a solvothermal reaction involving Cu(NO3)22.5H2O (47.2 mg, 0.203 mmol) and L5 (47.1 mg, 0.101 mmol) together with pyrid ine as a coordinating base (48 L, 0.599 mmol) in a molar ratio of one ligand to tw o metals to six pyridine mo lecules. All components, in addition to 2 mL of N, N -Dimethylformamide and 1 mL of odichlorobenzene, were added to a 20 mL scintillation vial which was sealed with aluminum foil and capped tightly. The vial was then pl aced in a sand bath and heated in a programmable oven. The heat profile was as follows: th e reaction temperature was raised from 30 C to 105 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours.

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190 The temperature was then slowly lowered back to 30 C at a rate of 1.0 C per minute. At this time the solution was a noticeable deep green color, but contained no precipitate or crystals. The reaction vial was then subjected to an additional round of heating, raised at rate of 1.5 C per minute to a holding temperature of 115 C. After 24 hours, the temperature was cooled again at a rate of 1.0 C per minute, and the vials again contained a deep green solution was no visible precipita te. The vials were left undisturbed on the lab bench, still capped, and after approximately three months, large prismatic green-blue crystals of compound [33] suitable for single crystal X-ray diffraction were observed to have formed (65 mg, 20.65% yield). In a typical reaction [Zn24( L5 )12(H2O)16(DMF)8]n [ 34 ], was synthesized from a solvothermal reaction involving Zn(NO3)26H2O (60 mg, 0.202 mmol) and L5 (46.78 mg, 0.100 mmol) together with pyridine as a coordinating base (48.52 L, 0.601 mmol) in a molar ratio of one ligand to tw o metals to six pyridine mo lecules. All components, in addition to 3 mL of N, N -Dimethylformamide and 1 mL of anisole, were added to a 20 mL scintillation vial which was sealed with aluminum foil and capped tightly. The vial was then placed in a sand bath and heated in a programmable oven. The heat profile was as follows: the reaction temperature was raised from 30 C to 115 C at a rate of 1.5 C per minute upon which time it was held at that temperature for 24 hours. The temperature was then slowly lowered back to 30 C at a rate of 1.0 C per minute. Upon cooling to room temperature, the reaction vials were removed from the oven and it was observed that large colorless cube shaped crystals [34] suitable for single crystal X-ray diffraction had formed (78 mg, 43% yield)

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191 4.4.4.2 X-ray Crystallography Single crystals of compound [33] (Fig. 4.28) suitable for X-ray crystallographic analysis were selected following examinati on under a microscope. Intensity data were collected on a Bruker-AXS SMART AP EX/CCD diffractometer using Mok\ radiation ( = 0.7107 ).281 The data were corrected for Lore ntz and polarization effects and for absorption using the SADABS program (SAINT).282 The structures were solved using direct methods and refined by fu ll-matrix least-squares on |F|2 (SHELXTL).283 Additional electron density, located in the void cavity sp ace, assumed to be disordered solvent, was unable to be adequately refined was removed using the SQUEEZE/PLATON program.284-286 Select crystallographic data is presented in tabular form in Appendix C20. Single crystals of compound [34] (Fig. 4.29) suitable for X-ray crystallographic analysis were selected following examinati on under a microscope. Intensity data were collected on a Bruker-AXS SMART APEX /CCD diffractometer using Mo k\ radiation ( = 0.7107 ).281 The data were corrected for Lore ntz and polarization effects and for Figure 4.28 Digital photographs depicting single crystals of compound [33]

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192 absorption using the SADABS program (SAINT).282 The structures were solved using direct methods and refined by fu ll-matrix least-squares on |F|2 (SHELXTL).283 Additional electron density, located in the void cavity sp ace, assumed to be disordered solvent, was unable to be adequately refined was removed using the SQUEEZE/PLATON program.284-286 Select crystallographic data is presented in tabular form in Appendix C21. 4.4.4.3 Powder X-ray Diffraction Powder samples suitable for powde r X-ray diffraction (PXRD), FT-IR spectroscopy, and Thermal Gravimetric Anal ysis (TGA) were obtained by removing a large amount of single crystals from the reacti on scintillation vial by using a glass Pasteur pipette and depositing these cr ystal (along with mother liquo r) in a small concave agar mortar. Excess solvent was removed via pipette, and surface solvent was removed by wicking action with a Kim-Wipe. Upon wick drying, the crysta ls were transferred to a small piece of filter paper which was subseque ntly folded over and they were dried Figure 4.29 Digital photograph depicting a single crystal of compound [34]

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193 further and slightly crushed with gently pr essure. The resulting dry powder (~30 mg) was then immediately applied to a PXRD samp le puck prepared with a small amount of vacuum grease to fixate the powder samp le, and the PXRD experiment performed without delay. The Cu(II) version of the linked nanoballs, compound [33], was characterized for bulk composition purity via PXRD. The samples were analyzed on a Bruker AXS D8 Discover X-ray diffractomet er, equipped with GADDS™ (General Area Diffraction Detection System) and a Bruker AXS HI-STAR area detector. The X-ray source was Cu ( = 1.54178 ) run on a generator operating at 50 kV and 40 mA. The data was collected within the 2 range of 3 – 40 , in continuous scan mode using a step-size of 0.05 per step and a rate of 0.5 sec onds per step. (Appendix B-38) The Zn(II) analogue of the linked nanoballs, compound [34], was also characterized for its bulk composition purity via PXRD. The samples of [34] were analyzed on a Bruker AXS D8 Discover X -ray diffractometer, equipped with GADDS™ (General Area Diffraction Detection System) and a Bruker AXS HI-STAR area detector. The X-ray source was Cu ( = 1.54178 ) run on a generato r operating at 50 kV and 40 mA. The data was collected in contin uous scan mode by sweeping through 2 angles of 3 – 40 and using a step-size of 0.05 a nd rate of 0.5 seconds per step respectively. (Appendix B-39)

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194 4.4.4.4 FT-IR Spectroscopy All compounds, including synthesi zed ligands, were characterized via infrared spectroscopy using a Nicolet Avatar 320 Four ier-Transform Infrared Spectrometer (FTIR). Before each sample was analyzed, a background spectrum was obtained for purposes of zeroing out ambient noise in the form of the laboratory atmosphere. Each sample was measured in the range from 4000 cm-1 to 500 cm-1 wavenumbers (wavelength of 2500 nm to 20000 nm respectively) and scanned 64 times. Results were recorded in % transmittance and the spectrum analyzed using the EZ OMNIC (V.5.1b, copyright 1992199 Nicolet Instruments Corporation) computer software suite. A typical sample was a analyzed as a neat, dry solid (~10 mg) obtained via either vacuum filtration and air drying or gently drying with laboratory grade filter paper. The FT-IR spectrum (Appendix B-5) for 1,3-bis(5-methoxy-1,3benzenedicarboxylic acid)benzene L5, illustrates the same broad featureless hump originating around 3300 cm-1 and bleeding into ~3000 cm-1 which is typical of carboxylic acids involved in hydrogen bonding, which would be expected in solid state samples such how the ligand was analyzed. The FT-IR spectru m for this ligand indicated the presence of the two ether groups by a moderate ly intense band appearing at 1044.65 cm-1 (expected 1040 cm-1).287, 288 The presence of the carboxylic acid groups was also confirmed by the strong sharp single band located at 1697.51 cm-1, exactly where an aromatic carboxylic acid should be found.

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195 [Cu24( L5 )12(H2O)16(N,N -Dimethylformamide)8]n [33]: IR (dry powder) max (cm-1): 3400 v br (-OH, alcohol solvent), 2922 very small, sh. (-CH, aliphatic), 2852 very small, sh. (-CH, aliphatic), 1637 m sh. (COO-, carboxylate), 1588 m sh. (C=O, carboxylate), 1379 v sh. (COO-, carboxylate). The most notab le changes between the IR spectrum for the ligand L5 and compound [ 33 ] is the disappearance of the broad OH stretch due to the carboxylic ac id that was centered around 3122 cm-1 and bleed into the 3000 cm-1 region. There are two very sm all, but sharp peaks at 2923 cm-1 and 2853 cm-1 which remained from the ligand IR spectrum and are due to the large presence of –CH2 and –CH3 groups. There is a strong sharp peak at 1014 cm-1 which is probably due to the presence of the ether group in the tetr acarboxylic acid ligand. Additionally, we notice drastic shifts in frequency for the C=O stre tches which is expect ed upon coordination of the carboxylate. (Appendix B-38) [Zn24( L5 )12(H2O)16(N,N -Dimethylformamide)8]n [34]: IR (dry powder) max (cm-1): 2922 very small (-CH, aliphatic), 2852 very small (-CH, aliphatic), 1641 m sh. (COO-, carboxylate), 1589 m sh. (C=O carboxylate), 1379 v sh. (COO-, carboxylate), 1053 m sh. (Ar-O-CH2-, ether). The most notable cha nges between the IR spectrum for the ligand L5 and compound [ 34 ] is the disappearance of the OH stretch due to the carboxylic acid that was centered around 3122 cm-1 and bleed into the 3000 cm-1 region as well as the two sharp peaks at 3535 cm-1 and 3451 cm-1 which arose from free acids. There are two very weak, but sharp peaks at 2922.81 cm-1 and 2852.29 cm-1 which remained from the ligand IR spectrum and are due to the presence of –CH2 groups.

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196 Additionally, we notice drastic shifts in frequency for the C=O stretches which is expected upon coordination of the carboxylate. (Appendix B-39) 4.4.4.5 Thermal Gravimetric Analysis Thermal gravimetric analysis for Cu(II) cross-linked nanoballs, [Cu24( L5 )12(H2O)16(N,N -Dimethylformamide)8]n [ 33 ], was conducted on a T.A. Instruments 2950 TGA operating under the Hi gh Resolution Dynamic mode. The heating program was run from 30 C up to 1000 C and was performed under a flow of N2 gas. The resulting data was graphed as a function of weight percent (wt. %) versus change in temperature. Upon acquisition the data was evaluated using T.A. Instruments Thermal Advantage suite of analyzing software. Initial weight loss of 3.26 % at 42.34 C was observed and interpreted to be loss of mother liquor still present on the crystalline sample. A small amount of further weight loss (1.43 %, 65 C) was observed and thought to be low boiling guest molecules in the crystal lattice. The first major weight loss results in a broad, rolling weight loss which may be do the loss of several different types of molecules at roughly the same temperatures over a broad range. This represen ts 24% of the sample and most likely was due to the various types of coordi nated solvent molecules (DMSO, H2O, etc.) being removed over a large temper ature range. (Appendix B-38) Thermal Gravimetric Analysis for [Zn24( L5 )12(H2O)16(N,N Dimethylformamide)8]n compound [ 34 ], the Zn(II) analogue of cross-linked nanoballs was performed on a PerkinElmer STA 6000 Simultaneous Thermal Analyzer. Data

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197 acquisition and analysis was pe rformed with the assistance of the Pyris Series suite of software. Roughly 10-20 mg of dry powder was pl aced in a sample crucible and heated at a rate of 10 C/min. form a temperature of 30 C up to 700 C. An immediate broad weight loss of ~ 3.7% for 30 C until ~100 C was taken to be the loss of mother liquor solvent still on the surface of the crystal and small amounts of interstitial solvent molecules from within the crystal structure. Over the temperature range of 100 C to 180 C, a weight loss of ~12.3 % was observed and is believed to be form solvent molecules trapped within the cavities of the framework, as well as some weaker bound solvent molecules (outside ax ially bound solvent molecules). At higher temperatures (~180 C until 240 C, ~240 C until 370 C) weight losses of ~10 % and ~7.5% were observed respectively and should be due to the loss of more tightly held solvent molecules, either trapped in the c onfines of the nanoballs or perhaps axially coordinated on the interior of the nanoballs or within the small interconnecting cages. After 370 C, the sample decomposed. (Appendix B-39) 4.5 Conclusion In summary, this chapter has attempted to emphasize the increased complexity of discrete metal-organic nanostructures based upon polyhedra, when co mpared to that of simple discrete polygons, 1-period ic architectures, and even mo st 2-periodic structures as 2-periodic tilings are often based upon so me polyhedral form. The reason for this increased complexity is the nature of how the regular polygons which make up the polyhedra can come together to generate the overall superstructure While generally not

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198 as complicated as 3-periodic structures, they are still rather important structures to investigate. First and foremost they represen t intriguingly beautiful structures that are fascinating on a purely aesthetic level. Second, being discrete nanoscale structures, they often have unique chemical and physical prope rties that can be exploited for the purpose of designing functional materials for specifi c applications. Finally, these nanoscale metalorganic polyhedra are essential to the investigation of MOMs in general due to the fact that many (if not all) of the more interesti ng 3-periodic structures can be interpreted as being constructed from polyhedral cage s related to metal-organic polyhedra. Three novel examples of nanoball derivatives the 5-dodecyloxy, the 5benzyloxy, and the 5-naphthylmethoxy have been synthesized and structurally characterized. From this it is demonstrated how these materials are not only complex in the way that they are generated through modular self-assembly, but also in the fact there is often a potential for inte resting packing of these na nospheres upon crystallization, a uniquely supramolecular phenomenon. For ex ample the distorted diamondoid packing and concomitant threading of dodecyloxy chai ns into the interior of the dodecyloxy derivative of the nanoball, was a somewhat unexpected although comp letely reasonably result of the noncovalent forces at work (s upramolecular chemistry) as these materials crystallize from solution. Additionally, the close pack ing of the aryloxy derivatives of the nanoball, in a manner much more predictable than was the case for the dodecyloxy form, resulted in a plethora of simultaneous weak noncovalent forces in the form of CH••• and stacking interactions that effectively alter the observed properties for these materials. As discrete

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199 architectures with the 24 aryloxy groups pos itioned around the periph ery of the sphere, these nanoballs were expected to exhibit increased solubility in common aromatic organic solvents. Alas, as a result of th e abundance of concerted weak noncovalent interactions, and the nature of the packing in general, these structures were, somewhat unpredictably, not soluble in any common laborat ory solvent. This is a strong illustration of the effect supramolecular chemistry can have of the properties of molecular structures. Finally, a new design strategy for the design and synthesis of extended metalorganic materials based upon the implementa tion of supermolecular building blocks (SBBs) was introduced. This concept is an extens ion of the use of SBUs in general, and is predicated upon the isolation of existing metal-organic polyh edra and then judiciously modifying these MOPs in a manner so as to facilitate their cross-linking into extended structures. The adoption of the SBB design stra tegy is practical for a number of reasons. The use of MOPs as nodes in extended MOMs will indubitably re sult in MOMs with enhanced scale. Additionally, SBBs can ofte n be designed in such a way as to adopt unique geometries or coordina tion numbers not possible with single metal ions or SBUs. Perhaps most importantly, SBBs may provide cr ystal engineers with increased control of the design and synthesis of novel ex tended metal-organic materials.

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200 Chapter 5 Conclusions and Future Directions 5.1 Summary and Conclusions In this dissertation I have attempted to su rvey the field of metal-organic materials through a sampling of my own research. Cla ssifications of what constitutes a metalorganic material were made. A brief histor y of the subject has been outlined, focusing upon the various design aspects which have been implemented throughout the years. Particular attention has been afforded to distinguishing between the several levels of complexity associated with various MOMs. In attempting to delineate this natural hierarchy of complexity, I have introduced several platforms of MOMs often related by their building components, but vastly different in thei r structural composition. Specifically, this dissertation has dealt with: i.) Two different platforms of 2-periodic networks, the 4.82 feslike structures which exhibit interdigitation between layers, and Kagom lattice structures which can be layered controllably and are capable of demonstrating intriguing supramolecular interactions in the solid state. ii.) The design strategy of pillaring has been exploited to fabricate 3-periodic materials with controllable dimensions and pore sizes. Additiona lly the concept of

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201 pillaring has been expanded upon to include appropriately designed ligands capable of interconnecting layers though ligand-to-l igand or axial-to-ligand methods. iii.) Novel examples of 0-periodic nanoscal e structures in the form of aryloxy and alkyloxy derivatives of nanoballs were descri bed along with some unique supramolecular chemistry associated with them. The ability of supramolecular chemistry to impact the observable properties of discrete structures was briefly explored. iv.) Finally, the concept of supermol ecular building blocks (SBBs) as a new design strategy for the fabric ation of extended metal-orga nic materials was introduced through two 3-periodic st ructures self-assembled via covalently cross-linking apt nanoballs. The benefits and implications of this new design strategy were also briefly expounded upon. To briefly summarize, the research pr esented within the confines of this dissertation deals with the desi gn, synthesis, and characteriza tion of several platforms of metal-organic materials (MOMs). These meta l-organic materials represent a bourgeoning class of hybrid material s which are constructed via the coordinate covalent bond between metal ions and organic molecules with the capacity to behave as ligands; typically appropriate exo-functional Ndonor or O-donor functional groups suffice. These hybrid materials are currently receiving an ever-expand ing level of interest, largely due to their myriad of interesting physical and chemical properties and potential useful applications. However, neither the mere existence of in triguing properties nor any potential toward future applications can fully explain the a ffection a large (and gr owing) population of

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202 crystal engineers have for these materials. I be lieve this to be a byproduct of the nature of these materials themselves; whereas many mate rials have in the pa st been looked upon with some interest and curiosity regarding th eir properties, for a la rge part it was done as spectator. A material was observed to have properties, and th en those properties were classified, categorized, and catalogued awa y. To be sure, chemists and materials scientists have probably always made observa tions about classes of materials and then attempted to generalize. And just as likely th ese same chemist often desired to be able to extend those generalizations in a manner such that they could ha rness control over the materials’ properties. In short the dream has b een the same. What is new is our ability to go about reaching those goals. Metal-organic materials, being particularly amenable to the principles of crystal engineering, represent a class of materials which not only beg for th e active participation of the synthetic chemist in their design they require it. It is wholly unsatisfactory to simply go about randomly making new materi als and then hoping for a diamond in the rough in terms of their abilities. 5.2 Future Directions The future of metal-organic materials is definitely bright. The amount of time and effort that goes into the study of MOMs is increasing (rap idly) every year. This is evidenced by the exponential growth in both the number of papers and the number of citations given to those papers. Hopefully this expansion can be sustained; and I believe it can. But for that to happen, I believe that th e field must branch out so to speak. To be

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203 sure there is already a great breadth of applications and us es of MOMs being investigated by the field. This merely needs to be conti nued, and supplemented, for the field to remain healthy and vibrant. Gone are the days when a new material can be fabricated and the potential properties or applic ations of it simply be specu lated upon with no further action. And the days of making a material and merely recording its properties will soon come to an end as well. As a scientific field we have successfully demonstrat ed that metal-organic materials can have a truly lasting impact on our technological soci ety. We have outlined numerous possibilities. It is now becoming time that we follow up on these possibilities, and so the next generation of metal-orga nic chemists will surely need to expound upon these ideas. While some in the field may make refe rence to separate “g enerations” of MOMs based upon either a material’s ability to acco mplish some specific goal (i.e. porosity), or conversely upon the nature and the stre ngth of the coordination bond involved in sustaining the framework, I find these demarca tions to be somewhat arbitrary and overtly subjective. For what other purpose, than an at tempt to segregate materials into classes of “proposed” usefulness these materials are promising and worthy of adulation, while those materials lack any real function can defining a material’s level of s ophistication be based on such narrow definitions of accomp lishment? These artificial classifications are mistaken, I believe, for another reas on. Generally, such defining of objects into groups is done in order to be beneficial in understanding these objec ts in some way. How does saying this material sorbs proficient amount s of gas or that material is made from

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204 the strongest coordination bonds help other research ers in the field move forward? Where is the benefit? Better, I would say, would be the classi fication of metal-organic materials on the natural hierarchy that occurs in the types of structural building units which are employed in their design and synthesis. At the very le ast this method has the benefit of following a loose, but nonetheless roughly linear timeline of when these materials were created; and the use of the word “generations” surely has connotations of order with respect to time. Additionally, using structural building units as a way of cl assifying MOMs is neutral to their properties and functions. It does not imply a material must meet some narrow criteria to be considered a significant adva ncement. A material made from single metal ion nodes may be just as promising (for some application anyway) as a material made from SBUs or SBBs. I see good things in store for the field of metal-organic materials, especially if collectively as a group we can take an honest look forward at what these materials could potentially be of use for, and try to get away from constantly redefini ng what it is that we are working with.

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205 References 1. Feynman, R. P. Plenty of Room at the Bottom http://www.its.caltech.edu/~feynman/plenty.html (September 29, 2009). 2. Webb, R. Symmetry: Culture and Science 2000, 11 (1-4), 231-268. 3. Webb, R. Stella4D v4.4; Melbourne, Australia, 2008 http://www.software3d.com/stella.html 4. Thoreau, H. D., Journal Volume VIII. In The Writings of Henry David Thoreau Torrey, B., Ed. Houghton Mifflin and Company: Boston, 1906; Vol. 14, pp 87-88. 5. Libbrecht, K. G. SnowCrystals.com http://www.its.caltech.edu/~atomic/snowcrystals/ (August 15, 2009). 6. Bentley, W. A.; Humphreys, W. J., Snow Crystals Dover Publicationhs, Inc.: New York, 1962 7. Kepler, J., A New Year's Gift or On the Six-Cornered Snowflake. In The SixCornered Snowflake Whyte, L. L., Ed. Clarendon Press: Oxford, 1966. 8. Bloss, F. D., Crystallography and Crystal Chemistry: an introduction Holt, Rinehart and Winston, Inc.: New York, 1971 9. Burke, J. G., Origins of the Science of Crystals University of California Press: Berkeley, California, 1966

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206 10. Bragg, L., The Crystalline State Cornell University Press: Ithaca, New York, 1965 ; Vol. 1. 11. Drexler, K. E., Nanosystems: Molecular Ma chinery, Manufacturing, and Computation John Wiley & Sons, Inc.: New York, 1992 12. Lehn, J.-M., Supramolecular Chemistry: Concepts and Perspectives VCH: Weinheim, 1995 13. Steed, J. W.; Turner, D. R.; Wallace, K. J., Core Concepts in Supramolecular Chemistry and Nanochemistry John Wiley & Sons, Ltd.: Chichester, West Sussex, England, 2007 14. Steed, J. W.; Atwood, J. L., Supramolecular Chemistry John Wiley & Sons, Ltd.: Chichester, West Sussex, England, 2000 15. Schneider, H.-J.; Yatsimirsky, A. K., Principles and Methods in Supramolecular Chemistry John Wiley & Sons, Ltd.: Chic hester, West Sussex, England, 2000 16. Ehrlich, P., Studies on Immunity Wiley: New York, 1906 17. Fischer, E. Ber. Deutsch Chem. Ges. 1894, 27 2985. 18. Pauling, L., The Nature of The Chemical Bond 3rd ed.; Cornell University Press: Ithaca, New York, 1960 19. Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101 (6), 1629-1658. 20. Hennigar, T. L.; MacQuarrie, D. C.; Losier, P.; Rogers, R. D.; Zaworotko, M. J. Angew. Chem., Int. Ed. 1997, 36 (9), 972-973. 21. Desiraju, G. R., Crystal Engineering: The Design of Organic Solids Elsevier: Amsterdam, 1989

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207 22. Schmidt, G. M. J. Pure Appl. Chem. 1971, 27 647-678. 23. Seddon, K. R.; Zaworotko, M. J., Crystal Engineering: The Design and Application of Functional Solids NATO ASI Series C: Mathematical and Physical Sciences, vol. 539 Kluwer Academic Publishers: Dordrecht, 1999 24. Desiraju, G. R. Journal of Molecular Structure 2003, 656 (1-3), 5-15. 25. Pepinsky, R. Phys. Rev. 1955, 100 971. 26. Desiraju, G. R. Angew.Chem., Int. Ed. 2007, 46 (44), 8342-8356. 27. Desiraju, G. R. Chem. Commun. 2005, (24), 2995-3001. 28. Desiraju, G. R. J. Molec. Struct. 2003, 656 (1-3), 5-15. 29. Desiraju, G. R. Acc. Chem. Res. 2002, 35 (7), 565-573. 30. Desiraju, G. R.; Steiner, T., The Weak Hydrogen Bond In Structural Chemistry and Biology Oxford University Press: Oxford, 1999 31. Nangia, A.; Desiraju, G. R. Design of Organic Solids 1998, 198 57-95. 32. Braga, D.; Grepioni, F.; Desiraju, G. R. Chem. Rev. 1998, 98 (4), 1375-1405. 33. Desiraju, G. R. Chem. Commun. 1997, (16), 1475-1482. 34. Thalladi, V. R.; Goud, B. S.; Hoy, V. J.; Allen, F. H.; Howard, J. A. K.; Desiraju, G. R. Chem. Commun. 1996, (3), 401-402. 35. Desiraju, G. R. Angew.Chem., Int. Ed. 1995, 34 (21), 2311-2327. 36. Desiraju, G. R. Acc. Chem. Res. 1991, 24 (10), 290-296. 37. Desiraju, G. R. J. Chem. Soc., Chem. Commun. 1990, (6), 454-455. 38. Desiraju, G. R.; Parthasarathy, R. J. Am. Chem. Soc. 1989, 111 (23), 8725-8726. 39. Sarma, J.; Desiraju, G. R. Acc. Chem. Res. 1986, 19 (7), 222-228.

PAGE 228

208 40. Theocharis, C. R.; Desiraju, G. R.; Jones, W. J. Am. Chem. Soc. 1984, 106 (12), 3606-3609. 41. Sarma, J.; Desiraju, G. R. J. Chem. Soc., Chem. Commun. 1984, (3), 145-147. 42. Desiraju, G. R.; Sarma, J. J. Chem. Soc., Chem. Commun. 1983, (1), 45-46. 43. Etter, M. C.; Reutzel, S. M. J. Am. Chem. Soc. 1991, 113 (7), 2586-2598. 44. Etter, M. C. J. Phys. Chem. 1991, 95 (12), 4601-4610. 45. Etter, M. C.; Urbanczyklipkows ka, Z.; Ziaebrahimi, M.; Panunto, T. W. J. Am. Chem. Soc. 1990, 112 (23), 8415-8426. 46. Etter, M. C.; Macd onald, J. C.; Bernstein, J. Acta Crystallogr. 1990, B46 (2), 256262. 47. Etter, M. C.; Adsmond, D. A. J. Chem. Soc., Chem. Commun. 1990, (8), 589-591. 48. Etter, M. C. Acc. Chem. Res. 1990, 23 (4), 120-126. 49. Bernstein, J.; Etter, M. C.; Macdonald, J. C. J. Chem. Soc., Perkin Trans. 2 1990, (5), 695-698. 50. Etter, M. C.; Baures, P. W. J. Am. Chem. Soc. 1988, 110 (2), 639-640. 51. Panunto, T. W.; Urbanczyklipkow ska, Z.; Johnson, R.; Etter, M. C. J. Am. Chem. Soc. 1987, 109 (25), 7786-7797. 52. Etter, M. C.; Urbanczyklipkowska, Z.; Jahn, D. A.; Frye, J. S. J. Am. Chem. Soc. 1986, 108 (19), 5871-5876. 53. Inorganic Crystal Structure Database http://icsd.fiz-k arlsruhe.de/icsd/ (September 19, 2009).

PAGE 229

209 54. Chen, B. L.; Ockwig, N. W.; Fronczek, F. R.; Contreras, D. S.; Yaghi, O. M. Inorg. Chem. 2005, 44 (2), 181-183. 55. Nucleic Acid Database http://ndbserver.rutgers.edu/ (September 19, 2009). 56. International Centre for Diffraction Data http://www.icdd.com/ (September 19, 2009). 57. Allen, F. H. Acta Crystallogr. 2002, B58 380-388. 58. Cambridge Structural Database http://www.ccdc.cam.ac.uk/products/csd/ (September, 10 2009). 59. Hall, S. R.; Allen, F. H.; Brown, I. D. Acta Crystallogr. 1991, A47 (6), 655-685. 60. International Union for Crystallography http://www.iucr.org/ (September 11, 2009). 61. Hall, S. R.; Allen, F. H.; Brown, I. D. Acta Crystallogr. 1991, A47 (6), 637-639. 62. Dunitz, J. D.; Gavezzotti, A. Chem. Soc. Rev. 2009, 38 (9), 2622-2633. 63. Robson, R. Dalton Trans. 2008, (38), 5113-5131. 64. Dunitz, J. D.; Gavezzotti, A. Cryst. Growth Des. 2005, 5 (6), 2180-2189. 65. Gavezzotti, A. CrystCngComm 2003, 5 439-446. 66. Motherwell, W. D. S.; Ammon, H. L.; Dunitz, J. D.; Dzyabchenko, A.; Erk, P.; Gavezzotti, A.; Hofmann, D. W. M.; Leusen, F. J. J.; Lommerse, J. P. M.; Mooij, W. T. M.; Price, S. L.; Scheraga, H.; Sc hweizer, B.; Schmidt, M. U.; van Eijck, B. P.; Verwer, P.; Williams, D. E. Acta Crystallogr. 2002, B58 647-661. 67. Lommerse, J. P. M.; Motherwell, W. D. S.; Ammon, H. L.; Dunitz, J. D.; Gavezzotti, A.; Hofmann, D. W. M.; Leusen, F. J. J.; Mooij, W. T. M.; Price, S.

PAGE 230

210 L.; Schweizer, B.; Schmidt, M. U.; van Eijck, B. P.; Verwer, P.; Williams, D. E. Acta Crystallogr. 2000, B56 697-714. 68. Gavezzotti, A.; Filippini, G. J. Am. Chem. Soc. 1996, 118 (30), 7153-7157. 69. Gavezzotti, A. J. Am. Chem. Soc. 1991, 113 (12), 4622-4629. 70. Desiraju, G. R.; Gavezzotti, A. Acta Crystallogr. 1989, B45 473-482. 71. Bryant, J. A., JR., The Tragedy of Romeo and Juliet The Signet Classic Shakespeare Signet Classic: New York, 1990 ; pp 75. 72. Rayner, J. H.; Powell, H. M. J. Chem. Soc. 1952 319-328. 73. Baur, R.; Schwarzenbach, G. Helv. Chim. Acta. 1960, 43 (3), 842-847. 74. Krishnamurty, K. V.; Harris, G. M. Chem. Rev. 1961, 61 (3), 213-246. 75. Griffin, W. P. Q. Rev. Chem. Soc. 1962, 16 (2), 188-207. 76. Billard, R. D.; Wilkinson, G. J. Chem. Soc. 1963 3193-3200. 77. Biondi, C.; Bonamico, M.; Torelli, L.; Vaciago, A. Chem. Commun. 1965, (10), 191-192. 78. Tomic, E. A. J. Appl. Polym. Sci. 1965, 9 (11), 3745-3752. 79. Walton, R. A. Q. Rev. Chem. Soc. 1965, 19 (2), 126-143. 80. Krishnamurty, K. V.; Harris, G. M. L.; Sastri, V. S. Chem. Rev. 1970, 70 (2), 171197. 81. Iwamoto, T.; Kiyoki, M.; Ohtsu, Y.; Takeshigekato, Y. Bull. Chem. Soc. Jpn. 1978, 51 (2), 488-491. 82. Nishikiori, S. I.; Iwamoto, T.; Yoshino, Y. Bull. Chem. Soc. Jpn. 1980, 53 (8), 2236-2240.

PAGE 231

211 83. Underhill, A. E.; Watkins, D. M. Q. Rev. Chem. Soc. 1980, 9 (4), 429-448. 84. Iwamoto, T.; Nakano, T.; Morita, M. ; Miyoshi, T.; Miyamoto, T.; Sasaki, Y. Inorg. Chim. Acta 1986, 2 313-316. 85. Kitazawa, T.; Nishikiori, S.; Kuroda, R.; Iwamoto, T. Chem. Lett. 1988, 17 (10), 1729-1732. 86. Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1989, 111 (15), 5962-5964. 87. Abrahams, B. F.; Hoskins, B. F.; Robson, R. J. Chem. Soc., Chem. Commun. 1990, (1), 60-61. 88. Gable, R. W.; Hoskins, B. F.; Robson, R. J. Chem. Soc., Chem. Commun. 1990, (10), 762-763. 89. Gable, R. W.; Hoskins, B. F.; Robson, R. J. Chem. Soc., Chem. Commun. 1990, (23), 1677-1678. 90. Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1990, 112 (4), 1546-1554. 91. Abrahams, B. F.; Hoskins, B. F.; Liu, J. P.; Robson, R. J. Am. Chem. Soc. 1991, 113 (8), 3045-3051. 92. Abrahams, B. F.; Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1991, 113 (9), 3606-3607. 93. Batten, S. R.; Hoskins, B. F.; Robson, R. J. Chem. Soc., Chem.Commun. 1991, (6), 445-447. 94. Abrahams, B. F.; Hardie, M. J.; Hoskins, B. F.; Robson, R.; Williams, G. A. J. Am. Chem. Soc. 1992, 114 (26), 10641-10643.

PAGE 232

212 95. Abrahams, B. F.; Hardie, M. J.; Hoskins, B. F.; Robson, R.; Sutherland, E. E. J. Chem. Soc., Chem. Commun. 1994, (9), 1049-1050. 96. Hoskins, B. F.; Robson, R.; Scarlett, N. V. Y. J. Chem. Soc., Chem. Commun. 1994, (18), 2025-2026. 97. Batten, S. R.; Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1995, 117 (19), 53855386. 98. Robinson, F.; Zaworotko, M. J. J. Chem. Soc., Chem.Commun. 1995, (23), 24132414. 99. Fujita, M.; Kwon, Y. J.; Miyazawa, M.; Ogura, K. J. Chem. Soc., Chem. Commun. 1994, (17), 1977-1978. 100. Fujita, M.; Kwon, Y. J.; Washizu, S.; Ogura, K. J. Am. Chem. Soc. 1994, 116 (3), 1151-1152. 101. Fujita, M.; Sasaki, O.; Watanabe, K. Y.; Ogura, K.; Yamaguchi, K. New J. Chem. 1998, 22 (2), 189-191. 102. Biradha, K.; Fujita, M. J. Chem. Soc., Dalton Trans. 2000, (21), 3805-3810. 103. Biradha, K.; Hongo, Y.; Fujita, M. Angew. Chem., Int. Ed. 2000, 39 (21), 38433845. 104. Umemoto, K.; Tsukui, H.; Kusukawa, T.; Biradha, K.; Fujita, M. Angew. Chem., Int. Ed. 2001, 40 (14), 2620-2622. 105. Kitagawa, S.; Matsuyama, S.; Munakata, M.; Emori, T. J. Chem. Soc., Dalton Trans. 1991, (11), 2869-2874. 106. Kitagawa, S.; Munakata, M.; Tanimura, T. Inorg. Chem. 1992, 31 (9), 1714-1717.

PAGE 233

213 107. Kitagawa, S.; Kawata, S.; Nozaka, Y.; Munakata, M. J. Chem. Soc., Dalton Trans. 1993, (9), 1399-1404. 108. Kawata, S.; Kitagawa, S.; Kondo, M.; Furuchi, I.; Munakata, M. Angew. Chem., Int. Ed. 1994, 33 (17), 1759-1761. 109. Kondo, M.; Yoshitomi, T.; Seki, K.; Matsuzaka, H.; Kitagawa, S. Angew. Chem.,. Int. Ed. 1997, 36 (16), 1725-1727. 110. Kondo, M.; Okubo, T.; Asami, A.; Nor o, S.; Yoshitomi, T.; Kitagawa, S.; Ishii, T.; Matsuzaka, H.; Seki, K. Angew. Chem., Int. Ed. 1999, 38 (1-2), 140-143. 111. Kondo, M.; Shimamura, M.; Noro, S.; Yoshitomi, T.; Minakoshi, S.; Kitagawa, S. Chem. Lett. 1999, (4), 285-286. 112. Noro, S.; Kondo, M.; Ishii, T.; Kitagawa, S.; Matsuzaka, H. J. Chem. Soc., Dalton Trans. 1999, (10), 1569-1574. 113. Noro, S.; Kondo, M.; Kitagawa, S.; Ishii, T.; Matsuzaka, H. Chem. Lett. 1999, (8), 727-728. 114. Macgillivray, L. R.; Subramanian, S.; Zaworotko, M. J. J. Chem. Soc., Chem. Commun. 1994, (11), 1325-1326. 115. Zaworotko, M. J. Chem. Soc. Rev. 1994, 23 (4), 283-288. 116. Carlucci, L.; Ciani, G. ; Proserpio, D. M.; Sironi, A. Angew. Chem., Int. Ed. 1995, 34 (17), 1895-1898. 117. Carlucci, L.; Ciani, G. ; Proserpio, D. M.; Sironi, A. J. Am. Chem. Soc. 1995, 117 (16), 4562-4569.

PAGE 234

214 118. Carlucci, L.; Ciani, G. ; Proserpio, D. M.; Sironi, A. Inorg. Chem. 1995, 34 (22), 5698-5700. 119. Carlucci, L.; Ciani, G. ; Proserpio, D. M.; Sironi, A. J. Am. Chem. Soc. 1995, 117 (51), 12861-12862. 120. Subramanian, S.; Zaworotko, M. J. Angew. Chem., Int. Ed. 1995, 34 (19), 21272129. 121. Blake, A. J.; Champness, N. R.; Chung, S. S. M.; Li, W. S.; Schroder, M. Chem. Commun. 1997, (17), 1675-1676. 122. Blake, A. J.; Champness, N. R.; Chung, S. S. M.; Li, W. S.; Schroder, M. Chem. Commun. 1997, (11), 1005-1006. 123. Blake, A. J.; Champness, N. R.; Khlobystov, A.; Lemenovskii, D. A.; Li, W. S.; Schroder, M. Chem. Commun. 1997, (21), 2027-2028. 124. Carlucci, L.; Ciani, G. ; Proserpio, D. M.; Sironi, A. Inorg. Chem. 1997, 36 (9), 1736-1737. 125. Carlucci, L.; Ciani, G.; vonGudenbe rg, D. W.; Proserpio, D. M.; Sironi, A. Chem. Commun. 1997, (6), 631-632. 126. Moulton, B.; Zaworotko, M. J. Curr. Opin. Solid State Mater. Sci. 2002, 6 (2), 117-123. 127. Spokoyny, A. M.; Kim, D. ; Sumrein, A.; Mirkin, C. A. Chem. Soc. Rev. 2009, 38 (5), 1218-1227. 128. O'Keeffe, M. Chem. Soc. Rev. 2009, 38 (5), 1215-1217. 129. Long, J. R.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38 (5), 1213-1214.

PAGE 235

215 130. Volkringer, C.; Meddouri, M.; Loisea u, T.; Guillou, N.; Marrot, J.; Ferey, G.; Haouas, M.; Taulelle, F.; Audebrand, N.; Latroche, M. Inorg. Chem. 2008, 47 (24), 11892-11901. 131. Larsen, R. W.; McManus, G. J.; Perr y, J. J.; Rivera-Otero, E.; Zaworotko, M. J. Inorg. Chem. 2007, 46 (15), 5904-5910. 132. Robin, A. Y.; Fromm, K. M. Coord. Chem. Rev. 2006, 250 (15-16), 2127-2157. 133. Cheetham, A. K.; Rao, C. N. R.; Feller, R. K. Chem. Commun. 2006, (46), 47804795. 134. Biradha, K.; Sarkar, M.; Rajput, L. Chem. Commun. 2006, (40), 4169-4179. 135. Shimizu, G. K. H. J. Solid State Chem. 2005, 178 (8), 2519-2526. 136. Rosseinsky, M. J. Micropor. Mesopor. Mater. 2004, 73 (1-2), 15-30. 137. James, S. L. Chem. Soc. Rev. 2003, 32 (5), 276-288. 138. Rosi, N. L.; Eddaoudi, M.; Kim, J.; O'Keeffe, M.; Yaghi, O. M. CrystEngComm 2002, 4 (68), 401-404. 139. Batten, S. R. Curr. Opin. Solid State Mater. Sci. 2001, 5 (2-3), 107-114. 140. Zaworotko, M. J. Nature Chemistry 2009, 1 (4), 267-268. 141. ISI Web of Science http://apps.isiknowledge.com/UA_Ge neralSearch_input.do?product=UA&search _mode=GeneralSearch&SID=1BBcKA83i cpCFEAbkKA&preferencesSaved= (August 2009). 142. Wells, A. F. Acta Crystallogr. 1954, 7 (8-9), 535-544. 143. Wells, A. F. Acta Crystallogr. 1954, 7 (8-9), 545-554.

PAGE 236

216 144. Wells, A. F. Acta Crystallogr. 1954, 7 (12), 842-848. 145. Wells, A. F. Acta Crystallogr. 1954, 7 (12), 849-853. 146. Wells, A. F. Acta Crystallogr. 1955, 8 (1), 32-36. 147. Wells, A. F. Acta Crystallogr. 1956, 9 (1), 23-28. 148. Wells, A. F.; Sharpe, R. R. Acta Crystallogr. 1963, 16 (9), 857-871. 149. Wells, A. F., Three-Dimensional Nets and Polyhedra John Wiley & Sons: New York, 1977 150. Tranchemontagne, D. J.; Mendoza-Cortes, J. L.; O'Keeffe, M.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38 (5), 1257-1283. 151. Kim, J.; Chen, B. L.; Reineke, T. M.; Li, H. L.; Eddaoudi, M.; Moler, D. B.; O'Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2001, 123 (34), 8239-8247. 152. Eddaoudi, M.; Moler, D. B.; Li, H. L.; Chen, B. L.; Reineke, T. M.; O'Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34 (4), 319-330. 153. Li, H.; Eddaoudi, M.; O'Keeffe, M.; Yaghi, O. M. Nature 1999, 402 (6759), 276279. 154. Baerlocher, C.; McCusker, L. B. Database of Zeolite Structures http://www.izastructure.org/databases/ (August 12, 2009). 155. Knight, C. T. G. Zeolites 1990, 10 (2), 140-144. 156. Meier, W. M.; Olson, D. H.; Baerlocher, C., Atlas of Zeolite Strucutre Types 5th ed.; Elsevier Science B.V.: Amsterdam, The Netherlands, 2001 157. Al-Rasbi, N. K.; Tidmarsh, I. S.; Ar gent, S. P.; Adams, H.; Harding, L. P.; Ward, M. D. J. Am. Chem. Soc. 2008, 130 (35), 11641-11649.

PAGE 237

217 158. Yoshizawa, M.; Nagao, M.; Umemot o, K.; Biradha, K.; Fujita, M.; Sakamoto, S.; Yamaguchi, K. Chem. Commun. 2003, (15), 1808-1809. 159. Chand, D. K.; Fujita, M.; Biradha, K.; Sakamoto, S.; Yamaguchi, K. Dalton Trans. 2003, (13), 2750-2756. 160. Chand, D. K.; Biradha, K.; Fujita, M.; Sakamoto, S.; Yamaguchi, K. Chem. Commun. 2002, (21), 2486-2487. 161. Yamanoi, Y.; Sakamoto, Y.; Kusukawa T.; Fujita, M.; Sakamoto, S.; Yamaguchi, K. J. Am. Chem. Soc. 2001, 123 (5), 980-981. 162. Fujita, M.; Umemoto, K.; Yoshizawa, M.; Fujita, N.; Kusukawa, T.; Biradha, K. Chem. Commun. 2001, (6), 509-518. 163. Umemoto, K.; Yamaguchi, K.; Fujita, M. J. Am. Chem. Soc. 2000, 122 (29), 71507151. 164. Fujita, M., Molecular Paneling through metal-directed self-assembly. In Molecular Self-Assembly: Organi c Versus Inorganic Approaches Fujita, M., Ed. Springer: Berlin, 2000; Vol. 96, pp 177-201. 165. Blatov, V. A. Acta Crystallogr. 2007, A63 (4), 329-343. 166. Delgado-Friedrichs, O.; O'Keeffe, M.; Yaghi, O. M. Acta Crystallogr. 2006, A62 (5), 350-355. 167. Blatov, V. A.; Proserpio, D. M. Acta Crystallogr. 2009, A65 (3), 202-212. 168. Delgado-Friedrichs, O.; O'Keeffe, M. J. Solid State Chem. 2005, 178 (8), 24802485.

PAGE 238

218 169. Delgado-Friedrichs, O.; O'Keeffe, M.; Yaghi, O. M. Phys. Chem. Chem. Phys. 2007, 9 (9), 1035-1043. 170. O'Keeffe, M.; Hyde, B. G., Crystal Structures: I. Patterns and Symmetry Mineralogical Society of Am erica: Washington, D.C., 1996 171. Grunbaum, B.; Shephard, G. C., Tilings and Patterns W. H. Freeman and Company: New York, 1987 172. Blatov, V. A.; Delgado-Friedrichs, O.; O'Keeffe, M.; Proserpio, D. M. Acta Crystallogr. 2007, A63 (5), 418-425. 173. Frondel, C.; Marvin, U. B. Nature 1967, 214 (5088), 587-589. 174. O'Keeffe, M.; Peskov, M. A.; Ramsden, S. J.; Yaghi, O. M. Acc. Chem. Res. 2008, 41 (12), 1782-1789. 175. Reticular Chemistry Structure Resource http://rcsr.anu.edu.au/ (September 2, 2009). 176. Delgado-Friedrichs, O. The Gavrog Project http://gavrog.sourceforge.net/ (August 10, 2009). 177. Barton, T. J.; Bull, L. M.; Klempere r, W. G.; Loy, D. A.; McEnaney, B.; Misono, M.; Monson, P. A.; Pez, G.; Scherer, G. W.; Vartuli, J. C.; Yaghi, O. M. Chem. Mater. 1999, 11 (10), 2633-2656. 178. Rouquerol, F.; Rouquerol, J.; Sing, K., Adsorption by Powders and Porous Solids Academic Press: London, 1999 179. Eddaoudi, M.; Li, H. L.; Yaghi, O. M. J. Am. Chem. Soc. 2000, 122 (7), 13911397.

PAGE 239

219 180. Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O'Keeffe, M.; Yaghi, O. M. Science 2002, 295 (5554), 469-472. 181. Rowsell, J. L. C.; Yaghi, O. M. Micropor. Mesopor. Mater. 2004, 73 (1-2), 3-14. 182. Fletcher, A. J.; Thomas, K. M.; Rosseinsky, M. J. J. Solid State Chem. 2005, 178 (8), 2491-2510. 183. Collins, D. J.; Zhou, H.-C. J. Mater. Chem. 2007, 17 (30), 3154-3160. 184. Maji, T. K.; Kitagawa, S. Pure Appl. Chem. 2007, 79 (12), 2155-2177. 185. Furukawa, H.; Yaghi, O. M. J. Am. Chem. Soc. 2009, 131 (25), 8875-8883. 186. Duren, T.; Bae, Y. S.; Snurr, R. Q. Chem. Soc. Rev. 2009, 38 (5), 1237-1247. 187. Thomas, K. M. Dalton Trans. 2009, (9), 1487-1505. 188. Murray, L. J.; Dinca, M.; Long, J. R. Chem. Soc. Rev. 2009, 38 (5), 1294-1314. 189. Han, S. S.; Mendoza-Cortes, J. L.; Goddard, W. A. Chem. Soc. Rev. 2009, 38 (5), 1460-1476. 190. Zhao, D.; Yuan, D. Q.; Zhou, H. C. Energy Environ. Sci. 2008, 1 (2), 222-235. 191. Ferey, G. Chem. Soc. Rev. 2008, 37 (1), 191-214. 192. Dinca, M.; Long, J. R. Angew. Chem., Int. Ed. 2008, 47 (36), 6766-6779. 193. Lin, X.; Jia, J. H.; Hubberstey, P.; Schroder, M.; Champness, N. R. CrystEngComm 2007, 9 (6), 438-448. 194. Collins, D. J.; Zhou, H. C. J. Mater. Chem. 2007, 17 (30), 3154-3160. 195. Dinca, M.; Yu, A. F.; Long, J. R. J. Am. Chem. Soc. 2006, 128 (27), 8904-8913. 196. Rowsell, J. L. C.; Yaghi, O. M. Angew. Chem., Int. Ed. 2005, 44(30), 4670-4679.

PAGE 240

220 197. Fletcher, A. J.; Thomas, K. M.; Rosseinsky, M. J. J. Solid State Chem. 2005, 178 (8), 2491-2510. 198. Yaghi, O. M.; O'Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. Nature 2003, 423 (6941), 705-714. 199. U.S. Department of Energy: Mult i-Year Research, Development and Demonstration Plan: Planned Program Activities for 2005-2015 http://www1.eere.energy.gov/ hydrogenandfuelcells/mypp/ (August, 2009). 200. Kurmoo, M. Chem. Soc. Rev. 2009, 38 (5), 1353-1379. 201. Pardo, E.; Ruiz-Garcia, R.; Cano, J. ; Ottenwaelder, X.; Lescouezec, R.; Journaux, Y.; Lloret, F.; Julve, M. Dalton Trans. 2008, (21), 2780-2805. 202. Miller, J. S. Dalton Trans. 2006, (23), 2742-2749. 203. Real, J. A.; Gaspar, A. B.; Munoz, M. C. Dalton Trans. 2005, (12), 2062-2079. 204. Murray, K. S.; Kepert, C. J., Coope rativity in spin crossover systems: Memory, magnetism and microporosity. In Spin Crossover in Tr ansition Metal Compounds I Springer-Verlag: Berlin, 2004; Vol. 233, pp 195-228. 205. Maspoch, D.; Ruiz-M olina, D.; Veciana, J. J. Mater. Chem. 2004, 14 (18), 27132723. 206. Maspoch, D.; Ruiz-Molina, D.; Wurst, K.; Domingo, N.; Cavallini, M.; Biscarini, F.; Tejada, J.; Rovira, C.; Veciana, J. Nature Mater. 2003, 2 (3), 190-195. 207. Ferey, G. Nature Mater. 2003, 2 (3), 136-137. 208. Batten, S. R.; Murray, K. S. Coord. Chem. Rev. 2003, 246 (1-2), 103-130.

PAGE 241

221 209. Batten, S. R.; Jensen, P.; Moubaraki, B.; Murray, K. S.; Robson, R. Chem. Commun. 1998, (3), 439-440. 210. Shultz, A. M.; Farha, O. K.; Hupp, J. T.; Nguyen, S. T. J. Am. Chem. Soc. 2009, 131 (12), 4204-4205. 211. Marat, K. SpinWorks v3.1; University of Manitoba: Winnipeg, Manitoba, Canada, 2009 212. Lee, J.; Farha, O. K.; Roberts, J. ; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Chem. Soc. Rev. 2009, 38 (5), 1450-1459. 213. Hong, D. Y.; Hwang, Y. K.; Serre, C.; Ferey, G.; Chang, J. S. Adv. Funct. Mater. 2009, 19 (10), 1537-1552. 214. Maspoch, D.; Ruiz-M olina, D.; Veciana, J. Chem. Soc. Rev. 2007, 36 (5), 770-818. 215. Hasegawa, S.; Horike, S.; Matsuda, R.; Furukawa, S.; Mochizuki, K.; Kinoshita, Y.; Kitagawa, S. J. Am. Chem. Soc. 2007, 129 (9), 2607-2614. 216. Dybtsev, D. N.; Nuzhdin, A. L.; Chun, H.; Bryliakov, K. P.; Talsi, E. P.; Fedin, V. P.; Kim, K. Angew. Chem., Int. Ed. 2006, 45 (6), 916-920. 217. Cho, S. H.; Ma, B. Q.; Nguyen, S. T.; Hupp, J. T.; Albrecht-Schmitt, T. E. Chem. Commun. 2006, (24), 2563-2565. 218. Wu, C. D.; Hu, A.; Zhang, L.; Lin, W. B. J. Am. Chem. Soc. 2005, 127 (25), 89408941. 219. Forster, P. M.; Cheetham, A. K. Top. Catalysis 2003, 24 (1-4), 79-86. 220. Evans, O. R.; Manke, D. R.; Lin, W. B. Chem. Mater. 2002, 14 (9), 3866-3874.

PAGE 242

222 221. Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim, K. Nature 2000, 404 (6781), 982-986. 222. Alkordi, M. H.; Liu, Y.; Lars en, R. W.; Eubank, J. F.; Eddaoudi, M. J. Am. Chem. Soc. 2008, 130 (38), 12639-12641. 223. Ingleson, M. J.; Barrio, J. P.; Basca, J.; Dickinson, C.; Park, H.; Rosseinsky, M. J. Chem. Commun. 2008, (11), 1287-1289. 224. Allendorf, M. D.; Bauer, C. A.; Bhakta, R. K.; Houk, R. J. T. Chem. Soc. Rev. 2009, 38 (5), 1330-1352. 225. McManus, G. J.; Perry, J. J.; Pe rry, M.; Wagner, B. D.; Zaworotko, M. J. J. Am. Chem. Soc. 2007, 129 (29), 9094-9101. 226. Chen, B. L.; Yang, Y.; Zapata, F.; Lin, G. N.; Qian, G. D.; Lobkovsky, E. B. Adv. Mater. 2007, 19 (13), 1693-1696. 227. Cahill, C. L.; de Lill, D. T.; Frisch, M. CrystEngComm 2007, 9 (1), 15-26. 228. Hill, R. J.; Long, D. L.; Hubberstey, P.; Schroder, M.; Champness, N. R. J. Solid State Chem. 2005, 178 (8), 2414-2419. 229. Bose, D.; Rahaman, S. H.; Mostafa, G.; Walsh, R. D. B.; Zaworotko, M. J.; Ghosh, B. K. Polyhedron 2004, 23 (4), 545-552. 230. Bose, D.; Banerjee, J.; Rahaman, S. H.; Mostafa, G.; Fun, H. K.; Walsh, R. D. B.; Zaworotko, M. J.; Ghosh, B. K. Polyhedron 2004, 23 (12), 2045-2053. 231. Wagner, B. D.; McManus, G. J.; Moulton, B.; Zaworotko, M. J. Chem. Commun. 2002, (18), 2176-2177.

PAGE 243

223 232. Reineke, T. M.; Eddaoudi, M.; Fehr, M.; Kelley, D.; Yaghi, O. M. J. Am. Chem. Soc. 1999, 121 (8), 1651-1657. 233. Birks, J. B., Photophysics of Aromatic Molecules Wiley-Interscience: London, 1970 234. Li, J. R.; Kuppler, R. J.; Zhou, H. C. Chem. Soc. Rev. 2009, 38 (5), 1477-1504. 235. Ferey, G.; Serre, C. Chem. Soc. Rev. 2009, 38 (5), 1380-1399. 236. Allendorf, M. D.; Houk, R. J. T.; A ndruszkiewicz, L.; Talin, A. A.; Pikarsky, J.; Choudhury, A.; Gall, K. A.; Hesketh, P. J. J. Am. Chem. Soc. 2008, 130 (44), 14404-14405. 237. Yaghi, O. M.; Davis, C. E.; Li, G. M.; Li, H. L. J. Am. Chem. Soc. 1997, 119 (12), 2861-2868. 238. Czaja, A. U.; Trukhan, N.; Muller, U. Chem. Soc. Rev. 2009, 38 (5), 1284-1293. 239. Liu, Y.; Li, G.; Li, X.; Cui, Y. Angew. Chem., Int. Ed. 2007, 46 (33), 6301-6304. 240. Maury, O.; Le Bozec, H. Acc. Chem. Res. 2005, 38 (9), 691-704. 241. Evans, O. R.; Lin, W. B. Acc. Chem. Res. 2002, 35 (7), 511-522. 242. Lacroix, P. G. Eur. J. Inorg. Chem. 2001, (2), 339-348. 243. Zhang, H.; Wang, X. M.; Zhang, K. C.; Teo, B. K. Coord. Chem. Rev. 1999, 183 (1), 157-195. 244. Struve, W. S., Fundamentals of Molecular Spectroscopy John Wiley & Sons: New York, 1989 245. Steinfeld, J. I., Molecules and Radiation: An In troduction to Modern Molecular Spectroscopy 2nd ed.; The MIT Press: Cambridge, Massachusetts, 1985

PAGE 244

224 246. Maji, T. K.; Kitagawa, S. Pure Appl. Chem. 2007, 79 (12), 2155-2177. 247. Mueller, U.; Schubert, M.; Teich, F.; Puetter, H.; Schierle-Arndt, K.; Pastre, J. J. Mater. Chem. 2006, 16 (7), 626-636. 248. Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43 (18), 23342375. 249. Janiak, C. Dalton Trans. 2003, (14), 2781-2804. 250. Uemura, T.; Yanai, N.; Kitagawa, S. Chem. Soc. Rev. 2009, 38 (5), 1228-1236. 251. Yoshizawa, M.; Kusukawa, T.; Fujita, M.; Sakamoto, S.; Yamaguchi, K. J. Am. Chem. Soc. 2001, 123 (43), 10454-10459. 252. Zou, X. Q.; Zhu, G. S.; Hewitt, I. J.; Sun, F. X.; Qiu, S. L. Dalton Trans. 2009, (16), 3009-3013. 253. Zacher, D.; Shekhah, O.; Woll, C.; Fischer, R. A. Chem. Soc. Rev. 2009, 38 (5), 1418-1429. 254. Yoo, Y.; Lai, Z. P.; Jeong, H. K. Micropor. Mesopor. Mater. 2009, 123 (1-3), 100106. 255. Horcajada, P.; Serre, C.; Grosso, D.; Boissiere, C.; Perruchas, S.; Sanchez, C.; Ferey, G. Adv. Mater. 2009, 21 (19), 1931-1935. 256. Allendorf, M. D.; Houk, R. J. T.; A ndruszkiewicz, L.; Talin, A. A.; Pikarsky, J.; Choudhury, A.; Gall, K. A.; Hesketh, P. J. J. Am. Chem. Soc. 2008, 130 (44), 14404-+. 257. Hermes, S.; Zacher, D.; Baunemann, A.; Woll, C.; Fischer, R. A. Chem. Mater. 2007, 19 (9), 2168-2173.

PAGE 245

225 258. Mahata, P.; Raghunathan, R.; Banerjee, D.; Sen, D.; Ramasesha, S.; Bhat, S. V.; Natarajan, S. Chem. Asian J. 2009, 4 (6), 936-947. 259. Nytko, E. A.; Helton, J. S.; Muller, P.; Nocera, D. G. J. Am. Chem. Soc. 2008, 130 (10), 2922-2923. 260. Mahata, P.; Sen, D.; Natarajan, S. Chem. Commun. 2008, (11), 1278-1280. 261. Horike, S.; Hasegawa, S.; Tanaka, D.; Higuchi, M.; Kitagawa, S. Chem. Commun. 2008, (37), 4436-4438. 262. Chun, H.; Moon, J. Inorg. Chem. 2007, 46 (11), 4371-4373. 263. Liu, Y. L.; Kravtsov, V. C.; Beauchamp, D. A.; Eubank, J. F.; Eddaoudi, M. J. Am. Chem. Soc. 2005, 127 (20), 7266-7267. 264. Rao, C. N. R.; Sampathkumaran, E. V.; Nagarajan, R.; Paul, G.; Behera, J. N.; Choudhury, A. Chem. Mater. 2004, 16 (8), 1441-1446. 265. Perry, J. J.; McManus, G. J.; Zaworotko, M. J. Chem. Commun. 2004, (22), 25342535. 266. Murugesu, M.; Clerac, R.; Anson, C. E.; Powell, A. K. J. Phys. Chem. Solids 2004, 65 (4), 667-676. 267. Behera, J. N.; Paul, G.; Choudhury, A.; Rao, C. N. R. Chem. Commun. 2004, (4), 456-457. 268. Barthelet, K.; Marrot, J.; Ferey, G.; Riou, D. Chem. Commun. 2004, (5), 520-521. 269. Srikanth, H.; Hajndl, R.; Moulton, B.; Zaworotko, M. J. J. Appl.Phys. 2003, 93 (10), 7089-7091.

PAGE 246

226 270. Shin, D. M.; Lee, I. S.; Chung, Y. K.; Lah, M. S. Inorg. Chem. 2003, 42 (18), 5459-5461. 271. Rusanov, E. B.; Ponomarova, V. V.; Komarchuk, V. V.; Stoeckli-Evans, H.; Fernandez-Ibanez, E.; Stoeckli, F.; Sieler, J.; Domasevitch, K. V. Angew. Chem., Int. Ed. 2003, 42 (22), 2499-2501. 272. Moulton, B.; Lu, J. J.; Hajndl R.; Hariharan, S.; Zaworotko, M. J. Angew. Chem., Int. Ed. 2002, 41 (15), 2821-2824. 273. Eddaoudi, M.; Kim, J.; Vodak, D.; Sudik, A.; Wachter, J.; O'Keeffe, M.; Yaghi, O. M. Proceedings of the National Academy of Sciences of the United States of America 2002, 99 (8), 4900-4904. 274. Diederich, F.; Schurmann, G.; Chao, I. J. Org. Chem. 1988, 53 (12), 2744-2757. 275. Schwende, C. F.; Sunday, B. R.; Shavel, J.; Giles, R. E. J. Med. Chem. 1974, 17 (10), 1112-1115. 276. Coco, S.; Cordovilla, C.; Donnio, B.; Espinet, P.; Garcia-Casas, M. J.; Guillon, D. Chem.-Eur. J. 2008, 14 (12), 3544-3552. 277. Valiyaveettil, S.; Enkelmann, V.; Mullen, K. J. Chem. Soc., Chem. Commun. 1994, (18), 2097-2098. 278. Valiyaveettil, S.; Gans, C.; Klapper, M.; Gereke, R.; Mullen, K. Polym. Bull. 1995, 34 (1), 13-19. 279. Valiyaveettil, S.; Mullen, K. New J. Chem. 1998, 22 (2), 89-95. 280. Kimura, K.; Yamashita, Y.; Sakaguchi, Y.; Takase, S. Alkoxysulfonic acid-groupcontaining polyarylene ether, compositi on containing the same, ion-conductive

PAGE 247

227 film, adhesive, composite, and fuel cell, and manufacture thereof. JP 2003272695 A September 26, 2003. 281. SMART v5.05; Siemens Analytical X-ray In struments Inc.: Madison, WI, USA, 1995 282. SAINT v6.28a; Bruker AXS Inc.: Madison, WI, USA, 1995 283. Sheldrick, G. M. Acta Crystallogr. 2008, A64 112-122. 284. Spek, A. L. J. Appl. Crystallogr. 2003, 36 (1), 7-13. 285. Spek, A. L. PLATON, A Multipurpose Crystallographic Tool v1.15; Utrecht University: Utrecht, The Netherlands, 2008 286. van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46 (3), 194-201. 287. Pretsch, E.; Buhlmann, P.; Affolter, C., Structure Determination of Organic Compounds Springer: Berlin, 2000 288. Silverstein, R. M.; Webster, F. X., Spectrometric Identification of Organic Compounds 6th ed.; John Wiley & Sons, Inc.: New York, 1998 289. Zhang, J.; Bu, X. H. Chem. Commun. 2009, (2), 206-208. 290. Zhang, R. F.; Wang, Q. F.; Yang, M. Q.; Wang, Y. R.; Ma, C. L. Polyhedron 2008, 27 (14), 3123-3131. 291. Zhang, J.; Chew, E.; Chen, S.; Pham, J. T. H.; Bu, X. Inorg. Chem. 2008, 47 (9), 3495-3497. 292. Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor R.; van de Streek, J.; Wood, P. A. J. Appl. Crystallogr. 2008, 41 (2), 466-470.

PAGE 248

228 293. Chen, S. M.; Zhang, J.; Bu, X. H. Inorg. Chem. 2008, 47 (13), 5567-5569. 294. Zhang, J.; Yao, Y. G.; Bu, X. H. Chem. Mater. 2007, 19 (21), 5083-5089. 295. Rood, J. A.; Boggess, W. C.; Noll, B. C.; Henderson, K. W. J. Am. Chem. Soc. 2007, 129 (44), 13675-13682. 296. Dybtsev, D. N.; Yutkin, M. P.; Pere sypkina, E. V.; Virovets, A. V.; Serre, C.; Ferey, G.; Fedin, V. P. Inorg. Chem. 2007, 46 (17), 6843-6845. 297. Zeng, M. H.; Wang, B.; Wang, X. Y. ; Zhang, W. X.; Chen, X. M.; Gao, S. Inorg. Chem. 2006, 45 (18), 7069-7076. 298. Thuery, P. Eur. J. Inorg. Chem. 2006, (18), 3646-3651. 299. Mulfort, K. L.; Hupp, J. T. Inorg. Chem. 2008, 47 (18), 7936-7938. 300. Brunauer, S.; Deming, L. S.; Deming, W. E.; Teller, E. J. Am. Chem. Soc. 1940, 62 1723-1732. 301. Byrnes, M. J.; Chisholm, M. H.; Patmore, N. J. Inorg. Chem. 2005, 44 (25), 93479352. 302. Olenyuk, B.; Whiteford, J. A.; Stang, P. J. J. Am. Chem. Soc. 1996, 118 (35), 8221-8230. 303. Stang, P. J.; Cao, D. H. J. Am. Chem. Soc. 1994, 116 (11), 4981-4982. 304. Stang, P. J.; Cao, D. H.; Saito, S.; Arif, A. M. J. Am. Chem. Soc. 1995, 117 (23), 6273-6283. 305. Stang, P. J.; Olenyuk, B. Angew. Chem., Int. Ed. 1996, 35 (7), 732-736. 306. Coxeter, H. S. M., Regular Polytopes MacMillan: New York, 1963 307. Torquato, S.; Jiao, Y. Nature 2009, 460 (7257), 876-879.

PAGE 249

229 308. Dalgarno, S. J.; Power, N. P.; Atwood, J. L. Coord. Chem. Rev. 2008, 252 (8-9), 825-841. 309. Hamilton, T. D.; MacGillivray, L. R. Cryst. Growth Des. 2004, 4 (3), 419-430. 310. Prakash, M. J.; Lah, M. S. Chem. Commun. 2009, (23), 3326-3341. 311. Tranchemontagne, D. J. L.; Ni, Z.; O'Keeffe, M.; Yaghi, O. M. Angew. Chem., Int.Ed. 2008, 47 (28), 5136-5147. 312. Wang, Y.; Okamura, T. A.; Sun, W. Y.; Ueyama, N. Crystal Growth & Design 2008, 8 (3), 802-804. 313. Zhu, H. F.; Fan, J.; Okamura, T.; Zhang, Z. H.; Liu, G. X.; Yu, K. B.; Sun, W. Y.; Ueyama, N. Inorganic Chemistry 2006, 45 (10), 3941-3948. 314. Umemoto, K.; Yamaguchi, K.; Fujita, M. Journal of the American Chemical Society 2000, 122 (29), 7150-7151. 315. Oppel, I. M.; Focker, K. Angewandte Chemie-In ternational Edition 2008, 47 (2), 402-405. 316. Umemoto, K.; Yamaguchi, K.; Fujita, M. J. Am. Chem. Soc. 2000, 122 (29), 71507151. 317. Chand, D. K.; Biradha, K.; Kawano, M.; Sakamoto, S.; Yamaguchi, K.; Fujita, M. Chemistry-an Asian Journal 2006, 1 (1-2), 82-90. 318. Sudik, A. C.; Millward, A. R.; Ockwi g, N. W.; Cote, A. P.; Kim, J.; Yaghi, O. M. J. Am. Chem. Soc. 2005, 127 (19), 7110-7118. 319. Yoshizawa, M.; Nagao, M.; Umemot o, K.; Biradha, K.; Fujita, M.; Sakamoto, S.; Yamaguchi, K. Chem. Commun. 2003, (15), 1808-1809.

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230 320. Roche, S.; Haslam, C.; Adams, H.; Heath, S. L.; Thomas, J. A. Chemical Communications 1998, (16), 1681-1682. 321. Sava, D. F.; Kravtsov, V. C.; Eckert, J.; Eubank, J. F.; Nouar, F.; Eddaoudi, M. Journal of the American Chemical Society 2009, 131 (30), 10394-+. 322. MacGillivray, L. R.; Atwood, J. L. Nature 1997, 389 (6650), 469-472. 323. Liu, Y. L.; Kravtsov, V. C.; Beauchamp, D. A.; Eubank, J. F.; Eddaoudi, M. Journal of the American Chemical Society 2005, 127 (20), 7266-7267. 324. Furukawa, H.; Kim, J.; Ockwig, N. W.; O'Keeffe, M.; Yaghi, O. M. Journal of the American Chemical Society 2008, 130 (35), 11650-11661. 325. Ke, Y. X.; Collins, D. J.; Zhou, H. C. Inorganic Chemistry 2005, 44 (12), 41544156. 326. Tominaga, M.; Suzuki, K.; Murase, T.; Fujita, M. Journal of the American Chemical Society 2005, 127 (34), 11950-11951. 327. Moulton, B.; Lu, J. J.; Mondal, A.; Zaworotko, M. J. Chemical Communications 2001, (9), 863-864. 328. Abourahma, H.; Coleman, A. W.; Moulton, B.; Rather, B.; Shahgaldian, P.; Zaworotko, M. J. Chemical Communications 2001, (22), 2380-2381. 329. Mohomed, K.; Abourahma, H.; Zaworotko, M. J.; Harmon, J. P. Chemical Communications 2005, (26), 3277-3279. 330. Larsen, R. W.; McManus, G. J.; Perr y, J. J.; Rivera-Otero, E.; Zaworotko, M. J. Inorganic Chemistry 2007, 46 (15), 5904-5910.

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231 331. Furukawa, H.; Kim, J.; Plass, K. E.; Yaghi, O. M. Journal of the American Chemical Society 2006, 128 (26), 8398-8399. 332. Jung, M.; Kim, H.; Baek, K.; Kim, K. Angewandte Chemie-International Edition 2008, 47 (31), 5755-5757. 333. Schweiger, M.; Yamamoto, T.; Stang, P. J.; Blaser, D.; Boese, R. Journal of Organic Chemistry 2005, 70 (12), 4861-4864. 334. Ni, Z.; Yassar, A.; Antoun, T.; Yaghi, O. M. J. Am. Chem. Soc. 2005, 127 (37), 12752-12753. 335. Furukawa, H.; Kim, J.; Plass, K. E.; Yaghi, O. M. Journal of the American Chemical Society 2006, 128 (26), 8398-8399. 336. Jung, M.; Kim, H.; Baek, K.; Kim, K. Angew. Chem., Int. Ed. 2008, 47 (31), 57555757. 337. vanGenderen, M. H. P.; Pfaadt, M.; Moller, C.; Valiyaveettil, S.; Spiess, H. W. J. Am. Chem. Soc. 1996, 118 (15), 3661-3665. 338. Venkataramanan, B.; Ning, Z.; Vittal, J. J.; Valiyaveettil, S. CrystEngComm 2005, 7 108-112. 339. Nishio, M.; Hirota, M.; Umezawa, Y., The CH/ Interaction: Evidence, Nature, and Consequences Wiley-VCH: New York, 1998 340. Desiraju, G. R. Accounts of Chemical Research 2002, 35 (7), 565-573. 341. Mohomed, K.; Abourahma, H.; Zaworotko, M. J.; Harmon, J. P. Chem. Commun. 2005, (26), 3277-3279.

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232 342. Mohomed, K.; Abourahma, H.; Zaworotko, M. J.; Harmon, J. P. Chem.Commun. 2005, (26), 3277-3279. 343. Perry, J. J.; Perman, J. A.; Zaworotko, M. J. Chem. Soc. Rev. 2009, 38 (5), 14001417. 344. Nouar, F.; Eubank, J. F.; Bousquet, T.; Wojtas, L.; Zaworotko, M. J.; Eddaoudi, M. J. Am. Chem. Soc. 2008, 130 (6), 1833-1835. 345. Cairns, A. J.; Perman, J. A.; Wojtas, L.; Kravtsov, V. C.; Alkordi, M. H.; Eddaoudi, M.; Zaworotko, M. J. J. Am. Chem. Soc. 2008, 130 (5), 1560-1561. 346. Abourahma, H.; Coleman, A. W.; Moulton, B.; Rather, B.; Shahgaldian, P.; Zaworotko, M. J. Chemical Communications 2001, (22), 2380-2381. 347. Eddaoudi, M.; Kim, J.; Wachter, J. B.; Chae, H. K.; O'Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2001, 123 (18), 4368-4369. 348. Moulton, B.; Lu, J. J.; Mondal, A.; Zaworotko, M. J. Chem.Commun. 2001, (9), 863-864. 349. McManus, G. J.; Wang, Z. Q.; Zaworotko, M. J. Cryst. Growth Des. 2004, 4 (1), 11-13. 350. Ke, Y. X.; Collins, D. J.; Zhou, H. C. Inorg. Chem. 2005, 44 (12), 4154-4156. 351. Furukawa, H.; Kim, J.; Plass, K. E.; Yaghi, O. M. J. Am. Chem. Soc. 2006, 128 (26), 8398-8399. 352. Ghosh, S.; Mukherjee, P. S. J. Org. Chem. 2006, 71 (22), 8412-8416. 353. Furukawa, H.; Kim, J.; Ockwig, N. W.; O'Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2008, 130 (35), 11650-11661.

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233 354. Tonigold, M.; Hitzbleck, J.; Bahn muller, S.; Langstein, G.; Volkmer, D. Dalton Trans. 2009, (8), 1363-1371. 355. Duriska, M. B.; Neville, S. M.; M oubaraki, B.; Cashion, J. A.; Halder, G. J.; Chapman, K. W.; Balde, C.; Letard, J. F.; Murray, K. S.; Kepert, C. J.; Batten, S. R. Angew. Chem., Int. Ed. 2009, 48 (14), 2549-2552. 356. Larsen, R. W. J. Am. Chem. Soc. 2008, 130 (34), 11246-11247. 357. Mohomed, K.; Gerasimov, T. G.; A bourahma, H.; Zaworotko, M. J.; Harmon, J. P. Mat. Sci. Eng., A 2005, 409 (1-2), 227-233. 358. Delgado-Friedrichs, O.; O'Keeffe, M. Acta Crystallogr. 2007, A63 (4), 344-347. 359. Wang, X. S.; Ma, S. Q.; Forster, P. M.; Yuan, D. Q.; Eckert, J.; Lopez, J. J.; Murphy, B. J.; Parise, J. B.; Zhou, H. C. Angew. Chem., Int. Ed. 2008, 47 (38), 7263-7266. 360. Zafar, A.; Yang, J.; Geib, S. J.; Hamilton, A. D. Tetrahedron Lett. 1996, 37 (14), 2327-2330.

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238 Appendices

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239 Appendix A. 1H NMR spectra for synthesized ligands. Appendix A-1. 1H NMR spectrum for L1: 5-benzyloxy-1,3-bdc 1H NMR spectrum of 5-benzyloxy1,3-benzenedicarboxylic acid ( L1 ) dissolved in Acetoned6. The spectrum was obtained on a Br uker DPX-250 MHz spectrometer. The FID data was processed and displayed using SpinWorks 3.1. 1H NMR (250 MHz, Acetoned6, ): 5.3(s, 2H, -O-CH2-), 7.4(m, 3 H, -ArH), 7.6(d, J = 7.4 Hz, 2H, -ArH), 7.9(d, J = 1.44 Hz, 2H, -ArH), 8.3(t, J = 1.4 Hz, 1H, -ArH), 11.2(br, 2H, -COOH). The carboxylic acid peak was so broad it is not shown in this spectrum, but was found upon increasing the vertical scale.

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240 Appendix A-2. 1H NMR spectrum for L2: 5-naphthyloxy-1,3-bdc 1H NMR spectrum of 5-naphthyloxy -1,3-benzenedicarboxylic acid ( L2 ) dissolved in DMSOd6. The spectrum was obtained on a Bruker DPX-250 MHz spectrometer. The FID data was processed and displayed using SpinWorks 3.1. 1H NMR (250 MHz, DMSOd6, ): 5.4(s, 2H, -O-CH2-), 7.6(m, 4 H, -ArH), 7.8(d, 2H, ArH), 7.98(m, 3H, -ArH), 8.0(s, 1H, -ArH), 8.1(t, J = 1.3 Hz, 1H, -ArH), 13.3(br, 2H, COOH, inset).

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241 Appendix A-3. 1H NMR spectrum for L3: 5-hexyloxy-1,3-bdc 1H NMR spectrum of 5-hexyloxy-1, 3-benzenedicarboxylic acid ( L3 ) dissolved in DMSOd6. The spectrum was obtained on a Bruker DPX-250 MHz spectrometer. The FID data was processed and displayed using SpinWorks 3.1. 1H NMR (250 MHz, DMSOd6, ): 0.9(t, J = 6.3 Hz, 3H, -CH3), 1.2(m, 6 H, -CH2-), 1.7(m, 2H, -CH2-), 4.1(t, J = 6.4 Hz, 2H, -O-CH2-), 7.6(s, 2H, -ArH), 8.1(t, J = 1.4 Hz, 1H, -ArH), 13.3(br, 2H, -COOH). The carboxylic acid peak was so broad that it is not shown on this spectrum, however it was found by increasing the vertic al scale quite a bit.

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242 Appendix A-4. 1H NMR spectrum for L4: 5-dodecyloxy-1,3-bdc 1H NMR spectrum of 5-dodecyloxy-1,3-benzenedicarboxylic acid ( L4 ) dissolved in DMSOd6. The spectrum was obtained on a Bruker DPX-250 MHz spectrometer. The FID data was processed and displayed using SpinWorks 3.1. 1H NMR (250 MHz, DMSOd6, ): 0.9(t, J = 6.3 Hz, 3H, -CH3), 1.2(m, 18 H, -CH2-), 1.7(m, 2H, -CH2-), 4.1(t, J = 6.4 Hz, 2H, -O-CH2-), 7.6(s, 2H, -ArH), 8.1(t, J = 1.4 Hz, 1H, -ArH), 13.3(br, 2H, -COOH, inset).

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243 Appendix A-5. 1H NMR spectrum for L5: 1,3-bis(5-methoxy-1,3-bdc)benzene 1H NMR spectrum of 1,3-bi s(5-methoxy-1,3-benzenedicarboxylic acid)benzene ( L5 ) dissolved in DMSOd6. The spectrum was obtained on a Bruker DPX-250 MHz spectrometer. The FID data was proce ssed and displayed using SpinWorks 3.1. 1H NMR (250 MHz, DMSOd6, ): 5.3(s, 4H, -O-CH2-), 7.5(d, J = 0.9 Hz, 3 H, -ArH), 7.6(s, 1H, -ArH), 7.8(d, J = 1.39 Hz, 4H, -ArH), 8.1(t, J = 1.38 Hz, 2H, -ArH), 13.4(br, 4H, -COOH, inset).

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244 Appendix B. FT-IR spectra for synthesize d ligands; FT-IR spectra, PXRD patterns, and Thermal Gravimetric Analys is for synthesized compounds. Appendix B-1. FT-IR spectrum for L1: 5-benzyloxy-1,3-bdc Appendix B-2. FT-IR spectrum for L2: 5-naphthyloxy-1,3-bdc

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245 Appendix B-3. FT-IR spectrum for L3: 5-hexyloxy-1,3-bdc Appendix B-4. FT-IR spectrum fo r L4: 5-dodecyloxy-1,3-bdc

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246 Appendix B-5. FT-IR spectrum for L5 : 1,3-bis(5-methoxy-1,3-bdc)benzene

PAGE 263

247 Appendix B-6. Experimental data for compound [1].

PAGE 264

248 Appendix B-7. Experimental data for compound [2].

PAGE 265

249 Appendix B-8. Experimental data for compound [3].

PAGE 266

250 Appendix B-9. Experimental data for compound [4].

PAGE 267

251 Appendix B-10. Experimental data for compound [5].

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252 Appendix B-11. Experimental data for compound [6].

PAGE 269

253 Appendix B-12. Experimental data for compound [7].

PAGE 270

254 Appendix B-13. Experimental data for compound [8].

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255 Appendix B-14. Experimental data for compound [9].

PAGE 272

256 Appendix B-15. Experimental data for compound [10].

PAGE 273

257 Appendix B-16. Experimental data for compound [11].

PAGE 274

258 Appendix B-17. Experimental data for compound [12].

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259 Appendix B-18. Experimental data for compound [13].

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260 Appendix B-19. Experimental data for compound [14].

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261 Appendix B-20. Experimental data for compound [15].

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262 Appendix B-21. Experimental data for compound [16].

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263 Appendix B-22. Experimental data for compound [17].

PAGE 280

264 Appendix B-23. Experimental data for compound [18].

PAGE 281

265 Appendix B-24. Experimental data for compound [19].

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266 Appendix B-25. Experimental data for compound [20].

PAGE 283

267 Appendix B-26. Experimental data for compound [21].

PAGE 284

268 Appendix B-27. Experimental data for compound [22].

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269 Appendix B-28. Experimental data for compound [23].

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270 Appendix B-29. Experimental data for compound [24].

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271 Appendix B-30. Experimental data for compound [25].

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272 Appendix B-31. Experimental data for compound [26].

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273 Appendix B-32. Experimental data for compound [27].

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274 Appendix B-33. Experimental data for compound [28].

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275 Appendix B-34. Experimental data for compound [29].

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276 Appendix B-35. Experimental data for compound [30].

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277 Appendix B-36. Experimental data for compound [31].

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278 Appendix B-37. Experimental data for compound [32].

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279 Appendix B-38. Experimental data for compound [33].

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280 Appendix B-39. Experimental data for compound [34].

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281 Appendix C. Crystal data and structu re refinement for select compounds. Appendix C-1. Crystal data and stru cture refinement for compound [1]. Empirical formula C40 H30 Cu2 N2 O10 Formula weight 825.74 Temperature 100(2) K Wavelength 0.71073 Crystal system Trigonal Space group P-3 Unit cell dimensions a = 18.4013(8) = 90. b = 18.4013(8) = 90. c = 9.6305(9) = 120. Volume 2824.1(3) 3 Z 3 Density (calculated) 1.457 Mg/m 3 Absorption coefficient 1.190 mm -1 F(000) 1266 Crystal size 0.20 x 0.15 x 0.05 mm 3 Theta range for data coll ection 1.28 to 28.30 Index ranges -23<=h<=22, -24<=k<=23, -12<=l<=8 Reflections collected 18160 Independent reflections 4496 [R(int) = 0.0411] Completeness to theta = 28.30 95.6 % Absorption correction multi-scan Max. and min. transmission 1.00000 and 0.783850 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4496 / 0 / 256 Goodness-of-fit on F 2 1.136 Final R indices [I>2sigma(I)] R1 = 0.0421, wR2 = 0.0970 R indices (all data) R1 = 0.0546, wR2 = 0.1094

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282 Appendix C-2. Crystal data and stru cture refinement for compound [2]. Empirical formula C42 H30 N2 O12 Zn2 Formula weight 885.42 Temperature 100(2) K Wavelength 0.71073 Crystal system Trigonal Space group P-3 Unit cell dimensions a = 18.476(3) = 90. b = 18.476(3) = 90. c = 9.528(3) = 120. Volume 2817.0(10) 3 Z 3 Density (calculated) 1.566 Mg/m 3 Absorption coefficient 1.347 mm -1 F(000) 1356 Crystal size 0.15 x 0.08 x 0.0 mm 3 Theta range for data coll ection 1.27 to 25.03 Index ranges -10<=h<=21, -21<=k<=10, -11<=l<=11 Reflections collected 8186 Independent reflections 3282 [R(int) = 0.2151] Completeness to theta = 25.03 98.2 % Absorption correction multi-scan Max. and min. transmission 1.0000 and 0.252832 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 3282 / 0 / 256 Goodness-of-fit on F 2 1.028 Final R indices [I>2sigma(I)] R1 = 0.1335, wR2 = 0.3249 R indices (all data) R1 = 0.1958, wR2 = 0.3701

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283 Appendix C-3. Crystal data and stru cture refinement for compound [3]. Empirical formula C42 H6 N2 O12 Cu2 Formula weight 860.57 Temperature 100(2) K Wavelength 0.71073 Crystal system Trigonal Space group P-3 Unit cell dimensions a = 18.8401(14) = 90. b = 18.8401(14) = 90. c = 11.2040 (18) = 120. Volume 3405.7(3) 3 Z 3 Density (calculated) 1.437 Mg/m 3 Absorption coefficient 1.088 mm -1 F(000) 1285 Crystal size 0.20 x 0.15 x 0.05 mm 3 Theta range for data coll ection 1.24 to 25.30 Index ranges -22<=h<=22, -19<=k<=22, -13<=l<=11 Reflections collected 18364 Independent reflections 3967 [R(int) = 0.0541] Completeness to theta = 26.30 97.6 % Absorption correction multi-scan Max. and min. transmission 1.00000 and 0.753650 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 3068 / 0 / 315 Goodness-of-fit on F 2 1.536 Final R indices [I>2sigma(I)] R1 = 0.1321, wR2 = 0.2670 R indices (all data) R1 = 0.1546, wR2 = 0.2894

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284 Appendix C-4. Crystal data and stru cture refinement for compound [4]. Empirical formula C42 H6 N2 O12 Zn2 Formula weight 861.23 Temperature 100(2) K Wavelength 0.71073 Crystal system Trigonal Space group P-3 Unit cell dimensions a = 18.8852(16) = 90. b = 18.8852(16) = 90. c = 11.1751(11) = 120. Volume 3451.6(5) 3 Z 3 Density (calculated) 1.243 Mg/m 3 Absorption coefficient 1.098 mm -1 F(000) 1284 Crystal size 0.20 x 0.15 x 0.10 mm 3 Theta range for data coll ection 1.82 to 25.11 Index ranges -22<=h<=22, -22<=k<=22, -11<=l<=13 Reflections collected 18331 Independent reflections 4090 [R(int) = 0.0333] Completeness to theta = 25.11 99.5 % Absorption correction multi-scan Max. and min. transmission 1.0000 and 0.645304 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4090 / 0 / 359 Goodness-of-fit on F 2 1.176 Final R indices [I>2sigma(I)] R1 = 0.0813, wR2 = 0.2385 R indices (all data) R1 = 0.0892, wR2 = 0.2449

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285 Appendix C-5. Crystal data and stru cture refinement for compound [5]. Empirical formula C48 H34 Cu2 N2 O10 Formula weight 925.85 Temperature 100(2) K Wavelength 1.54178 Crystal system Trigonal Space group P-3 Unit cell dimensions a = 18.6078(6) = 90. b = 18.6078(6) = 90. c = 12.2129(5) = 120. Volume 3662.2(2) 3 Z 3 Density (calculated) 1.259 Mg/m 3 Absorption coefficient 1.529 mm -1 F(000) 1422 Crystal size 0.50 x 0.30 x 0.20 mm 3 Theta range for data coll ection 2.74 to 67.82 Index ranges -19<=h<=20, -22<=k<=16, -14<=l<=13 Reflections collected 14420 Independent reflections 4235 [R(int) = 0.0801] Completeness to theta = 67.82 95.3 % Absorption correction multi-scan Max. and min. transmission 0.7496 and 0.5153 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4235 / 0 / 281 Goodness-of-fit on F 2 0.933 Final R indices [I>2sigma(I)] R1 = 0.0791, wR2 = 0.2004 R indices (all data) R1 = 0.1126, wR2 = 0.2193

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286 Appendix C-6. Crystal data and stru cture refinement for compound [6]. Empirical formula C58 H34 N2 O12 Zn2 Formula weight 1081.61 Temperature 100(2) K Wavelength 0.71073 Crystal system Trigonal Space group P-3 Unit cell dimensions a = 18.7097(12) = 90. b = 18.7097(12) = 90. c = 12.1704(11) = 120. Volume 3689.5(5) 3 Z 3 Density (calculated) 1.460 Mg/m 3 Absorption coefficient 1.044 mm -1 F(000) 1656 Crystal size 0.20 x 0.18 x 0.09 mm 3 Theta range for data coll ection 1.67 to 25.07 Index ranges -22<=h<=19, -19<=k<=22, -14<=l<=13 Reflections collected 19812 Independent reflections 4394 [R(int) = 0.0577] Completeness to theta = 25.07 99.9 % Absorption correction multi-scan Max. and min. transmission 1.00000 and 0.783850 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4394 / 0 / 328 Goodness-of-fit on F 2 1.533 Final R indices [I>2sigma(I)] R1 = 0.1015, wR2 = 0.3217 R indices (all data) R1 = 0.1105, wR2 = 0.3370

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287 Appendix C-7. Crystal data and stru cture refinement for compound [7]. Empirical formula C43.33 H43.33 Cl N2 O10.67 Zn2 Formula weight 928.99 Temperature 100(2) K Wavelength 0.71073 Crystal system Trigonal Space group P-3 Unit cell dimensions a = 18.9529(6) = 90. b = 18.9529(6) = 90. c = 10.7825(7) = 120. Volume 3354.3(3) 3 Z 3 Density (calculated) 1.380 Mg/m3 Absorption coefficient 1.190 mm-1 F(000) 1439 Crystal size 0.2 x 0.15 x 0.10 mm3 Theta range for data coll ection 1.89 to 28.28 Index ranges -25<=h<=24, -21<=k<=24, -11<=l<=14 Reflections collected 21567 Independent reflections 5329 [R(int) = 0.0434] Completeness to theta = 28.28 95.8 % Absorption correction Semi-empirical Max. and min. transmission 0.6427 and 0.5500 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 5329 / 14 / 270 Goodness-of-fit on F2 1.067 Final R indices [I>2sigma(I)] R1 = 0.0502, wR2 = 0.1374 R indices (all data) R1 = 0.0668, wR2 = 0.1449

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288 Appendix C-8. Crystal data and stru cture refinement for compound [8]. Empirical formula C25 H20 N2 O5 Zn Formula weight 493.80 Temperature 100(2) K Wavelength 1.54178 Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = 9.8421(5) = 90. b = 15.7560(7) = 94.132(3). c = 13.8865(7) = 90. Volume 2147.81(18) 3 Z 4 Density (calculated) 1.527 Mg/m 3 Absorption coefficient 1.940 mm -1 F(000) 1016 Crystal size 0.35 x 0.30 x 0.25 mm 3 Theta range for data coll ection 4.25 to 67.55 Index ranges -11<=h<=11, -18<=k<=18, -16<=l<=16 Reflections collected 15321 Independent reflections 3467 [R(int) = 0.0459] Completeness to theta = 67.55 89.5 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.6427 and 0.5500 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 3467 / 0 / 298 Goodness-of-fit on F 2 1.087 Final R indices [I>2sigma(I)] R1 = 0.0619, wR2 = 0.1461 R indices (all data) R1 = 0.0721, wR2 = 0.1512

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289 Appendix C-9. Crystal data and stru cture refinement for compound [9]. Empirical formula C25 H20 Co N2 O5 Formula weight 487.36 Temperature 100(2) K Wavelength 1.54178 Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = 9.8526(3) = 90. b = 15.7543(5) = 94.272(2). c = 13.8302(4) = 90. Volume 2140.77(11) 3 Z 4 Density (calculated) 1.512 Mg/m 3 Absorption coefficient 6.638 mm -1 F(000) 1004 Crystal size 0.20 x 0.20 x 0.05 mm 3 Theta range for data coll ection 4.26 to 60.00 Index ranges -11<=h<=10, -15<=k<=17, -15<=l<=15 Reflections collected 10322 Independent reflections 3143 [R(int) = 0.0813] Completeness to theta = 60.00 98.9 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.7325 and 0.3503 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 3143 / 0 / 299 Goodness-of-fit on F 2 1.030 Final R indices [I>2sigma(I)] R1 = 0.0489, wR2 = 0.1103 R indices (all data) R1 = 0.0634, wR2 = 0.1179

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290 Appendix C-10. Crystal data and struct ure refinement for compound [10]. Empirical formula C25 H20 Cd N2 O5 Formula weight 540.83 Temperature 100(2) K Wavelength 1.54178 Crystal system Monoclinic Space group P2(1)/c Unit cell dimensions a = 17.2395(5) = 90. b = 15.8856(4) = 104.6200(10). c = 16.8097(4) = 90. Volume 4454.4(2) 3 Z 8 Density (calculated) 1.613 Mg/m 3 Absorption coefficient 8.194 mm -1 F(000) 2176 Crystal size 0.30 x 0.20 x 0.10 mm 3 Theta range for data coll ection 3.84 to 68.04 Index ranges -19<=h<=20, -19<=k<=18, -19<=l<=20 Reflections collected 37840 Independent reflections 7911 [R(int) = 0.0479] Completeness to theta = 68.04 97.3 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.4946 and 0.1052 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 7911 / 0 / 584 Goodness-of-fit on F 2 1.027 Final R indices [I>2sigma(I)] R1 = 0.0518, wR2 = 0.1230 R indices (all data) R1 = 0.0591, wR2 = 0.1281

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291 Appendix C-11. Crystal data and structure refinement for compound [11]. Empirical formula C27 H24 N2 O5 Zn Formula weight 521.85 Temperature 100(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = 11.2273(13) = 90. b = 15.7208(18) = 97.471(2). c = 13.3310(15) = 90. Volume 2333.0(5) 3 Z 4 Density (calculated) 1.486 Mg/m 3 Absorption coefficient 1.095 mm -1 F(000) 1080 Crystal size 0.15 x 0.10 x 0.07 mm 3 Theta range for data coll ection 2.01 to 25.04 Index ranges -13<=h<=13, -9<=k<=18, -15<=l<=15 Reflections collected 12037 Independent reflections 4114 [R(int) = 0.0380] Completeness to theta = 25.04 99.7 % Absorption correction None Max. and min. transmission 1.0000 and 0.735425 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4114 / 0 / 316 Goodness-of-fit on F 2 0.925 Final R indices [I>2sigma(I)] R1 = 0.0317, wR2 = 0.0805 R indices (all data) R1 = 0.0361, wR2 = 0.0836

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292 Appendix C-12. Crystal data and struct ure refinement for compound [12]. Empirical formula C27 H24 Co N2 O5 Formula weight 515.41 Temperature 298(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = 11.1436(19) = 90. b = 15.910(3) = 98.614(3). c = 13.503(2) = 90. Volume 2367.1(7) 3 Z 4 Density (calculated) 1.446 Mg/m 3 Absorption coefficient 0.767 mm -1 F(000) 1068 Crystal size 0.10 x 0.10 x 0.04 mm 3 Theta range for data coll ection 1.99 to 25.12 Index ranges -13<=h<=13, -18<=k<=11, -15<=l<=16 Reflections collected 12091 Independent reflections 4184 [R(int) = 0.0819] Completeness to theta = 25.12 99.3 % Absorption correction None Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4184 / 0 / 317 Goodness-of-fit on F 2 0.941 Final R indices [I>2sigma(I)] R1 = 0.0570, wR2 = 0.1107 R indices (all data) R1 = 0.1115, wR2 = 0.1279

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293 Appendix C-13. Crystal data and struct ure refinement for compound [13]. Empirical formula C27 H24 Cd1 N2 O5 Formula weight 568.88 Temperature 100(2) K Wavelength 1.54178 Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = 11.5852(2) = 90. b = 15.6988(3) = 95.6450(10). c = 13.2064(2) = 90. Volume 2390.25(7) 3 Z 4 Density (calculated) 1.581 Mg/m 3 Absorption coefficient 7.666 mm -1 F(000) 1152 Crystal size 0.24 x 0.20 x 0.18 mm 3 Theta range for data coll ection 4.39 to 67.78 Index ranges -13<=h<=13, -18<=k<=18, -15<=l<=15 Reflections collected 18300 Independent reflections 4143 [R(int) = 0.0463] Completeness to theta = 67.78 95.7 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.3391 and 0.2606 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4143 / 0 / 318 Goodness-of-fit on F 2 1.054 Final R indices [I>2sigma(I)] R1 = 0.0357, wR2 = 0.1197 R indices (all data) R1 = 0.0368, wR2 = 0.1211

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294 Appendix C-14. Crystal data and struct ure refinement for compound [15]. Empirical formula C30 H46 Co2 N4 O10 Formula weight 740.57 Temperature 293(2) K Wavelength 1.54178 Crystal system Monoclinic Space group P2 Unit cell dimensions a = 13.4027(15) = 90. b = 9.4194(11) = 90.040 (6). c = 13.4730(15) = 90. Volume 1700.9(3) 3 Z 2 Density (calculated) 1.446 Mg/m 3 Absorption coefficient 8.144mm -1 F(000) 776 Crystal size 0.10 x 0.10 x 0.10 mm 3 Theta range for data coll ection 3.28 to 58.90 Index ranges -14<=h<=14, -9<=k<=10, -14<=l<=14 Reflections collected 7189 Independent reflections 3928 [R(int) = 0.0500] Completeness to theta = 58.90 92.2 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.4964 and 0.4964 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 3928 / 1 / 197 Goodness-of-fit on F 2 1.078 Final R indices [I>2sigma(I)] R1 = 0.0954, wR2 = 0.2568 R indices (all data) R1 = 0.1362, wR2 = 0.2833

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295 Appendix C-15. Crystal data and struct ure refinement for compound [16]. Empirical formula C30 H36 N2 O8 Zn2 Formula weight 683.35 Temperature 100(2) K Wavelength 0.71073 Crystal system Orthorhombic Space group I222 Unit cell dimensions a = 13.444(4) = 90. b = 13.444(4) = 90. c = 27.943(8) = 90. Volume 5050(2) 3 Z 4 Density (calculated) 0.899 Mg/m 3 Absorption coefficient 0.981 mm -1 F(000) 1416 Crystal size 0.10 x 0.10 x 0.10 mm 3 Theta range for data co llection 1.68 to 25.0 Index ranges -13<=h<=16, -16<=k<=15, -33<=l<=24 Reflections collected 7189 Independent reflections 4445 [R(int) = 0.0325] Completeness to theta = 25.02 99.9 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.4964 and 0.4964 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4445 / 4 / 195 Goodness-of-fit on F 2 1.115 Final R indices [I>2sigma(I)] R1 = 0.0623, wR2 = 0.1980 R indices (all data) R1 = 0.0790, wR2 = 0.2157

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296 Appendix C-16. Crystal data and struct ure refinement for compound [29]. Empirical formula C44 H40 Co2 N4 O12 Formula weight 934.66 Temperature 293(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P 2 Unit cell dimensions a = 13.291(5) = 90. b = 13.291(5) = 90.01(10). c = 22.084(6) = 90. Volume 3901(2) 3 Z 2 Density (calculated) 0.796 Mg/m 3 Absorption coefficient 0.462 mm -1 F(000) 964 Crystal size 0.1 x 0.1 x 0.1 mm 3 Theta range for data coll ection 0.92 to 23.25 Index ranges 14<=h<=13, -11<=k<=14, -24<=l<=24 Reflections collected 16925 Independent reflections 11205 [R(int) = 0.0331] Completeness to theta = 23.25 99.8 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.4946 and 0.1052 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 11205 / 3 / 88 Goodness-of-fit on F 2 1.045 Final R indices [I>2sigma(I)] R1 = 0.1062, wR2 = 0.2998 R indices (all data) R1 = 0.1183, wR2 = 0.3125

PAGE 313

297 Appendix C-17. Crystal data and struct ure refinement for compound [30]. Empirical formula C446.50 H579.50 Cu24 O144 Formula weight 9775.56 Temperature 296(2) K Wavelength 0.71073 Crystal system Tetragonal Space group P4(1)2(1)2 Unit cell dimensions a = 38.559(2) = 90. b = 38.559(2) = 90. c = 54.503(6) = 90. Volume 81035(11) 3 Z 4 Density (calculated) 0.801 Mg/m 3 Absorption coefficient 0.664 mm -1 F(000) 20426 Crystal size 0.2 x 0.15 x 0.1 mm 3 Theta range for data coll ection 0.91 to 16.00 Index ranges -29<=h<=29, -29<=k<=29, -42<=l<=20 Reflections collected 115996 Independent reflections 19801 [R(int) = 0.3397] Completeness to theta = 16.00 99.9 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 1.00 and 0.89 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 19801 / 449 / 775 Goodness-of-fit on F 2 1.317 Final R indices [I>2sigma(I)] R1 = 0.1873, wR2 = 0.4067 R indices (all data) R1 = 0.2226, wR2 = 0.4386

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298 Appendix C-18. Crystal data and struct ure refinement for compound [31]. Empirical formula C720 H432 Cu48 O288 Formula weight 16740.58 Temperature 100(2) K Wavelength 1.54178 Crystal system Tetragonal Space group P4/mnc Unit cell dimensions a = 27.974(5) = 90.000(5) . b = 27.974(5) = 90.000(5) . c = 39.321(5) = 90.000(5) . Volume 30770(9) 3 Z 2 Density (calculated) 0.903 Mg/m 3 Absorption coefficient 1.349 mm -1 F(000) 8448 Crystal size 0.10 x 0.10 x 0.10 mm 3 Theta range for data coll ection 1.94 to 39.96 Index ranges -15<=h<=22, -22<=k<=22, -32<=l<=31 Reflections collected 41589 Independent reflections 4548 [R(int) = 0.1175] Completeness to theta = 39.96 95.0 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.8769 and 0.8769 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 4548 / 7 / 232 Goodness-of-fit on F 2 1.113 Final R indices [I>2sigma(I)] R1 = 0.1097, wR2 = 0.2959 R indices (all data) R1 = 0.1504, wR2 = 0.3217

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299 Appendix C-19. Crystal data and struct ure refinement for compound [32]. Empirical formula C1248 H200 Cu48 N40 O352 Formula weight 24433.28 Temperature 100(2) K Wavelength 0.71073 Crystal system Tetragonal Space group I4/m Unit cell dimensions a = 27.654(20) = 90 . b = 27.654(20) = 90. c = 39.9159(60) = 90 . Volume 30524.7(60) 3 Z 2 Density (calculated) 0.984 Mg/m 3 Absorption coefficient 1.178 mm -1 F(000) 9845 Crystal size 0.10 x 0.10 x 0.10 mm 3 Theta range for data coll ection 1.90 to 24.45 Index ranges -15<=h<=22, -22<=k<=22, -32<=l<=31 Reflections collected 12235 Independent reflections 6342 [R(int) = 0.2237] Completeness to theta = 24.45 93.0 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.8769 and 0.8769 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 6342 / 17 / 751 Goodness-of-fit on F 2 2.13 Final R indices [I>2sigma(I)] R1 = 0.1794, wR2 = 0.2959 R indices (all data) R1 = 0.2617, wR2 = 0.3217

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300 Appendix C-20. Crystal data and structure refinement for compound [33]. Empirical formula C304 H216 Cu24 O144 S8 Formula weight 7954.21 Temperature 100(2) K Wavelength 0.71073 Crystal system Tetragonal Space group I422 Unit cell dimensions a = 28.885(4) = 90. b = 28.885(4) = 90. c = 28.305(6) = 90. Volume 23616(7) 3 Z 2 Density (calculated) 1.119 Mg/m 3 Absorption coefficient 1.159 mm -1 F(000) 8032 Crystal size 0.1 x 0.08 x 0.07 mm 3 Theta range for data coll ection 2.23 to 23.50 Index ranges -32<=h<=21, -32<=k<=31, -31<=l<=28 Reflections collected 52801 Independent reflections 8752 [R(int) = 0.3244] Completeness to theta = 23.50 99.7 % Absorption correction Semi-empirical Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 8752 / 635 / 520 Goodness-of-fit on F 2 1.000 Final R indices [I>2sigma(I)] R1 = 0.1032, wR2 = 0.2570 R indices (all data) R1 = 0.2820, wR2 = 0.2874

PAGE 317

301 Appendix C-21. Crystal data and structure refinement for compound [34]. Empirical formula 4441 H376 N32 O152 Zn24 Formula weight 10126.48 Temperature 293(2) K Wavelength 0.71073 Crystal system Tetragonal Space group I4/m Unit cell dimensions a = 30.144(7) = 90. b = 30.144(7) = 90. c = 27.944(11) = 90. Volume 25391(13) 3 Z 2 Density (calculated) 1.325 Mg/m 3 Absorption coefficient 1.193 mm -1 F(000) 10366 Crystal size 0.1 x 0.1 x 0.1 mm 3 Theta range for data coll ection 1.68 to 20.82 Index ranges -30<=h<=29, -29<=k<=14, -17<=l<=27 Reflections collected 19407 Independent reflections 6832 [R(int) = 0.1146] Completeness to theta = 20.82 99.7 % Absorption correction semi-empirical Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 6832 / 530 / 717 Goodness-of-fit on F 2 1.047 Final R indices [I>2sigma(I)] R1 = 0.1006, wR2 = 0.2329 R indices (all data) R1 = 0.1464, wR2 = 0.2555

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About the Author John Jackson Perry IV was born in Tampa, Florida U.S.A., in 1980. He was salutatorian of his graduati ng class from the Academy of Health Professions located on the campuses of Tampa Bay Technical High School in 1999. He received two B.A. degrees in chemistry and mathematics (gradu ating from the Honors College) from the University of South Florida in 2003. In August of 2003, he was admitted into the Ph.D. program in the Department of Chemistry at USF, upon which time he joined the research group of Dr. Michael J. Zaworotko. He is a member of the American Chemical Society, the American Association for the Advancem ent of Science, and the Mathematical Association of America. In addition to co-aut horing six scientific papers in peer-reviewed journals, he has presented his research at numerous local, st ate, regional, national, and international scientific conf erences. He has received several awards and recognitions for his research and in 2005 he wa s awarded the George Bursa award, given annually to an exceptional graduate student in the Departme nt of Chemistry at USF. In 2008 he was selected to be one of approximately 30 gra duate student / post-doctoral fellows to attend the International Center for Material s Research summer school workshop on Periodic Materials and Crystal Chemistry where he was afforded the opportunity to interact with some of the current luminaries as well as with future leaders in the field.


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Hierarchical complexity in metal-organic materials :
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Dissertation (Ph.D.)--University of South Florida, 2009.
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ABSTRACT: The design and synthesis of novel functional materials with fine-tunable physical and chemical properties has been an aspiration of materials scientists since at least Feynman's famous speech "There's Plenty of Room at the Bottom" which has fittingly been credited with ushering in the nanotechnology era. Crystal engineering, as the solid-state manifestation of supramolecular chemistry, is well positioned to make substantial contributions to this worthwhile endeavor. Within the realm of crystal engineering resides the subdiscipline of metal-organic materials (MOMs) which pertains most simplistically to the coordination bond and includes such objects as coordination polymers, metal-organic frameworks (MOFs), and discrete architectures, each of which share the common aspect that they are designed to be modular in nature.While metal-organic materials have been studied for quite some time, only recently have they enjoyed an explosion in significance and popularity, with much of this increased attention being attributed to two realizations; that this inherent modularity ultimately results in an almost overwhealming degree of diversity and subsequently, that this diversity can give rise to effective control of the properties of functional materials. At long last the goal of attaining fine-tunablity may be within our grasp. In addition to high levels of diversity, MOMs are also characterized by a broad range of complexity, both in their overall structures and in the nature of their constituents. From the simplest molecular polygons to extended 3-periodic frameworks of unprecedented topologies, MOMs have the capacity to adopt an array of structural complexities. Moreover, there has been a recent trend of increasing complexity of the very building blocks that construct the framework.It is the aim of the research presented in this dissertation to survey these two principle aspects of MOMs, diversity and complexity, by focusing upon the use of polycarboxylates and first row transition metals to synthesize several series of closely related materials imbued with varied levels of complexity. Through the use of single crystal X-ray diffraction and the charcterization of the materials' properties, the structure-function relationship has been probed. Finally, novel design strategies incorporating supermolecular building blocks for the creation of a new generation of MOMs has been addressed.
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