MATERIALS Today Perspectives of Crystal Engineering "Is Materials Science going soft?" photochemical reactions of cinnamic The most successful strategies of This question is raised by George acids? A broad and more meaningful crystal engineering are based on a Marsh in the first issue of Materials definition of crystal engineering was building block (or supramolecular Today and certainly deserves further provided by G. R. Desiraju in 1989 as synthon) approach, which simplifies consideration. Crystal Engineering, "the understanding of intermolecular the complex problem of structure one of these 'soft' areas in materials interactions in the context of crystal prediction into a simple problem of science, has recently been emerging packing and in the utilisation of such network architecture (like making as a major cross-disciplinary field of understanding in the design of new things out of LEGO ® blocks). For all basic and applied inquiry. solids with desired physical and practical purposes, the crystal chemical properties". 3 Crystal structures are assumed to be Let's examine the scope of this engineering is now a rapidly networks, where molecules, metals, exciting field as it applies to materials developing interdisciplinary field ions, etc., are considered as nodes and science. with a wide scope for basic research the intermolecular interactions or and promising industrial applications coordination bonds represent node Crystals are comprised of which may also drive the basic connections. 4 The design of one, two, molecules or ions, and the physical research effort. A few of the key or three-dimensional crystalline and chemical properties of the crystals research areas under the purview of network structures can thus be depend upon the geometrical crystal engineering include: achieved by choosing the desired arrangement of these internal building combination of nodes and connectors. blocks. To the materials scientist, • and Color of Solids For example, metal cations as the control of both the physical and • Separation Science nodes, coordinated to simple linear chemical properties of the materials • Catalysis bifunctional ligands as connectors would be a natural outcome of the • Optical Materials (NLO, will form a variety of 1D, 2D, and 3D ability to predict the Octupolar, Switches) architectures depending upon the of a given compound. The ability to • Electronic Materials and Sensors metal coordination geometry and fine-tune such features as color, • Conducting and Magnetic metal to ligand ratio as shown by point, polarity, polymorphism, Materials Mike Zaworotko in reference 5 and or conductivity would offer unlimited • Nanotechnology redrawn in Figure 1. Interestingly, potential for materials modification. • Crystal Growth, Polymorphism many of these simple new • Liquid Crystals frameworks have no precedence in Unfortunately, it is not yet possible • Molecular Modeling naturally occurring solids and the to predict solid state structure merely • Drug Design bulk properties of these compounds from chemical composition. This was • Protein-Receptor Binding remains largely unexplored.5 the subject of John Maddox's, 1988 • Surfactants, Monolayers, and Nature editorial where he indicated Multilayers Two separate branches of crystal that "One of the continuing scandals in • Supramolecular Devices engineering independently deal with the physical sciences is that it remains • Solid State Chemical Reactivity design principles for organic solids in general impossible to predict the structure of even the simplest Metal crystalline solids from a knowledge of 0 their chemical composition". 1 While Bifunctional ligand m these statements may still be true in a - i i strict sense even today, continuing Linear Chain Ladder efforts of various research groups _ ! l around the globe to achieve the T:i:i objective of crystal structure :EL E]Z prediction have afforded significant Brick Square Grid Honeycomb progress toward this goal.

The term crystal engineering was coined by G. M. J. Schmidt in the 1970s to address the problem of crystal structure prediction in the Figure 1. Control of metal ion coordination geometry and reaction context of organic solid state stoichiometry can lead to controllable ID, 2D, and 3D architectures. Page 27 NATEIiIA~ Today and inorganic solids (or coordination polymers). The organic solids are o o____._o .... o o____._o designed by considering molecular shape, symmetry, and intermolecular interactions such as O-H, N-H, and Figure 2. The 1:1 complex of 4-nitrobenzoic acid and 4-(N~V- C-H hydrogen bonding, or weaker dimethylamino)benzoic acid. The linear ribbon structure is stabilized by halogen...halogen, electrostatic, or centric O-H...O dimers and acentric C-H...O hydrogen bonded dimersJ ° van der Waals interactions. Inorganic solids are designed primarily by concerning the nature of weak one of nature's laws: "nature abhors a considering metal coordination intermolecular interactions such as C- vacuum". Despite these hurdles, quite geometry, chemical structure of the H---O and C-H...N interactions has a number of open porous networks organic ligand, metal to ligand ratio, been dispelled by crystallographic have been recently constructed. and the coordinating nature of the statistical analysis: it has been anions. 4,5 More recently, design o" o unequivocally proven that these strategies relying on a combination of interactions are directional and organic and inorganic synthons, electrostatic in nature like any other O~O" metal-organic solids, have become strong hydrogen bonds. 8,9 For increasingly prominent. Regardless example, the 1:1 molecular complex of the basic approach, in order to of 4-nitrobenzoic acid and 4-(N,N- design materials with reliable and dimethylamino)benzoic acid shows a 1 predictable crystalline networks, linear ribbon, that is stabilized by consideration of symmetry and robust acentric O-H-.-O dimers and C-H..-O and directional non-covalent hydrogen bonded dimers (Figure 2).1° interactions are paramount. Although The non-centrosymmetric nature of currently more difficult, it is also the C-H.-.O hydrogen bonded dimer possible to design solid state between the electron donating, and architecture with weak withdrawing functionalities serves as intermolecular interactions by careful a useful building block in efforts consideration of the interplay among toward the design of non- various intermolecular interactions. centrosymmetfic crystals with second CN CN 2 harmonic generation (SHG) Crystal engineering of organic properties. Very recently, C-H---O solids, especially with respect to NH2 hydrogen bonds have been used to understanding the nature of various construct trigonal acentric layered intermolecular interactions, has structures to generate a new class of profoundly influenced the concepts of SHG active octupolar solids, n . It is now well accepted that the organic crystal The design of nanoporous solids a is the best example of a (both organic and inorganic) with supermolecule, and crystal controlled sizes and shapes and engineering has become an integral chemical environments using the The 1:3 complex of trimesic acid part of supramolecular chemistry, the principles of crystal engineering has and N,N-dicyclohexylamine forms an chemistry of the 21st century.4,6,7 generated enormous interest in recent open porous hexagonal network years because such designer solids (effective cavity size 12.7 ,~) stabilized The voluminous (and ever may be exploited for separations, by rigid hydrogen bonding between growing) crystallographic informa- shape selective catalysis, and trimesate anions, 1, and ammonium tion stored in the Cambridge optoelectronic applications.~2 In cations (Figure 3). 13 Interestingly, Structural Database (CSD) is the general, strategies for the synthesis of Yaghi and co-workers used the same primary source for an extremely porous solids rely upon propagation trimesate anions to generate porous reliable description of intermolecular of molecular symmetry into inorganic layered structures with interactions for the design of organic crystalline symmetry through rigid transition metals coordinated to solids. The statistical analysis of directional forces (hydrogen bonds carboxylates. The crystalline lattice of structural and chemical information and/or metal coordination bonds) these compounds is thermally stable provides accurate and unambiguous such that an open porous network up to 350°C, even after the removal of information on interrnolecular may result. The down side of this included aromatic guest molecules! TM interactions that no other strategy is that such open networks Moore and co-workers used a spectroscopic method (NMR, UV, IR) always tend to interpenetrate to obey somewhat similar strategy by could provide. The controversy

Page 28 MATERIALS Today

~.o[~:: =4i'_°-.~ N N °° ~ .°~ ~.°° .~ ° .W• ..o• .W..o• . • •.'~ ~'.: - "--~ ~'.: N N :0.• •O: e ~.. :Ooe %0: ~ ~" . .~ ~" . --.*-- ,¢V•-.~*• °3 tie• .,Co %~ go...~_. ~.. :Q

% ~.e • e% ooe'~ t-e • •o. -.~ ~,-.o._ .~- .o,,,~ ~, .o.•

%=-.4"-' Figure 4. Angular bifunctional ligands, such as pyrimidine, and metal ions with a preference for linear coordination can be used to construct Figure 3. The 1:3 complex of square complexes. Here, the 1:1 Ag(I):pyrimidine complex forms trimesic acid and N,N- tetracationic supramolecular squares which face-to-face stack at the ligand dicyclohexylamine. Note the open, corners to form an open channel network in the solid state. 17 The nitrate porous hexagonal network stabilized anions reside over the channels and are exchangeable with pertechnetate. by rigid hydrogen bonding between trimesate anions and ammonium awareness of how the concepts of direction with the development of cations. 13 crystal engineering may be useful to new computational software, there chemists and material scientists of are many limitations to these considering Ag(I) complexes of 1,3,5- quite different research backgrounds. 18 approaches yet to be overcome.= tris(4-ethynylbenzonitrile)benzene, 2, This is a particularly encouraging sign, to generate rigid open porous since crystal engineering strategies Despite the absence of powerful honeycomb networks. ~5 The tecton 3, could be diversified to generate computational models to predict synthesized by Wuest and co-workers, various advanced materials and crystal structures with reasonable generated porous inclusion drastically expand the scope of the accuracy, the success of the building compounds in the solid state where subject. Indeed, recently, systematic block approach and the voluminous each tecton is held in position by 16 efforts have been initiated to design structural information available in the hydrogen bonds, thereby creating a magnetic, optical, and nanostructured literature have set the stage for the robust three-dimensional network that devices using crystal engineering design of new advanced materials is sustained even after the removal of principles. 18-20 using crystal engineering principles. It the guests molecules trapped inside the would thus not be surprising if crystal pores. 16 A number of interesting open Any overview of crystal engineering became an integral part of porous ladders, squares, and engineering would be incomplete every molecular material design effort octahedral coordination polymers that without mentioning polymorphism in the near future. successfully avoided interpenetration (i.e., a molecular structure yielding have been reported by Zaworotko and two or more different types of crystal Recently, Elsevier Science has co-workers.5 structures) and supramolecular established a new journal to publish isomerism (i.e., the existence of more contributions detailing the design, Recently, we have reported a simple than one network for the same characterization, and application of way to synthesize discrete inorganic building blocks). The phenomenon of engineered solids and the study of macrocycles with ion exchange polymorphism has been brought into noncovalent or covalent forces properties with the aid of angular the forefront recently with the responsible .for their structure. ligands. The 1:1 Ag(I):pyrimidine litigation surrounding the widely Crystal Engineering (currently a complex forms a tetracationic used ulcer drug Zantac and the huge supplement to the Materials Research supramolecular square and results in a commercial interests involved. 2~ Bulletin) is intended as a open channel network in the solid state Unfortunately, our understanding of multidisciplinary forum for (Figure 4). 17 These open channels the subjects of polymorphism and discussion of crystal engineering and facilitate the exchange of nitrate supramolecular isomerism remains as a focus for publications in this anions with radioactive TcO4- anions. scanty, and crystal engineers face the growing field. The first issue is same old question that has been highlighted by a lead article by Although crystal engineering conveniently forgotten with the Gautam Desiraju entitled, "Crystal studies tend at present to be somewhat advent of the building block Engineering: Some Further narrowly focused (mostly directed approach: "Can we predict the crystal Strategies." Joel Bernstein leads off toward the synthesis of various types structure from any given chemical issue #2 with an interesting article on of open networks and/or host-guest composition?"! While there is some polymorphism. Contributions are complexes), there is increasing evidence of advancement in this currently being accepted for future

Page 29 MATERIALS Today issues. Join us as Crystal Engineering The Design and Application of Functional Zaworotko, C. Bauer and R. D. Rogers, Angew. Chem. Int. Ed. Engl. 35, 2213 explores the frontiers of crystal Solids, (eds. K. R. Seddon and M. J. Zaworotko), NATO, ASI series, Kluwer, (1996). structure design and prediction. Dordecht, Netherlands, (1998) in press. 14. O. M. Yaghi, G. Li, and H. Li, Nature 378, 6. J. D. Duntiz, Pure Appl. Chem., 63, 177 703 (1995). C. V. Krishnamohan Sharma (1991). 15. G. B. Gardner, D. Venkataraman, J. S. and Robin D. Rogers* 7. J.-M. Lehn, Angew. Chem. Int. Ed. Engl., Moore, and S. Lee, Nature 374, 792 29, 1304 (1990). (1995). Department of Chemistry, 8. E A. Cotton, L. M. Daniels, G. T. Jordan 16. P. Brunet, M. Simard, and J. D. Wuest, J. The University of Alabama, IV and C. A. Murillo, Chem. Commun., Am. Chem. Soc., 119, 2737 (1997). Tuscaloosa, AL 35487, USA 1673 (1997). 17. C. V. K. Sharma, S. T. Griffin, and R. D. 9. T. Steiner and G. R. Desiraju, Chem. Rogers, Chem. Commun., 215 (1998). References Commun. 891 (1998). 18. P. Ball, Nature, 381,648 (1996). 10. C. V. K. Sharma, K. Paneerselvam, T. 19. R. Dagani, "The Shape of Things to 1. J. Maddox, Nature, 335, 201 (1988). Pilati and G. R. Desiraju, Chem. Commun., Come" Chemical & Engineering News, 2. G. M.J. Schmidt, Pure Appl. Chem. 27, 832 (1992). June 8, 35 (1998). 647 (1971). 11. V. R. Thalladi, S. Brasselet, D. Bl~iser, 20. See the first issue of Crystal Engineering 3. G. R. Desiraju, Crystal Engineering: The R. Boese, J. Zyss, A. Nangia and (1998, Elsevier) for various applications of Design of Organic Solids, Elsevier, G. R. Desiraju, Chem. Commun., 1841 crystal engineering. Amsterdam, (1989). (1997). 21. G. R. Desiraju, Science, 278,404 (1997). 4. G. R. Desiraju, Angew. Chem. Int. Ed. 12. V.A. Russel, C. C. Evans, W. Li and M. D. 22. Polymorph Predictor, Cerius2 Program Engl. 34, 2311 (1995). Ward, Science, 276, 575 (1997). (Molecular Simulations, San Diego, CA, 5. M. J. Zaworotko, in Crystal Engineering: 13. R. E. Melendez, C. V. K. Sharma, M. J. and Cambridge, UK).

CRYSTAL ENGINEERING For a free sample copy e-mail [email protected] 1998 Volume 1, Number 1 JUNE CONTENTS A. ANTHONY, G.R. DESIRAJU, R.K.R. JE'ITI, S.S. KUDUVA, E.J.BRANDON, A.M. ARIF, J.S. MILLER, K.-I, SUGIURA, N.N.L MADHAVI, A. NANGIA, R. THAIMATrAM, and V.R. and B.M. BURKHART THALLADI The Structure of Several Supramolecular Meso- Crystal Engineering: Some Further Strategies ...... 1 Tetraarrylpophinatomanganese(III) Tetracyanoethenide Magnets ...... 97 C.V.K. SHARMA and R.D. ROGERS Discrete Macrocycles to Infinite Polymeric Frames: Crystal B.M. FOXMAN, D.J. GUARRERA, L.D. TAYLOR, D. Engineering Studies of VANENGEN, and J.C. WARNER Ag(I): Pyrimidine Complexes ...... 19 Environmentally Benign Synthesis Using Crystal Engineering; C.B. AAKEROY and A.M, BEATTY Steric Accommodation in Non-Covalent Derivatives of Low-Dimensional Architectures of Silver Coordination Hydroquinones ...... 109 Compounds Assembled via Amide-Amide Hydrogen bonds39

R.D. BAILEY, L.L. HOOK, A.K. POWERS, T.W. HANKS, and For your free sample copy contact: W.T PENNINGTON Bis(Pyddyl)Cadium(II) Iodide Complexes: Thermal, Inclusion, and Structural Behavior ...... 51 Jo Enderby: e-mail: K. BIRADHA and M.J. ZAWOROTKO Supramolecular Isomerism and Polymorphism in j.enderby@ elsevier.co Dianion Salts of Pyromellitic Acid ...... 67 Tel: +44 1865 84378.' Fax: +44 1865 84392' F. HAJEK, E. GRAF, M.W. HOSSEINI. A. DE CIAN, and L FISCHER Crystal Engineering: Formation of 1D-Networks Based on the Self-Assembly of Serf-Complementary Hollow Molecular Modules in the Solid State ...... 79

L.R. MACGKJAVRAY, K.T. HO I:bqAN, and J.L. ATWOOD One-Dimen~cal Hydrogen Bonded Polymers Based on C-Methyl-Calix [4]Resorcinarene and a Crystal Engineering Design Strategy...... 87

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