Supramolecular structures databases

Supramolecular isomerism also lies at the heart of gaining a better understanding of supramolecular synthons and, by inference, how they develop and occur in other solid phases and even solution. The Cambridge Structural Database remains a very powerful tool in this context but it must be remembered that even such a large database will not necessarily be reflective of the full range of compounds that will be isolated and characterized in future years. 

Stoddart and coworkers reported the role of CH/O interactions as a control element in supramolecular complexes.Database studies demonstrated the importance of CH/O hydrogen bonds in the protein structure. 

The development of the supramolecular synthon concept from pattern recognition considerably simplifies the analysis and design of complicated crystal structures [9], as topological features and useful empirical rules can be derived by critical examination of the wealth of crystallographic information documented in structural databases [10],... 

Pidcock, E. Chisholm, J.A. Wood, P.A. Galek, P.T.A. Fabian, L. Korb, O. Cruz-Cabeza, A.J. Liebeschuetz, J.W. Groom, C.R. Allen, F.H. The Cambridge Structural Database System and its applications in supramolecular chemistry and materials design. In Supramolecular Chemistry, from Molecules to Nanomaterials. Steed, J.W. Gale, P.A., Eds WUey New York, 2012, 2927-2946. 

We have already seen several examples of supramolecular synthons in this chapter, such as patterns formed by carboxylic acid residues and urea functionalities (Section 4.3). The following section aims to explore in more detail how it is possible to recognise synthons and tailor their use within synthetic architectures. A particularly important source of information about the frequency of occurrence of particular synthons (and therefore their predictability) is the Cambridge Structured Database. 

The Cambridge Structural Database System and Its Applications in Supramolecular Chemistry and Materials Design... 

Thus, a brief and necessarily selective overview of the different types of interpenetration follows. For more comprehensive reviews on interpenetration, the reader is directed elsewhere." An understanding of basic network topology is assumed again, for discussions of network topology, the reader should consult other sources," including the chapter by Ohrstrom elsewhere in this volume (see The Cambridge Structural Database System and Its Applications in Supramolecular Chemistry and Materials Design, Supramolecular Materials Chemistry). 

Analysis of molecular properties in co-crystals revealed a preference for cocrystal formation between molecules of similar shapes and polarities. Statistical parameters, derived from co-crystals in the Cambridge Structural Database, were used to derive simple methods to select and rank likely co-crystal formers. Application of these methods has been demonstrated to improve the efficiency of screening experiments significantly. It has been shown that co-crystal formation is most likely if both supramolecular synthons and molecular shapes favour it. 

Solid state investigations are of great importance in particular in case of studying calixarene and calix-type compounds due to their great ability to form molecular inclusion complexes, co-crystals and supramolecular assemblies. In CSD (Cambridge Structural Database [1]) over 6000 structures of calix-type compounds are deposited so far. Approximately one-third of the entries are organometallic compounds and two-thirds are classified as organic compounds. 

Until 2003 [11] no single crystal to single crystal transformation of a monosubstituted diacetylene to polydiacetylenes had been reported [27]. The Cambridge Structural Database contains only four entries for terminal diacetylenes and none of these have the supramolecular structural features necessary for a topochemical 1,4-polymerization as outlined in Scheme 5.1. There are many reasons for the lack of information on the topochemical polymerization of unsymmetrical monosubstituted diacetylenes. One is that the oxidative coupling procedure, readily applied for the preparation of symmetrical diacetylenes, is not easily applied to the preparation of unsymmetrical diacetylenes. Another factor is that unsymmetrical diacetylenes lack a center of symmetry and are less likely to pack with simple translational symmetry, a structural feature commonly observed for diacetylenes that undergo a topochemical polymerization (see Scheme 5.1). 

This supramolecular structure arises as a result of the isonicotine rings stacking by 71-71 interactions. The question is whether or not this is a persistent supramolecular synthon that can be applied to the polymerization of trienes as well as triynes. Janiak has recently analyzed ti-ti stacking of pyridines [46]. It was observed in the Cambridge Structural Database that a common assembly of pyridines is for them to be oriented in opposite directions with a near-zero angle between the planes of the rings and a close contact distance of 3.57 A (Fig. 5.9). Although there was some... 

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