Supramolecular interactions crystal close packing

Figure 4.9. Schematic representations of the crystal structures of the salts of enantiopure 5 with / -substiluted 1-arylethylamines in success, (a) Less soluble salts, in which the formation of a stable supramolecular hydrogen-bond sheet, the realization of efficient CII—ti interaction, and the close packing of the sheets are achieved, (b) More soluble salts, in which efficient CH n interaction is not realized and the close packing of the supramolecular sheets a stable supramolecular hydrogen-bond sheet is not formed, (c) More soluble salts, in which a stable supramolecular hydrogen-bond sheet is formed and the close packing of the supramolecular sheets is achieved, while efficient interaction is not realized.

Creative concepts in crystal engineering make use of supramolecular synthons to define specific interactions in molecular solids, which may be employed to design crystal packings The synthon approach has been used to produce close packed structures, and, on the contrary, to build open network structures. In the packing motifs of high performance pigments several types of specific interactions (synthons) can be identified. 

The supramolecular formations and the molecular packing in the crystals show close resemblance, and the nature of the interactions involved is very much the same. There is great emphasis on weak interactions in both. According to Lehn, beyond molecular chemistry based on the covalent bond lies supramolecular chemistry based on molecular interactions—the associations of two or more chemical entities and the intermolecular bond [85], Dunitz expressed eloquently the relevance of supramolecular structures to molecular crystals and molecular packing [86] ... 

Figure 22 A linear example of Aufbau crystal packing for triorganotin 2-[(ZJ)-2-(2-hydroxy-5-methylphenyl)-l-diazenyl]benzoates. Molecules precipitate from solution and adopt orientations to optimize intermolecular interactions, in this case secondary Sn- -O contacts. When the steric bulk of the tin-bound substituents allows for the close approach of molecules, as in the R = methyl example, a supramolecular chain is formed comprising trans-C3Sn02 tin atom geometries. When the steric bulk precludes close association, monomeric packing is found with d -Cs Sn02 tin atom geometries. The linear repeat distance between successive tin atoms is 4.89 A for the R = methyl structure compared to 5.17 A for the R = cyclohexyl derivative.

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