A Novel Description of the Crystal Packing of Molecules

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• 作者：Elna Pidcock and W. D. Sam Motherwell
• 刊名：Crystal Growth & Design
• 出版年：2004
• 出版时间：May 2004
• 年：2004
• 卷：4
• 期：3
• 页码：611 - 620
• 全文大小：184K
• 年卷期：v.4,no.3(May 2004)
• ISSN：1528-7505

文摘

The question of why molecules pack to form particular crystal structures is occupying many researchersthroughout the scientific community. Much emphasis has been placed on the study of intermolecular interactionsand the search for "structure-directing" motifs. However, examination of experimental crystal structures containedwithin the Cambridge Structural Database has led us to propose a new, conceptually simple model of crystal packingthat describes the arrangements molecules adopt in unit cells. The model was inspired by consideration ofarrangements of boxes (with three unequal dimensions) stacked with faces touching and edges aligned. For a fixednumber of boxes, there are only a limited number of arrangements possible, and these arrangements, or packingpatterns, are of the same volume but different surface area. Applied to crystal structures, the model describes unitcells in terms of multiples (pattern coefficients) of molecular dimensions. The different packing patterns are notpopulated equally by experimental crystal structures, and it is found that the most populated packing patterns arethose that are characterized by low surface area. Correlations between broadly defined molecular shapes and packingpatterns have been observed which indicate that molecular aggregation is a useful method for moderating awkward(high surface area for volume) molecular shapes. A limited number of crystal structure prediction trials wereperformed with the reduced search space afforded by estimated unit cell dimensions (from molecular dimensions),and an increase in success rate was observed.