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[摘要]：Org. mols. are prone to polymorphic formation in the solid state due to the rich diversity of functional groups that results in comparable intermol. interactions, which can be greatly affected by the selection of solvent and other crystn. conditions. Intermol. interactions are typically weak forces, such as van der Waals and stronger short-range ones including hydrogen bonding, that are believed to det. the packing of org. mols. during the crystal-growth process. A different packing of the same mols. leads to the formation of a new crystal structure. To disclose the underlying causes that drive the mol. to have various packing motifs in the solid state, an electronic concept or function within the framework of conceptual d. functional theory has been developed, namely, crystn. force. The concept aims to describe the local change in electronic structure as a result of the self-assembly process of crystn. and may likely quantify the locality of intermol. interactions that directs the mol. packing in a crystal. To assess the applicability of the concept, 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile, so-called ROY, which is known to have the largest no. of solved polymorphs, has been examd. Electronic calcns. were conducted on the seven available crystal structures as well as on the single mol. The electronic structures were analyzed and crystn. force values were obtained. The results indicate that the crystn. forces are able to reveal intermol. interactions in the crystals, in particular, the close contacts that are formed between mols. Strong correlations exist between the total crystn. force and lattice energy of a crystal structure, further suggesting the underlying connection between the crystn. force and mol. packing. |
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