Symmetry Breaking in Molecular Crystal Structures

这个项目的目的是理解和操纵晶体堆积效应和晶体结构，基于一个称为Z‘的参数。广义地说，Z‘代表了产生一块积木所需的分子数量，该积木将在空间中镶嵌形成晶体结构。对于大多数分子化合物Z‘=1，因此少数具有Z’&gt；1的分子化合物(占已知有机小分子结构的8.8%)在某种程度上是例外。我们认为，例外情况证明了这一规则。为什么这个化合物的子集不能以正常的方式堆积呢？它们有什么特别之处？这一建议的主要重点是，为了理解晶体堆积，不仅具有指导意义，而且至关重要，超越空间群预测和调查，并在化学基础上审查多于一个分子占据晶体不对称单元的情况(Z‘&gt；1)。根据定义，这些分子之间的相互作用不具有通常的结晶学对称性，因此表明超分子合成子(一种具有预测效用的晶体堆积相互作用)足够强大，可以逆势而行。此外，这些结构有时可以被解释为“生长最快的晶核的化石遗迹”，因此也可以为晶体的成核和生长过程提供基本的洞察。

This project aims to understand and manipulate crystal packing effects and crystal structure based on a parameter termed Z'. Broadly, Z' represents the number of molecules it takes to produce a building block that will tesselate in space to produce a crystal structure. For most molecular compounds Z' = 1 and hence the few that have Z' > 1 (8.8% of known structures of small organic molecules) are exceptions in some way. We believe that the exceptions prove the rule. Why is it that this subset of compounds do not pack in a normal way? What is special about them? It is the primary focus of this proposal that in order to understand crystal packing it is not merely instructive, but vital to go beyond space group prediction and surveys, and to examine on a chemical basis, cases in which more than one molecule occupies the crystallographic asymmetric unit (Z' > 1). By definition, interactions between such molecules are not of the usual crystallographic symmetry and thus indicate cases in which a supramolecular synthon (a crystal packing interaction of predictive utility) is sufficiently robust to buck the trend. Moreover, these structures can sometimes be interpreted as 'fossil relics of the fastest growing crystal nucleus' and hence can also provide fundamental insight into crystal nucleation and growth processes.