The systematization of molecular crystal structures

A scheme of classification of molecular crystal structures is proposed. The structures are divided into homo-, hetero and quasiheteromolecular. The next step of the classification is the division into chiral types which define the character of the systems of equivalent positions occupied by the molecules. Finally, the subdivision into chiral classes reflects the equality or inequality of symmetrically unrelated molecules. Statistical data are given about the distribution of quasiheteromolecular structures into chiral classes. The concept of an expanded (non-Fedorov) space group is proposed to describe such structures.