On the Distribution of Molecular Crystals of Organic and Elementoorganic Compounds over Symmetry Space Groups

The geometric factors affecting the implementation rate of symmetry space groups in molecular crystals of organic and elementoorganic compounds have been analyzed. The structural features of crystals described within rare symmetry groups have been studied based on the data deposited at the Cambridge Crystallographic Data Centre (CCDC) (2019). It is proposed to classify symmetry groups with respect to the unit-cell volume V-c calculated for a given specific forbidden volume. It is shown that the most abundant symmetry groups are characterized by a small specific forbidden volume in comparison with rare symmetry groups (V-c < 10(3) angstrom(3)). In the case of packing of asymmetric molecules, the high fraction of the forbidden volume in the crystal space allows implementation of only crystals with large (V > 16 x 10(3) angstrom(3) on average) volumes of unit cells.