CSD Reveals Connections between Chemistry and Crystallography: Relations between Molecular Mass of Compounds and Probability of Space Groups of Their Crystals

Crystals for which no disorder was noted were selected from the Cambridge Structural Database (CSD version 5.45). For further analysis, they were divided into sets taking into account several criteria: the presence/absence of metal elements in the compounds; one or two chemically different residues (NRes) forming a crystal; presence/absence of ions (for crystals consisting of two residues). A total of nine different sets were considered, totaling 622,967 hits. Based on the chemical composition indicated in the CSD, the molecular masses of the compounds (MM) forming the crystals were calculated, and the dependences of the occurrence of space groups on MM were analyzed in different sets (for crystals with NRes = 2, the dependences for the heaviest component were analyzed, and in the sets with metals, the metal atom should have been present in this component). It was found that for the two most common among crystals of organic compounds space groups No. 2 (SG-2) and No. 14 (SG-14) there is a noticeable decrease in the ratio (φ) of the SG-14 group with increasing MM and a very significant increase in φ(SG-2) in all sets. Similar trends in changes in φ for sets with NRes = 1 were found for the dependences of φ(SG-2) and φ(SG-14) on the total number of atoms in molecules and on the number of non-hydrogen atoms. It has been established that in the case of a significant number of substances in sets (several tens of thousands), the parameters, characterizing the dependences of φ(SG-2) and φ(SG-14) on molecular mass or number of atoms, change little with a random change in the content of the sets. The influence of MM on the ratios of other widespread space groups was also noted. In addition, the previously discovered similarity in the distribution of space groups for the Organometallic sets (containing transition metals) and the Organics sets with elements 1A and 2A and the significant difference of these sets from the Organics sets without elements 1A and 2A was confirmed.