Learning from approximate periodic symmetry in organic P1 structures

Abstract

The article by Brock (2022) is the result of an ambitious 3+ year long project to study the occurrences of approximate symmetries in the space group P 1. Brock selected the November 2019 version of the Cambridge Structural Database (CSD; Groom et al. , 2016) where 2592 reports of organic crystal structures (based on Z , Z 0 and an R value (cid:2) 0.05) were found. Using a number of criteria this set was distilled down to 1407 Z = Z 0 > 1 and 1049 Z = Z 0 = 1. In the former group, molecules (including cations and anions) within asymmetric units were evaluated for possible approximate symmetries: 2, 2 1 , 3, 3 1 , translations, inversions or glides. Entries in the latter group were retained if some possible approximate symmetry was detected within the molecule(s). A subset of crystal structures was removed from both sets if the symmetry indicated these would be better described in a higher-symmetry space group. Brock’s conclusion is that approximate symmetry is pervasive in P 1 crystal structures.