Comparison of the frequencies of crystallographic space groups in organo-lanthanide and -actinide compounds

Abstract

Bibliographic and numeric data on 1540 organo-lanthanide and 895 organo-actinide crystalline compounds were derived from the Cambridge Structural Database. After removal of the double entries, the compounds were classified into the 230 crystallographic space groups according to their space-group numbers, and the relative frequency of occurrence of each space group was then determined. 10.0% of the lanthanide and 8.4% of the actinide compounds fall in space groups of tetragonal or higher symmetry. In both cases, only 71 of the space groups have at least one entry. Approximately two-thirds of the compounds crystallize in three space groups: 34.1% of the lanthanides in P2 1/ c (actinides: 38.5%), 22.1% (20.5%) in P 1 and 8.3% (9.0%) in C2/ c; in contrast, there are 46 space groups in the lanthanide group with five or fewer compounds assigned to them (55 for the actinides). The distribution of the lanthanides into the different crystal families corresponds well to that of the actinides. If the data are compared with a study on the space-group frequencies for organic compounds (Mighell et al., Acta Crystallogr., A 39 (1983), 737–740) there are a number of important differences: lanthanides and actinides tend to crystallize more in the triclinic crystal family than the organic compounds (22.6% for lanthanides and 21.0% for actinides vs. 14.8% for organic compounds) and less in the orthorhombic crystal family (15.4% for lanthanides and 17.0% for actinides vs. 25.8% for organic compounds). There is an increase in the number of compounds crystallizing in one of the centrosymmetric space groups (78.5% for lanthanides and 81.7% for actinides vs. 70.4% for organic compounds) and a decrease for the enantiomorphic space groups (11.5% for lanthanides and 10.1% for actinides vs. 23.1% for organic compounds). The number of compounds crystallizing in one of the symmorphic space groups is higher (27.9% for lanthanides and 24.7% for actinides vs. 18.6% for organic compounds), which corroborates the fact that the number of compounds crystallizing in the triclinic system has increased.