INTERMOLECULAR NONBONDED CONTACT DISTANCES IN ORGANIC-CRYSTAL STRUCTURES - COMPARISON WITH DISTANCES EXPECTED FROM VAN-DER-WAALS RADII

The conclusions derived from systematic analyses of intermolecular con tact distances in organic crystals may be affected by the values assum ed for van der Waals radii. The most widely used tabulations of van de r Waals radii date back 30 years or more. Moreover, many of the tabula ted values were chosen to reproduce volumes, not contact distances in crystals. Literally millions of nonbonded contact distances have been characterized by crystallography since the tabulations were compiled. A study has therefore been performed to establish the degree of consis tency between these accumulated crystallographic data and the van der Waals radii of the common nonmetallic elements, as compiled by Pauling and Bondi. For halogens and sulfur, the results show a remarkable agr eement between observed contact distances and the Bondi radii. Agreeme nt is slightly less good for carbon, nitrogen, and oxygen, but discrep ancies are still only about 0.05 Angstrom. However, there is a signifi cant difference for hydrogen, where the Bondi value of 1.2 Angstrom is probably too high by about 0.1 Angstrom. .