Rs. Rowland et R. Taylor, INTERMOLECULAR NONBONDED CONTACT DISTANCES IN ORGANIC-CRYSTAL STRUCTURES - COMPARISON WITH DISTANCES EXPECTED FROM VAN-DER-WAALS RADII, Journal of physical chemistry, 100(18), 1996, pp. 7384-7391
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. .