The lines-of-force landscape of interactions between molecules in crystals; cohesive versus tolerant and 'collateral damage' contact

Acta Cryst. (2010). B66, 396-406 (doi.org/10.1107/S0108768110008074)

A motif in the crystal structure of QIZHIQ [Archer, Goldberg, Lynch & Krische (2000). J. Am. Chem. Soc. 122, 5006]: N—H...N (blue-white-blue) hydrogen bonding brings collateral Cl...Cl (green-green) contact down to 3.29 Å. The interaction energy over this short contact is but slightly repulsive. Drawing by SCHAKAL (E. Keller).

Calculation of interaction energies between pairs of molecules in organic crystals shows as expected that intermolecular contact does not always occur at minimum energy, but also, somewhat unexpectedly, that short approach is very often irrelevant in terms of energy, and sometimes even repulsive. Caution should be exerted when analyzing crystal structures in terms of 'the shorter, the stronger' bonding criteria for atom-atom contacts.