WEAK INTERMOLECULAR INTERACTIONS BETWEEN NITROGEN AND OXYGEN-ATOMS

A recent study of organic crystalline compounds containing nitro group s, which concentrated on the intermolecular approach of oxygen to the N of the NO2 group, has revealed typical N...O distances much shorter than would be expected from the van der Waals radii. Ab initio dimer c alculations reported here substantiate this finding, and indicate that these interactions are comparable in strength with weak hydrogen bond s. Dimer binding energies of 10-13 kJ mol(-1) are obtained at the MP2/ 6-31++G(*) level, and the optimal N...O distance is approximate to 2. 85 Angstrom. The difference between one-electron (Hartree-Fock) and co rrelated treatments, combined with an atoms-in-molecules decomposition of the charge distribution, suggests that this interaction is dominat ed by dispersive forces.