Does single-electron chalcogen bond exist? Some theoretical insights.

Ab initio calculations have been carried out to investigate the σ-hole interaction in XHY···CH3 and XHY···CH2CH3 complexes, where X = F, Cl, Br and Y = S, Se. This interaction, termed "single-electron chalcogen bond interaction" was analyzed in terms of geometric, interaction energies and electronic features of the complexes. This interaction is a weak one, with an interaction energy that varies from a minimum of -1.7 kcal mol(-1) for BrHS···CH3 to -6.0 kcal mol(-1) for FHSe···CH2CH3 at the CCSD(T)/aug-cc-pVTZ level of theory. Energy decomposition analysis indicated that the dominant attraction energy originates in the electrostatic term which is larger for the Se complexes than for the S counterparts. However, the attractive polarization and dispersion components also make an important contribution to the interaction energy for the single-electron chalcogen bond interactions.