Chalcogen Bonds in Complexes of SOXY (X, Y = F, Cl) with Nitrogen Bases
SOF2, SOFCl, and SOCl2 were each paired with a series of N bases. The potential energy surface of the binary complexes were characterized by MP2 calculations with double and triple-ξ basis sets, extrapolated to complete sets. The most stable configurations contained a S···N chalcogen bond with interaction energies as high as 6.8 kcal/mol. These structures are stabilized by a Nlp → σ*(S–Z) electron transfer (Z = O, F, Cl), complemented by Coulombic attraction of N to the σ-hole opposite the Z atom. N···S–F and N···S–Cl chalcogen bonds are stronger than N···S═O interactions. Formation of each chalcogen bond elongates all of the internal covalent bonds within SOXY, especially the S–Cl bond. Halogen-bonded (N···Cl–S) complexes were also observed, but these are more weakly bound, by less than 3 kcal/mol.