Chalcogen bonds in complexes of SOXY (X, y = F, Cl) with nitrogen bases

SOF, SOFCl, and SOCl 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-ζ 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 N → 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.