σ-Hole bond tunability in YO2X2:NH3 and YO2X2:H2O complexes (X = F, Cl, Br; Y = S, Se): trends and theoretical aspects

A sigma-hole is defined as an electron-deficient region on the extension of a covalently bonded group IV-VII atoms. If the electronic density in the sigma-hole is sufficiently low, then this region will have a positive electrostatic potential, which allows attractive noncovalent interactions with negative sites. SO2X2 and SeO2X2 (X = F, Cl and Br) have three Lewis acid sites of sigma-hole located in the outermost of chalcogen atom and X end, participating in the chalcogen and halogen bonds with NH3 and H2O, respectively. MP2/aug-cc-pVTZ and M06-2X/aug-cc-pVTZ calculations reveal that for a given halogen atom, SeO2X2 forms stronger chalcogen bond interactions than SO2X2 counterpart. Almost a perfect linear relationship is evident between the interaction energies and the magnitudes of the product of most positive and negative electrostatic potentials. The interaction energies calculated by M06-2X and MP2 methods are almost consistent with each other.