A r-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 r-hole is suffi- ciently low, then this region will have a positive electro- static potential, which allows attractive noncovalent interactions with negative sites. SO 2 X 2 and SeO 2 X 2 (X = F, Cl and Br) have three Lewis acid sites of r-hole located in the outermost of chalcogen atom and X end, participating in the chalcogen and halogen bonds with NH 3 and H 2 O, respectively. MP2/aug-cc-pVTZ and M06-2X/ aug-cc-pVTZ calculations reveal that for a given halogen atom, SeO 2 X 2 forms stronger chalcogen bond interactions than SO 2 X 2 counterpart. Almost a perfect linear relation- ship 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.
