An Ab Initio Investigation of the Geometries and Binding Strengths of Tetrel-, Pnictogen-, and Chalcogen-Bonded Complexes of CO2, N2O, and CS2 with Simple Lewis Bases: Some Generalizations

Abstract

Geometries, equilibrium dissociation energies (De), and intermolecular stretching, quadratic force constants (kσ) are presented for the complexes B· · · CO2, B· · · N2O, and B· · · CS2, where B is one of the following Lewis bases: CO, HCCH, H2S, HCN, H2O, PH3, and NH3. The geometries and force constants were calculated at the CCSD(T)/aug-cc-pVTZ level of theory, while generation of De employed the CCSD(T)/CBS complete basis-set extrapolation. The non-covalent, intermolecular bond in the B· · · CO2 complexes involves the interaction of the electrophilic region around the C atom of CO2 (as revealed by the molecular electrostatic surface potential (MESP) of CO2) with non-bonding or π-bonding electron pairs of B. The conclusions for the B· · · N2O series are similar, but with small geometrical distortions that can be rationalized in terms of secondary interactions. The B· · · CS2 series exhibits a different type of geometry that can be interpreted in terms of the interaction of the electrophilic region near one of the S atoms and centered on the C∞ axis of CS2 (as revealed by the MESP) with the n-pairs or π-pairs of B. The tetrel, pnictogen, and chalcogen bonds so established in B· · · CO2, B· · · N2O, and B· · · CS2, respectively, are rationalized in terms of some simple, electrostatically based rules previously enunciated for hydrogen- and halogen-bonded complexes, B· · · HX and B· · · XY. It is also shown that the dissociation energy De is directly proportional to the force constant kσ, with a constant of proportionality identical within experimental error to that found previously for many B· · · HX and B· · · XY complexes.