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 (D_e), and intermolecular stretching, quadratic force constants (k_σ) 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 D_e 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 D_e is directly proportional to the force constant k_σ, with a constant of proportionality identical within experimental error to that found previously for many B⋯HX and B⋯XY complexes.