Quantum-mechanical investigation of tetrel bond characteristics based on the point-of-charge (PoC) approach

The point-of-charge (PoC) approach was employed to investigate the characteristics of the tetrel bond from an electrostatic perspective. W–T–XYZ···B nomenclature was suggested where T is a tetrel atom, W is the atom along the σ-hole extension, B is a Lewis base, and X, Y, and Z are three atoms on the same side of the σ-hole. Quantum-mechanical calculations were carried out on F–T–F3 systems (where T = C, Si, Ge, or Sn) at the MP2/aug-cc-pVTZ level of theory, with PP functions for Ge and Sn atoms. The tetrel bond strength was estimated via the molecular stabilization energy. Tetrel bond strength was found to increase with increasing PoC negativity (i.e., Lewis basicity) and the electronegativity of the W atom. Moreover, the effects of the T···PoC distance, the W–T···PoC angle, and the aqueous medium on the tetrel bond strength were also investigated. Correlations between tetrel bond strength and several atomic and molecular descriptors such as the natural charge on the tetrel atom, EHOMO, and the p-orbital contribution to W–T bond hybridization were observed. Contrary to expectations, the tetrel bond strength in F–C–X3 increased as the electronegativity of X decreased. The σ-node criteria for the studied molecules were also introduced and discussed. The ability of these molecules to simultaneously form more than one tetrel bond was examined via the σn-hole test. In conclusion, the tetrel bond strength was found to be governed by the strengths of (i) the attractive electrostatic interaction of the Lewis base with the σ-hole, (ii) the attractive/repulsive interaction between the Lewis base and the X, Y, and Z atoms, and (iii) the van der Waals interaction between the Lewis base and the X, Y, and Z atoms.