Two-Factor Rule for Distinguishing the Covalent and Tetrel Bonds

Understanding and exploring the existence of a recognizable boundary between the noncovalent tetrel bond (TtB) and the coordination or weakened covalent bond are important for the bonding characterization. We have developed a simple methodology for analysing the type of bonds based on comparison of the electrostatic and total static potentials along the bond line. For the typical σ-hole noncovalent bond formed by a Tt atom in a tetrahedral molecule, we have found that the space gap between positions of the maxima of the total static potential and the negative quantity of electrostatic potential is much wider than that for the coordination bonds in a trigonal bipyramid molecular system for the Cl-Tt/Cl⋅⋅⋅Tt and N-Tt/N⋅⋅⋅Tt (Tt=C, Si, Ge) bonds in molecules and molecular complexes. The distinction between the weakened covalent and strengthened noncovalent bonds is well reflected in behaviour of the Fermi hole along the bond line. Two-factor empirical rule based on the superposition of the electrostatic and total static potentials is suggested.