Ab Initio Investigation of Tetrel Bonds in Isolated Complexes Formed Between a Lewis Acid H3MX, M-O or M-S (M = Si, Ge, or Sn) and the Lewis Bases B = N2, CO, HCCH, PH3, C2H4, HCN, CS, HNC, NP, H2O, and NH3.

Abstract

Isolated complexes of the type B⋯A in which the noncovalent interaction is a tetrel bond have been characterized by ab initio calculations at the CCSD(T)(F12c)/cc-pVDZ-F12 level. The Lewis bases B involved were N2, CO, HCCH, PH3, C2H4, HCN, CS, HNC, NP, H2O and NH3. Two types of Lewis acid A were examined, each containing one of the tetrel atoms M = Si, Ge or Sn, The Lewis acids in the first series were the H3MX (X = F, Cl, CN, H), in each of which the most electrophilic region was found to lie on the C3 axis of the C3v molecules, near to the tetrel atom M. In the second series the Lewis acids were M-O and M-S. Graphs, consisting of calculated equilibrium dissociation energies De of each B⋯H3MX complex plotted against the nucleophilicities NB of the Lewis bases B, were used to obtain the electrophilicity EH3MX of each molecule H3MX (M = Si, Ge, Sn). The molecular electrostatic surface of potentials of the molecules M-S and M-O (M = Si, Ge, Sn) revealed that many of the B⋯M-S and B⋯M-O complexes should have a tetrel bond to M in which the axis of the M-S or M-O subunit should be approximately perpendicular to the axis of the nonbonding or π-bonding electron pair carried by B, a novel type of tetrel bond confirmed by geometry optimizations of the complexes.