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 N(2), CO, HCCH, PH(3), C(2)H(4), HCN, CS, HNC, NP, H(2)O and NH(3). 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 H(3)MX (X = F, Cl, CN, H), in each of which the most electrophilic region was found to lie on the C(3) axis of the C(3v) 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 D(e) of each B⋯H(3)MX complex plotted against the nucleophilicities N(B) of the Lewis bases B, were used to obtain the electrophilicity E(H3MX) of each molecule H(3)MX (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.