Variation of sigma-hole magnitude with M valence electron population in MXnY4−n molecules (n = 1–4; M = C, Si, Ge; X, Y = F, Cl, Br)

Abstract

Sigma holes are described as electron-deficient regions on atoms, particularly along the extension of covalent bonds, due to non-uniform electron density distribution on the surface of these atoms. A computational study of MX_nY_4−n molecules (n = 1–4; M = C, Si, Ge; X, Y = F, Cl, Br) was undertaken and it is shown that the relative sigma hole potentials on M due to X–M and Y–M can be adequately explained in terms of the variation in the valence electron population of the central M atom. A model is proposed for the depletion of the M valence electron population which explains the trends in sigma hole strengths, especially those that cannot be accounted for solely on the basis of relative electronegativities.