Σ-holes, π-holes and electrostatically-driven interactions

J Mol Model. 2012 Feb;18(2):541-8. doi: 10.1007/s00894-011-1089-1. Epub 2011 May 4.

Abstract

A positive π-hole is a region of positive electrostatic potential that is perpendicular to a portion of a molecular framework. It is the counterpart of a σ-hole, which is along the extension of a covalent bond to an atom. Both σ-holes and π-holes become more positive (a) in going from the lighter to the heavier atoms in a given Group of the periodic table, and (b) as the remainder of the molecule is more electron-withdrawing. Positive σ- and π-holes can interact in a highly directional manner with negative sites, e.g., the lone pairs of Lewis bases. In this work, the complexes of 13 π-hole-containing molecules with the nitrogen lone pairs of HCN and NH(3) have been characterized computationally using the MP2, M06-2X and B3PW91 procedures. While the electrostatic interaction is a major driving force in π-hole bonding, a gradation is found from weakly noncovalent to considerably stronger with possible indications of some degree of coordinate covalency.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Computer Simulation
  • Models, Molecular*
  • Static Electricity*