Polarization-induced σ-holes and hydrogen bonding

Abstract

The strong collinear polarizability of the A-H bond in A-H···B hydrogen bonds is shown to lead to an enhanced σ-hole on the donor hydrogen atom and hence to stronger hydrogen bonding. This effect helps to explain the directionality of hydrogen bonds, the well known cooperative effect in hydrogen bonding, and the occurrence of blue-shifting. The latter results when significant additional electron density is shifted into the A-H bonding region by the polarization effect. The shift in the A-H stretching frequency is shown to depend essentially linearly on the calculated atomic charge on the donor hydrogen for all donors in which A belongs to the same row of the periodic table. A further result of the polarization effect, which is also expected for other σ-hole bonds, is that the strength of the non-covalent interaction depends strongly on external electric fields.

Intuitive and counterintuitive noncovalent interactions of aromatic π regions with the hydrogen and the nitrogen of HCN

“…A good illustration of the importance of polarization was provided by Hennemann et al [55], who showed that the V S,max of a hydrogen in the water molecule could be increased from its ground state value of 57 kcal/mol to 75 kcal/mol just by putting a point charge of −0.4 at a distance of 1.9 Å from the hydrogen, and could be decreased to 38 kcal/mol by putting a point charge of +0.4 at the same distance. A very graphic demonstration of the role of polarization can also be had by looking at plots showing the difference between the electronic density of a complex and those of the components prior to interaction [56][57][58].…”

Electron density Laplacian and halogen bonds

“…[7][8][9] for typical examples) as well as by multifarious theoretical approaches [10]: molecular orbitals analysis [11], energetic decompositions [12], conceptual DFT [13,14], Bader's atoms-in-molecules (QTAIM) theory [15][16][17][18], etc., each of them conveying complementary insight to unravel their physical nature. Among them, the σ-hole concept [19][20][21][22][23][24], forged and developed by Politzer and coworkers, has achieved a high popularity, owing to its simplicity, its versatility and its ubiquity (since it is also at work in other non-covalent bonds like pnicogen and carbon bonds), and it has clearly represented a considerable breakthrough for the understanding of these non-conventional interactions.Let us recall that the σ-hole is plainly defined as a region of positive molecular electrostatic potential (MEP) on the outer side of the halogen atom. This space region is thus prone to interact with the lone electron pair(s) carried by the partner.…”

The electronic mechanism ruling the dihydrogen bonds and halogen bonds in weakly bound systems of H3SiH···HOX and H3SiH···XOH (X = F, Cl, and Br)

“…In a matter of fact, the analysis of the molecular electrostatic potential (MEP) [70,[74][75][76] delineates the preferential interaction sites upon the formation of the H 3 SiH•••XOH and H 3 SiH•••HOX complexes. Figure 4 outlines the MEP graphs of H 3 SiH and HOF monomers as well as of I and IV complexes.…”