Theoretical insight into the nature of the intermolecular charge-inverted hydrogen bond

The results of our further theoretical studies on the so-called charge-inverted hydrogen bond that is defined as an interaction between the partially negatively charged hydrogen atom of the X-H subunit and an atom possessing a lone pair vacancy are presented. It is shown that the elongation of the X-H bond and the red-shift of its stretching vibration frequency is caused by the charge transfer from the bonding sigma(XH) orbital to the empty p(z) orbital of the Y atom. The weakening of the X-H bond can also be reinforced by the small increase of the occupancy of the sigma(star)(XH) antibonding orbital. Based on quantum theory of atoms in molecules by Bader it is shown that the charge-inverted hydrogen bond is a closed-shell type interaction with significant contribution of covalent character. We found charge-inverted hydrogen bonds as a new type of interactions which are different than more common hydride or agostic-type interactions. (c) 2012 Elsevier B.V. All rights reserved.