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 σ 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 σ 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.