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 σXH orbital to the empty pz 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 σXH★ 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.

Highlights► Charge-inverted hydrogen bonds Xδ+-Hδ-⋯Y are investigated by means of NBO and QTAIM. ► A significant charge transfer from σXH to empty pz (=LP) orbital of Y is found. ► CIHBs are found to possess closed-shell character with significantly covalent contribution. ► CIHB are found to be distinct than either hydride or agostic-type interaction. ► CIHB should be treated as a new and individual type of interaction.