Delocalization indices for non-covalent interaction: Hydrogen and DiHydrogen bond

Delocalization indices (DI) can be considered a measure of the electron-pair sharing between two atoms. As these indices are related to the polarity of the bond, they can be used to classify hydrogen bonds (and dihydrogen bonds) from weak to strong ones. Correlations between structural, energetic and topological parameters are tested for a set of complexes with Hydrogen and Dihydrogen bonds. From energy decomposition scheme, the linear relationship between delocalization indices and orbital interaction energy reveals that the covalent contribution to the interaction energy is directly proportional to the number of electrons shared between the X and H atoms. Using topological parameters, definition of DI values will help to clarify the nature of HB as covalent or closed-shell interaction. Polarity of atoms linked to hydrogen in dihydrogen bonded complexes play an important role on the H2 formation. Delocalization indices are helping in the understanding the H⋯H bond in these potential H2 storage models.