Exploring hydride-π interactions and their tuning by σ-hole bonds: an ab initio study

In the present work, ab initio calculations are performed to investigate the geometry, interaction energy and bonding properties of binary complexes formed between metal-hydrides HMX (M = Be, Mg, Zn and X = H, F, CH3) and a series of pi-acidic heteroaromatic rings. In all the resulting complexes, the heteroaromatic ring acts as a Lewis acid (electron acceptor), while the H atom of the HMX molecule acts as a Lewis base (electron donor). The nature of this interaction, called 'hydride-pi' interaction, is explored in terms of molecular electrostatic potential, non-covalent interaction, quantum theory of atoms in molecules and natural bond orbital analyses. The results show that the interaction energies of these hydride-pi interactions are between -1.24 and -2.72 kcal/mol. Furthermore, mutual influence between the hydride-pi and halogen- or pnicogen-bonding interactions is studied in complexes in which these interactions coexist. For a given pi-acidic ring, the formation of the pnicogen-bonding induces a larger enhancing effect on the strength of hydride-pi bond than the halogen-bonding.