Atoms in molecules theory, electrostatic potential surface and frontier molecular orbital analyses on water multimers and pyridine – Water hydrogen bonded complexes

Abstract

Atoms in molecules theory, electrostatic potential surface and frontier molecular orbital analyses have been carried out on water multimers and their H – bonded complexes with pyridine (Py). The electron density ρr/Laplacian of electron density ∇2ρr values at the bond critical points (BCPs) of the classical/non-classical hydrogen bonds between water and Py exceed/subceed the proposed range of literature values. Based on the literature reports, the criteria for weak and medium H – bonds have been proposed. The ∇2ρr values indicate that the covalent character of the donor O-H bonds decrease/increase upon classical O-H⋯N/ non-classical O-H⋯π H – bonds. The electrostatic potential analysis shows that the nucleophilic nature of oxygen atoms becomes weaker with increase of multimer order. The bonding orbitals of the classical H – bonded Py – water complexes suffer severe change while that of the non-classical H – bonded complexes exactly resembles the Py monomer bonding orbitals.