{\sigma}/{\pi} character of H-bonding in water clusters

TL;DR

This paper investigates the dual {}/{} character of hydrogen bonds in water clusters, highlighting the previously overlooked  component and its role in collective effects within H-bond networks.

Contribution

It introduces the concept of -kind binding in water clusters, emphasizing the importance of  contributions from overlapping pre-lone pair orbitals, which was not considered before.

Findings

Identification of -character in water H-bonds.

Analysis of magnetic shielding tensors reveals electron density peculiarities.

Cluster orbital shapes illustrate the  contribution to H-bonding.

Abstract

Hydrogen bonds are typically treated as sufficiently localized directional intermolecular bonds, in which dispersion and electrostatic contributions can be distinguished. However, being formed chiefly due to the overlapping of p orbitals of electronegative atoms, the corresponding electronic bonds are characterized by both {\sigma}- and {\pi}-kind binding, the former determining the directionality of bonds, while the latter, the coupling of molecules and the collective effects in H-bond networks. The latter contribution was never considered previously and is predetermined by overlapping pre-lone pair orbitals of oxygen atoms. This is manifested in the peculiarities of the electron density distribution, which are quantified based on the analysis of magnetic shielding tensors of oxygen and bridge hydrogen nuclei and illustrated by the shapes of cluster orbitals of water aggregates.