Unexpected water-hydroxide ion structure and diffusion behavior in low hydration media

TL;DR

This study reveals that in low hydration environments, hydroxide ions form water-bridged double-hydroxide clusters, which differ from known structures and influence their diffusion behavior.

Contribution

It is the first computational investigation of hydroxide ions in low hydration media, uncovering unique double-hydroxide structures and their impact on diffusion.

Findings

Hydroxide ions form water-bridged double-hydroxide clusters in low hydration conditions.

These clusters disrupt hydrogen bonding networks, affecting ion diffusion.

Double-hydroxide structures increase ionic strength and alter diffusion behavior.

Abstract

Hydroxide ion transport and structure in aqueous media is fundamental to many chemical and biological processes. Research on hydroxide behavior has primarily focused on a single fully solvated hydroxide, either as an isolated cluster or in the bulk. This work presents the first computational study to consider a medium of low hydration levels where the hydroxide ion is microsolvated. Under such conditions, hydroxide ions are shown to be predominantly present as unique water-bridged double-hydroxide charged clusters, distinct from previously reported structures under hydrated conditions. Although layered double hydroxides were reported in the crystalline state, this is the first time to be seen in the disordered liquid state. These newly observed double-hydroxide structures presumably disrupt the hydrogen bonded network required for structural diffusion of hydroxide ions through water. These ion complexes have a higher ionic strength which may explain the unexpected diffusion behavior in comparison to the single hydroxide-water complex.