The hydration state of HO${}^{-}$(aq)

Abstract

The HO${}^{-}$(aq) ion participates in myriad aqueous phase chemical processes of biological and chemical interest. A molecularly valid description of its hydration state, currently poorly understood, is a natural prerequisite to modeling chemical transformations involving HO${}^{-}$(aq). Here it is shown that the statistical mechanical quasi-chemical theory of solutions predicts that $\mathrm{HO}\cdot [{\mathrm{H}}_2\mathrm{O}{]}_3{}^{-}$ is the dominant inner shell coordination structure for HO${}^{-}$(aq) under standard conditions. Experimental observations and other theoretical calculations are adduced to support this conclusion. Hydration free energies of neutral combinations of simple cations with HO${}^{-}$(aq) are evaluated and agree well with experimental values.

10 pages, 1 figure