Chemical effects in diffusion and structure of zinc chloride in aqueous solution

In the absence of neutron data, we have examined existing experimental data for X-ray, Raman scattering, EXAFS and thermodynamic activity studies in order to build up a consistent model of the structure of ZnCl₂ in aqueous solution in the range of molality from 2 up to saturation. The structure that emerges is that Zn is tetrahedrally coordinated and that in these coordination complexes the number of Cl ions per Zn ion increases with increasing molality, this implying the existence of extended Zn structures as the saturation concentration is approached. Relevant evidence in support of these structural models has been obtained by measuring the diffusion constants of Zn. Cl and H₂O when the stoichiometry of the solution is varied by replacing Zn by Li. This evidence strongly supports the model in which available Cl ions form complexes with Zn up to at least four Cl ions per Zn ion.