Microstructure and species distribution of aqueous zinc chloride solutions: results from Monte Carlo simulations

Abstract

Monte Carlo simulation results are reported for 1–5 mol kg^–1 aqueous zinc chloride solutions and compared to experimental data. The structural data from the simulations indicate the formation of ZnCl^(2–n)–_n complexes with n_max= 2, in contrast to the stronger CuCl^(2–n)–_n complexes observed up to n= 4. Besides these ‘contact ion pair’ complexes, solvent-separated (‘outer-sphere’) complexes are found, co-determining the physico-chemical properties of ZnCl₂ solutions. Formation constants for the ZnCl⁺ and ZnCl₂ species could be evaluated from the simulations. Structural details of the complexes are visualized by ligand distribution plots, showing a breakdown of the order of the hydration structure at salt concentrations of ca. 5 mol kg^–1, and a trans-conformation of the species ZnCl₂(H₂O)₄.