N.m.r. study of the solvation sphere of the Mg2+ ion in acetone + water solutions of magnesium perchlorate

Abstract

At temperatures below about 200 K, separate proton n.m.r. peaks have been observed for six hydrated forms of the magnesium ion dissolved in a mixed acetone + water solvent; the monohydrate peak is observed at lowest field and the hexahydrate peak at highest field. A “free” water peak is observed at still higher field. The resonances from “free” and “bound” acetone were also observed in certain solutions. The intensities and the temperature-dependence of the intensities of the peaks yield semiquantitative estimates of thermodynamic parameters for the individual steps in the hydration of magnesium ions. The spectral evidence indicates ion pair formation of Mg²⁺ with one perchlorate anion when little water is present.