Solutions of Mg(ClO4)2, Ca(ClO4)2 and Sr (ClO4)2 have been studied at a variety of concentrations up to saturation by means of infrared absorption, Raman scattering and multinuclear n.m.r. spectroscopy. For solutions of Mg(ClO4)2 there was little ion association up to saturation but for the other two salts association to both solvent shared anion- cation complexes and contact anion-cation complexes was identified. The nature of the association process was probed by using line broadening for the quadrupolar nuclei 17O, 35Cl and 43Ca . The extent of association to solvent shared anion-cation complexes was found to increase in the series Mg2+ < Ca2+ < Sr2+.

Solutions of Mg(ClO4)2 and Sr (ClO4)2 in acetone have been studied at various concentrations up to saturation by using infrared absorption, Raman scattering and multinuclear n.m.r (1H, 13C, 17O, 25Mg, 35Cl). Solvation numbers of c. 4.5 (Mg2+) and c. 5.5 (Sr2+) were determined from component band analysis of the c. 800 cm-1 acetone band in the Raman spectra. The solvent shell about the Mg2+ had a high level of steric crowding. There was a small amount of solvent-shared ion-pair formation at all oncentrations in solutions of Mg(ClO4)2 which showed little concentration dependence. In solutions of Sr (ClO4)2 there was evidence for the formation of both solvent-shared associated-ion species and ion-contact species. The solvent-shared species appeared to have two alternative configurations in one of which the anion was both polarized and highly hindered. There was a salt-promoted reaction in which the perchlorate was reduced to chloride and the solution darkened. This reaction prevented the use of Raman spectra to quantify the association equilibria.