Ion Ion Solvent Interactions in Solution .XI. Spectroscopic Studies of Group-2 Perchlorates in Acetone

Abstract

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.