Ion-ion-solvent interactions in solution. I. Solutions of LiClO₄ in acetone

Abstract

Vibrational spectra and ⁷Li, ¹³C and ³⁵Cl n.m.r. spectra have been obtained for solutions of LiClO₄ in acetone for salt concentrations from 0.05 to 6 M. Infrared spectra give qualitative indications of ion association. Analysis of the Raman band due to C-C stretching in acetone yields solvation numbers for the Li⁺ ion of the order of 3. Component band analysis of the ClO₄^- symmetric stretching vibrational band and the various n.m.r. spectra lead to the identification of solvent-separated ion pairs, contact ion pairs and ion aggregates, in addition to free solvated ions. The dependence on salt concentration of all four species has been determined. The association quotient for the association equilibrium

(Li⁺)_s(ClO₄)^- ↔ [Li+(acetone)ClO₄^-)_s

was determined to be 1.4 ± 0.3 dm³ mol^-1.