Solvation and ion association in solutions containing oxyanions

Abstract

Ion solvation and association behaviour has been studied for solutions of lithium perchlorate and lithium nitrate in N,N-dimethylformamide (DMF) methanol and ethanol. The techniques of Raman spectroscopy and multinuclear n.m.r. have been employed, and in some studies the cation has been caged in the cryptand Kryptofix 221. Solvation in DMF was examined through quantitative analysis of the OCN bending vibrational band of the DMF in the Raman spectra. A range of univalent and divalent cations was employed and solvation numbers and some information on solvation geometries were obtained. In alcohol solutions determination of solvation numbers was not possible but the involvement of Li⁺ and NO^–₃ produced observable spectroscopic changes, while the ClO^–₄ anion appeared to have only a weak solvation. Evidence for at least two associated species was obtained for both salts in DMF and ethanol and the concentration dependence of the species was determined. In methanol association was much less with the behaviour approaching that observed in aqueous solution.