Ion–ion–solvent interactions in solution. Part 6.—Aqueous solutions of metal nitrates having cations with incomplete valence shells

Abstract

The Raman spectra of aqueous solutions of AgNO₃, TlNO₃, Zn(NO₃)₂, Cd(NO₃)₂, La(NO₃)₃ and Th(NO₃)₄ are analysed as a function of concentration. For all solutes, bands due to aquated-nitrate ions, solvent-separated ion pairs (outer-sphere complexes) and contact ion pairs (inner-sphere complexes) are reported. The nature of the inner-sphere complex leads to a distinctly different band from contact ion pairs for simple monovalent cations. This difference is interpreted in terms of an electron-exchange mechanism. The inner-sphere complexes are discernable at all concentrations studied. The association quotients compare favourably with values from other measurements for solutions of Zn(NO₃)₂ and Th(NO₃)₄.