The effect of solvents on the equilibrium MX 4 2− + Y − ⇋ MYX 3 2− + X −, where M = Cd 2+ or Hg 2+ and X and Y = Cl −, Br −, I −, or CN −, has been studied by quantitative Raman spectrophotometry. This technique, employing LiClO 4 as internal reference, permits the direct determination of the decrease in concentration of the tetrahedral MX 4 2− due to the formation of MYX 3 2−. The fraction [1 − α( MX 4 2−)] is thus a direct measure of the solvent effect on the mixed complex stability. It is shown that bulk solvent properties are not relevant, and only solvent molecules in the immediate vicinity of the anionic complex have an effect on its stability. Selective solvation in this second coordination sphere is exhibited by several solvents, and water is not always the preferred solvent.