Partial molar volumes of hologeno complexes of platinum and palladium in aqueous solutions and differences in volume between tetra- and hexa-coordinated forms

Abstract

The partial molar volumes of dilute aqueous solutions of K2[PtX4], K2[PtX6], K2[PdX4] and K2[PdX6] complexes (X = Cl, Br or SCN), have been determined from density data measured at 298.15 K. The values of V02(K2[MX4]) and V02(K2[MX6]) can be predicted roughly by combining, respectively, the V02 values for K2[MCl4] and K2[MCl6] and the difference between V02(MX) and V02(KCl). Platinum and palladium complexes have quite similar V02, but the V02 values for the latter are larger by 1.7–1.9 cm3 mol–1 than those for the former. The increase of V02 with change of coordination number from four to six was compared for the ions Cl–, Br– and SCN–. For the hard ion, Cl–, the degree of volume increase was much smaller than for the soft ions Br– and SCN–.