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^–.