Partial molar compressibilities of halogeno complexes of platinum and palladium in aqueous solutions at 25 degrees C

Ultrasonic propagation velocities were measured at 25 degrees C for dilute aqueous solutions of K-2[PtX4], K-2[PtX6], K-2[PdX4], and K-2[PdX6] (X = Cl, Br, or SCN). The data obtained were combined with our previous density data to calculate the adiabatic compressibilities of each solution. Then, the infinite dilution values of partial molar adiabatic compressibilities K-s(o) were evaluated. By subtraction of the K-S(o) (K+) from those of the complexes, the values of K-S(o) for the halogeno complex ions [PtX4](2-), [PtX6](2-), [PdX4](2-) and [PdX6](2-) were determined. The values for the thiocyano complex ions [Pt(SCN)(4)](2-) and [Pt(SCN)(6)](2-) are positive, showing that the interaction of the ligand SCN- with the solvent water is very weak. Although the V-2(o) behavior of the complex ions [PtCl6](2-) and [PdCl6](2-) differed only slightly, compressibility measurement has indicated that the ion [PdCl6](2-) interacts more strongly than [PtCl6](2-).