The hydrolysis products of cis-diamminedichloroplatinum(II). I. The kinetics of formation and anation of the cis-diammine(aqua)chloroplatinum(II) cation in acidic aqueous solution

Abstract

The rate of loss of the first chloro ligand ( k 1) from cis-PtCl 2(NH 3) 2, to give an equilibrium cis-PtCl 2-(NH 3) 2, cis-PtCl(NH 3) 2(OH 2) + and Cl − mixture, has been measured spectrophotometrically in 0.1 M HClO 4, 1.0 MHClO 4 and 0.1 M HClO 4 plus 0.9 M NaClO 4 over a 22 °C temperature range. The absorbance versus time data were analysed in terms of first-order kinetics and the effect of [H +] and ionic strength (μ) in the above range, is small. At 25 °C (μ=1.0 M, HClO 4) kinetic parameters are k 1= 6.32 × 10 −5 s −1, E a=84.7±1.9 kJ mol −1, ΔS #= −49.4 ± 3 J K −1 mol −1. Removal of the released Cl − from the equilibrium solution (0.1 M HClO 4) by anion exchange chromatography with the resin in the ClO 4 − form gives a solution containing about 90% cis-PtCI(NH 3) 2(OH 2) +. Addition of known amounts of Cl − (as NaCl in HClO 4) to this solution allows a spectrophotometric measurement of the rate of the anation reaction ( k −1) to give a new equilibrium solution. At 25 °C (μ=1.0 M; NaCl, HClO 4), k −1= 6.26 × 10 −3 M −1 s −1, E a=77.2 ± 1.5 kJ mol −1 and δS #= −36.3 ± 3 J K −1 mol −1. A knowledge of the forward and reverse rate constants allows calculation of the equilibrium constant ( K 1) and from the variation of K 1 with temperature, Δ H° can be estimated. At 25 °C (μ=1.0 M) K 1=1.01 × 10 −2 and ΔH° for the endothermic forward reaction is +7.5 kJ mol −1