Kinetic and mechanistic studies on the substitution of aqua ligands from diaquaethylenediamineplatinum(II) ion by vicinal dioximes

Abstract

Kinetics of aqua ligand substitution from diaquaethylenediamineplatinum(II) ion by three vicinal dioximes, namely dimethylglyoxime, 1,2-cyclohexanedione dioxime, and α-furil dioxime have been studied spectrophotometrically in the 40–55 °C temperature range. All the above substitution reactions have been monitored at 297, 298, and 314 nm where the differences in absorbances between the reactant and products are maximum. At pH 4.0, all the three reactions have been found to proceed via two distinct consecutive steps, i.e., it shows a non-linear dependence on the concentrations of ligands: first step is [ligand] dependent but the second step is [ligand] independent. The rate constants for the processes are k 1 ~ 10−3 and k 2 ~ 10−5 s−1. The activation parameters, calculated from Eyring plots, suggest an associative mechanism for the interaction processes. From the temperature dependence of the outer sphere association equilibrium constants (K E) for the first step, the thermodynamic parameters were also calculated, which gives a negative Δ $$ G_{ 1}^{0} $$ value at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex in the first step. The products of the reactions have been characterized with the help of Job’s method, IR and ESI–MS spectroscopic analysis.