The Reactivity of vic-dioximes Towards the [(H2O)(tap)2RuORu(tap)2(H2O)]2+ Ion {tap = 2-(m-tolylazo)pyridine} at Physiological pH

Abstract

Kinetics of aqua ligand substitution from [(H2O)(tap)2RuORu(tap)2(H2O)]2+ {tap = 2-(m-tolylazo)pyridine}, by three vicinal dioximes, namely dimethylglyoxime (L1H), 1,2-cyclohexanedione dioxime (L2H) and α-furil dioxime (L3H), have been studied spectrophotometrically in the 35–50 °C temperature range. The reaction was monitored at 560 nm where the absorbance between the reactant and product is at a maximum. At pH 7.4, the reaction has been found to proceed via two distinct consecutive steps, i.e., it shows a non-linear dependence on the concentration of ligands: the first process is [ligand] dependent but the second step is [ligand] independent. The rate constants for the processes are: k 1 ~ 10−3 s−1 and k 2 ~ 10−4 s−1. The activation parameters, calculated from Eyring plots, suggest an associative mechanism for the interaction process. From the temperature dependence of the outer sphere association equilibrium constants, the thermodynamic parameters were also calculated, which give negative ΔG° values at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex. The product of the reaction has been characterized with the help of IR and ESI-mass spectroscopic analysis.