Reduction of the Adipato-Bridged Binuclear Iron(III) Complex, [(Fesalen)2adi] by Thioglycolic Acid: Kinetic and Mechanistic Study

Abstract

Reduction of the binuclear iron(III) complex ion, [(Fesalen)2adi] by β-mercaptoacetic acid was studied spectropotometrically at 495 nm. Kinetic runs were obtained at 302 K, under pseudofirst order conditions of a large excess of the reductant over the oxidant. At constant ionic strength, pseudo-first order rate constants increased with increase in concentration of the reductant and second rate constanst were fairly invariant at 4.67×10-2±0.017 dm3 mol-1s-1. Within the acid concentration 0.001≤[H+]≤0.15 mol dm-3 the rate of reaction increased with [H+]. The results are consistent with the general rate law: -d[Fe₂adiH]/dt = (? + m[?^– ])[??₂?][???]. Rate constant was not altered on varying ionic strength and dielectric constant of the reaction media.Addition of the small amounts of Mg²⁺ and CH₃COO^– did not affect the rate of reaction. Least square fits of Michaelis-Menten type plot of 1/k_obs versus. 1/[Red] was linear with intercept and analysis of products of reaction inferred formation of iron(III) and disulfides as products. The results point to plausible inner-sphere electron transfer path for the reduction of the iron(III) complex.