Kinetics and mechanism of the reduction of μ-adi-di[N,N′-bis{salicylideneethylenediaminatoiron(III)}] by dithionate ion

Abstract

The kinetics and mechanism of the reduction of the μ-adi-di[N,N′-bis{salicylideneethylenediaminatoiron(III)}] complex, [Fe2adi], by dithionate ion, S2O62−, have been investigated in aqueous perchloric acid at 29 °C, I = 0.05 mol dm−3 (NaClO4) and [H+] = 5.0 × 10−3 mol dm−3. Spectrophotometric titrations indicated that one mole of the reductant was oxidized per mole of oxidant. Kinetic profiles indicated first-order rate with respect to [Fe2adi] but zeroth-order dependence on [S2O62−]. The rate of reaction increased with increase in [H+], decreased with increased dielectric constant, but was invariant to changes in ionic strength of the medium. Addition of small amounts of AcO− and Mg2+ ions did not catalyse the reaction. A least-squares fit of rate against [H+]2 was linear (r2 = 0.984) without intercept. The reaction was analysed on the basis of a proton-coupled outer-sphere electron transfer mechanism.