Electron transfer mechanism for the oxidation of ternary N-(2-acetamido)iminodiacetatocobaltate(II) complexes involving succinate and maleate as secondary ligands by periodate

Abstract

The kinetics of oxidation of the ternary complexes [CoII(ADA)(Su)(H2O)]2− and [CoII(ADA)(Ma)(H2O)]2− (ADA = N-(2-acetamido)iminodiacetate, Su = succinate and Ma = maleate) by periodate have been investigated spectrophotometrically at 580 nm under pseudo-first-order conditions in aqueous medium over 30–50 °C range, pH 3.72–4.99, and I = 0.2 mol dm−3. The kinetics of the oxidation of [CoII(ADA)(Su)(H2O)]2− obeyed the rate law d[CoIII]/dt = [CoII(ADA)(Su)(H2O)]2−[H5IO6] {k4K5 + (k5K6K2/[H+)}, and the kinetics oxidation of [CoII(ADA)(Ma)(H2O)]2− obeyed the rate law d[CoIII]/dt = k1K2[CoII]T[IVII]T/{1 + ([H+]/K7) + K2[IVII]T}. The pseudo-first-order rate constant, kobs, increased with increasing pH, indicating that the hydroxo form of maleate complex, [CoII(ADA)(Ma)(OH)]3−, is the reactive species. The initial Co(III) products were slowly converted to the final products, fitting an inner-sphere mechanism. Thermodynamic activation parameters were calculated using the transition state theory equation. The initial cobalt(II) complexes were characterized by physicochemical and spectroscopic methods.