Mechanism of electron transfer reaction of ternary nitrilotriacetatocobalt(II) complexes involving succinate and malonate as secondary ligands

Abstract

AbstractThe mechanism of oxidation of ternary complexes, [CoII(nta)(S)(H2O)2]3− and [CoII(nta)(M)(H2O)]3− (nta = nitrilotriacetate acid, S = succinate dianion, and M = malonate dianion), by periodate in aqueous medium has been studied spectrophotometrically over the (20.0–40.0) ± 0.1°C range. The reaction is first order with respect to both [IO4−] and the complex, and the rate decreases over the [H+] range (2.69–56.20) × 10−6 mol dm−3 in both cases. The experimental rate law is consistent with a mechanism in which both the hydroxy complexes [CoII(nta)(S)(H2O)(OH)]4− and [CoII(nta)(M)(OH)]4− are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant for the oxidation of the [CoII(nta)(S)(H2O)2]3−, k1 (3.60 × 10−3 s−1), is greater than the value of k6 (1.54 × 10−3 s−1) for the oxidation of [CoII(nta)(M)(H2O)]3− at 30.0 ± 0.1°C and I = 0.20 mol dm−3. The thermodynamic activation parameters have been calculated. It is assumed that electron transfer takes place via an inner‐sphere mechanism. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 103–113, 2008