Mechanism of electron transfer reaction of ternary nitrilotriacetatocobalt(II) complexes involving succinate and malonate as secondary ligands |
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| Authors: | Hassan A Ewais |
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| Institution: | Chemistry Department, Faculty of Science, Beni‐Suef University, Beni‐Suef City, Egypt |
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| Abstract: | The 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 |
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