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

✍ Scribed by Hassan A. Ewais

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 357 KB
• Volume: 40
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20289

✦ Synopsis

Abstract

The mechanism of oxidation of ternary complexes, [Co^II^(nta)(S)(H~2~O)~2~]^3−^ and [Co^II^(nta)(M)(H~2~O)]^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 [IO~4~^−^] 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 [Co^II^(nta)(S)(H~2~O)(OH)]^4−^ and [Co^II^(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 [Co^II^(nta)(S)(H~2~O)~2~]^3−^, k~1~ (3.60 × 10^−3^ s^−1^), is greater than the value of k~6~ (1.54 × 10^−3^ s^−1^) for the oxidation of [Co^II^(nta)(M)(H~2~O)]^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