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Kinetic and mechanistic studies on the electron-transfer reactions between diaquabisethylenediaminecobalt(III) and ethylenediaminetetraacetatocobaltate(III) with promazine in acidic aqueous media

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Abstract

The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en)2(H2O)2]3+ in CF3SO3H solution ([CoIII] = (2–6) × 10−3 m, [ptz] = 2.5 × 10−4 m, [H+] = 0.02 − 0.05 m, I = 0.1 m (H+, K+, CF3SO 3 ), T = 288–308 K) and [Co(edta)] in aqueous HCl ([CoIII] = (1 − 4) × 10−3 m, [ptz] = 1 × 10−4 m, [H+] = 0.1 − 0.5 m, I = 1.0 m (H+, Na+, Cl), T = 313 − 333 K) were studied under the condition of excess CoIII using u.v.–vis. spectroscopy. The reactions produce a CoII species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k obs) on [CoIII] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en)2(H2O)2]3+ ion was found to be independent of [H+]. In the case of the [Co(edta)] ion, the k obs dependence on [H+] was linear and the increasing [H+] accelerates the rate of the outer-sphere electron-transfer reaction. The activation parameters were calculated as follows: ΔH = 105 ± 4 kJ mol−1, ΔS = 93 ± 11 J K−1mol−1 for [Co(en)2(H2O)2]3+; ΔH = 67 ± 9 kJ mol−1, ΔS = − 54 ± 28 J K−1mol−1 for [Co(edta)].

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Correspondence to Joanna Wiśniewska.

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Wiśniewska, J. Kinetic and mechanistic studies on the electron-transfer reactions between diaquabisethylenediaminecobalt(III) and ethylenediaminetetraacetatocobaltate(III) with promazine in acidic aqueous media. Transition Met Chem 32, 811–815 (2007). https://doi.org/10.1007/s11243-007-0258-7

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Keywords

  • Hedta
  • Observe Rate Constant
  • Promazine
  • Aqua Ligand
  • Phenothiazine Derivative