Abstract
The kinetics of the reactions between azido-pentacyanocobaltate(III), Co(CN)5N3 3−, and iron(II) polypyridyl complexes, Fe(LL)3 2+ (LL = bipy, phen), have been studied in both neutral and acidic aqueous solutions at I = 0.1 mol dm−3 NaCl. The reactions were carried out under pseudo-first-order conditions in which the concentration of Fe(LL)3 2+ was kept constant, and the second-order rate constants obtained for the reactions at 35 °C were within the range of 0.156–0.219 dm3 mol−1 s−1 for LL = bipy and 0.090–0.118 dm3 mol−1 s−1 for LL = phen. Activation parameters were measured for these systems. The dependence of reaction rates on acid was studied in the range [H+] = 0.001–0.008 mol dm−3. The reaction in acid medium shows interesting kinetics. Two reactive species were identified in acid medium, namely, the protonated cobalt complex and the azido-bridged binuclear complex. The electron-transfer process is proposed to go by mixed outer- and inner-sphere mechanisms in acid medium, in which electron transfer through the bridged inner-sphere complex (k 5) is slower than through the outer-sphere path (k 4).
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The authors wish to acknowledge the Organisation for the Prohibition of Chemical Weapons (OPCW) for the fund granted to carry out this research work at the University of Botswana, Gaborone, Botswana.
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Ogunlusi, G.O., Ige, J., Oyetunji, O.A. et al. Intermediate and ion-pair formation in the outer-sphere reactions between azido-pentacyanocobaltate(III) and iron(II) polypyridyl complexes in aqueous medium. Transition Met Chem 34, 483–491 (2009). https://doi.org/10.1007/s11243-009-9220-1
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DOI: https://doi.org/10.1007/s11243-009-9220-1