Kinetics of the Reductions of (Ethylenediaminetetraacetato)cobaltate(III) by 4,4‐Dipyridylamine Complexes of Pentacyanoferrate(II) and Pentaammineruthenium(II)

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The reactions of Fe(CN)5dpa3− and Ru(NH3)5dpa2+ (dpa = 4,4′‐dipyridylamine) with Co(edta)− have been investigated kinetically. For Fe(CN)5dpa3− complex, a linear relationship was observed between the pseudo‐First‐order rate constants and the concentrations of Co(edta) which leads to a specific rate 0.876 ± 0.006 M−1S−1 at T = 25°C., μ = 0.10 M and pH = 8.0. For the Ru(NH3)5dpa2+ system, the plots kobs vs [Co(edta)−] become nonlinear at concentrations of Co(edta) greater than 0.01 M and the reaction is interpreted on the basis of a mechanism involving the formation of an ion pair between Ru(NH3)5dpa2+ and Co(edta)− followed by electron transfer from Ru(II) to Co(III). The nonlinear least squares fit of the kinetic results shows that Qip = 10.6 ± 0.7 M−1 and ket = 93.9 ± 0.7 s−1 at pH = 8.0,μ = 0.10 M and T = 25°C.