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

The reactions of Fe(CN) 5 dpa 3− and Ru(NH 3 ) 5 dpa 2+ (dpa = 4,4′‐dipyridylamine) with Co(edta) − have been investigated kinetically. For Fe(CN) 5 dpa 3− 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 −1 S −1 at T = 25°C., μ = 0.10 M and pH = 8.0. For the Ru(NH 3 ) 5 dpa 2+ system, the plots k obs 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(NH 3 ) 5 dpa 2+ and Co(edta) − followed by electron transfer from Ru(II) to Co(III). The nonlinear least squares fit of the kinetic results shows that Q ip = 10.6 ± 0.7 M −1 and k et = 93.9 ± 0.7 s −1 at p H = 8.0,μ = 0.10 M and T = 25°C.