Kinetic studies of tris(2,2′-bipyridine)iron(III) perchlorate with cobaloxime, [Co(dmgBF 2) 2(H 2O) 2

Abstract

The kinetics of the reduction of Fe ( bipy ) 3 3 + by Co(dmgBF 2) 2(H 2O) 2 in 0.041 M HNO 3/NaNO 3 was found to be first-order in both the oxidizing and reducing agents and the second-order rate constant is given by k obs = k 1 + k 2 K[Cl −], with k 1=1.59 × 10 6 M −1 s −1and k 2 K = 1.83 × 10 8 M −2 s −1, at 25 °C. The term that is first-order in [Cl −] is attributed to the formation of an ion-pair between Fe ( bipy ) 3 3 + and Cl −. For k 1, the activation parameters Δ H* and Δ S* are 2.22 ± 0.02 kcal mol −1 and −22.7 ± 0.8 cal mol −1 K −1, respectively. The self-exchange rate constant of k 22 ≈ 8.7 × 10 −3 M −1 s −1 for Co ( dmgBF 2 ) 2 ( H 2 O ) 2 + / 0 was estimated using Marcus theory and the known self-exchange rate constant for Fe ( bipy ) 3 3 + / 2 + .