ELECTROCHEMISTRY AND HYDROLYSIS KINETICS OF 2,2'-BIPYRIDINE COMPLEXES OF IRON(3) AND IRON(2)

The electrochemistry and hydrolysis kinetics of the 2,2′-bipyridine (bipy) complexes of Fe(III) and Fe(II) have been studied by chronopotentiometry and cyclic voltammetry. The reduction of the brown, oxo-bridged Fe2(bipy)4O(H2O)24+ complex at prereduced gold and platinum electrodes is a one-electron, diffusion-controlled, irreversible process with an ana value of 0.46. Galvanostatic studies establish that the value of Et-0 for the complex shifts with pH and bipy concentration. The reduction product gives a reverse chronopotentiometric wave (at a potential 0.66 V anodic from the forward wave) which is due to the oxidation of the red Fe(bipy)32+ complex. The blue Fe(bipy)33+ complex is reduced at platinum and gold electrodes by a reversible, one-electron, diffusion-controlled process with a formal potential of +0.79 V vs. see which is independent of pH (pH 2-10) and of the concentration of bipy. The hydrolysis of Fe(bipy)33+ to Fe2(bipy)4O(H2O)24+ is first order in Fe(bipy)33+ and first order in base. The rate constants for three bases are: kH[H2O] = 8.4 X 10-5sec-1; Kbipy = 4.1 X 10-3 1. mol-1 sec-1; kOH- = 4.3 X 105 1. mol-1 sec-1. A mechanism consistent with the experimental data is proposed for the hydrolysis. The equilibrium constant for the hydrolysis reaction has an approximate value of 6 X 10-9 at low concentrations of bipy. © 1969, American Chemical Society. All rights reserved.