Studies in nickel(IV) chemistry. Electron transfer kinetics of the reaction between tris(dimethylglyoximato)nickelate(IV) and hexacyanoferrate(II) in aqueous medium

Abstract

The kinetics of electron transfer from hexacyanoferrate(I1) to tris(dimethylg1yoximato) -nickelate(IV), Ni(dmg)g-, to produce Fe(CN)t-and Ni(dmgH)2, follows a pseudo-first-order disappearance in the Ni(1V). The pseudo-first-order rate constants hob8 are linearly dependent on [Fe(CN);-]o in a fiftyfold range of 2 X 10-4-1 X 10-2M, and the average values of k,bl[Fe(CN){-]o range from 194M-'-s-' at pH = 5.20 to 0.2M-'-s-' at pH = 9.07 in aqueous medium at 35°C and fi = 0.57M. Results are interpreted in terms of a probable mechanism involving rate-determining outer sphere one-electron transfer steps from the reductant and one-protonated reductant species to the unprotonated and one-protonated Ni(1V) species present in solution. The more electrophilic one-protonated reductant species apparently reacts several orders of magnitude faster than the unprotonated one.