Two di-nickel complexes based on bis(salen) ligands are investigated by electrochemical and NMR techniques with respect to determination of their diffusion coefficients D and the number n of electrons involved in oxidation in organic electrolytes and at a Pt electrode. It is shown that in both cases the oxidation involves two electrons despite the appearance of the cyclic voltammograms which can not easily be distinguished from those of a one-electron process. The difference of the formal potentials of the two electron transfer processes is determined by simulation of the experimental cyclic voltammograms, and found to be below 60 mV. (C) 2016 Elsevier B.V. All rights reserved.