The electrochemical oxidation of osmocenewas investigated in dichloromethane (DCM) and acetonitrile (MeCN) in the presence of various electrolyte anions ([BF4] , [PF6] , and [B(C6F5)(4)] (TFAB)). The results showed that the reactivity of the electrogenerated osmocenium cation was dramatically affected by the coordinating properties of the electrolyte anion and the donor strength of the solvent. Cyclic voltammetry allowed the characterization of transient species and led to rationalization of some controversial mechanistic conclusions published before, which were in fact all correct, but referred to different conditions. Notably, the electrochemical signature of the dimer dication [Cp2Os](2)(2+) that appears as a crucial species to explain the voltammetric oxidative pattern of osmocene was detected for the first time. (C) 2016 Elsevier Ltd. All rights reserved.