The synthesis and voltammetric exploration of water-soluble ruthenocene sulfonate is reported. H-1 and C-13 NMR, mass spectroscopy and elemental analysis data are given to confirm the successful synthesis of this novel compound. Furthermore, it is found that the cyclic voltammetric response is strongly dependent on the size of anion in solution. Sodium toluene sulfonate is found to be capable of forming a charge-transfer complex with the oxidized ruthenocenium ion. In the presence of all other anions, follow-on reactions are observed. (c) 2007 Elsevier B.V. All rights reserved.