Electrochemistry of the tris(2,2′-bipyridine) complex of iron(II) in ionic liquids and aprotic molecular solvents

In this work, the electrochemistry of the tris(2,2'-bipyridine) complex of iron(II) was investigated, in order to develop a better understanding of the behaviour of this complex. Two ionic liquids (ILs), based on the 1-ethyl-3-methylimidazolium cation and two ILs based on the 1-butyl-1-methylpyrrolidinium cation, as well as three conventional aprotic solvents were used. The semi-integral electroanalysis was used to aid the interpretation of the results. The iron(II) complex presented a reversible oxidation reaction and three reduction reactions, which are normally considered to be reversible, however our results demonstrate that this is not always the case, with the reversibility of the reactions being highly dependent on the solvent used. A novel method for synthesising iron(III) tris(2,2'-bipyridine) is reported, and mixtures of the iron(II) and iron(III) complexes were used to determine the standard rate constants of the oxidation reaction. The long term stability of solutions of the iron(III) complex is also studied in this work, which is very important for possible electrochemical applications of this complex, such as in battery electrolytes. (C) 2016 Elsevier Ltd. All rights reserved.