Electrochemical behavior of several iron complexes in hydrophobic room-temperature ionic liquids

The electrochemical behavior of FeCp₂⁺/FeCp₂ (Cp^-, cyclopentadienyl), FeCl₄^-/FeCl₄^2-, FeBr₄^-/FeBr₄^2- and Fe(CN)₆^3-/Fe(CN)₆^4- couples was studied in the hydrophobic room-temperature ionic liquids based on bis(trifluoromethylsulfonyl)imide (TFSI^-) with 1-n-butyl-1-methylpyrrolidinium (BMP⁺) and other quaternary ammonium cations. The cyclic voltammetric data indicated that these complexes were stable in BMPTFSI and that the redox reactions between trivalent and divalent iron species of these complexes are electrochemically reversible. The diffusion coefficients of these complexes were found to be affected mainly by the size of the species. On the other hand, the redox potential of Fe(CN)₆^3-/Fe(CN)₆^4- couple depended on organic cations reflecting the difference in the acceptor properties of the organic cations.