The electrochemical behavior of FeCP2+/FeCp2 (Cp-, cyclopentadienyl), FeCl4-/FeCl42-, FeBr4-/FeBr42- 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 BMPTFS1 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. (c) 2006 Elsevier Ltd. All rights reserved.