Novel features associated with the electrochemically driven bis(η5-pentaphenylcyclopentadienyl)iron(II)-iron(III) redox transformation at an electrode-microcrystal-solvent (electrolyte) interface

Alan M. Bond, Axel Lamprecht, Vanda Tedesco, Frank Marken

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Electrochemical oxidation of microcrystals of the iron(II) compound, Fe(η5-C5Ph5)2 and reduction of the corresponding iron(III) [Fe(η5-C5Ph5)2]BF4 salt, mechanically attached to graphite and gold electrodes placed in aqueous media and in a (70:30) water:acetonitrile solvent mixture containing electrolyte has been investigated by voltammetric, electrochemical quartz crystal microbalance, and micro-analytical techniques. When interconversion of Fe(η5-C5Ph5)2 to [Fe(η5-C5Ph5)2]X (X-=ClO4-, BF4-, Cl-, F-) and vice versa occurs at the microcrystal-electrode-aqueous electrolyte interface via redox cycling of the electrode potential, then the reaction can be summarised by the process[Fe(η5-C5Ph5)2] +[X-](solid)+e-⇌Fe(η 5-C5Ph5)2(solid)+X- (solution)However, when CH3CN (in aqueous 0.1 M NaClO4) is present at the interface, data obtained are consistent with co-insertion of the organic solvent into the structure to give formally the [Fe(η5-C5Ph5)2] 1+/0.5+/0(solid) redox system containing interacting iron atoms in the solid structure. The formation of the new phase is voltammetrically associated with the conversion from the single chemically reversible one electron [Fe(η5-C5Ph5)2]+/0 process with a large separation in reduction and oxidation peak potentials (Epred=385 mV, Epox=980 mV) to two formally 0.5 electron processes with more closely spaced peak potentials (first 0.5 electron reduction: Epred=665 mV, Epox=715 mV; second 0.5 electron reduction: Epred=545 mV, Epox=610 mV). Mechanistic aspects of the substantial changes that are introduced by the incorporation of acetonitrile into the solid state structure are discussed.

Original languageEnglish
Pages (from-to)21-31
Number of pages11
JournalInorganica Chimica Acta
Issue number1-2
Publication statusPublished - 1 Aug 1999


  • Cyclopentadienyl complexes
  • Electrochemistry
  • Iron complexes

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