Voltammetric study of the interfacial electron transfer between bis(cyclopentadienyl)iron in 1,2-dichloroethane and in nitrobenzene and hexacyanoferrate in water

The electron transfer (ET) reaction between bis(cyclopentadienyl)iron(II) ([FeII(C5H5)2]) in 1,2-dichloroethane (1,2-DCE) and in nitrobenzene (NB) and hexacyanoferrate redox couple ([FeII/III(CN)6]4−/3−) in water (W) at the interface has been studied by use of normal-pulse voltammetry. The voltammetric results indicate that the ET reaction between [FeII(C5H5)2] in O (O = 1,2-DCE or NB) and [FeII/III(CN)6]4−/3− in W takes place not by way of the heterogeneous ET at O|W interface but by the mechanism in which a homogeneous ET reaction between [FeII(C5H5)2] (partially distributed from O) and [FeIII(CN)6]3− takes place in W phase and the resultant [FeIII(C5H5)2]+ ion is responsible for the current passage across the interface. From the limiting current, the forward rate constants of the homogeneous ET reaction: [Fe(C5H5)2] + [Fe(CN)6]3− = [Fe(C5H5)2]+ + [Fe(CN)6]4− in W phase, kfIT, were determined to be (3.2 ± 2.0) × 1010 M−1 s−1 and (2.0 ± 1.3) × 1010 M−1 s−1 with the 1,2-DCE|W (1.5 M Li2SO4) and NB|W (1.5 M Li2SO4) interfaces, respectively. These values are in the order of the rate constant of diffusion-controlled bimolecular reaction in solution. Also, the formal (standard) potentials of the transfer of [Fe(C5H5)2]+ ion at the interface, ΔOWϕFc+0, were determined to be −0.015 ± 0.014 V and −0.087 ± 0.015 V with the 1,2-DCE|W (1.5 M Li2SO4) and NB|W (1.5 M Li2SO4) interfaces, respectively.