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

Abstract

Abstract The electron transfer (ET) reaction between bis(cyclopentadienyl)iron(II) ([Fe II (C 5 H 5 ) 2 ]) in 1,2-dichloroethane (1,2-DCE) and in nitrobenzene (NB) and hexacyanoferrate redox couple ([Fe II/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 [Fe II (C 5 H 5 ) 2 ] in O (O = 1,2-DCE or NB) and [Fe II/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 [Fe II (C 5 H 5 ) 2 ] (partially distributed from O) and [Fe III (CN) 6 ] 3− takes place in W phase and the resultant [Fe III (C 5 H 5 ) 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(C 5 H 5 ) 2 ] + [Fe(CN) 6 ] 3− = [Fe(C 5 H 5 ) 2 ] + + [Fe(CN) 6 ] 4− in W phase, k f IT , were determined to be (3.2 ± 2.0) × 10 10 M −1 s −1 and (2.0 ± 1.3) × 10 10 M −1 s −1 with the 1,2-DCE|W (1.5 M Li 2 SO 4 ) and NB|W (1.5 M Li 2 SO 4 ) 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(C 5 H 5 ) 2 ] + ion at the interface, Δ O W ϕ Fc + 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 Li 2 SO 4 ) and NB|W (1.5 M Li 2 SO 4 ) interfaces, respectively.