Electrochemical and electrical properties of a mixed-valence bis(fulvalene)diiron salt in polyethylene glycol studied using an interdigitated array microelectrode

Abstract

Electron-transfer phenomena of a mixed-valence bis(fulvalene)diiron (BFD) salt, BFDBF₄ in 1.5 mol dm^–3 LiClO₄-polyethylene glycol dimethyl ether with m.w. = 400 are described, investigated by the four-probe interdigitated microarray electrode technique. The apparent electron diffusion coefficient D_app obtained from the limiting current caused by the concentration gradient between neighbouring fingers is 6.4 × 10^–9 cm²s^–1 for the BFD(2,3)⁺/BFD(2,2)^o couple and 1.3 × 10^–8 cm² s^–1 for the BFD(3,3)²⁺/BFD(2,3)⁺ couple at a BFD concentration of 5 mmol dm^–3. D_app decreases for both couples with increasing concentration of BFDBF₄, indicating that the physical diffusion coefficient, D_phys' of BFD(3,3)²⁺ is higher than that of BFD(2,2)^o. The conductivity vs. potential behaviour of the system is governed by the diffusive motion of electroactive species. The effect of electron hopping on D_app and that of solution non-ideality caused by ionic interaction of charged species on the conductivity vs. potential behaviour are discussed.