Electron Coupled Proton Transport Mediated by [Fe4S4(SC6H4-p-n-C8H17)4]2− in Liquid Membrane

Electrochemical reduction of [Fe4S4(SC6H4-p-n-C8H17)4]2− ([4-Fe]2−) dissolved in a CH2Cl2 phase of the CH2Cl2/H2O two phase system is followed by protonation to give [4-Fe]3−–H+ when the pH of the H2O phase is lower than 7.0, and protonated and deprotonated [4-Fe]3− exist as an equilibrium mixture in the CH2Cl2 phase. On the other hand, no protonation takes place upon the reduction of [4-Fe]2− in the CH2Cl2 phase contacting with the H2O phase with the pH higher than 7.0. The electron transport conducted in a liquid membrane composed of the H2O (W1), CH2Cl2, and H2O (W2) phases containing sodium dithionite as an electron donor, (n-Bu4N)2[4-Fe] as a mediator, and disodium anthraquinone-1,5-disulfonate (Na2AQS) as an electron acceptor, respectively, revealed that protonated [4-Fe]3−–H+ mediates electron coupled proton transport in the liquid membrane, while the deprotonated cluster has no ability of electron transport in the same system.