Electrochemical reduction of a binuclear dioxo-bridged molybdenum(V) complex with ethylenediaminetetraacetate*

Summary Electrochemical reduction of the binuclear, dioxo-bridged Mo(V) complex Mo 2 O 4 (EDTA) 2− has been studied at mercury electrodes in pH 7–10 borate, phosphate and NH 4 + /NH 3 buffers. The effect of pH, buffer composition and supporting electrolyte concentration on the reduction mechanism has been investigated. The complex is reduced by a concerted four-electron, four-proton transfer to a binuclear Mo(III) product, Mo 2 O 2 (H 2 O) 2 (EDTA) 2− . Protonated buffer species H 3 BO 3 . H 2 PO 4 − and NH 4 + are directly involved in the electrode reaction mechanism, which is postulated to be a pre-equilibrium transfer of two electrons followed by rate-limiting reaction between the proton donor and initial product and subsequent reduction to Mo(III). Interaction of unprotonated buffer species with the Mo(III) product facilitates the removal of protons upon reoxidation to Mo 2 O 4 (EDTA) 2− .