Electron Transfer Behavior of Multi‐Iron Sandwich‐Type Polyoxometalates and Electrocatalytic Reduction Reactions

Abstract

AbstractThe physicochemical and electrocatalytic behaviors of eight multi‐iron Wells−Dawson sandwich‐type polyoxometalates were studied with specific emphasis on the FeIII centers. Magnetization measurements were used to identify and quantify the antiferromagnetic interactions between the edge‐sharing FeIII units. Electrochemical studies show the stepwise reduction of the FeIII centers, in complete agreement with magnetization conclusions. The location of the potential of each wave depends on the pH of the solution, as well as the concentration and composition of the electrolyte. In addition, ion‐pairing studies show there is a positive shift of the FeIII centers with an increase in ion pairing (i.e. K+ > Na+ > Li+). The electrocatalytic reduction of dioxygen and hydrogen peroxide is efficient for all the complexes. However, there is a pronounced increase in efficiency as the number of FeIII centers in the complex increases (i.e. 4 FeIII > 3 FeIII > 2 FeIII). The mixed‐metal complexes [αββα‐Na14(MnIIOH2)2(FeIII)2(As2W15O56)2 and αββα‐Na14(MnIIOH2)2(FeIII)2(P2W15O56)2] are also efficient catalysts for the reduction of NO and HNO2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)