The reduction of (Ru(Hedta)(H2O)) at the mercury electrode and subsequent reactions

Abstract The reduction of [Ru(Hedta)(H2O)] at the mercury electrode and the subsequent chemical reactions in buffer solutions were investigated by AC and DC polarography and by large-scale electrolysis. Two polarographic steps were observed; the more positive step is discussed in this paper. The step was a diffusion-controlled, one-electron reduction of ruthenium(III) to ruthenium(II). For [H+]=(10−3–10−5) mol dm−3 the reduction was reversible, and it became less reversible if [H+]<10−5 mol dm−3. Large-scale electrolysis in formate buffer solutions at the potential of the polarographic diffusion current plateau confirmed that the reduction is a one-electron process. In formate buffer, the reduced form of the complex is deactivated. Furthermore, in the presence of perchlorate ions the reduced form is reoxidized to the original form. The rate constant for the reoxidation reaction at 25.0 °C was k2=(1.38±0.26)×10−3 mol−1 dm3 s−1. The activation parameters for the reoxidation reaction were ΔH\eweq=(94.1±17.6)×103J mol−1 and ΔS\eweq=(19.0±6.3) J K−1 mol−1.