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In situ X-Ray Absorption Near Edge Spectroscopy (XANES) and Extended X-Ray Absorption Fine Structure (EXAFS) techniques are applied to a metal center ionic liquid undergoing oxidation and reduction in a three electrode spectroscopic cell. Determination of the extent of reduction under negative bias on the working electrode and the extent of oxidation are determined after pulse voltammetry to quiescence. While the ionic liquid undergoes full oxidation, it undergoes only partial reduction, likely due to transport issues on the timescale of the experiment. Nearest neighbor Fe-O distances in the fully oxidized state match well to expected values for similarly coordinated solids, but reduction does not result in an extension of the Fe-O bond length, as would be expected from comparisons to the solid phase. Instead, little change in bond length is observed. We suggest that this may be due to a more complex interaction between the monodentate ligands of the metal center anion and the surrounding charge cloud, rather than straightforward electrostatics between the metal center and the nearest neighbor grouping. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the electrochemical behavior and the electrocatalytic properties towards the reduction of hydrogen peroxide, dioxygen and nitrate are compared for the two mixed sandwich-type complexes Ni2Fe2P4 and Ni2Fe2As4. In media of pH 3, Ni2Fe2P4 displayed two waves corresponding to the reduction of the two FeIII centers within the complex followed by four WVI based-waves. Compared to Ni2Fe2P4, Ni2Fe2As4 displayed only one Fe-based wave and three W-waves. In other words, the two FeIII waves and the first two WVI waves observed for Ni2Fe2P4 merge into one Fe-based wave and one W-wave in Ni2Fe2As4. This is probably related to a slight difference in acidity between the two complexes. In other words, Ni2Fe2P4 is slightly more basic than Ni2Fe2As4. This difference in acidity is also reflected in the position of the potentials. Compared to Ni2Fe2P4, the peak potentials of Ni2Fe2As4 are slightly shifted towards positive values, and the shift is more pronounced for the W-based waves than for the Fe-waves. The remarkable stability of the two complexes (roughly from pH 0 to 7) permitted to evaluate their catalytic behavior towards H2O2, O2 and . For the electrocatalytic reduction of H2O2, it is noticed that Ni2Fe2As4 is more efficient than Ni2Fe2P4. However, for O2 and it is observed that Ni2Fe2P4 is more efficient than Ni2Fe2As4. [ABSTRACT FROM AUTHOR]