Trapping an Iron(VI) Water-Splitting Intermediate in Nonaqueous Media

We report in situ spectroscopic measurements in nonaqueous media designed to trap an exceptionally strong oxidant generated electrochemically from an iron-containing nickel layered double hydroxide ([NiFe)-LDH) material. Anodic polarization of this material in acetonitrile produces metal-oxo vibrational spectroscopic signatures along with an extremely narrow near-infrared luminescence peak that strongly indicate that the reactive intermediate is cis-dioxo-iron(VI). Chemical trapping experiments reveal that addition of H2O to the polarized electrochemical cell produces hydrogen peroxide; and, most importantly, addition of HO- generates oxygen. Repolarization of the electrode restores the iron(VI) spectroscopic features, confirming that the high-valent oxo complex is active in the electrocatalytic water oxidation cycle.