RESUMEN
We report IR and UV/Vis spectroscopic signatures that allow discriminating between the oxidation states of the manganese-based water oxidation catalyst [(Mn4 O4 )(V4 O13 )(OAc)3 ]3- . Simulated IR spectra show that V=O stretching vibrations in the 900-1000â cm-1 region shift consistently by about 20â cm-1 per oxidation equivalent. Multiple bands in the 1450-1550â cm-1 region also change systematically upon oxidation/reduction. The computed UV/Vis spectra predict that the spectral range above 350â nm is characteristic of the managanese-oxo cubane oxidation state, whereas transitions at higher energy are due to the vanadate ligand. The presence of absorption signals above 680â nm is indicative of the presence of MnIII atoms. Spectroelectrochemical measurements of the oxidation from [Mn 2 III Mn 2 IV ] to [Mn 4 IV ] showed that the change in oxidation state can indeed be tracked by both IR and UV/Vis spectroscopy.