The analog of surface molybdenyl ion in Mo/SiO2 supported catalysts: The isopolyanion Mo6O193− studied by EPR and UV-visible spectroscopy. Comparison with other molybdenyl compounds

Electrochemical reduction of the isopolyanion Mo6O192− in solution leads to x-band EPR spectra at 77 K characterized by g⊥=1.930, g∥=1.919, A⊥=34.5 and A∥=80.5 G. The magnetic parameters were confirmed using a Q-band spectrometer. The EPR spectra are attributed to localized molybdenyl (Mo=0)3+ species surrounded by oxide ions in C4v symmetry with one short Mo–O bond. The magnitude of the g components g⊥≳g∥ confirms the earlier assignment made for reduced Mo/SiO2 supported catalysts where a similar type of molybdenyl Mo(V) species was found to be present on the surface. The magnetic parameters are discussed and compared with those obtained for other oxomolybdenum ions in the frame of the LCAO–MO theory.