Spectrosopic and paramagnetic properties of molybdenum oxyhydroxide films electrochemically formed from the Keggin-type (PMo₁₂O₄₀)³⁻ complex

Molybdenum-containing films electrochemically deposited from an aqueous solution of 12-molybdphosphate (PMo₁₂O₄₀)³⁻ (denoted as PMo₁₂) have been characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and electron spin resonance (ESR) techniques. XPS and FTIR data indicate that electrolysis of PMo₁₂ leads to the formation of Mo–O–Mo linkage by condensation of the polyanions accompanied by decomposition of the phosphate moiety. The ESR spectrum of the deposited film exhibits an asymmetric signal with g ∼1.92, indicative of pentavalent molybdenum (d¹). The feature of this signal is close to that for a MoV ion in the amorphous MoO₃ phase, but not in the PMo₁₂ framework. It is therefore suggested that the deposited film no longer has the Keggin structure PMo₁₂, but consists of a continuous structure containing molybdenum oxide.