SYNTHESIS OF DITUNGSTEN CARBIDE BY CONTROLLED DECOMPOSITION OF CP2W2(CO)(4) (DMAD) UNDER A HYDROGEN ATMOSPHERE

Controlled decomposition studies of the gsten(tetracarbonyl)dimethylac etylenedicarboxylate (Cp2W2(CO)(4)(dmad)) under flowing hydrogen show that it totally decomposes at 600 degrees C for 2 h to give a pure bul k W2C as revealed by X-ray diffraction. Excess oxygen and carbon at th e surface are detected by X-ray photoelectron spectroscopy. An in situ temperature-programmed X-ray diffraction experiment performed on Cp2W 2(CO)(4) (dmad) shows the detection temperature of W2C to be 600 degre es C, the sample being amorphous or microcrystalline below that temper ature. Based on previous results obtained for the decomposition of Cp2 Mo2(CO)(4)(dmad) on the one hand, and thermogravimetric and chromatogr aphic analyses performed on Cp2W2(CO)(4)(dmad), on the other, a decomp osition scheme of the latter under hydrogen has been proposed. (C) 199 8 Chapman & Hall.