Abstract

A combined in situ Mo K-edge extended X-ray absorption fine structure (EXAFS) and X-ray powder diffraction study has been carried out to follow the evolution of structure in the thermal decomposition of the ammonium thiomolybdates, (NH₄)₂Mo₃S₁₃·2H₂O and (NH₄)₂Mo₂S₁₂·2H₂O, under nitrogen. Additional information on the course of the decomposition reactions has been obtained from thermogravimetric and differential thermal analysis, and from IR spectroscopy. Molybdenum–molybdenum bonded triangular units are found to persist in all the amorphous intermediate decomposition products of (NH₄)₂Mo₃S₁₃·2H₂O, and are also formed during the decomposition of (NH₄)₂Mo₂S₁₂·2H₂O. Structural models for the intermediates are presented. The final decomposition product in both cases is poorly crystalline MoS₂.