therm0chimica acta ELSEVIER Thermochimica Acta 256 (1995) 325 338 Thermal and reductive decomposition of ammonium thiomolybdates Joaquin L. Brito *, Marcel Ilija, Petra Hernfindez Laboratorio de Fisicoquimica de Supet;ficies, Centro do Quimica Instituto Venecolano de lm;estigaciones Cient(ficas (1. V.I.C.) Apartado 21827, Caracas 1020-A, Venezuela Received 18 August 1994; accepted 25 October 1994 Abstract Thermal decomposition and hydrogen reduction of ammonium thiomolybdates of formu- las: (NH4)2[MoS4] (I), (NH4)z[M02(S2)61 - 2H20 (I[) and (NH4)2[M03S(S2)6] - 1.85H20 (III), were investigated using thermogravimetric analysis (TGA), either in pure N2 or in 10% H 2 in N 2, and temperature-programmed reduction (TPR). The thiomolybdate compounds were characterized by several physicochemical techniques, including FTIR, PAS/FTIR, UV-visible spectroscopy, XRD and CHNS elemental analyses. The decompositions of (I) and (lI) proceed in a similar way independently of the type of gas phase, with production of MoS~. However, the anion cluster of (III) is decomposed at lower temperatures in the presence of H 2. The amorphous MoS 3 compound is very sensitive to the presence of H> which also lowers the onset of its decomposition. These results seem to support a model for the structure of MoS 3 consisting of triangular Mo 3 cluster units, similar to those present in (lll). TPR could be used as a "fingerprint" technique for identification of the complexes, as they present strong differences in the shapes and characteristic temperatures of the reductograms. Keywords: Decomposition: Reducibility: Reductive decomposition: TGA; Thiomolybdate; TPR 1. Introduction Thiomolybdate complexes and clusters have recently gained increased attention, due to their relevance to the bioinorganic chemistry of molybdenum [1] and as * Corresponding author. 0040-6031/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0040-6031 (94)021 78-3