An oxomolybdenum complex with thiosemicarbazide (HTSC) of composition Mo2O4(TSC)2 has been prepared. The magnetic moment (0.51 BM) and the electronic spectral data indicate a dimeric structure with a 'Mo2O4' core. The negative shifts in v(NH) and v(CS) indicate the involvement of nitrogen and sulphur atoms in coordination. The IR bands at 970, 740 and 480 cm-1 indicate the presence of terminal (MoO) and bridging (MoO2Mo) oxygen atoms. XPS studies indicate the pentavalent state of molybdenum and the coordination of thiosemicarbazide through nitrogen and sulphur. The complex exhibits an irreversible cathodic wave at -1.05 V versus SCE characteristic of a Mo2O42+ core. The thermal decomposition behaviour of the complex in air, nitrogen and hydrogen atmospheres is discussed. A di-μ-oxo bridged oxomolybdenum(V) structure with thiosemicarbazide completing five coordination around each molybdenum atom is proposed. © 1987.