Syntheses and structures of tetranuclear cluster complexes of molybdenum [Mo₄(μ₃-S)₂(μ₂-S) ₄X₂-(PMe₃)₆] (X= SH, Cl, Br, I, SCN) and [Mo₄(μ₃-S)₂-(μ₂-S) ₄(dtc)₂(PMe₃)₄] (dtc = diethyldithiocarbamate)

A molybdenum cluster complex [Mo₄(μ₃-S)₂(μ₂-S) ₄(SH)₂(PMe₃)₆] has been synthesized by the reaction of (NH₄)₂Mo₃S₁₃ with trimethylphosphine. The cluster core is composed of lour molybdenum atoms arranged in the rhombus bridged by two capping and four bridging sulfur atoms. Two SH and six trimethylphosphinc ligands are coordinated to the terminal positions. The mean oxidation states of molybdenum is +3.5 and there are five Mo-Mo bonds consistent with ten metal cluster electrons. The complex has been converted into [Mo₄(μ₃-S)₂(μ₂-S) ₄X₂(PMe₃)₆] (X = Cl, Br, I, SCN) and [Mo₄(μ₃-S)₂(μ_{2 2}-S)₄ (dtc)₂(PMe₃)₄] (dtc = diethyldithiocarbamate). In the case of the dtc complex, two terminal trimethylphosphine ligands are displaced and dtc ligands are coordinated in chelate fashion. The structures of the SH, Cl, Br, and dtc complexes have been determined by X-ray crystallography. Molecular orbital calculations with DV-Xα method has shown large HOMO-LUMO gaps (1.52-1.74eV) for [Mo₄S₆X₂(PH₃)₄] (X = SH, Cl, and Br).