Electrochemical Generation of Complexes Containing Heterometallic Trinuclear Triangular Metal-Sulphur-Cubiodal {M’M2S2}4+ Core (where M and M’ = Mo and W): Synthesis and Study of Physico-chemical Behaviour

Abstract

Chromatographic separation of mixture leads to the isolation of molybdenum-tungsten mixed-metal clusters [MoW₂S₄(H₂O)₉]⁴⁺ and [WMo₂S₄(H₂O)₉]⁴⁺. From the aqua ion the corresponding oxalato-derivatives as [MoW₂S₄(C₂O₄)₃(H₂O)₃]^2- and [WMo₂S₄(C₂O₄)₃(H₂O)₃]^2- are isolated. The peak positions of the two big bands in each infrared spectrum of the four aqua clusters, [Mo₃S₄(H₂O)₉]⁴⁺, [W₃S₄(H₂O)₉]⁴⁺, [MoW₂S₄(H₂O)₉]⁴⁺ and [WMo₂S₄(H₂O)₉]⁴⁺ in the 550-400 cm^-1 region shift to lower wave number when the molybdenum atom is replaced by tungsten. The cyclic voltammogramms of Cs₂[MoW₂S₄(C₂O₄)₃(H₂O)₃] (1)B and Cs₂[WMo₂S₄(C₂O₄)₃(H₂O)₃] (2) shows three consecutive one-electron reduction steps in the aqueous medium with supporting electrolyte, KCl at -0.84, -1.40, -1.78 and -0.73, -1.22, -1.66 V, respectively. These steps correspond to the change of oxidation states of three metals in each cluster with the following electronic configuration {M₃}⁶ ® {M₃}⁷ ® {M₃}⁸ ® {M₃}⁹. The half wave potential E_1/2 are significantly dependent on the cluster metals. In all the reduction processes the [Mo_nW_3-nS₄(C₂O₄)₃(H₂O)₃]^2- clusters (n = 0-3) are easily reduced with the increase in the number of Mo(n) in the clusters. The proceeding reduction centre of themolybdenum-tungsten mixed metal clusters is mainly on the Mo atom(s) rather than Watoms.