Syntheses and Characterization of Cubane-Type Clusters with Molybdenum–Iron–Sulfur (Mo3FeS4) or Molybdenum–Nickel–Sulfur (Mo3NiS4) Cores. X-Ray Structures of [Mo3FeS4(H2O)10](CH3C6H4SO3)4·7H2O and [Mo3FeS4(H2O)(NH3)9]Cl4, and Discrete Variational (DV)-Xα Calculation of the Electronic Structures of [Mo3FeS4(H2O)10]4+, [Mo3FeS4(H2O)(NH3)9]4+, and [Mo3NiS4(H2O)10]4+

Reaction of the incomplete cubane-type cluster [Mo3S4(H2O)9]4+ (A) with iron gives a novel cubane-type aqua cluster [Mo3FeS4(H2O)10](CH3C6H4SO3)4·7H2O (B′). An ammonia coordinated derivative cluster [Mo3FeS4(H2O)(NH3)9]Cl4 (C′) is also synthesized. X-ray structural analyses of B′ and C′ revealed that the clusters, [Mo3FeS4(H2O)10]4+ (B) and [Mo3FeS4(H2O)(NH3)9]4+ (C), have an approximate symmetry of C3v. The iron atom has fairly regular tetrahedral geometry in both clusters. The effective magnetic moments of B′ at 2.16 K and 269.95 K are 2.78 and 3.26 B.M., respectively. 57Fe-Mössbauer spectroscopy showed that the oxidation states of iron in B′ and C′ were assignable to be +2.39 and +2.54, respectively, which indicates that the reaction is a reductive addition of an iron atom to the Mo3S4 core in A. The cyclic voltammograms of A, B, and [Mo3NiS4(H2O)10]4+ (D) show three consecutive one electron reductive steps, respectively, and the oxidation states of metals in B and D are assigned as MoIVMoIII2MII (M = Fe, Ni). Discrete variational (DV)-Xα calculation of B, C, and D explains the magnetic behavior, XPS spectra, and reactivity toward CO, C2H2, and C2H4.