CUBANE-TYPE MIXED-METAL CLUSTERS WITH MO3NIS4 CORES - SYNTHESES, CHARACTERIZATION, AND X-RAY STRUCTURES OF [MO3NIS4(H2O)10](CH3C6H4SO3)4.7H2O AND CA2.5[MO3NIS4(HNTA)(NTA)2CL].14H2O

Reaction of the incomplete cubane-type aqua ion [Mo3S4(H2O)9]4+ (A) with nickel metal gives a novel cubane-type mixed-metal cluster [Mo3NiS4(H2O)10]4+ (B') in high yields (75%), which is further converted to [Mo3NiS4(Hnta)(nta)2Cl]5- (C'; H3nta = nitrilotriacetic acid). The cluster B' is fairly stable toward air oxidation. Driving forces for the formation of the cubane-type mixed-metal clusters are discussed. The crystallographic results obtained are as follows. [Mo3NiS4(H2O)10](CH3C6H4SO3)4.7H2O (B): triclinic, P1BAR, a = 17.889 (6) angstrom, b = 19.601 (8) angstrom, c = 8.969 (4) angstrom, alpha = 102.83 (4)-degrees, beta = 103.78 (3)-degrees, gamma = 63.45 (3)-degrees, V = 2707.7 (19) angstrom 3, Z = 2, 7153 unique data (\F(o)\ greater-than-or-equal-to 3-sigma\F(o)\), R = 7.28%. Ca2.5[Mo3NiS4(Hnta)(nta)2Cl].14H2O (C), triclinic, P1BAR, a = 11.939 (5) angstrom, b = 18.379 (6) angstrom, c = 11.666 (3) angstrom, alpha = 103.60 (3)-degrees, beta = 106.13 (3)-degrees, gamma = 85.97 (3)-degrees, V = 2390.1 (15) angstrom 3, Z = 2, 7675 unique data (\F(o)\ greater-than-or-equal-to 3-sigma\F(o)\), R = 4.99%. If the Mo-Mo and Mo-Ni bonds are not counted, each molybdenum atom is octahedrally coordinated in B and C, and the nickel atom has fairly regular tetrahedral geometry in B and C. The magnetic moment of B is very low, indicating the presence of strong interaction between molybdenum and nickel atoms. The following stoichiometry was determined: Mo3NiS4(4+)(aq) + 2Fe3+(aq) --> Mo3S4(4+)(aq) + Ni2+(aq) + 2Fe2+(aq). No intermediate such as Mo3NiS4(5+)(aq) appeared. The electronic spectrum of the aqua ion B in 2 M HPTS has peaks at 680 nm (epsilon = 610 M-1 cm-1) and 500 nm (epsilon = 200). The peaks of B in 2 M HCl are at 800sh nm (epsilon = 360), 688 nm (epsilon = 488), and 498 nm (epsilon = 366). The peaks of C in water are at 703 nm (epsilon = 683 M-1 cm-1) and 500sh nm (epsilon = 280), while those of C in 2 M CaCl2 are at 810sh nm (epsilon = 455), 700 nm (epsilon = 535), and 502 nm (epsilon = 439). Coordination of chloride ion to nickel atom was observed; the formation constant K for the following equilibrium was determined to be 15 M-1: [Mo3NiS4(Hnta)(nta)2(H2O)]4- + Cl- reversible [Mo3NiS4-(Hnta)(nta)2Cl]5- + H2O. There exist three kinds of cubane-type cores: single cubane type (Mo3MS4), double cubane type (Mo3S4MMS4Mo3), and sandwich cubane type (Mo3S4MS4Mo3). The relationship between Mo-M distance and formal charge of the cores are discussed.