Defect {((WO7)-O-VI)W-4(VI)} and Full {((WO7)-O-VI)W-5(VI)} Pentagonal Units as Synthons for the Generation of Nanosized Main Group V Heteropolyoxotungstates

We report on the synthesis and characterization of three new nanosized main group V heteropolyoxotungstates KxNay[H-2((XW9O33)-O-VI)((W5O12)-O-VI)((X2W29O103)-O-VI)]center dot nH(2)O{X3W43} (x = 11, y = 16, and n = 115.5 for X = Sb-III; x = 20, y = 7, and n = 68 for X = Bi-III) and K-8 Na-15[H-16(Co-II(H2O)(2))(0.9)(Co-II(H2O)(3))(2)((W3.1O14)-O-VI)((SbW9O33)-W-III-O-VI) ((Sb2W30O106)-W-III-O-VI)(H2O)]center dot 53H(2)O {Co3Sb3W42}. On the basis of the key parameters for the one-pot synthesis strategy of {Bi3W43}, a rational step-by-step approach was developed using the known Krebs- type polyoxotungstat e ( POT) K-12[(Sb2W22O74)-W-V-O-VI(OH)(2)]center dot 27H(2)O {Sb2W22} as a nonlacunary precursor leading to the synthesis and characterization of {Sb3W43} and {Co3Sb3W42}. Solid-state characterization of the three new representatives {Bi3W43}, {Sb3W43}, and {Co3Sb3W42} by single-crystal and powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and elemental analysis, along with characterization in solution by UV/vis spectroscopy shows that {Bi3W43}, {Sb3W43}, and {Co3Sb3W42} represent the first main group V heteropolyoxotungstates encapsulating a defect {((WO7)-O-VI)W-4(VI)} ({X3W43}, X = BiIII and SbIII) or full {((WO7)-O-VI)W-5(VI)} ({Co3Sb3W42}) pentagonal unit. With 43 tungsten metal centers, {X3W43} (X = Bi-III and Sb-III) are the largest unsubstituted tungstoantimonate- and bismuthate clusters reported to date. By using time-dependent UV/vis spectroscopy, the isostructural representatives {Sb3W43} and {Bi3W43} were subjected to a comprehensive study on their catalytic properties as homogeneous electron-transfer catalysts for the reduction of K-3[Fe-III(CN)(6)] as a model substrate revealing up to 5.8 times higher substrate conversions in the first 240 min (35% for {Sb3W43}, 29% for {Bi3W43}) as compared to the uncatalyzed reaction (