Defect {(W(VI)O(7))W(VI)(4)} and Full {(W(VI)O(7))W(VI)(5)} Pentagonal Units as Synthons for the Generation of Nanosized Main Group V Heteropolyoxotungstates

[Image: see text] We report on the synthesis and characterization of three new nanosized main group V heteropolyoxotungstates K(x)Na(y)[H(2)(XW(VI)(9)O(33))(W(VI)(5)O(12))(X(2)W(VI)(29)O(103))]·nH(2)O {X(3)W(43)} (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)(H(2)O)(2))(0.9)(Co(II)(H(2)O)(3))(2)(W(VI)(3.1)O(14))(Sb(III)W(VI)(9)O(33))(Sb(III)(2)W(VI)(30)O(106))(H(2)O)]·53H(2)O {Co(3)Sb(3)W(42)}. On the basis of the key parameters for the one-pot synthesis strategy of {Bi(3)W(43)}, a rational step-by-step approach was developed using the known Krebs-type polyoxotungstate (POT) K(12)[Sb(V)(2)W(VI)(22)O(74)(OH)(2)]·27H(2)O {Sb(2)W(22)} as a nonlacunary precursor leading to the synthesis and characterization of {Sb(3)W(43)} and {Co(3)Sb(3)W(42)}. Solid-state characterization of the three new representatives {Bi(3)W(43)}, {Sb(3)W(43)}, and {Co(3)Sb(3)W(42)} 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 {Bi(3)W(43)}, {Sb(3)W(43)}, and {Co(3)Sb(3)W(42)} represent the first main group V heteropolyoxotungstates encapsulating a defect {(W(VI)O(7))W(VI)(4)} ({X(3)W(43)}, X = Bi(III) and Sb(III)) or full {(W(VI)O(7))W(VI)(5)} ({Co(3)Sb(3)W(42)}) pentagonal unit. With 43 tungsten metal centers, {X(3)W(43)} (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 {Sb(3)W(43)} and {Bi(3)W(43)} 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 {Sb(3)W(43)}, 29% for {Bi(3)W(43)}) as compared to the uncatalyzed reaction (<6% without catalyst after 240 min) under otherwise identical conditions.