Defect {(WO)W} and Full {(WO)W} 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 KNa[H(XWO)(WO)(XWO)]·HO ( = 11, = 16, and = 115.5 for X = Sb; = 20, = 7, and = 68 for X = Bi) and KNa[H(Co(HO))(Co(HO))(WO)(SbWO)(SbWO)(HO)]·53HO . On the basis of the key parameters for the one-pot synthesis strategy of , a rational step-by-step approach was developed using the known Krebs-type polyoxotungstate (POT) K[SbWO(OH)]·27HO as a nonlacunary precursor leading to the synthesis and characterization of and . Solid-state characterization of the three new representatives , , and 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 , , and represent the first main group V heteropolyoxotungstates encapsulating a defect {(WO)W} (, X = Bi and Sb) or full {(WO)W} () pentagonal unit. With 43 tungsten metal centers, (X = Bi and Sb) are the largest unsubstituted tungstoantimonate- and bismuthate clusters reported to date. By using time-dependent UV/vis spectroscopy, the isostructural representatives and were subjected to a comprehensive study on their catalytic properties as homogeneous electron-transfer catalysts for the reduction of K[Fe(CN)] as a model substrate revealing up to 5.8 times higher substrate conversions in the first 240 min (35% for , 29% for ) as compared to the uncatalyzed reaction (<6% without catalyst after 240 min) under otherwise identical conditions.