Extreme differences in oxidation states: synthesis and structural analysis of the germanide oxometallates A10[Ge9]2[WO4] as well as A(10+x)[Ge9]2[W(1–x)Nb(x)O4] with A = K and Rb containing [Ge9]4- polyanions.

Semitransparent dark-red or ruby-red moisture- and air-sensitive single crystals of A(10+x)Ge(9)[W(1-x)Nb(x)O(4)] (A = K, Rb; x = 0, 0.35) were obtained by high-temperature solid-state reactions. The crystal structure of the compounds was determined by single-crystal X-ray diffraction experiments. They crystallize in a new structure type (P2(1)/c, Z = 4) with a = 13.908(1) Å, b = 15.909(1) Å, c = 17.383(1) Å, and β = 90.050(6)° for K(10.35(1))Ge(9)[W(0.65(1))Nb(0.35(1))O(4)]; a = 14.361(3) Å, b = 16.356(3) Å, c = 17.839(4) Å, and β = 90.01(3)° for Rb(10.35(1))Ge(9)[W(0.65(1))Nb(0.35(1))O(4)]; a = 13.8979(2) Å, b = 15.5390(3) Å, c = 17.4007(3) Å, and β = 90.188(1)° for K(10)Ge(9)WO(4); and a = 14.3230(7) Å, b = 15.9060(9) Å, c = 17.8634(9) Å, and β = 90.078(4)° for Rb(10)Ge(9)WO(4). The compounds contain discrete Ge(9)(4-) Wade's nido clusters and WO(4)(2-) (or NbO(4)(3-)) anions, which are packed according to a hierarchical atom-to-cluster replacement of the Al(2)Cu prototype and are separated by K and Rb cations, respectively. The alkali metal atoms occupy the corresponding tetrahedral sites of the Al(2)Cu prototype. The amount of the alkali metal atoms on these diamagnetic compounds corresponds directly to the amount of W substituted by Nb. Thus, the transition metals W and Nb appear with oxidation numbers +6 and +5, respectively, in the vicinity of a Ge(9) polyanion. The crystals of the mixed salts were further characterized by Raman spectroscopy. The Raman data are in good agreement with the results from the X-ray structural analyses.