Extreme Differences in
Oxidation States: Synthesis
and Structural Analysis of the Germanide Oxometallates A<sub>10</sub>[Ge<sub>9</sub>]<sub>2</sub>[WO<sub>4</sub>] As Well As A<sub>10+<i>x</i></sub>[Ge<sub>9</sub>]<sub>2</sub>[W<sub>1–<i>x</i></sub>Nb<sub><i>x</i></sub>O<sub>4</sub>] with
A = K and Rb Containing [Ge<sub>9</sub>]<sup>4–</sup> Polyanions
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Abstract
Semitransparent dark-red or ruby-red moisture- and air-sensitive
single crystals of A<sub>10+<i>x</i></sub>[Ge<sub>9</sub>]<sub>2</sub>[W<sub>1–<i>x</i></sub>Nb<sub><i>x</i></sub>O<sub>4</sub>] (A = K, Rb; <i>x</i> = 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 (<i>P</i>2<sub>1</sub><i>/c</i>, <i>Z</i> = 4) with <i>a</i> = 13.908(1) Å, <i>b</i> = 15.909(1) Å, <i>c</i> = 17.383(1) Å,
and β = 90.050(6)° for K<sub>10.35(1)</sub>[Ge<sub>9</sub>]<sub>2</sub>[W<sub>0.65(1)</sub>Nb<sub>0.35(1)</sub>O<sub>4</sub>]; <i>a</i> = 14.361(3) Å, <i>b</i> = 16.356(3)
Å, <i>c</i> = 17.839(4) Å, and β = 90.01(3)°
for Rb<sub>10.35(1)</sub>[Ge<sub>9</sub>]<sub>2</sub>[W<sub>0.65(1)</sub>Nb<sub>0.35(1)</sub>O<sub>4</sub>]; <i>a</i> = 13.8979(2)
Å, <i>b</i> = 15.5390(3) Å, <i>c</i> = 17.4007(3) Å, and β = 90.188(1)° for K<sub>10</sub>[Ge<sub>9</sub>]<sub>2</sub>WO<sub>4</sub>; and <i>a</i> = 14.3230(7) Å, <i>b</i> = 15.9060(9) Å, <i>c</i> = 17.8634(9) Å, and β = 90.078(4)° for
Rb<sub>10</sub>[Ge<sub>9</sub>]<sub>2</sub>WO<sub>4</sub>. The compounds
contain discrete Ge<sub>9</sub><sup>4–</sup> Wade’s <i>nido</i> clusters and WO<sub>4</sub><sup>2–</sup> (or
NbO<sub>4</sub><sup>3–</sup>) anions, which are packed according
to a hierarchical atom-to-cluster replacement of the Al<sub>2</sub>Cu prototype and are separated by K and Rb cations, respectively.
The alkali metal atoms occupy the corresponding tetrahedral sites
of the Al<sub>2</sub>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<sub>9</sub>]<sup>4–</sup> 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