Synthesis and crystal structures of [K(18-crown-6)][Rb(18-crown-6)]2Ge9 · 6NH3, [Rb(18-crown-6)]3Ge9 · 9NH3 and [Cs(18-crown-6)]3Ge9 · 6NH3

The new compounds K(C₁₂H₂₄O₆)]Rb(C₁₂H₂₄O₆)]₂Ge₉ · 6NH₃, Rb(C₁₂H₂₄O₆)]₃Ge₉ · 9NH₃ and Cs(C₁₂H₂₄O₆)]₃Ge₉ · 6NH₃ were prepared by the extraction of binary and ternary phases of the nominal composition K₂Rb₂Ge₉, Rb₄Ge₉ and K₂Cs₂Ge₉ with liquid ammonia in the presence of 18-crown-6. The resulting crystals were characterized by low temperature X-ray structure analysis. All of them contain the 21 electron cluster , which is coordinated by alkali metal cations in ion-paired arrangements. The cages were assigned their specific point group symmetry and were compared with hitherto known structures.