Ge52− Zintl anions: synthesis and crystal structures of [K([2.2.2]-crypt)]2Ge5·4NH3 and [Rb([2.2.2]-crypt)]2Ge5·4NH3

Abstract

The new compounds [K(C₁₈H₃₆N₂O₆)]₂Ge₅·4NH₃ (1) and [Rb(C₁₈H₃₆N₂O₆)]₂Ge₅·4NH₃ (2) were prepared by the extraction of a binary phase of the nominal composition KGe_1.67 and a ternary phase of the composition Rb_0.5Cs_0.5Ge_2.25 with liquid ammonia in the presence of cryptand [2.2.2]. The resulting crystalline materials were characterized by low temperature X-ray structure analysis. Compounds 1 and 2 contain isolated trigonal-bipyramidal Ge₅²⁻ cage anions, the symmetries of which were investigated and compared to the previously reported pentagermanide anion. Despite the nearly identical formulae, the two compounds are not isotypic, as the space group type changes from the acentric group P1 (no. 1) for the potassium compound to P (no. 2) for the rubidium compound.