Conformation isomerism of nonagermanide ions. Crystal structures of brown and red [K-([2.2.2]crypt)]₆Ge₉Ge ₉-(ethylenediamine)_x (x = 0.5, 1.5)

A brown and a red form of the [K-([2.2.2]-crypt)]₊ salts of naked polyhedral nonagermanide anions were isolated by dissolving the alloy K₄Ge₉ in ethylenediamine. The compounds [K-([2.2.2]crypt)]₆Ge₉Ge₉(ethylenediamine) _x with x = 0.5 (2a, brown) and 1.5 (2b, red) crystallize in the P1̄ space group with two independent cluster anions and six [K-([2.2.2]-crypt)]₊ units. The structures are almost isotypic, but differ by their cell parameters at 233 K (2a, a = 14.397(1) Å,b= 19.765(2) Å, c = 28.898(2) Å, α = 87.485(9)°, β= 79.168(9)°, γ = 85.415(8)°; 2a, a = 14.503(1) Å,b= 19.924(2) Å, c = 28.935(3) Å, α = 87.43(1)°, β= 80.85(1)°, γ = 85.92(1)°) and atomic parameters. The differences arise with two additional ethylenediamine molecules in the case of red 2b. These solvent molecules were refined at 50% occupancy. The solvent molecules have a significant influence on the color of the crystals and the conformation of the deltahedral anions. The structures of the clusters correspond to C2_v distorted polyhedra that lie between the D_3h tricapped trigonal prism and the C_4v monocapped square antiprism. A geometrically deduced charge allocation Ge₉^2- and Ge₉^4- in an earlier study of a red compound with x = 2.5 and a less accurate structure refinement are not supported by the structures of the anions. EPR measurements on a single crystal of 2a reveal paramagnetic properties and presumably equal 3- charges for each of the two independent anions.