The germanides Er₅Pd₄Ge₈ and Tm₅Pd₄Ge₈. 3D [Pd₄Ge₈] polyanions with Ge₂ dumb-bells and Ge₄ chains in cis-conformation

Tm₅Pd₄Ge₈ was synthesized by melting of the elements in an arc-melting furnace. The new germanide was characterized by powder and single-crystal X-ray diffraction: own structure type, P2₁/m, a=574.3(1), b=1380.4(3), c=836.4(1) pm, β=107.57(2) , V=0.6321 nm³, wR2=0.0578, 2533 F² values, 86 variables. The palladium and germanium atoms built up a three-dimensional [Pd₄Ge₈]^15- polyanionic network which contains a unique germanium substructure composed of the Zintl anions Ge₂^6- dumb-bells and Ge₄^10- chains in cis-conformation. The palladium atoms within the network have distorted square pyramidal germanium coordination. The three crystallographically independent thulium atoms have coordination numbers 15, 16 and 17 with partial motifs of the Frank-Kasper type polyhedra. The isotypic germanide Er₅Pd₄Ge₈ forms only after annealing the arc-melted sample at 1070 K for 1 week: a=575.14(9), b=1386.3(3), c=838.4(1) pm, β=107.51(2) , V=0.6375 nm³.