Tribarium tetrahedro-tetragermanide acetylenide, Ba3[Ge4][C2]: Synthesis, structure, and properties

Article abstract of DOI:10.1002/zaac.199762301146

Ba₃Ge₄C₂ is formed at 1530 K from the elements or by reaction of BaC₂ with BaGe₂ (corundum crucible; steel ampoule). The compound is a semiconductor (grey colour; E_g = 1.1 eV), brittle, very sensitive to moisture, and reacts with NH₄Cl at about 400 K forming acetylene and germanes up to Ge₄H_n. The new Ba₃Ge₄C₂ structure type (space group I4/mcm, No. 140; a = 8.840(1) ?, c = 12.466(1) ?; Z = 4, Pearson code tI36), contains two kinds of isolated polyanions, namely tetrahedro-tetragermanide [Ge₄]^4- and acetylenide [C₂]^2- anions. The bond lengths are d(Ge-Ge) = 2.517 ? (4x) and 2.641 ? (2x), and d(C≡C) = 1.20 ?. The Ba₃[Ge₄][C₂] structure is a hierarchical derivative of the perovskite (CaTiO₃) generated by a partial atom/cluster replacement ([Ge₄] for Ca, [C₂] for Ti and Ba for O). The Raman spectrum shows bands at 168, 199 and 280 cm^-1, and at 1796 cm^-1 characteristic for [Ge₄]^4- and [C₂]² polyanions, respectively.