Ternary cobalt germanium pnictides CoGexPn1-x (Pn = P, As, Sb) and the structure of Co3Ge2Sb, an intermetallic compound with stuffed Sb2 pairs

The ternary,cobalt germanium pnictide systems CoGe(x)Pn(1-x), (Pn = P,:As, Sb; 0 < x < 1) were investigated. The ternary phosphides CoGexP1-x,, and arsenides CoGexAs1-x, adopt the MnP structure (Pnma) in the range 0 tn < 0.8, with Ge and Pn (Pn = P, As) disordering over the anion sites. Reactions in the antimonide system CoGexSb1-x,, result in a mixture of ternary phases, one with the NiAs structure (P6(3) /mmc) in which Ge and Sb disorder over the anion sites, and another that is a new intermetallic compound, Co3Ge2Sb. Single-crystal :X-ray diffraction reveals that Co3GexSb crystallizes in the hexagonal space group P6/mmm with a = 8.9128(13) A, c = 7.6312(8) A, and Z = 6 (T = 22 degrees C). The structure of Co3Ge2Sb comprises alternating kagome nets of Co atoms and 6(3) nets of Ge atoms, with Sb-2 pairs stuffed along the centres of the concentric hexagons of these nets. Co3Ge2Sb maybe regarded as an intermediate structure that is distorted from the limiting CoSn and CaCu5, structures.