Single-crystal Data of Ternary Germanides RE2Nb3Ge4 (RE = Sc, Y, Gd–Er, Lu) and Sc2Ta3Ge4 with Ordered Sm5Ge4-type Structure

Small single crystals of the Sm₅Ge₄-type (space group Pnma) germanides RE₂Nb₃Ge₄ (RE = Sc, Y, Gd–Er, Lu) and Sc₂Ta₃Ge₄ were synthesized by arc-melting of the respective elements. The samples were characterized by powder and single-crystal X-ray diffraction. In all structures, except for Sc_2.04Nb_2.96Ge₄ and Sc_2.19Ta_2.81Ge₄, the rare earth and niobium atoms show full ordering on the three crystallographically independent samarium sites of the Sm₅Ge₄ type. Two sites with coordination number 6 are occupied by niobium, while the slightly larger site with coordination number 7 is filled with the rare earth element. Small homogeneity ranges with RE/Nb and RE/Ta mixing can be expected for all compounds. The ordered substitution of two rare earth sites by niobium or tantalum has drastic effects on the coordination number and chemical bonding. This was studied for the pair Y₅Ge₄/Y₂Nb₃Ge₄. Electronic structure calculations show larger charge transfer from yttrium to germanium for Y₅Ge₄, contrary to Y₂Nb₃Ge₄ which shows stronger covalent bonding due to the presence of Nb replacing Y at two sites.