Er5Re2C7, Tm5Re2C7, and Lu5Re2C7 with Sc5Re2C7 Type, and Yb2ReC2 with Pr2ReC2 Type Structures

Z. Naturforsch. 52 b, 231-236 (1997); received November 15, 1996 Crystal Structure, Magnetic Properties, Rare Earth Metal Rhenium Carbides, Polymeric Rhenium-Carbon Polyanions ErsReiCy, TmsRe2C7, and LusReaC? were prepared by arc-melting of the elemental compo­ nents and subsequent annealing at 800 °C. ErsRe^Cy forms only after the annealing process, whereas the other two carbides were already present in the as cast samples. They crystallize with a ScsReiC? type structure, which was refined from single-crystal X-ray data of LusRe2C7: Cmmm, a = 791.44(5), b = 1418.08(8), c = 332.79(2) pm, Z = 2, R = 0.037 for 544 structure factors and 21 variable parameters. The structure contains linear centrosymmetric C3 units with a C-C bond length of 133(2) pm and isolated carbon atoms in octahedral coordination of four lutetium and two rhenium atoms. The rhenium atoms within the two-dimensionally infinite polymeric sheets [ReiC-tln are electronically saturated as is indicated by the diamagnetism and the semiconductivity of this carbide. Yf>2ReC2 was prepared by reacting the elements in a sealed tantalum tube with a high-frequency furnace. It crystallizes with a Pr2ReC2 type structure: Pnma, a = 645.91(6), b = 498.64(6), and c = 966.05(6) pm. Magnetic susceptibility measurements indicate the ytterbium atoms to be trivalent in this compound.