GDRUC2, A TERNARY CARBIDE WITH FILLED NIAS STRUCTURE

The new carbide GdRuC2 is a high-temperature phase prepared by are-mel ting of the elemental components. Its crystal structure was determined from single-crystal X-ray data to be Cmcm, a 436.5(1) pm, b = 927.7(1 ) pm, c = 520.2(1) pm, Z = 4, and R = 0.015 for 292 structure factors and 16 variable parameters. The unit cell corresponds to the orthorhom bic subgroup setting of the hexagonal NiAs structure with Ru and Gd at oms occupying the positions of the Ni and As atoms, respectively. The carbon atoms form pairs with a C-C distance of 137.9(6) pm, and togeth er with the Ru atoms they form two-dimensionally infinite polyanions, where the environment of the Ru atoms seems to be compatible with the 18-electron rule. GdRuC2 is ferromagnetic with a Curie temperature of T-C = 45(3) K and a paramagnetic moment of mu(exp) = 8.0(1) mu(B). Thi s moment compares well with the free ion value of Gd3+ mu(eff) = 7.94 mu(B), suggesting that the Ru atoms are nonmagnetic. (C) 1995 Academic Press, Inc.