GdRuC 2, a Ternary Carbide with Filled NiAs Structure

The new carbide GdRuC 2 is a high-temperature phase prepared by arc-melting 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 orthorhombic subgroup setting of the hexagonal NiA 5 structure with Ru and Gd atoms 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 together 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. GdRuC 2 is ferromagnetic with a Curie temperature of T c = 45(3) K and a paramagnetic moment of μ exp = 8.0(1) μ B. This moment compares well with the free ion value of Gd 3+ μ eff = 7.94 μ B, suggesting that the Ru atoms are nonmagnetic.