Preparation, crystal structure, and magnetic properties of rare earth ruthenium and osmium carbides with La3.67FeC6 type structure

The new carbides Gd3.67RuC6 and Ln(3.67)OsC(6) (Ln = La-Nd, Sm) were prepar ed by are-melting of cold-pressed pellets of the elemental components. Thei r hexagonal (P6(3)/m) La3.67FeC6 type crystal structure was refined from X- ray powder diffraction data of La3.67OsC6 (a = 889.1(1) pm, c = 535.1(1) pm ) and Pr3.67OsC6 (n = 874.9(2) pm, c = 523.7(1) pm). The occupancy paramete rs of one La and one Pr site were refined to 0.35(5) and 0.34(5), respectiv ely, in agreement. with the highest possible occupancy for steric reasons o f 1/3. The C-C distances in the C-2 pairs are 139(6) pm and 137(3) pm, resp ectively, indicating double bonds. The environment of the osmium atoms is c ompatible with the 18-electron rule. The magnetic properties of several car bides were determined with a SQUID magnetometer. The lanthanum compounds La 3.67RuC6 and La3.67OsC6 are Pauli paramagnetic. The magnetic properties of the other compounds are dominated by the magnetic moments of the rare earth atoms. Most order ferrimagnetically with Curie temperatures varying betwee n 5(+/-3) and 32(+/-6) K for Ce3.67OsC6 and Pr3.67RuC6, respectively. The c erium atoms in Ce3.67RuC6 and Ce3.67OsC6 are essentially trivalent, and the samarium compounds show Van Vleck behavior.