Preparation, properties, and crystal structure of the rare earth rutheniumcarbides R3Ru2C5 (R = Y, Gd-Er)

The title compounds were prepared from the elemental components by are-melt ing and subsequent annealing. While Gd3Ru2C5, and Tb3Ru2C5 are present in t he as-cast samples, the others are formed during the annealing process. The magnetic properties of the four compounds R3Ru2C5 (R = Gd-Ho) were investi gated with a SQUID magnetometer. They show very soft ferromagnetism. The hi ghest Curie temperature was observed for the gadolinium compound with T-C = 84(1) K. Electrical conductivity measurements for Tb3Ru2C5 indicate metall ic behavior. The crystal structure of these isotypic compounds has been det ermined from single-crystal X-ray data of Gd3Ru2C5: P6(3)/m, Z = 4, a = 114 7.0(1) pm, c = 504.7(1) pm, R = 0.052 for 500 F values and 43 variable para meters. Structure refinements of another crystal of the gadolinium compound with a slightly different composition and of the terbium compound gave sim ilar results. In all three structure refinements a ruthenium position on th e hexagonal axis had to be refined with split occupancy. The adjacent lanth anoid positions reflect this disorder. The refinement of the occupancy para meters of the three data sets resulted in the compositions Gd3Ru1.851(1)C4. 86(2), Gd3Ru1.862(2)C4.97(3), and Tb3Ru1.776(4)C4.95(1). The structure cont ains C-2 pairs and isolated carbon atoms. The C-C distances in the three re finements vary between 133(1) and 142(3) pm, close to the typical double-bo nd distance of 134 pm. The structure contains trigonal polyanionic clusters of the composition Ru3C10, and in addition there are ruthenium atoms which have no carbon neighbors. Chemical bonding in these compounds is briefly d iscussed on the basis of the 18- and 8-electron rules. (C) 2001 Academic Pr ess.