The lanthanoid ruthenium carbides Ln7Ru2C11 (Ln = Dy-Tm) with a superstructure caused by differences in ruthenium carbon interactions

Abstract

Abstract The new carbides Ln7Ru2C11 (Ln = Dy, Ho, Er, and Tm) were prepared by arc-melting and subsequent annealing. Their crystal structure was determined for Er7Ru2C11 from single-crystal X-ray data. It is orthorhombic with a very pronounced subcell of space group Amma and a superstructure of space group Pnma with the same cell dimensions: a = 1950.6(2) pm, b = 345.96(4) pm, c = 1650.3(2) pm; Z = 4. The structure refinements in the two space groups resulted in residuals of R = 0.030 (1074 structure factors, 50 variable parameters) and R = 0.026 (1343 F's, 91 variables), respectively. The structure contains isolated carbon atoms and C2 pairs with C–C distances varying between 128(2) pm and 136(2) pm approximately corresponding to double bonds. One half of the Ru atoms forms Ru(C2)4 units in the subcell which split to RuC6 and C2 units in the superstructure. The other half of the Ru atoms forms polymeric groups of composition RuC3. The magnetic susceptibility of Er7Ru2C11 shows Curie-Weiss behavior with complex field-dependent antiferromagnetic order at low temperatures. The experimentally determined magnetic moment per Er atom of μ exp = 9.1 (±0.1) μ B is only slightly lower than the moment of μ eff = 9.58 μ B expected for an Er3+ ion. The ruthenium-carbon polyanions do not seem to carry magnetic moments.