Carbides Ln10Ru10C19 (Ln = Y, Gd-Lu): Crystal Structure of their Subcells and the Superstructures of Er10Ru10C19

The nine new rare earth ruthenium carbides (10/10/19) were prepared by arc‐melting of the elemental components and subsequent annealing at 1173 K. Guinier powder patterns show these compounds to crystallize with a very pronounced subcell, which was solved from the single‐crystal X‐ray diffractometer data of Er10Ru10C19, erbium ruthenium carbide: Amm2, Z = 1, R = 0.031 for 1088 structure factors and 39 variable parameters. The single‐crystal film data of Er10Ru10C19 reveal several superstructures. Two of these were refined from the single‐crystal diffractometer data of multiple domain crystals; one of these in the space group Cm, Z = 2, R = 0.057 for 4848 F values and 147 variables; the other in Amm2, Z = 8, R = 0.078 for 2352 F values and 171 variables. In all of these structures most of the C atoms are paired with C—C distances corresponding to double bonds. Together with the Ru atoms, these C atoms form two‐dimensionally infinite layers, which are separated from each other by the Er atoms. In the third dimension the ruthenium–carbon layers are linked by single C atoms and carbon pairs. The subcell shows the superposition of these isolated and paired C atoms, whereas in the idealized superstructures these C atoms are fully ordered and their atomic environments reflect this order. Lu10Ru10C19 is a metallic conductor and Pauli‐paramagnetic. The carbides Ln10Ru10C19, with Ln = Gd–Tm, show Curie–Weiss behaviour with magnetic moments corresponding to the free Ln3+ ions. The magnetic ordering temperatures are all below 35 K. Chemical bonding in these compounds can be rationalized on the basis of simple concepts assuming the octet and the 18‐electron rules to be valid for the C and Ru atoms, respectively.