Preparation, Structure Refinement, and Properties of Some Compounds with Dy 2Fe 2Si 2C- and LaMn 11C 2- x-Type Structure

The new compounds Tm ₂Fe ₂Si ₂C and Lu ₂Fe ₂Si ₂C were prepared by are-melting cold-pressed pellets of the elemental components. They crystallize with the monoclinic Dy ₂Fe ₂Si ₂C-type structure. The crystal structure of Tm ₂Fe ₂Si ₂C was refined from single-crystal X-ray data: C2/ m, a = 1049.7(3) pm, b = 388.2(1) pm, c = 664.6(2) pm, β = 128.96(2)°, R = 0.020 for 296 structure factors, and 21 variable parameters. The structure may be considered as consisting of two-dimensionally infinite polyanionic layers of [Fe ₂Si ₂C ^6-] _n separated by the rare-earth cations. The hydrolysis of Er ₂Fe ₂Si ₂C with diluted hydrochloric acid yields mainly methane besides about 20 wt% of C ₂ and C ₃ hydrocarbons. Tm ₂Fe ₂Si ₂C orders antiferromagnetically at T_N = 2.7(2) K. The magnetization behavior for this compound suggests metamagnetism. Lu ₂Fe ₂Si ₂C is Pauli paramagnetic. Electrical conductivity measurements of polycrystalline samples of Tm ₂Fe ₂Si ₂C and Lu ₂Fe ₂Si ₂C indicate metallic conductivity. ThFe ₁₀SiC _{2- x} has a tetragonal LaMn ₁₁C _{2- x}-type structure with the lattice constants a = 1005.3(2) pm and c = 651.6(2) pm.