PREPARATION, STRUCTURE REFINEMENT, AND PROPERTIES OF SOME COMPOUNDS WITH DY2FE2SI2C- AND LAMN11C2-X TYPE-STRUCTURE

The new compounds Tm2Fe2Si2C and Lu2Fe2Si2C were prepared by arc-melting cold-pressed pellets of the elemental components. They crystallize with the monoclinic Dy2Fe2Si2C-type structure. The crystal structure of Tm2Fe2Si2C 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, beta = 128.96(2)degrees, 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 [Fe2Si2C6-](n) separated by the rare-earth cations. The hydrolysis of Er2Fe2Si2C with diluted hydrochloric acid yields mainly methane besides about 20 wt% of C-2 and C-3 hydrocarbons. Tm2Fe2Si2C orders antiferromagnetically at T-N = 2.7(2) K. The magnetization behavior for this compound suggests metamagnetism. Lu2Fe2Si2C is Pauli paramagnetic. Electrical conductivity measurements of polycrystalline samples of Tm2Fe2Si2C and Lu2Fe2Si2C indicate metallic conductivity. ThFe10SiC2-x has a tetragonal LaMn11C2-x. type structure with the lattice constants a = 1005.3(2) pm and c = 651.6(2) pm. (C) 1995 Academic Press, Inc.