CARBIDES WITH FILLED RE3B-TYPE STRUCTURE

The new compounds AFe2SiC (A = Y, Sm, Gd, Tb, Ho, Er, Tm, Lu, Th, U) w ere prepared by arc-melting cold-pressed pellets of the elemental comp onents. They are isotypic with the orthorhombic DyFe2SiC-type structur e, which was refined from single-crystal X-ray data of ThFe2SiC: Cmcm, a = 386.32(6) pm, b = 1080.6(1) pm, c = 695.0(1) pm, Z = 4, R = 0.020 for 559 structure factors and 17 variable parameters. The polyanionic iron-silicon-carbon network is three-dimensionally infinite. The carb on atoms are situated in octahedral voids formed by four thorium and t wo iron atoms. The hydrolysis of ErFe2SiC with diluted hydrochloric ac id yields mainly methane besides C2 and C3 hydrocarbons. A large numbe r of compounds can be classified to crystallize with a filled-up versi on of the Re3B-type structure. They are isotypic with V3AsC, where the positions of the vanadium and arsenic atoms correspond to the atomic positions of Re3B and the carbon atoms fill octahedral voids formed by the vanadium atoms. The DyFe2SiC-type structure also can be described as a filled-up Re3B structure; however, the carbon atoms of DyFe2SiC occupy different octahedral voids. (C) 1994 Academic Press, Inc.