HO4C7, Y4C7 - CARBIDES WITH C-3(4-) AND C 4- IONS

The new compounds Ho4C7 and Y4C7 have been prepared by reaction of sto ichiometric amounts of the metals and C in closed Ta capsules at 1450 and 1300 K, respectively. With HoF3 as a flux, black, needle like sing le crystals of Ho4C7 were obtained, which are air and moisture sensiti ve. Ho4C7 crystallizes in the space group P2(1)/n (No. 14) with lattic e constants a = 368.06(3), b = 1251.8(1), c = 1364.4(2) pm and beta = 96.62(1)degrees, Y4C7 with a = 370.08(5), b = 1258.9(1), c 1371.8(1) a nd beta = 96.61(1)degrees. Two different kinds of carbon species occur in the two structures: isolated C4- ions and C-3(4-) units, respectiv ely. The C4- ions are octahedrally surrounded by He-atoms, The Ho6C oc tahedra are condensed to form double chains parallel [100]. The chains are linked via C-3(4-) ions, which occupy positions above the edges o f the Ho octahedra. Additional Ho atoms are located in voids between t he C-3(4-) units. The compounds are electrically semiconducting. Ho4C7 has a magnetic Curie-Weiss behaviour with theta = -28(4) K and mu(eff ) = 8.8(2) mu(B).