Two extended metal chain compounds, yttrium iodide carbides (Y4I5C and Y6I7C2). Synthesis, structure, properties, and bonding

The title phases are obtained in high yield from the reactions of stoichiometric quantities of Y, YI/sub 3/, and graphite at 850-950/degree/C in welded Nb containers. The crystal structures of the two phases determined by standard x-ray diffraction means are related to those published for Er/sub 4/I/sub 5/ and Er/sub 6/I/sub 7/ (C2/m, Z = 2, /alpha/ = 18.479 (6) and 21.557 (8) /angstrom/, b = 3.947 (1) and 3.909 (1) /angstrom/, c = 8.472 (3) and 12.374 (6) /angstrom/, /beta/ = 103.22 (4) and 123.55 (3)/degree/, R/R/sub w/ = 4.6/5.4 and 3.2/3.7% for Y/sub 4/I/sub 5/C and Y/sub 6/I/sub 7/C/sub 2/, respectively). The two compounds contain infinite single and double chains of carbon-centered yttrium octahedra, respectively, condensed by edge-sharing and sheathed by edge-bridging iodine atoms together with square-planar iodine atoms that bridge between chains. Extended Hueckel MO band calculations were carried out for the empty and the carbon-centered compounds in both structures. Metal-based bands near E/sub F/ in the empty chains exhibit characteristic strong interactions with carbon valence orbitals that generate low-lying valence bands. E/sub F/ in both cases falls within a broad, metal-based conduction band. Resistivity and magnetic susceptibility measurements on Y/sub 6/I/sub 7/C/sub 2/ support the predictedmore » metallic character. 26 refs., 11 figs., 3 tabs.« less