Two extended metal chain compounds, yttrium iodide carbides (Y4I5C and Y6I7C2). Synthesis, structure, properties, and bonding
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The title phases are obtained in high yield from the reactions of stoichiometric quantities of Y, YI3, and graphite at 850-950 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 Er4I5 and Er6I7 (C2/m, Z = 2,a = 18.479 (6) and 21.557 (8) , b = 3.947 (1) and 3.909 (1) , c = 8.472 (3) and 12.374 (6) , = 103.22 (4) and 123.55 (3), R/Rw = 4.6/5.4 and 3.2/3.7% for Y4I5C and Y6I7C2, 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 Hckel MO band calculations were carried out for the empty and the carbon-centered compounds in both structures. Metal-based bands near Ef in the empty chains exhibit characteristic strong interactions with carbon valence orbitals that generate low-lying valence bands. Ef in both cases falls within a broad, metal-based conduction band. Resistivity and magnetic susceptibility measurements on Y6I7C2 support the predicted metallic character. 1988, American Chemical Society. All rights reserved.
