Inorganic Chemistry, Vol.45, No.26, 10728-10733, 2006
La(2)Tel(2): A new layered telluride iodide with unusual electrical properties
A new layered metal-rich telluride halide, La(2)Tel(2), has been synthesized by heating stoichiometric mixtures of Lal(3), La, and Te under argon at 900 degrees C, and its structure has been refined from X- ray powder diffraction data. The compound crystallizes in the 3R-Lu2CCl2 structure type (rhombohedral space group R (3) over barm with a = 4.5074(4) angstrom, c = 32.528(2) angstrom, and Z = 3). The crystal structure is composed of infinite layers of edge-sharing, Te-centered metal atom octahedra and iodine atoms separating these layers to form three close-packed I-Ln-Te-Ln-I slabs within the unit cell. The title compound is metallic at room temperature and exhibits an anomaly in the resistivity around 140 K which is closely related to changes in the a lattice parameter with temperature. The chemical bonding and metallic properties of La(2)Tel(2) can be plausibly understood in terms of an ionic description (Ln(3+))(2)Te2-(I-)(2)(e)(2) where two electrons are delocalized in the La 5d conduction band.