A Bismuth-Stabilized Metal-Rich Telluride Lu9Bi≈1.0Te≈1.0 – Synthesis and Characterization



Synthetic reactions aimed at bismuth incorporation into rare-earth-metal-rich tellurides yielded Lu9Bi≈1.00Te≈1.00 over a small range of compositions, but no analogues with Gd, Tb, Er, or Y. A single-crystal X-ray diffraction analysis gave the composition Lu9Bi0.99(3)Te1.01 in the acentric orthorhombic space group Cmc21 at ambient temperature. This is isostructural with the re-refined Sc9Te2 earlier reported in a monoclinic Cc structure. Lu9Bi≈1.00Te≈1.00 represents the first ternary compound in this structure type and the third lutetium-richest compound after Lu8Te and Lu7Te. The structure contains 3 × 3 columns of Lu in the form of condensed distorted trans-edge-sharing octahedral chains along a. The Te and Bi anions lie within tricapped trigonal prisms of Lu. Generally shorter Lu–Lu interactions lie in the interior of 3 × 3 metal columns compared with those on the periphery for which fewer Lu–Lu interactions and polar covalent bonding with neighboring tellurium weaken Lu–Lu bonding. Limiting Lu–Lu distances around 3.18 Å are by far the shortest among reduced lutetium tellurides. LMTO-type ab initio electronic structure calculations reveal a metallic nature and show that strong polar bonding of Lu to both the more electronegative Bi and Te leaves Lu relatively oxidized, many 5d states falling above the Fermi level. Stronger Lu–Lu bonding within the metal columns is also indicated by their larger individual Hamilton populations. The isostructural Lu9SbTe and Sc9BiTe were also shown to exist according to powder data.