Synthesis, crystal and electronic structure of BaLi Cd_13- (x ≈ 2)

A new ternary phase has been synthesized and structurally characterized. BaLi Cd_13- (x ≈ 2) adopts the cubic NaZn₁₃ structure type (space group Fm $$ c, Pearson symbol cF112) with unit cell parameter a = 13.5548 (10) Å. Structure refinements from single-crystal X-ray diffraction data demonstrate that the Li atoms are exclusively found at the centers of the Cd₁₂-icosahedra. Since a cubic BaCd₁₃ phase does not exist, and the tetragonal BaCd₁₁ is the most Cd-rich phase in the Ba-Cd system, BaLi Cd_13- (x ≈ 2) has to be considered as a true ternary compound. As opposed to the typical electron count of ca. 27e-per formula unit for many known compounds with the NaZn₁₃ structure type, BaLi Cd_13- (x ≈ 2) only has ca. 26e-, suggesting that both electronic and geometric factors are at play. Finally, the bonding characteristics of the cubic BaLi Cd_13- (x ≈ 2) and tetragonal BaCd₁₁ are investigated using the TB-LMTO-ASA method, showing metallic-like behavior.