A Three-Dimensional Extended Sb Network in the Metallic Antimonides (M‘,Ti)₅Sb₈ (M‘ = Zr, Hf, Nb, Mo)

(M‘,Ti)5Sb8 was prepared from the melt by arc-melting suitable mixtures of Ti, TiSb2, and M‘Sb2, respectively. This phase exists at least with M‘ = Zr, Hf, Nb, and Mo. A significant phase range for ZrδTi5-δSb8 was found to be within 1.10(8) ≤ δ ≤ 3.9(3). All (M‘,Ti)5Sb8 representatives investigated occur in the same, yet hitherto unknown structure type, as determined by single-crystal analyses. E.g., the lattice dimensions of ZrδTi5-δSb8 range from a = 654.49(3) pm, c = 2662.4(2) pm for δ = 1.10(8) to a = 671.06(6), c = 2679.7(4) pm for δ = 3.9(3) (space group I4122, No. 98, Z = 4). The three chemically inequivalent metal sites are statistically occupied by different mixtures of the M atoms M‘ and Ti, included in a three-dimensional network of Sb atoms on 6- to 8-fold Sb coordinated positions. Sb−Sb bonds of intermediate lengths occur in addition to the predominating heteronuclear M−Sb bonds. Physical property measurements of (Zr,Ti)5Sb8 reveal these phases being metallic exhibiting specific resistances of several mΩ·cm and a small Seebeck coefficient at room temperature, in agreement with the results of the electronic structure calculations on the LMTO and extended Hückel levels. The calculations indicate a possible change to semiconducting properties by heavy doping.