Instabilities in the linear Sb atom chain of the new binary antimonide Ti11-xSb8-y

The new binary antimonide Ti11-xSb8-y was prepared from directly reacting the elements in stoichiometric ratios, either by melting the reaction mixture in an arc furnace or by annealing it in a resistance furnace above 1000degreesC. Ti11-xSb8-y is a nonstoichiometric compound with a small phase range that cannot be prepared with the idealized Ti:Sb ratio of 11:8. Ti10.84(3)Sb7.74(1) crystallizes in the Cr11Ge8 type, isostructural with (Zr,V)(11) Sb-8: space group Pnma, lattice dimensions a = 1462.28(9) pm, b = 559.72(4) pm, c = 1764.4(1) pm, V = 1.4441(2) nm(3) (Z = 4). One can describe this type as an intergrowth of distorted fragments of the NiAs and W5Si3 types. In addition to the dominating heteronuclear Ti-Sb bonds, the structure of Ti11-xSb8-y comprises several homonuclear Ti-Ti and Sb-Sb bonding interactions. Short bonds of alternating 276 and 284 pm occur in a linear nonclassical chain of mainly Sb atoms (i.e., 87% Sb and 13% Ti). According to our experiments, the incorporation of Ti atoms into this chain, which consists solely of Sb atoms with shorter interatomic distances than those in the ternary Zr-V antimonide, is necessary for the formation of this compound to balance the mismatch of bond length and strength in this chain.