New Ternary Group-IV Tellurides with Extensive Te-Te Bonding: The Low-Dimensional Compounds Cs₃Ti₃Te₁₁ and Cs₅Hf₅Te₂₆

The new compounds Cs₃Ti₃Te₁₁ and Cs₅Hf₅Te₂₆ have been synthesized from a Cs₂Te_n reactive flux. Cs₃Ti₃Te₁₁ crystallizes in the monoclinic space group C_2h⁵-P2₁/n with four formula units in a cell of dimensions a = 10.776(4) Å, b = 15.281(5) Å, c = 14.843(5) Å, β= 92.29(1)○, V = 2442(2) ų (T = 115 K). The structure has been refined to an agreement index of R_w(F²) of 0.084 for 154 variables and 4812 observations; the value of R₁ (on F for F_o² > 2σ(F_o²)) is 0.034. Cs₅Hf₅Te₂₆ crystallizes in the monoclinic space group C_2h⁵-P2₁/c with four formula units in a cell of dimensions a = 19.256(10) Å, b = 9.487(6) Å, c = 27.94 (2) Å, β = 98.40(8)○, V = 5049(5) ų (T = 115 K). This structure has been refined to an agreement index of R_w(F²) of 0.171 for 145 variables and 3496 observations; the value of R₁ (on F for F_o² > 2σ(F_o²)) is 0.084. Both structures comprise chains of Te-bridged group-IV metals and both feature extensive Te-Te bonding within the chains. In Cs₃Ti₃Te₁₁ individual _∞¹[Ti₃Te₁₁^3-] chains are separated by Cs⁺ cations to form a truly one-dimensional structure. The chains in Cs₅Hf₅Te₂₆ on the other hand are tethered through Te-Te interactions to form a pseudolayered structure. Assignment of oxidation states by an assessment of Te-Te bonding is not possible, owing to the plethora of intermediate Te-Te interactions. The electrical conductivity of Cs₃Ti₃Te₁₁ is ≈9.2 × 10^-5 Ω^-1 cm^-1 at 25 °C.