Uranium Tellurides: New One- and Two-Dimensional Compounds CsUTe6, CsTiUTes, Cs₈Hf₅UTe_3o.6, and CsCuUTe₃

The new compounds CsUTe₆, CsTiUTe₅, Cs₈HfsUTe_30.6, and CsCuUTe₃ have been synthesized through the reaction of the metals with a Cs₂Te_n flux. CsUTe₆ crystallizes in space group D_2h¹⁶-Pnma of the orthorhombic system with eight formula units in a cell of dimensions a = 30.801(7), b = 8.143(2), and c = 9.174(2) Å and V = 2301(1) ų (T = 113 K). CsTiUTe₅ crystallizes in space group D₂h⁵-Pmma of the orthorhombic system with two formula units in a cell of dimensions a = 6.130(1), b = 8.240(2), and c = 10.363(2) Å and V = 523.4(2) ų (T = 113 K). Cs₈Hf₅UTe_30.6 crystallizes in space group C_2H⁵-P2_1/c of the monoclinic system with four formula units in a cell of dimensions a = 12.043(3), b = 18.724(4), and c = 30.496(6) Å, β = 97.64(3)°, and V = 6816(2) ų (T= 113 K). CsCuUTe3 crystallizes in space group D_2h¹⁷-Cmcm of the orthorhombic system with four formula units in a cell of dimensions a = 4.327(1), b = 16.661(4), and c = 11.337(3) Å, and V= 817.3(3) ų (T = 113 K). The structures of all four compounds were determined by single-crystal X-ray methods. CsUTe₆ has a one-dimensional structure that contains pairs of U/Te chains coupled by Te-Te bonds and separated by Cs⁺ cations. There are many Te-Te distances less than 3.1 Å; if an arbitrary maximum Te-Te single bond distance is taken as 2.98 Å, then the chains may be formulated ¹∞[U₂(Te₃)₃(Te₂)(Te)^2‒], with U in the +IV oxidation state. The U atoms are coordinated to nine Te atoms in a tricapped trigonal-prismatic arrangement. Electrical resistivity measurements give conductivities of 1.6(4) × 10^‒2 Ω^‒1 cm^‒1 (298 K) and 1.5(2) × 10^‒3 Ω^‒1 cm^‒1 (77 K). CsTiUTe₅ has a layered structure that contains UTe₈ bicapped trigonal prisms sharing a common edge and TiTe₆ octahedra sharing faces. Cs⁺ cations, located in pentagonal prisms of Te atoms, separate the layers. The structure contains an infinite linear Te-Te chain with a separation of 3.065(1) Å. Assignment from the structural results of formal oxidation states is difficult. Magnetic susceptibility data for CsTiUTe₅ give a curvilinear x^‒1 vs T plot. When fit to a modified Curie-Weiss law, the values C = 8.8(3) × 10^‒2 emu K/mol, ⦵ = −1.5(2) K, and x₀ = 2.11(8) × 10^‒3 emu/mol result. The value of μ_eff (300 K) is 2.23(1) μ_B for each CsTiUTe₅ unit. The resistivity of CsTiUTe₅ at 77 K is beyond the detection limits of our instrument, but it is 1.2(9) × 10^‒3 Ω^‒1 cm^‒1 at 298 K. Cs₈Hf₅UTe_30.6 is a one-dimensional compound with ordered Hf and U atoms and disordered Te atoms in two unique chains that may be formulated ¹∞[Hf₃Te_{15 6}^4_] and ^l∞[Hf₂UTe₁₅^4‒]. Cs⁺ cations separate the chains. The Hf and Uatoms are coordinated to Te atoms in a distorted trigonal prismatic framework. Since there are many short Te-Te distances the assignment of formal oxidation states is not possible. CsCuUTe₃ is a layered compound with no Te-Te bonding. Formal oxidation states are unambiguously Cs¹, Cu¹, U^IV, and Te^II‒. As expected, Cs⁺ cations separate the ²∞[CuUTe^3‒] layers, which contain UTe₆ octahedra and CuTe₄ tetrahedra. This structure differs markedly from the channel structure of CsAg₅Te₃ formed through an analogous synthesis with Cu replaced by Ag.