Synthesis, structure, and physical properties of the new group IV ternary tellurides, Cu₂MTe₃ (M = Ti, Zr, Hf)

The new close-packed compounds Cu₂TiTe₃, Cu₂ZrTe₃, and Cu₂HfTe₃ have been prepared through direct reactions of the elements. The compounds crystallize in space group C³_2h- C2 m of the monoclinic system with four formula units in cells of dimensions a = 19.73(3), b = 3.970(4), c = 7.076(4) Å, β = 95.7(1)° (T = 153 K) for Cu₂TiTe₃; a = 20.288(4), b = 4.065(2), c = 7.250(1) Å, β = 97.32(2)° (T = 153 K) for Cu₂ZrTe₃; a = 20.188(6), b = 4.054(1), c = 7.216(2) Å, β = 97.16(1)° (T = 111 K) for Cu₂HfTe₃. The Cu₂HfTe₃ structure has been solved by single crystal X-ray methods. The final R index on F²₀ for 1509 unique observations and 20 variables is 0.048. The Cu₂HfTe₃ structure is composed of distorted tetrahedral Cu atoms and distorted octahedral Hf atoms coordinated by Te atoms. These polyhedra are linked together through edge and face sharing. As there are no short Te···Te interactions the Cu atoms are in the +1 oxidation state and the Hf atoms are in the +4 oxidation state. The metal-metal interactions between the Cu atoms and the Hf and both Cu atoms form six-membered rings. These rings interconnect to create arsenic-like buckled sheets that run parallel to (201). Electrical resistivity measurements indicate that Cu₂HfTe₃ and Cu₂ZrTe₃ are metals with ρ{variant}₂₈₆ ≈ 3.8 × 10^-4 Ω cm and 2.0 × 10^-3 Ω cm, respectively. Cu₂ZrTe₃ exhibits Pauli-paramagnetic behavior with χ ≈ 3.5 × 10^-4 emu mol^-1.