Synthesis, Structure, and Physical Properties of a Novel Quaternary Niobium Telluride, Nb₂FeCu_0.35Te₄

Nb₂FeCu_0.35Te₄, the first solid-state quaternary niobium telluride, was prepared via chemical vapor transport reactions. The structure of this compound was determined by single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic system, space group Pmmn (No. 59). The unit cell dimensions are a = 12.576(1) Å, b = 3.8395(6) Å, c = 7.3012(9) Å, Z = 2, and V = 352.54(8) ų 123. Structural refinement with 433 observed reflections (I> 3 (σ(I)) and 40 variable parameters results in R = 4.0% and R_w = 4.8%. Nb₂FeCu_0.35Te₄ represents a novel three-dimensional structure type with interesting structural features and one-dimensional extended metal-metal bonds. The structure can be described as constructed from “Nb₄Fe₂Cu₂Te₁₁” building units. These building units stack on top of each other along the crystallographic b-axis to form a one-dimensional chain. The interchain connections are made through Cu-Te(3) bonds along the c-axis and Nb-Te(3) bonds along the a-axis resulting in a three-dimensional network with open channels running along the ¿-axis. The one-dimensional metal-metal bonds extend along the b-axis. A positional disorder was observed for both Nb and Fe sites, and all three metal atoms are partially occupied. Nb₂FeCu_0.35Te₄ shows degenerate semiconductor behavior with a room-temperature resistivity of 3.6(2) × 10^-3 Ω-cm and an antiferromagnetic ordering at 8 K. The temperature-dependent magnetic susceptibility follows modified (nonlinear) Curie-Weiss behavior with μ_eff = 1.26 μB.