NbFe_1.28Te₃, a quasi-layered ternary niobium telluride compound

NbFe_1.28Te₃, a new ternary niobium telluride compound, was synthesized via solid state reactions. The crystal structure of this compound was determined by single crystal X-ray diffraction methods. The structure belongs to the monoclinic space group P2₁/m (number 11) and is isostructural with TaFe_1.25Te₃. The following cell constants were obtained from the analysis: a = 7.373 A ̊, b = 3.648 A ̊, c = 9.965 A ̊, β = 108.81^o, Z = 2. The final refinement yielded R = 3.5% and R_w = 4.6%. The structure can be described as a quasi-two-dimensional layered type. It consists of an Nb-Fe1-Nb metal network "sandwiched" by the Te and Fe2 atoms from above and below. This would result in an "NbFe₂Te₃" layer if the Fe2 sites were fully occupied. Connections between the layers are made through Fe2-Te2 bonds. The Fe2 atoms reside in square pyramidal sites and are bonded to four basal Te atoms from one layer and an apical Te2 atom from the adjacent layer. The partial occupancy of the Fe2 sites leads to a non-stoichiometric formula NbFe_1.28Te₃. The metal-metal bonding in this structure is quite unusual.