Synthesis and physical properties of the new layered ternary tellurides MIrTe4 (M = Nb, Ta), and the structure of NbIrTe4

Two new ternary transition-metal chalcogenides, niobium iridium tetratelluride (NbIrTe4) and tantalum iridium tetratelluride (TaIrTe4), have been prepared by reaction of the elemental powders at 1000°C. The structure of NbIrTe4 has been determined by single-crystal X-ray diffraction methods. The compound crystallizes in space group C72v-Pmn21 of the orthorhombic system with four formula units in a cell of dimensions a = 3.768(3), b = 12.486(10), c = 13.077(9) Å at 294 K. NbIrTe4 is a layered compound with a structure closely related to those of WTe2 and β-MoTe2, variants of the CdI2 structure type. The layers comprise buckled sheets of Te atoms, with the Nb and Ir atoms residing in distorted octahedral sites. Metal-metal bonding appears to be responsible for a close association of the Nb and Ir atoms. From Weissenberg photography, the compound TaIrTe4 is found to be isostructural to NbIrTe4, with cell dimensions a = 3.77(3), b = 12.37(6), c = 13.17(3) Å. Electrical resistivity measurements along the a axis of both compounds show that they are metallic: ϱ298 = 8.1 × 10−5 and 1.2 × 10−4 Ω cm for NbIrTe4 and TaIrTe4, respectively. Magnetic susceptibility measurements indicate essentially temperature-independent Pauli paramagnetism for both compounds: χm = 1.9 × 10−3 and 8.9 × 10−4 emu mol−1 for NbIrTe4 and TaIrTe4, respectively. The compounds NbIrTe4 and TaIrTe4 appear to belong to a larger class of compounds MM′Te4 with M = Nb, Ta and M′ = Ru, Os, Rh, Ir.