Synthesis, structures, and conductivities of the new layered compounds Ta₃Pd₃Te₁₄ and TaNiTe₅

The new layered ternary chalcogenides Ta₃Pd₃Te₁₄ and TaNiTe₅ have been prepared by high-temperature reactions of the elements. They have been characterized by single crystal X-ray diffraction methods. The compound Ta₃Pd₃Te₁₄ crystallizes with two formula units in the monoclinic space groupC²_2h-P2₁m in a cell with dimensionsa = 14.088(19), b = 3.737(3), c = 20.560(19)Å, and β = 103.73(5)°. TaNiTe₅ crystallizes with four formula units in the orthorhombic space groupD¹⁷_2h-Cmcm in a cell with dimensionsa = 3.659(2), b = 13.122(10), c = 15.111(11)Å. Both are layer structures. TaNiTe₅ is isostructural with the previously synthesized compound NbNiTe₅. The layers for TaNiTe₅ contain Ta atoms in a bicapped trigonal prismatic Te environment and Ni atoms in an octahedral environment. The layers for Ta₃Pd₃Te₁₄ are made up of octahedral and bicapped trigonal prismatic Ta atoms and octahedral Pd atoms coordinated by Te. Electrical conductivity measurements indicate that both of these compounds are metallic; for Ta₃Pd₃Te₁₄,σ₂₉₇ ≈ 2.2 × 10³ Ω^-1cm^-1 and for TaNiTe₅,σ₂₉₇ ≈ 2.6 × 10⁴ Ω^-1cm^-1. Magnetic susceptibility measurements show that TaNiTe₅ is paramagnetic.