A series of new phases in the alkali metal–NbV/TaV–SeIV/TeIV–O systems

Abstract

Six new phases in the alkali metal-Nb^V/Ta^V–Se^IV/Te^IV–O systems have been prepared by solid-state reactions at high-temperatures. Their structures were determined by single-crystal X-ray diffraction studies. AM₃O₆(QO₃)₂ (A = K, Rb, M = Nb, Ta, Q = Te; A = K, M = Nb, Q = Se) are isomorphous and their structures feature a 3D network with 1D 4- and 6-MRs tunnels along the a-axis which is composed of 2D layers of corner-sharing MO₆ octahedra bridged by QO₃ groups. The alkali metal ions are located at the above 1D tunnels of 6-MRs. The structure of Cs₃Nb₉O₁₈(TeO₃)₂(TeO₄)₂ features a thick Nb–Te–O layer built of corner-sharing NbO₆ octahedra, TeO₃ and TeO₄ groups. The 2D layer of the NbO₆ octahedra with 1D tunnels of 6-MRs along the c-axis are formed by 1D chains of NbO₆ chains along the c-axis and linear Nb₄O₂₁ tetramers by corner-sharing. The TeO₃ and TeO₄ groups are grafted on both sides of the niobium-oxide layer via Nb–O–Te or/and Te–O–Te bridges. The caesium(I) ions are located at the above 1D tunnels of 6-MRs. TGA, UV-vis and infrared spectral measurements as well as electronic structure calculations have also been performed.