New niobium selenites, ANbO(SeO3)(2) (A = Na, K, Rb, and Cs): Effect of alkali metal cation size on the dimensionality and intraoctahedral distortion

Abstract

Four new alkali metal niobium selenites with both families of second-order Jahn-Teller distortive (SOJT) cations, ANbO(SeO3)(2) (A = Na, K, Rb, and Cs), have been synthesized through standard solid state reactions using A(2)CO(3), Nb2O5, and SeO2 in sealed fused silica tubes. Crystal structures of all four materials have been determined by single crystal X-ray diffraction. While NaNbO(SeO3)(2) is configured with corner-shared zigzag chains of NbO6 octahedra and SeO3 intrachain connectors, three isostructural ANbO(SeO3)(2) (A = K, Rb, and Cs) are arranged with corrugated layers that are composed of NbO6 octahedra and SeO3 trigonal pyramids. More detailed structural investigations indicate that the size and the coordination environment of alkali metal cations particularly affect the backbone geometries and the dimensions of the reported materials. With ANbO(SeO3)(2) (A = K, Rb, and Cs), the alkali metal cations in between the layers also influence the extent of octahedral distortions. Full characterizations including thermal analyses, infrared and UV-vis diffuse reflectance spectroscopy, intraoctahedral distortions, and local dipole moment calculations are also presented. (C) 2015 Elsevier B. V. All rights reserved.