Dimensionality variations in new zirconium iodates: hydrothermal syntheses, structural determination, and characterization of BaZr(IO3)6 and K2Zr(IO3)6

Abstract

Two new quaternary zirconium iodates, BaZr(IO₃)₆ and K₂Zr(IO₃)₆, have been synthesized through hydrothermal reactions using BaCO₃ (or K₂CO₃), ZrO₂, and HIO₃ as reagents. Single crystal and powder X-ray diffraction were used to determine crystal structures of the compounds. BaZr(IO₃)₆ exhibits infinite bands that are composed of ZrO₇ pentagonal bipyramids and IO₃ trigonal pyramids, in which Ba²⁺ cations are sandwiched by the bands. K₂Zr(IO₃)₆ exhibits a molecular structure that is composed of ZrO₆ octahedra and IO₃ groups. The dimensionality variations seem to be attributable to the flexible coordination numbers of Zr⁴⁺ cations with large ionic radii as well as the number of counter cations. Both of the materials are thermally stable up to approximately 440–450 °C and decompose to the corresponding metal zirconium oxides above these temperatures. The band gaps for BaZr(IO₃)₆ and K₂Zr(IO₃)₆ are calculated to be 3.1 and 3.0 eV, respectively, using the (K/S)-versus-E plots obtained from the UV-vis diffuse reflectance spectra. Infrared spectra and local dipole moment calculations are also presented.