New polymorphs of ternary sodium tellurium oxides: hydrothermal synthesis, structure determination, and characterization of β-Na₂Te₄O₉ and Na₂Te₂O₆·1.5H₂O.

Two new sodium tellurium oxide materials, β-Na2Te4O9 and Na2Te2O6·1.5H2O, have been synthesized through hydrothermal reactions using Na2CO3, TeO2, and H2TeO4·2H2O as reagents. The structures of the novel materials have been determined by single crystal X-ray diffraction. β-Na2Te4O9 is a new polymorph of ternary tellurite that is showing a three-dimensional framework structure containing only TeO4 polyhedra. Na2Te2O6·1.5H2O reveals an anionic layered backbone composed of Te(6+)O6 octahedra and Te(4+)O5 polyhedra. Thermogravimetric analyses and powder X-ray diffractions at different temperatures suggest that the frameworks of β-Na2Te4O9 and Na2Te2O6·1.5H2O are thermally stable up to 480 and 400 °C, respectively. The Na(+) cations in between the anionic layers in Na2Te2O6·1.5H2O are completely replaced by Li(+) cations through an ion-exchange reaction. The UV-vis diffuse reflectance and infrared spectra, elemental analyses, and local dipole moment calculations are also reported.