Synthesis, crystal structure and temperature-dependent properties of gallogermanate nitrite sodalite [Na8(NO2)2][GaGeO4]6

[Nas(NO2)(2)][GaGeO4](6) sodalite was synthesized in a two-step process, starting with the formation of gallogermanate basic-hydro-sodalite under mild hydrothermal conditions (1) followed by hydrothermal treatment in concentrated NaNO2 solution (2). The presence of NO in the sodalite framework was verified by FTIR and Raman spectroscopy. Crystal structure refinements were performed in the space group P (4) over bar 3n from X-ray powder diffraction data using the Rietveld method. a = 915.28(1) pm, V = 766.8(1) x 10(-6) pm(3), R-B = 1.92%. The nitrogen atoms were refined on the 8e (x, x, x) crystallographic position with 1/4 occupancy. Temperature-dependent properties were investigated by TG-DTA and in-situ X-ray powder diffraction. Debye-Anharmonicity model fit evaluation of the thermal expansion coefficient and the temperature-dependent cell volume behavior indicate intra-cage nitrite to nitrate oxidation around 850 K, confirmed by ex-situ FTIR spectroscopy. The sodalite framework decomposition follows around 935 K, resulting in the beryllonite-type NaGaGeO4. (C) 2014 Elsevier Inc. All rights reserved.