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

• Hydrothermal synthesis of |Na8(NO2)2|[GaGeO4]6 using a two-step process.
• Partial intra-cage oxidation of NaNO2 to NaNO3 starting around 850 K.
• Thermal expansion evaluation on Debye–Anharmonicity model fits.
• Sodalite framework decomposition from ∼935 K to beryllonite-type NaGaGeO4.

|Na8(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 NO2− in the sodalite framework was verified by FTIR and Raman spectroscopy. Crystal structure refinements were performed in the space group P4¯3n from X-ray powder diffraction data using the Rietveld method. a = 915.28(1) pm, V = 766.8(1) × 10−6 pm3, RB = 1.92%. The nitrogen atoms were refined on the 8e (x, x, x) crystallographic position with ¼ 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.

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