Temperature-dependent framework–template interaction of |Na6(H2O)8|[ZnPO4]6 sodalite

• The decomposition of |Na6(H2O)8|[ZnPO4]6 sodalite is a two-step process.
• Initial loss of two water molecule at 400 K stabilizes the sodalite (step 1).
• Further heating leads to complete loss of water and structural breakdown.
• Autocorrelation of temperature dependent FTIR-spectra gives structural information.

The partial dehydration followed by the decomposition of sodium-zincophosphate-hydrosodalite caused by the total water loss was examined by temperature-dependent X-ray powder diffraction, Fourier transform infrared (FTIR) and Raman spectroscopy as well as thermogravimetry combined with difference thermoanalysis. The dehydration causing the decomposition of this sodalite could be described in a two step-process. Initially two water molecules per unit-cell were lost, changing the interaction between the zincophosphate framework and the remaining water molecules as well as sodium cations as non-framework constituents. In this stage a 3+3 coordination of water molecules and sodium cations in the sodalite cage is observed. Using the autocorrelation function (AC) for the evaluation of the temperature-dependent FTIR spectra of sodalites is reported here for the first time. Calculating the changes in the AC broadness, structural features could well be analyzed due to its correlation with respective structural parameters. Temperature dependent Raman data was used to give a band assignment of bands at Raman shifts below 300 cm−1.

The thermal decomposition of |Na6(H2O)8|[ZnPO4]6 sodalite is a two-step process with an initial loss of two water molecules at 400 K, intermediately stabilizing the highly stressed framework. Further heating leads to a subsequent loss of the remaining six water molecules and a breakup of the sodalite framework. A beryllonite-type NaZnPO4 is the final product of this process.Figure optionsDownload as PowerPoint slide