Synthesis and characterization of the ultramarine-type analog Na(8-x)[Si6Al6O24] x (S2,S3,CO3)(1-2).

The use of nitrite sodalite as a precursor to prepare new blue ultramarine analogs has been investigated. The encapsulation of the chromophores inside of beta cages was achieved by heating the nitrite sodalite precursor with a mixture of sodium carbonate, sulfur, and a reducing agent at about 1000 K under airtight conditions. The obtained new blue ultramarine-type material was characterized by means of X-ray and neutron powder diffraction, transmission electron microscopy, 29Si magic-angle-spinning NMR, IR, Raman, and diffuse reflectance spectroscopies. Thermogravimetric analysis and magnetic measurements were performed in order to determine water and chromophore contents, respectively. On the basis of the spectroscopic results and Rietveld analysis of neutron powder data, the beta cage filling was found to be yellow S2(-) and blue S3(-) chromophores along with carbonate anions. The determined chromophore concentration, about 0.31 mol per formula unit, is enough to have greenish-blue ultramarines, which proves that ultramarine analogs can be obtained from nitrite sodalite.