Crystallization, characterization and structure of nitrite aluminogermanate sodalite Na8[AlGeO4]6(NO2)2

Nitrite aluminogermanate sodalite has been obtained from hydrothermal Synthesis at a temperature of 473 K. X-ray powder diffraction, and IR, Raman, and NMR spectroscopy of the Al-27 and Na-23 nuclei, and thermogravimetry were used to characterize these new sodalites. The cystallization field was studied in dependence of both the concentration of the NaNO2 'guest salt' and the concentration of the base NaOH. The investigation of the role of the hydroxide concentration in the starting solution and its effect upon the soldalite formation shows remarkable differences compared to the aluminosilicate system. It was found that increasing the hydroxide concentration led not only to a continuous decrease in the sodalite formation rate but also to an increase in the size and perfection of the crystals. The crystal structure of Na-8[AlGeO4](6)(NO2)(2) [cubic, a(o)=9.08571(1) Angstrom, space group P (4) over bar 3n was refined by the Rietveld method to a final residual of R-F=0.021 (R-P=0.064, R-wp=0.087). In contrast to the nitrite aluminosilicate sodalite, where the Si-O and Al-O distances are quite different, the Ge-O and Al-O distances are very similar and the O-Ge-O and O-Al-O angles are almost identical. The NMR investigations show increasing isotropic chemical shift for Na-23 and Al-27 nucleus of nitrite aluminogermanate sodalite and significantly lower values of quadrupole coupling parameters in comparison to nitrite aluminosilicate sodalite. (C) 1999 Published by Elsevier Science B.V. All rights reserved.