Synthesis and crystal structure of rhodanide-enclathrated sodalite Na-8[AlSiO4](6)(SCN)(2)

Rhodanide sodalite was synthesized hydrothermally in the system Na2O-SiO2-A l2O3-NaSCN-H2O at temperatures between 353 and 473 K. The products were cha racterized by X-ray powder diffraction and IR spectroscopy. A material of n early ideal composition was obtained after synthesis at 403 K and 24 h dura tion using highly alkaline conditions of 16-M NaOH-solution. The structural features of the socialite were investigated by MAS NMR spect roscopy of the nuclei Si-29, Al-27, and Na-23 and by Rietveld refinement of X-ray powder data. From these data the crystal structure of rhodanide soda lite Na-8[AlSiO4](6)(SCN)(2) has been refined in the space group P-43n: a = 907.67(3) pm, V = 0.74780(4) nm(3), R-WP = 0.054, R-P = 0.039, R-l = 0.020 , R-e = 0.027 for 4250 data points and 12 variable positional parameters. T he Si- and Al-atoms of the aluminosilicate framework are completely ordered . Whereas the carbon atoms of the rhodanide anions are located at the cente r of the sodalite cages, the sulfur and nitrogen atoms were refined on (x,0 ,0) positions near the three-fold axis of the cage. The guest anions are po sitionally disordered, but dynamic averaging of the rhodanide positions is suggested from the Na-23 MAS NMR spectrum. (C) 2001 Elsevier Science B.V. A ll rights reserved.