Synthesis and crystal structure of rhodanide-enclathrated sodalite Na8[AlSiO4]6(SCN)2

Rhodanide sodalite was synthesized hydrothermally in the system Na2O-SiO2-Al2O3-NaSCN-H2O at temperatures between 353 and 473 K. The products were characterized by X-ray powder diffraction and IR spectroscopy. A material of nearly ideal composition was obtained after synthesis at 403 K and 24 h duration using highly alkaline conditions of 16-M NaOH-solution. The structural features of the socialite were investigated by MAS NMR spectroscopy 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 sodalite 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. The Si- and Al-atoms of the aluminosilicate framework are completely ordered. Whereas the carbon atoms of the rhodanide anions are located at the center 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 positionally disordered, but dynamic averaging of the rhodanide positions is suggested from the Na-23 MAS NMR spectrum. (C) 2001 Elsevier Science B.V. All rights reserved.