CHANGES IN THE CRYSTAL STRUCTURE OF TSAREGORODTSEVITE [N(CH3)4][SI2(SI0.5AL 0.5)O6]2 ON HEATING

Abstract

Tsaregorodtsevite (N(CH3)4)(Si2(Si0.5Al0.5)O6)2 is a unique feldspathoid with a tetrame- thylammonium (TMA 1 ) organic cation in an ordered, sodalite-like framework of ortho- rhombic symmetry (I222) with a 5 8.984(3), b 5 8.937(2), and c 5 8.927(2) A ˚. Here, 13 C cross polarization MAS and 1 H MAS NMR spectra give direct evidence that the organic material in the cavities in tsaregorodtsevite is TMA 1 . The 27 Al and 29 Si MAS NMR spectra, and XRD data show that the framework is well ordered with Si in the T1 and T2 sites and both Si and Al in the T3 site. Upon heating, the colorless tsaregorodtsevite crystals change color becoming yellow, then brown, and finally black.