Crystal structures of the hydro-sodalite Na 6[AlSiO 4] 6 8H 2O and of the anhydrous sodalite Na 6[AlSiO 4] 6

Abstract

The most hydrate water rich form of the hydro-sodalites Na 6+ x [AlSiO 4] 6(OH) x nH 2O with x = O and n = 8 and the corresponding dehydrated form with x = O and n = O have studied by X-ray Rietveld analyses at 295 K and 675 K, respectively. The crystal structure of Na 6[AlSiO 4] 6. 8H 2O is strongly determined by hydrogen bonding between the non-framework hydrate water oxygens (donators) and the framework oxygens (acceptors). The hydrogen bonding scheme is destroyed during a two-step dehydratation reaction at 400–500 K, which yields a substantial relaxation of the aluminosilicate framework. The 9% volume expansion of the anhydrous sodalite Na 6[AlSiO 4] 6 is reflected by the increase of the SiOAl bridging angle from 136.2(3)° in the octahydrate to 156.3(6)° in the structure of the anhydrous high temperature product. The antagonistic effect of hydrogen bonding or hydroxo-configuration of the non-framework constituents in hydro-sodalites is discussed.