Crystal structures of hydrated and dehydrated forms of a Co(II)-exchanged chabazite

Abstract

Crystal structures were determined at room temperature in the rhombohedral space group R 3 m, for a cobalt(II)-exchanged chabazite from N.E. Azerbaijan, Iran (Co-chab(h): Co 1.7Na 0.4Al 3.8Si 8.2O 24·9.4H 2O), and its dehydrated form (Co-chab(d)). Unit cell parameters and R-indices were a = 9427(9) A ̊ , α = 94.02(7)° and 0.065 for Co-chab(h), and a = 9.351(9) A ̊ , α = 92.56(7)° and 0.046 for Co-chab(d). In Co-chab(h), Co ions were located in two sites of high occupancy on the triad axis, and in a third site of low occupancy in the centre of the D6R cage. Remaining extra-framework peaks were assigned to water molecules. Co ions moved during dehydration to two peaks of high occupancy, one on the triad axis near the 6-ring, the other in the centre of the D6R cage. Two other peaks of low occupancy near the 8-ring window were attributed to remaining Co and Na ions. Considerable distortion of the frame occurs during dehydration.