Position of cations and water molecules in hydrated chabazite. Natural and sodium, calcium, strontium, and potassium-exchanged chabazites

The crystal structures of natural and hydrated Na-, Ca-, Sr-, and K-exchanged chabazite from Keller (Germany) were refined at room temp. in the R‾3m space group. The most probable distribution of ions indicates the presence of 4 cation sites; 1 at the center of the hexagonal prism, 2 in the large cage along the [111] diagonal, and the 4th near the 8-ring window which is split into 2 sites close to each other in the monovalent exchanged forms. The site at the center of the D6R is empty in the Na and K-exchanged chabazites. In this last form, 1 of the 2 sites along [111] is also empty. H2O mols. are spread over a large no. of sites, 1 with 100% occupancy, at the center of the 8-ring window, the others, normally with low occupancy, inside the large cage. Occupancies of both cation and H2O mol. sites vary greatly in the different forms.