Cation site location in hydrated chabazites. Crystal structure of potassium- and silver- exchanged chabazites

Natural chabazite from N.E. Azerbaijan, Iran, was ion-exchanged to give K3.2Na0.75Al3.8Si8.2O24, n H2O and Ag3.7Al3.8Si8.3O24, m H2O respectively. After exchange crystals maintain the R3̄m symmetry with cell dimensions a = 9,459(9) Å, α = 94.06(7)o and a = 9.421 (10) Å, a = 94.20(8)o for the K- and Ag-exchanged chabazites. Full matrix least-squares refinement reduced the R index to 0.052 for (K)chab and 0.084 for (Ag)chab on the basis of 618 and 551 independent reflections. In both (Ag)- and (K)chab, the cations essentially occupy a site on the triad axis, in the large cavity facing the 6-ring oxygens of D6R units (site I) and a site near the 8-ring windows (site IV). In (K)chab an electron density peak is found near site IV, which is interpreted as due to another cation site (IV'). In (Ag)chab only 61% of the ions have been located in sites (I) and (IV), the remainder were assumed to be spread out in the zeolite cages.