Refinement of framework disorder in dehydrated CaA zeolite from single-crystal synchrotron data

An accurate knowledge of zeolite structure is required for understanding th eir selective sorption capacities and their catalytic properties. In partic ular, the positions of the exchangeable cations and their interactions with the framework are essential. The present study deals with the accurate cry stal structure determination of a fully exchanged and fully dehydrated CaA zeolite (Ca48Al96Si96O384,Fm (3) over bar c, a = 24.47 Angstrom) using sing le-crystal high-resolution synchrotron X-ray diffraction [(sin theta/lambda )(max) = 1.4 Angstrom(-1)]. It is shown that cation exchange severely disto rts the skeleton, especially around the O2 atom. The high-resolution synchr otron data reveal that this latter O atom is disordered and lies out of the mirror plane it occupies in other A-type zeolites. This feature is related to that observed for Ca2+ cations.