The location and ordering of fluoride ions in pure silica zeolites with framework types IFR and STF; implications for the mechanism of zeolite synthesis in fluoride media

Single-crystal X-ray diffraction studies carried out at a synchrotron radia tion source have allowed the structure solution and location of fluoride io ns inside as-made pure silica zeolites with the IFR and STF framework struc tures. The local environment of the fluoride has been identified, and unusu al ordering of the fluoride ions has been discovered in both cases. The det ails of the crystal structures are used to suggest structural features that are important in determining the ordering of fluoride ions in zeolites. A mechanism for how the fluoride ordering occurs is suggested for IFR and STF based on the local structure of small cages that make up these zeolites, a nd the implications for the mechanism of crystal growth are discussed.