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 radiation source have allowed
the structure solution and location of fluoride ions inside as-made pure silica zeolites with the IFR and STF
framework structures. The local environment of the fluoride has been identified, and unusual ordering of the
fluoride ions has been discovered in both cases. The details 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, and the implications for the mechanism of crystal growth are discussed.