title: Computational study of location and role of fluoride in zeolite structures.
abstract: The distribution of fluoride ions has been studied in the pure silica IFR, ITH, IWR, STF and STT zeolite structures using computational techniques. The interactions between the F- and SDA+ ions (where SDA is the organic structure directing agent) are able to explain the F- cage occupation found experimentally. While studying the short-range fluoride-framework interactions, a relationship was found between the Si atoms forming the pentacoordinated units and the lowest F- defect energies, which rationalizes the experimental Si-F bonding in terms of energetic stability. It is proposed that the F- location is governed by a two step process. In a first stage, the electrostatic long-range forces and, especially, the interactions between the F- and the SDA+ ions, decide which cage will be filled with F-; in a second stage, once the F- cage location is decided, the F- forms a covalent bond with a Si site to form an energetically stable pentacoordinated unit [SiO4/2F]-.
authors.affiliation: Instituto de Tecnologia Quimica, UPV-CSIC, Universidad Politecnica de Valencia, Avenida Los Naranjos s/n, 46022 Valencia, Spain.
authors.forename: Angeles
authors.initials: A
authors.lastname: Pulido
authors.forename: Avelino
authors.initials: A
authors.lastname: Corma
authors.forename: German
authors.initials: G
authors.lastname: Sastre