The encapsulation of a fluoride ion in an octaphenylsilsesquioxane cage is described by A. Bassindale, P. G. Taylor, and co-workers on the following pages. Viewed from above, the fluoride ion is shown to reside at the center of the cage, rather like the bird depicted; a tetrabutylammonium counterion is located between the phenyl groups of the cage.

Two fluoride-encapsulated octasilsesquioxane cage compounds have been prepared using the TBAF route as important molecular models for studying ion entrapment in siliceous zeolites. Analyses by X-ray crystal structure and solution 19F/29Si NMR spectroscopy reveal very similar environments for the encapsulated fluoride ion perfectly centered within each cage with evidence of weak silicon−fluoride ion interactions. By comparing our NMR and X-ray data with those of nonencapsulated cage analogues from the literature, we observe the effect the fluoride ion has on the geometry of the cage and use the findings of related studies in the literature to suggest reasons fluoride ion may be becoming entrapped in the silsesquioxane core.

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A range of fluoride-encapsulated octasilsesquioxane cage compounds have been prepared using the TBAF route. Our studies suggest that whilst it is relatively straightforward to prepare fluoride-encapsulated octasilsesquioxane cage compounds with adjacent sp(2) carbons, leading to a range of aryl and vinyl substituted compounds, the corresponding sp(3) carbon derivatives are more capricious, requiring an electron withdrawing group that can stabilize the cage whilst not acting as a leaving group. Analysis by X-ray crystallography and solution (19)F/(29)Si NMR spectroscopy of R(8)T(8)@F(-) reveal very similar environments for the encapsulated fluoride octasilsesquioxane cages. Migration of a fluoride ion from inside the cage to outside the cage without breaking the T(8) framework and the possibility of encapsulating other anions within silsesquioxane cages have been also investigated.