Location of Fluoride Counterion in As-Synthesized Silicalite-1 by Single Crystal X-ray Diffraction

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This paper presents results from single-crystal X-ray diffraction at room temperature on as-synthesized tetrapropylammonium fluoride silicalite. The fluoride counteranion lies in a [4 1 5 2 6 2 ] cage on a general position at an interacting distance from a silicon framework atom (Si−F = 1.915(3) Å). This silicon atom is close to the center of a slightly distorted trigonal bypyramid consisting of four oxygen framework atoms and a fluoride anion. The Si−O apical bond distance (1.667(2) Å) is clearly longer than the Si−O basal bond distances (1.62 ± 0.01 Å). The occluded TPA + cation is described using a disordered model at the channels intersection.