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| - A Study of Piperidinium Structure-Directing Agents in theSynthesis of Silica Molecular Sieves under Fluoride-BasedConditions
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| - This study is a continuation of our efforts to understand the interplay in the self-assembly chemistryfor formation of molecular sieves from guest organocations and inorganic silicon oxide. In this particularstudy we focus on the competitive interplay of the organocations and the synthesis cofactor fluoride anion.The anions play a key role in structure determination, as a function of net solution concentration. Theycompete with the role for the space-filling organocation in determining which molecular sieve host structurewill be specified. In this study we look at this competition in the synthesis for a series of 33 differentorganocations derived from the piperidine ring system. Derivatives were prepared which both fixedsubstituents on the carbon and nitrogen centers on the ring. Results were discussed in terms of productselectivity from synthesis as a function of solution concentration for the reactants. A total of 17 differenthost topologies were found in this series, and a correlation was seen for (a) open-framework lattices (lowframework densities) under the most concentrated reaction conditions and then (b) high framework densityproducts once the conditions were more dilute. Some surprising synthesis differences are seen in comparingthe performance of these structure directing agents (SDAs) in fluoride media vs hydroxide media (the moreconventional environment for zeolite/molecular sieve syntheses involving silicate chemistry). Finally molecularmodeling was used to understand some of the trends in product selectivity for closely related guest (SDA)candidates.
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