F-: A MULTIFUNCTIONAL TOOL FOR MICROPOROUS SOLIDS a) MINERALIZING, STRUCTURE DIRECTING AND TEMPLATING EFFECTS IN THE SYNTHESIS

The chemistry of phase selectivity in the synthesis of high-silica zeolites

“…Using fluoride as a mineralizing agent, Guth and Kessler also demonstrated that zeolites could be crystallized from gels with pH values 6 -8, that these zeolites often possessed unusually large crystals, and that the products possessed few lattice defects [29,30]. The recent studies of Camblor and Corma have demonstrated that synthesis in fluoride media [31 && -36] is an effective method for preparing new all-silica zeolite phases with fewer internal silanol/siloxy defects than those prepared in hydroxide media.…”

“…Also, a number of zeolites with previously unknown framework topologies have been synthesized by the fluoride route (see Tables 2 and 3). Many of the zeolites from these syntheses are ideal for crystallographic studies [37 -45] or 29 Si MAS NMR investigations to distinguish different T atom sites [46,47] because the fluoride method frequently produces large crystals with few internal defects.…”

Computational Study of 19F NMR Spectra of Double Four Ring‐Containing Si/Ge‐Zeolites

“…Second, it works as a catalyst in the condensation reactions that lead to the formation of SiÀOÀSi bonds. [5,9] Computational techniques, [10,11] NMR spectroscopy [12][13][14][15][16] and X-ray diffraction [9,[17][18][19] have been used to find the location of the fluoride in zeolites. So far, three general fluoride environments have been reported in pure silica zeolites: 1) Price et al [20] localise F À ions in close proximity to the charged structure-directing agent (SDA) as an ion pair in the main void volume of zeolite, although this result is subject to some controversy, [21] 2) the F À ions are separated from the SDA and are located inside small cages in the zeolite framework, but are not coordinated to any framework atom, [22] and 3) inside small cages but coordinated to a Si atom forming a pentacoordinated [SiO 4/2 F] À unit.…”

Towards Inorganic Porous Materials by Design: Looking for New Architectures

“…[ 18 ] The absence of D4R units in pure silica zeolites obtained by the hydroxide route, and its frequent existence in materials prepared by the fl uoride route, with fl uoride occluded in the D4R unit, suggested the hypothesis that fl uoride could exert a "structure-direction" effect towards structures featuring these units. [ 19 ] However, the rationale behind this effect and the apparent paradox that fl uoride would exert it precisely in cases in which there is less evidence for strong Si-F interactions in the fi nal material, i.e., when F is occluded in D4R, remained unexplained until the very recent works by Zicovich-Wilson, Camblor and coworkers. These authors fi rst showed that a signifi cant charge transfer between the guests (fl uoride and organic cations) and the silica host occurs [ 20 ] and then that the effect may effectively revert the order of stability of two silica frameworks.…”