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As the spacer length in 1,2‐dimethylimidazolium‐based dications increases beyond a specific point (six methylene units), they fail in structure‐directing towards STW zeolites in any synthetic conditions. These dications can instead produce, under fluoride concentrated conditions, either *BEA [in the case of the eight‐methylene‐unit structure‐directing agent (SDA)] or MWW (ten methylene units) zeolites. For any length of the dication, the default zeolite (MTW) is a relatively dense zeolite containing a unidimensional channel, whereas the zeolite demanding most specificity (STW, *BEA or MWW) is more porous, affording a larger concentration of the dication to be occluded. This work provides the first reported fluoride synthesis of pure silica MWW zeolites. Charge balance of the organic dications in this zeolite was achieved by combining "structural" silanolates, regular "connectivity defects" and occluded fluoride. Molecular mechanics calculations showed a perfect fit of the decamethylenebis(dimethylimidazolium) dication in the sinusoidal intralayer pore system of MWW. The calculations showed also that the dication is able to stabilize the interlayer space without disturbing the hydrogen‐bonding system that holds the layers together in the as‐made material. The 19F magic‐angle spinning (MAS) NMR presented two distinct resonances at −71 and −83 ppm, which, on the basis of DFT calculations, we tentatively assigned to fluoride occluded in [4662] and [415262] cages of the MWW structure, respectively. The same DFT study determines a different chemical shift of one methyl 13C nuclear magnetic resonance according to the imidazolium ring residing in the sinusoidal channels or in the large cup cavities, thus explaining an experimentally observed splitting of that resonance. Pure silica MWW zeolite was synthesized for the first time through the fluoride route by using dimethylimidazolium‐based long dications in highly concentrated conditions. DFT calculations suggested that the F− anions reside in both [415262] and [4662] cages, giving rise to two distinct 19F NMR signals. [ABSTRACT FROM AUTHOR]

Abstract: Molecular simulation, through the computation of adsorption isotherms, is a useful predictive tool for the selective capacity of nanoporous materials. Generally, adsorbents are modelled as rigid frameworks, as opposed to allowing for vibrations of the lattice, and this approximation is assumed to have negligible impact on adsorption. In this work, this approach was tested in an especially challenging system by computing the adsorption of the chiral molecules 2‐pentanol, 2‐methylbutanol and 3‐methyl‐2‐butanol in the all‐silica and germanosilicate chiral zeolites STW and studying their lattice vibrations upon adsorption. The analysis of single‐ and multicomponent adsorption isotherms showed the suitability of STW‐type zeolites as molecular sieves for chiral separation processes, which pose a challenging task in the chemical and pharmaceutical industries. Moreover, new experimental adsorption data validate the force field employed. The results reveal that the lattice vibrations of the all‐silica framework are sorbate‐independent, while those of germanosilicate STW show host–guest coupling modulated by uptake and sorbate type that disrupts the chiral recognition sites. This study indicates that the effects of intrinsic flexibility on the selective capacity of nanoporous materials may range from low to high impact, and some of them could not have been foreseen even after examination of the structural dynamics of an empty framework. [ABSTRACT FROM AUTHOR]

One common strategy in the search for new zeolites is the use of organic structure‐directing agents (OSDA). Typically, one seeks to achieve a high specificity in the structure‐directing effect of the OSDA. This study shows, however, that an OSDA lacking strong specificity towards any particular zeolite may provide opportunities for discovery when other synthesis parameters are systematically screened. Thus, 1‐methyl‐2‐ethyl‐3‐n‐propylimidazolium has allowed to crystallize the new large/medium pore zeolite HPM‐16 as well as the recently reported extra‐large pore ‐SYT and the medium/small pore and chiral STW. The sophisticated OSDA originally affording ‐SYT and the new simple OSDA have very little in common, both in terms of size, shape and flexibility, while both may still direct the synthesis of the same zeolite. In fact, molecular simulations show that the new OSDA is located in three different positions of the ‐SYT structure, including the discrete 8MR where the original organic could not fit. [ABSTRACT FROM AUTHOR]