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An organic cation lacking specificity in its structure-directing action offers the possibility, through the screening of other structure-directing parameters, to synthesize a variety of zeolites. In this work we show that the organic structure-directing agent 2-isopropyl-1,3-dimethylimidazolium (2iPr13DMI) can produce up to seven different zeolite phases depending on water concentration, the presence of inorganic impurities, crystallization temperature and time, and germanium molar fraction. The obtained phases are very different in terms of pore system, connectivity of the zeolite structure and structural units. At the pure SiO2 side, ZSM-12 and SSZ-35 dominate, with ZSM-12 being favored by the presence of potassium impurities and by less concentrated conditions. The introduction of Ge at low levels favors SSZ-35 over ZSM-12 and as the Ge fraction increases it successively affords CSV, -CLO and two distinct UOS zeolites, HPM-11 and HPM-6. These two zeolites have the same topology but distinct chemical compositions and display powder X-ray diffraction patterns that are much different from each other and from that of as-synthesized IM-16 (UOS reference material). They also show different symmetry at 96 K. Rietveld refinements of the three as-made UOS materials mentioned are provided. HPM-6 and HPM-11 are produced in distinct, non-adjacent crystallization fields. The frequent cocrystallization of the chiral STW zeolite, however, did not afford its synthesis as a pure phase. Molecular mechanics simulations of the location of the organic cation and host–guest interactions fail to explain the observed trends, but also considering the intrinsic stability of the zeolites and the effect of germanium help to rationalize the results. The study is completed by DFT calculations of the NMR chemical shifts of 13C in UOS (helping to understand splittings in the spectrum) and 19F in CSV (supporting the location of fluoride inside the new [4452], which is an incomplete double 4-ring). [ABSTRACT FROM AUTHOR]

The new zeolite NUD-3 possesses a three-dimensional system of large pore channels that is topologically identical to those of ITQ-21 and PKU-14. However, the three zeolites have distinctly different frameworks: a particular single 4-membered ring inside the denser portion of the zeolite is missing in PKU-14, disordered in ITQ-21 and fully ordered in NUD-3. We document these differences and use molecular simulations to unravel the mechanism by which a particular structure directing agent dication, 1,1′-(1,2-phenylenebis(methylene))bis(3-methylimidazolium), is able to orient this inner ring. [ABSTRACT FROM AUTHOR]

HPM-7, a germanosilicate synthesized using long imidazolium-based dications with two different linkers, is shown to possess the POS topology, although disorder may exist but it is very difficult to discern. First, three simple ordered polymorphs (POS-A to POS-C) with very similar energies and structural motifs could give rise to intergrowths that would be very difficult to recognize by powder X-ray diffraction, according to DIFFaX simulations. Another four structures (POS-D to POS-G) can be derived from POS by changing the orientation of two single four rings within the structure, possibly providing an additional source of disorder. While 3D EDT strongly suggests that HPM-7 basically possesses the POS-A (i.e. POS) topology, a detailed HR-STEM study demonstrates the rare existence of some disorder compatible with the polymorph POS-D. The general avoidance of polymorphs with very similar structural motifs and comparable energies points to a rather specific structure-direction by the organic dications used. [ABSTRACT FROM AUTHOR]

A short imidazolium based dication, with only three methylene units in the spacer linker, selectively directs the crystallization of zeolite HPM-12 (*UOE) as long as there is enough germanium present in the synthesis gel. The integrity of the dication is proved by dissolution of the zeolite and 1H and 13C NMR spectroscopy, where significant effects of organic dication concentration and the presence and concentration of HF need to be taken into account. For the as-made HPM-12 zeolite, a large shift of 9 ppm of one resonance in the 13C MAS NMR spectrum is due to the particular conformation of the dication imposed by confinement in the zeolite framework, as found by DFT calculations. The structure-directing ability of this kind of dication with varying length of the linker suggests that matching of the distance between positive charges (imidazolium moieties) and negative charges (double four rings in which fluoride resides) plays a crucial role during crystallization. [ABSTRACT FROM AUTHOR]

The whole compositional range (Gef = Ge/(Ge + Si) = 0 to 1) of zeolite STW has been synthesized and studied by a comprehensive combined experimental–theoretical approach. The yield of the zeolite goes through a maximum and then drops at the GeO2 side of the series, following the inverse of the calculated free energy curve. The unit cell generally expands, roughly linearly, as the Gef increases, but a notable resilience to expansion is observed at the high silica side. This can be attributed to the more rigid character of SiO2 and the ability of Ge units to deform. Density functional theory calculations provide a new assignment of the previously controversial 19F MAS NMR resonances for occluded fluoride, which is based not only on the number of Ge atoms in the double-4-ring units but also on the way they are associated (namely, no Ge, isolated Ge, Ge pairs or closed Ge clusters). While we found an overall good agreement between the experimental and theoretical trends in preferential occupation of different crystallographic sites by Ge, the theoretical models show more sharp and abrupt tendencies, likely due both to limitations of the approach and to kinetic factors that allow metastable configurations to actually exist. [ABSTRACT FROM AUTHOR]

Length-dependent structure direction of linear methylimidazolium-based dications towards MFI zeolite, previously known only for the tetramethylene spacer, has also been found for octamethylene and decamethylene spacers. This works only under highly concentrated conditions, whereas dilution always tends to favor TON, a default structure that is the only zeolite obtained with the other reported dications (with tri-, penta-, and hexamethylene spacers). The locations and conformations of the dications have been studied by molecular mechanics simulations. As longer dications introduce lower density of positive charges in the zeolite, the density of connectivity defects also decreases. Finally, these long dications cannot easily place each charged imidazolium ring in the two possible orientations (either parallel or perpendicular to 4MR close to F− sites) found for the tetramethylene case. Hence, although the three MFI materials display two 19F NMR resonances at similar chemical shifts, their relative intensities strongly vary as a function of the spacer length. [ABSTRACT FROM AUTHOR]

Dications consisting of 1,2-dimethylimidazolium units linked by chains of 4, 5 or 6 methylene groups display structure direction towards the chiral zeolite STW as racemic conglomerates with decreasing strength as the length of the linker increases. A phase transformation from the denser and less strained MTW to the less dense and more strained STW reveals significant stabilization in the case of the 4-methylene dication, which is able to produce STW even in the absence of germanium (i.e., for a pure silica composition), and to a lesser extent for the 5-methylene derivative. When Ge is introduced in the synthesis the crystallization is easier and the crystallization field is wider, with Ge preferentially occupying positions at the double four ring units of the STW framework, as revealed by Rietveld refinement from synchrotron data. Quantum mechanics calculations show that the interaction energy diminishes as the length of the linker increases, in agreement with the experimental findings. In addition, calculation of the 13C NMR chemical shieldings and comparison with experimental spectra allowed us to identify different conformations and orientations of the imidazolium rings in the asymmetric STW cavities, depending on the spacer length. An exploratory study strongly suggests that an asymmetric derivative with additional methyl groups at both sides of the tetramethylene chain could afford the crystallization of the homochiral zeolite even as a pure silica material. [ABSTRACT FROM AUTHOR]

The synthesis of microporous aluminophosphates using 1,2,3-trimethylimidazolium (123TMI) and fluoride produces three phases (HPM-3, PST-27 and triclinic AlPO4-34) depending on the amount of water and organic structure-directing agents in the synthesis mixture. Fluoride occluded in double 4-ring units was not detected by 19F MAS NMR spectroscopy in any product. While the structure of HPM-3 remains unknown, PST-27 has been determined to be a monoclinic version of AlPO4-5 with a distorted and likely complex structure. Rietveld analysis using synchrotron diffraction data for as-made triclinic AlPO4-34 reveals that each of its cha-cages holds two 123TMI cations, forming a displaced anti-parallel dimer with a short distance between aromatic rings (3.78 Å from center to center, 3.63 Å from plane to plane). This suggests that π–π interactions may play a role in the synthesis of this phase and related CHA-type systems. A study of the optical properties of PST-27, AlPO4-34 and other materials containing 123TMI cations shows their complex fluorescence behavior, sometimes displaying a red-edge effect, i.e., a red shift of the fluorescence as the excitation wavelength is shifted toward the red edge of the absorption band. An absorption band at 291 nm appears only in the dimer-containing triclinic AlPO4-34 and is sensitive to the introduction of Si into the framework. [ABSTRACT FROM AUTHOR]

We have synthesized an aluminosilicate RTH-type zeolite with Si/Al = 10 using 1,2,3-trimethylimidazolium (123TMI+) as an organic structure-directing agent (OSDA) together with Na+ or K+ in hydroxide media and without the use of seed crystals. The zeolite obtained is characterized by a cuboid morphology made of very small ill-defined crystallites, largely different from the plank-like morphology typically observed for RTH-type zeolite crystals thus far. More interestingly, we show experimental evidence demonstrating that two 123TMI+ ions are located within each [46586484] cavity of the RTH framework, forming antiparallel dimers, as found by Rietveld refinement. When hydrothermally aged at 1023 K, Cu-RTH is much less active for NO reduction with NH3 than Cu-SSZ-13, the best catalyst known for this reaction to date. However, while the CO2 uptake (3.2 mmol g−1) on Na-RTH at 298 K and 1.0 bar is lower than that (4.5 mmol g−1) on zeolite Na-Rho, a well-studied small-pore zeolite that selectively adsorbs CO2, it exhibits much faster CO2 sorption kinetics. This renders our RTH zeolite potentially useful as a selective CO2 adsorbent. [ABSTRACT FROM AUTHOR]

2-Ethyl-1,3,4-trimethylimidazolium is so far the fifth and largest imidazolium cation able to produce the pure silica zeolite ITW. The crystallization is not direct, but occurs as an in situ transformation from either the chiral HPM-1 (STW) zeolite or the new layered zeolite precursor HPM-2 (preMTF) and results in large interpenetrated crystals with a habit so far unseen in this zeolite. The results of chemical, physicochemical and structural characterization allow us to discuss structure-direction issues. The large cation is occluded intact in the zeolite, causing an expansion of the zeolite volume. The degree of polarization of the Si-O bond is similar to that observed in other as-made ITW zeolites. [ABSTRACT FROM AUTHOR]

An organic cation lacking specificity in its structure-directing action offers the possibility, through the screening of other structure-directing parameters, to synthesize a variety of zeolites. In this work we show that the organic structure-directing agent 2-isopropyl-1,3-dimethylimidazolium (2iPr13DMI) can produce up to seven different zeolite phases depending on water concentration, the presence of inorganic impurities, crystallization temperature and time, and germanium molar fraction. The obtained phases are very different in terms of pore system, connectivity of the zeolite structure and structural units. At the pure SiO 2 side, ZSM-12 and SSZ-35 dominate, with ZSM-12 being favored by the presence of potassium impurities and by less concentrated conditions. The introduction of Ge at low levels favors SSZ-35 over ZSM-12 and as the Ge fraction increases it successively affords CSV, -CLO and two distinct UOS zeolites, HPM-11 and HPM-6. These two zeolites have the same topology but distinct chemical compositions and display powder X-ray diffraction patterns that are much different from each other and from that of as-synthesized IM-16 (UOS reference material). They also show different symmetry at 96 K. Rietveld refinements of the three as-made UOS materials mentioned are provided. HPM-6 and HPM-11 are produced in distinct, non-adjacent crystallization fields. The frequent cocrystallization of the chiral STW zeolite, however, did not afford its synthesis as a pure phase. Molecular mechanics simulations of the location of the organic cation and host-guest interactions fail to explain the observed trends, but also considering the intrinsic stability of the zeolites and the effect of germanium help to rationalize the results. The study is completed by DFT calculations of the NMR chemical shifts of 13 C in UOS (helping to understand splittings in the spectrum) and 19 F in CSV (supporting the location of fluoride inside the new [4 4 5 2 ], which is an incomplete double 4-ring).

HPM-7, a germanosilicate synthesized using long imidazolium-based dications with two different linkers, is shown to possess the POS topology, although disorder may exist but it is very difficult to discern. First, three simple ordered polymorphs (POS-A to POS-C) with very similar energies and structural motifs could give rise to intergrowths that would be very difficult to recognize by powder X-ray diffraction, according to DIFFaX simulations. Another four structures (POS-D to POS-G) can be derived from POS by changing the orientation of two single four rings within the structure, possibly providing an additional source of disorder. While 3D EDT strongly suggests that HPM-7 basically possesses the POS-A (i.e. POS) topology, a detailed HR-STEM study demonstrates the rare existence of some disorder compatible with the polymorph POS-D. The general avoidance of polymorphs with very similar structural motifs and comparable energies points to a rather specific structure-direction by the organic dications used.

A short imidazolium based dication, with only three methylene units in the spacer linker, selectively directs the crystallization of zeolite HPM-12 (*UOE) as long as there is enough germanium present in the synthesis gel. The integrity of the dication is proved by dissolution of the zeolite and 1 H and 13 C NMR spectroscopy, where significant effects of organic dication concentration and the presence and concentration of HF need to be taken into account. For the as-made HPM-12 zeolite, a large shift of 9 ppm of one resonance in the 13 C MAS NMR spectrum is due to the particular conformation of the dication imposed by confinement in the zeolite framework, as found by DFT calculations. The structure-directing ability of this kind of dication with varying length of the linker suggests that matching of the distance between positive charges (imidazolium moieties) and negative charges (double four rings in which fluoride resides) plays a crucial role during crystallization.

Length-dependent structure direction of linear methylimidazolium-based dications towards MFI zeolite, previously known only for the tetramethylene spacer, has also been found for octamethylene and decamethylene spacers. This works only under highly concentrated conditions, whereas dilution always tends to favor TON, a default structure that is the only zeolite obtained with the other reported dications (with tri-, penta-, and hexamethylene spacers). The locations and conformations of the dications have been studied by molecular mechanics simulations. As longer dications introduce lower density of positive charges in the zeolite, the density of connectivity defects also decreases. Finally, these long dications cannot easily place each charged imidazolium ring in the two possible orientations (either parallel or perpendicular to 4MR close to F- sites) found for the tetramethylene case. Hence, although the three MFI materials display two 19F NMR resonances at similar chemical shifts, their relative intensities strongly vary as a function of the spacer length.

The synthesis of microporous aluminophosphates using 1,2,3-trimethylimidazolium (123TMI) and fluoride produces three phases (HPM-3, PST-27 and triclinic AlPO4-34) depending on the amount of water and organic structure-directing agents in the synthesis mixture. Fluoride occluded in double 4-ring units was not detected by (19)F MAS NMR spectroscopy in any product. While the structure of HPM-3 remains unknown, PST-27 has been determined to be a monoclinic version of AlPO4-5 with a distorted and likely complex structure. Rietveld analysis using synchrotron diffraction data for as-made triclinic AlPO4-34 reveals that each of its cha-cages holds two 123TMI cations, forming a displaced anti-parallel dimer with a short distance between aromatic rings (3.78 Å from center to center, 3.63 Å from plane to plane). This suggests that π-π interactions may play a role in the synthesis of this phase and related CHA-type systems. A study of the optical properties of PST-27, AlPO4-34 and other materials containing 123TMI cations shows their complex fluorescence behavior, sometimes displaying a red-edge effect, i.e., a red shift of the fluorescence as the excitation wavelength is shifted toward the red edge of the absorption band. An absorption band at 291 nm appears only in the dimer-containing triclinic AlPO4-34 and is sensitive to the introduction of Si into the framework.

Two imidazolium cations containing a benzyl group, 1-benzyl-3-methylimidazolium and 1-benzyl-2,3-dimethylimidazolium, generally produce the large pore zeolite MTW when used as structure directing agents in the synthesis of pure silica zeolites by the fluoride route. When working at low water contents only the smallest of these cations is able to crystallize MFI, a zeolite with crossing medium pore channels. In that case, MFI is metastable towards MTW, but the in situ transformation slows down as the water content is decreased. Structure-direction is discussed in terms of hydrophobicity, flexibility and size of the cations. A conformational analysis shows that the bulkier 1-benzyl-2,3-dimethylimidazolium is slightly more rigid than the smaller 1-benzyl-3-methylimidazolium, and thus could have been expected to depart more easily from crystallizing a default structure such as MTW. The different performance of both cations is investigated by molecular mechanics and the simulations show that the small increase in size brought about by a methyl group at position 2 of the imidazolium ring prevents an adequate sitting of the cation at channel intersections with the imidazolium ring close to the small cavity in which fluoride resides in MFI. The calculated interaction energies help to understand the phase selectivity and time evolution experimentally observed with both cations.

The synthetic details of a novel potassium gallosilicate natrolite with Si/Ga = 1.28, denoted PST-1, are described. The presence of K(+) and Ga with well-defined levels of concentration in the synthesis mixture is essential for directing its crystallisation. PST-1 transforms rapidly into TNU-6 under hydrothermal conditions, behaviour that contrasts sharply with its very high thermal and hydrothermal stability, which is unusual for a material of such a high Ga content. These stability issues are discussed and rationalized based on chemical composition, likely violations of Loewenstein's rule and the temperature of dehydration of as-made K-PST-1. The crystal structure of TNU-6 has been resolved through the combined use of synchrotron X-ray and electron diffraction data; it has the BaFeGaO(4) structure type with an additional radical 3a x radical 3a "GeAlO(4)" superstructure that arises from tilting of some of the tetrahedral units in all of the 6-rings.

The new synthetic form of microporous crystalline silica, denoted as ITQ-12, shows a high potential for the separation of propane and propene from its mixtures.