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Pure-silica and aluminosilicate sodalites of varying Si/Al ratios and containing a guest molecule, ethylene glycol, acting as a structure-directing agent and as a solvent were prepared and characterized. Specifically, x-ray diffraction, NMR, IR, Raman spectroscopic experiments were performed to elucidate the effect of intra- and intermolecular hydrogen bonding on the molecular conformation of ethylene glycol. The results proved the influence of aluminum concentration on the hydrogen bonding properties of ethylene glycol contained within the beta-cages of the sodalites.

The novel zeolite VPI-8 is prepared using hydrothermal techniques followed by calcining, and then structurally solved through combined X-ray diffraction, high resolution transmission electron microscopy and solid-state nuclear magnetic resonance spectroscopy (NMR). The structure of VPI-8 is characterized by five unusual T-atoms of atomic ratios 1:4:4:4:4 in each cell unit which highly correlates with the 29Si solid-state NMR spectra. The structure highlights a unique 'pinwheel' building unit that is usually used for extremely large-sized pore molecular sieves.

Periodic ab initio calculations including energy corrections for van der Waals interactions as well as zero-point and thermal effects are used to assess the relative stability of both SiO2 (calcined) phases and host-guest interactions in the as-made zeolites, as well as their relative stability. The proposed structure-directing role toward D4R materials for fluoride is attributed fundamentally in the ability to induce a global global polarization of the silica framework that allows relaxation of the strain associated with these units.

As-made and calcined ITQ-12 zeolites are structurally characterized by analyzing their vibrational modes. The vibrational analysis has highlighted several aspects of the host-guest interaction, structure-direction issues, which have included the role of fluoride anions in allowing the crystallization of silica structures with strained double-four rings and the role played by the framework flexibility.

The synthetic gallosilicate molecular sieves with the NAT topology and Si/Ga ratio close to but slightly higher than 1.50 undergo an in situ transformation under their crystallization condition. The materials are studied ex situ by using powder X-ray diffraction, elemental and thermal analyses and multinuclear MAS NMR.

The first synthesis of thermally stable inorganic electrides with cation to electron ratios of 1:1 as in organic electrides is reported. These electrides are powerful reducing agents in which alkali metals ionize to form bound alkali cations and excess electrons.

New research into zeolite Beta has been able to obtain a surface structure which could be a significant structure unit in the crystal growth process. This work produced the first experimental demonstration of the real existence of polytype C, which is a single-crystal pillar overgrown on ordinary Beta.

The effect of fluoride ions on template ordering in zeolite IFR is reported.

The small-pore pure silica zeolite ITQ-12 has been synthesized with fumed silica as the silica source in the presence of 1,3,4-trimethylimidazolium hydroxide and hydrofluoric acid under hydrothermal conditions at 448 K. Rietveld refinement using synchrotron X-ray diffraction data of the calcined ITQ-12 product taken at 298 K confirms the proposed topology, framework type code ITW, which can be described by a monoclinic unit cell (Si24O48] having Cm symmetry. Unit cell parameters are a = 10.3360(4), b = 15.0177(6), and c = 8.8639(4) Å, β = 105.356(3)°, and cell volume V = 1326.76(9) ų. For as-synthesized ITQ-12, the occluded fluoride anion is located inside the double four-membered ring, while the flat 1,3,4- trimethylimidazolium cation lies on the equatorial plane of the slit-shaped [44546484] cage, with its longest dimension in the [010] direction. The monoclinic unit cell [(C6N2H11)+2F-2][Si24O48], having Cm symmetry, has parameters a = 10.4478(3), b = 14.9854(4), and c = 8.8366(3) Å, β = 105.935(2)°, and cell volume V= 1330.34(7) ų at 298 K. Cooperative structure-directing effects during the crystallization of ITQ-12 are discussed in terms of the structure of the as-made material. [ABSTRACT FROM AUTHOR]

As-made and calcined ITQ-12 zeolites are structurally characterized by means of the analysis of their vibrational modes. The experimental IR spectra made on high crystalline samples are compared with accurate B3LYP periodic calculations performed with the CRYSTAL06 code. The fair agreement between both sets of data allows us to make a reliable assignment of the IR modes. Thanks to the detailed information provided by the theoretical calculations, the analysis of the IR intensities, the Born dynamic charges, and the whole set of vibrational frequencies at Γ-point shed light on several aspects of the host-guest interaction, structure-direction issues, including the role of fluoride anions in allowing the crystallization of silica structures with strained double-four rings, and the role played by the framework flexibility. [ABSTRACT FROM AUTHOR]

Under specific synthesis conditions the crystallization of a dense silica zeolite (TON) is followed by its in situ transformation into a less dense and, in the absence of occluded species, less stable zeolite (ITW). Periodic ab initio calculations including energy corrections for van der Waals interactions as well as zero-point and thermal effects are used first to assess the relative stability of both SiO2 (calcined) phases and then to investigate host-guest interactions in the as-made zeolites, as well as their relative stability. The less dense SiO2-ITW is less stable than SiO2-TON, with an energy difference that is significantly larger than expected from their difference in molar volume. This extra destabilization is ascribed to the strained double 4-ring units of silica tetrahedra (D4R). Regarding the as-made materials, the organic cation fills in more efficiently the zeolitic voids in ITW than in TON, bringing about a larger stabilization in the former owing to the extension of the long-range addition of dispersion force contributions. On the other hand, fluoride induces a polarization of the silica framework that is highly localized in TON (showing pentacoordinated [SiO4/2F]- units) but has a large global character in ITW (where fluoride is encapsulated into D4R units). We argue that the structure-directing role toward D4R materials that has been proposed for fluoride consists fundamentally in the ability to induce a global polarization of the silica framework that allows relaxation of the strain associated with these units. In this sense, fluoride stabilizes the otherwise strained D4R-SiO2 frameworks making them reachable for crystallization. This work documents a case in which the structure directing agents "choose" a structure not kinetically but through stabilization. [ABSTRACT FROM AUTHOR]

A series of doubly charged structure-directing agents based on two methylimidazolium moieties linked by a linear bridge of n = 3,4,5, or 6 methylene groups has been used in the synthesis of pure silica zeolites in the presence of fluoride. All of them yielded zeolite TON while only the one with n = 4 was able to produce also zeolite MFI at highly concentrated conditions. In this MFI zeolite, two distinct (19)F MAS NMR resonances with about equal intensity were observed, indicating two different chemical environments for occluded fluoride. With the singly charged 1-ethyl-3-methylimidazolium cation, which can be formally considered as the "monomer" of the bis-imidazolium cation with n = 4, TON and MFI were also obtained, and again two (19)F MAS NMR resonances now with largely dissimilar intensities were observed in MFI. Molecular mechanics simulations support a commensurate structure-direction effect for n = 4 in MFI, with each imidazolium ring, in two different orientations, sitting close to the [4(1)5(2)6(2)] cage. Periodic DFT calculations suggest that F in MFI resides always in the [4(1)5(2)6(2)] cages, with the different (19)F resonances observed being due to the different orientation of the closest imidazolium ring., (© 2012 American Chemical Society)