Ionothermal Synthesis and Structure of a New Layered Zirconium Phosphate

A new layered zirconium phosphate material has been synthesized ionothermally using <i>N</i>-ethylpyridinium (Epy) bromide as both the solvent and the template, and its structure has been solved from synchrotron X-ray powder diffraction data using the charge-flipping routine implemented in Superflip. Rietveld refinement coupled with difference electron density map analysis was used to locate the organic cations between the layers. In the final stages of refinement, it became clear that not only ethylpyridinium but also pyridinium ions were present between the zirconium phosphate layers. These findings were then corroborated using elemental analysis, TGA, and solid-state ¹³C CP/MAS NMR data

Locating Organic Guests in Inorganic Host Materials from X‑ray Powder Diffraction Data

Can the location of the organic structure-directing agent (SDA) inside the channel system of a zeolite be determined experimentally in a systematic manner? In an attempt to answer this question, we investigated six borosilicate zeolites of known framework structure (SSZ-53, SSZ-55, SSZ-56, SSZ-58, SSZ-59, and SSZ-60), where the location of the SDA had only been simulated using molecular modeling techniques in previous studies. From synchrotron powder diffraction data, we were able to retrieve reliable experimental positions for the SDA by using a combination of simulated annealing (global optimization) and Rietveld refinement. In this way, problems arising from data quality and only partially compatible framework and SDA symmetries, which can lead to indecipherable electron density maps, can be overcome. Rietveld refinement using geometric restraints were then performed to optimize the positions and conformations of the SDAs. With these improved models, it was possible to go on to determine the location of the B atoms in the framework structure. That is, two pieces of information that are key to the understanding of zeolite synthesisthe location of the organic SDA in the channel system and of the positions adopted by heteroatoms in the silicate frameworkcan be extracted from experimental data using a systematic strategy. In most cases, the locations of the SDAs determined experimentally compare well with those simulated with molecular modeling, but there are also some clear differences, and the reason for these differences can be understood. The approach is generally applicable, and has also been used to locate organic guests, linkers, and ligands in metal–organic compounds

SSZ-87: A Borosilicate Zeolite with Unusually Flexible 10-Ring Pore Openings

The structure of the as-synthesized borosilicate zeolite SSZ-87 has been solved by combining high-resolution X-ray powder diffraction (XPD) and rotation electron diffraction (RED) techniques. The unit cell and space group symmetry were found from the XPD data, and were essential for the initial analysis of the RED data. Although the RED data were only 15% complete, this proved to be enough for structure solution with the program <i>Focus</i>. The framework topology is the same as that of ITQ-52 (<b>IFW</b>), but for SSZ-87 the locations of the structure directing agent (SDA) and the B atoms could also be determined. SSZ-87 has large cages interconnected by 8- and 10-rings. However, results of hydroisomerization and Al insertion experiments are much more in line with those found for 12-ring zeolites. This prompted the structure analyses of SSZ-87 after calcination, and Al insertion. During calcination, the material is also partially deboronated, and the location of the resulting vacancies is consistent with those of the B atoms in the as-synthesized material. After Al insertion, SSZ-87 was found to contain almost no B and to be defect free. In its calcined and deboronated form, the pore system of SSZ-87 is more flexible than those of other 10-ring zeolites. This can be explained by the fact that the large cages in SSZ-87 are connected via single rather than double 10-ring windows and that there are vacancies in some of these 10-rings

Non-utopian optical properties computed of a tomographically reconstructed real photonic band gap crystal

State-of-the-art computational methods combined with common idealized structural models provide an incomplete understanding of experiments on real nanostructures, since manufacturing introduces unavoidable deviations from the design. We propose to close this knowledge gap by using the real structure of a manufactured crystal as input in computations to obtain a realistic comparison with observations on the same nanostructure. We demonstrate this approach on the structure of a real silicon inverse woodpile photonic bandgap crystal, obtained by previous synchrotron X-ray imaging. A 2D part of the dataset is selected and processed into a computational mesh suitable for a Discontinuous Galerkin Finite Element Method (DGFEM) to compute optical transmission spectra that are compared to those of a utopian crystal, i.e., a hypothetical model crystal with the same filling fraction where all pores are identical and circular. The nanopore shapes in the real crystal differ in a complex way from utopian pores, leading to a complex transmission spectrum with significant frequency speckle in and beyond the gap. The utopian model provides only a limited understanding of the spectrum: while it accurately predicts low frequency finite-size fringes and the lower band edge, the upper band edge is off, it completely misses the presence of speckle, the domination of speckle above the gap, and possible Anderson localized states in the gap. Moreover, unlike experiments where only external probes are available, numerical methods allow to study all fields everywhere. While the pore shapes hardly affect the fields at low frequency, major differences occur at high frequency such as localized fields deep inside the real crystal. In summary, using only external measurements and utopian models may give an erroneous picture of the fields and the LDOS inside a real crystal, which is remedied by our new approach

SSZ-45: A High-Silica Zeolite with Small Pore Openings, Large Cavities, and Unusual Adsorption Properties

Separations of small molecules such as CO₂ and N₂ or CH₄ and CO₂ are key to many industrial processes, but it is not always easy to find a molecular sieve that can discriminate between these molecules and withstand the harsh conditions often required. The high-silica zeolite SSZ-45, which was synthesized using <i>N</i>-cyclopentyldiazabicyclooctane as the structure directing agent (SDA), was found to exhibit excellent thermal stability and rather unusual adsorption properties under pressure. That is, it has potential in the area of small molecule separations. Of particular interest, therefore, was the structural basis for its peculiar adsorption behavior. The relatively complex silicate framework structure of SSZ-45 was determined from a combination of synchrotron powder diffraction and rotation electron diffraction data. Once the framework was known, it was possible to locate the organic SDA in the cavities and to better understand its contribution to the formation of the zeolite. Here we describe the synthesis of SSZ-45, the analysis of its structure, and the subsequent investigation of its small molecule separation properties

Multidimensional Disorder in Zeolite IM-18 Revealed by Combining Transmission Electron Microscopy and X‑ray Powder Diffraction Analyses

A new medium-pore germanosilicate, denoted IM-18, with a three-dimensional 8 × 8 × 10-ring channel system, has been prepared hydrothermally using 4-dimethylaminopyridine as an organic structure-directing agent (OSDA). Due to the presence of stacking disorder, the structure elucidation of IM-18 was challenging, and a combination of different techniques, including electron diffraction, high-resolution transmission electron microscopy (HRTEM), and Rietveld refinement using synchrotron powder diffraction data, was necessary to elucidate the details of the structure and to understand the nature of the disorder. Rotation electron diffraction data were used to determine the average structure of IM-18, HRTEM images to characterize the stacking disorder, and Rietveld refinement to locate the Ge in the framework and the OSDA occluded in the channels

Well-Defined Silanols in the Structure of the Calcined High-Silica Zeolite SSZ-70: New Understanding of a Successful Catalytic Material

The structure of the calcined form of the high-silica zeolite SSZ-70 has been elucidated by combining synchrotron X-ray powder diffraction (XRPD), high-resolution transmission electron microscopy (HRTEM), and two-dimensional (2D) dynamic nuclear polarization (DNP)-enhanced NMR techniques. The framework structure of SSZ-70 is a polytype of <b>MWW</b> and can be viewed as a disordered ABC-type stacking of <b>MWW</b>-layers. HRTEM and XRPD simulations show that the stacking sequence is almost random, with each layer being shifted by ±1/3 along the ⟨110⟩ direction with respect to the previous one. However, a small preponderance of ABAB stacking could be discerned. DNP-enhanced 2D ²⁹Si­{²⁹Si} <i>J</i>-mediated NMR analyses of calcined Si-SSZ-70 at natural ²⁹Si isotopic abundance (4.7%) establish the through-covalent-bond ²⁹Si–O-²⁹Si connectivities of distinct Si sites in the framework. The DNP-NMR results corroborate the presence of <b>MWW</b> layers and, more importantly, identify two distinct types of <i>Q</i>³ silanol species at the surfaces of the interlayer regions. In the first, an isolated silanol group protrudes into the interlayer space pointing toward the pocket in the adjacent layer. In the second, the surrounding topology is the same, but the isolated −SiOH group is missing, leaving a nest of three Si–O–H groups in place of the three Si–O–Si linkages. The analyses clarify the structure of this complicated material, including features that do not exhibit long-range order. With these insights, the novel catalytic behavior of SSZ-70 can be better understood and opportunities for enhancement recognized

Synthesis, Structural Elucidation, and Catalytic Properties in Olefin Epoxidation of the Polymeric Hybrid Material [Mo₃O₉(2-[3(5)-Pyrazolyl]pyridine)]_<i>n</i>

The reaction of [MoO₂Cl₂(pzpy)] (<b>1</b>) (pzpy = 2-[3(5)-pyrazolyl]­pyridine) with water in an open reflux system (16 h), in a microwave synthesis system (120 °C, 2 h), or in a Teflon-lined stainless steel digestion bomb (100 °C, 19 h) gave the molybdenum oxide/pyrazolylpyridine polymeric hybrid material [Mo₃O₉(pzpy)]_<i>n</i> (<b>2</b>) as a microcrystalline powder in yields of 72–79%. Compound <b>2</b> can also be obtained by the hydrothermal reaction of MoO₃, pzpy, and H₂O at 160 °C for 3 d. Secondary products isolated from the reaction solutions included the salt (pzpyH)₂(MoCl₄) (<b>3</b>) (pzpyH = 2-[3(5)-pyrazolyl]­pyridinium), containing a very rare example of the tetrahedral MoCl₄^2– anion, and the tetranuclear compound [Mo₄O₁₂(pzpy)₄] (<b>4</b>). Reaction of <b>2</b> with excess <i>tert</i>-butylhydroperoxide (TBHP) led to the isolation of the oxodiperoxo complex [MoO­(O₂)₂(pzpy)] (<b>5</b>). Single-crystal X-ray structures of <b>3</b> and <b>5</b> are described. Fourier transform (FT)-IR and FT Raman spectra for <b>1</b>, <b>4</b>, and <b>5</b> were assigned based on density functional theory calculations. The structure of <b>2</b> was determined from synchrotron powder X-ray diffraction data in combination with other physicochemical information. In <b>2</b>, a hybrid organic–inorganic one-dimensional (1D) polymer, _∞¹[Mo₃O₉(pzpy)], is formed by the connection of two very distinct components: a double ladder-type inorganic core reminiscent of the crystal structure of MoO₃ and 1D chains of corner-sharing distorted {MoO₄N₂} octahedra. Compound <b>2</b> exhibits moderate activity and high selectivity when used as a (pre)­catalyst for the epoxidation of <i>cis</i>-cyclooctene with TBHP. Under the reaction conditions used, <b>2</b> is poorly soluble and is gradually converted into <b>5</b>, which is at least partly responsible for the catalytic reaction