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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. [ABSTRACT FROM AUTHOR]

A study exploring the use of ionic liquid reactions based on imidazolium halides in molecular sieve synthesis has produced a novel zincoaluminophosphate material with an open DFO-type framework structure. This framework structure had only been observed previously in the magnesioaluminophosphate system (Mg-DAF-1) where decamethonium was used as the structure directing agent. The new Zn-DAF-1 material has been characterized using chemical and thermogravimetric analysis and 13C, 19F, 27Al and 31P MAS NMR techniques. Structure analysis (P6/mcc, a = 22.2244(1) Å, c = 42.3293(3) Å) using synchrotron powder diffraction data not only confirmed the framework structure, but also revealed the locations of the Al, P and Zn atoms in the framework, the N,N′-di-isopropyl-imidazolium (DIPI) ions in the pores, some fluoride ions associated with double 4-rings, and some water molecules and anions filling the remaining space. This level of structural detail had not been possible in the Mg-DAF-1 material. Four different locations for the DIPI cation were found in the two 12-ring channels and Zn was found to substitute for only one of the six crystallographically distinct Al sites to yield the approximate crystal chemical formula ☋(DIPI)17(OH,F)11(H2O)23☋[Zn6Al126P132O528]-DFO. [ABSTRACT FROM AUTHOR]

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 Focus. The framework topology is the same as that of ITQ-52 (IFW), 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. [ABSTRACT FROM AUTHOR]

The white-beam Laue diffraction experiment is an attractive alternative to the more conventional monochromatic one for single-crystal structure analysis, because it takes full advantage of the X-ray energy spectrum of a synchrotron source and requires no rotation of the crystal in the beam. Therefore, it could be used for structural characterizations under in situ or operando conditions. The potential of Laue diffraction was recognized and exploited by the protein community many years ago, and the methodology, which involved positioning and rotating the crystal in the beam, has been successfully applied to the determination of both protein and small-molecule crystal structures. Here, it is proposed that the specificities of Laue diffraction are exploited to study randomly oriented stationary microcrystals of inorganic materials. In order to determine the best strategy for collecting a reasonable quantity of data from stationary crystals, a series of simulations on four model structures for three experimental setups have been performed. It is shown that the structures of the four samples can be solved with the dual-space method in SHELX, even though the data sets are highly incomplete and much of the low-resolution part is missing. The experimental setup and data collection strategy for measuring such microcrystals have been developed on BL12.3.2 at the Advanced Light Source in Berkeley. The intensities of reflections with one and two harmonics can be extracted reliably by exploiting the tunable low-energy threshold of a Pilatus detector. In this way, the number of usable reflections can be increased from 75 to 95%. Such Laue microdiffraction data have been measured and used successfully to refine the structures of the model samples. [ABSTRACT FROM AUTHOR]

The program FOCUS [Grosse-Kunstleve, McCusker & Baerlocher (1997). J. Appl. Cryst. 30, 985-995] was originally developed to solve zeolite structures from X-ray powder diffraction data. It uses zeolite-specific chemical information (three-dimensional 4-connected framework structure with known bond distances and angles) to supplement the diffraction data. In this way, it is possible to compensate, at least in part, for the ambiguity of the reflection intensities resulting from reflection overlap, and the program has proven to be quite successful. Recently, advances in electron microscopy have led to the development of automated diffraction tomography (ADT) and rotation electron diffraction (RED) techniques for collecting three-dimensional electron diffraction data on very small crystallites. Reasoning that such data are also less than ideal (dynamical scattering, low completeness, beam damage) and that this can lead to failure of structure solution by conventional direct methods for very complex zeolite frameworks, FOCUS was modified to accommodate electron diffraction data. The modified program was applied successfully to five different data sets (four ADT and one RED) collected on zeolites of different complexities. One of these could not be solved completely by direct methods but emerged easily in the FOCUS trials. [ABSTRACT FROM AUTHOR]

A new zeolite (SSZ-52, ∣(C14H28N)6Na6(H2O)18∣[Al12Si96O216]), related to the DeNOx catalyst Cu-SSZ-13 (CHA framework type), has been synthesized using an unusual polycyclic quaternary ammonium cation as the structure-directing agent. By combining X-ray powder diffraction (XPD), high-resolution transmission electron microscopy (HRTEM) and molecular modeling techniques, its porous aluminosilicate framework structure (R3̅m, a = 13.6373(1) Å, c = 44.7311(4) Å), which can be viewed as an 18-layer stacking sequence of hexagonally arranged (Si,Al)6O6 rings (6-rings), has been elucidated. The structure has a three-dimensional 8-ring channel system and is a member of the ABC-6 family of zeolites (those that can be described in terms of 6-ring stacking sequences) like SSZ-13, but it has cavities that are twice as large. The code SFW has been assigned to this new framework type. The large cavities contain pairs of the bulky organic cations. HRTEM and XPD simulations show that stacking faults do occur, but only at the 5–10% level. SSZ-52 has considerable potential as a catalyst in the areas of gas conversion and sequestration. [ABSTRACT FROM AUTHOR]

The new X-ray free-electron laser source (SwissFEL) that is currently being developed at PSI will provide a broad-bandpass mode with an energy bandwidth of about 4%. By using the full energy range, a new option for structural studies of crystalline materials may become possible. The proof of concept of broad-bandpass diffraction presented here is based on Laue single-crystal microdiffraction and the experimental setup on BL12.3.2 at the Advanced Light Source in Berkeley. Diffraction patterns for 100 randomly oriented stationary crystallites of the MFI-type zeolite ZSM-5 were simulated assuming several bandwidths, and the statistical and structural results are discussed. With a 4% energy bandwidth, the number of reflection intensities measured in a single shot is significantly higher than with monochromatic radiation. Furthermore, the problem of partial reflection measurement, which is inherent to the monochromatic mode with stationary crystals, can be overcome. [ABSTRACT FROM AUTHOR]

In an attempt to overcome the reflection overlap problem, which is the primary hindrance to structure determination from powder diffraction data, an experimental approach that exploits preferred orientation was developed some years ago. Now both the experimental setup and the data analysis procedure have been optimized, with the result that the quality of the extracted reflection intensities has been improved significantly and the synchrotron beamtime required for the data collection reduced. The one-dimensional Si microstrip detector Mythen II on the Materials Science beamline at the Swiss Light Source and new features in the data analysis software MAUD [Lutterotti, Matthies & Wenk (1999). IUCr Commission on Powder Diffraction Newsletter, No. 21, pp. 14-15] have made these improvements possible. The main changes in the experimental setup are (1) using an optimized set of sample orientations, (2) placing the detector such that both positive and negative 2θ angles are measured simultaneously, and (3) introducing an additional sample tilt angle, to measure data that cannot be accessed otherwise. On the data analysis side, the program MAUD is now used for both the determination of the orientation of the crystallites and the intensity extraction. The evaluation of data obtained from a textured zirconium phosphate pyridinium sample shows a significant improvement in the reliability of the structure factor amplitudes derived from overlapping reflections. [ABSTRACT FROM AUTHOR]

The structure of the calcined borosilicate zeolite catalyst SSZ-82 ([Si61.3B4.7O132], Pmmn, a = 24.2783(4), b = 11.4665(2), and c = 14.1127(3) Å) has been solved from X-ray powder diffraction (XPD) data using the recently developed 2D-XPD charge flipping approach. The electron density maps generated with the more conventional powder charge flipping (pCF) algorithm could not be interpreted easily, so this new method, which begins by phasing low-resolution, 2D subsets of the data, was applied. Crystallographic phases were derived for the three main projections ([100], [010], and [001]) by using just the corresponding subsets of reflections (0kl, h0l, and hk0, respectively) from the full set of 3039 extracted intensities. These phases were then imposed on the (otherwise random) starting phases in the application of the pCF algorithm to the full data set. The framework structure, with 11 Si/B atoms in the asymmetric unit and a novel 12-/10-ring 2D channel system, could be seen clearly in the resulting electron density map. This is the first application of the 2D-XPD method to data collected on a material of unknown structure. Rietveld refinement of the structure revealed the positions of the B atoms in the framework and indicated that some water had been readsorbed in the pores. [ABSTRACT FROM AUTHOR]

Abstract: The zeolite framework structure of the germanosilicate SSZ-77 ([Si45.7Ge10.3O112], C2/m, a =13.2090(3)Å, b =13.3238(3)Å, c =21.5551(5)Å, β =123(2)°) has been re-examined using high-resolution synchrotron powder diffraction data collected with better counting statistics at higher angles. In the original Rietveld refinement, the geometry was strained and not all of the Ge atoms could be located. With the better data, both of these problems could be resolved. The powder charge-flipping algorithm in the program Superflip was used to determine that the space group should be reduced from C2/m to C2. With this symmetry reduction, the Ge atoms could be located more correctly, and the geometry became less strained. In the final structure, one of the 14 T sites (tetrahedrally coordinated atoms) is pure Ge, four are mixed Ge/Si positions, and the remaining nine are pure Si. Diffuse scattering under the Bragg peaks is clearly evident in the background correction. This is consistent with a Si/Ge substitutional disorder in which there is a positive correlation between neighboring unit cells. That is, adjacent unit cells are more likely to have the same ordering, so the crystal contains domains of similar unit cells rather than a completely random ordering from unit cell to unit cell. [Copyright &y& Elsevier]

The flexible, anionic, open-framework material NaLa[(PO3H)2CH-C6H4-CH(PO3H)2]·4H2O (NaLa(H4L)) exhibits an exceptional selectivity for monovalent metal cations. This study elucidates the relationship between the ion-exchange behavior and the framework flexibility of this recently discovered material. The exchange of the Na+ ions in NaLa(H4L) with alkaline-earth, alkaline, and selected transition metal ions was studied. EDX and ICP-OES elemental analysis revealed that ion exchange was successful with monovalent ions, while higher-valent ions were rejected. An explanation for this charge selectivity could be found in the site-specific role of the guest cation. X-ray diffraction and thermogravimetric studies on the reversible hydration and dehydration behavior demonstrate that NaLa(H4L) has a flexible framework. Contraction of the channels upon dehydration leads to a decrease in the cell volume of 15%. Rietveld refinement of the structure of the dehydrated form NaLa(H4L)dehyd revealed the key role played by the guest cation in the channel-shrinking mechanism. In the hydrated, expanded form, each Na+ ion guest shares three phosphonate oxygens with a La3+ ion in a lanthanum phosphonate chain that defines part of the wall of a rhombic channel. The Na+ ion completes its octahedral coordination sphere with two water molecules and a weaker bond to a fourth phosphonate oxygen. In the dehydrated, contracted form, the Na+ ion loses the two water molecules and moves toward a second La3+ ion, which is located in an adjacent lanthanum phosphonate chain, to share two more phosphonate oxygens, and becomes 5-coordinate. This results in the formation of an -La-O-Na-O-La- chain and a concomitant shrinking of the channels. A comparison of the monovalent metal (M(I)) ion-exchanged compounds, M(I)La(H4L), reveals that both the ionic radius and the enthalpy of hydration of the guest cation affect the equilibrium between the expanded and the contracted forms, and that the framework adapts specifically to the size of the guest cation. [ABSTRACT FROM AUTHOR]

High-resolution X-ray powder diffraction and electron microscopy techniques yield remarkably complementary information for crystal structure determination. By combining the two types of data, structures of polycrystalline materials that resist solution by more conventional methods can be tackled. In particular, crystallographic phase information extracted either from high-resolution transmission electron microscopy (HRTEM) images or from precession electron diffraction (PED) data has proven to be extremely useful in such cases. PED data can also be used to identify weak reflections in the diffraction pattern, and this information, in turn, can be exploited to improve the partitioning of the intensities of reflections that overlap in the powder diffraction pattern. The dual-space (diffraction and real space) structure determination programs Focus and pCF have been shown to be especially well-suited for combining the two different types of data. The power of this approach is illustrated with the details of the solutions of the structures of TNU-9, IM-5 and SSZ-74, the three most complex zeolite framework structures known. [ABSTRACT FROM AUTHOR]

A combination of advanced powder diffraction and NMR techniques have allowed the structure of the novel microporous aluminophosphate IST-1 (|(CH3NH2)4(CH3NH3+)4(OH−)4|[Al12P12O48]) to be elucidated. The framework structure was determined in the non-centrosymmetric space group Pca21 (a=9.61523(1) A˚, b=8.67024(1) A˚, c=16.21957(2) A˚) from high-resolution synchrotron powder diffraction data using the program FOCUS. Extra framework species were then located on difference electron density maps. A hydroxyl group was found to bridge between two of the framework Al atoms, and one methylamine species, presumably protonated, could be located in the channels where it H-bonds to three framework oxygens. The most unusual feature of the structure is the second methylamine molecule, which bonds directly to a framework Al atom. The structure is entirely consistent with 31P and 27Al MAS NMR studies, which showed there to be three P (all 4-coordinate) and three Al (one 4-, one 5- and one 6-coordinate) sites, and with 13C MAS NMR, which showed there to be two different types of methylamine species in equal amounts. Assignment of the 31P, 27Al and 13C MAS NMR signals could be deduced from the crystallographic data,31P-27Al HETCOR spectra and ab initio calculations. [Copyright &y& Elsevier]

Examines the use of structure envelopes in structure determination from powder diffraction data. Combination of the structure with direct-space methods to facilitate structure solution from powder data; Generation of an informative structure envelope; Assessment of the extension to molecular structures in combination with a simulated-annealing program.

The article discusses the use of three dimensional (3D) electron diffraction (ED) data derived from a single-crystal x-ray diffraction (XRD) experiment to determine hydrogen atom positions, referencing an article in the issue co-authored by scientist L. Palatinuse. The realtionship between the scattering power of an atom and its atomic number is discussed. [ABSTRACT FROM PUBLISHER]

The article discusses the new algorithm in determining crystal structures from diffraction data. Introduced in 2004, the algorithm was based on a very simple perturbation, called charge flipping, of electron-density maps that are generated during the structure solution process. Crystallographers tested the algorithm and the result is that the approach has found niches in areas in which traditional methods flounder.

Zeolites are crystalline aluminosilicate framework materials with corner sharing TO4 (T = Al, Si) tetrahedra forming well-defined pores and channels. Many zeolites are built from similar building units (i.e., isolated units, chains or layers), which are connected in different ways to form a variety of topologies. We have identified ten zeolite frameworks that share the same two-dimensional 'butterfly' net containing 5-, 6- and 10-rings: * MRE, FER, MEL, SZR, MFS, MFI, TUN, IMF, BOG and TON. Different orientations of the TO4 tetrahedra within the layer lead to different connectivities between neighboring layers. Some layers are corrugated and some are flat, resulting in different channel systems parallel to the layer. We found some interesting relationships between the unit cell parameters and this channel system that allow the size of the channels and their directions to be deduced from the unit cell dimensions. This may facilitate the prediction of new members of this zeolite family. In addition, other zeolites containing the 'butterfly' layers are also discussed. [ABSTRACT FROM AUTHOR]

While the powder charge flipping (pCF) algorithm has been applied successfully to a variety of inorganic compounds, reports on its application to organic structures, in particular those consisting of light atoms only, are rare. To investigate the reason for this apparent incongruity, a series of light-atom structures were tested using the pCF algorithm implemented in the program Superflip. The data sets, which covered varying degrees of reflection overlap, had resolutions of approximately 1 Å, and the structures ranged from 40 to 136 atoms per unit cell. Both centrosymmetric and noncentrosymmetric structures were investigated. A modified pCF approach, which was developed in a separate study, was tested on several compounds whose structures could not be solved by applying the basic pCF algorithm in Superflip. The results show that organic structures with no heavy atoms and low symmetry do indeed test the limits of the pCF algorithm in Superflip. The study has allowed a few guidelines for approaching such problems to be formulated. [ABSTRACT FROM AUTHOR]

Separationsof small molecules such as CO2and N2or CH4and CO2are key to many industrialprocesses, but it is not always easy to find a molecular sieve thatcan discriminate between these molecules and withstand the harsh conditionsoften required. The high-silica zeolite SSZ-45, which was synthesizedusing N-cyclopentyldiazabicyclooctane as the structuredirecting agent (SDA), was found to exhibit excellent thermal stabilityand rather unusual adsorption properties under pressure. That is,it has potential in the area of small molecule separations. Of particularinterest, therefore, was the structural basis for its peculiar adsorptionbehavior. The relatively complex silicate framework structure of SSZ-45was determined from a combination of synchrotron powder diffractionand rotation electron diffraction data. Once the framework was known,it was possible to locate the organic SDA in the cavities and to betterunderstand its contribution to the formation of the zeolite. Herewe describe the synthesis of SSZ-45, the analysis of its structure,and the subsequent investigation of its small molecule separationproperties. [ABSTRACT FROM AUTHOR]

Analysisof the structure of the zeolite ferrierite (frameworktype FER) synthesized using a combination of tetramethylammonium(TMA) and pyrrolidine as organic structure-directing agents (|((CH3)4N)0.4((CH2)4NH)3.6H1.7|[Si33.9Al2.1O72]) has revealed that TMA ions reside exclusively inthe [586682] cavities of the FERframework, whereas pyrrolidine species are found in boththe [586682] cavities and the main10-ring channel. A similar, but not identical, arrangement of pyrrolidinemolecules was found for a sample synthesized with pyrrolidine as theonly SDA (|((CH2)4NH)4.2H2.2|[Si33.8Al2.2O72])). A comparisonof the two structures shows the influence of TMA on the location ofpyrrolidine and the framework Al. Pyrrolidine species establish strongerinteractions with the zeolitic framework than does TMA, suggestinga different ability of the amine to exert an influence on the aluminumdistribution of the zeolite. These findings have implications in thecatalytic performance of the samples. [ABSTRACT FROM AUTHOR]

Over the past few years, the powder charge-flipping algorithm has proved to be a useful one for structure solution from powder diffraction data, so a semi-systematic study of the effect of the different input parameters on its success has been performed. Two data sets were studied in these tests: a zirconium phosphate framework material and D-ribose. The Superflip input parameters tested were the reflection overlap factor, the intensity repartitioning frequency, the isotropic displacement parameter, the threshold for charge flipping and the number of cycles/runs. By varying the values of these parameters within sensible ranges, an optimized set could be found for the zirconium phosphate case, but no combination of parameters allowed the D-ribose structure to be solved. Reasoning that starting with nonrandom phases might help, an approximate (but incorrect) structure was generated using the direct-space global-optimization method implemented in the program FOX. This structure was then used to calculate initial phase sets for Superflip by allowing the calculated phases to vary in a random fashion by a user-defined percentage. With such phases and reoptimized input parameters, some fully interpretable solutions with the correct symmetry could be produced, even with fairly low resolution data. Unfortunately, it was not possible to recognize these solutions using the Superflip R values, so other criteria were sought. Both cluster analyses and maximum entropy calculations of the solutions were performed, and the latter, in particular, look very promising. A set of guidelines derived from these two structures could be applied successfully to a further two inorganic and seven organic structures. [ABSTRACT FROM AUTHOR]

The article presents research on the structure of the zeolite SSZ-57, which exhibits adsorption and catalytic behavior somewhere between a medium- (10-ring) and large-pore (12-ring) zeolite. The authors determined that the silicate framework structure is related to ZSM-11 but shows commensurate modulation along the c axis. The use of SSZ-57 in creating products for fine chemicals is discussed. Figures are provided which show the idealized structure of SSZ-57, disorder in the crystal structure of SSZ-57, and an arrangement of cavities in the channel system of the zeolite.

Zn atoms have been incorporated into the STA-1 microporous framework (SAOframework type) for the first time. Pure Zn-containing STA-1 aluminophosphate has been obtained in the presence of either (S)-(−)-N-benzylpyrrolidine-2-methanol (BPM) or benzylpyrrolidine (BP) as structure-directing agent. Characterisation results have demonstrated that the organic molecules remain intact within the microporous framework after the hydrothermal treatment. The X-ray diffraction pattern has been indexed in the tetragonal space group I4m2 (a= 13.7828(1) Å and c= 21.9444(4) Å). Chemical analysis and 31P MAS NMR spectroscopy confirm the incorporation of ca. 4.5 Zn atoms per unit cell by isomorphous substitution of Al. This large-pore aluminophosphate has one of the lowest framework densities among the known zeolite structures, and is therefore of potential interest for applications in adsorption or catalytic processes involving bulky molecules. [ABSTRACT FROM AUTHOR]

Information derived from precession electron diffraction (PED) patterns can be used to advantage in combination with high-resolution X-ray powder diffraction data to solve crystal structures that resist solution from X-ray data alone. PED data have been exploited in two different ways for this purpose: (1) to identify weak reflections and (2) to estimate the phases of the reflections in the projection. The former is used to improve the partitioning of the reflection intensities within an overlap group and the latter to provide some starting phases for structure determination. The information was incorporated into a powder charge-flipping algorithm for structure solution. The approaches were first developed using data for the moderately complex zeolite ZSM-5, and then tested on TNU-9, one of the two most complex zeolites known. In both cases, including PED data from just a few projections facilitated structure solution significantly. [ABSTRACT FROM AUTHOR]

Physico-chemical characterization of the high-silica zeolite catalyst SSZ-74 (ref. 1) suggested that it, like the related materials TNU-9 (ref. 2) and IM-5 (ref. 3), has a multidimensional 10-ring channel system. Such pore systems are ideal for many petrochemical applications, and indeed SSZ-74 has been shown to be a good catalyst for a wide variety of reactions. The elucidation of its framework structure, however, proved to be difficult. Comparable problems were encountered with TNU-9 and IM-5, which were synthesized with related structure-directing agents. Their framework structures, which are the two most complex ones known, both have 24 Si atoms in the asymmetric unit, and were finally solved by combining high-resolution powder diffraction data with information derived from high-resolution electron microscopy images. Therefore, a similar approach, using the powder charge-flipping algorithm to combine the two types of data and molecular modelling to help to locate the structure-directing agent, was applied to SSZ-74. This procedure eventually revealed a most unusual 23-Si-atom framework structure (|(C16H34N2)4&Si92□4O184(OH)8]) with ordered Si vacancies. [ABSTRACT FROM AUTHOR]

Abstract: In an attempt to prepare a novel condensed silicate containing double 4-rings, a hydrothermal synthesis using a solution of octakis(tetramethylammonium) octasilsesquioxane hydrate as the starting material was performed. The product (DLM-2) was more thermally stable than the precursor, indicating that at least some condensation had taken place, but the solution of the structure of this polycrystalline material (∣((CH3)3N)8 (H2O)20∣[Si24O48(OH)8]) turned out to be more difficult than expected. This was primarily a result of the fact that the correct symmetry was unclear. However, the structure was finally solved from powder diffraction data collected on a textured sample using the powder charge flipping algorithm pCF in the program Superflip. This algorithm is symmetry independent, so the space group problem could be circumvented. The structure proved to be non-centrosymmetric (Ima2, a =11.5243(1)Å, b =8.4136(1)Å, c =27.9075(4)Å) and consists of silicate layers hydrogen-bonded to one another via water molecules with TMA+ cations encapsulated in the voids. However, there are no double 4-rings in the structure, suggesting that softer reaction conditions are needed for them to retain their structural integrity during the synthesis. The structure is very similar to that of the zeolite precursor RUB-15. [Copyright &y& Elsevier]

Abstract: The crystal structure of the potassium calcium silicate material, CAS-1 (|(Ca4K4(H2O)8)|[Si16O38]), has been determined from synchrotron powder diffraction data collected on a textured polycrystalline sample. It was not possible to solve the structure directly from normal high-resolution powder diffraction data, so the newly developed texture approach to structure solution using data collected in transmission mode was applied. Data analysis was performed using the computer program Expol, which has been developed to handle the large amount of data generated in transmission mode. The structure could then be solved by direct methods, and Rietveld refinement (using data collected on an untextured sample) converged with R F = 0.062 and R wp = 0.175 (R exp = 0.097). This structure is the first novel structure to be solved using the texture method in this configuration. As suggested by 29Si MAS NMR results (1 Q4 and 3 Q3 signals, all of equal intensity), CAS-1 (C2, a = 24.158 Å, b = 7.016 Å, c = 6.482 Å, β = 95.19°) proved to be a layer silicate. The structure can be described as a series of silicate double layers connected via chains of edge-sharing CaO5(H2O) octahedra. There is a two-dimensional eight-ring channel system within the silicate layer, and K+ ions, which balance the charge, are located in the eight-rings of the two 4.82 nets that form the double layer. One water molecule is located in the channel system and another bridges between K+ and Ca2+ ions. The structure is related to that of the natural mineral rhodesite. To cite this article: J.L. Jordá et al., C. R. Chimie 8 (2005). [Copyright &y& Elsevier]

The direct conversion of methane to methanol using oxygen is a challenging but potentially rewarding pathway towards utilizing methane. By using a stepwise chemical looping approach, copper‐exchanged zeolites can convert methane to methanol, but productivity is still too low for viable implementation. However, if the nature of the active site could be elucidated, that information could be used to design more effective catalysts. By employing anomalous X‐ray powder diffraction with support from theory and other X‐ray techniques, we have derived a quantitative and spatial description of the highly selective, active copper sites in zeolite omega (Cu‐omega). This is the first comprehensive description of the structure of non‐copper‐oxo active species and will provide a pivotal model for future development for materials for methane to methanol conversion. [ABSTRACT FROM AUTHOR]

The direct conversion of methane to methanol using oxygen is a challenging but potentially rewarding pathway towards utilizing methane. By using a stepwise chemical looping approach, copper‐exchanged zeolites can convert methane to methanol, but productivity is still too low for viable implementation. However, if the nature of the active site could be elucidated, that information could be used to design more effective catalysts. By employing anomalous X‐ray powder diffraction with support from theory and other X‐ray techniques, we have derived a quantitative and spatial description of the highly selective, active copper sites in zeolite omega (Cu‐omega). This is the first comprehensive description of the structure of non‐copper‐oxo active species and will provide a pivotal model for future development for materials for methane to methanol conversion. [ABSTRACT FROM AUTHOR]

Many industrially important materials, ranging from ceramics to catalysts to pharmaceuticals, are polycrystalline and cannot be grown as single crystals. This means that non-conventional methods of structure analysis must be applied to obtain the structural information that is fundamental to the understanding of the properties of these materials. Electron microscopy might appear to be a natural approach, but only relatively simple structures have been solved by this route. Powder diffraction is another obvious option, but the overlap of reflections with similar diffraction angles causes an ambiguity in the relative intensities of those reflections. Various ways of overcoming or circumventing this problem have been developed, and several of these involve incorporating chemical information into the structure determination process. For complex zeolite structures, the FOCUS algorithm has proved to be effective. Because it operates in both real and reciprocal space, phase information obtained from high-resolution transmission electron microscopy images can be incorporated directly into this algorithm in a simple way. Here we show that by doing so, the complexity limit can be extended much further. The power of this approach has been demonstrated with the solution of the structure of the zeolite TNU-9 (|H9.3|[Al9.3Si182.7O384]; ref. 10) with 24 topologically distinct (Si,Al) atoms and 52 such O atoms. For comparison, ITQ-22 (ref. 11), the most complex zeolite known to date, has 16 topologically distinct (Si,Ge) atoms. [ABSTRACT FROM AUTHOR]

Presents a report on the development of a method for solving structures from powder diffraction data. Demonstration of validity on three complex structures; Use of a textured sample that exploits the high intensity and parallel nature of synchrotron radiation; The principle of crystal structures; Results.

The high‐silica zeolite SSZ‐27 was synthesized using one of the isomers of the organic structure‐directing agent that is known to produce the large‐pore zeolite SSZ‐26 (CON). The structure of the as‐synthesized form was solved using multi‐crystal electron diffraction data. Data were collected on eighteen crystals, and to obtain a high‐quality and complete data set for structure refinement, hierarchical cluster analysis was employed to select the data sets most suitable for merging. The framework structure of SSZ‐27 can be described as a combination of two types of cavities, one of which is shaped like a heart. The cavities are connected through shared 8‐ring windows to create straight channels that are linked together in pairs to form a one‐dimensional channel system. Once the framework structure was known, molecular modelling was used to find the best fitting isomer, and this, in turn, was isolated to improve the synthesis conditions for SSZ‐27. [ABSTRACT FROM AUTHOR]

The high‐silica zeolite SSZ‐27 was synthesized using one of the isomers of the organic structure‐directing agent that is known to produce the large‐pore zeolite SSZ‐26 (CON). The structure of the as‐synthesized form was solved using multi‐crystal electron diffraction data. Data were collected on eighteen crystals, and to obtain a high‐quality and complete data set for structure refinement, hierarchical cluster analysis was employed to select the data sets most suitable for merging. The framework structure of SSZ‐27 can be described as a combination of two types of cavities, one of which is shaped like a heart. The cavities are connected through shared 8‐ring windows to create straight channels that are linked together in pairs to form a one‐dimensional channel system. Once the framework structure was known, molecular modelling was used to find the best fitting isomer, and this, in turn, was isolated to improve the synthesis conditions for SSZ‐27. [ABSTRACT FROM AUTHOR]

The adsorption and reaction properties of heterogeneous zeolite catalysts (e.g. for catalytic cracking of petroleum, partial oxidation of natural gas) depend strongly on the types and distributions of Al heteroatoms in the aluminosilicate frameworks. The origins of these properties have been challenging to discern, owing in part to the structural complexity of aluminosilicate zeolites. Herein, combined solid‐state NMR and synchrotron X‐ray powder diffraction analyses show the Al atoms locate preferentially in certain framework sites in the zeolite catalyst Al‐SSZ‐70. Through‐covalent‐bond 2D 27Al{29Si} J‐correlation NMR spectra allow distinct framework Al sites to be identified and their relative occupancies quantified. The analyses show that 94 % of the Al atoms are located at the surfaces of the large‐pore interlayer channels of Al‐SSZ‐70, while only 6 % are in the sub‐nm intralayer channels. The selective siting of Al atoms accounts for the reaction properties of catalysts derived from SSZ‐70. [ABSTRACT FROM AUTHOR]

The adsorption and reaction properties of heterogeneous zeolite catalysts (e.g. for catalytic cracking of petroleum, partial oxidation of natural gas) depend strongly on the types and distributions of Al heteroatoms in the aluminosilicate frameworks. The origins of these properties have been challenging to discern, owing in part to the structural complexity of aluminosilicate zeolites. Herein, combined solid‐state NMR and synchrotron X‐ray powder diffraction analyses show the Al atoms locate preferentially in certain framework sites in the zeolite catalyst Al‐SSZ‐70. Through‐covalent‐bond 2D 27Al{29Si} J‐correlation NMR spectra allow distinct framework Al sites to be identified and their relative occupancies quantified. The analyses show that 94 % of the Al atoms are located at the surfaces of the large‐pore interlayer channels of Al‐SSZ‐70, while only 6 % are in the sub‐nm intralayer channels. The selective siting of Al atoms accounts for the reaction properties of catalysts derived from SSZ‐70. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 MWW and can be viewed as a disordered ABC-type stacking of MWW-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} J-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 MWW layers and, more importantly, identify two distinct types of Q3 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. [ABSTRACT FROM AUTHOR]

The synthesis of the germanosilicate CIT-13, a molecular sieve that is the first to have a two-dimensional (2D) pore system possessing pores that are bounded by 14- and 10-rings, is accomplished using a family of monoquaternary, benzyl-imidazolium organic structure-directing agents (OSDAs) in aqueous media containing fluoride. CIT-13 is prepared using either hydrogen fluoride (HF) or ammonium fluoride (NH4F). The structure refinement suggests that most of the Ge atoms are located in the d4r (double-4-rings) units, and that there are framework disorders in the arrangement of those d4r units. Other characterizations of CIT-13 such as 29Si MAS NMR spectra, Ar-adsorption isotherms, and so forth are presented and compared to those of IM-12 (UTL), a previously reported germanosilicate with 14- and 12-ring pores. [ABSTRACT FROM AUTHOR]

A literature survey reveals a prominent reduction in the concentration of Brønsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple-quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI-type zeolites by desilication. The findings, subsequently generalized to FAU- and BEA-type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends. [ABSTRACT FROM AUTHOR]

A new layered zirconium phosphate material has been synthesized ionothermally using N-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. [ABSTRACT FROM AUTHOR]

A new layered zirconium phosphate material has been synthesized ionothermally using N-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. [ABSTRACT FROM AUTHOR]

Zeolites are important materials whose utility in industry depends on the nature of their porous structure. Control over microporosity is therefore a vitally important target. Unfortunately, traditional methods for controlling porosity, in particular the use of organic structure-directing agents, are relatively coarse and provide almost no opportunity to tune the porosity as required. Here we show how zeolites with a continuously tuneable surface area and micropore volume over a wide range can be prepared. This means that a particular surface area or micropore volume can be precisely tuned. The range of porosity we can target covers the whole range of useful zeolite porosity: from small pores consisting of 8-rings all the way to extra-large pores consisting of 14-rings. [ABSTRACT FROM AUTHOR]

Zeolites are important materials whose utility in industry depends on the nature of their porous structure. Control over microporosity is therefore a vitally important target. Unfortunately, traditional methods for controlling porosity, in particular the use of organic structure-directing agents, are relatively coarse and provide almost no opportunity to tune the porosity as required. Here we show how zeolites with a continuously tuneable surface area and micropore volume over a wide range can be prepared. This means that a particular surface area or micropore volume can be precisely tuned. The range of porosity we can target covers the whole range of useful zeolite porosity: from small pores consisting of 8-rings all the way to extra-large pores consisting of 14-rings. [ABSTRACT FROM AUTHOR]

The synthesis of the high-silica zeolite SSZ-61 using a particularly bulky polycyclic structure-directing agent and the subsequent elucidation of its unusual framework structure with extra-large dumbbell-shaped pore openings are described. By using information derived from a variety of X-ray powder diffraction and electron microscopy techniques, the complex framework structure, with 20 Si atoms in the asymmetric unit, could be determined and the full structure refined. The Si atoms at the waist of the dumbbell are only three-connected and are bonded to terminal O atoms pointing into the channel. Unlike the six previously reported extra-large-pore zeolites, SSZ-61 contains no heteroatoms in the framework and can be calcined easily. This, coupled with the possibility of inserting a catalytically active center in the channel between the terminal O atoms in place of H+, afford SSZ-61 intriguing potential for catalytic applications. [ABSTRACT FROM AUTHOR]

The synthesis of the high-silica zeolite SSZ-61 using a particularly bulky polycyclic structure-directing agent and the subsequent elucidation of its unusual framework structure with extra-large dumbbell-shaped pore openings are described. By using information derived from a variety of X-ray powder diffraction and electron microscopy techniques, the complex framework structure, with 20 Si atoms in the asymmetric unit, could be determined and the full structure refined. The Si atoms at the waist of the dumbbell are only three-connected and are bonded to terminal O atoms pointing into the channel. Unlike the six previously reported extra-large-pore zeolites, SSZ-61 contains no heteroatoms in the framework and can be calcined easily. This, coupled with the possibility of inserting a catalytically active center in the channel between the terminal O atoms in place of H+, afford SSZ-61 intriguing potential for catalytic applications. [ABSTRACT FROM AUTHOR]

The reaction of [MoO2Cl2(pzpy)] (1) (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)]n (2) as a microcrystalline powder in yields of 72-79%. Compound 2 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) (3) (pzpyH = 2-[3(5)-pyrazolyl]pyridinium), containing a very rare example of the tetrahedral MoCl42- anion, and the tetranuclear compound [Mo4O12(pzpy)4] (4). Reaction of 2 with excess tert-butylhydroperoxide (TBHP) led to the isolation of the oxodiperoxo complex [MoO(O2)2(pzpy)] (5). Single-crystal X-ray structures of 3 and 5 are described. Fourier transform (FT)-IR and FT Raman spectra for 1, 4, and 5 were assigned based on density functional theory calculations. The structure of 2 was determined from synchrotron powder X-ray diffraction data in combination with other physicochemical information. In 2, 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 2 exhibits moderate activity and high selectivity when used as a (pre)catalyst for the epoxidation of cis-cyclooctene with TBHP. Under the reaction conditions used, 2 is poorly soluble and is gradually converted into 5, which is at least partly responsible for the catalytic reaction. [ABSTRACT FROM AUTHOR]

The crystal structure of a novel open-framework gallogermanate, SU-66 {|(C6H18N2)18(H2O)32|[Ga4.8Ge87.2O208]}, has been solved from laboratory X-ray powder diffraction (XPD) data by using a direct-space structure solution algorithm and local structural information obtained from infrared (IR) spectroscopy. IR studies on 18 known germanates revealed that the bands in their IR spectra were characteristic of the different composite building units (CBUs) present in the structures. By comparing the bands corresponding to Ge-O vibrations in the IR spectra of SU-66 with those of the 18 known structures with different CBUs, the CBU of SU-66 could be identified empirically as the Ge10(O,OH)27 cluster (Ge10). The unit cell and space group (extinction symbol P-- a; a = 14.963, b = 31.593, c = 18.759 Å) were determined initially from the XPD pattern and then confirmed by selected-area electron diffraction. The structure of SU-66 was solved from the XPD data using parallel tempering as implemented in FOX [Favre-Nicolin & Černý (2002). J. Appl. Cryst. 35, 734-743] by assuming P21 ma symmetry and two Ge10 clusters in the asymmetric unit. Rietveld refinement of the resulting structure using synchrotron XPD data showed the framework structure to be correct and the space group to be Pmma. The framework has extra-large (26-ring) one-dimensional channels and a very low framework density of 10.1 Ge/Ga atoms per 1000 Å3. SU-66, with 55 framework atoms in the asymmetric unit, is one of the more complicated framework structures solved from XPD data. Indeed, 98% of the reflections were overlapping in the XPD pattern used for structure solution. Tests on other open-framework germanates (SU-62, SU-65, SU-74, PKU-12 and ITQ-37) for which the XPD data, unit cell, space group and IR spectra were available proved to be equally successful. In a more complex case (SU-72) the combination of FOX and powder charge flipping was required for structure solution. [ABSTRACT FROM AUTHOR]

Abstract: A microporous zirconium phosphate material with the chemical composition |(C4H12N+)6(H3O+)2(H2O)2|[Zr32P48O176F8(OH)16] (ZrPOF-DEA) has been synthesized ionothermally using diethylammonium chloride and oxalic acid to form the deep eutectic solvent. It is closely related to the analagous ethylammonium material ZrPOF-EA, which has already been shown to discriminate very well between CO2 and CH4. The framework structures, with two different 8-ring channels running parallel to the x-axis, one of which intersects a 7-ring channel running parallel to the z-axis, proved to be identical. Only the positions of the non-framework cations and water molecules differ. The structure of ZrPOF-DEA (Pbam, a =20.03757(1) Å, b =37.19099(1) Å, c =6.62488(1) Å) was solved from synchrotron powder diffraction data using the charge-flipping algorithm in Superflip. Difference Fourier analyses were then used to locate the non-framework species in the channels. Rietveld refinement of the final structure converged with R F =0.037 and R wp =0.138. Although this material, like ZrPOF-EA, is stable up to 410°C, it does not discriminate as well between CO2 and CH4. Thermogravimetric analysis shows that not all of the organic species have been removed at 410°C, and this is presumably the reason for the poorer adsorption results. [Copyright &y& Elsevier]

Two novel zirconium phosphate compounds, l(C9H8N)4(H2O)4I[Zr8P12O40(OH)8F5] and l(C9H8N)2l[Zr2P2O8 (OH)4F4], designated as ZrPOF-Q1 and ZrPOF-Q2, respectively, have been synthesized hydrothermaiy in the presence ot quinoline and HF and characterized by elemental and tharmogravimettc analyses, UV-vis spectroscopy, and scanning electron microscopy. Their crystal structures were determined troni powder X-ray diffraction data using a charge-flipping algorithm. The ZrPOF-Q1 structure [P¯I, a=10.7567(1) A, b = 13.8502(1) Å, c = 14.8995(1) Å, α =109.6(1)°, β=101.1(1 )°, and y=100.5(1)°] consists of zirconium phosphate layers with quinounium ions in between, The layers are unusual in that isolated ZrO2F4 octahedra are anchored on both sides of the layer and protrude into the interlayer space. The ZrPOF-Q2-structure [P¯I, a=7.7058(1) Å, b=12.3547(1) Å, c=6.5851(l) Å, α=97.0(1)°, fin 89.7(1)°, and γ= 101.9(1)°] consists of zirconium phosphate chains with an unusual Zr/P ratio of 1.0, interspersed with quinolinium ions. Both materials are stable up to 250 °C and exhibit Interesting photoluminescence in the UV-vis spectral region. This is attributed to the protonated quinoiine molecules, which are an Integral part of both structures. [ABSTRACT FROM AUTHOR]