The germanosilicate ITQ-24 (IWR framework type) was synthesized in fluoride medium using 1,3,5-tris(1,2-dimethylimidazolium) benzene as the structure directing agent (SDA). A structure analysis of the as-synthesized ITQ-24 material using synchrotron powder diffraction data and difference electron density calculations have allowed the fluoride ions and the germanium atoms to be located and the conformation of the SDA to be determined. The benzyl ring is perpendicular to the b axis with the three imidazolium moieties forming a "T-shaped" arrangement. Ge atoms replace some of the Si in the double-4-ring (d4r) and in one of the single-4-rings (s4r). The other s4r contains only Si. Fluoride ions are in the d4r units. Initially, the space group Cmmm (highest possible symmetry) was assumed, but the framework geometry was strained. An independent evaluation of the symmetry using the powder charge flipping algorithm in Superflip led to a successful refinement with reasonable geometry and a refined composition of |[(C6H3)(C7H10N2)3]2F2|[Si(40.2)Ge(15.8)O112] in the space group Pban.

So far, in the field of X-ray powder diffraction, the maximum entropy method (MEM) has been used to (i) solve the phase problem, (ii) estimate the intensities of overlapping reflections, (iii) predict the intensities of missing reflections, and (iv) improve electron density maps generated during Rietveld refinement. We found a new application for MEM in a recent study, in which the powder charge flipping algorithm [1] in Superflip was applied to all-light-atom structures [2]. It proved to be difficult to identify the few fully interpretable maps within in the 200 generated in a typical Superflip job using the standard evaluation criteria. In 1992, Sato reported that entropy could be used as a solution evaluation criterion if the basis set is large, the phases are close to the correct ones, and the structure contains a small molecule [3]. Reasoning that these requirements would be fulfilled by the better Superflip solutions, all solutions were input to the MEM program MICE to calculate the corresponding ME maps and their entropies. Tests performed on several datasets showed no direct correlation between entropy and the solution quality. However, it was noted that a certain number of solutions show entropy values significantly lower than the others. This group usually contained one fully interpretable map. Refinement of the approach led to a relatively straightforward method for recognizing the better solutions. Furthermore, phase recycling based on this approach proved to be useful. As a result, guidelines for solving structures of different levels of complexity using the pCF algorithm could be devised.

High-resolution synchrotron X-ray powder diffraction (SXPD) data alone are sometimes not enough to solve the structure of a complex polycrystalline material. Such was the case for the high-silica zeolites SSZ-61 and SSZ-87, where combining data from different sources, in particular XPD and electron microscopy, was vital to success. For SSZ-61, the SXPD data feature broad peaks and a resolution of ca. 1.2 Å. Although the pattern could be indexed, structure determination failed both with the charge flipping routine in SUPERFLIP [1] and with the zeolite-specific program FOCUS [2]. The unit cell parameters and HRTEM images indicated a relationship with ZSM-12 (MTW) and SSZ-59 (SFN), so several models derived from these two frameworks were built. Eventually, after considering Si-29 MAS NMR data and the size of the organic structure directing agent (SDA), a framework model that fits all the data emerged. To complete the structure, the SDA was included as a rigid-body, and its location and orientation optimized using simulated annealing. Subsequent Rietveld refinement confirmed the structure. In contrast to SSZ-61, the SXPD pattern for SSZ-87 was quite good, and it could be indexed with a C-centered cell. However, structure solution failed, probably because of the very high degree of reflection overlap (93%). Therefore, rotation electron diffraction (RED) data [3] were collected, but they proved to be of low resolution and poor quality. Only 2 of the 7 data sets could be indexed, and these had different unit cells. Neither fit the XPD pattern directly. The problem was traced to large errors in the RED cell parameters, and eventually one RED cell could be transformed to one similar to the SXPD cell. The RED data with this cell was only 15% complete up to a resolution of 1.22 Å. Even so, the structure could be solved using a recently developed version of FOCUS that works with ED data. The SDA was found as for SSZ-61, and the structure then confirmed by Rietveld refinement.

The synthesis of the polycrystalline niobium silicate catalyst AM-11 was first reported in 1998 [1], but its structure proved to be elusive. In 2007 we received two samples from the Aveiro group. At the time, we were looking for a material suitable for the application of the texture method of structure solution, and AM-11 seemed to be ideal for this purpose. One of the samples had needle and the other platelet morphology, and textured samples could be prepared in both cases. The conventional powder diffraction pattern could be indexed on a hexagonal, an orthorhombic or a monoclinic unit cell, so this was the first issue to be resolved. The texture measurements quickly revealed that the crystal system was orthorhombic, but the structure resisted solution. We then tried applying the precession electron diffraction technique in combination with high-resolution powder diffraction data, but beyond confirming the orthorhombic symmetry, these data did not help us to solve the structure. Another attempt was made with a new sample and an improved texture setup, but to no avail. Rotation electron diffraction data and high-resolution transmission electron microscopy images showed that some disorder was present and helped to define the space group, but the structure remained a mystery. The powder charge-flipping routine in Superflip [2], yielded tantalizingly clear electron density maps, but they could not be interpreted sensibly. The unit cell parameters were seen to be related to those of the titanium silicate zorite [3] (one axis doubled in AM-11), so the problem was taken up once again last year. By starting with a simplified zorite framework structure with Nb in place of Ti, and performing what amounts to manual Fourier recycling, the surprisingly simple structure (1Nb, 3 Si, 9 O), which is significantly different from zorite, finally revealed itself. There is some stacking disorder, but the structure is otherwise innocuous. What made it so difficult to solve?

X-ray free-electron laser (XFEL) sources create X-ray pulses of unprecedented brilliance and open up new possibilities for the structural characterization of crystalline materials. By exposing a small crystallite (100nm-10μm) to a single ultrafast pulse, a diffraction pattern can be obtained before the crystal is damaged. If such single-pulse diffraction patterns, collected sequentially on many randomly oriented crystallites, are combined, it is possible to determine the structure of the material accurately [1]. One of the drawbacks of this approach is that only a single position of the Ewald sphere is accessed in each pattern, so, because reflections have a finite width, the diffraction condition is not satisfied completely for any of the reflections recorded. The new XFEL source that is being developed in Switzerland (SwissFEL) will provide a broad-bandpass mode with an energy bandwidth of about 4% [2]. By using the full energy range of the SwissFEL beam, a new option for structural studies of crystalline materials becomes possible. In a recent study based on simulated data, we showed that a diffraction experiment with stationary crystallites in such an `extra pink' beam not only increases the number of reflection intensities that can be collected in a single shot, but also overcome the problem of `partial reflection' measurement [3]. To test the viability of the data processing with experimental data, attempts to simulate this 4% bandpass have been carried out on SNBL at ESRF and on the microXAS beamline at SLS. On SNBL, a single crystal was rotated over 360° and a continuous scan of the monochromator over the 4% energy range was performed every 1°. At SLS, a mirror was used to cut off the higher energies of the undulator beam and the energy threshold of a Pilatus detector to eliminate the lower ones. With this setup, a series of randomly oriented crystallites were measured. A comparison of the analysis of these datasets will be presented.

Mu-33, a new layered aluminophosphate with an Al/P ratio of 0.66, was obtained from a quasi non-aqueous synthesis in which tert-butylformamide (tBF) was the main solvent and only limited amounts of water were present. During the synthesis, tBF decomposed and the resulting protonated tert-butylamine is occluded in the as-synthesized material. The approximate structure was determined from data collected on a microcrystal (200 × 25 × 5 μm3) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, but the quality of these data did not allow satisfactory refinement. Therefore the structure was refined using high-resolution powder diffraction data, also collected at the ESRF. The structure (P21/c, a = 9.8922(6) Å, b = 26.180(2) Å, c = 16.729(1) Å and β = 90.4(1)°) consists of anionic aluminophosphate layers that can be described as a six-ring honeycomb of alternating corner-sharing AlO4 and PO4 tetrahedra with additional P-atoms above and below the honeycomb layer bridging between Al-atoms. The tert-butylammonium ions and water molecules located in the interlayer spacing interact via hydrogen-bonds with the terminal oxygens of the P-atoms. The characterization of this new aluminophosphate by 13C, 31P, 1H–31P heteronuclear correlation (HETCOR) and 27Al 3QMAS solid state NMR spectroscopy is also reported.

Two crystalline aluminophosphates have been synthesized under hydrothermal conditions using N-methyl-1,3-diaminopropane (MeDAP) as structure-directing molecule. The first one, denoted MDAP-1 is observed as an intermediate phase during the crystallization of the final product MDAP-2. The structure of MDAP-1, a 2D-layered compound with the empirical formula (C4H14N2)1.5[Al3P4O16] was refined using powder X-ray diffraction data. It crystallizes in the monoclinic space group P21/c (No. 14) with a=14.080(10)Å, b=8.4763(1)Å, c=18.9954(1)Å, β=100.95(5)° and Z=4. Inorganic sheets contain a novel 4×6 net, constructed from capped 6-membered rings. The sheets are held together by partially disordered, doubly protonated MeDAP molecules. Single crystal analysis showed that MDAP-2 is isostructural with AlPO4-21 and crystallizes in the monoclinic space group P21/n (No. 14) with a=8.488(6)Å, b=17.72(2)Å, c=9.024(6)Å, β=106.96(5)° and Z=4. MDAP-2 differs from AlPO4-21 by the presence of an octahedrally coordinated aluminum in the framework.

The structure of AlPO4-SOD, a microporous aluminophosphate synthesized in a quasi-nonaqueous system using dimethylformamide as template and solvent, was previously reported. Then, various solid state nuclear magnetic resonance techniques applied on the dehydrated compound at 200 degrees C were performed and suggested a rearrangement of one-third of the template molecules inside the sodalite cages and a tripling of the unit cell parameter c. We present here the structure determined from molecular modeling and Rietveld analysis on synchrotron data of AlPO4-SOD dehydrated under vacuum at 100 degrees C together with some solid state NMR experiments of the rehydrated product.

An aluminophosphate with the ERI framework topology, further denoted AIPO-ERI, has been synthesized in the presence of N,N,N',N'-tetramethyl-1,6-hexanediamine and its structure was solved by single crystal X-ray diffraction. It crystallizes in the monoclinic space group P2(1) (No. 4) with a = 13.163(14) angstrom, b = 14.793(15) angstrom, c = 13.215(14) angstrom, beta = 119.74(8)degrees. As compared to similar materials prepared with piperidine as template, extraframework hydroxyl groups are locally ordered in the structure. After calcination and rehydration, the aluminophosphate remains monoclinic and crystallizes in space group P2(1)/n (No. 14) with a = 13.283(17) angstrom, b = 14.910(14) angstrom, c = 22.76(3) angstrom and beta = 90.19(10)degrees. Both the as made and calcined rehydrated forms of AIPO-ERI have been characterized by multidimensional solid state NMR. (c) 2005 Academie des sciences. Published by Elsevier SAS. All rights reserved.

Two isotypes of a new layered aluminophosphate, further denoted MDAP-3 and MDAE-1, have been synthesized under hydrothermal conditions using N-methyl-1,3-propanediamine and N-methyl-ethylenediamine, respectively. MDAP-3, with the empirical formula [Al2(HPO4)(PO4)2](C4N2H14)(H2O), crystallizes in the orthorhombic space group Pna2(1) (No. 33) with a=9.602(16)Å, b=9.26(2)Å, c=16.03(3)Å, Z=4, R1=0.0498 and wR2=0.1217. The second solid, MDAE-1, with the empirical formula [Al2(HPO4)(PO4)2](C3N2H12)(H2O), crystallizes in the same space group with a=9.4250(19)Å, b=9.3170(19)Å, c=15.907(3)Å, Z=4, R1=0.0407 and wR2=0.0954. The two compounds possess the same layer topology. Inorganic layers contain PO3=O, PO3OH, AlO4 and AlO6 polyhedra, linked together to generate a new 4×8 net. MDAP-3 and MDAE-1 represent the first examples of two-dimensional layered aluminophosphates with the Al2P3O12 stoichiometry, and containing AlO6 octahedra.

The crystal structure of the potassium calcium silicate material, CAS-1 (vertical bar(Ca4K4(H2O)(8))vertical bar[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 Si-29 MAS NMR results (1 Q(4) and 3 Q(3) signals, all of equal intensity), CAS-1 (C2, a = 24.158 angstrom, b = 7.016 angstrom, c = 6.482 angstrom, beta = 95.19 degrees) 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 4.8(2) 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. (c) 2005 Academie des sciences. Published by Elsevier SAS. All rights reserved.

Additional information about the relative intensities of reflections that overlap in a powder diffraction pattern can be obtained from a polycrystalline sample in which the crystallites are preferentially oriented. If the data are collected and analyzed appropriately, more single-crystal-like reflection intensities can be extracted, and thereby more complex structures solved. This 'texture method' was implemented initially in reflection mode and its power demonstrated with the solution of the 117-atom structure of the hi-h-silica zeolite UTD-1F However, the experiment required a minimum of 3 days of synchrotron beamtime per sample. In an attempt to reduce the amount of beamtime needed and to simplify the experiment itself, a transmission mode alternative using an area detector was developed. Details of the sample preparation, data collection and data analysis for both geometries are described. The solution of the structures of the aluminophosphates Mu-9 (R(3) over bar c, a = 14.0696(1) Angstrom, c = 42.3113(4) Angstrom) and AIPO-M (Pbca, a = 9.7493(1) Angstrom, b = 29.1668(2) Angstrom, c = 9.3528(1) Angstrom) using reflection and transmission mode data, respectively, are provided as examples of the method.

A new layered aluminophosphate denoted AlPO-AEPP has been synthesized under hydrothermal conditions using N-(2-aminoethyl)-piperazine (AEPP) as structure directing molecule. The compound, with the empirical formula Al3P4O16C6N3H17H3O crystallizes in the orthorhombic space group P212121 (No. 19) with a=14.550(8)Å, b=16.163(8)Å, c=18.677(9)Å, Z=4, R1=0.0253 and wR2=0.0644. Inorganic sheets contain a 4×6 network previously found in a layered compound synthesized with 1,2-dimethylimidazole molecules. Layers stack in the ABAB sequence and are held together by doubly protonated organic molecules and H3O+ cations. AlPO-AEPP represents the second example of layered aluminophosphate for which protonated water acts as a co-template along with organic molecules.

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) Å, b=8.67024(1) Å, c=16.21957(2) Å) 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.