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The synthesis of polycrystalline, as opposed to single-crystalline, porous materials, such as zeolites and metal-organic frameworks (MOFs), is usually beneficial because the former have shorter synthesis times and higher yields. However, the structural determination of these materials using powder X-ray diffraction (PXRD) data is usually complicated. Recently, several methods for the structural investigation of zeolite polycrystalline materials have been developed, taking advantage of the structural characteristics of zeolites. Nevertheless, these techniques have rarely been applied in the structure determination of a MOF even though, with the electron-density contrast between the metal-containing units and pore regions, the construction of a structure envelope, the surface between high- and low-electron-density regions, should be straightforward for a MOF. Herein an example of such structure solution of MOFs based on PXRD data is presented. To start, a Patterson map was generated from powder diffraction intensities. From this map, structure factor phases for several of the strongest reflections were extracted and a structure envelope (SE) of a MOF was subsequently constructed. This envelope, together with all extracted reflection intensities, was used as input to the SUPERFLIP software and a charge-flipping (CF) structure solution was performed. This structure solution method has been tested on the PXRD data of both activated (solvent removed from the pores; dmin = 0.78 Å) and as-synthesized ( dmin = 1.20 Å) samples of HKUST-1. In both cases, our method has led to structure solutions. In fact, charge-flipping calculations using SE provided correct solutions in minutes (6 min for activated and 3 min for as-synthesized samples), while regular charge flipping or charge flipping with histogram matching calculation provided meaningful solutions only after several hours. To confirm the applicability of structure envelopes to low-symmetry MOFs, the structure of monoclinic PCN-200 has been solved via CF+SE calculations. [ABSTRACT FROM AUTHOR]

A bent Bragg-Laue monochromator (BLM) is proposed for high-energy X-ray (∼25-60 keV) beamlines. The BLM has the unique feature of bi-directional focusing. A sagittally bent Laue crystal can focus the large horizontal fan of a bending magnet or wiggler source. A meridionally bent Bragg crystal focuses the beam vertically and corrects for the anticlastic bending effects of the Laue crystal. This monochromator geometry relies on the crystal orientations being optimized. It is shown that the focusing condition and Rowland condition can be simultaneously satisfied at a given energy. Detailed ray tracings indicate that a BLM can provide similar energy resolution and higher flux density compared to a sagittally bent double-Laue monochromator configuration. A prototype BLM with a symmetric Bragg crystal and an asymmetric Laue crystal was tested. Matching of the bend radii of the two crystals in the meridional direction was demonstrated. In general, the horizontal acceptance of the sagittally bent Laue crystal is limited by the large curvature. This horizontal BLM acceptance could be increased by translating the Laue crystal along its sagittal bending axis. [ABSTRACT FROM AUTHOR]