Lesinurad,
a uric acid reabsorption inhibitor that received Food and Drug Administration
approval in 2015, is known to crystallize in three unsolvated crystal
forms and in a few solvated phases. The structures of the former have
been determined by state-of-the-art powder diffraction methods, highlighting
significant conformational as well as supramolecular differences,
resulting in hydrogen bonded centrosymmetric dimers (Form 1) or helical
chains (Form 2). In the complex crystal packing in Form 3, additional
one-dimensional (1D) ribbons held together by unexpected CO···Br
interactions of the halogen-bond type are found. Thermal analyses
and variable-temperature powder diffraction measurements (including
high-temperature synchrotron X-ray diffraction experiments) provided
evidence for the reversible formation of a new phase, Form 2hT, obtained
upon heating above 100 °C powders of Form 2. Structure solution
and refinement of the high-temperature phase made it possible to attribute
the structural change to a 60° rotation of the cyclopropyl residue,
leaving unaffected the conformation of the (longer) polar branch and
the supramolecular 1D helical chain arrangement found in the RT phase.
The use of metal−organic frameworks (MOFs) as precursors for the manufacture of heterogeneous catalysts has gained a great deal of attention over the last decade. By subjecting a given MOF to pyrolysis, electrochemical degradation, or other treatments under a controlled atmosphere, (supported) metal (oxide) nanoparticles with very narrow size distributions can be obtained, opening the door to the design of more efficient catalytic solids. Here, we demonstrate the benefits of steam during the controlled decomposition of two different MOF structures (Basolite F300(Fe) and In@ZIF-67(Co)) and the consequences of treatment under this mildly oxidizing atmosphere on the properties of the resulting catalysts for the direct hydrogenation of CO 2 to hydrocarbons and methanol. In-depth characterization demonstrates that steam addition helps to control the phase composition both before and after catalysis; additionally, it results in the formation of smaller nanoparticles, thus leading to more efficient catalysts in comparison with conventional pyrolysis.
Understanding adsorption processes at the molecular level, with multi‐technique approaches, is nowadays at the frontier of porous materials research. In this work it is shown that with a proper data treatment, in situ high‐resolution powder X‐ray diffraction (HR‐PXRD) at variable temperature and gas pressure can reveal atomic details of the accommodation sites, the framework dynamics as well as thermodynamic information (isosteric heat of adsorption) of the CO2 adsorption process in the robust iron(III) pyrazolate‐based MOF Fe2(BDP)3 [H2BDP = 1,4‐bis(1H‐pyrazol‐4‐yl)benzene]. Highly reliable “HR‐PXRD adsorption isotherms” can be constructed from occupancy values of CO2 molecules. The “HR‐PXRD adsorption isotherms” accurately match the results of conventional static and dynamic gas sorption experiments and Monte Carlo simulations. These results are indicative of the impact of the molecular‐level behavior on the bulk properties of the system under study and of the potential of the presented multi‐technique approach to understand adsorption processes in metal–organic frameworks.
Metal-Organic Frameworks (MOFs) are a class of synthetic porous crystalline materials based on metal ions connected through spacing ligands. They possess interesting properties such as high porosity [1], high concentration of metal centres and flexibility [2]. Additionally, MOFs can maintain their crystal structure upon removal, inclusion, exchange or reaction of a wide selection of guests, making them useful for multiple applications, e.g. in selective gas adsorption/separation. The synthesis of chemically and thermally stable MOFs, the comprehension of their properties and knowledge of their crystallographic features, are indispensable for the design and development of well performing materials. As MOFs' properties are intrinsically related to their crystal structure, a deep understanding of the host-guest interactions during adsorption processes is a fundamental aspect [3].
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