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The name of the third author of the article by Koch et al. [Acta Cryst. (2021). A77, 611-636] is corrected.
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Data reduction and correction steps and processed data reproducibility in the emerging single-crystal total-scattering-based technique of three-dimensional differential atomic pair distribution function (3D-ΔPDF) analysis are explored. All steps from sample measurement to data processing are outlined using a crystal of CuIr2S4 as an example, studied in a setup equipped with a high-energy X-ray beam and a flat-panel area detector. Computational overhead as pertains to data sampling and the associated data-processing steps is also discussed. Various aspects of the final 3D-ΔPDF reproducibility are explicitly tested by varying the data-processing order and included steps, and by carrying out a crystal-to-crystal data comparison. Situations in which the 3D-ΔPDF is robust are identified, and caution against a few particular cases which can lead to inconsistent 3D-ΔPDFs is noted. Although not all the approaches applied herein will be valid across all systems, and a more in-depth analysis of some of the effects of the data-processing steps may still needed, the methods collected herein represent the start of a more systematic discussion about data processing and corrections in this field.
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A new family of layered alkali uranyl borates, A2(UO2)B2O5 (A = Cs, Rb, K), was synthesized as high quality single crystals via high temperature flux growth methods. At room temperature, the compounds are structurally closely related although they crystallize in different monoclinic space groups, specifically P21/c (Cs), C2/m (Rb), and C2/c (K). At a low temperature (100 K), Cs2(UO2)B2O5 becomes isostructural with K2(UO2)B2O5 as the result of a reversible structure transition by Cs2(UO2)B2O5. The title phases represent the first examples of uranyl borates resulting from high temperature flux growth utilizing alkali halide fluxes. The synthesis, structures, and thermal, optical, and ion exchange properties are reported, and modeling of the atomic structure and disorder of the ion exchanged phases is discussed.
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Thermodynamic studies of actinide-containing metal-organic frameworks (An-MOFs), reported herein for the first time, are a step toward addressing challenges related to effective nuclear waste administration. In addition to An-MOF thermochemistry, enthalpies of formation were determined for the organic linkers, 2,2'-dimethylbiphenyl-4,4'-dicarboxylic acid (H2Me2BPDC) and biphenyl-4,4'-dicarboxylic acid (H2BPDC), which are commonly used building blocks for MOF preparation. The electronic structure of the first example of An-MOF with mixed-metal AnAn'-nodes was influenced through coordination of transition metals as shown by the density of states near the Fermi edge, changes in the Tauc plot, conductivity measurements, and theoretical calculations. The "structural memory" effect (i.e., solvent-directed crystalline-amorphous-crystalline structural dynamism) was demonstrated as a function of node coordination degree, which is the number of organic linkers per metal node. Remarkable three-month water stability was reported for Th-containing frameworks herein, and the mechanism is also considered for improvement of the behavior of a U-based framework in water. Mechanistic aspects of capping linker installation were highlighted through crystallographic characterization of the intermediate, and theoretical calculations of free energies of formation (ΔGf) for U- and Th-MOFs with 10- and 12-coordinated secondary building units (SBUs) were performed to elucidate experimentally observed transformations during the installation processes. Overall, these results are the first thermochemical, electronic, and mechanistic insights for a relatively young class of actinide-containing frameworks.
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Atomic pair distribution (PDF) analysis has proven to be an exceptionally robust tool for probing the structure of amorphous, crystalline and crystallographically challenged materials. This issue of IUCrJ features a significant step forward in X-ray PDF methodology for thin films, with substantial improvements in both sensitivity and time resolution.
