[en] Metal-organic UiO-66, UiO-66-NDC, and MOF-801 frameworks (MOFs) are produced via the solvothermal synthesis technique. The frameworks are composed of Zr₆O₄(OH)₄ clusters that are connected with appropriate linkers, as follows: UiO-66—terephthalic acid; UiO-66-NDC—1,4-naphthalenedicarboxilic acid; and MOF-801—fumaric acid. The single-phase composition of the samples is confirmed by X-ray powder diffraction. The identification of Zr₆O₄(OH)₄ clusters in all the synthesized MOFs is established using X-ray adsorption spectroscopy. The specific surface areas of UiO-66, UiO-66-NDC, and MOF-801 are evaluated, and their hydrogen adsorption–desorption isotherms are measured at 77 K, as well. Comprehensive preliminary characterization of the samples, together with hydrogen-storage-capacity data, allows one to make the following conclusions: (i) at relatively high pressures, the highest hydrogen-storage capacity is found for UiO-66 with the largest specific surface area; (ii) at relatively low pressures, MOF-801 with the smallest pores possesses the optimal structure for hydrogen sorption; (iii) a large π-system of aromatic UiO-66-NDC rings yields effective hydrogen sorption at low pressures, which is retained in pores during desorption.

[en] The data on the dynamics of structural changes in the composite cathode material based on iron(III) fluoride studied by the operando synchrotron X-ray spectroscopy and diffraction combined with the density functional theory (DFT) are reported. Based on the FeF₃ structure determined by X-ray crystallography the crystal structure of Li_xFeF₃ for 0 < x < 0.5 is modeled by the geometry optimization. The crystal structure models for 0.5 < x < 1 are predicted using the evolutionary algorithms. The Fe K-edge X-ray absorption spectra are calculated for these models and compared with the experimental data.

[en] A comprehensive study of the Jiddat Al Harasis 055 (L4-5 type) ordinary chondrite is conducted using 2D X-ray fluorescence spectroscopy, Mössbauer spectroscopy, X-ray absorption near edge structure (XANES) spectroscopy, X-ray diffraction, and vibrating sample magnetometry. The content of Fe, Ni, Si, Mg, S, Ca, Al, Mn, Ti, and Cr is determined; several components and areas with increased content of S, Ti, Cr, and Ni are detected along with several Ca–Al inclusions. According to XANES data, the Jiddat Al Harasis 055 sample contains iron with the average oxidation state 2.4+. This result is consistent with the data of Mössbauer spectroscopy used to identify iron phases which testifis that 46% and 54% of iron ions appear in Fe²⁺ and Fe³⁺ states, respectively. By comparing the pre-edge energy position and the area under the preedge peak of XANES spectra with literature data reported for geological materials, the average coordination number in the first coordination sphere of iron is found to be 5.3. According to the data of Xray diffraction and Mössbauer spectroscopy, the iron-containing meteorite phases consist mainly of olivine, pyroxene, hematite, and goethite. The observed magnetic properties of the sample can be attributed to small inclusions of ferromagnetic phases such as nickel nanoparticles, which cannot be reliably identified using laboratory spectral methods.

[en] Spectroscopic investigations of a ZnAl₂O₄ spinel doped with bivalent copper ions of 0.05% concentration have been carried out in the temperature range 4.2-290 K using a 3 cm^-1 range electron paramagnetic resonance (EPR) spectrometer having an operational frequency f = (9.241 ± 0.001) GHz. The spectrum can be represented as a superposition of two components: a low-temperature (LT) and a high-temperature (HT) one. Redistribution of integrated intensity between HT and LT components of the spectra occurs with temperature change that is typical of systems with multi-minimum adiabatic potential. Spectra observed are explained within the modified theory of crystalline field (MTCF). The electron levels of a Cu²⁺ ion placed in an octahedral coordination center with trigonal distortion [CuO₆]^10- have been calculated. The influence of possible types of oxygen octahedron distortions and possible displacement of copper ions from the symmetry center on the electron spectrum, as well as the shape of the adiabatic potential, has been analyzed. It is shown that in the low-temperature phase the multiple minima of the adiabatic potential occur due to tetragonal distortions while the depth of a minimum is determined by the degree of trigonal octahedron distortions. Tetragonal distortion values and multi-minimum potential barrier heights have been determined.

[en] Valence tautomer transition occurs mainly in 3d metalorganic complexes with redox-active ligands and makes them potential candidates for single-molecular switches. The transition occurs under temperature, pressure, or light-induced stimuli and is strongly affected by the intermolecular interactions. However single-crystal x-ray diffraction is not always applicable to such systems when crystal structure is destroyed upon transition or system is studied in the solution. Such an example is bis(o-semiquinonato) cobalt complex with TEMPO-functionalized iminopyridine ancillary ligand. In this work we apply two complementary techniques—ligand-sensitive Fourier transform infrared spectroscopy (FTIR) and metal sensitive Co K-edge x-ray absorption spectroscopy (XAS). In a solid state, a temperature hysteresis of magnetization larger than 40 K was observed upon cyclic cooling-heating. So, the temperature of phase transition upon cooling is about 40 K lower than that upon heating. In solution, the x-ray absorption spectra for high-temperature and low-temperature states were similar to that in the solid form, but the hysteresis was absent. Two methods are can probe valence tautomer transition, but XAS has an advantage for the liquid phase analysis and FTIR has larger sensitivity to the ligand related interactions in solid. (paper)