Kristallografiâ

A methodology for measuring and taking into account the background in a neutron single-crystal experiment with a position-sensitive detector is proposed. This methodology makes it possible to increase the ratio of integrated intensities to the standard deviation I/σ(I) for the diffraction reflection intensities and include in the array of experimental data the weak reflections that previously did not meet the condition I/σ(I)>3, and were not taken into account in crystallographic calculations. The methodology was tested on experimental data during structural studies of a Cs₄(HSO₄)₃(H₂PO₄) crystals on the MOND diffractometer at the IR-8 reactor of the National Research Center “Kurchatov Institute”.

The anthropogenic calcium fluorosilicate “kutyukhinite” Ca₅(SiO₄)₂F₂ from burnt dumps of the Chelyabinsk coal basin has been studied by single crystal and powder X-ray diffraction analyses in a wide temperature range. “Kutyukhinite” (P2₁/a, a = 11.4985(4), b = 5.0535(2), c = 8.7848(3) Å, β = 109.008(4)°, V = 482.63(3) ų, R₁ = 0.0183) is an anthropogenic analogue of kumtyubeite which belongs to the structural type of chondrodite. The empirical formula of “kutyukhinite” is Ca_5.02(Si_1.99O_7.98)F_2.04. Upon heating, its crystal structure expands anisotropically, with the direction of maximum thermal expansion close to the direction [100]. The relative change in bond lengths in silicon-oxygen tetrahedra with increasing temperature (27−927°C) is less than 0.6%, which is within the margin of error. At the same time, the relative increase in the average bond length of the varies from 1 () to 1.5% (). The largest relative change of 2% was found for the average bond length .

The paper presents data on synthesis of double borates crystallizing in the BaO–Lu₂O₃–B₂O₃ system and Eu³⁺-activated phosphors based on them as well as on finding of correlations between its chemical composition, crystal structure, thermal and optical properties. Based on results of the investigation of all currently known double Ba–Lu borates, it is shown that search for novel compounds in the system as well as development of optical materials based on them is a promising direction in a field of creating new functional materials for LED applications.

The metal-organic polymer of the composition Fe(OH)(BDC)×(H2O)2 – MIL-53(Fe) and the composite MIL-53(Fe)/GO (GO – graphene oxide) were obtained by the solvothermal method and characterized by X-ray diffraction and X-ray absorption and IR-Fourier spectroscopy, scanning electron microscopy. The presence of Fe²⁺ and Fe³⁺ ions in MIL-53(Fe) and MIL-53(Fe)/GO was established with a higher content of Fe²⁺ ions in MIL-53(Fe)/GO, which helps to increase the efficiency of the decomposition reaction of the RR195 dye, which is actively used in textile industry for dyeing fabrics in the photo-Fenton reaction.

Using neutron-diffraction methods implemented at the commissioned MOND experimental station installed on the thermal neutron beam of the IR-8 reactor of the Kurchatov Institute, crystals of hydrogen-contained compounds Cs₄(HSO₄)₃(H₂PO₄) and NH₄Cl∙2H₂SeO₃ have been studied. The obtained results demonstrate the capabilities of the techniques for localization with high accuracy of hydrogen atoms and characterization of hydrogen bonding systems, information about which is necessary for establishing correlations between atomic, real structure and physicochemical properties of the investigated crystals.

A new compound NaCu₁₂(Si₂O₇)₄Cl was synthesized by chemical deposition from gases. Using X-ray diffraction analysis, its crystal structure was established as containing 0-dimensional copper-oxide clusters Cu₁₂O₂₄ of a new type, which can be described as a truncated tetragonal bipyramid built from CuO₄ square groups connected by sharing common edges and vertices. The complexes are combined through the Si₂O₇ disilicate groups into a three-dimensional electroneutral framework [[Cu₁₂(Si₂O₇)₄]⁰, built on the principle of the bcc grid (body-centered cubic lattice). In the cavities of the framework disordered Na⁺ and Cl^– ions are located. The structure of the 12-nucleated copper-oxide clusters is similar to those of the Cu_nO_2n polyoxocuprates found in various minerals and inorganic compounds.

The transformation of PdBi compound at high temperatures was studied using in-situ high-temperature single-crystal X-ray diffraction. The new data about crystal structure of high temperature PdBi modification is obtained. The structure of PdBi at T = 293, 373, 423 and 473 К, is orthorhombic, space group Cmc2₁, unit cell parameters: a = 8.7160(3), b = 7.2031(3), c = 10.6631(4) Å, V = 669.45(4) ų, Z = 16 (293 К). Upon further heating, a phase transition to the high-temperature modification occurs. The structure of PdBi at T = 523 and 573 К was solved in orthorhombic space group Cmcm, a = 3.6162(3), b = 10.6446(8), c = 4.4208(4) Å, V = 170.17(3) ų, Z = 4 (523 К).

Crystals of new double sulfates (dmedaH₂)[Co(H₂O)₆](SO₄)₂ (1) and (dmedaH₂)[Ni(H₂O)₄(SO₄)₂] (2), as well as (dmedaH₂)₂(SO₄)₂⋅3H₂O (3), where dmeda is N,Nʹ-dimethylethylenediamine, were obtained by isothermal evaporation. The compounds crystallize in the triclinic symmetry, space group P$\overline{1}$, while compound 3 is characterized by the orthorhombic symmetry with the space group P2₁2₁2₁. The crystal structure of 1 contains isolated octahedral cations [Co(H₂O)₆]²⁺ and SO₄^2– tetrahedra, while the crystal structure of 2 contains complex anions trans-[Ni(H₂O)₄(SO₄)₂]^2–. Structures of 1 and 2 are compared with the structures of double cobalt and nickel sulfates with ethylenediammonium, where the opposite case is observed. The formation of both aqua- and aquasulfate complexes is quite typical for cations of transition metals of the 3d series. While for double sulfates of transition metals with inorganic cations the hydration number depends to a greater extent on the synthesis temperature and the ionic radius of the monovalent metal, for double sulfates with organic cations the picture is more complex. The crystal structure of compound 3 can also be considered as pseudolayered, with the cationic layer formed only by the organic component, while the anionic layer also includes water molecules. The anionic layer contains cavities, the volume of which allows us to assume that under certain conditions they can be occupied by water molecules, which would correspond to the composition (dmedaH₂)(SO₄)⋅2H₂O. Topological analysis of the obtained compounds showed that metal complexes with ethylenediammonium demonstrate a relatively high structural complexity of H-bonds with a lower complexity of structural units compared to N,N'-dimethylethylenediammonium.

In the presented work, the synthesis of a complex resulting from the reaction of 2,6-diaminopyridine with the Zn(II) ion in an alcohol solution of hydrochloric acid is described for the first time. The composition, molecular and crystal structure of the synthesized complex were determined by X-ray structural analysis. The structure of the new complex, its crystallographic data, and the geometry of hydrogen bonds in the crystal system were determined. The composition of the metal complex was confirmed by elemental analysis, and the existing chemical bonds were studied by IR spectroscopy. The surface of the crystals was studied according to Hirschfeld. To determine the stability of the obtained complex, its thermal analysis was carried out. The stability of the complex, caused by intramolecular hydrogen bonds, was confirmed.

The prediction of epitopes was carried out. The structural stability of the candidate vaccine was studied by the molecular dynamics method using the Gromacs-2023 software package. The results showed the preservation of the structural stability of all the studied subdomains. The final stage was the simulation of the cellular immune response using the C-IMMSIMM program. The results predict the ability of candidate vaccines to elicit both a vibrant primary and persistent secondary immune response.

The paper theoretically investigates TE and TM polarized surface plasmon polaritons in a metal film in contact with a semi-infinite periodic superlattice formed by alternating layers of two materials. It is shown that in a certain case, the frequency dependence of the impedances of such a bilayer superlattice can be of only two types out of three possible types of dependencies. The dispersion curves TE and TM of surface plasmon polaritons in a silver film have been calculated for a number of structures consisting of various combinations of bilayer superlattices containing layers of quartz and titanium oxide. The calculation results are compared with the conclusions of the general theory on the maximum number of surface plasmon polaritons. The effect of the absorption of electromagnetic waves in the film on the characteristics of surface plasmon polaritons is analyzed.

Complex structural studies of nanosized bismuth-doped yttrium iron garnet (BYIG) films were performed using X-ray diagnostics, scanning/transmission electron microscopy, and energy-dispersive X-ray microanalysis. The crystal structure of the film-substrate interface, the near-surface layers together with change in interplanar distances along the film thickness were determined. The features of the film microstructure were revealed: the presence of pores, the absence of misfit dislocations at the interface, the formation of maghemite (γ-Fe₂O₃) particles on the film surface and a decrease in the Bi content towards the film surface. Assumptions were made about the change in the Bi content depending on the film thickness, which can serve as an explanation for the mechanism of decreasing the magnitude of magneto-optical effects in these films with decreasing thickness.