Crystallography Reports最新文献

Crystals of lead monochloroacetate, Pb(ClCH₂COO)₂, were obtained in the reaction of lead carbonate and aqueous chloroacetic acid. The compound crystallizes in the monoclinic system (space group P2₁/c) with the unit-cell parameters a = 10.8346(6) Å, b = 7.7239(4) Å, c = 10.1484(5) Å, β = 106.542(5)°. Like in other medium- and long-chain lead carboxylates, the crystal structure of lead monochloroacetate is layered. Lead atoms are located in distorted seven-vertex PbO₇-polyhedra, which share edges and form layers. Features of the crystal structures of lead salts of carboxylic acids with unbranched hydrocarbon radicals are discussed. In particular, salts of lead(II) n-alkyl carboxylates with the general formula Pb(C_nH(_{{2n + 1}})COO)₂, despite belonging to different symmetry and space groups (monoclinic P2₁/m for n = 2 and 3, triclinic P(bar {1}) for n = 4–9, and monoclinic P2₁/c for Pb(ClCH₂COO)₂), are characterized by the same arrangement of molecules, so they can be considered structurally related.

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

The TE- and TM-polarized surface plasmon polaritons in a metal film contacting a semi-infinite periodic superlattice formed by alternating layers of two materials have been theoretically investigated. It is shown that, in a certain case, the frequency dependence of the impedances of this bilayer superlattice can be of only two types out of three possible types of dependences. The dispersion curves of ТE- and TM-polarized surface plasmon polaritons in a silver film have been calculated for a number of structures consisting of various combinations of bilayer superlattices containing quartz and titanium oxide layers. 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.

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,N'-dimethyl-ethylenediamine, were obtained by isothermal evaporation. The compounds crystallize in the triclinic symmetry, space group P(bar {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 ({text{SO}}_{4}^{{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, as compared to N,N'-dimethylethylenediammonium.

The thermal expansion of two modifications α- and β-Cs₂SO₄, as well as the compound Cs₂Ca₃(SO₄)₄, was studied for the first time by high-temperature powder X-ray diffraction method in the temperature ranges of 25–960 and 25–540°C, respectively. β-Cs₂SO₄ transforms into the high-temperature α-Cs₂(SO₄) modification through a two-phase region in the range of 600–750°C. The thermal expansion of all studied phases is sharply anisotropic: α_a = 37.3(10), α_b = 36.2(4), α_c = 12(5), α_V = 85.1(5) at 30°C for β-Cs₂SO₄; α_a = 55(5), α_c = 115(9), α_V = 224(12) × 10^–6 °С^–1 at 750°С for α-Cs₂SO₄. The thermal expansion coefficients for Cs₂Ca₃(SO₄)₄ are α₁₁ = 18.8(5), α_b = 18.2(5), α₃₃ = –7.5(2), αβ = –10.6(2), α_V = 29.6(9) × 10^–6 °С^–1 at 25°С. The continuity of the polymorphic transformation of Cs₂SO₄ is shown. It consists in the fact that, with an increase in temperature, the corrugated columns or rods elongated along the c axis in both modifications, consisting of Cs(SO₄)₆ microblocks, straighten due to the rotation of SO₄ tetrahedra. The interpretation of the anisotropy of the thermal expansion of Cs₂Ca₃(SO₄)₄ is based on the mechanism of rocking polyhedra. A hinge deformation at the level of Ca(SO₄)₆ microblocks, which leads to a large negative thermal expansion in the α₃₃ direction, is revealed.

Single crystals of two new complex hydroselenites with organic cations—(C₄H₁₂N₂)[Mn(HSeO₃)₂Cl₂] (1) and [(C₄N₁₂N₂)Br]₂[Mn(HSeO₃)₂Br₂] (2)—were obtained as the products of the reaction of piperazine, selenious acid, and manganese halide in an aqueous medium. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analysis; they are characterized by monoclinic symmetry (1: P2₁/c, a = 9.7557(7) Å, b = 7.3930(5) Å, c = 9.7660(6) Å, β = 116.839(7)°; 2: P2₁/c, a = 14.4093(3) Å, b = 7.3822(1) Å, c = 10.3051(3) Å, β = 101.553(2)°). The crystal structures of both compounds are constructed by alternating layers of the composition [Mn(HSeO₃)₂X₂]^2– (X = Cl, Br) and layers formed by piperazinium cations. Compound 1 is a structural analogue of the previously described compound (C₄H₁₂N₂)[Cd(HSeO₃)₂Cl₂], while the crystal structure of compound 2 belongs to a new structural type, is characterized by a modular structure, and contains layers including both piperazinium cations and bromine anions.

The images of the magnetic domain structure (DS) stray fields were obtained in the basal plane of Nd₂Fe₁₄B and Y₂(Fe_xCo(_{{1-x}}))₁₇ (x = 0.18, 0.41) bulk uniaxial crystal samples at different tip–sample lift heights z using a magnetic force microscope. A method for automated evaluation of magnetic force microscopy (MFM) images is proposed. The average number of extrema per unit length (n) was calculated, n(z) dependences were plotted, and an analytical expression for approximating experimental dependences was derived. The n₀ values, related to the z = 0 point, were obtained by approximating experimental data with the analytical expression. The values of the average domain width D and domain wall (DW) energy surface density γ were calculated based on the found n₀ values.

A holotype sample of keldyshite has been studied. It was found to consist of aggregates of partially protonated, Na-deficient parakeldyshite (which is dominant) and keldyshite itself. A series of laboratory experiments on the hydrolysis of parakeldyshite was performed, as a result of which the crystal structure of the keldyshite formed during this process was refined. A refined idealized formula was proposed for it: (Na(square ))ZrSi₂O₆(OH). As a result of the protonation of the oxygen atom at the О5 position and formation of strong hydrogen bonds (with an O5…O5 distance of 2.458 Å in keldyshite), a series of hinge transformations occurs, causing a significant distortion of the Zr–Si–O framework within the crystal structure. The existence of the transformation series from parakeldyshite to keldyshite in nature is confirmed. The mechanism of keldyshite formation can be described by the reaction scheme Na⁺ + O²⁻ → (square ) + (OH)⁻. The substitution reaction of parakeldyshite by keldyshite most likely occurs via a transition from single crystal to single crystal.

A new compound NaCu₁₂(Si₂O₇)₄Cl was synthesized by chemical vapor deposition. 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 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). Disordered Na⁺ and Cl^– ions are located in the cavities of the framework. 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.

African swine fever (ASF) has become a global threat to the pork industry, thus representing a great economic concern. A theoretical comparison of subunit vaccine candidates based on the transmembrane protein CD2v of the ASF virus was performed. Three outer-membrane subdomains of CD2v were evaluated using immunoinformatics, structure prediction, and molecular dynamics simulation methods. All candidates were shown to be non-toxic, non-allergenic and can induce a stable immune response, including the long-term antibody production. The subdomain А stands out as the most promising candidate due to its high immunogenicity despite potential difficulties in the expression in Escherichia coli. The immunomodulation confirmed the activation of both primary and secondary immune responses. An analysis of the structural stability showed the reliability of the candidates under physiological conditions. The study provides a theoretical basis for the further experimental development of subunit vaccines against ASF, combining the safety and efficacy.