Journal of Structural Chemistry最新文献

An aroylhydrazone compound N’-(2-hydroxy-4-methoxybenzylidene)-4-nitrobenzohydrazide (HL) was prepared. Reaction of the aroylhydrazone compound with zinc iodide afforded a dinuclear zinc(II) complex [Zn₂I₂L₂]∙2DMF. The aroylhydrazone compound and the zinc complex were characterized by CHN elemental analyses and infrared spectroscopy. Detailed structures are further confirmed by single crystal X-ray determination. The Zn atom in the complex is in square pyramidal coordination, with the phenolate O, imino N and carbonyl O atoms of one L ligand, and the phenolate O atom of the other L ligand in the basal plane, and with one I ligand at the apical position. The crystal structures of the aroylhydrazone and the zinc complex are stabilized by hydrogen bonds. The two compounds have been tested for their Jack bean urease activity. As a result, the zinc complex has effective activity with IC₅₀ value of 1.7 ± 0.3 μmol/L.

We report a comparative crystal chemical analysis of volatile homoligand complexes of Co(II), Ni(II), Cu(II), Pd(II), and Pt(II) with β-ketoimines utilized as precursors in the preparation of oxide and metal film coatings for various purposes using chemical vapor deposition. The crystal structures and intermolecular interactions of β-ketoiminates with the general formula M(L)₂ (L = (R1-C(O)CH-C(N-R3)-R2)₂; R1, R2 = CH₃, CF₃, C(CH₃)₃, C(OCH₃)(CH₂)₂ in various combinations; R3 = H, CH₃) are studied.

The key to the modification of the properties of carbon fibers is to understand how to control the structure of polyacrylonitrile-based precursors. Results of a mesoscale modeling of the structure formation processes in a mixture of polyacrylonitrile, dimethyl sulfoxide, and water (good and poor solvents for polymers) are reported. The system′s composition is chosen using the composition of precursor fibers at the later formation stages under coagulation bath conditions. All calculations are performed using the dynamic density functional theory. The proposed model considers effects caused by changes in the system composition, carbon nanotube filler, temperature, and shear flow. It is shown that the polymer structure can be significantly changed by varying the amount of water in the system (determined by the coagulation bath composition) and by introducing a carbon filler.

Results are reported about the molecular mechanics simulation of the structures of carbon–nitrogen solid solutions obtained by pyrolysis of a molten mixture of melamine with 50-100 wt.% high-temperature coal-tar pitch upon their slow heating to 500 °C. It is shown experimentally that the electrical conductivity of the solid solutions formed increases by several orders of magnitude with an increase in the nitrogen concentration from 0.4 wt.% to 22 wt.%. Structure simulation is the research stage required for understanding the conductivity mechanism. Starting data for the simulation are elemental, powder X-ray diffraction, pycnometric, simultaneous thermal analysis, infrared (IR) and X-ray photoelectron spectroscopy (XPS) results obtained for the materials under study. Apart from nitrogen and carbon atoms, hydrogen and oxygen atoms are present in the samples, which is explained by the presence of these elements in the initial components. According to XPS and Raman spectroscopy data, the materials have the graphite-like structure with carbon atoms that are mainly in the sp² hybridization state. The occurrence of four nitrogen atoms with different environments is detected by the XPS technique: graphite-, pyridine-, and pyrrole-like, and oxidized. The thermal analysis data support the conclusion about the absence of triazine islands in the samples prepared from mixtures with 80-100 wt.% coal-tar pitch and about their presence in the samples with 50-70 wt.% coal-tar pitch. The IR spectroscopic data confirm the absence of amino and cyano groups in all solid solutions. Based on the available experimental data, structure models are proposed for the materials studied, and common structural patterns are found.

Five new metal-organic frameworks based on 4,8-disulfo-2,6-naphthalenedicarboxylic acid (H₄dsndc) are obtained: [Cd₂(dsndc)(dmf)₆] (1), [Mn₂(dsndc)(dmf)₆] (2), [Zn₂(dsndc)(dmf)₆] (3), [Co₂(dsndc)(dmf)₆] (4), and [Cd₂(dsndc)(dma)₆] (5) (DMF = N,N-dimethylformamide, DMA = N,N-dimethylacetamide). The four of them (1–4) are isostructural layered coordination polymers. The structures of all compounds are determined by the single crystal X-ray diffraction analysis. Compounds 1–3 and 5 are obtained as chemically and phase-pure and are characterized by the standard complex of physicochemical techniques (powder XRD, IR, TGA, and CHN). Photoluminescence excitation and emission spectra are recorded for compound 3, and a quantum yield of 18% is obtained.

An original procedure is proposed to refine unit cell parameters (UCPs) of single crystals in Bond’s scheme. The procedure involves the use of a modern laboratory diffractometer equipped with a 2D detector and a three-circle goniometer. At the first stage, preliminary UCPs, diffraction class, and crystal orientation relative to goniometer axes are determined. Then φ and ω angles are calculated to bring an appropriate (occurrence of a well-resolved doublet, intensity) reflection hkl on the equatorial plane. The measurement in Bond’s scheme is carried out at two symmetric positions of the detector ±2θ_D ≈ 2θ_hkl. The principal difference from the measurement on a single crystal spectrometer consists in refusing to plot the reflection profile I(ω) and passing to ω-scans with a width of 3-4°, which allows the measurement of the Kα₁/Kα₂ doublet profile. After its processing by two independent 2D functions, coordinates of the maxima are determined, and then the 4θ_hkl. Angle is found based on angular sizes of the detector pixel and the difference in the coordinates of X Kα₁-component reflections obtained in symmetric positions. In this approach, measurement errors are related to the accuracy of placing the detector in two symmetric positions and the correctness of processing 2D reflection profiles. In the study of reference Si and Ge single crystals in the range of 2θ_D angles close to 100°, UCP deviations from the theoretical values are found to not exceed 0.0004 Å, and the relative measurement accuracy is 6·10^–5. The refinement of UCPs of single crystals grown in the Y₂O₃–Eu₂O₃ system by the melt-solution technique indicates the formation of the (Y_1–xEu_x)₂O₃ solid solution with the x value range of 0.27-0.40. A scheme is proposed to improve the measurement accuracy when the procedure is transferred to the diffractometer with synchrotron radiation.

Expressions are derived for the relationship between the metallicity index _m with the ratio of the absolute value of the potential electron energy density (V) to the kinetic energy density (G) at the bond critical point (BCP) using the quantum theory of atoms in molecules (QTAIM) and the electron localization function (ELF) value at the BCP. It is found that the ELF maximum (ELF^BCP = 1) is achieved at (xi _{m}^{text{BCP}}=-4). It is shown that calculated (xi _{m}^{text{BCP}}) values should not exist in a range (-4<xi _{m}^{text{BCP}}<-1). The (xi _{m}^{text{BCP}}) values are calculated and analyzed for some simple molecules and crystals.

Amorphous transparent SiC_x:H and SiC_xN_y:H films are prepared at a temperature of 200 °C and a discharge power of 200 W in an inductively coupled RF plasma reactor using hexamethyldisilane vapors and additional argon and/or nitrogen gases. The influence of N₂ flow rate on the morphology, chemical structure, elemental composition, transmittance, refractive index, contact angle, and film deposition rate is studied. Plasma components are determined by optical emission spectroscopy. It is shown by HRTEM and EDS mapping methods that the annealed Cu/SiC_x:H/Si(100) sample has distinct substrate/film and film/copper layer interfaces, no Cu diffusion occurs, and that the SiC_x:H the film can be considered as a promising diffusion barrier layer. Stability of the films during storage under ambient conditions is studied. The tendency of SiC_xN_y:H films to oxidize is revealed by EDS, IR spectroscopy, and XPS.

The In₂O₃–Ga₂O₃–ZnO ternary oxide is prospective for electronics applications. Promising methods of fabricating In₂O₃–Ga₂O₃–ZnO based transistors require a technique for the preparation of X-ray pure powders. Data on the influence of the studied organic complexing agent on the morphology of obtained powders are reported. It is shown that ethylene glycol is more preferable to use than citric acid since the powders prepared in the first case contain no admixture phases.

Single crystals of two new compounds, (L-CysH⋯L-Cys)(HC₂O₄) (I) and (L-CysH⋯L-Cys⋯L-CysH)(HC₂O₄)₂·0.5H₂O (II), were obtained. Crystal structures were solved and refined using single-crystal X-ray diffraction, and compared with the previously known orthorhombic and monoclinic modifications of the simple salt (L-CysH)(HC₂O₄). Compound I crystallizes in the triclinic crystal system (space group P1, Z = 2) and contains (L-CysH⋯L-Cys) dimeric cations with very short O⋯O interatomic distance of 2.434(2) Å. Hydrogen oxalate anions form head-to-tail type chains with very short hydrogen bonds, characterized by O⋯O distances of 2.422(2) Å and 2.417(3) Å. The crystal lattice of II is monoclinic with the space group C2, Z = 4. It contains a new type of cation, that has never been observed before for cysteine salts, i.e. trimeric (L-CysH⋯L-Cys⋯L-CysH) cation. Protonated L-cysteinium cations are connected to the zwitterionic L-cysteine moiety through the same oxygen atom of the carboxylate group via hydrogen bonds, with O···O distances of 2.6410(18) Å and 2.4888(19) Å. Similar to the structure I, the hydrogen oxalate anions form head-to-tail type chains linked by short hydrogen bonds with O⋯O distances of 2.4369(17) Å and 2.4330(17) Å, respectively. The crystals were characterized by IR and Raman spectroscopy. The batches obtained on crystallization were also characterized by X-ray powder diffraction, in order to check the phase purity of all the sample.