Journal of Structural Chemistry最新文献

This work presents the preparation of a hydrazone derivative of hydralazine (AA1) and its cyclic analogue triazophtalazine (AA2). The compounds were characterized using FTIR, mass spectrometry and elemental analysis. Crystal structures for both compounds were determined through single crystal X-ray diffraction analysis. While compound AA1 was found to crystallize in the triclinic crystal system with space group (Pbar{1}), compound AA2 crystallized in the monoclinic system with space group P2₁/c. Both structures are stabilized by π–π stacking interactions. Furthermore, UV-Vis absorption and fluorescence properties of the compounds were investigated in solution.

Two crystal modifications of the cocrystal of (Z)-4-amino-5-(hydroxyimino)-2,2-dimethyl-2,5-dihydro-1H-imidazole-3-oxide with 3,4-diaminoglyoxime in the 2:1 stoichiometric component ratio are studied by single-crystal XRD. It is established molecules of both modifications demonstrate highly similar geometric parameters. Noncovalent bonding in the crystals of both forms is analyzed comprehensively by constructing Hirshfeld surfaces. It is shown that 1H-imidazole-3-oxide chains are rearranged, the fraction of N–H⋯N interactions is diminished and their character is changed upon the introduction of a water molecule into the structure of one modification, while its calculated density and the coefficient of molecular packing in the crystal are not changed significantly.

This paper reports a comparative study of lithium and zinc adsorption on the surfaces of 2D carbon allotropes (biphenylene, irida-graphene, ψ-graphene and TPDH-graphene) using the density functional theory method. The cohesion energies of carbon monolayers and the binding energies of metal atoms with different carbon rings were calculated. All of the considered structures are characterized by cohesive energies close to those of graphene, but with a lower modulus, which indicates their lower thermodynamic stability. Lithium adsorption on the studied allotropes is always more favorable energetically than on graphene, with the energy being higher than the cohesive energy. Conversely, zinc manifests a weak interaction with carbon surfaces and its binding energies are significantly lower than the cohesive energies, indicating a tendency towards clusterization. The example of lithium adsorption on graphene shows that clusterization tendency cannot be estimated from cohesive energy values alone. Therefore, electrostatic repulsion of lithium ions plays a decisive role in the case of the lithium dimer.

Geometries and formation energies of (PhCl)_n (n = 2-6) clusters are computed by the density functional theory at the B3LYP/cc-pvdz level with D3 Grimme’s dispersion correction. Several geometric configurations with different types of interactions are considered for each n. The parallel arrangement of molecules is found to be more energetically favorable for the dimers and trimers. As the number of molecules increases in the cluster, the perpendicular orientation arises in combination with the parallel one. The formation of cyclic structures is not characteristic of (PhCl)_n clusters at n = 3-6. The obtained data on the cluster structures can be used to interpret the properties of liquid chlorobenzene and its solutions.

Coordination polymers (n{{(text{Pipy})}^{{2}+}}[text{A}{{text{g}}_{4}}{{(text{citr})}_{2}}]_{n}^{2-}cdot {2}n{{text{H}}_{2}}text{O}) (1) and {[Ag(bpy)]⁺[Ag₂(citr)(bpy)₂]^–}_n·10nH₂O (2) are formed by the interaction of silver acetate with citric acid (H₃citr) and piperazine (Pipy) / 4,4′-bipyridine (bpy) during slow diffusion. Their structures are determined by the single crystal X-ray diffraction (XRD) analysis. According to the single crystal XRD data, both compounds are ionic polymers. In the complexes, the Ag⁺ cations and bridging COO-groups of citric acid form eight-member cycles (–Ag–O–C–O–Ag–O–C–O–) with argentophilic interactions. Unlike complex 1 in which protonated piperazine fragments Pipy²⁺ occupy the outer-sphere positions, bpy coordinates to the complexing agent in 2, forming [Ag(bpy)]⁺ cationic chains. In the coordination polymers, the system of hydrogen bonds and π–π interactions participate in the additional stabilization of the structures. Simultaneous thermal analysis (STA) data show that complex 2 is the highly stable compound.

Polycrystalline rhodium Rh(poly) is oxidized in the O₂ atmosphere under the pressure P_O2 of 1 bar and a temperature of 1100 K, and then the morphology, microstructure and chemical composition of oxide phases were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). According to the XRD data, rhodium exists in the metallic state and contains subgrains with a size of ~43 nm and as large as ~10 µm in the bulk of the sample. The XPS data indicate that the recorded Rh 3d_5/2 and O 1s peaks with an electron binding energy (E_b) of 308.6 eV and 530.1 eV correspond to Rh³⁺ and O^2– in the composition of the surface Rh₂O₃ oxide. Morphology, phase and chemical compositions of a ~35 nm thick surface oxide layer and a rhodium corrosion layer located below the oxide layer at a depth of ~230 nm are characterized by SEM and EDS methods using the probe electron energy (E₀) of 5 keV and 20 keV. The Rh(poly) surface contains 20-50 nm (~35 nm) Rh₂O₃ oxide particles that are formed on ~43 nm rhodium subgrains and form a continuous oxide layer. This layer includes 20-50 µm regions containing spherical Rh₂O₃ oxide agglomerates with a size of ~150 nm. A corrosion rhodium layer containing 20-50 nm large Rh subgrains and nanocrystals is found under the oxide layer. The same layer contains 100-200 nm (~150 nm) rhodium crystals on which oxide agglomerates are formed.

The comparative computational study of perovskite oxides BaFeO_3–x, BaCoO_3–x, LaFeO_3–x, LaCoO_3–x, SrFeO_3–x, and SrCoO_3–x is performed using density functional theory (DFT). Cobalt- containing oxides are found to have a more flexible electronic structure as compared to iron oxides. Cobalt oxides demonstrate a tendency to a mixed spin state, charge disproportionation, and a distortion of the ideal cubic structure. Iron-containing oxides have a much weaker tendency to charge disproportionation. The ordering of brownmillerite-type vacancies is observed for all oxides studied, which is due to the interaction of adjacent vacancies.

Complexes of the alanyl-L–tyrosine zwitterion with neutral nucleoside (uridine, cytidine, adenosine, and guanosine) molecules are modeled by the quantum chemical DFT method. Different coordination modes of the peptide to nucleosides are considered, and the optimized structures of the complexes characterized by the most favorable values of changes in the free Gibbs energy are found. Changes in the energy and the free Gibbs energy during complexation are decomposed into contributions from the intermolecular interaction and structural reorganization of the peptide and nucleoside. Based on changes in the free Gibbs energy, the stability order of the alanyl–tyrosine complexes with nucleosides is determined: cytidine > adenosine > > guanosine > uridine. The energies of intermolecular H-bonds vary insignificantly on passing from the complexes of nucleic bases to those of nucleosides. However, the number of H-bonds is increased in the nucleoside complexes due to additional interactions with OH groups of the ribose residue. Additional stabilization effect of the complexes caused by π–π stacking is detected in the alanyl–tyrosine complexes with cytidine.

A comprehensive study of InGaZnO₄, InGaZn₃O₆, and InGaZn₄O₇ indium–gallium–zinc oxides (IGZO) prepared by the solid-phase synthesis is reported. The preparation technique is described in detail. The obtained samples are characterized by powder XRD, electron microscopy, inductively coupled plasma atomic emission spectroscopy (ICP-AES), IR and Raman spectroscopy methods. The vibrational spectra data are compared with the structure and composition of the samples.

Thin amorphous films of hydrogenated silicon carbonitride are prepared in a high-frequency plasma reactor using hexamethyldisilazane vapor and helium. SiC_xN_y:H films of various compositions are deposited by varying the substrate temperature and the precursor pressure in the reactor chamber. The dependences of growth rate, elemental composition, chemical structure, refractive index, and dielectric constant of the films on synthesis conditions are determined. Gas species are studied by optical emission spectroscopy. It is shown by HRTEM and EDS mapping methods that the annealed Cu/SiCNH/Si(100) sample has distinct substrate/SiCNH and SiCNH/copper interfaces; the copper diffusion was not registered. Thin SiCNH films with a low k value can be considered as a promising diffusion barrier layer for modern microcircuits.