Journal of Structural Chemistry最新文献

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.

Magnesium bis-(dipivaloylmethanato)(N,N,N′,N′-tetramethylethylenediamine) [Mg(tmeda)(thd)₂] is one of the most demanded volatile fluorine-free precursors to deposit MgO films. By means of single crystal and powder X-ray diffraction we have found for the first time that during recrystallization and vacuum sublimation different polymorphs of this complex are formed: space groups P2₁/n I (previously unknown) and C2/c II (new) respectively. The new modification is also stable upon storage but does not exhibit a low-temperature phase transition with crystal splitting and symmetry lowering to (Pbar{1}) III due to the ordering of tert-butyl groups. The thermal behavior of the new polymorph is analyzed by DSC and tensimetry (flow method), which enabled us to determine the thermodynamic parameters of transformations in the condensed phase and sublimation processes. It is determined that although molecules of the complex are packed closer in the P2₁/n crystals, it does not substantially affect the vapor pressure and thermal properties at temperatures used in deposition processes. By the density functional theory with periodic boundary conditions (Quantum Espresso 7.4, PBEsol-D3(BJ)/SSSP Precision) it is shown that differences in the crystal lattice energies of three polymorphs I–III studied do not exceed 2.4 kJ/mol.

A new [Zn(tr₂ad)₂(NO₃)₂]_n (I) (tr₂ad = 1,3-bis(1,2,4-triazole-1-yl)adamantane) metal-organic framework (MOF) is prepared by solvothermal synthesis. According to the XRD data, this MOF is formed by spiral chains, left- and right-handed ones present in equal amounts in the structure. Compound I is studied by powder XRD, elemental analysis, and thermogravimetry. Its photoluminescent properties are considered. It is shown that I exhibits emission with a maximum at 448 nm and a luminescence quantum yield of 7%.

A series of 2α, 2β, 3, 4β polymorphs of 2-, 3-, 4-aminophenylbenzothiazoles (2-pbt, 3-pbt, 4-pbt) is studied by XRD. The polymorphs crystallize in polar space groups. Static orientational disorder in their crystal structures is described. The disorder is a consequence of two factors: 1) presence of pseudosymmetry D_2h in the molecules; 2) absence of strong specific intermolecular interactions. The type of symmetry transformation relating disordered positions and the disorder degree are specific to each polymorph. The highest and lowest minor position occupancies are exhibited by 2α (30%) and 2β (2%), respectively. In the case of 2-pbt polymorphs, the assumption of dynamic or static disorder caused by the intramolecular transfer of the amino group′s H atom to the heterocyclic fragment′s N atom is rejected.