Journal of Structural Chemistry最新文献

A method of preparing tomographic images of multielectron (molecular) systems is theoretically substantiated. According to the current concepts, spin-spin coupling between resonating nuclei manifested in the NMR spectra is due to the electron motion inside the space of the molecule. Thus, it can be assumed that the interaction-containing space corresponds to the molecule′s size. Modern high-resolution NMR spectrometers allow studying low-energy (<1 Hz) interactions. From the experimental viewpoint, the inherently incorrect J → F(r, θ, φ, E) inverse problem should be solved. At the first stage, points of space occupied by some molecular (multielectron) system can be visualized using spin-spin coupling constants. At the next stage, tomographic images can be obtained from the calculated “exact” wave functions. This requires quite powerful computers and corresponding software programs. We propose a block diagram of a device for implementing a theoretically substantiated fundamentally new method of retrieving information about the spatial structure of substance at the molecular level.

The influence of weak microwave and ultraviolet radiation on the structure formation of zirconium oxyhydroxide prepared at different nucleation and growth rate ratios is studied. Thermal behavior, heat-induced phase changes, and morphology of the synthesized samples are studied by thermogravimetry, differential scanning calorimetry and mass spectrometry of gaseous thermolysis products, as well as by powder XRD and high-resolution transmission electron microscopy. It is established that such radiation promotes the decrease of the temperature of amorphous zirconium dioxide crystallization, formation of well-crystallized zirconium dioxide nanoparticles and can be therefore be used in the directed synthesis of nanocrystalline materials based on such compounds. The irradiation effect is most pronounced in the case of long-term hydrolysis of aqueous zirconium oxychloride.

A series of zinc complexes with 3-arylidene-1-pyrrolines and acetic or trifluoroacetic acid anions is obtained. Molecular and crystal structures are investigated and non-covalent interactions are analyzed for all synthesized compounds. The molecular structures of the complexes are shown to be similar. Minor differences are due to non-covalent interactions whose nature and amount is determined by the occurrence of active centers in the ligand compositions. It is revealed that for 3-arylidene-1-pyrroline complexes the main structure-forming interaction is π⋯π interactions of different topologies. The exceptions are only the crystals of compounds containing groups being donors of hydrogen bonds (e.g., hydroxyl groups), which results in the formation of hydrogen-bonded associates that in turn form the crystal packing mainly by π⋯π interactions. The molecular docking-modeling with the HER2 human receptor kinase domain indicates that the obtained complexes can bind with HER2 with an energy gain comparable with that for the previously studied copper trifluoroacetate complexes with 3-arylidene-1-pyrrolines. This fact suggests that they are effective in anticancer therapy.

The effect is studied of modifying dopants M = Fe, Cr, Ni, and Ga on the physicochemical and catalytic properties of copper-manganese catalysts for low-temperature CO oxidation under dry and wet reaction conditions. By means of X-ray diffraction and X-ray photoelectron spectroscopy the phase compositions and structural bulk characteristics of all catalysts before and after tests, as well as their surface compositions and states, are determined and compared. The catalysts are modified at the stage of preparing CuMn_1–xM_xO₂ nanocrystallites of the crednerite structure type with partial substitution at manganese positions. The final catalyst is obtained directly under the reaction conditions by pre-treatment at 350 °C that results in the phase transition of crednerite particles to cubic spinel structure (Cu,Mn,M)₃O₄. It is found that under dry conditions only nickel and gallium modifications substantially increase the specific rate of low-temperature CO oxidation whereas in the presence of water vapor, all CuMn catalysts studied are deactivated regardless of the nature of the modifying dopant.

This work discusses a mesoscale computer model based on the dissipative particle dynamics method. The model is aimed at studying the processes occurring at the initial stage of forming polyacrylonitrile-based chemical fibers by dry-jet wet spinning method. The model represents the appearance of structural inhomogeneities on the surface of a polymer solution jet as it passes through the air gap between the spinneret and the coagulation bath. According to the calculation results, a high-density polymer layer appears on the surface of the forming fiber the as a result of solvent evaporation, and this layer can significantly affect the polymer′s coagulation rate. The estimations of the layer thickness show that a ~0.5 µm thick layer is sufficient for making the spinning solution jet maintain in air for ~0.6 s. The obtained results can be useful in tuning the technological process of dry-jet wet method of chemical fiber spinning.

For the first time, the dependence of luminescent properties on temperature was investigated for the compound TbAl₃(BO₃)₄ with a huntite-like structure. Samples synthesized by the solution combustion synthesis (SCS) and grown from the flux were used for the study. There are significant differences in the thermal quenching behavior between the two types of materials. It was shown that the onset of thermal quenching strongly depends on the synthesis method: powders prepared by SCS exhibit higher luminescence efficiency at lower temperatures compared to flux-grown single crystals. The branching ratios for the ⁵D₄ to ⁷F₅ transition exceeded 50% under certain conditions, highlighting the potential of material for laser applications.

The existence of zero-dimensional layered bismuth(III) iodide hollow nanostructures is predicted; their models are constructed. Thermodynamic stability and electronic properties of BiI₃ fullerenes with tetrahedral, octahedral, and icosahedral morphologies and the number of atoms up to ~1000 are studied by the density functional theory method. The strain energy of BiI₃ fullerenes decreases with their increasing size, tetrahedral and octahedral morphologies being the most stable ones. Independently of the size and morphology, all the considered BiI₃ fullerenes are semiconductors with a bandgap smaller by 0.6-1.9 eV than that of the BiI₃ monolayer.

Thiourea (TU) has recently attracted attention as an effective additive for the improvement of phase stability (including defect passivation), recombination reduction, and increase of the lifetime of charge carriers in MAPbI₃/FAPbI₃ perovskites (MA–methylammonium, FA–formamidinium), but the molecular-level mechanisms of these processes are not yet fully clarified. In this work, we employ a multiscale theoretical approach, combining density functional theory (DFT) and molecular dynamics (MD), to investigate the role of TU in the stabilization of the black α-phase and the passivation of surface defects in formamidinium lead iodide. Calculations reveal that TU forms stable complexes with PbI₂ and the [PbI6]^4- octahedral fragment via Pb–S coordination and establishes stronger hydrogen bonds with FA⁺ cations than with MA⁺ cations. The adsorption energy of TU on the α-FAPbI₃(001) surface is higher than on the α-MAPbI₃(001) surface, indicating stronger binding and more effective defect passivation. The density of states analysis confirms the elimination of mid-gap trap states through passivation of undercoordinated Pb and I atoms. Also, TU reduces the free-energy difference between α- and δ-phases of FAPbI₃ by 5.79 kJ/mol per formula unit, thereby thermodynamically favoring the photoactive α-phase of FAPbI₃. MD simulations also demonstrate that TU slows down the nucleation and aggregation of PbI₆ and promotes the growth of larger grains. Thus, TU acts both as a phase stabilizer and as an electronic passivator, thus providing prospects for the rational design of additives aimed at enhancing the stability and efficiency of perovskite solar cells.

Organogold derivatives of nitronyl nitroxide, stabilized by phosphine ligands are obtained. Conformational features of the phosphine ligands and nitronyl nitroxide nuclei are analyzed by single crystal X-ray diffraction. Effective π–π stacking interactions are detected and described for the first time in the crystals of organogold derivatives.

The paper is devoted to the crystal structure refinement of two polymorphs of the active pharmaceutical ingredient sofosbuvir that is used to treat hepatitis C. The refinement is based on the powder X-ray diffraction data obtained from a synchrotron radiation source of the Kurchatov Institute Research Center. The Rietveld refinement of the structures was carried out using soft constraints. The effect of the model used to calculate optimal bond lengths and angles on the quality of the diffractogram description is demonstrated. Geometry is optimized using quantum chemical calculations with periodic boundary conditions, and it is shown that calculations using the PBE functional lead to a noticeable overestimation of bond lengths at the phosphorus atom. A noticeably better result is achieved using the SCAN hybrid functional. To verify and determine the accuracy of the obtained structures, standard deviations between experimental atomic positions and those optimized by quantum chemical calculations (RMSCD), as well as the HUW parameter (half uncertainty window), are calculated.