Journal of Structural Chemistry最新文献

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.

The crystal structures of 3,3-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-phenylpropan-1-one (1) and 3,3-bis(3,5- dimethyl-1H-pyrazol-1-yl)-1-(furan-2-yl)propan-1-one (2) are determined by single crystal X-ray diffraction (XRD). According to the single crystal XRD data, in the crystalline phases, the molecules of 1 and 2 are in the form of different conformers (cis and trans respectively), which is due to different orientations of pyrazolyl moieties. The rotational barriers of these moieties are estimated by quantum chemical calculations: they are 2.6 kcal/mol and 2.5 kcal/mol for 1 and 2 respectively. The contributions of different interatomic contacts to the crystal packings are estimated by the Hirshfeld surface analysis.

A new layered metal-organic framework (MOF) {[Tb₂(H₂O)₂L₃]·H₂O·CH₃CN}_n is obtained by the solvothermal synthesis from terbium(III) nitrate and bis(pyrazol-1-yl)methane-4,4′-dicarboxylic acid (H₂L). The compound is a layered framework formed of two types of binuclear secondary building units {Tb₂} linked by carboxylate groups of L^2– ligands. The layers are stabilized by intermolecular hydrogen bonds and contain channels occupied by water and acetonitrile molecules. The thermogravimetric analysis shows a high thermal MOF stability after the removal of guest molecules up to 400 °C. The luminescence quantum yield is 25%, and the excited-state lifetime is 1.19 ms. The high selectivity is demonstrated of the luminescence sensory response of the MOF suspension in acetonitrile to 2,6-pyridinedicarboxylic acid (DPA), a key biomarker of spore-forming bacteria.

A new aroylhydrazone compound 2-bromo-N’-(2-hydroxy-4-methoxybenzylidene)benzohydrazide (H₂L), was prepared and characterized by IR, UV-Vis and ¹H NMR spectra. Reaction of H₂L with bis(acetylacetonato)oxovanadium(IV) and bis(acetylacetonato)dioxomolybdenum(VI), respectively, in methanol afforded two new complexes [VOL(OMe)(MeOH)] (1) and [MoO₂L(MeOH)] (2). Both complexes have been characterized by elemental analysis, IR and UV-Vis spectra. Molecular structures of H₂L and the complexes have been determined by single crystal X-ray crystallography. In both complexes, the aroylhydrazone ligands coordinated to the metal atoms through phenolate oxygen, imino nitrogen and enolate oxygen atoms. The octahedral coordination of the V atom is furnished by one oxido oxygen, one methanol oxygen, and one methanolate oxygen atoms. The octahedral coordination of the Mo atom is furnished by two oxido oxygen and one methanol oxygen atoms. The complexes were assayed for antibacterial activities on Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens, and antifungal activities on Candida albicans and Aspergillus niger, and gave interesting results. Complex 1 has MIC value of 1.3 μM against B. subtilis.

The structure of the [Cu₂(S–C₆F₄–CF₃)₂(dmap)₄] (dmap - 4-dimethylaminopyridine) complex is determined by single crystal X-ray diffraction (XRD). It is found that when cooled below 230 K, the complex undergoes a phase transition forming another polymorph that is also characterized by single crystal XRD.

The series of H^5R N-tert-butyl-N-(1-alkyl-1H-pyrazole-5-yl)hydroxylamines (R = Me, iPr, nBu) (diamagnetic precursors of N^5R 5-R-pyrazolyl-substituted tert-butylnitroxides) is expanded. It is established that the interaction of H^5R with the copper(II) hexafluoroacetylacetonate Cu(hfac)₂ leads to the formation of individual mononuclear complexes and their cocrystals with H^5R. In the complexes, H^5R are coordinated in a monodentate mode via an N atom of the pyrazole ring, and the OH groups form intermolecular hydrogen bonds. It is shown by cyclic voltammetry that the peak at 720-750 mV corresponding to one-electron H^5R oxidation has a reduction response wave with a noticeably lower current, meaning that the process is partially reversible. Due to low values of potentials, the interaction with Cu(hfac)₂ in the solution can lead to the oxidation of H^5R by air oxygen and to the formation of complexes containing both H^5R and N^5R as ligands, thus allowing one to use the “one-pot” approach to prepare heterospin complexes with tert-butylnitroxides.

The work is aimed at the optimization of the preparation procedure of films and fibers from single-walled carbon nanotubes (SWCNTs) for their application as the electrode material. The multistage preparation procedure is proposed that includes thermal and chemical treatment (HCl_conc, 9% HNO₃ + H₂SO₄, 15% H₂O₂). The SWCNT films are synthesized by chemical vapor deposition from ethanol and ferrocene. The fibers are obtained by the wet pulling technique from SWCNT films. The effect of each stage on the structural and electrical characteristics of nanotubes is evaluated by TEM, Raman, and FTIR spectroscopy and the four-probe measurement of the surface resistance. By the TEM analysis a decrease is found in the fraction of catalytic particles after thermal treatment in the air at 330 °C in combination with HCl treatment. By the FTIR analysis it is found that thermal treatment of SWCNT films removes organic contaminations. The I_D/I_G ratio is estimated at each stage of the treatment using the Raman spectral data. The availability of the prepared fiber electrodes is evaluated electrochemically by chronopotentiometry and cyclic voltammetry. The obtained electrical capacitance values from 10 mF/cm² to 14 mF/cm² involve the substantial pseudocapacitive component due to the occurrence of surface functional groups, which allows the use of fibers in energy storage devices. The 15% H₂O₂ treatment of fibers provides the most acceptable results from the standpoint of minimization of background currents, which is necessary to take into account when using these fibers in analytical applications, e.g., for the voltammetric determination of electroactive compounds.