Journal of Structural Chemistry最新文献

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.

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.