卷 58, 编号 7 (2017)

The L and D isomers of the tryptophan (Trp) molecule and the (Trp)⁺ cation in the gas phase and water are calculated at the DFT level to reveal the effect of water considered in the dielectric continuum approximation on the electronic characteristics of the molecule. The distribution of effective atomic charges and bond lengths enables the prediction of the most probable parts of the chemical bond cleavage during the fragmentation of the molecule under the ionizing particle flux. These data are supplemented with a calculation of fragmentation energies. Zwitterionic structures characterized by the appearance of considerable dipole moments and a change in their orientation with respect to the ground state are distinguished among the possible isomeric forms in water.

The electronic structure and chemical bonding in Re₃F₃^2+/0/4− clusters are investigated using density functional theory (DFT) calculations. Out research results show that the ground state for the Re₃F₃^2+/0/4− clusters is found to be triplet state ³A′₁ with the D_3h symmetry, quintet state ⁵A′ with the C_s symmetry, and quintet state ⁵A′₁ with the D_3h symmetry, respectively. A detailed molecular orbital (MO) analysis reveals that the Re₃F²⁺₃ (D_3h, ³A′₁) dication possesses multiple (π_F and partial δ_Re) aromaticity that is respectively responsible for the triangular F₃ framework and the triangular Re₃ framework in the Re₃F²⁺₃ (D_3h, ³A′₁) dication. The neutral Re₃F₃ (C_s, ⁵A′) cluster possesses partial δ-aromaticity that is responsible for the triangular Re3 framework in the Re₃F₃ (C_s, ⁵A′) cluster. The Re₃F⁴⁻₃ (D_3h, ⁵A′₁) anion possesses multiple (σ and partial δ) aromaticity that is responsible for the triangular Re₃ framework in the Re₃F⁴⁻₃ (D_3h, ⁵A′₁) cluster. We also examined their hexagonal pyramidal-type Re₃F₃X⁺ (C_3v, ¹A′₁) (X = Li, Na, K) and Re₃F₃Y²⁺ (C_3v, ¹A′₁) (Y = Be, Mg, Ca) complexes containing the Re₃F₃ (D_3h, ¹A′₁) ligand to reveal that the Re₃F₃ (C_3h, ¹A′₁) structural unit is perfectly preserved in these Re₃F₃X⁺ (C_3v, ¹A′₁) and Re₃F₃Y²⁺ (C_3v, ¹A′₁) complexes also having the corresponding d-orbital aromatic characters.

Density functional theory is employed to study the interaction energies between dibenzothiophene (DBT) and 1-alkyl-3-methylimidazolium tetrafluoroborate ([C_nmim]⁺[BF₄]⁻). The structures of DBT, 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂mim]⁺[BF₄]⁻), 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim]+[BF₄]−), 1-hexyl-3-methylimidazolium tetrafluoroborate ([C₆mim]⁺[BF₄]⁻), 1-octyl-3-methylimidazolium tetrafluoroborate ([C₈mim]⁺[BF₄]⁻), [C₂mim]⁺[BF₄]⁻–DBT, [C₄mim]⁺[BF₄]⁻–DBT, [C₆mim]⁺[BF₄]⁻–DBT and [C₈mim]⁺[BF₄]⁻–DBT systems are optimized systematically at the B3LYP/6-31G(d,p) level, and the most stable geometries are obtained by NBO and AIM analyses. The results indicate that DBT and imidazolium rings of ionic liquids are parallel to each other. It is found that the [BF₄]⁻ anion prefers to be located close to a C1–H9 proton ring in the vicinity of the imidazolium ring and the most stable gas-phase structure of [C_nmim]⁺[BF₄]⁻ has four hydrogen bonds between [C_nmim]+ and [BF₄]−. There are hydrogen bonding interactions, π–π and C–H–π interactions between [C₈mim]⁺[BF₄]⁻ and DBT, which is confirmed by NBO and AIM analyses. The calculated interaction energies for the studied ionic liquids can be used to interpret a better extracting ability of [C₈mim]⁺[BF₄]⁻ to remove DBT, due to stronger interactions between [C₈mim]⁺[BF₄]⁻ and DBT, in agreement with the experimental results of dibenzothiophene extraction by [C_nmim]⁺[BF₄]⁻.

Mono-and mixed-ligand complexes with the composition [Ni(Cyt)₂(H₂O)₂]Cl₂, [Ni(Thr^–)₂(H₂O)₂] and [Ni(Thr^–)(Cyt)(H₂O)₂]Cl are synthesized and studied. Using IR spectroscopy it is determined that in the complex compounds, cytosine is bidentate (C=O group oxygen and heterocycle N3), threonine interacts with the Ni(II) ion due to amino and carboxyl groups. The models of the atomic structure of the studied compounds are proposed based on the EXAFS and XANES spectroscopy results.

X-ray crystallography images are used to perform DFT studies of the structural, electronic, intermolecular energies and IR frequencies of 6,8-dimethyl-3-(4-chlorophenyl)-7-oxo-7,8-dihydropyrimido[4,5-c]pyridazin-5(6H)-one (A) and 6,8-dimethyl-3-(4-chlorophenyl)-7-thioxo-7,8-dihydropyrimido[4,5-c]pyridazin-5(6H)-one (B) using Gaussian 98 and Crystal Explorer program packages. The optimization of A and B in vacuum and solvent (ethanol) phases represent negligible changes in the bond distances, bond angles, and torsion angles. Moreover, the optimization in ethanol is closer to the X-ray crystallography data as compared to the gas phase. Moreover, the Hirshfеld surface analysis reveals that the highest amount of close contact contributions relates to H—H contacts while the lowest amount goes to Cl—Cl/Cl—Cl and C—O/O—C close contacts for A and B, respectively. The corresponding calculated IR intensity values highly match the experimental data.

The molecular dynamics method is used to simulate argon solutions in water and a thin water film–argon system at low temperatures. The correlation in motions of two closely spaced argon atoms is of another nature than the correlation of two neon atoms in a neon solid solution in ice II. The structure of hydrate shells of argon atoms contains five-membered rings composed of water molecules. The solubility of argon in a water film at low temperatures is noticeably higher than at room temperature. If a water film is first cooled to the glassy state and then argon atoms are added to it, then approximately as many argon atoms are absorbed on the film surface as they are present in a cooled film in equilibrium with the argon atmosphere. Argon atoms migrate from one pit to another on the rough surface of a solid water film.

Resistance to heating above the boiling point of water of the molecular structure of a single-charged sodium cation hydration shell growing under the conditions of a model planar nanopore with a width of 5 Å is studied by computer simulation. Monte Carlo calculations of spatial correlation functions are performed in a detailed model with regard to many-body interactions between the ion and water molecules. The system demonstrates an increased resistance to thermal fluctuations along the pore plane and a decreased one in the transverse direction. The heating is accompanied by an enhanced coating effect of molecules around the ion and a diminished effect of extruding the ion out of its own hydration shell. The orientational molecular order due to strong spatial anisotropy inside the nanopore is much more stable than the hydrogen bonds between the molecules.

Stable hydrosols of copper sulfide nanoparticles are synthesized by heating aqueous solutions with different ratios of sodium thiosulfate and copper sulfate in the presence of polyvinylpyrrolidone and studied by a number of physicochemical methods in situ (optical spectroscopy, dynamic light scattering) and ex situ (transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy). The main product is CuS covellite nanoparticles with some impurities of other phases (Cu₂S, Cu_1,8S, Cu₇S₄). With an increase in the initial molar ratio S₂O ²⁻₃ / Cu from 0.2 to 5 the nanoparticle size increases from 1-5 nm to 30-50 nm and then decreases to 4 nm at a ratio of 10. A substantial increase in the intensity of plasmon absorption within 800-1500 nm is observed during the formation of planar nanoparticles with a lateral size of about 30 nm at S₂O ²⁻₃:Cu = 5. A band gap obtained from both direct and indirect optical absorption spectra of sulfides (2.6 eV and 1.7 eV respectively) remains constant for all particles.

The synthesis of zinc sulfide (ZnS) quantum dots (QDs) by microwave heating in a water-ethanol medium is proposed. The effect of the synthesis temperature (80 °C, 100 °C, 120 °C, and 150 °C) on the QD characteristics is examined. Based on the analysis of X-ray diffraction profiles the conclusion is drawn that the hexagonal ZnS phase of wurtzite type with an average nanocrystal size of 2.6-3.7 nm forms in the synthesized QDs. The nanocrystallite size is found to increase with the QD synthesis heating temperature. The analysis of X-ray absorption spectra (XANES) at the zinc K-edge indicates a higher crystallinity of the QD samples prepared at higher synthesis temperatures. The combined analysis of X-ray diffraction profiles, optical diffuse reflectance spectra, and X-ray absorption spectra implies the following possible QD structure: the pure hexagonal ZnS phase of wurtzite type in the bulk of nanoparticles and the amorphous ZnO phase in the surface layer of nanoparticles.

The diffusion of acetone vapor into a Na₇H[Nb₆O₁₉] solution at pH 9.5 results in the crystallization of the Na₁₀[{Na(H₂O)H₂Nb₆O₁₉}₂(μ-H₂O)₂]·46H₂O (1) complex characterized by X-ray diffraction. The sodium cation coordination to a triangular face of the anion enables the determination of anion protonation sites by blocking the disordering and the formation of strong hydrogen bonds between the anions.

The N,N′-bis[chromen-2,4-dione]-3-{2′-hydroxypropylenediamine-N,N′,O,O′}copper(II) solvate complex with dimethylsulfoxide is synthesized. The crystal and molecular structure of the complex is determined by X-ray diffraction. The coordination polyhedron of the copper atom is a square pyramid with the base formed by two oxygen atoms and two nitrogen atoms of the ligand and a vertex consisting of the oxygen atom of the coordinated DMSO molecule.

New dinuclear copper(II) complex [Cu₂(BTE)₂(N₃)₄] (1) (BTE = 1,1′-(2,2′-oxybis(ethane-2,1-diyl))bis(1H-1,2,4-triazole)) is synthesized and characterized using single crystal X-ray diffraction, IR spectroscopy, and elemental analysis. Single crystal X-ray diffraction reveals that complex 1 is a centrosymmetric dinuclear Cu(II) cluster unit with a Cu–Cu separation of 3.267(6) Å. In addition, complex 1 exhibits a high photocatalytic degradation activity for the degradation of rhodamine B.

The crystal structure of [NiEn₃]CrO₄ (En is ethylendiamine), C₆H₂₄CrN₆NiO₄ is studied: a = 9.0408(5) Å, c = 9.7466(4) Å, V = 689.92(8) ų, space group P6₃/mmc, Z = 2, d_x = 1.704 g/cm³, Ni–N 2.133(9) Å, ∠N–Ni–N 82.4(5)°. The thermal properties are determined. When it is heated in a hydrogen atmosphere, a mixture of nanocrystalline Ni and Cr₂O₃ powders with coherent scattering regions of 59 nm and 90 nm respectively is formed. It is demonstrated that thermal decomposition products consist of pseudomorphic particles that inherit the sizes and shapes of initial [NiEn₃]CrO₄ single crystals.

Complex [Pd(4,4′-bit)Cl₂] (1) is synthesized by the reaction of PdCl₂ and 4,4′-bithiazole (4,4′-bit) in acetonitrile and crystallized by vapor diffusion of methanol into a dimethyl sulfoxide solution of the complex. This complex is thoroughly characterized by elemental analysis, IR, ¹H NMR, UV-Vis, and luminescence spectroscopy and its structure is studied by the single crystal X-ray diffraction method. The X-ray structure determination shows that in the structure of this complex, the Pd(II) atom is fourcoordinated in a slightly distorted square-planar configuration by two nitrogen atoms from a bidentate 4,4′-bithiazole ligand and two chloride ions.

Sulfones are known to be biologically active compounds. X-ray diffraction is used to determine the crystal and molecular structure of methyl-(4-chlorophenyl)sulfone. The closest molecules are in pairs oriented to each other by their chlorine atoms. The crystal architecture is formed by endless ribbons of paired associates of the molecules under study.

A mixed-ligand iridium(I) complex with the imino-derivative of asymmetric β-diketone [Ir(cod)(Meitfac)] (cod = C₈H₁₂, cyclooctadiene-1,5; Mei-tfac = CF₃C(O)CHC(NMe)CH₃, 1,1,1-trifluoro-4-methyliminopentanoato-2) is synthesized for the first time. The compound is obtained by the interaction of [Ir(cod)Cl]₂ with sodium β-iminoketonate in diethyl ether in the inert atmosphere and is characterized by elemental analysis, IR and NMR spectroscopy. According to the single crystal X-ray diffraction analysis, the compound is a monomeric molecular complex. The coordination environment of iridium is a distorted square; the Ir–O and Ir–N bond lengths are 2.031(1) Å and 2.086(2) Å respectively; the average distance Ir–C′ = 1.994(8) Å (C′ is the center of the С=С bond of the cod ligand); the NIrO chelate angle is 91.30(6)°, and the C′IrC′ angle is 87.63°. The crystal packing contains dimers formed by weak F…H–C hydrogen interactions. The thermal properties of the complex are studied by thermogravimetry. The compound passes into the gas phase in the temperature range 150-260 °C (mass loss 93.5%) and is characterized by a lower volatility as compared with its β-diketonate analog [Ir(cod)(tfac)] (tfac = CF₃C(O)CHC(O)CH₃, 1,1,1-trifluoropentadionato-2,4).