Том 58, № 4 (2017)

By the structural representation of a chemical reaction in the form of a condensed graph a model allowing the prediction of rate constants (logk) of Diels–Alder reactions performed in different solvents and at different temperatures is constructed for the first time. The model demonstrates good agreement between the predicted and experimental logk values: the mean squared error is less than 0.75 log units. Erroneous predictions correspond to reactions in which reagents contain rarely occurring structural fragments. The model is available for users at https://cimm.kpfu.ru/predictor/.

The spin Hamiltonian parameters (g factors, hyperfine structure constants and superhyperfine parameters) and local structures for Ag²⁺ centers in AgCl and KCl crystals are theoretically studied using the high-order perturbation formulas for a tetragonally elongated 4d⁹ cluster. The impurity centers undergo relative elongations (≈0.05 Å and 0.23 Å for Ag²⁺ in AgCl and KCl, respectively) along the C₄ axis owing to the Jahn–Teller effect. All the calculated spin Hamiltonian parameters show good agreement with the experimental data, and the ligand contributions to the spin Hamiltonian parameters are important and should be taken into account. The unpaired spin densities in the superhyperfine parameters are determined from molecular orbital coefficients based on the cluster approach, instead of being taken as the adjustable parameters in the previous treatments. Increasing tetragonal elongation from AgCl to KCl is attributed to a decrease in chemical bonding (or lower force constant) with increasing Ag²⁺–Cl distance.

Halogen and solvent effects on the conformational, vibrational, and electronic characteristics of thiophene-2-carbaldehyde (T2C, C₅H₄OS) and thiophene-2-carbonyl-halogens [C₅H₃XOS, X = F (T2C-F), Cl (T2C-Cl), and Br (T2C-Br)] are analyzed by the density functional theory (DFT) and time dependent density functional theory (TDDFT), using the B3LYP functional and the 6-31++G(d,p) basis set. Computations consider two conformations of the compounds in both gas phase and solution. The present study aims at the exploration of the halogen and medium effects on the stability, structural parameters, dipole moment, carbonyl stretching vibration, frontier molecular orbitals, ultraviolet (UV) and density-of-states spectra of the conformers. The atypical characteristics of fluorine and chlorine affecting the electrical-optical band gaps, chemical hardness, partial density-of-states plot, absorption band, and the highest occupied molecular orbital are observed correspondingly. The findings of this research will provide insight for future studies considering conformations analogous to the compounds studied.

The g factors for Cu²⁺ in meta-zeunerite (Cu(UO₂)₂(AsO₄)₂·3H₂O), kroehnkite (Na₂Cu(SO₄)₂·2H₂O), copper benzoate (Cu(PhCO₂)₂·3H₂O) and diaboleite (Pb₂Cu(OH)₄Cl₂) of the tetragonal phase are uniformly treated by high order perturbation formulas for 3d⁹ ions in tetragonally elongated octahedra. The calculation results are in good agreement with the observed values and systematically analyzed in view of the local structures around Cu²⁺. The g anisotropies Δg (= g_‖−g_⊥) are largely ascribed to the local tetragonal elongations of the Cu²⁺ sites, characterized by the relative elongation ratios (R_‖−R_⊥)/R̅ ≈ 19%, 21%, 27% and 30% for metazeunertie, kroehnkite, copper benzoate and diaboletie, respectively. The anomalous valley (minimum) of relative g anisotropy for copper benzoate is attributed to the modification of the Cu²⁺ electronic states due to the phenyl ring. The ligand orbital contributions are found to be significant due to covalency, and should be taken into account. The present study would be helpful to the unified investigations of structures and properties of the copper oxygen compounds.

The work analyzes both literature data on the dependence of the internal liquid pressure on thermodynamic parameters of state and theoretical ideas of the nature of the internal pressure. The analysis enables the formulation of a hypothesis: the temperature coefficient of the internal liquid pressure corresponds to the state of its force field and the dynamics of this coefficient follows the course of changes in the macroscopic force field of liquids. The hypothesis underlies the construction of a scale of states of the own force field of liquids. To substantiate this scale, and consequently, the formulated hypothesis, the scale is verified with respect to water. A unified scale of states of force fields of associated liquids is proposed.

Crystals of bis(4-aminopyridinium) dichromate (C₅H₇N₂)₂[Cr₂O₇] (1) were isolated via slow solvent evaporation and characterized by energy dispersive spectroscopy (EDS), infrared (IR) and ultratviolet-visible (UV-Vis) spectroscopy, and single crystal X-ray diffraction. The room-temperature (RT; 298 K) phase of 1 crystallizes in the monoclinic space group P2₁/m. Its asymmetric unit consists of two crystallographically independent 4-aminopyridinium cations (A and B) and two halves of symmetry-independent dichromate anions (A and B). Cations and anions are linked with the aid of several moderate N–H⋯O hydrogen bonds and weak C–H⋯O interactions resulting in a three-dimensional supramolecular network. The crystal structure is further stabilized by extensive π–π stacking interactions between adjacent pyridine rings. A comparison of the structure of the RT phase of 1 and that of the low temperature (LT; 150 K) phase is described.

A new complex [Cu(L¹)(NCS)]SCN, where L¹ = 3,14-dimethyl-2,6,13,17-tetraazatricyclo( 16.4.0.0^7,12)docosane is prepared and characterized by single crystal X-ray crystallographic analysis. The complex crystallizes in the triclinic space group P1̅ with two mononuclear formula units in a cell of dimensions a = 7.9681(2) Å, b = 8.8644(2) Å, c = 18.8165(5) Å, α = 76.758(70)°, β = 78.490(2)° and γ = 77.679(2)°. The Cu(II) ion is five-coordinate in an axially elongated square pyramidal environment, with the four amine N atoms at the equatorial positions and the N atom of one thiocyanate at an apical site. The macrocyclic cyclam moiety adopts a stable trans-III configuration. The Cu–N basal plane bond length has a mean value of 2.037(2) Å. The coordinated Cu–NCS bond length is 2.322(3) Å. The N atom of the thiocyanate anion is connected to the macrocyclic ligand of the cation via an NH…N(CS) hydrogen bond. The UV-visible absorption and IR spectral properties are also discussed.

A new Mo₂O₃(dpm)₄ compound (I) is synthesized by the interaction of Mo(CO)₆ with 2,2,6,6-tetramethylheptanedione-3,5 (dpm). The structure of complex I determined by the XRD method is as follows: triclinic crystal system, space group P–1, a = 10.1780(7) Å, b = 10.1817(6) Å, c = 13.3255(9) Å, α = 110.562(2)°, β = 102.233(2)°, γ = 93.9041(19)°, V = 1248.17(14) ų. The compound is characterized by IR spectroscopy, mass-spectrometry and thermogravimetric analysis (TGA).

A number of physicochemical characteristics of ten 1,2,3,4-tetrahydroquinoline derivatives synthesized for the first time, along with their third order Wiener and Randič indices are calculated by quantum chemical methods. Correlations between the topological indices, physicochemical parameters, and retention factors of the mentioned compounds are obtained for conditions of reversed-phase high performance liquid chromatography on porous graphitized carbon.

A quantitative topological analysis of supramolecular structures in ethanol solutions with methanol, propanol, water, benzene, and hexane is performed by the MDGT method previously proposed by the authors. The method is based on a combination of molecular dynamics calculations and the graph theory, which enables the recognition and memorization of supramolecular structures observed in each snapshot of the molecular dynamic trajectory, the averaging of data for any number of these snapshots. Thus, the averaged concentrations of associates (dimers, trimers, etc.) are represented and then the concentrations and characteristics of isomers (e.g., chains, branched chains, rings, etc.), bond lengths, angles, etc. are determined in each group of associates.

A new caffeic acid derivative ((E)-3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)acrylic acid, HL¹)) is synthesized from caffeic acid, followed by the preparation of a Cu(II) complex, [Cu₂(L¹)₄DMSO₂]·2DMSO. The structure is determined by single crystal X-ray diffraction, and the urease inhibitory activity of the complex is studied. The results show that IC₅₀ of the complex is 0.56 μmol/L, which is superior to positive control acetohydroxamic acid (AHA, IC₅₀ was 10.95 μmol/l), i.e., the complex has strong inhibitory activity towards urease.

The crystal structures of isostructural fluoride complexes of indium(III) M[InF₄(H₂O)₂] (M = Rb, Cs) crystallizing in the monoclinic system, space group I2/a, are studied. The structures of M[InF₄(H₂O)₂] (M = Rb, Cs) are formed of isolated centrosymmetric complex [InF₄(H₂O)₂]^– anions with the trans-position of coordinated H₂O molecules and Rb⁺, respectively Cs⁺, cations. The In atom in the complex [InF₄(H₂O)₂]^– anion is surrounded by four F atoms and two oxygen atoms of coordinated H₂O molecules, forming the coordination polyhedron as a slightly distorted octahedron. Via a system of hydrogen O–H⋯F bonds the polyhedra of In atoms are arranged in a three-dimensional framework with the cations located in its channels.

Сrystals of the previously unknown polymorph of potassium tetrafluoroantimonate(III) (β-KSbF₄) are synthesized and their crystal structure is determined (orthorhombic crystal system: a = 8.1631(5) Å, b = 7.8563(5) Å, c = 6.5396(4) Å, V = 419.40(5) ų, Z = 4, d_calc = 3.751 g/cm³, F(000) = 424, space group Pmn2₁). The main structural units of β-KSbF₄ within the first coordination sphere are dimer complex [Sb₂F₈]^2– anions formed of trigonal SbF₄E and tetragonal SbF₅E bipyramids with a common vertex. The previously described α-KSbF₄ polymorph consists of tetrameric [Sb₄F₁₆]^4– complexes formed of SbF₅E bipyramids.

A new copper(II) complex with acetylacetone and ethylenediamine is obtained using the template synthesis. It is studied by single crystal X-ray diffraction. The crystals are monoclinic: а = 7.7563(4) Å, b = 24.0157(12) Å, c = 24.6353(13) Å, β = 91.9490(10)°, V = 4586.2(4) ų, space group P2(1)/c, Z = 2, d_calc = 1.713 g/cm³, R = 0.0695. The copper atom environment consists of two oxygen and two nitrogen atoms of the ligand, forming a slightly distorted square.

The [Zn(H₂O)₄]₃[Re₁₂CS₁₄(μ-SO₂)(μ-S)₂(CN)₆]_0.875[Re₁₂CS₁₄(μ-S)₃(CN)₆]_0.125•6H₂O compound (1) containing a new [Re₁₂CS₁₄(μ-SO₂)(μ-S)₂(CN)₆]^6– cluster anion is synthesized by the reaction of ZnCl₂ and K₆[Re₁₂CS₁₄(μ-S/SO/SO₂)₃(CN)6] in an aqueous solution and structurally characterized. Compound 1 crystallizes in a rhombic space group Pnma with the following unit cell parameters: a = 22.0834(7) Å, b = 28.2551(9) Å, c = 9.7775(3) Å, V = 6100.9(3) ų, Z = 4, d_calc = 3.806 g/cm³. The crystal structure consists of two cluster anions in the ratio 7:1, occupying the same position, distorted [Zn(H₂O)₄]²⁺ cations, and solvate H₂O molecules linked by hydrogen bonds.

A series of Ln(III) dipivaloylmethanates of the composition Ln(dpm)₃ (Ln = La, Tm, Yb) is obtained. It is established that Tm(dpm)₃ and Yb(dpm)₃ complexes are isostructural with Lu(dpm)₃. The crystal structure of [La(dpm)₃]₂ at 150(2) K is determined (space group P2₁/n, a = 12.4412(5) Å, b = 28.0579(12) Å, с = 21.9533(8) Å, β = 105.796(2)°, V = 7373.9(5) ų, Z = 4). The studied compound is isostructural with [Pr(dpm)₃]₂, [Eu(dpm)₃]₂, [Gd(dpm)₃]₂, and [Tb(dpm)₃]₂ complexes. The crystal structure of the complex is formed by dimeric [La(dpm)₃]₂ molecules. Thermogravimetric investigations show that the volatility of Ln(dpm)₃ increases in the series from [La(dpm)₃]₂ to Yb(dpm)₃. Melting points of the complexes are close to the known literature data.

The crystal structure of 2-(2-morpholinoacetyl)hydrazinocarbothioamide is determined by single crystal X-ray diffraction.