Home – Home – Jornals – Thermophysics and Aeromechanics 2008 number 2

The broken dam problem flow is tested to check accuracy of different procedures for gas-liquid interface resolution based on solution of the additional equation for the volume fraction of liquid phase. The study is focused on the numerical schemes used to approximate advection fluxes of this equation. In particular, the MUSCL scheme with QUICK interpolants and compressive minmod TVD limiters with the slope modification technique for the volume fraction fluxes is applied, as well as the upwind- downwind donor acceptor procedure designed in the VOF method. As the first stage, the quite simple and explicit procedure adopting the artificial compressibility method is used to solve the velocity and pressure equations. Computations are initially performed with a careful grid and time step independence studies. Importance of the wall boundary condition is also discussed. To present free surface motion, results of numerical investigation are shown in terms of contour plots for the volume fraction at successive times, as well as surge front and column height positions versus time.

Results of experimental investigation of a bubbly gas-liquid flow in horizontal and weakly inclined (from −20° to +20°) flat channel are presented. These measurements were carried out within the 0.2-1 m/s range of superficial velocities and volumetric gas flow rate ratio of up to 0.2. The hydrodynamic structure was measured by the electrochemical method with application of wall shear stress and conductivity microprobes. During the experiments signals of shear stress on the upper channel wall and local gas flow rate ratio were recorded completely. After numerical treatment of recorded signals the profiles of local gas flow rate ratio were obtained, average shear stress and its relative mean square pulsations on the upper channel wall were determined. It is shown that under the studied regimes the bubbles are grouped into clusters, and the bubbly flow is presented by alternation of bubbly clusters and single-phase liquid with separate bubbles and without them. Average wall shear stress and absolute shear stress pulsations in the range of bubbly clusters and beyond them were determined. Histograms of probability density distribution were obtained for the wall shear stress on the upper wall. It is shown that average shear stress and absolute pulsations in clusters are significantly higher than those in the flow zone free from bubbles.

The ideal gas exhaustion from an infinite volume into a gas at rest through a supersonic conical Laval nozzle is considered. The problem was solved numerically by steadying in time in a unified formulation for the regions inside the nozzle and in the ambient environment. In such a statement, the nozzle outlet section is no internal boundary of the region under consideration, and there is no need of specifying the boundary conditions here. Local subsonic zones arising in the flow lie inside the region under consideration, which eliminates the possibility of using a marching technique along one of the coordinates. The numerical solution is constructed by a unified algorithm for the entire flow region, which gives a possibility of obtaining a higher accuracy. The computations are carried out in the jet initial interval, where, according to monograph [1], the wave phenomena predominate over the viscous effects.
The exhaustion process is described by the system of gas dynamics equations. Their solution is constructed with the aid of a finite difference Harten's TVD (Total Variation Diminishing) scheme [2], which has the second approximation order in space. The second approximation order in time is achieved with the aid of a five-stage Runge−Kutta method. The solution algorithm has been parallelized in space and implemented on the multi-processor computer systems of the ITAM SB RAS and the MVS-128 of the Siberian Supercomputer Center of SB RAS.
The influence of the semi-apex angle of the nozzle supersonic part and the pressure jump between the nozzle outlet section and the ambient environment on the flow in the initial interval of a non-isobaric jet is investigated in the work. A comparison with experimental data is presented. The computations are carried out for the semi-apex angles of the nozzle supersonic part from 0 (parallel flow) to 20 degrees. For all considered nozzles, the Mach number in the nozzle outlet section, which was computed from the one-dimensional theory, equaled three. Computations showed that in the case of flow acceleration in a conical supersonic nozzle, its geometry is one of the main factors determining the formation of the jet initial interval in ambient environment.

Results of an experimental study of turbulent flow past a flat rib installed at an angle to the free-stream direction are reported. In the experiments, external flows with two different turbulence numbers were used, and the angle of rib inclination to the free stream was varied from 50 to 90°. The experiments were performed for ribs of various heights under conditions with natural and high (13.4 %) free-stream turbulence levels. Visualization tests were performed to elucidate the vortex formation pattern and the direction of flow streamlines. Deformations of the recirculation region and secondary-vortex zone as well as enhanced effects due to 3D flow structure observed on decreasing the angle φ, and also notable restructuring of the flow at a high free-stream turbulence intensity, were identified. A comparison between pressure coefficients in different longitudinal sections of the channel is reported for ribs of various heights installed at various angles φ. The influence of rib inclination angle, rib height, and free-stream turbulence number on local heat-transfer coefficients and heat-transfer intensification is analysed.

Experimental data on heat transfer in turbulent separation region behind obstacle in a broad frequency range of superimposed free-stream pulsations are reported. The heat-transfer coefficient was determined by solving an inverse non-stationary heat conduction problem based on experimentally measured wall transient temperature. Substantial heat-transfer intensification in the separation region of the pulsating flow was

Results of simulation study of evolution of solitary intensive second-sound waves spreading in superfluid helium are presented. Quantitative description was carried out on the basis of equations of hydrodynamics of superfluid turbulence (HST). HST equations with second-order accuracy (relative parameter deviation from equilibrium) were written for the cases of planar, cylindrical, and spherical geometries. The system of equations was solved using the disruption decay technique. Calculations were carried out for the temperature of undisturbed helium Т_{0 = 1.4 K. Simulation results were compared with experimental data.}

The model system of ordinary differential equations [1, 2] governing the behavior of a non-uniformly heated fluid in a tilted cavity is used for studying the stability of steady regimes of thermal convection at arbitrary (not small) tilting of the rectangular cavity. The bifurcation curve is constructed, which separates the region of parameters (the Rayleigh number ⎯ the cavity tilting angle) into two regions ⎯ the internal and external ones. In the external region, the system has one stable steady solution, and in the internal region, it has three steady solutions. One of them is always unstable in a monotone way, and two others may be both stable and unstable. The neutral curves are constructed, which determine the boundaries of the incipience of the oscillatory and monotone instabilities.

The reaction of the film interface to low-amplitude waviness of the wall was studied. A linearized version of the problem described by the Orr ⎯ Sommerfeld equation was considered; the solution was sought by asymptotic expansion in small parameter 1/Re, and usual spectral problem concerning stability to perturbations of exp[iα(x−ct)] type was solved. According to calculations, for some specially chosen wave numbers α the drift and dispersion effects balance each other, providing zero resulting velocity c_{R = 0. If we assume that a rigid wall is corrugated with the same α, we can say that stationary waves caused by the wavy wall are in resonance with intrinsic perturbations of the second kind.}

The results of theoretical and experimental studies of heat exchange at condensation of motionless steam on a vertical tube placed in a granular layer with different wetting angle are presented. Theoretical dependencies are obtained for the estimate of heat-exchange intensity, which account for the condensate slip on the surfaces of grains, and their satisfactory agreement with experimental data of the authors is shown.

The effect of liquid subcooling below the saturation temperature on the third heat transfer crisis was studied experimentally at pool boiling. Experimental data on the threshold values of superheating and heat fluxes, above which the evaporation front and third heat transfer crisis for acetone at subcooling from 0.3 to 10 K are formed, were shown. Formation of evaporation fronts is the necessary, but not sufficient condition for the third heat transfer crisis at subcooling. It was found that formation of a stable vapor film after propagation of condensation fronts over the heater surface is possible at heat fluxes considerably lower than the first critical one.

Ba[Co(heida)₂](HCO₃)⋅2H₂O crystals were grown (orthorhombic, a = 9.4491(5) Å, b = 10.9719(5) Å, c = 19.6077(9) Å, Z = 4, space group Pca2₁), and their structure was solved by X-ray diffraction. The Co atoms in the complex anion were coordinated by two N-(2-hydroxyethyl)iminodiacetate (heida) ligands via the N atom and two O atoms of each ligand. The Ba atoms and the complex anions form "honeycomb" layers linked via three О atoms. The "honeycombs" are additionally linked by their Ва atoms with the О atoms of the hydroxyethyl groups. The Ba atoms are aligned within a layer and linked via the bridging HCO₃ hydrocarbonate groups. The c.n. of Ва atoms is 10 (one water molecule; five О atoms of the complex anions, one from each of the nearest neighbors; and four О atoms of the hydrocarbonate ions).

Changes in the electronic structure and magnetic characteristics of Sr₂FeMO₆ double perovskites were studied by the FLAPW-GGA ab initio band structure method in relation to the type of the cation M = Sc, Ti, …, Ni, Cu.

The modified augmented plane wave method (WIEN2k program) was used to study the electronic energy structure and calculate the SK-absorption spectra of LiBiS₂, NaBiS₂, and KBiS₂. The crystal structures of the compounds were modeled using symmetric structures, in which each sulfur atom was surrounded by three alkali metal atoms and three bismuth atoms in such a way that the alkali metal-sulfur and bismuth-sulfur bond length differed. This difference between bond lengths was calculated from the sum of the ionic radii of the components of compounds and by the geometry optimization of the crystal lattice. The two variants of calculation allowed us to check the applicability of Pauling's idea about preservation of the bond lengths of elements in compounds for modeling the crystal structures of LiBiS₂, NaBiS₂, and KBiS₂. The SK absorption spectra and optically forbidden bands were calculated.

The electronic energy structure of MC, M₆C, and M₁₂C carbide systems and iron martensite in the absence of spin polarization was studied by the local coherent potential method using the cluster version of the МТ approximation in terms of multiple scattering theory. The local partial density of the electronic states of atoms in crystals was calculated and their electronic structures were compared. The peculiarities of chemical bonding in crystals are discussed.

The potential surfaces of the ground and lowest excited states of the [RuCl₅NO]^2- complex ion were studied by density functional theory. The conical intersections between the potential surfaces of the ground and lowest excited states were found and characterized. The possible routes from the conical intersection points to the ground state and metastable bond isomers were traced. A preliminary scheme, describing photoisomerizations in the complex, was suggested.

The results of B3LYP quantum-chemical calculations of the equilibrium structures of [(CX₃COOCu)₂]₃, [(CX₃COOCu)₂]₂, and (CX₃COOCu)₂ oligomers (X = H, F) using the cc-pVTZ correlation-consistent basis for C, O, and F atoms and the Stuttgart 1997 RSC basis and relativistic effective core potential for Cu(I) atoms are presented. The differences in the structures of the free dimer and dimer units in oligomers. The hexamer structure was chosen as the model of a fragment of the crystalline phase. Good agreement was obtained between the experimental and calculated differences between the geometrical parameters of the structures in the "gas phase−crystal" and "acetate−trifluoroacetate" series. Based on the calculated data, the increase in the Cu(I)-Cu(I) bond length in the silver acetate crystal compared with the gas phase can be explained by the effect of the neighboring dimer units of the polymer ribbon and the increase in the Cu(I)-Cu(I) bond length in gaseous trifluoroacetate compared with acetate, by the acceptor effect of fluorine atoms.

Density functional theory (DFT) calculations at B3LYP/6-31G(d,p) level were carried out to investigate the mechanism of the reaction of benzaldehyde (BA) or acetaldehyde (AD) with (1R)-2-endo-bromoacetyl-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ol (endo-2-bromoacetylisoborneol) 1 (Scheme 1). The calculations indicate that the reactions are diastereoselective, in good agreement with the experimental results [1]. Moreover, the calculations show that these reactions proceed via two steps: (1) an aldol-like reaction and (2) the formation of an epoxide. Our calculation study of the transition states demonstrate that the terminal hydroxyl group in compound 1 is vital to the stereoselectivity of the reactions.

The spatial and electronic structures of molecules with three substituents at the germanium atom (tricoordinated germanium) were calculated by the DFT method (Gaussian-98 program package, B3LYP functional, 6-311G(d,p) basis set). The main characteristics of Ge-X bonds in thee molecules were determined by NBO and AIM procedures. It is shown that Ge-X are weak, "intermediate" type bonds. The bond energies were calculated.

The molecular structure of nickel(II) and copper(II) N,N′-ethylene-bis(acetylacetoneiminates), NiO₂N₂C₁₂H₁₈ and CuO₂N₂C₁₂H₁₈, at 442(5) K and 425(5) K, respectively. Both molecules have С₂ symmetry with a nearly planar MN₂O₂ coordination site and internuclear distances r_h1(M-O) = 1.862(10)/1.923(17) Е and r_h1(M-N) = 1.879(10)/1.947(18) Е for Ni(acacen) and Cu(acacen), respectively. The structure of free molecules is close to the structure of molecules in crystal. The DFT/В3LYP quantum-chemical calculations (CEP-31G and 6-31G* basis sets) gave a molecular structure that agreed satisfactorily with the one found in experiment. The low-spin ¹А and high-spin ³А states of the Ni(acacen) molecule were considered. It was found that a change in multiplicity caused significant changes in the geometrical and electronic structure of the MN₂O₂ coordination site. As shown by experiment and calculations for the NiO₂N₂C₁₂H₁₈ molecule, the low-spin ¹А state is the ground state. The internal rotation of CH₃(CN) and CH₃(CO) methyl groups was studied by the В3LYP/CEP-31G method. It was shown that steric hindrances led to a high rotation barrier of the CH₃(CN) group.

The molecular structure of 2-chlorobenzenesulfonyl chloride was studied by electron diffraction and quantum-chemical (МР2/6-31G**, B3LYP/6-311++G**) methods at 337(3) K. Only one (C₁) conformer was found in the gas phase. The following structural parameters were obtained: r_h1(C-H)_av = 1.105(6) Е, r_h1(C-C)_av = 1.398(3) Е, r_h1(C-S) = 1.783(11) Е, r_h1(S=O)_av = 1.427(3) Е, r_h1(S-Cl) = 2.048(4) Е, r_h1(С-Cl) = 1.731(9) Е, ∠(С-S=O1) = 109.9(8)°, ∠(С-S=O2) = 106.9(8)°, ∠(Cl1-S-O1) = 107.3(4)°, ∠(Cl1-S-O2) = 106.4(4)°, ∠C-S-Cl = 102.1(6)°, ∠O=S=O = 122.3(11)°. The C2-C1-S-Cl1 torsion angle that defines the position of the S-Cl bond relative to the plane of the benzene ring was 69.7(8)°. The B3LYP/6-311++G** calculated barriers of internal rotation of the sulfonyl chloride group were V₀₁ = 9.7 kcal/mol and V₀₂ = 3.6 kcal/mol.

The binary molybdate Li₂Zn₂(MoO₄)₃ of a new crystal type was characterized by EPR, optical spectroscopy, and X-ray diffraction methods. The crystals have the Pnma symmetry group and the lattice parameters а = 5.1139(5) Е, b = 10.4926(13) Е, c = 17.6445(22) Е; Z = 4. The crystals possess scintillation properties; emission is caused by the presence of impurity levels in the forbidden band. The EPR studies of the nature of the impurity centers responsible for the scintillation characteristics of the crystal showed that the centers were Cu²⁺ ions substituted for zinc ions in the oxygen octahedra. The directions of the main values of the g and А tensors (g_zz, A_zz) correspond to the direction of O-Cu-O of the oxygen octahedron distorted along the Z axis. The EPR spectra of the copper ions are described by the spin Hamiltonian with the parameters g_|| = 2.38, g_⊥ = 2.06; A_|| = 116 G, А_⊥ = 0 G.

A method is suggested for analyzing the model structures of crystals by calculating the spherical coordinates of the normals to the simplex faces of the simplicial Delaunay partitioning of a set of points (atoms). The normals to the simplex faces of the Delaunay partitioning of the crystal structure characterize the structure at the local level. An algorithm for constructing the invariant of the crystal structure (crystal module) was considered. Crystals modules were constructed for hexagonal and cubic ices.

A simulation of crystallization and a structural study of an overcooled NaCl melt are reported. A criterion is suggested for classifying the structural states of ions in the transition mode of nucleation. It is shown that in the bulk of overcooled liquid, short-lived crystal phase germs appear and vanish. A distribution of the critical clusters according to form and size was found. It was assumed that crystal growth occurred by collective synchronization of particle motions in crystal and liquid near the interface. The NaCl nanocrystals formed during nucleation are cubic crystals with clear-cut faces and edges. Overcooling the liquid to a greater extent led to the formation of defective polycrystalline structures.

The Kirkwood factor g_K of a model polar liquid of dipolar hard spheres (DHSs) was approximated by analytical equations using the approximation of the interaction of the second neighbors within the hindered rotation model. The derived equations describe the temperature and density dependences of the dielectric functions of the DHS liquid.

Isoentropy compressibilities of aqueous magnesium chloride and sulfate were determined based on precision measurements of ultrasound velocity, density, and isobaric heat capacity at low to high concentrations at 278.15-323.15 K. The hydration numbers h and the molar parameters of volume and compressibility were calculated based on thermodynamically correct equations for hydration complexes (V_h, β_hV_h), water in the hydration shell (V_1h, β_1hV_1h), and the void containing a stoichiometric mixture of ions (V_2h, β_2hV_2h). The h and β_hV_h values were found to be independent of the temperature; the molar compressibility of the hydration sphere (β_1hV_1h) and the stoichiometric mixture of ions without a hydration shell (β_2hV_2h) were independent of the concentration under the stated conditions. The effect of the electrostatic field of ions on the temperature dependence of the molar volume of water in the hydration sphere was more significant than the effect of pressure on the temperature dependence of the molar volume of bulk water. This is attributed to changes in the dielectric constant of water in the vicinity of the electrolyte ions.

The results of previous studies of the increments ΔG⁰_CH2, ΔH⁰_CH2, TΔS⁰_CH2 and in hydrocarbon solution processes in water, evaporation, hydration, and transfer from vapor and water to surfactant micelles are summarized. The corresponding thermodynamic cycles were constructed. A micelle was shown to be a bistable structure formed by the contact and water-separated hydrophobic interactions of the alkyl groups of surfactants. The fraction in ΔG⁰_CH2M is -2.3 kJ⋅mol^-1 for the contact associate and -0.7 kJ⋅mol^-1 for the hydrated one. Water is involved in the hydrophobic interaction of each associate. In a dualist micelle, however, ΔG⁰_CH2 = -3.0 kJ⋅mol^-1 equals that of the dispersion interaction after condensation from vapor. The dual nature of the dynamic properties of micelles is discussed.

The crystal structure of the Os₃(μ,η²-O=CC₆H₅)(η³-C₃H₅)(CO)₉ cluster synthesized by the reaction of the (μ-H)Os₃(μ-O=CC₆H₅)(CO)₁₀ complex with allylamine in chloroform was determined by X-ray analysis. Prolonged storage of the reaction mixture led to N-C bond cleavage in allylamine and η³-addition of the allyl fragment at one of the Os atoms (Os-C 2.246 Е, 2.248 Е, and 2.273 Е). The unit cell parameters of the complex are a = 9.494(1) Е, b = 10.479(1) Е, c = 12.474(2) Е, α = 84.55(1)°, β = 70.08(1)°, γ =
70.72(1)°, V = 1255.8(4) Е³, space group Z = 2; C₁₉H₁₀O₁₀Os₃; d_calc = 2.922 g/cm³, 3085 I_hkl > 2σ_I of 3611 collected reflections; R = 0.0252. The structure of Os₃(μ,η²-O=CC₆H₅)(η³-C₃H₅)(CO)₉ is molecular. The plane of the Os₃ triangle and the OsCOOs plane are connected according to the "butterfly" principle with an angle of 103.4° between them. The Os-Os distances in the cluster core vary from 2.836(1) Е to 2.844(1) Е; the Os-C_carb distances are 1.88(1)-1.97(1) Е; the distances to the atoms of the bridging ligands are Os-C 2.11(1), Os-O 2.14(1) Е; the O-C bridging bond is 1.24(1) Е. The conformations of the Os₃(μ,η²-O=CC₆H₅)(η³-C₃H₅)(CO)₉ triosmium cluster were studied theoretically. The potential curve of the internal rotation of the allyl ligand relative to the Os(1)-С(9) bond was determined. The rotation barrier of the allyl ligand in crystal relative to the Os(1)-С(9) bond is 8.38 kJ/mol, and the rotation of the ligand is not hindered. The effects of the intra- and intermolecular interactions on the conformation state of the cluster complex is considered.

An X-ray study of the crystals of bicyclic compounds containing fluorinated aromatic and nonfluorinated heteroaromatic rings, 5,6,7,8-tetrafluoroquinoline, 5,6,8-trifluoroquinoline, 5,7-difluoroquinoline, 5,7,8-trifluoro-2-phenylquinoline, and 5,7,8-trifluoro-6-trifluoromethylquinoline, was carried out. The basic supramolecular motifs and the underlying intermolecular interactions that control the lattice structure of these compounds were investigated. B3LYP DFT quantum-chemical calculations (6-311G(d,p) basis set) and the topological analysis of the electron density distribution in terms of Bader's QTAIM theory were performed for the compounds. It is shown that the intermolecular interactions in question, traditionally regarded as nonvalent interactions, are related, to a definite extent, to the formation of very weak covalent chemical bonds in the intermolecular space due to the overlap of the "tails" of the molecular wave functions.

Three modifier compounds that stabilize the phase state of ammonium nitrate over a wide range of temperatures, 1,3,5-trihydroxyisocyanuric acid dihydrate (1), 4-aminouracil (2), and 4-aminouracil monohydrate (3) were studied by X-ray diffraction. Strong donor-acceptor intermolecular interactions were found for structures 2 and 3. The electronic parameters of the molecules were calculated by quantum-chemical methods, and it was found that additional intermolecular interactions were possible.

An X-ray study of (3Z)-(±)-4-(2′-hydroxypropyl)amino- and (3Z)-4-(2′-hydroxyethyl)aminopent-3-en-2-ones is reported. The bond lengths inside the H ring are equalized due to the classical N-H…O hydrogen bond between the carbonyl oxygen and the amino group. In the 4-(2′-hydroxyethyl)aminopent-3-en-2-one crystal, due to the classical N-H…O bonds, infinite zigzag chains are formed along the 0b axis and arranged into a layered structure due to the weak C-H…O interactions. In (±)-4-(2′-hydroxypropyl)amino-pent-3-en-2-one crystal, however, centrosymmetric dimers are formed, which are then linked by weak
C-H…O intermolecular interactions, which form a layered structure along the a0b plane.

Pseudohalogen-containing compounds have attracted significant interest among nonmetal chemists and theorists, not only owing to their potential use in various fields but also due to difficulties in their experimental preparation and characterization. Since its introduction in 1925, the pseudohalide principle has been used extensively and, therefore, a remarkable progress has been made in the experimental and theoretical research on the compounds of this kind. In this work, we review studies on structural investigations and theoretical characterizations of several pseudohalide-containing compounds in order to contribute to better understanding of the chemistry of many such species.

Non-empirical RHF/6-31G* and MP2/6-31G* quantum chemical methods are used to calculate the molecular structure of trichlorophosphazene compounds: Cl₃P=NC(CF₃)₃ (I) and Cl₃P=NCCl(CCl₃)₂ (II). The corresponding geometric parameters obtained from the calculations are compared with X-ray diffraction analysis data reported in the literature. Conformational differences between the molecules of I and II, previously found by X-ray diffraction in the crystals of these compounds, are confirmed by non-empirical calculations of the molecules in the free state. The features of their geometry caused by intramolecular interactions are discussed.

Based on graph theory fundamentals, a general formula to calculate formal unsaturation of chemical compounds that contain atoms of any valence is deduced and the mathematical meaning of this widely used chemical concept is shown.

Using the results of Monte Carlo simulation, equations of state of hard sphere liquids are calculated for 106 values of the fill factor η = 0.005-0.530 (step of 0.005). In the region of liquid phase stability the absolute accuracy of about 0.00001-0.00008 is reached. Correctness of the accuracy estimate is discussed. The results obtained are compared with reported equations of state of the hard sphere liquid.

Primary data of the X-ray diffraction experiment on DyBr₃ and YbBr₃ aqueous solutions in salt:water molar ratios of 1:20 are presented. The occurrence of a pre-main peak in the curves of normalized scattering intensities determines the average distance between cations in these solutions, and hence, directs to a model description of the structure of solutions. Based on the determination of boundaries of the cation complex and taking into account the deficit of solvent, the model of the cation complex is supposed to consist of two coordination shells involving at least two anions.

The crystal structure and the formation conditions of crystals of the LiFe₅O₈ ordered phase obtained from the solution-melt of the Bi₂O₃-Fe₂O₃-B₂O₃-LiCl quadruple system are refined. The crystals are black, octahedral, of cubic symmetry (space group P4₃32). Unit cell parameters: a = 8.3339(1) Е, V = 578.82(1) Е³, Z = 4, d_calc = 4.753 g/cm³. From 6046 of the collected array I_hkl 358 are independent (R_int = 0.0321). As a result of anisotropic refinement of structural parameters, R₁ factor is found to be 0.0186 (wR₂ = 0.0467). Lithium atoms are in octahedral environment, Li-O is 2.109(1) Е; iron atoms are of two types: in octahedra with Fe-O (by two) distances of 1.9586(9) Е, 2.0152(9) Е, and 2.0652(10) Е and tetrahedra with Fe-O (three) 1.8848(10) Е and 1.914(2) Е. The structure is of inverted spinel type.

Triclinic modification of trans-bis(trifluoroacetylacetonato)copper(II) has been studied by single crystal X-ray diffraction (diffractometer X8 APEX BRUKER, MoK_α radiation, T = 173(2) K). The structure is molecular. Square environment of the Cu atom (Сu-O_av 1.916 Е, ∠O-Сu-O_av 93.4°) is completed to a bi-pyramid by two Сγ atoms of neighboring molecules, Cu…Сγ 3.18 Е and 3.23 Е.

Crystal structure of acrylamide has been re-determined by single crystal X-ray diffraction (133(1) K, BRUKER SMART 1000 CCD, a = 8.228(1) Е, b = 5.759(1) Е, c = 9.760(1) Е, β = 120.04(1)°, V =
400.3(1) Е³, space group P2₁/c, Z = 4, R = 0.0543 for 867 reflections). In the structure strong hydrogen bonds N-H…O join the molecules of C₃H₅NO into bi-molecular layers, which make C…C molecular contacts. It has been demonstrated that the process of sold phase polymerization of acrylamide should proceed through the cleavage of double bonds С(1)=С(2) in the monomers and formation of bonds С(1)-С(1) and С(2)-С(2) between the closest carbon atoms of different layers.

Addition of trichloroacetonitrile to 2,5-dimethyl-1,5-hexadiene in presence of cuprous amine complexes has been studied. Single crystal X-ray diffraction unambiguously proves that the main product is a racemic mixture of the cyclic symmetric nitrile - (1r,3R,6S)- and (1r,3S,6R)-1,3,6-trichloro-3,6-dimethylcycloheptanecarbonitrile. Established relative configuration of the product confirms the ring closure mechanism suggested before. Also, a side product - 2,5-dimethyl-2,5-dichlorohexane has been isolated (the product of hydrochlorination of the starting alkadiene). Low-temperature (190 K) structural examination of this centrosymmetrical molecule indicates that the unit cell comprises one molecule.

The structure of (±)-2-[(1S,3S)-3-acetyl-2,2-dimethylcyclobutyl]-N-(p-tolyl)acetamide has been determined by single crystal X-ray diffraction analysis. The crystal belongs to triclinic system, space group P-1, a = 8.8700(18) Å, b = 10.331(2) Å, c = 10.363(2) Å, α = 71.11(3)°, β = 65.06(3)°, γ = 72.18(3)°, V = 798.6(3) ų, Z = 2, formula unit C₁₇H₂₃NO₂. The title compound has a fragment of 2,2-dimethylcyclobutane and its conformation represents semi-chair. The intermolecular hydrogen bonds N-H...O and C-H...O are revealed.