Geometry and energy calculations of the Hs-III polyhedral gas hydrate framework

Geometrical parameters of the HS-III hexagonal water framework in clathrate hydrates are calculated using Zimmerman-Pimentel's hydrogen-bond potential. Thermal expansion of an empty framework along the a and c axes is studied. Dependences of H-bond strain energies during the ice Ih—clathrate framework transition on hexagonal unit cell parameters are calculated. It is shown that water molecules occupying different crystallographic positions differ considerably in partial energies. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 3, pp. 488–493, May–June, 1995. Translated by L. Smolina     

Dependence of the structure of the gas hydrate framework on the parameters of guest-host interactions for lennard-jones guests

The energies of formation of hydrates from ice Ih and gaseous guests for 7 cubic and hexagonal frameworks are compared. The ranges of the parameters of the guest-host interaction potential within which one of the structures possesses lower energy than the others are determined. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 916–922, September–October, 1996. Translated by L. Smolina     

Crycom program for approximate symmetry recognition in crystal structures

The CRYCOM program was previously proposed for recognition of similarity between crystal structures. It compares unit cell parameters and atomic coordinates, taking into consideration all factors leading to various structure representations (the choice of basic lattice vectors, the origin of coordinates, segregation domain, and atomic displacements). The program can also be utilized for seeking approximate symmetry by comparing an original structure representation with its equivalent representations. Operation of the program is illustrated by an example of distorted hexagonal symmetry recognition in the monoclinic structure of strontium aluminate. L. Ya. Karpov Physicochemical Research Institute. Translated fromZhurnal Struktumoi Khimii, Vol. 35, No. 5, pp. 149–152, September–October, 1994. Translated by O. Kharlamova     

Preparation and characterization of hexagonal close-packed Ni nanoparticles

Hexagonal close-packed Ni nanoparticles were synthesized using a heat-treating technique with the precursors prepared by the sol-gel method. The synthesis condition, structure, and morphology of the samples were characterized and analysed by thermogravimetric analysis (TG), differential thermal analysis (DTA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicate that the hexagonal close packed Ni nanoparticles were synthesized at a heat-treating temperature of 300°C. The cell constants are calculated at a = 0.2652 nm and c = 0.4334 nm. The average grain size of the hexagonal close-packed Ni particles evaluated by Scherrer equation is about 12 nm. The phase transformation from a hexagonal close-packed Ni to a face-centered cubic Ni structure occurred when the heat-treating temperature was increased. __________ Translated from Chemical Journal of Chinese Universities, 2007, 28(7): 1232–1234 [译自: 高等学校化学学报]     

Kinetics of alkaline hydrolysis of ethylp-nitrophenyl ethylphosphonate in the reverse micellar system: sodium dodecyl sulfate-hexanol-water

The kinetics of alkaline hydrolysis of ethylp-nitrophenyl ethylphosphonate in the reverse micellar system sodium dodecyl sulfate—hexanol—water was studied. At high pH and low water content, the process occurs at the surface layer and can satisfactorily be described by the pseudo-phase model equation. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp 262–266, February, 2000.     

Comparative crystal chemistry of heavy metal fluorides and complex niobates and tantalates in terms of a new crystalline state concept

In many crystal structures of Nb (Ta) fluorides and complex oxides analyzed earlier, cationic sublattices of F, I, and AA types were found (face- and body-centered cubic and hexagonal monolayer sublattices, respectively). The density of anion packing in the cationic sublattice (N_a/N_c — the ration of the number of anions to that of cations) is close to two; this means that the mean valence of a cation is about two in fluorides and about four in oxides. These and other structural features are explained by the tendency of the atomic systems of the structures toward fewer degrees of freedom. The review of the structures suggests that there are stability regions of structures both in the field of cationic sublattice parameters and in the field of compositions. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 37, No. 5, pp. 907–915, September–October, 1996. Translated by L. Smolina     

Elution dynamics of adsorption of Chladon 113 and methyl bromide on active carbons

The elution dynamics of adsorption of Chladon 113 (at high contents of the adsorptive) and methyl bromide on active carbons with different lengths of the layer was studied. The adsorption isotherms were described by the equation of the theory of volume filling of micropores. The elution curves were calculated using the model of the equilibrium adsorption layer. The effective kinetic constant calculated in the framework of the model is 1.5 cm for Chladon 113 at a linear velocity of vapor-air flow of 1250 cm min⁻¹ and 1.0 cm for methyl bromide at the velocity of 700 cm min⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1353–1355, July, 1998.     

Structure of binary sulfides withD 2h 16 symmetry

CAS-PAN analysis for revealing close-packed cristallographic planes is performed to investigate the structures of a series of binary chalcogenides containing heavy cations and having D _2h ¹⁶ , symmetry with a short spacing perpendicular to the mirror plane. For chalcogenides with complex compositions, complex relationships between planes are typically observed. Absolute ordering of atoms by mirror planes generally coexists with ordering along the other two directions. By analogy with simple sulfides, these structures have cationic and anionic matrices of AA′ type, that is, one-layer hexagonal packing of trigon nets with a base plane split into two planes and with a doubled number of sites with respect to the number of atoms. Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 2, pp. 324–334, March–April, 2000.     

Benzenoid Molecules with Uniform Distribution of π-Electrons within Rings

Summary. In a recent work it was demonstrated that in linear hexagonal chains the distribution of π-electrons into rings (as computed by means of the Randić–Balaban method) is uniform, irrespective of the nature of the terminal fragments. We now establish that an analogous, yet somewhat more complex, uniformity in the π-electron distribution exists also in double linear hexagonal chains, as well as in some other benzenoid systems.     

Benzenoid Molecules with Uniform Distribution of π-Electrons within Rings

In a recent work it was demonstrated that in linear hexagonal chains the distribution of π-electrons into rings (as computed by means of the Randić–Balaban method) is uniform, irrespective of the nature of the terminal fragments. We now establish that an analogous, yet somewhat more complex, uniformity in the π-electron distribution exists also in double linear hexagonal chains, as well as in some other benzenoid systems.     

Simultaneous electron diffraction and mass spectrometric studies of molecular structure of manganese trifluoride

It is shown that two geometrical models of the MnF₃ molecule equally fit experimental electron diffraction data: a pyramidal model of C_3v symmetry and a planar model with nonequivalent F-F distances of C_2v symmetry. Ivanovo Chemical Technological Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 4. pp. 61–67, July–August, 1994. Translated by L. Smolina     

Estimation of the densities of solutions using the geometrical parameters of their component molecules

A new model based on certain physical concepts of interatomic interactions is proposed for simulating the volume characteristics of molecules that allow reliable estimations of the densities of substances and solutions. The model is used to calculate the solution densities for six substances within wide concentration ranges. Chelyabinsk State University. Translated fromZhurmal Strukturnoi Khimii, Vol. 36, No. 5, pp. 823–827, September–October, 1995. Translated by I. Izvekova     

Chemical bond and electronic structure anisotropies in the graphitic and rhombohedral modifications of boron nitride

The pseudopotential method is used to calculate the band spectra, valence charge densities, and electroneutrality levels in the graphitic (h-BN) and rhombohedral (r-BN) modifications of boron nitride. It is shown that these compounds are indirect-band insulators with the minimum energies of the indirect (4.65 and 4.8 eV) and direct (5.27 and 5.5 eV) forbidden zones in h- and r-BN, respectively. The band energies of h-BN correlate well with the experimental data. Both crystals are characterized by ionic-covalent chemical bonds. In the plane of hexagonal layers, the bonds are more covalent in h-BN. In h- and r-BN, the electroneutrality levels correspond to the energy of about 1.9 eV over the top of the valence band, which is responsible for the hole conductivity of the substances. In superlattices based on these compounds, the rhombohedral phase is a quantum well for holes and a barrier for electrons. Translated fromZhumal Strukturnoi Khimii, Vol. 38, No. 1, pp. 32–42, January–February, 1997.     

The role of the negatively charged (Si3−Si−F2)− complexes in interactions of fluorine with the (111) surface of silicon

We used the AM1 quantum chemical and cluster models to study the mechanism of formation of a SiF₂-like layer and dissociation of the Si−Si bond during the interaction of atomic fluorine with the (111) surface of silicon. It is shown that the negatively charged (Si₃−Si−F₂)⁻ complex with the five-coordinated centered silicon atom plays an important part in these processes. The above complex participates in the interaction of atomic fluorine with silicon to form a SiF₂-like layer and break the subsurface Si−Si bonds without penetration of fluorine atoms into the subsurface silicon layers. Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 14–21, January–February, 1996. Translated by I. Izvekova     

Computational modeling of amorphous silica. 4. Modeling the initial structures. Aerogel

A qualitative classification algorithm for constructing large clusters of aerogel model structures is used. According to this algorithm, aerogel is classified with polysilicas characterized by a packing of long chains of silicon-oxygen tetrahedra. A model of the aerogel structure is suggested, according to which aerogel is described as a set of cross-linked chains forming double or more complex ribbons. This model is in agreement with the conclusions drawn from analysis of the vibration spectra of its components. Institute of Surface Chemistry, Ukrainian Academy of Sciences. Russian University of Peoples' Friendship. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 35–38, May–June, 1994. Translated by O. Kharlamova     

Microstructure and surface composition of corn starch cryogels with sorbed organic flavoring agents

The surface composition and surface microtopography of corn starch cryogels obtained from a 3% starch sol containing organic flavoring agents were studied by X-ray photoelectron spectroscopy and scanning electron microscopy. The cryogels withn-octanol,n-octyl methyl ketone, andn-octyl acetate have a well-developed microtopography and their surface layer (5–20 nm) is enriched in sorbed compounds.n-Octyl acetate, unliken-butyl acetate, influences the composition and microstructure of the cryogel surface. The sorbedn-octyl acetate occupies 20–25% of the surface, which has a well-developed topography and a porous structure. Drying and evacuation do not change the concentration of the organic sorbates having a C₈ alkyl group in the surface layer. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 312–314, February 2000.     

The method of concentrating a substance from a solution in a stationary sorbent layer and its theoretical basis

The principle of concentrating a substance from a mixture flow in a stationary sorbent layer of infinite length that was previously developed for gas chromatography is extended to liquid chromatography. Translated fromIzevestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1063–1065, May, 1997.     

Spatial localization and dynamics of water molecules with good tetrahedral surroundings

The local structure of the molecular- dynamic model of water (729 particles at 300 K) is analyzed by isolating molecules whose surroundings differ slightly in configuration from a regular tetrahedron. These molecules are not randomly distributed in space but form nanometer clusters having a fractal structure. In these clusters, molecules are less mobile than the model molecules in general;their self- correlation function of rate and the density of vibrational states also differ from the average characteristics of the system. Translated fromZhumal Strukturnoi Khimii, Vol. 38, No. 4, pp. 713–722, July–August, 1997.     

Formation of a real structure of perovskites (La1−x , Sr x )CoO3−δ in the region of the morphotropic phase transition

Precision X-ray diffractometry with synchrotron radiation and transmission electron microscopy are used to show that the extent of hexagonal distortion of the perovskite cell of the (La_1−x, Sr _x )CoO₃−δ system decreases and the microstructure of the samples changes when La is substituted by Sr; these changes are due to increased microstrains in the structure and subsequent formation of microunits. The microunit structure of particles in the region of the morphotropic transition 0.3≤x≤0.4, which is a consequence of the metastable state of the system, may be the reason for the high catalytic activity of the samples which we found previously. G. K. Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 1, pp. 92–97, January–February, 1998. This work was supported by RFFR grants 96-03-33103 and 97-03-33497.     

High-temperature crystal chemistry of normal paraffins with even numbers of carbon atoms

Thermal deformations and phase transformations of evennumbered paraffins C_nH_2n+2(n=20, 22, and 24) have been investigated in a thermal X-ray diffraction study. In homologs with n=20 and 24, phase transformations occur in two steps: triclinic-to-orthorhombic and orthorhombic-to-hexagonal transitions. An orthorhombic rotator phase of even n-paraffins is described for the first time. A crystal-chemical model of the phase transformations of the homologs is suggested. St. Petersburg State University. Translated fromZhurnal Strukturmoi Khimii, Vol. 36, No. 5, pp. 790–798, September–October, 1995. Translated by L. Smolina