Hierarchical crystal-chemical analysis of binary intermetallic compounds

A modified Voronoi-Dirichlet polyhedra (VDP) method based on the clusterization of interatomic contacts in the crystal structure depending on contact strength is described. This method makes it possible to carry out crystal-chemical analysis hierarchically, consecutively recognizing atomic nets with different groups of interatomic contacts. The method is used to carry out the topological classification of structure representations for 547 intermetallic compounds of composition AX. Structural relations between various topologic types of intermetallic compounds are discovered and discussed.     

Comparative crystal-chemical analysis of d-metal sulfides, selenides, and tellurides and binary compounds

The structures of d-metal sulfides, selenides, and tellurides containing a tetrahedral complex anion have been compared to 1573 representatives of the topological types of binary compounds with the use of the TOPOS structural topological program package. The cases of similarity between these classes of compounds are found and discussed. Based on the results of topological analysis of ionic matrices, the rules are formulated that allow one to predict specific features of the structures of salts with complex chalcogen-containing anions.     

Comparative crystal-chemical analysis of anhydrous salts My(TQ4)z (T = Si, Ge, P, As; Q = S, Se, Te) and binary compounds

Topological analysis and crystal-chemical classification of 67 compounds with tetrahedral anions with the general formula M_y(TQ₄)_z (T = Si, Ge, P, As; Q = S, Se, Te) have been carried out. These compounds are classified into 36 topological and 38 structure types. Cases of similarity of ternary anhydrous salts M_y(TQ₄)_z to binary compounds A_yX_z are revealed and discussed with the use of the TOPOS structural topological program package. Analysis of the topology and uniformity of ionic matrices shows that the matrices of chalcogenide ions and tetrahedral TQ ₄ ^y? anions play, as a rule, a leading structural role in M_y(TQ₄)_z compounds.     

Formation and thermal stability of selenites and hydrogen selenites of samarium

The solubility isotherm of the Sm₂O₃-SeO₂-H₂O system was studied at 100°C. The two compounds obtained in the three-component system were identified by the Schreinemakers method as well as by chemical, thermoanalytical and X-ray diffraction analyses after their isolation in pure state.     

Comparative thermodynamic analysis of the binary system Bi−Sb

Results of the comparative thermodynamic analysis of the binary system Bi?Sb obtained by DTA measurements and predicting are presented in this paper. Activities, activity coefficients, partial and integral molar quantities for Bi and Sb at temperatures 973, 1073 and 1173 K in the investigated binary system Bi?Sb determined by DTA measurements and thermodynamic predicting are given. An excellent agreement between the experimental and predicted results is reached. Also, a phase diagram of the investigated system Bi?Sb obtained by DTA shows good agreement with literature and it can be concluded that DTA could be satisfactorily used for quantitative thermodynamic analysis of any binary system containing equilibrium between solid and liquid solutions. It was also determined that conclusion about linear dependence ofgKs constant for binary eutectic systems and systems with phase transformation is valid for binary system containing equilibrium between solid and liquid solutions too.     

Properties of binary complex compounds

The current state of studies on binary complex compounds [M¹L _a ] _x ·[M²A _b ] _y (M¹ and M² are the central ions, L and A are ligands) is considered, notably: synthesis, composition, structures, magnetic properties, and thermal decomposition.     

Comparative thermal analysis (CTA) of thermally-stable polymers and model compounds. Polyimides and model compounds

The method of comparative thermal analysis has been used to determine the thermal stability of polyimides and their model compounds. The extent of defects in the investigated polyimides was determined by gas chromatography. The dependence of the extent of the defects on the chemical structure of the initial components and the supermolecular structure of the polyimides was established.

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Zusammenfassung Die Methode der vergleichenden Thermoanalyse wurde zur Bestimmung der Hitzestabilität von Polyimiden und ihren Modellverbindungen eingesetzt. Das Ausmass der Defekte in den untersuchten Polyimiden wurde gaschromatographisch bestimmt. Die Abhängigkeit des Umfangs der Defekte von der chemischen Struktur der Ausgangskomponenten und der supermolekularen Struktur der Polyimide wurde festgestellt.

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Résumé La méthode d'analyse thermique comparée (CTA) a été utilisée pour étudier la stabilité thermique des polyimides et de leurs composés modèles. On a déterminé par chromatographie en phase gazeuse l'étendue des défauts dans les polyimides étudiés. On a établie de même les rapports qui existent entre l'étendue des défauts dans la structure chimique des composants initiaux et la structure supermoléculaire des polyimides.

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Structure and bonding in simple thiazyl compounds

The molcules NSF, NSO⁻, NSCl, HNSF⁺, HNSO, CH₃NSF⁺, CH₃NSO are investigated at the SCF level and partly with inclusion of electron correlation effects. Equilibrium geometries and relative stabilities of isomers and conformers are reported. Structure constants and relative energies are discussed in connection with the molecular electronic structure as characterized by the results of population analyses.     

A simple synthesis of tropones and related compounds

Cyclohexa-2,4- and 2,5-dienones bearing at position 2 or 4 α dihalomethyl group (halogen = chlorine or bromine) are smoothly reduced by tri-butyltin hydride to furnish appropriately substituted tropones. Modification of the substituents permits access to a tropolone and to less substituted tropones. The mechanism of this ring expansion process has been discussed.     

Structures and properties of functional metal selenites and tellurites

Metal selenites and tellurites are a class of very important compounds. In this paper, the structures and properties of metal selenites or tellurites combining with transition-metal (TM) ions with the d (0) electronic configuration or tetrahedral MO 4 building blocks of post-transition main-group elements were reviewed. Most compounds in the alkali or alkaline-earth-d (0) TM-Se (IV) (or Te (IV))-O systems exhibit extended anionic architectures composed of distorted octahedra of (d (0)) TM cations and tellurite or selenite groups. The distortion of the octahedron is always away from the lone-pair cation, and some of them exhibit excellent second-order nonlinear optical properties due to the adductive effects of two types of bond polarizations. Because of the high coordination number of Ln (III) ions, most of compounds in the Ln-d (0) TM-Se (IV) (or Te (IV))-O systems are not second-harmonic-generation active; however, they are able to emit strong luminescence in the visible or near-IR region; also in most cases, the d (0) TM cations are in tetrahedral geometry and are well separated from selenite or tellurite groups. It is also interesting to note that the selenite group is normally "isolated", whereas the TeO x ( x = 3-5) can be polymerized into a variety of discrete polynuclear anionic clusters or extended architectures via Te-O-Te bridges.     

Ionization potentials and structure of simple ionic compounds

Conclusions From the analysis we have presented here, we can state that the mutual influence of ions in simple diatomic and triatomic molecules essentially comes down to polarization effects similar to the Stark shift of levels. An expression for the Stark shift, obtained within the framework of perturbation theory, is valid only for weak fields. However, experiments indicate that phenomena similar to the Stark shift of levels occur for rather strong intramolecular fields as well.Translated from Zhurnal Strukturnoi Khimii, Vol. 26, No. 5, pp. 27–34, September–October, 1985.     

Mesophase behaviour of binary mixtures of bent-core and calamitic compounds

The mesophase behaviour of binary mixtures of bent-core and calamitic liquid crystals is presented. The nematogenic 4,6-dichloro-1,3-phenylene bis[4′-(10-undecen-1-yloxy)-1,1′-biphenyl-4-carboxylate] (I) was the banana-shaped component. As the calamitic compound ethyl 4′-(9-decen-1-yloxy)-1,1′-biphenyl-4-carboxylate (II), similar to one arm of the bent-core molecule, was used which exhibits smectic phases in a wide temperature range. A total of six mixtures with different compositions were prepared and studied by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction on non-oriented samples. In the mixtures, a nematic phase is not concomitant with smectic A phase, and the temperature range of both phases highly depends on the concentration of the comprising compounds. Lowered melting temperatures have been observed for all mixtures with respect to that of the pure compounds. Unforeseen finding is the induction of a monotropic SmC phase in mixtures with lowest concentration of the bent-core compound. Semi-empirical quantum-chemical calculations have also been performed. Based on the calculated molecular conformation, as well as on collected X-ray diffraction data, a model for a possible self-assembly of the banana-shaped and calamitic compounds is proposed.     

Velocity cross correlations in binary mixtures of simple fluids

The velocity cross correlation integrals $$D_{{\text{ab}}}^{\text{J}} = (N/3)\mathop \smallint \limits_{\text{o}}^\infty< {\text{v}}_{{\text{1a}}} ({\text{t}}) \cdot {\text{v}}_{{\text{2b}}} (0) > {\text{dt,}} {\text{a}} {\text{ = }} {\text{1,2;}} {\text{b}} {\text{ = }} {\text{1,2}}$$ can be estimated from the intradiffusion coefficients D ₁ ^° and D ₂ ^° at each mole fraction x₁ of component 1 on the basis of the exact relations among the Onsager phenomenological coefficients together with an assumed equation relating the joint diffusion coefficients D _ab ^J . The results from several such equations are compared with experimental data and with similar results derived by Hertz in a different way to represent the behavior of f _ab ≡D _ab ^J x _b in ideal reference systems. In some cases the agreement with experimental data for relatively ideal systems is even better than given by Hertz's results. For greater accuracy in predicting the D _ab ^J from D _a ^dg data one would need a prediction of the limiting value of D _aa ^J at x_a=0 for a=1,2. Presently known theory does not give a basis for estimating this limit reliably.     

Comparative molecular field analysis (CoMFA) of new herbicidal sulfonylurea compounds

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Electron-bombardment and pyrolysis of meso- and dl-hydrobenzoin cyclic sulfites

Only a minor yield of sulfur dioxide positive ions is eliminated from the meso- and dl-hydrobenzoin cyclic sulfite molecules under electron bombardment. Among the principal fragmentation products for both sulfites are very similar yields of ions with m/e 154 and 126, which contain sulfur most probably attached to a phenyl ring. Positive ions apparently corresponding to those of diphenylacetaldehyde, desoxybenzoin, and stilbene are minor products of the positive-ion fragmentation process of the sulfites. These three compounds along with sulfur dioxide are the products of the pyrolysis of the sulfites at 240-250°. The principal product from the meso-sulfite is desoxybenzoin, and from the dl-sulfite it is diphenylacetaldehyde. Mechanistic details are discussed.     

Thermal properties of the clathrate compounds of binary cyanides

The stoichiometry of thermal decomposition of a particular group of clathrate compounds, of the type Cd(en)Pd(CN)₄·2G, with the same coordination component but different clathrate-enclosed components, was investigated. Irrespective of the experimental conditions, the liberation of the enclosed component G always proceeded in one step. Thermal investigation of the decomposition stoichiometry under identical experimental conditions showed that the temperature intervals in which the enclosed components are given off shift to lower temperatures in the order C₆H₅OH=> C₆H₆ > > C₄H₅N > C₄H₄S. Diffraction measurements indicated a considerable change in the structures of the original clathrate compounds after thermal release of the enclosed componentG.

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Zusammenfassung Die Stöchiometrie der thermischen Zersetzung einer bestimmten Gruppe von Klathratverbindungen vom Typ Cd(en)Pd(CN)₄·2G mit der gleichen Koordinationskomponente und verschiedenen Klathrat-Einschlußkomponenten wurde in dieser Studie untersucht. Ungeachtet der Versuchsbedingungen vollzieht sich die Freisetzung der eingeschlossenen KomponenteG stets in einer Stufe. Die unter gleichen Versuchsbedingungen durchgeführte thermische Untersuchung der Zersetzungsstöchiometrie zeigte, daß die Temperaturbereiche, in denen die eingeschlossenen Komponenten freigesetzt werden in der Reihenfolge C₆H₅OH > C₆H₆ > C₄H₅N > C₄H₄S in Richtung der niedrigeren Temperaturwerte verschoben werden. Die Diffraktionsmessungen weisen darauf hin, daß eine beträchtliche Änderung der Struktur der ursprünglichen Klathratverbindung nach thermischer Freisetzung der eingeschlossenen KomponenteG sichtbar wird.

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Résumé Dans cette étude on a établi la stoechiométrie de la décomposition thermique d'un groupe particulier de clathrates du type Cd(en)Pd(CN)₄·2G, avec le même composant de coordination et différents composants occlus. Indépendamment des conditions d'expériences, la libération du composant occlusG s'effectue toujours en une étape. L'étude thermique de la stoechiométrie de la décomposition effectuée dans les mêmes conditions d'expériences, a montré que les intervalles des températures dans lesquels les composants occlus sont libérés, se déplacent vers les températures plus faibles dans l'ordre suivant: C₆H₅OH > C₆H₆ > > C₄H₅N > C₄H₄S. Les mesures de diffraction indiquent qu'après la libération thermique du composant occlusG, une variation considérable de la structure initiale des clathrates originaux apparaît.

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Cd(en)Pd(CN)₄. 2G . , G . , , , ] ₆₅>₆₆>C₄H₆N>C₄H₄S. - , G.