Thermal decomposition kinetics of iron(III), cobalt(II), nickel(II) and copper(II) complexes of a Schiff base derived from quinoxaline-2-carboxaldehyde and glycine

Quinoxaline-2-carboxalideneglycine complexes of iron(III), cobalt(II), nickel(II) and copper(II) complexes were subjected to a systematic TG/DTG analysis. The decomposition process consists of two stages for all these complexes. Kinetic parameters were evaluated for each of these stages using the Coats-Redfern equation. The rate of decomposition at the second stage seems to have a bearing on the catalytic effect of the metal oxides formed during this stage.

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-2- (III) (II), (II) (II) /. . - . , -, , .

     

Excited Π states of divinyl chalcogenides and chalcophenes

Electron transitions in divinyl chalcogenides (CH₂=CHXCH=CH₂, where X is S, Se, or Te) have been analyzed using UV absorption spectra of dialkyl and alkyl vinyl chalcogenides. The following relations for the orbital energies are found: ^* < ^* < ^* < ^* for Te and ^* < ^* < ^* < ^* for S and Se. For chalcophenes, a correlation between the energy of the excited state (E ^*) of specific symmetry, the ionization potential (I) and the electron affinity (EA) is obtained:E ^*=const+(I+EA)/2. The electron affinity of divinyl chalcogenides is estimated. The correlation between the excited ^* states of divinyl chalcogenides and chalcophenes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–835, May, 1994.     

The effect of outer sphere cations on the thermal stability of nitritocuprates(II)

Thermal analyses by Derivatograph were made for salts of the general formula M ₂ ^I M^II[Cu(NO₂)₆] where M^I=K⁺, Rb⁺ or Cs⁺; and M^II=Ca²⁺, Sr²⁺, Ba²⁺ or Pb²⁺. From the results and the chemical and diffractometric analysis of sinters of chosen salts, the mechanism of thermal decomposition was established. Some conclusions concerning the effects of outer sphere cations on the thermal stabilities of these salts are also drawn.

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Zusammenfassung Es wurden thermische Analysen mit einem Derivatographen für die Salze der allgemeinen Formel M₂ ^IM^II [Cu(NO₂)₆] durchgeführt [M^I=K⁺, Rb⁺, Cs⁺; M^II=Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺]. Aus den Ergebnissen dieser sowie der chemischen und diffraktometrischen Analysen der Sinterprodukte der jeweiligen Salze wurde der Mechanismus ihrer chemischen Zersetzung ermittelt. Einige Folgerungen bezüglich der Wirkung von Kationen der äusseren Sphäre auf die thermische Stabilität konnten ebenfalls gemacht werden.

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Résumé Le mécanisme de la décomposition thermique des sels de formule générale M₂ ^IM^II [Cu(NO₂)₆] où M^I=K⁺, Rb⁺, Cs⁺ et M^II=Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺ a été établi à partir des données thermiques obtenues à l'aide d'un Derivatograph, ainsi que par des analyses thermiques et diffractométriques sur les produits frittés. L'effet des cations de la couche externe sur la stabilité thermique de ces sels est discuté.

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M ₂ ^I M^II[Cu(NO₂)₆], M^I=K⁺, Rb⁺, Cs⁺; M^II=Ca²⁺, Sr²⁺, Ba²⁺, b²⁺. , , . , .

     

Intensity of the η(C≡C) Bands in the IR Spectra of Acetylene Derivatives and σR 0 Constants of Organosilicon,Organogermanium, and Organotin Substituents

The integral absorptivities of shape-characteristic (CC) bands in the IR spectra of 66 acetylene derivatives RCCX (R = H, Me₃M; X are inorganic and organic substituents) are related by a common linear equation to the _R ⁰ constants of the R and X substituents. The _R R⁰ constants of 10 Alk₃M substituents were calculated. The _R ⁰, _R , and _R ⁺ constants of Me₃M substituents were analyzed. The positive _R ⁰ values (0.12, 0.06, and 0.04 for R = Si, Ge, and Sn, respectively) suggest that in the ground electronic state of Me₃MCCX molecules the resonance acceptor effect of the Me₃M substituents (d, conjugation) prevails over donor (, conjugation). The first effect attenuates and the second enhances as the atomic number of M increases.     

Kinetic and mechanistic studies on the oxidation of sulfanilic acid by peroxomonophosphoric acid

Oxidation of sulfanilic acid to the corresponding azoxy derivative by peroxomonophosphoric acid (PMPA) has been studied in aqueous medium. The observed bell-shaped pH-rate profile has been rationalized on the basis of protonation of the amino group and ionization into different PMPA species and a suitable rate law has been proposed. The mechanism of oxidation involves the nucleophilic attack of nitrogen on the electrophilic peroxo oxygen.

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- (PMPA) . pH— , PMPA . .

     

Influence of some organic acids on the adsorption of PdX42? complexes on alumina

Results are presented concerning the role of oxalic acid, salicylic acid and glycine as coimpregnation ingredients in preparation of Pd/Al₂O₃ catalysts from PdCl ₄ ^2– and PdBr ₄ ^2– solutions.

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, , , Pd/Al₂O₃ PdCl ₄ ^2– PdBr ₄ ^2– .

     

Kinetics and mechanism of acetylene hydromethylation on organonickel catalysts

Kinetics of methane interaction with acetylene on Ziegler-Natta type organonickel catalysts has been studied. The reaction is first order with respect to methane. The kinetic isotope effect amounts to K_{CH 4}/K_{CD 4}=1.5 and K_{C 2}H₂,CH₄,H₂/K_{C 2}D₂,CD₄,D₂=2.0.

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-. -. K_{CH 4}/K_{CD 4}, K_{C 2}H₂,CH₄,H₂/K_{C 2}D₂,CD₄,D₂ 1,5; 2,0. .

     

Diacetylenic Derivatives of Fe2(CO)6(μ-EE′): Spectroscopic Investigations of Fe2(CO)6{μ-EC(H) = C(C≡ CMe)E′} (E = E′, E ≠ E′; E, E′ = S, Se, Te)

The diacetylenic adducts, Fe₂(CO)₆{-EC(H) = C(C CMe)E} (E = E, E E; E, E = S, Se, Te) (1–8) have been obtained from the room temperature stirring of Fe₂(CO)₆(-EE) with HC CC CMe in methanol solvent containing sodium acetate. Compounds 1–8 have been characterized by IR and multinuclear NMR (¹H, ¹³C, ⁷⁷Se, and ^l25Te) spectroscopy. Trends in the chemical shifts of ⁷⁷Se and ¹²⁵Te NMR spectra of Fe₂(CO)₆{-EC(H) = C(C CMe)E} with a variation of EE are discussed.     

Electronic effect of the 1-[η5-cyclgpentadienyl-η5-(3)-1,2-dicarbollyliron(II)] group

Conclusions The Taft method was used to determine the electronic effect of the 1-[⁵-cyclopenta-dienyl-⁵-(3)-1,2-dicarbollyliron(II) ] group which displays strong electron-donor properties: _I=–0.22 and _R=–0.20.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1449–1451, June, 1985.     

Charge control in the formation of complexes of phenol with unsaturated compounds containing organometallic substituents from group IV

The resonance donor effect of the , conjugation of R₃M and R₃MCH₂ (M = Si, Ge, Sn; R is an alklyl group) substituents with the triple bond in compounds R₃MC=CX and R₃MCH₂CCX (X = H, R) changes on passing from isolated molecules to their H-complexes. A partial ⁺ charge on the triple bond enhances , conjugation; a partial ^– charge on the triple bond has practically no effect on the resonance properties of R₃M substituents, whereas the , conjugation of R₃MCH₂ substituents diminishes owing to the effect of negative direct resonance interaction. The effect of , conjugation on the effective negative charges of the carbon atoms in the -CC- fragments was estimated quantitatively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1041–1046, June, 1994.This work was supported by the Russian Fundation for Basic Research (Grant 93-03-18372).     

Electron structure of the V2 molecule derived from DV-Xα data

Conclusions The electron structure of the V₂ molecule has been calculated by means of the DV-X method. The configuration 3_u ⁴6_g ²7_g ²(l_g)² has been obtained for the ground state, which corresponds to a quintuple bond, and the equilibrium state 1.78 Å. The term of the ground state³_g ^– and the bond length are in agreement with the experimental data.Translated from Izvestiya Akadeinii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 232–235, September, 1985.The authors wish to express their gratitude to A. N. Ivanov and V. K. Gryaznov for the provision of the program for the calculation of the atomic Hartree-Fock functions.     

Spin conversion of positronium in paramagnetic solutions studied by age-momentum-correlation method

Correlated measurement of the lifetime and of the lineshape of the 511 keV annihilation radiation of positrons (age-momentum correlation, AMOC) has become a powerful tool for investigating reactions of positron or positronium in condensed matter as a function of time. The beam-based ⁺ AMOC method installed at the Stuttgart relativistic positron beam facility (E _kin ^e+ 4MeV) offers substantial advantages over the conventional E coincidence technique resulting in a fast data taking due to the unity detection efficiency of the ⁺ scintillator which provides the start signal for the lifetime measurement. In this paper the application of AMOC to positronium chemistry is illustrated by the study of spin conversion of positronium in the system methanol/HTEMPO as a function of HTEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, a paramagnetic solute) concentration. The same technique can be applied to other systems and other reactions in positronium chemistry, e. g., oxidation or complex formation.     

First and second thermodynamic mixing properties of ethylbenzene +n-alkanes: Experimental and theory

Isobaric expansibilities _P and isothermal compressibilities _T have been determined at 25 and 45°C for binary mixtures of ethylbenzene + n-tetradecane and + n-hexadecane and the corresponding excess functions (V ^E /T)_P and (V ^E /P)_T have also been obtained. With these data and supplementary literature values, the following second order mixing properties are also reported at 25°C: _S ^E , (V ^E /P)_T, C_V and (VT). All mixing quantities have been compared with the results obtained at 25°C by using the Prigogine-Flory-Patterson theory of liquid mixtures. The predicted values suggest that the ability of ethylbenzene as a breaker of the pure n-C_n orientations is similar to what we found for toluene and higher than for p-xylene.     

SCF Xα DW nuclear magnetic screening tensor calculations

Conclusions Calculations have been performed on the nuclear magnetic screening tensors for molecules via perturbation theory and the X DW method, and a comparison is made with results from other methods. Although the absolute errors in the for the molecules are appreciable, the relative errors in determining the NR chemical shifts are much less (see for example, the shift for CO relative to CH₄), which is a hopeful factor leading one to expect that X DW can be widely used in analyzing NMR spectra. At the same time, X DW can closely reproduces the anisotropy, which is particularly important for compounds such as V₂O₅ or its derivatives, which show very large anisotropy in the magnetic screening tensors.Catalysis Institute, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 5, pp. 32–36, September–October, 1988.     

Crystal Structure of Hexa(μ-bromo)-#x03BC;4-oxo-tetrakis-(1-ethyltetrazole)-tetracopper(II)

The structure of the [Cu₄(-Br)₆(₄-O)(ettz)₄] complex of the monoclinic crystal system was investigated by X-ray diffraction analysis: a = 45.016(12), b = 9.363(4), c = 15.698(5) , = 100.28(2)°, V _cell = 6510(4) ³, space group C2/c, Z = 8,_calc = 2.330 g/cm³, R1 = 0.0697 for 714 F_hkl 4 (F). The copper atoms form a tetrahedron with an oxygen atom in the middle and bromine atoms on the edges. The coordination polyhedron around the copper atom is a distorted trigonal bipyramid (CuOBr₃N unit). All tetrazole ligands are monodentate and coordinated by the N⁴ atoms.     

Kinetic parameters of thermal decomposition of nitritocuprates (II)

Kinetic parameters of thermal decomposition of compounds of the general formula M ₂ ^I M^II[Cu(NO₂)₆] (where M^I=K⁺, Rb⁺ or Cs⁺; and M^II=Ca²⁺, Sr²⁺, Ba²⁺ or Pb²⁺) and K₂Pb[X(NO₂)₆] (where X=Co²⁺, Ni²⁺, Zn²⁺) are determined from the corresponding thermal curves. The order of reaction (n) and the activation energy (E _a) are derived. The kinetic data is discussed in terms of the effects of outer sphere cations and the central ion on the activation energy.

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Zusammenfassung Die kinetischen Parameter der thermischen Zersetzung von Verbindungen des allgemeinen Typs M ₂ ^I M^II[Cu(NO₂)₆] (M¹=K⁺, Rb⁺ oder Cs⁺; M^II=Ca²⁺, Sr²⁺, Ba²⁺ oder Pb²⁺) bzw. K₂Pb[X(NO₂)₆] (X=Co²⁺, Ni²⁺, Zn²⁺) werden aus den entsprechenden thermischen Kurven bestimmt. Die Reaktionsordnung (n) und die Aktivierungsenergie (E _a) werden abgeleitet. Die kinetischen Parameter werden hinsichtlich der Effekte der Kationen in der Äu\eren SphÄre und des zentralen Ions auf die Aktivierungsenergie diskutiert.

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Résumé Les paramètres cinétiques de la décomposition thermique des composés de formule générale M ₂ ^I M^II[Cu(NO₂)₆] où M^I=K⁺, Rb⁺ ou Cs⁺ et M^II=Ca²⁺, Sr²⁺, Ba²⁺ ou Pb² + et K₂Pb[X(NO₂)₆] où X=Co²⁺, Ni²⁺, Zn²⁺ ont été déterminés à partir des courbes thermoanalytiques correspondantes. L'ordre de réaction (n) et l'énergie d'activation (E _a) ont été calculés. Les effets des cations de la sphère externe et ceux de l'ion central sur l'énergie d'activation sont discutés.

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M ₂ ^I M^II[Cu(NO₂)₆, ^I=⁺, Rb⁺ Cs⁺; ^II=C²⁺, Sr²⁺, ^{2+ 2+}, K₂Pb[X(NO₂)₆], X=²⁺ Ni²⁺; Zn²⁺. (n) (E _a ). .

     

Quantum chemical study of the physical characteristics of the hydroxy groups of zeolites, III

The CNDO/2 method was applied to calculate the electronic structure of HY zeolite using cluster models Si₃AlO₁₂H ₈ ^– and Si₃AlO₁₂H₉. It has been shown that the probability of occurrence of H on a particular type of oxygen as well as the other physical characteristics of zeolite depend on both the type of oxygen and the position of the Al atom.

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/2 , Si₃AlO₁₂H₈ Si₃AlO₁₂H₉. , , , Al.

     

Interpretation of AC Conductivity of Lightly Doped Conducting Polymers in Terms of Hopping Conduction

The ac conduction of most disordered materials shows a regime of constant dc conductivity (0) at low frequencies and a crossover to a frequency-dependent regime of the type A ^s at high frequencies. We discuss the physical origin of this behavior and the interpretation of the onset frequency of excess ac conduction, _c , in terms of models for hopping conduction of polaronic carriers in a disordered medium. We emphasize the central role of the critical hopping rate in the percolation lattice for determining both (0) and _c . We show the behavior of () for lightly doped polypyrrole samples at different stages of doping, and we discuss the significance of frequency dispersion effects for electrochemical measurements.     

Nature of ethylene complexes on the surface of Ag/SiO2 as evidenced by13C NMR data

The formation of -complexes of C₂H₄ with Ag⁺ on oxidized Ag/SiO₂ catalysts is shown by¹³C NMR. These complexes are similar in nature to those of olefins with silver in solution.

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¹³C , Ag/SiO₂ - C₂H₄ Ag⁺, - .

     

Calculation of σ→π* and π→σ* transitions in vinylboranes

Calculations are presented of the energies of the ground and excited and electronic states of ethylene and substituted vinylboranes. The Pople-Segal-Santry method was employed throughout. It is concluded that the excited state of lowest energy in ethylene has * character whilst the lowest energy ultra-violet spectral bands of the latter compounds stem from ^* transitions.

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Zusammenfassung Valenzelektronenrechnungen nach Pople-Segal-Santry wurden für Äthylen und Vinylborane durchgeführt. Danach hat der niedrigste angeregte Zustand von Äthylen ^*-Charakter, während die längstwellige UV-Bande der Vinylborane einem ^* -Übergang entspricht.

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Résumé Calculs de l'énergie pour les états fondamentaux et excités et de l'éthylène et des vinylboranes substitués. Utilisation de la méthode de Pople-Ségal-Santry. L'état excité le plus bas pour l'éthylène résulte d'une transition ^* , alors qu'il résulte d'une transition ^* pour les vinylboranes.