Quantum-Chemical Calculation of the Electronic Structure and Ionic Conductivity of Lead Hexaferrite with a Magnetoplumbite Structure

The ab initio linear muffin-tin orbital method in a tight binding approximation (LMTO-TB) and semiempirical extended Hückel theory (EHT) were used to study the electronic structure, chemical binding, and ion conductivity of hexaferrite PbFe₁₂O₁₉. The analysis of chemical bonds showed that Fe–O interactions play the dominant role in the chemical bonding in hexagonal ferrites, the covalent component of the Pb–O bond being insignificant. The metallic Fe–Fe bonds have been found. The predicted increased mobility of Pb²⁺ ions in the structure of magnetoplumbite agrees well with the experimental parameters of lead diffusion and ion–electron conductivity in PbFe₁₂O₁₉. The mechanism of migration of lead ions in the structure of the hexaferrite is discussed.     

Molecular structure and interionic vibrations of the ion pairs of N-acetyloxypyridinium halides

The structure and interionic vibrations of the ion pairs of N-acetyloxypyridinium halides were investigated on the basis of joint use of methods of quantum chemistry, molecular mechanics, and long-wave IR spectroscopy. It was established that the indicated salts belong to the class of stereochemically nonrigid molecules, and their most probable geometrical configuration corresponds to a position of the anion above the plane of the pyridine ring in the region adjoining the nitrogen atom. A nonmonotonic dependence of the force constant of the interionic vibrations on the equilibrium distance between ions in N-acetyloxypyridinium halides was predicted theoretically and detected experimentally.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 22, No. 5, pp. 597–602, September–October, 1986.     

Analysis of ionic solids with SNMS

Summary The application of plasma-based SNMS to salt samples was examined to reveal the analytical features of this technique for the analysis of environmental material, which is frequently composed of ionic compounds. 10¹⁶ s^–1 cm^–2 argon ions of 300–500 eV energy were used to sputter halides, sulfates, nitrates and carbonates. The mass spectra are dominated by atomic signals of all elements of the salt and contain additional minor signals of binary homo- and heteroelemental clusters. The latter, such as salt monomers of alkali halides, are useful for compound identification. In sputter equilibrium the atomic mass signals can be used for elemental quantitation with a matrix dependence of about ±30% for the detection factors of most elements. As the average elemental detection factors are shown to be governed by atomic ionization probabilities the erosion flux from salts comprises mainly atoms. Results indicate that thermal release of atoms as well as emission of clusters are the main cause of the matrix dependence. The relative yield of the clusters was found to be strongly enhanced with increasing mass difference of the combined ions. The sputter yield of NaCl was determined to be 3.3 atoms/projectile at 490 eV argon ion energy which results in a depth propagation of 5 nm/s for the given sputter conditions.     

Electron structure and reactivity of organofluorine compounds. 3. Mndo and ami calculations of the ground state of perfluoroalkyl chlorides,bromides, and iodides

The semiempirical quantum chemical MNDO and AMI methods were used to determine the equilibrium geometries and electron properties of molecules of perfluoroalkyl halides (R_FX): CF₃X, CF₃CF₂X, (CF₃)₂CFX, (CF₃)₃CX for X=Cl, Br, and I. It was determined that the effective charge on the Cl atom in R_FCl is negative, positive on the I atom in R_FI, and depends on R_F for the Br atom in R_FBr. The CF₃ group can act as either an electron acceptor or donor in various perfluoroalkyl halides. The strongest C–I bond in the perfluoroalkyl halides occurs with a tertiary RF group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1059–1063, May, 1990.     

Electronic structure of polyphosphate ions

The electronic and stereochemical structure of the polyphosphate ions (PO₃) ₂ ^2– , P₂O₇ ^4–, and (PO₃)₃ ^3–, and also of model nucleoside polyphosphates, which play an important role in the accumulation and transport of energy in biosystems, were investigated by the MNDO quantum-chemical method. The electron density distribution in the systems is analyzed, and the centers most favorable for interaction with metal ions are identified. It is shown that the investigated ions are thermally stable systems, and this is largely due to the delocalization of the excess electron charge along the polyphosphate chain.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 6, pp. 673–679, November–December, 1987.     

The response of the chlorobenzene-ethanol-trimethylpentane dosimeter to medium energy X-rays

Energy dependence of the radiation chemical yield of hydrochloric acid, G(HCl), of chlorobenzene-ethanol-trimethylpentane (CET) dosimetry system was investigated to medium energy X-rays (210, 150 and 120 kV maximum energy). In the dose range 50–150 Gy the concentrations of chloride ions were determined spectrophotometrically. Reference dosimetry for all measurements was carried out by the Fricke dosimeter. There was no change of radiation chemical yield of chloride ions with photon energy throughout the X-ray energy range applied in this work, i.e. down to the mean energy of about 50 keV.     

Kinetics of Sulfur Oxide, Sulfur Fluoride, and Sulfur Oxyfluoride Anions with Ozone

Rate constants and product branching ratios were measured for eleven sulfur oxide, sulfur fluoride, and sulfur oxyfluoride anions reacting with O₃. The SO^– ₂ ion reacts rapidly to form –O^– ₃, SO^– ₃, and e^–. The temperature dependence of the branching ratio shows more reactive detachment and less SO^– ₃ formation at higher temperature. SO^– ₃ reacts with O₃, forming SO^– ₄ at 1/3 to 1/4 of the collisional rate from 200 to 500 K, respectively. At 300 K, SF^– ₆ charge transfers to O₃ at 20% of the collisional rate. F₂SO^– ₂ reacts with O₃ at a few percent of the collision rate, forming both O^– ₃ and FSO^– ₃; The ion F₃SO^– reacts slowly with O₃ to form F₃SO^– ₂. The ions SO^– ₄, SF^– ₅, FSO^– ₂, FSO^– ₃, F₃SO^–, and F₅SO^– are unreactive with O₃. A trend is noted relating the ion reactivity with the coordination of the central sulfur atom, i.e., the number of S–F bonds plus two times the number of S=O bonds. Only ions with a sulfur coordination of 4 or 6 are reactive, although the reaction rate constants are generally small. The reactivity trends appear to be partially explained by spin conservation. These reactions are all sufficiently slow, so O₃ reactions should not play a major role in SF₆/O₂ discharges. All ions studied have been found to be unreactive with O₂.     

Study of chemisorption equilibrium in the methanol-silica system

Quantitative IR spectroscopy and desorption mass spectrometry were used to study chemisorption equilibrium in the silica-methanol system. It was determined that the methoxylation of SiO₂ is endothermic. The enthalpy and the equilibrium constant were determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 85–87, January–February, 1992.     

Models having the thermodynamic properties of aqueous alkaline earth halides and NaCl-MgCl2 mixtures

A model studied earlier in relation to aqueous 1–1 electrolytes has been applied to the interpretation of the excess free energies of aqueous solutions of the alkaline earth halides up to 1 M ionic strength. Several variations on the model could be fitted to the data. In the one which seems most consistent with the other observations, the cospheres (hydration layers) on the M⁺⁺ ions were two water molecules thick rather than one as for the alkali metal, tetraalkylammonium, and halide ions. The overlap of cospheres of an M⁺⁺, M⁺⁺ pair was found to make a small attractive contribution to the interionic force, while the overlap of cospheres of an M⁺⁺, X^– pair makes a small positive contribution which is almost the same for X^–=Cl^–, Br^–, or I^–. Thus, ionic hydration shells which are not penetrated by other ions are not required to account for the observed excess free energies. The model is also fitted to NaCl-MgCl₂ mixtures to see whether the new cosphereoverlap parameter which must be determined is consistent with the others. The calculation also shows how the thermodynamic behavior of the mixtures is consistent with the mixture limiting law for unsymmetrical mixtures. The singularities in the mixing coefficients g₀ and w₀ at infinite dilution dominate their concentration dependence only up to ionic strengths of about 0.01 M in models which fit the data.Most of this report is abstracted from a thesis presented by A. Smitherman to the Graduate School of the State University of New York at Stony Brook in partial fulfillment of the requirements for the M.S. degree, August 1972.     

Effects of Concentration on Hexaaquacobalt(II)/Tetrachlorocobalt(II) Equilibrium. A Discovery-Oriented Experiment for Chemistry Students

A solution of cobalt(II) chloride in HCI is commonly used to examine various effects, such as changes in temperature and concentration, on the Co(H₂O)₆²⁺/CoCl₄^2– equilibrium (Lc Chaâtcliers principle). In aqucous solution the cobalt(II) ion exists as a mixture of two complex ions at equilibrium, blue CoCl₄^2– and pink Co(H2O)₆²⁺. As the ions have different colors, it is easy to determine the position of the equilibrium. A series of experiments was designed to allow students to examine the concentration of chloride ion, the dehydration effect, and how dissociation effects the equilibrium. Different compounds were added to the aqueous solution of cobalt(II) ion, and the position of the equilibrium was determined either visually or, more quantitatively, by means of UV–vis spectroscopy. This exercise is suitable for general chemistry students and is designed to introduce them to the complexity of the actual chemical reaction rather than presenting them with a simplistic model.     

Theoretical study of nonrigid rotation of the tetrahedral cation and anion in NH4BH4

Segments of the potential energy surface of NH₄BH₄ corresponding to nonrigid rotations of the NH₄ ⁺ cation and BH₄ ^– anion relative to each other were calculated using the SCF/3–21G approximation with complete geometrical optimization and MP3/6–31G^* approximation for special points. The barriers for these motions are only several kcal/mole and the molecule is very nonrigid relative to several types of intramolecular rotations (rotation about the B-N bond, rotations with change in the dentation of the cation and anion, and rotations of the cation and anion facilitating the formation of some H₃N-N..H-BH₃ bonds and the cleavage of other such bonds). The strong geometric deformation of the NH₄ ⁺ and BH₄ ^– ions, the polarization of the electron density in these ions, and the H-H interaction between the hydrogen atoms belonging to different ions were discussed. The structural nonrigidity of NH₄BH₄ is closely related to its stability relative to decomposition.Institute of New Chemical Products, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 27–34, September–October, 1989.     

An Aqueous Thermodynamic Model for the Complexation of Sodium and Strontium with Organic Chelators Valid to High Ionic Strength. II. N-(2-Hydroxyethyl)ethylenedinitrilotriacetic Acid (HEDTA)

This is the second paper in a two part series on the development of aqueous thermodynamic models for the complexation of Na⁺ and Sr²⁺ with organic chelators. In this paper, the development of an aqueous thermodynamic model describing the effects of ionic strength, carbonate concentration, and temperature on the complexation of Sr²⁺ by HEDTA under basic conditions is presented. The thermodynamic model describing the Na⁺ interactions with the HEDTA^3–chelate relies solely on the use of Pitzer ion-interaction parameters. The exclusive use of Pitzer ion-interaction parameters differs significantly from our previous model for EDTA, which required the introduction of a NaEDTA^3– ion pair. Estimation of the Pitzer ion-interaction parameters for HEDTA^3– and SrHEDTA^– with Na⁺ allows the extrapolation of a standard-state equilibrium constant for the SrHEDTA^– species, which is one order of magnitude greater than the 0.1 M reference state value available in the literature. The overall model is developed from data available in the literature on apparent equilibrium constants for HEDTA protonation, the solubility of salts in concentrated HEDTA solutions, and from new data on the solubility of SrCO₃(c) obtained as part of this study. The predictions of the final thermodynamic model for the Na-Sr-OH-CO₃-NO₃-HEDTA-H₂O system are tested by application to chemical systems containing competing metal ions (i.e., Ca²⁺).     

Tracer-diffusion of Co2+ ions in some transition metal chloride solutions

Tracer-diffusion coefficients of Co²⁺ ions have been determined in 1% agar gel containing transition metal chlorides, viz. ZnCl₂, NiCl₂ and MnCl₂ over the concentration range of 10^–6–0.15 M at 25°C using the zone-diffusion technique. The results are compared with calculated values on the basis of Onsager's theory and the deviations are accounted for on the basis of various types of interactions in the ion-gel water system. Further, activation energy for the tracer-diffusion of Co²⁺ ions in the above mentioned electrolytes has been obtained as a function of electrolyte concentration, using measurements in the temperature range of 25–50°C. The trend in activation energy is explained on the basis of the WANG's model.     

Nitrate ion transport across TBP-kerosene oil supported liquid membranes coupled with uranyl ions

The role of nitrate ions in uranyl ions transport across TBP-kerosene oil supported liquid membranes (SLM) at varied concentrations of HNO₃ and NaNO₃ has been studied. It has been found that nitrate ions move faster compared to uranyl ions at the uranium feed solution concentrations studied. The nitrate to uranyl ions flux ratio vary from 355 to 2636 under different chemical conditions. At low uranium concentration the nitrate ions transport as HNO₃ · TBP, in addition to as UO₂(NO₃)₂ · 2TBP type complex species. The flux of nitrate ions is of the order of 12.10 · 10^–3 mol · m^–2 · s^–1 compared to that of uranium ions (4.56 · 10^–6 mol · m^–2 · s^–1). The permeability coefficient of the membrane for nitrate ions varies with chemical composition of the feed solution and is in the order of 2.5 · 10^–10 m^–2 · s^–1. The data is useful to estimate the nitrate ions required to move a given amount of uranyl ions across such an SLM and in simple solvent extraction.     

Quantum chemical study of the mechanism of the reaction of tetraphosphorus with alcohol in the coordination sphere of copper(II)

We have used the CNDO Method to study ^–1-tetraphosphorus complexes of copper (II) containing MeOH, MeO^–, H₂O, HO^–, Cl^–, Br^–, I^–, formed during the new reaction of oxidative alkoxylation of P₄ to trialkylphosphates in alcohol-benzene solutions of Cu(II). We studied the nature of the activation of the coordinated molecules and ions by comparing the charges on al the atoms and the values of the total, vocalent, and ionic energies of the intramolecular and intermolecular bonds. We observed the effect of conversion of the tetraphosphorus (which does not display acid-base properties) to a strong electron acceptor, tending toward electrophilic addition of coordinated nucleophiles. The calculated quantum chemical characteristics of the tetraphosphorus complexes correlate well with experiment.D. V. Sokol'skii Institute of Organic Catalysis and Electrochemistry, Kazakh Academy of Sciences, Alma-Ata. Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 27, No. 6, pp. 659–672, November–December, 1991. Original article submitted April 19, 1990.     

Covalent nature of the metal-halogen bonds in trinuclear osmium carbonyl halides

Comparison of the results of the electrochemical reduction of trinuclear osmium carbonyl halides with linear structure, Os₃(CO)₁₂X₂, and nonlinear structure, Os₃(CO)₁₀(-X)₂ (X=I, Br, and Cl) with mononuclear carbonyl halides of transition metals indicates covalent nature of the metal-halogen bonds in these compounds. Chemical dissociation does not occur upon dissolving the trinuclear osmium carbonyl halides in acetonitrile and the cleavage of the Os-X bonds is a result of the electrochemical reduction. The observed order for ease of reduction of the trinuclear osmium carbonyl halides coincides with the change in the E_1/2 values in the reduction of the mononuclear carbonyl halides of transition metals and alkyl halides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 459–460, February, 1990.     

Kinetic studies on the bromate ion oxidation of 12-tungstocobaltate(II) in aqueous acid

The oxidation of Co^IIW by bromine(V) is a complex process involving an induction period. The reaction was found to be first-order in both [Co^IIW] and [Br^v], and exhibits a complex dependence on [H⁺]. These observations were successfully explained by considering HBrO₂, one of the intermediates formed in the direct but slow reaction between Co^IIW and bromine(V), as the reacting species. The first-order limiting dependence in [H⁺] was due to the involvement of a protic equilibrium of HBrO₂. The induction period appears due to the scavenging effect of Br^– inadvertently present in the medium. It appears to be the first report where HBrO₂ was found to be the reacting intermediate in the oxidation of metal ions and complexes by BrO^– ₃.     

Dissociation and rearrangements of the molecular ions of sulfides,sulfoxides, and sulfones generated by a strong electric field

The field mass spectra of 18 sulfides, sulfoxides, and sulfones were investigated, and the principles of charge localization in the dissociation and rearrangements of the molecular ions of these compounds were established. A new type of fragmentation leading to the elimination of S^+., SO^+., and SO₂. was observed. A new mechanism, according to which cleavage of two C-S bonds and the formation of one new C-C bond due to radical recombination cocur in the cyclic transition complex, is proposed. Prior migration of alkyl radicals from sulfur to oxygen with subsequent cleavage of the S-O and C-S bonds via the above-mentioned mechanism may also occur in the molecular ions of sulfoxides and sulfones.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 2, pp. 172–181, March–April, 1987.     

Exchange reactions in two-phase catalytic systems. Communication 2. Ion exchange with halides between the onium salt and solid alkali metal salts

Conclusions The ion exchange reaction between solutions of tetrabutylammonium halides in toluene and solid alkali metal halides has been studied. It is shown that no ion exchange takes place between the onium salt and solid-KCl; this is in agreement with the approximate calculation of the equilibrium constant for this reaction (K_eq10^–4).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimcheskaya, No. 2, pp. 314–316, February, 1988.     

1,1-Addition von Zinn- und Bleiverbindungen an Isonitrile Umsetzungen von Isonitrilen mit Halogeniden der IV. und V. Gruppe, 1. Mitt.

Zusammenfassung Isonitrile reagieren mit Zinntetrahalogeniden unter Einschiebung in Zinn-Halogen-Bindungen zu Halogencarbimino-zinnhalogeniden. Bei Umsetzungen mit organosubstituierten Zinnhalogeniden reagieren bevorzugt die Zinn-Halogen-Bindungen; nur Phenylisonitril wurde (unter forcierten Bedingungen) auch in Zinn-Kohlenstoff-Bindungen eingeschoben. In manchen Fällen entstehen dimere oder polymere Produkte. Triphenylbleibromid reagiert mit Phenylisonitril zur entsprechenden Tetracarbiminobleiverbindung.

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1,1-additions of tin and lead compounds to isonitriles

The reaction of isonitriles with tin(IV) halides yields halogenocarbiminotinhalides by insertion into tin-halogen bonds. In organosubstituted tin halides the tin-halogen bonds are more reactive towards insertion of isonitriles than the tin-carbon bonds. Under forced conditions however, phenylisonitrilisonitril also inserts into Sn–C bonds. A tetracarbimino-lead compound was obtained by reacting phenylisonitrile with triphenyllead bromide.