Peculiarities of Electrochemical Behavior of CsHSO4–SnO2 Composite System

Dependence of electronic and ionic components of conductance of CsHSO₄–SnO₂ systems on their composition is studied using the method of electrochemical impedance. The total electronic and ionic components of conductance nonmonotonically depend on the composition. To describe completely impedance diagrams of composite materials, an equivalent electrical circuit is proposed, which contains the bulk ionic conductance corresponding to the bulk of CsHSO₄ grains, and the conductance corresponding to the surface of tin dioxide grains. Each conductance component is separated out. The activation energies for the bulk and surface conduction equal 0.32 ± 0.02 and 0.36 ± 0.02 eV, respectively, and are independent of the system composition. The bulk ionic conductance monotonically decreases with increasing SnO₂ content and is well described wit percolation theory, whereas dependences of surface ionic and total electronic components have extremums.     

Molecular and ionic forms of salts and H-complexes in solutions

We generalize data collected in recent years on the effect of the properties of the medium on the state of salts and H-complexes in solutions. We examine current ideas about the molecular structure of these compounds in low-polarity media and the role of solvation effects in stabilization of ionic forms. We show the interconnection between changes in the electronic structure of the salts and H complexes occurring under the influence of the solvent and the thermodynamics of respectively ionic dissociation and proton transfer.Devoted to the 100th anniversary of the birthday of Academician A. I. Brodskii.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 5, pp. 271–283, September–October 1995.     

Electronic structure,energy of hydration,and stability of metal aquo ions

The stability of metal aquo ions with respect to redox reactions is determined by the ionization energies of the atoms and the Gibbs energies of hydration for the ions(–_hG⁰). We present critically selected values of –_hG⁰ for 55 metal ions, determined from electrochemical, thermochemical, and spectra data. We consider the factors determining the values of –_hG⁰ (charges, ionic radii, electronic structure, and relativistic effects). For isoelectronic ions, we observe correlations between the ratios of the Gibbs energies of hydration for these ions with different charges and the ratios of their ionic radii. Based on the use of these correlations, we find –_hG⁰ for a number of aquo ions not observed experimentally and we estimate the unknown oxidation-reduction potentials for the pairs of ions M³⁺/M²⁺. We formulate the principles for stabilization of unstable oxidation states of the metals by including the corresponding ions in complexes with certain classes of ligands.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 1, pp. 1–11, January–February, 1994.     

Quantum-chemical cluster models for hypervalency coordination environments in aluminum oxides

The MINDO/3 semiempirical approximation in SCF MO LCAO has been used to examine whether a cluster scheme can be used to calculate the electronic structures for aluminum oxides. Conditions are defined under which the hypervalent environment of the aluminum atom is stable under geometry optimization. A univalent pseudoatom model is compared with an uncharged ionic one to estimate the geometrical optimization. A univalent pseudoatom model is compared with an uncharged ionic one to estimate the geometrical and energy characteristics for clusters representing three-coordinated, four-coordinated, and six-coordinated Al.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 581–586, September–October, 1989.     

The virial theorem for the second derivatives of adiabatic potential and the dynamic instability of polyatomic molecules

The origin of dynamic instability of molecular configurations is investigated from the standpoint of the virial theorem for second derivatives and a new proof of this theorem is provided for an arbitrary polyatomic system. It is shown that the closeness of the energies of the excited and ground electronic states leads to a dynamic instability of the molecule by at least one vibrational coordinate. It is proposed that the instability of the solution of the Hartree-Fock equations under the condition of small positive numbers of instability can be an indication of dynamic instability of the equilibrium molecular configuration.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 3, pp. 257–262, May–June, 1986.The authors express their gratitude to G. E. Vaiman for the stimulating and helpful discussion.     

Quantum-chemical investigation into the geometric and energetic characteristics of kaolinite cluster models

A method of constructing molecular models for layered aluminosilicate crystals is put forward. The geometric and energetic characteristics of cluster models are calculated for the elementary kaolinite crystal layer using the MNDO approximation.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 3, pp. 214–218, May–June, 1993.     

Cluster structures for water adsorbed on SiO2

The MO LCAO SCF method has been used in the MNDO approximation to examine the electronic structures and formation energies for adsorption complexes for water on SiO₂ stabilized by hydrogen and coordination bonds. Stabilization by several hydrogen bonds cannot explain the high initial heats of adsorption for dehydrated silica. H₂O coordination complexes give higher energies, and hydroxylated silicon atoms on SiO₂ are considered as primary water-adsorption centers.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 532–545, September–October, 1988.     

Ionic liquids to the rescue? Overcoming the ionic conductivity limitations of polymer electrolytes

Polymer electrolytes – solid polymeric membranes with dissolved salts – are being intensively studied for use in all-solid-state lithium-metal-polymer (LMP) batteries to power consumer electronic devices. The low ionic conductivity at room temperature of existing polymer electrolytes, however, has seriously hindered the development of such batteries for many applications. The incorporation of salts molten at room temperature (room temperature ionic liquids or RTILs) into polymer electrolytes may be the necessary solution to overcoming the inherent ionic conductivity limitations of ‘dry’ polymer electrolytes.     

Investigation of molecule properties from electronic absorption spectra of solid and liquid crystals

Among the achievements of 20th century, there is the origin and violent development of the low-temperature technique and low-temperature spectroscopy of molecular crystals in the polarized light. Many obtained results became possible due to the close cooperation between experiment investigators and theorists. This short review traces the evolution of only one trend in the physics of molecular crystals, namely, the investigation of energetic and spatial structure of molecules from the analysis of electronic spectra of molecular crystals. First, for this purpose the possibilities of using the electronic spectra of molecular crystals at low temperatures benzene derivatives and the electronic spectra of liquid ionic crystals are considered. The results of investigations of the electronic absorption spectra for the new class of liquid crystals, namely, ionic metal-organic smectics are presented. Changes in the structure of doping molecules in the ionic liquid crystals under the influence of the dc electric field are analyzed.     

Nature of electronic states and mechanism of photocoloration of oxaindanespironaphthopyrans

The nature of the electronic states was studied, and the mechanism of photocoloration is discussed for spironaphthopyrans of the oxaindane series. The life times of the T states, the quantum yields, the quenching rate constants, and the activation energies of the photocoloration are determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 495–499, July–August, 1989.The authors express their sincere gratitude to V. A. Lokshin for providing the spiropyrans.     

Electronic structure of Co4(CO)12

The electronic structure of the Co₄(CO)₁₂ cluster has been studied by the extended semiempirical INDO method. The MO diagrams, atomic valences, and bond multiplicities are analyzed for the T_d and C_3v conformations of Co₄(CO)₁₂. Assignment of the electronic spectrum is suggested; the electronic structure of the lowest electronic-excited states is considered.St. Petersburg State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 20–30, November–December, 1993.Translated by L. Smolina     

Quantum-chemical investigation of hydrogen bond in complexes of ice-forming reagents with water

The MNDO method has been used in a quantum-chemical calculation of the electronic structure of complexes IFR...H₂O and IFR...2H₂O (IFR is an ice-forming reagent — 1,3,5-trihydroxybenzene, 1,5-dihyrdoxynapthalene, or 2,6-dihydroxynaphthalene), with complete optimization of geometry. The calculated results are compared with data on the ice-forming activity and structural features of the crystals of these IFRs.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 41–47, January–February, 1992.     

Electron-stimulated desorption from ionic crystal surfaces

Inelastic interactions of electrons with surfaces of ionic crystals result in emission of various particles such as ions, atoms and molecules. We will review such electron-stimulated desorption processes for the particular class of ionic crystals, namely for alkali halides. In this case, a dominant fraction of the emission is in the form of halogen and alkali atoms characterized by a thermal (Maxwellian) spectrum of translational energies. For several alkali halides (potassium and rubidium chlorides, bromides, and iodides), however, a significant part of the halogen atoms is ejected with nonthermal energies, i.e. energies of the order of 0.1 eV. The results of recent systematic studies of angular-resolved kinetic energy distributions of the emitted particles will be reported and current views on the electronic mechanisms of desorption will be described. In particular, it will be shown that the ESD mechanism can be understood in terms of the model involving a surface localisation of the so called “hot-holes” created by electron bombardment of alkali halides. A role of hot holes in ESD processes will further be discussed in relation to very recent experimental results obtained for the KBr crystals doped with In impurities which act as efficient hole traps.     

Quantum-chemical simulation of dicyanamide and tricyanomethanide ion solvation

SCF MO LCAO has been applied in the MNDO-WS approximation to calculate the spatial and electronic structures for solvates formed by dicyanamide and tricyanomethanide ions with alcohols, water, chloroform, and methylene chloride. The monosolvates formed by those anions are molecular complexes having medium-strength H bonds.Translated from Teoreticheskaya i Ékperimental'naya Khimiya, Vol. 25, No. 1, pp. 92–96, January–February, 1989.     

Structural and electronic properties of lithium ion battery anode material LiMN (M = Ni, Co, Cu)

The structural and electronic properties of anode materials LiMN (M = Ni, Co, Cu) for lithium ion batteries have been studied by the first-principles method. The calculations reveal different bonding characteristics for LiMN (M = Ni, Co, Cu). The Li–N bond on the LiN planes shows covalent mixed with ionic characters, with the covalent interaction strengthened and ionic one weakened gradually from LiNiN to LiCoN and then to LiCuN. In the direction of N–M chains, the bonding characteristics are analogous on the whole. The N–M bonding shows both ionic and covalent characters again, while the covalent interaction slightly weakened in sequence. Electronic structure calculations suggest that LiMN (M = Ni, Co, Cu) are all metallic, where the LiNiN is of anisotropic conductivity along the directions of N–Ni chains, while for LiCoN and LiCuN, electrons can also be feebly conductive on the LiN planes besides along the linear N–Co and N–Cu chains.     

Quasi-relativistic study of electronic structure of uranium tetrafluoride

Conclusions A comparison of the results obtained in a calculation of the electronic structure of UF₄, performed in the NR and QR approximations of the X-SW method, leads to a number of conclusions as to the role of relativistic effects in the electronic structure of molecules. a) An accounting for relativistic effects leads to changes in the spatial distribution of charge in the molecules and to a consequent change in the interpretation of the bond in terms of the ratio of ionic and covalent components. b) Relativistic compression of the wave functions of the s and p electrons (primary relativistic effects) and delocalization of the d and f functions (secondary relativistic effects) lead to substantial changes in the orbital energies and the corresponding ionization potentials in heavy molecules. c) Primary and secondary relativistic effects are responsible for considerable changes in the electronic excitation energies and the EA, changes that may account to as much as 200%. d) An accounting for spin-orbit interaction effects is extremely important in interpreting photoelectron and optical spectra. In the example of UF₄, it has been shown that NR wave functions are inadequate for use in calculating spin—orbit splittings in heavy molecules. Just as inadequate may be an accounting for spin—orbit interaction in first-order perturbation theory for systems of closelying MOs, the charge density of which is determined to a considerable degree by AOs of a single type (for example, 5f AOs of uranium in UF₄).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 20, No. 4, pp. 406–415, July–August, 1984.The authors wish to express their appreciation to M. I. Timokhin for assistance in performing the calculations.     

Electronic structure and N KVV Auger spectrum of the ammonium radical

A procedure for calculating multiplet-splitting energies in systems with an unpaired electron has been presented. The electronic structure and N KVV Auger spectrum of the ammonium radical have been calculated by the discrete-variation-X method. The results have been compared with experimental data.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 10–18, January–February, 1985.     

Thermodynamic properties of electrolyte solutions: An EMF study of the activity coefficients of KCl in the system KCl−KNO3−H2O at 25, 35 and 45°C

Electromotive force measurements were carried out on the system KCl–KNO₃–H₂O at constant total ionic strengths of 0.5, 1.0, 2.0 and 3.0 mol-kg^–1 and at 25, 35 and 45°C using a cell consisting of a potassium ionselective electrode and a Ag/AgCl electrode. The Harned coefficients and the Pitzer binary and ternary interaction parameters for the system have been evaluated at each temperature. The osmotic coefficients, excess free energies of mixing and heats of mixing of the system have been predicted at each of the experimental temperatures and ionic strengths. The solubility data at 25°C are also interpreted.     

A screened hybrid density functional study on energetic complexes: Alkaline-earth metal carbohydrazide perchlorates

The molecular geometries, electronic structures and stabilities of a series of alkaline-earth metal carbohydrazide perchlorates were investigated using the Heyd–Scuseria–Ernzerhof (HSE) screened hybrid density functional. The results show that Be and Mg complexes have six-coordinated octahedron features, as previously reported for the transition metal complexes. However, Ca, Sr and Ba complexes have additional coordinated oxygen atoms from the perchlorate ion. Detailed NBO analyses indicate that the metal–ligand interactions are essentially ionic and play an important role in the stabilities of these energetic complexes. The donor–acceptor interactions result in a reduction of occupancies of σ_C=O and σ_N–H bond orbitals, and also their subsequent impact on bond length and bond order.     

Thermal desorption of bromine from a graphite-bromine intercalation compound

Gas chromatography and static adsorption have been used to examine the bromine-graphite acceptor system, which has intercalant structures comparable with the adjacent graphite: layers. The bromine adsorption-desorption isobars and isotherms have been determined at 278–393 K, whose shapes indicate reversible phase transitions between intercalation stages 2 and 4. Measurements at 390–550 K give the desorption activation energies for the two forms of intercalated bromine; the heat involved in the conversion of the ionized intercalant form to the molecular one is 10.4 kJ/mole.Translated from Teoreticheskaya i Ékperimental'naya Khimiya, Vol. 25, No. 1, pp. 120–123, January–February, 1989.