Electrical conductivity in single-crystals of vanadium oxide bronzes

Single-crystal electrical conductivity of vanadium oxide bronzes of the type M_xV₂O₅ (β-phase), where M = Li, Na, K has been studied from 300 to 900°K. These compounds are found to exhibit a reversible semiconductor-metal transition along [010] in the region of 340°K. The phase transition observed seems to be caused by vanishing of the activation energy of carrier mobility due to the shift of some vanadium atoms in the planes perpendicular to the B axis.     

Preparative gas-solid adsorption chromatography. Part II. Selection of optimal conditions for separation in preparative chromatography

Summary The paper discusses the effects of the flow rate and the nature of the carrier gas, and the value of the Henry temperature coefficient on the capacity and effciency of preparative gas-solid adsorption columns.The theoretical relationship between the height equivalent of a theoretical plate (HETP) and the experimental parameters under overloaded conditions was obtained byDe Wet andPretorius [1] and somewhat modified by us [2]. Although it was derived under the assumption that the sorption isotherm is linear, the equation was shown to be in qualitative agreement with the experimental results when the separation took place in a partition column.Consequently we investigated the applicability of this equation for separation on gas-solid adsorption columns containing modified silica, further the optimum characteristics of the adsorbents and the optimal separation conditions. The dependence of the capacity on the separation conditions, theoretically derived by us in an earlier paper [3] has also been studied.

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Präparative Adsorptions-Fest-Gas-Chromatographie. Teil II: Wahl der optimalen Trennbedingungen in der präparativen Chromatographie

Zusammenfassung Die Arbeit befaßt sich mit der Wirkung von Strömungsgeschwindigkeit und Art des Trägergases, sowie mit dem Wert des Temperatur-Koeffizienten nach Henry auf die Kapazität und Wirksamkeit von Adsorptionssäulen für die präparative Fest-Gas-Chromatographie. Die theoretische Beziehung zwischen Bodenzahl (HETP) und Versuchsbedingungen bei Überladung wurde vonDe Wet undPretorius [1] emittelt und von uns etwas abgewandelt [2]. Obwohl sie unter der Voraussetzung einer linearen Adsorptionsisotherme abgeleitet wurde, zeigte die Gleichung gute Übereinstimmungmit den experimentell erhaltenen Ergebnissen bei der Trennung in einer Verteilungssäule. Daraufhin untersuchten wir die Anwendbarkeit dieser Gleichung für Trennungen auf Adsorptionssäulen für die Gas-Fest-Chromatographie, die mit modifiziertem Silicagel gefüllt waren; weiterhin versuchten wir die optimalen Eigenschaften der Adsorbentien und die optimalen Trennbedingungen zu ermitteln. Die Abhängigkeit der Belastbarkeit von den Trennbedingungen, die in einer früheren Arbeit [3] von uns schon theoretisch abgeleitet worden war, wurde ebenfalls untersucht.

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Chromatographie d'adsorption gaz-solide prépartive. 2ème Partie: Sélection des conditions optimales de séparation en chromatographie préparative

Résumé Dans ce travail on étudie les effets de la vitesse, de la nature du gaz vecteur, ainsi que de la valeur du coefficient de température selon Henry, sur la capacité et l'efficacité de colonnes adsorbantes en chromatographie préparative gaz-solide. La relation théorique entre la hauteur équivalente d'un plateau théorique (HETP) et les paramètres expérimentaux, dans des conditions de surcharge, a été établie parDe Wet etPretorius [1] et légèrement modifiée par nous [2]. Bien que cette relation füt obtenue en supposant que l'isotherme d'adsorption est linéaire, on trouve une bonne concordance qualitative avec les résultats expérimentaux de la chromatographie de partage. Par conséquent nous avons étudié la validité de cette équation pour des séparations sur colonnes adsorbantes en chromatographie gaz-solide (silice modifié); en outre nous avons essayé d'établir les caractéristiques optimales des adsorbants et les conditions de séparation optimales. On a étudié la relation existant entre la capacité et les conditions de séparation, en tenant compte des équations théoriques établies par nous dans un travail antérieur [3].

     

The standard enthalpies of formation of crystalline N-(carboxymethyl)aspartic acid and its aqueous solutions

The energy of combustion of N-(carboxymethyl)aspartic acid (CMAA) was determined by bomb calorimetry in oxygen. The standard enthalpies of combustion and formation of crystalline N-(carboxymethyl)aspartic acid were calculated. The heat effects of solution of crystalline CMAA in water and a solution of sodium hydroxide were measured at 298.15 K by direct calorimetry. The standard enthalpies of formation of CMAA and its dissociation products in aqueous solution were determined.     

1‐Oxa‐nido‐dodecaborate [OB11H12]− from the Controlled Oxidation of the closo‐Borates [B11H11]2− and [B12H12]2−

The closo‐dodecaborate [B₁₂H₁₂]^2? is degraded at room temperature by oxygen in an acidic aqueous solution in the course of several weeks to give B(OH)₃. The degradation is induced by Ag²⁺ ions, generated from Ag⁺ by the action of H₂S₂O₈. Oxa‐nido‐dodecaborate(1?) is an intermediate anion, that can be separated from the reaction mixture as [NBzlEt₃][OB₁₁H₁₂] after five days in a yield of 18 %. The action of FeCl₃ on the closo‐undecaborate [B₁₁H₁₁]^2? in an aqueous solution gives either [B₂₂H₂₂]^2? (by fusion) or nido‐B₁₁H₁₃(OH)^? (by protonation and hydration), depending on the concentration of FeCl₃. In acetonitrile, however, [B₁₁H₁₁]^2? is transformed into [OB₁₁H₁₂]^? by Fe³⁺ and oxygen. The radical anions [B₁₂H₁₂] ^{˙ ?} and [B₁₁H₁₁] ^{˙ ?} are assumed to be the primary products of the oxidation with the one‐electron oxidants Ag²⁺ and Fe³⁺, respectively. These radical anions are subsequently transformed into [OB₁₁H₁₂]^? by oxygen. The crystal structure analysis shows that the structure of [OB₁₁H₁₂]^? is derived from the hypothetical closo‐oxaborane OB₁₂H₁₂ by removal of the B3 vertex, leaving a non‐planar pentagonal aperture with a three‐coordinate O vertex, as predicted by NMR spectra and theory.     

EPR Spectra of Some Salts of Bis[η5-1,2-Dicarbollyl]nickeliate(III)(1-) Anion [NiIII (η 5-1,2-B9C2H11)2]?

Some salt-like complexes of the cluster anion [Ni^III (η⁵-1,2-B₉C₂H₁₁ )₂]⁻ ([NiCb₂]⁻), containing paramagnetic Ni³⁺ ion, with cations Cs⁺, (CH₃)₄N⁺, [MnPhen₃]²⁺ (where Phen is 1,10-phenanthroline) are studied by EPR method at 77 K and 300 K. A neutral complex [MnPhen₂(NCS₂] is also studied for comparison. The synthesis procedure and X-ray diffraction analysis of [MnPhen₃][NiCb₂]₂ complex with paramagnetic ions Mn²⁺ (3d ⁵) and Ni³⁺ (3d ⁷) are described. The EPR data of isostructural complexes [MnPhen₃][NiCb₂]₂ and [MnPhen₃][CoCb₂]₂ are reported. No exchange or dipole-dipole interaction was observed between two paramagnetic ions (Mn²⁺ and Ni³⁺) simultaneously present in a complex structure. The temperature changes in EPR spectra of solid compounds are caused by rearrangements in the Mn²⁺ surrounding. In the case of a salt with a compact spherical Cs⁺ ion, the local perturbation in a second coordination sphere of [NiCb₂]⁻ anion leads to redistribution of the electron density and changes in g-factor.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 6, 2005, pp. 403–414.Original Russian Text Copyright © 2005 by Nadolinny, Polyanskaya, Volkov, Drozdova.     

Electrochemical properties and state of paramagnetic centers in copper-modified complex vanadium and titanium oxides

Complex vanadium and titanium oxides modified by copper ions are studied by the electrochemical and ESR methods. Oxides Cu _x V_2?y Ti _y O_5?δ·nH₂O (0<y<1.33) have a layered structure and oxides Cu _x Ti_1?y V _y O_5+δ·nH₂O (0<y<0.25), an anatase structure. The intercalation of cations Cu²⁺ into the hydrates leads to oxidation of V⁴⁺. According to ESR data, V⁴⁺ exists in the oxides in the form of VO²⁺ and an octahedral surround of oxygen (V⁴⁺?O₆), respectively. The electroreduction of ions of d-elements and chemisorbed oxygen in the oxides is analyzed. The intercalation of cations Cu²⁺ alters the content of V⁴⁺ and the chemisorption ability of the oxides. Possible reasons for this phenomenon are discussed.     

Electronic structure and chemical bonding in K<Subscript>2</Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript>

The calculations of the electronic structure of layered polyvanadate K₂V₃O₈ were made employing the spin-polarized tight-binding LMTO method. Calculated magnetic moment for K₄V₆O₁₆ compound phase equals 1.97 μ_B. V-O interactions were established to be dominating in the chemical bonding generation in this polyvanadate according to the estimated crystal orbital overlap population. The covalent bonds V(2)-V(2) in V(2)₂O₇ groups and electron density localization on vanadium atoms in isolated pyramids V(1)O₅ were found.     

X-Ray and X-ray Photoelectron Spectroscopy Studies of the Electronic Structure of Borane Derivatives

This paper reviews the results of electronic structure studies of a number of typical members of borane series by X-ray and X-ray photoelectron spectroscopy using quantum chemical calculations. Fragment analysis of the molecular orbital structure is given. The nature of chemical interaction in boron cluster compounds is studied on models: simple molecules NH₃, BH₃, and BF₃ and their adducts NH₃BH₃ and NH₃BF₃. The electronic structure of B₁₀H₁₂L₂ type compounds with Lewis bases L = NH₃, (CH₃)₂S, (C₆H₅)₃P is analyzed. The complexes are considered in terms of the concept of donor–acceptor interactions between the fragments. The donor–acceptor bond has contributions from both occupied and vacant acceptor orbitals. X-ray photoelectron data on the charged states of atoms in the compounds are overviewed. Electron distribution in complex compounds with transition metals [(1,2-B₉C₂H₁₁)₂M]^–, M = Fe^III, Co^III, Ni^III, and Ni^IV and chain type polycobaltocarborane anions {[(3)-1,2-B₉C₂H₁₁]₂Co _n [(3,6)-1,2-B₈C₂H₁₀]_n-1} ^n– , n = 2-7, is considered.     

Electrode System Ni/Na y Al x V12O30/Al3+: An Impedance Spectroscopy Study

The impedance of electrochemical cells Ni/VOB/Al³⁺, Ni/VOB/Na⁺, and Ni/VOB/Ni (where VOB stands for vanadium oxide bronzes of the general formula Na _y Al _x V₁₂O₃₀, with 0 < x 1.7) is studied both at equilibrium and a constant-current polarization. Variations in the VOB composition and aqueous electrolytic solutions in contact with the bronze as a result of the passing of the current are monitored. The results of these measurements are employed to substantiate a model that describes the occurrence of processes of current production in the Ni/VOB/Al³⁺ electrode system. The overvoltage is defined to a substantial degree by the aluminum diffusion. The diffusion coefficients for aluminum, its partial conductivity, and transport number are estimated.