Barium oxoaluminate hydride

The crystal structure of Ba₃(AlO₄)H is isotypic with Ba₃SiS₅ and contains AlO₄^5? and H^? anions. The hydride and oxide anions are coordinated by six Ba and five Ba/one Al atoms in an octahedral geometry. The hydrogen content was ex­amined by MAS–NMR experiments of the deuterated compound.     

The electronic structures of polymeric beryllium hydride and polymeric boron hydride

The band structure of linear polymeric beryllium hydride is here calculated by anab initio technique. The doubly-degenerate valence band has symmetry and is composed of a berylliump orbital and an antisymmetric combination of the appropriate hydrogen 1s orbitals. The Koopmans' ionization potential is calculated to be 16.1 eV and the direct band gap, found atX, is 15.2 eV. The charge distribution shows an electron drift of approximately 0.15 electrons from beryllium to the hydrogen atoms. The total energy calculation indicates that polymeric beryllium hydride is more stable than the monomer while polymeric boron hydride is less stable than the monomeric species. From the polymeric boron hydride system, an alternating-bond model is more stable than a symmetric bond model. The energy band structures of both models reveal that electron delocalization along the polymer chain is weak.     

Tributylgermanium hydride as a replacement for tributyltin hydride in radical reactions

Tributylgermanium hydride (Bu(3)GeH) can be used as an alternative to tributyltin hydride (Bu(3)SnH) as a radical generating reagent with a wide range of radical substrates. Tributylgermanium hydride has several practical advantages over tributyltin hydride, e.g. low toxicity, good stability and much easier work-up of reactions. The reagent can be easily prepared in good yield and stored indefinitely. Suitable substrates include iodides, bromides, activated chlorides, phenyl selenides, tert-nitroalkanes, thiocarbonylimidazolides and Barton esters. Alkyl, vinyl and aryl radicals can be generated in radical reactions including reduction and cyclisation processes. Common radical initiators such as ACCN and triethylborane can be used. The slower rate of hydrogen abstraction by carbon-centred radicals from Bu(3)GeH as compared to Bu(3)SnH facilitates improved cyclisation yields. Polarity reversal catalysis (PRC) with phenylthiol can be used in reactions which generate stable radical intermediates which will not abstract hydrogen from Bu(3)GeH.     

Enantioselective organocatalytic hydride reduction

The first enantioselective organocatalytic hydride reduction has been accomplished. The use of iminium catalysis has provided a new organocatalytic strategy for the enantioselective reduction of beta,beta-substituted alpha,beta-unsaturated aldehydes to generate beta-stereogenic aldehydes. The use of imidazolidinone 2 as the asymmetric catalyst has been found to mediate the transfer of hydrogen to a large class of enal substrates from ethyl Hantzsch ester. The capacity of catalyst 2 to accelerate E-Z isomerization prior to selective E-olefin reduction allows the implementation of geometrically impure enals in this operationally simple protocol.     

Hydrated hydride anion clusters

On the basis of density functional theory (DFT) and high level ab initio theory, we report the structures, binding energies, thermodynamic quantities, IR spectra, and electronic properties of the hydride anion hydrated by up to six water molecules. Ground state DFT molecular dynamics simulations (based on the Born-Oppenheimer potential surface) show that as the temperature increases, the surface-bound hydride anion changes to the internally bound structure. Car-Parrinello molecular dynamics simulations are also carried out for the spectral analysis of the monohydrated hydride. Excited-state ab initio molecular dynamics simulations show that the photoinduced charge-transfer-to-solvent phenomena are accompanied by the formation of the excess electron-water clusters and the detachment of the H radical from the clusters. The dynamics of the detachment process of a hydrogen radical upon the excitation is discussed.     

Trinuclear rhodium hydride complexes

Three novel trinuclear rhodium hydride complexes of the type {[Rh(PP*)H](3)(μ(2)-H)(3)(μ(3)-H)}[BF(4)](2) containing diphosphines Tangphos, t-Bu-BisP* and Me-DuPHOS have been synthesised. The new compounds are very stable. Their structures have been characterized by X-ray analysis in the solid state and by NMR-spectroscopic investigations in solution.     

Electrochemical hydride generation for the determination of hydride forming elements by atomic fluorescence spectrometry

The determinations of As, Bi, Ge, Sb and Se were performed by atomic fluorescence spectrometry following their electrochemical hydride generation. An electrochemical hydride generator based on a screw-thread seal arrangement, working in a continuous flow mode was used. The effects of cathode material, shape and area of material, catholyte, sample flow rate, applied current, catholyte solution concentration and interference of transition metals on signal intensity were studied. Five kinds of materials including lead, graphite, copper, tungsten and platinum with different shapes were tested as cathode materials. The signal obtained from a 3-dimensional electrode was higher than that from a 2-dimensional electrode under the same conditions. The signal intensity of Ge in HNO₃ medium within a narrow concentration range of 0.05–0.10 mol L^− 1 was stronger than that in other acidic medium, such as HCl and H₂SO₄. However, the signal intensity of Ge was rapidly decreased with HNO₃, HCl and H₂SO₄ concentration increasing, and then reached approximately zero. In general, limits of detection and a precision were improved using a graphite cathode in H₃PO₄ medium. The analysis of the reference materials showed good agreement with the certified values for As, Bi, Ge, Sb and Se. The method was successfully applied in the determination of As, Bi, Ge, Sb and Se in traditional Chinese medicine samples.     

Electrochemical hydride generation for the determination of hydride forming elements by atomic fluorescence spectrometry

The determinations of As, Bi, Ge, Sb and Se were performed by atomic fluorescence spectrometry following their electrochemical hydride generation. An electrochemical hydride generator based on a screw-thread seal arrangement, working in a continuous flow mode was used. The effects of cathode material, shape and area of material, catholyte, sample flow rate, applied current, catholyte solution concentration and interference of transition metals on signal intensity were studied. Five kinds of materials including lead, graphite, copper, tungsten and platinum with different shapes were tested as cathode materials. The signal obtained from a 3-dimensional electrode was higher than that from a 2-dimensional electrode under the same conditions. The signal intensity of Ge in HNO₃ medium within a narrow concentration range of 0.05–0.10 mol L^{− 1} was stronger than that in other acidic medium, such as HCl and H₂SO₄. However, the signal intensity of Ge was rapidly decreased with HNO₃, HCl and H₂SO₄ concentration increasing, and then reached approximately zero. In general, limits of detection and a precision were improved using a graphite cathode in H₃PO₄ medium. The analysis of the reference materials showed good agreement with the certified values for As, Bi, Ge, Sb and Se. The method was successfully applied in the determination of As, Bi, Ge, Sb and Se in traditional Chinese medicine samples.     

Isoelectronic sequences of hydride molecules

The theory of the electronic structure of diatomic hydrides in which the nuclear charge of the second nucleus is varied freely is investigated. By the use of a scale factor which varies with both the nuclear charge and the internuclear distance, the electronic equation can be put into a form suitable for a perturbation expansion. The zero and first order energies are computed for á number of isoelectronic sequences but comparisons with experiment show that higher order terms are needed in order to explain the basic properties of the molecules.

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Zusammenfassung Die Theorie der Elektronenstruktur zweiatomiger Hydride wird untersucht, wobei die zweite Kernladungszahl frei veränderbar bleibt. Durch Einführung eines Maßstabfaktors, der sowohl von Kernladungszahl als auch zwischenatomarem Abstand abhängt, läßt sich die Schrödingergleichung in eine die Durchführung einer Störungsrechnung möglich machende Form bringen. Die Energien nullter und erster Näherung werden für eine Anzahl isoelektrischer Reihen berechnet, allein der Vergleich mit dem Experiment zeigt, daß Terme höherer Ordnung in die Rechnung mit einbezogen werden müssen, um Grundeigenschaften der Moleküle deuten zu können.

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Résumé La théorie de la structure électronique des hydrures diatomiques est étudiée, où la charge nucléaire du second noyau est variable. A l'aide d'un facteur d'échelle dépendant de la charge nucléaire et de la distance internucléaire l'équation de Schrödinger peut être mise dans une forme convenable à un calcul perturbateur. Les énergies de nullième et de premier ordre sont calculées pour quelques séquences isoélectroniques; mais la comparaison de l'expérience montre qu'il faut des termes de plus grand ordre pour expliquer les propriétés fondamentales des molécules.

     

Relativistic calculations on thallium hydride

The spectroscopic parameters of the ground state of thallium hydride are obtained using the four-component relativistic Dirac–Coulomb–Gaunt–coupled-cluster wave function with single and double excitations and an estimated triples correction method. Core correlation effects make the bond weaker but have little effect on the bond length. Inclusion of the distance dependence of the Gaunt part of the two-electron Breit interaction has an opposite but smaller effect on these properties. Received: 8 September 2000 / Revised version: 5 October 2000 / Published online: 21 December 2000     

Electrochemical hydride generation of thallium

An electrochemical hydride generation (ECHG) technique was developed to improve the determination of thallium by atomic spectrometry. The technique is based on the catholyte variation system for production of thallium hydride. Using Pb-Sn alloy as cathode, a transient peak shaped signal was achieved and its height, the maximum absorbance value, was taken as an analytical parameter. Parameters that might affect the hydride generation efficiency were investigated and the analytical performance of the method under the optimized experimental conditions was assessed. The linear range was 1-250 ng mL⁻¹ for thallium and the relative standard deviation of the method was 4.2% (RSD, n = 7). The LOD for thallium was found to be 0.8 ng mL⁻¹, showing a significant improvement relative to conventional chemical hydride generation techniques. The proposed method was applied to the determination of thallium in unalloyed zinc standard reference material. This method offers high sensitivity, simplicity, rapidness, freeness from reagent and low acid consumption.     

Heat capacity of copper hydride

The heat capacity of copper hydride has been measured in the temperature range 2–60 and 60–250 K using two adiabatic calorimeters. Special procedure for the purification of CuH has been applied and a careful analysis of sample contamination has been performed. The experimental results have been extrapolated up to 300 K due to instability of the copper hydride at room temperature. From the temperature dependence of heat capacity the values of entropy S°(T), thermal part of enthalpy H°(T)−H°(0) and Gibbs function [−(G°(T)−H°(0))] have been calculated assuming S°(0)=0. The standard absolute entropy, standard entropy of formation from the elements and enthalpy of decomposition of copper hydride from the elements have been calculated and found to be 130.8 J K⁻¹ mol⁻¹ (H₂), −85.1 J K⁻¹ mol⁻¹ (H₂), −55.1 kJ mol⁻¹ (H₂), respectively. These new results gave the possibility of discussion on thermodynamic properties of copper hydride. Debye temperature has been for the first time determined experimentally.     

Manganese hydride potential energy curves

The potential energy curves of the ⁷Σ⁺ and the ⁵Σ⁺ states of MnH are calculated using restricted Hartree-Fock, unrestricted Hartree-Fock and the perfect pairing generalized valence bond methods. Both of these states are bound, with the ⁷Σ⁺ lowest in energy. The bonding for both states is to the 4s² shell rather than to any of the five singly occupied d orbitals. The MnH bonding orbitals are sp hydribs. These results are compared to similar studies of H on Sc, Fe, Ni and Cu. The implications of these results to hydrocarbon catalysis by first row transition metal catalysis are considered.