Structure and energy studies of β-diketonates. XIII. Molecular structure of gadolinium tris-hexafluoroacetylacetonate Gd(C5O2HF6)3

In a mass spectrometric study, it was found that the saturated vapor over gadolinium tris-hexafluoroacetylacetonate Gd(C₅O₂HF₆)₃ contains molecular forms with a mass exceeding the mass of the dimer. The vapor overheated to 250–300°C contains only the monomer form. Simultaneous electron diffraction and mass spectrometric experiment aimed at investigating the structure of the Gd(hfa)₃ monomer molecule was carried out at 284(5)°C. The Gd(hfa)₃ molecule was found to have the symmetry of the equilibrium D ₃ configuration. The basic structural parameters are r _h1(Gd-O) = 2.291(10) Å, r _h1(O-C) = 1.257(10) Å, r _h1(C-C_r) = 1.404(6) Å, r _h1(C_F-F)_av = 1.341(3) Å, ∠OGdO = 72.8(0.4)°. The GdO₆ coordination polyhedron has the structure of a distorted antiprism. The rotation angle of the O-O-O trigonal faces relative to their position in a regular prism is 18.7(0.9)°. Quantum chemical calculations (HF/SBK, 6-31G*) generally reproduce the experimental structure, but the Gd-O internuclear distance is exaggerated by 0.04 Å.     

Thermoanalytical studies of 2,2,6,6-tetramethyl-4-oxy-4-ethynylpiperidin-1-oxyl polymerization

The structure transition temperature, monomer melting point and critical temperatures of polymerization and decomposition of 2,2,6,6-tetramethyl-4-oxy-4-ethynylpiperidin-1-oxyl were determined by means of thermal analysis. Some features of the polymerization of the acetylenic monomer were studied via thermal analysis, and IR and ESR spectroscopy.It was shown that, during non-isothermal temperature increase, the mass loss of the sample associated with the exothermic effect of polymerization occurred at the expense of the monoacetylene sublimation process (42%), a reagent explosion and decomposition of the reaction products formed (15%).

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Zusammenfassung Mittels Thermoanalyse wurde die Strukturumwandlungstemperatur, der Monomerschmelzpunkt und die kritischen Temperaturen für Polymerisierung und Zersetzung von 2,2,6,6-Tetramethyl-4-oxy-4-ethynylpiperidin-1-oxyl bestimmt. Mit Hilfe von Thermo-analyse, IR- und ESR-Spektroskopie wurden einige Eigenschaften der Polymerisierung des Acethylen-Monomers untersucht.Es wurde gezeigt, daß bei einem nichtisothermen Temperaturanstieg der Massenverlust der Probe zunimmt, verbunden mit einem exothermen Effekt der eingetretenen Polymerisierung auf Kosten des Monoacetylen-Sublimierungsprozesses [42%], der Explosion und der Zersetzung der gebildeten Reaktionsprodukte [15%].

     

Scaling of the energy gap withT c in Bi2Sr2CaCu2O8+δ

The results of a high-resolution photoemission study using synchrotron radiation of two single crystals of Bi₂Sr₂CaCu₂O₈₊, with different critical temperaturesT _c due to a variation in oxygen stoichiometry are reported. Within experimental accuracy, the energy gap 2 is found to scale withT _c , amounting to a reduced gap parameter of 2/k _BT_c7.4. Employing resonant photoemission at the O–2s and Cu–3p thresholds, two spectral peaks at binding energies of 180 meV and 320 meV were identified as predominantly O–2p-and Cu–3d 4s-derived states, respectively.     

Chemical deposition of smooth nanocrystalline Y2O3 films from solutions of metal-organic precursors

A series of (Y(AcO)₃·4H₂O—Q—Solv) solutions (Q is monoethanolamine (MEA), diethanolamine (DEA), en, dien; Solv = MeOH, EtOH, Pr_iOH, BuOH) was studied to choose the metal-organic precursor for surface smoothing treatment of metallic tapes by chemical deposition of nanocrystalline yttria films. Based on the results of viscosity, wetting angle, and thermal stability measurements, a solution (Y(AcO)₃·4H₂O—dien—PrⁱOH) was proposed as a new metal-organic precursor. After chemical deposition of nanocrystalline yttria films about 300 nm thick on a Hastelloy C-276 metallic tape the surface roughness was reduced by a factor of 11 (from 9.0 to 0.8 nm on a surface area of 5×5 μm²).     

Unusual Structure,Fluxionality, and Reaction Mechanism of Carbonyl Hydrosilylation by Silyl Hydride Complex [(ArN)Mo(H)(SiH2Ph)(PMe3)3]

The reactions of bis(borohydride) complexes [(RN?)Mo(BH₄)₂(PMe₃)₂] ( 4 : R=2,6‐Me₂C₆H₃; 5 : R=2,6‐iPr₂C₆H₃) with hydrosilanes afford new silyl hydride derivatives [(RN?)Mo(H)(SiR′₃)(PMe₃)₃] ( 3 : R=Ar, R′₃=H₂Ph; 8 : R=Ar′, R′₃=H₂Ph; 9 : R=Ar, R′₃=(OEt)₃; 10 : R=Ar, R′₃=HMePh). These compounds can also be conveniently prepared by reacting [(RN?)Mo(H)(Cl)(PMe₃)₃] with one equivalent of LiBH₄ in the presence of a silane. Complex 3 undergoes intramolecular and intermolecular phosphine exchange, as well as exchange between the silyl ligand and the free silane. Kinetic and DFT studies show that the intermolecular phosphine exchange occurs through the predissociation of a PMe₃ group, which, surprisingly, is facilitated by the silane. The intramolecular exchange proceeds through a new non‐Bailar‐twist pathway. The silyl/silane exchange proceeds through an unusual Mo^VI intermediate, [(ArN?)Mo(H)₂(SiH₂Ph)₂(PMe₃)₂] ( 19 ). Complex 3 was found to be the catalyst of a variety of hydrosilylation reactions of carbonyl compounds (aldehydes and ketones) and nitriles, as well as of silane alcoholysis. Stoichiometric mechanistic studies of the hydrosilylation of acetone, supported by DFT calculations, suggest the operation of an unexpected mechanism, in that the silyl ligand of compound 3 plays an unusual role as a spectator ligand. The addition of acetone to compound 3 leads to the formation of [trans‐(ArN)Mo(OiPr)(SiH₂Ph)(PMe₃)₂] ( 18 ). This latter species does not undergo the elimination of a Si? O group (which corresponds to the conventional Ojima′s mechanism of hydrosilylation). Rather, complex 18 undergoes unusual reversible β‐CH activation of the isopropoxy ligand. In the hydrosilylation of benzaldehyde, the reaction proceeds through the formation of a new intermediate bis(benzaldehyde) adduct, [(ArN?)Mo(η²‐PhC(O)H)₂(PMe₃)], which reacts further with hydrosilane through a η¹‐silane complex, as studied by DFT calculations.     

Factors Affecting the Determination of Fluorine in Rocks by X-Ray Fluorescence Spectrometry Using Pressed Pellets

Journal of Analytical Chemistry - We studied a possibility of determining fluorine in rocks by the X-ray fluorescence spectrometry using pressed pellets as emitters. The most important factors...     

The effects of lipid A on gamma-irradiated human peripheral blood lymphocytes in vitro

The modulatory effects of lipid A (diphosphoryl lipid A (DLA) and monophosphoryl lipid A (MLA)) on apoptosis induction and DNA structure damage (single and double-strand breaks (SSBs and DSBs, respectively)) in peripheral human blood lymphocytes are studied for ⁶⁰Co gamma-irradiation. It is shown that in the presence of these agents the amount of apoptotic cells increases compared with the irradiated control samples. The effect is most strongly pronounced for DLA. In its presence, a significant increase is observed in the number of radiation-induced DNA SSBs and DSBs. Possible mechanisms are discussed of the modifying influence of the used agents on radiation-induced cell reactions     

The comparative study of mosaic structure of ZnO crystals by γ-ray diffraction and conoscopic methods

It has been carried out the investigation of the mosaic structure of ZnO crystals by two methods providing the information on mosaic structure and inner stresses (γ-ray diffraction and conoscopic method). It has been observed a certain correlation between the results obtained by the two methods.     

Debye-Waller Factors and Elastic Constants for Beryllium Oxide at Temperatures between 10 and 720 K (I). Anisotropy of Inoic Mean-Square Displacements

The Debye-Waller factors and the mean-square dynamics displacements of the Be and O ions in beryllium oxide are obtained from X-ray diffraction powder data over the temperature range from 10 to 720 K for different crystallographic directions. The observed anisotropy of these mean-square displacements is discussed.