Parameters and Form of the Mössbauer Spectra of Iron(III) β-Diketonates: New Data

Mössbauer spectra have been measured at 295 and 78 K for ten ⁵⁷Fe-enriched iron(III) -diketonates differing in the type of radical in the chelate ring. Since the literature data for compounds of this class are incomplete and contradictory, a repeated analysis of spectrum shape and parameters has been performed. The chemical shift and quadrupole splitting are virtually independent of the type of radical in the chelate ring whereas the line width and asymmetry exhibit a pronounced dependence on the temperature and composition of the compounds. The available concepts on the nature of quadrupole splitting and relaxation mechanisms determining the lineshape for the given compounds are refined. It is concluded that electron spin relaxation is longitudinal or transverse relative to the principal axis of the electric field gradient in different compounds.     

Crystal structure of copper(II) <Emphasis Type="Italic">trans</Emphasis>-bis-(4-phenyliminopentan-2-onate)

trans-Bis-(4-phenyliminopentan-2-onato)Cu(II) (5), which is a phenyl-substituted ketoimine, was synthesized, and an X-ray study was performed for this compound. Crystal data for CuN₂O₂C₂₂H₂₄: a = 11.4557(3) Å, b = 26.6845(9) Å, c = 14.2976(5) Å, β = 113.2270(10)°; space group P2₁/n, Z = 8, d _calc = 1.363 g/cm³, R = 0.033. The structure is molecular and built of isolated trans complexes. The central copper atom is surrounded by four atoms (2O+2N) with the average distances Cu-O 1.904(3) Å and Cu-N 1.962(3) Å. The polyhedron around the copper atom is a distorted tetrahedron; the average values of the O-Cu-O and N-Cu-N trans bond angles are 147(2)° and 150(2)°, respectively. The average value of the O-Cu-N angles is 94(1)°.     

Reaction of a stable silylene with tetrahydrofuran

Reduction of 1,3-di-tert-butyl-2,2-dichloro-2,3-dihydro-1H-1,3,2-diazasilole with metallic potassium gave, instead of a stable silylene, 1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2λ²-diazasilylolene, a product of insertion of the latter into the carbon-oxygen bond of tetrahydrofuran, 1,4-di-tert-butyl-6-oxa-1,4-diaza-5-silaspiro[4,5]dec-2-ene.     

Thermal Behavior of Mixtures of Zirconium(IV) and Yttrium(III) Dipivaloylmethanates

Russian Journal of Applied Chemistry - The thermal properties of individual precursors, zirconium(IV) and yttrium(III) dipivaloylmethanates, and of their mixtures [Zr(thd)4–Y(thd)3, Hthd =...     

Synthesis and spectroscopic properties of (N/O) mono- and dispirocyclotriphosphazene derivatives with benzyl pendant arms: study of biological activity

The Cl replacement reactions of hexachlorocyclotriphosphazene (trimer; N ₃ P ₃ Cl ₆ ) with sodium (N-benzyl)- aminopropanoxides (1 and 2) produced monospiro- (3 and 4), cis-, and trans-dispirocyclotriphosphazenes (13–16). The monospiro tetrakis-aminocyclotriphosphazenes (5–12) were obtained by the Cl substitutions of 3 and 4 with different secondary amines. The cis- (13 and 14) and trans-dispirophosphazenes (15 and 16) possessed 2 chiral P centers, and they were able to present meso and racemic forms, respectively. Moreover, the structures of compounds 5 and 14 were designated using X-ray data. The absolute configuration of compound 14 was found as SR in the solid state. Analytical and spectroscopic data of the phosphazenes were consistent with their suggested structures. Antimicrobial activities of the benzyl-pendant-armed cyclotriphosphazenes were scrutinized against G(+) and G(−) bacteria and yeast strains. The bacterium most affected by the synthesized compounds was Pseudomonas aeruginosa . Minimum inhibitory concentrations and minimal bacterial concentrations were in the range of 125–500 μM. Interactions between the phosphazenes (3–12 and 15) and plasmid DNA were studied with agarose gel electrophoresis. The phosphazene- DNA interaction studies of the cyclotriphosphazenes revealed that phosphazenes 3, 4, and 15 had a substantial effect on supercoiled DNA by cleavage of the double helix.     

Volatile Phthalocyanines: Vapor Pressure and Thermodynamics

The current review summarizes the data of saturated vapor pressure and thermodynamic parameters of the sublimation process of different phthalocyanines as reported in the literature as well as in our work. The volatility of phthalocyanines is analyzed from the standpoint of their molecular and crystal structure. The differences in the saturated vapor pressure value of the investigated phthalocyanines may reach some orders of magnitude and are determined by the Van der Waals and electrostatic interaction of the peripheral atoms of adjacent molecules, as well as to a specific interaction, the type and number of which depend on the type of molecules packing in the crystal.     

Thermal investigation of bis(methoxy-β-diketonates) of copper(II) — novel CVD precursors of copper films. Crystal structure of bis(2,2,6,8-tetramethyl-6-methoxynonan-3,5-dionato)copper(II)

Seven copper(II) bis-chelates derived from novel sterically hindered ligands — methoxy-β-diketones     

The sub-micrometer thickness n-InSb/i-GaAs epilayers for magnetoresistor applications at room temperatures of operation

Magnetotransport at fields up to 500 mT and LF-noise characteristics are reported for miniature magnetoresistors with ferrite concentrators based on Sn-doped n-InSb/i-GaAs heterostructures grown by MBE. The thickness of the InSb epilayers lie in the range 0.55–1.5 μm giving room temperature mobilities of 2.5–5.5 m² V⁻¹ s⁻¹ with carrier densities of (0.5–1.5)×10¹⁷ cm⁻³. The room temperature magnetoresistance (MR) for our two terminal devices could be as high as 115% at 50 mT which is comparable to the extraordinary MR (ExMR) recently reported in microscopic composite van der Pauw disks four terminal devices [Science 289 (2000) 1530]. In addition, a high signal-to-noise ratio and a good temperature stability of R(B)/R₀=0.5–0.83% K⁻¹ was observed for B<60 mT (below the saturation field B_sat for ferrite). Device resistance stability R₀(T) was equal to 0.27–0.66% K⁻¹ in zero field with a nominal device resistance R₀=197–224 Ω for DC currents in the range I=0.01–1.0 mA. The minimum detectable magnetic field is estimated from the reduced differential MR (∂R/∂B)/R=2000% T⁻¹ at B=31 mT and normalised 1/f current noise power spectral density measured at the same field. The resolution limit B_min=2.6 nT at 10² Hz and B_min=0.82 nT at 10³ Hz. These resolution limits are seven times better than those recently reported for the same material n-InSb/i-GaAs and ferrite fabricated Hall sensors [Magnetotransport and Raman characterization of n-InSb/i-GaAs epilayers, for Hall sensors applications over extremely wide ranges of temperature and magnetic field, Proceedings NGS 10, IPAP Conference Series 2, IPAP, Tokyo, 2001, pp. 151–154].     

Volatile zirconium compounds: Prospects for use in gas-phase isotope separation

Data on volatile zirconium(IV) complexes are considered from the viewpoint of search for compounds exhibiting the required thermal parameters for centrifugal separation of stable isotopes. The results of studies concerning thermodynamics of vaporization of volatile zirconium compounds with inorganic and organic ligands are summarized and analyzed. The influence of the electronic structure of the central atom and of the molecular and crystal structure on the volatility of zirconium compounds is discussed. Promising lines of searching for volatile zirconium compounds for the development of low-activation materials based on isotopically altered elements are outlined.