[Fe2(μ-SC5H4N)2(NO)4] as a New Potential NO Donor: Synthesis,Structure, and Properties

A new potential donor of nitrogen monoxide, a binuclear iron sulfur nitroso complex, was prepared by exchange reaction of Na₂Fe₂(S₂O₃)₂(NO)₄ with pyridine-2-thiol in the presence of sodium thiosulfate at pH 12. The molecular and crystal structures of [Fe₂(-SC₅H₄N)₂(NO)₄] were studied by X-ray diffraction analysis. The type of iron coordination by pyridine-2-thiol in the presence of a coordinated NO molecule was determined. In vacuum, the structure of the complex is destroyed, which is accompanied by NO evolution, while exposure to UV radiation results in decomposition of the complex and in a release of N₂O.     

Continuous Process for Obtaining Carbon Nanofibers

A continuous laboratory installation with a horizontal reactor for obtaining carbon nanofibers by catalytic pyrolysis of methane was developed and tested. The conversion of methane at 600°C was studied and the nanofiber output capacity of the continuous installation under the optimal conditions on a Ni-La₂O₃ catalyst was determined.     

Atom-transfer radical polymerization of poly(ethylene oxide) macromonomers in aqueous media

Soluble comb-shaped and swelling network polymers based on monomethacrylate (M = 2080) and bismethacrylate (M = 4000) poly(ethylene oxide) macromonomers, have been synthesized by the controlled atom-transfer radical polymerization in aqueous media. PEG 2000 methyl ether ethyl-2-bromoisobutyrate and 2-bromoisobutyrate, in combination with CuBr, CuBr₂, and 2,2′-bipyridyl, have been used as initiators. The length of the main chain of comb-shaped polymers, as estimated with multidetector chromatography, is in good agreement with the calculated values in the 15–20 range at M _w /M _n = 1.42–1.89. The polymerization of the methacrylate macromonomer proceeds at a high rate and with a nearly quantitative conversion. The replacement of 10–80 mol % CuBr with CuBr₂ appreciably decelerates polymerization and decreases polydispersity to 1.14–1.21, while the experimental and calculated values of chain lengths remain equal. This finding indicates a higher level of process control. The polymer networks thus prepared manifest Gaussian elastic behavior, as is evident from the relationship between the elastic modulus G and the swelling degree Q that is consistent with the classical prediction G ～ Q ^m , where m = ?1/3. Within the framework of the accepted model of networks of this type, this fact suggests the short length of polymethacrylate chains. In addition, the relationship between the time of attainment of the gelation point and the composition of the initiation system agrees with the atomtransfer controlled polymerization mechanism. The efficiencies of various radical polymerization methods for controlling the network structure are compared.     

TEM and HREM of diamond crystals grown on Si tips: structure and results of ion-beam-treatment

Diamond single crystals were grown on the silicon whiskers by a hot filament chemical vapor deposition technique at the filament temperature about 2100 degrees C and the temperature of support 800 degrees C. Specimens were examined by SEM, TEM, HRTEM and SAED. When the filament temperature was about 1900 degrees C globular polycrystalline diamond particles were grown. At a support temperature more then 800 degrees C SiC nanoparticles were formed. To investigate the ion etching process of the silicon tip/diamond system, tips were treated with an Ar(+) beam with energy up to 30 kV. The results depend on fluence: at 4 x 10(18)ion/cm(2) diamonds and partially Si tips were destroyed, amorphous layer was formed (sometimes with nanometric size fragments of diamond); at 1 x 10(18)ion/cm(2) sharpened diamonds (radius of curvature about 20 nm) covered with amorphous layer (radius about 80 nm) probably with nanoclusters of diamond were observed; at 4.4 x 10(17) ion/cm(2) there was no visible tip sharpening but formation of amorphous thick layer occurred. The emission characteristics of Si tips covered with diamond were improved due to ion treatment. Since such tips in our case were covered with amorphous layer containing nanometric size fragments of diamond, we suppose this layer is responsible for electron emission improvement.     

Synthesis and structure of halogen derivatives of 9-dimethylsulfonium-7,8-dicarba-nido-undecaborane [9-Me2S-7,8-C2B9H11]

Halogenation of 9-dimethylsulfonium-7,8-dicarba-nido-undecaborane [9-SMe₂-7,8-C₂B₉H₁₁] with N-chlorosuccinimide, bromine and iodine gave the expected corresponding halogen derivatives [9-SMe₂-11-X-7,8-C₂B₉H₁₀], where X = Cl (1), Br (2), I (3). In the bromination reaction, [9-SMe₂-6-Br-7,8-C₂B₉H₁₀] (4) was isolated as a minor product being the first example of substitution at a “lower” belt of the 7,8-dicarba-nido-undecaborate cage. The use of excess of bromine resulted in dibromo derivative [9-SMe₂-6,11-Br₂-7,8-C₂B₉H₉] (5). Structures of the compounds prepared were determined using ¹¹B-¹¹B COSY NMR spectroscopy (for all halogen derivatives) and single crystal X-ray diffraction (for compounds 2, 3, and 5).     

Nucleation and growth of crystalline diamond particles on silicon tips

The data on the deposition, structure, and electric properties of crystalline diamond particles at silicon tips grown on single-crystal silicon substrates obtained over the last decade, mainly at the Institute of Crystallography of the Russian Academy of Sciences, have been reviewed. It is shown that silicon emitters coated with crystalline diamond are highly electrically stable. They are used to prepare long-life cathodoluminescence light sources.     

[Bu4N]2[Fe2(μ-S2O3)2(NO)4]: Synthesis,Structure, Redox Properties,and EPR Study

The [n-Bu₄N]₂[Fe₂(-S₂O₃)₂(NO)₄] complex was studied using X-ray diffraction analysis, cyclic voltammetry, and EPR spectroscopy, and its crystal structure was determined. The redox properties of the [Fe₂(-S₂O₃)₂(NO)₄]^2–anion in CH₃CN and CH₂Cl₂solutions were studied. An addition of excess reducer (sodium thiosulfate) to the thiosulfate complex was shown to produce an EPR signal with g= 2.03 typical of the mononuclear iron dinitrosyl complexes. The mechanism for [Fe₂(-S₂O₃)₂(NO)₄]^2–reduction was suggested.