Insulating tubular BN sheathing on semiconducting nanowires

An effective method was developed for generation of insulating tubular boron nitride (BN)-sheathed nanostructures. ZnS nanowires and multilayered Si-SiO2 nanowires were successfully sheathed with insulating tubular BN-forming nanocables. Both the semiconductor nanowire cores and the BN sheaths are crystalline with well-uniform morphologies.     

Kinetics of the grignard reaction with silanes in diethyl ether and ether-toluene mixtures

Kinetics of the reactions of butylmagnesium chloride and phenylmagnesium bromide with tetraethoxysilane and methyltrichlorosilane was investigated in diethyl ether and diethyl ether-toluene mixtures. Replacement of ether by toluene significantly accelerates the reaction with alkoxysilanes, while no effect was found for the reaction with chlorosilanes. We established that the reaction with alkoxysilanes consists of replacement of a donor molecule at the magnesium center by the silane followed by subsequent rearrangement of the complex to products through a four-center transition state. Chlorosilanes react differently without solvent molecule replacement but also via a four-center transition state. Large negative activation entropies are consistent with formation of cyclic transition states. Small activation enthalpy values together with remarkable exothermicity point to early transition states of the reactions.     

Synthesis of 2,3,9,10,16,17,23,24-Octaalkynylphthalocyanines and the Effects of Concentration and Temperature on Their (1)H NMR Spectra

The syntheses of 3,4- and 4,5-diiodophthalonitriles are described. Coupling of the latter compound with Pd(PPh(3))(2)Cl(2) and 1-octyne, 1-heptyne, 1-hexyne, 1-pentyne, and 3,3-dimethyl-1-butyne gave a series of 4,5-dialkynylphthalonitriles. Hydrogenation of 4,5-bis(1-pentynyl)phthalonitrile and 4,5-bis(3,3-dimethyl-1-butynyl)phthalonitrile gave 4,5-dipentylphthalonitrile and 4,5-bis(3,3-dimethylbutyl)phthalonitriles. Condensation of the dialkynylphthalonitriles with lithium 1-pentoxide in 1-pentanol gave 2,3,9,10,16,17,23,24-octaalkynylphthalocyanines, while intervention of the intermediate dilithium phthalocyanines with zinc acetate gave the related zinc(II) phthalocyanines. (1)H NMR spectroscopy of these octaalkynylphthalocyanines exhibited large chemical shifts (1-2 ppm) of the internal and aromatic protons at concentrations ranging from 10(-)(2) to 10(-)(5) M and at temperatures from 27 to 147 degrees C. The effects of aggregation phenomena are discussed. The importance of reporting concentration and temperature values for NMR spectra of phthalocyanines is stressed.     

Platinum nanoparticles generated in functionality-enhanced reaction media based on polyoctadecylsiloxane with long-chain functional modifiers

Functionality-enhanced nanostructured matrices generated by intercalating polyoctadecylsiloxane (PODS) with octadecene (ODC) or octadecylamine (ODA) are employed as reaction media in which to grow Pt nanoparticles. Small-angle X-ray scattering (SAXS) signatures confirm that the amphiphilic PODS matrix orders into lamellae with a periodicity (d) of 5.24 nm, which corresponds to the siloxy bilayer and a double layer of alkyl tails. The regular packing of the hydrophobic tails becomes distorted upon introduction of ODC or ODA. Incorporation of K[(C2H4)PtCl3].H2O (a Zeise salt) into the PODS/ODC matrix, followed by reduction of the Pt ions by NaBH4 or H2, results in the localization of Pt compounds and nanoparticles along the siloxy bilayers, which remain dimensionally unchanged. Electron density profiles deduced from PODS/ODA, however, provide evidence for considerable structural reorganization upon metalation with H2PtCl6.6H2O. In this case, the siloxy bilayers broaden due to the presence of PtCl62- ions, and the hydrophobic layers become distorted due to the formation of (PtCl62-)(ODAH+)2 complexes. Subsequent reduction by NaBH4 restores the inherent PODS organization, while H2 reduction partially preserves the distorted matrix, indicating that some Pt nanoparticles form in close proximity to the siloxy bilayer. Transmission electron microscopy reveals that relatively monodisperse Pt nanoparticles measuring approximately 1 nm in diameter are located along the siloxy bilayers, whereas anomalous SAXS further indicates that nanoparticles form aggregates of comparable size to d within the PODS double layers.     

Catalyzed collapse and enhanced hydrogen storage of BN nanotubes

The novel morphology of BN nanotubes with a collapsed structure has been discovered by a metal-catalyzed treatment. The collapse causes the dramatic enlargement of a specific surface area of BN nanotubes and remarkably enhances the hydrogen storage capacity of BN nanotubes.     

Reactions of Fused Carbonyl-containing Spirodihydrofurans with Hydrogen Sulfide and Acids

Reactions were studied of fused spirodihydrofurans originating from 1,3-cyclohexanedione with hydrogen sufide arising in situ. Depending on a substituent at the atom C ³ of the heterocycle the reaction ended by thionation of the conjugated carbonyl group followed by heterocyclization involving the spirodimedonyl fragment. A quantum-chemical forecasting of the protonation stages of substrates and their thionated analogs was performed applying the semiempirical PM3 procedure. A probable mechanism of investigated transformations of the spirodihydrofurans was suggested.     

Crystal structure of 1,2-bis-(phenylseleno)-1,2-dichlorethene

Vladimir State Pedagogical Institute. Institute for Elementorganic Compounds, Russian Academy of Sciences. Irkutsk Institute for Organic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 4, pp. 153–154, July–August, 1992.     

Triterpene glycosides from Kalopanax septemlobum. VII. Minor glycosides from stems of Kalopanax septemlobum var. maximowiczii and Kalopanax septemlobum var. typicum

Sixteen triterpene glycosides, three of which were new, hederagenin 28-O-β-D-glucuronopyranosyl ester and 28-O-β-D-gentiobiosyl ester and oleanolic acid 3-O-α-L-arabinopyranoside, were isolated from stem bark of Kalopanax septemlobum. The glycoside contents in stem bark of two varieties, maximowiczii and typicum, were compared. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 49–53, January–February, 2006.     

Measurement of adsorption heats of nitrogen on metal nitrides

Adsorption heats q and activation energies of the nitrogen exchange on several metal nitrides have been compared. For the systems capable of changing readily their composition upon varying conditions, the isotope exchange is suggested to be the most reliable method of the determination of q.

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Design of pure heterodinuclear lanthanoid cryptate complexes

Heterolanthanide complexes are difficult to synthesize owing to the similar chemistry of the lanthanide ions. Consequently, very few purely heterolanthanide complexes have been synthesized. This is despite the fact that such complexes hold interesting optical and magnetic properties. To fine-tune these properties, it is important that one can choose complexes with any given combination of lanthanides. Herein we report a synthetic procedure which yields pure heterodinuclear lanthanide cryptates LnLn*LX₃ (X = NO₃⁻ or OTf⁻) based on the cryptand H₃L = N[(CH₂)₂N CH–R–CH N–(CH₂)₂]₃N (R = m-C₆H₂OH-2-Me-5). In the synthesis the choice of counter ion and solvent proves crucial in controlling the Ln–Ln* composition. Choosing the optimal solvent and counter ion afford pure heterodinuclear complexes with any given combination of Gd(iii)–Lu(iii) including Y(iii). To demonstrate the versatility of the synthesis all dinuclear combinations of Y(iii), Gd(iii), Yb(iii) and Lu(iii) were synthesized resulting in 10 novel complexes of the form LnLn*L(OTf)₃ with LnLn* = YbGd 1, YbY 2, YbLu 3, YbYb 4, LuGd 5, LuY 6, LuLu 7, YGd 8, YY 9 and GdGd 10. Through the use of ¹H, ¹³C NMR and mass spectrometry the heterodinuclear nature of YbGd, YbY, YbLu, LuGd, LuY and YGd was confirmed. Crystal structures of LnLn*L(NO₃)₃ reveal short Ln–Ln distances of ∼3.5 Å. Using SQUID magnetometry the exchange coupling between the lanthanide ions was found to be anti-ferromagnetic for GdGd and YbYb while ferromagnetic for YbGd.

We present a synthetic strategy to prepare the first heterodinuclear lanthanide(iii) cryptate complexes. The cryptate design ensures that the complexes are stable in solution for days. The exchange coupling in YbYb, GdGd and YbGd is investigated.