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961.
Zvereva EA Evstigneeva MA Nalbandyan VB Savelieva OA Ibragimov SA Volkova OS Medvedeva LI Vasiliev AN Klingeler R Buechner B 《Dalton transactions (Cambridge, England : 2003)》2012,41(2):572-580
Two synthetic routes-ion-exchange preparation from layered Na(3)Ni(2)SbO(6) at 300 °C and direct solid-state synthesis at 1150 °C resulted in layered Li(3)Ni(2)SbO(6), a cation-ordered derivative from the rocksalt type. The Fddd form reported earlier could not be reproduced. According to the XRD Rietveld analysis, Li(3)Ni(2)SbO(6) is a pseudohexagonal monoclinic structure, C2/m, with a = 5.1828(2) ?, b = 8.9677(3) ?, c = 5.1577(2) ?, β = 109.696(2)°. No Li/Ni mixed occupancy was detected. At high temperatures, the magnetic susceptibility follows the Curie-Weiss law with a positive value of Weiss temperature, ~8 K, indicating a predominance of ferromagnetic interactions. However, Li(3)Ni(2)SbO(6) orders antiferromagnetically at T(N)~ 15 K. The effective magnetic moment is 4.3 μ(B)/f.u. which satisfactorily agrees with theoretical estimations assuming high-spin configuration of Ni(2+) (S = 1). Electron spin resonance (ESR) spectra show single Lorentzian shape line attributed to Ni(2+) ion in octahedral coordination. The absorption is characterized by isotropic temperature independent effective g-factor g = 2.150 ± 0.005. In accordance with the layered honeycomb crystal structure determined for Li(3)Ni(2)SbO(6), the superexchange interaction between Ni(2+) ions through Ni-O-Ni pathways within Ni(2)SbO(6) layers are assumed to be ferromagnetic, while the dominant interaction between layers is antiferromagnetic. 相似文献
962.
Shakirova JR Grachova EV Gurzhiy VV Koshevoy IO Melnikov AS Sizova OV Tunik SP Laguna A 《Dalton transactions (Cambridge, England : 2003)》2012,41(10):2941-2949
The reactions between trinuclear gold complex tppmAu(3)Cl(3) (tppm = tris(diphenylphosphino)methane), arylacetylenes HC(2)C(6)H(4)X and Cu(+) under basic conditions result in formation of the heterometallic complexes [tppm(AuC(2)C(6)H(4)X)(3)Cu](+), X = H (1), COOMe (2), CN (3), OMe (4), NH(2) (5). These compounds belong to one structural motif and consist of the heterometallic {(AuC(2)C(6)H(4)X)(3)Cu} core stabilized by the tridentate phosphine. Compounds 1-5 were characterized by polynuclear NMR and IR spectroscopy, ESI-MS and single-crystal X-ray analysis. Luminescence properties of these complexes have been studied and revealed a substantial red shift of the emission maxima with the increase in the electron donicity of the alkynyl ligands substituents in the 550-680 nm range. The theoretical calculations of the electronic structures showed that variations of the substituents on the alkynyl ligands display very little effect on the molecular structural parameters but show appreciable influence on the orbital energies and luminescence characteristics of the compounds under study. 相似文献
963.
Câmpian MV Perutz RN Procacci B Thatcher RJ Torres O Whitwood AC 《Journal of the American Chemical Society》2012,134(7):3480-3497
Three ruthenium complexes Λ-[cis-Ru((R,R)-Me-BPE)(2)(H)(2)] Λ-R,R-Ru1H(2), Δ-[cis-Ru((S,S)-Me-DuPHOS)(2)(H)(2)] Δ-S,S-Ru2H(2), and Λ-[cis-Ru((R,R)-Me-DuPHOS)(2)(H)(2)] Λ-R,R-Ru2H(2) (1 = (Me-BPE)(2), 2 = (Me-DuPHOS)(2)) were characterized by multinuclear NMR and CD spectroscopy in solution and by X-ray crystallography. The chiral ligands allow the full control of stereochemistry and enable mechanistic studies not otherwise available. Oxidative addition of E-H bonds (E = H, B, Si, C) was studied by steady state and laser flash photolysis in the presence of substrates. Steady state photolysis shows formation of single products with one stereoisomer. Solid state structures and circular dichroism spectra reveal a change in configuration at ruthenium for some Δ-S,S-Ru2H(2)/Λ-R,R-Ru2H(2) photoproducts from Λ to Δ (or vice versa) while the configuration for Λ-R,R-Ru1H(2) products remains unchanged as Λ. The X-ray structure of silyl hydride photoproducts suggests a residual H(1)···Si(1) interaction for Δ-[cis-Ru((R,R)-Me-DuPHOS)(2)(Et(2)SiH)(H)] and Δ-[cis-Ru((R,R)-Me-DuPHOS)(2)(PhSiH(2))(H)] but not for their Ru(R,R-BPE)(2) analogues. Molecular structures were also determined for Λ-[cis-Ru((R,R)-Me-BPE)(2)(Bpin)(H)], Λ-[Ru((S,S)-Me-DuPHOS)(2)(η(2)-C(2)H(4))], Δ-[Ru((R,R)-Me-DuPHOS)(2)(η(2)-C(2)H(4))], and trans-[Ru((R,R)-Me-DuPHOS)(2)(C(6)F(5))(H)]. In situ laser photolysis in the presence of p-H(2) generates hyperpolarized NMR spectra because of magnetically inequivalent hydrides; these experiments and low temperature photolysis with D(2) reveal that the loss of hydride ligands is concerted. The reaction intermediates [Ru(DuPHOS)(2)] and [Ru(BPE)(2)] were detected by laser flash photolysis and have spectra consistent with approximate square-planar Ru(0) structures. The rates of their reactions with H(2), D(2), HBpin, and PhSiH(3) were measured by transient kinetics. Rate constants are significantly faster for [Ru(BPE)(2)] than for [Ru(DuPHOS)(2)] and follow the substrate order H(2) > D(2) > PhSiH(3) > HBpin. 相似文献
964.
Intermolecular Rh-catalyzed reactions of cyclic α-diazocarbonyl compounds with chemoselectivity over β-hydride elimination are described. These methods represent the first general intermolecular reactions of Rh-carbenoids that are selective over tertiary β-C-H bond migration. Successful transformations include cyclopropanation, cyclopropenation, and various X-H insertion reactions with a broad scope of substrates. We propose that the intermolecular approach of substrates to carbenes from acyclic diazo precursors may be relatively slow due to a steric interaction with the ester function, which is perpendicular to the π-system of the carbene. For carbenes derived from five- and six-membered cyclic α-diazocarbonyls, it is proposed that the carbene is constrained to be more conjugated with the carbonyl, thereby relieving the steric interaction for intermolecular reactions, and accelerating the rate of intermolecular reactivity relative to intramolecular β-hydride migration. However, attempts to use α-diazo-β-ethylcaprolactone in intermolecular cyclopropanation with styrene were unsuccessful. It is proposed that the conformational flexibility of the seven-membered ring allows the carbonyl to be oriented perpendicular to Rh-carbene. The significant intermolecular interaction between the carbonyl and approaching substrate is in agreement with the poor ability of α-diazo-β-ethylcaprolactone to participate in intermolecular cyclopropanation reactions. DFT calculations provide support for the mechanistic proposals that are described. 相似文献
965.
J.J.H. Lancastre N. Fernandes F.M.A. Margaça I.M. Miranda Salvado L.M. Ferreira A.N. Falcão M.H. Casimiro 《Radiation Physics and Chemistry》2012,81(9):1336-1340
Polydimethylsiloxane-silicate based hybrid materials have recognized properties (high flexibility, low elastic modulus or high mechanical strength) for which there are a large number of applications in development, such as for the bioapplications field. The hybrids addressed in the present study were prepared by gamma irradiation of a mixture of polydimethylsiloxane (PDMS) with tetraethylorthosilicate (TEOS) and zirconium propoxide (PrZr) without addition of any solvent or other product. The materials are homogeneous, transparent, monolithic and flexible. The structure dependence on the PrZr content is addressed. A combination of X-ray diffraction (XRD) and Infrared Spectroscopy (IR) was used. The results reveal that the polymer in the hybrids prepared with PrZr, in a content≤5 wt%, shows a structure similar to that in the irradiated pure polymer sample. In these samples the presence of ordered polymer regions is clearly found. For samples prepared with higher content of Zr almost no ordered polymer regions are observed. The addition of PrZr plays an important role on polymer conformation in these hybrid materials. 相似文献
966.
Olga Ershova Elisabete V. da Costa António J. S. Fernandes M. Rosário Domingues Dmitry V. Evtuguin Herbert Sixta 《Cellulose (London, England)》2012,19(6):2195-2204
The effect of urea on the cellulose degradation under conditions of alkaline pulping has been studied using purified cellulose powder. The increased cellulose yield in the presence of urea was assigned essentially to the carbamation reactions which were confirmed by elemental analysis, UV-resonance Raman and solid-state 13C nuclear magnetic resonance spectroscopy. The stabilizing effect of urea on the cellulose peeling reactions during heating up period of pulping process was suggested based on kinetic studies and additionally confirmed in model reactions using cellobiose. The reaction products formed in alkaline urea solutions were analysed by tandem electrospray ionization mass spectrometry and the occurrence of Maillard type reactions between reducing end groups of cellobiose and urea were evidenced. Both Maillard type reactions and carbamation of reducing end groups were proposed to be a part of cellulose protection mechanism against peeling under the conditions of alkaline pulping. 相似文献
967.
Ferreira M Legrand FX Machut C Bricout H Tilloy S Monflier E 《Dalton transactions (Cambridge, England : 2003)》2012,41(28):8643-8647
Mixtures of randomly methylated cyclodextrins of various sizes have been evaluated in the rhodium-catalysed hydroformylation of higher olefins in an aqueous biphasic medium. A marked positive non-linear effect on 1-tetradecene conversion is observed when the CD molar ratio in the mixture is modified. The formation of 2:1 ternary inclusion complexes between RAME-CDs and the olefin is supposed to be responsible for the extra conversion observed. 相似文献
968.
MG Uchuskin AS Pilipenko OV Serdyuk IV Trushkov AV Butin 《Organic & biomolecular chemistry》2012,10(36):7262-7265
Indolo[3,2-c]quinolines are pharmacologically attractive class of heterocyclic compounds. The method of their synthesis, based on transformation of furfural, which is a large-scale product of treatment of biomass including agricultural and forestry wastes, has been developed. This method was utilized for the total synthesis of antimalarial alkaloid isocryptolepine and its derivatives. 相似文献
969.
We consider systems of ODEs with the right-hand side being Laurent polynomials in several non-commutative unknowns. In particular,
these unknowns could be matrices of arbitrary size. An important example of such a system was proposed by M. Kontsevich (private
communication). We prove the integrability of the Kontsevich system by finding a Lax pair, corresponding first integrals and
commuting flows. We also provide a pre-Hamiltonian operator which maps gradients of integrals for the Kontsevich system to
symmetries. 相似文献
970.
Comparative ultrastructural study of spermatozoa in some oyster species from the Asian-Pacific Coast
Yurchenko OV 《Micron (Oxford, England : 1993)》2012,43(2-3):365-373
Sperm organization in the oysters Crassostrea gigas, Crassostrea nippona, Crassostrea cf. rivularis and Saccostrea cf. mordax inhabiting Asian Pacific coast was studied. The spermatozoa of all studied species had a number of common morphological characters such as a cup-like acrosome with heterogeneous matrix on its top, an axial rod in the subacrosomal space, a barrel-shaped nucleus, four mitochondria in the midpiece, pericentriolar complexes, and a 9+2-organized flagellum. The spermatozoa of C. cf. rivularis differed from the other species by having cytoplasm processes in the midpiece region. Such structures have never been described in the Ostreidae. Additionally, each species could be identified by the shape and size of sperm compartments (acrosome, nucleus, anterior nuclear fossa). The most significant interspecific difference was found in the size of an anterior nuclear fossa. The smallest anterior nuclear fossa was found in C. cf. rivularis (about 0.24 μm in length reaching about 22% of the nuclear length) while the biggest in C. gigas from the Sea of Japan (about 0.53 μm in length reaching about 46% of the nuclear length). The spermatozoa of C. gigas collected from the Sea of Japan and Taiwan Strait differed significantly in almost all the studied parameters. Since sperm morphology has been successfully used for species differentiation, this suggests the existence of two species rather than two populations. The data obtained indicate the species-specific difference in the sperm ultrastructure within the Ostreidae, which may be identified both ultrastructurally and morphometrically. 相似文献