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61.
Dinuclear nickel complexes with bidentate N,O ligands: synthesis, structure, and catalytic oligomerization of ethylene 总被引:2,自引:0,他引:2
The new dicationic dinuclear complexes [Ni(micro-Cl)(2)(N,OH)(2)]Cl(2) (11, N,OH = 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-propan-2-ol; 12, N,OH = 2-pyridin-2-yl-propan-2-ol) were prepared in good yields and evaluated as precatalyts in the oligomerization of ethylene, using MAO or AlEtCl(2) as cocatalyst. These paramagnetic complexes were characterized by single-crystal X-ray diffraction in the solid state and in solution with the help of the Evans method, which revealed agreement between the octahedral coordination spheres found in solution and in the solid state. The N donor atoms of each chelating ligand are in mutual cis position, and the OH donors are mutually trans situated. Selectivities for 1-butene within the C(4) fraction of 61% (11) and 58% (12) were observed in the presence of 200 equiv of MAO, but better turnover frequencies (28 300 (11) and 20 400 (12) mol of C(2)H(4)/(mol of Ni.h)) were obtained when 800 equiv of MAO was used. In the presence of 6 equiv of AlEtCl(2), the activities were considerably increased, up to 174 300 (11) and 97 100 (12) mol of C(2)H(4)/(mol of Ni.h), and the selectivity for C(4) olefins was 70% and 64%, respectively. 相似文献
62.
Brackmann C Nygren J Bai X Li Z Bladh H Axelsson B Denbratt I Koopmans L Bengtsson PE Aldén M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(14):3347-3356
Formaldehyde (CH2O) is an important intermediate species in combustion processes and it can through laser-induced fluorescence measurements be used for instantaneous flame front detection. The present study has focussed on the use of the third harmonic of a Nd:YAG laser at 355 nm as excitation wavelength for formaldehyde, and different dimethyl ether (C2H6O) flames were used as sources of formaldehyde in the experiments. The investigations included studies of the overlap between the laser profile and the absorption lines of formaldehyde, saturation effects and the potential occurrence of laser-induced photochemistry. The technique was applied for detection of formaldehyde in an internal combustion engine operated both as a spark ignition engine and as a homogenous charge compression ignition engine. 相似文献
63.
Aurore Boscher Cédric GuignardTerence Pellet Lucien HoffmannTorsten Bohn 《Journal of chromatography. A》2010,1217(41):6394-6404
A simple multi-residue method was developed for detecting and quantifying 33 analytes from 13 classes of antibiotics (tetracyclines (3), quinolones (7), penicillins (3), ionophore coccidiostats (7), macrolides (3), sulfonamides (1), quinoxalines (2), phenicols (2), lincosamides (1), diaminopyrimidines (1), polypeptides (1), streptogramins (1) and pleuromutilins (1)) in animal feeds. Extraction and clean-up procedures were optimized with spiked piglet feed. Samples were extracted by ultrasonic-assisted extraction with a mixture of methanol/acetonitrile/McIlvaine buffer at pH 4.6 (37.5/37.5/25, v/v/v) containing 0.3% of EDTA-Na2, followed by a clean up using a dispersive solid-phase extraction (d-SPE) with PSA (primary secondary amine). Detection of antibiotics was achieved by liquid chromatography-electrospray tandem mass spectrometry (LC–ESI-MS/MS) within 28 min using both positive and negative ESI mode. Average recoveries ranged from 51% (oxytetracycline) to 116% (tilmicosin) with associated relative standard deviations of 7.3% and 9.0% and an overall mean of 87%. Limits of quantification ranged from 3.8 ng g−1 (lincomycin) to 65.0 ng g−1 (bacitracin). Following optimization, the method was further verified for bovine and lamb feedingstuffs; negative matrix effects were evaluated and overcome by a standard addition method. 相似文献
64.
Christian Klemps Dipl.‐Chem. Elina Payet Lionel Magna Dr. Lucien Saussine Dr. Xavier F. Le Goff Dr. Pascal Le Floch Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(33):8259-8268
Chromium(III) complexes bearing R′N(CH2PR2)2 (PCNCP) ligands have been prepared. Upon activation with methylaluminoxane, these complexes proved to be effective in the selective tri‐ and tetramerization of ethylene. The formation of either 1‐hexene or 1‐octene was found to be highly dependent on the steric bulk of the substituents R on the phosphine moieties. This observation was rationalized by using density functional theory calculations on selected steps of the metallacyclic mechanism of the ethylene oligomerization reaction. 相似文献
65.
François-Xavier d'Abzac Anne-Magali Seydoux-Guillaume Jérôme Chmeleff Lucien Datas Franck Poitrasson 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(9-10):671-680
The characteristics of infra red femtosecond laser-induced aerosols are studied for monazite (LREE, Th(PO4)) ablation and correlations are established with inductively coupled plasma-mass spectrometry (ICP-MS) signals. Critical parameters are tested within wide ranges of values in order to cover the usual laser ablation -ICP-MS analysis conditions: pulse energy (0.15 < E0 < 1 mJ/pulse), pulse width (60 < τ < 3000 fs), ablation time (t ≤ 10 min) and transport length (l ≤ 6.3 m). Transmission electron microscopy reveals that aerosols are made of agglomerates of ~ 10 nm particles and 20–300 nm phosphorus depleted condensed spherical particles. These structures are not affected by any laser ablation parameter. Particle counting is performed using electronic low pressure impaction. Small changes on particle size distribution are noticed. They may be induced either by a peak of ablation rate in the first 15 s at high fluence (larger particles) or the loss of small particles during transport. We found a positive correlation between I (ICP-MS mean signal intensity in cps) and N (particle density in cm? 3) when varying E0 and t, suggesting that N is controlled by the irradiance (P0 in W·cm? 2). Elemental ratio measurements show a steady state signal after the initial high ablation rate (mass load effect in the plasma torch) and before a late chemical fractionation, induced by poor extraction of bigger, early condensed spherical particles from the deepening crater. Such chemical fractionation effects remain within uncertainties, however. These effects can be limited by monitoring E0 to shorten the initial transient state and delay the attainment of an unfavorable crater aspect ratio. Most adopted settings are for the first time deduced from aerosol characteristics, for infra red femtosecond laser ablation. A short transport (l < 4.0 m) limits the agglomeration of particles by collision process along the tube. Short τ is preferred because of higher P0, yet no benefit is found on ICP-MS signal intensity under 200 fs. Under such pulse widths the increased particle production induces more agglomeration during transport, thereby resulting in higher mass load effects that reduce the ionization efficiency of the plasma torch. Thus, pulse energy must be set to get an optimal balance between the need for a high signal/background ratio and limitation of mass load effects in the plasma torch. 相似文献
66.
Sebastian Wendl Lucien Eisenburger Dr. Philipp Strobel Daniel Günther Dr. Jonathan P. Wright Dr. Peter J. Schmidt Prof. Dr. Oliver Oeckler Prof. Dr. Wolfgang Schnick 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(32):7292-7298
The nitridophosphates AEP8N14 (AE=Ca, Sr, Ba) were synthesized at 4–5 GPa and 1050–1150 °C applying a 1000 t press with multianvil apparatus, following the azide route. The crystal structures of CaP8N14 and SrP8N14 are isotypic. The space group Cmcm was confirmed by powder X-ray diffraction. The structure of BaP8N14 (space group Amm2) was elucidated by a combination of transmission electron microscopy and diffraction of microfocused synchrotron radiation. Phase purity was confirmed by Rietveld refinement. IR spectra are consistent with the structure models and the chemical compositions were confirmed by X-ray spectroscopy. Luminescence properties of Eu2+-doped samples were investigated upon excitation with UV to blue light. CaP8N14 (λem=470 nm; fwhm=1380 cm−1) and SrP8N14 (λem=440 nm; fwhm=1350 cm−1) can be classified as the first ultra-narrow-band blue-emitting Eu2+-doped nitridophosphates. BaP8N14 shows a notably broader blue emission (λem=417/457 nm; fwhm=2075/3550 cm−1). 相似文献
67.
68.
Hill [6] showed that the largest cap in PG(5,3) has cardinality 56. Using this cap it is easy to construct a cap of cardinality 45 in AG(5,3). Here we show that the size of a cap in AG(5,3) is bounded above by 48. We also give an example of three disjoint 45-caps in AG(5,3). Using these two results we are able to prove that the Steiner triple system AG(5,3) is 6-chromatic, and so we exhibit the first specific example of a 6-chromatic Steiner triple system. 相似文献
69.
70.
Paul Gonnard François Bauer Michel Troccaz Yves Fetiveau Lucien Eyraud 《Applied Physics A: Materials Science & Processing》1974,3(4):299-305
Hydrostatic pressure acting on doped lead titanate-zirconate materials with a considerable proportion of zirconium induces a phase transition between ferroelectric and antiferroelectric states, which causes the previously poled specimens to depolarize. Measurements using a capacitance and those made on short-circuited specimens allow us to draw phase diagrams of the following types: “pressure-electric field” and “pressure-composition”. A thermodynamic investigation of the phenomenon permits us to define new characteristic coefficients for this type of depolarization. 相似文献