Search results for "complex"
showing 10 items of 5889 documents
Chemistry of lanthanide–metal carbonyl systems: the ytterbium–chromium carbonyls interaction
2001
Abstract The interaction of the chromium carbonyl hydrides HCr2(CO)10− or HCr(CO)5− with Yb(acac)3·3H2O has been investigated, and the experimental conditions leading to the isolation of ytterbium–chromium carbonyl complex species are reported. Formulation of the coordination compounds produced by such interactions has been proposed on the basis of analytical data and IR spectroscopy.
"Table 2" of "Measurement of differential Z / gamma* + jet + X cross sections in p anti-p collisions at s**(1/2) = 1.96-TeV"
2008
Measured cross section as a function of the jet rapidity.
Determination at low ppm levels of dithiocarbamate residues in foodstuff by vapour phase-liquid phase microextraction-infrared spectroscopy
2010
Abstract A methodology based on the vapour phase (VP) generation of carbon disulphide from non-volatile dithiocarbamate compounds has been developed for determination of pesticide residues in foodstuff at low ppm levels. The method involves a selective reaction combined with liquid phase microextraction (LPME) and transmission infrared measurements. The use of a home made transmission cell improved the detection limits (LOD) compared to the use of attenuated total reflectance measurements by a factor of approximately 80. Using the most appropriate experimental conditions for the CS2 generation and LPME preconcentration, the precision of the methodology, expressed as the relative standard de…
Zirconium & Hafnium: Organometallic ChemistryBased in part on the article Zirconium & Hafnium: Organometallic Chemistry by Bernard Gautheron,…
2006
This review considers the main aspects of organometallic chemistry of zirconium and hafnium during the last 10 years. It is complementary to the first edition of Encyclopedia of Inorganic Chemistry. The material is presented in two major parts divided in five and three sections respectively. The first part is devoted to syntheses: the first section, by far the largest, covers in a systematic manner bis and mono cyclopentadienyl complexes with +4, +3, and +2 oxidation states and more especially constrained-geometry (CG) complexes, cationic complexes, and anionic or zwitterionic 18-electron complexes; unusual coordination geometries at carbon stabilized by group 4 metallocenes are presented i…
Complexes of titanium and zirconium containing a tridentate linked amido–cyclopentadienyl ligand with a soft donor group: synthesis, structure, and e…
1999
Abstract Group 4 metal complexes M(η5:η1-C5R4SiMe2NCH2CH2SMe)Cl2 (R=H, M=Ti; R=Me, M=Ti, Zr) containing the thioether-functionalized linked amido–cyclopentadienyl ligand were synthesized and characterized by 1H- and 13C-NMR spectroscopy, mass spectrometry, and elemental analysis. The crystal structures of the complexes Ti(η5:η1-C5H4SiMe2NCH2CH2SMe)Cl2 and Zr(η5:η1:η1-C5Me4SiMe2NCH2CH2SMe)Cl2 were determined by single-crystal X-ray diffraction studies. The titanium complex is a conventional three-legged piano-stool molecule without an intramolecular interaction between the sulfur donor group and the titanium center, whereas the zirconium complex adopts a trigonal bipyramidal structure, with …
Magnesium chloride modified with organoaluminium compounds as a support of the zirconocene catalyst for ethylene polymerisation
2004
Abstract This work describes the influence of the modification of the MgCl2(THF)2 and MgCl2 magnesium supports with the AlEt2Cl, MAO, AlEt3, AlMe3, and AlEt2Cl alkylaluminium compounds on heterogenisation of the bis(cyclopentadienyl) zirconium(IV) dichloride Cp2ZrCl2 catalyst. It was found that only the MgCl2(THF)2 support modified with AlEt2Cl gave the heterogeneous catalyst. On the contrary, application of a magnesium carrier modified by AlEt3, AlMe3, and MAO compounds only results in a homogeneous zirconocene catalyst.
Heterogeneous zirconocene catalyst on magnesium support MgCl2(THF)2 modified by AlEt2Cl for ethylene polymerisation
2005
Abstract The heterogeneous bis(cyclopentadienyl)zirconium(IV) dichloride catalyst of the composition MgCl2(THF)/(AlEt2Cl)0.34/(Cp2ZrCl2)0.01 as determined by FTIR, XRD, and AAS analyses was synthesised and, after activation by MAO, applied for ethylene polymerisation. The catalyst turned out to be stable and more active than those magnesium supported catalysts already known from the literature. The polyethylene produced has a relatively high molecular weight (Mw > 200,000 g/mol), a narrow and monomodal molecular weight distribution (MWD = 2.4), a bulk density of about 180 g/dm3, and monomodal particle size distribution. Application of a ternary Al(i-Bu)3/MAO/B(C6F5)3 activator decreased the…
Novel group 4b ansa-metallocene complexes with the shortest bridge: [1,1′-isopropylydene-3,3′-di-t.Bu-bis(η5-cyclopentadienyl)] Ti and Zr dichlorides
1997
Abstract Reaction of [1,1′-isopropylidene-3,3′-di-tert.butyl-bis(η5-cyclopentadienide)] dilithium with TiCl3, followed by treatment with HCl, and ZrCl4 in various solvent mixtures in the temperature range 0–50°C gives corresponding ansa-metallocene dichlorides as mixtures of the anti/syn-isomers, 1:1. The crystal and molecular structures of three of the four isomers were determined, i.e. rac(anti)-[1,1′-isopropylidene-3,3′-di-tert.butyl-bis(η5-cyclopentadienyl)]TiCl2, space group B2/b, rac(anti)-[1,1′-isopropylidene-3,3′-di-tert.butyl-bis(η5-cyclopentadienyl)]ZrCl2, space group P212121, and meso(syn)-1,1′-[isopropylidene-3,3′-di-tert.butyl-bis(η5-cyclopentadienyl)]ZrCl2, space group P21/n.
Zaleplon displays a selectivity to recombinant GABAA receptors different from zolipdem, zopiclone and benzodiazepines
1999
A chemically heterogeneous group of compounds acts at the benzodiazepine (BZ) recognition site of the γ-aminobutyric acid type A (GABAA) receptor complex. Whereas most 1,4-BZs recognize all GABAA/BZ receptors with similar affinity, other compounds differentiate between the large number of native GABAA receptors which assemble from the more than 14 known subunits. Here we describe the in vitro binding properties of the BZs lorazepam and Ro 15-4513 plus the three hypnotics zaleplon, zolpidem and zopiclone to eight receptors subtypes. Lorazepam fits well into the general shceme for other 1,4-BZs with respect to its receptor subtype selectivity in spite of its clinically different use. Zaleplon…
Data structures and algorithms for topological analysis
2014
International audience; One of the steps of geometric modeling is to know the topology and/or the geometry of the objects considered. This paper presents different data structures and algorithms used in this study. We are particularly interested by algebraic structures, eg homotopy and homology groups, the Betti numbers, the Euler characteristic, or the Morse-Smale complex. We have to be able to compute these data structures, and for (homotopy and homology) groups, we also want to compute their generators. We are also interested in algorithms CIA and HIA presented in the thesis of Nicolas DELANOUE, which respectively compute the connected components and the homotopy type of a set defined by…