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Metal Precursor (metal + precursor)
Selected AbstractsTripyrrinatocadmium Complexes: Enforcing Supramolecular Aggregation by a Large IonEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2007Martin Bröring Abstract A newly developed method for the preparation of free base tripyrrin ligands HTrpy by cyanide-promoted demetalation of nickel chelates TrpyNiNCO was used in order to explore the chemistry of cadmium tripyrrins TrpyCdX with a variety of anionic co-ligands X. The introduction of the large CdII ion into the tripyrrin N3 coordination site was accomplished by the use of cadmium acetate as the metal precursor. Ligand exchange experiments using sodium salts of different anions disclose a marked tendency for pentacoordination, which is achieved either by the formation of chelates or of 1D coordination polymers that form as a consequence of the size of the central metal. The attempted introduction of chlorido, iodido, or cyanato ligands thus leads mainly to decomposed material, while the use of 1,1,1-trifluoracetylacetonate, salicylate, and acetate ligands results in stable, pentacoordinate and monomeric complexes with the external ligand bound as a four- or six-membered O,O -chelate ring. With the pseudohalogenido ligands thiocyanate, selenocyanate, and azide as well as with the weakly coordinating trifluoroacetate 1D coordination polymers with a variety of chain structures were obtained and investigated by X-ray diffraction studies. Interestingly TrpyCdN3 is present in the crystal as a coordinatively and hydrogen-bonded methanol adduct with a dimeric repeating subunit. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Aerogel and Xerogel Catalysts Based on ,-Alumina Doped with Silicon for High Temperature ReactionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2005Aurelien Florin Popa Abstract Numerous materials (supports and catalysts) based on alumina have been prepared using the sol-gel process and carbon dioxide supercritical drying. In this work two types of solids, i.e. xerogels and aerogels, were systematically compared and a way of introducing platinum metal with a content of 5% percent by weight was examined. The structural data, the surface area, Pt dispersion and catalytic activity for the decomposition of the propellant were measured for the various samples. The (Al2O3)0.88(SiO2)0.12 samples prepared show very interesting porosity values, especially for the aerogel. For this reason, they were chosen as supports for the synthesis of 5 wt% platinum on alumina catalysts. The results presented in this work allowed us to obtain an overall view of the influence of the preparation mode on the properties of platinum on alumina supported catalysts. The dispersion of the metal phase is directly dependent on the specific surface of the support. A significant value for the surface area implies a large amount of centers for interaction with the metal precursor and, consequently, the appearance of more centres of simultaneous germination. Although aerogels obtained by carbon dioxide supercritical drying always show superior properties compared with xerogels, for catalytic decompositions the xerogels still remain superior. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Enantioselective CpRu-Catalyzed Carroll Rearrangement , Ligand and Metal Source ImportanceEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 34 2008David Linder Abstract The addition of unstabilized carbonyl nucleophiles to unsymmetrical allyl-metal fragments still represents a challenge to generate stereogenic centers enantio- and regioselectively. In this context, the decarboxylative Carroll rearrangement of allyl ,-keto esters is particularly interesting, since chiral ,,,-unsaturated ketones are obtained. Herein, we show that CpRu half-sandwich complexes can, with selected enantiopure pyridine-monooxazoline ligands, catalyze this transformation and afford complete conversions along with good levels of regioselectivity and enantioselectivity. Even more challenging (electron-poor) substrates react (up to 86,% ee, branched/linear ratio , 97:03). In addition, the use of an air-stable metal precursor, namely [CpRu(,6 -naphthalene)][PF6], allows the reaction to be carried out reproducibly evenin non-anhydrous THF with a catalyst loading as low as2 mol-%. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] [Ru(0)]@SiO2 and [RuO2]@SiO2 Hybrid Nanomaterials: From Their Synthesis to Their Application as Catalytic Filters for Gas SensorsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Victor Matsura Abstract [Ru(0)]@SiO2 and [RuO2]@SiO2 hybrid nanomaterials are produced following a facile method consisting of the synthesis of size-controlled ruthenium nanoparticles as elemental bricks. This route takes advantage of the organometallic approach and the use of a bifunctional ligand for the synthesis of ruthenium nanoparticles from [Ru(COD)(COT)](COD,=,1,3-cyclooctadiene, COT,=,1,3,5-cyclooctatriene) as metal precursor and (PhCH2)2N(CH2)11O(CH2)3Si(OEt)3 (benzenemethanamine) as stabilizer. Hydrolysis and polycondensation steps via a sol,gel approach lead to the formation of the silica materials containing the metal nanoparticles. A final calcination step in air at 400,°C yields the [RuO2]@SiO2 nanocomposites. Such hybrid nanomaterials display a good dispersion of the nanoparticles inside the silica matrix and interesting porosity properties making them attractive materials for catalytic applications. This is shown by using [RuO2]@SiO2 hybrid nanomaterials as catalytic filters for gas sensors. [source] Nanocrystal Shape Control: Synthesis and Structure,Property Correlation in Shape-Controlled ZnO Nanoparticles Prepared by Chemical Vapor Synthesis and their Application in Dye-Sensitized Solar Cells (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Mater. Chemical vapor synthesis is a convenient one-step synthesis process for the production of nanocrystalline powders. On page 875, Bacsa et al. report that by controlled variation of experimental parameters, tetrapods (as in image) or spherical ZnO nanocrystals can be selectively obtained directly from Zn metal precursor. Shape control leads to improved optical properties and a better performance when applied as electrodes in dye sensitized solar cells. [source] Efficient iridium and rhodium-catalyzed asymmetric transfer hydrogenation using 9-amino(9-deoxy) cinchona alkaloids as chiral ligandsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2006Wei He Abstract 9-Amino (9-deoxy) cinchona alkaloids, derived from natural cinchona alkaloids, were applied in asymmetric transfer hydrogenation in both iridium and rhodium catalytic systems using i -propanol as the hydrogen source. A series of aromatic ketones was examined, and good to excellent conversions and enantioselectivities were observed. The best results were achieved using 9-amino(9-deoxy) epicinchonine 2a as the ligand and [Ir(COD)Cl]2 as the metal precursor, and for the isobutylphenone, the conversion and enantioselectivity were obtained in 90 and 97% e.e. respectively. Copyright © 2006 John Wiley & Sons, Ltd. [source] N,N -Dimethylformamide as a Reaction Medium for Metal Nanoparticle SynthesisADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Isabel Pastoriza-Santos Abstract The versatility of wet chemical methods has rendered them extremely popular for the preparation of metal nanoparticles with tailored size and shape. This Feature Article reviews the use of N,N -dimethylformamide (DMF) for the reduction of metal salts, mainly Au and Ag, while also acting as a solvent. Apart from describing the ability of DMF to reduce metal salts, the effect of different parameters, such as the concentration of capping agent and metal precursors, the presence of preformed seeds acting as catalysts or their crystalline structure, on particle morphology are analyzed. Published reports on the use of different capping agents are summarized, with particular emphasis on the role of poly(vinylpyrrolidone) to determine the morphology of the particles. Finally, a brief overview is provided on the modulation of the optical response in DMF-based metal nanoparticle colloids with tunable size and shape. [source] Ultrathin Te Nanowires: An Excellent Platform for Controlled Synthesis of Ultrathin Platinum and Palladium Nanowires/Nanotubes with Very High Aspect RatioADVANCED MATERIALS, Issue 18 2009Hai-Wei Liang Uniform ultrathin Pt nanotubes, Pt and Pd nanowires with diameters of only several nanometers and a very-high aspect ratio of ,10,000 can be fabricated using ultrathin Te nanowires as both reducing agent and sacrificial template in ethylene glycol. The valences of metal precursors have a crucial effect on the morphology of the nanostructures. [source] Influence of the stacking order on structural features of the Cu-In-Ga-Se precursors for formation of Cu(In,Ga)Se2 thin films prepared by thermal reaction of InSe/Cu/GaSe alloys to elemental Se vapor and diethylselenide gasPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006F.B. Dejene Abstract A novel partway for the fabrication of copper-indium (gallium) diselenide has been developed. This two-stage process consists of the formation of Cu-In-(Ga)-Se precursors and subsequent selenization to form CuIn(Ga)Se2. In this work, we have investigated and compared the possible interactions in Cu-In-Ga-Se systems, using sequentially stacked precursors premixed with Se, in order to get a better understanding of the Cu(In,Ga)Se2 thin film formation. Comparison of these SEM micrographs clearly revealed that the surface morphologies and hence surface roughness of the resulting Cu(In,Ga)Se2 absorber films were significantly influenced by the structure of the precursor films prior to selenization. XRD analyses revealed the presence of a graded CuIn1-xGaxSe structure, irrespective of the stacking order during the precursor formation step for samples selenized using elemental Se vapor. It was established that distinct from the case of using Se vapor, a single-phase Cu(In,Ga)Se2 films were obtained by diethylselenide (DESe) selenization from Cu-In-Ga metal precursors premixed Se irrespective of the stacking order during the precursor formation step. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A comparative study of defect states in evaporated and selenized CIGS(S) solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 7 2005P. K. Johnson Abstract Current-voltage, admittance spectroscopy, and drive-level capacitance profiling measurements were taken on Cu(In1,xGax)(Se1,ySy)2 solar cell devices. The devices were made using two different types of absorbers. One set of absorbers was deposited via physical vapor deposition, while the other set of absorbers was made by selenization of metal precursors. Additionally, each type of absorber was completed with one of two different types of buffer treatments: a CdS layer or a cadmium partial electrolyte surface modification. The devices with the evaporated absorbers had larger values of VOC, higher carrier densities, lower densities of trapping defects, and likely shallower gap states. Results were qualitatively similar for the CdS and partial electrolyte buffers. Copyright © 2005 John Wiley & Sons, Ltd. [source] The Atomic Layer Deposition of HfO2 and ZrO2 using Advanced Metallocene Precursors and H2O as the Oxygen Source,CHEMICAL VAPOR DEPOSITION, Issue 11-12 2008Charles L. Dezelah IV Abstract The atomic layer deposition (ALD) of HfO2 and ZrO2 thin films is investigated using (MeCp)2HfMe2, (MeCp)2Hf(OMe)(Me), (MeCp)2ZrMe2, and (MeCp)2Zr(OMe)(Me) as the precursors at deposition temperatures between 300 and 500,°C, with water vapor as the oxygen source. A self-limiting growth mechanism is confirmed at 350,°C for all the metal precursors examined. The processes provide nearly stoichiometric HfO2 and ZrO2 films with carbon and hydrogen concentrations below 0.5 and 1.0 at.-%, respectively, for representative samples. All films are polycrystalline as deposited, and possess a thin interfacial SiO2 layer. The capacitance-voltage (C - V) and current density-voltage (I - V) behavior is reported and discussed for capacitor structures containing films from this study. [source] Ultrasonochemical-assisted fabrication and evaporation- induced self-assembly (EISA) of POSS-SiO2@Ag core/ABA triblock copolymer nanocomposite filmPOLYMER COMPOSITES, Issue 9 2010Murugan Veerapandian Poly(ethylene glycol)-octafunctionalized polyhedral oligomeric silsesquioxane (POSS) (Mn = 5576.6 g/mol) alloying agent stabilized amphiphilic silica@silver metalloid nanocomposite blended with a triblock copolymer poly(p -dioxanone- co -caprolactone)- block -poly(ethylene oxide)- block -poly(p -dioxanone- co -caprolactone) (POSS-SiO2@Ag/PPDO- co -PCL- b -PEG- b -PPDO- co -PCL) has been synthesized in both water and in organic medium utilizing ultrasonochemical reaction. The POSS stabilized pre-made metalloid was successfully dispersed in amphiphilic PPDO- co -PCL- b -PEG- b -PPDO- co -PCL (ABA) triblock copolymer matrix of molecular weight 45.9 × 104 g/mol. The mechanism of synthesis of high concentration of SiO2@Ag nanocomposite from TEOS/AgNO3 (in the presence of NH4OH as catalyst/NaBH4 as reductant) nonmetal/metal precursors and the successful EISA of POSS-SiO2@Ag/ABA nanocomposite into films has been discussed. The successful synthesis of metalloid nanocomposite was morphologically accessed by field emission-scanning electron microscopy, transmission electron microscopy and atomic force microscopy. Surface plasmon resonance was ensured from UV,visible spectral analysis. Identity and the crystallinity of as prepared nanocomposite were studied by X-ray diffractometer. Structural and luminescence properties of the nanocomposite were examined by Fourier transform infrared spectroscopy and photoluminescence. Thermogravimetric analysis was carried out to study the thermal stability of the resulting hybrid nanocomposite. The resultant inorganic,organic nanocomposite can be easily suspended in water and would be useful in variety of applications. POLYM. COMPOS., 31:1620,1627, 2010. © 2009 Society of Plastics Engineers [source] | |||||||||||||