Vapor synthesis methods

Dihydro-lH-l,5,2-azasilaboroles derive from the 2,5-dihydro-lH-l,2-aza-boroles ( 6.5.3.3) by substitution of the carbon neighboring N by a silicon atom. They may act as four-electron donors using electron density from the C=C double bond and the N atom. The B atom behaves as an acceptor center. Two pathways are known for complex synthesis reaction with a generated transition-metal complex fragment and reaction with metal atoms by the metal-vapor synthesis method. 

The structurally related bright-red crystalline iron compound [Fe2(PF3)6(/i-PF2)2] has been obtained by Timms by metal vapor synthesis (method B) in which iron atoms and PF3 are cocondensed at liquid nitrogen temperature (340, 341). A similar reaction using cobalt... 

The most generally applicable route to diene or triene metal PF3 complexes is via metal vapor synthesis (method D), in which the metal vapors are cocondensed with PF3 and the polyene at liquid nitrogen temperatures. 

More recent developments have utilized metal vapor synthesis (method F) involving cocondensation at low temperature of the metal, cyclopentadiene (or other dienes), and PF3. The hydrido-cyclooctadienyl complex [Cr( 5-C8Hn)(PF3)3H] 125) (see Section IX) made in this fashion exhibits variable-temperature NMR spectra which establish the existence of an exchange between the hydrido atom and a methylenic hydrogen bound to an sp3 carbon adjacent to the diene unit. 

The technique of metal vapor synthesis (method C) is obviously restricted to volatile ligands and has only been utilized so far in the synthesis of [Ni(PF3)2(PH3)2] and [Ni(PF3)3(PH3)]. 

Figure 5 shows high-resolution electron microscope images of several gold nanoparticles formed by this metal vapor synthesis method, often called Solvated Metal Atom Dispersion (SMAD). 

Metal-containing polymers may be produced by various methods, such as chemical reactions of precursors— in particular, reactions of metal salts in polymer solutions, the treatment of polymers with metal vapors, or the polymerization of various metal-monomer systems [1-4], Depending on the metal nature and the polymer structure, these processes lead to organometallic units incorporated into polymer chains, metal-polymer complexes, or metal clusters and nanoparticles physically connected with polymer matrix. Of special interest are syntheses with the use of metal vapors. In this case, metal atoms or clusters are not protected by complexones or solvate envelopes and consequently have specific high reactivity. It should be noted that the apparatus and principles of metal vapor synthesis techniques are closely related to many industrial processes with participation of atomic and molecular species [5]—for example, manufacturing devices for microelectronic from different metals and metal containing precursors [6]. Vapor synthesis methods employ varying metals and... 

Nonpowder Synthesis. Many ceramic composites (qv) under iavestigation utilize reinforcing ceramic whiskers or fibers to achieve toughening (19). Whiskers (17,19,20) are produced by vapor-synthesis techniques. SiC whiskers can be produced by the rice hull or vapor—soHd (VS) method whereby rice hulls are pyrolyzed to produce a mixture of carbon, C, and Si02, and whiskers are produced by directional growth by vapor... 

The direct linking of carbon nanotubes to graphite and the continuity in synthesis, structure and properties between carbon nanotubes and vapor grown carbon fibers is reviewed by the present leaders of this area, Professor M. Endo, H. Kroto, and co-workers. Further insight into the growth mechanism is presented in the article by Colbert and Smalley. New synthesis methods leading to enhanced production... 

The most important nanomaterial synthesis methods include nanolithography techniques, template-directed syntheses, vapor-phase methods, vapor-liquid-solid (VLS) methods, solution-liquid-solid (SLS) approaches, sol-gel processes, micelle, vapor deposition, solvothermal methods, and pyrolysis methods [1, 2]. For many of these procedures, the control of size and shape, the flexibility in the materials that can be synthesized, and the potential for scaling up, are the main limitations. In general, the understanding of the growth mechanism of any as-... 

Guerin S, Hayden BE. 2006. Physical vapor deposition method for the high-throughput synthesis of solid-state material libraries. J Comb Chem 8 66-73. 

Purified MeHNL was crystallized by the sitting-drop vapor-diffusion method. The 10-20 mm bipyramidal crystals formed were cross-linked with glutaraldehyde and used as biocatalyst for the synthesis of optically active cyanohydrins. The cross-linked crystals were more stable than Celite-immobilized enzymes when incubated in organic solvents, especially in polar solvents. After six consecutive batch reactions in dibutyl ether, the remaining activity of the cross-linked crystals was more than 70 times higher than for the immobilized enzymes. Nevertheless, the specific activity of the cross-linked crystals per milligram protein was reduced compared with the activity of Celite-immobilized enzymes [53],... 

Liu J, Czerw R, Carroll DL (2005a) Large-scale synthesis of highly aligned nitrogen doped carbon nanotubes by injection chemical vapor deposition methods. Journal of Materials Research 20 538-543. 

Fig. 2.2 Bottom-up synthesis methods, (a) Catalytic vapor deposition (b) epitaxial growth from SiC.

Cloke et al. presented the elegant metal-vapor synthesis for the preparation of linear 14 valence-electron complexes [M°(NHC)2] 73 (M = Ni, Pd, Pt) (Fig. 24a) [186]. The method was subsequently improved [187] and the interesting electronic and catalytic properties of Pd° and Pt° biscarbene complexes have been studied in detail [188-191]. 

Niobium Products Co., 50 m /g). Many different synthesis methods have been used to prepare supported metal oxide catalysts. In the case of supported vanadium oxide catalysts, the catalysts were prepared by vapor phase grafting with VOCI3, nonaqueous impregnation (vanadium alkoxides), aqueous impregnation (vanadium oxalate), as well as spontaneous dispersion with crystalline V2O5 [4]. No drastic reduction of surface area of the catalysts was observed. 

Ullrafine particles (UFPs) of metal and semiconductor nitrides have been synthesized by two major techniques one is the reactive gas condensation method, and the other is the chemical vapor condensation method. The former is modified from the so-called gas condensation method (or gas-evaporation method) (13), and a surrounding gas such as N2 or NII2 is used in the evaporation chamber instead of inert gases. Plasma generation has been widely adopted in order to enhance the nitridation in the particle formation process. The latter is based on the decomposition and the subsequent chemical reaction of metal chloride, carbonate, hydride, and organics used as raw materials in an appropriate reactive gas under an energetic environment formed mainly by thermal healing, radiofrequency (RF) plasma, and laser beam. Synthesis techniques are listed for every heal source for the reactive gas condensation method and for the chemical vapor condensation method in Tables 8.1.1 and 8.1.2, respectively. 

Nanosized metal sulfide powders of Ag2S, CuS, FeS, Ga2S3. In2S3, MnS, NiS, and ZnS were synthesized for use as gas- and liquid-phase mercury sorbents. An aqueous-based synthesis method using the surfactant cetyltrimethylammonium bromide (CTAB) is described. The vapor- and aqueous-phase mercury-sorption characteristics of the nanocrystalline powders synthesized and of commercially produced Ag2S, AU2S. and AU2S3 are presented. 

One of the modem methods is associated with the application of pyrophoric metals formed, for examle, as a result of low-temperature gas phase codeposition with toluene vapor (MVS-metal vapor synthesis) [757],... 

Zeolite-supported Re catalysts have been synthesized by chemical vapor deposition (CVD) ofMTO (CH3Re03) (3) on various zeolites such as HZSM-5, H-Beta, H-USY and H-Mordenite. HZSM-5 samples with different A1 contents were prepared by a hydrothermal synthesis method. For comparison, conventional impregnated catalysts were also prepared by an impregnation method using an aqueous solution of NH4Re04. All catalysts were pretreated at 673 K in a flow of He before use as catalyst. 

Lanthanide triflates, for allylic tin reactions, 9, 354 Laser beam heating, in metal vapor synthesis, 1, 224 Laser methods, in mechanistic studies, 1, 248 Laser photochemical vapor deposition, with organometallic complexes, 1, 259... 

Our experiment has demonstrated the possibility of the carbon nanotubes synthesis by low temperature (substrate temperature was 500°C) vapor deposition method from the ethanol vapor. Field emission samples were produced with different catalyst distribution on the substrate surface. 

Not surprisingly, in recent years the technique of metal vapor synthesis, in which the metal vapor and PF3 are cocondensed at liquid nitrogen temperatures, has found general application since PF3 is readily condensible (in contrast to CO) and the high volatility of the resulting metal-PF3 complexes facilitates their isolation (method H). 

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