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Spectroscopic studies zinc species

At high temperatures (> 170 K), the water desorbs and so the autocatalytic reaction cannot be sustained and is an explanation for why the H2 + 02 reaction slows, the formation of OH species now being solely dependent on the H(a) + O(a) reaction, which is the slowest step in the above scheme. That the water + oxygen reaction was fast and facile was evident from the spectroscopic studies at both nickel and zinc surfaces, when the oxygen surface coverage was low and involving isolated oxygen adatoms. [Pg.89]

Ito and co-workers observed the formation of zinc bound alkyl carbonates on reaction of carbon dioxide with tetraaza macrocycle zinc complexes in alcohol solvents.456 This reversible reaction was studied by NMR and IR, and proceeds by initial attack of a metal-bound alkoxide species. The metal-bound alkyl carbonate species can be converted into dialkyl carbonate. Spectroscopic studies suggested that some complexes showed monodentate alkyl carbonates, and varying the macrocycle gave a bidentate or bridging carbonate. Darensbourg isolated arylcarbonate compounds from zinc alkoxides as a by-product from work on polycarbonate formation catalysis.343... [Pg.1184]

In situ spectroscopic studies have identified a variety of species, such as formate, dioxymethylene, carbonate, and methoxide, to coexist under methanol synthesis conditions on Cu/ZnO-based catalysts [22, 23], Fourier transform infrared spectroscopy studies of CuZn-based catalysts under H2/C02 identified the presence of formate bound to both Cu and ZnO, whereas methoxide was found on ZnO only. Carbonates were found to form via C02 adsorption on ZnO [24] and partially oxidized Cu [23], and were quickly converted into formate via Cu-activated hydrogen. Upon exposure to CO mixtures, only zinc-bound formate was observed [22], The hydrogenation of these formates to methoxide is thought to be rate determining in methanol synthesis. [Pg.420]

Denmark et al. studied the effect of zinc iodide on the catalytic, enantioselective cyclopropanation of allylic alcohols with bis(iodomethyl)-zinc as the reagent and a bismethanesulfonamide as the catalyst 17]. They found significant rate enhancement and an increased enantiomeric excess of the product cyclopropane upon addition of 1 equivalent zinc iodide. Their studies and spectroscopic investigations showed that the Schlenk equilibrium appears to lie far on the left (IZnCHjI). Charette et al. used low temperature - C-NMR spectroscopy to differentiate several zinc-carbenoid species [18]. They also found evidence that in the presence of zinc iodide, bis(iodomethyl)zinc is rapidly converted to (io-domethyOzinc iodide. Solid-state structures of (halomethyl)zinc species have been described by Denmark for a bis(iodomethyl)zinc ether complex (6a) [19] and Charette for an (iodo-methyl)zinc iodide as a complex with 18-crown-6 (6b) [20] (Fig. 2). [Pg.4]

Mass spectrometry has been used to identily complexes formed in the gas phase by reaction of oxyanions and carbanions with 1,3,5-triazine. Spectroscopic studies and DFT calculations on the species formed by reaction of ethylamine with 2,4-dinitrotoluene in DMSO indicate that transfer of a methyl proton rather than nucleophilic attack is the major interaction. Two methods for the detection of 2,4,6-trinitrotoluene (TNT) using fluorescence techniques rely on the formation of its complexes with amines. Also cobalt-doped zinc sulfide quantum dots have been used to interact with complexes formed from TNT and L-cysteine allowing detection of the nitro compound. A complex between 2,4-dinitroanisole and L-cysteine methyl ester has been identified by surface-enhanced Raman spectroscopy. ... [Pg.251]

Two distinct classes of promoters have been identified for the reaction simple iodide complexes of zinc, cadmium, mercury, indium and gallium, and carbonyl complexes of tungsten, rhenium, ruthenium and osmium. The promoters exhibit a unique synergy with iodide salts, such as hthium iodide, under low water conditions. Both main group and transition metal salts can influence the equilibria of the iodide species involved. A rate maximum exists under low water conditions and optimization of the process parameters gives acetic acid with a selectivity in excess of 99% based upon methanol. IR spectroscopic studies have shown that the salts abstract iodide from the ionic methyl iridium species and that in the resulting neutral species the migration is 800 times faster [127]. [Pg.350]

Zn and N K-edge XANES have been used to distinguish the coordination geometries in (1,2-ethanediylidene)-bis(5 -methylhydrazonecarbodithionate) zinc complexes (109). The technique distinguished between tetrahedral species, square pyramidal dimers, and square pyramidal monomers, formed when pyridine was present. These studies were in conjunction with spectroscopic characterization and X-ray single-crystal data where possible.53 The results demonstrated the value of this technique when single crystals could not be obtained. [Pg.1226]

The potentiometric pH titration disclosed monodeprotonation with a pK value of 7.6 at 25°C. On the basis of NMR spectroscopic and anionbinding studies of 13, the monodeprotonated species was assigned to the OH -bound ZnL complex 14, rather than the pendent alkoxide complex as seen with [12]aneN3 8b. Nevertheless, among all past zinc(II) complexes, 14 seems to be the most active catalyst for NA hydrolysis. From kinetic studies in 10% (v/v) CH3CN at 25°C and pH... [Pg.235]

Zinc proteins are common, but the absence of any accessible oxidation states apart from Zn(II) means that they cannot act as redox proteins. One of the problems in working with with Zn(II) is that it is, as a d10 system, spectroscopically silent , which limits the type of studies that can be used to probe its chemistry in biomolecules. However, several zinc proteins are relatively low molecular weight species and these were characterized by crystal structure analysis some decades ago. [Pg.242]


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See also in sourсe #XX -- [ Pg.2 ]




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Species studied

Spectroscopic studies

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