A STUDY OF THE PHOTOCHEMISTRY AND PHOTOCATALYSIS OF GROUP VIB HEXACARBONYLS ADSORBED TO A POROUS GLASS MATRIX.
Item
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Title
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A STUDY OF THE PHOTOCHEMISTRY AND PHOTOCATALYSIS OF GROUP VIB HEXACARBONYLS ADSORBED TO A POROUS GLASS MATRIX.
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Identifier
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AAI8409418
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identifier
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8409418
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Creator
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SIMON, ROBERT C.
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Contributor
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Harry D. Gafney
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Date
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1984
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Inorganic
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Abstract
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The Group VIB hexacarbonyls have been adsorbed onto transparent, porous Vycor glass, PVG, to investigate the photophysical and photochemical properties of the adsorbed complexes and their potential as photocatalysts of various reactions.;The bound hexacarbonyls retain spectral properties similar to those in fluid solution which suggests that the complexes are physisorbed. UV photolysis of M(CO)(,6)ads (M = Cr, Mo, and W) leads to the quantitative formation of the corresponding pentacarbonyls which have UV-visible spectra equivalent to spectra of these species generated in low-temperature matrices. The pentacarbonyls have lifetimes > 48 hours in vacuo at room temperature. Stability arises from coordination to the PVG, but does not occur at the expense of subsequent thermal and photochemical activity. The addition of either thoroughly degassed or vapor phase mono and bidentate ligands to the pentacarbonyl leads to the qualitative formation of M(CO)(,5)Lads or M(CO)(,4)Lads which were characterized by their absorption and emission spectra. Comparison of the kinetic and thermodynamic parameters calculated from the rates of reaction of M(CO)(,5)ads with those from fluid solution studies suggest that the incoming ligand must overcome the apparent matrix bond the glass has with the pentacarbonyl.;Quantum yields for decomposition of M(CO)(,6), which are dependent on the excitation wavelength, formation of M(CO)(,5)ads and various photoproducts were measured at 254, 310, and 350-nm.;Photolysis of M(CO)(,5)ads at 310 and 254-nm causes further CO evolution along with H(,2), CH(,4), and CO(,2) evolution. Periodic examination of the gaseous effluent surrounding the photolyzed piece, in conjunction with spectral analysis, established that CH(,4) evolution is mediated by a monomeric M(CO)(,4)ads species. The latter is irreversibly oxidized, and initially, the complex oxidized is in a 1:1 stoichiometric ratio with the CH(,4) evolved. The hydrogen source is adsorbed H(,2)O since replacement with D(,2)O leads to CH(,2)D(,2) and CHD(,3) evolution. The metal complex is essential to CH(,4) formation, but in contrast to what is assumed in the temperature programmed decomposition of the complexes on silica gel, isotopic labelling establishes that in these photochemical experiments CH(,4) originates from carbonaceous residue in PVG rather than from coordinated CO.;The photocatalyzed isomerization and hydrogenation of olefins by these hybrid systems yields a distribution of products which contrasts with that found in solution and with other hybrid systems.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Chemistry
