Hexametalates as Catalysts for Photochemical Oxidation Reactions

Earley, Clarke Wesley

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Description

Title

Hexametalates as Catalysts for Photochemical Oxidation Reactions

Author(s)

Earley, Clarke Wesley

Issue Date

1987

Doctoral Committee Chair(s)

Klemperer, Walter G.

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Chemistry, Inorganic

Abstract

• The reaction of TiCl$\sb4$ with WO$\sb4$((n-C$\sb4$H$\sb9$)$\sb4$N) $\sb2$ in acetonitrile yields ClTiW$\sb5$O$\sb $ ((n-C$\sb4$H$\sb9$)$\sb4$N) $\sb3$. The complexes ROTiW$\sb5$O$\sb $ (n-C$\sb4$H$\sb9$)$\sb4$N) $\sb3$ (R = CH$\sb3$, C$\sb2$H$\sb5$, and (CH$\sb3$)$\sb2$CH) are prepared in an analogous fashion by acidification of Ti(OR)$\sb4$ and WO$\sb4$ ((n-C$\sb4$H$\sb9$)$\sb4$N) $\sb2$. Spectroscropic data (IR, $\sp $O, and $\sp{183}$W NMR) indicate that these anions all have structures related to the C$\sb5$H$\sb5$TiW$\sb5$O$\sb \sp{3-}$ structure by replacement of the C$\sb5$H$\sb5$ ligand by a chloride or alkoxide ligand. Hydrolysis of ROTiW$\sb5$O$\sb \sp{3-}$ results in formation of O(TiW$\sb5$O$\sb $)$\sb2$ ((n-C$\sb4$H$\sb9$)$\sb4$N) $\sb6$. This salt can also be prepared by the reaction of ClTiW$\sb5$O$\sb \sp{3-}$ with hydroxide ion. Spectroscopic data indicates that the structure of this anion is based on two TiW$\sb5$O$\sb \sp{2-}$ units linked through an oxide bridging two titanium atoms.
• The electronic structure of the series of hexametalate anions W$\sb6$O$\sb \sp{2-},$ VW$\sb5$O$\sb \sp{3-}$, NbW$\sb5$O$\sb \sp{3-}$, TaW$\sb5$O$\sb \sp{3-}$, ROTiW$\sb5$O$\sb \sp{3-}$, and O(TiW$\sb5$O$\sb )\sb2\sp{6-}$ as their tetrabutylammonium salts in acetonitrile was probed using cyclic voltammetry and electronic spectroscopy. The reduction potentials for all of the trianions except VW$\sb5$O$\sb \sp{3-}$ occur within a range of 0.3 V, which suggests that these reductions occur at tungsten sites. The electronic spectra of all of the anions were qualitatively similar. The observed differences could all be related to structural changes in the anions. In an effort to understand the electronic spectra, an electronic structure calculation on the W$\sb6$O$\sb \sp{2-}$ anion was performed using the self-consistent field X$\alpha$ scattered wave method. Assignments for the observed spectra were made by comparison with the calculated transition energies and intensities.
• Quantum yields for the photochemical production of acetone were measured for each of these anions. These values were compared with the relative amounts of acetone produced after several turnovers of the catalyst. Some features of the catalytic behavior could be explained by comparison with the observed electronic properties.

Graduation Semester

1987

Type of Resource

text

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