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    INVESTIGATION OF THE ENERGY OF THE DITHIOLENE FOLDING INTERACTION IN METALLOCENE-­DITHIOLENE COMPLEXES USING SPECTROSCOPIC AND COMPUTATIONAL ANALYSIS

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    Author
    Wiebelhaus, Nicholas John
    Issue Date
    2011
    Keywords
    Chemistry
    Advisor
    Enemark, John H.
    Lichtenberger, Dennis L.
    
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    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    The studies presented in this dissertation focus on elucidating key aspects of the interaction of metals and dithiolenes. The interaction is probed in a series of metallocene-dithiolene compounds (CpML where Cp = cyclopentadienyl, M = Mo, V, Ti and L = benezedithiolato and quinoxalinedithiolato) that have relatively simple electronic structures. The straightforward electronic structures were selected for assigning spectral features and correlating changes in electronic structure with changes in geometry, specifically the dithiolene fold angle. The experimental methods used to investigate the electronic structures include gas-phase photoelectron spectroscopy, X-ray absorption spectroscopy (XAS), resonance Raman (rR), and cyclic voltammetry (CV). Results from the experiment were supported by computational modeling with density functional theory.Results from the first part of the dissertation attempt to quantify the orbital interaction energy of the metal and dithiolene by comparing gas-phase X-ray and UV photoelectron (XPS/UPS) ionization energies. However, it was found that the metallocene compounds exhibit significant mixing of cyclopentadienyl orbital character with the frontier metal and dithiolene orbitals, which affects the orbital energies. Though unexpected, the implications for observing mixing between the dithiolene and other ligand orbitals can impact the understanding of Mo enezyme active sites as well as other synthetic systems.The next set of experiments looked at the effects of altering the electronic nature of the dithiolene ligand. The effect on the orbital energies of the molecules was probed by gas-phase UPS and CV. These results show no overall effect on the interaction between the dithiolene and the metal despite definite differences in the ligand electronic structure. Further experiments to probe the metal-ligand covalency using XAS also showed little change in the metal-ligand interaction.Finally, the relationship between geometric and electronic structure was investigated by comparing results from UPS vibrational structure with those from rR data. These data sets suggest that a metal-sulfur core breathing mode maybe active in electron transfer to and from the metal center in these types of compounds. The vibrational mode assigned to a dithiolene folding motion was shown to have a significant dependence on the metal electron count of the complexes as expected from basic molecular orbital theory.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Chemistry
    Degree Grantor
    University of Arizona
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