Investigation of molybdenum sulfur interactions via single crystal EPR and photoelectron spectroscopy: Implications to molybdoenzymes

Persistent Link:
http://hdl.handle.net/10150/282444
Title:
Investigation of molybdenum sulfur interactions via single crystal EPR and photoelectron spectroscopy: Implications to molybdoenzymes
Author:
Westcott, Barry Lee, 1972-
Issue Date:
1997
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:
A series of MoS(n) complexes were studied to afford a better understanding of the factors which affect the electronic structures in these complexes. Molybdenum sulfur interactions are of interest because of their importance in biology, and because of the utility of such complexes as catalysts in the petroleum industry. The He I gas phase photoelectron spectra (PES) of the series LMo(E)(OR)₂ [(L=hydrotris(3,5-dimethylpyrazolyl)borate), (E=O, NO)] were explored as a point of reference to the analogous thiolate complexes. These studies show that the nitrosyl complexes (formally Mo(II)) are 0.8 eV more difficult to ionize than the oxo analogues (formally Mo(V)). This counterintuitive result is ascribed to the differing π interactions of the nitrosyl and oxo ligands. The first single crystal EPR study of an oxo-Mo(V) complex with a single diothiolene-type ligand, LMoO(bdt) [bdt = 1,2-benzenedithiol], is reported. The principal g tensor elements was found to be oriented in the MoS₂ plane nearly perpendicular to the Mo-O vector, with a magnitude of 2.004. This large g value is attributed to contributions from sulfur spin-orbit coupling. These findings suggest that the singly occupied molecular orbital (SOMO), which is expected to be primarily metal in character, contains a significant amount of S character. The HeI, HeII, and NeI PES of LMoE(SPh)₂ and LMoE(tdt) [E = O, NO, S; tdt = 3,4-toluenedithiol] show that the ligand E and the formal oxidation state of the metal have little effect on the position of the first ionization potential, suggesting that the Mo-S interaction is the dominant factor in the electronic structure. An empirical equation is developed to quantify the relative amount of sulfur character in the "metal" orbitals. The results of these studies suggest that thiolate donors act as "electronic buffers" to a Mo center because of the close energy matching between Mo 4d and S 3p orbitals. This energy matching can be invoked to explain the utility of MoS(n) complexes as effective biological and industrial catalysts.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Chemistry, Inorganic.; Chemistry, Physical.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Enemark, John H.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleInvestigation of molybdenum sulfur interactions via single crystal EPR and photoelectron spectroscopy: Implications to molybdoenzymesen_US
dc.creatorWestcott, Barry Lee, 1972-en_US
dc.contributor.authorWestcott, Barry Lee, 1972-en_US
dc.date.issued1997en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © 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.en_US
dc.description.abstractA series of MoS(n) complexes were studied to afford a better understanding of the factors which affect the electronic structures in these complexes. Molybdenum sulfur interactions are of interest because of their importance in biology, and because of the utility of such complexes as catalysts in the petroleum industry. The He I gas phase photoelectron spectra (PES) of the series LMo(E)(OR)₂ [(L=hydrotris(3,5-dimethylpyrazolyl)borate), (E=O, NO)] were explored as a point of reference to the analogous thiolate complexes. These studies show that the nitrosyl complexes (formally Mo(II)) are 0.8 eV more difficult to ionize than the oxo analogues (formally Mo(V)). This counterintuitive result is ascribed to the differing π interactions of the nitrosyl and oxo ligands. The first single crystal EPR study of an oxo-Mo(V) complex with a single diothiolene-type ligand, LMoO(bdt) [bdt = 1,2-benzenedithiol], is reported. The principal g tensor elements was found to be oriented in the MoS₂ plane nearly perpendicular to the Mo-O vector, with a magnitude of 2.004. This large g value is attributed to contributions from sulfur spin-orbit coupling. These findings suggest that the singly occupied molecular orbital (SOMO), which is expected to be primarily metal in character, contains a significant amount of S character. The HeI, HeII, and NeI PES of LMoE(SPh)₂ and LMoE(tdt) [E = O, NO, S; tdt = 3,4-toluenedithiol] show that the ligand E and the formal oxidation state of the metal have little effect on the position of the first ionization potential, suggesting that the Mo-S interaction is the dominant factor in the electronic structure. An empirical equation is developed to quantify the relative amount of sulfur character in the "metal" orbitals. The results of these studies suggest that thiolate donors act as "electronic buffers" to a Mo center because of the close energy matching between Mo 4d and S 3p orbitals. This energy matching can be invoked to explain the utility of MoS(n) complexes as effective biological and industrial catalysts.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectChemistry, Inorganic.en_US
dc.subjectChemistry, Physical.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorEnemark, John H.en_US
dc.identifier.proquest9806835en_US
dc.identifier.bibrecord.b37557105en_US
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