EPR studies of oxo-molybdemun(V) complexes with sulfur donor ligands: Synthesis, X-band EPR spectra and approaches to single crystal host lattices.

Persistent Link:
http://hdl.handle.net/10150/187084
Title:
EPR studies of oxo-molybdemun(V) complexes with sulfur donor ligands: Synthesis, X-band EPR spectra and approaches to single crystal host lattices.
Author:
Dhawan, Ish Kumar.
Issue Date:
1995
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 well characterized mononuclear oxo-molybdenum(V) complexes with bidentate sulfur donor ligands, which possess the minimal structural feature for the Mo(V) state of the proposed molybdenum cofactor (Moco) have been investigated by X-band electron paramagnetic resonance (EPR) spectroscopy in fluid and frozen solutions. The complete EPR parameters (anisotropic g(i) and A(^(95,97)Mo) hyperfine splittings) were obtained by rigorous spectral simulations using the QPOW program. Comparison of the EPR parameters of LMoO(bdt) and LMoO{S(CH₂)ₓ)S}, x = 2, 3, 4 complexes reveals similar anisotropic g and A(^(95,97)Mo) values, and indicates that it is the sulfur ligation rather than the chelate skeleton that is the primary factor dictating these parameters. Fenske-Hall calculations show that the oxo-molybdenum(V) complexes of the type LMoO{S(C)ₓS}, x = 1,2 have similar electronic structures and indicate that the first electronic transition will be a charge transfer (CT) transition from Sπ to d(xy). Such a low lying charge transfer band accounts for one of the g(i) values being greater than the free electron value (gₑ = 2.0023) for complexes LMoO(bdt) and LMoO{S(CH₂)ₓ)S}, x = 2, 3, 4. The EPR spectrum of the low and high pH forms of sulfite oxidase have been reinvestigated due to its qualitative similarities with our well characterized model compounds. Complete EPR parameters, including anisotropic A(^(95,97)Mo) hyperfine splittings were reported for the first time for the low and high pH forms of the sulfite oxidase. Comparison of the EPR parameters for the model compounds to those of the low and high pH forms of sulfite oxidase reveals that these minimal structural models for Moco mimic the anisotropic g values and A₁ values, but the A₂ and A₃ components in the models are distinctly different from those in the enzyme. Preliminary single crystal EPR studies on LMoO(bdt) doped into the diamagnetic LMo(NO(bdt) and LMo(NO)(tdt) host lattices are reported. A series of mononuclear and binuclear molybdenum complexes of the neutral facially coordinating hydrotris(3,5-dimethyl-1-pyrazolyl)methane (L*) ligand have been prepared and characterized by X-ray crystallography and spectroscopic techniques. An unusual feature of the chemistry of L*, compared to other related facially coordinating tridentate nitrogen ligands, is the facile formation of novel unsymmetrical di-μ-oxo dimers such as L*Mo₂O₄Cl₂, which contain both five-coordinate and six-coordinate oxo-molybdenum centers.
Type:
text; Dissertation-Reproduction (electronic)
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemistry; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Enemark, John

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleEPR studies of oxo-molybdemun(V) complexes with sulfur donor ligands: Synthesis, X-band EPR spectra and approaches to single crystal host lattices.en_US
dc.creatorDhawan, Ish Kumar.en_US
dc.contributor.authorDhawan, Ish Kumar.en_US
dc.date.issued1995en_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 well characterized mononuclear oxo-molybdenum(V) complexes with bidentate sulfur donor ligands, which possess the minimal structural feature for the Mo(V) state of the proposed molybdenum cofactor (Moco) have been investigated by X-band electron paramagnetic resonance (EPR) spectroscopy in fluid and frozen solutions. The complete EPR parameters (anisotropic g(i) and A(^(95,97)Mo) hyperfine splittings) were obtained by rigorous spectral simulations using the QPOW program. Comparison of the EPR parameters of LMoO(bdt) and LMoO{S(CH₂)ₓ)S}, x = 2, 3, 4 complexes reveals similar anisotropic g and A(^(95,97)Mo) values, and indicates that it is the sulfur ligation rather than the chelate skeleton that is the primary factor dictating these parameters. Fenske-Hall calculations show that the oxo-molybdenum(V) complexes of the type LMoO{S(C)ₓS}, x = 1,2 have similar electronic structures and indicate that the first electronic transition will be a charge transfer (CT) transition from Sπ to d(xy). Such a low lying charge transfer band accounts for one of the g(i) values being greater than the free electron value (gₑ = 2.0023) for complexes LMoO(bdt) and LMoO{S(CH₂)ₓ)S}, x = 2, 3, 4. The EPR spectrum of the low and high pH forms of sulfite oxidase have been reinvestigated due to its qualitative similarities with our well characterized model compounds. Complete EPR parameters, including anisotropic A(^(95,97)Mo) hyperfine splittings were reported for the first time for the low and high pH forms of the sulfite oxidase. Comparison of the EPR parameters for the model compounds to those of the low and high pH forms of sulfite oxidase reveals that these minimal structural models for Moco mimic the anisotropic g values and A₁ values, but the A₂ and A₃ components in the models are distinctly different from those in the enzyme. Preliminary single crystal EPR studies on LMoO(bdt) doped into the diamagnetic LMo(NO(bdt) and LMo(NO)(tdt) host lattices are reported. A series of mononuclear and binuclear molybdenum complexes of the neutral facially coordinating hydrotris(3,5-dimethyl-1-pyrazolyl)methane (L*) ligand have been prepared and characterized by X-ray crystallography and spectroscopic techniques. An unusual feature of the chemistry of L*, compared to other related facially coordinating tridentate nitrogen ligands, is the facile formation of novel unsymmetrical di-μ-oxo dimers such as L*Mo₂O₄Cl₂, which contain both five-coordinate and six-coordinate oxo-molybdenum centers.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairEnemark, Johnen_US
dc.contributor.committeememberWigley, Daviden_US
dc.contributor.committeememberWalker, F. Annen_US
dc.contributor.committeememberTollin, Gordonen_US
dc.contributor.committeememberVemulapalli, Krishnaen_US
dc.identifier.proquest9531105en_US
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