Mechanistic Studies of Salt Effects on Bimolecular Electron-Transfer Reactions of Pentaamine Ruthenium Pyridyl Complexes Studied by 19F NMR Line-Broadening and T2 Spin-Echo Techniques

<p>Kinetic salt effects on the bimolecular ET self-exchange reaction between pentaamineruthenium(II)(3-trifluoromethylpyridine)²⁺, (NH₃)₅Ru^IItfmp²⁺, and pentaamineruthenium(III)(3-trifluoromethylpyridine)³⁺, (NH₃)₅Ru^IIItfmp³⁺, have been measured using both ¹⁹F NMR line-broadening and CPMG T₂ spin-echo relaxation techniques in H₂O and D₂O. Over the equimolar reactants concentration range of 0.10 mM – 8.00 mM there was a definite “self-salting” rate increase arising from the increased solution ionic strengths due to the reactants and counterions themselves. The magnitude of this effect diverged significantly, however, from predictions based on the classical Debye-Huckle-Bronsted theory of kinetic salt effects. In agreement with earlier stopped-flow work, addition of alkali-metal fluoride salts increased the rate of ET between the like-charged redox reactants in good quantitative agreement with the quantitative predictions of the Debye-Huckle-Bronsted theory of ion atmosphere charge screening effects, but the other halides exhibited progressively-increasing, non-linear upward deviations from theory in the order Cl^- < Br^- < I^- . Catalytic effects on the rate of ET from the addition of various dicarboxylate salts were also found to deviate in a non-linear fashion from theory. In sharp contrast to previous stopped-flow work wherein addition of the trans,trans-muconate dianion showed a uniquely-large catalytic affect, NMR investigations established a complete loss in catalytic efficacy for muconate. Numerous control experiments force us to conclude that it is the presence of the magnetic field itself which quenches the catalysis as probed by NMR. Similar investigations showed that additions of even miniscule amounts of metal-hexacyano salts of formulation K₄M<strong>^II</strong>(CN)₆ (M = Fe, Os, Ru) caused <em>much</em> larger ET catalytic effects than those seen with any of the added halides or dicarboxylates. Consideration of the redox thermodynamics of the metal centers involved supports an interpretation of the catalysis based on hole-transfer quantum super-exchange mediation by virtual states corresponding to hole creation on the bridging anions in presumed ternary ionic assemblies involved in the ET transition state.</p>

Name thesis:degree_name

Master of Science in Chemistry

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Chemistry

Year dc:date.available

2014

Author dc:creator

• Magarian, Nicholas J

Contributors dc:contributor

• Jeff Curtis

• NMR
• T2
• 19F NMR
• Electron Transfer
• Activation parameters
• physical inorganic chemistry
• Inorganic Chemistry
• Physical Chemistry

Repository record dc:identifier

https://repository.usfca.edu/thes/101

OAI identifier oai:identifier

oai:repository.usfca.edu:thes-1113