Mechanistic Studies of Bimolecular Electron Transfer Self-Exchange Rates of Ruthenium Ammine Pyridyl Complexes Measured by NMR Line Broadening Techniques

<p>The electron transfer (ET) self-exchange rates on a series of complexes of (NH₃)₅Ru^II/IIIL^2+/3+ in D₂O (where L is a substituted pyridyl ligand) were investigated by dynamic NMR measurements. Significant rate enhancement was observed for the cases of L = 3-phenylpyridine and 4-phenylpridine due to possible π-π stacking between Phpy ligands. These observations matche well with recent stopped-flow work by Mehmood on a similar set of related pseudo-self exchange reactions. Kinetics of the (NH₃)₅Ru^II/III(3-trifluoromethylpyridine)^2+/3+ self-exchange reactions with addition of various simple/complex salts and hexacyano salts (K₄M(CN)₆ with M = Fe, Os and Ru) were also studied. The halide ions showed qualitatilvely-similar behavior compared to the stopped-flow work by Sista and the same quantitative decrease in the magnitude of salt effect as reported by Inagaki. The hexacyano salts were found to have a striking effect on the ET rate with a clear trend of Fe > >Os > Ru. This could be explained as a probable “superexchange” type mechanism dominated by the “hole-transfer” pathway based on the trend between the catalytic effect and the redox potential of the particular M(CN)^4- ion. Kinetic modeling data also show the strongest catalytic effect of Fe which gives a k_etx/k_et of 126. Temperature-dependent experiments show that the rate enhancement of hexacyano series is due to a increased enthalpic barrier and less negative entropic barrier.</p>

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Chemistry

Year dc:date.available

2013

Author dc:creator

• Qin, Yishun

Contributors dc:contributor

• Jeff Curtis
• Kim Summerhays
• Larry Margerum

• superexchange
• pyridyl ligand substituent effects
• ion pair
• Inorganic Chemistry

Repository record dc:identifier

https://repository.usfca.edu/thes/74

OAI identifier oai:identifier

oai:repository.usfca.edu:thes-1081