Date of Graduation
Master of Science in Chemistry
College of Arts and Sciences
Kinetic salt effects on the bimolecular ET self-exchange reaction between pentaamineruthenium(II)(3-trifluoromethylpyridine)2+, (NH3)5RuIItfmp2+, and pentaamineruthenium(III)(3-trifluoromethylpyridine)3+, (NH3)5RuIIItfmp3+, 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 K4MII(CN)6 (M = Fe, Os, Ru) caused much 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.
Magarian, Nicholas J., "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" (2014). Master's Theses. 101.