Solvent Relaxation in Electron-Transfer Reactions: Comparisons between Barrier-Crossing Dynamics in Water and Polar Aprotic Media

Rate constants, k sub ex, for electron self exchange of three metallocene redox couples, carboxymethyl (cobaltocenium-cobaltocene) CpCO2Me2) 2Co+o, hydroxymethyl (ferrocenium-ferrocene) (Cp (dot) CpCH2OH)Fe+/o, and trimethylaminomethyl (ferrocenium-ferrocene) (Cp (dot) CpCH2NMe3)Fe2+/2, obtained usi...

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Bibliographic Details
Main Authors: Nielson, Roger M, McManis, George E, Weaver, Michael J
Format: Report
Language:English
Subjects:
ACETONES
ACETONITRILE
ACETYLENE/BIFERROCENYL
ACETYLENES
CARBINOLS
COBALTOCENE/CARBOXYMETHYL COBALTOCENIUM
CONSTANTS
COUPLING(INTERACTION)
DYNAMICS
ELECTRON TRANSFER
ELECTRONS
EXCHANGE REACTIONS
FERROCENE/ HYDROXYMETHYL FERROCENIUM
FERROCENE/TRIMETHYLAMINOMETHYL FERROCENIUM
FERROCENES
HIGH FREQUENCY
Inorganic Chemistry
MAGNETIC RESONANCE
METALLOCENES
MIXING
NITROMETHANE
OPTICAL PROPERTIES
Physical Chemistry
POLARITY
RATES
RELAXATION
SENSITIVITY
SOLVATION
SOLVENTS
VALENCE
WATER
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Summary:Rate constants, k sub ex, for electron self exchange of three metallocene redox couples, carboxymethyl (cobaltocenium-cobaltocene) CpCO2Me2) 2Co+o, hydroxymethyl (ferrocenium-ferrocene) (Cp (dot) CpCH2OH)Fe+/o, and trimethylaminomethyl (ferrocenium-ferrocene) (Cp (dot) CpCH2NMe3)Fe2+/2, obtained using proton NMR line broadening, are utilized along with optical electron-transfer energies for the mixed-valence biferrocenylacetylene cation to obtain solvent-dependent frequencies, (Kappa sub el)(n sub n), in water relative to those in methanol and six aprotic solvents. While (Kappa sub el)(n sub n) for the ferrocene couples is insensitive to the solvent, indicative of nonadiabatic behavior (K sub el 1), K sub el (n sub n) vn for the cobaltocene couple is responsive to the solvent dynamics. While rapid barrier-crossing dynamics are obtained in water, comparable to acetonitrile, acetone, and nitromethane, the influence of high-frequency relaxation components in water is less marked than for methanol. Keywords: Nuclear: Magnetic resonance: Metallocene redox couples: Line broadening: Biferrocenylacetylene cation: Aprotic solvents: Solvent dynamics: Mixed valence.