DEUTERIUM NMR KINETIC MEASUREMENTS OF SOLVENT EFFECTS ON THE BIMOLECULAR ELECTRON-TRANSFER SELF-EXCHANGE RATES OF RUTHENIUM AMMINE COMPLEXES - A DOMINANT ROLE FOR SOLVENT-SOLUTE HYDROGEN-BONDING
Wl. Mao et al., DEUTERIUM NMR KINETIC MEASUREMENTS OF SOLVENT EFFECTS ON THE BIMOLECULAR ELECTRON-TRANSFER SELF-EXCHANGE RATES OF RUTHENIUM AMMINE COMPLEXES - A DOMINANT ROLE FOR SOLVENT-SOLUTE HYDROGEN-BONDING, Journal of the American Chemical Society, 118(13), 1996, pp. 3247-3252
Electron transfer self-exchange rate constants for a series of three r
uthenium ammine complexes have been determined in a range of solvents
using deuterium NMR line-broadening measurements. It is found for all
three complexes that the observed rates slow dramatically in solvents
of strong Lewis basicity as measured by the Gutman donor number. The r
ates do not correlate significantly with either the dielectric continu
um-based Pekar factor, (1/n(2) - 1/D-s), or the solvent longitudinal r
elaxation time known to frequently characterize solvent dynamical effe
cts on electron transfer rates. The nature of the self-exchange rate s
low down is discussed within the context of Marcus-Hush theory and is
attributed to redox-state-dependent rearrangements of hydrogen bonds b
etween solvent and solute in the second coordination sphere. Quantitat
ive comparisons between the observed donor-number effect on rate and r
elevant optical electron transfer data from chemically similar systems
reveal evidence of an additional donor-number-dependent contribution
to the work of reactant preassociation in the bimolecular process.