Ion atmosphere relaxation control of electron transfer dynamics in a plasticized carbon dioxide redox polyether melt

The sorption Of CO2 into the highly viscous, semisolid hybrid redox polyether melt, [Co(phenanthroline)(3)](MePEG-SO3)(2), where MePEG-SO3 is a MW 350 polyether-tailed sulfonate anion, remarkably accelerates charge transport in this molten salt material. Electrochemical measurements show that as CO2 pressure is increased from 0 to 800 psi (54 atm) at 23 degreesC, the physical diffusion coefficient D-PHYS of the Co(II) species, the rate constant k(EX) for Co(II/I) electron self-exchange, and the physical diffusion coefficient of the counterion D-COUNTERION all increase, from 4.3 x 10(-10) to 6.4 x 10(-9) cm(2)/S 4.1 X 10(6) to 1.6 x 10(7) M-1 s(-1), and 3.3 x 10(-9) to 1.6 x 10(-8) cm(2)/S, respectively. Plots of log(k(EX)) versus log(D-PHYS) and of log(k(EX)) versus log(D-COUNTERION) are linear, showing that electron self-exchange rate constants are closely associated with processes that also govern D-PHYS and D-COUNTERION. Slopes of the plots are 0.68 and 0.98, respectively, indicating a better linear correlation between k(EX) and D-COUNTERION. The evidence indicates that k(EX) can be controlled by relaxation of the counterion atmosphere about the Co complexes in the semisolid redox polyether melts. Because the counterion relaxation is in turn controlled by polyether solvent fluctuations, this is a new form of solvent dynamics control of electron transfer.