Solvent Dynamics and Pressure Effects in the Kinetics of the Tris(bipyridine)cobalt(III/II) Electrode Reaction in Various Solvents

Abstract

The volume of activation ∆V el q for the Co(bpy) 3 3+/2+ electrode reaction in aqueous NaCl (0.2 mol L -1 ) is -8.6 ( 0.4 cm 3 mol -1 at 25.0 °C, as expected on theoretical grounds and by analogy with Co(en) 3 3+/2+ and Co(phen) 3 3+/2+ , and neither the rate constant k el at various pressures nor ∆V el q correlate with the corresponding mean diffusion coefficients D for the couple and the diffusional activation volume ∆V diff q , respectively. In organic solvents, however, ∆V el q is strongly positiVe (9.1 ( 0.3, 10.2 ( 0.7, and 12.2 ( 0.9 cm 3 mol -1 for CH 3 CN, acetone, and propylene carbonate, respectively, with 0.2 mol L -1 [(C 4 H 9 ) 4 N]ClO 4 at 25 °C) and correlates with ∆V diff q , while k el correlates with D. These results support the proposition of Murray et al.

Multiple Mechanisms for Electron Transfer at Metal/Self‐Assembled Monolayer/Room‐Temperature Ionic Liquid Junctions: Dynamical Arrest versus Frictional Control and Non‐Adiabaticity

“…These values are theoretically well interpretable for these patterns. [14,15,17,50,51] The case of c (n + 1) = 4 is almost similar to that of c (n + 1) = 3. For c (n + 1) = 6 and 8, intermediate values of + 2.4 and À4.2 cm 3 mol À1 , respectively, were found (Table 1), and according to other available signatures (see above), c (n + 1) = 6 and 8 are the intermediate occurrences.…”

“…For the volumes of activation (see refs. [14], [15], [17], [50] and [51] for the corresponding theoretical background) in the extreme cases of c (n + 1) = 3 and 12 to be considered as well-shaped non-adiabatic and adiabatic occurrences, huge values of + 25.3 and À21.7 cm 3 mol À1 were found (Table 1; some preliminary results have been published in ref. [25]).…”

High‐Pressure Probing of a Changeover in the Charge‐Transfer Mechanism for Intact Cytochrome c at Gold/Self‐Assembled Monolayer Junctions

“…(1) and (4)], and again omitting the minor terms, one arrives at Equation (7), [3,44] DV aðADÞ ¼ bRT…”

“…This is the case for all known liquids except water. [3,6,44] Actually, for most solvents, h increases exponentially with pressure and yields a maximum net viscosity-related contribution as high as + 20 cm 3 mol…”

“…(as the upper limit [3,44] ). In addition, we assume that for composite multicomponent systems, as in the present case, the overall medium reorganization energy can be roughly reproduced by summation over individual components [Eq.…”