TEMPERATURE AND PRESSURE EFFECTS ON THE OUTER-SPHERE ELECTRON-TRANSFER REACTION BETWEEN HEXACYANOFERRATE(II) AND PENTAAMMINECOBALT(III) COMPLEXES IN AQUEOUS-SOLUTION - COMPARISON OF EXPERIMENTAL AND THEORETICAL VOLUMES OF ACTIVATION

The kinetics of a series of outer-sphere electron-transfer reactions of the type [formula-omitted] were studied as a function of temperature and pressure. It was possible to separate the ion-pair formation constant and the electron-transfer rate constant in a kinetic way, and the corresponding thermodynamic and activation parameters were determined. For the electron-transfer process, the rate and activation parameters lie in the ranges 0.06 ≤ k X 102≤ 20 s-1, 84 ≤ ΔH‡≤ 118 kJ mol-1, + 11 ≤ ΔS‡≤ 113 J K-1mol-1, and + 19 ≤ AV* ≤ +34 cm3mol-1. The experimentally observed activation volumes are in good agreement with those predicted theoretically on the basis of an average λ‡value of 0.48 ± 0.07. The results are discussed in reference to related studies reported in the literature. © 1990, American Chemical Society. All rights reserved.