The electron self-exchange reaction via the outer-sphere pathway of V(OH2)62+/3+, Ru(OH2)62+/3+, V(OH2)63+/4+, and Ru(OH2)63+/4+ was investigated with quantum chemical methods. The reorganizational energy (λ) and the nuclear frequency factor (νn) were computed on the basis of M(OH2)6·(OH2)12n+ (M = V, Ru; n
= 2, 3, 4) model compounds, in which the 12 water molecules represent the second coordination sphere. The constant for the association of the reactants (KA) was calculated via the Fuoss equation. The electronic coupling matrix element (Hab) was computed on the basis of [M(OH2)6]2n+
(M = V, Ru; n
= 5, 7) dimers, and the electronic frequency factor (νel) was determined from Hab and λ. Because, for the present redox couples, νn is much greater than νel, the second-order rate constant (k) is equal to KAνele−ΔE‡/RT (whereby ΔE‡
=
λ/4). The experimental rate constant for the V(OH2)62+/3+ self-exchange reaction is too low because side reactions involving ClO4−, the anion of the supporting electrolyte, have not been considered. The present computations suggest a rate constant in the range of 0.14–0.19 M−1 s−1 (25 °C, I
= 2.0 M). The calculated
rate constant for the Ru(OH2)62+/3+ self-exchange reaction agrees with experiment. For the V(OH2)63+/4+ self-exchange reaction, an estimated rate constant of (1–6) × 10−6 M−1 s−1 (25 °C, I
= 2.0 M) is predicted. The second-order rate constant for the Ru(OH2)63+/4+ self-exchange process is estimated as 0.07 or 18 M−1 s−1 (25 °C, I
= 5.0 M), respectively, for a δ or a σ donor–acceptor interaction, whereby the preferred pathway is yet unknown.