IONIC-STRENGTH EFFECTS ON ELECTRON-TRANSFER IN THE INVERTED REGION

Rate constants (k) for the intramolecular electron transfer reaction fac-[Re(I)(bpy.-)(CO)3(py-PTZ.+)](PF6) --> fac-[Re(I)(bpy)(CO)3(py-PTZ)](PF6), which occurs in the inverted region, were measured at 295 K in 1,2-dichloroethane solutions at different ionic strengths with [N(n-C4H9)4](PF6) as the added electrolyte (bpy is 2,2'-bipyridine, py-PTZ is 10-(4-picolyl)phenothiazine). The rate constant for electron transfer varies with ionic strength from 1.05 X 10(7) s-1 (mu = 0.0002 m) to 1.65 x 10(7) s-1 (mu = 0.32 m). The variation of k with ionic strength is consistent with an energy gap law dependence for the electron transfer reaction. Based on conductivity measurements at a series of concentrations, the related salt fac-[Re(I)(bpy)(CO)3(4-Etpy)](PF6) (4-Etpy is 4-ethylpyridine) is nearly completely ion-paired in 1,2-dichloroethane even in the absence of added supporting electrolyte.