Abstract
The temperature-jump method has been used to determine the rate constants for a series of rapid, “outer-sphere” oxidation- reduction reactions of the type
ki (M~l sec. *)
—I redi5- + ox23 + kr(M-lsec.~l)
The symbol oxi2- represents IrCle2-, IrBrs2-, or RhCL2-. The symbol red2i + represents a substituted phenanthroline or
bipyridine complex of iron(II) or ruthenium(II). It has been found that a diffusion-controlled limit of about 2 X 109
(Af-1 sec.-1) is approached when the equilibrium quotient is equal to or greater than unity. The rate of reaction for a given electron donor is then independent of the relative acceptor strength once the diffusional limit has been reached. Evidence was also found that steric restrictions can affect a diffusion-controlled electron-transfer reaction, causing the rate constant to fall somewhat short of the theoretical value.