The Solvent Effect on the Electron-Transfer Reactions of Cobalt(III) Complexes. The Reduction of the cis-Chloro-2-aminoethanolbis(ethylenediamine)cobalt(III) Ion by Iron(II) in Aqueous Solutions of Organic Solvents

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Abstract
The solvent effect on the reduction of the textitcis-chloro-2-aminoethanolbis(ethylenediamine)cobalt(III) ion by iron(II) was investigated in aqueous solutions of dimethylsulfoxide (DMSO), dimethylformamide (DMF), ethanol, and acetone. The second-order rate constants for the reduction are 4.4×10−5 M−1sec−1 in the absence of an organic solvent, 1.4×10−3 M−1sec−1 in 0.20 Mf DMSO, 7.3×10−4 M−1sec−1 in 0.20 Mf DMF, 1.1×10−4 M−1sec−1 in 0.20 Mf ethanol, and 1.0×10−4 M−1sec−1 in 0.20 Mf acetone, at 25°C and at 0.16 M HClO4 and Σ[ClO4−]=0.60 M (Mf= mol fraction of organic solvent). From the kinetic and spectral data, it is suggested that the increase in the rate upon the addition of an organic solvent may be mainly due to a change in the solvation sphere of the reductant by replacing the water molecules by the organic molecules.