Electron-Transfer Reactions of Multidentate-ligand Cobalt(III) Complexes. III. The Reductions of Several Chloro- and Bromo(nitrilopolycarboxylato)cobaltate(III) Ions by Iron(II)

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Abstract
The reductions of chloro- and bromo(ethylenediaminetriacetatoacetic acid)cobaltate(III), chloro- and bromo (N-hydroxy ethy lethy lenediamine-N,N′, N′-triacetato)cobaltate (III), and dichloro(ethylenediaminediacetato) cobaltate(III) ions by iron(II) in perchloric acid solutions obey the second-order rate expression: –d-[Co(III)]/dt=kc[Co(III)][Fe2+]. The second-order rate constants, kc, and activation parameters for these reactions were determined spectrophotometrically. For the cases of all the Co(III) complexes investigated, an increase in the rate constant with the hydrogen-ion concentration at a constant ionic strength is expressed by: logkc=logk0+A[H+], where k0 and A are constants for the given complex at a constant ionic strength and temperature. The hydrogen-ion dependence can be explained by the difference in the degree of stabilization of the Co(III) anion between that by hydrogen ions and that by sodium ions.