Influence of Polyvalent Cations on the Rate of Electro-reductio n and Aquation of Co(NH₃)₅Xⁿ⁺ Complexes

Abstract

IN previous communications^1,2 the influence of the nature and concentration of anions on the rate of electroreduction of Co(NH₃)₅Xⁿ⁺ complexes has been reported. The influence exerted depends on the nature of the ligand X. This phenomenon has been explained by the assumption that the complex particle does not behave as a conducting sphere with uniform charge distribution (as assumed usually) but that the non-homogeneous charge distribution contributes considerably to the electrostatic free energy of activation and has to be taken into account. The ligand X represents the region of maximum non-homogeneity which induces an opposite non-homogeneity in the ionic atmosphere, the cations of the supporting electrolyte being preferentially attracted into the parts of the ionic atmosphere near the negative pole of the central particle. This increased concentration of cations shields the negative pole of the complex particle or might lead to the formation of an ion-pair between the positively charged complex particle and the cation. Both these effects make the attainment of the favourable orientation (that is, with ligand X removed from the positively charged electrode surface²) of the particle in the activated complex depolarizer-electrode² much easier and increase the rate of electro-reduction.