Influence of conformational changes of co(III)–poly‐N‐vinyl‐2‐methylimidazole complexes on electron‐transfer reactions of the complexes

Abstract

AbstractIn order to study the effect of conformational changes in electron‐transfer reactions of Co(III)–polymer complexes, cis‐[Co(III)(en)2LCl]Cl2, where the ligand L is PVI(poly‐N‐vinyl‐2‐methylimidazole) or NEI (N‐ethylimidazole), was prepared. Electrontransfer reactions with ferrous sulfate or FeEDTA2− were examined mainly with respect to the effects of the degree of coordination, ionic strength, composition of reaction solvent, in relation to the conformational changes. In the reduction by FeEDTA2−, an increase in the degree of coordination of Co(III)–PVI brought about an extreme increase in its reactivity, while it was almost unity in the reduction by ferrous sulfate. With an increase in the ionic strength, the reactivity decreased due to the electrostatic shielding in the reduction by FeEDTA2−. It was noticed that the reaction of Co(III)–PVI was much more enthalpically disadvantageous due to the shrinkage of the polymer chain than that of Co(III)–NEI, when neutral salts were added. In an aqueous alcoholic solvent, an increase in the alcohol concentration accelerated the reaction with FeEDTA2−, and especially in the reaction of Co(III)‐PVI, the maximum and minimum points of the reactivity were observed. On increasing the reaction temperature, the maximum and minimum points shifted to lower alcohol concentration. These phenomena are discussed in regard to the conformational changes of Co(III)–PVI.