Electron-transfer Reactions between Cobalt (III)-Partially-quaternized-Poly (4-vinylpyridine) Complexes and Ferrous EDTA

In order to study the electrostatic effect of polymer complex on its reactivity, the rate constants and the activation parameters for the electron-transfer reactions of cis-[Co(III) (en)₂L Cl] • Cl₂ were determined (L = QPVP: partially-quaternized-poly(4-vinylpyridine) by benzylchloride; PVP: poly (4-vinylpyridine); Py: pyridine). The reduction rates of Co(III)-polymer complexes by ferrous sulfate were almost the same as that of Co(III)-Py complex (Table 2). The rate constants of the reduction by Fe(II)EDTA^2– decreased in the following order: Co(III)-QPVP >Co(III)-PVP>Co(III)-Py (Table 3). An increase in degree of coordination and in that of quaternization brought about an increase in reactivity of QPVP complex (Fig. 1). The acceleration for polymer complex was found to be due to a decrease in activation enthalpy and an increase in activation entropy. These results were interpreted in terms of the electrostatic attraction between FeEDTA^2– and polymer metal complex, viz., a polycation. For QPVP complex the electrostatic effect was considered to be more pronounced by pyridinium cation situated on QPVP chain.