Outer-sphere electron-transfer reactions of co(III)–polymer complexes in relation to its polymer effects

The outer-sphere electron-transfer reactions between Co(III)(NH₃)₅L] (CIO₄)₃ L = polyethyleneimine (PEI), L = NH₃(Amm)] or cis-Co(III)(en)₂L′Cl]Cl₂ L′ = poly-N-vinyl-2-methylimidazole(PVI), poly-4-vinylpyridine (PVP), N-ethylimidazole (NEI), pyridine (Py)] and various Fe(II) were studied. In the reaction with Fe(II)-(phen)₃²⁺, the reactivity of Co(III)–PEI was smaller than that of Co(III)–Amm due to the larger electrostatic repulsion. On the other hand, the reactivity of Co(III)–PEI was larger by a factor of 80 in the reaction with Fe(II)(H₂O)₆²⁺. From the results of rapid-scanning spectroscopy, the higher reactivity of Co(III)–PEI is caused by the coordination of free ethyleneimine residues in the Co(III)–PEI to Fe(II)–ion. Further more, the hydrophobic interaction between heteroaromatic polymer ligands and Fe(II)-(phen)₃²⁺ brought about the higher reactivities of Co(III)–PVI and Co(III)–PVP. Three interactions caused by the essential properties of polymers are discussed in relation to conformational changes.