Effect of changing the charge of an iron(II) chelate on electron transfer to a cobalt(III) complex-containing poly(methacrylic acid-co-styrenesulfonic acid) in aqueous solution

Abstract

Three different poly(methacrylic acid-co-styrenesulfonic acid)-bound cis-Co^III(en)₂(OH₂)L species (CoPMAS)(en = ethylenediamine, L = methacrylate residue on the polymer) having different degrees of copolymerization and varying amounts of bound Co^III were synthesized. The effect of charge on the iron(II) chelate on the electron transfer between CoPMAS and [Fe(edta)]^2–(H₄edta = ethylenediamine-N,N,N′,N′-tetraacetic acid) or [Fe(hedta)]^–(H₃hedta =N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid) was investigated. The Co^III was reduced via electron transfer from Fe^II to CoPMAS. The degree of reduction of Co^III by both iron(II) chelates, R_Co, and the electron-transfer rate significantly depend on the proportion of functional groups having a negative charge on the polymer chain. The α′-dependence of R_Co for both iron(II) chelates was similar, but their reaction rates differed: the rate for [Fe(hedta)]^– being larger than that for [Fe(edta)]^2–. The value of R_Co was independent of the charge of the iron(II) chelate, but the reaction rate was influenced by the charge.