Effect of the polymeric ligand on electron‐transfer reactions: Iron(II) reduction of cis‐chloropoly‐4‐vinylpyridinebis(ethylenediamine)‐cobalt(III) complexes

Water‐soluble Co(III)–PVP complexes (where PVP = poly‐4‐vinylpyridine) were prepared, and the specific rates and activation parameters for the iron(II) reductions of cis‐Co(en)2XCl2+ (where X = PVP or pyridine and en = ethylenediamine) were determined in dilute sulfuric acid solutions. Under the conditions [H2SO4] = 0.50M, Σ[SO42−] = 1.25 M at 25°C, the second‐order rate constants and activation entropies, respectively, for the cis‐Co(en)2−XCl2+ are (4.10 ± 0.05) × 10−3l./mole‐sec and −14 ± 0.6 eu for × = pyridine, (2.1 ± 0.1) × 10−3l./mole‐sec and −6.0 ± 1 eu for × = PVP (Pn = 19), and (2.42 ± 0.08) × 10−3 l./mole‐sec and −2.5 ± 0.8 eu for × = PVP (Pn = 98), where Pn is the degree of polymerization of the PVP. The main feature of the polymer effect in the electron‐transfer reactions of the PVP complexes in which uncoordinated pyridine rings are present may be attributed to greater activation entropy. Such a greater entropy for the PVP complex may be partly ascribed to the intricate structure of the PVP ligand in the solution.