Reactions of OH radicals with tris(1,10-phenanthroline)iron(II) studied by pulse radiolysis

The reaction of OH radicals with aqueous tris(1,10-phenanthroline)iron(II) leads to the formation of an adduct, which exhibits a broad absorption band at rmpH = 6, λ_{max = 460 nm}, and ϵ₄₆₀ = 6700 (molar, decadic, 1 mol⁻¹ cm⁻¹). The rate of formation of the adduct is first order in complex concentration with a bimolecular rate constant $\text{k = (1 >}\text{s}\text{̇}\text{;05±0 >}\text{s}\text{̇}\text{;03)× 10}{}^{10}\text{1 mol}{}^{\mathrm{-1}}\text{s}{}^{\mathrm{-1}}$ independent of pH in the range pH 3–11. The adduct decays by mixed-order kinetics, but at 310 nm a second-order formation of a decay product can be directly observed.

The reaction of OH radicals with aqueous 1,10-phenanthroline leads also to the formation of an adduct which absorbs in the whole visible region with a maximum at 425 nm and ε₄₂₅ = 2612 (molar, decadic, 1 mol⁻¹ cm⁻¹) in neutral solution. The adduct exhibits a red shift in acidic and alkaline media. The formation is first order in 1,10-phenanthroline with a bimolecular rate constant $\text{k = (8 >}\text{s}\text{̇}\text{;6±0 >}\text{s}\text{̇}\text{;7)×10}{}^9\text{1 mol}{}^{\mathrm{-1}}\text{s}{}^{\mathrm{-}}$ at pH = 6; the rate of formation is pH dependent. The adduct decays according to second-order kinetics leading to the formation of a product that exhibits the presence of an additional functional group. A similar product, determined to have pK⋟4 > ṡ;2 and pK₂⋟8 > ṡ;1, has been isolated after γ-radiolysis of 1,10-phenanthroline.