Reduction of the [(NH)-2,2′-bipyrid-3-ylium-C ³,N′]bis(2,2′-bipyridine-N,N′)iridium(III) trication in aqueous solutions: A pulse radiolytic study

The specific rates of reduction of the title complex by e_aq^- and ·C(CH₃)₂OH radicals are reported. The reduced complex thus produced at pH 0.5 has an absorption spectrum with λ_max = 395 ± 5 nm, ∈_max = 10 600 M^-1 cm^-1, and a shoulder around 450 nm. This reduced species has a pK_a value of about 0.9 and is relatively stable in the absence of oxidants. It decays with a half-life ≥ 100 s, and its decomposition reaction involves water reduction with evolution of dihydrogen. This reduced complex is oxidized by O₂ and Br₂^-· at rates approaching the diffusion-controlled limit.