Some dicopper complexes of benzimidazole-containing ligands

Dicopper complexes of the following benzimidazole-containing ligands have been studied as possible models for the active site of hemocyanin: EDTB (N,N,N′,N′-tetrakis-(2-benzimidazolylmethyl)-1,2-ethanediamine), EGTB (1,1,10,10-tetrakis-(2-benzimidazolylmethyl)-1,10-diaza-4,7-dioxadecane), and MEGTB (1,1,10,10-tetrakis-(1-methylbenzimidazol-2-ylmethyl)-1,10-diaza-4,7-dioxadecane). The initial oxygenation product of Cu 2(EDTB)(ClO 4) 2 in Me 2SO gives optical absorption maxima at 315 nm (ϵ = 3750 M −1 cm −1) and 690 nm (ϵ = 100 M −1 cm −1). The fluorescence emission intensities of Cu 2(EDTB)(ClO 4) 2 at 400 and 700 nm (excitation at 350 nm) decreases rapidly on exposure to air. This suggests oxidation of Cu 2(I) to Cu2(II). The x-ray absorption edge spectra suggest that both coppers in the oxygenation product, analyzed as Cu 2(EDTB)(ClO 4) 2(O) · 3H 2O, are Cu(II). From spectrophotometric titration of Cu 2(MEGTB)Cl 4 with azide, formation constant of the Cu 2(MEGTB)N 3Cl 3, complex has been obtained. Data from cyclic voltammetry experiments suggest that in the presence of azide, Cu(II)(N 3)Cu(II) species is present.