Abstract
Several Mn, Cu, and Zn chelates of etiobiliverdin-IV-γ, mesobiliverdin-IXα, and its dimethyl ester are studied. The results show that the chemical constitution of the Cu biliverdin chelate corresponds to a formal metal oxidation state of (II) coordinated to a neutral radical of the NH trideprotonated biliverdin. The reactivity of the Cu(II) bilindione chelates in nucleophilic solvents agrees with that expected for a π neutral radical structure of the ligand; in CH3OH, they undergo oxidation towards dimethoxybilipurpurins. The magnetic behaviour of Cu(II) etiobiliverdinate-IV-γ in the solid state shows an intramolecular weak antiferromagnetic coupling d9Cu-to-π-radical (J=−23 cm−1) and an intermolecular weak antiferromagnetic coupling π-radical-to-π-radical (J=−45 cm−1). The analogy of this magnetic behaviour to that of the π cation radical of metalloporphyrins is discussed.
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