VOLTAMMETRIC AND SPECTROSCOPIC STUDY OF THE IRON(II) COMPLEXES WITH THE SEMIQUINONE OF 2-HYDROXY-1,4-NAPHTHOQUINONE (LAWSONE) IN APROTIC MEDIUM

The electrochemical and spectroscopic characterization of the species formed upon interaction of iron(II) with 2-hydroxy-1,4-naphthoquinone (Lawsone) and its reduced form has been studied in dimethylsulphoxide. Neither the protonated nor the anionic form of the ligand interacts with iron(II) to form complexes of reasonable stability. The reduced species of the ligand (semiquinone) forms a very stable complex with iron(II), which has a 1:2 stoichiometry and presents a formation constant of 3.5 x 10(25). The magnetic susceptibility measurements of the iron(II)-semiquinone system indicate the existence of an intramolecular charge transfer between the metal ion and one of the radical ligands, so that the metal centre has the character of iron(III). The presence of the metal ion stabilizes the radical species formed upon reduction of the quinone, which may be relevant to understand the mechanisms involved in charge-transfer processes in biological systems.