Electrochemical and spectroelectrochemical studies of ruthenium–edta complexes with aromatic diamines and their α-diimine derivatives

This paper focuses on the electron transfer reaction, in water, between aquaethylenediaminetetraacetatoruthenate(III) and aromatic diamines, particularly 9,10-diaminophenanthrene (pha), as well as on the chemical characterization of the corresponding α-diimine ruthenium(II) complexes. The redox chemistry of these complexes at all their accessible metal- and ligand-centered oxidation states in slightly acidic (pH 4.7) aqueous solutions was investigated by means of electrochemistry and spectroelectrochemistry. All these redox species were found to be rather stable in solid state or aqueous solutions and totally interconvertible in reversible chemical/electrochemical processes. Comparison of the metal-centered redox potentials of the [RuIII/II(edta)(L)]−/2− (L=9,10-phenanthrenequinone diimine, o-benzoquinone diimine, 1,10-phenanthroline and 2,2′-bipyridine) complexes revealed that the quinone diimines possess stronger π-acceptor abilities than 1,10-phenanthroline and 2,2′-bipyridine, supporting a more efficient stabilization of the Ru(II) species, by means of π-backbonding interactions, in the cases of the quinonoid ligands.