Synthesis and characterization of a dinuclear ferric complex with redox-active ligands

A dinuclear ferric complex with the redox-active ligand ( L Cl 2 ) 2 - ( H 2 L Cl 2 = N,N′-dimethyl-bis(3,5-dichloro-2-hydroxybenzyl)-1,2-diaminoethane), was synthesized and characterized. The two iron(III) ions are six-coordinate in a distorted octahedral environment of the N 2 O 2 Ph donor set of one ( L Cl 2 )2− and one amine and one phenolate donor of a second ( L Cl 2 )2−, which bridges the two complex halves. The relatively low-symmetric complex 1 crystallizes in the space group R 3 ¯ . The crystal structure contains hexagonal, one-dimensional channels parallel to the c axis with diameters of ∼13 Å. The absorption spectrum of 1 exhibits strong characteristic features of pπ → d π ∗ , pπ → d σ ∗ , phenolate-to-metal CTs, and π → π∗ ligand transitions. Electrochemical studies on 1 reveal the redox-activity of the coordinated ligand ( L Cl 2 )2− by showing irreversible oxidative electron-transfer waves. The reductive electron transfers at negative potentials seem to originate from metal-centered processes. A detailed comparison to complexes with similar donor sets provides new insights into the electrochemical properties of these kinds of complexes.