Electrochemical and Spectroscopic Characterization of a Series of Mixed-Ligand Diruthenium Compounds

The electrochemistry and spectroelectrochemistry of a novel series of mixed-ligand diruthenium compounds were examined. The investigated compounds having the formula Ru2(CH3CO2)x(Fap)4−xCl where x = 1−3 and Fap is 2-(2-fluoroanilino)pyridinate anion were made from the reaction of Ru2(CH3CO2)4Cl with 2-(2-fluoroanilino)pyridine (HFap) in refluxing methanol. The previously characterized Ru2(Fap)4Cl as well as the three newly isolated compounds represented as Ru2(CH3CO2)(Fap)3Cl (1), Ru2(CH3CO2)2(Fap)2Cl (2), and Ru2(CH3CO2)3(Fap)Cl (3) possess three unpaired electrons with a Ru25+ dimetal core. Complexes 1 and 2 have well-defined Ru25+/4+ and Ru25+/6+ redox couples in CH2Cl2, but 3 exhibits a more complicated electrochemical behavior due to equilibria involving association or dissociation of the anionic chloride axial ligand on the initial and oxidized or reduced forms of the compound. The E1/2 values for the Ru25+/4+ and Ru25+/6+ processes vary linearly with the number of CH3CO2− bridging ligands on Ru2(CH3CO2)x(Fap)4−xCl and plots of reversible half-wave potentials vs the number of acetate groups follow linear free energy relationships with the largest substituent effect being observed for the oxidation. The major UV−visible band of the examined compounds in their neutral Ru25+ form is located between 550 and 800 nm in CH2Cl2 and also varies linearly with the number of CH3CO2− ligands on Ru2(CH3CO2)x(Fap)4−xCl. The electronic spectra of the singly oxidized and singly reduced forms of each diruthenium species were characterized by UV−visible spectroelectrochemistry in CH2Cl2.