Ruthenium(II) Thiacrown Complexes Incorporating Noninnocent Redox Active Ligands: Synthesis, Electrochemical Properties, and Theoretical Studies

The synthesis and characterization of a series of nine new complexes incorporating [RuIICl­([n]­aneS3)] (n = 12,14, 16) metal centers coordinated to redox active catechol ligands is reported. The solid-state structure of one of these complexes has been determined by X-ray crystallography. The redox properties of these complexes have been probed experimentally through absorption spectroscopy, cyclic voltammetry, and spectroelectrochemistry, as well as computationally through density functional theory calculations. These studies reveal that, whereas the tetrachlorocatechol-based complexes are isolated with the dioxolene unit in the catechol form, the rest of the complexes are isolated in the semiquinone oxidation state. It was also found that the RuIII/II-based couple for the complexes is dependent on the nature of the thiacrown ligand coordinated to the metal center. A combination of optical and theoretical studies revealed that the absorption spectra of the complexes contain contributions from a variety of charge transfer processes; in the case of the tetrachlorocatechol complexes these transitions include catechol-to-thiacrown ligand-to-ligand charge transfer.