Resonance Raman spectroelectrochemical and structural study of reduced ruthenium(II) complexes with binaphthyridine-based ligands

The spectroscopy of electrochemically reduced ruthenium(II) complexes with 2,2′-biquinoline and 2,2′-binaphthyridine ligands have been investigated. These compounds are: [Ru(bn)(bpy)2][BF4]2 (where bn = 2,2′-bi-1,8-naphthyridine and bpy = 2,2′-bipyridyl); [Ru(dbn)(bpy)2][BF4]2 (where dbn = 3,3′-dimethylene-2,2′-bi-1,8-naphthyridine); [Ru(dbn)3][BF4]2; [Ru(dbq)(bpy)2][BF4]2 (where dbq = 3,3′-dimethylene-2,2′-biquinoline). Resonance Raman spectra of the parent species showed the bichromophoric nature of the visible absorptions of the heteroleptic complexes; both bpy and non-bpy ligand vibrations are enhanced depending on the excitation wavelength. Changes in the electronic absorption spectra for the complexes upon electrochemical reduction suggest the reducing electron is localised on the non-bpy ligand. For the complexes with the dimethylenebinaphthyridine ligand the second reduction also appears localised on the non-bpy ligand. Resonance Raman spectra of the reduced species confirm that the first and second reduction are based on the dbn ligand. Single crystal structures of [Ru(bn)(bpy)2][BF4]2 and [Ru(dbn)(bpy)2][BF4]2 have been determined and significant distortions of the ligands are apparent.