Three Bis-BODIPY Analogous Diruthenium Redox Series: Characterization and Electronic Structure Analysis.

The dianion derived from (2Z,6Z)-3,7-diphenyl-N2,N6-di(pyridin-2-yl)pyrrolo[2,3-f]indole-2,6(1H,5H)-diimine (H BL), a modified BODIPY ligand precursor, is shown to be capable of bridging two metal complex fragments RuL , L=2,4-pentanedionato (acac ), 2,2'-bipyridine (bpy) or 2-phenylazopyridine (pap) in [Ru(acac) Ru(μ-BL)Ru(acac) ] (1/2), Ru(bpy) Ru(μ-BL)Ru(bpy) (3 ) and Ru(pap) Ru(μ-BL)Ru(pap) (4 ). The compounds, including a diastereoisomeric pair 1 (meso) and 2 (rac) were spectroscopically and structurally characterized. Reversible electron transfers as revealed by cyclic and differential pulse voltammetry allowed for an EPR and UV-vis-NIR spectroelectrochemical investigation of several neighboring charge states. Together with susceptibility measurements and TD-DFT calculations the assignment of oxidation states reveals that 1, 2 are diruthenium(III) species which can be oxidized or reduced by one electron whereas 3 and 4 contain ruthenium(II) and get reduced or oxidized mainly at the dianionic bridge (3 ) or are reduced at the ancillary ligands pap (4 ).