Redox series of the complexes [Ru(L)(L')(2)](n), L = 1,5-diphenyl-3-(4-tolyl)-formazanate and L' = 2,4-pentanedionate (acac(-)), 2,2'-bipyridine (bpy), or 2-phenylazopyridine (pap), were studied by cyclic and differential pulse voltammetry and by TD-DFT-supported spectroelectrochemistry (UV-vis-NIR, EPR). The precursors [Ru-II(L-)(acac(-))(2)], [Ru-II(L-)(bpy)(2)]ClO4, and [Ru-II(L-)(pap)(2)]ClO4 were identified in their indicated oxidation states by X-ray crystal structure determination. The six-membered formazanato-ruthenium chelate rings have an envelope conformation with puckering of the metal. DFT calculations indicate a pronounced sensitivity of the N-N bond lengths toward the ligand oxidation state. Several electrochemically accessible charge states were analyzed, and the derived oxidation numbers Ru-II, Ru-III, or Ru-IV, L' or (L')(center dot-), and L-, L center dot 2-, or the new formazanyl ligand L-center dot for the two-way noninno cent formazanate reflect the increasing acceptor effect of the ancillary ligands L' in the series acac(-) < bpy < pap.