Redox series of the complexes [Ru(L)(L′)<sub>2</sub>]<sup><i>n</i></sup>, L = 1,5-diphenyl-3-(4-tolyl)-formazanate
and L′ = 2,4-pentanedionate (acac<sup>–</sup>), 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<sup>III</sup>(L<sup>–</sup>)(acac<sup>–</sup>)<sub>2</sub>], [Ru<sup>II</sup>(L<sup>–</sup>)(bpy)<sub>2</sub>]ClO<sub>4</sub>, and [Ru<sup>II</sup>(L<sup>–</sup>)(pap)<sub>2</sub>]ClO<sub>4</sub> 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<sup>II</sup>, Ru<sup>III</sup>, or Ru<sup>IV</sup>, L′ or (L′)<sup>•–</sup>, and L<sup>–</sup>, L<sup>•2–</sup>, or the new formazanyl ligand L<sup>•</sup> for the two-way
noninnocent formazanate reflect the increasing acceptor effect of
the ancillary ligands L′ in the series acac<sup>–</sup> < bpy < pap