Evidence for Bidirectional Noninnocent Behavior of a Formazanate Ligand in Ruthenium Complexes MandalAbhishek SchwederskiBrigitte FiedlerJan KaimWolfgang LahiriGoutam Kumar 2015 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.