Metal‐to‐Ligand Charge Transfer Induced Valence Tautomeric Forms of Non‐Innocent 2,2′‐Azobis(benzothiazole) in Ruthenium Frameworks

Abstract

AbstractThe impact of metal‐to‐ligand charge transfer towards the redox noninnocence of 2,2′‐azobis(benzothiazole) (abbt) has been highlighted on coordination to {RuII(acac)2} (acac=2,4‐pentanedionato). It led to the authentication of a series of mononuclear and dinuclear complexes incorporating variable oxidation states of abbt (abbt0/.−/2−). Mononuclear 1 was identified as [RuIII(abbt.−)], a MLCT excited state of [RuII(abbt)]. Dinuclear 2 was however recognized as two discrete redox isomers: (i) radical bridged mixed‐valent meso‐[Ru2.5(μ‐abbt.−)Ru2.5] (2a) and (ii) dianionic ligand bridged isovalent meso‐[RuIII(μ‐abbt2−)RuIII] (2b), demonstrating unprecedented structural confirmation of valence tautomerism in azo‐based ligand systems. A crystal structure of [2]ClO4 validated the formation of [RuIII(μ‐abbt.−) RuIII]ClO4. Analysis of electronic structural forms of 1 and 2 in accessible redox states via spectroelectrochemistry and DFT revealed their electron reservoir feature.