Inner-Sphere Electron Transfer Induced Reversible Electron Reservoir Feature of Azoheteroarene Bridged Diruthenium Frameworks.

This article demonstrates the stabilization of ground- and redox-induced metal-to-ligand charge transfer excited states on coordination of azo-coupled bmpd(L4) [bmpd = ()-1,2-bis(1-methyl-1-pyrazol-3-yl)diazene; L4 = -N═N-] to the electron-rich {Ru(acac)} (acac = acetylacetonate) unit in mononuclear Ru(acac)(L4) () and diastereomeric dinuclear (acac)Ru(μ-L4)Ru(acac) [, ΔΔ/ΛΛ ()/, ΔΛ ()] complexes, respectively. It also develops further one-step intramolecular electron transfer induced L4 bridged isovalent higher analogue [(acac)Ru(μ-L4)Ru(acac)]ClO in diastereomeric forms, -[]ClO-[]ClO. On the contrary, under identical reaction conditions electronically and sterically permuted bimpd [L5, ()-1,2-bis(4-iodo-1-methyl-1-pyrazol-3-yl)diazene)] delivered mononuclear Ru(acac)(L5) () as an exclusive product. Further, the generation of unprecedented heterotrinuclear complex [(acac)Ru(μ-L4)Ag(μ-L4)Ru(acac)]ClO ([]ClO) involving unreduced L4 via the reaction of and AgClO revealed the absence of any inner-sphere electron transfer (IET) as in precursor , which in turn reaffirmed an IET (at the interface of electron-rich Ru(acac) and acceptor L4) mediated stabilization of . Structural authentication of the complexes with special reference to the tunable azo distance (N═N, N-N, N-N) of and their spectro-electrochemical events in accessible redox states including the reversible electron reservoir feature of → → were evaluated in conjunction with density functional theory/time-dependent density functional theory calculations. The varying extent of IET as a function of heteroaromatics appended to the azo group of L (L1 = abpy = 2,2'-azobipyridine, L2 = abbt = 2,2'-azobis(benzothiazole), L3 = abim = azobis(1-methylbenzimidazole), L4 and L5, Schemes 1 & 2) in the Ru(acac)-derived respective molecular setup has been addressed.