Indazole-Derived Mono-/Diruthenium and Heterotrinuclear Complexes: Switchable Binding Mode, Electronic Form, and Anion Sensing Events.

The article deals with the newer classes of mononuclear: [(acac)Ru(H-Iz)(Iz)] , [(acac)Ru(H-Iz)]ClO []ClO/[]ClO, and [(bpy)Ru(H-Iz)(Iz)]ClO []ClO, mixed-valent unsymmetric dinuclear: [(acac)Ru(μ-Iz)Ru(bpy)]ClO []ClO, and heterotrinuclear: [(acac)Ru(μ-Iz)M(μ-Iz)Ru(acac)] (M = Co:, Ni:, Cu:, and Zn:) complexes (H-Iz = indazole, Iz = indazolate, acac = acetylacetonate, and bpy = 2,2'-bipyridine). Structural characterization of all the aforestated complexes established their molecular identities including varying binding modes (N and N donors and 1-indazole versus 2-indazole) of the heterocyclic H-Iz/Iz in the complexes. Unlike []ClO containing two NH protons at the backface of H-Iz units, the corresponding []ClO was found to be unstable due to the deprotonation of its positively charged quaternary nitrogen center, and this resulted in the eventual formation of the parent complex . A combination of experimental and density functional theory calculations indicated the redox noninnocent feature of Iz in the complexes along the redox chain. The absence of intervalence charge transfer transition in the near-infrared region of the (Iz)-bridged unsymmetric mixed-valent RuRu state in []ClO suggested negligible intramolecular electronic coupling corresponding to a class I setup (Robin and Day classification). Heterotrinuclear complexes () exhibited varying spin configurations due to spin-spin interactions between the terminal Ru(III) ions and the central M(II) ion. Though both []ClO and - displayed ligand (Iz/Iz)-based oxidation, reductions were preferentially taken place at the bpy and metal (Ru/Ru) centers, respectively. Unlike or []ClO containing one free NH proton at the backface of H-Iz, []ClO with two H-Iz units could selectively and effectively recognize F, OAc, and CN among the tested anions: F, OAc, CN, Cl, Br, I, SCN, HSO, and ΗPΟ in CHCN via intermolecular NH···anion hydrogen bonding interaction. The difference in the sensing feature between []ClO and /[]ClO could be rationalized by their p values of 8.4 and 11.3/10.8, respectively.