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

• Published in: Inorganic chemistry 2022-10, Vol.61 (40), p.16122-16140
• Main Authors: Kumari, Maya, Dey, Krishnendu, Bera, Sudip Kumar, Lahiri, Goutam Kumar
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.2c02628

The article deals with the newer classes of mononuclear: [(acac)2RuIII(H-Iz)­(Iz–)] 1, [(acac)2RuIII(H-Iz)2]­ClO4 [1]­ClO4/[1′]­ClO4, and [(bpy)2RuII(H-Iz)­(Iz–)]­ClO4 [2]­ClO4, mixed-valent unsymmetric dinuclear: [(acac)2RuIII(μ-Iz–)2RuII(bpy)2]­ClO4 [3]­ClO4, and heterotrinuclear: [(acac)2RuIII(μ-Iz–)2MII(μ-Iz–)2RuIII(acac)2] (M = Co:4a, Ni:4b, Cu:4c, and Zn:4d) 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 (Na and Nb donors and 1H-indazole versus 2H-indazole) of the heterocyclic H-Iz/Iz– in the complexes. Unlike [1′]­ClO4 containing two NH protons at the backface of H-Iz units, the corresponding [1]­ClO4 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 1. 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–)2-bridged unsymmetric mixed-valent RuIIIRuII state in [3]­ClO4 suggested negligible intramolecular electronic coupling corresponding to a class I setup (Robin and Day classification). Heterotrinuclear complexes (4a–4d) exhibited varying spin configurations due to spin–spin interactions between the terminal Ru­(III) ions and the central M­(II) ion. Though both [3]­ClO4 and 4a–4d displayed ligand (Iz–/Iz•)-based oxidation, reductions were preferentially taken place at the bpy and metal (RuIII/RuII) centers, respectively. Unlike 1 or [2]­ClO4 containing one free NH proton at the backface of H-Iz, [1′]­ClO4 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–, HSO4 –, and Η2PΟ4 – in CH3CN via intermolecular NH···anion hydrogen bonding interaction. The difference in the sensing feature between [1′]­ClO4 and 1/[2]­ClO4 could be rationalized by their pK a values of 8.4 and 11.3/10.8, respectively.