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Indazole-Derived Mono-/Diruthenium and Heterotrinuclear Complexes: Switchable Binding Mode, Electronic Form, and Anion Sensing Events
Journal
Inorganic Chemistry
ISSN
00201669
Date Issued
2022-10-10
Author(s)
Kumari, Maya
Dey, Krishnendu
Bera, Sudip Kumar
Lahiri, Goutam Kumar
Abstract
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 (Naand Nbdonors and 1H-indazole versus 2H-indazole) of the heterocyclic H-Iz/Iz-in the complexes. Unlike [1′]ClO4containing two NH protons at the backface of H-Iz units, the corresponding [1]ClO4was 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 RuIIIRuIIstate in [3]ClO4suggested 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]ClO4and 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]ClO4containing one free NH proton at the backface of H-Iz, [1′]ClO4with 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 - 2PΟ4-in CH3CN via intermolecular NH···anion hydrogen bonding interaction. The difference in the sensing feature between [1′]ClO4and 1/[2]ClO4could be rationalized by their pKavalues of 8.4 and 11.3/10.8, respectively.