title: A structurally characterised redox pair involving an indigo radical: indigo based redox activity in complexes with one or two [Ru(bpy)2] fragments.
abstract: The reaction between indigo, H2Ind, and {Ru(bpy)2(EtOH)2}2+in EtOH/NaOH produced the compounds [Ru(bpy)2(HInd)]ClO4[1]ClO4, rac-{[Ru(bpy)2]2(μ-Ind)}(ClO4)2[2](ClO4)2, and meso-{[Ru(bpy)2]2(μ-Ind)}(ClO4)3[2](ClO4)3, which were structurally characterised, the latter as the first stable, isolable radical complex of indigo. The redox pair 22+/23+showed little structural difference, as confirmed using DFT calculations. The redox series 1nand 2nwere investigated using voltammetry and spectroelectrochemistry (EPR, UV-vis-NIR). Remarkably, the EPR results for 1, 12+, 2+and 23+revealed mostly ligand based spin in ruthenium(ii) complexes of the indigo-derived radical ligands HInd˙2-, HInd˙, Ind˙3-and Ind˙-, in agreement with the DFT calculated spin densities. The dominance of the frontier orbitals by the metal-stabilised indigo chromophore was also confirmed via the TD-DFT based assignment of near-infrared absorptions as intra-indigo or ligand-to-ligand charge transfer transitions.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. lahiri@chem.iitb.ac.in.
authors.forename: Madhumita
authors.initials: M
authors.lastname: Chatterjee
authors.forename: Prasenjit
authors.initials: P
authors.lastname: Mondal
authors.forename: Katharina
authors.initials: K
authors.lastname: Beyer
authors.forename: Alexa
authors.initials: A
authors.lastname: Paretzki
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kaim
authors.forename: Goutam Kumar
authors.initials: GK
authors.lastname: Lahiri