title: Uncommon cis configuration of a metal-metal bridging noninnocent Nindigo ligand.
abstract: In contrast to several reported coordination compounds of trans-Nindigo ligands [Nindigo = indigo-bis(N-arylimine) = LH2] with one or two six-membered chelate rings involving one indole N and one extracyclic N for metal binding, the new diruthenium complex ion [(acac)2Ru(μ,η(2):η(2)-L)Ru(bpy)2](2+) = 2(2+) exhibits edge-sharing five- and seven-membered chelate rings in the first documented case of asymmetric bridging by a Nindigo ligand in the cis configuration [L(2-) = indigo-bis(N-phenylimine)dianion]. The dication in compound [2](ClO4)2 displays one Ru(α-diimine)3 site and one ruthenium center with three negatively charged chelate ligands. Compound [2](ClO4)2 is obtained from the [Ru(bpy)2](2+)-containing cis precursor [(LH)Ru(bpy)2]ClO4 = [1]ClO4, which exhibits intramolecular H-bonding in the cation. Four accessible oxidation states each were characterized for the 1(n) and 2(n) redox series with respect to metal- or ligand-centered electron transfer, based on X-ray structures, electron paramagnetic resonance, and ultraviolet-visible-near-infrared spectroelectrochemistry in conjunction with density functional theory calculation results. The structural asymmetry in the Ru(III)/Ru(II) system 2(2+) is reflected by the electronic asymmetry (class I mixed-valence situation), leaving the noninnocent Nindigo bridge as the main redox-active site.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Prasenjit
authors.initials: P
authors.lastname: Mondal
authors.forename: Sebastian
authors.initials: S
authors.lastname: Plebst
authors.forename: Ritwika
authors.initials: R
authors.lastname: Ray
authors.forename: Shaikh M
authors.initials: SM
authors.lastname: Mobin
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kaim
authors.forename: Goutam Kumar
authors.initials: GK
authors.lastname: Lahiri