title: 1,5-Diamido-9,10-anthraquinone, a Centrosymmetric Redox-Active Bridge with Two Coupled β-Ketiminato Chelate Functions: Symmetric and Asymmetric Diruthenium Complexes.
abstract: The dinuclear complexes {(μ-H2L)[Ru(bpy)2]2}(ClO4)2 ([3](ClO4)2), {(μ-H2L)[Ru(pap)2]2}(ClO4)2 ([4](ClO4)2), and the asymmetric [(bpy)2Ru(μ-H2L)Ru(pap)2](ClO4)2 ([5](ClO4)2) were synthesized via the mononuclear species [Ru(H3L)(bpy)2]ClO4 ([1]ClO4) and [Ru(H3L)(pap)2]ClO4 ([2]ClO4), where H4L is the centrosymmetric 1,5-diamino-9,10-anthraquinone, bpy is 2,2'-bipyridine, and pap is 2-phenylazopyridine. Electrochemistry of the structurally characterized [1]ClO4, [2]ClO4, [3](ClO4)2, [4](ClO4)2, and [5](ClO4)2 reveals multistep oxidation and reduction processes, which were analyzed by electron paramagnetic resonance (EPR) of paramagnetic intermediates and by UV-vis-NIR spectro-electrochemistry. With support by time-dependent density functional theory (DFT) calculations the redox processes could be assigned. Significant results include the dimetal/bridging ligand mixed spin distribution in 3(3+) versus largely bridge-centered spin in 4(3+)-a result of the presence of Ru(II)-stabilizig pap coligands. In addition to the metal/ligand alternative for electron transfer and spin location, the dinuclear systems allow for the observation of ligand/ligand and metal/metal site differentiation within the multistep redox series. DFT-supported EPR and NIR absorption spectroscopy of the latter case revealed class II mixed-valence behavior of the oxidized asymmetric system 5(3+) with about equal contributions from a radical bridge formulation. In comparison to the analogues with the deprotonated 1,4-diaminoanthraquinone isomer the centrosymmetric H2L(2-) bridge shows anodically shifted redox potentials and weaker electronic coupling between the chelate sites.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Mohd Asif
authors.initials: MA
authors.lastname: Ansari
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Mandal
authors.affiliation: Institut für Anorganische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
authors.forename: Alexa
authors.initials: A
authors.lastname: Paretzki
authors.affiliation: Institut für Anorganische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Beyer
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic , Dolejškova 3, CZ-18223 Prague, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Fiedler
authors.affiliation: Institut für Anorganische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kaim
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India.
authors.forename: Goutam Kumar
authors.initials: GK
authors.lastname: Lahiri