title: Noninnocently Behaving Bridging Anions of the Widely Distributed Antioxidant Ellagic Acid in Diruthenium Complexes.
abstract: Dinuclear compounds [L2Ru(μ-E)RuL2](n) where L is acetylacetonate (acac(-), 2,4-pentanedionate), 2,2'-bipyridine (bpy), or 2-phenylazopyridine (pap) and EH4 is ellagic acid, an antioxidative bis-catechol natural product, were studied by voltammetric and spectroelectrochemical techniques (UV-vis-NIR and electron paramagnetic resonance (EPR)). The electronic structures of the isolated forms (NBu4)2[(acac)2Ru(μ-E)Ru(acac)2] ((NBu4)2[1]), [(bpy)2Ru(μ-E)Ru(bpy)2]ClO4 ([2]ClO4), and [(pap)2Ru(μ-E)Ru(pap)2] ([3]) were characterized by density functional theory (DFT) in conjunction with EPR and UV-vis-NIR measurements. The crystal structure of (NBu4)2[1] revealed the meso form and a largely planar Ru(μ-E)Ru center. Several additional charge states of the compounds were electrochemically accessible and were identified mostly as complexes with noninnocently behaving pap(0/•-) or bridging ellagate (E(n-)) anions (n = 2, 3, 4) but not as mixed-valence intermediates. The free anions E(n-), n = 1-4, were calculated by time-dependent DFT to reveal NIR transitions for the radical forms with n = 1 and 3 and a triplet ground state for the bis(o-semiquinone) dianion E(2-).
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: Anita
authors.initials: A
authors.lastname: Grupp
authors.affiliation: Institut für Anorganische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Schwederski
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
mesh_terms: D000838:Anions / Q000737:chemistry; D000975:Antioxidants / Q000737:chemistry*; D004610:Ellagic Acid / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D000838:Anions; D000975:Antioxidants; D009942:Organometallic Compounds; D004610:Ellagic Acid; D012428:Ruthenium