Noninnocently Behaving Bridging Anions of the Widely Distributed Antioxidant Ellagic Acid in Diruthenium Complexes

• Published in: Inorganic chemistry 2015-10, Vol.54 (20), p.10049-10057
• Main Authors: Mandal, Abhishek, Grupp, Anita, Schwederski, Brigitte, Kaim, Wolfgang, Lahiri, Goutam Kumar
• Format: Article
• Language: English
• Subjects: Accessibility; Anions; Anions - chemistry; Antioxidants - chemistry; Bridging; Crystal structure; Density functional theory; Electron paramagnetic resonance; Ellagic Acid - chemistry; Mathematical analysis; Models, Molecular; Molecular Structure; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Quantum Theory; Radicals; Ruthenium - chemistry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.5b01868

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 pap0/•– 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 E2–.