title: Mononuclear and dinuclear complexes of dibenzoeilatin: synthesis, structure, and electrochemical and photophysical properties.
abstract: This work describes a study of Ru(II) and Os(II) polypyridyl complexes of the symmetrical, fused-aromatic bridging ligand dibenzoeilatin (1). The synthesis, purification, and structural characterization by NMR of the mononuclear complexes [Ru(bpy)(2)(dbneil)](2+) (2), [Ru(tmbpy)(2)(dbneil)](2+) (3), and [Os(bpy)(2)(dbneil)](2+) (4), the homodinuclear complexes [[Ru(bpy)(2)](2)[micro-dbneil]](4+) (5), [[Ru(tmbpy)(2)](2)[micro-dbneil]](4+) (6), and [[Os(bpy)(2)](2)[micro-dbneil]](4+) (7), and the heterodinuclear complex [[Ru(bpy)(2)][micro-dbneil][Os(bpy)(2)]](4+) (8) are described, along with the crystal structures of 4, 6, and 7. Absorption spectra of the mononuclear complexes feature a low-lying MLCT band around 600 nm. The coordination of a second metal fragment results in a dramatic red shift of the MLCT band to beyond 700 nm. Cyclic and square wave voltammograms of the mononuclear complexes exhibit one reversible metal-based oxidation, as well as several ligand-based reduction waves. The first two reductions, attributed to reduction of the dibenzoeilatin ligand, are substantially anodically shifted compared to [M(bpy)(3)](2+) (M = Ru, Os), consistent with the low-lying pi orbital of dibenzoeilatin. The dinuclear complexes exhibit two reversible, well-resolved, metal-centered oxidation waves, despite the chemical equivalence of the two metal centers, indicating a significant metal-metal interaction mediated by the conjugated dibenzoeilatin ligand. Luminescence spectra, quantum yield, and lifetime measurements at room temperature in argon-purged acetonitrile have shown that the complexes exhibit (3)MLCT emission, which occurs in the IR-region between 950 and 1300 nm. The heterodinuclear complex 8 exhibits luminescence only from the Ru-based fragment, the intensity of which is less than 1% of that observed in the corresponding homodinuclear complex 5; no emission from the Os-based unit is observed, and an intramolecular quenching constant of k(q) > or = 3 x10(9) s(-)(1) is evaluated. The nature of the quenching process is briefly discussed.
authors.affiliation: The School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: Sheba D
authors.initials: SD
authors.lastname: Bergman
authors.forename: Israel
authors.initials: I
authors.lastname: Goldberg
authors.forename: Andrea
authors.initials: A
authors.lastname: Barbieri
authors.forename: Francesco
authors.initials: F
authors.lastname: Barigelletti
authors.forename: Moshe
authors.initials: M
authors.lastname: Kol
mesh_terms: D000465:Algorithms; D000470:Alkaloids / Q000737:chemistry; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D008024:Ligands; D049449:Luminescence; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D009992:Osmium / Q000737:chemistry*; D010618:Phenanthrolines / Q000138:chemical synthesis* / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D000470:Alkaloids; D008024:Ligands; D009942:Organometallic Compounds; D010618:Phenanthrolines; C485542:dibenzoeilatin; D009992:Osmium; D012428:Ruthenium