title: A homoleptic trisbidentate Ru(II) complex of a novel bidentate biheteroaromatic ligand based on quinoline and pyrazole groups: structural, electrochemical, photophysical, and computational characterization.
abstract: We synthesized a new homoleptic, tris-bidentate complex [Ru(QPzH)3](2+) based on the novel biheteroaromatic, 8-(3-pyrazolyl)-quinoline ligand QPzH. The QPzH ligand was designed to reduce the distortions typically observed in complexes incorporating the 8-quinolinyl group into the ligand framework. This was indeed observed, and was also, as anticipated, found to facilitate the formation of tris-homoleptic Ru(II) complexes; [Ru(QPzH)3](2+) is the first reported tris-homoleptic complex with ligands based on the 8-quinolinyl group. The synthesis can either result in a statistical 3:1 mer/fac ratio of the complex, or, through controlled exposure to light, be tweaked to allow isolation of the pure mer isomer only. X-ray crystallography reveals three nonequivalent ligands, with significantly less strain than other quinoline-based bidentate ligands. The complex exhibits a nearly octahedral coordination geometry but shows large differences in bond lengths between the Ru core and the quinoline and pyrazoles, respectively. The Ru-N(pyrazole) bond distances are ∼2.04 Å, while the corresponding distances for Ru-N(quinoline) are ∼2.12 Å. Structural, photophysical, electrochemical, and theoretical characterization revealed a mer-Ru(II) complex with a low oxidation potential (0.57 V vs ferrocene(0/+)) attributed to the incorporation of the pyrazolyl group, a ground state absorption that is sensitive to the local environment of the complex, and a short-lived (3)MLCT excited state.
authors.affiliation: Centre for Analysis and Synthesis, Department of Chemistry and ‡Theoretical Chemistry Division, Chemical Center, Lund University , Box 124, SE-22100 Lund, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Jarenmark
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Fredin
authors.forename: Joachim H J
authors.initials: JH
authors.lastname: Hedberg
authors.forename: Isa
authors.initials: I
authors.lastname: Doverbratt
authors.forename: Petter
authors.initials: P
authors.lastname: Persson
authors.forename: Maria
authors.initials: M
authors.lastname: Abrahamsson