title: A triangular prismatic hexanuclear iridium(III) complex bridged by flavin analogues showing reversible redox processes.
abstract: [Ir(6)(μ-alloCl(2)(2-))(3)(Cp*)(6)(OH)(3)](PF(6))(3) (1) having 7,8-dichloroalloxazine dianion (alloCl(2)(2-)) as bridging ligands was synthesized and characterized by X-ray crystallography, spectroscopic and electrochemical measurements. The alloxazine ligands showed unprecedented coordination modes to link the six Ir(III) centres. The complex exhibited remarkable stability and reversible six-electron redox processes at the bridging alloxazine ligands in organic solvents. The first reversible reduction process occurred on each of three alloxazine ligands in 1 to produce a three-electron-reduced species, [Ir(III)(6)Cp*(6)(μ-alloCl(2)˙(3-))(3)(OH)(3)], and was observed as an apparent one-step reduction process at -0.65 V (vs. Fc(0/+)). The second reversible reduction process on each of the three alloxazine ligands in 1 was recorded at almost the same potential, -0.78 V (vs. Fc(0/+)), to afford the six-electron-reduced form, [Ir(III)(6)Cp*(6)(μ-alloCl(2)(4-))(3)(OH)(3)](3-). The radical anion of the alloxazine derivative was detected by EPR measurements at room temperature. After the six-electron reduction of 1 with cobaltocene, the backward oxidation processes of reduced forms with p-chloranil were traced by UV-Vis spectroscopy to confirm the recovery of the original spectrum of 1.
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, and ALCA (JST), 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Inui
authors.forename: Motoo
authors.initials: M
authors.lastname: Shiro
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kusukawa
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Takahiko
authors.initials: T
authors.lastname: Kojima
mesh_terms: D018360:Crystallography, X-Ray; D005415:Flavins / Q000737:chemistry*; D007495:Iridium / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D010084:Oxidation-Reduction; D011789:Quantum Theory
chemical_list: D005415:Flavins; D009942:Organometallic Compounds; D007495:Iridium