title: Selective detection of multicarboxylate anions based on "turn on" electron transfer by self-assembled molecular rectangles.
abstract: Two new large molecular rectangles (4 and 5) were obtained by the reaction of two different dinuclear arene ruthenium complexes [Ru(2)(arene)(2)(OOOO)(2)Cl(2)] (arene = p-cymene; OOOO = 2,5-dihydroxy-1,4-benzoquinonato (2), 6,11-dihydroxy-5,12-naphthacene dionato (3)) with the unsymmetrical amide NN (N-[4-(pyridin-4-ylethynyl)phenyl]isonicotinamide) donor ligand 1 in methanol in the presence of AgO(3)SCF(3), forming tetranuclear cations of the general formula [Ru(4)(arene)(4)(NN)(2)(OOO O)(2)](4+). Both rectangles were isolated in good yields as triflate salts and were characterized by multinuclear NMR, ESI-MS, UV/Vis, and photoluminescence spectroscopy. The crystal structure of 5 was determined by X-ray diffraction. Luminescent rectangle 5 was used for anion sensing with an amide ligand as a hydrogen-bond donor and an arene-ruthenium acceptor as a signaling unit. Rectangle 5 strongly bound multicarboxylate anions, such as oxalate, tartrate, and citrate, in UV/Vis titration experiments in 1:1 ratios, in contrast to monoanions, such as F(-), Cl(-), NO(3)(-), PF(6)(-), CH(3)COO(-), and C(6)H(5)COO(-). The fluorescence titration experiment showed a large fluorescence enhancement of 5 upon binding to multicarboxylate anions, which could be attributed to blocking of the photoinduced electron transfer process from the arene-ruthenium moiety to the amidic donor in 5; this was likely to be a result of hydrogen bonding between the ligand and the anion. On the other hand, rectangle 5 was not selective towards any other anions. To the naked eye, multicarboxylate anions in a solution of 5 in methanol appear greenish upon irradiation with UV light.
authors.affiliation: Department of Chemistry, University of Ulsan, Ulsan 680-749, Republic of Korea.
authors.forename: Anurag
authors.initials: A
authors.lastname: Mishra
authors.forename: Sunmi
authors.initials: S
authors.lastname: Lee
authors.forename: Hyunuk
authors.initials: H
authors.lastname: Kim
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Cook
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Stang
authors.forename: Ki-Whan
authors.initials: KW
authors.lastname: Chi
mesh_terms: D000838:Anions / Q000737:chemistry; D002264:Carboxylic Acids / Q000032:analysis*; D056831:Coordination Complexes / Q000737:chemistry; D004579:Electron Transport; D004583:Electrons; D008968:Molecular Conformation; D012428:Ruthenium / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000838:Anions; D002264:Carboxylic Acids; D056831:Coordination Complexes; D012428:Ruthenium