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Sökning: WFRF:(Akermark B)

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  • [1]234567Nästa
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1.
  • Huang, P., et al. (författare)
  • Photo-induced oxidation of a dinuclear Mn-2(II,II) complex to the Mn-2(III,IV) state by inter- and intramolecular electron transfer to Ru-III tris-bipyridine
  • 2002
  • Ingår i: Journal of Inorganic Biochemistry. - : Elsevier. - 0162-0134 .- 1873-3344. ; 91:1, s. 159-172
  • Tidskriftsartikel (refereegranskat)abstract
    • To model the structural and functional parts of the water oxidizing complex in Photosystem 11, a dimeric manganese(II,11) complex (1) was linked to a ruthenium(II)tris-bipyridine (Ru-II(bpy)3) complex via a substituted L-tyrosine, to form the trinuclear complex 2 [J. Inorg. Biochem. 78 (2000) 15]. Flash photolysis of 1 and Ru-II(bpy), in aqueous solution, in the presence of an electron acceptor, resulted in the stepwise extraction of three electrons by Ru-III(bpy), from the Mn-2(II,II) dimer, which then attained the Mn-2(III,IV) oxidation state. In a similar experiment with compound 2, the dinuclear Mn complex reduced the photo-oxidized Ru moiety via intramolecular electron transfer on each photochemical event. From EPR it was seen that 2 also reached the Mn-2(III,IV) state. Our data indicate that oxidation from the Mn-2(II,II) state proceeds stepwise via intermediate formation of Mn-2(II,III) and Mn-2(III,III). In the presence of water, cyclic voltammetry showed an additional anodic peak beyond Mn-2(II,III/III,III) oxidation which was significantly lower than in neat acetonitrile. Assuming that this peak is due to oxidation to Mn-2(III,IV), this suggests that water is essential for the formation of the Mn-2(III,IV) oxidation state. Compound 2 is a structural mimic of the water oxidizing complex, in that it links a Mn complex via a tyrosine to a highly oxidizing photosensitizer. Complex 2 also mimics mechanistic aspects of Photosystem 11, in that the electron transfer to the photosensitizer is fast and results in several electron extractions from the Mn moiety.
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2.
  • Borgstrom, M., et al. (författare)
  • Electron donor-acceptor dyads and triads based on tris(bipyridine)ruthenium(II) and benzoquinone : Synthesis, characterization, and photoinduced electron transfer reactions
  • 2003
  • Ingår i: Inorganic Chemistry. - 0020-1669 .- 1520-510X. ; 42:17, s. 5173-5184
  • Tidskriftsartikel (refereegranskat)abstract
    • Two electron donor-acceptor triads based on a benzoquinone acceptor linked to a light absorbing [Ru(bpy)(3)](2+) complex have been synthesized. In triad 6 (denoted Ru-II-BQ-Co-III), a [Co(bpy)(3)](3+) complex, a potential secondary acceptor, was linked to the quinone. In the other triad, 8 (denoted PTZ-Ru-II-BQ), a phenothiazine donor was linked to the ruthenium moiety. The corresponding dyads Ru-II-BQ (4) and PTZ-Ru-II (9) were prepared for comparison. Upon light excitation in the visible band of the ruthenium moiety, electron transfer to the quinone occurred with a rate constant k(1) = 5 x 10(9) s(-1) (tau(1) = 200 ps) in all the quinone containing complexes. Recombination to the ground state followed, with a rate constant k(b) similar to 4.5 x 10(8) s(-1) (tau(b) similar to 2.2 ns), for both Ru-II-BQ and Ru-II-BQ-Co-III with no indication of a charge shift to generate the reduced Coll moiety. In the PTZ-Ru-II-BQ triad, however, the initial charge separation was followed by a rapid (k > 5 x 10(9) s(-1)) electron transfer from the phenothiazine moiety to give the fairly long-lived PTZ(.+)-Ru-II-BQ(.-) state (tau = 80 ns) in unusually high yield for a [Ru(bPY)(3)](2+)- based triad (> 90%), that lies at DeltaGdegrees = 1.32 eV relative to the ground state. Unfortunately, this triad turned out to be rather photolabile. Interestingly, coupling between the oxidized PTZ(.+) and the BQ(.-) moieties seemed to occur. This discouraged further extension to incorporate more redox active units. Finally, in the dyad PTZ-Ru-II a reversible, near isoergonic electron transfer was observed on excitation. Thus, a quasiequilibrium was established with an observed time constant of 7 ns, with ca. 82% of the population in the PTZ-Ru-*(II) state and 18% in the PTZ(.+)Ru(II)(bpy(.-)) state. These states decayed in parallel with an observed lifetime of 90 ns. The initial electron transfer to form the PTZ(.+)-Ru-II(bpy(.-)) state was thus faster than what would have been inferred from the Ru-*(II) emission decay (tau = 90 ns). This result suggests that reports for related PTZ-Ru-II and PTZ-Ru-II-acceptor complexes in the literature might need to be reconsidered.
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3.
  • Wolpher, H., et al. (författare)
  • Synthesis of a Ru(bpy)(3)-type complex linked to a free terpyridine ligand and its use for preparation of polynuclear bimetallic complexes
  • 2004
  • Ingår i: Catalysis Today. - : Elsevier. - 0920-5861 .- 1873-4308. ; 98:4, s. 529-536:98, s. 529-536
  • Tidskriftsartikel (refereegranskat)abstract
    • A terpyridine ligand has been covalently linked to a Ru(bpy)(3) complex via an amide bond. By using this functionalized terpyridine ligand, a series of multinuclear bimetallic complexes have been synthesized and characterized. One of these complexes has the structure of di-mu-oxobridged Mn dimer. EPR spectra of this complex showed that, depending on the procedure for the preparation, the oxidation states of the Mn dimer is either a Mn-2(III,IV) dimer or a mixture of this and Mn-2(IV,IV) dimer. Water oxidation catalyzed by this complex has been performed.
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4.
  • Abrahamsson, M., et al. (författare)
  • A new strategy for the improvement of photophysical properties in ruthenium(II) polypyridyl complexes. Synthesis and photophysical and electrochemical characterization of six mononuclear ruthenium(II) bisterpyridine-type complexes
  • 2005
  • Ingår i: Inorganic Chemistry. - 0020-1669 .- 1520-510X. ; 44:9, s. 3215-3225
  • Tidskriftsartikel (refereegranskat)abstract
    • The synthesis and characterization of six ruthenium(II) bistridentate polypyridyl complexes is described. These were designed on the basis of a new approach to increase the excited-state lifetime of ruthenium(II) bisterpyridine-type complexes. By the use of a bipyridylpyridyl methane ligand in place of terpyridine, the coordination environment of the metal ion becomes nearly octahedral and the rate of deactivation via ligand-field (i.e., metal-centered) states was reduced as shown by temperature-dependent emission lifetime studies. Still, the possibility to make quasi-linear donor-ruthenium-acceptor triads is maintained in the complexes. The most promising complex shows an excited-state lifet me of tau = 15 ns in alcohol solutions at room temperature, which should be compared to a lifetime of tau = 0.25 ns for [Ru(tpy)(2)](2+). The X-ray structure of the new complex indeed shows a more octahedral geometry than that of [Ru(tpy)(2)](2+). Most importantly, the high excited-state energy was retained, and thus, so was the potential high reactivity of the excited complex, which has not been the case with previously published strategies based on bistridentate complexes.
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5.
  • Abrahamsson, M. L. A., et al. (författare)
  • Ruthenium-manganese complexes for artificial photosynthesis : Factors controlling intramolecular electron transfer and excited-state quenching reactions
  • 2002
  • Ingår i: Inorganic Chemistry. - : The American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 41:6, s. 1534-1544
  • Tidskriftsartikel (refereegranskat)abstract
    • Continuing our work toward a system mimicking the electron-transfer steps from manganese to P-680(+) in photosystem II (PS II), we report a series of ruthenium(II)-manganese(II) complexes that display intramolecular electron transfer from manganese(II) to photooxidized ruthenium(III). The electron-transfer rate constant (k(ET)) values span a large range, 1 X 10(5)-2 x 10(7) s(-1), and we have investigated different factors that are responsible for the variation. The reorganization energies determined experimentally (lambda = 1.5-2.0 eV) are larger than expected for solvent reorganization in complexes of similar size in polar solvents (typically lambda approximate to 1.0 eV). This result indicates that the inner reorganization energy is relatively large and, consequently, that at moderate driving force values manganese complexes are not fast donors. Both the type of manganese ligand and the link between the two metals are shown to be of great importance to the electron-transfer rate. In contrast, we show that the quenching of the excited state of the ruthenium(II) moiety by manganese(II) in this series of complexes mainly depends on the distance between the metals. However, by synthetically modifying the sensitizer so that the lowest metal-to-ligand charge transfer state was localized on the nonbridging ruthenium(II) ligands, we could reduce the quenching rate constant in one complex by a factor of 700 without changing the bridging ligand. Still, the manganese(II)-ruthenium (III) electrontransfer rate constant was not reduced. Consequently, the modification resulted in a complex with very favorable properties.
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6.
  • Johansson, O., et al. (författare)
  • Electron donor-acceptor dyads based on ruthenium(II) bipyridine and terpyridine complexes bound to naphthalenediimide
  • 2003
  • Ingår i: Inorganic Chemistry. - 0020-1669 .- 1520-510X. ; 42:9, s. 2908-2918
  • Tidskriftsartikel (refereegranskat)abstract
    • Two series of photosensitizer-electron acceptor complexes have been synthesized and fully characterized: ruthenium(11) tris(bipyridine) {[Ru-II(bpy)(2)(bpy-X-NDI)], where X = -CH2-, tolylene, or phenylene, bpy is 2,2'-bipyridine, and NDI is naphthalenediimide} and ruthenium(II) bis(terpyridine) {[Ru-II(Y-tpy)(tpy-X-NDI)], where Y = H or tolyl and X = tolylene or phenylene, and tpy = 2,2':6',2-terpyridine}. The complexes have been studied by cyclic and differential pulse voltammetry and by steady state and time-resolved absorption and emission techniques. Rates for forward and backward electron transfer have been investigated, following photoexcitation of the ruthenium(II) polypyridine moiety. The terpyridine complexes were only marginally affected by the linked diimide unit, and no electron transfer was observed. In the bipyridine complexes we achieved efficient charge separation. For the complexes containing a phenyl link between the ruthenium(II) and diimide moieties, our results suggest a biphasic forward electron-transfer reaction, in which 20% of the charge-separated state was formed via population of the naphthalenediimide triplet state.
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7.
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8.
  • Karlsson, E. A., et al. (författare)
  • Synthesis and Electron-Transfer Processes in a New Family of Ligands for Coupled Ru-Mn-2 Complexes
  • 2014
  • Ingår i: ChemPlusChem. - 2192-6506. ; 79:7, s. 936-950
  • Tidskriftsartikel (refereegranskat)abstract
    • A series of [Ru(bpy)(3)](2+)-type (bpy= 2,2'-bipyridine) photosensitisers have been coupled to a ligand for Mn, which is expected to give a dinuclear complex that is active as a water oxidation catalyst. Unexpectedly, photophysical studies showed that the assemblies had very short lived excited states and that the decay patterns were complex and strongly dependent on pH. One dyad was prepared that was capable of catalysing chemical water oxidation by using [Ru(bpy)(3)](3+) as an oxidant. However, photochemical water oxidation in the presence of an external electron acceptor failed, presumably because the short excited-state lifetime precluded initial electron transfer to the added acceptor. The photophysical behaviour could be explained by the presence of an intricate excited-state manifold, as also suggested by time-dependent DFT calculations.
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9.
  • Liu, T. B., et al. (författare)
  • Synthesis, structures and electrochemical properties of nitro- and amino-functionalized diiron azadithiolates as active site models of Fe-only hydrogenases
  • 2004
  • Ingår i: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 10:18, s. 4474-4479
  • Tidskriftsartikel (refereegranskat)abstract
    • Complex [{(mu-SCH2)(2)N(4-NO2C6H4)}Fe-2(CO)(6)] (4) was prepared by the reaction of the dianionic intermediate [(mu-S)(2)Fe-2(CO)(6)](2-) and N,N-bis(chloromethyl)-4-nitroaniline as a biomimetic model of the active site of Fe-only hydrogenase. The reduction of 4 by Pd-C/H-2 under a neutral condition afforded complex [{(mu-SCH2)(2)N(4-NH2C6H4)}Fe-2(CO)(6)] (5) in 67% yield. Both complexes were characterized by IR, H-1 and C-13 NMR spectroscopy and MS spectrometry. The molecular structure of 4, as determined by X-ray analysis, has a butterfly 2Fe2S core and the aryl group on the bridged-N atom slants to the Fe(2) site. Cyclic voltammograms of 4 and 5 were studied to evaluate their redox properties. It was found that complex 4 catalyzed electrochemical proton reduction in the presence of acetic acid. A plausible mechanism of the electrocatalytic proton reduction is discussed.
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10.
  • Schmitt, H., et al. (författare)
  • Synthesis, redox properties, and EPR spectroscopy of manganese(III) complexes of the ligand N,N-bis(2-hydroxybenzyl)-N '-2-hdroxybenzylidene-1,2-diaminoethane : Formation of mononuclear, dinuclear, and even higher nuclearity complexes
  • 2002
  • Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlag. - 0947-6539 .- 1521-3765. ; 8:16, s. 3757-3768
  • Tidskriftsartikel (refereegranskat)abstract
    • The synthesis and characterization of the title trisphenolate ligand are described. From its reaction with manganese(iii) three complexes were isolated. The crystal structures revealed one pentacoordinate monomer and two similar dimers with different solvents of crystallization. In the dimers the metal ions are hexacoordinate and connected through bridging of two phenolates. A combination of electrochemistry and EPR spectroscopy showed that, in acetonitrile, the isolated batches were all identical and mainly monomeric, indicating that the mononuclear complex is in equilibrium with the dimer and perhaps also with complexes of higher nuclearity, as suggested by the detection of both the trimer and the tetramer by electrospray ionization mass spectrometry (ESI-MS). The successful use of the monomer batch as an epoxidation catalyst indicated that a high-valent manganese-oxo species can be formed, although it is probably short-lived. This is also suggested by EPR studies of the species formed by electrochemical oxidation of the complex. Upon one-electron oxidation, a manganese(iv) species was formed, which was at least partly converted to another species containing a phenoxy radical.
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  • Resultat 1-10 av 62
  • [1]234567Nästa

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