| 1. |
- Huang, Ping, et al.
(författare)
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Light-induced multistep oxidation of dinuclear manganese complexes for artificial photosynthesis
- 2004
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 98:5, s. 733-745
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Tidskriftsartikel (refereegranskat)abstract
- Two dinuclear manganese complexes, [Mn2BPMP(mu-OAc)(2)] . ClO4 (1, where BPMP is the anion of 2,6-bis {[N,N-di(2-pyridinemethyl)amino]methyl}-4-methylphenol) and [Mn2L(mu-OAc)(2)] . ClO4 (2, where L is the trianion of 2,6-bis{[N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N-(2-pyridinemethyl)amino]methyl}-4-methylphenol), undergo several oxidations by laser flash photolysis, using ruthenium(II)-tris-bipyridine (tris(2,2-bipyridyl)dichloro-ruthenium(II) hexahydrate) as photo-sensitizer and penta-amminechlorocobalt(III) chloride as external electron acceptor. In both complexes stepwise electron transfer was observed. In 1, four Mn-valence states from the initial Mn-2(II,II) to the Mn-2(III,IV) state are available. In 2, three oxidation steps are possible from the initial Mn-2(III,III) state. The last step is accomplished in the Mn-2(IV,IV) state, which results in a phenolate radical. For the first time we provide firm spectral evidence for formation of the first intermediate state, Mn-2(II,III) in 1 during the stepwise light-induced oxidation. Observation of Mn-2(II,III) is dependent on conditions that sustain the mu-acetato bridges in the complex, i.e., by forming Mn-2(II,III) in dry acetonitrile, or by addition of high concentrations of acetate in aqueous solutions. We maintain that the presence of water is necessary for the transition to higher oxidation states, e.g., Mn-2(III,III) and Mn-2(III,IV) in 1, due to a bridging ligand exchange reaction which takes place in the Mn-2(II,III) state in water solution. Water is also found to be necessary for reaching the Mn-2(IV,IV) state in 2, which explains why this state was not reached by electrolysis in our earlier work (Eur. J. Inorg. Chem (2002) 2965). In 2, the extra coordinating oxygen atoms facilitate the stabilization of higher Mn valence states than in 1, resulting in formation of a stable Mn-2(IV,IV) without disintegration of 2. In addition, further oxidation of 2, led to the formation of a phenolate radical (g = 2.0046) due to ligand oxidation. Its spectral width (8 mT) and very fast relaxation at 15 K indicates that this radical is magnetically coupled to the Mn-2(IV,IV) center.
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| 2. |
- Huang, Ping, et al.
(författare)
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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
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Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 91:1, s. 159-172
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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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| 3. |
- Johansson, A., et al.
(författare)
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Synthesis and photophysics of one mononuclear Mn(III) and one dinuclear Mn(III,III) complex covalently linked to a ruthenium(II) tris(bipyridyl) complex
- 2003
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42, s. 7502-7511
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Tidskriftsartikel (refereegranskat)abstract
- The preparation of donor (D)-photosensitizer (S) arrays, consisting of a manganese complex as D and a ruthenium tris(bipyridyl) complex as S has been pursued. Two new ruthenium complexes containing coordinating sites for one (2a) and two manganese ions (3a) were prepared in order to provide models for the donor side of photosystem II in green plants. The manganese coordinating site consists of bridging and terminal phenolate as well as terminal pyridyl ligands. The corresponding ruthenium-manganese complexes, a manganese monomer 2b and dimer 3b, were obtained. For the dimer 3b, our data suggest that intramolecular electron transfer from manganese to photogenerated ruthenium(III) is fast, k(ET) > 5 x 10(7) s(-1).
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| 4. |
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| 5. |
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| 6. |
- Magnuson, Ann, et al.
(författare)
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High-valent Ruthenium-Manganese Complexes for Solar Energy Production.
- 2001
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Ingår i: PS2001 Proceedings.
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Konferensbidrag (refereegranskat)abstract
- We present progress in the development of artificial photosynthesis, as a means to harvesting and storage of solar energy. The plan is to compose molecular systems that combine known photochemistry with emerging functional model compounds. A photochemical device for solar energy conversion contains a photosensitizer, an electron acceptor system and a donor system that prevents charge recombination. Our goal is to utilize water as sacrificial electron donor, which will allow a net production of reducing equivalents, and the ultimate production of fuel. The only light-driven molecular catalyst for water oxidation exists in Photosystem II (PSII), which has a tetranuclear Mn-cluster in the active site. Here we present several Mn-compounds, that we have developed for the purpose of creating water-oxidizing catalysts. Our idea is to link Ru-tris(bipyridine) derivatives, which mimicks the function of the primary donor in PS II, with manganese complexes, mimicking the tetra-Mn cluster on the PSII donor side. We have constructed a number of heteronuclear complexes, containing a Ru-photosensitizer and various Mn-complexes. The compounds have been characterized with regards to their photophysical and photochemical properties, redox potentials and structure. The most promising compounds are capable of undergoing several electron transfers from the Mn-complex to the photosensitizer, leaving 3 to 4 oxidizing equivalents on the Mn. In the latest development, we have constructed ligands that stabilize higher oxidation states in Mn, in order to promote formation of Mn(V) which many believes is an intermediate in the water oxidation mechanism.
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| 7. |
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| 8. |
- Schmitt, H., et al.
(författare)
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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
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Ingår i: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 8:16, s. 3757-3768
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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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| 9. |
- Sun, Licheng C., et al.
(författare)
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Towards an artificial model for Photosystem II : a manganese(II,II) dimer covalently linked to ruthenium(II) tris-bipyridine via a tyrosine derivative
- 2000
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Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 78:1, s. 15-22
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Tidskriftsartikel (refereegranskat)abstract
- In order to model the individual electron transfer steps from the manganese cluster to the photooxidized sensitizer P-680(+) in Photosystem II (PS II) in green plants, the supramolecular complex 4 has been synthesized. In this complex, a ruthenium(II) tris-bipyridine type photosensitizer has been linked to a manganese(II) dimer via a substituted L-tyrosine, which bridges the manganese ions. The trinuclear complex 4 was characterized by electron paramagnetic resonance (EPR) and electrospray ionization mass spectrometry (ESI-MS). The excited state lifetime of the ruthenium tris-bipyridine moiety in 4 was found to be about 110 ns in acetonitrile, Using flash photolysis in the presence of an electron acceptor (methylviologen), it was demonstrated that in the supramolecular complex 4 an electron was transferred from the excited state of the ruthenium tris-bipyridine moiety to methylviologen, forming a methylviologen radical and a ruthenium(III) tris-bipyridine moiety. Next, the Ru(III) species retrieved the electron from the manganese(II/II) dimer in an intramolecular electron transfer reaction with a rate constant k(ET)>1.0X10(7) s(-1), generating a manganese(II/III) oxidation state and regenerating the ruthenium(II) photosensitizer. This is the first example of intramolecular electron transfer in a supramolecular complex, in which a manganese dimer is covalently linked to a photosensitizer via a tyrosine unit, in a process which mimics the electron transfer on the donor side of PS II.
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