| 1. |
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| 2. |
- Arafa, Wael A. A., et al.
(författare)
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Dinuclear manganese complexes for water oxidation : evaluation of electronic effects and catalytic activity
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:24, s. 11950-11964
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Tidskriftsartikel (refereegranskat)abstract
- During recent years significant progress has been made towards the realization of a sustainable and carbon-neutral energy economy. One promising approach is photochemical splitting of H2O into O-2 and solar fuels, such as H-2. However, the bottleneck in such artificial photosynthetic schemes is the H2O oxidation half reaction where more efficient catalysts are required that lower the kinetic barrier for this process. In particular catalysts based on earth-abundant metals are highly attractive compared to catalysts comprised of noble metals. We have now synthesized a library of dinuclear Mn-2 (II,III) catalysts for H2O oxidation and studied how the incorporation of different substituents affected the electronics and catalytic efficiency. It was found that the incorporation of a distal carboxyl group into the ligand scaffold resulted in a catalyst with increased catalytic activity, most likely because of the fact that the distal group is able to promote proton-coupled electron transfer (PCET) from the high-valent Mn species, thus facilitating O-O bond formation.
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| 3. |
- Das, Biswanath, et al.
(författare)
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Water oxidation catalyzed by molecular di- and nonanuclear Fe complexes: importance of a proper ligand framework
- 2016
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Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 45:34, s. 13289-13293
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of two molecular iron complexes, a dinuclear iron(III,III) complex and a nonanuclear iron complex, based on the di-nucleating ligand 2,2-(2-hydroxy-5-methyl-1,3-phenylene)bis(1H-benzo[d]imidazole-4-carboxylic acid) is described. The two iron complexes were found to drive the oxidation of water by the one-electron oxidant [Ru(bpy)(3)](3+).
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| 4. |
- Gao, Weiming, et al.
(författare)
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Attachment of a Hydrogen-Bonding Carboxylate Side Chain to an FeFe -Hydrogenase Model Complex : Influence on the Catalytic Mechanism
- 2010
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Ingår i: Chemistry - A European Journal. - Weinheim : Wiley. - 0947-6539 .- 1521-3765. ; 16:8, s. 2537-2546
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Tidskriftsartikel (refereegranskat)abstract
- Azapropanedithiolate (adt)-bridged model complexes of [FeFe]-hydrogenase bearing a carboxylic acid functionality have been designed with the aim of decreasing the potential for reduction of protons to hydrogen. Protonation of the bisphosphine complexes 4-6 has been studied by in situ IR and NMR spectroscopy, which revealed that protonation with triflic acid most likely takes place first at the N-bridge for complex 4 but at the Fe Fe bond for complexes 5 and 6. Using an excess of acid, the diprotonated species could also be observed, but none of the protonated species was sufficiently stable to be isolated in a pure state. Electrochemical studies have provided an insight into the catalytic mechanisms under strongly acidic conditions, and have also shown that complexes 3 and 6 are electro-active in aqueous solution even in the absence of acid, presumably due to hydrogen bonding. Hydrogen evolution, driven by visible light, has been observed for three-component systems consisting of [Ru(bpy)(3)](2+), complex 1, 2, or 3, and ascorbic acid in CH3CN/D2O solution by on-line mass spectrometry.
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| 5. |
- Gao, Yan, et al.
(författare)
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Nucleophilic Attack of Hydroxide on a Mn-V Oxo Complex : A Model of the O-O Bond Formation in the Oxygen Evolving Complex of Photosystem II
- 2009
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 131:25, s. 8726-
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Tidskriftsartikel (refereegranskat)abstract
- A manganese(III) corrole complex, 1, has been synthesized and used to study a potential mechanism for oxidation of water to molecular oxygen. Oxidation by t-BuOOH gave the Mn-V=O complex 2. Addition of hydroxide Led to release of oxygen via the Mn-IV complex 4 and regeneration of complex 1. It could be shown that the oxygen from O-18-labeted water was incorporated in both the formed molecular oxygen and the peroxy intermediate 4.
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| 6. |
- Huang, Yong, et al.
(författare)
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An Air-Stable Fe3S4 Complex with Properties Similar to Those of the HOXair State of the Diiron Hydrogenases
- 2012
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :27, s. 4259-4263
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Tidskriftsartikel (refereegranskat)abstract
- A Fe3S4 complex bridged by azapropanedithiolate (adt), complex 6, was prepared as a potential model of the HOXair state of [FeFe]-hydrogenases. Complex 6 was characterized by IR and 1H NMR spectroscopy, and its structure was determined by X-ray crystallography. The electrochemical studies show that complex 6 is redox-active under acidic conditions, which provides insight into the catalytic mechanism. Hydrogen evolution, driven by visible light, was observed in CH3CN/D2O solution by online mass spectroscopy.
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| 7. |
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| 8. |
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| 9. |
- Karlsson, Erik A., et al.
(författare)
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Synthesis and Electron-Transfer Processes in a New Family of Ligands for Coupled Ru-Mn2 Complexes
- 2014
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Ingår i: ChemPlusChem. - : Wiley. - 2192-6506. ; 79:7, s. 936-950
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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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| 10. |
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| 11. |
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| 12. |
- Kärkäs, Markus D., 1984-, et al.
(författare)
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Light-Induced Water Oxidation by a Ru complex Containing a Bio-Inspired Ligand
- 2011
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 17:28, s. 7953-7959
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Tidskriftsartikel (refereegranskat)abstract
- The new Ru complex 8 containing the bio-inspired ligand 7 was successfully synthesized and characterized. Complex 8 efficiently catalyzes water oxidation using Ce(IV) and Ru(III) as chemical oxidants. More importantly, this complex has a sufficiently low overpotential to utilize ruthenium polypyridyl-type complexes as photosensitizers.
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| 13. |
- Kärkäs, Markus D., et al.
(författare)
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Molecular ruthenium water oxidation catalysts carrying non-innocent ligands : mechanistic insight through structure-activity relationships and quantum chemical calculations
- 2016
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Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 6:5, s. 1306-1319
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Tidskriftsartikel (refereegranskat)abstract
- Robust catalysts that mediate H2O oxidation are of fundamental importance for the development of novel carbon-neutral energy technologies. Herein we report the synthesis of a group of single-site Ru complexes. Structure-activity studies revealed that the individual steps in the oxidation of H2O depended differently on the electronic properties of the introduced ligand substituents. The mechanistic details associated with these complexes were investigated experimentally along with quantum chemical calculations. It was found that O-O bond formation for the developed Ru complexes proceeds via high-valent Ru-VI species, where the capability of accessing this species is derived from the non-innocent ligand architecture. This cooperative catalytic involvement and the ability of accessing Ru-VI are intriguing and distinguish these Ru catalysts from a majority of previously reported complexes, and might generate unexplored reaction pathways for activation of small molecules such as H2O.
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| 14. |
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| 15. |
- Laine, Tanja M., et al.
(författare)
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Efficient photochemical water oxidation by a dinuclear molecular ruthenium complex
- 2015
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Ingår i: Chemical Communications. - : Royal Society of Chemistry. - 1359-7345 .- 1364-548X. ; 51:10, s. 1862-1865
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Tidskriftsartikel (refereegranskat)abstract
- Herein is described the preparation of a dinuclear molecular Ru catalyst for H2O oxidation. The prepared catalyst mediates the photochemical oxidation of H2O with an efficiency comparable to state-of-the-art catalysts.
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| 16. |
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| 17. |
- Rabbani, Faiz, et al.
(författare)
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Cobalt selenium oxohalides : catalysts for water oxidation
- 2014
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Ingår i: Dalton Transactions. - 1477-9226 .- 1477-9234. ; 43:10, s. 3984-33989
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Tidskriftsartikel (refereegranskat)abstract
- Two new oxohalides Co4Se3O9Cl2 and Co3Se4O10Cl2 have been synthesized by solid state reactions. They crystallize in the orthorhombic space group Pnma and the monoclinic space group C2/m respectively. The crystal structure of the two compounds are made up of similar building blocks; Co4Se3O9Cl2 is made up of [CoO4Cl2], [CoO5Cl] and [SeO3] polyhedra and Co3Se4O10Cl2 is made up of [CoO4Cl2] and [SeO3] polyhedra. As several Co-containing compounds have proved to be good catalysts for water oxidation, the activities of the two new compounds were compared with the previously found oxohalide Co5Se4O12Cl2 in reference to CoO and CoCl2. The one electron oxidant Ru(bpy)33+ was used as oxidizing species in a phosphate buffer and it was found that the activities of the oxohalide species were in between CoO and CoCl2. The roles of Cl− and PO43− ions are discussed.
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| 18. |
- Rabten, Wangchuk, et al.
(författare)
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A ruthenium water oxidation catalyst based on a carboxamide ligand
- 2016
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45:8, s. 3272-3276
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Tidskriftsartikel (refereegranskat)abstract
- Herein is presented a single-site Ru complex bearing a carboxamide-based ligand that efficiently manages to carry out the fourelectron oxidation of H2O. The incorporation of the negatively charged ligand framework significantly lowered the redox potentials of the Ru complex, allowing H2O oxidation to be driven by the mild oxidant [Ru(bpy)(3)](3+). This work highlights that the inclusion of amide moieties into metal complexes thus offers access to highly active H2O oxidation catalysts.
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| 19. |
- Rabten, Wangchuk, et al.
(författare)
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Catalytic Water Oxidation by a Molecular Ruthenium Complex : Unexpected Generation of a Single-Site Water Oxidation Catalyst
- 2015
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 54:10, s. 4611-4620
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Tidskriftsartikel (refereegranskat)abstract
- The increasing energy demand calls for the development of sustainable energy conversion processes. Here, the splitting of H2O to O-2 and H-2, or related fuels, constitutes an excellent example of solar-to-fuel conversion schemes. The critical component in such schemes has proven to be the catalyst responsible for mediating the four-electron oxidation of H2O to O-2. Herein, we report on the unexpected formation of a single-site Ru complex from a ligand envisioned to accommodate two metal centers. Surprising N-N bond cleavage of the designed dinuclear ligand during metal complexation resulted in a single-site Ru complex carrying a carboxylate amide motif. This ligand lowered the redox potential of the Ru complex sufficiently to permit H2O oxidation to be carried out by the mild one-electron oxidant [Ru(bpy)(3)](3+) (bpy = 2,2'-bipyridine). The work thus highlights that strongly electron-donating ligands are important elements in the design of novel, efficient H2O :oxidation catalysts.
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| 20. |
- Verho, Oscar, et al.
(författare)
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Application and mechanistic studies of a water-oxidation catalyst in alcohol oxidation by employing oxygen-transfer reagents
- 2012
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:52, s. 16947-16954
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Tidskriftsartikel (refereegranskat)abstract
- By using a dimeric ruthenium complex in combination with tert-butyl hydrogen peroxide (TBHP) as stoichiometric oxidant, a mild and efficient protocol for the oxidation of secondary benzylic alcohols was obtained, thereby giving the corresponding ketones in high yields within 4 h. However, in the oxidation of aliphatic alcohols, the TBHP protocol suffered from low conversions owing to a competing Ru-catalyzed disproportionation of the oxidant. Gratifyingly, by switching to Oxone (2 KHSO5⋅KHSO4⋅K2SO4 triple salt) as stoichiometric oxidant, a more efficient and robust system was obtained that allowed for the oxidation of a wide range of aliphatic and benzylic secondary alcohols, giving the corresponding ketones in excellent yields. The mechanism for these reactions is believed to involve a high-valent RuV–oxo species. We provide support for such an intermediate by means of mechanistic studies.
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| 21. |
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| 22. |
- Verho, Oscar, et al.
(författare)
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Well-Defined Palladium Nanoparticles Supported on Siliceous Mesocellular Foam as Heterogeneous Catalysts for the Oxidation of Water
- 2015
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 21:15, s. 5909-5915
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we describe the use of Pd nanoparticles immobilized on an amino-functionalized siliceous mesocellular foam for the catalytic oxidation of H2O. The Pd nanocatalyst proved to be capable of mediating the four-electron oxidation of H2O to O-2, both chemically and photochemically. The Pd nanocatalyst is easy to prepare and shows high chemical stability, low leaching, and recyclability. Together with its promising catalytic activity, these features make the Pd nanocatalyst of potential interest for future sustainable solar-fuel production.
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| 23. |
- Xu, Yunhua, et al.
(författare)
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A New Dinuclear Ruthenium Complex as an Efficient Water Oxidation Catalyst
- 2009
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 48:7, s. 2717-2719
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Tidskriftsartikel (refereegranskat)abstract
- A dinuclear ruthenium complex, which acts as a molecular catalyst for water oxidation, has been synthesized and characterized. The electronic and electrochemical properties were studied by UV-vis spectroscopy and cyclic voltammetry. The oxidation potentials of the complex are significantly lowered by introducing a negatively charged carboxylate ligand, in comparison with those of the reported complexes that have neutral ligands. The catalytic activity of the complex toward water oxidation using Ce(NH4)(2)(NO3)(6) as a chemical oxidant was investigated by means of an oxygen electrode and mass spectrometry. The turnover number of this catalyst with Ce-IV as the chemical oxidant was found to be ca. 1700. The mass spectroscopic analysis of the isotopomer distribution in oxygen evolved from O-18-labeled water indicates that O atoms in the evolved oxygen originate from water.
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| 24. |
- Xu, Yunhua, et al.
(författare)
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Synthesis and Catalytic Water Oxidation Activities of Ruthenium Complexes Containing Neutral Ligands
- 2011
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 17:34, s. 9520-9528
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Tidskriftsartikel (refereegranskat)abstract
- Two dinuclear and one mononuclear ruthenium complexes containing neutral polypyridyl ligands have been synthesised as pre-water oxidation catalysts and characterised by (1)H and (13)C NMR spectroscopy and ESI-MS. Their catalytic water oxidation properties in the presence of [Ce(NH(4))(2)(NO(3))(6)] (Ce(IV)) as oxidant at pH 1.0 have been investigated. At low concentrations of Ce(IV) (5 mm), high turnover numbers of up to 4500 have been achieved. An (18)O-labelling experiment established that both O atoms in the evolved O(2) originate from water. Combined electrochemical study and electrospray ionisation mass spectrometric analysis suggest that ligand exchange between coordinated 4-picoline and free water produces Ru aquo species as the real water oxidation catalysts.
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| 25. |
- Abdel-Magied, Ahmed F., et al.
(författare)
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Substituent Effects in Molecular Ruthenium Water Oxidation Catalysts Based on Amide Ligands
- 2017
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Ingår i: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 9:9, s. 1583-1587
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Tidskriftsartikel (refereegranskat)abstract
- The production of clean and sustainable energy is considered as one of the most urgent issues for our society. Mastering the oxidation of water to dioxygen is essential for the production of solar fuels. A study of the influence of the substituents on the catalytic activity of a series of mononuclear Ru complexes (2a-e) based on a tetradentate ligand framework is presented. At neutral pH, using [Ru(bpy)(3)](PF6)(3) (bpy=2,2'-bipyridine) as the terminal oxidant, a good correlation between the turnover frequency (TOF) and the Hammett sigma(meta) parameters was obtained. Additionally, a general pathway for the deactivation of Ru-based catalysts 2a-e during the catalytic oxidation of water through poisoning by carbon monoxide was demonstrated. These results highlight the importance of ligand design for fine-tuning the catalytic activity of water oxidation catalysts.
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| 26. |
- Abrahamsson, Maria, et al.
(författare)
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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
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 44:9, s. 3215-3225
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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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| 27. |
- Abrahamsson, Maria, et al.
(författare)
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Steric influence on the excited-state lifetimes of ruthenium complexes with bipyridyl-alkanylene-pyridyl ligands.
- 2008
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Ingår i: Inorganic Chemistry. - : ACS. - 0020-1669 .- 1520-510X. ; 47:9, s. 3540-3548
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Tidskriftsartikel (refereegranskat)abstract
- The structural effect on the metal-to-ligand charge transfer (MLCT) excited-state lifetime has been investigated in bis-tridentate Ru(II)-polypyridyl complexes based on the terpyridine-like ligands [6-(2,2'-bipyridyl)](2-pyridyl)methane (1) and 2-[6-(2,2'-bipyridyl)]-2-(2-pyridyl)propane (2). A homoleptic ([Ru(2)(2)](2+)) and a heteroleptic complex ([Ru(ttpy)(2)](2+)) based on the new ligand 2 have been prepared and their photophysical and structural properties studied experimentally and theoretically and compared to the results for the previously reported [Ru(1)(2)](2+). The excited-state lifetime of the homoleptic Ru-II complex with the isopropylene-bridged ligand 2 was found to be 50 times shorter than that of the corresponding homoleptic Ru-II complex of ligand 1, containing a methylene bridge. A comparison of the ground-state geometries of the two homoleptic complexes shows that steric interactions involving the isopropylene bridges make the coordination to the central Ru-II ion less octahedral in [Ru(2)(2)](2+) than in [Ru(1)(2))(2+). Calculations indicate that the structural differences in these complexes influence their ligand field splittings as well as the relative stabilities of the triplet metal-to-ligand charge transfer ((MLCT)-M-3) and metal-centered ((MC)-M-3) excited states. The large difference in measured excited-state lifetimes for the two homoleptic Ru-II complexes is attributed to a strong influence of steric interactions on the ligand field strength, which in turn affects the activation barriers for thermal conversion from (MLCT)-M-3 states to short-lived (MC)-M-3 states.
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| 28. |
- Anderlund, Magnus, 1973-
(författare)
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Dinuclear Manganese Complexes for Artificial Photosynthesis : Synthesis and Properties
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the synthesis and characterisation of a series of dinuclear manganese complexes. Their ability to donate electrons to photo-generated ruthenium(III) has been investigated in flash photolysis experiments followed by EPR-spectroscopy. These experiment shows several consecutive one-electron transfer steps from the manganese moiety to ruthenium(III), that mimics the electron transfer from the oxygen evolving centre in photosystem II.The redox properties of these complexes have been investigated with electro chemical methods and the structure of the complexes has been investigated with different X-ray techniques. Structural aspects and the effect of water on the redox properties have been shown.One of the manganese complexes has been covalently linked in a triad donor-photosensitizer-acceptor (D–P–A) system. The kinetics of this triad has been investigated in detail after photo excitation with both optical and EPR spectroscopy. The formed charge separated state (D––P–A+) showed an unusual long lifetime for triad based on ruthenium photosensitizers.The thesis also includes a study of manganese-salen epoxidation reactions that we believe can give an insight in the oxygen transfer mechanism in the water oxidising complex in photosystem II.
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| 29. |
- Anderlund, Magnus F., et al.
(författare)
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A new, dinuclear high spin manganese(III) complex with bridging phenoxy and methoxy groups. Structure and magnetic properties
- 2006
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Ingår i: Inorganic Chemistry Communications. - : Elsevier BV. - 1387-7003 .- 1879-0259. ; 9:12, s. 1195-1198
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Tidskriftsartikel (refereegranskat)abstract
- A new mu-phenoxy-mu-metoxy di-manganese(III) complex with the trisphenolic ligand, 2,6-bis[((2-hydroxybenzyl)(2-pyridylmethyl)amino)methyl]-4-methylphenol, was isolated as a perchlorate salt. The X-ray structure shows that the two manganese(III) ions are in a distorted octrahedral enviroment with approximately perpendicular Jahn-Teller axes. Investigation of the molar magnetic susceptibility reveals a ferromagnetic coupling between the two high-spin manganese(III) ions. Fitting of the data led to g = 2 and J = 12.5 cm(-1).
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| 30. |
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| 31. |
- Anderlund, Magnus F., et al.
(författare)
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Redox chemistry of a dimanganese(II,III) complex with an unsymmetric ligand : Water binding, deprotonation and accumulative light-induced oxidation
- 2006
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :24, s. 5033-5047
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Tidskriftsartikel (refereegranskat)abstract
- A dinuclear manganese complex {[(Mn2L)-L-II,IIII(mu-OAc)(2)]-ClO4} has been synthesised, where L is the dianion of 2-{[bis-(pyrid-2-ylmethyl)amino]methyl}-6-{[(3,5-di-tert-butyl-2- hydroxybenzyl)(pyrid-2-ylmethyl)amino]methyl)-4-methylphenol, an unsymmetric binucleating ligand with two coordinating phenol groups. The two manganese ions, with a Mn-Mn distance of 3.498 angstrom, are bridged by the two bidentate acetate ligands and the 4-methylphenolate group of the ligand, resulting in a N3O3 and N2O4 donor set of Mn-II and Mn-II, respectively. Electrochemically [Mn2(II,III)L(mu-OAc)(2)](+) is reduced to [(Mn2L)-L-II,II(mu-OAc)(2)] at E-1/2(1)=-0.53 V versus Fc(+/0) and oxidised to [(Mn2L)-L-III,III(mu-OAC)(2)](2+) at E-1/2(2)=0.38 V versus Fc(+/0). All three redox states have been characterised by EPR, IR and UV/Vis spectroscopy. Subsequent oxidation of [(Mn2L)-L-II,III(mu-OAc)(2)](2+) [E-1/2(3)=0.75 V vs. Fc(+/0)] in dry acetonitrile results in an unstable primary product with a lifetime of about 100 ins. At high scan rates quasireversible voltammetric behaviour is found for all three electrode processes, with particularly slow electron transfer for the II,III/II,II [k(o)(1) = 0.002 cms(-1) and III,III/II,III [k(o)(2) = 0.005 cms(-1)] couples, which can be rationalised in terms of major distortions of the Mn-II centres. In aqueous media the bridging acetates are replaced by water-derived ligands. Deprotonation of these stabilises higher valence states, and photo-induced oxidation of the manganese complex results in a (Mn2L)-L-IlI,IV complex with oxo or hydroxo bridging ligands, which is further oxidised to an EPR-silent product. These results demonstrate that a larger number of metal-centred oxidations can be compressed in a narrow potential range if build up of charge is avoided by charge-compensating reactions.
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| 32. |
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| 33. |
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| 34. |
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| 35. |
- Berggren, Gustav, et al.
(författare)
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Tetraethylammonium [12,12-diethyl-2,2,9,9-tetramethyl-1,4,7,10-tetraza-5,6-benzotridecane-3 ,8,11,13-tetraone(4-)]oxidomanganate(V)
- 2007
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Ingår i: Acta Crystallographica Section E. - 1600-5368. ; 63:11, s. M2672-M2673
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Tidskriftsartikel (refereegranskat)abstract
- The Mn-V complex in the title compound, (C8H20N)[ Mn(C21H26N4O4)O], is interesting as it has been suggested that Mn-V oxospecies are intermediates both in epoxidation of alkenes and in water oxidation in PSII, i.e. photosystem II, the protein found in oxygenic photosynthetic organisms, which uses light to split water into O-2, protons and electrons. The Mn atom has a square-pyramidal coordination of four N atoms with an apical O atom. The four N atoms coordinating to Mn [Mn-N = 1.872 (2)-1.882 (2) angstrom] form a plane within 0.03 (3) angstrom from which the Mn ion is displaced by 0.582 (2) angstrom.
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| 36. |
- Berglund-Baudin, Helena, et al.
(författare)
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Intramolecular Electron Transfer from Manganese(II) Coordinatively Linked to a Photogenerated Ru(III)-Polypyridine Complex: A Kinetic Analysis
- 1998
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Ingår i: The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory. - : American Chemical Society (ACS). - 1520-5215. ; 102:15, s. 2512-2518
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Tidskriftsartikel (refereegranskat)abstract
- For further investigations in the field of artificial photosynthesis, a model compound, 1, has been developed to mimic the electron-transfer steps from the manganese cluster to P680+ in photosystem II. In this model compound the photosensitizer ruthenium(II)-trisbipyridyl was linked to a manganese(II) ion through a bridging ligand. Photoexcitation of 1 in the presence of the electron acceptor methyl viologen (MV2+) lead to electron transfer from the Ru moiety to MV2+. Laser flash photolysis experiments at different concentrations of 1 were performed in order to follow the subsequent reduction of the photooxidized Ru(III) species. A kinetic model, taking different parallel reactions into account, could explain the experimental data. It was shown that the major part of the photooxidized Ru(III) created was reduced again by intramolecular electron transfer from the attached Mn(II), with a rate constant of 1.8 × 105 s-1. However, Mn(II) was partially dissociated from 1, giving a fraction of Ru(III) without Mn(II) attached. In these complexes electron transfer could occur only after a rate-limiting reassociation of Mn(II), with a rate constant 2.9 × 109 M-1 s-1. In the analysis of the data, the fraction of dissociated Mn(II) could be determined independently at each concentration of 1, utilizing the fact that bound Mn(II) quenched the excited state, probably by energy transfer.
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| 37. |
- Blomberg, Margareta R A, et al.
(författare)
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A Quantum Chemical Study of Hydrogen Abstraction from Manganese-Coordinated Water by a Tyrosyl Radical: A Model for Water Oxidation in Photosystem II
- 1997
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 119:35, s. 8285-8292
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Tidskriftsartikel (refereegranskat)abstract
- Recently, water oxidation in photosystem II was proposed to involve direct abstraction of hydrogen atoms from water molecules terminally ligated to manganese ions in the oxygen-evolving complex by the oxidized tyrosine radical, TyrZ. This model is tested here by performing quantum chemical calculations. An empirically parametrized hybrid density functional method is used, and both monomeric and dimeric manganese model systems are studied. It is found that, by coordination to a manganese center, the first O-H bond strength of water is lowered from 113.4 to 84.3 kcal/mol. This O-H bond strength is only 2.8 kcal/mol stronger than that in tyrosine. Using an extended basis set, we find that this difference decreases still further. The second hydrogen abstraction energy is quite similar. Since thermoneutrality in the reaction (or a weak exothermicity) is a requirement for the hydrogen abstraction model, the present calculations support this model. Possible functions of a coordinated chloride and a nearby calcium complex are suggested. Five- or six-coordination and ferro- or antiferromagnetic spin couplings of the manganese centers are discussed.
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| 38. |
- Blondin, Geneviève, et al.
(författare)
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Electron paramagnetic resonance study of the S=1/2 ground state of a radiolysis-generated manganese(III)-trimanganese(IV) form of [Mn-IV;O-4(6)(bipy)(6)](4+) (bipy=2,2'-bipyridine). Comparison with the photosynthetic Oxygen Evolving Complex
- 1997
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Ingår i: Journal of the Chemical Society. Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1472-7773 .- 0300-9246 .- 1364-5447. ; 1997:21, s. 4069-4074
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Tidskriftsartikel (refereegranskat)abstract
- gamma-Ray irradiation at liquid nitrogen temperature of a dimethylformamide solution of the tetranuclear complex [(Mn4O6)-O-IV(bipy)(6)](4+) (bipy = 2,2'-bipyridine) allowed the generation of the first mixed-valence tetranuclear system containing Mn-III and Mn-IV ions and exhibiting a S = 1/2 ground state. The X-band EPR spectrum of this tetranuclear system has been obtained. Simulations have been undertaken and the Mn hyperfine coupling tensors determined clearly show a (MnMn3IV)-Mn-III, composition for the EPR active species. A general approach for the analysis of the isotropic components of the Mn hyperfine tensors is presented in detail. This allowed the determination of the spin projection value for each Mn site. A three J coupling scheme assuming that the linear topology of the starting compound remains is able to reproduce these spin projection values if and only if the Mn-III ion is located at a terminal position in a N4O2 environment. The EPR signal of this [Mn4O6(bipy)(6)](3+) species is compared with the multiline signal observed in the S-2 state of the photosynthetic Oxygen Evolving Complex.
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| 39. |
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| 40. |
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| 41. |
- Brandt, Peter, et al.
(författare)
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Molecular Mechanics (MM3) Parameters for Ruthenium(II)-Polypyridyl Complexes.
- 1998
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Ingår i: Inorganic Chemistry. - 0020-1669 .- 1520-510X. ; 37:16, s. 4120-4127
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Tidskriftsartikel (refereegranskat)abstract
- We have developed molecular mechanics parameters for Ru(II)-polypyridyl coordination compounds with the MM3 force field in MacroModel. X-ray structures, together with a B3LYP frequency calculation on a model system, have been utilized in the parametrization. The performance of the force field and the quality of each parameter is analyzed. A clear qualitative correlation have been found between coordination geometry and emission properties for the ruthenium polypyridyl complexes examined in this paper.
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| 42. |
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| 43. |
- Das, Biswanath, et al.
(författare)
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Bifunctional and regenerable molecular electrode for water electrolysis at neutral pH
- 2023
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 11:25, s. 13331-13340
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Tidskriftsartikel (refereegranskat)abstract
- The instability of molecular electrodes under oxidative/reductive conditions and insufficient understanding of the metal oxide-based systems have slowed down the progress of H2-based fuels. Efficient regeneration of the electrode's performance after prolonged use is another bottleneck of this research. This work represents the first example of a bifunctional and electrochemically regenerable molecular electrode which can be used for the unperturbed production of H2 from water. Pyridyl linkers with flexible arms (–CH2–CH2–) on modified fluorine-doped carbon cloth (FCC) were used to anchor a highly active ruthenium electrocatalyst [RuII(mcbp)(H2O)2] (1) [mcbp2− = 2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine]. The pyridine unit of the linker replaces one of the water molecules of 1, which resulted in RuPFCC (ruthenium electrocatalyst anchored on –CH2–CH2–pyridine modified FCC), a high-performing electrode for oxygen evolution reaction [OER, overpotential of ∼215 mV] as well as hydrogen evolution reaction (HER, overpotential of ∼330 mV) at pH 7. A current density of ∼8 mA cm−2 at 2.06 V (vs. RHE) and ∼−6 mA cm−2 at −0.84 V (vs. RHE) with only 0.04 wt% loading of ruthenium was obtained. OER turnover of >7.4 × 103 at 1.81 V in 48 h and HER turnover of >3.6 × 103 at −0.79 V in 3 h were calculated. The activity of the OER anode after 48 h use could be electrochemically regenerated to ∼98% of its original activity while it serves as a HE cathode (evolving hydrogen) for 8 h. This electrode design can also be used for developing ultra-stable molecular electrodes with exciting electrochemical regeneration features, for other proton-dependent electrochemical processes.
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| 44. |
- Das, Biswanath, et al.
(författare)
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Cobalt Electrocatalyst on Fluorine Doped Carbon Cloth – a Robust and Partially Regenerable Anode for Water Oxidation
- 2022
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Ingår i: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 14:18
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Tidskriftsartikel (refereegranskat)abstract
- The low stability of the electrocatalysts at water oxidation (WO) conditions and the use of expensive noble metals have obstructed large-scale H2 production from water. Herein, we report the electrocatalytic WO activity of a cobalt-containing, water-soluble molecular WO electrocatalyst [CoII(mcbp)(OH2)] (1) [mcbp2−=2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine] in homogeneous conditions (overpotential of 510 mV at pH 7 phosphate buffer) and after anchoring it on pyridine-modified fluorine-doped carbon cloth (PFCC). The formation of cobalt phosphate was identified only after 4 h continuous oxygen evolution in homogeneous conditions. Interestingly, a significant enhancement of the stability and WO activity (current density of 5.4 mA/cm2 at 1.75 V) was observed for 1 after anchoring onto PFCC, resulting in a turnover (TO) of >3.6×103 and average TOF of 0.05 s−1 at 1.55 V (pH 7) over 20 h. A total TO of >21×103 over 8 days was calculated. The electrode allowed regeneration of∼ 85 % of the WO activity electrochemically after 36 h of continuous oxygen evolution.
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| 45. |
- Das, Biswanath, et al.
(författare)
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The Impact of Ligand Carboxylates on Electrocatalyzed Water Oxidation
- 2021
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Ingår i: Accounts of Chemical Research. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 54:17, s. 3326-3337
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Forskningsöversikt (refereegranskat)abstract
- Fossil fuel shortage and severe climate changes due to global warming have prompted extensive research on carbon-neutral and renewable energy resources. Hydrogen gas (H-2), a clean and high energy density fuel, has emerged as a potential solution for both fulfilling energy demands and diminishing the emission of greenhouse gases. Currently, water oxidation (WO) constitutes the bottleneck in the overall process of producing H-2 from water. As a result, the design of efficient catalysts for WO has become an intensively pursued area of research in recent years. Among all the molecular catalysts reported to date, ruthenium-based catalysts have attracted particular attention due to their robust nature and higher activity compared to catalysts based on other transition metals. Over the past two decades, we and others have studied a wide range of ruthenium complexes displaying impressive catalytic performance for WO in terms of turnover number (TON) and turnover frequency (TOF). However, to produce practically applicable electrochemical, photochemical, or photo-electrochemical WO reactors, further improvement of the catalysts' structure to decrease the overpotential and increase the WO rate is of utmost importance. WO reaction, that is, the production of molecular oxygen and protons from water, requires the formation of an O-O bond through the orchestration of multiple proton and electron transfers. Promotion of these processes using redox noninnocent ligand frameworks that can accept and transfer electrons has therefore attracted substantial attention. The strategic modifications of the ligand structure in ruthenium complexes to enable proton-coupled electron transfer (PCET) and atom proton transfer (APT; in the context of WO, it is the oxygen atom (metal oxo) transfer to the oxygen atom of a water molecule in concert with proton transfer to another water molecule) to facilitate the O-O bond formation have played a central role in these efforts. In particular, promising results have been obtained with ligand frameworks containing carboxylic acid groups that either are directly bonded to the metal center or reside in the close vicinity. The improvement of redox and chemical properties of the catalysts by introduction of carboxylate groups in the ligands has proven to be quite general as demonstrated for a range of mono- and dinudear ruthenium complexes featuring ligand scaffolds based on pyridine, imidazole, and pyridazine cores. In the first coordination sphere, the carboxylate groups are firmly coordinated to the metal center as negatively charged ligands, improving the stability of the complexes and preventing metal leaching during catalysis. Another important phenomenon is the reduction of the potentials required for the formation of higher valent intermediates, especially metal-oxo species, which take active part in the key O-O bond formation step. Furthermore, the free carboxylic acid/carboxylate units in the proximity to the active center have shown exciting proton donor/acceptor properties (through PCET or APT, chemically noninnocent) that can dramatically improve the rate as well as the overpotential of the WO reaction.
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| 46. |
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| 47. |
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| 48. |
- Fryxelius, Jacob, 1974-
(författare)
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Design and Synthesis of Ligands for High-Valent Metal Oxidation Catalysts
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes several approaches towards the design of a water oxidation catalyst. Different aspects of coordination and water oxidation chemistry are adressed and result in various syntheses of ligands and their metal complexes.
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| 49. |
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| 50. |
- Gao, Weiming, et al.
(författare)
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An azadithiolate bridged Fe2S2 complex as active site model of FeFe-hydrogenase covalently linked to a Re(CO)(3)(bpy)(py) photosensitizer aiming for light-driven hydrogen production
- 2008
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Ingår i: Comptes rendus. Chimie. - : Elsevier BV. - 1631-0748 .- 1878-1543. ; 11:8, s. 915-921
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Tidskriftsartikel (refereegranskat)abstract
- In order to create photoactive catalysts for hydrogen production, a novel trimetallic Re-Fe2S2 complex 4 was synthesized by the coordination of the free -PPh2 group of the ligand of the rhenium photosensitizer 6 to an azadithiolate (ADT)-bridged diiron complex 8 with the assistance of the decarbonylation reagent Me3NO. Complex 4 was characterized by H-1, C-13, P-31 NMR and HRMS spectra. The IR, UV-vis and electrochemical data indicate some interactions between Re and Fe2S2 moieties, and the photo-induced electron transfer from the excited state of the Re moiety to the Fe2S2 catalyst is thermodynamically feasible.
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