| 1. |
- Berggren, Gustav, et al.
(författare)
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Mechanistic Studies on the Water-Oxidizing Reaction of Homogeneous Manganese-Based Catalysts : Isolation and Characterization of a Suggested Catalytic Intermediate
- 2011
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 50:8, s. 3425-3430
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis, isolation, and characterization of two high-valent manganese dimers with isomeric ligands are reported. The complexes are synthesized and crystallized from solutions of low-valent precursors exposed to tert-butyl hydroperoxide. The crystal structures display centrosymmetric complexesconsisting of Mn2 IV,IV(μ-O)2 cores, with one ligand coordinating to each manganese. The ligands coordinate with the diaminoethane backbone, the carboxylate, and one of the two pyridines, while the second pyridine is noncoordinating. The activity of these complexes, under water oxidation conditions, is discussed in light of a proposed mechanism for water oxidation, in which this type of complexes have been suggested as a key intermediate.
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| 2. |
- 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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| 3. |
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| 4. |
- 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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| 5. |
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| 6. |
- 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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| 7. |
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| 8. |
- Beckmann, K., et al.
(författare)
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Formation of stoichiometrically O-18-labelled oxygen from the oxidation of O-18-enriched water mediated by a dinuclear manganese complex : a mass spectrometry and EPR study
- 2008
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 1:6, s. 668-676
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen formation was detected for the oxidations of various multinuclear manganese complexes by oxone (HSO5-) in aqueous solution. To determine to what extent water was the source of the evolved O-2, (H2O)-O-18 isotope-labelling experiments coupled with membrane inlet mass spectrometry (MIMS) were carried out. We discovered that during the reaction of oxone with [Mn-2(OAc)(2)(bpmp)](+) (1), stoichiometrically labelled oxygen (O-18(2)) was formed. This is the first example of a homogeneous reaction mediated by a synthetic manganese complex where the addition of a strong chemical oxidant yields O-18(2) with labelling percentages matching the theoretically expected values for the case of both O-atoms originating from water. Experiments using lead acetate as an alternative oxidant supported this finding. A detailed investigation of the reaction by EPR spectroscopy, MIMS and Clark-type oxygen detection enabled us to propose potential reaction pathways.
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| 9. |
- Berggren, Gustav, et al.
(författare)
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FTIR Study of Manganese Dimers with Carboxylate Donors As Model Complexes for the Water Oxidation Complex in Photosystem II
- 2012
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 51:4, s. 2332-2337
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Tidskriftsartikel (refereegranskat)abstract
- The carboxylate stretching frequencies of two high-valent, di-mu-oxido bridged, manganese dimers has been studied with IR spectroscopy in three different oxidation states. Both complexes contain one monodentate carboxylate donor to each Mn ion, in one complex, the carboxylate is coordinated perpendicular to the Mn-(mu-O)(2)-Mn plane, and in the other complex, the carboxylate is coordinated in the Mn-(mu-O)(2)-Mn plane. For both complexes, the difference between the asymmetric and the symmetric carboxylate stretching frequen-cies decrease for both the Mn-2(IV,IV) to Mn-2(III,IV) transition and the Mn-2(III,IV) to Mn-2(III,III) transition, with only minor differences observed between the two arrangements of the carboxylate ligand versus the Mn-(mu-O)(2)-Mn plane. The IR spectra also show that both carboxylate ligands are affected for each one electron reduction, i.e., the stretching frequency of the carboxylate coordinated to the Mn ion that is not reduced also shifts. These results are discussed in relation to FTIR studies of changes in carboxylate stretching frequencies in a one electron oxidation step of the water oxidation complex in Photosystem II.
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| 10. |
- Berggren, Gustav, 1980-
(författare)
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Mimicking Nature – Synthesis and Characterisation of Manganese Complexes of Relevance to Artificial Photosynthesis
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of efficient catalyst for water oxidation is of paramount importance to artificial photosynthesis, but before this can be achieved a deeper understanding of this reaction is essential. In nature this reaction occurs in a tetranuclear Mn-cluster which serves as the work-horse of oxygenic photosynthesis. This thesis summarises my efforts at developing molecular systems capable of mimicking this complex employing a biomimetic approach. Three different approaches towards this goal are described here-in. The first section describes a screening study, in which a number of manganese complexes were tested to see whether or not they were capable of catalysing the formation of dioxygen when treated with different oxidants (Papers I). For those reactions in which dioxygen formation was observed the reactions were repeated in labelled water and the incorporation of labelled O-atoms was studied by mass spectrometry. This allowed us to determine to what extent water was the source of the evolved dioxygen (Papers II-III). In Chapter three a reported catalyst and a derivative thereof is studied in depth. The influence of changes to the ligand on the oxygen–oxygen bond forming reaction could unfortunately not be reliably addressed, because of the instability of the complexes under “catalytic” conditions. Nevertheless, the study allowed us to revise the “carboxylate shift”-mechanism suggested in the literature (Papers IV-V). Chapter four describes the continuation of my work on ligands featuring the carboxylate ligand motif first introduced in Chapter three. In this study ligands containing multiple binding pockets were designed and synthesised (Paper VI). A better understanding of the mechanism in the natural water oxidising enzyme will facilitate the design of biomimetic complexes, this is discussed in Chapter five. In this work model complexes (Paper VII) are used to study the mechanism by which natures own water oxidising catalyst performs this reaction.
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| 11. |
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| 12. |
- Berggren, Gustav, et al.
(författare)
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Synthesis and characterisation of low valent Mn-complexes as models for Mn-catalases
- 2010
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 39:45, s. 11035-11044
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report the synthesis of two novel manganese complexes, [L1(3)Mn(6)(II)](ClO4)(6) (1 center dot(ClO4)(6)) and [L2Mn(2)(II)(mu-OAc)(mu-Cl)](ClO4)(2) (2 center dot(ClO4)(2)), where L1(2-) is the 2,2'-(1,3-phenylenebis(methylene))bis-((2-(bis(pyridin-2-ylmethyl)amino)ethyl)azanediyl)diacetic acid anion and L2 is N1,N1'-(1,3-phenylenebis(methylene))bis(N2,N2'-bis(pyridin-2-ylmethyl)ethane-1,2-diamine). The ligands Na(2)L1 and L2 are built on the same backbone, L2 only contains nitrogen donors, while two carboxylate arms have been introduced in Na(2)L1. The two complexes have been characterized by single-crystal X-ray diffraction, magnetic susceptibility, EPR spectroscopy, and electrochemistry. X-Ray crystallography revealed that 1 is a manganese(II) hexamer and 2 is a manganese(II) dimer featuring an unprecedented mono-mu-acetato, mono-mu-chlorido bridging motif. The ability of the complexes to catalyse H2O2 disproportionation, thereby acting as models for manganese catalases, has been investigated and compared to the activity of two other related manganese complexes. The introduction of carboxylate donors in the ligands, leading to increased denticity, resulted in a drop in H2O2 disproportionation activity.
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| 13. |
- Berggren, Gustav, et al.
(författare)
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Synthesis, Characterization and Reactivity Study of a New Penta-Coordinated Mn(II) Complex
- 2009
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Ingår i: Applied Magnetic Resonance. - : Springer Science and Business Media LLC. - 0937-9347 .- 1613-7507. ; 36:1, s. 9-24
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Tidskriftsartikel (refereegranskat)abstract
- A penta-coordinated Mn(II) compound [dqpMnCl2] (1) (dqp = 2,6-di-(8-quinoline-yl)-pyridine) has been synthesized and its X-ray crystallographic structure is reported here. Magnetic susceptibility measurements confirmed a high-spin Mn(II) (S = 5/2) center in 1. The X-band EPR spectrum of 1 in dimethylformamide solution exhibits widely distributed transitions in the spectral range from 0 to 700 mT with particularly well-resolved hyperfine lines due to the 55Mn (I = 5/2) nucleus. The abundance of highly resolved transition lines in the spectrum facilitated the electron paramagnetic resonance spectral simulation which revealed large zero-field splitting and g-anisotropies. When dissolved, 1 exists in equilibrium with a hexa-coordinated species, the latter probably resulting from disassociation of one chlorido-ligand allowing ligation of two solvent molecules. The redox behavior of 1 was studied and was compared to that of a structural analog for which water oxidation in the presence of a chemical oxidant has been shown. The results from water oxidation trials of 1 are discussed
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| 14. |
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| 15. |
- Koroidov, Sergey, et al.
(författare)
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First turnover analysis of water-oxidation catalyzed by Co-oxide nanoparticles
- 2015
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 8:8, s. 2492-2503
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Tidskriftsartikel (refereegranskat)abstract
- Co-oxides are promising water oxidation catalysts for artificial photosynthesis devices. Presently, several different proposals exist for how they catalyze O2 formation from water. Knowledge about this process at molecular detail will be required for their further improvement. Here we present time-resolved 18O-labelling isotope-ratio membrane-inlet mass spectrometry (MIMS) experiments to study the mechanism of water oxidation in Co/methylenediphosphonate (Co/M2P) oxide nanoparticles using [Ru(bpy)3]3+ (bpy = 2,2'-bipyridine) as chemical oxidant. We show that 16O–Co/M2P-oxide nanoparticles produce 16O2 during their first turnover after simultaneous addition of H218O and [Ru(bpy)3]3+, while sequential addition with a delay of 3 s yields oxygen reflecting bulk water 18O-enrichment. This result is interpreted to show that the O–O bond formation in Co/M2P-oxide nanoparticles occurs via intramolecular oxygen coupling between two terminal Co–OHn ligands that are readily exchangeable with bulk water in the resting state of the catalyst. Importantly, our data allow the determination of the number of catalytic sites within this amorphous nanoparticular material, to calculate the TOF per catalytic site and to derive the number of holes needed for the production of the first O2 molecule per catalytic site. We propose that the mechanism of O–O bond formation during bulk catalysis in amorphous Co-oxides may differ from that taking place at the surface of crystalline materials.
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| 16. |
- Koroidov, Sergey, et al.
(författare)
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Mechanism of water oxidation catalyzed by Co/M2P-oxides studied by isotope-ratio membrane inlet mass spectrometry
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Co-oxides are promising water oxidation catalysts for artificial photosynthesis devices. Their catalytic mechanism was studied previously both experimentally and theoretically, but there is presently no agreement whether the O-O bond formation occurs via nucleophilic attack or by direct coupling, and whether or not bridging oxygens participate as substrate during O-O bondformation. Here we present time-resolved 18O-labelling isotope-ratio membrane-inlet massspectrometry experiments employing the previously introduced Co/methylenediphosphonate (Co/M2P) system in combination with [Ru(bpy)3]3+ (bpy = 2,2’-bipyridine) as chemical oxidant. Our data demonstrate that for Co/M2P-oxide O-O bond formation occurs between two pre-bound, fast exchanging oxygen species, i.e. likely via direct coupling between two terminal water-derived oxygen ligands. Detailed modeling of the dependence of the O2-isotope ratios on the [Ru(bpy)3]3+ concentration revealed that in the Co/M2P-oxidenanoparticles almost all Co ions are catalytically active (2.35 Co per catalytic site) and that, starting from a ‘resting state‘, 3.5 electrons need to be removed from each catalytic site for thefirst O2 formation. Since it was previously demonstrated that in the resting state most Co ions are in the oxidation state Co(III), we conclude that the coupling mechanism involves at least one Co(IV)-O• radical.
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| 17. |
- Kurz, Philipp, et al.
(författare)
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Oxygen evolving reactions catalysed by synthetic manganese complexes : A systematic screening
- 2007
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :38, s. 4258-4261
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Tidskriftsartikel (refereegranskat)abstract
- A set of six multinuclear manganese complexes was screened for the ability to catalyse reactions yielding O(2) under coherent experimental conditions; we identify a much larger number of manganese compounds than previously known that catalyse oxygen formation.
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| 18. |
- Kurz, Philipp, et al.
(författare)
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Redox reactions of a dinuclear manganese complex : the influence of water
- 2008
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :5, s. 762-770
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Tidskriftsartikel (refereegranskat)abstract
- The redox properties of the dinuclear manganese complex [(Mn2L)-L-III,III(mu-OAC)(2)](+) (1) (where L is the trianion of the heptadentate ligand 2,6-bis{[(3,5-di-tert-butyl-2-hydroxybenzyl)(2-pyridylmethyl)amino]methy l)-4-methylphenol) were studied in acetonitrile solutions containing different concentrations of water. Electrochemical reactions as well as reactions with different chemical and photochemical redox reagents were monitored, using a variety of analytical techniques, namely cyclic voltammetry, UV/Vis spectroelectrochemistry, and EPR spectroscopy. We found that even small concentrations of water influence the compound's redox behaviour significantly, especially the oxidation reactions. As a consequence, the presence of water reduces the overall potential span needed to reach the highest oxidation state observed for 1 (M-2(III,IV)) from its most reduced state (Mn-2(II,II)) to about 1.1 V Higher oxidation states of I are stabilized, most likely by water coordination and the formation of mu-oxido bridge(s) between the two manganese atoms. For reducing conditions, an unprecedented 25-line EPR signal was observed, which might originate from reduced 1 in its Mn-2(II,II) or Mn-2(II,II) state after considerable ligand rearrangement. As complexes like I have been designed to act as potential water oxidation catalysts, the complicated redox- and ligand-exchange chemistry found for 1 in the presence of water, its intended substrate, might be exemplary for many of the dinuclear manganese compounds currently under investigation.
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| 19. |
- Risch, Marcel, et al.
(författare)
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Atomic structure of cobalt-oxide nanoparticles activein light-driven catalysis of water oxidation
- 2012
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 37:10, s. 8878-8888
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Tidskriftsartikel (refereegranskat)abstract
- The atomic structure of water-oxidizing nanoparticles (10-60 nm) formed from cobalt(II)salts and methylenediphosphonate (M2P) is investigated. These amorphous nanoparticles are of high interest for production of solar fuels. They facilitate water oxidation in a directly light-driven process using [Ru(bpy)3]2+ (bpy = 2,2’-bipyridine) as a photosensitizer and persulfate (S2O82-) as an electron acceptor. By X-ray absorption spectroscopy (XAS) at the cobalt K-edge, cobalt L-edge and oxygen K-edge, we investigate the light-driven transition from the CoII/M2P precursor to the active catalyst, which is a layered cobalt(III) oxide with structural similarities to water-oxidizing electrocatalysts. The M2P ligand likely binds at the periphery of the nanoparticles, preventing their further agglomeration during the catalytic reaction. This system opens a possibility to link the catalytically active nanoparticles via a covalent bridge to a photosensitizer and build an artificial photosynthetic system for direct utilization of solar energy for fuel production without production of electricity as an intermediate step.
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| 20. |
- Shevchenko, Denys, et al.
(författare)
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Photochemical water oxidation with visible light using a cobalt containing catalyst
- 2011
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Ingår i: Energy and Environmental Science. - : RSC Publishing. - 1754-5692 .- 1754-5706. ; 4:4, s. 1284-1287
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Tidskriftsartikel (refereegranskat)abstract
- Artificial photosynthesis aims at using solar light energy to oxidatively split water to oxygen, protons and electrons and store the energy in a chemical fuel. Here we present a cobalt phosphonate material that can split water catalytically, driven by visible light in aqueous solutions of pH 7.
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| 21. |
- Shevchenko, Denys, et al.
(författare)
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Synthesis, crystal structure, mass spectrometry, electrochemistry and magnetism of a Mn-III-substituted trilacunary Keggin tungstosilicate
- 2013
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 42:14, s. 5130-5139
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Tidskriftsartikel (refereegranskat)abstract
- A rare example of a "monomeric" triple transition-metal substituted Keggin anion has been synthesized and characterized by various methods including X-ray crystallography, ESI and MALDI mass spectrometry, electrochemistry, EPR, and SQUID.
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| 22. |
- Shevchenko, Denys, et al.
(författare)
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Water oxidation by manganese oxides formed from tetranuclear precursor complexes : the influence of phosphate on structure and 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. 11965-11975
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Tidskriftsartikel (refereegranskat)abstract
- Two types of manganese oxides have been prepared by hydrolysis of tetranuclear Mn(III) complexes in the presence or absence of phosphate ions. The oxides have been characterized structurally using X-ray absorption spectroscopy and functionally by O-2 evolution measurements. The structures of the oxides prepared in the absence of phosphate are dominated by di-mu-oxo bridged manganese ions that form layers with limited long-range order, consisting of edge-sharing MnO6 octahedra. The average manganese oxidation state is +3.5. The structure of these oxides is closely related to other manganese oxides reported as water oxidation catalysts. They show high oxygen evolution activity in a light-driven system containing [Ru(bpy)(3)](2+) and S2O82- at pH 7. In contrast, the oxides formed by hydrolysis in the presence of phosphate ions contain almost no di-mu-oxo bridged manganese ions. Instead the phosphate groups are acting as bridges between the manganese ions. The average oxidation state of manganese ions is +3. This type of oxide has much lower water oxidation activity in the light-driven system. Correlations between different structural motifs and the function as a water oxidation catalyst are discussed and the lower activity in the phosphate containing oxide is linked to the absence of protonable di-mu-oxo bridges.
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| 23. |
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