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Lomoth, Reiner
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Publications (10 of 76) Show all publications
Kjmer, K. S., Kaul, N., Prakash, O., Chabera, P., Rosemann, N. W., Honarfar, A., . . . Wärnmark, K. (2019). Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime. Science, 363(6424), 249-253
Open this publication in new window or tab >>Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime
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2019 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 363, no 6424, p. 249-253Article in journal (Refereed) Published
Abstract [en]

Iron's abundance and rich coordination chemistry are potentially appealing features for photochemical applications. However, the photoexcitable charge-transfer states of most iron complexes are limited by picosecond or subpicosecond deactivation through low-lying metal-centered states, resulting in inefficient electron-transfer reactivity and complete lack of photoluminescence. In this study, we show that octahedral coordination of iron(Ill) by two mono-anionic facial tris-carbene ligands can markedly suppress such deactivation. The resulting complex [Fe(phtmeimb)(2)](+), where phtmeimb is {phenyl[tris(3-methylimidazol-1-ylidene)]borate}(-), exhibits strong, visible, room temperature photoluminescence with a 2.0-nanosecond lifetime and 2% quantum yield via spin-allowed transition from a doublet ligand-to-metal charge-transfer ((LMCT)-L-2) state to the doublet ground state. Reductive and oxidative electron-transfer reactions were observed for the (2)LMCTstate of [Fe(phtmeimb)(2)](+) in bimolecular quenching studies with methylviologen and diphenylamine.

Place, publisher, year, edition, pages
AMER ASSOC ADVANCEMENT SCIENCE, 2019
National Category
Theoretical Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-376883 (URN)10.1126/science.aau7160 (DOI)000456140700029 ()30498167 (PubMedID)
Funder
Swedish Foundation for Strategic Research Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg FoundationSwedish National Infrastructure for Computing (SNIC)Stiftelsen Olle Engkvist ByggmästareCarl Tryggers foundation Wenner-Gren FoundationsThe Crafoord Foundation
Available from: 2019-02-12 Created: 2019-02-12 Last updated: 2019-02-12Bibliographically approved
Aster, A., Wang, S., Mirmohades, M., Esmieu, C., Berggren, G., Hammarström, L. & Lomoth, R. (2019). Metal vs. ligand protonation and the alleged proton-shuttling role of the azadithiolate ligand in catalytic H-2 formation with FeFe hydrogenase model complexes. Chemical Science, 10(21), 5582-5588
Open this publication in new window or tab >>Metal vs. ligand protonation and the alleged proton-shuttling role of the azadithiolate ligand in catalytic H-2 formation with FeFe hydrogenase model complexes
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2019 (English)In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 10, no 21, p. 5582-5588Article in journal (Refereed) Published
Abstract [en]

Electron and proton transfer reactions of diiron complexes [Fe(2)adt(CO)(6)] (1) and [Fe(2)adt(CO)(4)(PMe3)(2)] (4), with the biomimetic azadithiolate (adt) bridging ligand, have been investigated by real-time IR- and UV-vis-spectroscopic observation to elucidate the role of the adt-N as a potential proton shuttle in catalytic H-2 formation. Protonation of the one-electron reduced complex, 1(-), occurs on the adt-N yielding 1H and the same species is obtained by one-electron reduction of 1H(+). The preference for ligand vs. metal protonation in the Fe-2(i,0) state is presumably kinetic but no evidence for tautomerization of 1H to the hydride 1Hy was observed. This shows that the adt ligand does not work as a proton relay in the formation of hydride intermediates in the reduced catalyst. A hydride intermediate 1HHy(+) is formed only by protonation of 1H with stronger acid. Adt protonation results in reduction of the catalyst at much less negative potential, but subsequent protonation of the metal centers is not slowed down, as would be expected according to the decrease in basicity. Thus, the adtH(+) complex retains a high turnover frequency at the lowered overpotential. Instead of proton shuttling, we propose that this gain in catalytic performance compared to the propyldithiolate analogue might be rationalized in terms of lower reorganization energy for hydride formation with bulk acid upon adt protonation.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-390686 (URN)10.1039/c9sc00876d (DOI)000474412700015 ()31293742 (PubMedID)
Funder
Swedish Research Council, 621-2014-5670Swedish Research Council, 2016-04271Swedish Research Council Formas, 213-2014-880
Available from: 2019-08-16 Created: 2019-08-16 Last updated: 2019-08-16Bibliographically approved
Liu, T., Guo, M., Orthaber, A., Lomoth, R., Lundberg, M., Ott, S. & Hammarström, L. (2018). Accelerating proton-coupled electron transfer of metal hydrides in catalyst model reactions. Nature Chemistry, 10(8), 881-887
Open this publication in new window or tab >>Accelerating proton-coupled electron transfer of metal hydrides in catalyst model reactions
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2018 (English)In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 10, no 8, p. 881-887Article in journal (Refereed) Published
Abstract [en]

Metal hydrides are key intermediates in catalytic proton reduction and dihydrogen oxidation. There is currently much interest in appending proton relays near the metal centre to accelerate catalysis by proton-coupled electron transfer (PCET). However, the elementary PCET steps and the role of the proton relays are still poorly understood, and direct kinetic studies of these processes are scarce. Here, we report a series of tungsten hydride complexes as proxy catalysts, with covalently attached pyridyl groups as proton acceptors. The rate of their PCET reaction with external oxidants is increased by several orders of magnitude compared to that of the analogous systems with external pyridine on account of facilitated proton transfer. Moreover, the mechanism of the PCET reaction is altered by the appended bases. A unique feature is that the reaction can be tuned to follow three distinct PCET mechanisms-electron-first, proton-first or a concerted reaction-with very different sensitivities to oxidant and base strength. Such knowledge is crucial for rational improvements of solar fuel catalysts.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-357209 (URN)10.1038/s41557-018-0076-x (DOI)000439420400015 ()30013192 (PubMedID)
Funder
Swedish Research Council, 2016-04271Knut and Alice Wallenberg Foundation, 2011.0067
Available from: 2018-08-13 Created: 2018-08-13 Last updated: 2019-01-04Bibliographically approved
Chabera, P., Kjaer, K. S., Prakash, O., Honarfar, A., Liu, Y., Fredin, L. A., . . . Warnmark, K. (2018). Fe-II Hexa N-Heterocyclic Carbene Complex with a 528 ps Metal-to-Ligand Charge-Transfer Excited-State Lifetime. Journal of Physical Chemistry Letters, 9(3), 459-463
Open this publication in new window or tab >>Fe-II Hexa N-Heterocyclic Carbene Complex with a 528 ps Metal-to-Ligand Charge-Transfer Excited-State Lifetime
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2018 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 9, no 3, p. 459-463Article in journal (Refereed) Published
Abstract [en]

The iron carbene complex [Fe-II(btz)(3)](PF6)(2) (where btz = 3,3'-dimethyl-1,1'-bis(p-tolyl)-4,4'-bis(1,2,3-triazol-5-ylidene)) has been synthesized, isolated, and characterized as a low-spin ferrous complex. It exhibits strong metal-to-ligand charge transfer (MLCT) absorption bands throughout the visible spectrum, and excitation of these bands gives rise to a (MLCT)-M-3 state with a 528 ps excited-state lifetime in CH3CN solution that is more than one order of magnitude longer compared with the MLCT lifetime of any previously reported Fe-II complex. The low potential of the [Fe(btz)(3)](3+)/[Fe(btz)(3)](2+) redox couple makes the (MLCT)-M-3 state of [Fe-II(btz)(3)](2+) a potent photo-reductant that can be generated by light absorption throughout the visible spectrum. Taken together with our recent results on the [Fe-III(btz)(3)](3+) form of this complex, these results show that the Fe-II and Fe-III oxidation states of the same Fe(btz)(3) complex feature long-lived MLCT and LMCT states, respectively, demonstrating the versatility of iron N-heterocyclic carbene complexes as promising light-harvesters for a broad range of oxidizing and reducing conditions.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-348923 (URN)10.1021/acs.jpclett.7b02962 (DOI)000424315900001 ()29298063 (PubMedID)
Funder
Knut and Alice Wallenberg FoundationSwedish Energy AgencySwedish Research CouncilStiftelsen Olle Engkvist ByggmästareThe Crafoord FoundationCarl Tryggers foundation
Available from: 2018-04-26 Created: 2018-04-26 Last updated: 2018-04-26Bibliographically approved
Lomoth, R., Liu, T., Wang, S., Ott, S. & Hammarström, L. (2018). Probing the elementary steps of PCET catalysis. Paper presented at 255th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nexus of Food, Energy, and Water, MAR 18-22, 2018, New Orleans, USA.. Abstract of Papers of the American Chemical Society, 255
Open this publication in new window or tab >>Probing the elementary steps of PCET catalysis
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2018 (English)In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 255Article in journal, Meeting abstract (Other academic) Published
Place, publisher, year, edition, pages
Washington, D.C.: American Chemical Society (ACS), 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-368927 (URN)000435539903446 ()
Conference
255th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nexus of Food, Energy, and Water, MAR 18-22, 2018, New Orleans, USA.
Note

Meeting Abstract: 1173

Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2018-12-11Bibliographically approved
Wang, S., Aster, A., Lomoth, R. & Hammarström, L. (2018). Structural and Kinetic Studies of Intermediates of a Biomimetic Diiron Proton-Reduction Catalyst. Inorganic Chemistry, 57(2), 768-776
Open this publication in new window or tab >>Structural and Kinetic Studies of Intermediates of a Biomimetic Diiron Proton-Reduction Catalyst
2018 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, no 2, p. 768-776Article in journal (Refereed) Published
Abstract [en]

One-electron reduction and subsequent protonation of a biomimetic proton-reduction catalyst [FeFe(μ-pdt)(CO)6] (pdt = propanedithiolate), 1, were investigated by UV-vis and IR spectroscopy on a nano- to microsecond time scale. The study aimed to provide further insight into the proton-reduction cycle of this [FeFe]-hydrogenase model complex, which with its prototypical alkyldithiolate-bridged diiron core is widely employed as a molecular, precious metal-free catalyst for sustainable H2 generation. The one-electron-reduced catalyst was obtained transiently by electron transfer from photogenerated [Ru(dmb)3]+ in the absence of proton sources or in the presence of acids (dichloro- or trichloroacetic acid or tosylic acid). The reduced catalyst and its protonation product were observed in real time by UV-vis and IR spectroscopy, leading to their structural characterization and providing kinetic data on the electron and proton transfer reactions. 1 features an intact (μ22-pdt)(μ-H)Fe2 core in the reduced, 1-, and reduced-protonated states, 1H, in contrast to the Fe-S bond cleavage upon the reduction of [FeFe(bdt)(CO)6], 2, with a benzenedithiolate bridge. The driving-force dependence of the rate constants for the protonation of 1- (kpt = 7.0 × 105, 1.3 × 107, and 7.0 × 107 M-1 s-1 for the three acids used in this study) suggests a reorganization energy >1 eV and indicates that hydride complex 1H is formed by direct protonation of the Fe-Fe bond. The protonation of 1- is sufficiently fast even with the weaker acids, which excludes a rate-limiting role in light-driven H2 formation under typical conditions.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-343862 (URN)10.1021/acs.inorgchem.7b02687 (DOI)000422810900029 ()29297686 (PubMedID)
Funder
Swedish Research Council, 2016-04271Stiftelsen Olle Engkvist Byggmästare, 2016/3
Available from: 2018-03-02 Created: 2018-03-02 Last updated: 2019-03-26
Chabera, P., Liu, Y., Prakash, O., Thyrhaug, E., El Nahhas, A., Honarfar, A., . . . Warnmark, K. (2017). A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence. Nature, 543(7647), 695-+
Open this publication in new window or tab >>A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence
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2017 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 543, no 7647, p. 695-+Article in journal (Refereed) Published
Abstract [en]

Transition-metal complexes are used as photosensitizers(1), in light-emitting diodes, for biosensing and in photocatalysis(2). A key feature in these applications is excitation from the ground state to a charge-transfer state(3,4); the long charge-transfer-state lifetimes typical for complexes of ruthenium(5) and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron(6) and copper(7) being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs(6,8-10), it remains a formidable scientific challenge(11) to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered(12) photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers(13-15). Here we present the iron complex [Fe(btz)(3)](3+) (where btz is 3,3'-dimethyl-1,1'-bis(p-tolyl)-4,4'-bis(1,2,3-triazol-5-ylidene)), and show that the superior sigma-donor and pi-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(III) d(5) complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer ((LMCT)-L-2) state that is rarely seen for transition-metal complexes(4,16,17). The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2017
National Category
Chemical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-320033 (URN)10.1038/nature21430 (DOI)000397619700051 ()28358064 (PubMedID)
Funder
Knut and Alice Wallenberg FoundationSwedish Energy AgencyThe Crafoord FoundationSwedish National Infrastructure for Computing (SNIC)Stiftelsen Olle Engkvist Byggmästare
Available from: 2017-04-13 Created: 2017-04-13 Last updated: 2017-04-18Bibliographically approved
Hammarström, L., Lomoth, R. & Ott, S. (2017). Capturing intermediates of molecular solar fuels catalysts by time-resolved mid-IR spectroscopy. Paper presented at 253rd National Meeting of the American-Chemical-Society (ACS) on Advanced Materials, Technologies, Systems, and Processes, APR 02-06, 2017, San Francisco, CA. Abstract of Papers of the American Chemical Society, 253
Open this publication in new window or tab >>Capturing intermediates of molecular solar fuels catalysts by time-resolved mid-IR spectroscopy
2017 (English)In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 253Article in journal, Meeting abstract (Other academic) Published
Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-377528 (URN)000430569103735 ()
Conference
253rd National Meeting of the American-Chemical-Society (ACS) on Advanced Materials, Technologies, Systems, and Processes, APR 02-06, 2017, San Francisco, CA
Available from: 2019-02-25 Created: 2019-02-25 Last updated: 2019-02-25Bibliographically approved
Mijangos, E., Roy, S., Pullen, S., Lomoth, R. & Ott, S. (2017). Evaluation of two- and three-dimensional electrode platforms for the electrochemical characterization of organometallic catalysts incorporated in non-conducting metal-organic frameworks. Dalton Transactions, 46(15), 4907-4911
Open this publication in new window or tab >>Evaluation of two- and three-dimensional electrode platforms for the electrochemical characterization of organometallic catalysts incorporated in non-conducting metal-organic frameworks
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2017 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 46, no 15, p. 4907-4911Article in journal (Refereed) Published
Abstract [en]

The development of a reliable platform for the electrochemical characterization of a redox-active molecular diiron complex, [FeFe], immobilized in a non-conducting metal organic framework (MOF), UiO-66, based on glassy-carbon electrodes is reported. Voltammetric data with appreciable current responses can be obtained by the use of multiwalled carbon nanotubes (MWCNT) or mesoporous carbon (CB) additives that function as conductive scaffolds to interface the MOF crystals in "three-dimensional" electrodes. In the investigated UiO-66-[FeFe] sample, the low abundance of [FeFe] in the MOF and the intrinsic insulating properties of UiO-66 prevent charge transport through the framework, and consequently, only [FeFe] units that are in direct physical contact with the electrode material are electrochemically addressable.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2017
National Category
Inorganic Chemistry Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-321800 (URN)10.1039/c7dt00578d (DOI)000398888700006 ()28345708 (PubMedID)
Funder
Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg FoundationWenner-Gren FoundationsEU, European Research Council, ERC-CoG2015-681895_MOFcat
Available from: 2017-05-11 Created: 2017-05-11 Last updated: 2017-05-11Bibliographically approved
Fredin, L., Chabera, P., Lomoth, R., Sundstrom, V., Warnmark, K. & Persson, P. (2017). Photochemistry of iron(III) carbenes. Paper presented at 254th National Meeting and Exposition of the American-Chemical-Society (ACS) on Chemistry's Impact on the Global Economy, AUG 20-24, 2017, Washington, DC. Abstract of Papers of the American Chemical Society, 254
Open this publication in new window or tab >>Photochemistry of iron(III) carbenes
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2017 (English)In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 254Article in journal, Meeting abstract (Other academic) Published
Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2017
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-357071 (URN)000429556700154 ()
Conference
254th National Meeting and Exposition of the American-Chemical-Society (ACS) on Chemistry's Impact on the Global Economy, AUG 20-24, 2017, Washington, DC
Available from: 2018-08-13 Created: 2018-08-13 Last updated: 2018-08-13Bibliographically approved
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