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Title: Probing the oxidation state of transition metal complexes: a case study on how charge and spin densities determine Mn L-edge X-ray absorption energies

Transition metals in inorganic systems and metalloproteins can occur in different oxidation states, which makes them ideal redox-active catalysts. To gain a mechanistic understanding of the catalytic reactions, knowledge of the oxidation state of the active metals, ideally in operando, is therefore critical. L-edge X-ray absorption spectroscopy (XAS) is a powerful technique that is frequently used to infer the oxidation state via a distinct blue shift of L-edge absorption energies with increasing oxidation state. A unified description accounting for quantum-chemical notions whereupon oxidation does not occur locally on the metal but on the whole molecule and the basic understanding that L-edge XAS probes the electronic structure locally at the metal has been missing to date. We quantify how charge and spin densities change at the metal and throughout the molecule for both redox and core-excitation processes. We explain the origin of the L-edge XAS shift between the high-spin complexes Mn II(acac) 2 and Mn III(acac) 3 as representative model systems and use ab initio theory to uncouple effects of oxidation-state changes from geometric effects. The shift reflects an increased electron affinity of Mn III in the core-excited states compared to the ground state due to a contraction of the Mnmore » 3d shell upon core-excitation with accompanied changes in the classical Coulomb interactions. This new picture quantifies how the metal-centered core hole probes changes in formal oxidation state and encloses and substantiates earlier explanations. The approach is broadly applicable to mechanistic studies of redox-catalytic reactions in molecular systems where charge and spin localization/delocalization determine reaction pathways.« less
Authors:
ORCiD logo [1] ; ORCiD logo [2] ;  [3] ;  [4] ;  [2] ; ORCiD logo [5] ;  [1] ; ORCiD logo [6] ; ORCiD logo [7] ; ORCiD logo [8] ;  [4] ; ORCiD logo [9] ;  [6] ; ORCiD logo [6] ; ORCiD logo [2] ; ORCiD logo [1]
  1. Helmholtz-Zentrum Berlin (HZB), (Germany). German Research Centre for Materials and Energy and Inst. for Methods and Instrumentation for Synchrotron Radiation Research
  2. Uppsala Univ. (Sweden). Angstrom Lab. and Dept. of Chemistry
  3. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
  4. Helmholtz-Zentrum Berlin (HZB), (Germany). German Research Centre for Materials and Energy and Inst. for Nanometre Optics and Technology
  5. Univ. of Manchester (United Kingdom). The School of Chemistry
  6. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Biophysics and Integrated Bioimaging Division
  7. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Biophysics and Integrated Bioimaging Division; SLAC National Accelerator Lab., Menlo Park, CA (United States). Linac Coherent Light Source (LCLS)
  8. Helmholtz-Zentrum Berlin (HZB), (Germany). German Research Centre for Materials and Energy and Inst. for Methods and Instrumentation for Synchrotron Radiation Research; Univ. of Potsdam (Germany). Inst. of Physics and Astronomy
  9. SLAC National Accelerator Lab., Menlo Park, CA (United States). Photon Ultrafast Laser Science and Engineering Inst. (PULSE)
Publication Date:
Grant/Contract Number:
AC02-76SF00515; AC02-05CH11231; RGP0063/2013; P41GM103393; KAW-2013.0020; GM110501; GM55302
Type:
Accepted Manuscript
Journal Name:
Chemical Science
Additional Journal Information:
Journal Volume: 9; Journal Issue: 33; Journal ID: ISSN 2041-6520
Publisher:
Royal Society of Chemistry
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; Human Frontier Science Program (HFSP), Strasbourg (France); Swedish Research Council (SRC); Knut and Alice Wallenberg Foundation (Sweden); National Institutes of Health (NIH)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1476324

Kubin, Markus, Guo, Meiyuan, Kroll, Thomas, Löchel, Heike, Källman, Erik, Baker, Michael L., Mitzner, Rolf, Gul, Sheraz, Kern, Jan, Föhlisch, Alexander, Erko, Alexei, Bergmann, Uwe, Yachandra, Vittal, Yano, Junko, Lundberg, Marcus, and Wernet, Philippe. Probing the oxidation state of transition metal complexes: a case study on how charge and spin densities determine Mn L-edge X-ray absorption energies. United States: N. p., Web. doi:10.1039/c8sc00550h.
Kubin, Markus, Guo, Meiyuan, Kroll, Thomas, Löchel, Heike, Källman, Erik, Baker, Michael L., Mitzner, Rolf, Gul, Sheraz, Kern, Jan, Föhlisch, Alexander, Erko, Alexei, Bergmann, Uwe, Yachandra, Vittal, Yano, Junko, Lundberg, Marcus, & Wernet, Philippe. Probing the oxidation state of transition metal complexes: a case study on how charge and spin densities determine Mn L-edge X-ray absorption energies. United States. doi:10.1039/c8sc00550h.
Kubin, Markus, Guo, Meiyuan, Kroll, Thomas, Löchel, Heike, Källman, Erik, Baker, Michael L., Mitzner, Rolf, Gul, Sheraz, Kern, Jan, Föhlisch, Alexander, Erko, Alexei, Bergmann, Uwe, Yachandra, Vittal, Yano, Junko, Lundberg, Marcus, and Wernet, Philippe. 2018. "Probing the oxidation state of transition metal complexes: a case study on how charge and spin densities determine Mn L-edge X-ray absorption energies". United States. doi:10.1039/c8sc00550h. https://www.osti.gov/servlets/purl/1476324.
@article{osti_1476324,
title = {Probing the oxidation state of transition metal complexes: a case study on how charge and spin densities determine Mn L-edge X-ray absorption energies},
author = {Kubin, Markus and Guo, Meiyuan and Kroll, Thomas and Löchel, Heike and Källman, Erik and Baker, Michael L. and Mitzner, Rolf and Gul, Sheraz and Kern, Jan and Föhlisch, Alexander and Erko, Alexei and Bergmann, Uwe and Yachandra, Vittal and Yano, Junko and Lundberg, Marcus and Wernet, Philippe},
abstractNote = {Transition metals in inorganic systems and metalloproteins can occur in different oxidation states, which makes them ideal redox-active catalysts. To gain a mechanistic understanding of the catalytic reactions, knowledge of the oxidation state of the active metals, ideally in operando, is therefore critical. L-edge X-ray absorption spectroscopy (XAS) is a powerful technique that is frequently used to infer the oxidation state via a distinct blue shift of L-edge absorption energies with increasing oxidation state. A unified description accounting for quantum-chemical notions whereupon oxidation does not occur locally on the metal but on the whole molecule and the basic understanding that L-edge XAS probes the electronic structure locally at the metal has been missing to date. We quantify how charge and spin densities change at the metal and throughout the molecule for both redox and core-excitation processes. We explain the origin of the L-edge XAS shift between the high-spin complexes MnII(acac)2 and MnIII(acac)3 as representative model systems and use ab initio theory to uncouple effects of oxidation-state changes from geometric effects. The shift reflects an increased electron affinity of MnIII in the core-excited states compared to the ground state due to a contraction of the Mn 3d shell upon core-excitation with accompanied changes in the classical Coulomb interactions. This new picture quantifies how the metal-centered core hole probes changes in formal oxidation state and encloses and substantiates earlier explanations. The approach is broadly applicable to mechanistic studies of redox-catalytic reactions in molecular systems where charge and spin localization/delocalization determine reaction pathways.},
doi = {10.1039/c8sc00550h},
journal = {Chemical Science},
number = 33,
volume = 9,
place = {United States},
year = {2018},
month = {7}
}

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