TY  - GEN
A1  - Kubin, Markus
A1  - Guo, Meiyuan
A1  - Kroll, Thomas
A1  - Löchel, Heike
A1  - Källman, Erik
A1  - Baker, Michael L.
A1  - Mitzner, Rolf
A1  - Gul, Sheraz
A1  - Kern, Jan
A1  - Föhlisch, Alexander
A1  - Erko, Alexei
A1  - Bergmann, Uwe
A1  - Yachandra, Vittal
A1  - Yano, Junko
A1  - Lundberg, Marcus
A1  - Wernet, Philippe
T1  - Probing the oxidation state of transition metal complexes
BT  - a case study on how charge and spin densities determine Mn L-edge X-ray absorption energies
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - 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. Here 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 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.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 656 
KW  - electronic-structure
KW  - atomic multiplet
KW  - water-oxidation
KW  - iron complexes
KW  - photosystem-II
KW  - spectroscopy
KW  - manganese
KW  - spectra
KW  - ligand
KW  - FE
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-425057
SN  - 1866-8372
IS  - 656
ER  - 
TY  - GEN
A1  - Fondell, Mattis
A1  - Eckert, Sebastian
A1  - Jay, Raphael Martin
A1  - Weniger, Christian
A1  - Quevedo, Wilson
A1  - Niskanen, Johannes
A1  - Kennedy, Brian
A1  - Sorgenfrei, Florian
A1  - Schick, Daniel
A1  - Giangrisostomi, Erika
A1  - Ovsyannikov, Ruslan
A1  - Adamczyk, Katrin
A1  - Huse, Nils
A1  - Wernet, Philippe
A1  - Mitzner, Rolf
A1  - Föhlisch, Alexander
T1  - Time-resolved soft X-ray absorption spectroscopy in transmission mode on liquids at MHz repetition rates
T2  - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe
N2  - We present a setup combining a liquid flatjet sample delivery and a MHz laser system for time-resolved soft X-ray absorption measurements of liquid samples at the high brilliance undulator beamline UE52-SGM at Bessy II yielding unprecedented statistics in this spectral range. We demonstrate that the efficient detection of transient absorption changes in transmission mode enables the identification of photoexcited species in dilute samples. With iron(II)-trisbipyridine in aqueous solution as a benchmark system, we present absorption measurements at various edges in the soft X-ray regime. In combination with the wavelength tunability of the laser system, the set-up opens up opportunities to study the photochemistry of many systems at low concentrations, relevant to materials sciences, chemistry, and biology.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 780 
KW  - l-edge xas
KW  - electronic-structure
KW  - molecular-structure
KW  - spin-state
KW  - dynamics
KW  - complexes
KW  - probe
KW  - water
KW  - iron(II)
KW  - spectra
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-437529
SN  - 1866-8372
IS  - 780
ER  -