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Speaker: Dr. Olesya Ablyasova
Program Description
Olesya S. Ablyasova1,2, Mihkel Ugandi3, Esma Birsen Boydas3, Mayara da Silva Santos1,2, Max Flach1,2,
Vicente Zamudio-Bayer1, Michael Römelt3, J. Tobias Lau1,2, Konstantin Hirsch1
1Abteilung für Hochempfindliche Röntgenspektroskopie, Helmholtz-Zentrum Berlin für Materialien und Energie,
Albert-Einstein-Straße 15, 12489 Berlin, Germany.
2Physikalisches Institut, Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, Germany
3Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489 Berlin, Germany
The CaMn4O5 cluster’s electronic structure plays a crucial role in understanding dioxygen formation in the Kok cycle. The S4 state, responsible for O2 formation, is difficult to observe because of the millisecond time scale of the S3-S0 transition [1]. Two main widely discussed models for the S4 state feature different oxidation states of +4 and +5 of the manganese atom at the reaction site [2]. Despite the fact that the spin states of the manganese atoms in state S4 are still under debate, the reactivity of the CaMn4O5 cluster is believed to be spin-dependent [3].
We report on the characterization of cold cationic gas-phase manganese oxide complexes via X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). We identify oxidation and spin states by
comparison with reference spectra of manganese compounds with known oxidation states, accompanied by
multireference and density functional theory calculations. We demonstrate that cationic Mn(V)O+2, recently identified as a species with the high oxidation state of manganese atom [4], is only the second manganese oxo complex to exist in a high-spin state. Our most important result is the identification of a Mn2O+3 species with Mn(V) in a high-spin state. This is the first observation of the elusive manganese(V) high-spin state in a polymagnanese oxido complex [5, 7]. The
observed result might have implications for the oxidation and spin states of the CaMn4O5 complex in the S4 state.
References
[1] N. Cox et al, Science (2014), 345, 804.
[2] J. Barber, Nature Plants (2017), 3(4), 17041.
[3] V. Krewald et al, Inorganic Chemistry (2016), 55(2), 488.
[4] M. G. Delcey, et al, Phys. Chem. Chem. Phys (2022), 24, 3598.
[5] R. Gupta, Proceedings of the National Academy of Sciences (2015), 112, 53
[6] T. Taguchi, et al, Journal of the American Chemical Society (2012), 134(4), 1996.
