Electronic state of a manganese oxide clusters revealed by soft x-ray spectroscopy

Speaker: Dr. Olesya Ablyasova

Program Description
Olesya S. Ablyasova^1,2, Mihkel Ugandi³, Esma Birsen Boydas³, Mayara da Silva Santos^1,2, Max Flach^1,2, Vicente Zamudio-Bayer¹, Michael Römelt³, J. Tobias Lau^1,2, 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.