26. Deutsche Physikerinnentagung 2022 (German Conference of Women in Physics)

Disproportionation in gas-phase di-manganese oxide cluster revealed by X-ray absorption spectroscopy

Nov 26, 2022, 10:15 AM

15m

Otto-Lehmann Hörsaal (KIT Campus South)

Talk Physics talks Physics Talks - Quantum Effects, Materials Physics

Speaker

Olesya Ablyasova (Helmholtz-Zentrum Berlin für Materialien und Energie)

Description

Photosystem II, with its active center a CaMn${}_4$O${}_5$ cluster (OEC), is essential for photosynthesis and therefore O${}_2$ production in nature [1]. The understanding of the electronic structure and properties of this complex plays an important role in designing artificial water-oxidizing complexes. During oxygen formation the OEC undergoes five distinct states called S${}_0$-S${}_4$ forming the Kok cycle. Despite detailed knowledge of S${}_0$ through S${}_3$ there is still a lack of information on S${}_4$ due to challenges preparing OEC in this state [2]. However, two major competing models for S${}_4$ have been proposed in the literature which involve distinctively different oxidation states namely Mn(IV) (and an oxygen radical) and Mn(V), respectively.
We performed X-ray absorption spectroscopy (XAS) in ion yield mode at the manganese L-edge and oxygen K-edge on a series of cryogenically cooled, mass-selected manganese oxide ions at 20 K.
Here, we report on Mn${}_2$O${}_3^{+}$ – a high-valent species with two μ-oxo bridges and a terminal oxo ligand, which forms a subunit of the OEC. Using XAS we find an unusual charge disproportionation in Mn${}_2$O${}_3^{+}$,where one manganese atom is in a high oxidation state, and stability of this complex in a H${}_2$O ligand presence. The oxidation states were identified by by comparison to reference X Ray absorption spectra of other manganese compounds.

[1] N. Cox and et al. Electronic structure of the oxygen-evolving complex in Photosystem II prior to O–O bond formation. Science, 2014, 345, 804.
[2] J. Barber. A mechanism for water splitting and oxygen production in photosynthesis. Nature Plants, 2017, 3(4), 17041.

Presentation materials

WStalkAblyasova.pdf