Soft X-ray signatures of cationic manganese–oxo systems, including a high-spin manganese(v) complex

Mickaël G. Delcey,Bernd von Issendorff,Christine Bülow,Vicente Zamudio-Bayer,Rebecka Lindblad,Marcus Lundberg,Martin Timm,J. Tobias Lau

doi:10.1039/d1cp03667j

Abstract

Manganese-oxo species catalyze key reactions, including C-H bond activation or dioxygen formation in natural photosynthesis. To better understand relevant reaction intermediates, we characterize electronic states and geometric structures of [MnOn]+ manganese-oxo complexes that represent a wide range of manganese oxidation states. To this end, we apply soft X-ray spectroscopy in a cryogenic ion trap, combined with multiconfigurational wavefunction calculations. We identify [MnO2]+ as a rare high-spin manganese(V) oxo complex with key similarities to six-coordinated manganese(V) oxo systems that are proposed as reaction intermediates in catalytic dioxygen bond formation.

Highlights

University, SE-75121 Uppsala, Sweden e Institut fur Optik und Atomare Physik, Technische Universitat Berlin, Hardenbergstr. 36, 10623 Berlin, Germany f Physikalisches Institut, Albert-Ludwigs-Universitat Freiburg, Hermann-Herder-Str. 3, 79104, Freiburg, Germany † Electronic supplementary information (ESI) available
Accurate spectral simulations can be used to identify electronic structure based on spectral fingerprints, and enable a clear separation of electronic and geometric effects on spectral shape and edge position
The good agreement between experimental and calculated L-edge X-ray absorption spectra allows for definite assignments of electronic state and oxidation state, and give insight into how the oxidation state is expressed in ligand K-edge and metal L-edge X-ray absorption spectra

Summary

Introduction

University, SE-75121 Uppsala, Sweden e Institut fur Optik und Atomare Physik, Technische Universitat Berlin, Hardenbergstr. 36, 10623 Berlin, Germany f Physikalisches Institut, Albert-Ludwigs-Universitat Freiburg, Hermann-Herder-Str. 3, 79104, Freiburg, Germany † Electronic supplementary information (ESI) available. University, SE-75121 Uppsala, Sweden e Institut fur Optik und Atomare Physik, Technische Universitat Berlin, Hardenbergstr. 36, 10623 Berlin, Germany f Physikalisches Institut, Albert-Ludwigs-Universitat Freiburg, Hermann-Herder-Str. 3, 79104, Freiburg, Germany † Electronic supplementary information (ESI) available. DFT calculations predict the formation of high-spin manganese–. Oxo species, typically in the form of a manganese(IV)–oxyl radical.[20,21,22,23] These predictions require experimental confirmation, not least because relative spin-state energetics and the amount of radical character depend on the density functional.[24,25,26] Other proposals invoke nucleophilic attack on a triplet manganese(V)–oxo group or even the involvement of manganese(VII) species.[10,11,12] For synthetic manganese complexes proposed as oxygen evolution catalysts, no reactive species have been trapped and their identities are often under debate.[13,14,15,16,17,18,19]

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Discussion

Conclusion