Ablyasova, O.S.; Zamudio-Bayer, V.; Flach, M.; da Silva Santos, M.; Lau, J.T.; Hirsch, K.: Direct spectroscopic evidence for the high-spin state of dioxidomanganese(v). Physical Chemistry Chemical Physics 26 (2024), p. 5830-5835
10.1039/d3cp05468c
Open Access Version
Abstract:
The spin state of metal centers in many catalytic reactions has been demonstrated to be a rate limiting factor when high-valent metal centers such as manganese are involved. Although numerous manganese(V) complexes, including a few manganese(V) oxo complexes, have been identified, thus far only one of these, [MnVH3 buea(O)], has been directly confirmed to exist in a high spin state. Such a high-spin manganese(V) center may play a crucial role in the dioxygen formation process in the elusive S4 state of the Kok cycle in photosystem II. In this study, we provide direct experimental evidence, using X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectroscopy (XAS), of gas phase [OMnO]+ as the second known high-spin manganese(V) oxo complex. We conclusively assign the ground state as 3B1 (C2v). Additionally, we provide fingerprint spectra not only for [OMnV O]+, but also for the high-spin hydroxidooxidomanganese(IV) ion [OMnIV OH]+ in its 4A′′ (Cs) ground state that is expected to exhibit similar XAS and XMCD spectral signatures to neutral dioxidomanganese(IV).