da Silva Santos, Mayara: R for Reactive: Revealing Rhodium, Ruthenium, and Rhenium’s Rare Oxides through X-ray Absorption Spectroscopy. , Dissertation, Albert-Ludwigs-Universität Freiburg im Breisgau, 2025
https://freidok.uni-freiburg.de/data/262615
10.6094/UNIFR/262615
Open Access Version
Abstract:
Discovering compounds that present transition metals with high oxidation states or reactive oxygen species, such as the oxygen-centered radical, is of great scientific interest, as they have key applications as oxidizing agents, catalysts, or reaction intermediates. Due to the high reactivity of such chemical entities, experimental investigations of their electronic structures are limited. The study of small systems as models can be used to understand their properties and expand the applicability of related materials. This work aims to investigate highly oxidized transition metals, bringing a new perspective towards their electronic structure and properties. For that, X-ray absorption spectroscopy, at the oxygen K and metal M3 or N3 edges of [MOn]+ molecular ions (M=transition metal, n=integer), is used to identify the spectroscopic signatures of oxygen ligands and assign the oxidation state of the metal. The highly oxidized [MOn]+ gas phase species are produced by argon sputtering of a metal target in the presence of oxygen. The X-ray absorption spectroscopy, performed in ion yield mode, is used here as a tool to directly probe the electronic ground state structure of the investigated samples, that are analysed in stable conditions in their lowest energy states. The highest oxidation state of rhodium is here presented for the first time in the trioxidorhodium(VII) cation, for which the rhodium M3 edge shows the chemical shift corresponding to its high oxidation state, while the oxygen K edge shows the spectral signature of oxo ligands. Further, the oxygen-centered radical tetroxidoruthenium(VIII) cation and diradical tetroxidorhenium(VII) cation are here investigated by X-ray absorption spectroscopy for the first time, where the oxygen-centered singly occupied molecular orbitals are identified by a low energy transition at the oxygen K edge, which is suppressed upon hydrogenation. Computational studies corroborate the experimental observations, that will hopefully contribute to the scientific knowledge of these species and their oxidative properties.