Spectroscopic and Theoretical Elucidation of Oxygen-Activating Transition Metal Centers – Developing Magnetic Raman Spectroscopy as a new Experimental Method

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The iron-containing systems that are of central importance for the present FOR5215 research initiative feature a large array of challenging spectroscopic and electronic structure problems. The iron centers can exist in up four different oxidation states over the course of a single turnover, each of which can be associated with a variety of spin states. Also, changes between high-spin and low-spin surfaces are rather common in such systems (two-state reactivity). Predicting the geometric and electronic structures of these states theoretical is still highly challenging, even for the most powerful quantum chemical methods. A careful combination of advanced spectroscopy and state-of-the-art quantum chemistry is the best way forward in determining the catalytic mechanisms of these systems. Thus, any information that spectroscopy can provide is of paramount importance. Our main goals for this project are i.) to establish a magnetic (resonance) Raman spectrometry as a novel spectroscopic tool in transition metal chemistry, and ii.) to explore the molecular and electronic structures of most interesting catalytically active iron complexes arising from scientific collaboration within the FOR5215 initiative. For the first part of this proposal, we will build a dedicated magnetic resonance Raman setup, develop the so far unknown theory for this method, provide benchmark results on simple, well-understood systems and finally apply this methodology to the problems pursued by the FOR5215 research initiative. For the second part of this proposal, we will combine the substantial array of spectroscopic methods available in our department (Mössbauer, EPR, CD/MCD, UV/vis, resonance Raman, SQUID) with the powerful quantum chemical machinery contained in the ORCA electronic structure package to study selected systems and reactions mechanisms inside FOR5215.