Electronic Spectra of Iron–Sulfur Complexes Measured by 2p3d RIXS Spectroscopy

Abstract

Iron sulfur (FeS) proteins perform a wide range of biological functions including electron transfer and catalysis. Understanding the complex reactivity of these systems requires a detailed understanding of their electronic properties, which are encoded in the low-energy d-d excited states. Here we demonstrate that iron L-edge 2p3d resonant inelastic X-ray scattering (RIXS) can measure d-d excitation spectra in a series of monomeric, dimeric, and tetrameric FeS model complexes. RIXS provides advantages over traditional optical spectroscopies, because it is capable of measuring low-energy electronic excitations (0-10 000 cm) and spin-flip transitions. RIXS reveals the dense manifold of d-d excited states in dimeric [2Fe-2S] and tetrameric [MFeS] (M = V or Mo) complexes resulting from covalency and exchange coupling. These results support recent ab initio theoretical predictions that FeS clusters possess a much greater number of low-lying excited states than predicted by model Hamiltonians.

Spin-Pure Stochastic-CASSCF via GUGA-FCIQMC Applied to Iron–Sulfur Clusters

“…Especially, because direct experimental measurements targeting the electronic structures of these systems are often hindered by the large number of overlapping electronic states and corresponding vibrational modes at finite temperatures. 83 − 85 In addition, some energetically low-lying excited states are inaccessible by accurate optical absorption experiments due to being electric-dipole-forbidden transitions. 86 …”

Resonant Inelastic X-ray Scattering (RIXS) Studies in Chemistry: Present and Future

“…We want to mention that further interesting studies of LF excitations in metal compounds and catalytic systems were recently reported by the groups of DeBeer (Van Kuiken et al, 2016, Van Kuiken et al, 2018 and deGroot (Hunault et al, 2018, van Schooneveld et al, 2013b and others (Asakura et al, 2014, Bokarev et al, 2015.…”

Computational and data driven molecular material design assisted by low scaling quantum mechanics calculations and machine learning

“…This finding is later supported by indirect experimental evidence from iron L-edge 2p3d resonant inelastic X-ray scattering (RIXS). 194 In 2019, Cho et al 195 further performed ultraviolet (UV) absorption spectroscopy and stimulated X-ray Raman spectroscopy (SXRS) for [2Fe–2S] complexes, which complement each other by accessing different parts of the electronic spectrum and together can effectively probe the dense d – d electronic states in the Fe–S clusters. The simulated spectra presented clear signatures of the theoretically predicted dense low-lying excited states within the d – d manifold.…”