Unveiling the Redox Noninnocence of Metallocorroles: Exploring K‑Edge X‑ray Absorption Near-Edge Spectroscopy with a Multiconfigurational Wave Function Approach

X-ray
absorption near-edge spectroscopy (XANES) is an advanced
technique for probing the local electronic structure of catalysts,
effectively identifying the noninnocent nature of ligands in transition-metal
complexes. Metallocorroles with noninnocent corrole rings exhibit
unusual electronic structures that challenge traditional density functional
theory (DFT) methods, necessitating more rigorous approaches to describe
electron correlation accurately. We explored K-edge XANES spectra
of Fe, Mn, and Co metallocorroles using TDDFT and wave function-based
methods. This is the first investigation employing multireference
methods, specifically RASSCF, RASPT2, and MC-PDFT, to analyze the
redox noninnocent nature of metallocorroles reflected in their XANES
spectra. We quantified the noninnocent character of the corrole and
the oxidation states of the metals, capturing more than singly excited
excitations responsible for the pre-edge peak. Our findings demonstrate
the importance of these advanced computational techniques for accurately
predicting XANES spectra, providing a reliable understanding of the
electronic properties of such complexes. This study offers a new strategy
for investigating ligand redox noninnocence via integrated experimental
and computational XANES.