Unveiling the\nRedox Noninnocence of Metallocorroles:\nExploring K‑Edge X‑ray Absorption Near-Edge Spectroscopy\nwith a Multiconfigurational Wave Function Approach

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