Unveiling the redox non-innocence 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 and is particularly effective in identifying the non-innocent nature of ligands in transition metal complexes. Metallocorroles with non-innocent corrole rings exhibit unusual electronic structures that challenge traditional density functional theory (DFT) methods, necessitating more rigorous methods that provide a reliable description of electron correlation. Herein, we explored the K-edge XANES spectra of metallocorroles of Fe, Mn, and Co using TDDFT and wavefunction-based methods. This is the first investigation to employ multireference methods, specifically RASSCF, RASPT2, and MC-PDFT, to study the redox noninnocent nature of metallocorroles reflected in their XANES spectra. We quantified the percentage of the non-innocent character of the corrole and the oxidation states of the metal in these complexes. Additionally, we captured more than singly excited excitations responsible for the pre-edge peak in the K-edge XANES spectra using multireference methods, that are beyond the capabilities of DFT. Our findings demonstrate that these advanced computational techniques are crucial for accurately predicting the XANES spectra, thereby providing a more reliable understanding of the electronic properties of such complexes. Furthermore, this study provides a new strategy for investigating the ligand redox noninnocence via integrated experimental and computational XANES.