Computational Insights into O 2 Capture by Cobalt salen and Its Derivatives

We present a detailed computational study of O 2 binding thermodynamics, spinstate preferences and redox properties of cobalt salen (Co(salen)) and its methoxy substituent analog (OMe-Co(salen)). Starting with a DLPNO-CCSD(T) benchmarking study, we used the r 2 SCAN-3c functional to quantify the energetics of superoxo and µ-peroxo adduct formation across various charge states, solvents, and ligand environments. We find that µ-peroxo species are consistently more stable than their superoxo counterparts, with binding free energies twice as exergonic under typical conditions. Our results show that weak-field ligands such as DMF promote slightly stronger binding O 2 than pyridine, particularly in the peroxo configuration. We show that methoxy substitution further enhances O 2 affinity, especially for the peroxo adduct, with increased stabilization on the order of 0.1-0.2 eV compared to Co(salen). Binding constants (K eq), derived from free energy calculations, elucidate the impact of various factors on the efficiency of capture and release of O 2. To facilitate the rational design of Co(salen) systems for O 2 separation, these insights are combined into thermodynamic schemes using reduction potentials and equilibrium constants.