Electronic Descriptors Governing Binding Energies of Bidentate Aromatic Ligands with Metal Cations: Insights from DFT...

The binding energy (BE) of metal-ligand complexes is a fundamental parameter that governs the stability, reactivity, and selectivity in catalysis and separation processes. For bidentate coordination of aromatic ligands with metal cations, it is still unclear what fundamental electronic and structural properties govern the metal-ligand binding. Here, density functional theory (DFT) calculations combined with statistical analysis were used to uncover the key descriptors that control metal-ligand binding. Fourteen descriptors were selected to represent the physicochemical properties of metals/ligands. Electron affinity of metals (EA_M) and the ionization energy of ligands (IE_L) were identified as the dominant descriptors because they capture the process of electron transfer from ligands to metals. Their strong correlation with binding energy was also supported by HOMO-LUMO orbital theory and thermodynamic analysis. Incorporation of atomic radius (r_M) accounted for covalent stabilization in soft-soft interactions, while the $\frac{{\mathrm{EA}}_M}{{\mathrm{IE}}_L}$ ratio emphasized hard-hard electrostatic attractions. Together, these findings establish quantitative relationships between the binding energy and descriptors, which provide new physical insight into how electron transfer and orbital overlap determine metal-ligand binding behavior. These descriptors can facilitate the empirical screening of ligand-metal pairs in the design of catalysts and metal adsorbents.