Quantum chemical study of the photocatalytically active Mo-quercetin complex

The electronic and structural nature of the photocatalytically active Mo-quercetin complex was investigated using quantum chemical methods. According to DFT calculations performed at the B3LYP/6-31G(d,p) level, the HOMO energy of the complex was found to be –5.81 eV, while the LUMO energy was –3.28 eV. The corresponding band gap was determined to be approximately 464 nm. Additionally, the reactive character of the molecule can be revealed by the electrostatic potential surface area analysis. It was estimated that 42% of the complex's surface area had ESP values less than -25 kcal/mol. This suggests that there are many nucleophilic areas available for interactions like conjugation with biomolecules, coordination with other metal centers, and hydrogen bonding. On the other hand, it was discovered that about 18% of the surface area exceeded +20 kcal/mol. These results indicate that the complex exhibits semiconducting behavior and can be effectively used as a photocatalyst in the visible light region. Moreover, under standard conditions, the Gibbs free energy (ΔG°) of the complex was calculated to be –75.7 kJ/mol, and the standard enthalpy change (ΔH°) was –114.2 kJ/mol, reflecting an exothermic interaction between the molybdenum center and the quercetin ligand. The standard entropy change (ΔS°) was found to be –105.4 J/mol·K, indicating a decrease in disorder upon complex formation. These thermodynamic parameters confirm that the Mo-quercetin complex is thermodynamically stable. Structurally, the stability of the complex was further assessed based on its intermolecular interaction energies.

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