Crystal structure, Spectroscopic Studies, DFT Calculations, Cyclic Voltammetry and Catalytic Activity of a Copper Schiff Base Complex

Herein, we describe the synthesis of a novel tetradentate Schiff base ligand, H₂L, with a diaminotoluene spacer, and its corresponding mononuclear copper complex, CuL, in methanol solvent. The characterization of all new compounds was conducted using various spectroscopic techniques, such as FT-IR, UV-vis, ¹H, ¹³C, ¹H-¹H COSY-NMR and MS. Single-crystal X-ray diffraction analysis of the CuL complex revealed a monoclinic system with a Cc space group, comprising four molecules per unit cell. Conductivity measurements indicated the nonelectrolytic nature of the complex, while the electrochemical behavior exhibited a quasi-reversible redox process. Quantum calculations, performed using DFT and TD-DFT theory at the M062X/6-311**G/ SDD level, demonstrated good agreement with the experimental data. Notably, the copper compound displayed larger static and dynamic hyperpolarizability values compared to urea, suggesting potential as an excellent second- and third-order nonlinear optical (NLO) material.

Furthermore, the prepared complex effectively catalyzed the homogeneous oxidation reaction of cyclohexene in the presence of H₂O₂ as an oxidant, achieving a high conversion rate of 98% with CuL as the catalyst. The bromoperoxidase activity was explored in the oxidative bromination of phenol red as a trap, employing the studied complex which can be considered as a potential functional model of bromoperoxidase, with the reaction rate constant k equal to 2.203 × 10⁵ (mol L^-1)^-2s^-1.