Two new square-planar Cu(II) complexes derived from a heterocyclic pyrazolone ligand: synthesis, in vitro anticancer activity, DFT and Hirshfeld analysis

The current work describes the synthesis of two Cu(II) complexes [Cu(LA_I)₂] complex-1 and [Cu(LA_II)₂] complex-2 based on σ-donating acylpyarazolone ligands. Both complexes were thoroughly investigated using FTIR, UV–Vis, TGA and ESR spectroscopy methods. Additionally, single-crystal X-ray diffraction analysis was employed to determine their structures. The analysis indicates that the Cu²⁺ ion in both complexes occupies a centre of inversion symmetry and exhibits square-planar geometry. The examined complexes [Cu(LA_I)₂] complex-1 and [Cu(LA_II)₂] complex-2 crystallize in the P2₁/c Monoclinic and P2₁/n Monoclinic space groups, respectively, according to the X-ray single-crystal investigation. In addition to the experimental and spectroscopic investigations, DFT calculations were performed using the B3LYP functional with the LANL2DZ basis set for optimization. The bond lengths and bond angles determined from the DFT calculations are consistent with the X-ray data. HOMO–LUMO energy, natural bonding orbital and spin density analyses were also conducted to provide the best possible correlation and comparison with the experimental data. Intermolecular and non-covalent interactions were examined using Hirshfeld surface analysis. Furthermore, a cytotoxicity assay of the synthesized [Cu(LA_II)₂] complex-2 was performed against three different cancer cell lines: NCI-H23 (lung carcinoma cell line—lung cancer), SH-SY5Y (neuroblastoma cell line—neuroblastoma cancer) and HepG2 (hepatocellular carcinoma cell line—liver cancer), where notable cell death was observed, demonstrating the effectiveness of the complex against cancer cells.

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