Comparative investigation of Cu(II) complexes with dithiocarbazate: Structural design, theoretical calculation, and in vitro antitumor activity

The present work reports the synthesis and investigation by semi-empirical Density Functional Theory (DFT), physical chemistry, and spectroscopic methods of two dithiocarbazates, 2-acetylpyridine-S-p-bromobenzyl-dithiocarbazate (HL1) and 2-acetylpyridine-S-p-nitrobenzyl-dithiocarbazate (HL2) and their Cu(II) complexes, [Cu(L1)Cl] (1), [Cu(L1)Br] (2), [Cu(L2)Cl] (3) and [Cu(L2)Br] (4). Single crystal X-ray analyzes showed distorted square planar geometry to the metal centers, which tridentate ligands coordinated by the NNS system and an additional halogen (Cl− or Br−) to complete the coordination sphere. Mass spectrometry data indicated the presence of [Cu(L1)(DMF)]+ and [Cu(L2)(DMF)]+, due to the exchanging of chloride/bromide ions and characteristic fragmentations of the compounds. The DFT composite method B97-3c was employed to optimize the geometries of ligands and complexes and IR spectra were calculated revealing good agreement with experimental data. Hydrogen bonds and π⋅⋅⋅π stacking interactions upon the molecular packing were investigated by Hirshfeld surface and fingerprint plots with the main interactions attributed to the H⋅⋅⋅H contacts. The biological activity of the dithiocarbazates and their Cu(II) complexes were evaluated in vitro against the human glioma U251 cells. Results revealed that the free dithiocarbazates present great in vitro antitumor activity that is increased after the complexation with copper. The measurement of cytotoxicity of the compounds showed biological activity in a low range of concentration, which indicates high efficiency as potential drugs.