Copper(II) complexes derived from 3,5-dibromosalicylaldehyde semicarbazone: Crystal structures, spectra and in vitro cytotoxicity studies

Two mononuclear Cu(II) complexes of ONO donor 3,5-dibromosalicylaldehyde semicarbazone (H₂dbsc) were synthesized and characterized. Tridentate nature of the ligand 3,5-dibromosalicylaldehyde semicarbazone to Cu(II) was realized from different physiochemical techniques. In both complexes, phenolic hydrogen of the semicarbazone deprotonates and is coordinated to copper in the phenolate form. The azomethine nitrogen and the amido oxygen serves the other two coordination sites, with chlorido/bromido atom occupies the fourth coordination position. Both the Cu(II) complexes, [Cu(Hdbsc)Cl]·H₂O (1) and [Cu(Hdbsc)Br]·H₂O (2) are crystallized and their structures are determined by SCXRD. A molecule of water is present in the lattice in both complexes. Extensive hydrogen bonding, C–Br···π and π···π interactions make the complexes more rigid in crystal lattice, and they generate supramolecular network. IR spectra indicate tridentate behavior of the semicarbazone in copper(II) complexes. EPR spectra of both complexes in frozen DMF solution at 77 K indicate axial geometry with metal-ligand bonds largely covalent in nature. The in vitro cytotoxicity study of the synthesized Cu(II) complexes 1 and 2 was performed on HepG2 and HeLa cells using CCK-8 assay. It is found that metal complexation increases the cytotoxicity against HeLa cells.