Synthesis and crystal structure of cytotoxic copper(II) complex with 1,10-phenanthroline-5,6-dione and isothiazole derivative

Oligopyridine based copper(II) complexes are of interest to scientists as possible anticancer agents due to promising cytotoxic and DNA binding/cleaving properties. In this study, copper(II) complex [Cu(phendione)L2]·C2H5OH with 1,10-phenanthroline-5,6-dione (phendione) and 4,5-dichloro-isothiazole-3-carboxylic acid (HL) was synthesized and characterized by elemental analysis, IR-spectroscopy, X-ray powder diffraction and single-crystal X-ray diffraction. According to X-ray diffraction data, obtained compound is mononuclear complex with square pyramidal coordination environment of the central atom which is surrounded by two isothiazolate molecules and one phendione ligand. The X-ray diffraction data are confirmed by IR-spectroscopy data showing the presence of characteristic stretching vibration bands of the carbonyl and carboxyl groups of oligopyridine ligand and isothiazolate ions, respectively. Density functional theory (DFT) calculations for complex were carried out using the ADF software package to perform geometry optimization and frequency calculations that were in a good agreement with experimental IR spectrum. Cytotoxicity of complex and initial reagents was tested in vitro against HepG2 (human hepatocellular carcinoma) and MCF-7 (human breast adenocarcinoma) cell lines. The complex showed high dose-dependent cytotoxic activity with the IC50 values of 0.60±0.03 µM and 0.96±0.13 µM, respectively, which is higher than the activity of cisplatin against these cell lines. The activity of the complex is due to the presence of phendione ligand, which exhibits a similar cytotoxic activity.