Synthesis, crystal structures, and cytotoxicity against cancer cell lines of metal (Co, Cu, Zn, Cd) complexes containing 1,1′-diaryl-2,2′dipyridylethene derivatives

A series of complexes between bis(2-pyridyl)-di(4-n-butylphenyl)ethene (KT4) and bis(2-pyridyl)-di(3-methoxyphenyl)ethene (KT18) with transition metals Co(II), Cu(II), Zn(II), and Cd(II) were synthesized and crystallized. The structures of these compounds were confirmed based on IR, NMR, and MS spectra. Moreover, crystals were obtained for ZnKT18, CoKT18, CuKT18, CdKT18, and CdKT4. Single-crystal X-ray diffraction (XRD) demonstrated the ability of these pyridine-based ligands to coordinate to metal ions via two nitrogen atoms in the aromatic heterocycles. Depending on the central metal, they can form different structures. Zn(II) and Co(II) form mononuclear complexes with KT18, where the metal coordinates to two N atoms and two chloride ions in a tetrahedral geometry (coordination number 4). The complexes CuKT18, CdKT18, and CdKT4 are binuclear complexes with one pendant chloride and two bridging chlorides coordinating with the metal ion (coordination number 5). The cytotoxic properties of free ligands and complexes were tested on four cancer lines, including KB, Hep-G2, Lu, and MCF-7. In general, the free ligands have no cytotoxic activity, while all complexes present strong to medium effects on these cancer lines. Several complexes are comparable in activity to cisplatin, a commercial drug used in the treatment of cancer. Specifically, ZnKT4 selectively inhibits the activities of the KB and Hep-G2 cell lines. CdKT4 has a high impact on Hep-G2 and Lu (IC50 < 5 μM) while CdKT18 exhibits effective anticancer activity against the KB and MCF-7 cell lines. CuKT18 strongly inhibits the growth progress of the KB cancer cell (IC50 = 9.52 μM). These IC50 values are lower than those of cisplatin.