Synthesis and cytotoxicity evaluation of copper(II) complexes with polypyridines and 5-benzyltetrazole

•First Cu(II) complexes with 5-benzyltetrazole and polypyridines were synthesized.•SCXRD showed that bipyridine based complexes are binuclear due to tetrazolate bridges.•Phenanthroline based complexes exhibited significant dose-dependent cytotoxicity. In the present study, four new mixed-ligand copper(II) complexes with 5-benzyltetrazole (HL) and polypyridine ligands (phen – 1,10-phenanthroline, dmphen – 4,7-dimethyl-1,10-phenanthroline, bipy – 2,2’-bipyridine, dmbipy – 2,2’-bi-4-picoline), namely, [Cu2(bipy)2(L)4] (1), [Cu2(dmbipy)2(L)4]·H2O (2·H2O), [Cu(phen)(L)2] (3), [Cu(dmphen)(L)2] (4), have been synthesized. Complexes have been characterized by EPR and IR-spectroscopy, elemental, thermogravimetric and powder X-ray diffraction analysis. Two crystal structures of the copper(II) complexes with 5-benzyltetrazole, namely [Cu2(bipy)2(L)4] (1) and [Cu2(dmbipy)2(L)4] (2), were established for the first time by a single-crystal X-ray diffraction study. All complexes have been screened in vitro for their cytotoxic activity against two cancer cell lines: larynx carcinoma (Hep2), hepatocellular carcinoma (HepG2) and breast adenocarcinoma (MCF-7). The order of efficacy was 4 > 3 > 2·H2O > 1. Complexes [Cu(phen)(L)2] (3) and [Cu(dmphen)(L)2] (4) demonstrated the highest cytotoxicity.