Two complexes [Cu4L4] (1) and [Zn2Cl4L]·2[N(CH2CH3)4] (2) are synthesized and characterized with UV–Vis, IR, PXRD and TGA using a symmetrical flexible Schiff base ligand 2,2′-(1,4-phenlenebis(nitrilomethylylidene)-bis(6- methoxyphenol) (H2L). Crystallographic analysis reveals that complex 1 is a mirror symmetric single molecule with a rhombic crossing structure linked by four Cu(II) ions and four ligands encircling each other. Complex 2 is a centrosymmetric single molecule with one ligand connecting two zinc chloride salts to form an anion framework with two tetraethylammonium cations to balance charge. Antiproliferative activity of both complexes against four cancer cells and two normal cells was investigated, and the results show that complex 2 had the strongest inhibitory effect on A549 cells with IC50 value much lower than cisplatin and lower toxicity to two normal cells. Mechanistic studies showed that complex 2 could induce apoptosis of A549 cells, and inhibit cell invasion and migration of SMMC-7721 cells and A549 cells at a low concentration effectively. This work could provide a basis for developing novel metal-based anticancer agents.