Synthesis, crystal structures and anticancer studies of Ni (Ⅱ), Co (Ⅲ) and Zn (Ⅱ) complexes based on 5-bromosalicylaldehyde- 2-(2-aminophenyl)benzimidazole Schiff base

•Three Schiff base metal complexes were synthesized and characterized.•Co(Ⅲ) complex is mononuclear molecule, Ni(Ⅱ) and Zn(Ⅱ) complexes are binuclear molecules.•Co(Ⅱ) was oxidized to Co(Ⅲ) by coordinating three deprotonated groups.•Co(Ⅲ) complex was potently cytotoxic against breast cancer cells than cisplatin.•Co(Ⅲ) complex could induce cell apoptosis and inhibit DNA replication.