DNA binding, molecular docking and apoptotic inducing activity of nickel(ii), copper(ii) and zinc(ii) complexes of pyridine-based tetrazolo[1,5-a]pyrimidine ligandsElectronic supplementary information (ESI) available: Table S1 shows crystal data and structure refinement for ligands L1&2 and complex 6, Tables S2-S5 show the data of bond length, bond angles and hydrogen bond parameters for ligands L1&2, Fig. S1-S4 show crystal packing and hydrogen bonding parameters of ligands L1&2, Fig. S5-S8 sho

Six mononuclear copper( ii ), nickel( ii ) and zinc( ii ) complexes, [ML 1 Cl 2 ] ( 1-3 ) and [M(L 2 ) 2 Cl 2 ] ( 4-6 ), of two biologically active tetrazolo[1,5- a ]pyrimidine core ligands, ethyl 5-methyl-7-pyridine-2-yl-4,7-dihydrotetrazolo[1,5- a ]pyrimidine-6-carboxylate (L 1 ) and ethyl-5-methyl-7-pyridine-4-yl-4,7-dihydrotetrazolo[1,5- a ]pyrimidine-6-carboxylate (L 2 ), have been synthesized and characterized. The molecular structure of the ligands (L 1&2 ) and complex 6 were determined by single crystal X-ray diffraction. The X-ray crystal structure of 6 confirms that it has a distorted tetrahedral structure with a ZnN 2 Cl 2 coordination environment. All of the complexes exhibit an unusually strong luminescence at room temperature. Electroparamagnetic resonance spectra of copper( ii ) complexes ( 2 and 5 ) show four lines, characteristic of square planar geometry, with nuclear hyperfine spin 3/2. DNA binding studies of complexes with calf-thymus DNA suggest that complexes 2 and 5 bind in the grooves of the DNA. These results were further supported by molecular docking studies. In vitro cytotoxic activities of the ligands (L 1&2 ) and complexes ( 1-6 ) against human cancer cell lines such as lung (A549), cervical (HeLa), colon (HCT-15) and a non-cancer human embryonic kidney cell line revealed that the complexes selectively inhibit the growth of cancer cells and are inactive against non-cancer cell lines, whereas the ligands were found to be inactive with both cancer and non-cancer cell lines. The IC 50 values of the complexes revealed that the copper( ii ) complexes ( 2 and 5 ) exhibit high cytotoxic activity against colon (HCT-15) cells when compared to the standard drug cisplatin. Furthermore, the live cell and fluorescent imaging of cancer cells show that complexes 2 and 5 induce cell death through apoptosis. The biological activity of metal( ii ) complexes of tetrazolo[1,5- a ]pyrimidine ligands show that the copper( ii ) complexes may act as promising anticancer agents.