In this study, the authors report the synthesis of a new Mannich base formed by the condensation of pyrrole (C4H5N), 4-hydroxybenzaldehyde (C7H6O2) and phthalimide (C8H5NO2) and the respective copper (II) (Cu2+), nickel (II) (Ni2+) and cobalt (II) (Co2+) transition metal complexes derived from the ligand. The synthesized ligand and the metal complexes were characterized using elemental analysis, electrical conductivity studies and spectral studies. The geometry of the Mannich base metal (II) complexes was studied by ultraviolet–visible and electron spin resonance spectroscopy, and all the complexes were found to adopt square planar geometry. Among all the complexes, the cobalt complex was observed to show better antioxidant properties. It is noteworthy to mention that the copper complex is observed to exhibit better deoxyribonucleic acid cleavage activity at all concentrations compared with other complexes.