Ligational behavior of a bidentate coumarin derivative towards CoII, NiII, and CuII : synthesis, characterization, electrochemistry, and antimicrobial studies

A series of new Co(II), Ni(II), and Cu(II) complexes of Schiff base derived from coumarin have been prepared and characterized by analytical and spectral methods. The Schiff base is synthesized by the condensation of 2,6-diaminopyridine and 3-acetylcoumarin in 1:1 stoichiometric ratio. All complexes have 1:1 metal : ligand ratio except the nickel complex, where it was found to be 1:2. UV-Vis spectra and magnetic moment studies confirm the existence of tetrahedral and octahedral geometries around cobalt(II) and nickel(II) metal ions, respectively, but copper(II) chloride/nitrate/sulfate complexes have square-planar geometry and copper(II) acetate complex is distorted octahedral. ESR spectra of copper complexes at room temperature and liquid nitrogen temperature were tetragonal. All the complexes were found to be more active against bacteria except Ni(II) complex; only CuLSO4 and CuL(CH3COO)(2) have shown the enhanced activity against fungi.