Synthesis, spectroscopic characterization, electrochemistry and biological activity evaluation of some metal (II) complexes with ONO donor ligands containing indole and coumarin moieties

Cu(II), Co(II), Ni(II) and Zn(II) complexes of ligands 5-substituted-N′-((7-hydroxy-4-methyl-2-oxo-2H-chromen-8-yl)methylene)-3-phenyl-1H-indole-2-carbohydrazides were synthesized, characterized by elemental analysis and various spectroscopic techniques like, IR, 1H NMR, ESI-mass, UV–Visible, thermogravimetry–differential thermal analysis, magnetic measurements, molar conductance and powder-XRD data. Spectral analysis indicates octahedral geometry for all the complexes. Cu(II) and Zn(II) complexes of both the ligands have 1:1 stoichiometry of the type [M(L)(Cl)(H2O)2], whereas Co(II) and Ni(II) complexes of both the ligands have 1:2 stoichiometric ratio of the type [M(L)2]. The bonding sites are the oxygen atom of amide carbonyl, nitrogen of azomethine function and phenolic oxygen for the Schiff base ligands. The thermogravimetry–differential thermal analysis studies gave evidence for the presence of coordinated water molecules in the composition of Cu(II) and Zn(II) complexes of both the ligands, which were further supported by IR measurements. All the complexes were investigated for their electrochemical activity, but only the Cu(II) complexes showed the redox property. In order to evaluate the effect of antimicrobial potency of metal ions upon chelation, ligands and their metal complexes along with their respective metal chlorides were screened for their antibacterial and antifungal activities by the minimum inhibitory concentration (MIC) method. The results showed that the metal complexes were found to be more active than free ligands. Ligand 1 and its complexes were screened for free radical scavenging activity by the DPPH method and DNA cleavage activity using supercoiled plasmid DNA.