Synthesis, Characterization, DFT of novel, symmetrical, N/O-donor tetradentate Schiff’s base, its Co(II), Ni(II), Cu(II), Zn(II) complexes and their in-vitro human pathogenic antibacterial activity

Abstract

A novel tetradentate Schiff’s base ligand Bis(furfural)-1,8-naphthalenediimine (L) was synthesized and characterized by physical, analytical and spectral data. Complexes of Co(II), Ni(II), Cu(II) and Zn(II) of general composition MLX2 [L = C20H14N2O2 and X = Cl– , NO3– and OAc–] have been synthesized in 1:1 molar ratio of metal to ligand. The elemental analysis, molar conductance measurements, magnetic susceptibility measurements, Mass, IR, UV-Visible, NMR and EPR spectral studies of the compounds led to the conclusion that the ligand acts in a tetradentate manner in Co(II), Ni(II) and Cu(II) complexes, while in bidentate fashion in Zn(II) complex. Octahedral geometry was assigned to Co(II) and Ni(II) complexes, Tetragonal geometry for Cu(II) complexes and tetrahedral geometry for Zn(II) complexes of the Schiff’s base ligand. The thermal studies suggested that the complexes are more stable as compared to ligand and absence of coordinated water molecules in metal complexes. The geometries of Schiff’s base and metal complexes were optimized with respect to the energy taking the 6-31+g(d,p) basis set in Gaussian 09W programme in gaseous phase. The antibacterial studies of the compounds were examined against the human pathogenic, Gram negative bacteria i.e. Escherichia coli, Yersinia enterocolitica, Klebsiella pneumoniae, and Salmonella typhi and Gram positive bacteria i.e. Listeria monocytogenes and Enterococcus faecalis.