Co(II), Ni(II), Cu(II) and Zn(II) complexes of acenaphthoquinone 3-(4-benzylpiperidyl)thiosemicarbazone: Synthesis, structural, electrochemical and antibacterial studies.

An interesting series of four complexes of acenaphthoquinone 3-(4-benzylpiperidyl) thiosemicarbazones (HL), with a general formula [Co II L 2 ]( 1 ), [Ni II L 2 ]( 2 ), [Cu II L 2 ]( 3 ), and [Zn II L 2 ]( 4 ), were prepared. The complexes were characterized by means of elemental analysis, IR, UV–Vis spectroscopy and ESI-MS methods. In all the complexes the ligand (HL) coordinate as a monobasic ligand in tridentate fashion. The crystal structure of the compounds 1 and 2 were determined by single crystal X-ray diffraction experiment. The geometry and bonding parameters of the compound 3 were determined from EPR spectra. The g values of 3 , calculated from EPR at 77 K, indicate a rhombic coordination geometry about copper(II). The room temperature magnetic moment of the cobalt(II) complex 1 , indicate that it is in high spin state, while the nickel(II) complex, 2 , is paramagnetic. The redox behavior of the ligand and its complexes were studied by cyclic voltammetry. The density functional theory (DFT) was used for geometry optimization, determination of HOMO and LUMO energies, HOMO–LUMO energy gap and dipole moment of the compounds. Antibacterial activity of the ligand and complexes 1 – 4 , have been screened against two gram negative bacteria Escherichia coli , Pseudomonas aeruginosa and two gram positive bacteria Staphylococcus aureus and Bacillus subtilis. The electron micrograph images display damage to microbial cell wall upon treatment with the compounds. [ABSTRACT FROM AUTHOR]