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Abstract
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Copper, cobalt and zinc-salophen complexes 3–8 were prepared from the reaction of N,N-bis(salicylidene)4-chloro-1,2-phenylendiamine (1) or N,N-bis(salicylidene)4-bromo-1,2-phenylendiamine (2) with their respective acetate salts. All compounds were characterized with common techniques. In additional, optical, electrochemical, thermal and antibacterial properties of ligands and their complexes were studied. Schiff base ligands 1 and 2 showed the intense emission band at 476 nm in the fluorescence spectra. The emission process of these ligands is related to the excited state intramolecular proton transfer phenomenon (and also π→π* transitions). In general, after the incorporation of copper, cobalt and zinc metal ions into the structure of ligands 1 and 2, the emission intensity of the ligands totally quenched. It can be attributed to the changes in the conformational rigidity of the structure of ligands upon complexation. Thermal stability of complexes was proved by TGA analysis. The cyclic voltammogrames of Cu (II) complexes displayed quasi-reversible one electron Cu(II)/Cu(I) redox process, while those of their cobalt counterparts exhibited two reversible redox couples of Co(II)/Co(I) and Co(III)/Co(II). The investigation of antibacterial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and carbapenem &colistin resistant Klebsiella pneumoniae showed both Co(II) complexes 4 and 7 have remarkable antibacterial activity. The antibacterial effect of cobalt complexes against K. pneumoniae is of high interest as the bacterium, is resistant to two most important therapeutic options for treatment of multi-drug resistant Gram-negative bacteria, including polymyxins and carbapenems. Moreover, DFT investigations were performed to obtain a better understanding of structure of compounds 1–8. The values of band gap energies revealed ability of all compounds for using in optical devices. Finally, the electronic spectra of compounds are analyzed by TD
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