Synthesis, Characterization, and Antibacterial Activity of Cu(II), Ni(II), and Zn(II)Complexes of 14-Membered MacrocyclicTetraazaLigand

The macrocyclic 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-7,14-dienium bromide salt (LBr) was synthesisedfor use in complexationreactions with various metal salts of copper, nickel, and zinc. Twelve complexes were synthesised; five of them were successfully obtained in a crystal form that was suitable for X-ray crystallographic analysis. All the complexes were analysedby microelemental analysis, Fourier Transform infrared spectroscopy, ultravioletvisible spectroscopy,and magnetic susceptibility. The metals formed coordination bonds to the four aza nitrogen atoms,during the process of which the azomethine nitrogen atoms were deprotonated. The cationic charge in each complexwasbalanced with a bromide anion from the macrocyclic ligand. Deprotonation of the azomethine nitrogen atoms led to the formation of an acid/base complex with the metal salts.Preliminary studies for biological activity, based on the minimum inhibitory concentration (MIC) method, indicated that the macrocyclic complexes showed greater antibacterial activity than the bromide macrocyclicligand, which showedlower MIC valueswith S. aureus(6.3 mg/mL) andE. aerogenes and B. Subtilis (3.1 mg/mL).