Thermal and spectral studies of transition metal complexes of 2-bromo-3-hydroxynaphthalene-1,4-dione: Evaluation of antibacterial activity against six bacterial strains

Abstract

Synthesis, thermal, spectral, electrochemical, and magnetic properties of transition metal complexes of 2-bromo-3-hydroxynaphthalene-1,4-dione(abbreviated as L) are discussed. The complexes viz, [Zn(L)2(H2O)2]; ZnL, [Cu(L)2(H2O)2]; CuL, [Ni(L)2(H2O)2]; NiL, [Co(L)2(H2O)2]; CoL, are resulted from the reactions of L with respective metal chlorides in methanol. The carbonyl frequency (1633 cm-1) of the ligand remains the same in ZnL, whereas it is observed at a higher wavenumber (17 cm-1) in CuL and lower wavenumber (3 cm-1) in NiL and CoL. The thermal decomposition of the complexes was studied by thermogravimetry. Powder X-ray diffraction studies further analyzed the respective metal oxide formed in TG studies. Redox potentials of all complexes are determined by cyclic voltammetry studies. It is difficult to reduce or oxidize the ligand after complexation. The frozen solution (DMSO) spectrum (133 K) of CuL shows four 63Cu hyperfine lines in the gllregion with All = -155 G in CuL. The ligand, as well as all-metal complexes, showed considerable antibacterial activity against six strains viz. Staphylococcus aureus NCIM (National Collection of Industrial Microorganisms) 2079, Bacillus subtilis NCIM 2423, Escherichia coli NCIM 2065, Proteus vulgaris NCIM 2027, Pseudomonas aeruginosa MTCC (Microbial Type Culture Collection and Gene Bank) 2297, P. putida MTCC 2463.