Syntheses, crystal structures, antioxidant SOD-like properties and in-vitro antimicrobial studies of Cu(II) and Ni (II) complexes with 2-((E)-(4-bromo-2-chlorophenylimino) methyl)-6-bromo-4-nitrophenol and (E)-1-(3, 5-dichloro-2-hydroxybenzylidene)-4, 4-dimethylthiosemicarbazide

Abstract

Three new salen-type copper (II) and nickel (II) complexes viz. [Cu(L)2] (1); [Ni(L)2] (2); [Ni(L1) (DMF)] (3), where HL = 2-((E)-(4-bromo-2-chlorophenylimino) methyl)-6-bromo-4-nitrophenol and HL1= (E)-1-(3,5-dichloro-2-hydroxybenzylidene)-4,4-dimethylthiosemicarbazide; DMF = N, N-dimethylformamide, have been successfully achieved and structurally characterized by single crystal X-ray analysis. The salen-type ligands (HL and HL1) are able to provide the most plausible geometry for 1:2 complexes which appeared to be a square planar (four coordinated) geometry around the M (II) ions. The FT-IR spectra, UV–Vis spectra and magnetic susceptibility measurements agree with the observed crystal structures. X-band Electron paramagnetic resonance (EPR) spectra indicate a dx2–y2ground state (g||>g⊥> 2.0023 and A||>A⊥) for (1) at RT and LNT. The salen-type ligands were behaves as monobasic bidentate-N, O ligand (HL) or tridentate ligand (HL1) possessing N, O and S donor atoms. Electrochemical properties for complexes (1)-(3) yielded an irreversible couple that can be assigned to an M (II)/M (I) redox process. These complexes exhibit effective antioxidant activity towards the dismutation of superoxide anions. The complex (1) exhibits more active scavenging effects against O2− than HL and other complexes (2) and (3) under the same conditions. These complexes were also tested for their in vitro microbiological screening activities against two bacteria (Streptococcus aureus, Escherichia coli) and two fungi (Aspergillus sp., Penicillium sp.) comparing with the salen-type ligands and the control. The biological property of salen-type complexes at the minimum inhibitory concentration (MIC) indicates that most of the metal chelates exhibits slightly higher antimicrobial activity than the free Schiff base ligands.