Spectral, NLO and antimicrobial studies of Co(II), Ni(II) and Cu(II) complexes of Schiff base ligands of 2-amino-6-nitrobenzothiazole

Novel series of Co(II), Ni(II) and Cu(II) transition metal complexes were synthesized from the Schiff base ligands HL 1 – HL 4  derived from 2-amino-6-nitrobenzothiazole with various aromatic aldehydes, i.e ., 4-methylbenzaldehyde, 4-ethylbenzaldehyde, 2-hydroxybenzaldehyde and 4-hydroxybenzaldehyde, respectively. The ligands HL 1 – HL 4  and their metal (II) complexes were characterized by atomic absorption spectroscopy (AAS), magnetic susceptibility and molar conductance measurements, and UV–Vis, FT-IR and NMR spectroscopic techniques. The spectroscopic studies revealed that the complexes of HL 1 – HL 3  coordinated in an octahedral environment and L 4  in square planar/tetrahedral geometry. The ligands HL 1 – HL 4  and their metal(II) complexes were screened for their antimicrobial activities against Staphylococcus aureus , Escherichia coli , Pseudomonas aeruginosa and Candida albicans . The results suggest that the complexes of HL 4  possess greater inhibition activity towards C. albicans . The nonlinear optics (NLO) activities of ligands HL 1 – HL 4  were determined. The obtained results showed that ligands HL 1  and HL 2  have greater second harmonic generation (SHG) efficiency than HL 3 and HL 4 .