Co(II), Ni(II), Cu(II) and Zn(II) complexes of 1,8-naphthalimide-based ligand: syntheses, characterizations and evaluation of antibacterial activities

Abstract

Mononuclear later first-row transition metal complexes, [M(L)₂] (1–4), where M = Co(II) (1), Ni(II) (2), Cu(II) (3), and Zn(II) (4) incorporating 1,8-naphthalimide based ligand were designed. The complex preparation was achieved by reacting metal nitrates with ligand (L) in 1:2 stoichiometry. The ligand and complexes were characterized with analytical and photophysical techniques. Single crystal X-ray diffraction determines that 3 is square planar. The complexes are highly fluorescent compared to the free ligand. The synthesized ligand (L) and complexes (1–4) were screened for their antibacterial activities against gram-positive [Streptococcus mutans (SM), Staphylococcus aureus (SA)] and gram-negative [Escherichia coli (EC), Klebsiella pneumoniae (KL)] bacterial strains. Ni(II) and Cu(II) complexes exhibited good activity against K. pneumonia and S. aureus compared to the free ligand. Particularly effective against gram-negative bacteria (Klebsiella pneumoniae), Ni(II) complex (2) has a MIC value of 6.25 µM and exhibits similar activity to standard ciprofloxacin. Cu(II) complex (3) is two times more effective than the common antibiotic ciprofloxacin with a MIC value of 3.125 µM against gram-positive bacteria (S. aureus).

KEYWORDS:

• Mononuclear
• square planar
• 1,8-naphthalimide
• antibacterial activity

Disclosure statement

No potential conflict of interest was reported by the authors.

Acknowledgements

The authors acknowledge the Directorate of Minorities Government of Karnataka (DOMWDD/Ph.D/M.Phil/FELLOWSHIP/CR-01/2019-20) and DST PURSE Phase II program (Ref. No. KU/PMEB/HJK/2017-18/128/818) for financial support. The authors thank USIC Karnatak University Dharwad, India for providing spectral data. The authors thank SAIF, Dharwad for providing NMR spectral data. The authors are also grateful to the Department of Studies in Physics, University of Mysore, for providing spectral and X-ray diffraction data of the synthesized compound and JAIN (Deemed-to-be University) for sanctioning the funds under the minor project JU/MRP/SET/7/2022.