Synthesis, thermal, photo-physical, and biological properties of mononuclear Yb³⁺, Nd³⁺, and Dy³⁺ complexes derived from Schiff base ligands

Abstract

Six new lanthanide complexes, [Ln(NO₃)₂(L₁H₂)](NO₃).xCHCl₃.yH₂O {Ln = Yb (1), x = 1, y = 2; Nd (3), x = 2, y = 3 and Dy (5), x = 2, y = 2} and [Ln(NO₃)₂(L₂H₂)](NO₃).xCHCl₃ {Ln = Yb (2), x = 1; Nd (4), x = 2 and Dy (6), x = 2}, were prepared by NNNOO-donor pentadentate Schiff base ligands N,N′-bis(3-methoxysalicylidene)−2,2′-diaminoethylamine (L₁H₂) and N,N′-bis(2-hydroxynaphthalidene)−2,2′-diaminoethylamine (L₂H₂). These synthesized complexes were characterized by elemental analysis, FT-IR, ¹H NMR, UV-vis spectroscopy, and mass spectrometry. The thermal characteristics of complexes were studied by TGA technique. The observation of the fluorescence emission properties of ligands L₁H₂ and L₂H₂ and its Ln(III) complexes in DMSO solution at excitation wavelength of 320 nm shows that the ligands favor energy transfers to the emitting energy level of Ln(III) complexes. The computational calculations using density functional theory of ligands and its Yb((III) complexes were performed to obtain optimized molecular geometry, the highest occupied molecular orbital, the lowest unoccupied molecular orbital and other parameters. The Schiff bases, metal salts, and its Ln(III) complexes were screened for their in vitro antibacterial studies against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Salmonella typhi bacterial strains. The results of the antibacterial investigation show that the lanthanide complexes possess more potent bactericide properties than ligands and metal salts.

Graphical Abstract

Keywords:

• Lanthanide complexes
• Schiff bases
• UV-vis
• DFT
• fluorescence studies
• antibacterial studies

Acknowledgements

The authors are grateful to the Department of Chemistry, University of Allahabad, Allahabad, for providing laboratory facilities. The author (Sikandar Paswan) would like to thank UGC, New Delhi for financial support and award of Senior research fellowship (SRF). The authors would like to thank Prof. GopalNath, Department of Microbiology, IMS, BHU for antibacterial testing, MRC - MNIT Jaipur for IR, mass, and fluorescence analysis, SAIF Chandigarh for NMR and IISER Pune for TGA analysis.

Disclosure statement

No potential conflict of interest was reported by the authors.