Syntheses, characterization, biological activities and photophysical properties of lanthanides complexes with a tetradentate Schiff base ligand

A tetradentate Schiff base ligand L (N,N′-bis(1-naphthaldimine)-o-phenylenediamine) was prepared from the condensation of 2-hydroxy-1-naphthaldehyde with o-phenylenediamine in a molar ratio of 2:1. New eight lanthanide metal complexes [LnL(NO3)2(H2O)x](NO3) {Ln(III) = Nd, Dy, Sm, Pr, Gd, Tb, La and Er, x = 0 for Nd, Sm, 1 for La, Gd, Pr, Nd, Dy, and 2 for Tb} were prepared. The characterization and nature of bonding of these complexes were elucidated by elemental analysis, spectral analysis (1H NMR, FT-IR, UV–vis), molar conductivity measurements, luminescence spectra and thermogravimetric studies. Analytical and spectral data revealed that the ligand L coordinates to the central Ln(III) ions by its two imine nitrogen atoms and two phenolic oxygen atoms with 1:1 stoichiometry. Under the excitation with 329 nm at room temperature, Tb and Dy complexes exhibited characteristic luminescence of the central metal ions attributed to efficient energy transfer from the ligand to the metal center. Most of Ln(III) complexes found to exhibit antibacterial activities against a number of pathogenic bacteria. We found that the antioxident activity of Ln(III) complexes on DPPH is concentration dependent and higher than that of the free ligand L.

Eight new Ln(III) complexes [LnL(NO3)2(H2O)y](NO3) (Ln(III) = Nd, Dy, Sm, Pr, Gd, Tb, La and Er, y = 0 for Nd, Sm, 1 for La, Gd, Pr, Nd, Dy, and 2 for Tb, L = N,N′-bis(1-naphthaldimine)-o-phenylenediamine) are described and discussed. Luminescent spectra of Tb and Dy complexes exhibit characteristic metal-centered fluorescence.Figure optionsDownload as PowerPoint slideHighlights
• A Schiff base ligand L {N,N′-bis(1-naphthaldimine)-o-phenylenediamine} was synthesized.
• Eight new [LnL(NO3)2(H2O)y]NO3 (Ln(III): Nd, La, Eu, Sm, Pr, Gd, Dy, Pr) complexes were synthesized.
• Tb and Dy complexes exhibited characteristic luminescence of the central Ln(III) ions.
• Most of Ln(III) complexes showed good antibacterial activity against different types of bacteria.
• The antioxidant activity of Ln(III) complexes on DPPH is significantly more than the free L.