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

Six new lanthanide complexes, [Ln(NO3)(2)(L1H2)](NO3).xCHCl(3).yH(2)O {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).xCHCl(3) {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, H-1 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.