Synthesis, characterization, biological activities, and luminescent properties of lanthanide complexes with N,N′-bis(2-hydroxy-1-naphthylidene)-1,6-hexadiimine

A series of lanthanide complexes with a Schiff base ligand, L (N,N′-bis(2-hydroxy-1-naphthylidene)-1,6-hexadiimine) are presented. The ligand and its complexes were synthesized and characterized based on elemental analyses, molar conductance, IR, 1H and 13C NMR, UV–Vis, and TGA studies. These analytical and spectral data reveal that the ligand L coordinates to the central Ln(III) ion by its two imine nitrogen atoms and two phenolic oxygen atoms and the general formula of the complex is [LnL(NO3)2·2H2O]NO3, Ln = [Ln = La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III) and Er(III)] Under the excitation at 396 nm, the luminescence emission properties for Sm, Tb, and Eu complexes are observed. These observations show that the ligand favors energy transfers to the emitting energy level of these lanthanide ions. Furthermore, the antimicrobial activities of all complexes were studied against a number of pathogenic bacteria. The antimicrobial activity results show that most of the synthesized Ln(III) complexes possessed good antibacterial activity and in most cases higher than that of the corresponding ligand L.