Probing the variations of synthesis, antimicrobial activity, and optical properties of new lanthanide and transition metal complexes of salicylaldehyde-dipropylenetriamine ligand

Due to their notable antimicrobial activity and optical properties, Schiff base ligands, along with their lanthanide and transition metal complexes, have seen extensive use in various applications. However, despite their potential, a comprehensive investigation into lanthanide and transition metal complexes using the same Schiff base ligand has not been reported to date. In this study, coordination compounds of lanthanide and transition metal ions were synthesized from the Schiff base ligand salicylaldehyde-dipropylenetriamine. These complexes were characterized by elemental analysis, ¹H and ¹³C NMR, mass spectroscopy, Fourier-transform infrared spectroscopy ultraviolet–visible spectroscopy (UV–Vis), fluorescence spectroscopy, molar conductivity measurements, and thermogravimetric studies. Furthermore, the molecular structure of the Co (II) complex was determined by means of X-ray crystallography. Thermogravimetric studies illustrated endothermic and non-spontaneous degradation pathways of the complexes. UV–Vis spectra showed a new absorption band attributed to the ligand-to-metal charge transfer peak supporting the complexation between the ligand and metals. The lanthanide complexes exhibited distinctive luminescence emissions in the Sm (III), Tb (III), and Eu (III) complexes. This observation suggests that the ligand possesses the capability to absorb and efficiently transfer energy to the metal center of these lanthanide ions, thereby resulting in their characteristic luminescent properties. Additionally, antimicrobial investigations revealed that transition metal complexes generally exhibited antimicrobial activity against both gram-positive and gram-negative bacterial strains compared to lanthanide metal complexes, in most cases. However, it is noteworthy that the Dy (III) complex displayed the lowest minimum inhibitory concentration and minimum biocidal concentration values of 16 μg/ml against Staphylococcus epidermidis, indicating its potential as a candidate for the treatment of this pathogenic bacterium. The main purpose of this article is to investigate the variations in the synthesis and characterization of lanthanide and transition metal complexes utilizing the same Schiff base ligand suitable for applications in the pharmaceutical industry and optical material sciences.