Synthesis, Structure, Thermochemical Properties, and Luminescent Performance of Dual-Ligand Rare Earth Complexes With Organic Carboxylic Acids and Nitrogen-Containing Pyridine Ligands

Abstract

Using aromatic carboxylic acid (2-chloro-6-fluorobenzoic acid) as the primary ligand and a nitrogen-containing pyridine compound (4,4′-dimethyl-2,2′-bipyridyl) as the auxiliary ligand, three dual-ligand lanthanide complexes were successfully synthesized. X-ray single-crystal diffraction measurements revealed that these three complexes belong to the Pbca space group of the orthorhombic crystal system and share identical structural characteristics, with the central ions located in a consistent coordination environment and a coordination number of 9. Their general molecular formula can be uniformly expressed as [Ln(2-Cl-6-FBA)₂(4,4′-DM-2,2′-bipy)(NO₃)]₂, where Ln represents different rare earth elements, specifically Sm(1), Eu(2), and Pr(3); 2-Cl-6-FBA = 2-chloro-6-fluorobenzoate; and 4,4′-DM-2,2′-bipy = 4,4′-dimethyl-2,2′-bipyridine. To further investigate the properties of these complexes, various characterization techniques such as elemental analysis, infrared spectroscopy, and Raman spectroscopy were employed. The thermal stability and pyrolysis products of the three complexes were thoroughly studied using TG-DTG-DSC/FTIR/MS combined technology. Additionally, the energy transfer mechanism between the ligands and lanthanide ions was explained based on density functional theory (DFT), and the luminescent properties of Complexes 1 and 2 were investigated.