Crystal structure, thermodynamic behavior, and luminescence properties of a new series of lanthanide halogenated aromatic carboxylic acid complexes

Abstract

Five lanthanide complexes with polydentate coordination were successfully synthesized by volatilization of 2,4-difluorobenzoate and o-phenanthroline ligands. The structure general formula is [Ln(2,4-DFBA) 3 (phen)] 2 , (Ln = La( 1 ), Gd( 2 ), Tb( 3 ), Dy( 4 ), Ho( 5 ); 2,4-DFBA = 2,4-difluorobenzoate, phen = o-phenanthroline). The crystal structures of five complexes were determined, and supramolecular structures were probed. Characterization was performed by elemental analysis, IR, Raman spectroscopy and XRD, followed by an examination of the fluorescence and heat capacity properties. The molar heat capacities of complexes 4 and 5 were determined in detail by the DSC apparatus, and the thermodynamic functions were calculated. Finally, the fluorescence properties of complexes 3 and 4 were investigated. Using DFT, the HOMO, LUMO energy levels of the ligands and their single and triplet state energy levels were calculated at the level of the valence layer cleavage 6-311G(d,p) basis group, and the fluorescence enhancement mechanism was explained from the energy transfer perspective.