Novel Lanthanide Complexes Synthesized from 3-Dimethylamino Benzoic Acid and 5,5′-Dimethyl-2,2′ Bipyridine Ligand: Crystal Structure, Thermodynamics, and Fluorescence Properties

Two isostructural lanthanide complexes were synthesized by solvent evaporation with 3-dimethylaminobenzoic acid and 5,5 '-dimethyl-2,2 '-bipyridine as ligands. The general formula of the structure is a [Ln(3-N,N-DMBA)3(5,5 '-DM-2,2 '-bipy)]2 center dot 2(3-N,N-DMHBA), Ln = (Gd(1), Tb(2)), 3-N,N-DMBA = 3-Dimethylamino benzoate, 5,5 '-DM-2,2 '-bipy = 5,5 '-dimethyl-2,2 ' bipyridine. Both complexes exhibited dimeric structures based on X-ray diffraction analysis. At the same time, infrared spectroscopy and Raman spectroscopy were used to measure the spectra of the complex. A thermogravimetric infrared spectroscopy experiment was performed to investigate the thermal stability and decomposition mechanism of the complexes. Measurements of the low-temperature heat capacity of the complexes were obtained within the temperature range of 1.9 to 300 K. The thermodynamic function was calculated by heat capacity fitting. In addition, the fluorescence spectra of complex 2 were studied and the fluorescence lifetime values were determined, and the energy transfer mechanism of complex 2 was elucidated.