Lanthanide Complexes With 4‐Acetylbenzoic Acid and 1,10‐Phenanthroline: Synthesis, Structural Characterization, Thermal Decomposition, and Fluorescence Properties

Four novel lanthanide complexes, [Ln 2 (4‐ABA) 6 (phen) 2 (H 2 O) 4 ]·2H 2 O (Ln = La(1), Ce(2), Nd(3), and Tb(4)), were successfully synthesized. In these complexes, 4‐acetylbenzoate (4‐ABA) acts as the primary ligand, while 1,10‐phenanthroline (phen) serves as a neutral auxiliary ligand. Slow evaporation at room temperature yielded single crystals of the compound. Single‐crystal X‐ray diffraction analysis revealed that all four complexes are isomorphous. The physicochemical composition of the complexes was systematically investigated using elemental analysis (EA), Raman spectroscopy, and infrared spectroscopy. Powder X‐ray diffraction (PXRD) confirmed the consistency between powder patterns and the single‐crystal structures. A multi‐method approach, incorporating TG‐DTG‐DSC and simultaneous FTIR‐MS, was applied to study the thermal decomposition process and elucidate the underlying mechanism of the powdered complexes through evolved gas analysis. At the same time, the luminescence properties of Tb complexes were studied, and the ligands exhibited significant antenna effects, effectively sensitizing the luminescence of lanthanide ions. DFT calculations reveal that the triplet energy level of the ligand aligns with the excited state ( 5 D 4 ) of Tb 3+ , ensuring the driving force for ligand‐to‐metal energy transfer in the “antenna effect.”