Five lanthanide complexes based on hydrogen bond interactions: fluorescence properties, thermal analysis, and DFT calculations

At room temperature, five novel complexes were synthesized with the following specific formulas: [Ln(4-FBA)₃(5,5′-DM-2,2′-bipy)(H₂O)]₂, (Ln = Sm(1), Tb(2), Eu(3),Gd(4)); [Ln(4-FBA)₃(5,5′-DM-2,2′-bipy)]₂·6(H₂O)·2(C₂H₆O)·2(5,5′-DM-2,2′-bipy), (Ln = Er(5); 4-FBA = 4-fluorobenzoate; 5,5′-DM-2,2′-bipy = 5,5′-dimethyl-2,2′-bipyridine). All of the complexes exhibit a consistent triclinic structure. The binuclear units of each complex can be connected by hydrogen bonding interactions. It is worth mentioning that, irrespective of the differences in their complex architectures, the central metal maintains a consistent coordination number. The measurement of the fluorescence spectra for complexes 1–3 was conducted, revealing the luminescent properties of the corresponding ions. The luminescence mechanism is confirmed by the rationalization of density functional theory (DFT). Finally, TG-DSC/FTIR/MS was used to study the detailed decomposition mode of the complexes.