Crystal structure, luminescence properties and thermochemistry of a new series of dual-ligand lanthanide complexes

Six lanthanide complexes, featuring 2,2′:6′,2″-terpyridine as the neutral ligand and benzoic acid in its deprotonated form (BA) as the acidic ligand, were synthesized via both ultrasonic dissolution and conventional solution methodologies. These complexes denoted as [Ln(BA)₃·(H₂O)·(terpy)]₂·2HBA, (Ln = Eu(1),Gd(2),La(3),Pr(4),Nd(5),Sm(6), terpy = (2,2′:6′,2″-terpyridine) were meticulously characterized to elucidate their structural and properties. Elemental analysis, X-ray single crystal diffraction, infrared and Raman spectroscopy studies, and X-ray diffraction (XRD) techniques were used to probe the properties of these complexes. The X-ray single crystal diffraction data revealed that complexes 1–6 exhibit an isomorphic binuclear molecular structure, with the central lanthanide ions occupying identical coordination environments and boasting the same coordination number across the series. To gain insights into their thermal stability, thermogravimetric analysis (TGA) was performed on all six complexes. The activation energy of the Sm (6) complexes during the second-step decomposition was calculated by using the nonlinear isoconversional integration method (NL-INT) and the (M.J. Starink) modified method. Furthermore, the luminescent properties of the Eu(1) and Sm(6) complexes were investigated through fluorescence spectroscopy, offering valuable information on their optical behavior.