Crystal structures and fluorescence properties of lanthanide complexes prepared with 2,2′-biphenyldicarboxylic acid and 2,2′:6′,2″-terpyridine

Five lanthanide complexes of Ln2(dpdc)2(tpy)2(NO3)2(H2O)2 [Ln=La (1), Ce (2), Pr (3), Sm (4), Gd (5), H2dpdc=2,2’-biphenyldicarboxylic acid and tpy=2,2′:6′,2″-terpyridine] were prepared at room temperature and characterized by X-ray diffraction, FT-IR and thermo-gravimetric analysis. The results showed that complexes 1–5 were isostructural and consisted of dinuclear units [Ln2(dpdc)2(tpy)2(NO3)(H2O)2] bridged by two dpdc2− ligands. The dinuclear units with strong intramolecular hydrogen bonds were assembled into 2D supramolecular layers by the weak π…π staking interactions between pyridine rings of tpy. The TG analysis showed that the complexes 1–5 behaved higher thermal stability with no mass loss at < 320 °C. The lanthanide contraction effect and the solid state luminescence properties of complexes 1–5 were also investigated. The luminescence emission spectra of complexes 1–5 exhibited ligands emission bands and complex 3 and 4 had no typical emission in the visible region.