Crystal structures and luminescence properties of lanthanide complexes with 4-bromobenzoate and nitrogen heterocyclic ligands

Five crystals of lanthanide complexes with 4-bromobenzoate (p-BrBA), 2,4,6-tri(2-pyridyl)-1,3,5-trianzine (TPTZ) and 1,10-phenanthroline (Phen) ligands were synthesized. The structures of the complexes [Sm2(TPTZ-TPTZ)(p-BrBA)4] (1), [Eu2(TPTZ)2(p-BrBA)6] (2), [Tb(TPTZ)(p-BrBA)3(H2O)] (3), [Tb2(Phen)2(p-BrBA)2Ac4] (4) and [Dy2(Phen)2(p-BrBA)6] (5) were determined by single-crystal X-ray diffraction. The crystals 1, 5 belong to monoclinic crystal system, and the other three crystals belong to triclinic crystal system. The dinuclear compound [Sm2(TPTZ-TPTZ)(p-BrBA)4] possesses a coupled [TPTZ-TPTZ]2- ligand that coordinates with two Sm3+ ions in both tridentate and bidentate coordination modes. To investigate the luminescence properties of the complexes, six complexes with similar composition in the powder form were also synthesized, whose formulas are [Eu(TPTZ)(p-BrBA)3(H2O)2], [Tb(TPTZ)(p-BrBA)3(H2O)], [Eu2(Phen)(p-BrBA)3Ac3], [Tb(Phen)(p-BrBA)3], [Sm(TPTZ)(p-BrBA)3(H2O)] and [Dy(Phen)(p-BrBA)3]. The luminescence intensity, luminescence lifetime and quantum efficiency of Eu and Tb complexes with Phen ligand are remarkably superior to the corresponding TPTZ complexes. This difference may mainly result from the stronger structural rigidity of the Phen ligand, which reduces the non-radiative transition of the complexes.