Structures and Photoluminescent Properties of the Lanthanide Coordination Complexes with Hydroxyquinoline Carboxylate Ligands

A series of luminescent lanthanide coordination complexes, [Eu2(hqc)6(H2O)4]·8H2O (1), [Ln2(hqc)6(H2O)2(DMF)2]·2H2O (Ln = Eu (2), Dy (3), Ho (4)), and [Ln2(hqc)6(H2O)4]·2H2O·2DMF (Ln = Ce (5), La (6), Pr (7); Hhqc =2-hydroxyquinoline-4-carboxylic acid), have been synthesized via evaporative crystallization and then characterized by single-crystal X-ray diffraction. Complexes 1−7 are nine-coordinated lanthanide(III) complexes with distorted tricapped trigonal prism geometry around each metal center. The dinuclear units in 1−7 form the two-dimensional square networks and further extend to three-dimensional supramolecular frameworks through the π−π stacking and strong hydrogen bonding interactions. The optical properties of complexes 1−7 in both the solid state and solution state were investigated in detail at room temperature and 10 K. The results show that the Eu3+ ions in 1 and 2 could be highly sensitized by the hqc− ligands and thus emit intense red luminescence with long lifetimes, while complexes 3 and 5−7 exhibit the characteristic blue luminescence. Furthermore, X-ray diffraction and thermogravimetric analysis of 1−7 are also studied, which demonstrate their high purities and good thermal stabilities.