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

A series of luminescent lanthanide coordination complexes, [Eu-2(hqc)(6)(H2O)(4)]center dot 8H(2)O (1), [Ln(2)(hqc)(6)(H2O)(2)-(DMF)(2)]center dot 2H(2)O (Ln = Eu (2), Dy (3), Ho (4)), and [Ln(2)(hqc)(6)(H2O)(4)]center dot 2H(2)O.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 pi-pi 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.