Syntheses, Structures, and Luminescence Properties of a Series of LnIII−BaII Heterometal-Organic Frameworks

Abstract

Ten novel LnIII−BaII heterometal-organic frameworks, {[Ln2Ba2(PDA)5(H2O)12]·mH2O}n (Ln = Pr (1, m = 9); Sm (2, m = 6); PDA = pyridine-2,6-dicarboxylic anion), {[LnBa1.5(PDA)3(H2O)8]·2H2O}n (Ln = Eu (3); Gd (4); Tb (5)), {[Ln4Ba6(PDA)12(H2O)x]·mH2O}n (Ln = Dy (6, x = 27.5, m = 12); Lu (7, x = 27, m = 11.5)), {[Eu4Ba4(PDA)10(H2O)23]·16H2O}n (3a), {[TbBa3(PDA)4(NO3)(H2O)6]·2H2O}n (5a), and {[DyBa1.5(PDA)3(H2O)7]·2H2O}n (6a), have been successfully synthesized under hydrothermal conditions, and the various structures are constructed from 1D chain, 2D layer, to 3D framework. Compounds 1 and 2 exhibit 1D ribbonlike structures. Compounds 3−5 display 2D layers constructed by 1D BaII chains and [Ln(PDA)3] units. Compounds 6 and 7 exhibit complicated 2D structures different from those of 3−5. When the amount of Ba(OH)2 changes during the syntheses of 3, 5, and 6, three novel coordination polymers 3a, 5a, and 6a were obtained. Compound 3a consists of a 1D chain different from those in 1 and 2. Compound 5a displays a 3D framework, which was constructed through the 2D Ba layers and [Tb(PDA)3] linkers. Compound 6a is isostructural to those of 3−5, although synthetic conditions are different from each other. The significant differences in structure from 1 to 7, and from 3a to 6a, may result from the lanthanide contraction effect, whereas the structural divergences between 3 and 3a, 5 and 5a, and 6 and 6a originate from different amounts of Ba(OH)2 in the synthetic process. The luminescence studies of 2, 3, 5, 6, 3a, 5a, and 6a were applied in the solid state at room temperature, showing intense characteristic emission bands of lanthanide ions, and the results reveal that PDA ligand as an “antenna” may effectively sensitize the luminescence of lanthanide ions.