Syntheses, Structures, and Luminescence Properties of a Series of Ln^III−Ba^II Heterometal-Organic Frameworks

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.本研究通过水热合成法成功制备了10种新型三价镧系-二价钡异金属有机框架（heterometal-organic frameworks），具体包括：{[Ln₂Ba₂(PDA)₅(H₂O)₁₂]·mH₂O}ₙ（其中Ln为Pr（化合物1，m=9）、Sm（化合物2，m=6）；PDA指吡啶-2,6-二羧酸根（pyridine-2,6-dicarboxylic anion））、{[LnBa₁.₅(PDA)₃(H₂O)₈]·2H₂O}ₙ（其中Ln为Eu（化合物3）、Gd（化合物4）、Tb（化合物5））、{[Ln₄Ba₆(PDA)₁₂(H₂O)ₓ]·mH₂O}ₙ（其中Ln为Dy（化合物6，x=27.5，m=12）、Lu（化合物7，x=27，m=11.5）），以及三种衍生配位聚合物：{[Eu₄Ba₄(PDA)₁₀(H₂O)₂₃]·16H₂O}ₙ（3a）、{[TbBa₃(PDA)₄(NO₃)(H₂O)₆]·2H₂O}ₙ（5a）和{[DyBa₁.₅(PDA)₃(H₂O)₇]·2H₂O}ₙ（6a）。这些化合物的结构涵盖一维链、二维层状至三维骨架构型。化合物1和2呈现一维带状结构。化合物3~5由一维钡链与[Ln(PDA)₃]结构单元构筑得到二维层状骨架。化合物6和7的二维结构更为复杂，与3~5的二维结构存在显著差异。在合成化合物3、5和6的过程中，通过改变氢氧化钡（Ba(OH)₂）的投料量，我们得到了另外三种新型配位聚合物3a、5a和6a。化合物3a为一维链状结构，与1、2的一维带状结构有所区别。化合物5a呈现三维骨架结构，由二维钡层与[Tb(PDA)₃]连接单元构筑而成。尽管合成条件存在差异，但化合物6a与3~5具有相同的骨架结构。化合物1~7以及3a~6a之间的结构差异可归因于镧系收缩效应；而3与3a、5与5a以及6与6a之间的结构分歧，则源于合成过程中氢氧化钡投料量的不同。本研究在室温固态条件下对化合物2、3、5、6、3a、5a及6a开展了发光性能测试，结果显示这些化合物呈现出强的镧系离子特征发射峰，表明PDA配体可作为“天线”分子有效敏化镧系离子的发光。