New europium coordination polymers with efficient energy transfer from conjugated tetracarboxylate ligands to Eu3+ ion: syntheses, structures, luminescence and magnetic properties
作者:Li-Feng Wang、Ling-Chen Kang、Wen-Wei Zhang、Fang-Ming Wang、Xiao-Ming Ren、Qing-Jin Meng
DOI:10.1039/c1dt10693g
日期:——
Two novel lanthanide coordination polymers, [Eu2(EBTC)(DMF)5(NO3)2]·DMF (1) and [Eu2(BBTC)1.5(CH3OH)2(H2O)2]·7DMF·HNO3 (2) (EBTC4− = 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylate; BBTC4− = 1,1′-butadiynebenzene-3,3′,5,5′-tetracarboxylate), were successfully synthesized from conjugated ligands of EBTC4− and BBTC4−. Although the two tetracarboxylate ligands have similar structures, their different rigidity/flexibility results in quite different networks upon complexation. Complex 1 has a two-dimensional (2-D) layered structure with two crystallographically independent Eu3+ ions, one in a distorted monocapped square-antiprism and the other in a distorted square-antiprism coordination geometry. Complex 2 exhibits a three-dimensional (3-D) porous framework, with one type of Eu3+ in a distorted square-antiprism and the other in a trigondodecahedron environment. Both 1 and 2 emit the intensely red characteristic luminescence of Eu3+ ion at room temperature, with a long lifetime of up to 1.3 and 0.7 ms, respectively, during which the ligand emission of EBTC4−/BBTC4− was quenched by the Eu3+ ion, indicating the existence of efficient energy transfer between the conjugated ligand of EBTC4−/BBTC4− and the Eu3+ ion. Thus, both EBTC4− and BBTC4− are ideal ligands with an “antenna” effect for the Eu3+ ion. The two complexes show the single-ion magnetic behaviors of Eu3+ with strong spin–orbit coupling interactions even if there are shorter distances (5.714 Å for 1versus 4.275 and 5.360 Å for 2) between the neighboring Eu3+ ions connected by oxygen atoms of the tetracarboxylates.
两种新型镧系元素配位聚合物,[Eu2(EBTC)(DMF)5(NO3)2]-DMF (1)和[Eu2(BBTC)1.5(CH3OH)2(H2O)2]-7DMF-HNO3(2)(EBTC4- = 1,1′-乙基苯-3,3′,5,5′-四甲酸酯;成功合成了 EBTC4- 和 BBTC4- 的共轭配体。尽管这两种四羧酸配体具有相似的结构,但由于它们的刚性/柔性不同,在络合时会形成截然不同的网络。络合物 1 具有二维(2-D)层状结构,其中有两个在晶体学上独立的 Eu3+ 离子,一个呈扭曲的单帽方倒棱配位几何形状,另一个呈扭曲的方倒棱配位几何形状。配合物 2 显示出三维(3-D)多孔框架,其中一种 Eu3+ 位于扭曲的方倒棱中,另一种位于三十二面体环境中。1 和 2 在室温下都能发出 Eu3+ 离子的强烈红色特征发光,寿命分别长达 1.3 毫秒和 0.7 毫秒,在此期间,EBTC4-/BBTC4- 的配体发光被 Eu3+ 离子淬灭,这表明 EBTC4-/BBTC4- 的共轭配体与 Eu3+ 离子之间存在有效的能量转移。因此,EBTC4- 和 BBTC4- 都是理想的配体,对 Eu3+ 离子具有 "天线 "效应。即使四羧酸氧原子连接的相邻 Eu3+ 离子之间的距离较短(1 为 5.714 Å,2 为 4.275 Å 和 5.360 Å),这两种配合物也能显示出 Eu3+ 的单离子磁性行为,并具有很强的自旋轨道耦合相互作用。