Three-Dimensional Extended Frameworks Constructed from Dinuclear Lanthanide(III) 1,4-Naphthalenedicarboxylate Units with Bis(2,2′-biimidazole) Templates: Syntheses, Structures, and Magnetic and Luminescent Properties

Eight unprecedented Ln-NDC coordination polymers with BBI as templates {[HBBI]­[Ln­(NDC)2(H2O)]·H2O [Ln = La (1), Pr (2)], [HBBI]2[Sm­(NDC)2(H2O)]2·1/2H2O (3), and [HBBI]­[Ln­(NDC)2(H2O)] [Ln = Eu (4), Gd (5), Tb (6), Dy (7), Er (8)] [Ln = lanthanide, H2NDC = 1,4-naphthalenedicarboxylic acid, BBI = bis­(2,2′-biimidazole)]} have been hydrothermally synthesized and structurally characterized by elemental analyses, IR spectra, and single-crystal X-ray diffraction. Complexes 1–8 crystallize in the monoclinic space group P21/c and display similar (8,8)-connected 3-D frameworks with different dinuclear Ln secondary building units due to the effect of Ln contraction and diverse coordination modes of NDC2– ligands. As the ionic radii of Ln ions decrease, the coordination numbers of Ln ions decrease from 10, to 9, to 8. The variable-temperature magnetic properties of 2–8 have been investigated. The strong fluorescent emissions of 4 demonstrate that ligand-to-EuIII energy transfer is efficient. In addition, thermogravimetric analyses and optical diffuse reflectance spectra of these compounds are also described.

以双(2,2′-联咪唑)（bis(2,2′-biimidazole)，缩写BBI）为模板剂，合成了8种前所未有的镧系元素（lanthanide，缩写Ln）-1,4-萘二甲酸配位聚合物，其通式分别为：{[HBBI]·[Ln(NDC)₂(H₂O)]·H₂O [Ln=La(1)、Pr(2)]、[HBBI]₂[Sm(NDC)₂(H₂O)]₂·1/2H₂O(3)以及[HBBI]·[Ln(NDC)₂(H₂O)] [Ln=Eu(4)、Gd(5)、Tb(6)、Dy(7)、Er(8)]}，其中1,4-萘二甲酸（1,4-naphthalenedicarboxylic acid，缩写H₂NDC）为有机配体。上述配合物均通过水热法合成，并借助元素分析、红外光谱（IR spectra）以及单晶X射线衍射（single-crystal X-ray diffraction）完成了结构表征。配合物1~8均结晶于单斜晶系P2₁/c空间群，展现出相似的(8,8)连接型三维骨架结构，但由于镧系收缩效应以及NDC²⁻配体多样的配位模式，其双核Ln次级结构单元存在差异。随着Ln离子半径逐渐减小，其配位数从10依次降至9、8。对配合物2~8的变温磁学性质进行了研究。配合物4展现出强荧光发射特性，表明配体到Eu³+的能量转移过程高效。此外，本文还对上述配合物的热重分析（thermogravimetric analyses）以及光学漫反射光谱（optical diffuse reflectance spectra）进行了表征与讨论。