A Molecular Basketwork: Self-Assembly of Coordination Polymers from Zn(II) and Biphenyl-3,4′-dicarboxylate Regulated by Different Flexible Bridging and Chelating N-Donor Ancillary Ligands

Four low-dimensional coordination polymers, [Zn2(bpdc)2(dib)2]n·nH2O (1), [Zn(bpdc)(phen)]n·2nH2O (2), [Zn(bpdc)(bpy)]n·2nH2O (3), and [Zn(bpdc)(H2O)]n (4), (H2bpdc = biphenyl-3,4′-dicarboxylic acid, dib = 1,4-di(1H-imidazol-2-yl)butane, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine), have been successfully prepared under hydrothermal conditions and characterized by IR, single crystal X-ray diffraction, thermogravimetric analysis (TGA), and luminescence analyses. Self-assembly behaviors of these polymers were entirely directed by N-donor ancillary coligands (bridging or chelating). Complex 1 displays an interesting novel two-dimensional (2D) basketwork, in which Zn(II) ions are knitted by both organic molecules, biphenyl-3,4′-dicarboxylic acid and 1,4-di(1H-imidazol-2-yl)butane, to form an infinite network. Polymers 2 and 3 are infinite zigzag helical chains, and both terminated ligands in 2 and 3 prevent self-assembly to higher dimensional polymers. In 4, a water molecule occupies one of four coordinated positions of Zn(II), and it shows an infinite alternating subloop chains consisting of 8- and 24-membered rings. New coordination modes of the rarely used 3,4-bpdc ligand are reported in 1−4. The results reveal that different secondary building units could tune the process of self-assembly to form low-dimensional structures, and the observed structural motifs can be well regulated by the different chelating or bridging N-donor ancillary ligands. Moreover, complexes 1−4 exhibit strong solid-state luminescence emissions at room temperature.

本研究通过水热法成功合成了四种低维配位聚合物，分别为[Zn₂(bpdc)₂(dib)₂]ₙ·nH₂O(1)、[Zn(bpdc)(phen)]ₙ·2nH₂O(2)、[Zn(bpdc)(bpy)]ₙ·2nH₂O(3)以及[Zn(bpdc)(H₂O)]ₙ(4)。其中，H₂bpdc为联苯-3,4'-二羧酸（biphenyl-3,4′-dicarboxylic acid），dib为1,4-二(1H-咪唑-2-基)丁烷（1,4-di(1H-imidazol-2-yl)butane），phen为1,10-邻菲啰啉（1,10-phenanthroline），bpy为2,2'-联吡啶（2,2′-bipyridine）。所有产物均通过红外光谱（IR）、单晶X射线衍射、热重分析（TGA）以及发光分析完成了表征。此类聚合物的自组装行为完全由氮给体辅助配体（桥联型或螯合型）调控。配合物1呈现出新颖有趣的二维篮状骨架，其中Zn(II)离子被联苯-3,4'-二羧酸与1,4-二(1H-咪唑-2-基)丁烷两种有机配体桥联，形成无限延伸的网络结构。聚合物2与3均为无限锯齿状螺旋链，二者的端基配体阻止了其进一步自组装为更高维度的聚合物。在配合物4中，一个水分子占据了Zn(II)离子的四个配位位点之一，其骨架为由8元环与24元环交替构成的无限亚环链。本研究报道了1~4中罕见使用的3,4-bpdc配体的新型配位模式。研究结果表明，不同的次级结构单元可调控自组装过程以形成低维结构，且所观测到的结构基元可通过不同的螯合型或桥联型氮给体辅助配体得到有效调控。此外，配合物1~4在室温下均表现出较强的固态发光性能。