Assembly of Chiral/Achiral Coordination Polymers Based on 2-(Pyridine-3-yl)-1H-4,5-imidazoledicarboxylic Acid: Chirality Transfer between Chiral Two-Dimensional Networks Containing Helical Chains

Three kinds of new coordination polymers, [Mn­(μ3-HPyIDC)­(H2O)]n (1a and 1b), {[Cd3(μ4-PyIDC)2(H2O)4]·H2O}n (2), and [Ca­(μ4-HPyIDC)­(H2O)]n (3a and 3b), were synthesized from the solvothermal reactions of 2-(pyridine-3-yl)-1H-4,5-imidazoledicarboxylic acid (H3PyIDC) with the corresponding metal salts. Crystal structure analysis showed that all coordination polymers were based on an analogical chiral two-dimensional (2D) secondary building unit (SBU) containing helical chains. The chirality of the 2D SBU was transferred to neighboring 2D SBUs via hydrogen bonds and coordination bonds in 1 and 3, respectively, resulting in two homochiral frameworks. When opposite chirality was transferred between neighboring 2D SBUs via Cd­(II) ions, an achiral framework was generated, resulting in 2D nets packed in alternating P and M chirality in compound 2. Furthermore, compounds 1, 2, and 3 feature 2D (82·10), 3D (62·82)­(62·82·102), and cds network topologies, respectively. Circular dichroism (CD) measurements also confirmed that the resulting crystals of 1 and 3 are racemic mixtures. Compounds 2 and 3 showed strong fluorescent emissions at room temperature.

三种新型配位聚合物，分别为[Mn(μ3-HPyIDC)(H2O)]n（记为1a与1b）、{[Cd3(μ4-PyIDC)2(H2O)4]·H2O}n（记为2）以及[Ca(μ4-HPyIDC)(H2O)]n（记为3a与3b），均由2-(吡啶-3-基)-1H-咪唑-4,5-二羧酸（H3PyIDC）与对应金属盐经溶剂热反应合成。晶体结构分析显示，所有配位聚合物均基于一类含螺旋链的类手性二维（2D）次级结构基元（secondary building unit, SBU）。化合物1与3中，二维次级结构基元的手性分别通过氢键与配位键传递至相邻的二维次级结构基元，最终得到两种同手性骨架。当相邻二维次级结构基元之间通过Cd(II)离子发生相反手性传递时，会生成非手性骨架，使得化合物2中的二维网络以P型与M型手性交替堆积。此外，化合物1、2和3分别具有2D (82·10)、3D (62·82)(62·82·102)以及cds网络拓扑结构。圆二色谱（CD）测试进一步证实，化合物1和3的所得晶体为外消旋混合物。化合物2与3在室温下表现出较强的荧光发射。