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
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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.
