Syntheses and Properties of One–Three-Dimensional Coordination Polymers Constructed by Metallohelicates of Purin-Containing Carboxylate

An acetate-functionalized purine-containing ligand, 2-(6-oxo-6,9-dihydro-1H-purin-1-yl) acetic acid (H2L), and its six new one–three-dimensional (1–3D) coordination polymers, [La­(HL)2(NO3)­(H2O)2]n (1), [Ce­(HL)2(NO3)­(H2O)2]n (2), [Pb­(HL)2(H2O)2]n (3), [Cd­(HL)2(H2O)2]n (4), [Cd­(L)]n (5), and [Zn­(L)]n (6), were synthesized and characterized. Single-crystal X-ray diffraction analyses reveal that the architectures of complexes 1–6 are built from the metal–organic helixes of ligands H2L. The overall structures range from the double helical chains of 1 and 2, and the 2D helical networks of 3 and 4, to the 3D coordination polymers of 5 and 6, containing 2D homochiral layers based on 1D metal–organic helixes. In those meso compounds, ligands H2L display differently anionic states, bridge modes, and especially unsymmetrical configurations with the sharp distortion between the acetate and purin in favor of constructing helical assemblies as expected. The plentiful hydrogen-bonding sites and π···π interactions originating from the bioactive purin group of ligand H2L greatly contribute to the formation of helical structures and the structural dimension, showing an intriguing ability in the supramolecular assembly. At room temperature, complexes 1–6 exhibit solid-state photoluminescences, with their emission wavelengths and intensities varying according to the central metal ions and the coordination patterns of ligand H2L. Additionally, the thermostabilities of these new complexes have been discussed in detail. In particular, 3D polymers 5 and 6 have extra high thermostabilities and stronger blue emissions, indicating potential applications in photoluminescent materials.