Design and synthesis of diverse Cd2+/Zn2+/Cu2+ coordination polymers tuned by dicarboxylate and auxiliary 1,4-bis(pyridin-4-ylmethyl)piperazine ligands with luminescence and Hirshfeld surface analyses

Abstract

Four new coordination polymers, including 1D, 2D and 3D structures, were synthesized via a hydrothermal method using Cd2+/Zn2+/Cu2+ metal salts as nodes. These polymers were formed through self-assembly of four different dicarboxylic acid ligands, namely adamantane-1,3-dicarboxylic acid (H2adc), glutaric acid (H2glu), 5-hydroxyisophthalic acid (H2hip) and fumaric acid (H2fum), in conjunction with the auxiliary ligand [1,4-bis(pyridin-4-ylmethyl)piperazine (bpmp). The corresponding formulae are [Cd3(adc)2(bpmp)Cl2(H2O)2] n (1), {[Cd2(glu)2(bpmp)2(H2O)2]·8H2O·2CH3OH} n (2), [Zn(hip)(bpmp)(H2O)] n (3) and [Cu(fum)(bpmp)(H2O)2] n (4). Single-crystal X-ray diffraction studies revealed that the Cd2+ centers in complex 1 all adopt a six-coordinate mode but two distinct {CdO2N2Cl2} and {CuO5Cl} units. The 3D network of complex 1 can be simplified to a binodal (4.6)-connected underlying net with the point symbol (3·42·5·62)4(32·62·72·88·10). Each Cd2+ cation in complex 2 adopts a seven-coordinate {CdO5N2} center, forming an asymmetric pentagonal bipyramidal coordination. Its stacking structure is formed by the interaction of hydrogen bonds between 2D supramolecular layers, with the adjacent layers exhibiting mirror symmetry. Each Zn2+ ion in complex 3 displays a {ZnO3N} four-coordinate unit. Its stacking structure is formed by one-dimensional [Zn(hip)(bpmp)(H2O)] n chains connected through hydrogen bonds. On the other hand, complex 4 features a Jahn–Teller distorted {CuO4N2} octahedral coordination. Subsequently, the thermal stability of these complexes was investigated. The solid-state fluorescence spectroscopy was employed to analyze complexes 1, 2 and 3. Additionally, a Hirshfeld surface analysis was performed on complex 3.