Design and synthesis of diverse Cd 2+ /Zn 2+ /Cu 2+ coordination polymers tuned by dicarboxylate and auxiliary 1,4-bis(pyridin-4-ylmethyl)piperazine ligands with luminescence and Hirshfeld surface analyses.

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 (H2 adc), glutaric acid (H2 glu), 5-hydroxyisophthalic acid (H2 hip) and fumaric acid (H2 fum), in conjunction with the auxiliary ligand [1,4-bis(pyridin-4-ylmethyl)piperazine (bpmp). The corresponding formulae are [Cd3 (adc)2 (bpmp)Cl2 (H2 O)2 ]n (1), {[Cd2 (glu)2 (bpmp)2 (H2 O)2 ]·8H2 O·2CH3 OH}n (2), [Zn(hip)(bpmp)(H2 O)]n (3) and [Cu(fum)(bpmp)(H2 O)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 {CdO2 N2 Cl2 } and {CuO5 Cl} 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 {CdO5 N2 } 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 {ZnO3 N} four-coordinate unit. Its stacking structure is formed by one-dimensional [Zn(hip)(bpmp)(H2 O)]n chains connected through hydrogen bonds. On the other hand, complex 4 features a Jahn-Teller distorted {CuO4 N2 } 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.