Design and synthesis of diverse Cd/Zn/Cu 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 Cd/Zn/Cu metal salts as nodes. These polymers were formed through self-assembly of four different dicarboxylic acid ligands, namely adamantane-1,3-dicarboxylic acid (Hadc), glutaric acid (Hglu), 5-hydroxyisophthalic acid (Hhip) and fumaric acid (Hfum), in conjunction with the auxiliary ligand [1,4-bis(pyridin-4-ylmethyl)piperazine (bpmp). The corresponding formulae are [Cd(adc)(bpmp)Cl(HO)] (1), {[Cd(glu)(bpmp)(HO)]·8HO·2CHOH} (2), [Zn(hip)(bpmp)(HO)] (3) and [Cu(fum)(bpmp)(HO)] (4). Single-crystal X-ray diffraction studies revealed that the Cd centers in complex 1 all adopt a six-coordinate mode but two distinct {CdONCl} and {CuOCl} units. The 3D network of complex 1 can be simplified to a binodal (4.6)-connected underlying net with the point symbol (3·4·5·6)(3·6·7·8·10). Each Cd cation in complex 2 adopts a seven-coordinate {CdON} 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 Zn ion in complex 3 displays a {ZnON} four-coordinate unit. Its stacking structure is formed by one-dimensional [Zn(hip)(bpmp)(HO)] chains connected through hydrogen bonds. On the other hand, complex 4 features a Jahn-Teller distorted {CuON} 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.