A Cu(II) complex-driven supramolecular array: synthesis, crystal structure, Hirshfeld surface analysis and application in dyes adsorption

Using benzilic acid (BA) and 1-Methylimidazole (1-Me-Imi) ligands, a new Cu(II) complex is prepared, formulated as, [Cu(BA)2(1-Me-Imi)2(H2O)] (1). In the structure, the Cu(II) metal ion adopted a distorted square-pyramidal geometry, completed by two BA ligands, two 1-Me-Imi ligands, and one coordinated water molecule. Furthermore, the supramolecular structure is formed 1, and the coordinated axial water (with a Cu1–O4 distance of 2.681 Å) interacted with other coordinated water molecules in the lattice to generated a hydrogen-bonded chain. Under optimized conditions, the complex 1 delivered high adsorption efficiencies of 84.87% for methylene blue (MB) and 82.32% for methyl orange (MO). The Freundlich Isotherm model provided the best fit to the adsorption data, with R2 values of 0.994 for MB while the Langmuir isotherm model supplied the best fit to the adsorption data for MO with R2 values of 0.999 for MO. The corresponding BT (heat of adsorption) values were 10.58 J/mol and 9.85 J/mol for MB and MO, respectively, which shows the nature of the adsorption process is physisorption. The adsorption process is mainly controlled by electrostatic interactions, hydrogen bonding, and π–π interactions between complex 1 and the dye molecules, consistent with a physisorption mechanism. The positive entropy change suggests the involvement of interfacial rearrangement, including the release/reorganization of water molecules during dye adsorption. Hirshfeld surface analysis (HSA) was performed to determine various types of interactions.