Luminescent Zn(II) and Cd(II) coordination polymers based on naphthalene tetracarboxylic acid and 4,4'-bipyridine for sensing of nitrobenzene, Fe³⁺ and Cr₂O₇²⁻ ions

Two luminescent Zn(II) and Cd(II) metal-organic frameworks (MOFs) containing 1,4,5,8-naphthalene tetracarboxylic acid (H4L’) and 4,4'-bipyridine (4bpy), [ZnL(4bpy)0.5(DMA)]n (1) and [CdL(4bpy)0.5]n (2) (L = 1,8-monoanhydride-1,4,5,8-naphthalenetetracarboxylate, DMA = N,N-dimethyl acetamide), were synthesized and characterized through X-ray diffraction, IR, and UV-Vis spectroscopy. 1 shows a 1D linear chain structure, while 2 shows a 2D baluster structure. Both show multiple H bonding and π-stacking interactions. Both compounds show ligand-based luminescence in the range 400-500 nm with contributions from both ligands. The luminescence is strongly dependent on the presence of potentially coordinating molecules. Luminescence quenching experiments show good sensitivities in detecting nitrobenzene (NB), Fe3+ and Cr2O72−.