A two-dimensional mixed ligands based coordination polymer of cadmium: Synthesis, single crystal structure and luminescence quenching based sensing behaviors towards Fe3+, Cr3+, Al3+ ions and TNP in aqueous phase

A new Cd (II)-based compound [Cd(BTCH)(L)] (BTCH = di-anionic 1,3,5-benzene tricarboxylic acid and L = 2,4,5-tri-4-pyridyl-1H-imidazole), 1, has been synthesized by hydrothermal method. The structure determined by single-crystal X-ray diffraction revealed two dimensional extended assemblies based on connectivity of Cd²⁺ ions with two ligands. The presence of one free carboxylic acid groups of each BTCH ligand and one non-bonded pyridine ring of each L ligand makes the two-dimensional layer structure stabilized through the hydrogen bond interactions. The compound has been characterized by powder X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). Aqueous dispersion of compound 1 showed emission at 400 nm upon excitation at 300 nm. The compound 1 also exhibited photoluminescence-based sensing behaviors towards Fe³⁺, Al³⁺ and Cr³⁺ ions in aqueous medium based on luminescence quenching effect. However, photoluminescence studies in presence of other common metal ions showed either negligible quenching effect or moderate to low turn on effect for Ni²⁺, K⁺, Zn²⁺, Cd²⁺ Cu²⁺, Ca²⁺, Mn²⁺, Na⁺, Co²⁺, Fe²⁺, Pb²⁺, Mg²⁺ in aqueous. The limit of detection for Fe³⁺, Al³⁺, Cr³⁺ ions are 0.568 μM, 1.721 μM and 0.840 μM respectively. Compound 1 also showed significant quenching effect in the presence of 2,4,6-trinitrophenol (TNP) with detection limit of 0.302 μM.