A four-coordinate cadmium(II) polymer for efficient adsorption of Congo red, kinetic, isotherm, fluorescence and antibacterial activity

A 3-D cadmium-based coordination polymer, [CdCl₂L]_n (1) (where L = 1,1-(1,6-hexanediyl)bis(1,3-dihydro-3-methyl-1H-imidazole-2-thione), was synthesized and structurally characterized. The capability of the polymer as an efficient sorbent for Congo red (CR) removal from aqueous solution has been evaluated. Compound 1 has a tetrahedral arrangement with a CdS₂Cl₂ core. L in 1 is bidentate to two neighboring Cd^II centers via the methimidazole sulfurs to create 1D chains propagating along the c-axis. The remaining coordination sites are occupied by two terminal chlorides. The chains are further stabilized by intermolecular C–H⋯Cl hydrogen bonds between the chlorides and hydrogens of the imidazole rings. Parallel chains stack in the 3-D structure. The Cd^II polymer sorbent was characterized by infrared spectroscopy, elemental analysis, UV–vis, solid fluorescence and X-ray single-crystal diffraction. Sorption kinetics were studied by three kinetic models, second order, Elovich and intraparticle diffusion. The results indicate that the mechanism of the sorption process followed Elovich kinetic model. Sorption equilibrium was also studied with Langmuir, Temkin, and Freundlich isotherm models. The sorption process followed the Temkin isotherm. MIC, MBC, and DNA cleavage activities of 1 were also studied. Furthermore, the UV–vis and solid state fluorescence spectra of 1 were measured.