Catalytic activation of persulfate by 3D Cd(II) coordination polymers based on a flexible cyclotriphosphazene-functionalized ligand

Dye removal in wastewater can be done by catalytic reaction with coordination polymers. Herein, Two 3D Cd(II) coordination polymers, namely, {[Cd₃(L)(H₂O)₄].(H₂O)(DMF)}_n (GTU-1) and {[Cd₃(L)(4,4-bpy))(H₂O)₂].(H₂O)}_n (GTU-2), were prepared with a novel hexapod-shaped molecular building block, hexakis(methyl-2-(4-phenoxyphenyl)acetatebenzene) cyclotriphosphazene (H₆L), by solvothermal reactions in dimethylformamide with nitric acid as the modulator. Cd(II) coordination polymers were characterized by Fourier transform infrared spectroscopy, thermal analysis, scanning electron microscopy, powder X-ray diffraction analysis and single crystal X-ray diffraction technique. GTU-1 represents a 3D pillared-layered coordination polymer structure containing 2D Cd-carboxylate (Cd(COO)_n)-based inorganic building unit (IBU) whereas GTU-2 is a 3D coordination polymer derived from 1D IBU bridged together by deprotonated L^6- and judiciously chosen ancillary linker 4,4-bipyridine (4,4-bpy). In both complexes, the flexible multisite cyclotriphosphazene bridging ligand (H₆L) is completely deprotonated. GTU-2 exhibited relatively good catalytic activity towards rhodamine B (RhB), Methylen Blue (MB) and Acid Red 17 (AR-17) removal in aqueous solution.