Functionalized Cyclotriphosphazene-Based Cobalt Coordination Polymer: Synthesis, Characterization, and Catalytic Efficiency Evaluation

Metal-containing-cyclic phosphazenes can function as catalytic materials in diverse applications. Despite their distinctive structural, catalytic, and electronic properties, the development of metal-based phosphazenes has lagged behind that of other metal-containing materials. Here, a flexible hexapod-shaped molecular building block, known as hexakis(methyl-2-(4-phenoxyphenyl)acetatebenzene) cyclotriphosphazene (H₆L₁), was utilized to synthesize a Co(II) coordination polymer. This Co(II) framework, referred to as {[Co3(L)(4,4′-bpy)(H₂O)₂]}n (GTU-4), was obtained through a solvothermal reaction between H₆L₁ and 4,4′-bipyridine (4,4′-bpy) pincer ligand in dimethylformamide (DMF). The Co(II) coordination polymer was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), powder X-ray diffraction analysis (PXRD), and single crystal X-ray diffraction (SC-XRD) techniques. The asymmetric unit of the complex includes three crystallographically different Co(II) ions, one completely deprotonated cyclophosphazene-based linker (L), one 4,4′-bipyridine (4,4′-bpy), and two coordinated aqua molecules. The synthesized coordination polymer (GTU-4, GTU denotes Gebze Technical University.) showed high catalytic efficiency in the removal of different groups of pollutants in the presence of peroxymonosulfate (PMS) oxidant so that pollutants with the concentration of 50 mg/L of RhB, MB, AR17 dyes, and Rif pharmaceutical were degraded by 97.6%, 98.5%, 100%, and 97.8%, respectively. This high degradation efficiency could be attributed to the synergistic effect of the simultaneous presence of GTU-4 catalyst and PMS oxidant. It was also shown that the degradation process obeyed pseudo-first-order kinetic with a k_app value of 0.0537 min⁻¹.