Syntheses, characterizations and luminescence-based iron(iii) ions detection of mixed-ligand zinc(II) coordination polymers

In this thesis study, four novel Zn(II)-based coordination polymers were synthesized via solvothermal methods using bis(3,5-dicarboxyphenyl)terephthalamide (H 4 L) and bis(imidazole)-type auxiliary ligands. The synthesized structures were identified as {[Zn(µ 4 -L) 0,5 (µ-obix)]·2DMF} n (EK1), {[Zn(µ 4 -L) 0,5 (µ-mbix)]·3H₂O} n (EK2), {[Zn 2 (µ 4 - L)(µ-pbix) 2 ]·5H₂O} n (EK3) and {[Zn 2 (µ 4 -L)(µ-bib) 2 ]·4H 2 O} n (EK4). EK1-4 were comprehensively characterized using FT-IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction (SCXRD). Additionally, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and topological analyses were also performed. EK1-4 exhibited structural diversity based on the rotation of imidazole rings around the –CH 2 – linkers in the bis(imidazole) ligands. Specifically, EK1-4 featured a 2- fold interpenetrated 3D framework, a 2D structure, a 3D framework and a 3-fold interpenetrated 3D framework, respectively with high phase purity and thermal stability. The luminescent properties of the complexes were examined in both solid-state and in various solvents, showing strong emission behavior. Based on these findings, the feasibility of using the complexes as fluorometric sensors for Fe 3+ ion detection was investigated. The fluorescence of all complexes was significantly quenched in the presence of Fe 3+ ions, while exhibiting high selectivity over a wide range of competing metal ions. The calculated detection limits (LOD) were 4.14 × 10 -5 M for EK1, 9.23 × 10 -5 M for EK2, 4.67 × 10 -5 M for EK3, and 4.69 × 10 -5 M for EK4, indicating their potential application as sensitive fluorometric sensors in environmental monitoring and biosensing technologies. The quenching mechanism was attributed to the competitive light absorption between Fe 3+ ions and the complexes. This study highlights the effectiveness of Zn(II)-based coordination polymers, modulated by bis(imidazole) ligands, in the design of selective and sensitive fluorescence-based detection systems. Keywords: Coordination polymer, luminescence, Fe 3+ detection, Zn(II) complexes, bis(imidazole) ligands, bis(3,5-dicarboxyphenyl)terephthalamide (H 4 L)