Fluorine-Substituted Regulation in Two Comparable Isostructural Cd(II) Coordination Polymers: Enhanced Fluorescence Detection for Tetracyclines in Water

Abstract

The two functional fluorinated ligands 2-fluoro-4-(1H-tetrazol-5-yl)benzoic acid (2-F-H2tzba) and 3-fluoro-4-(1H-tetrazol-5-yl)benzoic acid (3-F-H2tzba) were obtained by modifying 4-(1H-tetrazol-5-yl)benzoic acid (H2tzba) embedded with fluorine. Two isostructural 3D Cd2+ coordination polymers (CPs), {[Cd(2-F-tzba)(H2O)]·1.5H2O}n (1) and {[Cd(3-F-tzba)(H2O)]·1.5H2O}n (2), were constructed using the hydrothermal method, in which the binuclear clusters [Cd2(tetrazolate)2] serving as 6-connected secondary building units (SBUs) are linked by six ligands to generate (3,6)-connected (4·62)2(42·610·83)-rtl binodal 3D nets. Compounds 1 and 2 simultaneously show excellent chemical and thermal stability in water systems at different pH levels (pH 3–10). The calculated structures for the ligands and compounds were further investigated by density functional theory (DFT) calculations to compare the structures and fluorescence properties of two fluorine-decorated skeletons. In comparison to 2, 1 displayed more efficient fluorescence sensing toward tetracycline (TET), doxycycline (DOX), oxytetracycline (OTC), and chlortetracycline (CTC) in water systems with a lower low detection limit (LOD) and a rapid response. The fluorescence quenching mechanism was explored through a combination of experimental data and DFT calculations.