A Zn(II) Coordination Polymer for Fluorescent Turn-Off Selective Sensing of Heavy Metal Cation and Toxic Inorganic Anions

Abstract

A novel coordination polymer [Zn(atyha)₂]_n (1) (Hatyha = 2-(2-aminothiazole-4-yl)-2- hydroxyiminoacetic acid) was constructed by hydrothermal reaction of Zn²⁺ with Hatyha ligand. CP 1 exhibits a 2D (4,4)-connected topological framework with Schläfli symbol of {4⁴·6²}, where atyha^- anions serve as tridentate ligands, bridging with Zn²⁺ through carboxylate, thiazole and oxime groups. CP 1 displays a strong ligand-based photoluminescence at 390 nm in the solid state, and remains significantly structurally stable in water. Interestingly, it can be utilized as a fluorescent probe for selective and sensitive sensing of Fe³⁺, Cr₂O₇^2- and MnO₄^- through the fluorescent turn-off effect with limit of detection (LOD) of 3.66 × 10^-6, 2.38 × 10^-5 and 2.94 × 10^-6 M, respectively. Moreover, the efficient recyclability for detection of Fe³⁺ and Cr₂O₇^2- is better than that for MnO₄^-. The mechanisms of fluorescent quenching involve reversible overlap of UV-Vis absorption bands of the analytes (Fe³⁺, Cr₂O₇^2- and MnO₄^-) with fluorescence excitation and emission bands for CP 1, respectively.

Keywords: coordination polymer; fluorescent; inorganic anion; metal cation; selective sensing.

Figure 1

(a) A drawing showing the coordination environment about Zn²⁺; (b) octahedral coordination configuration of Zn²⁺; (c) 2D-layered structure; (d) 3D supramolecular structure; (e) bridged atyha⁻ ligand-based node; (f) 4-c node of Zn²⁺; (g) topological structure.

Figure 1

(a) A drawing showing the coordination environment about Zn²⁺; (b) octahedral coordination configuration of Zn²⁺; (c) 2D-layered structure; (d) 3D supramolecular structure; (e) bridged atyha⁻ ligand-based node; (f) 4-c node of Zn²⁺; (g) topological structure.

Figure 2

Fluorescence excitation and emission spectra of (a) free Hatyha ligand and (b) CP 1.

Figure 3

(a) Fluorescence spectra of CP 1 and (b) fluorescence intensities in different solutions of metal ions.

Figure 4

Fluorescence intensities of CP 1 in solutions with different interfering metal ions before and after addition of Fe³⁺.

Figure 5

(a) Fluorescence responses of CP 1 in solutions with different concentrations of Fe³⁺ and (b) Stern–Volmer plot.

Figure 6

Recyclability of CP 1 for sensing of Fe³⁺.

Figure 7

(a) PXRD pattern of CP 1 soaked in Fe³⁺ solution; (b) UV-Vis absorption spectrum of Fe³⁺, fluorescence excitation and emission spectra of CP 1.

Figure 8

(a) Fluorescence spectra and (b) fluorescence intensities of CP 1 in different anionic solutions.

Figure 9

Fluorescence intensities of CP 1 in solutions with different interfering anions before and after addition of (a) Cr₂O₇²⁻ and (b) MnO₄⁻.

Figure 10

(a) Fluorescence responses of CP 1 in solutions with different concentrations of Cr₂O₇²⁻ and (b) Stern–Volmer plot.

Figure 11

(a) Fluorescence responses of CP 1 in solutions with different concentrations of MnO₄⁻ and (b) Stern–Volmer plot.

Figure 12

Cyclic experiments using CP 1 for detection of (a) Cr₂O₇²⁻ and (b) MnO₄⁻.

Figure 13

(a) PXRD patterns of CP 1 soaked in Cr₂O₇²⁻ and MnO₄⁻ solution, respectively; (b) UV-Vis absorption spectra of Cr₂O₇²⁻ and MnO₄⁻, fluorescence excitation and emission spectra of CP 1.