Novel Multifunctional Samarium-Organic Framework for Fluorescence Sensing of Ag+, MnO4 -, and Cimetidine and Electrochemical Sensing of o-Nitrophenol in Aqueous Solutions

Abstract

A novel Sm-metal-organic framework (MOF) sensor with the molecular formula Sm₈(HDBA)₆·H₂O has been prepared based on a penta-carboxyl organic ligand (H₅DBA = 3,5-di(2',4'-dicarboxylphenyl)benzoic acid) and samarium nitrate under solvothermal conditions. Sm-MOF is characterized by single-crystal X-ray diffraction analysis, elemental analysis, thermogravimetric analysis, and powder X-ray diffraction analysis. Structural analysis shows that the dimer metal units are alternately connected to form a one-dimensional chain, and this chain is connected by the bridging carboxyl oxygen of the ligand H₅DBA to form a two-dimensional double-layer plane, which then expands into a three-dimensional microporous framework. Fluorescence detection studies show that Sm-MOF can detect Ag⁺ ions, MnO₄ ^- anions, and cimetidine tablets with high sensitivity and selectivity and can also be used to electrochemically detect o-nitrophenol in water. High-sensitivity detection capability of the Sm-MOF can enrich the application of samarium complexes in multifunctional sensors.

Figure 1

(a) Coordination environment of Sm1 (symmetry codes: a: 1/3 + x – y, −1/3 + x, −1/3-z; b: 1/3 + x – y, −1/3 + x, 2/3 – z; c: 2/3 – y, 1/3 + x – y, −2/3 + z; d: y, −x + y, −z; e: 1/3 – x + y, 2/3 – x, −4/3 + z; f:1/3 – x + y, 2/3 – x, −1/3 + z); (b) one-dimensional chains based on adjacent Sm1 dimer units; (c) coordination environment of Sm2 (symmetry codes: a:-x+y, 1-x, 1+z; h:2/3-x, 4/3-y, 1/3-z; i:-1/3+y, 1/3-x+y, 1/3-z); (d) six core metal clusters based on Sm2 ions; (e) six-angle group based on six nuclear clusters, six DBA ligands, and binuclear units; and (f) 3D microporous framework.

Scheme 1. Coordination Modes of DBA^5– Ligands in the Complex of κ₁κ₂-κ₂κ₂-κ₁κ₁-κ₁κ₁-κ₁κ₁-μ₈

Figure 2

Solid-state fluorescence spectra of Sm-MOF and H₅DBA at room temperature (λ_ex = 279 nm).

Figure 3

(a) Relative fluorescence intensity of the Sm-MOF immersed in 16 nitrate solutions and (b) nonlinear graph of the Sm-MOF sensing the Ag⁺ ions.

Figure 4

(a) Relative fluorescence intensity of the Sm-MOF immersed in 16 anionic solutions and (b) nonlinear and linear graph of the Sm-MOF sensing MnO₄^– anions.

Figure 5

(a) Luminescence spectra of the Sm-MOF, cimetidine, and the Sm-MOF immersed in different drug aqueous solutions and (b) luminescence spectra of the Sm-MOF immersed in the cimetidine aqueous solution with different concentrations and the nonlinear graph of sensing and detecting cimetidine by the Sm-MOF.

Figure 6

(a) Cyclic voltammogram of the Sm-MOF/CPE bare electrode and the working electrode with o-nitrophenol and (b) cyclic voltammogram with different concentrations of o-nitrophenol.