Two Stable Terbium–Organic Frameworks Based on Predesigned

Jul 22, 2019 - (28) Remarkably, lanthanide MOFs (Ln-MOFs) have more significant ... Different functional groups can change the crystal structure and ...
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Two Stable Terbium−Organic Frameworks Based on Predesigned Functionalized Ligands: Selective Sensing of Fe3+ Ions and C2H2/CH4 Separation Weize Wang,†,‡ Ning Gong,†,‡ Hong Yin,† Bin Zhang,§ Panyue Guo,† Bo Liu,*,† and Yao-Yu Wang§ †

College of Chemistry & Pharmacy, Northwest A&F University, Yangling, 712100, P. R. China Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, College of Chemistry & Materials Science, Northwest University, Xi’an 710069, P. R. China

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S Supporting Information *

ABSTRACT: To construct desired metal−organic framework (MOF) sensors, the predesigned functionalized ligands 2,5-bis(2′,5′-dicarboxylphenyl)pyridine (L-N) and 2,5bis(2′,5′-dicarboxylphenyl)difluorobenzene (L-F) with pyridine- and fluorine-decorated tetracarboxylic acids were used, and two stable terbium−organic frameworks, H3O[(Tb(L-N)(H2O)2]·2H2O (Tb-N) and [Tb3(L-F)2(HCOO)(H2O)4]·6H2O (Tb-F), have been synthesized. The structures of Tb-N and Tb-F contain 1D open channels, which are functionalized by pyridine N or F atoms, respectively. Both of them show intense fluorescence in water and exhibit excellent selectivity and sensitivity to Fe3+ ions. The effects of different functional group sites on the stability and fluorescence sensing performance of MOFs have also been studied. In addition, a gas adsorption study demonstrates that Tb-N is capable of adsorbing C2H2 over CH4 selectively.

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INTRODUCTION As a promising class of porous crystalline materials, high surface areas, proper pore structures, and a variety of chemical compositions make metal−organic frameworks (MOFs) extremely attractive for an array of applications.1−6 One of the biggest advantages of MOFs is their adjustable and modifiable frameworks. The modification of organic ligands and metal centers as an effective strategy has been used in the construction of functionalized MOFs, especially used in selective adsorption/separation, catalysis, and sensing properties.7−15 The sensing properties of MOFs are mainly based on the active sites in the structures, such as the introduction of pyridine N atoms for sensing Fe3+ ions;16−19 thus, many sensors have been synthesized by introducing preactive sites in ligands.20−24 On the other hand, in practical applications, the stability plays an important parameter for evaluating MOFs as potential materials.25−27 Although a large number of MOFs have been synthesized that show excellent properties in some aspects, their poor stabilities limit their applications.28 Remarkably, lanthanide MOFs (Ln-MOFs) have more significant advantages and characteristics. What the Ln3+ ions possess are intense luminescent signals and bright luminescent colors, especially for Eu3+ and Tb3+, which make Ln-MOFs promising sensor materials.29−34 Meanwhile, the high oxidation number of a hard acid Ln3+-ion-formed framework usually has high stability in aqueous solution, which satisfies the application of MOFs as sensors in practical detection. Moreover, although various types of Ln-MOF sensors have been reported, there has been little research on the design of © XXXX American Chemical Society

materials such as organic ligands with different functional group sites. Different functional groups can change the crystal structure and luminescence behavior of MOFs, such as improving the sensitivity of analytical detection.16,35 It is necessary to carry out work on the effect of different functional group sites of organic ligands and Ln3+ ions to construct functional MOFs as fluorescent probes. In this work, when two ligands, 2,5-bis(2′,5′dicarboxylphenyl)pyridine (L-N) and 2,5-bis(2′,5′dicarboxylphenyl)difluorobenzene (L-F), were applied with pyridine- and fluorine-decorated tetracarboxylic acids (Scheme 1), Tb3+ ions reacted under solvothermal conditions to Scheme 1. Structures of L-N and L-F

synthesize two terbium−organic frameworks with the formulas H3O[(Tb(L-N)(H2O)2]·2H2O (Tb-N; CCDC 1917048) and [Tb 3 (L-F) 2 (HCOO)(H 2 O) 4 ]·6H 2 O (Tb-F; CCDC 1917049). Both Tb-N and Tb-F display good water stability and exhibit excellent selectivity and high sensitivity to Fe3+ ions in aqueous solution. In addition, gas adsorption behavior Received: May 20, 2019

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DOI: 10.1021/acs.inorgchem.9b01465 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. Coordination modes of L-N (a) and the 3D framework of Tb-N (b). corrections were collected using the SADABS program. The structure was settled with a simple approach and improved using the SHELXTL package and the OLEX2 software suite. All non-H atoms were refined using anisotropic filtration techniques, and the entire structure was refined by adding H atoms to their geometrically desirable positions. The SQUEEZE method of the PLATON program36 reduced the disordered solvent molecules from the numerous reflected data to obtain the final crystal structure. Table S1 shows the structural refinement parameters and crystallographic data of the crystals. Fluorescence Measurements. Solid-state and solution fluorescences were tested at room temperature. Tb-N and Tb-F solid particles were ground into powder, 3 mg each was respectively immersed in various M(NO3)x (M = K+, Pb2+, Ba2+, Zn2+, Cd2+, Co2+, Ni2+, Al3+, Fe3+) aqueous solutions (10−2 M, 5 mL), and the luminescent data were collected after 12 h. In the test of the sensitivity for Fe3+ ions, a pipet was used to continuously add Fe3+ (10−2 M) into the aqueous solutions (5 mL) of Tb-N and Tb-F. In the selective experiment, the concentration of the selective metal ion was 10−2 M, then the grounded sample was added, and the fluorescence intensity before and after the addition of Fe3+ ions (10−2 M) was recorded. During the cycle experiment, the ground sample was immersed in a Fe3+ ion (10−2 M) solution for 12 h, then the fluorescence of the ground sample, which had been washed by water a few times, was tested, and this was repeated five times. Before all of the solution fluorescence testing, an ultrasound was performed on the solution for 10 min to ensure the formation of a suspension. Gas Adsorption Measurements. The freshly prepared sample was soaked in methanol, the fresh methanol was changed every 12 h, and the solvent was exchanged for 3 days. The guest and solvent molecules were removed by drying on a vacuum apparatus at 120 °C for 12 h to activate. All N2, C2H2, and CH4 adsorption isotherms were performed on a Micromeritics ASAP 2020 HD88 physisorption analyzer.

demonstrates that Tb-N is capable of adsorbing C2H2 over CH4 selectively.

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EXPERIMENTAL SECTION

Materials and Instrumentation. The reagents were commercially purchased and could be used directly. C, H, and N elemental analysis was tested by utilizing the PerkinElmer 2400C elemental analyzer. Powder X-ray diffraction (PXRD) patterns were carried out over 2θ ranging from 5 to 30° on a Bruker D8 ADVANCE diffractometer. Thermogravimetric analyses (TGA) were acquired by gradual heating from 30 to 800 °C at a rate of 5 °C min−1 under a N2 atmosphere on a NETZSCH TG 209 thermal analyzer. Fluorescent spectra were implemented using an F-4500 spectrophotometer (Hitachi). UV−vis absorption spectra were recorded on a U-3900H spectrophotometer (Hitachi). X-ray photoelectron spectroscopy (XPS) was accomplished on a Thermo Scientific ESCALAB 250Xi photoelectron spectrometer. The IR spectral data were recorded on a Nicolet Avatar 360 Fourier transform infrared spectrometer, in the area of 400−4000 cm−1. Synthesis of H3O[(Tb(L-N)(H2O)2]·2H2O (Tb-N). A mixture of Tb(NO3)3·6H2O (0.05 mmol, 22.7 mg), L-N (0.025 mmol, 10.2 mg), 1.5 mL of N,N-dimethylformamide (DMF), 1.5 mL of deionized water, and 0.5 mL of a nitric acid solution (1 mL of HNO3 in 2 mL of H2O) was sealed in a glass vial (10 mL), which was capped tightly at room temperature. After the contents were well mixed, the glass vial was heated to 100 °C for 3 days and then slowly cooled to room temperature. Light-yellow crystals were filtered, washed with a small amount of DMF, and air-dried (the yield was 70% by L-N). Anal. Calcd for C21H20NO13Tb: C, 38.61; N, 2.14; H, 3.09. Found: C, 38.74; N, 2.30; H, 2.82. IR (KBr, cm−1): 3746 (w), 3048 (w), 2882 (w), 2349 (m), 1566 (s), 1383 (s), 1303 (w), 1257 (w), 1156 (w), 1051 (w), 1012 (w), 926 (w), 890 (w), 837 (m), 801 (m), 770 (s), 709 (w), 638 (w), 553 (s), 478 (w), 421 (w). Synthesis of [Tb3(L-F)2(HCOO)(H2O)4]·6H2O (Tb-F). A mixture of Tb(NO3)3·6H2O (0.05 mmol, 22.7 mg), L-F (0.025 mmol, 11.1 mg), 2.5 mL of DMF, and 0.6 mL of a nitric acid solution (1 mL of HNO3 in 3 mL of H2O) was sealed in a glass vial (10 mL), which was capped tightly at room temperature. After the contents were well mixed, the glass vial was heated to 110 °C for 3 days and then slowly cooled to room temperature. White crystals were filtered, washed with a small amount of DMF, and air-dried (the yield was 53% by L-F). Anal. Calcd for C44H37F4O28Tb3: C, 33.74; H, 2.38. Found: C, 33.85; H, 2.55. IR (KBr, cm−1): 3739 (w), 3622 (m), 2940 (m), 2872 (w), 2805 (m), 2353 (s), 1650 (s), 1566 (s), 1480 (s), 1380 (s), 1285 (w), 1245 (s), 1168 (s), 1095 (s), 1025 (m), 901 (w), 849 (s), 773 (s), 724 (m), 678 (s), 525 (s), 439 (w). X-ray Crystallography. Diffraction data were recorded at room temperature on a Bruker-AXS SMART CCD area detector diffractometer using Mo Kα radiation (λ = 0.71073). Absorption

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RESULTS AND DISCUSSION Crystal Structure of Tb-N. Single-crystal X-ray diffraction analysis reveals that Tb-N crystallizes in the monoclinic space group P21/n, showing a 3D framework based on Tb−COO− Tb chain units. The asymmetric unit of Tb-N is assembled from one Tb3+ atom, one L-N ligand, and two coordinated H2O molecules. Each Tb3+ atom is coordinated with eight O atoms, in which six O atoms are from five different L-N ligands and the other two O atoms are from two coordinated H2O molecules (Figure S1). As shown in Figure 1a, the L-N ligands show two kinds of connect modes, the carboxylate groups of which exhibit η0:η1-μ1 and η1:η1-μ2 in one and η0:η1-μ1 and η1:η1-μ1 in the other. The neighboring Tb3+ atoms are connected by the carboxylate groups in a η1:η1-μ2 fashion to B

DOI: 10.1021/acs.inorgchem.9b01465 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 2. Coordination modes of L-F (a) and the 3D framework of Tb-F (b).

Figure 3. PXRD profiles of Tb-N (a) and Tb-F (b) after being soaked in water, acidic, and basic solutions.

Figure 4. Excitation and emission fluorescence spectra of Tb-N (a) and Tb-F (b) at room temperature.

five different L-F ligands and two O atoms from one HCOO− and one coordinated H2O, respectively (Figure S3). Tb2 is eight-coordinated and bonds to O atoms from two L-F ligands, two HCOO− anions, and four coordinated H2O molecules. Similar to the bridging modes of L-N in the structure of Tb-N, L-F also exhibits two kinds of bridging modes in Tb-F. The carboxylate groups of L-F show η1:η1-μ1 and η1:η2-μ2 in one mode and η0:η1-μ1 and η1:η1-μ2 in the other mode (Figure 2a). Two Tb1 atoms are bridged by four carboxylate groups to give a dimer Tb2 unit. Interestingly, the neighboring Tb2 unit and Tb2 atom are connected through HCOO− to form a 1D chain (Figure S4). These 1D chains are further bridged by L-F ligands to build a 3D framework (Figure 2b), which contains

generate a 1D chain (Figure S2). The 1D chains are further connected through L-N ligands to form a 3D framework (Figure 1b). Along the b axis, small open channels can be found in which the isolated pyridyl N atoms and uncoordinated carboxylate O atoms exist in the interior as potential functionalized points. The effective free volume is ∼9.8%, as calculated by PLATON. Crystal Structure of Tb-F. Tb-F crystallizes in the monoclinic space group P1̅ , whose asymmetric unit is constructed by one and half Tb3+ atoms, one L-F ligand, half a HCOO−, and two coordinated H2O molecules. The HCOO− anions are derived from the decomposition of DMF molecules. Tb1 is nine-coordinated by seven carboxylate O atoms from C

DOI: 10.1021/acs.inorgchem.9b01465 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 5. Fluorescence intensities of Tb-N (a) and Tb-F (b) at 549 nm in different metal-ion solutions (10−2 M). Tb-N (c) and Tb-F (d) with Fe3+ ion solutions (10−2 M) continuously added in 5 mL of water (insets show color changes before and after the addition of Fe3+ under UV light).

Figure 6. Relative luminescence intensities of Tb-N (a) and Tb-F (b) at 549 nm in different Fe3+ ion concentrations. Relationship between the luminescence intensities of Tb-N (c) and Tb-F (d) at 549 nm and the Fe3+ ion concentration.

temperature range of 30−150 °C, and this loss is consistent with the release of lattice and coordinated H2O molecules (calcd 11.3%). After further heating, a good platform could be observed until 420 °C. For Tb-F, in the temperature range of 30−210 °C, the total weight loss was 13.9% (calcd 11.4%). The structure gradually collapsed because of continuous heating, indicating the poor thermal stability of Tb-F. Notably, both Tb-N and Tb-F show excellent chemical stability in different pH conditions. As shown in Figure 3, the diffraction

1D rectangle channels, and the effective free volume is about 29.2%. It should be noted that these free F atoms point toward the inner side of the channels as potential functionalized sites. Thermal and Chemical Stability. The experimental PXRD patterns of Tb-N and Tb-F match with the simulated ones from the respective crystal structures, indicating that they are isomorphic compounds with a single phase. TGA of Tb-N and Tb-F were performed under a N2 atmosphere (Figure S5). For Tb-N, the total weight loss was about 11.3% in the D

DOI: 10.1021/acs.inorgchem.9b01465 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 7. Comparison of the fluorescence intensities at 549 nm between Tb-N (a) and Tb-F (b) before and after the addition of Fe3+ ions (10−2 M) in different metal-ion (10−2 M) solutions. (c) Recyclability of the quenching ability of Tb-N with the application of a 10−2 M Fe3+ aqueous solution. (d) PXRD patterns of Tb-N after five rounds of circulation.

According to the Stern−Volmer equation, KSV for Tb-N and Tb-F are found to be 7.93 × 103 and 1.39 × 104 M−1, respectively (Figure 6a,b). When the values of KSV are compared, it can be seen that the Fe3+ ion sensitivity detection for Tb-F is higher than that for Tb-N, which may be due to the fact that there are massive F atoms located on the surface of the pores, leading to a better quenching effect on the Fe3+ ions. Furthermore, their KSV constants are comparable or higher than those of most reported MOF sensors (Table S2). Interestingly, the fluorescence intensities of Tb-N and Tb-F and the concentration of Fe3+ ions at 549 nm are in line with the single-logarithmic function, indicating that the fluorescence quenching behavior of Fe3+ ions is a process of diffusion control (Figure 6c,d).37 As is known to all, the selectivity is a key factor to be considered in practical applications for metal-ion sensors. Thus, we soaked the finely ground samples in five groups of different metal ions in aqueous solutions. As shown in Figure 7a,b, the mixed ions had little impact on the fluorescence intensities of Tb-N and Tb-F. Conversely, the fluorescence intensities of Tb-N and Tb-F showed an apparent decrease immediately upon the addition of Fe3+ ions, indicating that TbN and Tb-F can exclusively sense Fe3+ ions in the existence of other metal ions. Considering the importance of recyclablility for a sensor in environmental protection, circulation experiments of the two compounds were carried out. After washing quenched Tb-N with deionized water several times, its fluorescence intensity was restored immediately (Figure 7c). Notably, after five cycles, the fluorescence intensity of Tb-N could be wellretained, and the framework completely remained, showing good stability and recyclability (Figure 7d), while the recyclability of Tb-F was poor, which could be due to the formation of Fe3+@Tb-F. The larger channel of Tb-F allows Fe3+ ions to enter more easily and leads a certain interaction

peak of the crystal does not obviously change after solution treatments with pH = 1−13 and 2−13 for Tb-N and Tb-F, respectively. Fluorescence Properties and Sensing of Metal Ions. The solid states of Tb-N and Tb-F show characteristic emission peaks of Tb3+ ions at 495, 550, and 606 nm upon excitation at room temperature (Figure 4). They both show sharp emission bands at 550 nm attributed to f−f from the 5D4 → 7F5 transition and emit bright-green luminescence of Tb3+ via UV radiation. Notably, compared with Tb-F, in the fluorescence spectra of Tb-N, a broad emission peak at 408 nm is observed, which may be due to the π*−π or π*−n molecular interaction of the ligand. This phenomenon further indicates the influence of different substituents of ligands on the luminescence efficiency of rare-earth ions. By virtue of the advantages of massive bare Lewis base sites on the surface, favorable green luminescent properties, and superior structural stability, Tb-N and Tb-F can act as one kind of fluorescent probe with great potential to detect metal ions under a water solution. Then their luminescent responses toward various metal ions were explored. By observation of the fluorescence spectra of crystals in aqueous solutions of different M(NO3)x (M = K+, Pb2+, Ba2+, Zn2+, Cd2+, Co2+, Ni2+, Al3+, Fe3+), it can be clearly seen that Fe3+ ions show a significant quenching effect on the fluorescence intensity of both Tb-N and Tb-F, and the quenching efficiency can reach 99.9% by calculation. In contrast to the original intensity, other metal ions display negligible influence for the fluorescence intensity of Tb-N (Figure 5a). However, for Tb-F, the fluorescence intensity is decreased by almost of the metal ions to some extent (Figure 5b). Those results suggest that Tb-N and Tb-F can efficiently sense Fe3+ ions in water. To further quantitatively evaluate the quenching effect of Fe3+ ions, the quenching constants (KSV) were calculated using the linear Stern−Volmer equation (I0/I = 1 + KSV[Fe]). E

DOI: 10.1021/acs.inorgchem.9b01465 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 8. Comparison of the XPS spectra of Tb-N before (a) and after (b) treatment with Fe3+ ions: overall spectra (left); N 1s (middle); O 1s (right).

Figure 9. Comparison of the XPS spectra of Tb-F before (a) and after (b) treatment with Fe3+ ions: overall spectra (left); F 1s (middle); O 1s (right).

between Fe3+ ions and the framework, which makes it difficult for Fe3+ ions to leave. In addition, the formation of Fe3+@Tb-F is also illustrated by the change in color before and after soaking of the Fe3+ ions (Figures S6 and S7). Luminescence Quenching Mechanism. According to previous studies, the quenching mechanism toward metal ions of MOFs is divided into the following two main reasons: (1) the collapse of the structure; (2) the impact between the admitted metal ions and the structure.38−40 The PXRD patterns of both the Tb-N and Tb-F samples before and after soaking of the metal ions are consistent, so it is not the result of structural collapse (Figures S8 and S9). Thus, the primary reason for causing the quenching effect is the impact between the admitted metal ions and the structure. As is wellknown, this kind of quenching is generally caused by photoinduced electron transfer and fluorescence resonance energy transfer, as observed in other known MOFs.41 To verify the mechanism, UV−vis and XPS studies were performed. According to the UV−vis absorption spectra (Figures S10 and S11), the absorption spectra of Fe3+ ions in aqueous solution overlap with the excitation spectra of Tb-N, implying that the excitation wavelength energy prevents energy transfer from the

ligand to the Tb3+ ions and ultimately brings about luminescence quenching, the explanation of which could also be applied to Tb-F. Furthermore, when the XPS spectra of the Fe3+ ion solution are compared before and after treatment (Figures 8 and 9), the N 1s peak at 410.16 eV in Tb-N is shifted to 401.25 eV, and the peak of O 1s does not change. The binding energy varies greatly and is higher than that reported in the literature,42 indicating that there exist weak bonding interactions between the pyridine N atoms and Fe3+ ions. Similarly, the F 1s peak in Tb-F shifted from 686.73 to 686.64 eV, and the O 1s peak shifted from 531.31 to 532.12 eV. The change of the binding energy is similar to the values in the literature,43 indicating the weak interaction of Fe3+ ions with F and O atoms of the ligands. From the above results, the bond of Fe−N is stronger than that of Fe−F or Fe−O, and Fe atoms are also likely to bond with N atoms. Likewise, the Fe3+ ion has an unfilled 3d orbital that accepts electrons. After excitation, electrons are transferred to the lowest unfilled molecular orbital through the nonradiation path, leading to fluorescence quenching. It is worth noting that the pyridine N atom and F atom in the para position can also provide a pair of lone-pair electrons to form a F

DOI: 10.1021/acs.inorgchem.9b01465 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 10. (a) C2H2 and CH4 sorption isotherms of Tb-N at 273 and 298 K. (b) IAST sorption selectivity of Tb-N for C2H2/CH4 at 298 K. (c) Isosteric heat of C2H2 in Tb-N.

coordination bond with the Fe3+ ion, which improves the recognition efficiency. Thus, the interaction of weak bonds could increase the electronic energy levels of the ligand, further forbidding energy transfer between the ligand and Tb3+ ion and leading to luminescence quenching. Sorption Properties. The PXRD patterns indicate that the desolvated Tb-N keeps the framework integrity, whereas the framework of Tb-F becomes nonporous after the removal of guest molecules (Figure S12). Thus, the porosity of Tb-N was further evaluated. N2 sorption isotherm of Tb-N shows only surface absorption (Figure S13), and the reason should be the small open channel sizes, which hinder the entry of N2 molecules. Furthermore, the stable and small open channel sizes of Tb-N encourage us to examine its potential application for C2H2/CH4 separation. As shown in Figure 10a, the C2H2 and CH4 adsorption properties on Tb-N under ambient temperature were investigated. The C2H2 uptakes are 32.3 cm3 g−1 at 273 K and 21.8 cm3 g−1 at 298 K and 1 bar. Meanwhile, negligible amounts of uptake of CH4 (4.2 and 3.0 cm3 g−1 at 273 and 298 K, respectively), bespeaking Tb-N, prefer selective adsorption of C2H2 over CH4. To estimate the practical separation ability for C2H2, a theoretical gas mixture of C2H2/CH4 is guided by the ideal absorbed solution theory (IAST) model (Figure S14). As shown in Figure 10b, the C2H2/CH4 selectivity for an equimolar mixture is 43, and the value is superior among those MOFs that are reported to possess high C2H2 selectivity.44−47 The good selectivity of C2H2 in Tb-N may be attributed to the small window size, which is not sufficient for the inclusion of CH4 molecules (C2H2, 3.3 Å; CH4, 3.8 Å). Moreover, free carboxylate O atoms, pyridine N atoms, and the anionic framework generate negatively charged electric fields,48 thereby enhancing interaction between the framework and quadrupolar C2H2 molecule. The isosteric heat of adsorption for C2H2 derived from virial analysis illuminates a strong guest−host interaction (29.6 kJ mol−1) between C2H2 molecules with TbN (Figure 10c).

the small window sizes and good stability make Tb-N possess high C2H2/CH4 separation performance.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b01465. Additional figures, supplementary PXRD patterns, TGA plots, and UV−vis spectra (PDF) Accession Codes

CCDC 1917048 and 1917049 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Yao-Yu Wang: 0000-0002-0800-7093 Author Contributions ‡

These authors contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for support from the NSFC (Grants 21601145, 21531007, and 31600275). REFERENCES

(1) Zhou, H.-C.; Long, J.-R.; Yaghi, O. M. Introduction to Metal− Organic Frameworks. Chem. Rev. 2012, 112, 673−674. (2) Kirchon, A.; Feng, L.; Drake, H. F.; Joseph, E. A.; Zhou, H.-C. From fundamentals to applications: a toolbox for robust and multifunctional MOF materials. Chem. Soc. Rev. 2018, 47, 8611− 8638. (3) Drout, R. J.; Robison, L.; Farha, O. K. Catalytic applications of enzymes encapsulated in metal−organic frameworks. Coord. Chem. Rev. 2019, 381, 151−160. (4) Chen, X.; Peng, Y.; Han, X.; Liu, Y.; Lin, X.; Cui, Y. Sixteen isostructural phosphonate metal-organic frameworks with controlled Lewis acidity and chemical stability for asymmetric catalysis. Nat. Commun. 2017, 8, 2171. (5) Zhou, W.; Huang, D.-D.; Wu, Y.-P.; Zhao, J.; Wu, T.; Zhang, J.; Li, D.-S.; Sun, C.; Feng, P.; Bu, X. Stable Hierarchical Bimetal− Organic Nanostructures as High Performance Electrocatalysts for the

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CONCLUSION In summary, under the guidance of predesigned ligands, two stable 3D terbium−organic frameworks, Tb-N and Tb-F, were successfully prepared. Both terbium−organic framework materials own high selectivity and sensitivity to Fe3+ ions in aqueous solution. The detection study shows that the quenching coefficient of Tb-F is higher than that of Tb-N but the stability and repeatability of Tb-N are better than those of Tb-F. These results would be useful for the design and synthesis of new fluorescence sensing materials. In addition, G

DOI: 10.1021/acs.inorgchem.9b01465 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

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DOI: 10.1021/acs.inorgchem.9b01465 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.9b01465 Inorg. Chem. XXXX, XXX, XXX−XXX