Communication Cite This: Cryst. Growth Des. XXXX, XXX, XXX−XXX
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A Highly Stable Dual Functional Zinc Phosphite Carboxylate as Luminescent Sensor of Fe3+ and Cr2O72− Si-Fu Tang*,† and Xiaomin Hou‡ †
College of Chemistry and Pharmaceutical Sciences and ‡Shandong Province Key Laboratory of Applied Mycology, College of Life Science, Qingdao Agricultural University, Changcheng Road 700, Chengyang District, Qingdao 266109, China
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S Supporting Information *
ABSTRACT: One new organic−inorganic hybrid zinc phosphite carboxylate, namely, [H2N(CH3)2]2[Zn2L(HPO3)2] (1), where H2L= 2′,3′,5′,6′-tetramethyl-[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid, was synthesized and thoroughly characterized. It has a three-dimensional anionic framework structure with protonated dimethylamine as counter cations accommodated in the channels. It shows good thermal stability and remarkable aqueous stability in the pH range of 3−11 and can behave as a chemical sensor of Fe3+ and Cr2O72−. The sensing mechanism is also discussed.
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more organic linkers to enrich the structural diversity and enhance their performances. Therefore, 2′,3′,5′,6′-tetramethyl[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid (H2L) was selected with the following considerations: (1) it is longer than BDC and would be expected to form a porous framework; (2) it possesses four methyl groups on the middle benzene ring, which is beneficial to the water resistance of the formed materials. One new zinc phosphite carboxylate, [H2N(CH3)2]2[Zn2L(HPO3)2], was successfully obtained. Herein, we report on the synthesis, crystal structure, thermal and chemical stability, and optical sensing toward Fe3+ and Cr2O72−. Colorless plate crystals of compound 1 were obtained hydro(solvo)thermally from the reaction of H2L (0.0936 g, 0.25 mmol), Zn(NO3)2·6H2O (0.0745 g, 0.25 mmol), H3PO3 (0.0410 g, 0.5 mmol), 100 μL of 2-(2-aminoethoxy)ethanol, and four drops of HF (40%) at 140 °C for 3 days (see the details in the Supporting Information). The powder X-ray diffraction (XRD) pattern of compound 1 confirms the purity of the bulk sample (see Figure S1). Compound 1 crystallizes in monoclinic P21/c space group (see Table S1) and has a three-dimensional framework structure. There is one zinc(II) ion, one phosphite anion (HPO3)2−, a half deprotonated carboxylate ligand (L2−), and one protonated dimethylamine cation (NH2(CH3)2)+ (see Figure 1(a)) in the asymmetric unit, indicating a formula of [H2N(CH3)2]2[Zn2L(HPO3)2]. The zinc ion is tetrahedrally coordinated by one carboxylate oxygen atom and three phosphite oxygen atoms with the Zn−O bond lengths ranging from 1.9326(19) to 1.9715(18) Å and O−Zn−O bond angles from 100.32(8) to 127.62(11)° (see Tables S2 and S3). In the
etal−organic frameworks (MOFs) have been extensively researched and have found many potential applications in the gas adsorption/separation, optical, magnetic, catalysis, and sensors fields, among others.1−4 Tremendous efforts have been made in the design and synthesis of MOF materials with interesting crystal structures and applications. One great challenge on their way to practical application that must be conquered is their moderate stability.5 Many MOF materials collapse during activation or decompose in acidic/basic solutions. Thus, enhancing their thermal and chemical stability becomes an urgent issue. Some strategies have been developed, such as the employment of high oxidation state metal ions6 or N-heterocycle organic linkers.7 Recently, one type of organic−inorganic hybrid zinc phosphate/phosphite carboxylate framework has emerged as a new method to synthesize highly stable MOFs.8−11 These frameworks are usually constructed from inorganic onedimensional zinc phosphite chains/nanotubes or two-dimensional zinc phosphate layers and organic dicarboxylate linkers. They combine both the advantages of zeolite-related compounds and organic rigid linkers. One distinctive character of these compounds is their outstanding stability. For example, NOTU-4, which is assembled from one-dimensional zincophosphite chains and benzene-1,4-dicarboxylate linkers, is stable up to 400 °C and shows resistance to seawater, acidic and basic aqueous solutions (pH 3−11), and boiling organic solvents.8 Undoubtedly, organic−inorganic hybrid zinc phosphite/phosphate carboxylates are very promising functional crystalline porous materials. However, the development of this kind of material is still at its infant stage. Up to date, only very rare compounds have been reported in the literature. The construction of new compounds remains a great challenge. In previous work, only benzene-1,4-dicarboxylic acid (BDC) and biphenyl-4,4′-dicarboxylate (BPDC) have been employed for the construction of organic−inorganic hybrid zinc phosphite/phosphate carboxylates. It is desirable to explore © XXXX American Chemical Society
Received: October 9, 2018 Revised: December 5, 2018 Published: December 11, 2018 A
DOI: 10.1021/acs.cgd.8b01517 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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Communication
Figure S1), and a wide pH range (3−11) of HCl and NaOH solutions for 1 day (see Figure 2), demonstrating its
Figure 2. Simulated and recorded PXRD patterns of compound 1 at varying pH conditions. Figure 1. (a) The coordination environments of the ligand L2− and zinc ion in 1. Symmetry codes: A = x, 1.5 − y, −0.5 + z; B = 1 − x, 1 − y, 2 − z; C = x, 1.5 − y, 0.5 + z. (b) 2D zinc phosphite layer in bcplane. (c) 3D packing structure viewing along b-axis.
remarkable chemical stability. As we know, the number of chemical stable MOF compounds is still limited. The present work suggests that zinc phosphite carboxylates could be an alternative strategy for the development of stable MOF materials. The solid state emission spectra of compound 1 and ligand H2L were recorded at room temperature (see Figure S4). By exciting at 315 nm, compound 1 displays a broad emission band with a maximum lying at about 359 nm, which could be attributed to the intraligand π* → π transition, because it resembles the free ligand (355 nm) and the character of Zn(II) ions, which are difficult to oxidize or reduce.13,14 The slight red shift compared with H2L could be ascribed to the coordination of the ligand to the metal centers. The excellent luminescent property as well as the thermal and chemical stability of compound 1 make it an ideal candidate as a chemical sensor toward metal cations or anions. To research the sensing property of compound 1, the solvent effect on luminescence was first investigated. Compound 1 (2 mg) was dispersed in different solvents (2 mL) and subjected to ultrasonication for 10 min before luminescence measurements. It was found that compound 1 could display intense luminescence in H2O and moderate emission in CH2Cl2 and acetonitrile with a slight blue shift but is quenched in ethanol, acetone, and DMF (see Figure S5). Therefore, water was selected as the solvent for the following luminescence measurements. Sensing properties of compound 1 toward various metal ions (Cr3+, Al3+, Na+, Ca2+, Mg2+, Fe2+, Co2+, Cd2+, Cu2+, Ni2+, and Fe3+) were investigated by recording the emission spectra of the suspensions of powder 1 (2 mg) in 2 mL of different aqueous solutions of nitrate salts (10−3 M, the Fe2+ solution was prepared from ferrous chloride). Interestingly, Fe3+ can significantly quench the luminescence, while other metal ions have a moderate or negligible quenching effect on the emission intensity (see Figure 3), suggesting that compound 1 could act as a sensor of Fe3+ with high selectivity. To check the sensitivity of 1 toward Fe3+, fluorescence titration experiments were performed. The emission intensity of compound 1 shows a clear negative correlation with the increasing concentration of Fe3+, suggesting a diffusion-controlled quenching process.15 The quenching efficacy can be calculated using the Stern− Volmer (SV) equation16 and plotted as a function of
phosphite anion, the P−O bond lengths are in the range of 1.511(2) to 1.5212(19) Å, and the P−H bond length is 1.37(2) Å, showing a pseudopyramid geometry. The O−P−O and O−P−H bond angles range from 103.9(10) to 127.62(11)°, which are all comparable to those of other zinc phosphites.8−12 Each phosphite group bridges three zinc(II) ions via its three oxygen atoms. These ZnO4 and HPO3 tetrahedrons assemble via a corner sharing mode into a twodimensional (2D) layer in the bc-plane with Zn4P4 eightmembered rings (see Figure 1(b)). The dicarboxylic acid ligand is fully deprotonated and shows a trans bis-monodentate coordination mode, which is similar to BDC and BPDC. The 2D zinc phosphite layers are further connected by these carboxylate ligands to form a three-dimensional (3D) framework structure with narrow channels (4.743(0) × 21.937(11) Å2) running along the b-axis and methyl groups dangling on the walls (see Figure 1(c)). The total potential solvent area volume is determined to be 359.3 Å3, which is about 21.9% of the unit cell volume (1643.3 Å3). The channels are filled with protonated dimethylamine cations, which originate from the hydrolysis of DMF and form plenty of N−H···O and C−H···O interactions with neighboring carboxylate oxygen atoms and phosphite oxygen atoms (see Table S4). Weak π···π interactions between neighboring phenyl rings are also observed (see Table S5). N2 sorption/desorption analyses were carried out to examine the porosity of compound 1 at 77 K. It shows typical type-I gas uptake isotherms (see Figure S2). The total N2 uptake and BET surface area are determined to be 19.925 cm3 g−1 (STP) and 17.701 m2 g−1, respectively. Compound 1 is thermal stable up to 280 °C (see Figure S3). Upon further heating, two overlapping weight losses (69.4%) occur in the range of 280−600 °C, corresponding to the removal of one dicarboxylate ligand and two protonated dimethylamine molecules in each formula (61.5%). The chemical stability of compound 1 was also investigated by immersing the crystalline samples into water, boiling water, HCl, and NaOH solutions. It was found that it could retain its crystallinity in water for 1 week, boiling water for 2 days (see B
DOI: 10.1021/acs.cgd.8b01517 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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Previous studies have revealed that four possible processes22,23 may lead to luminescence quenching, including collapse of the framework, replacement of the metal ions in the sensor by the analytes, strong interaction between the ions and the framework, and competitive absorption of excitation energy or other excitation energy transfer/distribution processes. To understand the underlying sensing mechanism, further analyses were carried out. First, the PXRD patterns of compound 1 recovered from Fe(NO3)3 or K2Cr2O7 aqueous solutions (5 mg of compound 1 dispersed in 5 mL of 10−3 M solutions for 6 h) are in good accordance with the simulated pattern (Figure S6), suggesting the luminescence quenching is not incurred by the destruction of the crystal framework. Second, the ICP measurements show that the concentrations of Zn2+ ions in the supernatants of 10 mg of compound 1 dispersed in 10 mL of Fe3+ and Cr2O72− solutions for 6 h are negligible (1.24 and 0.66 mg/L, respectively) compared with the element content (173.12 mg/L) in compound 1. Therefore, it can be concluded that there is no ion exchange between Fe3+/Cr2O72− and Zn2+ ions in the examined time period. Third, no obvious difference can be observed between the IR spectra of original 1 and 1 recovered from Fe(NO3)3 or K2Cr2O7 aqueous solutions (10−3 M) (see Figure S7), suggesting no detectable interaction between the target ions and the framework or formation of new chemical bonding. Finally, the UV−vis absorption spectra of compound 1, Fe3+, and Cr2O72− aqueous solutions were measured and are shown in Figure S8. Intense absorptions can be observed for Fe3+ and Cr2O72− solutions in the range of 200−450 nm, which have overlapping range with the absorption spectrum of compound 1. The energy transfer to the emissive segment would be interrupted by Fe3+ and Cr2O72−. Therefore, the remarkable fluorescence quenching observed for Fe3+ and Cr2O72− ions could be ascribed to their strong absorption of energy.17 In summary, one highly stable MOF compound has been synthesized from the assembly of inorganic zinc phosphite layers and organic rigid dicarboxylic linkers. It shows excellent thermal stability and good resistance to aqueous solutions in the pH range of 3−11. It can behave as a luminescent sensor toward Fe3+ and Cr2O72− with high selectivity. This work presents a new method for the development of stable MOF materials.
Figure 3. Luminescence intensity comparison of the dispersions of 1 in different aqueous solutions of metal ions (a) or anions (d). Emission spectra of compound 1 after gradual addition of Fe3+ (b) or Cr2O72− solutions (e). Stern−Volmer plot of compound 1 with the addition of Fe3+ (c) or Cr2O72− (f) in water.
concentration of Fe3+ as shown in Figure 3(c). It is clear that the I0/(I − 1) value shows a good linear relationship with Fe3+ concentration in the range of 2.25−30 μM (R2 = 0.9974). The KSV is calculated to be 3.96 × 105 M−1, suggesting a strong quenching effect on luminescence. The detection limit is 1.16 × 10−4 mM (Table S6), which is comparable with those of other luminescent sensors of Fe3+ ions.17,18 The sensing property of compound 1 toward various anions (NO3−, IO3−, BrO3−, SO42−, I−, Br−, Cl−, F−, and Cr2O72−, as potassium salts) was also tested. The suspension was prepared by adding 2 mg of powder 1 into 2 mL aqueous solutions of different anions (10−3 M). From Figure 3(d), it is clear that compound 1 shows a selective quenching response toward Cr2O72− but has no remarkable response to other anions. Titration experiments were also conducted by gradual addition of Cr2O72− solution to the suspension of 2 mg of compound 1 in 2 mL of water. The emission intensity of the suspension decreases gradually with the addition of Cr2O72− in the range of 0−300 μL. The linear fit of (I0/I − 1) to the micromolar concentration of Cr2O72− shows a good linear dependence in the concentration range of 2.25−40 μM and reveals a correlation coefficient of 0.9981 and a KSV value of 4.44 × 104 M−1. The detection limit is determined to be 1.09 × 10−3 mM (Table S6), which is also comparable to those of some luminescent sensors of the Cr2O72− anion reported in the literature.19−21
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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.cgd.8b01517. Experimental details, crystal parameters, XRD patterns, weak interactions, BET isotherms, and IR and UV−vis spectra (PDF) Accession Codes
CCDC 1865374 contains 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]. C
DOI: 10.1021/acs.cgd.8b01517 Cryst. Growth Des. XXXX, XXX, XXX−XXX
Crystal Growth & Design
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ORCID
(16) Sahoo, S. K.; Sharma, D.; Bera, R. K.; Crisponi, G.; Callan, J. F. Iron(III) selective molecular and supramolecular fluorescent probes. Chem. Soc. Rev. 2012, 41, 7195−7227. (17) Fan, K.; Bao, S.-S.; Nie, W.-X.; Liao, C.-H.; Zheng, L.-M. Iridium(III)-Based Metal−Organic Frameworks as Multiresponsive Luminescent Sensors for Fe3+, Cr2O72−, and ATP2− in Aqueous Media. Inorg. Chem. 2018, 57, 1079−1089. (18) Zhang, Q.; Wang, J.; Kirillov, A. M.; Dou, W.; Xu, C.; Xu, C.; Yang, L.; Fang, R.; Liu, W. Multifunctional Ln−MOF Luminescent Probe for Efficient Sensing of Fe3+, Ce3+, and Acetone. ACS Appl. Mater. Interfaces 2018, 10, 23976−23986. (19) Lv, R.; Wang, J.; Zhang, Y.; Li, H.; Yang, L.; Liao, S.; Gu, W.; Liu, X. An amino-decorated dual-functional metal-organic framework for highly selective sensing of Cr(III) and Cr(VI) ions and detection of nitroaromatic explosives. J. Mater. Chem. A 2016, 4, 15494−15500. (20) Liu, J.; Ji, G.; Xiao, J.; Liu, Z. Ultrastable 1D europium complex for simultaneous and quantitative sensing of Cr(III) and Cr(VI) ions in aqueous solution with high selectivity and sensitivity. Inorg. Chem. 2017, 56, 4197−4205. (21) Gu, T.; Dai, M.; Young, D. J.; Ren, Z.; Lang, J. Luminescent Zn(II) coordination polymers for highly selective sensing of Cr(III) and Cr(VI) in water. Inorg. Chem. 2017, 56, 4668−4678. (22) Mahata, P.; Mondal, S. K.; Singha, D. K.; Majee, P. Luminescent rare-earth-based MOFs as optical sensors. Dalton Trans 2017, 46, 301−328. (23) Wen, G.; Wu, Y.; Dong, W.; Zhao, J.; Li, D.; Zhang, J. An ultrastable europium(III)−organic framework with the capacity of discriminating Fe2+/Fe3+ ions in various solutions. Inorg. Chem. 2016, 55, 10114−10117.
Si-Fu Tang: 0000-0002-7151-9876 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors acknowledge financial support from the Natural Science Foundation of China (No. 21171173) and the Advanced Talents Foundation of Qingdao Agricultural University.
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REFERENCES
(1) Li, J.-R.; Sculley, J.; Zhou, H.-C. Metal−Organic Frameworks for Separations. Chem. Rev. 2012, 112, 869−932. (2) Cui, Y.; Yue, Y.; Qian, G.; Chen, B. Luminescent Functional Metal−Organic Frameworks. Chem. Rev. 2012, 112, 1126−1162. (3) Kreno, L. E.; Leong, K.; Farha, O. K.; Allendorf, M.; Van Duyne, R. P.; Hupp, J. T. Metal−Organic Framework Materials as Chemical Sensors. Chem. Rev. 2012, 112, 1105−1125. (4) Zhu, L.; Liu, X.-Q.; Jiang, H.-L.; Sun, L.-B. Metal−Organic Frameworks for Heterogeneous Basic Catalysis. Chem. Rev. 2017, 117, 8129−8176. (5) Burtch, N. C.; Jasuja, H.; Walton, K. S. Water Stability and Adsorption in Metal−Organic Frameworks. Chem. Rev. 2014, 114, 10575−10612. (6) Wang, B.; Lv, X.-L.; Feng, D.; Xie, L. H.; Zhang, J.; Li, M.; Xie, Y.; Li, J.-R.; Zhou, H.-C. Highly Stable Zr(IV)-Based Metal−Organic Frameworks for the Detection and Removal of Antibiotics and Organic Explosives in Water. J. Am. Chem. Soc. 2016, 138, 6204− 6216. (7) Herm, Z. R.; Wiers, B. M.; Mason, J. A.; van Baten, J. M.; Hudson, M. R.; Zajdel, P.; Brown, C. M.; Masciocchi, N.; Krishna, R.; Long, J. R. Separation of Hexane Isomers in a Metal-Organic Framework with Triangular Channels. Science 2013, 340, 960−964. (8) Wang, C.-M.; Lin, Y.-J.; Pan, M.-F.; Su, C.-K.; Lin, T.-Y. A Highly Stable Framework of Crystalline Zinc Phosphite with Selective Removal, Recovery, and Turn-On Sensing Abilities for Mercury Cations in Aqueous Solutions. Chem. - Eur. J. 2018, 24, 9729−9734. (9) Wang, C.-M.; Pan, M.-F.; Chen, Y.-C.; Lin, H.-M.; Chung, M.Y.; Wen, Y.-S.; Lii, K.-H. Two Polymorphs of an Organic− Zincophosphate Incorporating a Terephthalate Bridging Ligand in an Unusual Bonding Mode. Inorg. Chem. 2017, 56, 7602−7605. (10) Wang, C.-M.; Pan, M.-F.; Lin, Y.-J.; Chung, M.-Y.; Wen, Y.-S.; Chang, Y.; Lin, H.-M.; Hsu, T. A Series of Organic−Inorganic Hybrid Zinc Phosphites Containing Extra-Large Channels. Inorg. Chem. 2018, 57, 2390−2393. (11) Wang, G.-M.; Zhao, X.-M.; Zhang, X.; Bao, Z.-Z. The inorganic−organic hybrid zinc phosphite poly[(μ3-hydrogen phosphito-κ3O:O’:O’’)(piperidin-1-ium-4-carboxylate-κO)zinc(II)]. Acta Crystallogr., Sect. C: Struct. Chem. 2014, C70, 289−291. (12) Ni, A.-Y.; Mu, Y.; Pan, J.; Han, S.-D.; Shang, M.-M.; Wang, G.M. An organic−inorganic hybrid zinc phosphite framework with room temperature phosphorescence. Chem. Commun. 2018, 54, 3712− 3714. (13) Sun, D.; Han, L.-L.; Yuan, S.; Deng, Y.-K.; Xu, M.-Z.; Sun, D.-F. Four New Cd(II) Coordination Polymers with Mixed Multidentate N-Donors and Biphenyl-Based Polycarboxylate Ligands: Syntheses, Structures, and Photoluminescent Properties. Cryst. Growth Des. 2013, 13, 377−385. (14) He, X.; Lu, X.-P.; Li, M.-X.; Morris, R. E. Tuning Different Kinds of Entangled Networks Formed by Isomers of Bis(1,2,4-triazol1-ylmethyl)benzene and a Flexible Tetracarboxylate Ligand. Cryst. Growth Des. 2013, 13, 1649−1654. (15) Zhang, X.; Wang, Z.-J.; Chen, S.-G.; Shi, Z.-Z.; Chen, J.-X.; Zheng, H.-G. Cd-Based metal−organic frameworks from solvothermal reactions involving in situ aldimine condensation and the highly sensitive detection of Fe3+ ions. Dalton Trans 2017, 46, 2332−2338. D
DOI: 10.1021/acs.cgd.8b01517 Cryst. Growth Des. XXXX, XXX, XXX−XXX
