Article pubs.acs.org/IC
Adsorption of Iodine Based on a Tetrazolate Framework with Microporous Cages and Mesoporous Cages Zhi-Qiang Jiang,†,‡ Fei Wang,† and Jian Zhang*,† †
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 35002, China ‡ Deep-Processing of Fine Flake Grapgite Sichuan Province Key Laboratory of Colleges and Universities, Panzhihua University, Panzhihua, Sichuan 617000 China S Supporting Information *
ABSTRACT: A three-dimensional tetrazolate framework was synthesized with solvothermal reaction. Single-crystal X-ray diffraction analysis shows that the framework is fabricated by a microporous cage (1.35 nm) and mesoporous cage (2.85 nm) via vertex-sharing packing mode. This compound shows permanent porosity and excellent performance of absorbing iodine.
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INTRODUCTION Iodine has become an increasingly important component and is in great demand on account of its essential role in the fields of bioscience, environmental chemistry, functional materials, and so on.1,2 As 129I is one kind of important radioactive element, the emission of 129I from the developing nuclear industry leads to serious environmental pollution. For this reason, the study of adsorption of iodine has received increasing attention and is more significant. Some porous materials, including activated carbons, porous silicas, and organic polymers, have been used to adsorb iodine species.3 The porosity of activated carbon and porous silica is usually determined by their physical or chemical synthetic methods, while the structure of organic polymer is affected by some related monomers. Therefore, the pores of these materials are not regular. Recently, porous metal−organic frameworks (MOFs) with high specific surface area, unique architecture, controlled pore size, and regular pore shape have been developed, which display potential applications in the fields of sorption/separation, catalysis, luminescence, etc.4,5 In particular, employing a polyhedron-like cage as a building block to fabricating a new type of MOFs is of great interest and a daunting challenge because of their intriguing structure, satisfying stability, and exciting property.6,7 Although the reports are still limited, MOFs have also been paid some attention for the enrichment and release of iodine.8 The 1,3,5-benzenetricarboxylate (btc) ligand is usually used to form three-dimensional (3D) MOFs with large surface area.9 In many cases, a secondary ligand is often used to construct new MOFs based on the btc ligand. However, the auxiliary ligand should be relatively short and curved with the purpose of forming a cage structure. According to the analysis, the btc mixing azole ligand is an effective © XXXX American Chemical Society
strategy for building cage-based structure to enrich or encapsulate some guest molecules.10 In this work, we employ Zn2+ ion, 5-amino-tetrazole, and 1,3,5-benzenetricarboxylic acid as linkers to assemble a (3,4)connencted anionic MOF, namely, Zn9(btc)4(atz)12 (1, atz = 5amino-tetrazole). Notably, the 1.35 nm octahedral microporous cages and 2.85 nm octahedral mesoporous cages adopt a vertexsharing packing mode to form a 3D porous framework with effective iodine adsorption.
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EXPERIMENTAL SECTION
Materials and Instrumentation. All reagents were purchased commercially and used without further purification. Single-crystal Xray diffraction data were collected on a Smart Apex II single-crystal diffractometer with graphite-monochromatic Mo Kα (λ = 0.71073 Å) at room temperature. The structure was solved by the direct method and refined on F2 by full-matrix least-squares methods using the SHELX-2014 program package. X-ray powder diffraction (XRD) analysis was finished on a MiniFlex-II diffractometer with Cu Kα radiation (λ = 1.54056 Å) with a step size of 1°. A thermal stability study was performed on a NETSCHZ STA-449C thermoanalyzer with a heating rate of 15 °C/min under an N2 atmosphere. The adsorption experiments were performed on a Micromeritics ASAP 2020 surface area and pore size analyzer. Synthesis of Compound 1. A mixture of 5-amino tetrazole (atz, 0.0200g, 0.22 mmol), Zn(NO3)2·6H2O (0.1600g, 0.55 mmol), pyrazine(0.0300g, 0.37 mmol), 1,3,5-benzenetricarboxylic acid (btc, 0.1400g, 0.45 mmol), tetraethylammonium bromide (TEA, 0.1200g, 0.57 mmol), ethanolamine (1.0000g, 16 mmol), N,N-dimethylacetamide (DMA, 6 mL), and methanol (3 mL) was stirred for 20 min, transferred into the oven of 120 °C for 5 days, and then cooled to room temperature. The resulting colorless transparent crystals were Received: November 7, 2016
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DOI: 10.1021/acs.inorgchem.6b02696 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry obtained, washed with DMA and methanol, and dried at room temperature. Crystal Data for 1. Space group Fd-3, cubic, a = 41.393(2) Å, V = 70922(6) Å3, T = 293(2) K, Z = 48, 9 0347 reflections measured, 6645 independent reflections (Rint = 0.1172). The final R1 value was 0.1444 (I > 2σ(I)). The final wR(F2) value was 0.4236 (I > 2σ(I)). The goodness of fit on F2 was 1.909. The structure was solved by the direct method and refined by full-matrix least-squares on F2 using the SHELXTL-2014 program. Crystallographic data have been submitted to the Cambridge Structural Database with deposition number CCDC 1498404.
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RESULTS AND DISCUSSION Single crystals of 1 were prepared by the solvothermal reaction of Zn(NO3)2·6H2O, btc, atz, pyrazine, TEA, and ethanolamine in mixed N,N-dimethylacetamide (DMA) and methanol solvent at 120 °C for 5 days. Single-crystal X-ray diffraction was used to determine the structural feature of 1, and the disordered dissociative molecules within the framework were removed by employing the SQUEEZE program of PLATON. Powder X-ray diffraction (PXRD) revealed the purity, while thermogravimetric analysis (TGA) characterized the thermal stability of 1. The result of single-crystal X-ray diffraction measurement shows that compound 1 has high symmetry in cubic Fd3̅. As depicted in Figure 1, although both two Zn atoms adopt
Figure 2. Two kinds of octahedral cages and the corresponding topological sketch in 1: (a and b) 1.35 nm octahedral microporous cage; (c and d) 2.85 nm octahedral mesoporous cage.
Figure 1. Coordination environment of the Zn atom and bridging mode of atz and btc ligands in 1. Hydrogen atoms were omitted for clarity.
tetrahedral coordination modes, their coordination environments are entirely different. The Zn1 atom links three atz ligands and one btc ligand, while the Zn2 center is tetrahedrally coordinated by two oxygen atoms from two btc ligands and two nitrogen atoms from two atz ligands. In the structure of 1, four btc ligands bridge six Zn2 centers to form an interestingly octahedral microporous cage with the vertex distance being 1.35 nm (Figure 2a and 2b). It is worth noting that 6 Zn2 centers as the vertex are connected by 36 atz linkers, 4 btc linkers, and 24 Zn1 atoms, which leads to a bigger octahedral mesoporous cage. The size of this mesoporous cage is about 2.85 nm (Figure 2c and 2d). Except for the disordered dissociative organic cations and solvent molecules, the inner space is unoccupied by coordinated molecules, which is perhaps beneficial to absorb or encapsulate other components. Therefore, compound 1 has a large pore void comprising ∼62.7% of the cell volume as estimated by PLATON. As depicted in Figure 3a, two neighboring microporous cages that share the vertexes of the same mesoporous cage link microporous cage and mesoporous cage along the vertical direction. Other cages without a sharing vertex were bridged by
Figure 3. (a, b) Connected mode of cages without sharing vertex and its extension along the same direction; (c) vertex-sharing packing mode between microporous cage and mesoporous cage in 1; (d) view of new topology of 1.
Zn1 atoms and atz ligands (Figure 3b). Both a microporous cage and a mesoporous cage use Zn2 as the vertex of the octahedron (Figure 3c), which resulted in one mesoporous cage bridging six microporous cages in vertex-sharing fashion and generated an unusual 3D framework. From the viewpoint of structural topology, if the btc ligand is reduced as a 3connected node and 4-coordinate zinc center is looked at as a 4-connected node, the resulted 3D framework displays a (3,4)connected topology with a vertex symbol of (63)4(66)9 (Figure 3d), which is unknown in previously reported MOFs. The as-synthesized sample of 1 was immersed in dichloromethane (CH2Cl2) at ambient temperature for 72 h to B
DOI: 10.1021/acs.inorgchem.6b02696 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
To investigate the performance of absorbing I2, 100 mg of single crystals of 1 was immersed in a cyclohexane solution of I2 (0.1 M/L) in a sealed vial at ambient temperature. As shown in Figure 5a, the crystal slowly changed color from colorless to dark brown, while solutions of I2 also gradually changed its color from dark red to pale brown. The mass of compound 1 after loading iodine increased by ca. 39.5 wt %, which is slightly above that of zeolite 13X (0.32−0.38) and below those of activated carbon and some MOFs.8a,d,11 Notably, this kind of I2 adsorption process is invertible. The loaded I2 can easily be released from compound 1 when the I2-loaded single crystals are soaked in organic solvents, which is proved by the change that the color of the EtOH sequentially varied from colorless to pale brown (Figure 5b). To further investigate the releasing process of I2 from the crystals with a nonaqueous solution, very little I2-loaded single crystals of 1 were placed in 9 mL of ethanol, and the iodine content is estimated by UV−vis spectroscopy at room temperature with time over the first 1 h (Figure 5c). The absorbance of I2 extracted into ethanol at 204, 288, and 360 nm normally increases within 1 h. Complete release of I2 lasts 1.5 h and then reaches a dynamic equilibrium.
exchange high boiling point solvent molecules, followed by evacuation at 40 °C for 24 h, which resulted in an entirely hollow compound 1 for gas-adsorption measurement. The structural integrity was measured by PXRD, while the TGA measurement was carried out for proving that full activation was achieved (Figures S1 and S2). For activated sample, almost all of the diffraction peaks can be well matched with the simulated signals, proving that the integrity of framework of 1 was well retained. The TGA curves for fresh and activated samples display a similar process of weight loss. The first weight loss belongs to removing the free solvents. The second process from 200 to 300 °C may be assigned to loss of the organic cations. Then the weight loss is due to decomposition of the organic ligands, accompanying the collapse of the whole framework. To confirm the permanent porosity, gas-adsorption measurements (N2, CO2) of 1 were accomplished on a Micromeritics ASAP 2020 surface-area and pore-size analyzer. The CH2Cl2 activated samples of 1 were degassed at 60 °C until no further reducing weight. The N2 adsorption/desorption studies reveal that compound 1 has a reversible type-I isotherm, which demonstrates that there are micropores in 1. The Brunauer− Emmett−Teller and Langmuir surface areas for 1 are 229.7 and 321.7 m2·g−1, respectively (Figure 4). The adsorption isotherm of CO2 for 1 was performed up to 1 bar at 0 °C, and the adsorptive quantity is 27 cm3·g−1 (Figure S3).
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CONCLUSIONS In summary, we employ 5-amino tetrazole as an auxiliary ligand with 1,3,5-benzenetricarboxylic acid to assemble a threedimensional tetrazolate framework. It shows that a microporous cage (1.35 nm) and a mesoporous cage (2.85 nm) share the same vertex to generate a porous structure, which displays outstanding performance of enriching iodine.
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02696. TGA plot, powder X-ray diffraction, CO2 sorption isotherm, pore size distribution (PDF) (CIF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Fax: (+86)-591-83714946. Phone: (+86)-591-83715030.
Figure 4. N2 sorption isotherms (■, adsorption; □, desorption) of 1 at 77 K.
ORCID
Fei Wang: 0000-0001-8432-0009
Figure 5. (a) Photos of I2-absorbed process. (b) Photos of I2-released process of 1 (10 mg) immersed in 1.5 mL of EtOH. (c) Temporal evolution of absorbance for the I2-released process from 1 in 9 mL of EtOH. C
DOI: 10.1021/acs.inorgchem.6b02696 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
Substitution Strategy for the Preparation of Metal-Organic Polyhedral. Nat. Chem. 2010, 2, 893−898. (8) (a) Zeng, M. H.; Wang, Q. X.; Tan, Y. X.; Hu, S.; Zhao, H. X.; Long, L. S.; Kurmoo, M. Rigid Pillars and Double Walls in a Porous Metal-Organic Framework: Single-Crystal to Single-Crystal, Controlled Uptake and Release of Iodine and Electrical Conductivity. J. Am. Chem. Soc. 2010, 132, 2561−2563. (b) Liu, Q. K.; Ma, J. P.; Dong, Y. B. Highly Efficient Iodine Species Enriching and Guest-Driven Tunable Luminescent Properties Based on a Cadmium(II)-Triazole MOF. Chem. Commun. 2011, 47, 7185−7187. (c) Yin, Z.; Wang, Q. X.; Zeng, M. H. Iodine Release and Recovery, Influence of Polyiodide Anions on Electrical Conductivity and Nonlinear Optical Activity in an Interdigitated and Interpenetrated Bipillared-Bilayer Metal-Organic Framework. J. Am. Chem. Soc. 2012, 134, 4857−4863. (d) Cui, P.; Ren, L.; Chen, Z.; Hu, H.; Zhao, B.; Shi, W.; Cheng, P. TemperatureControlled Chiral and Achiral Copper Tetrazolate Metal-Organic Frameworks: Syntheses, Structures, and I2 Adsorption. Inorg. Chem. 2012, 51, 2303−2310. (e) He, J.; Duan, J. J.; Shi, H. T.; Huang, J.; Huang, J. H.; Yu, L.; Zeller, M.; Hunter, A. D.; Xu, Z. T. Immobilization of Volatile and Corrosive Iodine Monochloride (ICl) and I(2) Reagents in a Stable Metal-Organic Framework. Inorg. Chem. 2014, 53, 6837−6843. (9) (a) Chui, S. S. Y.; Lo, S. M. F.; Charmant, J. P. H.; Orpen, A. G.; Williams, I. D. A Chemically Functionalizable Nanoporous Material. Science 1999, 283, 1148−1150. (b) Yang, H.; Wang, F.; Tan, Y. X.; Kang, Y.; Li, T. H.; Zhang, J. Charge Matching on Designing Neutral Cadmium-Lanthanide-Organic Open Frameworks for Luminescence Sensing. Chem. - Asian J. 2012, 7, 1069−1073. (10) (a) Liu, Z. Y.; Zou, H. A.; Hou, Z. J.; Yang, E. C.; Zhao, X. J. Structural Motif-Dependent Magnetic Diversity Observed in ThreeDimensional Tetrazolyl-Based MMOFs: Synthesis, Structures and Magnetism. Dalton Trans. 2013, 42, 15716−15725. (b) Wang, F.; Fu, H. R.; Hou, D. C.; Zhang, J. Assembly of Four Kinds of Cages into Porous Metal-Organic Framework for Selective Sorption of Light Hydrocarbons. Cryst. Growth Des. 2014, 14, 6467−6471. (c) Cai, H.; Li, M.; Lin, X. R.; Chen, W.; Chen, G. H.; Huang, X. C.; Li, D. Spatial, Hysteretic, and Adaptive Host-Guest Chemistry in a Metal-Organic Framework with Open Watson-Crick Sites. Angew. Chem., Int. Ed. 2015, 54, 10454−10459. (11) Murthi, M.; Snurr, R. Q. Effects of Molecular Siting and Adsorbent Heterogeneity on the Ideality of Adsorption Equilibria. Langmuir 2004, 20, 2489−2497.
Jian Zhang: 0000-0003-3373-9621 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We are thankful for the support of this work by NSFC (21425102, 21573236), Open Foundation of State Key Laboratory of Structural Chemistry (20150012), and Science and Technology Planning Project in Sichuan Province and Panzhihua City (2014GZ0030, 2015RZ0029, 2014CY-G-24, 2016CY-G-4).
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REFERENCES
(1) Carpenter, L. J. Iodine in the Marine Boundary Layer. Chem. Rev. 2003, 103, 4953−4962. (2) Huang, R. J.; Hoffmann, T. Development of a Coupled Diffusion Denuder System Combined with Gas Chromatography/Mass Spectrometry for the Separation and Quantification of Molecular Iodine and the Activated Iodine Compounds Iodine Monochloride and Hypoiodous Acid in the Marine Atmosphere. Anal. Chem. 2009, 81, 1777−1783. (3) (a) Hu, J. M.; Zhai, J. P.; Wu, F. M.; Tang, Z. K. Molecular Dynamics Study of the Structures and Dynamics of the Iodine Molecules Confined in AlPO(4)-11 Crystals. J. Phys. Chem. B 2010, 114, 16481−16486. (b) Hayakawa, C.; Urita, K.; Ohba, T.; Kanoh, H.; Kaneko, K. Physico-Chemical Properties of Iodine-Adsorbed SingleWalled Carbon Nanotubes. Langmuir 2009, 25, 1795−1799. (c) Sava, D. F.; Rodriguez, M. A.; Chapman, K. W.; Chupas, P. J.; Greathouse, J. A.; Crozier, P. S.; Nenoff, T. M. Capture of Volatile Iodine, a Gaseous Fission Product, by Zeolitic Imidazolate Framework-8. J. Am. Chem. Soc. 2011, 133, 12398−12401. (4) (a) Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae, T. H.; Long, J. R. Carbon Dioxide Capture in Metal-Organic Frameworks. Chem. Rev. 2012, 112, 724− 781. (b) Liu, J. W.; Chen, L. F.; Cui, H.; Zhang, J. Y.; Zhang, L.; Su, C. Y. Applications of Metal-Organic Frameworks in Heterogeneous Supramolecular Catalysis. Chem. Soc. Rev. 2014, 43, 6011−6061. (c) Cui, P.; Hu, H. S.; Zhao, B.; Miller, J. T.; Cheng, P.; Li, J. A Multicentre-bonded [Zn(I)]8 Cluster with Cubic Aromaticity. Nat. Commun. 2015, 6, 6331. (d) Hu, H. C.; Hu, H. S.; Zhao, B.; Cui, P.; Cheng, P.; Li, J. Metal-Organic Frameworks (MOFs) of a Cubic Metal Cluster with Multicentered Mn(I)-Mn(I) Bonds. Angew. Chem., Int. Ed. 2015, 54, 11681−11685. (e) Gu, Z. G.; Zhan, C. H.; Zhang, J.; Bu, X. H. Chiral Chemistry of Metal-Camphorate Frameworks. Chem. Soc. Rev. 2016, 45, 3122−3144. (5) (a) Cui, Y. J.; Yue, Y. F.; Qian, G. D.; Chen, B. L. Luminescent Functional Metal-Organic Frameworks. Chem. Rev. 2012, 112, 1126− 1162. (b) Li, J. R.; Sculley, J.; Zhou, H. C. Metal-Organic Frameworks for Separations. Chem. Rev. 2012, 112, 869−932. (c) Lu, H. S.; Bai, L.; Xiong, W. W.; Li, P.; Ding, J.; Zhang, G.; Wu, T.; Zhao, Y.; Lee, J.; Yang, Y.; Geng, B.; Zhang, Q. Surfactant Media to Grow New Crystalline Cobalt 1,3,5-Benzenetricarboxylate Metal-Organic Frameworks. Inorg. Chem. 2014, 53, 8529−8537. (6) (a) Zheng, S. T.; Bu, J. T.; Li, Y.; Wu, T.; Zuo, F.; Feng, P. Y.; Bu, X. H. Pore Space Partition and Charge Separation in Cage-within-cage Indium-Organic Frameworks with High CO2 Uptake. J. Am. Chem. Soc. 2010, 132, 17062−17064. (b) Zheng, S. T.; Wu, T.; Irfanoglu, B.; Zuo, F.; Feng, P. Y.; Bu, X. H. Multicomponent Self-Assembly of a Nested Co24@Co48 Metal-Organic Polyhedral Framework. Angew. Chem., Int. Ed. 2011, 50, 8034−8037. (7) (a) Li, J. R.; Timmons, D. J.; Zhou, H. C. Interconversion between Molecular Polyhedra and Metal-Organic Frameworks. J. Am. Chem. Soc. 2009, 131, 6368−6369. (b) He, Q. T.; Li, X. P.; Liu, Y.; Yu, Z. Q.; Wang, W.; Su, C. Y. Copper(I) Cuboctahedral Coordination Cages: Host-Guest Dependent Redox Activity. Angew. Chem., Int. Ed. 2009, 48, 6156−6159. (c) Li, J. R.; Zhou, H. C. Bridging-LigandD
DOI: 10.1021/acs.inorgchem.6b02696 Inorg. Chem. XXXX, XXX, XXX−XXX
