DOI: 10.1002/chem.201405676
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& Synthetic Methods
Organic–Inorganic Hybrid Zinc Phosphate with 28-Ring Channels Chih-Min Wang,*[a] Li-Wei Lee,[c] Tsung-Yuan Chang,[b] Yen-Chieh Chen,[a] Hsiu-Mei Lin,[b] Kuang-Lieh Lu,[c] and Kwang-Hwa Lii*[a, c] Abstract: An organic–inorganic hybrid zinc phosphate with 28-ring channels was synthesized by use of an organic ligand instead of organic amine template under a hydro(solvo)thermal condition. This crystalline zinc phosphate contains large channels constructed from 28 zinc and phosphate tetrahedral units. The walls of the channels consist of two types of zincophosphate chains, in which the Zn atoms are coordinated by 2,4,5-tri(4-pyridyl)-imidazole ligands as pendent groups. This compound exhibits yellow emission and interesting properties of removing cobalt, cadmium, and mercury cations from aqueous solution. A new two-dimensional organic–inorganic hybrid zincophosphate was also obtained by changing the solvent mixture ratios in the synthesis.
The discovery of iron phosphates and aluminophosphates, such as cacoxenite and VPI-5, has inspired researchers to synthesize new crystalline open-framework compounds with large structural channels and pores.[1, 2] These compounds are interesting not only because of rich structural chemistry but also potential applications in ion exchange, gas storage, catalysis, and luminescence.[1–3] Many approaches toward the design and synthesis of inorganic frameworks have been explored; however, compounds containing extra-large channels are still limited.[2, 4, 6–8] In comparison with metal–organic frameworks (MOFs), the inorganic building units comprising various geometric polyhedra, flexible coordination behaviors, and assorted connectivities make the synthesis of inorganic frameworks with large pore sizes and channels difficult. One of the synthesis methods to prepare materials with open framework structures is the template-directed synthesis based on the charge density matching of the organic ammonium ions and the inorganic frameworks. In the liquid-crystal templating concept, organic ammonium molecules assemble as a central structure, [a] Dr. C.-M. Wang, Y.-C. Chen, Prof. K.-H. Lii Department of Chemistry National Central University, Jhongli, 320 (Taiwan) E-mail: [email protected] [email protected] [b] T.-Y. Chang, Prof. H.-M. Lin Institute of Optoelectronic Sciences National Taiwan Ocean University, Keelung, 202 (Taiwan) [c] L.-W. Lee, Prof. K.-L. Lu, Prof. K.-H. Lii Institute of Chemistry, Academia Sinica, Nankang, Taipei, 115 (Taiwan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201405676. Chem. Eur. J. 2015, 21, 1878 – 1881
around which inorganic units grow, resulting in the formation of nanostructured materials.[5] The landmark structures in the presence of organic amines as templates exhibit a very large channel opening of 72-membered rings (72 MR) in phosphites,[6] 30 MR in germanates,[7] 18 MR in silicates,[2] and 24 MR in metal phosphates.[8] The structural building unit of phosphites, HPO32, may reduce the M-O-P connectivity and lead to the formation of more open, interrupted structures. In the structure of the gallophosphate with extra-large 24 ring channels, [Ga2(DETA)(PO4)2]·2 H2O (DETA = diethylenetriamines), the organic amine plays an interrupted role of binding in a tridentate fashion to the Ga atoms. Herein, we report a new organic–inorganic hybrid zinc phosphate with 28 ring channels, Zn5(H2L)(HPO4)3(PO4)2·3.5 H2O (denoted as NCU-1; L = 2,4,5-tri(4pyridyl)-imidazole).[9] This finding not only enlarges the maximum channel size of a metal phosphate from 24 to 28 MR but also provides a new route for the synthesis of inorganic frameworks with large channels through the use of organic amine ligands instead of amine templates. Typically, organic ligands as linkers bind to central metal atoms to form coordination compounds, whereas organic amines are as space-filling counterions or structure-directing agents in the formation of porous materials. A new layered compound, Zn2(HL)(HPO4)(PO4)·4 H2O (NCU-1 a), was also obtained under the same reaction conditions as those for NCU-1, except that the solvent mixture ratio was different. This work reports the synthesis, structural diversity in different solvent mixture ratios, and photoluminescence properties of NCU-1, as well as its ability to remove metal cations from aqueous solutions. Orange needle-like crystals of NCU-1 were obtained by heating a mixture of Zn(NO3)2·6 H2O (0.5 mmol), 2,4,5-tri(4-pyridyl)imidazole (0.2 mmol), HF(aq.) (0.4 mmol, 48 % solution), H3PO4 (3 mmol), dimethylformamide (0.5 mL), and H2O (1.5 mL) under hydro(solvo)thermal reaction conditions at 150 8C for two days. The X-ray powder-pattern data of the bulk product is in good agreement with the calculated pattern for NCU-1 based on the structure analysis results from single-crystal X-ray diffraction (Figure S1 in the Supporting Information). The yield was 81 % based on Zn. The elemental analysis results were consistent with the formula Zn5(H2L)(HPO4)3(PO4)2·3.5 H2O (elemental analysis calcd (%): C 18.49, H 2.16, N 5.99; found: C 18.36, H 2.16, N 5.88). The structure of NCU-1 is a close-packed array of channels of 28 MR in an elliptical shape, which are constructed from four ZnO3N tetrahedra, ten ZnO4 tetrahedra, six phosphate groups, and eight hydrogen phosphate units (Figures 1 and S2 in the Supporting Information). The P(1) and P(4) atoms are both bonded to four Zn atoms through four oxygen atoms,
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Figure 2. Two types of chains in NCU-1: a) the inorganic 1[Zn4(HPO4)2(PO4)] + chain with three-, four-, and six-membered rings; b) the organic–inorganic hybrid 1[Zn(H2L)(HPO4)(PO4)] chain. Blue and black circles represent N and C atoms, respectively. The H atoms are omitted for clarity.
Figure 1. Perspective view of the inorganic framework of NCU-1 along the a axis, showing 28 MR channels. The H atoms, water, and organic molecules are omitted for clarity in the plot. The ZnO3N and ZnO4 tetrahedra are indicated in yellow; phosphate and hydrogen phosphate units are in green.
and P(2), P(3), and P(5) bridge three Zn atoms through three oxygen atoms with a POH group being directed toward the center of channel. Bond-valence calculations indicated that O(6), O(9), and O(18) are hydroxo oxygen atoms, and the H atoms associated with them could be located in difference Fourier maps. The maximum free atom-to-atom distance across the channel was 23.5 , and the non-framework space within the structure was estimated to be 49.3 % of the unit cell. The framework metal density for NCU-1 was 11.5 M atoms (M = Zn, P) per 1000 3. For comparison, the framework metal densities of several metal phosphates with extra-large channels, such as VPI-5, CLO, ND-1, VSB-5, NTHU-1, and cacoxenite, are 11.8, 14.2, 11.1, 12.1, 18.5, and 10.9, respectively.[2, 4a, 8] The walls of the channels in NCU-1 consist of two kinds of 1D zincophosphate chains through P-O-Zn connections. One kind of chain is the positively charged [Zn4(HPO4)2(PO4)] + chain containing three-, four-, and six-membered rings (Figures 2 a and S3 in the Supporting Information), and the other is an negatively charged organic–inorganic hybrid chain (Figure 2). The 2,4,5-tri(4-pyridyl)-imid1[Zn(H2L)(HPO4)(PO4)] azole ligands coordinate in a monodentate fashion to Zn atoms and extend away from inorganic framework into the intrachannel region as pendent ligands (Figure S4 in the Supporting Information). The distance between the centroids of the rings of adjacent ligands is 5.12 (Figure 2 b). The voids of the channels are filled with water molecules. Interestingly, a new zinc phosphate with a 2 D layer structure, Zn2(HL)(HPO4)(PO4)·4 H2O (NCU-1 a), was synthesized by changing the solvent mixture ratio from 1.5 mL H2O/0.5 mL DMF to 1.5 mL H2O/1.0 mL DMF. The structure of NCU-1 a consists of Chem. Eur. J. 2015, 21, 1878 – 1881
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inorganic chains of zinc phosphate with 4 MR, which are connected by the organic ligands to form an organic–inorganic hybrid sheet (Figure S5 in the Supporting Information).[10] Thermogravimetric analysis of NCU-1 showed a weight loss of 4.92 % between 40 and 200 8C, which is close to the calculated value of 5.39 % for 3.5 H2O molecules per formula unit (Figure S6 in the Supporting Information). The observed total weight loss of 35.72 % between 40 and 1000 8C is close to the calculated value of 34.84 % for the loss of one L ligand and six H2O molecules. The structure of NCU-1 is thermally stable up to 250 8C, as was indicated by the powder X-ray diffraction patterns of the powder samples of NCU-1 after being heated at 100, 200, and 250 8C for 4 h (Figure S7 in the Supporting Information). The as-synthesized and dehydrated powder samples of NCU-1 at different temperatures showed different intensities of yellow luminescence when these powder samples were irradiated with l = 365 nm UV light from a handheld UV lamp. The spectra display broad emission at approximately 540 nm in the range from 450 to 700 nm under excitation at 374 nm. The spectral intensity of the as-synthesized NCU-1 was lower than that of other dehydrated samples, which can be ascribed to the reduction of the quenching effect of water molecules (Figure 3).[11] The development of new materials emitting yellow light is interesting and critical, because combination of yellow-light phosphor and blue-light LED to generate white light is the mainstream of current lighting technology. The yellow emission of phosphate materials may originate from complex processes. Two metal phosphates, NTHU-4 and NTHU6, have been reported to emit yellow light, and their emissions were respectively caused by a defect in the host material and the organic molecules used as a sensitizer to assist energy absorption and transfer.[12] The emission of NCU-1 is redshifted relative to that of the free L ligand (a weak emission band at 520 nm under excitation at 374 nm), therefore, the yellow emission can be related to the intraligand fluorescent emission. Heavy-metal pollutions in wastewater from a variety of industries are easily transported through water into the environment, and these pollutions may cause harmful effects on envi-
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Communication bonded to Zn atoms as pendent groups in the 28 MR channel. The synthesis of NCU-1 not only enlarges the maximum channel size of metal phosphate from 24 to 28 MR, but also provides a new route for the synthesis of inorganic frameworks with large channels by the use of organic amine ligands instead of amine templates. A change of the solvent mixture ratio results in the formation of a new zinc phosphate with 2D layer structure. NCU-1 also exhibits yellow emission and the potential ability to remove cobalt, cadmium, and mercury cations from aqueous solutions. Further research on this theme is in progress.
Experimental Section Figure 3. Luminescence spectra of NCU-1 excited at l = 347 nm. The black, red, and blue curves represent the emission spectra of the as-synthesized compound and the compounds dehydrated at 100 and 200 8C for 2 h, respectively.
ronmental toxicity and human health. Therefore, NCU-1 was explored for the removal of metal ions from aqueous solutions. A powder sample (0.05 g) of NCU-1 was respectively added to 10 mL of 0.01 m aqueous solution of Co(NO3)2, Cd(ClO4)2, and Hg(NO3)2 at room temperature with constant stirring for 1 h. The color of Co(NO3)2 (aq.) changed from deep pink to light pink, indicating that Co2 + cations were partly removed from solution by NCU-1. The solid was separated from the solution by centrifugation. The X-ray powder patterns of the solids showed that their structures were retained (Figure S8 in the Supporting Information). The ICP-OES analysis of the solutions showed that the Co, Cd, and Hg metal contents decreased by 22.42 % (adsorption capacity ca. 1.32 mg g1), 63.38 % (7.12 mg g1), and 80.17 % (16.08 mg g1), respectively. To determine the positions of metal cations in the crystal structure, several single crystals of NCU-1 after being immersed in aqueous solution of Hg(NO3)2 overnight were indexed on a diffractometer, but their peak profiles showed that they were no longer suitable for crystal structure analysis. The non-coordinated N atoms of 2,4,5-tri(4-pyridyl)-imidazole in the wall of NCU-1 may play a key role for the interaction with incoming metal ions. Recently, Tang et al. reported that one MOF compound containing an organic ligand with Lewis basic sites allowed complexation with Lewis acidic analytes.[13] Attempts to synthesize the analogues of NCU-1 by using Co(NO3)2, Cd(ClO4)2, and Hg(NO3)2 instead of Zn(NO3)2·6 H2O in the same synthetic condition were unsuccessful. To the best of our knowledge, all of the previously reported crystalline phosphate materials with extra-large pores ( 20membered rings, 20 MR) were synthesized in the presence of organic amine molecules.[4a, 8] To date, the largest pore size has been 24 MR in nickel, zinc, and gallium phosphates.[8] Instead of using organic amines as templates in the synthesis, we prepared an organic–inorganic hybrid zinc phosphate with 28-ring channels by including large organic linkers in the inorganic framework. The 2,4,5-tri(4-pyridyl)-imidazole ligands are Chem. Eur. J. 2015, 21, 1878 – 1881
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The hydro(solvo)thermal reactions were carried out in Teflon-lined stainless steel Parr acid digestion bombs at 150 8C for 2 d, followed by slow cooling to RT at 6 8C h1. Orange needle-like crystals of NCU-1 were obtained by heating a mixture of Zn(NO3)2·6 H2O (0.5 mmol), 2,4,5-tri(4-pyridyl)-imidazole (0.2 mmol), HF(aq.; 0.4 mmol, 48 % solution), H3PO4 (3 mmol), dimethylformamide (0.5 mL), and H2O (1.5 mL); white plate crystals of NCU-1 a were obtained by heating a mixture of Zn(NO3)2·6 H2O (0.5 mmol), 2,4,5tri(4-pyridyl)-imidazole (0.2 mmol), HF(aq.; 0.4 mmol, 48 % solution), H3PO4 (3 mmol), dimethylformamide (1.0 mL), and H2O (1.5 mL). CCDC-1019899 (NCU-1) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements We thank the Ministry of Science and Technology of Taiwan for financial support (MOST 103-2113-M-008-011-MY2 and NSC 101-2113-M-008-006-MY3), and Dr. Y. S. Wen at the Institute of Chemistry, Academia Sinica for X-ray data collection. Keywords: crystals · hydro(solvo)thermal synthesis · organic– inorganic hybrid composites · phosphorus · zinc
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[1] P. B. Moore, J. Shen, Nature 1983, 306, 356. [2] M. F. Davis, C. Saldarriaga, C. Montes, J. M. Garces, C. Crowder, Nature 1988, 331, 698. [3] a) Q. Hu, R. Xu, S. Li, Z. Ma, J. M. Thomas, R. H. Jones, A. M. Chippindale, Chem. Commun. 1992, 875; b) J. Zhu, X. Bu, P. Feng, G. D. Stucky, J. Am. Chem. Soc. 2000, 122, 11563; c) X. Wang, L. Liu, A. J. Jacobson, Angew. Chem. Int. Ed. 2003, 42, 2044; Angew. Chem. 2003, 115, 2090; d) A. Corma, Chem. Rev. 1997, 97, 2373; e) A. K. Cheetham, G. Frey, T. Loiseau, Angew. Chem. Int. Ed. 1999, 38, 3268; Angew. Chem. 1999, 111, 3466; f) M. E. Davis, Nature 2002, 417, 813; g) S. Natarajan, S. Mandal, Angew. Chem. Int. Ed. 2008, 47, 4798; Angew. Chem. 2008, 120, 4876, and references therein. [4] a) M. Estermann, L. B. McCusker, C. Baerlocher, A. Merrouche, H. Kessler, Nature 1991, 352, 320; b) J. Plvert, T. M. Gentz, A. Laine, H. Li, V. G. Young, O. M. Yaghi, M. O’Keeffe, J. Am. Chem. Soc. 2001, 123, 12706; c) J. Liang, J. Li, J. Yu, P. Chen, Q. Fang, F. Sun, R. Xu, Angew. Chem. Int. Ed. 2006, 45, 2546; Angew. Chem. 2006, 118, 2608; d) Y. L. Lai, K. H. Lii, S. L. Wang, J. Am. Chem. Soc. 2007, 129, 5350; e) J. Jiang, J. L. Jorda, J. Yu, L. A. Baumes, E. Mugnaioli, M. J. Diaz-Cabanas, U. Kolb, A. Corma, Science 2011, 333, 1131. [5] a) B. M. Lok, T. R. Cannon, C. A. Messina, Zeolites 1983, 3, 282; b) E. M. Flanigen, R. L. Patton, S. T. Wison, Stud. Surf. Sci. Catal. 1988, 37, 13; 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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[6] [7]
[8]
[9]
c) A. Sayari, Stud. Surf. Sci. Catal. 1996, 102, 1; d) M. E. Davis, R. F. Lobo, Chem. Mater. 1992, 4, 756. H. Y. Lin, C. Y. Chin, H. L. Huang, W. Y. Huang, M. J. Sie, L. H. Huang, Y. H. Lee, C.-H. Lin, K. H. Lii, X. Bu, S. L. Wang, Science 2013, 339, 811. a) X. Zou, T. Conradsson, M. Klingstedt, M. S. Dadachov, M. O’Keeffe, Nature 2005, 437, 716; b) J. Sun, C. Bonneau, . Cantn, A. Corma, M. J. Daz-CabaÇas, M. Moliner, D. Zhang, M. Li, X. Zou, Nature 2009, 458, 1154. a) G. Y. Yang, S. C. Sevov, J. Am. Chem. Soc. 1999, 121, 8389; b) C. H. Lin, S. L. Wang, K. H. Lii, J. Am. Chem. Soc. 2001, 123, 4649; c) N. Guillou, Q. Gao, P. M. Forster, J. S. Chang, M. Nogus, S. E. Park, G. Frey, A. K. Cheetham, Angew. Chem. Int. Ed. 2001, 40, 2831; Angew. Chem. 2001, 113, 2913. Crystal data for Zn5(H2L)(HPO4)3(PO4)2·3.5 (H2O) (NCU-1): monoclinic, space group P21/n, Z = 4, Mr = 1169.13 g mol1, and a = 5.1242(2), b = 25.0641(14), c = 27.1877(15) , b = 90.940(2)8, V = 3491.3(3) 3, 1calcd = 2.224 g cm3, l = 0.71073 , m = 3.72 mm1, 5805 unique reflections with
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[10]
[11] [12] [13]
[I > 2s(I)], GOF = 1.102, D1max, min = 1.56, 1.24 e 3, R1 = 0.0493, wR2 = 0.1208. Crystal data for Zn2(HL)(HPO4)(PO4)·4 (H2O) (NCU-1a): monoclinic, space group P21/n, Z = 4, Mr = 698.13 g mol1, a = 5.1813(6), b = 26.849(3), c = 18.546(2) , b = 94.443(4)8, V = 2572.2(5) 3, 1calcd = 1.824 g cm3, l = 0.71073 , m = 2.06 mm1, 4416 unique reflections with [I > 2s(I)], GOF = 1.062, D1max, min = 0.76, 0.70 e 3, R1 = 0.0695, wR2 = 0.1835. C. M. Wang, Y. Y. Wu, C. H. Hou, C. C. Chen, K. H. Lii, Inorg. Chem. 2009, 48, 1519. a) Y. C. Liao, C. H. Lin, S. L. Wang, J. Am. Chem. Soc. 2005, 127, 9986; b) Y. C. Yang, S. L. Wang, J. Am. Chem. Soc. 2008, 130, 1146. Q. Tang, S. Liu, Y. Liu, J. Miao, Z. Li, L. Zhang, Z. Shi, Z. Zheng, Inorg. Chem. 2013, 52, 2799.
Received: October 16, 2014 Published online on December 3, 2014
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Organic–Inorganic Hybrid Zinc Phosphate with 28-Ring Channels Chih-Min Wang,*[a] Li-Wei Lee,[c] Tsung-Yuan Chang,[b] Yen-Chieh Chen,[a] Hsiu-Mei Lin,[b] Kuang-Lieh Lu,[c] and Kwang-Hwa Lii*[a, c] Abstract: An organic–inorganic hybrid zinc phosphate with 28-ring channels was synthesized by use of an organic ligand instead of organic amine template under a hydro(solvo)thermal condition. This crystalline zinc phosphate contains large channels constructed from 28 zinc and phosphate tetrahedral units. The walls of the channels consist of two types of zincophosphate chains, in which the Zn atoms are coordinated by 2,4,5-tri(4-pyridyl)-imidazole ligands as pendent groups. This compound exhibits yellow emission and interesting properties of removing cobalt, cadmium, and mercury cations from aqueous solution. A new two-dimensional organic–inorganic hybrid zincophosphate was also obtained by changing the solvent mixture ratios in the synthesis.
The discovery of iron phosphates and aluminophosphates, such as cacoxenite and VPI-5, has inspired researchers to synthesize new crystalline open-framework compounds with large structural channels and pores.[1, 2] These compounds are interesting not only because of rich structural chemistry but also potential applications in ion exchange, gas storage, catalysis, and luminescence.[1–3] Many approaches toward the design and synthesis of inorganic frameworks have been explored; however, compounds containing extra-large channels are still limited.[2, 4, 6–8] In comparison with metal–organic frameworks (MOFs), the inorganic building units comprising various geometric polyhedra, flexible coordination behaviors, and assorted connectivities make the synthesis of inorganic frameworks with large pore sizes and channels difficult. One of the synthesis methods to prepare materials with open framework structures is the template-directed synthesis based on the charge density matching of the organic ammonium ions and the inorganic frameworks. In the liquid-crystal templating concept, organic ammonium molecules assemble as a central structure, [a] Dr. C.-M. Wang, Y.-C. Chen, Prof. K.-H. Lii Department of Chemistry National Central University, Jhongli, 320 (Taiwan) E-mail: [email protected] [email protected] [b] T.-Y. Chang, Prof. H.-M. Lin Institute of Optoelectronic Sciences National Taiwan Ocean University, Keelung, 202 (Taiwan) [c] L.-W. Lee, Prof. K.-L. Lu, Prof. K.-H. Lii Institute of Chemistry, Academia Sinica, Nankang, Taipei, 115 (Taiwan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201405676. Chem. Eur. J. 2015, 21, 1878 – 1881
around which inorganic units grow, resulting in the formation of nanostructured materials.[5] The landmark structures in the presence of organic amines as templates exhibit a very large channel opening of 72-membered rings (72 MR) in phosphites,[6] 30 MR in germanates,[7] 18 MR in silicates,[2] and 24 MR in metal phosphates.[8] The structural building unit of phosphites, HPO32, may reduce the M-O-P connectivity and lead to the formation of more open, interrupted structures. In the structure of the gallophosphate with extra-large 24 ring channels, [Ga2(DETA)(PO4)2]·2 H2O (DETA = diethylenetriamines), the organic amine plays an interrupted role of binding in a tridentate fashion to the Ga atoms. Herein, we report a new organic–inorganic hybrid zinc phosphate with 28 ring channels, Zn5(H2L)(HPO4)3(PO4)2·3.5 H2O (denoted as NCU-1; L = 2,4,5-tri(4pyridyl)-imidazole).[9] This finding not only enlarges the maximum channel size of a metal phosphate from 24 to 28 MR but also provides a new route for the synthesis of inorganic frameworks with large channels through the use of organic amine ligands instead of amine templates. Typically, organic ligands as linkers bind to central metal atoms to form coordination compounds, whereas organic amines are as space-filling counterions or structure-directing agents in the formation of porous materials. A new layered compound, Zn2(HL)(HPO4)(PO4)·4 H2O (NCU-1 a), was also obtained under the same reaction conditions as those for NCU-1, except that the solvent mixture ratio was different. This work reports the synthesis, structural diversity in different solvent mixture ratios, and photoluminescence properties of NCU-1, as well as its ability to remove metal cations from aqueous solutions. Orange needle-like crystals of NCU-1 were obtained by heating a mixture of Zn(NO3)2·6 H2O (0.5 mmol), 2,4,5-tri(4-pyridyl)imidazole (0.2 mmol), HF(aq.) (0.4 mmol, 48 % solution), H3PO4 (3 mmol), dimethylformamide (0.5 mL), and H2O (1.5 mL) under hydro(solvo)thermal reaction conditions at 150 8C for two days. The X-ray powder-pattern data of the bulk product is in good agreement with the calculated pattern for NCU-1 based on the structure analysis results from single-crystal X-ray diffraction (Figure S1 in the Supporting Information). The yield was 81 % based on Zn. The elemental analysis results were consistent with the formula Zn5(H2L)(HPO4)3(PO4)2·3.5 H2O (elemental analysis calcd (%): C 18.49, H 2.16, N 5.99; found: C 18.36, H 2.16, N 5.88). The structure of NCU-1 is a close-packed array of channels of 28 MR in an elliptical shape, which are constructed from four ZnO3N tetrahedra, ten ZnO4 tetrahedra, six phosphate groups, and eight hydrogen phosphate units (Figures 1 and S2 in the Supporting Information). The P(1) and P(4) atoms are both bonded to four Zn atoms through four oxygen atoms,
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Figure 2. Two types of chains in NCU-1: a) the inorganic 1[Zn4(HPO4)2(PO4)] + chain with three-, four-, and six-membered rings; b) the organic–inorganic hybrid 1[Zn(H2L)(HPO4)(PO4)] chain. Blue and black circles represent N and C atoms, respectively. The H atoms are omitted for clarity.
Figure 1. Perspective view of the inorganic framework of NCU-1 along the a axis, showing 28 MR channels. The H atoms, water, and organic molecules are omitted for clarity in the plot. The ZnO3N and ZnO4 tetrahedra are indicated in yellow; phosphate and hydrogen phosphate units are in green.
and P(2), P(3), and P(5) bridge three Zn atoms through three oxygen atoms with a POH group being directed toward the center of channel. Bond-valence calculations indicated that O(6), O(9), and O(18) are hydroxo oxygen atoms, and the H atoms associated with them could be located in difference Fourier maps. The maximum free atom-to-atom distance across the channel was 23.5 , and the non-framework space within the structure was estimated to be 49.3 % of the unit cell. The framework metal density for NCU-1 was 11.5 M atoms (M = Zn, P) per 1000 3. For comparison, the framework metal densities of several metal phosphates with extra-large channels, such as VPI-5, CLO, ND-1, VSB-5, NTHU-1, and cacoxenite, are 11.8, 14.2, 11.1, 12.1, 18.5, and 10.9, respectively.[2, 4a, 8] The walls of the channels in NCU-1 consist of two kinds of 1D zincophosphate chains through P-O-Zn connections. One kind of chain is the positively charged [Zn4(HPO4)2(PO4)] + chain containing three-, four-, and six-membered rings (Figures 2 a and S3 in the Supporting Information), and the other is an negatively charged organic–inorganic hybrid chain (Figure 2). The 2,4,5-tri(4-pyridyl)-imid1[Zn(H2L)(HPO4)(PO4)] azole ligands coordinate in a monodentate fashion to Zn atoms and extend away from inorganic framework into the intrachannel region as pendent ligands (Figure S4 in the Supporting Information). The distance between the centroids of the rings of adjacent ligands is 5.12 (Figure 2 b). The voids of the channels are filled with water molecules. Interestingly, a new zinc phosphate with a 2 D layer structure, Zn2(HL)(HPO4)(PO4)·4 H2O (NCU-1 a), was synthesized by changing the solvent mixture ratio from 1.5 mL H2O/0.5 mL DMF to 1.5 mL H2O/1.0 mL DMF. The structure of NCU-1 a consists of Chem. Eur. J. 2015, 21, 1878 – 1881
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inorganic chains of zinc phosphate with 4 MR, which are connected by the organic ligands to form an organic–inorganic hybrid sheet (Figure S5 in the Supporting Information).[10] Thermogravimetric analysis of NCU-1 showed a weight loss of 4.92 % between 40 and 200 8C, which is close to the calculated value of 5.39 % for 3.5 H2O molecules per formula unit (Figure S6 in the Supporting Information). The observed total weight loss of 35.72 % between 40 and 1000 8C is close to the calculated value of 34.84 % for the loss of one L ligand and six H2O molecules. The structure of NCU-1 is thermally stable up to 250 8C, as was indicated by the powder X-ray diffraction patterns of the powder samples of NCU-1 after being heated at 100, 200, and 250 8C for 4 h (Figure S7 in the Supporting Information). The as-synthesized and dehydrated powder samples of NCU-1 at different temperatures showed different intensities of yellow luminescence when these powder samples were irradiated with l = 365 nm UV light from a handheld UV lamp. The spectra display broad emission at approximately 540 nm in the range from 450 to 700 nm under excitation at 374 nm. The spectral intensity of the as-synthesized NCU-1 was lower than that of other dehydrated samples, which can be ascribed to the reduction of the quenching effect of water molecules (Figure 3).[11] The development of new materials emitting yellow light is interesting and critical, because combination of yellow-light phosphor and blue-light LED to generate white light is the mainstream of current lighting technology. The yellow emission of phosphate materials may originate from complex processes. Two metal phosphates, NTHU-4 and NTHU6, have been reported to emit yellow light, and their emissions were respectively caused by a defect in the host material and the organic molecules used as a sensitizer to assist energy absorption and transfer.[12] The emission of NCU-1 is redshifted relative to that of the free L ligand (a weak emission band at 520 nm under excitation at 374 nm), therefore, the yellow emission can be related to the intraligand fluorescent emission. Heavy-metal pollutions in wastewater from a variety of industries are easily transported through water into the environment, and these pollutions may cause harmful effects on envi-
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Communication bonded to Zn atoms as pendent groups in the 28 MR channel. The synthesis of NCU-1 not only enlarges the maximum channel size of metal phosphate from 24 to 28 MR, but also provides a new route for the synthesis of inorganic frameworks with large channels by the use of organic amine ligands instead of amine templates. A change of the solvent mixture ratio results in the formation of a new zinc phosphate with 2D layer structure. NCU-1 also exhibits yellow emission and the potential ability to remove cobalt, cadmium, and mercury cations from aqueous solutions. Further research on this theme is in progress.
Experimental Section Figure 3. Luminescence spectra of NCU-1 excited at l = 347 nm. The black, red, and blue curves represent the emission spectra of the as-synthesized compound and the compounds dehydrated at 100 and 200 8C for 2 h, respectively.
ronmental toxicity and human health. Therefore, NCU-1 was explored for the removal of metal ions from aqueous solutions. A powder sample (0.05 g) of NCU-1 was respectively added to 10 mL of 0.01 m aqueous solution of Co(NO3)2, Cd(ClO4)2, and Hg(NO3)2 at room temperature with constant stirring for 1 h. The color of Co(NO3)2 (aq.) changed from deep pink to light pink, indicating that Co2 + cations were partly removed from solution by NCU-1. The solid was separated from the solution by centrifugation. The X-ray powder patterns of the solids showed that their structures were retained (Figure S8 in the Supporting Information). The ICP-OES analysis of the solutions showed that the Co, Cd, and Hg metal contents decreased by 22.42 % (adsorption capacity ca. 1.32 mg g1), 63.38 % (7.12 mg g1), and 80.17 % (16.08 mg g1), respectively. To determine the positions of metal cations in the crystal structure, several single crystals of NCU-1 after being immersed in aqueous solution of Hg(NO3)2 overnight were indexed on a diffractometer, but their peak profiles showed that they were no longer suitable for crystal structure analysis. The non-coordinated N atoms of 2,4,5-tri(4-pyridyl)-imidazole in the wall of NCU-1 may play a key role for the interaction with incoming metal ions. Recently, Tang et al. reported that one MOF compound containing an organic ligand with Lewis basic sites allowed complexation with Lewis acidic analytes.[13] Attempts to synthesize the analogues of NCU-1 by using Co(NO3)2, Cd(ClO4)2, and Hg(NO3)2 instead of Zn(NO3)2·6 H2O in the same synthetic condition were unsuccessful. To the best of our knowledge, all of the previously reported crystalline phosphate materials with extra-large pores ( 20membered rings, 20 MR) were synthesized in the presence of organic amine molecules.[4a, 8] To date, the largest pore size has been 24 MR in nickel, zinc, and gallium phosphates.[8] Instead of using organic amines as templates in the synthesis, we prepared an organic–inorganic hybrid zinc phosphate with 28-ring channels by including large organic linkers in the inorganic framework. The 2,4,5-tri(4-pyridyl)-imidazole ligands are Chem. Eur. J. 2015, 21, 1878 – 1881
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The hydro(solvo)thermal reactions were carried out in Teflon-lined stainless steel Parr acid digestion bombs at 150 8C for 2 d, followed by slow cooling to RT at 6 8C h1. Orange needle-like crystals of NCU-1 were obtained by heating a mixture of Zn(NO3)2·6 H2O (0.5 mmol), 2,4,5-tri(4-pyridyl)-imidazole (0.2 mmol), HF(aq.; 0.4 mmol, 48 % solution), H3PO4 (3 mmol), dimethylformamide (0.5 mL), and H2O (1.5 mL); white plate crystals of NCU-1 a were obtained by heating a mixture of Zn(NO3)2·6 H2O (0.5 mmol), 2,4,5tri(4-pyridyl)-imidazole (0.2 mmol), HF(aq.; 0.4 mmol, 48 % solution), H3PO4 (3 mmol), dimethylformamide (1.0 mL), and H2O (1.5 mL). CCDC-1019899 (NCU-1) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements We thank the Ministry of Science and Technology of Taiwan for financial support (MOST 103-2113-M-008-011-MY2 and NSC 101-2113-M-008-006-MY3), and Dr. Y. S. Wen at the Institute of Chemistry, Academia Sinica for X-ray data collection. Keywords: crystals · hydro(solvo)thermal synthesis · organic– inorganic hybrid composites · phosphorus · zinc
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[1] P. B. Moore, J. Shen, Nature 1983, 306, 356. [2] M. F. Davis, C. Saldarriaga, C. Montes, J. M. Garces, C. Crowder, Nature 1988, 331, 698. [3] a) Q. Hu, R. Xu, S. Li, Z. Ma, J. M. Thomas, R. H. Jones, A. M. Chippindale, Chem. Commun. 1992, 875; b) J. Zhu, X. Bu, P. Feng, G. D. Stucky, J. Am. Chem. Soc. 2000, 122, 11563; c) X. Wang, L. Liu, A. J. Jacobson, Angew. Chem. Int. Ed. 2003, 42, 2044; Angew. Chem. 2003, 115, 2090; d) A. Corma, Chem. Rev. 1997, 97, 2373; e) A. K. Cheetham, G. Frey, T. Loiseau, Angew. Chem. Int. Ed. 1999, 38, 3268; Angew. Chem. 1999, 111, 3466; f) M. E. Davis, Nature 2002, 417, 813; g) S. Natarajan, S. Mandal, Angew. Chem. Int. Ed. 2008, 47, 4798; Angew. Chem. 2008, 120, 4876, and references therein. [4] a) M. Estermann, L. B. McCusker, C. Baerlocher, A. Merrouche, H. Kessler, Nature 1991, 352, 320; b) J. Plvert, T. M. Gentz, A. Laine, H. Li, V. G. Young, O. M. Yaghi, M. O’Keeffe, J. Am. Chem. Soc. 2001, 123, 12706; c) J. Liang, J. Li, J. Yu, P. Chen, Q. Fang, F. Sun, R. Xu, Angew. Chem. Int. Ed. 2006, 45, 2546; Angew. Chem. 2006, 118, 2608; d) Y. L. Lai, K. H. Lii, S. L. Wang, J. Am. Chem. Soc. 2007, 129, 5350; e) J. Jiang, J. L. Jorda, J. Yu, L. A. Baumes, E. Mugnaioli, M. J. Diaz-Cabanas, U. Kolb, A. Corma, Science 2011, 333, 1131. [5] a) B. M. Lok, T. R. Cannon, C. A. Messina, Zeolites 1983, 3, 282; b) E. M. Flanigen, R. L. Patton, S. T. Wison, Stud. Surf. Sci. Catal. 1988, 37, 13; 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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c) A. Sayari, Stud. Surf. Sci. Catal. 1996, 102, 1; d) M. E. Davis, R. F. Lobo, Chem. Mater. 1992, 4, 756. H. Y. Lin, C. Y. Chin, H. L. Huang, W. Y. Huang, M. J. Sie, L. H. Huang, Y. H. Lee, C.-H. Lin, K. H. Lii, X. Bu, S. L. Wang, Science 2013, 339, 811. a) X. Zou, T. Conradsson, M. Klingstedt, M. S. Dadachov, M. O’Keeffe, Nature 2005, 437, 716; b) J. Sun, C. Bonneau, . Cantn, A. Corma, M. J. Daz-CabaÇas, M. Moliner, D. Zhang, M. Li, X. Zou, Nature 2009, 458, 1154. a) G. Y. Yang, S. C. Sevov, J. Am. Chem. Soc. 1999, 121, 8389; b) C. H. Lin, S. L. Wang, K. H. Lii, J. Am. Chem. Soc. 2001, 123, 4649; c) N. Guillou, Q. Gao, P. M. Forster, J. S. Chang, M. Nogus, S. E. Park, G. Frey, A. K. Cheetham, Angew. Chem. Int. Ed. 2001, 40, 2831; Angew. Chem. 2001, 113, 2913. Crystal data for Zn5(H2L)(HPO4)3(PO4)2·3.5 (H2O) (NCU-1): monoclinic, space group P21/n, Z = 4, Mr = 1169.13 g mol1, and a = 5.1242(2), b = 25.0641(14), c = 27.1877(15) , b = 90.940(2)8, V = 3491.3(3) 3, 1calcd = 2.224 g cm3, l = 0.71073 , m = 3.72 mm1, 5805 unique reflections with
Chem. Eur. J. 2015, 21, 1878 – 1881
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[10]
[11] [12] [13]
[I > 2s(I)], GOF = 1.102, D1max, min = 1.56, 1.24 e 3, R1 = 0.0493, wR2 = 0.1208. Crystal data for Zn2(HL)(HPO4)(PO4)·4 (H2O) (NCU-1a): monoclinic, space group P21/n, Z = 4, Mr = 698.13 g mol1, a = 5.1813(6), b = 26.849(3), c = 18.546(2) , b = 94.443(4)8, V = 2572.2(5) 3, 1calcd = 1.824 g cm3, l = 0.71073 , m = 2.06 mm1, 4416 unique reflections with [I > 2s(I)], GOF = 1.062, D1max, min = 0.76, 0.70 e 3, R1 = 0.0695, wR2 = 0.1835. C. M. Wang, Y. Y. Wu, C. H. Hou, C. C. Chen, K. H. Lii, Inorg. Chem. 2009, 48, 1519. a) Y. C. Liao, C. H. Lin, S. L. Wang, J. Am. Chem. Soc. 2005, 127, 9986; b) Y. C. Yang, S. L. Wang, J. Am. Chem. Soc. 2008, 130, 1146. Q. Tang, S. Liu, Y. Liu, J. Miao, Z. Li, L. Zhang, Z. Shi, Z. Zheng, Inorg. Chem. 2013, 52, 2799.
Received: October 16, 2014 Published online on December 3, 2014
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