CRYSTAL GROWTH & DESIGN
Photoluminescent Zn(II) Metal-Organic Frameworks Built from Tetrazole Ligand: 2D Four-Connected Regular Honeycomb (4363)-net
2007 VOL. 7, NO. 7 1227-1229
Xian-Wen Wang,*,† Jing-Zhong Chen,† and Jian-Hong Liu‡ Faculty of Materials Science and Chemical Engineering, China UniVersity of Geoscience, Hubei, Wuhan 370007, P. R. China, and College of Chemistry and Chemical Engineering, Shengzhen UniVersity, Guangdong, Shengzhen 518060, P. R. China ReceiVed April 5, 2007; ReVised Manuscript ReceiVed May 10, 2007
ABSTRACT: Two metal-organic frameworks, [Zn2(ATA)3(ATA)2/2] (1) and [Zn(OH)(ATA)2] (2), have been synthesized by the hydrothermal reactions of Zn(II) salts with HATA. 1 displays a unique four-connected 2D bilayer “hcb” 43.63 topological network, and shows a strong blue fluorescence at room temperature. Great interest has been focused on the rapidly expanding field of supramolecular chemistry and crystal engineering of the metalorganic frameworks (MOFs)1 in recent years because of their intriguing network topologies as well as their potential application as functional materials in many areas such as separations and catalysis,2 gas storage,3 and magnetism.4 Many higher dimensionality metal-organic frameworks represent themselves as realistic targets of inorganic compounds or minerals in nature with topologies such as R-polonium or NaCl, CdSO4, PtS, Pt3O4, NbO, diamond, rutile, boracite, and so on.5 Particular attention has been attracted to the isolation and characterization of two-dimensional (2D) topologies that contain three-, four-, five- or six-sided polygons with the features as (6,3) honeycomb, (4,4) squre grid, brick wall, bilayer, etc.5,6 However, the networks that consist of mixed polygons or nodes in the 2D arrangement are rarely observed in the literature.6c Herein, we report a four-connected regular 2D bilayer “hcb” 43.63 topological network, which to the best of our knowledge represents the first example of a 2D four-connected network containing a mix of four- and six-sided polygons. Exploring highly symmetrical multitopic ligands and suitable metal salts to construct supramolecular architectures is of great interest.7 Rigid polytopic ligands are often employed to produce extended frameworks with high structural stability and special topologies due to the predictability of the resulting networks. Tetrazoles with various interesting coordination chemistry and a strong networking ability have been extensively used as organic linkers for construction novel MOFs.8 Remarkably, as they have highest content of nitrogen among the organic substances and show surprisingly high thermal stabilities, aminotetrazoles are prospective materials for the generation of gases, such as blowing agents, solid propellants, and other combustible and thermally decomposing systems.9-11 5-Amino-1H-tetrazole (HATA) has received by far the most attention in the literature and is used as a gas generator and key intermediate in many organic syntheses.12 Furthermore, the HATA is isosteric with the carboxylate group and has good coordination ability; from a crystal engineering view, the amino group of the tetrazole ligand is quite important for orientation of adjacent ligands within the metal coordination sphere and could be involved as a factor controlling the framework structure.13 However, it has scarcely been utilized as multifunctional organic linkers for generating MOFs.14 Accordingly, our interest focuses on assembling novel topological MOFs with rigid multitopic ligands, which contain heterocyclic nitrogen or carboxylate oxygen atoms.15 Here, we carried the reactions of Zn(II) salts with HATA under hydrothermal conditions for assembling extended coordination polymer (Scheme 1) and successfully isolated two complexes, [Zn2(ATA)3(ATA)2/2] (1) and * Corresponding author. E-mail:
[email protected]. † China University of Geoscience. ‡ Shengzhen University.
Scheme 1
[Zn(OH)(ATA)2] (2), with two-dimensional unique four-connected regular “hcb” 43.63 topological network and two-dimensional “sql” (square lattice) structure, respectively. 2 has been reported by Xiong and his group, where the ATA- ligand was afforded from the reaction of N,N′-dicyanohydrazine with ZnCl2 and NaN3 in water.14a The hydrothermal reaction of Zn(NO3)2‚6H2O with HATA in aqua at 160 °C for 4 days afforded colorless crystals of 1,16 which are characterized by elemental analysis, IR spectra, TGA, and XPRD pattern (see the Supporting Material). Single-crystal X-ray analysis17 revealed that the asymmetric unit of compound 1 contains two Zn2+ cations (Zn1 and Zn2), three crystallographically independent anionic ATA- ligands, and two crystallographically different halves of ATA- groups. Each ATA anion serves as µ2bridge linking two Zn atoms, and each Zn atom is surrounded by four ATA- ligands, where the four-coordinated Zn atom adopts a tetrahedral geometry (see the Supporting Information, Figure S1). The Zn1-N and Zn2-N bond lengths range from 1.970(5) to 2.005(7) Å and 1.982(5) to 2.013(6) Å, respectively, and the mean Zn1-N bond length (1.988(1) Å) is slightly shorter than that of Zn2-N (1.991(8) Å). All the Zn-N bond lengths are comparable to those of the reported Zn(II)-tetrazole complex.14a,18 The cisangles at the central Zn1 and Zn2 atoms fall in range of 101.8(3)-114.3(2)° and 99.7(3)-114.5(2)°, respectively, indicating that the tetrahedral geometries are slightly distorted. Parallel to (010), the tetrahedrally coordinated Zn atoms are bridged by the µ2-ATA- into (6,3) topological networks, which are interlinked by the mirror plane symmetric µ2-ATA- ligands along the [010] direction to form a bilayer honeycomb feature (Figure 1). One of the most intriguing features regarding the network is that 1 shows unique four-connected hexagonal bilayer “hcb” topology (honeycomb network),19 with the Schla¨fli symbol20 of 4.363 and the vertex symbol or long symbol21 of 4.62.4.62.4.62. The network is of the type (6,3)Ia according to the classification of the double-net sphere packing graphs for layer group22 (Figure 1c). Although many 2D complexes display three-connected (6,3) nets, four-connected (4,4) nets, five-connected (34,5) nets, six-connected (3,6) nets, some mixed connected nets such as (5, 34) and (5, 36) nets, and so on, there are few reported complexes exhibiting highly regular 2D bilayer topology that possess four-connected nodes and a mix of squares and hexagons.5,6 To the best of our knowledge, compound 1 is the first example of a 2D four-connected 4.363 network containing a mix of four- and six-sided polygons.
10.1021/cg070330w CCC: $37.00 © 2007 American Chemical Society Published on Web 05/24/2007
1228 Crystal Growth & Design, Vol. 7, No. 7, 2007
Figure 1. (a) Two-dimensional honeycomb bilayer viewed down the b-axis. (b) Polyhedron drawing showing the tetrahedral coordinated Zn atoms linked by ATA- groups into hexagonal prism building block. (c) Unique fourconnected topology suggesting the highly regular 2D bilayer “hcb” topological network. (d) Space-filling mode showing the π···π stacking interactions and the open channels.
Within the crystal structure of 1, the N-H‚‚‚N hydrogen-bonding interactions play a key role in forming the unique framework (see the Supporting Information, Table S1). The terminal amino groups of each ATA-, which is parallel to (010), donate H atoms to the adjacnt noncoordinated tetrazole N atoms to generate intramolecular N-H‚‚‚N hydrogen bonding interactions with S(6) and R 66(15) motifs,23 as shown in the Supporting Information, Figure S2. These specific hydrogen-bonding interactions may be involved as a factor controlling the entire hexagonal honeycomb framework.13,14b,24 Remarkably, the 2D bilayers further pack along [010] direction into 3D porous supramolecular structure via strong π···π stacking interactions between the neighboring ATA- ligands, where the distance between the centroids of the tetrazole rings is 3.371(2) Å. Large open channels of dimensions of 3 × 3 Å2 (after exclusion of the van der Waals radii of the surface atoms) were generated along the [001] direction (Figure 1d). A calculation with PLATON25 reveals that the solvent accessible void is 259.00 Å3 per unit cell, which indicates that 1 could potentially accommodate hydrogenbonded H2O molecules and small molecules such as methanol, ethanol, dichloromethane, toluene, and so on. Compound 2 was prepared by a procedure similar to that for 1.26 The crystal structure of 2 is confirmed by X-ray analysis27 to be equal to the one reported by Xiong, et al.14a 2 is a 2D square lattice structure, where the tetra-coordinated Zn(II) atoms are bridged by the µ2-ATA- ligands and µ2-OH groups into “sql” topology with the Schla¨fli symbol of 44.62 and the vertex symbol or long symbol of 4.4.4.4.62.62 (Figure 2). The 2D layers are stabilized by the strong intramolecular N-H‚‚‚N hydrogen bonding interactions, via the amino groups donating H5A atoms to tetrazole N3 atoms, to form S(6) motifs (Figure 2).23 The resultant layers are further interlinked by the weak N-H‚‚‚N and O-H‚‚‚N hydrogen-bonding interactions into a 3D supramolecular framework (see the Supporting Information, Table S1). Thermogravimetric analysis (TGA) reveals that 1 possesses high thermal stability. There is no weight loss from room temperature to 300 °C in the TGA curve. The compound starts decomposing above 300 °C, and the compound suffers complete decomposition until it reaches a temperature of 600 °C; the total mass loss of 59.25% corresponds to the removal of the tetrazole fragments (58.46%), with the residue of Zn(CN)2. The solid-state fluorescence spectra of 1 and 2 at room temperature are depicted in Figure 3. When excited at 320 nm at room temperature, 1 shows blue luminescence with a weak emission peak centered at ca. 485 nm that would be assigned to the ligandto-metal charge transfer (LMCT) and/or metal-to-ligand charge transfer (MLCT) and significantly strong emission with the
Communications
Figure 2. Two-dimensional “sql” network of 2 (the dashed lines indicating N-H‚‚‚N hydrogen bonds).
Figure 3. Photoluminescence emission spectra for 1 and 2 in the solid state at room temperature.
maximum peak at ca. 392 nm that would originate from intraligand πL f πL* transitions emission (LLCT). The free HATA ligand has a very weak emission centered at ca. 325 nm. The strong fluorescence emission and significant red-shift are mainly due to the coordination interactions and the deprotonation of the HATA ligand, which effectively increase the rigidity of the ligand and reduce the loss of energy by radiationless decay of the intraligand emission excited state. Furthermore, the strong π-π interactions between the adjacent tetrazole rings of the layers may also be favorable to reduction of the energy π-π* transition to some extent and enhance the photoluminescence.28 Along with the fact that compound 1 has high thermal stability and is virtually insoluble in most common solvents such as acetone, ethanol, chloroform, water, etc., the emission property makes 1 a potential blue fluorescence material. Comparable with 1, compound 2 exhibits a weak fluorescence emission with the λmax ) 320 nm upon excitation at λmax ) 274 nm. In conclusion, two metal-organic frameworks, [Zn2(ATA)3(ATA)2/2] (1) and [Zn(OH)(ATA)] (2), have been afforded from the hydrothermal reactions of Zn(II) salts with HATA. 1 displays a unique four-connected regular 2D bilayer “hcb” 43.63 topological network, which is to the best of our knowledge the first example of a 2D network that exhibits highly regular 2D bilayer topology possessing four-connected nodes and a mix of four- and six-sided polygons. Compound 1 may be a potential blue fluorescence material. Acknowledgment. This work is supported by the Natural Science Foundation of China (NSFC 60508012). Supporting Information Available: X-ray crystallographic files for 1 and 2 in CIF format. IR spectra (Figure S3), PXRD patterns (Figure S4),
Communications
Crystal Growth & Design, Vol. 7, No. 7, 2007 1229
and TGA diagram (Figure S5) for complexes 1 (PDF). This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) (a) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1461. (b) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319. (c) Papaefstathiou, G. S.; MacGillivray, L. R.; Coord. Chem. ReV. 2003, 246, 169. (d) Evans, O. R.; Lin, W. Acc. Chem. Res. 2002, 35, 511. (e) Oh, M.; Carpenter, G. B.; Sweigart, D. A. Acc. Chem. Res. 2004, 37, 1. (a) Dybtsev, D. N.; Chun, H.; Yoon, S. H.; Kim, D.; Kim, K. J. Am. Chem. Soc. 2004, 126, 32. (b) Pan, L.; Sander, M. B.; Huang, X.; Li, J.; Smith, M.; Bittner, E.; Bockrath, B.; Johnson, J. K. J. Am. Chem. Soc. 2004, 126, 1308. (2) (a) Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim, K. Nature 2000, 404, 982. (b) Evans, O. R.; Ngo, H. L.; Lin, W. J. Am. Chem. Soc. 2001, 123, 10395. (3) (a) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, O. M. Science 2002, 295, 469. (b) Rowsell, J. L. C.; Spencer, E. C.; Eckert, J.; Howard, J. A. K.; Yaghi, O. M. Science 2005, 309, 1350. (c) Li, H.; Eddaoudi, M.; O’Keeffe, M.; Yaghi, O. M. Nature 1999, 402, 276. (4) (a) Tasiopoulos, A. J.; Vinslava, A.; Wernsdorfer, W.; Abboud, K. A.; Christou, G. Angew. Chem., Int. Ed. 2004, 43, 2117. (b) Murugesu, M.; Habrych, M.; Wernsdorfer, W.; Abboud, K. A.; Christou, G. J. Am. Chem. Soc. 2004, 126, 4766. (c) Halder, G. J.; Kepert, C. J.; Moubaraki, B.; Murray, K. S.; Cashion, J. D. Science 2002, 298, 1762. (5) Wells, A. F. Three-Dimensional Nets and Polyhedra; Wiley: New York, 1977. (6) (a) Keller, S. W.; Lopez, S. J. Am. Chem. Soc. 1999, 121, 6306. (b) Moulton, B.; Lu, J.; Zaworotko, M. J. J. Am. Chem. Soc. 2001, 123, 9224. (c) Wells, D. The Penguin Dictionary of Curious and Interesting Geometry; Penguin: London, 1991. (d) Moulton, B.; Zaworotko, M. J. Chem. ReV. 2001, 101, 1629. (7) (a) Gardner, G. B.; Ventakaraman, D.; Moore, J. S.; Lee, S. Nature 1995, 374, 792. (b) Chen, B. L.; Eddaoudi, M.; Hyde, S. T.; O’Keeffe, M.; Yaghi, O. M. Science 2001, 291, 1021. (c) Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002, 35, 972. (d) Muller, A. Science 2003, 300, 749. (e) Chae, H. K.; Siberio-Perez, D. Y.; Kim, J.; Go, Y.; Eddaoudi, M.; Matzger, A. J.; O’Keeffe, M.; Yaghi, O. M. Nature 2004, 427, 523. (8) (a) Huang, X.-C.; Zhang, J.-P.; Chen, X.-M. J. Am. Chem. Soc. 2004, 126, 13218. (b) Masciocchi, N.; Ardizzoia, G. A.; Brenna, S.; Castelli, F.; Galli, S.; Maspero, A.; Sironi, A. Chem. Commun. 2003, 2018. (c) Stassen, A. F.; Grunert, M.; Mills, A. M.; Spek, A. L.; Haasnoot, J. G.; Reedijk, J.; Linert, W. Dalton Trans. 2003, 3628. (d) Xiong, R.-G.; Xue, X.; Zhao, H.; You, X.-Z.; Abrahams, B. F.; Xue, Z.-L. Angew. Chem., Int. Ed. 2002, 41, 3800. (e) Wang, L.-Z.; Qu, Z.-R.; Zhao, H.; Wang, X.-S.; Xiong, R.-G.; Xue, Z. Inorg. Chem. 2003, 42, 3969. (f) Steel, P. J. Coord. Chem. ReV. 1990, 106, 227. (9) Lesnikovich, A. I.; Ivashkevich, O. A.; Levchik, S. V.; Balabanovich, A. I.; Gaponik, P. N.; Kulak, A. A. Thermochim. Acta 2002, 388, 233. (10) Gao, A.; Oyumi, Y.; Brill, T. B. Combust. Flame 1991, 83, 345. (11) Levchik, S. V.; Balabanovich, A. I.; Ivashkevich, O. A.; Gaponik, P. N.; Costa, L. Polym. Degrad. Stab. 1995, 47, 333. (12) (a) Neutz, J.; Grosshardt, O.; Schaeufele, S.; Schuppler, H.; Schweikert, W. Propellants, Explos., Pyrotech. 2003, 28 (4), 181. (b) Demko, Z. P.; Sharpless, K. B. Org. Lett. 2002, 4 (15), 2525. (c) Katritzky, A. R.; Rogovoy, B. V.; Kovalenko, K. V. J. Org. Chem. 2003, 68, 4941. (13) (a) Aakero¨y, C. B.; Seddon, K. R. Chem. Soc. ReV. 1993, 22, 397. (b) Etter, M. C. Acc. Chem. Res. 1990, 23, 120. (c) Subramanian, S.; Zaworotko, M. J. Coord. Chem. ReV. 1994, 137, 357. (d) Zaworotko, M. J. Nature 1997, 386, 220.
(14) (a) Xue, X.; Abrahams, B. F.; Xiong, R.-G.; You, X.-Z. Aust. J. Chem. 2002, 55, 495. (b) He, X.; Lu, C.-Z.; Yuan, D.-Q. Inorg. Chem. 2006, 45, 5760. (15) (a) Wang, X.-W.; Dong, Y.-R.; Zheng, Y.-Q.; Chen, J.-Z. Cryst. Growth Des. 2007, 7, 613. (b) Wang, X.-W.; Li, X.; Zheng, G.; Hong, H.-L.; Chen, J.-Z. Cryst. Growth Des. 2007, submitted. (16) Preparation of 1: The mixture of Zn(NO3)2‚6H2O (0.285 g, 1.0 mmol), HATA (0.108 g, 1.0 mmol), and H2O (18.0 ml) was sealed in a 25 ml stainless-steel reactor with Teflon liner; it was heated to 160 °C, kept at constant temperature for 120 h, and then slowly cooled to room temperature. Colorless block crystals of [Zn2(ATA)3(ATA)2/2] (1) were abtained (yield: 65% based on the initial HATA input). Anal. Calcd for C4H7Zn2N20 (%): C, 10.28; H, 1.71; N, 59.95. Found: C, 10.25; H, 1.65; N, 59.93. IR data (cm -1, KBr): 3341s, 3195s, 1655s, 1606s, 1571s, 1471s, 1448m, 1421m, 1375m, 1331w, 1166w, 1094m, 1007w, 905w, 786w, 754w, 494s. (17) Crystal data for C4H7Zn2N20 1: monoclinic, space group P21/m, M ) 467.04, a ) 10.3400(12) Å, b ) 19.931(2) Å, c ) 10.3723(12) Å, β ) 119.8130(10)°, V ) 1854.6(4) Å3, Z ) 4, T ) 173 K, Dc ) 1.673 g cm-3, F(000) ) 928, Mo-KR radiation (λ ) 0.71073 Å), µ ) 2.623 mm-1, R1 ) 0.0543 and wR2 ) 0.1584, S ) 1.069. (18) (a) Wang, X.-S.; Tang, Y.-Z.; Huang, X.-F.; Qu, Z.-R.; Che, C.-M.; Chan, P. W. H.; Xiong, R.-G. Inorg. Chem. 2005, 44, 5278. (b) Dinca, M.; Yu, A. F.; Long, J. R. J. Am. Chem. Soc. 2006, 128, 8904. (19) (a) Friedrichs, O. D.; O’Keeffe, M.; Yaghi, O. M. Acta Crystallogr., Sect. A 2003, 59, 22. (b) Friedrichs, O. D.; O’Keeffe, M.; Yaghi, O. M. Acta Crystallogr., Sect. A 2006, 62, 350. (c) Friedrichs, O. D.; O’Keeffe, M. Acta Crystallogr., Sect. A 2005, 61, 358. (20) Smith, J. V. Am. Mineral. 1978, 63, 960. (21) (a) O’Keeffe, M.; Hyde, B. G. Crystal Structures I: Patterns and Symmetry; Mineralogical Society of America: Washington, DC, 1996. (b) O’Keeffe, M.; Hyde, S. T. Zeolites 1997, 19, 370. (22) Koch, E.; Fischer, W. Z. Kristallogr. 1978, 148, 107. (23) (a) Bernstein, J.; Davis, R. E.; Shimoni, L.; Chang, N.-L. Angew. Chem., Int. Ed. 1995, 34, 1555. (b) Etter, M. C. Acc. Chem. Res. 1990, 23, 120. (c) Etter, M. C.; MacDonald, J. C. Acta Crystallogr., Sect. B 1990, 46, 256. (24) Ga´lvez-Ruiz, J. C.; Holl, G.; Karaghiosoff, K.; Klapo¨tke, T. M.; Lo¨hnwitz, K.; Mayer, P.; No¨th, H.; Polborn, K.; Rohbogner, C. J.; Suter, M.; Weigand, J. J. Inorg. Chem. 2005, 44, 4327. (25) Spek, A. L. PLATON, version 1.62; University of Utrecht: Utrecht, The Netherlands, 1999. (26) Preparation of 2: The mixture of ZnSO4‚6H2O (0.269 g, 1.0 mmol), HATA (0.108 g, 1.0 mmol), NaOH (0.040 g, 1.0 mmol), and H2O (18.0 ml) was sealed in a 25 mL stainless-steel reactor with Teflon liner; it was heated to 160 °C, kept at constant temperature for 120 h, and then slowly cooled to room temperature. Colorless rod-shaped crystals of [Zn(OH)(ATA)] (2) were abtained (yield: 85% based on the initial ZnSO4‚6H2O input). Anal. Calcd for CH3ZnN5O (%): C, 7.21; H, 1.80; N, 42.05. Found: C, 7.25; H, 1.86; N, 42.02. IR data (cm -1, KBr): 3397s, 3338s, 3245s, 3204s, 1663s, 1587s, 1571s, 1506w, 1471s, 1448m, 1396w, 1302w, 1160w, 1112m, 1094s, 1015m, 905s, 833w, 765w, 748w, 489s. (27) Crystal data for CH3ZnN5O:orthorhombic, space group Pbcm, M ) 166.45, a ) 6.3449(5) Å, b ) 10.4301(7) Å, c ) 6.6211(5) Å, V ) 438.17(6) Å3, Z ) 4, T ) 298(3) K, Dc ) 2.523 g cm-3, F(000) ) 328, Mo-KR radiation (λ ) 0.71073 Å), µ ) 5.481 mm-1, R1 ) 0.02 and wR2 ) 0.0556, S ) 1.157. (28) (a) Yersin, H.; Vogler, A. Photochemistry and Photophysics of Coordination Compounds: Springer: Berlin, 1987. (b) Wang, S.-N. Coord. Chem. ReV. 2001, 215, 79. (c) Zheng, S.-L.; Yang, J.-H.; Yu, X.-L.; Chen, X.-M.; Wong, W.-T. Inorg. Chem. 2004, 43, 830.
CG070330W
