- Email: [email protected]
Two new microporous coordination polymers constructed by ladder-like and ribbon-like molecules with cavities
Journal of Molecular Structure 693 (2004) 11–15 www.elsevier.com/locate/molstruc
Two new microporous coordination polymers constructed by ladder-like and ribbon-like molecules with cavities Haitao Xu, Yadong Li* Department of Chemistry, The Key Laboratory of Atomic and Molecular Nanosciences (China Ministry of Education), Tsinghua University, Haidian Dist., Beijing 100084, China Received 2 December 2003; revised 3 January 2004; accepted 8 January 2004
Abstract Two novel microporous coordination polymers constructed by ladder-like and ribbon-like molecules with cavities: 21{[Zn(C8H3NO6)·(C10H8N2)1/2·(H2O)2]·(H2O)} (1) and 21[Zn(C8H3NO6)·H2O] (2) are obtained through assemble of the corner ligand and the metal Zn2þ ion. The metal Zn2þ ion of the coordination polymer (1) is in trigonal bipyramid environment: two O atoms from carboxyl groups and one N atom furnishing the equatorial plane and the other two O atoms in axes sites. For coordination polymer (2), the metal Zn2þ ion center is in tetrahedron environment: three O atoms from carboxyl groups in bottom plane and another O atom from coordination water in axis site. These infinite ladder-like or ribbon-like molecules are orderly arranged to furnish hydrophilic microporous by molecular interaction and hydrogen bonds from water molecules and carboxyl groups. And their properties are studied in this paper. q 2004 Elsevier B.V. All rights reserved. Keywords: Hydrothermal synthesis; Coordination polymers; Crystal-structure; The cavity material
1. Introduction Due to the metal – organic complex’s interesting structural topologies and the potential applications in absorption, separation, catalysis, magnetism, nonlinear optics [1 – 8], the design and the synthesis of metal – organic open frameworks (MOFs) with large pores or cavities have rapidly developed in recent years. Furthermore, the synthesis of coordination polymer with extra-large porous has made great progress: some excellent examples in dblock transition metal carboxylate cluster: Zn4O(BDC)3· (DMF)8(C6H5Cl) [9a], Zn(BDC)·(DMF)(H2O) [9b], Zn3 (BDC)3·6CH3OH (BDC ¼ 1,4-benzenedicarboxylate), [9c] Zn 4O(tpdc) 3 ·(DMF) 8 [9d], and [Co3 (bpdc) 3bpy] (bpdc ¼ 4,40 -biphenyldicarboxylate)·4DMF·H2O [6] of the dicarboxylate cluster, Cu3(BTB)3·(H2O)3(DMF)8(H2O)2 (BTB ¼ 4,40 ,400 -benzene-1,3,5-triyl-tribenzoiclate) [10] of the tricarboxylate cluster and Cu2[o –Br –C6H3(CO2)2]2(H2O)2·(DMF)8(H2O)2 [11] of the modifying dicarboxylate cluster. As reported in literature, the metal – organic * Corresponding author. Tel.: þ86-106-277-2350; fax: þ 86-106-2788765. E-mail address: [email protected] (Y. Li). 0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2004.01.007
structural topology depend on the coordination geometry of the metal, the metal to ligand ratio, the chemical structure of the organic ligands, and the solvent [12b]. In different environment, the metal – organic complex structure could be chain [12], ladder [13], grid [14], brick wall [15], honeycomb [16], diamond [17], and channel [18]. So the rational control of the synthesis conditions is very important for the formation of new metal – organic networks, and the key to the construction of the desired frameworks is the selection of metal – organic building blocks. As we know, the high coordination number metal ions would be difficult to form open frameworks. This is cause that the condensed structures of lanthanide coordination polymers are usually reported. The transition metal (like Zn2þ or Cu2þ ion) is present the low coordination number, and they are propitious to furnish metal – organic open frameworks (MOFs) with large pores or cavities. On the other hand, the chemical structure of the organic ligands including ligand symmetry and modifying group’s steric effect would make coordination structure change and construct novel open frameworks. According to what mentioned above, the metal Zn2þ ion and the corner ligand with modifying groups are chosen to assemble the MOFs and obtain two new coordination polymers with cavities.
12
H. Xu, Y. Li / Journal of Molecular Structure 693 (2004) 11–15
2. Experimental
3. Results and discussion
2.1. Materials and methods
The crystals are all stable in air and insoluble in water and common organic solvent. The infrared spectra [19,20] show the expected strong characteristic peaks ca 1624 (vs), 1570 (s) cm21 due to the stretching-vibration of carboxyl groups. No absorptions of any protonated 5-nitroisophthalate (1715 – 1680 cm21) confirm that 5-nitroisophthalic is completely deprotonated by NaOH. The absorption peaks beyond 3000 cm21 would be depicted to y O – H of waters. As shown in Fig. 1a, the coordination polymer (1) is constructed by novel 2D ladder-like molecules with cavities. The metal Zn2þ ion center is in trigonal bipyramid environment (Fig. 1b); two O atoms (O(1) and O(3A)) from carboxyl groups of 5-nitroisophthalic acid and one N(2) atom from 4,4-bipy construct the equatorial plane and the other two O(7) and O(8) atoms from coordination waters acting as the terminal ligands occupy axes sites. Each metal Zn2þ ion bonds three organic ligands, and each organic ligand links two metal Zn2þ ions. To our best knowledge, this is the rare example of five-coordinated number for the metal Zn2þ ion. Both carboxyl groups of the ligand link the metal Zn2þ ion in mono-dentate fashion, and they are all deprotonated which is in agreement with the IR data (no absorption peak 1715 –1680 cm21). The bond length in axes sites is slightly longer than that in the equatorial plane. The hydrogen bonds exist among coordination-waters, latticewaters and the uncoordination oxygen from carboxyl groups. Due to hydrogen bonds and molecular interaction, these ladders are arranged to layer-structure along b-axis. The layers pile up to furnish 1D microporous structures down a-axis (Fig. 1c). The micro-porous with coordination waters and lattice waters are hydrophilic. The ˚ . The cavity is about 10 £ 11 layered distance is about 3 A ˚ 2 (Fig. 1a). A The complex (2) is furnished by ribbon-like molecules with cavities (Fig. 2a). The metal Zn2þ ion center is in tetrahedron environment (Fig. 2b), carboxyl groups provide three O atoms in bottom plane and another from coordination water is in axis site. Each Zn2þ ion links three ligands, and each ligand bonds three Zn2þ ions: one carboxyl group bridging two Zn2þ ions and the other bonding third Zn2þ ion in mono-dentate mode, which construct ribbon-like structure with cavities. The ribbons arrangement in the crystal is similar to what mentioned in the complex (1), and results in 1D hydrophilic micro-porous structures down b-axis (Fig. 2c), which are about ˚ 2. 4.5 £ 6.5 A According to open-frameworks of complexes (1) and (2) mentioned above, we got to know that the organic buildingblock is of importance for the formation of open-frameworks due to changing the coordination number and the coordination geometry of the metal Zn2þ ion and the coordination model of O atoms from the carboxyl groups of 5-nitroisophthalic acid. Compared with the complex (2), the porous size of the complex (1) is the same 2 times as that of
Starting regents used in this study were purchased without further purification. IR spectra were determined within the frequency range 4000 –400 cm21 on a NICOLET 560 FT – IR spectrophotometer as KBr pallets. TGA experiment was carried out with a TGA2050 thermal analyzer under an 80-ml/min N2 atmosphere. The final temperature was 900 8C at a heating rate of 10 8C/min. The investigation of the emission spectra and excited spectra of pure solid-powder was performed on Hitachi F-4500 spectrometer. The pressure – composition – temperature (P –C – T) curves for hydrogen adsorption and desorption were measured using a computer controlled ‘Gas Reaction Controller’ apparatus, which was manufactured by the Advanced Materials Corporation (AMC, Pittsburgh). The samples of 100 –500 mg (depending on the total amount and the density) in weight were placed into a stainless steel vacuum system. The volume in hydrogen adsorption– desorption process had been carefully calibrated before the actual measurement. The hydrogen adsorption and desorption were carried out at the fixed temperatures under the hydrogen pressure ranged from 0.01 to 40 atm. Ultra-high purity hydrogen (99.999%) was used. The hydrogen adsorption amount was defined as the ratio of the mass gain and the mass of the starting sample plus adsorbed hydrogen. The single-crystal structure data was collected on Bruker SMART CCD diffractometer with graphite-mono˚ ) radiation at room chromated Mo Ka ( l ¼ 0:7173 A temperature. The crystal structure was solved by Bruker SHELXTL. 2.2. Preparation of the complexes These crystals were obtained by hydrothermal technique: a mixture of 5-nitroisophthalic acid (0.208 g), NaOH (0.078 g) and distillated water (20 ml) was heated till boiling. When it was cooled, the solution was put into a 40ml bomb added ZnCl2 (0.147 g), then added 4,4-bipy (0.091 g) dissolved in ethanol (10 ml). The bomb was sealed and heated at 142 8C for 24 h., and then it was cooled to room temperature. The colorless crystals of the coordination polymer (1) 21{[Zn(C8H3NO6)·(C10H8N2)1/2·(H2O)2]·(H2O)} [19] were yielded (78.8%). Elemental analyses results of the crystal were consistent with the stoichiometry of the crystal. Calc. C, 38.3; H, 3.2; N, 6.9%. Found: C, 38.4; H 3.1; N, 6.8%. The synthesis of the crystal (2) [20] was similar to the procedure above: ZnCl2 (0.081 g) was added to a mixture of 5-nitroisophthalic acid (0.217 g), NaOH (0.080 g). The light-yellow crystals of the complex (2) 2 1[Zn(C8H3NO6)·H2O] were obtained (95.6%) at 142 8C for 72 h. Elemental analyses results of the crystal were consistent with the stoichiometry of the crystal. Calc. C, 32.8; H, 1.7; N, 4.8%. Found: C, 32.9; H 1.7; N, 4.7%.
H. Xu, Y. Li / Journal of Molecular Structure 693 (2004) 11–15
13
Fig. 1. (a) Space-filling views of complex (1) and (b) An ORTEP view of the complex (1) crystal structure showing the coordination environment around the Zn (1) atom. (c) Perspective view of the complex (1) along a-axis showing the cavities.
complex (2) when the rigid club-shaped ligand (4,4-bipy) is added to assemble open-frameworks. The metal Zn2þ ion coordination-number augment is due to terminal ligands (H2O) increasing, and the terminal ligands (such as H2O, CH3OH and CH3CH2OH) are propitious to fill up the coordination-atom vacancy of the metal ion so as to increase the stability of the open-frameworks. TGA shows two weight-loss steps in 1: 12.88% weight loss from 50 to 120 8C ascribing to the removal of three water molecules (calculated: 13.28%), 65.94% weight loss up 340 8C due to organic ligand decomposing (calculated: 64.93%). The results of 2 reveal the complex 2 is stability in high temperature (till 200 8C), and 6.01% weight loss from 200 to 260 8C equivalents to the removal of one coordination water molecules (calculated: 6.15%).
The frameworks’ decomposing and the solid – vapor transition [21] appear to be in the second-step, which occurred at 450 8C. The remaining produce is 10.5% weight. TAG reveals the thermal stability of the openframeworks is involved in the cavity-size and watermolecule status of the crystal packing. The coordination polymer with porous or cavities would become new energy-storage material with the development of material science. Due to its favorable absorption for some small molecules, the material would be required to store large amounts of energy-resource matter (such as H2, CH4, CO) at ambient temperature and relatively low pressures with small volume, low weight and fast kinetics for recharging. In order to study the cavities, the hydrogenstorage capacity of complex (1) is measured and the result is
14
H. Xu, Y. Li / Journal of Molecular Structure 693 (2004) 11–15
Fig. 2. (a) Space-filling views of complex (2) and (b) An ORTEP view of the complex (2) crystal structure showing the coordination environment around the Zn(1) atom. (c) Perspective view of the complex (2) along b-axis showing the cavities.
shown that the maximum hydrogen storage will reach weight 0.48% at low pressures (30 bar) and room temperature, which is equivalent to 0.98 H2 per formula unit. The observed uptake of H2 at lower pressure indicates sorption interaction between the open framework with cavities, and it could take up more H2 at higher pressure. Further studies about this property are in progress. The emission spectra and excited spectra of pure solidpowder (1) and (2) at room temperature reveal that the emission spectra and excited spectra of complex (1) are very similar to those of complex (2). The bright emission peak ðl ¼ 451Þ is achieved when excited at l ¼ 422 nm. The emission is neither metal-to-ligand charge transfer nor ligand-to-metal charge transfer, and could be assigned to the fluorescence from the intra ligand emission excited state. The emission spectrum of complex (1) and (2) is very similar, and the fluorescence would be related to 5nitroisophthalic acid. In summary, two new microporous coordination polymers constructed by ladder-like and ribbon-like molecules
with cavities are reported in this paper. And it illustrates that the organic-building-block is key to the porous size of the metal – organic open-frameworks. Their properties are well studied too.
Acknowledgements This work was financially supported by the NSFC (20025102, 50028201, 20151001).
References [1] C. Kahn, Martinez, Science 279 (1998) 44. [2] O. Sato, T. Lyoda, A. Fujishima, K. Hashimoto, Science 271 (1996) 49. [3] M.J. Zaworotko, Nature 386 (1997) 220. [4] O.M. Yaghi, G. Li, H. Li, Nature 374 (1995) 703. [5] Y. Tian, G.D. Li, J.S. Chen, J. Am. Chem. Soc. 125 (2003) 6622.
H. Xu, Y. Li / Journal of Molecular Structure 693 (2004) 11–15 [6] L. Pan, H. Liu, X. Lei, X. Huang, D.H.N. Olson, J. Turro, J. Li, Angew. Chem. Int. Ed. 42 (2003) 542. [7] B.F. Hoskins, R. Robson, J. Am. Chem. Soc. 112 (1990) 1546. [8] (a) R-G. Xiong, J-L. Zuo, X-Z. You, H-K. Fun, S. Raj, New J. Chem. 23 (1999) 1051. (b) D.B. Leznoff, B-Y. Xue, B.O. Patrick, V. Sanchez, R.C. Thompson, Chem. Commun. (2001) 259. [9] (a) H. Li, M. Eddaoudi, M. O’keeffe, O.M. Yaghi, Nature 402 (1999) 276. (b) H. Li, M. Eddaoudi, T.L. Groy, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 8571. (c) H. Li, C.E. Davis, T.L. Groy, D.G. Kelley, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 218. (d) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. wacher, M. O’keeffe, O.M. Yaghi, Science 295 (2002) 469. [10] B. Chen, M. Eddaoudi, S.T. Hyde, M. O’keeffe, O.M. Yaghi, Science 291 (2001) 1021. [11] M. Eddaoudi, J. Kim, M. O’keeffe, O.M. Yaghi, J. Am. Chem. Soc. 124 (2001) 376. [12] (a) X-M. Zhang, H-S. Wu, X-M. Chen, Eur. J. Inorg. Chem. 16 (2003) 2959. (b) J. Fan, M-H. Shu, T. Okamura, Y-Z. Li, W-Y. Sun, W-X. Tang, N. Ueyama, New J. Chem. (2003) 27. (c) Q-H. Zhao, H-F. Li, X-F. Wang, Z-D. Chen, New J. Chem. 26 (2002) 1709. (d) H-F. Zhu, W. Zhao, T. Okamura, B-L. Fei, W-Y. Sun, N. Ueyama, New J. Chem. 26 (2002) 1277. (e) H-P. Wu, C. Janiak, G. Rheinwald, H. Lang, J. Chem. Soc. Dalton Trans. (1999) 183. (f) L-N. Zhu, L-Z. Zhang, WZ. Wang, D-Z. Liao, P. Cheng, Z-H. Jiang, S-P. Yan, Inorg. Chem. Commun. 5 (2002) 1017. [13] (a) B-W. Sun, S. Gao, Z-M. Wang, Chem. Lett. (2001) 2. (b) P. Losier, M.J. Zaworotko, Angew Chem. Int. Ed. 35 (1996) 2779. (c) L. Mao, S.J. Retting, R.C. Thompson, J. Trotter, S. Xia, Can. J. Chem. 74 (1996) 2413. [14] L-M. Zheng, Y. Wang, X. Wang, J.D. Korp, A.J. Jacobson, Inorg. Chem. 40 (2001) 1380.
15
[15] I. Weissbuch, P.N.W. Baxter, S. Cohen, H. Cohen, K. Kjaer, P.B. Howes, J. Als-Nielsen, G.S. Hanan, U.S. Schuber, J.M. Lehn, M. Lahav, J. Am. Chem. Soc. 120 (1998) 4850. [16] M. Fujita, Y.J. Kwon, O. Sasaki, K. Ogura, J. Am. Chem. Soc. 117 (1995) 7287. [17] V. Tangoulis, C.P. Raptopoulou, V. Psycharis, A. Terzis, K. Skorda, S.P. Perlepes, O. Cador, O. Kahn, E.G. Bakalbassis, Inorg. Chem. 39 (2000) 2522. [18] (a) G.B. Gardner, D. Venkataraman, J.S. Moore, S. Lee, Nature 374 (1995) 792. (b) S-M. Ying, J.-G. Mao, B.-P. Yang, Z.-M. Sun, Inorg. Chem. Commun. 6 (2003) 1319. [19] Crystal 1 data C13 H13 N2 O9 Zn M ¼ 406:62; monoclinic, space ˚. b ¼ group C2=c; a ¼ 18:151ð7Þ; b ¼ 9:636ð3Þ; c ¼ 18:712ð7Þ A ˚ 3, DC ¼1.789 g cm23, ((Mo112.672(5)8.Z ¼ 8; V ¼ 3019:9ð18Þ A ˚ , T ¼293(2) K, m ¼1.682 mm21, 2.368 , 2u , Ka) ¼ 0.71073 A 26.438, R1½I . 2ððIÞ ¼ 0:0395; wR2 (all data) ¼ 0.0959, GOF ¼ 1.003, Deposited in CCDC-212760. IR (KBr pellet cm21): 3573 (s), 3338 (s), 3087 (s), 1624 (vs), 1570 (s), 1518 (s), 1456 (s), 1349 (vs), 1224 (w), 1070 (m), 827 (s), 788 (s). 731 (vs), 642 (s). [20] Crystal 2 data C8H5NO7 Zn M ¼ 292:50; Triclinic, space group ˚ . a ¼ 107:718ð6Þ; P 2 1; a ¼ 7:338ð3Þ; b ¼ 8:224ð3Þ; c ¼ 8:347ð3Þ A ˚ 3, DC ¼ b ¼ 105:094ð5Þ8; g ¼ 95:014ð6Þ: Z ¼ 2; V ¼ 455:6ð3Þ A ˚ , T ¼293(2) K, m ¼ 2.132 g cm23 , ((Mo-Ka) ¼ 0.71073 A 2:723 mm21, 2.648 , 2u , 25.028, R1½I . 2ððIÞ ¼0.0276, wR2 (all data) ¼ 0.0732, GOF ¼ 1.046, Deposited in CCDC-212603. IR (KBr pellet cm21): 3419 (s), 3201(s), 3093(s), 1627 (vs), 1570 (vs), 1519 (s), 1460 (vs), 1379 (s), 1348 (s), 1093 (m), 939 (m), 788 (s), 739(vs). [21] W.S. Rees Jr., O. Just, S.L. Castro, J.S. Matthews, Inorg. Chem. 39 (2000) 3736.
Two new microporous coordination polymers constructed by ladder-like and ribbon-like molecules with cavities Haitao Xu, Yadong Li* Department of Chemistry, The Key Laboratory of Atomic and Molecular Nanosciences (China Ministry of Education), Tsinghua University, Haidian Dist., Beijing 100084, China Received 2 December 2003; revised 3 January 2004; accepted 8 January 2004
Abstract Two novel microporous coordination polymers constructed by ladder-like and ribbon-like molecules with cavities: 21{[Zn(C8H3NO6)·(C10H8N2)1/2·(H2O)2]·(H2O)} (1) and 21[Zn(C8H3NO6)·H2O] (2) are obtained through assemble of the corner ligand and the metal Zn2þ ion. The metal Zn2þ ion of the coordination polymer (1) is in trigonal bipyramid environment: two O atoms from carboxyl groups and one N atom furnishing the equatorial plane and the other two O atoms in axes sites. For coordination polymer (2), the metal Zn2þ ion center is in tetrahedron environment: three O atoms from carboxyl groups in bottom plane and another O atom from coordination water in axis site. These infinite ladder-like or ribbon-like molecules are orderly arranged to furnish hydrophilic microporous by molecular interaction and hydrogen bonds from water molecules and carboxyl groups. And their properties are studied in this paper. q 2004 Elsevier B.V. All rights reserved. Keywords: Hydrothermal synthesis; Coordination polymers; Crystal-structure; The cavity material
1. Introduction Due to the metal – organic complex’s interesting structural topologies and the potential applications in absorption, separation, catalysis, magnetism, nonlinear optics [1 – 8], the design and the synthesis of metal – organic open frameworks (MOFs) with large pores or cavities have rapidly developed in recent years. Furthermore, the synthesis of coordination polymer with extra-large porous has made great progress: some excellent examples in dblock transition metal carboxylate cluster: Zn4O(BDC)3· (DMF)8(C6H5Cl) [9a], Zn(BDC)·(DMF)(H2O) [9b], Zn3 (BDC)3·6CH3OH (BDC ¼ 1,4-benzenedicarboxylate), [9c] Zn 4O(tpdc) 3 ·(DMF) 8 [9d], and [Co3 (bpdc) 3bpy] (bpdc ¼ 4,40 -biphenyldicarboxylate)·4DMF·H2O [6] of the dicarboxylate cluster, Cu3(BTB)3·(H2O)3(DMF)8(H2O)2 (BTB ¼ 4,40 ,400 -benzene-1,3,5-triyl-tribenzoiclate) [10] of the tricarboxylate cluster and Cu2[o –Br –C6H3(CO2)2]2(H2O)2·(DMF)8(H2O)2 [11] of the modifying dicarboxylate cluster. As reported in literature, the metal – organic * Corresponding author. Tel.: þ86-106-277-2350; fax: þ 86-106-2788765. E-mail address: [email protected] (Y. Li). 0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2004.01.007
structural topology depend on the coordination geometry of the metal, the metal to ligand ratio, the chemical structure of the organic ligands, and the solvent [12b]. In different environment, the metal – organic complex structure could be chain [12], ladder [13], grid [14], brick wall [15], honeycomb [16], diamond [17], and channel [18]. So the rational control of the synthesis conditions is very important for the formation of new metal – organic networks, and the key to the construction of the desired frameworks is the selection of metal – organic building blocks. As we know, the high coordination number metal ions would be difficult to form open frameworks. This is cause that the condensed structures of lanthanide coordination polymers are usually reported. The transition metal (like Zn2þ or Cu2þ ion) is present the low coordination number, and they are propitious to furnish metal – organic open frameworks (MOFs) with large pores or cavities. On the other hand, the chemical structure of the organic ligands including ligand symmetry and modifying group’s steric effect would make coordination structure change and construct novel open frameworks. According to what mentioned above, the metal Zn2þ ion and the corner ligand with modifying groups are chosen to assemble the MOFs and obtain two new coordination polymers with cavities.
12
H. Xu, Y. Li / Journal of Molecular Structure 693 (2004) 11–15
2. Experimental
3. Results and discussion
2.1. Materials and methods
The crystals are all stable in air and insoluble in water and common organic solvent. The infrared spectra [19,20] show the expected strong characteristic peaks ca 1624 (vs), 1570 (s) cm21 due to the stretching-vibration of carboxyl groups. No absorptions of any protonated 5-nitroisophthalate (1715 – 1680 cm21) confirm that 5-nitroisophthalic is completely deprotonated by NaOH. The absorption peaks beyond 3000 cm21 would be depicted to y O – H of waters. As shown in Fig. 1a, the coordination polymer (1) is constructed by novel 2D ladder-like molecules with cavities. The metal Zn2þ ion center is in trigonal bipyramid environment (Fig. 1b); two O atoms (O(1) and O(3A)) from carboxyl groups of 5-nitroisophthalic acid and one N(2) atom from 4,4-bipy construct the equatorial plane and the other two O(7) and O(8) atoms from coordination waters acting as the terminal ligands occupy axes sites. Each metal Zn2þ ion bonds three organic ligands, and each organic ligand links two metal Zn2þ ions. To our best knowledge, this is the rare example of five-coordinated number for the metal Zn2þ ion. Both carboxyl groups of the ligand link the metal Zn2þ ion in mono-dentate fashion, and they are all deprotonated which is in agreement with the IR data (no absorption peak 1715 –1680 cm21). The bond length in axes sites is slightly longer than that in the equatorial plane. The hydrogen bonds exist among coordination-waters, latticewaters and the uncoordination oxygen from carboxyl groups. Due to hydrogen bonds and molecular interaction, these ladders are arranged to layer-structure along b-axis. The layers pile up to furnish 1D microporous structures down a-axis (Fig. 1c). The micro-porous with coordination waters and lattice waters are hydrophilic. The ˚ . The cavity is about 10 £ 11 layered distance is about 3 A ˚ 2 (Fig. 1a). A The complex (2) is furnished by ribbon-like molecules with cavities (Fig. 2a). The metal Zn2þ ion center is in tetrahedron environment (Fig. 2b), carboxyl groups provide three O atoms in bottom plane and another from coordination water is in axis site. Each Zn2þ ion links three ligands, and each ligand bonds three Zn2þ ions: one carboxyl group bridging two Zn2þ ions and the other bonding third Zn2þ ion in mono-dentate mode, which construct ribbon-like structure with cavities. The ribbons arrangement in the crystal is similar to what mentioned in the complex (1), and results in 1D hydrophilic micro-porous structures down b-axis (Fig. 2c), which are about ˚ 2. 4.5 £ 6.5 A According to open-frameworks of complexes (1) and (2) mentioned above, we got to know that the organic buildingblock is of importance for the formation of open-frameworks due to changing the coordination number and the coordination geometry of the metal Zn2þ ion and the coordination model of O atoms from the carboxyl groups of 5-nitroisophthalic acid. Compared with the complex (2), the porous size of the complex (1) is the same 2 times as that of
Starting regents used in this study were purchased without further purification. IR spectra were determined within the frequency range 4000 –400 cm21 on a NICOLET 560 FT – IR spectrophotometer as KBr pallets. TGA experiment was carried out with a TGA2050 thermal analyzer under an 80-ml/min N2 atmosphere. The final temperature was 900 8C at a heating rate of 10 8C/min. The investigation of the emission spectra and excited spectra of pure solid-powder was performed on Hitachi F-4500 spectrometer. The pressure – composition – temperature (P –C – T) curves for hydrogen adsorption and desorption were measured using a computer controlled ‘Gas Reaction Controller’ apparatus, which was manufactured by the Advanced Materials Corporation (AMC, Pittsburgh). The samples of 100 –500 mg (depending on the total amount and the density) in weight were placed into a stainless steel vacuum system. The volume in hydrogen adsorption– desorption process had been carefully calibrated before the actual measurement. The hydrogen adsorption and desorption were carried out at the fixed temperatures under the hydrogen pressure ranged from 0.01 to 40 atm. Ultra-high purity hydrogen (99.999%) was used. The hydrogen adsorption amount was defined as the ratio of the mass gain and the mass of the starting sample plus adsorbed hydrogen. The single-crystal structure data was collected on Bruker SMART CCD diffractometer with graphite-mono˚ ) radiation at room chromated Mo Ka ( l ¼ 0:7173 A temperature. The crystal structure was solved by Bruker SHELXTL. 2.2. Preparation of the complexes These crystals were obtained by hydrothermal technique: a mixture of 5-nitroisophthalic acid (0.208 g), NaOH (0.078 g) and distillated water (20 ml) was heated till boiling. When it was cooled, the solution was put into a 40ml bomb added ZnCl2 (0.147 g), then added 4,4-bipy (0.091 g) dissolved in ethanol (10 ml). The bomb was sealed and heated at 142 8C for 24 h., and then it was cooled to room temperature. The colorless crystals of the coordination polymer (1) 21{[Zn(C8H3NO6)·(C10H8N2)1/2·(H2O)2]·(H2O)} [19] were yielded (78.8%). Elemental analyses results of the crystal were consistent with the stoichiometry of the crystal. Calc. C, 38.3; H, 3.2; N, 6.9%. Found: C, 38.4; H 3.1; N, 6.8%. The synthesis of the crystal (2) [20] was similar to the procedure above: ZnCl2 (0.081 g) was added to a mixture of 5-nitroisophthalic acid (0.217 g), NaOH (0.080 g). The light-yellow crystals of the complex (2) 2 1[Zn(C8H3NO6)·H2O] were obtained (95.6%) at 142 8C for 72 h. Elemental analyses results of the crystal were consistent with the stoichiometry of the crystal. Calc. C, 32.8; H, 1.7; N, 4.8%. Found: C, 32.9; H 1.7; N, 4.7%.
H. Xu, Y. Li / Journal of Molecular Structure 693 (2004) 11–15
13
Fig. 1. (a) Space-filling views of complex (1) and (b) An ORTEP view of the complex (1) crystal structure showing the coordination environment around the Zn (1) atom. (c) Perspective view of the complex (1) along a-axis showing the cavities.
complex (2) when the rigid club-shaped ligand (4,4-bipy) is added to assemble open-frameworks. The metal Zn2þ ion coordination-number augment is due to terminal ligands (H2O) increasing, and the terminal ligands (such as H2O, CH3OH and CH3CH2OH) are propitious to fill up the coordination-atom vacancy of the metal ion so as to increase the stability of the open-frameworks. TGA shows two weight-loss steps in 1: 12.88% weight loss from 50 to 120 8C ascribing to the removal of three water molecules (calculated: 13.28%), 65.94% weight loss up 340 8C due to organic ligand decomposing (calculated: 64.93%). The results of 2 reveal the complex 2 is stability in high temperature (till 200 8C), and 6.01% weight loss from 200 to 260 8C equivalents to the removal of one coordination water molecules (calculated: 6.15%).
The frameworks’ decomposing and the solid – vapor transition [21] appear to be in the second-step, which occurred at 450 8C. The remaining produce is 10.5% weight. TAG reveals the thermal stability of the openframeworks is involved in the cavity-size and watermolecule status of the crystal packing. The coordination polymer with porous or cavities would become new energy-storage material with the development of material science. Due to its favorable absorption for some small molecules, the material would be required to store large amounts of energy-resource matter (such as H2, CH4, CO) at ambient temperature and relatively low pressures with small volume, low weight and fast kinetics for recharging. In order to study the cavities, the hydrogenstorage capacity of complex (1) is measured and the result is
14
H. Xu, Y. Li / Journal of Molecular Structure 693 (2004) 11–15
Fig. 2. (a) Space-filling views of complex (2) and (b) An ORTEP view of the complex (2) crystal structure showing the coordination environment around the Zn(1) atom. (c) Perspective view of the complex (2) along b-axis showing the cavities.
shown that the maximum hydrogen storage will reach weight 0.48% at low pressures (30 bar) and room temperature, which is equivalent to 0.98 H2 per formula unit. The observed uptake of H2 at lower pressure indicates sorption interaction between the open framework with cavities, and it could take up more H2 at higher pressure. Further studies about this property are in progress. The emission spectra and excited spectra of pure solidpowder (1) and (2) at room temperature reveal that the emission spectra and excited spectra of complex (1) are very similar to those of complex (2). The bright emission peak ðl ¼ 451Þ is achieved when excited at l ¼ 422 nm. The emission is neither metal-to-ligand charge transfer nor ligand-to-metal charge transfer, and could be assigned to the fluorescence from the intra ligand emission excited state. The emission spectrum of complex (1) and (2) is very similar, and the fluorescence would be related to 5nitroisophthalic acid. In summary, two new microporous coordination polymers constructed by ladder-like and ribbon-like molecules
with cavities are reported in this paper. And it illustrates that the organic-building-block is key to the porous size of the metal – organic open-frameworks. Their properties are well studied too.
Acknowledgements This work was financially supported by the NSFC (20025102, 50028201, 20151001).
References [1] C. Kahn, Martinez, Science 279 (1998) 44. [2] O. Sato, T. Lyoda, A. Fujishima, K. Hashimoto, Science 271 (1996) 49. [3] M.J. Zaworotko, Nature 386 (1997) 220. [4] O.M. Yaghi, G. Li, H. Li, Nature 374 (1995) 703. [5] Y. Tian, G.D. Li, J.S. Chen, J. Am. Chem. Soc. 125 (2003) 6622.
H. Xu, Y. Li / Journal of Molecular Structure 693 (2004) 11–15 [6] L. Pan, H. Liu, X. Lei, X. Huang, D.H.N. Olson, J. Turro, J. Li, Angew. Chem. Int. Ed. 42 (2003) 542. [7] B.F. Hoskins, R. Robson, J. Am. Chem. Soc. 112 (1990) 1546. [8] (a) R-G. Xiong, J-L. Zuo, X-Z. You, H-K. Fun, S. Raj, New J. Chem. 23 (1999) 1051. (b) D.B. Leznoff, B-Y. Xue, B.O. Patrick, V. Sanchez, R.C. Thompson, Chem. Commun. (2001) 259. [9] (a) H. Li, M. Eddaoudi, M. O’keeffe, O.M. Yaghi, Nature 402 (1999) 276. (b) H. Li, M. Eddaoudi, T.L. Groy, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 8571. (c) H. Li, C.E. Davis, T.L. Groy, D.G. Kelley, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 218. (d) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. wacher, M. O’keeffe, O.M. Yaghi, Science 295 (2002) 469. [10] B. Chen, M. Eddaoudi, S.T. Hyde, M. O’keeffe, O.M. Yaghi, Science 291 (2001) 1021. [11] M. Eddaoudi, J. Kim, M. O’keeffe, O.M. Yaghi, J. Am. Chem. Soc. 124 (2001) 376. [12] (a) X-M. Zhang, H-S. Wu, X-M. Chen, Eur. J. Inorg. Chem. 16 (2003) 2959. (b) J. Fan, M-H. Shu, T. Okamura, Y-Z. Li, W-Y. Sun, W-X. Tang, N. Ueyama, New J. Chem. (2003) 27. (c) Q-H. Zhao, H-F. Li, X-F. Wang, Z-D. Chen, New J. Chem. 26 (2002) 1709. (d) H-F. Zhu, W. Zhao, T. Okamura, B-L. Fei, W-Y. Sun, N. Ueyama, New J. Chem. 26 (2002) 1277. (e) H-P. Wu, C. Janiak, G. Rheinwald, H. Lang, J. Chem. Soc. Dalton Trans. (1999) 183. (f) L-N. Zhu, L-Z. Zhang, WZ. Wang, D-Z. Liao, P. Cheng, Z-H. Jiang, S-P. Yan, Inorg. Chem. Commun. 5 (2002) 1017. [13] (a) B-W. Sun, S. Gao, Z-M. Wang, Chem. Lett. (2001) 2. (b) P. Losier, M.J. Zaworotko, Angew Chem. Int. Ed. 35 (1996) 2779. (c) L. Mao, S.J. Retting, R.C. Thompson, J. Trotter, S. Xia, Can. J. Chem. 74 (1996) 2413. [14] L-M. Zheng, Y. Wang, X. Wang, J.D. Korp, A.J. Jacobson, Inorg. Chem. 40 (2001) 1380.
15
[15] I. Weissbuch, P.N.W. Baxter, S. Cohen, H. Cohen, K. Kjaer, P.B. Howes, J. Als-Nielsen, G.S. Hanan, U.S. Schuber, J.M. Lehn, M. Lahav, J. Am. Chem. Soc. 120 (1998) 4850. [16] M. Fujita, Y.J. Kwon, O. Sasaki, K. Ogura, J. Am. Chem. Soc. 117 (1995) 7287. [17] V. Tangoulis, C.P. Raptopoulou, V. Psycharis, A. Terzis, K. Skorda, S.P. Perlepes, O. Cador, O. Kahn, E.G. Bakalbassis, Inorg. Chem. 39 (2000) 2522. [18] (a) G.B. Gardner, D. Venkataraman, J.S. Moore, S. Lee, Nature 374 (1995) 792. (b) S-M. Ying, J.-G. Mao, B.-P. Yang, Z.-M. Sun, Inorg. Chem. Commun. 6 (2003) 1319. [19] Crystal 1 data C13 H13 N2 O9 Zn M ¼ 406:62; monoclinic, space ˚. b ¼ group C2=c; a ¼ 18:151ð7Þ; b ¼ 9:636ð3Þ; c ¼ 18:712ð7Þ A ˚ 3, DC ¼1.789 g cm23, ((Mo112.672(5)8.Z ¼ 8; V ¼ 3019:9ð18Þ A ˚ , T ¼293(2) K, m ¼1.682 mm21, 2.368 , 2u , Ka) ¼ 0.71073 A 26.438, R1½I . 2ððIÞ ¼ 0:0395; wR2 (all data) ¼ 0.0959, GOF ¼ 1.003, Deposited in CCDC-212760. IR (KBr pellet cm21): 3573 (s), 3338 (s), 3087 (s), 1624 (vs), 1570 (s), 1518 (s), 1456 (s), 1349 (vs), 1224 (w), 1070 (m), 827 (s), 788 (s). 731 (vs), 642 (s). [20] Crystal 2 data C8H5NO7 Zn M ¼ 292:50; Triclinic, space group ˚ . a ¼ 107:718ð6Þ; P 2 1; a ¼ 7:338ð3Þ; b ¼ 8:224ð3Þ; c ¼ 8:347ð3Þ A ˚ 3, DC ¼ b ¼ 105:094ð5Þ8; g ¼ 95:014ð6Þ: Z ¼ 2; V ¼ 455:6ð3Þ A ˚ , T ¼293(2) K, m ¼ 2.132 g cm23 , ((Mo-Ka) ¼ 0.71073 A 2:723 mm21, 2.648 , 2u , 25.028, R1½I . 2ððIÞ ¼0.0276, wR2 (all data) ¼ 0.0732, GOF ¼ 1.046, Deposited in CCDC-212603. IR (KBr pellet cm21): 3419 (s), 3201(s), 3093(s), 1627 (vs), 1570 (vs), 1519 (s), 1460 (vs), 1379 (s), 1348 (s), 1093 (m), 939 (m), 788 (s), 739(vs). [21] W.S. Rees Jr., O. Just, S.L. Castro, J.S. Matthews, Inorg. Chem. 39 (2000) 3736.