CRYSTAL GROWTH & DESIGN
Three Unprecedented Entangled Metal-Organic Frameworks: Self-Penetration and Hydrothermal in Situ Ligand Formation
2009 VOL. 9, NO. 7 2995–2998
Li-Xin Sun,† Yan Qi,† Yun-Xia Che,*,† Stuart R. Batten,‡ and Ji-Min Zheng*,† Department of Chemistry, Nankai UniVersity, Tianjin 300071, China, and School of Chemistry, Monash UniVersity, Victoria 3800, Australia ReceiVed March 6, 2009; ReVised Manuscript ReceiVed May 13, 2009
ABSTRACT: Three unprecedented entangled systems are successfully obtained. Compounds 1 and 2 are self-penetrating networks with
intracatenated [M2bimh2] loops and two-dimensional [M2(bptc)] sheets ((H4bptc ) biphenyl-3,3′,4,4′-tetracarboxylic acid, bimh ) 1,6bis(imidazol-1-yl)-hexane), while compound 3 is a three-dimensional self-penetrating network which results from the hydrothermal in situ formation of a new tetradentate ligand, 1,2,4,5-tetra(4-pyridyl)benzene, through dehydrogenative coupling of 1,3-bis(4-pyridyl)propane molecules. Particular attention has been recently devoted to entangled systems because of their undisputed beauty and potential applications as materials for gas storage, separation, and catalysis.1,2 A large number of fascinating entangled families are now recognized, such as the common types of interpenetrating networks and the more sophisticated cases of self-penetrated arrays, Borromean architectures, and polyrotaxane-like species, whose topological classification is in progress.3,4 Conformationally flexible ligands, showing varied geometries, are often featured in these new classes of compounds. We are continuing to investigate the use of flexible N,N′-bidentate ligands along with metal aromatic polycarboxylates, and these spacers have already shown a preference for the formation of M2L2 rings when adopting cis conformations.5 We report here three remarkable entangled frameworks, namely, [M2(bptc)(bimh)2] (M ) CoII(1), ZnII(2)) and [Co2(bptc)(tpb)] (3) (H4bptc ) biphenyl3,3′,4,4′-tetracarboxylic acid, bimh ) 1,6-bis(imidazol-1-yl)-hexane and tpb ) 1,2,4,5-tetra(4-pyridyl)benzene). All the compounds contain 2D [M(bptc)0.5]n sheets. Those sheets in compounds 1 and 2 are catenated with [M2bimh2] loops to generate a two-dimensional (2D) self-penetrating network, while those in the three-dimensional (3D) self-penetrating framework of compound 3 are interlocked with [Co2tpb2]n ribbons of rings that result from the in situ formation of a new tetradentate ligand, tpb, through dehydrogenative coupling of 1,3-bis(4-pyridyl)propane (bpp) molecules under hydrothermal conditions.
Experimental Section. Materials and General Procedures. Solvents and starting materials for synthesis were purchased commercially and used as received. The ligand bimh was prepared according to reported procedures.6 Elemental analysis for C, H, and N was performed on a Perkin-Elmer 240 analyzer. The thermogravimetric analysis was performed with a Shimadzu TGA50H TG analyzer in the range of 25-800 °C under a nitrogen flow at a heating rate of 5 °C/min for all measurements. The photoluminescence measurements were carried out on crystalline samples at room temperature, and the spectra were collected with a Hitachi F-2500FL spectrophotometer.
X-ray Crystallographic Measurements for 1-3. Suitable single crystals of 1-3 were selected and mounted in air onto thin glass fibers. Accurate unit cell parameters were determined by a least-squares fit of 2θ values, and intensity data were measured on a Rigaku r-axis rapid IP area detector with Mo KR radiation (λ ) 0.71073 Å) at room temperature. The intensities were corrected for Lorentz and polarization effects as well as for empirical * Corresponding author: Tel: +86-22-23508056; fax:+86-22-23508056; e-mail:
[email protected]. † Nankai University. ‡ Monash University.
Table 1. Crystallographic Data and Structure Refinement Details for 1-3
formula formula weight T/K crystal system space group a /Å b /Å c /Å β /deg V /Å3 Z D/mg m-3 F(000) no. of reflns collected/unique GOF R1 [I > 2σ(I)] wR2 (for all data)
1
2
3
C20H21CoN4O4 440.34 298 monoclinic P21/c 8.2499(16) 12.370(3) 19.628(5) 108.48(3) 1899.8(8) 4 1.540 912 4346
C20H21ZnN4O4 446.78 298 monoclinic P21/c 8.2795(17) 12.504(3) 19.464(5) 108.73(3) 1908.3(8) 4 1.555 924 4273
C21H12CoN4O2 411.26 298 orthorhombic Pbam 11.115(2) 20.780(4) 9.910(2)
1.024 R1 ) 0.0377 wR2 ) 0.0885
1.054 R1 ) 0.0337 wR2 ) 0.0836
1.019 R1 ) 0.0831 wR2 ) 0.2824
2288.9(8) 4 1.205 844 2763
absorption based on multiscan techniques; all structures were solved by direct methods and refined by full-matrix least-squares fitting on F2 by SHELX-97. All non-hydrogen atoms were refined with anisotropic thermal parameters. Crystallographic data for compounds 1-3 are suummarized in Table 1, and selected bond lengths and bond angles for compounds 1-3 are listed in Table S1 (see Supporting Information). Synthesis of [Co2(bptc)(bimh)2] (1). The mixture of CoCl2 · 6H2O (0.24 g, 1.0 mmol), H4bptc (0.33 g, 0.5 mmol), and bimh (0.21 g, 1.0 mmol) was dissolved in 10 mL of distilled water. The pH was adjusted to 5.0 by addition of 1 M NaOH solution. Consequently, the resulting mixture was transferred and sealed in a 25 mL Teflon-lined stainless steel vessel, which was sealed and heated at 180 °C for 72 h. After the reactor was slowly cooled to room temperature, purple crystals of 1 were obtained and in yield: 52% (based on Co). Elemental analysis (%): Calcd. For 1: C 47.51, H 3.84, N 12.31; Found: C 47.58, H 3.78, N 12.36. Selected FTIR (KBr): ν (cm-1) ) 3130(m), 3089(m), 1606(s), 1574(m), 1405(m), 1092(m), 839(m), 659(m). Synthesis of [Zn2(bptc)(bimh)2] (2). The mixture of Zn(NO3)2 · 6H2O (0.30 g, 1.0 mmol), H4bptc (0.33 g, 0.5 mmol), and bimh (0.21 g, 1.0 mmol) was dissolved in 10 mL of distilled water. The pH was adjusted to 5.0 by addition of 1 M NaOH solution. Consequently, the resulting mixture was transferred and sealed in a 25 mL Teflon-lined stainless steel vessel, which was sealed and heated at 180 °C for 72 h. After the reactor was slowly cooled to room temperature, colorless crystals of 2 were obtained and in yield: 55% (based on Zn). Elemental analysis (%): Calcd. For 2: C 53.76,
10.1021/cg9002719 CCC: $40.75 2009 American Chemical Society Published on Web 06/01/2009
2996
Crystal Growth & Design, Vol. 9, No. 7, 2009
Communications
Figure 1. (a) The immediate coordination environment around the Co(II) center in 1; (b) the view of the 2D self-penetrated sheet of 1.
H 4.74, N 12.54; Found: C 53.72, H 4.79, N 12.48. Selected FTIR (KBr): ν (cm-1) ) 3132(m), 3093(m), 1608(s), 1585(m), 1404(m), 1096(m), 831(m), 663(m). Synthesis of [Co2(bptc)(tpb)] (3). The mixture of CoCl2 · 6H2O (0.24 g, 1.0 mmol), H4bptc (0.33 g, 0.5 mmol), and bpp (0.20 g, 1.0 mmol) was dissolved in 10 mL of distilled water. The pH was adjusted to 5.0 by addition of 1 M NaOH solution. Consequently, the resulting mixture was transferred and sealed in a 25 mL Teflonlined stainless steel vessel, which was sealed and heated at 180 °C for 72 h. After the reactor was slowly cooled to room temperature, purple crystals of 3 were obtained and in yield: 38% (based on Co). Elemental analysis (%): Calcd. For 3: C 61.33, H 2.94, N 13.62; Found: C 61.40, H 2.92, N 13.58. Selected FT-IR (KBr): ν (cm-1) ) 3130(m), 1604(s), 1552(m), 1408(s), 847(m), 672(m).
Results and Discussion. Crystal Structure of [Co2(bptc)(bimh)2] (1). Crystallographic analysis revealed that compounds 1 and 2 are isostructural. Hence, only the crystal structure of compound 1 is described here in detail. Each Co(II) ion in 1 is four-coordinate with a distorted tetrahedral geometry, composed of two carboxylic O atoms from two bptc4- anions (Co-O ) 1.9616(15) Å and 1.9946(16) Å) and two N atoms from two bimh ligands (Co-N ) 2.018(2) Å and 2.0467(19)Å) (Figure 1a). All the bimh ligands adopt a cis conformation, with the dihedral angle of the two imidazolyl rings being 59.70°. Two bimh ligands connect two Co(II) atoms to achieve a 26-membered [Co2(bimh)2] metallacyclic ring exhibiting maximum dimensions (corresponding to the Co · · · Co distance and shortest intracycle C...C separation) of 12.741 Å × 7.499 Å (Figure S1, Supporting Information). Furthermore, the four carboxylic groups of each completely deprotonated bptc4- anion adopt monodentate modes and coordinate to four Co atoms to generate a 2D layer (Figure S2, Supporting Information). Notably, the two types of windows are catenated, as
Figure 2. (a) The immediate coordination environment around the Co(II) center in 3; (b) the view of 1D loop-containing [Co4(tpb)] chain in 3; the front (c) and side (d) views of the 3D self-penetrated framework of compound 3.
Communications
Crystal Growth & Design, Vol. 9, No. 7, 2009 2997 Scheme 1
shown in Figure 1b, but also connected by shared Co atoms. That is to say, all the [Co2bimh2] loops are threaded by the longer CobptcCo rods (node-to-node distance of 12.472 Å) of the 2D net. The entanglement found here is unprecedented. One might initially describe it as a polyrotaxane4,7 due to the extensive and prominent rotaxane-like interactions, but caution should be exercised. In all self-penetrating and interpenetrating networks, by definition, rotaxane-like interactions can be defined (and also for all molecular catenanes). However, in true polyrotaxanes, by analogy to molecular rotaxanes, the ring and rod components should not be connected except by the rotaxane mechanical bond, and there should be no catenane type interactions. Both these conditions are clearly violated here, and thus the net is classified as a self-penetrating net, which can be thought of as the polymeric equivalent of a molecular knot. Furthermore, the self-catenated layer is one more example for which a special notation is needed to describe the topology: the introduction of 2-connected nodes in the point/Schlafli symbol. Such notation is the 2-membered rings (i.e., the “loops”), introduced by Ma and Batten.8 Therefore, the whole net is trinodal 2,4-connected (4 · 83 · 102)2(4)2(85 · 10) network. Crystal Structure of [Co2(bptc)(tpb)] (3). The structure of 3 is a 3D self-penetrating framework containing ribbons of rings catenated with 2D layers. In 3, each Co(II) atom is fivecoordinated by three carboxylic O atoms from two bptc4- anions (Co-O ) 1.997(7)-2.212(7) Å) and two N atoms from one tpb molecule (Co-N ) 2.090(4) Å) (Figure. 2a). Notably, the formation of 3 involves an interesting tetradentate dye molecule, 1,2,4,5-tetra(4-pyridyl)benzene (tpb), which was formed in situ hydrothermally via oxidative coupling of 1,3-bis(4-pyridyl)propane (bpp) molecules (Scheme 1).9 The in situ formation of tpb from bpp is still rare, with only three examples of the coupling of bpp into tpb reported.9 The tpb ligand connects four Co ions to generate ribbons of rings running along the c axis (Figure 2b). Neighboring chains are almost perpendicular. Meanwhile, the bptc4- anions form 2D sheets similar to those in 1. The overall 3D array of 3 is formed by the intersection, at the shared Co nodes, of the 1D [Co2(tpb)]n ribbons and the 2D [Co2(bptc)]n sheets (Figure 2c,d). As shown in Figure 2c, each loop of the 1D [Co2(tpb)]n chain is threaded by a Cobptc-Co rod of the 2D [Co2(bptc)]n layer to afford the 3D self-penetrating motif. The structure can also be described in terms of 2D self-penetrating layers (Figure S4, Supporting Information), similar to compounds 1 and 2, which are further linked by benzene rings formed between two bpp units. Evidently, the oxidative coupling between two bpp units is essential in establishing the 3D framework in 3. From the view of the topology, such 3D self-catenated framework is a trinodal 4-connected network with the Schla¨fli symbol (4 · 85)2(42 · 82 · 102)(86). Thermal Analyses. To study the stability of the supramolecular architecture, thermogravimetric analyses experiment (TGA) of compounds 1-3 were carried out in the temperature range of 30-700 °C. As shown in Figure 3, 1, 2, and 3 all begin to collapse from about 320 °C. At about 620 °C, 1 and 3 decomposed completely and the remaining residues are CoO (calcd: 17.01%, found: 17.82% for 1; calcd: 18.22%, found: 18.02% for 3). The resulting residue of 2 remains as ZnO (calcd: 18.32%, found: 18.60%) after the complete decomposition of the organic ligands.
Figure 3. The TG plots of these MOFs.
Figure 4. The emission spectra of 2 at room temperature (λex ) 343 nm).
Photoluminescent measurement of compound 2 was carried out in the solid state at room temperature. The solid-state photoluminescent spectrum of 2 is depicted in Figure 4. It can be seen that the intense photoluminescence emission at 425 nm (λex ) 343 nm) is exhibited, which is tentatively assigned to the intraligand transition fluorescence.10 In conclusion, three unprecedent self-penetrated systems have been presented. This work may give an impetus to the further exploration of new types of entanglement.
Acknowledgment. This work was supported by the National Natural Science Foundation of China (50872057). Supporting Information Available: X-ray crystallographic file in CIF format, tables of bond lengths and angles for all the compounds (Table S1) and some figures of compounds 1-3 (Figures S1-S4) are available free of charge via the Internet at http://pubs.acs.org.
References (1) (a) Janiak, C. Angew. Chem., Int. Ed. 1997, 36, 1431. (b) Noro, S.; Kitagawa, S.; Kondo, M.; Seki, K. Angew. Chem., Int. Ed. 2000, 39, 2081. (c) Zaworotko, M. J. Angew. Chem., Int. Ed. 2000, 39, 2113. (d) Kitaura, R.; Seki, K.; Akiyama, G.; Kitagawa, S. Angew. Chem., Int. Ed. 2003, 42, 428. (2) (a) Eddaoudi, M.; Li, H.; Yaghi, O. M. J. Am. Chem. Soc. 2000, 122, 1391. (b) Kepert, C. J.; Prior, T. J.; Rosseinsky, M. J. J. Am. Chem. Soc. 2001, 123, 10001. (c) Noro, S.; Kitaura, R.; Kondo, M.; Kitagawa, S.; Ishii, T.; Matsuzaka, H.; Yamashita, M. J. Am. Chem. Soc. 2002, 124, 2568. (3) (a) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460. (b) Batten, S. R. CrystEngComm 2001, 3, 67.
2998
Crystal Growth & Design, Vol. 9, No. 7, 2009
(4) (a) Carlucci, L.; Ciani, G.; Proserpio, D. M. Coord. Chem. ReV. 2003, 246, 247. (b) Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. CrystEngComm 2004, 6, 377. (c) Baburin, I. A.; Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. J. Solid State Chem. 2005, 178, 2452. (d) Baburin, I. A.; Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. Cryst. Growth Des. 2008, 8, 519. (5) (a) Qi, Y.; Che, Y. X.; Zheng, J. M. Cryst. Growth Des. 2008, 8, 3602. (b) Qi, Y.; Luo, F.; Che, Y. X.; Zheng, J. M. Cryst. Growth Des. 2008, 8, 606. (c) Luo, F.; Che, Y. X.; Zheng, J. M. Cryst. Growth Des. 2006, 6, 2432. (6) So, Y. H. Macromolecules 1992, 25, 516. (7) (a) Hoskins, B. F.; Robson, R.; Slizys, D. A. J. Am. Chem. Soc. 1997, 119, 2952. (b) Gao, X. M.; Li, D. S.; Wang, J. J.; Fu, F.; Wu, Y. P.; Hu, H. M.; Wang, J. W. CrystEngComm 2008, 10, 479. (c) Wang, X. L.; Qin, C.; Wang, E. B.; Li, Y. G.; Su, Z. M.; Xu, L.; Carlucci,
Communications L. Angew. Chem., Int. Ed. 2005, 44, 5824. (d) Carlucci, L.; Ciani, G.; Proserpio, D. M. Cryst. Growth Des. 2005, 5, 37. (e) Hoskins, B. F.; Robson, R.; Slizys, D. A. Angew. Chem., Int. Ed. 1997, 36, 2336. (f) Goodgame, D. M. L.; Menzer, S.; Smith, A. M.; Williams, D. J. Angew. Chem., Int. Ed. 1995, 34, 574. (8) Yang, J.; Ma, J. F.; Batten, S. R.; Sua, Z. M. Chem. Commun. 2008, 2233. (9) (a) Zheng, N. F.; Bu, X. H.; Feng, P. Y. J. Am. Chem. Soc. 2002, 124, 9688. (b) Zhang, J.; Wu, T.; Feng, P. Y.; Bu, X. H. Chem. Mater. 2008, 20, 5457. (c) Han, L.; Zhao, W. N.; Zhou, Y.; Li, X.; Pan, J. G. Cryst. Growth Des. 2008, 8, 3504. (10) Wang, J. J.; Gou, L.; Hu, H. M.; Han, Z. X.; Li, D. S.; Xue, G. L.; Yang, M. L.; Shi, Q. Z. Cryst. Growth Des. 2007, 7, 1514.
CG9002719
