Assembly of Metal-Organic Frameworks with Helical Layer: From 2D Parallel Interpenetrated Layer to 3D Self-Penetrating Network Lei Han,*,† Yan Zhou,† Wen-Na Zhao,‡ Xing Li,† and Yun-Xiao Liang† State Key Laboratory Base of NoVel Functional Materials & Preparation Science, Faculty of Materials Science & Chemical Engineering, Ningbo UniVersity, Ningbo, Zhejiang, 315211, P. R. China, and Key Laboratory for Molecular Design and Nutrition Engineering of Ningbo, Ningbo Institute of Technology, Zhejiang UniVersity, Ningbo, Zhejiang 315100, P. R. China
CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 2 660–662
ReceiVed August 27, 2008; ReVised Manuscript ReceiVed December 9, 2008
ABSTRACT: Two novel Co(II)-organic frameworks with helical structures, [Co(hfipbb)(py)]n (1) and {[Co4(OH)(H2O)(hfipbb)3(Hhfipbb)(bpp)2] · H2O}n (2) (H2hfipbb ) 4,4′-(hexafluoroisopropylidene)bis(benzoic acid), py ) pyridine, bpp ) 1,3-bis(4-pyridyl)propane), have been assembled from flexible bent ligands. Complex 1 displays a 2-fold parallel interpenetrated layer network with one-dimensional double helical channels, while 2 exhibits a three-dimensional pillared helical-layer open framework with six-connected self-penetrating topology based on a mixed dinuclear paddle-wheel cluster and tetranuclear [Co4(µ3-OH)2(µ2-OH2)2] steplike cluster. . Helical assemblies such as protein bundles and DNA are prevalent in biological systems and play key roles in molecular recognition, replication, and catalysis.1 Several approaches have been developed for constructing abiological helices for potential applications in chiral separations, asymmetric catalysis, and nonlinear optics. One promising approach is the use of coordination chemistry to direct the assembly of small component molecules into extended polymeric materials exhibiting helical structures.2 Larger numbers of helical coordination polymers, such as onedimensional (1D) n-stranded helices, two-dimensional (2D) helical layers, and 3D metal-organic frameworks containing helical features, as well as three-dimensional (3D) entangled frameworks from single helical chains, have been systemically investigated in recent years.2-5 The helical layer has already been reported several years ago as a new 2D structure,5 whereas studies on entangling it into interpenetrated networks or extending it into 3D open frameworks remained less explored.3d Another fascinating structure feature in the field of metal-organic frameworks is the construction of entangled systems, which are discussed in several excellent reviews.6 Of the many reported types of entanglement in polymeric architectures, the phenomenon of selfpenetration has attracted much attention.7 The construction of 3D self-penetrating frameworks has been proven to be an effective and controllable approach to design functional polymeric materials with novel topology. However, the occurrence of self-penetrating networks with helical character, especially 2D helical layers, is particularly rare. Inspired by the aforementioned considerations, our current synthetic strategy is to construct 3D self-penetrating networks by linking the parallel interpenetrating helical layers with high-connected metal cluster nodes. As is well-known, metal clusters with substituted single metal atoms have been used as nodes for high-connected metal-organic frameworks.8 The crucial step for the design of helical coordination polymers is the choice of ligands. The ligands should be ditopic and thus capable of bridging metal atoms in certain directions and should also contain steric information that can be interpreted by the arrangement of the bound metal centers, resulting in the formation of helical structures. Along with our research of assembly of helical coordination polymers2b,3b,5a and entangled networks9 based on conformational flexible ligands, herein we employed a long and bent ligand, 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) (H2hfipbb) (Scheme 1), as an excellent candidate for the construction of targeted frameworks. This selection is adopted not only * To whom correspondence should be addressed. E-mail:
[email protected]. † Ningbo University. ‡ Zhejiang University.
Scheme 1. The Ligands
because the long and bent features benefit the formation of helical and self-penetrating networks, but also because the synthesis of metal cluster nodes is usually by the controlled hydrolysis of metal salts with the aid of caboxylate ligands. On the other hand, the assemblies of extended solids from the long and bent arenedicarboxylate linkers are considerably less studied even though they would likely offer new topologies with channels.10 As expected, we successfully isolated a novel 2D Co(II)-organic complex with dinuclear paddle-wheel cluster as node, [Co(hfipbb)(py)]n (1), which displays a 2-fold parallel 2D f 2D interpenetrated helical layer network with 1D helical channels. Then by introducing another flexible exo-bisdentate ligand, 1,3-bis(4-pyridyl)propane (bpp) (Scheme 1), into linking to layers, an unprecedented 3D open framework, {[Co4(OH)(H2O)(hfipbb)3(Hhfipbb)(bpp)2] · H2O}n (2), was obtained. Interestingly, 2 exhibits a novel six-connected selfpenetrating topology with helical layers based on mixed dinuclear paddle-wheel cluster and tetranuclear [Co4(µ3-OH)2(µ2-OH2)2] steplike clusters. The thermal analyses of all complexes have also been investigated. The hydrothermal reaction of CoCl2 · 6H2O, H2hfipbb, and pyridine in aqua afforded deep-blue crystals of 1,11 which are characterized by elemental analysis, IR spectra, and XPRD (see Supporting Information). Single-crystal X-ray analysis12 revealed that 1 is composed of an interpenetrated polymeric structure without the presence of any solvent molecule. Its asymmetric unit consists of one cobalt atoms, one hfipbb ligand, and one pyridine (Figure S1, Supporting Information). The basic secondary building unit (SBUs) is composed of dimetallic tetracarboxylate paddle-wheel clusters bridged by hfipbb moieties. Among the class of metal carboxylates, the tetracarboxylate-bridged dimetallic (e.g., Cu24+, Zn24+, and Mo24+) paddle-wheels have been envisaged as SBUs for the construction of metal-organic frameworks that display nanosized porosity and magnetic properties.13 In the dimetallic structure, Co-O bond distances are in the range of 2.019(2)-2.073(2) Å, Co-N bond distances are 2.063(2) Å, and the intradimer Co-Co separation is 2.8165(9) Å, which are all within the normal range found in other reported experiments.13f,g The hfipbb ligand in bent conformation presents a dihedral angle of 75.9° between the two
10.1021/cg800945m CCC: $40.75 2009 American Chemical Society Published on Web 12/24/2008
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Figure 2. Two distinct metal clusters in 2 as six-connected nodes.
Figure 1. (Top) View of 2-fold parallel interpenetration of 1 with double-stranded helical structures. (Bottom) Schematic representation of 1D double helical channels in 2D layers of 1.
benzene rings. Significantly, the bent hfipbb moieties link each paddle-wheel cluster to another four neighboring paddle-wheel clusters, which results into an undulating (4,4) net with a rhombic window. The dimensions of the net are 14.138 × 14.138 Å, corresponding to the distance between adjacent centers of dinuclear cobalt subunits at their corner. As shown in Figure 1, the covalent skeleton of this 2D sheet can also be described as a unique helical tubular double layer in which the left and right helical chains appear alternatively by sharing the paddle-wheel clusters. The pitch of helix is about 15.2 Å based on cluster cores. The interesting feature of 1 is the occurrence of a parallel 2D f 2D interpenetrating feature consisting of two identical helical layers (Figure 1). Upon 2-fold parallel interpenetration, the 1D double helical channels in skeleton are formed, and the PLATON14 calculation shows that the effective void volume has been drastically reduced to 544.6 Å3, which approximately corresponds to 11.8% of the crystal volume (4618.0 Å3). To extend the parallel interpenetrating helical double layers into 3D frameworks, we employed the conformational flexible exobisdentate bpp ligand as coligand to replace the monodentate pyridine molecules in 1. The hydrothermal reaction of CoCl2 · 6H2O, H2hfipbb, and bpp in aqua afforded purple crystals of 2.15 Singlecrystal X-ray analysis16 revealed that 2 is a 3D network with an unprecedented structural features. The first interesting structural feature is that 2 contains two distinct metal clusters for construction of this polymer. One is dimetallic tetracarboxylate paddle-wheel clusters, similar to that in 1. In the two paddle-wheel clusters of 2, the intradimer Co-Co separations are 2.775 and 2.816 Å. The other metal cluster is a unique tetranuclear [Co4(µ3-OH)2(µ2-OH2)2] unit (Figure S2, Supporting Information). The tetranuclear cluster locates on a center of inversion. All of four Co atoms have distorted octahedral coordination geometry. The Co3 atom coordinates to two N atoms of bpp ligands, two O atoms of carboxylate groups, one µ3-OH and one µ2-OH2, while Co4 center links to three O atoms of carboxylate groups, two µ3-OH and one µ2-OH2 moieties. The Co-O bond distances range from 2.002 to 2.327 Å, the Co-N bond distances vary from 2.114 to 2.133 Å. Consequently, the [Co4(µ3-OH)2(µ2-OH2)2] subunit presents a unique distorted steplike
Figure 3. The 3D network structure and schematic representation of the six-connected self-penetrating network of 2 (the interpenetrating helical layers are shown by red and green lines).
structure, with each of the 10 edges of the Co4O4 step defined by a Co-O bond. Meanwhile, all four edges of the rhombic tetranuclear Co4 cluster core are also bridged by the µ2(η1,η1) carboxylate group of ligands, respectively. Although a number of discrete Co(II) clusters have been reported as single molecular magnets, extended coordinated networks formed by such kinds of tetranuclear Co4 clusters are unusual.17 The second striking structural feature of 2 is the presence of the 2-fold parallel 2D f 2D interpenetrated helical layer network with 1D double helical channels. As expected, the helical layer is identical to that of 1, which indicates that we have successfully extended the interpenetrating helical layers into 3D frameworks. The neighboring layers are pillared by tetranuclear clusters and bpp ligands. The third structural feature is that the H2hifpbb ligands display various coordinated modes, and the bpp ligands exhibit different conformations in 2. Three coordinated modes of H2hifpbb ligands present as bridged tetradentate, bridged tridentate, and terminal bidentate. Meanwhile, the highly flexible bpp ligand presents two kinds of conformations, trans-trans (TT) and transgauche (TG), with respect to the relative orientations of the CH2 groups. Both ligands could cooperate with each other by adjusting their coordinations and conformations to generate the final framework. The last striking structural fearture is that 2 exhibits a novel sixconnected self-penetrating topology. The di- and tetranuclear cluster units are linked by organic ligands to another six neighboring metal clusters, respectively, which can be considered as six-connected nodes shown in Figure 2. It is noteworthy that the neighboring tetranuclear Co clusters are connected by double organic linkers to give a 1D double chains structure in 2. Because of the occurrence of the interpenetrated helical layers in 2, so the overall structure gives an unprecedented six-connected self-penetrating network (Figure 3). Taking into account these structural features of complex 2, to the best of our knowledge, it is the first 3D metal-organic framework with six-connected self-penetrating topology based on helical layers and mixed paddle-wheel cluster, tetranuclear [Co4(µ3OH)2(µ2-OH2)2] steplike clusters.
662 Crystal Growth & Design, Vol. 9, No. 2, 2009 To further identify the stability of the whole frameworks of 1 and 2, thermal gravimetric analyses (TGA) measurements were performed (Figures S7 andS8, Supporting Information). The results show that the frameworks of 1 and 2 are stable up to 220 and 360 °C, respectively, demonstrating the higher stability of 3D structure of 2 with mixed metal clusters than 1. In conclusion, we have demonstrated the successful assembly of two novel Co(II)-organic frameworks with helical structures from flexible bent ligands. This work represents a unique example of synthetic strategy that the construction of 3D self-penetrating networks from parallel interpenetrating helical layers with highconnected metal cluster nodes. We are currently extending this work into additional metal ions.
Acknowledgment. This work is supported by the National Natural Science Foundation of China (20701022), Natural Science Foundation of Zhejiang Province (Y4080435), Natural Science Foundation of Ningbo Municipal (2007A610024, 2008A610045, 2008A610048), Open Foundation of Municipal Key Laboratory of Ningbo (2007A22003), and the K. C. Wong Magna Fund in Ningbo University. Supporting Information Available: TGA, XRPD, other figures, and crystallographic data in CIF for 1 and 2. These materials are available free of charge via the Internet at http://pubs.acs.org.
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(b) Pan, L.; Olson, D. H.; Ciemnolonski, L. R.; Heddy, R.; Li, J. Angew. Chem., Int. Ed. 2006, 45, 616. (c) Yuen, T.; Lin, C. L.; Pan, L.; Huang, X.-Y.; Li, J. J. Appl. Phys. 2006, 99, 08J501. (d) Monge, A.; Snejko, N.; Gutie´rrez-Puebla, E.; Medina, M.; Cascales, C.; RuizValero, C.; Iglesias, M.; Go´mez-Lor, B. Chem. Commun. 2005, 1291. (e) Ga´ndara, F.; Gomez-Lor, B.; Gutie´rrez-Puebla, E.; Iglesias, M.; Monge, M. A.; Proserpio, D. M.; Snejko, N. Chem. Mater. 2008, 20, 72. (f) Ga´ndara, F.; Andre´s, A. D.; Go´mez-Lor, B.; Gutie´rrez-Puebla, E.; Iglesias, M.; Monge, M. A.; Proserpio, D. M.; Snejko, N. Cryst. Growth Des. 2008, 8, 378. Synthesis of complex 1: A mixture of CoCl2 · 6H2O (24 mg, 0.1 mmol), H2hfipbb (80 mg, 0.2 mmol), pyridine (80 mg, 1 mmol), and water (8 mL) was homogenized at room temperature for 30 min, and then the final solution was sealed in a 20 mL stainless-steel autoclave at 170 °C for 72 h. A quantity of deep-blue single crystals of 1 was obtained after the solution was cooled to room temperature. The yield of 1 is ca. 74% based on CoCl2 · 6H2O. Anal. Calcd. for C22H13CoF6NO4 (%): C, 50.02; H, 2.48; N 2.65. Found (%): C, 50.73; H, 2.84; N, 2.19. IR (KBr, ν/cm-1): 3420(m), 2920(vw), 2358(m), 1628(vs), 1538(s), 1410(vs), 1252(s), 1174(s), 959(w), 725(m). Crystal data for 1: C22H13CoF6NO4, M ) 528.26, monoclinic, space group C2/c (No. 15), a ) 30.102(6), b ) 7.6184(15), c ) 23.820(5) Å, β ) 122.29(3)°, V ) 4618.0(16) Å3, Z ) 8, Dc ) 1.520 g/cm3, F000 ) 2120, Mo-KR radiation, λ ) 0.71073 Å, T ) 293(2) K, µ ) 0.819 mm-1. Final GOF ) 1.086, R1 ) 0.0428, wR2 ) 0.0969. (a) Del Sesto, R. E.; Arif, A. M.; Miller, J. S. Inorg. Chem. 2000, 39, 4894. (b) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34, 10–758. (c) Chui, S. S.-Y.; Lo, S. M.-F.; Charamant, J. P. H.; Orpen, A. G.; Williams, I. D. Science 1999, 283, 1148. (d) Vos, T. E.; Liao, Y.; Shum, W. W.; Her, J.-H.; Stephens, P. W.; Reiff, W. M.; Miller, J. S. J. Am. Chem. Soc. 2004, 126, 11630. (e) Moulton, B.; Abourahma, H.; Bradner, M. W.; Lu, J. J.; McManus, G. J.; Zaworotko, M. J. Chem. Commun. 2003, 1342. (f) Lee, D. W.; Hung, P.-L.; Spingler, B.; Lippard, S. J. Inorg. Chem. 2002, 41, 521. (g) Eremenko, I. L.; Nefedov, S. E.; Sidorov, S. E.; Golubnichaya, M. A.; Danilov, P. V.; Ikorskii, P. V.; Shvedenkov, Y. G.; Novotortsev, V. M.; Moiseev, I. I. Inorg. Chem. 1999, 38, 3764. Dolomanov, O. V.; Blake, A. J.; Champness, N. R.; Schro¨der, M. J. Appl. Crystallogr. 2003, 36, 1283. Synthesis of complex 2: A mixture of CoCl2 · 6H2O (0.0331 g, 0.14 mmol), H2hfipbb (0.0455 g, 0.12 mmol), and 1,3-bis(4-pyridyl)propane) (0.0280 g, 0.14 mmol) in 8 mL of deionized water was homogenized at room temperature for 30 min. Then the final solution was sealed in a 20 mL stainless-steel autoclave at 170 °C for 72 h. A quantity of platelet purple crystals of 2 was obtained after the solution was cooled to room temperature. The crystals were filtered, washed, with deionized water and dried at room temperature. The yield of 2 is ca. 63% based on CoCl2.6H2O. Anal. Calcd. for C94H59Co4F24N4O19 (%): C, 50.40; H, 2.65; N 2.50. Found (%): C, 50.82; H, 3.01; N, 2.91. IR (KBr, ν/cm-1): 3462(m), 2941(vw), 2360(w), 1618(vs), 1545(s), 1411(vs), 1246(vs), 1202(s), 1172(vs), 970(w), 777(m), 727(m). Crystal data for 2: C94H59Co4F24N4O19, M ) 2240.17, monoclinic, space group P21/c (No. 14), a ) 29.450(6), b ) 15.409(3), c ) 23.393(5) Å, β ) 111.80(3)°, V ) 9856(3) Å3, Z ) 4, Dc ) 1.510 g/cm3, F000 ) 4508, Mo-KR radiation, λ ) 0.71073 Å, T ) 293(2) K, µ ) 0.775 mm-1. Final GOF ) 1.104, R1 ) 0.0982, wR2 ) 0.2409. The high R(F) is in part related to the disorder of flexible bpp ligands, which limits the resolution of the diffraction data. (a) Chiang, R. K.; Huang, C. C.; Wur, C. S. Inorg. Chem. 2001, 40, 3237. (b) Xiang, S. C.; Wu, X. T.; Zhang, J. J.; Fu, R. B.; Hu, S. M.; Zhang, X. D. J. Am. Chem. Soc. 2005, 127, 16352. (c) Luo, J. H.; Zhao, Y. S.; Xu, H. W.; Kinnibrugh, T. L.; Yang, D. L.; Timofeeva, T. V.; Daemen, L. L.; Zhang, J. Z.; Bao, W.; Thompson, J. D.; Currier, R. P. Inorg. Chem. 2007, 46, 9021.
CG800945M
