First Three-Dimensional Self-Penetrating Coordination Polymer

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First Three-Dimensional Self-Penetrating Coordination Polymer Containing Rare (10,3)‑d Subnets: Synthesis, Structure, and Properties Li-Hui Cao,† Qing-Qing Xu,† Shuang-Quan Zang,*,† Hong-Wei Hou,† and Thomas C. W. Mak†,‡ †

College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, P. R. China Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, P. R. China

‡

S Supporting Information *

ABSTRACT: Hydrothermal assembly of ZnII ion, a tripodal ligand with both flexible imidazole and rigid carboxylate groups [HL = 3,5bis(imidazol-1-ylmethyl)benzoic acid hydrochloride], and rigid bidentate linker 5-iodoisophthalic acid (5-iipa) yields a novel threedimensional (3D) self-penetrating metal−organic framework [Zn2(L)2(5-iipa)]n (1). Complex 1 exhibits a (62·8)(63·8·102) topology that is unprecedented with the rare (10,3)-d (or utp) subnets. In addition, photoluminescence was also performed on 1.

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in 2011.10 To the best of our knowledge, the self-penetrating networks based on (10,3)-d nets have not been reported. Over the past few years, our group has focused on a systematic synthetic and structural investigation of transition metal complexes containing carboxylate-based ligands11 or polycarboxylic acids with additional pyridyl functional bindingsite ligands.12 These kinds of ligands have been exploited by our group and other groups13 to construct a wide variety of metal−organic frameworks. As far as we know, assembly of coordinated polymers containing bifunctional ligands with both nitrogen donors and carboxylate groups have received less attention and limited examples have been reported.12,14 In this work, the ligand 3,5bis(imidazol-1-ylmethyl)benzoic acid hydrochloride (HL) was chosen to present a framework with rare (10,3)-d (or utp) subnets based on the following considerations: (i) it is a tripodal ligand with both flexible imidazole and rigid carboxylate groups which may be efficient to construct (10,3) nets and (ii) the skew coordination orientation of the flexible imidazol group provides the potential to form a helical coordination polymer. Hydrothermal reaction of HL and Zn(NO3)2·4H2O at the presence of 5-iipa resulted in the formation of colorless block crystals, [Zn2(L)2(5-iipa)]n (1). The phase purity of the bulk sample was confirmed by elemental analysis and powder X-ray

onstruction of metal−organic frameworks (MOFs) has become an increasingly popular field of research over the past decades, owing to their intriguing aesthetic architectures, topological features, and their promising applications as functional materials.1,2 Topological approach not only is a powerful tool for the simplification, analysis, and comparison of multitudinous framework structures but also plays an instructive role in the rational design of some functional materials with desired properties.3 One approach is to perform reactions with a mixed ligand in the same system, and a great number of new intriguing structures are obtained.4 Among many three-dimensional (3D) MOFs, the three-connected (10,3) nets are widely investigated because of their tendency to form large voids, in which (10,3)a, (10,3)-d, and (10,3)-f nets are very similar in the four-fold axis direction.5 Triangular ligands [such as 1,3,5-benzenetricarboxylic acid and 1,3,5-tris(2H-tetrazole-5-yl)benzene] have proven to be good candidates for constructing MOFs with (10,3) nets, and some complexes containing (10,3) nets with such ligands were reported recently.6 However, the (10,3)-d species containing alternate left- and right-handed helices are very few.7 Self-penetrating networks, in which the smallest circuits are passed through by rods of the same net, are not very common within coordination polymers. Compared with the widely studied interpenetrating networks,8 the investigation of selfpenetrating networks remains less explored.3b,9 Alexandrov et al. have summarized 12 cases of interpenetrating (10,3)-d nets © 2013 American Chemical Society

Received: January 31, 2013 Revised: April 16, 2013 Published: April 19, 2013 1812

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diffraction. The single-crystal X-ray diffraction result reveals that complex 1 crystallizes in the orthorhombic space group Pccn and has a self-penetrating 3D framework. The asymmetric unit consists of one ZnII cation, one L− ligand, and half a 5-iipa ligand, as shown in Figure 1. In complex 1, the ZnII center

Figure 1. Asymmetric unit and atom labeling in complex 1. All hydrogen atoms are omitted for clarity. Symmetry codes: A: 0.5 + x, − 0.5 + y, − z; B: 1.5 − x, y, 0.5 + z; C: 1.5 − x, − 0.5 − y, z.

Figure 3. One independent single (10,3)-d net in the self-penetrating framework of 1. One 10-membered shortest circuit is highlighted by orange.

adopts a distorted tetrahedral geometry surrounded by one carboxylate oxygen atom from 5-iipa ligand and two nitrogen atoms and one carboxylate oxygen atom from two L− ligands. As for the L− ligand, the two imidazole groups at the N1 and N4 positions make dihedral angles of 74.72° and 62.98°, respectively, with the corresponding linked benzene rings. In the crystal structure of complex 1, ZnII centers are connected together through L − ligands to give a 3D substructure, which contains interesting helixes with different chirality (Figure 2). On the basis of the distance from their

ligands, resulting in the unusual 3D self-penetrating architecture, as illustrated in Figure S1 of the Supporting Information. Interestingly, the distance between the nearest O and I atoms in the whole structure is 3.13 Å, indicating the existence of strong O···I halogen bonding, as shown in Figure S1c of the Supporting Information. As illustrated in Figure 3, from the topological point of view, complex 1 can be simplified as a self-penetrating (3,4)connected network with an unprecedented (62·8)(63·8·102) topology. In this topology, taking no account of the 5-iipa ligands between two identical 3D frameworks, the ZnII center can be looked at as a 3-connected nonplanar node with trigonal-pyramid geometry. Because the L− ligand can be looked at as a planar 3-connected node, the whole network can thus be represented topologically by two types of 3-connected nodes (trigonal-pyramidal and trigonal-planar nodes, respectively). The left- and right-handed helices in this topology arrange in the cross-linkage. On the basis of the above connection mode, the two identical 3D frameworks can be extended to two 3D unusual (10,3)-d nets, which are assigned to the utp nets. As shown in Figure 4, the main original feature of the utp net is the unprecedented self-penetration. We note that two (10,3)d subnets are catenated together by 5-iipa ligands to give a selfpenetrated framework. To our knowledge, interpenetrated and noninterpenetrated (10,3)-d nets have been known to be present in coordination polymers, but such a self-penetrating framework with utp subnets has not been reported yet. We

Figure 2. One 3D substructure with the arrangement of the left- and right-handed helical chains along the b axis in 1.

axes, these helical chains can be distinguished as smaller and bigger helices. One imidazole group and carboxylate group from the same L− anion coordinate to two ZnII cations to form the smaller infinite Zn-L helical chain along the b axis with a pitch of 17.69 Å. On the other hand, two ZnII cations which are bridged by two imidazole groups from the L− anion are linked together by the imidazole group and carboxylate groups from another L− anion to form the bigger infinite Zn-L helical chain along the b axis. The nearest Zn···Zn distances through the L− ligands are 9.51 Å. As shown in Figure 3, four bigger helical chains with different chirality are linked together by one smaller helical chain, and at the same time, every bigger helical chain links four smaller helical chains with different chirality to form a 3D substructure. As we usually find, in order to stabilize the framework and minimize the big void cavities, the potential voids formed by a single 3D subnetwork incorporate with another identical network, thus giving a two-fold interpenetrating framework. The adjacent 3D frameworks are bridged by the auxiliary 5-iipa

Figure 4. Self-penetrating (3,4)-connected network containing two (10,3)-d subnets in 1. (Red lines represent 5-iipa ligands). 1813

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(2) (a) Brizard, A.; Stuart, M.; Bommel, K. V.; Friggeri, A.; Jong, M. D.; Esch, J. V. Angew. Chem., Int. Ed. 2008, 47, 2063. (b) Duriska, M. B.; Neville, S. M.; Lu, J.-Z.; Iremonger, S. S.; Boas, J. F.; Kepert, C. J.; Batten, S. R. Angew. Chem., Int. Ed. 2009, 48, 8919. (3) (a) Wang, X.-L.; Qin, C.; Wang, E.-B.; Li, Y.-G.; Su, Z.-M. Chem. Commun. (Cambridge, U.K.) 2005, 5450. (b) Kathalikkattil, A. C.; Bisht, K. K.; Aliaga-Alcalde, N.; Suresh, E. Cryst. Growth Des. 2011, 11, 1631. (c) Lan, Y.-Q.; Li, S.-L.; Qin, J.-S.; Du, D.-Y.; Wang, X.-L.; Su, Z.-M.; Fu, Q. Inorg. Chem. 2008, 47, 10600. (d) Ke, X.-J.; Li, D.-S.; Du, M. Inorg. Chem. Commun. 2011, 14, 788. (4) (a) Du, M.; Jiang, X.-J.; Zhao, X.-J. Inorg. Chem. 2007, 46, 3984. (b) Fang, S.-M.; Hu, M.; Zhang, Q.; Du, M.; Liu, C.-S. Dalton Trans. 2011, 40, 4527. (5) (a) Liu, Q.-Y.; Wang, Y.-L.; Shan, Z.-M.; Cao, R.; Jiang, Y.-L.; Wang, Z.-J.; Yang, E.-L. Inorg. Chem. 2010, 49, 8191. (b) Li, M.-N.; Du, D.-Y.; Yang, G.-S.; Li, S.-L.; Lan, Y.-Q.; Shao, K.-Z.; Qin, J.-S.; Su, Z.-M. Cryst. Growth Des. 2011, 11, 2510. (6) (a) Prior, T. J.; Rosseinsky, M. J. Inorg. Chem. 2003, 42, 1564. (b) Sun, D.; Ke, Y.; Collins, D. J.; Lorigan, G. A.; Zhou, H.-C. Inorg. Chem. 2007, 46, 2725. (7) (a) Black, C. A.; Hanton, L. R. Cryst. Growth Des. 2007, 7, 1868. (b) Zhang, J.; Chen, Y.-B.; Chen, S.-M.; Li, Z.-J.; Cheng, J.-K.; Yao, Y.G. Inorg. Chem. 2006, 45, 3161. (8) (a) Wu, H.; Yang, J.; Su, Z.-M.; Batten, S. R.; Ma, J.-F. J. Am. Chem. Soc. 2011, 133, 11406. (b) Yang, J.; Ma, J.-F.; Batten, S. R. Chem. Commun. (Cambridge, U.K.) 2012, 48, 7899. (9) (a) Carlucci, L.; Ciani, G.; Proserpio, D. M. Coord. Chem. Rev. 2003, 246, 247. (b) Zhang, L.-P.; Ma, J.-F.; Yang, J.; Pang, Y.-Y.; Ma, J.-C. Inorg. Chem. 2010, 49, 1535. (c) Yang, J.; Li, B.; Ma, J.-F.; Liu, Y.Y.; Zhang, J.-P. Chem. Commun. (Cambridge, U.K.) 2010, 46, 8383. (10) (a) Tong, M.-L.; Chen, X.-M.; Batten, S. R. J. Am. Chem. Soc. 2003, 125, 16170. (b) Blake, K. M.; Lucas, J. S.; LaDuca, R. L. Cryst. Growth Des. 2011, 11, 1287. (c) Xiao, D.-R.; Chen, H.-Y.; Zhang, G.-J.; Sun, D.-Z.; He, J.-H.; Yuan, R.; Wang, E.-B. CrystEngComm 2011, 13, 433. (d) Alexandrov, E. V.; Blatov, V. A.; Kochetkova, A. V.; Proserpio, D. M. CrystEngComm 2011, 13, 3947. (11) (a) Zang, S.-Q.; Liang, R.; Fan, Y.-J.; Hou, H.-W.; Mak, T. C. W. Dalton Trans. 2010, 39, 8022. (b) Cao, L.-H.; Li, H.-Y.; Zang, S.-Q.; Hou, H.-W.; Mak, T. C. W. Cryst. Growth Des. 2012, 12, 4299. (12) (a) Zang, S.-Q.; Cao, L.-H.; Liang, R.; Hou, H.-W.; Mak, T. C. W. Cryst. Growth Des. 2012, 12, 1830. (b) Ji, C.; Li, B.; Ma, M.-L.; Zang, S.-Q.; Hou, H.-W.; Mak, T. C. W. CrystEngComm 2012, 14, 3951. (13) (a) Farnum, G. A.; Pochodylo, A. L.; LaDuca, R. L. Cryst. Growth Des. 2011, 11, 678. (b) Bisht, K. K.; Suresh, E. Inorg. Chem. 2012, 51, 9577. (14) (a) Su, Z.; Chen, M.; Okamura, T. A.; Chen, M.-S.; Chen, S.-S.; Sun, W.-Y. Inorg. Chem. 2011, 50, 985. (b) Su, Z.; Fan, J.; Chen, M.; Okamura, T. A.; Sun, W.-Y. Cryst.Growth Des. 2011, 11, 1159. (15) (a) Wang, S. Coord. Chem. Rev. 2001, 215, 79. (b) Zheng, S.-L.; Yang, J.-H.; Yu, X.-L.; Chen, X.-M.; Wong, W.-T. Inorg. Chem. 2004, 43, 830.

have applied a name for this new topology to the authors of RCSR and TOPOS TTD databases, and its name (zjc1) has been added to the TOPOS Web site in the personal.ttd file. Photoluminescence properties (Figure S3 of the Supporting Information) of complex 1 and the free ligand HL12b in the solid state at room temperature show that the free HL ligand exhibits a broad emission band at 451 nm (λex = 326 nm), and the complex displays a strong broad fluorescence emission band at 585 nm when irradiated at 326 nm, which is highly redshifted by 134 nm compared with that of the L− ligand. This result indicates that the fluorescence of 1 may be due to the coordination interactions of the L− ligand, which effectively increase the rigidity of the ligand and reduce the loss of energy by radiation-less decay of the intraligand emission excited state. On the other hand, the strong π−π interactions between the adjacent benzene rings of the layers may also contribute to reducing the energy π−π* transition.15 To characterize this complex in terms of thermal stability, thermalgravimetric analysis (TGA) of 1 was carried out in nitrogen atmosphere. In accordance with Figure S4 of the Supporting Information, no obvious weight loss was observed until the temperature reached 300 °C, where the framework of the structure began to collapse. X-ray powder diffraction (XRD) was used to check the purity of 1. As shown in Figure S5 of the Supporting Information, all the peaks displayed in the (b) measured patterns are similar to those in the (a) simulated patterns generated from singlecrystal diffraction data, indicating single phases of 1 are formed. In summary, we have demonstrated that the tripodal ligand with both flexible imidazole and rigid carboxylate groups can be used to create metal−organic frameworks composed of mixed ligands, thereby forming the first 3D self-penetrating framework containing 103-utp subnets. In addition, this coordination polymer displays modest thermal stability and solid state fluorescent emission. Further studies based on this and related ligands are underway in our laboratory and will be reported in due course.

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ASSOCIATED CONTENT

S Supporting Information *

Synthetic details, X-ray diffraction data, tables of crystallographic information, structural details, fluorescent emission spectra, thermalgravimetric curve, powder XRD patterns, and crystallographic information files in CIF format (that has been also deposited as CCDC 905684 in the Cambridge Crystallographic Data Centre). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the National Natural Science Foundation of China (Grant 20901070) and Zhengzhou University (P. R. China).

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REFERENCES

(1) Special issues for metal-organic frameworks: (a) Chem. Soc. Rev. 2009, 38, 1201−1508. (b) Chem. Rev. 2012, 112, 673−1268. 1814

dx.doi.org/10.1021/cg400191x | Cryst. Growth Des. 2013, 13, 1812−1814