3D copper coordination polymers based on N-heterocyclic ligands with different topology

Inorganic Chemistry Communications 13 (2010) 417–420

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3D copper coordination polymers based on N-heterocyclic ligands with different topology Xiang He a,*, Zhao-Xi Wang a, Fei-Fei Xing a, Ming-Xing Li a,b,* a b

Department of Chemistry, College of Sciences, Shanghai University, Shanghai 200444, China State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China

a r t i c l e

i n f o

Article history: Received 15 October 2009 Accepted 7 January 2010 Available online 11 January 2010 Keywords: Copper N-Heterocycle Coordination polymer Crystal structure

a b s t r a c t Two novel three-dimensional (3D) coordination polymers ½CuII3 ðmttaÞ6 n (1) and ½CuII2 CuI3 ðtrzÞ4 Br3 n nH2O (2) (mtta = 5-methyltetrazolate, trz = 1,2,4-triazole) were synthesized and structurally characterized. Complex 1 shows a 3D porous metal–organic framework. By the topology analysis, the complicated architecture of 1 can be simplified to be the 4-connected diamond-type net. Compound 2 is a two-fold interpenetrating 3,5-connected 3D framework with new topology. Ó 2010 Elsevier B.V. All rights reserved.

The design and synthesis of metal-organic frameworks is of great interest due to their intriguing topologic architecture and significant application in many fields [1–3]. As members of the N-heterocyclic class of compounds, tetrazole and triazole species are significant not only for their application in the medicine biology field but also for their widespread use as bridging ligands in coordination chemistry. These ligands possess extensive abilities to bridge metal ions into polynuclear clusters or high-dimensional intricate structures, which are always difficult to recognize and analyze their structures. However, a particularly useful tool is the analysis of network topology, which reduces multidimensional structures to simple node-and-connection reference nets [4]. This might be an important and essential approach to understanding the structure at a molecular or an atomic resolution [5–8]. Recently, a series of coordination polymers assembled by suitable tetrazolates via in situ ligand synthesis have been studied, which exhibit intriguing structural motifs and luminescent properties [9–14]. So far, most of the work in the field of constructing tetrazole coordination frameworks has been done by varying the metal ions, especially ZnII, CdII, CoII, FeII, CuI/CuII, and AgI have been used extensively. However, copper ions always present lower valence in most of copper-tetrazolates system [15,16]. Here, we report two novel 3D coordination polymers ½CuII3 ðmttaÞ6 n (1) and ½CuII2 CuI3 ðtrzÞ4 Br3 n nH2O (2) [17] (mtta = 5-methyltetrazolate, trz = 1,2,4-

* Corresponding authors. Address: Department of Chemistry, College of Sciences, Shanghai University, Shanghai 200444, China. Tel.: +86 21 66132803; fax: +86 21 66134594 (X. He). E-mail addresses: [email protected] (X. He), [email protected] (M.-X. Li). 1387-7003/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.01.001

triazole), in which copper ions show higher valence and mixvalence. The blue prism crystals of 1 and green prism crystals of 2 were obtained via hydrothermal synthetic method and structurally characterized by X-ray diffraction analysis [18]. Complex 1 shows a 3D porous metal–organic framework. There are two crystallographically independent Cu(II) ions in an asymmetric unit with distorted octahedral coordination geometries (Fig. S1). The Cu(1) at (1/2, 3/4, 1/8) is at a site with 4 axis symmetry, Cu(2) at (1/2, 1, 0) is at a site with 1 symmetry. The mtta ligand lies in a mirror plane with N(1) at a site with two-fold symmetry. The role of the 5-methyltetrazole ligand, in which the methyl group show significant disorder, is a tridentate spacer connector bridging three Cu(II) ions together to form a 3D network (Fig. 1a). The skeleton framework consists of a fundamental repeating unit [Cu3(mtta)6], in which each of Cu(1) and Cu(2) is octacoordinated by six tetrazolate ligands in l3-tetrazolyl coordination mode via N(2), N(3) and N(4). The Cu–N lengths ranging from 2.046(6) to 2.347(9) Å are close to those reported for copper(II)nitrogen compounds [19]. Both Cu(1) and Cu(2) centers show Jahn–Teller distortion with four equatorially ligated tetrazoles (Cu(1)–N(2) = 2.046(6) Å; Cu(2)–N(4) = 2.027(7) Å, Cu(2)–N(3) = 2.070(8) Å) and axially ligated tetrazoles (Cu(1)–N(1) = 2.347(9), Cu(2)–N(5) = 2.310(8) Å). Each Cu(1) bridged by tetrazolate ligands connects with other four Cu(2) atoms to form the block A (Fig. 1b), which connect each other by sharing their metal apices to form the one-dimensional chain as unit B (Fig. 1c). Viewed down from the baxis, it can be found that each of unit B shared by tetrazolate ligands with four other adjacent unit B to form a tetragonal channel. This channel was also made by two kinds of copper-nitrogen

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Fig. 1. (a) The 3D framework of compound 1, viewed down from b-axis; (b) each Cu1 bridged by tetrazolate ligands to connected with other four Cu2 atoms to form the block A; and (c) one-dimensional chain as unit B.

helices chains in opposite direction (Fig. S2). Finally, compound 1 exhibits a 3D porous framework constructed by these units B. Calculations using PLATON [20] show that the effective volume for the inclusion is about 126.7 Å3 per unit cell in compound 1. Thermogravimetric analysis (Fig. S3) shows that 1 is thermally stable up to about 123 °C. Further heating led to decomposition of 1 and the final inorganic residue was formed. Compound 1 adopts similar structure as {[Cd3(ta)6]6H2O}n [14], the different lie on the following points, (1) The space group is I4(1)/a for compound 1, while is Fd-3m for the latter; (2) The tetragonal channel is occupied by six gust water molecules in the latter compound, while there is no water molecule in compound 1, due to the methyl groups on 5-position of tetrazole filling the space. Better insight of the complicated 3D architecture can be achieved by topology analysis. This net contains two types of node (Cu(1) and Cu(2)) and one type of link (tetrazolate ligand). It may be considered as a four-connected dia-type net with the 66 topology, because each Cu(1) connects to four other Cu(1) through Cu(2) (Fig. 2). When the Cu(1) centers are treated as four-connected nodes, the Cu(2) can be treated as two-connected nodes. An investigation of the topologic structure shows the tetrahedral coordina-

tion of Cu(1) in 1 is similar to that of carbon atoms in diamond. The distance of Cu(1)  Cu(1) is 7.557(2) Å and the Cu(1)  Cu(1)   Cu(1) angles are in the range of 102.31(2)113.17(2)°, which represents a slight distortion from the ideal tetrahedral angle of 109.5° in a diamond net [21]. Compare the structure of 1 to compound {[Cu(Mtta)]0.17H2O}n [15], the latter compound can only be considered as three-connected topological net. This net has short and long Schafli symbol of 83 and 828181 that contain 3-fold helices and pseudo-5-fold helices. The Cu ions also present the lower valence in the latter compound. It is interesting that the structure of 2 is a two-fold interpenetrated 3D framework. As shown in Fig. 3, the structure of 2 possesses four unique metal sites, which adopt three kinds of coordination modes, namely five-, three- and two-coordination. CuII(3) and CuII(4) centers are all coordinated by four nitrogen atoms from different triazole ligands and one l2-bridging bromido ligand in distorted square-pyramidal geometries, in which CuII(3),

Fig. 2. Schematic illustration of the 4-connected dia-type net with the 66 topology symbol in 1.

Fig. 3. ORTEP drawing of 2, showing the coordination environment of copper(II) centers.

X. He et al. / Inorganic Chemistry Communications 13 (2010) 417–420

CuII(4) and Br(1) atoms are located at a symmetric plane. CuI(2) is in a distorted trigonal sphere, surrounding by two nitrogen donors from diverse triazole ligands (Cu–N: 1.929(7), 1.930(6) Å) and one bromido ligand with N–Cu–Br bond angles ranging from 101.4(2)° to 104.0(2)°. With respect to CuI(1), the linear geometry is provided by two l2-bridging bromido anions. The deprotonated triazole ligands exhibit l3-bridging mode in 2 via N(1), N(2) and N(4). CuII(3) and CuII(4) centers are linked by two triazoles and one l2-bridging bromido ligand with Cu  Cu separation of 3.5212(2) Å. This unit is further connected by two triazole ligands with Cu  Cu separation of 3.7332(2) Å to form a 1D chain (Fig. S4). The {Cu2N4} ring formed by CuII(3), CuII(4) atoms and the 1- and 2nitrogen donors of the triazole ligands is nonplanar with the dihedral angles of 60.35(2)° between Cu(3)Cu(4)N(4)N(5) and Cu(3)Cu(4)N(4B)N(5B), and of 56.59(2)° between Cu(3)Cu(4)N(1)N(2) and Cu(3)Cu(4)N(1B)N(2B). These chains are further connected each other via N4 site of triazole ligands bonding to Cu(2) atoms to construct unusual 2D layer (Fig. S5). The dihedral angle between C(1)N(1)N(2)C(2)N(3) and C(3)N(4)N(5)C(4)N(6) is 58.54(2)°. Viewed down to the c-axis, these 2D layers are further connected each other by Br–Cu(1)–Br unit to form the final 3D structure that including 1D channel with approximate 10.91  5.93 Å2 dimension (van der Waals radii are accounted). These channels were constructed by left- or right-handed helix chains respectively (Fig. 4). To the best of our knowledge, 3D porous MOFs contain 1D helix chains are rarely reported. Furthermore, these 3D architectures pass through each other to generate the interpenetrating 3D network (Fig. 5). This is consistent with the fact that crystal structures with such large cavities are stabilized either by inclusion of suitable guests or by interpenetrating lattices [22]. Compare the structure of 2 to Cu(I)Cu(II)(trz)X complexes reported by Jon Zubieta and coworkers [19]. We can see the copper atom has a labile metal center with versatile coordination properties, normally adopts two-, three-, four-, five- or six-coordination to form diversity geometric constraints, which is the main reason to construct a variety of copper-1,2,4-triazole coordination polymers, while 1,2,4-trz ligand and anion X also play an important role to generate interesting compounds that may exhibit intriguing topological architectures. These results can be proven distinctly by the Cu(I)Cu(II)(trz)Br system, the copper atom only adopt two kinds of coordination modes in [CuIICuI(trz)Br2]n, while adopt three kinds of coordination modes in complex 2. Versatile coordination modes might result in the special two-fold interpenetrated 3D framework of compound 2. From the viewpoint of network topology, compound 2 can be simplified as a new 3,5-connected 4-nodal network as shown in Fig. S6. The triazole ligands can be treated as a 3-connected node with two kinds of Schafli symbol (4,82) and (3,82). Then, the

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Fig. 5. Schematic representation of the interpenetrated 3D framework in 2.

Cu(2) becomes 3-connected node with (8,102) Schafli symbol, and Cu(3), Cu(4) become 5-connected nodes. The Schafli symbol for this 3,5-connected uniform network is (3,82)(32,42, 82,92,102)(4,82)(8,102) [23]. Comparing with reported 3,5-connected 4-nodal example [24], we find a ocu-d-a net. However, ocu-d-a net is usually characterized by three-, four-, six- and twelve-membered rings. Whereas the present net shows features of three-, four-, eight-, nine- and ten-membered rings. Magnetic susceptibility measurement of the crystalline sample of 1 was carried out on a Quantum Design MPMS-XL7 SQUID magnetometer in an applied magnetic field of 2 kOe over the temperature range 1.8300 K. Variable-temperature magnetic susceptibilities in the forms of vMT and n1 M versus T are shown in Fig. S7. The vMT value at room-temperature is 1.07 emu K mol1. As temperature is lowered to 50 K, vMT decreases slowly. Then it sharply downs to 0.48 emu K mol1 upon cooling to 1.8 K. This is a typical behavior for an antiferromagnetic interaction. It is in agreement with Curie-Weiss law, and the magnetic susceptibility fitting in the whole temperature range gave a Weiss constant h = 12.0 K and a Curie constant C = 1.12 emu K mol1. In summary, we have hydrothermally synthesized and characterized two MOFs. The single crystal X-ray diffraction suggests that polymer 1 and 2 are all three-dimensional frameworks. Compound 1 exhibits a four-connected dia-type porous architecture. Compound 2 shows an interpenetrating 3D MOFs with first reported 3,5-connected topology. From both compounds, we find polydentate tetrazole and triazole species can construct high-dimensional porous structures. If increasing the length of these ligands, perhaps, we can obtain some new compounds with adjustable cavities. The variable-temperature magnetic susceptibilities of 1 suggest that there is an antiferromagnetic coupling between copper(II) ions transferred through tetrazolate.

Acknowledgments

Fig. 4. Nanotube with approximate 10.91  5.93 Å2 dimension constructed by 1D left- or right-handed helix chains in compound 2.

Financially supported by the Science Foundation for the Excellent Youth Scholars of Higher Education of Shanghai, the Innovation Foundation of Shanghai University, Natural Science Foundation of Shanghai (10ZR1411100) and the Leading Academic

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Discipline Project (J50102) of Shanghai Municipal Education Commission. Appendix A. Supplementary material CCDC 713303 and 713301 contain the supplementary crystallographic data for compounds 1 and 2, respectively. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2010.01.001. References [1] N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O’Keeffe, O.M. Yaghi, Science 300 (2003) 1127. [2] L. Pan, M.B. Sander, X. Huang, J. Li, M. Smith, E. Bittner, B. Bockrath, J.K. Johnson, J. Am. Chem. Soc. 126 (2004) 1308. [3] S.R. Batten, R. Robson, Angew. Chem., Int. Ed. 37 (1998) 1460. [4] A.F. Wells, Further Studies of Three-Dimensional Nets, American Crystallographic Association, Pittsburgh, PA, 1979. [5] (a) X.M. Zhang, Y.T. Zhao, W.X. Zhang, X.M. Chen, Adv. Mater. 19 (2007) 2843; (b) X.M. Zhang, Y.F. Zhao, H.S. Wu, S.R. Batten, S.W. Ng, Dalton Trans. (2006) 3170. [6] C.Y. Su, A.M. Goforth, M.D. Smith, P.J. Pellechia, H.C.Z. Loye, J. Am. Chem. Soc. 126 (2004) 3576. [7] (a) M. Dinca, W.S. Han, Y. Liu, A. Dailly, C.M. Brown, J.R. Long, Angew. Chem., Int. Ed. 46 (2007) 1419; (b) A. Rodriguez-Dieguez, A. Salinas-Castillo, S. Galli, N. Masciocchi, J.M. Gutierrez-Zorrilla, P. Vitoria, E. Colacio, Dalton Trans. (2007) 1821. [8] (a) X. He, C.D. Wu, M.X. Li, S.R. Batten, Inorg. Chem. Commun. 11 (2008) 1378; (b) X.W. Wang, J.Z. Chen, J.H. Liu, Cryst. Growth Des. 7 (2007) 1227; (c) Y.L. Yao, L. Xue, Y.X. Che, J.M. Zheng, Cryst. Growth Des. 9 (2009) 606; (d) Q.Y. Chen, Y. Li, F.K. Zheng, W.Q. Zou, M.F. Wu, G.C. Guo, A.Q. Wu, J.S. Huang, Inorg. Chem. Commun. 11 (2008) 969. [9] R.G. Xiong, X. Xue, H. Zhao, X.Z. You, B.F. Abrahams, Z. Xue, Angew. Chem., Int. Ed. 41 (2002) 3800. [10] H. Zhao, Z.R. Qu, H.Y. Ye, R.G. Xiong, Chem. Soc. Rev. 37 (2008) 84. [11] T. Wu, M. Li, D. Li, X.C. Huang, Cryst. Growth Des. 8 (2008) 568.

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