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Two unusual 3D and 2D zinc coordination polymers containing 2D or 1D [Zn2(btec)]n based on flexible bis(triazole) and rigid benzenetetracarboxylate co-ligands
Inorganic Chemistry Communications 26 (2012) 37–41
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Two unusual 3D and 2D zinc coordination polymers containing 2D or 1D [Zn2(btec)]n based on flexible bis(triazole) and rigid benzenetetracarboxylate co-ligands Shan Zhao, Xia Zhu, Ju Wang, Zhi Yang, Bao-Long Li ⁎, Bing Wu Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, P.R. China
a r t i c l e
i n f o
Article history: Received 30 July 2012 Accepted 21 September 2012 Available online 27 September 2012 Keywords: Coordination polymer (3,4)-Connected three-dimensional network (4,4)-Connected two-dimensional network Flexible bis(1,2,4-triazole) ligand Benzenetetracarboxylate
a b s t r a c t In order to investigate the influence of flexible bis(triazole) ligands on the motifs, two zinc coordination polymers {[Zn2(bte)(btec)(H2O)4]•2H2O}n (1) and {[Zn2(btp)2(btec)]•10H2O}n (2) were synthesized by the self-assembly reaction of 1,2,4,5-benzenetetracarboxylate (btec), 1,2-bis(1,2,4-triazol-1-yl)ethane (bte), or 1,3-bis(1,2,4-triazol-1-yl)propane (btp). In 1, the bte ligands connect the 2D [Zn2(btec)]n networks to generate an unusual (3,4)-connected 3D network. The Schläfli symbol of the 3D network is (6•10 2)(6210 4). In 2, each btp ligand links two [Zn2(btec)]n 1D belts to form a (4,4)-connected 2D network with the 1D channels ca. 8.0 × 10.0 Å 2 along the a-axis. The btp ligands of each 2D network interpenetrate into two adjacent identical 2D networks to form a 3D supramolecular network in 2. The luminescences and thermal stabilities of 1 and 2 were also investigated. © 2012 Elsevier B.V. All rights reserved.
Recently, the rational design and synthesis of novel coordination polymers is of great interest in modern inorganic chemistry stemming not only from their potential applications as functional materials in fields such as gas storage, chemical separation, catalysis and ion exchange but also from their intriguing variety of topologies [1–5]. Because of the diversity of the coordination modes and high structural stability, polycarboxylate ligands are frequently used for metal– organic networks [6–12]. 1,2,4,5-Benzenetetracarboxylate (btec) is a rigid, planar molecule and has been used as a bridging ligand in the synthesis of novel metal–organic frameworks [13–17]. To design coordination polymers with interesting structure and performance, the match of metal centers with suitable ligands is one of the most important factors. Ligands containing N donors and carboxylic groups have been employed to construct many metal–organic frameworks with novel structure and properties [6–17]. On the other hand, polytriazole derivatives are good ligands for the construction of metal–organic frameworks [18–22]. We are interested in the construction of novel topologies and functional materials using flexible bis(triazole) ligands [23–26]. The ligands 1,2bis(1,2,4-triazol-1-yl)ethane (bte) and 1,3-bis(1,2,4-triazol-1-yl)propane (btp), which can adopt different conformations respect to the relative orientations of the CH2 groups, have be proven the good bridging ligands to construct novel metal–organic frameworks [27–29]. For examples, {[Zn(btp)(1,4-bdc)][Zn(btp)(1,4-bdc)0.5Cl]•H2O}n (1,4-bdc= 1,4-benzenedicarboxylate) represents a new type of entanglement that only a half of the loops of 2D networks are polythreading by 1D chains
⁎ Corresponding author. Tel.: +86 512 65880324; fax: +86 512 65880089. E-mail address: [email protected] (B.-L. Li). 1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.inoche.2012.09.024
containing alternating rings and rods [29]. In addition, the d10 metal coordination polymers are found to exhibit interesting photoluminescent properties [10,13,21,24,23,29]. In order to extend our work on the synthesis novel topological frameworks and functional materials and investigate the influence of the flexible bte, btp and rigid btec co-ligands on the coordination networks, in the present work, we synthesized two zinc(II) coordination polymers {[Zn2(bte)(btec)(H2O)4]•2H2O}n (1) and {[Zn2(btp)2(btec)]• 10H2O}n (2) by the reaction of rigid btec, flexible bte, or btp and zinc salt. 1 consists of an unusual (3,4)-connected 3D network by the bte
Chart 1. The 3-connected Zn(II) atom and 4-connected btec in 1.
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S. Zhao et al. / Inorganic Chemistry Communications 26 (2012) 37–41
Fig. 1. (a) The [Zn2(btec)]n two-dimensional network in 1. (b) The three-dimensional network in 1. (c) Schematic of the three-dimensional network in 1. The bright green sticks present the bte ligand. The black balls at the benzene ring center of the btec ligands exhibit the 4-connected btec ligands.
S. Zhao et al. / Inorganic Chemistry Communications 26 (2012) 37–41
ligands joining 2D [Zn2(btec)]n. 2 consists of (4,4)-connected 2D coordination networks by the btp ligands connecting [Zn2(btec)]n 1D belts and a 3D supramolecular network. Here we report the syntheses, crystal structures, and luminescences and thermal stabilities. Coordination polymers 1 and 2 [30] were synthesized by the slow diffusion method in CH3OH/H2O media. The crystal structure of 1 [31] shows that 1 has an unusual (3,4)-connected 3D network. The asymmetry unit contains one Zn(II) atom, half btec, half bte, and two coordination water and a lattice water. The coordination geometry of the Zn(II) atom is a distorted octahedron, coordinated by one triazole nitrogen atom from one bte ligand, three carboxylate oxygen atoms from two btec and two oxygen atoms from two coordination water molecules (Fig. S1). Each Zn(II) center links two btec and one bte and each btec connects four Zn(II) atoms. Therefore, the Zn(II) atom is 3-connected and the btec is 4-connected (Chart 1). Two COO groups (O1O2) of one btec ligand show a monodentate coordination mode and join two Zn(II) atoms. The other two COO groups (O3O4) of one btec exhibit a bidentate chelating mode and coordinate two Zn(II) atoms. Each btec ligand connects four Zn(II) atoms through its four carboxylate groups, resulting in a two-dimensional [Zn2(btec)]n network (Fig. 1a) with the Zn1…Zn1A and Zn1…Zn1B distances of 5.7583(7) and 9.4219(15) Å, respectively. Each bte ligand exhibits the gauche conformation with the dihedral angle between two triazol rings being 48.15(2)° and the torsion angle (N(1)-C(1)-C(2)-N(4)) being 42.2(2)°. Each Zn(II) atom links a Zn(II) atom through one bte molecule with a Zn …Zn distance of 6.6295(12) Å. The bte ligands connect the 2D [Zn2(btec)]n networks to generate an unusual (3,4)-connected 3D network (Fig. 1b). The Schläfli symbol of the 3D network is (6•102)(6 2104) (Fig. 1c). As far as we know, it is quite unusual to observe (3,4)-connected 3D network. For example, Li and coworkers synthesize an interesting self-catenated coordination frameworks [Cd2(nip)2(dpa)(H2O)3]·2H2O with (3,4)connected (4•62)2(42•62•82) topology using the V-shaped ligands 5-nitroisophthalic acid (H2nip) and 4,4′-dipyridylamine (dpa) [32]. {Cd(mpda)(biim-6)0.5(H2O)}n (mpda=1,3-phenylenediacetate, biim6=1,1′-(1,6-hexanedidyl)bis(imidazole)) constructs a (3,4)-connected (42•63•8)(42•6) V2O5-type 2D network [33]. 2 consists of (4,4)-connected 2D coordination networks and a 3D supramolecular network. The asymmetry unit contains one Zn(II) atom, half btec, one btp, and five disordered lattice water molecules. Each Zn(II) atom displays a distorted tetrahedral coordination geometry, coordinated by two carboxylate oxygen atoms from two btec and two nitrogen atoms from two btp ligands (Fig. S2). Each zinc(II) atom connects two btec and two btp ligands and is 4-connected (Chart 2). Each btec shows the four-monodentate mode bridging four zinc(II) atoms (The btec is 4-connected.) and extend to form a [Zn2(btec)]n one-dimensional belt (Fig. 2a). Such [Zn2(btec)]n one-dimensional belt is rarely observed [13–17].
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The long and flexible ligands btp exhibit the anti-gauche conformation with the dihedral angle between two triazol rings being 96.2(2)°. The torsion angle N(1)-C(1)-C(2)-C(3) and C(1)-C(2)-C(3)-N(4) are −169.8(4) and −67.8(6)°, respectively. Each bridge ligand btp shows a bis-monodentate coordination mode. Each Zn(II) atom connects two Zn(II) atoms from two adjacent [Zn2(btec)]n one-dimensional belts. Each [Zn2(btec)]n one-dimensional belt join two adjacent [Zn2(btec)]n one-dimensional belts through btp bridges and form a two-dimensional network [Zn2(btp)2(btec)]n (Fig. 2b) with the 1D channels ca. 8.0×10.0 Å2 along the a-axis (Fig. 2c). An interesting structural feature of 2 is that the btp ligands of each 2D network interpenetrate into two adjacent identical 2D networks to form a 3D supramolecular network (Fig. 2d). The solid state luminescence spectra of 1 and 2 at room temperature were determined (Fig. S3). The free bte and btp ligands in the solid state display the emission band maxima approximate at 390 and 410 nm upon excitation at 340 nm. The (4,8)-connected [Zn(btec)0.5]n compound in the solid state shows a broad band emission with a maximum at 420 nm when irradiated at 340 nm at room temperature. The fluorescence emission may originate from the intraligand emission excited state [13]. 1 and 2 exhibit the luminescence maxima at 454 and 464 nm, respectively, upon excitation at 310 nm. The emissions can be tentatively attributed to the emission of ligand-to-metal charge-transfer (LMCT) [10,13,21,24,23,29]. To characterize the compounds more fully in terms of thermal stability, the thermal behaviors of 1 and 2 were examined by TGA. The experiments were performed on samples consisting of numerous single crystals with a heating rate of 10 °C/min (Fig. S4). The coordination and lattice water molecules of 1 were lost from 60 to 135 °C (calculated: 16.54%, found: 16.38%) and the anhydrous product was stable upon to approximate 275 °C. Then the weight loss occurred and continuously and did not stop upon ca. 680 °C. The weight of residue of 1 is 25.22% at 792 °C which may be ZnO (calculated: 24.80%). The lattice water molecules of 2 were lost from 40 to 125 °C (calculated: 19.62%, found: 19.78%) and the anhydrous product was stable upon to approximate 252 °C. Then the weight loss occurred and continuously and did not stop upon ca. 675 °C. The weight of residue of 2 is 17.92% at 800 °C which may be ZnO (calculated: 17.66%). In summary, two zinc coordination polymers were successfully synthesized with flexible bte or btp and rigid btec co-ligands. 1 forms an unusual (3,4)-connected 3D network by the bte ligands connecting the [Zn2(btec)]n 2D networks. 2 constructs a (4,4)-connected 2D coordination network by the btp ligands joining [Zn2(btec)]n 1D belts. The bte ligands show the gauche conformation in 1 and the btp ligands exhibit the anti-gauche conformation in 2. These results show that the flexible ligands can adopt different conformations according to the geometric needs of the different metal ions and may induce coordination polymers with novel topologies. 1 and 2 are also the good candidates of the luminescent materials. Further syntheses and structural studies of novel coordination polymer with flexible triazole ligands and rigid carboxylate ligands are also under way in our laboratory.
Acknowledgment This work was supported by the Natural Science Foundation of China (21171126), the Priority Academic Program Development of Jiangsu Higher Education Institutions and the Funds of Key Laboratory of Organic Synthesis of Jiangsu Province.
Appendix A. Supplementary material
Chart 2. The 4-connected Zn(II) atom and the 4-connected btec ligand in 2.
Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.inoche.2012.09.024.
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Fig. 2. (a) The 1D belt [Zn2(btec)]n in 2. (b) The 2D network [Zn2(btp)2(btec)]n in 2. (c) Viewing the 2D network [Zn2(btp)2(btec)]n along the a-axis and showing the 1D channels in 2. (d) The three-dimensional supramolecular network in 2.
S. Zhao et al. / Inorganic Chemistry Communications 26 (2012) 37–41
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[20] G.A.V. Albada, R.C. Guijt, J.G. Haasnoot, M. Lutz, A.L. Spek, J. Reedijk, Two examples of novel and unusual double-layered, two-dimensional CuII compounds with bridging 1,3-bis(1,2,4-triazol-1-yl)propane, Eur. J. Inorg. Chem. (2000) 121–126. [21] X.L. Wang, C. Qin, E.B. Wang, Z.M. Su, Metal nuclearity modulated four-, six, and eight-connected entangled frameworks based on mono-, bi-, and trimetallic cores as nodes, Chem. Eur. J. 12 (2006) 2680–2691. [22] Y. Garcia, C. Bravic, C. Gieck, D. Chasseau, W. Tremel, P. Gutlich, Crystal structure, magnetic properties and 57Fe Mössbauer spectroscopy of the two-dimensional coordination polymers: [M((1,2-bis-triazol-4-yl)ethane)2(NCS)2] (M = Fe, Co), Inorg. Chem. 44 (2005) 9723–9730. [23] B.L. Li, Y.F. Peng, B.Z. Li, Y. Zhang, Supramolecular isomers in the same crystal: a new type of entanglement involving ribbons of rings and 2D (4,4) networks polycatenated in a 3D architecture, Chem. Commun. (2005) 2333–2335. [24] X.G. Liu, K. Liu, Y. Yang, B.L. Li, Syntheses, structures and luminescence of zinc and cadmium coordination polymers with bis(1,2,4-triazol-1-yl)butane and benzenedicarboxylate, Inorg. Chem. Commun. 11 (2008) 1273–1275. [25] N. Liang, J. Wang, D.Y. Yuan, B.L. Li, H.Y. Li, A novel three-dimensional network silver coordination polymer with flexible bis(1,2,4-triazol-4-yl)ethane, Inorg. Chem. Commun. 13 (2010) 844–846. [26] Y. Zhang, X.G. Liu, L.Y. Wang, J.G. Ding, B.L. Li, An unusual (4,6)-connected three dimensional framework and a two-dimensional (6,3) network based on flexible and rigid co-ligands, Inorg. Chem. Commun. 21 (2012) 76–79. [27] J.H. Zhou, X. Zhu, Y.N. Zhang, Y. Zhang, B.L. Li, Two novel manganese coordination polymers containing both double-stranded chain and single chain or double-stranded chain, Inorg. Chem. Commun. 7 (2004) 949–952. [28] X. Zhu, X.Y. Wang, B.L. Li, J. Wang, S. Gao, Syntheses, structures and magnetic properties of five iron(II) coordination polymers with flexible bis(imidazole) and bis(triazole) ligands, Polyhedron 31 (2012) 77–81. [29] J. Wang, X. Zhu, Y.F. Cui, B.L. Li, H.Y. Li, A polythreading coordination array formed from 2D grid networks and 1D chains, CrystEngComm 13 (2011) 3342–3344. [30] Syntheses of 1 and 2: A solution of H4btec (0.1 mmol) in 10 mL H2O was adjusted to approximately pH 6 with dilute NaOH solution. Then bte (0.2 mmol) or btp (0.2 mmol) in 10 mL CH3OH was added. This mixture was added to one side of the “H-shape” tube, and Zn(NO3)2.6H2O (0.2 mmol) in 20 mL water was added to the other side of the “H-shape” tube. Colorless crystals 1 and 2 were obtained after two weeks at room temperature. Anal. Calcd. for C16H22N6O14Zn2 (1): C, 29.42; H, 3.40; N, 12.87%. Found: C, 29.37; H, 3.36; N, 12.83. Anal. Calcd. for C24H42N12O18Zn2 (2): C, 31.42; H, 4.61; N, 18.32%. Found: C, 31.35; H, 4.56; N, 18.2 [31] X-ray single crystal diffraction data collection for 1 and 2 were performed on a Rigaku Mercury or Saturn CCD. The structures were solved by direct methods and refined with full-matrix least-squares technique (SHELXTL-97). Crystal data for C16H22N6O14Zn2 (1): Mr=653.14, monoclinic, C2/c, a=16.411(3), b=9.8620(16), c=16.667(3) Å, β=111.678(3)°, V=2506.6(8) Å3, Z=4, Dc =1.731 g/cm3, μ=1.993 mm-1, F(000)=1328, S=1.096, R=0.0878, wR=0.2162. Crystal data for C24H42N12O18Zn2 (2): Mr=917.44, triclinic, P 1, a=9.6491(17), b=10.7245(17), c=10.9775(16) Å, α=92.771(3), β=98.955(3), γ=114.076(3)°, V=1016.6(3) Å3, Z=1, Dc =1.499 g/cm3, μ=1.263 mm-1, F(000)=474, S=1.079, R=0.0497, wR=0.157. [32] J. Zhao, D.S. Li, Z.Z. Hu, W.W. Dong, K. Zou, J.Y. Lu, Unprecedented (3,4)-connected self-catenated network based on V-shaped building blocks, Inorg. Chem. Commun. 14 (2011) 771–774. [33] Y.P. Wu, D.S. Li, J. Zhao, Z.F. Fang, W.W. Dong, G.P. Yang, Y.Y. Wang, Isomeric phenylenediacetates as modular tectons for a series of ZnII/CdII coordination polymers incorporating flexible bis(imidazole) co-ligands, CrystEngComm 14 (2012) 4745–4755.
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Two unusual 3D and 2D zinc coordination polymers containing 2D or 1D [Zn2(btec)]n based on flexible bis(triazole) and rigid benzenetetracarboxylate co-ligands Shan Zhao, Xia Zhu, Ju Wang, Zhi Yang, Bao-Long Li ⁎, Bing Wu Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, P.R. China
a r t i c l e
i n f o
Article history: Received 30 July 2012 Accepted 21 September 2012 Available online 27 September 2012 Keywords: Coordination polymer (3,4)-Connected three-dimensional network (4,4)-Connected two-dimensional network Flexible bis(1,2,4-triazole) ligand Benzenetetracarboxylate
a b s t r a c t In order to investigate the influence of flexible bis(triazole) ligands on the motifs, two zinc coordination polymers {[Zn2(bte)(btec)(H2O)4]•2H2O}n (1) and {[Zn2(btp)2(btec)]•10H2O}n (2) were synthesized by the self-assembly reaction of 1,2,4,5-benzenetetracarboxylate (btec), 1,2-bis(1,2,4-triazol-1-yl)ethane (bte), or 1,3-bis(1,2,4-triazol-1-yl)propane (btp). In 1, the bte ligands connect the 2D [Zn2(btec)]n networks to generate an unusual (3,4)-connected 3D network. The Schläfli symbol of the 3D network is (6•10 2)(6210 4). In 2, each btp ligand links two [Zn2(btec)]n 1D belts to form a (4,4)-connected 2D network with the 1D channels ca. 8.0 × 10.0 Å 2 along the a-axis. The btp ligands of each 2D network interpenetrate into two adjacent identical 2D networks to form a 3D supramolecular network in 2. The luminescences and thermal stabilities of 1 and 2 were also investigated. © 2012 Elsevier B.V. All rights reserved.
Recently, the rational design and synthesis of novel coordination polymers is of great interest in modern inorganic chemistry stemming not only from their potential applications as functional materials in fields such as gas storage, chemical separation, catalysis and ion exchange but also from their intriguing variety of topologies [1–5]. Because of the diversity of the coordination modes and high structural stability, polycarboxylate ligands are frequently used for metal– organic networks [6–12]. 1,2,4,5-Benzenetetracarboxylate (btec) is a rigid, planar molecule and has been used as a bridging ligand in the synthesis of novel metal–organic frameworks [13–17]. To design coordination polymers with interesting structure and performance, the match of metal centers with suitable ligands is one of the most important factors. Ligands containing N donors and carboxylic groups have been employed to construct many metal–organic frameworks with novel structure and properties [6–17]. On the other hand, polytriazole derivatives are good ligands for the construction of metal–organic frameworks [18–22]. We are interested in the construction of novel topologies and functional materials using flexible bis(triazole) ligands [23–26]. The ligands 1,2bis(1,2,4-triazol-1-yl)ethane (bte) and 1,3-bis(1,2,4-triazol-1-yl)propane (btp), which can adopt different conformations respect to the relative orientations of the CH2 groups, have be proven the good bridging ligands to construct novel metal–organic frameworks [27–29]. For examples, {[Zn(btp)(1,4-bdc)][Zn(btp)(1,4-bdc)0.5Cl]•H2O}n (1,4-bdc= 1,4-benzenedicarboxylate) represents a new type of entanglement that only a half of the loops of 2D networks are polythreading by 1D chains
⁎ Corresponding author. Tel.: +86 512 65880324; fax: +86 512 65880089. E-mail address: [email protected] (B.-L. Li). 1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.inoche.2012.09.024
containing alternating rings and rods [29]. In addition, the d10 metal coordination polymers are found to exhibit interesting photoluminescent properties [10,13,21,24,23,29]. In order to extend our work on the synthesis novel topological frameworks and functional materials and investigate the influence of the flexible bte, btp and rigid btec co-ligands on the coordination networks, in the present work, we synthesized two zinc(II) coordination polymers {[Zn2(bte)(btec)(H2O)4]•2H2O}n (1) and {[Zn2(btp)2(btec)]• 10H2O}n (2) by the reaction of rigid btec, flexible bte, or btp and zinc salt. 1 consists of an unusual (3,4)-connected 3D network by the bte
Chart 1. The 3-connected Zn(II) atom and 4-connected btec in 1.
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S. Zhao et al. / Inorganic Chemistry Communications 26 (2012) 37–41
Fig. 1. (a) The [Zn2(btec)]n two-dimensional network in 1. (b) The three-dimensional network in 1. (c) Schematic of the three-dimensional network in 1. The bright green sticks present the bte ligand. The black balls at the benzene ring center of the btec ligands exhibit the 4-connected btec ligands.
S. Zhao et al. / Inorganic Chemistry Communications 26 (2012) 37–41
ligands joining 2D [Zn2(btec)]n. 2 consists of (4,4)-connected 2D coordination networks by the btp ligands connecting [Zn2(btec)]n 1D belts and a 3D supramolecular network. Here we report the syntheses, crystal structures, and luminescences and thermal stabilities. Coordination polymers 1 and 2 [30] were synthesized by the slow diffusion method in CH3OH/H2O media. The crystal structure of 1 [31] shows that 1 has an unusual (3,4)-connected 3D network. The asymmetry unit contains one Zn(II) atom, half btec, half bte, and two coordination water and a lattice water. The coordination geometry of the Zn(II) atom is a distorted octahedron, coordinated by one triazole nitrogen atom from one bte ligand, three carboxylate oxygen atoms from two btec and two oxygen atoms from two coordination water molecules (Fig. S1). Each Zn(II) center links two btec and one bte and each btec connects four Zn(II) atoms. Therefore, the Zn(II) atom is 3-connected and the btec is 4-connected (Chart 1). Two COO groups (O1O2) of one btec ligand show a monodentate coordination mode and join two Zn(II) atoms. The other two COO groups (O3O4) of one btec exhibit a bidentate chelating mode and coordinate two Zn(II) atoms. Each btec ligand connects four Zn(II) atoms through its four carboxylate groups, resulting in a two-dimensional [Zn2(btec)]n network (Fig. 1a) with the Zn1…Zn1A and Zn1…Zn1B distances of 5.7583(7) and 9.4219(15) Å, respectively. Each bte ligand exhibits the gauche conformation with the dihedral angle between two triazol rings being 48.15(2)° and the torsion angle (N(1)-C(1)-C(2)-N(4)) being 42.2(2)°. Each Zn(II) atom links a Zn(II) atom through one bte molecule with a Zn …Zn distance of 6.6295(12) Å. The bte ligands connect the 2D [Zn2(btec)]n networks to generate an unusual (3,4)-connected 3D network (Fig. 1b). The Schläfli symbol of the 3D network is (6•102)(6 2104) (Fig. 1c). As far as we know, it is quite unusual to observe (3,4)-connected 3D network. For example, Li and coworkers synthesize an interesting self-catenated coordination frameworks [Cd2(nip)2(dpa)(H2O)3]·2H2O with (3,4)connected (4•62)2(42•62•82) topology using the V-shaped ligands 5-nitroisophthalic acid (H2nip) and 4,4′-dipyridylamine (dpa) [32]. {Cd(mpda)(biim-6)0.5(H2O)}n (mpda=1,3-phenylenediacetate, biim6=1,1′-(1,6-hexanedidyl)bis(imidazole)) constructs a (3,4)-connected (42•63•8)(42•6) V2O5-type 2D network [33]. 2 consists of (4,4)-connected 2D coordination networks and a 3D supramolecular network. The asymmetry unit contains one Zn(II) atom, half btec, one btp, and five disordered lattice water molecules. Each Zn(II) atom displays a distorted tetrahedral coordination geometry, coordinated by two carboxylate oxygen atoms from two btec and two nitrogen atoms from two btp ligands (Fig. S2). Each zinc(II) atom connects two btec and two btp ligands and is 4-connected (Chart 2). Each btec shows the four-monodentate mode bridging four zinc(II) atoms (The btec is 4-connected.) and extend to form a [Zn2(btec)]n one-dimensional belt (Fig. 2a). Such [Zn2(btec)]n one-dimensional belt is rarely observed [13–17].
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The long and flexible ligands btp exhibit the anti-gauche conformation with the dihedral angle between two triazol rings being 96.2(2)°. The torsion angle N(1)-C(1)-C(2)-C(3) and C(1)-C(2)-C(3)-N(4) are −169.8(4) and −67.8(6)°, respectively. Each bridge ligand btp shows a bis-monodentate coordination mode. Each Zn(II) atom connects two Zn(II) atoms from two adjacent [Zn2(btec)]n one-dimensional belts. Each [Zn2(btec)]n one-dimensional belt join two adjacent [Zn2(btec)]n one-dimensional belts through btp bridges and form a two-dimensional network [Zn2(btp)2(btec)]n (Fig. 2b) with the 1D channels ca. 8.0×10.0 Å2 along the a-axis (Fig. 2c). An interesting structural feature of 2 is that the btp ligands of each 2D network interpenetrate into two adjacent identical 2D networks to form a 3D supramolecular network (Fig. 2d). The solid state luminescence spectra of 1 and 2 at room temperature were determined (Fig. S3). The free bte and btp ligands in the solid state display the emission band maxima approximate at 390 and 410 nm upon excitation at 340 nm. The (4,8)-connected [Zn(btec)0.5]n compound in the solid state shows a broad band emission with a maximum at 420 nm when irradiated at 340 nm at room temperature. The fluorescence emission may originate from the intraligand emission excited state [13]. 1 and 2 exhibit the luminescence maxima at 454 and 464 nm, respectively, upon excitation at 310 nm. The emissions can be tentatively attributed to the emission of ligand-to-metal charge-transfer (LMCT) [10,13,21,24,23,29]. To characterize the compounds more fully in terms of thermal stability, the thermal behaviors of 1 and 2 were examined by TGA. The experiments were performed on samples consisting of numerous single crystals with a heating rate of 10 °C/min (Fig. S4). The coordination and lattice water molecules of 1 were lost from 60 to 135 °C (calculated: 16.54%, found: 16.38%) and the anhydrous product was stable upon to approximate 275 °C. Then the weight loss occurred and continuously and did not stop upon ca. 680 °C. The weight of residue of 1 is 25.22% at 792 °C which may be ZnO (calculated: 24.80%). The lattice water molecules of 2 were lost from 40 to 125 °C (calculated: 19.62%, found: 19.78%) and the anhydrous product was stable upon to approximate 252 °C. Then the weight loss occurred and continuously and did not stop upon ca. 675 °C. The weight of residue of 2 is 17.92% at 800 °C which may be ZnO (calculated: 17.66%). In summary, two zinc coordination polymers were successfully synthesized with flexible bte or btp and rigid btec co-ligands. 1 forms an unusual (3,4)-connected 3D network by the bte ligands connecting the [Zn2(btec)]n 2D networks. 2 constructs a (4,4)-connected 2D coordination network by the btp ligands joining [Zn2(btec)]n 1D belts. The bte ligands show the gauche conformation in 1 and the btp ligands exhibit the anti-gauche conformation in 2. These results show that the flexible ligands can adopt different conformations according to the geometric needs of the different metal ions and may induce coordination polymers with novel topologies. 1 and 2 are also the good candidates of the luminescent materials. Further syntheses and structural studies of novel coordination polymer with flexible triazole ligands and rigid carboxylate ligands are also under way in our laboratory.
Acknowledgment This work was supported by the Natural Science Foundation of China (21171126), the Priority Academic Program Development of Jiangsu Higher Education Institutions and the Funds of Key Laboratory of Organic Synthesis of Jiangsu Province.
Appendix A. Supplementary material
Chart 2. The 4-connected Zn(II) atom and the 4-connected btec ligand in 2.
Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.inoche.2012.09.024.
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S. Zhao et al. / Inorganic Chemistry Communications 26 (2012) 37–41
Fig. 2. (a) The 1D belt [Zn2(btec)]n in 2. (b) The 2D network [Zn2(btp)2(btec)]n in 2. (c) Viewing the 2D network [Zn2(btp)2(btec)]n along the a-axis and showing the 1D channels in 2. (d) The three-dimensional supramolecular network in 2.
S. Zhao et al. / Inorganic Chemistry Communications 26 (2012) 37–41
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