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Spacer length effect on the formation of different zinc coordination polymers of 1,4-benzenedicarboxylate and flexible bipyrazolyl ligands
Inorganic Chemistry Communications 29 (2013) 70–75
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Spacer length effect on the formation of different zinc coordination polymers of 1,4-benzenedicarboxylate and flexible bipyrazolyl ligands Ming Dai a, Lian-Wen Zhu a, Ju-Hua Yang a, Hong-Xi Li a,⁎, Min-Min Chen a, Zhi-Gang Ren a, Jian-Ping Lang a, b,⁎⁎ a b
College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, Jiangsu, People's Republic of China State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, People's Republic of China
a r t i c l e
i n f o
Article history: Received 30 October 2012 Accepted 30 November 2012 Available online 29 December 2012 Keywords: Solvothermal synthesis Zinc complexes Crystal structures Spacer length effect Bipyrazolyl ligand Luminescence
a b s t r a c t The solvothermal reactions of Zn(NO3)2∙6H2O with 1,4-benzenedicarboxylic acid (1,4-H2bdc) and 1,4bis(3,5-dimethyl-1H-pyrazol-1-yl)butane (dmpzb) or 1,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)hexane (dmpzh) afforded two three-dimensional coordination polymers [Zn3(1,4-bdc)3(dmpzb)]n (1) and [Zn2(1,4-bdc)2(dmpzh)]n (2), respectively. Compounds 1 and 2 were characterized by elemental analysis, IR, powder X-ray diffraction, and single crystal X-ray diffraction. Compound 1 has an 8-connected 3D net (a 364185262 Schläfli symbol) assembled from trinuclear [Zn3(1,4-bdc)3] units and 1,4-bdc and dmpzb bridges. Compound 2 has a 6-connected 3D net (with a 485463 Schläfli symbol) constructed from binuclear [Zn2(1,4-bdc)2] units and 1,4-bdc and dmpzh linkers. The solid state luminescent and thermal stability properties of 1 and 2 at ambient temperature were also investigated. The results showed that the spacer lengths of bipyrazol-based ligands did affect the topological structures of zinc(II) coordination polymers. © 2012 Elsevier B.V. All rights reserved.
In the past decades, the design and construction of coordination polymers have attracted considerable attention due to their diverse structural topologies as well as their potential applications in catalysis, adsorption, separation, magnetism and luminescence [1–6]. However, it still remains a great challenge to control the formation and the structures of functional coordination polymers. As we know, the formation of coordination polymers may be affected by many subtle factors such as temperatures, solvents, pH values, N-donor/O-donor organic ligands, metal ions, and so on [7]. Among them, the flexibility and rigidity of the N-donor ligands can directly influence the final structures of the resulting coordination polymers [8]. This is because flexible ligands can bend or rotate in some degrees, which may lead to the formation of the resulting products with different topologies, though their reactions look quite similar. The flexible N-heterocyclic ligand is one of such ligands that could form various coordination polymers with excellent physical and/or chemical properties [9]. Recently, we have been involved in the syntheses, structures and luminescent properties of copper(I) complexes with various poly(pyrazolyl)alkanes [10] and found that the spacer lengths could impose great effects on the structures and properties of the resulting Cu(I) compounds. For example, when a family of pyrazolyl-based ligands with
⁎ Corresponding author. Tel./fax: +86 512 65882865. ⁎⁎ Correspondence to: J.P. Lang, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, Jiangsu, People's Republic of China. Tel./fax: + 86 512 65882865. E-mail address: [email protected] (J.-P. Lang). 1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.inoche.2012.11.038
different spacer lengths [(dmpz)(CH2)n(dmpz)] (dmpz=3,5-dimethylpyrazole; n=1, dmpzm; n =2, dmpze; n=3, dmpzpr; n =4, dmpzb; n=5, dmpzp; n =6, dmpzh) were employed to react with CuCN, the framework of the bulk CuCN could be cleaved to form different [CuCN]n motifs, which were further linked by these ligands to form a set of [CuCN]n-based coordination polymers with different topological structures and luminescent properties [10a]. On the other hand, 1,4benzenedicarboxylic acid (1,4-H2bdc) is known as a popular O-donor ligand which displays abundant coordination modes (Scheme 1). Can the spacer lengths of N-donor ligands affect the coordination modes of 1,4-bdc and the structures of the final coordination polymers when they work in the same system? With this question in mind, we employed two bipyrazolyl-based ligands with different spacer lengths, dmpzb and dmpzh (Scheme 1g), and carried out their reactions with Zn(NO3)2 and 1,4-H2bdc under solvothermal conditions. Two unique three-dimensional coordination polymers [Zn3(1,4-bdc)3(dmpzb)]n (1) and [Zn2(1,4-bdc)2(dmpzh)]n (2) were isolated and structurally characterized. Herein we report their syntheses, crystal structures and luminescent properties. Solvothermal reaction of a mixture of Zn(NO3)2∙6H2O, 1,4-H2bdc, dmpzb (molar ratio 1:1:1) in H2O and MeCN at 150°C in a sealed Pyrex glass tube for 1 day afforded colorless blocks of 1 in 83% yield [11]. Similar reaction of Zn(NO3)2∙6H2O, 1,4-H2bdc, dmpzh generated colorless crystals of 2 in 75% yield [11]. The different outcomes of the two similar reactions may be ascribed to the spacer lengths of dmpzb and dmpzh ligands, which will be described later in this article. Compounds 1 and 2 are air and moisture stable and insoluble in common
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Scheme 1. (a)–(f) Several possible coordination modes of the 1,4-bdc ligand. (g) Structure of the dmpzb and dmpzh ligands.
organic solvents such as CHCl3, MeCN, and DMF and DMSO. The elemental analyses were consistent with their chemical formula. For 1 or 2, the PXRD showed that the observed patterns for each compound correlate well with the simulated ones generated from single-crystal X-ray diffraction data (Fig. S1). In the IR spectra of 1 and 2, the strong bonds at 1560–1622 cm −1 and 1350–1435 cm −1 represent the coordinated carboxyl groups. The identities of 1–2 were finally confirmed by X-ray crystallography [12]. Compound 1 crystallizes in the triclinic space group Pī and its asymmetric unit consists of half an independent [Zn3(1,4-bdc)3(dmpzb)] molecule. As shown in Fig. 1a and b, the Zn1 atom is octahedrally coordinated by six O atoms from six 1,4-bdc ligands, while the Zn2 atom adopts a tetrahedral geometry coordinated by three O atoms from three 1,3-bdc ligands, and one N atom from one dmpzb ligand. For Zn1, the average Zn1\O bond length (2.013(2) Å) is slightly shorter than that found in [Zn4(μ-OH)2(1,2-PDA)3(1,4-bpeb)2]n (2.157(3) Å, for 1,2-PDA=1,2-phenylenediacetate; 1,4-bpeb=1,4-bis[2-(4-pyridyl) ethenyl]benzene) [13]. For Zn2, the mean Zn1\N and Zn1\O bond lengths (1.991(3) Å vs 1.964(2) Å) are comparable to the corresponding ones of [Zn(OH2)(5-HO-1,3-BDC)(1,4-bpeb)]n (2.027(2) Å vs 1.961(2) Å for 5-HO-1,3-BDC=5-hydroxy-1,3-benzenedicarboxylate) [14]. The 1,4-bdc ligands display two coordination modes bis-bidentate (mode a) and bis-monodentate (mode b) shown in Scheme 1. Four bis-bidentate 1,4-bdc and two bis-monodentate 1,4-bdc ligands combine two tetrahedral Zn and one octahedral Zn to form a trinuclear [Zn3(1,4-bdc)6] unit (Fig. 1c). Each unit is connected to its equivalent ones by bis-bidentate 1,4-bdc and bis-monodentate 1,4-bdc ligands, generating a 2D grid extending along the bc plane (Fig. 1d). Such a 2D layer is further linked to its neighboring ones by dmpzb bridges to afford a unique 3D net (Fig. 1e). If the trinuclear [Zn3(1,4-bdc)6(dmpzb)2] unit is considered as an 8-connecting node, the whole net can be simplified into an 8-connected net with a 364185262 topology (Fig. 1f). Compound 2 crystallizes in the monoclinic space group P21/c and its asymmetric unit contains one [Zn2(1,4-bdc)2(dmpzh)] molecule. Each Zn shows a square pyramidal geometry, which is coordinated by four O atoms from four 1,4-bdc ligands at the basal positions, and one N atom from a dmpzh ligand at the apical position (Fig. 2a). The contact between Zn1 and Zn2 is 3.095(13) Å. The mean Zn1\N length (2.049(3) Å) is shorter than that of [Fe(η 5-C5H4-1-C5H4N)2]2Zn2(OAc)4 (2.178(3) Å) [15], while the average Zn1\O bond length (2.036(2) Å) is slightly longer than that in [Fe(η 5-C5H4-1-C5H4N)2]2Zn2(OAc)4 (2.026(2) Å) [15]. In 2, all the four 1,4-bdc ligands adopt coordination mode a in Scheme 1 and they bridge Zn1 and Zn2 to form a dinuclear [Zn2(1,4-bdc)4] unit (Fig. 2b). These units are interlinked by 1,4-bdc bridges, forming a 1D [Zn2(1,4-bdc)2]n chain along the a axis (Fig. 2c). Such a chain
connects its adjacent ones by other 1,4-bdc bridges to form a 2D (4,4) layer extending along the ab plane (Fig. 2d). This layer is further linked to its neighboring ones by dmpzh bridges to afford a 3D net (Fig. 2e). If the [Zn2(1,4-bdc)4(dmpzh)2] unit is considered as a six-connecting node, the whole structure of 2 can be described as a 6-connected net with a 4 85 46 3 Schläfli symbol (Fig. 2f). The photoluminescent properties of 1 and 2 in solid state at room temperature were investigated (Fig. S2). Upon excitation at 327 nm (1) or 330 nm (2), 1 and 2 exhibited photoluminescence with emission maxima at 375 nm (1) and 420 nm (2), respectively. 1,4-H2bdc did not show photoluminescence under the above-mentioned exciation wavelengths. The maximum emission wavelengths for dmpzb and dmpzh (λex = 220 nm) both appeared at 330 nm [9b]. Thus the emission maxima of 1 and 2 are red-shifted related to them, which may be ascribed to the zinc(II)-to-ligand charge transfer (MLCT) with electrons being transferred from the Zn(II) to pyrazolyl groups [10a]. The thermogravimetric analyses revealed that 1 and 2 were stable up to 449 °C (1) and 248 °C (2), respectively (Fig. S3). After 449 °C, the ligands in 1 started to decompose and the weight of the final residue (27.07%) was assumed to be ZnO (calcd. 26.11%). 2 got its first weight loss corresponding to one coordinated 1,4-bdc ligand (obsd. 21.84%, calcd. 22.36%) from 248 to 286 °C. It continuously lost weight above 361 °C, and the final residue was also assumed to be ZnO (obsd. 22.03%; calcd. 22.09%). In summary, we demonstrated that solvothermal reactions of Zn(NO3)2 with 1,4-bdc and two flexible bipyrazolyl ligands (dmpzb and dmpzh) with different spacer lengths led to the formation of two different Zn coordination polymers 1 and 2. For 1, three zinc centers are held together by four bis-bidentate and two bis-monodentate 1,4-bdc ligands to form a trinuclear [Zn3(1,4-bdc)6] unit, which is further linked to its equivalent ones by 1,4-bdc and dmpzb ligands to form a 3D net with a 3 64 185 26 2 topology. For 2, two zinc centers are linked by four bis-bidentate 1,4-bdc ligands to afford a dinuclear [Zn2(1,4-bdc)2] unit that is further connected to its equivalent ones to afford a 3D net with a 4 85 46 3 topology. The results provided an interesting insight into the effect of the spacer length of the bipyrazolyl ligands on the coordination modes of 1,4-bdc, and the zinc/1,4-bdc units and the final topological structures of the Zn(II) coordination polymers. Acknowledgments The authors thanked the National Natural Science Foundation of China (90922018 and 21171124), the Nature Science Key Basic Research of Jiangsu Province for Higher Education (09KJA150002), the Specialized Research Fund for the Doctoral Program of Higher
72 M. Dai et al. / Inorganic Chemistry Communications 29 (2013) 70–75 Fig. 1. (a) View of the coordination environment of the Zn1 center in 1 with a labeling scheme. Symmetry code: (A) −x, −y, −z + 1. All H atoms have been omitted for clarity. (b) View of the coordination environment of the Zn2 center in 1 with a labeling scheme. Symmetry code: (B) −x + 1, −y, −z + 1. (c) View of a trinuclear [Zn3(1,4-bdc)6(dmpzb)2] unit in 1. (d) View of a 2D network extending along the bc plane. (e) View of a single 3D net of 1 looking along the b axis. (f) Schematic view of the topological net of 1. The cyan spheres represent [Zn3(1,4-bdc)6(dmpzb)2] units, while the purple and blue lines represent 1,4-bdc and dmpzb ligands, respectively.
M. Dai et al. / Inorganic Chemistry Communications 29 (2013) 70–75 Fig. 2. (a) View of the coordination environment of the Zn1 center in 2 with a labeling scheme. Symmetry code: (A) −x + 2, −y, −z. All H atoms have been omitted for clarity. (b) View of a structure of the dinuclear [Zn2(dmpzh)2(1,4-bdc)4] unit in 2. (c) View of a section of the 1D chain extending along the a axis. The red and blue balls represent O and N atoms, respectively. Each cyan square pyramid represents one Zn atom. (d) View of a 2D network extending along the ab plane. (e) View of a single 3D net of 2 looking along the a axis. (f) Schematic view of the topological net of 2. The cyan spheres represent [Zn2(1,4-bdc)4(dmpzh)] units, while the purple and blue lines represent 1,4-bdc and dmpzh ligands, respectively.
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Education of the Ministry of Education (20093201110017), and the State Key Laboratory of Organometallic Chemistry of Shanghai Institute of Organic Chemistry (201201006) for the financial support. J. P. Lang highly appreciated the support by the Priority Academic Program Development of Jiangsu Higher Education Institutions. The authors also greatly thanked the editor and the reviewers for the helpful comments.
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Abrahams, Single-crystal-to-single-crystal transformations of two three-dimensional coordination polymers through regioselective [2+2] photodimerization reactions, Angew. Chem. Int. Ed. 49 (2010) 4767–4770. To a 10 mL Pyrex glass tube was loaded Zn(NO3)2∙6H2O (30 mg, 0.1 mmol), 1,4-H2bdc (17 mg, 0.1 mmol), dmpzb (25 mg, 0.1 mmol), 2.5 mL of H2O and 0.5 mL of MeCN. The tube was sealed and then heated in an oven to 150 °C for one day. It was cooled to ambient temperature at the rate of 5 °C/h, to form colorless crystals of 1, which were washed with water and Et2O and dried in air. Yield: 29 mg (83% based on Zn). Anal. Calcd. for C38H34N4O12Zn3: C, 48.82; H, 3.66; N, 5.99%. Found: C, 48.64; H, 3.61; N, 5.74%. IR (KBr, cm−1): 3448m, 3156w, 1636m, 1601m, 1556s, 1502m, 1392s, 1295m, 1122s, 1018m, 819m, 744s, 604m, 544m. Compound 2 (colorless blocks) was prepared as above starting from Zn(NO3)2∙6H2O (30 mg, 0.1 mmol), 1,4-H2bdc (17 mg, 0.1 mmol), dmpzh (28 mg, 0.1 mmol), 2.5 mL of H2O and 0.5 mL of MeCN. Yield: 27 mg (75% yield based on Zn). Anal. Calcd. for C32H34N4O8Zn2: C, 52.40; H, 4.67; N, 7.64%. Found: C, 52.55; H, 4.48; N, 7.59%. IR (KBr, cm−1): 2940m, 1647s, 1557m, 1501m, 1387s, 1052m, 1018m, 885m, 823s, 746s, 539s. Crystal data for 1 : C38H34N4O12Zn3, Mr =934.86, 0.50×0.30×0.20 mm, trinilic, space group Pī, a=9.843(2) Å, b=10.052(2) Å, c=11.240(2) Å, α=98.98(3)°, β=110.25(3)°, γ=110.25(3)°, V=900.6(3) Å3, Z=1, Dc =1.724 g·cm-3, F(000)=476 and μ=2.055 mm-1, T=223 K, 8360 reflections collected, 4016 unique (Rint =0.0483). R1 =0.0397, wR2 =0.1127 and S=1.048 based on 3072 observed reflections with I>2σ(I). For 2: C32H34N4O8Zn2, Mr =733.41, 0.60× 0.60×0.40 mm, monoclinic, space group P21/c, a=10.909(2) Å, b=21.370(4) Å, c=16.575(5) Å, α=90.00 °, β=124.24(2)°, γ=90.00 °, V=3194.4(13) Å3, Z=4, Dc =1.525 g·cm-3, F(000)=1512 and μ=1.559 mm-1, T=223 K, 29294 reflections collected, 7220 unique (Rint =0.0656). R1 =0.0565, wR2 =0.1576 and S=1.124 based on 6230 observed reflections with I>2σ(I).
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Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Spacer length effect on the formation of different zinc coordination polymers of 1,4-benzenedicarboxylate and flexible bipyrazolyl ligands Ming Dai a, Lian-Wen Zhu a, Ju-Hua Yang a, Hong-Xi Li a,⁎, Min-Min Chen a, Zhi-Gang Ren a, Jian-Ping Lang a, b,⁎⁎ a b
College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, Jiangsu, People's Republic of China State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, People's Republic of China
a r t i c l e
i n f o
Article history: Received 30 October 2012 Accepted 30 November 2012 Available online 29 December 2012 Keywords: Solvothermal synthesis Zinc complexes Crystal structures Spacer length effect Bipyrazolyl ligand Luminescence
a b s t r a c t The solvothermal reactions of Zn(NO3)2∙6H2O with 1,4-benzenedicarboxylic acid (1,4-H2bdc) and 1,4bis(3,5-dimethyl-1H-pyrazol-1-yl)butane (dmpzb) or 1,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)hexane (dmpzh) afforded two three-dimensional coordination polymers [Zn3(1,4-bdc)3(dmpzb)]n (1) and [Zn2(1,4-bdc)2(dmpzh)]n (2), respectively. Compounds 1 and 2 were characterized by elemental analysis, IR, powder X-ray diffraction, and single crystal X-ray diffraction. Compound 1 has an 8-connected 3D net (a 364185262 Schläfli symbol) assembled from trinuclear [Zn3(1,4-bdc)3] units and 1,4-bdc and dmpzb bridges. Compound 2 has a 6-connected 3D net (with a 485463 Schläfli symbol) constructed from binuclear [Zn2(1,4-bdc)2] units and 1,4-bdc and dmpzh linkers. The solid state luminescent and thermal stability properties of 1 and 2 at ambient temperature were also investigated. The results showed that the spacer lengths of bipyrazol-based ligands did affect the topological structures of zinc(II) coordination polymers. © 2012 Elsevier B.V. All rights reserved.
In the past decades, the design and construction of coordination polymers have attracted considerable attention due to their diverse structural topologies as well as their potential applications in catalysis, adsorption, separation, magnetism and luminescence [1–6]. However, it still remains a great challenge to control the formation and the structures of functional coordination polymers. As we know, the formation of coordination polymers may be affected by many subtle factors such as temperatures, solvents, pH values, N-donor/O-donor organic ligands, metal ions, and so on [7]. Among them, the flexibility and rigidity of the N-donor ligands can directly influence the final structures of the resulting coordination polymers [8]. This is because flexible ligands can bend or rotate in some degrees, which may lead to the formation of the resulting products with different topologies, though their reactions look quite similar. The flexible N-heterocyclic ligand is one of such ligands that could form various coordination polymers with excellent physical and/or chemical properties [9]. Recently, we have been involved in the syntheses, structures and luminescent properties of copper(I) complexes with various poly(pyrazolyl)alkanes [10] and found that the spacer lengths could impose great effects on the structures and properties of the resulting Cu(I) compounds. For example, when a family of pyrazolyl-based ligands with
⁎ Corresponding author. Tel./fax: +86 512 65882865. ⁎⁎ Correspondence to: J.P. Lang, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, Jiangsu, People's Republic of China. Tel./fax: + 86 512 65882865. E-mail address: [email protected] (J.-P. Lang). 1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.inoche.2012.11.038
different spacer lengths [(dmpz)(CH2)n(dmpz)] (dmpz=3,5-dimethylpyrazole; n=1, dmpzm; n =2, dmpze; n=3, dmpzpr; n =4, dmpzb; n=5, dmpzp; n =6, dmpzh) were employed to react with CuCN, the framework of the bulk CuCN could be cleaved to form different [CuCN]n motifs, which were further linked by these ligands to form a set of [CuCN]n-based coordination polymers with different topological structures and luminescent properties [10a]. On the other hand, 1,4benzenedicarboxylic acid (1,4-H2bdc) is known as a popular O-donor ligand which displays abundant coordination modes (Scheme 1). Can the spacer lengths of N-donor ligands affect the coordination modes of 1,4-bdc and the structures of the final coordination polymers when they work in the same system? With this question in mind, we employed two bipyrazolyl-based ligands with different spacer lengths, dmpzb and dmpzh (Scheme 1g), and carried out their reactions with Zn(NO3)2 and 1,4-H2bdc under solvothermal conditions. Two unique three-dimensional coordination polymers [Zn3(1,4-bdc)3(dmpzb)]n (1) and [Zn2(1,4-bdc)2(dmpzh)]n (2) were isolated and structurally characterized. Herein we report their syntheses, crystal structures and luminescent properties. Solvothermal reaction of a mixture of Zn(NO3)2∙6H2O, 1,4-H2bdc, dmpzb (molar ratio 1:1:1) in H2O and MeCN at 150°C in a sealed Pyrex glass tube for 1 day afforded colorless blocks of 1 in 83% yield [11]. Similar reaction of Zn(NO3)2∙6H2O, 1,4-H2bdc, dmpzh generated colorless crystals of 2 in 75% yield [11]. The different outcomes of the two similar reactions may be ascribed to the spacer lengths of dmpzb and dmpzh ligands, which will be described later in this article. Compounds 1 and 2 are air and moisture stable and insoluble in common
M. Dai et al. / Inorganic Chemistry Communications 29 (2013) 70–75
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Scheme 1. (a)–(f) Several possible coordination modes of the 1,4-bdc ligand. (g) Structure of the dmpzb and dmpzh ligands.
organic solvents such as CHCl3, MeCN, and DMF and DMSO. The elemental analyses were consistent with their chemical formula. For 1 or 2, the PXRD showed that the observed patterns for each compound correlate well with the simulated ones generated from single-crystal X-ray diffraction data (Fig. S1). In the IR spectra of 1 and 2, the strong bonds at 1560–1622 cm −1 and 1350–1435 cm −1 represent the coordinated carboxyl groups. The identities of 1–2 were finally confirmed by X-ray crystallography [12]. Compound 1 crystallizes in the triclinic space group Pī and its asymmetric unit consists of half an independent [Zn3(1,4-bdc)3(dmpzb)] molecule. As shown in Fig. 1a and b, the Zn1 atom is octahedrally coordinated by six O atoms from six 1,4-bdc ligands, while the Zn2 atom adopts a tetrahedral geometry coordinated by three O atoms from three 1,3-bdc ligands, and one N atom from one dmpzb ligand. For Zn1, the average Zn1\O bond length (2.013(2) Å) is slightly shorter than that found in [Zn4(μ-OH)2(1,2-PDA)3(1,4-bpeb)2]n (2.157(3) Å, for 1,2-PDA=1,2-phenylenediacetate; 1,4-bpeb=1,4-bis[2-(4-pyridyl) ethenyl]benzene) [13]. For Zn2, the mean Zn1\N and Zn1\O bond lengths (1.991(3) Å vs 1.964(2) Å) are comparable to the corresponding ones of [Zn(OH2)(5-HO-1,3-BDC)(1,4-bpeb)]n (2.027(2) Å vs 1.961(2) Å for 5-HO-1,3-BDC=5-hydroxy-1,3-benzenedicarboxylate) [14]. The 1,4-bdc ligands display two coordination modes bis-bidentate (mode a) and bis-monodentate (mode b) shown in Scheme 1. Four bis-bidentate 1,4-bdc and two bis-monodentate 1,4-bdc ligands combine two tetrahedral Zn and one octahedral Zn to form a trinuclear [Zn3(1,4-bdc)6] unit (Fig. 1c). Each unit is connected to its equivalent ones by bis-bidentate 1,4-bdc and bis-monodentate 1,4-bdc ligands, generating a 2D grid extending along the bc plane (Fig. 1d). Such a 2D layer is further linked to its neighboring ones by dmpzb bridges to afford a unique 3D net (Fig. 1e). If the trinuclear [Zn3(1,4-bdc)6(dmpzb)2] unit is considered as an 8-connecting node, the whole net can be simplified into an 8-connected net with a 364185262 topology (Fig. 1f). Compound 2 crystallizes in the monoclinic space group P21/c and its asymmetric unit contains one [Zn2(1,4-bdc)2(dmpzh)] molecule. Each Zn shows a square pyramidal geometry, which is coordinated by four O atoms from four 1,4-bdc ligands at the basal positions, and one N atom from a dmpzh ligand at the apical position (Fig. 2a). The contact between Zn1 and Zn2 is 3.095(13) Å. The mean Zn1\N length (2.049(3) Å) is shorter than that of [Fe(η 5-C5H4-1-C5H4N)2]2Zn2(OAc)4 (2.178(3) Å) [15], while the average Zn1\O bond length (2.036(2) Å) is slightly longer than that in [Fe(η 5-C5H4-1-C5H4N)2]2Zn2(OAc)4 (2.026(2) Å) [15]. In 2, all the four 1,4-bdc ligands adopt coordination mode a in Scheme 1 and they bridge Zn1 and Zn2 to form a dinuclear [Zn2(1,4-bdc)4] unit (Fig. 2b). These units are interlinked by 1,4-bdc bridges, forming a 1D [Zn2(1,4-bdc)2]n chain along the a axis (Fig. 2c). Such a chain
connects its adjacent ones by other 1,4-bdc bridges to form a 2D (4,4) layer extending along the ab plane (Fig. 2d). This layer is further linked to its neighboring ones by dmpzh bridges to afford a 3D net (Fig. 2e). If the [Zn2(1,4-bdc)4(dmpzh)2] unit is considered as a six-connecting node, the whole structure of 2 can be described as a 6-connected net with a 4 85 46 3 Schläfli symbol (Fig. 2f). The photoluminescent properties of 1 and 2 in solid state at room temperature were investigated (Fig. S2). Upon excitation at 327 nm (1) or 330 nm (2), 1 and 2 exhibited photoluminescence with emission maxima at 375 nm (1) and 420 nm (2), respectively. 1,4-H2bdc did not show photoluminescence under the above-mentioned exciation wavelengths. The maximum emission wavelengths for dmpzb and dmpzh (λex = 220 nm) both appeared at 330 nm [9b]. Thus the emission maxima of 1 and 2 are red-shifted related to them, which may be ascribed to the zinc(II)-to-ligand charge transfer (MLCT) with electrons being transferred from the Zn(II) to pyrazolyl groups [10a]. The thermogravimetric analyses revealed that 1 and 2 were stable up to 449 °C (1) and 248 °C (2), respectively (Fig. S3). After 449 °C, the ligands in 1 started to decompose and the weight of the final residue (27.07%) was assumed to be ZnO (calcd. 26.11%). 2 got its first weight loss corresponding to one coordinated 1,4-bdc ligand (obsd. 21.84%, calcd. 22.36%) from 248 to 286 °C. It continuously lost weight above 361 °C, and the final residue was also assumed to be ZnO (obsd. 22.03%; calcd. 22.09%). In summary, we demonstrated that solvothermal reactions of Zn(NO3)2 with 1,4-bdc and two flexible bipyrazolyl ligands (dmpzb and dmpzh) with different spacer lengths led to the formation of two different Zn coordination polymers 1 and 2. For 1, three zinc centers are held together by four bis-bidentate and two bis-monodentate 1,4-bdc ligands to form a trinuclear [Zn3(1,4-bdc)6] unit, which is further linked to its equivalent ones by 1,4-bdc and dmpzb ligands to form a 3D net with a 3 64 185 26 2 topology. For 2, two zinc centers are linked by four bis-bidentate 1,4-bdc ligands to afford a dinuclear [Zn2(1,4-bdc)2] unit that is further connected to its equivalent ones to afford a 3D net with a 4 85 46 3 topology. The results provided an interesting insight into the effect of the spacer length of the bipyrazolyl ligands on the coordination modes of 1,4-bdc, and the zinc/1,4-bdc units and the final topological structures of the Zn(II) coordination polymers. Acknowledgments The authors thanked the National Natural Science Foundation of China (90922018 and 21171124), the Nature Science Key Basic Research of Jiangsu Province for Higher Education (09KJA150002), the Specialized Research Fund for the Doctoral Program of Higher
72 M. Dai et al. / Inorganic Chemistry Communications 29 (2013) 70–75 Fig. 1. (a) View of the coordination environment of the Zn1 center in 1 with a labeling scheme. Symmetry code: (A) −x, −y, −z + 1. All H atoms have been omitted for clarity. (b) View of the coordination environment of the Zn2 center in 1 with a labeling scheme. Symmetry code: (B) −x + 1, −y, −z + 1. (c) View of a trinuclear [Zn3(1,4-bdc)6(dmpzb)2] unit in 1. (d) View of a 2D network extending along the bc plane. (e) View of a single 3D net of 1 looking along the b axis. (f) Schematic view of the topological net of 1. The cyan spheres represent [Zn3(1,4-bdc)6(dmpzb)2] units, while the purple and blue lines represent 1,4-bdc and dmpzb ligands, respectively.
M. Dai et al. / Inorganic Chemistry Communications 29 (2013) 70–75 Fig. 2. (a) View of the coordination environment of the Zn1 center in 2 with a labeling scheme. Symmetry code: (A) −x + 2, −y, −z. All H atoms have been omitted for clarity. (b) View of a structure of the dinuclear [Zn2(dmpzh)2(1,4-bdc)4] unit in 2. (c) View of a section of the 1D chain extending along the a axis. The red and blue balls represent O and N atoms, respectively. Each cyan square pyramid represents one Zn atom. (d) View of a 2D network extending along the ab plane. (e) View of a single 3D net of 2 looking along the a axis. (f) Schematic view of the topological net of 2. The cyan spheres represent [Zn2(1,4-bdc)4(dmpzh)] units, while the purple and blue lines represent 1,4-bdc and dmpzh ligands, respectively.
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Education of the Ministry of Education (20093201110017), and the State Key Laboratory of Organometallic Chemistry of Shanghai Institute of Organic Chemistry (201201006) for the financial support. J. P. Lang highly appreciated the support by the Priority Academic Program Development of Jiangsu Higher Education Institutions. The authors also greatly thanked the editor and the reviewers for the helpful comments.
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Abrahams, Single-crystal-to-single-crystal transformations of two three-dimensional coordination polymers through regioselective [2+2] photodimerization reactions, Angew. Chem. Int. Ed. 49 (2010) 4767–4770. To a 10 mL Pyrex glass tube was loaded Zn(NO3)2∙6H2O (30 mg, 0.1 mmol), 1,4-H2bdc (17 mg, 0.1 mmol), dmpzb (25 mg, 0.1 mmol), 2.5 mL of H2O and 0.5 mL of MeCN. The tube was sealed and then heated in an oven to 150 °C for one day. It was cooled to ambient temperature at the rate of 5 °C/h, to form colorless crystals of 1, which were washed with water and Et2O and dried in air. Yield: 29 mg (83% based on Zn). Anal. Calcd. for C38H34N4O12Zn3: C, 48.82; H, 3.66; N, 5.99%. Found: C, 48.64; H, 3.61; N, 5.74%. IR (KBr, cm−1): 3448m, 3156w, 1636m, 1601m, 1556s, 1502m, 1392s, 1295m, 1122s, 1018m, 819m, 744s, 604m, 544m. Compound 2 (colorless blocks) was prepared as above starting from Zn(NO3)2∙6H2O (30 mg, 0.1 mmol), 1,4-H2bdc (17 mg, 0.1 mmol), dmpzh (28 mg, 0.1 mmol), 2.5 mL of H2O and 0.5 mL of MeCN. Yield: 27 mg (75% yield based on Zn). Anal. Calcd. for C32H34N4O8Zn2: C, 52.40; H, 4.67; N, 7.64%. Found: C, 52.55; H, 4.48; N, 7.59%. IR (KBr, cm−1): 2940m, 1647s, 1557m, 1501m, 1387s, 1052m, 1018m, 885m, 823s, 746s, 539s. Crystal data for 1 : C38H34N4O12Zn3, Mr =934.86, 0.50×0.30×0.20 mm, trinilic, space group Pī, a=9.843(2) Å, b=10.052(2) Å, c=11.240(2) Å, α=98.98(3)°, β=110.25(3)°, γ=110.25(3)°, V=900.6(3) Å3, Z=1, Dc =1.724 g·cm-3, F(000)=476 and μ=2.055 mm-1, T=223 K, 8360 reflections collected, 4016 unique (Rint =0.0483). R1 =0.0397, wR2 =0.1127 and S=1.048 based on 3072 observed reflections with I>2σ(I). For 2: C32H34N4O8Zn2, Mr =733.41, 0.60× 0.60×0.40 mm, monoclinic, space group P21/c, a=10.909(2) Å, b=21.370(4) Å, c=16.575(5) Å, α=90.00 °, β=124.24(2)°, γ=90.00 °, V=3194.4(13) Å3, Z=4, Dc =1.525 g·cm-3, F(000)=1512 and μ=1.559 mm-1, T=223 K, 29294 reflections collected, 7220 unique (Rint =0.0656). R1 =0.0565, wR2 =0.1576 and S=1.124 based on 6230 observed reflections with I>2σ(I).
M. Dai et al. / Inorganic Chemistry Communications 29 (2013) 70–75 [13] D. Liu, Y.J. Chang, J.P. Lang, Ligand geometry-driven formation of different coordination polymers from Zn(NO3)2, 1,4-bpeb and phenylenediacetic acids, CrystEngComm 13 (2011) 1851–1857. [14] D. Liu, H.X. Li, L.L. Liu, H.M. Wang, N.Y. Li, Z.G. Ren, J.P. Lang, How do substituent groups in the 5-position of 1,3-benzenedicarboxylate affect the construction of supramolecular frameworks, CrystEngComm 12 (2010) 3708–3716.
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