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Solvothermal synthesis, crystal structure and magnetic properties of a 3D CoII framework based on 2-p-isopropylphenyl imidazole dicarboxylate
Inorganic Chemistry Communications 36 (2013) 86–89
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Solvothermal synthesis, crystal structure and magnetic properties of a 3D CoII framework based on 2-p-isopropylphenyl imidazole dicarboxylate Li Li, Bei-Bei Guo, Jiao Zhang, Gang Li ⁎ College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, Henan, P. R. China
a r t i c l e
i n f o
Article history: Received 1 July 2013 Accepted 22 August 2013 Available online 30 August 2013 Keywords: Imidazole dicarboxylate Cobalt Polymer Crystal structure Property
a b s t r a c t Self-assembly of CoSO4 salt and 2-(p-isopropylphenyl)-1H-imidazole-4,5-dicarboxylic acid (H3PPhIDC), results in the formation of a metal-organic framework, [Co(HPPhIDC)(CH3OH)]n (1), which has been characterized by elemental analysis, IR, X-ray powder diffraction (XRPD), thermogravimetric analysis and single-crystal X-ray diffraction. Polymer 1 is a meso-compound and displays a (3,3)-connected 3D structure with 1D channels and cages, which are composed of left- and right-handed helices pillared by Co2+ linkers. Moreover, the antiferromagnetic coupling between the neighboring Co(II) ions in 1 can be observed. © 2013 Elsevier B.V. All rights reserved.
Generally, the crystal structure and dimensionality of the metalorganic framework (MOF) are driven by the functionality of the organic ligand and the coordination geometry of the metal center [1,2]. In this context, polydentate ligand is particularly important because it can connect multiple metal centers by multi-coordination sites and various coordination modes to form an infinite array. To obtain one desirable polydentate linker, the modification method has been witnessed to be the most efficient way [3]. By the method, people have obtained a large variety of organic linkers to construct intriguing polymeric structures. As well known, imidazole-4,5-dicarboxylic acid (H3IDC) ligand contains N, O-multidentate coordination sites and can display various bridging modes, which is a useful polydentate linker and heavily favored by chemistry researchers recently [4]. Therefore, modifications based on the H3IDC ligand are underway. More recently, our group has strong and continuous interest in introducing aromatic groups such as phenyl, m-methoxyphenyl, p-bromophenyl and 3,4-dimethylphenyl units into 2-position of imidazole dicarboxylate ligands [5]. With the employment of these modified organic ligands, a number of attractive MOFs have been reported [5], which further demonstrates the feasibility of modifications. To investigate the modifications more comprehensively, another 2-(p-isopropylphenyl)-1H-imidazole-4,5-dicarboxylic acid (H3PPhIDC) was designed and synthesized under the guidance of the literature [6]. What's more, considering the significant role played by center metals, people prefer to select the metals with well-defined coordination geometries as nodes. For this purpose, the transition metals attract extensive attention. According to the literatures, we find that only seven ⁎ Corresponding author. Tel./fax: +86 371 67781764. E-mail address: [email protected] (G. Li). 1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.inoche.2013.08.018
Co complexes including four 0D, one 1D, one 2D, and one 3D structures have been obtained on the basis of the imidazole dicarboxylate ligands bearing 2-position aromatic groups [5]. This prompted us to give much attention on the preparation and investigation of the related Co complexes. Hence, to enrich the researches of the Co(II) polymers, the assembly of Co(II) ion with H3PPhIDC ligand is explored by us. Fortunately, one 3D Co polymer [Co(HPPhIDC)(CH3OH)]n (1) [7] was solvothermally synthesized and structurally characterized. The phase purity of the crystalline sample has been confirmed by elemental analysis and powder X-ray diffraction. Furthermore, its thermal and magnetic properties have been further investigated as well. The single-crystal X-ray diffraction result [8] reveals that complex 1 crystallizes in the tetragonal space group I41/a, and presents a fascinating mesomer 3D framework with 1D infinite channels. As shown in Fig. S1 (supporting information), the asymmetric unit of complex 1 consists of one Co(II) cation, one HPPhIDC2− and one CH3OH ligands. Each Co(II) ion has a distorted octahedron [CoO4N2] geometry, which is defined by three individual HPPhIDC2− and one CH3OH ligands. The Co–O and Co–N bond distances are in the ranges of 2.105(5)–2.211(5) Å and 2.057(4)–2.080(4) Å, respectively, which are comparable with the values of previous complexes [9]. The bond angles around the Co(II) ion vary from 75.43(16) to 164.87(18)° without exception. Each HPPhIDC2− ligand adopts a μ3-kN,O: kO′: kN′,O′ mode (Scheme S1, supporting information), which bridges Co ions to form interesting helical chains with different chirality along c-axis. The intra-chain distance of two adjacent Co ions is 6.3809(7) Å. As shown in Fig. 1a, the carboxyl groups act as the linkers and combine two types of helical chains. Furthermore, via the junctions among the helical chains, one
L. Li et al. / Inorganic Chemistry Communications 36 (2013) 86–89
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Fig. 1. (a) View of the two types of helical chains along c-axis. (b) The unique 3D structure of 1. (c) Perspective of the simplified 3D structure with left- and right-handed helices. (d) Features of the 3D compound displayed by tiling. (e) View of the cage in compound 1. (f) View of the (3,3)-connected topological net (Color scheme for b, c, e: carbon = yellow, nitrogen = blue, oxygen = red, metal = green, purple).
unique 3D structure containing left- and right-handed helices are arranged in the cross-linkage is revealed to us (Fig. 1b,c and d). Meanwhile, the 1D infinite channels are surrounded by four helical chains with different chirality, which is very rare. Moreover, it should be noted that irregular cages are emerged in the channels (Fig. 1e). In this 3D framework, only one type of intra-molecular H-bond, [O(2)–H(2)…O(3)] within the imidazole dicarboxylate ligand can be observed (supporting information, Table 3), which may influence the polymer's thermogravimetric ability. To understand the framework topology, it is necessary to simplify the building blocks of compound 1. Each Co atom is surrounded by three HPPhIDC2− ligands, which can be represented by a 3-connected unit, and the ligand linking three Co atoms can be represented by a 3connected unit (Fig. 1f). Therefore the whole structure can be simplified as a (3,3)-connected topology with a point symbol of (4.8.10). Owing to the magnetic properties of Co coordination polymers, there are continuous researches about them. However, there solely have seven imidazole dicarboxylate-based Co(II) complexes in the references [5]. In the reported 0D, 1D, 2D structures, the imidazole dicarboxylate ligands always display 1- or 2-connected coordination modes, and in the 3D structures, the imidazole dicarboxylate ligands exhibit 3-connected coordination modes. Therefore, complicated coordination modes will induce high-dimensional frameworks. It is to be noted that the coordination mode (μ3-kN,O: kO′: kN′,O′) of HPPhIDC2− ligand herein is first
reported. Polymer 1 is a meso-compound, which is composed of leftand right-handed helical chains and displays a 3D non-interpenetrated topology with 1D open channels, which is rare. The IR spectrum of polymer 1 displays characteristic absorption bands for carboxylate, imidazole and phenyl units (Fig. S2, supporting information). There is a weak peak around 1700 cm−1, which is a characteristic peak of protonated carboxylate group. The absorption bands in the frequency range 1700, 1575 cm−1 should be attribute to the vibrations of νas(COO−) and νs(COO−), respectively. Bands in the range of 1000–1500 cm −1 are attributed to C–N and C–C vibrations. The characteristic IR band of the phenyl ring can be found at 787 cm −1 for the δ(C–H) vibrations. In conclusion, the infrared spectral data of 1 are consistent with crystal structure analysis. The stability of 1 was examined by thermogravimetric analysis in air atmosphere from the temperature of 25–830 °C (Fig. 2). It shows a low thermal stability and a two main steps loss weight. First, a gradual loss weight of 9.12% (calculated 8.82%) is from 53 to 189 °C corresponding to the release of the coordinated CH3OH molecule. Subsequently, it keeps losing the remaining complex from 336 to 497 °C (observed 69.98, calculated 70.55%). Finally, residual weight of 20.90% corresponds to the percentage (calculated 20.63%) of the Co and O components, indicating that the final product is CoO. X-ray powder diffraction (XRD) was used to check the purity of 1. As shown in Fig. 3, all the peaks displayed in the (b) measured patterns are
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Fig. 2. The TG curve of compound 1.
similar to those in the (a) simulated patterns generated from single crystal diffraction data, indicating single phase of 1 is formed. Variable-temperature magnetic study on 1 is carried out over the temperature range of 2.0 – 300 K on a MPMS-7 SQUID magnetometer. The variation of the inverse of the magnetic susceptibility, χ−1 M and χMT of 1 is shown in Fig. 4. At 300 K, the effective magnetic moment (μeff) per cobalt(II) is 4.630 μB, is higher than the expected value for the spin-only S = 3/2 system (3.87 μB) due to the orbital contribution [10]. −1 The thermal evolution of χM obeys Curie–Weiss law, χM = C/(T − θ) in the temperature range of 300–8.5 K with Weiss constant, θ, of − 21.79 K and Curie constant, CM, of 2.94 cm3 K mol −1. On lowering the temperature, the χMT value decreases smoothly to a minimum of 0.589 cm3 K mol −1 at 2 K. Such the χMT vs T curve and the negative θ value can be referred to the presence of typical antiferromagnetic exchange interactions between neighbor Co(II) ions in polymer 1 or the contribution of the spin-coupling and the zero-splitting. According to the aforementioned structural discussion, the μ3– HPPhIDC2− units link Co(II) ions into a 3D network. Till now, no appropriate theory model has been established to determine the magnetic coupling constant between metal ions for a 3D net polymeric complex. In order to evaluate the magnetic interactions in 1, the magnetic susceptibility of 1 has been fitted to the Fisher model [11] of the isotropic Heisenberg antiferromagnet, or the 1D – J1J2J1J2 – mode [12] or the dinuclear Co(II) mode [13]. Unfortunately, we could not get satisfactory result. Obviously, the magnetic pathways between neighbor Co(II) ions of 1 are complicated, which could not be simply dealt with. The results
Fig. 3. Powder X-ray pattern of compound 1.
are according with those of the previous Co(II) polymer based on the similar imidazole dicarboxylate ligand [5c]. In summary, the extended architecture of polymer 1 has been synthesized under solvothermal condition. The thermal and magnetic properties of 1 have been investigated. The H3PPhIDC ligand in this work shows a new kind of coordination mode. Apparently, further studies based on the H3PPhIDC ligand and related ligands need to be done and will be reported in due course. Acknowledgments We gratefully acknowledge the financial support by the National Natural Science Foundation of China (21071127 and J1210060), and Program for New Century Excellent Talents in University (NCET-10-0139). Appendix A. Supplementary material CCDC 940682 contains the supplementary crystallographic data for this paper. The 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 http://dx.doi.org/10.1016/j.inoche.2013.08.018. References [1] (a) S.H. Jhung, N.A. Khan, Z. Hasan, Analogous porous metal-organic frameworks: synthesis, stability and application in adsorption, CrystEngComm 14 (2012) 7099–7109; (b) L.F. Song, J. Zhang, L.X. Sun, F. Xu, F. Li, H.Z. Zhang, X.L. Si, C.L. Jiao, Z.b. Li, S. Liu, Y.L. Liu, H.y. Zhou, D.l. Sun, Y. Du, Z. Cao, Z. Gabelica, Mesoporous metal-organic frameworks: design and applications, Energy Environ. Sci. 5 (2012) 7508–7520; (c) H.L. Jiang, Q. Xu, Porous metal-organic frameworks as platforms for functional applications, Chem. Commun. 47 (2011) 3351–3370. [2] (a) D. Sun, L.L. Han, S. Yuan, Y.K. Deng, M.Z. Xu, D.F. Sun, Four new Cd(II) coordination polymers with mixed multidentate N-donors and biphenyl-based polycarboxylate ligands: syntheses, structures, and photoluminescent properties, Cryst. Growth Des. 13 (2013) 377–385; (b) F.A. Almeida Paz, J. Klinowski, S.M.F. Vilela, J.P.C. Tomé, J.A.S. Cavaleiro, J. Rocha, Ligand design for functional metal-organic frameworks, Chem. Soc. Rev. 41 (2012) 1088–1110; (c) S.R. Halper, L. Do, J.R. Stork, S.M. Cohen, Topological control in heterometallic metal–organic frameworks by anion templating and metalloligand design, J. Am. Chem. Soc. 128 (2006) 15255–15268; (d) L.Q. Han, Y. Yan, F.X. Sun, K. Cai, T. Borjigin, X.J. Zhao, F.Y. Qu, G.S. Zhu, Single- and double-layer structures and sorption properties of two microporous metal-organic frameworks with flexible tritopic ligand, Cryst. Growth Des. 13 (2013) 1458–1463. [3] (a) N. Stock, S. Biswas, Synthesis of Metal-Organic Frameworks (MOFs): routes to various MOF topologies, morphologies, and composites, Chem. Rev. 112 (2012) 933–969; (b) O.K. Farha, J.T. Hupp, Rational design, synthesis, purification, and activation of metal–organic framework materials, Acc. Chem. Res. 43 (2010) 1166–1175. [4] (a) S.L. Cai, S.R. Zheng, Z.Z. Wen, J. Fan, N. Wang, W.G. Zhang, Two types of new three-dimensional d-f heterometallic coordination polymers based on 2-(pyridin-3-yl)-1H-imidazole-4,5-dicarboxylate and oxalate ligands:
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syntheses, structures, luminescence, and magnetic properties, Cryst. Growth Des. 12 (2012) 4441–4449; J.H. Deng, D.C. Zhong, X.Z. Luo, H.J. Liu, T.B. Lu, 2-Propyl-4,5-dicarboxylateimidazole (H3PPHIDC) based cadmium(II) coordination compounds stabilized by supramolecular interactions: from mononuclear and tetranuclear oligomers to one-dimensional (1D) chain and two-dimensional (2D) layer polymers, Cryst. Growth Des. 12 (2012) 4861–4869; L.X. Xie, X.W. Hou, Y.T. Fan, H.W. Hou, Four three-dimensional coordination polymers constructed by 2-((1H-1,2,4-triazol-1-yl)methyl)-1H-imidazole-4,5dicarboxylate: syntheses, topological structures, and magnetic properties, Cryst. Growth Des. 12 (2012) 1282–1291. Z.F. Xiong, R.M. Gao, Z.K. Xie, B.B. Guo, L. Li, Y.Y. Zhu, G. Li, Assembly of a series of MOFs based on the 2-(m-methoxyphenyl)imidazole dicarboxylate ligand, Dalton Trans. 42 (2013) 4613–4624; Y. Zhang, B.B. Guo, L. Li, S.F. Liu, G. Li, Construction and properties of six MOFs based on the newly designed 2-(p-bromophenyl)-imidazole dicarboxylate ligand, Cryst. Growth Des. 13 (2013) 367–376; C.J. Wang, T. Wang, W. Zhang, H.J. Lu, G. Li, Two unprecedented transitionmetal–organic frameworks showing one dimensional-hexagonal channel open network and two-dimensional sheet structures, Cryst. Growth Des. 12 (2012) 1091–1094; C.J. Wang, T. Wang, L. Li, B.B. Guo, Y. Zhang, Z.F. Xiong, G. Li, MOFs constructed with the newly designed imidazole dicarboxylate bearing 2-position aromatic substituent: hydro(solvo)thermal syntheses, crystal structures and properties, Dalton Trans. 42 (2013) 1715–1725; Z. Xiong, H.L. Jia, B. Ma, G. Li, Syntheses, crystal structures and properties of three Co(II) supramolecules constructed from phenyl imidazole icarboxylates, Synth. React. Inorg. Met.-Org. Chem. 42 (2012) 1204–1210; Z.F. Xiong, B.B. Shi, L. Li, Y.Y. Zhu, G. Li, Construction of transition-metal coordiantion polymers using multifunctional imidazole dicarboxylates as spacers, CrystEngComm 15 (2013) 4885–4899.
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[6] A.V. Lebedev, A.B. Lebedeva, V.D. Sheludyakov, E.A. Kovaleva, O.L. Ustinova, V.V. Shatunov, Synthesis and N-alkylation of 2-alkyland 2-arylimidazole-4,5-dicarboxylic acid esters, Russ. J. Gen. Chem. 77 (2007) 949–953. [7] Synthesis of [Co(HPPHIDC)(CH3OH)]n (1): A mixture of CoSO4·7H2O (28.1 mg, 0.1 mmol), H3PPHIDC (27.4 mg, 0.1 mmol) and CH3OH/H2O (3/4, 7 mL), Et3N (0.014 mL, 0.1 mmol) was sealed in a 25 mL Teflon-lined stainless steel autoclave, heated at 160 °C for 72 h, and then cooled to room temperature. After decanting the mother liquor, aubergine crystals of 1 were isolated, washed with distilled water and dried in air (69% yield based on Co). Anal. Calcd. For C15H16CoN2O5: C, 49.60; H, 4.44; N, 7.71%. Found: C, 49.46; H, 4.27; N, 7.90%. IR (cm−1, KBr): 3422 (m), 2961 (s), 1700 (w), 1575 (s), 1447 (s), 1406 (w), 1272 (s), 1124 (s), 1054 (m), 842 (s), 787 (s), 757 (s), 621 (w), 541 (w). [8] Crystal data for 1: Tetragonal, I41/a, a = 20.7782(6) Å, b = 20.7782(6) Å, c = 15.7899(5) Å, α = 90.00° β = 90.00° γ = 90.00° V = 1334.9(3) Å3, Z = 16, F(000) = 2992, GOF = 1.046, R1 = 0.0707, wR2 = 0.1907. [9] (a) J.H. Cui, Y.Z. Li, Z.J. Guo, H.G. Zheng, Six new co-coordination polymers based on a tripodal carboxylate ligand, Cryst. Growth Des. 12 (2012) 3610–3618; (b) H.L. Wang, D.P. Zhang, D.F. Sun, Y.T. Chen, L.F. Zhang, L.J. Tian, J.Z. Jiang, Z.H. Ni, Co(II) metal − organic frameworks (MOFs) assembled from asymmetric semirigid multicarboxylate ligands: synthesis, crystal structures, and magnetic properties, Cryst. Growth Des. 9 (2009) 5273–5282. [10] H.Y. Mao, C.Z. Zhang, G. Li, H.Y. Zhang, H.W. Hou, L.K. Li, Q.A. Wu, Y. Zhu, E.B. Wang, New types of the flexible self-assembled metal–organic coordination polymers constructed by aliphatic dicarboxylates and rigid bidentate nitrogen ligands, Dalton Trans. (2004) 3918–3925. [11] M.E. Fisher, Magnetism in one-dimensional systems — the heisenberg model for infinite spin, Am. J. Phys. 32 (1964) 343–345. [12] O. Kahn, Molecular Magnetism, VCH, New York, 1993. [13] H. Sakiyama, R. Ito, H. Kumagai, K. Inoue, M. Sakamoto, Y. Nishida, M. Yamasaki, Eur. J. Inorg. Chem. (2001) 2027–2032.
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Solvothermal synthesis, crystal structure and magnetic properties of a 3D CoII framework based on 2-p-isopropylphenyl imidazole dicarboxylate Li Li, Bei-Bei Guo, Jiao Zhang, Gang Li ⁎ College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, Henan, P. R. China
a r t i c l e
i n f o
Article history: Received 1 July 2013 Accepted 22 August 2013 Available online 30 August 2013 Keywords: Imidazole dicarboxylate Cobalt Polymer Crystal structure Property
a b s t r a c t Self-assembly of CoSO4 salt and 2-(p-isopropylphenyl)-1H-imidazole-4,5-dicarboxylic acid (H3PPhIDC), results in the formation of a metal-organic framework, [Co(HPPhIDC)(CH3OH)]n (1), which has been characterized by elemental analysis, IR, X-ray powder diffraction (XRPD), thermogravimetric analysis and single-crystal X-ray diffraction. Polymer 1 is a meso-compound and displays a (3,3)-connected 3D structure with 1D channels and cages, which are composed of left- and right-handed helices pillared by Co2+ linkers. Moreover, the antiferromagnetic coupling between the neighboring Co(II) ions in 1 can be observed. © 2013 Elsevier B.V. All rights reserved.
Generally, the crystal structure and dimensionality of the metalorganic framework (MOF) are driven by the functionality of the organic ligand and the coordination geometry of the metal center [1,2]. In this context, polydentate ligand is particularly important because it can connect multiple metal centers by multi-coordination sites and various coordination modes to form an infinite array. To obtain one desirable polydentate linker, the modification method has been witnessed to be the most efficient way [3]. By the method, people have obtained a large variety of organic linkers to construct intriguing polymeric structures. As well known, imidazole-4,5-dicarboxylic acid (H3IDC) ligand contains N, O-multidentate coordination sites and can display various bridging modes, which is a useful polydentate linker and heavily favored by chemistry researchers recently [4]. Therefore, modifications based on the H3IDC ligand are underway. More recently, our group has strong and continuous interest in introducing aromatic groups such as phenyl, m-methoxyphenyl, p-bromophenyl and 3,4-dimethylphenyl units into 2-position of imidazole dicarboxylate ligands [5]. With the employment of these modified organic ligands, a number of attractive MOFs have been reported [5], which further demonstrates the feasibility of modifications. To investigate the modifications more comprehensively, another 2-(p-isopropylphenyl)-1H-imidazole-4,5-dicarboxylic acid (H3PPhIDC) was designed and synthesized under the guidance of the literature [6]. What's more, considering the significant role played by center metals, people prefer to select the metals with well-defined coordination geometries as nodes. For this purpose, the transition metals attract extensive attention. According to the literatures, we find that only seven ⁎ Corresponding author. Tel./fax: +86 371 67781764. E-mail address: [email protected] (G. Li). 1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.inoche.2013.08.018
Co complexes including four 0D, one 1D, one 2D, and one 3D structures have been obtained on the basis of the imidazole dicarboxylate ligands bearing 2-position aromatic groups [5]. This prompted us to give much attention on the preparation and investigation of the related Co complexes. Hence, to enrich the researches of the Co(II) polymers, the assembly of Co(II) ion with H3PPhIDC ligand is explored by us. Fortunately, one 3D Co polymer [Co(HPPhIDC)(CH3OH)]n (1) [7] was solvothermally synthesized and structurally characterized. The phase purity of the crystalline sample has been confirmed by elemental analysis and powder X-ray diffraction. Furthermore, its thermal and magnetic properties have been further investigated as well. The single-crystal X-ray diffraction result [8] reveals that complex 1 crystallizes in the tetragonal space group I41/a, and presents a fascinating mesomer 3D framework with 1D infinite channels. As shown in Fig. S1 (supporting information), the asymmetric unit of complex 1 consists of one Co(II) cation, one HPPhIDC2− and one CH3OH ligands. Each Co(II) ion has a distorted octahedron [CoO4N2] geometry, which is defined by three individual HPPhIDC2− and one CH3OH ligands. The Co–O and Co–N bond distances are in the ranges of 2.105(5)–2.211(5) Å and 2.057(4)–2.080(4) Å, respectively, which are comparable with the values of previous complexes [9]. The bond angles around the Co(II) ion vary from 75.43(16) to 164.87(18)° without exception. Each HPPhIDC2− ligand adopts a μ3-kN,O: kO′: kN′,O′ mode (Scheme S1, supporting information), which bridges Co ions to form interesting helical chains with different chirality along c-axis. The intra-chain distance of two adjacent Co ions is 6.3809(7) Å. As shown in Fig. 1a, the carboxyl groups act as the linkers and combine two types of helical chains. Furthermore, via the junctions among the helical chains, one
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Fig. 1. (a) View of the two types of helical chains along c-axis. (b) The unique 3D structure of 1. (c) Perspective of the simplified 3D structure with left- and right-handed helices. (d) Features of the 3D compound displayed by tiling. (e) View of the cage in compound 1. (f) View of the (3,3)-connected topological net (Color scheme for b, c, e: carbon = yellow, nitrogen = blue, oxygen = red, metal = green, purple).
unique 3D structure containing left- and right-handed helices are arranged in the cross-linkage is revealed to us (Fig. 1b,c and d). Meanwhile, the 1D infinite channels are surrounded by four helical chains with different chirality, which is very rare. Moreover, it should be noted that irregular cages are emerged in the channels (Fig. 1e). In this 3D framework, only one type of intra-molecular H-bond, [O(2)–H(2)…O(3)] within the imidazole dicarboxylate ligand can be observed (supporting information, Table 3), which may influence the polymer's thermogravimetric ability. To understand the framework topology, it is necessary to simplify the building blocks of compound 1. Each Co atom is surrounded by three HPPhIDC2− ligands, which can be represented by a 3-connected unit, and the ligand linking three Co atoms can be represented by a 3connected unit (Fig. 1f). Therefore the whole structure can be simplified as a (3,3)-connected topology with a point symbol of (4.8.10). Owing to the magnetic properties of Co coordination polymers, there are continuous researches about them. However, there solely have seven imidazole dicarboxylate-based Co(II) complexes in the references [5]. In the reported 0D, 1D, 2D structures, the imidazole dicarboxylate ligands always display 1- or 2-connected coordination modes, and in the 3D structures, the imidazole dicarboxylate ligands exhibit 3-connected coordination modes. Therefore, complicated coordination modes will induce high-dimensional frameworks. It is to be noted that the coordination mode (μ3-kN,O: kO′: kN′,O′) of HPPhIDC2− ligand herein is first
reported. Polymer 1 is a meso-compound, which is composed of leftand right-handed helical chains and displays a 3D non-interpenetrated topology with 1D open channels, which is rare. The IR spectrum of polymer 1 displays characteristic absorption bands for carboxylate, imidazole and phenyl units (Fig. S2, supporting information). There is a weak peak around 1700 cm−1, which is a characteristic peak of protonated carboxylate group. The absorption bands in the frequency range 1700, 1575 cm−1 should be attribute to the vibrations of νas(COO−) and νs(COO−), respectively. Bands in the range of 1000–1500 cm −1 are attributed to C–N and C–C vibrations. The characteristic IR band of the phenyl ring can be found at 787 cm −1 for the δ(C–H) vibrations. In conclusion, the infrared spectral data of 1 are consistent with crystal structure analysis. The stability of 1 was examined by thermogravimetric analysis in air atmosphere from the temperature of 25–830 °C (Fig. 2). It shows a low thermal stability and a two main steps loss weight. First, a gradual loss weight of 9.12% (calculated 8.82%) is from 53 to 189 °C corresponding to the release of the coordinated CH3OH molecule. Subsequently, it keeps losing the remaining complex from 336 to 497 °C (observed 69.98, calculated 70.55%). Finally, residual weight of 20.90% corresponds to the percentage (calculated 20.63%) of the Co and O components, indicating that the final product is CoO. X-ray powder diffraction (XRD) was used to check the purity of 1. As shown in Fig. 3, all the peaks displayed in the (b) measured patterns are
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T/K −1 −1 Fig. 4. Plots of χM and χM T vs T for 1.
Fig. 2. The TG curve of compound 1.
similar to those in the (a) simulated patterns generated from single crystal diffraction data, indicating single phase of 1 is formed. Variable-temperature magnetic study on 1 is carried out over the temperature range of 2.0 – 300 K on a MPMS-7 SQUID magnetometer. The variation of the inverse of the magnetic susceptibility, χ−1 M and χMT of 1 is shown in Fig. 4. At 300 K, the effective magnetic moment (μeff) per cobalt(II) is 4.630 μB, is higher than the expected value for the spin-only S = 3/2 system (3.87 μB) due to the orbital contribution [10]. −1 The thermal evolution of χM obeys Curie–Weiss law, χM = C/(T − θ) in the temperature range of 300–8.5 K with Weiss constant, θ, of − 21.79 K and Curie constant, CM, of 2.94 cm3 K mol −1. On lowering the temperature, the χMT value decreases smoothly to a minimum of 0.589 cm3 K mol −1 at 2 K. Such the χMT vs T curve and the negative θ value can be referred to the presence of typical antiferromagnetic exchange interactions between neighbor Co(II) ions in polymer 1 or the contribution of the spin-coupling and the zero-splitting. According to the aforementioned structural discussion, the μ3– HPPhIDC2− units link Co(II) ions into a 3D network. Till now, no appropriate theory model has been established to determine the magnetic coupling constant between metal ions for a 3D net polymeric complex. In order to evaluate the magnetic interactions in 1, the magnetic susceptibility of 1 has been fitted to the Fisher model [11] of the isotropic Heisenberg antiferromagnet, or the 1D – J1J2J1J2 – mode [12] or the dinuclear Co(II) mode [13]. Unfortunately, we could not get satisfactory result. Obviously, the magnetic pathways between neighbor Co(II) ions of 1 are complicated, which could not be simply dealt with. The results
Fig. 3. Powder X-ray pattern of compound 1.
are according with those of the previous Co(II) polymer based on the similar imidazole dicarboxylate ligand [5c]. In summary, the extended architecture of polymer 1 has been synthesized under solvothermal condition. The thermal and magnetic properties of 1 have been investigated. The H3PPhIDC ligand in this work shows a new kind of coordination mode. Apparently, further studies based on the H3PPhIDC ligand and related ligands need to be done and will be reported in due course. Acknowledgments We gratefully acknowledge the financial support by the National Natural Science Foundation of China (21071127 and J1210060), and Program for New Century Excellent Talents in University (NCET-10-0139). Appendix A. Supplementary material CCDC 940682 contains the supplementary crystallographic data for this paper. The 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 http://dx.doi.org/10.1016/j.inoche.2013.08.018. References [1] (a) S.H. Jhung, N.A. Khan, Z. Hasan, Analogous porous metal-organic frameworks: synthesis, stability and application in adsorption, CrystEngComm 14 (2012) 7099–7109; (b) L.F. Song, J. Zhang, L.X. Sun, F. Xu, F. Li, H.Z. Zhang, X.L. Si, C.L. Jiao, Z.b. Li, S. Liu, Y.L. Liu, H.y. Zhou, D.l. Sun, Y. Du, Z. Cao, Z. Gabelica, Mesoporous metal-organic frameworks: design and applications, Energy Environ. Sci. 5 (2012) 7508–7520; (c) H.L. Jiang, Q. Xu, Porous metal-organic frameworks as platforms for functional applications, Chem. Commun. 47 (2011) 3351–3370. [2] (a) D. Sun, L.L. Han, S. Yuan, Y.K. Deng, M.Z. Xu, D.F. Sun, Four new Cd(II) coordination polymers with mixed multidentate N-donors and biphenyl-based polycarboxylate ligands: syntheses, structures, and photoluminescent properties, Cryst. Growth Des. 13 (2013) 377–385; (b) F.A. Almeida Paz, J. Klinowski, S.M.F. Vilela, J.P.C. Tomé, J.A.S. Cavaleiro, J. Rocha, Ligand design for functional metal-organic frameworks, Chem. Soc. Rev. 41 (2012) 1088–1110; (c) S.R. Halper, L. Do, J.R. Stork, S.M. Cohen, Topological control in heterometallic metal–organic frameworks by anion templating and metalloligand design, J. Am. Chem. Soc. 128 (2006) 15255–15268; (d) L.Q. Han, Y. Yan, F.X. Sun, K. Cai, T. Borjigin, X.J. Zhao, F.Y. Qu, G.S. Zhu, Single- and double-layer structures and sorption properties of two microporous metal-organic frameworks with flexible tritopic ligand, Cryst. Growth Des. 13 (2013) 1458–1463. [3] (a) N. Stock, S. Biswas, Synthesis of Metal-Organic Frameworks (MOFs): routes to various MOF topologies, morphologies, and composites, Chem. Rev. 112 (2012) 933–969; (b) O.K. Farha, J.T. Hupp, Rational design, synthesis, purification, and activation of metal–organic framework materials, Acc. Chem. Res. 43 (2010) 1166–1175. [4] (a) S.L. Cai, S.R. Zheng, Z.Z. Wen, J. Fan, N. Wang, W.G. Zhang, Two types of new three-dimensional d-f heterometallic coordination polymers based on 2-(pyridin-3-yl)-1H-imidazole-4,5-dicarboxylate and oxalate ligands:
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