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A inorganic-organic hybrid material constructed from the monolacunary polyoxomolybdates and multi-nuclear copper clusters
Inorganic Chemistry Communications 76 (2017) 118–121
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Short communication
A inorganic-organic hybrid material constructed from the monolacunary polyoxomolybdates and multi-nuclear copper clusters Xiao-Yuan Wu, Wen-Bin Yang, Wei-Ming Wu, Jian-Zhen Liao, Sa-Sa Wang, Can-Zhong Lu ⁎ Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Provincial Key Laboratory of Nanomaterials, Fujian Institute of the Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China
a r t i c l e
i n f o
Article history: Received 13 December 2016 Received in revised form 10 January 2017 Accepted 17 January 2017 Available online 18 January 2017 Keywords: Polyoxometalate Multi-nuclear Cu cluster Inorganic-organic hybrid material Magnetism Photocatalytic property
a b s t r a c t A novel polyoxometalate (POM)-based inorganic-organic hybrid material constructed from the monolacunary Keggin-type polyoxomolybdates and the multi-nuclear copper clusters, namely, V {[Cu8(tz)8(Htz)4(H2O)5][PMoVI 10Mo O39]}∙~10H2O (1) (Htz = 1H-tetrazole) has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, IR spectra, PXRD analysis. In 1, the six-nuclear copper clusters in the roof shape were bridged by the tz ligands. These clusters are extended into the wave-like layers by the μ2-Htz ligands and the copper atoms in octahedron coordination geometry. The polyoxomolybdate anions act as the eight-connected node to link the layers into a 3D framework. In addition, the magnetic and photocatalytic properties of compound 1 have been investigated. © 2017 Elsevier B.V. All rights reserved.
Inorganic organic hybrid materials are of great current interest and importance due to their intriguing structures as well as wide-ranging applications in gas storage, catalysis, chemical separation, optics and materials science [1–5]. Polyoxometalates (POMs), as an important kind of inorganic building units, have a lot of superiorities for constructing multifunctional inorganic organic hybrid materials, such as abundant topologies and compositions, acid/base tenability, oxygen-rich surface and controllable sizes [6–22]. In addition, polyoxometalates possess strong capacity to bear and release electrons, and therefore often serve as electron reservoirs in various types of chemical reactions, which renders POMs and their hybrid materials to be excellent homogeneous and heterogeneous catalysts [6–10]. In the big family of POMs, Keggin- and Dawson-type heteropolyoxometalates, as well as [Mo8O26]4− octamolybdate isomers, are most frequently used to construct POM-based hybrid materials with intriguing structure due to their commercial availability or easy in-situ generation from reaction precursors under hydrothermal conditions [9–14]. To date, a large number of inorganic-organic hybrid materials based on polyoxometalates have been synthesized and reported, in which the polyoxometalates are either coordinated to secondary metal atoms via metal-oxygen coordination bonds, or act as guests/templates/counter ions through non-covalent interactions [15–22]. However, examples of POMs-based hybrid materials with high dimensional frameworks constructed by the multi-nuclear transition metal clusters are scare, indicating that the research area on POMs-based hybrids is still in its infancy, and ⁎ Corresponding author. E-mail address: [email protected] (C.-Z. Lu).
http://dx.doi.org/10.1016/j.inoche.2017.01.026 1387-7003/© 2017 Elsevier B.V. All rights reserved.
POM chemists still face challenge to rationally design and synthesize inorganic-organic hybrid materials with high dimensional structures. It is well-known that organic ligand play significant roles in the construction of inorganic-organic hybrids with novel structures and properties. Herein, we choose the simplest 1H-tetrazole (Htz) as rigid multifunational ligands to build POM-based inorganic-organic hybrid materials, because it exhibits diverse coordination/bridging modes as reported recently in metal-organic frameworks [23–24]. Not only can providing with four sequent electron-donating N-donors to coordinate metal atoms, the 1H-tetrazole (Htz) ligand also possesses the smaller steric hindrance, showing the superiority in the construction of multinuclear clusters and high dimensional structures. Many metal-organic frameworks based on Htz ligands exhibit intriguing topologies and interesting magnetic, absorptive and photophysical properties. Secondary metal ions are another important factor in building functional hybrid materials. The copper ions are chosen due to their various coordination arrangements. Furthermore, the copper compounds, as a kind of environmentally benign catalysts, were widely used in eliminating the organic pollutants with green oxidants, such as molecular oxygen and hydrogen peroxide [25–26]. Using Keggin POMs as building blocks in the presence of polydentate triazolate or tetrazolate ligands, our research group has synthesized and reported recently a series of POM-based copper (or silver)–organic pseudorotaxane frameworks, POM-based supramolecular aggregates and POM-MOF host-guest hybrids [27–30]. As a part of continuous works in this POM/Cu/tetrazolate system, we herein report another new POM-based hybrid compound V {[Cu8(tz)8(Htz)4(H2O)5][PMoVI 10Mo O39]}∙~10H2O (1), which is built
X.-Y. Wu et al. / Inorganic Chemistry Communications 76 (2017) 118–121
from copper-tetrazolate coordination polymeric wave-like layers extended by monolacunary Keggin heteropolyoxometalates via copper-oxygen coordination bonds to form a 3-D framework. Furthermore, the magnetic and photocatalytic properties of 1 have been investigated. Green crystals of compound 1 were obtained by heating a mixture of H3PMo12O40, Cu(NO3)2·3H2O and Htz in water under hydrothermal conditions [31]. The formula of the product was determined to be {[Cu8(tz)8(Htz)4(H2O)5][PMoVI10MoVO39]}∙~10H2O on the basis of the combined results of X-ray single-crystal structure analysis, elemental analysis and thermal analysis. Single-crystal X-ray diffraction analysis revealed that 1 crystallizes in the orthorhombic system with the Pmmn space group [32]. There are one P atom and four Mo atoms in the asymmetry unit. It is noted that the occupancies of the Mo4 and O14 atoms are nearly 50%. Thus the polyoxoanion {PMo11O39} is disordered in X-ray crystallography to give a Keggin-like structure based on two times of mirror symmetry operation. Bond valence sum calculations revealed that the Mo1, Mo2 and Mo3 atoms are in +VI oxidation state and Mo4 atom is in +V oxidation state [33]. The polyoxoanion is therefore determined as [PMoVI10MoVO39]8 − in the type of monolacunary keggin heteopolyoxomolybdate. To our best knowledge, compound 1 is the first example exhibiting the unsubstituted monolacunary Keggin-type polyoxomolybdates. The three crystallographically independent Cu ions are all six-coordinated in distorted octahedron geometry. The Cu1 ion lies in a plane and is coordinated by five N atoms from five tz ligands and one bridging water molecule. The bond distances around Cu1 are 2.017(7)–2.340(9) Å for Cu1\\N and 2.308(7) Å for Cu1\\O. The Cu2 ion is coordinated by four N atoms from four tz ligands and two O atoms from the [PMo11O39]8 − anion and water molecule respectively. The bond distances around Cu2 are 1.984(7)–2.309(7) Å for Cu2\\N and 2.023(6)–2.476(4) Å for Cu2\\O. The Cu3 ion lies on a symmetry center and is coordinated by four N atoms from four tz ligands and two O atoms from two [PMo11O39]8 − anions with bond distances of 1.971(7)–2.021(6) Å (Cu3\\N) and 2.546(2) Å (Cu3\\O). In compound 1, the tetrazole ligands adopt four types of coordination modes: μ2-N2, N4; μ3-N1, N3, N4; μ3-N1, N2, N3; μ4-N1, N2, N3, N4 (as shown in Scheme 1). Basing on the charge balance and the coordination modes, the μ3- and μ4-tz ligands are deprotonation, while the μ2-Htz ligands keep neutral. As shown in Fig. 1, the triangle-type copper cluster is constructed with one Cu1 atom, two Cu2 atoms, one ligand in coordination model II and two ligands in coordination model III. Two such copper clusters are bridged by the μ4-tz ligands and the water molecule into the six-nuclear cluster in the roof shape, which is further extended to form a chain by the μ2-Htz ligands. Furthermore, the Cu3 atoms connected the chains into the wave-like layers in ab plane. The polyoxomolybdate anions act as the eight-connected nodes to link the layers into a 3D framework (as shown in Fig. 2). In the IR spectrum of 1 (Fig. S1), the vibrations at 1058, 981, 944, 861, 802 cm−1 are the characteristic bands of the Keggin-type heteropolyoxomolybdate, while the vibrations in the region of 1700– 1100 cm−1 can be attributed to the characteristic peaks of tz ligands. In addition, the strong and broad peaks at 3138 cm−1 can be assigned to the telescopic oscillations of water molecules. To estimate the purity and thermal stability of complex 1, XRPD patterns and TGA were performed on polycrystalline samples of 1. The XRPD patterns for the assynthesized sample of 1 are in good agreement with the one simulated
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from the single-crystal X-ray data (Fig. S2), confirming the crystalline phase purity of 1. Upon heating under nitrogen stream, complex 1 displays a multistep process of weight loss in the temperature of 30– 700 °C (Fig. S3); the first weigh loss of 7.1% occurring below 270 °C is attributed to the removal of the lattice water molecules and the coordinated water molecules (calcd. 8.1%). The successive weight loss between 250 °C and 500 °C belongs to the decomposition of the hybrid framework of 1, followed by the plateau without further weight loss to give the final oxide product of Cu and Mo. As shown in Fig. 3, preliminary magnetic studies were performed on powdered samples of 1 under an applied field of 1000 Oe in the temperature range of 2–300 K. The experimental χmT value at room temperature is 3.1 emu K mol− 1 per formula unit, slightly higher than the theoretical value (i.e. 3.0 emu K mol−1) for eight uncoupled Cu2+ ions (S = 1/2, g = 2). The slightly higher measured χmT is ascribable to an appreciable orbital contribution. Upon cooling, the χmT value continuously decreases, indicating the presence of the antiferromagnetic exchange interactions. The magnetic data of 1 obey the Curie-Weiss law in the range 100–300 K temperature region, giving the Curie constant C = 3.65 emu mol−1 K and the Weiss constant θ = −24.4 K. The negative Weiss constant also suggests that the dominative interactions between Cu2+ ions are antiferromagnetic interactions mediated through bridging tetrazolate ligands and bridging water molecules. For it is not soluble in water and common organic solvents like methanol, ethanol and so on, the title compound may act as a heterogeneous catalyst in degrading the organic dyes in the waste water. To investigate the photocatalytic activities of 1, the methyl orange (MO) was evaluated under visible light irradiation with hydrogen peroxide as oxidant. In the experiments, 100 mg of 1 was dispersed in 100 mL MO aqueous solution (20 mg L−1) containing 2 mL of hydrogen peroxide (30%) as oxidant, and the reaction mixture was stirred and irradiated with 300 W Xe lamp as the visible light source. After every 30 min time interval, 5.0 mL of solution was collected and used to monitor the degradation of MO− through testing the characteristic absorption peak of MO− with UV–vis spectra. Control experiments were also carried out without 1 or H2O2. As shown in Fig. 4, the degradation of MO− reaches up to 90.1% within 2.5 h in the presence of 1 and H2O2. In comparison, there is no any observable change of the concentration of MO in the absence of H2O2 oxidant, while in the presence of hydrogen peroxide but without 1, the degradation ratio of MO is less than 21.7%. Moreover, the PXRD patterns of the powder solid recycled after degradation of MO are the same as the original (Fig. S2), suggesting that the framework structure of 1 remain intact in the process of degrading MO. These results indicate that 1 may be a good heterogenous photocatalyst on the degradation of MO organic dye. In conclusion, we report here a novel polyoxometalate (POM)-based inorganic-organic hybrid material with 3D framework structure, which is constructed from the unsubstituted monolacunary Keggin-type polyoxomolybdates and the multi-nuclear copper clusters. Moreover, compound 1 exhibits excellent photocatalytic activity in degradation of MO under visible light irradiation. Acknowledgements This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB20000000), the Frontier Sciences Research Program of the Chinese Academy of Sciences (QYZDJ-
Scheme 1. The four coordination modes of the tz/Htz ligands in compound 1.
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X.-Y. Wu et al. / Inorganic Chemistry Communications 76 (2017) 118–121
Fig. 1. The layer structure of the {Cu8(tz)8(Htz)4(H2O)5}n in the compound 1.
SSW-SLH033), the National Natural Science Foundation of China (21373221, 21521061, 21403236) and the Natural Science Foundation of Fujian Province (2006L2005).
Fig. 2. The 3D framework of compound 1.
Fig. 3. Temperature dependence of the molar magnetic susceptibility χm (□) and the product of the molar magnetic susceptibility and the temperature χmT (▲) for compound 1 between 2.0 and 300 K.
X.-Y. Wu et al. / Inorganic Chemistry Communications 76 (2017) 118–121
Fig. 4. Photocatalytic degradation of MO solution under different conditions.
Appendix A. Supplementary material Crystal data, PXRD patterns, IR curves, TG curves, tables of X-ray crystallographic data in CIF format for compounds 1 are available free of charge via the Internet at http://www.sciencedirect.com. CCDC reference numbers are 983604 for 1. Supplementary data associated with this article can be found, in the online version doi: 10.1016/j.inoche. 2017.01.026.
References [1] H.C. Zhou, S. Kitagawa, Metal-Organic Frameworks (MOFs), Chem. Soc. Rev. 43 (2014) 5415–5418. [2] K. Sumida, D.L. Rogow, J.A. Mason, T.M. McDonald, E.D. Bloch, Z.R. Herm, T.-H. Bae, J.R. Long, Carbon dioxide capture in metal-organic frameworks, Chem. Rev. 112 (2012) 724–781. [3] S.T. Zheng, G.Y. Yang, Recent advances in paramagnetic-TM-substituted polyoxometalates (TM = Mn, Fe, Co, Ni, Cu), Chem. Soc. Rev. 41 (2012) 7623–7646. [4] D.Y. Du, J.S. Qin, S.L. Li, Z.M. Su, Y.Q. Lan, Recent advances in porous polyoxometalate-based metal-organic framework materials, Chem. Soc. Rev. 43 (2014) 4615–4632. [5] J.R. Li, R.J. Kuppler, H.C. Zhou, Selective gas adsorption and separation in metal-organic frameworks, Chem. Soc. Rev. 38 (2009) 1477–1504. [6] S.S. Wang, G.Y. Yang, Recent advances in polyoxometalate-catalyzed reactions, Chem. Rev. 115 (2015) 4893–4962. [7] R. Neumann, Polyoxometalate complexes in organic oxidation chemistry, Prog. Inorg. Chem. 47 (1998) 317–370. [8] Q.X. Han, B. Qi, W.M. Ren, C. He, J.Y. Niu, C.Y. Duan, Polyoxometalate-based homochiral metal-organic frameworks for tandem asymmetric transformation of cyclic carbonates from olefins, Nat. Commun. 6 (2015) 10007. [9] A. Alsalme, N. Alzaqri, A. Alsaleh, M.R.H. Siddiqui, A. Alotaibi, E.F. Kozhevnikova, I.V. Kozhevnikov, Efficient Ni-Mo hydrodesulfurization catalyst prepared through Keggin polyoxometalate, Appl. Catal. B Environ. 182 (2016) 102–108. [10] W.J. Xuan, C. Botuha, B. Hasenknopf, S. Thorimbert, Chiral Dawson-type hybrid polyoxometalate catalyzes enantioselective diels-alder reactions, Chem. Eur. J. 21 (2015) 16512–16516. [11] X. Rong, H.Y. Lin, D.N. Liu, X. Wang, G.C. Liu, X.L. Wang, Solvothermal synthesis, structures and properties of two new octamolybdate-based compounds with tetrazole- and pyridyl-containing asymmetric amide ligands, Inorg. Chem. Commun. 71 (2016) 9–14. [12] X.L. Hao, S.F. Jia, Y.Y. Ma, H.Y. Wang, Y.G. Li, Two new Keggin-type polyoxometalatebased entangled coordination networks constructed from metal-organic chains with dangling arms, Inorg. Chem. Commun. 72 (2016) 132–137.
121
[13] J.C. Liu, J. Yu, Q. Han, B. Shao, Y. Wen, L.J. Chen, J.W. Zhao, Syntheses, structures and properties of four inorganic-organic hybrid heteropolymolybdates functionalized by chiral serine ligands, Inorg. Chem. Commun. 70 (2016) 136–139. [14] Y.H. Sun, G.D. Li, X.B.J.Q. Cui, Z.M.M. Xu, A novel two-dimensional coordination polymer constructed from bi-capped Keggin molybdenum-vanadium polyoxoanions and nickel ethylenediamine complexes, Inorg. Chem. Commun. 66 (2016) 24–27. [15] I.V. Kozhevnikov, Catalysis by heteropoly acids and multicomponent polyoxometalates in liquid-phase reactions, Chem. Rev. 98 (1998) 171–198. [16] H.N. Miras, V.-N. Laia, L. Cronin, Polyoxometalate based open-frameworks (POMOFs), Chem. Soc. Rev. 43 (2014) 5679–5699. [17] Y.T. Zhang, X.L. Wang, E.L. Zhou, X.S. Wu, B.Q. Song, K.Z. Shao, Z.M. Su, Polyoxovanadate-based organic inorganic hybrids: from {V5O9Cl} clusters to nanosized octahedral cages, Dalton Trans. 45 (2016) 3698–3701. [18] J.W. Zhao, Y.Z. Li, L.J. Chen, G.Y. Yang, Research progress on polyoxometalate-based transition-metal-rare-earth heterometallic derived materials: synthetic strategies, structural overview and functional applications, Chem. Commun. 52 (2016) 4418–4445. [19] Y.Y. Hu, T.T. Zhang, X. Zhang, D.C. Zhao, X.B. Cui, Q.S. Huo, J.Q. Xu, New organic-inorganic hybrid compounds constructed from polyoxometalates and transition metal mixed-organic-ligand complexes, Dalton Trans. 45 (2016) 2562–2573. [20] X.L. Wang, X. Rong, H.Y. Lin, J.J. Cao, G.C. Liu, Z.H. Chang, A novel Wells-Dawson polyoxometalate-based metal-organic framework constructed from the uncommon in-situ transformed bi(triazole) ligand and azo anion, Inorg. Chem. Commun. 63 (2016) 30–34. [21] J.W. Zhang, Q. Li, M.Y. Zeng, Y.C. Huang, J. Zhang, J. Hao, Y.G. Wei, The proton-controlled synthesis of unprecedented diol functionalized Anderson-type POMs, Chem. Commun. 52 (2016) 2378–2381. [22] X.L. Wang, J.J. Sun, H.Y. Lin, Z.H. Chang, X. Wang, G.C. Liu, G.C. Liu, A series of Anderson-type polyoxometalate-based metal-organic complexes: their pH-dependent electrochemical behaviour, and as electrocatalysts and photocatalysts, Dalton Trans. 45 (2016) 12465–12478. [23] Z.J. Hou, Z.Y. Liu, N. Liu, E.C. Yang, X.J. Zhao, Four tetrazolate-based 3D frameworks with diverse subunits directed by inorganic anions and azido coligand: hydro/ solvothermal syntheses, crystal structures, and magnetic properties, Dalton Trans. 44 (2015) 2223–2233. [24] P. Cui, H.S. Hu, B. Zhao, J.T. Miller, P. Cheng, J. Li, A multicenter-bonded [ZnI]8 cluster with cubic aromaticity, Nat. Commun. 6 (2015) 6331. [25] K.H. Kim, S.K. Ihm, Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: a review, J. Hazard. Mater. 186 (2011) 16–34. [26] D.W. Fickel, J.M. Fedeyko, R.F. Lobo, Copper coordination in Cu-SSZ-13 and Cu-SSZ16 investigated by variable-temperature XRD, J. Phys. Chem. C 114 (2010) 1633–1640. [27] X. Kuang, X. Wu, R. Yu, J.P. Donahue, J. Huang, C.Z. Lu, Assembly of a metal–organic framework by sextuple intercatenation of discrete adamantane-like cages, Nat. Chem. 2 (2010) 461–465. [28] X. Kuang, X.Y. Wu, J. Zhang, C.Z. Lu, Surface modification of polyoxometalate host– guest supramolecular architectures: from metal–organic pseudorotaxane framework to molecular box, Chem. Commun. 47 (2011) 4150–4152. [29] X.Y. Wu, Q.K. Zhang, X.F. Kuang, W.B. Yang, R.M. Yu, C.Z. Lu, Two hybrid polyoxometalate-pillared metal–organic frameworks, Dalton Trans. 41 (2012) 11783–11787. [30] R.M. Yu, X.F. Kuang, X.Y. Wu, C.Z. Lu, J.P. Donahue, Stabilization and immobilization of polyoxometalates in porous coordination polymers through host–guest interactions, Coord. Chem. Rev. 253 (2009) 2872–2890. [31] Synthesis of 1. A mixture of Cu(NO3)2·3H2O (0.242 g, 1.0 mmol), Htz (0.050 g, 0.71 mmol), H3PMo12O40·xH2O (0.150 g) and H2O (10.0 mL) was stirred for 1 h. Then the solution was sealed in the 23 mL Teflon-lined auto clave and heated at 100 °C for 4 days. After slow cooling to room temperature, green crystals of 1 were filtered, washed with distilled water and ethanol, and dried at room temperature (68% yield based on Mo). Elemental analysis: C12H46Cu8Mo11N48O54P1 (3321.60). Anal. Calcd for 1: H, 1.40; C, 4.34; N, 20.24; O, 26.01; Cu, 15.31; Mo, 31.77%. Found: H, 1.38; C, 4.35; N, 19.86; O, 26.26; Cu, 14.76; Mo, 31.15%. [32] Crystal data for 1: C12H46Cu8Mo11N48O54P1, M = 3321.60, orthorhombic, a = 20.599(6) Å, b = 11.872(3) Å, c = 16.534(4) Å, V = 4043.3(19) Å3, space group Pmmn, Z = 2, Dc = 2.728 Mg/m3, μ = 3.844 mm−1, F(000) = 3190, GOF = 1.002, 25907 reflections measured, 3853 independent reflections (Rint = 0.0717). The final R1 value was 0.0548 (I N 2σ(I)). The X-ray diffraction data was collected with a Rigaku Saturn70 CCD Diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at T = 293(2) K. Absorption corrections were made using SADABS program. The structures were solved using direct method and refined by full-matrix least-squares methods on F2 by using SHELX-97 program package. All non-hydrogen atoms were refined anisotropically. Positon of the hydrogen atoms were attached to carbon atoms were fixed at their ideal positions. [33] H.H. Thorp, Bond valence sum analysis of metal-ligand bond lengths in metalloenzymes and model complexes, Inorg. Chem. 31 (1992) 1585–1588.
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Short communication
A inorganic-organic hybrid material constructed from the monolacunary polyoxomolybdates and multi-nuclear copper clusters Xiao-Yuan Wu, Wen-Bin Yang, Wei-Ming Wu, Jian-Zhen Liao, Sa-Sa Wang, Can-Zhong Lu ⁎ Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Provincial Key Laboratory of Nanomaterials, Fujian Institute of the Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China
a r t i c l e
i n f o
Article history: Received 13 December 2016 Received in revised form 10 January 2017 Accepted 17 January 2017 Available online 18 January 2017 Keywords: Polyoxometalate Multi-nuclear Cu cluster Inorganic-organic hybrid material Magnetism Photocatalytic property
a b s t r a c t A novel polyoxometalate (POM)-based inorganic-organic hybrid material constructed from the monolacunary Keggin-type polyoxomolybdates and the multi-nuclear copper clusters, namely, V {[Cu8(tz)8(Htz)4(H2O)5][PMoVI 10Mo O39]}∙~10H2O (1) (Htz = 1H-tetrazole) has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, IR spectra, PXRD analysis. In 1, the six-nuclear copper clusters in the roof shape were bridged by the tz ligands. These clusters are extended into the wave-like layers by the μ2-Htz ligands and the copper atoms in octahedron coordination geometry. The polyoxomolybdate anions act as the eight-connected node to link the layers into a 3D framework. In addition, the magnetic and photocatalytic properties of compound 1 have been investigated. © 2017 Elsevier B.V. All rights reserved.
Inorganic organic hybrid materials are of great current interest and importance due to their intriguing structures as well as wide-ranging applications in gas storage, catalysis, chemical separation, optics and materials science [1–5]. Polyoxometalates (POMs), as an important kind of inorganic building units, have a lot of superiorities for constructing multifunctional inorganic organic hybrid materials, such as abundant topologies and compositions, acid/base tenability, oxygen-rich surface and controllable sizes [6–22]. In addition, polyoxometalates possess strong capacity to bear and release electrons, and therefore often serve as electron reservoirs in various types of chemical reactions, which renders POMs and their hybrid materials to be excellent homogeneous and heterogeneous catalysts [6–10]. In the big family of POMs, Keggin- and Dawson-type heteropolyoxometalates, as well as [Mo8O26]4− octamolybdate isomers, are most frequently used to construct POM-based hybrid materials with intriguing structure due to their commercial availability or easy in-situ generation from reaction precursors under hydrothermal conditions [9–14]. To date, a large number of inorganic-organic hybrid materials based on polyoxometalates have been synthesized and reported, in which the polyoxometalates are either coordinated to secondary metal atoms via metal-oxygen coordination bonds, or act as guests/templates/counter ions through non-covalent interactions [15–22]. However, examples of POMs-based hybrid materials with high dimensional frameworks constructed by the multi-nuclear transition metal clusters are scare, indicating that the research area on POMs-based hybrids is still in its infancy, and ⁎ Corresponding author. E-mail address: [email protected] (C.-Z. Lu).
http://dx.doi.org/10.1016/j.inoche.2017.01.026 1387-7003/© 2017 Elsevier B.V. All rights reserved.
POM chemists still face challenge to rationally design and synthesize inorganic-organic hybrid materials with high dimensional structures. It is well-known that organic ligand play significant roles in the construction of inorganic-organic hybrids with novel structures and properties. Herein, we choose the simplest 1H-tetrazole (Htz) as rigid multifunational ligands to build POM-based inorganic-organic hybrid materials, because it exhibits diverse coordination/bridging modes as reported recently in metal-organic frameworks [23–24]. Not only can providing with four sequent electron-donating N-donors to coordinate metal atoms, the 1H-tetrazole (Htz) ligand also possesses the smaller steric hindrance, showing the superiority in the construction of multinuclear clusters and high dimensional structures. Many metal-organic frameworks based on Htz ligands exhibit intriguing topologies and interesting magnetic, absorptive and photophysical properties. Secondary metal ions are another important factor in building functional hybrid materials. The copper ions are chosen due to their various coordination arrangements. Furthermore, the copper compounds, as a kind of environmentally benign catalysts, were widely used in eliminating the organic pollutants with green oxidants, such as molecular oxygen and hydrogen peroxide [25–26]. Using Keggin POMs as building blocks in the presence of polydentate triazolate or tetrazolate ligands, our research group has synthesized and reported recently a series of POM-based copper (or silver)–organic pseudorotaxane frameworks, POM-based supramolecular aggregates and POM-MOF host-guest hybrids [27–30]. As a part of continuous works in this POM/Cu/tetrazolate system, we herein report another new POM-based hybrid compound V {[Cu8(tz)8(Htz)4(H2O)5][PMoVI 10Mo O39]}∙~10H2O (1), which is built
X.-Y. Wu et al. / Inorganic Chemistry Communications 76 (2017) 118–121
from copper-tetrazolate coordination polymeric wave-like layers extended by monolacunary Keggin heteropolyoxometalates via copper-oxygen coordination bonds to form a 3-D framework. Furthermore, the magnetic and photocatalytic properties of 1 have been investigated. Green crystals of compound 1 were obtained by heating a mixture of H3PMo12O40, Cu(NO3)2·3H2O and Htz in water under hydrothermal conditions [31]. The formula of the product was determined to be {[Cu8(tz)8(Htz)4(H2O)5][PMoVI10MoVO39]}∙~10H2O on the basis of the combined results of X-ray single-crystal structure analysis, elemental analysis and thermal analysis. Single-crystal X-ray diffraction analysis revealed that 1 crystallizes in the orthorhombic system with the Pmmn space group [32]. There are one P atom and four Mo atoms in the asymmetry unit. It is noted that the occupancies of the Mo4 and O14 atoms are nearly 50%. Thus the polyoxoanion {PMo11O39} is disordered in X-ray crystallography to give a Keggin-like structure based on two times of mirror symmetry operation. Bond valence sum calculations revealed that the Mo1, Mo2 and Mo3 atoms are in +VI oxidation state and Mo4 atom is in +V oxidation state [33]. The polyoxoanion is therefore determined as [PMoVI10MoVO39]8 − in the type of monolacunary keggin heteopolyoxomolybdate. To our best knowledge, compound 1 is the first example exhibiting the unsubstituted monolacunary Keggin-type polyoxomolybdates. The three crystallographically independent Cu ions are all six-coordinated in distorted octahedron geometry. The Cu1 ion lies in a plane and is coordinated by five N atoms from five tz ligands and one bridging water molecule. The bond distances around Cu1 are 2.017(7)–2.340(9) Å for Cu1\\N and 2.308(7) Å for Cu1\\O. The Cu2 ion is coordinated by four N atoms from four tz ligands and two O atoms from the [PMo11O39]8 − anion and water molecule respectively. The bond distances around Cu2 are 1.984(7)–2.309(7) Å for Cu2\\N and 2.023(6)–2.476(4) Å for Cu2\\O. The Cu3 ion lies on a symmetry center and is coordinated by four N atoms from four tz ligands and two O atoms from two [PMo11O39]8 − anions with bond distances of 1.971(7)–2.021(6) Å (Cu3\\N) and 2.546(2) Å (Cu3\\O). In compound 1, the tetrazole ligands adopt four types of coordination modes: μ2-N2, N4; μ3-N1, N3, N4; μ3-N1, N2, N3; μ4-N1, N2, N3, N4 (as shown in Scheme 1). Basing on the charge balance and the coordination modes, the μ3- and μ4-tz ligands are deprotonation, while the μ2-Htz ligands keep neutral. As shown in Fig. 1, the triangle-type copper cluster is constructed with one Cu1 atom, two Cu2 atoms, one ligand in coordination model II and two ligands in coordination model III. Two such copper clusters are bridged by the μ4-tz ligands and the water molecule into the six-nuclear cluster in the roof shape, which is further extended to form a chain by the μ2-Htz ligands. Furthermore, the Cu3 atoms connected the chains into the wave-like layers in ab plane. The polyoxomolybdate anions act as the eight-connected nodes to link the layers into a 3D framework (as shown in Fig. 2). In the IR spectrum of 1 (Fig. S1), the vibrations at 1058, 981, 944, 861, 802 cm−1 are the characteristic bands of the Keggin-type heteropolyoxomolybdate, while the vibrations in the region of 1700– 1100 cm−1 can be attributed to the characteristic peaks of tz ligands. In addition, the strong and broad peaks at 3138 cm−1 can be assigned to the telescopic oscillations of water molecules. To estimate the purity and thermal stability of complex 1, XRPD patterns and TGA were performed on polycrystalline samples of 1. The XRPD patterns for the assynthesized sample of 1 are in good agreement with the one simulated
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from the single-crystal X-ray data (Fig. S2), confirming the crystalline phase purity of 1. Upon heating under nitrogen stream, complex 1 displays a multistep process of weight loss in the temperature of 30– 700 °C (Fig. S3); the first weigh loss of 7.1% occurring below 270 °C is attributed to the removal of the lattice water molecules and the coordinated water molecules (calcd. 8.1%). The successive weight loss between 250 °C and 500 °C belongs to the decomposition of the hybrid framework of 1, followed by the plateau without further weight loss to give the final oxide product of Cu and Mo. As shown in Fig. 3, preliminary magnetic studies were performed on powdered samples of 1 under an applied field of 1000 Oe in the temperature range of 2–300 K. The experimental χmT value at room temperature is 3.1 emu K mol− 1 per formula unit, slightly higher than the theoretical value (i.e. 3.0 emu K mol−1) for eight uncoupled Cu2+ ions (S = 1/2, g = 2). The slightly higher measured χmT is ascribable to an appreciable orbital contribution. Upon cooling, the χmT value continuously decreases, indicating the presence of the antiferromagnetic exchange interactions. The magnetic data of 1 obey the Curie-Weiss law in the range 100–300 K temperature region, giving the Curie constant C = 3.65 emu mol−1 K and the Weiss constant θ = −24.4 K. The negative Weiss constant also suggests that the dominative interactions between Cu2+ ions are antiferromagnetic interactions mediated through bridging tetrazolate ligands and bridging water molecules. For it is not soluble in water and common organic solvents like methanol, ethanol and so on, the title compound may act as a heterogeneous catalyst in degrading the organic dyes in the waste water. To investigate the photocatalytic activities of 1, the methyl orange (MO) was evaluated under visible light irradiation with hydrogen peroxide as oxidant. In the experiments, 100 mg of 1 was dispersed in 100 mL MO aqueous solution (20 mg L−1) containing 2 mL of hydrogen peroxide (30%) as oxidant, and the reaction mixture was stirred and irradiated with 300 W Xe lamp as the visible light source. After every 30 min time interval, 5.0 mL of solution was collected and used to monitor the degradation of MO− through testing the characteristic absorption peak of MO− with UV–vis spectra. Control experiments were also carried out without 1 or H2O2. As shown in Fig. 4, the degradation of MO− reaches up to 90.1% within 2.5 h in the presence of 1 and H2O2. In comparison, there is no any observable change of the concentration of MO in the absence of H2O2 oxidant, while in the presence of hydrogen peroxide but without 1, the degradation ratio of MO is less than 21.7%. Moreover, the PXRD patterns of the powder solid recycled after degradation of MO are the same as the original (Fig. S2), suggesting that the framework structure of 1 remain intact in the process of degrading MO. These results indicate that 1 may be a good heterogenous photocatalyst on the degradation of MO organic dye. In conclusion, we report here a novel polyoxometalate (POM)-based inorganic-organic hybrid material with 3D framework structure, which is constructed from the unsubstituted monolacunary Keggin-type polyoxomolybdates and the multi-nuclear copper clusters. Moreover, compound 1 exhibits excellent photocatalytic activity in degradation of MO under visible light irradiation. Acknowledgements This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB20000000), the Frontier Sciences Research Program of the Chinese Academy of Sciences (QYZDJ-
Scheme 1. The four coordination modes of the tz/Htz ligands in compound 1.
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Fig. 1. The layer structure of the {Cu8(tz)8(Htz)4(H2O)5}n in the compound 1.
SSW-SLH033), the National Natural Science Foundation of China (21373221, 21521061, 21403236) and the Natural Science Foundation of Fujian Province (2006L2005).
Fig. 2. The 3D framework of compound 1.
Fig. 3. Temperature dependence of the molar magnetic susceptibility χm (□) and the product of the molar magnetic susceptibility and the temperature χmT (▲) for compound 1 between 2.0 and 300 K.
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Fig. 4. Photocatalytic degradation of MO solution under different conditions.
Appendix A. Supplementary material Crystal data, PXRD patterns, IR curves, TG curves, tables of X-ray crystallographic data in CIF format for compounds 1 are available free of charge via the Internet at http://www.sciencedirect.com. CCDC reference numbers are 983604 for 1. Supplementary data associated with this article can be found, in the online version doi: 10.1016/j.inoche. 2017.01.026.
References [1] H.C. Zhou, S. Kitagawa, Metal-Organic Frameworks (MOFs), Chem. Soc. Rev. 43 (2014) 5415–5418. [2] K. Sumida, D.L. Rogow, J.A. Mason, T.M. McDonald, E.D. Bloch, Z.R. Herm, T.-H. Bae, J.R. Long, Carbon dioxide capture in metal-organic frameworks, Chem. Rev. 112 (2012) 724–781. [3] S.T. Zheng, G.Y. Yang, Recent advances in paramagnetic-TM-substituted polyoxometalates (TM = Mn, Fe, Co, Ni, Cu), Chem. Soc. Rev. 41 (2012) 7623–7646. [4] D.Y. Du, J.S. Qin, S.L. Li, Z.M. Su, Y.Q. Lan, Recent advances in porous polyoxometalate-based metal-organic framework materials, Chem. Soc. Rev. 43 (2014) 4615–4632. [5] J.R. Li, R.J. Kuppler, H.C. Zhou, Selective gas adsorption and separation in metal-organic frameworks, Chem. Soc. Rev. 38 (2009) 1477–1504. [6] S.S. Wang, G.Y. Yang, Recent advances in polyoxometalate-catalyzed reactions, Chem. Rev. 115 (2015) 4893–4962. [7] R. Neumann, Polyoxometalate complexes in organic oxidation chemistry, Prog. Inorg. Chem. 47 (1998) 317–370. [8] Q.X. Han, B. Qi, W.M. Ren, C. He, J.Y. Niu, C.Y. Duan, Polyoxometalate-based homochiral metal-organic frameworks for tandem asymmetric transformation of cyclic carbonates from olefins, Nat. Commun. 6 (2015) 10007. [9] A. Alsalme, N. Alzaqri, A. Alsaleh, M.R.H. Siddiqui, A. Alotaibi, E.F. Kozhevnikova, I.V. Kozhevnikov, Efficient Ni-Mo hydrodesulfurization catalyst prepared through Keggin polyoxometalate, Appl. Catal. B Environ. 182 (2016) 102–108. [10] W.J. Xuan, C. Botuha, B. Hasenknopf, S. Thorimbert, Chiral Dawson-type hybrid polyoxometalate catalyzes enantioselective diels-alder reactions, Chem. Eur. J. 21 (2015) 16512–16516. [11] X. Rong, H.Y. Lin, D.N. Liu, X. Wang, G.C. Liu, X.L. Wang, Solvothermal synthesis, structures and properties of two new octamolybdate-based compounds with tetrazole- and pyridyl-containing asymmetric amide ligands, Inorg. Chem. Commun. 71 (2016) 9–14. [12] X.L. Hao, S.F. Jia, Y.Y. Ma, H.Y. Wang, Y.G. Li, Two new Keggin-type polyoxometalatebased entangled coordination networks constructed from metal-organic chains with dangling arms, Inorg. Chem. Commun. 72 (2016) 132–137.
121
[13] J.C. Liu, J. Yu, Q. Han, B. Shao, Y. Wen, L.J. Chen, J.W. Zhao, Syntheses, structures and properties of four inorganic-organic hybrid heteropolymolybdates functionalized by chiral serine ligands, Inorg. Chem. Commun. 70 (2016) 136–139. [14] Y.H. Sun, G.D. Li, X.B.J.Q. Cui, Z.M.M. Xu, A novel two-dimensional coordination polymer constructed from bi-capped Keggin molybdenum-vanadium polyoxoanions and nickel ethylenediamine complexes, Inorg. Chem. Commun. 66 (2016) 24–27. [15] I.V. Kozhevnikov, Catalysis by heteropoly acids and multicomponent polyoxometalates in liquid-phase reactions, Chem. Rev. 98 (1998) 171–198. [16] H.N. Miras, V.-N. Laia, L. Cronin, Polyoxometalate based open-frameworks (POMOFs), Chem. Soc. Rev. 43 (2014) 5679–5699. [17] Y.T. Zhang, X.L. Wang, E.L. Zhou, X.S. Wu, B.Q. Song, K.Z. Shao, Z.M. Su, Polyoxovanadate-based organic inorganic hybrids: from {V5O9Cl} clusters to nanosized octahedral cages, Dalton Trans. 45 (2016) 3698–3701. [18] J.W. Zhao, Y.Z. Li, L.J. Chen, G.Y. Yang, Research progress on polyoxometalate-based transition-metal-rare-earth heterometallic derived materials: synthetic strategies, structural overview and functional applications, Chem. Commun. 52 (2016) 4418–4445. [19] Y.Y. Hu, T.T. Zhang, X. Zhang, D.C. Zhao, X.B. Cui, Q.S. Huo, J.Q. Xu, New organic-inorganic hybrid compounds constructed from polyoxometalates and transition metal mixed-organic-ligand complexes, Dalton Trans. 45 (2016) 2562–2573. [20] X.L. Wang, X. Rong, H.Y. Lin, J.J. Cao, G.C. Liu, Z.H. Chang, A novel Wells-Dawson polyoxometalate-based metal-organic framework constructed from the uncommon in-situ transformed bi(triazole) ligand and azo anion, Inorg. Chem. Commun. 63 (2016) 30–34. [21] J.W. Zhang, Q. Li, M.Y. Zeng, Y.C. Huang, J. Zhang, J. Hao, Y.G. Wei, The proton-controlled synthesis of unprecedented diol functionalized Anderson-type POMs, Chem. Commun. 52 (2016) 2378–2381. [22] X.L. Wang, J.J. Sun, H.Y. Lin, Z.H. Chang, X. Wang, G.C. Liu, G.C. Liu, A series of Anderson-type polyoxometalate-based metal-organic complexes: their pH-dependent electrochemical behaviour, and as electrocatalysts and photocatalysts, Dalton Trans. 45 (2016) 12465–12478. [23] Z.J. Hou, Z.Y. Liu, N. Liu, E.C. Yang, X.J. Zhao, Four tetrazolate-based 3D frameworks with diverse subunits directed by inorganic anions and azido coligand: hydro/ solvothermal syntheses, crystal structures, and magnetic properties, Dalton Trans. 44 (2015) 2223–2233. [24] P. Cui, H.S. Hu, B. Zhao, J.T. Miller, P. Cheng, J. Li, A multicenter-bonded [ZnI]8 cluster with cubic aromaticity, Nat. Commun. 6 (2015) 6331. [25] K.H. Kim, S.K. Ihm, Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: a review, J. Hazard. Mater. 186 (2011) 16–34. [26] D.W. Fickel, J.M. Fedeyko, R.F. Lobo, Copper coordination in Cu-SSZ-13 and Cu-SSZ16 investigated by variable-temperature XRD, J. Phys. Chem. C 114 (2010) 1633–1640. [27] X. Kuang, X. Wu, R. Yu, J.P. Donahue, J. Huang, C.Z. Lu, Assembly of a metal–organic framework by sextuple intercatenation of discrete adamantane-like cages, Nat. Chem. 2 (2010) 461–465. [28] X. Kuang, X.Y. Wu, J. Zhang, C.Z. Lu, Surface modification of polyoxometalate host– guest supramolecular architectures: from metal–organic pseudorotaxane framework to molecular box, Chem. Commun. 47 (2011) 4150–4152. [29] X.Y. Wu, Q.K. Zhang, X.F. Kuang, W.B. Yang, R.M. Yu, C.Z. Lu, Two hybrid polyoxometalate-pillared metal–organic frameworks, Dalton Trans. 41 (2012) 11783–11787. [30] R.M. Yu, X.F. Kuang, X.Y. Wu, C.Z. Lu, J.P. Donahue, Stabilization and immobilization of polyoxometalates in porous coordination polymers through host–guest interactions, Coord. Chem. Rev. 253 (2009) 2872–2890. [31] Synthesis of 1. A mixture of Cu(NO3)2·3H2O (0.242 g, 1.0 mmol), Htz (0.050 g, 0.71 mmol), H3PMo12O40·xH2O (0.150 g) and H2O (10.0 mL) was stirred for 1 h. Then the solution was sealed in the 23 mL Teflon-lined auto clave and heated at 100 °C for 4 days. After slow cooling to room temperature, green crystals of 1 were filtered, washed with distilled water and ethanol, and dried at room temperature (68% yield based on Mo). Elemental analysis: C12H46Cu8Mo11N48O54P1 (3321.60). Anal. Calcd for 1: H, 1.40; C, 4.34; N, 20.24; O, 26.01; Cu, 15.31; Mo, 31.77%. Found: H, 1.38; C, 4.35; N, 19.86; O, 26.26; Cu, 14.76; Mo, 31.15%. [32] Crystal data for 1: C12H46Cu8Mo11N48O54P1, M = 3321.60, orthorhombic, a = 20.599(6) Å, b = 11.872(3) Å, c = 16.534(4) Å, V = 4043.3(19) Å3, space group Pmmn, Z = 2, Dc = 2.728 Mg/m3, μ = 3.844 mm−1, F(000) = 3190, GOF = 1.002, 25907 reflections measured, 3853 independent reflections (Rint = 0.0717). The final R1 value was 0.0548 (I N 2σ(I)). The X-ray diffraction data was collected with a Rigaku Saturn70 CCD Diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at T = 293(2) K. Absorption corrections were made using SADABS program. The structures were solved using direct method and refined by full-matrix least-squares methods on F2 by using SHELX-97 program package. All non-hydrogen atoms were refined anisotropically. Positon of the hydrogen atoms were attached to carbon atoms were fixed at their ideal positions. [33] H.H. Thorp, Bond valence sum analysis of metal-ligand bond lengths in metalloenzymes and model complexes, Inorg. Chem. 31 (1992) 1585–1588.