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Rational design of metal boron imidazolate cages to frameworks
Accepted Manuscript Research paper Rational Design of Metal Boron Imidazolate Cages to Frameworks Tian Wen, Jian Zhang PII: DOI: Reference:
S0020-1693(16)30527-8 http://dx.doi.org/10.1016/j.ica.2016.09.023 ICA 17268
To appear in:
Inorganica Chimica Acta
Received Date: Revised Date: Accepted Date:
22 July 2016 10 September 2016 12 September 2016
Please cite this article as: T. Wen, J. Zhang, Rational Design of Metal Boron Imidazolate Cages to Frameworks, Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.09.023
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Rational Design of Metal Boron Imidazolate Cages to Frameworks Tian Wen, Jian Zhang* State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China; E-mail: [email protected]
1
Abstract: The targeted construction strategy for discrete metal boron-imidazolate cages to 2D frameworks is successfully realized by tetradentate boron-imidazolate acting as cage ligands and bridge linker of frameworks. This work may help us to understand the formation mechanism of extended open frameworks. Also, the cubic cages exhibited the photocatalytic behaviour of MB.
2
1. Introduction Recently, metal-organic cages (MOCs) have been extensively investigated due to their unique structures, confined void and advanced applications like recognition and catalysis［1-5］. The discrete MOCs are often considered as ideal building blocks for the construction of extended porous metal organic frameworks (MOFs) ［6-9］. By taking advantage of organic molecules as linkers, the new MOFs materials were obtained based on MOCs. However，few reported examples use cubic MOCs targeted assembly to form infinite open structures. Actually, the cubic α-cage is a well-known secondary building unit in many zeolite structures［10］.To elucidate and mimic these cage-based self-assembly behaviour in zeolites and even other porous framew orks, it is imperative to dig the synthetic strategy for construction cubic cages with different organic ligands, especially explore cubic cages to extended open frameworks. Moreover, discrete cages with photocatalytic activity have seldom been investigated. Our previous studies have found that tetradentate boron-imidazolate ligands link tetrahedral metal centers into boron imidazolate frameworks (BIFs) with several zeolite-type topologies［11-13］. In addition, some tridentate boron imidazolate,
Zn2+ and auxiliary ligand like inorgnic ligands to link metal centers to gain interrupted zeolitie
structure［14］. Further, to anticipate zeolite-type BIFs with α or β cage-substructures, we have successfully obtained to a cubic cage(M4L4) and two dodecahedral cage(M6L8) by cheaper metal Zn and Cu according to principle of self-assembly of cages［8, 15 ］.Obviously, to understand the formation mechanism of extended open metal boron imidazolate frameworks, the segmented cages technology should be developed though it will be full of great challenges. In this paper, we present the novel design strategy for boron imidazolate cages to frameworks differs from that of the isolated cubic cage. Although the construction methods of boron imidazolate cages have been reported by Yaghi group［16］, cubic cages based on the metal boron imidazolate framworks are not reported. A feasible synthesis method for the formation of discrete cubic boron imidazolate cages involves divalent metal centers tetrahedral coordination geometry. In our previous report［15］, the typical isolated boron-imidazolate cage (M4L4) were designed by applying the tetrahedral Zn(II) centre and tridentate boron imidazolate ligands. Here, for the classic cubic cage, we have expanded tetrahedral metal centre from Zn2+ to Co2+, and even the different tridentate boron imidazolate ligands (Scheme 1-2).
3
However, to extend the cubic cage structure, new design idea is considered by applying tetradentate boron imidazolate ligands replacing tridentate boron imidazolate ligands (Scheme 1b). As a result, tetradentate boron-imidazolate not only can act as cage ligands but also extend cages to frameworks severing as bridge linkers. Scheme 1. Scheme 2.
2. Experimental section Synthesis of BIF-26: KBH(bim)3 (0.058 g) and Zn(NO3)2.3H2O (0.037 g) in a DMF (3mL) solution were placed in a 20 mL vial. The sample was heated at 80 oC for 72h, and then cooled to room-temperature. After washed by ethanol and distilled water, the colorless crystals were obtained. Synthesis of BIF-27: KBH(dm-bim)3 (0.0543 g) and ZnSO4.7H2O (0.015 g) in a N, N-dimethylactamide (DMA, 2 mL)/tetrahydrofuran (THF, 2mL)/(+/-)-2-amino-1-butanol (1.5 mL) solution were placed in a 20 mL vial. The sample was heated at 80 oC for 10 days, and then cooled to room-temperature. After washed by ethanol and distilled water, the colorless crystals were obtained. Synthesis of BIF-32: KB(im)4 (0.0234 g), tungstic acid (0.020 g) and ZnCl2 (0.0278 g) in a mixed 1,3-dimethy1-2imidazolidinone (DMI, 5.2123 g)/ammonia (2.5 mL) solution were placed in a 20 mL vial. The sample was heated at 80 oC for a week, and then cooled to room-temperature. After washed by ethanol and distilled water, the colorless crystals were obtained. Synthesis of BIF-58: KBH(bim)3 (0.0826 g), KBF4 (0.0340 g) and CoCl2.H2O (0.0336 g) in a mixed formamide (1.5ml )/tertiary butanol (1 mL)//N,N-dimethyl ethanolamine (1.5 mL) solution were placed in a 20 mL vial. The sample was heated at 100 oC for 3 days, and then cooled to room-temperature. After washed by ethanol and distilled water, the purple crystals were obtained.
Table 1: Summary of crystal data and refinement results.
4
Compound reference BIF-26 Chemical formula C87H73B4N29O14Zn4 Formula Mass 2053.48 Crystal system Cubic a/ Å 26.58980(10) b/ Å 26.58980(10) c/ Å 26.58980(10) α/° 90.00 β/° 90.00 γ/° 90.00 Unit cell volume/? 18799.45(12) Temperature/K 293(2) Space group Pa-3 No. of formula units 8 per unit cell, Z No. of reflections 127623 measured No. of independent 5558 reflections Rint 0.1462 Final R1 values (I > 0.0769 2σ(I)) Final wR(F2) values 0.2101 (I > 2σ(I)) Goodness of fit on F2 1.016
BIF-27 BIF-32 C112H108B4N24O10Zn4 C24H20B2Cl4N16Zn3 2254.94 892.09 Cubic Orthorhombic 29.1099(5) 16.290(6) 29.1099(5) 27.382(11) 29.1099(5) 41.705(16) 90.00 90.00 90.00 90.00 90.00 90.00 24667.3(7) 18602(12) 293(2) 293(2) Pa-3 Fddd 8 16
BIF-58 C84H73B5Co4F4N24O4 18404.3 Cubic 26.4022(5) 26.4022(5) 26.4022(5) 90.00 90.00 90.00
18907
29630
15401
8240
4089
6111
0.0662 0.0751
0.2322 0.0843
0.0718 0.0769
0.1982
0.2215
0.2323
0.878
0.974 2
2
R1 = ∑(|Fo|-|Fc|) /∑|Fo|; ωR = [∑w(Fo - Fc
18404.3(6)
100k Pa-3 8
0.882 2
)/∑w(Fo2)2]1/2
3. Results and discussion According to above construction principles, three cage-based boron imidazolate compounds (BIF-26/27/58) and a boron imidazolate framework (BIF-32) were successfully synthesized and structurally characterized by single-crystal X-ray diffraction. The phase purity and stability of these compounds were characterized (Fig S1-4 and S7). Here, the substituted group of imidazole and anions were responsible for the formation of such cages and cage-based frameworks. The details are discussed below. The boron imidazolate ligands for the construction of different BIFs were pre-synthesized according to literature［17］. The BH(bim)3- (bim = benzimidazolate) ligands and BH(dm-bim)3- (dm-bim = 5, 6-dimethylbenzimidazolate) ligands were used to synthesize Zn4[BH(bim)3]4.(NO3)4 (BIF-26) and Co4[BH(bim)3]4.(OH)3.BF4 (BIF-58), and Zn4[BH(dmbim)3]4.(CO2)4 (BIF-27), respectively. Single-crystal structural analysis reveals that BIF-26/27 and BIF-58 crystallize in the same cubic space group Pa-3 and possess a cubic cage framework containing different guests (Fig 1a-c). Each cubic cage in BIF-26 and BIF-27 is made up of four Zn(II) ions and four boron-imidazolate ligands (Fig 1a-b), where the Zn(II) 5
and B(III) was linked by benzimidazolate and dimethylbenzimidazolate building blocks, repectively. The two cubic cages were electronically balanced by four nitrate anions and formate anions respectively. Interestingly, anions show two distinct functions. Three of them are the ending ligands and bonded to three tetrahedral Zn centers, while the forth one is a special guest anion in the center of cage. Thus, the forth Zn center in the cage is coordinated by one additional water molecule and three symmetry-related imidazolate N atoms. In BIF-58, the framework is made up of four Co(II) ions and four BH(bim)3ligands. The cubic cage is electronically balanced by three OH- anions and one BF4-. In contrast, the packing of the three cubic cages, it was evident that different tridentate boron imidazolate ligands and different divalent metal ions have no impact on the packing mode, also indicating the coordination geometry of metal and ligands played important roles on tuning the cage structure and stacking, and fig. 1d was on behalf of the packing of cages in BIF-27.
Fig. 1. As a continuing study of metal boron imidazolate cages by using the tridentate boron-imidazolate ligands and tetrahedral Zn(II) centre self-assembly method under solvothermal reaction conditions, we attempted to assemble the metal boron imidazolate cages to extended porous boron imidazolate framworks. Recently, we have successfully obtained a porous frameworks BIF-33 by the self-assembly of Cu-boron imidazolate cages and inorganic anions I-［15］. Inspired by our previous work［8,15］, for the discrete structures of cages: 1) three coordination sites of tetrahedral Zn centers were coordinated by the ending boron midazolate ligands, while the forth one was bonded a special anion or guest molecule; 2) the isolated M6L8 cages can be linked by bridging linker I-. These properties indicated cubic cage may be formed the high dimensional porous frameworks by some linkers bridging the metal Zn2+. As a result, we attempted to linked the cubic cage to frameworks by some organic acid and other anionic such as SCN- and halide ion, while these trials failed. Consequently, the other approach is to add directly additional connectivity by ligands through applying the tetradentate boron imidazolate ligands. Because tetradentate boron imidazolate ligands are used, the forth imidazolate group may connect the formed cage sub-structures into extended frameworks. Luckily, A BIF-32 (Zn4[B(im)4]4Cl6) framework
6
with cubic cage sub-structure was successfully obtained by using tetradentate B(im)4- ligands (im = imidazolate). Singlecrystal X-ray diffraction analysis revealed that BIF-32 crystallized in the hexgonal space group R3c. It exhibits a twodimensional (2D) framework with ZnBH(im)4 cage sub-structure. In BIF-32, four B(im)4- ligands connect four Zn2+ ions to form the cubic Zn4[B(im)4]4Cl4 cage with four remaining imidazolate groups (Fig 2a). Furthermore, these remaining imidazolate groups are linked together by the ZnCl2 units, which lead to the formation of a two-dimensional (2D) framework with cubic cages (Fig 2b). It is interesting that the coordination linkage between four adjacent cubic cages generates additional porous space with dimension of 10.7×18.8 Å2 in the 2D structure. We tend to think that a strategy may be used to link the cages into frameworks.
Fig. 2. In contrast with the colorless BIF-26/27/32 including coordinated metal Zn2+, the purple BIF-58 with coordinated metal Co2+, which is of the potential catalytic activity due to the good absorption ability of visible light. As a result, we only chose the BIF-58 to explore its photocatalytic ability. The band-gap size of BIF-58 was investigated by UV-vis diffuse reflection measurement method at room temperature. The results give Eg (band gap energy) value of 1.89 eV (Fig S5). The photocatalytic activities of BIF-58 were further explored. Interestingly, BIF-58 showed excellent photocatalytic efficiency for the degradation of methylene blue (MB) in aqueous solution under xenon arc lamp irradiation. For the degradation of MB, the characteristic absorption of MB at about 650 nm was selected to monitor the adsorption and photocatalytic degradation process. The photocatalytic activity of BIF-58 was gradually enhanced with time increasing from 0 to 5 h. After 1 h, the degradation ration of MB reaches to almost 50%. The full degradation time for MB is about 5h, and the degradation of MB also reaches to 99% (Fig 3). After the photocatalytic degradation of MB, the color change of BIF-58 crystals and the PXRD patterns are almost the same as that of the as-prepared sample (Fig. S6-7). To investigate its reusability, three recycles of the activity were tested for BIF-58. The catalyst exhibits similar catalytic behaviour without obvious decrease in the degradation process (Fig. S8). In addition, the control experiment was performed, and ligands almost not have the
7
degradation effect. Also, we tentatively discussed the mechanism for the photocatalysis, and speculated the reactive radical species like ·OH- and ·O2- degrade the MB dye molecules by directly cleaving the aromatic ring (Fig. S9). It showed that the BIF-58 as visible light photocatalyst was feasible. Fig. 3.
4. Conclusions In summary, three cubic cages have been rationally designed by using tridentate boron imidazolate ligands to link tetrahedral metal centers Zn2+ and Co2+. Moreover, tetradentate boron-imidazolate ligands in the cage can be considered to add further connectivity, which realized the design strategy from boron imidazolate cages to boron-imidazolate frameworks. This work provided the evidence on understanding the building mechanism of cage-based structures, such as zeolites and other zeolitic metal-organic frameworks. Furthermore, BIF-58 can act as the photocatalytic catalyst to degrade organic dyes, which showed the potential application of cage-based BIF materials.
Acknowledgment We thank the support of this work by NSFC (21425102, 21601180) and CAS (XDA07070200).
Supplementary materials Experimental details, additional Figures, TGA, powder X-ray diffraction patterns, and CIF file (BIF-26: CCDC-1025828, BIF-27: CCDC-1025829 BIF-32:CCDC-1025834, and BIF-58:CCDC-1430217). Seehttp://dx.doi.org/xx.xxxx/x.xxxx.xxxx.xx.xxx.
References 8
[1] Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Chem. Rev. 111 (2011) 6810. [2] Han, M.; Michel, R.; He, B.; Chen, Y.-S.; Stalke, D.; John, M.; Clever, G. H. Angew. Chem., Int. Ed. 52 (2013) 1319. [3] Lewis, J. E. M.; Gavey, E. L.; Cameron, S. A.; Crowley, J. D. Chem. Sci. 3 ( 2012) 778. [4] Zhang, G.; Mastalerz, M. Chem. Soc. Rev. 43 (2014) 1934. [5] (a) Mitra, T.; Jelfs, K. E.; Schmidtmann, M.; Ahmed, A.; Chong, S. Y.; Adams, D. J.; Cooper, A. I. Nat. Chem. 5 (2013) 276; (b) Rostamnia, S.; Alamgholiloo, H.; Liu, X. J. Colloid Interface Sci. 469 (2016) 310; (c) Rostamnia, S.; Karimi, Z. Inorg. Chim. Acta 428 (2015) 133; (d) Rostamnia, S.; Morsali, A. Inorg. Chim. Acta 411 (2014) 113; (e) Rostamnia, S.; Xin, H. Appl. Organometal. Chem. 28 (2014) 359; (f) Rostamnia, S.; Xin, H. ; Nouruzi, N. Microporous Mesoporous Mater. 179 (2013) 99. [6] Chen, L.; Chen, Q.; Wu, M.; Jiang, F.; Hong, M. Acc. Chem. Res. 48 (2015) 201. [7] Guillerm, V.; Kim, D.; Eubank, J. F.; Luebke, R.; Liu, X.; Adil, K.; Lah, M. S.; Eddaoudi, M. Chem. Soc. Rev. 43 (2014) 6141 [8] Zhang, D.-X.; Zhang, H.-X.; Li, H.-Y.; Wen, T.; Zhang, J. Cryst. Growth Des. 15 (2015) 2433. [9] Li, J.-R.; Timmons, D. J.; Zhou, H.-C. J. Am. Chem. Soc. 131 (2009) 6368. [10] He, J. L.; Ba, Y.; Ratcliffe, C. I.; Ripmeester, J. A.; Klug, D. D.; Tse, J. S.; Preston, K. F. J. Am. Chem. Soc. 120 (1998) 10697. [11] Zhang, J.; Wu, T.; Zhou, C.; Chen, S.; Feng, P.; Bu, X. Angew. Chem., Int. Ed. 48(2009) 2542. [12] Wu, T.; Zhang, J.; Zhou, C.; Wang, L.; Bu, X.; Feng, P. J. Am. Chem. Soc. 131 (2009) 6111. [13] Wu, T.; Zhang, J.; Bu, X.; Feng, P. Chem. Mater. 21 (2009) 3830. [14] Zhang, H. X.; Wang, F.; Yang, H.; Tan, Y. X.; Zhang, J.; Bu, X. J. Am. Chem. Soc. 133 (2011) 11884. [15] Zhang, D.-X.; Zhang, H.-X.; Li, H.-Y.; Wen, T.; Zhang, J. Dalton Trans. 44 (2015) 9367. [16] Lu, Z.; Knobler, C. B.; Furukawa, H.; Wang, B.; Liu, G.; Yaghi, O. M. J. Am. Chem. Soc. 131(2009) 12532. [17] Trofimenko, S. J. Am. Chem. Soc. 89 (1967) 3170;
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Captions Scheme 1. Principle of self-assembly of M4L4 cage. (a) Discrete cubic cage. (b) Cubic cages to frameworks. Scheme 2. The pre-synthesized boron imidazolate ligands for the construction of different BIFs. Fig. 1. (a) The cubic cage in BIF-26. (b) The cubic cage in BIF-27. (c) The cubic cage in BIF-58. (d) The packing of cages in BIF-27. Color codes: Zn, pale blue; Co, lavender; B, purple; O, red; C, gray; N, blue; partial H atoms are omitted for clarity. Fig. 2.(a) The cubic cage with remaining imidazolate groups in BIF-32. (b) 2D structure of BIF-32. Color codes: Zn, pale blue; B, purple; O, red; C, gray; N, blue; Cl, brown; partial H atoms are omitted for clarity
Fig. 3. Photocatalysis decomposition of MB dyes in solution over BIF-58 (the inset is the color change photograph image of dyes solution).
Scheme 1. Principle of self-assembly of M4L4 cage. (a) Discrete cubic cage. (b) Cubic cages to frameworks.
Scheme 2. The pre-synthesized boron imidazolate ligands for the construction of different BIFs.
10
Fig. 1. (a) The cubic cage in BIF-26. (b) The cubic cage in BIF-27. (c) The cubic cage in BIF-58. (d) The packing of cages in BIF-27. Color codes: Zn, pale blue; Co, lavender; B, purple; O, red; C, gray; N, blue; partial H atoms are omitted for clarity.
Fig. 2. (a) The cubic cage with remaining imidazolate groups in BIF-32. (b) 2D structure of BIF-32. Color codes: Zn, pale blue; B, purple; O, red; C, gray; N, blue; Cl, brown; partial H atoms are omitted for clarity
11
Fig. 3. Photocatalysis decomposition of MB dyes in solution over BIF-58 (the inset is the color change photograph image of dyes solution).
12
Graphical abstract
13
Highlights
This work realized synthetic strategy for boron imidazolate ligands and Co or Zn metal to construct discrete cubic cage (M4L4) to mimic the -cage. This work showed that discrete cages exhibited a good the photocatalytic degradation behavour of MB. This work firstly realized facile synthesis of metal boron-imidazolate cages to 2D frameworks.
14
S0020-1693(16)30527-8 http://dx.doi.org/10.1016/j.ica.2016.09.023 ICA 17268
To appear in:
Inorganica Chimica Acta
Received Date: Revised Date: Accepted Date:
22 July 2016 10 September 2016 12 September 2016
Please cite this article as: T. Wen, J. Zhang, Rational Design of Metal Boron Imidazolate Cages to Frameworks, Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.09.023
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Rational Design of Metal Boron Imidazolate Cages to Frameworks Tian Wen, Jian Zhang* State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China; E-mail: [email protected]
1
Abstract: The targeted construction strategy for discrete metal boron-imidazolate cages to 2D frameworks is successfully realized by tetradentate boron-imidazolate acting as cage ligands and bridge linker of frameworks. This work may help us to understand the formation mechanism of extended open frameworks. Also, the cubic cages exhibited the photocatalytic behaviour of MB.
2
1. Introduction Recently, metal-organic cages (MOCs) have been extensively investigated due to their unique structures, confined void and advanced applications like recognition and catalysis［1-5］. The discrete MOCs are often considered as ideal building blocks for the construction of extended porous metal organic frameworks (MOFs) ［6-9］. By taking advantage of organic molecules as linkers, the new MOFs materials were obtained based on MOCs. However，few reported examples use cubic MOCs targeted assembly to form infinite open structures. Actually, the cubic α-cage is a well-known secondary building unit in many zeolite structures［10］.To elucidate and mimic these cage-based self-assembly behaviour in zeolites and even other porous framew orks, it is imperative to dig the synthetic strategy for construction cubic cages with different organic ligands, especially explore cubic cages to extended open frameworks. Moreover, discrete cages with photocatalytic activity have seldom been investigated. Our previous studies have found that tetradentate boron-imidazolate ligands link tetrahedral metal centers into boron imidazolate frameworks (BIFs) with several zeolite-type topologies［11-13］. In addition, some tridentate boron imidazolate,
Zn2+ and auxiliary ligand like inorgnic ligands to link metal centers to gain interrupted zeolitie
structure［14］. Further, to anticipate zeolite-type BIFs with α or β cage-substructures, we have successfully obtained to a cubic cage(M4L4) and two dodecahedral cage(M6L8) by cheaper metal Zn and Cu according to principle of self-assembly of cages［8, 15 ］.Obviously, to understand the formation mechanism of extended open metal boron imidazolate frameworks, the segmented cages technology should be developed though it will be full of great challenges. In this paper, we present the novel design strategy for boron imidazolate cages to frameworks differs from that of the isolated cubic cage. Although the construction methods of boron imidazolate cages have been reported by Yaghi group［16］, cubic cages based on the metal boron imidazolate framworks are not reported. A feasible synthesis method for the formation of discrete cubic boron imidazolate cages involves divalent metal centers tetrahedral coordination geometry. In our previous report［15］, the typical isolated boron-imidazolate cage (M4L4) were designed by applying the tetrahedral Zn(II) centre and tridentate boron imidazolate ligands. Here, for the classic cubic cage, we have expanded tetrahedral metal centre from Zn2+ to Co2+, and even the different tridentate boron imidazolate ligands (Scheme 1-2).
3
However, to extend the cubic cage structure, new design idea is considered by applying tetradentate boron imidazolate ligands replacing tridentate boron imidazolate ligands (Scheme 1b). As a result, tetradentate boron-imidazolate not only can act as cage ligands but also extend cages to frameworks severing as bridge linkers. Scheme 1. Scheme 2.
2. Experimental section Synthesis of BIF-26: KBH(bim)3 (0.058 g) and Zn(NO3)2.3H2O (0.037 g) in a DMF (3mL) solution were placed in a 20 mL vial. The sample was heated at 80 oC for 72h, and then cooled to room-temperature. After washed by ethanol and distilled water, the colorless crystals were obtained. Synthesis of BIF-27: KBH(dm-bim)3 (0.0543 g) and ZnSO4.7H2O (0.015 g) in a N, N-dimethylactamide (DMA, 2 mL)/tetrahydrofuran (THF, 2mL)/(+/-)-2-amino-1-butanol (1.5 mL) solution were placed in a 20 mL vial. The sample was heated at 80 oC for 10 days, and then cooled to room-temperature. After washed by ethanol and distilled water, the colorless crystals were obtained. Synthesis of BIF-32: KB(im)4 (0.0234 g), tungstic acid (0.020 g) and ZnCl2 (0.0278 g) in a mixed 1,3-dimethy1-2imidazolidinone (DMI, 5.2123 g)/ammonia (2.5 mL) solution were placed in a 20 mL vial. The sample was heated at 80 oC for a week, and then cooled to room-temperature. After washed by ethanol and distilled water, the colorless crystals were obtained. Synthesis of BIF-58: KBH(bim)3 (0.0826 g), KBF4 (0.0340 g) and CoCl2.H2O (0.0336 g) in a mixed formamide (1.5ml )/tertiary butanol (1 mL)//N,N-dimethyl ethanolamine (1.5 mL) solution were placed in a 20 mL vial. The sample was heated at 100 oC for 3 days, and then cooled to room-temperature. After washed by ethanol and distilled water, the purple crystals were obtained.
Table 1: Summary of crystal data and refinement results.
4
Compound reference BIF-26 Chemical formula C87H73B4N29O14Zn4 Formula Mass 2053.48 Crystal system Cubic a/ Å 26.58980(10) b/ Å 26.58980(10) c/ Å 26.58980(10) α/° 90.00 β/° 90.00 γ/° 90.00 Unit cell volume/? 18799.45(12) Temperature/K 293(2) Space group Pa-3 No. of formula units 8 per unit cell, Z No. of reflections 127623 measured No. of independent 5558 reflections Rint 0.1462 Final R1 values (I > 0.0769 2σ(I)) Final wR(F2) values 0.2101 (I > 2σ(I)) Goodness of fit on F2 1.016
BIF-27 BIF-32 C112H108B4N24O10Zn4 C24H20B2Cl4N16Zn3 2254.94 892.09 Cubic Orthorhombic 29.1099(5) 16.290(6) 29.1099(5) 27.382(11) 29.1099(5) 41.705(16) 90.00 90.00 90.00 90.00 90.00 90.00 24667.3(7) 18602(12) 293(2) 293(2) Pa-3 Fddd 8 16
BIF-58 C84H73B5Co4F4N24O4 18404.3 Cubic 26.4022(5) 26.4022(5) 26.4022(5) 90.00 90.00 90.00
18907
29630
15401
8240
4089
6111
0.0662 0.0751
0.2322 0.0843
0.0718 0.0769
0.1982
0.2215
0.2323
0.878
0.974 2
2
R1 = ∑(|Fo|-|Fc|) /∑|Fo|; ωR = [∑w(Fo - Fc
18404.3(6)
100k Pa-3 8
0.882 2
)/∑w(Fo2)2]1/2
3. Results and discussion According to above construction principles, three cage-based boron imidazolate compounds (BIF-26/27/58) and a boron imidazolate framework (BIF-32) were successfully synthesized and structurally characterized by single-crystal X-ray diffraction. The phase purity and stability of these compounds were characterized (Fig S1-4 and S7). Here, the substituted group of imidazole and anions were responsible for the formation of such cages and cage-based frameworks. The details are discussed below. The boron imidazolate ligands for the construction of different BIFs were pre-synthesized according to literature［17］. The BH(bim)3- (bim = benzimidazolate) ligands and BH(dm-bim)3- (dm-bim = 5, 6-dimethylbenzimidazolate) ligands were used to synthesize Zn4[BH(bim)3]4.(NO3)4 (BIF-26) and Co4[BH(bim)3]4.(OH)3.BF4 (BIF-58), and Zn4[BH(dmbim)3]4.(CO2)4 (BIF-27), respectively. Single-crystal structural analysis reveals that BIF-26/27 and BIF-58 crystallize in the same cubic space group Pa-3 and possess a cubic cage framework containing different guests (Fig 1a-c). Each cubic cage in BIF-26 and BIF-27 is made up of four Zn(II) ions and four boron-imidazolate ligands (Fig 1a-b), where the Zn(II) 5
and B(III) was linked by benzimidazolate and dimethylbenzimidazolate building blocks, repectively. The two cubic cages were electronically balanced by four nitrate anions and formate anions respectively. Interestingly, anions show two distinct functions. Three of them are the ending ligands and bonded to three tetrahedral Zn centers, while the forth one is a special guest anion in the center of cage. Thus, the forth Zn center in the cage is coordinated by one additional water molecule and three symmetry-related imidazolate N atoms. In BIF-58, the framework is made up of four Co(II) ions and four BH(bim)3ligands. The cubic cage is electronically balanced by three OH- anions and one BF4-. In contrast, the packing of the three cubic cages, it was evident that different tridentate boron imidazolate ligands and different divalent metal ions have no impact on the packing mode, also indicating the coordination geometry of metal and ligands played important roles on tuning the cage structure and stacking, and fig. 1d was on behalf of the packing of cages in BIF-27.
Fig. 1. As a continuing study of metal boron imidazolate cages by using the tridentate boron-imidazolate ligands and tetrahedral Zn(II) centre self-assembly method under solvothermal reaction conditions, we attempted to assemble the metal boron imidazolate cages to extended porous boron imidazolate framworks. Recently, we have successfully obtained a porous frameworks BIF-33 by the self-assembly of Cu-boron imidazolate cages and inorganic anions I-［15］. Inspired by our previous work［8,15］, for the discrete structures of cages: 1) three coordination sites of tetrahedral Zn centers were coordinated by the ending boron midazolate ligands, while the forth one was bonded a special anion or guest molecule; 2) the isolated M6L8 cages can be linked by bridging linker I-. These properties indicated cubic cage may be formed the high dimensional porous frameworks by some linkers bridging the metal Zn2+. As a result, we attempted to linked the cubic cage to frameworks by some organic acid and other anionic such as SCN- and halide ion, while these trials failed. Consequently, the other approach is to add directly additional connectivity by ligands through applying the tetradentate boron imidazolate ligands. Because tetradentate boron imidazolate ligands are used, the forth imidazolate group may connect the formed cage sub-structures into extended frameworks. Luckily, A BIF-32 (Zn4[B(im)4]4Cl6) framework
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with cubic cage sub-structure was successfully obtained by using tetradentate B(im)4- ligands (im = imidazolate). Singlecrystal X-ray diffraction analysis revealed that BIF-32 crystallized in the hexgonal space group R3c. It exhibits a twodimensional (2D) framework with ZnBH(im)4 cage sub-structure. In BIF-32, four B(im)4- ligands connect four Zn2+ ions to form the cubic Zn4[B(im)4]4Cl4 cage with four remaining imidazolate groups (Fig 2a). Furthermore, these remaining imidazolate groups are linked together by the ZnCl2 units, which lead to the formation of a two-dimensional (2D) framework with cubic cages (Fig 2b). It is interesting that the coordination linkage between four adjacent cubic cages generates additional porous space with dimension of 10.7×18.8 Å2 in the 2D structure. We tend to think that a strategy may be used to link the cages into frameworks.
Fig. 2. In contrast with the colorless BIF-26/27/32 including coordinated metal Zn2+, the purple BIF-58 with coordinated metal Co2+, which is of the potential catalytic activity due to the good absorption ability of visible light. As a result, we only chose the BIF-58 to explore its photocatalytic ability. The band-gap size of BIF-58 was investigated by UV-vis diffuse reflection measurement method at room temperature. The results give Eg (band gap energy) value of 1.89 eV (Fig S5). The photocatalytic activities of BIF-58 were further explored. Interestingly, BIF-58 showed excellent photocatalytic efficiency for the degradation of methylene blue (MB) in aqueous solution under xenon arc lamp irradiation. For the degradation of MB, the characteristic absorption of MB at about 650 nm was selected to monitor the adsorption and photocatalytic degradation process. The photocatalytic activity of BIF-58 was gradually enhanced with time increasing from 0 to 5 h. After 1 h, the degradation ration of MB reaches to almost 50%. The full degradation time for MB is about 5h, and the degradation of MB also reaches to 99% (Fig 3). After the photocatalytic degradation of MB, the color change of BIF-58 crystals and the PXRD patterns are almost the same as that of the as-prepared sample (Fig. S6-7). To investigate its reusability, three recycles of the activity were tested for BIF-58. The catalyst exhibits similar catalytic behaviour without obvious decrease in the degradation process (Fig. S8). In addition, the control experiment was performed, and ligands almost not have the
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degradation effect. Also, we tentatively discussed the mechanism for the photocatalysis, and speculated the reactive radical species like ·OH- and ·O2- degrade the MB dye molecules by directly cleaving the aromatic ring (Fig. S9). It showed that the BIF-58 as visible light photocatalyst was feasible. Fig. 3.
4. Conclusions In summary, three cubic cages have been rationally designed by using tridentate boron imidazolate ligands to link tetrahedral metal centers Zn2+ and Co2+. Moreover, tetradentate boron-imidazolate ligands in the cage can be considered to add further connectivity, which realized the design strategy from boron imidazolate cages to boron-imidazolate frameworks. This work provided the evidence on understanding the building mechanism of cage-based structures, such as zeolites and other zeolitic metal-organic frameworks. Furthermore, BIF-58 can act as the photocatalytic catalyst to degrade organic dyes, which showed the potential application of cage-based BIF materials.
Acknowledgment We thank the support of this work by NSFC (21425102, 21601180) and CAS (XDA07070200).
Supplementary materials Experimental details, additional Figures, TGA, powder X-ray diffraction patterns, and CIF file (BIF-26: CCDC-1025828, BIF-27: CCDC-1025829 BIF-32:CCDC-1025834, and BIF-58:CCDC-1430217). Seehttp://dx.doi.org/xx.xxxx/x.xxxx.xxxx.xx.xxx.
References 8
[1] Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Chem. Rev. 111 (2011) 6810. [2] Han, M.; Michel, R.; He, B.; Chen, Y.-S.; Stalke, D.; John, M.; Clever, G. H. Angew. Chem., Int. Ed. 52 (2013) 1319. [3] Lewis, J. E. M.; Gavey, E. L.; Cameron, S. A.; Crowley, J. D. Chem. Sci. 3 ( 2012) 778. [4] Zhang, G.; Mastalerz, M. Chem. Soc. Rev. 43 (2014) 1934. [5] (a) Mitra, T.; Jelfs, K. E.; Schmidtmann, M.; Ahmed, A.; Chong, S. Y.; Adams, D. J.; Cooper, A. I. Nat. Chem. 5 (2013) 276; (b) Rostamnia, S.; Alamgholiloo, H.; Liu, X. J. Colloid Interface Sci. 469 (2016) 310; (c) Rostamnia, S.; Karimi, Z. Inorg. Chim. Acta 428 (2015) 133; (d) Rostamnia, S.; Morsali, A. Inorg. Chim. Acta 411 (2014) 113; (e) Rostamnia, S.; Xin, H. Appl. Organometal. Chem. 28 (2014) 359; (f) Rostamnia, S.; Xin, H. ; Nouruzi, N. Microporous Mesoporous Mater. 179 (2013) 99. [6] Chen, L.; Chen, Q.; Wu, M.; Jiang, F.; Hong, M. Acc. Chem. Res. 48 (2015) 201. [7] Guillerm, V.; Kim, D.; Eubank, J. F.; Luebke, R.; Liu, X.; Adil, K.; Lah, M. S.; Eddaoudi, M. Chem. Soc. Rev. 43 (2014) 6141 [8] Zhang, D.-X.; Zhang, H.-X.; Li, H.-Y.; Wen, T.; Zhang, J. Cryst. Growth Des. 15 (2015) 2433. [9] Li, J.-R.; Timmons, D. J.; Zhou, H.-C. J. Am. Chem. Soc. 131 (2009) 6368. [10] He, J. L.; Ba, Y.; Ratcliffe, C. I.; Ripmeester, J. A.; Klug, D. D.; Tse, J. S.; Preston, K. F. J. Am. Chem. Soc. 120 (1998) 10697. [11] Zhang, J.; Wu, T.; Zhou, C.; Chen, S.; Feng, P.; Bu, X. Angew. Chem., Int. Ed. 48(2009) 2542. [12] Wu, T.; Zhang, J.; Zhou, C.; Wang, L.; Bu, X.; Feng, P. J. Am. Chem. Soc. 131 (2009) 6111. [13] Wu, T.; Zhang, J.; Bu, X.; Feng, P. Chem. Mater. 21 (2009) 3830. [14] Zhang, H. X.; Wang, F.; Yang, H.; Tan, Y. X.; Zhang, J.; Bu, X. J. Am. Chem. Soc. 133 (2011) 11884. [15] Zhang, D.-X.; Zhang, H.-X.; Li, H.-Y.; Wen, T.; Zhang, J. Dalton Trans. 44 (2015) 9367. [16] Lu, Z.; Knobler, C. B.; Furukawa, H.; Wang, B.; Liu, G.; Yaghi, O. M. J. Am. Chem. Soc. 131(2009) 12532. [17] Trofimenko, S. J. Am. Chem. Soc. 89 (1967) 3170;
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Captions Scheme 1. Principle of self-assembly of M4L4 cage. (a) Discrete cubic cage. (b) Cubic cages to frameworks. Scheme 2. The pre-synthesized boron imidazolate ligands for the construction of different BIFs. Fig. 1. (a) The cubic cage in BIF-26. (b) The cubic cage in BIF-27. (c) The cubic cage in BIF-58. (d) The packing of cages in BIF-27. Color codes: Zn, pale blue; Co, lavender; B, purple; O, red; C, gray; N, blue; partial H atoms are omitted for clarity. Fig. 2.(a) The cubic cage with remaining imidazolate groups in BIF-32. (b) 2D structure of BIF-32. Color codes: Zn, pale blue; B, purple; O, red; C, gray; N, blue; Cl, brown; partial H atoms are omitted for clarity
Fig. 3. Photocatalysis decomposition of MB dyes in solution over BIF-58 (the inset is the color change photograph image of dyes solution).
Scheme 1. Principle of self-assembly of M4L4 cage. (a) Discrete cubic cage. (b) Cubic cages to frameworks.
Scheme 2. The pre-synthesized boron imidazolate ligands for the construction of different BIFs.
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Fig. 1. (a) The cubic cage in BIF-26. (b) The cubic cage in BIF-27. (c) The cubic cage in BIF-58. (d) The packing of cages in BIF-27. Color codes: Zn, pale blue; Co, lavender; B, purple; O, red; C, gray; N, blue; partial H atoms are omitted for clarity.
Fig. 2. (a) The cubic cage with remaining imidazolate groups in BIF-32. (b) 2D structure of BIF-32. Color codes: Zn, pale blue; B, purple; O, red; C, gray; N, blue; Cl, brown; partial H atoms are omitted for clarity
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Fig. 3. Photocatalysis decomposition of MB dyes in solution over BIF-58 (the inset is the color change photograph image of dyes solution).
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Graphical abstract
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Highlights
This work realized synthetic strategy for boron imidazolate ligands and Co or Zn metal to construct discrete cubic cage (M4L4) to mimic the -cage. This work showed that discrete cages exhibited a good the photocatalytic degradation behavour of MB. This work firstly realized facile synthesis of metal boron-imidazolate cages to 2D frameworks.
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