Unique T-Shaped Ligand as a New Platform for MetalâOrganic

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Unique T-shaped Ligand as a New Platform for Metal-Organic Frameworks Tao He, Yong-Zheng Zhang, Xiang-Jing Kong, Xiu-Liang Lv, Lin-Hua Xie, and Jian-Rong Li Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01528 • Publication Date (Web): 03 Dec 2018 Downloaded from http://pubs.acs.org on December 3, 2018

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Crystal Growth & Design

Unique T-shaped Ligand as a New Platform for MetalOrganic Frameworks Tao He, Yong-Zheng Zhang, Xiang-Jing Kong, Xiu-Liang Lv, Lin-Hua Xie, and Jian-Rong Li* Beijing Key Laboratory for Green Catalysis and Separation, Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, P. R. China.

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ABSTRACT: The utilization of a rationally designed T-shaped ligand 4,4',4''-(1Hbenzo[d]imidazole-2,4,7-triyl)tribenzoic acid (H3BTBA) as the platform for constructing metalorganic frameworks (MOFs) with structure diversity was achieved. Five new MOFs, [Zn4O(BTBA)2] (BUT-34), [Fe2CoO(BTBA)2(H2O)3] (BUT-35), [Cu9(BTBA)4(H2O)(DMA)] (BUT-36), [Eu2(HBTBA)2(OH)2(H2O)6] (BUT-37), and [In(BTBA)(DMF)] (BUT-38) (BUT = Beijing University of Technology), have been solvothermally synthesized and structurally characterized. Combining with several popularly used metal-cluster secondary building units, the five MOFs show novel structural features. BUT-34 with typical tetranuclear Zn4O clusters shows three-dimensional (3D) networks with a new (3,6)-connected topology. BUT-35 exhibits a (3,6)connected flu-3 network with trinuclear [Fe2Co(μ3-O)] clusters. BUT-36 represents a mixed Cu(II)/Cu(I) based 3D framework, in which the T-shaped ligand adopts different coordination modes. However, BUT-37 and -38 consist of binuclear Eu2 paddle-wheel clusters and single In(III) ions with 2D layer structures, respectively. Clearly, the structural diversity of these MOFs can be attributed to the unique structure and variable coordination patterns of the T-shaped ligand. This work thus enriches the synthetic chemistry of MOFs in the structural design based on the low-symmetric ligands, and thereby function exploration.


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INTRODUCTION Metal-organic frameworks (MOFs), as a class of fascinating porous materials constructed by organic linkers and inorganic nodes, have attracted enormous research interest among scientific researchers and industrial engineers due to their great potential for applications in gas storage, separation, proton conduction, heterogeneous catalysis, and so on.1–6 Compared with conventional solid porous materials, a distinct advantage of MOFs is their modular nature, which allows their structures and properties to be tailored through the judicious design of ligand components and the variation of metal species. Definitely, the organic ligands used in the formation of MOFs play a crucial role in controlling the structure, porosity, and property of the resulting materials. Multiple factors such as the rigidity, length, geometry or symmetry of organic ligands can affect the architecture of resulting MOFs, thus the pre-design or selection of ligands is of critical concern in the construction

of

MOFs.7–12

Typical

high-symmetric

ligands,

such

as

linear

1,4-

benzenedicarboxylate (BDC2–),13 triangular 1,3,5-benzenetricarboxylate (BTC3–),14 tetrahedral 4,4',4'',4'''-methanetetrayl-tetrabenzolate

(MTB4–),14

square

tetrakis(4-carboxylatephenyl)-

porphyrin (TCPP4–),15–16 and rectangular 1,3,6,8-tetrakis(p-benzolate)pyrene (TBAPy4–)17 have been extensively used to build MOFs. In contrast, due to the unique geometry, thereby complicated synthetic route, the low-symmetric ligands were relatively less investigated. The desymmetrization strategy on tailoring substituent entities from high symmetry linkers has been reported in building new MOFs.18–21 It should be pointed out that some MOFs in previous reports were declared to be built with so-called “T-shaped” ligands, which actually should be coined “Yshaped” ligands.22–23 The standard/typical T-shaped ligand bearing both 90 and 180° bridging angles is totally different from the reported ones. Using such a low-symmetric ligand, the


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structures of resulting MOFs are much more unpredictable compared with those of popularly explored high-symmetric ones, opening another door to access more intriguing MOFs construction, thus being of great research significance. Simultaneously, metal ions/clusters offer a variety of inorganic secondary building units (SBUs), which can direct the construction of various MOFs on given organic ligands, especially in terms of topology, connectivity, and function. Plenty of classical metal cluster based SBUs, such as dodecahedral [Zr6O8(COO)12],24 octahedral [Zn4O(COO)6],25 trigonal prismatic [Fe3O(COO)6],26–27 paddle-wheel [Cu2(COO)4],28–29 and square-antiprismatic [In(COO)4]30–31 have been widely used in constructing a large library of MOFs with ligands of different geometries and sizes. Resulting MOFs exhibit diverse structures, fascinating properties, and extensive applications. Clearly, combining a unique ligand with these typical pre-designed SBUs, some MOFs with novel structures can be obtained, which not only create new materials for specific applications but also expand/enrich the synthetic chemistry of MOFs.32–33 Anyway, the construction of MOFs with exquisite structures is a significant and interesting task in MOFs field for ever. In this and our recently reported works, to investigate the actual effect of the geometry of organic ligands on MOF’s structure and property, a new low-symmetric ligand acid, 4,4',4''-(1Hbenzo[d]imidazole-2,4,7-triyl)tribenzoic acid (H3BTBA, Figure 1a), which possesses both 90 and 180° bridging angles and thus shows an overall configuration of “T”, was designed and synthesized in our laboratory. A novel Zr(IV)-MOF, BUT-39 (BUT = Beijing University of Technology), has been constructed based on this ligand, which features a (3,9)-connected network with rare 9-connected Zr6 clusters, being the first case in Zr(IV)-MOF (Figure 1b), and shows good performance in the detection and adsorption of Cr2O72– in water.34


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As a continuation of our study on this T-shaped ligand as a new platform for constructing MOFs, several other commonly used SBUs were employed to build MOFs in present work (Figure 1). As a result, we successfully obtained five new MOFs based on the ligand H3BTBA, namely,

[Zn4O(BTBA)2]

[Cu9(BTBA)4(H2O)(DMA)]

(BUT-34), (BUT-36),

[Fe2CoO(BTBA)2(H2O)3]

[Eu2(HBTBA)2(OH)2(H2O)6]

(BUT-35),

(BUT-37),

and

[In(BTBA)(DMF)] (BUT-38). The syntheses and crystal structures of these MOFs, associated with the discussion about the influence of ligand and metal node on the final structure are represented herein.

Figure 1. Structural representation of (a) the T-shaped BTBA3− ligand, diverse metal nodes, and resulting networks of (b) BUT-38, (c) BUT-34, (d) BUT-35, (e) BUT-36, (f) BUT-37.


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RESULTS AND DISCUSSION Synthesis and Structures BUT-34. With the attempt to vary metal species for synthesizing new MOFs using the Tshaped ligand H3BTBA, a new framework composing of the classical octahedral Zn4O(COO)6 SBU was originally desired. A solvothermal reaction of H3BTBA and Zn(NO3)2·6H2O in N,Ndimethylformamide (DMF), acetonitrile and water at 80 oC afforded colorless crystals of BUT34, Zn4O(BTBA)2. Single-crystal X-ray diffraction (SXRD) structural analysis revealed that BUT-34 crystallizes in I41/acd space group. In BUT-34, the typical Zn4O(COO)6 building units formed as wanted. Each Zn4O core connects to six tri-topic BTBA3− ligands through six carboxylate groups, and each BTBA3− coordinates with three Zn4O to give a three-dimensional (3D) framework with pores. Topologically, the Zn4O(COO)6 can be reduced to a 6-connected node, while the BTBA3− ligand can be simplified as a 3-connected linker (Figure 1c). BUT-34 thus exhibits a new (3,6)-connected topology with the point symbol of {4.82}2{42.812.10}. PLATON calculation shows that the solvent-accessible volume in the network of BUT-34 is 57.8%.35 BUT-35. M3(μ3-O)(COO)6 (M = Fe, Cr, Al) is one of the most common trimeric clusters in reported MOFs.26–27 Reaction between H3BTBA and preformed [Fe2Co(μ3-O)(CH3COO)6] with acetic acid as the modulator was then conducted in DMF, yielding block crystals of BUT-35, Fe2CoO(BTBA)2(H2O)3. SXRD analysis revealed that BUT-35 crystallizes in Pnma space group. As shown in Figure S1, each Fe2Co(μ3-O) core connects to six BTBA3− ligands through six carboxylate groups, and each BTBA3− bridges three Fe2Co(μ3-O) to afford the 3D structure of BUT-35. The resulting network has interconnected 1D channels along all three directions. A


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view along the a-axis reveals large rhombic channels with dimension of 19.2 × 15.3 Å formed through the [Fe2Co(μ3-O)] building blocks occupying four vertexes (Figure 2a). Smaller ellipse channels exist along the b-axis with the dimension of 20.5 × 7.3 Å (Figure 2b). Along the c-axis a grid perspective consisting of two kinds of small quadrangles segmented by ligands stretching towards different directions to link with clusters appears in Figure S2. SXRD analysis showed that the apical positions of the [Fe2Co(μ3-O)] building unit are statistically occupied by water molecules. Topologically, the [Fe2Co(μ3-O)] cluster can be simplified as a 6-connected node, while the tri-topic BTBA3− ligand can be viewed as a 3-connected linker. Then BUT-35 exhibits a (3,6)-connected flu-3 topology with the point symbol of {42.6}2{44.62.89} (Figure 1d). The solvent-accessible volume in BUT-35 is about 79.6%, as estimated by PLATON.

Figure 2. The framework structures of BUT-35 viewed along (a) the a-axis and (b) b-axis.


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BUT-36. Paddle-wheel Cu2(COO)4 is another very common SBU with four-connected square geometry.28–29 Attempting in the synthesis of an exclusive Cu2(COO)4-based MOF on this T-shaped ligand has failed. However, Cu9(BTBA)4(H2O)(DMA) (BUT-36) with mixed-valence Cu(II)/Cu(I) nodes was obtained on the solvothermal reaction between H3BTBA ligand and Cu(OAc)2·H2O in N,N-dimethylacetamide (DMA) using acetic acid as the modulator. BUT-36 crystallizes in P21/n space group. Nine Cu ions are involved in the asymmetric unit of its structure. As shown in Figure 3a, two types of Cu coordination geometries exist: one is the fivecoordinated Cu(II) (Cu1 and Cu2), and another is two-coordinated linear Cu(I) (Cu3−Cu9). The linear Cu(I) ions locate in three different coordination environments: Cu3 and Cu6 connect to one N atom of the imidazole moiety and one O atom from the monodentate carboxylate of BTBA3− ligand, Cu7 coordinates with two N atoms from two different imidazole moieties, Cu4, Cu5, Cu8 and Cu9 link to one N from the imidazole and one O atom from the bimonodentate carboxylate of BTBA3−, respectively. The two adjacent five-coordinated Cu1 and Cu2 atoms are bridged together by four carboxylates from four different BTBA3− ligands to generate a paddlewheel [Cu2(COO)4], the two axial sites of which are occupied by DMA and water molecules. While the Cu−O/Cu−N bond distance in the Cu(I) are in ranges of 1.833−1.882 and 1.850−1.884 Å, which are shorter than those observed in Cu(II), confirming the +1 oxidation state of Cu3−Cu9 (Table S1).36 The BTBA3− ligands with a free carboxylate are bridged into twodimensional (2D) layers through connecting with Cu3−Cu9 alternately (Figure S3), then the layers are further pillared by the shorter arms of BTBA3− through coordinating to the Cu(II) paddle-wheel clusters to form a 3D structure (Figure 3b). The resulting framework of BUT-36 has 1D slits along the b-axis with the dimension of ~3.5 × 22 Å, which are filled by disordered


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solvent molecules. Calculation using PLATON shows that BUT-36 has about 49.8% of the total volume available for guest inclusion.

Figure 3. (a) Coordination environment of Cu(II)/Cu(I) in BUT-36. (b) The structure of BUT-36 viewed along b-axis. BUT-37. Due to the existence of N atoms on the 1,3-imidazole moiety of the BTBA3− ligand, which are liable to coordinate with Cu ions, there exist mixed-valence Cu(II)/Cu(I) ions serving as metal nodes in BUT-36, thereby giving rise to the intricate structure. The coordination affinity of N-donor ligands to metals with higher valence (such as lanthanide) is relatively weaker than that to Cu(I/II) ion based on the Pearson’s hard/soft acid/base principle, which perhaps could allow the manipulation on the exclusive formation of di-nuclear paddle-wheel cluster in MOF synthesis.37–38 Fortunately, Eu2(HBTBA)2(OH)2(H2O)6 (BUT-37) was obtained


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as single crystals via the reaction of Eu(NO3)3·6H2O with H3BTBA ligand in DMF. BUT-37 consists of the Eu2 paddle-wheel cluster,39–40 which is anchored by four carboxylates from four different BTBA3− ligands with eight terminal H2O/OH entities occupying remaining coordination sites of the cluster. Each BTBA3− ligand bridges to two such Eu2 clusters by two bilateral carboxylates with the uncoordinated shorter arm disordered in the cavity, affording the final 2D network (Figure 1e).

Figure 4. (a) Coordination environment of In(III) in BUT-38. (b) The 2D layer structure of BUT-38. BUT-38. As another high-valence ion, single In(III) is a typical tetrahedral node when connected to four carboxylates, and was frequently used to design and synthesize single metal ion based MOFs with low connectivity and high surface area.30–31 In(BTBA)(DMA) (BUT-38)


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with single In(III) nodes and a 2D network structure was synthesized by the reaction between H3BTBA and In(NO3)3·6H2O in DMA using acetic acid as the modulator. As depicted in Figure 4a, the asymmetric unit of BUT-38 consists of an In(III) ion, a fully deprotonated BTBA3− ligand and a DMF molecule. The seven-coordinated In(III) ion is chelated to six O atoms from three different carboxylate groups of BTBA3− ligands and one O atom of terminal DMF molecule. The lengths of In−O bond range from 2.238(3) to 2.382(3) Å, which are close to reported In(III) complexes in the literature.30–31 In this framework, each In(III) ion links to three carboxylate groups from three BTBA3− ligands and each BTBA3− ligand connects to three In(III) ions to form a 2D layer extending along the ab plane (Figures 1f and 4b). The adjacent layers stack in an eclipsed fashion via intermolecular interactions to afford the 3D structure of BUT-38, leaving small 1D rhombic channels along the a-axis (~3.2 Å) (Figure S4).

Figure 5. Four ligands (a−d) with different configurations in the asymmetric unit of BUT-36 structure.


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Structural Comparison. As is well known, MOFs are distinguished from conventional porous materials due to their uniform framework structures as well as consequent appealing properties. In the construction of MOFs, high-symmetric ligands were preferentially designed and employed as building units thanks to their better adaptation to the coordination geometry of various typical metal-based nodes, from the perspective of synthetic chemistry. In comparison, the low-symmetric ligands, usually associated with inferior geometry matching ability, have presented a challenge to build new MOFs, but meanwhile unpredictability on distinctive structures. As mentioned above, a T-shaped ligand has been first employed to afford a unique Zr(IV)-MOF BUT-39 with the rare 9-connected Zr6O8 cluster in our previous report.34 In present work, by varying metal species with different valence and connectivity, five new MOFs, BUT-34 with 6-connected Zn4O cluster, BUT-35 with 6-connected Fe2Co cluster, BUT-36 with mixed Cu(II)/Cu(I) nodes, BUT-37 with 4-connected paddle-wheel Eu2 cluster, and BUT-38 with 3connected single In(III), have been successfully constructed, respectively. By comparing the structures of BUT-34−-39, it was found that different metal clusters lead to distinct structures of these MOFs even if the same ligand was used. The careful comparison between structures of BUT-34−-38 reveals that the T-shaped BTBA3− ligand, with the flexibility of C−C linkage between terminal phenyl groups and central benzimidazole nucleus, displays various dihedral angles through the free rotation of three peripheral aromatic rings. Except the structurally disordered BUT-34 and -37, the dihedral angles of ligand in other three MOFs are shown in Figure 5 and S5. In BUT-35, the dihedral angles between the central benzene plane and three terminal benzene rings of this T-shaped ligand are different (Φ1 = 45.062o, Φ2 = 44.718o, Φ3 = 34.421o, Figure S5a); while for BUT-36, there exist four independent ligands in the asymmetric unit and their dihedral angles are different (Φ1 = 54.922o, Φ2 = 55.184o, Φ3 =5.694o, Figure 5a;


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Φ1 = 63.091o, Φ2 = 53.964o, Φ3 = 7.104o, Figure 5b; Φ1 = 57.950o, Φ2 = 82.240o, Φ3 =17.729o, Figure 5c; Φ1 = 60.896o, Φ2 = 88.991o, Φ3 = 20.168o, Figure 5d); in BUT-38, the dihedral angles are Φ1 = 32.548o, Φ2 = 53.444o, Φ3 = 42.051o (Figure S5b), respectively. Such deviation of dihedral angles rather differs from those expected for the otherwise rigid backbone of this linker. The variable rotation patterns of BTBA3−, well matching the coordination geometries of [Zn4O(COO)6], [Fe2CoO(COO)6], [Cu2(COO)4], [Eu2(COO)4], [In(COO)3] nodes, have thus given rise to BUT-34−-38 despite the low symmetry. Furthermore, two types of hybrid N atoms are available on the associated 1,3-imidazole moiety, contributing to diverse coordination sites and thus coordination modes in this ligand. For the case of BUT-36, in addition to the effect of arm rotation, N atoms attached on the central benzimidazole moiety also take part in the coordination with Cu ions accompanied by the carboxylate groups, synergistically affording the complicated network structure. These two distinctions of BTBA3− donate to its good compatibility with various metal ions/clusters, thereby creating more structure diversity. Hence, this T-shaped ligand can provide plenty of new topologies when encountering different metal nodes with different symmetry and connectivity, serving as a facile platform for designing and discovering novel MOFs. Additional Characterizations and Properties All the prepared MOFs (BUT-34−-38) underwent detailed characterizations by powder Xray diffraction (PXRD), N2 adsorption/desorption measurements, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and elemental analysis. To check the phase purity, samples of BUT-34−-38 were examined by PXRD at room temperature. As shown in Figure S6, peak positions of the simulated patterns generated on the basis of SXRD structural data and those of experimental ones are in agreement with each other, demonstrating the good phase purity of


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these MOFs. The results of elemental analysis of all five MOFs are consistent with the calculations, which further proves their purity (see experimental section for elemental analysis). To assess the porosity, N2 sorption measurements were performed at 77 K. The adsorption/desorption isotherms are shown in Figure S7, which show N2 uptakes of 497, 480 and 432 cm3 g–1 for BUT-34, BUT-35 and BUT-36, and their Brunauer-Emmett-Teller (BET) surface areas evaluated from the N2 adsorption data are 1457, 1394 and 1206 m2 g–1, respectively. No obvious uptakes were observed for BUT-37 and BUT-38, which may be due to their framework collapse. Crystallinity of these two samples after sorption was also evaluated by PXRD. The poor diffraction patterns confirm their framework decomposition (Figure S8). MOF decomposition during activation can be usually attributed to its crystallinity loss due to the high surface tension and capillary forces exerted on the framework when trapped solvent molecules in pores are vaporizing.41–42 The structural damage can occur at any stage of the removal of activation solvents, in this case, it may happen during the degassing process under vacuum. The permanent porosity of BUT-34, BUT-35, and BUT-36 prompted us to investigate their sorption capacity for CO2 and CH4. The adsorption isotherms of CO2 and CH4 for three MOFs were recorded at 298 K and 1 atm, and the results are shown in Figure S9. BUT-34, BUT-35, and BUT-36 have maximum CO2 uptake of 37.6, 39.3, and 33.8 cm3 g−1, and CH4 uptake of 12.5, 13.3 and 10.7 cm3 g−1 under tested conditions, respectively. The FT-IR spectra of BUT-34−-38 are available in Figure S10. As can be seen from the spectra, the stretching vibration absorption peak of the carboxyl groups in H3BTBA is at 1730 cm–1. After these carboxyl groups being involved in coordination, their characteristic peaks appear in the range of 1653–1705 cm–1. TGA curves show that the activated samples are stable up to 403, 320, 283, 304, and 371 oC for BUT34, BUT-35, BUT-36, BUT-37 and BUT-38, respectively (Figure S11).


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CONCLUSIONS In summary, we have designed and synthesized five new MOFs through assembling a unique Tshaped ligand and various typical metal-cluster nodes. This initiatory research in crystal engineering of congenetic MOFs demonstrates that the unique geometry of this low-symmetric tri-topic ligand could present good adaptation to coordination behaviours of metal nodes with different symmetry and connectivity by modulating own configurations and coordination modes, giving rise to a series of novel MOFs with interesting structures. This work not only enriches the library of MOFs constructed with low-symmetric ligands, but also offers a new platform for designing and synthesizing MOFs with unique structure and particular function.

EXPERIMENTAL Materials and Instruments All reagents and solvents (AR grade) were commercially purchased and used as received. The ligand, H3BTBA was synthesized by a previously reported procedure.34 FT-IR spectra were recorded on an IRAffinity-1 instrument. TGA data were obtained on a TGA-50 (SHIMADZU) thermogravimetric analyzer with a heating rate of 10 °C min–1 under air atmosphere. The PXRD patterns were recorded on a Rigaku Smartlab3 X-ray Powder Diffractometer equipped with a Cu sealed tube (λ = 1.54178 Å) at room temperature (RT). Gas adsorption-desorption isotherms were obtained using a Micrometrics ASAP 2020. Elemental analysis was performed in vario EL cube (Elementar). Synthesis of BUT-34


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H3BTBA (0.01 mmol, 5 mg) and Zn(NO3)2·6H2O (0.017 mmol, 5 mg) were dissolved under ultrasound in 1 mL of DMF in a 4 mL glass vial. 0.1 mL of acetonitrile and 0.1 mL of deionized water were added to the solution. The vial was then tightly sealed and the mixture was sonicated for 15 minutes. This resulting solution was heated in an oven of 80 °C for 24 h. After cooling down to RT, the colorless crystals (4.6 mg of activated sample, 75% yield based on the H3BTBA ligand) were collected by filtration, and washed with DMF. Synthesis of BUT-35 [Fe2Co(μ3-O)(CH3COO)6] was prepared according to the literature.26 H3BTBA (0.01 mmol, 5 mg) was dissolved under ultrasound in 2 mL of DMF in a 4 mL glass vial. [Fe2Co(μ3O)(CH3COO)6] (0.013 mmol, 7 mg) followed by 100 μL of acetic acid as the modulator was added to the solution. The vial was then tightly sealed and the mixture was sonicated for 30 minutes. This resulting suspension was heated in an oven of 120 °C for 24 h. After cooling down to RT, the dark brown crystals (1.2 mg of activated sample, 21% yield based on the H3BTBA ligand) were collected by filtration, and washed with DMF. Synthesis of BUT-36 H3BTBA (0.01 mmol, 5 mg) and Cu(OAc)2·H2O (0.03 mmol, 6 mg) were dissolved under ultrasound in 2 mL of DMA in a 4 mL glass vial. 0.4 mL of acetic acid was added to the solution as the modulator. The vial was then tightly sealed and the mixture was sonicated for 10 minutes. This resulting solution was heated in an oven of 120 °C for 48 h. After cooling down to RT, the blue-green crystals (9.4 mg of activated sample, 73% yield based on the H3BTBA ligand) were collected by filtration, and washed with DMA.


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Synthesis of BUT-37 H3BTBA (0.01 mmol, 5 mg) and Eu(NO3)3·6H2O (0.034 mmol, 15 mg) were dissolved under ultrasound in 1 mL of DMF in a 4 mL glass vial. 0.1 mL of deionized water was added to the solution. The vial was then tightly sealed and the mixture was sonicated for 15 minutes. This resulting solution was heated in an oven of 80 °C for 48 h. After cooling down to RT, the colorless crystals (2.9 mg of activated sample, 42% yield based on the H3BTBA ligand) were collected by filtration, and washed with DMF. Synthesis of BUT-38 H3BTBA (0.01 mmol, 5 mg) and In(NO3)3·6H2O (0.015 mmol, 6 mg) were dissolved under ultrasound in 2 mL of DMA in a 4 mL glass vial. 40 μL of acetic acid was added to the solution as the modulator. The vial was then tightly sealed and the mixture was sonicated for 15 minutes. This resulting solution was heated in an oven of 120 °C for 24 h. After cooling down to RT, the light yellow crystals (1.9 mg of activated sample, 56% yield based on the H3BTBA ligand) were collected by filtration, and washed with DMA. Sample Activation and Gas Adsorption Prior to gas adsorption tests, BUT-34−-38 samples (about 80 mg for each) were immersed into 15 mL of DMF for 24 h at RT. These samples were then harvested carefully by decanting and next soaked into 15 mL of acetone for another 48 h, during which time fresh solvents were exchanged twice every day. When solvent exchange finished, the samples were loaded in a sample tube and degassed under high vacuum at an optimal heated temperature of 30 °C. Then,


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gas adsorption measurements were performed at 77 K in a liquid nitrogen bath and at 298 K in a water bath. Elemental Analysis After the activation and evacuation of BUT-34−-38, elemental analyses were measured. BUT-34: Anal. calc. for Zn4C56H30N4O13 C, 54.76; H, 2.46; N, 4.56; found C, 54.63; H, 2.91; N, 4.69. BUT-35: Anal. calc. for Fe2CoC56H36N4O16 C, 56.45; H, 3.05; N, 4.70; found C, 56.58; H, 3.57; N, 4.64. BUT-36: Anal. calc. for Cu9C116H71N9O26 C, 54.03; H, 2.78; N, 4.89; found C, 54.38; H, 3.23; N, 4.95. BUT-37: Anal. calc. for EuC28H23N2O10 C, 48.08; H, 3.31; N, 4.01; found C, 48.19; H, 4.10; N, 4.09. BUT-38: Anal. calc. for InC32H24N3O7 C, 56.74; H, 3.57; N, 6.20; found C, 56.44; H, 4.07; N, 6.33. X-ray Crystallographic Analysis The diffraction data of as-synthesized BUT-35−-38 were carried out using an Agilent Supernova CCD diffractometer (a mirror monochromator, Cu Kα source, λ = 1.54184 Å). The datasets were corrected by empirical absorption correction using spherical harmonics, implemented in the SCALE3 ABSPACK scaling algorithm. All the structures were solved using direct methods and refined by full-matrix least-squares on F2 with anisotropic displacement using the SHELXTL software package. Hydrogen atoms of ligands (except those in the imidazole N) were refined


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with isotropic displacement parameters. Those in the imidazole N atoms and coordinated water and hydroxyl groups were not added but were calculated into molecular formula of the crystal data. For these MOFs, the volume fractions of disordered solvents in pores could not be modeled in terms of atomic sites, but were treated by using the MASK routine in the Olex2 software package. Crystal parameters and structure refinement are summarized in Table S2−S6 (for details, see CCDC 1859559−1859563).

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge via the Internet at: http://pubs.acs.org/: Additional figures, PXRD, adsorption isotherms, FT-IR, TGA, the selected bond lengths, and tables of crystallographic data. Accession Codes CCDC 1859559−1859563 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: + 44 1223 336033. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Notes


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The authors declare no competing financial interest. ACKNOWLEDGMENTS We acknowledge financial support from the National Natural Science Foundation of China (No. 51621003, 21576006, 21771012).

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Table of Contents

A unique T-shaped ligand as a new platform for MOFs provides structural diversity when encountering various typical metal-based nodes, enriching the synthetic chemistry of MOFs.


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Unique T-Shaped Ligand as a New Platform for MetalâOrganic

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