Temperature- and solvent-dependent structures of three zinc(II) metal-organic frameworks for nitroaromatic explosives detection

Author’s Accepted Manuscript Temperature- and solvent-dependent structures of three zinc(II) metal-organic frameworks for nitroaromatic explosives detection Shu-Li Yao, Sui-Jun Liu, Chen Cao, Xue-Mei Tian, Meng-Na Bao, Teng-Fei Zheng www.elsevier.com/locate/yjssc

PII: DOI: Reference:

S0022-4596(18)30417-1 https://doi.org/10.1016/j.jssc.2018.09.032 YJSSC20393

To appear in: Journal of Solid State Chemistry Received date: 26 July 2018 Revised date: 8 September 2018 Accepted date: 21 September 2018 Cite this article as: Shu-Li Yao, Sui-Jun Liu, Chen Cao, Xue-Mei Tian, MengNa Bao and Teng-Fei Zheng, Temperature- and solvent-dependent structures of three zinc(II) metal-organic frameworks for nitroaromatic explosives detection, Journal of Solid State Chemistry, https://doi.org/10.1016/j.jssc.2018.09.032 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 galley proof before it is published in its final citable 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.

Temperature- and solvent-dependent structures of three zinc(II) metal-organic frameworks for nitroaromatic explosives detection

Shu-Li Yao, Sui-Jun Liu1*, Chen Cao, Xue-Mei Tian, Meng-Na Bao, Teng-Fei Zheng*

School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, Jiangxi Province, P.R. China [email protected] [email protected]

Abstract

Three zinc(II) metal-organic frameworks have been solvothermally synthesized with V-shaped 1,3-bis(1-imidazolyl)benzene (bib) and 4,4'-oxydibenzoic acid (4,4'-H2oba), namely

{[Zn(bib)(oba)]∙solvents} n

(1),

{[Zn(bib)(oba)]∙2H 2O}n

(2)

and

{[Zn2(bib)2(oba)2]∙2EtOH∙H2O}n (3). All of them are characterized by single-crystal X-ray diffraction, infrared spectra and powder X-ray diffraction. Complex 1 presents a two-fold interpenetrating three-dimensional structure with 4-connected (65.8) topology. While, complexes 2 and 3 exhibit double layer cavity and double chains based two-dimensional structure, respectively. Luminescent studies indicate that 2 and 3 display selectively sensitive to electron-deficient nitroaromatic explosives with excellent anti-interference abilities.

1

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Graphical abstract Three zinc(II) metal-organic frameworks have been synthesized by the regulation of temperatureand solvent. Complexes 2 and 3 show selectively sensitive to electron-deficient nitroaromatic explosives with excellent anti-interference abilities.

Keywords: MOFs; Mixed-Ligand; Solvothermal synthesis; Nitroaromatic explosives detection

1. Introduction As a unique class of crystalline materials constructed via self-assembly of metal ions/clusters and organic ligands [1-3], metal-organic frameworks (MOFs) have rapidly emerged in chemistry and materials science due to their new topological structure as well as versatile potential applications such as gas storage/separation [4-6], catalysis [7-9], magnetism [10-12], optics [13], and chemical sensing [14-16]. However, the rational design and synthesis of MOFs with targeted properties and functionality have been a challenge for the synthetic chemistry. In general, the self-assembly of well-designed metal ions/clusters nodes and organic ligands is one of the most effective and available methods for preparing targeted MOFs [17-19]. Among the various organic ligands, aromatic dicarboxylates have been extensively employed in the construction of MOFs [20], which are divided into two branches: the flexible ones and the rigid ones [21]. The construction of MOFs with the flexible ones is propitious to produce the versatile structures and/or structural transformations by external stimuli [22]. While, the rigid ones make for the preparation

2

of stable MOFs, offering permanent porosity. In addition, the shape of organic ligands also affects the topology of targeted MOFs [23]. On the other hand, the self-assembly of MOFs are influenced by many factors, such as metal-to-ligand molar ratios [24], coordination abilities of the ligands [25], the types of metal ions and solvent molecules [26,27], reaction temperatures [28], counter ions [29], pH values of the reaction systems [30] and reaction medium [31,32], etc. Therefore, the investigation of the relationship between reaction conditions and the final structures can lead us to design and synthesize MOFs with fantastic structures. Chemical sensing for MOFs has drawn much attention from analytical chemist and materials scientists due to the high efficient detection capability [33,34]. With the rapid development of society and economy, environmental protection is becoming a hot topic in the last few decades [35]. Therefore, the detection of hazardous substance is significant for environmental protection. The nitroaromatic explosives have been a serious issue in recent years because of their harm to human body and environment [36]. Among various nitroaromatics, nitrobenzene is the simplest and basic constituent of explosives [37]. Nitrobenzene is also a highly toxic environment pollutant, which could cause serious health problems [38]. Up to now, the prevailing detection of nitrobenzene is mainly based on sophisticated instrumental methods, including ion mobility spectroscopy (IMS), X-ray dispersion, Raman spectroscopy, and so on [39-41]. However, these methods are often time-consuming, high cost, limited portable and thus economical and convenient methods for the detection of nitrobenzene are urgently needed. Actually, the emerging MOF materials may provide a valid route to overcome the above obstacle. As one of the d10 ions, ZnII ion is environmentally friendly in the construction of luminescent MOFs, which are 3

extensively used for sensing organic pollutants and exhibit significant advantages such as high sensitivity and selectivity [42]. In our previous work, four MOFs based on 1,3-bis(1-imidazolyl)benzene (bib) with a series of analogous shape and flexible auxiliary ligands have been successfully prepared by a mixed-ligand strategy [43]. As one part of our ongoing interest in understanding the impact of synthetic conditions on the self-assembly of MOFs, V-shaped 4,4'-oxydibenzoic acid (H2oba) and bib ligands are selected. Furthermore, as the ether bond of H2oba is easily rotated to produce varied conformations, target complexes derived from bib and H2oba may exhibit various and interesting structures. Herein, the synthesis, structures and fluorescence properties of three new zinc(II) MOFs based on bib and 4,4'-H2oba (see Scheme 1) have been studied in detail.

2. Experimental 2.1. Materials and general methods All reagents were of analytical grade and used as purchased. The bib ligand was synthesized according to the literature [43]. Powder X-ray diffraction (PXRD) patterns were recorded on an Empyrean diffractometer (PANalytical B.V.) with a Cu-target tube and a graphite monochromator. The simulated PXRD spectra were from the single-crystal data and the Mercury (Hg) program obtained free from the Web site at http://www.iucr.org. The infrared (IR) spectra were obtained on a Bruker ALPHA FT-IR spectrometer with KBr pellets. Thermogravimetric analyses (TGAs) were carried out on a NETZSCH STA2500 (TG/DTA) thermal analyzer under nitrogen atmosphere at a heating rate of 10 °C min-1. The photoluminescence properties in suspension solutions and state were determined by a fluorescence spectrometer (Hitachi, Model F-4600). 4

2.2 Synthesis of complexes 1-3

Synthesis of {[Zn(bib)(oba)]∙solvents}n (1): A mixture of Zn(NO3)2∙6H2O (59 mg, 0.2 mmol), bib (21 mg, 0.1 mmol) and H2oba (26 mg, 0.1 mmol) in 6 mL of component solvent (VDMF/Vethanol = 2:1) was sealed in a 23 mL Teflon-lined autoclave and heated at 120 °C for 72 h. After the autoclave was cooled to room temperature (RT) in 24 h, colorless block crystals were obtained in ~30% yield based on bib. Notably, after separated from the parent solvents and exposed to the air, complex 1 was weathered into the powder within a few minutes. Synthesis of {[Zn(bib)(oba)]∙2H2O}n (2): A mixture of Zn(NO3)2∙6H2O (59 mg, 0.2 mmol), bib (42 mg, 0.2 mmol) and H2oba (52 mg, 0.2 mmol) in 10 mL of component solvent (VDMF/Vdeionized water/Vethanol

= 5:2:3) was sealed in a 23 mL Teflon-lined autoclave and heated at 120 °C for 72 h.

Then the autoclave was cooled to RT in 24 h, and colorless block crystals were obtained in ∼45% yield based on bib. IR (KBr, cm−1): 3441w, 3131w, 1666w, 1604s, 1563m, 1516m, 1376s, 1303w, 1239s, 1161m, 1113w, 1067m, 1009w, 950w, 875m, 783m, 748w, 657m, 510w. Synthesis of {[Zn2(bib)2(oba)2]∙2EtOH∙H2O}n (3): A mixture of Zn(CH3COO)2∙6H2O (44 mg, 0.2 mmol), bib (42 mg, 0.2 mmol) and H2oba (52 mg, 0.2 mmol) in 10 mL of component solvent (VDMF/Vdeionized water/Vethanol= 5:2:3) was sealed in a 23 mL Teflon-lined autoclave and heated at 160 °C for 72 h. Then the autoclave was cooled to RT in 24 h, and colorless block crystals were obtained in ∼35% yield based on bib. IR (KBr, cm−1): 3421w, 3135w, 1605s, 1564m, 1375s, 1238s, 1161m, 1117w, 1067m, 1008w, 938w, 875m, 780m, 755m, 753m, 558w, 508w.

2.3. X-ray crystallographic

5

All of crystallographic data were collected on a Bruker D8 QUEST diffractometer with Mo−Kα radiation (λ = 0.71073 Å) by ω scan mode. Program SAINT was used for integration of the diffraction profiles [44]. All structures were solved by direct method and refined by full-matrix least-squares methods through the SHELXTL program [45]. The non-hydrogen atoms were identified by successive difference Fourier syntheses and refined with anisotropic thermal parameters on F2. The hydrogen atoms of organic ligands were generated by the riding mode and refined isotropically with fixed thermal factors. The hydrogen atoms of ethanol in 3 were not assigned due to the limited quality and the hydrogen atoms of water in 2 and 3 were added automatically by SHELXL-97 using OLEX2 as a graphical user interface. The solvent molecules in the channels of 1 are highly disordered and were removed by the SQUEEZE program in PLATON [46]. The summary of the crystal data and structure refinements for 1–3 is given in Table 1. The selected bond lengths and angles of 1–3 are provided in Table S1 (SI).

3. Results and discussion 3.1. Syntheses By using a mixed-ligand strategy, three Zn-MOFs have been successfully synthesized. The solvothermal reactions with the same temperature and different solvents give rise to 1 and 2, while compared with 2 at the higher synthetic temperature 3 are obtained. Although we have successfully synthesized 3 by using Zn(NO3)2∙6H2O as ZnII ion source, its yield is very low.

Therefore,

3 was

synthesized

via

Zn(CH3COO)2·6H2O

rather than

Zn(NO3)2·6H2O, and the influence of anion on detailed structures is neglected. Based on the above discussions, we can safely assume that the temperature and solvent play important roles in the formation of targeted MOFs. 6

3.2. Description of the crystal structures As all of 1–3 are constructed from ZnII ions, bib and oba2– ligands, the comprehensive analysis of their structures are presented. Complexes 1–3 crystallize in C2/c, Ibca and P21/m space group, respectively. In these complexes, the ZnII ions are all four-coordinate and present the irregular [ZnO2N2] tetrahedral geometry (Fig. 1a) proved by SHAPE [47] analysis of ZnII ions (Table S2, SI). In addition, the detailed analyses of ligands indicate that the conformations of bib and oba2– ligands are different in complexes 1–3 (Fig. 1b-1c), which are proved by the values of these angles (Table S3, SI). In term of bib ligand, owing to the free rotation of covalent C-N bonds between B ring and I/I′ ring, the three aromatic rings are not on the same plane. Thus the values of and represent the rotation degree of two kinds of C-N bond, respectively. Additionally, the rotation degree of C-N bond may be related to the energy of molecular systems [48]. In other words, the change of the energy leads to the rotation of C-N bond. To our best knowledge, only one structural conformation of organic ligand frequently exists in the self-assembly of MOFs [49]. Interestingly, there are two different structural conformations of bib in 2 and 3. {[Zn(bib)(oba)]∙solvents}n (1). The oba2– ligands coordinate ZnII ions to form one-dimensional (1D) chains (Fig. 2a). As shown in Fig. 2b, one Zn-oba chain links the infinite chains of the neighbouring plane to form part of overall framework through bib ligands. The shape of self-assembled structure just likes the wave. Finally, the infinite chains are bridged by bib ligands to generate the 3D structure with open 1D channel along the b axis (Fig. 2c). To our knowledge, the 3D structure with the unimodal node and the “level” ligands is rare [50]. The framework can also be viewed as a “pillar-layer” structure. That is, the infinite chains in the neighbouring planes are projected to a waving plane, which is 7

viewed as the “layer”, and the bib ligand is considered as the “pillar”. As the interpenetrating structure always exists in the MOF materials with the smaller aperture, the further analysis indicates that complex 1 displays a two-fold interpenetrating structure (Fig. S1, SI). The accessible volume for 1 calculated by PLATON [46] is 2587.4 Å3 (39.3%) per unit cell volume when the solvent molecules were removed. The topological analysis of 1 suggests that a 4-connected net with a point symbol of (65.8) can be rationalized by TOPOS 4.0 [51] (Fig. 2d).

{[Zn(bib)(oba)]∙2H2O}n (2). The oba2– ligands coordinate ZnII ions to form 1D tortuous chains. Additionally, the bib ligand with the slighter rotation of C-N bond links the infinite chains to form the waving layer (Fig. 3a). The similar and neighbouring planes are further connected to generate a double layer-cavity structure by the bib with the same values of α and β, exhibiting small rectangle cavity along the a axis (Fig. 3b). Therefore, two different conformations may play two roles in the formation of 2. That is, one links the carboxylate-based chains to form the layer, and the other acts as the pillar to bridge the neighbouring layers to afford the final structure. Furthermore, the neighbouring layers can be packed to form the 3D supramolecular structure (Fig. S2, SI). {[Zn2(bib)2(oba)2]∙2EtOH∙H2O}n (3). The ZnII ions are linked by oba2– ligands to generate the linear chains (Fig. 4a), and two adjacent chains are further bridged to give rise to the 2D layer structure by bib ligands (Fig. 4b). The adjacent layers are packed through Van der Waals interactions to obtain the 3D supramolecular structure (Fig. S3, SI).

8

Although all of 1–3 were constructed from ZnII ions, bib and oba2– ligands, the changes of synthetic conditions result in the structural diversity. The structural analysis shows that there is small difference in the coordination geometries of ZnII ions, while a big difference in the conformations of organic ligands, leading to structural diversity of targeted complexes. In addition, there are two conformations for bib and oba2– ligands in 2, respectively. However, only one conformation for oba2- ligands exists in 1 and 3. With the varied rotation degree of C-N bond, bib in 1–3 could be viewed as the “pillar” or terminal ligand. On the basis of the synthetic conditions of 1 and 2, the structural differences between 1 and 2 are clearly related to the solvents. The solvent not only influences the deprotonation of carboxylate ligands but also could be a template during the synthetic process. The comparison between 2 and 3 shows the synthetic temperature has a critical impact on the construction of different MOFs. All above suggest that suitable solvent and temperature is favourable for the formation of multi-dimensional products. 3.3. PXRD Patterns and TGA

To confirm the phase purities of these complexes, the PXRD patterns were carried out on polycrystalline samples. The PXRD patterns of as-synthesized samples are well consistent with their corresponding simulated ones, indicating the phase purities of the bulk samples (Fig. S4, SI). To study the thermal stabilities of these complexes, they were carried out for TGA experiments from 20 to 600 °C under nitrogen atmosphere. As shown in Fig. S5 (SI), the TG curve of 2 shows a weight loss between 80–242 °C, corresponding to the release of solvent molecules. After that, the decomposition of the framework occurs up heating to 310 °C. The TG trace of 3 exhibits a 9

slight weight loss from room temperature to 140 °C, corresponding to the escape of the lattice water molecules. There exists a stable plateau covering a temperature range of 140–266 °C, indicating that the framework maintains its integrity after losing the lattice water molecules. Then the framework begins to collapse at 335 °C due to the decomposition of organic ligands.

3.4. Luminescence behaviors and sensing properties

Complexes 2 and 3 contain d10 metal ions and conjugated organic linkers, and may be promising candidates for potential photoactive materials [52]. At room temperature, the emission spectra of bib, H2oba, 2 and 3 were investigated. As shown in Fig. S6 (SI), bib and H2oba in solid state give a strong emission band with the maximum at 320 and 323 nm upon excitation at 280 nm, respectively. It is known that a double bond is composed of σ and π bonds, and the emissions of organic ligands are usually ascribed to π* -n or π-π* transitions [53]. Complexes 2 and 3 in solid state give strong emission band with the maximum at 387 and 381 nm upon excitation at 280 nm, respectively (Fig. S7, SI). Compared to the free ligands, the highly red-shifted were observed for 2 and 3. These emissions may be ascribed to ligand-to-ligand charge transfer (LLCT) [21], rather than metal-to-ligand charge transfer (MLCT) or ligand-to-metal charge transfer (LMCT) due to ZnII is hard to reduce or to oxidize. Furthermore, a small difference in their emission spectra of complexes 2 and 3 may be ascribed to the difference of crystal structures [54]. The strong emissions of 2 and 3 in solid state and the environmentally friendly Zn II ions encourage us to further investigate luminescent properties in different organic solvents. Herein, the samples of 2 and 3 were immersed in several common organic solvents, 10

including ethanol (EtOH), methanol (CH3OH), 1-proppanol, 2-propanol, dichloromethane (CH2Cl2), trichlormethane (CHCl3), tetrachlormethane (CCl4), N,N-dimethylformamide (DMF), N,N-Dimethylacetamide (DMAc), Tetrahydrofuran (THF), acetonitrile (CH3CN), toluene, benzene and nitrobenzene (NB). Then these samples were ultrasonicated for 30 minutes and then aged for 3 days to form a stable suspension solution [55]. Interestingly, the emission of 2 and 3 are only completely quenched by NB (Fig. 5 and Fig. S8 (SI)). This result indicates that 2 and 3 are new types of selective fluorescence sensors for NB. It is very meaningful considering that nitroaromatic explosives have become a serious issue due to the harm to human body and environment [55]. Since complexes 2 and 3 were synthesized with EtOH medium and showed good stabilities in this solvent proved by the PXRD patterns (Fig. S4, SI), EtOH was utilized as the dispersion medium. To further examine the sensing sensitivity towards NB, the emissive response was monitored by gradually increasing NB contents of the emulsion of 2 and 3 dispersed in EtOH. As shown Fig. 6, the emission intensities of the suspension were nearly completely quenched ( 80%) when the addition of NB was increased to 160 and 140 ppm, respectively. And such a quenching trend occurred even at the addition of 10 ppm of NB. In addition, the detections limit of the assay calculated with 3σ/k (k: slope, σ: standard) are about 8.7 and 7.2 ppm for 2 and 3 (Fig. S9 and S10, SI), respectively, revealing the high sensing sensitivity of 2 and 3 toward NB [55]. Moreover, the interference of other organic solvents on the emission intensity of 2 and 3 are also examined. As shown in Fig. 7, when 3000 ppm of the other organic solvents were added, no obvious changes occurred, and then the fluorescence intensities of these suspensions rapidly

11

decreased only after the addition of NB (300 ppm) (Fig. 8). These results firmly indicate that 2 and 3 can be used as fluorescence sensors for NB detection with excellent anti-interference ability. In addition, the possible sensing mechanism of 2 and 3 towards NB are also explored. The UV-vis spectra of NB exhibits absorption bands in the range of 275–325 nm [56], which suggests that the competition between the absorption of NB and the excitation of 2 and 3 (λex = 280 nm) may be responsible for the selective quenching behaviour. Moreover, the PXRD patterns of 2 and 3 immersed in NB also were measured (Fig. S4, SI), which are almost consistent with the simulated ones, proving that the framework of the samples did not collapse during the sensing operation. The nitro group of NB is a typical electron withdrawing substituent, while bib and oba2are electron rich ligands. Thus, when a light with certain energy illuminates on the samples of 2 and 3 dispersed in NB solution, the excited electron of 2 and 3 might be transferred to NB, leading to the fluorescence quenching phenomenon [56]. Based on the above analyses, both the competition absorption and electron transfer (ET) mechanism are responsible for the selective fluorescence sensing of 2 and 3. Considering the quenching efficiency of 300 ppm nitrobenzene, four analogues including 4-nitrotoluene, 1,4-dinitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene of 300 ppm were added to the emulsions of 2 and 3 dispersed in EtOH. The emission spectra shows that the four nitro-aromatic explosives can also efficiently quench the fluorescence of 2 and 3 (Fig. S11, SI). The result indicates that complexes 2 and 3 exhibit extremely high detection sensitivity towards nitroaromatic explosives.

4. Conclusions

12

By the employment of a mixed-ligand strategy, three new 4-connected 2D/3D Zn-MOFs have been successfully synthesized. The synthetic temperature and solvents affect the conformation of ligands and further result in the structural diversity of 1–3. Luminescent investigation suggests that complexes 2 and 3 exhibit selectively sensitive to electron-deficient nitroaromatic explosive with high anti-interference ability.

Acknowledgements This work was financially supported by the National Natural Science Foundation of China (No. 21501077), the China Postdoctoral Science Foundation (No. 2016M592107), the Natural

Science Foundation of Jiangxi Province (Nos. 20161ACB21013 and 20171BCB23066), the Postdoctoral Preferred Project of Jiangxi Province (No. 2015KY34), the Postdoctoral Daily Project of Jiangxi Province (No. 2016RC31), the Project of Jiangxi Provincial Department of Education (Nos. GJJ150634 and GJJ170497), and the Program for Qingjiang Excellent Young Talents, JXUST. Appendix A. Supplementary data CCDC 1850765-1850767 contain the supplementary crystallographic data for 1–3, respectively. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected].

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Scheme 1. Ligands bib and H2oba used for the synthesis of 1–3. Fig. 1. (a) Coordination environment of the ZnII ions in complexes 1–3 (H atoms omitted for clarity); (b) Conformational structures of bib ligand; (c) Conformational structures of oba2– ligand. Fig. 2. Views of (a) the carboxylate-based chains in neighboring planes of 1; (b) the infinite chains weaved by the ‘shuttles’ of bib (c) the 3D framework showing open 1D channel along the b axis; (d) the 4-connected topology net (H atoms omitted for clarity). Fig. 3. Views of (a) the 2D layer structure of 2; (b) The double-sided cavity structure (H atoms omitted for clarity). Fig. 4. Views of (a) the ladder chain structure in 3; (b) the 2D network of 3. (H atoms omitted for clarity). Fig. 5. The emission intensities of 2 (a) and 3 (b) dispersed in different organic solvents. Fig. 6. Fluorescence titration of 2 (a) and 3 (b) dispersed in EtOH with the addition of different concentrations of NB. Fig. 7. Emission spectra of 2 (a) and 3 (b) dispersed in EtOH with the addition of 3000 ppm different organics. Fig. 8. Fluorescene intensity ratio (F/F0) histograms of 2 (a) and 3 (b) dispersed in EtOH with the addition of different organic solvents (red) and subsequent addition of NB (blue). Emission intensities at the maximum were selected. Table 1. Crystal data and structure refinements for 1–3 Compound

1

2

3

formula

C26H18ZnN4O5

C78H62Zn3N12O21

C55H38Zn2N8O13

Mr

531.83

1699.57

1149.67

T (K)

297(2)

300(2)

298(2)

crystal system

Monoclinic

Orthorhombic

Monoclinic

17

space group

C2/c

Ibca

P21/m

a (Å)

27.017(6)

15.131(2)

8.283(1)

b (Å)

10.919(3)

29.085(3)

22.704(3)

c (Å)

34.189(6)

40.674(4)

14.481(2)

α (º)

90.00

90.00

90.00

β (º)

139.244(10)

90.00

91.070(8)

γ (º)

90.00

90.00

90.00

V (Å3)

6584(3)

17900(3)

2722.9(6)

Z

8

8

2

2176

6975

1176

Dcalc (g cm )

1.073

1.261

1.402

µ (mm–1)

0.779

0.869

0.952

reflections collected/unique

55879/5801

127233/7877

28609/4913

Rint

0.088

0.148

0.045

R1 /wR2 [I>2σ(I)]

0.055/0.154

0.080/0.251

0.061/0.173

GOF on F2

0.989

1.056

1.047

F(000) -3

a

b

a

R1 = Fo-Fc/Fo, bwR2 = [w(Fo2-Fc2)2/w(Fo2)2]1/2.

Highlights

• Complexes 1–3 exhibit 2D/3D structures derived from V-shaped bib and H2oba with different conformations. • Through the change of reaction conditions, the assembly of MOFs with novel structures and interesting properties has been successfully realized. • Complexes 2 and 3 exhibit selectively sensitive to electron-deficient nitroaromatic explosives with high anti-interference abilities.

18

Scheme 1.

19

(a)

(b)

(c)

Fig. 1

20

(a)

(b)

(c)

(d)

Fig. 2

21

(a)

(b)

Fig. 3

22

(a)

(b)

Fig. 4

23

(a)

(b)

Fig. 5

24

(a)

(b)

Fig. 6

25

(a)

(b)

Fig. 7

26

(a)

(b) Fig. 8

27