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Heterometallic Hybrid Open-Frameworks: Synthesis and Application for Selective Detection of Nitro Explosives Kangcai Wang, Xin Tian, Yunhe Jin, Jie Sun, and Qinghua Zhang Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b01808 • Publication Date (Web): 13 Feb 2017 Downloaded from http://pubs.acs.org on February 15, 2017

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Crystal Growth & Design

Heterometallic Hybrid Open-Frameworks: Synthesis and Application for Selective Detection of Nitro Explosives Kangcai Wang,‡ Xin Tian,‡ Yunhe Jin, Jie Sun,* and Qinghua Zhang* Research Center of Energetic Material Genome Science, Institute of Chemical Materials, China Academy of Engineering Physics (CAEP), Mianyang, 621900, P. R. China

ABSTRACT: Three inorganic-organic hybrid open-frameworks based on heterometallic cluster building

blocks,

formulated

as

Cd2Cs3(NDC)3(OAc)(DMA)2(H2O)

(1),

[NH2(CH3)2]2·Cd2Mg(NDC)4·Gx (2), and [NH2(CH3)2]3·Cd2K(NDC)4·Gx (3) (H2NDC = 2,6napthalenedicarboxylicacid, G = guest solvent molecule), were synthesized under solvothermal conditions. Compound 1 has a pillared layered structure featuring inorganic hcb-type layers with 14-ring windows, and simultaneously exhibits a 3D open-framework constructed from two types of heterometallic clusters, i.e., {Cd2Cs2O18} and {CdCs4O18}, and the NDC2- ligand. Compounds 2 and 3 are constructed from linear trinuclear {Cd2M} (M= Mg and K) building blocks and the NDC2- ligand, featuring 1D square channels with rld-z topology. Of three heterometallic hybrid open-frameworks, compounds 1 and 2 exhibited strong blue-light emission due to the presence of fluorescent organic ligands in the anionic frameworks, and more importantly their strong fluorescence could be selectively quenched towards the nitro explosive picric acid (PA).

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Mechanism study has demonstrated that the high fluorescence quenching selectivity of both hybrid materials towards PA might be due to resonance energy transfer (RET) and photoinduced electron transfer (PET) processes. 1. INTRODUCTION Rapid and selective detection of explosives has attracted considerable attention since the sensing technologies of nitroaromatic compounds are gaining increasing concerns with respect to terrorism threats, environmental protection, and public safety.1, 2 Of explosives widely used in the industry, picric acid (PA), like 2,4,6-trinitrotoluene (TNT), is one of the well-known nitro explosives. On the other hand, PA is also used in pharmaceutical industries and has been found in many unexploded land mines worldwide, which has become a potential pollutant and may cause serious environmental problems.3, 4 The rapid and selective sensing of PA in the field of sensors and analytical chemistry is therefore an interesting and urgent task but very difficult due to its electron deficient property.5, 6 Recently, fluorescent metal-organic frameworks (FMOFs) have been successfully used for the detection of nitro-containing compounds by virtue of their portability, rapid response time, low cost, and so on.7-11 The sensing selectivity of FMOFs is significantly affected by their structures including topologies, channels and specific surface areas.12-16 The connection of fluorescent ligands with d10 configured metal ions or main group metal ions is an efficient strategy to construct FMOFs as sensory materials.17,

18

For example, [Cd(NDC)0.5(PCA)]·Gx (G = guest

molecules, H2NDC = 2,6-napthalenedicarboxylic acid, PCA = 4-pyridinecaboxylic acid), a 3D


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luminescent metal-organic framework (MOF), displayed selective detection property towards the PA molecule.19 Another example is the [(CH3)2NH2]3[Zn4Na(BPTC)3]·4CH3OH·2DMF (BPTC = biphenyl-3,3',5,5'-tetracarboxylic acid),20 a 3D heterometallic MOF with interesting structure which also exhibited high detection selectivity towards PA. Another approach to obtain luminescent materials is the application of fluorescent metal ions as metal centre to construct MOFs. For example, [Tb(L)(OH)·x(solv)] (H2L = 5-(4-carboxyphenyl)pyridine-2-carboxylate), a water-stable FMOF, displayed excellent sensing ability towards nitro-containing compounds in aqueous solutions as well as in vapour phases.21 Despite great efforts were devoted to developing new FMOFs as sensory materials for highly efficient detection of nitro explosives, there is still enough space for assembling new structures to improve the detection selectivity and sensitivity.22, 23

In this work, we wish to report the synthesis and structural characterization of three new heterometallic hybrid open-frameworks and their potential applications for the sensing of nitrocontaining explosives, especially for PA. In the design of hybrid open-frameworks, a mixed metal Cd/M (M = main group metal ions) carboxylate systems were used to prepare FMOFs since they are more likely to display strong fluorescence. In our previous efforts, five fluorescent heterometallic hybrid open-frameworks were successfully synthesized.24 Of these compounds, [NH2(CH3)2]4Cd4Ca2(BDC)8(DMA)·Gx (G = guest solvent molecules) is able to selectively sense RDX (cyclotrimethylenetrinitriamine). In our continuing efforts to prepare interesting FMOFs as


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high-performing explosive sensors, three heterometallic inorganic-organic hybrid openframeworks,

formulated

as

Cd2Cs3(NDC)3(OAc)(DMA)2(H2O)

(1),

[NH2(CH3)2]2·Cd2Mg(NDC)4·Gx (2) and [NH2(CH3)2]3·Cd2K(NDC)4·Gx (G = guest solvent molecule) (3), were prepared through solvothermal methods in this study. Their structures, thermal stability, fluorescent properties, as well as the applications for selective detection of nitro explosives were fully studied.

2. EXPERIMENTAL SECTION Materials and Methods. The chemical reagents used in this work were purchased from commercial sources and used as received. Room temperature and temperature-dependence powder X-ray diffractions (PXRD) were carried out on Rigaku D/MAX-rA and D/MAX-22003KW diffractometer using Cu-Kα radiation, respectively. Themo-gravimetric analyses were performed using a Netzsch STA 449c instrument under a flow of nitrogen with a heated rate of 10 oC per minute. FT-IR (KBr pellets) spectra were recorded on a Nicolet Impact 410 FTIR spectrometer. Elemental analyses were measured with a Euro EA3000 analyzer. The N2 sorption analyses were measured on an ASAP 2020 apparatus. All the samples were activated at 200 oC for 4 hours before its characterization. Fluorescent behaviors of 1 and 2 were measured on a PTI QM-40 luminescent analyzer with a light source of xenon lamp. Synthesis of Cd2Cs3(NDC)3(OAc)(DMA)2(H2O) (1): Cd(OAc)2·2H2O (0.375 mmol, 99 mg), Cs2CO3 (0.065 mmol, 21 mg), 9-AC (9-anthracencarboxylic acid, 0.250 mmol, 55 mg), and


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H2NDC (0.250 mmol, 54 mg) were added into a mixed solvent of DMA (4 mL) and methanol (1 mL) in a 25 mL Teflon-lined stainless steel vessel. After enough mixing, the mixture was then heated to 150 oC for 4 days. The crystal was recovered by filtration, washed with DMA, ethanol, and finally dried in air (34.2 wt% yield based on H2NDC). CHN elemental analysis: anal. for 1: C 36.23 wt%, H 2.89 wt%, and N 1.78 wt%; calc. for 1: C 36.41 wt%, H 2.72 wt%, and N 1.85 wt%. IR (KBr, cm-1): 3380 (m), 3063 (w), 1605 (s), 1550 (s), 1495 (m), 1399 (s), 1354 (m), 1198 (m), 1093 (m), 1138 (w), 907 (m), 825 (m), 786 (m), 474 (m). Synthesis of [NH2(CH3)2]2·Cd2Mg(NDC)4·Gx (2): Similar to synthesis of compound 1, a same synthetic operation was used for the synthesis of 2 except that Cs2CO3 (0.065 mmol, 21 mg) was replaced by Mg(OH)2 (0.138 mmol, 8 mg). The yield of 2 based on H2BDC is 34.2%. CHN elemental analysis: anal. for 2: C 52.52 wt%, H 3.49 wt%, and N 2.31 wt%; calc. for 2: C 52.41 wt%, H 3.52 wt%, and N 2.26 wt%. IR (KBr, cm-1): 3402 (m), 1609 (m), 1564 (s), 1488 (m), 1397 (s), 1351 (m), 1192 (m), 1093 (m), 933 (w), 907 (m), 774 (m), 447 (w). Synthesis of [NH2(CH3)2]3·Cd2K(NDC)4·Gx (3): Similar to synthesis of compound 1, single crystal of 3 was obtained by using KOH (0.143 mmol, 8 mg) to replace Cs2CO3 (0.065 mmol, 21 mg). In this synthesis, colorless crystals of 3 and some unknown powers were obtained. X-ray crystallographic structure. Single-crystal data were collected on an Oxford Xcalibur diffractometer with a CCD detector Mo-Kα radiation (λ = 0.71073 Å) using a ω scan for 1-3 at 296 oC. The direct method and full-matrix least-squares method on F2 contained in SHELXTL program package were used to resolve and refine the structures of compounds 1-3,


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respectively.25 Crystallographic data of 1-3 were shown in Table 1. The CCDC numbers for 1-3 are 1484794, 1493444 and 1519610, respectively. Table 1. Crystallographic data of 1-3 1

2

3

Empirical formula

C46H39O17N2Cd2Cs3

C125H127O37N9Cd4Mg2

C100H64O34N1Cd4K2

Formula weight

1515.34

2845.62

2351.32

Crystal system

monoclinic

orthorhombic

orthorhombic

Space group

C2/c

Fdd2

Fdd2

a, Å

27.806(9)

33.5429(18)

30.4133(18)

b, Å

13.792(4)

34.1738(17)

34.5880(2)

c, Å

28.738(8)

24.3555(13)

27.5921(18)

α,

o

90.00

90.00

90.00

β,

o

108.289(6)

90.00

90.00

γ,

o

90.00

90.00

90.00

Volume, Å

10464(5)

27918(3)

29025(3)

Z

8

8

8

296

296

296

Dc, g cm

0.955

1.354

1.076

F(000)

1712.0

11615.0

9384.0

2θ [ ]

4.78 to 50.02

4.772 to 50.054

3.986 to 50.244

Reflections collected

40623

47320

40273

Independent reflections (Rint)

9220

10828

12744

1.022

1.088

1.026

R1 [I > 2σ(I)]

0.0723

0.0475

0.0494

wR2[I > 2σ(I)]

0.1800

0.1298

0.1297

3

T [K] -3

o

GOF on F

2

Sensing of nitro explosives. In typical experiment, 3 mg of 1 was dispersed in 20 mL acetonitrile, and ultrasonicated for 1 h and then aged for 3 days. The fluorescence of 1-based dispersions (λex = 355 nm) were measured with incremental addition of different nitro compound solutions (1mM) to 3 mL the acetonitrile dispersion of 1. 3. RESULTS AND DISCUSSION


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Structural analysis. The single crystals of compound 1 were collected by the solvothermal

reaction

of

Cd(OAc)2·2H2O,

Cs2CO3,

H2NDC,

and

9-AC

(9-

Anthracencarboxylic acid) in a mixed solvents of methanol and DMA at 150 oC for 4 days. The phase purity of 1 was determined by the PXRD analysis, as shown in Figure S1. Compound 1 crystallizes in monoclinic C2/c (no. 15) space group. Two independent Cd(II) ions, three Cs(I) ions, three NDC2- ligands, one OAc- ligands, one water, and two DMA molecules are comprised in the asymmetric unit of 1 (Figure S9). The Cd1 is eightcoordinated by three NDC2- and one OAc- ligands in an approximately monocapped pentagonal bipyramidal geometry. Cd2 is six-coordinated in a distorted octahedral environment. Cs1, Cs2, and Cs3 are coordinated by six, six and five oxygen atoms, respectively (Figure 1). Interestingly, the water molecule and DMA molecules in the framework are coordinated with Cs2 and Cs3 ions, respectively. The bond lengths of CdO [2.296(8)-2.515(10) Å], Cs-O [2.934(10)-3.498(10) Å] and Cs-O1w 3.701(17) Å are all within the normal ranges.26-28


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Figure 1. The coordination environment of Cd(II) and Cs(I) contained in compound 1.

In compound 1, the adjacent metal ions were connected via oxygen atoms of carboxyl groups from NDC2- ligands to form two types of clusters, i.e., {Cd2Cs2O18} and {CdCs4O18} (Figure 2a). These clusters were further connected by NDC2- ligands to assemble the 3D hybrid framework of 1. Viewed along [101] direction, compound 1 has 1D channels occupied by DMA and water molecules. After removing the guest molecules (i.e., H2O and DMA), the accessible volume of 1 is ca. 34.7% calculated using PLATON program.


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Figure 2. (a) View of the clusters contained in 1, left: {CdCs4O18} cluster; right: {Cd2Cs2O18} cluster. (b) View of the inorganic layer along [-111] direction. (c) View of the inorganic-organic hybrid layer along [-111] direction contained in 1. (d) Polyhedral view of the 3d hybrid framework of 1 along [101] direction. Polyhedral: Pink: CsO6, red: CsO5; blue: CdO8, green: CdO6.

Alternatively, the framework structure of 1 can also be understood as a pillared layered structure. As shown in Figure 2b, the heterometallic clusters are connected by oxygen atoms from NDC2- ligands, resulting in the formation of hcb-type layer structure parallel to the ab plane. Each 14-ring window contained in the layers is filled by two NDC2ligands (Figure 2c). The residual NDC2- ligands within the interlayer region act as pillars to connect adjacent layers, forming a sandwich-like hybrid framework. Therefore, the hybrid framework of 1 can be classified as I2O1 type.


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The entire structure of compound 1 is reminiscent of the sandwich frameworks [Er7(µ3O)(µ3-OH)6(bdc)3](ina)9[Cu3X4]29 (bdc = 1,2-benzenedicarboxylate, ina = isonicotinate, X=Cl or Br). As reported in the literature,29 the inorganic 2D layers in these hybrid frameworks are pillared by [Cu3X4(ina)6]4− to give 3D frameworks. It is notable that the inorganic layers in [Er7(µ3-O)(µ3-OH)6(bdc)3](ina)9[Cu3X4] are constructed by one type of metal atom, whereas in the structure of compound 1, the layers are constructed by two types of metal atoms. As compared to traditional MOFs, the heterometallic-organic frameworks have some advantages including designable structures and tunable properties via the strategy of changing the secondary metal centers.30-32 Structural analysis indicates that compounds 2 and 3 are iso-structural. Therefore, in this work we only described the detailed structure of compound 2. The phase purity of 2 was confirmed by PXRD (Figure S6.). Compound 2 crystallizes in the orthorhombic Fdd2 (no. 43) space group. Two Cd(II) ions, one Mg(II) ions, four NDC2- ligands, and two [CH3NH2]+ cations were comprised in the asymmetric unit of 2. Both Cd and Mg atoms were six-coordinated by the NDC2- ligands in a distorted octahedral environment, as shown in Figure 3. The Cd-O and Mg-O distances range from 2.188(6) to 2.420(7) Å and 2.014(10) to 2.121(6) Å, respectively.33-35


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Figure 3. The coordination environment of Cd(II) and Mg(II) contained in compound 2.

In compound 2, the adjacent metal ions were connected by carboxyl groups of NDC2- ligands to give a linear trinuclear {Cd2Mg} building blocks and each {Cd2Mg} cluster bridges eight neighboring clusters via surrounding NDC2- ligands, forming the 3D frameworks. Viewed along the [001] direction, compound 2 had regular 1D channels with a window size of ca. 9.65 × 9.75 Å2. These channels were occupied by the guest molecules (Figure 4c). The accessible volume of 2, after removing the guest molecules, was ca.47.2%, as calculated using PLATON program.


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Figure 4.(a) View of the diamondiod cage contained in 2; (b) View of the four-fold self-interpenetrated diamondoid topological network contained in 2; (c) View of the 3D structure of 2 with regular channels along [001] direction, green polyhedral: CdO6, pink polyhedral: MgO6; (d) View of the rld-z topological structure of 2. Black ball: Cd, red line: NDC2-, blue line: Mg2+.

The 3D structure of 2 is constructed by a four-fold self-interpenetrated diamondoid topological network of Cd(NDC)22- anion (Figure 4b) and Mg2+ ions. If we consider the Cd atoms as 5connected nodes, Mg atoms and NDC2- ligands as 2-connected linkers, compound 2 displays a 5connected rld-z topological structure (Figure 4d). It is noteworthy that this unprecedented rld-z topology was only found in the structure of a known compound, i.e., {[Ni(dpa)2(succinate)0.5]Cl} (dpa = 4,4'-dipyridylamine).36 Different from the positive framework charge of the networks in {[Ni(dpa)2(succinate)0.5]Cl}, compound 2 has the negative framework charge in this work. More importantly, the framework of {[Ni(dpa)2(succinate)0.5]Cl} is much dense, that is to say, compound 2 is the first open-framework with rld-z topology.


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Thermal stability. Both thermo-gravimetric analysis (TGA) and temperature-dependent PXRD (N2, heating rate: 10 oC·min-1) were used to study the stability of 1. As shown in Figure S3, the weight loss step from 30 to 220 oC may correspond to the escape of all of the water and half of DMA molecules. The observed weight loss value is well consistent with the calculated one (observed: 6.75 wt%, calculated: 6.91 wt%). Moreover, the weight loss of 1 from 220 oC to 240 o

C may be caused by the release of other DMA molecules (observed: 6.13 wt%, calculated: 5.73

wt%). Upon further heating from 240 to 380 oC, the framework of 1 begins to decompose, probably due to the decomposition of acetate (observed: 4.24 wt%, calculated: 3.88 wt%). Up to 800 oC, the observed total weight loss is 60.23 wt%. Temperature-dependence PXRD also confirmed that the framework of 1 remains stable, even when all of water and DMA molecules coordinated to Cs atoms have escaped from the channels (Figure S4). In compound 2, the TGA results showed two main weight loss steps from 30 to 800 oC (Figure S8). The first step (30-200 o

C) may correspond to the escape of guest molecules (observed: 13.01 wt%, calculated: 12.68

wt%). The weight loss from 200 to 500 oC may be attributed to the decomposition of the framework, and the possible decomposition products are CdO, MgO, and some unknown powders (observed: 32.61 wt%, calculated of CaO and MgO: 25.15 wt%). Fluorescent properties and selective detection of nitro explosives. The solid-state fluorescence of compounds 1, 2 and H2NDC were studied at room temperature. As shown in Figure S15-S17, compounds 1, 2 and H2NDC exhibit strong fluorescent emissions at 427, 426 and 443 nm (λex = 387, 371 and 373 nm, respectively), respectively. The very


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similar excitations and emissions to the H2NDC ligand indicated that the fluorescence of the as-synthesized compounds was mainly originated from the organic ligands. To demonstrate the capability of compounds 1 and 2 for explosives detection, the fluorescence spectra of 1 and 2-based acetonitrile dispersions were monitored by successive addition of small aliquots of nitro explosive molecules including PA, TNT, cyclotrimethylenetrinitriamine (RDX), cyclotetramethylenetetranitramine (HMX), 1,3,5trinitrobenzene

(TNB),

1,3-dinitrobenzene

(DNB),

and

2,4,6,8,10,12-hexanitro-

2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0.0]dodecane (CL-20). The fluorescence intensity of both 1 and 2-based dispersions were continuously decreased with successive addition of PA acetonitrile solution (Figure 5a and 5b). When 400 µL acetonitrile solution of PA (1 mM) was added to the 1-based dispersion, the percentage of fluorescence quenching (defined as (I0-I)/I0 × 100%; I0 = original peak maximum intensity, I = maximum intensity after exposure added) was ca. 74.5%. Under same conditions, the fluorescence quenching percentage of compound 2 was about 96%. Interestingly, when PA was replaced by some other nitro compounds, e.g., TNT, TNB, HMX, DNB, RDX, and CL-20, there was almost no fluorescence quenching for the 1based dispersion (Figure 5c). However, the 2-based dispersion still showed quenching behavior, but the efficiency is much lower than that of PA (Figure 5d).


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Figure5. (a) & (b) The emission spectra of 1- and 2-based dispersions upon increment addition of a PA acetonitrile solution (1 mM), λex = 355 nm and λex = 371 nm, respectively. Insert: photographs showing the fluorescence of the dispersions before and after addition of 200 µL PA acetonitrile solution (1 mM). (c) & (d) The fluorescence quenching efficiency for different nitro compounds acetonitrile solution with the concentration of 118 µM of 1 and 2.

The quenching constant and quenching efficiency for PA can be calculated via the S-V equation, (I0/I) = Ksv[A] +1, where Ksv represents quenching constant (M-1), and [A] represents molar concentration of the analyte. Compounds 1 and 2 give the quenching constants for PA of 2.2 × 104 M-1 and 2.7 × 104 M-1, respectively. These values are comparable with the highest quenching constants for the known MOFs.37-38 It is noteworthy that for compound 1, its quenching constant for PA is much higher than that for TNT and all other nitro compounds used in this work, i.e., the quenching constant for


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PA of 1 is above sixty times than that of TNT. As calculated by the 3σ/k equation (σ represents the standard deviation for intensity of 1 or 2 in the absence of PA and k represents slope of the equation),39-41 the detection limits (DL) of compounds 1 and 2 are 1.54 × 10-7 M (35 ppb) and 1.58 × 10-7 M (36 ppb), respectively. Both S-V plots of 1 and 2 for PA are nearly linear at low concentrations. And the plots deviated from linearity and begin to bend downwards upon further increasing the concentration (Figure S30). The non-linear behaviors observed from S-V plots of PA demonstrate that a combination of static and dynamic enhancement, self-absorption or energy transfer, may exist between PA and compounds 1 and 2.42, 43

Figure 6. Spectral overlap between the normalized emission spectra of 1, 2 and normalized absorption spectra of different nitro compounds.

To gain more insights into the high sensing selectivity of compounds 1 and 2 towards PA, the fluorescence quenching mechanism was also studied. It has been demonstrated that the resonance energy transfer (RET) is a widely-agreed fluorescent quenching


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mechanism which can explain the high selectivity of the sensory MOFs.19 In order to verify that whether RET exists in our sensing process or not, the UV-vis spectra of different nitro compounds in acetonitrile were first tested. Both emission spectra of 1 and 2-based acetonitrile dispersions and absorption spectra of different nitro compounds in acetonitrile were normalized and shown in Figure 6. Obviously, an overlap between the emission spectra of both 1 and 2-based dispersions and the absorption spectra of PA in acetonitrile solution was observed, demonstrating the probability of RET between the emission bands of 1 and 2 and the absorption band of PA. However, no such overlap was observed for other nitro compounds, indicating that no RET occurred between 1 and 2based dispersions and these nitro-containing analytes.

Figure 7. Photo-induced electron transfer mechanism between fluorescent sensor at excited state and analyte at ground state.

In order to explain the high sensing selectivity of compounds 1 and 2, theoretical studies were also performed using Dmol3 program Perdew-Burke-Ernzerhofpackage. In general, there is a driving force for the electron transfer process when the conduction


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band (CB) of a crystal material locates at higher energies than the LUMOs of analytes, thus resulting in the fluorescence quenching (Figure7).19 The experimental observation of the interactions between compounds 1 and 2 and the analytes (e.g., PA, TNT, and other nitro compounds) supports this calculation. As shown in Figure S31, the LUMOs energies of all the nitro compounds (except RDX and CL-20) used in this work are lower than the CB energies of 1 and 2, indicating the photo-induced electron transfer process (PET) may also occur when 1 and 2-based dispersions are excited by ultraviolet light in the present of nitro compounds. And the fluorescent quenching percentages of compounds 1 and 2 towards other nitro explosives are depressed by their direct interactions with analytes due to the short-range process of PET.19 4. CONCLUSION In summary, the assembly of both transition metal ion (Cd2+) and main group metal ion (Mg2+, K+ and Cs+) with the aromatic NDC2- ligand afforded three 3D inorganic-organic hybrid openframeworks under solvothermal condition. The framework structure of compound 1 exhibits a pillared layered structure which is constructed from inorganic hcb-type layer with 14-ring windows and NDC2- ligand. The inorganic layers in compound 1 are assembled by two type of heterometallic clusters, i.e., {Cd2Cs2O18} and {CdCs4O18}. Compound 2 and 3 are iso-structural and constructed by linear trinuclear {Cd2Mg} (M = Mg, K) building blocks featured with 1D quare channels with rld-z topology, which is first observed in porous open-frameworks reported to date. Moreover, compounds 1 and 2 displayed strong blue fluorescence and showed high


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detection selectivity and sensitivity towards PA. The fluorescence quenching constant of compound 1 towards PA is about sixty times higher than that of TNT and other nitro compounds. The high selectivity of 1 and 2 towards PA may be attributed to the RET and PET mechanisms. ASSOCIATED CONTENT Supporting Information. X-ray data in CIF format, IR spectra, TGA curves, powder XRD patterns, and additional figures. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]; *E-mail: [email protected]. Author Contributions ‡These authors contributed equally. Notes Caution: Some nitro compounds used in this work are dangerous and should be handled carefully and in small amounts. ACKNOWLEDGMENT The authors gratefully acknowledge the supports from the Development Foundation of CAEP (No. 2015B0302056) and China Postdoctoral Science Foundation (2016M590903). REFERENCES


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For Table of Contents Use Only：：

Heterometallic Hybrid Open-Frameworks: Synthesis and Application for Selective Detection of Nitro Explosives Kangcai Wang,‡ Xin Tian,‡ Yunhe Jin, Jie Sun,* and Qinghua Zhang*

Three fluorescent inorganic-organic hybrid framework containing inorganic hcb-type layers and rld-z topology were synthesized. The strong blue fluorescence of compounds 1 and 2 could be quenched much more efficiently towards PA than other nitroaromatics.


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Heterometallic Hybrid Open Frameworks ... - ACS Publications

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