A unique zinc-organic framework constructed through: In situ ligand synthesis for conversion of CO2 under mild conditions and as a luminescence sensor for Cr2O72-/CrO42-

Article abstract of DOI:10.1039/c7dt02819a

A novel zinc-organic framework, {[Zn₃(tza)₂(μ₂-OH)₂(H₂O)₂]·H₂O}_n (1) (H₂tza = 1H-tetrazolate-5-acetic acid), was synthesized through an in situ generated tetrazole ligand under hydrothermal conditions. In compound 1, tza^2- ligands and Zn²⁺ are interlinked to form 2D layers, which are further pillared through μ₂-OH groups to generate a 3D framework. Thermogravimetric analysis and powder X-ray diffraction confirm that 1 has high thermal stability, pH stability and solvent stability. Catalytic studies show that 1 exhibits excellent catalytic ability for the cycloaddition of CO₂ with epoxides under 50 °C and 0.1 MPa. Importantly, 1 can be reused at least six times. Furthermore, luminescence investigations indicate that 1 can serve as a recyclable luminescence sensor to efficiently detect Cr₂O₇^2-/CrO₄^2-, and the detection limit can reach 10^-6 mol L^-1 and 4 × 10^-6 mol L^-1, respectively.

Full text of DOI:10.1039/c7dt02819a

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January 2016 Pages 1–398
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Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
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a Zr-metal–organic
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A unique zincꢀorganic framework constructed through in situ
ligand synthesis for conversion of CO under mild conditions
2
2ꢀ
7
2ꢀ
4
and luminescent sensor for Cr O /CrO
2
a
b
a
a
b
TianꢀQun Song, Jie Dong, HongꢀLing Gao, JianꢀZhong Cui,* Bin Zhao*
Abstract
A novel zincꢀorganic framework, {[Zn
1) (H tza = 1Hꢀtetrazolateꢀ5ꢀacetic acid), was synthesized through in situ generated
tetrazole ligand under hydrothermal condition. In compound 1, tza ligands and Zn
are interlinked to form 2D layers, which are further pillared through ꢀ ꢀOH groups to
3
2 2 2 2 2 2 n
(tza) (ꢀ ꢀOH) (H O) ]·H O}
(
2
2
ꢀ
2+
2
generate a 3D framework. Thermogravimetric analysis and the powder Xꢀray
diffraction confirm that 1 has high thermal stability, pHꢀstability and solventꢀstability.
Catalytic studies show that 1 exhibits excellent catalytic ability for the cycloaddition
2
of CO with epoxides under 50 °C and 0.1 MPa. Importantly, 1 can be reused for at
least six times. Furthermore, luminescent investigations indicate that 1 can serve as a
2
ꢀ
2ꢀ
2 7 4
recyclable luminescent sensor to efficiently detect Cr O /CrO , and the detection
ꢀ6
ꢀ6
limit can reach 10 mol/L and 4×10 mol/L, respectively.
Introduction
It is commonly believed that the increasing emission of greenhouse gases, such as
carbon dioxide, is the main reason for global warming. Meanwhile, carbon dioxide is
1
an abundant, cheap and innoxious renewable C1 resource in producing chemicals.
Therefore, how to effectively use carbon dioxide is extremely significant and urgent.
As is wellꢀknown, cyclic carbonates can be used as polar aprotic solvents, degreaser,
and other applications in organic synthesis, such as electrolytes in lithiumꢀion
2
batteries and intermediates for linear dialkyl carbonates synthesis. The coupling
2
reaction between epoxides and CO is an effective method to obtain cyclic carbonates
a
Department of Chemistry, National Demonstration Center for Experimental Chemistry & Chemical engineering
Education, National Virtual Simulation Experimental Teaching Center for Chemistry & Chemical engineering
Education, Tianjin University, Tianjin 300072, P. R. China
Eꢁmail: cuijianzhong@tju.edu.cn (J.ꢁZ. Cui).
Department of Chemistry, Nankai University, Tianjin 300071, P. R. China.
b
Eꢁmail: zhaobin@nankai.edu.cn (B. Zhao).
1

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2
without other byproduct and realize reasonable utilization of CO . In this system, the
major barrier is the high thermodynamic stability of CO , which needs a catalyst to
2
2
promote the cycloaddition of CO and epoxides. The catalysts are always metal
3
4
5
6
oxides, alkali metal salts, quaternary ammonium salts, and ionic liquids. But some
of them have low catalytic performance or use of high pressures and/or high
7
temperatures. In recent years, MOFs acting as effective heterogeneous catalysts due
to unique structures and Lewis acidic sites have been widely investigated in CO
2
conversion with epoxides. Hence, greatly improving yields with the help of catalysts
under mild conditions are in demand in practical applications.
On the other hand, MOFꢀbased sensors have been widely studied and they are
8
9
always used to detect chemical pollutants, such as metal ions, anions, small
10
11
2ꢀ
7
2ꢀ
molecules, and explosive molecules. Cr O and CrO4 with high toxicity and
2
carcinogenesis have been used in industrial processes. The random discharge of
2
ꢀ
2ꢀ
Cr
2 7 4
O /CrO may lead to serious threats to the ecological balance and human health.
2ꢀ
7
2ꢀ
Hence, it is meanful to effectively detect Cr O /CrO . However, sensor materials
2
4
still exist the deficiencies of bad sensitivity, poor regeneration or low chemical
stability to some extent. Until now, it is still a big challenge to develop new MOFs
2
ꢀ
2ꢀ
2 7 4
with high sensitivity and recyclability to detect Cr O /CrO .
The tetrazole functional groups have been widely used as ligands in coordination
chemistry, because tetrazole through the four nitrogen electronꢀdonating atoms allows
1
2
it to coordinate with either bridging or multidentate modes in selfꢀassemble process.
However, bifunctional carboxylateꢀintroduced 5ꢀsubstituted tetrazolate ligands with
1
3
more coordination modes than tetrazolyl ligands are less studied. Recently, we
synthesized 3D pillaredꢀlayerꢀlike 5ꢀsubstituted tetrazole framework,
[Zn (tza) (ꢀ ꢀOH) (H O) ]·H O} (1) (H tza = 1Hꢀtetrazolateꢀ5ꢀacetic acid). In
a
{
3
2
2
2
2
2
2
n
2
particular, 1Hꢀtetrazolateꢀ5ꢀacetic acid ligand was in situ generated using cyanoacetic
acid and NaN under hydrothermal method (Scheme 1), which is called the
3
14
DemkoꢀSharpless [2+3] cycloaddition reaction. This zincꢀorganic framework has
high thermal stability, pHꢀstability and solventꢀstability. It can largely improve the
activity of the cycloaddition of CO
2
to epoxides in mild conditions and recycle for at
2

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least six times. In addition, 1 can selectively, efficiently and circularly detect
2
ꢀ
2ꢀ
Cr O /CrO .
2
7
4
2
Scheme 1 In situ synthesis of the H tza ligand.
Experimental section
Materials and characterization methods
All chemicals were commercially available. Elemental analysis (EA) was made on
a Perkin Elmer 240 CHN analyzer. The infrared (IR) spectra were obtained on a
Nicolet Nexus 670 spectrometer (KBr pellet). The Powder Xꢀray diffraction (PXRD)
were performed on a Ultima IV Xꢀray diffractometer using Cu Kα radiation (λ =
0
.15406 nm). Thermogravimetric analysis (TGA) data was collected using a Netzsch
TG 209 TGꢀDTA apparatu. Fluorescent analyses were measured on a Cary Eclipse
luminescence spectrophotometer. The content of metal was detected by ICP atomic
emission spectrometric analysis. UVꢀVis spectra were obtained on shimadzu
UVꢀ3600 spectrophotometer.
Synthesis of {[Zn (tza) (µ ꢀOH) (H O) ]·H O} (1)
3
2
2
2
2
2
2
n
2 3
ZnBr (0.3 mmol, 0.0675 g), cyanoacetic acid (0.3 mmol, 0.0255 g), NaN (0.6
mmol, 0.039g) were mixed with 5 mL distilled water, and the pH value was tuned to
approximately 5 using 1M NaOH solution, then the mixture was sealed into a 25 mL
stainless autoclave. The autoclave was heated at 120 °C for 72 hours and then cooled
slowly down to 30 °C. Colorless block single crystals were obtained. The yield was
7
5% (based on ZnBr
2
). Elemental analysis (%) for compound 1, Calcd: C 13.43, H
−
1
2
.23, N 20.90. Found: C 13.67, H 2.17, N 21.13. IR (cm ) (Fig. S1 in the Supporting
Information): 3424(vs), 2951(m), 2889(m), 2140(m), 1605(vs), 1505(vs), 1469(s),
1
5
395(s), 1264(vs), 1138(w), 1096(w), 1038 (w), 955(m), 803(s), 745(s), 640(m),
77(vw), 536(vs).
3
Caution! Only a small amount of NaN should be carefully used and handled,
3

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3
because NaN exists the potential explosiveness!
Xꢀray single crystal structure determination
The crystal structure data of 1 was collected on a Bruker SMARTꢀ1000 CCD
diffractometer with Mo Kα radiation (λ = 0.71073 Å) using a ω−ϕ scan. The
singleꢀcrystal structure was solved by direct methods with the SHELXTLꢁ97 program
15
package and all nonꢀH atoms were refined anisotropy through fullꢀmatrix
2
leastꢀsquares methods based on F . The number of free H
2
O molecules was confirmed
by TG analysis and elemental analysis. Table 1 listed crystal data collection and
refinement details, and Table S1 showed the selected bond lengths and angles. CCDC
(
1542487, 1) contain crystallographic data and these data can be obtained free of
charge from the Cambridge Crystallographic Data Center via
www.ccdc.cam.ac.uk/data request/cif.
Table 1 Crystallographic data and structure refinements for 1
Compound
1
Formula
C
6
H
12
N O Zn
8 9 3
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
536.33
120.00(10)
0.71073
Monoclinic
P2 /c
1
7.5917(11)
14.645(3)
6.4975(11)
90
b (Å)
c (Å)
α
β
(deg)
(deg)
96.645(15)
90
γ (deg)
3
Volume (Å )
717.5(2)
2
Z
ꢀ
3
Calculated density (Mg m )
2.399
ꢀ
1
Absorption coefficient (mm )
5.037
F (000)
512.0
θ
range for data collection (deg) 3.038 to 24.999
Reflections collected
2364
Independent reflection
Data / restraints / parameters
1263 [R(int)=0.0542]
1263 / 8 / 116
1.149
2
Goodnessꢀofꢀfit on F
4

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Final R indices [I>2σ(I)]
R indices (all data)
R
1
= 0.0677,
wR = 0.1807
2
R
1
= 0.0865,
wR = 0.1984
2
Result and discussion
Crystal structure
Singleꢀcrystal structural analysis reveals that 1 crystallizes in the monoclinic
2
+
2ꢀ
system, P2 /c. The asymmetric unit of 1 exists one and a half Zn , one tza ligand,
1
2
one ꢀ ꢀOH group and one water molecule. As shown in Fig. 1a, Zn1 displays a nearly
2
2
ideal octahedron, completed by two O atoms (O4, O4 ) and two N atoms (N11, N11 )
2
ꢀ
2
of two tza ligands, and two O atoms (O7, O7 ) of H O, while Zn2 is
2
2
ꢀ
tetraꢀcoordinated by one O atom (O1) and one N atom (N1) from two tza ligands,
2
2ꢀ
and two O atoms (O3, O3 ) from two ꢀ
2
ꢀOH groups. Each tza ligand is a tridentate
linker, adopting one single ꢀ ꢀκN11, O4 : κN1 : κO1 coordination mode. Interestingly,
3
2
ꢀ
2+
tza ligand interlinks with Zn to form 2D layers, then the 2D layers are futher
bridged through ꢀ ꢀOH group to obtain a 3D framework (Fig. 1b). Besides, the
2
2
ꢀ
intramolecular hydrogen bonds between the coordinated water and tza ligand are
observed (Table S2), which contribute to the stability of 3D framework of 1 (Fig. 1c).
5

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2
+
2+
Fig. 1 (a) The polyhedra of Zn and the coordinated environments of Zn ; (b) 3D framework
of 1 formed by 2D layers; (c) 3D framework of 1 with hydrogen bonds shown by dashed lines
along b and c axes. All hydrogen atoms were omitted for clarity. cyan: Zn; red: O; blue: N; gray:
C.
PXRD analysis and TG analysis
The PXRD pattern of compound 1 was shown in Fig. S2. High similarity between
the simulated and measured peaks revealed that 1 was pure phase. In order to evaluate
the solvent and acidꢀbase stabilities of 1, the solid sample was immersed in ten
common solvents about 15 h, respectively, and the PXRD patterns had almost no
change compared with the simulated one from 1. When the sample was immersed in a
series of solutions with pH values from 1 to 14 about 4 h, only the peaks in the pattern
disppeared partly under pH = 14, revealing that the sample became amorphous. In
order to study the thermal stability, TGA was measured and the picture was shown in
Fig. S3. A weight loss of 3.17% could be observed from room temperature to 130 °C,
owing to the loss of free H O molecules (Calcd: 3.35%). Then, compound 1 was
2
decomposed gradually above 300 °C. The remaining weight of 42.22% may
correspond to ZnO (calcd: 42.02%).
Catalytic properties
2
Catalytic experiments were focused on the transformation of CO with epoxides
and styrene oxide was employed as an initial substrate to study the optimized reaction
conditions. The corresponding results were listed in Table 2. The reaction was carried
out using 2 mmol styrene oxide, about 5 mol % compound 1 (based on Zn) and in the
presence of 2.5 mol % coꢀcatalyst (tetrabutylammonium bromide, TBAB) under
6

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2
solventꢀfree condition and CO pressure of 0.1 MPa for 12 h. When reaction was
conducted at 50 °C, the yield of the desired epoxide reached 86% (entry 1, Table 2),
much higher than under 2.5 mol % TBAB without compound 1 (20%, entry 2, Table
ꢀ
2
). The increased yield suggests that nucleophilic attack of Br to epoxides is
16
tremendously promoted with the help of Lewis acid sites. The reaction was also
conducted at other higher temperatures (entries 3ꢀ5, Table 2), but the yield had less
obvious enhancement. Taking energy into consideration, we chose a moderate
temperature (50 °C) to continue our research. In order to investigate whether the
increase of TBAB can enhance yield, 5 mol % TBAB was carried out under the same
conditions. The result proved that the yield had no obvious increase (entry 6, Table 2).
Besides, the yield was reduced to 64% when crystal was no grinding, which probably
c
attributed to less exposed metal sites (entry 1 , Table 2). When raction was carried out
for 6 h, the yield was decreased by 30% (entry 7, Table 2). Therefore, 5 mol % sample
with grinding and 2.5 mol % TBAB were selected to react at 50 °C for 12 h.
Under the optimized conditions, we chose other epoxide substrates to evaluate the
catalytic universality of 1. The higher yields (89%, 91%) were obtained with the
presence of an electronꢀwithdrawing group in the structure of substrates (entries 2ꢀ3,
Table 3), which contributed to easy ringꢀopening of substrates by nucleophilic
17
attack. In turn, substrates possessing electronꢀdonating groups were less reactive
(entries 4ꢀ8, Table 3). Moreover, cyclohexene oxide has two rings leading to high
steric hindrance, and the corresponding yield was more lower (entry 8, Table 3).
The reuse of catalyst is one of the significant aspects to evaluate catalyst
performance. Here, 1 possessed recyclability for at least six times with slightly loss in
activity (Fig. 2). From the FTꢀIR spectra analysis of the asꢀsynthesized and reused 1
−
1
(
Fig. S1), there appeared one new absorption peaks at 1650 cm , which attributed to
18
the stretching vibration of C═O in carbonate slightly adsorbed in 1. Hence, the
residual product partially covering the active sites of the catalyst is one of the reason
for the slight decrease of catalytic activity after recycle. The PXRD plots of reused
catalyst were almost no change compared with simulated one from 1 (Fig. S4),
indicating that the framework of 1 still remained intact. The reaction mixture filtrate
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of the last time recycling was analyzed by inductively coupled plasma (ICP) and only
.69 ppm of leakage from the framework 1 was found (Table S3). Therefore, 1 is a
promising catalyst with high stability, activity and recyclability.
0
2
Fig. 2 Recycle tests of 1 for the transformation reaction of CO with styrene oxide.
In order to explore the mechanism of this process, only 20 mg catalyst without
TBAB was conducted using styrene oxide as substrate and the yield was lower than
1
%, suggesting that the ringꢀopening process needs to overcome high energy barriers
19
without nucleophiles (entry 8, Table 2). When inorganic salts Zn(NO
3 2 2
) , Zn(OAc) ,
ZnSO and organic salt Zn(acac) as catalysts replaced compound 1 to conduct the
4
2
reaction, the yield was just 18%, 27%, 38% and 42%, respectively (entries 9ꢀ12,
Table 2). The results showed that inorganic salts with different anions and organic
salts could not effectively catalyze the cycloaddition reaction. Therefore, the plausible
mechanism is that epoxides are adsorbed onto 1 and activated by the unsaturated Zn
ꢀ
sites, and the selective ring opening occurs with nucleophilic Br attacking methylene
2
0ꢀ21
C−O bond of the terminal epoxides.
Then, CO and the oxygen anion of opened
2
epoxy ring interact to form alkylcarbonate salts. At last, the corresponding products of
cycloaddition reaction are got through ring closure (Fig. S6).
2
Table 2 Yields of Cycloaddition Reaction of CO with Styrene Oxide under
a
Various Reaction Conditions
8

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b
Entry Catalyst 1 (mg) TBAB (mol %) T(°C) t (h) Yield (%)
1
20
20
0
2.5
2.5
2.5
2.5
2.5
2.5
5.0
2.5
0
50
50
50
60
70
80
50
50
50
50
50
50
50
12
12
12
12
12
12
12
6
86
64
20
89
93
97
88
56
<1
18
27
38
42
c
1
2
3
4
5
6
7
8
20
20
20
20
20
20
0
12
12
12
12
12
d
9
2.5
2.5
2.5
2.5
e
10
0
f
11
0
g
12
0
a
Reaction conditions: styrene oxide (0.240 g, 2.0 mmol), catalyst, TBAB, solventꢀfree, CO (0.1
2
b
1
MPa); Determined by H NMR spectroscopy using 1,3,5ꢀtrimethoxybenzene as an internal
c
d
e
f
3 2 2 4
standard; crystal 1 without grinding; Zn(NO ) (5 mmol); Zn(OAc) (5 mmol); ZnSO (5
g
mmol); Zn(acac) (5 mmol).
2
Table 3 Yields of Cycloaddition Reaction of CO with Various Epoxides under
2
a
Optimized Conditions
b
Entry
1
Subs
Prod
Yield(%)
86
2
89
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3
4
5
6
7
8
91
57
51
42
33
27
a
Reaction conditions: epoxides (2.0 mmol), catalyst 1 (20 mg, about 5 mol %, based on Zn),
b
1
2
TBAB (0.016 g, 2.5 mol %), solventꢀfree, CO (0.1 MPa). Determined by H NMR spectroscopy
using 1,3,5ꢀtrimethoxybenzene as an internal standard.
Luminescent behaviors and sensing properties
Under excitation at 270 nm, the characteristic emission peak of 1 appears at 419
21
nm (Fig. S7), which is probably caused by intraligand transition. In order to
investigate whether 1 can probe anions, 12 mg sample of 1 and 1.95 mL of deionized
n n
water mixed to form a suspension, and then 50 ꢁL of Na X (K X) solution (0.1 mol/L)
ꢀ
ꢀ
ꢀ
3ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
ꢀ
2ꢀ
2ꢀ
2ꢀ
ꢀ
(
X = I , NO , Br , PO , OAc , BF , Cl , ClO , SO , F , C O , SO , CO , BrO ,
3 4 4 4 4 2 4 3 3 3
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
2ꢀ
N
3 3 4 4 2 7 4
, SCN , IO , MnO , IO , Cr O , CrO , respectively) was added into the above
ꢀ3
solution to obtain 1ꢀX suspension (2×10 mol/L). The corresponding luminescence
intensity was shown in Fig. 3. It was obvious that the luminescence of 1 decreased
2
ꢀ
2ꢀ
tremendously in the presence of Cr
2
O
7
/CrO
4
compared with other anions and
responsive time was about a few seconds, indicating that compound 1 can be seen as a
2
7
ꢀ
2ꢀ
high selectivity sensor of Cr O /CrO among various anions. On the other hand,
2
4
2
7
ꢀ
2ꢀ
mixed anions containing Cr
2
O
/CrO
4
were investigated for luminescence (Fig. S8).
The emission of 1 was quenched when mixed anions were added. So it was difficult to
2
7
ꢀ
2ꢀ
influence quenching effect of Cr
anions.
2
O
/CrO
4
on the emission by other introduced
1
0

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ꢀ3
Fig. 3 The luminescence intensity of 1 at 419 nm in 10 mol/L different anions.
2
ꢀ
2ꢀ
In order to explore the detection limit of the Cr O /CrO sensor, different
2
7
4
2
ꢀ
2ꢀ
ꢀ5
ꢀ1
concentration gradients of Cr
2
O
7
/CrO
4
(1×10 to 1×10 mol/L) solutions were
2
ꢀ
added into the suspension of 1, respectively, obtaining a series of 1ꢀCr
2
O
7
or
2
ꢀ
ꢀ7
ꢀ3
1
ꢀCrO4 (1×10 to 1×10 mol/L) suspensions. As shown in Fig. 4, luminescence
2
7
ꢀ
2ꢀ
intensity of 1 gradually reduced when the concentration of Cr
2
O
/CrO
4
increased.
The decrease of luminescence intensity still could be clearly seen under the
2
7
ꢀ
ꢀ6
2ꢀ
4
ꢀ6
concentration of Cr
2
O
at 10 mol/L and CrO
at 4×10 mol/L, manifesting that
ꢀ6
2ꢀ
7
the detection limit of 1 as a sensor can reach 10 mol/L for detecting Cr
2
O
and
ꢀ6
2ꢀ
4
×10 mol/L for detecting CrO
4
. In addition, to further study relationship between
2
ꢀ
2ꢀ
the quenching effect and the concentration of Cr
2
7 4
O /CrO , luminescence intensity
2ꢀ
2ꢀ
versus the Cr O /CrO concentration plots linearly obey the equation Ι /Ι = 1.087 +
2
7
4
0
2
7
ꢀ
2ꢀ
4
Ksv[Cr
2
O
] and Ι
0
/Ι = 0.93 + Ksv[CrO
] (the inset of Fig. 4) (I
0
and I represent the
2
7
ꢀ
2ꢀ
luminescence intensity of 1 before and after existing Cr
2
O
/CrO
4
, respectively;
2
ꢀ
2ꢀ
2ꢀ
2ꢀ
[
Cr O ]/[CrO ] represents the Cr O /CrO concentration, and K represents the
2 7 4 2 7 4 sv
quenching rate constant), which approach the SternꢀVolmer equation I
0
/I = 1 +
2
ꢀ
2ꢀ
3
2ꢀ
3
K
2 7 4 2 7
sv[Cr O /CrO ]. The Ksv value is 5.02 × 10 mol/L for Cr O and 3.02 × 10
2
4
ꢀ
2ꢀ
7
2ꢀ
mol/L for CrO
, indicating that Cr
2
O
/CrO
4
can efficiently quench on the
emission of 1.
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2
7
ꢀ
2ꢀ
Fig. 4 Emission spectra of 1 with different concentrations of Cr
2
O
ions (a) and CrO
4
ions (b),
2
ꢀ
2ꢀ
2 7 4
the inset: luminescence intensity vs the Cr O /CrO concentrations plots.
As is well known, it is important to reuse luminescent sensor in practical
2
ꢀ
2ꢀ
applications. Hence, recyclability of 1 as a Cr O /CrO luminescent sensor was
2
7
4
2
ꢀ
2ꢀ
4
ꢀ3
investigated. The 1ꢀCr
2
O
7
/1ꢀCrO
(2×10 mol/L) suspension was washed with
deionized water for three times, and the luminescence intensity of 1 and PXRD were
measured (Fig. 5, S9). It was clearly observed that after being recycled six times, the
luminescence intensity of 1 and PXRD plot were almost the same as the one without
1
2

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DOI: 10.1039/C7DT02819A
2
ꢀ
2ꢀ
dropping Cr
2 7 4
O /CrO , revealing that 1 can be recycled for at least six times with
negligible loss in luminescence response. In addition, the ICP results indicated that
2
7
ꢀ
2ꢀ
2ꢀ
2ꢀ
reused sample do not contain Cr
2
O
/CrO
4
2 7 4
(Table S3). Therefore, Cr O /CrO
can be removed completely by a rapid method.
Fig. 5 The luminescence intensity of compound 1 after six times of recycling under excitation at
2
ꢀ
2ꢀ
2
2 7 4
70 nm (blue: Cr O , orange: CrO ).
Here, the reasonable mechanism of quenching effect on the emission of 1 with the
2
7
ꢀ
2ꢀ
introduction of Cr
2
O
/CrO
4
is discussed. There are several reasons for quenching
9a,22
effect according to literatures:
(a) MOFs frameworks are destroyed. (b)
2
ꢀ
2ꢀ
2 7 4
Cr O /CrO
solution absorbs the energy of the excited light. (c) The collision
between ions and MOFs leads to energy losing. As for compound 1, after being
recycled six times, the PXRD plot was wellꢀmatched with the original one from 1,
which indicated the intact framework of 1. Hence, the quenching does not result from
the collapse of framework. On the other hand, UVꢀVis spectra of K
2 2
Cr O
7
and
K
2
CrO solution display the strong absorption at 257 and 352 nm for K
4
2
2 7
Cr O , 273
and 373 nm for K CrO (Fig. S10). Because the strong excitation wavelength of 1 is
2
4
2
7
ꢀ
2ꢀ
2
70 nm, Cr
2
O
/CrO
4
solution can remarkably absorb the energy of the excited light,
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3

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DOI: 10.1039/C7DT02819A
leading to the luminescence reduction or quenching of 1. Besides, the fluorescence
intensity of 1 can fit SternꢀVolmer equation, showing that the quenching effect is
23
attributed to dynamic quenching (that is, the collision interaction). Hence, the
2
7
ꢀ
2ꢀ
energy adsorption of Cr
2
O
/CrO
4
and the collision interaction between
2
7
ꢀ
2ꢀ
Cr O /CrO and framework expend the energy during energy transmission, and
2
4
finally result in the fluorescence quenching.
Conclusion
In summary, a new Znꢀtetrazole framework was synthesized by in situ ligand
synthesis under hydrothermal condition. The structure analysis reveals that compound
1
is a 3D framework, which is generated by ꢀ
2
ꢀOH group bridging adjacent 2D layers.
to epoxides under
0 °C and 0.1 MPa, and can be reused for at least six times. As a bifunctional material,
Furthermore, 1 can efficiently catalyze the cycloaddition of CO
2
5
2
ꢀ
2ꢀ
1
2 7 4
can act as a high selective, efficient and recyclable luminescent Cr O /CrO
ꢀ6
ꢀ6
sensor, and the detection limit can reach 10 mol/L and 4×10 mol/L, respectively.
Acknowledgements
This work was supported by the NSFC (Grants 21625103, 21571138 and
1473121) and the Key Laboratory of Advanced Energy Materials Chemistry
2
(
Ministry of Education, Nankai University, Opening Foundation).
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A novel 3D pillared-layer-like zinc-organic framework was synthesized through in situ generated
tetrazole ligand, displaying significant catalyst activity for conversion of CO and luminescent
2
2
-
2-
2 7 4
detection of Cr O / CrO .