Cadmium(II)–Triazole Framework as a Luminescent Probe for Ca2+and Cyano Complexes

Article abstract of DOI:10.1002/chem.201600209

A bidentate ligand, 1-{4-[4-(1H-1,2,4-triazol-1-yl)phenoxy]phenyl}-1H-1,2,4-triazole (TPPT), has been designed and synthesized. By using TPPT as a building block for self-assembly with Cd(NO₃)₂?4 H₂O and CdCl₂?10.5 H₂O, novel 1D double-chain {[Cd(TPPT)(NO₃)₂]?3 H₂O}_n(1) and 2D (4,4) layer [Cd(TPPT)Cl₂(H₂O)]_n(2) have been constructed. When 1 was employed as a precursor and exposed to DMF or N,N′-dimethylacetamide (DMAC), the crystals of 1 dissolved and reassembled into two types of brown block-shaped crystals of 1D double chains: {[Cd(TPPT)₂(NO₃)₂]?DMF}_n(1 a) and {[Cd(TPPT)₂(NO₃)₂]?DMAC}_n(1 b). The anion-exchange reactions of complex 2 have also been investigated. After gently stirring crystals of 2 in CHCl₃/C₂H₅OH/H₂O containing NaBr, NaI?2 H₂O, or NaOAc?3 H₂O, the crystals retained their crystalline appearances. A remarkable single crystal to single crystal transformation was observed and 1D double chains of {[Cd(TPPT)Br₂]?C₂H₅OH}_n(2 a) and {[Cd(TPPT)₂I₂]?CHCl₃}_n(2 b), and 1D single chains of [Cd(TPPT)(H₂O)₂(CH₃COO)₂]_n(2 c), can be obtained. Luminescent properties indicate that 1 shows excellent selectivity for Ca²⁺and cyano complexes. To the best of our knowledge, this is the first example of a luminescent probe for Ca²⁺based on triazole derivatives.

Full text of DOI:10.1002/chem.201600209

DOI: 10.1002/chem.201600209
Full Paper
&
Self-Assembly
2
+
Cadmium(II)–Triazole Framework as a Luminescent Probe for Ca
and Cyano Complexes
[a, c]
[a]
[a]
[a]
[a]
[a]
Ying Wang,
Ping Xu, Qiong Xie, Qing-Qing Ma, Yan-Hui Meng, Zi-Wen Wang,
[b, c]
[a]
[c]
[d]
Shaowei Zhang,*
Xiao-Jun Zhao,* Jun Chen,* and Zhong-Liang Wang*
Abstract: A bidentate ligand, 1-{4-[4-(1H-1,2,4-triazol-1-yl)-
phenoxy]phenyl}-1H-1,2,4-triazole (TPPT), has been designed
and synthesized. By using TPPT as a building block for self-
assembly with Cd(NO ) ·4H O and CdCl ·10.5H O, novel 1D
tions of complex 2 have also been investigated. After gently
stirring crystals of 2 in CHCl /C H OH/H O containing NaBr,
3
2
5
2
NaI·2H O, or NaOAc·3H O, the crystals retained their crystal-
2
2
line appearances. A remarkable single crystal to single crystal
transformation was observed and 1D double chains of
{[Cd(TPPT)Br ]·C H OH} (2a) and {[Cd(TPPT) I ]·CHCl } (2b),
3
2
2
2
2
double-chain {[Cd(TPPT)(NO ) ]·3H O} (1) and 2D (4,4) layer
3
2
2
n
[
Cd(TPPT)Cl (H O)] (2) have been constructed. When 1 was
2 2 n
2
2
5
n
2 2
3 n
employed as a precursor and exposed to DMF or N,N’-dime-
thylacetamide (DMAC), the crystals of 1 dissolved and reas-
sembled into two types of brown block-shaped crystals of
and 1D single chains of [Cd(TPPT)(H O) (CH COO) ] (2c), can
2 2 3 2 n
be obtained. Luminescent properties indicate that 1 shows
2
+
excellent selectivity for Ca and cyano complexes. To the
best of our knowledge, this is the first example of a lumines-
1D
double chains: {[Cd(TPPT) (NO ) ]·DMF} (1a) and
2 3 2 n
2
+
{
[Cd(TPPT) (NO ) ]·DMAC} (1b). The anion-exchange reac-
cent probe for Ca based on triazole derivatives.
2
3 2
n
Introduction
days, porous metal–organic frameworks (PMOFs) with dynamic
behavior have received considerable interest because these
functional coordination frameworks can exhibit guest-induced
Metal–organic frameworks (MOFs), a class of emerging porous
materials, are built from metal ions/clusters connected by or-
ganic building blocks, in which the pore structures and func-
[8]
structural changes of the host lattice. These porous frame-
works contain potential or strain energy and undergo dramatic
changes in functional properties and structure with the release
[
1–3]
tionalities are designable and predictable.
Because there are
[9,10]
numerous organic and inorganic functional moieties incorpo-
rated into the porous materials, MOFs demonstrate remarkable
properties for applications in many fields, such as lumines-
of energy in response to specific external stimuli.
An appro-
priate external stimulus can perturb the coordination sites of
porous frameworks and its connectivity by inducing the break-
[
4–7]
[11]
cence, gas storage, sensing, magnetics, and catalysis.
Nowa-
ing and generation of coordination bonds. Such a specific
system can offer researchers an experimentally unexplored
field to investigate and expand the subtle intermediate region
between flexibility and robustness through dynamic single-
crystal to single-crystal (SC–SC) and/or solid transformation
processes, involving cooperative movements of atoms in the
solid state, which has attracted considerable attentions in
[
a] Prof. Y. Wang, P. Xu, Q. Xie, Q.-Q. Ma, Y.-H. Meng, Dr. Z.-W. Wang,
Prof. Dr. X.-J. Zhao
Key Laboratory of Inorganic-Organic
Hybrid Functional Material Chemistry, Ministry of Education
College of Chemistry, Tianjin Normal University, Tianjin 300387 (P.R. China)
E-mail: hxxyzxj@mail.tjnu.edu.cn
[12]
recent years. The SC–SC transformation is extremely desira-
[b] Dr. S. Zhang
ble and useful, although it occurs relatively rarely, because it
Key Laboratory of Theoretical Organic Chemistry
and Functional Molecule of the Ministry of Education
School of Chemistry and Chemical Engineering
Hunan University of Science and Technology, Xiangtan 411201 (P.R. China)
E-mail: swzhang@hnust.edu.cn
[13]
allows unequivocal assignment of the obtained product.
Recent research in our group has mainly focused on the study
of anion- or solvent-exchange properties and organic-group-
[14]
functionalized aromatic guest loaded host–guest complex.
[
c] Prof. Y. Wang, Dr. S. Zhang, Prof. Dr. J. Chen
Key Laboratory of Advanced Energy Materials Chemistry
Ministry of Education, Nankai University, Tianjin 300071 (P.R. China)
E-mail: chenabc@nankai.edu.cn
Along this line, many researchers are interested in developing
novel metal-based guest receptors that can function efficiently
and selectively in aqueous or organic solvent environments.
Recently, significant progress has been made in the use of
the luminescence properties of MOFs for the sensing of small
[d] Prof. Dr. Z.-L. Wang
Tianjin Key Laboratory of Water Resources and Environment Tianjin Normal
University, Tianjin 300387 (P.R. China)
E-mail: wangying790601@163.com
[15]
[16]
[17]
molecules, metal ions, and explosives. Generally, diverse
pore topologies and functional sites make MOFs suitable sen-
sory materials through molecular-level interactions between
zhongliang_wang@163.com
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201600209.
[16g]
the framework and the analytes.
An efficient strategy to
Chem. Eur. J. 2016, 22, 1 – 17
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2
prepare MOFs for the use in metal-ion sensing is to use aro-
matic organic molecules with nonbonded functional ligand
sites, in which the aromatic part provides luminescence, and
ligand TPPT with L symmetry has never been reported in coor-
dination chemistry up to now. The continuous development of
new ligand systems is important for the development of MOF
[18]
II
the nonbonded functional sites interact with the metal ions.
chemistry. By using the phenoxy-based ligand TPPT, two Cd
However, immobilization of functional sites within the MOFs is
still challenging due to their high reactivity during the synthe-
complexes, {[Cd(TPPT)(NO ) ]·3H O} (1) and [Cd(TPPT)Cl (H O)]
n
3
2
2
n
2
2
(2), have been constructed (Scheme 1). When 1 was employed
as a precursor and exposed to DMF or DMAC, through
our careful observation, the crystals of 1 were dissolved
and reassembled into two types of yellow crystals:
{[Cd(TPPT) (NO ) ]·DMF} (1a) and {[Cd(TPPT) (NO ) ]·DMAC}
[
16n]
sis of MOFs.
However, the design and synthesis of such materials is still
a tremendous challenge for researchers because of many fac-
tors, such as reaction temperature, solvent, anion, and molar
ratio, although much progress has been made in practical and
theoretic approaches. Among the strategies used, judiciously
choosing a suitable polydentate organic ligand to construct
the desirable product for self-assembly between metal ions
2
3 2
n
2
3 2
n
(1b; Scheme 1). We also investigated the anion-exchange reac-
tions of complex 2. After gently stirring crystals of 2 in a mix-
ture of CHCl /C H OH/H O containing NaBr, NaI·2H O, and
3
2
5
2
2
NaOAc·3H O, the crystals retained their crystalline appearan-
2
[
19]
and ligands has been receiving increasing attention. General-
ly, the preparation of such materials can be influenced by
a number of factors, such as crystallization conditions, ligand/
metal ratio, reaction systems of different solvents, and the
nature of organic linkers. Particularly, the organic building
blocks play an important role in the construction of MOFs with
versatile structures. It is widely known that five-membered het-
erocycles, such as imidazole, pyrazole, triazole, and tetrazole,
are good candidates in the design and synthesis of functional
MOFs. Among them, 1,2,4-triazole and its derivatives have at-
tracted great interest as multidentate ligands, which can
bridge different metal centers to construct many novel coordi-
nation functional frameworks because of their versatile bridg-
ces. A remarkable SC–SC transformation was observed and
two 1D double chains of {[Cd(TPPT)Br ]·CH CH OH} (2a),
2
3
2
n
and {[Cd(TPPT) I ]·CHCl } (2b), and a 1D single chain of
2
2
3 n
[Cd(TPPT)(H O) (CH COO) ] (2c; Scheme 1), could be obtained.
2
2
3
2 n
Luminescent properties indicate that 1 shows excellent selec-
2
+
tivity for Ca . Complexes 1, 2, and 2c exhibit strong ligand-
originated photoluminescence emissions, which are selectively
sensitive to electron-deficient nitroaromatic explosives, such as
nitrobenzene (NB), 1,4-dinitrobenzene (p-DNB), 1,3-dinitroben-
zene (m-DNB), and 1-fluoro-4-nitrobenzene (FNB). These prop-
erties make complexes 1, 2, and 2c potential fluorescence sen-
sors for these chemicals. Furthermore, complex 2 can detect
cyano complexes, such as K [Cr(CN) ], K [W(CN) ], K [Mn(CN) ],
3
6
4
8
3
6
[
20]
ing features.
On the basis of the above considerations,
Na [W(CN) ], Na [Mo(CN)] , Cs [W(CN)] , [NBu ][Mo(CN) ], [NBu ]
3 8 3 8 3 8 3 8 3
herein, we describe the design and synthesis of a new biden-
[W(CN) ], and Rb [W(CN) ]. To the best of our knowledge, this
8 3 8
tate ligand, 1-{4-[4-(1H-1,2,4-triazol-1-yl)phenoxy]phenyl}-1H-
is the first report on the application of MOFs for the sensing of
cyano complexes.
1,2,4-triazole (TPPT). To the best of our knowledge, the flexible
Scheme 1. Synthesis of complexes 1, 1a, 1b, 2, 2a, 2b, and 2c.
Chem. Eur. J. 2016, 22, 1 – 17 www.chemeurj.org
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Results and Discussion
Structural descriptions of TPPT
TPPT crystallizes in the monoclinic crystal system with space
group P21/c. The fundamental structural unit of TPPT is shown
in Figure 1. The dihedral angles between the triazole and ben-
zene rings are 10.2 and 1.98, respectively, while the dihedral
angle between the two benzene rings is 668. Crystallographic
data, selected bond lengths, and bond angles of TPPT are
listed in Tables S1 and S2.
Figure 2. The fundamental structural unit of 1.
The CdꢀN bond lengths are 2.326(3) and 2.361(1) ꢁ (Table 2),
respectively, whereas the axial CdꢀO distance is 2.344(3) ꢁ,
which is shorter than that of CdꢀO (2.373 ꢁ) in [Cd (m -
2
2
1
1
1
L ) (L ) (NO )(m -NO )(H O) ](NO ) ·1.75H O (L =4-(pyrid-2-yl)-
3
2
3
2
21]
3
2
2
3 2
2
[
1
,2,4-triazole) and CdꢀO (2.3563(18) ꢁ) in Cd(L) (NO ) ·2(THF)
2
3 2
[22]
(
L=3,5-bis[3-pyridyl-3-(3’-methylphenyl)-1,3,4-oxadiazole]).
II
The Cd nodes are connected to each other to form an infinite
D chain that consists of a 32-membered bimetallic macrocy-
1
Figure 1. The fundamental structural unit of TPPT. Light gray, C; medium
gray, N; dark gray, O.
cle-containing building block (Figure S1a), in which the termi-
nal triazole groups on each cis-TPPT ligand are basically per-
pendicular to each other. The dihedral angle between the tria-
zole and benzene rings is 10.2 and 19.48, respectively, much
less than that of two terminal triazole groups (78.68).
Structural descriptions of complex 1
Complex 1 crystallizes in the triclinic crystal system with space
group P 1¯ (Table 1). As shown in Figure 2, the fundamental
In each elliptical ring, the Cd···Cd contact is around 16 ꢁ,
whereas the opposite phenoxy O···O distance is around 10 ꢁ.
These 1D macrocycle-containing double chains (Figure 3) stack
together in an ꢀAAꢀ fashion along the crystallographic a axis
to generate distorted quadrangle-like channels (Figure S1b), in
structural unit of 1 contains one crystallographically independ-
II
ꢀ
ent Cd ion, one TPPT ligand, two terminally coordinated NO3
II
anions, and three crystal lattice water molecules. Each Cd
center lies on a crystallographic inversion center and adopts
a slightly distorted octahedral {CdN O } environment, involving
ꢀ
which the coordinated NO3 anions and water guest molecules
are located; this is further confirmed by thermogravimetric
analysis (TGA). TGA revealed that the encapsulated water mol-
ecules could be completely removed at temperatures ranging
4
2
four N atoms from four TPPT ligands and two O atoms from
two monodentate nitrate.
[
a,b]
Table 1. Crystallographic data and details of refinements for complexes 1, 1a, 1b, 2, 2a, 2b, and 2c.
1
1a
1b
2
2a
2b
2c
formula
C
32
H
30CdN14
O
11
C
35
H
31CdN15
O
9
C
36
H
33CdN15
O
9
C
16
H
18CdCl
2
N
6
O
3
C
18
H
18Br
2
CdN
6
O
2
C
33
H
25CdCl
3
I
2
N
12
O
2
20 6 7
C H22CdN O
ꢀ
1
M
r
[gmol
]
899.10
triclinic
P1¯
918.15
triclinic
P1¯
932.17
triclinic
P1¯
525.66
triclinic
P1¯
622.60
triclinic
P1¯
1094.20
triclinic
P1¯
570.84
monoclinic
P21/c
crystal system
space group
T [K]
296(2)
173(2)
173(2)
173(2)
296(2)
296(2)
296(2)
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
8.0811(9)
10.6838(10)
12.4221(13)
110.930(2)
105.489(2)
98.246(2)
930.74(17)
1
7.8147(10)
12.3663(16)
19.775(2)
82.610(2)
82.357(2)
73.666(2)
1809.2(4)
2
7.8957(5)
12.4931(8)
19.8295(12)
82.1260(10)
83.0880(10)
75.4730(10)
1868.1(2)
2
7.6240(6)
11.5346(9)
7.8782(9)
11.9129(13)
12.6519(15)
103.229(2)
107.760(2)
104.294(2)
1034.6(2)
2
8.2403(4)
12.4512(6)
13.4303(19)
10.7261(15)
16.355(2)
90
104.988(2)
90
12.6334(10)
104.2300(10)
106.0110(10)
103.4370(10)
979.92(13)
2
19.8409(10)
82.8880(10)
84.2980(10)
72.6360(10)
1923.80(16)
2
b [8]
g [8]
3
V [ꢁ ]
2275.8(6)
4
Z
F (000)
456
1.604
0.666
932
1.685
0.684
948
1.657
0.664
524
1.782
1.418
604
1.999
4.945
1056
1.889
2.429
1152
1.666
1.014
ꢀ
3
1
calcd [mgm
]
ꢀ
1
m [mm
]
data/restraints/parameters
3283/0/250
1.006
0.0346
6368/88/561
1.051
0.0706
6583/0/553
1.040
0.0318
3423/0/235
1.083
0.0194
3627/42/276
1.050
0.0458
6723/60/491
1.050
0.0364
4011/0/309
1.049
0.0210
0.0586
2
GOF on F
[
a]
R
1
(I=2s(I))
(all data)
[
b]
wR
2
0.0753
0.1775
0.0690
0.0509
0.1254
0.1009
2
2
c
2
2 2 1/2
o
[a] R
1
=Sj jF
o
jꢀjF
c
j j/jF
o
j. [b] wR
2
=[Sw(jF
o
j ꢀjF j /wj F j ]
.
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[
a]
Table 2. Selected bond lengths [ꢁ] and angles [8] for complexes 1, 1a, 1b, 2, 2a, 2b, and 2c.
1
Cd1ꢀN3
2.326(2)
180.00(12)
97.45(8)
94.22(7)
Cd1ꢀO2#1
2.344(2)
97.45(8)
180.0
Cd1ꢀN6#2
2.361(2)
N3-Cd1-N3#1
N3#1-Cd1-O2
N3#1-Cd1-N6#2
N3-Cd1-O2#1
O2#1-Cd1-O2
O2#1-Cd1-N6#2
N3#1-Cd1-O2#1
N3-Cd1-N6#2
O2-Cd1-N6#2
82.55(8)
85.78(7)
98.65(8)
81.35(8)
1
a
Cd1ꢀO6
2.259(6)
2.334(5)
83.1(2)
85.44(19)
177.70(19)
81.94(19)
101.8(2)
Cd1ꢀN12#1
Cd1ꢀO3
2.302(5)
2.349(5)
99.8(2)
96.49(17)
81.06(18)
92.40(16)
80.29(18)
Cd1ꢀN3
2.326(5)
2.363(5)
Cd1ꢀN9
Cd1ꢀN6#1
O6-Cd1-N12#1
O6-Cd1-N9
O6-Cd1-O3
N12#1-Cd1-N6#1
O6-Cd1-N6#1
O6-Cd1-N3
N12#1-Cd1-N9
N3-Cd1-O3
N9-Cd1-O3
O3-Cd1-N6#1
N12#1-Cd1-N3
N3-Cd1-N9
N12#1-Cd1-O3
N3-Cd1-N6#1
N9-Cd1-N6#1
171.44(17)
91.79(17)
96.34(18)
89.57(18)
172.27(17)
1
b
Cd1ꢀN9
2.312(2)
2.3316(19)
93.48(7)
94.35(7)
83.55(7)
97.93(7)
89.55(7)
Cd1ꢀN12#1
2.318(2)
171.59(7)
82.69(7)
80.87(7)
176.42(8)
82.74(7)
Cd1ꢀO6
2.359(2)
97.60(7)
99.31(7)
79.92(8)
178.67(8)
97.92(7)
Cd1ꢀO4
N3-Cd1-N12#1
N3-Cd1-O4
N9-Cd1-O4
N12#1-Cd1-O4
N12#1-Cd1-O6
O4-Cd1-O6
N3-Cd1-O6
N9-Cd1-N3
N9-Cd1-N12#1
N9-Cd1-O6
O6-Cd1-N6#1
N3-Cd1-N6#1
O4-Cd1-N6#1
N9-Cd1-N6#1
N12#1-Cd1-N6#1
2
Cd1ꢀN3
2.2970(18)
2.6119(6)
103.42(7)
163.55(5)
83.36(5)
Cd1ꢀN6#1
2.314(2)
2.6939(6)
87.90(5)
86.43(5)
88.79(5)
86.55(5)
108.171(17)
Cd1ꢀCl2#2
2.5935(5)
2.8322(6)
155.55(5)
88.181(19)
114.287(19)
81.50(5)
Cd1ꢀCl1
Cd1ꢀCl1#3
Cd1ꢀCl2
N3-Cd1-N6#1
N3-Cd1-Cl1
N3-Cd1-Cl1#3
Cl1-Cd1-Cl1#3
Cl2#2-Cd1-Cl2
N3-Cd1-Cl2#2
N6#1-Cd1-Cl1
N6#1-Cd1-Cl1#3
N3-Cd1-Cl2
N6#1-Cd1-Cl2#2
Cl2#2-Cd1-Cl1
Cl2#2-Cd1-Cl1#3
N6#1-Cd1-Cl2
Cl1#3-Cd1-Cl2
83.710(18)
77.589(19)
Cl1-Cd1-Cl2
164.003(18)
2
a
Br1ꢀCd1#1
2.7329(5)
2.8181(6)
2.7329(5)
95.149(17)
160.09(10)
89.150(16)
108.359(19)
83.48(10)
Br1ꢀCd1
2.9970(6)
2.316(4)
Br2ꢀCd1
2.7523(6)
2.335(3)
101.765(18)
87.99(7)
87.89(10)
90.98(10)
86.96(10)
168.758(16)
Br2ꢀCd1#2
Cd1ꢀN6#3
Cd1ꢀN3
Cd1ꢀBr1#1
Cd1ꢀBr2#2
2.8181(6)
98.92(13)
167.22(10)
84.24(10)
84.850(17)
104.640(17)
Cd1#1-Br1-Cd1
N6#3-Cd1-Br1#1
N3-Cd1-Br2
N3-Cd1-Br2#2
N6#3-Cd1-Br1
Br2#2-Cd1-Br1
Cd1-Br2-Cd1#2
N3-Cd1-Br1#1
Br1#1-Cd1-Br2
Br1#1-Cd1-Br2#2
N3-Cd1-Br1
N6#3-Cd1-N3
N6#3-Cd1-Br2
N6#3-Cd1-Br2#2
Br2-Cd1-Br2#2
Br2-Cd1-Br1
2
b
Cd2ꢀN12#1
2.380(4)
2.423(4)
Cd2ꢀN9
2.385(4)
Cd2ꢀN3
2.409(4)
Cd2ꢀN6#2
Cd2ꢀI1
2.9174(5)
90.06(14)
84.55(16)
92.64(11)
89.41(10)
91.18(11)
Cd2ꢀI2
2.9400(5)
173.63(15)
90.26(15)
91.15(10)
89.89(11
N12#1-Cd2-N9
N12#1-Cd2-N6#2
N12#1-Cd2-I1
N6#2-Cd2-I1
N3-Cd2-I2
95.16(15)
179.34(14)
88.39(10)
91.03(11)
86.51(10)
N12#1-Cd2-N3
N9-Cd2-N6#2
N9-Cd2-I1
N12#1-Cd2-I2
N6#2-Cd2-I2
N9-Cd2-N3
N3-Cd2-N6#2
N3-Cd2-I1
N9-Cd2-I2
I1-Cd2-I2
176.789(15)
2
c
Cd1ꢀO4
2.2550(16)
2.3333(19)
103.31(6)
95.36(7)
82.32(6)
93.30(6)
Cd1ꢀO6
2.3137(16)
2.3355(15)
98.75(7)
Cd1ꢀN6#1
Cd1ꢀO7
2.3331(18)
2.3641(17)
87.39(7)
164.89(7)
93.90(6)
Cd1ꢀN3
Cd1ꢀO2
O4-Cd1-O6
O4-Cd1-N3
O4-Cd1-O2
N3-Cd1-O2
N6#1-Cd1-O7
O4-Cd1-N6#1
O6-Cd1-N3
O6-Cd1-O2
O4-Cd1-O7
N3-Cd1-O7
O6-Cd1-N6#1
N6#1-Cd1-N3
N6#1-Cd1-O2
O6-Cd1-O7
O2-Cd1-O7
84.13(7)
173.99(6)
169.35(6)
86.35(7)
87.32(6)
87.09(6)
80.78(7)
[
a] Symmetry transformations used to generate equivalent atoms: for 1: #1 ꢀx+2, ꢀy, ꢀzꢀ1 #2 ꢀx+1, ꢀy, ꢀz #3 x+1, y, zꢀ1 #4 xꢀ1, y, z+1; for 1a: #1
xꢀ1, yꢀ1, z #2 x+1, y+1, z; for 1b: #1 x+1, y+1, z #2 xꢀ1, yꢀ1, z; for 2: #1 x+2, y, z+1 #2 ꢀx+2, ꢀy, ꢀz+2 #3 ꢀx+3, ꢀy, ꢀz+2 #4 xꢀ2, y, zꢀ1; for
a: #1 ꢀxꢀ1, ꢀy+1, ꢀz #2 ꢀx, ꢀy+1, ꢀz #3 xꢀ2, y, zꢀ1 #4 x+2, y, z+1; for 2b: #1 x+1, y+1, z #2 xꢀ1, yꢀ1, z; for 2c: #1 xꢀ1, y, zꢀ1 #2 x+1, y, z+1.
2
from 200 to 2208C (calculated 6.00%, observed 5.81%; Fig-
ure 4a). The powder X-ray diffraction (PXRD) patterns (Fig-
ure 4b) based on the desolvated sample of 1 confirm that the
framework of 1 is stable.
&
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Figure 3. The 1D double-chain structure of 1 along the a axis. Black, Cd; light gray, C; medium gray, N; dark gray, O.
Figure 5. The fundamental structural unit of 2 (30% displacement ellipsoids
for the non-hydrogen atoms).
tween 1 and 2 lies in the location of the anions. As mentioned
ꢀ
above, the NO3 anions in 1 serving as terminal-coordinated li-
ꢀ
gands face toward the center of the channel, whereas the Cl
anions in 2 act as bridging ligands to connect two neighboring
II
Cd ions, forming a 2D four-connected network with (4,4) top-
ology (Figure S2). Again, the PXRD pattern indicated that the
as-synthesized complex 2 was pure (Figure 7b).
Figure 4. a) TGA trace of 1. The calculated and observed weight losses corre-
sponding to three encapsulated crystal lattice water molecules are 6.00 and
Molecular reassembly during the solvent-exchange process
5.81%, respectively. b) PXRD patterns of 1. Black straight line, simulated;
black dotted line, as-synthesized.
[14c]
In our previous work,
we employed mononuclear complex
[
Mn(tatrz) (SCN) (CH OH)]·2H O (tatrz=1-[9-(1H-1,2,4-triazol-1-
2
2
3
2
yl)anthracen-10-yl]-1H-1,2,4-triazole) to synthesize the reactive,
organic-group-functionalized, aromatic-guest-loaded, host–
guest 2D layer {[Mn(tatrz) (SCN) ]·(atan)} (atan= anthracene).
Structural descriptions of complex 2
Complex 2 is characterized by X-ray single-crystal analysis and
crystallizes in the monoclinic system, space group P21/
c (Table 1<xtabr1). As depicted in Figure 5, Cd1 is six-coordi-
nated by three chloride anions (Cl1, Cl2, and Cl2A), two nitro-
gen atoms from two TPPT ligands (N3 and N6B), and one coor-
dinated aqua oxygen O2 atoms, forming slightly distorted oc-
2
2
n
II
After gently stirring the mononuclear Mn complex for 6 h, the
complex dissolved and a remarkable reassembly process oc-
II
curred. The mononuclear Mn complex was converted into the
novel 2D coordination framework, encapsulating atan as an or-
ganic template. Encouraged by our results in reassembly,
herein, we exposed the light-yellow crystals of complex 1 to
DMF or DMAC for 6 h. We observed that crystals of 1 dissolved
and reassembled into another two brown crystals of an iso-
morphic solvate of 1a or 1b. X-ray analysis revealed that the
1D chain families of 1a and 1b were supramolecular isomers,
although they are topologically equivalent (Figures S3 and S4).
tahedral coordination geometry. Every TPPT adopts m -briding
2
modes and the dihedral angles between the benzene ring and
triazole moiety are 18.5 and 33.38, respectively, which indicates
a spatial distortion effect. Two m -bridging chloride anions con-
2
II
II
nect two neighboring Cd ions to form a binuclear Cd cluster,
in which the Cd···Cd separation is 3.849(3) ꢁ.
II
13
1
Such binuclear Cd clusters, {Cd Cl }, act as secondary build-
On the other hand, the C and H NMR spectra (Figures S5
and S6), together with TGA measurements (Figures S7 and S8)
on the exchanged sample, demonstrated that the encapsulat-
ed water molecules were simultaneously replaced by DMF or
DMAC molecules when the reaction was performed in DMF or
DMAC. The structures of 1a and 1b are essentially isostructural
to that of 1, with similar cell dimensions and the same gross
structural features (detailed bond parameters can be obtained
from the archived CIF files). Single-crystal XRD analysis revealed
2
2
ing blocks (SBUs) and can be further linked through four bridg-
ing TPPT ligands to form a 2D porous framework (Figure 6).
Topologically, if each {Cd Cl } cluster is considered as a basic
2
2
node of a simplified network, then the topology of 2 can be
regarded as a four-connected node and m -TPPT tecton linker.
2
The TGA trace indicated that the coordinated water molecule
could be removed by heating from 100 to 1508C (calcd:
3.42%, obsd: 3.79%; Figure 7a). The remarkable difference be-
Chem. Eur. J. 2016, 22, 1 – 17
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Figure 6. The 2D porous framework of 2 along the c axis. Black, Cd; light gray, C; medium gray, N; dark gray, O; white, Cl.
reveal that the ligand TPPT can provide favorable conditions
for the formation of CdꢀN coordination bonds through the
free torsion of CꢀN bonds.
Anion-exchange properties and transformation from a 2D
layer to 1D double- or single-chain structures
The SC–SC structural transformations, which involve coopera-
tive movements of atoms in the solid state, have received con-
[23]
siderable attention in recent years. The SC–SC transforma-
tion is extremely useful and desirable, although it occurs rela-
tively rarely, because it allows unequivocal assignment of the
[13]
product obtained. Usually, through the SC–SC transforma-
tion, new complexes, which cannot be obtained under conven-
[24]
tional conditions, can be formed in high yield. Materials that
show reversible structure transformations and a characteristic
[25]
response toward specific external stimuli, such as light, tem-
[26]
[27]
perature, and guest molecules, are vitally important for
applications in sensing, molecular capture, switches, and so
[28]
on. However, studies on the changes in metal coordination
geometry caused by the removal and addition of ligands from
the network itself through the SC–SC transformation remain
[29]
less common.
Generally, MOFs have low solubility and high stability in
common solvents; therefore, these frameworks can retain their
morphology through a solvent-assisted solid-state reaction, al-
though in some examples the solid materials may lose their
crystallinity. In recent years, previous research also demonstrat-
ed that solvent molecules could induce SC–SC transformations.
In most examples, guest moieties of diverse shapes and sizes
can be encapsulated in the MOFs cavities through various in-
termolecular interactions. Therefore, MOF products in such
conversion processes exhibit a certain shape flexibility and size
specificity, and have wide applications in many fields, such as
selective molecular/ion recognition, separation, and molecular/
2
Figure 7. a) TGA trace of 2. The calculated amount of coordinated H O for 2
is 3.42%, and the observed amount is 3.79%. b) PXRD patterns of 2. Black
straight line, simulated; black dotted line, as-synthesized.
that the Cd···Cd separations in 1a and 1b were 16.381 and
16.368 ꢁ, respectively. The dihedral angles between benzene
rings and triazole moieties are 23.5, 45.2, 19.9, and 2.38 in 1a
and 6.8, 43.4, 4.2, and 24.18 in 1b. The flexible dihedral angles
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[
30]
ion sensors. Although some related research in the construc-
tion of MOFs with framework structures by deliberately tuning
dimensions of 9.766(10)ꢂ11.021(13) ꢁ, than those of 1 (9.715
(9)ꢂ9.822(11) ꢁ), due to the larger size of encapsulated guest
molecules of C H OH than H O. TGA (Figure 9a) revealed that
[
31,32]
different kinds of solvent molecules
or different compo-
2
5
2
[
33]
nent ratios of mixed solvents have been reported, a particu-
lar series of MOF species that can be systematically tuned by
the two factors in combination and also undergo structural
transformations remain largely unexplored thus far. To further
investigate the effect of solvent–molecule exchange on the
SC–SC transformation, anion-induced crystal transformations,
especially SC–SC transformations, have been widely investigat-
encapsulated C H OH could be completely removed at temper-
2 5
atures ranging from 200 to 2698C (calcd: 8.75%, obsd: 8.64%).
The PRXD patterns (Figure 9b) based on the desolvated
sample of 2a confirm that the [Cd(TPPT) ] framework is stable.
2
Single-crystal analysis revealed that complexes 2b and
1 were isostructural (Figures S9 and S10). They all crystallized
II
II
in the triclinic space group P 1¯ (Table 1). The Cd ···Cd distance
[
14b,c,34]
ed for coordination frameworks recently.
Herein, PXRD
was about 16 ꢁ and encapsulated CHCl was located in the
3
2
and well-defined single-crystal diffraction analysis methods
were employed to monitor related dynamic conversions be-
tween some crystalline solids. Notably, for related dynamic
conversions between other MOFs, the product cannot be defi-
nitely characterized by the available methods; thus they are
quadrangle channels with dimensions of 9.828(5)ꢂ9.929(4) ꢁ .
not referred to herein. Recently, we obtained {[Cu(tatrz) -
2
ꢀ
(
NO ) ]·(CH OH)·4H O} , in which NO3 anions could be
3
2
3
2
n
ꢀ
completely exchanged by ClO4 in an irreversible SC–SC trans-
formation, as evidenced by the anion-exchange products of
[
14c]
{[Cu(tatrz) (H O) ](ClO ) ·4CH OH} .
Taking inspiration from
2
2
2
4 2
3
n
[
35]
the aforementioned points,
herein we investigated the
anion-exchange reaction of the 2D architecture of 2. After
gently stirring crystals of 2 (0.5 mmol) in a 1:8:1 solution of
CHCl /C H OH/H O containing NaBr·2H O, NaI·2H O, or NaOA-
3
2
5
2
2
2
c·3H O (5 mmol) for 6 h, the crystals retain their crystalline ap-
2
pearances, excluding dissolution or recrystallization processes.
A remarkable anion- and solvent-exchange in a SC–SC transfor-
mation was observed and two 1D double chains of 2a and
2
b, and a 1D single chain of 2c, can be obtained.
Single-crystal XRD studies revealed that 2a crystallized in
the triclinic crystal system with space group P 1¯ (Table 1). In 2a,
Cd1 coordinates to two nitrogen atoms (N3 and N6) from two
TPPT ligands and three bromide ions (Br1, Br2, and Br2A). The
bond lengths of CdꢀN and CdꢀBr are 2.316(4)–2.335(3) and
2
.7329(5)–2.9970(6) ꢁ (Table 2), respectively. As demonstrated
II
in Figure 8, the coordination environment of the Cd ion can
be viewed as a distorted tetragonal pyramid.
ꢀ
II
II
Two m -Br connect two Cd ions to form the binuclear Cd
2
cluster {Cd Br N }, which is extended into a 1D infinite chain
2
4
4
through four m -TPPT ligands. Careful investigation shows that
2
ꢀ
the intercalated C H OH molecules and coordinated Br play
2
5
key roles in differentiating between the two structures 2 and
a. The corresponding dihedral angles between the benzene
rings and triazole moieties in 2a are 10.8 and 22.38, respective-
ly. Interestingly, complex 2a has larger 1D channels, with the
Figure 9. a) TGA trace of 2a. The calculated amount of encapsulated
2
C
2
H
5
OH in {[Cd(TPPT)Br
.64%. b) PXRD patterns of 2a. Black straight line, simulated; black dotted
line, as-synthesized.
2 2 5 n
]·C H OH} is 8.75%, and the observed amount is
8
Figure 8. The 1D nanotubular structure of 2a encapsulating guest water molecules. Black, Cd; white, Br; dark gray, O; light gray, C; medium gray, N.
Chem. Eur. J. 2016, 22, 1 – 17 www.chemeurj.org ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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The dihedral angles between benzene and triazole rings in 2b
are 5.0 and 40.38, respectively. TGA (Figure S11a) revealed that
encapsulated C H OH could be completely removed at temper-
2
5
atures ranging from 150 to 2408C (calcd: 10.91%, obsd:
0.90%). The PRXD patterns based on the desolvated sample
1
of 2b confirmed that the 1D chain was stable (Figure S11b).
As shown in Figure 10, the asymmetric unit of 2c contains
II
one crystallographically independent Cd ion, one TPPT ligand,
ꢀ
two terminally coordinated CH COO anions, and two termi-
3
nally coordinated water molecules. The geometry of the Cd1
atom can be regarded as a distorted octahedron, which is co-
ordinated by two triazole nitrogen atoms from two TPPT (N3
ꢀ
and N6A), two terminally coordinated CH COO anions (O2
3
and O4), and two terminally coordinated water molecules (O6
and O7). The CdꢀN bond lengths are in the range of 2.333(1)–
2.333(3) ꢁ (Table 2), which are typical values for these bonds.
As illustrated in Figure 11, each TPPT bridges two neighboring
II
Cd ions to form the 1D single chain with a Cd···Cd distance of
18.282(23) ꢁ. TGA (Figure 12a) revealed that the coordinated
H O molecules could be completely removed at temperatures
2
ranging from 150 to 2508C (calcd: 3.15%, obsd: 3.35%). The
PRXD patterns (Figure 12b) based on the desolvated sample of
2
c confirmed that the 1D single chain was stable.
2
Figure 12. a) TGA trace of 2c. The calculated amount of coordinated H O
molecules in [Cd(TPPT)(H O) (CH COO) ] is 3.15%, and the observed
2 2 3 2 n
amount is 3.35%. b) PXRD patterns of 2c. Black straight line, simulated;
black dotted line, as-synthesized.
Figure 10. The fundamental structural unit of 2c (30% displacement ellip-
soids for the non-hydrogen atoms).
pected that the double-bond-based ligand TPPT will exhibit
photoluminescence properties. Previous research also con-
firmed that coordination polymers had the ability to affect the
emission strength and wavelength of organic materials
through the judicious incorporation of different central metal
Luminescence behavior and sensing properties
Aromatic organic molecules and inorganic–organic hybrid co-
ordination complexes were investigated for their photolumi-
nescent properties and for potential applications as lumines-
[38]
ions. Herein, the luminescent properties of TPPT and com-
plexes 1, 1a, 1b, 2, 2a, 2b, and 2c in the solid state and in
DMF have been investigated.
[
36]
cent materials, such as light-emitting diodes (LEDs). Owing
to the ability to adjust the emission strength and wavelength
of organic materials, the construction of inorganic–organic co-
ordination complexes through the judicious incorporation of
transition-metal centers and conjugated organic spacers can
be an efficient strategy to synthesize new kinds of photolumi-
nescent materials. It is known that a double bond is composed
of s and p bonds, and the emissions of organic ligands are
At ambient temperature, strong green fluorescence for TPPT
and complexes 1, 1a, 1b, 2, 2a, 2b, and 2c in the solid state
is visible in daylight by irradiation with UV light. The emission
spectra are shown in Figure 13; all of the complexes and TPPT
were excited at l=(385ꢁ2) nm. The main emission bands of
TPPT and complexes 1, 1a, 1b, 2, 2a, 2b, and 2c are located
at l=525, 515, 511, 492, 487, 518, 526, and 546 nm, respec-
[
37]
usually ascribed to p*!n or p!p* transitions. It is then ex-
Figure 11. The infinite 1D single chain of 2c. Black, Cd; dark gray, O; light gray, C; medium gray, N.
Chem. Eur. J. 2016, 22, 1 – 17 www.chemeurj.org
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tively, exhibiting strong green fluorescence with a slightly dif-
ferent band shape. All complexes also exhibit some low-
energy emission bands. The different band shapes in the lumi-
nescent emissions might be due to different structural topolo-
gies. The emissions of complexes 1, 1a, 1b, 2, 2a, 2b, and 2c
are neither metal-to-ligand charge transfer (MLCT) nor ligand-
to-metal charge transfer (LMCT) in nature and can probably be
assigned to intraligand fluorescent emission because very simi-
lar emissions are also observed for the free TPPT ligand. The
enhancement of intraligand fluorescence in complexes 1, 1a,
1
b, 2, 2a, 2b, and 2c is probably due to the coordination of
II
TPPT to Cd , which increases the conformational rigidity of the
ligand, thereby reducing the nonradiative decay of the intrali-
[
39]
gand (p–p*) excited state.
Figure 14. Emission spectra of TPPT and complexes 1, 1a, 1b, 2, 2a, 2b, and
ꢀ
3
ꢀ1
2
c in DMF at room temperature (1ꢂ10 molL ).
stand this experimental phenomenon, the same experiments
2
+
2+
were performed with the introduction of Mg (MgCl ), Ni
2
2
+
(
NiCl ), and Zn
(ZnCl ) ions into the system. The results
2
2
reveal that the luminescence bands are not enhanced, but
rather the luminescent intensities of 1 decrease. It is interest-
2
+
2+
ing that, upon adding Cd (CdCl ) or Co (CoCl ) ions, the
2
2
emission intensity of 1 exhibits almost the same intensity as
that of 1. The above experimental results support the idea that
the luminescent emission of 1 shows excellent selectivity for
2
+
Ca . This is the first example of a 1D coordination complex
2
+
based on triazole derivates as a luminescent probe of Ca
.
2
+
However, when adding one to three equivalents of M ions
2
+
2+
2+
2+
2+
2+
Figure 13. Emission spectra of TPPT, complexes 1, 1a, 1b, 2, 2a, 2b, and 2c
in the solid state at room temperature. All compounds were excited at
l=(385ꢁ2) nm.
(M=Cd , Ca , Co , Mg , Ni , and Zn ) with respect to
a, 1b, and 2, 2a, 2b, and 2c, the luminescence bands are
1
not enhanced, but rather decrease, as illustrated in Figur-
es S12–S17.
As displayed in Figure 14, TPPT and complexes 1, 1a, 1b, 2,
a, 2b, and 2c exhibit broad blue fluorescence in DMF. All of
the complexes in DMF are excited at l=(365ꢁ5) nm. The
main emission bands of the complexes are located at l=540,
In addition, we have examined the plausible modulation of
its porous network by means of ion-exchange processes of the
extra-framework cations. The results show that the ion-ex-
change processes in these systems lead to profound changes
2
2
+
2+
2+
4
34, 446, 438, 477, 508, 516, and 522 nm, respectively, exhibit-
in the luminescent properties. The radii of Cd , Ca , Co ,
2
+
2+
2+
ing strong green fluorescence with slightly different band
shapes. The fluorescent emissions can probably be assigned to
intraligand fluorescent emission because similar behavior is
also observed for the free TPPT ligand in DMF. Coordination of
the complexes leads to slight redshifts of the emissions. Com-
pared with the fluorescent emissions of 1, 1a, 1b, 2, 2a, 2b,
and 2c in solution, the emissions are redshifted and narrow;
this can be attributed to intermolecular interactions in the
solid state, most likely p–p* stacking interactions.
Mg , Ni , and Zn are 95, 100, 90, 57, 72, 69, and 74 pm, re-
2
+
spectively. Among these ions, perhaps the size of Cd may
coincide with the size of the cavity of the 1D double chain and
increase the luminescent intensity of 1.
With the development of modern society and industry, haz-
ardous chemicals, such as toxic ions and organic small mole-
cules, are increasingly released from industrial facilities and
other anthropogenic activities; these have adverse effects on
human health and the environment. Environmental pollutants,
such as poisonous gases, organic solvent vapors, heavy metals,
and anions, have both acute and chronic effects on human
health and consequently lead to heart attacks, lung cancer,
In our previous studies, the selectivity and sensitivity to
2
+
2+
2+
[14b,c]
Mg , Cd , and Zn were mainly investigated.
Inspired
by the aforementioned progress in the study of luminescent
probes based on triazole derivatives, herein, luminescent inves-
[40]
hepatosis, and other serious diseases. It is challenging and
of great significance to identify and monitor these environ-
mental pollutants through direct detection by the naked eye
through the development of advanced materials. Considering
the intense luminescent signal and visible luminescent colors,
Cd MOFs could be good candidates as luminescent sensing
materials for environmental pollutants. To explore the lumines-
2
+
tigations reveal that 1 can detect Ca ions with relatively high
sensitivity and selectivity. The emission intensity of 1 signifi-
2
+
cantly increases upon adding one to three equivalents of Ca
ions (from CaCl ) with respect to 1 (Figure 15). The highest
2
band at l=434 nm is about four times as intense as the corre-
2
+
sponding band in DMF without Ca ions. To further under-
Chem. Eur. J. 2016, 22, 1 – 17
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ꢀ
3
2+
Figure 15. Emission spectra of complex 1 in DMF (10 m) at room temperature (excited at l=400 nm) in the presence of 0–3 equivalents of Cd (top left),
2
+
2+
2+
2+
2+
Ca (top middle), Co (top right), Mg (bottom left), Ni (bottom middle), and Zn (bottom right).
2
+
cent properties of Cd MOFs in sensing, luminescent Cd cen-
ters and judiciously selected ligands are key factors to obtain
luminescent Cd MOFs with proper porosity and functional
groups to provide potential open Lewis acid or base sites for
specific host–guest interactions that can tune the luminescent
properties. There are several reported Cd MOFs for sensing
functions, which highlight the significance of luminescent
MOFs (Table 3). Importantly, a series of G ꢂCdL (L=4-amino-
the highest quenching efficiencies were 99.78%, 99.85%, and
99.92%, respectively. With the addition of the same amount of
other organic compounds, including alcohols (methanol, etha-
nol, n-propanol, and 2-propanol), amides (DMAC), ketones
(acetone), chloroalkanes (CH Cl and CHCl ), nitriles (CH CN), ni-
2
2
3
3
troaliphatics (e.g., nitromethane (NM) and tris(hydroxymethyl)-
nitromethane (THMNM)), and even other aromatic complexes
and heterocycles (toluene, pyridine, and morpholine), the max-
imum change in the emission intensity was no more than
44.3% for 1, 52.2% for 2, and 56.5% for 2c. The properties
make complexes 1, 2, and 2c potential fluorescence sensors
for nitroaromatic explosives.
n
2
3
,5-bis(4-pyridyl-3-phenyl)-1,2,4-triazole; n=1, 2) host–guest
[
41]
II
complexes reported by Dong et al. and Cd –guanazole (3,5-
[
42]
diamino-1,2,4-triazole) hybrid family reported by Yao et al.
exhibit interesting sensing of organic small-molecule solvents
and anions, respectively. The porosity and potential open
metal/organic group sites within Cd MOFs have played a signifi-
To further investigate the sensing properties of 1, 2 and 2c,
the emissive response was monitored by gradually increasing
the p-DNB content in emulsions of 1, 2, and 2c dispersed in
DMF. As displayed in Figure 17, the emission intensity de-
creased upon the addition of 5 ppm p-DNB and was nearly
completely quenched at a concentration of 150 ppm with
a high quenching efficiency of 90.6% for 1, 88.6% for 2, and
93.4% for 2c; these values are comparable to other MOF sen-
2
+
cant role on their sensing functionality, such as open Cd
sites for small-molecule sensing, hydrogen-bonding interac-
ꢀ
2+
tions for X , and open Lewis basic triazole sites for Cd
.
The fluorescence sensing ability of 1, 2, and 2c were exam-
ined with the addition of different organic compounds to the
suspension of the complexes. As shown in Figure 16, the addi-
tion of 4000 ppm nitroaromatics, such as NB, p-DNB, m-DNB,
and FNB, could almost quench the emissions of 1, 2, and 2c;
[
46]
1
1
sors for NB.
For [Zn (tib)(HL )(H L ) ]·2H O (tib=1,3,5-tris-
2 2 0.5 2
1
(1-imidazolyl)benzene; H L =biphenyl-3,3’,4,4’-tetracarboxylic
4
Table 3. Selected luminescent Cd MOF materials for sensing applications.
Cd MOF luminescent materials
Luminescent substrates
Ref.
[
a]
CdL
2
organic small molecules
TNP
derivatives of NB
anions
[41]
[45]
[43c]
[43b]
[
b]
[
[
[
Cd(NDC)0.5(PCA)]·Gx
NH (CH [Cd17(L)12(m
Cd (datrz)
[
c]
2
3
)
2
]
2
3
-H
2
O)
4
(DMF)
2
(H
2
O)
2
]·solvent
[
d]
5
4 4 2
X (OH) ]
[a] L=4-amino-3,5-bis(4-pyridyl-3-phenyl)-1,2,4-triazole. [b] NDC=2,6-napthalenedicarboxylic acid, PCA=4-pyridinecarboxylic acid, G=guest molecules,
TNP=2,4,6-trinitrophenol. [c] H
Chem. Eur. J. 2016, 22, 1 – 17
3
L=2,4,6-tris[1-(3-carboxylphenoxy)ylmethyl]mesitylene. [d] Hdatrz=3,5-diamino-1,2,4-triazole; X=Cl, Br.
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of NB was only 2000 ppm, the fluorescence intensity of the
II
suspension of this Zn complex at l=450 nm was decreased
by 90%. Furthermore, another 3D luminescent MOF,
[
NH (CH ) ] [Cd (L) (m -H O) (DMF) (H O) ]·solvent, shows high
2 3 2 2 17 12 3 2 4 2 2 2
sensitivity and a quick response toward the presence of a trace
amount of NB in solution or vapor state, which may be used
[43c]
II
for NB sensing applications.
Meanwhile, such a 3D Cd com-
plex can also detect trace amounts of derivatives of nitroben-
zene, such as 4-nitrotoluene (4-NT), m-DNB, and p-DNB. The
emission intensity decreased upon the addition of 5 ppm NB
and was nearly completely quenched at a concentration of
100 ppm with a high quenching efficiency of 92.5%, which
was higher than or comparable to other MOF sensors for
[43a,b,d]
NB.
As illustrated in Figures S18–S20, among the six nitro com-
pounds, complexes 1, 2, and 2c are more sensitive to p-DNB
than five other nitro compounds at room temperature, espe-
cially nitroaliphatics, such as NM and THMNM. Complexes 1, 2,
and 2c exhibit extremely high detection sensitivity towards p-
DNB explosives with high quenching efficiencies of 99.78,
99.81, and 99.90%, respectively. To date, several MOF-based
fluorescence sensors have been developed for the detection of
nitroaromatic explosives. For example, Li et al. reported two
[44]
highly luminescent MOFs,
[Zn (oba) (bpy)]·3DMA (H oba=
2 2 2
4
,4’-oxybis(benzoic acid)) and [Zn (bpdc) (bpee)]·2DMF
2
2
(
bpdc=4,4’-biphenyldicarboxylate, bpee=1,2-bipyridylethene),
which exhibit unique selectivity in the detection of nitroaro-
matics with different groups and high explosives. The excellent
fluorescence quenching response to 2,3-dimethyl-2,3-dinitro-
butane (DMNB, a taggant required by law in all commercial
plastic explosives) can be further attributed to pore confine-
ment of the analyte inside the molecular-sized cavities of such
II
Zn complexes; this facilitates stronger interactions between
DMNB and the host framework, as reflected by the relatively
small difference in the quenching percentages for NB, which
exhibits only 10% higher sensitivity (94% quenching at 10 s)
than that of DMNB. In [Zn (oba) (bpy)]·3DMA, NB quenches
2
2
the emission by as much as 84%, and the order of quenching
efficiency for selected nitroaromatics is NB>m-DNB>NTꢃp-
DNB>dinitrotoluene (DNT). Notably, this order is not fully in
accordance with the trend of electron-withdrawing groups,
but it is fully consistent when the vapor pressure of each ana-
lyte is also taken into consideration. The fact that NB exhibits
the strongest quenching effect can be attributed to two fac-
tors: the high vapor pressure and the strongly electron-with-
drawing ꢀNO group. Although the vapor pressure of NT is
2
comparable to that of NB, the quenching efficiency (29%) is
significantly less because of the presence of the electron-do-
Figure 16. Emission spectra of: a) 1, b) 2, and c) 2c dispersed in DMF with
the addition of 4000 ppm of different organic compounds.
nating ꢀCH group. Similarly, although m- and p-DNB have two
3
strongly electron-withdrawing ꢀNO groups, both have very
2
[
43a]
acid),
the photoluminescent intensity decreased to 50% at
low vapor pressures at room temperature. Interestingly,
Ghosh’s group demonstrated another luminescent 3D MOF
[Cd(NDC) (PCA)]·G (G=guest molecules; PCA=4-pyridineca-
a concentration of only 200 ppm, which allowed us to detect
II
small amounts of NB in solution. Another 2D Zn complex,
0.5
x
[45]
[
Zn (L)(bipy)(H O) ]·(H O) (DMF)
nyl)terephthalamide; bipy=4,4’-bipyridine), reported by Bu’s
(H L=bis-(3,5-dicarboxyphe-
4
boxylic acid) for the highly selective detection of TNP. To ex-
2
2
2
2
3
2
II
plore the ability of such a Cd complex to sense a trace quanti-
group could selectively detect NB through a redox fluores-
ty of nitro explosives, fluorescence-quenching titrations were
performed with the incremental addition of analytes to such
[
43b]
cence quenching mechanism.
When the additional amount
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quenching titrations were also performed with nitroaromatics,
such as 2,4,6-trinitrotoluene (TNT), 2,4-DNT, 2,6-DNT, m-DNB,
and NB, and nitroaliphatic compounds, such as DMNB, NM,
and 1,3,5-trinitro-1,3,5-triazacyclohexane. All other nitro com-
pounds showed little effect on the fluorescence intensity.
II
These results demonstrate that such a Cd compound has high
selectivity for TNP compared with other nitro compounds.
As shown in Figure 16, among the tested aromatic organic
compounds (toluene, benzene, and nitro compounds), the
emissions of 1, 2, and 2c can only be quenched by nitroaro-
matic explosives. Therefore, the fluorescence responses of 1, 2,
and 2c to nitro compound explosives were attributed to the
electron-transfer quenching mechanism, that is, in the pres-
ence of nitro compounds, the excited electron of complexes 1,
2
, and 2c would undergo a transfer to nitro compounds, in-
stead of relaxation to the ground state with fluorescence emis-
sion. Because the photoluminescence of 1, 2, and 2c originat-
ed from the ligand, the sensitive response of 1, 2, and 2c to ni-
troaromatic explosives could be attributed to the electron-rich
properties of the ligand, which facilitated the excited-state
electron-transfer process. Although there are cavities in the
framework of 1, the absence of an accessible path excludes
the possibility of analyte encapsulation during the sensing pro-
cess. Therefore, the sensing mechanism of 1 should be not
guest-induced quenching, in which analyte molecules are in-
cluded in the pores as guests and interact directly with the flu-
orophore.
Cyanide poisoning is less frequent than mercury or strych-
nine poisoning, although during recent years the death rate
from cyanide poisoning has been increasing. Cyano-containing
molecules show interesting reactivity due to the strong elec-
[46]
tron-withdrawing capability of the cyano group. Cyano com-
plexes are also hypothesized to be intermediates in the forma-
[47,48]
tion of biologically relevant molecules.
However, none of
the complexes proved active against the replication of retrovi-
ruses (human immunodeficiency virus, murine sarcoma virus)
at concentrations that were not toxic to the host cells. Ferric
ꢀ
heme systems can be ligated by CN , a strong-field ligand,
which places the heme into a low-spin state that is generally
thought to be very stable and that does not undergo photo-
[49]
dissociation. Therefore, the development of the detection of
the cyano group is very important for environmental and
safety considerations. Additionally, the application of MOFs for
the sensing of cyano groups is limited because most porous
MOFs used for the detection of cyano groups must be activat-
ed to evacuate the pores before sensing because the presence
of solvent or other guest molecules diminishes the per-
formance of the MOFs. On the other hand, the introduction of
electron-rich aromatic ligands could improve sensor perform-
ances effectively because quenching sensing is generally realiz-
ed by the transfer of photoexcited electrons from the MOFs to
the electron-deficient analytes. Inspired by our previous experi-
Figure 17. Fluorescence titrations of: a) 1, b) 2, and c) 2c dispersed in DMF
with the addition of different concentrations of p-DNB.
II
a Cd complex dispersed in MeCN. Fast and high fluorescence
quenching was observed upon the incremental addition of
[50]
a solution of TNP (1 mm). The visible bright-blue emission of
ences, we now carry out our work in the field of selective
recognition toward cyano-containing molecules.
II
such a Cd complex in UV light vanished upon the addition of
the solution of TNP, which quenched nearly 78% of the initial
fluorescence intensity. Fluorescence quenching by TNP could
be easily discerned at a low concentration (4 mm). Fluorescence
The fluorescent sensing ability of 2 was first examined with
the addition of different molecules to a suspension of 2. The
addition of cyano-containing molecules, such as K [W(CN) ],
4
8
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2
+
K [Mn(CN) ], Na [W(CN) ], Na [Mo(CN)] , Cs [W(CN)] , [NBu ]
of a triazole derivative as a luminescent probe of Ca . More-
3
6
3
8
3
8
3
8
3
[
Mo(CN) ], [NBu ][W(CN) ], and Rb [W(CN) ], at 400 ppm could
over, the luminescent emissions of 1, 2, and 2c could be
quenched by trace amounts of nitroaromatic explosives, such
as m-DNB, NB, and FNB. The quenching mechanism is attribut-
ed to electron transfer from the excited-state electron-donat-
ing MOF framework to electron-withdrawing nitroaromatic ex-
plosives, as well as the dispersible nature of the MOF particles.
8
3
8
3
8
almost entirely quench the emission of 2 (Figure 18). The maxi-
mum decrease in the emission intensity was more than
9
9.85% with the addition of [NBu ][Mo(CN) ], which indicated
3 8
that 2 had a selective response to cyano-containing molecules,
especially to [NBu ][Mo(CN) ]. To investigate the sensing prop-
3
8
erties of 2 further, the emissive response was monitored by
gradually increasing the [NBu ][Mo(CN) ] content of emulsions
3
8
Experimental Section
of 2 dispersed in DMF. The emission intensity decreased upon
the addition of 5 ppm of [NBu ][Mo(CN) ] and was nearly com-
3
8
Materials and methods
pletely quenched at a concentration of 100 ppm, with a high
quenching efficiency of 99.95% (Figure S22). To the best of our
knowledge, no other examples of selective sensors toward
All reagents are commercially available and used without further
purification. The elemental analysis of C, N, and H has been mea-
sured on a PerkinElmer 240 elemental analyzer. The photolumines-
cence spectra have been recorded by using an MPF-4 fluorescence
spectrophotometer with a xenon arc lamp as the light source.
Powder XRD analysis has been determined on a D/Max-2500 X-ray
diffractometer by using CuKa radiation. The photoluminescence
spectra were recorded by using an MPF-4 fluorescence spectro-
[
51]
cyano-containing molecules have been reported. The emis-
sions of 2 can be quenched by cyano-containing molecules.
Therefore, the fluorescence responses of 1 to cyano-containing
molecules were attributed to the electron-transfer quenching
mechanism, that is, in the presence of cyano-containing mole-
cules, the excited electron of 1 would undergo transfer to the
cyano complex, instead of relaxation to the ground state with
fluorescence emission. Because the photoluminescence of
1
photometer with a xenon arc lamp as the light source. H NMR
spectra have been measured by using a Bruker Avance 400 MHz
spectrometer. Chemical shifts are reported in d relative to tetrame-
thylsilane (TMS). Thermal analyses (under an oxygenated atmos-
1
originates from the ligand, the sensitive response of 1 to
ꢀ1
phere at a heating rate of 58Cmin ) were carried out by using
cyano complexes can be attributed to the electron-rich proper-
ties of the ligand, which facilitate the excited-state electron-
transfer process. Although there are cavities in the framework
of 1, the absence of an accessible path excludes the possibility
of analyte encapsulation during the sensing process. Therefore,
the sensing mechanism of 1 should not be guest-induced
quenching, in which analyte molecules are included in the
pores as guests and interact directly with the fluorophore.
a Labsys NETZSCH TG 209 Setaram apparatus. The fluorescence
quantum yields of complexes 1, 1a, 1b, 2, 2a, 2b, and 2c were
measured by using an Edinburgh Instruments FLS 920 device.
Caution! Nitroaromatics, such as NB, m-DNB, and p-DNB, and nitro-
aliphatics, such as NM and THMNM, are highly explosive and
should be handled carefully and in small amounts.
X-ray crystallography
Single-crystal XRD determination was performed on an APEX II
CCD area detector and a Bruker Smart CCD diffractometer. A
graphite crystal monochromator was equipped in the incident
beam for data collection at a temperature of 296(2) K for TPPT, 1,
2, 2a, 2b, and 2c and at 173(2) K for 1a, 1b, and 2. The w–f scan
technique was applied. Direct methods were applied to solve the
structures. Full-matrix least-squares methods by using the SHELXL-
9
7 and SHELXS-97 programs were used to refine the crystal struc-
[52,53]
tures.
For all coordination complexes, anisotropic thermal pa-
rameters were applied to all non-hydrogen atoms. Anomalous dis-
persion corrections were incorporated and analytical expressions
of neutral-atom scattering factors were also used. These crystallo-
graphic data, selected bond lengths, and bond angles of these
complexes are listed in Tables 1 and 2.
CCDC-1424630 (TPPT), 1016243 (1), 1055207 (1a), 1016244 (1b),
1
044214 (2), 1016246 (2a), 1016247 (2b), and 1016248 (2c) contain
Figure 18. Emission intensities of 2 in DMF with different cyano complexes.
the supplementary crystallographic data for this paper. These data
are provided free of charge by The Cambridge Crystallographic
Data Centre.
Conclusions
Synthesis of 4,4’-dibromodiphenyl ether
A new bidentate ligand, TPPT, has been designed and synthe-
sized. By using TPPT as a building block in self-assembly with
Cd(NO ) ·4H O and CdCl ·10.5H O, novel 1D double-chain
4
,4’-Dibromodiphenyl ether was prepared by reacting an excess of
Br with diphenyl ether in methanol. Br (3.99 g) was added drop-
2
2
3
2
2
2
2
wise to diphenyl ether (2.04 g), which was dissolved in methanol
10 mL). The reaction mixture was then stirred at 608C for an addi-
1
and 2D (4,4)-layer 2 have been constructed. Anion-exchange
(
experiments for 2 occurred in a SC–SC transformation manner.
Luminescent measurements indicate that 1 is the first example
tional 1 h. After cooling to room temperature, the product precipi-
tated. Yield: 70%; m.p. 59–618C.
Chem. Eur. J. 2016, 22, 1 – 17
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Synthesis of TPPT
Synthesis of 2a
The synthetic method used to prepare TPPT was the same as that
A suspension mixture of 2 (0.5 mmol) and NaBr (5 mmol) in CHCl3/
[54]
reported previously.
A mixture of 4,4’-dibromodiphenyl ether
C H OH/H O (1:8:2 v/v/v; 11 mL) was stirred for 6 h. Well-shaped
2
5
2
(
1.63 g, 5 mmol), 1H-1,2,4-triazole (0.69 g, 10 mmol), potassium car-
colorless block crystals suitable for XRD analysis were isolated.
Yield: 30%; elemental analysis calcd (%) for C H Br CdN O : C
34.72, H 2.91, N 13.50; found: C 34.68, H 2.87, N 13.56.
bonate (5.52 g, 40 mmol), and CuO (0.16 g, 2 mmol) were heated
with stirring in DMSO (20 mL) at 1508C for 48 h. The resulting
slurry was cooled to room temperature and solids were removed
by filtration. DMSO was removed by distillation under reduced
pressure. Dichloromethane was added to the remaining filtrate
and the mixture was then washed with water and dried over
sodium sulfate. Dichloromethane was then removed. The products
were recrystallized in methanol and water, and light-yellow solids
18
18
2
6
2
Synthesis of 2b
A suspension of 2 (0.5 mmol) and NaI (5 mmol) in CHCl
O (v/v/v 1:8:2; 11 mL) was stirred for 6 h. Well-shaped colorless
block crystals suitable for XRD analysis were isolated. Yield: 32%;
elemental analysis calcd (%) for C33 : C 40.37, H 2.57,
/C H OH/
2 5
3
H
2
were obtained. Yield: 12%; m.p. 192–1958C. As shown in Fig-
ure S21 in the Supporting Information, H NMR (400 MHz, CDCl ):
H25CdCl I N O
3 2 12 2
1
N 17.12; found: C 40.28, H 2.22, N 17.33.
3
d=8.56 (s, 2H), 8.12 (s, 2H), 7.68–7.70 (d, 4H), 7.17–7.20 ppm (d,
4
H). TPPT (0.0304 g, 0.1 mmol) was dissolved in CH Cl and CH OH
2 2 3
Synthesis of 2c
(
1:1 v/v). Under slow evaporation of the filtrate at room tempera-
ture, well-shaped colorless crystals of TPPT suitable for XRD were
obtained within one month in 90% yield. Elemental analysis calcd
A suspension of 2 (0.5 mmol) and NaOAc (5 mmol) in CHCl3/
C H OH/H O (v/v/v 1:8:2; 11 mL) was stirred for 6 h. Well-shaped
2
5
2
colorless block crystals suitable for XRD analysis were isolated.
Yield: 40%; elemental analysis calcd (%) for C H CdN O : C 42.08,
(
%) for C N OH : C 63.15, H 3.97, N 27.62; found: C 63.19, H 4.06,
16 6 12
N 27.50.
20 22
6
7
H 3.88, N 14.72; found: C 42.10; H 3.97, N 14.76.
Synthesis of 1
Acknowledgements
Complex 1 was prepared by slow diffusion at room temperature of
a solution of TPPT (0.0609 g, 0.2 mmol) in CHCl3 (10 mL) at the
bottom of the tube and CH OH (4 mL) containing Cd(NO ) ·6H O
This work was supported financially by the NSFC (41372373,
1421001, 21471113 and 21531005), the innovation team plan
3
3 2
2
2
(
0.1164 g, 0.4 mmol) on the top. After a few weeks, well-shaped
of the Tianjin Education Committee (TD12-5037), and the
Opening Fund of Key Laboratory of Advanced Energy Materials
Chemistry (Ministry of Education), Nankai University.
yellow rodlike crystals suitable for X-ray analysis were obtained.
Yield: 30%; elemental analysis calcd (%) for C H CdN O : C
32
30
14 11
4
2.75, H 3.36, N 21.81; found: C 42.72, H 3.38, N 21.79.
Keywords: crystal growth
frameworks · self-assembly · sensors
· fluorescence · metal–organic
Synthesis of 1a
A suspension of 1 (0.2628 g, 0.5 mmol) in DMF (10 mL) was stirred
for 6 h. Through our careful observations, well-shaped yellow rod-
like crystals dissolved and brown block crystals suitable for XRD
analysis were isolated after one week. Yield: 45%; elemental analy-
sis calcd (%) for C H CdN O : C 45.79, H 3.40, N 22.88; found: C
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A mixture of CdCl ·10.5H O (0.0745 g, 0.2 mmol), TPPT (0.0304 g,
2
2
[
0
.1 mmol), CHCl (1 mL), H O (1 mL), and CH OH (8 mL) was placed
3 2 3
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Published online on && &&, 0000
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&
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Full Paper
FULL PAPER
&
Self-Assembly
Y. Wang, P. Xu, Q. Xie, Q.-Q. Ma,
Y.-H. Meng, Z.-W. Wang, S. Zhang,*
X.-J. Zhao,* J. Chen,* Z.-L. Wang*
&& – &&
Go for the quench: A bidentate ligand,
Cd(NO ) ·4H O and CdCl ·10.5H O, 1D
3 2 2 2 2
Cadmium(II)–Triazole Framework as
a Luminescent Probe for Ca and
Cyano Complexes
2
+
1-{4-[4-(1H-1,2,4-triazol-1-yl)phenoxy]-
double-chain and 2D (4,4)-layer com-
pounds have been constructed. These
phenyl}-1H-1,2,4-triazole (TPPT), has
been designed and synthesized (see
scheme). By using TPPT as a building
block for self-assembly with
2
+
complexes are used to detect Ca and
cyano complexes.
Chem. Eur. J. 2016, 22, 1 – 17
www.chemeurj.org
17
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ