A luminescent zinc(II) coordination polymer as a highly selective and sensitive chemosensor for Fe(III) cation and Cr(VI) anions detection in aqueous solution

Article abstract of DOI:10.1016/j.ica.2020.119940

A double-bent-mixed-ligand supported 2-periodic coordination polymer (CP) {[Zn₂(FDA)₂(4-abpt)₂(H₂O)₂]}_n (1) has been synthesized from the unique combination of a bent furan-2,5-dicarboxylic acid (H₂FDA) ligand and a bent 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole (4-abpt) coligand. The CP 1 demonstrates readily dispersible two-dimensional (2D) 2-periodic layer structure and considerable chemostability in aqueous media. Luminescence titration experiments indicate that CP 1 can serve as chemosensors for sensitively and selectively detecting Fe³⁺ cation, CrO₄^2? and Cr₂O₇^2? anions in water solution via an environmentally friendly manner. Besides, the luminescent selective quenching mechanism of CP 1 toward Fe³⁺ cation, CrO₄^2? and Cr₂O₇^2? anions is comprehensively investigated in the light of absorption of the excitation energy of the host framework by individual analytes.

Full text of DOI:10.1016/j.ica.2020.119940

Journal Pre-proofs
Research paper
A luminescent zinc(II) coordination polymer as a highly selective and sensi‐
tive chemosensor for Fe(III) cation and Cr(VI) anions detection in aqueous
solution
Ling Li, Zhao-Yang Deng, Xin Xie, Ji-Yong Zou, Sheng-Yong You, Kai-
Hong Chen, Jin-Feng Le
PII:
DOI:
Reference:
S0020-1693(20)31140-3
https://doi.org/10.1016/j.ica.2020.119940
ICA 119940
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
14 June 2020
28 July 2020
28 July 2020
Please cite this article as: L. Li, Z-Y. Deng, X. Xie, J-Y. Zou, S-Y. You, K-H. Chen, J-F. Le, A luminescent
zinc(II) coordination polymer as a highly selective and sensitive chemosensor for Fe(III) cation and Cr(VI)
anions detection in aqueous solution, Inorganica Chimica Acta (2020), doi: https://doi.org/10.1016/j.ica.
2
020.119940
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover
page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version
will undergo additional copyediting, typesetting and review before it is published in its final form, but we are
providing this version to give early visibility of the article. Please note that, during the production process, errors
may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
©
2020 Published by Elsevier B.V.

A luminescent zinc(II) coordination polymer as a highly selective and
sensitive chemosensor for Fe(III) cation and Cr(VI) anions detection in
aqueous solution
a
a
a
a
a
a
Ling Li, Zhao-Yang Deng, Xin Xie, Ji-Yong Zou,* Sheng-Yong You* Kai-Hong Chen and Jin-Feng
Lea,b
a
Institute of Applied Chemistry, Jiangxi Academy of Sciences, Nanchang, 330096, P.R. China
b
High Performance Modified Starch Research Center of Jiangxi, Nanchang, 330096, P.R. China
*
Corresponding author. E-mail address: zoujiyong@jxas.ac.cn; youshengyong@jxas.ac.cn
Abstract
A
double-bent-mixed-ligand
(FDA) (4-abpt) (H O) ]} (1) has been synthesized from the unique combination of a bent
FDA) ligand and a bent 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole (4-abpt)
supported
2-periodic
coordination
polymer
(CP)
{
[Zn
2
2
2
2
2
n
furan-2,5-dicarboxylic acid (H
2
coligand. The CP 1 demonstrates readily dispersible two-dimensional (2D) 2-periodic layer structure
and considerable chemostability in aqueous media. Luminescence titration experiments indicate that CP
3
+
2-
2-
1
can serve as chemosensors for sensitively and selectively detecting Fe cation, CrO
4
and Cr
2
O
7
anions in water solution via an environmentally friendly manner. Besides, the luminescent selective
3
+
2-
2-
quenching mechanism of CP 1 toward Fe cation, CrO
4
and Cr
2
O
7
anions is comprehensively
investigated in the light of absorption of the excitation energy of the host framework by individual
analytes.
Keywords: a double-bent-mixed-ligand strategy; luminescence chemosensors; Zn(II) coordination
polymer; Fe(III) cations recognition; Cr(VI) anions detection
1

Introduction
While sophisticated analytical instruments such as atomic absorption spectroscopy, mass
spectrometry, inductively coupled plasma and chromatography have played an increasingly important
role in the detection of hazardous substances,[1-3] the use of simple, fast and readily available detection
techniques continues to offer fascinating new approaches and at the same time offers deeper insight into
the structural parameters and individual analytes in the detection process.[4-6] Such a fact is especially
true for luminescence detection techniques, which have been widely investigated for chemosensing
applications. This is because in comparison with other analytical techniques, luminescence detection
techniques are superior in simple operating procedures, excellent selectivity and sensitivity, low cost,
online monitoring detection and high-efficiency response.[7-9] Significantly, among the various candidate
luminescence detection techniques, luminescence coordination polymers (LCPs) have attracted much
attention.[10-12] Specifically in sensing applications, LCPs have been proved to be optimal candidates as
chemosensor for detecting explosives, corrosive gases, antibiotics, cancer markers, neurotransmitters,
pH and so on because of their selective and sensitive response to the individual analytes. [13-15] This
superior performance in chemosensing applications may largely depend on their versatile components
and highly tunable morphology. [16-18] More importantly, the excellent sensitivity, high selectivity and
reusability of LPCs could also benefit their sensing applications in comparison with other the
luminescence detection techniques.
Additionally, severe pollution caused by the abuse of hazardous chemicals has raised global concerns
because the abused chemicals can seriously harm human health and severely contaminate natural
3
+
environment and ecological systems. For instance, as an indispensable trace element, Fe cations have
played an important role in the oxygen-transfer and physiological processes and participated in the
hemoglobin formation and the synthesis processes of DNA and RNA.[19,20] However, the deficiency and
3
+
excess of Fe cations has lethal effects on organisms and could cause several adverse human health
2
-
2-
problems. Likewise, CrO
4
and Cr
2
O
7
anions are notorious chromium(VI) species because of their
high toxicity, nonbiodegradablity and facile accumulation during the wide applications in industry,
2

resulting in human lesion such as cancer and deformity.[21,22]Thus, it is of significant importance to
3
+
2-
2-
investigate an effective approach for detecting Fe cations, CrO
4
and Cr O
2 7
anions in aqueous media
via highly sensitive, fast-responsive detection, of which LCPs are considered as optimized candidates to
efficiently detect them.
Based on the reasons discussed above, we develop a luminescence detection approach based on LCPs
3
+
2-
2-
to detect Fe cations, CrO
4
and Cr
2
O
7
anions in aqueous media rapidly and sensitively. Herein, a
]} (1) is designed via a double-bent-mixed-ligand strategy
2
-periodic CP {[Zn (FDA)
2
2
(4-abpt)
2
(H
2
O)
2
n
based on a bent dicarboxylic acid ligand and a bent pyridyl ligand (Scheme 1), which exhibits readily
dispersible 2D sql layer structure and considerable chemostability in aqueous media. Moreover,
luminescent exploration reveals that CP 1 represents superior luminescent properties, which can
sensitively and selectively detect Fe3+ cations, CrO
2-
and Cr
O
7
2-
anions in aqueous media. Further
4
2
3
+
2-
2-
exploration of luminescence quenching mechanism toward Fe cations, CrO
4
and Cr
2
O
7
anions has
been investigated by the UV-Vis spectral overlap experiment.
Scheme 1 Molecular structures of H FDA and 4-abpt.
2
Experimental Section
General Methods and Materials
All reagents and solvents were purchased from commercial sources and used as received without
further purification. Elemental analyses of C, H and N were performed using a Perkin-Elmer 240 CHN
elemental analyzer. IR spectra were recorded in the range 400–4000 cm−1 with a Bruker Tensor 27
spectrometer on KBr disks. Powder X-ray diffraction measurements were carried out using a
D/Max-2500 X-ray diffractometer with Cu/Kα radiation. The luminescence spectrum was measured on
a Varian Cary Eclipse Fluorescence spectrophotometer. UV/Vis spectra were recorded on a Agilent
3

Cary100 spectrophotometer.
Synthesis of 4-abpt. A mixture of 4-cyanopyridine (10 mmol, 1.04 g) and hydrazine monohydrate
(
80% 1.5 mL) in 2 mL C
20 °C for 3 days and subsequently cooled to room temperature at a rate of 1.25 °C h . Colorless
crystals of 4-abpt were collected by washing with C OH, and dried in air. Yield: 86%. Anal. Calcd for
: C 60.50; N 35.27; H 4.23 Found: C 60.67; N 35.01; H 4.32%.
2
H
5
OH was sealed in a 23 mL Teflon-lined stainless autoclave and heated at
-1
1
2
H
5
C
12
H
10
N
6
Synthesis of {[Zn
2
(FDA)
2
(4-abpt)
2
(H
2
O)
2
]}
n
(1). A mixture of H
2
FDA (0.100 mmol, 0.0156 g),
4
-abpt (0.100 mmol, 0.0368g) and Zn(NO
3
)
2
.6H
2
O (0.100 mmol, 0.0297 g) in 4 mL DMA and 2 mL
C
2
5
H OH was sealed in a 23 mL Teflon-lined stainless autoclave and heated at 90 °C for 3 days and
-1
subsequently cooled to room temperature at a rate of 1.25°C h . Colorless block crystals of CP 1 were
collected by washing with DMA several times and dried in air. Yield: 63% based on Zn. Anal. Calcd for
-1
C
36
H
28
N
12
O
12Zn : C 45.44; N 17.66; H 2.97. Found: C 45.27; N 17.41; H 3.24%. IR (KBr, cm ): 3358w,
2
3
118s, 2928w, 1610vs, 1359vs, 1210s, 1019m, 834m, 793m, 598m.
Table 1 Crystal data and Structure Refinements for 4-abpt and 1.
4

compound
formula
formula weight
temperature (K)
crystal system
space group
a (Å)
4-abpt
1
C
12
H
10
N
6
36 28 12 2
C H N O12Zn
238.25
951.50
150(10)
150(10)
monoclinic
orthorhombic
Aea2
1
P2 /c
13.1496(4)
7.0195(2)
11.7924(4)
90
14.8200(8)
32.601(3)
19.2529(12)
90
b (Å)
c (Å)
α (°)
ß (°)
106.259(3)
90
90
γ (°)
90
V (Å3)
1044.95(6)
4
9301.9(10)
8
Z
-
3
D
c
( g cm )
1.514
1.357
-
1
μ (mm )
F(000)
0.813
1.850
496.0
3864.0
2
θ range (°)
7.002 to 131.994
1.068
8.002 to 131.986
1.057
GOF on F2
reflections collected / unique
2913/1801
0.0267
6324 / 4252
0.0813
R
R
R
int
,a wR
b
[I > 2σ(I)]
0.0425, 0.1078
0.1340, 0.3285
0.1481, 0.3490
1
1
2
, wR
2
( all data)
0.0470, 0.1140
1 0 c 0 2 0 c 0
= ∑(|F | - |F |) / ∑|F = [∑{w(|F | ) ]]
|. bwR |2 - |F |2)2} / ∑[w(|F
a
2 2 1/2
R
X-ray Structure Determination. Data collections of 4-abpt and CP 1 were carried out using an
Oxford Supernova diffractometer equipped with graphite-monochromated Cu-Kα radiation (λ = 1.54178
Å). The temperature was cooled by a cryoject controller attached to an Oxford Supernova diffractometer.
Starting models for structure refinement were found using direct methods (Olex2,[23] and
SHELXT-2014[24]). All non-hydrogen atoms were found from the different Fourier maps and refined by
2
[25]
full-matrix least-squares techniques on F using the SHELXL-2014 programs.
Anisotropic thermal
parameters were assigned to all non-hydrogen atoms. The hydrogen atoms were placed in idealized
positions and located in the difference Fourier map. CCDC 2002379 for 4-abpt and CCDC 2002381 for
CP 1 contain the supplementary crystallographic data of this paper. The data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data request/cif. The
crystallographic data for 4-abpt and CP 1 are summarized in Table 1.
Luminescence Experiments. In a typical experiment, 5 mg CP 1 samples were powdered and
5

-2
3+
2+
2+
2+
2+
2+
2+
2+
2+
immersed in 2.5 mL MCl metal salts (10 M) (M = Al , Ba , Ca , Cd , Co , Cu , Ni , Mg , Pd ,
x
3
+
3+
Fe and Cr ) aqueous solution with ultrasonication for 30 min to obtain the suspension of CP 1. Then,
the obtained suspension was transferred to a quartz cuvette, and the photoluminescence spectra were
recorded by a fluorescence spectrophotometer under excitation of 285 nm at room temperature.
As for the luminescence titration experiment, 5 mg crystalline powders CP 1 were dispersed in 2.5
mL water with ultrasonication for 30 min, forming stable suspensions. Then, the obtained suspension
was transferred to a quartz cuvette, and 10-3 M MCl
corresponding emission spectra were monitored.
metal salts were added slowly, and the
x
As for the anti-interference ability of CP 1, 5 mg of crystalline powders CP 1 was dispersed in 2.5 mL
-2
of water, forming stable suspensions, then 100 μL of the corresponding MCl
x
metal salts (10 M) were
added to the suspension of CP 1, and the corresponding emission spectra were monitored. With the
-2
subsequent addition of 100 μL FeCl
3
(10 M) into the parallel tests, the corresponding emission spectra
was monitored.
As for the luminescence quenching experiment of CrO 2-
and Cr
O
7
2-
anions, similar procedures have
4
2
3
+
been performed as the luminescence quenching experiment of Fe cation.
Results and Discussion
Description of the Crystal Structure
Scheme 2 Synthesis of 4-abpt crystals.
The solvothermal reaction of 4-cyanopyridine and excess hydrazine monohydrate in C
2
5
H OH at
1
20 °C affords the crystals of 4-abpt (Scheme 2), which crystallize in the monoclinic system with space
.6H
O, H FDA and 4-abpt at
group P2
1
/c (Table 1). While the solvothermal treatment of Zn(NO
3
)
2
2
2
9
0 °C for 3 days in a mixture solution of DMA and C
2
5
H OH harvests colorless crystals of CP 1.
6

Single-crystal X-ray diffraction study revealed that CP 1 crystallized in the orthorhombic system with
space group Aea2 (Table 1). Each asymmetric unit is composed of two crystallographically independent
2
-
Zn(II) ions, two FDA ligands, two 4-abpt ligands and two water molecules, of which partial Zn(II)
2
-
2+
ions, FDA ligands and 4-abpt ligands are disordered (Figure 1a). Each Zn ion is hexacoordinated by
2
-
three oxygen atoms from two FDA ligands, one oxygen atom from water molecule and two nitrogen
atoms from two 4-abpt ligands, generating a distorted distorted octahedral {ZnN2O4} coordination
geometries. The Zn–O bond distances range from 2.041 (8) to 2.405(5) Å and the Zn–N bond distances
are in the range of 2.126 (9) to 2.164 (5) Å, which are comparable to those distances reported for
Zn-based CPs[26-28]. And each FDA ligand with the (ƞ )-(ƞ )-µ
coordination mode, supported by the
2-
2
1
2
2
+
infrared spectra (Figure S1 of the supporting information) connects with two separate Zn ions. As a
result, a 2D sql 2-periodic layer structure is formed due to the partial disordered structure of the
asymmetric unit (Figure 1b and Figure 1c), which stacks along the b-axis in an –AABB– fashion
(Figure 1d). The consecutive 2-periodic layer structures can be bridged together via direct inter-layer
hydrogen bonds involving the coordinated water molecules of one layer and carboxylate groups as well
as the oxygen atoms of furan groups of a neighboring layer (O11-H11E···O9, O11-H11F···O6,
O11-H11F···O8, O12A-H12A···O5, O12A-H12B···O2, O12A-H12C···O2, O12A-H12C···O3 and
O12A-H12D···O5) (Table S1 of the supporting information), which support the 3D supermolecular
structure of CP 1.
7

Figure 1. (a) The asymmetric unit in CP
hydrogen atoms were omitted for clarity. [Symmetry code: (#) 3/2-X, Y, 1/2+Z; (##) 1+X, +Y, +Z]; (b) 2D
-periodic layer structure of CP 1 (part of disordered molecules were omitted for clarity); (c) The 2-periodic sql
1 (thermal ellipsoids are drawn at the 30% probability level). All
2
square grid of CP 1. (d) Overrall packing of the structure of CP 1. All hydrogen atoms were omitted for clarity;
Powder X-ray Diffraction (PXRD) Measurement
The crystalline phase purity of CP 1 has been performed at room temperature and confirmed by
comparing the simulated PXRD pattern from the single crystal data with the experimental pattern. The
current result indicates one crystalline phase is present in sample CP 1 (Figure S2 of the supporting
information). The slight difference may be derived from the variation of preferred orientation of CP 1.
-2
3+
2-
2-
Moreover, when samples CP 1 were dispersed in 10 M Fe cations, CrO
4
and Cr
2
O
7
anions of
aqueous solution, the PXRD patterns are consistent with the simulated pattern, which suggest the
3
+
2-
2-
structure of CP 1 is undecomposed and can be stable in Fe cations, CrO
4
and Cr
2
O
7
anions.
Thermogravimetric (TG) Measurement
The thermal stability of sample CP 1 has been performed under an N atmosphere in the temperature
2
8

range of 25–800 °C (Figure S3 of the supporting information). The curve shows a steady plateau
from room temperature to 140 °C, indicating that there are no free solvent molecules in CP
1.
Then, a weight loss of ca. 4.26% (calcd. 3.78%) before 270 °C is observed, indicative of the removal of
two coordinated water molecules. As the temperature is raised, the whole structure begins to
decompose.
Luminescence Measurement
The luminescence measurements of H
2
FDA, 4-abpt and CP 1 have been performed in the solid state
FDA and 4-abpt
at room temperature. Upon excitation at 300 nm, the luminescence emission band of H
2
shows a main emission peak with the maximum value of 365 nm and 378 nm, respectively. This
luminescence phenomenon could be ascribed to ligand-to-lignand charge transfer transition (π*→π or
π*→n). Compared to H FDA and 4-abpt ligands, a strong luminescence emission at 380 nm is observed
2
upon the excitation of 285 nm (Figure S4 of the supporting information), resulting in a red shift of 15
nm and 2 nm, respectively. Such luminescence emission phenomenon could be attributed to neither
metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge transfer (LMCT) due to the fact of
the difficulty of being oxidized or reduced regarding as Zn2+ ions d configuration. Therefore, the
luminescence emission band of CP 1 could be reasonably speculated to the mixed contribution of the
intra-ligand charge transfer transition of π-electron-rich linkers and ligand-to-lignand charge transfer
transition (π*→π or π*→n) of the organic ligands.[29]
10
It is well-known that much work has been devoted to developing luminescence detection approaches
based on LCPs because of their superior performance for the effective response and sensing of
hazardous analytes such as toxic anions and cations.[30-33] Of particular concern to the Zn-based LCPs
are the favorable advantage in sensing applications. In this contribution, CP 1 is exploited as the
3
+
2-
2-
luminescence chemosensor to recognize Fe cations, CrO
4
and Cr
2
O
7
anions via the luminescence
quenching effects.
3
+
Fe Cations Recognition
-2
The 5 mg tiny samples of CP 1 were dispersed into 10 M cations (AlCl
3
, BaCl
2
, CaCl
2
, CdCl ,
2
9

CoCl
2
, CuCl
2
, NiCl
2
, MgCl
2
, PdCl
2
, FeCl
3
and CrCl ) of 2.5 mL water solution by 30 min ultrasonic
3
process, forming suspension solutions. As demonstrated in Figure 2a, different cations have significant
influences on the luminescence intensities of the CP 1 suspension, along with the slightly red-shifted or
blue-shifted luminescence peaks due to the contribution of the interaction between the guest cations and
the host skeletons of CP 1. Particularly, Fe3+ cations have the most significant influences on the
luminescence intensities, demonstrating the most noticeable turn-off quenching effect, and the
luminescence of CP 1 is totally quenched. Compared with the phenomenon of Fe3+ cations on the
influences of CP 1, other cations have a moderate effect on the luminescence of CP 1. This fact suggests
3
+
CP 1 could be qualified as a promising luminescence chemosensor for selective Fe cations detection.
To evaluate the anti-interference sensing ability of CP 1, the competing experiments have been
performed (Figure 2b and Figure S5-S15 of the supporting information). The experimental results reveal
3
+
that CP 1 shows visible luminescent quenching effects in the case of Fe cations as well as outstanding
3
+
selectivity to Fe cations.
Figure 2. (a) The luminescence of CP 1 dispersed in different cations; (b) The luminescence intensity (348 nm) of CP
1
dispersed in H
2
O with the addition of different competing cations (green) and subsequent addition of Fe3+ cations
O with different concentration of Fe3+ cations; (d) The linear
(purple); (c) The luminescence of CP 1 dispersed in H
2
1
0

3
+
correlation between the luminescence of CP 1 and the low concentration of Fe cations.
3
+
To further explore the sensing sensitivity and better understand the quenching effects of Fe cations,
the titration experiments have been carried out. As expected, the luminescence behaviour of CP 1 is in
accordance with the concentration of Fe3+ cations (Figure 2c). The luminescence curve shows the
luminescence changes of the intensities in different degrees could be clearly present and the existence of
turn-off quenching phenomenon simultaneously became remarkable. Moreover, the intensities could
3
+
gradually decrease with the increasing concentration of Fe cations, endowing CP 1 with the capacity
3
+
of the quantitative detection of Fe cations. The relationship between the luminescence intensities and
3
+
the concentration of Fe cations is illustrated in Figure 2d and Figure S16 of the supporting information.
3
+
A best fit of I
0
/ I vs the low concentration of Fe cations is evaluated based on the equation of I
0
/ I =
0
.98596 + Ksv [Fe3+ cations] with the correlation coefficient of 0.9989, where the values of I
0
and I
3
+
represent the initial and ultimate luminescence intensity of CP 1, [Fe cations] is the molarity of the
−
1
corresponding anions (mM) and Ksv stands for the quenching constant (M ), respectively. The result
3
+
shows a linear correlation of luminescence quenching and the low concentration of Fe cations and is in
close proximity to the Stern−Volmer (SV) equation: I
0
/ I = 1 + Ksv[Fe3+ cations]. The Ksv value is
4
-1
quantitatively calculated to be 1.23 × 10 M by the linear regression of the curve, indicating the
3
+
significant quenching efficiency of CP 1. The detection limit for Fe cations can be calculated by using
δ / k, in which δ is standard error and k is slope according to the SV equation with a value of 12.4 µM
3
3
+
for CP 1, further indicative of an excellent sensitivity for sensing Fe cations. The superior Ksv value
and low detection limit of CP 1 qualifies CP 1 as a high-efficiency luminescence chemosensor for
3
+
quantitative Fe cations detection. Furthermore, the recyclable performance demonstrates the negligible
changes of luminescence intensity after four cycles, revealing the high recyclability of CP 1 for Fe3+
cations detection (Figure S17 of the supporting information).
CrO 2
Likewise, the influences of different anions (KCl, KBr, KF, KI, KNO
MoO , K WO , K Cr , K CrO and K PO ) on the luminescence intensities of CP 1 have been
-
and Cr
O
2-
anions Detection
4
2
7
3
, KSCN, K
2
SO
4
, K
2
CO ,
3
K
2
4
2
4
2
2
O
7
2
4
3
4
1
1

explored (Figure 3). The result proves that different anions have significant influences on the
luminescence signal of CP 1. The luminescence signal can completely disappear in the presence of
CrO 2
-
and Cr
O
7
2-
anions, whereas the luminescence signal can negligibly change in the presence of
4
2
other anions. The completely quenched luminescence signal in the case of CrO 2-
and Cr
O
7
2-
anions for
4
2
CP 1 indicates CP 1 can also be exploited as a possible luminescence chemosensor for selectively
sensing CrO 2
-
and Cr
O
7
2-
anions. The anti-interference sensing ability experiments also show CrO
2-
4
2
4
2
-
and Cr
2
O
7
anions can dramatically quench the luminescence signal, while other anions can scarcely
2
-
influence the luminescence intensities of CP 1, further indicative of the superior selectivity to CrO
4
2
-
and Cr
2
O
7
anions (Figure 4a-4b and Figure S18-S28 of the supporting information). The sensitivity
ability of CP 1 has been demonstrated by the titration experiments (Figure 4c-4d). It turns out that
2
-
significant luminescence quenching variation is implemented with the gradual addition of CrO
4
and
2
-
anions, indicating CP 1 has the capacity of the quantitative detection of CrO 2-
2-
Cr
2
O
7
4
and Cr O
2 7
2
-
anions. The relationship between the luminescence intensities and the concentration of CrO
4
and
2
-
Cr
2
O
7
anions is illustrated in Figure 4e-4f and Figure S29-30 of the supporting information. Similarity
3
+
2-
2-
with the case of Fe cations, the best fit of I
0
/ I vs the low concentration of Cr
2
O
7
anions and CrO
4
anions could also be calculated based on the equations of I
0
/ I = 0.99179 + Ksv [CrO 2-
4
anions] with the
2
-
correlation coefficient of 0.9949 and I
0
/ I = 0.98469 + Ksv [Cr
2
O
7
anions] with the correlation
coefficient of 0.9913, respectively. The fitting result shows a linear correlation of luminescence
2
-
2-
quenching and the low concentration of Cr
the SV equation: I / I = 1 + Ksv[Cr(VI) anions]. Accordingly, the Ksv values can be quantitatively
calculated to be 7.20 × 10 M for CrO
2
O
7
anions and CrO
4
anions, which is in close proximity to
0
3
-1
2-
3
-1
2-
4
anions and 7.92 × 10 M for Cr
2
O
7
anions and the detection
2
-
2-
limits are as low as 101 µM for CrO
4
anions and 120 µM for Cr
2
O
7
anions, which further indicate that
CP 1 serves as selective and sensitive chemosensors for sensing CrO 2-
anions and Cr
O
7
2-
anions in
4
2
aqueous solution. Moreover, the recyclable performance demonstrates the negligible changes of
2
-
luminescence intensity after four cycles, revealing the high recyclability of CP 1 for sensing CrO
4
2
-
anions and Cr
2
O
7
anions (Figure S17 of the supporting information).
1
2

3
+
Comparatively, the superior Ksv value and low detection limit for Fe cations of CP 1 is superior to
the values of Cr(VI) anions and previous reports (Table S2 of the supporting information). The
phenomenon of the superior sensitivity determination is likely to be caused by the fact that the amino
and triazolyl nitrogen atoms are anchored in the skeleton. Additionally, it should be noted that the Ksv
value and detection limit is comparable or superior to the reported LCPs as luminescence chemosensors
3
+
[34-36]
to recognize Fe cations and Cr(VI) anions in aqueous solution.
Such fact clearly indicates the
3
+
high selectivity and superior sensitivity of CP 1 for sensing Fe cations and Cr(VI) anions in aqueous
solution.
Figure 3. The luminescence of CP 1 dispersed in different anions.
1
3

Figure 4. (a) The luminescence intensity (348 nm) of CP 1 dispersed in H O with the addition of different competing
2
2
-
anions (green) and subsequent addition of Cr
2
O
7
anions (purple); (b) The luminescence intensity (348 nm) of CP 1
dispersed in H
2
O with the addition of different competing anions (green) and subsequent addition of CrO 2-
4
anions
anions; (d) The
anions; (e) The linear correlation
2-
(purple); (c) The luminescence of CP 1 dispersed in H
2
O with different concentration of Cr
2
O
7
2
-
luminescence of CP 1 dispersed in H
2
O with different concentration of CrO
4
2-
between the luminescence of CP 1 and the low concentration of Cr
2
O
7
anions; (f) The linear correlation between the
2
-
luminescence of CP 1 and the low concentration of CrO
4
anions.
Quenching Mechanism
3
+
The possible luminescent turn-off sensing mechanism of CP 1 caused by Fe cations and Cr(VI)
anions has been investigated. The PXRD patterns before and after the sensing performance reveal that
CP 1 is still intact, excluding the structural collapse of the framework during the sensing process.
3
+
Additionally, there is almost no obvious overlap between the absorption spectra of Fe cations, Cr(VI)
1
4

anions and the emission spectrum of CP 1, also excluding the luminescence resonance energy transfer
FRET) process between the donor of CP 1 and the Fe3+ cations, Cr(VI) anions acceptor. However,
(
3
+
UV–visible absorption spectroscopy of Fe cations and Cr(VI) anions have an effective overlap with
the excitation spectrum of CP 1 (Figure S31 in the Supporting information), clearly indicating the fact
3
+
that Fe cations and Cr(VI) anions could absorb the energy of the irradiated light of CP 1 and weaken
2
+
the effective energy transfer from the organic ligands to the central Zn ions. This may be the reason for
the luminescence quenching phenomenon with the increase of Fe3+ cations and Cr(VI) anions and
promote the sensing performance of CP 1.
Conclusion
In summary, a 2-periodic 2D sql CP with a considerable chemostability in aqueous media is designed
via a double-bent-mixed-ligand strategy. The result of the luminescence performance demonstrates CP 1
has the promisingly potential capacity to be used as an efficient luminescence turn-off chemosensor for
quantitatively sensing Fe3+ cations and Cr(VI) anions with superior selectivity and advantageous
sensitivity. Further analysis of luminescence quenching mechanism interprets the competitive
absorption between the Fe3+ cations or Cr(VI) anions and CP 1 may dominates the luminescence
quenching response of CP 1 based on the UV-Vis spectral overlap experiments. All evidence support the
fact that a facile access to synthesize luminescence chemosensors for the practical application in sensing
3
+
Fe cations and Cr(VI) anions in aqueous solution have been realized. And the result promotes us a new
horizon for exploiting superior chemosensor materials for hazardous analytes recognition.
Acknowledgements
Financial support from the National Natural Science Foundation of China (No. 21561014 and
2
1562023), the Key Research Project of Jiangxi Province (No.20171BEM26002 and 20192BBF60038)
and the Project of Jiangxi Academy of Sciences (No. 2018-YZD2-11 and 2020-YZD-3).
References
1
J.M. Sylvia, J.A. Janni, J.D. Klein, K.M.Spencer, Surface-enhanced Raman detection of 2,
-dinitrotoluene impurity vapor as a marker to locate landmines. Anal. Chem. 72 (2000) 5834-5840.
4
1
5

2
3
4
K. Hakansson, R.V. Coorey, R.A. Zubarev, V.L. Talrose P. Hakansson, Low-mass ions observed in
plasma desorption mass spectrometry of high explosives. J. Mass Spectrom. 35 (2000) 337-346.
S.Y. Wu, H. Min, W. Shi, P. Cheng, Multicenter Metal-Organic Framework‐Based Ratiometric
Fluorescent Sensors. Adv. Mater. 31 (2019) 1805871.
Z.S. Han, K.Y. Wang, Y.F. Guo, W.J. Chen, J.L. Zhang, X.R. Zhang, G. Siligardi, S.H.Yang, Z. Zhou,
P.C. Sun, W. Shi, P. Cheng, Cation-induced chirality in a bifunctional metal-organic framework for
quantitative enantioselective recognition. Nat. Commun. 10 (2019) 5117-5123.
5
6
7
8
9
1
1
1
1
1
1
S.Y. Zhang, W. Shi, P. Cheng, M.J. Zaworotko, A mixed-crystal lanthanide zeolite-like metal-organic
framework as a fluorescent indicator for lysophosphatidic acid, a cancer biomarker. J. Am. Chem. Soc.
1
37 (2015) 12203-12206.
J.Y. Zou, L. Li, S.Y. You, Y.W. Liu, H.M. Cui, J.Z. Cui, S.W. Zhang, Two luminescent lanthanide (III)
metal-organic frameworks as chemosensors for high-efficiency recognition of Cr (VI) anions in aqueous
solution. Dalton Trans. 47 (2018) 15694-15702.
Y. Takashima, V.M. Martínez, S. Furukawa, M. Kondo, S. Shimomura, H. Uehara, M. Nakahama, K.
Sugimoto, S. Kitagawa, Molecular decoding using luminescence from an entangled porous framework.
Nat. Commun. 2 (2011) 168-175.
Z.H. Jiao, X.L. Jiang, S.Li Hou, M.H. Tang, B. Zhao, Highly Sensitive and Selective Luminescence
Sensor Based on Two-Fold Interpenetrated MOFs for Detecting Glutamate in Serum. Inorg. Chem. 59
(
2020) 2171-2177.
N.N. Wang, Z.Y. Wang, L.Z. Chen, W.W. Chen, Y.W. Quan, Y.X. Cheng,; H.X. Ju, Dual resonance
energy transfer in triple-component polymer dots to enhance electrochemiluminescence for highly
sensitive bioanalysis. Chem. Sci. 10 (2019) 6815-6820.
0 L. Li, J.Y. Zou, S.Y. You, H.M. Cui, G.P. Zeng, J.Z. Cui, Tuning the luminescence of two
3
d–4fmetal–organic frameworks for the fast response and highly selectivedetection of aniline Dalton
Trans. 46 (2017) 16432-16438.
1 T. Gong, P. Li, Q. Sui, J.Q. Chen, J.H. Xu, E.Q. Gao, A stable electron-deficient metal-organic
framework for colorimetric and luminescence sensing of phenols and anilines. J. Mater. Chem. A 6 (2018)
9
236-9244.
2 J.Y. Zou, L. Li, S.Y. You, K.H. Chen, X.N. Dong, Y.H. Chen, J.Z. Cui, A usf Zinc (II) Metal-Organic
Framework as a Highly Selective Luminescence Probe for Acetylacetone Detection and Its Postsynthetic
Cation Exchange. Cryst. Growth Des. 18 (2018) 3997-4003.
3 L. Wang, G.L. Fan, X.F. Xu, D.M. Chen, L. Wang, W. Shi, P. Cheng, Detection of polychlorinated
benzenes (persistent organic pollutants) by a luminescent sensor based on a lanthanide metal-organic
framework. J. Mater. Chem. A 5 (2017) 5541-5549.
4 S.Y. Wu, Y.N. Lin, J.W. Liu, W. Shi, G.M. Yang, P. Cheng, Rapid detection of the biomarkers for
carcinoid tumors by a water stable luminescent lanthanide metal-organic framework sensor. Adv. Funct.
Mater. 28 (2018) 1707169.
5 X.M. Kang, R.R. Cheng, H. Xu, W.M. Wang, B. Zhao, A Sensitive Luminescent Acetylacetone Probe
Based on Zn-MOF with Six-Fold Interpenetration. Chem.-Eur. J. 23 (2017) 13289-13293.
1
6

1
1
1
1
6 S.Li Hou, J. Dong, M.H. Tang, X.L. Jiang, Z.H. Jiao, B. Zhao, Triple-interpenetrated lanthanide-organic
framework as dual wave bands self-calibrated pH luminescent probe. Anal. Chem. 91 (2019) 5455-5460.
7 Z.C. Hu, B.J. Deibert, J. Li, Luminescent metal-organic frameworks for chemical sensing and explosive
detection. Chem. Soc. Rev. 43 (2014) 5815-5840.
8 T.F. Xia, Y.J. Cui, Y.Yang, G.D. Qian, A luminescent ratiometric thermometer based on thermally
coupled levels of a Dy-MOF. J. Mater. Chem. C 5 (2017) 5044-5047.
9 Y.J. Cui, D. Yue, Y.K. Huang, J. Zhang, Z.Y. Wang, D. Yang, G. D. Qian, Photo-induced electron
transfer in a metal-organic framework: a new approach towards a highly sensitive luminescent probe for
3
+
Fe . Chem. Commun. 55 (2019) 11231-11234.
2
2
0 L. Guo, Y. Liu, R.M. Kong, G. Chen, Z. Liu, F.L. Qu, L. Xia, W.H. Tan, A Metal-Organic Framework as
3+
Selectivity Regulator for Fe and Ascorbic Acid Detection. Anal. Chem. 91 (2019) 12453-12460.
1 W. Liu, X. Huang, C. Xu, C.Y. Chen, L.Z. Yang, W. Dou, W.M. Chen, H. Yang, W.S. Liu, A
3+
VI
Multi-responsive Regenerable Europium-Organic Framework Luminescent Sensor for Fe , Cr Anions,
and Picric Acid. Chem. Eur. J. 22 (2016) 18769-18776.
2
2 J.Y. Zou, L. Li, S.Y. You, H.M. Cui, Y.W. Liu, K.H. Chen, Y.H. Chen, J.Z. Cui, S.W. Zhang, Sensitive
luminescent probes of aniline, benzaldehyde and Cr (VI) based on a zinc (II) metal-organic framework
and its lanthanide (III) post-functionalizations. Dyes Pigm. 159 (2018) 429-438.
2
2
3 O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, OLEX2: a complete
structure solution, refinement and analysis program. J. Appl. Cryst. 42 (2009) 339-341.
4 G.M. Sheldrick, SHELXT-Integrated space-group and crystal-structure determination. Acta Cryst. A71
(
2015) 3-8.
2
2
5 G.M. Sheldrick, Crystal structure refinement with SHELXL. Acta Cryst. C71 (2015) 3-8.
6 R. Ochi, S.I. Noro, K. Kubo, T. Nakamura, A Zn(ii) metal-organic framework with dinuclear
[
Zn
2
(N-oxide) ] secondary building units. Dalton Trans. 48 (2019) 6314-6318.
2
2
2
2
7 S. Jensen, K. Tan, W. Lusting, D. Kilin, J. Li, Y. J. Chabal, T. Thonhauser, Quenching of
photoluminescence in a Zn-MOF sensor by nitroaromatic molecules. J. Mater. Chem. C 7 (2019)
2
625-2632.
8 B. Parmar, K.K. Bisht, Y. Rachuri, E. Suresh. Zn(ii)/Cd(ii) based mixed ligand coordination polymers as
fluorosensors for aqueous phase detection of hazardous pollutants. Inorg. Chem. Front. 7 (2020)
1
082-1107.
9 H. Cai, L.L. Xu, H.Y. Lai, J. Y. Liu, S.W. Ng, D. Li, A highly emissive and stable zinc(ii) metal-organic
framework as a host-guest chemopalette for approaching white-light-emission. Chem. Commun. 53 (2017)
7
917-7920.
0 Y.Q. Chen, G.R. Li, Z. Chang, Y.K. Qu, Y.H. Zhang, X.H. Bu, A Cu(I) metal-organic framework with
-fold helical channels for sensing anions. Chem. Sci. 4 (2013) 3678-3682.
3
3
4
1 Y.L. Wu, G.P. Yang, X. Zhou, J. Li, Y. Ning, Y.Y. Wang, Three new luminescent Cd(ii)-MOFs by
regulating the tetracarboxylate and auxiliary co-ligands, displaying high sensitivity for Fe3+ in aqueous
solution. Dalton Trans. 44 (2015) 10385-10391.
1
7

3
3
2 K.S. Asha, R. Bhattacharjee, S. Mandal, Complete transmetalation in a metal-organic framework by
metal ion metathesis in a single crystal for selective sensing of phosphate ions in aqueous media. Angew.
Chem. Int. Ed. 55 (2016) 11528-11532.
3 B. Parmar, Y. Rachuri, K.K. Bisht, R. Laiya, E. Suresh, Mechanochemical and conventional synthesis of
Zn (II)/Cd (II) luminescent coordination polymers: Dual sensing probe for selective detection of
chromate anions and TNP in aqueous phase. Inorg. Chem. 56 (2017) 2627-2638.
3
3
4 R. Lv, H. Li, J. Su, X. Fu, B. Yang, W. Gu, X. Liu, Zinc metal-organic framework for selective detection
and differentiation of Fe (III) and Cr (VI) ions in aqueous solution. Inorg. Chem. 56 (2017) 12348-12356.
5 X.Y. Guo, Z.P. Dong, F. Zhao, Z.L. Liu, Y.Q. Wang, Zinc (II)-organic framework as a multi-responsive
photoluminescence sensor for efficient and recyclable detection of pesticide 2, 6-dichloro-4-nitroaniline,
Fe (III) and Cr (VI). New J. Chem. 43(2019) 2353-2361.
3
6 T. Wiwasuku, J. Boonmak, K. Siriwong, V. Ervithayasuporn, S. Youngme, Highly sensitive and
selective fluorescent sensor based on a multi-responsive ultrastable amino-functionalized Zn (II)-MOF
for hazardous chemicals. Sensor Actuat B-Chem, 284(2019) 403-413.
Research Highlights
a 2-periodic sql coordination polymer is designed via a double-bent-mixed-ligand strategy.
3
+
2-
2-
This coordination polymer can sensitively and selectively detects Fe cations, CrO
anions in aqueous media.
4
and Cr
2
O
7
1
8

The luminescence quenching mechanism has been investigated by the UV-Vis spectral overlap
experiment.
Graphical Abstract
Ling Li: Experiments, Conceptualization, Methodology, Software, Writing - original
draft. Zhao-Yang Deng: Experiments. Xin Xie: Experiments. Sheng-Yong You: Data
curation. Investigation, Visualization. Kai-Hong Chen: Data curation. Investigation.
Jin-Feng Le: Investigation, Visualization. Ji-Yong Zou: Supervision, Funding
acquisition, Writing - review & editing.
1
9