A multifunctional Eu-based coordination polymer luminescent sensor for highly sensitive and selective detection of Fe3+ and acetone

Article abstract of DOI:10.1016/j.poly.2019.114216

A new 3D Eu-based coordination polymer, ([Eu(L)(H₂O)₃]Cl·H₂O)_n (1) (H₂L = (4-(pyridyl-N-oxide)methylphosphonic acid), was successfully self-assembled via diffusion method at room temperature and characterized by single-crystal X-ray diffraction, elemental analyses, powder X-ray diffraction, thermogravimetric analyses and FT-IR. Single-crystal X-ray diffraction analysis shows that 1 features 3D (4,5)-connected (3·4·5·6²·7)(3²·4²·5·6³·7²) topological framework with large 1D channels. Photoluminescent spectra of 1 exhibit the strong characteristic luminescence of Eu³⁺. More importantly, sensing experiments exhibit that 1 can be used as a fluorescence sensor for detecting Fe³⁺ and acetone with excellent sensitivity, great selectivity, reproducibility and low detection limits for Fe³⁺, and acetone are 0.21 μM and 0.0246 vol percent. It is the first example of Eu-based phosphonate sensor for simultaneous detection of Fe³⁺ and acetone.

Full text of DOI:10.1016/j.poly.2019.114216

Journal Pre-proofs
A Multifunctional Eu-based Coordination Polymer Luminescent Sensor for
3
+
Highly Sensitive and Selective Detection of Fe and Acetone
Cheng-Bo Yang, Chun-Bo Jiang, Mu-Yin Zhang, Xue Chen, Ping Zou, Rui-Wu
Yang, Han-Bing Rao, Guang-Tu Wang
PII:
S0277-5387(19)30661-8
DOI:
https://doi.org/10.1016/j.poly.2019.114216
POLY 114216
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
19 June 2019
21 October 2019
25 October 2019
Please cite this article as: C-B. Yang, C-B. Jiang, M-Y. Zhang, X. Chen, P. Zou, R-W. Yang, H-B. Rao, G-T. Wang,
A Multifunctional Eu-based Coordination Polymer Luminescent Sensor for Highly Sensitive and Selective
3
+
Detection of Fe and Acetone, Polyhedron (2019), doi: https://doi.org/10.1016/j.poly.2019.114216
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A Multifunctional Eu-based Coordination Polymer Luminescent Sensor for Highly Sensitive and
3
+
Selective Detection of Fe and Acetone
[
a]
[a]
[a]
[a]
[a]
[b]
Cheng-Bo Yang, Chun-Bo Jiang, Mu-Yin Zhang, Xue Chen, Ping Zou, Rui-Wu Yang,
[
a]
[a]
Han-Bing Rao, and Guang-Tu Wang*
a
College of Science, Sichuan Agriculture University, Ya’an 625014, China
b
College of Life Science, Sichuan Agriculture University, Ya’an 625014, China
Abstract
A
new
3D
Eu-based
coordination
polymer,
([Eu(L)(H
2
O)
3
]Cl·H
2
O)
n
(1)
(
H L=(4-(pyridyl-N-oxide)methylphosphonic acid), was successfully self-assembled via diffusion
2
method at room temperature and characterized by single-crystal X-ray diffraction, elemental analyses,
powder X-ray diffraction, thermogravimetric analyses and FT-IR. Single-crystal X-ray diffraction anal-
2
2
2
3
2
ysis shows that 1 features 3D (4,5)-connected (3·4·5·6 ·7)(3 ·4 ·5·6 ·7 ) topological framework with
3
+
large 1D channels. Photoluminescent spectra of 1 exhibit the strong characteristic luminescence of Eu .
More importantly, sensing experiments exhibit that 1 can be used as a fluorescence sensor for detecting
3
+
Fe and acetone with excellent sensitivity, great selectivity, reproducibility and low detection limits for
3
+
Fe , and acetone are 0.21 μM and 0.0246 vol%. It is the first example of Eu-based phosphonate sensor
3
+
for simultaneous detection of Fe and acetone.
3
+
Keywords: Coordination Polymer; Luminescence; Sensor; Fe ; Acetone
Corresponding author.
E-mail address: gtwang@sicau.edu.cn
1

Introduction
Coordination polymers (CPs) are among the most active research fields in the design and preparation
of novel inorganic-organic hybrid materials,[1] which are widely used in the areas of catalysis , gas
[2]
[
3]
[4]
[5]
[6]
[7]
storage and separation , bioimaging , proton conduction , magnetism and fluorescence . So far, a
large number of fluorescent CPs with infinite three-dimensional structures have been successfully
[
8]
[9]
self-assembled , by rationally designed ligands as linkers and carefully selected metal ions as nodes.
For example, Liu et al. used transition metal [Zn(ClO ·6H O], 2,2'-bipyridine and
-(3',5'-dicarboxylphenoxy)phthalic acid to form Zn-coordination polymer material with strong photo-
4
)
2
2
3
luminescence by hydrothermal reaction.[10] Compared with the transition metal CPs, lanthanide metals
feature excellent inherent photoluminescence features, i.e., the narrow emission peak, large Stokes shift,
long fluorescence lifetime and pure chromaticity.[11] Thus, the design, synthesis and characterization of
luminescent lanthanide CPs (Ln-CPs) are one of the fastest-growing fields in material research today.[12]
Particularly, they are used to detect different types of analytes, including small organic molecules[13]
metal cations[14], anions[15] and explosives[16].
,
Ferric ions, widely found in environmental and biological systems, play crucial roles in almost all
3
+
types of biosystems like cell metabolism, synthesis of DNA and RNA. However, Fe level above and
below the normal allowable limits can cause serious illness. Acetone is one of the most common organ-
ic solvents used in the laboratory and industrial production [17]. It is flammable, toxic, explosive and
harmful to the environment [14a,18]. Conventional methods of detecting Fe and acetone include spec-
trophotometry, atomic absorption spectroscopy, ion mobility spectroscopy, inductively coupled plasma
atomic emission spectroscopy, electrochemical methods gas chromatography and mass spectrometry.
However, these methods sometimes mainly require complicated pre-processing and expensive instru-
ments.[13a, 14b, 17a, 19] In contrast, Ln-CPs fluorescence sensors are convenient and economical in detect-
3+
2

3
+
ing Fe and acetone. Not long ago, Ma et al. reported a luminescent Tb-CPs which can be used as a
3
+
[1f]
multifunctional probe to simultaneously sense Fe and acetone. Despite a variety of Ln-CPs sensors
reported to date, more efforts were focused on the lanthanide carboxylic acid complexes.[18b, 20] Lantha-
nide phosphonate sensors are rarely developed.[21] Compared with carboxylates, phosphonates form
stronger bonds with metal atoms, which exhibit higher thermal and chemical stabilities. [20b] Moreover,
phosphonate groups have more coordination centers, which can yield rich structural diversities and fas-
cinating luminescent properties.[21c] To the best of our knowledge, lanthanide phosphonates have not
3
+
been explored as multifunctional sensors for the detection of Fe and acetone. So, it is of significance
to study the synthesis, structure, properties and sensing applications of lanthanide phosphonates.
In previous work, we reported series of lanthanide phosphonates constructed by
2
-(pyridyl-N-oxide)methylphos-phonic acid ligand. Among them, [Eu(HL)((C
2
O
4
)
0.5
)
2
(H
2
O)]·3H O
2
have been confirmed to have excellent photoluminescence properties.[22] However, the construction of
an infinite 3D network requires a second ligand assist. Speculatively, this may be because the
phosphonate group and the pyridyl group of the ortho-phosphonate ligand are closer, hindering the
further growth of the complex in three dimensions. With the further increase of the distance between
pyridine and phosphonate, the components may construct a 3D network without the second ligand, and
4
-(pyridyl-N-oxide)methylphosphonic acid (H
Fortunately, H
L and Eu3+ form a new type of Eu-based lanthanide coordination polymer at room
temperature (just using one tube). Structural analysis reveals the complex displays (4,5) two-node 3D
2
L) could be designed and synthesized (Scheme 1).
2
2
2
2
3
2
network with 1D channels, the point symbol of (3·4·5·6 ·7) (3 ·4 ·5·6 ·7 ). The solid-state
luminescence behavior of 1 indicates that H
L can effectively sensitize Eu3+ characteristic red
luminescence. Further studies of the sensing behavior of 1 show that 1 can detect Fe and acetone by
2
3
+
3
+
fluorescence emission and quenching, and has high Ksv values and low detection limits for Fe and
3

acetone.
Experimental Section
Materials and methods
All chemicals and reagents are commercially available as reagent grades and are used without fur-
-1
ther purification. FT-IR spectra were carried out in the range of 4000-500 cm using DGTS detector (32
scans) by using KBr disks. Elemental analysis data of C, H, N was collected with an Elementar Vario
1
ELIII analyzer. H NMR spectra were measured using a DRX-400 MHz (Bruker) superconduct-
ing-magnet NMR spectrometer. Thermal analyses were conducted on a Perkin-Elmer STA 6000 with a
heating rate of 10 °C/min at the temperature ranging from 40 to 650 °C under air. Powder X-ray diffrac-
tion patterns (PXRD) were carried out on a D/MAX-3C X-ray diffractometer using Cu Kα radiation
with 2θ range of 5-50° and scanning rate of 0.02°/s (2θ) at room temperature. UV−vis absorption spec-
tra are measured with an Agilent 8453 spectrometer. The luminescent excitation/emission spectra of the
powdered solid samples were recorded at room temperature on an Edinburgh FL920. The absolute ex-
ternal luminescent quantum yield and fluorescence lifetime were determined using an integrating sphere
equipped on an Edinburgh FLS 920 phosphorimetry. Adsorption data was collected on outgassed sam-
ples (160°C for 12 h) on a Micromeritics ASAP 2460 gas adsorption analyzer.
Synthesis of 4-chloromethylpyridine(I).
Firstly, a sample of 4-chloromethylpyridine hydrochloride (5.00 g, 30.48 mmol) was dissolved in
water (15 mL), and dichloromethane (25 mL) was added under stirring conditions. Then, saturated
aqueous NaHCO solution was added dropwise to give a pH=8 solution. After a while, the phases were
3
separated, and the organic compounds were extracted with dichloromethane (6 × 30 mL). Finally, the
4

organic layers were combined and dried with anhydrous magnesium sulfate before the solvent was re-
moved.
Synthesis of (4-pyridylmethyl) diethyl phosphate(II).
Diethyl phosphite (8 mL, 62.19 mmol) and sodium (1.2 g, 52.19 mmol) were added to a toluene
(30 mL) under nitrogen. Then, 4-chloromethylpyridine (I) in toluene (15 mL) was added to the mixture
at room temperature. The resulting suspension was stirred in the dark for 24 hours. After that, the or-
ganic compounds were extracted with ethyl acetate (4 × 20 mL). The organic layers were combined and
concentrated. The light yellow oil (6.46 g, 28.20 mmol) was purified by flash chromatography on silica
1
gel (PE:EA (4:1 V/V)). Yield: 92.50%. H NMR (400 MHz, CDCl
3
) δ = 8.48-8.03 (m, 2H), 7.08 (d,
J=28.1, 2H), 4.08-3.69 (m, 4H), 2.99 (ddd, J=28.3, 15.6, 12.3, 2H), 1.22-0.85 (m, 6H).
Synthesis of 4-((diethoxyphosphoryl)methyl)pyridine-1-oxide(III).
m-CPBA (7.8 g, 33.90 mmol) and II (6.46 g, 28.20 mmol) in DCM (50 mL) were stirred at room
temperature overnight, then the solvent was evaporated under vacuum. Purification of the residue was
achieved using flash chromatography (PE:EA (2:1 V/V)) to give the oily liquid (5.88 g, 23.99 mmol).
1
Yield: 85.07%. H NMR (400 MHz, CDCl
3
) δ = 8.11 (d, J=6.0, 2H), 7.22-7.14 (m, 2H), 4.02 (dq,
J=14.3, 7.1, 4H), 3.10 (s, 1H), 3.04 (s, 1H), 1.27–1.15 (m, 6H).
Synthesis of 4-(pyridyl-N-oxide)methylphosphonic acid (H L).
2
III (4-((diethoxyphosphoryl)methyl)pyridine-1-oxide) (5.88 g, 23.99 mmol) in HCl (25 mL, 18%)
o
was stirred at 90 C for 24 h. The resulting solution was concentrated under reduced pressure to give oil.
Then, the oil in acetone (50 mL) was stirred vigorously at room temperature and a white powder solid
5

was formed. Finally, the filtrate was removed by filtration, and the white solid was dried under vacuum
1
(
3.40 g, 17.97 mmol). Yield: 74.89%. Mp: 147.7-148.5 °C. H NMR (400 MHz, D
2
O) δ = 8.31 (dd,
J=11.8, 5.5, 2H), 7.61-7.34 (m, 2H), 3.21-2.96 (m, 2H).
Synthesis of ([Eu(L)(H
2
O)
3
]Cl·H
2
O)
n
(1).
The aqueous solutions of H
2
L (1 mL, 0.10 mmol) and EuCl
3
·6H O (0.5 mL, 0.10 mmol) were
2
placed in a test tube, and then acetonitrile was diffused into the mixture. Thereafter, the test tube was
sealed and stored for 15 days at room temperature. Colorless crystals of 1 were obtained in 49.51%
yield (based on Eu). Elemental analysis (%) Calcd for 1 (C
6
H
14ClNO PEu: 446.56): C, 16.12%; H,
8
-
1
3
1
5
.14%; N, 3.14%. Found: C, 16.19% ; H, 3.11% ; N, 3.11% . IR (KBr, cm ): 3440s, 1647s, 1490s,
450m, 1423m, 1236vs, 1215s, 1195s, 1151m, 1115m, 1053m, 997m, 850v, 790m, 702vs, 601v, 547vs,
03s.
X-ray Crystallography.
The diffraction data of the complex was collected through a Bruker APEX-II CCD with graphite
monochromated Mo Kα radiation (λ = 0.71073 Å). Empirical absorption corrections were operated us-
ing the SADABS program. The structure was solved and the refined by the direct method and
full-Matrix least-squares method on F , respectively [23]. All non-hydrogen atoms were refined with an-
isotropic thermal parameters. And hydrogen atoms attached to the carbon atoms were placed in the cal-
culation position and refined using a ride model.
2
6

Results and Discussion
Crystal structure description
Single-crystal X-ray diffraction analysis reveals that the 1 crystallizes in the monoclinic system
with the P12
1
/c1 space group. As shown in Fig. 1a, the asymmetric unit of 1 consists of one crystallo-
graphically independent Eu3+ ion, one L , three coordinating water molecules and one lattice water
2-
3
+
molecule and one chloride ion. The unique Eu ion is eight-coordinated in a Snub diphenoid J84 ge-
2
-
ometry defined by five oxygen atoms (O1C, O2B, O3B, O3A, O4) from four L , and the remaining
three coordination sites are occupied by three oxygen atoms from the coordinating water molecule
(
Figure S1).[24] O4 and O3A are derived from the phosphonate of two ligands, respectively. O2B and
2
-
2-
O3B are derived from a phosphonate of L . O1C is derived from the N-O oxides of the L . O5W, O6W,
and O7W are from three coordinating water molecules. Similar to other reported Eu complexes based
on phosphonate ligands, [25] the bond distances between Eu-O (L ) are 2.318(3) and 2.678(3) Å with the
average bond length of 2.414 Å. Moreover, the crystallographic and structural data of 1 are summa-
rized in Table S1-S2.
2-
3
+
In the complex 1, the neighbouring Eu ions are connected by ligand phosphate groups to produce
a chain structure with an infinite corrugated shape along the a-axis. The distance between Eu···Eu is
4
.1782(5) Å and 5.4344(4)Å, respectively. Eu-O-Eu angle is 112.60° (Fig 1b). Each chain is further
bonded to one another by ligands to form a three-dimensional framework with 1D channels along the
2
-
3+
a-axis direction (Fig 1c). The L acts as a four-coordination linker, coordinating to four Eu via its
three phosphonate oxygen atoms and one pyridine N-O oxygen atom with bridging and coupling modes,
3
+
wherein the phosphate group is coordinated to three Eu ions; nitrogen oxide pyridine oxygen atom is
7

3
+
linked to a Eu ion (Fig S2). Furthermore, the porosity of the 1 was calculated by PLATON to be 20%,
after removing the lattice water molecules and Cl-[26]
.
To simplify the three-dimensional structure of complex 1, a topological analysis was executed.
3
+
2-
Eu and L can be regarded as five- and four-coordinated node, respectively. Thence this framework
could be simplified as a 3D (4,5)-connected bimodal topological structure with the Schläfli symbol as
2
2
2
3
2
[27]
(
3·4·5·6 ·7) and (3 ·4 ·5·6 ·7 ) calculated by the TOPOS program (Fig. 1d).
Thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD)
In order to investigate the phase purity and the stability of the entire skeleton of complex 1, powder
X-ray diffraction (PXRD) and thermogravimetric (TG) measurements were carried out. The PXRD pat-
tern for 1 is presented in Fig.S3. The diffraction peaks of both simulated and experiment patterns are in
good agreement with each other, indicating the phase purities of 1.
The thermal stability test of complex 1 was performed under air conditions at the temperatures
ranging from 40 to 650 °C (Fig. S4). The initial weight loss of 15.7% corresponds to the loss of four
water molecule (one solvent water molecule and three coordinating water molecules) during 40-250 °C
(calcd. 16.1%). Further heating to 400 °C shows little loss of weight, indicating the dehydrated frame-
work of 1 is thermally stable over this temperature range. Finally, the residue weight is 69.4%, probably
due to the formation of a mixture of Eu
2
O
3
and EuPO in a molar ratio of 1:1 (calcd. 67.1%).
4
Photoluminescence properties
The solid-state excitation and emission spectra of complex 1 have been measured at ambient tem-
3
+
perature (Fig. 2). The emission spectrum of 1 shows photoluminescence with four typical Eu emission
5
→7F
(j=1, 2, 3 and 4) tran-
peaks at 592 nm, 612 nm, 651 nm, and 701 nm (λex= 293 nm) due to the D
0
j
sition originating from antenna effects. The most intense emission peak is located at 612 nm, corre-
8

5
→7F transition [28]. The fluorescence lifetime of 1 is 2.36 ms, which is in line with
sponding to the D
0
2
the single exponential curve. The fluorescence quantum yield of this complex is 9.3%.
Sensing of Fe3+
In order to study the potential of complex 1 for the sensing of metal cations, the finely ground
powder sample of 1 (4mg) was dispersed in a series of DMF (4mL) solutions containing M(NO
)
3 X
x+
+
2+
+
2+
2+
2+
2+
2+
3+
+
2+
3+
2+
(
concentration = 1mM; M = Na , Ca , Ag , Ni , Pb , Mg , Ba , Cd , Al , K , Zn , Cr , Co ,
2
+
3+
2+
3+
2+
Cu , Fe ; since Fe can be easily oxidized to Fe , the influence of Fe is not discussed herein), then
treated with ultrasonication for 30 min, and aged for 12 h to form a stable suspension. Finally, the ul-
trasonication was performed for 30 min before the fluorescence detection. The fluorescence results
show that the fluorescence intensity of 1 is almost completely quenched in the Fe3+ nitrate solution,
while other metal ions have no such significant effect (Fig. 3). This phenomenon implies that 1 can
3
+
3+
sense Fe selectively. Moreover, when 1, Fe and other various metal ions (including the same con-
3
+
centration of Fe ) exist simultaneously, the fluorescence intensity of 1 is also significantly quenched
(Fig. S7a). The results indicate that the fluorescence quenching effect of 1 is not inhibited by other met-
3
+
al ions while detecting Fe . That is, the anti-interference ability of 1 is strong.
3
+
To further study the detection limit of complex 1 for Fe , the fluorescence intensity of 1 in the
presence of different concentrations of Fe3+ was measured using a fluorescence titration method. As
3
+
-4
shown in Fig. 4a, as the concentration of Fe increases from 0 to 2.5×10 M, the fluorescence intensity
-6
3+
of 1 decreases continuously. The detection limit reaches 5×10 M; the quenching effect of Fe reaches
4.5% (The quenching effect is defined by (I −I)/I ×100%, where I and I refer to the fluorescence in-
tensity of 1 before and after the addition of Fe , respectively[14c]). When the Fe3+ concentration is
1
0
0
0
3
+
-4
3+
2
.5×10 M, the quenching effect reaches 83.4%. The fluorescence quenching effect of Fe on 1 was
9

further evaluated using the Stern-Volmer formula I
0
/I =1+Ksv × [Q] [29] (I
0
and I refer to the fluorescence
3
+
3+
intensity of 1 at 612 nm before and after the addition of Fe , [Q] refers to the concentration of Fe , and
K
sv is the fluorescence quenching constant). The Ster-Volmer plot (Figure 4b) shows a good linear cor-
3
+
2
relation between the fluorescence intensity of 1 and the concentration of Fe at low concentrations (R
4
-1
=
0.9961): the Ksv is estimated to be 1.2549×10 M , and the detection limit is calculated to be 0.21 μM.
The Ksv value of 1 is comparable to those reported in the previous literature (Table S3)[30]
.
Sensing of Acetone molecules
3
+
Inspired by the complex 1 sensing behavior of Fe , the sensing ability of 1 for different small or-
3
+
ganic molecules is further explored. Similar to the previous 1 for Fe sensing, the powder sample of 1
(4 mg) was added to 4 mL various organic small molecules (methanol, ethanol, DMF, acetonitrile, ethyl
acetate, methyl tert-butyl ether, DCM, chloroform, THF, dioxane, cyclohexane and acetone). After that,
the mixture was treated by ultrasonication for 30 min and then aged for 12 h to form a stable suspension.
The results show that (Fig. 5), acetone can completely quench the emission of 1, indicating that 1 can be
used as a fluorescent sensor for acetone. Of course, the 1 has also been studied the ability to selectively
detect acetone. When 1, acetone and other small organic molecules (the same volume of each small or-
ganic molecule) are present simultaneously, the fluorescence intensity of 1 is also quenched (Fig. S7b).
It indicates that 1 has good anti-interference ability for other organic small molecules in sensing ace-
tone.
The detection limit of complex 1 for acetone is also explored. In Fig. 6, the fluorescence emission
intensity of 1 decreases with the increased volume fraction of acetone (0-4.8%): the detection limit is
0
.1% and the quenching effect reaches 12.7%. When the volume fraction of acetone reaches 4.8%, the
quenching effect achieves 98.1%. Further testing the acetone detection limit using the Stern-Volmer
1
0

2
formula with a linear correlation of R = 0.9855 at low concentrations, the Ksv reaches 1.25 and the de-
tection limit is calculated to be 0.0246 vol% (Table S3) [31]
.
Regeneration performance
It is well known that the recyclability of sensing materials is one important parameter in evaluating
3
+
the usability of a sensor. Therefore, the regeneration performance of 1 for the detection of Fe and ace-
3
+
tone are also investigated. As shown in Fig. 7, after 1 sensed Fe and acetone, the samples were simply
3
+
washed several times with DMF to remove residual Fe and acetone, and then recovered by centrifuga-
tion. The fluorescence detection results show that the fluorescence intensity of 1 can be recovered sub-
3
+
stantially at least 5 times for the detection of Fe and acetone. It can be seen from the PXRD pattern
3
+
that the crystal structure of 1 does not collapse significantly after five cycles of detection of Fe and
acetone.
3
+
3+
Interestingly, the characteristic diffraction peaks of 1@Fe , 1(5)@Fe and 1(5)@Acetone are
slightly shifted from 1, while the diffraction peaks of 1@Acetone fit well with 1 (Fig.S3). Therefore, the
PXRD of 1@DMF is collected to verify if DMF causes these shifts. The results show that the PXRD of
3
+
3+
1
@DMF can be fitted with 1@Fe , 1 (5)@Fe and 1 (5)@Acetone diffraction peaks. In other words,
DMF causes these PXRD diffraction peak shifts. If DMF is removed, the shift of this PXRD character-
3
+
istic diffraction peak may be restored. As expected, the diffraction peaks shift of 1@Fe after washing
with an acetonitrile/H O (V/V:5/1) mixed solvent was recovered. This phenomenon further indicates
2
that the displacement of the characteristic diffraction peak of PXRD may be caused by DMF solvent
molecules (Fig.S3).
Mechanism of fluorescence sensing
11

In prior literature data, the generation of fluorescence quenching for 1 may come from the follow-
ing aspects: (i) the collapse of crystal structure;[32] (ii) the absorption and/or excitation spectra of 1
overlap with absorption spectra of analytes;[1f, 19c] (iii) the exchange of central metal ions of 1 and target
cations inter-ion;[33] (iv) the interaction between metal cations and organic ligands.[34]
3
+
Firstly, the PXRD patterns of 1@Fe and 1@DMF show that the PXRD patterns of the two fits
3
+
well (Fig. S3), indicating that the crystal structure of 1 does not change before and after Fe treatment.
3
+
Therefore, the crystal structure collapse is first excluded. Secondly, in the Fe limit detection experi-
3
+
ment, it is found that the Fe concentration increased slightly, and the fluorescence intensity of 1 de-
3
+
creased slightly in a short time, suggesting that 1 has a fast response to Fe , thus excluding ion ex-
change between central metal ions of 1 and target cations. Simultaneously, the fluorescence perfor-
mance of 1 after simple cleaning with DMF restored, and it also suggests that cation exchange is not the
3
+
fluorescence quenching mechanism of 1 sensing Fe .
3
+
Thirdly, it is found by UV-visible absorption experiments that the absorption spectrum of Fe has
a large coverage with the excitation spectrum of 1 (Fig. S5a), while other metal ions have no large cov-
3
+
erage. This phenomenon indicates that competition for energy absorption by 1 and Fe is one of the
reasons for 1 fluorescence quenching.
3
+
Fourthly, for 1 before and after treatment with Fe , the O1s peak in the XPS spectrum is desig-
nated as O in the ligand pyridine oxynitride and phosphonate groups, and the N1S peak is designated as
the ligand pyridine ring (Fig.S6). The N1S peak changes from 403.1 eV to 402.5 eV and the O1S peak
changes from 531.4 eV to 531.8 eV , due to the weak interaction of N and O atom in Fe3+ and 1.
3
+
Therefore, there is a weak interaction between Fe and the ligand of 1, and the energy absorbed by the
3
+
ligand is partially transferred to Fe , which also causes a decrease in fluorescence intensity.
1
2

For acetone, the mechanism of fluorescence quenching that occuring through previous literatures
show that effective sense acetone based on 1 is often attributed to energy absorption competition[1g, 21c,
35].
Therefore, we first tested the PXRD pattern of acetone-treated 1 and found that it can be well fitted,
which proves that the crystal structure of 1 does not collapse, excluding the reason of crystal structure
damage.
After the UV absorption test of each organic solvent, it is found that the absorption spectrum of
acetone and the excitation spectrum of 1 were greatly covered, while other organic small molecules
were weaker than acetone (Fig. S5b). It is obvious that the energy absorption of 1 and acetone is the
main reason for the quenching of 1.
3
+
These phenomena indicate that the 1 can be used as potential fluorescent sensors for Fe and ace-
tone, with high sensitivity, high selectivity and regenerability.
Conclusions
In summary, a new coordination polymer ([Eu(L)(H
self-assembled by 4-(pyridyl-N-oxide)methylhosphonic acid (H L) ligand via using diffusion method at
room temperature. 1 displays a three-dimensional network structure with 1D channels, presenting a
2
O)
3
]Cl·H O)
2 n
was successfully
2
2
2
2
3
2
(
4,5)-connected topological framework with a point symbol of (3·4·5·6 ·7) (3 ·4 ·5·6 ·7 ). The lumi-
nescence sensing experiments of 1 demonstrate excellent selectivity and high sensitivity for the detec-
3
+
3+
tion of Fe and acetone, and the detection limits for Fe and acetone are 0.21μM and 0.0246 vol%, re-
spectively. In addition, the sensor can be easily and quickly regenerated, indicating good recyclability
3
+
for the detection of Fe and acetone. These properties indicate that the 1 functional material has great
3
+
potential for detecting acetone and Fe .
1
3

Acknowledgments
This work was supported by Two-Way Support Programs of Sichuan Agricultural University (Nos.
3572832 and 03572227).
0
Appendix A. Supplementary data
CCDC 1872143 contains the supplementary crystallographic data for complex 1. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk.
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1
9

Figure Captions
Scheme 1. Synthesis of H L.
2
3
+
Figure 1. (a) Coordination environment of Eu in 1; (b) The 1D chain bridged by phosphoric acid; (c)
3
D stacked view of 1 along the a-axis; (d) the topology of 1.
2
0

Figure 2. Fluorescence excitation and emission spectra of 1.
5
→7F
transition of 1 dispersed in DMF solutions of dif-
Figure 3. Luminescence intensities of the D
0
2
ferent metal ions. Excitation wavelength: 280 nm.
2
1

3
+
Figure 4. (a) Response of fluorescence emission spectra of 1 to various concentrations of Fe ; (b) line-
3
+
ar fitting curves of luminescence intensities quenched by Fe with different concentrations. Excitation
wavelength: 280 nm.
5
→7F
transition of 1 dispersed in different small organic
Figure 5. Luminescence intensities of the D
0
2
molecules. Excitation wavelength: 280 nm.
2
2

Figure 6. (a) Response of fluorescence emission spectra of 1 to various concentrations of Acetone; (b)
linear fitting curves of luminescence intensities quenched by Acetone with different concentrations. Ex-
citation wavelength: 280 nm.
3
+
Figure 7. (a) Five cycle tests of 1 towards sensing Fe in DMF; (b) Five cycle tests of 1 towards sens-
ing acetone in DMF. Excitation wavelength: 280 nm.
Mandatory graphical abstract
A new Eu-based phosphonate coordination polymer was successfully synthesized by diffusion at room
temperature. The obtained coordination polymer can be used as a fluorescent sensor to sensitively and
2
3

3
+
selectively sense Fe and acetone.
2
4