One-dimensional channel-structured Eu-MOF for sensing small organic molecules and Cu2+ ion

Article abstract of DOI:10.1039/c3ta12270k

Two new lanthanide metal-organic frameworks Ln(FBPT)(H₂O)(DMF) (FBPT = 2′-fluoro-biphenyl-3,4′,5-tricarboxylate, Ln = Eu and Tb) were prepared under solvothermal conditions. Single crystal X-ray diffraction analyses reveal that the two compounds are isostructurally related with the same one-dimensional channel structure on the basis of FBPT as an organic linker. Herein, the Eu(FBPT)(H₂O)(DMF) (EuL) is selected as a representative sample for luminescent measurements. Study of the photoluminescence properties reveals that the EuL exhibits red emission, corresponding to the ⁵D₀ → ⁷F_J (J = 1-4) transitions of the Eu³⁺ ion under UV light excitation. Most interestingly, when this compound was immersed in the different organic solvents and metal ion DMF solutions, it shows highly selective and sensitive sensing for small organic molecules and Cu²⁺ ions. In connection to this, a probable sensing mechanism was also discussed in this paper.

Full text of DOI:10.1039/c3ta12270k

Journal of
Materials Chemistry A
View Article Online
View Journal | View Issue
PAPER
One-dimensional channel-structured Eu-MOF for
sensing small organic molecules and Cu2+ ion†
Cite this: J. Mater. Chem. A, 2013, 1,
11043
Zhaomin Hao,ab Xuezhi Song,ab Min Zhu,ab Xing Meng,ab Shuna Zhao,ab
a
a
a
Shengqun Su,ab Weiting Yang, Shuyan Song and Hongjie Zhang
*
Two new lanthanide metal–organic frameworks Ln(FBPT)(H2O)(DMF) (FBPT ¼ 20-fluoro-biphenyl-3,40,5-
tricarboxylate, Ln ¼ Eu and Tb) were prepared under solvothermal conditions. Single crystal X-ray
diffraction analyses reveal that the two compounds are isostructurally related with the same one-
dimensional channel structure on the basis of FBPT as an organic linker. Herein, the Eu(FBPT)(H2O)(DMF)
(EuL) is selected as
a representative sample for luminescent measurements. Study of the
photoluminescence properties reveals that the EuL exhibits red emission, corresponding to the 5D0
/
Received 12th June 2013
Accepted 12th July 2013
7FJ (J ¼ 1–4) transitions of the Eu3+ ion under UV light excitation. Most interestingly, when this
compound was immersed in the different organic solvents and metal ion DMF solutions, it shows highly
selective and sensitive sensing for small organic molecules and Cu2+ ions. In connection to this, a
probable sensing mechanism was also discussed in this paper.
DOI: 10.1039/c3ta12270k
www.rsc.org/MaterialsA
for host–guest recognition and to tune their functional properties,
however, it is still a challenge to get the desired microporous Ln-
1 Introduction
Over the last two decades, extensive efforts on metal–organic
frameworks (MOFs) have not only led to the creation of a huge
number of diverse topologies with aesthetic beauty, but also
initiated rational design strategies to construct porous materials
with high surface areas, predictable structure, and tunable pore
sizes for use in some important applications, such as gas storage,
separation, heterogeneous catalysis, sensing and drug delivery.1–7
Among the diverse MOFs, microporous lanthanide metal–organic
frameworks (Ln-MOFs) are well known for their unique optical
and magnetic properties, as well as their characteristic coordi-
nation preferences.8 Taking advantage of the optical properties,
microporous Ln-MOFs possess lots of fascinating features, such
as Stokes' shis, high color purity, and relatively long lumines-
cence lifetimes, which originate from f–f transitions via an
“antenna effect” can be investigated.9–11 These optical properties
of microporous Ln-MOFs make them especially attractive for
potential applications in uorescence probes and luminescence
bioassays.12 Meanwhile, such progress in the optical properties of
microporous Ln-MOFs also guides and inspires us to rationally
design and synthesize more characteristic microporous Ln-MOFs
MOFs. This is because lanthanide ions have a larger coordination
sphere and more exible coordination geometry, and the open
lanthanide sites formed in situ during activation/de-solvation tend
to bind back with the oxygen and/nitrogen donors from the
organic linkers to form a condensed structure.
Nonetheless, the above problems did not deter researchers
from exploring the luminescent microporous Ln-MOFs for their
sensing applications. Over the past few years, a wide range of
luminescent lanthanide-based MOFs, for sensing cations,
anions, small molecules and vapors have been realized and
reported by Chen, Lee, Harbuzaru and Liu et al.13 In fact, to make
use of the luminescent Ln-MOFs for the unique recognition of
small molecules and cations, our group have also recently real-
ized a few microporous luminescent Ln-MOFs for sensing
applications.14 Throughout recent years, we have been constantly
dedicated to expanding and improving the luminescent micro-
porous Ln-MOFs for their sensing applications. As far as we
know, reports about uorinated microporous Ln-MOFs as lumi-
nescent probes for sensing small organic molecules and metal
ions are still relatively rare. Herein, we present a uorinated
luminescent material Eu(FBPT)(H2O)(DMF) (EuL) as a highly
selective uorescent probe targeting small organic molecules and
Cu2+ ions, and the possible sensing mechanism is also discussed.
aState Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's
Republic of China. E-mail: hongjie@ciac.jl.cn; Fax: +86 43185685653; Tel: +86
43185262127
2 Experimental
2.1 Materials and measurements
bGraduate University of Chinese Academy of Sciences, Beijing, 100049, People's
Republic of China
† Electronic supplementary information (ESI) available. CCDC 923447 and
923448. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3ta12270k
All chemicals were commercially available and used as
received without further purication. Scheme S1† shows the
This journal is ª The Royal Society of Chemistry 2013
J. Mater. Chem. A, 2013, 1, 11043–11050 | 11043

View Article Online
Journal of Materials Chemistry A
Paper
synthetic route to the ligand FBPT. Elemental analyses of the 39.22; H, 2.74; N, 2.54; Tb, 28.83. Found: C, 39.01; H, 2.93; N,
C, H, N, and Ln ions were carried out on a VarioEL analyzer 2.41; Tb, 28.56.
(Elementar Analysensysteme GmbH) and via inductively
coupled plasma (ICP) atomic emission spectrometric analysis
(POEMS, TJA), respectively. 1H NMR spectra were recorded on
a Mercury Plus-400 spectrometer in DMSO-d6. Mass spectra
(MS) were run on a Thermo Scientic LXQ mass spectrometer
equipped with an electrospray source. Absorption measure-
ments were carried out using a Shimadzu UV-3600 spectro-
photometer. XPS data was obtained using an ESCALAB 250
X-ray photoelectron spectrometer. Thermogravimetric anal-
ysis (TGA) was carried out using a SDT 2960 Simultaneous
DSC-TGA of TAꢁi1nstruments up to 900 ꢀC, and the heating rate
2.3 X-ray crystal structure determination
Suitable single crystals with dimensions of 0.24 ꢂ 0.21 ꢂ
0.19 mm3 for EuL and 0.25 ꢂ 0.21 ꢂ 0.18 mm3 for TbL were
selected for single-crystal X-ray diffraction analyses. Crystallo-
graphic data was collected at 185 K on a Bruker Apex II CCD
diffractometer with graphite monochromated Mo-Ka radiation
˚
(l ¼ 0.71073 A). The crystal structure was deduced by means of
direct methods and rened employing full-matrix least squares
on F2 (SHELXTL-97).15 All the hydrogen atoms were generated
geometrically and rened isotropically using the riding model.
All non-hydrogen atoms were rened with anisotropic displace-
ment parameters. In the compound EuL, the distance between
C18 and N1 in the disordered DMF molecule was restrained (with
the restraint command “DFIX”) to a target value of 1.54 with an
estimated standard deviation of 0.02. In the compound of TbL, a
few lighter atoms (C and N) were restrained with the “ISOR”
command due to their unreasonable anisotropic Ueq parameters
and obvious ADP problems. These atoms are as follows: C16, C17,
C18, N1. Furthermore, the bond length of C17–N1 in the disor-
dered DMF molecule of compound TbL was also xed with the
restraint command “DFIX”. In EuL and TbL, all these restrained
commands led to the restraint number, but these treatments are
necessary for the reasonable structural model. The crystal data
and details of the structure determination for compounds EuL
and TbL are listed in Table 1. Selected bond lengths and angles
are given in Table 2.
was 10 C min under an air ow of 100 mL minꢁ1. Powder
ꢀ
X-ray power diffraction (XRD) patterns were performed on a D8
Focus (Bruker) diffractometer with Cu-Ka radiation Field-
emission (l ¼ 0.15405 nm, continuous, 40 kV, 40 mA, incre-
ment 0.02ꢀ).
2.2 Synthesis
Synthesis of 20-uoro-biphenyl-3,40,5-tricarboxylate (FBPT).
1-Bromo-2-uoro-4-methylbenzene (0.99 g, 5.275 mmol), 3,5-
dimethylphenylboronic acid (0.95 g, 6.325 mmol) and tetra-
kis(triphenylphosphine)palladium0 (0.19 g, 0.16 mmol) were
dissolved in 20 mL of THF in a round-bottomed ask. Aer
15 mL of aqueous 2 M ꢀNa2CO3 was added, the reaction
mixture was heated at 70 C for 24 h under a nitrogen atmo-
sphere. The cooled mixture was poured into water, extracted
with CH2Cl2 (30 mL ꢂ 3 times) and then dried over anhydrous
magnesium sulfate. Finally silica column purication
(n-hexane as eluent) gave the product of 20-uoro-3,40,5-tri-
methylbenzene (0.85 g, 3.96 mmol) with 75% yield. Then a
mixture of 20-uoro-3,40,5-trimethylbenzene (0.5 g), concen-
trated HNO3 (1 mL) and deionized H2O (8 mL) water was
Table 1 Crystal data collection and refinement details for EuL and TbL
Compound
Formula
EuL
TbL
C18H15EuFNO8
C18H15TbFNO8
551.24
sealed in a 15 mL Teon-lined stainless steel container. The Mr
544.28
Cryst. size, mm3
0.24 ꢂ 0.21 ꢂ 0.19 0.25 ꢂ 0.21 ꢂ 0.18
ꢀ
container was heated to 160 C and held at that temperature
for 24 h, and then cooled to room temperature. Finally, a pale
yellow product was obtained in 90% yield. 1H NMR (400 MHz,
DMSO-d6, Fig. S1 in ESI†) d ¼ 13.51 (s, 3H), 8.72–8.49 (m, 1H),
Crystal system
Space group
Monoclinic
C2/c
Monoclinic
C2/c
24.605(2)
12.9653(12)
14.6200(14)
96.727(2)
˚
a, A
24.6841(13)
12.9554(7)
14.6905(8)
96.6580(10)
8
1.549
2128
ꢁ30 # h # 30
0 # k # 16
0 # l # 18
1.66 to 26.05
˚
b, A
8.46–8.27 (d, 2H), 8.01–7.67 (m, 3H). HRMS: calculated [M+] c, A
˚
304.04; observed [M+] 304.01.
b, deg
Z
8
Synthesis of EuL. FBPT (0.045 mmol, 13 mg), Eu(NO3)3$6H2O
(0.045 mmol, 20 mg), DMF (2 mL), H2O (1.3 mL) and
ethanol (2 mL) were placed in a 10 mL glass vial, which was
Dcalcd, g cmꢁ3
F(000), e
hkl range
1.575
2144
ꢁ18 # h # 29
ꢁ15 # k # 15
ꢁ14 # l # 17
1.67 to 25.00
11 186/4090
4090/33/272
1.063
R1 ¼ 0.0597
uR2 ¼ 0.1697
R1 ¼ 0.0750
uR2 ¼ 0.1793
2.397 and ꢁ4.304
ꢀ
sealed and heated to 80 C for 48 h, and then cooled to room
temperature at a rate of 10 ꢀC minꢁ1. The pH value of the
reaction mixtures changed from 3.6 to 5.5. The colorless
crystals formed were collected and air-dried (73% based on
FBPT). Anal. calcd (%) for C18H15EuFNO8 (Mr ¼ 544.28): C,
q range, deg
Reections collected/unique 4615/4604
Data/restraints/parameters
4604/1/272
1.097
GoFa (F2)
39.72; H, 2.78; N, 2.57; Eu, 27.92. Found: C, 39.48; H, 3.09; N, R1/uR2 [I > 2s (I)]
R1 ¼ 0.0568
uR2 ¼ 0.1636
R1 ¼ 0.0675
uR2 ¼ 0.1636
2.754 and ꢁ4.208
2.43; Eu, 28.22.
R1/uR2b (all data)
Synthesis of TbL. This compound was synthesized following
the same synthetic procedure as that for compound EuL except
that Tb(NO3)3$6H2O was used instead of Eu(NO3)3$6H2O.
Colorless crystals of TbL were obtained with 69% yield based
on FBPT. Anal. calcd (%) for C18H15TbFNO8 (Mr ¼ 551.24): C,
ꢁ3
˚
Largest diff. peak/hole/e A
a
2
b
GoF ¼ [Su(Fo ꢁ Fc2)2/(nobc ꢁ nparam)]1/2
.
R1 ¼ ||Fo| ꢁ |Fc||/S|Fo|,
uR2 ¼ [Su(Fo ꢁ Fc2)2/Su(Fo2)2]1/2
.
2
11044 | J. Mater. Chem. A, 2013, 1, 11043–11050
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Paper
Journal of Materials Chemistry A
to its higher yield than TbL. The strongest emission wave-
lengths for EuL were located at 616 nm when excited at 320 nm.
For the experiment of sensing small organic molecules, the
EuL–solvent emulsions were prepared by introducing 5 mg of
EuL powder into 5.00 mL of methanol, ethanol, 2-propanol,
acetone, acetonitrile, chloroform, DMF and THF, benzene,
methylbenzene, p-xylene, chlorobenzene, 1-phenylethanone,
and benzaldehyde, respectively; for the experiment of sensing
metal ions, the EuL–solvent emulsions were prepared by
introducing 5 mg of EuL powder into 5.00 mL of M(NO3)x (M ¼
Na+, K+, Mg2+, Ca2+, Mn2+, Cd2+, Zn2+,Co2+, Cu2+, Gd3+) DMF
solution for the luminescence studies.
2.4 Luminescent measurements
The luminescence spectra were recorded on a Hitachi F-4500
uorescence spectrophotometer. The photomultiplier tube
(PMT) voltage was 700 V, the scan speed was 1200 nm minꢁ1
,
the slit width of excitation and emission is 5 nm. In this paper,
the EuL is selected as test sample for systematic research, owing
Table 2 Selected bond lengths and angles for EuL and TbLa,b
Compound EuL
Eu(1)–O(5)
Eu(1)–O(6)
Eu(1)–O(7)
2.353(6)
2.394(6)
2.438(10)
2.458(6)
2.717(6)
2.448(6)
74.4(2)
132.8(2)
138.2(3)
149.4(3)
73.8(3)
124.3(2)
90.5(2)
73.0(4)
76.1(2)
94.4(3)
83.0(2)
71.4(2)
71.1(3)
127.1(2)
76.2(2)
67.9(2)
108.2(3)
126.7(2)
Eu(1)–O(2)
Eu(1)–O(8)
Eu(1)–O(1)#1
Eu(1)–O(3)
O(5)–Eu(1)#2
2.365(6)
2.414(8)
2.448(6)
2.521(7)
2.717(6)
3 Results and discussion
3.1 Structure description
Eu(1)–O(4)
Eu(1)–O(5)#2
Single-crystal X-ray diffraction analysis reveals that the poly-
mer consists of 20-uoro-biphenyl-3,40,5-tricarboxylate (FBPT),
lanthanide atom, coordinated H2O and DMF molecules
(Fig. 1a). EuL and TbL are isostructural and crystallize in the
monoclinic space group C2/c. In the EuL, the Eu3+ ion is nine
coordinated by seven oxygen atoms from the carboxyl groups
of FBPT, one oxygen atom (O8) from DMF and one oxygen
atom (O7) from the terminal water molecule, forming a dis-
torted tricapped trigonal prism. The average Eu–O bond
O(1)–Eu(1)#3
O(5)–Eu(1)–O(2)
O(2)–Eu(1)–O(6)
O(2)–Eu(1)–O(8)
O(5)–Eu(1)–O(7)
O(6)–Eu(1)–O(7)
O(5)–Eu(1)–O(1)#1
O(6)–Eu(1)–O(1)#1
O(7)–Eu(1)–O(1)#1
O(2)–Eu(1)–O(4)
O(8)–Eu(1)–O(4)
O(1)#1–Eu(1)–O(4)
O(2)–Eu(1)–O(3)
O(8)–Eu(1)–O(3)
O(1)#1–Eu(1)–O(3)
O(5)–Eu(1)–O(5)#2
O(6)–Eu(1)–O(5)#2
O(7)–Eu(1)–O(5)#2
O(4)–Eu(1)–O(5)#2
O(5)–Eu(1)–O(6)
O(5)–Eu(1)–O(8)
O(6)–Eu(1)–O(8)
O(2)–Eu(1)–O(7)
O(8)–Eu(1)–O(7)
O(2)–Eu(1)–O(1)#1
O(8)–Eu(1)–O(1)#1
O(5)–Eu(1)–O(4)
O(6)–Eu(1)–O(4)
O(7)–Eu(1)–O(4)
O(5)–Eu(1)–O(3)
O(6)–Eu(1)–O(3)
O(7)–Eu(1)–O(3)
O(4)–Eu(1)–O(3)
O(2)–Eu(1)–O(5)#2
O(8)–Eu(1)–O(5)#2
O(1)#1–Eu(1)–O(5)#2
O(3)–Eu(1)–O(5)#2
80.5(2)
81.9(2)
74.0(3)
135.9(3)
75.3(4)
72.7(2)
147.5(2)
129.6(2)
146.7(2)
73.0(3)
80.6(2)
142.2(2)
110.2(3)
51.5(2)
67.7(2)
138.4(2)
50.08(19)
137.0(2)
˚
˚
length is 2.565 A within a range of 2.353–2.717 A (2.318–
˚
2.729 A in TbL) (Table 2). The bond angles for O–Eu–O are in
the range of 50.1–149.4ꢀ (50.2–148.9ꢀ in TbL) (Table 2). All
O–Eu–O bond angles and Eu–O bond lengths are within the
expected ranges.
Notably, further study into the structure of EuL (or TbL)
showed that the compound was a three-dimensional (3D) open
framework. A better insight into the nature of the intricate
framework can be achieved by the application of a topological
approach, which is necessary to simplify the building blocks. As
shown in Fig. 2, each [FBPT]3ꢁ ligand can be considered as a
three-connecting node since it links three binuclear-Eu units
and each binuclear-Eu unit in turn links six [FBPT]3ꢁ ligands,
which can be regarded as a six-connecting node. The resulting
(3,6)-connected net resembles the uorite structure with the
Compound TbL
Tb(1)–O(4)#4
Tb(1)–O(8)
Tb(1)–O(3)
Tb(1)–O(5)
2.318(7)
2.365(9)
2.412(7)
2.437(7)
2.729(7)
2.318(7)
74.9(2)
138.6(3)
132.8(3)
124.6(2)
146.7(3)
148.9(3)
74.6(4)
73.0(3)
75.7(3)
146.6(3)
73.0(3)
71.0(3)
142.8(3)
110.3(3)
76.1(2)
138.6(3)
50.2(2)
Tb(1)–O(2)
Tb(1)–O(1)#4
Tb(1)–O(7)
Tb(1)–O(6)
O(1)–Tb(1)#4
2.338(7)
2.375(7)
2.420(9)
2.503(8)
2.375(7)
Tb(1)–O(4)
O(4)–Tb(1)#4
O(4)#4–Tb(1)–O(2)
O(2)–Tb(1)–O(8)
O(2)–Tb(1)–O(1)#4
O(4)#4–Tb(1)–O(3)
O(8)–Tb(1)–O(3)
O(4)#4–Tb(1)–O(7)
O(8)–Tb(1)–O(7)
O(3)–Tb(1)–O(7)
O(2)–Tb(1)–O(5)
O(1)#4–Tb(1)–O(5)
O(7)–Tb(1)–O(5)
O(2)–Tb(1)–O(6)
O(1)#4–Tb(1)–O(6)
O(7)–Tb(1)–O(6)
O(4)#4–Tb(1)–O(4)
O(8)–Tb(1)–O(4)
O(3)–Tb(1)–O(4)
O(4)#4–Tb(1)–O(8)
O(4)#4–Tb(1)–O(1)#4
O(8)–Tb(1)–O(1)#4
O(2)–Tb(1)–O(3)
O(1)#4–Tb(1)–O(3)
O(2)–Tb(1)–O(7)
O(1)#4–Tb(1)–O(7)
O(4)#4–Tb(1)–O(5)
O(8)–Tb(1)–O(5)
O(3)–Tb(1)–O(5)
O(4)#4–Tb(1)–O(6)
O(8)–Tb(1)–O(6)
O(3)–Tb(1)–O(6)
O(5)–Tb(1)–O(6)
O(2)–Tb(1)–O(4)
O(1)#4–Tb(1)–O(4)
O(7)–Tb(1)–O(4)
81.9(3)
80.6(2)
74.4(3)
73.1(3)
89.4(3)
135.9(3)
73.7(3)
129.9(2)
94.6(3)
83.0(3)
80.4(3)
71.6(3)
127.5(3)
51.9(3)
67.6(2)
67.7(2)
108.8(3)
2
4
2
7
2
¨
Schlai symbol of (4 $6)2(4 $6 $8 $10 ). What is most inter-
esting is that one-dimensional (1D) ellipsoidal shaped channels
exist along the c axis (Fig. 1b). As shown in Fig. 1c and d, water
molecules and uorine atoms, which can be the potential sites
for their sensing functions of small organic molecules, or metal
ions are regularly distributed in the channel. The solvent-
3
3
˚
˚
accessible volume of 1317.3 A out of the 4666.2 A unit cell
volume (28.2% of the total crystal volume), calculated by PLA-
TON, and the moderate pore sizes indicating such 1D channels
are accessible to a variety of small organic molecules or metal
ions.16
3.2 Gas and I2 sorption
To examine the existence of the 1D channel, gas and I2 sorption
were studied. The EuL was activated at a temperature of 120 ꢀC
under vacuum for gas sorption studies. As shown in Fig. S3 and
a
Symmetry codes: (#1) ꢁx + 1/2, y + 1/2, ꢁz ꢁ 1/2; (#2) ꢁx + 1/2, ꢁy + 3/2,
ꢁz; (#3) ꢁx + 1/2, y ꢁ 1/2, ꢁz ꢁ 1/2. b Symmetry codes: (#4) ꢁx + 1/2, ꢁy +
3/2, ꢁz + 1.
This journal is ª The Royal Society of Chemistry 2013
J. Mater. Chem. A, 2013, 1, 11043–11050 | 11045

View Article Online
Journal of Materials Chemistry A
Paper
Fig. 1 (a) ORTEP representation of compound EuL (hydrogen atoms were omitted for clarity), (b) the space-filling view of EuL along the c axis, (c) a view of the one-
dimensional channel structure, and (d) a schematic illustration of the one-dimensional channel structure.
3.3 Thermal stability
In order to examine the thermal stability of EuL and TbL,
thermaꢀl gravimetric analyses (TGA) (Fig. 4) were studied from 46
to 900 C. The TGA diagrams of the two compounds are quite
similar, and both show two main weight losses in the curves. In
EuL, the TGA curve shows that the rst weight loss was at
ꢀ
13.82% in the temperature range 46–255 C, corresponding to
the loss of DMF and water molecules (calculated value of
14.17%). The second weight loss was at 56.01% from 445 to
ꢀ
505 C, ascribed to the release of the ligand composite (calcu-
lated value of 55.34%). For compound EuL, the nal product
was Eu2O3, which is conrmed by PXRD studies. The weight
loss of compound TbL with the increase of temperature is
similar to EuL, and both t well with the calculated value.
Fig. 2 Schematic illustration of the topology of the 3D network of EuL (black
and blue balls represent three-connected FBPT ligands and six-connected paddle-
wheel building blocks, respectively).
3.4 Sensing of small organic molecules
To examine the potential of the EuL for the sensing of small
S4,† both the N2 and H2 sorption isotherm at 77 K show that molecules, the compound was immersed in methanol, ethanol,
there is certain porosity in the compound of EuL. According to 2-propanol, acetone, acetonitrile, chloroform, DMF and THF
the reported literature, the experiment of I2 sorption is also a solvent emulsions for luminescence studies. The emission
very good and effective way to verify the existence of micro-sized spectra of EuL excited at 320 nm reveals the well-resolved
pores.17 As shown in Fig. 3, when the outgassed sample of EuL magnied luminescence of the f–f transitions, attributed to the
(100 mg) was immersed in a hexane (10 mL) solution of I2 (0.1 energy transfer from FBPT ligands to Eu3+. Characteristic tran-
mol Lꢁ1), the color of the crystals intensied from pale yellow to sitions of the Eu3+ ion are also evident for EuL, at 590, 616, 651
5
7
5
7
brown gradually. Notably, the photographs and XRD for EuL and 698 nm, which are ascribed to the D0 / F1, D0 / F2,
releasing I2, demonstrate that the I2 sorption progress of EuL is 5D0 / 7F3 and 5D0 / 7F4 transitions, respectively. As shown in
reversible. Besides, the TG curve of I2-incorporated EuL shows a Fig. 5, the photoluminescence (PL) intensity is largely depen-
hysteresis for the loss of the iodine, suggesting that there are dent on the solvent molecules, especially in the case of acetone,
some interactions between the guest molecules and the which showed a signicant quenching effect. The EuL were
framework (Fig. S5†). Undoubtedly, the experiment of I2 sorp- dispersed in DMF as the standard suspension, while the
tion provides additional proof of the 1D channel for the acetone content was gradually increased to monitor the emis-
compound EuL.
sive response. As shown in Fig. 6, the luminescent intensity of
11046 | J. Mater. Chem. A, 2013, 1, 11043–11050
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Paper
Journal of Materials Chemistry A
Fig. 3 Photographs of EuL for the adsorption and release of I2. For adsorption, the outgassed sample of EuL (100 mg) was immersed in a hexane (10 mL) solution of I2
(0.1 mol Lꢁ1). For release, the sample of I2–EuL was soaked in 20 mL hexane, and replaced hexane (20 mL) per 20 min over 8 h.
versus the volume ratio of acetone could be well tted with a
rst-order exponential decay (Fig. S7†), indicating that lumi-
nescence quenching of EuL by acetone is diffusion-
controlled.13e
Such solvent-dependent luminescence properties are very
interesting and important for the selective sensing of solvent
molecules. The above results evoked by the acetone solvent
molecules, led us to an exploration of more small organic mole-
cules. As shown in Fig. 7, the solvents used were benzene,
methylbenzene, p-xylene, chlorobenzene, 1-phenylethanone and
benzaldehyde, and all of them have an aromatic ring. EuL has
been demonstrated to show a selective sieving function with
respect to 1-phenylethanone and benzaldehyde. When the
1-phenylethanone or benzaldehyde solvent content was gradually
added and increased to the EuL DMF standard emulsion, the
Fig. 4 Thermal gravimetric analyses curves for EuL and TbL.
luminescent intensity also gradually decreased with the addition
of 1-phenylethanone or benzaldehyde.
Powder XRD was employed to study the structural data of the
original and exchanged compounds. The powder XRD pattern
of the acetone–EuL, 1-phenylethanone–EuL, and benzalde-
hyde–EuL are similar to that of EuL, suggesting that the basic
frameworks remain in the compounds (Fig. S6†). In the solvents
we used, acetone, 1-phenylethanone and benzaldehyde all have
a strong absorbing range from 250 to 350 nm, while other
Fig.
5
PL spectra of EuL introduced into methanol, ethanol, 2-propanol,
acetone, THF, chloroform, CH3CN and DMF.
the suspension signicantly decreased with the addition of
acetone, and it almost disappeared at an acetone content of
5.0 vol%. This decreasing trend of the luminescent intensity
may be signicant to identify the presence of small amounts of
acetone in solution. Besides, the decreasing trend of the lumi-
Fig. 6 The PL spectra of EuL DMF emulsion in the presence of various contents
nescent intensity of the 5D0 / 7F2 transition of Eu3+ at 616 nm of acetone solvent.
This journal is ª The Royal Society of Chemistry 2013
J. Mater. Chem. A, 2013, 1, 11043–11050 | 11047

View Article Online
Journal of Materials Chemistry A
Paper
form metal-ion-incorporated EuL as microcrystalline solids for
luminescence studies. The PL spectra of Cu2+-incorporated EuL
are shown in Fig. 10, and exhibit typical Eu3+ ion transitions.
The most important feature is that the luminescence intensities
of the different suspensions are strongly dependent on the
identities of the metal ions. Zn2+, Mg2+, Ca2+, Cd2+, Gd3+ ions,
possessing a closed-shell electron conguration, have a trivial
effect on the luminescence intensity, whereas the other metal
ions with different electron congurations produce varying
degrees of quenching of the luminescence intensity, especially
the Cu2+ ion (Fig. 9). The emitted visible red light of the EuL
suspension containing Cu2+ ion is signicantly darker than the
original one under UV light (Fig. 10), which allowed us to
identify easily the existence of a small amount of Cu2+ ion in
DMF solution. It is very remarkable that this material features
such highly selective and sensitive sensing of Cu2+ ion in DMF
solution.
Fig. 7 PL spectra of EuL introduced into benzene, methylbenzene, p-xylene,
chlorobenzene and 1-phenylethanone.
solvents have no signicant absorption band in this range. As
shown in Fig. 8, the strong absorption band of FBPT is located
from 250 to 310 nm, which is largely overlapped by the
absorbing band of acetone (1-phenylethanone or benzalde-
hyde). The physical interaction of the solute and solvent plays
an important role in such luminescence quenching effects of
small solvent molecules. Upon excitation, there is competition
of the absorption of the light source energy between acetone
(1-phenylethanone or benzaldehyde) molecules and FBPT from
250 to 310 nm. Combined with the absorption and luminescent
spectra, it was suggested that the energy absorbed by the FBPT
is transferred to the acetone (1-phenylethanone or benzalde-
hyde) molecules, resulting in a decrease in the luminescence
intensity, even quenching, of EuL. The quenching mechanism
is in agreement with that proposed previously by Chen et al.14d,18
3.5 Sensing of metal ions
Fig. 9 A comparison of the luminescence intensities of the 5D0
/
7F2 transitions
The EuL was immersed in DMF solutions containing M(NO3)x
(M ¼ Na+, K+, Mg2+, Ca2+, Mn2+, Cd2+, Zn2+,Co2+, Cu2+, Gd3+) to
of EuL exchanging with 0.01 M DMF solution with different metal ions.
Fig. 10 The PL spectra of EuL in Cu(NO3)2 DMF solution at different concen-
trations. The inset shows the luminescence change after the addition of Cu2+ ion
in EuL suspension under UV light.
Fig. 8 The UV/vis absorption spectra for acetone, 1-phenylethanone, benzal-
dehyde and FBPT.
11048 | J. Mater. Chem. A, 2013, 1, 11043–11050
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Paper
Journal of Materials Chemistry A
Fig. 11 F1s X-ray photoelectron spectroscopy (XPS) spectra of the EuL (blue) and Cu2+-incorporated EuL (red).
According to the reported literature, the examples of porous 2011AA03A407) and National Natural Science Foundation for
MOFs with Lewis basic sites, such as pyridyl sites,13d,19 amide Creative Research Group (Grant no. 21221061).
sites,20 anionic sulfonate sites,21 and so on, could have an effect
on metal ions. As for the reason of the quenching by Cu2+, we
speculate that it might be related to the interaction between the
Cu2+ ions and the uorine, carboxylate and/or terminal water
Notes and references
Lewis basic sites on the EuL, similar to that observed in the
1 (a) M. Eddaoudi, D. B. Moler, H. Li, B. Chen, T. M. Reineke,
reported literature.14c,22 The interaction between the Cu2+ ions
M. O'Keeffe and O. M. Yaghi, Acc. Chem. Res., 2001, 34, 319;
and the FBPT ligands minimizes the energy transfer efficiency
(b) S. Kitagawa, R. Kitaura and S. I. Noro, Angew. Chem., Int.
from FBPT to the Eu3+ ions within EuL, thus decreasing the
˘
Ed., 2004, 43, 2334; (c) L. J. Murray, M. Dinca and J. R. Long,
luminescent intensity. To check the results, F1s X-ray photo-
electron spectroscopy (XPS) was selected to study the EuL and
Cu2+-incorporated EuL. The F1s peak from free uorine atoms
at 686.27 eV in EuL is shied to 686.81 eV on the addition of
Cu2+ (Fig. 11), indicating the weak interaction of uorine atoms
with Cu2+ in the Cu2+-incorporated EuL.
Chem. Soc. Rev., 2009, 38, 1294; (d) S. Ma and H. C. Zhou,
Chem. Commun., 2010, 46, 44; (e) J. R. Li, R. J. Kuppler and
H. C. Zhou, Chem. Soc. Rev., 2009, 38, 1477; (f) L. Ma,
C. Abney and W. Lin, Chem. Soc. Rev., 2009, 38, 1248; (g)
B. Chen, S. C. Xiang and G. Qian, Acc. Chem. Res., 2010, 43,
1115; (h) H. L. Jiang and Q. Xu, Chem. Commun., 2011, 47,
3351.
4 Conclusions
2 S. Chen, J. Zhang, T. Wu, P. Feng and X. Bu, J. Am. Chem. Soc.,
2009, 131, 16027.
In conclusion, two new 3D lanthanide metal–organic frame-
works were synthesized by means of solvothermal methods
using uorinated tricarboxylic acid as an organic ligand. These
materials exhibited a one-dimensional channel structure in
which uorine atoms and coordinated water molecules are
regularly distributed. EuL shows a remarkable quenching effect
in the luminescence emission of Eu3+ upon the introduction of
the small organic molecules (acetone, 1-phenylethanone and
benzaldehyde) and Cu2+ ion. It is expected that the easy access
to luminescent one-dimensional channel MOFs with a variety of
organic solvents and metal ions will render this strategy very
practical and useful in exploring luminescent microporous
organic-molecule and metal-ion sensors. This research can be
considered as a work that is devoted to the potential applica-
tions of Ln-MOFs, and further work on this theme is currently
under way.
3 A. Lan, K. Li, H. Wu, D. H. Olson, T. J. Emge, W. Ki,
M. C. Hong and J. Li, Angew. Chem., Int. Ed., 2009, 48, 2334.
4 S. Horike, D. Tanaka, K. Nakagawa and S. Kitagawa, Chem.
Commun., 2007, 3395.
5 Y. K. Hwang, D. Y. Hong, J. S. Chang, S. H. Jhung, Y. K. Seo,
´
J. Kim, A. Vimont, M. Daturi, C. Serre and G. Ferey, Angew.
Chem., Int. Ed., 2008, 47, 4144.
6 Y. B. Zhang, W. X. Zhang, F. Y. Feng, J. P. Zhang and
X. M. Chen, Angew. Chem., Int. Ed., 2009, 48, 5287.
7 G. Huang, C. Yang, Z. Xu, H. Wu, J. Li, M. Zeller,
A. D. Hunter, S. S. Y. Chui and C. M. Che, Chem. Mater.,
2009, 21, 541.
8 (a) J. Kido and Y. Okamoto, Chem. Rev., 2002, 102, 2357; (b)
N. Marques, A. Sella and J. Takats, Chem. Rev., 2002, 102,
2137.
9 (a) M. D. Allendorf, C. A. Bauer, R. K. Bhakta and
R. J. T. Houk, Chem. Soc. Rev., 2009, 38, 1330; (b) Y. J. Cui,
Y. F. Yue, G. D. Qian and B. L. Chen, Chem. Rev., 2012,
112, 1126; (c) J. Rocha, L. D. Carlos, F. A. A. Paz and
D. Ananias, Chem. Soc. Rev., 2011, 40, 926; (d) L. D. Carlos,
R. A. S. Ferreira and S. J. L. Ribeiro, Adv. Mater., 2009, 21,
509; (e) K. Binnemans, Chem. Rev., 2009, 109, 4283.
Acknowledgements
The authors are grateful to the nancial aid from the National
Natural Science Foundation of China (Grant nos 21071140,
91122030 and 21210001), 863'-National High Technology
Research and Development Program of China (Grant no.
This journal is ª The Royal Society of Chemistry 2013
J. Mater. Chem. A, 2013, 1, 11043–11050 | 11049

View Article Online
Journal of Materials Chemistry A
Paper
10 (a) K. A. White, D. A. Chengelis, M. Zeller, S. J. Geib,
J. Szakos, S. Petoud and N. L. Rosi, Chem. Commun., 2009,
4506; (b) K. A. White, D. A. Chengelis, K. A. Gogick,
J. Stehman, N. L. Rosi and S. Petoud, J. Am. Chem. Soc.,
1080; (e) B. L. Chen, Y. Yang, F. Zapata, G. Lin, G. Qian
and E. B. Lobkovsky, Adv. Mater., 2007, 19, 1693; (f)
E. Y. Lee, S. Y. Jang and M. P. Suh, J. Am. Chem. Soc., 2005,
127, 6374.
2009, 131, 18069; (c) H. L. Jiang, N. Tsumori and Q. Xu, 14 (a) Z. Y. Guo, H. Xu, S. Q. Su, J. F. Cai, S. Dang, S. C. Xiang,
Inorg. Chem., 2010, 49, 10001; (d) W. J. Rieter,
K. M. L. Taylor, H. An, W. Lin and W. Lin, J. Am. Chem.
Soc., 2006, 128, 9024; (e) Q. G. Meng, R. J. Witte,
Y. J. Gong, E. L. Day, J. C. Chen, P. S. May and M. T. Berry,
Chem. Mater., 2010, 22, 6056; (f) H. L. Guo, Y. Z. Zhu,
S. L. Qiu, J. A. Lercher and H. J. Zhang, Adv. Mater., 2010,
G. D. Qian, H. J. Zhang, M. O'Keeffe and B. L. Chen, Chem.
Commun., 2011, 47, 5551; (b) S. Dang, E. Ma, Z. S. Sun and
H. J. Zhang, J. Mater. Chem., 2012, 22, 16920; (c)
W. T. Yang, J. Feng and H. J. Zhang, J. Mater. Chem., 2012,
22, 6819; (d) W. T. Yang, J. Feng, S. Y. Song and
H. J. Zhang, ChemPhysChem, 2012, 13, 2734.
22, 4190; (g) Y. J. Cui, G. D. Qian and B. L. Chen, J. Am. 15 G. M. Sheldrick, SHELXL-97, Program for Renement of Crystal
¨
Structures, University of Gottingen, Germany, 1997.
Chem. Soc., 2012, 134, 3979.
11 (a) S. I. Weissman, J. Chem. Phys., 1942, 10, 214; (b) 16 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7.
F. J. Steemers, W. Verboom, D. N. Reinhoudt, E. B. van 17 (a) Z. J. Zhang, W. Shi, Z. Niu, H. H. Li, B. Zhao, P. Cheng,
der Tol and J. W. Verhoeven, J. Am. Chem. Soc., 1995,
117, 9408.
12 (a) P. Horcajada, R. Gref, T. Baati, P. K. Allan and C. Serre,
Chem. Rev., 2012, 112, 1232; (b) L. E. Kreno, M. Allendorf
and J. T. Hupp, Chem. Rev., 2012, 112, 1105; (c)
W. J. Rieter, K. M. L. Taylor and W. B. Lin, J. Am. Chem.
D. Z. Liao and S. P. Yan, Chem. Commun., 2011, 47, 6425;
(b) Q. K. Liu, J. P. Ma and Y. B. Dong, Chem. Commun.,
2011, 47, 7185; (c) M. H. Zeng, Q. X. Wang, Y. X. Tan,
S. Hu, H. X. Zhao, L. S. Long and M. Kurmoo, J. Am. Chem.
Soc., 2010, 132, 2561; (d) Z. Yin, Q. X. Wang and
M. H. Zeng, J. Am. Chem. Soc., 2012, 134, 4857.
Soc., 2007, 129, 9852; (d) K. Hanaoka, K. Kikuchi, 18 Y. Q. Xiao, L. B. Wang, Y. J. Cui, B. L. Chen, F. Zapata and
H. Kojima, Y. Urano and T. Nagano, Angew. Chem., 2003,
115, 3104.
13 (a) W. Liu, T. Jiao, Y. Li, Q. Liu, M. Tan, H. Wang and
G. D. Qian, J. Alloys Compd., 2009, 484, 601.
19 J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon and
K. Kim, Nature, 2000, 404, 982.
L. Wang, J. Am. Chem. Soc., 2004, 126, 2280; (b) B. Chen, 20 S. Hasegawa, S. Horike, R. Matsuda, S. Furukawa,
L. Wang, F. Zapata, G. Qian and E. B. Lobkovsky, J. Am.
Chem. Soc., 2008, 130, 6718; (c) B. Chen, L. Wang, Y. Xiao,
K. Mochizuki, Y. Kinoshita and S. Kitagawa, J. Am. Chem.
Soc., 2007, 129, 2607.
F. R. Fronczek, M. Xue, Y. Cui and G. Qian, Angew. Chem., 21 S. Horike, S. Bureekaew and S. Kitagawa, Chem. Commun.,
Int. Ed., 2009, 48, 500; (d) B. V. Harbuzaru, A. Corma, 2008, 471.
F. Rey, P. Atienzar, J. L. Jorda, H. Garcıa, D. Ananias, 22 Y. Q. Xiao, Y. J. Cui, Q. Zheng, S. C. Xiang, G. D. Qian and
L. D. Carlos and J. Rocha, Angew. Chem., Int. Ed., 2008, 47, B. L. Chen, Chem. Commun., 2010, 46, 5503.
´
´
11050 | J. Mater. Chem. A, 2013, 1, 11043–11050
This journal is ª The Royal Society of Chemistry 2013