Lanthanide-Potassium Biphenyl-3,3′-disulfonyl-4,4′-dicarboxylate Frameworks: Gas Sorption, Proton Conductivity, and Luminescent Sensing of Metal Ions

Article abstract of DOI:10.1021/acs.inorgchem.6b00928

A novel sulfonate-carboxylate ligand of biphenyl-3,3′-disulfonyl-4,4′-dicarboxylic acid (H₄-BPDSDC) and its lanthanide-organic frameworks {[LnK(BPDSDC)(DMF)(H₂O)]·x(solvent)}_n (JXNU-2, where JXNU denotes Jiangxi Normal University, DMF indicates dimethylformamide, and Ln = Sm³⁺, Eu³⁺, and Pr³⁺) were synthesized and structurally characterized. The three isomorphous lanthanide compounds feature three-dimensional frameworks constructed from one-dimensional (1D) rod-shaped heterometallic Ln-K secondary building units and are an illustration of a Kagome-like lattice with large 1D hexagonal channels and small 1D trigonal channels. The porous material of the representive JXNU-2(Sm) has an affinity to quadrupolar molecules such as CO₂ and C₂H₂. In addition, the JXNU-2(Sm) compound exhibits humidity-and temperature-dependent proton conductivity with a large value of 1.11 × 10^-3 S cm^-1 at 80 °C and 98% relative humidity. The hydrophilic sulfonate group on the surface of channels facilitates enrichment of the solvate water molecules in the channels, which enhances the proton conductivity of this material. Moreover, the JXNU-2(Eu) material with the characteristic bright red color shows the potential for recognition of K⁺ and Fe³⁺ ions. The enhancing Eu³⁺ luminescence with the K⁺ ion and quenching Eu³⁺ luminescence with the Fe³⁺ ion can be associated with the functional groups of the organic ligand.

Full text of DOI:10.1021/acs.inorgchem.6b00928

Article
pubs.acs.org/IC
Lanthanide−Potassium Biphenyl-3,3′-disulfonyl-4,4′-dicarboxylate
Frameworks: Gas Sorption, Proton Conductivity, and Luminescent
Sensing of Metal Ions
Li-Juan Zhou,†,§ Wei-Hua Deng,‡,§ Yu-Ling Wang,*,† Gang Xu,‡ Shun-Gao Yin,† and Qing-Yan Liu*,†
†College of Chemistry and Chemical Engineering, Key Laboratory of Small Functional Organic Molecule of Ministry of Education,
Jiangxi Normal University, Nanchang, Jiangxi 330022, P. R. China
‡State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou, Fujian 350002, P. R. China
S
* Supporting Information
ABSTRACT: A novel sulfonate−carboxylate ligand of biphenyl-3,3′-disulfonyl-
4,4′-dicarboxylic acid (H4−BPDSDC) and its lanthanide−organic frameworks
{[LnK(BPDSDC)(DMF)(H2O)]·x(solvent)}n (JXNU-2, where JXNU denotes
Jiangxi Normal University, DMF indicates dimethylformamide, and Ln = Sm3+,
Eu3+, and Pr3+) were synthesized and structurally characterized. The three
isomorphous lanthanide compounds feature three-dimensional frameworks
constructed from one-dimensional (1D) rod-shaped heterometallic Ln−K
secondary building units and are an illustration of a Kagome-like lattice with
large 1D hexagonal channels and small 1D trigonal channels. The porous
material of the representive JXNU-2(Sm) has an affinity to quadrupolar
molecules such as CO2 and C2H2. In addition, the JXNU-2(Sm) compound
exhibits humidity- and temperature-dependent proton conductivity with a large
value of 1.11 × 10−3 S cm−1 at 80 °C and 98% relative humidity. The hydrophilic
sulfonate group on the surface of channels facilitates enrichment of the solvate
water molecules in the channels, which enhances the proton conductivity of this material. Moreover, the JXNU-2(Eu) material
with the characteristic bright red color shows the potential for recognition of K+ and Fe3+ ions. The enhancing Eu3+ luminescence
with the K+ ion and quenching Eu3+ luminescence with the Fe3+ ion can be associated with the functional groups of the organic
ligand.
products and may enable solid-state dynamics for the resulting
frameworks.11 In this contribution, a novel sulfonate−
carboxylate ligand, biphenyl-3,3′-disulfonyl-4,4′-dicarboxylic
acid (H4−BPDSDC), was synthesized. The H4−BPDSDC
ligand with a biphenyl backbone and two carboxyl and two
sulfonyl functional groups can be considered as a remarkable
organic precursor for preparation of the functional MOFs.
Moreover, the H4−BPDSDC ligand with strong coordination
ability of carboxylate groups and weak coordination ability of
sulfonate groups can coordinate to the metal ions synergisti-
cally, which will give some interesting physical properties.
Herein, three LnOFs {[LnK(BPDSDC)(DMF)(H2O)]·x(sol-
vent)}n (JXNU-2, where JXNU denotes Jiangxi Normal
University, DMF indicates dimethylformamide, and Ln =
Sm3+, Eu3+, and Pr3+) were synthesized and structurally
characterized. The sulfonate groups attached to the π-rich
biphenyl backbones in these MOFs are on the surface of the
one-dimensional (1D) channels, which endows the present
INTRODUCTION
■
The lanthanide−organic framework (LnOF) solids offer great
promise for the development of materials with potential
applications in photoluminescence,1 molecular magnets,2
adsorption,3 proton conduction,4 and sensing.5 Their aestheti-
cally appealing structural topologies are associated with the
high coordination number and flexible coordination geometry
of the lantahanide ions.6 In contrast to the transition metal-
based metal−organic frameworks (MOFs), the LnOFs are
highly sought after because they can display distinct intrinsic
optical and magnetic properties endowed by the lanthanide
ions with 4f configuration.7
However, the selection of the organic ligand is very
important for the preparation of the functional MOFs.8 For
oxygen-containing organic ligand, the carboxylate ligands
provide the most successful functional ligands due to the
carboxylate group, which can exhibit various coordination
modes when coordinated to the metal centers.9 In comparison
with carboxylate group, the coordination chemistry of sulfonate
has been less well-investigated due to the perception that
sulfonate is a poor ligand.10 However, the weaker ligation
nature of the sulfonate group facilitates formation of crystalline
Received: April 14, 2016
© XXXX American Chemical Society
A
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yl. 1H NMR (DMSO-d6, ppm): 7.86 (s, 4H), 8.12 (s, 2H); IR
spectrum (cm−1, KBr pellet): 3521 (s), 2924 (m), 1715 (s), 1597 (m),
1547 (w), 1505 (m), 1400 (m), 1384 (m), 1372 (m), 1287 (m), 1265
(m), 1213 (s), 1183 (w), 1135 (m), 1046 (s), 1021 (s), 900 (m), 825
(s), 809 (m), 732 (m), 648 (s), 626 (s).
MOFs with some interesting physical properties such as gas
adsorption, proton conduction, and luminescent sensing.
EXPERIMENTAL SECTION
■
Physical Measurements. IR (KBr pellets) spectra were recorded
in the 400−4000 cm−1 range using a PerkinElmer Spectrum One FT-
IR spectrometer. Elemental analyses were performed on Elementar
PerkinElmer 2400CHN microanalyzer. Thermogravimetric analyses
were performed on a PE Diamond TG/DTA unit at a heating rate of
10 °C/min under a nitrogen atmosphere. Powder X-ray diffraction
patterns were performed on a Rigaku Miniflex Π powder
diffractometer using Cu Kα radiation (λ = 1.5418 Å). Gas sorption
isotherms were measured using a Micromeritics ASAP2020 gas
adsorption instrument up to 1 atm of gas pressure. The highly pure N2
(99.999%) and CO2 (99.999%) gases were used in the sorption
experiments. The proton conductivity data were interrogated by the
conventional quasi-four-probe method using gold paste and gold wires
(50 μm diameter) with an Impedance/Gain-Phase Analyzer (Solartron
SI 1260) under different environmental conditions. The electro-
chemical impedance spectroscopy (EIS) was taken by applying 100
mV of alternating current amplitude voltage over the frequency from 1
to 1 × 106 Hz in 10 steps on a logarithmic scale. The impedance
results were analyzed in ZView2 (Scribner Associates), which was used
to generate Nyquist plots with the real parts (Z′) as the abscissa and
the imaginary part (Z″) as the ordinate. A pellet of JXNU-2(Sm) (2.5
mm in diameter and 1.27 mm in thickness) was compressed under a
pressure of ∼500 MPa and exposed to controlled humidity and
temperature environments, which was performed using an XK-
CTS80Z incubator (Shenzhen selenium control testing equipment
corp). Fluorescence spectra were measured at room temperature with
a single-grating Edinburgh EI980 fluorescence spectrometer.
Synthesis of {[LnK(BPDSDC) (DMF)(H2O)]·x(solvent)}n (JXNU-
2) (Ln = Sm3+, Eu3+ and Pr3+). The same process was employed to
prepare these compounds, as follows. A mixture of lanthanide salt
(SmCl3·6H2O (36.4 mg, 0.1 mmol), or Eu(NO3)3·6H2O (44.6 mg, 0.1
mmol), or Pr(NO3)3·6H2O (41.7 mg, 0.1 mmol)) and biphenyl-3,3′-
disulfonyl-4,4′-dicarboxylic acid (40.2 mg, 0.1 mmol) in 8 mL of
dimethylformamide (DMF) and 2 mL of H2O was introduced into a
25 mL Parr Teflon-lined stainless steel vessel and heated at 85 °C for 4
d. Then the mixture was cooled naturally to form crystals. Crystalline
product was filtered, washed with DMF, and dried at ambient
temperature. Yield: 31.5 mg for JXNU-2(Sm); 30.2 mg for JXNU-
2(Eu); 32.3 mg for JXNU-2(Pr). IR spectrum (cm−1, KBr pellet): for
JXNU-2(Sm), 3429 (s), 2935 (w), 1644 (s), 1601 (w), 1566 (w),
1534 (w), 1499 (w), 1480 (w), 1406 (s), 1253 (s), 1182 (m), 1088
(s), 1023 (s), 903 (w), 866 (m), 793 (m), 755 (m), 726 (w), 672 (m),
626 (m), 585 (w), 432 (m); for JXNU-2(Eu), 3415 (s), 2936 (w),
1655 (s), 1536 (w), 1499 (w), 1479 (w), 1394 (s), 1249 (m), 1179
(m), 1087 (s), 1022 (s), 903 (w), 887 (w), 853 (m), 793 (m), 753
(m), 726 (w), 626 (m), 585 (w), 530 (m), 430 (m); for JXNU-2(Pr),
3423 (s), 2937 (w), 1644 (s), 1600 (w), 1566 (m), 1534 (w), 1480
(w), 1398 (s), 1250 (m), 1179 (m), 1087 (s), 1021 (s), 902 (w), 888
(w), 861(s), 793 (m), 755 (m), 698 (w), 626 (m), 550 (w), 432 (m).
X-ray Crystallography. X-ray diffraction data of compounds
JXNU-2 were collected on a Bruker Apex II CCD diffractometer
equipped with a graphite-monochromated Mo Kα radiation (λ =
0.710 73 Å). Data reduction was performed using SAINT and
corrected for Lorentz and polarization effects. Adsorption corrections
were applied using the SADABS routine.12 The structures were solved
by the direct methods and successive Fourier difference syntheses and
refined by the full-matrix least-squares method on F2 (SHELXTL
Version 5.1).13 All non-hydrogen atoms were refined with anisotropic
thermal parameters except for the oxygen, carbon, and nitrogen atoms
of the coordination solvent molecules, which were kept isotropic
thermal parameters due to poor thermal behavior. Aromatic hydrogen
atoms were assigned to calculated positions. Hydrogen atoms of the
solvent molecules were not located. For compounds JXNU-2(Sm) and
JXNU-2(Eu), the coordinated water and DMF molecules, except for
the oxygen atom of the DMF, could not be located in the difference
Fourier map due to their disorder, but they are included in the
formulas. The unit cell includes a large region of disordered guest
solvent molecules, which could not be modeled and were treated by
the SQUEEZE routine.14 The structures were then refined again using
the data generated. Note that the formulas do not include the guest
solvent molecules. The R1 values are defined as R1 = ∑||Fo| − |Fc||/∑|
Chemicals. All chemicals were of reagent grade and used as
commercially obtained. The biphenyl-3,3′-disulfonyl-4,4′-dicarboxylic
acid (H4−BPDSDC) ligand was prepared as follows (Scheme 1).
Scheme 1. Preparation of H4−BPDSDC Ligand
Synthesis of H4−BPDSDC Ligand. (1) Synthesis of 3,3′-
Disulfonyl-4, 4′-dimethylbiphenyl. Sulfuric acid (30 mL; 98%) was
placed in a 100 mL three-necked flask. The flask was immersed in an
ice bath for 0.5 h, and then 10 g of 4,4′-dimethylbiphenyl was slowly
added into the flask. The mixture was stirred at 60 °C for 1 h, 80 °C
for 3 h, and 90 °C for 3 h. After it cooled to room temperature, the
white powder product was obtained by adding lots of acetonitrile and
2
2
Fo| and wR2 = {∑[w(Fo − Fc2)2]/∑[w(Fo )2]}1/2. The details of the
crystal parameters, data collection, and refinement are summarized in
Table 1, and the selected bond lengths are listed in Table S1.
RESULTS AND DISCUSSION
■
1
methylene chloride. Yield: ∼86% based on 4,4′-dimethylbiphenyl. H
Crystal Structure. Single-crystal X-ray diffraction analyses
revealed that compounds JXNU-2(Sm), JXNU-2(Eu), and
JXNU-2(Pr) are isomorphous and crystallize in a rhombohe-
dral space group R3c (Table 1). There are one Ln3+ ion, one K+
ion, and one tetraanionic BPDSDC4− ligand in the asymmetric
unit. Note that these compounds contain the K+ ion, which
derives from the H4−BPDSDC ligand containing a small
amount of K+ impurity. As shown in Figure 1, Ln atom is nine-
coordinated by six carboxylate O atoms and two sulfonate O
atoms from four BPDSDC4− ligands and one O atom of a DMF
molecule. The coordination gemometry of the Ln atom can be
described as a singly capped square antiprism with O7F at the
capped position (Figure S1 in Supporting Information). The
Ln−O bond distances vary from 2.380(4) to 2.674(4) Å (Table
NMR (deuterated dimethyl sulfoxide (DMSO-d6), ppm): 2.50 (s, 6H),
7.23 (d, 2H), 7.46 (d, 2H), 8.00 (s, 2H); IR spectrum (cm−1, KBr
pellet): 3430 (s), 2244 (w), 1722 (m), 1476 (s), 1373 (m), 1184 (m),
1093 (m), 1071 (s) (OSO of −SO3H group), 815 (s), 720 (s),
629 (s) (C−S), 588 (w), 535 (m), 514 (m).
(2) Synthesis of Biphenyl-3,3′-disulfonyl-4,4′-dicarboxylic Acid.
3,3′-disulfonyl-4,4′-dimethylbiphenyl (7.5 g), NaOH (0.5 g), and
deionized water (75 mL) were placed in a three-necked flask. The
mixture was stirred at 70 °C. Then 4.5 g of NaOH was slowly added
into the mixture (pH = 12). The resulting mixture became clear, and
after it stayed 1 h, finely powdered KMnO4 (12.3 g) was added into
the flask in small portions. After it stirred at 90 °C for 9 h, the mixture
was cooled to room temperature and filtrated. The filtrate was acidified
with 12 M HCl. White solid was obtained from the resulting mixture
after 10 h. Yield: ∼67% based on 3,3′-disulfonyl-4,4′-dimethylbiphen-
B
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Table 1. Crystallographic Data for JXNU-2
Sm
Eu
Pr
formula
fw
C17H15NO12S2KSm
678.87
296(2)
trigonal
R3c
C17H15NO12S2KEu
680.48
296(2)
trigonal
R3c
C17H15NO12S2KPr
669.43
296(2)
trigonal
R3c
temp (K)
cryst syst
space group
Z
18
18
18
a (Å)
48.832(2)
48.832(2)
8.4834(6)
90
48.7999(3)
48.7999(3)
8.45290(10)
90
48.884(2)
48.884(2)
8.5632(6)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Dcalcd (g·cm−3
90
90
90
120
120
120
17 519(2)
1.158
17 433.1(3)
1.167
17 721(2)
1.129
)
μ (mm−1
)
1.760
1.872
1.486
no. of reflns collected
independent reflns
obsd reflns.(I > 2σ(I))
F(000)
42 323
8874
32 991
8884
35 014
8607
8435
8342
8116
5994
6012
5940
R[int]
0.0434
0.0341
0.0974
1471126
0.0302
0.0290
0.0808
1471127
0.0400
0.0337
0.0937
1471128
a
R1 (I > 2σ(I))
a
wR2 (all data)
CCDC no.
a
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo| and wR2 = {∑[w(Fo − Fc2)2]/∑[w(Fo )2]}1/2
.
Figure 2. 3D framework showing the trigonal and hexagonal channels
highlighting the heterometallic rod-shaped SBU.
Figure 1. Coordination environments of Ln3+ and K+ ions.
S1). The K+ ion is six-coordinated by four sulfonate O atoms
from three BPDSDC4− ligands, one carboxylate O of the fourth
BPDSDC4− ligand, and one coordinated water molecule. The
K−O bond distances range from 2.564(5) to 2.896(5) Å. As
schemed in Figure S2, the BPDSDC4− ligand bridges four Ln3+
and four K+ ions through its four η2-O atoms and five
unidentate O atoms. The Ln3+ and K+ ions are interconnected
by the BPDSDC4− ligands to give a three-dimensional (3D)
framework constructed from the 1D rod-shaped secondary
building units (SBUs) running alone the c axis (Figure 2). The
1D rod-shaped SBU is constructed by the heterometallic Ln3+
and K+ ions bridged by the carboxylate and sulfonate groups,
which is distinct from the common observed rod-shaped SBUs
based on the homometallic carboxylate rods.15 Each rod-shaped
heterometallic SBU is connected with four adjacent SBUs
through the biphenyl linkers, resulting in the final 3D
framework with two kinds of 1D channels propagating along
the c axis: small trigonal channels and large hexagonal channels
(Figure 2). This 3D structure is an illustration of a Kagome-like
lattice16 and reminiscent of vanadium-based terephthalate
compound of MIL-68 (V(OH) (terephthalate)) based on the
1D rod-shaped vanadium(III)-hydroxyl−carboxylate SBUs.17
The trigonal channel has an approximate dimensionality of 13.5
Å, and the diameter of the hexagonal channel is ∼28.2 Å (based
on the Ln ions). As depicted in Figure 2, the free sulfonate O10
atoms protrude into the channels in the small trigonal channels,
while the sulfonate atoms of O4 and O5 atoms point into the
hexagonal channels. These channels are occupied by large
amounts of highly disordered solvated water and DMF
molecules, which could not be located from the sing-crystal
X-ray diffraction data (XRD).
Gas Adsorption Properties. The experimental powder
XRD patterns match well with the simulated ones, indicative of
the phase purity of these compounds (Figure S3). Since the
C
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Figure 3. (a) The N2 sorption isotherm at 77 K and (b) CO2 sorption isotherms at 273 and 293 K (solid symbols: adsorption, open symbols:
desorption) for JXNU-2(Sm). (inset) The enthalpy of adsorption (Qst) as a function of CO2 uptake.
three compounds are isomorphous, the JXNU-2(Sm) is
described here representatively to illustrate their gas adsorption
and proton conductivity. The total solvent-accessible volume
for JXNU-2(Sm) is estimated to be 58% using the PLATON
program.14 The resulting thermogravimetric analyses revealed
that the removal of solvent molecules occurs between 40 and
220 °C, and no further weight loss is observed below 380 °C
(Figure S4). The activated sample of JXNU-2(Sm) was
prepared by evacuation at 30 °C for 10 h and then at 150
°C for 10 h. The stability of the guest-free material is confirmed
by the PXRD patterns (Figure S3a). The permanent porosity of
JXNU-2(Sm) is verifieded by its N2 sorption isotherms at 77 K,
which exhibits a typical reversible type I behavior and a very
sharp uptake at P/P0 < 0.05 (Figure 3a), corroborating the
microporous nature of JXNU-2(Sm). JXNU-2(Sm) takes up
230 cm3 (STP) g−1 of N2 at 1 atm with a Langmuir and BET
surface areas of 985.6 and 738.6m2 g−1, respectively. As shown
in Figure 3b, CO2 uptakes of JXNU-2(Sm) at 273 and 293 K (1
atm) are 66.6 and 41.2 cm3 g−1, respectively. Furthermore, the
CO2 isotherms measured at 273 and 293 K were fitted using
the virial equation (Figure S5), which gives the CO2 isosteric
heat of adsorption (Qst) of 27 kJ mol−1 at zero loading and 26.4
kJ mol−1 at the maximum measured loading (Figure 3b inset).
The Qst value for CO2 does not change appreciably with
loading, indicating uniformity of the binding sites. Additionally,
the Qst value for the present compound is moderately high,
which is larger than those of MOFs with no open metal sites or
polar functional groups (with Qst of 16−20 kJ mol−1),18 but it is
comparable to those of MAF-25 (26.3(5) kJ mol−1)19 and
InOF-1(29 kJ mol−1).20 The sorption performance of JXNU-
2(Sm) for CO2 prompted us to study the sorption of several
fuel molecules such as CH4, C2H6, C3H8, and C2H2. At 273 K,
JXNU-2(Sm) takes up less CH4 but adsorbs some amounts of
C2H6, C3H8, and C2H2. Its uptake capacity for C2H6, C3H8, and
C2H2 is 38.3, 60.7, and 79.1 cm3 g−1 at 1 atm, respectively
(Figure 4). A hysteresis profile is observed in the isotherms of
C2H2, which indicates a strong interaction between the
adsorbed C2H2 molecules and the sulfonate-containing pore
surface.21 The micropore surface is decorated with the sulfonate
groups, which has a polarized environment and has a high
affinity to C2H2.
Figure 4. CH4, C2H6, C3H8, and C2H2 sorption isotherms at 273 K
(solid symbols: adsorption, open symbols: desorption) for JXNU-
2(Sm).
molecules will provide the proton-conducting pathways for
the proton transfer, indicating that these compounds with the
hydrophilic channels can potentially be a proton-conducting
material. The proton conductivity of JXNU-2(Sm) was
therefore evaluated by the AC impedance method using a
compacted pellet of the powdered sample. The Nyquist plots of
the pellet samples were obtained at 30 °C under different
relative humidity (RH). As shown in Figure S6, the Nyquist
plots displayed a semicircle in the high-frequency component
and an inclined tail in the low-frequency component, which is a
fingerprint of proton conductor and shows two distinct charge
transport regimes. The semicircle corresponds to the bulk
resistance, which is attributed to the grain interior contribution,
and the tail corresponds to the pile-up of protons at the
electrodes.23 A noticeable decrease of the size of the semicircle
with increasing humidity was observed in the Nyquist plots
(Figure S6), which indicates that the conductivity of JXNU-
2(Sm) is highly humidity-dependent and increases by raising
humidity. As shown in Figure 5, the proton conductivity of
JXNU-2(Sm) is 6.64 × 10−7 S cm−1 at 30 °C and 50% RH,
which is significantly less than that obtained at 98% RH by 2
orders of magnitude. The conductivity of 4.69 × 10−5 S cm−1 at
98% RH and 30 °C for JXNU-2(Sm) is comparable to those of
other LnOFs such as Gd(III)-compound with hydrophilic
channels formed by carboxylate oxygen atoms and coordinated
water molecules (6.3 × 10−5 S cm−1 at 25 °C and 97% RH)24
and layered La3+ compound (4.24 × 10−5 S cm−1 at 25 °C and
95% RH).25 The abundant hydrophilic sulfonate groups are
arranged at surface of channels, which would facilitate
enrichment of the solvate water molecules for this high-proton
Proton Conduction. It is well-known that the organic
polymers with sulfonate group, like Nafion, are an important
kind of solid-state proton-conductive materials.22 We were
inspired by the structural features that the sulfonate oxygen
atoms lined in the surfaces of the channels of these compounds.
The sulfonate groups along with the coordinated water
D
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be 0.628 eV from the linear fitting of the Arrhenius plot of
ln(σT) versus T−1 (Figure 6). The value is too large to assume
that the conduction mechanism is only of the Grotthuss
fashion.27 Instead, a vehicle mechanism could operate for the
proton conduction of JXNU-2(Sm).27 The hydrophilic sites
present in the channels would facilitate enrichment of the
solvate water molecules in the channels, which movement as a
solvated H+. Thus, the solvated water uptake induces a vehicle-
type proton transfer.
Luminescent Properties. The Eu-containing compounds
can show characteristic luminescent properties in the visible
region. Thus, the luminescent spectra of compound JXNU-
2(Eu) suspended in DMF solution were measured. JXNU-
2(Eu) emits the characteristic bright red color of Eu3+ upon
excitation at 316 nm (Figure S8). The emission peaks at 579,
593, 618, 652, and 696 nm can be attributed to 5D0 → 7Fn (n =
Figure 5. Plots of log(σ) vs RH of JXNU-2(Sm) at 30 °C with three
cycles.
0, 1, 2, 3, 4) transitions of Eu3+ ions, respectively.28 The D0
5
emission decay curve for JXNU-2(Eu) in the solid state was
monitored within the 5D0 → 7F2 transition under the excitation
wavelength (Figure S9). The lifetime for 5D0 → 7F2 of Eu3+ ion
was calculated to be 0.864 ms. The absolute emission quantum
yield for the Eu3+ compund is 5.49%. The sulfonate groups on
the surface of the 1D channels may capture the additional metal
ions and serve as the fluorescent sensing sites for the metal
ions. The as-prepared crytalline sample of JXNU-2(Eu) was
ground and dispersed in DMF solution to form a suspension by
ultrasound method. Then the interesting metal ions were added
into the above resulting mixture. As shown in Figure S8, the
well-resolved Eu3+-luminescence was observed in the emission
spectra of the metal-incorported JXNU-2(Eu) in DMF
suspension (metal ion concentration: 1 mM) upon excitation
at 316 nm. The luminescence intensities of the dominant
emission peaks (618 nm) are shown in Figure 7. The Li+, Na+,
conductivity. As shown in Figure 5, the humidity-dependent
proton conductivity of JXNU-2(Sm) can be measured
repeatedly by decreasing and increasing the humidity in the
range of 50−98% without distinct change in their curves
shapes. This observation suggests JXNU-2(Sm) is stable under
impedance measurements and can reach equilibrium quickly, a
property that is essential for sensor applications. Thus, JXNU-
2(Sm) could be a good candidate as a promising humidity
sensor.
To study the temperature effect and ensure meaningful
correlation to proton conduction measurements, we further
interrogated them with impedance as a function of temperature.
Temperature dependence of the conductivity of JXNU-2(Sm)
was measured from 40 to 80 °C at 98% RH for pellet sample
(Figure S7). The Nyquist plots showed the decreased size of
the semicircle when switching temperature from 40 to 80 °C,
which displayed a noticeable increase in the conductivity (σ)
when increasing temperature. The sample at 80 °C and 98%
RH shows the highest proton conductivity with the value of
1.11 × 10−3 S cm−1 (Figure 6), which is comparable to that of
the highest conductive hydrated metal−organic framework
(MOF) material.26 The activation energy Ea was estimated to
Figure 7. Luminescence intensity of the transition (618 nm) of JXNU-
2(Eu) with addition of different metal ions (1 mM). I and I0 denote
the fluorescence intensity of JXNU-2(Eu) with and without metal ions
of interest, respectively.
Mg2+, Ba2+, and Co2+ ions have a negligible effect on the
luminescence intensity. The addition of Fe3+ and Cu2+ ions to
the suspension of JXNU-2(Eu) can weaken the emission
intensity of JXNU-2(Eu). Remarkably, the emission intensity of
JXNU-2(Eu) was enhanced significantly after the addition of
K+. The luminescence intensity increases as the concentration
of K+ increases, while the emission intensity decreases with
increasing the concentration of Fe3+ (Figure 8). The PXRD
patterns of the K+ and Fe3+-ion-incorporated JXNU-2(Eu) both
are in good agreement with the parent JXNU-2(Eu) (Figure
Figure 6. Arrhenius-type plots of ln(σT) vs 1000/T for JXNU-2(Sm)
at a RH of 98%. The black solid lines represent the best fit of the data.
The measurements were performed at 10 °C intervals over a
temperature range from 40 to 80 °C, with each data point
corresponding to three independent tests. (inset) Nyquist plot for
JXNU-2(Sm) at 80 °C and 98% RH.
E
DOI: 10.1021/acs.inorgchem.6b00928
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 8. Emission spectra of JXNU-2(Eu) with different concentrations of K+ (a) and Fe3+ (b) in DMF solution.
S3b), suggesting that the framework of JXNU-2(Eu) remains
intact when metal ions are added in. A few reports have been
documented that some transition metal ions such as Cu2+ and
Fe3+ can quench the lanthanide luminescence of the MOFs.29
For the present case, it is likely that the Cu2+ and Fe3+ entered
into the channels and were captured by the sulfonate groups on
the channels. The electronic structure of the ligand was
perturbed by the introduction of metal-ion guests into the
MOF channels, which reduces the energy transfer from ligand
to the Eu3+ center, resulting in luminescent quenching.
However, for K+ ion, it is not the case. The K+ ion has a
large ionic radius and may form a cation−π interaction with the
phenyl of the ligand when entering into the channel, which is
similar to the Ag+ ion.30 It has been reported that the cation−π
interaction can enhance the intersystem crossing (ISC) and
increase the population of the excited triplet state of a
fluorophore,31 which subsequently increases the population of
AUTHOR INFORMATION
Corresponding Authors
*E-mail: ylwang@gmail.com. Fax: +86-791-88336372. (Y.-
L.W.)
■
*E-mail: qyliuchem@hotmail.com. (Q.-Y.L.)
Author Contributions
§These authors contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the NNSF of China (Grant Nos.
21361011, 21101081, 51402293, and 21561015), the NSF of
Jiangxi (Grant No. 20151BAB203002), NSF of Fujian for
Distinguished Young Scholar (Grant No. 2016J06006), and the
Young Scientist Training Project of Jiangxi Province (Grant
No. 20153BCB23017).
5
the D0 excited state of the Eu3+ ion. Thus, the addition of K+
ion into the compound JXNU-2(Eu) increases the Eu3+
emission. To our knowledge, the luminescence sensitivity to
K+ ion with MOF has not been reported previously.
Concerning material of JXNU-2(Eu), it serves as a turn-on
emission, which is preferred for detecting an analyte, high-
lighting the potential for recognition of K+ ion.
REFERENCES
■
(1) (a) Rocha, J.; Carlos, L. D.; Almeida Paza, F. A.; Ananias, D.
Chem. Soc. Rev. 2011, 40, 926−940. (b) Cui, Y.; Yue, Y.; Qian, G.;
Chen, B. Chem. Rev. 2012, 112, 1126−1162.
(2) (a) Sorace, L.; Benelli, C.; Gatteschi, D. Chem. Soc. Rev. 2011, 40,
3092−3104. (b) Lin, P.-H.; Burchell, T. J.; Clerac, R.; Murugesu, M.
Angew. Chem., Int. Ed. 2008, 47, 8848−8851.
(3) (a) Duan, J.; Higuchi, M.; Foo, M. L.; Horike, S.; Rao, K. P.;
Kitagawa, S. Inorg. Chem. 2013, 52, 8244−8249. (b) Xue, D.-X.;
Belmabkhout, Y.; Shekhah, O.; Jiang, H.; Adil, K.; Cairns, A. J.;
Eddaoudi, M. J. Am. Chem. Soc. 2015, 137, 5034−5040.
(4) (a) Colodrero, R. M. P.; Olivera-Pastor, P.; Losilla, E. R.; Aranda,
M. A. G.; Leon-Reina, L.; Papadaki, M.; McKinlay, A. C.; Morris, R. E.;
Demadis, K. D.; Cabeza, A. Dalton Trans. 2012, 41, 4045−4051.
(b) Yoon, M.; Suh, K.; Natarajan, S.; Kim, K. Angew. Chem., Int. Ed.
2013, 52, 2688−2700. (c) Sadakiyo, M.; Yamada, T.; Kitagawa, H. J.
Am. Chem. Soc. 2009, 131, 9906−9907. (d) Taylor, J. M.; Dawson, K.
W.; Shimizu, G. K. H. J. Am. Chem. Soc. 2013, 135, 1193−1196.
(e) Wang, R.; Dong, X.-Y.; Xu, H.; Pei, R.-B.; Ma, M.-L.; Zang, S.-Q.;
Hou, H.-W.; Mak, T. C. W. Chem. Commun. 2014, 50, 9153−9156.
(5) (a) Wong, K.-L.; Law, G.-L.; Yang, Y.-Y.; Wong, W.-T. Adv.
Mater. 2006, 18, 1051−1054. (b) Wu, Z.-L.; Dong, J.; Ni, W.-Y.;
Zhang, B.-W.; Cui, J.-Z.; Zhao, B. Inorg. Chem. 2015, 54, 5266−5272.
(c) Zhou, Y.; Chen, H.-H.; Yan, B. J. Mater. Chem. A 2014, 2, 13691−
13697. (d) Dong, X.-Y.; Wang, R.; Wang, J.-Z.; Zang, S.-Q.; Mak, T. C.
W. J. Mater. Chem. A 2015, 3, 641−647.
CONCLUSIONS
■
In conclusion, the lanthanide-organic frameworks JXNU-2
based on the novel biphenyl-3,3′-disulfonyl-4,4′-dicarboxylate
ligand have been synthesized and characterized. The 3D
frameworks feature 1D hexagonal channels and 1D trigonal
channels and exhibit affinity to quadrupolar molecules such as
C2H2 and CO2, revealing potential for application in gas
separation. Moreover, the JXNU-2 framework shows highly
humidity-dependent proton conductivity associated with the
hydrophilic channels, which has a potential application for an
impedance humidity sensor. Finally, the JXNU-2(Eu) material
acts as a turn-on emission for K+ ion, highlighting the potential
for K+ ion sensor.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.6b00928.
(6) (a) Maji, T. K.; Mostafa, G.; Chang, H.-C.; Kitagawa, S. Chem.
Commun. 2005, 2436−2438. (b) Shiga, T.; Ito, N.; Hidaka, A.; Okawa,
H.; Kitagawa, S.; Ohba, M. Inorg. Chem. 2007, 46, 3492−3501.
(c) Thirumurugan, A.; Natarajan, S. Dalton Trans. 2004, 2923−2928.
Table about bond lengths; PXRD patterns; TG curves;
luminescence plots; and proton condutivity data (PDF)
X-ray structure data (CIF)
(d) Long, D. L.; Blake, A. J.; Champness, N. R.; Wilson, C.; Schroder,
̈
F
DOI: 10.1021/acs.inorgchem.6b00928
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
M. Angew. Chem., Int. Ed. 2001, 40, 2443−2447. (e) Pan, L.; Zheng, N.
W.; Wu, Y. G.; Han, S.; Yang, R. Y.; Huang, X. Y.; Li, J. Inorg. Chem.
2001, 40, 828−830. (f) Sun, Y.-Q.; Zhang, J.; Yang, G.-Y. Chem.
Commun. 2006, 1947−1949. (g) Benelli, C.; Gatteschi, D. Chem. Rev.
(18) Bastin, L.; Bar
́
cia, P. S.; Hurtado, E. J.; Silva, J. A. C.; Rodrigues,
A. E.; Chen, B. J. Phys. Chem. C 2008, 112, 1575−1581.
(19) Lin, J.-B.; Zhang, J.-P.; Chen, X.-M. J. Am. Chem. Soc. 2010, 132,
6654−6656.
(20) Qian, J.; Jiang, F.; Yuan, D.; Wu, M.; Zhang, S.; Zhang, L.;
Hong, M. Chem. Commun. 2012, 48, 9696−9698.
(21) Horike, S.; Bureekaew, S.; Kitagawa, S. Chem. Commun. 2008,
471−473.
2002, 102, 2369−2388. (h) Canadillas-Delgado, L.; Martín, T.;
̃
Fabelo, O.; Pasan
C. Chem. - Eur. J. 2010, 16, 4037−4047.
(7) (a) Serre, C.; Ferey, G. J. Mater. Chem. 2002, 12, 3053−3057.
(b) Serpaggi, F.; Ferey, G. J. Mater. Chem. 1998, 8, 2749−2755.
(c) Jiang, H.-L.; Tsumori, N.; Xu, Q. Inorg. Chem. 2010, 49, 10001−
10006. (d) Henry, N.; Costenoble, S.; Lagrenee, M.; Loiseau, T.;
́ ́
, J.; Delgado, F. S.; Lloret, F.; Julve, M.; Ruiz-Perez,
́
(22) (a) Schuster, M.; Meyer, W. H.; Wegner, G.; Herz, H. G.; Ise,
M.; Schuster, M.; Kreuer, K. D.; Maier. Solid State Ionics 2001, 145,
85−92. (b) Li, G. H.; Lee, C. H.; Lee, Y. M.; Cho, C. G. Solid State
Ionics 2006, 177, 1083−1090. (c) Karadedeli, B.; Bozkurt, A.; Baykal,
A. Phys. B 2005, 364, 279−284.
́
́
Abraham, F. CrystEngComm 2011, 13, 251−258. (e) Cai, B.; Yang, P.;
Dai, J.-W.; Wu, J.-Z. CrystEngComm 2011, 13, 985−991. (f) Reineke,
T. M.; Eddaoudi, M.; Fehr, M.; Kelley, D.; Yaghi, O. M. J. Am. Chem.
Soc. 1999, 121, 1651−1657.
(23) (a) Ordinario, D. D.; Phan, L.; Walkup, W. G., IV; Jocson, J.-M.;
Karshalev, E.; Husken, N.; Gorodetsky, A. A. Nat. Chem. 2014, 6,
̈
596−602. (b) Soboleva, T.; Xie, Z.; Shi, Z.; Tsang, E.; Navessin, T.;
Holdcroft, S. J. Electroanal. Chem. 2008, 622, 145−152. (c) Karim, M.
R.; Hatakeyama, K.; Matsui, T.; Takehira, H.; Taniguchi, T.; Koinuma,
M.; Matsumoto, Y.; Akutagawa, T.; Nakamura, T.; Noro, S.; Yamada,
T.; Kitagawa, T.; Hayami, S. J. Am. Chem. Soc. 2013, 135, 8097−8100.
(d) Bao, S.-S.; Li, N.-Z.; Taylor, J. M.; Shen, Y.; Kitagawa, H.; Zheng,
L.-M. Chem. Mater. 2015, 27, 8116−8125.
(8) (a) Eddaoudi, M.; Moler, D. B.; Li, H. L.; Chen, B. L.; Reineke,
T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319−330.
(b) Deng, Y.-K.; Su, H.-F.; Xu, J.-H.; Wang, W.-G.; Kurmoo, M.; Lin,
S.-C.; Tan, Y.-Z.; Jia, J.; Sun, D.; Zheng, L.-S. J. Am. Chem. Soc. 2016,
̌
138, 1328−1334. (c) Liu, F.-L.; Kozlevcar, B.; Strauch, P.; Zhuang, G.-
L.; Guo, L.-Y.; Wang, Z.; Sun, D. Chem. - Eur. J. 2015, 21, 18847−
18854. (d) Li, X.-Y.; Su, H.-F.; Zhou, R.-Q.; Feng, S.; Tan, Y.-Z.;
Wang, X.-P.; Jia, J.; Kurmoo, M.; Sun, D.; Zheng, L.-S. Chem. - Eur. J.
2016, 22, 3019−3028. (e) Dong, X.-Y.; Hu, X.-P.; Yao, H.-C.; Zang,
S.-Q.; Hou, H.-W.; Mak, T. C.W. Inorg. Chem. 2014, 53, 12050−
12057.
(24) Liang, X. Q.; Zhang, F.; Zhao, H. X.; Ye, W.; Long, L. S.; Zhu,
G. S. Chem. Commun. 2014, 50, 6513−6516.
(25) Bao, S.-S.; Otsubo, K.; Taylor, J. M.; Jiang, Z.; Zheng, L.-M.;
Kitagawa, H. J. Am. Chem. Soc. 2014, 136, 9292−9295.
(26) Xu, G.; Otsubo, K.; Yamada, T.; Sakaida, S.; Kitagawa, H. J. Am.
Chem. Soc. 2013, 135, 7438−7441.
(27) Shigematsu, A.; Yamada, T.; Kitagawa, H. J. Am. Chem. Soc.
2011, 133, 2034−2036.
(28) (a) Kirby, A. F.; Foster, D.; Richardson, F. S. Chem. Phys. Lett.
1983, 95, 507−512. (b) Nogami, M.; Abe, Y. J. Non-Cryst. Solids 1996,
197, 73−78.
(29) (a) Chen, B. L.; Wang, L. B.; Xiao, Y. Q.; Fronczek, F. R.; Xue,
M.; Cui, Y. J.; Qian, G. D. Angew. Chem., Int. Ed. 2009, 48, 500−503.
(b) Xu, H.; Hu, H.-C.; Cao, C.-S.; Zhao, B. Inorg. Chem. 2015, 54,
4585−4587. (c) Wang, R. M.; Zhang, M. H.; Liu, X. B.; Zhang, L. L.;
Kang, Z. X.; Wang, W.; Wang, X. Q.; Dai, F. N.; Sun, D. F. Inorg.
Chem. 2015, 54, 6084−6086. (d) Tang, Q.; Liu, S. X.; Liu, Y. W.;
Miao, J.; Li, S. J.; Zhang, L.; Shi, Z.; Zheng, Z. P. Inorg. Chem. 2013,
52, 2799−2801. (e) Zhou, J.-M.; Shi, W.; Xu, N.; Cheng, P. Inorg.
Chem. 2013, 52, 8082−8090.
(9) (a) Deria, P.; Chung, Y. G.; Snurr, R. Q.; Hupp, J. T.; Farha, O.
K. Chem. Sci. 2015, 6, 5172−5176. (b) Taylor, J. M.; Komatsu, T.;
Dekura, S.; Otsubo, K.; Takata, M.; Kitagawa, H. J. Am. Chem. Soc.
2015, 137, 11498−11506. (c) Yang, F.; Huang, H.; Wang, X.; Li, F.;
Gong, Y.; Zhong, C.; Li, J.-R. Cryst. Growth Des. 2015, 15, 5827−5833.
(d) Xue, D.-X.; Cairns, A. J.; Belmabkhout, Y.; Wojtas, L.; Liu, Y.;
Alkordi, M. H.; Eddaoudi, M. J. Am. Chem. Soc. 2013, 135, 7660−
7667. (e) Zhang, Y.-B.; Furukawa, H.; Ko, N.; Nie, W.; Park, H. J.;
Okajima, S.; Cordova, K. E.; Deng, H.; Kim, J.; Yaghi, O. M. J. Am.
Chem. Soc. 2015, 137, 2641−2650.
̂ ́
(10) (a) Cote, A. P.; Shimizu, G. K. H. Coord. Chem. Rev. 2003, 245,
49−64. (b) Shimizu, G. K. H.; Vaidhyanathan, R.; Taylor, J. M. Chem.
Soc. Rev. 2009, 38, 1430−1449. (c) Sun, D.; Liu, F.-J.; Hao, H.-J.; Li,
Y.-H.; Zhang, N.; Huang, R.-B.; Zheng, L.-S. CrystEngComm 2011, 13,
5661−5665. (d) Meng, X.; Song, S.-Y.; Song, X.-Z.; Zhu, M.; Zhao, S.-
N.; Wu, L.-L.; Zhang, H.-J. Chem. Commun. 2015, 51, 8150−8152.
(e) Dong, X.-Y.; Wang, R.; Li, J.-B.; Zang, S.-Q.; Hou, H.-W.; Mak, T.
C. W. Chem. Commun. 2013, 49, 10590−10592.
(30) Xue, Y.; Davis, A. V.; Balakrishnan, G.; Stasser, J. P.; Staehlin, B.
M.; Focia, P.; Spiro, T. G.; Penner-Hahn, J. E.; O'Halloran, T. V. Nat.
Chem. Biol. 2008, 4, 107−109.
(31) Isaac, M.; Denisov, S. A.; Roux, A.; Imbert, D.; Jonusauskas, G.;
(11) (a) Xiao, B.; Byrne, P. J.; Wheatley, P. S.; Wragg, D. S.; Zhao,
X.; Fletcher, A. J.; Thomas, K. M.; Peters, L.; Evans, J. S. O.; Warren, J.
E.; Zhou, W.; Morris, R. E. Nat. Chem. 2009, 1, 289−294. (b) Horike,
S.; Matsuda, R.; Tanaka, D.; Mizuno, M.; Endo, K.; Kitagawa, S. J. Am.
Chem. Soc. 2006, 128, 4222−4223. (c) Sun, D. F.; Cao, R.; Sun, Y. Q.;
Bi, W. H.; Yuan, D. Q.; Shi, Q.; Li, X. Chem. Commun. 2003, 1528−
1529. (d) Miao, X.-H.; Zhu, L.-G. CrystEngComm 2009, 11, 2500−
2509. (e) Liu, Q.-Y.; Wang, W.-F.; Wang, Y.-L.; Shan, Z.-M.; Wang,
M.-S.; Tang, J. K. Inorg. Chem. 2012, 51, 2381−2392. (f) Papadaki, I.;
Malliakas, C. D.; Bakas, T.; Trikalitis, P. N. Inorg. Chem. 2009, 48,
9968−9970.
McClenaghan, N. D.; Sen
11453−11456.
́
eq
̀
ue, O. Angew. Chem., Int. Ed. 2015, 54,
(12) APEX2, SADABS, SAINT; Bruker AXS Inc: Madison, WI, 2008.
(13) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, A64, 112−122.
(14) Spek, A. L. PLATON: A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 2001.
(15) (a) Rosi, N. L.; Kim, J.; Eddaoudi, M.; Chen, B.; O’Keeffe, M.;
Yaghi, O. M. J. Am. Chem. Soc. 2005, 127, 1504−1508. (b) Zhang, J.;
Wu, T.; Chen, S. M.; Feng, P. Y.; Bu, X. H. Angew. Chem., Int. Ed.
2009, 48, 3486−3490. (c) Guo, X.; Zhu, G.; Sun, F.; Li, Z.; Zhao, X.;
Li, X.; Wang, H.; Qiu, S. Inorg. Chem. 2006, 45, 2581−2587.
(16) Pati, S. K.; Rao, C. N. R. Chem. Commun. 2008, 4683−4693.
(17) Barthelet, K.; Marrot, J.; Fer
2004, 520−521.
́
ey, G.; Riou, D. Chem. Commun.
G
DOI: 10.1021/acs.inorgchem.6b00928
Inorg. Chem. XXXX, XXX, XXX−XXX