Cd(II)-MOF: Adsorption, separation, and guest-dependent luminescence for monohalobenzenes

Article abstract of DOI:10.1021/ic501100p

A series of isostructural 2-fold interpenetrating 2D Cd(II)-MOFs, namely G?CdL₂(OTs)₂ (G = THF (1), PhF (2), PhCl (3), PhBr (4), PhI (5), L = 1,2-bis[(3-(pyridin-4-yl)phenoxy]ethane, and OTs^- = p-toluenesulfonate anion), have been successfully synthesized from the flexible ethylene glycol ether-bridging ligand L and Cd(OTs)₂ in solution. The CdL₂(OTs)₂ framework contains squarelike nonpolar channels, and the encapsulated guest molecules can be removed by heating (150°C) to generate a guest-free host framework which is able to reversibly adsorb monohalobenzenes PhX (X = F, Cl, Br, I) in the liquid phase under ambient conditions without loss of framework integrity. Furthermore, it can effectively separate these monohalobenzenes and exhibits a clear affinity for monohalobenzenes according to the following order: PhI > PhBr > PhCl > PhF. In addition, PhX?CdL₂(OTs)₂ exhibits guest-dependent luminescence properties.

Full text of DOI:10.1021/ic501100p

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Article
pubs.acs.org/IC
Cd(II)-MOF: Adsorption, Separation, and Guest-Dependent
Luminescence for Monohalobenzenes
Lei Wang,†,‡ Yan-An Li,† Fan Yang,† Qi-Kui Liu,† Jian-Ping Ma,† and Yu-Bin Dong*,†
†College of Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Center of Functionalized Probes for
Chemical Imaging, Key Laboratory of Molecular and Nano Probes, Ministry of Education, Shandong Normal University, Jinan
250014, People’s Republic of China
‡Department of Pharmacy, Binzhou Medical University, Yantai 264003, People’s Republic of China
S
* Supporting Information
ABSTRACT: A series of isostructural 2-fold interpenetrating 2D
Cd(II)-MOFs, namely G⊂CdL2(OTs)2 (G = THF (1), PhF (2), PhCl
(3), PhBr (4), PhI (5), L = 1,2-bis[(3-(pyridin-4-yl)phenoxy]ethane,
and OTs− = p-toluenesulfonate anion), have been successfully
synthesized from the flexible ethylene glycol ether-bridging ligand L
and Cd(OTs)2 in solution. The CdL2(OTs)2 framework contains
squarelike nonpolar channels, and the encapsulated guest molecules
can be removed by heating (150 °C) to generate a guest-free host
framework which is able to reversibly adsorb monohalobenzenes PhX
(X = F, Cl, Br, I) in the liquid phase under ambient conditions without
loss of framework integrity. Furthermore, it can effectively separate
these monohalobenzenes and exhibits a clear affinity for mono-
halobenzenes according to the following order: PhI > PhBr > PhCl >
PhF. In addition, PhX⊂CdL2(OTs)2 exhibits guest-dependent luminescence properties.
enrichment and separation are very highly demanded and
important.
INTRODUCTION
■
Metal−organic frameworks (MOFs), as an emerging class of
porous inorganic−organic hybrid materials, have attracted
considerable interest in materials science due to their diverse
potential applications. One of the most promising applications
for MOFs might be their use as porous materials for adsorption
and separation.1 In principle, the specific pore size and inner
microenvironment in MOFs could be realized by judicious
choice of the organic ligands and inorganic metal nodes. Such
MOFs might offer a possibility to selectively uptake and
separate some specific substrates under ambient conditions.
To date, numerous porous MOFs with adsorption and
separation properties, generally gas species (such as hydrogen,
nitrogen, methane, carbon dioxide, and so on) MOF separators,
have been reported.2 In contrast, the selective adsorption and
separation of aromatics,3 especially halogenated aromatics,4 is a
relatively unexplored field. As we know, monohalobenzenes
(C6H5X, X = F, Cl, Br, I) have been extensively used in fine
chemical synthesis and in the pharmaceutical industry.5 Since
halogenated compounds are used on a wide scale, their disposal
results in a large accumulation in our environment. However,
they are not friendly to our environment and may cause
harmful health effects. The Environment Protection Agency
(EPA) and the Food and Drug Administration (FDA) found
that these halogenated aromatics have some toxic effects on our
ecosystem and health.6a For example, bromobenzene could
cause liver necrosis in various animals;6b therefore, their
In this contribution, we report a series of isostructural
organic guest loaded Cd(II)-MOFs, namely CdL2(OTs)2·
2THF (1), CdL2(OTs)2·2C6H5F (2), CdL2(OTs)2·C6H5Cl
(3), CdL2(OTs)2·2C6H5Br (4), and CdL2(OTs)2·1.5C6H5I·
0.5H2O (5), generated from 1,2-bis[(3-(pyridin-4-yl)phenoxy]-
ethane and Cd(OTs)2 (OTs− = p-toluenesulfonate anion) in
solution. After removal of the guest molecules, the guest-free
CdL2(OTs)2 framework can reversibly adsorb and separate
PhF, PhCl, PhBr, and PhI at room temperature in the liquid
phase. Furthermore, it exhibits a guest-dependent luminescent
property.
EXPERIMENTAL SECTION
■
Materials and Methods. All chemicals were commercially
purchased and used as obtained without further purification. Infrared
(IR) samples were prepared as KBr pellets, and spectra were obtained
in the 400−4000 cm−1 range using a PerkinElmer 1600 FTIR
spectrometer. Elemental analyses for C, H, and N were performed on
1
a PerkinElmer Model 2400 analyzer. H NMR data were collected
using an AM-300 spectrometer. Chemical shifts are reported in δ units
relative to TMS. All fluorescence measurements were carried out on a
Cary Eclipse spectrofluorimeter (Varian, Belrose, Australia) equipped
with a xenon lamp and quartz carrier at room temperature.
Thermogravimetric analyses were performed on a TA Instrument
Received: May 12, 2014
© XXXX American Chemical Society
A
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Scheme 1. Synthesis of L and 1-5
SDT 2960 simultaneous DTA-TGA under flowing nitrogen at a
heating rate of 10 °C/min. Powder X-ray diffraction (PXRD)
measurements were carried out on a D8 ADVANCE diffractometer
with Cu Kα radiation (λ = 1.5405 Å). GC analysis was performed on a
7890A gas chromatograph (Agilent Technologies, Santa Clara, CA,
USA) equipped with a flame ionization detector (FID) and a split/
splitless injector. The GC capillary column (DB-WAX) with
dimensions of 30 m length × 0.53 mm i.d. and a film thickness of
1.0 μm was purchased from Agilent Technologies.
(s), 1161 (s), 1036 (s), 821 (m), 775 (s), 681 (s), 622 (m), 564 (s).
Anal. Calcd for C70H70CdN4O12S2: C, 62.88; H, 5.24; N, 4.19. Found:
C, 62.44; H, 4.87; N, 4.01.
Synthesis of [CdL2(OTs)2]·2C6H5F (2). A solution of Cd(OTs)2
(10 mg, 0.022 mmol) in MeOH (2 mL) was carefully layered on a
solution of L (5 mg, 0.013 mmol) in C6H5F (2 mL). The solution was
left for 1 month at room temperature, and colorless crystals of 2 were
obtained. Yield: 50% (based on L). IR (KBr pellet, cm−1): 3069 (w),
2930 (w), 1607 (s), 1548 (s), 1479 (m), 1418 (m), 1299 (s), 1244 (s),
1205 (s), 1161 (s), 1036 (s), 821 (m), 776 (s), 681 (s), 622 (m), 564
(s). Anal. Calcd for C74H64CdF2N4O10S2: C, 64.17; H, 4.62; N, 4.05.
Found: C, 63.83; H, 4.65; N, 3.84.
Synthesis of [CdL2(OTs)2]·C6H5Cl (3). A solution of Cd(OTs)2
(27 mg, 0.060 mmol) in MeOH (8 mL) was carefully layered on a
solution of L (15 mg, 0.040 mmol) in C6H5Cl (8 mL). The solution
was left for 1 week at room temperature, and colorless crystals of 3
were obtained. Yield: 65% (based on L). IR (KBr pellet, cm−1): 3067
(w), 2932 (w), 1607 (s), 1549 (s), 1477 (m), 1419 (m), 1298 (m),
1244 (s), 1206 (s), 1161 (s), 1036 (s), 821 (m), 776 (s), 680 (s), 621
(m), 564 (s). Anal. Calcd for C68H59CdClN4O10S2: C, 62.57; H, 4.52;
N, 4.29. Found: C, 62.13; H, 4.56; N, 3.95.
Synthesis of [CdL2(OTs)2]·2C6H5Br (4). A solution of Cd(OTs)2
(27 mg, 0.060 mmol) in MeOH (8 mL) was carefully layered on a
solution of L (15 mg, 0.040 mmol) in C6H5Br (8 mL). The solution
was left for 1 week at room temperature, and colorless crystals of 4
were obtained. Yield: 68% (based on L). IR (KBr pellet, cm−1): 3068
(w), 2932 (w), 1608 (s), 1548 (s), 1476 (m), 1419 (m), 1298 (m),
1244 (s), 1205 (s), 1161 (s), 1036 (s), 822 (m), 776 (s), 680 (s), 621
(m), 564 (s). Anal. Calcd for C74H64CdBr2N4O10S2: C, 58.98; H, 4.25;
N, 3.72. Found: C, 58.88; H, 4.35; N, 3.34.
Synthesis of [CdL2(OTs)2]·1.5C6H5I·0.5H2O (5). A solution of
Cd(OTs)2 (10 mg, 0.022 mmol) in MeOH (2 mL) was carefully
layered on a solution of L (5 mg, 0.013 mmol) in C6H5I (2 mL). The
solution was left for 1 month at room temperature, and light yellow
crystals of 5 were obtained. Yield: 30% (based on L). IR (KBr pellet,
cm−1): 3069 (w), 2921 (w), 1607 (s), 1548 (s), 1479 (m), 1418 (m),
1299 (m), 1245 (s), 1206 (s), 1162 (s), 1036 (s), 821 (m), 820 (m),
776 (s), 681 (s), 622 (m), 564 (s). Anal. Calcd for
C71H62.5CdI1.5N4O10.5S2: C, 56.55; H, 4.15; N, 3.72. Found: C,
56.19; H, 4.05; N, 3.75.
Synthesis of Intermediate 3-(Pyridin-4-yl)phenol (A).7
A
solution of 3-bromophenol (3.46 g, 20.0 mmol), pyridine-4-boronic
acid (2.95 g, 24.0 mmol), K2CO3 (17.25 g, 125.0 mmol), and
Pd(PPh3)4 (1.16 g, 1.0 mmol) in EtOH/H2O was refluxed for 40 h
(Scheme 1). After removal of solvent under vacuum, the residue was
purified by column chromatography to afford A in 82% yield. IR (KBr
pellet, cm−1): 3415 (m), 3053 (m), 1603 (s), 1544 (s), 1511 (w), 1476
(s), 1419 (m), 1368 (s), 1309 (s), 1210 (s), 1067 (m), 1010 (s), 897
(s), 879 (s), 833 (s), 775 (s), 725 (m), 694 (m), 665 (m), 616 (w),
538 (m). 1H NMR (300 MHz, DMSO-d6, 25 °C, TMS, ppm): 9.69 (s,
1H, −OH), 8.60−8.59 (d, 2H, −C6H4−), 7.62−7.60 (d, 2H,
−C6H4−), 7.33−7.28 (t, 1H, −C5H4N), 7.20−7.17 (d, 1H,
−C5H4N), 7.12 (s, 2H, −C5H4N), 6.87−6.85 (d, 2H, −C5H4N).
Anal. Calcd for C11H9NO: C, 77.17; H, 5.30; N, 8.18. Found: C,
77.21; H, 5.42; N, 8.05.
Synthesis of L. A mixture of A (1.88 g, 11.0 mmol), NaOH (0.44
g, 11.0 mmol) and 1,2-bis(p-tolylsulfonyl)ethane (1.85 g, 5.0 mmol)
was stirred in DMF (50 mL) at 358 K for 24 h and then cooled to
room temperature (Scheme 1). The mixture was poured into ice−
water, filtered, and washed with water. The raw product was purified
by column chromatography to afford white solids in 80% yield. IR
(KBr pellet, cm−1): 3446 (s), 2360 (w), 1594 (s), 1580 (s), 1547 (s),
1472 (m), 1443 (w), 1409 (w), 1300 (s), 1279 (w), 1208 (s), 1175
(w), 1058 (s), 1039 (w), 994 (w), 875 (w), 819 (w), 790 (s), 727 (m),
1
699 (m), 615 (w), 537 (w). H NMR (300 MHz, DMSO-d6, 25 °C,
TMS, ppm): 8.62−8.60 (d, 4H, −C5H4N), 7.72−7.71 (d, 4H,
−C5H4N), 7.48−7.42 (t, 2H, −C6H4−), 7.39 (s, 4H, −C6H4−),
7.11−7.09 (d, 2H, −C6H4−), 4.40 (s, 4H, −CH2−). Anal. Calcd for
C24H20N2O2: C, 78.24; H, 5.47; N, 7.60. Found: C, 78.09; H, 5.68; N,
7.41.
Synthesis of [CdL2(OTs)2]·2THF (1). A solution of Cd(OTs)2 (27
mg, 0.060 mmol) in MeOH (8 mL) was carefully layered on a solution
of L (15 mg, 0.040 mmol) in THF (8 mL). The solution was left for 1
week at room temperature, and colorless crystals of 1 were obtained.
Yield: 72% (based on L). IR (KBr pellet, cm−1): 3067 (w), 2931 (w),
1607 (s), 1548 (s), 1480 (m), 1418 (m), 1299 (m), 1244 (s), 1205
Compounds 1−5 are insoluble in common organic solvents such as
acetone, THF, benzene, toluene and xylene, but they are dissociated in
DMSO at room temperature.
X-ray Crystallography. The X-ray diffraction data for single
crystals of 1−5 were measured at different temperatures (1 at 105 K, 2
B
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Table 1. Crystal Data and Structural Refinement Parameters for 1−5
1
2
3
4
5
formula
fw
C70H70CdN4O12S2
1335.82
0.71073
monoclinic
C2/c
C74H64CdF2N4O10S2
1383.81
0.71073
monoclinic
C2/c
C68H59CdClN4O10S2
1304.16
0.71073
monoclinic
C2/c
C74H64CdBr2N4O10S2
1505.63
0.71073
monoclinic
C2/c
C71H62.5CdI1.5N4O10.5S2
1506.62
0.71073
monoclinic
C2/c
λ (Å)
cryst syst
space group
T (K)
105(7)
99.96(10)
28.3154(9)
13.4934(4)
18.3088(5)
90.00
119.97(13)
28.5373(7)
13.5012(3)
18.2192(4)
90.00
119.99(11)
28.6004(10)
13.4741(3)
18.3173(8)
90.00
99.93(16)
28.561(2)
13.4161(5)
18.0696(8)
90.00
a (Å)
28.5077(12)
13.4136(4)
18.1780(7)
90.00
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
106.675(4)
90.00
106.868(3)
90.00
107.342(2)
90.00
107.463(4)
90.00
106.976(4)
90.00
6658.8(4)
4
6694.3(3)
4
6700.5(3)
4
6733.5(4)
4
6622.2(6)
4
ρcakd (g cm−3
)
1.332
1.373
1.293
1.485
1.511
μ (mm−1
F(000)
GOF
)
0.454
0.457
0.486
1.636
1.155
2776
2856
2688
3064
3040
1.062
1.104
1.130
1.040
1.033
no. of data/restraints/params
R1 (I > 2σ(I))
5867/0/448
0.0551
5900/0/482
0.0571
5907/0/534
0.0541
5885/0/486
0.0824
6149/91/479
0.0601
wR2 (all data)
0.1626
0.1755
0.1769
0.2274
0.1646
Figure 1. (a) ORTEP figure of 1. (b) 2D network of 1 with a twist-boat-like window. The single twist-boat unit is highlighted by a dashed line in
green.
and 5 at 100 K, 3 and 4 at 120 K) on an Agilent Technologies
SuperNova Single Crystal Diffractometer with graphite-monochro-
mated Mo Kα radiation (λ = 0.71073 Å). Corrections for incident and
diffracted beam absorption effects were applied using CrysAlisPro.8
None of the crystals showed evidence of crystal decay during data
collection. The structures were solved by direct methods using the
SHELXS program and refined by full matrix least squares on F2,
including all reflections (SHELXL97).9 The crystal data, refinement
parameters, and bond lengths and angles are summarized in Table 1
and in the Supporting Information.
consisting of MeOH and the corresponding monohalobenzene
in 30−68% yields. The results demonstrated that THF and
monohalobenzenes (PhF, PhCl, PhBr, and PhI) can be the
templates to facilitate the formation of the porous frameworks
of 1−5. X-ray single-crystal analyses revealed that compounds
1−5 are isostructural and all crystallize in the triclinic space
group C2/c (Table 1, Figures S1−S5 (Supporting Informa-
tion)). The cell volumes of 1−5 are slightly different (variation
from 6622.2(6) to 6733.5(4) Å3, Table 1) due to the
encapsulation of different guest species. Therefore, only the
structure of 1 is described in detail herein.
As shown in Figure 1, the asymmetric unit cell of 1 consists
of half of a Cd(II) ion, one L ligand, one OTs− anion, and one
THF guest molecule. Each Cd(II) node lies in a distorted-
octahedral coordination environment which consists of four N
atoms from four L ligands in the equatorial plane and two O
atoms from two OTs− anions in the axial positions. The Cd−N
bond lengths vary from 2.333(3) to 2.328(3) Å, while the Cd−
RESULTS AND DISCUSSION
■
Synthesis and Crystal Structures. Compound 1
(2THF⊂CdL2(OTs)2) was obtained by the combination of L
and Cd(OTs)2 in a THF/MeOH mixed-solvent system in 72%
yield, while compounds 2 (2C6H5F⊂CdL2(OTs)2), 3
(C6H5Cl⊂CdL2(OTs)2), 4 (2C6H5Br⊂CdL2(OTs)2), and 5
(1.5C6H5I·0.5H2O⊂CdL2(OTs)2) were prepared by the
combination of L with Cd(OTs)2 in the mixed-solvent systems
C
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Figure 2. (left) Single 2-fold interpenetrating layers of 1. The different sets of 2D nets are shown in different colors for clarity. (right) Interlayer
hydrogen bonding systems.
Figure 3. (left) Stacking of 2D layers in an −ABAB− fashion into a 3D framework with 1D channels along the crystallographic c axis, in which THF
guest molecules are located. The encapsulated THF molecules are shown as space-filling models for clarity. (right) 1H NMR (DMSO-d6) spectrum
and XRPD patterns of 1. The H peaks corresponding to the encapsulated THF molecules are marked with asterisks.
Figure 4. Synthesis of the hollow framework CdL2(OTs)2 (1′) and reversible adsorption of monohalobenzenes based on 1′. The encapsulated PhF,
PhCl, PhBr, and PhI are shown in green, cyan, orange, and purple, respectively. The TGA traces of 1 and 1′ (the observed THF mass loss in 1 is
1
9.9%, calculated 10.8%) and H NMR ((DMSO-d6) of 1′ are shown as inserts.
O bond length is 2.306(3) Å (Tables S1−S5 (Supporting
Information)). In 1, each L adopts a gauche conformation with
a torsion angle (−O−CH2−CH2−O−) of 73.004(4)°. As a
node, each Cd(II) atom connects to four adjacent Cd(II)
atoms via four bidentate L ligands, forming a four-connected
(4,4) network structure. The 2D layered net contains a twist-
D
dx.doi.org/10.1021/ic501100p | Inorg. Chem. XXXX, XXX, XXX−XXX