Three resorcin[4]arene-based complexes with Cu(ii)-exchange characteristics and fluorescence sensing of polyoxometalates in aqueous solutions

Article abstract of DOI:10.1039/c4ce01376j

Three new resorcin[4]arene-based coordination polymers, [Cd₃L(H₂L)(H₂O)₂]·2DMF·11.5H₂O (1), [Zn₄L₂(H₂O)₄]·2DMF·10H₂O (2) and [Mn₉L

Full text of DOI:10.1039/c4ce01376j

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PAPER
Three resorcin[4]arene-based complexes with
Cu(II)-exchange characteristics and fluorescence
sensing of polyoxometalates in aqueous solutions†
Cite this: CrystEngComm, 2014, 16,
9638
a
a
Wei Jiang, Hang Zhang, Jin Yang, a Ying-Ying Liu,a Hai-Yan Liub
*
a
*
and Jian-Fang Ma
Three new resorcin[4]arene-based coordination polymers, [Cd3L(H2L)(H2O)2]·2DMF·11.5H2O (1),
[Zn4L2(H2O)4]·2DMF·10H2O (2) and [Mn9L4(HCOO)2(H2O)12·(DMF)2]·2DMF·10H2O (3) (H4L = tetrakis(ω-
carboxybutyl)methylene resorcin[4]arene, DMF = N,N′-dimethylformamide), have been solvothermally
synthesized. Compounds 1–3 are all bilayer structures constructed by secondary building units (SBUs),
where trinuclear clusters are found in 1 and infinite rod-shaped chains are observed in 2 and 3. Strikingly,
compounds 1–3 display partial Cu(II)-exchange characteristics. The solid-state emission spectra and fluores-
cence sensing abilities of 1 and 2 to detect polyoxometalates (POMs) in aqueous solutions were studied.
Received 4th July 2014,
Accepted 18th August 2014
DOI: 10.1039/c4ce01376j
www.rsc.org/crystengcomm
inorganic–organic hybrid chemistry.7 Polyoxometalates
(POMs) are a crucial class of metal oxide clusters. Usually,
Introduction
Calixarenes, which are constructed from different phenol
moieties and various substituents, are some of the most
important supramolecular hosts due to their wide applica-
tions in molecular recognition, self assembly, chemical sen-
sors and catalysis.1 Resorcin[4]arenes modified by eight arms
at the upper rim and four legs at the lower rim are a subclass
of calixarenes, and these features provide them with wide
potential modifications at both rims.2 However, only limited
supramolecular structures and metal complexes based on res-
orcin[4]arenes have been investigated up to now.3
Metal ion exchange through post-synthetic modification
(PSM) has become one hot issue in recent years due to its
potential to achieve novel complexes and modify properties.4
At present, reports about the partial or complete replacement
of metal ions are relatively rare because it is hard to maintain
the crystalline structure during PSM.5 Most notably, there is
still no systematic study on the PSM behavior of calixarene
complexes as far as we know.6
titrimetric analyses and sophisticated instrumental methods
are used to detect POMs.8 Recently, a study on the use of
luminescent complexes for sensing POMs in aqueous solu-
tions has been reported.9 Inspired by this experimental tech-
nique, we investigated for the first time the potential of
resorcin[4]arene-based compounds for sensing POMs in
aqueous solutions.
In this paper, a new flexible tetracarboxylate functional-
ized resorcin[4]arene ligand, tetrakis(ω-carboxybutyl)methy-
lene resorcin[4]arene (H4L), has been prepared. The arms
are bridged by methylene groups to display a crown-like
configuration. The legs are modified using four carboxylic
acids to provide various potential coordination modes
(Chart 1).10 Herein, three novel bilayer complexes have
been synthesized successfully, namely, [Cd3L(H2L)
(H2O)2]·2DMF·11.5H2O (1), [Zn4L2(H2O)4]·2DMF·10H2O (2)
and [Mn9L4(HCOO)2(H2O)12·(DMF)2]·2DMF·10H2O (3). For
all complexes, partial Cu(II)-exchanges of the metal cations,
maintaining the crystallinity, have been achieved. Solid-
state fluorescence properties of 1 and 2 were detected,
and their ability to sense POMs in aqueous solutions was
also demonstrated.
Nowadays, the study of luminescent complexes to detect
cations, anions and small molecules has become popular in
a Key Lab of Polyoxometalate Science, Department of Chemistry, Northeast
Normal University, Changchun 130024, PR China. E-mail: yangj808@nenu.edu.cn,
majf247@yahoo.com; Fax: +86 431 85098620
b Department of Chemistry and Pharmaceutical Engineering, Suihua University,
Suihua 152061, People's Republic of China
Results and discussion
Structure of [Cd3L(H2L)(H2O)2]·2DMF·11.5H2O (1)
† Electronic supplementary information (ESI) available: Experimental section,
selected bond lengths and angles, pores of 1 along the c axis, thermogravimetric
curve of 2, photographs of crystals a, time-dependent ICP data and emission
spectra of 1 and 2. CCDC 1012007–1012009. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c4ce01376j
Single-crystal X-ray diffraction reveals that 1 crystallized in
the tetragonal space group P4212 (Table 1). The asymmetric
unit of 1 consists of one and a half Cd(II) ions, two kinds of
unique quarter-occupied L anions, half a H2L anion, one
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The bilayer network of 1 can be simplified as a (4,5)-
connected network with the (46)(42·58) topology (Fig. 1e).
Structure of [Zn4L2(H2O)4]·2DMF·10H2O (2)
Compound 2 crystallized in the orthorhombic space group
Pca21. The asymmetric unit of 2 is composed of four Zn(II)
ions, two L anions, four coordinated water molecules, two
free DMF molecules, and ten free water molecules. The
SQUEEZE function in PLATON was applied during the refine-
ment because of the highly disordered solvents.11 In the orig-
inal data, two DMF molecules are defined by the electron
densities from difference Fourier maps. The amount of free
water molecules are calculated and confirmed by
thermogravimetric analysis (Fig. S2†) and elemental analysis
of the data. As shown in Fig. 2a, each Zn(II) ion is five-
coordinated in a distorted square-pyramidal geometry, and
is defined by three different L anions and one water
molecule. Adjacent Zn(II) ions are held together by carboxyl-
ate groups of the L anions to result in an infinite Zn(II)-
carboxylate chain, which can be taken as a rod-shaped
Chart 1 The synthesis of ligand H4L.
coordinated water molecule, one lattice DMF molecule, and
five and three quarters free water molecules. Cd1 is seven-
coordinated in a decahedral geometry by six carboxylate oxy-
gen atoms from one H2L anion, two L anions and one water
molecule. Cd2 lies in an inversion center, and is coordinated
in an octahedral geometry by six carboxylate oxygen atoms
from two H2L anions and two L anions (Fig. 1a). Two Cd1
ions and one Cd2 ion are surrounded by three water mole-
cules and six carboxylate groups to form a trinuclear cluster,
which serves as a structural secondary building unit (SBU)
(Fig. 1b). Both of the L anions lie in inversion centers, and
adopt the same μ8–η1:η2:η2:η1:η1:η2:η2:η1 coordination mode.
The H2L anion also lies in an inversion center, and adopts a
μ4–η1:η2:η1:η0:η1:η2:η1:η0 coordination mode (Fig. 1c). In this
way, the SBUs are bridged by H2L and L anions to generate a
bilayer framework (Fig. 1d). These anions take a head to head
arrangement, and channels are formed on the top of the
cavities of resorcin[4]arenes, which are filled with free DMF
and water molecules (Fig. S1†).
SBU (Fig. 2b). Both
L
anions adopt the same
μ6–η1:η1:η1:η1:η1:η1:η1:η1 mode (Fig. 2c). On the basis of this
mode, parallel rod-shaped SBUs are linked by the L anions to
generate a bilayer structure (Fig. 2d). Topologically, if the two
dinuclear Zn(II) units (Zn1 and Zn2, and Zn3 and Zn4) and each
L anion are respectively considered as a 4-connected node,
the layer structure of 2 can be simplified as a 4-connected
network with the (46)(42·84)2 topology (Fig. 2e).
Structure of [Mn9L4(HCOO)2(H2O)12·(DMF)2]·2DMF·10H2O (3)
Single-crystal X-ray diffraction reveals that 3 crystallized in
From the topological view, each H2L anion acts as a linker,
each L anion is regarded as a 4-connected node, and each
trinuclear Cd(II) cluster is reduced to a 5-connected node.
¯
the triclinic space group P1. The asymmetric unit of 3
Table 1 Crystal data and structure refinements for complexes 1–3
1
2
3
Formula
Mr
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
C102H131O47.5N2Cd3
2482.35
Tetragonal
P4212
22.9973(4)
22.9973(4)
22.5955(7)
90
C102H130O48N2Zn4
2413.74
Orthorhombic
Pca21
17.6923(7)
15.6746(7)
42.5940(11)
90
C206H250O94N4Mn9
4780.60
Triclinic
¯
P1
11.8811(6)
20.9902(14)
21.3711(11)
79.558(5)
81.534(4)
86.360(5)
5180.6(5)
1
90
90
90
90
γ (°)
V (Å3)
Z
11 950.2(6)
4
1.382
11 812.2(8)
4
1.174
Dcalc (g cm−3
F(000)
)
1.532
2491
5080
4320
Rint
0.0884
1.024
14 377
0.1146
0.2048
0.2649
0.3376
0.0693
1.0110
15 528
0.1020
0.1243
0.2696
0.2953
0.0602
1.0220
23 519
0.0957
0.2061
0.2144
0.2799
GOF on F2
Nreaf
R1 [I > 2σ(I)]
R1 (all data)
wR2b[I > 2σ(I)]
wR2 (all data)
P
P
P
P
a
2
R1 = ‖Fo| − |Fc‖/ |Fo|. b wR2 = { [w(Fo − Fc2)2]/ w(Fo2)2]}1/2
.
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coordinated water molecules, one coordinated DMF mole-
cule, one free DMF molecule, and five free water molecules.
The HCOO− anion results from the hydrolysis of DMF during
the reaction. Five Mn(II) ions are all six-coordinated in
distorted octahedral geometries, but with entirely different
coordination environments. Mn1 is coordinated by four L
anions and two water molecules. Both Mn2 and Mn3 ions are
surrounded by three L anions, one water molecule, and one
HCOO− anion. Mn4 is ligated by four different L anions and
one water molecule. The oxygen atoms surrounding Mn5 are
provided by three different L anions, two water molecules,
and one DMF molecule (Fig. 3a and S3†). Mn1–Mn5 are
bridged by HCOO− anions and the carboxylate groups of the
L anions to give a [Mn]5 cluster. With Mn1 as the symmetric
center, two [Mn]5 clusters are held together to give a [Mn]9
cluster. Neighboring [Mn]9 clusters are further linked by
the carboxylate groups of the L anions to generate a Mn(II)-
carboxylate chain, which can be regarded as an infinite
rod-shaped SBU (Fig. 3b). Two unique L anions adopt
μ9–η1:η1:η1:η2:η0:η2:η2:η0 and μ6–η1:η2:η1:η1:η2:η0:η1:η1 coor-
dination modes, respectively (Fig. 3c). In these modes, the
SBUs are linked by the L anions to produce a bilayer frame-
work (Fig. 3d). Topologically, two L anions with μ6 and μ9
coordination modes are considered as one linker and a
3-connected node, respectively, and nine-nuclear cluster
[Mn]9 is taken as an 8-connected node. The bilayer network
of 3 can be described as a (3,8)-connected network with the
(3·42)(34·44·616·84) topology (Fig. 3e).
Thermal analyses
Thermogravimetric analysis of compounds 1–3 was con-
ducted to study their thermal behavior (Fig. S2†). For com-
pound 1, the first weight loss before 220 °C corresponds to
the removal of water and DMF molecules (obsd 14.1%,
calcd 15.7%). In the temperature range of 305–450 °C, the
weight loss can be attributed to the decomposition of the
organic ligands. The remaining solid is possibly assigned as
CdO (obsd 16.8%, calcd 15.5%). For compound 2, the weight
loss from room temperature to 258 °C can be attributed to
the removal of water and DMF molecules (obsd 16.58%). The
decomposition of organic ligands occurs at 350 °C. The
residual composition corresponds to ZnO (obsd 12.0%,
calcd 13.5%). For compound 3, the weight loss of 13.9%
before 212 °C is attributed to the loss of water and DMF
molecules (calcd 14.4%). The network begins to decompose
at 302 °C. The remaining residue is ascribed to the formation
of MnO2 (obsd 15.1%, calcd 16.3%).
Fig. 1 (a) View of the coordination environments of the Cd(II) ions in 1.
Symmetry codes: #1 −x, −y, z; #2 y, x, −z + 1. (b) View of the trinuclear
Cd(II) cluster. (c) View of the coordination modes of the L and H2L
anions. (d) View of the bilayer network of 1. (e) View of the (4,5)-
connected network of 1 with the (46)(42·58) topology.
Ion exchange
Compounds 1–3 are stable in both DMF and methanol solu-
tions (Fig. S4†). In order to study the possibility of ion
exchange, as-synthesized crystals of 1–3 (20 mg) were
immersed in a 0.3 M DMF–methanol (6 mL, V1 : 1) solution of
CuCl2·2H2O, CoCl2·6H2O and NiCl2·6H2O, respectively. After
about 10 minutes, the Cu(II)-immersed crystals of 1–3 turned
contains five crystallographically independent Mn(II) ions,
two kinds of L anions, one coordinated HCOO− anion, six
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Fig. 2 (a) View of the coordination environments of the Zn(II) ions in 2.
Symmetry codes: #1 x − 1/2, −y, z; #2 x + 1/2, −y, z; #3 x, y − 1, z;
#4 x + 1/2, −y − 1, z. (b) View of the rod-shaped SBU. (c) View of the
coordination mode of the L anion. (d) View of the bilayer structure of 2.
(e) View of the 4-connected (46)(42·84)2 network of 2.
Fig. 3 (a) View of the coordination environments of the Mn(II) ions in
3. (b) View of the rod-shaped SBU. (c) View of the coordination modes
of the L anions. (d) View of the bilayer framework of 3. (e) View of the
(3,8)-connected network with the (3·42)(34·44·616·84) topology.
blue (Fig. S5, Table S4†). However, the color changes
were not observed in Co(II) and Ni(II)-immersed crystals for
several days.
To monitor the Cu(II)-exchange process, time-dependent
powder X-ray diffraction (PXRD) patterns were tested every
twenty minutes. The PXRD patterns indicated that the
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exchange frameworks of complexes 1a–3a were in accordance
with their parent structures within 120, 120 and 180 minutes,
respectively (Fig. 4). But when the soakage time was more
than 140, 140 and 200 minutes, respectively, they lost their
crystallinity (Fig. S6†). Time-dependent ICP analyses were
measured to confirm the compositions of metal ions in the
crystals. As shown in Fig. 5 and S7,† the Cu(II) content finally
increased to 47.0%, 51.6% and 47.9% for 1a–3a, respectively.
As far as we know, this is the second research study on the
metal-ion exchange occurring in calixarene-based complexes.6
Even if 100% of the transformed crystalline bulks have not
been harvested, this metal-ion exchange could be used as a
new strategy for the preparation of new analogue structures.
Fig. 5 Time-dependent ICP data for the Cu(II) composition during the
ion-exchanging process for 1–3.
Luminescent properties
Solid-state photoluminescent properties of 1, 2 and H4L
were analyzed (Fig. 6). The main emission peak of H4L is
at 504 nm (λex = 374 nm), which could be attributed to the
π* → n or π* → π transitions.12 The main emission peaks
of 1 and 2 are located at 467 and 460 nm (λex = 374 nm),
respectively. Compared with H4L, 1 and 2 display obvious
blue shift, which can be ascribed to the coordination effect
of the H4L ligand to the metal ion.13
H3PMo12O40] aqueous solutions. A small amount of cyanoac-
rylate adhesive was dropped onto a quartz slide (12 × 45 nm),
and 4 mg of grounded crystals of 1 and 2 were laid gently
on the surface of the slide. Then the slide was put into a
Suprasil cuvette and 2 mL POM aqueous solution was
dropped into the cuvette slowly. After keeping the solution
at room temperature for 10 min, the measurement of
photoluminescence was taken.9 The emission spectra of
the crystals in pure water were taken to act as the compari-
son. As shown in Fig. 7, the emission intensities decrease
in different degrees when the three POMs were used. In
contrast, the H3PMo12O40 solution shows the most obvious
quenching effect.
To study the potential of complexes 1 and 2 to sense
POMs, their luminescence properties were investigated in
different POM [(NH4)6Mo7O24, H3PW12O40, H4SiW12O40 and
Recently, Bo and co-workers reported a sensitive lumi-
nescent complex [Eu(5-tert-butylisophthalate)1.5 2n
displayed a quenching effect on several POMs such as
] , which
9
(NH4)6Mo7O24, H3PW12O40 and H4SiMo12O40
. In compari-
son, compounds 1 and 2 only have quenching effects on
H3PMo12O40. The results reveal that 1 and 2 are sensitive
to H3PMo12O40 and can be considered to be potential fluo-
rescent probes for H3PMo12O40.
Fig. 4 Simulated (black), experimental (blue) and Cu(II)-exchanged
(red) PXRD patterns within 120, 120 and 180 minutes for 1–3,
respectively.
Fig. 6 Solid-state emission spectra of H4L, 1 and 2.
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Fig. 7 Emission spectra of 1 (a) and 2 (b) with the addition of 10 mM
of the various POMs in aqueous solutions (1 k = 1000, inner: detecting
at 467 nm and 460 nm, respectively).
Fig. 8 Emission spectra of 1 (a) and 2 (b) in different concentrations of
H3PMo12O40 aqueous solutions (λex = 374 nm).
To further investigate the sensing properties for
H3PMo12O40, the emission spectra of 1 and 2 in different con-
centrations of H3PMo12O40 were studied (Fig. 8). The emis-
sion intensities of 1 and 2 decrease with the increase of
H3PMo12O40 concentration. When the concentration of
H3PMo12O40 is 5 mM, the emission intensities are almost
completely quenched with quenching efficiencies of 99.93%
and 99.67% for 1 and 2, respectively. The results suggest that
1 and 2 have good sensitivity in detecting H3PMo12O40 in
aqueous solutions.
and the tetracarboxylic acids at the lower rim of the H4L
ligand lead to its tendency to generate bilayer structures. A
PSM process by partially exchanging Cu(II) with M(II) ions in
complexes 1–3 has been observed. PXRD patterns and ICP
analysis confirm the success of the metal exchange. The
luminescence properties of 1 and 2 show selectivity and
sensitivity to H3PMo12O40. The result shows that 1 and 2 may
be used as sensors for detecting H3PMo12O40. Further study
in fluorescence sensing is underway.
Acknowledgements
Conclusion
This work was supported by the National Natural Science
Foundation of China (grant no. 21277022, 21371030,
21301026, 21201128) and the Fundamental Research Funds
for the Central Universities of China.
In summary, three bilayer coordination polymers based on
resorcin[4]arene ligand, H4L, and transition metals have been
synthesized. The crown-like conformation at the upper rim
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