Polyoxometalate-templated lanthanide-organic hybrid layers based on 6 3-honeycomb-like 2D nets

Article abstract of DOI:10.1039/c1dt10139k

The reaction of a double-betaine-containing ligand with LnPMo ₁₂O₄₀·nH₂O (Ln = Dy, Tb and Er) led to the isolation of new polyoxometalate-templated lanthanide-organic hybrid layers with the molecular formula [Ln(L)_1.5(H₂O) ₅][PMo₁₂O₄₀]·1.5CH₃CN· 2H₂O (Ln = Dy (1), Tb (2) and Er (3); L = 1,4-bis(pyridinil-4- carboxylato)-l,4-dimethylbenzene). All compounds were characterized by elemental analyses, TG analyses, IR and the single-crystal X-ray diffraction. Compounds 1-3 are isostructural and possess a 2D undulating cationic network [Ln(L) _1.5(H₂O)₅]_n³ⁿ⁺ with the honeycomb-like cavities. Interestingly, the interval 2D networks are further connected by the H-bonds to form a 3D supramolecular framework. Moreover, two of such identical supramolecular frameworks are 2-fold interpenetrated with each other and encapsulate the α-Keggin-type [PMo₁₂O ₄₀]^3- anionic templates and the solvent molecules. These composite compounds display both luminescent properties (induced by organic ligands and/or lanthanide ions) and electrocatalytic activities towards the reduction of nitrite.

Full text of DOI:10.1039/c1dt10139k

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PAPER
Polyoxometalate-templated lanthanide–organic hybrid layers based on
63-honeycomb-like 2D nets†
Xiu-Li Hao, Ming-Fa Luo, Wei Yao, Yang-Guang Li,* Yong-Hui Wang* and En-Bo Wang
Received 25th January 2011, Accepted 29th March 2011
DOI: 10.1039/c1dt10139k
The reaction of a double-betaine-containing ligand with LnPMo12O40·nH2O (Ln = Dy, Tb and Er) led
to the isolation of new polyoxometalate-templated lanthanide–organic hybrid layers with the molecular
formula [Ln(L)1.5(H2O)5][PMo12O40]·1.5CH3CN·2H2O (Ln = Dy (1), Tb (2) and Er (3); L =
1,4-bis(pyridinil-4-carboxylato)-l,4-dimethylbenzene). All compounds were characterized by elemental
analyses, TG analyses, IR and the single-crystal X-ray diffraction. Compounds 1–3 are isostructural
3n+
and possess a 2D undulating cationic network [Ln(L)1.5(H2O)5]n with the honeycomb-like cavities.
Interestingly, the interval 2D networks are further connected by the H-bonds to form a 3D
supramolecular framework. Moreover, two of such identical supramolecular frameworks are 2-fold
interpenetrated with each other and encapsulate the a-Keggin-type [PMo12O40]3- anionic templates and
the solvent molecules. These composite compounds display both luminescent properties (induced by
organic ligands and/or lanthanide ions) and electrocatalytic activities towards the reduction of nitrite.
lanthanide ions usually possess high reactivity with oxygen-
enriched POMs, which always leads to precipitate instead of
Introduction
crystallization;11 (ii) lanthanide ions exhibit relatively low coor-
dination ability with many N-donor linking ligands, especially in
the acidic media; (iii) When using the anionic O-donor ligands, for
example, the multi-carboxylate-containing ligands, the reaction
competition between polyoxoanions and anionic organic O-donor
ligands with lanthanide ions can not be easily avoided and often
Metal–organic coordination polymers with cavities, pores and/or
channels are of great interest due to not only their chemical
and structural diversities but also their promising applications
in catalysis, gas storage, separation, and molecular recognition.1
During the synthesis, an important strategy is the use of various
templates to assemble such type of hybrid compounds.2,3 In recent
years, many anions have been employed as templates.3 In this
aspect, polyoxometalates (POMs), as one type of unique nano-
sized metal-oxo clusters, can be the outstanding anionic templates
due to their controllable shape, size, high negative charges and
abundant chemical combinations with multiple functionalities.4–9
In this sub-family, most POM-templated metal–organic networks
or frameworks are constructed by the transition metal (TM) ions
and various neutral organic N-donor ligands.5–7 In comparison,
the analogues based on lanthanide–organic hybrid moieties and
POM templates have rarely been reported9 and become a currently
new research focus especially considering that the lanthanide
complexes may endow new POM-based composite materials
with “value-added” functionalities such as luminescent, magnetic,
and/or catalytic properties.10 However, several problems have
arisen during the synthesis of such compounds: (i) the oxophilic
12
leads to unexpected results; (iv) furthermore, using neutral O-
donor ligands might provide a solution for the above problem
(iii) but such neutral O-donor linkers remains far unexplored
in contrast to the neutral N-donor ligands.9a Therefore, the
design and synthesis of new POM-templated lanthanide–organic
networks or frameworks is still a great challenge.
Based on aforementioned considerations, the double betaine-
containing ligands may be one of suitable organic linkers for
the assembly of such POM-templated lanthanide–organic hybrid
compounds. The betaine-type ligands usually contain both an-
ionic carboxylate groups and cationic amino groups, exhibiting
the zwitterionic properties and overall charge neutrality.13 In
comparison to the anionic double-carboxylate-containing ligands,
the double-betaine-type ligands may not only keep the versatile
coordination modes of carboxylate groups but also provide
a new type of neutral O-donor linkers.13 So far, such type
of O-donor ligands have never been used to construct POM-
based metal–organic hybrid compounds. Herein, we synthesized
a flexible double-betaine-containing ligand, that is, the 1,4-
bis(pyridinil-4-carboxylato)-l,4-dimethylbenzene (L) (see Scheme
1). The slow reaction of L with LnPMo12O40·nH2O (Ln = Dy,
Tb or Er) resulted in the isolation of three new POM-templated
lanthanide-organic 2D networks with the molecular formula
Key Laboratory of Polyoxometalate Science of Ministry of Education, Fac-
ulty of Chemistry, Northeast Normal University, Changchun 130024, P. R.
China. E-mail: liyg658@nenu.edu.cn,wangyh319@nenu.edu.cn; Fax: +86
43185098787; Tel: +86 43185099193
† Electronic supplementary information (ESI) available: Additional struc-
tural figures, IR, TG and CV. CCDC reference numbers 808504, 808505
and 808506 for compounds 1–3. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c1dt10139k
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of acetonitrile and water (v/v = 3 : 1) was slowly layered over the
buffer layer. The tube was sealed and left undisturbed at room
temperature. After one month, the yellow block crystals were
isolated in the buffer layer and collected by filtration (Yield: 55%
based on Mo). Anal. calcd for C33H42.5N4.5O53PMo12Dy: C 14.64,
H 1.56, N 2.37. Found: C 14.69, H 1.58, N 2.34. Selected IR
(KBr pellet, cm-1): 3118(w), 3059(w), 1634(m), 1563(m), 1458(w),
1384(m), 1063(s), 957(s), 878(m), 800(s), 687(w).
Scheme 1 The structure of double-betaine-containing ligand (L =
1,4-bis(pyridinil-4-carboxylato)-l,4-dimethylbenzene).
[Ln(L)1.5(H2O)5][PMo12O40]·1.5CH3CN·2H2O (Ln = Dy (1), Tb (2)
and Er (3)). The double-betaine-type ligand as neutral linkers is
firstly introduced into the POM-based lanthanide-organic hybrid
materials. The luminescent and electrocatalytic properties of these
composite compounds were investigated.
[Tb(L)1.5(H2O)5][PMo12O40]·1.5CH3CN·2H2O
pound was prepared in the same way as
(2). Com-
except
2
1
that TbPMo12O40·nH2O (0.033 mmol) was used instead of
DyPMo12O40·nH2O. After one month, the yellow block crystals
were isolated and collected by filtration (Yield: 50% based on
Mo). Anal. calcd for C33H42.5N4.5O53PMo12Tb: C 14.68, H 1.61, N
2.36. Found: C 14.72, H 1.58, N 2.34. Selected IR (KBr pellet,
cm-1): 3102(w), 3060(w), 1635(m), 1565(m), 1457(w), 1364(s),
1063(s), 958(s), 871(m), 771(s), 654(w).
Experimental
Materials and methods
All chemicals and organic solvents used for synthesis were
of reagent grade without further purification. The lanthanide
chlorides LnCl3·6H2O (Ln = Dy, Tb, Er) were prepared by
dissolving Ln2O3 (99.9%) in hydrochloric acid, followed by
concentration and crystallization. The a-H3PMo12O40·14H2O14
and LnPMo12O40·nH2O (Ln = Dy, Tb, Er)9a were prepared
according to the literature methods. Elemental analyses (C, H
and N) were analyzed on a Perkin–Elmer 2400 CHN elemental
analyzer. The FT-IR spectra were performed on a Mattson Alpha-
Centauri spectrometer with KBr pellets in the range of 4000–
400 cm-1. TG analyses were carried out on a Pyris Diamond TG
[Er(L)1.5(H2O)5][PMo12O40]·1.5CH3CN·2H2O
(3). Com-
pound 3 was prepared in the same way as 1 except that
ErPMo12O40·nH2O (0.033 mmol) was used instead. After one
month, the yellow block crystals were isolated and collected
by filtration (Yield: 62% based on Mo). Anal. calcd for
C33H42.5N4.5O53PMo12Er: C 14.65, H 1.59, N 2.31. Found: C 14.67,
H 1.57, N 2.33. Selected IR (KBr pellet, cm-1): 3118(w), 3058(w),
1636(m), 1568(m), 1459(w), 1377(m), 1062(s), 956(s), 878(m),
799(s), 686(w).
X-Ray crystallography
◦
instrument in flowing N2 with a heating rate of 10 C min-1.
The crystallographic data of three compounds were collected
at 150 K on the Rigaku R-axis Rapid IP diffractometer using
graphite monochromatic Mo-Ka radiation (l = 0.71073 A) and
Electrochemical experiments were measured on a BAS Epsilon
Analyzer in a three-electrode cell: glassy carbon electrode (GCE,
diameter 3 mm) as a working electrode, platinum wire as a counter
electrode, and Hg/HgCl as a reference electrode. The solid-state
emission/excitation spectra of compounds 1–3 were measured on
a SPEX FL-2T2 spectrofluorimeter equipped with a 450 W xenon
lamp as the excitation source.
˚
IP techniques. A multi-scan absorption correction as applied. The
crystal data of 1, 2 and 3 were solved by the direct method
and refined by a full-matrix least-squares method on F2 using
the SHELXTL-97 crystallographic software package.16 All non-
H atoms were refined anisotropically except the disordered solvent
water molecules. H atoms on the C atoms were fixed in calculated
positions. H atoms on the coordinated water molecules were found
from the difference Fourier maps and fixed in reasonable positions.
However, the H atoms on the lattice water molecules cannot be
found from the residual peaks but were directly included in the
final molecular formula. The detailed crystal data and structure
refinement for 1–3 are given in Table 1. Selected bond lengths and
angles of 1–3 are listed in Table S1–S3, respectively.†
Synthesis
1,4-Bis(pyridinil-4-carboxylato)-l,4-dimethylbenzene (L). The
flexible double betaine ligand was prepared in a modified way
similar to that in the literature.15 1,4-Bis-chloromethyl-benzene
(1.75 g, 10 mmol) (instead of 1,4-bis-bromomethyl-benzene) was
dissolved in the acetone solution of ethyl isonicotinate (3.1 mL,
20 mmol). The mixture was refluxed and filtered to give a white
precipitate, which was hydrolyzed by dilute hydrochloric acid (5%,
50 mL). Then, the chloride ions were removed by the fresh silver(I)
oxide (prepared by the reaction of AgNO3 and NaOH in aqueous
solution) and the white powder of L were obtained. Anal. calcd
(%) for L (C20H16N2O4): C 68.96, H 4.63, N 8.04. Found (%): C
68.82, H 4.68, N 8.13. IR (KBr, cm-1): 3112(w), 3035(w), 2997(w),
1633(s), 1567(m), 1519(m), 1458(m), 1432(m), 1356(s), 781(s),
756(s); 693(s).
Results and discussion
Synthesis
During the preparation of compounds 1, 2 and 3, the starting ma-
terials LnPMo12O40·nH2O (Ln = Dy, Tb or Er) can not be directly
mixed with L ligand, otherwise plenty of precipitates would be
immediately isolated from the solution. These precipitates exhibit
very low solubility in water and common organic solvents such
as acetonitrile, methanol and ethanol. Furthermore, the L ligand
will decompose in aqueous solutions if the reaction temperature
is higher than 80 ◦C. Hence, the hydrothermal technique can not
be employed in such a reaction system. In this case, the slow
[Dy(L)1.5(H2O)5][PMo12O40]·1.5CH3CN·2H2O (1). A solvent
mixture (10 mL) of acetonitrile and water (v/v = 3 : 2) was used as
a buffer layer and very carefully layered over an aqueous solution
(4 mL) of L ligand (35 mg, 0.1 mmol) in a long and thin tube.
Then, DyPMo12O40·nH2O (67 mg, ~0.033 mmol) in 4 mL mixture
5972 | Dalton Trans., 2011, 40, 5971–5976
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Table 1 Crystal data and structure refinement for 1–3
Compounds
1
2
3
Formula
Mr
C33H42.5N4.5O53PMo12Dy
2694.97
150(2)
C33H42.5N4.5O53PMo12Tb
2691.39
150(2)
C33H42.5N4.5O53PMo12Er
2699.73
150(2)
T/K
Crystal system
Triclinic
Triclinic
Triclinic
¯
¯
¯
Space group
P1
P1
P1
˚
a/A
11.900(2)
15.167(3)
21.059(4)
100.61(3)
90.83(3)
102.67(3)
3639.0(12)
2
11.921(2)
15.142(3)
21.053(4)
100.51(3)
90.91(3)
102.78(3)
3637.6(12)
2
11.921(2)
15.166(3)
21.020(4)
100.49(3)
90.79(3)
102.89(3)
3636.7(12)
2
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
m/mm-1
3.134
2562
28 656
3.080
2560
28 122
3.263
2566
28 272
F(000)
Reflections
Independent Reflections (Rint
)
12 732 (0.0623)
1.032
0.0595
0.1662
1.163/-1.521
12 589 (0.0962)
1.035
0.0718
0.1829
1.103/-1.291
12 635 (0.0711)
1.007
0.0674
0.1895
1.195/-0.970
GOF
R1 [I > 2s(I)]a
wR2 (all data)b
-3
˚
Drmax/min/e A
a R1 = RꢀFo| - |Fcꢀ/R|Fo|. b wR2 = R[w(Fo - Fc2)2]/R[w(Fo2)2]1/2
.
2
diffusion method is employed for the assembly of new POM-
templated lanthanide–organic networks. As to such a method,
the density and polarity of the solvent media play an important
role for the preparation of single crystals with good qualities. In
our experiments, water is chosen as the heavy solvent to dissolve
the organic ligands in the bottom layer of the tube. The density of
the middle buffer layer is adjusted by the mixture of CH3CN : H2O
(v/v = 3 : 2). The top LnPMo12O40 salts are dissolved in the solvent
mixture of CH3CN : H2O (v/v = 3 : 1). The increase of the amount
of CH3CN from bottom to top can keep the three layers well
separated in the tube and maintain a relatively slow diffusion
speed. It is worth emphasizing that the middle buffer layer should
keep a little higher so as to avoid the quick reaction between top
LnPMo12O40 and bottom organic ligands.
Fig. 1 The structure of cationic 2D lanthanide–organic network in
1. Each honeycomb-like cavity encapsulates two Keggin-type POM
templates. The blue lines show that such a 2D network exhibits a 63-hcb
net topology. The H atoms and solvent molecules are omitted for clarity.
Crystal structures
Single-crystal X-ray diffraction analyses show that compounds
1–3 are isostructural, thus, 1 is described here as the represen-
tative example. Compound 1 crystallizes in the triclinic space
ligands to form an undulating 2D network with honeycomb-like
cavities. From a topological perspective, each Dy center can be
viewed as a 3-connected node and the L ligands are linear linkers.
Thus, such a 2D network can be regarded as a honeycomb-like
63-hcb net (Fig. 1 and Fig. S4).† Interestingly, each six-membered
ring in the 2D net is large enough to contain two Keggin-type
polyoxoanion templates, which has rarely been observed.7a
In the packing arrangement, all of these identical 2D layers are
parallel with each other, and two adjacent nets have no obvious
intermolecular interactions. However, the typical hydrogen bonds
occur between the coordination water molecules (O5w) and the
carboxylate groups (O42) from the interval networks (See Fig.
¯
group P1, and the basic structural unit consists of the cationic
complex moiety [Dy(L)1.5(H2O)5]3+, the Keggin-type polyoxoanion
[PMo12O40]3-, one and a half crystalline acetonitrile molecules, and
three water molecules (ESI, Fig. S1–S3).† In 1, the guest poly-
oxoanion [PMo12O40]3- shows the typical a-Keggin type structural
feature with the approximate Td symmetry (see Fig. S1).† In the
cationic dysprosium–organic layer of 1, each Dy3+ ion coordinates
with three oxygen atoms derived from the carboxylate groups of
three different L ligands and five coordinated water molecules and
exhibits a distorted square anti-prismatic coordination geometry
(Fig. 1 and Fig. S4).† The bond distances of Dy–O are in the range
˚
2a). The typical H-bond length of O5w-H5aw ◊ ◊ ◊ O42 is 2.486 A.
The interval 2D networks are then hydrogen-bonded with each
other to form a 3D supramolecular framework (see Fig. 2b–c and
Fig. S5).† More interestingly, two independent but identical 3D
supramolecular frameworks are entangled with each other in a
2-fold interpenetration mode. (Fig. 2d and Fig. S5).† The large
voids of the 3D supramolecular framework are occupied by the
˚
of 2.237(1) – 2.389(1) A. Furthermore, all L ligands adopt a trans-
configuration and each carboxylate group on the L ligand displays
a monodentate coordination mode with one Dy center. (Fig. 1).
˚
The Dy ◊ ◊ ◊ Dy separation across the L ligand is ca. 19.87 A. Based
on above coordination mode, the Dy centers are linked by the L
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cationic metal–organic networks.5d–f,6,7 Herein, the electrochemical
behaviours of compounds 1–3 were studied with the 1-, 2- and
3-modified carbon paste electrodes (1-, 2- and 3-CPEs) since
these composite compounds are dissoluble in water and common
organic solvents.17,18 The cyclic voltammetry (CV) measurements
of 1-, 2- and 3-CPEs at different scan rates were recorded in the
potential range from +700 to -200 mV in 1 M H2SO4 (Fig. 4a and
Fig. S8b–S9b).† The CV behaviours of three samples are similar
and only that of 1-CPE is described here. As shown in Fig. 4a,
three pairs of reversible redox peaks of 1-CPE appear in the range
of +700 to -200 mV, and the mean peak potentials (E1/2 = (Ecp
+
Eap)/2) are 400, 252 and -15 mV with the scan rate of 100 mV s-1
(Fig. S7). The reversible peaks I–I¢, II–II¢, and III–III¢ correspond
to a two-, four-, and six-electron redox process of [PMo12O40]3-
unit, respectively, which is similar to the reported Keggin-type
[PMo12O40]3- species.19 The peak currents are proportional to the
scan rate up to 200 mV s-1, indicating that the redox process of
1-CPE is surface-controlled (Fig. 4a insert).
Fig. 2 (a) The typical hydrogen bonding interactions between two interval
˚
˚
layers in 1 (O5w–H5bw ◊ ◊ ◊ O44 1.966 A; O5w–H5aw ◊ ◊ ◊ O42 2.126 A,
˚
O5w–H5aw . . . O42¢ 2.486 A with the symmetry operation: -x, -y + 2,
-z + 1). (b) Interval lanthanide-organic networks in 1 are linked by the
H-bonds to form a 3D supramolecular framework. (c) Schematic views of
3D supramolecular framework in 1. (d) Schematic view of the entangled
3D supramolecular framework in a 2-fold interpenetration mode.
Keggin-type POM templates and solvent MeCN and water
molecules (Fig. 3 and Fig. S6).† To our knowledge, compounds
1–3 represent the first POM-templated lanthanide-organic hybrids
exhibiting the entangled 3D supramolecular frameworks.
Fig. 3 Structural view of the host lanthanide–organic supramolecular
framework encapsulating the POM templates in 1. The H atoms and
solvent molecules are omitted for clarity.
Fig. 4 (a) The cyclic voltammograms (CV) of 1-CPE in 1 M H2SO4 at
different scan rates (from inner to outer: 50, 75, 100, 125, 150, 175 and
200 mV s-1). The inset shows plots of the dependence of anodic peak and
cathodic peak (II–II¢) current on scan rates; (b) CVs of the 1-CPE in 1 M
H2SO4 solution containing 0.0–0.8 mM KNO2 and a bare CPE in 0.50 mM
KNO2 + 1 M H2SO4 solution.
Electrochemical and electrocatalytic properties
Polyoxometalates usually undergo reversible multi-electron redox
processes, especially the Keggin-type polyoxomolybdates repre-
sent one of good models for the electrochemical investigation.17
Moreover, it is also interesting to explore the electrochemical
behaviours and changes of such Keggin-type polyoxomolybdates
when these multi-electron carriers are encapsulated into various
In the electrochemical studies of POM-based hybrid materials,
one of the most interesting works is to discover the potential
electrocatalytic properties of such compounds since many of them
5974 | Dalton Trans., 2011, 40, 5971–5976
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can be used as good electrocatalysts for the reduction of polluting
substances in aqueous solutions such as nitrite, hydrogen peroxide
and iodate.5d,6,7,20 In contrast to the CPEs modified by the soluble
alkali salts of POMs, the POM-templated metal–organic hybrid
materials may both avoid the partial loss of POMs in aqueous
and/or organic media (that is, stabilize the POMs due to their low
solubility) and keep the electrocatalytic activity of POMs, which
thus represent one type of ideal electrocatalysts. Therefore, the
electrocatalytic properties of compounds 1–3 modified CPEs were
further investigated towards the reduction of nitrite in an aqueous
solution. The CV for the electrocatalytic reduction of nitrite at
1-CPE in a 1 M H2SO4 aqueous solution is shown in Fig. 4b.
-
On addition of NO2 , all three reduction peak currents increased
while the corresponding oxidation peak currents dramatically
decreased, indicating that nitrite was reduced by all three reduced
polyoxoanion species.17 It is noteworthy that the third reduced
species shows the best electrocatalytic activity, which suggests that
the increase of reduction extent of the Keggin anion species may
enhance their catalytic activities. In contrast, the reduction of
nitrite at a bare electrode generally requires a large overpotential
and no obvious response was observed in the range +700 to
-200 mV on a bare CPE (Fig. 4b). It is also worth mentioning
that the peak currents of 1-CPE maintain almost unchanged over
100 cycles at a scan rate of 100 mV s-1 when the potential range is
kept between +700 and -200 mV, revealing that 1-CPE possesses
a relatively high stability.20 Similar behaviours were also observed
for 2- and 3-CPEs (Fig. S8d–S9d).†
Luminescent properties
Fig. 5 (a) Emission spectra of free L (black), compound 1 (red), 2 (blue)
and 3 (green) excited at 368 nm. (b) The characteristic luminescence
spectrum of Tb(III) in compound 2 excited at 260 nm.
The luminescent properties of compounds 1–3 have also been
explored, considering that both lanthanide ions and the organic
ligands may induce the luminescent behaviours. Actually, two
kinds of emission regions were observed for compound 2, and
only one emission region is found for 1 and 3 (Fig. 5). The first
emission region of compound 2 was obtained with an excitation
wavelength of 260 nm and involves a low-intensity emission
band at 494 nm and a high-intensity emission peak at 559 nm,
honeycomb-like nets. Based on the present work, it can be expected
that the design and use of new double or multiple betaine-
containing ligands and/or other POM templates in such reaction
systems can assemble more new types of POM-based lanthanide–
organic hybrid materials with multifunctional properties in lumi-
nescence, electrochemistry, magnetism and catalysis. This work is
ongoing in our group.
corresponding to the 5D4
→
7F6 and 5D4
→
7F5 transitions
of Tb3+ ion, respectively. (Fig. 5b).21 Moreover, another intense
emission peak of compound 2 is located at 423 nm upon excitation
at 368 nm (Fig. 5a) and can be assigned to organic ligand-
based emission according to the luminescence spectrum of the
free L ligand (Fig. 5a). This emission band can be ascribed to
a p–p* or p–n ligand-centered electronic transition within the
aromatic systems of the L ligand.22 Furthermore, the emission
peak positions at ca. 423 nm for compounds 1 and 3 are similar to
that of 2 (Fig. 5a), but the characteristic emission bands of Dy3+
and Er3+ ions cannot be observed. It is presumed that the aqua
ligands on these lanthanide ions may lead to the fluorescence
quenching.23 The above observations suggest that these POM-
based composite materials of 1–3 may be suitable candidates for
potential fluorescent materials.
References
1 (a) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keeffe
and O. M. Yaghi, Science, 2002, 295, 469; (b) R. Matsuda, R. Kitaura, S.
Kitagawa, Y. Kubota, R. V. Belosludov, T. C. Kobayashi, H. Sakamoto,
T. Chiba, M. Takata, Y. Kawazoe and Y. Mita, Nature, 2005, 436, 238;
(c) R. Banerjee, A. Phan, B. Wang, C. Knobler, H. Furukawa, M.
O’Keeffe and O. M. Yaghi, Science, 2008, 319, 939; (d) J. J. Perry IV,
J. A. Perman, J. Michael and M. J. Zaworotko, Chem. Soc. Rev., 2009,
38, 1400; (e) X.-M. Zhang, Z.-M. Hao, W.-X. Zhang and X.-M. Chen,
Angew. Chem., Int. Ed., 2007, 46, 3456; (f) H.-L. Guo, G.-S. Zhu, Ian
J. Hewitt and S.-L. Qiu, J. Am. Chem. Soc., 2009, 131, 1646; (g) X.-L.
Wang, C. Qin, S.-X. Wu, K.-Z. Shao, Y.-Q. Lan, S. Wang, D.-X. Zhu,
Z.-M. Su and E.-B. Wang, Angew. Chem., Int. Ed., 2009, 48, 5291.
2 (a) A. K. Cheetham, G. Fe´rey and T. Loiseau, Angew. Chem., Int. Ed.,
1999, 38, 3268; (b) J. H. Yu and R. R. Xu, Acc. Chem. Res., 2003, 36,
481; (c) Y. Song, J. Yu, Y. Li, G. Li and R. Xu, Angew. Chem., Int. Ed.,
2004, 43, 2399.
Conclusions
3 (a) P. J. Hagrman, D. Hagrman and J. Zubieta, Angew. Chem., Int. Ed.,
1999, 38, 2638; (b) R. Vilar, D. M. P. Mingos, A. J. P. White and D. J.
Williams, Angew. Chem., Int. Ed., 1998, 37, 1258; (c) L. C. Tabares, J.
A. R. Navarro and J. M. Salas, J. Am. Chem. Soc., 2001, 123, 383.
In summary, the introduction of a double-betaine-containing
ligand into the lanthanide-POMs reaction system results in the
new POM-templated lanthanide–organic hybrid layers with 63-
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4 (a) M. T. Pope, Heteropoly and Isopoly Oxometalates, Springer, Berlin,
1983; (b) M. T. Pope and A. Mu¨ller, Polyoxometalates: From Platonic
Solids to Anti-Retroviral 414 Activity, Kluwer, Dordrecht, 1993; (c) C.
L. Hill, Chem. Rev., 1998, 98, 1 , Ed. Special Issue on Polyoxometalates;
(d) T. Yamase and M. T. Pope, Polyoxometalate Chemistry for Nano-
Composite Design, Kluwer, Dordrecht, 2002; (e) D.-L. Long, E.
Burkholder and L. Cronin, Chem. Soc. Rev., 2007, 36, 105; (f) A.
Dolbecq, E. Dumas, C. R. Mayer and P. Mialane, Chem. Rev., 2010,
110, 6009.
5 (a) C. Inman, J. M. Knaust and S. W. Keller, Chem. Commun., 2002,
156; (b) L. Lisnard, A. Dolbecq, P. Mialane, J. Marrot, E. Codjovi
and F. Se´cheresse, Dalton Trans., 2005, 3913; (c) X.-J. Kong, Y.-P. Ren,
P.-Q. Zheng, Y.-X. Long, L.-S. Long, R.-B. Huang and L.-S. Zheng,
Inorg. Chem., 2006, 45, 10702; (d) A.-X. Tian, J. Ying, J. Peng, J.-Q.
Sha, H.-J. Pang, P.-P. Zhang, Y. Chen, M. Zhu and Z.-M. Su, Inorg.
Chem., 2009, 48, 100; (e) X.-L. Wang, C. Qin, E.-B. Wang and Z.-M.
Su, Chem. Commun., 2007, 4245; (f) H.-J. Pang, J. Peng, C.-J. Zhang,
Y.-G. Li, P.-P. Zhang, H.-Y. Ma and Z.-M. Su, Chem. Commun., 2010,
46, 5097; (g) S.-T. Zheng and G.-Y. Yang, Dalton Trans., 2010, 39, 700.
6 (a) L. M. Rodriguez-Albelo, A. R. Ruiz-Salvador, A. Sampieri, D. W.
Lewis, A. Go´mez, B. Nohra, P. Mialane, J. Marrot, F. Se´cheresse, C.
Mellot-Draznieks, R. N. Biboum, B. Keita, L. Nadjo and A. Dolbecq,
J. Am. Chem. Soc., 2009, 131, 16078; (b) X.-L. Wang, Y.-F. Bi, B.-K.
Chen, H.-Y. Lin and G.-C. Liu, Inorg. Chem., 2008, 47, 2442; (c) X.-Y.
Zhao, D.-D Liang, S.-X. Liu, C.-Y Sun, R.-G. Cao, C.-Y. Gao, Y.-H.
Ren and Z.-M. Su, Inorg. Chem., 2008, 47, 7133.
7 (a) Y.-G. Li, L.-M. Dai, Y.-H. Wang, X.-L. Wang, E.-B. Wang, Z.-M.
Su and L. Xu, Chem. Commun., 2007, 2593; (b) L.-M. Dai, W.-S. You,
Y.-G. Li, E.-B. Wang and C.-Y. Huang, Chem. Commun., 2009, 2721.
8 (a) M.-L. Wei, C. He, W.-J. Hua, C.-Y. Duan, S.-H. Li and Q.-J. Meng,
J. Am. Chem. Soc., 2006, 128, 13318; (b) C.-Y. Sun, S.-X. Liu, D.-D.
Liang, K.-Z. Shao, Y.-H. Ren and Z.-M. Su, J. Am. Chem. Soc., 2009,
131, 1883; (c) A. Dolbecq, P. Mialane, L. Lisnard, J. Marrot and F.
Se´cheresse, Chem.–Eur. J., 2003, 9, 2914.
9 (a) M.-L. Wei, C. He, Q.-Z. Sun, Q.-J. Meng and C.-D. Duan, Inorg.
Chem., 2007, 46, 5957; (b) C.-H. Li, K.-L. Huang, Y.-N. Chi, X. Liu,
Z.-G. Han, L. Shen and C.-W. Hu, Inorg. Chem., 2009, 48, 2010; (c) X.-
D. Yang, C.-H. Zhang, D.-P. Wang and Y.-G. Chen, Inorg. Chem.
Commun., 2010, 13, 1350; (d) X.-L. Wang, Y.-Q. Guo, Y.-G. Li, E.-
B. Wang, C.-W. Hu and N.-H. Hu, Inorg. Chem., 2003, 42, 4135.
10 (a) C. Boglio, G. Lemie`re, B. Hasenknopf, S. Thorimbert, E. Lacote and
M. Malacria, Angew. Chem., Int. Ed., 2006, 45, 3324; (b) N. Dupre´, P.
Re´my, K. Micoine, C. Boglio, S. Thorimbert, E. Lacoˆte, B. Hasenknopf
and M. Malacria, Chem. Eur. J., 2010, 16, 7256; (c) Y. Kikukawa, S.
Yamaguchi, Y. Nakagawa, K. Uehara, S. Uchida, K. Yamaguchi and
N. Mizuno, J. Am. Chem. Soc., 2008, 130, 15872.
11 C.-D. Wu, C.-Z. Lu, H.-H. Zhuang and J.-S. Huang, J. Am. Chem. Soc.,
2002, 124, 3836.
12 (a) H.-Y. An, Z.-B. Han and T.-Q. Xu, Inorg. Chem., 2010, 49, 11403;
(b) J. Lu¨, E.-H. Shen, Y.-G. Li, D.-R. Xiao, E.-B. Wang and L. Xu,
Cryst. Growth Des., 2005, 5, 65.
13 (a) D.-D. Wu and T. C. W. Mak, J. Chem. Soc., Dalton Trans., 1995,
139; (b) J.-G. Mao, H.-J. Zhang, J.-Z. Ni, S.-B. Wang and T. C. W. Mak,
Polyhedron, 1999, 18, 1519; (c) X. Zhang, G.-C. Guo, F.-K. Zheng,
G.-W. J.-G. Zhou, Z.-C. Dong, J.-S. Huang and T. C. W. Mak, J. Chem.
Soc., Dalton Trans., 2002, 1344; (d) A.-Q. Wu, Y. Li, F.-K. Zheng, G.-C.
Guo and J.-S. Huang, Cryst. Growth Des., 2006, 6, 444.
14 R. D. Claude, F. Michel, F. Raymonde and T. Rene, Inorg. Chem., 1983,
22, 207.
15 F.-K. Zheng, A.-Q. Wu, Y. Li, G.-C. Guo and J.-S. Huang, Chin. J.
Struct. Chem., 2005, 24, 940.
16 (a) G. M. Sheldrick, SHELXL97, Program for Crystal Structure
Refinement, University of Go¨ttingen, Go¨ttingen, Germany, 1997; (b) G.
M. Sheldrick, SHELXS97, Program for Crystal Structure Solution,
University of Go¨ttingen, Go¨ttingen, Germany, 1997.
17 M. Sadakane and E. Stechhan, Chem. Rev., 1998, 98, 219.
18 S. Don, X. Xi and M. Tian, J. Electroanal. Chem., 1995, 385, 227.
19 K. Unoura and N. Tanaka, Inorg. Chem., 1983, 22, 2963.
20 (a) X.-L. Wang, Z.-H. Kang, E.-B. Wang and C.-W. Hu, J. Electroanal.
Chem., 2002, 523, 142; (b) L. Cheng, X.-M. Zhang, X.-D. Xi and S.-J.
Dong, J. Electroanal. Chem., 1996, 407, 97.
21 B. Zhao, X.-Y. Chen, P. Cheng, D.-Z. Liao, S.-P. Yan and Z.-H. Jiang,
J. Am. Chem. Soc., 2004, 126, 15394.
22 (a) F.-Y. Yi, N. Zhao, W. Wu and J.-G. Mao, Inorg. Chem., 2009, 48,
628; (b) X.-X. Zhou, Y.-P. Cai, S.-Z. Zhu, Q.-G. Zhan, M.-S. Liu, Z.-Y.
Zhou and L. Chen, Cryst. Growth Des., 2008, 8, 2076; (c) B. Xu, J. Lu¨
and R. Cao, Cryst. Growth Des., 2009, 9, 3003.
23 W.-K. Wong, X.-P. Yang, Richard A. Jones, Joseph H. Rivers, Vince
Lynch, Wing-Kit Lo, D. Xiao, Michael M. Oye and Archie L. Holmes,
Inorg. Chem., 2006, 45, 4340.
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