Anionic porous metal-organic framework with novel 5-connected vbk topology for rapid adsorption of dyes and tunable white light emission

Article abstract of DOI:10.1039/c3tc32001d

A novel porous metal-organic framework, {[Zn₂(L)·H ₂O]·3H₂O·3DMAc·NH₂(CH ₃)₂}_n (Zn(ii)-MOF), was synthesized under solvothermal conditions using a flexible multicarboxylic acid (H₅L = 3,5-bis(1-methoxy-3,5-benzene dicarboxylic acid)benzoic acid). Zn(ii)-MOF contains 1D nanotubular channels of 13.8 A × 16.4 A and exhibits a rare 5-connected vbk net with a Schlaefli symbol of {4 ⁵.6⁵} topology. Notably, Zn(ii)-MOF can adsorb toluidine blue fast and effectively, and trap lanthanide ions such as Eu³⁺ and Tb³⁺ to sensitize their emissions in the solid state through a Ln³⁺-exchanged approach. Furthermore, we successfully obtained white light emitting materials.

Full text of DOI:10.1039/c3tc32001d

Journal of
Materials Chemistry C
View Article Online
View Journal
PAPER
Anionic porous metal–organic framework with
novel 5-connected vbk topology for rapid
adsorption of dyes and tunable white light
emission†
Cite this: DOI: 10.1039/c3tc32001d
Ming-Li Ma,a Jian-Hua Qin,a Can Ji,a Hong Xu,a Rui Wang,a Bao-Jun Li,a
a
Shuang-Quan Zang, Hong-Wei Houa and Stuart R. Battenb
*
A novel porous metal–organic framework, {[Zn2(L)$H2O]$3H2O$3DMAc$NH2(CH3)2}n (Zn(II)–MOF), was
synthesized under solvothermal conditions using a flexible multicarboxylic acid (H5L ¼ 3,5-bis(1-
methoxy-3,5-benzene dicarboxylic acid)benzoic acid). Zn(II)–MOF contains 1D nanotubular channels of
Received 10th October 2013
Accepted 13th November 2013
13.8 A˚ ꢀ 16.4 A˚ and exhibits a rare 5-connected vbk net with a Schlafli symbol of {45.65} topology.
¨
Notably, Zn(II)–MOF can adsorb toluidine blue fast and effectively, and trap lanthanide ions such as Eu3+
DOI: 10.1039/c3tc32001d
and Tb3+ to sensitize their emissions in the solid state through
a
Ln3+-exchanged approach.
www.rsc.org/MaterialsC
Furthermore, we successfully obtained white light emitting materials.
amount of attention because of their adsorbing applications.
Although a host of applications that utilize the capability of
MOFs for physical absorption have been explored, work about
rapid dye adsorption of MOFs has been rarely reported.2g–m
White-light-emitting materials deserve particular attention
due to their potential applications in solid-state lighting (SSL),
full-color displays, and backlights.6 White emission should
ideally be composed of two (blue and yellow) or three (blue,
green, and red) primary colors and cover the whole visible range
from 400 to 700 nm, and the emitters should have the ability to
emit primary colors simultaneously and be comparable in
intensity to produce white light and the pure colors separately
in a tunable way.7 Different approaches have been reported to
obtain efficient white-light-emitting materials. They mainly
focus on metal-doped or hybrid inorganic materials,8 nano-
materials,9 organic molecules,10 and metal complexes.11 In the
photo- and electroluminescence elds, lanthanide-containing
materials, which exhibit excellent sharp-emission luminescence
properties with suitable sensitization, have attracted much
interest and have been effectively used in designing white-light
emitting materials.12 However, the design and synthesis of
hetero-lanthanide MOFs is very hard due to the inherent diffi-
culty of synthesis of organic ligands with specic recognition
sites required by the different lanthanide cations. So, with
judiciously chosen red, green and blue-emissive ions incorpo-
rated in a suitable host, it is possible to obtain luminescent
materials which emit across the entire visible spectrum with
high color purity.13 However, as to the white-light-emitting
materials study of MOFs, there are few reports about the
encapsulation of lanthanide ions to generate white light emis-
sion through a Ln3+-exchanged approach.
Introduction
Recently, metal–organic frameworks (MOFs) have met with
great interest owing to their enormous variety of interesting
molecular topologies and a wide range of potential applications
as functional materials.1 A key feature in MOFs is their porosity,
which plays a signicant role in the functional properties,
typically in guest species recognition and adsorption.2 Most of
the functionalities derive from the ability of MOFs to recognize
specic guest substrates through elusive host–guest interac-
tions. Furthermore, the highly regular channel structures and
controllable pore sizes of MOFs permit their applications in
adsorption of guest molecules/ions, such as dyes or lanthanide
ions.
With the development of the dyeing and nishing industry,
dye effluent is emerging as an environmentally challenging
issue worldwide, particularly in China.3 Many dyes are consid-
ered to be toxic and even carcinogenic, and most toxic dyestuffs
are stable to light and oxidants, which make them difficult to
degrade.4 Although several techniques, such as biological
treatments, membrane processes, advanced oxidation
processes, electrochemical techniques, and adsorption proce-
dures,5 have been proposed, materials containing nanometer
sized pores and channels are currently receiving a considerable
aCollege of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou
450001, P. R. China. E-mail: zangsqzg@zzu.edu.cn; Fax: +86 371-67780136
bSchool of Chemistry, Monash University, Vic 3800, Australia
† Electronic supplementary information (ESI) available. CCDC 962887. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3tc32001d
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. C

View Article Online
Journal of Materials Chemistry C
Paper
Based on the above consideration, we have been developing
a program for the preparation of porous MOFs. The MOF built
from a bulky ligand which enables the formation of large
channels can serve as a host for adsorbing dyes effectively and
an antenna for generating luminescent lanthanide MOFs. In
this contribution, we present a novel porous metal–organic
framework {[Zn2(L)$H2O]$3H2O$3DMAc$NH2(CH3)2}n (Zn(II)–
MOF), which is generated from H5L (3,5-bis(1-methoxy-3,5-
benzene dicarboxylic acid)benzoic acid) and ZnCl2 under
solvothermal conditions. Zn(II)–MOF is anionic, and dimethy-
lammonium cations reside in its 1D pores. Furthermore, we can
replace the dimethylammonium cations with specic cations in
a post synthetic fashion.14 Thus, we successfully obtained multi-
functional MOF materials which can adsorb toluidine blue fast
and effectively, and we also obtained white-light emitting
materials through trapping of Eu3+ and Tb3+ ions into the pores
of the Zn(II)–MOF material.
Scheme 1 The synthesis of ligand H5L.
Experimental
Materials and physical measurements
ester. Then, the product and NaOH (3.6 g, 0.09 mol) were dis-
solved in 60 mL of methanol and 60 mL of water and reuxed
overnight. The methanol was removed by distillation under
reduced pressure and the resulting aqueous solution was acidi-
ed to pH ꢃ 2.0 by 6 M HCl solution. A white solid was precipi-
tated and ltered. Next the solid was dried under vacuum
overnight. Yield: 1.22 g, 86%. Elemental analysis (%): calcd for
All reagents and solvents employed in the present work were of
analytical grade as obtained from commercial sources and used
without further purication. Elemental analysis for C, H, and N
were performed on a Perkin-Elmer 240 elemental analyzer. The
FT-IR spectra were recorded from KBr pellets in the range from
4000 to 400 cmꢁ1 on a Nicolet NEXUS 470-FTIR spectrometer.
Thermogravimetric analysis (TGA) was performed on an SDT
2960 thermal analyzer under air from room temperature to
800 ꢂC with a heating rate of 20 ꢂC minꢁ1. Data for Zn(II)–MOF
were collected using the MX1 beamline at the Australian
C
25H18O12: C, 58.83; H, 3.55; O, 37.62. Found: C, 58.73; H, 3.61; O,
37.66. 1H NMR (300 MHz, DMSO-d6): d 8.10 (s, 2H), 8.03 (d, 2H),
7.88 (s, 1H), 7.77 (s, 4H), 5.35 (m, 4H). IR (KBr, cmꢁ1): 3443(s),
1693(vs), 1596(vs), 1465(m), 1418(s), 1301(s), 1264(m), 1127(m),
1072(m), 1042(w), 883(w), 775(s), 728(m), 488(w).
˚
Synchrotron operating at 15.995 keV (l ¼ 0.71073 A) for the
100 K structure. Luminescence spectra for the solid samples
were recorded on a Hitachi 850 uorescence spectrophotom-
eter. UV-visible absorption spectra were recorded on a TU-1900
double-beam UV-Vis spectrophotometer. Inductively coupled
plasma spectroscopy (ICP) was performed on a Thermo ICAP
6500 DUO spectrometer. The Commission International de
I'Eclairage (CIE) color coordinates were calculated on the basis
of the international CIE standards.15
Preparation of {[Zn2(L)$H2O]$3H2O$3DMAc$NH2(CH3)2}n
(Zn(II)–MOF)
A mixture of H5L (0.0153 g, 0.03 mmol), ZnCl2 (0.0272 g,
0.2 mmol), and DMAc–methanol (1/1.5) (DMAc ¼ N,N0-dime-
thylacetamide) was stirred for 10 min in air at room tempera-
ture. Then the mixture was transferred and sealed inꢂ a
Teon-lined stainless steel vessel (18 mL) and heated at 90 C
for 3 days. Aer the mixture was cooled to room temperature at
4 ꢂC hꢁ1, colorless crystals of Zn(II)–MOF were obtained (57.2%
yield based on H5L). Elemental analysis (%): calcd for
Preparation of 3,5-bis(1-methoxy-3,5-benzene dicarboxylic
acid)benzoic acid (H5L)
C
39H56O19N4Zn2: C, 46.12; H, 5.56; N, 5.52. Found: C, 46.18; H,
5.96; N, 5.61. IR (KBr, cmꢁ1): 3426(s), 1622(vs), 1578(vs),
1455(m), 1403(s), 1364(s), 1262(m), 1126(m), 1036(m), 963(w),
889(w), 780(s), 726(m), 594(w).
The ligand was prepared by the reaction of methyl 3,5-bis(bromo-
methyl)benzoate16 with dimethyl-5-hydroxy-benzene-1,3-dio-
ate17 (Scheme 1). A mixture of methyl 3,5-bis(bromomethyl)-
benzoate (0.96 g, 3 mmol), dimethyl-5-hydroxy-benzene-1,3-
dioate (1.79 g, 8.5 mmol), K2CO3 (1.80 g, 13 mmol) and DMF Experimental details for dye adsorption
(50 mL) were placed in a 100 mL round-bottom ask and the
Freshly prepared Zn(II)–MOF (30 mg) was immersed for 30 min
reaction completed aer the solution was stirred at 50 ꢂC for 48
hours under a N2 atmosphere. The product mixture was poured
into H2O (100 mL), and the aqueous solution was extracted by
CH2Cl2 (2 ꢀ 100 mL). The combined CH2Cl2 layer was washed
with saturated NaHCO3 solution (3 ꢀ 100 mL), dried over MgSO4,
ltered and evaporated on a rotary evaporator to give a 3,5-bis(1-
in 3 mL DMAc solutions with different toluidine blue concen-
trations (10ꢁ3, 10ꢁ4, 10ꢁ5, and 10ꢁ6 M).
Encapsulation of lanthanide(III) cations in Zn(II)–MOF
Soakage of Zn(II)–MOF in DMAc solutions of lanthanide
methoxy-3,5-benzene dicarboxylic acid)benzoic acid dimethyl hydrochloride. Freshly prepared Zn(II)–MOF (30 mg) was soaked
J. Mater. Chem. C
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry C
in DMAc solutions (3 mL) of hydrochloride of Eu3+ and Tb3+,
respectively. Aer one day of soakage at 50 ꢂC, the crystals were
washed with DMAc to remove residual lanthanide(III) cations on
the surface.
Soakage of Zn(II)–MOF in DMAc solutions of europium(III)/
terbium(III) hydrochloride with different Eu3+/Tb3+ ratios.
Freshly prepared Zn(II)–MOF (30 mg) was soaked in DMAc
solutions (3 mL) of lanthanide hydrochloride with different
molar ratios of Eu3+/Tb3+. Aer one day of soakage at 50 ꢂC, the
crystals were washed with DMAc to remove residual lanthani-
de(III) cations on the surface.
X-ray crystallography
Fig. 1 Coordination environment of the Zn(II) center in Zn(II)–MOF.
Symmetry code: #1 x, 1.5 ꢁ y, 0.5 + z; #2 ꢁx, 1 ꢁ y, 1 ꢁ z; #3 x, 1 + y + 2,
1 + z; #4 1 ꢁ x, 0.5 + y, 0.5 ꢁ z (all of the H atoms and solvent
molecules are omitted for clarity).
Single-crystal X-ray diffraction data of Zn(II)–MOF was con-
ducted on the MX1 beamline at the Australian Synchrotron
˚
operating at 15.995 keV (l ¼ 0.71073 A) for the 100 K structure.
The sample was mounted on a 0.1 mm cryo-loop using viscous
oil and the temperature was maintained using an open-ow N2
cryostream. Data were collected from a single phi scan using the
Bluice interface program.18 Initial data processing was carried
out using XDS.19 The structure was solved by direct methods
with SHELXS-97 (ref. 20) and rened with the full-matrix least-
squares technique using the SHELXL-97 (ref. 21) program. All
non-hydrogen atoms were rened anisotropically. The
hydrogen atoms of the ligand were included in the structure
factor calculation at idealized positions by using a riding model
and rened isotropically. The unit cell includes a large region of
disordered solvent molecules, which could not be modelled as
discrete atomic sites. We employed PLATON/SQUEEZE to
calculate the diffraction contribution of solvent molecules and
thereby to produce a set of solvent-free diffraction intensities.
The structure was then rened again using the data generated.
Analytical expressions of neutral atom scattering factors were
employed, and anomalous dispersion corrections were incor-
porated. Crystal data, data collection parameters, and rene-
ment statistics for Zn(II)–MOF are listed in Table S1.† Relevant
bond distances and bond angles for Zn(II)–MOF are given in
Table S2.†
distinct L5ꢁ ligands, while the ZnO5 pentacoordination in Zn2 is
provided by four carboxylate oxygen atoms from four separate
L5ꢁ ligands (Zn–O ¼ 1.901(3)–2.079(5) A) and one coordinated
˚
˚
water molecule (Zn–O1W ¼ 2.172(6) A). The two Zn(II) ions are
held together by three bis-bidentate carboxylate groups from
three different L5ꢁ ligands, forming a triple lamella “paddle-
wheel” secondary building unit (SBU) (Fig. S2†). In the crystal
structure of Zn(II)–MOF, these SBUs are connected together
through L5ꢁ ligands to give a 3D structure (Fig. 2), which
contains two different kinds of channels along the b-axis:
˚
˚
smaller quadrilateral channels of 7.7 A ꢀ 5.4 A (measured
between opposite atoms) and larger quadrilateral channels of
˚
˚
13.8 A ꢀ 16.4 A (measured between opposite atoms) in size, as
shown in Fig. 3. Both ends of the L5ꢁ ligands are linked together
with the binuclear SBUs to form the larger channel, while only
one end of the L5ꢁ ligands connect the binuclear SBUs to form
the smaller 1D channel. The total solvent accessible volume
calculated using PLATON is 68.1% of the unit cell volume.
A better insight into the nature of the intricate framework
can be achieved by the application of a topological approach,
reducing multidimensional structures to simple nodes and
Results and discussion
Synthesis and crystal structure
The reactions of ZnCl2 and H5L in a mixed solvent system of
ꢂ
DMAc–methanol at 90 C for 72 h produced colourless crystals
of Zn(II)–MOF. A single crystal X-ray diffraction study reveals
that Zn(II)–MOF crystallizes in monoclinic space group P21/c
and has a non-interpenetrated three-dimensional framework.
As shown in Fig. 1, the asymmetric unit of Zn(II)–MOF consists
of two Zn(II) cations, one L5ꢁ anion, one coordinated water
molecule, three free water molecules, three free DMAc mole-
+
cules, and one free dimethylammonium cation (Me2NH2 )
which results from the hydrolysis of DMAc under the reaction
condition.22 The ve carboxylate groups of the L5ꢁ ligand bind
the metal ions via the m8-h1:h1:h1:h0:h1:h1:h1:h1:h1:h0 mode as
depicted in Fig. S1.† The Zn1 center adopts a distorted tetra-
hedral geometry surrounded by four oxygen atoms from four Fig. 2 Three-dimensional network structure of Zn(II)–MOF.
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. C

View Article Online
Journal of Materials Chemistry C
Paper
230 ꢂC. The residue was ZnO (experimental: 16.31% and
calculated: 16.03%).
Host–guest system
Single-crystal X-ray diffraction revealed that the framework of
Zn(II)–MOF is anionic, with dimethylammonium cations and
DMAc molecules residing in the 1D channels. The solvent
molecules could not be removed completely by solvent
exchange and subsequent drying in vacuum. Furthermore, gas
sorption measurements gave low sorption values, though this
technique can be of limited value in demonstrating porosity in
certain systems.25 Thus, to further probe the permanent
porosity and accessibility of Zn(II)–MOF, the dye-adsorptions
were measured with a range of different dyes.26 When immersed
into DMAc solutions of toluidine blue (TB), methylene blue
(MB), and rhodamine 6G (R6G) at different times at room
temperature, respectively, Zn(II)–MOF presents different
adsorption behaviors toward these dyes as monitored by UV-Vis
absorption spectroscopy (Fig. 5, S5 and S6†), in the order of TB >
MB > R6G, which could be mainly ascribed to the anionic nature
of the framework of Zn(II)–MOF. Their molecular structures are
shown in Fig. S7.† It is noteworthy that the solution color of TB
decreased in the process with the increased time and nearly
disappeared aer 30 min, and the corresponding absorbance of
the solution almost decreased to zero. It is also worth
mentioning that when the mixtures are shaken adsorption is
instantaneous. These adsorption phenomenon clearly show
that Zn(II)–MOF possesses rapid adsorption of organic dye TB
molecules.
Fig. 3 Representation of the two kinds of quadrilateral nanotube-like
channels of Zn(II)–MOF viewed along the a-axis.
connection nets. If the paddle-wheel cluster (which bonds to
ve separate L5ꢁ ligands) is considered as a ve-connecting
node, and the L5ꢁ ligand is also considered as a ve-connecting
node, the structure displays the unusual 3D 5-connected vbk net
(both nodes are topologically equivalent) with the point
5
5
(Schlai) symbol of {4 .6 } calculated with TOPOS23 (Fig. 4). To
the best of our knowledge, only a few examples of frameworks
with 5-connected networks have been reported to date.24
¨
Thermogravimetric analysis
The thermal stability of Zn(II)–MOF was examined by ther-
mogravimetric analysis (TGA) in the temperature range of 30–
ꢁ1
Exposure of Zn(II)–MOF to a solution of TB in DMAc (3 mL,
10ꢁ3 M) indicated that Zn(II)–MOF adsorbs TB quickly. TB
belongs to the class of thiazine dyes, and it exhibits strong
absorption in the visible region. Fig. 6 shows the uorescence
spectra for TB@Zn(II)–MOF. Obviously, the strongest emission
peak for TB@Zn(II)–MOF is at 704 nm with the excitation peak
at 640 nm at room temperature, which is similar to the previous
ꢂ
ꢂ
800 C with a heating rate of 10 C min under an air atmo-
sphere, as shown in Fig. S4.† The curve exhibits three major
losses in the temperature range of 30–510 ꢂC, the weight loss of
5.35% during the rst step between 30 and 98 ꢂC corresponds to
the loss of three lattice H2O (calculated 5.32%), and the weight
ꢂ
loss of 32.13% during the second step between 98 and 230 C
corresponds to the loss of three guest DMAc molecules, one free
dimethylammonium cation and one coordinated H2O molecule
(calculated 32.04%). Decomposition of Zn(II)–MOF began above
Fig. 4 Novel 5-connected network with {45.65} topology of Zn(II)– Fig. 5 UV-Vis spectra of the original and Zn(II)–MOF treated (30 mg)
MOF (the purple nodes represent the Zn paddle-wheel SBUs, the light organic dye TB (5.0 ꢀ 10ꢁ5 M, 2 mL) solution at various times. The
blue nodes represent the L5ꢁ ligands).
insets are photos of the corresponding solutions at various times.
J. Mater. Chem. C
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry C
Fig. 6 Fluorescence spectra of TB@Zn(II)–MOF at room temperature.
results obtained on TB-doped materials.27 Furthermore,
TB@Zn(II)–MOF can also be obtained by immersing Zn(II)–MOF
in solutions of TB in DMAc with different concentrations (10ꢁ4
,
10ꢁ5, and 10ꢁ6 M) for 30 min. We can see that the emission
peaks present a blue shi (703 nm, 680 nm, and 657 nm,
respectively) when the concentration of the TB solution used to
prepare TB@Zn(II)–MOF is decreased from 10ꢁ3 to 10ꢁ6
M
(Fig. S8†), which implies that the TB in the crystals is present as
free monomer molecules and shows ne uorescence proper-
ties.28 The PXRD patterns of dye-included MOFs are virtually the
same as the pristine Zn(II)–MOF (Fig. S3†), indicating that the
structural integrity and open channels of the porous Zn(II)–MOF
are maintained aer exposure to the solution.
Zn(II)–MOF was then placed into an apparatus to lter DMAc
solutions of TB (Fig. 7a). The much decreased color of the
outow compared with original solution shows successfully
removal of TB from the DMAc solution. Furthermore, Zn(II)–
MOF exhibits the highest efficiency and it maintains a lter
efficiency of 100% for TB until a critical concentration of
120 mL gꢁ1 (Fig. 5b and inset). Aer that the efficiency drops
rapidly due to the penetration of dye molecules.
Fig. 7 (a) UV-Vis spectra and images of (a) the original (3.0 ꢀ 10ꢁ5 M)
and filtered TB solution with Zn(II)–MOF. (b) Filtrate collected at
different filter amounts of TB DMAc solution. The amount of adsorbent
was 50 mg.
Zn(II)–MOF was maintained upon the lanthanide ion adsorp-
tion (Fig. S3†). Upon excitation with a standard laboratory UV
lamp (365 nm), the europium and terbium loaded samples
emitted their respective red and green colors, which can be
readily observed by the naked eye as a qualitative indication of
lanthanide sensitization. The excitation and emission spectra
measured at room temperature for the powder samples of H5L
and Zn(II)–MOF are displayed in Fig. 8. The free H5L ligand
Luminescence properties
As mentioned above, the porous Zn(II)–MOF contains quadri- exhibits a strong emission at 419 nm presumably due to p–p*
˚
˚
lateral-like channels (dimensions ca. 13.8 A ꢀ 16.4 A) and transitions under 366 nm UV light excitation. Zn(II)–MOF
dimethylammonium cations reside in its 1D pores, which exhibits more enhanced blue light emission and shis slightly
makes it suitable for the trapping of different Ln3+ cationic to 424 nm with the excitation at 359 nm. The 0.470Eu3+@Zn(II)–
species into the host framework to form a heterometallic host– MOF exhibits the characteristic transitions of Eu3+ excited at
guest system, and sensitize their emissions to exhibit mono- or 359 nm, which are assigned to the transitions between the rst
dual-emission. Lanthanide(III) ions were introduced into the excited state (5D0) and the ground multiplet (7FJ, J ¼ 0–4) for
pores of Zn(II)–MOF, by soaking the samples in DMAc solutions Eu3+ at 578, 591, 615, 649 and 698 nm (Fig. 8c). The quantum
(3 mL) of hydrochloride salts of Eu3+ or Tb3+ (0.1 mmol) yield of 0.470Eu3+@Zn(II)–MOF is 5%. Similarly, the
(0.470Eu3+@Zn(II)–MOF, 0.470Tb3+@Zn(II)–MOF). The doped 0.470Tb3+@Zn(II)–MOF displays additional characteristic tran-
amounts of the lanthanide ions were conrmed by inductively sitions of Tb3+ excited at 359 nm, which are attributed to the
coupled plasma spectroscopy (ICP). The PXRD patterns of the transitions between the rst excited state (5D4) and the ground
Eu3+, Tb3+ loaded samples conrmed that the structure of multiplet (7FJ, J ¼ 6–3) at 488, 542, 582 and 620 nm for Tb3+
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. C

View Article Online
Journal of Materials Chemistry C
Paper
Fig. 8 (a) Excitation and emission spectra of the H5L ligand. (b) Exci-
tation and emission spectra of Zn(II)–MOF. (c) Emission spectra of
Eu3+@Zn(II)–MOF excitation at 359 nm. (d) Emission spectra of
Tb3+@Zn(II)–MOF excitation at 359 nm.
(Fig. 8d). The quantum yield of 0.470Tb3+@Zn(II)–MOF is 17%.
We can see that the intensity of the ligand nearly disappears.
These results suggest that the energy transfer from Zn(II)–MOF
to the lanthanide centers is very effective when the Eu3+ or Tb3+
emitters are brought into the Zn(II)–MOF. The luminescent
lifetimes of 0.470Eu3+@Zn(II)–MOF and 0.470Tb3+@Zn(II)–MOF
were measured and found to be 1.1022 ns and 2.4648 ns,
respectively, and they have shown much shorter lifetimes
compared with other strong uorescence materials.29 Despite
this limitation, the doped materials displayed strong lumines-
cence which can be easily observed by the naked eye and a high
quantum yield.
Fig. 9 The emission spectra for Zn(II)–MOF in DMAc solution of Eu3+
(a) and Tb3+ (b) at 0.5 h, 1 h, 4 h, 8 h, 12 h and 24 h and photographs
showing the crystals of Eu3+@Zn(II)–MOF and Tb3+@Zn(II)–MOF with
natural light (inset, top) and 365 nm laboratory UV light (inset, bottom).
colors from blue to blue-green, green, green-yellow. The corre-
In order to investigate the Eu3+ and Tb3+ adsorption sponding CIE chromaticity photographs of the tunable colors
processes, fresh samples of Zn(II)–MOF with the same quality generated from the doped Eu3+@Zn(II)–MOF and Tb3+@Zn(II)–
(30 mg) were immersed in 3 mL DMAc solution with 0.1 mmol MOF excited under 359 nm are shown in Fig. S9.†
Ln3+ for different times (0, 0.5 h, 1 h, 4 h, 8 h, 12 h, 24 h),
It is expected that trapping two kinds of lanthanide ions into
respectively. This adsorption process was then monitored by porous MOFs for developing compounds with tunable lumi-
photoinduced emission spectra. The emission monitoring nescent properties is a promising approach. Notably, devel-
indicated that with the increase of immersion time, the entry of oping high performance white-light emitting compounds has
Eu3+ or Tb3+ ions into the Zn(II)–MOF host framework led to a attracted much attention due to their important applications in
distinct increase of the emission intensity as the guest loading general lighting sources. Recently, signicant efforts have been
increased. Upon excitation with a standard UV lamp (lex
¼
made towards the design and synthesis of hetero-lanthanide-
365 nm), Eu3+@Zn(II)–MOF and Tb3+@Zn(II)–MOF emit their based materials.30 However, f–f hybrid coordination
corresponding red and green emission (Fig. 9), which can be compounds are very hard to prepare selectively. A new approach
readily observed by the naked eye as a qualitative indication of via a simple cation exchange based on porous MOFs31 perhaps
lanthanide sensitization.
could provide an alternative way to access to white-light emit-
As expected, when the amount of Eu3+ or Tb3+ introduced ting materials.
into Zn(II)–MOF increases, the corresponding emissions
The tunable colors from the doped Eu3+@Zn(II)–MOF and
increase gradually. We can see that the Eu3+-exchanged mate- Tb3+@Zn(II)–MOF provided the basis for us to compensate the
rials generate tunable colors from blue, blue-red, red, red- blue color from Zn(II)–MOF, green color from Tb3+ and red color
yellow, and the Tb3+-exchanged materials generate tunable from Eu3+ in the co-doped xEu3+/yTb3+@Zn(II)–MOF by adjusting
J. Mater. Chem. C
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry C
with the corresponding CIE coordinates being (0.312, 0.335) and
(0.339, 0.327), respectively; both are very close to the coordinates
for pure white-light (0.333, 0.333), according to the 1931 CIE
coordinate diagram (Fig. 10).
Conclusion
In conclusion, we have successfully synthesized an anionic
porous
metal–organic
framework,
{[Zn2(L)$H2O]$
3H2O$3DMAc$NH2(CH3)2}n (Zn(II)–MOF), with large 1D nano-
˚
˚
tubular channels of 13.8 A ꢀ 16.4 A and a rare 5-connected vbk
net {45.65} topology, constructed from “paddle-wheel”
secondary building units. The MOF was also shown to readily
and quickly adsorb toluidine blue dye molecules. In addition,
white light emitting materials were obtained based on the
porous Zn(II)–MOF by a cation exchanged approach. It is
believed that these results will further facilitate the exploration
of such MOFs as new types of functional materials for appli-
cations in elds such as environmental issues and optical
materials. Further investigations in this domain are underway.
Acknowledgements
We gratefully acknowledge nancial support by the National
Natural Science Foundation of China (no. 20901070 and
21371153), the Program for Science and Technology Innovation
Talents in Universities of Henan Province (no. 13HASTIT008),
Key Scientic and Technological Project of Henan Province
(132102210411) and Zhengzhou University (P. R. China). Part of
this research was undertaken on the MX1 beamline at the
Australian Synchrotron, Victoria, Australia.
Fig. 10 (a) Emission spectra of 0.183Eu3+/0.408Tb3+@Zn(II)–MOF and
0.127Eu3+/0.432Tb3+@Zn(II)–MOF excitation at 359 nm. (b) CIE
chromaticity diagram for the xEu3+/yTb3+@Zn(II)–MOF monitored
under 359 nm ((A) x ¼ 0.127, y ¼ 0.432 and (B) x ¼ 0.183, y ¼ 0.408).
References
different amounts of the doped Eu3+ and Tb3+ ions. A series of
Ln3+-exchanged materials with different guest Ln3+ ratios were
obtained. The PXRD patterns on the resulted heterometallic
materials are identical to that of Zn(II)–MOF, so the framework is
stable during the different lanthanide species adsorption
(Fig. S3†). The emission spectra of these loaded samples excited
at 359 nm are listed in Fig. S10.† The emission spectra of the
Ln3+-exchanged materials exhibit characteristic emissions of the
Eu3+ and Tb3+ and the blue emission of the Zn(II)–MOF. We can
see that the emission spectra of Tb3+ exhibits signicant
decrease along with the decrease of Tb3+ concentration, while the
emission spectrum of Eu3+ is largely enhanced along with the
increase of Eu3+ concentration and these results herein conrms
that energy transfer does occur from Tb3+ to Eu3+ when the two
kinds of lanthanide species co-exist in the Zn(II)–MOF.2b Such
multiband emissions from the heterolanthanide doped Zn(II)–
MOF might be a barcoded luminescent material.32 When the
emission intensities at 434, 543, and 616 nm can be compen-
sated, white light emission can be readily produced. Accordingly,
the best combination of Eu3+ and Tb3+ concentration in the Ln3+-
exchanged materials for white light emission is 0.127Eu3+/
0.432Tb3+@Zn(II)–MOF (the quantum yield is h ¼ 7%) and
0.183Eu3+/0.408Tb3+@Zn(II)–MOF (the quantum yield is h ¼ 8%)
1 (a) N. W. Ockwig, O. Delgado-Friederichs, M. O'Keeffe and
O. M. Yaghi, Acc. Chem. Res., 2005, 38, 176; (b) B. Moulton
and M. J. Zaworotko, Chem. Rev., 2001, 101, 1629; (c)
S. R. Batten and R. Robson, Angew. Chem., 1998, 110, 1558;
Angew. Chem., Int. Ed., 1998, 37, 1460; (d) G. F-rey,
C. Mellot-Draznieks, C. Serre and F. Millange, Acc. Chem.
Res., 2005, 38, 217; (e) X. Zhao, B. Xiao, A. J. Fletcher,
K. M. Thomas, D. Bradshaw and M. J. Rosseinsky, Science,
2004, 306, 1012; (f) 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; (g) A. J. Blake, N. R. Champness, P. Hubberstey,
W. S. Li, M. A. Withersby and M. SchrRder, Coord. Chem.
Rev., 1999, 183, 117; (h) Y. Yuan, H. Ren, F. X. Sun,
X. F. Jing, K. Cai, X. J. Zhao, Y. Wang, Y. Wei and
G. S. Zhu, J. Mater. Chem., 2012, 22, 24558; (i) C. Janiak,
Y. Sun, Y. Wei, S. L. Qiu and R. R. Xu, Angew. Chem., 2005,
117, 3913; Angew. Chem., Int. Ed., 2005, 44, 3845; (j)
H. Y. Zhao, Z. Jin, H. M. Su, J. L. Zhang, X. D. Yao,
H. J. Zhao and G. S. Zhu, Chem. Commun., 2013, 49, 2780;
(k) W. M. Bloch and C. J. Sumby, Chem. Commun., 2012,
48, 2534; (l) C. Y. Su, A. M. Goforth, M. D. Smith,
P. J. Pellechia and H. C. zur Loye, J. Am. Chem. Soc., 2004,
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. C

View Article Online
Journal of Materials Chemistry C
Paper
126, 3576; (m) W. W. He, S. L. Li, W. L. Li, J. S. Li, G. S. Yang,
S. R. Zhang, Y. Q. Lan, P. Shen and Z. M. Su, J. Mater. Chem.
A, 2013, 1, 11111.
8 (a) W. H. Green, K. P. Le, J. Grey, T. T. Au and M. J. Sailor,
Science, 1997, 276, 1826; (b) P. P. Lima, F. A. Almeida Paz,
R. A. S. Ferreira, V. de Zea Bermudez and L. D. Carlos,
Chem. Mater., 2009, 21, 5099; (c) L. Luo, X. X. Zhang,
K. F. Li, K. W. Cheah, J. X. Shi, W. K. Wong and
M. L. Gong, Adv. Mater., 2004, 16, 1664; (d) Y. C. Liao,
C. H. Lin and S. L. Wang, J. Am. Chem. Soc., 2005, 127, 9986.
9 (a) M. J. Bowers, J. R. McBride and S. J. Rosenthal, J. Am.
Chem. Soc., 2005, 127, 15378; (b) T. Uchino and T. Yamada,
Appl. Phys. Lett., 2004, 85, 1164; (c) H. S. Chen,
S. J. J. Wang, C. J. Lo and J. Y. Chi, Appl. Phys. Lett., 2005,
86, 131905; (d) X. M. Sui, C. L. Shao and Y. C. Liu, Appl.
Phys. Lett., 2005, 87, 113115.
2 (a) J. An, C. M. Shade, D. A. Chengelis-Czegan, S. Petoud and
N. L. Rosi, J. Am. Chem. Soc., 2011, 133, 1220; (b) C. X. Chen,
Q. K. Liu, J. P. Ma and Y. B. Dong, J. Mater. Chem., 2012, 22,
9027; (c) W. W. He, S. L. Li, G. S. Yang, Y. Q. Lan, Z. M. Su and
Q. Fu, Chem. Commun., 2012, 48, 10001; (d) G. L. Zheng,
Y. Y. Li, H. D. Guo, S. Y. Song and H. J. Zhang, Chem.
Commun., 2008, 4918; (e) W. M. Bloch, R. Babarao,
M. R. Hill, C. J. Doonan and C. J. Sumby, J. Am. Chem. Soc.,
2013, 135, 10441; (f) H. N. Wang, X. Meng, G. S. Yang,
X. L. Wang, K. Z. Shao, Z. M. Su and C. G. Wang, Chem.
Commun., 2011, 47, 7128; (g) Y. Q. Lan, H. L. Jiang, S. L. Li 10 (a) Y. S. Zhao, H. B. Fu, F. Q. Hu, A. D. Peng, W. S. Yang and
and Q. Xu, Adv. Mater., 2011, 23, 5015; (h) L. Chen, K. Tan,
Y. Q. Lan, S. L. Li, K. Z. Shao and Z. M. Su, Chem.
Commun., 2012, 48, 5919; (i) Q. R. Fang, G. S. Zhu, Z. Jin,
Y. Y. Ji, J. W. Ye, M. Xue, H. Yang, Y. Wang and S. L. Qiu,
Angew. Chem., Int. Ed., 2007, 46, 1; (j) K. Gedrich,
J. N. Yao, Adv. Mater., 2008, 20, 79; (b) J. Y. Li, D. Liu,
C. W. Ma, O. Lengyel, C. S. Lee, C. H. Tung and S. T. Lee,
Adv. Mater., 2004, 16, 1538; (c) M. Mazzeo, V. Vitale,
F. D. Sala, M. Anni, G. Barbarella, L. Favaretto, G. Sotgiu,
R. Cingolani and G. Gigli, Adv. Mater., 2005, 17, 34.
¨
M. Heitbaum, A. Notzon, I. Senkovska, R. Frohlich, 11 (a) P. Coppo, M. Duati, V. N. Kozhevnikov, J. W. Hofstraat
J. Getzschmann, U. Mueller, F. Glorius and S. Kaskel,
Chem.–Eur. J, 2011, 17, 2099; (k) L. B. Sun, H. Z. Xing,
Z. Q. Liang, J. H. Yu and R. R. Xu, Chem. Commun., 2013,
49, 11155; (l) H. N. Wang, F. H. Liu, X. L. Wang, K. Z. Shao
and Z. M. Su, J. Mater. Chem. A, 2013, 1, 13060; (m)
L. N. Li, F. X. Sun, J. T. Jia, T. Borjigina and G. S. Zhu,
CrystEngComm, 2013, 15, 4094; (n) A. A. Ayi, A. D. Burrows,
M. F. Mahona and V. M. Sebestyena, CrystEngComm, 2013,
15, 9301.
3 National Bureau of Statistics of China, 2007. http://
www.stats.gov.cn/tjsj/ndsj/2007/html/L1205e.htm.
4 S. H. Chen, J. Zhang, C. L. Zhang, Q. Y. Yue, Y. Li and C. Li,
Desalination, 2010, 252, 149.
and L. De Cola, Angew. Chem., Int. Ed., 2005, 44, 1806; (b)
K. Jayaramulu, P. Kanoo, S. J. George and T. K. Maji, Chem.
Commun., 2010, 46, 7906; (c) H. B. Xu, X. M. Chen,
Q. S. Zhang, L. Y. Zhang and Z. N. Chen, Chem. Commun.,
2009, 7318; (d) G. L. Law, K. L. Wong, H. L. Tam,
K. W. Cheah and W. T. Wong, Inorg. Chem., 2009, 48,
10492; (e) D. Sykes, I. S. Tidmarsh, A. Barbieri,
I. V. Sazanovich, J. A. Weinstein and M. D. Ward, Inorg.
Chem., 2011, 50, 11323; (f) A. C. Wibowo, S. A. Vaughn,
M. D. Smith and H. C. zur Loye, Inorg. Chem., 2010, 49,
11001; (g) H. T. Cao, G. G. Shan, X. M. Wen, H. Z. Sun,
Z. M. Su, R. L. Zhong, W. F. Xie, P. Li and D. X. Zhu,
J. Mater. Chem. C, 2013, 1, 7371; (h) M. L. Ma, C. Ji and
S. Q. Zang, Dalton Trans., 2013, 42, 10579; (i) H. B. Zhang,
X. C. Shan, L. J. Zhou, P. Lin, R. F. Li, E. Ma, X. G. Guo
and S. W. Du, J. Mater. Chem. C, 2013, 1, 888.
5 (a) Y. H. Lin and J. Y. Leu, Biochem. Eng. J., 2008, 39, 457; (b)
S. A. Avlonitis, I. Poulios, D. Sotiriou, M. Pappas and
K. Moutesidis, Desalination, 2008, 221, 259; (c) L. Young
and J. Yu, Water Res., 1997, 31, 1187; (d) A. G. Vlyssides, 12 (a) G. Glaspell, J. Anderson, J. R. Wilkins and M. S. El-Shall,
D. Papaioannou, M. Loizidoy, P. K. Karlis and A. A. Zorpas,
Waste Manage., 2000, 20, 569; (e) Y. C. Sharma and Uma,
J. Chem. Eng. Data, 2010, 55, 435.
J. Phys. Chem. C, 2008, 112, 11527; (b) S. Sivakumar,
F. C. J. M. van Veggel and M. Raudsepp, J. Am. Chem. Soc.,
2005, 127, 12464.
´
´
´
6 (a) B. W. D'Andrade and S. R. Forrest, Adv. Mater., 2004, 16, 13 (a) P. Escribano, B. Julian-Lopez, J. Planelles-Arago,
1585; (b) H. C. Su, H. F. Chen, F. C. Fang, C. C. Liu, C. C. Wu,
K. T. Wong, Y. H. Liu and S. M. Peng, J. Am. Chem. Soc., 2008,
130, 3413; (c) Y. H. Niu, M. S. Liu, J. W. Ka, J. Bardeker,
M. T. Zin, R. Schoeld, Y. Chi and A. K. Y. Jen, Adv. Mater.,
2007, 19, 300.
E. Cordoncillo, B. Viana and C. Sanchez, J. Mater. Chem.,
2008, 18, 23; (b) R. C. Evans, L. D. Carlos, P. Douglas and
J. Rocha, J. Mater. Chem., 2008, 18, 1100; (c) J. Kido and
Y. Okamoto, Chem. Rev., 2002, 102, 2357; (d)
R. Shunmugam and G. N. Tew, Polym. Adv. Technol., 2007,
18, 940.
7 (a) R. Abbel, C. Grenier, M. J. Pouderoijen, J. W. Stouwdam,
`
P. E. L. G. Leclere, R. P. Sijbesma, E. W. Meijer and 14 Z. Q. Wang and S. M. Cohen, Chem. Soc. Rev., 2009, 38, 1315.
A. P. H. J. Schenning, J. Am. Chem. Soc., 2009, 131, 833; (b) 15 T. Smith and J. Guild, Trans. Opt. Soc., 1931, 33, 73.
J. Luo, X. Li, Q. Hou, J. B. Peng, W. Yang and Y. Cao, Adv. 16 T. Routasalo, J. Helaja, J. Kavakka and A. M. P. Koskinen,
Mater., 2007, 19, 1113; (c) A. Ajayaghosh, V. K. Praveen,
S. Srinivasan and R. Varghese, Adv. Mater., 2007, 19, 411; 17 J. P. Collman, X. M. Zhang, K. Wong and J. I. Braman, J. Am.
(d) J. H. Kim, P. Herguth, M. S. Kang, A. K. Y. Jen, Chem. Soc., 1994, 116, 6245.
Y. H. Tseng and C. F. Shu, Appl. Phys. Lett., 2004, 85, 1116; 18 T. M. McPhillips, S. E. McPhillips, H. J. Chiu, A. E. Cohen,
Eur. J. Org. Chem., 2008, 3190.
(e) A. C. A. Chen, S. W. Culligan, Y. Geng, S. H. Chen,
K. P. Klubek, K. M. Vaeth and C. W. Tang, Adv. Mater.,
2004, 16, 783.
A. M. Deacon, P. J. Ellis, E. Garman, A. Gonzalez,
N. K. Sauter, R. P. Phizackerley, S. M. Soltis and P. J. Kuhn,
Synchrotron Radiat., 2002, 9, 401.
J. Mater. Chem. C
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry C
¨
¨
19 W. J. Kabsch, Appl. Crystallogr., 1993, 26, 795.
26 (a) R. Grunker, V. Bon, A. Heerwig, N. Klein, P. Muller,
U. Stoeck, I. A. Baburin, U. Mueller, I. Senkovska and
S. Kaskel, Chem.–Eur. J., 2012, 18, 13299; (b) G. Q. Kong,
S. Ou, C. Zou and C. D. Wu, J. Am. Chem. Soc., 2012, 134,
19851; (c) G. Nickerl, A. Notzon, M. Heitbaum,
I. Senkovska, F. Glorius and S. Kaskel, Cryst. Growth Des.,
2013, 13, 198; (d) J. C. Yu, Y. J. Cui, C. D. Wu, Y. Yang,
Z. Y. Wang, M. O'Keeffe, B. L. Chen and G. D. Qian, Angew.
Chem., Int. Ed., 2012, 51, 10542; (e) Y. J. Cui, Y. F. Yue,
G. D. Qian and B. L. Chen, Chem. Rev., 2012, 112, 1126; (f)
Q. R. Fang, G. S. Zhu, Z. Jin, Y. Y. Ji, J. W. Ye, M. Xue,
H. Yang, Y. Wang and S. L. Qiu, Angew. Chem., Int. Ed.,
2007, 46, 1.
20 (a) G. M. Sheldrick, Acta Crystallogr., Sect. A: Found.
Crystallogr., 1990, 46, 457; (b) G. M. Sheldrick, SHELXS-97,
Program for Solution of Crystal Structures, University of
¨
Gottingen, Germany, 1997.
21 G. M. Sheldrick, SHELXL-97, Program for renement of crystal
¨
structures, University of Gottingen, Germany, 1997.
22 (a) S. M. Hawxwell and L. Brammer, CrystEngComm, 2006, 8,
473; (b) C. G. Carson, K. Hardcastle, J. Schwartz, X. T. Liu,
C. Hoffmann, R. A. Gerhardt and R. Tannenbaum, Eur. J.
Inorg. Chem., 2009, 2338.
23 V. A. Blatov and M. V. Peaskov, Acta Crystallogr., Sect. B:
Struct. Sci., 2006, 62, 457.
24 (a) G. J. Xu, Y. H. Zhao, K. Z. Shao, Y. Q. Lan, P. Li and 27 (a) L. Guo, G. Y. Li, J. S. Liu, S. M. Ma and J. F. Zhang, J. Chem.
Z. M. Su, Inorg. Chem. Commun., 2010, 13, 932; (b)
K. M. Blake, L. L. Johnston, J. H. Nettleman,
Eng. Data, 2011, 56, 1875; (b) Y. Hirano, M. Hattori and
K. Takahashi, J. Agric. Food Chem., 2005, 53, 9800.
R. M. Supkowski and R. L. LaDuca, CrystEngComm, 2010, 28 K. Yurekli, E. Conley and R. Krishnamoorti, Langmuir, 2005,
12, 1927; (c) Z. H. Li, L. P. Xue, S. H. Li, J. G. Wang, 21, 5825.
B. T. Zhao, J. Kan and W. P. Su, CrystEngComm, 2013, 15, 29 (a) Y. H. Zhang, X. Li and S. Song, Chem. Commun., 2013, 49,
2745; (d) X. W. Wang, Y. R. Dong, Y. Q. Zheng and
J. Z. Chen, Cryst. Growth Des., 2007, 7, 613; (e) H. L. Sun,
B. Q. Ma, S. Gao and S. R. Batten, Cryst. Growth Des., 2005,
5, 1331; (f) R. J. Hill, D. L. Long, M. S. Turvey, A. J. Blake,
N. R. Champness, P. Hubberstey, C. Wilson and
¨
10397; (b) Y. Q. Lan, H. L. Jiang, S. L. Li and Q. Xu, Adv.
Mater., 2011, 23, 5015; (c) X. Ma, X. Li, Y. E. Cha and
L. P. Jin, Cryst. Growth Des., 2012, 12, 5227; (d) J. Yang,
C. M. Zhang, C. X. Li, Y. N. Yu and J. Lin, Inorg. Chem.,
2008, 47, 7262.
¨
M. Schroder, Chem. Commun., 2004, 1792; (g) R. J. Hill, 30 (a) C. Piguet and J. C. G. Bunzli, Chem. Soc. Rev., 1999, 28,
¨
D. L. Long, P. Hubberstey, M. Schroder and
347; (b) S. Faulkner and S. J. A. Pope, J. Am. Chem. Soc.,
2003, 125, 10526; (c) M. S. Tremblay and D. Sames, Chem.
Commun., 2006, 4116; (d) J. P. Costes, F. Dahan, A. Dupuis,
S. Lagrave and J. P. Laurent, Inorg. Chem., 1998, 37, 153.
N. R. Champness, J. Solid State Chem., 2005, 178, 2414; (h)
J. G. Wang, C. C. Huang, X. H. Huang and D. S. Liu, Cryst.
Growth Des., 2008, 8, 795; (i) Z. R. Pan, J. Xu, X. Q. Yao,
Y. Z. Li, Z. J. Guo and H. G. Zheng, CrystEngComm, 2011, 31 J. C. Yu, Y. J. Cui, C. D. Wu, Y. Yang, Z. Y. Wang, M. O'Keeffe,
13, 1617. B. L. Chen and G. D. Qian, Angew. Chem., Int. Ed., 2012, 51, 1.
25 K. Gedrich, M. Heitbaum, A. Notzon, I. Senkovska, 32 K. A. White, D. A. Chengelis, K. A. Gogick, J. Stehman,
R. Frçhlich, J. Getzschmann, U. Mueller, F. Glorius and
N. L. Rosi and S. Petoud, J. Am. Chem. Soc., 2009, 131,
S. Kaskel, Chem.–Eur. J., 2011, 17, 2099.
18069.
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. C