Synthesis of isoreticular zinc(II)-phosphonocarboxylate frameworks and their application in the Friedel-Crafts benzylation reaction

Article abstract of DOI:10.1002/chem.201101239

Three isoreticular zinc(II)-phosphonocarboxylate frameworks, namely {[Zn₃(pbdc)₂]·2 H₃O}_n (ZnPC-2), {[Zn₃(pbdc)₂]·Hpd·H ₃O·4 H₂O}_n (Hpd@ZnPC-2) and {[Co

Full text of DOI:10.1002/chem.201101239

FULL PAPER
DOI: 10.1002/chem.201101239
Synthesis of Isoreticular Zinc(II)-Phosphonocarboxylate Frameworks and
Their Application in the Friedel–Crafts Benzylation Reaction
Mingli Deng, Yun Ling, Bing Xia, Zhenxia Chen, Yaming Zhou,* Xiaofeng Liu,
Bin Yue, and Heyong He*[a]
Abstract: Three isoreticular zinc(II)-
phosphonocarboxylate frameworks,
namely {[Zn3A(pbdc)2]·2H3O}n (ZnPC-
2), {[Zn3A(pbdc)2]·Hpd·H3O·4H2O}n
(Hpd@ZnPC-2)
(pbdc)2]·2H3O}n
(H4pbdc=5-phosphonobenzene-1,3-di-
carboxylic acid, pd=pyrrolidine), were
solvothermally synthesized. ZnPC-2
has a 3D structure based on trinuclear
ZnII clusters (Zn3-SBU) showing 3D in-
terconnected channels. Hpd@ZnPC-2
contains an isoreticular framework of
ZnPC-2 with small channels blocked
by Hpd molecules. In CoZnPC-2, ZnII
ions in ZnPC-2 are partially substituted
by CoII ions. The Friedel–Crafts benzy-
lation reactions were carried out over
these isoreticular porous materials. The
catalytic results reveal that ZnPC-2 is
an excellent heterogeneous Lewis acid
catalyst with a high selectivity (>90%)
towards less bulky para-oriented prod-
ucts. The catalytic reaction has been
proved to occur inside the pore of
ZnPC-2, and the immobilized Zn3-
SBUs are the active sites.
CHTUNGTRENNUNG
CHTUNGTRENNUNG
and
{[Co1.5Zn1.5-
(CoZnPC-2)
ACHTUNGTRENNUNG
Keywords: heterogeneous catalysis ·
isoreticular structure · metal–organ-
ic frameworks
·
phosphonate
ligands · zinc
Introduction
kylation of bulky aromatic molecules. Therefore, increasing
interests have been focused on the porous metal–organic
frameworks (MOFs).
Catalytic alkylation of aromatics is a very important C–C
coupling reaction and has been undertaken on a large scale
in both petrochemical and chemical industries.[1–3] The para-
oriented dialkylated aromatics, such as para-diisopropylben-
zene, para-ethyltoluene, para-diethylbenzene, para-cymenes
and 4-tert-butyltoluene, are very important chemical materi-
als. The Friedel–Crafts reaction is a typical catalytic alkyla-
tion reaction and generally results the mixture of para-,
meta- and ortho-oriented products. Traditionally, strong min-
eral acids (such as HF and H2SO4) and Lewis acids (such as
AlCl3, FeCl3 and ZnCl2) have been used as the catalysts.
These traditional catalysts, however, not only cause undesir-
able economic and environmental problems in separating
and handling of the acid waste,[4–5] but also suffer low selec-
tivity towards the para products.[6] Thus, there is a strong
demand to replace these catalysts with green and efficient
heterogeneous catalysts. H-form zeolites have been studied
as the catalysts in the Friedel–Crafts alkylation reactions,[7–8]
because of their strong acidity and microporosity. However,
the small pore size of zeolites limits its application in the al-
MOFs have attracted tremendous interest during the past
decades due to their potential applications in gas storage
and/or separation, molecular recognition, ion exchange,
drug delivery and so on.[9–14] Compared with other porous
materials, the unique features of MOFs, are their designable
structures,[15–17] adjustable pore sizes (from microspore to
mesopore)[18–24] and controllable host–guest interactions
inside the pores (from hydrophobic to hydrophilic, polarity
to no polarity).[25–26] On the other hand, MOFs possess inher-
ent advantages as no additional support is needed for the
heterogenization, and the organic microenvironment provid-
ed by the framework often allows the metal active sites to
behave in a manner reminiscent of enzymes.[27–29] However,
it must be realized that only limited investigations of MOFs
have been carried out in heterogeneous catalysis compared
with the number of structures discovered and the achieve-
ments in gas storage and separation.[30–33] Recently, the Frie-
del–Crafts benzylation reactions using MOFs (such as
MOF-n and MIL-n) as the catalysts have been ex-
plored.[6,34–37] However, this study has been generally fo-
cused on the catalytic performance of certain reported
MOFs. The use of the approach of isoreticular MOFs as cat-
alysts to explore catalytic active sites, as far as we know, is
rarely reported due to the challenges to obtain isoreticular
MOFs.[17,38–40]
[a] M. Deng,+ Dr. Y. Ling,+ B. Xia, Dr. Z. Chen, Dr. Y. Zhou, X. Liu,
Dr. B. Yue, Dr. H. He
Department of Chemistry and Shanghai Key Laboratory of
Molecular Catalysis and Innovative Materials
Fudan University, 220 Handan Road
Shanghai 200433, (P. R. China)
The present work aims to synthesize isoreticular frame-
works and explore their catalytic reaction and related active
sites in the Friedel–Crafts benzylation reaction. {[Zn3-
E-mail: ymzhou@fudan.edu.cn
heyonghe@fudan.edu.cn
[+] M. L. Deng and Y. Ling contributed equally to this paper.
AHCTUNGTRENNUNG
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101239.
Chem. Eur. J. 2011, 17, 10323 – 10328
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
10323

structed by six-connected Zn
G
E
scribed as a (3,6)-connected rutile-type network with ap-
proximately 6ꢁ6 ꢂ channels along the c axis and approxi-
mately 4ꢁ4 ꢂ along a and b axes by the taking van der
Waals radius in consideration. SEM images of ZnPC-2 show
the clear rodlike crystals with micrometer sizes (Figure 1b).
PXRD patterns of the as-made and 1108C activated samples
are given in Figure 1c and both are well in agreement with
the simulated data. No significant difference was observed
from the different batch samples. Thermal stability of
ZnPC-2 (see Figure S1 in the Supporting Information) was
studied with TG analysis in the temperature range of 30–
8008C, showing a weight loss of about 5.0% from 30 to
1508C ascribed to the loss of water molecules. To study the
surface area and pore size of ZnPC-2, N2 and Ar adsorption
at 77 K were carried out, but no adsorption datum was ob-
tained. The single-component vapor-phase adsorption of
water, methanol and toluene were carried out on an auto-
matic gravimetric adsorption apparatus at 298 K (see Fig-
ure S2 in the Supporting Information and Figure 1d). The
adsorption curves of both methanol and water show a two-
step weight increase (methanol at P/P0 =0.2 and water at P/
P0 =0.7), which can be ascribed to the further uptake of
guest molecules in the small channels of ZnPC-2 along the a
and b axes. The adsorption behaviour of toluene on ZnPC-2
shows a type-I curve. The uptake amount increases rapidly
and reaches 1.5 wt% (ca. 0.9 toluene/cell) at 0.04 P/P0, then
increases linearly and reaches 3.8 wt% at P/P0 of 0.94 (P0 =
3700 Pa at 298 K), which may be ascribed to the further con-
densation of toluene on ZnPC-2. Thus, the analysis results
show that the pure ZnPC-2 phase is obtained by the im-
proved preparation method and the pore size of the product
is enough to be accessed by toluene.
ing blocks (Zn3-SBU) and tritopic 5-phosphonobenzene-1,3-
dicarboxylic acid, showing 3D interconnected regular chan-
nels (ca. 6ꢁ6 ꢂ along the c axis, ca. 4ꢁ4 ꢂ along a and b
axes). {[Zn3ACHTUNGTRENNUNG(pbdc)2]·Hpd·H3O·4H2O}n (pd=pyrrolidine,
named as Hpd@ZnPC-2) is an isoreticular framework with
only 1D channels along the axis (ca. 5ꢁ5 ꢂ) and
{[Co1.5Zn1.5A(pbdc)2]·2H3O}n is a
E
ZnPC-2 (CoZnPC-2). The catalytic results show that the
ZnPC-2 is an efficient heterogeneous acid catalyst for the
Friedel–Crafts benzylation reaction with a high selectivity
(>90%) to the para-oriented product. The catalytic reaction
and the active sites of ZnPC-2 have been studied for the
first time based on the isoreticular frameworks of
Hpd@ZnPC-2 and CoZnPC-2.
Results and Discussion
Synthesis and characterization: Crystalline samples of rutile-
type porous ZnPC-2 (Figure 1a) with high yields were pre-
pared according to our previous method[41] with some modi-
fication described in the Experimental Section. ZnPC-2 con-
sists of trimeric zinc-phosphonocarboxylate clusters (Zn3-
The isoreticular Hpd@ZnPC-2[42] crystals were synthesized
through a similar procedure as that of ZnPC-2, except by re-
placing triethylamine by pyrrolidine. The protonated pyrroli-
dine guests, based on single-crystal X-ray diffraction results
(Figure 2), replace the hydrated protons of ZnPC-2, block-
ing the small channels along the a and b axes, but serving as
walls of the large channels along the c axis. Because of the
Figure 1. a) Crystal structure of ZnPC-2 constructed by a 6-connected tri-
nuclear ZnII cluster and 3-connected ligand. b) The SEM image of ZnPC-
2 showing the rodlike structure of the crystals. c) The PXRD patterns of
ZnPC-2 compared with that of simulated one. d) The adsorption amounts
of toluene on activated ZnPC-2 at 298 K.
ACHTUNGTRENNUNG(CO2)4ACHTUNGTRENNUNG(PO3)2, Zn3-SBU) and pbdc linkers (Figure 1a). The
three ZnII ions in the Zn3-SBU form an isoscelestriangle
with Zn(1)···Zn(1)i (i: x, 1/2Ày, 1/4Àz) and Zn(1)/
Zn(1)i···Zn(2) distances of 4.61 and 3.56 ꢂ, respectively. The
oxygen atoms from the phosphonate of pbdc tridentately
capture the isoscelestriangle. Considering the Zn3-SBU as a
6-connected node formed with four C atoms from four car-
boxylates and two P atoms from two phosphonates as verti-
ces and the pbdc as a 3-connected node, ZnPC-2 may be de-
Figure 2. a) Perspective view of ZnPC-2 along the c axis (left) and ortho-
graphic view of ZnPC-2 along b axis (left). b) The perspective view of
Hpd@ZnPC-2 along the c axis showing the shrunken pore size (left) and
orthographic view of Hpd@ZnPC-2 along the a axis (left) showing the
position of Hpd (water molecules are omitted for clarity).
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Reticular Zinc(II)-Phosphonocarboxylate Frameworks
FULL PAPER
bulkier Hpd guests, the pore size of channels along the c
axis is approximately 5ꢁ5 ꢂ. The PXRD pattern (see Fig-
ure S3 in the Supporting Information) shows the product is
pure. To identify the thermal stability of Hpd guest mole-
cules in the framework, TGMS analysis results (see Fig-
ure S4 in the Supporting Information) show that the amine
molecules are stable in the framework till 3008C. Pyrroli-
dine molecules were detected after further increasing the
temperature due to the collapse of the framework. Com-
pared with the low thermal stability of amine-modified
MOFs through the cation-exchange procedure,[43] the high
thermal stability of the amine guests in the ZnPC-2 frame-
work may be ascribed to the strong hydrogen-bond interac-
tion between the guest molecule and the host framework in
restricted small channels along the a and b axes (see Fig-
ure S5 in the Supporting Information).
4CBB at a certain temperature and the molar ratio of tolu-
ene to 4CBB was fixed to 50:1. The traditional Lewis acid
catalyst of ZnCl2 was used as a reference. The reaction mix-
ture was analyzed at certain intervals by gas chromatogra-
phy with nonane as a reference.
Effects of reaction temperature on the conversion of
4CBB were firstly studied in the range of 70–1108C. As
shown in Figure 3, the reaction at 708C reached a conver-
The CoZnPC-2 crystal sample was prepared by following
a similar procedure with additional CoACHTUNTGRNEUNG(OAc)2·4H2O as the
cobalt source described in the Experimental Section. The
molar ratio of Zn/Co was varied from 8:1 to 1:2. Blue crys-
tals of CoZnPC-2 were obtained when the ratio was set to
2:1 and the pure bulk sample was confirmed by PXRD pat-
terns. Lowering or increasing the molar ratio will lead to the
formation of other compounds besides CoZnPC-2 (see Fig-
ure S6 in the Supporting Information). Single-crystal X-ray
diffraction (see Figures S7a and S7b and Table S1 in the
Supporting Information) studies reveal that CoZnPC-2 is
still a 3D rutile-type framework constructed of 6-connected
trinuclear metal clusters and 3-connected pbdc ligands with
the same coordination geometry. It has the Fdd2 space
group, which is different from that of ZnPC-2 and
Hpd@ZnPC-2 in the I-42d space group. EDS analysis shows
that the ratio of Zn/Co is about 1:1 in the product (see Fig-
ure S7c and S7d in the Supporting Information). Taking the
single-crystal X-ray diffraction results into consideration,
the CoII and ZnII ions are metal-atom disordered in the tri-
nuclear metal cluster. The hydrated protons in CoZnPC-2
are filled in the large channels.
&
Figure 3. Catalytic performance of ZnPC-2 at 70, 90, and 1108C.
:
~
*
1108C, : 908C, : 708C.
sion of 29% after 6.5 h, and a longer reaction time (18 h)
was required to achieve much higher conversion (78%).
With increasing the temperature to 908C, the conversion
boosted to be 41% after 6.5 h. At 1108C, the >99% conver-
sion of 4CBB was achieved within only 3 h, whereas the
conversion was only 81% for ZnCl2. The high catalytic ac-
tivity of ZnPC-2 is comparable to that of MOF-5.[6] After
the catalytic reaction, ZnPC-2 was centrifugally separated,
and the PXRD pattern confirms its framework integrity
after the reaction (see Figure S8 in the Supporting Informa-
tion).
To prove whether or not the reaction occurs heterogene-
ously, the reaction solution was centrifugally separated from
the catalyst after a one hour reaction time at 1108C, trans-
ferred to a new vessel and then stirred for an additional 4 h
at 1108C. The GC result shows that there is no further con-
version of 4CBB (see Figure S9 in the Supporting Informa-
tion), which suggests that there is no contribution from
leached active species,[34] confirming the catalytic reaction is
a heterogeneous process.
Catalytic reaction of ZnPC-2: The catalytic activity of
ZnPC-2 was assessed by studying the Friedel–Crafts benzy-
lation reaction of toluene with 4-chlorobenzyl bromide
(4CBB) to form isochlorobenzyltoluene (CBT) products
under ambient conditions (Scheme 1). The initial reaction
was carried out by using 3 mol% ZnPC-2 catalyst relative to
High catalytic selectivity is one of the crucial performan-
ces for catalysts. The selectivity of Friedel–Crafts benzyla-
tion reactions with traditional solid Lewis acidic catalysts,
such as AlCl3, ZnCl2 etc., is unsatisfactory. Therefore, the
porous acidic catalysts with shape selectivity are highly de-
sirable. In previous reports of MOF-5, the selectivity to-
wards para-oriented products varied from 65 to 85% (de-
pendent on reactants),[6,34] which is higher than that of tradi-
tional Lewis catalysts. In our case, ZnPC-2 exhibits a high
selectivity (>90%) for the less bulky p-CBT (Table 1),
whereas ZnCl2 is only about 54%, which is similar to previ-
ous reports.[34] Generally, the high selectivity towards the
Scheme 1. Friedel–Crafts benzylation reaction investigated by using
ZnPC-2 as the catalyst.
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H. He, Y. Zhou et al.
Table 1. Selectivity of the products of the Friedel–Crafts benzylation re-
action of toluene with 4CBB (ZnPC-2 compared with the reference cata-
lyst of ZnCl2).
zyl)-1,4-dimethylbenzene. Although the kinetic diameter of
p-xylene (5.8 ꢂ, size of the ellipsoid structure: ca. 4.6ꢁ
6.9 ꢂ) is smaller than the pore size of ZnPC-2, the size of
the product, 2-(4-chlorobenzyl)-1,4-dimethylbenzene (size of
its ellipsoid structure ca. 6.2ꢁ13.1 ꢂ) is larger than the pore
size of ZnPC-2. In addition, in a restricted space in ZnPC-2,
the two methyl groups of p-xylene can be only placed paral-
lel to the channel, which inhibits the Friedel–Crafts benzyla-
tion reaction of p-xylene with 4CBB due to the steric hin-
drance (Scheme 2). With the same reaction conditions as
Selectivity [%]
Catalyst
p-CBT
m-CBT
o-CBT
ZnPC-2
ZnCl2
91.4
53.1
7.3
39.1
1.3
7.8
para-oriented product in porous MOFs is assumed to occur
inside the pore, inhibiting the formation of large-size meta-
and ortho- counterparts due to the steric-hindrance in re-
stricted channels.[6] However, direct evidence to prove this
assumption has been rarely reported.
To investigate whether or not the catalytic reaction occurs
inside the pore of ZnPC-2, benzylation reactions of toluene
with different molecular sizes of 4CBB (11.3ꢁ4.3 ꢂ, mea-
sured based on the ellipsoid structure), 3-biphenylmethyl-
bromide (3BPMB, 12.7ꢁ5.7 ꢂ) and 3,5-di-tert-butylbenzyl
bromide (35TBBB, 10.4ꢁ7.3 ꢂ) were carried out for 24 h.
ZnCl2 was still used as a reference catalyst with a conversion
of >99% in all reactions involving 4CBB, 3BPMB and
35TBBB. ZnPC-2 exhibits a size-related selectivity towards
these reactants to give a conversion of >99% for 4CBB,
89% for 3BPMB, and no conversion for 35TBBB. Based on
these results, the selectivity of ZnPC-2 seems to be related
to the regular channels along the c axis, which highly limits
the diffusion of larger reactants and the formation of larger
intermediates and products inside the pore. However, the
external surface of ZnPC-2 also possibly contains active
sites for 3BPMB. Therefore, an isoreticular framework with
a shrunk pore size is necessary for further exploring the cat-
alytic reaction.
Isoreticular frameworks with shrunk pore size can be pre-
pared through two feasible approaches. One is to adjust the
rigid organic linkers by the way similar to IRMOFs[20] and
the other is to post-modify the pore size with an organo re-
action[44] or guest exchange. However, it is a great challenge
to obtain isoreticular frameworks based on phosphonate li-
gands because of its multidentate coordination nature. In
our case, the isoreticular structure of Hpd@ZnPC-2 with the
shrunk pore sizes was directly synthesized by using the pyr-
rolidine as the template. In Hpd@ZnPC-2, the Hpd guests
block small channels along the a and b axes, and serve as
the wall along the c axis. Because of its bulky size, the pore
size is shrunk from approximately 6ꢁ6 ꢂ in ZnPC-2 to ap-
proximately 5ꢁ5 ꢂ in Hpd@ZnPC-2, which is smaller than
the kinetic diameter of toluene (5.2 ꢂ, size of the ellipsoid
structure: ca. 4.6ꢁ5.7 ꢂ). The Friedel–Crafts benzylation re-
action of toluene with 4CBB over Hpd@ZnPC-2 shows an
extremely low conversion of 4CBB (<1%) after 10 h, con-
firming that the catalytic reaction indeed occurs inside the
pore of ZnPC-2.
Scheme 2. A snapshot of random uploading of guest molecules in a 2ꢁ
2ꢁ2 cell of ZnPC-2 (top: the 4CBB and toluene; bottom: the 4CBB and
p-xylene. A Drieding force field was used to describe the interactions).
that of toluene, the catalytic result shows that there is no de-
tectable conversion of 4CBB after 10 h, confirming that the
benzylation reaction of toluene with 4CBB occurred inside
the restricted channels of ZnPC-2, leading to the formation
of the para-oriented product.
Understanding the active sites is very important for the
design of high-performance heterogeneous catalysts. In the
literature, the catalytic active sites of MOF-5 are ascribed to
the structural defects,[35] leading to the generation of Lewis
acid sites. Recently, CoII-substituted MOF-5 was reported
for gas storage,[45] which offers us a feasible method to ex-
plore the catalytic active sites of MOFs by metal-ion-substi-
tuted isoreticular frameworks. In our case, the catalytic
active sites of ZnPC-2 are either related to the ligand or the
Zn3-SBU. With the same reaction conditions as those used
for ZnPC-2, the Friedel–Crafts benzylation reaction was car-
ried out by using the ligand as the catalyst. The result shows
that there is no conversion of 4CBB after 10 h. Isoreticular
frameworks of CoZnPC-2, in which part of ZnII in Zn3-SBU
has been substituted by CoII ions, was used as the catalyst.
The results show that the conversion of 4CBB is near zero
after 6 h, reaches 2% after 10 h and 7% after 18 h, which
indicates that changing the constitution of Zn3-SBU affects
the catalytic performance. Taking the catalytic results of li-
gands and CoZnPC-2 into consideration, the immobilized
Instead of toluene, p-xylene was further used to study
whether or not the reaction occurs inside the pore of ZnPC-
2. Generally, the Friedel–Crafts benzylation reactions of p-
xylene with 4CBB form a pure product of 2-(4-chloroben-
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Reticular Zinc(II)-Phosphonocarboxylate Frameworks
FULL PAPER
with anisotropic thermal parameters for all non-hydrogen atoms on F2.
Generally, C-bonded H atoms were placed geometrically and refined as
riding modes, the hydrogen atoms of hydroprotons were not added due
to their disordering. Crystallographic data including ZnPC-2,
Hpd@ZnPC-2 and CoZnPC-2 are listed in Table S1 in the Supporting In-
formation. CCDC-746203 (ZnPC-2), -776925 (Hpd@ZnPC-2) and
-808302 (CoZnPC-2) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
and regular distributed Zn3-SBUs in ZnPC-2 are the catalyt-
ic active sites.
Conclusion
Three rutile-type porous zinc(II)-phosphonocarboxylate iso-
reticular frameworks of ZnPC-2, Hpd@ZnPC-2 and
CoZnPC-2 have been successfully synthesized. In compari-
son with the conventional Lewis acid catalyst ZnCl2, ZnPC-
2 exhibits remarkable catalytic performance on the Friedel–
Crafts benzylation reaction of toluene with 4-chlorobenzyl
bromide, showing a high selectivity (>90%) to the para
product because of its adaptable pore size. With the isoretic-
ular frameworks of Hpd@ZnPC-2 and CoZnPC-2, it is
proved that the catalytic reaction occurs inside the pore of
ZnPC-2 and the catalytic active sites are the Zn3-SBUs.
Catalytic reactions: All the catalysts were degassed at 383 K for 3 h
under 10À3 Pa before catalytic reactions. The Friedel–Crafts alkylation re-
actions were carried out under ambient conditions. In a typical reaction,
a
mixture of toluene (5 mL), 4-chlorobenzyl bromide (200.25 mg,
0.97 mmol) and nonane (0.2 mL) as an internal standard was added into
a 50 mL flask containing the ZnPC-2 catalysts (17.50 mg, 0.024 mmol).
The mixture was stirred at a desired temperature for a certain time. The
products were analyzed by using gas chromatography at certain intervals
and further confirmed by GCMS. The ZnPC-2 catalyst was separated
from the reaction mixture by simple centrifugation, washed with anhy-
drous toluene, dried under vacuum at 383 K for 3 h and reused if neces-
sary. An Agilent GC equipped with a flame-ionization detector (FID)
and a DB-5 column was used for the reaction analyses by using nonane
as an internal standard. The temperature program for GC analysis was
settled as follows: held at 1008C for 2 min., then heated from 100 to
2508C at 208CminÀ1 and held at this temperature for 10 min. Inlet and
detector temperatures were set at 250 and 2808C, respectively. The prod-
ucts were also identified by the ThermoFocus DSQ GC-MS chromato-
graph equipped with a FID and a HP-5 capillary column. MS results
were compared with the data in the NIST library.
Experimental Section
Chemicals: All starting materials were obtained from commercial sources
and used as received without any further purification unless otherwise
noted. 4-Chlorobenzyl bromide was purchased from Acros and 3,5-di-
tert-butylbenzyl bromide was purchased from TCI. Toluene and p-xylene
were distilled before use. H4pbdc was synthesized by the method de-
scribed previously.[41]
Characterization: Powder X-ray diffraction (PXRD) patterns were ob-
tained on a Bruker D8 powder diffractometer by using a CuKa1 radiation
(l=1.5405 ꢂ) at 40 kV, 40 mA with a scan speed of 0.2 s/step and a step
size of 0.028 (2q). To identify the accessible pore size for toluene, the
sorption isotherms were measured with an automatic gravimetric adsorp-
tion apparatus (IGA-001 series, Hiden Isochema Ltd.) at 298 K after
samples were degassed at 383 K for 12 h. SEM images and EDS were ob-
tained on a Philips XL-30 scanning electron microscope.
Synthesis of ZnPC-2, Hpd@ZnPC-2, and CoZnPC-2 catalysts: The lay-
ered-solvothermal synthesis method[41] was used to obtain high quality
crystals
of
{[Zn
(pbdc)2]·2H3O}n
(ZnPC-2)
and
{[Zn3-
ACHTUNGTRENNUNG
procedure was introduced for large-scale synthesis of the samples. For
the synthesis of ZnPC-2, triethylamine (0.121 g, 1.21 mmol) was added to
an isopropanol (5 mL) solution of H4pbdc (0.075 g, 0.31 mmol). The
white mixture was stirred until it became a clear solution. Then, the solu-
tion was added dropwise to another solution of ZnACTHNUTRGNE(UNG CH3COO)2·2H2O
(0.101 g, 0.46 mmol) in deionized water (5 mL) for 10 min. After that the
solution was stirred at room temperature for another 10 min and then
transferred into a teflon-lined stainless steel autoclave (15 mL). After
having been heated at 1408C for 2 d, the autoclaves were cooled down to
room temperature. The product of ZnPC-2 was collected by filtration
(yield of 56% based on H4pbdc). By replacing triethylamine by pyrroli-
dine, the product of Hpd@ZnPC was obtained (yield of 61% based on
H4pbdc).
Acknowledgements
We gratefully acknowledge the NSF of China (nos. 21041009 and
91027044) and the Ministry of Sciences and Technology (no.
2009CB623506) for financial support.
CoZnPC-2 was synthesized by the following procedure: Zn-
ACHTUNGTRENNUNG(CH3COO)2·2H2O (0.044 g, 0.20 mmol) and CoCAHTUNGTRNE(NUGN CH3COO)2·4H2O
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heated at 508C for 30 min. The resulting pink solution was transferred to
a teflon-lined stainless steel autoclave (15 mL) and then a solution of
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Received: April 22, 2011
Published online: August 4, 2011
10328
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