a 9-connected metal–organic framework with gas adsorption properties
TRANSCRIPT
Dynamic Article LinksC<Journal ofMaterials Chemistry
Cite this: J. Mater. Chem., 2011, 21, 15909
www.rsc.org/materials PAPER
Publ
ishe
d on
22
Aug
ust 2
011.
Dow
nloa
ded
by U
nive
rsity
of
Mic
higa
n L
ibra
ry o
n 30
/10/
2014
18:
18:4
1.
View Article Online / Journal Homepage / Table of Contents for this issue
A 9-connected metal–organic framework with gas adsorption properties†
Guojian Ren, Shuxia Liu,* Fengji Ma, Feng Wei, Qun Tang, Yuan Yang, Dadong Liang, Shujun Liand Yaguang Chen
Received 20th June 2011, Accepted 19th July 2011
DOI: 10.1039/c1jm12834e
A 9-connected, trinuclear cluster-based microporous metal–organic framework, Ni3(OH)
(Ina)3(BDC)1.5 (Ina ¼ isonicotinate and BDC ¼ 1,4-benzenedicarboxylate) (1), was synthesized and
characterized. The structure is constructed from a 3D channel and two kinds of cages (tetrahedron and
triangular pyramid cages). Compound 1 is microporous with a BET surface area of 1255 m2 g�1. It has
been observed that the amount of adsorbed benzene (22.60%) is much higher than that of cyclohexane
(1.40%), showing its potential to separate benzene and cyclohexane.
Introduction
Metal–organic frameworks (MOFs) and porous coordination
polymers (PCPs)1 have attracted intense interest due to their
aesthetics of diverse network structures and potential applica-
tions in gas storage,2 separation3 and catalysis.4 Despite the rapid
development of MOFs, the construction of MOFs with high
connectivity numbers (>6) remains challenging5 because
the construction of such systems are severely hampered by the
available number of coordination sites of metal centers and the
sterically demanding nature of organic ligands. MOFs with high
connectivity may show an enhanced stability and permanent
porosity for reversible gas adsorption. A few high-connected
MOFs with remarkable adsorption capacities have been repor-
ted.6 One developed way to construct high-connected frame-
works is using clusters as building blocks, since they can enhance
coordination number and reduce the steric hindrance of organic
ligands.7 Trinuclear clusters of the type [M3(m3-O)(O2C)6(X)3]n(M ¼ Cr, Fe, Ni, In, Sc, etc.)8 have been reported as building
blocks for MOF construction. Among most reported cases,
metal ions usually bonded to terminal molecules hamper further
connection.9 Two routes have been developed to replace the
terminal molecules so as to construct high-connected MOFs: (1)
Angular pyridyldicarboxylate ligands would not only act as
a bridging carboxylate but also involve the terminal pyridyl
N-donor to replace X in the trinuclear fragment.10 (2) Mixed
ligand applications is the other way of constructing high-con-
nectedMOFs, which are composed of dicarboxylate and pyridyl-
carboxylate ligands.11 ‘‘Simple, high-symmetry’’ structures are
always the most important plausible targets for the construction
Key Lab of Polyoxometalate Science, Department of Chemistry, NortheastNormal University, Changchun, 130024, P. R. China. E-mail: [email protected]
† Electronic supplementary information (ESI) available: Additionalfigures, tables of selected bond lengths and angles, bond valence andmagnetic susceptibility data, IR spectrum, H2, ethanol adsorption of 1.CCDC reference number 808418. See DOI: 10.1039/c1jm12834e
This journal is ª The Royal Society of Chemistry 2011
of MOFs.12 Here, we report a 9-connected MOF, Ni3(OH)
(Ina)3(BDC)1.5, with an ncb net and a high-symmetry I�43m space
group. The topology of the framework is (312,412,512), which was
confirmed by OLEX.13 The mixed-valence Ni3(OH)(CO2)6(N)3clusters act as 9-connected uninodal nodes. The adsorption
properties of the title compound for N2 and H2 are studied, and
the vapour adsorptions of ethanol, benzene (C6H6) and cyclo-
hexane (C6H12) are also measured. 1 exhibits a selective
adsorption property for C6H6 over C6H12.
Experimental section
Materials and methods
All the starting materials were purchased commercially as
reagent grade and used without further purification. The IR
spectra in KBr pellets were recorded in the range 400–4000 cm�1
with an Alpha Centaurt FT/IR spectrophotometer. Thermog-
ravimetric analyses were carried out by using a Perkin-Elmer
TGA7 instrument with a heating rate of 10 �C min�1 under
a nitrogen atmosphere. Powder X-ray diffraction measurements
were performed on a Rigaku D/MAX-3 instrument with Cu-KR
radiation. Magnetic susceptibility data were collected over the
temperature range 300–2 K at a magnetic field of 1000 Oe on
a Quantum Design MPMS-5 SQUID magnetometer.
Synthesis of 1
A mixture of Ni(NO3)2$6H2O (0.15 g, 0.5 mmol), BDC (0.10 g,
0.6 mmol) and Ina (Ina ¼ isonicotinate, 0.06 g, 0.5 mmol) were
dissolved in 12 mL DMF (N,N-dimethylformamide) and then
heated to 140 �C for 3 d in a stainless steel reactor with a Teflon
liner. After cooling to room temperature, green block crystals of
1 were obtained in 42% yield based on Ni.
J. Mater. Chem., 2011, 21, 15909–15913 | 15909
Table 1 Crystal data and structure refinement for 1
Formula C30H18N3Ni3O13
Formula weight 804.54 g mol�1
Crystal system CubicSpace group I�43m (no. 217)Unit cell dimensions a ¼ 21.6623(19) �A, a ¼ 90�
b ¼ 21.6623(19) �A, b ¼ 90�c ¼ 21.6623(19) �A, g ¼ 90�
Volume, Z 10165.1(15) A3, 8Density (calc.) 1.043 g cm�1
Absorption coefficient 1.148 mm�1
F(000) 3159Crystal size 0.271 � 0.212 � 0.192 mm3
Theta range for data collection 1.33 to 28.35�Limiting indices �28 # h # 28,
�27 # k # 28,�27 # l # 22
Publ
ishe
d on
22
Aug
ust 2
011.
Dow
nloa
ded
by U
nive
rsity
of
Mic
higa
n L
ibra
ry o
n 30
/10/
2014
18:
18:4
1.
View Article Online
Single-crystal X-ray crystallography
The reflection intensity data of 1 were collected on a SMART
CCD diffractometer equipped with graphite monochromatic
Mo-KR radiation (l ¼ 0.71073 �A) at 293 K. The linear
absorption coefficients, scattering factors for the atoms and
anomalous dispersion corrections were taken from the Interna-
tional Tables for X-Ray Crystallography. The structure was
solved by the direct method and refined by the full-matrix least-
squares method on F2 using the SHELXTL crystallographic
software package. All H atoms were placed geometrically for 1.
Anisotropic thermal parameters were used to refine all non-
hydrogen atoms. Solvents within the channels were not crystal-
lographically well defined, and these data were treated with the
SQUEEZE routine within PLATON.
Reflections collected 31197Independent reflections 2340 [Rint ¼ 0.1408]Refinement method Full-matrix least-squares on F2Data/restraints/parameters 2340/0/88Goodness-of-fit on F2 0.903Final R indices [I > 2s(I)] R1 ¼ 0.0388,
wR2 ¼ 0.0580R indices (all data) R1 ¼ 0.0559,
wR2 ¼ 0.0610Absolute structure parameter 0.01(2)Largest diff. peak and hole 0.208 and �0.305 e �A�3
Gas sorption measurements
Gas adsorption measurements were performed with a Hiden
Isochema Intelligent Gravimetric Analyser (IGA-100B). The
sample (ca. 100 mg) was out-gassed to a constant weight at 423 K
under a high vacuum (10–6 mbar) prior to the measurement of
isotherms. High purity gases (N2, 99.999%; H2, 99.9995%) were
used for the gas adsorption measurements performed at 77 K.
Temperatures were maintained with liquid nitrogen and
a constant-temperature water bath, respectively. All data were
rigorously corrected for the buoyancy of the system, samples and
adsorbates.
Fig. 1 (a) 9-Connected trinuclear cluster. (b) The trinuclear cluster unit
and a simplification of the two kinds of ligands (hydrogen atoms have
been omitted for clarity). (c) Two kinds of cages: orange (tetrahedral) and
yellow (triangular pyramid). (d) The 3D channel of 1 (purple column).
Results and discussion
Synthesis and crystal structure
The solvothermal reaction of Ni(NO3)2$6H2Owith BDC and Ina
in DMF gave block green crystals. It is worth noting that a little
water, excess BDC and control of the temperature are key to the
formation of 1. Partly deliquescent Ni(NO3)2$6H2O was chosen
as the Ni source, which may introduce a little water into this
reaction. It was observed that the Ina : BDC ratio in the
molecular formula was 2 : 1, while the excess BDC used probably
lead to a weakly acidity environment in DMF. Control of the
temperature in the reaction process was also essential. After
being heated to 140 �C under autogenous pressure for 3 d, the
bomb was cooled down to 100 �C at a rate of 10 �C h�1 and
maintained at this temperature for 10 h. After this, the bomb was
cooled to room temperature naturally.
The title compound was formulated as Ni3(OH)
(Ina)3(BDC)1.5 (1), established by a single-crystal X-ray diffrac-
tion analysis (Table 1). X-Ray crystallography revealed that 1
crystallizes in the highly symmetric cubic space group I�43m. Its
asymmetric unit consists of one crystallographically-independent
Ni, one m3-oxo, half a BDC and half an Ina. The O(2) atoms are
located on the crystallographic C3 axis. Ni(1) is ligated by four
oxygen atoms of four carboxylates, which are from two BDC and
two Ina, a nitrogen atom, which is located in the terminal posi-
tion from Ina, and a m3-O, showing an octahedral geometry.
Bond lengths around Ni(1) are Ni(1)–O(3) 2.0419(18) �A, Ni(1)–
O(1) 2.0712(17) �A, Ni(1)–N(1) 2.105(3) �A and Ni(1)–O(2) 2.0104
(6) �A. The angle of Ni(1)–O(2)–Ni(1) is 119.12(4)�. A trinuclear
15910 | J. Mater. Chem., 2011, 21, 15909–15913
cluster is constructed through three Ni atoms connecting with
a m3-oxo, 3 N-atoms and 6 carboxylates.
The trinuclear cluster is ligated by 3 BDC and 6 Ina (three Ina
are carboxylate-connected and the other three Ina are N-con-
nected) (Fig. 1(a)). The 9-connected trinuclear cluster could be
viewed as a tricapped trigonal prismatic node (Fig. 1(b)). A
tetrahedral cage is constructed from 4 nodes connected with
This journal is ª The Royal Society of Chemistry 2011
Publ
ishe
d on
22
Aug
ust 2
011.
Dow
nloa
ded
by U
nive
rsity
of
Mic
higa
n L
ibra
ry o
n 30
/10/
2014
18:
18:4
1.
View Article Online
6 BDC ligands, and each face of the tetrahedron is further con-
nected by 3 Ina ligands and a trinuclear cluster, forming
a triangular pyramid cage. A cage unit is composed of one
tetrahedron and 4 adjacent triangular pyramids, which contains
an 8 trinuclear cluster, 6 BDC and 12 Ina (Fig. 1(c)). It is well-
known that JABULANI (the ball of the FIFA World Cup 2010)
was made from eight spherically-moulded panels. It is observed
that each trinuclear cluster of the cage unit points to one of the
eight panels in the JABULANI sphere. The 9-connected MOF is
constructed through further connection of the cage unit, forming
a 3D channel (Fig. 1(d)). The diameter of the 3D channel is 7.0�A,
while the interior diameters of the tetrahedral cage and the
triangular pyramid cage are 7.8 and 7.0 �A, respectively.
MOFs with the same net and similar connection mode have
been reported by Chen and Xu.11 They adopted a strategy that
applied longer ligands for constructing the MOF with a larger
cage and channel. Generally speaking, highly connected MOFs
constructed by shorter ligands bear a stronger tensile force,
which may cause a reduction in stability. Here a 9-connected
MOF with shorter ligands, BDC and Ina, has been assembled.
Characterization
The TGA curve shows the main weight loss of about 24% under
220 �C, corresponding to the release of H2O and DMF guest
molecules. No weight loss is observed until 350 �C, and the
framework decomposes completely at about 430 �C (Fig. 2(a)).
As shown in Fig. 2(b), the power X-ray diffraction (PXRD) data
match the calculated X-ray pattern derived from the single
crystal structure very well, indicating that the bulk sample is the
Fig. 2 TGA curve and power X-ray diffraction (PXRD).
This journal is ª The Royal Society of Chemistry 2011
same as the single crystal. Compound 1 is insoluble in common
organic solvents such as DMF, EtOH, MeOH, chloroform,
acetone and 1,4-dioxane.
Adsorption of gases
The permanent porosity was evaluated by N2 adsorption at 77 K.
The N2 adsorption measurements indicate a reversible type-I
isotherm (Fig. 3(a)) characteristic of microporous materials.
The BET surface area and pore volume are 1255 m2 g�1 and
0.413 cm3 g�1. A Dubinin–Astakhov (DA) analysis of the
isotherm data reveals that the pore size is consistent with the X-
ray analysis (Fig. 3(a), insert). The high porosity and stable
framework make 1 a good candidate for gas storage. Hydrogen
sorption was measured under 1 bar and 20 bar at 77 K in order to
evaluate the hydrogen storage performance. As shown in Fig. 3
(b), 1 can adsorb 1.40 wt% (162 cm3 g�1) at 77 K. The amount
adsorbed is comparable with that of other reported MOFs
having similar trinuclear clusters, which is inferior to 12-con-
nected trinuclear cluster frameworks (1.99 wt%),6a comparable
with MCP-19 (1.56 wt%)11a and higher than PCN-19 (0.95 wt
%).9a When the pressure is increased to 20 bar, the hydrogen
uptake of 1 can reach 2.30 wt% at 77 K (Fig. S3, ESI†).
The porosity of 1 was further verified by vapour adsorption.
The adsorption isotherm of ethanol vapour was measured at
298 K. The ethanol adsorption isotherm exhibits a two-step
Fig. 3 (a) N2 volumetric adsorption isotherm of 1 at 77 K. Insert: pore
size distributions calculated from the DA equation. (b) H2 gravimetric
adsorption isotherm of 1 at 77 K. Filled and open symbols for (a) and (b)
represent adsorption and desorption, respectively.
J. Mater. Chem., 2011, 21, 15909–15913 | 15911
Fig. 4 (a) Benzene (C) and (b) cyclohexane (:) sorption isotherms of 1
at 298 K.
Publ
ishe
d on
22
Aug
ust 2
011.
Dow
nloa
ded
by U
nive
rsity
of
Mic
higa
n L
ibra
ry o
n 30
/10/
2014
18:
18:4
1.
View Article Online
adsorption.14 As shown in Fig. S4, ESI†, it shows a stepwise
isotherm that represents a sharp increase when the relative
pressure is 0.19. The amount adsorbed was 29.90 wt% when
relative pressure reached 0.95, which is equivalent to the
adsorption of 7.40 molecules of ethanol per formula unit. In
order to further characterize the adsorption of 1, C6H6 and
C6H12 adsorption studies were carried out. As shown in Fig. 4(a)
and 4(b), the amount adsorbed for C6H6 and C6H12 was 22.60
and 1.40 wt%, respectively (respectively, 3 and 0.14 molecules per
formula unit). It is obvious that C6H6 adsorption is 16-times that
of C6H12, which is higher than the 12-times and 2-times values
previously reported.15,16b Compared with other porous adsorp-
tion materials, such as molecular sieves, compound 1 also shows
an advantageous adsorption of C6H6.19 At the beginning range
of the sorption isotherm, the amount of C6H6 adsorbed is much
higher than that of C6H12, probably because of p–p interactions
between the C6H6 guest and the phenyl ring of BDC.16 As p/p0increases, the adsorption of C6H6 also increases. It is assumed
that the number of C6H6 molecules in the tetrahedral cages (the
larger cages) increases when p/p0 is increased; that is, the C6H6
molecules first enter into the small cages and then go into the
larger ones. Such a process has been clarified through inelastic
neutron scattering in other MOF adsorption performances that
also contain two kinds of cage.17 Meanwhile, the adsorption of
C6H12 is not evidently increased along with p/p0 increases,
probably because of only particle surface adsorption. It is well
known that C6H6 and C6H12 have similar boiling points and are
difficult to separate. The selective sorption of C6H6 over C6H12
provides a separation opportunity in the petroleum industry and
in the industrial hydrogenation of benzene to cyclohexane.18
Conclusions
In summary, a 9-connected trinuclear cluster-based metal–
organic framework has been rationally synthesized and charac-
terized. Two simple ligands, Ina and BDC, were applied during
the solvothermal reaction. The title compound shows a two-step
adsorption towards ethanol, probably due to the distribution of
the channel and cages of the framework. Due to p–p interactions
between the benzene and phenyl ring of BDC, and the two kinds
of cages of the framework, it can selectively adsorb C6H6 over
C6H12, which have similar boiling points, providing a potential
15912 | J. Mater. Chem., 2011, 21, 15909–15913
industrial application. Further work is planned to construct
more ‘‘simple, high-symmetry’’ MOFs that may have gas
adsorption, separation, catalysis or other applications.
Acknowledgements
This work was supported by the NSFC (Grant nos. 20871027
and 20973035), the Program for New Century Excellent Talents
in University (NCET - 07 - 0169), the Fundamental Research
Funds for the Central Universities (Grant no. 09ZDQD0015)
and the Program for Changjiang Scholars and Innovative
Research Team in University.
References
1 G. F�erey, Chem. Soc. Rev., 2008, 37, 191; D. J. Tranchemontagne,J. L. Mendoza-Cort�es, M. O’Keeffe and O. M. Yaghi, Chem. Soc.Rev., 2009, 38, 1257; J. J. Perry IV, J. A. Perman andM. J. Zaworotko, Chem. Soc. Rev., 2009, 38, 1400.
2 Y. L. Liu, V. C. Kravtsov and M. Eddaoudi, Angew. Chem., Int. Ed.,2008, 47, 8446; C. S. Lim, J. K. Schnobrich, A. J. Wong-Foy andA. J. Matzger, Inorg. Chem., 2010, 49, 5271.
3 N. Dybtsev, H. Chun, S. H. Yoon, D. Kim and K. Kim, J. Am. Chem.Soc., 2004, 126, 32; J. R. Li and H. C. Zhou, Chem. Soc. Rev., 2009,38, 1477; S. Q. Ma, D. F. Sun, D. Q. Yuan, X. S. Wang andH. C. Zhou, J. Am. Chem. Soc., 2009, 131, 6445.
4 J. Lee, O. K. Farha, J. Roberts, K. A. Scheidt, S. T. Nguyen andJ. T. Hupp, Chem. Soc. Rev., 2009, 38, 1450; K. Gedrich,M. Heitbaum, A. Notzon, I. Senkovska, R. Fr€ohlich,J. Getzschmann, U. Mueller, F. Glorius and S. Kaskel, Chem.–Eur.J., 2011, 17, 2099; S. H. Cho, B. Ma, S. T. Nguyen, J. T. Hupp andT. E. Albrecht-Schmitt, Chem. Commun., 2006, 2563.
5 T. T. Luo, H. L. Tsai, S. L. Yang, Y. H. Liu, R. D. Yadav, C. C. Su,C. H. Ueng, L. G. Lin and K. L. Lu,Angew. Chem., Int. Ed., 2005, 44,6063; H. Chun, D. Kim, D. N. Dybtsev and K. Kim, Angew. Chem.,Int. Ed., 2004, 43, 971; Z. J. Zhang, S. C. Xiang, Q. Zheng, X. T. Rao,J. U. Mondal, H. D. Arman, G. D. Qian and B. L. Chen, Cryst.Growth Des., 2010, 10, 2372; J. J. Morris, B. C. Noll andK. W. Henderson, Chem. Commun., 2007, 5191.
6 J. H. Jia, X. Lin, C. Wilson, A. J. Blake, N. R. Champness,P. Hubberstey, G. Walker, E. J. Cussen and M. Schr€oder, Chem.Commun., 2007, 840; L. Hou, J. P. Zhang, X. M. Chen andS. W. Ng, Chem. Commun., 2008, 4019.
7 H. Li, M. Eddaoudi, M. O’Keeffe and O. M. Yaghi, Nature, 1999,402, 276; P. Horcajada, S. Surbl�e, C. Serre, D. Y. Hong, Y. K. Seo,J. S. Chang, J.-M. Gren�eche, I. Margiolaki and G. F�erey, Chem.Commun., 2007, 2820; L. H. Xie, S. X. Liu, B. Gao, C. D. Zhang,C. Y. Sun, D. H. Li and Z. M. Su, Chem. Commun., 2005, 2402;L. H. Xie, S. X. Liu, C. Y. Gao, R. G. Cao, J. F. Cao, C. Y. Sunand Z. M. Su, Inorg. Chem., 2007, 46, 7782.
8 G. F�erey, C. Mellot-Draznieks, C. Serre, F. Millange, J. Dutour,S. Surbl�e and I. Margiolaki, Science, 2005, 309, 2040; A. C. Sudik,A. P. Cot�e, A. G. Wong-Foy, M. O’Keeffe and O. M. Yaghi,Angew. Chem., Int. Ed., 2006, 45, 2528; S. Q. Ma, X. S. Wang,E. S. Manis, C. D. Collier and H. C. Zhou, Inorg. Chem., 2007, 46,3432; Y. L. Liu, J. F. Eubank, A. J. Cairns, J. Eckert,V. C. Kravtsov, R. Luebke and M. Eddaoudi, Angew. Chem., Int.Ed., 2007, 46, 3278; I. A. Ibarra, X. Lin, S. Yang, A. J. Blake,G. S. Walker, S. A. Barnett, D. R. Allan, N. R. Champness,P. Hubberstey and M. Schr€oer, Chem.–Eur. J., 2010, 16, 13671.
9 S. Q. Ma, J. M. Simmons, D. Q. Yuan, J. R. Li, W. Weng, D. J. Liuaand H. C. Zhou, Chem. Commun., 2009, 4049; A. C. Sudik, A. P. Cot�eand O. M. Yaghi, Inorg. Chem., 2005, 44, 2998.
10 X. M. Zhang, Y. Z. Zheng, C. R. Li, W. X. Zhang and X. M. Chen,Cryst. Growth Des., 2007, 7, 980.
11 Y. B. Zhang, W. X. Zhang, F. Y. Feng, J. P. Zhang and X. M. Chen,Angew. Chem., Int. Ed., 2009, 48, 5287; X. J. Gu, Z. H. Lu and Q. Xu,Chem. Commun., 2010, 46, 7400.
12 O. D. Friedrichs, M. O’Keeffe and O. M. Yaghi, Acta Crystallogr.,Sect. A: Found. Crystallogr., 2003, 59, 22; O. D. Friedrichs,M. O’Keeffe and O. M. Yaghi, Acta Crystallogr., Sect. A: Found.
This journal is ª The Royal Society of Chemistry 2011
Publ
ishe
d on
22
Aug
ust 2
011.
Dow
nloa
ded
by U
nive
rsity
of
Mic
higa
n L
ibra
ry o
n 30
/10/
2014
18:
18:4
1.
View Article Online
Crystallogr., 2003, 59, 515; X. C. Huang, Y. Y. Lin, J. P. Zhang andX.M. Chen,Angew. Chem., Int. Ed., 2006, 45, 1557; J. P�erez-Pellitero,H. Amrouche, F. R. Siperstein, G. Pirngruber, C. Nieto-Draghi,G. Chaplais, A. Simon-Masseron, D. Bazer-Bachi, D. Peralta andN. Bats, Chem.–Eur. J., 2010, 16, 1560.
13 O. V. Dolomanov, A. J. Blake, N. R. Charmpness and M. Schr€oder,J. Appl. Crystallogr., 2003, 36, 1283.
14 S. Horike, D. Tanaka, K. Nakagawa and S. Kitagawa, Chem.Commun., 2007, 3395; L. Hou, Y. Y. Lin and X. M. Chen, Inorg.Chem., 2008, 47, 1346.
15 R. Yang, L. Li, Y. Xiong, J. R. Li, H. C. Zhou and C. Y. Su, Chem.–Asian J., 2010, 5, 2358.
This journal is ª The Royal Society of Chemistry 2011
16 H. Ren, T. Ben, E. S. Wang, X. F. Jing, M. Xue, B. B. Liu, Y. Cui,S. L. Qiu and G. S. Zhu, Chem. Commun., 2010, 46, 2913; J. B. Lin,J. P. Zhang, W. X. Zhang, W. Xue, D. X. Xue and X. M. Chen,Inorg. Chem., 2009, 48, 6652.
17 V. K. Peterson, Y. Liu, C. M. Brown and C. J. Kepert, J. Am. Chem.Soc., 2006, 128, 15578; Y. Liu, C. M. Brown, D. A. Neumann,V. K. Peterson and C. J. Kepert, J. Alloys Compd., 2007, 446–447, 385.
18 D.W. Breck, Zeolite Molecular Sieves: Structure, Chemistry, and Use,Wiley, Toronto, 1974, ch. 8.
19 M. Hartmann and C. Bischof, J. Phys. Chem. B, 1999, 103, 6230;S. P. Mirajkar, A. Thangaraj and V. P. Shirakar, J. Phys. Chem.,1992, 96, 3073.
J. Mater. Chem., 2011, 21, 15909–15913 | 15913