Design of novel bilayer compounds of the CPO-8 type containing 1D channels

Article abstract of DOI:10.1021/ic050662v

The reaction between Zn(NO₃)₂·6H₂O and 5-aminoisophthalic acid (aip) in a mixture of diethylformamide (DEF) and ethanol resulted in [Zn(C₈H₅NO₄)(C ₅H₁₁NO)]_n (CPO-8-DEF). This compound is composed of infinite 2D layers with tetrahedral Zn atoms and aip ligands in a triangular topology. The DEF molecules are bonded to Zn, and within each layer, the DEF molecules are oriented in the same direction, while in the subsequent layer, the DEF molecules are oriented in the opposite direction. By introduction of the pillaring ligands 4,4-bipyridine (BPY), 1,2-di-4-pyridylethylene (DPE), 1,2-di-4-pyridylethane (DPA), and 1,3-di-4-pyridylpropane (DPP) into mixtures of N,N′-dimethylformamide and water with Zn(NO₃)₂ and aip, we have successfully synthesized a series of related pillared bilayer compounds with the same common triangular Zn(aip) layer structural motif as that observed in CPO-8-DEF. The compounds are denoted as CPO-8-BPY ([Zn(C ₈H₅NO₄)(C₁₀H₈N ₂)_0.5]_n·3nH₂O), CPO-8-DPE ([Zn(C₈H₅NO₄)-(C₁₂H ₁₀N₂)_0.5]_n·2.5nH ₂O), CPO-8-DPA ([Zn(C₈H₅NO₄)(C ₁₂H₁₂N₂)_0.5]_n·2. 5nH₂O), and CPO-8-DPP ([Zn(C₈H₅NO ₄)-(C₁₃H₁₄N₂)_0.5] _n·3nH₂O). In all cases, the pillars create spaces inside the bilayers that result in 1D channels running along the [010] directions with dimensions of 3.5 x 6.7 A². These channels contain water molecules that can be removed on heating to 150°C, resulting in porous structures. The crystal structures of these porous high-temperature variants have been determined on the basis of powder X-ray diffraction data. All of the compounds show preferential adsorption of H₂ over N ₂ at 77 K.

Full text of DOI:10.1021/ic050662v

Inorg. Chem. 2006, 45, 2424−2429
Design of Novel Bilayer Compounds of the CPO-8 Type Containing 1D
Channels
Kjell Ove Kongshaug and Helmer Fjellvåg*
Department of Chemistry, UniVersity of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway
Received April 29, 2005
The reaction between Zn(NO3)2‚6H2O and 5-aminoisophthalic acid (aip) in a mixture of diethylformamide (DEF)
and ethanol resulted in [Zn(C8H5NO4)(C5H11NO)]n (CPO-8-DEF). This compound is composed of infinite 2D layers
with tetrahedral Zn atoms and aip ligands in a triangular topology. The DEF molecules are bonded to Zn, and
within each layer, the DEF molecules are oriented in the same direction, while in the subsequent layer, the DEF
molecules are oriented in the opposite direction. By introduction of the pillaring ligands 4,4-bipyridine (BPY), 1,2-
di-4-pyridylethylene (DPE), 1,2-di-4-pyridylethane (DPA), and 1,3-di-4-pyridylpropane (DPP) into mixtures of N,N′-
dimethylformamide and water with Zn(NO3)2 and aip, we have successfully synthesized a series of related pillared
bilayer compounds with the same common triangular Zn(aip) layer structural motif as that observed in CPO-8-DEF.
The compounds are denoted as CPO-8-BPY ([Zn(C8H5NO4)(C10H8N2)0.5 n
]
‚
3nH2O), CPO-8-DPE ([Zn(C8H5NO4)-
2.5nH2O), and CPO-8-DPP ([Zn(C8H5NO4)-
3nH2O). In all cases, the pillars create spaces inside the bilayers that result in 1D channels running
6.7 Å2. These channels contain water molecules that can be
C, resulting in porous structures. The crystal structures of these porous high-temperature
(C12H10N2)0.5 n
]
‚
‚
2.5nH2O), CPO-8-DPA ([Zn(C8H5NO4)(C12H12N2)0.5 n
]
‚
(C13H14N2)0.5 n
]
along the [010] directions with dimensions of 3.5
removed on heating to 150
×
°
variants have been determined on the basis of powder X-ray diffraction data. All of the compounds show preferential
adsorption of H2 over N2 at 77 K.
Introduction
The MOF type of compounds offers great scope for the
rational design of solids with pores of defined size, shape,
and chemical environment. This represents the so-called
bottom-up method. However, synthetic chemistry is not yet
developed to a stage where pore structures can be designed.
Hence, the exploratory synthetic approach is still ruling the
field, where the discovery of novel compounds is mostly
serendipitous using methods referred to by critics as “shake
and bake” or “mix and wait”. A great motivation is thus to
develop controlled synthetic techniques for these extreme
complex systems.
Recently, the concept of the secondary building unit (SBU)
has been advanced for the understanding and prediction of
the topologies of MOF structures. Yaghi and co-workers12
have defined the concept of recticular synthesis, indicating
topological rules that govern the design of MOF types of
compounds. These concepts start from the existence of well-
defined inorganic SBUs and organic linker molecules that
maintain their structural integrity throughout the construction
The construction of polymeric metal-organic frameworks
(MOFs) is currently attracting considerable attention because
of the possible application for such compounds in areas such
as separation, catalysis, ion exchange, and gas storage.1-11
* To whom correspondence should be addressed. E-mail:
helmer.fjellvag@kjemi.uio.no. Tel: +4722855564. Fax: +4722855565.
(1) Yaghi, O. M.; Davis, C. E.; Li, G. M.; Li, H. L. J. Am. Chem. Soc.
1997, 119, 2861.
(2) Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim, K.
Nature 2000, 404, 982.
(3) Bennett, M. V.; Shores, M. P.; Beauvais, L. G.; Long, J. R. J. Am.
Chem. Soc. 2000, 122, 6664.
(4) Blom, R.; Heyn, R. H.; Swang, O.; Fjellvåg, H.; Kongshaug, K. O.;
Nielsen, R. K. B. Chem. Eng. Trans. 2004, 4, 325.
(5) Janiak, C. Dalton Trans. 2003, 2781.
(6) Mori, W.; Takamizawa, S.; Kato, C. N.; Ohmura, T.; Sato, T.
Microporous Mesoporous Mater. 2004, 73, 31.
(7) Rosseinsky, M. J. Microporous Mesoporous Mater. 2004, 73, 15.
(8) Ferey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F. Acc. Chem.
Res. 2005, 38, 217.
(9) Ferey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F.; Dutour, J.;
Surble, S.; Margiolaki, I. Science 2005, 309, 2040.
(10) Kitagawa, S.; Uemura, K. Chem. Soc. ReV. 2005, 34, 109.
(11) Rowsell, J. L. C.; Yaghi, O. M. Angew. Chem., Int. Ed. 2005, 44,
4670.
(12) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi,
M.; Kim, J. Nature 2003, 423, 705.
2424 Inorganic Chemistry, Vol. 45, No. 6, 2006
10.1021/ic050662v CCC: $33.50
© 2006 American Chemical Society
Published on Web 02/11/2006

Design of Bilayer Compounds
based on Zn. Anal. Calcd for C13H16N2O5Zn (%): C, 45.17; H,
4.66; N, 8.11. Found (%): C, 44.27; H, 4.56; N, 8.02.
process of the solid. Different combinations of inorganic
SBUs and organic linker molecules may assemble by strong
bonding to ordered structures showing topologies of dense
structures. Ferey and co-workers13 have developed these
concepts further by the introduction of a computational
approach for the enumeration of the possible frameworks
accessible from the building blocks. They proved the strength
of the method by being able to define structures known in
the literature by starting from their organic and inorganic
building blocks, and, interestingly, they also predicted
topologies for which no material is yet synthesized.
In the concept of recticular synthesis of porous MOF
structures, the inorganic SBUs tend to consist of a limited
number of metal centers. However, larger structural motifs
might also lead to porous MOF structures. In particular, 2D-
layered structural motifs can be pillared into 3D porous
pillared layer structures. This approach has been applied by
Kitagawa et al.,14 Seki and Mori,15 and Kim et al.16 to obtain
3D porous MOF compounds. Clearfield and co-workers have
also used this approach to produce porous zirconium diphos-
phate compounds.17,18 Such synthetic systems might be very
attractive because they enable possible control of both the
pore size and chemical functionality of the pores via
modification of the pillar module.
Synthesis of [Zn(C8H5NO4)(C10H8N2)0.5]n‚3nH2O (CPO-8-
BPY). The reagent mixture along with 4,4′-bipyridine (BPY; 0.094
g, 0.6 mmol), N,N′-dimethylformamide (DMF; 8.0 mL), and water
(8.0 mL) was heated to 120 °C for 24 h. The yield was 70% based
on Zn. Anal. Calcd for C13H15N2O7Zn (%): C, 41.45; H, 4.01; N,
7.43. Found (%): C, 43.09; H, 3.63; N, 7.18.
Synthesis of [Zn(C8H5NO4)(C12H10N2)0.5]n‚2.5nH2O (CPO-8-
DPE). The reagent mixture along with 1,2-di-4-pyridylethylene
(DPE; 0.109 g, 0.6 mmol), DMF (8.0 mL), and water (8.0 mL)
was heated to 105 °C for 24 h. The yield was 60% based on Zn.
Anal. Calcd for C28H30N4O13Zn2 (%): C, 44.17; H, 3.97; N, 7.36.
Found (%): C, 44.60; H, 3.81; N, 7.09.
Synthesis of [Zn(C8H5NO4)(C12H12N2)0.5]n‚2.5nH2O (CPO-8-
DPA). The reagent mixture along with 1,2-di-4-pyridylethane
(DPA; 0.111 g, 0.6 mmol), DMF (8.0 mL), and water (8.0 mL)
was heated to 120 °C for 24 h. The yield was 55% based on Zn.
Anal. Calcd for C28H32N4O13Zn2 (%): C, 44.05; H, 4.22; N, 7.34.
Found (%): C, 45.10; H, 3.95; N, 7.11.
Synthesis of [Zn(C8H5NO4)(C13H14N2)0.5]n‚3nH2O (CPO-8-
DPP). The reagent mixture along with 1,3-di-4-pyridylpropane
(DPP; 0.357 g, 1.8 mmol), DMF (8.0 mL), and water (8.0 mL)
was heated to 100 °C for 24 h. The yield was 50% based on Zn.
Anal. Calcd for C29H36N4O14Zn2 (%): C, 43.78; H, 4.56; N, 7.04.
Found (%): C, 44.25; H, 4.23; N, 6.90.
Single-Crystal X-ray Diffraction Analysis. Single-crystal X-ray
diffraction data for the CPO-8 type compounds were collected at
room temperature on a Siemens diffractomer equipped with a
Bruker-Nonius ApexII CCD detector. Data reduction and empirical
absorption correction were carried out using the programs SAINT19
and SADABS,20 respectively. The crystal structures were solved by
direct methods and refined using the WinGX program.21 Non-H
atoms was refined anisotropically. The organic H atoms were
generated geometrically and refined in the riding mode. The
refinements for the structures CPO-8-DEF and CPO-8-DPA ended
in relatively high reliability factors (0.089 and 0.114), despite several
data collections on different crystals. The crystallographic data and
details on the refinements for all compounds are listed in Table 1.
Powder X-ray Diffraction Analysis. Powder X-ray diffraction
data for all of the dehydrated CPO-8 type compounds (except CPO-
8-DEF) were collected in transmission mode with a Siemens D5000
diffractometer using Cu KR1 (λ ) 1.540 598 Å) radiation selected
with an incident-beam germanium monochromator. The detector
was a Braun position-sensitive detector. The samples were dehy-
drated at 150 °C for 8 h, and then they were kept in a 0.5-mm-
diameter sealed borosilicate capillary. The diffraction patterns were
collected over 24 h for the 2θ range of 5-80°.
In this paper, we present a synthetic system that provides
a structure type denoted as CPO-8. Four different pillars have
been introduced into the system, all leading to this structure
type that consists of porous pillared bilayers with 1D
channels.
Experimental Section
All syntheses were performed in Teflon-lined steel autoclaves
under autogenous pressure. Reagents were purchased commercially
and used without further purification. Thermogravimetric analysis
(TGA) measurements were carried out on a Perkin-Elmer thermo-
gravimetric analyzer in a N2 gas stream using a heating rate of 5
°C/min. The N2 and H2 gas sorption isotherm measurements were
carried out at 77 K. The experiments for N2 were performed using
a BELSORP mini instrument, while the H2 experiments were done
using a Quantachrome Autosorb-1 instrument. Prior to the measure-
ments, the samples were dried under a high vacuum at 150 °C for
18 h to remove the solvated water molecules.
For all compounds, Zn(NO3)2‚6H2O (179 mg, 0.6 mmol) and
5-aminoisophthalic acid (aip; 110 mg, 0.6 mmol) were used as
reagents. The light-brown crystalline products (brown for CPO-8-
DEF) were washed with water (DEF for CPO-8-DEF) and dried in
air at room temperature. Additional specific information is given
in the following:
The diffraction patterns were all indexed from the first 20 Bragg
reflections with the program TREOR-90.22 In all cases, the unit
cell dimensions are quite similar to those of the as-synthesized
compounds, and hence good starting models for the structures could
be built. By means of the Accelrys software, the water molecules
were removed from the structure descriptions. The starting models
were transferred into the GSAS program23 for Rietveld analysis.
Refinements of scale, background, zero point, and unit cell
Synthesis of [Zn(C8H5NO4)(C5H11NO)]n (CPO-8-DEF). The
reagent mixture along with ethanol (2.5 mL) and diethylformamide
(DEF; 7.5 mL) was heated to 95 °C for 24 h. The yield was 65%
(13) Mellot-Draznieks, C.; Dutour, J.; Ferey, G. Angew. Chem., Int. Ed.
2004, 43, 6290.
(14) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43,
(19) SAINT, version 7.06a; Bruker AXS Inc.: Madison, WI.
(20) SADABS, version 2.10; Bruker AXS Inc.: Madison, WI.
(21) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(22) Werner, P. E.; Eriksson, L.; Westdahl, J. J. Appl. Crystallogr. 1985,
18, 367.
2334.
(15) Seki, K.; Mori, W. J. Phys. Chem. B 2002, 106, 1380.
(16) Dybtsev, D. N.; Chun, H.; Kim, K. Angew. Chem., Int. Ed. 2004, 43,
5033.
(17) Wang, Z.; Heising, J. M.; Clearfield, A. J. Am. Chem. Soc. 2003, 125,
10375.
(18) Clearfield, A.; Wang, Z. K. J. Chem. Soc., Dalton Trans. 2002, 2937.
(23) Larson, A. C.; von Dreele, R. B. Los Alamos National Laboratory
Report LA-UR-86-784; Los Alamos National Laboratory: Los Ala-
mos, NM, 1987.
Inorganic Chemistry, Vol. 45, No. 6, 2006 2425

Kongshaug and Fjellvåg
Table 1. Crystal and Structure Refinement Data for CPO-8-Type Compoundsa
CPO-8-DEF
CPO-8-BPY
CPO-8-DPE
CPO-8-DPA
CPO-8-DPP
formula
fw
C13H16N2O5Zn
345.65
C13H15N2O7Zn
376.64
C28H30N4O13Zn2
761.30
C28H32N4O13Zn2
763.32
C29H36N4O14Zn2
795.36
T (K)
298
298
298
298
298
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
11.2615(18)
7.6501(12)
16.284(3)
90
92.921(5)
90
1401.0(4)
4
monoclinic
P21/c
12.4676(9)
7.6792(6)
16.1832(12)
90
108.963(2)
90
1465.31(19)
4
monoclinic
C2/c
26.5106(19)
7.4518(5)
16.3890(12)
90
114.0290(10)
90
2957.1(4)
4
monoclinic
C2/c
26.544(6)
7.4487(16)
16.339(4)
90
113.588(5)
90
2960.6(11)
4
orthorhombic
Pna21
16.205(4)
7.6783(16)
25.247(5)
90
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
90
90
3141.2(12)
4
1.682
1.606
1.61, 20.81
23654
Dc (g/cm3)
1.639
1.776
1.81, 23.26
13989
1.707
1.716
1.73, 26.51
18034
1.710
1.699
1.68, 26.41
16594
1.713
1.697
1.67, 27.24
19000
µ (mm-1
)
θ
min, θmax (deg)
no. of reflns
no. of unique reflns (Rint
no. of obsd reflns [I > 2σ(I)]
no. of param
)
2015 (0.0983)
1242
208
3021 (0.0360)
2394
219
3000 (0.0353)
2501
213
3268 (0.0406)
2789
213
3288 (0.1873)
3288
442
GOF
0.956
1.056
1.058
1.088
0.923
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
∆F (e/Å3)
0.0478, 0.1177
0.0890, 0.1332
0.496, -0.647
0.0377, 0.0933
0.0510, 0.1007
0.847, -0.824
0.0317, 0.0825
0.0417, 0.0866
0.691, -0.581
0.0404, 0.1034
0.0486, 0.1085
0.684, -0.615
0.0573, 0.1298
0.1138, 0.1494
0.312, -0.699
a The calculated standard deviations are given in parentheses.
Table 2. Experimental Conditions and Relevant Data for Rietveld Refinements of CPO-8 Types of Compounds at 150 °Ca
CPO-8-BPY-150
CPO-8-DPE-150
CPO-8-DPA-150
CPO-8-DPP-150
formula
fw
C13H9N2O4Zn
322.61
6-80
C28H20N4O8Zn2
671.22
5-80
C28H22N4O8Zn2
673.24
5-80
C29H24N4O8Zn2
687.26
5-80
0.015 43
1.540 598
orthorhombic
Pna21
16.0405(4)
7.65135(18)
25.1087(5)
90
pattern range 2θ (deg)
step size ∆2θ (deg)
wavelength (Å)
cryst syst
space group
a (Å)
0.015 43
1.540 598
monoclinic
P21/c
11.58082(32)
7.70682(20)
15.9980(4)
90
107.6361(19)
90
1360.74(6)
4
0.015 43
1.540 598
monoclinic
C2/c
25.9183(9)
7.43553(30)
16.2652(6)
90
113.1355(24)
90
2882.47(20)
4
0.015 43
1.540 598
monoclinic
C2/c
26.0448(9)
7.44817(29)
16.2399(6)
90
113.3305(24)
90
2892.74(19)
4
b (Å)
c (Å)
R (deg)
â (deg)
90
90
γ (deg)
V (Å3)
3081.64(12)
4
Z
no. of obsns
no. of reflns
no. of refined param
Rp
4817
856
92
0.0609
0.0789
0.0756
4872
965
94
0.0342
0.0498
0.0582
4872
949
97
0.0702
0.0948
0.0772
4943
1058
160
0.0423
0.0566
0.0671
Rwp
2
RF
a The calculated standard deviations are given in parentheses.
dimensions were followed by refinements of the atomic coordinates.
The atomic coordinates were refined with soft constraints being
introduced: d(C-C) ) 1.39(2) Å, d(C-N) ) 1.35(2) Å, and d(C-
O) ) 1.26(2) Å. In addition, d(C-C) ) 2.41(3) Å and d(C-N) )
2.39(3) Å were constrained in order to keep the angles in the
aromatic rings near 120°. Isotropic displacement parameters were
refined, and common parameters were adopted for C, N, and O.
The contribution of the H atoms to the scattered intensity was
neglected. The weight on the soft constraints could not be
completely relaxed. For details of the refinements, see Table 2.
The observed, calculated, and difference diffraction profiles from
the refinements are shown in Figure 1.
thermal synthesis with water as the solvent. Its crystal
structure contains infinite 2D layers with tetrahedral Zn atoms
and aip ligands in a triangular topology (Figure 2a). Each
Zn is coordinated to three different aip ligands through two
monodentate carboxylate groups and one amino group. A
terminal water molecule constitutes the fourth coordination
bond of Zn. All terminal water molecules of a given layer
are oriented in the same direction (Figure 2b). In the
subsequent layer, the water molecules are oriented in the
opposite direction. These layers are linked into pairs by
strong H-bonding interactions.
By replacing water as a solvent in the synthesis reported
by Wu et al. with a mixture of DEF and ethanol, we obtained
Results and Discussion
Recently, Wu et al.24 obtained a novel coordination
polymer based on Zn and aip, [Zn(aip)(H2O)]n, by hydro-
(24) Wu, C. D.; Lu, C. Z.; Yang, W. B.; Zhuang, H. H.; Huang, J. S. Inorg.
Chem. 2002, 41, 3302.
2426 Inorganic Chemistry, Vol. 45, No. 6, 2006

Design of Bilayer Compounds
Figure 1. Observed, calculated, and difference powder X-ray diffraction profiles for (a) CPO-8-BPY, (b) CPO-8-DPE, (c) CPO-8-DPA, and (d) CPO-8-
DPP.
a compound denoted as CPO-8-DEF, whose the crystal
structure is related to that of [Zn(aip)(H2O)]n. In CPO-8-
DEF, one finds the same type of 2D dense triangular layers;
however, DEF molecules now replace the terminal water
molecules. Within each layer, the DEF molecules are oriented
in the same direction (Figure 3), while in the subsequent
layer, the DEF molecules are oriented in the opposite
direction. This leads to increased interlayer distance com-
pared with that of [Zn(aip)(H2O)]n simply because the more
spacious DEF molecules replace the water molecules; see
Figure 3. The layers are connected by H bonds between the
amino groups of one layer and the carboxylate O atoms of
the subsequent layer [d(N‚‚‚O1) ) 3.041(6) Å and d(N‚‚‚
O3) ) 3.019(6) Å]. The ethyl groups of the DEF molecules
are disordered.
On the basis of synthetic reports and the crystal structures
of [Zn(aip)(H2O)]n and CPO-8-DEF, there are two distinct
observations that act as guidelines for a more general route
toward the construction of novel structures. First, the
triangular layer appears as a preferred reaction product in
reactions between Zn salts and the aip ligand under different
synthetic conditions. Second, for this layer component, the
fourth coordination bond around Zn is directed toward the
interlamellar space and is exchangeable. By the introduction
of bifunctional ligands into a synthetic system that forms
Zn(aip) triangular layers, one would expect the formation
of a pillared bilayer framework structure with 1D channels.
We have indeed discovered such a system. By the introduc-
tion of BPY, DPE, DPA, and DPP into mixtures of DMF
and water with Zn(NO3)2 and aip, we have successfully
synthesized a series of related pillared bilayer compounds
with a common triangular Zn(aip) layer structural motif.
The crystal structure of CPO-8-BPY is a unique pillared
bilayer structure. The same triangular layers as those
identified in [Zn(aip)(H2O)]n and CPO-8-DEF are present.
The bilayers formed with BPY ligands as the connectors are
stacked along the [100] direction (Figure 4). These bilayers
are, furthermore, interconnected by H bonds between the
amino groups and the carboxylate O atoms {d[N(1)‚‚‚O(2)]
) 3.049(3) Å and d[N(1)‚‚‚O(3)] ) 3.100(3) Å}. The BPY
pillars create spaces inside the bilayers that result in 1D
channels running along the [010] direction with dimensions
of 3.5 × 6.7 Å2 (Figure 4). These channels contain three
water molecules per formula unit. One of the water molecules
is disordered over two positions. All of the water molecules
are involved in an extensive H-bonding scheme that also
involves the carboxylate O atoms.
The thermal stability of CPO-8-BPY was examined using
TGA. The TGA curve indicates the release of water
molecules up to 150 °C (obsd weight loss 10.5%; calcd
14.3%). The compound is stable up to 350 °C, where a
second weight loss starts that indicates decomposition of the
organic ligands. The powder X-ray diffraction pattern of
CPO-8-BPY dehydrated at 150 °C shows sharp diffraction
Inorganic Chemistry, Vol. 45, No. 6, 2006 2427

Kongshaug and Fjellvåg
Figure 4. Stacking of bilayers along [100] in CPO-8-BPY.
It turned out to be possible to exchange the pillaring BPY
module in CPO-8-BPY by either of three similar molecules,
resulting in three new compounds in the CPO-8 series,
namely, CPO-8-DPE, CPO-8-DPA, and CPO-8-DPP; see
Figure 5. The increase in the length of the pillars from BPY
to DPP does, however, not lead to any significant increase
in the pore dimension along [010]. Actually, the orientation
of the Zn tetrahedra forces the pillaring molecules into a
bent position along [100] ([001] for CPO-8-DPP) and thus
increases the pore dimensions along [001] ([100] for CPO-
8-DPP) instead. The dimensions of the pores in this direction
still remain small compared with the channels along [010].
The thermal properties of CPO-8-DPE, CPO-8-DPA, and
CPO-8-DPP are similar to those of CPO-8-BPY. The TGA
curves show two distinct weight losses. The first stage with
a water loss from channels takes place up to 150 °C (CPO-
8-DPE obsd weight loss 11.70%, calcd 11.83%; CPO-8-DPA
obsd 10.71%, calcd 11.80%; CPO-8-DPP obsd 11.60%, calcd
13.59%). Thermal decomposition of the frameworks starts
around 350 °C. Analogous to CPO-8-BPY, dehydrated
samples at 150 °C appear as porous on the basis of powder
X-ray patterns with sharp reflections. Rietveld analyses of
such diffraction data confirmed for all three compounds that
the frameworks are virtually unchanged after the dehydra-
tions, resulting in porous structures with the following free
volumes: CPO-8-DPE, 23.5%; CPO-8-DPA, 23.5%; CPO-
8-DPP, 25.5%.
Figure 2. (a) Tetrahedral Zn and aip ligands linked into 2D layers in a
triangular topology. (b) Stacking of 2D layers in [Zn(aip)(H2O)]n.
The isotherms of N2 measured at 77 K for the CPO-8 types
of compounds showed no sorption for any of the compounds.
However, at the same temperature, a small but significant
sorption of H2 was observed for all of the compounds. This
preferential sorption of H2 over N2 is shown for CPO-8-
DPP in Figure 6. The uptake of H2 at 1 atm was as follows:
CPO-8-BPY, 11.3 cm3(STP)/g (0.093 wt %); CPO-8-DPE,
9.6 cm3(STP)/g (0.079 wt %); CPO-8-DPA, 10.8 cm3(STP)/g
(0.089 wt %); CPO-8-DPP, 24.0 cm3(STP)/g (0.197 wt %).
The H2 uptake for CPO-8-DPP is in the same range as that
for the MOF structure CPL-1,26 while the uptake for the other
compounds is similar to the uptake of the nanoporous nickel
phosphate VSB-1.27 Preferential adsorption of H2 over N2
Figure 3. Stacking of 2D layers in CPO-8-DEF.
peaks, indicating that the framework is maintained even after
removal of the water molecules from the channels. The
Rietveld refinement analysis of the powder X-ray data
confirmed that the framework is virtually unchanged after
the dehydration, giving CPO-8-BPY-150 a porous structure.
The free volume was estimated by the program PLATON25
to be 20.7% of the unit cell volume, while the effective
dimensions of the pores are 3.5 × 6.7 Å2.
(26) Kubota, Y.; Takata, M.; Matsuda, R.; Kitaura, R.; Kitagawa, S.; Kato,
K.; Sakata, M.; Kobayashi, T. C. Angew. Chem., Int. Ed. 2005, 44,
920.
(27) Forster, P. M.; Eckert, J.; Chang, J. S.; Park, S. E.; Ferey, G.;
Cheetham, A. K. J. Am. Chem. Soc. 2003, 125, 1309.
(25) Spek, A. L. Acta Crystallogr., Sect A 1990, 46, C34.
2428 Inorganic Chemistry, Vol. 45, No. 6, 2006

Design of Bilayer Compounds
Figure 6. N2 and H2 gas sorption isotherms at 77 K for CPO-8-DPP.
P/P0 is the ratio of the gas pressure (P) to the saturation pressure (P0), with
P0 ) 1.0 bar.
Å) are larger than the smallest channel aperture size (3.5
Å). The kinetic diameter of H2 of 2.8 Å30 is, however, small
enough for the molecules to enter the channels.
Conclusion
In conclusion, the CPO-8 series of compounds demonstrate
the use of a unique, pillared bilayer motif for the rational
synthesis of novel porous coordination polymers. This
approach will allow the construction of novel coordination
polymers with the potential for various applications because
modification of the pillaring ligands may enable systematic
control of the pore size as well as pore functionality.
Acknowledgment. This work has received support from
the Research Council of Norway, Project No. 151502, as
part of the Klimatek research effort. Dr. Richard Blom and
Aud I. Spjelkavik at SINTEF are thanked for performing
the H2 sorption isotherm experiments.
Supporting Information Available: X-ray crystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
Figure 5. Stacking of bilayers along [100] in (a) CPO-8-DPE and (b)
CPO-8-DPA and along [001] in (c) CPO-8-DPP.
IC050662V
in MOF compounds has just been observed before for Mn-
(HCO2)228 and Mg3ndc329 (ndc ) 2,6-naphthalenedicarboxy-
late). This behavior may be explained by the fact that the
apertures of the channels are too small to allow N2 molecules
to enter because the kinetic diameters of the molecules30 (3.64
(28) Dybtsev, D. N.; Chun, H.; Yoon, S. H.; Kim, D.; Kim, K. J. Am.
Chem. Soc. 2004, 126, 32.
(29) Dinca, M.; Long, J. R. J. Am. Chem. Soc. 2005, 127, 9376.
(30) Beck, D. W. Zeolite Molecular SieVes; John Wiley & Sons: New
York, 1974.
Inorganic Chemistry, Vol. 45, No. 6, 2006 2429