An unprecedented twofold interpenetrating (3,4)-connected 3-D metal-organic framework

Article abstract of DOI:10.1039/b702216f

An unprecedented twofold interpenetrating (3,4)-connected topology of the Cu₃L₄-type metal-organic framework was prepared using N,N′,N″-tris(4-pyridinyl)-1,3,5-benzenetricarboxamide (L) as a trigonal three-connection node and the cop

Full text of DOI:10.1039/b702216f

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An unprecedented twofold interpenetrating (3,4)-connected 3-D metal–
organic framework{
Seunghee Hong,{ Yang Zou,{ Dohyun Moon and Myoung Soo Lah*
Received (in Cambridge, UK) 12th February 2007, Accepted 23rd March 2007
First published as an Advance Article on the web 30th March 2007
DOI: 10.1039/b702216f
An unprecedented twofold interpenetrating (3,4)-connected
topology of the Cu L -type metal–organic framework was
as an augmented square planar tetratopic node. To our surprise,
there have been no reports of (3,4)-connected MOFs with a simple
square planar node.
3
4
prepared using N,N9,N0-tris(4-pyridinyl)-1,3,5-benzenetricar-
boxamide (L) as a trigonal three-connection node and the
copper(II) ion as a square planar four-connection node, where
the framework contains remarkably large 1-D solvent channels.
Here we describe the synthesis, and structure, of a (3,4)-
2
+
connected MOF with a Cu ion as a simple square planar
four-connection node and a ligand, N,N9,N0-tris(4-pyridinyl)-1,3,5-
benzenetricarboxamide (L), as a trigonal three-connection node.
This work is part of our research program aimed at the systematic
In recent years, there has been considerable interest in porous
metal–organic frameworks (MOFs) with regular and accessible
cavities. Although this field aims at the discovery and synthesis of
new materials for practical applications that use their functional
aspects, including catalysis, storage, separation, sensors, and
12
study of (3,4)-connected open-framework architectures.
The reaction of L with copper(II) nitrate trihydrate (4 : 3) in
DMSO produced, after standing undisturbed for three days, blue
needle-like crystals of 1 in 31.6% yield.§ The asymmetric unit of the
crystal structure of 1 is shown in Fig. 1." Two crystallographically
1
electronics, it would be difficult to achieve a major advance
2
+
without understanding the structural aspects of such materials.
Recent reviews on the framework topologies and other geometrical
independent four-connected Cu centers, one in the general
position and the other in the crystallographic twofold axis site, and
two crystallographically independent but topologically equivalent
three-connected ligands lead to a novel twofold interpenetrating
1,2
characteristics of network solids reflect this importance. The
classification of structures by Wells lays the foundation for the
3
general understanding of inorganic solids, as well as MOFs.
(3,4)-connected Cu3L4 network structure. The coordination
Many 3-D structures with mineral topologies, such as CdSO
4
,
geometry of the Cu1 atom is Jahn–Teller distorted octahedral
with four N atoms of the pyridine groups from four different L
13
3 4
NbO, Pt O , pyrite, quartz, rutile, halite, and sodalite have been
reported recently as the result of attempts to obtain geometric
4
characteristics with designable functionalities.
ligands occupying the corners of a square. The bond lengths of
˚
Cu1–N range from 1.971(6) to 2.028(6) A (Table S2{). The two
apical positions of the Cu1 atom are occupied by two oxygens
The key steps in building coordination frameworks are to
rationally design the appropriate ligands and to choose metal ions
14
from a water molecule and a nitrate anion, with Cu1–O4A and
˚
Cu1–O1N bond lengths of 2.447(8) and 2.711(9) A, respectively.
2
,5
with suitable coordination geometries. In the synthetic design of
metal–organic open frameworks, a low coordination number (,6)
with more directional covalent bonds is desirable for creating an
The coordination environment of the other Jahn–Teller distorted
octahedral Cu2 atom, which is in the crystallographic twofold axis
13
site, is similar to that of the Cu1 center except for the two water
14
molecules ligated at the apical positions instead of a water
6
open architecture. There has been increasing interest in the use of
three-connected centers as basic structural units for the construc-
7
tion of open-framework materials. Three-connected centers, when
molecule and a nitrate anion. The bond lengths of Cu2–N of the
˚
pyridine groups are 1.876(7) and 1.967(6) A and the bond length of
˚
Cu2–O4N of the water molecule is 2.545(4) A.
used alone, tend to form low-dimensional structures, and when
used in combination with four-connected centers lead to a variety
8
of 3-D open-framework architectures. However, most of the
studies have focused on the (3,4)-connected nets with tetrahedral
9
four-connected centers. If all square planar four-connected nodes
are linked exclusively to trigonal three-connected nodes and vice
versa, two distinct (3,4)-connected nets are obtained: Pt
3
O
4
and a
Until now, only five examples of (3,4)-
connected MOFs with square planar four-connected motifs were
2b,10
twisted boracite net.
7a,11
known.
All of them are either augmented Pt O or augmented
3 4
twisted boracite nets, where the paddle wheel Cu(II) center serves
Department of Chemistry and Applied Chemistry, College of Science and
Technology, Hanyang University, Ansan, Kyunggi-Do 426-791, Korea.
E-mail: mslah@hanyang.ac.kr
{
ligand and MOF, simplified view of network, crystal information,
Electronic supplementary information (ESI) available: Synthesis of
Fig. 1 ORTEP view of the asymmetric unit of 1 with thermal ellipsoids
at 20% probability displacement; the hydrogen atoms and the unligated
solvent molecules are omitted for clarity.
hydrogen-bonding table, and XRD pattern. See DOI: 10.1039/b702216f
{
The first and the second authors contributed equally to this paper.
This journal is ß The Royal Society of Chemistry 2007
Chem. Commun., 2007, 1707–1709 | 1707

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Despite the simplicity of the building blocks, the overall
structure of 3-D network 1 is quite complicated (Fig. 2A). In a
simplified view, it is composed of alternating planar four-
2
+
connection Cu and trigonal three-connection L nodes. The
two types of nodes are linked to each other to form an extended
3
framework (Fig. S1{). According to Wells, such networks with
three- and four-connection nodes belong to the (3,4)-connected net
family.
The individual (3,4)-connected net in 1 can be specified by the
2b,10
Schl a¨ fli symbol
2
(4.8 )(8 )(4 .8 .10 ) (Fig. 2B), which is different
6
2
2
2
from the other (3,4)-connected nets with square planar tetratopic
3
6
3
2
2
2 15
3 4
nodes: Pt O net (8 )(8 ) and twisted boracite net (6 )(6 .8 .12 ).
To the best of our knowledge, this is the first example of a (3,4)-
connected net that has two topologically different square planar
four-connected vertices.
Fig. 3 View of the 3-D network illustrating the intermolecular hydrogen
…
The trigonal units (representing the central benzene ring of L) of
the two discrete nets in the network structure are displaced from
˚
each other by 6.65 A. The rings of one net are penetrated by links
bonding, shown as yellow dashed lines: d(H4B O2N [2x, 2y + 1, 2z +
1]) = 2.22 A˚ and / N4B–H4B…O2N [2x, 2y + 1, 2z + 1] = 162.0u.
of the other so that they are truly catenated. As shown in Fig. 2A
and 3, the two interpenetrating nets hold each other through
hydrogen bonding between the N–H of the amide group of the
ligand and the oxygen atom of the adjacent nitrate (Table S3{),
mentioned above work together to influence the formation of two
topologically different four-connected nodes.
˚
The large channels with a diameter of y18 A (Fig. 2A) are filled
with water and disordered DMSO, whose presence was supported
by FT-IR spectroscopy. The solvent volume is 71% of the crystal
volume, a value seldom observed for interpenetrating networks,
which generally incorporate either very little (up to 20% of the
2+
which is coordinated with a four-connected node (Cu ) of the
other net. The van der Waals interactions between the nets
provides further stabilization of the interwoven nets. This
interweaving allows mutual reinforcement of the exceptionally
large L moieties. The two different coordination environments of
16
crystal volume) or no free volume.
Interpenetration has been considered a major obstacle in the
achievement of porous crystalline structures with large free
volume. In other words, the smaller the degree of interpenetration
2
+
Cu and the non-covalent interactions between the two nets
(n = 3 or 2 in the MOF), the greater the optimum amount of
available free volume that can be achieved. As shown in Fig. 4, the
diameter of the ring of one net (red), which another net (blue) has
˚
interpenetrated, is 14.3 A and the length of the three-connected
ligand (from the center of the benzenes to the nitrogen atom of
˚
pyridine) is 7.93 A. On the other hand, the diameter of the four-
˚
connected node [Cu(pyr) ] is 9.6 A, which is too large to let a third
4
net fit in the space remaining after two interpenetrating frame-
works form. This results in wide channels and large void volume.
However, the net is not robust enough to sustain its porosity. The
XRD data of the air-dried network 1 showed an amorphous
pattern with an extremely broad but high intensity band around
2
2u in 2h, which suggests the presence of a large number of
˚
interatomic distances around 4 A (Fig. S2{).
Fig. 2 (A) 3-D porous network of 1, with solvent molecules omitted for
clarity. Rhombic channels are observed along the b-axis. Two individual
nets are indicated by different colors (blue and red). The diameter of the
2
6
2
2
2
˚
yellow balls inside the channels is 18 A. (B) The (4.8 )(8 )(4 .8 .10 ) net of
, three types of nodes are differentiated by color: yellow refers to three-
1
Fig. 4 A space-filling version of the part that highlights the interwoven
nature of the 3-D network. Hydrogen atoms have been omitted. Atoms of
different nets are shown in different colors (blue and red).
connected nodes; blue and green refer to two topologically different four-
connected nodes.
1
708 | Chem. Commun., 2007, 1707–1709
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6
7
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3 4
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was obtained. We think the nitrate-mediated hydrogen-bonding
interaction between the two nets, where the nitrate is weakly
2
+
ligated at the apical position of the Cu center (the green colored
node in Fig. 2B), influences the formation of two topologically
different square planar four-connected nodes. This MOF shows an
extremely large solvent volume, which is due to the long trigonal
linking ligand and the limited interpenetration (twofold). This
might offer a new way to explore the synthesis of MOFs with large
free volumes. If it can be made robust, this may offer new gas
storage or catalytic potential.
We gratefully acknowledge the financial assistance offered by
KRF (KRF–2005–070–C00068), KOSEF (R01–2005–000–10490–
8
9
0) and CBMH. The authors also acknowledge PAL for beam line
use (2006–2041–15).
Notes and references
§ A total of 0.1403 g (0.3200 mmol) of ligand, 0.0465 g (0.248 mmol) of
Cu(NO ?3H O, and 15 mL of dimethyl sulfoxide (DMSO) were mixed
3
)
2
2
and stirred for ca. 10 min, then filtered. Blue needle-like crystals were
obtained after standing undisturbed at room temperature for three days.
1
996, 118, 3039; (g) X. H. Bu, N. F. Zheng, Y. Q. Li and P. Y. Feng,
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R. Robson, Angew. Chem., Int. Ed. Engl., 1996, 35, 1690; (j)
D. N. Dybtsev, H. Chun and K. Kim, Chem. Commun., 2004, 1594.
Yield 0.0673 g, 31.6%. Elemental analysis: [Cu
NO ?3(DMSO)?3(H O) (C102 Cu , fw = 2658.93): calcd
C, 46.08; H, 3.87; N, 15.80%. Found: C, 46.18; H, 3.39; N, 15.47%. IR
3 4 3 2 2 3
L (NO ) (H O) ]
(
3
)
4
2
H N O S
102 30 39 3
3
2
1
21
(
"
KBr): n(CLO), 1695 cm ; n(N–H), 3170 cm .
17
Crystal data for [Cu
3 4 3 2 2 3 3 4 96 3 30
L (NO ) (H O) ](NO ) : C H72Cu N O30, M =
1
0 M. O’Keeffe and S. T. Hyde, Zeolites, 1993, 13, 592.
2316.46, orthorhombic, T = 100(2) K, space group Pnna, a = 56.792(11),
b = 14.331(3), c = 32.170(6) A, V = 26 183(9) A , Z = 4, m = 0.279 mm
1
1 (a) S. S.-Y. Chui, S. M.-F. Lo, J. P. H. Charmant, A. G. Orpen and
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3
21
,
˚
˚
˚
synchrotron radiation (l = 0.70000 A), 49 789 reflections measured, 13 803
unique [Rint = 0.2134] which were used in all calculations. Structure
refinement following modification of the data for the non-framework
region as disordered electron densities with the SQUEEZE routine in
16474; (c) V. V. Komarchuk, V. V. Ponomarova, H. Krautscheid and
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1
8
PLATON: final R1 = 0.0787 (I . 2s(I)), wR2 = 0.1739, GOF = 0.687,
23
˚
max./min. residual electron densities 0.212/20.506 e A . CCDC 631720.
12 D. Moon, S. Kang, J. Park, K. Lee, R. P. John, H. Won, G. H. Seong,
Y. S. Kim, G. H. Kim, H. Rhee and M. S. Lah, J. Am. Chem. Soc.,
For crystallographic data in CIF or other electronic format see DOI:
10.1039/b702216f
2006, 128, 3530.
13 The Jahn–Teller distorted octahedral Cu center (Cu1) is directly bonded
1
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coordination at Cu1 is completed by N3A which is related by lattice
translation (x, 1 + y, z), N2B, related by a combination of an a-glide
operation and a lattice translation (1/2 + x, y, 1 2 z), and N3B related
by another combination of the same a-glide operation and another
lattice translation (1/2 + x, 1 + y, 1 2 z). The other octahedral Cu center
(Cu2) is bonded to three atoms (N2A, N1B, and O4N) from the
asymmetric unit and the remaining three atoms are related by a twofold
axis operation (x, 1/2 2 y, 3/2 2 z).
2
14 We have tentatively assigned these electron densities as those of the
oxygen atoms of the coordinated water molecules because no further
residual densities corresponding to DMSO molecules or nitrate anions
were found in the vicinity of these electron densities.
3
4, 319; (e) O. R. Evans and W. Lin, Acc. Chem. Res., 2002, 35, 511; (f)
15 Long vertex symbols for net 1: (4.8.8)
(4.4.8 .8 .1630.1630); Pt net: (8 .8 .8 (8 .8
boracite net: (6.6.6) (6 .6 .8 .12 .12
4
(8
.8
2
.8
.8 .8
2
.8
4
.8
2
.8
2
.8
; twisted
2 2 2
.8 ) -
O. M. Yaghi, M. O’Keeffe, N. W. Ockwig, H. K. Chae, M. Eddaoudi
and J. Kim, Nature, 2003, 423, 705.
3
3
3
O
2
.8
4
5
5
5
)
4
2
2
4
4
4
)
3
4
2
2
2
2
2 3
) .
3
4
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17 All non-hydrogen atoms in the framework of the structure were found
from the difference Fourier map, but additional nitrate ions and some
solvent molecules (DMSOs and waters) could not be confirmed easily
from only the difference Fourier map. The details of the structural
analysis are given in the supporting information{.
6063; (b) H. Chun, D. Kim, D. N. Dybtsev and K. Kim, Angew. Chem.,
Int. Ed., 2004, 43, 971 and references therein.
5
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18 PLATON program: A. L. Spek, Acta Crystallogr., Sect. A: Found.
Crystallogr., 1990, 46, 194.
This journal is ß The Royal Society of Chemistry 2007
Chem. Commun., 2007, 1707–1709 | 1709