Novel one-dimensional tubelike and two-dimensional polycatenated metal-organic frameworks

Article abstract of DOI:10.1021/ic020461g

Two novel metal-organic frameworks (MOFs) [Zn(TITMB)(OAc)](OH)·8.5H₂O (1) and [Ag(TITMB)N₃]·H₂O (2) [TITMB = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene, OAc = acetate anion] were synthesized and their structures were determined by X-ray crystallography. Complex 1 crystallizes in tetragonal space group P4 with a = 23.2664(7) and c = 11.9890(3) A and Z = 8.1 has a one-dimensional tubelike structure with large inner pore size of ～17 A. Complex 2 crystallizes in monoclinic space group C2 with a = 20.7193(10), b = 11.5677(8), and c = 12.2944(6) A, β = 125.5770(10)°, and Z = 4. 2 consists of two-dimensional honeycomb networks that interpenetrate each other to generate a polycatenated structure. In these two complexes, both zinc(II) and silver(I) atoms are four-coordinated with the same tetrahedral coordination geometry. The topologies of 1 and 2 are predominated by the conformations of TITMB, which are cis, trans, trans in 1 and cis, cis, cis in 2, respectively.

Full text of DOI:10.1021/ic020461g

Inorg. Chem. 2003, 42, 158−162
Novel One-Dimensional Tubelike and Two-Dimensional Polycatenated
Metal−Organic Frameworks
,†
Jian Fan,† Hui-Fang Zhu,† Taka-aki Okamura,‡ Wei-Yin Sun,* Wen-Xia Tang,† and Norikazu Ueyama‡
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry,
Nanjing UniVersity, Nanjing 210093, China, and Department of Macromolecular Science,
Graduate School of Science, Osaka UniVersity, Toyonaka, Osaka 560-0043, Japan
Received July 16, 2002
Two novel metal−organic frameworks (MOFs) [Zn(TITMB)(OAc)](OH)‚8.5H O(1) and [Ag(TITMB)N ]‚H O(2) [TITMB
2
3
2
) 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene, OAc ) acetate anion] were synthesized and their structures
were determined by X-ray crystallography. Complex 1 crystallizes in tetragonal space group P4h with a )
23.2664(7) and c ) 11.9890(3) Å and Z ) 8. 1 has a one-dimensional tubelike structure with large inner pore size
of ∼17 Å. Complex 2 crystallizes in monoclinic space group C2 with a ) 20.7193(10), b ) 11.5677(8), and c )
12.2944(6) Å, â ) 125.5770(10)°, and Z ) 4. 2 consists of two-dimensional honeycomb networks that interpenetrate
each other to generate a polycatenated structure. In these two complexes, both zinc(II) and silver(I) atoms are
four-coordinated with the same tetrahedral coordination geometry. The topologies of 1 and 2 are predominated by
the conformations of TITMB, which are cis, trans, trans in 1 and cis, cis, cis in 2, respectively.
Introduction
counteranions. Especially in the case of flexible tripodal
ligands such as 1,3,5-tris(4-pyridylmethyl)benzene,5 1,3,5-
tris(pyrazol-1-ylmethyl)-2,4,6-triethylbenzene,6 and 1,3,5-tris-
(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (TITMB),7,8 in
which the coordinating pyridyl, pyrazol, or imidazole groups
were connected to the central aromatic ring through the
methylene groups, a variety of MOFs can be expected since
such flexible ligands can adopt different conformations
according to the different geometric requirements of metal
atoms. The TITMB ligand has cis, cis, cis and cis, trans,
trans conformations (Chart 1) as observed in the cagelike
The construction of metal-organic frameworks (MOFs)
with novel structures and topologies has attracted great
interest from chemists in the past decade because of their
potential applications in many fields such as material science,
medicine, and chemical technology.1 From the reported
studies, tripodal ligands with an arene core have been found
to be one of the most useful organic building blocks in
construction of MOFs. For example, metallocages or cap-
sules, infinite one-dimensional (1D) chain, two-dimensional
(2D) honeycomb networks, and three-dimensional (3D)
architectures have been obtained by assembly reactions of
tripodal ligands with transition metal salts.2-4 The results
demonstrated that the formation of MOFs strongly depends
on the nature of organic ligands and metal ions as well as
-
-
- 7
complexes [Ag3(TITMB)2]X3 (X ) ClO4 , BF4 , NO3 ) and
2D network complex [(dien)3Cu3(TITMB)2](ClO4)6 (dien )
diethylenetriamine),8 respectively. Extending this approach,
we now have constructed 1D tubelike complex [Zn(TITMB)-
(4) (a) Zeng, F.; Zimmerman, S. C. Chem. ReV. 1997, 97, 1681. (b) Wu,
Q.; Hook, A.; Wang, S. Angew. Chem., Int. Ed. 2000, 39, 3933. (c)
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1995, 34, 820. (d) Batten, S. R.; Hoskins, B. F.; Robson, R. J. Am.
Chem. Soc. 1995, 117, 5385. (e) Hennigar, T. J.; MacQuarrie, D. C.;
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Chem.sEur. J. 2001, 7, 2557. (b) Liu, H. K.; Sun, W. Y.; Tang, W.
X.; Yamamoto, T.; Ueyama, N. Inorg. Chem. 1999, 38, 6313.
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Chim. Acta 1999, 295, 129.
* To whom correspondence should be addressed. E-mail: sunwy@
nju.edu.cn. Fax: 86-25-3314502. Telephone: +86-25-3593485.
† Nanjing University.
‡ Osaka University.
(1) (a) Baxter, P. N. W.; in ComprehensiVe Supramolecular Chemistry;
Lehn, J.-M., Ed.; Pergamon: Oxford, 1996, Vol. 9, Chapter 5. (b)
Caulder, D. L.; Raymond, K. N.; Acc. Chem. Res. 1999, 32, 975. (c)
Stang, P. J.; Olenyuk, B.; Acc. Chem. Res. 1997, 30, 502.
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Abrahams, B. F.; Egan, S. J.; Robson, R. J. Am. Chem. Soc. 1999,
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295. (e) Yaghi, O. M.; Li, G.; Li, H. Nature 1995, 378, 703.
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158 Inorganic Chemistry, Vol. 42, No. 1, 2003
10.1021/ic020461g CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/10/2002

Tubelike/Polycatenated Metal-Organic Frameworks
Chart 1
Table 1. Crystal Data and Refinement Results for Complexes 1 and 2
param
1
2
chem formula
fw
C23H45N6O11.5Zn
655.02
C21H26AgN9O
528.38
space group
a, Å
b, Å
P4h (No. 81)
C2 (No. 5)
20.7193(10)
11.5677(8)
12.2944(6)
125.5770(10)
2396.6(2)
4
23.2664(7)
c, Å
11.9890(3)
â, deg
V, Å3
Z
6490.0(3)
8
T, K
93
200
λ, Å
0.7107
1.341
8.19
0. 0635
0. 1303
0.7107
1.464
8.72
0.0447
D
calcd, g cm-3
µ(Mo KR), cm-1
R1 [I > 2σ(I)]a
wR2 [I > 2σ(I)]b
(OAc)](OH)‚8.5H2O (1) (OAc ) acetate anion) and 2D
polycatenated honeycomb network [Ag(TITMB)N3]‚H2O (2)
by assembly reactions of TITMB with zinc(II) acetate
dihydrate and [Ag(NH3)2N3], respectively. Here we report
the self-assembly and X-ray crystal structures of the novel
MOFs. It is interesting that the TITMB has a cis, trans, trans
conformation in 1 while the conformation of TITMB in 2 is
cis, cis, cis.
0.1219
2
2
a R1 ) Σ||Fo| - |Fc||/Σ|Fo|. b wR2 ) |Σw(|Fo| - |Fc| )|/Σ|w(Fo)2|1/2
,
2
2
2
where w ) 1/[σ2(Fo ) + (aP)2 + bP]. P ) (Fo + 2Fc )/3.
Table 2. Selected Bond Distances (Å) and Angles (deg) for Complexes
1 and 2
Compound 1
Zn1-O71
Zn1-N302
Zn2-O73
Zn2-N102
1.975(5)
2.012(5)
1.952(4)
2.020(5)
Zn1-N12
Zn1-N502
Zn2-N52
Zn2-N32
2.009(5)
2.012(5)
2.004(5)
2.030(5)
Experimental Section
Materials and Measurements. All commercially available
chemicals are of reagent grade and used as received without further
purification. TITMB was synthesized as reported previously.8
Ag(NH3)2N3 was prepared in situ by addition of diluted ammonia
solution to silver azide, which was obtained by the reaction of silver
nitrate and sodium azide, until the silver azide was dissolved.
Solvents were purified by standard methods prior to use. Elemental
analyses of C, H, and N were taken on a Perkin-Elmer 240C
elemental analyzer, at the Center of Materials Analysis, Nanjing
University. Electrospray mass spectral (ES-MS) measurements were
carried out on an LCQ System (Finnigan MAT) using methanol as
the mobile phase. Thermogravimetric analysis was performed on
a simultaneous SDT 2960 thermal analyzer under flowing N2 with
a heating rate of 10 °C/min. The 500 MHz 1H NMR spectra were
measured on a Bruker DRX-500 NMR spectrometer at room
temperature.
Preparation of the Complexes. [Zn(TITMB)(OAc)](OH)‚
8.5H2O (1). In a typical synthesis, an ethanolic solution (40 mL)
of zinc(II) acetate dihydrate (110 mg, 0.5 mmol) was added slowly
to a solution of TITMB (180 mg, 0.5 mmol) in ethanol (20 mL)
and the mixture was stirred for 5 h at room temperature to give a
colorless powder with ca. 30% yield. Single crystals suitable for
X-ray analysis were obtained by recrystallization from aqueous
solution. Anal. Calcd for C23H45N6O11.5Zn: C, 42.18; H, 6.92; N,
12.83. Found: C, 42.14; H, 7.08; N, 12.65.
O71-Zn1-N12
O71-Zn1-N502
N12-Zn1-N502
O73-Zn2-N52
O73-Zn2-N32
N32-Zn2-N52
104.0(2)
114.5(2)
110.4(2)
114.5(2)
117.3(2)
110.0(2)
O71-Zn1-N302
N12-Zn1-N302
N502-Zn1-N302
O73-Zn2-N102
N102-Zn2-N52
N102-Zn2-N32
116.0(2)
100.9(2)
109.8(2)
107.9(2)
107.4(2)
97.9(2)
Compound 2a
2.293(5)
2.329(4)
Ag1-N1
Ag1-N52#1
Ag1-N12
2.300(4)
2.341(4)
Ag1-N32#2
N1-Ag1-N52#1
N52#1-Ag1-N32#2
N52-Ag1-N12#1
121.08(19)
105.99(15)
100.89(16)
N1-Ag1-N32#2
N1-Ag1-N12
109.8(2)
112.8(2)
104.84(17)
N32-Ag1-N12#2
a Symmetry transformations used to generate equivalent atoms: #1, x
- 0.5, y - 0.5, z - 1; #2, x, y, z - 1.
methods using SIR929 and expanded using Fourier techniques.10
All data were refined anisotropically by the full-matrix least-squares
method for non-hydrogen atoms. In complex 2, atoms N2 and N3
in the azide anion disordered into two positions with the site
occupancy factors (sof) of 0.577(8) and 0.423(8), respectively. The
hydrogen atoms except for those of water molecules were generated
geometrically. All calculations were carried out on an SGI
workstation using the teXsan crystallographic software package.11
The crystal parameter, data collection, and refinement results for
compounds 1 and 2 are summarized in Table 1. Selected bond
length and angles are listed in Table 2. Further details are provided
in the Supporting Information.
[Ag(TITMB)N3]‚H2O (2). A solution of TITMB (18.0 mg, 0.05
mmol) in acetonitrile (5 mL) was carefully layered over an aqueous
solution of freshly prepared Ag(NH3)2N3 (0.05 mmol). Colorless
crystals were isolated by filtration after several weeks. Yield: 47%.
Anal. Calcd for C21H26AgN9O: C, 47.74; H, 4.96; N, 23.86.
Found: C, 47.97; H, 5.03; N, 23.51.
Results and Discussion
X-ray crystallographic analysis revealed that each zinc-
(II) atom in 1 is coordinated by three N atoms of imidazole
Caution! Azide salts of metal complexes are toxic and potentially
explosiVe and should be handled with care.
(9) SIR92: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.;
Giacovazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystallogr. 1994,
27, 435.
(10) DIRDIF94: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman,
W. P.; de Gelder, R.; Israel, R.; Smits, J. M. M. The DIRFID-94
program system; Technical Report of the Crystallography Laboratory;
University of Nijmegen: Nijmegen, The Netherlands, 1994.
(11) teXsan: Crystal Structure Analysis Package; Molecular Structure
Corporation: The Woodlands, TX, 1999.
Crystallographic Analyses. A crystal of 1 with approximate
dimensions 0.45 × 0.30 × 0.30 mm was mounted, and data
collection was carried out on a Rigaku RAXIS-RAPID imaging
plate diffractometer at 93 K, using graphite-monochromated Mo
KR radiation (λ ) 0.7107 Å). The intensity data for 2 were collected
on the same machine at 200 K. The structures were solved by direct
Inorganic Chemistry, Vol. 42, No. 1, 2003 159

Fan et al.
Figure 1. A 48-membered macrocyclic ring for complex 1. The thermal
ellipsoids were drawn at the 50% probability level.
from three different TITMB ligands and one O atom of
acetate anion to complete its tetrahedral coordination envi-
ronment. As a result of such coordination mode, the
[Zn(ImCH2R)3(OAc)] (where Im ) imidazol-1-yl, R )
aromatic ring) unit has a positive charge. A hydroxide anion
is present as a counteranion for the charge balance. The
presence of hydroxide anion was confirmed by electrospray
mass spectral (ES-MS) spectrometry. Prominent peaks of
[(TITMB)2Zn2(OAc)(OH)]2+ and [(TITMB)3Zn2(OAc)(OH)-
(H2O)]2+ were observed with reasonable isotopic distribution
in aqueous solutions of 1.12 Four zinc(II) atoms and four
TITMB ligands (each TITMB using two of the three pendant
arms connects two zinc atoms) form a 48-membered mac-
rocyclic ring through Zn-N coordination bonds (Figure 1).
The key point for the formation of such a macrocyclic ring
is the cis, trans, trans conformation of TITMB ligand in 1,
while TITMB with cis, cis, cis conformation formed
Figure 2. (a) 1D tubelike structure of 1. (b) Schematic drawing of the
tubelike structure of 1 in which the TITMB ligands are simplified by straight
lines from the centroid of the central benzene ring to the coordinated zinc
atom and water molecules are omitted for clarity.
coordinated metal atoms, e.g. [Zn3(TIB)2(OAc)6] (4) [TIB
) 1,3,5-tris(imidazol-1-ylmethyl)benzene]13 and [(en)3Pd3L2]-
(NO3)6 [en ) ethylenediamine, L ) 1,3,5-tris(4-pyridyl-
methyl)benzene],5 two coordination sites of each metal atom
were occupied by two acetate anions or by one ethylenedi-
amine as ancillary ligands. Furthermore, it is noteworthy that
TITMB and TIB react with the same zinc(II) acetate
dihydrate to form two entirely different MOFs 1 and 4; the
structural difference between TITMB and TIB is just that
there are three methyl groups at the 2,4,6-positions of the
central benzene ring of TITMB. Reactions of TITMB and
TIB with copper(II) acetate also give different MOFs with
2D honeycomb and 3D porous structures.7b,14 The results
imply that even subtle changes of a ligand may have great
influence on the formation of MOFs. The steric hindrance
of methyl groups in TITMB and the differences in solubilities
between TITMB and TIB may contribute to the formation
of the 1D chain structure of 1 rather than an individual cage.
Three methyl substituents make the TITMB ligand and its
zinc(II) complex 1 have lower solubility than TIB and 4 in
common solvents such as ethanol, acetonitrile, water, etc.
The discrete compound must be unfavorable because of the
additional methyl groups of the TITMB preventing the
entropically favored [Zn3(TITMB)2]6+ structure.
-
-
individual cages [Ag3(TITMB)2]X3 (X ) ClO4 , BF4 ,
-
NO3 ) or a 2D honeycomb network [Cu3(TITMB)2(OAc)6]‚
H2O (3) assemblied with the corresponding transition metal
salts.7
The macrocyclic rings are connected still by Zn-N
coordination bonds to give an infinite 1D tubelike chain
(Figure 2) with large inner channel. The intermetallic
separations of Zn1-Zn2 and Zn1-Zn2A are 13.725(1) Å
and 13.595(1) Å [diagonal distances of Zn1-Zn1A and
Zn2-Zn2A: 16.380(2) and 18.309(2) Å, respectively], and
the distances of C101-C10B and C11-C11A are 11.80(1)
and 10.51(2) Å, respectively (atom numbering scheme shown
in Figure 1). A previously reported silver(I) coordination
polymer containing nanometer-sized tubes was obtained by
reaction of 2,4,6-tris[(4-pyridyl)methylsulfanyl]-1,3,5-triazine
with silver(I) salts.3
Complex 1 contains a lot of water molecules (8.5 H2O/
zinc atom, most of which are inside the channel; see Figure
S1) as revealed by the crystal structure determined at low
There is only one acetate anion as an ancillary ligand
coordinated with the zinc(II) atom in 1. However, in the
reported cagelike architectures with tripodal ligands and four-
(13) Liu, H. K.; Sun, W. Y.; Ma, D. J.; Yu, K. B.; Tang, W. X. Chem.
Commun. 2000, 591.
(12) A recent example with hydroxide as a counteranion: Satcher, J. H.,
Jr.; Olmstead, M. M.; Droege, M. W.; Parkin, S. R.; Noll, B. C.; May,
L.; Balch, A. L. Inorg. Chem. 1998, 37, 6751.
(14) Liu, H. K.; Tan, H. Y.; Cai, J. W.; Zhou, Z. Y.; Chan, A. S. C.; Liao,
S.; Xiao, W.; Zhang, H. X.; Yu, X. L.; Kang, B. S. Chem. Commun.
2001, 1008.
160 Inorganic Chemistry, Vol. 42, No. 1, 2003

Tubelike/Polycatenated Metal-Organic Frameworks
Figure 3. Top view (a) and side view (b) of the 2D network of 2. Water molecules are omitted for clarity.
temperature (93 K). Distances of C-O and O-O ranging
from 2.18(7) to 3.599(8) Å indicate the formation of
C-H---O(water), (water)O-H---O(water), and (water)O-
H---O(acetate) hydrogen bonds, although most of the hy-
drogen atoms of the water molecules could not be found.
TGA data for 1 exhibited a weight loss of 18.0% (calcd
17.9%) from 25 to 110 °C, representing the loss of
uncoordinated water molecules (6.5 H2O), and no further
weight loss was observed until 260 °C. Unfortunately the
tubelike structure collapsed after removing the water mol-
ecules. The tubelike structure of 1 is expected to have affinity
for guest inclusion, which was studied by 1H NMR in D2O.
Upfield shifts of 0.15-0.2 ppm were observed for the methyl
and methylene signals of 1-dodecanol when it was added to
the D2O solution of 1 as a guest. The results indicate that 1
may have a capacity for inclusion of an alkyl chain.
To further investigate the assembly of TITMB with
transition metal salts, we carried out the reaction of TITMB
with Ag(NH3)2N3. A complex with the same structure and
topology as 1 can be expected if the silver(I) takes a four-
coordinated tetrahedral geometry. In this case the coordinated
acetate anion in 1 will be replaced by an azide anion and
the complex is neutral with one silver(I) and one azide anion.
In fact, the crystallographic analysis of 2 indicates that the
silver(I) atom is indeed four-coordinated with the same
tetrahedral geometry as that of zinc(II) in 1 and the azide
anion coordinated to the silver(I) atom as a monodentate
ligand as that of acetate anion in 1. However, the conforma-
tions of the TITMB ligand in complexes 1 and 2 are different.
In complex 2 the conformation of TITMB is cis, cis, cis while
TITMB in 1 has cis, trans, trans conformation. Namely the
topologies of MOFs 1 and 2 are predominated by the
conformations of the organic ligand. Each TITMB acts as
an exo-tridentate ligand and connects three silver(I) atoms
to form an infinite 2D honeycomb network in complex 2 as
illustrated in Figure 3a. The silver(I) atoms are located in
the same layer which was separated from benzene ring plane
with a distance of 4.00(1) Å, and the azide anions act as
Figure 4. (a) Crystal packing diagram of 2 along the c axis. (b) Schematic
drawing of the polycatenated framework of 2.
Inorganic Chemistry, Vol. 42, No. 1, 2003 161

Fan et al.
appending groups from the side view of the network as
shown in Figure 3b. In the reported 2D honeycomb network
[Cu3(TITMB)2(OAc)6]‚H2O (3), the distance between two
planes formed by the copper(II) atoms and by benzene rings
is 5.00(1) Å,7 while, in the case of [Ag(TCB)(CF3SO3)] (5)
(TCB ) 1,3,5-tricyanobenzene), the silver(I) atoms are
trigonally coordinated to three nitriles and fall into the
benzene ring plane since the TCB is a tripodal planar
ligand.15
In the 2D network of complex 2, three silver(I) atoms form
triangles which are “filled” with TITMB ligand (e.g. Ag1A,
Ag1B, and Ag1C) and “empty” (e.g. Ag1B, Ag1C, and
Ag1D) alternatively as exhibited in Figure 3a. The edge
lengths of the triangles, i.e., the intermetallic distance
between two silver(I) atoms in Figure 3a, are 11.865(1)
(Ag1B-Ag1C), 11.989(1) (Ag1B-Ag1A), and 12.294(1)
(Ag1B-Ag1D) Å, respectively. The crystal packing diagram
of complex 2 is shown in Figure 4a. The remarkable
structural feature of this complex is that the “empty” triangle
is large enough to allow the inclusion of another 2D sheet
generating a polycatenated network structure (Figure 4b).
The dihedral angle between two polycatenated sheets, for
example sheets A and C in Figure 4b, is 68.9° implying an
inclined interpenetration. Two parallel sheets A and B are
separated by a distance of 9.537(1) Å.
In conclusion, a 1D tubelike or 2D honeycomb structure
can be formed on the basis of the conformation of the flexible
TITMB ligand. The results of present and previous studies
show that TITMB is a versatile ligand that can provide MOFs
with specific topologies as well as interesting properties.7,8,16
The large inner pore size (∼17 Å) of the tubelike structure
of 1 creates a localized chemical microenvironment in which
a compound may have properties different from that of the
bulk phase.17 Further studies, such as chemistry inside the
tubelike structure and functionalization of MOFs, are now
in progress in our laboratory.
Acknowledgment. The authors are grateful to the Na-
tional Natural Science Foundation of China for financial
support of this work.
Supporting Information Available: Figure S1, showing the
tubelike structure of 1 with water molecules inside and outside of
the channel, and X-ray crystallographic files, in CIF format. This
material is available free of charge via Internet at http://pubs.acs.org.
IC020461G
(16) Fan, J.; Sun, W. Y.; Okamura, T.; Xie, J.; Tang, W. X.; Ueyama, N.
New J. Chem. 2002, 26, 199.
(17) See for example: (a) Warmuth, R.; Yoon, J. Acc. Chem. Res. 2001,
34, 95. (b) Yoshizawa, M.; Takeyama, Y.; Kusukawa, T.; Fujita, M.
Angew. Chem., Int. Ed. 2002, 41, 1347.
(15) Gardner, G. B.; Venkataraman, D.; Moore, J. S.; Lee, S. Nature 1995,
374, 792.
162 Inorganic Chemistry, Vol. 42, No. 1, 2003