Syntheses, crystal structures and anion-exchange properties of copper(II) and cadmium(II) complexes containing a novel tripodal ligand

Article abstract of DOI:10.1039/b317043h

Four novel metal-organic frameworks (MOFs), [Cu(3)₂](ClO ₄)₂ · 0.67H₂O (4), [Cu(3) ₂][Cu(mal)₂] · 6H₂O (mal^2- = ^-OCOCH₂COO^-) (5), [Cd(3)₂](NO ₃)₂ · H₂O, (6) and [Cd(3)(OAc) ₂] · 6H₂O (7), were obtained by self-assembly of the corresponding metal salts with a novel flexible tripodal ligand, 1-(1-imidazolyl)-3,5-bis(imidazol-1-ylmethyl)benzene (3), and their structures were determined by single crystal X-ray diffraction analyses. Complex 4 has a 2D network structure in which 3 shows two different coordination modes, one kind of 3 acts as a three-connecting ligand and the other one serves as a two-connecting (bridging) ligand using its two flexible arms. Complex 5 has an infinite 1D hinged chain structure in which only two of three imidazole groups of 3 are coordinated with the metal atoms while the last one is uncoordinated. In complexes 6 and 7, the metal centers are all six-coordinated; 6 has a 2D honeycomb and 7 has a 2D grid network structure, respectively. Ligand 3 has a trans conformation in 7, which is different from that in complexes 4 (cis and L-shaped), 5 (cis) and 6 (cis). The anion-exchange properties of complex 6 were investigated.

Full text of DOI:10.1039/b317043h

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P A P E R
Syntheses, crystal structures and anion-exchange properties of
copper(II) and cadmium(II) complexes containing a novel tripodal
ligandw
Wei Zhao,a Jian Fan,a Taka-aki Okamura,b Wei-Yin Sun*a and Norikazu Ueyamab
a Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing
University, Nanjing 210093, P. R. China. E-mail: sunwy@nju.edu.cn
b Department of Macromolecular Science, Graduate School of Science, Osaka University,
Toyonaka, Osaka, 560-0043, Japan
Received (in Montpellier, France) 29th December 2003, Accepted 7th April 2004
First published as an Advance Article on the web 20th July 2004
.
.
Four novel metal-organic frameworks (MOFs), [Cu(3)2](ClO4)2 0.67H2O (4), [Cu(3)2][Cu(mal)2] 6H2O
(mal2ꢀ = ꢀOCOCH2COOꢀ) (5), [Cd(3)2](NO3)2 H2O, (6) and [Cd(3)(OAc)2] 6H2O (7), were obtained by
self-assembly of the corresponding metal salts with a novel flexible tripodal ligand, 1-(1-imidazolyl)-3,5-
bis(imidazol-1-ylmethyl)benzene (3), and their structures were determined by single crystal X-ray diffraction
analyses. Complex 4 has a 2D network structure in which 3 shows two different coordination modes, one
kind of 3 acts as a three-connecting ligand and the other one serves as a two-connecting (bridging) ligand
using its two flexible arms. Complex 5 has an infinite 1D hinged chain structure in which only two of three
imidazole groups of 3 are coordinated with the metal atoms while the last one is uncoordinated. In
complexes 6 and 7, the metal centers are all six-coordinated; 6 has a 2D honeycomb and 7 has a 2D grid
network structure, respectively. Ligand 3 has a trans conformation in 7, which is different from that in
complexes 4 (cis and L-shaped), 5 (cis) and 6 (cis). The anion-exchange properties of complex 6 were
investigated.
.
.
4,40-bipyridine.11a In this complex, most of the nitrate ions can
be exchanged by SO42ꢀ and BF4ꢀ 11a Yip and co-workers have
also reported the anion exchange of coordination polymers
with silver(I) and flexible ligands.11b
Introduction
.
In the past decade, much progress has been achieved in the
metal-directed assembly of supramolecular frameworks with
suitable metal ions and rationally designed organic ligands.1
Metal-organic frameworks (MOFs) with specific topologies
such as cage-like structures, honeycomb and interpenetrating
networks have been obtained by self-assembly of suitable metal
salts with rigid or flexible tripodal ligands, for example, 1,3,5-
tricyanobenzene,2 2,4,6-tris(4-pyridyl)-1,3,5-triazine,3 1,3,5-
benzenetribenzoate,4 1,3,5-tris(4-pyridylmethyl)benzene5 and
1,3,5-tris(benzimidazole-1-ylmethyl)-2,4,6-trimethylbenzene.6
In contrast to the rigid ligands that show little or no con-
formational changes when they interact with metal salts, the
flexible tripodal ligands have many more possible coordination
modes due to their flexibility and they can adopt different
conformations according to the geometric requirements of
different metal ions. Accordingly, we designed and synthesized
a series of flexible tripodal ligands with aromatic core as
spacers and systematically investigated their reactions with
metal salts.7
Most recently, interest in porous metal-organic frameworks
has been driven by the prospect of generating a wide range of
materials with useful properties for applications such as ad-
sorption, ion and molecular recognition, ion-exchange and
catalysis.8–10 Supramolecular architectures have attracted
much attention not only because of their various structures,
but also because of their potential applications.11–15 Yaghi and
co-workers have reported MOFs containing large rectangular
channels obtained by self-assembly of Cu(NO3)2 ꢁ 2.5H2O with
In our previous studies, we reported two tripodal ligands,
1,3,5-tris(1-imidazolyl)benzene (1, Scheme 1) and 1,3-bis(1-im-
idazolyl)-5-(imidazol-1-ylmethyl)benzene (2, Scheme 1) and
demonstrated that they can form organic-inorganic hybridized
coordination complexes with reversible anion-exchange prop-
erties.12 The results show that such tripodal ligands are versa-
tile and can adopt different conformations when they interact
with metal salts and the self-assembly process depends on
many and/or even subtle factors and is often difficult to predict
exactly.13 This encouraged us to undertake further studies on
analogs/derivatives of 1 and 2 as organic ligands, which may
lead to a great variety of structures. Following this approach,
we now expand this system with a new tripodal ligand,
1-(1-imidazolyl)-3,5-bis(imidazol-1-ylmethyl)benzene (3, Sche-
me 1). Four non-interpenetrating organic-inorganic hybridized
coordination complexes, [Cu(3)2](ClO4)2 ꢁ 0.67H2O (4), [Cu(3)2]
[Cu(mal)2]ꢁ6H2O (5), [Cd(3)2](NO3)2ꢁH2O (6) and [Cd(3)(OAc)2]ꢁ
6H2O (7), were successfully isolated; their structures and the
anion-exchange behavior of complex 6 were investigated.
Experimental
Materials and methods
All commercially available chemicals were of reagent grade
and were used as received without further purification. Sol-
vents were purified according to the standard methods. C, H
and N analyses were made on a Perkin–Elmer 240C elemental
analyzer at the analysis center of Nanjing University. 1H NMR
spectral measurements were performed on a Bruker DRX-500
{ Electronic supplementary information (ESI) available: crystal pack-
ing diagrams and hydrogen bonding for 4–7; XPD of 6 and its ion-
exchanged analogs. See http://www.rsc.org/suppdata/nj/b3/b317043h/
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
1142
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 1 4 2 – 1 1 5 0

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Scheme 1
NMR spectrometer at room temperature. Infrared (IR) spectra
were recorded on a Bruker Vector22 FT-IR spectrophotometer
by using KBr discs. Powder X-ray diffraction patterns were
taken on a Rigaku D/max-RA rotating anode X-ray diffract-
ometer with graphite-monochromated Cu-Ka (l ¼ 1.542 A)
radiation at room temperature. Thermogravimetric and differ-
ential thermal analyses were performed on a simultaneous SDT
2960 thermal analyzer. Powder samples were loaded into alum-
the aqueous solution and 3 (15.2 mg, 0.05 mmol) in methanol
(2.5 ml) at room temperature. Yield: 47%. Single crystals
suitable for X-ray analysis were obtained by recrystallization
from a mixed solution of H2O (5 ml) and acetonitrile (5 ml) at
room temperature for 7 days. Anal. calcd for C40H48Cu2-
N12O14: C, 45.84; H, 4.62; N, 16.04%. Found: C, 45.88; H,
4.66; N, 16.03%. IR (KBr, cmꢀ1): 3385 s, 3133 m, 1605 s,
1605 s, 1561 s, 1531 m, 1501, 1420 m, 1400 m, 1371 m, 1316 m,
1245 m, 1233 m, 1094 m, 1060 m, 835 m, 749 m, 737 m, 686 m,
664 m, 635 m. The TGA data of 5 show an initial weight loss of
10.1% (calcd. 10.3%) from 30 to 80 1C, representing the loss of
uncoordinated water molecules; no further weight loss was
observed over the temperature range 80–175 1C.
ina pans and heated under N2at a heating rate of 10 1C minꢀ1
.
Syntheses
1-(1-Imidazolyl)-3,5-bis(imidazol-1-ylmethyl)benzene (3). 1-
Bromo-3,5-dimethylbenzene was treated with N-bromosucci-
nimide to give 1-bromo-3,5-bis(bromomethyl)benzene, which
was then treated with imidazole in DMSO to generate
1-bromo-3,5-bis(imidazole-1-ylmethyl)benzene. 1-Bromo-3,5-bi-
s(imidazole-1-ylmethyl)benzene (2.52 g, 8.0 mmol), imidazole
(1.63 g, 24.0 mmol), K2CO3 (1.46 g, 10.4 mmol), and CuSO4
(0.05 g, 0.20 mmol) were mixed and heated at 180 1C for 12 h
under a nitrogen atmosphere. The mixture was cooled to room
temperature and was then washed with water. The residue was
extracted with CH2Cl2 (5 ꢂ 30 ml). The organic layer was
separated, dried over sodium sulfate and evaporated to dryness
to give the crude product 3, which was recrystallized from
water and methanol. Yield: 40%. 1H NMR [CDCl3] d: 7.79
(s, 1H), 7.61 (s, 2H), 7.22 (s, 1H), 7.19 (s, 1H), 7.17 (s, 2H), 7.10
(s, 2H), 6.93 (s, 2H), 6.89 (s, 1H), 5.19 (s, 4H). Elem. anal. for 3,
C17H16N6: C, 66.90; H, 5.65; N, 27.45%; calcd: C, 67.09; H,
5.30; N, 27.61%.
[Cd(3)2](NO3)2 ꢁ H2O (6). This complex was prepared by
slow diffusion between two layers of an aqueous solution (10
ml) of Cd(NO3)2 ꢁ 4H2O (15.4 mg, 0.05 mmol) and 3 (15.2 mg,
0.05 mmol) in methanol (10 ml) at room temperature. About
two weeks later, colorless platelet crystals suitable for X-ray
analysis were obtained in 50% yield. Anal. calcd for
C34H34CdN14O7: C, 47.31; H, 3.97; N, 22.72%. Found: C,
47.32; H, 3.94; N, 22.68%. IR (KBr, cmꢀ1): 3446 m, 3121 m,
1609 m, 1510 m, 1439 m, 1384 s, 1336 m, 1231 m, 1108 m, 1086 m,
1069 m, 1035 m, 933 m, 830 m, 738 m, 660 m, 634 m. The TGA
data of 6 show an initial weight loss of 2.0% (calcd. 2.1%)
from 20 to 100 1C, representing the loss of uncoordinated water
molecules; no further weight loss was observed over the
temperature range 100–320 1C.
[Cd(3)(OAc)2] ꢁ 6H2O (7). In a typical synthesis, an aqueous
solution (5 ml) of Cd(OAc)2 ꢁ 2H2O (13.3 mg, 0.05 mmol) was
added slowly to a solution of 3 (15.2 mg, 0.05 mmol) in H2O
(5 ml) and the mixture was stirred for 5 h at room temperature
to give a colorless powder in ca. 80% yield. Single crystals
suitable for X-ray analysis were obtained by recrystallization
from methanol solution. Anal. calcd for C21H34CdN6O10: C,
39.23; H, 5.33; N, 13.07%. Found: C, 39.42; H, 5.44; N,
13.07%. IR (KBr, cmꢀ1): 3405 s, 3125 m, 1607 m, 1563 s,
1508 s, 1437 m, 1415 m, 1437 m, 1415 m, 1314 m, 1227 m,
1109 m, 1092 m, 1069 m, 1015 m, 935 m, 838 m, 748 m, 660 m,
620 m. The TGA data of 7 show an initial weight loss of 16.5%
(calcd. 16.8%) from 20 to 110 1C, representing the loss of
uncoordinated water molecules; no further weight loss was
observed over the temperature range 110–300 1C.
[Cu(3)2](ClO4)2 ꢁ 0.67H2O (4). The title compound was
synthesized by a hydrothermal reaction. A mixture of 0.5
mmol (21.7 mg) of [Cu(dien)im](ClO4)2(dien ¼NH2CH2
CH2NHCH2CH2NH2; im ¼ imidazole), 0.5 mmol (15.2 mg)
of 3 and 10.0 ml of deionized water was sealed into a bomb
equipped with a Teflon liner and then heated at 100 1C for 4
days. After slow cooling of the reaction mixture to room
temperature, blue crystals of compound 4 were obtained in
ca. 62% yield as a single phase. Anal. calcd for C34H33.13
Cl2CuN12O8.67: C, 46.25; H, 3.78; N, 19.04%. Found: C, 46.10;
H, 3.66; N, 18.85%. IR (KBr, cmꢀ1): 3386 m, 3133 m, 1610 m,
1524 m, 1442 m, 1237 m, 1094 s, 948 m, 828 m, 754 m, 739 m,
659 m, 622 m. The TGA data of 4 show an initial weight loss of
1.5% (calcd. 1.4%) from 30 to 100 1C, representing the loss of
0.67 uncoordinated water molecules.
Anion-exchange reactions
Caution! Perchlorate salts of metal complexes with organic
ligands are potentially explosive and should be handled with
care.
Well-ground powder of [Cd(3)2](NO3)2 ꢁ H2O (6, 200.0 mg) was
suspended in water (20 mL), then NaClO4 (1.5 g) was added.
The mixture was stirred for 1 day at room temperature, then
filtered, washed with water several times and dried. Elem. anal.
for the exchanged powder: C, 43.48; H, 3.61; N, 17.80%; calcd
for [Cd(3)2](ClO4)2 ꢁ H2O: C, 43.54; H, 3.65; N, 17.92%. The
exchanged solid (200.0 mg) was suspended in water (20 mL)
and NaNO3 (1.5 g) was added. The mixture was stirred for
[Cu(3)2][Cu(mal)2] ꢁ 6H2O (mal2ꢀ ¼ ꢀOCOCH2COOꢀ) (5).
An aqueous solution (10 ml) of CuO (4.0 mg, 0.05 mmol)
and H2mal (5.2 mg, 0.05 mmol) was refluxed and stirred for
about 8 h. The aqueous solution was filtered and cooled down
to room temperature. A blue powder was obtained after mixing
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 1 4 2 – 1 1 5 0
1143

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Table 1 Crystallographic data for complexes 4, 5, 6 and 7
Compound
4
5
6
7
Chemical formula
M
C34H33.13Cl2CuN12O8.67
883.27
C40H48Cu2N12O14
1047.98
Triclinic
P-1
C34H34CdN14O7
863.15
Triclinic
P-1
C21H34CdN6O10
642.94
Crystal system
Space group
Z
Monoclinic
P21/c
Triclinic
P-1
4
1
2
2
a/A
b/A
19.693(9)
8.996(5)
20.591(8)
90.00
8.860(6)
10.518(7)
12.331(8)
81.71(5)
76.18(5)
82.76(5)
200
12.301(13)
12.992(17)
13.221(14)
70.85(9)
66.48(8)
78.79(8)
200
11.2414(6)
12.1178(2)
12.2494(6)
60.400(2)
77.0554(16)
70.382(3)
200
c/A
a/1
b/1
g/1
T/K
U/A3
m/mmꢀ1
Data collected
Independent data
Rint
97.57(3)
90.00
200
3616(3)
0.826
35 596
1099.2(12)
1.050
10 942
1825(4)
0.668
17 657
1363.20(10)
0.863
12 953
8229
0.1873
5010
0.0558
3419
8221
0.1054
2532
6172
0.0284
Observed data
R1 [I 4 2s(I)]
wR2 [I 4 2s(I)]
R1 (all data)
wR2 (all data)
3274
0.0560
0.0885a
0.1579
0.1080
5613
0.0266
0.0686d
0.0311
0.0702
0.0379
0.0766b
0.0625
0.0803
d
0.0472
0.0659c
0.1558
0.0744
a
b
c
w ¼ 1/[s2(F0)2]. w ¼ 1/[s2(F0)2 þ (0.0359P)2], P ¼ (F20 þ 2Fc2)/3. w ¼ 1/[s2(F0)2]. w ¼ 1/[s2(F0)2 þ (0.0428P)2 þ 0.4550P], P ¼ (F02 þ 2F2c)/3.
1 day at room temperature, then filtered, washed with water
several times and dried to give a colorless powder. Elem. anal.
for this powder: C, 45.58; H, 3.89; N, 20.17%; calcd for
[Cd(3)2](ClO4)(NO3) ꢁ H2O: C, 45.30; H, 3.78; N, 20.21%.
Well-ground powder of [Cd(3)2](NO3)2 ꢁ H2O (6, 200.0 mg)
was suspended in water (20 mL), then NaNO2 (1.5 g) was
added. The mixture was stirred for 1 day at room temperature,
then filtered, washed with water several times and dried. Elem.
anal. for the exchanged product: C, 49.20; H, 4.18; N, 23.55%;
calcd for [Cd(3)2](NO2)2 ꢁ H2O: C, 49.13; H, 4.12; N, 23.59%.
The exchanged solid (200.0 mg) was suspended in water (20
mL) and NaNO3 (1.5 g) was added. The mixture was stirred for
1 day at room temperature, then filtered, washed with water
several times, and dried to give a colorless powder. Elem. anal.
for the exchanged powder: C, 47.35; H, 3.95; N, 22.70%; calcd
for [Cd(3)2](NO3)2 ꢁ H2O: C, 47.31; H, 3.97; N, 22.72%.
Results
Crystal structures
.
[Cu(3)2](ClO4)2 0.67H2O (4). The title complex crystallizes
in the monoclinic form with space group P21/c. As shown in
Fig. 1, each copper(II) atom in complex 4 is coordinated by five
N atoms from five different 3 ligands. Due to the presence of
two flexible arms, ligand 3 can coordinate to the metal center
comfortably to meet the geometric requirements of Cu(II). The
coordination geometry of the Cu(II) center can be described as
a tetragonal pyramid with an N5 donor set. The Cu–N bonds
in the equatorial plane have very similar bond lengths ranging
from 1.983(4) to 1.997(4) A, while the ligand at the apical
position shows an elongated bond length of Cu1–N52 ¼
2.253(4) A. The N–Cu–N coordination angles range from
87.27(15) to 173.92(17)1 (Table 2). The Cu1 atom locates
approximately within the plane formed by the N12, N32,
N132 and N152 atoms with a deviation of 0.20 A. It is
interesting that there are two kinds of ligands 3 with different
conformations. Ligand 3A has a cis conformation since the two
coordinating atoms N52A and N32A from the two flexible
arms locate above the central benzene ring plane with distances
of 3.13 and 2.13 A, respectively. In the case of ligand 3B, the
atom N15B locates above the central benzene ring plane at a
distance of 2.32 A and the corresponding distance between
N132 and the central benzene ring plane is only 0.27 A. This
means that ligand 3B has a near-L shape (Scheme 2), rather
than the cis or trans conformation, in complex 4. For ligand
3A, the three imidazolyl rings are inclined to the phenyl ring
with angles of 77.11, 93.41 and 107.71 and the corresponding
angles are 43.61, 85.61, 89.71 for ligand 3B. Neglecting the
interactions with ligand 3B, three copper(II) atoms are linked
by ligand 3A to form a triangle with metal-metal separations
(Cuꢁ ꢁ ꢁCu) of 9.00, 10.59 and 12.18 A, respectively; therefore
ligand 3A acted as a three-connecting ligand. Such units repeat
in the ab plane to generate an infinite 2D honeycomb network
as shown in Fig. 2(a). In addition, two such 2D networks are
further linked by ligand 3B bridges to form an independent
layer [Fig. 2(b)]; the copper atoms between two sublayers
bridged by ligand 3B have a Cuꢁ ꢁ ꢁCu separation of 10.89 A.
It is noteworthy that ligand 3B has only two flexible imidazole
groups coordinated with the metal atoms while the rigid one
X-Ray crystallography
The collection of crystallographic data for the complexes 4, 5, 6
and 7 was carried out on a Rigaku RAXIS-RAPID Imaging
Plate diffractometer at 200 K, using graphite-monochromated
Mo-Ka radiation (l ¼ 0.7107 A). The structures were solved by
direct methods with SIR9216 and expanded using Fourier
techniques.17 All non-hydrogen atoms were refined anisotro-
pically by the full-matrix least-squares method. The hydrogen
atoms except for those of water molecules were generated
geometrically. In complex 4, eight oxygen atoms of two per-
chlorate anions are disordered into two positions with site
occupancy factors (SOF) of 0.734(5) for O1, O2, O3, O4,
0.266(5) for O1B, O2B, O3B, O4B, 0.810(10) for O5, O6, O7,
O8 and 0.190(10) for O5B, O6B, O7B, O8B. All calculations
were carried out on an SGI work station using the teXsan
crystallographic software package of Molecular Structure
Corporation.18 Details of the crystal parameters, data collec-
tion and refinement are summarized in Table 1; selected bond
lengths and angles with their estimated standard deviations are
listed in Table 2.z
{ CCDC reference numbers 236959–236962. See http://www.rsc.org/
suppdata/nj/b3/b317043h/ for crystallographic data in .cif or other
electronic format.
1144
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 1 4 2 – 1 1 5 0

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Table 2 Selected bond distances (A) and angles (1) for compounds 4,
5, 6 and 7
Compound 4
Cu1–N132
1.983(4)
1.985(4)
2.253(4)
Cu1–N12
Cu1–N152
1.983(4)
1.997(4)
Cu1–N32
Cu1–N52
N132–Cu1–N12
N12–Cu1–N32
N12–Cu1–N152
N132–Cu1–N52
N32–Cu1–N52
173.92(17)
91.82(15)
87.27(15)
93.35(15)
97.99(15)
N132–Cu1–N32
N132–Cu1–N152
N32–Cu1–N152
N12–Cu1–N52
N152–Cu1–N52
Compound 5
Cu1–N52a
91.59(15)
87.89(15)
161.28(16)
91.16(15)
100.72(15)
2.019(2)
2.025(2)
1.912(2)
1.927(2)
180.0
Cu1–N52
Cu1–N32a
Cu2–O3b
2.019(2)
2.025(2)
1.912(2)
1.927(2)
87.61(9)
92.39(9)
180.0
Cu1–N32
Cu2–O3
Cu2–O1b
Cu2–O1
N52a–Cu1–N52
N52–Cu1–N32
N52–Cu1–N32a
O3–Cu2–O3b
O3b–Cu2–O1b
O3b–Cu2–O1
Compound 6
Cd1–N132
N52a–Cu1–N32
N52a–Cu1–N32a
N32–Cu1–N32a
O3–Cu2–O1b
O3–Cu2–O1
O1b–Cu2–O1
92.39(9)
87.61(9)
180.0
85.48(9)
94.52(9)
180.0
94.52(9)
85.48(9)
2.298(5)
2.326(5)
2.379(5)
Cd1–N152
Cd1–N32
Cd1–N12
2.319(5)
2.334(5)
2.377(5)
86.94(19)
177.40(19)
94.69(18)
91.02(17)
88.1(2)
Cd1–N52
Cd1–N112
N132–Cd1–N152
N152–Cd1–N52
N152–Cd1–N32
N132–Cd1–N112
N52–Cd1–N112
N132–Cd1–N12
N52–Cd1–N12
N112–Cd1–N12
Compound 7
Cd1–N52
89.42(18)
173.51(17)
89.15(18)
94.08(19)
83.89(17)
86.73(19)
97.59(18)
178.36(17)
N132–Cd1–N52
N132–Cd1–N32
N52–Cd1–N32
N152–Cd1–N112
N32–Cd1–N112
N152–Cd1–N12
N32–Cd1–N12
Fig. 1 Coordination environment around the copper(II) atom in 4
with the perchlorate anions, lattice water molecules and hydrogen
atoms omitted for clarity.
87.56(17)
91.0(2)
supplementary information); the distances of Cꢁ ꢁ ꢁO are in the
range of 3.031(8)–3.478(7) A and the C–H–O angles are in the
range from 1241 to 1591.19 The hydrogen-bonding data are
summarized in Table S1 (see ESI). The distances of 2.77 and
2.80 A between the O atom of solvated water and the O atom
of perchlorate or the N atom of the imidazole indicate the
presence of the O–Hꢁ ꢁ ꢁO and O–Hꢁ ꢁ ꢁN hydrogen bonds,
respectively, although the hydrogen atoms of the water mole-
cule could not be found.
2.278(2)
2.302(2)
2.394(2)
169.61(6)
84.89(6)
88.45(6)
102.49(6)
143.58(6)
81.00(6)
96.04(5)
52.71(5)
Cd1–N32
Cd1–N12
Cd1–O82
2.300(2)
2.320(2)
2.500(2)
88.19(6)
90.39(6)
131.72(6)
87.64(6)
83.49(6)
107.40(6)
131.31(6)
Cd1–O72
Cd1–O81
N52–Cd1–N32
N32–Cd1–O72
N32–Cd1–N12
N52–Cd1–O81
O72–Cd1–O81
N52–Cd1–O82
O72–Cd1–O82
O81–Cd1–O82
a
N52–Cd1–O72
N52–Cd1–N12
O72–Cd1–N12
N32–Cd1–O81
N12–Cd1–O81
N32–Cd1–O82
N12–Cd1–O82
.
[Cu(3)2][Cu(mal)2] 6H2O (5). The title complex crystallizes
in the triclinic form with P-1 space group; the coordination
environment around the copper(II) center in complex 5 is
shown in Fig. 4(a). The asymmetric unit of 5 contains two
distinct Cu centers, in which Cu1 and Cu2 sit on inversion
centers [Fig. 4(a)]. Each Cu1 center coordinates to four N
atoms from different 3 ligands with N–Cu–N bond angles in
the range of 87.61(9)–180.01 and Cu–N bond distances of
2.019(2) and 2.025(2) A. The Cu1 atom locates within the
plane defined by N32, N32A, N52 and N52A atoms without
deviation. Therefore, the local coordination geometry around
Cu1 can be regarded as square-planar with an N4 donor set,
which is different from that in 4. Each ligand 3 in turn binds to
two metal atoms using its two flexible arms to generate an
infinite 1D hinged chain structure [Fig. 4(b)] and ligand 3 has a
b
Symmetry transformation: ꢀx, 2 ꢀ y, ꢀz. Symmetry transforma-
tion: 1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
keeps free of coordination; thus, this ligand served as a two-
connecting (bridging) ligand, without a dimensionality in-
crease. In short, each independent 2D layer in complex 4
contains two sublayers, which are connected by ligand 3B
bridges. Disordered perchlorate anions are located between
the two sublayers of an independent layer (Fig. 3) and held
there by C–Hꢁ ꢁ ꢁO (ClO4ꢀ) hydrogen bonds to produce a 3D
framework as exhibited in Figs. S1 and S5 (see Electronic
Scheme 2
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 1 4 2 – 1 1 5 0
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Fig. 2 (a) 2D honeycomb network in 4 formed by the coordination of the three-connecting ligands 3A and the copper(II) atoms with the ligand 3B;
perchlorate anions, lattice water molecules and hydrogen atoms omitted for clarity. (b) Side view of the 2D network of 4 with the perchlorate anions,
lattice water molecules and hydrogen atoms omitted for clarity.
cis conformation (Scheme 2). For ligand 3, the three imidazolyl
rings are inclined to the phenyl ring with angles of 85.11, 93.81
and 142.21, respectively. Intrachain metal-metal distances in
complex 5 are 12.87 A. It is noteworthy that ligand 3 in
complex 5 has only two of its three imidazole groups coordi-
nated with metal atoms; the third one is uncoordinated, which
is similar to the ligand 3B in complex 4. The two benzene rings
from two opposing 3 ligands in the Cu2(3)2 macrocyclic ring
adopt a face-to-face conformation and are strictly parallel to
each other with a centroid-centroid distance of 5.32 A. In
addition, in the dianion Cu(mal)22ꢀ, each copper(II) center co-
ordinates to four O atoms from two malonates with O–Cu–O
bond angles ranging from 85.48(9)1 to 180.01 and Cu–O band
distances of 1.912(2) and 1.927(2) A, respectively. It is obvious
that a similar coordination geometry is found for Cu1 and
Cu2; the Cu2 atom is in the plane composed of O1, O3, O1A,
2ꢀ
O3A without deviation. Cu(mal)2 and five uncoordinated
water molecules are joined together by O–Hꢁ ꢁ ꢁO hydrogen
bonds with Oꢁ ꢁ ꢁO distances in the range of 2.732(4)–2.903(3) A
to form an interesting 2D hydrogen-bonded structure in the ab
plane [Fig. 4(c)]. Such 2D anionic layers are located in the
voids formed between two adjacent cationic chains as exhibited
in Fig. 5. Infinite 1D hinged chains and 2D hydrogen-bonded
layers are repeated and joined by C–Hꢁ ꢁ ꢁO hydrogen bonds
with Cꢁ ꢁ ꢁO distances in the range of 3.224(4)–3.437(4) A to
give a 3D structure for complex 5 as illustrated in Fig. S2
(Table S1; see the ESI). A previously reported malonato-
bridged copper(II) complex, {(H2bpe)[Cu(mal)2]}n ꢁ 4nH2O
[bpe ¼ 1,2-bis(4-pyridyl)ethylene], consists of anionic malona-
to-bridged copper(II) chains that are connected through hydro-
gen bonds involving malonato oxygen atoms, uncoordinated
water molecules and H2bpe21 cations.20
[Cd(3)2](NO3)2 ꢁ H2O (6). In addition to the synthesis of
Cu(II) complexes with a coordination number of four or five,
reactions of 3 with Cd(II) salts (cadmium is generally six-
coordinated) were also carried out and complexes 6 and 7 were
obtained. The polymeric structure of 6 was confirmed by X-ray
single crystal structure analysis. The complex crystallizes in
triclinic space group P-1 and Fig. 6 shows the asymmetric
unit of 6 with atom numbering scheme. Each cadmium(II) atom
is coordinated by six imidazole N atoms derived from six
different 3 ligands. The coordination geometry of the Cd(II)
center is a slightly distorted octahedral with coordination angles
Fig. 3 Crystal packing diagram for complex 4.
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 1 4 2 – 1 1 5 0
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Fig. 4 (a) Coordination environment around the copper(II) atoms in 5 with the hydrogen atoms omitted for clarity. (b) 1D hinged chain structure
in 5 with Cu(mal)22ꢀ, lattice water molecules and hydrogen atoms omitted for clarity. (c) 2D hydrogen-bonded structure in the ab plane in 5
2ꢀ
obtained by the connectivity of Cu(mal)2 and water molecules through O–Hꢁ ꢁ ꢁO hydrogen bonds.
(N–Cd–N) ranging from 83.89(17)1 to 178.36(17)1 and the Cd–N
bond lengths varying from 2.298(5) to 2.379(5) A (Table 2).
Each ligand 3 in turn connects three Cd(II) atoms, which form a
triangle with edge lengths (Cdꢁ ꢁ ꢁCd) of 12.99 A (e.g.,
Cd1Bꢁ ꢁ ꢁCd1C), 9.85 A (e.g., Cd1Bꢁ ꢁ ꢁCd1G) and 8.77 A (e.g.,
Cd1Cꢁ ꢁ ꢁCd1G), respectively. Such a coordination mode makes
the compound a 2D network with honeycomb structure [Fig.
7(a)], and a schematic drawing is shown in Fig. 7(b). It is
obvious that all 3 ligands in the network have cis conformation
with alternating up and down orientations (Scheme 2). The
distance between the two benzene ring planes of the up and
down orientations is 10.83 A and they are parallel each other.
The crystal packing diagram of complex 6 is illustrated in
Fig. 8. The nitrate anions and the lattice water molecules are
located in the voids formed between two adjacent cationic
layers. As shown in Fig. S3 (ESI), the nitrate anions and the
lattice water molecules are held there by C–Hꢁ ꢁ ꢁO hydrogen
bonds as tabulated in Table S1 (ESI).
[Cd(3)(OAc)2] ꢁ 6H2O (7). The crystallographic study pro-
vides direct evidence for the structure of 7. As listed in Table 1,
the complex crystallizes in triclinic space group P-1 and Fig. 9
shows the asymmetric unit of 7 with atom numbering scheme.
Each cadmium(II) atom is coordinated with three N atoms of
the imidazole unit from three different 3 ligands with N–Cd–N
bond angles varying from 88.45(6)1 to 169.61(6)1 and Cd–N
bond distances ranging from 2.278(2) to 2.320(2) A (Table 2).
The Cd1 atom locates within the plane formed by N12, N32,
Fig.
5
1D polymeric chain representation of complex
5
with
2ꢀ
Cu(mal)2 and water molecules located in the voids formed between
two adjacent cationic chains shown; hydrogen atoms are omitted for
clarity.
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 1 4 2 – 1 1 5 0
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Fig. 8 Crystal packing diagram for complex 6.
Fig. 6 Coordination environment around the cadmium(II) atom in 6
with the hydrogen atoms omitted for clarity.
Fig. 9 Coordination environment around the cadmium(II) atom in 7
with the hydrogen atoms omitted for clarity.
Fig. 7 (a) 2D honeycomb network in 6; nitrate anions, lattice water
molecules and hydrogen atoms are omitted for clarity. (b) Schematic
drawing of the two-dimensional network of 6, in which the ligands are
represented by three spokes radiating from a point and the cadmium
centers by black balls.
N52 atoms without deviation. Three additional positions are
occupied by three O atoms from two different acetate anions
with O–Cd–O bond angles of 143.58(6)1, 96.04(5)1 and
52.71(5)1 and Cd–O bond distances of 2.302(2), 2.394(2) and
2.500(2) A, respectively (Table 2). Therefore the coordination
environment of the cadmium(II) atom is N3O3, which is
different from that in 6. In turn, each 3 ligand links three metal
atoms to form a triangle with edge lengths (Cdꢁ ꢁ ꢁCd) of 12.12,
11.24 and 13.48 A, respectively. The three imidazolyl rings are
inclined to the phenyl ring with angles of 77.21, 107.91 and
162.21. As shown in Fig. 10, such a coordination mode gen-
erates an infinite 2D grid network structure based on (6,3) nets
and the 3 ligand has a trans conformation (Scheme 2), which is
different from that in 4, 5, and 6.
Fig. 10 2D polymeric grid network of complex 7.
The crystal packing diagram of complex 7 is illustrated in
Fig. 11. The 2D sheets are further connected by O–Hꢁ ꢁ ꢁO
hydrogen bonds to give a 3D structure as shown in Fig. S4(a)
(ESI). It is noteworthy that the connectivity of the water
molecules with the acetate ligands generates an interesting 3D
framework [Fig. S4(b), ESI]; the hydrogen bonding data are
listed in detail in Table S1 (ESI). There are large open channels
in complex 7, which are occupied by water molecules held there
by C–Hꢁ ꢁ ꢁO and O–Hꢁ ꢁ ꢁO hydrogen bonds (Table S1).
1148
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Fig. 11 Crystal packing diagram for complex 7 with the lattice water
molecules and hydrogen atoms omitted for clarity.
Comparison of structures. The results showed that the nature
of the metal ion has an important influence on the structures of
the MOFs with ligand 3. Due to the different coordination
geometry requirements of the metal ions, coordination com-
pounds 4, 5 and 6, 7 have different structures, in which ligand
3B in 4 and ligand 3 in 5 both have only two of the three
imidazole groups coordinated with metal atoms while the third
one keeps free of coordination. In addition to the role of the
metal atoms, counter anions with different shapes, coordina-
tion and bridging abilities also have a remarkable impact on
the structure of the MOFs; for example, complexes 6 and 7
with nitrate and acetate anions have different structures,
though Cd(II) in 6 and 7 has the same six-coordination. It is
noteworthy that in complex 7, ligand 3 has a trans conforma-
tion and leads to a 2D grid network structure.
The present study also shows that the reactions of flexible
organic ligands with various metal salts can afford a variety of
fascinating self-assembled polymeric frameworks. The differ-
ence between ligands 3 and 1 is that the former is more flexible
than the latter. Flexible ligand 3 can adjust its conformation to
fit with the geometrical needs of metal ions. For example, in
complex 4, ligand 3A adopts a cis conformation to give a 2D
honeycomb network, while in a previously reported complex
Fig. 12 FT-IR spectra of (a) complex 6, (b) complex 6 treated with an
aqueous solution of NaClO4, (c) complex 6 treated with an aqueous
solution of NaClO4 and then with NaNO3, (d) complex 6 treated with
an aqueous solution of NaNO2, (e) complex 6 treated with an aqueous
solution of NaNO2 and then with NaNO3.
12
[Cu(1)2(H2O)2](ClO4)2 obtained by reaction of Cu(ClO4)2 ꢁ
the reversibility of such anion-exchange processes in more
detail, the exchanged solid was suspended in an aqueous
solution of NaNO3 with stirring to allow anion eꢀxchange
6H2O with ligand 1, each ligand 1 coordinates to two copper(II)
atoms as a bidentate ligand rather than as a tridentate one.
Such a difference is caused by the introduction of methylene
groups between the imidazole and central benzene groups in 3.
Previous studies showed that 1D hinged chain and 2D network
structures were obtained by reactions of another flexible
tripodal ligand 2 with MnSO4 ꢁ H2O and Mn(ClO4)2 ꢁ 6H2O,12
which are similar with complexes 5 and 6, respectively. The
results show that the nature of the organic ligand has a great
impact on the structures of the assembly products.
ꢀ
again. It is interesting that both the ClO4 and NO3 bands
appeared in the FT-IR spectrum of the obtained solid (trace c
in Fig. 12). The result of elemental analysis suggests ca. 50%
ꢀ
exchange of ClO4 by NO3ꢀ, namely the exchange product
would be [Cd(3)2](ClO4)(NO3) ꢁ H2O (see Experimental). The
anion exchange was also carried out between complex 6 and
NaNO2. The FT-IR spectrum of the exchanged solid is shown
as trace d in Fig. 12. Intense bands at n ¼ 1335 to 1250 cmꢀ1
,
which originate from the NO2ꢀ ion, appeared while the intense
bands from 1384 to 1356 cmꢀ1 of the NO3ꢀ ion disappeared in
the spectrum of the exchanged solid, implying complete anion
exchange. The exchanged solid was again suspended in an
aqueous solution of NaNO3 with stirring to allow anion
Anion-exchange properties of complex 6
As revealed by the crystal structure of 6, the anions are located
within the open structure between the cationic layers through
hydrogen bonds (Fig. 8). Since complex 6 is insoluble in
common solvents, this cationic layered compound is expected
to display anion-exchange properties. Excess NaClO4 was
added to a well-ground powder of complex 6 suspended in
water at room temperature. The mixture was stirred for 24 h to
allow anion exchange, then it was filtered and washed with
water several times. The FT-IR spectra of the exchanged solid
and the original 6 are shown in Fig. 12 as traces b and a,
respectively. Intense bands at n ¼ꢀ 1112 to 1091 cmꢀ1 appeared,
which originate from the ClO4 ion,ꢀwhile the intense bands
from 1384 to 1356 cmꢀ1 of the NO3 ion disappeared in the
spectrum of the exchanged solid. The result of elemental
analysis also suggests complete anion exchange (see Experi-
mental). The anion-exchange reactions were also monitored by
X-ray powder diffraction (XPD) techniques (Fig. S6 in ESI).
The similar XPD patterns observed for the exchanged product
suggest that the solid state structure is retained. To investigate
ꢀ
ꢀ
exchange. The NO2 bands disappeared and the NO3 bands
appeared in the FT-IR spectrum of the obtained solid (trace e
in Fig. 12), which is almost the same as the spectrum of the
original material 6 (trace a in Fig. 12). The XPD pattern of
exchanged product closely resembles the experimental one of 6
[cf.Fig. S6(e) with Fig. S6(a) in the ESI]. The FT-IR and
elemental analysis confirm the reversible anion exchange be-
ꢀ
ꢀ
tween NO3 and NO2 anions.
In complex 6, the nitrate anions could be exchanged by the
perchlorate anions, however, the perchlorate anions could only
be partially exchanged by the nitrate anions, probably dꢀue to
the different environments around the two ClO4 in
[Cd(3)2](ClO4)2 ꢁ H2O. As discussed by Yip et al.,11b the ex-
ꢀ
change of [Cd(3)2](NO3)2 ꢁ H2O by ClO4 is favored since the
ꢀ
hydration energy (DGh) of NO3 (ꢀ300 kJ molꢀ1) is higher
than that of ClO4ꢀ (ꢀ205 kJ molꢀ1). On the other hand, rever-
sible anion exchange between complexes [Cd(3)2](NO3)2 ꢁ H2O
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 1 4 2 – 1 1 5 0
1149

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and [Cd(3)2](NO2)2 ꢁ H2O may be due to the comparability of
(g) J. Fan, H. F. Zhu, T. Okamura, W.-Y. Sun, W.-X. Tang and
N. Ueyama, Inorg. Chem., 2003, 42, 158; (h) S.-Y. Wan, Y.-Z. Li,
T. Okamura, J. Fan, W.-Y. Sun and N. Ueyama, Eur. J. Inorg.
Chem., 2003, 3783.
the nitrate anions and the nitrite anions.
8
9
(a) S. I. Noro, S. Kitagawa, M. Yamashita and T. Wada, Chem.
Commun., 2002, 222; (b) M. Munakata, L. P. Wu and T. Kuroda-
Sowa, Bull. Chem. Soc. Jpn., 1997, 70, 1727.
(a) R. H. Groeneman, L. R. MacGilliray and J. L. Atwood, Chem.
Commun., 1998, 2735; (b) Y. Cui, O. R. Evans, H. L. Ngo, P. S.
White and W. B. Lin, Angew. Chem., Int. Ed., 2002, 41, 7; (c) D.
M. L. Goodgame, D. A. Grachvogel and D. J. Williams, Angew.
Chem., Int. Ed., 1999, 38, 153.
Acknowledgements
The authors are grateful to the National Natural Science
Foundation of China (Grant No. 20231020) for financial
support of this work.
10 (a) C. V. K. Sharma and M. J. Zaworotko, Chem. Commun., 1996,
2655; (b) D. L. Long, A. J. Blake, N. R. Champness, C. Wilson
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