Metal-organic frameworks containing flexible bis(benzimidazole) ligands

Article abstract of DOI:10.1002/ejic.200700833

Eleven coordination polymers constructed from three structurally related flexible bis(benzimidazole) ligands, 1,1′-(1,4-butanediyl)bis(2- methylbenzimidazole) (L¹), 1,1′-(1,4-butanediyl) bis(2-ethylbenzimidazole) (L²), and 1,1′-(1,4-butanediyl) bis(2-benzylbenzimidazole) (L³), have been synthesized: [Zn(cin) ₂(L¹)]·H₂O (1), [Zn(cin) ₂(L²)] (2), [Cd(cin)₂(L¹)] ·H₂O (3), [Cd(cin)₂(L²)] (4), [Ag(MES)(L¹)_0.5] (5), [Ag(MES)(L²) _0.5]·H₂O (6), [Zn(adi)(L¹)] ·H₂O (7), [Zn(adi)(L²)_0.5] (8), [Cd(adi)(L¹)]·2H₂O (9), [Cd(adi)(L²)] (10), and [Cd(adi)(L³)]·2H₂O (11), where cin = cinnamate anion, MES = 2-(N-morpholino)ethanesulfonate anion, and adi = adipate dianion. For compounds 1-4, the cin anions are coordinated to metal ions in monodentate mode or bidentate chelating mode, and metal cations are bridged by L¹ or L² ligands to form 1-D chain structures. Compound 5 shows a 1-D chain structure which comprises a dimeric unit that is built from two silver ions and two MES anions. In compound 6, silver ions are bridged by MES anions and L² ligands to form a 2-D (6, 3) network while compounds 7-9 possess 2D (4, 4) networks. In the structure of compound 8, there exists a dimeric unit which is built from two zinc ions bridged by four carboxylate groups. Compound 10 exhibits a fourfold interpenetrating diamondoid net, and compound 11 displays a noninterpenetrating diamondoid framework. The luminescent properties for 1-11 are also discussed in detail. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200700833

FULL PAPER
DOI: 10.1002/ejic.200700833
Metal–Organic Frameworks Containing Flexible Bis(benzimidazole) Ligands
Hui Jiang,[a] Jian-Fang Ma,*[a] Wen-Li Zhang,[a] Ying-Ying Liu,[a] Jin Yang,[a]
Guang-Ju Ping,[a] and Zhong-Min Su[a]
Keywords: Coordination polymers / Flexible ligands / Supramolecular chemistry / Luminescence
Eleven coordination polymers constructed from three struc-
turally related flexible bis(benzimidazole) ligands, 1,1Ј-(1,4-
butanediyl)bis(2-methylbenzimidazole) (L1), 1,1Ј-(1,4-but-
structures. Compound 5 shows a 1-D chain structure which
comprises a dimeric unit that is built from two silver ions and
two MES anions. In compound 6, silver ions are bridged by
anediyl)bis(2-ethylbenzimidazole) (L2), and 1,1Ј-(1,4-butane- MES anions and L2 ligands to form a 2-D (6, 3) network while
diyl)bis(2-benzylbenzimidazole) (L3), have been synthesized:
[Zn(cin)2(L1)]·H2O (1), [Zn(cin)2(L2)] (2), [Cd(cin)2(L1)]·H2O
(3), [Cd(cin)2(L2)] (4), [Ag(MES)(L1)0.5] (5), [Ag(MES)(L2)0.5]·
compounds 7–9 possess 2D (4, 4) networks. In the structure
of compound 8, there exists a dimeric unit which is built from
two zinc ions bridged by four carboxylate groups. Compound
H2O (6), [Zn(adi)(L1)]·H2O (7), [Zn(adi)(L2)0.5] (8), [Cd(adi)(L1)]· 10 exhibits a fourfold interpenetrating diamondoid net, and
2H2O (9), [Cd(adi)(L2)] (10), and [Cd(adi)(L3)]·2H2O (11),
where cin = cinnamate anion, MES = 2-(N-morpholino)eth-
anesulfonate anion, and adi = adipate dianion. For com-
pounds 1–4, the cin anions are coordinated to metal ions in
monodentate mode or bidentate chelating mode, and metal
cations are bridged by L1 or L2 ligands to form 1-D chain
compound 11 displays a noninterpenetrating diamondoid
framework. The luminescent properties for 1–11 are also dis-
cussed in detail.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Ongoing research in our laboratory has been directed to-
ward the design and synthesis of novel frameworks with
flexible ligands.[6] To further investigate the influence of
bis(benzimidazole) ligands on the formation of supramolec-
ular architectures, in this paper, we have synthesized three
flexible ligands: 1,1Ј-(1,4-butanediyl)bis(2-methylbenzimid-
azole) (L1), 1,1Ј-(1,4-butanediyl)bis(2-ethylbenzimidazole)
(L2), and 1,1Ј-(1,4-butanediyl)bis(2-benzylbenzimidazole)
(L3) (Scheme 1). Three kinds of acids, cinnamic acid
(Hcim), 2-(N-morpholino)ethanesulfonic acid (HMES),
and adipic acid (H2adi) (Scheme 2) are selected as anions
for the reason that their coordination chemistry has rarely
been investigated.[7]
Introduction
In the field of supramolecular chemistry, great interest
has been focused on the crystal engineering of coordination
frameworks due to their new topologies, intriguing architec-
tures, intertwining phenomena, and potential applica-
tions.[1] Studies in this field have been focused on the design
and construction of novel coordination frameworks and the
relationships between their structures and properties. It is
still a great challenge to predict the exact structures and
compositions of the assembly products built by coordina-
tion bonds and/or hydrogen bonds in crystal engineering.[2]
The construction of molecular architecture depends on the
combination of several factors, such as the coordination na-
ture of the metal ions, ligand structures, counterions, and
so on. Therefore, systematic research on this topic is impor-
tant for understanding the role of these factors in the for-
mation of metal coordination frameworks.
The rigid ligands, such as 4,4Ј-bipyridine[3] and pyr-
azine,[4] have been extensively employed in the construction
of a rich variety of intriguing architectures. However, there
are an increasing number of recently characterized interest-
ing interwoven frames incorporating with flexible ligands.[5]
Scheme 1.
In this work, 11 coordination polymers, namely, [Zn-
(cin)2(L1)]·H2O (1), [Zn(cin)2(L2)] (2), [Cd(cin)2(L1)]·H2O
(3), [Cd(cin)2(L2)] (4), [Ag(MES)(L1)0.5] (5), [Ag(MES)-
(L2)0.5]·H2O (6), [Zn(adi)(L1)]·H2O (7), [Zn(adi)(L2)0.5] (8),
[Cd(adi)(L1)]·2H2O (9), [Cd(adi)(L2)] (10), and [Cd(adi)-
(L3)]·2H2O (11), have been synthesized by both solution
and solvothermal reactions. The crystal structures of these
[a] Key Lab of Polyoxometalate Science, Department of Chemistry,
Northeast Normal University,
Changchun 130024, People’s Republic of China
Fax: +86-431-85098620
E-mail: jianfangma@yahoo.com.cn
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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J.-F. Ma et al.
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shows a three-coordinate configuration.[10a,10b] For com-
pound 1, the water molecule shows a two-coordinate mo-
de.[10c,11a]
Scheme 2.
compounds and topological analyses, along with the sys-
tematic investigation of the modulated effect of bis(benz-
imidazole) ligands on the ultimate frameworks, will be rep-
resented and discussed in this paper.
Results and Discussion
Syntheses of the Compounds
As is well known, the reactions of metal ions with car-
boxylates or sulfonates and neutral ligands in aqueous solu-
tion often result in the formation of insoluble substances,
presumably because of the fast coordination of them to
form polymeric structures. In this paper, solution reaction
and solvothermal synthesis were used to synthesize the
compounds. Compounds 5 and 6 are insoluble in water and
common organic solvents, but they can be dissolved in a
concentrated solution of ammonia by segregating the li-
gands from metal cations. The crystals of these compounds
were obtained by using a crystallization process through
evaporating an ammoniacal solution of them. Compounds
1–4 and 7–11 were synthesized by solvothermal synthesis.
All compounds are stable in air and are insoluble in com-
mon solvents such as ethanol, benzene, acetone, and aceto-
nitrile.
Figure 1. (a) ORTEP diagram showing the coordination environ-
ment for the Zn atom in 1. (b) The infinite 1-D zigzag chain of 1.
Table 1. Selected hydrogen-bonding geometry data [Å, deg].
D–H···A
d(D–H)
d(H···A) d(D···A) Є(D–H···A)
Compound 1
O(1W)–H(1A)···O(2)
O(W1)–H(1A)···O(1)
0.93(5)
2.16(15) 2.876(6) 133(16)
Compound 3
0.99(7)
1.97(7) 2.960(8) 173(11)
Compound 6
Descriptions of Crystal Structures
O(1W)–H(1A)···O(4)#3
O(1W)–H(1B)···O(3)
0.90(5)
0.93(5)
2.01(5) 2.866(4) 158(4)
1.82(5) 2.717(4) 162(4)
Structure Description of 1
Compound 9
In the structure of 1, each zinc ion is coordinated by two
nitrogen atoms from two L1 ligands and two oxygen atoms
from two cin anions, showing a distorted tetrahedral coor-
dination geometry (Figure 1, a). The Zn(1)–N distances of
2.033(2) Å and the Zn(1)–O distances of 1.951(2) Å fall in
O(1W)–H(1B)···O(3)
O(1W)–H(1A)···O(2W)
O(2W)–H(2A)···O(2)#5
0.83(5)
0.91(5)
0.91(5)
2.05(6) 2.796(5) 150(9)
1.94(5) 2.797(6) 156(8)
1.97(5) 2.777(5) 147(6)
2.31(5) 3.110(8) 151(6)
O(2W)–H(2B)···O(1 W)#6 0.88(4)
#3
#5
Symmetry codes for 6:
–x + 5/2, y + 1/2, –z – 1/2; 9:
–x +
the range of normal Zn–N and Zn–O distances.[8,9] Each 2, –y + 1, –z; –x + 2, –y + 2, –z.
cin anion coordinates to one zinc center through one car-
#6
boxylate O atom, and the zinc ions are bridged by L1 li-
gands to form an infinite chain (Figure 1, b). There exist
Structure Description of 2
lattice water molecules in the structure of 1. The water
The structure of 2 is similar to that of compound 1 ex-
molecule donates hydrogen bonds to the carboxylate O cept L1 is replaced by L2. Part of the structure of 2 is shown
atoms of the cin anion. The geometric parameters of the in Figure 2. The Zn–O and Zn–N bond lengths and related
hydrogen bonds are summarized in Table 1. As is well angles for 1 and 2 are slightly different. Zinc ions are
known, a water molecule has two hydrogen atoms and two bridged by L2 ligands to form a 1D chain the same as that
lone-electron pairs which enable it to participate in four hy- observed in compound 1 (see Figure S1, Supporting Infor-
drogen bonds in a tetrahedral configuration, but it often mation).
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Flexible Ligands in Metal–Organic Frameworks
normal Cd–O distances.[12] The cin anion in 3 exhibits a
bidentate chelating coordination mode. Cadmium centers
are bridged by L1 ligands to form a 1-D infinite zigzag
chain (Figure 3, b).
In the structure of 3, there exist lattice water molecules
which show a two-coordinate mode (Table 1). The adjacent
polymeric chains are bridged by the hydrogen-bonding in-
teractions between the water molecules and the carboxylate
oxygen atoms to form a wavelike 2-D supramolecular layer
(Figure 3, c). These layers stack in a parallel mode to form
the overall structure of 3 (Figure S2).
Figure 2. ORTEP diagram showing the coordination environment
for the Zn atom in 2.
Structure Description of 4
In the structure of 4, each cadmium center is coordinated
by four oxygen atoms from two cin anions and two nitrogen
atoms from two L2 ligands, showing a distorted octahedral
geometry (Figure 4, a). The cin anion adopts a bidentate
chelating coordination mode, and CdII atoms are connected
by L2 ligands to form a 1-D zigzag chain (Figure 4, b). The
polymeric chains are arranged in a parallel mode to form a
2D sheet (Figure S3).
Structure Description of 3
In the structure of 3, each cadmium center is coordinated
by two nitrogen atoms [Cd–N 2.261(3) Å] from two L1 li-
gands and four carboxylate O atoms [Cd–O 2.339(6)–
2.526(6) Å] from two cin anions (Figure 3, a). The geometry
around the cadmium center can be described as a distorted
octahedron. The Cd–O distances are quite similar to the
Figure 4. (a) ORTEP diagram showing the coordination environ-
ment for the Cd atom in 4. (b) The infinite 1-D zigzag chain of 4.
Structure Description of 5
As shown in part a of Figure 5, the silver ion in 5 is
coordinated by two oxygen atoms [Ag–O 2.479(2)–
2.516(2) Å] from two MES anions and two nitrogen atoms
[Ag–N 2.155(2)–2.285(2) Å] from one MES anion and one
L1 ligand, showing a distorted tetrahedral coordination ge-
ometry. The Ag–O bond lengths are similar to the values in
the related compound.[13]
As illustrated in part b of Figure 5, the coordination of
MES anion to silver ion results in a [Ag2(MES)2] unit with
two kinds of rings. The eight-membered ring (Ag2O4S2) is
composed of two silver ions and two sulfonate groups, with
the Ag···Ag distance of 7.06 Å, while the six-membered ring
is formed by one silver ion and one MES anion. The
[Ag2(MES)2] units are linked by L1 ligands to form a 1-D
Figure 3. (a) ORTEP diagram showing the coordination environ-
ment for the Cd atom in 3. (b) The infinite 1-D zigzag chain of 3.
(c) The 2-D layer containing hydrogen bonds between cin anions
and water molecules of 3 (H-bonds: dashed lines).
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J.-F. Ma et al.
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chain structure (Figure 5, c). Compound 5 displays a
unique supramolecular organization of the polymeric
chains. These polymeric chains are arranged on parallel
levels in different propagating directions, rotated by 72.5°
on passing from one level to the successive one, thus re-
sulting in an ABAB sequence (Figure 5, d). Similar packing
fashions of 1-D chain polymers have rarely been ob-
served.[11]
Figure 6. (a) ORTEP diagram showing the coordination environ-
ment for the Ag atom in 6. (b) The infinite 1-D zigzag chain com-
posed of silver ions and MES anions. (c) View of the 2-D (6, 3)
network.
Structure Description of 7
In compound 7, the zinc ion is coordinated by two oxy-
gen atoms [Zn–O 1.955(5)–1.979(5) Å] from two mono-
dentate adi anions and two nitrogen atoms [Zn–N 2.048(5)–
2.050(5) Å] from two L1 ligands (Figure 7, a), showing a
distorted tetrahedral geometry. The zinc ions are bridged
by adi anions to form an infinite chain, and these chains
are connected by L1 ligands to form a 2-D wavelike (4, 4)
network (Figure 7, b).
Figure 5. (a) ORTEP diagram showing the coordination environ-
ment for the Ag atom in 5. (b) View of the dimeric unit consisting
of two Ag ions and two MES anions. (c) The infinite 1D chain of 5.
(d) Rod-packing diagram of the 1D chains spanning two different
directions (light gray and medium gray) in 5.
Structure Description of 6
In the structure of 6, the silver ion is coordinated by one
oxygen atom from one MES anion and two nitrogen atoms
from one MES anion and one L2 ligand, showing a dis-
torted T-shaped geometry (Figure 6, a). The silver ions are
bridged by MES anions to form a 1-D polymeric chain
(Figure 6, b). These chains are further extended by L2 li-
gands to result in a 2-D (6, 3) network (Figure 6, c). The 2-
D polymeric networks stack in a parallel mode to form the
overall structure of 6 (Figure S4). The lattice water mole-
cules are hydrogen-bonded to the oxygen atoms of the MES
anions.
Figure 7. (a) ORTEP diagram showing the coordination environ-
ment for the Zn atom in 7. (b) The 2-D wavelike polymeric layer.
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Flexible Ligands in Metal–Organic Frameworks
Structure Description of 8
In the structure of 8, the zinc center is coordinated by
four oxygen atoms from four adi anions and one nitrogen
atom from a L2 ligand to furnish a distorted square-pyrami-
dal geometry (Figure 8, a). Each adi anion is coordinated
to four zinc ions, adopting a bis(bidentate-bridging) coordi-
nation mode. A pair of ZnII ions are bridged by four car-
boxylate groups from four adi anions to give a dinuclear
[Zn2(CO2)4] unit in which the Zn···Zn distance is 3.01 Å.
The [Zn2(CO2)4] units are linked by adi anions to form a
double-chain structure (Figure 8, b). These chains are fur-
ther connected by L2 ligands to form a 2-D (4, 4) network
(Figure 8, c).
Figure 9. (a) ORTEP diagram showing the coordination environ-
ment for the Cd atom in 9. (b) The infinite 2-D wavelike layer. (c)
View of the (H2O)4 cluster. (d) The packing diagram of 9 (dashed
lines represent hydrogen bonds).
Figure 8. (a) ORTEP diagram showing the coordination environ-
ment for the Zn atom in 8. (b) The infinite 1-D double chain com-
posed of Zn ions and adi anions. (c) View of the 2D layer.
Structure Description of 9
Structure Description of 10
In compound 9, the cadmium ion is six-coordinate by
In the structure of 10, the cadmium center is coordinated
two nitrogen atoms from two L1 ligands and four carboxyl- by two nitrogen atoms from two L2 ligands and four oxygen
ate O atoms from two adi anions, showing a distorted octa- atoms from two adi anions, showing a distorted octahedral
hedral geometry (Figure 9, a). Cadmium ions are bridged geometry (Figure 10, a). The topological analysis of 10 re-
by the bis(bidentate-chelating) adi anions to form an infi- veals that it is a typically diamondoid framework contain-
nite chain. These chains are further connected by L1 ligands ing large adamantanoid cages (Figure 10, b).[11c] The
to form a 2-D wavelike (4, 4) network (Figure 9, b).
Cd···Cd distances separated by the adi anion and L2 ligand
In the structure of 9, there exist (H2O)4 clusters (Fig- are 11.39 and 14.50 Å, respectively. In order to minimize
ure 9, c). Hydrogen bond data indicate that O1W donates the big void cavities and stabilize the framework, the poten-
hydrogen bonds to the carboxylate oxygen atom (O3) and tial voids formed by a single 3D network show incorpora-
water molecule (O2W#5) which in turn donates to O2#4 and tion of another three identical networks, thus giving a four-
O1W#5. The polymeric layers are linked by hydrogen-bond- fold interpenetrating diamondoid array (Figure 10, c). This
ing interactions to form two interpenetrating 3-D supramo- kind of fourfold interpenetrating structure has been de-
lecular structures (Figure 9, d).
scribed in previous reports.[14]
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Cd ions, adopting a bis(bidentate-chelating) coordination
mode.[15] The topological analysis of 11 reveals that it is
also a diamondoid framework (Figure 11, b). In principle,
the exploration of long ligands usually leads to large voids
that may further result in interpenetrating or entangled
structures. It is somewhat unexpected that no interpen-
etration occurs between the networks of 11. This may be
caused by the existence of the bulky benzyl groups of the
L3 ligand. There exist π-π stacking interactions between the
phenyl rings and benzimidazole rings of adjacent L3 li-
gands, with the centroid-to-centroid distance of 3.65 Å and
face-to-face distance of 3.40 Å (Figure 11, c).
The Effect of the Neutral Ligands on the Structure of the
Complexes
L1–L3 show similar structural features and display the
same bidentate bridging coordination mode with two aro-
matic N atoms coordinating to two different metal ions in
compounds 1–11. The similar frameworks may be expected
when L1, L2, and L3 are used, respectively. Indeed, com-
pounds 1 and 2 have similar structures; and compounds 3
and 4 also show similar frameworks.
Figure 10. (a) ORTEP diagram showing the coordination environ-
ment for the Cd atom in 10. (b) Single adamantanoid cage. (Light
gray lines represent the adi ligands and dark gray lines represent the
L2 ligands). (c) View of the fourfold interpenetrating diamondoid
framework.
Structure Description of 11
However, sometimes changes in the substituting groups
in the 2- and 2Ј-positions of the bis(benzimidazole) ligands
can result in changes in several aspects of the final frame-
works.
In compound 11, the cadmium ion is coordinated by four
oxygen atoms from two adi anions and two nitrogen atoms
from two L3 ligands, showing a distorted octahedral geome-
try (Figure 11, a). Each adi anion is coordinated to two
1. A change in dimensionalities for the coordination poly-
mers. Compounds 9 and 10 contain the same cadmium ion
and the same adi anion, and all adi anions display the same
coordination mode with each carboxylate group chelating
one cadmium ion. The replacement of the methyl group by
the ethyl group results in the change of frameworks from
the 2-D (4, 4) net to the 3-D diamondoid framework
through the fusion of the adjacent layers of 9. A change of
dimensionalities also occurs in compounds 5 and 6.
2. A change in interpenetrations for the frameworks. Al-
though both compounds 10 and 11 display the same dia-
mondoid framework, the replacement of the ethyl group by
the benzyl group results in a change from the fourfold inter-
penetrating framework of 10 to the noninterpenetrating
framework of 11 due to the larger volume of the benzyl
group compared to the ethyl group.
3. A change in M/L ratios for the compounds. The similar
synthetic conditions gave two compounds 7 and 8 with dif-
ferent M/L ratios (1:1 for 7 and 2:1 for 8) due to the change
of the substituting groups from the methyl to the ethyl
group.
4. A change in coordination modes of the anions. For com-
pounds 5 and 6, the change of the substituting groups from
the methyl to the ethyl group results in a change of the
coordination modes for the MES anions. A similar change
also occurred in 7 and 8.
Figure 11. (a) ORTEP diagram showing the coordination environ- The Effect of the Anions on the Structure of the Complexes
ment for the Cd atom in 11. (b) Single adamantanoid cage. (Light
From the structures of 1–11, it can be seen that the
anions play a very important role in the construction of the
gray lines represent the adi ligands and dark gray lines represent
the L2 ligands). (c) View of the π-π interaction.
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Flexible Ligands in Metal–Organic Frameworks
frameworks. The cin anion contains one carboxylate group, ture to 97 °C (obsd. 2.0%, calcd. 2.6%). The anhydrous
and coordinates to only one metal ion, acting as a terminal compound begins to decompose at 240 °C. For compound
ligand. And the related complexes (1–4) contain only one 3, the weight loss corresponding to the release of water
kind of connector (L1 or L2), and show 1-D chain struc- molecules is observed from room temperature to 149 °C
tures. The adi anion contains two carboxylate groups, act- (obsd. 2.4%, calcd. 2.7%). The anhydrous compound be-
ing as a bridging ligand. Complexes 7–11 have two kinds of gins to decompose at 278 °C. The TGA curve of 7 shows
bridging ligands [adi anion and bis(benzimidazole) ligand], that it undergoes dehydration in the range of 52–83 °C
and display 2-D or 3-D polymeric structures. The MES (obsd. 2.7%, calcd. 3.3%). The decomposition of the anhy-
anion adopts two kinds of coordination modes. Compound drous compound occurs at 231 °C. For compound 9, the
6 exhibits a 2-D polymeric structure, with the MES anion weight loss in the range of room temperature to 100 °C cor-
acting as a bidentate bridging ligand. In compound 5, the responds to the departure of water molecules (a weight loss
MES anion acts as an interesting tridentate ligand, and sil- of 2.1% is smaller than the calculated value, 5.9%, probably
ver ions are linked by MES anions to form dinuclear sub- resulting from a very slow liberation of the water molecules
units that are further bridged by bidentate L1 ligands to from 9 at room temperature).[16] For compound 11, the
form a 1-D chain structure.
weight loss in the range of 60–255 °C corresponds to the
departure of water molecules (obsd. 3.0%, calcd. 4.7%).
The removal of the organic components occurs at 283 °C.
The Effect of the Metal Ions on the Structure of the
Complexes
Luminescent Properties
From the structures of compounds 1–11, it can be seen
that the coordination behavior of metal ions have a great
influence on the structures of the complexes. In compounds
1–11, the metal ions display a variety of coordination num-
bers (from 3 to 6). Both ZnII and CdII ions have a closed
d10 electronic shell, and there is no crystal field stabilization
energy for them when their complexes are formed. The co-
ordination numbers of ZnII and CdII ions are mainly deter-
mined by the steric repulsion between different ligands.
Since the radius of the CdII ion is larger than that of the
ZnII ion, the coordination numbers of the CdII ions in 3, 4,
and 9–11 are larger than those of the ZnII ions in 1, 2, 7,
and 8. Although the radius of the AgI ion is larger than
that of the CdII ion, the coordination numbers of the AgI
ions in 5 and 6 are lower than those of the CdII ions because
the AgI ion and CdII ion have different valences.
On the basis of the above discussion, many factors, such
as the stoichiometric ratio of the components, the radii of
metal ions, the versatility of the metal coordination geome-
tries, and the donor characters of nitrogen and oxygen
atoms to the metals, play fundamental roles in the forma-
tion of the final products. Since these factors work together
to affect the structures, it is difficult to separate and ratio-
nalize them, and it is hard to propose definitive reasons as
to why each compound adopts a different configuration
with our present state of knowledge.
Luminescent compounds are of great current interest be-
cause of their various applications in chemical sensors, pho-
tochemistry, and electroluminescent (EL) display.[17] The
photoluminescent properties of compounds 1–11 were
studied at room temperature. The solid-state photolumines-
cent spectra of 1–11, and L1–L3 are depicted in Figure S10.
The wavelengths of the emission maxima and excitation are
listed in Table 2.
Table 2. Wavelengths λ [nm] of the emission maxima and exci-
tation.
Compound
1
2
3
4
5
6
λem
λex
423
358
465
405
438
375
408
358
479
420
363
296
Compound
7
8
9
10
11
λem
λex
412, 441 390
280 332
365, 441 360
292 295
445
396
The free L1, L2, and L3 ligands display luminescence with
emission maxima at 371, 365, and 413 nm (λex = 295 nm
for L1 and L2, λex = 340 nm for L3), respectively, which are
attributed to the πǞπ* transitions. The free Hcin shows an
emission maximum at 365 nm with two shoulder peaks at
384 and 405 nm (Figure S11). The emission peaks of com-
pounds 1–5, 7–9, and 11 are attributed to charge transfer
transition and the intraligand transition.[18,19] For com-
pounds 1–5, 8, and 11, the emission peaks of charge trans-
fer transition and the intraligand transition are mixed to-
gether, showing only one emission peak. Compounds 7 and
Thermal Analysis
In order to characterize the compounds more fully in 9 exhibit a main peak with a shoulder at 412 and 441 nm
terms of thermal stability, their thermal behaviors were for 7, and 365 and 441 nm for 9 upon excitation at 280 and
studied by thermogravimetric analysis (TGA). The experi- 292 nm, respectively. The peaks at 412 and 365 nm would
ments were performed on samples consisting of numerous be assigned to intraligand transitions of bis(benzimidazole)
single crystals of 1, 3, 7, 9, and 11 under N2 atmosphere ligands, while the shoulder peaks at 441 nm may be attrib-
with a heating rate of 10 °C/min (Figures S5–S9 and Table uted to the emission of charge transfer transitions. The
S2 in the Supporting Information).
emission peaks of compounds 6 and 10 are probably due
For compound 1, the weight loss corresponding to the to πǞπ* transitions of L2 ligands because similar peaks
release of water molecules is observed from room tempera- also appear for the free bis(benzimidazole) ligands.
Eur. J. Inorg. Chem. 2008, 745–755
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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751

J.-F. Ma et al.
FULL PAPER
68.02, H 5.75, N 8.01. IR (KBr): ν = 3416 (w), 2979 (w), 2939 (w),
˜
Conclusions
1687 (m), 1642 (s), 1610 (m), 1577 (m), 1465 (s), 1357 (s), 1306 (s),
In summary, 11 coordination polymers based on L1–L3
ligands and three different anions have been synthesized
and characterized. The results of this study not only illus-
trate that the changes of the substituting groups of bis(ben-
zimidazole) ligands play an important role in the construc-
1280 (m), 1191 (s), 1012 (w), 982 (m), 749 (s), 711 (w), 682 (w) cm–1.
Synthesis of [Cd(cin)2(L1)]·H2O (3):
A mixture of Cd(OH)2
(0.035 g, 0.2 mmol), Hcin (0.059 g, 0.4 mmol), and L1 (0.064 g,
0.2 mmol) in EtOH/H2O (1:4, v/v) (10 mL) was placed in a Teflon
reactor (15 mL). The mixture was heated at 160 °C for 3 d, then it
tion of coordination polymers, but also illustrate that the was gradually cooled to room temperature at a rate of 10 °Ch–1.
Colorless crystals of 3 were obtained. Yield 56% based on Cd-
coordination modes of anions and the coordination behav-
ior of metal ions can also have an influence on the final
frameworks. It is anticipated that more metal complexes
containing flexible divergent ligands with interesting struc-
tures as well as physical properties will be synthesized.
(OH)2 (0.083 g). C38H38CdN4O5 (743.12): calcd. C 61.42, H 5.15,
N 7.54; found C 61.29, H 5.05, N 7.49. IR (KBr): ν = 3737 (m),
˜
3680 (w), 3622 (w), 1742 (w), 1692 (m), 1645 (s), 1547 (s), 1513 (s),
1462 (m), 1397 (s), 1244 (w), 744 (w), 677 (s) cm–1.
Synthesis of [Cd(Cin)2(L2)] (4): The same synthetic method as for
3 was used except that L1 was replaced by L2 (0.070 g, 0.2 mmol).
Yield 50% based on Cd(OH)2 (0.075 g). C40H40CdN4O4 (753.16):
calcd. C 63.79, H 5.35, N 7.44; found C 63.68, H 5.26, N 7.49. IR
Experimental Section
General: All reagents and solvents for syntheses were purchased
from commercial sources and used without further purification.
The C, H, and N elemental analysis was conducted with a Perkin–
Elmer 240C elemental analyzer. The FT-IR spectra were recorded
from KBr pellets in the range 4000–400 cm–1 on a Mattson Alpha-
Centauri spectrometer. TGA was performed with a Perkin–Elmer
TG-7 analyzer heated from room temperature to 600 °C under ni-
trogen. The solid-state luminescent properties of compounds 1–11
were measured with a Perkin–Elmer LS55 spectrometer at room
temperature.
(KBr): ν = 3847 (w), 3736 (m), 3680 (m), 3621 (m), 1742 (w), 1693
˜
(m), 1644 (s), 1547 (s), 1512 (s), 1462 (s), 1391 (s), 1242 (m), 1066
(w), 745 (m), 678 (s) cm–1.
Synthesis of [Ag(MES)(L1)0.5] (5): A mixture of Ag2CO3 (0.028 g,
0.1 mmol), HMES (0.043 g, 0.2 mmol), and L1 (0.032 g, 0.1 mmol)
in ethanol (10 mL) was stirred for 30 min at room temperature.
The mixture was dissolved by dropwise addition of ammonia (5 ).
Colorless single crystals were obtained by slow evaporation of the
solution at room temperature. Yield 66% based on Ag2CO3
(0.030 g). C16H23AgN3O4S (461.30): calcd. C 41.66, H 5.03, N 9.11;
Synthesis of 1,1Ј-(1,4-Butanediyl)bis(2-methylbenzimidazole) (L1): A
mixture of NaOH (1.18 g, 30 mmol) and 2-methylbenzimidazole
(3.96 g, 30 mmol) in acetone (50 mL) was stirred at room tempera-
ture to give a clear solution, then 1,4-dibromobutane (3.24 g,
15 mmol) and NaI (0.1 g) were added. The mixture was stirred at
50 °C for 10 h. After removing the acetone, 50 mL of water was
added and a brown solid formed. The solid was recrystallized from
a mixture of water and ethanol (4:1, v/v) to give L1 as a light brown
crystalline solid. Yield 85% based on 2-methylbenzimidazole.
found C 41.68, H 5.04, N 9.09. IR (KBr): ν = 3848 (m), 3738 (s),
˜
3680 (m), 3619 (m), 2925 (m), 2801 (m), 2470 (w), 1741 (w), 1686
(m), 1645 (s), 1548 (s), 1513 (s), 1464 (m), 1060 (s), 672 (s), 630
(w), 487 (w) cm–1.
Synthesis of [Ag(MES)(L2)0.5]·H2O (6): The same synthetic
method as for 5 was used except that L1 was replaced by L2
(0.035 g, 0.1 mmol). Yield 68% based on Ag2CO3 (0.034 g).
C17H27AgN3O5S (493.35): calcd. C 41.39, H 5.52, N 8.52; found C
41.48, H 5.64, N 8.78. IR (KBr): ν = 3829 (m), 3736 (s), 3620 (m),
˜
Synthesis of 1,1Ј-(1,4-Butanediyl)bis(2-ethylbenzimidazole) (L2):
The same synthetic method as for L1 was used except that 2-meth-
ylbenzimidazole was replaced by 2-ethylbenzimidazole (4.38 g,
30 mmol). Yield 80% based on 2-ethylbenzimidazole.
3034 (m), 2933 (s), 1611 (w), 1513 (s), 1462 (s), 1408 (s), 1367 (m),
1323 (w), 1245 (w), 1152 (w), 747 (w), 672 (w) cm–1.
Synthesis of [Zn(adi)(L1)]·H2O (7): A mixture of ZnCO3 (0.025 g,
0.2 mmol), H2adi (0.029 g, 0.2 mmol), L1 (0.064 g, 0.2 mmol) in
EtOH/H2O (1:4, v/v) (10 mL) was placed in a Teflon reactor. The
mixture was heated at 180 °C for 3 d, and then it was gradually
cooled to room temperature at a rate of 10 °Ch–1. Colorless crystals
of 7 were obtained. Yield 50% based on ZnCO3 (0.055 g).
C26H32N4O5Zn (545.93): calcd. C 57.20, H 5.91, N 10.26; found C
Synthesis of 1,1Ј-(1,4-Butanediyl)bis(2-benzylbenzimidazole) (L3):
The same synthetic method as for L1 was used except that 2-meth-
ylbenzimidazole was replaced by 2-benzylbenzimidazole (6.25 g,
30 mmol). Yield 78% based on 2-benzylbenzimidazole.
Synthesis of [Zn(cin)2(L1)]·H2O (1): A mixture of ZnCO3 (0.025 g,
0.2 mmol), Hcin (0.059 g, 0.4 mmol), L1 (0.064 g, 0.2 mmol) in
EtOH/H2O (1:4, v/v) (10 mL) was placed in a Teflon reactor. The
mixture was heated at 180 °C for 3 d, and then it was gradually
cooled to room temperature at a rate of 10 °Ch–1. Colorless crystals
of 1 were obtained. Yield 50% based on ZnCO3 (0.070 g).
C38H38N4O5Zn (696.09): calcd. C 65.57, H 5.50, N 8.05; found C
55.30, H 6.05, N 9.89. IR (KBr): ν = 3736 (w), 3621 (w), 3444 (m),
˜
2941 (m), 2864 (w), 1614 (s), 1512 (s), 1463 (s), 1389 (s), 1288 (m),
1244 (m), 1014 (m), 938 (w), 851 (w), 745 (s), 672 (m), 430
(m) cm–1.
Synthesis of [Zn(adi)(L2)0.5] (8): A mixture of ZnCO3 (0.025 g,
0.2 mmol), H2adi (0.029 g, 0.2 mmol), L2 (0.069 g, 0.2 mmol) in
65.30, H 5.65, N 8.25. IR (KBr): ν = 3726 (w), 1645 (s), 1605 (m), EtOH/H2O (1:4, v/v) (10 mL) was placed in a Teflon reactor. The
˜
1497 (w), 1461 (m), 1417 (m), 1362 (s), 1012 (w), 978 (m), 749 (s),
mixture was heated at 160 °C for 3 d, and then it was gradually
cooled to room temperature at a rate of 10 °Ch–1. Colorless crystals
of 8 were obtained. Yield 54% based on ZnCO3 (0.041 g).
C17H21N2O4Zn (382.73): calcd. C 53.35, H 5.53, N 7.32; found C
685 (w) cm–1.
Synthesis of [Zn(cin)2(L2)] (2): A mixture of ZnCO3 (0.025 g,
0.2 mmol), Hcin (0.059 g, 0.4 mmol), L2 (0.069 g, 0.2 mmol) in
EtOH/H2O (1:4, v/v) (10 mL) was placed in a Teflon reactor. The
mixture was heated at 170 °C for 3 d, and then it was gradually
cooled to room temperature at a rate of 10 °Ch–1. Colorless crystals
of 2 were obtained. Yield 53% based on ZnCO3 (0.075 g).
C40H40N4O4Zn (706.13): calcd. C 68.04, H 5.71, N 7.93; found C
53.30, H 5.52, N 7.34. IR (KBr): ν = 3894 (w), 3847 (w), 3736 (s),
˜
3621 (m), 1836 (w), 1742 (m), 1692 (s), 1647 (s), 1513 (s), 1532 (s),
1548 (s), 1463 (m), 1389 (m), 675 (s) cm–1.
Synthesis of [Cd(adi)(L1)]·2H2O (9):
(0.035 g, 0.2 mmol), H2adi (0.029 g, 0.2 mmol), L1 (0.064 g,
A mixture of Cd(OH)2
752
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 745–755

Flexible Ligands in Metal–Organic Frameworks
0.2 mmol) in EtOH/H2O (1:4, v/v) (10 mL) was placed in a Teflon
reactor. The mixture was heated at 160 °C for 3 d, and then it was
gradually cooled to room temperature at a rate of 10 °Ch–1. Color-
less crystals of 9 were obtained. Yield 50% based on Cd(OH)2
(0.070 g). C26H30CdN4O6 (606.94): calcd. C 51.45, H 4.98, N 9.23;
Synthesis of [Cd(adi)(L3)]·2H2O (11): A mixture of Cd(OH)2
(0.035 g, 0.2 mmol), H2adi (0.029 g, 0.2 mmol), L3 (0.094 g,
0.2 mmol) in EtOH/H2O (1:4, v/v) (10 mL) was placed in a Teflon
reactor. The mixture was heated at 140 °C for 3 d, and then it was
gradually cooled to room temperature at a rate of 10 °Ch–1. Color-
found C 51.44, H 4.90, N 9.35. IR (KBr): ν = 3736 (w), 3597 (w), less crystals of 11 were obtained. Yield 58% based on Cd(OH)2
˜
2934 (w), 1676 (w), 1646 (m), 1623 (m), 1549 (s), 1512 (s), 1483 (s),
1415 (s), 1389 (s), 1304 (m), 1241 (w), 1126 (w), 744 (m), 674 (s),
425 (m) cm–1.
Synthesis of [Cd(adi)(L2)] (10): A mixture of Cd(OH)2 (0.035 g,
0.2 mmol), H2adi (0.029 g, 0.2 mmol), L2 (0.069 g, 0.2 mmol) in
EtOH/H2O (1:4, v/v) (10 mL) was placed in a Teflon reactor. The
mixture was heated at 180 °C for 3 d, and then it was gradually
cooled to room temperature at a rate of 10 °Ch–1. Colorless crystals
of 10 were obtained. Yield 53% based on Cd(OH)2 (0.070 g).
C28H34CdN4O4 (602.99): calcd. C 55.77, H 5.68, N 9.29; found C
(0.070 g). C38H42CdN4O6 (763.16): calcd. C 59.80, H 5.55, N 7.34;
found C 59.75, H 5.59, N 7.39. IR (KBr): ν = 3846 (w), 3736 (s),
˜
3670 (m), 1742 (w), 1643 (s), 1547 (s), 1512 (s), 1462 (s), 1391 (s),
1242 (m), 1067 (m), 979 (m), 745 (m), 678 (s), 423 (w) cm–1.
X-ray Crystallography: Single-crystal X-ray diffraction data for
compounds 3 and 11 were recorded with a Bruker Apex CCD dif-
fractometer with graphite-monochromated Mo-Kα radiation (λ =
0.71073 Å) at 293 K. Diffraction data for compounds 1, 2, and 4–
10 were collected with a Rigaku RAXIS-RAPID single-crystal dif-
fractometer with Mo-Kα radiation (λ = 0.71073 Å) at 293 K. Ab-
55.68, H 5.60, N 9.33. IR (KBr): ν = 3847 (w), 3736 (s), 3621 (m), sorption corrections were applied using the multi-scan technique.
˜
1692 (m), 2926 (m), 1741 (m), 1646 (s), 1565 (m), 1548 (s), 1532 All the structures were solved by direct methods using SHELXS-
(m), 1512 (s), 1464 (w), 1061 (s), 673 (s), 604 (w), 483 (w) cm–1.
97[20] and refined by full-matrix least-squares techniques using the
Table 3. Crystal data and structure refinements for compounds 1–4.
1
2
3
4
Empirical formula
Formula mass
Crystal system
Space group
C38H38N4O5Zn
696.09
monoclinic
P2/c
C40H40N4O4Zn
706.13
monoclinic
P2/c
C38H38CdN4O5
743.12
monoclinic
P2/c
C40H40CdN4O4
753.16
monoclinic
P2/c
a [Å]
b [Å]
c [Å]
α [°]
10.796(3)
8.987(3)
19.052(7)
90
10.861(4)
8.856(3)
19.466(6)
90
10.214(1)
9.160(1)
19.048(2)
90
11.290(5)
9.000(3)
18.711(6)
90
β [°]
94.20(2)
90
1843.5(11)
2
1.254
728
95.51(2)
90
878.3(1)
2
1.258
740
103.40(2)
90
1733.6(3)
2
1.424
764
94.67(2)
90
1894.9(13)
2
1.320
776
γ [°]
V [Å3]
Z
Dcalcd. [gcm–3]
F(000)
Reflections collected/unique
17611/4196
1.037
0.0523
0.1540
17688/4241
1.042
0.0651
0.1659
10599/4194
1.046
0.0623
0.1764
18095/4323
1.077
0.0479
0.1352
GOF on F2
[a]
R1 [I Ͼ 2σ(I)]
[b]
wR2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = |Σw(|Fo|2 – |Fc|2)|/Σ|w(Fo2)2|1/2
.
Table 4. Crystal data and structure refinements for compounds 5–8.
5
6
7
8
Empirical formula
Formula mass
Crystal system
Space group
C16H23AgN3O4S
461.30
monoclinic
C2/c
C17H27AgN3O5S
493.35
monoclinic
P21/n
C26H32N4O5Zn
545.93
C17H21N2O4Zn
382.73
triclinic
triclinic
¯
¯
P1
P1
a [Å]
b [Å]
c [Å]
α [°]
21.379(9)
9.867(3)
19.558(6)
90
117.36(1)
90
3664(2)
8
1.672
8.421(3)
11.803(6)
19.51(1)
90
93.83(2)
90
1934.8(16)
4
1.694
8.459(5)
9.507(7)
17.48(1)
81.10(2)
84.06(2)
69.11(2)
1295.9(14)
2
9.040(5)
9.366(5)
11.322(5)
81.10(2)
112.24(2)
99.87(2)
835.9(7)
2
β [°]
γ [°]
V [Å3]
Z
Dcalcd. [gcm–3]
F(000)
1.399
572
1.521
398
1880
1012
Reflections collected/unique
17527/4198
1.043
0.0252
0.0610
16479/4418
1.139
0.0349
12669/5834
1.102
0.0920
0.1827
8208/3779
1.049
0.0565
0.0851
GOF on F2
[a]
R1 [I Ͼ 2σ(I)]
[b]
wR2
0.0703
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = |Σw(|Fo|2 – |Fc|2)|/Σ|w(Fo2)2|1/2
.
Eur. J. Inorg. Chem. 2008, 745–755
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
753

J.-F. Ma et al.
FULL PAPER
Table 5. Crystal data and structure refinements for compounds 9–11.
9
10
11
Empirical formula
Formula mass
Crystal system
Space group
C26H34CdN4O6
610.97
C28H34CdN4O4
602.99
orthorhombic
Pbca
C38H42CdN4O6
763.16
monoclinic
Cc
triclinic
¯
P1
a [Å]
b [Å]
c [Å]
α [°]
8.608(3)
9.584(4)
17.451(8)
82.53(2)
85.05(2)
69.76(2)
1338.0(10)
2
18.294(3)
15.498(3)
19.285(4)
90
90
90
5467.7(19)
8
1.465
10.540(3)
22.909(4)
14.916(8)
90
102.09(2)
90
3522(2)
4
1.439
β [°]
γ [°]
V [Å3]
Z
Dcalcd. [gcm–3]
F(000)
1.516
628
2480
1576
Reflections collected/unique
13240/6061
1.064
0.0355
0.0888
48852/6232
1.023
0.0355
0.0737
10990/6306
0.987
0.0410
0.0760
GOF on F2
[a]
R1 [I Ͼ 2σ(I)]
[b]
wR2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = |Σw(|Fo|2 – |Fc|2)|/Σ|w(Fo2)2|1/2
.
SHELXL-97 program.[21] Non-hydrogen atoms were refined with
anisotropic temperature parameters. The disordered ligands in
compounds 4, 7, and 9 were refined using isotropic C atoms split
over two sites, with a total occupancy of 1. The hydrogen atoms of
the organic ligands were refined as rigid groups. Some water H
atoms in compound 11 could not be positioned reliably. Other H
atoms of water molecules were located from difference Fourier
maps. The detailed crystallographic data and structure refinement
parameters for 1–11 are summarized in Tables 3, 4 and 5. Selected
bond lengths and angles for compounds 1–11 are listed in Table S1
(see the Supporting Information).
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CCDC-656673 (for 1), -656674 (for 2), -656675 (for 3), -656676 (for
4), -656677 (for 5), -656678 (for 6), -656679 (for 7), -656680 (for
8), -656681 (for 9), -656682 (for 10), -656683 (for 11) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supporting Information (see also the footnote on the first page of
this article): Selected bond lengths and angles. View of the infinite
1-D zigzag chain of compound 2. Packing diagrams of compounds
3, 4, and 6. TGA diagrams of compounds 1, 3, 7, 9, and 11. The
solid-state photoluminescent spectra of 1–11, L1, L2, L3, and the
Hcin ligand.
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Acknowledgments
We thank the National Natural Science Foundation of China (No.
20471014), Program for New Century Excellent Talents in Chinese
University (NCET-05-0320), Program for Changjiang Scholars and
Innovative Research Teams in Chinese University, the Science
Foundation for Young Teachers of NENU (No. 20050310 and
20060304), and the Analysis and Testing Foundation of Northeast
Normal University for support.
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Received: August 8, 2007
Published Online: December 17, 2007
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