Syntheses, structures, luminescent and magnetic properties of a novel class of metal complexes constructed from 2-(2-pyridyl)benzimidazole and 5-hydroxy-1,3-benzenedicarboxylic acid

Article abstract of DOI:10.1016/j.ica.2011.02.092

Four novel metal coordination polymers, [Zn(2-PBIM)(OH-BDC)]_n (1), [Cd(2-PBIM)(OH-BDC)]_n (2), [Mn(2-PBIM)(OH-BDC)] _n·1.5nH₂O (3), [Cu(2-PBIM)(OH-BDC)] _n·nH₂O (4) [2-PBIM = 2-(2-pyridyl)benzimidazole; OH-H₂BDC = 5-hydroxy-1,3-benzenedicarboxylic acid], have been synthesized under hydrothermal conditions and structurally characterized by single crystal X-ray diffraction analysis, elemental analysis, IR spectroscopy, and thermogravimetric analysis. Compound 1 possesses left-handed screw (M-helix) and right-handed screw (P-helix) chains that are further connected though intermolecular hydrogen bonds and π-π stacking interactions resulting in a three-dimensional (3D) network. Compound 2 has a two-dimensional metal-organic framework which is connected into a 3D network by intermolecular hydrogen bonds and π-π stacking interactions. Compounds 3 and 4 are isostructural and possess one-dimensional (1D) channels. Free 2-PBIM and OH-H₂BDC ligands and complexes 1, 2 show fluorescent emissions in the visible and near-infrared region. Magnetic susceptibility measurements indicate that both 3 and 4 exhibit antiferromagnetic coupling between adjacent center atoms.

Full text of DOI:10.1016/j.ica.2011.02.092

Inorganica Chimica Acta 371 (2011) 27–35
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Syntheses, structures, luminescent and magnetic properties of a novel class
of metal complexes constructed from 2-(2-pyridyl)benzimidazole and
5-hydroxy-1,3-benzenedicarboxylic acid
Jing Li a, Chang-Chun Ji a, Liang-Fang Huang a, Yi-Zhi Li a, He-Gen Zheng a,b,
⇑
a State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructures,
Nanjing University, Nanjing 210093, PR China
b State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 April 2010
Received in revised form 18 February 2011
Accepted 27 February 2011
Available online 4 March 2011
Four novel metal coordination polymers, [Zn(2-PBIM)(OH-BDC)]n (1), [Cd(2-PBIM)(OH-BDC)]n (2),
[Mn(2-PBIM)(OH-BDC)]nꢀ1.5nH2O (3), [Cu(2-PBIM)(OH-BDC)]nꢀnH2O (4) [2-PBIM = 2-(2-pyridyl)benz-
imidazole; OH-H2BDC = 5-hydroxy-1,3-benzenedicarboxylic acid], have been synthesized under hydro-
thermal conditions and structurally characterized by single crystal X-ray diffraction analysis, elemental
analysis, IR spectroscopy, and thermogravimetric analysis. Compound 1 possesses left-handed screw
(M-helix) and right-handed screw (P-helix) chains that are further connected though intermolecular
Keywords:
hydrogen bonds and
2 has a two-dimensional metal-organic framework which is connected into a 3D network by intermolec-
ular hydrogen bonds and stacking interactions. Compounds 3 and 4 are isostructural and possess
p–p stacking interactions resulting in a three-dimensional (3D) network. Compound
X-ray crystal structures
Left-handed screw
Right-handed screw
Magnetic properties
Photoluminescent properties
p–p
one-dimensional (1D) channels. Free 2-PBIM and OH-H2BDC ligands and complexes 1, 2 show fluorescent
emissions in the visible and near-infrared region. Magnetic susceptibility measurements indicate that
both 3 and 4 exhibit antiferromagnetic coupling between adjacent center atoms.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
In this work, we chose 5-hydroxy-1,3-benzenedicarboxylic acid
(OH-H2BDC) as a bridging ligand and 2-(2-pyridyl)benzimidazole
Metal-organic coordination frameworks with various intriguing
structural motifs have been extensively studied for their versatile
chemical and physical properties and potential applications in
catalysis, molecular adsorption, magnetism, nonlinear optics,
molecular sensing and heterogeneous catalysis [1–9]. The rational
design and synthesis of coordination architectures is still in an ac-
tive research area with the current focus mainly on understanding
the factors to determine the crystal packing [10–12]. Additionally,
(2-PBIM) (Scheme 1) as a 2,20-bipyridyl-like chelating ligand to
construct new frameworks based on three characteristics as fol-
lows: (1) the phenol hydroxyl, carboxylic groups of OH-H2BDC
and amino groups of 2-PBIM can act as H-bond acceptors and
donors which can link subunits or low-dimensional entities into
high-dimensional supramolecular networks [23–26]. (2) 2-PBIM
ligand has larger conjugated
therefore, stacking interactions may play important roles in
p
-system than pyridine or 2,20-bipy,
p–p
some weak interactions, such as hydrogen bonds [13–17], C–Hꢀ ꢀ ꢀ
p
the formations of their complexes. (3) The carboxylic groups can
propagate magnetic superexchange between metal centers, as a
result some material with magnetism properties may be synthe-
sized [27,28]. In the present work, we synthesized four new
compounds with the OH-H2BDC and 2-PBIM ligands under hydro-
thermal conditions, and their photoluminescent properties and
magnetic properties have also been researched.
and stacking [18–20] interactions greatly control the supra-
p–p
molecular architecture of transition metal complexes and may lead
to the formation of oligomers, polymers, or porous frameworks
possessing unusual structures and fascinating properties. Consid-
ering all the aspects above, the skillful combination of bridging car-
boxylates, 2,20-bipyridyl-like chelating ligands and metal atoms
have generated many interesting coordination architectures
[21,22].
2. Experimental
2.1. Materials and measurements
⇑
Corresponding author at: State Key Laboratory of Coordination Chemistry,
School of Chemistry and Chemical Engineering, Nanjing National Laboratory of
Microstructures, Nanjing University, Nanjing 210093, PR China. Tel.: +86 25
83686155; fax: +86 25 83314502.
The 2-(2-pyridyl)benzimidazole (2-PBIM) ligand was synthe-
sized as reported previously [29,30]. All other starting materials
were of reagent quality and were obtained from commercial
E-mail address: zhenghg@nju.edu.cn (H.-G. Zheng).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.092

28
J. Li et al. / Inorganica Chimica Acta 371 (2011) 27–35
2.3. Preparation of the complexes
2.3.1. [Zn(2-PBIM)(OH-BDC)]n (1)
ZnSO4ꢀ7H2O (0.029 g, 0.10 mmol) was added into a solution of
2-PBIM (0.019 g, 0.10 mmol) and OH-H2BDC (0.021 g, 0.10 mmol)
in CH3OH (2 mL) and H2O (6 mL), which was adjusted to pH 8.0
with Et3N. The mixture was sealed in a 15 mL PTFE-lined stain-
less-steel acid digestion bomb and heated at 160 °C for 72 h. The
colorless crystals of 1 were collected by filtration and washed with
water. Yield: 45% based on 2-PBIM. Anal. Calc. for C20H13N3O5Zn: C,
54.50; N, 9.53; H, 2.97. Found: C, 54.59; N, 9.49; H, 3.04%. IR (KBr,
cmꢁ1): 3063(s), 1697(m), 1447(s), 1399(s), 1117(vs), 745(m),
618(w).
Scheme 1. Structures of OH-H2BDC and 2-PBIM ligand.
sources without further purification. The IR absorption spectra of
the complexes were recorded in the range of 400–4000 cmꢁ1 by
means of a Nicolet (Impact 410) spectrometer with KBr pellets
(5 mg of sample in 500 mg of KBr). Element analyses (C, H, N) were
carried out on a Perkin-Elmer model 240C analyzer. Luminescent
spectra were recorded with a SHIMAZU VF-320 X-ray fluorescence
spectrophotometer at room temperature (25 °C). PXRD measure-
ments were performed on a Bruker D8 Advance X-ray diffractom-
2.3.2. [Cd(2-PBIM)(OH-BDC)]n (2)
Compound 2 was prepared in the same way as that for 1 but
using CdSO4ꢀ6H2O (0.032 g, 0.10 mmol) to replace ZnSO4ꢀ7H2O,
and colorless crystals of 2 were obtained and collected by filtration,
washed with water, then dried in air, 60% yield (based on 2-PBIM).
Anal. Calc. for C20H13N3O5Cd: C, 49.25; H, 2.69; N, 8.62. Found: C,
49.31; H, 2.73; N, 8.54%. IR (KBr, cmꢁ1): 3404(s), 1647(vs),
1583(s), 1443(m), 1304(m), 741(s), 619(m), 551(w).
eter using Cu Ka radiation (0.15418 nm), in which the X-ray tube
was operated at 40 kV and 30 mA. Thermogravimetric analyses
were performed on a TGA V5.1A Dupont 2100 instrument from
room temperature to 750 °C with a heating rate of 10 °C/min under
N2 atmosphere. Temperature dependent magnetic susceptibility
data for polycrystalline 3 and 4 were obtained on a SQUID XL-7
magnetometer under an applied field of 2000 Oe over the temper-
ature range of 1.8–300 K.
2.3.3. [Mn(2-PBIM)(OH-BDC)]nꢀ1.5nH2O (3)
Mn(OAc)2ꢀ4H2O (0.025 g, 0.10 mmol) was added into a solution
of 2-PBIM (0.019 g, 0.10 mmol), OH-H2BDC (0.021 g, 0.10 mmol)
and Et3N (0.1 mmol) in CH3OH (2 mL) and H2O (6 mL). The resul-
tant mixture was placed in a Teflon-lined autoclave with a capacity
of 15 mL which was heated to 120 °C for 72 h. The yellow crystals
of 3 were collected by filtration and washed with water. Yield: 40%
based on 2-PBIM. Anal. Calc. for C20H16MnN3O6.5: C, 52.53; N, 9.19;
H, 3.53. Found: C, 52.62; N, 9.25; H, 3.44%. IR (KBr, cmꢁ1): 3420(s),
1552(m), 1440(m), 1382(vs), 789(m), 746(s).
2.2. Crystal structure determination
The crystal structures were determined by single-crystal X-ray
analyses. Data collections were performed using a Bruker-APS
SMART CCD area detector diffractometer with Mo K
a radiation
with an mode (k = 0.71073 Å). The structures were solved
u–x
with direct methods using the SHELXTL program [31] and refined
anisotropically with SHELXTL using full-matrix least squares proce-
dures. The structural plots were drawn using SHELXTL and Diamond
[32]. Crystal data and experimental details for the complexes are
given in Table 1. Selected bond lengths and angles are given in Ta-
ble S1.
2.3.4. [Cu(2-PBIM)(OH-BDC)]nꢀnH2O (4)
Compound 4 was prepared in the same way as that for 3
but using Cu(NO3)2ꢀ3H2O (0.024 g, 0.1 mmol) to replace
Mn(OAc)2ꢀ4H2O, and green crystals of
4 were obtained and
collected by filtration, washed with distilled water, then dried in
air. Yield: 40% based on 2-PBIM. Anal. Calc. for C20H15N3O6Cu: C,
Table 1
Crystallographic data and structure refinement details for compounds 1–4.
Compound
1
2
3
4
Formula
C
20H13N3O5Zn
C20H13N3O5Cd
487.73
monoclinic
P21/c
10.515(2)
10.041(2)
17.275(4)
90.00
C20H16N3O6.5Mn
457.30
monoclinic
C 2/c
15.711(4)
21.040(5)
14.319(3)
90.00
C20H15N3O6Cu
456.89
monoclinic
C 2/c
12.6291(13)
24.488(3)
14.2851(17)
90.00
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
440.70
monoclinic
P 21/n
7.3528(14)
10.835(2)
22.136(4)
90.00
a
(°)
b (°)
94.611(4)
90.00
1757.7(6)
4
1.665
1.438
98.187(4)
90.00
1805.4(7)
4
1.794
1.249
102.903(5)
90.00
4613.8(19)
8
1.317
0.612
108.074(3)
90.00
4199.9(8)
8
1.445
1.081
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
l
(Mo K
a
) (mmꢁ1
)
F(0 0 0)
896
968
1872
1864
Crystal size (mm)
Total unique data
0.22 ꢂ 0.26 ꢂ 0.28
8580, 3086
0.0647
0.20 ꢂ 0.22 ꢂ 0.28
9497, 3541
0.0372
0.22 ꢂ 0.24 ꢂ 0.28
12 325, 4531
0.0417
0.22 ꢂ 0.24 ꢂ 0.28
11 026, 4094
0.0401
(Rint
)
Observed data [I > 2
r
(I)]
2218
2972
3523
3057
Nref, Npar
3086, 293
0.0561, 0.0778
1.007
ꢁ0.409, 0.516
3541, 263
0.0463, 0.1004
1.056
ꢁ0.966, 0.363
4531, 278
0.0538, 0.1200
1.071
ꢁ0.528, 0.428
4094, 281
0.0578, 0.1376
1.071
ꢁ0.751, 0.632
R, wR2 (all data)
S (all data)
Minimum and maximum resd. densisty (e Åꢁ3
)

J. Li et al. / Inorganica Chimica Acta 371 (2011) 27–35
29
52.58; N, 9.20; H, 3.31. Found: C, 52.65; N, 9.31; H, 3.42%. IR (KBr,
cmꢁ1): 3420(s), 1635(s), 1543(m), 1406(m), 1383(s), 1271(w),
982(w), 744(m), 715(m).
3. Results and discussion
3.1. Crystal structure descriptions
3.1.1. [Zn(2-PBIM)(OH-BDC)]n (1)
Single-crystal X-ray diffraction analysis reveals that compound
1 is a 1D structure consisting of helical chains. The asymmetric unit
of compound 1 contains one zinc atom, one OH-BDC ligand and
one 2-PBIM ligand (Fig. 1a). Each Zn atom is six-coordinated by
four carboxylate O atoms from two OH-BDC ligands and two N
atoms from one 2-PBIM ligand. The geometry of the Zn atom is dis-
torted octahedral, with Zn–O and Zn–N distances in the ranges of
2.050(3)–2.124(4) Å and 2.073(3)–2.203(3) Å. Each OH-BDC ligand
coordinates to two Zn atoms via its carboxylate groups in a chelat-
ing fashion (Scheme 2a) to result in one-dimensional chains. While
the 2-PBIM ligand acts as a chelating ligand and arranges at the
sides of the chains (Fig. 1b). As to the OH-BDC ligand, the twisting
is observed that two carboxylate groups are not in the plane of
phenyl ring, with the dihedral angle between them being
14.415(3)° and 28.570(2)°, respectively. As a result, the left-handed
screw (M-helix) and right-handed screw (P-helix) chains can be
found (Fig. 1b). It should be noted that there are two types of
hydrogen bonds in this structure, N3–H6ꢀ ꢀ ꢀO1 and O5–H5Aꢀ ꢀ ꢀO2
with the distances [d(Dꢀ ꢀ ꢀA)] being 2.794(5) and 2.700(4) Å, with
angles of 154.47(4)° and 150.72(2)° (Table 2). Through these
O5–H5Aꢀ ꢀ ꢀO2 hydrogen bonds the above cited 1D chains are inter-
connected forming a wavelike layer (a 2D structure) in ab plane, as
shown in Fig. 1c. Furthermore, these layers are extended into a
three-dimensional (3D) network through intercalation between
the lateral 2-PBIM ligands from adjacent layers with the face-
to-face distance of 3.4941(4) Å (Fig. 1d), indicating significant
Fig. 1b. Left-handed screw (M-helix) and right-handed screw (P-helix) chains in 1
(hydrogen atoms are omitted for clarity).
interlayer
p–p stacking interaction. Similar intercalations have
been reported previously in some three-dimensional coordination
architectures constructed by two-dimensional layers [33]. Addi-
tionally, there are interlayer N–Hꢀ ꢀ ꢀO hydrogen bonds between N
Fig. 1c. Perspective views of the two-dimensional layers constructed by the helix
chains and O–Hꢀ ꢀ ꢀO hydrogen bonds (purple dotted lines) in 1 (part of H atoms and
2-PBIM ligands are omitted for clarity).
atoms from 2-PBIM ligands and O atoms from the carboxylate
groups of OH-BDC ligands, which further stabilize the structure,
as shown in Fig. 1d.
3.1.2. [Cd(2-PBIM)(OH-BDC)]n (2)
Single-crystal X-ray analysis reveals that compound 2 is a
two-dimensional (2D) framework in which the asymmetric unit
Fig. 1a. An ORTEP drawing of 1 showing 50% ellipsoid probability. Symmetry code:
#1 = 0.5 ꢁ x, 0.5 + y, 0.5 ꢁ z. (hydrogen atoms are omitted for clarity).

30
J. Li et al. / Inorganica Chimica Acta 371 (2011) 27–35
Fig. 1d. The three-dimensional network via
PBIM ligands between two adjacent layers is 3.4941(4) Å (part of H atoms are omitted for clarity).
p
–
p
stacking interaction and N–Hꢀ ꢀ ꢀO hydrogen bonds (purple dotted lines) in 1 that the face-to-face distance of the lateral 2-
Scheme 2. The OH-BDC ligand employs three different coordination modes in these four new complexes. (a) and (b) Represent the coordination modes of the ligand in 1 and
2, respectively; (c) represents the coordination mode of the ligand in 3 and 4.
Table 2
Hydrogen-bonding geometry (Å, °) for compounds 1–4.
D–Hꢀ ꢀ ꢀA
d(Dꢀ ꢀ ꢀA)
\D–Hꢀ ꢀ ꢀA
Complex 1a
N3–H6ꢀ ꢀ ꢀO1i
O5–H5Aꢀ ꢀ ꢀO2ii
Complex 2b
2.794(5)
2.700(4)
154(4)
150.8
N3–H3Aꢀ ꢀ ꢀO3i
O5–H5Aꢀ ꢀ ꢀO2ii
Complex 3c
2.776(5)
2.700(4)
147.0
162.8
N3–H3ꢀ ꢀ ꢀO4i
O5–H5Aꢀ ꢀ ꢀO4ii
O1W–H1Xꢀ ꢀ ꢀO2Wiii
Complex 4d
2.801(3)
2.753(3)
3.222(9)
160.4
117.2
128.6
N2–H2Aꢀ ꢀ ꢀO4i
2.674(4)
2.713(4)
166.4
113.1
O3–H3Bꢀ ꢀ ꢀO4ii
a
b
c
Symmetry codes: (i) ꢁx, ꢁy, ꢁz; (ii) x ꢁ 1, y, z.
Symmetry codes: (i) 1 ꢁ x, y + 1/2, ꢁz + 3/2; (ii) 2 ꢁ x, y + 1/2, ꢁz + 3/2.
Symmetry codes: (i) x + 1/2, y + 1/2, z; (ii) ꢁx, y, ꢁz + 3/2; (iii) ꢁx + 3/2, ꢁy + 3/2,
1ꢁz.
d
Symmetry codes: (i) 1 ꢁ x, ꢁy, ꢁz; (ii) 1 ꢁ x, y, ꢁz + 1/2.
Fig. 2a. An ORTEP drawing of 2 showing 50% ellipsoid probability (hydrogen atoms
are omitted for clarity). Symmetry codes: #1 = 2 ꢁ x, 0.5 + y, 1.5 ꢁ z; #2 = 2 ꢁ x,
ꢁ0.5 + y, 1.5 ꢁ z; #3 = x, 0.5 ꢁ y, 0.5 + z; #4 = x, 0.5 ꢁ y, ꢁ0.5 + z.
contains one Cd atom, one 2-PBIM ligand and one OH-BDC ligand.
All Cd atoms are equivalent and six-coordinated by two N atoms
from one 2-PBIM ligand and four O atoms from three OH-BDC li-
gands. As shown in Fig. 2a, 2-PBIM ligand also acts as a typical che-
lating ligand to coordinate to the Cd atom with the Cd–N bond
distances ranging from 2.312(4) to 2.393(4) Å and the N–Cd–N an-
gle being 70.77(14)°. Different from 1, the OH-BDC ligand adopts
the l3 chelating-bridging bidentate fashion to connect two Cd
atoms (Scheme 2b). Compound 2 contains Cd2O4 units that are
linked by four OH-BDC ligands to form a 2D network structure
(Fig. 2b), which is decorated with 2-PBIM ligands alternately at
two sides. Additionally, there exist O5–H5Aꢀ ꢀ ꢀO2 hydrogen bonds
the
l4-bridge mode with three Cd atoms: one carboxylate group
links one Cd atom in a monodentate mode and the other one in

J. Li et al. / Inorganica Chimica Acta 371 (2011) 27–35
31
Fig. 2b. (Left) View of 2D crystalline framework and O–HꢀꢀꢀO hydrogen bonds (purple dotted lines) in 2. (Right) Illustration of the (4, 4) 2D network structure. (2-PBIM ligands
are omitted for clarity, polyhedral representation of the structure of Cd2O4).
Fig. 2c. The 3D network formed by N–HꢀꢀꢀO hydrogen bonds (yellow dotted lines),
p–p stacking interaction between 2D sheets in 2 (green dotted lines).
Fig. 3a. An ORTEP drawing of 3 showing 30% ellipsoid probability (hydrogen atoms
and solvated water molecules are omitted for clarity). Symmetry codes: #1 = 1 ꢁ x,
y, 1.5 ꢁ z; #2 = 0.5 ꢁ x, 0.5 ꢁ y, 1 ꢁ z.
with the distances [d(Dꢀ ꢀ ꢀA)] being 2.700(4) Å (Fig. 2b, Table 2) in
the layer structure of 2 which further stabilize the structure of 2. In
order to facilitate viewing, the Cd2O4 units can be regarded as 4-
connected nodes and OH-BDC ligands act as 2-connected nodes.
Therefore, the whole structure can be represented as (4, 4) net,
as displayed in Fig. 2b (right). Furthermore, such layers are assem-
bled into a three-dimensional (3D) supramolecular network via
and the 8-membered rings (B rings) with the Mnꢀ ꢀ ꢀMn distances
of 7.6090(15) and 3.7414(10) Å, respectively (Fig. 3b). It should
be noted that the O(4) atoms of OH-BDC ligands are uncoordinated
but act as hydrogen-bonding acceptors to form O5–H5Aꢀ ꢀ ꢀO4
hydrogen bonds with hydroxy groups of the OH-BDC ligands, in
which O5ꢀ ꢀ ꢀO4 separations of 2.753(3) Å, and O5–H5Aꢀ ꢀ ꢀO4 angles
of 117.242(17)° (Table 2). The 1D chains mentioned above are
interconnected though these hydrogen bonds to result in a 2D
layer (Fig. 3c). While 2-PBIM ligand still acts as a chelating ligand
and alternately decorated at both sides of the layers (Fig. 3d). There
interlayer N3–H3Aꢀ ꢀ ꢀO3 hydrogen bonds (Table 2) and
p–p stack-
ing interactions between benzene-imidazole rings or pyridyl rings
of 2-PBIM ligands with the interplanar separation of 3.418 Å
(Fig. 2c).
3.1.3. [Mn(2-PBIM)(OH-BDC)]nꢀ1.5nH2O (3) and [Cu(2-PBIM)-
(OH-BDC)]nꢀnH2O (4)
are aromatic p–p stacking interactions between 2-PBIM groups of
adjacent layers [the distance between layers is 3.4850(25) Å],
which induce adjacent layers interdigitated in a claylike fashion
Single-crystal X-ray diffraction analysis reveals that compounds
3 and 4 are isostructural and crystallize in the monoclinic C2/c
space group. Only structure
3 is described here in detail.
[34] to form
a three-dimensional supramolecular network
Compound 3 has a three-dimensional supramolecular framework
formed by one-dimensional zigzag [Mn(2-PBIM)(OH-BDC)]n
chains. Asymmetric unit contains one Mn atom, one 2-PBIM ligand,
one OH-BDC ligand and one and a half lattice water molecules
(Fig. 3a). Each Mn atom is five-coordinated by three carboxylate
O atoms from three different OH-BDC ligands and two N atoms
from the 2-PBIM ligand. In this structure, the OH-BDC ligand
adopts only one kind coordination fashion (Scheme 2c): one car-
boxylate group adopts bis-monodentate coordination mode to
bridge two Mn(II) centers, and another carboxylate group acts as
a monodentate ligand. There exist binuclear Mn2(CO2)2 unit in
compound 3 that are bridged by four OH-BDC ligands to form 1D
double chains, which include the 16-membered rings (A rings)
Fig. 3b. View of one-dimensional chain structure of complex 3 with two kinds of
interlocking rings (H atoms and 2-PBIM ligands are omitted for clarity).

32
J. Li et al. / Inorganica Chimica Acta 371 (2011) 27–35
Fig. 3e. View of the 3D supramolecular network showing 1D channels in 3.
Fig. 3c. 2D layer structure of 3 connected by hydrogen bonds (black dotted lines, 2-
PBIM ligands are omitted for clarity).
3.2. Luminescent properties
(Fig. 3d). Additionally, there is one type of intermolecular
N3–H3ꢀ ꢀ ꢀO4 hydrogen bonds with the distances [d(Dꢀ ꢀ ꢀA)] being
2.801(3) Å (Fig. 3d, Table 2) between N atoms from 2-PBIM ligands
and O atoms from the carboxylate groups of OH-BDC ligands,
which further stabilize the supramolecular network. It is interest-
ing to find that there exist one-dimensional channels sized ca.
13.8 ꢂ 7.2 Å in the supramolecular network, which are occupied
by water molecules, as depicted in Fig. 3e. Calculation by PLATON
[35] shows that the channels occupy 31% of the crystal volume.
Structure of compound 4 is similar to compound 3 except that 4
contains only one lattice water in asymmetric unit, as shown in
Fig. S5. So we do not describe it here in detail.
During the past few years, the photoluminescent properties of
many d10 metal coordination polymers have been studied, and
the studies reveal that their luminescence behaviors are closely
associated with the central metal ions and the ligands coordinated
with them [36–38]. Taking into account the excellent lumines-
cence properties of d10 metal coordination polymers, the photolu-
minescent properties of the free 2-PBIM ligand, OH-H2BDC ligand
and compounds 1–4 have been investigated in the solid state at
room temperature (Fig. 4). The free OH-H2BDC ligand displays
luminescence with an emission maximum at 362 nm (kex
=
350 nm), while free 2-PBIM ligand displays luminescence with
two emission maximum at 397 and 449 nm (kex = 350 nm), which
Fig. 3d. Side view of the three-dimensional supramolecular network connected by hydrogen bonds (yellow dotted lines) and p–p stacking interaction in 3 (a = 3.4850(25) Å,
b = 3.4922(28) Å).

J. Li et al. / Inorganica Chimica Acta 371 (2011) 27–35
33
bridged Mn(II) ions, whereas the superchange interactions
between Mn(II) ions through the OH-BDC ligands can be ignored
because of the long length of the OH-BDC ligands. The magnetic
susceptibility data were fitted assuming that the carboxylate
bridges of the Mn(II) ions form an isolated spin dimer system
[40]. When the intermolecular magnetic coupling constants zj0
were taken into account, the magnetic susceptibility in the whole
temperature range was fitted to Eqs. (1) and (2), which are
ˆ
ˆ ˆ
deduced from the spin Hamiltonian H = ꢁ2J S1ꢀS2,
2Ng2b2
kT
v
¼
55e30J=kT þ 30e20J=kT þ 14e12J=kT þ 5e6J=kT þ e2J=kT
ꢂ
ð1Þ
ð2Þ
11e30J=kT þ 9e20J=kT þ 7e12J=kT þ 5e6J=kT þ 3e2J=kT þ 1
Fig. 4. Fluorescent emission spectra of 2-PBIM, OH-H2BDC ligands, 1 and 2 in the
v
solid state at room temperature.
vM
¼
1 ꢁ ð2zj0=Ng2b2Þ
v
can be assigned to the
p
ꢀ ꢀ ꢀ ⁄ transitions of the benzene-imidazole
p
where all symbols have their normal meanings. The best fitting gave
J = ꢁ2.24 cmꢁ1 and zj0 = ꢁ1.81 cmꢁ1 with a reasonable g-factor
(2.15) [41]. These results indicate that there exists antiferromag-
netic interaction within the Mn2 unit.
rings or pyridyl rings. When ligands are coordinated to zinc or cad-
mium centers, blue luminescence are observed. Compound 1 has a
slightly broader emission band with a kmax value of 435 nm and is
red-shifted by 73 nm compared to the free OH-H2BDC ligand. The
emission spectra of 2 show a broad and a slightly weaker emission
(bandwidth at half-height about 60 nm) centered at 440 nm. It is
clear that a significant red shift of the emission occurs in 1 and 2
compared with ligand, which is probably due to the ligand-to-me-
tal charge-transfer (LMCT) transition [39]. Emissions of 3 and 4 are
not observed in the solid state at room temperature, which may be
attributed to the effect of the central metal ion and coordinated
water molecules.
For 4 as shown in Fig. 6, upon lowering the temperature,
vMT
continuously decreases and reaches 0.014 cm3 K molꢁ1 at 1.8 K,
indicating the antiferromagnetic coupling between Cu ions. The va-
lue of
v
MT at 300 K is 0.74 cm3 K molꢁ1 which is closed to the ex-
pected value of 0.75 cm3 K molꢁ1 for two isolated high-spin Cu(II)
ions (g = 2 and s = 1/2). The single-crystal structure suggests that
4 is a uniform 1D chain and can be considered as an isolated spin
dimer system. When considering the impact of impurities and the
mean-field corrections zj0, the magnetic susceptibility in whole
temperature range was fitted to Eqs. (3) and (4) which is deduced
3.3. Magnetic properties
ˆ
ˆ ˆ
from spin Hamiltonian H = ꢁ2J S1ꢀS2.
The magnetic measurements were performed on polycrystalline
samples of 3 and 4 using a SQUID magnetometer under an applied
field of 2000 Oe over the temperature range of 1.8–300 K. The tem-
perature dependence of magnetic susceptibility of 3 in the forms of
2Ng2b2
kT
1
Ng2b2
2kT
v
¼ ð1 ꢁ
q
Þ
ꢂ
þ
q
ð3Þ
ð4Þ
3 þ eꢁ2J=kT
v
MT and vM versus T is displayed in Fig. 5. As the temperature
cools,
MT continuously decreases from 8.79 cm3 K molꢁ1 at
300 K to 0.09 cm3 K molꢁ1 at 1.8 K, indicating antiferromagnetic
v
v
vM
¼
1 ꢁ ð2zj0=Ng2b2Þ
v
coupling between Mn ions. The value of
vMT at 300 K is closed to
the expected value of 8.75 cm3 K molꢁ1 for two isolated high-spin
Mn(II) ions (g = 2 and s = 5/2). From the viewpoint of crystal struc-
ture, it could be presumed that the main magnetic interactions
between the metal centers might happen between two carboxylate
All symbols have their normal meanings. The best fit leads to the
parameter values J = ꢁ8.83 cmꢁ1, zj0 = ꢁ0.52 cmꢁ1
, q = 0.04% and
g = 2.14 cmꢁ1. The negative J value shows antiferromagnetic cou-
pling between metal atoms.
Fig. 5. Temperature dependence of magnetic susceptibility in the form of vM and
Fig. 6. Temperature dependence of magnetic susceptibility in the form of vM and
vMT vs. T for compound 3. The solid lines are the fits of the data.
vMT vs. T for compound 4. The solid lines are the fits of the data.

34
J. Li et al. / Inorganica Chimica Acta 371 (2011) 27–35
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2010.
Acknowledgments
This work was supported by grants from the Natural Science
Foundation of China (Nos. 20971065; 91022011; 21021062) and
National Basic Research Program of China (2007CB925103;
2010CB923303).
Appendix A. Supplementary material
CCDC 762028–762031 contain the supplementary crystallo-
graphic data for compounds 1–3. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.02.092.
Fig. 7. The TGA diagram of compounds 1–4.
3.4. Thermogravimetric analyses and X-ray powder diffraction
In order to examine the thermal stabilities of these compounds,
we carried out TG analyses (Fig. 7). Samples 1–4 were heated to
750 °C under N2 atmosphere with a heating rate of 10 °C/min.
The TGA study of compound 1 shows no weight loss from room
temperature to 325 °C, suggesting that the framework is thermally
stable. Above 325 °C, a rapid weight loss is observed which is
attributed to the decomposition of the organic ligands. The TGA
curve for 2 shows that compound 2 is more stable than compound
1, it can be stable up to 400 °C and above that the decomposition of
the compound 2 occurred. For compound 3, it shows three steps of
weight loss. The first weight loss of 6.0% between 22 and 300 °C
corresponds to the loss of one and a half lattice water molecules
(calcd 5.9%). The other two steps correspond to the decomposition
of two kinds of organic ligands which began above 305 °C. For com-
pound 4, the first weight loss is observed from 44 to 125 °C which
is attributed to the loss of one lattice water molecules, with a
weight loss of 3.0% (calcd 3.31%). No further weight loss was ob-
served until it reached 293 °C, at which a rapid weight loss oc-
curred, corresponding to the decomposition of the organic
ligands. The purities of polymers are confirmed by X-ray power dif-
fraction analyses, in which the experimental spectra of polymers
1–4 are almost consistent with their simulated spectra (Figs. S1–
S4, Supporting information).
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4. Conclusions
In summary, we successfully synthesized four novel coordina-
tion polymers based on 2-PBIM and OH-H2BDC ligands with differ-
ent metals by solvothermal method. All these compounds get the
3D supramolecular structures through intermolecular interactions.
It demonstrates that the weakly intermolecular interactions, such
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