Two different dimensional bbbm-based cobalt(II) coordination polymers tuned by benzenedicarboxylates: Assembly, structures and properties

Article abstract of DOI:10.1016/j.ica.2012.11.024

Two new metal-organic coordination polymers [Co₄(bbbm) ₄(1,2-BDC)₄(H₂O)]·2H₂O (1) and [Co(bbbm)(1,4-BDC)] (2) (bbbm = 1,1-(1,4-butanediyl)bis-1H-benzimidazole, 1,2-H₂BDC = 1,2-benzenedicarboxylic acid and 1,4-H₂BDC = 1,4-benzenedicarboxylic acid) were obtained under hydrothermal conditions and structurally characterized. Polymer 1 exhibits a two-dimensional (2D) 4-connected network with the Co^II ions as four-connected nodes, and the bbbm and 1,2-BDC ligands as linkers. Polymer 2 possesses a novel three-dimensional (3D) 3-fold interpenetrated framework. The position of carboxyl groups for benzenedicarboxylates dominates the final structures of 1 and 2. Furthermore, elemental analysis, IR spectroscopy, thermogravimetric analysis, electrochemical properties and solid state fluorescence for 1 and 2 were investigated.

Full text of DOI:10.1016/j.ica.2012.11.024

Inorganica Chimica Acta 397 (2013) 88–93
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Two different dimensional bbbm-based cobalt(II) coordination polymers tuned
by benzenedicarboxylates: Assembly, structures and properties
⇑
⇑
Xiu-Li Wang , Li-Li Hou, Ju-Wen Zhang , Guo-Cheng Liu, Bao Mu, Hong-Yan Lin
Department of Chemistry, Bohai University, Liaoning Province Silicon Materials Engineering Technology Research Center, Jinzhou 121000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 July 2012
Received in revised form 5 November 2012
Accepted 16 November 2012
Available online 12 December 2012
Two new metal–organic coordination polymers [Co4(bbbm)4(1,2-BDC)4(H2O)]Á2H2O (1) and
[Co(bbbm)(1,4-BDC)] (2) (bbbm = 1,1-(1,4-butanediyl)bis-1H-benzimidazole, 1,2-H2BDC = 1,2-benzen-
edicarboxylic acid and 1,4-H2BDC = 1,4-benzenedicarboxylic acid) were obtained under hydrothermal
conditions and structurally characterized. Polymer 1 exhibits a two-dimensional (2D) 4-connected net-
work with the CoII ions as four-connected nodes, and the bbbm and 1,2-BDC ligands as linkers. Polymer
2 possesses a novel three-dimensional (3D) 3-fold interpenetrated framework. The position of carboxyl
groups for benzenedicarboxylates dominates the final structures of 1 and 2. Furthermore, elemental anal-
ysis, IR spectroscopy, thermogravimetric analysis, electrochemical properties and solid state fluorescence
for 1 and 2 were investigated.
Keywords:
Bis(benzimidazole)-based ligand
Benzenedicarboxylate
Coordination polymer
Crystal structure
Ó 2012 Elsevier B.V. All rights reserved.
Electrochemical property
1. Introduction
flexible 1,1-(1,4-butanediyl)bis-1H-benzimidazole (bbbm) ligand,
two types of benzenedicarboxylic acids, namely, 1,2-benzenedi-
The construction of novel metal–organic coordination polymers
(MOCPs) has received much attention due to their promising appli-
cation in chemical separation [1,2], proton conductivity [3–5],
selective adsorption [6,7], luminescence [8–10], magnetic materi-
als [11–13], etc. The selection of suitable organic ligands plays cru-
cial roles in the constructions of desirable MOCPs. In the past
decade, the self-assembly of MOCPs based on the flexible
bis(imidazole), bis(triazolyl) and bis(tetrazole) derivatives and
polycarboxylates mixed ligands has been of an attractive area of
research [14–16], which is usually based on the following reasons:
(i) the flexible N-donor linkers may adopt diverse conformation
when they are coordinated to the central metal ions [17]; (ii) mul-
tidentate carboxylate ligands are extensively applied in the con-
structions of high dimensional MOCPs due to their various
coordination modes [18–20]. As is known, the constructions of
MOCPs based on the flexible bis(benzimidazole) and auxiliary
polycarboxylate system have been already reported [21–26]. How-
ever, the systematic studies on the effect of position of carboxyl
groups for aromatic polycarboxylates on the structures of MOCPs
based on the flexible bis(benzimidazole)-based ligands are still
limited in the literatures.
carboxylic acid (1,2-H2BDC) and 1,4-benzenedicarboxylic acid
(1,4-H2BDC) were selected as auxiliary ligands to construct the tar-
get coordination polymers (Scheme 1). As a result, two coordination
polymers [Co4(bbbm)4(1,2-BDC)4(H2O)]Á2H2O (1) and [Co(bbbm)
(1,4-BDC)] (2), were obtained and their syntheses, crystal structures,
electrochemical and luminescent properties were reported.
2. Experimental
2.1. Materials and measurements
All reagents were purchased from commercial sources and used
without further purification. Ligand bbbm was synthesized accord-
ing to the literature method [27]. FT-IR data were collected on a
Magna FT-IR 560 spectrometer (KBr pellets). Elemental analyses
were performed on a Perkin-Elmer 2400 CHN elemental analyzer
(C, H and N). Thermogravimetric analyses (TGA) were measured
on a Pyris Diamond TG/DTA under a N2 atmosphere with a heating
rate of 10 °C minÀ1. Fluorescence spectra were recorded on a Hit-
achi F-4500 fluorescence/phosphorescence spectrophotometer at
room temperature. Electrochemical measurements were carried
out on a CHI 440 electrochemical workstation. A conventional
three-electrode system was used at room temperature. The title
polymer chemically bulk-modified carbon paste electrodes (CPE)
were used as the working electrodes. A saturated calomel electrode
(SCE) was used as the reference electrode, and a platinum wire as
the auxiliary electrode.
In this work, in order to explore the effect of carboxyl position of
polycarboxylate linkers on the structures of MOCPs based on the
⇑
Corresponding authors. Tel.: +86 416 3400158 (X.-L. Wang), tel.: +86 416
3400308 (J.-W. Zhang).
E-mail addresses: wangxiuli@bhu.edu.cn (X.-L. Wang), juwenzhang@yahoo.cn
(J.-W. Zhang).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.11.024

X.-L. Wang et al. / Inorganica Chimica Acta 397 (2013) 88–93
89
Table 1
The crystal and structure refinement data for polymers 1 and 2.
Complexes
1
2
Formula
C
104H94Co4N16O19
C26H22CoN4O4
513.41
monoclinic
C2/c
16.225(5)
18.445(5)
16.083(5)
90
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
2107.66
monoclinic
P21/c
27.993(5)
10.587(2)
33.716(6)
90
a
(°)
b (°)
107.199(3)
90
9545(3)
4
1.465
0.764
108.718(5)
90
4559(2)
8
1.496
0.795
c
(°)
V (Å3)
Z
Dcalc (g cmÀ3
)
Scheme 1. The bbbm ligand and benzenedicarboxylic acids in this paper.
l
(mmÀ1
)
2.2. Syntheses of 1 and 2
F(000)
4351.0
0.0880
0.2303
0.998
2120.0
0.0774
0.1497
1.015
a
R1 (I > 2
r
(I))
b
wR2 (all data)
2.2.1. Synthesis of [Co4(bbbm)4(1,2-BDC)4(H2O)]Á2H2O (1)
GOF on F2
Polymer 1 was synthesized by hydrothermal reaction. A mix-
ture of CoCl2Á6H2O (0.024 g, 0.10 mmol), bbbm (0.015 g,
0.05 mmol), 1,2-H2BDC (0.008 g, 0.05 mmol), H2O (10 mL) and
NaOH (0.10 mol LÀ1, 2 mL) was stirred for 1 h in air, and then
sealed in a 25 mL Teflon-lined stainless-steel autoclave at 150 °C
for 72 h. The reaction system was then slowly cooled to room tem-
perature at a rate of 4 °C hÀ1. Purple block crystals of 1 were col-
lected from the final reaction system by filtration and washed
with distilled water and acetone. Yield: 56% (based on Co). Anal.
Calc. for C104H94Co4N16O19 (2107.66): C, 59.26; H, 4.50; N, 10.63.
Found: C, 59.43; H, 4.37; N, 10.75%. IR (KBr, cmÀ1): 3128 w, 2364
s, 2329 m, 1612 m, 1580 s, 1539 m, 1510 m, 1394 s, 1300 w,
1257 w, 829 m, 810 w, 743 s, 671 w, 545 s.
a
R1
wR2 = [
=
R
||Fo| À |Fc||/
R|Fo|.
b
2
R
w(Fo À Fc2)2/
R .
w(Fo2)2]1/2
electrical contact was established with a copper stick [28]. The same
procedure was used for the preparation of bare CPE and 2-CPE.
2.4. X-ray crystallography study
X-ray diffraction data for 1 and 2 were collected on a Bruker
Smart Apex CCD diffractometer with Mo
K
a
radiation
(k = 0.71073 Å for 1 and k = 0.71069 Å for 2). The structures were
solved by direct methods using the program SHELXS-97, and all
non-hydrogen atoms were refined anisotropically on F2 by the
full-matrix least-squares technique using the SHELXL-97 crystallo-
graphic software package [29]. The hydrogen atoms except for
those of water molecules were generated geometrically and re-
fined with isotropic thermal parameters. The crystal data and
structure refinements for 1 and 2 are listed in Table 1. Selected
bond distances (Å) and angles (°) for 1 and 2 are provided in
Table S1. Crystallographic data for 1 and 2 have been deposited
in the Cambridge Crystallographic Data Center with CCDC refer-
ence numbers 882695 and 882696 for 1 and 2, respectively.
2.2.2. Synthesis of [Co(bbbm)(1,4-BDC)] (2)
Synthesis of 2 is similar to that of 1 except that 1,4-H2BDC
(0.025 g, 0.15 mmol) was used instead of 1,2-H2BDC. Purple block
crystals of 2 were obtained in a 47% yield based on Co. Anal. Calc.
for C26H22CoN4O4 (513.41): C, 60.82; H, 4.32; N, 10.91. Found: C,
60.98; H, 4.21; N, 11.07%. IR (KBr, cmÀ1): 2357 s, 1619 m, 1556
m, 1494 w, 1385 s, 1170 m, 828 s, 739 s, 650 s, 596 w, 559 w.
2.3. Preparation of 1 and 2-CPEs
Polymer 1 bulk-modified carbon paste electrode (1-CPE) was fab-
ricated as follows: 0.030 g of 1 and 0.500 g of graphite powder were
mixed and ground together by the agate mortar and pestle to
achieve an even mixture, and then 0.15 mL of paraffin oil was added
into the mixture with stirring. The resulting mixture was packed
into a glass tube with 3 mm inner diameter to a length of 8 mm,
and the tube surface was wiped with the weighing paper. The
3. Results and discussion
3.1. Crystal structure description
3.1.1. Crystal structure of 1
Single crystal X-ray diffraction analysis reveals that polymer 1
crystallizes in the monoclinic space group P21/c. The asymmetric
Fig. 1. Coordination environment of the CoII ions in 1. All hydrogen atoms and interstitial water molecules are omitted for clarity. Symmetry codes: #1 Àx + 1, y À 1/2, Àz + 1/
2; #2 Àx + 1, y + 1/2, Àz + 1/2; #3 x + 1, y, z + 1.

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X.-L. Wang et al. / Inorganica Chimica Acta 397 (2013) 88–93
Fig. 3. Coordination environment of the CoII ion in 2. All hydrogen atoms are
omitted for clarity.
one 1,4-BDC anion. As depicted in Fig. 3, Co1 is six-coordinated
by two nitrogen atoms from two bbbm ligands and four oxygen
atoms from two 1,4-BDC anions, furnishing a distorted octahedron
geometry. The Co–N bond distances are 2.056(6) (Co1–N1) and
2.069(6) (Co1–N5) Å, and the Co–O bond distances vary in the
range of 2.066(5)–2.264(5) Å (Table S1), which are similar to those
of 1.
As shown in Fig. 4a, the CoII ions are connected by the bbbm
bridges to form a 1D chain in 2. The adjacent 1D chains are linked
by the 1,4-BDC ligands to give rise to a 2D layer along the ab plane
(Fig. 4b). It is interesting that, in the 2D layer, there are two kinds
of cycles, namely, the small Co4bbbm2BDC2 rings and large Co8-
bbbm6BDC2 rings. The 2D layers are further connected by the
1,4-BDC ligands to build a 3D framework (Fig. 4c). If we define
the CoII ion as a 4-connected node, and the bbbm and 1,4-BDC li-
gands as spacers, the 3D framework structure with a Schfäli sym-
bol (42Á63Á8) can be schematically represented by Fig. 5a. By
Fig. 2. (a) 1D chain formed by the CoII ions and bbbm ligands in 1. (b) 2D layer of 1
constructed from the 1D chains and 1,2-BDC anions along the ab plane. (c) 2D 4-
connected topological structure of 1.
unit consists of four CoII ions, four bbbm ligands, four 1,2-BDC an-
ions, one coordinated water molecule and two interstitial water
molecules. The coordination environment of four crystallographi-
cally independent CoII ions is given in Fig. 1. Co1 is five-coordinated
by two nitrogen atoms from two bbbm ligands and three oxygen
atoms from two 1,2-BDC anions, completing a distorted square
pyramid geometry. Co2 is six-coordinated by two nitrogen atoms
from two bbbm ligands and four oxygen atoms from two 1,2-
BDC anions and one water molecule in a distorted octahedron
geometry. The coordination environment of Co3 and Co4 is similar
to that of Co1. The Co–N and Co–O bond distances are in the range
of 2.023(7)–2.081(7) and 1.936(6)–2.381(6) Å (Table S1), respec-
tively, which are comparable to those of the similar cobalt com-
plexes [30,31].
In 1, each CoII ions is bridged by the bbbm ligands to form 1D
chains (Fig. 2a), which are further extended by the 1,2-BDC anions
into a 2D layer (Fig. 2b). As shown in Fig. 2b, the Co1 and Co3 ions
are connected by the 1,2-BDC anions to generate 1D Co1–1,2-BDC
and Co3–1,2-BDC chains, respectively, and the 1,2-BDC anions link
the Co2 and Co4 ions from adjacent 1D Co-bbbm chains to give the
1D Co2–1,2-BDC–Co4 chains. The Co1–1,2-BDC, Co2–1,2-BDC–Co4
and Co3–1,2-BDC chains are alternately arrayed in the 2D layer. If
each CoII ion is considered as a four-connected node, and the bbbm
and 1,2-BDC ligands as linkers, polymer 1 possesses a 2D 4-con-
nected topological structure (Fig. 2c) with a Schfäli symbol of
(44Á62). In 1, the 1,2-BDC anion only adopts one type of coordina-
tion mode (chelating-monodentate) (Scheme S1), which have been
observed in the reported 1,2-BDC metal complexes [32,33].
3.1.2. Crystal structure of 2
Fig. 4. (a) 1D chain formed by the CoII ions and bbbm ligands in 2. (b) 2D layer of 2
constructed from the 1D chains and 1,4-BDC anions. (c) 3D framework built by the
2D layers and 1,4-BDC anions.
Polymer 2 crystallizes in the monoclinic space group C2/c. The
asymmetric unit consists of one CoII ion, one bbbm ligand and

X.-L. Wang et al. / Inorganica Chimica Acta 397 (2013) 88–93
91
Obviously, the position of carboxyl groups for benzenedicarboxy-
lates plays an important role in the final structures of 1, 2 and 3
(Fig. 6).
3.3. Thermogravimetric analyses
To assess the thermal stability of 1 and 2, thermogravimetric
analysis was performed under nitrogen atmosphere in the temper-
ature range of 25–800 °C with a heating rate of 10 °C minÀ1. As can
be seen from the thermal curves (Fig. S1), polymer 1 exhibits three
separate steps of weight losses, while polymer 2 features one main
step. For 1, the first weight loss step is observed in the range of 50–
130 °C, corresponding to the release of coordinated and interstitial
water molecules (found, 2.28 wt.%; calcd, 2.56 wt.%). The second
and third successive weight losses from 325 to 750 °C may be
attributed to the decomposition of bbbm and 1,2-BDC ligands
(found, 83.08 wt.%; calcd., 83.22 wt.%). The crystal networks of 2
are stable up to 430 °C. The successive weight losses in the range
of 430–780 °C correspond to the decomposition of bbbm and 1,4-
BDC ligands (found, 85.05 wt.%, calcd., 85.40 wt.%). The remaining
residues (14.64% for 1, 14.95% for 2) correspond to CoO.
Fig. 5. (a) Single 3D topological framework for 2. (b) Schematic representation of
the 3D 3-fold interpenetrated topological nets for 2.
careful inspection of the structure for 2, the single 3D framework
incorporating with another two identical networks, gives a 3-fold
interpenetrated network (Fig. 5b). To the best of our knowledge,
polymer 2 is the rare 3D 3-fold interpenetrated network con-
structed from the flexible bis(benzimidazole)-based ligand
[34,25]. In 2, the 1,4-BDC anion only adopts one type of chelat-
ing-bis(bidentate) coordination mode (Scheme S1), which have
been observed in the reported 1,4-BDC metal complexes [35,18].
3.4. Electrochemical properties
Redox properties of 1 and 2 were investigated in 0.5 M Na2SO4
aqueous solution with title complexes bulk-modified CPEs as
working electrodes, because polymers 1 and 2 are stable and insol-
uble in 0.5 M Na2SO4 aqueous solution. As shown in Fig. 7 and
Fig. S2, the electrochemical behaviors for 1 and 2 are similar except
for some slight potential shifts. Thus, only the 1-CPE is representa-
tively described in detail here. Fig. 7a displays the cyclic voltam-
mograms for 1-CPE at different scan rates in the potential range
of 0 to 900 mV. A pair of reversible redox peaks are observed,
which can be attributed to the redox of CoIII/CoII [37], and the mean
peak potential E1/2 = (Epa + Epc)/2 is +380 mV (100 mV sÀ1). As seen
in Fig. 7a, with the scan rates increasing from 40 to 500 mV sÀ1, the
peak potentials changed gradually: the cathodic peak potentials
gradually shift to the negative direction, and the corresponding
anodic peak potentials shift to the positive direction. Fig. 7b shows
the plots of peak currents versus scan rates, which indicates the re-
dox process of 1-CPE is surface-controlled.
3.2. Effect of benzenedicarboxylates on the structures of 1 and 2
In this work, bbbm was used as the main ligand, and two kinds
of benzenedicarboxylates were used as the auxiliary ligands, aim-
ing at exploring the effect of position of carboxyl groups for ben-
zenedicarboxylates on the assembly of 1 and 2. According to the
above structural description, bbbm uniformly behaves as the
bidentate spacers to link the CoII ions in 1 and 2. When 1,2-BDC an-
ion was used as an ancillary ligand, a 2D 4-connected network of 1
was obtained. In order to investigate the influence of position of
carboxyl groups for benzenedicarboxylates on the structures of
target compounds, 1,4-BDC was employed as auxiliary ligand in
the synthesis of 2, and a 3D 3-fold interpenetrated framework
was constructed. In addition, we have obtained and structurally
characterized another bbbm-based cobalt(II) polymer using 1,3-
BDC anion as auxiliary ligand, i.e. [Co(bbbm)(1,3-BDC)]ÁH2O (3) in
our previous work, which exhibits a 2D (4,4) network [36]. Poly-
mers 1 and 3 possess the different 2D network structures, whereas
polymer 2 displays a novel 3D 3-fold interpenetrated structure.
3.5. Photoluminescent properties
Previous studies have shown that the metal–organic
coordination polymers display photoluminescent properties, and
may have potential application as fluorescence materials [38].
Fig. 6. Effect of carboxyl position of auxiliary benzenedicarboxylates on the structures of 1–3.

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X.-L. Wang et al. / Inorganica Chimica Acta 397 (2013) 88–93
Comparing with the free bbbm ligand, the emission maxima of 1
and 2 uniformly are blue-shifted. They are 399 nm (kex = 250 nm)
for 1 (Fig. 8), 406 nm (kex = 250 nm) for 2 (Fig. S3). The emission
bands of 1 and 2 might be attributed to the intraligand charge
transfer transitions [39,40].
4. Conclusions
Two new CoII coordination polymers constructed from flexible
bbbm and different benzenedicarboxylates have been hydrother-
mally obtained under similar synthetic conditions. The position
of carboxyl groups for auxiliary benzenedicarboxylates shows a
great influence on the final structures of 1 and 2. The polymers 1
and 2 exhibit good electrochemical and photoluminescent proper-
ties, demonstrating their potential applications in the electrochem-
ical and luminescent field.
Acknowledgments
This research was financially supported by the National Natural
Science Foundation of China (Nos. 21171025 and 21101015), the
Program for New Century Excellent Talents in University (NCET-
09-0853) and the Natural Science Foundation of Liaoning Province
(201102003).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2012.11.024.
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