A novel 2D tubular polymer based on flexible bis-methylbenzimidazole ligand

Article abstract of DOI:10.1080/15533174.2011.615783

A novel metal-organic polymer [Cd(bmb)(p-bdc)]_n (1) (bmb = (1,4-bis(2-methylbenzimidazol-1-ylmethyl) benzene); p-H₂bdc = p-benzenedicarboxylic acid) has been hydrothermally synthesized and structural characterized. Crystal data: 1, monoclinic, space group C2/c, a = 22.786(5) A, b = 15.712(3) A, c = 18.305(4) A, β = 18.305(4)°, Z = 4. Polymer 1 exhibits a 2D puckered layer structure with two different elongated tubular channels. In addition, the thermal stability, PXRD pattern, and photoluminescence properties of 1 in the solid state have also been investigated.

Full text of DOI:10.1080/15533174.2011.615783

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Synthesis and Reactivity in Inorganic, Metal-Organic,
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A Novel 2D Tubular Polymer Based on Flexible Bis-
Methylbenzimidazole Ligand
Chunying Xu a , Xianjuan Wang a , Qianqian Guo a , Chuntong Li a , Hongwei Hou a & Yaoting
Fan a
a Department of Chemistry , Zhengzhou University , Zhengzhou , P. R. China
Accepted author version posted online: 27 Mar 2012.Published online: 04 Jun 2012.
To cite this article: Chunying Xu , Xianjuan Wang , Qianqian Guo , Chuntong Li , Hongwei Hou & Yaoting Fan (2012) A Novel
2D Tubular Polymer Based on Flexible Bis-Methylbenzimidazole Ligand, Synthesis and Reactivity in Inorganic, Metal-Organic,
and Nano-Metal Chemistry, 42:5, 741-745
To link to this article: http://dx.doi.org/10.1080/15533174.2011.615783
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:741–745, 2012
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.615783
A Novel 2D Tubular Polymer Based on Flexible
Bis-Methylbenzimidazole Ligand
Chunying Xu, Xianjuan Wang, Qianqian Guo, Chuntong Li, Hongwei Hou, and
Yaoting Fan
Department of Chemistry, Zhengzhou University, Zhengzhou, P. R. China
of the ligand. We anticipate that the novel ligand 1,4-bis(2-
methylbenzimidazol-1-ylmethyl) benzene (bmb) would have
good cooperative coordination abilities with polycarboxylate.
In addition, bmb with a rigid spacer of phenyl ring and two
freely rotating methylbenzimidazol arms can freely rotate to
form diverse conformations and meet the requirement of coor-
dination geometries of metal ions.[9] In view of the characters,
bmb has the potential to produce unique structural motifs with
beautiful channels or cavities.
A novel metal-organic polymer [Cd(bmb)(p-bdc)]n (1) (bmb
= (1,4-bis(2-methylbenzimidazol-1-ylmethyl) benzene); p-H2bdc =
p-benzenedicarboxylic acid) has been hydrothermally synthesized
and structural characterized. Crystal data: 1, monoclinic, space
group C2/c, a = 22.786(5) Å, b = 15.712(3) Å, c = 18.305(4) Å,
β = 18.305(4)◦, Z = 4. Polymer 1 exhibits a 2D puckered layer
structure with two different elongated tubular channels. In addi-
tion, the thermal stability, PXRD pattern, and photoluminescence
properties of 1 in the solid state have also been investigated.
In this work, by introducing p-benzenedicarboxylic acid into
the Cd(II)-bmb hydrothermal synthesis process, a 2D polymer
[Cd(bmb)(p-bdc)]n (1) with different tubular channels was ob-
tained. Thermal analysis indicates that polymer 1 is stabile up
to 324◦C. Moreover, an intense fluorescent emission bond is
obtained at 441 nm for 1.
Keywords flexible, photoluminescence, tubular channel
INTRODUCTION
During the past decades, intense interest has been focused on
the design and synthesis functional metal-organic frameworks
(MOFs) owing to their variety of intriguing topologies[1] and po-
tential applications in the areas of anion/guest exchange,[2] catal-
ysis,[3] magnetism,[4] luminescence,[5] and gas storage.[6] Up to
now, many researches demonstrate that using mixed organic lig-
ands, especially the mixed polycarboxylate and N-containing
ones, with more tunable factors, are good strategies for the con-
struction of novel MOFs.[7] However, unfortunately, it is difficult
to get their mixed-ligand complexes for some excellent candi-
date ligands, such as 1,4-bis(benzimidazol-1-ylmethyl) benzene
(bbb).[8] So, it is very necessay to make some modifictions of
such ligands and enhance their cooperative coordination abili-
ties with organic carboxylic acids. With this understanding, we
introduce substituent methyl to the 2-position of benzimidazole
ring, which would greatly enhance the donated-electrons ability
EXPERIMENTAL
Materials and Physical Measurements
All reagents and solvents were commercially available except
for bmb, which was synthesized according to the literature.[10]
The FT-IR spectra were recorded from KBr pellets in the range
of 400–4000 cm−1 on a Bruker Tensor 27 spectrophotometer
(Germany). Elemental analyses (C, H, and N) were carried out
on a FLASH EA 1112 elemental analyzer (USA). PXRD pat-
terns were recorded using Cu Kα1 radiation on a PANalytical
X’Pert PRO diffractometer (USA). Thermal analyses were per-
formed on a Netzsch STA 449C thermal analyzer (Germany)
from room temperature at a heating rate of 10◦C min−1 in air.
The luminescence spectra for the powdered solid samples were
measured at room temperature on a Hitachi F-4500 Fluores-
cence Spectrophotometer (Japan). The excitation slit and the
emission slit were 2.5 nm.
Received 22 March 2011; accepted 14 August 2011.
This work was financially supported by the National Natural Sci-
ence Foundation (Nos. 20971110 and 91022013), Program for New
Century Excellent Talents of Ministry of Education of China (NCET-
07-0765), and the Outstanding Talented Persons Foundation of Henan
Province.
Address correspondence to Hongwei Huou, Department of Chem-
istry, Zhengzhou University, Zhengzhou 450052, P. R. China. E-mail:
houhongw@zzu.edu.cn
Synthesis of [Cd(bmb)(p-bdc)]n (1)
A mixture of Cd(NO3)·4H2O (61.7 mg,0.2mmol), p-H2bdc
(33.2 mg, 0.2 mmol), NaOH (8.0 mg, 0.2 mmol), and bmb (36.6
mg, 0.1 mmol) in 10 mL distilled H2O was sealed in a 25 mL
Teflon-lined stainless steel container and heated at 160◦C for
4 days. After the mixture cooled to room temperature at a rate
of 5◦C/h, colorless block crystals of 1 were obtained with a
741

742
C. XU ET AL.
TABLE 1
Crystallographic Data Collection and Structure
Determination
Crystallographic data for 1a
The data of polymer 1 was collected on a Rigaku Saturn 724
CCD diffractometer (Japan) (Mo-Kα, λ = 0.71073 Å) at temper-
ature of 20 1◦C. Absorption corrections were applied by using
multiscan program. The data was corrected for Lorentz and po-
larization effects. The structures were solved by direct methods
and refined with a full-matrix least-squares technique based
on F2 with the SHELXL-97 crystallographic software package
(Germany).[11] The hydrogen atoms were placed at calculated
positions and refined as riding atoms with isotropic displace-
ment parameters. Crystallographic crystal data and structure
processing parameters for 1 is summarized in Table 1. Selected
bond lengths and bond angles of 1 are listed in Table 2.
1
Formula
Formula mass
Temperature [K]
Wavelength [Å]
Crystal system
Space group
a (Å)
C32H26CdN4O4
642.97
293(2)
0.71073
monoclinic
C2/c
22.786(5)
15.712(3)
18.305(4)
90
119.13(3)
90
5724(12)
4
1.492
b (Å)
c (Å)
α (◦)
β (◦)
γ (◦)
V (Å3)
RESULTS AND DISCUSSION
Z
Crystal Structure of [Cd(bmb)(p-bdc)]n (1)
Dcalcd.(g·cm−3
)
Single-crystal X-ray analysis reveals that polymer 1 crys-
tallizes in the monoclinic C2/c space group, which consists of
two half bmb, one p-bdc2−, and one Cd(II) ion in the asym-
metric unit. As shown in Figure 1, the center Cd(II) ion is six-
coordinated in a badly distorted octahedral geometry, ligated by
four oxygen atoms (O1, O2, O3, and O4) from two symmetry-
related p-bdc2− and two nitrogen atoms (N1, N4) from two
distinct bmb. The Cd-O bond lengths vary from 2.242(2) to
2.572(2) Å, while the Cd-N bond lengths are 2.247(2) and
2.344(2) Å, which are in the normal range.[12] The p-bdc2−anion
with bi-chelate mode bridges adjacent Cd(II) ions to form a com-
mon zigzag chain, which is further linked by bmb to generate
a 2D puckered network (Figure 2). Interestingly, viewing from
the c-axis, the 2D layer shows two kinds of tubular channel,
elongated into different directions (Figure 3). Further investiga-
tion indicates that it is due to the various conformations of bmb.
In 1, bmb exhibits two different cis-conformations. One adopts
a Ndonor···N-Csp3···Csp3 torsion angle of 73.45◦ and neighboring
Cd/p-bdc zigzag chains are associated together by this type of
µ (mm−1
F(000)
θ (◦)
)
0.807
2608.0
1.65–25.00
5040 / 0 / 372
1.088
Data / restraints / parameters
GOF
R1 (I >2sigma(I))
wR2 (I >2sigma(I))
0.0352
0.0839
ꢀ
ꢀ
ꢀ
ꢀ
2
2 2
aR1 =
ꢁ F0 | − | Fc ꢁ /
| F0 |; wR2 = [ w(F0 − Fc ) /
2 2 1/2
w(F0 ) ]
.
yield of 25% (based on Cd). Anal. Calcd. For C32H26N4O4Cd
(%): C, 59.77; H, 4.08; N, 8.71. Found: C, 59.59; H, 3.92; N,
8.57. IR (KBr, cm−1): 3440(m), 2924(w), 2853(w), 1562(s),
1509(m), 1475(w), 1456(m), 1382(s), 1290(m), 1258(w),
1223(w), 1159(w), 1015(m), 991(w), 8369s), 751(s), 739(m),
527(m), 474(w), 431(w).
TABLE 2
Selected bond lengths (Å) and angles (◦) for 1
Cd(1)-O(2)
Cd(1)-O(3)#4
Cd(1)-O(4)#4
2.240(2)
2.288(2)
2.386(2)
104.99(8)
104.18(9)
147.93(9)
95.35(9)
94.32(9)
95.96(9)
144.87(10)
92.37(9)
Cd(1)-N(4)
Cd(1)-N(1)
Cd(1)-O(1)
N(1)-Cd(1)-O(4)#4
O(2)-Cd(1)-O(1)
N(4)-Cd(1)-O(1)
O(3)#4-Cd(1)-O(1)
N(1)-Cd(1)-O(1)
O(4)#4-Cd(1)-O(1)
O(3)#4-Cd(1)-O(4)#4
2.247(2)
2.344(3)
2.572(2)
113.84(10)
54.05(8)
98.07(9)
88.41(9)
149.05(8)
93.92(9)
55.73(9)
O(2)-Cd(1)-N(4)
O(2)-Cd(1)-O(3)#4
N(4)-Cd(1)-O(3)#4
O(2)-Cd(1)-N(1)
N(4)-Cd(1)-N(1)
O(3)#4-Cd(1)-N(1)
O(2)-Cd(1)-O(4)#4
N(4)-Cd(1)-O(4)#4
Symmetry transformations used to generate equivalent atoms: #1 −x, y, −z + 1/2, #4 x, −y + 1, z − 1/2.

TUBULAR POLYMER [Cd(bmb)(p-bdc)]n
743
FIG. 1. The asymmetric unit of 1 with hydrogen atoms omitted for clarity.
(thermal ellipsoids at 50% probability level). Symmetry codes: A x, 1 − y, −0.5
+ z.
bmb facing opposite directions alternatively to form the hor-
izontally elongated tubular channel. By the same connection
way, the other type of bmb with a bigger Ndonor···N-Csp3···Csp3
torsion angle of 81.96◦ forms the vertically elongated tubular
channel.
XRD patterns and thermal analyses
FIG. 2. The 1D Cd/p-bdc2− zigzag chains are linked by bmb to generate a 2D
puckered network.
In order to confirm the phase purity of polymer 1, the PXRD
pattern was recorded for 1, and it was comparable to the cor-
responding simulated one calculated from the single-crystal tial breakdown of the organic moieties ranging from 324◦C to
diffraction data (Figure 4), indicating a pure phase of bulky 360◦C. Then bmb starts to loss until 580◦C. The final products
sample.
The thermal stability of 1 was also estimated. As shown in
Figure 5, no obvious weight loss is observed for anhydrous
CdO (20.70%, calcd.: 19.97%) are obtained.
Photoluminescence properties
polymer 1 until the decomposition of the framework occurs at
Coordination polymers with d10 metal centers and conjugated
324◦C. The sharp weight loss (26.38%) attributes to the com- organic linkers are promising candidates for photoactive mate-
bustion of p-bdc2− (calcd.: 25.51%) accompanied by the ini- rials with potential applications such as chemical sensors and
FIG. 3. Viewing from the c-axis, the 2D layer of 1 shows two kinds of tubular channel, elongated into different directions.

744
C. XU ET AL.
FIG. 6. Photoluminescence of free ligands and polymer 1.
CONCLUSION
In summary, a 2D fluorescent polymer [Cd(bmb)(p-bdc)]n (1)
has been synthesized under the hydrothermal reaction condition.
In 1, flexible bmb shows two kinds of cis-conformations with
different Ndonor···N-Csp3···Csp3 torsion angles, which lead to the
formation of two different elongated tubular channels. Photolu-
minescence investigation reveals that a large red-shift more than
100 nm of 1 takes place, compared with p-benzenedicarboxylic
acid, and it can be assigned to LMCT.
FIG. 4. Experimental and simulated PXRD patterns of polymer 1.
photochemistry.[13] Hence, the solid-state photoluminescence
properties of Cd(II) polymer 1, together with the free bmb lig-
and and p-H2bdc, were investigated at room temperature. As
shown in Figure 6, polymer 1, free ligands p-H2bdc and bmb
show intense emission bands at 441 nm (λex = 336 nm), 383 nm
(λex = 314 nm), and 309 nm (λex = 293 nm), respectively. Ob-
viously, the emission band of 1 is likely to that of p-H2bdc, but
with a large red-shift more than 100 nm. So, such broad band of 1
may be tentatively assigned to ligand(p-H2bdc)-to-metal charge
transfer (LMCT) as reported for other d10 metal polymers.[14] In
addition, further investigation indicates that the fluorescent in-
tensity of 1 decrease compared with the corresponding ligands
p-H2bdc. It may be attributed to ligand coordination to the metal
center, which reduce the rigidity of the ligand, and enhance the
loss of energy by radiationless decay.[15]
SUPPLEMENTARY MATERIALS
Complete crystallographic data has been deposited with the
Cambridge Crystallographic Data Center, CCDC No.818125
for polymer 1. Copies of this information can be obtained free
of charge from The Director, CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, U.K. (fax: +44-1223-336033. E-mail: de-
posit@ccdc.cam.ac.uk. www: http://www.ccdc. cam.ac.uk).
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