Synthesis and crystal structure of a new Zn(II) interpenetrating complex based on 1,4-bis(2-methyl-imidazol-1-yl)butane and 5-bromoisophthalic acid

Article abstract of DOI:10.1080/15533174.2013.809753

A new interpenetrating complex, [Zn(5-Br-ip)(bmib)]_n (5-Br-H₂ip = 5-bromoisophthalic acid, bmib = 1,4-bis(2-methyl- imidazol-1-yl)butane), has been synthesised by hydrothermal reactions of Zn(NO₃)₂·6H₂O and bmib in the presence of 5-bromoisophthalic acid, and characterized by elemental analysis and single-crystal X-ray analysis. X-ray diffraction reveals that it belongs to the orthorhombic system, Pnna space group, a = 8.7335(18) A, b = 17.358(4) (10) A, c = 14.769(3) A, α = β = γ = 90°, F(000) = 1064. R1 = 0.0389, wR2 = 0.0946. Complex 1 exhibits a fascinating 3-fold interpenetrating three-dimensional framework with the topological symbol of 6⁵·8. Copyright

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Synthesis and Crystal Structure of a New Zn(II)
Interpenetrating Complex Based on 1,4-bis(2-methyl-
imidazol-1-yl)butane and 5-bromoisophthalic Acid
Hua-Rui Wanga & Hui Guoa
a College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang, P. R.
China
Accepted author version posted online: 21 Jan 2014.Published online: 02 Jun 2014.
To cite this article: Hua-Rui Wang & Hui Guo (2014) Synthesis and Crystal Structure of a New Zn(II) Interpenetrating Complex
Based on 1,4-bis(2-methyl-imidazol-1-yl)butane and 5-bromoisophthalic Acid, Synthesis and Reactivity in Inorganic, Metal-
Organic, and Nano-Metal Chemistry, 44:10, 1457-1460, DOI: 10.1080/15533174.2013.809753
To link to this article: http://dx.doi.org/10.1080/15533174.2013.809753
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 44:1457–1460, 2014
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2013.809753
Synthesis and Crystal Structure of a New Zn(II)
Interpenetrating Complex Based
on 1,4-bis(2-methyl-imidazol-1-yl)butane
and 5-bromoisophthalic Acid
Hua-Rui Wang and Hui Guo
College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang, P. R. China
interpenetrating MOFs is to use long and low steric hindrance
ligands.[14]
Inspired by the previous idea, we employed a long and flexi-
ble ligand 1,4-bis(2-methyl-imidazol-1-yl)butane (bmib) in the
self-assembly with organic carboxylic acid 5-bromoisophthalic
acid and Zn(II) ions to synthesize interpenetrating MOFs. Fortu-
nately, a 3-fold interpenetrating three dimensional (3D) frame-
work [Zn(5-Br-ip)(bmib)]n was obtained. The topological sym-
bol is 65·8.
A new interpenetrating complex, [Zn(5-Br-ip)(bmib)]n (5-
Br-H2ip = 5-bromoisophthalic acid, bmib = 1,4-bis(2-methyl-
imidazol-1-yl)butane), has been synthesised by hydrothermal re-
actions of Zn(NO3)2·6H2O and bmib in the presence of 5-
bromoisophthalic acid, and characterized by elemental analysis
and single-crystal X-ray analysis. X-ray diffraction reveals that
it belongs to the orthorhombic system, Pnna space group, a =
8.7335(18) Å, b = 17.358(4) (10) Å, c = 14.769(3) Å, α = β = γ =
90◦, F(000) = 1064. R1 = 0.0389, wR2 = 0.0946. Complex 1 exhibits
a fascinating 3-fold interpenetrating three-dimensional framework
with the topological symbol of 65·8.
EXPERIMENTAL
Keywords 1, 4-bis(2-methyl-imidazol-1-yl)butane, crystal structure,
Materials and Physical Measurements
hydrothermal synthesis, interpenetrating
All reagents used in the syntheses were of analytical grade.
Elemental analyses for carbon, hydrogen, and nitrogen were
performed on a Vario EL III (Germany, Elementar Analy-
sensysteme GmbH) elemental analyzer. The infrared spectra
(4,000–600 cm–1) were recorded by using KBr pellet on an
Avatar 360 E. S. P. (Maryland, USA, Thermo-Nicolet) IR spec-
trometer. The crystal determination was performed on a Bruker
SMART APEX II CCD diffractometer (Germany) equipped
with graphite-monochromatized MoKα radiation (λ= 0.71073
Å). Thermogravimetric analyses (TG) were carried out on a
STA449C integration (Germany, NETZSCH) thermal analyzer.
Fluorescent analyses were performed on a Hitachi F-4500
(Japan, Hitachi) analyzer.
INTRODUCTION
As one of the major themes of supramolecular chemistry,
entangled structures are common in nature, such as catenanes,
rotaxanes, and molecular knots.[1,2] Owing to their numerous
practical applications, physical and chemical properties, and
aesthetic and usually complicated architectures and topologies,
entangled metal–organic frameworks (MOFs) have received
tremendous attention from chemists.[3–5] Among diverse entan-
gled MOFs, interpenetration is the most familiar phenomenon.
To date, considerable efforts have been invested in interpene-
trating MOFs and a great many interpenetrating networks have
been reported by many groups[6–9] and some comprehensive re-
views have been made by Robson, Batten, and Ciani et al.[10–12]
Summarizing from the large amount of reported works, we can
draw a conclusion that long and low steric hindrance ligands will
lead to larger voids that may result in high-fold interpenetrating
structures.[13] Therefore, the effective strategy for constructing
Syntheses of Complex 1
[Zn(5-Br-ip)(bmib)]n (1)
This complex was prepared under hydrothermal conditions.
A mixture of 5-Br-H2ip (24.3 mg, 0.1 mmol), bmib (21.8 mg,
0.1 mmol), Zn(NO3)2·6H2O (29.7 mg, 0.1 mmol), KOH (5.6 mg,
0.2 mmol), and H2O (16 mL) was placed in a Teflon-lined
stainless-steel vessel, heated to 160◦C for 72 h, and then cooled
to room temperature over 36 h. Yellow block crystals of 1 were
collected by filtration, washed with water, and dried in air. Anal.
Calcd. (%) for C20H21BrN4O4Zn: C, 45.61; H, 4.02; N, 10.64.
Found (%): C, 45.85; H, 3.88; N, 10.75. IR (cm–1): 3125 (w),
2937 (w), 1624 (m), 1559 (w), 1423 (w), 1372 (w), 1335 (s),
Received 22 April 2013; accepted 27 May 2013.
Address correspondence to College of Chemistry and Chemical En-
gineering, Luoyang Normal University, Luoyang 471022, P. R. China.
E-mail: wanghrly@126.com
1457

1458
H.-R. WANG AND H. GUO
TABLE 1
Crystallographic data
Empirical formula
Formula weight
Temperature (K)
Crystal system
C20H21BrN4O4Zn
526.69
296(2)
Orthorhombic
Pnna
Space group
Unit cell dimensions
a = 8.7335(18) Å
b = 17.358(4) Å
c = 14.769(3) Å
α = β = γ = 90◦
2238.9(8)
V (Å3)
Z
4
Dc (Kg·m–3)
1.563
1064
F(000)
FIG. 1. Coordination environment of the Zn(II) ion in 1.
GOF
1.017
Crystal size (mm3)
θ range for data collection (º)
Reflections collected
Independent reflections
Final R indices (I > 2σ(I))
R indices (all data)
Largest diff. peak and hole (e Å–3)
0.26 × 0.09 × 0.06
Table 1 shows crystallographic crystal data of 1. Selected bond
lengths and angles are listed in Table 2.
2.71–25.50
15560
2094 (Rint = 0.0686)
R = 0.0389, wR2 = 0.0946
R = 0.0667, wR2 = 0.1101
0.661 and –0.435
RESULTS AND DISCUSSION
Crystal Structure Description
[Zn(5-Br-ip)(bmib)]n (1)
2
2
2 2 1/2
R1 = [|F0|-|Fc|]/|F0|. wR2 = [w(|Fo | − |Fc |)2 / w|Fo | ]
.
X-ray structural analysis shows that 1 crystallizes in the or-
thorhombic system, space group Pnna, and features a 3-fold
interpenetrating three-dimensional (3D) framework. Its asym-
metric unit contains one Zn(II) ion, one bmib ligand, and one
5-Br-ip2– anion. The coordination environment around Zn(II) is
shown in Figure 1. Each Zn(II) ion sits in a distorted tetrahedron
geometry defined by two nitrogen atoms [Zn−N = 2.012 Å] of
two bmib ligands and two oxygen atoms [Zn−O = 1.935 Å]
1304 (w), 1280 (m), 1157 (w), 1123 (w), 1003 (w), 902 (w),
774 (w), 762 (m), 753 (m), 723 (s), 693(m).
Crystallographic Data Collection and Structural
Determination
Single-crystal X-ray diffraction analyses of the complex 1 from two separated 5-Br-ip2– anions. The Zn−O/N bond lengths
were carried out on a Bruker SMART APEX II CCD diffrac- are all consistent with corresponding bond lengths found in the
tometer equipped with a graphite-monochromated Mo Kα radi- literature.[3,18]
ation (λ = 0.71073 Å) by using the φ/ω scan technique at room
Each bmib ligand links two Zn(II) ions to form a 1D wave-
temperature. The structure were solved by direct methods with like chain (Zn−bmib chain) with an adjacent Zn···Zn distance
SHELXS-97.[15] Empirical absorption corrections were applied of 13.394 Å (Figure 2). The two carboxylic groups of 5-Br-
with SADABS program.[16] All non-hydrogen atoms were re- ip2– take a uniform coordination mode, in a μ1-η1:η0 fashion.
fined anisotropically. The hydrogen atoms were assigned with Zn(II) ions are connected by 5-Br-ip2– anions to form a 1D
common isotropic displacement factors and included in the final chain (Zn−5-Br-ip2– chain) with a Zn···Zn distance of 10.587
refinement by use of geometrical restrains. A full-matrix least- Å (Figure 2). The combination of 1D chains of Zn–bmib and
squares refinement on F2 was carried out using SHELXL-97.[17] Zn–5-Br-ip2– leads to the formation of a 3D network (Figure 3).
TABLE 2
Selected bond lengths (Å) and bond angles (◦)
Zn(1)-O(1)#1
Zn(1)-O(1)
Zn(1)-N(1)
Zn(1)-N(1)
O(1)#1-Zn(1)-O(1)
1.935(3)
1.935(3)
2.012(3)
2.012(3)
116.97(19)
O(1)#1-Zn(1)-N(1)
O(1)-Zn(1)-N(1)
O(1)#1-Zn(1)-N(1)#1
O(1)-Zn(1)-N(1)#1
N(1)-Zn(1)-N(1)#1
98.52(13)
120.06(12)
120.05(13)
98.52(13)
103.3(2)
Symmetry transformations used to generate equivalent atoms: #1 x, –y + 3/2, –z + 1/2; #2 –x – 1/2, –y + 1, z; #3 –x + 1, –y + 1, –z.

HYDROTHERMAL SYNTHESIS INTERPENETRATING
1459
FIG. 2. (a) View of the 1D Zn–bmib wave-like chain. (b) View of the 1D
Zn–5-Br-ip2– chain.
Owing to the long distance of Zn···Zn, there is a large unoc-
cupied void space existing in the single 3D framework, which
shows a possibility that 1 may display interpenetrating struc-
tural characteristics. As can be seen, the maximum dimensions
(corresponding to the longest intracage Zn···Zn distances) are
21.929 × 18.171 × 30.542 Å. The potential voids are filled
via mutual interpenetration of two other independent equivalent
frameworks, generating a 3-fold interpenetrating 3D architec-
FIG. 4. Schematic view showing the 3-fold interpenetrated 3D topological
network for 1.
in Figure 5, complex 1 is stable up to about 400◦C. Then the
framework begins to disintegrate upon elevating the tempera-
ture.
ture (Figure 4). This feature can greatly enhance the stability of Photoluminescence Properties
the whole structure.
The emission spectra of compound 1 have been investigated
in the solid state at room temperature. The emission peaks of 1
are shown in Figure 6. Upon exciting at 333 nm, the maximum
emission peaks at about 442 nm were observed for compounds
1. Free 5-Br-H2ip and bmib ligands fluoresced in the solid state
with their emission peaks at 500 nm[19] and 465 nm,[20] respec-
tively. Compared to free ligands, complex 1 shows obvious blue
To further demonstrate the overall 3D structure of 1, we
consider each Zn(II) ion as a four-connecting node, which is
linked by two 5-Br-ip2– anions and two bmib ligands. Moreover,
the bmib and 5-Br-ip2– anions are simplified as a linear linker.
With further topological analysis by the OLEX program, the
whole structure of 1 can be simplified to a 3-fold 3D framework
with its topological notation of 65·8.
Thermal Analysis
To investigate the thermal stability of 1, their thermogravi-
metric analyses were examined in air atmosphere with the rate
of 10◦C min−1 from room temperature to 1000◦C. As shown
FIG. 3. Left: View of the 3D framework constructed by 1D Zn–bmib and
Zn–5-Br-ip2– chains. Right: Schematic view showing the single 3D framework.
FIG. 5. TG curve of complex 1.

1460
H.-R. WANG AND H. GUO
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CONCLUSIONS
In summary, based on a long and flexible ligand 1,4-bis(2-
methyl-imidazol-1-yl)butane (bmib), a new interpenetrating
complex [Zn(5-Br-ip)(bmib)]n has been successfully synthe-
sised with Zn(II) salt in the presence of ancillary ligand 5-
bromoisophthalic acid. The complex manifests a 3D framework
with large void space, which is penetrated by two other indepen-
dent equivalent frameworks to give rise to 3-fold interpenetrat-
ing 3D architecture. Further systematic studies for the design
and syntheses of interpenetrating polymers are underway in our
laboratory.
SUPPLEMENTAL MATERIAL
Crystallographic data for the structural analysis has been
deposited with the Cambridge Crystallographic Data Centre,
CCDC No. 929613. Copies of this information may be ob-
tained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44-1223-336-033; E-mail:
deposit@ ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
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photoluminescence of five zinc(II) coordination polymers based on 5-
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