Two zinc(II) coordination polymers based on the ligand 1, 4-bis[(2-methyl-imidazol-1-yl)methyl]benzene: Syntheses, crystal structures and properties

Article abstract of DOI:10.1002/zaac.201200341

Two coordination polymers (CPs), {[Zn₂(BMB)(5-AIPA) ₂]·2H₂O}_n(1) and [Zn(BMB)(5-NIPA)] _n(2) {BMB = 1, 4-bis[(2-methyl-imidazol-1-yl)methyl]benzene, 5-AIPA = 5-aminoisophthalic acid, 5-NIPA = 5-nitroisophthalic acid}, were synthesized under hydrothermal conditions. Compound 1 displays a 2D double-layer structure, which is packed into a 3D supramolecule by interlayer hydrogen bonds and π-π stacking interactions. Compound 2 displays a threefold interpenetrating 3D network, which is composed of left-handed helical chains and two types of meso-helical chains along different directions. Copyright

Full text of DOI:10.1002/zaac.201200341

ARTICLE
DOI: 10.1002/zaac.201200341
Two Zinc(II) Coordination Polymers Based on the Ligand
1,4-Bis[(2-methyl-imidazol-1-yl)methyl]benzene: Syntheses, Crystal
Structures and Properties
Jing-Tao Shi,[a] Chun-Sheng Zhou,[a,b] Yong-Liang Liu,[a] Zhi-Guo Fang,[a]
Rui-Li Zhao,[a] Li-Li Xu,[a] and Ke-Fen Yue*[a]
Keywords: Bisimidazole ligand; Interpenetration; Zinc; Coordination polymers
Abstract. Two coordination polymers (CPs), {[Zn2(BMB)(5-AIPA)2]·
2H2O}n(1) and [Zn(BMB)(5-NIPA)]n(2) {BMB = 1,4-bis[(2-methyl- π–π stacking interactions. Compound 2 displays a threefold interpen-
imidazol-1-yl)methyl]benzene, 5-AIPA = 5-aminoisophthalic acid, 5- etrating 3D network, which is composed of left-handed helical chains
is packed into a 3D supramolecule by interlayer hydrogen bonds and
NIPA = 5-nitroisophthalic acid}, were synthesized under hydrothermal and two types of meso-helical chains along different directions.
conditions. Compound 1 displays a 2D double-layer structure, which
1,4-bis[(2-methyl-imidazol-1-yl)methyl]benzene (BMB). It has
Introduction
shown the ability to produce unique meso-helical features be-
The rational synthesis of hybrid coordination polymers (CPs)
cause of two freely rotating –CH2– groups and a rigid spacer
of phenyl ring.[24] The meso-helical chains contain both left-
and right-handed helical loops in each chain like a lemniscate,
and display a “ϱ” shape.[25]
has attracted immense attention because of their various struc-
tural topologies and potential application in many areas such
as molecular magnetism, catalysis, and gas absorbents.[1–6]
The multiple structures and unique properties of coordination
polymers have relation to the organic and inorganic compo-
nents.[7–11] Flexible bisimidazole ligands as good candidates
for the formation of novel CPs easily form interpenetrating
structures and helical modes, since they are able to twist and
Herein, we report on two CPs, {[Zn2(BMB)(5-AIPA)2]·
2H2O}n(1) and [Zn(BMB)(5-NIPA)]n(2), which were obtained
under hydrothermal conditions and exhibit interesting 2D
double-layer and 3D threefold interpenetrating topologies,
respectively. They were characterized by elemental analysis,
IR spectroscopy, and X-ray crystallography. Additionally, the
thermal and photoluminescence properties are presented.
rotate freely to adopt a suitable conformation in constructing
[12–16]
process
.
Recently, bisimidazole ligands have attracted much attention
in the field of crystal engineering. Some coordination polymers
contained bisimidazole ligands have been documented in the
literatures.[17,18] However, CPs constructed by BMB has not
been well studied to date.[19,20] In our previous work, we have
designed and synthesized systematically topologically interest-
ing coordination structures based on flexible bisimidazole li-
gands, 1,4-bis(2-methyl-imidazol-1-yl)butane and 1,6-bis(2-
methyl-imidazole-1-yl)hexane.[21–23] To expand our investi-
gations in this field, we select the other bisimidazole ligand,
Results and Discussion
Description of Crystal Structures
Structure of {[Zn2(BMB)(5-AIPA)2]·2H2O}n (1)
X-ray diffraction analysis revealed that compound 1 crys-
tallizes in the monoclinic space group P21/c (Table 1). The
asymmetric unit of 1 consists of one ZnII ion, a half of a BMB,
and one 5-AIPA molecule (Figure 1). The central ZnII atom
has a slightly distorted trigonal bipyramidal arrangement and
is surrounded by one nitrogen atom (N1) from the BMB mole-
cule, two oxygen atoms, and one nitrogen atom (N3) from
different 5-AIPA ligands. The Zn–O bond lengths are 1.948(2)
and 1.999(2) Å. The Zn–N1 bond length is 2.008(2) Å and the
Zn–N3 bond length is 2.067(2) Å. Selected bond lengths and
angles are given in Table 2. Thus, each 5-AIPA links three ZnII
ions to form an infinite 2D layer. The BMB ligands are at-
tached to the two layers to construct double-layer as shown in
Figure 2. The double-layers are further connected together by
* Prof. Dr. K.-F. Yue
Fax: +86-29-88302604
E-Mail: ykflyy@nwu.edu.cn
[a] Key Laboratory of Synthetic and Natural Functional Molecule
Chemistry of the Ministry of Education
Shaanxi Key Laboratory of Physico-Inorganic Chemistry
College of Chemistry and Materials Science, Northwest University
XiЈan 710069, P. R. China
[b] Department of Chemistry
Shang Luo University
Shang Luo 726000, P. R. China
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201200341 or from the au-
thor.
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K.-F. Yue et al.
ARTICLE
Table 1. Crystal data and structure refinements for compounds 1
and 2.
1
2
Molecular formula
Fw
Temperature
C16H16N3O5Zn
395.69
296(2)
C24H21N5O6Zn
540.83
150
Crystal system
Space group
monoclinic
P21/c
Monoclinic
P2/c
a /Å
b /Å
c /Å
α /°
12.7129(10)
7.8758(6)
15.9859(13)
90
17.795(6)
7.305(2)
24.447(6)
90
Figure 1. Coordination environment of the ZnII ion in 1.
β /°
91.3320(10)
90
1600.1(2)
4
133.221(15)
90
2315.8(12)
4
γ /°
V /Å3
Z
ρ /g·cm–3
1.642
1.551
F(000)
812
1112
Reflections collected /
unique
7764 / 2846
[0.0222]
1.11
13684 / 5577
[0.0649]
1.03
[R(int)]
Goodness-of-fit on F2
Final R indices
[I Ͼ 2σ(I)]
R1 = 0.0268,
wR2 = 0.0803
R1 = 0.0351,
wR2 = 0.0953
R1 = 0.0568,
wR2 = 0.1393
R1 = 0.1063,
wR2 = 0.1765
Figure 2. Schematic representation of the 2D double-layer of com-
pound 1.
R indices (all data)
Structure of [Zn(BMB)(5-NIPA)]n (2)
two kinds of hydrogen bonding interactions between the amino
The asymmetric unit of 2 contains two half ZnII atoms, one
group (–N3) and carboxylate oxygen atoms (N3···O1, 3.049 Å, BMB, one 5-NIPA ligand and belongs to the monoclinic space
N3···O2, 3.153 Å) (Figure 3a,b). Meanwhile, there are strong group P2/c (Table 1). As illustrated in Figure 4, the two ZnII
π–π stacking interactions between the benzene rings of inter- atoms exhibit similar coordination arrangements. Zn1II is four-
layers with a face-to-face distance of 3.368 Å (Figure 3a,c). coordinate with two oxygen atoms (O1) of two 5-NIPA ligands
Besides, O–H···O hydrogen bonds (O1W···O2, 2.918 Å; besides two nitrogen atoms (N3) from two BMB ligands, and
O1W···O3, 2.995 Å) exist between protonated carboxylate Zn2II is coordinated by two O3 and two N1 atoms. The Zn–N
groups and uncoordinated water molecules (Table S1; Support- and Zn–O bond lengths are all within the reasonable ranges. Se-
ing Information). Finally, the 2D double-layers are further ex- lected bond lengths and angles are given in Table 2. In 2, Zn1
tended into a 3D supramolecular architecture through hydro- and Zn2 are bridged by BMB ligands to form two similar 1D
gen bonds and π–π stacking interactions.
meso-helical chains, namely (Zn1–BMB)n and (Zn2–BMB)n
Table 2. Selected bond lengths /Å and angles /° for 1 and 2.
1a
Zn(1)–O(4)#1
Zn(1)–N(1)
O(4)–Zn(1)#3
O(4)#1–Zn(1)–O(1)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(3)#2
2b
1.9478(17)
2.008(2)
1.9478(17)
106.10(7)
108.49(8)
105.85(7)
Zn(1)–O(1)
Zn(1)–N(3)#2
N(3)–Zn(1)#4
O(4)#1–Zn(1)–N(1)
O(4)#1–Zn(1)–N(3)#2
N(1)–Zn(1)–N(3)#2
1.9991(16)
2.0670(18)
2.0670(18)
105.75(8)
108.08(7)
121.66(8)
Zn(1)–O(1)
Zn(1)–N(3)#1
Zn(2)–O(3)#2
Zn(2)–N(1)
O(1)–Zn(1)–O(1)#1
O(1)#1–Zn(1)–N(3)#1
O(1)#1–Zn(1)–N(3)
O(3)#2–Zn(2)–O(3)
O(3)–Zn(2)–N(1)
O(3)–Zn(2)–N(1)#2
1.959(5)
2.022(5)
1.968(4)
2.052(5)
121.0(3)
94.2(2)
123.4(2)
122.9(3)
111.73(19)
106.0(2)
Zn(1)–O(1)#1
Zn(1)–N(3)
Zn(2)–O(3)
Zn(2)–N(1)#2
O(1)–Zn(1)–N(3)#1
O(1)–Zn(1)–N(3)
N(3)#1–Zn(1)–N(3)
O(3)#2–Zn(2)–N(1)
O(3)#2–Zn(2)–N(1)#2
N(1)–Zn(2)–N(1)#2
1.959(5)
2.022(5)
1.968(4)
2.052(5)
123.4(2)
94.2(2)
101.5(3)
106.0(2)
111.73(19)
95.1(3)
Symmetry transformations used to generate equivalent atoms: a: #1 x, –y+1/2, z+1/2; #2 x, y+1, z; #3 x, –y+1/2, z–1/2; #4 x, y–1, z; #5 –x,
–y+2, –z b: #1 –x+1, y, –z+3/2; #2 –x+2, y, –z+3/2; #3 –x+2, –y, –z+1; #4 –x, –y+3, –z+1.
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ZnII Coordination Polymers with 1,4-Bis[(2-methyl-imidazol-1-yl)methyl]benzene
Figure 3. (a). Schematic representation of hydrogen bonding and π–π interactions between the double-layers in 1. (b) Packing of the 3D
framework by hydrogen bonds. (c) Packing diagram showing π–π interactions between the 5-AIPA molecules.
with a pitch of 25.85 and 24.35 Å respectively (Figure 5a). Photoluminescent Properties
Each 5-NIPA ligand connects the atoms Zn1 and Zn2 in a
monodentate coordination mode to form a 1D left-handed heli-
The solid-state luminescent properties of the ligands as well
as compounds 1, and 2 were investigated at room temperature
cal chain (Zn-5-NIPA)n (see Figure 5b). The (Zn1–BMB)n,
as shown in Figure 7. As previously reported,[26,27] the solid
(Zn2–BMB)n, and (Zn–5-NIPA)n helical chains are joined to-
aromatic carboxylate ligands (5-AIPA, 5-NIPA) are nearly
gether to a 3D network (Figure 5c). Finally, the independent
non-fluorescent in the range 400–600 nm, and the free co-li-
equivalent 3D frameworks give rise to a threefold interpen-
gand BMB shows a maximum emission band at 505 nm (λex
= 280 nm). The emission bands of 1, 5-AIPA, and BMB are
etrating net with the point symbol 65.8 and the long symbol
6.6.6.6.62.83, as seen in Figure 5d.
observed at 344, 439, and 505 nm, respectively. The emission
bands of 2 and BMB are observed at 465 and 505 nm, respec-
tively. The emission peaks of 1 and 2 are both blue-shifted
compared to ligands. The weak luminescent properties of 5-
NIPA and 2 may originate from the obvious decrease of the
electron density of the ligand affected by electron-withdrawing
nitryl group.[28] Since Zn2+ ion is difficult to oxidize or to
reduce owing to its d10 configuration, these bands can probably
be assigned to the (π–π*) intraligand fluorescent emis-
sion.[18,29–31]
Figure 4. Coordination environment of the ZnII ion in 2.
Thermal Behaviors and PXRD Results
Meanwhile, the atoms Zn1II and Zn2II are alternatingly
linked via two types of BMB and 5-NIPA ligands extending
into meso-helical chains, which can be described as (Zn1– of 5.35% (calcd. 4.55%) before 200 °C, due to the loss of two
N3···N3BMB–Zn1–NIPA–Zn2–N1···N1BMB–Zn2–NIPA– lattice water molecules. The decomposition of its coordination
Thermogravimetric analysis for 1 shows a small weight loss
Zn1)n (Figure 6a). In the structure of 3D frameworks, the rigid framework occurred during 445–535 °C, which can be attrib-
benzene rings of BMB between three meso-helical chains form uted to the organic ligands released progressively. For 2, the
π–π interactions with an intercentroid distance of 3.703 Å decomposition of the framework occurred when the tempera-
(Figure 6b).
ture is above 365 °C (Figure S1, Supporting Information). The
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K.-F. Yue et al.
ARTICLE
Figure 5. (a) View of the a type of ZnII and BMB meso-helical chain and the “ϱ” shape of the meso-helices. (c) Left helical chain of ZnII and
5-NIPA. (c) View of the 3D network accomplished by connecting three types of helical chains. (d) 3D threefold interpenetration topology in 2.
Figure 6. (a) View of the meso-helical chains of ZnII, BMB, and NIPA (Zn1–N3···N3BMB–Zn1–NIPA–Zn2–N1···N1BMB–Zn2–NIPA–Zn1)n
and the “ϱ” shape of the meso-helices along the b axis in 2. (b) Three strands meso-helices (Zn1–N3···N3BMB–Zn1–NIPA–Zn2–N1···N1BMB–
Zn2–NIPA–Zn1)n in threefold interpenetration framework and π–π interactions between 3D networks.
PXRD experiments for 1 and 2 were carried out to confirm terns of the corresponding complexes are shown in Figure S2.
whether the crystal structures are truly representative of the We can see that the synthesized bulk materials and the mea-
bulk materials. The experimental and computer-simulated pat- sured single crystals are the same.
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ZnII Coordination Polymers with 1,4-Bis[(2-methyl-imidazol-1-yl)methyl]benzene
Synthesis of {[Zn2(BMB)(5-AIPA)2]·2H2O}n (1): A mixture of BMB
(0.266 g, 1 mmol), 5-AIPA (0.181 g, 1 mmol), and Zn(NO3)2·6H2O
(0.149 g, 0.5 mmol) was dissolved in DMF/H2O = 4:1 (10 mL). The
mixture was stirred for about 30 min and THF (0.05 mL) was slowly
added. The mixture was transferred to a 25 mL stainless steel reactor
with Teflon liner and heated to 150 °C automatically. The temperature
was kept at 150 °C for 4 d and cooled to room temperature at the rate
of 5 K·h–1. Colorless block crystals of 1 were obtained. Yield: 72%.
Elemental analysis: calcd: C 48.50; H 4.03; N 10.65%; found: C
48.52; H 4.04; N 10.61%. IR (KBr): ν˜ = 3452 s, 3143 s, 1575 s, 1507
w, 1399 s, 1250 w, 1137 m, 1006 w, 962 w, 887 w, 781 m, 744 m,
670 w cm–1.
Synthesis of [Zn(BMB)(5-NIPA)]n (2): The synthesis of 2 was similar
to the above description for 1 except that 5-AIPA was replaced by 5-
NIPA. Colorless block crystals of 2 were obtained. Yield: 77%. Ele-
mental analysis: calcd: C 52.24; H 3.87; N 12.96%; found: C, 53.25;
H, 3.82; N, 12.94%. IR (KBr): ν˜ = 3440 s, 3128 s, 1638 s, 1536 w,
1400 s, 1338 m, 1273 w, 1114 w, 1001 w, 923 w, 870 w, 725 m,
666 w cm–1.
Figure 7. Solid-state photoluminescent spectra at room temperature.
Supporting Information (see footnote on the first page of this article):
TGA curves of compounds 1 and 2. XRPD spectra of 1 and 2 at room
temperature.
Conclusions
Two novel CPs based on co-ligand BMB and dicarboxylate
acid were synthesized under hydrothermal conditions. The co-
ligand BMB could bend and rotate to construct novel CPs as
a potential building block. The 2D double-layer of 1 is packed
by interlayer hydrogen bonds and π–π stacking interactions to
extend to a 3D supramolecule. Compound 2 generates a three-
fold interpenetrating 3D net containing left-handed helical
chains and two types of meso-helical chains along different
directions.
Acknowledgements
This work was supported by the Natural Scientific Research Founda-
tion of Shaanxi Provincial Education Office (No. 11JK0590), the Natu-
ral Science Foundation of Shaanxi Province (No. 2009JZ001), the
National Science Fund for Fostering Talents in Basic Science (No.
J1210057), and the State Key Program of National Natural Science of
China (No. 20931005).
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Published Online: November 9, 2012
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