Crystal structure and characterization of a double-helical-chain coordination polymer zinc complex constructed by flexible dicarboxylate ligand 2-nitrobenzene-1,4-di(oxyacetate) and rigid 2,2′-bipyridine ligand

Article abstract of DOI:10.1002/zaac.200700490

A novel double-helical-chain coordination polymer [Zn(nbdoa)(2,2′- bipy)(H₂O)]_n constructed by flexible 2-nitro-benzene-1,4- di(oxyacetate) ligand and rigid 2,2′-bipyridine ligand was obtained by hydrothermal reaction. The crystal structure demonstrates that there is a double-helical chain with an inner channel running parallel to the helix axis without any interpenetration, which is connected to network via π-π stacking and hydrogen bond interactions. The thermal analysis shows that the infinite helical structure is stable up to 536 K. The luminescence property is investigated and the complex shows photoluminescence in the solid state at room temperature.

Full text of DOI:10.1002/zaac.200700490

DOI: 10.1002/zaac.200700490
Crystal Structure and Characterization of a Double-helical-chain Coordination
Polymer Zinc Complex Constructed by Flexible Dicarboxylate Ligand 2-Nitro-
benzene-1,4-di(oxyacetate) and Rigid 2,2Ј-Bipyridine Ligand
Wei Yua,b, Tong-Lai Zhanga,*, Jian-Guo Zhanga, Li Yanga, Shao-Zong Wanga, Rui-Feng Wua
a Beijing / P. R. China, Beijing Institute of Technology, State Key Laboratory of Explosion Science and Technology
b Shanghai / P. R. China, Shanghai Second Polytechnic University, School of Urban Construction and Environment Engineering
Received October 16th, 2007.
Abstract.
A
novel double-helical-chain coordination polymer
interactions. The thermal analysis shows that the infinite helical
structure is stable up to 536 K. The luminescence property is inves-
tigated and the complex shows photoluminescence in the solid state
at room temperature.
[Zn(nbdoa)(2,2Ј-bipy)(H2O)]n constructed by flexible 2-nitro-ben-
zene-1,4-di(oxyacetate) ligand and rigid 2,2Ј-bipyridine ligand was
obtained by hydrothermal reaction. The crystal structure demon-
strates that there is a double-helical chain with an inner channel
running parallel to the helix axis without any interpenetration,
which is connected to network via π-π stacking and hydrogen bond
Keywords: Coordination polymers; 2-Nitro-benzene-1,4-di(oxy-
acetate); Zinc; Fluorescent emission
Introduction
chain coordination polymer [Zn(nbdoa)(2,2Ј-bipy)(H2O)]n
is obtained, which is characterized by X-ray single-crystal
diffraction, thermal analysis and spectral analysis in this
paper.
The control of helicity at supramolecular level is a fasci-
nation challenge for chemists [1], because helix is ubiqui-
tous in nature as well as in human art and architecture,
such as the double-helical structure for DNA [2] and right
or left-handed quartz [3], which provides an important im-
petus for the creation of artificial helical structures in supra-
molecular chemistry and material science with potential ap-
plications in the fields of asymmetric catalysis, nonlinear
optical materials and the aesthetically appealing topologies
of helicalcompounds [4Ϫ6]. Consequently, many single-,
double- and higher-order stranded helical complexes have
been generated by self-assembly processes [7Ϫ12].
The judicious choice of suitable ligand is an important
factor that greatly influences the structure of the coordi-
nation and functionality of the complex formed, and for
constructing helical polymers the ligands with a little flexi-
bility and spacial hidrance are very efficient [13]. 2-Nitro-
benzene-1,4-di(oxyacetate) (nbdoa2Ϫ) is a multidentate flex-
ible ligand with versatile coordination modes, which maybe
an excellent candidate for the construction of supramolecu-
lar helical polymers. There have been numerous reports on
the zinc helix because zinc coordination in DNA domain is
a common topic [14Ϫ16]. As expected, a double-helical-
Results and Discussion
Crystallographic and refinement parameters are given in
Table 1, and the selected bond distances and angles of the
Table 1 Crystal data and details of the structure determination a)
Empirical formula
Formula weight
Temperature /K
Crystal size /mm
Crystal system
Space group
C20 H17 Zn N3 O9
508.74
153(2)
0.27 ϫ 0.27 ϫ 0.12
monoclinic
P 2(1)/n
0.71073
14.1255(3)
˚
λ/ A
˚
a/ A
˚
b/ A
10.2035(3)
14.8227(3)
˚
c/ A
β /°
108.759(1)
2022.90(8)
4
1.670
1.276
3.05 to 27.50
Ϫ18ՅhՅ17, Ϫ13ՅkՅ13, Ϫ19ՅlՅ19
19330
3
˚
Volume/A
Z
Density (calculated) /g/cm3
Absorption coefficient /mmϪ1
θrange for data collection /°
Limiting indices
Reflections collected
Unique reflections
4638 [R(int) ϭ 0.0288]
1.005
R1 ϭ 0.0282, wR2 ϭ 0.0765
R1 ϭ 0.0298, wR2 ϭ 0.0775
0.525 and Ϫ0.661
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R indices (all data)
Ϫ3
˚
Largest diff. peak and hole (e A
)
* Prof. Tong-Lai Zhang
State Key Laboratory of Explosion Science and
Technology
Beijing Institute of Technology
5 South Zhongguancun Street, Haidian District,
Beijing / P. R. China
TEL & Fax: (ϩ) 86-10-68913818
E-mail: ztlbit@bit.edu.cn
a) Crystallographic data (excluding structure factors) for the struc-
ture in this paper have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publication no. CCDC-
663152. Copies of the data can be obtained free of charge on appli-
cation to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax:
(internat.) ϩ44(1223)336-033, E-mail: deposit@ccdc.cam.ac.uk].
754
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 634, 754Ϫ757

Double-helical-chain Coordination Polymer Zinc Complex
title complex are given in Table 2. The molecular structure
of the complex is illustrated in Figure 1. Each Zn2ϩ ion
is penta-coordinated by two nitrogen atoms from 2,2Ј-bipy
tice, and it displays the flexible characterization different
from the rigid ligands due to the existence of OCH2.
Each nbdoa2Ϫ group serves as a bridging ligand to link
two ZnII atoms, giving rise to a one-dimensional helical
chain structure (Figure 2). The helix has a straight-line axis
˚
ligand (Zn-N ϭ 2.0816(12) and 2.1717(13) A, N(2)-Zn-
N(3) ϭ 77.39(5)°), two oxygen atoms from two nbdoa2Ϫ
˚
˚
(Zn-O ϭ 1.9786(11) and 2.0193(11) A, O(2)-Zn-O(8) ϭ
with a pitch of 20.407 A, and in each helical cycle there are
93.47(5)°) and one oxygen atom from coordinated water
three ZnII atoms and two bridging nbdoa2Ϫ groups. The
˚
molecule (Zn-O
ϭ
2.0137(11) A, O(2)#1-Zn-O(9)
ϭ
adjacent Zn···Zn(1) (symmetry code: Ϫxϩ1/2, yϩ1,
˚
137.21(5)°, O(9)-Zn-O(8) ϭ 94.03(5)°), and the local co-
ordination environment around ZnII atom can be best de-
scribed as a distorted triangle bipyramidal coordination
with atoms N(2), N(3) and O(8) defining the equatorial
Ϫzϩ1/2) distance within the polymeric chain is 12.917 A,
and the angle of three neighboring ZnII atoms in the
cycle is 104.34°, which is similar to the structure of
[Cu(nip)(phen)]n [17]. As expected, two N atoms from 2,2Ј-
bipy have occupied two coordination positions of one metal
atom to prevent the formation of network in this direction.
Along the helix axis, 2,2Ј-bipy planes on the same side are
absolutely parallel one another, but they have a dihedral
angle of 13.28° with those on the other side. It is interesting
that two helical chains intercross with each other to form a
double-helical-chain structure (Fig. 2), and there is an inner
channel running parallel to the helix axis without any inter-
penetration, which is similar to the structure in [Zn(2,2Ј-
bpy)(1,2-BDC)(H2O)]n [18]. Although its effective void is
not big enough for practical use, it hints a possible way for
designing functional molecular channels. The ligands 2,2Ј-
bipy protrude out of the helix channel, which point differ-
ent direction to sustain the crystal lattice and minimize the
steric hindrance.
˚
plane, and Zn (II) atom deviates by 0.0793 A out of the
plane, and O(2) and O(8) occupies the apical site.
˚
Table 2 Selected bond lengths/A and bond angles/° for the title
a)
complex
Zn(1)-O(2)#1
Zn(1)-O(8)
Zn(1)-N(2)
C(8)-O(2)
1.9786(11)
2.0193(11)
2.1717(13)
1.264(2)
Zn(1)-O(9)
Zn(1)-N(3)
C(10)-O(8)
C(10)-O(7)
2.0137(11)
2.0816(12)
1.254(2)
1.247(2)
C(8)-O(3)
1.238(2)
O(2)#1-Zn(1)-O(9)
O(9)-Zn(1)-O(8)
O(9)-Zn(1)-N(3)
O(2)#1-Zn(1)-N(2)
O(8)-Zn(1)-N(2)
C(4)-O(6)-C(9)-(10)
137.21(5)
94.03(5)
119.06(5)
92.86(5)
168.02(5)
170.25(13)
O(2)#1-Zn(1)-O(8)
O(2)#1-Zn(1)-N(3)
O(8)-Zn(1)-N(3)
O(9)-Zn(1)-N(2)
N(3)-Zn(1)-N(2)
C(1)-O(1)-C(7)-C(8)
93.47(5)
102.81(5)
91.29(5)
88.19(5)
77.39(5)
82.3(2)
a) Symmetry operations: #1 ϭ Ϫxϩ1/2, yϩ1, Ϫzϩ1/2.
Figure 1 The molecular structure of the title complex.
˚
The distances C(10)-O(8) (1.254(2) A) and C(8)-O(2)
˚
(1.264(2) A) are slightly longer than those of C(10)-O(7)
˚
˚
(1.247(2) A) and C(8)-O(3) (1.238(2) A), in accord with the
monodentate coordination mode of carboxyl groups. The
torsion angle of C(4)-O(6)-C(9)-C(10) is Ϫ170.25(13)°,
whereas another oxyacetate group C(1)-O(1)-C(7)-C(8) is
obviously twisted out the phenyl ring plane with the torsion
angle 82.3(2)°. At the same time, the angle between C10
carboxyl plane and benzene ring plane is 19.6°, while that
between C8 carboxyl plane and benzene ring plane is
106.6°, two carboxyl planes are almost vertical with the an-
gle 87.2°, demonstrating the two oxyacetate groups have
different space orientation to sustain the whole crystal lat-
Figure 2 View of the double-helical chain (2,2Ј-bipy and hydrogen
atoms omitted for clarity).
Due to the double-helical-chain, π-π stacking interac-
tions are not between the two adjacent parallel chains, but
are among several adjacent chains, which exist between the
aromatic rings of 2,2Ј-bipy and benzene rings to generate a
Z. Anorg. Allg. Chem. 2008, 754Ϫ757
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
755

W. Yu, T.-L. Zhang, J.-G. Zhang, L. Yang, S.-Z. Wang, R.-F. Wu
3-D supramolecular network (Fig. 3). Except for the π-π
stacking interactions, there are hydrogen bond interactions
between water and the uncoordinated O atoms of the car-
boxyl groups, which is shown in Table 3.
begins to collapse, which is similar to the decomposition of
the polymer [Cu(p-BDOA)(2,2Ј-bipy)(H2O)]n [19].The final
residue may be ZnO (found 16.46 %, Calc. 16.00 %).
Figure 3 π-π stacking interactions in the title complex.
Figure 5 The TG-DTG curve of the title complex.
˚
In IR spectra of the title complex, 1633 and 1420 cmϪ1
are the characteristic adsorption bands of νas(OCO) and
νs(OCO). 1521 and 1344 cmϪ1 attribute to νas(ONO) and
νs(ONO), respectively, and 1278 and 1056 cmϪ1 can be as-
signed to νas(C-O-C) and ν (C-O-C), respectively. The fluor-
escent spectrum study shows that the title complex has in-
tense emission occurred at 468 and 574 nm upon excitation
at 320 nm, which can be assigned to the intraligand fluor-
escent emission since a very similar emission is also ob-
served for free H2nbdoa.
Table 3 Selected bond lengths/A and bond angles/° for the title
complex
a)
D-H···A
d(D-H)
d(H-A)
d(D-A)
Є(D-H···A)
O9-H9B···O3#3
O9-H9A···O7#4
0.814(10)
0.823(10)
1.974(12)
1.822(10)
2.751(2)
2.643(2)
160(2)
174(2)
a) Symmetry operations: #3 xϩ1/2, Ϫyϩ1, zϩ1/2; #4 Ϫxϩ1, Ϫyϩ2, Ϫzϩ1.
Figure 4 The DSC curve ofthe title complex.
Figure 6 Emission spectrum of the complex in the solid state at
room temperature.
In the DSC curve (Fig. 4) of the complex there are one
endothermic and two exothermic processes. The TG-DTG
curve (Fig. 5) demonstrates that there are three main mass
loss stages. The first weight loss from 433 to 467 K is attri-
buted to the loss of coordinated water molecules with the
mass loss 3.21 % (Cal. 3.54 %), which is corresponding to
the endothermic process in the DSC curve. The second
mass loss stage from 536 to 720 K is predicted as the loss
of the nitro group, two phenoxyacetate radicals (OCH2) and
2,2Ј-bipy with the mass loss 50.38 % (Calc. 51.55 %), and
in this process the framework of the coordination polymer
Conclusion
In summary, a double-helical chain Zn coordination poly-
mer constructed by flexible ligand 2-nitro-benzene-1,4-di
(oxyacetate) and rigid ligand 2,2Ј-bipy was successfully syn-
thesized under hydrothermal condition. It is noticeable that
the ligand nbdoa2Ϫ displays a good flexibility, which dem-
onstrates some different characteristics from the rigid li-
756
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 754Ϫ757

Double-helical-chain Coordination Polymer Zinc Complex
Acknowledgements. The authors thank the National Natural Sci-
ence Foundation of China (20471008) and the Excellent Young
Scholars Research Fund of Beijing Institute of Technology
(000Y02-8) for financial supports.
gand, and there is an inner channel running parallel to the
helix axis. The double-helical chains are connected to 3-D
network through π-π sacking and hydrogen bond interac-
tions. The thermal analysis showed the coordinating water
molecule was lost at 433 K, and no chemical decomposition
occurred up to 536 K, indicating that the one-dimensional
infinite helical structure was quite stable. The complex is
luminescent and displays an emissive maximum at 468 and
574 nm upon excitation at 320 nm in the solid state at
room temperature.
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Experimental Section
Elemental analysis was carried out on Carlo Erba 1106 full-auto-
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pullet in the range of 400 ϳ 4000 cmϪ1. A Perkin-Elmer Pyris1
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2-Nitro-benzene-1,4-di(oxyacetic) acid was prepared by the ni-
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the reaction of hydroquinone with chloroacetic acid in a molar ra-
tio of 1:2 at 373 K [22]. A mixture of ZnCl2 (0.3 mmol), H2nbdoa
(0.3 mmol), NaOH (0.6 mmol), 2,2Ј-bipy (0.3 mmol) and 15 mL
H2O was sealed in a 25 mL Teflon-lined reactor and kept at 373 K
for 3 days under autogenous pressure. After being cooled slowly to
room temperature, yellow crystals were collected in 83 % yield
(based on Zn). Anal. Calcd (%) for C20H17ZnN3O9: C, 47.22; H,
3.37; N, 8.26. Found (%): C, 47.14; H, 3.29; N, 8.29.
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Z. Anorg. Allg. Chem. 2008, 754Ϫ757
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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