A tubular luminescent Zn(II) coordination polymer with unsymmetrical bridge ligand

Article abstract of DOI:10.1016/j.inoche.2009.10.040

A novel 1D tubular coordination polymer [ZnL(dca)₂]_n (dca = dicyanamide, L = 2-(3-pyridylmethylthio)-5-(4-pyridyl)-1,3,4-oxadiazole) constructed by the unsymmetrical bridge ligands L spirally winding around two double-chain pillars Zn(dca)₂ was synthesized and characterized.

Full text of DOI:10.1016/j.inoche.2009.10.040

Inorganic Chemistry Communications 13 (2010) 157–159
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
A tubular luminescent Zn(II) coordination polymer with unsymmetrical
bridge ligand
*
*
Ben-Lai Wu , Rui-Ying Wang, E. Ye, Hong-Yun Zhang, Hong-Wei Hou
Department of Chemistry, Zhengzhou University, Zhengzhou 450052, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel 1D tubular coordination polymer [ZnL(dca)2]n (dca = dicyanamide, L = 2-(3-pyridylmethylthio)-
5-(4-pyridyl)-1,3,4-oxadiazole) constructed by the unsymmetrical bridge ligands L spirally winding
around two double-chain pillars Zn(dca)2 was synthesized and characterized.
Ó 2009 Elsevier B.V. All rights reserved.
Received 23 August 2009
Accepted 27 October 2009
Available online 31 October 2009
Keywords:
1,3,4-Oxadiazole derivative
Unsymmetrical ligand
1D tubular coordination polymer
Fluorescence properties
1,3,4-Oxadiazole exhibiting excellent luminous property and
biological activity such as antiphlogosis and antisepsis, has drawn
recent great attention in organic synthesis, medicinal chemistry
and materials science [1–4]. For example, in combination of an
dicyanamide), together with its electrooptical and fluorescent
properties.
Ligand L shown in Scheme 1 was synthesized via a nucleophilic
substitution reaction of 5-(4-pyridyl)-2-mercapto-1,3,4-oxadiazole
and 3-(chloromethyl)pyridine under alkaline condition [3,9,10,13].
Compound 1 was synthesized as colorless block crystals by slow
evaporation of an ethanol/methanol solution of L, Na(dca)2 and
Zn(NO3)2Á6H2O [14]. IR spectra disclose characteristic absorptions
of 2313, 2261 and 2186 cmÀ1 for dca and 1623, 1546 and
1459 cmÀ1 for aromatic rings in 1. Crystallographic analysis [15]
reveals that compound 1 is a discrete 1D tubular architecture
extending along the b-axis (Fig. 1).
In the structure, each zinc(II) atom locates at a distorted octahe-
dral environment with four nitrogen atoms from dca in the equa-
torial plane, and a 3-pyridyl nitrogen atom and a 4-pyridyl
nitrogen atom from different L at the axial sites (Fig. 2). The bond
lengths of Zn–N range from 2.065(7) to 2.234(7) Å, and among
which the Zn–N5dca of 2.234(7) Å is slight longer compared with
those in literature [16–20]. The widely used versatile ligand dca
anions acting as bidentate bridges adopt an end-to-end coordina-
tion mode, and doubly link with Zn(II) metal centers to form 1D
electron transporting moiety 1,3,4-oxadiazole with
transporting moiety carbazole, Huang et al. created a fascinating
compound 2-(4-biphenylyl)-5-(4-carbazole-9-yl)phenyl-1,3,4-
a hole
oxa-diazole to design high-performance blue electroluminescent
devices [4]. As for coordination chemistry, it has been a hotspot
to tailor polytopic ligands based on the intentional modification
of 1,3,4-oxadiazole through introducing functional groups such
as mercapto, pyridyl and sulfanilamide to enforce/enhance the de-
sired properties and coordination flexibility, and some metal-or-
ganic complexes with novel structures and properties have been
reported [5–8]. However, 1,3,4-oxadiazole-containing unsymmet-
rical ligands and their coordination compounds are comparatively
uncommon [9,10]. As well known, using unsymmetrical bridging
ligands as building blocks is currently selection for assembling no-
vel helical architectures and optical materials [11,12]. Thus we
simultaneously introduce mercapto and pyridyl groups into the
backbone of 1,3,4-oxadiazole, and hope that the unsymmetrical
configuration, coordination variety and flexibility of the resulting
multifunctional ligands are in favor of construction for aesthetic
structural motifs with gracious functions. Here we wish to commu-
nicate a novel 1D tubular coordination polymer [ZnL(dca)2]n (1)
(L = 2-(3-pyridylmethylthio)-5-(4-pyridyl)-1,3,4-oxadiazole, dca =
annular structures with
a
separation of Zn(II)Á Á ÁZn(II) being
7.463 Å. The double chain is almost linear and every cycle in the
chain is a 12-membered Zn(dca)2Zn ring with a flat configuration,
being similar to the double dca-bridged 1D polymers [16–18]. A
striking structural feature of 1 is that unsymmetrical ligands L
select the double-chain Zn(dca)2 as pillars, wind around two pillars
through its 3-pyridyl and 4-pyridyl nitrogen atoms ligating to
metal centers in different pillars, and form a 1D tubular polymer
with a 21 axis running through the tube (Fig. 1). Half dca anions
of every pillar reside in the tube, which mainly results in the
* Corresponding authors. Tel.: +86 0371 67763675 (Ben-Lai Wu and Hong-Wei
Hou).
E-mail addresses: wbl@zzu.edu.cn (B.-L. Wu), houhongw@zzu.edu.cn
(H.-W. Hou).
1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2009.10.040

158
B.-L. Wu et al. / Inorganic Chemistry Communications 13 (2010) 157–159
Scheme 1. Schematic representation of ligand L.
Fig. 2. Perspective view of the coordination environment of the Zn(II) ion in 1.
Selected bonds (Å) and angles (°): Zn1–N1 2.117(9), Zn1–N5 2.220(7), Zn1–N7
2.074(7), Zn1–N5C 2.220(7), Zn1–N7C 2.074(7), Zn1–N4B 2.153(9), N7–Zn1–N1
92.7(3), N7–Zn1–N5 90.3(4), N1–Zn1–N5 90.6(3), N7–Zn1–N7C 98.4(4), N7C–
Zn1–N1 92.7(3), N7–Zn1–N4B 91.2(2), N1–Zn1–N4B 174.0(3), N1–Zn1–N5C
90.6(3), N7C–Zn1–N5 170.5(3), N7C–Zn1–N4B 91.2(2), N7–Zn1–N5C 170.5(3),
N7C–Zn1–N5C 90.3(4), N4B–Zn1–N5C 84.8(3), N4B–Zn1–N5 84.8(3), N5C–Zn1–N5
80.8(6). A x, 1/2-y, z; B -x, y-1/2, -z; C x, -y-1/2, z; D x, y-1, z.
Fig. 1. (a) View of dca-bridged double-chain pillars Zn(dca) and (b) 1D tubular
coordination polymer constructed by bridges
L spirally winding around two
double-chain pillars in 1.
disorder of C12 in the half dca anions. The Zn(II)Á Á ÁZn(II) distance
bridged by L is 7.085 Å. Notably, every unsymmetrical ligand L al-
lows a spiral configuration with the 4-pyridyl group being coplanar
with the oxadiazole group (the dihedral angle being 6.3°) and the
S-bonded 3-(methyl)pyridyl group reversely being perpendicular
with the oxadiazole group (the dihedral angle being 91.5°), being
obviously different from the almost flat configuration of analogue
[9,10]. Especially, the thioether moiety embedded in the backbone
of L not only constrains the C–S–C angle being close to 90°
(96.6(5)°) but also allows the free rotation of the two bound groups
along C–S bonds, thereby endowing ligand
L with flexible
conformations to cater for assembling requirement. Perhaps the
Fig. 3. View of discrete tubular polymeric units aligning in parallel along b-axis and complementary interchain interdigitation through the p–p stacking interactions between
neighbouring tubes to result in an overall 2D sheet.

B.-L. Wu et al. / Inorganic Chemistry Communications 13 (2010) 157–159
159
unsymmetrical bridge ligand L containing biologically active group
1,3,4-oxadiazole.
Supplementary material
CCDC 743772 contains the supplementary crystallographic data
for complex 1. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Acknowledgements
We gratefully acknowledge financial support from the National
Natural Science Foundation of China (20771094), the Science and
Technology Key Task of Henan Province (0524270061), and the
China Postdoctoral Science Foundation (20070410877).
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Fig. 4. Solid state photoluminescent spectra of 1 (solid line) and free ligand L
(dotted line) at room temperature.
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role in the construction of the tubular structure. In a sense, com-
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size about 14 Â 6 Å2 and a pitch of 7.463 Å, being dissimilar to
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rigidity of L and reducing the nonradiative relaxation process.
In summary, we have successfully synthesized a novel 1D
tubular luminescent Zn(II) coordination polymer with the designed
q
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