A 3D luminescent Zn(II) coordination polymer with rutile-type topology

Article abstract of DOI:10.1016/j.inoche.2013.03.010

A new coordination network, namely {[Zn(bce)(H₂O)]}_n (1) (H₂bce = 1,2-bis(4-carboxy-phenoxy)ethane), is reported. Complex 1 shows a 3D (3,6)-connected rutile (rtl) topology. The luminescence study indicates that the title compound emits bright green fluorescence and possesses moderate fluorescence lifetimes (τ = 2.26 ns).

Full text of DOI:10.1016/j.inoche.2013.03.010

Inorganic Chemistry Communications 31 (2013) 87–89
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
A 3D luminescent Zn(II) coordination polymer with rutile-type topology
Jian Wu a,1, Jian-Qiang Liu b, ,1, Fu-min Wang c, Tie Wu b, Wang Jun d
⁎
a
Guangxi Key Laboratory of Chemistry and Engineering of Forest Products, and College of Chemistry and Ecological Engineering, Guangxi University for Nationalities,
Nanning, Guangxi 530006, PR China
b
Guangdong Medical College, School of Pharmacy, Dongguan 523808, PR China
College of Chemistry & Life Science, Weinan Teachers University Shannxi, China
College of Chemistry and Pharmaceutical Engineering, Sichuan University of Science & Engineering, Zigong 643000, PR China
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
A new coordination network, namely {[Zn(bce)(H2O)]}n (1) (H2bce = 1,2-bis(4-carboxy-phenoxy)ethane),
is reported. Complex 1 shows a 3D (3,6)-connected rutile (rtl) topology. The luminescence study indicates
that the title compound emits bright green fluorescence and possesses moderate fluorescence lifetimes
(τ = 2.26 ns).
Received 30 January 2013
Accepted 13 March 2013
Available online 21 March 2013
© 2013 Elsevier B.V. All rights reserved.
Keywords:
Luminescence
Structure
Topology
Dicarboxylate
The rational design and construction of metal-organic frameworks
(MOFs) from metal ions and flexible organic ligands have been receiving
increasing interest for fascinating structural topologies, interesting con-
formations such as pillared-layer structure, and potential applications
[1]. Until recently, research on coordination polymers has focused on in-
corporation of flexible dicarboxylate ligands due to its flexuous geometry
and various binding modes [2–8]. Inspired by our previous experience,
we have been interested in the syntheses and characterizations of differ-
ent polymers containing 1,3-bis(4-carboxy-phenoxy)propane (H2bcp)
and 4,4′-oxybis(benzoic acid) (H2oba) [9–12]. Between the two types of
flexible dicarboxylate ligands, the segments of \O\(X)n\O\ chains
are different with the relative orientation of CH2 groups (X = CH2;
n = 0 for H2oba; and n = 3 for H2bcp). Herein, we explore a similar flex-
ible dicarboxylate ligand 1,2-bis(4-carboxy-phenoxy)ethane (bce) to
construct new type of motifs and infer the relationship between the fea-
ture of functions and structural characters.
Herein, we report the synthesis and characterization of a new 3D
coordination polymer, in which bce ligands work as pillars and link
the inorganic \Zn\CO2\Zn\ layers, resulting in (3,6)-connected
rutile-type framework. The as-synthesized sample of compound 1
has also been measured by IR, PXRD, elemental, TG analyses and 3D
luminescence.
Colorless crystals of compound 1 were thermally synthesized by
reacting Zn(OAC)2∙4H2O and H2bce in molar ratio 1:1 and mixed
methanol/deionised water solvent at 150 °C for 72 h [13].
The structure of 1 contains one unique Zn atom, one unique bce,
and one coordinated water molecule. Fig. 1a shows the stick view
of the local octahedral-coordination geometry around the Zn(II)
atom. The axial positions are occupied by two oxygen atoms from
different carboxyl groups, whereas the three oxygen atoms from car-
boxyl groups in bridging bidentated [(k1–k1)-μ2] and tridentated
[(k2–k1)-μ3] fashions and one oxygen atom from coordinated water
molecule are on the equatorial plane. Thus, each Zn(II) ion is coordi-
nated by five carboxylate oxygen atoms from three different bce li-
gands, in which is similar with the reported complexes with oba
[14]. The bond distances of Zn\O are in the range of 2.152(5) to
2.361(5) Å and the O\Zn\O bond angles vary from 55.59(18) to
168.1(2)°, which is coincident with the reported values of the corre-
sponding Zn–carboxylate compounds. Carboxylate groups link the
Zn(II) center to form 2D sheets which runs parallel bc-plane
(Fig. 2b). The 2D layer consists of dimmers of edge sharing ZnO6
polyhedron that are corner-shared hexagon to form the layer. The
distance between the Zn(II) atoms in each dimmer is 3.72(12) Å,
while the distance between the Zn atoms of corner-shared interac-
tion is 4.87(11) Å. Each bce ligand links to three Zn(II) atoms in
bridging bidentated [(k1–k1)-μ2] and tridentated [(k2–k1)-μ3]
modes. To the best of our knowledge, this type of coordinating
mode of bce ligand is not observed in the previously reported com-
plexes. The usual mode is bridging bidentated [(k1–k1)-μ2] and
monodentated [(k1)-μ] modes for carboxyl groups. The layers are sepa-
rated by the biphenyl dicarboxylate groups with the biphenyl rings lay-
ered along the ab-plane. The flexible bce ligands along the a axis act as a
pillar and serve to connect adjacent layer to shape an extended 3D coor-
dination motif, as shown in Fig. 2a. Unfortunately, the adjacent pillars
are too close to each other, and there is no solvent accessible void in 1.
⁎
Corresponding author. Tel./fax: +86 769 22896547.
E-mail address: Jianqiangliu2010@126.com (J.-Q. Liu).
J.Q. Liu and J. Wu have equal contribution on the work and they are co-first authors.
1
1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2013.03.010

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J. Wu et al. / Inorganic Chemistry Communications 31 (2013) 87–89
Fig. 1. The coordination geometry of the metal center and the ligand geometry of com-
pound 1. (Symmetric codes: (i) x, −y + 1/2, z + 1/2; (ii) −x + 1, −y + 1, −z + 1.)
A better insight into the nature of 1 can be achieved by the appli-
cation of topological approach, reducing multidimensional structures
to simple node-and-linker nets. As discussed above, the dinuclear Zn
subunits can be regarded as one node. Each subunit is surrounded by
six adjacent bce ligands, thus, each subunit is taken as a six-connected
node. On the other hand, each bce ligand can be considered as a
three-connecting node since it links three subunits. Consequently,
according to the calculation of TOPOS [15], the framework of 1 be-
longs to a uninodal (3,6)-connected rtl type of topology with Schläli
symbol of (4 · 62)2(42 · 610 · 83) (Fig. 3) [16]. This is a new topolog-
ical motif in the MOFs with bce ligand.
As to FTIR spectra, the compound shows a broad band center
around 3437 cm−1 attributable to the O\H stretching frequency of
the water molecule in 1. As shown in Fig. S1. To study the stability
of the polymer, thermogravimetric analysis (TGA) of complex 1 was
performed (Fig. S2). The compound 1 has two observed weight loss,
first weight loss of 4.6% is corresponding to the loss of the crystalliza-
tion water (calcd 4.7%). Additionally, to confirm the phase purity of
compound, the original sample was characterized by X-ray powder
diffraction (XRPD) at room temperature. The pattern that was simu-
lated from the single-crystal X-ray data of compound was in agree-
ment with those that was observed, as shown in Fig. S3. For
compound 1 after heating at 190 °C for 5 h, the coordinated water
molecule was removed (the evacuated framework is defined as 1′).
The XRPD pattern of 1′ is similar to compound 1, although minor dif-
ferences can be seen in the positions, intensities, and widths of some
peaks, which indicates that the framework of compound 1 is retained
after the removal of the water molecule.
Fig. 3. Schematic representation of the 3D rtl topology net of 1.
emission bands, the fluorescent spectrum of bce ligand has been
also measured, which shows a relatively broad band at 348 nm
(
= 260 nm) (Fig. 4b). The emission bands of these carboxylates
λex
can be assigned to the p* → n transition as previously reported. The
luminescence decay curve of 1 was obtained at room temperature.
The decay curves are well fitted into an exponential function. As
shown in Fig. S4. The corresponding lifetime for 1 is about τ =
2.26 ns at 364 nm. The χ2 value is found to be close to 1 in this
work. Deng and his co-worker reported a Zn(beta) complex and its
lifetime (τ = 13.81 ns), which is longer than that of 1. The difference
may be attributed to the 3D connection feature and more rigid frame-
works between complexes Zn(beta) and title compound 1, in which
also results in less vibrations of the skeleton and less radiation
decay of energy [18].
In conclusion,
a
new Zn(II) coordination polymer of
{[Zn(bce)(H2O)]}n, has been successfully synthesized, in which
shows a 3D (3,6)-connected rutile (rtl) topological motif. In addi-
tion, the luminescence behavior and lifetime of 1 at room temper-
ature are discussed.
Acknowledgment
Organic–inorganic coordination polymers, especially those with
d10 metal centers, have been investigated for their fluorescent prop-
erties and potential applications as fluorescent-emitting materials,
such as light-emitting diodes (LEDs) [17]. Therefore, the complex 1
and bce were studied in the solid-state at room temperature. Excita-
tion of the microcrystalline sample at 266 nm leads to the generation
of fluorescent emission, with the peak maxima occurring at 364 nm
for 1, as shown in Fig. 4a. To further understand the origin of these
This work was partially supported by the grants from the National
Natural Science Foundation of China (21201044), Natural Science
Foundation of Guangdong Province (S2012040007835), Guangdong
Medical College (B2010009), Foundation for Distinguished Young
Talents in Higher Education of Guangdong Province (LYM11069),
Technologies R & D program of Zhanjiang (2011C3108013 and
2012C3106016), Guangxi University for Nationalities (2011DQ022),
Fig. 2. (a) View of the 3D pillared-layer network along the a-axis for 1; (b) the 2D layer of 1 with Zn bridged by oxygen atoms from the carboxylate groups of bce ligands.

J. Wu et al. / Inorganic Chemistry Communications 31 (2013) 87–89
89
Fig. 4. (a) View of the 3-D fluorescence spectrum of 1 and (b) the 3-D fluorescence spectrum of bce ligand at room temperature.
(b) Y.X. Li, M. Xue, L.J. Guo, L. Huang, S.R. Chen, S.L. Qiu, A unique (4,12)-
connected lanthanide metal-organic framework based on tetranuclear build-
ing blocks: topological analysis, fluorescence and magnetism properties,
Inorg. Chem. Commun. 28 (2013) 25–30.
Science & Technology Innovation Fund of Guangdong Medical College
(STIF201112), and Scientific Research Plan Projects of Shaanxi Educa-
tion Department (12JK608).
[8] Q. Chen, J.B. Lin, W. Xue, M.H. Zeng, X.M. Chen, A porous coordination polymer as-
sembled from 8-connected CoII3(OH) clusters and isonicotinate: multiple active
metal sites, apical ligand substitution, H2 adsorption, and magnetism, Inorg.
Chem. 50 (2011) 2321–2328.
Appendix A. Supplementary material
[9] J.Q. Liu, Y.Y. Wang, P. Liu, Z. Dong, Q.Z. Shi, S.B. Batten, Two coordination polymers
displaying unusual threefold 1D → 1D and threefold 2D → 3D interpenetration
topologies, CrystEngComm 11 (2009) 1207–1209.
[10] J.Q. Liu, B. Liu, Y.Y. Wang, P. Liu, G.P. Yang, R.T. Liu, Q.Z. Shi, S.B. Batten, An unusual
3D entangled Co(II) coordination polymer directed by ferromagnetic molecular
building block, Inorg. Chem. 49 (2010) 10422–10426.
[11] J.Q. Liu, Y.Y. Wang, Y.S. Huang, Structural variability of Co(II) and Ni(II) entangled
metal–organic frameworks: effect of N-donor ligands and metal ions, CrystEngComm
3 (2011) 3733–3740.
[12] J.Q. Liu, Y.Y. Wang, Z.B. Jia, An unusual 3D metal-organic framework with multi-
form helical chains, Inorg. Chem. Commun. 14 (2011) 519–521.
[13] A mixture of Zn(OAC)2∙4H2O (0.027 g, 0.1 mmol), H2bce (0.023 g, 0.1 mmol),
CH3OH (5 mL) and deionised water (10 mL) was stirred for 30 min in air. The
pH of the resulting solution was adjusted to 7 using dilute NaOH (0.1 mol/L)
and kept at 150 °C for 72 h. The solution was then cooled to room tempera-
ture at rate of 5 °C h−1, to colorless crystalline product 1 in 41% yield based
on Zn. C16H14ZnO7 (383.64). Calcd: C, 50.08; H, 3.68; Found C, 50.16; H,
3.882. IR (KBr, cm−1): 3437(vs); 2968(m), 1605(s), 1506(s), 1402(vs),
1251(s), 1164(s), 1054(m), 857(s), 781(m), 659(m). Crystal data for 1:
Supplementary data(including four figures and supplementary
crystallographic data in CIF for this paper) to this article can be
found online at http://dx.doi.org/10.1016/j.inoche.2013.03.010.
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