Hydrothermal synthesis, crystal structures, and photoluminescent properties of two cadmium(II) coordination polymers derived from dicarboxylates and N-donor ligands

Article abstract of DOI:10.1080/00958972.2013.813493

Two metal coordination polymers, [Cd(ipa)(L₁)(H ₂O)]_n(1) and [Cd(ipa)(L₂)]_n(2) [H₂ipa=isophthalic acid, L₁= 3,5-bis(imidazole-1-yl) pyridine and L2 = 3,5-bis(benzoimidazo-1-ly)pyridine], have been synthesized and structurally characterized by IR, elemental analysis, XRD, and X-ray single-crystal diffraction. Complex 1 shows a twofold cds topological net and 2 features a 3-D pcu topological net. Luminescent properties of 1 and 2 were investigated in the solid state at room temperature.

Full text of DOI:10.1080/00958972.2013.813493

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Hydrothermal synthesis, crystal structures and
photoluminescent properties of two cadmium(II)
coordination polymers derived from dicarboxylates and
N-donor ligands
JIAKUN XU a b , XIAOCHUN SUN c , CAIXIA JU a d , LIRONG YANG e , CAIFENG BI b & MI SUN a
a Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences , Qingdao ,
266071 , China
b Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean
University of China , Qingdao , 266100 , China
c National Oceanographic Center , Qingdao , 266071 , China
d College of Food Science and Technology, Shanghai Ocean University , Shanghai , 201306 ,
China
e College of Chemistry and Chemical Engineering, Henan University , Kaifeng , 475004 ,
China
Accepted author version posted online: 11 Jun 2013.
To cite this article: JIAKUN XU , XIAOCHUN SUN , CAIXIA JU , LIRONG YANG , CAIFENG BI & MI SUN (2013): Hydrothermal
synthesis, crystal structures and photoluminescent properties of two cadmium(II) coordination polymers derived from
dicarboxylates and N-donor ligands, Journal of Coordination Chemistry, DOI:10.1080/00958972.2013.813493
To link to this article: http://dx.doi.org/10.1080/00958972.2013.813493
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Hydrothermal synthesis, crystal structures and photoluminescent properties of
two cadmium(II) coordination polymers derived from dicarboxylates and
N-donor ligands
JIAKUN XUa, b, XIAOCHUN SUNc, CAIXIA JUa, d, LIRONG YANGe, CAIFENG BIb and MI SUN*a
aYellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, China
bKey Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China,
Qingdao 266100, China
cNational Oceanographic Center, Qingdao 266071, China
dCollege of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China
eCollege of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, China
Two metal coordination polymers, [Cd(ipa)(L1)(H2O)]n (1) and [Cd(ipa)(L2)]n (2) [H2ipa =
isophthalic
acid,
L1
=
3,5-bis(imidazole-1-yl)pyridine
and
L2
=
3,5-bis(benzoimidazo-1-ly)pyridine], have been synthesized and structurally characterized by IR,
elemental analysis, XRD and X-ray single-crystal diffraction. Complex 1 shows a two-fold cds
topological net and 2 features a 3D pcu topological net. Luminescent properties of 1 and 2 were
investigated in the solid state at room temperature.
Keywords: Cd Coordination polymers; Crystal structures; Luminescent properties
1. Introduction
Construction of metal-organic frameworks (MOFs) based on metal ions and organic bridging
ligands has attracted attention for intriguing structures and applications in storage [1, 2],
luminescence [3, 4], magnetism [5], drug delivery [6], catalysis [7, 8], sensors [9] and
separations [10]. The functionalities of MOFs could be designed and fine-tuned through
judicious choices of bridging ligands and metal centers. Rigid ligands, such as
benzenedicarboxylates, have been utilized to construct MOFs: (a) it can be partially or
completely deprotonated to generate H2ipa, Hipa− and ipa2− by controlling the pH, which allows
*Corresponding author. Email: hhsunmi@yeah.net
1

H2ipa to display various acidity-dependant coordination modes. (b) H2ipa has a rigid 120° angle
between the benzene ring and the two carboxylate groups, and therefore may provide various
coordination modes to form discrete metal complexes under appropriate synthesis conditions.
(c) flexible, multidentate coordination sites provide possibility of formation of
higher-dimensional structures. Typical coordination modes of H2ipa are reported [11-14].
Flexible ligands have been employed for construction of MOFs with special properties and
structures [15-17]. Comparatively, far less research has been devoted to semi-rigid ligands.
Nevertheless, MOFs based on semi-rigid ligands have received increasing attention owing to
slight conformational changes during assembly, making it easy to control architectures of MOFs
[18-21].
SBUs, (3,5-bis(imidazole-1-yl)pyridine) and 3,5-bis(benzoimidazo-1-ly)pyridine, exhibit
interesting properties: (i) As semi-rigid bifunctional ligands, they have been employed to
construct one-dimensional and two-dimensional linear polymeric chains and, therefore, are
excellent candidates for construction of supramolecular architectures. (ii) Considering the
orientation of pyridine rings, they are effective as targets in formation of lower dimensional to
high-dimensional networks. (iii) The pyridine rings are useful in formation of hydrogen-bonding
and π-π stacking interactions, which are important in assembling high-dimensional networks. We,
herein, report two new Cd(II) coordination polymers based on semi-rigid L1 and L2 and the rigid
dicarboxylate (H2ipa).
2. Experimental
2.1. Materials and physical measurements
All reagents and solvents were commercially available and used as received. Elemental analyses
were carried out on a Carlo Erba 1106 full-automatic trace organic elemental analyzer.
Fourier-transform infrared spectra (FT-IR) were recorded on a Bruker Tensor-27 FT-IR
spectrometer using dry KBr pellets from 400~4000 cm-1. Solid-state fluorescence spectra were
recorded on a Hitachi F-4600 equipped with a xenon lamp and a quartz carrier at room
2

temperature. X-ray powder diffraction (XRPD) measurements were performed on a Bruker D8
diffractometer operated at 40 kV and 40 mA using Cu-Kα radiation (λ = 0.15418 nm).
2.2. Syntheses
2.2.1. [Cd(ipa)(L1)(H2O)]n (1). A mixture of Cd(CH3COO)2·2H2O (1 mmol), H2ipa (1 mmol),
L1 (1 mmol), NaOH (2 mmol) and deionized water (18 mL) was sealed in a 25 mL Teflon-lined
stainless steel vessel and heated at 160 °C for 96 h. After cooling to room temperature, colorless
block crystals were obtained and washed with ethanol several times. Elemental Anal. Calcd. (%)
for C19H15CdN5O5: C, 45.12; H, 2.99; N, 13.85. Found: C, 45.14; H, 3.00; N, 13.84. IR: 3118 br,
1602 s, 1545 m, 1505 m, 1441 m, 1383 m, 1310 m, 1245 m, 1115 m1, 1067 m, 931 m, 827 m,
725 m.
2.2.2. [Cd(ipa)(L2)]n (2). A similar procedure as for 1 was employed to prepare 2 by changing L1
to L2 (1 mmol). Colorless block crystals of 2 were collected by filtration and washed with
ethanol several times. Elemental Anal. Calcd. (%) for C27H17CdN5O4: C, 55.17; H, 2.92; N,
11.91. Found: C, 55.09; H, 2.89; N, 11.93. IR: 1600 s, 1541 s, 1466 m, 1361 m, 910 m, 827 w,
719 m.
2.3. X-ray Crystallography
Diffraction intensity data of the single crystals of 1 and 2 were collected on a Bruker SMART
APEX II CCD diffractometer equipped with graphite monochromated Mo-Kα radiation (λ =
0.71073 Å) using a ω-scan mode. Empirical absorption correction was applied using SADABS
[22]. The structures were solved by direct methods and refined by full-matrix least-squares on F2
using SHEXL 97 [23]. All non-hydrogen atoms were refined anisotropically. Hydrogens were
located by geometric calculations and their positions and thermal parameters fixed during the
structure refinement. The crystallographic data are summarized in table 1 and bond distances and
angles in table 2.
3

3. Results and discussion
3.1. Description of crystal structures
3.1.1. [Cd(ipa)(L1)(H2O)]n (1). The structure of 1 is determined by X-ray single crystal
diffraction. As shown in figure 1, each Cd(II) is six-coordinate by four oxygens and two
nitrogens, showing decahedral geometry. The Cd-O bond distances range from 2.199 Å to
2.437 Å and the Cd-N distances are 2.305 Å and 2.320 Å. The coordination environment of the
complex is shown in figure 1a, suggesting that the central Cd(II) bonds to two ipa ligands and
two L1 ligands simultaneously, each ipa ligand and each L1 connects two Cd(II) ions to form the
plane hexagon Cd6(ipa)2(L1)4 with dimension of 21.59×10.42 Å2. Remarkably, the coplanar
Cd6(ipa)2(L1)4 generates a large nanoscale cage which can be considered as consisting of six
Cd(II) vertices, four bended L2 edges and two bended ipa molecules, as depicted in figure 1b.
Thus, a 3D framework is prolongated along a, b and c axes through cage-to-cage connections.
One left-handed helical chain (with a pitch of 10.539 Å) running along the b axis in the 3D
framework of 1 is observed. The adjacent left-handed helical chains entangle reciprocally
through ipa and L1 bridges to give an unprecedented interwoven double helix architecture, see
figure 1c. If the Cd(II) ions and the organic ligands can be viewed as nodes and linkers, the 3D
framework can be simplified as a cds net. Two identical layers penetrate each other in
interpenetrating modes to give a two-fold interpenetrating network, as illustrated in figures 1d
and 1e.
3.1.2. [Cd(ipa)(L2)]n (2). Single crystal X-ray diffraction analysis reveals that 2 is a 3D pcu
topological net. As shown in figure 2, Cd(II) adopts an octahedral geometry in which four
carboxylate oxygens form three different carboxylate ligands and two nitrogens from L2. In
MOF 2, the carboxylates are bis-monodentate(μ2-η1: η1) and bidentate/chelating(μ1-η1: η1)
coordination, as shown in figure 2a. The μ2-η1: η1 carboxylate groups connect Cd(II) ions to form
dinuclear units with Cd-Cd distance of 4.435 Å. In the framework, Cd(II) ions are connected
4

through carboxylic oxygen bridges in μ2-η1: η1 fashion to propagate an infinite one-dimensional
looped ribbon in which two types of rings are alternately arranged in the pattern (ABAB)∞.
16-Membered ring A is comprised by Cd–ipa–Cd–ipa and 8-membered ring B by
Cd–CO2–Cd–CO2 units, respectively, as depicted in figure 2b. If the dinuclear Cd(II) and organic
ligands can be viewed as nodes and linkers, the 3D framework can be simplified as a pcu net, see
figure 2c.
3.2. XRPD analysis and luminescent properties
Simulated and experimental X-ray powder diffraction patterns of 1 and 2 are shown in figure 3.
All the peaks observed in the measured curves approximately match the simulated curves
generated from single-crystal diffraction data, which clearly confirms the phase purity of the
as-synthesized products.
Fluorescence emission spectra of 1 and 2 were measured in the solid state at room
temperature. Intense luminescence emissions are observed at 408 nm (λex = 280 nm) for 1 and
409 nm (λex = 290 nm) for 2 (figure 4). L1 and L2 have an emission band at 411 nm and 352 nm,
respectively. The luminous mechanism for 1 and 2 might be intraligand fluorescent emission
(π-π*) [24]. The different emission positions and intensities of 1 and 2 might be attributed to the
significant difference in their structures. The ligand coordination to the metal center might
contribute to enhancement of luminescence, which effectively increases the asymmetry and
rigidity of the ligands, and thereby reduces the non-radiative decay of the intraligand excited
state [25].
4. Conclusions
A number of Cd(II) coordination polymers of different network structures have been constructed
by utilization of different N-heterocyclic ligands and other auxiliary ligands as building blocks,
most of which coordinate to metal ions in chelating or monodentate fashions [26-34]. Through
self-assembly of rigid H2ipa with Cd(II) in the presence of semi-flexible N-donor ligands L1 and
5

L2, we constructed two new coordination polymers [Cd(ipa)(L1)(H2O)]n (1) and
[Cd(ipa)(L2)]n (2). Complex 1 shows a two-fold cds topological interpenetrating network, while
2 features a 3D pcu topological net, as reported [33]. The ligand exhibits remarkable versatility
to link metals in different coordination modes, which could affect the architecture of the
coordination polymers and form different topological frameworks. Moreover, 1 and 2 also
exhibit emission in the solid state at room temperature.
Supplementary materials
Crystallographic data for the structural analysis have been deposited with the Cambridge
Crystallographic Data Center, CCDC reference numbers: 913558 and 913559. These data can be
obtained free of charge at http://www.ccdc.cam.ac.uk (or Cambridge Crystallographic Data
Center, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44-1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk).
Acknowledgement
We thank the support of this work by NSFC (No. 31200642 and No. 41106146), Special Funds
for the Basic R&D Program in the Central Non-profit Research Institutes (No. 20603022012018),
Special Scientific Research Funds for Central Non-profit Institutes, Chinese Academy of Fishery
Sciences (No. 2013A1002) and Qingdao Municipal Science and Technology Plan Project
(No. 12-1-4-12-(2)-jch).
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8

Table 1. Crystallographic data and structure refinement summary for 1 and 2.
Empirical formula
Formula weight
Crystal system
C19N5O5CdH15
505.76
C27N5O4CdH17
587.86
Monoclinic
C2/c
Monoclinic
C2/c
Space group
Unit cell dimensions
a = 34.966(2) Å
b = 20.643(1) Å
c = 26.328(2) Å
β = 126.408(1)°
a = 20.876(2) Å
b = 14.164(1) Å
c = 20.012(1) Å
β = 128.877(1)°
Volume (Å3)
15294(1)
4607(2)
Z
8
8
Calculated density (mg/ mm3)
1.757
1.695
Independent reflections (I>2σ(I))
F(000)
13554
5215
8064
2352
θ range for data collection
Limiting indices
1.22-25.05
1.81-27.53
-41≤h≤41
-20≤k≤24
-31≤l≤25
-26≤h≤25
-18≤k≤13
-22≤l≤21
Goodness-of-fit on F2
1.032
1.045
a
R1 ,wR2 b [I>2σ(I)]
R1 = 0.0371, wR2 = 0.0784
R1 = 0.0641, wR2 = 0.0930
R1 = 0.0221, wR2 = 0.0582
R1 = 0.0249, wR2 = 0.0600
0.41 and -0.50
a
R1 ,wR2 b (all data)
Largest diff. peak and hole (e/Å3)
1.07 and -0.81
2
aR = Σ(||F0|−|FC||)/Σ|F0|. bwR = [Σw(|F0|2−|FC|2)2/Σw(F0 )]1/2.
9

Table 2. Selected bond lengths (Å) and angles (°) for 1 and 2.
Compound 1
Cd(1)-O(1)
2.199(3)
Cd(1)-O(16)
2.401(3)
Cd(1)-O(1W)
2.437(4)
Cd(1)-N(1)
2.305(4)
Cd(1)-O(15)
2.382(4)
Cd(1)-N(3)i
2.320(4)
N(1)-Cd(1)-N(3)i
N(1)-Cd(1)-O(15)
N(1)-Cd(1)-O(16)
N(1)-Cd(1)-O(1W)
N(3)i-Cd(1)-O(15)
N(3)i-Cd(1)-O(16)
N(3)i-Cd(1)-O(1W)
O(1)-Cd(1)-N(1)
90.18(14)
97.83(13)
85.37(13)
160.76(15)
146.14(12)
93.61(13)
74.95(15)
106.09(14)
O(1)-Cd(1)-N(3)i
O(1)-Cd(1)-O(15)
O(1)-Cd(1)-O(16)
O(1)-Cd(1)-O(1W)
O(15)-Cd(1)-O(16)
O(15)-Cd(1)-O(1W)
O(16)-Cd(1)-O(1W)
126.21(14)
83.06(12)
137.60(12)
92.68(16)
54.70(11)
88.47(14)
83.50(15)
Compound 2
Cd(1)-N(1)
Cd(1)-N(3)ii
Cd(1)-O(1)iii
2.252(2)
2.443(2)
2.387(1)
170.28(5)
116.72(6)
86.62(6)
102.90(5)
142.28(5)
88.90(5)
84.00(5)
87.19(5)
Cd(1)-O(2)
Cd(1)-O(3)i
Cd(1)-O(4)i
2.207(2)
2.325(1)
2.376(2)
55.79(5)
94.84(6)
83.54(6)
92.86(6)
84.64(5)
100.20(6)
153.65(5)
O(1)iii-Cd(1)-N(3)v
O(2)-Cd(1)-N(1)
O(2)-Cd(1)-N(3)v
O(2)-Cd(1)-O(1)iii
O(2)-Cd(1)-O(3)iv
O(2)-Cd(1)-O(4)iv
O(3)iv-Cd(1)-N(3)v
O(3)iv-Cd(1)-O(1)iii
O(3)iv-Cd(1)-O(4)iv
O(4)iv-Cd(1)-N(3)v
O(4)iv-Cd(1)-O(1)iii
N(1)-Cd(1)-N(3)v
N(1)-Cd(1)-O(1)iii
N(1)-Cd(1)-O(3)iv
N(1)-Cd(1)-O(4)iv
i
i
ii
Symmetry codes for 1: 1/2+X, 3/2-Y, 1/2+Z; for 2: -1/2+X, 1/2-Y, -1/2+Z; +X, -Y,
-1/2+Z; iii3/2-X, 1/2-Y, 1-Z; iv1/2+X, 1/2-Y, 1/2+Z; v+X, -Y, 1/2+Z.
10

Figure 1.
(a)
(b)
(c)
11

Figure 1 (continued)
(d)
(e)
Figure 1. (a) The coordination environment for Cd(II) in 1; (b) The coplanar hexagon
Cd6(ipa)2(L1)4; (c) The double-stranded helices; (d) The 3D topological cds net; (e) The two-fold
interpenetrating cds net of 1.
12

Figure 2.
(a)
(b)
(c)
Figure 2. (a) The coordination environment for Cd(II) in 2; (b) View of one-dimensional looped
ribbon comprising ring A and ring B; (c) Diagram of the 3D pcu net for 2.
13

Figure 3.
(a)
(b)
Figure 3. The XRPD for (a): 1; (b) 2 in the solid state at room temperature.
14

Figure 4.
Figure 4. Fluorescence emission spectra for 1 and 2 in the solid state at room temperature.
15