Construction of 1D to 3D cadmium(II) coordination polymers from 4-(imidazol-1-yl)-benzoic acid: Effect of bridging anions

Article abstract of DOI:10.1016/j.ica.2014.01.014

Three Cd(II) coordination polymers, [Cd(IBA)Cl(H₂O)]_n (1), [Cd(IBA)(CH₃COO)]_n (2) and [Cd(IBA)N ₃]_n (3) derived from HIBA (HIBA = 4-(imidazol-1-yl)- benzoic acid), have been designed and prepared in the existence of different anions. 1 is a 1D chain and consists of Cd₂Cl₂ units bridged by imidazolyl nitrogen atom and chelating carboxylate of IBA. In 2, the adjacent Cd(II) are bridged by acetate to form a bis(carboxylate-O,O′)- Cd(II) dimeric unit, which is inter-connected by exo-tridentate IBA into a 2D layer, in which carboxylate of acetate and IBA alternatively bridge Cd(II) generating carboxylate-O,O′-Cd(II) chains. In 3, μ_1,1-azide bridges Cd(II) forming a helical chain, which is further inter-connected by exo-tridentate IBA into a two-folded interpenetrated 3D network with unusual seh-3,5-P4₃2₁2 topology. These results show significant anion-dependent effect on the formation of network structures. Solid-state photoluminescence investigation at room temperature indicates complexes 1-3 emit the intense photoluminescence around 450 nm.

Full text of DOI:10.1016/j.ica.2014.01.014

Inorganica Chimica Acta 413 (2014) 187–193
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Construction of 1D to 3D cadmium(II) coordination polymers from
4-(imidazol-1-yl)-benzoic acid: Effect of bridging anions
⇑
Ying Feng, Da-Bin Wang, Bo Wan, Xin-Hua Li, Qian Shi
Nanomaterials & Chemistry Key Laboratory, College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three Cd(II) coordination polymers, [Cd(IBA)Cl(H2O)]n (1), [Cd(IBA)(CH3COO)]n (2) and [Cd(IBA)N3]n (3)
derived from HIBA (HIBA = 4-(imidazol-1-yl)-benzoic acid), have been designed and prepared in the exis-
tence of different anions. 1 is a 1D chain and consists of Cd2Cl2 units bridged by imidazolyl nitrogen atom
and chelating carboxylate of IBA. In 2, the adjacent Cd(II) are bridged by acetate to form a bis(carboxylate-
O,O0)-Cd(II) dimeric unit, which is inter-connected by exo-tridentate IBA into a 2D layer, in which
carboxylate of acetate and IBA alternatively bridge Cd(II) generating carboxylate-O,O0-Cd(II) chains. In
Received 16 September 2013
Received in revised form 1 January 2014
Accepted 6 January 2014
Available online 23 January 2014
Keywords:
3,
l1,1-azide bridges Cd(II) forming a helical chain, which is further inter-connected by exo-tridentate
Cadmium(II) polymer
Anion-dependent effect
Crystal structure
IBA into a two-folded interpenetrated 3D network with unusual seh-3,5-P43212 topology. These results
show significant anion-dependent effect on the formation of network structures. Solid-state
photoluminescence investigation at room temperature indicates complexes 1–3 emit the intense
photoluminescence around 450 nm.
Luminescence property
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
other factors, such as coordination geometry of metal ions, coun-
ter anions, temperature, the solvent system and pH value of the
The design and synthesis of metal–organic frameworks (MOFs)
with unusual and tailorable structures are fundamental steps for
the discovery and fabrication of various functional supramolecu-
lar devices or materials [1]. Molecular self-assembly based on
the principle of crystal engineering has proven to be an efficient
approach for the formation of 1D, 2D and 3D frameworks. The
judicial selection of multifunctional organic ligands with different
coordination sites linked by appropriate spacers is important for
the design and construction of the desirable frameworks [2–4].
In the context, multidenate N,O-organic ligands containing nitro-
gen and carboxylate groups are excellent candidates to construct
MOFs by closely controlling the properties of spacers, such as the
length, shape, symmetry, flexibility and functionality [5]. For
examples, Lin et al. have obtained a series of Cd(II) complexes,
using ligands containing pyridyl and carboxylate groups [6]. Hong
et al. reported a series of Ag(I), Cd(II) and Mn(II) MOFs with beau-
tiful aesthetics and useful properties using aminobenzoic acids
[5d–f]. However, the mechanism of molecular self-assembly is
still unclear, the exact prediction and modification of target prod-
ucts are still difficult. The main reason is the assembly process of
organic ligands and metal ions is also highly influenced by lots of
solution [7]. Sometimes, a subtle alteration in any of these factors
can result in new MOFs with different structural topologies and
functions. Thus, understanding the factors that govern the assem-
bly process is crucial to the development of MOFs. It is a common
strategy to carry out a special study by only changing one of reac-
tion conditions.
In the designed synthesis of MOFs, the imidazolyl unit is a
promising building block owing to its ready availability and strong
coordination ability [8–10]. Various MOFs were constructed from
transition metal ions and organic ligands containing imidazolyl
and carboxylate groups. In our study of imidazolyl-based func-
tional materials, we are interested in 4-(imidazol-1-yl)-benzoic
acid (HIBA) due to the non-linear property. It was known that
the anion can not only balance the electron charge in the system,
but also plays an important role on the coordination mode of the
ligands in MOFs [11]. Recently, Co(II) [12] and Cd(II) [13–14] MOFs
were constructed, but the anionic effect on the structures and
properties have no been studied. In this work, we chose Clꢀ,
CH3COOꢀ, and N3ꢀ as the anions to construct the frameworks with
IBA, and reported three Cd(II) coordination polymers,
[Cd(IBA)Cl(H2O)]n (1), [Cd(IBA)(CH3COO)]n (2) and [Cd(IBA)N3]n
(3) (HIBA = 4-(imidazol-1-yl)-benzoic acid), in which the anions
have an important effect on their structures and properties.
⇑
Corresponding author. Tel.: +86 577 86596013; fax: +86 577 86596059.
E-mail address: shiq@wzu.edu.cn (Q. Shi).
http://dx.doi.org/10.1016/j.ica.2014.01.014
0020-1693/Ó 2014 Elsevier B.V. All rights reserved.

188
Y. Feng et al. / Inorganica Chimica Acta 413 (2014) 187–193
Table 1
Crystallographic data for the complexes.
1
2
3
Molecular formula
Formula weight
T (K)
C
10H9CdClN2O3
C12H10CdN2O4
358.62
173(3)
C10 H7CdN5O2
341.61
173(3)
353.04
173(3)
Cryst color and form
Cryst system
space group
yellow blocks
monoclinic
C2/c
colorless blocks
monoclinic
C2/c
pale yellow blocks
orthorhombic
Pbca
a (Å)
19.487(7)
9.189(3)
18.803(9)
8.128(4)
15.967(6)
6.815(3)
0
b (AÅ)
0
12.856(5)
16.328(8)
20.113(8)
c (AÅ)
a
(°)
90
90
90
b (°)
93.505(6)
90
2297.9(14)
8
2.041
1376
103.930(5)
90
2422(2)
8
1.967
1408
90
90
c
(°)
V (A3)
2188.6(14)
8
2.074
1328
27.49
Z
Dcalc (Mg mꢀ3
F(000)
hmax (°)
)
27.48
27.46
Collected/unique
9382/2610
164
0.874
R1 = 0.0217
wR2 = 0.0473
R1 = 0.0289
wR2 = 0.0487
0.540 and ꢀ0.432
8904/2750
174
1.113
R1 = 0.0182
wR2 = 0.0496
R1 = 0.0212
wR2 = 0.0514
0.772 and ꢀ0.548
15842/2509
164
1.117
R1 = 0.0228
wR2 = 0.0526
R1 = 0.0247
wR2 = 0.0537
0.970 and ꢀ0.480
No. of parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)a,b
Largest peak and hole (e Åꢀ3
r
(I)]a,b
)
P
P
a
R1
¼
jjFoj ꢀ jFcjj= jFoj.
1
2
ꢀ1
P
P
2
2
2
2
wR2 ¼ ½ wðjFoj ꢀ jFcjÞ = wjFoj ꢁ ; w ¼ ½r2ðFoÞ þ ð0:1ðmaxðFo2; 0Þ þ 2Fc2Þ=3Þ ꢁ
.
b
Table 2
Selected bond lengths (Å) and Angles (°) for the complexes.a
Complex 1
Cd(1)–O(1)
Cd(1)–O(2A)
Cd(2)–O(1W)
Cd(2)–N(1C)
O(2)–Cd(1)–O(1)
O(1)–Cd(1)–Cl(1)
O(2)–Cd(1)–Cl(1A)
N(1B)–Cd(2)–O(1W)
N(1B)–Cd(2)–Cl(1A)
N(1B)–Cd(2)–Cl(1)
O(1WA)–Cd(2)–Cl(1)
Complex 2
2.365(2)
2.3522(18)
2.392(2)
2.233(2)
55.58(7)
90.15(6)
148.02(5)
85.18(8)
99.68(6)
91.78(7)
83.64(6)
Cd(1)–O(1A)
Cd(1)–Cl(1)
2.365(2)
2.5500(9)
2.392(2)
2.6796(9)
119.83(7)
93.73(5)
164.00(12)
104.49(11)
83.64(6)
Cd(1)–O(2)
Cd(1)–Cl(1A)
Cd(2)–N(1B)
Cd(2)–Cl(1A)
O(2)–Cd(1)–O(2A)
O(2)–Cd(1)–Cl(1)
N(1C)–Cd(2)–O(1W)
N(1B)–Cd(2)–Cl(1)
O(1WA)–Cd(2)–Cl(1)
O(1W)–Cd(2)–Cl(1)
2.3522(18)
2.5500(9)
2.233(2)
2.6796(9)
94.17(9)
94.42(6)
85.04(8)
91.78(7)
170.95(6)
170.95(5)
Cd(2)–O(1WA)
Cd(2)–Cl(1)
O(2)–Cd(1)–O(1A)
O(1)–Cd(1)–Cl(1A)
N(1B)–Cd(2)–N(1C)
O(1W)–Cd(2)–O(1WA)
O(1W)–Cd(2)–Cl(1)
N(1C)–Cd(2)–Cl(1)
Cl(1)–Cd(2)–Cl(1A)
99.68(6)
88.56(4)
Cd(1)–O(2)
Cd(1)–O(3A)
Cd(2)–O(1D)
Cd(2)–O(4A)
N(1B)–Cd(1)–O(2)
N(1C)–Cd(1)–O(2)
N(1B)–Cd(1)–O(3)
N(1C)–Cd(1)–O(3A)
O(2A)–Cd(1)–O(3)
O(1D)–Cd(2)–O(4)
O(1D)–Cd(2)–O(4A)
Complex 3
2.3261(15)
2.3775(16)
2.2390(14)
2.2569(15)
91.54(5)
98.64(5)
83.61(5)
83.61(5)
177.62(4)
91.94(6)
Cd(1)–O(2A)
Cd(1)–N(1B)
Cd(2)–O(1AA)
2.3261(15)
2.2620(17)
2.2390(14)
Cd(1)–O(3)
Cd(1)–N(1C)
Cd(2)–O(4)
2.3775(16)
2.2620(17)
2.2569(15)
N(1C)–Cd(1)–O(2A)
N(1B)–Cd(1)–N(1C)
N(1B)–Cd(1)–O(3A)
O(2)–Cd(1)–O(3)
O(2A)–Cd(1)–O(3A)
O(1AA)–Cd(2)–O(4A)
O(4)–Cd(2)–O(4A)
91.54(5)
166.59(7)
86.35(5)
97.79(7)
97.79(7)
91.94(6)
144.96(7)
N(1B)–Cd(1)–O(2A)
O(2)–Cd(1)–O(2A)
N(1C)–Cd(1)–O(3)
O(2)–Cd(1)–O(3A)
O(3)–Cd(1)–O(3A)
O(1AA)–Cd(2)–O(4)
O(1AA)–Cd(2)–O(1D)
98.64(5)
81.44(8)
86.35(5)
177.62(4)
83.08(9)
98.93(6)
143.38(7)
98.93(6)
Cd(1)–O(1A)
Cd1–N(3)
N(1)–Cd(1)–N(3)
N(1)–Cd(1)–O(2B)
N(1)–Cd(1)–O(1A)
O(2B)–Cd(1)–O(1A)
2.2933(18)
2.255(2)
120.10(8)
87.23(7)
91.25(7)
171.81(7)
Cd(1)–N(1)
Cd1–N(3C)
N(1)–Cd(1)–N(3C)
N(3)–Cd(1)–O(2B)
N(3)–Cd(1)–O(1A)
2.233(2)
2.247(2)
110.56(7)
88.44(7)
91.67(8)
Cd1–O(2B)
2.2848(17)
N(3)–Cd(1)–N(3C)
N(3C)–Cd(1)–O(2B)
N(3C)–Cd(1)–O(1A)
129.29(3)
96.40(8)
85.36(7)
a
Symmetry operations. For 1: (A) ꢀx + 1, y, ꢀz + 3/2 (B) x ꢀ 1/2, ꢀy + 3/2, z + 1/2 (C) ꢀx + 3/2, y + 3/2, ꢀz + 1; For 2: (A) xꢀ1/2, ꢀy + 3/2, zꢀ1/2 (B) x + 3/2, ꢀy + 3/2, ꢀz + 2 (C)
ꢀx + 1, y, ꢀz + 3/2 (D) ꢀx + 1, yꢀ1, ꢀz + 3/2 (AA) x, y ꢀ 1, z; For 3: (A) ꢀx + 2, y + 1/2, ꢀz + 3/2 (B) x + 1/2, ꢀy + 1/2, ꢀz + 1, (C) ꢀx + 3/2, ꢀy, z + 1/2.
IR spectra were measured from KBr pellets on a Bruker-Tensor
27FT-IR spectrometer. Photoluminescence spectra were recorded
ona Thermo Aminco-Bowan2spectrometerwith450-Wxenonlamp
monochromatized by double grating (1200 gr/mu) at room temper-
ature. Thermal stability studies were carried out on a NETSCHZ STA
2. Experimental
2.1. Materials and physical measurements
All chemicals were purchased and used as received. Elemental
analyses were performed with a Thermo 1112 elemental analyzer.
449C thermoanalyzer under N2 at a heating rate of 10 °C minꢀ1
.

Y. Feng et al. / Inorganica Chimica Acta 413 (2014) 187–193
189
Scheme 1. Schematic drawing of the reactions between HIBA and Cd(II) salts.
2.2. Synthesis of [Cd(IBA)Cl(H2O)]n (1)
3. Results and discussion
A mixture of CdCl2ꢂ2.5H2O (0.143 g, 0.6 mmol), HIBA (0.0376 g,
0.2 mmol) and H2O (15 ml) was sealed in a 30 ml Teflon-lined
autoclave and heating to 120 °C for 3 days, followed by slow cool-
ing (10 °C hꢀ1) to room temperature during 24 h. The yellow block
crystals were obtained (yield: 51%). Anal. Calc. for C10H9CdClN2O3:
C, 34.02; H, 2.57; N, 7.93. Found: C, 34.13; H, 2.52; N, 7.98%.
3.1. Preparation
Solvothermal reaction is preference to the other methods in this
system because of the poor solubility of HIBA in water and most
common organic solvents. A series of experiments were carried
out in order to get the suitable reaction temperature. It has been
found that the best temperature for the crystal growth of the Cd(II)
complexes is at 120 °C in the mixed solvent. In the reaction of
Cd(II) salts and HIBA, one-dimensional complex 1 and two-dimen-
sional complex 2 were formed in theꢀexistence of Clꢀ or CH3COOꢀ.
2.3. Synthesis of [Cd(IBA)(CH3COO)]n (2)
The colorless crystals of 2 were formed using Cd(OAc)2ꢂ2H2O
(0.160 g, 0.6 mmol) instead of CdCl2ꢂ2.5H2O in the same reaction
conditions as described above (yield: 78.8%). Anal. Calc. for C12H10-
CdN2O4: C, 40.19; H, 2.81; N, 7.81. Found: C, 40.18; H, 2.70; N,
7.87%.
When the anion is NO3 and N3ꢀ, N3 participates in coordination
ꢀ
ꢀ
instead of NO3
(Scheme 1). The result indicates that anions have an important ef-
fect on the structure of complexes.
, forming an three-dimensional complex 3
The IR spectrum of complex 1 shows typical antisymmetric
v
asym(CO2) and symmetric
ate group at 1523 and 1406 cmꢀ1, respectively. The separation be-
tween asym(CO2) and
sym(CO2) is 117 cmꢀ1, indicating a chelating
vsym(CO2) stretching bands of carboxyl-
2.4. Synthesis of [Cd(IBA)N3]n (3)
v
v
The pale yellow block crystals of 3 were obtained using
Cd(NO3)2ꢂ4H2O (0.185 g, 0.6 mmol) and NaN3 (0.013 g, 0.2 mmol)
instead of CdCl2ꢂ2.5H2O in the same reaction conditions as de-
scribed above (yield: 73%). Anal. Calc. for C10H7CdN5O2: C, 35.16;
H, 1.81; N, 20.38. Found: C, 35.16; H, 1.95; N, 20.50%.
coordination mode of carboxylate group [5d]. However, the charac-
teristic bands of the carboxylate group of IBA are shown at 1545
and 1397 cmꢀ1 for 2, at 1544 and 1400 cmꢀ1 for 3. The separations
(D
) between vasym (CO2) and
respectively, suggesting a 2-carboxylate bridging mode. The pres-
ence of a sharp peak of 2071 cmꢀ1 in IR spectrum of 3 shows that
the azide anion adopts a 2-1,1-bridging mode.
v ,
sym(CO2) are 148 and 144 cmꢀ1
l
2.5. X-ray crystallography
l
In complex 1, Cd(1) is in a six-coordinated mode and is bonded
by two cis-coordinated Clꢀ and four oxygen atoms from the chelat-
ing carboxylate of different IBA. Cd(2) is coordinated by two trans-
coordinated imidazolyl nitrogen atoms, two water molecules and
Crystal and intensity data were collected on a Bruker Smart
APEX II CCD diffractometer with graphite-monochromated Mo
Ka radiation (k = 0.71073 Å) at 173 K. Empirical absorption correc-
tions were applied using the SADABS program. The structures were
solved by direct methods and refined by the full-matrix least-
squares based on F2 using SHELXTL-97 program. Crystal data as well
as details of data collection and refinement for the complexes are
summarized in Table 1. Selected bond lengths and angles are listed
in Table 2.
two cis-coordinated Clꢀ in
a distorted octahedral geometry
(Fig. 1a). The CdꢂꢂꢂCd distance bridged by IBA is 12.363 Å. The twist-
ing angle between imidazoly ring and phenyl ring is 11.6°, while
the twisting angle between phenyl ring and ꢀCO2ꢀ is 6.8°. Clꢀ acts
as a
l2-bridge between different Cd(II) to form a Cd2Cl2 building
unit. The separation of Cdꢂ ꢂ ꢂCd is 3.651 Å. IBA connect Cd2Cl2 units

190
Y. Feng et al. / Inorganica Chimica Acta 413 (2014) 187–193
Fig. 1. (a) ORTEP view of the Cd(II) coordination environments in 1 (30% probability ellipsoids). (b) Perspective view of 3D hydrogen bonding network in 1.
into a 1D chain consisting of rectangular grids (Scheme 1). It
should be noted that the water ligands form strong hydrogen
bonds with carboxylate oxygen atoms of IBA [O1W–H1Wꢂ ꢂ ꢂO2i
2.749 Å, symmetry code: (i) ꢀx + 1, y ꢀ 1, ꢀz + 3/2]. The hydrogen
bonding interactions further extend 1D chains into a 2D network,
which is further extended into a 3D network by the hydrogen
bonding interactions between water and Clꢀ [O1W–H2Wꢂ ꢂ ꢂCl1ii
3.449 Å, symmetry code: (ii) x, ꢀy + 1, z + 1/2]. (Fig. 1b).
acetate bridge Cd(1) and Cd(2) forming a dicarboxylate-Cd(II)
eight-membered ring with Cdꢂ ꢂ ꢂCd distance of 4.037 Å. Different
from that in 1, IBA adopts an exo-tridentate bridging mode through
imidazolyl nitrogen atom and l2,g
2-carboxylate group
(Scheme 1b). The imidazolyl ring is slightly distorted with respect
to the phenyl ring with the dihedral angle between them being
ꢀ
9.5°, while the twisting angle between phenyl ring and ꢀCO2 is
19.8°, which are much different from those in 1. Each pair of adja-
cent Cd(1) and Cd(2) is alternatively bridged by carboxylate-O,O0 of
acetate and IBA to generate an infinite Cd(II)-carboxylate chain
(Fig. 2b). The chain is inter-connected by IBA into a 2D network
(Scheme 1). There are no other short contacts or noteworthy
aryl-aryl interactions between the adjacent 2D layers.
Complex 2 is a 2D coordination polymer based on bicarboxy-
late-O,O0-bridged Cd(II) chains. Cd(1) is in a distorted octahedral
geometry and is coordinated by four carboxylate oxygen atoms
from two IBA and two acetate, respectively, and two nitrogen
atoms from different IBA (Fig. 2a). Four carboxylate oxygen atoms
comprise the equatorial plane and Cd(1) is coplanar with their
mean plane, two imidazolyl nitrogen atoms occupy the axial posi-
tions with the N–Cd–N bond angle of 166.59(7)°. The bond angles
between the cis donors around Cd(1) range from 81.44(8)° to
98.93(6)°. The Cd(1)–N bond length of 2.2620(17) Å is slightly
shorter than that of Cd(1)–O bond length of 2.3261(15) and
2.3775(16) Å, suggesting a compressed octahedron. Cd(2) is a dis-
torted tetrahedral geometry and is coordinated by four carboxylate
oxygen atoms from two IBA and two acetate. Cd(2)–O bond
distances of 2.2390(14) and 2.2569(15) Å are shorter than those
In complex 3, the asymmetric unit contains one Cd(II), one IBA
and one azide. As shown in Fig. 3a, Cd(II) is in a distorted trigonal–
bipyramidal geometry with
s = 0.71 [15]. The equatorial plane
comprises two azide nitrogen atoms [N(3) and N(3C)] and one
imidazolyl nitrogen atom (N1). Two carboxylate oxygen atoms
[O(1A) and O(2B)] from different IBA occupy the axial positions
with O(1A)–Cd(1)–O(2B) bond angle of 171.81(7)°. IBA adopts an
exo-tridentate bridging mode (Scheme 1b). The dihedral angle be-
tween imidazoly ring and phenyl ring is 30.8°, which is larger than
that in 1 and 2, while the twisting angle between phenyl ring and
ꢀ
of Cd(1)–O. Acetate serves as a l2
,g
2-carboxylate bridge. Two
ꢀCO2 is 4.0°.
l1,1-Azide connects Cd(II) into a helical chain

Y. Feng et al. / Inorganica Chimica Acta 413 (2014) 187–193
191
Fig. 2. (a) ORTEP view of the Cd(II) coordination environments in 1 (30% probability ellipsoids). (b) Perspective view of the Cd(II)-carboxylate chain in 2.
(Fig. 3b), in which the adjacent Cd(II) are further bridged by l2,g2
-
Fluorescence spectra were performed on at room temperature.
carboxylate of IBA through the formation a (Cd–N–Cd–O–C–O) six-
membered ring. IBA further extend the chain into a 3D network
(Scheme 1). However, because of the absence of larger guest mol-
ecules to fill the larger void space, the potential voids are filled via
mutual interpenetration to generate a twofold interpenetrating
architecture. Topologically, in 3, the Cd(II) center can be simplified
as a 5-connected node, while IBA connecting three Cd(II) can be re-
garded as a 3-connected node. Therefore the whole framework 3
can be designated as a twofold interpenetrating (3,5)-connected
seh-3,5-P43212 topology with point symbol (372)(327583) and long
vertex symbol (3.7.7)(3.3.7.7.7.7.7.8.8.82) [16] (Fig. 3c). Comparing
with (3,4)- and (3,6)-connected nets, (3,5)-connected nets are not
commonly observed in coordination polymers. Moreover, for
known (3,5)-connected nets, the framework with gra and hms
topologies have been well investigated [17], however, seh-3,5-
P43212 topology is observed only in very few compounds [18].
In complexes 1–3, strong blue fluorescence at 450 nm was ob-
served upon the excitation at 370 nm (Fig. 4). To understand the
nature of the emission band, the photoluminescence of HIBA was
also determined. While the HIBA ligand displays fluorescence at
440 nm. Although the maximum emission wavelengths of com-
plexes 1–3 undergo a slight blue-shift, the emission bands for com-
plexes 1–3 are very similar to that found for the free ligand in
terms of position and band shape. Therefore, the emission bands
of complexes 1–3 are mainly due to an intraligand emission state
as reported for Cd(II) or other d10 metal complexes with N-donor
ligands. The enhancement of luminescence in the complex 1 is,
perhaps, may be attributed to the rigidity of 1. This rigidity is favor
of energy transfer and reduces the loss of energy through a radia-
tionless pathway [19,20].
Thermogravimetric analyses (TGA) of complexes 1–3 were per-
formed on polycrystalline samples in a nitrogen atmosphere

192
Y. Feng et al. / Inorganica Chimica Acta 413 (2014) 187–193
Fig. 3. (a) ORTEP view of the Cd(II) coordination environments in 3 (30% probability ellipsoids). (b) Perspective view of the Cd-NN3 helical chain in 3. (c) Twofold
interpenetrating network in 3.
(Supporting information, Fig. S1). For 1, the weight loss of 12.2%
from 156 to 180 °C corresponds to the loss of coordination water
molecule and Cl- (calcd: 11.5%), subsequent decomposition occurs
after 365 °C. However, 2 and 3 are stabled up to 370 and 390 °C,
respectively.
4. Conclusion
Three cadmium(II) coordination polymers based on IBA and
bridging anions (Cl, CH3COOꢀ, N3ꢀ) have been synthesized and
structurally characterized. In 1, IBA bridges two Cd(II) through
its imidazolyl nitrogen atom and chelating carboxylate group.
IBA and Clꢀ link Cd(II) into a 1D chain, which is further extended
into a 3D network by hydrogen bonding interactions. IBA in 2 and
3 adopts an exo-tridentate bridging mode through imidazolyl
Fig. 4. The solid emission spectra of free HIBA ligand and complexes 1–3 at room
temperature.
nitrogen atom and l2,g2-carboxylate group. In 2, IBA and

Y. Feng et al. / Inorganica Chimica Acta 413 (2014) 187–193
193
2-acetate link Cd(II) into a 2D layer consisting of carboxylate-
Cd(II) chains alternatively bridged by carboxylate of acetate and
IBA. However, IBA and 1,1-azide in 3 link Cd(II) into a two-folded
interpenetrating 3D network consisting of N3–Cd(II) helical
2904.;
l2,g
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Acknowledgments
We thank the National Natural Science Foundation of China
(20971101 and 21271142) for financial support of this study. Help-
ful discussions with Prof. Ruihu Wang (Fujian Institute of Research
on the Structure of Matter, Chinese Academy of Sciences) are also
acknowledged.
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Appendix A. Supplementary material
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CCDC 816070, 816069 and 794750 contains the supplementary
crystallographic data for 1–3. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2014.01.014.
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