Cd(II) complexes from imidazole substitute isophthalate ligand: Syntheses, structural characterization, and fluorescence property

Article abstract of DOI:10.1080/00958972.2013.867025

The hydrothermal reaction of Cd(II) salt with 5-[(2-methyl-1H-imidazol-1- yl)methyl]isophthalic acid (H2L) leads to the formation of a new complex [Cd(L)(H2O)] (1). While in the presence of 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) as auxiliary ligands, complexes [Cd(L)(bpy)]H2O (2) and [Cd(L)(phen)]2H2O (3) were obtained. Complexes 1-3 have been characterized by single crystal and powder X-ray diffractions, IR, and elemental and thermogravimetric analyzes. As a result, complex 1 exhibits twofold interpenetrated 3-D (10,3)-a architecture, 2 displays chain structure, and 3 shows uninodal 3-connected hcb network with (6³) topology. The impact of auxiliary ligands on the structures of resultant complexes is discussed. Moreover, luminescence property of 1-3 was investigated. 2013

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Cd(II) complexes from imidazole
substitute isophthalate ligand:
syntheses, structural characterization,
and fluorescence property
Hai-Wei Kuaia, Xing-You Xua, Xiao-Chun Chenga, Liang-Dong Fenga
& Xiao-Hong Zhua
a Faculty of Life Science and Chemical Engineering, Jiangsu
Provincial Engineering Laboratory for Advanced Materials of Salt
Chemical Industry, Huaiyin Institute of Technology, Huaian, China
Published online: 04 Dec 2013.
To cite this article: Hai-Wei Kuai, Xing-You Xu, Xiao-Chun Cheng, Liang-Dong Feng & Xiao-Hong
Zhu (2013) Cd(II) complexes from imidazole substitute isophthalate ligand: syntheses, structural
characterization, and fluorescence property, Journal of Coordination Chemistry, 66:24, 4304-4315,
DOI: 10.1080/00958972.2013.867025
To link to this article: http://dx.doi.org/10.1080/00958972.2013.867025
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Journal of Coordination Chemistry, 2013
Vol. 66, No. 24, 4304–4315, http://dx.doi.org/10.1080/00958972.2013.867025
Cd(II) complexes from imidazole substitute isophthalate
ligand: syntheses, structural characterization, and
fluorescence property
HAI-WEI KUAI, XING-YOU XU, XIAO-CHUN CHENG*, LIANG-DONG FENG and
XIAO-HONG ZHU
Faculty of Life Science and Chemical Engineering, Jiangsu Provincial Engineering Laboratory for
Advanced Materials of Salt Chemical Industry, Huaiyin Institute of Technology, Huaian, China
(Received 1 June 2013; accepted 14 November 2013)
The hydrothermal reaction of Cd(II) salt with 5-[(2-methyl-1H-imidazol-1-yl)methyl]isophthalic acid
(H2L) leads to the formation of a new complex [Cd(L)(H2O)] (1). While in the presence of
2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) as auxiliary ligands, complexes [Cd(L)(bpy)]
∙H2O (2) and [Cd(L)(phen)]∙2H2O (3) were obtained. Complexes 1–3 have been characterized by
single crystal and powder X-ray diffractions, IR, and elemental and thermogravimetric analyzes. As
a result, complex 1 exhibits twofold interpenetrated 3-D (10,3)-a architecture, 2 displays chain
structure, and 3 shows uninodal 3-connected hcb network with (63) topology. The impact of
auxiliary ligands on the structures of resultant complexes is discussed. Moreover, luminescence
property of 1–3 was investigated.
Keywords: Cd(II) complex; Structural characterization; Fluorescence
1. Introduction
Metal-organic frameworks (MOFs) have been increasingly focused on, which is justified
not only due to their fascinating structures and topologies, but also for their potential appli-
cations in many fields [1]. Consequently, a great number of MOFs have been deliberately
prepared and discussed in some comprehensive reviews [2]. It is known that one of the
effective strategies for construction of MOFs is to select suitable organic ligands as building
blocks to bridge metal centers into infinite frameworks [3]. Among the well employed
organic ligands, N- and/or O-multidentate donors ligands are often regarded as excellent
building blocks for desirable frameworks. Meanwhile, many influential factors can impact
on self-assembly process, including the nature of metal ions and ligands, acidic or basic
media, and other experimental conditions such as solvent, reaction temperature, and ratio of
metal-to-ligand [4]. Therefore, it still seems a great challenge to achieve controllable
assembly of a target structure driven by the global energy minimization of one system under
specific condition.
*Corresponding author. Email: hxldh@126.com
© 2013 Taylor & Francis

Cd(II) coordination polymers
4305
Recently, we have been focusing our attention on the utilization of a new methylimidazol-
1-yl and carboxylate-containing ligand: 5-[(2-methyl-1H-imidazol-1-yl)methyl]isophthalic
acid (H2L) as a building block for construction of MOFs with different structures. One main
goal is to investigate the impact of synthetic conditions on the structures and properties of
resultant complexes. The arene-cored ligand H2L exhibits a advantage over other N- or
O-donor ligands since it contains two coordination groups, namely rigid carboxylate and
flexible methylimidazole. Given the relative orientation of these two carboxylate groups and
their variable coordination patterns such as μ1-η1 : η0-monodentate and μ1-η1 : η1-chelating
modes, the H2L ligand can act as a multi-connector in formation of complexes [5].
Furthermore, the flexible coordination group in H2L has more spatial freedom to adopt
different orientations, which is originated from its freely axial rotation on the demand of
coordinating requirements [6]. The potential variable coordination modes of H2L provide the
feasibility to assemble complexes with various structures by adjusting synthetic conditions,
which may be helpful to further comprehend the correlation between experimental conditions
and the structure of resultant complexes and would lay a solid groundwork for finally
achieving the goal of controllable self-assembly.
We report herein syntheses and structural characterization of three new coordination
polymers [Cd(L)(H2O)] (1), [Cd(L)(bpy)]∙H2O (2), and [Cd(L)(phen)]∙2H2O (3). These com-
plexes exhibited structural diversity dependent on the presence and alteration of auxiliary
ligands. In addition, fluorescence properties of complexes 1–3 have been examined.
2. Experimental
2.1. Materials and methods
All commercially available chemicals are of reagent grade and were used as received with-
out further purification. Elemental analysis of C, H, and N were taken on a Perkin–Elmer
240C elemental analyzer. Infrared spectra (IR) were recorded on a Bruker Vector22 FT-IR
spectrophotometer using KBr pellets. Thermogravimetric analysis (TGA) was performed on
a simultaneous SDT 2960 thermal analyzer under nitrogen atmosphere with a heating rate
of 10 °C min−1. Powder X-ray diffraction (PXRD) patterns were measured on a Shimadzu
XRD-6000 X-ray diffractometer with Cu Kα (λ = 1.5418 Å) radiation at room temperature.
The luminescence spectra for the powdered solid samples were measured on an Aminco
Bowman Series 2 spectrofluorometer with a xenon arc lamp as the light source. In the
measurements of emission and excitation spectra the pass width is 5 nm, and all the
measurements were carried out under the same experimental conditions.
2.2. Preparation of ligand
The H2L was synthesized via similar experimental procedure to that reported for preparation
of other imidazole substitute isophthalate ligands [7]. Potassium hydroxide (0.56 g, 10 mM)
was added to a solution of 2-methyl-1H-imidazole (0.82 g, 10 mM) in 10 mL DMF.
The mixture was then stirred for 10 h at room temperature, following which dimethyl
5-(bromomethyl)isophthalate (1.44 g, 5 mM) was added and the solution was stirred further
at room temperature for 24 h. Then, 200 mL water and potassium hydroxide
(1.12 g, 20 mM) were added into the resulting mixture. The reaction mixture was refluxed
for 10 h, and then poured into ice water, acidified with acetic acid to pH 5–6. After filtration,

4306
H.-W. Kuai et al.
the product was dried at 100 °C under vacuum and obtained as a pale yellow solid (1.06 g,
1
82%). H NMR (500 MHz, DMSO-d6, 25 °C): δ = 8.40 (s, 1H); 7.92 (s, 2H); 7.26 (s, 1H);
6.92 (s, 1H); 5.36 (s, 2H); 2.27 (s, 3 H). Calcd for C13H12N2O4 (%): C, 60.00; H, 4.65; N,
10.76. Found (%): C, 60.26; H, 4.38; N, 10.98.
2.3. Preparation of [Cd(L)(H2O)] (1)
Reaction mixture of Cd(NO3)2·4H2O (61.8 mg, 0.2 mM), H2L (26.0 mg, 0.1 mM), and
KOH (11.2 mg, 0.2 mM) in 10 mL H2O was sealed in a 16 mL Teflon-lined stainless steel
container and heated at 180 °C for 72 h. After cooling to the room temperature, colorless
needle crystals of 1 were collected by filtration and washed by water and ethanol for several
times with the yield of 30% (11.6 mg) based on the H2L. Calcd for C13H12N2O5Cd (%): C,
40.17; H, 3.11; N, 7.21. Found (%): C, 39.90; H, 3.38; N, 6.98. IR (KBr pellet, cm−1):
3213 (m), 1609 (s), 1548 (s), 1458 (s), 1422 (s), 1373 (s), 1284 (s), 1255 (m), 1227 (m),
1159 (m), 1146 (m), 1130 (m), 1106 (m), 1008 (m), 801 (m), 769 (s), 733 (s), 688 (m), 664
(m), 640 (m).
2.4. Preparation of [Cd(L)(bpy)]∙H2O (2)
Complex 2 was obtained under the same reaction condition as that for preparation of 1
except that bpy (15.6 mg, 0.1 mM) was introduced into the synthetic system as auxiliary
ligand. Colorless plate-shaped crystals of 2 were obtained with the yield of 25% (13.6 mg)
based on the H2L. Calcd for C23H20N4O5Cd (%): C, 50.70; H, 3.70; N, 10.28. Found (%):
C, 50.40; H, 3.45; N, 10.55. IR (KBr pellet, cm−1): 3416 (m), 1620 (s), 1600 (s), 1567 (s),
1498 (m), 1474 (m), 1441 (s), 1409 (m), 1360 (s), 1316 (m), 1284 (m), 1158 (m), 1016
(m), 814 (m), 785 (m), 761 (s), 724 (s), 700 (m), 663 (m), 635 (m).
2.5. Preparation of [Cd(L)(phen)]∙2H2O (3)
Complex 3 was obtained under the same reaction condition as that for preparation of 1
except that phen (18.0 mg, 0.1 mM), instead of bpy, was used as auxiliary ligand. Colorless
block crystals of 3 were obtained with the yield of 32% (18.7 mg) based on the H2L. Calcd
for C25H22N4O6Cd (%): C, 51.16; H, 3.78; N, 9.55. Found (%): C, 51.40; H, 3.50; N, 9.66.
IR (KBr pellet, cm−1): 3449 (m), 1617 (s), 1565 (s), 1512 (s), 1475 (m), 1452 (m), 1423
(s), 1366 (s), 1309 (m), 1281 (m), 1236 (m), 1131 (m), 1102 (m), 998 (m), 847 (s), 807
(m), 778 (m), 758 (m), 730 (s), 669 (m), 636 (m).
2.6. X-ray crystallography
The crystallographic data collections for complexes 1–3 were carried out on a Bruker Smart
ApexII CCD area-detector diffractometer using graphite-monochromated Mo-Kα radiation
(λ = 0.71073 Å) at 293 K. The diffraction data were integrated using the SAINT program
[8], which was also used for the intensity corrections for the Lorentz and polarization
effects. Semi-empirical absorption correction was applied using the SADABS program [9].
The structure of 1–3 was solved by direct methods and all non-hydrogen atoms were
refined anisotropically on F2 by the full-matrix least-squares technique using the
SHELXL-97 crystallographic software package [10]. For complexes 1–3, all hydrogen

Cd(II) coordination polymers
4307
atoms attached to C were generated geometrically using the riding model. The hydrogen
atoms of lattice water in 2 were excluded from the refinement, as the directions of H atoms
towards O acceptors and the O–H bond distances are outside normal ranges, and deliber-
ately artificial restraints always make the structural refinement unstable and arouse many
crystallographic errors. Besides, other hydrogen atoms of water molecules in 1 and 3 were
found at reasonable positions in the difference fourier maps and located there. The details
of crystal parameters, data collection, and refinements for the complexes are summarized in
table 1; the selected bond lengths and angles are listed in table S1 (see online supplemental
material at http://dx.doi.org/10.1080/00958972.2013.867025).
3. Results and discussion
3.1. Crystal structure description of [Cd(L)(H2O)] (1)
X-ray structural analysis showed that complex 1 is composed of 3-D frameworks in ortho-
rhombic crystal system with Pbca space group (table 1). As shown in figure 1(a), the asym-
metric unit of 1 contains one Cd(II), one L2− ligand, and one coordinated water molecule.
Each Cd(II) is six-coordinated by one nitrogen atom from methylimidazolyl of L2−, four
carboxylate oxygen atoms from two different L2− ligands, and one oxygen atom from the
coordinated water molecule to show a greatly distorted octahedral coordination geometry.
Both carboxylate groups of the L2− in 1 adopt μ1-η1 : η1-chelating coordination mode
(scheme 1). Thus in complex 1 each L2− ligand bridges three different Cd(II) atoms and
each Cd(II) is also coordinated by three different L2− ligands. This kind of interconnection
repeats infinitely to construct a neutral 3-D architecture (figure 1(b)), where 2-D layer
structure can be isolated (figure 1(b) and (c)). Within this 2-D structure five L2− ligands and
five metal atoms are connected together via coordination bonds to form a 48-membered
Table 1. Crystallographic data and structure refinement details for complexes 1–3.
1
2
3
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
b/Å
c/Å
α/°
β/°
C
13H12N2O5Cd
C23H20N4O5Cd
544.83
293(2)
Monoclinic
P21/c
10.3236(5)
14.3355(8)
15.3792(8)
90.00
95.3350(10)
90.00
2266.2(2)
4
C25H22N4O6Cd
586.87
293(2)
Triclinic
P-1
8.791(2)
10.174(3)
15.061(4)
89.355(4)
83.637(4)
67.995(4)
1240.5(6)
2
388.65
293(2)
Orthorhombic
Pbca
10.637(5)
13.702(5)
18.612(5)
90.000(5)
90.000(5)
90.000(5)
2712.7(18)
8
γ/°
V (Å3)
Z, DCalcd/(Mg m−3
F (000)
)
1536
1096
592
θ Range/°
2.19–27.50
15,439
3069
1.080
0.0300
1.95–28.35
16,254
5660
1.033
0.0360
1.36–28.00
8669
5896
1.068
0.0335
Reflections collected
Independent reflections
Goodness-of-fit on F2
R1 [I > 2σ (I)]a
wR2 [I > 2σ (I)]b
0.0831
0.1124
0.0952
aR1 = Σ||Fo| − |Fc||/Σ|Fo|.
bwR2 = |Σw(|Fo|2 − |Fc|2)|/Σ|w(Fo)2|1/2, where w = 1/[σ2(Fo2) + (aP)2 + bP], P = (Fo2 + 2Fc2)/3.

4308
H.-W. Kuai et al.
Figure 1. (a) The coordination environment of Cd(II) ions in complex 1 with the ellipsoids drawn at the 30%
probability level. Hydrogen atoms are omitted for clarity, (b) view of 3-D architecture of 1. The red circle high-
lights 2-D network in 1, (c) view of 2-D network in 1, (d) schematic illustrating the uninodal 3-connected architec-
ture of 1 with (10,3)-a topology; the bigger balls (red): metal centers; the smaller balls (green): the L2− ligands, and
(e) topological representation of twofold interpenetrating framework of
00958972.2013.867025 for color version).
1 (see http://dx.doi.org/10.1080/
macrocyclic ring. In 1, both L2− ligand and metal atom act as 3-connected nodes, then the
3-D framework can be simplified as uninodal 3-connected (10,3) a net which is intrinsically
chiral [11] (figure 1(d)). But the twofold interpenetrating networks are of the opposite hands
and form an enantiomeric pair of racemate (figure 1(e)).

Cd(II) coordination polymers
4309
Scheme 1. The coordination modes of the L2− appearing in complexes 1–3.
3.2. Crystal structure description of [Cd(L)(bpy)]∙H2O (2)
Complex 2 exhibits double-stranded chain structure in the monoclinic system with P21/c space
group (table 1). There are one Cd(II), one L2− ligand, one coordinated bpy, and one lattice
water molecules in the asymmetric unit of 2. As shown in figure 2(a), each Cd(II) is seven-
coordinated by one methylimidazole N atom, two N atoms from coordinated bpy, and four car-
boxylate O atoms from two different L2− ligands to furnish a distorted pentagonal bipyramidal
geometry. Two apexes are occupied by methylimidazole and bpy N atoms and the equatorial
plane can be well defined by four carboxylate O atoms and the other bpy N atom. Both car-
boxylate groups in the L2− ligand exhibit μ1-η1 : η1-chelating coordination modes (scheme 1).
As depicted in figure 2(b), each L2− ligand bridges three Cd(II) centers to construct a double-
stranded chain structure with the nearest intrachain Cd···Cd distance of 10.101 Å. Because of
the flexibility of the L2− ligand, the double chain extends along the a-axis direction in a spiral
way. If some organic moieties are ignored, a pair of right- and left-handed helical chains could
be distinguished in the neutral double-stranded chain (figure 2(c)).
3.3. Crystal structure description of [Cd(L)(phen)]∙2H2O (3)
When phen was introduced into hydrothermal reaction system as auxiliary ligand instead of
bpy, complex 3 was obtained, which consists of 2-D networks based on Cd(II), L2−, and
phen in triclinic P-1 space group (table 1). The asymmetric unit of 3 contains one Cd(II),
one L2−, one coordinated phen molecule, and two lattice water molecules. Each Cd(II) is
seven-coordinated (figure 3(a)), with a distorted pentagonal bipyramidal geometry, by four
carboxylate O atoms and three N atom from methylimidazole and phen. Just as in 2, both
carboxylate groups in the L2− ligand exhibit μ1-η1 : η1-chelating coordination modes, respec-
tively, and thus the L2− can be described as a μ3-bridge. Each metal ion is also surrounded
by three L2− ligands. The interconnection of Cd(II) and L2− infinitely extends to form a
2-D network (figure 3(b)). Both of L2− ligand and metal center can be treated as a
3-connected node. Thus the structure of 3 can be simplified as a uninodal 3-connected 2-D
hcb network with (63) topology (figure 3(c)).
3.4. Coordination modes of H2L ligand and structural comparison of 1–3 with previously
reported Cd(II) complexes
All carboxylate groups of the L2− in the three complexes are found to be completely depro-
tonated and involved in coordination showing the same μ1-η1 : η1-chelating coordination
modes (scheme 1) and the flexible coordination groups coordinate to a single metal atom,

4310
H.-W. Kuai et al.
Figure 2. (a) The coordination environment of Cd(II) in complex 2 with the ellipsoids drawn at the 30%
probability level. Hydrogen atoms and lattice water are omitted for clarity, (b) view of the 1-D chain structure of 2
along a-axis, and (c) view of the right- and left-handed helical chains in 2.
and thus, the L2− ligands act as μ3-linkers in 1–3. Given the flexibility of the μ3-linkers, the
dihedral angles between the phenyl and imidazole rings are 81.32°, 75.89°, and 83.98° for
complexes 1–3. The metal coordination numbers are six for 1 and seven for 2 and 3. The
difference of the dihedral angles and coordination numbers may subtly impact on the

Cd(II) coordination polymers
4311
Figure 3. (a) The coordination environment of Cd(II) in complex 3 with the ellipsoids drawn at the 30%
probability level. Hydrogen atoms and lattice water are omitted for clarity, (b) view of the 2-D network of 3, and
(c) topological view of the 2-D network of 3; the bigger balls (red): metal centers; the smaller balls (green): the
L
2− ligands (see http://dx.doi.org/10.1080/00958972.2013.867025 for color version).

4312
H.-W. Kuai et al.
diversity of structures: 1 shows 3-D framework architecture; 2 is 1-D structure; 3 displays
2-D network structure. All carboxylate in complexes 1–3 show chelating coordination
modes, but they are asymmetrically chelating ones, reflected by dramatically different
Cd–O bond distances within each chelating moiety, such as in complex 1, Cd1–O1 = 2.173 Å,
Cd1–O2 = 2.673 Å, Cd1–O3 = 2.237 Å and Cd1–O4 = 2.706 Å (table S1). Despite the
existence of the longer Cd–O distances, they are still much shorter than the sum of van der
Waals radii of Cd and O atoms (3.70 Å). Therefore, these longer Cd–O interactions are
regarded as coordination bonds here. The Cd–N distances in 1 are 2.176(3) Å, and the aver-
age ones are 2.962 and 2.949 Å for 2 and 3, which are much shorter than the sum of van der
Waals radii of Cd and N atoms (3.71 Å). Because the coordination geometries of 1–3 are
greatly distorted, bond angles around Cd(II) are also dramatically different (table S1).
To further comprehend the coordintion chemisty of Cd(II) Complexes with imidazole and
carboxylate-containing ligands, we would here like to carry out a structural comparison of
1–3 with the Cd(II) complexes previously reported by Sun et al. [12–14]:
(1) Three Cd(II) complexes [Cd(L1)(DMF)(H2O)] ∙H2O (R1), [Cd(L1)(H2O)2]2∙5H2O
(R2), and [Cd2(L1)2(H2O)2]2∙H2O (R3) show 1-D, 2-D (63) network and 3-D
(4.62)2(42.610.83) framework structure, respectively (H2L1 = 5-(imidazol-1-ylmethyl)iso-
phthalic acid) [12]. In complex R1, both carboxylate groups show μ1-η1 : η1-chelating
coordination modes. The bond distances are in the range of 2.283(3)–2.588(3) Å and the
average bond distance is 2.379 Å. In complex R2, the coordination mode of carboxylate is
also chelating one. The longest bond distance is 2.636(3) Å; the shortest is 2.241(3) Å;
the average one is 2.392 Å. In complex R3, carboxylate groups exhibit μ1-η1 : η1-chelating
and μ2-η1 : η1-bridging coordination modes. The bond distances differ from 2.235(5) to
2.537(3) Å which can be averaged to 2.322 Å. The Cd–N distances in complexes R1–R3
are 2.292(3), 2.241(3) and 2.263(4), and 2.235(5) Å, respectivley.
(2) Two homochiral Cd(II) complexes were obtained from a one-pot reaction L-[Cd(tib)
(BDC)]∙2H2O (R4) and R-[Cd(tib)(BDC)]∙2H2O (R5) (tib = 1,3,5-tris(1-imidazolyl)benzene
and BDC2− = 1,4-benzenedicarboxylate) [13]. Complexes R4 and R5 display the 3-D
(83)2(86) framework structures and contain the left- and right-handed helical chains. The
ranges of bond distance for R4 and R5 are 2.272(5)–2.612(5) Å and 2.280(4) Å–2.621(4)
Å. The average Cd–O and Cd–N distances are 2.468 and 2.330 Å for R4, which are almost
identical to R5 (2.468 and 2.333 Å).
(3) Two 3-D Cd(II) complexes D-[Cd6(L2)4(D-Cam)4(H2O)4]·2H2O (R6) and
L-[Cd6(L2)4(L-Cam)4(H2O)4]·2H2O (R7) with chiral chains constructed by Cd(II) cations
and camphorate anions, which are a pair of enantiomers [HL = 3,5-di(imidazol-1-yl)benzoic
acid, D-H2Cam = D-camphoric acid, L-H2Cam = L-camphoric acid]. The Cd–O distances
differ from 2.312(2) to 2.641(5) for R6 and 2.320(3) to 2.648(4) R7. The average Cd–O
and Cd–N distances are 2.476 and 2.327 Å for R6 and 2.479 and 2.363 Å for R7.
In summary, the bond distances of the complexes 1–3 are comparable to the reported
Cd(II) complexes including Cd–O and Cd–N distances. Just as those reported instances, the
structures of 1–3 vary from chain structure to 3-D twofold interpenetrating framework
architecture under different synthetic conditions.
3.5. PXRD and TGA
PXRD patterns of complexes 1–3 consist with the simulated ones based on the single-crys-
tal X-ray diffraction analysis, as shown in figure S1. The diffraction peaks correspond well
in positions, indicating the phase purity of the as-synthesized samples.

Cd(II) coordination polymers
4313
Figure 4. Fluorescence of 1–3 and H2L in the solid state at room temperature: (a) excitation spectra, and
(b) emission spectra.
To estimate the thermal stability of 1–3, TGA were carried out under N2 atmosphere with
a heating rate of 10 °C min−1 and the TGA curves of 1–3 were recorded from 30 to 800 °C
(figure S2). Complex 1 shows a weight loss (4.36%) in the temperature range of
180–267 °C, corresponding to the loss of coordinated water (Calcd 4.63%), and the residue
is stable up to about 360 °C. For complex 2, there is a weight loss (3.10%) from 80 to
117 °C, attributed to the release of lattice water (Calcd 3.30%), and the decomposition of
the residue can be observed at 360 °C nearby. The TGA curve of 3 displays an initial
weight loss of 5.85% from 72 to 123 °C, suggesting the loss of lattice water (Calcd 6.13%)
and the framework can be stable up to 350 °C. When temperature approaches at 800 °C,
the total weight losses for 1–3 are 63.10, 75.63, and 73.76%. However, the continuous
decomposition of 1–3 does not terminate at 800 °C, so the final residuals of them are not
characterized.

4314
H.-W. Kuai et al.
3.6. Luminescent property
Previous studies have shown that coordination compounds containing d10 metal centers
such as Cd(II) may exhibit excellent luminescent properties and have potential applications
as photoactive materials [15]. In the present work, luminescence of complexes 1–3 and the
H2L has been investigated in the solid state at room temperature. As shown in figure 4,
intensive fluorescent emission can be observed with emission bands at 410 nm (λex = 327 nm)
for 1, 421 nm (λex = 323 nm) for 2, 388 nm (λex = 320 nm) for 3, and 403 nm (λex = 348 nm)
for H2L ligand, respectively. Moreover, the emission spectra of bpy and phen have also
been recorded with emission bands at 526 nm (λex = 337 nm) and 521 nm (λex = 369 nm)
(figure S3). The fluorescent emission of 1–3 may be tentatively assigned to intra-ligand
transition of coordinated L2− ligands, since similar emission was observed for free H2L
[15]. Meanwhile, the emission of the L2− ligands in 1–3 may be affected by their incorpora-
tion into the Cd(II)-containing polymeric compounds, as evidenced by the red- or blue-shift
compared with free H2L ligand. The observation of red- (1 and 2) or blue- (3) shifts of the
emission maximum in 1–3 may originate from the coordination of the ligands to the metal
centers [16]. Accordingly, complexes 1–3 could be potentially used as luminescent
materials due to their good thermal stabilities and strong photoluminescence.
4. Conclusion
In summary, three new Cd(II) coordination polymers have been synthesized under the
hydrothermal synthetic conditions. The structures of complexes 1–3 varied from chain
structure to 3-D twofold interpenetrating framework architecture with different topologies.
The structural diversity of resultant complexes is achieved by the presence and alteration of
auxiliary ligands. The results imply that auxiliary ligands can subtly impact on formation of
complexes.
Supplementary material
Crystallographic data (excluding structure factors) for the structures reported in this paper have
been deposited with the Cambridge Crystallographic Data Centre as supplementary publication
[CCDC 942463-942465 for 1–3]. Copies of the data can be obtained free of charge on applica-
tion to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44 1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk).
Funding
This work was supported by the Huaian Administration of Science and Technology of Jiangsu
Province of China [HAG201222] and [HC201216].
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