Syntheses, structures and fluorescence properties of three new polymers based on a flexible tripodal ligand

Article abstract of DOI:10.1016/j.molstruc.2009.09.024

Three new polymers, namely, {[Cd(TTTMB)(bdic^2-)(H₂O)]·H₂O}_n (1), {[Cd(TTTMB)(Hbtrc^2-)(H₂O)]·2H₂O}_n (2) and [Zn(TTTMB)(Hbtrc^2-)(H₂O)]_n

Full text of DOI:10.1016/j.molstruc.2009.09.024

Journal of Molecular Structure 938 (2009) 185–191
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Syntheses, structures and fluorescence properties of three new polymers based on
a flexible tripodal ligand
a
Xia Wang a,b, Weiyin Wang a, Shumin Liu a, Hongwei Hou a, , Yaoting Fan
*
a Department of Chemistry, Zhengzhou University, Henan 450052, China
b Henan University of Traditional Chinese Medicine, Henan 450008, China
a r t i c l e i n f o
a b s t r a c t
Three new polymers, namely, {[Cd(TTTMB)(bdic2À)(H2O)]ÁH2O}n (1), {[Cd(TTTMB)(Hbtrc2À)(H2O)]Á2H2O}n
(2) and [Zn(TTTMB)(Hbtrc2À)(H2O)]n (3) based on a flexible tripodal ligand 1,3,5-tris(triazol-1-ylmethyl)-
2,4,6-trimethylbenzene (TTTMB) have been synthesized by choosing H2bdic and H3btrc as auxiliary
ligands under hydrothermal reaction (H2bdic = 1,3-benzenedicarboxylic acid and H3btrc = 1,3,5-benzen-
etricarboxylic acid). The structures of the polymers were determined by single-crystal X-ray diffraction
analyses, and the results reveal that 1 and 2 exhibits a two-dimensional (4,4) network. While the crystal
structure of 3 shows one-dimensional zigzag chain. Additionally, the solid-state fluorescent properties of
these three polymers and ligand TTTMB were investigated at room temperature.
Article history:
Received 20 February 2009
Received in revised form 2 September 2009
Accepted 14 September 2009
Available online 17 September 2009
Keywords:
Tripodal ligand
Polymers
Crystal structures
Fluorescence
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
1,3-benzenedicarboxylic acid (H2bdic) and 1,3,5-benzenetricarb-
oxylic acid (H3btrc) are good organic building blocks in construct-
The design and construction of metal–organic frameworks
(MOFs) have attracted much attention in the fields of supramolecu-
larchemistryandcrystalengineeringinrecentyearsduetotheirver-
satile intriguing architectures and their potential applications in
optical, electronic, magnetic and biomimetic materials [1–6]. Gener-
ally, the diversity in the framework structures of such MOFs depends
on many factors, such as the selection of metal centers, organic
ligands and the reaction pathways [7]. Among these factors, the de-
sign and selection of organic ligands with suitable binding groups
are especially crucial [8]. Flexible tripodal ligands with an arene core
have been found to be one of the most useful organic building blocks
in construction of MOFs, such as 1,3,5-tris(4-pyridylmethyl)ben-
zene [9], 1,3,5-tris(pyrazol-1-ylmethyl)-2,4,6-triethylbenzene [10],
1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene [11–14],
1,3,5-tris(benzimidazole-1-ylmethyl)-2,4,6-trimethylbenzene
[15]. These flexible tripodal ligands can adopt different conforma-
tions and coordination modes according to the geometric require-
ments of different metal ions, so they are helpful to construct
intriguing architectures and topologies.
ing metal–organic frameworks [7]. H2bdic and H3btrc have two or
three carboxyl groups, which can be completely or partially depro-
tonated, and they may serve as potential anion groups. This makes
it very appealing for the design of MOFs with interesting structures
and properties. Hence, our group started on a program aimed at
constructing new MOFs by rational utilization of flexible tripodal
ligands and selection of aromatic acids H2bdic and H3btrc as auxil-
iary ligands.
In the present work, we selected a novel flexible tripodal com-
pound with aromatic core 1,3,5-tris(triazol-1-ylmethyl)-2,4,6-
trimethylbenzene (TTTMB) [8,17] as a functional ligand, and three
polymers {[Cd(TTTMB)(bdic2À)(H2O)]ÁH2O}n (1), {[Cd(TTTMB)
(Hbtrc2À)(H2O)]Á2H2O}n (2) and [Zn(TTTMB)(Hbtrc2À)(H2O)]n (3)
were obtained by choosing H2bdic and H3btrc as auxiliary ligands
under hydrothermal reaction. Herein, we report the syntheses,
crystal structures as well as fluorescence properties of these
polymers.
Considerable progress has been made on the design and
construction of MOFs using this kind of flexible tripodal ligands
[9–15]. However, using the aromatic acids as auxiliary ligands,
the study on the structures of coordination complexes containing
flexible tripodal ligands is extremely rare [16,17]. In addition, the
2. Experimental
2.1. Materials and physical techniques
1,3,5-Tris(triazol-1-ylmethyl)-2,4,6-trimethylbenzene (TTTMB)
was prepared according to literature method [18]. All other staring
materials were of reagent-grade quality and were obtained from
commercial sources and used without further purification.
* Corresponding author. Tel./fax: +86 371 67761744.
E-mail address: houhongw@zzu.edu.cn (H. Hou).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.09.024

186
X. Wang et al. / Journal of Molecular Structure 938 (2009) 185–191
Table 1
Elemental analyses (C, H and N) were carried out on a FLASH EA
1112 elemental analyzer. Infrared spectra data were recorded on
a Bruker TENSOR 27 spectrophotometer with KBr pellets in the
400–4000 cmÀ1 region.
Crystal data and structure refinement for polymers 1–3.
Polymers
1
2
3
Formula
C52H58Cd2N18O12 C54H62Cd2N18O18 C27H27ZnN9O7
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
1351.96
293(2)
1476.02
293(2)
654.95
293(2)
0.71073
Monoclinic
P2(1)/n
8.6070(17)
20.393(4)
15.481(3)
90
91.28(3)
90
2716.6(9)
4
2.2. Preparation of polymer {[Cd(TTTMB)(bdic2À)(H2O)]ÁH2O}n (1)
0.71073
Triclinic
0.71073
Triclinic
A
mixture of TTTMB (0.037 g, 0.1 mmol), Cd(NO3)2Á4H2O
ꢀ
ꢀ
P1
P1
(0.031 g, 0.1 mmol) and H2bdic (0.017 g, 0.1 mmol) in H2O
(10 mL) was kept in a Teflon-lined autoclave at 130 °C for 3 days.
After the mixture was cooled to room temperature, colorless crys-
tals suitable for X-ray diffraction were obtained. Yield: 78%. Anal.
Calcd for C52H58Cd2N18O12 (%): C, 46.19; H, 4.32; N, 18.65. Found:
C, 46.27; H, 4.35; N, 18.57. IR (KBr, cmÀ1): 3427(m), 3123(w),
2364(w), 1693(w), 1605(s), 1548(s), 1479(w), 1443(s), 1386(s),
1276(s), 1216(w), 1134(s), 1076(m), 1010(w), 750(m), 726(m),
675(m), 642(w).
10.158(2)
10.654(2)
15.477(3)
106.43(3)
91.56(3)
115.34(3)
1430.6(5)
1
10.388(2)
11.619(2)
14.162(3)
67.89(3)
86.21(3)
70.39(3)
1488.2(5)
1
1.647
16,238
5843
0.0271
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dc (g/cm3)
1.569
1.601
29,623
5368
0.0824
5368/0/406
Reflections collected 15,712
Unique reflections
Rint
Data/restraints/
parameters
5610
0.0326
5610/24/398
2.3. Preparation of polymer {[Cd(TTTMB)(Hbtrc2À)(H2O)]Á2H2O}n (2)
5843/0/439
GOF
1.024
1.072
1.004
a
A mixture of TTTMB (0.037 g, 0.1 mmol), 3CdSO4Á8H2O (0.026 g,
0.03 mmol) and H3btrc (0.021 g, 0.1 mmol) in H2O (10 mL) was
kept in a Teflon-lined autoclave at 120 °C for 3 days. Then the reac-
tion system was cooled to room temperature slowly, and colorless
crystals of 2 were obtained. The crystals were collected and were
further used for single-crystal analysis and physical measure-
ments. Yield: 67%. Anal. Calcd for C54H62Cd2N18O18 (%): C, 43.94;
H, 4.23; N, 17.08. Found: C, 43.37; H, 4.20; N, 17.35. IR (KBr,
cmÀ1): 3430(m), 3128(w), 2364(w), 1712(s), 1614(s), 1566(s),
1439(s), 1371(s), 1279(m), 1226(w), 1136(s), 1012(w), 986(w),
879(w), 759(w), 731(m), 675(s), 641(w), 527(w).
R1 [I > 2
r
(I)]
0.0442
0.1061
0.0511
0.1114
0.0448
0.1079
0.0489
0.1111
0.0884
0.2044
0.1119
0.2230
b
wR2 [I > 2
r(I)]
a
R1 (all data)
b
wR2 (all data)
a
R1 = ||Fo| À |Fc||/|Fo|.
wR2 = [w(|Fo2| À |Fc2|)2/w|Fo2|2]1/2, w = 1/[
r
2(Fo)2 + 0.0297P2 + 27.5680P], where
b
P = (Fo2 + 2Fc2)/3.
Table 2
Selected bond lengths (Å) and bond angles (°) for polymers 1–3.
2.4. Preparation of polymer [Zn(TTTMB)(Hbtrc2À)(H2O)]n (3)
Polymer 1
Cd(1)–N(1)
2.279(3)
2.306(3)
2.356(3)
2.596(3)
95.46(12)
93.51(12)
81.98(10)
81.18(14)
141.22(12)
91.47(12)
53.93(9)
87.98(12)
52.67(9)
84.26(12)
Cd(1)–N(6)#1
Cd(1)–O(4)#2
Cd(1)–O(3)#2
2.299(3)
2.340(3)
2.485(3)
Cd(1)–O(2)
Cd(1)–O(5)
Cd(1)–O(1)
The synthesis was the same as that for 2, except using
Zn(NO3)2Á4H2O (0.030 g, 0.1 mmol) instead of and 3CdSO4Á8H2O.
Yield: 79%. Anal. Calcd for C27H27ZnN9O7 (%): C, 49.51; H, 4.16; N,
19.25. Found: C, 49.77; H, 4.20; N, 19.07. IR (KBr, cmÀ1):
3428(m), 3138(w), 2964(m), 2367(w), 1720(s), 1620(s), 1582(m),
1542(s), 1439(m), 1352(s), 1281(m), 1211(s), 1161(s), 1138(s),
997(m), 893(w), 760(m), 720(m), 671(s), 641(m), 551(w).
N(1)–Cd(1)–N(6)#1
N(6)#1–Cd(1)–O(2)
N(6)#1–Cd(1)–O(4)#2
N(1)–Cd(1)–O(5)
O(2)–Cd(1)–O(5)
N(1)–Cd(1)–O(3)#2
O(2)–Cd(1)–O(3)#2
O(5)–Cd(1)–O(3)#2
N(6)#1–Cd(1)–O(1)
O(4)#2–Cd(1)–O(1)
O(3)#2–Cd(1)–O(1)
168.97(13)
90.79(12)
96.36(13)
88.04(13)
136.48(12)
90.36(11)
135.83(10)
87.34(12)
88.61(12)
134.50(9)
171.49(9)
N(1)–Cd(1)–O(2)
N(1)–Cd(1)–O(4)#2
O(2)–Cd(1)–O(4)#2
N(6)#1–Cd(1)–O(5)
O(4)#2–Cd(1)–O(5)
N(6)#1–Cd(1)–O(3)#2
O(4)#2–Cd(1)–O(3)#2
N(1)–Cd(1)–O(1)
O(2)–Cd(1)–O(1)
O(5)–Cd(1)–O(1)
2.5. X-ray crystallographic study
Single crystals of 1, 2 and 3 were selected for indexing and
Polymer 2
intensity data collection on a Rigaku Saturn 724 CCD diffractome-
Cd(1)–N(1)
Cd(1)–O(5)#1
Cd(1)–N(6)#2
N(1)–Cd(1)–O(5)#1
N(1)–Cd(1)–O(7)
O(5)#1–Cd(1)–O(7)
O(1)–Cd(1)–N(6)#2
O(7)–Cd(1)–N(6)#2
2.251(3)
2.300(3)
2.374(3)
136.29(11)
94.22(14)
85.19(13)
88.11(12)
168.98(13)
Cd(1)–O(1)
Cd(1)–O(7)
2.267(3)
2.339(3)
ter using graphite-monochromated Mo
Ka
X-radiation
N(1)–Cd(1)–O(1)
O(1)–Cd(1)–O(5)#1
O(1)–Cd(1)–O(7)
N(1)–Cd(1)–N(6)#2
O(5)#1–Cd(1)–N(6)#2
132.85(11)
90.84(10)
90.68(12)
94.63(13)
83.88(12)
(k = 0.71073 Å) at room temperature. A single crystal suitable for
X-ray diffraction was mounted on a glass fiber. The data were inte-
grated using the Siemens SAINT program [19]. Absorption correc-
tions were applied. The structures were solved by direct methods
and refined on F2 by full-matrix least-squares using SHELXTL
[20]. All non-hydrogen atoms were refined with anisotropic ther-
mal parameters. Hydrogen atoms were located at geometrically
calculated positions and refined with isotropic thermal parame-
ters. Crystallographic and refinement details are listed in Table 1,
with selected bond lengths and angles in Table 2.
Polymer 3
Zn(1)–N(1)
Zn(1)–O(7)
O(1)–Zn(1)–O(7)
O(7)–Zn(1)–N(1)
O(7)–Zn(1)–N(6)#2
2.019(5)
1.971(5)
102.73(18)
114.5(2)
100.3(2)
Zn(1)–O(1)
Zn(1)–N(6)#2
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(6)#2
N(1)–Zn(1)–N(6)#2
1.965(4)
2.023(5)
113.22(19)
118.36(19)
107.2(2)
Symmetry transformations used to generate equivalent atoms. Polymer 1: #1 x, y,
z + 1; #2 x + 1, y, z; #3 x, y, z À 1; #4 x À 1, y, z. Polymer 2: #1 x + 1, y, z; #2 x, y À 1,
z; #3 x, y + 1, z; #4 x À 1, y, z. Polymer 3: #1 x + 1/2, Ày + 3/2, z À 1/2; #2 x À 1/2,
Ày + 3/2, z + 1/2.
2.6. Determination of fluorescent properties
The fluorescent spectra were measured on powder samples at
room temperature using a F-4500 HITACHI Fluorescence Spectro-
photometer. The excitation slit was 5 nm and the emission slit
was 5 nm too, the response time was 2 s. The different concentra-
tion of TTTMB and polymers 1–3 were obtained by adding the KBr,
because the KBr does not show any fluorescence upon excitation at
284 nm.

X. Wang et al. / Journal of Molecular Structure 938 (2009) 185–191
187
3.2. Description of crystal structures
3. Results and discussion
3.2.1. Crystal structure of polymer {[Cd(TTTMB)(bdic2À)(H2O)]ÁH2O}n
3.1. Syntheses
(1)
X-ray diffraction analysis reveals that polymer 1 crystallizes in
the triclinic space group P1. Each Cd(II) ion is seven-coordinated
As far as we know, hydrothermal synthesis at mild temperature
(100–200 °C) under autogenous pressure was proven to be a pow-
erful approach in the preparation of low-soluble organic–inorganic
hybrid materials [21–23]. The ligands H2bdic, H3btrc and TTTMB
suit for hydrothermal reactions due to the high structural stability.
Thus, we believe that the new structures of metal–organic frame-
works could be obtained using these mixed-ligands under hydro-
thermal reaction. As anticipated, treatment of TTTMB as
functional ligand with Cd(NO3)2Á4H2O, H2bdic as auxiliary ligand
yielded polymer 1 at 130 °C hydrothermal reactions. Polymer 2
and 3 was obtained successfully by using TTTMB, H3btrc and intro-
ducing 3CdSO4Á8H2O or Zn(NO3)2Á4H2O at 120 °C hydrothermal
reactions.
ꢀ
by one oxygen atom from a water molecule, four oxygen atoms
from two bdic2À groups and two nitrogen donors arising from
two TTTMB ligands (Fig. 1a). The equatorial position is occupied
by O1AA, O2AA, O3AC, O4AC and O5AA (the mean deviation is
0.0538 Å) and N1AA, N6AB are in axial position. So the local
coordination environment of Cd(II) can be described as a distorted
pentagonal bipyramid (Fig. 1b). The Cd–N bond lengths are 2.279
and 2.299 Å, and Cd–O bond lengths are in the range of 2.306–
2.596 Å. They are in conformity with those found in reported
corresponding cadmium complexes [24–27]. The ligand TTTMB is
the cis,trans,trans-conformation (Scheme 1) and each TTTMB
Fig. 1. (a) The coordination environment of Cd(II) in polymer 1. (b) Perspective view of the (4,4) coordination layer of 1 with the Cd(II) centers highlighted as grey polyhedron.
The lattice water molecules and H atoms are omitted for clarity in (a) and (b).

188
X. Wang et al. / Journal of Molecular Structure 938 (2009) 185–191
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
cis,trans,trans
cis,cis,cis
Scheme 1. Schematic drawing for tripodal ligand TTTMB with cis,cis,cis- and cis,trans,trans-conformation.
molecule coordinates to two Cd(II) ions as a bidentate ligand rather
than a tridentate ligand that connects three metal ions. The ligand
TTTMB adopts similar coordination mode to the other tripodal li-
gands of the reported complexes [28]. Each bdic2À group as the
bidentate ligand also links two Cd(II) ions. Such coordination
modes of TTTMB and bdic2À groups result in the formation of an
infinite two-dimensional network structure as shown in Fig. 1b.
Four Cd(II) ions, two bdic2À groups and two TTTMB units form a
40-membered ring (Fig. 1a). Thus the framework of polymer 1
can be regarded as a (4,4) network. The distance between Cd1A
and Cd1B is 15.477 Å, whereas the distance between Cd1A and
Cd1C is 10.158 Å. All the Cd(II) ions in one layer of 1 are in the same
plane, and the layers are parallel (Fig. 2). The benzene ring planes
of TTTMB and bdic2À are deflected from the Cd(II) ions plane with
the dihedral angles of 65.1° and 77.3°, respectively.
Additionally, the adjacent layers are linked together through
hydrogen bonds between coordinated oxygen atoms of the bdic2À
groups and coordinated water molecules, O(carboxylate) and solvent
H2O molecules resulting in a three-dimensional network (Fig. 3).
The benzene rings of bdic2À groups and triazole rings in adjacent
layers are parallel with the average interplanar distance of 3.623,
and 3.571 Å, respectively. These distances are slightly longer than
the
[29], thus
p
–
p
stacking distances of 3.33–3.53 Å reported elsewhere
interactions between adjacent layers in this com-
p–p
plex are very weak [30,31].
3.2.2. Crystal structure of polymer
{[Cd(TTTMB)(Hbtrc2À)(H2O)]Á2H2O}n (2)
Single-crystal structural determination reveals that polymer 2
has the same space group as polymer 1. As shown in Fig. 4a.
Fig. 2. Schematic representation of the layer stacking in 1.
Fig. 3. View of the infinite three-dimensional supramolecular structure of polymer 1, generated through extensive hydrogen bonding. Hydrogen atoms are omitted for clarity.

X. Wang et al. / Journal of Molecular Structure 938 (2009) 185–191
189
deprotonated and coordinated to two Cd(II) ions in a monodentate
mode. Thus the framework of polymer 2 is the same as 1 exhibiting
a two-dimensional network (Fig. 4b). The distances of Cd1AÁÁÁCd1B
and Cd1AÁÁÁCd1C are 11.619 and 10.388 Å, respectively. Moreover,
the triazole rings are parallel between the adjacent layers
(Fig. 5). The adjacent layers are linked through hydrogen bonds be-
tween uncoordinated oxygen atoms of the Hbtrc2À groups and
coordinated H2O molecules, solvent H2O molecules and oxygen
atoms of the Hbtrc2À groups resulting in a three-dimensional net-
work. Although the hydrogen bonds are weak, they are important
in the molecular assembly.
3.2.3. Crystal structure of polymer [Zn(TTTMB)(Hbtrc2À)(H2O)]n (3)
The crystal structure of 3 is significantly different from 2: it
exhibits one-dimensional zigzag chain as shown in Fig. 6, and this
complex crystallizes in the monoclinic space group P2(1)/n. Each
Zn(II) ion is four-coordinated in a distorted tetrahedron geometry
with one oxygen atom from a terminal Hbtrc2À group, one oxygen
atom from a water molecule and two nitrogen donors from two
TTTMB molecules. The Zn–N bond lengths are 2.019 and 2.023 Å,
and Zn–O bond lengths (1.965 and 1.971 Å) compare well with
the distances found in the reported zinc complexes [32]. The bond
angles around each Zn(II) ion range from 100.3° to 118.4°. Hence,
average bond angle at Zn(1) is 109.3°, which is slightly smaller
than 109.5° for an ideal tetrahedron. Two carboxyl groups of
H3btrc are deprotonated, but only one carboxyl group coordinated
to a Zn(II) ion in a monodentate mode. The coordination mode of
ligand TTTMB in 3 is in conformity with those in polymers 1 and
2. Each ligand TTTMB coordinates to two Zn(II) ions as a bidentate
ligand forming one-dimensional chain, and between the adjacent
chains, the triazole rings are parallel with the average interplanar
distance of 3.494 Å. Similarly, p–p interaction exists in the benzene
rings of Hbtrc2À groups and benzene rings of TTTMB ligands with
the average interplanar distance of 3.537 Å. So, the adjacent layers
Fig. 4. (a) The coordination environment of Cd(II) in polymer 2. (b) Perspective
view of the two-dimensional layer of 2 with the Cd(II) centers highlighted as grey
polyhedron. The lattice water molecules and H atoms are omitted for clarity in (a)
and (b).
Cd1A is five-coordinated in a slightly distorted trigonal bipyramid
environment by binding two O atoms (O1AA and O5AB) from two
Hbtrc2À groups, one O atom (O7AA) from a water molecule and
two nitrogen donors (N1AA and N6AB) arising from two TTTMB li-
gands. The Cd–N bond lengths are 2.251 and 2.374 Å. The Cd–O
bond lengths are in the range of 2.267–2.340 Å, and these distances
are slightly shorter than those of 1. The distance of Cd1ÁÁÁO2
(2.691 Å) is longer than the common Cd–O(carboxyl) bond length.
In other words, the O2 atom coordinates to the Cd(II) ion very
weakly. The coordination mode of ligand TTTMB in 2 is in confor-
mity with that in polymer 1. Two carboxyl groups of H3btrc are
Fig. 5. Two layers of the structure of 2. The lattice water molecules and H atoms are
omitted for clarity.

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X. Wang et al. / Journal of Molecular Structure 938 (2009) 185–191
Fig. 6. One-dimensional zigzag chain structure of polymer 3. Hydrogen atoms are omitted for clarity.
Fig. 7. View of the infinite three-dimensional supramolecular structure of polymer 3, generated through extensive hydrogen bonding. Hydrogen atoms are omitted for clarity.
are linked through hydrogen bonds and
in a three-dimensional network (Fig. 7).
p
–
p
interactions resulting
cent with a main emission band at 301 nm upon excitation at
284 nm. Polymers 2 and 3 give broad strong fluorescence center
at 308 and 318 nm under the same experimental conditions,
respectively. However, polymer 1 gives two peaks at 312 and
381 nm upon excitation at 284 nm. The peak at 381 nm which
can be attributed to the auxiliary ligand H2bdic since the ligand
H2bdic shows one strong emission band at 380 nm. In addition,
we investigated the solid-state fluorescent spectra of TTTMB and
polymers under the different concentration [33]. The result shows
the main emission bands of the TTTMB and polymers 1–3 with dif-
ferent concentration do not change, and the fluorescence intensi-
ties of TTTMB and polymers 1–3 are falling along with reduction
of the concentration (such as Fig. 9). The fluorescent spectra of
all polymers exhibit slight red-shift in contrast to free ligands,
In polymers 1, 2 and 3, the ligand TTTMB is the cis,trans,trans-
conformation and each TTTMB molecule coordinates to two Cd(II)
ions as a bidentate ligand rather than a tridentate ligand that con-
nects three metal ions. Additionally, bdic2À and Hbtrc2À as biden-
tate bridging ligand or monodentate ligand coordinates to metal
ions, and they all serve as anion groups to keep the equilibrium
of charges in these three polymers.
3.3. Fluorescence properties
The solid-state fluorescent spectra of 1–3 and TTTMB at room
temperature are shown in Fig. 8. The free TTTMB ligand is fluores-

X. Wang et al. / Journal of Molecular Structure 938 (2009) 185–191
191
Appendix A. Supplementary data
CCDC numbers 711653, 711654 and 711655 contain the supple-
mentary crystallographic data for 1, 2 and 3, respectively. These
data can be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2009.09.024.
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We gratefully acknowledge the financial support by the Na-
tional Natural Science Foundation of China (Nos. 20671082 and
20971110), NCET and the Outstanding Talents Foundation by the
Henan Province.