Four ZnII/CdII coordination polymers based on 3,3′-(pyridine-3,5-diyl) dibenzoic acid: Syntheses, crystal structures and photoluminescence property

Article abstract of DOI:10.1016/j.poly.2013.10.022

Four new coordination polymers namely, [Zn(pddb)(H₂O)] _n (1), [Zn(pddb)]_n (2), {[Cd₂(pddb) ₂]·H₂O}_n (3) and [Cd(pddb)(H ₂O)₂]_n (4), have been solvothermally obtained. Among which, complexes 1 and 3 were prepared in presence of 4-nitrobenzoic acid, and complexes 2 and 4 not, respectively. Complex 1 shows a binodal 3,3-connected wavelike layer structure with the point symbol of (6 ³)₂. However, 2 performs a binodal 3,6-connected 3D coordination framework with the point symbol of (4·6²) ·(4²·6⁸·8⁵). 3 exhibits a more complicated 3D periodic structure built on an infinite rod-shape secondary blocking units (SBUs), while 4 shows a double-chain structure, extended into 3D supramolecular framework through strong hydrogen bonding interactions. Furthermore, the study about photoluminescence properties of these four complexes and H₂pddb ligand reveals that these diverse structures have significant influence on the photoluminescence signals.

Full text of DOI:10.1016/j.poly.2013.10.022

Polyhedron 68 (2014) 138–143
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Four ZnII/CdII coordination polymers based on 3,30-(pyridine-3,5-diyl)
dibenzoic acid: Syntheses, crystal structures and photoluminescence
property
⇑
Bei Zhao, Hui-Jun Li, Yan-Yuan Jia, Qian-Qian Guo, Hong-Wei Hou , Yao-Ting Fan
The College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou, Henan 450052, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 May 2013
Accepted 16 October 2013
Available online 31 October 2013
Four new coordination polymers namely, [Zn(pddb)(H2O)]n (1), [Zn(pddb)]n (2), {[Cd2(pddb)2]ꢀH2O}n (3)
and [Cd(pddb)(H2O)2]n (4), have been solvothermally obtained. Among which, complexes 1 and 3 were
prepared in presence of 4-nitrobenzoic acid, and complexes 2 and 4 not, respectively. Complex 1 shows
a binodal 3,3-connected wavelike layer structure with the point symbol of (63)2. However, 2 performs a
binodal 3,6-connected 3D coordination framework with the point symbol of (4ꢀ62)ꢀ(42ꢀ68ꢀ85). 3 exhibits a
more complicated 3D periodic structure built on an infinite rod-shape secondary blocking units (SBUs),
while 4 shows a double-chain structure, extended into 3D supramolecular framework through strong
hydrogen bonding interactions. Furthermore, the study about photoluminescence properties of these four
complexes and H2pddb ligand reveals that these diverse structures have significant influence on the pho-
toluminescence signals.
Keywords:
3,30-(Pyridine-3,5-diyl) dibenzoic acid
Crystal structures
Photoluminescence signals
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
which carboxylate groups adopt simple monodentate and chelate
coordination moods [20]. Compared with rigid pyridine-3,5-
Recent decades have seen increasing issues upon the design and
syntheses of various coordination polymers, not only due to their
attracting structures and new fascinating topologies [1–4], but also
due to some potential applications, such as gas adsorption [5–7],
chemical sensors [8], molecular recognition, photochromism [9],
gas separation [10], chemical stability and medical drug [11]. How-
ever, how to obtain desired structures with specific properties is
still a challenge, because the self-assembly processes can be
affected by many factors, for instance, temperature, metal ions,
ligands, metal–ligand ratios, solvents, and counterions [12–15].
Among these influential factors, the judicious selections of organic
ligands play an indispensable role in the construction and struc-
tural diversity of coordination polymers, due to their adjustable
flexibility and connectivity information. Recent decade, bifunc-
tional pridine-carboxylate ligands [16–18] have captured the
chemistry’ s attention, because they possess N– and O– potential
electron-donating centers which can exhibit diverse coordination
modes with metal centers and various structures. Notably, carbox-
ylate groups on the ligands may facilitate the formation of discrete
multinuclear clusters and infinite building blocks by M–COO–M
linkage [19]. Lu et al. have reported four metal–organic frameworks
by varying water content based on pyridine-3,5-dicarboxylate in
dicarboxylate, H2pddb (3,30-(pyridine-3,5-diyl)dibenzoic acid) is a
semirigid ligand, owing to the different dihedral angles between
two benzene rings and the versatile coordination orientation of two
carboxylate groups, which may result into the very distinct structures.
Although many transition metal complexes of pyridinedicarboxylates
have been previously reported, no ZnII/CdII complexes based on 3,30-
(pyridine-3,5-diyl)dibenzoic acid have been described [21].
Herein, we utilized H2pddb and ZnII/CdII salts under solvother-
mal condition and successfully synthesized four new distinct
frameworks, namely, [Zn(pddb)(H2O)]n (1), [Zn(pddb)]n (2), {[Cd2
(pddb)2]ꢀH2O}n (3) and [Cd(pddb)(H2O)2]n, (4), among which com-
plexes 1 and 3 were obtained in presence of 4-nitrobenzoic acid,
while 2 and 4 were not. Further, the photoluminescence studies
of these four complexes and H2pddb were carried out, and the
results reveal that the diverse structures had significant effect on
the behaviors of photoluminescence.
2. Experimental
2.1. Materials and physical measurements
All reagents and solvents were purchased commercially and
used without further purification. The rigid ligand 3,30-(pyridine-
3,5-diyl) dibenzoic acid (H2pddb) was also purchased. The
FT-IR spectra were recorded from KBr pellets in the range of
⇑
Corresponding author.
E-mail address: houhongw@zzu.edu.cn (H.-W. Hou).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.10.022

B. Zhao et al. / Polyhedron 68 (2014) 138–143
139
400–4000 cmꢁ1 on a Bruker Tensor 27 spectrophotometer. Ele-
mental analyses (C, H and N) were carried out on a FLASH EA
1112 elemental analyzer. PXRD Patterns were recorded using Cu
program. The data were corrected for Lorentz and polarization
effects. The structures were solved by direct methods and refined
with a full-matrix least-squares technique based on F2 with the
SHELXL-97 crystallographic software package [22]. All non-hydrogen
atoms were refined anisotropically. The hydrogen atoms of ligands
were included in the structure factor calculation at idealized posi-
tions by using a riding model and refined isotropically. The hydro-
gen atoms of coordinating water molecules and solvent water
molecules were located from the difference Fourier maps,
restrained at fixed positions and refined isotropically. Crystallo-
graphic crystal data and structural parameters for 1–4 are summa-
rized in Table 1, and selected bond lengths and angles of 1–4 are
listed in Table S1 in SI (Supporting Information).
Ka1 radiation on a PANalytical X’Pert PRO diffractometer. Thermal
analyses were performed on a Netzsch STA 449C thermal analyzer
from room temperature at a heating rate of 10 °C minꢁ1 in air. The
luminescence spectra for the powdered solid samples were measured
at room temperature on a Hitachi 850 Fluorescence Spectrophotom-
eter. The excitation slit, as well as the emission slit was 2 nm.
2.2. Preparation of the complexes
2.2.1. Synthesis of [Zn(pddb)(H2O)]n (1)
A mixture of H2pddb (0.0128 g, 0.04 mmol), Zn(NO3)2ꢀ6H2O
(0.0297 g, 0.1 mmol), 4-nitrobenzoic acid (0.0146 g, 0.10 mmol),
water (6 mL), and DMA (1 mL) was heated in 25 mL Teflon-lined
stainless steel container at 160 °C for three days, and slowly cooled
to room temperature at a rate of 5 °C/h. Then colorless block crys-
tals 1 were obtained with a 75% yield (based on H2pddb) after
being washed several times by water. Elemental analysis: Anal.
Calc. for C19H13NO5Zn: C, 56.95; H, 3.17; N, 3.50. Found: C,
56.79; H, 3.34; N, 3.33%. IR (KBr, cmꢁ1): 3421 (bw), 3053 (bw),
1612 (w), 1542 (s), 1397 (s), 1277 (w), 1172 (w), 820 (w), 766
(m), 690 (m).
3. Results and discussion
3.1. Crystal structures of [Zn(pddb)(H2O)]n (1)
Single-crystal X-ray analysis reveals that 1 crystallizes in mono-
clinic space group P21/c, and exhibits a wavelike layer structure.
The asymmetric unit contains one Zn center, one pddb2ꢁ ligand
and one coordinating water molecule. As shown in Fig. 1a, Zn1 is
four-coordinated by three oxygen atoms (O1A, O2, and O4B) from
three pddb2ꢁ ligands with the ZnꢁO bond lengths of 1.959–1.978 Å
and an oxygen atom (O5) from one water molecule with the ZnꢁO
bond length of 1.978 Å, and the ZnꢁO distances are in a normal
range according to previous reports for ZnII coordination polymers
[23–26]. It is worth noting that the nitrogen atoms from pddb2ꢁ li-
gand do not participate in coordination. Furthermore, from the
view of pddb2ꢁ ligand, two carboxylate groups from the same
pddb2ꢁ ligand adopt two different coordination modes. One adopts
monodentate coordination mode to coordinate with one ZnII ion,
2.2.2. Synthesis of [Zn(pddb)]n (2)
A mixture of H2pddb (0.0128 g, 0.04 mmol), Zn(NO3)2ꢀ6H2O
(0.0297 g, 0.1 mmol), water (6 mL), and DMA (1 mL) was heated
in 25 mL Teflon-lined stainless steel container at 160 °C for three
days, and slowly cooled to room temperature at a rate of 5 °C/h.
Meanwhile, colorless stick crystals were collected, with yield of
60% (based on H2pddb). Elemental analysis: Anal. Calc. for C19H11
NO4Zn: C, 59.63; H, 2.90; N, 3.66. Found: C, 59.74; H, 2.82; N,
3.76%. IR (KBr, cmꢁ1): 3049 (w), 2360 (w), 1608 (w), 1540 (s),
1395 (s), 820 (w), 764 (m), 682 (m).
and the other adopts l2 g1 g1 bridging mode with two ZnII ions
- :
(ZnꢀꢀꢀZn = 4.220 Å). If the potential weak ZnꢁO3 bonds with the
bond length of 2.566Å are taken into consideration, the coordina-
tion number of Zn center changes to five and the carboxylate group
containing O3 adopts bidentate chelating coordination mode to
one ZnII ion instead of monodentate mode. ZnII ions link the car-
boxylate groups from pddb2ꢁ ligands to form a wavelike chain by
coordinating with O2 and O4 atoms (Fig. 1b), and adjacent chains
are linked together to produce a wavelike layer by sharing the
O1 atoms from one carboxylate group (Fig. 1c). From the view of
topology, if Zn centers are regarded as 3-connected nodes, and
pddb2ꢁ ligands as 3-connected nodes, the structure of complex 1
is a binodal 3,3-connected wavelike layer with a point symbol of
(63)2, as depicted in Fig. 1d. Finally, 3D supramolecular structure
is packed through two sorts of hydrogen bonding (classical hydro-
gen bonding: O5ꢀꢀꢀN1 = 2.704 Å), as shown in Fig. 1e.
2.2.3. Synthesis of {[Cd2(pddb)2]ꢀH2O}n (3)
A mixture of H2pddb (0.0128 g, 0.04 mmol), CdI2 (0.0366 g,
0.1 mmol), 4-nitrobenzoic acid (0.0146 g, 0.10 mmol), water
(6 mL), and MeCN (2 mL) was heated in 25 mL Teflon-lined stain-
less steel container at 160 °C for three days, and slowly cooled to
room temperature at a rate of 5 °C/h. Thus, colorless block crystals
3 were achieved with a pure yield of 70% (based on H2pddb). Ele-
mental analysis: Anal. Calc. for C38H24N2O9Cd2: C, 52.12; H, 2.76; N,
3.19. Found: C, 52.21; H, 2.93; N, 3.02%. IR (KBr, cmꢁ1): 3433 (bw),
3081 (w), 2928 (w), 2484 (w), 2249 (w), 1704 (w), 1604 (m), 1557
(s), 1455 (m), 1395 (s), 1349 (s), 1260 (w), 926 (w), 764 (m), 684
(m).
2.2.4. Synthesis of [Cd(pddb)(H2O)2]n (4)
A mixture of H2pddb (0.0128 g, 0.04 mmol), CdI2 (0.0366 g,
0.1 mmol), water (6 mL), and MeCN (2 mL) was heated in 25 mL
Teflon-lined stainless steel container at 160 °C for three days, and
slowly cooled to room temperature at a rate of 5 °C/h. Colorless
block crystal 4 were collected, and then filtered to get a yield of
58% (based on H2pddb). Elemental analysis: Anal. Calc. for C19H15
NO6Cd: C, 49.00; H, 3.25; N, 3.01. Found: C, 48.82; H, 3.40; N,
3.08%. IR (KBr, cmꢁ1): 3391 (bw), 3080 (w), 2926 (w), 1696 (w),
1605 (m), 1557 (s), 1435 (m), 1351 (s), 1253 (w), 1174 (w), 892
(bw), 765 (m), 688 (m), 567 (w).
3.2. Crystal structure of [Zn(pddb)]n (2)
When 4-nitrobenzoic acid was absent in the syntheses process
of 1, a structurally different complex 2 was obtained. Single-crystal
X-ray analysis reveals that 2 also crystallizes in monoclinic space
group P21/c, but exhibits a distinct 3D framework. The asymmetric
unit of 2 contains one Zn center and one pddb2ꢁ ligand. As shown
in Fig. 2a, Zn centers are in a distorted five-coordinated geometry,
which is defined by four oxygen atoms from three different pddb2ꢁ
ligands with the ZnꢁO bond lengths of 1.984–2.271 Å and one
nitrogen atom from another pddb2ꢁ ligand with the ZnꢁN bond
lengths of 2.059Å. The ZnꢁO/N distances are normal as reported
for other ZnII coordination polymers [23–26]. Moreover, different
from complex 1, two carboxylate groups from the same pddb2ꢁ
ligand adopt two different coordination modes, one of which
adopts chelating mode to coordinate with one ZnII ion, and the
2.3. Crystal data collection and refinement
The data of the four polymers were collected on a Rigaku Saturn
724 CCD diffractomer (Mo K
a, k = 0.71073 Å) at temperature of
20 1 °C. Absorption corrections were applied by using multi-scan

140
B. Zhao et al. / Polyhedron 68 (2014) 138–143
Table 1
Crystallographic data and structure refinement details for 1–4.
Complex
1
2
3
4
Formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
a (Å)
C
19H13NO5Zn
C19H11NO4Zn
382.66
293(2)
0.71073
Monoclinic
12.409(3)
11.979(2)
10.352(2)
90
C38H24N2O9Cd2
877.39
293(2)
0.71073
Monoclinic
17.332(4)
17.988(4)
10.660(2)
90
C19H15NO6Cd
465.72
293(2)
0.71073
Monoclinic
17.764(4)
12.648(3)
8.1797(16)
90
400.67
293(2)
0.71073
Monoclinic
15.883(3)
12.631(3)
8.0124(16)
90
b (Å)
c (Å)
a
(°)
b (°)
91.69(3)
90
1606.8(6)
4
1.656
1.561
107.10(3)
90
1470.9(5)
4
1.728
1.696
94.12(4)
90
3315.0(11)
4
1.454
1.345
106.40(3)
90
1763.1(6)
4
1.755
1.276
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
l
(mmꢁ1
)
F (000)
Goodness-of-fit on F2
R1 [I > 2
(I)]a
wR2 (all data)b
816
1.043
0.0702
0.1376
776
1.153
0.0684
0.1713
1736
1.168
0.0584
0.1512
928
1.081
0.0308
0.0925
r
a
R1
wR2
=
R
¼
||Fo| ꢁ |Fc||/
R|Fo|.
h
i
1=2
P
P
2
2
wðF2o ꢁ Fc2Þ = wðFo2Þ
.
b
Fig. 1. (a) Coordination environments of the ZnII ions in 1. Hydrogen atoms and free water molecule are omitted for clarity; (b) the infinite 1D chain formed by ZnII ions and
pddb2ꢁ ligand. (c) polyhydral view of the 2D layer in 1; (d) The 3,3-connected topology of the 2D layer viewed by b axis; (e) Perspective view of the supermolecular
framework through two kinds of hydrogen-bonding interaction.
other adopts l2
ions. As shown in Fig. 2b, two carboxylate groups from pddb2ꢁ li-
gand link three ZnII ions in 3-bridging mode to form a sheet struc-
-
g1
:
g1 bridging mode to coordinate with two ZnII
3.3. Crystal structure of {[Cd2(pddb)2]ꢀH2O}n (3)
l
Single-crystal X-ray analysis indicates that 3 crystallizes in
monoclinic space group C2/c and exhibits a complicated 3D peri-
odic framework. The asymmetric unit in complex 3 includes two
half of distinct Cd centers, one pddb2ꢁ ligand, and one guest water
molecule. As shown in Fig. 3a, Cd1 is in a distorted octahedral fash-
ion and surrounded by four oxygen atoms (O2C, O2D, O4E, and O4)
from four different pddb2ꢁ ligands with Cd1ꢁO distances of 2.289–
2.297 Å and two nitrogen atoms (N1A and N1B) from another two
pddb2ꢁ ligands with CdꢁN bond length of 2.362 Å. Unlike Cd1, Cd2
is also in a distorted octahedral fashion but defined by six oxygen
atoms (O1, O1d, O3c, O3e, O4a and O4b) from six different pddb2ꢁ
ligands with the Cd2ꢁO bond lengths of 2.226–2.388 Å. The CdꢁO
bond lengths are in normal range according to previous reports for
ture along ab plane. Comparing with that of complex 1, the
architecture of this sheet is composed of infinite linear chains
based on a paddle-wheel dinuclear unit [Zn2(COO)2] with the
ZnꢀꢀꢀZn distance of 3.917 Å. The sheets are connected together into
3D framework by ZnꢁN connections (Fig. 2c). A better insight into
the present 3D framework can be accessed by the topological
method. Each dinuclear [Zn2(COO)2] unit links six pddb2ꢁ ligands
and can be simplified as a 6-connected node, and one pddb2ꢁ links
three dinuclear [Zn2(COO)2] unit, serving as a 3-connected node,
therefore, the structure of complex 2 is a binodal 3,6-connected
3D framework with a point symbol of (4ꢀ62)(42ꢀ68ꢀ85) , as depicted
in Fig. 2d.

B. Zhao et al. / Polyhedron 68 (2014) 138–143
141
Fig. 2. (a) Coordination environments of the ZnII ions in 2. (b) Perspective view of the 2D layer in 2. (c) Perspective view of the 3D framework extended by ZnII coordinating
with nitrogen atoms, viewed by the c axis. (d) The 3,6-connected topology of the 3D framework. Hydrogen atoms and free water molecule are omitted for clarity.
Fig. 3. (a) Coordination environments of the CdII ions in 3. (b) The rod SBU unit formed by CdII ions and carboxylate groups from the pddb2ꢁ ligand. (c) polyhydral view of the
rod SBU in 3; (d) Perspective view of the 3D framework formed by the rod SBU linking with four neighbor SBU units by pddb2ꢁ ligand. Hydrogen atoms and free water
molecule are omitted for clarity.
CdII coordination polymers [27–29]. As for pddb2ꢁ ligand, the two
carboxylate groups from the same pddb2ꢁ ligand adopt two dis-
tinct coordination modes in Scheme 1c. One adopts chelating mode
the valid void occupancy after the removal of uncoordinated sol-
vents is 18%, calculated by the PLATON software.
to coordinate with one CdII ion, and the other adopts l3 g2 1 coor-
- :g
3.4. Crystal structure of [Cd(pddb)(H2O)2]n (4)
dination mode to coordinate with three CdII ions, which favors to
the formation of rod secondary building units (SBUs). Along c axis,
there is a infinite (Cd1ꢁOꢁCꢁOꢁCd2)n rod SBU composed by alter-
native six-coordinated CdII ions and the carboxylate groups (Fig. 3b
and c), according to the previous records [30–32]. The rods connect
four neighboring rods by the skeleton of pddb2ꢁ along the ab plane,
resulting in 3D nanovoid framework, in which each cube-type
channel of 4.82 ꢂ 9.76 Å2 in size is surrounded by four adjacent
rectangle-type of 9.76 ꢂ 11.21 Å2 in size, as depicted in Fig. 3d.
The guest water molecules are located inside the channels, and
In the absent of 4-nitrobenzoic acid, complex 4 with distinct
structure was obtained. Single-crystal X-ray analysis reveals that
4 crystallizes in monoclinic space group C2/c and exhibits a dou-
ble-chain structure. The asymmetric unit is composed of one Cd
center, half of the pddb2ꢁ ligand, and one coordinating water mol-
ecule. As shown in Fig. 4a, Cd1 is seven-coordinated by four oxygen
atoms (O1B, O2B, O1C, and O2C) from two different pddb2ꢁ ligands
with CdꢁO bond lengths of 2.342–2.495 Å, two oxygen atoms (O3
and O3A) from two water molecules with CdꢁO bond lengths of

142
B. Zhao et al. / Polyhedron 68 (2014) 138–143
Scheme 1. The coordination modes of pddb2ꢁ in these four complexes: (1a) the coordination modes of pddb2ꢁ in complex 1 by introduction of 4-nitrobenzoic acid; (1b) the
coordination modes of pddb2ꢁ in complex 2 without any other agents; (1c) the coordination modes of pddb2ꢁ in complex 3 in the present of 4-nitrobenzoic acid; (1d) the
coordination modes of pddb2ꢁ in complex 4 without any other agents.
2.347 Å, and one nitrogen atom (N1) from another pddb2ꢁ ligand
with the CdꢁN bond length of 2.276 Å. And the CdꢁO/N distances
are in normal range according to previous reports for CdII coordina-
tion polymers [27–29]. Different from that in complex 3, the
pddb2ꢁ ligand in complex 4 adopts trans-conformation and both
the carboxylate groups from the same ligands employ bidentate
chelating mode to coordinate with one CdII ion. Therefore, the car-
boxylate groups from pddb2ꢁ ligands link the CdII ions to form a
chain which is extended into double chain by CdIIꢁN connections
(Fig. 4b). Through two sorts of strong hydrogen bonds
(O3ꢀꢀꢀO1#4 = 2.819 Å, and O3ꢀꢀꢀO1#5 = 2.739 Å, #4 ꢁx + 1, ꢁy + 1,
ꢁz + 1; #5 x, ꢁy + 1, z + 1/2), these double chains are extended into
3D supermolecular framework along the bc plane, as depicted in
Fig. 4c. It is these strong hydrogen bonding interactions that help
to further reinforce the 3D supermolecular framework (Fig. 4d).
these four coordination polymers, thermogravimetric analyses
(TGA) were carried out. The curves show that all these complexes
are of good thermal stability, which can endure more than 400 °C
after losing the coordinated water or the lattice water molecules,
as shown in the Fig. S2 (Supporting Information). A slow weight
loss of 4.51% in complex 1 from 135 to 210 °C takes place, which
is resulted from the loss of coordinating water molecules. A plateau
phase occurs until the framework starts to collapse at 427 °C, it is
the strong coordination ability between metal ions and pddb2ꢁ
ligand that stabilizes the structure. For complex 2, there is no obvi-
ous weight loss until the framework begins to decompose at
417 °C. With regard to the complex 3, the loss weight of 2.86%
before 265 °C can be assigned to the loss of the lattice water mol-
ecule (Calc., 2.78%), and then the framework begins to decompose
at 483 °C. For the complex 4, the weight loss of 7.3% can be ob-
served in the range of 150–280 °C, which can be seen as the loss
of two coordinated water molecules, and the framework can be
stable up to 475 °C.
3.5. PXRD studies and thermal analyses
To confirm the phase purity of these four complexes, the PXRD
patterns were recorded and comparable to the corresponding sim-
ulated ones calculated from the single-crystal diffraction data (as
shown in Fig. S1 (Supporting Information)), indicating a pure phase
of each bulky sample. In addition, to estimate thermal stability of
3.6. Photoluminescence properties
Coordination polymers with d10 metal centers and conjugated
organic linkers are considered as
a promising option for
Fig. 4. (a) Coordination environments of the CdII ions in 4. (b) The infinite 1D double chain viewed by the c axis. (c) The 3D supermolecular frameworks through by two sorts
of hydrogen bonding interaction; (d) Perspective view of the supermolecular 3D framework. Hydrogen atoms and free water molecule are omitted for clarity.

B. Zhao et al. / Polyhedron 68 (2014) 138–143
143
Appendix A. Supplementary data
Crystallographic data for the structures in the form of CIF files
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication Nos. CCDC: 920566–920569
for 1ꢁ4, respectively. Copies of these data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html or from the
Cambridge Crystallographic Data Centre, 12, Union Road, Cam-
bridge CB21EZ, UK (fax: (+44) 1223-336-033; Email: depos-
it@ccdc.cam.ac.uk). Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.poly.2013.10.022.
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? p electronic transitions. Since
the ZnII/CdII ions are difficult to oxidize or reduce, the photolumi-
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4 (kem = 409 nm, kex = 334 nm) are mainly contributed to the inter-
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but necessary effect on the photoluminescence signals.
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Based on a new type of pridine-carboxylate ligand 3,30-(pyri-
dine-3,5-diyl) dibenzoic acid (H2pddb), four new coordination
polymers have been solvothermally synthesized in the present or
absent of 4-nitrobenzoic acid. Complex 1 shows a binodal 3,3-con-
nected wavelike layer structure, and 2 performs a binodal 3,6-con-
nected 3D coordination framework. 3 exhibits a more complicated
3D periodic structure built on an infinite rod-shape secondary
blocking units (SBUs), while 4 shows a double-chain structure, ex-
tended into 3D supramolecular framework through strong hydro-
gen bonding interactions. Furthermore, the fluorescence study of
these four polymers and H2pddb ligand indicates that the diverse
structures have subtle but necessary effect on the photolumines-
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Acknowledgements
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This work is financially supported by the National Natural Sci-
ence Foundation of China (Grant No. 20971110 and Grant No.
91022013) and Research Fund for the Doctoral Program of Higher
Education of China (Grant No. 20124101110002).