Tuning structural topologies of five photoluminescent Cd(II) coordination polymers through modifying the substitute group of organic ligand

Article abstract of DOI:10.1016/j.jssc.2012.11.026

Five new Cd(II) coordination polymers based on mixed 5-position substituted 1,3-benzenedicarboxylate ligands (R=NO₂/OH/CH₃) and 1,4-bis(imidazol-1-yl)benzene (L₁)or 1,4-bis(1-imidazol-yl) -2,5- dimethyl benzene (L₂), namely [Cd(5-NO₂-ip)(L ₁)·H₂O] (1), [Cd(5-OH-ip)(L₁)] _n (2), [Cd(5-NO₂-ip) (L₁)_0.5(H ₂O)₂]_n (3), {[Cd(5-NO₂-ip)(L ₂)_0.5(H₂O)]·H₂O} (4), [Cd(5-CH₃-ip)(L₂)(H₂O)₂] _n (5), have been synthesized hydrothermally and structurally characterized. With different substituted groups in the organic ligands, five compounds exhibit five distinct framework structures. By changing the pH value, compound 1 with 2-fold interpenetrating (4,4)-layer structure and compound 3 with three-dimensional diamond-type framework are obtained, respectively, from the assembly of Cd(NO₃)₂·4H₂O, 5-NO ₂-ip and L₁ ligand. The replacement of 5-NO₂-ip with 5-OH-ip leads to a compound 2 which features a doubly pillared layered structure with pcu topology. Compounds 4 and 5 are constructed from L ₂ ligand with 5-NO₂-ip or 5-CH₃-ip, respectively. Compound 4 has non-interpenetrating (4,4) layer, while compound 5 shows unusual 2D->3D polycatenation of bilayers. The results reveal a new approach toward tuning structural topologies of coordination polymers through modifying the substitute groups in organic ligands. Furthermore, the photoluminescent properties of compounds 1-5 have been studied in the solid state at room temperature.

Full text of DOI:10.1016/j.jssc.2012.11.026

Journal of Solid State Chemistry 199 (2013) 42–48
Contents lists available at SciVerse ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Tuning structural topologies of five photoluminescent Cd(II) coordination
polymers through modifying the substitute group of organic ligand
nn
Feng Guo a,n, Baoyong Zhu a, Guilan Xu a, Miaomiao Zhang a, Xiuling Zhang a, Jian Zhang b,
a Key Laboratory of Coordination Chemistry and Functional Materials in Universities of Shandong, Dezhou University, Shandong 253023, PR China
b State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Five new Cd(II) coordination polymers based on mixed 5-position substituted 1,3-benzenedicarbox-
ylate ligands (R¼–NO2/–OH/–CH3) and 1,4-bis(imidazol-1-yl)benzene (L1)or 1,4-bis(1-imidazol-yl) -
2,5- dimethyl benzene (L2), namely [Cd(5-NO2-ip)(L1) ꢀ H2O] (1), [Cd(5-OH-ip)(L1)]n (2), [Cd(5-NO2-ip)
(L1)0.5(H2O)2]n (3), {[Cd(5-NO2-ip)(L2)0.5(H2O)] ꢀ H2O} (4), [Cd(5-CH3-ip)(L2)(H2O)2]n (5), have been
synthesized hydrothermally and structurally characterized. With different substituted groups in the
organic ligands, five compounds exhibit five distinct framework structures. By changing the pH
value, compound 1 with 2-fold interpenetrating (4,4)-layer structure and compound 3 with three-
dimensional diamond-type framework are obtained, respectively, from the assembly of Cd(NO3)2 ꢀ
4H2O, 5-NO2-ip and L1 ligand. The replacement of 5-NO2-ip with 5-OH-ip leads to a compound 2 which
features a doubly pillared layered structure with pcu topology. Compounds 4 and 5 are constructed
from L2 ligand with 5-NO2-ip or 5-CH3-ip, respectively. Compound 4 has non-interpenetrating (4,4)
layer, while compound 5 shows unusual 2D-43D polycatenation of bilayers. The results reveal a new
approach toward tuning structural topologies of coordination polymers through modifying the
substitute groups in organic ligands. Furthermore, the photoluminescent properties of compounds 1–
5 have been studied in the solid state at room temperature.
Received 12 October 2012
Received in revised form
21 November 2012
Accepted 25 November 2012
Available online 5 December 2012
Keywords:
Coordination polymer
Cadmium (II)
Luminescence
& 2012 Elsevier Inc. All rights reserved.
1. Introduction
different structures and properties [26–29]; (II) the rigid bis(imi-
dazole ) shows the good ability to coordinated to the metal center
Recently, the self-assembly of coordination polymers (CPs) have
been given considerable attention not only for their potential
applications in gas storage, luminescence, magnetism, catalysis
and separation [1–10], but also for their structural diversities and
intriguing topological net [11–14]. It has been recognized that the
construction of CPs is influenced by many structural and experi-
mental factors, such as the nature of the organic ligands, the metal
centers, and the reaction conditions (pH value, template and
solvents) [15–18]. The organic carboxylate and imidazole-
containing ligands have been proven to be good candidates for
the construction of CPs [19–25]. Among mentioned above, we
selected the 5-position substituted 1,3-benzenedicarboxylate
ligands (R¼–NO2/–OH/–CH3) as organic anions, 1,4-bis(imidazol-
1-yl) benzene and 1,4-bis(1-imidazol-yl) -2,5- dimethyl benzene as
neutral ligands based on the following considerations:(I) The dif-
ferent electron-donating (–OH/–CH3)/accepting (–NO2) noncoordi-
nating groups in 5-position groups might generate compounds with
and can adopt two type coordination modes: cis-configuration and
trans-configuration. Moreover, the rigid bis(imidazole) ligands are
good framework pillars to sustain the structures [30–33]. Five new
Cd(II) coordination polymers, [Cd(5-NO2-ip)(L1) ꢀ H2O] (1), [Cd
(5-OH-ip)(L1)]n (2), [Cd(5-NO2-ip) (L1)0.5(H2O)2]n (3), {[Cd(5-
NO2-ip)(L2)0.5(H2O)] ꢀ H2O} (4), [Cd(5-CH3-ip)(L2)(H2O)2]n (5), have
been synthesized hydrothermally and structurally characterized. It
is interesting that five compounds exhibit five distinct framework
structures. The results reveal a new approach toward tuning
structural topologies of coordination polymers through modifying
the substitute groups in organic ligands. The luminescent properties
of these compounds have been studied in the solid state at room
temperature.
2. Experimental
2.1. Materials and physical measurements
All reagents and solvents employed were commercially avail-
able and used without further purification. Elemental analysis
was carried out on a Carlo Erba 1106 full-automatic trace organic
n Corresponding author. Fax: þ86 534 8985835.
nn Corresponding author. Fax: þ86 591 83714946.
E-mail addresses: guofeng1510@yeah.net (F. Guo), zhj@fjirsm.ac.cn (J. Zhang).
0022-4596/$ - see front matter & 2012 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jssc.2012.11.026

F. Guo et al. / Journal of Solid State Chemistry 199 (2013) 42–48
43
elemental analyzer. FT-IR spectra were recorded with a Bruker
Equinox 55 FT-IR spectrometer as a dry KBr pellet in the 400–
4000 cmꢁ1 range. Solid-state fluorescence spectra were recorded
on a Hitachi F-4600 equipped with a xenon lamp and a quartz
carrier at room temperature. The powder X-ray powder diffrac-
tion (XRPD) measurements were performed on a Bruker D8
equipped with
˚
a
graphite monochromated Mo-K
a
radiation
(
l¼0.71073 A) by using a o-scan mode. Empirical absorption
correction was applied using the SADABS programs [34]. All the
structures were solved by direct methods and refined by full-
matrix least-squares methods on F2 using the program SHEXL 97
[35]. All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were located by geometrically calculations, and
their positions and thermal parameters were fixed during the
structure refinement. The crystallographic data and experimental
details of structural analyses for coordination polymers are
summarized in Table 1. Selected bond and angle parameters are
listed in Table S1.
diffractometer operated at 40 kV and 40 mA using Cu-K
tion (
¼0.15418 nm).
a radia-
l
2.2. Syntheses of complexes
[Cd(5-NO2-ip)(L1) ꢀ H2O] (1):The mixtures of Cd(NO3)2 ꢀ 4 H2O
(0.5 mmol, 0.145 g), 5-NO2-ip (0.5 mmol,0.106 g), L1(0.5 mmol,
0.105 g) and 12 mL of water were placed in a 25 mL Teflon
reactor, then the pH value was adjusted to 6.8 by addition of
NaOH solution (1 mmol/4 mL), the mixtures were heated to
160 1C for 4 days, and then cooled to room-temperature. The
colorless crystals were obtained in pure phase, washed with
water and ethanol, and dried at room temperature (Yield: 53%
based on Cd). Anal. Calc. for C20 H17CdN5O8: C, 42.30 N, 12.33; H,
3.02. Found: C, 41.87; N,12.26; H, 3.03. IR/cmꢁ1(KBr):3100 br,
1608 s, 1527 s, 1441 s, 1372 m, 1258 m, 1112 m, 1062 m, 961 m,
843 m, 787 m.
3. Results and discussion
3.1. Description of crystal structures
3.1.1. [Cd(5-NO2-ip)(L1) ꢀ H2O]n (1)
Compound 1 crystallizes in the triclinic space group Pꢁ1. As
shown in Fig. 1a, each cadmium atom is coordinated by four
˚
oxygen atoms (Cd(1)-O, 2.257(2)–2.572(2) A) and two nitrogen
[Cd(5-OH-ip)(L1)]n (2):The mixtures of Cd(NO3)2 ꢀ 4 H2O
(0.5 mmol, 0.145 g), 5-OH-ip (0.5 mmol, 0.106 g), L1(0.5 mmol,
0.105 g) and 12 mL of water were placed in a 25 mL Teflon
reactor. After pH was adjusted 5.1, the mixtures were heated to
160 1C for 4 days, and then cooled to room-temperature. The
colorless crystals were obtained in pure phase, washed with
water and ethanol, and dried at room temperature (Yield: 57%
based on Cd). Anal. Calc. for C20H14CdN4O5: C, 47.78; H,2.81; N,
11.14. Found: C, 47.69; N, 11.15; H, 2.80. IR/cmꢁ1 (KBr): 0.1559 s,
1383 m,1273 m, 1126 m, 1061 m, 991 m, 832 m, 787 m, 649 m.
[Cd(5-NO2-ip) (L1)0.5(H2O)2]n (3):The compound 3 was obtained
by the similar method as described for 2 by using of 5-NO2-ip
(0.5 mmol, 0.106 g) in place of 5-OH-ip (pH¼4.8). The colorless
crystals were obtained in pure phase, washed with water and
ethanol, and dried at room temperature (Yield: 47% based on Cd).
Anal. Calc. for C C14H16CdN3O8: C, 36.34; H, 2.61; N, 9.08. Found: C,
36.41; H, 2.60; N, 9.06. IR/cmꢁ1 (KBr): 3138 br, 1612 s, 1530 s,
1446 m, 1348 m, 1256 m, 1063 m, 930 m, 842 m, 789 m, 649 m.
{[Cd(5-NO2-ip)(L2)0.5(H2O)] ꢀ H2O} (4): The compound 4 was
obtained by the similar method as described for 2 by using of
5-NO2-ip (0.5 mmol, 0.106 g) andL2 (0.5 mmol, 0.119 g) in place
of 5-OH-ip and L1, respectively (pH¼4.5). The colorless crystals
were obtained in pure phase, washed with water and ethanol, and
dried at room temperature (Yield: 47% based on Cd). Anal. Calc.
for C C15H14CdN3O8: C, C, 37.79; H, 2.96; N, 8.82. Found: C, 37.70;
H, 2.94; N, 8.86. IR/cmꢁ1(KBr): 3438 br, 1621 s, 1533 s, 1430 m,
1310 m, 1230 m, 1153 m, 1023 m, 950 m, 836 m, 727 m, 660 m.
[Cd(5-CH3-ip)(L2)(H2O)2]n (5):The mixtures of Cd(NO3)2 ꢀ 4
H2O (0.5 mmol, 0.145 g ), 5-CH3-ip (0.5 mmol, 0.09 g), L2
(0.5 mmol, 0.119 g ) and 12 mL of water were placed in a 25 mL
Teflon reactor. After pH was adjusted 6.8, the mixtures were
˚
(Cd(1)–N(1)¼2.366(2) and Cd(1)–N(3)¼2.271(2) A), exhibiting a
distorted octahedral geometry. Three carboxylate oxygen atoms
and one nitrogen atom construct equatorial plane and the axis
positions are occupied by one water molecule and one nitrogen
atoms. The structure of compound 1 is comprised of (4, 4)
undulated layers. The size of the windows in the layer can be
˚
estimated as 10.173 ꢂ 14.031 A from the distance of the Cd atoms.
The undulated layers are associated in pairs to give (2D-2D)
2-fold interpenetrated sheets. The intermolecular interactions
play a significant role in the packing of the layers. Firstly,
the interpenetrated sheets are interacted via C–Hy
p bonds
˚
(C–Hy
p
¼2.79 A, the angle of 1701) and the dihedral angle of
two phenyl rings is 86.841. Secondly, there are
pyp interactions
between the phenyl rings of 5-NO2-ip ligands with a centroid-to-
centroid distance of 3.591(3) A, and the interplane distance of
3.380 A as well as the dihedral angles of 01. Thirdly, the
interactions also exist between the phenyl rings of 5-NO2-ip and
L1 ligands with a centroid-to-centroid distance of 3.836(3) A, and
the shortest interplane distance of 3.558 A as well as the dihedral
angles of 7.7751. Such layer packing results in a 3D supramole-
cular structure. It is no doubted that the supramolecular interac-
tions contribute to the stability of the structure.
˚
˚
pyp
˚
˚
3.1.2. [Cd(5-OH-ip)(L1)]n (2)
The replacement of 5-NO2-ip with 5-OH-ip leads to a com-
pound 2 which features a doubly pillared layered structure with
pcu topology. Single-crystal X-ray diffraction analysis reveals that
compound 2 crystallizes in the monoclinic space group P21/n.
Each Cd (II) is coordinated by three oxygen atoms (Cd–O,
˚
2.254(3)–2.252(3) A) and two nitrogen atoms (Cd(1)–N(1)¼
heated to 160 1C for
4 days, and then cooled to room-
˚
˚
2.293(3) A and Cd(1)–N(4)¼2.302(4) A), showing
a trigonal
temperature. The colorless crystals were obtained in pure phase,
washed with water and ethanol, and dried at room temperature
(Yield: 53% based on Cd). Anal. Calc. for C30 H31CdN6O6: C, 52.68;
H, 4.57; N, 12.28. Found: C, 52.73; N,12.29; H, 4.58. IR/cmꢁ1(KBr):
3268 br, 1625 m, 1533 m, 1428 s, 1375 s, 1110 m, 1060 m, 927 m,
832 m, 773 m, 654 m.
bipyramidal geometry. Two Cd (II) atoms, related by a twofold
axis, are bridged by one pair of 5-OH-ip into a dinuclear unit with
˚
CdyCd distance of 4.078 A. The dinuclear cadmium moieties are
linked by four 5-OH-ip ligands to four adjacent dinuclear cad-
mium clusters, thus generating a (4,4) layer (Fig. 2b). The L1
ligand bridges two metal centers and further connects adjacent
2.3. X-ray crystallography
layers into a 3D framework. From a topological view, the
[Cd2(CO2)3] dimeric unit can be treated as a 6-connected node,
Single crystal X-ray diffraction analyses of compounds 1–5
were carried out on a Bruker SMART APEX/CCD diffractometer
the 5-OH-ip and L1 ligands are taken as linkers, the 3D structure
can be classified as a pcu net (a-Po topology).

44
F. Guo et al. / Journal of Solid State Chemistry 199 (2013) 42–48
Table 1
Crystallographic Data and Structure Refinement Summary for Complexes 1–5.
Empirical formula
C20 H17CdN5O8
C20H14CdN4O5
C14H16CdN3O8
C15H14CdN3O8
C30 H31CdN6O6
Formula weight
567.79
502.75
925.33
476.69
684.01
Crystal system, Space group
Unit cell dimensions
Triclinic, Pꢁ1
a¼10.173 (7) A
b¼11.810 (8) A
Monoclinic, P21/n
Monoclinic, P2(1)/c
Triclinic, Pꢁ1
a¼7.843(3) A
Triclinic, Pꢁ1
a¼10.311 (6) A
b¼11.229 (6) A
˚
˚
˚
˚
˚
a¼9.866 (2) A
b¼14.137 (3) A
c¼13.808 (3) A
a¼9.616 (4) A
b¼28.514 (11) A
c¼12.458 (5) A
˚
˚
˚
˚
˚
b¼10.053(4) A
˚
˚
˚
˚
˚
c¼11.810 (8)A
c¼11.639(5) A
c¼14.021 (8) A
a
b
g
¼117.148 (7)1
¼104.809 (7)1
¼99.441(6)1
a
b
g
¼90.144(5)1
¼94.641(5)1
¼109.953(4)1
a
b
g
¼107.475 (7)1
¼96.101 (7)1
¼96.513 (7)1
b
¼94.019 (3)1
b¼106.009(5)1
3
1063.67 (12)
1921.1 (7)
3283 (2)
859.3 (8)
1521.5 (11)
˚
Volume(A )
Z, Calculated density(mg/m3)
2, 1.773
4322
4, 1.738
3245
4, 1.872
6288
2, 1.842
3591
2, 1.493
5870
Independent reflections
(I42s(I))
F(0 0 0)
568
1000
1832
474
698
2.56–27.48
ꢁ13rhr13
ꢁ12rkr14
ꢁ15rlr15
1.056
2.06–27.48
ꢁ12rhr12
ꢁ18rkr15
ꢁ17rlr17
1.045
1.43–27.46
ꢁ12rhr11
ꢁ36rkr28
ꢁ16rlr15
1.100
1.76–27.51
ꢁ10rhr6
ꢁ8rkr12
ꢁ14rlr14
1.069
2.56–27.49
ꢁ13rhr13
ꢁ14rkr11
ꢁ18rlr17
1.019
y
range for data collection
Limiting indices
Goodness-of-fit on F2
R1a, wR2 [I42
b
s(I)]
R1¼0.0260,
wR2¼0.0653
R1¼0.0292,
wR2¼0.0673
0.617 and ꢁ0.600
R1¼0.0413,
wR2¼0.0970
R1¼0.0614,
wR2¼0.1067
1.008 and ꢁ1.208
R1¼0.0357,
wR2¼0.0704
R1¼0.0456,
wR2¼0.0738
0.616 and ꢁ0.633
R1¼0.0217,
wR2¼0.0586
R1¼0.0231,
wR2¼0.0596
0.568 and ꢁ0.599
R1¼0.0331,
wR2¼0.0760
R1¼0.0405,
wR2¼0.0803
0.551 and ꢁ0.519
R1a,wR2 (all data)
b
3
˚
Largest diff. peak and hole (e/A )
a
R¼S(JF09ꢁ9FCJ)/S9F09.
b
wR¼[
S
w(9F092ꢁ9FC92)2/ w(F02)]1/2
S .
Fig. 1. (a) The coordination environment of Cd(II) atom in compound 1 (50% thermal ellipsoids); (b) the 2-fold interpenetrating layers (left ) and the C–Hy
p interactions
between phenyl rings; (c) the 2-fold interpenetrating topology for compound 1 and (d) the 3D supramolecular structure of compound 1 via interactions.
pyp

F. Guo et al. / Journal of Solid State Chemistry 199 (2013) 42–48
45
3.1.3. [Cd(5-NO2-ip)(L1)0.5(H2O)2]n (3)
both Cd1 and Cd2 ions show similar coordination environment.
Each Cd ion is coordinated by five oxygen atoms [Cd–O, ranging
Compared to 1, the synthesis of 3 was performed under low
pH value, which results in the formation of a new 3D structure
with 4-connected dia topology. It is interesting that the structure
of 3 is based on the dinuclear Cd2 unit bonded by four 5-NO2-ip
ligands and two L1 ligands (Fig. 3a). In each dinuclear Cd2 unit,
˚
from 2.226 (2)–2.528(3) A] and one nitrogen atoms [Cd(1)–
˚
˚
N(4)¼2.210(3) A and Cd(2)–N(1)¼2.233(3) A], showing a dis-
torted octahedral geometry. The two 5-NO2-ip anions adopting
bridging/chelating-bidentate mode connect two adjacent Cd(II)
Fig. 2. (a) The coordination environment of Cd(II) atom in compound 2 (50% thermal ellipsoids); (b) The 2D layer structure formed by 5-OH-ip ligands and (c) the pcu
topology of compound 2.
Fig. 3. (a) The coordination environment of Cd (II) atom in compound 3 (50% thermal ellipsoids) and (b) the dia topology for compound 3.

46
F. Guo et al. / Journal of Solid State Chemistry 199 (2013) 42–48
centers to form a dinuclear Cd2 unit with a CdyCd distance of
polycatenation of bilayers. Compound 5 crystallizes in triclinic
space group Pꢁ1. In compound 5, the central Cd(II) ion coordinates
with three oxygen atoms from two carboxylate groups (one
˚
3.881 A (Scheme 1c). The resulting dinuclear Cd2 unit further bonds
to four adjacent ones through four 5-NO2-ip ligands and two L1
ligands, leading to the formation of a 3D framework. Two adjacent
dinuclear Cd2 units are doubly linked by two 5-NO2-ip ligands. If
each dinuclear Cd2 unit is reduced into a 4-connected node, the 3D
framework of 3 can be topologically simplified as a dia net (Fig. 3b).
˚
monodentate: Cd (1)–O(1)¼2.288(2) A and one chelating biden-
˚
˚
tate: Cd (1)–O(3)¼2.578(2) A and Cd (1)–O(4)¼2.344(2) A) and
˚
three nitrogen atoms (Cd–N, 2.291(2)–2.317(2) A ) to form a
distorted octahedron (Fig. 5a). The L2 ligands link Cd (II) ions to
form a ladder-like chain, and the chains are further connected by 5-
CH3-ip to form a bilayer structure with the topological symbol of
(48.62). The Cd(II) ions are joined by 5-CH3-ip and L2 ligands to give
one-dimensional nanotube containing large cubelike box of approx-
3.1.4. {[Cd(5-NO2-ip)(L2)0.5(H2O)] ꢀ H2O} (4)
In the structure of compound 4, each Cd (II) ion is six-coordinated
by five oxygen atoms and one nitrogen atom to afford the CdNO5
octahedral geometry (Fig. 4a). The Cd–O bond lengths are in the
˚
imate dimensions 10.311 ꢂ 13.964 ꢂ 14.021 A (Fig. 5b) in the
bilayer. The adjacent bilayers are interlocked each other in a parallel
fashion (along the b axis) to give rise to a 3D polycatenated
structure (Fig. 5c).
˚
range of 2.211(2)–2.518 (2) A. The carboxylate groups from two 5-
NO2-ip ligands adopt bis-monodentate coordinate mode to connect
two Cd(II) ions to form a dinuclear Cd(II) unit (Fig. 4b and
Scheme 1a). The dinuclear Cd(II) units are further connected by the
5-NO2-ip ligands to form a ladder-like chain. The parallel chains are
further connected by the L2 ligand into a layer (Fig. 4c).
3.2. Influence of organic ligands or reaction conditions on the
structures
From the above descriptions, it is clear that different reaction
conditions or organic ligands with different substitute groups
may effectively tune the framework structures of the coordina-
tion polymers. By changing the pH value, compound 1 with 2-fold
3.1.5. [Cd(5-CH3-ip)(L2)(H2O)2]n (5)
The replacement of 5-NO2-ip with 5-CH3-ip results in the
generation of
a
new compound
5
with unusual 2D-43D
OH
NO2
Cd
O
O
O
O
Cd
O
Cd
Cd
Cd
O
O
Cd
O
NO2
CH3
O
O
O
O
O
Cd
Cd
Cd
O
O
O
Cd
Scheme 1. Coordination modes of carboxylate ligands in compounds 1–5: (a) for compounds 1 and 4; (b) for compound 2; (c) for compound 3 and (d) for compound 5.
Fig. 4. (a) The coordination environment of Cd (II) atom in compound 4 (50% thermal ellipsoids); (b) The ladder-like chain via 5-NO2-ip ligands and (c) the layer structure
for compound 4.

F. Guo et al. / Journal of Solid State Chemistry 199 (2013) 42–48
47
Fig. 5. (a) The coordination environment of Cd(II) atom in compound 5 (50% thermal ellipsoids); (b) the bilayer containing nanotubes paralleled to the a axis and (c) 3D
polycatenated structure.
Fig. 6. The solid state emission spectra of complexes 1–5 at the room temperature.
interpenetrating (4,4)-layer structure and compound 3 with three-
dimensional diamond-type framework are obtained, respectively,
from the assembly of Cd(NO3)2 ꢀ 4 H2O, 5-NO2-ip and L1 ligand. The
replacement of 5-NO2-ip with 5-OH-ip leads to a compound 2 which
features a doubly pillared layered structure with pcu topology.
Compounds 4 and 5 are constructed from L2 ligand with 5-NO2-ip
or 5-CH3-ip, respectively. Compound 4 has non-interpenetrating (4,
4) layer, while compound 5 shows unusual 2D-43D polycatenation
of bilayers. From compound 3 to compound 4, inducing the CH3
groups into 1,4-bis(imidazol-1-yl) benzene also dramatically chan-
ged the dia net in 3 to a (4,4) layer structure in 4. The preparation of
compound 5 is similar to compound 1 except changing L1 to L2 with
additional CH3 groups, but their structures are also different.
d
10 configuration, the emission of these complex is neither metal-to-
ligand charge transfer nor ligand-to-metal charge transfer in nature
Compared with free L1 and L2 ligands [lem¼456 nm (lex¼341 nm)
for L1 and lem¼421 nm (lex¼362 nm) for L2], the enhancement
of luminescence intensity in the complexes 1–5 in is probably due
to the coordination of the N-donors to the Cd(II) center, increasing
the rigidity of the ligands, reducing the nonradiative decay of the
intraligand (
carboxylate ligands originated from the
and it was considered that the carboxylate ligands have no significant
contribution to the luminescent emission peaks of complexes 1–5 in
the presence of the N-donor ligands.
p–p
n) excited state[36,37]. The emission bands of the
p*ꢁn transition are weak,
3.3. Photoluminescent properties
4. Conclusions
The solid-state photoluminescent properties of compounds 1–5
have been investigated at room temperature. As shown in Fig. 6,
complexes 1–5 exhibit luminescent emission peaks at 423 nm
In summary, we presented here five new Cd(II) coordination
polymers based on mixed 5-position substituted 1,3-benzenedicar-
boxylate (R¼–NO2/–OH/–CH3) and N-donor ligands (L1¼1,4-bis
(imidazol-1-yl)benzene or L2¼1,4-bis(1-imidazol-yl)-2,5-dimethyl
benzene). With different substituted groups in the organic
ligands, five compounds exhibit five distinct framework structures.
(
lex¼331 nm) for 1, 415 nm (lex¼334 nm) for 2, 413 nm (lex¼329
nm) for 3, 410 nm (lex¼354 nm) for 4 and 408 nm (lex¼357 nm)
for 5. Because the Cd(II) ion is difficult to oxidize or reduce because of

48
F. Guo et al. / Journal of Solid State Chemistry 199 (2013) 42–48
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organic ligands can result in distinct framework topologies of
coordination polymers. It also provides a new approach toward
tuning structural topologies of coordination polymers through mod-
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Acknowledgment
We thank the support of this work by National Basic Research
Program of China (973 Programs 2011CB932504 and 2012-
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