Four cadmium(II) coordination polymers with an N- and O-donor ligand: Structural characterization, in situ reaction and fluorescent property

Article abstract of DOI:10.1016/j.poly.2013.01.038

Cadmium nitrate tetrahydrate reacts with 5-(1H-benzotriazol-1-ylmethyl) isophthalic acid (H₂L) under hydrothermal conditions to yield four complexes, [Cd(L¹)(py)₂(H₂O)] (1), [Cd(L)(DMF)(H₂O)] (2), [Cd(L)] (3) and [Cd(L)] (4) [L¹ = in situ generated 5-(2H-benzotriazol-2-ylmethyl)isophthalate, py = pyridine, DMF = N,N-dimethylformamide], which have been characterized by single crystal and powder X-ray diffraction, IR, elemental and thermogravimetric analyses. Complexes 1-4 exhibit structural diversity, which is dependent upon different experimental conditions. As a result, complex 1 has a chain structure, which can be further linked by hydrogen bonding and C-H?π interactions to form a 2D network structure; 2 displays a double-stranded chain structure and a 3D supramolecular framework can be built via hydrogen bonding and π-π stacking interactions; 3 and 4 are a pair of isomers: 3 is a binodal (3,6)-connected 2D kgd network with (4³)₂(4 ⁶·6⁶·8³) topology, while 4 displays a binodal (3,6)-connected 3D rtl (4·6²) ₂(4²·6¹⁰·8³) framework architecture. Significantly, an in situ rearrangement reaction of H ₂L to H₂L¹ occurs during the synthesis of 1. The influential factors of the synthetic strategies on the coordination modes of the ligand and the structures of resultant complexes are discussed. Furthermore, the fluorescent properties of 1-4 were preliminarily investigated.

Full text of DOI:10.1016/j.poly.2013.01.038

Polyhedron 53 (2013) 113–121
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Four cadmium(II) coordination polymers with an N- and O-donor ligand: Structural
characterization, in situ reaction and fluorescent property
⇑
Hai-Wei Kuai , Xiao-Chun Cheng, Xiao-Hong Zhu
Faculty of Life Science and Chemical Engineering, Huaiyin Institute of Technology, Huaian 223003, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Cadmium nitrate tetrahydrate reacts with 5-(1H-benzotriazol-1-ylmethyl)isophthalic acid (H2L) under
hydrothermal conditions to yield four complexes, [Cd(L1)(py)2(H2O)] (1), [Cd(L)(DMF)(H2O)] (2), [Cd(L)]
(3) and [Cd(L)] (4) [L1 = in situ generated 5-(2H-benzotriazol-2-ylmethyl)isophthalate, py = pyridine,
DMF = N,N-dimethylformamide], which have been characterized by single crystal and powder X-ray dif-
fraction, IR, elemental and thermogravimetric analyses. Complexes 1–4 exhibit structural diversity,
which is dependent upon different experimental conditions. As a result, complex 1 has a chain structure,
Received 24 November 2012
Accepted 8 January 2013
Available online 8 February 2013
Keywords:
Cadmium
Coordination polymers
Characterization
In-situ reaction
Fluorescence
which can be further linked by hydrogen bonding and C–HÁ Á Á
ture; 2 displays a double-stranded chain structure and a 3D supramolecular framework can be built via
hydrogen bonding and stacking interactions; 3 and 4 are a pair of isomers: 3 is a binodal (3,6)-con-
p interactions to form a 2D network struc-
p–p
nected 2D kgd network with (43)2(46Á66Á83) topology, while 4 displays a binodal (3,6)-connected 3D rtl
(4Á62)2(42Á610Á83) framework architecture. Significantly, an in situ rearrangement reaction of H2L to
H2L1 occurs during the synthesis of 1. The influential factors of the synthetic strategies on the coordina-
tion modes of the ligand and the structures of resultant complexes are discussed. Furthermore, the fluo-
rescent properties of 1–4 were preliminarily investigated.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
there is a vast domain of potentially multifunctional materials [6].
Among many influential factors, the intrinsic nature of the organic
In recent years, coordination supramolecular chemistry has
mainly been concerned with the design and assembly of crystalline
materials based on metal centers and bridging ligands, and conse-
quently, exploration of such hybrid materials with interesting prop-
erties and potential applications has been becoming the main aim
of crystal engineering of coordination chemistry [1]. It is known
that the functional properties of complexes are largely dependent
on the nature of the metal centers and bridging ligands, and their
architectures. For example, complexes with porous framework
architectures may show sorption or catalytic properties [2]; metal
ions possessing unpaired electrons, such as Mn(II), Co(II), Ni(II)
and Cu(II) etc., could be bridged by ligands to form polynuclear sub-
units which may mediate magnetic interactions [3]; moreover,
complexes containing metal centers with a d10 electron configura-
tion, such as Zn(II) and Cd(II), may exhibit luminescent properties
[4]. Therefore, it may be significant to pursue structural diversity
by attempting to use different experimental conditions, though it
is still a great challenge to assemble complexes with target struc-
tures because of complicated factors influencing the assembly pro-
cess [5]. However, the complexity of self-assembly may also give
access to composite polymers with novel functional properties as
ligands has been proven to play a decisive role in the formation of
complexes [7].
In previous research, rigid carboxylate ligands, such as iso-
phthalate, terephthalate and 1,3,5-benzetricarboxylate, have been
well studied in the syntheses of complexes due to their fine coor-
dinating capacities and appropriate connectivity [8]. Meanwhile,
benzotriazole and its benzene ring-substituted derivatives may in-
duce new coordination insight for structural evolution in crystal
engineering based on their steric hindrance and more potential
coordination sites [9]. However, the combination of both benzo-
triazolyl and carboxylate functional groups in a single organic
ligand remains less investigated. Recently, we have been focusing
our attention on the coordination reactions of metal salts with an
N- and O-donor ligand: 5-(1H-benzotriazol-1-ylmethyl)isophthalic
acid (H2L). Our main goals are to synthesize complexes with fasci-
nating structures and interesting properties and to seek for further
comprehension of the relationship between the experimental con-
ditions and the structures of the resultant complexes. The H2L
ligand has an advantage over other N- or O-donor ligands since it
possesses two functional groups, namely carboxylate and flexible
benzotriazol-1-ylmethyl groups. Due to the relative orientation
of the two carboxylate groups and their potential mutable
coordination patterns, such as l1
1-chelating and l2 1-bridging modes, H2L can act as a
– : g – :
g1 0-monodentate, l1 g1
⇑
Corresponding author. Tel./fax: +86 517 83559044.
E-mail address: hyitshy@126.com (H.-W. Kuai).
g
– : g
g1
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.01.038

114
H.-W. Kuai et al. / Polyhedron 53 (2013) 113–121
multi-connector in the assembly of complexes [10]. Furthermore,
the flexible benzotriazol-1-ylmethyl arm in H2L has more spatial
freedom to adopt different orientations [11], which originates from
its axial rotation to a different angle to satisfy coordinating
requirements. The potential variable coordination modes and con-
formations of H2L provide the feasibility to assemble complexes
with various structures by regulating the experimental conditions.
We report herein the syntheses and characterization of four new
coordination polymers, [Cd(L1)(py)2(H2O)] (1), [Cd(L)(DMF)(H2O)]
(2), [Cd(L)] (3) and [Cd(L)] (4) [py = pyridine, DMF = N,N-dimethyl-
formamide]. The fluorescence of 1–4 was also examined.
stainless steel container and heated at 210 °C for 72 h. The oven
was then turned off and cooled down naturally to ambient temper-
ature. After cooling to room temperature, colorless slender crystals
of 1 were obtained in an approximate yield of 20% based on H2L.
Anal. Calc. for C25H21N5O5Cd: C, 51.43; H, 3.63; N, 11.99. Found:
C, 51.16; H, 3.42; N, 11.79%. IR (KBr pellet, cmÀ1): 3422 (br, m),
1615 (s), 1603 (s), 1568 (s), 1552 (s), 1447 (s), 1376 (s), 1302
(w), 1275 (w), 1243 (m), 1220 (m), 1098 (m), 1071 (w), 1036
(w), 778 (m), 751 (s), 727 (s), 700 (s).
2.3. Synthesis of [Cd(L)(DMF)(H2O)] (2)
2. Experimental
The reaction mixture of Cd(NO3)2Á4H2O (61.8 mg, 0.2 mmol),
H2L (29.7 mg, 0.1 mmol) and 5 mL DMF in 5 mL H2O was sealed
in a 16 mL Teflon-lined stainless steel container and heated at
100 °C for 48 h. The oven was then cooled down at a rate of
10 °C/h. After cooling to room temperature, colorless plate crystals
of 2 were obtained in an approximate yield of 25% based on H2L.
Anal. Calc. for C18H18N4O6Cd: C, 43.35; H, 3.64; N, 11.23. Found:
C, 43.56; H, 3.52; N, 11.49%. IR (KBr pellet, cmÀ1): 3332 (br, m),
1646 (m), 1615 (m), 1556 (s), 1497 (m), 1454 (s), 1438 (s), 1372
(s), 1242 (m), 1219 (m), 1113 (m), 930 (w), 789 (m), 773 (s), 757
(s), 722 (s), 676 (m).
2.1. Materials and measurements
All commercially available chemicals and solvents are of
reagent grade and were used as received without further purifica-
tion. According to the reported literature [12], a similar experimen-
tal procedure was used to synthesize the H2L ligand. Elemental
analyses for C, H and N were performed on a Perkin-Elmer 240C
elemental analyzer. Thermogravimetric analyses (TGA) were per-
formed on a simultaneous SDT 2960 thermal analyzer under nitro-
gen with a heating rate of 10 °C minÀ1. FT-IR spectra were recorded
in the range 400–4000 cmÀ1 on a Bruker Vector22 FT-IR spectro-
photometer using KBr pellets. Powder X-ray diffraction (PXRD)
patterns were obtained on a Shimadzu XRD-6000 X-ray diffrac-
tometer with Cu Ka (k = 1.5418 Å) radiation at room temperature.
2.4. Synthesis of [Cd(L)] (3)
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 emis-
sion and excitation spectra the pass width was 5 nm, and all the
measurements were carried out under the same experimental
conditions.
The reaction mixture of Cd(NO3)2Á4H2O (61.8 mg, 0.2 mmol),
H2L (29.7 mg, 0.1 mmol) and KOH (11.2 mg, 0.2 mmol) in 10 mL
H2O was sealed in a 16 mL Teflon-lined stainless steel container
and heated at 180 °C for 72 h. The oven was then turned off and
cooled down naturally to ambient temperature. After cooling to
room temperature, colorless needle crystals of 3 were obtained
in an approximate yield of 20% based on H2L. Anal. Calc. for C15H9-
N3O4Cd: C, 44.19; H, 2.23; N, 10.31. Found: C, 44.46; H, 2.44; N,
10.52%. IR (KBr pellet, cmÀ1): 1616 (s), 1561 (s), 1457 (s), 1386
(s), 1314 (w), 1290 (w), 1243 (w), 1227 (m), 1171 (w), 808 (w),
783 (m), 768 (s), 744 (s), 728 (s), 593 (w).
2.2. Synthesis of [Cd(L1)(py)2(H2O)] (1)
A solution of Cd(NO3)2Á4H2O (61.8 mg, 0.2 mmol) and H2L
(29.7 mg, 0.1 mmol) in pyridine/H2O (2:8, 10 mL) was stirred for
30 min. Then reaction mixture was placed in a 16 mL Teflon-lined
Table 1
Crystal data and structure refinements for complexes 1–4.
Compound
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
25H21N5O5Cd
C18H18N4O6Cd
498.76
triclinic
C15H9N3O4Cd
407.65
monoclinic
P21/c
8.439(5)
11.404(5)
17.255(5)
90.00
119.279(17)
90.00
C15H9N3O4Cd
407.65
monoclinic
P21/c
11.3010(6)
9.1272(5)
16.8393(7)
90.00
127.069(3)
90.00
583.87
monoclinic
P21/c
15.5435(10)
10.3174(7)
17.9635(9)
90.00
119.374(4)
90.00
ꢀ
P1
9.7945(3)
10.4765(3)
11.3523(4)
73.84
65.96
64.10
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
T (K)
293(2)
2510.4(3)
4
1.545
0.915
293(2)
949.82(5)
2
1.744
1.194
293(2)
1448.4(11)
4
1.869
1.532
293(2)
1385.90(12)
4
1.954
1.601
V (Å3)
Z
Dcalc (g cmÀ3
)
l
(mmÀ1
)
F(000)
1176
500
800
800
h (°)
1.50–28.32
17748
6243
1.025
0.0541, 0.1351
0.0688, 0.1368
2.18–28.24
6794
4606
1.090
0.0187, 0.0499
0.0193, 0.0502
2.24–28.35
10220
3608
1.006
0.0273, 0.0688
0.0322, 0.0709
2.26–28.33
9683
3452
1.062
0.0386, 0.1047
0.0436, 0.1083
Reflections collected
Unique reflections
Goodness-of-fit (GOF) F2
R1a, wR2 [I > 2
r(I)]
b
R1, wR2 (all data)
a
R1
wR2 = |
=
R
||Fo| À |Fc||/
R|Fo|.
b
R
w(|Fo|2 À |Fc|2)|/
R
|w(Fo)2|1/2, where w = 1/[2(Fo2) + (aP)2 + bP]. P = (Fo2 + 2Fc2)/3.

H.-W. Kuai et al. / Polyhedron 53 (2013) 113–121
115
Scheme 3. The proposed mechanism of the rearrangement reaction of the
(L1)2À ligand in complex 1.
Scheme 1. Schematic representation of the hydrothermal syntheses of complexes
1–4.
structures were 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 [15]. In 1–4, all hydrogen atoms bonded to C were gener-
ated geometrically; hydrogen atoms in the water molecules in 1
and 2 were found at reasonable positions in the difference Fourier
maps and located there. The details of crystal parameters, data col-
lection and refinements for the complexes are summarized in Table
1; selected bond lengths and angles are listed in Table S1; hydrogen
bonds in 1 and 2 are listed in Table S2.
3. Results and discussion
3.1. Preparation
As is shown in Scheme 1, the hydrothermal reactions of a stoi-
chiometric amount of cadmium nitrate tetrahydrate with H2L un-
der different experimental conditions provided single crystalline
materials of 1–4, which are stable in air. The ligand H2L/H2L1
exhibits varied coordination modes as observed in complexes
1–4 (Scheme 2). The crystal structures of 1–4 are discussed in de-
tail in the following sections.
3.2. Crystal structural description of [Cd(L1)(py)2(H2O)] (1)
Scheme 2. Coordination modes of the ligands in complexes 1–4.
It is noteworthy that the rearrangement of H2L to H2L1 (vide su-
pra) occurred in the formation of 1. As shown in Scheme 3, the
rearrangement reaction takes places under alkaline conditions, as
reported previously [16]. Considering the synthetic conditions of
complexes 1–4, a high concentration of hydroxyl may be crucial
for the occurrence of the rearrangement. The complete deprotona-
tion of the in situ generate H2L1 ligand could be further confirmed
by IR spectroscopy because of no characteristic vibration band in
the range 1680–1760 cmÀ1 was observed.
Crystallographic analysis reveals that complex 1 exhibits a
chain structure with the asymmetric unit containing one Cd(II)
center, one (L1)2À ligand, two coordinated pyridine molecules
and one coordinated water molecule. As shown in Fig. 1a, each
Cd(II) center is seven-coordinated with a distorted pentagonal
bipyramidal geometry by two N atoms (N21, N31) from two coor-
dinated pyridine molecules, with Cd–N bond distances of 2.352(4)
and 2.323(4) Å, and five O atoms from two carboxylate groups and
one coordinated water molecule, with Cd–O bond lengths in the
range 2.314(3) to 2.566(3) Å. The Cd–O and Cd–N bond distances
are comparable to previously reported values for Cd(II) complexes.
The coordinating bond angles around Cd(II) vary from 51.91(10)°
to 176.13(12)° (Table S1). Both carboxylate groups in the
2.5. Synthesis of [Cd(L)] (4)
Complex 4 was synthesized by the same hydrothermal proce-
dure as that used for the preparation of 3, except raising the reac-
tion temperature to 210 °C. Colorless block crystals of 4 were
obtained in an approximate yield of 20% based on H2L. Anal. Calc.
for C15H9N3O4Cd: C, 44.19; H, 2.23; N, 10.31. Found: C, 44.36; H,
2.07; N, 11.12%. IR (KBr pellet, cmÀ1): 1618 (s), 1552 (s), 1497
(m), 1455 (s), 1430 (w), 1380 (s), 1356 (m), 1282 (m), 1250 (w),
1219 (m), 1170 (m), 804 (m), 780 (m), 765 (s), 740 (s), 722 (s),
596 (m).
2.6. X-ray crystallography
The crystallographic data collections for complexes 1–4 were
carried out on a Bruker Smart Apex CCD area-detector diffractome-
ter using graphite-monochromated Mo Ka radiation (k = 0.71073 Å)
at 293(2) K. The diffraction data were integrated by using the SAINT
program [13], which was also used for the intensity corrections
for the Lorentz and polarization effects. A semi-empirical absorp-
tion correction was applied using the SADABS program [14]. The

116
H.-W. Kuai et al. / Polyhedron 53 (2013) 113–121
Fig. 1. (a) The coordination environment of the Cd(II) ions in 1 with the ellipsoids drawn at the 30% probability level. The hydrogen atoms are omitted for clarity. (b) The 1D
structure of 1. (c) The double-chain structure in 1 extended by hydrogen bonding interactions. (d) The 2D network of 1 extended by hydrogen bonding and C–HÁ Á Á
p stacking
interactions.
(L1)2À ligand adopt l1
–
g1
:
g
1-chelating coordination modes
(Fig. 1b). Moreover, hydrogen bonding and C–HÁ Á Á
p interactions
(Scheme 2A), exhibiting almost identical C–O bond lengths,
consistent with electron delocalization, and with the angles sub-
tended at cadmium being 51.91(10)° and 53.61(10)°, respectively.
The in situ generated benzotriazol-2-ylmethyl group is free of
are available in 1 to arrange the molecular building blocks, which
are very important for the construction and stabilization of the
resultant molecular structure: (1) O(5)–H(20)Á Á ÁO(3)#1 [#1:
1 À x, 1Ày, 2 À z; O(5)Á Á ÁO(3)#1 = 2.731(5) Å; \O(5)–H(20)–
O(3)#1 = 139°], hydrogen bonding interactions between H atoms
in water molecules and carboxylate O atoms from adjacent chains
(Table S2). The hydrogen bonding interactions link the adjacent
chains to form a double-chain structure (Fig. 1c). (2) Stacking
coordination. Therefore, each (L1)2À ligand acts as a
l2-bridge to
link two Cd(II) atoms; meanwhile each metal atom is surrounded
by two different (L1)2À ligands. This interconnection repeats infi-
nitely to give rise to a chain structure along the [100] direction

H.-W. Kuai et al. / Polyhedron 53 (2013) 113–121
117
Fig. 2. (a) The coordination environment of the Cd(II) ions in 2 with the ellipsoids drawn at the 30% probability level. The hydrogen atoms are omitted for clarity. (b) The
neutral double-stranded chain of 2. (c) Schematic view of the right- and left-handed helical chains in 2. (d) The 2D network of 2 extended by hydrogen bonding interactions.
(e) The 3D framework of 2 constructed through hydrogen bonding and p–p stacking interactions.
interactions between C24–H12 and the central benzene ring (sym-
metry code: Àx, À1/2 + y, 3/2Àz; the distance between H12 and the
centroid of the central benzene ring plane is 2.643 Å), and then
adjacent double-stranded chains can be further linked to yield a
L2À ligands to furnish a distorted octahedral coordination geome-
try. The DMF oxygen atom and the benzotriazolyl nitrogen atom
occupy the apices and the other four oxygen atoms are located in
the equatorial plane. The coordinating bond lengths vary from
2.2148(11) to 2.3921(13) Å and the coordinating bond angles are
in the range 56.37(4)° to 172.13(5)°. One of carboxylate groups
2D supramolecular network by taking the C–HÁ Á Á
p stacking inter-
actions into account (Fig. 1d).
in the L2À ligand exhibits the l1 0-monodentate coordination
–
g1
:
g
3.3. Crystal structural description of [Cd(L)(DMF)(H2O)] (2)
mode, and the other is a l2– : g
g1 1-chelating one (Scheme 2B). As
depicted in Fig. 2b, each L2À ligand bridges three Cd(II) centers to
construct a double-stranded chain structure with a nearest intra-
chain CdÁ Á ÁCd distance of 9.543 Å. Interestingly, because of the
flexibility of the L2À ligand, the double-chain extends along the
[100] direction in a spiral way. If some organic moieties are
ignored, a pair of right- and left-handed helical chains could be
isolated from the neutral double-stranded chain (Fig. 2c). Each
Complex 2 exhibits a double-stranded chain structure. There
are one Cd(II), one L2À ligand, one coordinated DMF and one coor-
dinated water molecule in the asymmetric unit of 2. As shown in
Fig. 2a, each Cd(II) center is six-coordinated by one benzotriazolyl
nitrogen atom, one coordinated DMF, one coordinated water oxy-
gen atom and three carboxylate oxygen atoms from two different

118
H.-W. Kuai et al. / Polyhedron 53 (2013) 113–121
Fig. 3. (a) The coordination environment of the Cd(II) ions in 3 with the ellipsoids drawn at the 30% probability level. The hydrogen atoms are omitted for clarity. (b) View of
secondary building unit SBU [Cd2(COO)2] in 3. (c) View of the 2D network of 3. (d) View of nodes representing the SBU and the L2À ligand in 3. (e) View of the binodal (3,6)-
connected 2D kgd network of 3.
chain is interlinked to form a supramolecular layer motif via
hydrogen-bonding interactions between water molecules and
carboxylate oxygen atoms (Fig. 2d, Table S2). Another structural
feature in 2 is that the adjacent layers recognize each other
through strong offset p–p stacking interactions, ultimately leading
to a 3D supramolecular framework (Fig. 2e). The centroid–centroid
coordinating bond angles are in the range 56.24(7)° to
157.02(7)°. The carboxylate groups in L2À adopt l1 0-mono-
dentate and l2
1-bridging coordination modes, resulting in
–
g1
: g
–
g1
: g
the formation of the carboxylate-bridged binuclear secondary
building unit (SBU) [Cd2(COO)2] with a CdÁ Á ÁCd distance of 3.84 Å
(Fig. 1a), which is shorter than the sum of two van der Waals radii
(4.60 Å) [17]. In 3, each L2À ligand links three SBUs; each SBU is
surrounded by six L2À ligands. This kind of connection proceeds
infinitely to generate a 2D network structure (Fig. 3c). If using
topology to analyze the structure, each SBU could be regarded as
a 6-connector node and the L2À ligand as a 3-connector node
(Fig. 3d), and thus the resultant structure of 3 could be simplified
as a binodal (3,6)-connected 2D kgd network with (43)2(46Á66Á83)
topology (Fig. 3e) [18].
distance between the central benzene rings is 3.643 Å.
3.4. Crystal structural description of [Cd(L)] (3)
Complex 3 shows a 2D network structure based on Cd(II) and
the L2À ligand. The asymmetrical unit is composed of one Cd(II)
ion and one L2À ligand. In complex 3, each Cd(II) center is tetraco-
ordinated by one benzotriazolyl N atom and four carboxylate O
atoms from three different L2À ligands to furnish a distorted tetrag-
onal pyramid coordination geometry (Fig. 3a). The best equatorial
plane is defined by the O1, O2, O3 and O4 atoms from three
L2À ligands, and the metal is deviated by 0.497 Å toward N13 from
the mean plane. The axial positions are occupied by one benzo-
triazolyl nitrogen atom (N13) from another L2À ligand. The coordi-
nating bond lengths vary from 2.1747(17) to 2.3273(18) Å; the
3.5. Crystal structure description of [Cd(L)] (4)
Complexes 3 and 4 are a pair of isomers. The asymmetric unit of
4 is also composed of one Cd(II) and one L2À ligand. As shown in
Fig. 4a, each metal atom is coordinated by one benzotriazolyl nitro-
gen atom and five carboxylate oxygen atoms from three

H.-W. Kuai et al. / Polyhedron 53 (2013) 113–121
119
Fig. 4. (a) The coordination environment of the Cd(II) ions in 4 with the ellipsoids drawn at the 30% probability level. The hydrogen atoms are omitted for clarity. (b) View of
SBU [Cd2(COO)2] in 4. (c) View of the 2D network in 4. (d) View of the 3D framework of 4. (e) View of nodes representing the SBU and the L2À ligand in 4. (f) View of the
binodal (3,6)-connected 3D rtl framework architecture of 4.
L2À ligands, with a Cd–N bond length of 2.275(4) Å and an average
Cd–O distance of 2.342 Å. The bond angles around the Cd(II) atom
are in the range 54.97(9)° to 150.68(10)°, and thus the Cd(II) atom
displays a distorted octahedral coordination geometry with the
[NO5] donors set. The coordination mode of the L2À ligand in 4
benzotriazolyl groups (Fig. 4c). Topological analysis can be used
for a better comprehension of the structural features. Each SBU
can be viewed as a 6-connected node and each L2À ligand can be
considered as a 3-connector bridge (Fig. 4e). According to the rules
of simplification, the 3D architecture of 4 can be simplified as a
binodal (3,6)-connected rtl framework with (4Á62)2(42Á610Á83)
topology (Fig. 4f).
can be described as follows: one carboxylate adopts a l2
1-chelating/bridging coordination mode, resulting in the forma-
– :
g2
g
tion of the carboxylate-bridged binuclear secondary building unit
(SBU) [Cd2(COO)2], with a CdÁ Á ÁCd distance of 3.84 Å (Fig. 4b);
3.6. Coordination modes of the H2L ligand and structural comparisons
of 1–4
the other carboxylate shows the l1
–
g1
:g
1-chelating mode; each
benzotriazolyl group is bound to a Cd(II) ion. So the L2À ligand dis-
plays a l4
–
g2
:
g1
–
g1
:
g1
–
g1 mode to bridge four different metal
All the carboxylate groups of L2À/(L1)2À in the four complexes
are found to be completely deprotonated and involved in coordina-
tion. The carboxylate coordination modes of the ligands in com-
atoms. Each Cd(II) center is also surrounded by four different L2À
ligands. The interconnections of metals and ligands repeat infi-
nitely to yield a 3D framework architecture (Fig. 4d), within which
2D networks can be isolated with the free-of-coordination
plexes 1–4 are different from each other, that is l2
1, and l3 1, respectively
– : : : ,
g1 g1 g1 g1
l2–
g1
:
g1
:
g1
:
g0
,
l3–
g1
:
g1
:
g1
:g
– : : :g
g2 g1 g1

120
H.-W. Kuai et al. / Polyhedron 53 (2013) 113–121
(Scheme 2). As for the flexible benzotriazolylmethyl group, it
undergoes an in situ rearrangement reaction in 1, emerging as
the 2H-benzotriazol-2-ylmethyl group and being free of coordina-
tion. In 2–4, the bidentate N-donor group just coordinates to a
single metal atom. The L2À/(L1)2À ligands exhibit a variety of coor-
dination modes in 1–4, which demonstrates influential factors of
the synthetic strategies on the coordination modes of the ligands.
The Cd(II) centers in 1–4 are seven-, six-, five- and five-coordi-
nated, respectively. As a result, complexes 1–4 exhibit different
structures: 1 and 2 are 1D structures; 3 displays a 2D network
structure; 4 shows a 3D framework architecture. The results show
that the synthetic strategies can efficiently influence the coordina-
tion modes of the ligand and the structures of the resultant com-
plexes. Certainly, the potential variable coordination modes and
conformations of H2L provide the feasibility to assemble com-
plexes with various structures by adjusting the experimental
conditions.
4. Conclusion
A carboxylate and benzotriazolyl-containing ligand, 5-(1H-ben-
zotriazol-1-ylmethyl)isophthalic acid (H2L), was selected as an or-
ganic block which can display potential variable coordination
modes. Hydrothermal reactions of the H2L ligand with a Cd(II) salt
under different experimental conditions provide four complexes
with different structures, varying from 1D to 3D, whilst the L2À li-
gand in the complexes is found to show a variety of coordination
modes. Moreover, an in situ rearrangement reaction of H2L to
H2L1 occurs during the synthesis of complex 1. The results might
illustrate the aesthetic diversity of coordinative supramolecular
chemistry, although more investigations are needed to understand
the essential reasons for this difference. As expected, these cad-
mium polymers exhibit strong luminescent emissions.
Acknowledgment
The authors gratefully acknowledge Huaian Administration of
Science & Technology of Jiangsu Province of China (HAG2012022)
for financial support of this work.
3.7. Thermal stabilities and PXRD of complexes 1–4
The phase purity of 1–4 could be proved by powder X-ray dif-
fraction (PXRD) analyses. As shown in Fig. S1, each pattern of the
bulk sample was in agreement with the simulated pattern from
the corresponding single crystal data.
Appendix A. Supplementary material
CCDC 910152–910154 and 893793 contains the supplementary
crystallographic data for 1–4. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail: 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.2013.01.038.
Thermogravimetric analyses (TGA) were carried out for com-
plexes 1–4, and the results are shown in Fig. S2. Complex 1 shows
a weight loss of 3.26% from 96 to 120 °C, corresponding to the re-
lease of coordinated water molecules (calcd 3.08%), and a continu-
ous weight loss starting at 167 °C could be assigned to the
liberation of pyridine molecules, accompanied by the subsequent
decomposition of the framework. For 2, a weight loss of 3.33%
was found between 92 and 140 °C due to the release of water mol-
ecules (calcd 3.61%), and a weight loss of 14.36% in the tempera-
ture range 210–273 °C corresponds to the liberation of
coordinated DMF molecules (calcd 14.65%). The decomposition
temperature of 2 is 363 °C. As for 3 and 4, no obvious weight loss
can be observed before the decomposition of the frameworks oc-
curred at 406 °C for 3 and 455 °C for 4.
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