The nature of the metal ions influenced formation of coordination polymers based on asymmetric semi-rigid 3-(4-carboxyphenoxy)phthalic acid with N-heterocyclic ligands

Article abstract of DOI:10.1016/j.ica.2013.01.037

Three new coordination complexes, namely [Cd(HL)(μ-bpp)(H ₂O)]_n·(H₂O)_n (1), [Co(HL)(μ-bpp)]_n·(H₂O)_n (2), and [Ag₂(L)_2/3(μ-bpp)]_n (3) [H₃L = 3-(4-carboxyphenoxy)phthalic acid and bpp = 1,3-bis(4-pyridyl)propane], have been successfully synthesized by using H₃L and accessory bridging ligand. The predominant influence in 1-3 may be the nature of different metal ions, which result in the complexes assembling into supramolecular frameworks with different topological nets. Structural analysis reveals that the structure of 1 can be described as a 2D network with Point (Scha?lfli) symbol for net: {6⁶} topology. Complex 2 shows the similar 2D 4⁴ grid-like layers by the intermolecular hydrogen bonds, whereas dinuclear Ag(I) clusters in 3 act as coordination nodes, forming a sandwich-like 2D structure. In addition, the magnetic behavior of 2 was also studied.

Full text of DOI:10.1016/j.ica.2013.01.037

Inorganica Chimica Acta 400 (2013) 7–12
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
The nature of the metal ions influenced formation of coordination polymers
based on asymmetric semi-rigid 3-(4-carboxyphenoxy)phthalic acid with
N-heterocyclic ligands
Jun Chen a, Guo-Ping Yang a, Wen-Huan Huang a, Ling-Yan Pang a, Cui-Ping Zhang b, Yao-Yu Wang a,
,
⇑
Qi-Zhen Shi a
a Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, College of Chemistry
& Materials Science, Northwest University, Xi’an 710069, PR China
b The Affiliated Hospital of Medical College, Qingdao University, Qingdao 266003, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 October 2012
Received in revised form 19 December 2012
Accepted 20 January 2013
Available online 13 February 2013
Three new coordination complexes, namely [Cd(HL)(
(2), and [Ag2(L)2/3(l-bpp)]n (3) [H3L = 3-(4-carboxyphenoxy)phthalic acid and bpp = 1,3-bis(4-pyri-
l
-bpp)(H2O)]nÁ(H2O)n (1), [Co(HL)( -bpp)]nÁ(H2O)n
l
dyl)propane], have been successfully synthesized by using H3L and accessory bridging ligand. The pre-
dominant influence in 1–3 may be the nature of different metal ions, which result in the complexes
assembling into supramolecular frameworks with different topological nets. Structural analysis reveals
that the structure of 1 can be described as a 2D network with Point (Schälfli) symbol for net: {66} topol-
ogy. Complex 2 shows the similar 2D 44 grid-like layers by the intermolecular hydrogen bonds, whereas
dinuclear Ag(I) clusters in 3 act as coordination nodes, forming a sandwich-like 2D structure. In addition,
the magnetic behavior of 2 was also studied.
Keywords:
Coordination polymers
Metal ions
Helix
Hydrogen bonding
Topology
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
value in crystalline MOFs [12–14]. It is a good choice to construct
various complexes by using mixed ligands. Many types of bridging
Recently, the construction of coordination polymers using or-
ganic ligands and transition metals, has attracted increasing atten-
tion from chemists, not only for their intriguing variety of
architectures and topologies but also due to their potential applica-
tion in industry [1–4]. Crystalline metal–organic frameworks
(MOFs) has proven that aromatic carboxylic acids and pyridine
derivatives are widely used for constructing various structural
and topological coordination polymers [5–9]. In these complexes,
high-dimensional structures usually possess stable 3D framework
by coordination bond. In contrast, the 3D supramolecular struc-
tures of low-dimensional frameworks are sustained by weak inter-
ligands have been extensively used for the construction of diverse
multidimensional architectures [15–17], as seen in Scheme 1 in
this paper. The asymmetric semi-rigid V-shaped 3-(4-carboxy-
phenoxy)phthalic acid (H3L) ligand is considered to be a potential
candidate as a linker to produce versatile coordination polymers
with fascinating architectures. Firstly, two benzene rings of H3L
can rotate freely around the –O– groups with different angles to
meet the requirement of the coordination geometries of the metal
ions [18,19]. Furthermore, H3L is seen as bridging ligand that have
also been used to expand the dimension of coordination polymer.
Jiang and co-workers have reported a large family of the asymmet-
ric semi-rigid V-shaped 3-(4-carboxyphenoxy)phthalic acid with
N-donor co-ligands that led to a series of (1D ? 3D) coordination
polymers with the general formula, [M(H3L)(bpy)] (M = Co(II),
Ni(II), and Cd(II)) [20–24]. However, it has been seldom reported
that under the same reaction condition, the nature of metal ions
lead to varieties of final structures of complexes. In this work, at
the same hydrothermal condition (H2O/145 °C/pH = 6.5), we com-
bine H3L ligand and pyridine derivant co-ligand (bpp = 1,3-bis
(4-pyridyl)propane) with different transition metals, to construct
three complexes with different 1D–2D frameworks [Cd(HL)
actions such as hydrogen-bonding,
p–p stacking, and van der
Waals interactions. In the previous study, it is found that low
dimensional complexes also can show good selective adsorption
and separate applications [10,11].
How to control dimension of the resultant complex with selec-
tive synthesis is still a challenge. It has been proven that the resul-
tant structures can be changed by solvent, temperature and pH
⇑
Corresponding author. Tel.: +86 29 88303097; fax: +86 29 88303798.
E-mail address: wyaoyu@nwu.edu.cn (Y.-Y. Wang).
(l
-bpp)(H2O)]nÁ(H2O)n (1), [Co(HL)( -bpp)]nÁ(H2O)n (2), and
l
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.01.037

8
J. Chen et al. / Inorganica Chimica Acta 400 (2013) 7–12
COOH
HOOC
O
N
N
COOH
3-(4-carboxyphenoxy)phthalic Acid (H3L)
1,3-bis(4-pyridyl)propane (bpp)
Scheme 1. Molecular structures of N-heterocyclic ligand and H3L ligand.
[Ag2(L)2/3
also been probed.
(
l
-bpp)]n (3). Moreover, the magnetic properties of 2 has
and other pertinent information for the complexes are listed in Ta-
ble 1 and Tables S1 and S2. Crystallographic data for the structural
analysis have been deposited with the Cambridge Crystallographic
Data Centre. CCDC reference numbers: 901988 for 1, 874962 for 2
and 874966 for 3.
2. Experimental
2.1. Materials and physical measurements
2.3. General synthesis procedure for complexes 1–3
All reagents used in the syntheses were of analytical grade. All
other starting materials were commercially available and used
without further purification. Elemental analyses were recorded on
a Perkin–Elmer model 240C instrument [25]. IR spectra were re-
corded by a Perkin–Elmer Spectrum One spectrometer in the region
4000–400 cmÀ1 using KBr pellets. Thermal Gravimetric Analysis
(TGA) were performed on a NETZSCH STA 449C microanalyzer un-
der a flowing N2 atmosphere at a heating rate of 10 °C minÀ1. Vari-
able-temperature magnetic susceptibility measurements were
performed on a Quantum Design MPMS SQUID magnetometer
[26]. The experimental susceptibilities were corrected for the dia-
magnetism of the constituent atoms (Pascal’s tables).
The target complexes were obtained by utilizing the hydrother-
mal method with the same stoichiometric ratio for the starting
materials. A Teflon-lined stainless steel container (25 mL) was em-
ployed as a reaction vessel containing all starting materials, which
was heated to an appropriate temperature (145 °C) and held for
72 h, then cooled to 50 °C at a descent rate of 10 °C hÀ1. Finally,
the oven was cut off and kept for another 10 h, and perfect crystals
were isolated with a high yield based on the metals.
2.4. Synthesis of [Cd(HL)(
l
-bpp)(H2O)]nÁ(H2O)n (1)
The mixture of Cd(CH3COO)2Á2H2O (0.0266 g, 0.1 mmol), H3L
(0.0302 g, 0.1 mmol) and bpp (0.0198 g, 0.1 mmol) was dissolved
in 10 mL of distilled water. The pH value was then adjusted to
6.5 with 1 M NaOH solution and the resulting mixture was trans-
ferred and sealed in a 25 mL Teflon-lined stainless steel vessel. This
was then heated at 145 °C for 4 days and cooled to room tempera-
ture at 10 °C hÀ1. Colorless crystals of 1 were collected in 46% yield
(based on Cd). Elemental Anal. Calc. for C28H25CdN2O9: C, 63.04; H,
4.72; N 5.25. Found: C, 62.59; H, 4.36; N 5.73%. IR (KBr, cmÀ1):
3446 s, 1608 w, 1543 m, 1387 s, 1240 s, 1151 m, 1019 w, 880 w,
767 w, 702 w, 513 w.
2.2. X-ray crystallography materials
Single crystal X-ray diffraction data of the three complexes were
collected on a Bruker SMART APEX II CCD diffractometer equipped
with a graphite monochromated Mo-Ka radiation (k = 0.71073 Å) at
room temperature. All structures were solved by direct methods
and refined by full-matrix least squares fitting on F2 by SHELX-97
[27]. Absorption corrections were applied using SADABS. All of the
non-hydrogen atoms were refined anisotropically. The hydrogen
atoms of the organic ligands were placed in calculated positions
and refined with a riding model [28]. The crystallographic data
2.5. Synthesis of [Co(HL)(
l
-bpp)]nÁ(H2O)n (2)
Table 1
The synthesis procedure of 2 is similar to that for 1, except
Cd(CH3COO)2Á2H2O (0.0266 g, 0.1 mmol) was replaced by
Co(CH3COO)2 Á4H2O (0.0249 g, 0.1 mmol). Violet crystals of 2 were
collected in 58% yield (based on Co). Elemental Anal. Calc. for
Crystal data and structure refinement for 1–3.
Complex No.
Formula
1
2
3
C
28H25CdN2O9
C28H26CoN2O9
593.44
triclinic
C41H35Ag2N4O7
911.47
monoclinic
P21/n
16.9556(15)
9.0102(8)
24.685(2)
90
106.846(2)
90
3609.4(5)
4
1.677
1.144
1836
0.0740
0.1883
1.180
FW (g molÀ1
System
Space group
a (Å)
)
645.90
monoclinic
C2/c
26.164(4)
9.2330(15)
23.666(4)
90
108.410(3)
90
5424.3(15)
8
1.582
0.863
2616
0.0662
0.1560
1.078
C
28H26CoN2O9: C, 56.67; H, 4.41; N, 4.72. Found: C, 56.57; H,
4.47; N, 4.83%. IR (KBr, cmÀ1): 3438 (s), 3082 (w), 2936 (w),
2864 (w), 2599 (w), 2469 (w), 1689 (m), 1591 (s), 1495 (m),
1389 (s), 1236 (s), 1164 (m), 835 (w), 777 (s), 519 (w), 487 (m).
ꢀ
P1
10.9809(13)
11.7784(13)
12.1259(14)
63.892(2)
83.120(2)
77.689(2)
1375.3(3)
2
1.433
0.681
614
0.0759
b (Å)
c (Å)
a
(o)
b (o)
2.6. Synthesis of [Ag2(L)2/3(l-bpp)]n (3)
c
(o)
V (Å3)
The synthesis procedure of 3 is also similar to that for 1, except
Cd(CH3COO)2Á2H2O (0.0266 g, 0.1 mmol) was replaced by
Ag(CH3COO) (0.0167 g, 0.1 mmol). Colorless crystals of 3 were
collected in a 39% yield (based on Ag). Elemental Anal. Calc. for
Z
Dcalc (g cmÀ3
)
l
(mmÀ1
)
F(000)
a
R1 [I > 2h]
C
41H35Ag2N4O7: C, 54.53; H, 3.87; N, 6.55. Found: C, 54.66; H,
b
3.83; N, 6.63%. IR (KBr, cmÀ1): 3437 (s), 3067 (w), 2925 (m),
2855 (w), 1605 (s), 1504 (m), 1426 (w), 1372 (s), 1238 (s), 1160
(w), 1067 (w), 1028 (w), 856 (w), 817 (m), 770 (m), 692 (w), 574
(w), 512 (m).
wR2 [I > 2h]
0.1781
1.053
Goodness-of-fit (GOF)
P
P
a
R1
=
||F0| À |Fc||/ |F0|.
P
P
b
2
wR2 = { [w(F0 À Fc2)2]/ (F02)2}1/2
.

J. Chen et al. / Inorganica Chimica Acta 400 (2013) 7–12
9
further connected together by Cd(II) ions and HL2À ligands [30].
At the end of this paragraph, it is worth noting that the structure
of 1 supports the fact that these helical chains construct two-
dimensional layer through the connections of the bpp ligands in
ab plane (Fig. 1b), and array in the alternation of left- and right-
handed helixes (Fig. 1c). From the topological view, H3L ligand
and N-auxiliary ligand can be considered as 2-connected nodes
(green, blue), and the Cd(II) centre can be considered as 4-con-
nected nodes (violet), the bpp ligand is simplified as a linker be-
tween the metal centres and the structure of 1 can be described
as a 2D network with Point (Schälfli) symbol for net: {66} topology
(Fig. 1d).
3. Results and discussion
3.1. Structural descriptions
3.1.1. [Cd(HL)(l-bpp)(H2O)]nÁ(H2O)n (1)
The skeleton structure of 1 is shown in Fig. 1a. The asymmetric
unit contains one Cd(II) ion, one HL2À ligand, one bpp ligand, one
coordinated water molecule and one free water molecule. Each
Cd(II) ion adopts a seven-coordinate environment, which is coordi-
nated by two nitrogen atoms from two bpp ligands (Cd1–
N1 = 2.348(6) and Cd1–N2 = 2.309(6) Å), four oxygen atoms from
two chelating carboxylate group (Cd1–O1 = 2.359(5), Cd1–O2 =
2.497(5) Å, Cd1–O3 = 2.441(5) Å, and Cd1–O4 = 2.386(5) Å) and
one coordinated water molecule (Cd1–O5 = 2.459(5) Å). If the bpp
ligand is neglected, each partly deprotonated HL2À anion acts a l2
bridging ligand, linking two Cd(II) ions [29]. The neighboring Cd(II)
ions are linked by bpp ligands with the average distance of
13.278 Å, generating an infinitely 1D helical chain. On the basis of
this conductive way, these neighboring 1D helical chains are
3.1.2. [Co(HL)(
l
-bpp)]nÁ(H2O)n (2)
The asymmetric unit of 2 consists of one Co(II), one bpp, one
HL2À ligand and one lattice-water molecule (Fig. 2a). Co atom re-
veals a distorted tetrahedral geometry with two O atoms from car-
boxyl groups [Co–O, 1.957(4) and 1.960(4) Å] and two N atoms
from the terminal bpp ligand [Co–N, 2.053(5) and 2.061(5) Å]. It
Fig. 1. (a) ORTEP representation (30% thermal probability ellipsoids) of the structure of 1. Hydrogen atoms and guest molecules are omitted for clarity. (b) A 2D network
formed through bpp ligands in 1. (c) The alternation of left- and right-handed helixes. (d) Topological view showing the equivalent 2D framework with Point (Schälfli) symbol
for net: {66}.

10
J. Chen et al. / Inorganica Chimica Acta 400 (2013) 7–12
Fig. 2. (a) ORTEP of molecular structure of 2 (30% thermal probability ellipsoids). (b) The 2D 44-sql layer of 2. Hydrogen bonds are shown as dashed lines. Hydrogen atoms and
the lattice waters are omitted for clarity. (c) Schematic view of the (4,4)-connected topological structure. (d) 3D supramolecular structure via hydrogen bonds with free water.
is worth noting that the individual novel chains are connected into
a 3D intricate network via hydrogen bonding interactions. There
are abundant hydrogen-bond donors (free water molecules) and
hydrogen-bond acceptors (deprotonated carboxyl groups and
undeprotoned carboxylic groups) to construct a hydrogen bond
network (Table S2). The repeated [bpp–M–(HL)] units extend along
the b axis to be a 1D chain. The individual chains generate a 2D
honeycomb-like layered structure with small windows formed
via weak intermolecular hydrogen bonding interactions (2.601(7)
Å). (Fig. 2b). Tubular channels are observed in 2 and possess a void
volume (5.5%) per unit cell by PLATON analysis [31,32], which are
occupied by the intercalated water. Furthermore, there are some
other weak hydrogen bonding interactions between the 2D layers
[33,34]. The two dimensional structure is simplified to (4,4) con-
nected topology network (Fig. 2c). These weak interactions extend
the 2D layers into a 3D supramolecular structure (Fig. 2d). It is
worth noting that a complicated supramolecular architecture
assembled via hydrogen bond interactions from simple chains still
remain rare, to the best of our knowledge.
and one carboxyl oxygen atom (Ag–O 2.481(6) Å) with T-shape.
Interestingly, the 2D layers on the top and at the bottom are com-
posed of Ag ions and H3L; while the 2D layer in the middle consists
of Ag ions and bpp. The three layers are connected by Ag–O bonds
and form a sandwich-like 2D structure (Fig. 3b). The yellow inter-
layer in Fig 3b is simplified as Fig 3c, which the interlayer shows a
3-connected faveolate net. (both ends of pink bonds are silver
atoms) (Fig. 3c).
3.2. Comparison of structures of coordination polymers
In 1–3, the three types of different coordination modes for H3L
exist as shown in Scheme 2. It is noteworthy that in complex 1,
H3L ligand displays the l1 l1 l1 l1
: : : :g2 mode with two carboxylate
groups deprotonated and both adopt bidentate chelate coordinated
modes. In 2, the coordination fashion of the H3L ligand is the
l1
:
l1
:
g2 mode with two of carboxyl groups are deprontonated
and both adopt monodentate coordinated modes [35,36]. In 3, the
H3L ligand exhibits the l1
g3 mode to bridge three metal
:
l1 l1
: :
ions. At the same hydrothermal condition, complexes 1–3 are dif-
ferent structure frameworks with different metal ions and same
auxiliary ligands (bpp). Therefore, the different metal centers
maybe play an important role with the presence of the same auxil-
iary ligand in the formation process of coordination polymer.
3.1.3. [Ag2(L)2/3(l-bpp)]n (3)
The single crystal X-ray structural analysis reveals that complex
3 crystallizes in the monoclinic space group P21/n, and that there
are two types of coordination environments around the Ag(I) ions
in the crystal structure (Fig. 3a). Ag1 represents the tetrahedral
environment, coordinated by two carboxyl oxygen atoms (Ag–O
2.602(5), 2.649(5) Å) from two H3L ligands and two nitrogen atoms
(Ag–N 2.186(6), 2.193(6) Å) from bpp ligands. However, the
distance between the carboxylic oxygen (O1, O6A) atom and the
Ag1 atom is in unusual and regarded as a non-negligible weak
interaction. These weak interactions (Ag1–O1 and Ag1–O6A) may
play an important role in fixing the metal centers in a definite con-
formation in 3. Compared with the Ag1 atom, the Ag2 ion is three-
coordinated to two nitrogen atoms (Ag–N 2.191(6) and 2.226(7) Å)
3.3. IR spectroscopy
The IR spectra for complexes 1–3 are recorded in the region
4000–400 cmÀ1. In the area of functional groups, the absorption
band at 3446 cmÀ1 for 1, 3438 cmÀ1 for 2, and 3437 cmÀ1 for 3
can be assigned to the O–H stretching vibrations of water molecules
or carboxyl group. The C–H stretching vibrations are observed as
sharp, weak bands close to 3000 cmÀ1 for 1–3. The bands at 1608,
1543, 1387 cmÀ1 for 1, 1689, 1591, 1495, 1389 cmÀ1 for 2, and

J. Chen et al. / Inorganica Chimica Acta 400 (2013) 7–12
11
Fig. 3. (a) ORTEP diagram showing the coordination environment of 3 with thermal ellipsoids at 30% probability. All H atoms are omitted for clarity. (b) The 2D network
structure. (c) Schematic view of the (6,3)-connected topological structure of yellow interlayer of Fig. 3(b). (For interpretation of reference to colours in this figure legend the
reader is referred to the web version of this article.)
M
O
M
O
M
O
O
O
O
O
O
O
M
O
O
M
O
M
O
O
O
OH
OH
O
M
O
O
O
(1)
(2)
(3)
Scheme 2. Coordination modes of H3L ligands with different metal ions in complexes 1–3.
1605, 1504, 1426, 1372 cmÀ1 for 3 can be assigned to the stretching
1.875 cm3 K molÀ1 [one isolated Co(II) ions, S = 3/2] for 2 [38–42].
bands of the pyridyl rings of bpp ligands.
The temperature dependence of the reciprocal susceptibilities
(1/
v
M) obeys the Curie–Weiss law [
v
M = C/(T À h)] [43,44]. Above
5 K with negative Weiss constant h = À2.4 K, Curie constant
C = 2.5 cm3 K molÀ1 for 2, the complex exhibits the weak anti-fer-
romagnetic. Such behavior is characteristic for the complex, essen-
tially due to the single ion anisotropy, and anti-ferromagnetic
exchange between the ions centers [45,46].
3.4. Thermal gravimetric analysis
In order to characterize the thermal stability of the complexes,
thermal gravimetric analyses (TGA) for 1–3 were performed in N2
atmosphere between 30 and 800 °C. The results are presented in
Fig. S1. For 1, in the temperature range 100–700 °C, it correspond
to consecutive loss of guest water molecules, bpp and HL ligands.
The remaining weight of 8.95% is in accord with the mass of CdO
residue (calcd 8.61%). The residual of complexes 2–3 also results
in metallic oxide at temperatures close to 700 °C. The TGA curve
of 2 shows the first weight loss of 3.69% at 80–276 °C correspond
to the loss of one water molecule (calcd 3.53%). When the temper-
ature increase to 280 °C, the bpp and HL ligands decompose. In the
case of 3, there is a weight loss of 21.67% in the range of 30–210 °C
correspond to the release of bpp (calcd 21.72%), the framework
decompose at about 220 °C.
4. Conclusions
In summary, a series of interesting coordination polymers have
been hydrothermally synthesized by the asymmetric semi-rigid
H3L and N-heterocyclic ligand with transition metal ions from
low-dimensional to high-dimensional networks. Importantly,
structural investigation demonstrates that with the same reaction
condition and H3L ligand, structures of complexes present promi-
nent changes by different metal ions. The nature of metal ions
may lead to the diversities of resultant complexes. However, all
the variable factors cannot be accurately forecasted at this stage.
The further research works are underway based on H3L and other
N-heterocyclic ligands.
3.5. Magnetic properties
The solid-state direct-current magnetic susceptibilities of 2 is
measured over the temperature range of 1.8–300 K under an outer
field of 1000 Oe [37]. The changing tendencies for temperature
dependence of magnetic susceptibility for complex 2 is shown as
Acknowledgments
This work is supported by the National Natural Science Founda-
tion of China (No. 20771090), State Key Program of National Natu-
ral Science of China (No. 20931005), Key Research Planning
vM and
vMT versus T plots in Fig. S2. The room temperature value
of
v
MT, 2.513 cm3 K molÀ1 for 2, is close to the spin only value of

12
J. Chen et al. / Inorganica Chimica Acta 400 (2013) 7–12
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CCDC 901988, 874962 and 874966 contain the supplementary
crystallographic data for the complexes 1–3, 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 http://dx.doi.org/10.1016/j.ica.2013.01.037.
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