Structural diversity and properties of six coordination polymers derived from 1,2/1,3-phenylenedioxydiacetic acids and varied N-donor co-ligands

Article abstract of DOI:10.1016/j.ica.2013.12.027

Based on two positional isomers of phenylenedioxydiacetate ligands and different N-containing co-ligands, six novel coordination polymers, formulated as {[Zn(o-PDOA)(bpp)]·2H₂O}_n (1), {[Cd(o-PDOA)(bix)]·3H₂O}_n (2), [Cd(m-PDOA)(bix)] _n (3), [Cd(m-PDOA)(bib)]_n (4), [Zn(m-PDOA)(bix)] _n (5), {[Zn(m-PDOA)(bib)]·2H₂O}_n (6), (o/m-H₂PDOA = 1,2/1,3-phenylenedioxydiacetic acid; bix = 1,4-bis(imidazol-ylmethyl)benzene; bib = 1,4-bis(1H-imidazol-1-yl)-butane; bpp = 1,3-bis(4-pyridyl)propane), have been synthesized under hydrothermal conditions. Compound 1 features a three-dimensional (3D) 2-fold interpenetrating cds topology. In 2, the (H₂O)₆ clusters interlink the 1D double [Cd₂(o-PDOA)₂(bix)₂]_n chains into a 3D supramolecular network. Compound 3 is a (3,5)-connected 2D layer with (4².6)(4².6⁷.8) topology. Compound 4 exhibits a 3-fold interpenetrating pcu topological network, while, 5 is a 2D puckered meso-helical 4⁴-sql layer built by alternately arranged right-handed and left-handed helical chains. In contrast to 1-5, compound 6 possesses a 1D loop-like chain and, interestingly, rare D4 tetrameric (H₂O) ₄ cluster extends the chains into a 3D supramolecular framework. Moreover, the thermal stabilities and luminescent properties of compounds 1-6 have also been investigated.

Full text of DOI:10.1016/j.ica.2013.12.027

Inorganica Chimica Acta 413 (2014) 6–15
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Structural diversity and properties of six coordination polymers derived
from 1,2/1,3-phenylenedioxydiacetic acids and varied N-donor
co-ligands
a
a
a
b,
Jun Zhao a, Dong-Sheng Li a, , Ya-Pan Wu , Wen-Wen Dong , Liang Bai , Jack Y. Lu
⇑
⇑
a College of Materials and Chemical Engineering, Research Institute of Materials, China Three Gorges University, Yichang, PR China
b Department of Chemistry, University of Houstons-Clear Lake, Houston, TX 77058, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Based on two positional isomers of phenylenedioxydiacetate ligands and different N-containing
co-ligands, six novel coordination polymers, formulated as {[Zn(o-PDOA)(bpp)]ꢀ2H2O}n (1), {[Cd(o-PDOA)
(bix)]ꢀ 3H2O}n (2), [Cd(m-PDOA)(bix)]n (3), [Cd(m-PDOA)(bib)]n (4), [Zn(m-PDOA)(bix)]n (5), {[Zn(m-
PDOA)(bib)]ꢀ2H2O}n (6), (o/m-H2PDOA = 1,2/1,3-phenylenedioxydiacetic acid; bix = 1,4-bis(imidazol-
ylmethyl)benzene; bib = 1,4-bis(1H-imidazol-1-yl)-butane; bpp = 1,3-bis(4-pyridyl)propane), have been
synthesized under hydrothermal conditions. Compound 1 features a three-dimensional (3D) 2-fold
interpenetrating cds topology. In 2, the (H2O)6 clusters interlink the 1D double [Cd2(o-PDOA)2(bix)2]n
Received 7 November 2013
Received in revised form 26 December 2013
Accepted 26 December 2013
Available online 3 January 2014
Keywords:
Coordination polymer
o/m-Phenylenedioxydiacetic acid
Luminescent property
chains into
a 3D supramolecular network. Compound 3 is a (3,5)-connected 2D layer with
(42.6)(42.67.8) topology. Compound 4 exhibits a 3-fold interpenetrating pcu topological network, while,
5 is a 2D puckered meso-helical 44-sql layer built by alternately arranged right-handed and left-handed
helical chains. In contrast to 1–5, compound 6 possesses a 1D loop-like chain and, interestingly, rare D4
tetrameric (H2O)4 cluster extends the chains into a 3D supramolecular framework. Moreover, the thermal
stabilities and luminescent properties of compounds 1–6 have also been investigated.
Crown Copyright Ó 2014 Published by Elsevier B.V. All rights reserved.
1. Introduction
as 1,2/1,3/1,4-benzenedicarboxylic acid and 1,2/1,3/1,4-phenylene-
diacetate acid, to construct coordination polymers and to promote
Crystal engineering to synthesize rationally coordination
polymers (CPs) or metal–organic frameworks (MOFs) has evoked
an immense amount interest as a result of the fascinating architec-
tures and topologies as well as the potential applications in the
areas of magnetism, luminescence, catalysis, gas storage/separa-
tion, sensing, ion exchange and optics [1–3]. Up to now, many effec-
tive synthetic approaches have been applied to construct desired
and attractive CPs through the assembly of various metal centers
and elaborately designed organic spacers. In this context, some
excellent organic tectons, mainly including the rigid multicarboxy-
late ligands, such as 1,2/1,3/1,4-benzenedicarboxylic acid, 1,3,
5-benzene tricarboxylic acid, and 1,3,5-tri(4-carboxyphenyl) ben-
zene, have been extensively used for fabricating functional crystal-
line materials [4–6]. However, the combination study on positional
isomeric effects of organic linkers and the diversity of structure in
assembly of CPs remains less explored yet, which is of great impor-
tance in understanding the relationship between their structure
and intrinsic properties [7]. For these reasons, we have focused on
utilizing positional isomeric benzenedicarboxylate ligands, such
the investigation of the structure–property relationship. Many
interesting frameworks with diverse topologies and desired proper-
ties have been observed [8]. To evaluate the influence of positional
isomeric effect on the formation of the coordination frameworks,
here we select a couple of positional isomeric dicarboxylate ligands,
1,2-phenylenedioxydiacetic acid (o-H2PDOA) and 1,3-phenylene-
dioxydiacetic acid (m-H2PDOA) as multidentate ligands based on
the following reason: The –OCH2– group makes these ligands more
flexible and more coordination modes in comparison with the
corresponding benzenedicarboxylate, whilst the existence of the
benzene ring provides a rigid element.
On the other hand, polymeric d10 metal (CuI, AgI, AuI, ZnII, or
CdII) complexes have extensive interests in recent years because
they not only exhibit appealing structures but also possess photo-
luminescent properties [9]. A search of the Cambridge Structural
Database (CSD version 5.34, may 2013) reveals only 13 coordina-
tion polymers constructed by a d10 metal and o/m-PDOA ligand
have been reported hitherto (seven for o-PDOA, six for m-PDOA).
Moreover, because of the strong coordination affinity and mediat-
ing geometric need of metal centers, it is effective to introduce
auxiliary connectors in preparing metal carboxylate coordination
polymers with novel topology and properties [10]. In view of the
⇑
Corresponding authors. Tel./fax: +86 717 6397516 (D.-S. Li).
E-mail addresses: lidongsheng1@126.com (D.-S. Li), Lu@uhcl.edu (J.Y. Lu).
0020-1693/$ - see front matter Crown Copyright Ó 2014 Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.12.027

J. Zhao et al. / Inorganica Chimica Acta 413 (2014) 6–15
7
above experience, two isomeric phenylenedioxydiacetate ligands,
1,2/1,3-phenylenedioxydiacetic acid (Scheme 1), were used to
assemble with Zn(II) or Cd(II) salt in this work, incorporating dif-
ferent secondary N-donor spacers. As a result, six coordination
polymers with distinct topological motifs, that is, {[Zn(o-PDOA)
(bpp)]ꢀ2H2O}n (1), {[Cd(o-PDOA)(bix)]ꢀ3H2O}n (2), [Cd(m-PDOA)
(bix)]n (3), [Cd(m-PDOA)(bib)]n (4), [Zn(m-PDOA)(bix)]n (5), {[Zn
(m-PDOA)(bib)]ꢀ2H2O}n (6), are reported. Their syntheses, crystal
structures, thermal stabilities, and photoluminescent properties
have also been investigated.
reaction mixture was placed in a 23 mL Teflon-lined stainless steel
autoclave and was sealed and heated at 140 °C for 120 h. The
autoclave was allowed to cool to room temperature for 48 h. Pale
yellow crystals of compound 2 were obtained (35.0 mg). Yield:
55.7% (based on Cd). Anal. Calc. for C24H28CdN4O9 (Mr = 628.90):
C, 45.83; H, 4.49; N, 8.91. Found: C, 45.42; H, 4.63; N, 8.76%. IR
(KBr pellet, cmꢁ1): 3412 m, 2937 w, 1615 s, 1502 m, 1422 s,
1329 m, 1182 s, 1250 m, 1213 m, 1133 m, 1040 m, 924 w, 825
m, 755 s.
2.4. Synthesis of [Cd(m-PDOA)(bix)]n (3)
2. Experimental
The same synthetic method as that of 2 was used except that o-
H2PDOA (22.6 mg, 0.1 mmol)was replaced by m-H2PDOA(22.6 mg,
0.1 mmol). Colorless crystals were obtained (32.2 mg). Yield: 56%
(based on Cd). Anal. Calc. for C24H22CdN4O6 (Mr = 574.86): C,
50.14; H, 3.86; N, 9.75. Found: C, 50.36; H, 3.58; N, 9.91%. IR
(KBr pellet, cmꢁ1): 3139 s, 2894 s, 2362 m, 2336 m, 1618 s, 1592
s, 1509 m, 1416 s, 1329 m, 1293 w, 1183 s, 1080 s, 1060 m, 931
m, 825 m, 732 s, 688 m.
2.1. Materials and methods
All the chemicals were received as reagent grade and used with-
out any further purification. FT-IR spectra were recorded as KBr
pellets on a Thermo Electron NEXUS 670 FTIR spectrometer. Ele-
mental analyses were performed on a Perkin-Elmer 2400 Series II
analyzer. Thermogravimetric (TG) curves were recorded on a
NETZSCH 449C thermal analyzer with a heating rate of 10 °C minꢁ1
under an air atmosphere. Power X-ray diffraction (PXRD) analyses
2.5. Synthesis of [Cd(m-PDOA)(bib)ꢀH2O]n (4)
were recorded on a Rigaku Ultima IV diffractometer (Cu Ka radia-
The same synthetic method as that of 3 was used except that
bix (23.8 mg, 0.1 mmol) was replaced by bib (19.0 mg, 0.1 mmol,).
Colorless crystals were obtained (31.1 mg). Yield: 57% (based on
Cd). Anal. Calc. for C20H24CdN4O7 (Mr = 544.83): C, 44.09; H, 4.44;
N, 10.28. Found: C, 44.31; H, 4.12; N, 10.46%. IR (KBr pellet,
cmꢁ1): 3516 s, 3116 s, 2900 w, 2342 w, 1625 s, 1558 m, 1482 m,
1406 s, 1313 s, 1286 s, 1183 s, 1097 s, 964 m, 841 s, 778 m, 695 m.
tion, k = 1.5406 Å). Solid-state fluorescence spectra were recorded
on a FLS920 fluorescence spectrophotometer at room temperature.
The simulated powder patterns were calculated using Mercury 2.0.
The purity and homogeneity of the bulk products were determined
by comparison of the simulated and experimental X-ray powder
diffraction patterns.
2.2. Synthesis of {[Zn(o-PDOA)(bpp)]ꢀ2H2O}n (1)
2.6. Synthesis of [Zn(m-PDOA)(bix)]n (5)
A
mixture of Zn(CH3COO)2ꢀ2H2O (21.9 mg, 0.1 mmol),
The same synthetic method as that of 3 was used except that
Cd(CH3COO)2ꢀ2H2O(26.7 mg, 0.1 mmol) was replaced by
Zn(CH3COO)2ꢀ2H2O (21.9 mg, 0.1 mmol). Pale yellow crystals were
obtained (26.9 mg). Yield 51% (based on Zn). Anal. Calc. for C24H22-
ZnN4O6 (Mr = 527.83): C, 54.61; H, 4.20; N, 10.61. Found: C, 54.87;
H, 4.03; N, 10.76%. IR (KBr pellet, cmꢁ1): 3425 w, 3242 w, 1681 m,
1502 s, 1446 m, 1349 m, 1280 s, 1226 s, 1077 s, 924 m, 818 m, 768
s, 748 s, 675 s.
o-H2PDOA (22.6 mg, 0.1 mmol), bpp (19.8 mg, 0.1 mmol,) and
NaOH (8.0 mg, 0.2 mmol) in H2O (8 mL) was stirred for 30 min.
The reaction mixture was placed in a 23 mL Teflon-lined stainless
steel autoclave and was sealed and heated at 120 °C for 120 h.
The autoclave was allowed to cool to room temperature for 48 h.
Pale yellow crystals of compound 1 were obtained (30.9 mg). Yield:
59.0% (based on Zn). Anal. Calc. for C23H26ZnN2O8 (Mr = 523.83): C,
52.71; H, 5.00; N, 5.35. Found: C, 52.12; H, 4.86; N, 5.42%. IR (KBr
pellet, cmꢁ1): 3458 w, 2933 w, 1622 s, 1509 m, 1432 m, 1329 w,
1250 s, 1210 s, 1137 s, 1105 m, 1021 m, 821 m, 752 m.
2.7. Synthesis of {[Zn(m-PDOA)(bib)]ꢀ2H2O}n (6)
The same synthetic method as that of 5 was used except that
bix (23.8 mg, 0.1 mmol) was replaced by bib (19.0 mg, 0.1 mmol).
Pale yellow crystals were obtained (21.7 mg). Yield: 42% (based
on Zn). Anal. Calc. for C20H26ZnN4O8 (Mr = 515.82): C, 46.57; H,
5.08; N, 10.86. Found: C, 46.91; H, 4.83; N, 11.04%. IR (KBr pellet,
cmꢁ1): 3123 m, 2362 m, 1635 s, 1602 s, 1532 s, 1495 m, 1396 s,
1273 m, 1183 s, 1107 m, 1050 m, 957 w, 838 s, 758 m.
2.3. Synthesis of {[Cd(o-PDOA)(bix)]ꢀ3H2O}n (2)
A
mixture of Cd(CH3COO)2ꢀ2H2O (26.7 mg, 0.1 mmol),
o-H2PDOA (22.6 mg, 0.1 mmol), bix (23.8 mg, 0.1 mmol) and NaOH
(8.0 mg, 0.2 mmol) in H2O (8 mL) was stirred for 30 min. The
2.8. Crystal structure determination and refinement
Single crystal X-ray diffraction analyses of compounds 1–6 were
carried out on a Rigaku XtaLAB mini diffractometer with graphite
monochromated Mo Ka radiation (k = 0.71073 Å). The collected
data were reduced using the program CRYSTALCLEAR [11] and an
empirical absorption correction was applied. The structure was
solved by direct methods and refined based on F2 by the full matrix
least-squares methods using SHELXTL [12,13]. All non-H atoms were
refined anisotropically. The position of hydrogen atoms attached to
carbon atoms were generated geometrically. The crystallographic
data and structural refinementsfor complexes 1–6 are summarized
in Table 1. Selected bond lengths and angles for 1–6 are listed in
Table S1.
Scheme 1. Schematic molecular structures of the ligands.

8
J. Zhao et al. / Inorganica Chimica Acta 413 (2014) 6–15
as
l
2-bridging mode with one carboxylate group in a l1
- :g
g1 1 che-
3. Results and discussion
lating mode and the other in a l1
-
g1
:
g0 monodentate mode(mode
Il in Scheme 2). The Zn(II) ions are bridged by o-PDOA2ꢁ ligands to
generate zigzag neutral [Zn(o-PDOA)]n chains with the Znꢀ ꢀ ꢀZn dis-
tance of 8.850(9) Å. The chains are linked by TT conformational
bpp ligands which adopt two different orientations (N1–Zn1–N2,
109.0(1)°), thus extending the chains into a 3D 65.8-cds framework
(Fig. 1b). Furthermore, the cds-topological architecture of 1 pro-
duces large channels that have an opening of about
13.0 ꢂ 16.3 Å2 along the crystallographic a axis (Fig. 1b). So, a pair
of cds-nets is interlocked with each other, leading to the formation
of the 2-fold interpenetrated 3D ? 3D architecture (Fig. 1c, d).
Although a number of cds frameworks have been reported, there
are only a few compounds that exhibit interpenetration [14]. The
2-fold interpenetration in the crystal effectively reduces the void
3.1. Description of the crystal structures
3.1.1. {[Zn(o-PDOA)(bpp)]ꢀ2H2O}n (1)
Single-crystal X-ray diffraction analysis reveals that 1 crystal-
lizes in the orthorhombic space group of Pbcn and the asymmetric
unit of 1 contains one Zn(II) ion, one o-PDOA2ꢁ ligand, one bpp
ligand and two lattice water molecules (Fig. 1a). The Zn(II) ion is
five-coordinated by three carboxylate oxygen atoms from two
o-PDOA2ꢁ
ligands
(Zn1–O1 = 2.151(4),
Zn1–O2 = 2.218(4),
Zn1–O6#1 = 2.009(4) Å, #1: x + 1/2,ꢁy + 1/2,ꢁz + 1) and two nitro-
gen atoms from two bpp ligands (Zn1–N1 = 2.065(4),
Zn1–N2#2 = 2.047(4) Å, #2: x ꢁ 1/2,y ꢁ 1/2,ꢁz + 1/2) in a distorted
square pyramid coordination geometry. Each o-PDOA2ꢁ ligand act
Table 1
Crystallographic data and structure refinement details for 1–6.
Compound
1
2
3
4
5
6
Formula
Formula weight
Crystal system
a (Å)
b (Å)
c (Å)
C
23H26ZnN2O8
C24H28CdN4O9
628.90
C24H22CdN4O6
574.86
C20H24CdN4O7
544.83
C24H22ZnN4O6
527.83
C20H26ZnN4O8
515.82
523.83
orthorhombic
14.094(2)
17.093(8)
20.192(9)
90.00
90.00
90.00
4864.9(7)
8
1.430
triclinic
9.605(2)
12.262(3)
12.708(3)
66.916(3)
72.173(3)
84.090(4)
1310.5(5)
2
triclinic
10.034(8)
10.942(5)
12.101(7)
67.629(1)
78.023(1)
79.469(1)
1194.14(1)
2
triclinic
9.601(9)
10.713(8)
11.565(7)
110.919(2)
97.986(2)
92.316(2)
1095.37(1)
2
monoclinic
20.728(4)
13.207(2)
16.843(3)
90.00
106.30(3)
90.00
4425.5(1)
8
triclinic
9.908(2)
10.501(1)
12.880(3)
105.483(8)
93.881(8)
113.079(1)
1165.4(4)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
F(000)
)
1.594
640
1.599
580
1.652
552
1.584
2176
1.470
536
2176
Data/restraints/parameters
Rint
4270/21/319
0.0556
4584/9/361
0.0113
4143/144/316
0.1142
5261/121/289
0.0402
5401/0/317
0.0213
4090/0/299
0.1599
GOF
1.033
0.0677
0.1918
1.050
0.0228
0.0617
1.093
0.0682
0.2110
1.019
0.0518
0.0783
1.011
0.0331
0.0814
1.046
0.0597
0.1531
a
R1 (I > 2
r
(I))
(I))
b
wR2 (I > 2
r
R1 (all data)
0.0910
0.0249
0.0724
0.0658
0.0547
0.0648
wR2 (all data)
D
0.2073
1.470/ꢁ0.861
0.0633
0.364/ꢁ0.384
0.2181
2.244/ꢁ1.786
0.0827
0.903/ꢁ0.559
0.0902
0.328/ꢁ0.498
0.1605
1.265/ꢁ0.641
qmaximum,minimum (e Åꢁ3
)
a
R1
wR2 = {
=
R
||F0|| ꢁ |Fc|/
R|F0|.
b
2
R
[w(F0 ꢁ Fc2)2]/
R
[w F02]2}1/2
.
Fig. 1. (a) The coordination environment of Zn(II) ion in 1 (symmetry codes: A: ꢁ1/2 + x,ꢁ1/2 + y,1/2 ꢁ z; B: 1/2 + x,1/2 ꢁ y,1 ꢁ z). (b) The view of 3D cds network. (c) The 3D
packing of 2-fold cds network. (d) Schematic representation of 2-fold cds topology.

J. Zhao et al. / Inorganica Chimica Acta 413 (2014) 6–15
9
Scheme 2. Diverse coordination modes of o/m-PDOA in complexes 1–6 and previously reported polymers.
space, and it still shows a porous structure. After removal of the
lattice water molecules, the effective free void space of 1 is calcu-
lated by PLATON program [15] as being 15.6% of the crystal volume
(757.1 Å3 out of the 4864.9 Å3 unit cell volume). In addition, intra-
molecular O–Hꢀ ꢀ ꢀO hydrogen-bonding interactions (Table S2) exist
among the lattice water molecules and carboxylate oxygen atoms,
which further stabilized the 3D structure.
aromatic rings between the o-PDOA2ꢁ molecules (centroid-to-cen-
troid distance = 3.976(2) Å), resulting a 2D supramolecular network
as shown in Fig. 2c. It is worth noting that an interesting hexameric
water cluster (Fig. 2e) self-assembled by means of hydrogen bond-
ing interactions (Table S2) between lattice water molecules is ob-
served in the solid structure of 2. Each hexameric water cluster
consists of a cyclic water tetramer and two dangling water mono-
mers. Within the cluster, the four water molecules are fully copla-
nar in the plane and each water monomer acts as both a single
hydrogen bond donor and acceptor. The remaining hydrogen atom
of O1WA is below/above of the ring, while the remaining hydrogen
atom of O1WC is above/below the ring. In addition, the hanged
water molecules also form hydrogen bonds with carboxylate group
of PDOA2ꢁ ligand, resulting in a 3D supramolecular network
(Fig. 2d).
3.1.2. {[Cd(o-PDOA)(bix)]ꢀ3H2O}n (2)
Single-crystal X-ray diffraction analysis reveals that
ꢀ
2 crystallizes in the triclinic space group of P1. The structure of 2
exhibits a double-stranded chain and each asymmetric unit of 2
contains one Cd(II) ion, one o-PDOA2ꢁ ligand, one bix ligand and
three lattice water molecules. As shown in Fig. 2a, Cd(II) ion
displays distorted pentagonal bipyramidal coordination geometry,
defined by three carboxyl oxygen atoms and two ether oxygen
atoms from two different o-PDOA2ꢁ ligands (Cd(1)–O(1) = 20291
(1), Cd(1)–O(3) = 2.637(3), Cd(1)–O(4) = 2.647(2), Cd(1)–O(5) =
2.367(0), Cd(1)–O(5)#1 = 2.331(4) Å, #1: ꢁx + 2,ꢁy + 1,ꢁz), as well
as two nitrogen atoms from two bix ligands (Cd(1)–
N(1) = 2.221(9), Cd(1)–N(4)#2 = 2.235(5) Å, #2: x + 1,y ꢁ 1,z). One
carboxylate group of PDOA2ꢁ ligand acts as bridging ligand, which
3.1.3. [Cd(m-PDOA)(bix)]n (3)
ꢀ
Compound 3 crystallized in triclinic space group of P1. As
shown in Fig. 3a, there are one crystallography independent Cd(II)
ion, one m-PDOA2ꢁ ligand and one bix ligand. Each Cd(II) center
adopts distorted octahedral coordination geometry completed by
four O atoms from two m-PDOA2ꢁ ligands and two N atoms from
links the two Cd(II) ions in l2
-
g2
:
g0 mode, the other carboxylate
two bix liangs. Each m-PDOA2ꢁ anion acts as a
l
3-bridge (mode
IIl in Scheme 2) linking three Cd(II) ions, in which one carboxylate
group adopts a l2
1 bridging mode to connect two Cd(II) ions,
while the other adopts a l1
group adopts l1
-
g1
:g
0 mode, resulting the pentadentate coordina-
tion mode (mode Im in Scheme 2), with the addition of two coordi-
nated ether oxygen atoms. In the structure, two Cd(II) ions are
connected by a pair of pentadentate o-PDOA2ꢁ ligands to form a
binuclear unit (Cdꢀ ꢀ ꢀCd = 3.848(9) Å). Then such binuclear blocks
are linked through trans conformational bix ligands in two different
directions giving rise to a unique 1D infinite double [Cd2(o-
PDOA)2(bix)2]n chain (Fig. 2b). If viewed along the b-axis, these dou-
- :g
g1
-
g1 g1 mode to chelate one Cd(II) ion.
:
The adjacent Cd(II) ions are bridged by m-PDOA2ꢁ ligands to form
a 1D [Cd2(m-PDOA)2]n ribbon chain. The infinite chain comprises 8-
and 24-membered rings built up by Cd(II) ion and m-PDOA2ꢁ an-
ion. The 8-membered ring is formed by two symmetry related
bridging carboxylate groups with
4.710(3) Å. Such 1D chains are further interlinked by trans confor-
a
Cdꢀ ꢀ ꢀCd distance of
ble chains have interesting
pꢀ ꢀ ꢀp packing interactions of adjacent

10
J. Zhao et al. / Inorganica Chimica Acta 413 (2014) 6–15
Fig. 2. (a) The coordination environment of Cd(II) ion in 2 (symmetry codes: A: 2 ꢁ x,1 ꢁ y,ꢁz; B: 1 + x,ꢁ1 + y,z); (b) The view of 1D infinite double chain like structure. (c)
The 2D supramolecular packing sheet constructed by packing interactions. (d) The view of H-bonded 3D network. (e) The enlarged view of the hexameric (H2O)6 cluster
pꢀ ꢀ ꢀp
formed by a planar water tetramer and two dangling water monomers.
Fig. 3. (a) The coordination environment of Cd(II) ion in 3 (symmetry codes: A: 1 ꢁ x,ꢁy,1 ꢁ z; B: 1 + x,y,ꢁ1 + z; C: 1 + x,ꢁ1 + y,z). (b) The view of the 2D layer. (c) Schematic
representation of (3,5)-connected (42.6)(42.67.8) topology. (d) The view of the 3D supramolecular network linked by hydrogen bonding and
pꢀ ꢀ ꢀp packing interactions.
mational bix ligands with a dihedral angle between imidazole and
phenyl of 87.45(7)° and 79.31(1)° to form a 2D layer (Fig. 3b).
Analysis of the network topology of 3 reveals that each Cd(II) cen-
ter acts as a 5-connected node to connect three m-PDOA2ꢁ ligands
and two bix spacers. And the m-PDOA2ꢁ ligands serve as the 3-con-
nected nodes. Thus, a (3,5)-connected 2D network with the point
symbol of (42.6)(42.67.8) is constituted (Fig. 3c). The 2D layers are
further linked by hydrogen bonding between the C atom and the
carboxylate O atom (C7–H7Aꢀ ꢀ ꢀO5#1, #1: ꢁx,1 ꢁ y,2 ꢁ z), as well
as the
p p packing interactions of adjacent imidazole rings be-
ꢀ ꢀ ꢀ

J. Zhao et al. / Inorganica Chimica Acta 413 (2014) 6–15
11
tween the m-PDOA2ꢁ molecules (centroid-to-centroid dis-
tance = 3.898 (6) Å), resulting in a 3D supramolecular network
(Fig. 3d).
3.1.5. [Zn(m-PDOA)(bix)]n (5)
The single-crystal X-ray diffraction study performed on com-
pound 5 reveals that it is a 2D framework, crystallizing in the
monoclinic space group C2/c. As shown in Fig. 5a, the asymmetric
unit consists of two crystallographically independent Zn(II) ions,
one m-PDOA2ꢁ ligand, a pair of half bix liand. Each Zn(II) center
is tetra-coordinated by two carboxyl O atoms from two m-PDOA2ꢁ
ligands and two imidazolyl N atoms from two bix ligands, showing
a distorted tetrahedral coordination geometry. The two carboxyl-
3.1.4. {[Cd(m-PDOA)(bib)]ꢀH2O}n (4)
X-ray single-crystal diffraction analysis reveals that 4 is a 3-fold
interpenetrated pcu network and crystallizes in the triclinic space
ꢀ
group of P1. The asymmetric unit contains one Cd(II) ion, one
ate groups of m-PDOA2ꢁ ligand all exhibit l1
mode (mode IIe in Scheme 2). The Zn(II) ions are linked by
1-bridging m-PDOA2ꢁ ligands to form the alternate left- and
- :
g1 g0 monodentate
m-PDOA2ꢁ ligand and a pair of half bbi ligand as well as one lattice
water molecule. The structure contains a centrosymmetric binu-
clear Cd(II) unit (Fig. 4a) built through two bridging carboxylates
(Cd1–O6 2.240(1) Å), while the other four coordination sites of
each metal ion are occupied by two chelating carboxylate O atoms
and two imidazole N atoms forming a distorted octahedral geom-
etry (Cd1–O1 2.290(5), Cd1–O2 2.598(2), Cd1–N1 2.281(3), Cd1–
l
right-handed [Zn(m-PDOA)]n helical chains running along the crys-
tallographic a axis(Fig. 5b) with a pitch of 20.728(4) Å. Right-
handed and left-handed helical chains are alternately arranged
and interlinked by trans-bix ligands, resulting a 2D puckered
meso-helical (4,4) layer (Fig. 5c) with grid dimensions
10.3 ꢂ 14.9 Å2 (based on the separation of the metal ions). Further-
more, the C–Hꢀ ꢀ ꢀO and C–Hꢀ ꢀ ꢀCg weak bonding interactions which
is ranging from 3.176 (6) to 3.306(2) Å not only bring further sta-
bility for the structure but also link the 2D layer structure to form
a 3D supramolecular architecture (Fig. 5d, S1).
N3 2.231(2) Å). Each m-PDOA2ꢁ anion acts as a
three Cd(II) ions (mode IIm in Scheme 2), in which one carboxylate
group adopts a l2
0 bridging mode to connect two Cd(II) ions,
while the other adopts a l1
g1 mode to chelate one Cd(II) ion.
l3-bridge linking
-
g2
:g
-
g1
:
The m-PDOA2ꢁ ligands link the binuclear Cd(II) units to form a
1D double chain with the [Zn2(m-PDOA)2]n ring arranging alter-
nately, which is then connected by the TTT conformational bbi
ligands into a loop-like ladder 2D network along the (111) plan
(Fig. 4b). Further, these 2D layers are pillared by the GTG
(G = gauche, T = trans) conformational bbi spacers to result in an
interesting 3D pillar-layered framework with 1D rectangular chan-
nels with dimensions of 14.597(6) ꢂ 13.098(8) Å2. Because of the
spacious nature of the single network, the potential voids are filled
via mutual interpenetration of an identical 3D framework generat-
ing a 3-fold interpenetrating architecture (Fig. 4c). Topologically, if
we consider the dimeric Cd(II)-unit as six-connected node, while
m-PDOA2ꢁ and bbi ligands serve as linkers. Thus, the whole frame-
work is a 3-fold interpenetrating pcu network (Fig. 4d).
3.1.6. {[Zn(m-PDOA)(bib)]ꢀ2H2O}n (6)
Single-crystal X-ray diffraction analysis reveals that complex 6
ꢀ
crystallizes in the triclinic P1 space group. As shown in Fig. 6a, each
Zn(II) center displays a distorted tetrahedral coordination geome-
try, where two oxygen atoms (O1, O5A) are part of two separate
m-PDOA2ꢁ ligands and two nitrogen atoms (N1, N4B) belong to
two different bib ligands. The two carboxylate groups of m-PDOA2ꢁ
ligand all exhibit l1- :
g1 g0 monodentate mode (mode IIe in
Scheme 2), whereas the GTT conformational bib ligand with its ter-
minal nitrogen atom coordinate two Zn(II) centers, and the dihe-
dral angle between two imidazolyl ring is 64.62°. In this way,
Fig. 4. (a) The coordination environment of Cd(II) ion in 4 (symmetry codes: A: ꢁx,1 ꢁ y,ꢁ1 ꢁ z; B: 1 + x,1 + y,1 + z; C: 1 ꢁ x,2 ꢁ y,ꢁz). (b) The view of the 2D sheet. (c) The
packing view of 3-fold interpenetrating pcu network. (d) Schematic representation of 3-fold interpenetrating pcu network.

12
J. Zhao et al. / Inorganica Chimica Acta 413 (2014) 6–15
Fig. 5. (a) The coordination environment of Zn(II) ion in 5 (symmetry codes: A: 1 ꢁ x,y,1/2 ꢁ z; B: ꢁx,y,1/2 ꢁ z). (b) The view of 1D infinite right-handed and left-handed
helical [Zn(m-PDOA)]n chains along the crystallographic a axis. (c) The view of 2D puckered meso-helical (4, 4) layer constructed by helical chains and interlinked bix ligands.
(d) View of 3D crystal packing of 5.
Fig. 6. (a) Coordination environment of Zn(II) ion in 6 (symmetry codes: A: ꢁx,1 ꢁ y,ꢁ1 ꢁ z; B: ꢁx,ꢁy,ꢁ1 ꢁ z). (b) The view of 1D loop-like chain formed by Zn(II) ions and
organic ligands. (c), (d) The 3D supramolecular framework constructed by 1D chains and (H2O)4 water clusters viewed along the b (or a) axis. (e) View of the tetramer water
cluster which links the four adjacent chains; (f) The enlarged view of the tetramer water cluster.

J. Zhao et al. / Inorganica Chimica Acta 413 (2014) 6–15
13
Table 2
two bib ligands link two Zn(II) centers into a -Zn-bib-Zn-bib-
Summary about the coordinated geometry of metal centers in 1–6.
22-member ring in head-to-tail mode with the Znꢀ ꢀ ꢀZn distance
being 9.362(9) Å. The bis-monodentate m-PDOA2ꢁ ligands further
extend the metal rings into a 1D loop-like chain (Fig. 6b).
Formula
Dimension
Coordination
atoms
Geometry of
metal
Most strikingly, the two symmetric independent lattice water
molecules (O7, and O8) are assembled into a curved tetrameric
cluster (H2O)4 notated as D4 according to Infantes’ classification
[16] by hydrogen bonding interactions with the Oꢀ ꢀ ꢀO distances
of 2.706 (8) Å (O7ꢀ ꢀ ꢀO8) and 2.756 (6) Å (O8ꢀ ꢀ ꢀO8A) and an
Oꢀ ꢀ ꢀOꢀ ꢀ ꢀO angle of 122.94° (O7ꢀ ꢀ ꢀO8ꢀ ꢀ ꢀO8A). As we know, such an
arrangement has scarcely observed so far [17], although cyclic
(H2O)4 consisting of two or four independent water molecules have
been reported [18]. In this structure, the guest water cluster,
(H2O)4, just like a ‘‘glue’’ agglutinates and supports the host 1D
loop-like chains to form a 3D supramolecular framework (Fig. 6c,
d) by abundant hydrogen bonding interactions involving carbox-
ylic oxygen atoms and crystallization water molecules (Fig. 6e, f).
1
2
3
4
5
6
C
C
C
23H26ZnN2O8
24H28CdN4O9
24H22CdN4O6
3D
1D
2D
3D
2D
1D
N2O3
N2O5
N2O4
N2O4
N2O2
N2O2
square pyramid
pentagonal bipyramid
octahedron
octahedron
tetrahedron
C20H24CdN4O7
C
C
24H22ZnN4O6
20H26ZnN4O8
tetrahedron
link 1D double [Cd2(m-PDOA)2]n chains into a 2D layer with
(42.6)(42.67.8) topology. In 4, when a flexible spacer (bib) was ta-
ken into the reaction, a 3D threefold interpenetrating pcu net-
work was obtained. In 5 and 6, semi-rigid bix and flexible bib
was used in the reactions, respectively. 5 is a puckered meso-
helical (4,4) layer network wihle 6 exhibits a 1D loop-like chain
structure; (iii) the versatile coordinated geometries of Zn(II)/
Cd(II) centers maybe benefit the structural diversification of
the resultant extended networks of coordination polymers (Ta-
ble 1). For example, with regard to the m-PDOA-bib- bridged
CPs 4 and 6 in this series of crystalline materials, along with
the variation of metal centers (from Cd(II) to Zn(II) ion), their
network arrays are changed from 3D 3-fold interpenetrating
pcu topology to1D loop-like chain motif. The results mentioned
above indicate that the backbone of phenylenedioxydiacetate li-
gands, the different flexibility of the N-containing auxiliary
bridging ligands as well as the coordination geometry of the me-
tal centers play a key role in governing the ultimate crystalline
architectures.
3.2. The diverse coordination modes of o/m-PDOA
The coordination chemistry of H2PDOA is interesting, since its
two carboxylate groups can be partially or fully deprotonated to
generate HPDOAꢁ and PDOA2ꢁ anions under different synthesis
conditions. Therefore, it can coordinate with metal ions in multiple
ways to form a series of coordination polymers with interesting
topologies and properties. Furthermore, the flexible –O–CH2–COO
group can twist to meet different coordination modes. As shown
in Scheme 2, according to the search of the Cambridge Structural
Database (CSD version 5.34, may 2013), so far 26 kinds of coordi-
nation mode of o/m-PDOA ligands were observed in the previously
reported ones and complexes 1–6 [19,20]. In 1, the o-PDOA ligand
3.4. XRPD and TG results
takes the
l
2-bridging mode with one carboxylate group in a
l1
-
g1
:
g1 chelating mode and the other in a l1 g1
- :
g0 monodentate
To check the purity and homogeneity of the bulk products of
compounds 1–6, the as-synthesized samples were measured by
X-ray powder diffraction (XRPD) at room temperature. As shown
in Figs. S2ꢁS7 (ESI), the peak positions of the experimental pat-
terns are in good agreement with the simulated patterns generated
from single-crystal diffraction data, which clearly indicate the good
purity and homogeneity of the compounds.
mode (see mode Il in Scheme 2). In 2, the m-PDOA ligand displays a
first reported pentadentate mode (see mode Im in Scheme 2). In 3,
the o-PDOA ligand acts the
group in a l1
g1 chelating mode and the other in a l2
bridging mode (see mode IIl in Scheme 2). In 4, the m-PDOA ligand
acts as 3-bridging mode with one carboxylate group in a l1
chelating mode and the other in a l2
g0 bridging mode (see
mode IIm in Scheme 2). In 5 and 6, the m-PDOA ligands fearture
2-bridging modes with two carboxylate groups in l1
0 mono-
l
3-bridging mode with one carboxylate
-
g1
:
-
g1
:
g1
l
-
g1
:
g1
-
g2
:
To investigate the thermal stability of these compounds, the
thermogravimetric analyses were carried out on under an air
atmosphere. As shown in Fig. S8 (ESI), compound 1 shows the first
mass loss of 6.47% below 135 °C due to the release of the two guest
water molecules (calcd 6.87%); the further weight loss of 78.41%
between 230 and 450 °C is attributed to the loss of organic
ligands(calcd 80.63%), and the residual weight at ca. 15.12% (calcd
for ZnO, 15.54%). For 2, the first mass loss of 9.31% below 175 °C
due to the release of the three guest water molecules (calcd
8.59%), the residual weight at ca. 21.32% above 550 °C (calcd for
CdO, 20.41%). For 3, the framework is stable up to 290 °C, and then
a sharp weight loss (75.41%) from 290 to 700 °C corresponding to
the decomposition of the organic ligands, and the residual weight
at ca. 22.58% (calcd for CdO, 22.33%). For 4, the first mass loss of
3.51% below 110 °C due to the release of the one guest water mol-
ecule (calcd 3.30%), and the residual weight at ca. 23.71% (calcd for
CdO, 23.56%). For 5, the framework is stable up to 240 °C, and the
residual weight at ca. 15.15% (calcd for ZnO, 15.42%)). For 6, the
first mass loss of 7.36% below 120 °C due to the release of the
two guest water molecules (calcd 6.98%); the second step is from
250 to 600 °C, where the organic ligands began to decompose with
the residual weight of 17.54% (calcd for ZnO, 15.72).
l
- :g
g1
dentate mode (see mode IIe in Scheme 2). In comparison with the
reported compounds, as we know, the coordination modes Im, IIl
and IIm are first reported in this presentation.
3.3. Structural diversity of 1–6
It is noteworthy that a variety of framework structures can be
achieved on the basis of the choice of the phenyl dicarboxylate
isomers with differently oriented carboxyl groups and N-contain-
ing auxiliary bridging ligands. The phenomenon of structural
diversification in 1–6, may arise from three different sources:
(i) the positional isomeric effect of the PDOA ligands. The pheny-
lenedioxydiacetate isomers with different orientations, torsions,
and binding modes of the carboxylate groups can adopt the che-
lating and bridging modes. From PDOA-containing CPs 1–6,
PDOA ligand shows five types of coordination modes: mode Il
for 1, mode Im for 2, mode IIl for3, mode IIm for 4, mode IIe
for 5 and 6, resulting in three different dimensional frameworks
(two for 1D, two for 2D, and two for 3D, Table 2); (ii) the N-con-
taining co-ligands with different flexibility were employed to
investigate their influence on the structure of the polymers,
which will influence the final coordination architectures.
Compare 3 and 4: when a semi-rigid ligand, bix was chosen as
an auxiliary ligand, and is found to act as a pillar connector to
3.5. Photoluminescent properties
The emission spectra of 1–6 were examined in the solid state at
room temperature and shown in Fig. 7. According to the previous

14
J. Zhao et al. / Inorganica Chimica Acta 413 (2014) 6–15
tetrameric (H2O)4 water clusters. The effects of the positions of
the carboxylate groups, the flexibility of the N-containing co-li-
gands as well as the coordination geometry of the metal centers
are discussed in detail. Many more systematic studies for the de-
sign and construction of such crystalline materials with isomeric
H2PDOA and other N-containing building blocks are underway in
our group.
Acknowledgements
This work was financially supported by the NSF of China
(Nos: 21201109, 21373122 and 21301106), the NSF of Hubei Prov-
ince of China (No: 2011CDA118), the Project of Hubei Provincial
Education Office (Q20131304).
Appendix A. Supplementary material
CCDC 932838–932843 contain the supplementary crystallo-
graphic data for 1–6. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif. X-ray crystallographic files in CIF for-
mat for compounds 1–6, selected bond lengths and angles, hydro-
gen bond distances and angles for 1 and 2, PXRD, TG curves for 1–6,
respectively. Supplementary data associated with this article can
be found, in the online version, at http://dx.doi.org/10.1016/
j.ica.2013.12.027.
Fig. 7. Solid-state emission spectrum of 1–6 at room temperature.
Table 3
Luminescent properties of free ligands and 1–6 in the solid state.
Compound
kex/kem (nm)
Compound
kex/kem (nm)
o-H2PDOA
m-H2PDOA
284/568
350/394
373/508
379/451
278/320
440/503
2
3
4
5
6
375/461
315/429
315/441
388/452
372/431
bpp
bix
bib
1
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