Synthesis, structural diversities and properties of a series of transition metal-organic frameworks based on asymmetric dicarboxylic acid and N-donor auxiliary ligand

Article abstract of DOI:10.1016/j.inoche.2012.12.037

Four new metal-organic frameworks, namely, [Zn(pimb)(hpht)]·H ₂O (1), Cd(pimb)_0.5(hpht)(H₂O) (2), [Co(pimb)(hpht)(H₂O)₂]·H₂O (3) and [Ni(pimb)(hpht)(H₂O)₂]·H₂

Full text of DOI:10.1016/j.inoche.2012.12.037

Inorganic Chemistry Communications 30 (2013) 5–12
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Feature article
Synthesis, structural diversities and properties of a series of transition metal-organic
frameworks based on asymmetric dicarboxylic acid and N-donor auxiliary ligand
a
a
Yan Wang a,b, , Song-Quan Shen , Ju-Hong Zhou
⁎
a,⁎⁎
, Tao Wang , Su-Na Wang b,c, Guang-Xiang Liu a,b
a
School of Chemistry and Chemical Engineering, Anhui Key Laboratory of Functional Coordination Compounds, Anqing Teachers College, Anqing 246011, China
State Key Laboratory of Coordination Chemistry, National Laboratory of Microstructures, Nanjing University, Nanjing 210093, China
School of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252059, China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Four new metal-organic frameworks, namely, [Zn(pimb)(hpht)]·H2O (1), Cd(pimb)0.5(hpht)(H2O) (2),
[Co(pimb)(hpht)(H2O)2]·H2O (3) and [Ni(pimb)(hpht)(H2O)2]·H2O (4), (pimb=1,4-bis(imidazol-1-yl-
methyl)benzene, H2hpht=homophthalic acid) have been synthesized by using hydrothermal method
based on mixed ligands of asymmetric dicarboxylate and N-donor auxiliary ligand. The networks show
diverse structures and coordination modes at the metal ions. Complex 1 is a 2D corrugated network bridged
by C\H···O hydrogen bond to generate a 3D framework, whereas the complex 2 features rare (3,4)-
connected V2O5 topological net and stacks to give a 3D structure by C\H···π interactions. Complexes 3
and 4 are isomorphous and isostructural, where the X–H···π (X=C, O) interactions exist and stabilize the
stack of their (4,4)-topological network. The factors causing structural diversities are discussed. The TGA
and XPRD patterns as well as photoluminescent properties of complexes 1 and 2 are also studied in the
solid state at room temperature.
Received 22 November 2012
Accepted 21 December 2012
Available online 11 January 2013
Keywords:
Asymmetric carboxylate
Imidazole-based ligand
Transition metal complex
Structural diversity
Luminescence
© 2013 Elsevier B.V. All rights reserved.
Contents
6
6
6
6
6
7
7
7
7
7
7
8
8
8
8
9
9
Introduction
Experimental
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
11
Materials and physical measurements
Synthesis of the complexes
Synthesis of [Zn(pimb)(hpht)]·(H2O) (1) .
Synthesis of Cd(pimb)0.5(hpht)(H2O) (2) .
Synthesis of [Co(pimb)(hpht)(H2O)2]·H2O (3) .
.
.
.
.
.
.
Synthesis of [Ni(pimb)(hpht)(H2O)2]·H2O (4)
X-Ray crystallography
Results and discussion .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Synthesis and characterization .
Description of crystal structures .
[Zn(pimb)(hpht)]·(H2O) (1) .
Cd(pimb)0.5(hpht)(H2O) (2) .
[Co(pimb)(hpht)(H2O)2]·H2O (3) and [Ni(pimb)(hpht)(H2O)2]·H2O (4)
Structural diversities of MOFs 1 to 4
XRD patterns and thermal properties
Photoluminescent properties of 1 and 2 .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
10
⁎
Correspondence to: Y. Wang, School of Chemistry and Chemical Engineering, Anhui Key Laboratory of Functional Coordination Compounds, Anqing Teachers College, Anqing
246011, China. Tel./fax: +86 556 5500090.
⁎⁎ Corresponding author.
E-mail addresses: njwangy@live.com (Y. Wang), zhoujh@aqtc.edu.cn (J.-H. Zhou).
1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2012.12.037

6
Y. Wang et al. / Inorganic Chemistry Communications 30 (2013) 5–12
Conclusions
Acknowledgment .
Appendix A.
References .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
10
10
10
11
Supplementary material .
. . . . . . . . . . . . .
.
Introduction. Crystal engineering based on metal-organic frame-
works (MOFs) has recently attracted considerable interest, owing to
their variety of intriguing structures, topologies as well as their po-
tential applications in molecular magnetism, catalysis, gas sorption,
fluorescent sensing, and optoelectronic devices [1–3]. Studies in this
field have focused on the design and preparation, as well as the struc-
ture–property relationships. Although significant progress has been
made in recent decades, rational prediction and controllable synthesis
of MOFs are still a great challenge for chemists, mainly due to the
complexity of the factors influencing the self-assembly progress, in-
cluding the nature of ligand, coordination requirement of the central
metal ions, metal–ligand ratio, pH value, solvent, temperature, etc
[4]. Literature survey shows that the most important aspect in the con-
struction of these MOFs is the proper design and selection of organic
ligands with suitable binding groups. In recent years, as an important
type of multidentate O-donor ligands, organic aromatic rigid poly-
carboxylate ligands have been extensively studied because of their
diversity coordination modes and sensitivity to pH values of the
carboxylate groups, and many polymers with multidimensional
networks as well as interesting properties have been reported [5].
However, asymmetrical flexible polycarboxylate ligands remain less
developed [6].
Meanwhile, flexible imidazole-based ligands containing alkyl
spacers are proved to be good candidates for constructing various
MOFs, due to the structural diversities caused by the flexibly nature,
which allows the ligands to adjust their conformation and coordination
modes when they coordinate to metal centers [7]. But studies about
coordination polymers constructed with bis-imidazole/triazole spacers
and asymmetric dicarboxylate are relatively few [8].
Taking all the considerations mentioned above in count, we pay our
attentions on the constructions of MOFs based on an asymmetric
dicarboxylate acid, namely, homophthalic acid (H2hpht) and flexible
imidazole-based spacer ligand, namely, 1,4-bis(imidazol-1-yl-methyl)
benzene (pimb) (Scheme 1). A series of new transition metal-organic
polymers: [Zn(pimb)(hpht)]·H2O (1), Cd(pimb)0.5(hpht)(H2O) (2),
[Co(pimb)(hpht)(H2O)2]·H2O (3) and [Ni(pimb)(hpht)(H2O)2]·H2O
(4) were successfully synthesized and characterized. Herein, we report
their syntheses, structure diversities and luminescent properties.
Experimental. Materials and physical measurements. Commercially
available reagents were used as received without further purification.
The ligand pimb was prepared according to reported procedures [4b].
Elemental analysis (EA) for C, H, and N was performed on Elementar
Vario EL-III elemental analyzer. Infrared spectra were performed on a
Nicolet AVATAR-350 spectrophotometer with KBr pellets in the 400–
4000 cm−1 region. Powder X-ray diffraction patterns were recorded
on a Rigaku D/max-RA rotating anode X-ray diffractometer with graph-
ite monochromatic Cu-Kα (λ=1.542 Å) radiation at room temperature.
Thermal gravimetric analysis (TGA) was performed on a Netzsch
STA-409PC instrument in flowing N2 with a heating rate of 20 °C/min.
The luminescence spectra for the powdered solid samples were
measured at room temperature on a Hitachi F-4500 fluorescence spec-
trophotometer with a xenon arc lamp as the light source. In the mea-
surements of emission and excitation spectra the pass width is 5 nm.
All the measurements were carried out under the same experimental
conditions.
Synthesis of the complexes. Synthesis of [Zn(pimb)(hpht)]·(H2O) (1). A
mixture of ZnBr2 (22.5 mg, 0.1 mmol), Homophthalic acid (18.0 mg,
0.1 mmol), pimb (23.8 mg, 0.1 mmol) and Na2CO3 (10.6 mg,
0.1 mmol) was placed in a Teflon-lined stainless steel vessel. The mix-
ture was sealed and heated at 120 °C for 3 days, and then the reaction
system was cooled to room temperature. Colorless crystals were
obtained in yield (based on Zn): 56%. Elemental analysis (%): Calcd.
Scheme 1. Coordination modes of hpht2− ligands observed in the title complexes.

Y. Wang et al. / Inorganic Chemistry Communications 30 (2013) 5–12
7
for (C23H22N4O5Zn1): C 55.26, H 4.44, and N 11.20. Found: C 55.33, H
4.78, and N 11.13. FT-IR (KBr pellet, cm−1): 3403(br), 3055(m),
1607(s), 1569(s), 1513(s) 1369(s), 1222(w), 970(w), 846(w),
798(w), 709(w), 624(m), and 462(w).
52.20, H 4.96, and N 10.58. Found: C 52.10, H 4.88, and N 10.43.
FT-IR (KBr pellet, cm−1): 3604(br), 3058(m), 1621(s), 1569(s),
1466(w), 1322(s), 1255(m), 1216(w), 1130(m), 1002(m), 927(w),
883(w), 775(m), 678(w), 634(w), and 489(w).
Synthesis of Cd(pimb)0.5(hpht)(H2O) (2). A mixture of CdCl2·2H2O
(22.5 mg, 0.1 mmol), Homophthalic acid (18.0 mg, 0.1 mmol), pimb
(23.8 mg, 0.1 mmol) and LiOH (8.2 mg, 0.2 mmol) was placed in a
Teflon-lined stainless steel vessel. The mixture was sealed and heated
at 120 °C for 3 days, and then the reaction system was cooled to room
temperature. Colorless crystals were obtained in yield (based on Cd):
56%. Elemental analysis (%): Calcd. for (C16H15Cd1N2O5): C 44.93,
H 3.54, and N 6.55. Found: C 45.01, H 3.41, and N 6.79. FT-IR (KBr
pellet, cm−1): 3155(br), 1625(s), 1556(s), 1519(m), 1469(w),
1440(m), 1373(s), 1309(m), 1259(w), 1164(m), 1022(w), 956(w),
848(w), 755(m), 673(w), 607(m), 571(w), and 457(w).
X-Ray crystallography. X-ray diffraction data were collected on a Bruker
Smart Apex II CCD equipped with a Mo-Kα radiation (λ=0.71073 Å).
The data were integrated by using the SAINT program [9], which was
also used for the intensity corrections for the Lorentz and polarization
effects. An empirical absorption correction was applied using the
SADABS program [10]. The structures were solved by direct methods
with SHELXS-97 program and refined with SHELXL-97 by full-matrix
least-squares techniques on F2. All non-hydrogen atoms were refined
anisotropically and hydrogen atoms isotropically. The hydrogen atoms
except for those of water molecules were generated geometrically. All
calculations were performed on
a personal computer with the
SHELXL-97 crystallographic software package [11]. The details of the
crystal parameters, data collection and refinement for the compounds
are summarized in Table 1. Selected bond lengths and angles with
their estimated standard deviations are listed in Table 2.
Synthesis of [Co(pimb)(hpht)(H2O)2]·H2O (3). A mixture of CoCl2·6H2-
O (23.8 mg, 0.1 mmol), Homophthalic acid (18.0 mg, 0.1 mmol), pimb
(23.8 mg, 0.1 mmol) and Na2CO3 (10.6 mg, 0.1 mol) was placed in a
Teflon-lined stainless steel vessel. The mixture was sealed and heated
at 120 °C for 3 days, and then the reaction system was cooled to room
temperature. Colorless crystals were obtained in yield (based on Co):
68%. Elemental analysis (%): Calcd. for (C23H26Co1N4O7): C 52.18, H
4.96, and N 10.58. Found: C 52.34, H 5.03, and N 10.31. FT-IR (KBr pellet,
cm−1): 3412(br), 3008(w), 1615(s), 1583(s), 1522(s), 1464(w),
1442(w), 1319(m), 1226(m), 1168(w), 1097(w), 968(m), 923(w),
817(w), 761(m), 673(w), and 512(w).
Results and discussion. Synthesis and characterization. Due to the
quick precipitation in traditional aqueous reactions of metal salts and
carboxylate solutions, hydrothermal synthesis at mild temperature
(100–200 °C) under autogenous pressure was proven to be a powerful
approach in the preparation of low-soluble MOFs, which can cause the
reactions to shift from the kinetic to the thermodynamic domain [12].
In our work, complexes 1, 3 (Zn/Co complexes) were obtained when
only Na2CO3 was used to adjust the pH value, while the other com-
plexes (2 and 4 based on Cd/Ni) were synthesized when only the
LiOH was used as base, because suitable crystals cannot be obtained
with other different bases. Thus, the different bases play important
roles in the construction of the title complexes, which is also the case
for some reported carboxylate compounds [13].
Synthesis of [Ni(pimb)(hpht)(H2O)2]·H2O (4). A mixture of NiCl2·6H2O
(23.7 mg, 0.1 mmol), Homophthalic acid (18.0 mg, 0.1 mmol), pimb
(23.8 mg, 0.1 mmol) and LiOH (8.2 mg, 0.2 mmol) was placed in a
Teflon-lined stainless steel vessel. The mixture was sealed and heated
at 120 °C for 3 days, and then the reaction system was cooled to
room temperature. Colorless crystals were obtained in yield (based
on Ni): 63%. Elemental analysis (%): Calcd. for (C23H26N4Ni1O7): C
No bands at around 1700 cm−1 were found in the IR spectrum
of title complexes indicating the complete deprotonation of the
Table 1
Crystal data and structure refinements for complexes 1–4.
1
2
3
4
Empirical formula
Formula weight
C
23H22N4O5Zn1
C16H15Cd1N2O5
427.70
C23H26Co1N4O7
529.41
C23H26N4Ni1O7
529.19
499.82
Temperature (K)
298(2)
298(2)
298(2)
298(2)
Crystal system
Space group
Triclinic
Pī
Monoclinic
C2/c
Monoclinic
P 21/c
Monoclinic
P 21/c
a/Å
b/Å
c/Å
α/(°)
8.3560(8)
10.8110(11)
13.1530(14)
94.6630(10)
96.2750(10)
105.18(2)
1132.4(2)
2
19.9441(19)
8.2380(8)
19.4769(17)
90.00
98.8010(10)
90.00
3162.4(5)
8
1.797
11.3278(9)
13.2079(14)
18.9925(14)
90.00
122.189(4)
90.00
2404.8(4)
4
1.462
11.2950(10)
13.1770(12)
18.9798(13)
90.00
122.218(4)
90.00
2389.9(3)
4
1.471
β/(°)
γ/(°)
V/Å3
Z
Dc/g·cm−3
1.466
Absorption coefficient/mm
θ range/(°)
F(000)
1.127
2.37–25.00
516
1.410
2.68–27.50
1704
0.765
2.37–28.31
1100
0.863
2.63–27.49
1104
Reflections collected
Unique reflections
Rint
5510
3848
0.0393
9102
3603
0.0326
14937
5909
0.0530
14116
5464
0.0424
Reflections observed [I>2σ(I)]
Goodness-of-fit on F2
R1, wR2 [I>2σ(I)]
R1, wR2 (all data)
2322
1.076
2986
1.080
3321
1.011
3471
1.088
0.1438, 0.3854a
0.1932, 0.4302
0.0303, 0.0681b
0.0406, 0.0732
0.0395, 0.0836c
0.0906, 0.1076
0.0359, 0.0845d
0.0727, 0.1098
a
w=1/[s2(F02)+(0.1605P)2+13.2125P], where P=(F02+2Fc2)/3.
w=1/[s2(F02)+(0.0331P)2+1.9547P], where P=(F02+2Fc2)/3.
w=1/[s2(F02)+(0.0297P)2+1.1001P], where P=(F02+2Fc2)/3.
w=1/[s2(F02)+(0.0436P)2+0.5889P], where P=(F02+2Fc2)/3.
b
c
d

8
Y. Wang et al. / Inorganic Chemistry Communications 30 (2013) 5–12
Table 2
Description of crystal structures. [Zn(pimb)(hpht)]·(H2O) (1). Single-
crystal X-ray structural analysis shows that the structure of 1 is a
two-dimensional complex. The coordination environment around
Zn(II) atom is depicted in Fig. 1a. The Zn(II) is in distorted tetrahedron
geometry and coordinated by two carboxyl O atoms from two hpht2−
and two N atoms from two pimb ligands in N2O2 donor set. The coordi-
nation bond lengths and angles around Zn(II) are in the range of
1.935(13) to 2.014(14) Å and 95.5(5)° to 119.7(6)°, respectively. In 1,
each hphp2− connects two Zn(II) atoms with Zn···Zn separation
of 8.36 Å to form one-dimensional chain structure, where the carboxyl-
ate groups are all coordinated to one Zn(II) with μ1−η1:η0 monodentate
mode (Scheme 1a). The chains are further expanded to two-dimensional
corrugated net structure with the pillar coordination effect of pimb
(Fig. 1b). The pimb ligands in 1 adopt trans-conformation, where the
two imidazole rings are parallel to each other and corresponding dihe-
dral angle between imidazole and benzene is 72.00°. There are abundant
strong hydrogen bond interactions in 1 involving free water molecules,
carboxylate O atoms and C atoms on the skeleton (Table 3), which trap
water molecules around the inflection points of the layers (Fig. 1c).
These 2D layers are stacked along b axis to form its 3D framework
(Fig. A.1) and stabilized by C\H···O interactions (Table 3) [15].
Selected bond lengths (Å) and bond angles (°) for complexes 1–4.
1
Zn1-O1
Zn1-N2
O1-Zn1-O3
O1-Zn1-N4
O3-Zn1-N4
1.935(13)
2.006(12)
95.5(5)
119.7(6)
106.1(6)
Zn1-O3
Zn1-N4
O1-Zn1-N2
O3-Zn1-N2
N2-Zn1-N2
1.946(11)
2.014(14)
107.9(5)
118.5(6)
109.2(5)
2
Cd1-O1#1
Cd1-O3
Cd1-O1W
2.368(2)
2.234(2)
2.577(3)
55.36(7)
94.37(9)
107.59(8)
87.35(8)
162.27(8)
77.95(8)
161.03(9)
84.34(9)
Cd1-O2#1
Cd1-O4#2
Cd1-N2
O1#1-Cd1-O3
O1#1-Cd1-O1W
O2#1-Cd1-O3
O2#1-Cd1-O1W
O3-Cd1-O4#2
O3-Cd1-N2
2.356(2)
2.330(2)
2.220(2)
126.26(8)
70.69(8)
84.99(8)
93.16(8)
120.94(9)
111.48(9)
89.42(9)
O1#1-Cd1-O2#1
O1#1-Cd1-O4#2
O1#1-Cd1-N2
O2#1-Cd1-O4#2
O2#1-Cd1-N2
O3-Cd1-O1W
O4#2-Cd1-O1W
O1W-Cd1-N2
O4#2-Cd1-N2
3
Co1-O2#3
Co1-N4#3
Co1-O1W#3
Co2-O4
Co2-N2#5
Co2-O2W
O2#3-Co1-O2
O2-Co1-N4#3
O2-Co1-N4
O2#3-Co1-O1W#3
N4#3-Co1-O1W#3
O2#3-Co1-O1W
N4#3-Co1-O1W
O1W#3-Co1-O1W
O4-Co2-N2#5
O4-Co2-N2#6
N2#5-Co2-N2#6
O4#4-Co2-O2W
N2#6-Co2-O2W
O4#4-Co2-O2W#4
N2#6-Co2-O2W#4
2.0683(17)
2.132(2)
2.181(2)
2.1089(18)
2.122(2)
2.145(2)
180.00(11)
88.40(8)
91.60(8)
87.95(8)
91.97(8)
92.05(8)
88.03(8)
179.999(1)
87.52(8)
92.48(8)
180.00(15)
89.89(9)
91.33(8)
90.11(9)
88.67(8)
Co1-O2
Co1-N4
Co1-O1W
Co2-O4#4
Co2-N2#6
Co2-O2W#4
2.0684(17)
2.132(2)
2.181(2)
2.1089(18)
2.122(2)
2.145(2)
91.60(8)
88.40(8)
179.998(1)
92.05(8)
88.03(8)
87.95(8)
91.97(8)
180.0
92.48(8)
87.52(8)
90.11(9)
88.67(8)
89.89(9)
91.33(8)
179.999(1)
Cd(pimb)0.5(hpht)(H2O) (2). When the Zinc(II) was replaced by
Cadmium(II), new polymer with different structures was obtained.
The polymeric structure of 2 was confirmed by X-ray single crystal
structure analysis. The complex 2 crystallizes in monoclinic space
group C2/c. The asymmetric unit of 2 contains one Cd(II) center,
half pimb, one hpht2− and one coordinated water molecules
(Fig. 2a). The Cd(II) is six-coordinated in distorted octahedral geom-
O2#3-Co1-N4#3
O2#3-Co1-N4
N4#3-Co1-N4
O2-Co1-O1W#3
N4-Co1-O1W#3
O2-Co1-O1W
N4-Co1-O1W
O4-Co2-O4#4
O4#4-Co2-N2#5
O4#4-Co2-N2#6
O4-Co2-O2W
N2#5-Co2-O2W
O4-Co2-O2W#4
N2#5-Co2-O2W#4
O2W-Co2-O2W#4
etry with four carboxylate O atoms from three different hpht2−
one water molecule and one atom from pimb ligand. The
,
N
corresponding bond lengths and angles around Cd(II) center are in
the range of 2.220(2) to 2.577(3) Å and 55.36(7)° to 162.27(8)°, re-
spectively, which is comparable with the reported Cd\O/N bond
[16]. The carboxylate groups of hpht2− adopt μ1 −η1:η1 chelating
mode and μ2 −η1:η1 bridging mode, respectively (Scheme 1b). Two
Cd(II) atoms and two bridging carboxylate groups form a bimetallic
subunit with Cd···Cd distance of 4.06 Å, which are linked by
hpht2− to give rise to a 1D ladder-like chain structure (Fig. 2b)
along the b axis with separation of 5.33 Å. The pimb ligands are in
cis-conformation, the dihedral angles between two imidazole and
benzene rings are 13.1° and 83.4°, respectively, and the angle of the
methylene arm (e.g. the angle of C10–C13-N1) is 110.5°. The neigh-
boring chains are connected by pimb ligands to build a 2D network
spreading along the bc plane. If the Cd atom is considered as a
four-connected node (three hphp2− and one pimb), the hpht2− and
pimb can be considered as three-connected node and pillar, respec-
tively. Thus the 2D network of 2 can be classified as 2-nodal net of
(42·63·8)(42·6) topology (Fig. 2c) [17]. Although some similar topol-
ogies have been reported, such V2O5 topology based on asymmetric
polycarboxylate and Zinc(II) is rare [18]. The intermolecular packing
is further controlled by C\H···π interaction among the C atom in
5-positon of imidazole and neighboring benzene ring of hpht2−
(H16···Centroid=2.74 Å, C16···Centroid=3.556(3) Å and ∠C16–
H16···Centroid=147°) to generate a 3D supramolecular architec-
ture in ···ABAB··· mode (Fig. A.2) [19].
4
Ni1-O2#3
Ni1-N4#3
Ni1-O1W#3
Ni2-O4
Ni2-N2#5
Ni2-O2W
O2#3-Ni1-O2
O2-Ni1-N4#3
O2-Ni1-N4
O2#3-Ni1-O1W#3
N4#3-Ni1-O1W#3
O2#3-Ni1-O1W
N4#3-Ni1-O1W
O1W#3-Ni1-O1W
O4-Ni2-N2#5
O4-Ni2-N2#6
N2#5-Ni2-N2#6
O4#4-Ni2-O2W
N2#6-Ni2-O2W
O4#4-Ni2-O2W#4
N2#6-Ni2-O2W#4
2.0600(16)
2.082(2)
2.1249(19)
2.0765(16)
2.081(2)
2.1153(18)
179.997(1)
88.48(7)
91.52(7)
88.77(8)
92.15(8)
91.23(8)
87.85(8)
179.999(1)
88.11(8)
91.88(8)
180.00(14)
91.06(8)
90.84(8)
88.94(8)
89.17(8)
Ni1-O2
Ni1-N4
Ni1-O1W
Ni2-O4#4
Ni2-N2#6
Ni2-O2W#4
2.0599(16)
2.082(2)
2.1248(19)
2.0765(16)
2.081(2)
2.1153(18)
91.52(7)
88.48(7)
180.00(10)
91.23(8)
87.85(8)
88.77(8)
92.15(8)
180.0
91.89(8)
88.11(8)
88.94(8)
89.16(8)
91.06(8)
90.83(8)
179.998(1)
O2#3-Ni1-N4#3
O2#3-Ni1-N4
N4#3-Ni1-N4
O2-Ni1-O1W#3
N4-Ni1-O1W#3
O2-Ni1-O1W
N4-Ni1-O1W
O4-Ni2-O4#4
O4#4-Ni2-N2#5
O4#4-Ni2-N2#6
O4-Ni2-O2W
N2#5-Ni2-O2W
O4-Ni2-O2W#4
N2#5-Ni2-O2W#4
O2W-Ni2-O2W#4
Symmetry codes: #1 x, 1−y, 0.5+z; #2 x, −y, 0.5+z; #3 −x+2, −y+2, −z+2;
#4 −x+2, −y+3, −z+2; #5 −x+1, y+1/2, −z+3/2; #6 x+1, −y+5/2, z+1/2.
[Co(pimb)(hpht)(H2O)2]·H2O (3) and [Ni(pimb)(hpht)(H2O)2]·H2O
(4). Similar cell parameters with the same space group P 21/c as listed
in Table 1 and the results of crystallographic analysis indicate that com-
plexes 3 and 4 are isomorphous and isostructural, and thus only the
structure of 3 is presented here as an example. The asymmetric unit
of 3 contains two Co(II) atoms locating at inversion centers , one
hpht2− ligand, one pimb ligand, two coordinated water molecules and
one free water molecule (Fig. 3a). The Co1/Co2 is all six-coordinated in
octahedral geometry of O4N2 set composed of two water molecules,
carboxylic acid ligands, which is also consistent with the X-ray single-
crystallographic analysis. Strong absorptions bands between 1350
and 1630 cm−1 in the IR can be assigned to the coordinated carbox-
ylate groups [14].

Y. Wang et al. / Inorganic Chemistry Communications 30 (2013) 5–12
9
(a)
(b)
Fig. 1. (a) Coordination environment around Zn(II) in 1, where the ellipsoids were drawn at 30% and hydrogen atoms were omitted for clarity. Symmetric code: A x+1, y, z; B −
x+3, −y+2, −z+1; C −x+1, −y+2, −z. (b) Top view of 2D sheet in 1 along the b axis.
H···π (H8B···Centroid=2.59 Å, C8···Centroid=3.560(4)
∠C8–H8B···Centroid=177°) between two adjacent layers, which
expand the 2D layers to its 3D architecture (Fig. A.3) [19].
Å and
two carboxyl O atoms and two N atoms from different ligands with dif-
ferent bond lengths and angles. The Co\O/N bond lengths in the range
of 2.0683(17)–2.181(2) Å are comparable with those of the reported
ones [20]. The hpht2− displays bis-monodentate coordination fashion
(Scheme 1a), while the pimb ligand adopts cis-conformation with the
dihedral angles between three aromatic rings of 80.79°, 88.10° and
45.22°, respectively.
Structural diversities of MOFs 1 to 4. It is notable that, by proper choice
of the asymmetric dicarboxylic acid and similar N-donor based li-
gands as building blocks, various frameworks were obtained. The di-
versification in polymers 1–4 may be due to different sources as
discussed below: (i) the nature and versatile coordination geometry
of the metal ions. In title complexes, four different metal ions lead
to four different architectures, although the synthetic conditions are
almost the same. For instance, in complexes 1 and 2, the Zn(II) is in
tetrahedron geometry with N2O2 donor set, while the Cd(II) is all in
octahedron geometry with O5N1 donor set. The diverse coordination
geometries of Zn/Cd centers may be propitious to the structural diversi-
fication of the MOFs. (ii) Different conformations of pimb ligand includ-
ing different coordination patterns that the hpht2− ligands adopt, in
which the hpht2− ligand can be regarded as μ2- and μ4-linker with di-
verse coordination modes of carboxylate groups. The versatile coordi-
nation behaviors of ligands allow them to make adjustment during
assembly process to result in diverse frameworks. However, in general,
the further extension of these factors mentioned above may mainly in-
fluence their final structural diversities, which cannot be precisely pre-
dicted and it still needs more experimental accumulations [22].
The Co(II) ions are bridged by hpht2−
,
which adopts
bis(monodentate) coordination mode (Scheme 1a), to generate a
neutral one-dimensional (1D) S-shape double-helix chain along the
b axis with Co···Co distance of 6.60 Å (Fig. 3b). Such chains are
further connected by pimb via Co\N coordination bond along a axis
to form a two-dimensional sheet in the ab plane (Fig. 3c) consisting
of M4L4 (four Co(II), two hpht2− and two pimb) 42-menbered macro-
cyclic unit. The free water molecules (O3W) are trapped in the cyclic
units and stabled by strong hydrogen bonds as indicated in Fig. 3c
(Table 3). It is noteworthy that, although the H3WB does not partici-
pate in any hydrogen bond interactions, it forms O\H···π interactions
with adjacent benzene rings of hpht2− in the same layer (e.g. H3WB···
Centroid=2.73(6) Å, O3···Centroid=3.470(3) Å and ∠O3–H3WB···
Centroid=148(5)°) [21]. Furthermore, there are an additional C\
Table 3
Hydrogen bond lengths (Å) and bond angles (°) for 1–4.
XRD patterns and thermal properties. In order to confirm that the phase
purity of these bulk materials can be represented by the crystal struc-
tures, powder XRD experiments were carried out for complexes 1–4
(Supplementary material, Fig. A.4–A.7). Despite a few unindexed dif-
fraction lines and some lightly broadened peaks, the experimental
patterns of the as-synthesized samples can be considered comparable
to corresponding simulated ones, indicating the phase purity of each
sample.
D\H···A
d(D\H)
d(H···A)
d(D···A)
∠DHA
1
O1W-H1WA···O4#1
O1W-H1WB···O2
C13-H13···O1W
C15-H15···O1W
C21-H21B···O3#2
0.85
0.85
0.93
0.93
0.97
1.79
2.24
2.42
2.47
2.50
2.60(4)
3.05(4)
3.30(4)
3.27(5)
3.34(3)
159
161
157
145
145
3
Thermal gravimetric analysis (TGA) was also carried out to examine
the thermal stabilities of 1–4 (Supplementary material, Fig. A.8–A.11).
The results show that the weights of title complexes are very stable in
air at ambient temperature making them potential candidates for prac-
tical applications. For complex 1, the decomposition of the compound
occurs at ca. 300 °C. The remaining weight corresponds to the forma-
tion of ZnO (obsd. 17.05%, calcd. 16.28%). For 2, a weight loss of 4.26%
(calcd. 4.21%) is observed from ca. 189 to 263 °C, which is attributed
O3W-H3WA···O1
O2W-H2WA···O3W#3
0.85
0.83(5)
2.10
1.99(5)
2.951(4)
2.792(4)
179
165(4)
4
O3W-H3WA···O1
O2W-H2WB···O3W#3
0.88
0.89(5)
2.08
1.93(5)
2.954(4)
2.803(4)
173
168(5)
Symmetric codes: #1 −1+x, y, z; #2 −x+, −y+1, −z+1; #3 −x+1, y+1/2,
−z+3/2.

10
Y. Wang et al. / Inorganic Chemistry Communications 30 (2013) 5–12
(a)
(b)
(c)
Fig. 2. (a) Coordination environment around Cd(II) in 2 with the thermal ellipsoids at 30% with additional atoms drawn to finish the coordination sphere and integrity of ligand,
where the hydrogen atoms were omitted for clarity. Symmetric code: A −x+1/2, −y+3/2, −z+1; B −x+1/2, −y+1/2, −z+1; C −x, y, −z+1/2. (b) View of 1D chain in 2
with the distances marked. (c) View of 2D 2-nodal V2O5 topological framework, where the Cd(II) and hpht2− ligands are presented by four- and three-spoke radiation from solid
points, respectively.
to the loss of coordinated water molecules. The next weight loss follows
closely, corresponding to the decomposition of the anhydrous complex.
For complexes 3 and 4, there is no significant loss up to about 300 °C,
and then a sharp weight-loss step occurs.
Conclusions. In this paper, we present a family of transition metal
(Zn/Cd/Co/Ni) MOFs based on asymmetric polycarboxylate ligand
and N-donor auxiliary ligands. These four MOFs have different
structures. In general, the diverse coordination patterns that the
phenyl dicarboxylate groups are adopting and the coordination
need of metal centers play dominating roles in the construction
of these compounds. Our present results will further enrich the
strategy of crystal engineering and offer the possibility of controlla-
ble synthesis on desired architectures. Meanwhile, this work may
also give us an opportunity to get more functional crystalline
products by such reliable synthetic route by employing aromatic
polycarboxylate ligands and N-donor spacers, and further investiga-
tions are still undergoing.
Photoluminescent properties of 1 and 2. For MOFs containing Zinc and
Cadmium as metal centers, the luminescent properties have attracted
more interest due to their good applications in various areas, includ-
ing chemical sensor, photochemistry and electroluminescent display,
etc [23]. Thus, the solid-state photoluminescent properties of com-
plexes 1 and 2 have been investigated at room temperature. As
depicted in Fig. 4, the intense broad emission bands at 420 nm for 1
and 412 nm for 2 are observed with excitation wavelength of
342 nm. Meanwhile, the free H2hpht, pimb exhibits fluorescent emis-
sions at 443 nm and 423 nm, respectively, with the same excitation
condition. Due to the d10 configuration of Zn(II) and Cd(II) ions, neither
metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge
transfer (LMCT) can easily occur, the emission spectra for the com-
plexes should be assigned to the intraligand fluorescent emission. The
enhancement of luminescence may be attributed to coordination effect,
which increases the rigidity of the ligand and reduces to loss of energy
by radiationless decay [23]. These results show that complexes 1 and
2 may be candidates for potential photoactive materials.
Acknowledgment. We are very thankful for the financial support
from the National Natural Science Foundation of China (grant no.
20901004, 20971004) and the Science Foundation for Young Teachers
of AQTC (KJ201016).
Appendix A. Supplementary material. Crystal packing diagrams,
TGA curves and XPRD patterns of title complexes. CCDC 853420,
853421, 862176 and 862180 contain the supplementary crystallo-
graphic data for 1, 2, 3 and 4. These data can be obtained free of

Y. Wang et al. / Inorganic Chemistry Communications 30 (2013) 5–12
11
(a)
(b)
(c)
Fig. 3. (a) Asymmetric unit in 3 with additional atoms drawn to complete the coordination environments around Co(II). The thermal ellipsoids were drawn at 30% and the H atoms
were omitted for charity. Symmetric code: A −x+2, −y+3, −z+2; B −x+1, y+1/2, −z+3/2; C x+1, −y+5/2, z+1/2; D −x+2, −y+2, −z+2. (b) View of 1D chain of 3
along the c axis. (c) View of 2D sheet in complex 3 along c axis, where the hydrogen bonds and O\H···π interactions were indicated by black and red dashed lines, respectively.
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif. Supplementary data to this article can
be found online at http://dx.doi.org/10.1016/j.inoche.2012.12.037.
References
[1] Z.L. You, X.Y. Qiu, D.M. Xian, M. Zhang, Unprecedented preparation of dinuclear
nickel(II) and zinc(II) complexes with shciff-base ligands transformation under
solvothermal conditions, Inorg. Chem. Commun. 26 (2012) 11–16.
[2] M. Yoon, R. Srirambalaji, K. Kim, Homochiral metal-organic frameworks for asym-
metric heterogeneous catalysis, Chem. Rev. 112 (2012) 1196–1231.
[3] C. Adhikary, S. Koner, Structural and magnetic studies on copper(II) azido com-
plexes, Coord. Chem. Rev. 254 (2010) 2933–2958.
2
1
[4]
a
L.L. Zhang, J. Guo, Q.G. Meng, H.D. Pang, Z. Chen, D.F. Sun, Two novel
isostructural Ln(III) 3D frameworks supported by 3,6-dibromobenzene-
1,2,4,5-tetracarboxylic acid and in situ generated oxalate: synthesis, character-
ization and photoluminescent property, Inorg. Chem. Commun. 26 (2012)
51–55;
pimb
b
H.F. Zhu, J. Fan, T. Okamura, W.Y. Sun, N. Ueyama, Syntheses and structures of
Zinc(II), Silver(I), Copper(II), and Cobalt(II) complexes with imidazole-
containing ligand: 1-(1-imidazoly)-4-(imidazole-1-ylmethyl)benzene, Cryst.
Growth Des. 5 (2005) 289–294.
H2hpht
[5] C.A. Williams, A.J. Blake, C. Wilson, P. Hubberstey, M. Schröder, Novel metal-
organic frameworks derived from group II metal cations and aryldicarboxylate
anionic ligands, Cryst. Growth Des. 8 (2008) 911–922.
[6] M.S. Chen, Z.S. Bai, T. Okamura, Z. Su, S.S. Chen, W.Y. Sun, N. Ueyama,
Metal-organic frameworks with pyridyl- and carboxylate-containing ligands:
synthesis, structures and properties, CrystEngComm 12 (2010) 1935–1944.
[7] L. Koskinen, S. Jääskeläinen, L. Oresmaa, M. Haukka, Argentophilic interactions in
multinuclear Ag complexes of imidazole containing Schiff bases, CrystEngComm
14 (2012) 3509–3514.
[8] X.L. Wang, L.L. Hou, J.W. Zhang, J.X. Zhang, G.C. Liu, S. Yang, Assembly and properties
of coordination polymers modulated by substituted 1,3-benzenedicarboxylates,
CrystEngComm 14 (2012) 3936–3944.
350
400
450
500
550
600
650
Wavelength (nm)
Fig. 4. Photoluminescent properties of complexes 1 and 2 and free ligands.
[9] SAINT, Version 6.02a; Bruker AXS Inc., Madison, WI, 2002.

12
Y. Wang et al. / Inorganic Chemistry Communications 30 (2013) 5–12
[10] G.M. Sheldrick, SADABS, Program for Bruker Area Detector Absorption Correction,
University of Göttingen, Göttingen, Germany, 1997.
ligand: diverse structural topology and photoluminescent and magnetic proper-
ties, Cryst. Growth Des. 11 (2011) 1475–1485.
[11]
a
G.M. Sheldrick, SHELXS-97, Program for Crystal Structure Solution, University
of Göttingen, Göttingen, Germany, 1997.;
G.M. Sheldrick, SHELXL-97, Program for Crystal Structure Refinement, Univer-
sity of Göttingen, Göttingen, Germany, 1997.
[19] M.K. Rofouei, J.A. Gharamaleki, M.R. Melardi, S.M. Hosseini, F. Hosseinzadeh, M.
Peyman, A. Ghannadan, B. Notash, G. Bruno, H.A. Rudbari, Synthesis, characterization
and crystal structures of HgII complexes with asymmetric ortho-functionalized
1,3-bis(aryl)triazenide ligands, Polyhedron 44 (2012) 138–142.
b
[12] M.P. Suh, Y.E. Cheon, E.Y. Lee, Syntheses and functions of porous
metallosupramolecular network, Coord. Chem. Rev. 252 (2008) 1007–1026.
[13] X.L. Wang, C. Qin, E.B. Wang, Polythreading of infinite 1D chains into different
structural motifs: two poly(pseudo-rotaxane) architectures constructed by con-
[20] A.D. Burrows, L.C. Fisher, D. Hodgson, M.F. Mahon, N.F. Cessford, T. Düren, C.
Richardson, S.P. Rigby, The synthesis, structures and reactions of zinc and cobalt
metal-organic frameworks incorporating an alkyne-based dicarboxylate linker,
CrystEngComm 14 (2012) 188–192.
comitant coordinative and hydrogen bonds, Cryst. Growth Des.
6
(2006)
[21] G. Matisz, A. Kelterer, W.M.F. Fabian, S. Kunsάgi-Mάte, Coordination of methanol
439–443.
clusters to benzene: a computational study, J. Phys. Chem. A 115 (2011)
[14] G.H. Wang, Z.G. Li, H.Q. Jia, N.H. Hu, J.W. Xu, Topological diversity of coordination
polymers containing the rigid terephthalate and a flexible N, N′-type ligand: in-
terpenetration, polyrotaxane and polythreading, Cryst. Growth Des. 8 (2008)
1932–1939.
10556–10564.
[22]
[23]
a
b
a
D.C. Wu, F. Xu, R.W. Fu, K. Hong, K. Matyjaszewski, Design and preparation of
porous polymers, Chem. Rev. 112 (2012) 3959–4015;
D.F. Weng, Z.M. Wang, S. Gao, Framework-structured weak ferromagnets,
Chem. Soc. Rev. 40 (2011) 3157–3181.
H.J. Hao, D. Sun, F.J. Liu, R.B. Huang, L.S. Zheng, Discrete octamer water cluster and
1D T5(2) water tape trapped in two luminescent Zn(II)/1,2-bis(imidazole-1′-yl)
ethane/dicarboxylate hosts: from 2D (4,4) net to 3D 5-fold interpenetrated dia-
mond network, Cryst. Growth Des. 11 (2011) 5475–5482;
[15] D. Saha, T. Maity, T. Dey, S. Koner, One-dimensional chain copper(II) complex:
X-ray crystal structure and catalytic activity in the epoxidation of styrene, Polyhe-
dron 35 (2012) 55–61.
[16] A. Pramanik, G. Das, Aryl azo imidazole assisted self-assembly of d10 metal com-
plexes: influence of halogen substitution and counter ions, Polyhedron 29 (2010)
2999–3007.
b
c
S.S. Chen, J. Fan, T. Okamura, M.S. Chen, Z. Su, W.Y. Sun, N. Ueyama, Synthesis,
crystal structure, and photoluminescence of a series of Zinc(II) coordination
polymers with 1,4-Di(1H-imidazol-4-yl)benzene and varied carboxylate li-
gands, Cryst. Growth Des. 10 (2010) 812–822;
Z.S. Bai, G.X. Liu, Y. Lu, W.Y. Sun, Preparation, structure, magnetic and
photoluminescence properties of copper(II) and cadmium(II) frameworks
with 4,4′-bipyridine-2,2′,6,6′-tetracarboxylate, Inorg. Chem. Commun. 11
(2008) 513–517.
[17]
a
V.A. Blatov, A.P. Shevchenko, TOPOS-Version 4.0 Professional (Beta Evalua-
tion), Samara State University, Samara, Russia, 2006.;
b
D. Zhao, D.J. Timmons, D.Q. Yuan, H.C. Zhou, Tuning the topology and function-
ality of metal-organic frameworks by ligand design, Acc. Chem. Res. 44 (2011)
123–133.
[18] B.Y. Li, F. Yang, G.H. Li, D. Liu, Q. Zhou, Z. Shi, S.H. Feng, Construction of coordina-
tion polymers based on bent 4-amino-3,5-bis(3-carboxyphenyl)-1,2,4-triazole