Three 3D complexes constructed from azelaic aci and rigid bis(imidazole) ligand: Syntheses, structures, thermal and photoluminescent properties

Article abstract of DOI:10.1016/j.inoche.2012.07.012

Three new 3D transition metal coordination complexes, namely, [Co(Aze)(L)] (1), [Cu(Aze)(L)]₂ (2) and [Cd(Aze)(L)]·3H₂O (3) (Aze = azelaic acid, L = 1,4-bis (1-imidazolyl)-benzene) have been synthesized hydrothermally from the self-assembly of the transition metal ions (M ^{2 +}) with flexible aliphatic dicarboxylate ligand (Aze) and the rigid bis(imidazole) ligand (L). All complexes display three-dimensional (3D) structures. Complex 1 shows a three-fold interpenetrating 4-connected dmp net. Complex 2 shows a noninterpenetrating 4-connected cds net. Complex 3 shows the pcu net built on 6-connected Cd₂ units and particularly there exists weave-like water chains penetrating the channels of the pcu net along b direction. Furthermore, thermogravimetric studies of 1, 2 and 3, and photoluminescent property of 3 have also been investigated.

Full text of DOI:10.1016/j.inoche.2012.07.012

Inorganic Chemistry Communications 24 (2012) 200–204
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Three 3D complexes constructed from azelaic aci and rigid bis(imidazole) ligand:
Syntheses, structures, thermal and photoluminescent properties
⁎
Fang-Hua Zhao, Yun-Xia Che, Ji-Min Zheng
Department of chemistry, Nankai University, Tianjin300071, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new 3D transition metal coordination complexes, namely, [Co(Aze)(L)] (1), [Cu(Aze)(L)]2 (2) and
[Cd(Aze)(L)]·3H2O (3) (Aze = azelaic acid, L = 1,4-bis (1-imidazolyl)-benzene) have been synthesized
hydrothermally from the self-assembly of the transition metal ions (M2+) with flexible aliphatic dicarboxylate
ligand (Aze) and the rigid bis(imidazole) ligand (L). All complexes display three-dimensional (3D) structures.
Complex 1 shows a three-fold interpenetrating 4-connected dmp net. Complex 2 shows a noninterpenetrating
4-connected cds net. Complex 3 shows the pcu net built on 6-connected Cd2 units and particularly there
exists weave-like water chains penetrating the channels of the pcu net along b direction. Furthermore,
thermogravimetric studies of 1, 2 and 3, and photoluminescent property of 3 have also been investigated.
© 2012 Elsevier B.V. All rights reserved.
Received 31 May 2012
Accepted 2 July 2012
Available online 10 July 2012
Keywords:
Coordination complexes
Azelaic acid
Bis(imidazole) ligand
Photoluminescent property
The design and synthesis of coordination complexes is now of great
interest owing to their intriguing topologies and potential applications
in many fields such as gas storage, ion exchange, catalysis and magne-
tism [1]. In construction of the coordination complexes, the selection
of appropriate organic linkers is central to determining the structures
of the resulting coordination complexes. It is well known that the
carboxylate-containing ligands play an important role in coordination
chemistry. And so far, extensive work has been carried out using rigid
carboxylate ligands; for example, benzoic acid and its derivative ligands
such as 1,4-benzenedicarboxylate and 1,3,5-benzenetricarboxylate,
have been extensively employed to construct high-dimensional
structures [2,3]. As good carboxylate ligands, the flexible carboxylate
ligands have also received considerable attention in the construction
of coordination complexes, the flexibility and conformational freedoms
of such ligands may produce diverse frameworks with unique
structures and useful properties [4].
On the other hand, the ligands containing N-donor such as
imidazole, pyridine and their derivatives have also attracted great
attention to construct metal–organic complexes [5]. The rigid
1,4-bis(1-imidazolyl)-benzene (L) ligand, as good N-donor ligand,
has already proven a certain ability to give interpenetrating networks in
our previous works [6]. And several other complexes based on L and
polycarboxylate ligands have also been reported [7]. Upon careful
inspection of such reported complexes, most of them are focused
on the metal–L–aromatic polycarboxylate system; by contrast, the
exploration of metal–L–flexible polycarboxylate system is less
documented [7e,8]. In our recent work, we have reported three
2D metal–L–Pim complexes with helical chains using flexible
pimelic acid with L ligand [8]. In this work, we use the longer
azelaic acid instead of pimelic acid (Pim) with rigid L ligand to
construct complexes. Three metal–L–Aze complexes are sucessfully
prepared under the hydrothermal conditions, [Co(Aze)(L)] (1),
[Cu(Aze)(L)]2 (2) and [Cd(Aze)(L)]·3H2O (3). Interestingly, com-
pared to the three 2D structures of metal–L–Pim complexes, the
three metal–L–Aze complexes all display 3D structures which can
be attributed to the longer length of the Aze acid than Pim acid.
The syntheses, structures, thermal and photoluminescent studies
in detail are listed below.
The purple block-shaped crystals of complex 1 were prepared by
the reaction of Co(NO3)2·6H2O with Aze and L in a 1:1:1 molar
ratio under hydrothermal conditions [9]. Single crystal X-ray analysis
[10] reveals that complex 1 crystallizes in the orthorhombic space
group Pnna. In the asymmetric unit, there are half a Co2+ ion, half
an Aze2− anion and half an L ligand. As shown in Fig. 1a, the Co(II)
ion is coordinated by four oxygen atoms of two Aze2− anions and
two nitrogen atoms of two L molecules to give the distorted CoO4N2
octahedral geometry. The Co–O/N bond lengths in the range of
2.089(3)–2.253(3) Å (Table S1) are comparable with the normal
Co–O/N bond lengths. Each completely deprotonated Aze2− anion
connects two Co(II) centers with the μ2–η2:η2 coordinated mode
(Scheme 1, I), and each L connects two Co(II) centers in the trans
fashion with the two imidazole rings being almost coplanar (dihedral
angle=0.36°). The Co(II) ions are connected by the two types of ligands
into a 3D framework with Co⋅⋅⋅Co separation of 11.929(3) Å and
13.413(2) Å, respectively. (Fig. 1b). From the topological view, the
Aze2− and L ligands can be regarded as the linear two-connected linker,
each Co atom is linked by two Aze2− anions and two L ligands with the
same ligands arranging on the same side, so it can be considered as the
four-connected node, the 3D framework can be simplified into a
⁎
Corresponding author. Tel./fax: +86 22 23508056.
E-mail address: jmzheng@nankai.edu.cn (J.-M. Zheng).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.07.012

F.-H. Zhao et al. / Inorganic Chemistry Communications 24 (2012) 200–204
201
Scheme 1. Coordination modes of Aze2−
.
framework constructed from long Aze2− and L ligands has a large
enough vacancy to allow the inclusion of another two identical 3D
frameworks. Therefore, the overall structure of 1 is a three-fold inter-
penetrating dmp net (Fig. 1d).
Complex 2 crystallizes in the triclinic space group P-1. In the asym-
metric unit, there are two types of Cu2+ ions with the occupancy of 0.5,
one independent Aze2− anion and one independent L ligand. From
Fig. 2a, both the Cu1 and Cu2 atoms are coordinated by four Aze2−
oxygen atoms and two L nitrogen atoms to give the distorted CuO4N2
octahedral geometry. The Cu–O/N bond lengths are in the range of
1.9541(14)–2.6560(18) Å. The completely deprotonated Aze2− ligands
and L ligands display the same coordinated modes as those in 1. The L
ligands also exhibit trans fashion with the two imidazole rings being
almost coplanar (dihedral angle=0.00° and 0.26°). However, the
arrangement of the two types of ligands around the metal center are
different from that in 1, the same ligands arrange in the two sides of
the Cu center in complex 2. Thus a different 3D framework is
constructed (Fig. 2b). From the topological view, the 3D framework
of 2 also represents a uninodal four-connected net with the same
Point Schläfli symbol of (65·8) but different extended Schläfli symbol
of 6·6·6·6·62·8∞ (Fig. 2c). Such topology is assigned to cds net
which is obviously different from that of 1. The reason why such differ-
ence can be related to the different arrangement of the two types of
ligands around the metal center.
Complex 3 crystallizes in the monoclinic space group P21/c. The
asymmetric unit consists of one independent Cd(II) ion, one Aze2−
anion, one L ligand and three free water molecules. As shown in
Fig. 3a, the Cd(II) ions are coordinated by five Aze2− oxygen atoms
and two L nitrogen atoms to give the distorted CdO5N2 pentagonal
bipyramid geometry. The Cd–O/N bond lengths are in the range of
2.271(5)–2.502(5) Å. The completely deprotonated Aze2− ligands
adopt the μ3–η3:η2 coordinated mode (Scheme 1, II). The L ligands
exhibit trans fashion with the two imidazole rings being nearly copla-
nar (dihedral angle=6.74°). Two adjacent Cd(II) ions are bridged by
carboxyl group into the Cd2 units with Cd⋅⋅⋅Cd distance of 3.794(4) Å.
Each Cd2 unit is connected with six identical Cd2 units via four single
Aze2− bridges along b and c direction and two double L bridges along
a direction, finally forming a 3D framework (Fig. 3b) which displays a
6-connected pcu net with (412·63) topology symbol (Fig. 3c).
Although lots of complexes with pcu net have been reported, they
all contain one kind of edge (all single or all double) [12], while this
unusual pcu net contains both single and double edges. More inter-
estingly, the three free water molecules are connected by O–H⋅⋅⋅O
hydrogen bonds (Table S2) and short O⋅⋅⋅O contacts into 1D
weave-like water chain penetrating the channels of the 3D frame-
work along b direction (Fig. 3d) (O5⋅⋅⋅O6 2.768(5) Å, O6⋅⋅⋅O7
2.802(1) Å, O7⋅⋅⋅O5A 2.745(3) Å). The free water molecules occupy
the space with a total volume of 375.0 Å3 estimated by Platon [13],
which represents 15.6% of the cell volume. The water chains are
connected with the host framework by the O–H⋅⋅⋅O hydrogen
bonds between the water molecules and the carboxyl groups of
Aze2− (Table S2), which further stablize the 3D structure of 3.
Comparing the structures of the three metal–L–Aze complexes with
those of our recent reported metal–L–Pim complexes [8], only the
Fig. 1. (a) The immediate coordination environment around the Co(II) center in 1,
symmetry code: #1=x, 0.5−y, 1.5−z; #2=1.5−x, −y, z; 3#=−x, 1−y, 1−z;
(b) the 3D framework of 1 viewed along b direction; (c) schematic description of
the 4-connected (65·8) dmp net of 1. Aze, green; L, pink. (d) The schematic view of
3-fold interpenetrating dmp net of 1.
uninodal four-connected dmp net with Point Schläfli symbol of (65·8)
and extended Schläfli symbol of 6·6·6·6·62·83 (Fig. 1c). The
4-connected nets such as dia, cds, qtz nets are very common, while
dmp net is rare in coordination complexes [11]. Moreover, the 3D

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F.-H. Zhao et al. / Inorganic Chemistry Communications 24 (2012) 200–204
Fig. 3. (a) The immediate coordination environment around the Cd(II) center in 3,
symmetry code: #1=2−x, −y, 1−z; #2=1+x, y, z; 3#=x, 0.5−y, 0.5+z; (b) the
3D structure of complex 3. (c) The 3D 6-connected pcu net with (412·63) topology of 3.
Aze, green; L, pink. (d) The 1D weave-like water chain in 3.
Fig. 2. (a) and (b) The immediate coordination environment around the Cu(II) center
in 2, symmetry code: #1=1−x, 1−y, −z; #2=−x, 1−y, −1−z; 3#=2−x, −y,
1−z; 4#=3−x, −1−y, 1−z; (c) the 3D framework of 2; (d) schematic description
of the 4-connected (65·8) cds net of 2.
flexible dicarboxylate acid is changed from pimelic to azelaic acid, the
final dimension of the complexes becomes 3D from 2D. In our reported
metal–L–Pim complexes, all consist of left- and right-handed helical
chains, while no helical chains can be observed in the metal–L–Aze
complexes of this work. Therefore, it is evident that the different lengths
of the flexible dicarboxylate ligands (Pim and Aze) play a significant
role in determining the structures of the two groups of complexes.
To study the stability of the three complexes, thermogravimetric
analysis (TGA) was performed on the single crystal samples of the
three complexes under N2 atmosphere with a heating rate of 5 °C/min.
As shown in Fig. S1, complex 1 shows no weight loss until the tempera-
ture reaches 303 °C, and after that, it begins to chemically decompose, it
does not decompose completely until 800 °C. For complex 2, it can be
stable up to 245 °C, and above that a rapid weight loss occurred,

F.-H. Zhao et al. / Inorganic Chemistry Communications 24 (2012) 200–204
203
lengths of Pim and Aze ligands play a significant role in constructing
the novel structures.
Acknowledgements
This work was supported by the National Natural Science Founda-
tion of China under Project 50872057.
Appendix A. Supplementary data
CCDC-883021-883023 contain the supplementary crystallographic
data for 1–3. The data can be obtained free of charge via bhttp://
www.ccdc.cam.ac.uk/conts/retrieving.html>, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk. Additional
thermogravimetric curves of 1–3, materials and measurements, selected
bonds data are available as electronic supplementary information in the
online version, at http://dx.doi.org/10.1016/j.inoche.2012.07.012.
Fig. 4. Excitation (left) and emission (right) spectra of 3 and L ligand.
Appendix B. Supplementary data
corresponding to the decomposition of the organic ligands, after 354 °C,
it shows slow weight loss without completely decomposing until
800 °C. For complex 3, it shows a weight loss of 9.43% from 30 °C to
125 °C, corresponding to the loss of three free water molecules (calcd.
9.59%), and there is almost no weight loss from 125 °C to 285 °C; and
after that, a rapid weight loss is observed which is attributed to the
decomposition of the organic ligands. And finally, the remnants are
22.87%, which should be CdO (calcd. 22.81%).
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.inoche.2012.07.012.
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[9] Synthesis of 1: a mixture of Co(NO3)2·6H2O (145 mg, 0.5 mmol), Aze (94 mg,
0.5 mmol), L (105 mg, 0.5 mmol) was dissolved in 8 mL distilled water. The pH
value was adjusted to 6.0 with 1 M NaOH solution. The resulting mixture was
sealed in a 25 mL teflon-lined stainless steel vessel and heated at 160 °C for
3 days in an oven and then slowly cooled to room temperature. Purple
block-shaped crystals of 1 were obtained in 62% yield (based on Co). Elemental
analysis(%): Calcd. for (1): C 55.39, H 5.31, N 12.30. Found: C 55.32, H 5.37,
N 12.35. IR (KBr): ν (cm−1)=3090.22(w) 2924.75(w) 2852.10(w) 1557.14(s)
1532.62(s) 1419.69(m) 1307.62(w) 1275.12(w) 1251.67(w) 1128.82(w) 1069.87(m)
960.52(m) 834.93(m) 737.03(w) 661.19(w) 538.24(w). Synthesis of 2: Simi-
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lar procedures to complex
1
were performed except that Co(NO3)2·6H2O
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was replaced by Cu(NO3)2·4H2O (122 mg, 0.5 mmol). Blue block-shaped crys-
tals of 2 were obtained in 76% yield (based on Cu). Elemental analysis(%):
Calcd. for (2): C 54.83, H 5.26, N 12.18. Found: C 54.87, H 5.20, N 12.12. IR
(KBr): ν (cm−1)=3101.77(w) 2926.02(w) 2851.51(w) 1572.00(s) 1527.32(s)
1498.16(w) 1399.95(m) 1305.83(m) 1266.82(w) 1238.64(w) 1142.78(w)
1061.80(m) 959.98(m) 835.21(m) 654.04(w). Synthesis of 3: Similar proce-
dures to complex 1 were performed except that Co(NO3)2·6H2O was replaced
by Cd(NO3)2·4H2O (154 mg, 0.5 mmol). Colourless needle-like crystals of
3 were obtained in 54% yield (based on Cd). Elemental analysis(%): Calcd.
for (3): C 44.81, H 5.37, N 9.95. Found: C 44.87, H 5.31, N 9.99. IR (KBr): ν
(cm−1)=3406.91(w) 3120.02(w) 2930.00(w) 2855.30(w) 1533.50(s) 1411.82(s)
1307.13(m) 1247.47(w) 1134.13(w) 1068.50(m) 961.07(m) 840.98(w) 646.25(w).
[10] Suitable single crystals of 1 to 3 were selected and mounted in air onto thin glass
fibers. Accurate unit cell parameters of the three complexes were determined by
a least-squares fit of 2θ values, and intensity data were measured on a Rigaku
r-axis rapid IP area detector with Mo-Kα radiation (λ=0.71073 Å) at 113 K.
The intensity was corrected for Lorentz and polarization effects as well as for
empirical absorption based on multi-scan technique. The structures were solved
by direct method and refined by full-matrix least-squares fitting on F2 with the
program SHELXL-97. All nonhydrogen atoms were refined anisotropically. The
hydrogen atoms bound to carbon atoms were calculated theoretically and
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