Syntheses, crystal structure, and luminescence properties of three new Cd(II) polymers based on different conformational carboxylates

Article abstract of DOI:10.1016/j.molstruc.2010.12.006

Three new coordination polymers, namely, {[Cd₃(L ₁)₂(IP)₂(H₂O)₄]} _n (1), {[Cd₂(L₂)₂(IP) ₂]·(CH₃OH)(DMF)}_n (2) an

Full text of DOI:10.1016/j.molstruc.2010.12.006

Journal of Molecular Structure 987 (2011) 126–131
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Syntheses, crystal structure, and luminescence properties of three new Cd(II)
polymers based on different conformational carboxylates
a
b
Jian-Qiang Liu a, , Zhen-Bin Jia , Yao-Yu Wang
⇑
a Guangdong Medical College, School of Pharmacy, Dongguan 523808, PR China
b Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, Shaanxi Key Laboratory of Physico-Inorganic
Chemistry, Department of Chemistry, Northwest University, Xi’an 710069, 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 coordination polymers, namely, {[Cd3(L1)2(IP)2(H2O)4]}n (1), {[Cd2(L2)2(IP)2]ꢀ(CH3OH)(DMF)}n
(2) and [Cd(L3)(IP)]n (3) (H3L1 = benzene-1,2,4-tricarboxylic acid, H2L2 = 2,2-bis(4-carboxyphenyl)hexa-
fluoropropane, H2L3 = 1,3-phenylenediacetic acid and IP = 1H-imidazo[4,5-f][1,10]-phenanthroline), were
prepared via self-assembly of pharmaceutical agent IP with cadmium sulfate in the presence of the dif-
ferent backbones of carboxylate linkers under mild conditions. All the polymers possess 2D structural
motifs. The rigid tricarboxylate ligand links the metal centers to form a tetranuclear core in 1. In 2, the
2D network with trinuclear cores is further extended into 3D supramolecular arrays through aromatic
stacking interactions. Interestingly, IP ligand acts in a tridentate mode via the two N atoms of pyridyl
rings and the third N atom of imidazole ring and connects metal atoms into 1D zigzag chain in 3. The
structural analysis reveals that the backbones of carboxylates have critical effect on the construction
of the complexes. Solid-state luminescent spectra of the Cd(II) complexes indicate intense fluorescent
emissions.
Received 1 November 2010
Received in revised form 6 December 2010
Accepted 6 December 2010
Available online 13 December 2010
Keywords:
Crystal structure
Cd(II) complex
Self-assembly
Luminescent property
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
we employ other types of backbones of carboxylates and explore
their effects on metal–organic frameworks. In this context, we will
The flourishing realm of crystal engineering has provided a
sound junction between aesthetics of crystalline architectures
and their potential functions [1–3], of which the ultimate destina-
tion is to successfully achieve the target materials with tailored
structures and/or physicochemical properties. In a general way,
the diversity in the networks of such materials greatly depends
on the selection of metal centers with kinds of coordination prefer-
ence and organic spacers with modifiable backbones and connec-
tivity information [4–10]. The selection of the organic ligand to
be bonded to the metal atom plays a pivotal role in the resulting
structure of MOF. For example, the bent configuration or angular
disposition of coordinating sites of the ligand could generate to a
grid motif [4b]. Nevertheless, it is still a great challenge to predict
the exact structures and compositions of compounds by careful
selection of organic ligands[11–19].
describe three new Cd(II) coordination polymers with different
structural characters. The thermal stabilities and solid-state prop-
erties for these crystalline materials will also be investigated.
2. Experimental abbreviations
H3L1 = benzene-1,2,4-tricarboxylic acid, H2L2 = 2,2-bis(4-car-
boxyphenyl)hexafluoropropane, H2L3 = 1,3-phenylenediacetic acid
and IP = 1H-imidazo[4,5-f][1,10]-phenanthroline.
2.1. Materials and physical measurements
All the reagents were purchased from commercial sources and
used as received. FT-IR spectra (KBr pellets) were taken on a FT-
IR 170SX (Nicolet) spectrometer. The luminescent spectra of the
solid samples were acquired at ambient temperature by using a JO-
BIN YVON/HORIBA SPEX Fluorolog t3 system (slit: 0.2 nm). Ele-
Recently, a comprehensive analysis of the predicted diversity of
coordination polymers with IP has been carried out by us [20].
These results reveal that the backbones of carboxylates and nat-
ures of metal ions are reliable to obtain unusual frameworks with
particular properties. As a continuation of this attractive project,
mental analyses were performed on
analyzer. TG analyses were carried out with a Mettler-Toledo TA
50 in dry nitrogen (60 mL min–1) at a heating rate of 5 °C min–1
X-ray power diffraction (XRPD) data were recorded on a Rigaku
RU200 diffractometer at 60 kV, 300 mA for Cu K radiation
a Perkin–Elmer 240C
.
⇑
Corresponding author.
E-mail address: deposit@ccdc.cam.ac.uk (J.-Q. Liu).
a
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.12.006

J.-Q. Liu et al. / Journal of Molecular Structure 987 (2011) 126–131
127
Table 2
(k = 1.5406 Å), with a scan speed of 2 °C/min and a step size of
0.02° in 2h.
Selected bond distances (Å) and angles (°).
Complex 1
Cd1–O2
Cd1–O4
Cd1–N2
Cd2–O1
Cd2–O7#1
Cd2–O6#3
O2–Cd1–O4
O2–Cd1–N1
O2–Cd1–O5#2
O3–Cd1–O5#2
2.224(4)
2.277(5)
2.354(5)
2.336(4)
2.175(4)
2.401(4)
113.81(18)
87.66(16)
84.74(15)
177.35(15)
Cd1–O3
Cd1–N1
Cd1–O5#2
Cd2–O6
Cd2–O1#3
Cd2–O7#1
O6–Cd2–O7#1
O2–Cd1–N2
O3–Cd1–O4
O4–Cd1–N1
2.335(5)
2.388(4)
2.333(4)
2.401(4)
2.336(4)
2.175(4)
80.22(15)
157.48(16)
89.82(19)
158.50(18)
3. X-ray crystallography
Single crystal X-ray diffraction analyses of the three compounds
were carried out on a Bruker SMART APEX II CCD diffractometer
equipped with
a
graphite monochromated Mo
Ka radiation
scan technique at room temperature.
(k = 0.71073 Å) by using //
x
The intensities were corrected for Lorentz and polarization effects
as well as for empirical absorption based on multi-scan tech-
niques; all structures were solved by direct methods and refined
by full-matrix least-squares fitting on F2 by SHELX-97 [21]. Absorp-
tion corrections were applied by using multi-scan program SADABS
[22].The hydrogen atoms of organic ligands were placed in calcu-
lated positions and refined using a riding on attached atoms with
isotropic thermal parameters 1.2 times those of their carrier atoms.
The water hydrogen atoms were located from difference maps and
refined with isotropic thermal parameters 1.5 times those of their
carrier atoms. Table 1 shows crystallographic data of 1–3. Selected
bond distances and bond angles are listed in Table 2.
#1: x, ꢁ1 + y, z; #2: 1 + x, y, z; #3: 1 ꢁ x, 1 ꢁ y, ꢁz
Complex 2
Cd1–O1
Cd1–N1
Cd1–O3#1
Cd2–O2
Cd2–O4#1
Cd2–O6#2
O1–Cd1–O5
O1–Cd1–N1
O1–Cd1–O3#1
O1–Cd1–O4#1
2.182(3)
2.308(4)
2.463(4)
2.267(3)
2.318(3)
2.272(4)
97.03(15)
114.49(15)
146.49(13)
92.72(13)
Cd1–O5
Cd1–N2
Cd1–O4#1
Cd2–O6
Cd2–O2#2
Cd2–O4#1
O6–Cd2–O6#2
O4–Cd2–O6
O4–Cd2–O6#2
O4–Cd2–O4#1
2.197(4)
2.349(4)
2.329(3)
2.272(4)
2.267(3)
2.318(3)
180.00
86.15(13)
86.15(13
180.00
#1: x, y, ꢁ1 + z; #2: 1/2 ꢁ x, 1/2 ꢁ y, 1 ꢁ z
4. Synthesis of the complexes
Complex 3
Cd1–O1
4.1. {[Cd3(L1)2(IP)2(H2O)4]}n (1)
2.511(7)
2.394(7)
2.451(8)
2.377(8)
52.9(2)
94.1(2)
133.4(2)
96.0(2)
Cd1–O2
Cd1–N2
Cd1–O4#1
2.395(7)
2.369(7)
2.363(8)
Cd1–N1
Cd1–O3#1
Cd1–N3#2
O–Cd1–O2
O1–Cd1–N2
O1–Cd1–O4#1
O2–Cd1–N1
O2–Cd1–O3#1
Compound 1 was prepared as follows: a mixture of CdSO4H2O
(0.027 g, 0.11 mmol), IP (0.022 g, 0.1 mmol), H3L1 (0.021,
0.1 mmol), NaOH (0.1 mmol), CH3OH (2 mL) and DMF (1 mL) and
deionised water (8 mL) was stirred for 20 min in air, then trans-
ferred and sealed in a 25-mL Teflon reactor, which was heated at
150 °C for 72 h. The solution was then cooled to room temperature
at rate of 5 °C hꢁ1, to yield pale yellow crystalline product of 1 in
45% yield based on Cd. C22H15Cd1.50N4O8 (1) (1544.28) Calcd: C,
41.81; H, 2.39; N, 8.87. Found C, 41.67; H, 2.42; N, 8.85. IR (KBr,
cm–1): 3569(m), 2291(w), 1512(s), 1205(m), 648(s).
O1–Cd1–N1
77.1(2)
O1–Cd1–O3#1
N1–Cd1–N3#2
O2–Cd1–N2
167.9(3)
146.5(3)
146.8(2)
85.5(2)
125.9(3)
O2–Cd1–O4#1
#1: 1 ꢁ x, 1/2 + y, 5/2 ꢁ z; #2: x, 3/2 ꢁ y, 1/2 + z
46.56; H, 2.94; N, 6.39. Found C, 46.60; H, 2.98; N, 6.51. IR (KBr,
cmꢁ1): 3212(m), 2591(m),1569(s), 1288(m), 655(s).
4.2. {[Cd2(L2)2(IP)2]ꢀ(CH3OH)(DMF)}n (2)
4.3. [Cd(L3)(IP)]n (3)
The synthesis procedure of 2 is similar to that for 1 except that
H3L1 is replaced by H2L2. C56.67H42.67Cd2F12N6.67O12 (2) Calcd: C,
The synthesis procedure of 3 is similar to that for 1 except that
H3L1 is replaced by H2L3. C23H16CdN4O4 (3) Calcd: C, 52.63; H, 3.07;
Table 1
Crystal data and structure refinement information for compounds 1–3.
Compounds
1
2
3
Formula
Fw
C22H15Cd1.50N4O8
631.98
C56.67H42.67Cd2F12N6.67O12
1461.77
C23H16CdN4O4
524.80
Temp. (K)
Cryst system
Space group
a (Å)
b (Å)
c (Å)
298(2)
Trinlinic
P ꢁ 1
298(2)
Monoclinic
C2/c
24.1063(17)
25.1877(18)
14.5654(10)
90
101.0930(10)
90
298(2)
Monoclinic
P21/c
1.2116(13)
16.029(3)
17.056(3)
90
98.882(2)
90
7.5213(12)
9.5403(15)
15.238(2)
73.893(2)
79.037(2)
81.934(2)
1026.9(3)
2
a
(°)
b (°)
c
(°)
V (Å3)
8678.6(11)
6
1948.0(6)
4
Z
F(0 0 0)
622
2.044
4376
1.678
1048
1.789
Dc (g/cm3)
GOF
0.875
1.089
0.965
Reflections collected
Unique reflections
3599
7788
3479
5121(Rint = 0.0225)
R1 = 0.0398
wR2 = 0.1124
R1 = 0.0557
wR2 = 0.1286
21,745(Rint = 0.0349)
R1 = 0.0457
wR2 = 0.1434
R1 = 0.0457
wR2 = 0.1600
9458 (Rint = 0.1021)
R1 = 0.0769
wR2 = 0.2025
R1 = 0.0904
wR2 = 0.2167
Final R indices
a
(R (I > 2
r(I))
R indices
(All data)
P
P
P
P
aR1
=
||F0| ꢁ |Fc||/ |F0|, wR2 = { [w(F20 ꢁ F2c )2]/ (F02)2}1/2
.

128
J.-Q. Liu et al. / Journal of Molecular Structure 987 (2011) 126–131
N, 10.68. Found C, 52.60; H, 3.12; N, 10.61. IR (KBr, cm–1): 2028(m),
1618(s), 1216(m), 638(s).
ligands (Cd–O bond distances range from 2.267(3) to 2.318(3) Å),
whereas the terminal Cd1 atom is coordinated by four oxygen
atoms (Cd–O bond distances range from 2.182(4) to 2.463(4) Å)
and two nitrogen atoms (Fig. 2a). Similar trinuclear Cd3(RCO2)6
cluster has been reported, in which is assembled from Cd atom
and flexible organic unit[4,23]. In the asymmetric unit, there are
two types of L2(1) and L2(2) ligands. The L2(1) adopts (k1–k1)–
(k1–k1)–l4 fashion and links the tri-metallic core to form a 1D
5. Results and discussion
5.1. Crystal structure of {[Cd3(L1)2(IP)2(H2O)4]}n (1)
Single-crystal X-ray structural analysis reveals that the asym-
metric unit of 1 contains one and a half Cd(II) atoms, one L1 ligand,
one IP and two coordination water molecules. Fig. 1a shows the
view of the local coordination geometries around the Cd(II) atoms.
The two Cd(II) atoms have different coordinative environments. As
for Cd1, the axial positions are occupied by one oxygen atom from
one bidentate carboxylate group and one oxygen atom from one
coordinative water molecule, whereas two oxygen atoms from
one coordinative water molecule and one bidentate carboxylate
end and two nitrogen atoms from one chelating IP ligand are on
the equatorial plane. The Cd2 has ideal octahedral coordination
geometry. The axial positions are occupied by two oxygen atoms
from two symmetric monodentate carboxylate groups, while the
four oxygen atoms from carboxylate groups of two different L1 li-
gands locate on the equatorial plane. The Cd–O bond distances
range from 2.175(4) to 2.401(4) Å, and the Cd–N bond distances
range from 2.354(5) to 2.388(5) Å. The three carboxylate groups
exhibit two kinds of coordination modes (monodentate and bridg-
ing bidentate fashions). Based on these connection nodes, four
chain along the c direction, while L2(2) adopts (k1–k1)–(k2–
l2)–l4
mode and connects the trinuclear unit to shape another 1D chain
along the a axis.
View from the ac plane reveals a (4, 4) topology structure
(Fig. 2b). The space is occupied by the guest CH3OH and DMF mol-
ecules. Each layer is slightly offset compared to adjacent layers
(Fig. 2d). A striking feature of 2 is the alternating arrangement of
three types of helices along a axis, which are formed by Cd2 and
two types of L2(1) and L2(2) ligands (Fig. 2c). The strong aromatic
stacking interaction of neighboring IP molecules is ca. 3.63(6) Å),
which further extended the structure into 3D framework (Fig. 2e).
5.3. Crystal structure of [Cd(L3)(IP)]n (3)
To further investigate the effect of assistant ligand on the
framework, the angular backbone of organic ligand was deliber-
ately employed. 1,3-Phenylenediacetic acid was introduced into
the Cd-IP system. A new compound 3 was obtained. The structure
of 3 has neutral sheet of [Cd(L3)(IP)]n. The Cd(II) ion is coordinated
by four oxygen atoms from two carboxylate groups and three
nitrogen atoms from two pyridine rings and one imidazole ring
(Fig. 3a). The Cd(II) metal centers are connected to each other by
L3 with syn–syn fashion into a 1D helical chain (Fig. 3c). In 3, IP
Cd(II) ions are bridged by four l2–carboxylate ends to give tetranu-
clear units, which are further extended by monodentate carboxyl-
ate ends into 2D layers along the ab plane, as shown in Fig. 1b.
From the [1 0 1] direction, nano-channels are directed by Cd ions
and L1 ligands (Fig. 1c and d). As presented in Fig. 1e, the Cd1
and Cd2 atoms are linked by O2C–C–CO2 groups of L1 ligand to
form the left- and right-handed helical chains running along the
c axis with a pitch of 12.86 Å. In addition, the interplanar distance
between pyridyl rings of IP ligands is ca. 3.86(5) Å, indicating the
adopts a
l2-bridging mode, linking the adjacent metal ions into a
zigzag chain (Fig. 3d). Ultimately, the whole structure displays a
2D framework. As shown in Fig. 3b. Each layer is slightly offset
compared to adjacent layers (Fig. 3e and f).
presence of weak
p–p stacking interaction that further stabilizes
the crystal structure (Fig. 1f).
5.4. Comparison of the structures of coordination polymers
5.2. Crystal structure of {[Cd2(L2)2(IP)2]ꢀ(CH3OH)(DMF)}n (2)
As a matter of fact, the coordination frameworks of most com-
plexes are not only influenced by metal ions, but also depend on
the reliable coordinative sites of carboxylate ligands. In this work,
we select three kinds of rigid/flexible carboxylic acid with H3L1,
H2L2 and H2L3, and intend to explore their effects on the assembly
In the structure, there are two crystallographically unique Cd(II)
atoms. The central Cd2 atom in each unit lies on an inversion cen-
tre and is coordinated by six oxygen atoms from separated L2
Fig. 1. (a) Stick representation of the coordination environments of the Cd(II) ions in 1 (i: x, ꢁ1 + y, z; ii: 1 + x, y, z; ii: 1 ꢁ x,1 ꢁ y, ꢁz). Hydrogen atoms have been omitted for
clarity; (b) view of the 2D layer along ab plane; (c) the 2D layer long ac direction; (d) view of 1D nano-tube channels along ac plane; (e) Schematic view of the double helical
chains; (f) the 3D supramolecular framework formed by aromatic stacking interactions.

J.-Q. Liu et al. / Journal of Molecular Structure 987 (2011) 126–131
129
Fig. 2. (a) Stick representation of the coordination environments of the Cd(II) ions in 2 (i: x, y, ꢁ1 + z; ii: 1/2 ꢁ x, 1/2 ꢁ y, 1 ꢁ z). Hydrogen atoms have been omitted for clarity;
(b) perspective view of 2D layer in 2; (c) three types of helical chains directed by Cd(2) ions and L2 ligands; (d) view of the adjacent offset grid sheet; (e) 3D supramolecular
net formed by strong aromatic stacking interactions.
Fig. 3. (a) Stick representation of the coordination environment of the Cd(II) ion in 3(i: 1 ꢁ x, 1/2 + y, 5/2 ꢁ z; ii: x, 3/2 ꢁ y, 1/2 + z); hydrogen atoms have been omitted for
clarity; (b) perspective view of 2D layer in 3; (c) view of 1D helical chain; (d) view of the 1D zigzag chain; (e) cross section of 3 viewed along ac plane; (f) the butterfly-like
layers.
of the Cd-IP coordination system (see Scheme 1). In compound 1,
the small backbone makes it possible for L1 to provide more chance
to bind more metal ions and form polynuclear core. In addition, the
formation of tetranuclear Cd(II) cores may reduce the coordinative
chance of N atom from imidazole ring of IP to bond to metal atoms.
As for compound 3, the N atom from imidazole ring coordinates to
metal atom. Finally, a new grid layer is shaped. The incorporation
of the changeable backbone length between L2 and L3 determines
the difference of the pitch of the helices and helical degree in 2
and 3. Consequently, 2 features undulating Cd(II)/L2 layer from
three types of helical chains; in 3, only one helical chain was direc-
ted by Cd(II) ions and L3 ligands(Scheme 1).
Taking the coordinated sites of backbones for organic ligands,
the influence of dicarboxylates on the nets is also revealed by the
structural differences. For example, Complex {[Cd(1,4-BDC)(I-
P)(H2O)]ꢀ0.5H2O}(1,4-H2BDC = 1,4-benzendicarboxylic acid) has a
1D undulating structure with [Cd(1,4-BDC)(IP)] as its repeating
unit[20]. When an additional coordinative site was introduced into
the benzene ring, a higher dimension of compound 1 was obtained
herein. This result indicates that the coordinative backbones can
manipulate the nuclear numbers and final resulting structures.
This phenomenon is also observed in flexible organic carboxylate
and Cd-IP system [20].
5.5. TGA and photoluminescence properties
The decomposition behaviors of 1–3 were examined via ther-
mogravimetric analysis (TGA) (Fig. S1). For 1, first weight loss of
4.9% is detected over the range 35–190 °C, corresponding to the
loss of the coordinated water molecules (calcd. 5.2%). The polycrys-
talline sample is stable up to 405 °C which the decomposition
starts. For 2, the TGA reveals there is a weight loss (found:
7.53%) from ca. 45 to 320 °C, corresponding to the loss of the free
CH3OH and DMF molecules (calcd: 7.1%). For 3, the TGA reveals
the polycrystalline sample is stable up to 298 °C above which the
decomposition starts.
In order to confirm the phase of the bulk materials, X-ray pow-
der diffraction (XRPD) experiments were carried out on com-
pounds 1–3 (Fig. S2). The XRPD experimental and computer-
simulated patterns of all them are shown in Fig. S2. Although the
experimental patterns have a few unindexed diffraction lines and
some slightly broadened in comparison with those simulated

130
J.-Q. Liu et al. / Journal of Molecular Structure 987 (2011) 126–131
Scheme 1. Schematic representation of the ligands and nuclear number.
patterns, it can also be considered that the as-synthesized materi-
als are homogeneous. For compound 1, after heating at 200 °C for
5 h, the coordinative water molecules were removed (the evacu-
ated framework is defined as 1’). The XRPD pattern of 1’ is similar
to compound 1, although minor differences can be seen in the posi-
tions, intensities, and widths of some peaks, which indicates that
the framework of compound 1 is retained after the removal of
the coordinative water molecules.
weaker than those of the
the carboxylate ligands almost have no contribution to the fluores-
cent emission of the complexes. For the emission bands of 1–3 are
located in red-shift positions, which may be assigned to the
transitions, whereas the significant redshifts of these bands in
comparison to that of IP would be attributed to the metal–ligand
coordinative behaviors and their different conjugated structures.
p
⁄ ?
p transition n of the IP ligand, thus,
p⁄ ?
p
Organic–inorganic coordination polymers, especially those with
d10 metal centers, have been investigated for their fluorescent
properties and potential applications as fluorescent-emitting
materials, such as light-emitting diodes(LEDs)[24–25]. Therefore,
the complexes 1–3 were studied in the solid-state at room temper-
ature. Excitation of the microcrystalline samples at 350 nm leads to
the generation of fluorescent emissions (Fig. 4), with the peak max-
ima occurring at 501 nm for 1, 458 nm for 2, 514 nm for 3. The
fluorescent spectrum of IP has been also measured, which behaves
a relatively broad band at 460 nm (kex = 315 nm)[20]. The emission
6. Conclusion
In summary, the simultaneous use of carboxylate ligands and
the pharmaceutical agent IP ligand reacting with Cd(II) ions affords
three new polymers. Although the polymers possess 2D structural
motifs, the tridentate mode of IP ligand is only observed in com-
plex 3. All the complexes have high stabilities and intense fluores-
cent emissions. This work shows that tuning the backbone of
organic ligand is an effective strategy in crystal engineering of pre-
paring metal–organic frameworks.
bands of these carboxylates can be assigned to the
tion as previously reported. The fluorescent emission of the car-
boxylate ligands deriving from the
⁄ ? n transition is very
p⁄ ? n transi-
Acknowledgment
p
We gratefully acknowledge financial support of this work by
the Guangdong Medical College.
Appendix A. Supplementary material
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre, CCDC
No. 768703–768705 for compounds 1–3. Copies of this informa-
tion may be obtained free of charge on application to CCDC, 12 Un-
ion Road, Cambridge CB2 1EZ, UK (fax: +44 1223 336 033; e-mail:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2010.12.006.
References
[1] (a) O.M. Yaghi, J.L.C. Rowsell, J. Am. Chem. Soc. 128 (2006) 1304;
(b) X. Zhao, B. Xiao, A.J. Fletcher, K.M. Thomas, D. Bradshaw, M.J. Rosseinsky,
Science. 306 (2004) 1012;
(c) N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O0. Keeffe, O.M. Yaghi,
Science. 300 (2003) 1127.
Fig. 4. Solid-state emission spectra of compounds 1–3 at room temperature.
[2] Y.W. Li, R.T. Yang, J. Am. Chem. Soc. 128 (2006) 726.

J.-Q. Liu et al. / Journal of Molecular Structure 987 (2011) 126–131
131
[3] Y. Kubota, M. Takata, R. Matsuda, R. Kitaura, S. Kitagawa, K. Kato, M. Sakata,
T.C. Kobayashi, Angew. Chem., Int. Ed. 44 (2005) 920.
[14] D.R. Xiao, E.B. Wang, H.Y. An, Y.G. Li, Z.M. Su, C.Y. Sun, Chem. Eur. J. 12 (2006)
6528.
[4] (a) F.Y. Lian, F.L. Jiang, D.Q. Yuan, J.T. Chen, M.Y. Wu, M.C. Hong, Cryst Eng
Comm 10 (2008) 905;
(b) R. Mondal, M.K. Bgunia, K. Dhara, Cryst Eng Comm 10 (2008) 1167.
[5] X.-M. Zhang, M.-L. Tong, M.-L. Gong, X.-M. Chen, Eur. J. Inorg. Chem. (2003)
138.
[15] X.L. Wang, C. Qin, E.B. Wang, Z. M. Su 12 (2006) 2680.
[16] Y. Xiong, X.-F. He, X.-H. Zou, J.-Z. Wu, X.-M. Chen, L-N. Ji, R.-H. Li, J.-Y. Zhou, K.-
B. Yu, J. Chem.Soc., Dalton Trans. (1999) 19.
[17] B. Zhao, P. Cheng, Y. Dai, C. Cheng, D.Z. Liao, S.P. Yan, Z.H. Jiang, G.L. Wang,
Angew. Chem., Int. Ed. 42 (2003) 943.
[6] L.-M. Duan, F.-T. Xie, X.-Y. Chen, Y. Chen, Y.-K. Lu, P. Cheng, J.-Q. Xu, Cryst.
Growth & Des. 6 (2006) 1101.
[7] A. Beghidja, P. Rabu, G. Rogez, R. Welter, Chem. Eur. J. 12 (2006) 7627.
[8] M.-L. Tong, H.–K. Lee, Y.–X. Tong, X.–M. Chen, T.C.W. Mak, Inorg. Chem. 39
(2000) 4666.
[9] R.P. Davies, R.J. Less, P.D. Lickiss, A.J.P. White, Dalton Trans. (2007) 2528.
[10] Y. Wei, H.W. Hou, L.K. Li, Y.T. Fan, Y. Zhu, Cryst. Growth Des. 5 (2005) 1405.
[11] G.B. Che, C.B. Liu, B. Liu, Q.W. Wang, Z.L. Xu, Cryst Eng Comm 10 (2008) 184.
[12] T.L. Hu, R.Q. Zou, J.R. Li, X.H. Bu, Dalton Trans. (2008) 1302.
[13] Z.-H. Zhou, G.-F. Wang, S.-Y. Hou, H.-L. Wan, K.-R. Tsai, Inorg. Chim. Acta. 314
(2001) 184.
[18] M.D. Stephenson, T.J. Prior, M.J. Hardie, Cryst. Growth Des. 8 (2008) 643.
[19] X.L. Wang, H.Y. Lin, T.L. Hu, J.L. Tian, X.H. Bu, J. Mol. Struct 798 (2006) 34.
[20] J.Q. Liu, Y.N. Zhang, Y.Y. Wang, J.C. Jin, E.L. Lermontova, Q.Z. Shi, Dalton Trans.
(2009) 5365.
[21] G. M. Sheldrick, SHELXL-97; University of Göttingen: Germany, 1997.
[22] G.M. Sheldrick, SADABS 2.05; University of Göttingen: Germany, 2002.
[23] J. Tao, M.L. Tong, J. Shi, X.M. Chen, Wen. Ng, S. Chem. Commun. (2000) 2043.
[24] X. Ouyang, D. Liu, T. Okamura, H. Bu, W. Sun, W. Tang, N. Ueyanma, Dalton
Trans. (2003) 1836.
[25] K. Balasubramanian, RelatiVistic Effects in Chemistry⁄ Part A: Theory and
Techniques; Part B: Applications, Wiley, New York, 1997.