Dicarboxylate-controlled three Zn(II) coordination polymers incorporating flexible 1,2-bis(imidazol-1′-yl)ethane ligand: Syntheses, structures, thermal stabilities and photoluminescent properties

Article abstract of DOI:10.1016/j.molstruc.2011.12.030

Three mixed-ligand Zn(II) coordination polymers (CPs) of the formula {[Zn₂(bime)₂(adip)₂](H₂O) ₅}_n (1), {[Zn(bime)(ipa)](H₂O) ₃}_n (2), {[Zn(bime)(tpa)](H

Full text of DOI:10.1016/j.molstruc.2011.12.030

Journal of Molecular Structure 1012 (2012) 131–136
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Dicarboxylate-controlled three Zn(II) coordination polymers incorporating flexible
1,2-bis(imidazol-10-yl)ethane ligand: Syntheses, structures, thermal stabilities
and photoluminescent properties
a
Hong-Jun Hao a,1, Di Sun b, ,1, Fu-Jing Liu a, Rong-Bin Huang a, , Lan-Sun Zheng
⇑
⇑
a State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen,
Fujian 361005, China
b School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three mixed-ligand Zn(II) coordination polymers (CPs) of the formula {[Zn2(bime)2(adip)2]ꢀ(H2O)5}n (1),
{[Zn(bime)(ipa)]ꢀ(H2O)3}n (2), {[Zn(bime)(tpa)]ꢀ(H2O)ꢀ(CH3OH)}n (3) (bime = 1,2-bis(imidazol-10-yl)ethane,
H2adip = adipic acid, H2ipa = isophthalic acid and H2tpa = terephthalic acid) were synthesized. All CPs have
been characterized by element analysis, powder X-ray diffraction (PXRD), IR and X-ray single-crystal diffrac-
tion. Complexes 1 and 2 exhibit similar wavy two-dimensional (2D) sheets with 44-sql topology. Compared
to 1, complex 2 contains a larger window owing to the different conformation of bime ligand. In both 1 and 2,
we observed 1D water chain filling in the 44-sql net. In 3, the bime acts as a bidentate ligand and the tpa
Received 12 November 2011
Received in revised form 18 December 2011
Accepted 19 December 2011
Available online 5 January 2012
Keywords:
Zinc(II)
1,2-Bis(imidazol-10-yl)ethane
Dicarboxylate
adopts a l2- ,g
g1 1 coordinated mode which links the Zn(II) ions to form a 2D 63-hcb net. The results suggest
that the dicarboxylates play crucial roles in the formation of the different structures. In addition, the thermal
stabilities and the photoluminescence properties of them were also investigated.
Ó 2012 Elsevier B.V. All rights reserved.
Photoluminescence
1. Introduction
[25,26], there are only four Zn/bime CPs. In view of above consid-
eration, herein we wish to report the syntheses, crystal structures,
Particular attention has been recently devoted to coordination
polymers (CPs) due to not only their undisputed structural beauty
but also promising applications in the fields of catalysis, storage,
conduction, luminescence, conductivity, non-linear optics (NLOs),
ferroelectricity and magnetism [1–13]. The construction of CPs
depends on the combination of several factors, such as solvent
system [14–16], counteranion [17–20], pH value of the solution
[21–23], reaction temperature, ratio of ligand to metal ion, coordi-
nation geometry of central metals and organic ligands [24]. Thus,
understanding how these considerations affect metal coordination
and influence supramolecular assembly is at the forefront of con-
trolling coordination supramolecular arrays.
To the best of our knowledge, the bime, bearing alkyl spacers is
a good choice of N-donor ligands, the flexible nature of spacers al-
lows the ligands to bend and rotate when it coordinates to metal
centers, and this often causes the structural diversity. As a conse-
quence of the free rotation of the ethyl group, it possesses gauche
and anti conformations which favor the possibility of generating
fascinating structures. However, as indicated by CSD (Cambridge
Structure Database) survey with the help of ConQuest version 1.3
characterizations and photoluminescences of three Zn(II) mixed-li-
gand CPs, namely, {[Zn2(bime)2(adip)2]ꢀ(H2O)5}n (1), {[Zn(bime)
(ipa)]ꢀ(H2O)3}n (2), {[Zn(bime)(tpa)]ꢀ(H2O)ꢀ(CH3OH)}n (3) (bime = 1,2-
bis(imidazol-10-yl)ethane, H2adip = adipic acid, H2ipa = isophthalic
acid and H2tpa = terephthalic acid).
2. Experimental
2.1. Materials and physical measurements
All the reagents and solvents employed were commercially
available and used as received without further purification. Infra-
red spectra were recorded on a Nicolet AVATAT FT-IR330 spec-
trometer as KBr pellets in the frequency range 4000–400 cmꢁ1
.
The elemental analyses (C, H, N contents) were determined on a
CE instruments EA 1110 analyzer. Photoluminescence measure-
ments were performed on a Hitachi F-7000 fluorescence spectro-
photometer with solid powder on a 1 cm quartz round plate.
Thermogravimetric analyses were performed on a NETZSCH TG
209 F1 IrisÒ Thermogravimetric Analyser from 30 to 800 °C at a
heating rate 10 °C/min under the N2 atmosphere (20 mL/min).
X-ray powder diffractions were measured on a Panalytical X-Pert
⇑
Corresponding authors. Fax: +86 592 2183047.
E-mail addresses: dsun@sdu.edu.cn (D. Sun), rbhuang@xmu.edu.cn (R.-B. Huang).
These authors contributed equally to this work.
1
pro diffractometer with CuKa radiation.
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.12.030

132
H.-J. Hao et al. / Journal of Molecular Structure 1012 (2012) 131–136
Table 1
2.2. Synthesis of complex {[Zn2(bime)2(adip)2]ꢀ(H2O)5}n (1)
Crystallographic data for complexes 1–3.
A mixture of Zn(OOCCH3)2ꢀ2H2O (43.8 mg, 0.2 mmol), bime
Complexes
1
2
3
(32.4 mg, 0.2 mmol) and H2adip (26.4 mg, 0.2 mmol) was treated
Formula
Mr
Crystal system
Space group
a (Å)
Zn2C28H45N8O13 ZnC16H14N4O7 ZnC17H20N4O6
in DMF-H2O mixed solvent (6 mL, v/v: 2/1) under ultrasonic irradi-
832.46
Monoclinic
Pc
8.2138(16)
17.491(3)
12.260(2)
90.00
90.234(4)
90.00
2
439.70
Monoclinic
P2(1)/c
10.231(2)
21.874(4)
8.8151(18)
90.00
103.52(3)
90.00
4
441.74
Triclinic
P-1
9.4794(17)
10.3579(19)
10.682(2)
74.805(3)
73.450(3)
76.959(3)
2
ation at ambient temperature. Then aqueous NH3 solution (25%,
10 d) was dropped into the mixture to give a clear solution under
ultrasonic treatment. The resultant solution was allowed to evapo-
rate slowly in darkness at room temperature for several days to give
pale-yellow crystals of 1 (yield: 56%, based on Zn(OOCCH3)2ꢀ2H2O).
Anal. Calc. (found) for Zn2C28H45N8O13: C, 40.40 (40.34); H, 5.45
b (Å)
c (Å)
a
(deg)
b (deg)
c
(deg)
(5.54); N, 13.46 (13.35)%. IR (KBr): m
(cmꢁ1) = 3453 (s), 3123 (s),
2940 (w), 1571 (s), 1535 (w), 1425 (m), 1241 (w), 1107 (w), 960
(w), 643 (w).
Z
V (Å3)
1761.3(6)
1.570
1.436
1918.1(6)
1.523
1.326
957.2(3)
1.533
1.325
Dc (g cmꢁ3
)
l
(mmꢁ1
)
F (000)
No. of unique reflns
No. of obsd reflns
866
5121
5019
896
3728
2252
456
3281
3194
2.3. Synthesis of complex {[Zn(bime)(ipa)]ꢀ(H2O)3}n (2)
The synthesis of 2 was similar to that of 1, but with H2ipa
(42.4 mg, 0.2 mmol) in place of H2adip in DMF-H2O mixed solvent
(6 mL, v/v: 2/1) under ultrasonic irradiation at ambient tempera-
[I > 2r(I)]
Parameters
GOF
461
0.816
R1 = 0.0350,
254
1.088
R1 = 0.0758
262
1.099
R1 = 0.0284
Final R indices
ture. Pale-yellow crystals of 2 were obtained in 75% yield based
on Zn(OOCCH3)2ꢀ2H2O. Anal. Calc. (found) for ZnC16H20N4O7: C,
43.11 (43.04); H, 4.52 (4.44); N, 12.57 (12.45)%. IR (KBr):
[I > 2r
(I)]a,b
wR2 = 0.1052
R1 = 0.0357
wR2 = 0.1060
0.563 and
ꢁ0.320
wR2 = 0.1612
R1 = 0.1413
wR2 = 0.2379
1.396 and
ꢁ1.602
wR2 = 0.0788
R1 = 0.0290,
wR2 = 0.0792
0.701 and
R indices (all data)
m
(cmꢁ1) = 3429 (s), 3319 (s), 3123 (s), 1608 (s), 1559 (s), 1376
Largest difference peak
(s), 1241 (w), 1107 (w), 948 (w), 740 (m), 643 (w).
and hole (e Åꢁ3
)
ꢁ0.790
P
P
a
R1
¼
kFoj ꢁ jFck= jFoj.
wðF2o ꢁ F2c Þ
2.4. Synthesis of complex {[Zn(bime)(tpa)]ꢀ(H2O)ꢀ(CH3OH)}n (3)
h
.
i
0:5
P
P
2
2
wðF2o Þ
.
b
wR2
¼
The synthesis of 3 was similar to that of 1, but with H2tpa
(42.4 mg, 0.2 mmol) in place of H2adip in DMF-H2O mixed solvent
(6 mL, v/v: 2/1) under ultrasonic irradiation at ambient tempera-
Table 2
Selected bond distances (Å) and angles (°) for 1–3.
ture. Pale-yellow crystals of 3 were obtained in 62% yield based
on Zn(OOCCH3)2ꢀ2H2O. Anal. Calc. (found) for ZnC17H20N4O6: C,
46.22 (46.14); H, 4.56 (4.47); N, 12.68 (12.65)%. IR (KBr):
Complex 1
Zn1–O3i
1.965(3)
1.983(3)
1.983(4)
2.024(4)
Zn2–O7
Zn2–N8
1.968(3)
1.983(4)
2.019(3)
(cmꢁ1) = 3429 (s), 3123 (s), 1596 (s), 1376 (s), 1229 (w), 1107
Zn1–O5
m
Zn1–N1
Zn2–O2
(w), 960 (w), 826 (w), 735 (w), 643 (w).
Zn1–N3ii
Zn2–N6iii
2.041(4)
O3i–Zn1–O5
O3i–Zn1–N1
O5–Zn1–N1
O3i–Zn1–N3ii
O5–Zn1–N3ii
N1–Zn1–N3ii
105.43(14)
125.33(17)
111.09(15)
100.19(16)
99.04(16)
112.26(18)
O7–Zn2–N8
O7–Zn2–O2
N8–Zn2–O2
O7–Zn2–N6iii
N8–Zn2–N6iii
O2–Zn2–N6iii
126.58(16)
102.09(14)
116.89(14)
96.58(14)
109.30(18)
100.93(16)
3. X-ray crystallography
Single crystals of the complexes 1–3 with appropriate dimen-
sions were mounted on a glass fiber and used for data collection.
Data were collected on a Bruker-AXS CCD diffractometer equipped
Symmetry codes: (i) x, y + 1, z; (ii) x + 1, y, z; (iii) x ꢁ 1, y, z
Complex 2
with
(k = 0.71073 Å) for 1 and 3, and a Rigaku R-AXIS RAPID Imaging
Plate single-crystal diffractometer equipped with graphite-
monochromated MoK radiation source (k = 0.71073 Å) for 2.
a
graphite-monochromated MoK
a
radiation source
Zn1–N3
1.992(7)
1.994(7)
123.4(3)
103.1(2)
105.3(3)
Zn1–O3ii
2.021(6)
1.995(6)
100.7(2)
110.6(2)
110.7(3)
Zn1–N2i
Zn1–O2
a
N3–Zn1–N2i
N3–Zn1–O2
N2i–Zn1–O2
O2–Zn1–O3ii
N3–Zn1–O3ii
N2i–Zn1–O3ii
a
The crystal structures were solved by direct methods and refined
with the full-matrix least-squares technique on F2 using the SHEL-
XS-97 and SHEXL-97 programs [27,28]. The crystallographic details
of 1–3 are summarized in Table 1. Selected bond lengths and an-
gles for 1–3 are collected in Table 2.
Symmetry codes: (i) ꢁx + 1, y + 1/2, ꢁz + 1/2; (ii) x ꢁ 1, y, z
Complex 3
Zn1–O3
Zn1–O2
O3–Zn1–O2
O3–Zn1–N4i
O2–Zn1–N4i
1.9494(15)
1.9901(15)
107.20(7)
113.71(7)
115.31(7)
Zn1–N4i
Zn1–N1
O3–Zn1–N1
O2–Zn1–N1
N4i–Zn1–N1
1.9957(19)
2.0101(19)
97.21(7)
110.87(7)
111.05(8)
4. Results and discussion
Symmetry codes: (i) ꢁx + 1, ꢁy, ꢁz
4.1. Syntheses and IR
The syntheses of complexes 1–3 were carried out in the room
temperature. The infrared spectra and elemental analyses of 1–3
are fully consistent with their formations. The IR spectra (Fig. S4)
of complexes 1–3 show features attributable to the carboxylic
group stretching vibrations. No band in the region 1690–
1730 cmꢁ1, indicates complete deprotonation of the carboxyl
groups. The characteristic bands of the carboxylic groups are
shown in the range 1541–1625 cmꢁ1 for asymmetric stretching
and 1345–1492 cmꢁ1 for symmetric stretching. The splitting of
m
as(COO) indicates the different coordination modes of carboxyl
group [29], being in agreement with their crystal structures.
4.2. Crystal structures
4.2.1. Crystal structure of {[Zn2(bime)2(adip)2]ꢀ(H2O)5}n (1)
Single-crystal X-ray diffraction analysis reveals that complex 1
crystallizes in the monoclinic space group Pc and is a 2D wavy

H.-J. Hao et al. / Journal of Molecular Structure 1012 (2012) 131–136
133
44-sql net of rectangular grids with lattice water molecules. The
asymmetric unit of 1 was comprised of two Zn(II) ions, two bime li-
gands, two adip anions and five lattice water molecules. As shown
in Fig. 1a, Zn1 is four-coordinated by two O atoms from two adip
anions and two N atoms from two different bime ligands to furnish
all nodes in one net have the identical connectivity, then according
to Wells it is a platonic uniform net and can be represented by the
symbol (n, p), where n is the size of the shortest circuit and p is the
connectivity of the nodes [35]. In the sheet of 1, all Zn(II) ions are
4-connecting and the shortest circuit is a four-membered ring. So
this 2D sheet can be simplified to a 44-sql net.
The most fascinating feature of 1 is that five crystallographically
independent lattice water molecules (O1W, O2W, O3W, O4W and
O5W) within the void are hydrogen bonded to each other, forming
an infinite water chain with a curl conformation (Fig. 1d). The
arrangement mode of five water molecules within a water chain
can be described as ꢀ ꢀ ꢀO1Wꢀ ꢀ ꢀO4Wꢀ ꢀ ꢀO2Wꢀ ꢀ ꢀO5Wꢀ ꢀ ꢀO3Wꢀ ꢀ ꢀO1W
ꢀ ꢀ ꢀO4Wꢀ ꢀ ꢀO2Wꢀ ꢀ ꢀO5Wꢀ ꢀ ꢀO3Wꢀ ꢀ ꢀ. The Oꢀ ꢀ ꢀO distances in the chain
are in the range 2.789(7)–2.907(7) Å with an average value of
2.838(7) Å. Moreover, the average Oꢀ ꢀ ꢀOꢀ ꢀ ꢀO angle is 133.56(2)°,
which is slightly larger than the corresponding value of 109.3 in
ice Ih. The water aggregates in 1 can be seen as intercalation of guests
into voids of the 3D framework host. (Symmetry codes: (i) x, y + 1, z;
(ii) x + 1, y, z; (iii) x ꢁ 1, y, z.)
a
distorted tetrahedron geometry (Zn1–O3i = 1.965(3), Zn1–
O5 = 1.983(3), Zn1–N1 = 1.983(4), Zn1–N3ii = 2.024(4) Å). The max-
imum and minimum bond angles for Zn1 are 125.33(17) and
112.26(18)°, respectively. The distortion of the tetrahedron can be
indicated by the calculated value of the s4 parameter introduced
by Yang et al. [30] to describe the geometry of a four-coordinate
metal system, which is 0.87 (for ideal tetrahedron s4 = 1). The Zn2
is also located in a tetrahedral geometry and coordinated by two
N atoms from two bime ligands and two O atoms from two adip li-
gands (Zn2–O7 = 1.968(3), Zn2–N8 = 1.983(4), Zn2–O2 = 2.019(3),
Zn2–N6iii = 2.041(4) Å), which the value of s4 is 0.83. Both Zn–N
and Zn–O bond lengths are well-matched to those observed in sim-
ilar complexes [31–33]. According to the stereochemistry terminol-
ogy [34], the conformation of the bime in 1 belongs to gauche with a
torsion angle of 47.3(5)° defined by N2–C17–C16–N4 atoms. The
flexible adip shows a anti-anti-anti conformation due to three tor-
sion angles of the carbon chain of being 178.6(4), 178.3(5) and
175.8(4)°.
4.2.2. Crystal structure of {[Zn(bime)(ipa)]ꢀ(H2O)3}n (2)
When using H2ipa instead of the H2adip, we obtained a similar
2D infinite 44-sql net. Single crystal X-ray analysis reveals that 2
crystallizes in a monoclinic space group P21/c. As shown in
Fig. 2a, there are one Zn(II) ion, one bime ligand, one ipa anion
and three lattice water molecules in the asymmetric unit of 2.
The Zn(II) ion adopts a distorted tetrahedron geometry completed
by two N atoms from two bime ligands and two O atoms from two
ipa anions with the value of s4 being 0.89. The bond lengths and
The Zn(II) ions are bridged by
l2-bime and l2- ,g
g1 1-adip
ligands to form a 2D infinite undulated sheet (Fig. 1b) incorporat-
ing a [Zn4(bime)2(adip)2] window of 8.21 ꢂ 11.39 Å (Fig. 1c) based
on the Znꢀ ꢀ ꢀZn distances. This sheet exhibits an undulated charac-
ter with a thickness of about 7.04 Å (Fig. S1). To better understand
the structure of 1, the topological analysis approach is employed. If
Fig. 1. (a) The coordination environment of the Zn(II) ion and the linkage modes of ligands in 1 with 50% thermal ellipsoid probability. Hydrogen atoms are omitted for clarity.
(b) The 2D sheet structure along c axis. (c) Representation of the 44-sql net (red stick: adip; green stick: bime). (d) The structure of 1D water chain in 1. (For interpretation of
the references to color in this figure legend, the reader is referred to the web version of this article.)

134
H.-J. Hao et al. / Journal of Molecular Structure 1012 (2012) 131–136
Fig. 2. (a) The coordination environment of the Zn(II) ion and the linkage modes of ligands in 2 with 50% thermal ellipsoid probability. Hydrogen atoms are omitted for clarity.
(b) A view of the 2D 44-sql net in the structure of 2. (c) Side view of the single 44-sql net in the structure of 2. (d) The structure of 1D water chain in 2.
bond angles around Zn(II) ion fall in the range of 1.992(7)–
2.021(6) Å and 100.7(2)–123.4(3)°, respectively. The conformation
of the bime in 2 is anti which is different from that of in 1 with a
torsion angle of 166.1(7)°. Similar to 1, the basic structure of 2 is
also a 44-sql net which is constructed by Zn(II) ions, bidentate
bime and ipa ligands (Fig. 2b). This 44-sql net also contains one
type of node (four-connected Zn(II) ions) and two types of linkers
(two-connected bime and ipa ligands). Compared to the net of 1,
the net in 2 contains a larger window of 10.23 ꢂ 11.33 Å which is
due to the different conformations of bime. The bime belonging
to an anti conformation in 2 is much longer than that in 1 with
gauche conformation. Meanwhile, the net exhibits a slightly undu-
lated character with a thickness of about 1.92 Å (Fig. 2c).
There is also a 1D infinite water chain in 2 and a clear insight into
this water structure is shown in Fig. 2d. Three crystallographically
independent lattice water molecules (O1W, O2W and O3W) and
their symmetry-related ones compose of the 1D water chain by
H-bonds. O1W and O2W act as hydrogen donors to bond with car-
boxylate oxygen atoms O1 and O4 from coordination sheet, respec-
tively. As a result, the water chains serve as ‘‘glue’’ to reinforce the
2D sheets forming an overall 3D supramolecular framework. The
Oꢀ ꢀ ꢀO distances in the chain are in the range 2.65(2)–2.847(15) Å
with an average value of 2.752(6) Å, moreover, the Oꢀ ꢀ ꢀOꢀ ꢀ ꢀO angles
fall in the range 84.93(5)–119.01(5)°.
tpa anions to complete a tetrahedron geometry (Zn1–O3 =
1.9494(15), Zn1–O2 = 1.9901(15), Zn1–N1 = 2.0101(19), Zn1–
N4i = 1.9957(19) Å). The maximum and minimum bond angles for
Zn(II) ion are 115.31(7) and 97.21(7)°, respectively. The conforma-
tion of the bime in 3 is the same to that of in 1 with a torsion angle
of 54.6(2)°. As shown in Fig. 3b, the bime acts as a bidentate ligand
and the tpa adopts a l2- ,
g1 g1 coordinated mode which links the
Zn(II) ions to form a 2D sheet. To better understand the structure
of 3, the topological analysis is employed [36]. We can consider
the Zn(II) ions as 3-connecting nodes, and each two neighboring
Zn(II) ions were linked via bridging ligands (bime or tpa ligand) to
form Zn6 hexagonal rings. On the basis of above analysis, the 2D
structure can be simplified to a hexagonal 63-hcb net with the grid
dimensions of 7.32 ꢂ 10.97 Å (Fig. 3c). The uncoordinated methanol
molecules and lattice water molecules are filled in the windows and
hydrogen-bonded to carboxyl groups to extend the 2D sheet to 3D
supramolecular framework. (Symmetry codes: (i) ꢁx + 1, ꢁy, ꢁz.).
4.3. Effect of bime and dicarboxylates ligands on assembly
As it is shown in the descriptions above, three novel Zn(II) CPs
1–3 with the bime and different dicarboxylates were successfully
synthesized and characterized. Based on the X-ray analysis results,
although 1 and 2 have the similar 2D infinite 44-sql net structure,
they contain different sizes of windows. For 1 and 2, the auxiliary
4.2.3. Crystal structure of {[Zn(bime)(tpa)]ꢀ(H2O)ꢀ(CH3OH)}n (3)
Complex 3 crystallizes in the triclinic space group P-1. As shown
in Fig. 3a, the asymmetric unit of 3 contains one independent Zn(II)
ion, one bime ligand, one tpa anion, one lattice water molecule and
one uncoordinated methanol molecule. The Zn(II) ion is bound by
two N atoms from two bime ligands and two O atoms from two
dicarboxylates (adip and ipa) with the same l2- ,g
g1 1 coordination
mode possess different lengths and the main ligand bime adopts
the identical l2 bridging coordination mode but belonging to dif-
ferent conformations with different lengths. The structure of 3 is
a 2D sheet which can be simplified to a hexagonal 63-hcb net with
the grid dimensions of 7.32 ꢂ 10.97 Å. In 3, the bime acts as a

H.-J. Hao et al. / Journal of Molecular Structure 1012 (2012) 131–136
135
Fig. 3. (a) The coordination environment of the Zn(II) ion and the linkage modes of ligands in 3 with 50% thermal ellipsoid probability. Hydrogen atoms are omitted for clarity.
(b) The 2D sheet structure. (c) Representation of the hexagonal 63-hcb net grid (yellow stick: tpa; amaranth stick: bime). (For interpretation of the references to color in this
figure legend, the reader is referred to the web version of this article.)
bidentate ligand with a gauche conformation and the tpa adopts a
1 coordinated mode. In all, the different auxiliary dicarbox-
ylates as well as bime with different conformations significantly
generated from the results of single-crystal diffraction data
(Fig. S3), indicative of pure products. The Thermogravimetric (TG)
analysis was performed in N2 atmosphere on polycrystalline sam-
ples of 1–3. As shown in Fig. 5, in 1, the framework is stable to
350 °C and then the framework begins to collapse, accompanying
the release of coordinated bime and ipa ligands. There exists a
gradual weight loss of 2 occurring from 30 to 200 °C which is
l2- ,g
g1
contributed to the different structures of 1–3.
4.4. Photoluminescence properties
The photoluminescence spectra of the complexes 1–3 are
shown in Fig. 4. The free ligand bime displays photoluminescence
with emission maximum at 356 nm (kex = 300 nm, Fig. S2). It can
be presumed that this peak originate from the p⁄
? p transition.
To the best of our knowledge, the emission of dicarboxylate be-
longs to p⁄ ? n transitions which is very weak compared to that
of the p⁄
? p transition of the bime, so the dicarboxylates almost
have no contribution to the fluorescent emission [37]. Upon com-
plexation of these ligands with Zn(II) ions, intense emissions are
observed at 427 nm for 1, 433 nm for 2 and 436 nm for 3, under
300 nm excitation, respectively. The resemblance between the
emissions of 1–3 and that of the free bime indicates that the emis-
sions of 1–3 originate from p⁄
? p electronic transition of bime
ligand.
4.5. X-ray powder diffraction analyses and thermal analyses
Powder X-ray diffraction (PXRD) has been used to check the
phase purity of the bulky samples in the solid state. For 1–3, the
measured PXRD patterns closely match the simulated patterns
Fig. 4. Emission spectra of the complexes 1–3.

136
H.-J. Hao et al. / Journal of Molecular Structure 1012 (2012) 131–136
Appendix A. Supplementary material
CCDC 853480, 853481 and 853482 contain the supplementary
crystallographic data for 1–3 respectively in this paper. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB 21EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.molstruc.2011.12.030.
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Acknowledgments
This work was financially supported by the National Natural Sci-
ence Foundation of China (No. 20721001), 973 Project (Grant
2007CB815301) from MSTC, Independent Innovation Foundation
of Shandong University(2011GN030), and the Special Fund for Post-
doctoral Innovation Program of Shandong Province (201101007).