Construction of three low dimensional Zn(II) complexes based on different organic-carboxylic acids

Article abstract of DOI:10.1016/j.ica.2008.07.015

Three new Zn(II) complexes based on different organic-carboxylic acids, [Zn(mba)₂(2,2′-bipy)] (1), [Zn(mpdaH)₂(H₂O)₄] · 4H₂O (2) and [Zn(cda)₂(H₂O)₂]_n (3) (

Full text of DOI:10.1016/j.ica.2008.07.015

Inorganica Chimica Acta 362 (2009) 1441–1447
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Construction of three low dimensional Zn(II) complexes based on different
organic-carboxylic acids
*
Xiu-Xia Zhou, Mao-Sheng Liu, Xiao-Ming Lin, Hua-Cai Fang, Jian-Qiao Chen, Ding-Qiao Yang, Yue-Peng Cai
Key Lab of Technology on Electrochemical Energy Storage and Power Generation in Guangdong Universities, School of Chemistry and Environment, South China Normal
University, Guangzhou 510006, PR China
a r t i c l e i n f o
a b s t r a c t
Three new Zn(II) complexes based on different organic-carboxylic acids, [Zn(mba)2(2,20-bipy)] (1),
[Zn(mpdaH)2(H2O)4] ꢀ 4H2O (2) and [Zn(cda)2(H2O)2]n (3) (Hmba = 4-methylbenzoic acid, H2mpda =
2,6-dimethylpyridine-3,5-dicarboxylic acid and H2cda = chelidonic acid) have been synthesized success-
fully under hydrothermal conditions. X-ray single crystal diffractions show that compounds 1 and 2 are
the mononuclear and 3 is one-dimensional chain, in which the Zn(II) centers have different coordination
Article history:
Received 14 March 2008
Received in revised form 18 June 2008
Accepted 4 July 2008
Available online 16 July 2008
geometries with octahedron for 1 and 2 and tetrahedron for 3. Through
p–p stacking and/or hydrogen
Keywords:
bonding (O–Hꢀ ꢀ ꢀO and O–Hꢀ ꢀ ꢀN) interactions, different supramolecular structures are assembled, namely,
2D supramolecular layer for 1 and 3D supramolecular networks for 2 and 3. Furthermore, the IR, TGA and
luminescent properties are also investigated in this work.
Three Zn(II) complexes based on different
organic-carboxlic acids
Synthesis and characterization
Supramolecular structure
Luminescence
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
have been prepared and explored by the use of such heterocyclic
dicarboxylic acids, there are still a great deal of uncharacterized
The rational design and synthesis of metal-organic frameworks
(MOFs) with carboxylic acids using various secondary building
units (SBUs) connected through coordination bonds, supramolecu-
compounds with novel crystal structures emerged under various
reaction conditions, and these new compounds mostly are seren-
dipitous, especially the emergence of fancy and intricate supramo-
lecular architectures assembled by small building blocks through
lar contacts (hydrogen bonding,
pꢀ ꢀ ꢀp stacking, etc.), or their com-
bination, continue to be interesting and attractive due to not only
their potential properties in catalysis, magnetic behavior, optical
material and adsorption, but also their intriguing network archi-
tectures [1–5]. A large number of different dimensional coordina-
tion polymers have been prepared and characterized using a
variety of carboxylic acids. Of the many such kinds of compounds
investigated, those containing benzene-core carboxylic acids con-
stitute an important family as they have proven to be good candi-
dates for the rich coordination modes, such as terminal
monodentate, chelating to one metal center and various modes
of bridging coordination of two, three, four or even five metal cen-
ters [6], and also function as hydrogen-bond acceptors as well as
donors in assembling supramolecular complexes [7–8]. In recent
years, the scope of the investigations on benzene-core carboxylic
acids has been enhanced enormously by using N- or O-heterocyclic
dicarboxylic acids such as pyridine-, pyran-dicarboxylic acids
which can use their carboxylate oxygens and nitrogen or oxygen
atoms on the heterocycle to approach metal ions, to form interest-
ing frameworks [9–10]. Although quite a number of compounds
hydrogen bonding and
attract chemists’ attention.
p p stacking interactions, which greatly
ꢀ ꢀ ꢀ
In the past years, we have prepared a series of new metal-or-
ganic frameworks in the presence of heterocyclic multi-carboxylic
acids via the hydrothermal synthesis, and their supramolecular
architectures have also been investigated [11]. In order to continue
and extend our work, we have recently synthesized three new
Zn(II) complexes with 4-methylbenzoic acid, pyridine- and pyr-
an-dicarboxylic acids, that is, [Zn(mba)2(2,20-bipy)] (1),
[Zn(mpdaH)2(H2O)4] ꢀ 4H2O (2) and [Zn(cda)2(H2O)2]n (3). Com-
pounds 1 and 2 are prepared from 4-methylbenzoic acid (Hmba)
and 2,6-dimethylpyridine-3,5-dicarboxylic acid (H2mpdc), respec-
tively, and they are both zero-dimensional structures, while com-
pound 3 is synthesized from chelidonic acid (H2cda) and it
possesses a one-dimensional linear structure. Through
p p stack-
ꢀ ꢀ ꢀ
ing or hydrogen bonding (O–Hꢀ ꢀ ꢀO) interactions, compounds 1 and
3 are further assembled into 2D layer and 3D network supramolec-
ular structures, respectively. However, compound 2 is connected
into three-dimensional supramolecular structure through hydro-
gen bonding (O–Hꢀ ꢀ ꢀO and O–Hꢀ ꢀ ꢀN) and
p p stacking interac-
tions. To the best of our knowledge, these three carboxylic acids
ꢀ ꢀ ꢀ
* Corresponding author. Tel.: +86 020 33033475; fax: +86 20 85215865.
E-mail address: ypcai8@yahoo.com (Y.-P. Cai).
(Hmba, H2mpdc and H2cda) and their supramolecular coordination
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.07.015

1442
X.-X. Zhou et al. / Inorganica Chimica Acta 362 (2009) 1441–1447
chemistry have been less explored up to now [9]. Thus, it is inter-
esting to study the hydrothermal synthesis and coordination
chemistry of these ligands and explore the photoluminescence of
the resulted coordination frameworks. In this work, we describe
the synthesis, characteristic and properties of the three new
complexes.
2.5. X-ray crystallography
The three complexes 1–3 were determined by single crystal X-
ray diffraction. Suitable single crystals were mounted on a glass
fiber and the intensity data were collected on a Bruker APEX II
diffractometer at 298 K using graphite monochromated Mo K
a
radiation (k = 0.71073 Å). Absorption corrections were performed
using the SADABS program [12]. The structures were solved by di-
rect methods and refined by full-matrix least-squares against F2
of data using SHELXTL software [13]. Anisotropic thermal parame-
ters were applied to all non-hydrogen atoms. The organic hydro-
gen atoms were generated geometrically, the aqua hydrogen
atoms were located from difference maps and refined with isotro-
pic temperature factors. A summary of parameters for the data
collection and refinements for three complexes are given in Table
1. Selected bond lengths and angles for complexes 1–3 are listed
in Table 2. Hydrogen-bonding data of complexes 1–3 are listed in
Table 3.
2. Experimental
2.1. Materials and measurements
All materials were reagent grade, obtained from commercial
sources and used without further purification. Elemental analyses
were performed on a Perkin–Elmer 240C analytical instrument.
The metal analysis was performed on an ICP AES Liberty Series II
Varian apparatus. IR spectra in the 4000–400 cmꢁ1 range were
measured with a Thermo Nicolet 320 FT-IR spectrometer using
KBr discs. Thermal analyses (under nitrogenated atmosphere, heat-
ing rate of 5 °C/min) were carried out in a Labsys NETZSCH TG 209
Setaram apparatus. The luminescent spectra for the solid-state
were recorded at room temperature on an Aminco Bowman Series
2 spectrofluorometer with a xenon arc lamp as the light source. In
the measurements of emission and excitation spectra the pass
width is 5.0 nm.
Table 1
Crystal data and structure refinement for compounds 1–3
Complex
1
2
3
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C26H22N2O4Zn
491.83
298(2)
C18H32N2O16Zn
597.83
298(2)
C7H6O8Zn
283.49
298(2)
2.2. Preparation of complex [Zn(mba)2(2,20bipy)] (1)
0.71073
triclinic
0.71073
0.71073
triclinic
triclinic
A
mixture of Hmba (0.135 g, 1.0 mmol), Zn(ClO4)2 ꢀ
ꢀ
ꢀ
ꢀ
6H2O(0.186 g, 0.50 mmol), 2,20-bipy (0.078 g, 0.50 mmol) and
H2O (10 cm3) was placed in a 20 cm3 Teflon reactor and kept un-
der autogenous pressure at 160 °C for 3 days, and then slowly
cooled to room temperature at a rate of 0.5 °C minꢁ1. Colourless
block crystals of 1 suited for single crystal X-ray diffraction anal-
yses were formed with a yield of approximately 22% (based on
Zn). Anal. calc. for C26H22N2O4Zn: C, 63.49; H, 4.51; N, 5.70.
Found: C, 63.46; H, 4.55; N, 5.63; Zn, 13.32%. Zn, 13.29%. Se-
lected IR data (KBr, cmꢁ1): 3035(w), 2937(m), 1632(s), 1553(s),
1472(w), 1435(m), 1401(m), 1376(m), 1313(s), 1276(m),
1192(m), 1160(w), 1121(w), 1089(s), 1017(vs), 926(s), 793(w),
768(s), 661(m).
P1
P1
P1
7.6208(4)
9.8140(6)
15.7439(9)
79.148(3)
83.929(3)
79.936(3)
1135.4(1)
2
7.6312(4)
8.6555(4)
10.7260(5)
69.635(2)
69.686(2
83.593(2)
622.9(1)
1
5.1098(2)
9.3271(4)
9.8661(4)
104.937(2)
95.279(2)
93.442(2)
450.7(1)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
qcalc. (mg mꢁ3
)
1.439
1.117
1.594
1.067
2.089
2.753
l
(mꢁ1
)
F(000)
508
312
284
Crystal size (mm)
h Range for data
collection (°)
h/k/l (maximum,
minimum)
0.26 ꢂ 0.22 ꢂ 0.17 0.22 ꢂ 0.20 ꢂ 0.17 0.28 ꢂ 0.26 ꢂ 0.22
2.70–25.50
2.71–25.50
2.15–27.50
ꢁ9,9/ꢁ11,7/
ꢁ19,18
ꢁ9,9/ꢁ10,10/
ꢁ12,12
ꢁ6,6/ꢁ12,11/
ꢁ12,12
2.3. Preparation of complex [Zn(mpdcH)2(H2O)4] ꢀ 4H2O (2)
Reflections
5245
3767
5675
Similar to the preparation of 1, the hydrothermal reaction of
H2mpdc (0.181 g, 1.0 mmol), Zn(ClO4)2 ꢀ 6H2O (0.186 g, 0.50
mmol), 2,20-bipy (0.078 g, 0.50 mmol) and H2O (10 cm3) in a
20 cm3 Teflon reactor under autogenous pressure was performed
at 160 °C for 72 h and then was cooled to room temperature at a
rate of ca. 0.5 °C minꢁ1 to give colorless prism crystals of 2 (yield:
31% based on Zn). Zn, 11.02. Anal. calc. for C18H32N2O16Zn: C, 36.16;
H, 5.40; N, 4.69; Zn, 10.94. Found: C, 36.09; H, 5.49; N, 4.72%. Se-
lected IR data (KBr, cmꢁ1): 3439(br), 1645(s), 1595(s), 1434(m),
1385(s), 1359(s), 1196(m), 1124(w), 1060(w), 1029(w), 932(w),
794(w), 746(m).
collected
Unique (Rint
Completeness to
q = 27.13 (%)
Absorption
correction
Maximum and
minimum
)
3766 (0.0227)
99.10
2284 (0.0207)
98.10
2033 (0.0178)
98.10
empirical
empirical
empirical
full-matrix least-
full-matrix least-
full-matrix least-
squares on F2
squares on F2
squares on F2
transmission
Data/restraints/
parameters
Goodness-of-fit on
F2
3766/0/300
1.046
2284/12/196
1.081
2033/6/158
1.028
Final R1a, wR2
0.0424, 0.0975
0.0274, 0.0753
0.0203, 0.0534
b
indices
[I > 2r(I)]
2.4. Preparation of complex [Zn(cda)2(H2O)2]n (3)
R1, wR2 indices (all
data)
0.0596, 0.1072
0.0276, 0.0756
0.0211, 0.0538
Compound 3 was obtained using the same reaction procedure
as described for compound 2 taking H2cda in place of H2mpdc.
The colorless block crystals of 3 were isolated in about 38% yield
(based on Zn). Anal. calc. for C7H6O8Zn: C, 29.66; H, 2.13; Zn,
23.06. Found: C, 29.62; H, 2.25; Zn, 23.12%. Selected IR data (KBr,
cmꢁ1): 3419(br), 1625(s), 1575(m), 1520(m), 1429(s), 1387(s),
1337(m), 1202(w), 1190(m), 1120(m), 1060(m), 856(m), 748(m),
726(m).
Largest difference
in peak and hole
0.341/ꢁ0.306
0.354/ꢁ0.334
0.366/ꢁ0. 502
(e Åꢁ3
)
P
a
R = |Fo| ꢁ |Fc|/S|Fo|.
P
P
wR = [ w(|Fo|2 ꢁ |Fc|2)2/ w(F2o)2]1/2. w = 1/[
r
2(F2o) + (0.0472P)2 + 0.3107P] for
2(F2o) + (0.0282P)2 + 0.2805P]
b
1, w = 1/[
r
2(F2o) + (0.0389P)2 + 0.2999P] for 2, w = 1/[
r
for 3, P = (F2o þ 2Fc2)/3.

X.-X. Zhou et al. / Inorganica Chimica Acta 362 (2009) 1441–1447
1443
Table 2
Selected atomic distances (Å) and bond angles (°) for compounds 1–3a
Compound 1
Zn(1)–O(1)
Zn(1)–O(2)
Zn(1)–O(3)
Zn(1)–O(4)
Zn(1)–N(1)
Zn(1)–N(2)
O(1)–Zn(1)–O(4)
O(3)–Zn(1)–O(4)
1.985(2)
2.509(3)
2.066(2)
2.202(2)
2.088(3)
2.103(3)
100.99(9)
61.24(9)
O(1)–Zn(1)–O(3)
O(1)–Zn(1)–N(1)
O(3)–Zn(1)–N(1)
O(1)–Zn(1)–N(2)
O(3)–Zn(1)–N(2)
N(1)–Zn(1)–N(2)
N(1)–Zn(1)–O(4)
N(2)–Zn(1)–O(4)
145.1(1)
105.6(1)
96.5(1)
103.1(1)
107.8(1)
78.1(1)
153.4(1)
94.4(1)
Compound 2
Zn(1)–O(3)
Zn(1)–O(3)#1
Zn(1)–O(6)#1
Zn(1)–O(6)
2.0240(13)
2.0240(13)
2.0764(14)
2.0764(14)
2.1864(14)
2.1864(14)
O(3)–Zn(1)–O(6)#1
O(3)–Zn(1)–O(6)
O(3)#1–Zn(1)–O(6)
O(3)–Zn(1)–O(5)
O(6)–Zn(1)–O(5)
90.5(1)
89.5(1)
90.5(1)
88.3(1)
88.3(1)
Zn(1)–O(5)
Zn(1)–O(5)#1
Compound 3
Zn(1)–O(7)
Zn(1)–O(2)#2
Zn(1)–O(6)
Zn(1)–O(8)
O(3)–C(6)
O(3)–C(2)
C(2)–C(3)
1.9296(12)
1.9541(12)
1.9723(12)
1.9910(14)
1.3518(18)
1.3554(18)
1.340(2)
1.443(2)
1.243(2)
1.443(2)
1.339(2)
O(7)–Zn(1)–O(2)#2
O(7)–Zn(1)–O(6)
O(2)#2–Zn(1)–O(6)
O(7)–Zn(1)–O(8)
O(2)#2–Zn(1)–O(8)
O(6)–Zn(1)–O(8)
C(6)–O(3)–C(2)
C(3)–C(2)–O(3)
C(2)–C(3)–C(4)
124.5(1)
121.1(1)
95.3(1)
Fig. 1. Coordination environment of Zn(II) ion in 1 with 50% probability thermal
ellipsoids.
104.8(1)
105.3(1)
103.3(1)
118.2(1)
123.1(1)
120.4(1)
114.5(1)
120.4(1)
123.1(1)
C(3)–C(4)
O(4)–C(4)
C(4)–C(5)
C(5)–C(4)–C(3)
C(6)–C(5)–C(4)
C(5)–C(6)–O(3)
C(5)–C(6)
a
Symmetry transformations used to generate equivalent atoms: #1 ꢁx, ꢁy,
ꢁz + 2; #2 x, y, z ꢁ 1.
Table 3
Distances (Å) and angles (°) of hydrogen bonds for compounds 1–3
D–Hꢀ ꢀ ꢀA
Distance
(D–H)
Distance
(Hꢀ ꢀ ꢀA)
Distance
(Dꢀ ꢀ ꢀA)
Angle
(D–Hꢀ ꢀ ꢀA)
Compound 2
O(5)–H(5A)ꢀ ꢀ ꢀO(7)#2
O(5)–H(5B)ꢀ ꢀ ꢀO(4)#1
O(6)–H(6D)ꢀ ꢀ ꢀO(2)#3
O(6)–H(6E)ꢀ ꢀ ꢀO(2)#4
O(7)–H(7A)ꢀ ꢀ ꢀO(1)#5
O(7)–H(7B)ꢀ ꢀ ꢀO(1)
O(8)–H(8A)ꢀ ꢀ ꢀO(5)#6
O(8)–H(8B)ꢀ ꢀ ꢀO(2)#5
N(1)–H(1)ꢀ ꢀ ꢀO(8)#4
0.847(9)
0.846(9)
0.836(9)
0.842(9)
0.850(9)
0.850(10)
0.843(10)
0.836(10)
0.861(9)
1.928(10)
1.890(10)
1.934(12)
1.917(12)
2.055(14)
1.998(14)
2.029(12)
2.098(12)
1.875(11)
2.773(2)
2.713(2)
2.7518(19)
2.7478(19)
2.863(2)
2.812(2)
2.858(2)
2.919(2)
2.729(2)
176(2)
164(2)
166(2)
168(2)
159(2)
160(2)
168(2)
167(2)
175(2)
Fig. 2. 2D supramolecular layer of 1 constructed through
viewed along a-axis.
pꢀ ꢀ ꢀp packing interactions
Compound 3
nation geometry. The Zn–O distances range from 1.985 to 2.509 Å
and the Zn–N distances from 2.088 to 2.103 Å (Table 2).
In complex 1, mbaꢁ and 2,20-bipy acting as terminal ligands
O(7)–H(7A)ꢀ ꢀ ꢀO(1)#7
O(7)–H(7A)ꢀ ꢀ ꢀO(3)#7
O(7)–H(7B)ꢀ ꢀ ꢀO(5)#7
O(8)–H(8B)ꢀ ꢀ ꢀO(4)#8
O(8)–H(8A)ꢀ ꢀ ꢀO(6)#9
0.844(9)
0.844(9)
0.846(9)
0.842(9)
0.832(9)
1.868(10)
2.66(2)
1.879(10)
1.788(10)
2.018(11)
2.7103(18)
3.0407(16)
2.7193(18)
2.6207(18)
2.8172(18)
175(2)
109(2)
172(2)
169(2)
161(2)
ˆ
ˆ
adopt chelating modes (OO/NN) to coordinate with one Zn(II)
ion, forming mononuclear unit with three bite angles of O1–Zn1–
O2 57.12°, O3–Zn1–O4 61.24° and N1–Zn1–N2 78.05° as secondary
building units (SBUs), and then these SBUs are further linked by the
Symmetry transformation used to generate equivalent atoms: #1 ꢁx, ꢁy, ꢁz + 2; #2
x, y ꢁ 1, z; #3 x, y ꢁ 1, z + 1; #4 ꢁx + 1, ꢁy + 1, ꢁz + 1; #5 ꢁx + 1, ꢁy + 2, ꢁz + 1; #6
x + 1, y + 1, z; #7 ꢁx + 1, ꢁy + 1, ꢁz; #8 ꢁx, ꢁy + 2, ꢁz; #9 x + 1, y, z.
p p
stacking interactions among the adjacent parallel 2,20-bpy
ꢀ ꢀ ꢀ
molecules or benzene rings with the distance of 3.918 Å, 3.923 Å
for 2,20-bipy rings and 4.058 Å for benzene rings to give rise to
2D layer supramolecular structure which is shown in Fig. 2.
3. Results and discussion
3.1. Description of crystal structures
3.1.2. [Zn(mpdcH)2(H2O)4] ꢀ 4H2O (2)
The monocarboxylate ligand mbaꢁ in 1 is replaced by dicarbox-
ylate ligand mpdc2ꢁ, giving complex 2. Single crystal X-ray diffrac-
tion analysis shows that the complex 2 is still mononuclear with
3.1.1. [Zn(mba)2(2,20bipy)] (1)
Single crystal X-ray diffraction analysis reveals that complex 1
consists of [Zn(mba)2(2,20bipy)] and coordination environment of
Zn(II) ion is shown in Fig. 1. Zn(II) ion is six-coordinated by four
oxygen atoms (O1, O2 and O3, O4) from two different carboxylic
groups of two mbaꢁ ligands and two nitrogen atoms (N1 and N2)
of one 2,20-bipy molecule, exhibiting a distorted octahedral coordi-
ꢀ
space group P1, and the molecular ORTEP plot is shown in Fig. 3.
Each dicarboxylate ligand mpbc2ꢁ gives one oxygen atom (g1
-
O3/O3a) to coordinate to the central Zn(II) atom, and the octahe-
dral coordination environments of the Zn(II) ions are further satis-
fied by the coordination of four water molecules (O5, O6, O5a and

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X.-X. Zhou et al. / Inorganica Chimica Acta 362 (2009) 1441–1447
Fig. 3. The molecular structure of complex 2, shown with 50% probability displacement ellipsoids. Uncoordinated water molecules have been omitted for clarity. Unlabelled
atoms are related to labelled atoms by ꢁx, ꢁy, ꢁz + 2.
Fig. 4. 2D supramolecular layer of 2 assembled by
pꢀ ꢀ ꢀp packing interactions viewed along b-axis.
Fig. 5. 3D supramolecular network of 2 fabricated through
pꢀ ꢀ ꢀp packing and hydrogen bonding O–Hꢀ ꢀ ꢀO and N–Hꢀ ꢀ ꢀO interactions viewed along a-axis.
O6a). O3 and O3a are at the axis, while the other four oxygen
atoms are located on the plane. The average distances of Zn–O
are 2.0956(14) Å. The angles of O(3)–Zn(1)–O(3)#1, O(3)–Zn(1)–
O(6) and O(3)–Zn(1)–O(5) are 180°, 89.54(6)° and 88.31(5)°,
respectively (Table 2). So the coordination geometry of the central
Zn(II) ion may be accurately described as the canonical octahedron.
The intermolecular interactions play significant roles in the for-
mation and stability of compound 2. As shown in Fig. 4, at first,
4.035 Å, which results in 2D layer-like supramolecular structure,
and latticed water molecules reside in the interlayers (Fig. 5).
The nitrogen atom in the central pyridinyl ring is protonated with-
out coordinating under the reaction conditions employed and may
be attributed to the steric hindrance of two methyl groups situated
ortho- to nitrogen atom. Considering ligand mpbc2ꢁ in 2 adopting
monodentate
g
1 mode to coordinate to one Zn(II) ion and the sec-
ond carboxyl group of ligand mpbc2ꢁ remaining free, consequently
there are a lot of versatile hydrogen bonds in the crystal lattice of
compound 2 (see Table 3): between the lattice water molecules
and the uncoordinated carboxylate oxygen atoms, the lattice water
these discrete Zn1 units (as SBUs) are packed through the
stacking interactions between pyridine rings of the adjacent Zn1
p p
ꢀ ꢀ ꢀ
units with the centroid-to-centroid distance of 3.717 Å or

X.-X. Zhou et al. / Inorganica Chimica Acta 362 (2009) 1441–1447
1445
Fig. 6. Coordination environment of Zn(II) ion in 1D compound 3 with 50% probability thermal ellipsoids.
As shown in Table 2 and Fig. 6, the average lengths of C–C and
C–O bonds in the central -pyranone ring are 1.391 and 1.354 Å,
respectively. Six internal angles of -pyranone ring range from
c
c
114.54 to 123.14° with a mean of 119.96° very close to 120°. Seven
atoms of C2, C3, C4, C5, C6, O3, O4 are almost in the same plane
with mean deviation of 0.0296 Å. These data lead to the conclusion
that there is a delocalization of the electrons in seven atoms C2–
C3–C4–C5–C6–O3–O4 c-pyranone portion.
As compared with compound 2, although there are no free
water molecules in crystal lattice, two coordinated water mole-
cules in compound 3 with five oxygen atoms of multifunctional
chelidonate ligand cda2ꢁ are equally engaged in the rich hydrogen
bonding network (Table 3). Through these hydrogen bonding inter-
actions between the coordinated water molecules and the coordi-
nated/uncoordinated carboxylate O atoms, the 1D chains are
packed alternatively to brick-wall-like three-dimensional network
containing 1D channels with the pore size of 3 ꢂ 9 Å2 (Fig. 7). Un-
Fig. 7. A view of 3D molecular network with 1D channels constructed by
intermolecular O–Hꢀ ꢀ ꢀO hydrogen interactions viewed along c-axis.
molecules and the coordinated carboxylate oxygen atoms, the lat-
tice water molecules and the coordinated water molecules, the
coordinated water molecules and the uncoordinated carboxylate
oxygen atoms as well as among the lattice water molecules. One
the right side of these hydrogen bonding interactions, 2D layers
are assembled into 3D supramolecular network (see Fig. 5).
like 1 and 2, no significant
in 3.
pꢀ ꢀ ꢀp stacking interactions are observed
It is obvious from the above descriptions that the organic car-
boxylate ligands have significant effect on the formation and
architecture of the resulting Zn(II) complexes (Scheme 1). In com-
plexes 1, mba2ꢁ acts as terminal ligand adopting chelate mode
ˆ
(OO) to coordinate with Zn(II) ion cooperated with the co-ligand
2,20-bipy, which prevents the structure from being extended into
higher dimensionality. Compared to the terminal ligand mba2ꢁ in
1, the multidentate dicarboxylate ligands mpbc2ꢁ in 2 and cda2ꢁ
in 3 exclude the co-ligand 2,20-bipy from coordination to Zn(II)
ions, resulting in the existence of the coordinated water mole-
cules and plentiful hydrogen bonds in crystal lattice, which fur-
ther conduce the differences of the supramolecular structures of
compounds 1–3. Both compounds 2 and 3 have 3D spramolecular
networks; however, compound 1 is only assembled into 2D
3.1.3. [Zn(cda)2(H2O)2]n (3)
Compound 3 is a one-dimensional chain-like structure, which is
constructed by hybridization of organic ligands cda2ꢁ with inor-
2þ
ganic units ZnðH2OÞ2
(Fig. 6). The selected bond angles and
lengths are depicted in Table 2. The coordination geometry of Zn(II)
ion, which completely differs from the ones in compounds 1 and 2,
is a slightly distorted tetrahedron with two oxygen atoms from
two water molecules and the other two oxygen atoms from differ-
ent bridging ligands cda2ꢁ. The bond angles around the Zn(II) ion
are in the range of 95.28–124.54°, and the Zn–O bond lengths
range from 1.930 to 1.991 Å.
supramolecular structure by
two benzene rings.
pꢀ ꢀ ꢀp stacking interactions between
COOH
...
π
π
0D compound [Zn(mba)2(2,2'-bipy)] (1)
2 D supramolecular layer
N
N
Hmba or H2cda
or H2mpda
N
O
...
O-H
π
π
hydrothermal
HOOC
COOH
COOH
...
N
synthesis
3 D supramolecular
network
2+
.
0D compound [Zn(mpdaH)2(H2O)4] 4H2O (2)
Zn
...
O-H
O
160 ºC, 3 days
2,2'-bipy
HOOC
...
O-H
O
3D supramolecular network
conatining 1D channel
1D chain-like compound [Zn(cda)2(H2O)2]n (3)
Scheme 1.

1446
X.-X. Zhou et al. / Inorganica Chimica Acta 362 (2009) 1441–1447
Fig. 8. TG curve of complex 2.
Fig. 9. Luminescent emission spectra: (a) for compound
2 (Em = 396 nm,
Ex = 291 nm) and (b) for compound 3 (Em = 363 nm, Ex = 291 nm) in the solid
state at room temperature. Em, emission; Ex, excitation.
3.2. Thermal properties
To examine the thermal stability of the complexes, the thermo-
gravimetric analyses of complexes 2 and 3 were carried out from
20 to 800 °C. In 2 and 3, uncoordinated and coordinated water mol-
ecules were lost at first. And then, complicated decomposition
reaction took place when the heating continued. Take complex 2
as an example. The TG curve of complex 2 showed that the first
weight loss of 12.20% (calc. 12.05%) from 88 to 142 °C corresponds
to the loss of four uncoordinated water molecules, the residue
weight approximates to the formula of [Zn(mpdaH)2(H2O)4]. And
then the weight loss of 12.11% (calc. 12.05%) between 154 and
255 °C ascribes to the loss of four coordinated water molecules,
and the residue weight corresponds to Zn(mpdaH)2. Another major
weight loss occurred in the range 295–800 °C, which may corre-
spond to complete burning of mpdaH group. The final residue
weight is 14.08% (calc. 13.56%) corresponding to ZnO (Fig. 8).
9. The results exhibit that every compound has two peaks (at
335 nm and 396 nm for 2, 325 nm and 363 nm for 3) with strong
maximal emission bands at 396 nm and 363 nm, respectively,
upon excitation at 291 nm in the same experimental environment.
The lifetime, s, for the emissions is 0.027 and 0.035 ns for 2 and 3,
respectively. This indicates that the luminescence should be as-
signed to fluorescence. As a comparison, luminescence of the cor-
responding ligands H2mpda and H2cda has been measured, and
their emission spectra are also demonstrated in Fig. 9, from which,
the emission maximum at 468 nm for H2mpda and 460 nm for
H2cda can be attributable to the
p
* ? n transition [8]. Thus, the
blue-shifted fluorescent emission of compounds 2 and 3 compared
to the free corresponding ligands can be assigned as ligand-to-me-
tal charge transfer (LMCT) [15]. The much more enhanced fluores-
cent intensities of 2 and 3 are presumably attributed to more
rigidity of the ligand coordinating to Zn(II) ions than that of the
free ligands, which effectively reduces the loss of energy [16]. As
can be seen, the main emission bands of 2 and 3 are similar in
the band shapes but with differences in the positions of the located
emission bands, which have been attributed to the same coordi-
3.3. IR spectra
The IR spectrum of 1 indicates the typical bands of carboxylic
groups at 1632 cmꢁ1 for the antisymmetric stretching and at
1553 cmꢁ1 for symmetric stretching. The values of (masym
ꢁ
msym)
nated mode (g
1) of two heterocyclic dicarboxylate ligands. The dif-
clearly indicate the presence of chelating (79 cmꢁ1) coordination
mode of carboxylic groups [14], which is consistent with the single
crystal X-ray diffraction. While the IR spectra of complexes 2 and 3
ferences in the band positions might also be due to the differences
in the structures of the central heterocycles of two dicarboxylate
ligands and coordination environment around central Zn(II) ions,
because luminescence behavior is closely associated with the local
environments around metal ions [17–19]. In addition, the different
topologies (0D and 1D) and the intricate hydrogen bonds may also
influence the emission spectra. Considering that the luminescence
properties of the two complexes exhibit a broad range of visible
light, giving the observed blue luminescence, therefore, both 2
and 3 may have potential application as luminescent materials in
organic light-emitting devices.
In summary, three new low dimensional Zn(II) complexes con-
taining organic-carboxylic acids have been successfully demon-
strated. X-ray single crystal diffraction displays that three
compounds 1–3 have the different topologies and supramolecular
architectures, which may be attributed to the organic carboxylate
ligands having significant effect on the formation and architecture
of the resulting Zn(II) complexes. Obviously the results presented
here offer the intriguing strategy of constructing the complexes
with the different topologies and supramolecular architectures.
Furthermore, the intense blue luminescent properties of complex
show the common characteristic absorption, such as mH absorp-
2O
tion in the wide range of about 3600–3100 cmꢁ1, centered at
3439 cmꢁ1 for 2, 3419 cmꢁ1 for 3, which approves the existence
ꢁ
of water molecules in 2 and 3. In complex 2, the msCOO absorptions
appear at 1412–1345 cmꢁ1, while the unco-ordinated carboxyl
absorption of the ligand is not presented, which may be caused
ꢁ
by the strong hydrogen-bonding. In complex 3, the msCOO absorp-
tions appear at 1432–1358 cmꢁ1. It is really a pity that the
ꢁ
masCOO absorptions in complexes 2 and 3 are submerged in the
range of 1650–1500 cmꢁ1 because the skeleton vibrations of C@O
and C@N bonds of aromatic rings appear at the same range. The ab-
sence of strong bands ranging from 1690 to 1730 cmꢁ1 in com-
pounds 1–3 indicates that all ligands are deprotonated.
3.4. Luminescent properties
Room-temperature solid-state luminescent studies performed
on powdered samples of complexes 2 and 3 are presented in Fig.

X.-X. Zhou et al. / Inorganica Chimica Acta 362 (2009) 1441–1447
1447
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2 and 3 at room temperature suggest that they have great potential
application as luminescent materials.
(b) L.-P. Sun, S.-Y. Niu, J. Jin, G. –D Yang, L. Ye, Inorg. Chem. Commun. 9 (2006)
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Acknowledgements
[7] (a) H.W. Roesky, M. Andruh, Coord. Chem. Rev. 236 (2003) 91;
(b) K. Biradha, Cryst. Eng. Comm. 5 (2003) 374;
(c) X.M. Chen, G.F. Liu, Chem. Eur. J. 8 (2002) 4811.
[8] K.L. Huang, Y.T. He, D.Q. Wang, W.L. Pan, C.W. Hu, J. Mol. Struct. 832 (2007)
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[9] (a) J.F. Eubank, V.C. Kravtsov, M. Eddaoudi, J. Am. Chem. Soc. 129 (2007)
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(b) M. Fainerman-Melnikova, J.K. Clegg, R. Codd, Acta Crystallogr., Sect. E 62
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We are grateful to the National Natural Science Foundation of P.
R. China (Grant No. 20772037), Science and Technology Planning
Project of Guangdong Province (Grant No. 2006A10902002) and
the N.S.F. of Guangdong Province (Grant No. 06025033) for finan-
cial support.
Appendix A. Supplementary material
(b) H.-P. Xiao, B.-L. Liu, X.-Q. Liang, J.-L. Zuo, X.-Z. You, Inorg. Chem. Commun.
11 (2008) 39.
[11] (a) Y.-P. Cai, G.-B. Li, Q.-G. Zhan, F. Sun, J.-G. Zhang, S. Gao, A.-W. Xu, J. Solid
State Chem. 178 (2005) 3729;
(b) Y.-P. Cai, C.-Y. Su, G.-B. Li, Z.-W. Mao, C. Zhang, A.-W. Xu, B.-S. Kang, Inorg.
Chim. Acta 358 (2005) 1298.
[12] G.M. Sheldrick, SADABS Program for Scaling and Correction of Area Detector
Data, University of Göttingen, Göttingen, Germany, 1996.
[13] SHELXTL SHELXTL, Ver. 5.10, Bruker Analytical X-ray Systems, Madision, WI, USA,
1998.
CCDC 677378, 677379 and 677380 contain the supplementary
crystallographic data for 1, 2 and 3. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. X-ray crystallographic files
in CIF format for compounds 1–3 are available. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2008.07.015.
[14] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds;, John Wiley and Sons, New York, 1997.
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