Hydrothermal synthesis, crystal structure and heterogeneous catalytic activity of a novel inorganic-organic hybrid complex, possessing infinite La-O-La linkages

Article abstract of DOI:10.1016/j.ica.2013.01.026

In this paper, a novel lanthanum coordination polymer formulated as {[La₂(Hpdc)₃(H₂O)₄]·2H ₂O}_n (1, H₃pdc = 3,5-pyrazoledicarboxylic acid) has been synthesized by the reaction of H₃pdc with chloride salt of La(III) under hydrothermal conditions and characterized by elemental analysis, FT-IR, TGA and single-crystal X-ray diffraction. The complex crystallized in the monoclinic system Cc space group. The single-crystal X-ray structural analysis revealed that central metal La atoms are nine-coordinate and linked by bridging μ₂-O_COO^- groups to form [La(1)- (μ₂-O_COO^-)₂-La(2)]_n inorganic-organic chains that produce a supramolecular polymeric framework structure. The three-dimensional structure of 1 is accompanied by non-coordinating water molecules. Thermal behavior and catalytic performance of 1 have also been studied. The complex 1 showed 100% selectivity and a conversion rate of 24% on the oxidation of thymol (T) to thymoquinone (TQ).

Full text of DOI:10.1016/j.ica.2013.01.026

Inorganica Chimica Acta 399 (2013) 208–213
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Hydrothermal synthesis, crystal structure and heterogeneous catalytic activity
of a novel inorganic–organic hybrid complex, possessing infinite La–O–La linkages
Burak Ay , Emel Yildiz , John D. Protasiewicz , Arnold L. Rheingold c
a
a,
⇑
b
a
Department of Chemistry, Arts and Science Faculty, Cukurova University, Balcali 01330, Adana, Turkey
Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, USA
Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, CA 92093, USA
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 October 2012
Received in revised form 24 January 2013
Accepted 28 January 2013
Available online 10 February 2013
In this paper, a novel lanthanum coordination polymer formulated as {[La (Hpdc) (H O) ]Á2H O} (1,
2
3
2
4
2
n
H
3
3
pdc = 3,5-pyrazoledicarboxylic acid) has been synthesized by the reaction of H pdc with chloride salt
of La(III) under hydrothermal conditions and characterized by elemental analysis, FT-IR, TGA and single-
crystal X-ray diffraction. The complex crystallized in the monoclinic system Cc space group. The single-
crystal X-ray structural analysis revealed that central metal La atoms are nine-coordinate and linked by
-
À
2
bridging
2 2 n
l -OCOO groups to form [La(1)-(l -OCOO ) -La(2)] inorganic–organic chains that produce a
Keywords:
supramolecular polymeric framework structure. The three-dimensional structure of 1 is accompanied
by non-coordinating water molecules. Thermal behavior and catalytic performance of 1 have also been
studied. The complex 1 showed 100% selectivity and a conversion rate of 24% on the oxidation of thymol
(T) to thymoquinone (TQ).
Hydrothermal synthesis
Inorganic–organic hybrid compound
Crystal structure
Lanthanide coordination polymer
Thymoquinone
Ó 2013 Elsevier B.V. All rights reserved.
1
. Introduction
Lanthanide coordination polymers containing carboxylate
The metal pyridinecarboxylate and pyrazolecarboxylate com-
plexes are effective catalysts for oxidation of organic substrates
[15,16]. Oxidation of T to TQ is a significant commercial reaction.
TQ is widely used in different areas, especially in the medical field,
as an active component [17]. Especially last four years, several
studies have been conducted to investigate anticancer [18], anti-
tumor [19], antioxidant [20] and antimicrobial [21] properties of
TQ (see Scheme 2).
Hydrothermal synthesis is an efficient method for the prepara-
tion of coordination polymers because of advantages over other
methods. For example, water is environmentally friendly com-
pound using as the solvent under the hydrothermal conditions. Un-
der the conditions of the hydrothermal syntheses, even insoluble
reagents, which are unsuitable to synthesize complexes by conven-
tional means, can often provide pure crystalline metastable novel
compounds and materials directly from reaction mixtures upon
cooling [22].
bridged have attracted great interest due to their well-rounded
properties and applications such as catalysis [1], luminescent [2]
and fluorescent [3] technologies, magnetism [4] and molecular rec-
ognition [5]. Because of the different and interesting coordination
modes ligand to the metal centers, studies including lanthanide
metals and carboxyl groups have been increasing constantly. Many
of these compounds, the metal ions are bridged by carboxylate
groups to produce different structures such as dimers, 1D chains,
2
D-layer and 3D [6–10]. The lanthanide ions which are containing
oxygen or hybrid oxygen–nitrogen atoms have high affinity for
hard donor atoms. Carboxylate moieties in pyridine and pyrazole
compounds are widely used in the construction of lanthanide coor-
dination polymers due to their capability of bridging metal centers
in various coordination modes [11]. In particular, H
functional ligand and there are three different acidic hydrogens
Ha, Hb, Hc, Scheme 1), whose ionization can allow metal ions to
3
pdc is a multi-
We report the hydrothermal synthesis and crystal structure
(
characterization of
(H O) O} (1). It was prepared the reaction of LaCl
]Á2H
and H pdc by hydrothermal synthesis in alkali medium. The com-
a
novel lanthanide complex {[La
2
(Hpdc)
3
be coordinated to the different coordination sites in varying se-
quences to synthesize diverse new heterometallic complexes
2
4
2
n
3 2
Á7H O
3
[
12–14].
plex was obtained higher yield and more different conditions such
as pH, reaction temperature and time than that of similar empirical
formulas [23,24]. Also, the molecular geometry of 1 has one more
oxygen bridge unlike Ref. [23] (Fig. 1). This metal catalyst acts as an
efficient heterogeneous catalyst in oxidation of T to TQ. Thermal
stability of the compound also has been investigated.
⇑
Corresponding author. Tel.: +90 3223386084x2442; fax: +90 3223386070.
E-mail address: eeyildiz@cu.edu.tr (E. Yildiz).
0
020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.01.026

B. Ay et al. / Inorganica Chimica Acta 399 (2013) 208–213
209
NaOH (0.041 g, 1.0 mmol) and H
2
O (5 mL) was placed in a 23 mL
Teflon-lined Parr acid digestion bomb and heated for two days at
1
80 °C under autogenous pressure. Upon cooling to room temper-
ature, solution was separated from the solid phase, and after filtra-
tion precipitate washed with water and acetone, respectively. The
product was dried at ambient temperature. The colorless crystals
of 1 were obtained with high yield and the synthesized single crys-
tals suited for X-ray diffraction analysis. Yield ca. 86% (based on
La). Initial pH was 2.50; final pH was 1.88. Crystalline 1 is insoluble
in water and common solvents and stable in air. Anal. Calc. for
Scheme 1.
C
15
H
15La
2
N
6
O
18: C, 21.29; H, 1.78; N, 9.93. Found: C, 21.18; H, 2.18;
À1
2
. Experimental
.1. Materials and methods
All chemicals and solvents employed were commercially avail-
N, 9.67%. IR data (KBr pellet, cm ): 3410(m), 3160(m), 1593(vs),
1458(m), 1352(vs), 1311(vs), 1017(s), 837(w), 783(s), 629(w).
2
2.3. Crystal structure determination
able and used as received without further purification. Parr acid
reactors with 23 mL PTFE lined were used for the complex synthe-
sis. All chemicals were stirred before reactions at the room temper-
ature then initial pH values of the reactions were determined. At
Single crystal X-ray data were collected on a Bruker AXS SMART
CCD diffractometers using monochromatic Mo K
a radiation at
100 K with omega scanned technique. The unit cell was deter-
mined using APEX2 Crystallographic Suite. All structures were
solved by direct methods and refined by full matrix least squares
the end of the reactions final pH values were measured with Hanna
À1
2
2
11 pH meter. The IR spectra were recorded in the 400–4000 cm
against F with all reflections using SHELXTL software package.
region using KBr pellets on a Perkin–Elmer RX-1 spectrometer.
Thermo gravimetric analysis (TGA) of the sample was carried out
with a Perkin Elmer Pyris Diamond system at a rate of 10 °C/min
from ambient temperature to 800 °C in a nitrogen atmosphere.
Thermo Scientific ISQ Single Quadrupole headspace GC–MS system
Refinement of extinction coefficients was found to be insignificant.
All non-hydrogen atoms were refined anisotropically. Data collec-
tion parameters and refinement details are summarized in Table 1,
and selected bond distances, and bond angles are given in Table 2.
Full lists of bond lengths and angles, atomic coordinates and equiv-
alent isotropic displacements and other parameters are given in
the supporting information (Tables S1–S4). Powder X-ray diffrac-
tion (XRD) of the metal complex was carried out on a BRUKER
AXS D8 ADVANCE model diffractometer.
(
TR5MS capillary columns: 60 m  0.25 mm i.d.; 25
lm film thick-
ness) was used for the determination of % selectivity and charac-
terization of the oxidation product TQ. Chromatography and
mass spectrometry (head space GC–MS) circumstances were as fol-
À1
lows: first temperature: 50 °C; heating rate: 3 °C min ; last tem-
perature: 250 °C; temperature of the injector: 240 °C. The
corresponding peak areas were used for the percentage of T and
TQ in the reaction mediums. High-performance liquid chromatog-
raphy (HPLC) analyses were performed with a SHIMADZU LC-10AD
2
.4. Thymol oxidation
T oxidation was performed at 20, 40 and 60 °C in a multi-necked
flask (250 mL) equipped with a temperature controller, a magnetic
stirrer and a reflux condenser in an oil bath. T (3.0 g, 20 mmol) and
system equipped with
250 mm  4.6 mm I.D., 5
conversion studies of TQ. Samples (20
a
reversed phase C18 column
Ò
(
l
m particle sizes, Phenomenex ) for %
l) were injected for per
2
0 mL acetonitrile were transferred to glass vessel. Afterward, the
essential amount of 30% wt. H (7 mL) was added to supply the re-
quired T-to-H stoichiometric ratio although 0.4 mL H was
l
2 2
O
injection, and separation was performed with an isocratic mobile
2
O
2
2 2
O
À1
phase with a flow-rate of 1.0 mL min and at 30 °C column tem-
used for 0.325 mmol substrate [25]. After heating this mixture to
be 20–60 °C, the catalyst (0.1–0.3 g) was added to the flask to begin
the reaction. The reaction mixture was stirred continuously for 1, 5,
perature. The ultraviolet visible (UV–Vis) detector was set up at
2
54 nm considering of the retention times of T and TQ because
the substrate and the oxidation product exhibit the maximum
absorbance of at that wavelength. Before the injection, the column
was balanced with the methanol:acetonitrile:water (60:20:20 v/v)
for 30 min. until a straight line was obtained.
9
and 24 h. The products of the oxidation reactions were collected at
different time intervals and were identified and quantified by HPLC.
3
. Results and discussion
2.2. Synthesis of compound 1
3.1. Crystal structure of {[La
2 3
(Hpdc) (H
O)
2 4
2 n
]Á2H O} (1)
The complex was prepared by hydrothermal method. A mixture
Crystals of the lanthanum coordination polymer 1 was obtained
of LaCl Á7H
3 2
O (0.187 g, 0.5 mmol), H
3
pdc (0.175 g, 1.0 mmol),
directly from slow cooling of the contents of the hydrothermal
Scheme 2.

2
10
B. Ay et al. / Inorganica Chimica Acta 399 (2013) 208–213
Fig. 1. (a) The coordination environment of the La atom in complex. (b) Grid motif in the ac plane. La, pink; O, red; N, blue; C, gray; H, white.
reaction of LaCl
3
Á7H
2
O, H
3
pdc, and NaOH in a 1:2:2 stoichiometric
values in other found La(III) complexes [28,29]. The chelated
3,5-pyrazoledicarboxylic acid (H pdc) acid is coordinated in such
ratios. The single-crystal X-ray analysis showed that the coordina-
tion polymer crystallized in the monoclinic system and Cc space
group. The asymmetric unit of 1 (Fig. 1) contains two different
types of lanthanum atoms. La(1) is nine-coordinate by five carbox-
ylate O atoms (O(1), O(3), O(7), O(8), and O(12)), and four are water
oxygen atoms. The carboxylate oxygen atoms are all engaged
bridging to La(2). Three different bridging modes are utilized, a
3
a manner that each oxygen atom is not only bond to one central
La atom with La–O distances range from 2.4433(18) to
2.6721(17) Å. As seen in Fig. 1, La atoms are coordinated to pdc3
ligands to yield a 3D layer structure, where the nine-coordinated
À
La1 and La2 are bridged by
2 2
l -OCOO- atoms to from [La(1)–(l -
O
COO-
)
2
–La(2)] arrangement, the La–La distance is 4.0582(2) Å
n
2
2
j
-O,O’-
carboxylato
O(12) + N(6)), and a
l
-O,O-carboxylato mode (O(3) + O(4)),
a
j
-O,N-l-O-
and La–O–La angle is 101.62° for La(1)#5–O(1)–La(2)#5 and
102.90° for La(1)–O(12)–La(2). Fig. 2 represents view of the layer
structure along the ac plane. Each La atom in the chain is bonded
of the pyridine carboxylate group of the upper chain.
l
-N-pryazolyl mode (O(1) + N(1), O(5) + N(3),
3
j
-O,O’-l-O,l2-O-carboxylato mode (O(7) +
O(8)). La(2) is also nine-coordinate but by six carboxylic O atoms
and three pryazolyl nitrogen atoms. The La–O and La–N bond
lengths are in the range of 2.4433(18)–2.6721(17) Å and
3.2. IR spectra
2
.642(2)–2.659(2) Å, respectively, which are similar to those in
related La nine-coordinate complexes [26,27]. The O–La–O bond
The infrared spectra of the ligand and complex 1 are available in
angles range from 49.13° to 149.94°, which are similar to the
the supporting information (Figs. S1–S2). The infrared spectrum of

B. Ay et al. / Inorganica Chimica Acta 399 (2013) 208–213
211
À1
Table 1
m
(C–OH) at 1276 cm shows the –OH coordinates to La atoms
Crystal data and structure refinement for the {[La
2
(Hpdc)
3
(H
2
O)
4
]Á2H
2
O}
n
.
[
33].
Formula
15 2 6 18
C H15La N O
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
845.13
100(2)
0.71073
monoclinic
Cc
15.7754(8)
8.8617(4)
18.3791(9)
90
98.326(2)
90
2542.3(2)
4
2.205
3.412
1616
3.3. Thermal behaviors
TGA analysis was performed to determine the thermal behavior
of the metal complex (Supporting Information Fig. S3). The data of
the complex displayed three steps weight losses from 90 °C to
b (Å)
c (Å)
6
30 °C. The first stage for weight loss observed between 90 °C
and 127 °C, is attributed for removal of non-coordinated water
molecules from the crystal lattice (4.45% measured, 4.15% calcu-
lated). The subsequent mass loss of 25.25% between 192 °C and
258 °C, corresponds to the loss of three coordinated water mole-
cules and one Hpdc ligand (calc. 24.64%). The third weight loss of
32.06% between 411 °C and 625 °C, corresponds to the decomposi-
tion of other Hpdc ligands (calc. 33.55%). The remaining solid is
a
(°)
b (°)
(°)
c
3
Volume (Å )
Z
3
Density (calculated) (g/cm )
Absorption coefficient (mm
F(000)
Crystal size (mm )
Theta range for data collection (°) 3.18–25.53
Index ranges
À1
)
3
0.38 Â 0.28 Â 0.23
2 3
likely La O (residue weight: found, 38.03%; calc. 38.62%). As a re-
sult of the thermal studies, the results elementarily consistent with
the structural formula of the coordination compound and similar
to be reported related compounds involving water molecules and
lanthanum [34,35].
À18 6 h 6 19, À10 6 k 6 10,
À22 6 l 6 21
Reflections collected
13109
Independent reflections
Completeness to theta = 25.00°
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F
Final R indices [I > 2
R indices (all data)
4502 [R(int) = 0.0181]
99.8%
multi-scan
0.5024 and 0.3572
Full-matrix least-squares on F
4502/14/406
3.4. Catalytic activity
2
Lanthanide coordination polymers have rarely been used as a
2
1.071
heterogeneous catalyst for the oxidation of phenols to quinones
36]. There have been no reports on the oxidation of T to TQ using
r
(I)]
R
R
1
= 0.0112, wR
= 0.0113, wR
2
2
= 0.0289
= 0.0289
[
1
lanthanide complex although T oxidation reactions catalyzed by
other types of the first row complexes in homogeneous and heter-
ogeneous mediums [37]. In general, homogeneous lanthanide cat-
alysts have been used for catalytic conversions. A major drawback
of the homogeneous catalysts is the difficulty of their recovery
from the reaction medium; also they have poor thermal stability.
To prevent the loss of catalyst, many measures have been taken
such as encapsulation [38], linking the catalysts to matrix [39]
and employing the steric hindrance [40,41].
In Fig. S4 (Supporting Information), GC/MS data of the TQ are gi-
ven. La catalyst exhibited 100% selectivity for oxidation of T to TQ.
HPLC analysis technique was used for the catalytic performance of
3 2 2
the metal complex for the oxidation of T using CH CN and H O .
Table 3 summarizes the results, i.e., percentage of T conversion
in the different reaction conditions. These values were calculated
Absolute structure parameter
Extinction coefficient
Largest diff. peak and hole (e Å
0.002(6)
0.00129(5)
0.337 and À0.402
À3
)
Table 2
Selected bond lengths (Å) and angles (°) for the {[La
2
(Hpdc)
3
(H
2
O)
4
]Á2H
2 n
O} .
La(1)–O(3)
2.4433(18)
2.4510(19)
2.5533(17)
2.5572(19)
2.5660(18)
2.6139(16)
2.6204(19)
2.6230(19)
2.6721(17)
2.4897(17)
2.6220(17)
2.6228(17)
2.642(2)
O(16)–La(1)–O(12)
O(3)–La(1)–O(1)#1
O(16)–La(1)–O(1)#1
O(12)–La(1)–O(1)#1
O(14)–La(1)–O(7)
O(15)–La(1)–O(7)
O(16)–La(1)–O(7)
O(12)–La(1)–O(7)
O(3)–La(1)–O(13)
O(15)–La(1)–O(8)
O(7)–La(1)–O(8)
O(4)#2–La(2)–O(5)#4
O(4)#2–La(2)–O(8)
O(9)#3–La(2)–O(12)
O(5)#4–La(2)–O(12)
O(1)#1–La(2)–O(12)
O(9)#3–La(2)–N(1)#1
O(8)–La(2)–N(1)#1
O(1)#1–La(2)–N(1)#1
O(5)#4–La(2)–N(6)
O(1)#1–La(2)–N(3)#4
N(6)–La(2)–N(3)#4
137.81(6)
145.78(6)
74.75(6)
66.31(6)
135.59(7)
135.52(6)
71.65(7)
103.49(6)
74.86(7)
133.50(6)
49.13(5)
84.24(6)
80.98(6)
149.94(6)
126.06(6)
65.39(5)
71.18(6)
109.10(7)
60.86(6)
73.56(7)
77.41(6)
70.54(7)
La(1)–O(14)
La(1)–O(15)
La(1)–O(16)
La(1)–O(12)
La(1)–O(1)#1
La(1)–O(7)
La(1)–O(13)
La(1)–O(8)
La(2)–O(8)
La(2)–O(1)#1
La(2)–O(12)
La(2)–N(1)#1
La(2)–N(6)
from
Fig. S5). H
its reduction product is H
dation product using only H
T
and TQ calibration curves (Supporting Information
is a cheap and an eco-friendly compound because
O, which is harmless. There was no oxi-
as an oxidant and this result is in
2 2
O
2
2 2
O
2.649(2)
agreement with the studies published by another scientists. As a
result of the HPLC analysis, there was no by product at the end
of the catalytic studies (Supporting Information Fig. S6). Even so, the
formation of 2-hydroxy-3-isopropyl-6-methyl-1,4-benzoquinone,
La(2)–N(3)#4
O(1)–La(1)#5
O(1)–La(2)#5
O(4)–La(2)#6
O(5)–La(2)#7
O(9)–La(2)#8
N(1)–La(2)#5
N(3)–La(2)#7
2.659(2)
2.6140(16)
2.6221(17)
2.4548(17)
2.4763(17)
2.4689(18)
2.642(2)
2
-hydroxy-6-isopropyl-3-methyl-1,4-benzoquinone, 4-hydroxy-3-
isopropyl-6-methyl-1, 2-benzoquinone and unknown compounds
have been reported in the same catalytic investigations [36,37]. It
is also remarkable that under same reaction conditions with LaCl3-
2.659(2)
Á7H
2
O in place 1, no oxidation products were detected during the
first 10 h of reaction.
the exhibits strong and broad absorption bands in the range of
À1
2
900–3500 cm which are assigned as the characteristic peaks
To specify the activity of the catalyst, T conversion was plotted
as a function of different temperatures, catalyst amount and reac-
tion time. When the catalytic performance of the La catalyst was
investigated, the conversion ratio was 24% but the selectivity was
100%. In order to determination of the effect of the catalyst on oxi-
dation reaction, the HPLC was acquired before and after reactions
(1, 5, 9 and 24 h) (Supporting Information Fig. S6). When working
60 °C temperature 0.3 g complex, catalyst activity was optimized
giving the maximum T conversion of 24% after 24 h with proximate
to 100% selectivity.
of
m
(O–H) and
m
(N–H) vibrations. The IR spectrum of 1 also exhibits
À1
strong bands at 3410 and 837 cm due to the vibrations of the
non-coordinated water molecules. The strong vibration appearing
À1
at ꢀ3100 cm corresponds to stretching vibrations of the
m(N–
H), which is neighbor of the carboxylate group [30,31]. The very
strong vibrations appearing at 1593–1558 cm
À1
are associated
with the symmetric and asymmetric stretching vibrations of
m
(C@O) [32], indicate that coordinated oxygen atoms to the La cen-
À1
ter. The absence of
m(O–H) of carboxylic group at 1492 cm and

2
12
B. Ay et al. / Inorganica Chimica Acta 399 (2013) 208–213
Fig. 2. View of the layer structure of complex on ac plane. La, pink; O, red; N, blue; C, gray; H, white.
Table 3
Thymol conversion values catalyzed with La(III) complex.
Temperature
°C)
Catalyst amount
(g)
Reaction time
(h)
Thymol conversion
(%)
(
2
2
2
2
4
4
4
4
6
6
6
6
0
0
0
0
0
0
0
0
0
0
0
0
0.2
0.1
0.2
0.3
0.2
0.2
0.1
0.3
0.2
0.1
0.2
0.3
1
5
9
24
1
5
9
24
1
5
9
4.10
5.50
8.20
12.8
4.40
7.30
5.30
16.3
7.20
5.60
7.80
24.0
24
Fig. 3. Powder XRD patterns of the catalyst before (A) and after reaction (B).
Table 4
The reusability of the catalyst.
(
20 mL) water (100 mL) and acetone (20 mL) then dried in a vac-
Recycle number
Thymol conversion (%)
Acetonitrile
uum oven at 50 °C and reused. No traces of La in the filtrate. After
three tests, the conversion values did not change considerably (Ta-
ble 4). Powder XRD patterns were recorded before and after reac-
tions. There were no significant changes in the XRD pattern of
the catalyst. Consequently, no loss of crystallinity was observed
First reuse
Second reuse
Third reuse
24.03
24.01
23.84
(Fig. 3).
3.5. Separation and stability of catalyst
4. Conclusion
The biggest advantage of using heterogeneous catalysts is to get
In summary, we have successfully prepared a supramolecular
lanthanide coordination polymer as metal–organic framework so-
back the catalyst from the reaction medium by filtration and re-
cycle. The phase purity of the sample was proved by filtration,
powder X-ray diffraction (XRD) data and elemental analysis (Sup-
porting Information Table S5) for recycling experiments. Catalyst
was tested running three consecutive reactions in the same condi-
tions. To determine the reusability of the catalyst, is a crucial fea-
ture for a heterogeneous catalyst, the catalyst was separated from
the reaction mixture and filtered off, washed with methanol
lid from the reaction mixture of H
3
pdc and LaCl
3
Á7H
2
O by facile
hydrothermal method which is often result in unusual structures
with variations in stoichiometry, pH, reaction temperature and
time. The lanthanum centers are nine-coordinated and linked by
À
À
2
2 2 n
l -OCOO groups to form the [La(1)–(l -OCOO ) –La(2)] inor-
ganic–organic chains and polymer have a three-dimensional struc-
ture is occupied by non-coordinating water molecules. The crystal

B. Ay et al. / Inorganica Chimica Acta 399 (2013) 208–213
213
structure of the complex is different from that of the previous pub-
lished studies with the similar composition, {[La (Hpdc) (H O)
Á2H O} [24]. The synthesized complex 1 has higher catalytic activ-
[5] G.-X. Liu, K. Zhu, H. Chen, R.-Y. Huang, H. Xu, X.-M. Ren, Inorg. Chim. Acta 362
2009) 1605.
(
2
3
2
4
]
[
[
6] A. Rohde, W. Urland, Dalton Trans. 24 (2006) 2974.
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2
n
ity than the first row transition metal complexes containing pyri-
dine or pyrazole dicarboxylic acid ligands as a heterogeneous
catalyst. Due to the presence of the three oxygen bridges, our La
complex is insoluble at different solvents such as ethanol, metha-
nol and etc. (Supporting Information Table S6). The insoluble fea-
ture is one of the most important factors for application of the
heterogeneous catalysts.
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19.
(
[
[
2
[
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1
According to our catalytic studies, T converted to TQ using eco-
friendly and inexpensive oxidizing agent H O and the synthesized
2 2
[
[
15] R.S. Dowining, H. van Bekkum, R.A. Sheldon, Cattech 95, 1997.
16] Sopharma USA Coorporation, 2001. <http://www.sopharma.com>.
catalyst. The catalytic performance of the study shows that the
conversion from T to TQ is 24% and selectivity is 100%. To the best
of our knowledge, this is the first report on the oxidation of T to TQ
using a lanthanum catalyst. This percent conversion is higher than
[17] B. Ay, E. Yildiz, S. Jones, J. Zubieta, Inorg. Chim. Acta 387 (2012) 15.
[
[
18] X. Lei, X. Lv, M. Liu, Z. Yang, M. Ji, X. Guo, W. Dong, Biochem. Biophys. Res.
Commun. 417 (2012) 864.
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2
0% and 18% those of related catalytic studies [36,37]. Moreover, La
(
2011) 1469.
catalyst exhibited similar performance after three times used. In
this aspect, our investigations are going onto synthesize original
framework lanthanide metal complexes constructed by pyridine
or pyrazine dicarboxylic acid groups. Their catalytic and lumines-
cence properties will be examined.
[
[
22] J. Maa, X. Huang, R. Wei, L. Zhou, W. Liu, Inorg. Chim. Acta 362 (2009) 3440.
23] P. Long, X. Huang, J. Li, Y. Wu, N. Zheng, Angew. Chem., Int. Ed. 39 (2000) 527.
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Yan, Inorg. Chem. 46 (2007) 3450.
[
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[
25] R.R.L. Martins, M.G.P.M.S. Neves, A.J.D. Silvestre, A.M.S. Silva, J.A.S. Cavaleiro, J.
Mol. Catal. A: Chem. 137 (1999) 41.
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27] C. Brouca-Cabarrecq, J. Dexpert-Ghys, A. Fernandes, J. Jaud, J.C. Trombe, Inorg.
Chim. Acta 361 (2008) 2909.
Acknowledgement
The authors gratefully acknowledge financial support from the
Research Unit of Cukurova University (Grant No. FEF 2010 BAP15).
[28] G. Peng, L. Ma, B. Liu, J. Cai, H. Deng, Inorg. Chem. Commun. 13 (2010) 599.
[
[
[
29] Y. Wang, G. Liu, Y. Chen, K. Wang, S. Meng, Inorg. Chim. Acta 363 (2010) 2668.
30] H. Yue, D. Zhang, Y. Chen, Z. Shi, S. Feng, Inorg. Chem. Commun. 9 (2006) 959.
31] M. Tabatabaee, M.A. Sharif, F. Vakili, S. Saheli, J. Rare Earth 27 (2009) 356.
Appendix A. Supplementary material
[32] G. Cui, J. Li, R. Zhang, X. Bu, J. Mol. Struct. 740 (2005) 187.
[
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33] X. He, M. Bi, K. Ye, Q. Fang, P. Zhang, J. Xu, Y. Wang, Inorg. Chem. Commun. 9
2006) 1165.
34] Y. Li, F. Liang, C. Jiang, X. Li, Z. Chen, Inorg. Chim. Acta 361 (2008) 219.
(
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2013.01.026.
[35] D. Hu, Chen, P.F. Luo, Y. Che, J. Zheng, J. Mol. Struct. 837 (2007) 179.
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