Synthesis, spectral and thermal studies on dicarboxylate-bridged palladium(II) coordination polymers. Part II

Article abstract of DOI:10.1007/s10973-009-0249-3

The synthesis and thermal behavior of the new [Pd(fum)(bipy)] _n ?2nH₂O (1), [Pd(fum)(bpe)] _n ?nH₂O (2) and [Pd(fum)(pz)] _n ?3nH₂O (3) {bipy = 4,4'-bipyridine, bpe = 1,2-bis(4-pyridyl)ethene

Full text of DOI:10.1007/s10973-009-0249-3

J Therm Anal Calorim (2009) 97:153–156
DOI 10.1007/s10973-009-0249-3
Synthesis, spectral and thermal studies on dicarboxylate-bridged
palladium(II) coordination polymers. Part II
R. L. Fernandes Æ P. M. Takahashi Æ
R. C. G. Frem Æ A. V. G. Netto Æ A. E. Mauro Æ
J. R. Matos
ICTAC2008 Conference
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract The synthesis and thermal behavior of the new
[Pd(fum)(bipy)]nꢀ2nH2O (1), [Pd(fum)(bpe)]nꢀnH2O (2) and
[Pd(fum)(pz)]nꢀ3nH2O (3) {bipy = 4,40-bipyridine, bpe = 1,
2-bis(4-pyridyl)ethene and pz = pyrazine} fumarate com-
plexes are described in this work as well their characterization
by IR and 13C CPMAS NMR spectroscopies. TG curves
showed that the compounds released organic ligands
and lattice water molecules in the temperature range of
46–491 °C. In all the cases, metallic palladium was identified
as the final residue.
In the present study, we describe the synthesis, spectro-
scopic characterization and thermal studies on the polymeric
species [Pd(fum)(bipy)]nꢀ2nH2O (1), [Pd(fum)(bpe)]nꢀnH2O
(2) and [Pd(fum)(pz)]nꢀ3nH2O (3) {fum = fumarate, bipy =
4,40-bipyridine, bpe = 1,2-bis(4-pyridyl)ethane, pz = pyr-
azine} as a part of our ongoing research interest in thermal
behavior of palladium-based compounds [9].
Experimental
Keywords Palladium(II) ꢀ Fumarate ꢀ N-based linear
spacers ꢀ Thermal studies ꢀ Coordination polymers
Preparation of the complexes
Compounds 1–3 were synthesized from the dropwise addi-
tion of a methanolic mixture containing the appropriate
amounts of the N-based ligand (76.8 mmols) and sodium
fumarate (61.6 mg, 38.5 mmol) to a solution of the precursor
[PdCl2(CH3CN)2] (100 mg, 38.5 mmols) in methanol.
Yellow suspensions were obtained, filtered off and the solids
were washed with water, methanol and dried in vacuum.
Introduction
Research on metal-directed supramolecular compounds has
rapidly been expanding duo to their interesting topologies
and potential applications as functional materials [1, 2].
Recently the use of organic spacers, particularly the
dicarboxylic acid, as superexchange pathways between the
metal ions is of growing interest in the field of catalysis [3],
gas sorption and desorption [4–6], opto-electronic devices
[7], and molecular magnetism [8].
Methods
The elemental analysis (carbon, nitrogen and hydrogen)
were performed on a CE Instruments, model EA 1110-
CHNS-O microanalyser.
Infrared spectra were recorded on a Nicolet FTIR-
Impact 400 spectrophotometer in the 4000–400 cm-1
spectral range using KBr pellets.
R. L. Fernandes ꢀ P. M. Takahashi ꢀ R. C. G. Frem (&) ꢀ
A. V. G. Netto ꢀ A. E. Mauro
´
Instituto de Quımica de Araraquara, UNESP, P.O. Box 355,
The 13C CP NMR spectra were obtained on a Varian
Unity INOVA spectrometer operating at 300 MHz for
carbon. Samples were packed in a silicon nitride rotor
(OD = 7 mm). Chemical shift values were referenced
externally to tetramethylsilane at 0 ppm.
Araraquara, SP 14801-970, Brazil
e-mail: rcgfrem@iq.unesp.br
J. R. Matos
Instituto de Quımica-USP-SP, P.O. Box 26077, Sa˜o Paulo, SP,
Brazil
´
123

154
R. L. Fernandes et al.
Table 2 Selected vibrational data (cm-1) of the palladium(II) com-
plexes 1–3
TG experiments were carried out using a Shimadzu
system model TGA-50. The TG curves were recorded in
dry synthetic air flow (100 mL min-1), with temperature
up to 900 °C and at a heating rate of 20 °C min-1 in
platinum sample holders.
vꢀ/cm-1
1
2
3
Assignment
X-ray powder diffraction patterns of the residues were
measured using SIEMENS D-5000 diffractometer equip-
ped with a proportional counter and pulse height discrim-
inator. The Bragg–Bretano arrangement was adopted using
3446s
3090w
1610ms
1416m
815m
–
3425s
3092w
1605ms
1423m
833m
–
3454s
3091w
–
m(OH)
m(CH)ar
m(CC)
1423m
817m
–
m(CN)
˚
CuKa radiation (k = 1.541 A) and setting of 34 kV and
20 mA. The peaks were identified using PDF bases [10].
d(CH)
m(Pd–O)
mas(COO-)
ms(COO-)
d(O–C–O)
1647ms
1382m
–
1643ms
1376m
–
1643ms
1382m
–
Results and discussion
m medium, s strong, ms medium–strong, w weak
The fumarate-bridged palladium polymers 1–3 were char-
acterized through elemental analyses, thermogravimetric
data, IR and 13C CPMAS NMR spectroscopies, leading us
to suggest the formulae illustrated in the Fig. 1 to the
isostructural compounds. The analytical data are presented
in Table 1.
13C CPMAS NMR spectra
Table 3 lists the 13C CPMAS NMR results obtained to 1–3.
The presence of coordinated fumarate in 1 and 2 is inferred
due to the existence of 13C=O signal at 185.72 and
187.83 ppm, respectively [14]. The 13C signals at 153.60
Infrared spectra
0
0
(CA, CA ), 147.37 (Cq), and 124.47 ppm (CB, CB ) agree
well with the presence of 4,40-bipyridine in 1 (see num-
bering scheme in Table 3). For the compound 2, the
The principal IR data of the complexes are presented in
Table 2. The bis-monodentate coordination mode of the
fumarate ligand was evidenced in the IR spectra of 1–3 by
the appearance of its characteristic bands at 1640–
1650 cm-1 (masCOO-) and 1375–1385 cm-1 (msCOO-)
[11]. Infrared vibrational studies also revealed the coordi-
nation of the linear spacers in these compounds by the
presence of the typical mCN absorptions at 1423–
1416 cm-1 and dCH bands at 815–833 cm-1 [12, 13].
Table 3 13C CPMAS NMR data (ppm) for compounds 1 and 2
Numbering scheme
Compound Chemical Assignment
shift/ppm
1
185.72
153.36
147.37
133.54
124.47
C=O
CA
CB
Cq Cq′
CB
CA
0
CA, CA
N
N
0
Cq, Cq
CA′
CB′
CA′
CB′
bipy
–CH=CH–
O
0
CB, CB
C=O
O
O
Pd
O
N
N
O
N
N
O
Pd
O
O
2
187.83
150.93
144.78
132.48
125.53
=
CA
CB
Cq′
CB′
CA
CB
Cq
N
H
C
0
CA, CA
N
N
C
N
H
0
Cq, Cq
CA′
CB′
CA′
bpe
–CH = CH–
[Pd(fum)(L)]n
0
CB, CB
Fig. 1 Proposed structural formulae for the complexes 1–3
Table 1 Results of elemental analysis of the compounds 1–3
Compound
Color
Formula
Carbon/%
Found
Nitrogen/%
Found
Hydrogen/%
Found
Calc.
Calc.
Calc.
[Pd(l-fum)(l-4,40-bipy)]nꢀ2nH2O 1
[Pd(l-fum)(l-bpe)]nꢀnH2O 2
[Pd(l-fum)(l-pz)]nꢀ3nH2O 3
Yellow
Yellow
Yellow
C14H10N2O4Pd
C16H12N2O4Pd
C8H6N2O4Pd
40.2
45.5
27.4
40.6
45.6
27.0
7.0
7.3
7.1
6.8
6.6
7.9
3.6
3.9
3.0
3.6
3.6
3.7
123

Synthesis, spectral and thermal studies
155
Thermogravimetric analysis
The TG curves for 1–3 are illustrated in Fig. 2. Table 4
shows the results of the thermal investigations in dry
synthetic air atmosphere of these compounds together with
the assignments of each decomposition stage based on
mass calculation.
Compound 1 undergoes decomposition to Pd0 by a
gradual elimination started at 46 °C followed by an abrupt
mass loss completed at 462 °C, associated to the elimina-
tion of bipy, fum and H2O molecules and uptake of O2,
yielding a mixture of Pd0 (05-0681) and PdO (ASTM 06-
0515) [10]. The formation of additional PdO is noticed by a
slight progressive mass loss up to 818 °C. The decompo-
sition of PdO to Pd0 is observed in the last mass loss
between 818 and 864 °C.
Compound 2 started to degrade at higher temperature
(70 °C) than 1. Afterwards, a mass change of 70.91% is
caused by the thermal breakdown of the main chain,
leading to a mixture of Pd (ASTM 05-0681) and PdO
(ASTM 06-0515) [10] at 491 °C. A progressive mass gain
of 0.97% up to 819 °C is ascribed to the formation of
additional PdO which further decomposed into Pd (Calcd.
25.92%, Found 26.42%) over the range 819–876 °C.
The coordination polymer 3 started to decompose at
50 °C. A further heating to 450 °C resulted in a mass loss
of 66.55% associated with the degradation of the main
polymeric chain and elimination of H2O molecules,
yielding a mixture of Pd (ASTM 05-0681) and PdO
(ASTM 06-0515) [10] as residue. A slight mass gain of
1.55%, between 450 and 818 °C, is ascribed to the oxida-
tion of Pd0 to PdO. The decomposition of PdO to metallic
palladium is observed in the last mass loss (4.68%)
between 818 and 860 °C (Calcd. 4.52%).
Fig. 2 TG curves for the complexes 1–3
Table 4 Thermal analysis data for compounds 1–3
Complex Step
DT/°C
Dm/%
Assignment
Obt.
Calc.
1
2
3
1
46–462 -72.74 -72.28 -2 H2O; -1 bipy;
-1 fum
2
462–818 ?0.66 ?1.94 ?0.25 O2
818–864 -2.92 -3.87 -0.50 O2
3
Residue
1
25.00
25.79 Pd
70–491 -70.91 -72.81 -1 H2O; -1 bpe;
-1 fum
Conclusions
2
491–819 ?0.97 ?1.91 ?0.25 O2
819–876 -3.64 -3.18 -0.50 O2
3
The novel coordination polymers [Pd(fum)(bipy)]nꢀ2nH2O
(1), [Pd(fum)(bpe)]nꢀnH2O (2) and [Pd(fum)(pz)]nꢀ3nH2O
(3) are described in this work. TG curves showed that the
thermal degradation pattern of 1–3 consists of the elimi-
nation of solvent occlusion (water) during the initial
decomposition step. Further increase temperature resulted
in the degradation of linear bridging ligand and fumarate
group.
Residue
1
26.42
25.92 Pd
50–450 -66.55 -67.69 -3 H2O; -1 pz;
-1 fum
2
450–818 ?1.55 ?2.26 ?0.25 O2
818–860 -4.68 -4.52 -0.50 O2
3
Residue
30.51
30.05 Pd
TG studies also showed that the nature of the N-based
linear spacers does not affect significantly their thermal
stability of the coordination polymers. After the release of
water molecules, the dehydrated form of polymer 1 is
stable up to 205 °C whereas the decomposition of the main
polymeric chain started at about 181 °C and 179 °C for the
dehydrated compounds 2 and 3, respectively.
coordination of 1,2-bis(4-pyridyl)ethane (bpe) is evidenced
0
by the aromatic signals at 150.93 (CA, CA ), 144.78 (Cq),
0
and 125.53 ppm (CB, CB ) as well the resonance of
–CH=CH– moiety at 132.48 ppm [15]. The 13C CPMAS
NMR spectrum of 3 could not be registered due to its lower
yield synthesis.
123

156
R. L. Fernandes et al.
Acknowledgements The authors acknowledge CNPq, FAPESP and
CAPES for financial support.
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