Synthesis and thermal behavior study of complexes of the type [Pd(μ-X)(4-eb-p-phen)]2(X = Cl, Br, I, N3, NCO, SCN) and 4-eb-p-phen [bis(4-ethylbenzyl)p-phenylenediimine]

Article abstract of DOI:10.1007/s10973-014-4015-9

The Schiff base bis(4-ethylbenzyl) p-phenylenediimine, 4-eb-p-phen (1), and six new dimeric Pd(II) complexes of the type [Pd(μ-X)(4-eb-p-phen)]₂{X = Cl (2), Br (3), I (4), N₃(5), NCO (6), SCN (7)} have been synthesized and characterized by elemental analysis, IR spectroscopy, and ¹H and ¹³C{¹H}-NMR experiments. The thermal behavior of the complexes 2-7 has been investigated by means of thermogravimetry and differential thermal analysis. From the final decomposition temperatures, the thermal stability of the complexes can be ordered in the following sequence: 3 > 4 > 7 > 2 ≈ 5 > 6. The final products of the thermal decompositions were characterized as metallic palladium by X-ray powder diffraction (XRD).

Full text of DOI:10.1007/s10973-014-4015-9

J Therm Anal Calorim (2014) 118:67–74
DOI 10.1007/s10973-014-4015-9
Synthesis and thermal behavior study of complexes of the type
[Pd(l-X)(4-eb-p-phen)]2 (X 5 Cl, Br, I, N3, NCO, SCN) and 4-eb-
p-phen [bis(4-ethylbenzyl)p-phenylenediimine]
•
Gabriela Francini Bozza Luis Eduardo Sarto
•
•
•
Claudia Torres Adelino Vieira de Godoy Netto
Eduardo Tonon de Almeida
Received: 14 January 2014 / Accepted: 4 July 2014 / Published online: 24 August 2014
´
´
Ó Akademiai Kiado, Budapest, Hungary 2014
Abstract The Schiff base bis(4-ethylbenzyl) p-phenyl-
enediimine, 4-eb-p-phen (1), and six new dimeric Pd(II)
complexes of the type [Pd(l-X)(4-eb-p-phen)]2 {X = Cl (2),
Br (3), I (4), N3 (5), NCO (6), SCN (7)} have been syn-
thesized and characterized by elemental analysis, IR
spectroscopy, and 1H and 13C{1H}-NMR experiments. The
thermal behavior of the complexes 2–7 has been investi-
gated by means of thermogravimetry and differential
thermal analysis. From the final decomposition tempera-
tures, the thermal stability of the complexes can be ordered
in the following sequence: 3 [ 4 [ 7 [ 2 & 5 [ 6. The
final products of the thermal decompositions were char-
acterized as metallic palladium by X-ray powder diffrac-
tion (XRD).
Cyclometalated complexes of palladium(II) have often
been considered to be interesting organometallic molecules
because they show properties that may have useful appli-
cations in several domains of Chemistry, Physics, or
Biology. Studies have demonstrated that palladium deriv-
atives exhibit a noticeable cytotoxic activity, similar to
standard platinum-based drugs used as a reference, and
show fewer side effects relative to other heavy metal
anticancer compounds [2].
Palladium(II) compounds show ligand-exchange kinetics
105 times greater than the platinum(II) analogs, which may
facilitate the hydrolysis of the leaving groups that dissociate
readily in solution, before the complex reaches the phar-
macological target. To overcome their high lability, chelat-
ing ligands have been used to afford high thermodynamically
stable and kinetically inert Pd(II) complexes [3].
Keywords Cyclopalladated Á Iminic ligands Á IR and
NMR spectroscopy Á TG–DTA
In particular, palladacycles result in an interesting bio-
logical activity because of their possible capacity to inhibit
the replication of DNA by single or simultaneous interac-
tions, such as insertion and/or coordination with DNA
structure by its metallic center [4].
Introduction
Cyclometalated compounds have been the subject of many
studies over the last decades because of their numerous
applications in organic synthesis and catalysis of metallo-
mesogens in liquid crystals, synthesis of supramolecules,
and as biologically active compounds [1].
Schiff bases are compounds characterized by the pre-
sence of at least one imine functional group. These com-
pounds are obtained by the condensation of primary amines
and aldehydes or ketones. These bases play an important
role in coordination chemistry because the C=N group is
suitable for many coordinated reactions. Also the bidentate
imines are an important class of chelating ligands [5–7].
As a part of our research program in this area, we report
in the present study the synthesis, characterization, and
thermal behavior of the compounds 4-eb-p-phen (1), [Pd(l-
Cl)(4-eb-p-phen)]2 (2), [Pd(l-Br)(4-eb-p-phen)]2 (3),
[Pd(l-I)(4-eb-p-phen)]2 (4), [Pd(l-(N3))(4-eb-p-phen)]2
(5), [Pd(l-(NCO)(4-eb-p-phen)]2 (6), and [Pd(l-(SCN))(4-
eb-p-phen)]2 (7).
G. F. Bozza Á L. E. Sarto Á C. Torres Á E. T. de Almeida (&)
´
UNIFAL - MG - Univ Federal de Alfenas, Instituto de Quımica,
CEP, Alfenas, MG 37130-000, Brazil
e-mail: tonon@unifal-mg.edu.br
A. V. de Godoy Netto
UNESP - Univ Estadual Paulista, Instituto de Quımica, CEP,
Araraquara, SP 14801-970, Brazil
´
123

68
G. F. Bozza et al.
Experimental
washed with distilled water and ethyl ether, and vacuum
dried, obtaining a yield of 91 %.
All syntheses were carried out at room temperature. All
reagents were obtained from commercial suppliers and
used without further purification.
Compounds 3–7 were readily obtained by metatheti-
cal reactions of [Pd(l-Cl)(4-eb-p-phen)]2 (2) (0.35 g;
0.364 mmol) with 0.728 mmol of the appropriate salts
(KBr, KI, NaN3, KNCO, and KSCN, respectively) in
50 mL of acetone under constant stirring for 2 h. The
resulting suspensions were filtered off, and the obtained
solids were washed with distilled water and ethyl ether, and
vacuum dried. The yields of the compounds are as follows:
85 % (3), 81 % (4), 77 % (5), 83 % (6), and 68 % (7). The
proposed structure for the complexes 3–7 is shown in
Fig. 2.
Preparation of Schiff base (1)
To a solution of p-phenylenediamine (2.77 mmol) in eth-
anol (100 mL),
a solution of 4-ethyl-benzaldehyde
(5.54 mmol) in ethanol (5 mL) was added slowly for 3 h.
The yellow solid formed was filtered off and dried in
vacuum, obtaining a reaction yield of 97 %. The proposed
structure for the ligand is shown in Fig. 1.
Instrumentation
Preparation of the complexes 2–7
Elemental analysis of carbon, hydrogen, and nitrogen was
performed on Elemental Analyzer, Leco Instruments
LTD—TruSpec model CHNS-O. The absorption spectra in
the infrared region were recorded on spectrophotometer,
Thermo Scientific—IS-Nicolet FT-IR 50, in the
4000–400 cm-1 spectral range. The spectra of nuclear
magnetic resonance of 1H and 13C were recorded on Bruker
AC-200 spectrometer working at 300 MHz for 1H and
75 MHz for 13C{1H}, using CDCl3 for (1) and (2) or
DMSO-d6 for 3–7 for dissolution of samples. The melting
or decomposition points were obtained using the MARTE
(PFM II) equipment. Simultaneously, thermal analyses
(TG–DTA) were carried out using a thermobalance, TA
Instruments—SDT Q600, under flow of dry synthetic air
(100 mL min-1), temperature up to 1,100 °C, and heating
rate of 20 °C min-1, in a-alumina sample holders, using
sample masses of about 10 mg. The reference was pure a-
alumina in DTA measurements. The patterns of powder
X-ray diffraction were obtained by Rigaku Ultima IX
For the synthesis of the compound [Pd(l-Cl)(4-eb-p-
phen)]2 (2), the following methodology has been
employed: Firstly, 1.00 g (5.65 mmol) of palladium chlo-
ride was partially solubilized in 100.00 mL of methanol at
50 °C. To this solution, 0.50 g (11.77 mmol) of lithium
chloride was added. After that the mixture was left under
stirring at 50 °C until the solution turned reddish brown.
The mixture was cooled and filtered off. Then, 1.92 g
(5.76 mmol) of the ligand 4-eb-p-phen was added, fol-
lowed by the slow addition of 0.82 mL (5.82 mmol) of
triethylamine in 8.00 mL of methanol. Lastly, the mixture
was stirred for 8 h, forming an orange solid. The yellow
suspension was filtered off, and the obtained solid was
N
H3C
N
CH3
˚
equipment using KaCu wavelength (k = 1.5418 A) setting
of 34 kV and 20 mA.
Fig. 1 Proposed structure for the ligand 4-eb-p-phen
CH3
Fig. 2 Proposed structure for
the compounds [Pd(l-X)(4-eb-
p-phen)]2 (X = Cl (2); Br (3);
I (4); N3 (5), NCO (6), SCN (7)
CH3
N
PD
N
X
X
N
PD
N
CH3
CH3
123

Synthesis and thermal behavior study
69
Table 1 Results of the elemental analyses and melting or decomposition point of the compounds 1–7
Compound
m.p./°C
Carbon/%
Calc.
Nitrogen/%
Calc.
Hydrogen/%
Calc.
Obt.
Obt.
8.66
Obt.
1
2
3
4
5
6
7
153
86.67
59.89
54.82
50.33
59.08
61.54
59.58
83.98
59.18
53.67
49.19
58.98
59.98
58.38
8.23
5.82
5.33
4.89
14.35
8.61
8.34
6.66
4.82
4.41
4.05
4.75
4.75
4.60
7.11
5.07
4.17
3.98
4.97
4.23
4.91
271 (dec.)
315 (dec.)
260 (dec.)
198 (dec.)
210 (dec.)
170 (dec.)
6.11
5.86
5.16
13.87
8.47
9.38
Results and discussion
(5)
[Pd(μ–N3)(4–eb–p–phen)]2
100
80
The results of elemental analysis supported the proposal for
the compounds 1–7 (Table 1).
60
40
Spectroscopy
20
[Pd(μ–C1)(4–eb–p–phen)]2 (2)
100
The IR absorption spectrum of the ligand 4-eb-p-phen (1),
in Fig. 3, presented an intense band at 1623 cm-1 assigned
to the stretching mode of the characteristic imine C=N
bond, confirming its formation [8]. Compared with the
spectrum of the starting primary amine, the disappearance
of the bands corresponding to the characteristic asymmetric
(*3300 cm-1) and symmetric (*3200 cm-1) stretching
NH bond is observed. Moreover, when compared with the
spectrum of the precursor aldehyde, there is a disappear-
ance of the intense stretching band characteristic of the
C=O bond of the aromatic aldehyde (*1700 cm-1). These
spectral data indicated the formation of a new compound
from the starting materials.
80
60
40
20
4–eb–p–phen (1)
100
80
60
40
20
4000 3500 3000 2500 2000 1500 1000
Wavenumber/cm–1
500
For the regiospecific substitutions, the replacement of
the chloro ligand in (2) by Br (3) and I (4) was not observed
in the spectrum in the analyzed IR region, in Fig. 3. For the
pseudohalides, the IR spectrum of the azido complex
[Pd(l-(N3))(4-eb-p-phen)]2 (5) exhibited a characteristic
masN3 band at 2062 cm-1, consistent with end-on azido
groups [9]. The pseudohalides NCO and SCN are also
versatile ligands that can bind as monodentate ligands or
bridging groups. The IR spectrum of the compound [Pd(l-
(NCO)(4-eb-p-phen)]2 (6) showed an intense band at
2175 cm-1 assigned to the asymmetric stretching vibra-
tional mode of NCO group, indicating that the NCO is
coordinated in an end-on fashion [8]. With regard to the IR
spectrum of complex [Pd(l-(SCN))(4-eb-p-phen)]2 (7), the
presence of an absorption band was noticed between the
2146 and 2114 cm-1 region which may suggest the end-to-
end coordination mode of the SCN group [10].
Fig. 3 IR spectra for compounds 1–7
a quadruplet at 2.72 ppm (H3C–CH2–), a singlet at
8.48 ppm (–HC=N–), and the typical multiplets associated
with the symmetrical aromatic rings between 7.25 and
8.50 ppm. The 13C NMR spectrum of (1) showed the major
signals in 15.39 ppm (H3C–CH2–), 28.98 ppm (H3C-CH2-),
159.65 ppm (–HC=N–), and between 121 and 150 ppm
(symmetrical aromatic rings).
The formulation of (2) and (4) as [Pd(l-X)(4-eb-p-
phen)]2 due to the appearance of two signals at ca. 9.94 and
*8.48 ppm in 1:1 ratio indicates the presence of distinct
–HC=N– groups in their molecular structures. The signal at
8.48 ppm remains unchanged at the same position in both
1H NMR spectra of the 4-eb-p-phen ligand and complexes
(2) and (4). This fact strongly supports that one imino
group does not participate in coordination. On the other
hand, the downfield shift of the –HC=N– proton from
Analyzing the 1H NMR spectrum of the Schiff base (1),
in Fig. 4, a triplet was observed at 1.28 ppm (H3C–CH2–),
123

70
G. F. Bozza et al.
[Pd(μ–I)(4–eb–p–phen)]2 (4)
[Pd(μ–I)(4–eb–p–phen)]2 (4)
[Pd(μ–C1)(4–eb–p–phen)]2
(2)
[Pd(μ–C1)(4–eb–p–phen)]2
(2)
(1)
4–eb–p–phen
(1)
4–eb–p–phen
10
8
6
4
2
0
200
150
100
δ /ppm
50
0
δ /ppm
Fig. 4 1H NMR spectra for compounds (1) and (2) in CDCl3 and (4)
in DMSO-d6
Fig. 5 13C{1H} NMR spectra for compounds (1) and (2) in CDCl3
and (4) in DMSO-d6
8.48 ppm (free ligand) to ca. 9.94 ppm strongly supports
the coordination to the Pd atom through the iminic nitro-
gen. This deshielding is attributed to the removal of the
electron density from the ligand to the palladium center via
r-charge donation from the imine-like N-donor atom. The
existence of different distinct –HC=N– groups was also
evidenced by 13C{1H} NMR spectra; in Fig. 5 the 13C
signal at *160 ppm is associated with the non-coordinated
imine group, whereas the low field resonance at
192.05 ppm (2)/193.17 ppm (4) is related to the coordi-
nated –HC=N– groups. The presence of a complicated
series of multiplets in the aromatic region of both 1H NMR
spectra has hindered their assignment. NMR spectra of
compounds (3), (5), (6), and (7) could not be recorded due
to their low solubility in common deuterated solvents.
TG and DTA curves of the organic compound 4-eb-p-
phen are shown in Fig. 6. TG curve shows that the com-
pound is thermally stable up to 260 °C. Then three steps of
mass loss are observed: the first one occurs over the tem-
perature range of 260–468 °C, followed by two consecu-
tive steps up to 716 °C. These events are also indicated in
the DTA curve through exothermic peaks at 450 and
665 °C with shoulder at 590 °C. Furthermore, the DTA
curve also shows an endothermic peak at 160 °C before
decomposition, corresponding to the melting of the com-
pound, which was confirmed by melting point analysis. The
residual mass obtained was 0.41 %, indicating complete
decomposition.
TG and DTA curves of the compound [Pd(l-Cl)(4-eb-p-
phen)]2 (2) are shown in Fig. 7. TG curve shows that the
compound is thermally stable up to 110 °C. The mass-loss
steps occurring in the range of 110–553 °C can be assigned
to the removal of ligands 4-eb-p-phen and Cl, in addition to
0.66 O2 uptake, corresponding to a mass loss of 73.95 %
(calc. 75.69 %). Exothermic peaks appear at 249 and
508 °C, and an endothermic at 321 °C, in the DTA curve,
corresponding to these successive decomposition steps.
Between 553 and 793 °C, a mass gain of 1.06 % was
observed, which can be attributed to oxidation of the
remainder of Pd0 to PdO with 0.34 O2 uptake. The decom-
position of PdO to Pd0 is observed between 793 and 821 °C
with a mass loss of 3.13 % (calc. 3.32 %), corroborated by an
endothermic peak in the DTA curve at 809 °C. The residual
mass obtained was 23.18 % (calc. 22.11 %).
Thermal analysis
The ranges of temperature (°C), mass loss (%), and the
DTA peak for each of the steps proposed for the decom-
position of compounds 2–7, and assignment related to mass
loss are presented in Table 2. These assignments (Dm -
Calc.) are based on the structural fragments from the the-
oretical formulae of the compounds 2–7, Fig. 2. This
implies that the groups proposed in the right column of
Table 2 are not necessarily the gaseous decomposition
products generated. The final residues were analyzed
by X-ray powder diffraction (XRD), and peaks were
identified on the basis of ICDD to Pd0 (05-0681) and PdO
(06-0515) [11].
123

Synthesis and thermal behavior study
71
Table 2 Thermal analysis data of compounds [Pd(l-X)(4-eb-p-phen)]2 {X = Cl (2), Br (3), I (4), N3 (5), NCO (6), SCN (7)}
Compounds
Step
DT/°C
Dm/%
Peaks DTA/°C
Assignment
Obt.
Calc.
Endo
Exo
2
1
110–553
553–796
793–821
-73.96
?1.06
-3.13
23.18
-75.69
?1.12
-3.32
22.11
321
–
249/508
-2Cl-. -2(4-eb-p-phen). ?0.66O2
2
–
–
?0.34O2
3
809
-O2
Pd0
Residue
3
4
5
1
130–693
797–834
-76.87
-2.42
20.79
-76.71
-3.04
20.24
386
818
263/636
–
-2Br-. -2(4-eb-p-phen). ?O2
2
-O2
Pd0
Residue
1
114–666
666–792
792–825
-80.46
?1.22
-2.01
18.61
-81.2
?1.8
–
251/636
-2I-.-2(4-eb-p-phen). ?0.39O2
2
–
–
–
?0.61O2
3
-2.79
18.58
807
-O2
Pd0
Residue
1
118–551
796–831
-74.91
-3.08
21.82
-74.9
-3.28
21.81
–
164/508
–
-2N3-. -2(4-eb-p-phen). ?O2
2
826
-O2
Pd0
Residue
6
7
1
115–535
598–794
794–814
-74.68
?1.71
-3.21
22.14
-76.55
?1.75
-3.28
21.81
–
271/471
-2(NCO)-. -2(4-eb-p-phen). ?0.47O2
2
–
–
–
?0.53O2
3
816
-O2
Pd0
Residue
1
116–598
598–794
794–819
-75.31
?1.33
-3.13
21.3
-77.06
?1.35
-3.17
21.12
–
271/541
-2(SCN)-. -2(4-eb-p-phen). ?0.57O2
2
–
–
–
?0.43O2
-O2
Pd0
3
809
Residue
30
12
10
8
TG
DTA
Exo
100
80
100
80
60
40
20
TG
DTA
Exo
25
20
15
10
5
6
60
40
20
4
2
0
0
0
0
0
200
400
600
800
1000
200
400
600
800
1000
Temperture/°C
Temperture/°C
Fig. 7 TG and DTA curves of the complex [Pd(l-Cl)(4-eb-p-phen)]2
Fig. 6 TG and DTA curves of the ligand 4-eb-p-phen
and 636 °C, and endothermic, at 386 °C, peaks. This mass
loss is related to the elimination of Br ligands and 4-eb-p-
phen. Simultaneously with the end of the elimination of the
ligands, there is an O2 uptake resulting in the oxidation of
Pd0 to PdO. The decomposition of PdO to Pd0, between
797 and 834 °C, resulting in a decrease of 2.42 % of mass
Figure 8 presents the TG and DTA curves of the com-
plex [Pd(l-Br)(4-eb-p-phen)]2 (3). This compound is
thermally stable up to 130 °C. Between 130 and 693 °C,
successive stages of decomposition can be observed in the
TG curve, resulting in a mass loss of 76.87 % (calc.
77.23 %), and the DTA curve presented exothermic, at 263
123

72
G. F. Bozza et al.
30
25
TG
TG
20
15
10
5
100
80
100
80
DTA
DTA
Exo
Exo
20
15
10
60
60
40
20
40
20
5
0
0
0
200
400
600
800
1000
0
200
400
600
800 1000 1200
Temperture/°C
Temperture/°C
Fig. 11 TG and DTA curves of the complex [Pd(l-(NCO))(4-eb-p-
phen)]2
Fig. 8 TG and DTA curves of the complex [Pd(l-Br)(4-eb-p-phen)]2
30
16
100
TG
DTA
Exo
TG
100
25
20
15
DTA
Exo
14
12
10
80
60
80
60
40
8
6
10
40
20
4
5
0
2
0
20
0
200
400
600
800
1000
0
200
400
600
800
1000
Temperture/°C
Temperture/°C
Fig. 12 TG and DTA curves of the complex [Pd(l-(SCN))(4-eb-p-
phen)]2
Fig. 9 TG and DTA curves of the complex [Pd(l-I)(4-eb-p-phen)]2
35
(calc. 3.94 %) is in agreement with the endothermic peak at
818 °C in the DTA curve. The residual mass of Pd0
obtained was 20.79 % (calc. 20.24 %).
TG
DTA
100
30
Exo
25
80
TG and DTA of the compound [Pd(l-I)(4-eb-p-phen)]2
(4) resulted in the curves presented in Fig. 9. This com-
pound is considered to be thermally stable at temperatures
up to 114 °C. Consecutive mass-loss steps can be observed
between 115 and 666 °C, resulting in 80.46 % of mass loss
(calc. 81.20 %). These steps are in agreement with DTA
curve which presented two exothermic peaks at 251 and
636 °C, assigned to the removal of iodides and 4-eb-p-phen
ligand, in addition to 0.39 O2 uptake, between 666 and
792 °C; a mass gain of 1.22 % occurs due to the oxidation
of the remainder of Pd0 to PdO with 0.61 O2. The
decomposition of PdO to Pd0 between 792 and 825 °C,
with a mass loss of 3.08 % (calc. 3.28 %), is corroborated
20
15
10
5
60
40
20
0
–5
0
200
400
600
800
1000
Temperture/°C
Fig. 10 TG and DTA curves of the complex [Pd(l-(N3))(4-eb-p-
phen)]2
123

Synthesis and thermal behavior study
73
100
90
Fig. 13 Thermogravimetric
curves for the thermal
decomposition of compounds
2–7, highlighting the final
temperatures of step 1
2
3
4
5
35
25
80
70
60
6
7
2
3
15
500
50
40
550
600
650
700
Temperture/°C
4
5
6
7
30
20
10
50
150
250 350 450
550 650 750
850 950 1050
Temperture/°C
by an endothermic peak in the DTA curve at 807 °C. The
residual mass obtained was 18.61 % (calc. 18.58 %).
Figure 10 shows TG and DTA curves of [Pd(l-N3)(4-
eb-p-phen)]2 complex (5). Being thermally stable up to
118 °C, the compound exhibits successive decomposition
steps up to 551 °C to form PdO. These steps result in a
mass loss of 74.91 % (calc. 74.90 %), equivalent to the
elimination of N3 ions, the 4-eb-p-phen ligands, and reac-
tion with O2. In this temperature range, by DTA curve, the
existence of exothermic peaks at 164 and 508 °C has been
observed. The reduction of PdO to Pd occurs between 796
and 831 °C, and is confirmed by an endothermic peak at
826 °C and a mass loss of 3.08 % (calc. 3.28 %). The mass
residue of Pd0 obtained was 21.72 % (calc. 21.81 %). It is
important to note that the thermal behavior of (5) is similar
to that observed for other Pd(II) compounds containing
coordinated azide, which exhibit inherent tendency of
highly exothermic decomposition, yielding Pd and/or PdO
and gaseous products, such as N2. In some cases, these
compounds are potential explosives [12–14].
Figure 12 shows TG and DTA curves of the [Pd(l-
(SCN))(4-eb-p-phen)]2 compound (7). This complex starts
its thermal decomposition at 116 °C and subsequently
consecutive mass loss steps, up to 598 °C, can be observed
in the TG curve, with a 75.31 % (calc. 77.06 %) mass loss,
which are in agreement with the exothermic peaks, at 271
and 541 °C, presented in the DTA curve. This mass loss is
equivalent to the elimination of SCN and 4-eb-p-phen
ligands, and to the 0.57 O2 uptake. The next step extends to
785 °C and is characterized by a slight increase of 1.33 %
mass, as well as the compounds (2), (4), and (6). This effect
occurs by oxidation of the remaining Pd0 to PdO. The last
step is due to the reducing of PdO to Pd0, with a 3.13 %
mass loss (calc. 3.17 %) and final residue of 21.30 % (calc.
21.12 %). This last step is corroborated by an endothermic
peak in the DTA curve at 807 °C.
On analyzing the TG and DTA curves of all synthesized
complexes, it is possible to note that there are no significant
differences in various steps. Overall, the TG curves pre-
sented characteristic thermal behavior of palladium coor-
dination compounds [15]. The oxidation of Pd0 to PdO and
subsequent decomposition events, most visible in the TG
curves of compounds (2), (4), (6), and (7), are also char-
acteristic of these types of compounds [16, 17].
TG and DTA curves of the compound [Pd(l-(NCO))(4-
eb-p-phen)]2 (6) are illustrated in Fig. 11. This complex
presents thermal stability at temperatures up to 115 °C;
above this temperature, it undergoes several stages of mass
loss up to 535 °C, resulting in a total mass loss of 74.68 %
(calc. 76.55 %). This mass loss is equivalent to the elimi-
nation of two NCO pseudohalides and two 4-eb-p-phen
ligands, in addition to 0.47 O2 uptake. In this temperature
range, DTA curve shows two exothermic peaks at 271 and
471 °C. In the second step (535–795 °C), a mass gain of
1.71 % occurs due to the oxidation of the remaining Pd0 to
PdO with 0.53 O2. The final step, between 795 and 831 °C,
corresponds to the reduction of PdO to Pd0, characterized
by a mass loss of 3.21 % (calc. 3.28 %) and to the exis-
tence of an endothermic peak at 816 °C. The final mass
after total decomposition was 22.14 % (calc. 21.81 %).
The substitution of Cl ions by other halides (Br and I)
and pseudohalides (N3, NCO and SCN) has not signifi-
cantly altered the initial decomposition temperatures of the
compounds. On the other hand, an interesting trend can be
observed from the inspection of final decomposition tem-
peratures (Table 2):
3
(693 °C) [ 4 (666 °C) [ 7
(598 °C) [ 2 (553 °C) & 5(551 °C) [ 6 (535 °C)
Compounds 3 (693 °C), 4 (666 °C), and 7 (598 °C)
showed higher final temperatures, when compared with the
others, in Fig. 13. This can be explained by the fact that the
ions Br, I, and SCN have higher affinity with Pd(II),
according to the theory of acidity and basicity of Pearson
123

74
G. F. Bozza et al.
6. Prasad KS, Kumar LS, Chandan S, Kumar RMN, Revanasidd-
appa HD. Palladium(II) complexes as biologically potent metal-
lo-drugs: synthesis, spectral characterization, DNA interaction
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organometallic, and bioinorganic chemistry. 6th ed. Hoboken:
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[18], resulting in a greater bond stability, thereby increas-
ing the final temperature of the decomposition step.
The residual mass of Pd0 has also changed with the
substitution of the chloride in the compounds, in the fol-
lowing order: 2 [ 5 & 6 [ 7 [ 3 [ 4. This order is
explained because the palladium content of the compounds
is inversely proportional to the mass of the substituent ions.
9. Moro AC, Mauro AE, Ananias SR. Clivagem dos ciclopala-
´
´ ´ ´
etilbenzilamina; X = Cl, N3, NCO) por tioureia. Eclet Quım.
Conclusions
dados dimericos [Pd(dmba)(l-X)]2 (dmba = N, N-dim-
The thermal behavior of the complexes of general formula
[Pd(l-X)(4-eb-p-phen)]2 was described satisfactorily. From
the final decomposition temperatures, the thermal stability of
the complexes can be ordered in the following sequence:
3 > 4 > 7 > 2 & 5 > 6. The difference in the temperatures
in some stages of decomposition and mainly the residual
masses of Pd0 evidences that the substitution reactions
occurred. The combination of TG and DTA with other
techniques such as FT-IR, NMR, and CHN elemental ana-
lysis, enabled the characterization of the compounds formed.
2004;29:57–61.
10. Lucca Neto VA. Mauro AE, Caires ACF, Ananias SR, de
Almeida ET. Synthesis, characterization and thermal behavior of
cyclopalladated compounds of the type [Pd{C6H4CH2 N(CH3)
2}(l-X)]2 (X = Cl, NCO, SCN, CN). Polyhedron. 1999;18:
413–7.
11. Powder Diffraction File of the Joint Committee on Powder Dif-
fraction Standards. Sets 1-32, published by the International
Center of Diffraction Data Swarthmore, PA 19081, USA, 1982.
12. Netto AVG, Takahashi PM, Frem RCG, Mauro AE, Zorel HE Jr.
Thermal decomposition of palladium(II) pyrazolyl complexes.
Part I. J Anal Appl Pyrolysis. 2004;72:183–9.
13. Netto AVG, Santana AM, Mauro AE, Frem RCG, de Almeida
ET, Crespi, Zorel HE Jr. Thermal decomposition of palladium(II)
pyrazolyl complexes, part II. J Therm Anal Calorim. 2005;79:
339–42.
Acknowledgements We thank CAPES, CNPq, FINEP, and FAP-
EMIG for financial support and scholarship: Bozza GF (CAPES),
Sarto LE (FAPEMIG).
14. De Almeida ET, Santana AM, Netto AVG, Torres C, Mauro AE.
Thermal study of cyclopalladated complexes of the type [Pd2(-
dmba)2X2(bpe)] - (X = NO3, Cl, N3, NCO, NCS; bpe = trans-
1,2-bis(4-pyridyl)ethylene). J Therm Anal Calorim. 2005;82:
361–4.
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