Thermal and spectroscopic investigation on N,N-dimethylbenzylamine based cyclopalladated compounds containing isonicotinamide

Article abstract of DOI:10.1007/s10973-009-0251-9

Synthesis, spectroscopic characterization and thermal analysis of the [Pd(dmba)(Cl)(iso)] (1), [Pd(dmba)(NCO)(iso)] (2), [Pd(dmba)(N ₃)(iso)] (3) and [Pd(dmba)(Br)(iso)] (4) (dmba = N,N′- dimethylbenzylamine; iso = isonicotinamide) compounds ar

Full text of DOI:10.1007/s10973-009-0251-9

J Therm Anal Calorim (2009) 97:149–152
DOI 10.1007/s10973-009-0251-9
Thermal and spectroscopic investigation
on N,N-dimethylbenzylamine based cyclopalladated
compounds containing isonicotinamide
Alessandra Stevanato Æ Antonio E. Mauro Æ
Adelino V. G. Netto
ICTAC2008 Conference
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract Synthesis, spectroscopic characterization and
thermal analysis of the [Pd(dmba)(Cl)(iso)] (1), [Pd(dmba)
(NCO)(iso)] (2), [Pd(dmba)(N3)(iso)] (3) and [Pd(dmba)
(Br)(iso)] (4) (dmba = N,N0-dimethylbenzylamine; iso =
isonicotinamide) compounds are described in this work.
The complexes were investigated by infrared spectroscopy
(IR), differential thermal analysis (DTA) and thermogravi-
metry (TG) and the residues of the thermal decomposition
were identified as Pdo by X-ray powder diffraction.
The thermal stability order of the complexes varied as
[Pd(dmba)(Cl)(iso)] (1) [ [Pd(dmba)(Br)(iso)] (4) [ [Pd
(dmba)(NCO)(iso)] (2) [ [Pd(dmba)(N3)(iso)] (3).
obtained by the cleavage of orthopalladated dimers of
general formulae [Pd(dmba)(l-X)]2 (X = bridging anionic
group; dmba = N,N-dimethylbenzylamine) by isonicoti-
namide. Following up our interest on the thermal behavior
of palladium(II) compounds [5–8] herein the synthesis,
spectroscopic characterization and thermal investigation of
the [Pd(dmba)(Cl)(iso)] (1), [Pd(dmba)(NCO)(iso)] (2),
[Pd(dmba)(N3)(iso)] (3) and [Pd(dmba)(Br)(iso)] (4) com-
pounds using TG and DTA techniques is reported.
Experimental
Keywords Palladium(II) ꢀ Isonicotinamide ꢀ
Spectroscopy ꢀ Thermal behavior
General comments
All the synthesis have been carried out at room tempera-
ture. All reagents were obtained from commercial suppli-
ers. The starting complexes [Pd(dmba)(l-X)]2 (X = Cl,
NCO, N3, Br) were prepared as described in [9].
Introduction
Vigorous research efforts have been devoted to synthesize
new cyclopalladated compounds mainly due to their
potential uses as technologically relevant materials (e.g.
liquid crystals) [1], catalysts [2], and antitumor drugs [3].
Despite the increased attention on the field of Pd(II) cy-
clometallated species less attention have been paid to their
derivatives containing isonicotinamide, a pyridine deriva-
tive with an amide group (–CONH2) in c-position, which
possesses strong anti-tubercular, anti-pyretic, fibrinolytic
and anti-bacterial properties [4]. It was assumed that
new interesting biologically active compounds could be
Preparation of the complexes [Pd(dmba)X(iso)];
X = Cl (1), NCO (2), N3 (3), Br (4)
Isonicotinamide (40 mg; 0.327 mmol) was dissolved in
5 mL of methanol and then was added to a solution con-
taining 0.27 mmol of the appropriate [Pd(dmba)(l-X)]2
(X = Cl, NCO, N3, Br) precursor dissolved in 15 mL of
methanol/acetone (2:1 vol:vol). The mixtures were stirred
magnetically for 1 h. The obtained white suspensions were
filtered off and the solids were washed thoroughly with
methanol. The synthesized compounds with general for-
mulae [Pd(dmba)(X)(iso)] (X = Cl (1), NCO (2), N3 (3),
Br (4)) were recrystallized from dichloromethane/pentane
(1:1) and then dried in vacuo. The yields varied from 80%
to 90%.
A. Stevanato ꢀ A. E. Mauro (&) ꢀ A. V. G. Netto
´
Instituto de Quımica de Araraquara, UNESP, C.P. 355,
Araraquara, SP 14801-970, Brazil
e-mail: mauro@iq.unesp.br
123

150
A. Stevanato et al.
to that one of the free ligand (993 cm-1) [11]. It is worth
mentioning that characteristic bands of amide group at
3417–3332 cm-1 (mN–H) and 1666–1681 cm-1 (mC=O) in
the IR spectra of 1–4 did not essentially alter when com-
pared to those observed for the free ligand, suggesting that
the amide group does not take part in coordination [12].
Concerning to the pseudohalide ligands, the presence of
terminal N-cyanate group in (2) was evidenced by the
masNCO band at 2212 cm-1 whereas the terminal azide
ligand in (3) was inferred on basis of the masNNN absorp-
tion at 2036 cm-1 [13]. The proposed molecular structures
for cyclopalladated complexes 1–4 are shown in Fig. 1.
Instrumentation
Melting points were determined using a Mettler model
MQAPF-302 microscope. Elemental analyses of carbon,
nitrogen and hydrogen were performed on a microanalyser
elemental analyser CHN, model 2400 PerkinElmer. Infra-
red spectra were recorded in KBr pellets on a Nicolet
model SX-FT-Impact 400 spectrophotometer in the 4000–
400 cm-1 spectral range. Thermal analyses (TG) and dif-
ferential thermal analyses (DTA) were carried out using a
TA Instruments model SDQ 600, under flow of dry syn-
thetic air (50 mL min-1), temperature up to 900 °C and at
heating rate of 20 °C min-1 in a-alumina sample holders.
The reference substance was pure a-alumina in DTA
measurements. X-ray powder diffraction patterns were
measured on a Siemens D-5000 X-ray diffractometer using
Thermogravimetric analysis
The TG and DTA curves for the compounds [Pd(dmba)(-
Cl)(iso)] (1), [Pd(dmba)(NCO)(iso)] (2), [Pd(dmba)(-
N3)(iso)] (3) and [Pd(dmba)(Br)(iso)] (4) are shown in
Fig. 2. Table 2 lists the results of the thermal studies of
these compounds together with the assignments of each
decomposition stage based on mass calculation. Therefore
the groups indicated at the right column of the Table 2 do
not correspond necessarily to the gaseous final products of
decomposition.
˚
CuKa radiation (k = 1.541 A) and setting of 34 kV and
20 mA. The peaks were identified using ICDD bases [10].
Results and discussion
The results of the elemental analyses and the thermo-
gravimetric data together with IR spectroscopy data, con-
firmed the proposed formulae for the compounds 1–4. The
results of the analyses and melting points are shown in
Table 1.
Comparison of X-ray powder diffractograms of the final
products obtained after the pyrolysis of the ligands in the
thermal decomposition of 1 and 4 with ICDD data bases,
showed the characteristic peaks of a mixture of Pd (card 05-
0681) and PdO (card 06-0515) [10]. After this stage, the TG
curves of 1 and 4 exhibited a slight mass increase up to ca.
800 °C due to the oxidation of the remaining Pd0 to PdO,
which was also identified by X-ray powder diffraction.
Finally, the decomposition of PdO to Pd0 is completed at ca.
860 °C. Complexes 2 and 3 degrade into PdO (card
06-0515) [10] which further decomposes into Pd0 at ca.
860 °C. The TG-DTA curves of the compounds [Pd(dmba)
(X)(iso)] showed that the anionic X group has a significant
influence on thermal decomposition. Taking into account
Infrared spectra
The maintenance of the structural integrity of the ortho-
metallatted ring after the interaction with isonicotinamide
was clearly evidenced by comparison of the IR spectra of
1–4 with those ones of the precursors [Pd(dmba)(l-X)]2
(X = Cl, NCO, N3, Br) [9]. The characteristic bands of the
cyclometallated ring at 3049–3197 cm-1 (mCHring), 2923–
2979 cm-1 (masCH3), 2885–2896 cm-1 (msCH3) in IR
spectra of 1–4 were found unchanged when compared to
those observed for the precursors. The coordination of
isonicotinamide through pyridinic-type nitrogen atom was
inferred by the shift of the absorption band attributed to
the ring breathing vibrational mode to higher frequency
(ca. 1053 cm-1) in the IR spectra of 1–4 when compared
CH
H3C
3
X
N
Pd
N
Table 1 Elemental analyses and melting points for compounds 1–4
Complex M.P. (°C) Carbon (%)
Nitrogen (%) Hydrogen (%)
NH2
Calc. Found Calc. Found Calc. Found
1
2
3
4
208–209 49.52 49.24 10.27 10.55 4.28 4.56
190–191 46.77 47.48 12.01 13.84 4.30 4.48
183–185 45.02 44.51 20.49 20.76 4.65 4.48
O
X = Cl (1), NCO (2), N3 (3), Br (4)
Fig. 1 Proposed structure of the compounds [Pd(dmba)X(iso)];
X = Cl (1), NCO (2), N3 (3), Br (4)
213 dec. 40.70 42.64
9.49 9.70 4.10 4.34
123

Thermal and spectroscopic investigation
151
Fig. 2 TG and DTA curves
of the complexes
[Pd(dmba)(X)(iso)] (X = Cl
(1), NCO (2), N3 (3), Br (4))
Table 2 Thermal analysis data for compounds [Pd(dmba)(X)(iso)] (X = Cl (1), NCO (2), N3 (3), Br (4))
Complex
Step
DT (°C)
Dm (%)
DTA Peaks (°C)
Assignment
Found
Calc.
Endo
Exo
1
1
224–240
240–441
441–798
798–864
–
-30.63
-39.69
?2.05
-4.02
27.71
-30.84
-40.50
?2.01
-4.01
26.66
224
–
240
372
–
–iso
2
–dmba, –Cl, ?0.25 O2
? 0.25 O2
3
–
4
834
–
–0.5 O2
Pdo
Residue
2
1
194–329
329–463
801–867
–
-55.35
-13.46
-4.36
26.83
-57.23
-12.60
-3.94
26.23
192
–
207
419
–
–0.5 dmba, –NCO, –iso
–0.5 dmba, ?0.5 O2
–0.5 O2
2
3
811
Residue
Pdo
3
4
1
190–379
780–856
–
-69.34
-3.95
26.71
-69.76
-4.01
26.23
184
824
195, 262–329
–
–dmba, –N3, –iso, ?0.5 O2
2
–0.5 O2
Pdo
Residue
1
216–233
233–357
357–525
525–805
805–863
–
-27.94
-31.15
-14.29
?1.93
-3.87
24.68
-27.75
-33.14
-13.32
?1.80
-3.60
23.99
227
351
–
–
–iso
2
–
–0.5 dmba, –Br
–0.5 dmba, ?0.25 O2
?0.25 O2
–0.5 O2
3
529
–
4
–
5
823
–
Residue
Pd8
the initial temperature of the decomposition process, the
thermal stability of the complexes [Pd(dmba)(X)(iso)]
(X = Cl (1), NCO (2), N3 (3), Br (4)) varies in the sequence
of Cl [ Br [ NCO&N3. The lower thermal stability of 3
and 4 could be probably associated to the higher reactivity
of the polyatomic and unsaturated pseudohalide groups
than the monoatomic halide ions [13]. Such behaviour was
similar to those observed in our previous studies on the
thermal behaviour of other Pd(II) complexes containing
halides and pseudohalides as ligands [5, 6].
The first decomposition step observed in TG curve of 1
is attributed, by mass calculation, to the pyrolysis of iso-
nicotinamide, followed by the elimination of dmba and
Cl ligands together with uptake of O2. TG curves of the
123

152
A. Stevanato et al.
Acknowledgements We thank the CNPq, CAPES, and FAPESP for
financial support.
pseudohalide-based compounds 2 and 3 exhibit a differ-
ent pattern of decomposition. The cyanato-compound 2
degrades in two steps whereas two consecutive and over-
lapped mass losses characterize a single stage of decom-
position of the azido-derivative 3. Complex 4 started to
degrade at slightly lower temperature (216 °C) than 1. The
first stage is assigned, by mass calculation, to the pyrolysis
of isonicotinamide whereas the elimination of Br group
together with the partial degradation of dmba ligand are
probably suggested to take place during the second
decomposition stage. The last step of the degradation is
attributed, by mass calculation, to the gradual elimination
of the remaining dmba fragment as a carbonaceous residue
of varied composition.
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