Thermal and spectroscopic investigation of new binuclear Pt(II) complexes with carboxylic acids

Article abstract of DOI:10.1007/s10973-008-9069-0

The thermal decomposition of the binuclear Pt(II) complexes with acetate, propionate, valerate and izovalerate ligands were studied by TG and DTA techniques. The Pt(II) complex with acetic acid (PtAA) was stable up to 343.15 K, Pt(II) complex with propion

Full text of DOI:10.1007/s10973-008-9069-0

Journal of Thermal Analysis and Calorimetry, Vol. 96 (2009) 2, 593–597
THERMAL AND SPECTROSCOPIC INVESTIGATION OF NEW
BINUCLEAR Pt(II) COMPLEXES WITH CARBOXYLIC ACIDS
*
Adriana Bakalova
Department of Chemistry, Faculty of Pharmacy, Medical University – Sofia, 2 Dunav Str., 1000 Sofia, Bulgaria
The thermal decomposition of the binuclear Pt(II) complexes with acetate, propionate, valerate and izovalerate ligands were studied
by TG and DTA techniques. The Pt(II) complex with acetic acid (PtAA) was stable up to 343.15 K, Pt(II) complex with propionic
acid (PtPrA) was stable up to 323.15 K, Pt(II) complex with valeric acid (PtVA) was stable up to T=313.15 K and Pt(II) complex
with isovaleric acid (PtIvA) was stable up to 408.15 K. The PtAA complex was investigated again after a year by thermogravimetric
analysis. After the thermal decomposition of the Pt(II) complexes with carboxylic acids, only in the PtVA complex and PtAA com-
plex (investigated after a year) the final residue contains only platinum, while in the rest complexes the solid residue was a mixture
of platinum and platinum carbides (PtC2, Pt2C3).
Keywords: carboxylic acids, Pt(II) complexes, thermal analysis
Introduction
they could be considered as biologically active. On
the basis of the IC50 values obtained it could be drawn
out, that the Pt(II) complex with acetate ligands
proved to be the most potent cytotoxic agent with rel-
ative potency equal or even exceeding that of the ref-
erent drug cisplatin. The increase of the alkyl chain in
the organic ligands is invariably related to a
pronounced loss of efficacy.
Cisplatin is one of most widely used anticancer drugs,
effective against several solid tumors such as ovarian,
lung, head and neck and bladder cancers [1–3]. De-
spite the high antitumor activity its clinical applica-
tion is limited from severe side effects such as
nephrotoxicity, cumulative neurotoxicity, ototoxicity
and extreme emetogenic potential [2–4]. In recent
years, there has been an intense interest in synthesiz-
ing new Pt(II) complexes with an aim to reduce the
toxicity and/or to achieve a broader antitumor spec-
trum [5, 6].
In this paper I present the thermal and spectro-
scopic behavior of the binuclear Pt(II) complexes
with acetate (PtAA) (1), propionate (PtPrA) (2),
valerate (PtVA) (3) and isovalerate lig-
ands (PtIvA) (4).
Such class of platinum complexes are the com-
pounds containing two, three or four platinum centres
with both cis and/or trans configurations. A represen-
tative trinuclear complex BBR3464 has entered a
phase II clinical trial and exhibits activity against pan-
creatic, lung and melanoma cancers [6].
Experimental
The synthesis and the physicochemical methods for
the characterization of the new Pt(II) complexes with
acetate, propionate, valerate and isovalerate ligands
were described in our previous works [7–11]. On the
basis of the obtained results, the following most prob-
able schematic formulae of the Pt(II) complexes with
some carboxylate ligands were proposed (Fig. 1).
TG and DTA studies were carried out in an air
atmosphere and the heating rate was fixed at
5°C min–1 on a Q 1500 C Derivatograph (MOM, Hun-
gary) with a simultaneous DTA-TG module. The tem-
perature range employed was 293.15–1173.15 K.
The mass of the samples used in this study was
80–345 mg. a-Al2O3 was used as a reference material.
In our previous works [7–11], we reported the
synthesis and characterization by physico-chemical
methods of new Pt(II) complexes with acetic,
propionic, valeric and isovaleric acids. The new Pt(II)
complexes were studied pharmacologically and it was
found that they exert concentration-dependent
cytotoxic effect in a panel of human tumour cell lines.
The experimental data retrieved from the cytotoxicity
screening program show that all of the novel
binuclear platinum complexes, despite of the differ-
ences in respect to relative potency, exert
antineoplastic activity and since they cause more than
50% inhibition of the malignant cell proliferation,
*
adrigebk@abv.bg
1388–6150/$20.00
© 2008 Akadémiai Kiadó, Budapest
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands

BAKALOVA
Fig. 2 TG, DTG and DTA curves of PtAA
Fig. 1 Scematic structures of the investigated Pt(II) complexes
PtAA, PtPrA, PtVA and PtIvA
This exothermic effect is due to the passing of
the complex from one polymorphous form to another.
In the TG curve in the range 403.15–423.15 K the
mass loss is registered Dm=7.00%, but the theoretical
mass loss is Dm=7.61%, which may correspond to the
disconnection of two molecules of crystal water and
one molecule NH3 according to the scheme:
The X-ray data are obtained on DRON VM-1
powder diffractometer using CuKa radiation
(l=1.5418 ).
The IR spectra were recorded on IFS 113 v
Bruker FTIR spectrophotometer in the range of
4000–400 cm–1 in KBr tablets.
cis-[Pt2(NH3)2(CH3COO)4]·2H2O®
cis-[Pt2(NH3)(CH3COO)4]+2H2O+NH3
Results and discussion
The next endothermic effect in the range
453.15–478.15 K with maximum at T=468.15 K in-
cludes further break down of the complex and discon-
nection of further molecule NH3 and four molecules
CO2.
Thermogravimetric analysis is a very valuable
method used for studying the thermal decomposition
of solid substances, such as complex compounds
[12–14]. The curves obtained depict the decrease in
sample mass with linear increase in the treatment tem-
perature.
cis-[Pt2(NH3)(CH3COO)4]®
NH3(g)+4CO2(g)+solid residue
In the present investigation, the heating rate was
fixed at 5°C min–1. Depending on the total mass loss
within the framework of 593.15–1103.15 K, the sam-
ple mass was monitored in the range 80–345 mg dur-
ing the experimental runs.
The experimental mass loss during the mainte-
nance of these processes in the range
453.15–478.15 K is Dm=27.50%, while the theoreti-
cal mass loss should be Dm=27.73%. The second
stage of the decomposition of the binuclear complex
is in the temperature interval 483.15–593.15 K and
the mass loss Dm=55.60%.
A stepped thermal decomposition of the coordi-
nation compounds occurred in the range
293.15–1173.15 K. The results of the thermal analy-
sis revealed two distinct steps of mass loss.
Of certain interest is the DTA curve in which af-
ter endothermic effect in the range 453.15–478.15 K
two successive high exothermic effects in the range
503.15–588.15 K with maximums at 523.15 and
573.15 K were observed. The existence of these two
effects is evidence, that except the decomposition
process of the compound, new compounds were
formed. Pt and platinum carbides were most probably
obtained as final residue.
Pt(II) complex with acetic acid –
bis(acetato)diammine-bis-m-acetato diplatinum(II)
dihydrate –
cis-[Pt2(NH3)2(CH3COO)2(m-CH3COO)2]·2H2O (1)
The PtAA complex is stable up to 343.15 K. Its
two-stage decomposition begins after this tempera-
ture (Fig. 2). The first stage is in the temperature in-
terval 343.15–483.15 K. An initial exothermic effect
can be observed in the DTA curve, which overlaps
with an endothermic effect in the range
403.15–423.15 K with a maximum at T=413.15 K.
As in a very small temperature interval a lot of
successive effects were obtained, it was impossible to
separate and identify the different substances at this
heating rate 5°C min–1. If the final residue was plati-
num then theoretically Dm=43.97%. From the TG
594
J. Therm. Anal. Cal., 96, 2009

NEW BINUCLEAR Pt(II) COMPLEXES WITH CARBOXYLIC ACIDS
curve the registered mass loss of Dm=55.60%, gives
us the reason to suggest that the final residue consists
of platinum and platinum carbides [15, 16].
Certain differences were observed at comparing
the IR spectra of the PtAA complex when the sub-
stance was not heated (at room temperature) and then
the same complex was heated at T=413.15 K and
cooled to room temperature. At room temperature in
the IR spectra of the PtAA complex two intensive
as
s
bands, characteristics for g
and 1398 cm–1, one quite intensive band at 894 cm–1,
and g
at 1569
(COO–
)
(COO–
)
characteristic for rNH and one weakly intensive wide
3
band in the range 1300–1021 cm–1 were observed,
as
where most probably d(NH ) and d(NH ) bands were
s
3
3
Fig. 3 TG, DTG and DTA curves of PtAA after a year
overlapped. In the IR spectra of the heating complex
at T=413.15 K, the band at 1569 cm–1 was smaller in-
tensive, which was probably due to the changes of the
DTA curve at this temperature. Endothermic effect
was observed. The shoulder in the range
1300–1021 cm–1 disappeared, which was connected
with the elimination of one molecule ammonia. Only
one weakly intensive band at 875 cm–1, characteristic
for rNH and one intensive band at 1375 cm–1, charac-
connection of two molecules ammonia, one molecule
CO2 and probably one molecule CO.
The second stage of the decomposition is
described with the horizontal part in the TG curve. In
the DTA curve in this part one small exothermic effect
in the range 490.15–593.15 K is observed which is
overlapped with the endothermic effect with maximum
at T=511.15 K. In this temperature interval the
experimental mass loss in the TG curve is Dm=33.05%,
which can be explained with the release of the two
molecules CO2. Especially interestingly is the DTA
curve in which after endothermic affect with maximum
at T=511.15 K one strong exothermic effect with
maximum at T=568.15 K is observed. The availability
of this exothermic effect is evidence, that along with
the decomposition process of the platinum complex,
new compounds have been formed. Platinum is the
most probable final residue. This fact is well corre-
sponding to the mass loss Dm=43.18% of the obtained
solid residue. If the final residue is platinum then
theoretically Dm=43.97%. This gives us the reason to
suggest that the final residue consists only platinum.
These changes in final products of the complex
investigated immediately and one year later probably
were obliged to variation of the composition.
3
s
teristic for g
were remained. The results confirm
)
(COO–
the assumption that the endothermic effect at
T=413.15 K was connected with the elimination of
the molecule ammonia and the change of the structure
of the initial complex. In the IR spectra of the heating
complex at T=573.15 K only one middle intensive
band at 1400 cm–1 and one weakly intensive band at
875 cm–1 were remained. This may be explained with
the fact, that the probable new compound with the
structure PtC2 was formed.
The same PtAA complex was investigated again
after a year by thermogravimetric analysis. At com-
paring the DTA curve with those made immediately it
is evident that the curve followed the analogous
movement.
The complex is stable up to T=313.15 K (Fig. 3).
After this temperature, begins the decomposition in
two stages. The first stage is in the temperature inter-
val 313.15–490.15 K and the second stage is –
490.15–593.15 K. At the first stage in the DTA curve
two consecutive small endothermic effects in the
range 398.15–481.15 K with the maximums at
T=416.15 and 469.15 K were observed. In the TG
curve in the range 398.15–445.15 K the mass loss is
registered Dm=5.68%, but the theoretical mass loss
Dm=5.17%, which may be corresponded to the dis-
connection of two molecules of crystal water. The
second endothermic effect in the range
456.15–481.15 K is connecting with the decomposi-
tion of the platinum complex. The experimental mass
loss at the TG curve is Dm=19.6% but the theoretical
mass loss Dm=20.4%, which corresponds to the dis-
Pt(II) complex with propionic acid – potassium
dichlorido propionato ammine-bis-m-propionato
diplatinate (II) –
K[Pt2(NH3)(C2H5COO)Cl2(m-C2H5COO)2] (2)
The PtPrA complex is stable up to T=323.15 K. After
this temperature in the DTA curve one pronounced en-
dothermic effect in the temperature interval
453.15–483.15 K with maximum at T=473.15 K can be
observed which overlaps into exothermic effect because
the process gives by burning in air (Fig. 4). At this tem-
perature the experimental mass loss of Dm=29.00%,
which is due to the decomposition of the platinum com-
plex. In this range one molecule NH3, three molecules
J. Therm. Anal. Cal., 96, 2009
595

BAKALOVA
Fig. 4 TG, DTG and DTA curves of PtPrA
Fig. 5 TG, DTG and TDA curves of PtVA
carbon dioxide and one molecule chlorine are probably
eliminated according to the scheme:
in the range 613.15–833.15 K is observed. All these
exothermic effects are connected with the decrease in
mass. The existence of exothermic effects is evidence,
that except the decomposition process of the compound,
new compounds are formed.
cis-K[Pt2(NH3)Cl2(C2H5COO)3]®
NH3(g)+3CO2(g)+Cl2(g)+solid residue
The theoretical mass loss is Dm=29.88%. After this
endothermic effect two salient exothermic effects with
maximums at T=503.15 and 573.15 K were observed.
The availability of these two exothermic effects is
due to the fact that except the decomposition process of
the platinum complex, new compounds are formed. This
fact is well corresponding to the mass loss Dm=44.04%
of the obtained solid residue. If the final residue is plati-
num then theoretically Dm=52.99%. This gives us the
reason to suggest that the final residue contains platinum
and platinum carbides.
If the final residue is platinum then theoretically
Dm=51.33%. From the TG curve the registered mass
loss of Dm=50.80%, gives us the reason to suggest
that the final residue consists of platinum [15, 16].
Pt(II) complex with isovaleric acid – potassium
chlorido-bis(isopentanoato)ammine-bis-m-isopenta-
noato diplatinate(II) –
K[Pt2(NH3)(C4H9COO)2Cl(m-C4H9COO)2] (4)
The PtIvA complex is stable up to T=408.15 K. Its
two-stage decomposition begins after this tempera-
ture (Fig. 6). The first stage (in the temperature inter-
val T=408.15–578.15 K is connected with mass loss
of Dm=49.28%. The second stage is in the tempera-
ture interval T=408.15–743.15 K and the mass loss
Dm=69.57%.
Pt(II) complex with valeric acid – potassium
chlorido-bis(pentanoato)ammine-bis-m-pentanoato
diplatinate(II) –
K[Pt2(NH3)(C4H9COO)2Cl(m-C4H9COO)2] (3)
The PtVA complex is stable up to T=313.15 K. Its
two-stage decomposition begins after this temperature
with pronounced endothermic effect in the range
373.15–413.15 K with a maximum at T=393.15 K
(Fig. 5). In the TG curve in this range the experimental
mass loss is Dm=9.80%, but the theoretical mass loss is
Dm=9.50%, which corresponds to the disconnection of
two molecules CO2. The next endothermic effect in
DTA curve is in the range 433.15–453.15 K with maxi-
mum at T=443.15 K, which is connected with the exper-
imental mass loss Dm=28.87%, at the theoretical mass
loss Dm=28.12%. This endothermic effect is most prob-
ably due to the disconnection of four molecules CO2,
one molecule NH3 and two molecules CO.
In the range 393.15–453.15 K two successive
exothermic effects with maximums at T=416.15 and
443.15 K. The second exothermic effect is connected
with the mass loss of Dm=4.35%. A broad endother-
mic effect is observed in the DTA curve in the range
478.15–513.15 K where the mass loss of Dm=24.64%
Of certain interest is the DTA curve after this tem-
perature T=443.15 K. It is observed a high exothermic
effect overlapping into second exothermic effect in the
range 533.15–573.15 K with maximum at 568.15 K. Af-
ter this temperature third rather wide exothermic effect
Fig. 6 TG, DTG and DTA and T curves of PtIvA
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NEW BINUCLEAR Pt(II) COMPLEXES WITH CARBOXYLIC ACIDS
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The TG/DTA curves of the four binuclear Pt(II) com-
plexes were different in character. There was a
two-stage mass loss on heating. The complex PtAA
was stable up to 343.15 K, the complex PtPrA was
stable up to 323.15 K, the PtVA was stable up to
T=313.15 K and the PtIvA was stable up to 408.15 K.
After the thermal decomposition of the Pt(II) com-
plexes with carboxylic acids, only in the PtVA com-
plex and PtAA complex (investigated after a year) the
final residue consisted only platinum, while in the rest
complexes the solid residue was a mixture of plati-
num and platinum carbides (PtC2, Pt2C3).
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Received: February 20, 2008
Accepted: May 29, 2008
Online First: September 19, 2008
DOI: 10.1007/s10973-008-9069-0
J. Therm. Anal. Cal., 96, 2009
597