STUDY OF THE THERMAL DECOMPOSITION ON Pt(II) COMPLEXES
includes the decomposition and disconnection of two
nitrate anions, two amine groups and the initial
destruction of the two organic ligands, ending with
the obtainment of Pt and most probably two
hydantoin fragments.
The theoretical mass loss during the
maintenance of these processes should be 43.97%,
while the experimental loss is Dm=45.28%. The
endothermic effect that follows at 366°C (639 K) is
registered as a very broad peak and can be assigned to
the destruction of the hydantoin residue. The final
residue contains only platinum and carbon –24.27%
(
calcd–25.25%).
The second ligand cycloheptanespiro-5’-hyd-
antoin starts to melt at 208°C (481 K) ( Fig. 3). After
this temperature, begins the decomposition of the
substance and an endothermic effect in the TG curve
is observed with a mass loss Dm=79.48%. Next a
multistep destruction with a sufficiently lower speed
takes place. In the DTA curve several weak
endothermic peaks are outlined in the temperature
region 319–585°C (592–858 K). A mixture of several
Fig. 4 TG, DTG and DTA curves of PtCHTH
to a small exothermic effect with two maximums at
272°C (545 K) and 293°C (566 K). The existence of
these two effects is evidence that except the decompo
sition processes of the compound, new compounds are
formed. As in a very small temperature interval a lot of
successive effects are obtained, it is impossible to
separate and identify the different substances at this
gases are detached (CO, CO , N , NH , water vapour).
2 2 3
At the end of the process no solid residue is left.
On Fig. 4 the results from the thermal analyses of
PtCHTH are given. This DTA curve is much more
complicated than that of the ligand discussed above.
This fact is to be expected in connection with
coordination ability of Pt(II). The complex is stable
up to 150°C (423 K), followed by its decomposition
in two steps. The first step, taking place between
–
1
heating rate (5°C min ). If the final residue is Pt then
theoretically Dm=64.87%. From the TG curve a mass
loss of 46.92% is registered. At the final temperature
formation of PtO is not possible as it decomposes at
much lower temperature T=500°C (773 K) [10]. The
registered mass loss Dm=46.92% gives us the reason
to suggest that the final residue consists of platinum
and platinum carbides. In the literature two kinds of
150–240°C (423–513 K), is connected with a change
of the mass Dm=19.70%. The second step is in the
platinum carbides are announced – PtC
Pt C [11, 12], but no X-ray data are available for
their characterization. There are some data about the
existing of PtN [13], but obtained at quite different
conditions, then this taking place with the
decomposition of the complex.
2
and
temperature interval from 240°C (513 K) to 350°C
(
2
3
623 K) and with a mass loss Dm=31.25%.
Of certain interest is the DTA curve in which the
endothermic effect at Tmax=160°C (433 K) proceeds
Conclusions
The TG/DTA curves of the two complexes were
different in character. A three-stage mass loss of
PtCBH on heating was observed, while PtCHTH
decomposed in two stages going through new
compounds. The two complexes investigated were
more stable than the ligands due to the coordination
process. During the decomposition of PtCBH a
polymorphous change was detected. After the thermal
decomposition of PtCBH the solid residue was
platinum, while the decomposition of PtCHTH gave a
mixture of platinum carbides (PtC , Pt C ).
2 2 3
Fig. 3 TG, DTG and DTA curves of CHTP
J. Therm. Anal. Cal., 89, 2007
259
Bakalova
