A THERMAL DECOMPOSITION STUDY ON NICKEL(II) COMPLEXES OF 1,2-(DIIMINO-4’-ANTIPYRINYL) ETHANE
the removal of the remaining half of GA and one bro-
mide ion. The decomposition gets completed at
6
29°C and the final reside is qualitatively proved to
be anhydrous metal oxide.
The iodide complex, [Ni(GA)]I
two stage decomposition process in the range
68–599°C. The first stage begins at 168 and ends at
34°C. The observed mass loss (45.01%) is due to the
, undergoes a
2
1
4
decomposition of half of the molecule of GA and one
iodide ion. The infrared spectrum of the residue after
this stage shows the presence of GA indicating only
partial removal of the ligand at this stage. The second
stage starts at 434 and comes to an end at 599°C and
the corresponding mass loss (45.70%) is due to the
decomposition of the remaining half of GA and one
iodide ion. The rate of mass loss is found to be maxi-
mum at 276 and 537°C respectively for the first and
second stages of decompositions as indicated by the
DTG peaks. The decomposition gets completed at
Fig. 4 TG and DTG curves of [Ni(GA)]Br
2
5
99°C and the final residue is qualitatively proved to
be anhydrous metal oxide.
The TG results show that all the nickel(II) com-
plexes of GA follow a two stage decomposition pat-
tern. Even though the anions are not involved in coor-
dination in these complexes, they exhibit a wide
range in stability. Among the series the iodide com-
plex is the least stable and the nitrate complex is the
most stable. The difference in thermal stability of the
complexes indicates that even though the anions are
not involved in coordination they may have some
marked influence on the thermal stability of the
complexes and it is found in the order:
nitrate>bromide>chloride>iodide
Fig. 5 TG and DTG curves of [Ni(GA)]I
2
4
56 and comes to an end at 768°C, and the corre-
Kinetic aspects
sponding mass loss (38.38%) is due to the decomposi-
tion of the remaining half of the ligand molecule. The
rate of mass loss is found to be maximum at 289 and
All the well characterized decomposition stages were
selected for the study of the kinetics of decomposi-
tion. The kinetic parameters like the activation energy
6
75°C respectively for the first and second stages of
(
E) and the pre-exponential factor (A) were calculated
Table 2) using Coats–Redfern equation [10].
decomposition as indicated by the DTG peaks. The fi-
nal residue is anhydrous metal chloride as confirmed
by qualitative analysis.
(
log⎡g(α)⎤
AR ⎡ 2RT ⎤ –
1–
E
= log
The bromide complex, [Ni(GA)]Br , undergoes
2
⎢
2
⎥
⎢
⎥
T
⎦
ϕE ⎣
E ⎦ 2.303RT
⎣
a two stage decomposition pattern and there is no
mass loss up to 221°C revealing the absence of either
water or solvent molecules in this complex. The first
stage of decomposition starts at 221 and ends at
where, T – temperature, A – pre-exponential factor,
R – gas constant, f – heating rate and E – activation
energy.
2
4
71°C with the DTG peak at 313°C. The observed
In3 the present investigation log[g(a )/T ] plotted
mass loss (44.63%) is due to the decomposition of
half of the ligand molecule and one bromide ion. The
infrared spectrum of the residue after this stage shows
the presence of GA indicating only a partial removal
of the ligand at this stage. The second stage begins at
vs. 10 /T gives straight lines whose slope and inter-
cept are used to evaluate the kinetic parameters by the
least squares method. The goodness of fit is checked
by calculating the correlation coefficient.
The entropy of activation (DS) is also calculated
for each stage of thermal decomposition in these com-
plexes using the relationship,
4
71 and ends at 629°C with the DTG peak at 564°C.
The corresponding mass loss (44.28%) is attributed to
J. Therm. Anal. Cal., 84, 2006
609
Madhu
