Kinetics of thermolysis of some transition metal perchlorate complexes with 1,4-diaminobutane ligand

Article abstract of DOI:10.1016/j.tca.2005.06.009

Three metal perchlorate complexes of general formula [M(dab) ₂](ClO₄)₂·xH₂O (where M = Zn, Cu and Ni; dab = 1,4-diaminobutane) have been prepared and characterized by gravimetry, infrared spectroscopy (IR) and elemental analysis. Thermolysis has been studied by thermogravimetry (TG) in air and simultaneous thermogravimetry-differential thermogravimetry-differential thermal analysis (TG-DTG-DTA) and differential scanning calorimetry (DSC) in N₂ atmosphere. Isothermal gravimetry over the temperature range of initial decomposition of the complexes has been done to evaluate the kinetics. Both model fitting and isoconversional methods have been used for the evaluation of the kinetics. Model fitting gives a single value of activation energy (E) whereas the isoconversional method yields a series of E values which vary with extent of conversion. Ignition with varying amounts of the complexes was measured to see the response to rapid heating. The thermal stability order of the complexes is [Zn(dab)₂](ClO₄)₂ ? [Cu(dab)₂](ClO₄)₂.2H₂O ≈ [Ni(dab)₂](ClO₄)₂.

Full text of DOI:10.1016/j.tca.2005.06.009

Thermochimica Acta 437 (2005) 21–25
Kinetics of thermolysis of some transition metal perchlorate
complexes with 1,4-diaminobutane ligandଝ
Gurdip Singha,∗, Chandra Prakash Singha, S.M. Mannanb
a
Chemistry Department, DDU Gorakhpur University, Gorakhpur 273 009, India
b
Department of explosives, Nagpur 440006, India
Received 29 May 2005; received in revised form 4 June 2005; accepted 7 June 2005
Available online 14 July 2005
Abstract
Three metal perchlorate complexes of general formula [M(dab)2](ClO4)2·xH2O (where M = Zn, Cu and Ni; dab = 1,4-diaminobutane) have
been prepared and characterized by gravimetry, infrared spectroscopy (IR) and elemental analysis. Thermolysis has been studied by ther-
mogravimetry (TG) in air and simultaneous thermogravimetry–differential thermogravimetry–differential thermal analysis (TG–DTG–DTA)
and differential scanning calorimetry (DSC) in N2 atmosphere. Isothermal gravimetry over the temperature range of initial decomposition of
the complexes has been done to evaluate the kinetics. Both model fitting and isoconversional methods have been used for the evaluation of the
kinetics. Model fitting gives a single value of activation energy (E) whereas the isoconversional method yields a series of E values which vary
with extent of conversion. Ignition with varying amounts of the complexes was measured to see the response to rapid heating. The thermal
stability order of the complexes is [Zn(dab)2](ClO4)2 ꢀ [Cu(dab)2](ClO4)2.2H2O ≈ [Ni(dab)2](ClO4)2.
© 2005 Elsevier B.V. All rights reserved.
Keywords: 1,4-Diaminobutane; Metal perchlorate complex; Thermolysis; Kinetics; Ignition delay
1. Introduction
hexammine metal perchlorates [6,10], bis(ethylenediamine)
metal nitrates [8,11] and perchlorates [12] and bis(pro-
pylenediamine) metal nitrates [13]. Hexammine metal per-
chlorate complexes were found to be potential burning rate
modifiers for composite solid propellants. We report here
the preparation, characterization, kinetics and mechanism
of thermolysis of bis(1,4-diaminobutane) metal perchlorate
complexes. Simultaneous thermogravimetry–differential
thermogravimetry–differential thermal analysis (TG–DTG–
DTA), DSC, TG, isothermal gravimetry and ignition delay
measurements have been done to investigate the effect of
slow and fast heating of complexes under various conditions.
When 1,4-diaminobutane (dab), a neutral bidentate ligand,
complexes to metal ions having ClO4 as counterion, the
−
resultant complex undergoes self-propagative decomposition
reactions due to presence of both oxidizing (ClO4) and reduc-
ing (dab) groups in the same molecule [1,2]. On the basis
of their sensitivity, amine complexes lie between primary
and secondary explosives [3,4]. These complexes may have
applications in propellants, explosives and pyrotechnics.
Some energetic transition metal complexes [5–8] and salts
of NTO (5-nitro-2,4-dihydro-3H-1,2,4-triazole-3-one) [9]
have proved to be potential ballistic modifiers for composite
solid propellants. In previous studies, we have reported the
thermolysis, kinetics and decomposition mechanism of some
2. Experimental
2.1. Materials
ଝ
Part 48.
∗
Corresponding author. Tel.: +91 551 2200745/2202856;
AR grade commercially available chemicals were used
as received, zinc carbonate (Thomas Baker), copper car-
fax: +91 551 2340459.
E-mail address: gsingh4us@yahoo.com (G. Singh).
0040-6031/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2005.06.009

22
G. Singh et al. / Thermochimica Acta 437 (2005) 21–25
bonate (BDH), nickel carbonate (Thomas Baker), 70% per-
chloric acid and methanol (Ranbaxy), ethanol (Hayman),
1,4-diaminobutane (Merck) and silica gel TLC grade (Quali-
gens).
2.2. Preparation of the complexes
Hexahydrated metal perchlorates were obtained by treat-
ing metal carbonates with 70% perchloric acid, washing
the salts with petroleum ether, recrystallizing from distilled
water and drying over fused calcium chloride. The metal per-
chlorate complexes were prepared by treating an ethanolic
solution of metal perchlorate hexahydrates with an ethanolic
solution of 1,4-diaminibutane in desired [14–18]. The precip-
itated complexes were washed with methanol, recrystallized
and dried over fused calcium chloride.
2.3. Thermal decomposition studies
TG was done at 5 ◦C/min in static air (sample
mass ≈ 30 mg) on indigenously fabricated TG apparatus
[19]. Iso-thermal gravimetry was performed in static air
with the same TG apparatus (mass ≈ 30 mg). Simultane-
ous TG–DTG–DTA curves were recorded on a Pyris Dia-
mond Star system in flowing nitrogen (flow rate 100 mL/min,
sample mass 3–5 mg, heating rate 10 ◦C/min). DSC was
done in inert atmosphere (flowing nitrogen at a rate of
50 mL/min) on a Mettler Toledo Star system (sample
mass 2–4 mg, heating rate 10 ◦C/min). Ignition delay was
recorded with the tube furnace technique [20–23] (mass 20
and 7 mg).
Fig. 1. TG curves of complexes in air atmosphere.
3.2. TG
TG curves obtained in air are shown in Fig. 1. In all the
three complexes, the initial rate of thermolysis is slow but
later thermolysis is fast.
3.3. Simultaneous TG–DTG–DTA in flowing N2
atmosphere
Simultaneous TG–DTG–DTA curves are presented in
Fig. 2 Complexes of Zn and Ni decompose in single step
giving a corresponding DTG peak and exothermic peak
in DTA. The copper complex decomposes in two steps
in the temperature range 60–92 and 153–262 ◦C giving
mass losses of 7.2 and 76%, respectively. TG and DTA
data show the stability of the complexes decreases in
the order [Zn(dab)2](ClO4)2 ꢀ [Cu(dab)2](ClO4)2·2H2O ≈
[Ni(dab)2](ClO4)2.
3. Results
3.1. Characterization
The purity of complexes was checked by thin layer chro-
matography. The mass percent of metal was estimated gravi-
metrically [24]. The mass percent of other elements (C, H
and N) was obtained on an Heraeus Carlo Erba 1108 instru-
ment. The complexes were characterized by their infrared
spectra (impact 400, KBr pellet). Results are reported in
Table 1.
3.4. DSC in flowing N2 atmosphere
DSC curves for all the three complexes are analogous
to their corresponding DTA curves having exothermic peak
Table 1
Physical, elemental and spectral parameters of the complexes
Compound
Color
% observed (calculated)
IR (␯ cm−1
)
C
H
N
M
N
H
N
H
C H C H H2C NH2 Cl O Cl O ClO4 M N
str.
bend str.
bend
[Zn(dab)2](ClO4)2 White
[Cu(dab)2](ClO4)2· Blue
2H2O
22.1 (21.8) 5.3 (5.4) 13.3 (12.7) 14.4 (14.8) 3271 1457 2926 1384 1088
20.7 (20.2) 5.4 (5.9) 12.6 (11.8) 12.9 (13.3) 3243 1466 2950 1442 1084
1117 673
1116 690
629 469
630 480
[Ni(dab)2](ClO4)2
Sky blue 21.8 (22.) 5.8 (5.5) 13.4 (12.9) 13.8 (13.5) 3314 1467 2910 1446 1087
1119 712
628 496

G. Singh et al. / Thermochimica Acta 437 (2005) 21–25
23
Fig. 3. DSC thermograms of complexes in N2 atmosphere.
Fig. 2. Simultaneous TG–DTG–DTA curves of complexes in N2 atmo-
sphere.
model results in nearly the same activation energy (E). The
average E for Zn, Cu and Ni complexes are 176, 43 and
144 kJ/mol, respectively. Application of the isoconversional
method results in a series of E values (Fig. 5), which vary
with extent of conversion (α). The E for Zn is higher than Cu
and Ni complex.
temperature at 336, 245 and 245 ◦C for Zn, Cu and Ni com-
pound, respectively (Fig. 3.). For Cu complex, one additional
endotherm is present at 86 ◦C due to loss of water.
3.5. Isothermal gravimetry
Mass loss was recorded at five temperatures in the decom-
position range for early thermolysis (∼33% weight loss),
Fig. 4.
3.7. Ignition delay measurements
Ignition delay (τ) at various temperatures was recorded
with different amounts (20 and 7 mg) to see the self-heating
effect of sample particles in comparison to the glass igni-
tion tube (Table 2). Zn complex does not ignite in less than
10 min at 350 ◦C, so ignition delay is recorded at 420,435,
450,465 and 480 ◦C. The ignition delay for all the com-
plexes is less for sample mass 7 mg, compared with that of
3.6. Kinetic evaluation of isothermal gravimetry data
The kinetics of the early decomposition of the complexes
(α = 0.33) has been evaluated by model fitting [13,19] as
well as by the model-free isoconversional method [25]. Each

24
G. Singh et al. / Thermochimica Acta 437 (2005) 21–25
Fig. 5. Variation of activation energy with extent of conversion (α).
where E* is the activation energy for thermal ignition, A, the
pre-exponential factor and T is the absolute temperature. E*
was determined from the slope of a plot of ln(τ) versus 1/T,
see Table 2. The activation energy (E*) is not varying much
with the variation of sample mass.
4. Discussion
The analytical data presented in Table 1 agree with the cal-
culated mass percent of each element. Also, the characteristic
absorption frequencies of atoms/groups match the standard
texts[29,30]. ZnandNicomplexesareanhydrouswhereasCu
complex is hydrated. TG curves obtained in static air atmo-
sphere (Fig. 1) show that Zn and Ni complexes decompose
in one step.
A comparison of the TG curves, in air and in nitrogen
shows that in N2 the mass loss is sudden while in air, initial
mass loss (∼20%) is slow. This is because of slow heating
rate (5 ◦C/min) in air and fast heating rate (10 ◦C/min) in N2.
Also, a large sample mass (∼30 mg) was used in air and a
small mass in N2 (4–5) mg. Initial 20% weight loss (in case of
Cu 27%) corresponds to one dab molecule (for Cu 2H2O and
one dab molecule). During data recording, the characteristic
odorofdabwasobserved. Aftertheremovalofthesemoieties,
the residue left is [M(dab)](ClO4)2 which ignites at elevated
temperatures giving a sharp mass loss (60%) and gaseous
products. Finally the metal oxide is left as residue, although
in curve less residue is shown (10%) because some of residue
is thrown outside the crucible. Due to fast heating rate in inert
atmosphere, the mass loss is sudden (∼80%) leaving residue
Fig. 4. Isothermal TG thermograms of complexes in air atmosphere.
20 mg. τ for Cu and Ni complexes is nearly the same which
shows equal thermal stability. Thus, the thermal stability
order is [Zn(dab)2](ClO4)2 ꢀ [Cu(dab)2](ClO4)2·2H2O ≈
[Ni(dab)2](ClO4)2.
The τ was fitted to [26–28]:
E∗
τ = A exp
RT
Table 2
Ignition delay (τ), ignitionn temperature (TE) and activation energy for thermal explosion (E*) of complexes (sample mass 7 mg)
Compounda Mass (mg) τ (s) at various temperatures
E* (kJ/mol)
r
320
340
360
380
400
420
435
450
465
480
104 ± 1 22.5
1
2
3
20
7
–
–
–
–
–
–
–
–
–
–
140
131
1
1
136
127
1
1
126
121
1
1
110
109
1
1
0.9974
0.9789
98 ± 1
22.4
20
7
139
127
1
1
121
110
1
1
105
86
1
1
84
72
1
1
64
55
1
1
–
–
–
–
–
–
–
–
–
–
31.6
34.7
0.9816
0.9920
20
7
150
142
1
1
121
112
1
1
92
81
1
1
74
67
1
1
56
52
1
1
–
–
–
–
–
-
–
–
–
–
40.8
41.9
0.9974
0.9979
a
1: [Zn(dab)2](ClO4)2; 2: [Cu(dab)2](ClO4)2·2H2O; 3: [Ni(dab)2](ClO4)2.

G. Singh et al. / Thermochimica Acta 437 (2005) 21–25
25
of metal oxides (19%). Thus, the mechanism of thermolysis
may be proposed as:
Explosives, Ministry of commerce and Industry, Govt. of
India for providing lab facility at Departmental Testing Sta-
tion Gondkhairy, Nagpur for the studies on TG, DTA and
DSC.
[M(dab)2](ClO4)2xH2O → [M(dab)2](ClO4)2 + xH2O
[M(dab)2](ClO4)2 → [M(dab)](ClO4)2 + dab
[M(dab)](ClO4)2 → MO + gaseous products
The formation of monoligand intermediates has been seen
earlier during thermal studies of bis(ethylenediamine)-
copper chloride/bromide monohydrates [31], bis(ethylene-
diamine)metal nitrate [8,11] complexes.
Comparison of the DTA and DSC exothermic peak tem-
peratures (Table 2) shows the decreasing trend as [Zn(dab)2]
(ClO4)2 ꢀ [Cu(dab)2](ClO4)2·2H2O ≈[Ni(dab)2](ClO4)2
for early thermolysis (α = 0.33).
Analysis of kinetics from isothermal TG data using model
fitting method, values of E obtained from different models for
particular sample are nearly equal irrespective of the equa-
tions used. It is difficult to assign a single value of E to a
particular process taking place in such a complex solid state
decomposition. Model-free isoconversional method shows
that the thermolysis of these complexes is not as simple as
indicated by model fitting method. As can be seen from Fig. 5,
the value of E changes with α but in all the α range, E for Zn
complex is higher than Cu and Ni which indicates the stabil-
ity of Zn complex is higher than Cu and Ni. Except in lower
α range, E for Ni is greater than Cu indicating the greater
stability of Ni over Cu complex.
To examine the effect of rapid heating on the complexes,
ignition delay was measured. A perusal of Table 2 reveals
that, at a particular temperature, τ for Cu and Ni complex are
nearly the same. This shows their similar thermal stability.
Thus, the thermal stability order is same as indicated earlier.
This thermal stability order can be directly correlated with the
cation size. Comparison of τ data for 20 and 7 mg of sample
for all three complexes indicates that it is lower for 7 mg. This
emphasizes that the self-propagative heating effect of sample
particles are less than the contact heating to the ignition tube
wall. Although the τ are different for different sample masses,
activation energies for ignition (E*) are almost the same.
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Acknowledgements
Thanks to Head, Chemistry department of DDU Gorakh-
pur University for lab facility and DRDO, ARMREB, New
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Anbunathan, Chief Controller of Explosives, Department of
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