Thermal studies of cobalt(II), nickel(II) and copper(II) complexes of 4-(sulfonylazido phenylazo) pyrazolones

Article abstract of DOI:10.1023/A:1010148706396

The thermal decompositions of cobalt(II), nickel(II) and copper(II) complexes of 4-(3′-sulfonylazido-6′-methoxyphenylazo)-1-phenyl-3-methyl- 2-pyrazolin-5-one H(D¹-SO₂N₃) and 4-(4′-sulfonylazido phenylazo)-3-phenyl-3-methy

Full text of DOI:10.1023/A:1010148706396

Journal of Thermal Analysis and Calorimetry, Vol. 63 (2001) 173–180
THERMAL STUDIES OF COBALT(II), NICKEL(II)
AND COPPER(II) COMPLEXES OF
4-(SULFONYLAZIDO PHENYLAZO) PYRAZOLONES
S. S. Kandil, F. I. Abdel-Hay and R. M. Issa
Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt
(
Received December 22, 1999; in revised form May 22, 2000)
Abstract
The thermal decompositions of cobalt(II), nickel(II) and copper(II) complexes of 4-(3’-sulfonyl-
1
azido-6’-methoxyphenylazo)-1-phenyl-3-methyl-2-pyrazolin-5-one H(D –SO
2
N
3
) and 4-(4’-sulfo-
2
2 3
nylazido phenylazo)-3-phenyl-3-methyl-2-pyrazolin-5-one H(D –SO N ) were studied by thermo-
gravimetry. The decomposition in all cases takes place along two stages. The first stage is due to the
elimination of water and nitrogen molecules with the formation of tetracoordinate complexes con-
2 2
taining nitrene reactive species [M(DSO N:) ]. The second stage represents the decomposition of the
material to the metal oxide. The kinetics of the decomposition were examined by using Coats–Red-
fern, the decomposition in all complexes was found to be first order for the first and second stages.
*
*
*
The activation energies and other activation parameters (∆H and ∆S and ∆G ) were computed and
related to the bonding and stereochemistry of the complexes.
Keywords: azopyrazolones, decomposition, kinetics, metal complexes, TG-DTG
Introduction
Azopyrazolones have attracted attention of many investigators because of their po-
tential uses in different areas of chemistry such as in medicinal chemistry as anti-
microbial and therapeutic agents [1, 2], in analytical chemistry as complexing agents
for the determination of some metal ions spectrophotometrically [3, 4], and in indus-
trial chemistry as dyestuffs [1, 5–7]. Metal complexes of these compounds have
shown improved dyeing properties [8, 9] and are anticipated to show increased bio-
logical activity in comparison to the unmetallized forms [10, 11].
In continuation to a recent publication [12] on the magnetic and spectral proper-
ties of Co(II), Ni(II) and Cu(II) complexes of sulphonylazido arylazopyrazolones
1
2
H(D –SO N ) and H(D –SO N ), the present investigation aims to study the thermal
2
3
2
3
decomposition of these complexes in order to throw more light on the influence of the
structural properties of such ligands on the decomposition mechanism as well as on
the values of the activation parameters.
1
418–2874/2001/ $ 5.00
2001 Akadémiai Kiadó, Budapest
Akadémiai Kiadó, Budapest
©
Kluwer Academic Publishers, Dordrecht

1
74
KANDIL et al.: AZOPYRAZOLONES
1
H(D –SO
2
2
N
3
)
2 3
H(D –SO N )
Scheme 1
Experimental
All reagents used for the preparation of the complexes were of analytical grade. The
free ligands and their cobalt(II), nickel(II) and copper(II) complexes were prepared
according to the published procedure [12, 13]. Thermoanalytical curves of the com-
–
1
plexes were recorded by using a Shimadzu DT-50 at a heating rate of 10°C min , us-
ing 3–6 mg of powdered samples in a nitrogen atmosphere.
Methods of calculations
*
The orders n and the activation energies E of the different stages of the thermal de-
composition reactions have been evaluated from TG curves by using Coats–Redfern
method [14]. The equation is used in the form:
1
−n
*

1−(1−α )

AR  2RT 
=log 1− −
E
log

2

*
*
T (1−n)
aE 
E
 2.303RT


where α is the fraction of the material decomposed at a given temperature T/K, A is
the frequency factor, R is the gas constant, a is the rate of heating 10°C min and E is
–
1
*
the activation energy of the reaction.
1
–n
2
Plots of log{[1–(1–α) ]/[T (1–n)]} vs. 1/T for different values of n have been
2
tested, except for n=1, where log{[–ln(1–α)]/T } vs. 1/T has been tested. The correct
value of n for the thermal reaction is the one which gives the best straight line, assum-
*
*
ing that the term logAR/(aE )(1–2RT/E ) would be constant within the temperature
range, over which the thermal reaction occurs. From the slope of the straight line the
*
activation energy E could be calculated, where the slope= –E /(2.303R). The change
*
*
*
in the activation enthalpy ∆H is calculated from the relation ∆H=E –RT and the
*
change in the activation entropy from ∆S =R{ln[Ah/(KT)–1]}, where K is
Boltzmann’s constant and h is Planck’s constant; the transmission coefficient is as-
*
sumed to be equal unity [15–17]. The change in the free energy of activation ∆G is
*
*
*
calculated from the relation ∆G =∆H –T∆S .
J. Therm. Anal. Cal., 63, 2001

KANDIL et al.: AZOPYRAZOLONES
175
Results and discussion
1
The complexes [M(D –SO N ) (H O) ] where n=0, 1 and 2 for M=Co(II), Cu(II) and
2
3
2
2
n
2
Ni(II), respectively, and [M(D –SO N ) (H O) ] were precipitated from the reaction
2
3
2
2
2
media as brown microcrystalline solids. Based on the elemental analyses, molar con-
ductances, magnetic susceptibilities, infrared and electronic spectral measurements
[
12], the structures of these complexes were proposed as follows:
1
Co(D –SO
2
[M(D –SO
[
2
N
3
)
2
]
2 3 2 2
N )(H O) ] M=Co(II), Ni(II) and Cu(II)
Scheme 2
The thermal behaviour of the complexes can be summarized as follows: Figure 1
1
shows the tracing of the TG curve obtained for [Co(D –SO N ) ] under conditions of
2
3 2
–
N flow and a heating rate of 10°C min . It could be seen that, under these conditions,
1
2
two major thermal processes exist. The first of them, lying in the region 175–240°C,
has a mass loss of 6.5% corresponding to the loss of 2N moles per mole of
2
1
Co(D –SO N ) ] (mass of mole=883) which is consistent with the reported decom-
[
position of azo sulphonylazido compounds into nitrene species (D–SO N:) and N
2
3 2
2
2
1
Fig. 1 TG and DTG curves of [Co(D –SO
2
N
3
)
2
]
J. Therm. Anal. Cal., 63, 2001

1
76
KANDIL et al.: AZOPYRAZOLONES
gas above 130°C in air [13]. The onset of decomposition of such sulphonylazido
group at 175°C and not somewhat above 130°C is due to the fact that the process was
performed under N flow, rather than in air. This suppresses the decomposition of
2
(
D–SO N ) into (D–SO N:) species and N gas. The second thermal process is in the
2 3 2 2
region 280–590°C and corresponds to the formation of CoO as revealed by the mass
percentage of the end product. The thermal decomposition stages can be represented
as follows:
1
Co(D –SO
240°C
1
[
2
N
3
)
2
]   [Co(D –SO N:) ]+2N
2 2 2
1
585°C
[
Co(D –SO N:) ]   decomposition products+CoO
2
2
1
The TG curves for the aqua complexes [Ni(D –SO N )(H O) ] and
2
3
2
2
1
[
Cu(D –SO N )(H O)] (Figs 2 and 3) also show two distinct thermal stages. The first
2 3 2
of them has a mass loss corresponding to the elimination of 2H O+2N and 1H O+N
2
2
2
2
moles per one mole of the complex, respectively. The second stage of the thermal de-
1
Fig. 2 TG and DTG curves of [Ni(D –SO
2
N
3
)
2
(H
2
O)
2
]
1
Fig. 3 TG and DTG curves of [Cu(D –SO
2
N
3
)
2
(H
2
O)]
J. Therm. Anal. Cal., 63, 2001

–
Table 1 Temperatures of decomposition and activation parameters (kJ mol ) of decomposition for the complexes
1
*
T
s
/°C (DTG peak)
stage
E
stage
First stage
Second stage
Complex
*
*
*
*
*
*
(
1)
(2)
(1)
76.55
95.69
108.45
57.41
88.32
68.89
(2)
∆S
∆H
∆G
∆S
∆H
∆G
1
Co(D –SO
[
[
[
[
[
[
2
N
3
)
2
]
220
217
222
212
205
211
486
448
438
439
445
395
89.51
94.49
90.91
–0.14
–0.16
–0.14
–0.11
–0.13
–0.11
72.45
91.62
104.34
53.38
84.35
64.87
141.47
170.02
173.64
106.73
146.49
118.11
–0.21
–0.20
–0.20
–0.20
–0.19
–0.19
83.21
88.50
85.00
99.34
101.20
93.97
242.60
232.49
227.20
241.74
237.62
220.89
1
Ni(D –SO
2
N
3
)
2
(H
2
O)
2
]
1
Cu(D –SO
2
N
3
3
)
)
2
(H
(H
2
2
O)]
O)
2
Co(D –SO
2
N
2
2
]
105.26
107.17
99.52
2
Ni(D –SO
2
N
3
)
2
(H
2
O)
2
]
2
Cu(D –SO
2
N
3
)
2
(H
2
O)
2
]

1
78
KANDIL et al.: AZOPYRAZOLONES
composition for all complexes gives MO as final product. The following equations
1
for [Ni(D –SO N ) (H O) ], as a representative example, illustrate the two stages of
the thermal decompositions of these aqua complexes:
2
3
2
2
2
1
225°C
1
[
Ni(D –SO N ) (H O) ]   [Ni(D –SO N:) ]+2H O+2N
2
3 2
2
2
2
2
2
2
1
575°C
[
Ni(D –SO N:) ]   decomposition products+NiO
2
2
It was found that the first and second stages of the thermal decompositions for
all complexes obey the equations of first-order decomposition reactions, on applying
*
*
*
Coats–Redfern method as shown in Fig. 4. The activation parameters E , ∆H , ∆S
*
and ∆G for the decomposition steps of the complexes are given in Table 1. The nega-
*
tive value of ∆S means that the activated complex is more ordered than that of the re-
*
*
actants and that the reactions are slow [18]. The values of ∆H and ∆G of the com-
plexes refer to the effect of changing the structure of the ligand and the metal ion on
the thermal stability of the complexes.
1
Fig. 4 Coats–Redfern plots for thermal decompositions of H(D –SO
a – first stage; b – second stage
2
N
3
) complexes;
*
For cobalt(II) complexes, the difference between ∆G values is quite obvious
1
1
*
–1
2
*
(
1
for [Co(D –SO N ) ]; ∆G =141.47 kJ mol and for [Co(D –SO N ) (H O) ]; ∆G =
06.73 kJ mol ). This variation in ∆G for the two complexes may be due to the dif-
2
3
2
1
–1 *
2
3
2
2
2
1
1
ferences in the nature of their organic ligands and the stereochemical arrangements.
They influence the bonding between water molecules and metal cations. Since volati-
J. Therm. Anal. Cal., 63, 2001

KANDIL et al.: AZOPYRAZOLONES
179
lisation of water molecules precedes the decomposition of sulphonylazido group as
revealed by DTA curves of the aqua complexes [12]. It is apparent that volatilisation
of these water molecules would destruct the crystal packing of the aqua complex [19],
*
thereby assists the decomposition of SO N as shown by lowering of its ∆G value.
For copper(II) complexes, the same arguments can be given for the difference be-
2
3
1
*
1
*
–1
tween ∆G1 for [Cu(D –SO N ) (H O)]; ∆G =173.64 kJ mol
and for
2
3
2
2
1
2
*
–1
[
Cu(D –SO N ) (H O) ]; ∆G =118.11 kJ mol . In nickel(II) complexes, the differ-
2
3
2
2
2
1
*
1
*
–1
ence between ∆G values for [Ni(D –SO N ) (H O) ]; ∆G =170.02 kJ mol and for
Ni(D –SO N ) (H O) ]; ∆G =146.94 kJ mol is pronounced, though it is smaller
1
2
3
2
–1
2
2
1
2
*
[
2
3
2
2
2
1
*
than in the cases of copper(II) and cobalt(II) complexes. Since the ∆H values are
reasonably similar as consequences of each having the same kinds and number of do-
1
*
nors, the difference in ∆G for the two complexes should be attributed to the differ-
1
*
*
ence in the ∆S values or more strictlyT∆S . The former complex which has o-OCH
substituent needs more energy to be ordered in structure than that needed for the latter
1
1
3
one which has no o-substituents, in the activated state with respect to the reactants
and/or the reaction of o-CH substituted complex is relatively slow. The close values
3
*
of ∆G of the complexes of the two ligands with the same cation e.g. for
2
1
*
–1
2
*
[
2
Co(D –SO N ) ]; ∆G =242.60 kJ mol and for [Co(D –SO N ) (H O) ]; ∆G =
41.74 kJ mol suggest that the tetracoordinate complexes [M(D–SO N:) ] produced
2 2
2
3
–1
2
2
2
3
2
2
2
2
from the first stage would have the same electronic and geometric structures so that
thermal activation in this stage involves mostly similar groups. On the other hand, the
*
difference in ∆G from one cation to the other for the same ligand is not pronounced.
This suggests that the effect of the ligand is more than the cation on the second stage
decomposition of the complexes.
2
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