Thermal and kinetic study of nickel trifluoromethanesulphonate, trifluoroacetate and acetate

Article abstract of DOI:10.1007/s10973-007-8633-3

The reason of comparing thermal behaviour and kinetics of some nickel compounds, is justified by the influence of anion on it, besides supplying information on the stability of the salts. In this work, Ni(TMS) ₂?6H₂O, Ni(TFA)₂

Full text of DOI:10.1007/s10973-007-8633-3

Journal of Thermal Analysis and Calorimetry, Vol. 93 (2008) 3, 959–962
THERMAL AND KINETIC STUDY OF NICKEL TRIFLUOROMETHANE-
SULPHONATE, TRIFLUOROACETATE AND ACETATE
Hiléia K. S. de Souza*, E. A. Sousa, M. D. M. Paiva, F. M. M. Borges, D. M. A. Melo
and H. Scatena Jr.
Universidade Federal do Rio Grande do Norte, Departamento de Química, C. P. 1662, 59078-970 Natal, RN, Brasil
The reason of comparing thermal behaviour and kinetics of some nickel compounds, is justified by the influence of anion on it, be-
sides supplying information on the stability of the salts. In this work, Ni(TMS)2·6H2O, Ni(TFA)2·3H2O and Ni(Ac)2·2H2O, were
synthesized and characterized by microanalysis, atomic absorption molar, conductance and thermal analysis. Thermogravimetric
curves indicate that the decomposition of the salts occurs in the range 295–1169 K and the NiO is the final residue. Non-isothermal
kinetic evaluation from thermogravimetric data was used to determine energies of activation and pre-exponential factors.
Keywords: kinetic study, nickel complexes, thermal analysis
Introduction
Experimental
The interest for nickel chelated CF SO– (TMS) results
Nickel trifluoromethanesulphonates (TMS), TFA and
Ac salts were obtained from pentahydrated nickel
chloride and characterized by microanalytical proce-
dure (CHN), atomic absorption, nuclear electrolytic
conductance and thermal analysis (TG and DSC). Car-
bon and hydrogen were determined with a Perkin
Elmer 2400 Elemental Analyzer. Nickel percentages
were measured on a SpectrAA 110 Varian atomic ab-
sorption spectrophotometer and molar conductance on
Quimis E405 equipment. TG curves were obtained in a
N2 dynamic air atmosphere with 0.17 K s–1 heating rate
and 0.83 cm3 s–1 flow in a Shimadzu TGA-50H system.
DSC curves were obtained under the same heating and
flow rate conditions with a Shimadzu DSC-50H equip-
ment. Finally, kinetic study of the compounds was
achieved using a domestic computer program devel-
oped in QBASIC using TG data.
3
3
from its thermal stability and also from the possibility of
being a mono-, bi- or tridentates ligand [1]. Trifluoro-
acetates CF3COO– (TFA) and acetates CH3COO– (Ac)
may behave in a similar way, albeit forming nickel com-
pounds with different amounts of hydration. Garner [2]
was a precursor of the study of the whole series of tran-
sition metal trifluoromethane compounds with salts
showing three hydration water molecules. Fujinaga and
Sakamoto have been studied the electrochemical char-
acteristics of trifluoro- methanesulphonic acid and its
salts in nonaqueous solvents [3].
Transition complexes containing trifluoroacetate
compounds with formulas: Tm(CF3COO)3·3H2O,
Tm2(CF3COO)6·2CF3COOH·3H2O
[4]
and
Ln(TFA)3·3MMNO [5] were synthesized and studied.
Trifluoroacetate compounds and their structures also
have been described already [6].
Acetates complexes with several organic neutral
ligands as heterocyclicamines [7], phenol derived [8],
pyrazines [9], salicylidene derivatives [10],
phenazone [11] dimethylaminobenzoic derivatives
[12] were also prepared and characterized. In the
solid-state, nickel acetates have been used as precur-
sors for obtaining mixed nickel oxides with ‘d’ transi-
tion metals and also rare earths [13].
Basic kinetic theory
Several methods have been used for obtaining kinetic
parameters through TG techniques [14, 15].
Vyazovkin [16] and Scatena Jr. [17] analyzed the dif-
ficulty in obtaining kinetic parameters with small er-
rors. In this work, custom-made software was used,
simulating thermogravimetric data using the follow-
ing kinetic equation in each process step:
This work tries to correlate dehydration with
thermal stability and to evaluate kinetic parameters,
activation energies and pre-exponential factors from
thermogravimetric curves of the nickel salts with dif-
ferent anions.
k
E
M
DT + i + 1 Dm
M
é
ù
Dm =- 0,i exp -
m
(1)
ai
i,j
i,j–1
j
i,j–1
ê
b
ë
ú
û
RT
i
*
Author for correspondence: hileiak@yahoo.com
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2008 Akadémiai Kiadó, Budapest

DE SOUZA et al.
where Dmi,j is the mass increase of the compound i af-
environments. Thermogravimetric curves were re-
corded to evaluate the thermal stability of the salts.
For Ni(TFA)2·3H2O and Ni(Ac)2·2H2O salts, the
thermogravimetric curves show four-step decomposi-
tion. For the Ni(TMS)2·6H2O, the decomposition pro-
cess show five-step (Fig. 1). The first mass loss region
for all salts is due to anhydrous salts formation. TMS
compound starts the decomposition at 716 K, while
the TFA and Ac compounds at 545 and 563 K, respec-
tively. This clearly suggests a high stability of the
TMS salt. Finally, nickel oxide was obtained as final
residue for all the salts (Table 3).
ter the step j; k0,i is the pre-exponential factor and Ea,i
is the activation energy of compound i, Mi is the mo-
lar mass of compound i; b is the heating rate and DTj
is the temperature increase for step j.
The initial mass for the first compound is m1. For
the remaining components the initial mass is zero.
With the use of block activation energies and pre-ex-
ponential factors it is possible to approximate visually
the theoretical mass and the experimental one. The
theoretical mass is given by:
(2)
m =åm
j
i,j
DSC curves (300–780 K range), obtained under
the same condition as TG exhibit different behavior
and showed endothermic peaks as indicative of dehy-
dration of the compounds (Fig. 2). The exothermic
process observed in acetate compounds is probably
related to the evolution of acetate molecules. This
exothermic peak evidence a less stability of the ace-
i
where mj is the total mass at step j. A reaction order of
one was proposed for basic kinetic theory, since any
other is theoretically difficult to justify.
The quality criterion for the approximation of
calculated and observed curves is visual and therefore
the first and second derivatives are helpful.
The advantages of determining the kinetic pa-
rameters by this method are:
Table 2 Molar electrolytic conductance results
• It is possible to study the whole temperature range
of the thermogravimetric curve even with parallel
or consecutive reactions.
Compounds
LM/W–1 cm–2 mol–1
Ni(TMS)2·6H2O
Ni(TFA)2·3H2O
Ni(Ac)2·2H2O
206.5
153.0
265.3
• It is possible to predict the quantity and the molar
mass of the reaction intermediate.
• Using the mechanistic proposal it is possible to de-
termine the experimental curve and test the initial
hypothesis.
105
90
75
60
45
30
Results and discussion
From the CHN microanalysis and atomic absorp-
tion (AA) results shown in Table 1, the following
stoichiometrics are suggested for the salts:
Ni(TMS)2·6H2O, Ni(TFA)2·3H2O and Ni(Ac)2·2H2O.
Conductance measurements in 10–3 mol L–1 wa-
ter solution at 298 K indicate the existence of 1:2
electrolytes for the compounds TMS and AC. Electro-
lytes (1:1) to the TFA according to the intervals ad-
mits by Geary [18] (Table 2).
Ac
TFA
TMS
15
Thermal stability depends on the anions types,
structure and chartered of the bond between ligands
and central atom. The complexation of the different
anions can be distinct effects on the thermal stability
of the complexes as results of the different chemical
250
500
750
1000
1250
Temperature/K
Fig. 1 TG curves for the TMS, TFA and Ac salts under flow-
ing N2 (50 cm3 min–1). Heating rate 0.083 K s–1
Table 1 Elemental analysis results
Ni/%
C/%
H/%
Compounds
exp.
calc.
exp.
calc.
exp.
calc.
Ni(TMS)2·6H2O
Ni(TFA)2·3H2O
Ni(Ac)2·2H2O
9.8
7.8
8.5
9.9
7.5
8.4
5.4
15.3
22.2
5.2
15.0
22.6
2.6
1.9
4.8
2.6
1.3
4.7
960
J. Therm. Anal. Cal., 93, 2008

NICKEL TRIFLUOROMETHANESULPHONATE, TRIFLUOROACETATE AND ACETATE
105
300
600
900
1200
90
75
60
45
30
15
st
1
derivative
300
600
900
1200
Fig. 2 DSC curve for salts (TMS, TFA and Ac), under flowing
N2 (50 cm3 min–1). Heating rate 0.083 K s–1
nd
2
derivative
Observed
Calculated
tate compound in comparison with another ones. Due
to the temperature range limited in DSC, was not pos-
sible to observe the final decomposition process of
the TMS and TFA compounds.
200
400
600
800
1000
1200
Temperature/K
Fig. 3 Observed and calculated TG curves for the
Ni(TMS)2·6H2O salt
According TG and DSC data, it is possible to
suggest the following decomposition reactions:
Ni(TMS)2·6H2O, Ni(TFA)2·3H2O and Ni(Ac)2·2H2O
is coherent with:
Ni(TMS)2·6H2O
• Molar mass obtained from TG curves and
• Mass balance of each step.
Ni(CF3SO3)2·6H2O®Ni(CF3SO3)2·3H2O+3H2O-
Ni(CF3SO3)2·3H2O®Ni(CF3SO3)2·2H2O+H2O-
Ni(CF3SO3)2·2H2O®Ni(CF2O)2+2H2O+2FSO3
Ni(CF2O)2®NiO+C2F4O-
Table 4 summarizes the thermodynamic parame-
ters obtained from these plots as explained in the ex-
perimental section. Studies show that Ac is least hy-
drated and have major Ea in the step dehydrated
(step 1) returning least stable. Step 2 only the TMS
continue hydrated, while of the Ac and TFA starts the
salts decomposition respectively, observed through
values Ea. In this step, the value major Ea of the TFA
is related due the fluor compound. In step 3 continue
the salts Ac and TFA decomposition with Ea values
400 and 205 kJ mol–1, respectively. The decomposi-
Ni(TFA)2·3H2O
According Pedrosa et al. [5], the decomposition of TFA
evolve gaseous products, especially CO, CO2, CF3OF
and (CF3CO)2O. The decomposition of TFA continues
up 1160 K, with the formation of NiO as final residue.
300
600
900
1200
100
Ni(Ac)2·2H2O
The decomposition of AC also evolves gaseous prod-
ucts, especially CO, CO2, CH3COO, C2H6CO2 and
C2H5CHO with NiO as final residue.
80
st
1
derivative
Figures 3–5 shows the observed and calculated
thermogravimetric curves obtained by TG and kinetic
studies respectively for the thermal decomposition of
60
the
Ni(TMS)2·6H2O,
Ni(TFA)2·3H2O
and
300
600
900
1200
Ni(Ac)2·2H2O. These figures also show the first and
second derivatives of both calculated and observed
TG curves for the three salts. Ea, k0, and intermediate
molar masses were determined by fitting the observed
curves assuming that the reaction order was one. The
first and second derivatives help with a visual ap-
proach between observed and calculated curves. The
usual molar mass of the intermediate allows good ap-
proximation between observed and calculated curves.
The proposed mechanism for thermoanalysis of the
nd
40
2
derivative
Observed
Calculated
20
200
400
600
800
1000
1200
Temperature/K
Fig. 4 Observed and calculated TG curves for the
Ni(TFA)2·3H2O salt
J. Therm. Anal. Cal., 93, 2008
961

DE SOUZA et al.
Table 3 Kinetic study results
TMS
Step
TFA
Ac
k0/s–1
Ea/kJ mol–1
k0/s–1
Ea/kJ mol–1
k0/s–1
Ea/kJ mol–1
1
2
3
4
2.1·1013
8.5·105
1.3·1029
3.0·102
108.8
66.4
4.6·106
3.5·1014
8.0·1010
–
67.0
196.0
205.0
–
1.1·1026
3.0·109
1.0·1031
–
165.0
75.0
400.0
–
471.5
88.7
105
References
300
600
900
1200
1 D. M. A. Melo, ‘Synthesis, properties, structure and
thermochemistry of addition compounds of lanthanide
(III) trifluoromethanesulphonates and
90
75
60
45
30
N,N-dimethylformamide(DMF)’ (in Portuguese).
Ph.D. Thesis, University of S. Paulo, 1989.
2 C. D. Garner and B. Hughes, Adv. Inorg. Chem.
Radiochem., 17 (1975) 1.
st
1
derivative
3 T. Fujinaga and I. Sakamoto, Pure Appl. Chem.,
52 (1980) 1387.
300
600
900
1200
4 S. I. Gutnikov, E. V. Karpova, M. A. Zakharov and
A. I. Boltalin, Russ. J. Inorg. Chem., 51 (2006) 541.
5 A. M. Garrido Pedrosa, M. S. C. C-mara,
F. M. M. Borges, H. K. S. Souza, H. Scatena Jr.,
D. M. A. Melo and L. B Zinner, J. Therm. Anal. Cal.,
73 (2003) 895.
nd
2
derivative
Observed
Calculated
6 O. Tokareva, D. S. Tereshchenko, A. I. Boltalin and
S. I. Troyanov, Russian J. Coord. Chem., 32 (2006) 663.
7 V. Zele×ák, Z. Vargová, Katalin Györyová,
E. Ve¹erníková and V. Balek, J. Therm. Anal. Cal.,
82 (2005) 747.
200
400
600
800
1000
1200
Temperature/K
Fig. 5 Observed and calculated TG curves for the
Ni(Ac)2·2H2O salt
8 K. Shanmuga Bharathi, S. Sreedaran, A. Kalilur Rahiman,
K. Rajesh and V. Narayanan, Polyhedron, 26 (2007) 3993.
9 N. Schultheiss, D. R. Powell and E. Bosch, J. Chem.
Crystallogr., 34 ( 2004) 785.
tion of TFA and Ac continues in step 4 with the for-
mation of NiO as a final residue. In the TMS case the
NiO residue was obtained in step 5.
10 R. M. Issa, S. A. Amer, I. A. Mansour and
A. I. Abdel-Monsef, J. Therm. Anal. Cal., 90 (2007) 261.
11 E. Szunyogová, K. Györyová, D. Hudecová, L. Piknová,
J. Chomi¹, Z. Vargová and V. Zele×ák. J. Therm. Anal.
Cal., 88 (2007) 219.
Conclusions
12 B. S. Garg, R. K. Sharma and E. Kundra, Transition Metal
Chem., 30 (2005) 552.
Thermal behavior of the nickel TMS, TFA and Ac
salts have not been described in the literature. The
thermal characterization was carried out by TG, DSC
while the kinetic study using a QBASIC program in-
fer the TG data as input. The proposed three mecha-
nism for the observed thermal decomposition consists
of consecutive of the organic intermediates. The
method previously introduced [8] showed a good
agreement with the plotted curves and suggests that
each peak correspond to more than one reaction. The
first and second derivatives indicated the high quality
of the optimization of the mass curves.
13 A .M. L. Silva, M. F. V. Moura, L. P. Mercuri,
A. M. E. Santo and J. R. Matos, Anais Assoc. Bras.
Quim., 47 (1998) 133.
14 W. W. Wendlant, Thermal Analysis, 3rd Ed., John Wiley
& Sons, Houston 1964.
15 M. E. Brown, Introduction to Thermal Analysis:
Techniques and Applications, Chapman and Hall, London
1988.
16 S. V Vyazovkin and A. I. Lesnikovich, Thermochim.
Acta, 165 (1990) 11.
17 A. M. G. Pedrosa, P. M. Pimentel, D. M. A Melo,
H. Scatena Jr., F. M. M. Borges, A. G. Souza and
L. B. Zinner, J. Therm. Anal. Cal., 67 (2002) 397.
18 W. J. Geary, Coord. Chem. Rev., 7 (1971) 81.
The thermal decompositions and kinetic studies
show that trifluoromethanesulphonate anion is much
more stable than other anions taking into account the
remarkable resistance to thermal decomposition.
Received: July 11, 2007
Accepted: March 11, 2008
OnlineFirst: June 25, 2008
DOI: 10.1007/s10973-007-8633-3
962
J. Therm. Anal. Cal., 93, 2008