A comparative study on the thermal decomposition of some transition metal maleates and fumarates

Article abstract of DOI:10.1007/s10973-005-7473-2

Thermal decomposition of M(mal/fum)?xH₂O (M=Mn, Co, Ni) has been studied in static air atmosphere from ambient to 500°C employing TG-DTG-DTA, XRD and IR spectroscopic techniques. After dehydration the anhydrous maleate salts decompose to metal oxalate in the temperature range of 320-360°C, which at higher temperature undergo an abrupt oxidative pyrolysis to oxides. The anhydrous fumarate salts have been found to decompose directly to oxide phase. A comparison of thermal analysis reveals that fumarates are thermally more stable than maleates.

Full text of DOI:10.1007/s10973-005-7473-2

Journal of Thermal Analysis and Calorimetry, Vol. 89 (2007) 1, 251–255
A COMPARATIVE STUDY ON THE THERMAL DECOMPOSITION OF
SOME TRANSITION METAL MALEATES AND FUMARATES
B. S. Randhawa* and M. Kaur
Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, India
Thermal decomposition of M(mal/fum)×xH2O (M=Mn, Co, Ni) has been studied in static air atmosphere from ambient to 500°C em-
ploying TG-DTG-DTA, XRD and IR spectroscopic techniques. After dehydration the anhydrous maleate salts decompose to metal
oxalate in the temperature range of 320–360°C, which at higher temperature undergo an abrupt oxidative pyrolysis to oxides. The
anhydrous fumarate salts have been found to decompose directly to oxide phase. A comparison of thermal analysis reveals that
fumarates are thermally more stable than maleates.
Keywords: metal fumarates, metal maleates, TG-DTG-DTA, thermal decomposition, XRD
Introduction
determined titrimetrically using Eriochrome Black-T
as indicator whereas cobalt and nickel contents were
determined electrogravimetrically [10].
Thermal decomposition of transition metal
carboxylates has become a fascinating subject of re-
cent interest due to the technological importance of
these studies. The final thermolysis products (metal
oxides) find extensive applications as catalysts, ce-
ramic colorants, photoconductors, etc. [1–5]. Al-
though the thermolysis of transition metal oxa-
lates [6–8] has been extensively studied, a similar
interest on transition metal maleates and fumarates
that are geometrical isomers is lacking. The thermal
analysis of copper and zinc maleates/fumarates has
already been reported [9]. In continuation of that
work the present investigation on thermolysis of other
transition metal (M=Mn, Co, Ni) maleates and
fumarates has been undertaken, with a view to study
the effect of geometry (cis, trans) on their thermal sta-
bilities and mode of decomposition.
Simultaneous TG-DTG-DTA curves were re-
corded on a Stanton Red Craft Model (STA-780) in
static air atmosphere at a heating rate of 10°C min–1.
For isothermal decomposition, transition metal ma-
leates and fumarates were calcined isothermally at
450°C in static air atmosphere for a duration of 2 h to
obtain the final thermolysis residue for its character-
ization. IR spectra of parent carboxylates and their
thermolysis products were recorded in the range
4000–200 cm–1 on PYE-UNICAM SP3-300 IR
spectrophotometer using KBr matrix. The room tem-
perature XRD powder patterns (using CuKa radia-
tion) were recorded at USIC, IIT Roorkee.
Table 1 Microanalytical data of transition metal maleates
and fumarates
Salt
C/%
H/%
M/%
obs.
cal.
20.90
21.52
3.42
3.58
24.63
24.66
Mn(mal)×3H2O
Experimental
obs.
cal.
28.22
28.40
1.09
1.18
32.48
32.54
Mn(fum)
Transition metal maleates and fumerates were prepared
by mixing vigorously the equimolar solutions of re-
spective transition metal carbonate and carboxylic acid
(maleic, fumaric). The resultant solution was concen-
trated on a water bath after filtering off the excess
unreacted carboxylic acid. The precipitates of transi-
tion metal maleate and fumarate were obtained by the
addition of acetone (in excess). The precipitates were
filtered, dried and stored in a vacuum desiccator. The
identity of these compounds was established by ele-
mental analysis (Table 1). The manganese content was
obs.
cal.
15.80
16.05
5.26
5.35
19.56
19.73
Co(mal)×7H2O
Co(fum)×4H2O
Ni(mal)×4H2O
Ni(fum)×4H2O
obs.
cal.
18.90
19.59
4.81
4.08
23.88
24.08
obs.
cal.
19.09
19.59
4.01
4.08
23.95
24.08
obs.
cal.
19.21
19.59
4.02
4.08
23.75
24.08
*
Author for correspondence: balwinderrandhawa@yahoo.co.in
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2007 Akadémiai Kiadó, Budapest

RANDHAWA, KAUR
Results and discussion
IR spectrum of manganese maleate trihydrate exhibits
a broad band centered at about 3400 cm–1 marking the
presence of nO–H of lattice water. A small shoulder
lies at 2960 cm–1 due to nC–H of the ligand. An over-
lapping of bands due to nC=C and nasym(C=O) exist in the
range 1570–1600 cm–1, whereas a strong band at
1390 cm–1 is assigned to nsym(C=O) of the coordinated
carboxylate group. Bands in the range 1210–985 cm–1
are attributed to the (O–H) bending modes. A sharp
and distinct band at 815 cm–1 is due to cis(C–H) wag-
ging and bands at 585 and 330 cm–1 indicate the pres-
ence of Mn–O bonding [11, 12]. The infrared spectra
of manganese fumarate and other transition metal
carboxylates are almost similar to that of manganese
maleate. The compound-wise discussion on thermal
decomposition studies follows.
Fig. 1 DTA, TG and DTG curves of manganese maleate
trihydrate
tained by isothermal calcination of parent compound
at 320°C for 15 min. Manganese oxalate undergoes an
abrupt oxidative decomposition accompanied by a
steep mass loss i.e. 68% at 410°C revealing the for-
mation of manganese oxide, MnO (calc. loss=68.2%).
The respective DTA (strong exotherm) and DTG
peaks lie at 360 and 355°C, respectively. The identity
of the final thermolysis product has been confirmed
from XRD data which agree to that reported for
MnO [15]. IR spectrum of the residue, obtained by
calcining the parent complex at 450°C for 2 h shows
characteristic bands at 589 and 290 cm–1 due to nMn–O
bonding [16]. Manganese oxalate is reported to de-
compose directly to MnO [6].
Manganese maleate trihydrate, Mn(C2H2C2O4)×3H2O
Figure 1 shows the simultaneous thermal curves
(TG-DTG-DTA) of manganese maleate trihydrate at a
heating rate of 10°C min–1. The compound undergoes
decomposition in three steps. The first step is the de-
hydration which commences at 95°C and is com-
pleted at 187°C as indicated by a mass loss of 24%
(calc. loss=24.2%), DTA and DTG show correspond-
ing peaks at 157°C (endothermic) and 155°C, respec-
tively. In the second step, the anhydrous compound
undergoes a gradual decomposition process until a
mass loss of 32% is reached at 320°C suggesting the
formation of manganese oxalate from manganese
maleate after the removal of an acetylene molecule.
The respective DTG peak lies at 290°C which is endo
in DTA. The liberation of acetylene has been reported
during ‘Kolbe electrolysis’ of metal maleate in solu-
tion phase [13, 14]. The presence of manganese oxa-
late, MnC2O4 as an intermediate has been confirmed
from XRD powder data of the residue (Table 2) ob-
Manganese fumarate, Mn(C2H2C2O4)
Figure 2 shows the simultaneous (TG, DTG, DTA)
curves of manganese fumarate at a heating rate of
10°C min–1. The compound is anhydrous and under-
goes a single step decomposition. The anhydrous
compound remains stable up to 380°C and then un-
dergoes an oxidative decomposition. A large exother-
Table 2 XRD powder data of the intermediate obtained at 320°C by isothermal calcination of Mn(mal)×3H2O
Experimental
ASTM* data
d/
Irel
h k l
d/
Irel
Assignment
5.826
5.575
4.886
3.539
2.921
2.753
2.286
2.011
100
58
23
47
14
28
17
10
0 1 0
0 1 1
0 1 1
2 0 0
0 2 0
1 0 3
3 0 1
1 2 3
5.830
5.570
4.890
3.550
2.928
2.761
2.297
2.015
100
60
25
50
17
30
20
12
MnC2O4
MnC2O4
MnC2O4
MnC2O4
MnC2O4
MnC2O4
MnC2O4
MnC2O4
*ASTM Card No. 32-646
252
J. Therm. Anal. Cal., 89, 2007

SOME TRANSITION METAL MALEATES AND FUMARATES
spectively. In the second step the anhydrous salt under-
goes a rapid oxidative decomposition as shown by a
steep mass loss i.e. 74% at 400°C revealing the forma-
tion of cobalt oxide, CoO. The accompanying DTG
and DTA (exothermic) peaks lie at 375 and 365°C, re-
spectively. The presence of CoO has been confirmed
by XRD powder pattern of the final thermolysis prod-
uct [17]. IR spectrum also shows characteristic bands
at 570 and 280 cm–1 due to nCo–O bonding.
Cobalt fumarate tetrahydrate: Co(C2H2C2O4)×4H2O
Figure 4 shows the STA curves (TG-DTG-DTA) of
cobalt fumarate tetrahydrate at a heating rate of
10°C min–1. The compound undergoes decomposition
in two steps as shown by TG curve. The first step is
the dehydration, which starts at 110°C and completes
at 180°C as indicated by a mass loss of 29%
(calc. loss=29.4%). DTG shows corresponding peak
at 145°C which is endo in DTA. The anhydrous com-
pound remains stable up to 330°C and then undergoes
rapid oxidative decomposition process until a mass
loss of 69% is attained at 380°C suggesting the forma-
tion of CoO (calc. loss=69.4%). The respective DTG
peak lies at 350°C which is exothermic in DTA.
Fig. 2 DTA, TG and DTG curves of manganese fumarate
mic peak at 400°C is associated with the decomposi-
tion process. The corresponding DTG peak lies at
395°C. A mass loss of 58% (calc. loss=58%) at 440°C
suggests the presence of manganese oxide (MnO).
The formation of manganese oxalate intermediate, as
observed in manganese maleate, has not been de-
tected in fumarate salt. This is due to the fact that the
carboxylate groups of fumarate present at trans posi-
tion, do not facilitate the formation of oxalate. Forma-
tion of manganese oxide, MnO as the end product has
been confirmed by IR spectrum and XRD powder dif-
fraction pattern of the final thermolysis residue.
Cobalt maleate heptahydrate, Co(C2H2C2O4)×7H2O
The mode of decomposition of this compound is simi-
lar to that of manganese maleate trihydrate. The com-
pound undergoes decomposition in two steps (Fig. 3).
The first step is dehydration which commences at 107
and is completed at 225°C as indicated by a mass loss
of 42% (calc. loss=42%). DTA and DTG show corre-
sponding peaks at 147 (endothermic) and 145°C, re-
Fig. 4 DTA, TG and DTG curves of cobalt fumarate tetrahydrate
Nickel maleate tetrahydrate: Ni(C2H2C2O4)×4H2O
The compound undergoes a multistep dehydration pro-
cess as shown by the DTG curve (Fig. 5) and there is a
corresponding endothermic region in DTA from 70 to
210°C. TG shows a plateau at a mass loss of 22% sug-
gesting the removal of three water molecules (calc.
loss=22.2%). A further slackening of TG curve at a
mass loss of 29% suggests the removal of fourth water
molecule at 210°C (calc. loss=29.4%). The anhydrous
compound undergoes a gradual decomposition until a
mass loss of 40% is reached at 360°C indicating the for-
Fig. 3 DTA, TG and DTG curves of cobalt maleate heptahydrate
J. Therm. Anal. Cal., 89, 2007
253

RANDHAWA, KAUR
Fig. 5 DTA, TG and DTG curves of nickel maleate tetrahydrate
Fig. 6 DTA, TG and DTG curves of nickel fumarate tetrahydrate
mation of nickel oxalate (calc. loss=40.3%). The respec-
tive DTG peak exists at 340°C which is exo in DTA.
The identity of nickel oxalate, NiC2O4 formed has been
revealed by recording XRD powder data of the residue
obtained by isothermal heating of the parent salt at
360°C for 15 min (Table 3). Being unstable, nickel oxa-
late immediately undergoes an oxidative decomposition
until a mass loss of 69.5% is reached at 420°C revealing
the formation of NiO (calc. loss= 69.4%). There are cor-
responding DTA and DTG peaks at 395 (exo) and
400°C, respectively. The presence of NiO has been con-
firmed by XRD powder data of the final thermolysis res-
idue [18]. IR spectrum shows characteristic bands at 565
and 282 cm–1 due to nNi–O bonding.
loss of 29% (calc. loss=29.4%). The corresponding
DTG peak lies at 175°C which is endo in DTA. In the
second step the anhydrous compound undergoes
rapid oxidative decomposition as shown by an abrupt
mass loss i.e. 69% up to 390°C indicating the forma-
tion of nickel oxide (NiO) directly from nickel
fumarate. DTA shows an exotherm at 370°C for this
oxidative decomposition step and the corresponding
DTG peak lies at 365°C. XRD powder data of the fi-
nal thermolysis product confirms the existence of
nickel oxide, NiO.
On the basis of various thermoanalytical studies,
the following mechanism may be proposed for the ae-
rial decomposition of transition metal maleates:
dehydration, 187–225°C
M(C2H2C2O4)×xH2O¾¾¾¾¾®
M(C2H2C2O4)+xH2O
Nickel fumarate tetrahydrate: Ni(C2H2C2O4)×4H2O
Figure 6 displays the simultaneous thermal curves
(TG-DTG-DTA) of nickel fumarate tetrahydrate at a
heating rate of 10°C min–1. The compound decom-
poses in two steps as shown by TG curve. The first
step is dehydration which commences at 130 and
completes at 225°C as shown by a plateau at a mass
decomposition, 320–360°C
¾¾¾¾¾¾®MC2O4+HCºCH
decomposition, 390–440°C
MC2O4¾¾¾¾¾¾®MO+CO+CO2
Table 3 XRD powder data of the intermediate obtained at 360°C by isothermal calcination of Ni(mal)×4H2O
Experimental
ASTM* data
d/
Irel
h k l
d/
Irel
Assignment
4.765
3.932
3.045
2.938
2.615
2.510
1.575
1.512
1.470
100
15
12
37
10
26
28
20
20
2 0 2
0 0 4
1 1 4
4 0 0
1 1 5
0 2 2
3 3 2
2 0 0
1 3 6
4.770
3.940
3.080
2.959
2.642
2.528
1.589
1.518
1.480
100
16
14
40
11
25
30
18
20
NiC2O4
NiC2O4
NiC2O4
NiC2O4
NiC2O4
NiC2O4
NiC2O4
NiC2O4
NiC2O4
*ASTM Card No. 25-0582
254
J. Therm. Anal. Cal., 89, 2007

SOME TRANSITION METAL MALEATES AND FUMARATES
5 R. Sasikala and S. K. Kulshreshtha, J. Therm. Anal. Cal.,
78 (2004) 723.
However, anhydrous fumarate salts decompose
directly to the oxide phase. The formation of oxalate
intermediate from fumarate is not possible due to the
‘trans’ location of carboxylate groups in the latter.
6 D. Dollimore and D. L. Griffiths, J. Thermal Anal.,
2 (1970) 229.
7 B. Malecka, E. D. Ciesla and A. Malechi,
J. Therm. Anal. Cal., 68 (2002) 819.
8 O. Carp, L.Patron, G. Marinescu, G. Pascu, P. Budrugeau
and M. Brezeanu, J. Therm. Anal. Cal., 72 (2003) 263.
9 P. S. Bassi, B. S. Randhawa, C. M. Khajuria and S. Kaur,
J. Thermal Anal., 32 (1987) 569.
Conclusions
A comparison of thermal analysis shows that the
fumarate compounds are more stable than the corre-
sponding maleate salts. A similar trend has also been
observed [7] for copper and zinc carboxylates (ma-
leates, fumarates). This is attributed to the structure of
these carboxylates. The fumarate, being a trans iso-
mer, can crystallize either as a three dimensional or as
linear polymer whereas only dimeric structure is ex-
pected for the cis-isomer (maleate).
The highest thermal stability of manganese
fumarate (395°C) is attributed to its existence as anhy-
drous salt whereas all other carboxylates are hydrated.
Being anhydrous, it does not have to undergo any reor-
ganization/restructuring prior to decomposition.
10 A. I. Vogel, A Textbook of Quantitative Inorganic Analysis
Including Elementary Instrumental Analysis, Longman,
London 1973.
11 K. Nakamoto, Infrared spectra of inorganic and coordina-
tion compounds, 2nd Ed., Wiley Intersci., New York 1970.
12 C. N. R. Rao, Chemical Applications of Infrared Spectros-
copy, Academic Press, New York 1967.
13 S. N. Dhawan, P. N. Kapil, S. C. Kheterpal and
R. S. Nandwani, New Course Chemistry, Pradeep Publ.,
11th Ed., New Delhi 1999, pp. 15–16.
14 S. P. Jauhar and S. K. Malhotra, Modern Approach to
Chemistry, Modern Publ., New Delhi 1999, p. 804.
15 ASTM Card Number 7-230.
16 R. A. Nyquist and R. O. Kagel, Infrared Spectra of Inor-
ganic Compounds, Academic Press, 1971.
17 ASTM Card Number 9-402.
18 ASTM Card Number 78-0643.
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Received: December 12, 2005
Accepted: April 24, 2006
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OnlineFirst: August 11, 2006
DOI: 10.1007/s10973-005-7473-2
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J. Therm. Anal. Cal., 89, 2007
255