Synthesis, characterization and thermal behaviour on solid tartrates of some bivalent metal ions

Article abstract of DOI:10.1016/j.tca.2009.07.015

Solid-state M-L compounds, where M stands for bivalent Mn, Fe, Co, Ni, Cu, Zn and L is tartrate, have been synthesized. Thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, infr

Full text of DOI:10.1016/j.tca.2009.07.015

Thermochimica Acta 496 (2009) 156–160
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Thermochimica Acta
journal homepage: www.elsevier.com/locate/tca
Synthesis, characterization and thermal behaviour on solid tartrates
of some bivalent metal ions
Emanuel C. Rodriguesa,∗, Claudio T. Carvalhob, Adriano B. de Siqueirac,
Gilbert Bannachd, Massao Ionashirob
a Centro Universitário da Fundac¸ ão Educacional de Barretos, UNIFEB, CEP 14780-226, Barretos, SP, Brazil
b Instituto de Química, UNESP, C.P. 355, CEP 14801-970, Araraquara, SP, Brazil
c Universidade Federal do Mato Grosso, UFMT, CEP 78698-000, Cuiabá, MT, Brazil
d Instituto de Química de São Carlos, USP, CEP 13560-970, São Carlos, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 May 2009
Received in revised form 9 July 2009
Accepted 24 July 2009
Available online 3 August 2009
Solid-state M–L compounds, where M stands for bivalent Mn, Fe, Co, Ni, Cu, Zn and L is tartrate, have
been synthesized. Thermogravimetry and differential thermal analysis (TG–DTA), differential scanning
calorimetry (DSC), X-ray powder diffractometry, infrared spectroscopy, elemental analysis and complex-
ometry were used to characterize and to study the thermal behaviour of these compounds. The TG–DTA
and DSC curves show that the manganese, cobalt and nickel compounds are hydrated while iron, copper
and zinc ones are anhydrous. The thermal stability of the anhydrous compounds depends on the nature of
the metal ion, and it follows the order: Zn > Cu > Mn = Co > Ni > Fe. These curves also show that the thermal
decomposition occurs in a single step to the respective metal oxides. The results led to information about
the composition, dehydration, ligand denticity and thermal decomposition of the isolated compounds.
© 2009 Elsevier B.V. All rights reserved.
Keywords:
Bivalent metals
Tartrate
Characterization
Thermal behaviour
1. Introduction
complexometry, elemental analysis, X-ray powder diffractome-
try, infrared spectroscopy, simultaneous thermogravimetry and
Tartaric acid (dihydroxybutanedioic acid) is an organic com-
pound which has not an ample utilization as citric and malic acids,
but it has a great importance in the provision industry. It is used as
acidulant in some food [1].
differential thermal analysis (TG–DTA) and differential scanning
calorimetry. The results allowed us to acquire information con-
cerning these compounds in the solid-state including their thermal
stability, ligand’s denticity and crystallinity.
Tartaric acid (C4H6O6) is found in the grape in the form L(+) and
among the organic acids of the grape, it is more strong [2].
A survey of the literature shows that the thermal studies
involving compounds derivative of tartrate, reported the ther-
mal decomposition and kinetics of dehydration of praseodymium
(III), neodymium (III) and gadolinium (III) tartrates [3,4], TG and
DSC studies on Sm(III) and Tb(III) tartrates [5], thermal decom-
position behaviour of lanthanum (III), tris-tartrate lanthanide (III)
decahydrate [6], studies on kinetics and mechanism of thermal
decomposition of yttrium tartrate trihydrate crystals [7] and kinet-
ics, mechanism of thermal decomposition of strontium tartrate
crystals [8] and thermoanalytical study of some salts of 3d metals
with tartaric acid [9–11].
2. Experimental
The sodium tartrate dibasic dihydrate (C4H4O6Na2·2H2O) 99%
purity was obtained from Sigma and aqueous solution 0.20 mol L−1
was prepared by direct weighing of the solid salt. Aqueous solutions
of bivalent metal ions 0.20 mol L−1 were prepared by dissolving the
corresponding chlorides.
The solid-state compounds were obtained by adding equiva-
lent quantities of sodium tartrate to the respective metal chloride
and the resulting solutions were heated and maintained in water
bath until total precipitation of the metal tartrates. The precipi-
tates were washed with hot distilled water until chloride ions were
eliminated, filtered through and dried on Whatman no. 42 filtered
papers, and kept in a desiccator over anhydrous calcium chloride.
To avoid oxidation of Mn(II) and Fe(II), all their solutions as well
as the water employed for washing their precipitates were purged
with nitrogen gas, even in the solutions maintained in the water
bath.
In the present paper, solid-state compounds of bivalent
manganese, iron, cobalt, nickel, copper and zinc with tartrate
(C4H4O62−) were prepared. The compounds were investigated by
∗
Corresponding author.
E-mail address: emanuelbarretos@bol.com.br (E.C. Rodrigues).
0040-6031/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2009.07.015

E.C. Rodrigues et al. / Thermochimica Acta 496 (2009) 156–160
157
Table 1
Analytical data for the ML·nH2O compounds.
Compounda
Metal oxide (%)
Ligand lost
Calcd.
Water (%)
Calcd.
Carbon (%)
Calcd.
Hydrogen (%)
Calcd.
Final
Calcd.
TG
EDTA
TG
TG
4.21
E.A
E.A
Residueb
MnL·0.5H2O
FeL
CoL·0.5H2O
NiL·2.5H2O
CuL
37.23
39.16
37.15
29.67
37.59
38.12
36.91
38.8
36.85
29.32
37.73
38.03
36.46
38.77
36.95
29.45
37.84
37.82
58.33
60.84
58.68
52.44
62.41
61.88
58.88
61.20
58.64
53.11
62.27
61.97
4.44
–
4.17
17.89
–
22.66
23.56
22.24
19.08
22.70
22.51
22.90
23.70
21.90
19.32
23.15
22.40
2.38
1.98
2.34
3.61
191
2.01
1.61
2.49
3.66
1.51
2.11
Mn2O3
Fe2O3
Co3O4
NiO
CuO
ZnO
–
4.51
17.57
–
ZnL
–
–
1.89
a
L means tartrate.
All the residues was confirmed by X-ray powder diffractometry.
b
In the solid-state compounds, metal ions, water and tartrate
contents were determined from TG curves. The metal ions were
also determined by complexometry with standard EDTA solutions
[12,13] after igniting the compounds to the respective oxides and
their dissolution in hydrochloric acid.
Simultaneous TG–DTA and DSC curves were obtained with two
thermal analysis system, models SDT 2960 and Q 10, both from
TA Instruments. The purge gas was an air flow of 150 mL min−1. A
heating rate of 20 ◦C min−1 was adopted, with samples weighing
about 7–8 mg. Alumina and aluminum crucibles, the latter with
perforated covers, were used for TG–DTA and DSC, respectively.
Carbon and hydrogen contents were determined by microan-
alytical procedures, with an EA 1110 CHNS-O Elemental Analyzer
from CE Instruments.
X-ray powder patterns were obtained with a Siemens D-5000 X-
ray diffractometer using Cu K␣ radiation (ꢀ = 1.544 Å) and settings
of 40 kV and 20 mA.
Infrared spectra for tartrate (sodium salt) as well as for its metal
ioncompoundswere runonaNicolet model Impact 400 FTIRinstru-
ment, within the 4000–400 cm−1 range. The solid samples were
pressed into KBr pellets.
range because this region is potentially the most informative
in attempting to assign coordination sites. The IR spectrum of
acid shows a peak at 1743 cm−1 which is indicative of free car-
boxyl groups. The spectrum of the compounds show peaks at
lower wavenumbers which is indicative of coordination carboxy-
late groups. The spectrum of tartaric acid also shows a peak
at 1088 cm−1 indicative of a C–O stretching (alcohol group).
The spectrum of the compounds also show a split or doublet
bands, both shifted to lower frequencies in the complexes, namely
1092–1041 cm−1, suggesting metals coordination by carboxylate
with participation of the alcoholic hydroxyl groups of the ligand.
Simultaneous TG–DTA and DSC curves of the compounds are
shown in Figs. 2–7. The TG–DTA curves show mass losses in a single
or two steps, corresponding to endothermic peaks due to dehydra-
tion and exothermic ones attributed to the oxidation of organic
matter. The thermoanalytical data of TG–DTA curves are shown
in Table 3. The DSC curves also show endothermic and exothermic
peaks, corresponding to the mass losses displayed by the TG curves.
The differences observed concerning the peak temperature or the
profiles of these curves are undoubtedly due to the perforated cover
used to obtain the DSC curves, while the TG–DTA ones are obtained
without cover.
The thermal stability of the anhydrous compounds (I) as well as
the final temperature of thermal decomposition (II) as shown by
the TG–DTA curves depend on the nature of the metal ion, and they
3. Results and discussion
The analytical and thermoanalytical (TG) data are shown
in Table 1. These results establish the stoichiometry of these
compounds, which are in agreement with the general formula:
ML·nH2O, where M represents Mn(II), Fe(II), Co(II), Ni(II), Cu(II) or
Zn(II), L is tartrate and n = 0 (Fe, Cu, Zn), 0.5 (Mn, Co) and 2.5 (Ni).
The X-ray diffraction powder patterns (Fig. 1) show that all the
compounds have a crystalline structure, without evidence of the
formation of isomorphous compounds.
Infrared spectroscopic data on tartrate and its compounds with
the metal ions considered in this work are shown in Table 2.
The investigation was focused mainly within the 1750–1000 cm−1
Table 2
Spectroscopic data.
␯
(COO−
)
␯
sym
(COO−
)
␯
ax
(C–O) alcohol
as
Acid
1743*
1088
Sodium salt
MnL·0.5H2O
FeL
CoL·0.5H2O
NiL·2.5H2O
CuL
1619s
1608s
1587s
1616s
1608s
1623s
1606s
1410m
1412m
1404m
1415m
1398m
1365m
1419m
1113/1066
1084/1045
1086/1041
1086/1043
1086/1047
1074/1059
1092/1049
ZnL
␯
␯
␯
(COO−): symmetrical vibrations of the COO− group.
sym
(COO−): anti-symmetrical vibrations of the COO− group.
as
(C–O): axial stretching of C–O of the alcohol group.
Free carboxyl groups.
Strong.
ax
*
s
Fig. 1. X-ray powder diffraction patterns of the compounds: MnL·0.5H2O; FeL;
CoL·0.5H2O; NiL·2.5H2O; CuL and ZnL.
m
Medium.

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E.C. Rodrigues et al. / Thermochimica Acta 496 (2009) 156–160
Fig. 2. TG–DTA and DSC curves of MnL·0.5H2O (L = tartrate).
Fig. 3. TG–DTA and DSC curves of FeL (L = tartrate).
follow the order:
organic matter. The total mass loss up to 405 ◦C is in agreement
with the formation of Mn2O3, as final residue (Calcd. = 62.77%;
TG = 63.09%) and confirmed by X-ray powder diffractometry. The
residue at 420 ◦C is in agreement with Ref. [9]. However the decom-
position to Mn3O4 was not observed.
Iron compound: The simultaneous TG–DTA and DSC curves are
shown in Fig. 3. These curves show that the compound is anhydrous
and stable up to 175 ◦C. Above this temperature the thermal decom-
position occurs in two steps between 175–245 ◦C and 245–360 ◦C,
with loss of 60.31% and 0.9% respectively corresponding to the large
and sharp exothermic peak at 245 ◦C and small exothermic event at
340 ◦C (DTA) or the broad exotherm between 185 and 350 ◦C (DSC)
attributed to the oxidation of Fe(II) to Fe(III) and organic matter.
(I)and(II) : Zn > Mn : Co > Ni > Fe > Cu.
The thermal behaviour of the compounds is heavily dependent
on the nature of the metal ion and so the features of each of these
compounds are discussed individually.
Manganese compound: The simultaneous TG–DTA and DSC
curves are shown in Fig. 2. The first mass loss observed between
65 and 110 ◦C, corresponding to the endothermic peak at 100 ◦C
(DTA) or 115 ◦C (DSC) is due to dehydration, with loss of 0.5H2O
(Calcd. = 4.44%; TG = 4.21%). The anhydrous compound is stable up
to 315 ◦C and the thermal decomposition occurs in a single step
between 350 and 460 ◦C (DSC) attributed to the oxidation of the
Table 3
Temperature ranges (ꢁ), mass losses or gain (%) and peak temperatures observed for each step of TG–DTA curves of the compounds.
Compound
TG–DTA steps
First
DSC peaks
First
Second
Third
Second
MnL·0.5H2Oa
ꢁ/◦C
65–110
4.21
100 (endo)
315–405
58.88
400 (exo)
Loss/%
Peak/◦C
115 (endo)
350–460 (exo; broad)
185–350 (exo; broad)
350 – 475 (exo; broad)
335–450 (exo; broad)
220–390 (exo; broad)
380–475 (exo; broad)
FeL
ꢁ/◦C
175–245
60.31
245 (exo)
245–360
0.9
340 (exo)
Loss/%
Peak/◦C
–
CoL·0.5H2O
NiL·2.5H2O
CuL
ꢁ/◦C
65–145
4.51
100 (endo)
315–405
58.64
405 (exo)
Loss/%
Peak/◦C
107; 141 (endo)
ꢁ/◦C
75–140
17.57
130 (endo)
310–370
70.33
365 (exo)
370–650
0.35b
Loss/%
Peak/◦C
144 (endo)
ꢁ/◦C
205–280
65.84
270 (exo)
280–500
3.57b
–
Loss/%
Peak/◦C
–
–
ZnL
ꢁ/◦C
325–435
61.77
415 (exo)
–
–
–
Loss/%
Peak/◦C
a
L means tartrate.
Mass gain.
b

E.C. Rodrigues et al. / Thermochimica Acta 496 (2009) 156–160
159
Fig. 4. TG–DTA and DSC curves of CoL·0.5H2O (L = tartrate).
Fig. 6. TG–DTA and DSC curves of CuL (L = tartrate).
The profiles of the TG–DTA curves corresponding to the first mass
loss show that the oxidation of the organic matter occurs with com-
bustion. The total mass loss up to 360 ◦C is in agreement with the
formation of Fe2O3, as final residue (Calcd. = 60.84%; TG = 61.20%)
and confirmed by X-ray powder diffractometry. These results are in
agreement with the thermal decomposition of the iron compound
as described by Dranca [9] and Venkataraman [10].
Cobalt compound: The simultaneous TG–DTA and DSC curves are
shown in Fig. 4. The mass loss that occurs between 65 and 145 ◦C,
corresponding to small endothermic event at 100 and 130 ◦C (DTA)
or 107 ◦C or 141 ◦C (DSC) is due to dehydration that occurs in two
steps, with loss of 0.5H2O (Calcd. = 4.17%; TG = 4.51%). The anhy-
drous compound is stable up to 315 ◦C and above this temperature
the thermal decomposition occurs in a single step up to 405 ◦C with
loss of 58.64%, corresponding to exothermic peak at 405 ◦C (DTA)
or the broad exotherm between 350 and 475 ◦C (DSC), attributed to
the oxidation of organic matter. The profiles of the TG–DTA curves
also show that the oxidation of the organic matter occurs with com-
bustion. The total mass loss up to 405 ◦C is in agreement with the
formation of Co3O4, as final residue (Calcd. = 62.85%; TG = 63.15%)
and confirmed by X-ray powder diffractometry. The results are
in agreement with the literature [9]. However the formation of
Fig. 5. TG–DTA and DSC curves of NiL·2.5H2O (L = tartrate).
Fig. 7. TG–DTA and DSC curves of ZnL (L = tartrate).

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E.C. Rodrigues et al. / Thermochimica Acta 496 (2009) 156–160
stable anhydrous compound and the thermal decomposition of
the anhydrous compound, without formation of intermediate are
in disagreement with the results described in Ref. [11]. The dis-
agreement undoubtedly is due to the different condition used for
obtaining these curves, even for preparation the compound.
Nickel compound: The simultaneous TG–DTA and DSC curves are
shown in Fig. 5. The first mass loss between 75 and 140 ◦C corre-
sponding to the endothermic peak at 130 ◦C (DTA) or 144 ◦C (DSC)
is due to dehydration, which occurs in a single step with loss of
2.5 H2O (Calcd. = 17.89%; TG = 17.57%). The anhydrous compound is
stable up to 310 ◦C and above this temperature the thermal decom-
position occurs in a single step up to 370 ◦C with loss of 74.49%
corresponding to the exothermic peak at 365 ◦C (DTA) or the broad
exotherm between 335 and 450 ◦C (DSC) attributed to the oxidation
of the organic matter. The total mass loss up to this step suggests
the formation of a mixture of Ni and NiO, as residue. The mass gain
observed between 370 and 650 ◦C, is attributed to oxidation of Ni to
NiO, although no exothermic event due to this oxidation is observed
in DTA curve, probably because the oxidation occurs through a slow
process and the heat evolved is not enough to procedure the ther-
mal event. The total mass loss up to 650 ◦C is in agreement with the
formation of NiO, as final residue (Calcd. = 70.33%; TG = 70.68%) and
confirmed by X-ray powder diffractometry.
(DTA) or the broad exotherm between 380 and 475 ◦C (DSC)
attributed to oxidation of the organic matter. The total mass loss
up to 435 ◦C is in agreement with the formation of ZnO, as final
residue (Calcd. = 61.88%; TG = 61.77%) and confirmed by X-ray pow-
der diffractometry.
Although the copper and zinc compound were obtained in anhy-
drous state the thermal decomposition of nickel, copper and zinc
compound are in agreement with the literature [9]. Small difference
in the TG–DTA profiles and the temperatures of thermal decom-
position undoubtedly were due to different condition used for
obtaining these curves.
4. Conclusion
From TG–DTA, complexometry and elemental analysis data, a
general formula could be established for the compounds involving
some bivalent metal ions and tartrate. The X-ray powder patterns
pointed out that the synthesized compounds have a crystalline
structure, without evidence concerning the formation of isomor-
phous series. The infrared spectroscopic data suggest that both
carboxylic and alcoholic group act as coordination sites.
The TG–DTA and DSC curves provided previously unreported
information about the thermal stability and thermal decomposition
of these compounds.
Copper compound: The simultaneous TG–DTA and DSC curves
are shown in Fig. 6. These curves show that the compound is anhy-
drous and stable up to 205 ◦C. Above this temperature the thermal
decomposition occurs in a single step up to 280 ◦C with loss of
65.84%, corresponding to the exothermic peak at 270 ◦C (DTA) or
the broad exotherm between 220 and 390 ◦C (DSC) attributed to
oxidation of the organic matter. The mass loss up to this step is in
agreement with the formation of Cu2O as residue (Calcd. = 66.19%;
TG = 65.84%).
Acknowledgements
The authors thank UNESP Postdoctoral Program and FAPESP,
CNPQ, CAPES Foundations (Brazil) for financial support.
References
The mass gain observed between 280 and 500 ◦C is attributed
to the oxidation of Cu2O to CuO, and as already observed in
the nickel compound, no exothermic event due to this oxida-
tion is also observed in the DTA curve. The total mass loss up
to 500 ◦C is in agreement with the formation of CuO as final
residue (Calcd. = 62.41%; TG = 62.27%) and confirmed by X-ray pow-
der diffractometry.
Zinc compound: The simultaneous TG–DTA and DSC curves are
shown in Fig. 7. These curves also show that the compound is
anhydrous and stable up to 325 ◦C. Above this temperature the
thermal decomposition occurs in a single step up to 435 ◦C, with
loss of 61.77% corresponding to the exothermic peak at 415 ◦C
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