Synthesis, characterisation and thermal behaviour of solid state compounds of 4-methylbenzylidenepyruvate with some bivalent metal ions

Article abstract of DOI:10.1016/S0040-6031(02)00498-7

Solid state M-4-Me-BP compounds, where M stands for bivalent Mn, Fe, Co, Ni, Cu, Zn, Pb and 4-Me-BP is 4-methylbenzylidenepyruvate, have been synthesized. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorime

Full text of DOI:10.1016/S0040-6031(02)00498-7

Thermochimica Acta 400 (2003) 187–198
Synthesis, characterisation and thermal behaviour of solid
state compounds of 4-methylbenzylidenepyruvate
with some bivalent metal ions
I.A. Petroni, F.L. Fertonani, C.B. Melios, M. Ionashiro∗
Instituto de Qu´ımica, UNESP, C.P. 355, CEP 14801-970, Araraquara, SP, Brazil
Received 5 June 2002; received in revised form 26 September 2002; accepted 29 September 2002
Abstract
Solid state M-4-Me-BP compounds, where M stands for bivalent Mn, Fe, Co, Ni, Cu, Zn, Pb and 4-Me-BP is 4-methylben-
zylidenepyruvate, have been synthesized. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), differen-
tial scanning calorimetry (DSC), X-ray powder diffractometry, infrared spectroscopy, elemental analysis, and complexometry
were used to characterise and to study the thermal behaviour of these compounds. The results led to information about the
composition, dehydration, thermal stability and thermal decomposition of the isolated complexes.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Bivalent metals; 4-Methylbenzylidenepyruvate; Coordination sites; Thermal behaviour
1. Introduction
λmax), associated with 1:1 complex species, analyt-
ical applications of the ligands, e.g., in gravimetric
analysis and as metallochromic indicators, while in
the solid state, the establishment of the stoichiometry
and detailed knowledge of the thermal behaviour of
the ligands and their metal-ion compounds have been
the main purposes of these studies.
Synthesis of benzylidenepyruvic acid (HBP), as
well as of phenyl-substituted derivatives of HBP, have
been reported [1,2]. These acids are of continuing
interest as intermediates in pharmacological, indus-
trial and chemical syntheses, in the development of
enzyme inhibitors and drugs, as model substrates of
enzymes, and in other ways [2–7].
Preparation and investigation of several metal-ion
complexes of phenyl-substituted derivatives of BP,
have been carried out in aqueous solutions [8–11],
and in the solid state [12–18]. In aqueous solutions,
these works reported mainly the thermodynamic
In the present paper, solid state compounds of bi-
valent manganese, iron, cobalt, nickel, copper, zinc
and lead with 4-methylbenzylidenepyruvate (4-CH3–
−
=
C6H4–CH CH–COCOO ) were prepared. The com-
pounds were investigated by complexometry, elemen-
tal analysis, X-ray powder diffractometry, infrared
spectroscopy, simultaneous thermogravimetry-differ-
ential thermal analysis (TG-DTA) and differential
scanning calorimetry (DSC). The data provide in-
formation concerning the thermal stability and ther-
mal decomposition of these compounds in the solid
state.
stability (β1) and spectroscopic parameters (ε1 max
,
∗
Corresponding author. Tel.: +55-16201-6617;
fax: +55-16222-7932.
E-mail address: massaoi@iq.unesp.br (M. Ionashiro).
0040-6031/03/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0040-6031(02)00498-7

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I.A. Petroni et al. / Thermochimica Acta 400 (2003) 187–198
2. Experimental
cator over anhydrous calcium chloride, under reduced
pressure (103 Pa), to constant mass.
In the solid state compounds, metal ions, water
and 4-Me-BP contents were determined from the TG
curves. The metal ions were also determined by com-
plexometry with standard EDTA solution [20,21] after
igniting the compounds to the respective oxides and
their dissolution in hydrochloric or nitric acid.
Simultaneous TG-DTA and DSC curves were ob-
tained with two thermal analysis systems, models SDT
2960 and DSC 2010, both from TA Instruments. The
purge gas was an air flow of 150 ml min−1. A heat-
ing rate of 10 ◦C min−1 was adopted, with samples
weighing about 7–8 mg. Alumina and aluminium cru-
cibles, the latter with perforated covers, were used for
TG-DTA and DSC, respectively.
The sodium salt of 4-methylbenzylidenepyruvic
acid (4-Me-BP) was prepared from 4-methylbenzal-
dehyde and sodium pyruvate in the presence of an
alkaline catalyst as described in the literature [19].
Aqueous solutions of the bivalent metal ions were
prepared by dissolving the corresponding chlorides,
except for lead, where the nitrate was used.
The solid state compounds were prepared by adding
slowly, with continuous stirring, the ligand solution
to the respective metal-ion solutions until complete
precipitation of the metal ions. 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.
Carbon and hydrogen contents were determined by
microanalytical procedures, with an EA1110 CHNS-0
Elemental Analyser from CE Instruments.
The precipitates were washed until chloride (or ni-
trate) ions were eliminated, filtered through and dried
on Whatman no. 42 filter paper and kept in a desic-
Table 1
Analytical data for the ML2·nH2O compoundsa
M (%)
L (lost) (%)
H2O (%)
Calcd.
C (%)
Calcd.
H (%)
Calcd.
Final residue
Calcd.
EDTA
TG
Calcd.
TG
TG
7.70
7.59
7.63
10.90
7.41
10.80
–
EA
EA
MnL2·2H2O
FeL2·2H2O
CoL2·2H2O
NiL2·3H2O
CuL2·2H2O
ZnL2·3H2O
PbL2
11.70
11.88
12.45
11.95
13.30
13.13
34.38
11.35
11.54
11.93
11.95
13.70
12.96
35.35
11.81
11.90
12.34
12.02
13.61
13.10
35.30
76.05
75.36
76.56
73.78
75.82
72.80
61.89
75.93
75.18
76.74
73.80
75.90
72.90
61.95
7.68
7.66
7.61
11.01
7.54
10.86
–
56.29
56.18
55.82
53.79
55.28
53.07
45.12
56.52
56.67
55.86
53.41
56.03
52.59
45.06
4.73
4.72
4.69
4.94
4.65
4.87
3.10
4.65
4.66
4.72
4.16
4.33
4.46
3.26
Mn3O4
Fe2O3
CoO
NiO
CuO
ZnO
PbO
a M: metal; L: 4-methylbenzylidenepyruvate.
Table 2
Spectroscopic data for sodium 4-methylbenzylidenepyruvate (4-Me-BP) and compounds with some bivalent metal ionsa
νas(COO−)b (cm−1
)
ꢀνas(COO−)c
νsym(COO−) (cm−1
)
ν(C O) (cm−1
)
ꢀν(C O)
b
d
e
=
=
Compound
4Me-BP-Na·0.5H2O
Mn(4Me-BP)2·2H2O
Fe(4Me-BP)2·2H2O
Co(4Me-BP)2·2H2O
Ni(4Me-BP)2·3H2O
Cu(4Me-BP)2·2H2O
Zn(4Me-BP)2·3H2O
Pb(4Me-BP)2
1635s; 1605s
1635s; 1601s
1635s; 1594s
1635s; 1590s
1585s; 1563s
1564s
–
0; 4
1411m
1413m
1407m
1407m
1400m
1384m
1409m
1397m
1673m
1673sh
1667sh
1664sh
1645s
1623m
1631sh
1626sh
–
0
6
0; 11
0; 15
50; 42
71
46; 42
37; 43
9
28
50
42
47
1589s; 1563s
1598s; 1562s
a s: strong, m: medium, sh: shoulder.
b νsym(COO−) and νas(COO−): symmetrical and anti-symmetrical vibrations of the COO− group, respectively.
c νas(COO−) (Na salt) − νas(COO−) (metal complex).
d Ketonic carbonyl stretching frequency.
e
=
=
ν(C O) (Na salt) − ν(C O) (metal complex).

I.A. Petroni et al. / Thermochimica Acta 400 (2003) 187–198
189
X-ray powder patterns were obtained with a
3. Results and discussion
Siemens D-500 X-ray diffractometer using Cu K␣
radiation (λ = 1.544 Å) and settings of 40 kV and
20 mA.
Infrared spectra for 4-Me-BP (sodium salt) as
well as for its metal-ion compounds, were run on a
Nicolet model Impact 400 FT-IR instrument, within
the 4000–400 cm−1 range. The solid samples were
pressed into KBr pellets.
The analytical and thermoanalytical (TG) data are
shown in Table 1. These results establish the stoi-
chiometry of these compounds, which are in agree-
ment with the general formula: M(4-Me-BP)2·nH2O,
where M represents Mn(II), Fe(II), Co(II), Ni(II),
Cu(II), Zn(II) or Pb(II), 4-Me-BP is 4-methylbenzyli-
denepyruvate and n = 0, 2 or 3.
Fig. 1. X-ray powder diffraction patterns of (a) Mn(4-Me-BP)2·2H2O, (b) Fe(4-Me-BP)2·2H2O, (c) Co(4-Me-BP)2·2H2O, (d)
Ni(4-Me-BP)2·3H2O, (e) Cu(4-Me-BP)2·2H2O, (f) Zn(4-Me-BP)2·3H2O and (g) Pb(4-Me-BP)2.

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The X-ray diffraction powder patterns (Fig. 1) show
most informative in attempting to assign coordination
sites.
that all the compounds have a crystalline structure,
without evidence of the formation of isomorphous
series.
Infrared spectroscopic data on 4-methylbenzylide-
nepyruvate and its compounds with the metal ions
considered in this work are shown in Table 2. The
investigation was focused mainly within the 1700–
1400 cm−1 range because this region is potentially
In 4-Me-BP (sodium salt), strong doublet bands
(at 1635 and 1605 cm−1) and a medium intensity
band located at 1411 cm−1 are attributed to the
anti-symmetrical and symmetrical frequencies of the
carboxylate groups, respectively [22,23]. The band
centered at 1673 cm−1 is typical of a conjugated ke-
tonic carbonyl group [22–24]. This is in line with the
Fig. 2. TG-DTA and DSC curves of Mn(4-Me-BP)2·2H2O (m = 7.191 and 6.521 mg, respectively).

I.A. Petroni et al. / Thermochimica Acta 400 (2003) 187–198
191
observed carbonyl stretching frequency for s-trans-
benzylidene acetone (i.e., 1674 cm−1) [23].
coordination centres in the metal compounds [24,25].
The data displayed in Table 2 show that these shifts
are dependent on the metal ions and the magnitudes of
the shifts follow the well-known Irving–Williams or-
der: Mn(II) < Fe(II) < Co(II) < Ni(II) < Cu(II) >
Zn(II). Overall, the information conveyed by the in-
frared spectra is in line with that gathered for the
1:1 complexes of the same ligand with several metal
ions in aqueous solution, where linear free energy
Except for the Cu(II) compound, the doublet bands
assigned to the anti-symmetrical stretching carboxy-
late frequencies are retained in the complexes. Both
these bands as well as that assigned to the ketonic
carbonyl are shifted to lower values relative to the
corresponding frequencies in 4-Me-BP itself (sodium
salt). This behaviour indicates that both groups act as
Fig. 3. TG-DTA and DSC curves of Fe(4-Me-BP)2·2H2O (m = 7.643 and 7.604 mg, respectively).

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I.A. Petroni et al. / Thermochimica Acta 400 (2003) 187–198
Fig. 4. TG-DTA and DSC curves of Co(4-Me-BP)2·2H2O (m = 7.638 and 7.899 mg, respectively).
relationships, also suggest the –COCOO− moiety as
the bidentate metal binding site of 4-Me-BP [11].
Simultaneous TG-DTA and DSC curves of the com-
pounds are shown in Figs. 2–8. The TG-DTA curves
show mass losses in three, four or six steps, corre-
sponding to endothermic peaks due to dehydration
and exothermic peaks attributed to the oxidation of
organic mater. The DSC curves, also show endother-
mic and exothermic peaks, corresponding to the mass
losses displayed by the TG curves. Small differences
observed concerning the peak temperatures obtained
by TG-DTA and DSC for the endothermic peaks 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 decom-
position (II) as shown by the TG-DTA curves, depend

I.A. Petroni et al. / Thermochimica Acta 400 (2003) 187–198
193
Fig. 5. TG-DTA and DSC curves of Ni(4-Me-BP)2·3H2O (m = 7.807 and 3.906 mg, respectively).
on the nature of the metal ion, and they follow the
order:
• Manganese compound. The simultaneous TG-DTA
curves and the DSC curve as well are shown in
Fig. 2. The first mass loss observed between 100
and 150 ◦C (TG), corresponding to an endother-
mic peak at 150 ◦C (DTA) and 160 ◦C (DSC) is
due to hydration water; it reflects the loss of 2H2O
(calcd. = 7.68%, TG = 7.70%). The thermal de-
composition of the anhydrous compound occurs in
two overlapping steps: between 150 and 380, and
380 and 520 ◦C, with losses of 30.54 and 45.39%,
(I) Ni > Zn > Co > Pb > Cu > Mn ≈ Fe
(II) Zn > Pb > Cu > Mn ≈ Co > Fe > Ni
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 below.

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I.A. Petroni et al. / Thermochimica Acta 400 (2003) 187–198
peak at 950 ◦C (DTA), is assigned to the reduction of
Mn2O3 to Mn3O4 (calcd. = 0.57%, TG = 0.63%)
and confirmed by X-ray powder diffractometry.
Literature reports on the thermal stability and re-
duction temperature of Mn2O3 are in disagreement
among themselves [26–28] and with the data ob-
tained in this work. This behaviour concerning man-
ganese oxides has already been pointed out [26]; it
is reported that the properties significantly depend
on the preparation conditions, structural properties
of the oxides and upon operational parameters dur-
ing the reduction step [26].
• Iron compound. The simultaneous TG-DTA and
DSC curves are shown in Fig. 3. The first mass
loss observed between 80 and 150 ◦C (TG), cor-
responding to endothermic peak at 150 ◦C (DTA)
and 155 ◦C (DSC) is due to dehydration with loss
of 2H2O (calcd. = 7.66%, TG = 7.59%). Im-
mediately after the dehydration, the anhydrous
compounds show mass losses in three overlapping
steps: between 150 and 180 ◦C (6.27%), 180 and
350 ◦C (24.36%), and 350 and 480 ◦C (44.55%),
corresponding to the exothermic peaks at 210 and
415 ◦C (DTA) and 200, 420 and 530 ◦C (DSC), at-
tributed to oxidation of Fe(II) to Fe(III) and of the
organic matter. The total mass loss up to 480 ◦C is in
agreement with the formation of Fe2O3 as the final
residue (calcd. = 83.02%, TG = 82.77%) which
was confirmed by X-ray powder diffractometry.
• Cobalt compound. The simultaneous TG-DTA and
DSC curves are shown in Fig. 4. The first mass
loss that occurs between 120 and 185◦C (TG), cor-
responding to endothermic peak at 180 ◦C (DTA)
or 190◦C (DSC), is due to dehydration with loss of
2H2O (calcd. = 7.61%, TG = 7.63%). The ther-
mal decomposition of the anhydrous compound
occurs in two overlapping steps: between 190 and
350, and 350 and 520 ◦C, with losses of 30.45 and
45.07%, respectively, corresponding to exother-
mic peaks at 340 and 470 ◦C (DTA) or the broad
exotherms between 220 and 600 ◦C, attributed to
the oxidation of the organic matter. The total mass
loss up to 520 ◦C is in agreement with the formation
of Co3O4 (calcd. = 83.04%, TG = 83.15%). The
last mass loss that occurs between 900 and 930 ◦C,
corresponding to the endothermic peak at 920 ◦C
(DTA), is attributed to reduction of Co3O4 to CoO
(calcd. = 1.18%, TG = 1.22%), in agreement with
Fig. 6. TG-DTA and DSC curves of Cu(4-Me-BP)2·2H2O
(m = 7.585 and 3.906 mg, respectively).
respectively, corresponding to the exothermic peaks
at 300 and 460 ◦C (DTA) or the broad exotherms
between 200 and >600 ◦C (DSC), which are at-
tributed to oxidation of the organic matter. The to-
tal mass loss up to 520 ◦C is in agreement with
the formation of Mn2O3 (calcd. = 83.76%, TG =
83.61%). The last mass loss observed between 920
and 980 ◦C, corresponding to the small endothermic

I.A. Petroni et al. / Thermochimica Acta 400 (2003) 187–198
195
Fig. 7. TG-DTA and DSC curves of Zn(4-Me-BP)2·3H2O (m = 7.159 and 5.626 mg, respectively).
the literature [29,30]. The X-ray powder pattern of
the residue obtained at 950 ◦C, is coincident with
that obtained for Co3O4, this is due to the reoxi-
dation reaction of CoO to Co3O4 which occurs on
cooling the former in an air atmosphere at room
temperature [29,30].
70 and 170 ◦C (TG), corresponding to endothermic
peak at 150 ◦C (DTA) or 165 ◦C (DSC), is due to
dehydration with loss of 3H2O (calcd. = 11.01%,
TG = 10.90%). The anhydrous compound is stable
up to 220 ◦C, and above this temperature the ther-
mal decomposition occurs in two consecutive steps:
between 220 and 295, and 295 and 425 ◦C with
losses of 29.45 and 44.35%, respectively. These
• Nickel compound. The TG-DTA and DSC curves are
shown in Fig. 5. The mass loss that occurs between

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I.A. Petroni et al. / Thermochimica Acta 400 (2003) 187–198
Fig. 8. TG-DTA and DSC curves of Pb(4-Me-BP)2 (m = 7.141 and 7.102 mg, respectively).
mass losses correspond to exothermic peaks at 280
to 130 ◦C (TG), with evidence of two consecutive
steps, corresponding to an endothermic peak at
120◦C (DTA) (Fig. 6), or 100 and 130 ◦C (DSC),
is due to dehydration with loss of 2H2O (calcd. =
7.54%, TG = 7.41%). Aiming at a closer exami-
nation of the dehydration process, TG-DTA curves
were obtained up to 150 ◦C in static air atmo-
sphere, sample mass: 5.387 mg, and heating rate
of 2 ◦C min−1 (Fig. 6). These curves confirmed
and 400 ◦C (DTA) or the broad exotherms between
220 and >600 ◦C (DSC), attributed to oxidation
of the organic matter. The total mass loss up to
425 ◦C, is in agreement with the formation of NiO
as final residue (calcd. = 84.79%, TG = 84.70%),
and confirmed by X-ray powder diffractometry.
• Copper compound. The TG-DTA and DSC curves
are shown in Fig. 6. The mass loss observed up

I.A. Petroni et al. / Thermochimica Acta 400 (2003) 187–198
197
that the dehydration occurs in two steps: between
30 and 60, and 75 and 100 ◦C, corresponding to
endothermic peaks at 55 and 95 ◦C; dehydration in
two steps is also pointed out by the DSC curve.
The anhydrous compound is stable up to 170 ◦C,
and above this temperature the thermal decom-
position occurs in four consecutive and/or over-
lapping steps with losses of 9.02% (170–220 ◦C),
8.97% (220–240 ◦C), 21.31% (240–320 ◦C) and
36.60% (320–530 ◦C). These mass losses corre-
spond to exothermic peaks at 190, 220, 260 and
430 ◦C (DTA), although the DSC curve shows
five exothermic peaks (160–320 ◦C) and a large
exotherm between 320 and 600 ◦C. The total mass
loss up to 530 ◦C is in agreement with the forma-
tion of CuO as the final residue (calcd. = 83.36%,
TG = 83.31%), which was confirmed by X-ray
powder diffractometry.
TG = 61.95%); this was further confirmed by
X-ray powder diffractometry.
4. Conclusion
From TG, complexometry and elemental analysis
data, a general formula could be established for the
binary compounds involving some bivalent metal ions
and 4-Me-BP. The X-ray powder patterns pointed out
that the synthesized compounds have a crystalline
structure, without evidence concerning the formation
of isomorphous series. The infrared spectroscopic
data suggest that 4-Me-BP acts as a bidentate ligand
towards the metal ions considered in this work.
The TG-DTA and DSC curves, provided previously
unreported information about the thermal stability and
thermal decomposition of these compounds.
• Zinc compound. The TG-DTA and DSC curves are
shown in Fig. 7. The mass loss observed between 70
and 130 ◦C (TG), corresponding to the endothermic
peak at 120 ◦C (DTA) or 130 ◦C (DSC), is due to hy-
dration water with loss of 3H2O (calcd. = 10.86%,
TG = 10.80%). The anhydrous compound is stable
up to 195 ◦C, and above this temperature the thermal
decomposition occurs in two overlapping steps with
mass losses of 28.84% (195–395 ◦C) and 44.06%
(395–550 ◦C), corresponding to exothermic peaks
at 380 and 460 ◦C (DTA) or the exotherms between
300 and >600 ◦C (DSC), attributed to oxidation of
organic matter. The total mass loss up to 550 ◦C is
in agreement with the formation of ZnO, as the fi-
nal residue (calcd. = 83.66%, TG = 83.70%); this
was confirmed by X-ray powder diffractometry.
• Lead compound. The TG-DTA and DSC curves
are shown in Fig. 8. These curves show that this
compound was obtained in the anhydrous state and
it is stable up to 180 ◦C. Above this temperature
up to 535 ◦C, the TG-DTA curves suggest mass
losses in four overlapping steps, while the DSC
curve suggests five steps. The mass loss that oc-
curs between 180 and 305 ◦C (18.28%), and 305
and 535 ◦C (43.67%), corresponding to exothermic
peaks at 220, 250, 300 and 510 ◦C (DTA) or 200,
250, 305, 460 and >600 ◦C (DSC), are attributed
to oxidation of the organic matter. The total mass
loss up to 535 ◦C, is in agreement with the forma-
tion of PbO, as the final residue (calcd. = 61.89%,
Acknowledgements
The authors thank FAPESP (Procs. 97/12646-8 and
98/12794-0) and CNPq Foundations (Brazil) for finan-
cial support and Ms. Rosemary Camargo for aid in the
preparation of this compuscript.
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