Synthesis, characterization and thermal behaviour of solid-state compounds of 4-methoxybenzoate with some bivalent transition metal ions

Article abstract of DOI:10.1007/s10973-005-0058-2

Solid-state M-4-MeO-Bz compounds, where M stands for bivalent Mn, Co, Ni, Cu and Zn and 4-MeO-Bz is 4-methoxybenzoate, have been synthesized. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), X-

Full text of DOI:10.1007/s10973-005-0058-2

Journal of Thermal Analysis and Calorimetry, Vol. 79 (2005) 323–328
SYNTHESIS, CHARACTERIZATION AND THERMAL BEHAVIOUR OF
SOLID-STATE COMPOUNDS OF 4-METHOXYBENZOATE WITH SOME
BIVALENT TRANSITION METAL IONS
E. C. Rodrigues, A. B. Siqueira, E. Y. Ionashiro, G. Bannach and M. Ionashiro*
Instituto de Química, UNESP, C. P. 355, CEP 14801 – 970 Araraquara, SP, Brazil
Solid-state M-4-MeO-Bz compounds, where M stands for bivalent Mn, Co, Ni, Cu and Zn and 4-MeO-Bz is 4-methoxybenzoate,
have been synthesized. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorime-
try (DSC), X-ray powder diffractometry, infrared spectroscopy, elemental analysis and complexometry were used to characterize
and to study the thermal behaviour of these compounds. The results led to have information about the composition, dehydration,
thermal stability and thermal decomposition of the isolated compounds.
Keywords: bivalent transition metals, 4-methoxybenzoate, thermal behaviour
Introduction
methoxybenzoates of heavy lanthanides and yttrium us-
ing elemental analysis, IR spectroscopy, thermo-
gravimetric studies and X-ray diffraction measurements.
Ionashiro et al. [11, 12] reported the thermal studies on
solid compounds of phenyl substituted derivatives of
benzylidenepyruvates with several metal ions.
In the present paper, solid-state compounds of
Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with
4-methoxybenzoate were prepared and investigated
using complexometric titration, elemental analysis,
X-ray powder diffractometry, infrared spectroscopy,
differential scanning calorimetry (DSC) and simulta-
neous thermogravimetry-differential thermal analysis
(TG-DTA). The results allowed us to acquire infor-
mation concerning these compounds in the solid-
state, including their thermal stability and thermal
decomposition.
Several metal-ion salts of benzoic acid, as well as
some benzoic acid derivatives, have been investigated
in aqueous solutions and in solid-state.
In aqueous solutions, Yun et al. [1] reported the
thermodynamics of complexation of lanthanides by
some benzoic acid derivatives. Wang et al. [2] re-
ported the spectroscopic study of trivalent lanthanides
with several carboxylic acids, including benzoic acid.
Arnaud and Georges [3] described the influence of
pH, surfactant and synergic agent on the luminescent
properties of terbium chelates with benzoic acid de-
rivatives. Choppin et al. [4] reported the thermody-
namic of complexation of lanthanides by benzoic and
isophthalic acids. Lam et al. [5] described the synthe-
sis, crystal structure and photophysical and magnetic
properties of dimeric and polymeric lanthanide com-
plexes with benzoic acid and its derivatives.
In the solid-state, Wendlandt synthesized and re-
ported the thermal stability and thermal decomposi-
tion of thorium salts with several organic acids, in-
cluding 4-methoxybenzoic acid [6], as well as ben-
zoic and m-hydroxybenzoic acids [7].
Glowiack et al. [8] reported the reaction of bivalent
copper, cobalt and nickel with 3-hydroxy-4-methoxy
and 3-methoxy-4-hydroxybenzoic acids and a structure
for these compounds has been proposed on the basis of
spectroscopic and thermogravimetric data. Brzyska and
Karasinski [9] described the thermal decomposition of
thorium salts of benzoic and 4-methoxybenzoic acids in
air atmosphere. Ferenc and Walkow-Dziewulska [10]
wrote about the synthesis and characterization of 2,3-di-
Experimental
The 4-methoxybenzoic acid (4-MeO-Bz) 98% was ob-
tained from Acros organics and purified by re-
crystallization. Thus, aqueous suspension of 4-MeO-Bz
was heated near ebullition until total dissolution and
cooled to ambient temperature. The crystal in needle
form was isolated and after kept in dry in a plastic flask.
The hydrated basic carbonates of Mn(II), Co(II), Ni(II),
Cu(II) and Zn(II) were prepared by adding slowly with
continuous stirring satured sodium carbonate solution to
the corresponding metal chloride solutions, sulphate for
copper, until total precipitation of the metal ions. The
precipitates were washed with distilled water until elim-
*
Author for correspondence: massaoi@iq.unesp.br
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2005 Akadémiai Kiadó, Budapest

RODRIGUES et al.
ination of chloride or sulphate ions and maintained in an
aqueous suspension.
Solid-state Mn(II), Co(II), Ni(II), Cu(II) and
bles, the latter with perforated covers, were used for
TG-DTA and DSC, respectively.
Zn(II) compounds were prepared by mixing the corre-
sponding metal basic carbonates with 4-methoxyben-
zoic acid, in slight excess. The aqueous suspension
was heated slowly up to near ebullition, until total
neutralization of the respective basic carbonates. The
resulting solutions after cooling were maintained in
an ice bath to recrystallize the acid in excess and fil-
tered through a Whatman nº 40 filter paper. Thus, the
aqueous solutions of the respective metal-4-methoxy-
benzoates were evaporated in a water bath until near
dryness and kept in a desiccator over anhydrous cal-
cium chloride. All attempts to synthesize the iron(II)
compound were unsuccessful, due to the oxidation re-
action of Fe(II) to Fe(III) during the drying of the
compound, even by using nitrogen atmosphere.
In the solid-state compounds, metal ions, water and
4-methoxybenzoate contents were determined from TG
curves. The metal ions were also determined by
complexometry with standard EDTA solution [13, 14]
after igniting the compounds of the respective oxides
and their dissolution in hydrochloric acid solution. Car-
bon and hydrogen contents were determined by micro-
analytical procedures, with an EA 1110 CHNS-O Ele-
mental Analyzer from CE Instruments.
Results and discussion
The analytical data are shown in Table 1. These re-
sults establish the stoichiometry of these compounds,
which are in agreement with the general formula
ML2×nH2O, where M represents Mn(II), Co(II),
Ni(II), Cu(II) or Zn(II), L is 4-methoxybenzoate and
n=2; 2; 3.5; 3 and 1.75, respectively. The X-ray dif-
fraction powder patterns (Fig. 1) show that all the
compounds have a crystalline structure, without evi-
dence for formation of an isomorphous series.
X-ray powder patterns were obtained with a
SIEMENS D-500 X-ray diffractometer using CuKa ra-
diation (l=1.544 Å) and setting of 40 kV and 20 mA.
Infrared spectra for sodium 4-methoxybenzoate
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.
Fig. 1 X-ray powder diffraction patterns of the compounds:
a – MnL2×2H2O; b – CoL2×2H2O; c – NiL2×3.5H2O;
d – CuL2×3H2O; e – ZnL2×1.75H2O
Infrared spectroscopic data on 4-methoxybenzoate
and its compounds with the bivalent metal ions consid-
ered in this work are shown in Table 2. The investiga-
tion was focused mainly within the 1700–1400 cm–1
range because this region is potentially most informative
to assign coordination sites. In sodium 4-methoxy-
benzoate, strong band at 1543 cm–1 and a medium inten-
Simultaneous TG-DTA and DSC curves were
obtained 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
heating rate of 20°C min–1 was adopted with samples
weighing about 7 mg. Alumina and aluminium cruci-
Table 1 Analytical, thermoanalytical (TG) and elemental analysis data of the compounds, ML2·nH2O
Metal/%
EDTA
L loss/%
Water/%
Carbon/%
calcd EA
Hydrogen/%
calcd EA
Compounds
Mn(L)2·2H2O
Residuea
calcd
TG
calcd
TG
calcd
TG
b
13.97
13.97
14.83
13.84
15.13
13.79
13.79
15.20
13.90
14.88
16.01
14.18
13.70
14.52
13.76
15.21
16.61
71.44
70.77
70.73
67.51
68.18
71.71
71.08
71.08
71.08
9.16
9.16
9.07
9.28 48.86 48.54 4.62
9.28 48.86 48.54 4.62
9.08 48.37 48.77 4.58
4.85 Mn3O4
4.85 Mn2O3
b
c
Co(L)2·2H2O
Ni(L)2·3.5 H2O
Cu(L)2·3H2O
4.38
5.12
5.02
4.23
Co3O4
NiO
67.60 14.87 14.89 45.31 46.04 5.00
68.08 12.87 12.99 45.76 45.52 4.81
CuO
ZnO
Zn(L)2·1.75H2O 16.38
71.33
7.90
7.99 48.13 48.53 4.43
L – means 4-methoxybenzoate
aall the residues was confirmed by X-ray powder diffractometry; bmixture of Mn3O4 and Mn2O3; cCo3O4 up to 800°C
324
J. Therm. Anal. Cal., 79, 2005

SOLID-STATE COMPOUNDS OF 4-METHOXYBENZOATE WITH SOME BIVALENT TRANSITION METAL IONS
Table 2 Spectroscopic data for sodium 4-methoxybenzoate and compounds with some bivalent metal ions. IR spectra/cm–1
Compound
nOH(H2O)
nasymCOO–
nsymCOO–
Na4MeO-Bz
3383 br
3472 br
3179 br
3469 br
3167 br
3547 br
1543 s
1533 s
1562 m
1547 s
1531 s
1560 m
1416 m
1408 s
1421 m
1439 s
1435 s
1412 s
Mn(4MeO-Bz)2·2H2O
Co(4MeO-Bz)2×2H2O
Ni(4MeO-Bz)2·3.5H2O
Cu(4MeO-Bz)2·3H2O
Zn(4MeO-Bz)2·1.75H2O
br – broad; m – medium; s – strong; 4MeO-Bz=4-methoxybenzoate; nOH=hydroxyl group stretching frequency; nsym COO– and
nasymCOO–=symmetrical and anti-symmetrical vibrations of the COO– structure.
sity band located at 1416 cm–1 are attributed to the anti-
symmetrical and symmetrical frequencies of the
carboxylate groups, respectively [15, 16]. The manga-
nese, cobalt, nickel, copper and zinc compounds, pre-
sented practically the same symmetrical and anti-sym-
metrical vibrations of the COO– groups, when compared
with the sodium salt, suggesting that the compounds
have ionic character. The data displayed in Table 2
show that these shifts are dependent on the metal ions
and the magnitudes of the shifts do not follow the
well-known Irving–Williams series.
peaks due to dehydration and the exothermic peaks
attributed to oxidation of the organic matter. In all the
TG-DTA curves, the final mass loss profile shows
that the sample temperature is greater than the oven
temperature, indicating that the oxidation of the or-
ganic matter is accompanied by the combustion.
The thermal stability of the anhydrous com-
pounds (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 follow
the order:
Simultaneous TG-DTA curves of the com-
pounds are shown in Figs 2–4. These curves show
mass losses in steps, corresponding to endothermic
(I) Mn»Zn>Cu>Co>Ni
(II) Zn>Co>Mn>Ni>Cu
Fig. 2 TG-DTA curves of MnL2·2H2O
(L=4-methoxybenzoate) m=7.1425 mg
Fig. 4 TG-DTA of NiL2·3.5H2O
(L=4-methoxybenzoate) m=7.0521 mg
The thermal behaviour of the compounds is heavi-
ly dependent on the nature of the metal ion and so the
features of each compound are discussed individually.
Manganese compound
The simultaneous TG-DTA curves are shown in Fig. 2.
These curves show mass losses in three steps between
80 and 456°C and thermal events corresponding to these
losses. The first mass loss observed between 80 and
150ºC, corresponding to an endothermic peak at 139ºC
is due to dehydration with loss of 2H2O (calcd.=9.16%;
Fig. 3 TG-DTA curves of the Co(L)2·2H2O
(L=4-methoxybenzoate) m=7.1170 mg
J. Therm. Anal. Cal., 79, 2005
325

RODRIGUES et al.
TG=9.28%). The thermal decomposition of the anhy-
(calcd.=82.38%; TG=82.49%) and confirmed by
X-ray powder diffractometry.
drous compound occurs in two overlapping steps be-
tween 240–390°C, and 390–456°C, with losses of
32.70% and 38.38%, respectively, corresponding to the
exothermic peak at 456°C. The profiles of the TG and
DTA curves, in these steps show that the oxidation of
the organic matter is accompanied by combustion. The
total mass loss up to 456ºC is in agreement with the for-
mation of Mn3O4 or Mn2O3 as final residue
Copper compound
The TG-DTA curves are shown in Fig. 5. These
curves show mass losses in four steps between 70
and 415°C and thermal events corresponding to these
losses. The first mass loss observed between 70
and 120°C, corresponding to the endothermic peak
at 105°C is due to dehydration with loss of 3H2O
(calcd.=12.87%; TG=12.99%). The anhydrous com-
pound is stable up to 235ºC, and above this tempera-
ture the thermal decomposition occurs in three steps
with losses of 14.50% (235–262°C), 21.76%
(262–350°C) and 31.82% (350–415°C), correspond-
ing to exothermic peaks at 278°C, 319°C and 415°C,
respectively, attributed to the oxidation of the organic
matter and for the last step oxidation and combustion
of the carbonaceous material. The total mass loss up
to 415°C is in agreement with the formation of CuO,
as final residue (calcd.=81.05%; TG=81.07%), and
confirmed by X-ray powder diffractometry.
(calcd.=80.60%
–
Mn3O4, 79.93%
–
Mn2O3;
TG=80.36%). The X-ray powder diffractometry showed
that the final residue of the thermal decomposition is a
mixture of Mn3O4 and Mn2O3.
Cobalt compound
The TG-DTA curves are shown in Fig. 3. The mass
loss observed between 30 and 170°C corresponding to
endothermic peaks at 120and 160°C is due to dehydra-
tion that occurs in two steps, with loss of 1H2O in each
step (calcd.=9.07%; TG=9.08%). After dehydration,
the thermal decomposition of the anhydrous compound
occurs in a single step between 170 and 460°C, with
loss of 71.08%, corresponding to exothermic peak at
455°C, attributed to oxidation and combustion of the
organic substance. The total mass loss up to 460°C is
in agreement with the formation of Co3O4, as final resi-
due (calcd.=79.82%; TG=80.16%) and confirmed by
X-ray powder diffractometry. The small endothermic
peak at 290°C is attributed to the fusion of the com-
pound. The last mass loss that occurs between 900 and
930°C corresponding to the endothermic peak at
920°C, is attributed to reduction of Co3O4 to CoO, as
already observed during the thermal decomposition of
the cobalt 4-methylbenzylidenepyruvate [17].
Fig. 5 TG-DTA curves of the Cu(L)2·3H2O
(L=4-methoxybenzoate) m=7.0498 mg
Nickel compound
The TG-DTA curves are shown in Fig. 4. The mass
loss that occurs between 100 and 160ºC, correspond-
ing to the endothermic peak at 143ºC, is due to dehy-
dration with loss of 3.5H2O (calcd.=14.87%;
TG=14.89%). Immediately after the dehydration, the
anhydrous compound shows mass loss that begins
with a slow process (up to 320ºC), followed by a fast
process to give the oxide level beginning at 430°C,
with losses of 5.60 and 62.00%, respectively, corre-
sponding to the exothermic event with two peaks at
410 and 415°C, attributed to the oxidation and com-
bustion of the organic matter. In both temperatures
(410 and 415°C), the anomaly observed in the
TG-DTA curves is due to the combustion of the or-
ganic matter, where the sample temperature exceed
the oven's one. The total mass loss up to 430°C, is in
agreement with the formation of NiO as final residue
Zinc compound
The TG-DTA curves are shown in Fig. 6. The mass
loss observed between 100 and 200°C, corresponding
to the endothermic peaks at 120 and 180°C is attrib-
uted to dehydration with loss of 0.75 and 1H2O, re-
spectively (calcd.=7.90%; TG=7.99%). After dehy-
dration the anhydrous compound shows mass loss in
two overlapping steps with losses of 17.58%
(240–350°C) and 53.75% (350–470°C), correspond-
ing to exothermic peak at 335 and 450°C, attributed to
oxidation of organic matter and oxidation followed by
combustion of the carbonaceous residue, respec-
tively. The total mass loss up to 470°C is in agreement
with the formation of ZnO, as final residue
(calcd.=79.61%; TG=79.32%).
326
J. Therm. Anal. Cal., 79, 2005

SOLID-STATE COMPOUNDS OF 4-METHOXYBENZOATE WITH SOME BIVALENT TRANSITION METAL IONS
The temperature range and the percentage mass
loss observed in each step of the thermal decomposi-
tion are shown in Table 3.
The DSC curves of the compounds are shown in
Fig. 7 These curves show endothermic and exothermic
peaks that all accord with the mass losses observed in
TG curves. The endothermic peaks are in the range
110–160°C (Mn); 105–140 and 140–170°C (Co);
110–180°C (Ni); 85–150°C (Cu) and 105–150 and
150–195°C (Zn) is ascribed to dehydration. The dehy-
dration enthalpies found were: 111.2 kJ mol–1 (Mn);
16.3 kJ and 20.9 kJ mol–1 (Co); 144.7 kJ mol–1 (Ni);
118.3 kJ mol–1 (Cu); 10.4 kJ and 8.8 kJ mol–1 (Zn).
The endothermic peaks observed only for cobalt,
Fig. 6 TG-DTA curves of the ZnL2·1.75 H2O
nickel and zinc compounds are in the temperature range
of 275–305, 340–365 and 250–280°C, are ascribed to
(L=4-methoxybenzoate) m=7.2888 mg
Fig. 7 DSC curves of the compounds: a – MnL2·2H2O (5.4 mg); b – CoL2·2H2O (4.8 mg); c – NiL2·3.5H2O (5.3 mg);
d – CuL2·3H2O (5.6 mg) and e – ZnL2·1.75H2O (4.5 mg)
J. Therm. Anal. Cal., 79, 2005
327

RODRIGUES et al.
Table 3 Temperature ranges (DT), mass losses (%) and peak temperatures observed for each step of the TG-DTA curves of
the compounds, ML2·nH2O, where M=metal and L=4–methoxybenzoate
Steps
Compound
First
Second
Third
Fourth
Fusion
DT/°C
Loss/%
Peak/°C
80–150
9.28
139 (endo)
240–390
32.70
–
390–456
38.38
456 (exo)
–
–
–
–
–
–
MnL2·2H2O
CoL2·2H2O
NiL2·3.5H2O
CuL2·3H2O
ZnL2·1.75H2O
DT/°C
Loss/%
Peak/°C
30–170
9.08
120, 160 (endo)
170–460
71.08
455 (exo)
–
–
–
–
–
–
–
–
290 (endo)
DT/°C
Loss/%
Peak/°C
100–160
14.89
143 (endo)
160–320
5.60
–
320–430
62.00
410, 415 (exo)
–
–
–
–
–
–
DT/°C
Loss/%
Peak/°C
70–120
12.99
105 (endo)
235–262
14.50
278 (exo)
262–350
21.76
319 (exo)
350–415
31.82
415 (exo)
–
–
–
DT/°C
Loss/%
Peak/°C
100–200
7.99
120, 180 (endo)
240–350
17.58
335 (exo)
350–470
53.75
450 (exo)
–
–
–
–
–
270 (endo)
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Conclusions
From TG, complexometric titration and elemental
analysis data, a general formula could be established
for the binary compounds involving Mn(II), Co(II),
Ni(II), Cu(II) and Zn(II), and 4-methoxybenzoate.
The X-ray powder patterns pointed out that the
synthesized compounds have a crystalline structure
without evidence concerning the formation of iso-
morphous series.
The infrared spectroscopy data suggest that the
compounds considered in this work have an ionic
character.
The TG-DTA and DSC provided previously un-
reported information about the thermal stability and
thermal decomposition of these compounds.
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328
J. Therm. Anal. Cal., 79, 2005