Synthesis, characterization and thermal behaviour of solid-state compounds of europium(III) and gadolinium(III) 3-methoxybenzoate

Article abstract of DOI:10.1007/s10973-009-0281-3

Solid-state Ln-C₈H₇O₃ compounds, where Ln stands for Eu(III) and Gd(III) and C₈H₇O₃ is 3-methoxybenzoate, have been synthesized. Simultaneous thermogravimetry and differential thermal analy

Full text of DOI:10.1007/s10973-009-0281-3

J Therm Anal Calorim (2009) 97:765–768
DOI 10.1007/s10973-009-0281-3
Synthesis, characterization and thermal behaviour of solid-state
compounds of europium(III) and gadolinium(III)
3-methoxybenzoate
Patr ´ı cia R. Dametto Æ Beatriz Ambrozini Æ
Adriano B. Siqueira Æ Cl a´ udio T. Carvalho Æ
Massao Ionashiro
ICTAC2008 Conference
Ó Akad e´ miai Kiad o´ , Budapest, Hungary 2009
Abstract Solid-state Ln–C H O compounds, where Ln
8
powder diffractometry, infrared spectroscopy, simultaneous
TG-DTA, DSC, elemental analysis and complexometry.
7 3
stands for Eu(III) and Gd(III) and C H O is 3-methoxy-
7 3
8
benzoate, have been synthesized. Simultaneous thermo-
gravimetry and differential thermal analysis (TG-DTA),
differential scanning calorimetry (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 information about the composition, dehydration, thermal
stability and decomposition of the isolated compounds.
Experimental
The 3-methoxybenzoic acid (C H O ) with 99% purity was
8 8 3
obtained from Aldrich. Aqueous solution of Na–C H O
7 3
8
-
0.1 mol L was prepared from aqueous (C H O ) sus-
1
8
8 3
-
1
pension by adding sodium hydroxide solution 2.5 mol L
up to near total neutralization, followed by NaOH solution
-
0.1 mol L up to pH 8.7.
1
Keywords Eu(III) Á Gd(III) Á 3-Methoxybenzoate Á
Thermal behaviour
Europium(III) and gadolinium(III) chlorides were pre-
pared from the corresponding metal oxides by treatment
with concentrated hydrochloric acid. The resulting solu-
tions were evaporated to near dryness, the residues were
again dissolved in distilled water, transferred to a volu-
Introduction
-
1
Benzoic acid and some of its derivatives are used as pre-
servative, catalyst precursors, in pharmaceutical industries,
beyond other applications. A survey of the literature shows
that the complexes of rare earth elements with benzoic acid
and some of its derivatives have been investigated in solid
state. These works reported the thermal and spectral
behaviour on solid compounds of benzoates and its deriva-
tives with rare earth elements [1–8], the vibrational and
electronic spectroscopic study of lanthanides and effect of
sodium on the aromatic system of benzoic acid [9, 10].
In this work the 3-methoxybenzoates of europium(III) and
gadolinium(III) were synthesized and characterized by X-ray
metric flask and diluted in order to obtain ca. 0.1 mol L
solutions, whose pH were adjusted to 5.5 by adding diluted
sodium hydroxide or hydrochloric acid solutions.
The solid state compounds were prepared by adding
slowly, with continuous stirring, the aqueous solution of the
ligand (Na–C H O ) to the respective metal chloride until
8
7 3
total precipitation of the metal ions. The precipitates were
washed with distilled water until elimination of chloride ions,
filtered through and dried on Whatman no. 42 filter paper and
kept in a desiccator over anhydrous calcium chloride.
In the solid state compounds hydration water, ligand and
metal ion content were determined from TG curves. The
metal ions were also determined by complexometric titra-
tions with standard EDTA solution using xylenol orange as
indicator [11].
P. R. Dametto (&) Á B. Ambrozini Á A. B. Siqueira Á
C. T. Carvalho Á M. Ionashiro
X-ray powder patterns were obtained by using a SIE-
Instituto de Qu ´ı mica da Universidade Estadual Paulista
‘
‘J u´ lio de, Mesquita Filho’’, Araraquara, SP, Brazil
e-mail: pdametto@gmail.com
MENS D-5000 X-ray diffractometer employing Cu Ka
˚
radiation (k = 1.541 A) and setting of 40 kV and 20 mA.
123

7
66
P. R. Dametto et al.
Infrared spectra for Na–C H O as well as for its metal
8
7
3
(a)
ion compounds were run on a Nicolet model Impact 400
1
-
FT-IR Instrument, within the 4000–400 cm range. The
solid samples were pressed into KBr pellets.
Simultaneous TG-DTA curves and DSC curves were
obtained with two thermal analysis systems, models 2960
and Q10 both from TA Instruments, respectively. The
-
1
purge gas was an air flow of 100 mL min (TG-DTA) and
-
1
-1
5
0 mL min (DSC). A heating rate of 20 K min and
with samples weighing about 7 mg (TG-DTA) and about
mg (DSC). Alumina and aluminium crucibles, the latter
(b)
5
with perforated cover were used for TG-DTA and DSC,
respectively.
Carbon and hydrogen contents were determined by
microanalytical procedures, with an EA 1110 CHNS-O
Elemental Analyser from CE Instruments.
0
20
40
60
80
Results and discussion
2θ
The analytical and thermoanalytical (TG) results are shown
in 1. These results establish the stoichiometry of these
compounds, which are in agreement with the general
formula, Ln (C H O ) ÁnH O, where Ln represents euro-
Fig. 1 X-ray powder diffraction patterns of: (a) Eu(C
(b) Gd(C O. C = 3-methoxybenzoate
Á2H
8 7 3 3
H O ) ,
8 7 3
H O )
3
2
8 7 3
H O
8
7
3 3
2
pium(III) or gadolinium(III), C H O is 3-methoxybenzoate
8
7 3
and n = 2 (Gd).
Table 2 Spectroscopic data for sodium 3-methoxybenzoate and
compounds with lighter trivalent lanthanides
The X-ray diffraction powder patterns ( 1) show that
the europium(III) and gadolinium(III) compounds have a
crystalline structure, without evidence for formation of
isomorphous compounds.
Compound
m
(O–H)
(cm
H
)
2
O mas(COO
-
)
sym(COO )
m - Dm(mas - msym)
-1
-
1
-1
-1
(cm
)
(cm
)
(cm )
Na(C
Eu(C
Gd(C
8
H
7
O
3
)
–
1568
1529
1537
s
s
s
1402
1400
1408
s
s
s
166
129
129
Infrared spectroscopic data on sodium-3-methoxyben-
zoate (Na–C H O ) and its compounds with europium(III)
8
H
7
O
3
)
3
3439br
8
7 3
8
H
O
7
O
3
)
3
Á 3501br
and gadolinium(III) are shown in 2. The investigation was
2
H
2
-
1
focused mainly within the 1700–1400 cm range because
the region is potentially most informative in attempting to
assign coordination sites. In the Na–C H O , strong bands
br Broad, s strong, C
group stretching frequency, msym(COO
8
H
7
O
3
3-methoxybenzoate, m(O–H) hydroxyl
and mas(COO symmetrical
and anti-symmetrical vibrations of the COO group, respectively
-
)
-
)
-
8
7
3
-
1
located at 1568 and 1400 cm
are attributed to anti-
symmetrical (m ) and symmetrical (msym) frequencies of the
as
carboxylate groups, respectively [12, 13]. In the Eu(III) and
The TG-DTA curves of the europium(III) and gadolin-
ium(III) complex are shown in 2. The first mass loss up to
363 K(Eu) and 373 K(Gd), corresponding to the endo-
thermic peak at 353 K(Eu) and 362 K(Gd) is due to the
release of 0.25 hygroscopic water molecule and two
hydration water molecules, respectively.
Gd(III) compounds, analysis of the frequencies of the m
as
-
and msym (COO ) bands, where m - msym = 129, shows
as
that the lanthanides are linked to the carboxylate group by
a bidentate bond with an incomplete equalization of bond
lengths in the carboxylate anion [6–9].
Table 1 Analytical data for Ln(L)
3
2
ÁnH O
Compound
Water (%)
Calcd.
Ligand lost (%)
Metal oxide (%)
Carbon (%)
Hydrogen (%)
Residue
TG
Calcd.
TG
Calcd.
TG
EDTA
Calcd.
E.A.
Calcd.
E.A.
Eu(L)
3
–
–
70.93
66.40
71.25
66.51
29.07
28.03
28.75
27.85
29.57
28.41
47.61
44.57
47.85
44.68
3.50
3.90
3.52
3.79
Eu
2 3
O
Gd(L)
3
Á2H
2
O
5.57
5.64
Gd
2 3
O
Ln Europium(III) or gadolinium(III), L 3-methoxybenzoate
1
23

Synthesis, characterization and thermal behaviour of solid-state compounds
767
(a)
TG
DSC
DTA
4
W
(b)
(a)
(b)
exo up
873
exo up
273
373
473
573
Temperature/K
673
773
273
473
673
873
1073 1273 1473
Temperature/K
Fig. 3 DSC curves of: (a) Eu(C
= 3-methoxybenzoate
8 7
H O
3
)
3 8 7
, (b) Gd(C H O
3
)
3
Á2H
2
O.
8 7 3
C H O
Fig. 2 TG-DTA curves of: (a) Eu(C
= 3-methoxybenzoate
8 7
H O
3 3 8 7
) , (b) Gd(C H O
3
)
3
Á2H
2
O.
8 7 3
C H O
1
1
2
0
8
6
4
2
0
2
523
473
exo up
After their dehydration the anhydrous compounds are
4
23
73
23
273
stable up to 583 K and the endothermic peak at 471 K(Eu)
and 470 K(Gd) are attributed to the reversible crystalline
phase transition confirmed by X-ray powder diffraction and
DSC analysis.
3
-
-4
3
-6
0
10
20
30
Time/min
40
50
60
The thermal decomposition of the anhydrous com-
pounds occurs in two steps. The first mass loss that occurs
through a fast process with loss of 68.72% up to 693 K(Eu)
and 62.18% up to 723 K(Gd), corresponding to exothermic
peaks at 683 and 703 K, respectively, is attributed to the
oxidation of the organic matter. The TG-DTA profiles also
show that the oxidation of the organic matter is accompa-
nied by combustion, with formation of a mixture of Ln O
Fig. 4 DSC curves of heating and cooling of the compound
Eu(C . C = 3-methoxybenzoate
8 7
H O
3
)
3
8 7 3
H O
curves and endothermic peaks due to the reversible crys-
talline phase transition ( 4). The endothermic peak at
360 K(Eu) and 377 K(Gd) is due to dehydration. The
dehydration enthalpy found for the gadolinium(III) com-
2
3
-
1
and Ln O CO (Ln = Eu, Gd) in no simple stoichiometric
2
pound was: 49.8 kJ mol , respectively.
2
3
composition. The formation of dioxycarbonate as inter-
mediate was based on the mass losses observed in the TG
curves and tests with hydrochloric acid solution on samples
heated up to the formation temperature of the intermediate
as indicated by the TG curves, confirming the elimination
The broad exothermic event observed above 573 K(Eu)
and 623 K(Gd), without appearance of definitive peaks are
ascribed to the thermal decomposition of the anhydrous
compounds where the oxidation of the organic matter takes
place in overlapping steps.
of CO . The last mass loss step is attributed to the thermal
2
The endothermic peak at 472 K (Eu, Gd) are due to
decomposition of the dioxycarbonate to the respective
oxides, Eu O and Gd O . The formation of lanthanides
crystalline phase transition and the enthalpies found were:
-
27.9 and 28.0 kJ mol , respectively.
1
2
3
2 3
oxides was confirmed by X-ray diffraction. No peak was
observed in the DTA curves under the applied experi-
mental settings, which is probably due to the small heat
effect of this step.
Conclusions
The DSC curves of the compounds are shown in 3.
These curves show endothermic and exothermic events that
are in agreement with the mass losses observed in the TG
From analytical and thermoanalytical (TG) results a
general formula could be established for these compounds
in the solid state.
123

7
68
P. R. Dametto et al.
The X-ray powder patterns showed that the europium
lanthanides(III) and yttrium(III). J Therm Anal Calorim. 2005;
7
. Kula A. Thermal analysis of lanthanide(III) and Y(III) complexes
with 4-hydroxy-3-methoxybenzoic acid. J Therm Anal Calorim.
2005;81:381–5.
9:145–50.
and gadolinium compounds exist in crystalline state, with-
out evidence for formation of isomorphous compounds.
The infrared spectroscopic data suggest that the C H O
7 3
5
8
acts as a bidentate ligand towards the europium and
gadolinium ions.
6. Rodrigues EC, Siqueira AB, Ionashiro EY, Bannach G, Ionashiro
M. Synthesis, characterization and thermal behaviour of solid-
state compounds of 4-methoxybenzoate with lanthanum(III) and
trivalent lighter lanthanides. Eclet Quim. 2006;31:21–30.
7. Rodrigues EC, Siqueira AB, Ionashiro EY, Bannach G, Ionashiro
M. Synthesis, characterization and thermal behaviour of solid 4-
methoxybenzoates of heavier trivalent lanthanides. Thermochim
Acta. 2006;451:149–55.
The TG-DTA and DSC curves provided information
about the thermal stability and thermal behaviour of these
compounds.
Acknowledgements The authors thank FAPESP, CNPq and
CAPES Foundations (Brazil) for financial support.
8
. Dametto PR, Siqueira AB, Carvalho CT, Ionashiro M. Synthesis,
characterization and thermal studies on solid state 3-methoxy-
benzoate of lighter trivalent lanthanides. Eclet Quim. 2007;
3
2:17–21.
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