Synthesis, characterization and thermal behaviour of solid-state compounds of yttrium and lanthanide benzoates

Article abstract of DOI:10.1007/s10973-005-7380-6

Solid-state Ln(Bz)₃?H₂O compounds where Ln stands for trivalent yttrium or lanthanides and Bz is benzoate have been synthesized. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), X-ray powder diffractometry, infra

Full text of DOI:10.1007/s10973-005-7380-6

Journal of Thermal Analysis and Calorimetry, Vol. 90 (2007) 3, 737–746
SYNTHESIS, CHARACTERIZATION AND THERMAL BEHAVIOUR OF
SOLID-STATE COMPOUNDS OF YTTRIUM AND LANTHANIDE
BENZOATES
1
J. R. Locatelli , E. C. Rodrigues , A. B. Siqueira , E. Y. Ionashiro , G. Bannach and
2
2
2
2
2
*
M. Ionashiro
1
Academia da For¸a Aérea, AFA. Estrada de Aguaí; s/n, CEP 13630-000 Pirassununga, SP, Brazil
Instituto de Química, UNESP, C. P. 355, CEP 14801 – 970 Araraquara, SP, Brazil
2
3 2
Solid-state Ln(Bz) ·H O compounds where Ln stands for trivalent yttrium or lanthanides and Bz is benzoate have been synthesized.
Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), X-ray powder diffractometry, infrared spectroscopy and
chemical analysis 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 thermal decomposition of the isolated compounds.
Keywords: benzoate, lanthanides, thermal behaviour
Introduction
[9–12, 14–17]. The vibrational and electronic spec-
troscopic study of lanthanides and effect of sodium on
the aromatic system of benzoic acid is surveyed in
[13, 16]; 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 spec-
troscopic and thermogravimetric data [18]; the ther-
mal decomposition of thorium salts of benzoic and
4-methoxybenzoic acids in air atmosphere [19]; the
thermal and spectral behaviour on solid compounds
of 5-chloro-2-methoxybenzoate with rare earth and
d-block elements [20–23]; the synthesis and charac-
terization of 2,3-dimethoxybenzoates of heavy
lanthanides and yttrium [24]; the thermal studies on
solid compounds of phenyl substituted derivates of
benzylidenepyruvates with several metal ions
[25, 26]; the spectral and magnetic studies of
2-chloro-5-nitrobenzoates of rare earth elements [27];
thermal behaviour of solid state 2-methoxybenzoates,
3-methoxybenzoates, 4-methoxybenzoates of some
bivalent transition metal ions [28–30]; and thermal
behaviour of solid state 4-methoxybenzoates of triva-
lent lanthanides [31, 32].
Benzoic acid and some of its derivatives are used as
preservative, catalyst polymer precursor, in pharma-
ceutical industries, etc. A survey of the literature
shows that the complexes of rare earth and d-block el-
ements with benzoic acids and some of their deriva-
tives have been investigated in aqueous solution and
in solid state.
The papers report on the thermodynamics of
complexation of lanthanides by some benzoic acid
derivatives [1] in solution, on the spectroscopic study
of trivalent lanthanides with several carboxylic acids
including benzoic acid [2], the influence of pH,
surfactant and synergic agent on the luminescent
properties of terbium chelates with benzoic acid de-
rivatives [3]. The thermodynamic of complexation of
lanthanides by benzoic and isophthalic acids is dealt
in [4], while the synthesis, crystal structure,
photophysical and magnetic properties of dimeric and
polymeric lanthanide complexes with benzoic acid
and its derivatives were described in [5].
Among the solid state properties the thermal sta-
bility and thermal decomposition of thorium salts
with several organic acids, including 4-methoxy-
benzoic acid is reported in [6], as well as benzoic and
m-hydroxybenzoic acids in [7]; the thermal decompo-
sition of nickel benzoate and of the nickel salt of
cyclohexane carboxylic acid in [8]; the thermal and
spectral behaviour on solid compounds of benzoates
and its methoxy derivates with rare earth elements in
In the present study benzoates of Y(III) and tri-
valent lanthanides, except Pm, were synthesized. The
compounds were investigated by means of infrared
spectroscopy, X-ray powder diffractometry, simulta-
neous thermogravimetry-differential thermal analysis
(TG-DTA) and other analytical methods.
*
Author for correspondence: massaoi@iq.unesp.br
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2007 Akadémiai Kiadó, Budapest

LOCATELLI et al.
Experimental
complexometric titrations with standard EDTA solu-
tion using xylenol orange as indicator [34].
The benzoic acid (HBz) with 99.9% purity was obtained
X-ray powder patterns were obtained by using a
Siemens D-5000 X-ray diffractometer with CuK ra-
diation (l=1.541 ) and under 40 kV and 20 mA set-
–1
from Merck. Aqueous solution of Na-Bz (0.1 mol L )
was prepared by neutralization aqueous HBz suspension
a
–1
with 0.1 mol L sodium hydroxide solution.
tings. Infrared spectra for NaBz (sodium salt) as well
as for its metal-ion compounds were recorded on a
Nicolet model Impact 400 FTIR instrument in the
Yttrium(III) and lanthanide(III) chlorides were
prepared from the corresponding metal oxides (except
for cerium) by treatment with concentrated hydro-
chloric acid. The resulting solutions were evaporated
to near dryness, the residues were redissolved in dis-
tilled water and the solutions have been again evapo-
rated to near dryness to eliminate the excess of hydro-
chloric acid. Then, the residues were again dissolved
in distilled water, transferred to a volumetric flask and
diluted in order to obtain ca. 0.10 M solutions, whose
pH were adjusted to 5.0 by adding diluted sodium hy-
droxide or hydrochloric acid solutions. Ca. 0.10 M
aqueous solution of cerium(III) nitrate was made by
direct weighing of the solid salt according to [33].
The solid-state compounds were prepared by slow
addition of the aqueous solution of NaBz with continu-
ous stirring to the respective metal chloride or nitrate so-
lutions, until total precipitation of the metal ions. The
precipitates were washed with distilled water to elimi-
nate the chloride (or nitrate ions), then filtered through
–
1
4000–400 cm range. The solid samples were
pressed into KBr pellets.
Simultaneous TG-DTA curves were obtained
applying TA SDT 2960 thermoanalytical unit
(TA Instruments, USA) with air purging (flow rate:
–
1
–1
100 mL min ) and at a heating rate of 20°C min .
The initial sample mass was about 7 mg and platinum
crucibles were used for the TG-DTA experiments.
Computational strategy
To calculation of the theoretical infrared spectrum of
lanthanum benzoate, it is necessary to evaluate the
structure and wave function computed by the ab initio
SCF Hartree–Fock–Roothan method [35] using a split
valence (LanL2DZ) basis set [36–39]. The performed
molecular calculations in this work were done by us-
ing the Gaussian 98 routine [40] and the hardware
used was IBM power 3. The crystal geometry of lan-
thanum benzoate is unknown. The geometrical opti-
mization was carried out without any constraints. The
o
and dried on Whatman n 42 filter paper, and kept in a
desiccator over anhydrous calcium chloride, under re-
duced pressure to obtain a constant mass.
In the solid state compounds hydration water,
ligand and metal ion content was determined from TG
curves. The metal ions were also determined by
benzoate
molecule
contains
rings
with
conformational flexibility and all variables were opti-
mized. The optimization proceeded more uniformly
when all variables were optimized.
Table 1 Analytical data for Ln(Bz)
3 2
·nH O
Water/%
Ligand lost/%
Metal oxide/%
TG
Compound
Residue
Calcd.
TG
Calcd.
TG
Calcd.
EDTA
La(Bz)
3
·2H
·2H
·2H
·2.5H
·2H
·1.5H
·1.5H
·H
2
O
6.70
6.68
6.67
8.15
6.56
4.98
4.94
3.34
1.68
–
6.73
6.70
6.84
7.90
6.65
5.15
5.03
3.40
1.72
–
63.04
61.42
61.82
61.41
61.73
62.57
61.96
62.06
63.45
64.24
63.96
63.75
63.27
63.10
75.03
63.48
61.30
61.76
61.55
61.49
62.50
61.78
62.14
63.28
64.18
63.83
63.65
63.34
62.86
74.99
30.26
31.90
31.51
30.44
31.71
32.45
33.10
34.60
34.87
35.76
36.04
36.24
36.73
36.90
24.97
29.79
32.00
31.40
30.55
31.86
32.35
33.19
34.46
35.00
35.82
36.17
36.35
36.66
37.14
25.01
30.35
31.76
31.74
30.03
31.62
32.21
32.88
34.60
34.55
35.57
36.01
36.58
36.85
36.71
24.90
La
CeO
Pr
Nd
Sm
2
O
3
Ce(Bz)
3
2
O
2
Pr(Bz)
3
2
O
6
O
11
Nd(Bz)
3
2
O
2
O
3
Sm(Bz)
3
2
O
2 3
O
Eu(Bz)
3
2
O
Eu
2 3
O
Gd(Bz)
3
2
O
2 3
Gd O
Tb(Bz)
Dy(Bz)
Ho(Bz)
3
2
O
Tb
Dy
Ho
4 7
O
3
3
·0.5H
2
O
2
O
3
3
2
O
Er(Bz)
Tm(Bz)
Yb(Bz)
Lu(Bz)
Y(Bz)
3
–
–
Er
Tm
Yb
Lu
2
O
3
3
–
–
2
O
3
3
–
–
2 3
O
3
–
–
2 3
O
3
–
–
2 3
Y O
Ln=Yttrium(III), or trivalent lanthanides; Bz=benzoate
7
38
J. Therm. Anal. Cal., 90, 2007

YTTRIUM AND LANTHANIDE BENZOATES
Results and discussion
The X-ray diffraction powder patterns (Fig. 1)
show that all the compounds have a crystalline struc-
ture, except lanthanum(III), cerium(III) and dyspro-
sium(III) compounds, evidencing the formation of
two isomorphous series: being the praseodymium(III)
to terbium(III) compounds the first one and the hol-
mium(III) to lutetium(III) and yttrium(III) compounds
the other series.
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 Ln(Bz) ·nH O general formula,
3 2
where Ln represents trivalent yttrium and lanthanides,
Bz is benzoate and n=2.5 (Nd), 2 (La, Ce, Pr, Sm), 1.5
(
Eu, Gd), 1 (Tb), 0.5 (Dy) and 0 (Ho to Lu and Y).
Infrared spectroscopic data on sodium benzoate
and its compounds and with the metal ions considered
in this work are shown in Table 2. The investigation
a
–
1
was focused mainly in the 1700–1400 cm range be-
cause this region is potentially the most informative
to assign the coordination sites.
The anti-symmetrical and symmetrical vibration
bands of carboxylate anions appeared in the spectra of
yttrium(III) and lanthanide(III) compounds within the
b
–
–1
ranges
n
n
as(COO )=1539–1522
–1
cm ,
(COO )=1427–1416 cm ; for the sodium benzoate
–
s
–
at nas(COO )=1551 cm and n
–1
–
(COO )=1414 cm
–1
s
c
frequencies.
–
(COO ) bands shows
Analysis of the nas and n
s
that the lanthanides(III) are linked to the carboxylic
group by a bidentate bond with an incomplete equal-
ization of bond lengths in the carboxylate anion; this
is in agreement with the literature data [41, 42].
d
3 2
The theoretical infrared spectrum of La(Bz) ·3H O
was calculated by using a harmonic field [43] and the
obtained frequencies were not scaled. The geometry op-
timization was computed by the optimized Berny algo-
rithm [44]. The obtained geometry from calculations is
presented in Fig. 2 and Table 3.
e
The theoretical infrared spectrum (electronic
1
–1
state A) was obtained with frequency values (cm ),
relative intensities, assignments and description of vi-
brational modes.
1
0
20
30
40
50
60
70
2
/degree
Fig. 1 X-ray powder diffraction patterns of: a – La(Bz)
b – Ce(Bz) ·2H O; c – Dy(Bz) ·0.5H O;
d – Pr(Bz) ·2H O as representative of the Nd to Tb com-
pounds and e – Ho(Bz) as representative of Er to Lu and
Y compounds (Bz=benzoate)
3 2
·2H O;
A comparative analysis between the experimen-
tal and theoretical spectrum shows the following con-
clusions: (a) the first assignment shows a strong con-
3
2
3
2
3
2
3
–
1
–
tribution at 1535 cm suggesting a nasym(COO ) as-
H
H
C
C
H
C
C
C
H
C
O
C
H
O
H
H
O
La
H
C
C
C
H
C
C
C
O
C
C
C
H
O
C
C
H
C
H
C
H
C
H
H
Fig. 2 Proposed structure 3D of solid-state anhydrous compound lanthanum(III) with benzoate (optimized using
Hartree–Fock–Roothan method, LanL DZ basis set of Gaussian 98)
2
J. Therm. Anal. Cal., 90, 2007
739

LOCATELLI et al.
Table 2 Spectroscopic data for sodium benzoate and compounds with lanthanides(III) and yttrium(III)
Compounds
NaBz
u
(O–H)
H
2
O
u
s (COO–)
u
as(COO–)
D(us (COO–)– uas(COO–))
–
1414 s
1425 s
1427 s
1427 s
1417 s
1423 s
1423 s
1423 s
1419 s
1418 s
1416 s
1418 s
1418 s
1418 s
1419 s
1418 s
1551 s
1535 s
1533 s
1533 s
1531 s
1533 s
1537 s
1539 s
1539 s
1531 s
1522 s
1524 s
1526 s
1526 s
1523 s
1526 s
137
110
106
106
114
110
114
116
120
113
106
106
108
108
104
108
La(Bz)
3
·2H
·2H
·2H
·2.5H
·2H
·1.5H
·1.5H
·H
2
O
3449
3454
3448
3438
3462
3440
3442
3452
3450
–
Ce(Bz)
3
2
O
Pr(Bz)
3
2
O
Nd(Bz)
3
2
O
Sm(Bz)
3
2
O
Eu(Bz)
3
2
O
Gd(Bz)
3
2
O
Tb(Bz)
Dy(Bz)
Ho(Bz)
3
2
O
3
3
·0.5H
2
O
Er(Bz)
Tm(Bz)
Yb(Bz)
Lu(Bz)
Y(Bz)
3
–
3
–
3
–
3
–
3
–
s=strong, Bz=Benzoate; s strong; b broad; uas (O–H)=hydroxyl group stretching frequency; us (COO–) and uas (COO–)=symmetrical and
–
anti-symmetrical vibrations of the COO group respectively
signment, while the theoretical results show the corre-
–
Lanthanum(III), Neodymium(III), Samarium(III) and
Europium III) compounds
1
sponding peak at 1531 cm with 0.3% discrepancies;
b) the second assignment shows a strong contribu-
(
tion at 1425 cm suggesting a nsym(COO ) assign-
–
1
–
The TG–DTA curves of the lanthanum(III) and euro-
pium(III) as representative of these compounds are
shown in Fig. 3. The first mass loss up to 125°C (La),
120°C (Nd) and 110°C (Sm, Eu) with the corresponding
endothermic peaks at 115°C (La), 110°C (Nd), 105°C
ment, while the theoretical results show the corre-
–
1
sponding peak at 1386 cm with 2.7% discrepancies;
c) the third assignment shows both experimental and
(
–
–
theoretical Dn values (nasym(COO )–nsym(COO )) are
near the sodium benzoate Dn value (DnNa=127;
Dnexp=103; DnTheor=140) reinforcing the suggestion
that compounds considered in this work have a cova-
lent bidentate bond.
(
(
Sm) and 100°C (Eu) is due to the release of 2.5H
Nd), 2H O (La, Sm) and 1.5H O (Eu) moles of water.
After their dehydration the anhydrous com-
2
O
2
2
pounds are stable up to 320°C and the endothermic
peaks at 255°C (La), 250°C (Nd, Eu) and 320°C (Sm)
are attributed to the reversible crystalline phase tran-
sition confirmed by X-ray powder diffraction and
TG–DTA analysis.
The simultaneous TG–DTA curves of the com-
pounds are shown in Fig. 2. These curves exhibit
mass loss in steps and thermal events corresponding
to these losses or due to physical phenomenon. Three
thermal steps are observed for these compounds. At
first, similar TG–DTA profiles can be observed for
La(III), Nd(III), Sm(III) and Eu(III) compounds,
where the thermal decomposition occurs in four steps.
A close similarity was observed for the Ce(III),
Pr(III), Gd(III), Tb(III) and Dy(III) compounds,
where the thermal decomposition occurs in the three
steps. On the contrary, Ho(III) to Lu(III) and Y(III)
compounds display another set of very similar
TG–DTA profiles and the thermal decomposition
occurs in two steps.
Table 3 Theoretical geometries parameters of La(Bz)
compound
3
d
d
d
d
d
<
<
<
La – OCOO
–
2.54 
1.29 
1.47 
1.39 
1.07 
116.76°
64.34°
119.84°
CCOO
–
–
– OCOO
–
CCOO
– Cring
C
ring – Cring
Cring – Hring
OCOO
OCOO
–
– CCOO
–
– OCOO
–
–
– La – OCOO
–
C
ring – Cring – Cring
Thus the features of each of these compounds are
discussed on the base of their similar thermal profiles.
Key: La=lanthanum; Bz=benzoate; d=atoms distance;
<
–
=atoms angle; COO =carboxylate; ring=benzene ring
7
40
J. Therm. Anal. Cal., 90, 2007

YTTRIUM AND LANTHANIDE BENZOATES
Fig. 3 TG–DTA and TG/DTG curves of: a – La(Bz)
3
·2H
2
O (6.943 mg); b – Eu(Bz)
3
·1.5H
2
O (6.966 mg); c – Ce(Bz)
3 2
·2H O
(
6.964 mg); d – Gd(Bz) ·1.5H O (6.929 mg); e – Ho(Bz)
3
2
3
(7.029 mg) and f – Yb(Bz)
3
(7.244 mg) (Bz=benzoate)
J. Therm. Anal. Cal., 90, 2007
741

LOCATELLI et al.
Fig. 3 (continued)
The thermal decomposition of the anhydrous
shown in Fig. 3. The first mass loss that occurs up to
120°C (Ce, Pr), 105°C (Gd), 95°C (Tb) and 90°C
(Dy) accompanied by an endothermic peak at 105°C
(Ce, Pr), 95°C (Gd), 85°C (Tb) and 75°C (Dy) is for
the dehydration with loss of 2 (Ce, Pr), 1.5 (Gd); 1
(Tb) and 0.5 (Dy) mole of water, respectively.
compounds occurs in three steps. The first two corre-
sponding to exothermic peaks, attributed to the oxida-
tion of the organic matter. The TG–DTA profiles of
the second step show that the oxidation of organic
matter is accompanied by combustion with the forma-
tion of lanthanum dioxycarbonate, La
O
2
O
mixture of Ln and Ln CO (Ln=Nd, Sm, Eu),
2
CO
3
, or a
The anhydrous compounds are stable up to
260°C (Ce), 320°C (Pr) and 350°C (Gd, Tb, Dy) and
the endothermic peak at 250°C (Ce, Pr), 255°C (Gd)
and 270°C (Tb, Dy) is ascribed to the reversible crys-
talline phase transition, which was confirmed by
X-ray powder diffraction and TG–DTA curves.
2
3
2
O
2
3
however, not in a simple stoichiometric composition.
The formation of dioxycarbonate as intermediate 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 interme-
diate as indicated by the TG curves, confirming the
The less thermal stability of the cerium com-
pound is attributed to the oxidation reaction of Ce(III)
to Ce(IV) together with the oxidation of the organic
matter. This behaviour concerning to the thermal sta-
bility of the cerium compound has already been ob-
served for other cerium compounds, too [45, 46].
The thermal decomposition of the anhydrous com-
pounds takes place in two steps. The first one is accom-
panied by a small exothermic peak for the Gd(III),
Tb(III) and Dy(III) and no peak for the Ce(III) and
Pr(III) compounds, probably due to the simultaneous
thermal decomposition (endothermic) and oxidation of
the organic matter (exothermic). The resulting heat in
this step is sufficient to produce a small exothermic peak
or insufficient to produce a thermal event. The exother-
mic peak corresponding to the second step is attributed
to the oxidation of the organic matter and for the cerium,
elimination of CO
2
.
The formation of the
dioxycarbonate, as intermediate has already been ob-
served for other lanthanides compounds [45, 46]. The
last mass loss step is attributed to the thermal decom-
position of the dioxycarbonate to the respective
2 3
Ln O oxide (Ln=La, Nd, Sm, Eu). No peak was ob-
served in the DTA curves under the applied experi-
mental settings, which is probably due to the small
heat effect of this step.
Cerium(III), Praseodymium(III), Gadolinium(III),
Terbium(III) and Dysprosium(III) compounds
The TG-DTA curves of the cerium(III) and gadolin-
ium(III) as representative of these compounds are
7
42
J. Therm. Anal. Cal., 90, 2007

YTTRIUM AND LANTHANIDE BENZOATES
Table 4 Temperature ranges (°C), mass losses (%) and peak temperatures (°C) observed for each step of the TG–DTA curves
of the Ln(Bz) ·nH O compounds, where Ln=yttrium(III) and lanthanides(III), Bz=benzoate
3
2
Steps
Compound
Crystalline
transition
First
Second
Third
Fourth
La(Bz)
3
·2H
2
O
°C
40–125
6.73
320–510
26.67
510–555
630–720
Loss(%)
Peak (°C)
°C
35.62
4.19
115 (endo)
50–120
6.70
470 (exo)
260–400
28.97
555 (exo)
–
255 (endo)
250 (endo)
250 (endo)
250 (endo)
230 (endo)
250 (endo)
255 (endo)
270 (endo)
270 (endo)
280 (endo)
280 (endo)
280 (endo)
280 (endo)
275 (endo)
280 (endo)
Ce(Bz)
3
·2H
2
O
400–510
–
Loss(%)
Peak (°C)
°C
32.33
–
105 (endo)
50–120
6.84
–
460 (exo)
–
Pr(Bz)
3
·2H
2
O
320–520
30.06
520–560
–
Loss(%)
Peak (°C)
°C
31.70
–
105 (endo)
40–120
7.90
–
560 (exo)
–
Nd(Bz)
3
·2.5H
2
O
320–510
32.11
510–555
560–680
Loss(%)
Peak (°C)
°C
27.29
2.15
110 (endo)
40–110
6.65
500 (exo)
320–490
32.11
555 (exo)
–
Sm(Bz) ·2H
3
2
O
490–525
530–680
Loss(%)
Peak (°C)
°C
28.29
1.09
105 (endo)
40–110
5.15
470 (exo)
320–470
14.82
525 (exo)
–
Eu(Bz)
3
·1.5H
2
O
470–555
555–680
Loss(%)
Peak (°C)
°C
46.61
1.07
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
100 (endo)
40–105
5.03
470 (exo)
350–515
19.07
495, 530 (exo)
Gd(Bz)
3
·1.5H
2
O
515–550
Loss(%)
Peak (°C)
°C
42.71
95 (endo)
40–95
500 (exo)
350–490
30.20
550 (exo)
Tb(Bz)
Dy(Bz)
Ho(Bz)
3
·H
2
O
490–530
Loss(%)
Peak (°C)
°C
3.40
31.94
85 (endo)
40–90
450 (exo)
350–500
22.00
530 (exo)
3
3
·0.5H
2
O
500–590
Loss(%)
Peak (°C)
°C
1.72
41.28
75 (endo)
350–535
29.46
450 (exo)
535–580
32.72
535, 555 (exo)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Loss(%)
Peak (°C)
°C
460 (exo)
350–545
30.24
565 (exo)
545–570
33.59
Er(Bz)
3
Loss(%)
Peak (°C)
°C
460 (exo)
350–515
29.01
570 (exo)
515–545
34.64
Tm(Bz)
3
Loss(%)
Peak (°C)
°C
460 (exo)
350–515
36.00
545 (exo)
515–550
27.34
Yb(Bz)
3
Loss(%)
Peak (°C)
°C
470 (exo)
350–535
33.44
550 (exo)
535–560
29.42
3 2
Lu(Bz) ·1.5H O
Loss(%)
Peak (°C)
°C
460 (exo)
350–530
23.68
560 (exo)
530–560
51.31
Y(Bz)
3
Loss(%)
Peak (°C)
460 (exo)
560 (exo)
J. Therm. Anal. Cal., 90, 2007
743

LOCATELLI et al.
3 2 3 2 3 2 3
Fig. 4 TG–DTA curves of: a – La(Bz) ·2H O; b – Sm(Bz) ·2H O; c – Dy(Bz) ·0.5H O; d – Yb(Bz) (Bz=benzoate)
praseodymium and terbium compounds. In this step the
oxidation reaction of Ce(III) to Ce(IV), Pr(III) to Pr
and Tb(III) to Tb , respectively also occurs. The
TG–DTA profiles of this step also show that the oxida-
tion is accompanied by combustion and as final residue
Holmium(III) to Lutetium(III) and Yttrium(III)
compounds
O
6 11
4 7
O
The TG–DTA curves of the holmium(III) and ytter-
bium(III) as representative of these compounds are
shown in Fig. 3. These curves show that all the com-
pounds were obtained in anhydrous state and they are
stable up to 350°C. Above this temperature the anhy-
drous compounds show mass losses in two steps to-
gether with exothermic peaks attributed to the oxida-
tion of the organic matter. The TG–DTA profiles of
the last step also show that oxidation of the organic
matter is accompanied by combustion and with the
the formation of the respective oxide, CeO
Tb , Gd and Dy , without the formation of in-
termediate, Ln CO , as observed for the La(III),
2 6 11
, Pr O ,
4 7
O
2 3
O
2 3
O
2 2
O
3
Nd(III), Sm(III) and Eu(III) compounds. The lack of the
formation of the intermediate is undoubtedly due to the
large amount of evolved heat provoked either by the ox-
idation and combustion of the organic matter (Gd, Dy)
together with the oxidation reaction of the lanthanide
ions (Ce, Pr, Tb) and yet by a decreasing stability of this
intermediate with increasing atomic number of the
lanthanide ions [47].
2 3
formation of the respective oxide, Ln O (Ln=Ho to
Lu and Y) without formation of intermediate, too.
The endothermic peak at 280°C observed in
these compounds is attributed to the reversible crys-
talline phase transition as it can be seen in the
7
44
J. Therm. Anal. Cal., 90, 2007

YTTRIUM AND LANTHANIDE BENZOATES
TG–DTA curves (Fig. 4) as representative of the stud-
ied compounds.
The mass loss (Dm), temperature range and peak
temperature (°C) observed for each step of the
TG–DTA curves of all the compounds were collected
in Table 4.
17 G. N. Makushova and S. B. Pirkes, Russ. J. Inorg. Chem.,
2 (1987) 489.
8 T. Glowiak, H. Kozlowski, L. Strinna Erre, B. Gulinati,
G. Micera, A. Pozzi and S. Brunni, J. Coord. Chem.,
5 (1992) 75.
9 W. Brzyska and S. Karasinski, J. Thermal Anal.,
9 (1993) 429.
0 W. Ferenc and B. Bocian, J. Therm. Anal. Cal.,
2 (2000) 831.
21 B. Bocian, B. Czajka and W. Ferenc, J. Therm. Anal. Cal.,
6 (2001) 729.
2 B. Czajka, B. Bocian and W. Ferenc, J. Therm. Anal. Cal.,
7 (2002) 631.
3 W. Ferenc and B. Bocian, J. Therm. Anal. Cal.,
4 (2003) 521.
3
1
2
1
2
3
6
Conclusions
6
2
2
2
2
TG curves and chemical analysis can provide a gen-
eral formula for these compounds in the solid state.
The X-ray powder patterns showed that all the
synthesized compounds exist in crystalline state.
The infrared spectroscopic data suggest that the
benzoate acts as a bidentate ligand towards the metal
ions considered in this work.
6
7
4 W. Ferenc and A. Walkow-Dziewulska, J. Therm. Anal.
Cal., 71 (2003) 375.
5 N. S. Fernandes, M. A. S. Carvalho Filho, C. B. Melios
and M. Ionashiro, J. Therm. Anal. Cal., 73 (2003) 307.
The TG–DTA curves provided information on
the thermal stability and thermal behaviour of these
compounds.
26 N. S. Fernandes, M. A. S. Carvalho Filho, R. A. Mendes,
C. B. Melios and M. Ionashiro, J. Therm. Anal. Cal.,
76 (2004) 193.
2
2
7 W. Ferenc, B. Bocian and A. Walków-Dziewulska,
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8 E. C. Rodrigues, A. B. Siqueira, E. Y. Ionashiro,
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The authors thank FAPESP, CNPq and CAPES Foundations
(Brazil) for financial support and computational facilities of
IQ-UNESP and CENAPAD-UNICAMP.
2
9 A. C. Vallejo, A. B. Siqueira, E. C. Rodrigues,
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3
0 C. T. Carvalho, A. B. Siqueira, E. C. Rodrigues and
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J. Therm. Anal. Cal., 90, 2007