Synthesis, characterization and thermal behavior on solid tartrates of light trivalent lanthanides

Article abstract of DOI:10.1007/s10973-009-0329-4

Solid state Ln-L compounds, where Ln stands for light trivalent lanthanides (L-Gd) and L is tartrate, have been synthesized. Thermogravimetry and differential thermal analysis (TG/DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry,

Full text of DOI:10.1007/s10973-009-0329-4

J Therm Anal Calorim (2009) 97:761–764
DOI 10.1007/s10973-009-0329-4
Synthesis, characterization and thermal behavior on solid
tartrates of light trivalent lanthanides
B. Ambrozini Æ P. R. Dametto Æ A. B. Siqueira Æ
C. T. Carvalho Æ M. Ionashiro
ICTAC2008 Conference
Ó Akad e´ miai Kiad o´ , Budapest, Hungary 2009
Abstract Solid state Ln–L compounds, where Ln stands
for light trivalent lanthanides (L–Gd) and L is tartrate, have
been synthesized. Thermogravimetry and differential ther-
mal analysis (TG/DTA), differential scanning calorimetry
behaviour of lanthanum(III) tris-tartrato lanthanate (III)
decahydrate[6], studiesonkineticsandmechanismofthermal
decomposition of yttrium tartrate trihydrate crystals [7] and
kinetics and mechanism of thermal decomposition of stron-
tium tartrate crystals [8].
(
DSC), X-ray powder diffractometry, 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 and
thermal decomposition of the isolated compounds.
In the present article, solid state compounds of light triva-
lent lanthanides, except promethium, (La–Gd), with tartrate
-2
[(C H O ) ] were prepared. The compounds were investi-
4 4 6
gated by complexometry, elemental analysis, X-ray powder
diffractometry, simultaneous thermogravimetry and differ-
ential thermal analysis (TG–DTA) and differential scanning
calorimetry (DSC). The results allowed us to acquire infor-
mation concerning these compounds in the solid state
including their thermal stability and crystallinity.
Keywords Light lanthanides Á Tartrate Á
Characterization Á Thermal behaviour
Introduction
Tartaric acid (dihydroxybutanedioic acid) is an organic
compound 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].
Experimental
The sodium tartrate with 99% purity was obtained from
Sigma-Aldrich. Aqueous solution of sodium tartrate
-
1
Tartaric acid (C H O ) is found in the grape in form
4 6 6
0.20 mol L was made by direct weighing of the solid
salt.
L(?) and among the organic acids of the grape, it is the
strongest one [2].
Light lanthanide(III) chlorides were prepared from the
corresponding metal oxides (except for cerium) by treat-
ment with concentrated hydrochloric acid. The resulting
solutions were evaporated to near dryness, the residues
were re-dissolved in distilled water and the solutions have
been again evaporated to near dryness to eliminate the
excess of hydrochloric acid. The residues were again dis-
solved in distilled water, transferred to a volumetric flask
A surveying the literature thermal studies involving
derivatives of tartrate reported on results on the thermal
decomposition and kinetics of dehydration of gadolinium (III)
and praseodymium(III) tartarates [3, 4], TG and DSC studies
on Sm(III) and Tb(III) tartrates [5], thermal decomposition
-
1
and diluted in order to obtain 0.20 mol L
solutions,
B. Ambrozini (&) Á P. R. Dametto Á A. B. Siqueira Á
C. T. Carvalho Á M. Ionashiro
whose pH were adjusted to 5.0 by adding diluted sodium
hydroxide or hydrochloric acid solutions. Aqueous solution
Instituto de Qu ´ı mica, UNESP, C. P. 355, Araraquara,
SP CEP 14801 – 970, Brazil
e-mail: biaambro@gmail.com
-
1
of cerium(III) nitrate 0.20 mol L was made by direct
weighing of the solid salt.
123

7
62
B. Ambrozini et al.
The solid state compounds were prepared by slow
is undoubtedly related to the low solubility of these
compounds.
addition with continuous stirring the solutions of the ligand
to the respective metal chloride or nitrate solutions, until
total precipitation of the metal ions. The precipitates were
washed with distilled water until elimination of the chlo-
ride (or nitrate) ions, filtered through and dried on What-
man no. 42 filter paper, and kept in a desiccator over
anhydrous calcium chloride.
Simultaneous TG–DTA curves of the compounds are
shown in Fig. 1. These curves exhibit mass losses in two
(Ce), four (La, Pr, Eu, Gd) and five (Nd, Sm) steps between
50 and 780 °C. The first mass loss in the 50–180 °C (La–
Nd), 50–160 °C (Sm–Gd) range is ascribed to dehydration,
which occurs in a single step.
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 [9, 10] after igniting the com-
pounds to the respective oxides and their dissolution in
hydrochloric acid.
Simultaneous TG–DTA and DSC were obtained with
two thermal analysis systems, models SDT 2960 and Q 10,
both from TA Instruments. The purge gas was an air flow
-
1
-1
of 150 mL mim . A heating rate of 20 °C min was
adopted with sample masses about 7–8 mg. Alumina and
aluminium crucibles, the latter with perforated covers 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.
X-ray powder patterns were obtained by using a SIE-
MENS D-5000 X-ray diffractometer using CuK radiation
a
˚
(
k = 1.541 A) and setting of 40 kV and 20 mA.
Results and discussion
The analytical and thermoanalytical results of the synthe-
sized compounds are shown in Table 1. These data per-
mitted to establish the stoichiometry of the compounds,
which are in agreement with the general formula:
Ln (C H O ) ÁnH O, where Ln represents trivalent light
2
4
4
6 3
2
Fig. 1 TG–DTA curves of: (a) La
2
(L-Tar)
(L-Tar)
O, (g) Gd (L-Tar)
3
Á5H
2
O, (b) Ce
2
(L-Tar)
(L-Tar)
3
Á
Á
lanthanides and n = 5.0 (La–Sm) or 5.5 (Eu, Gd).
X-ray powder patterns showed that all the compounds
were obtained in amorphous state. The amorphous state
5
5
H
H
2
O, (c) Pr
O, (f) Eu
2
(L-Tar)
3
Á5H
2
O, (d) Nd
2
3
Á5H
2
O, (e) Sm
2
3
2
2
(L-Tar)
3
Á5.5H
2
2
3
Á5.5H
2
O, L-Tar =
2-
4 4 6
C H O
Table 1 Analytical data for the Ln (L)
2
3 2
.nH O
Compound
Water (%)
Calcd.
Ligand lost (%)
Metal oxide (%)
Carbon (%)
Hydrogen (%)
Residue
TG
Calcd.
TG
Calcd.
TG
EDTA
Calcd.
E.A.
Calcd.
E.A.
La
2
(L)
(L)
(L)
(L)
(L)
(L)
(L)
3
Á5H
Á5H
Á5H
Á5H
Á5H
Á5.5H
Á5.5H
2
O
11.09
11.06
11.04
10.95
10.79
11.70
11.55
10.96
10.97
10.95
11.17
10.95
11.61
11.77
48.79
46.68
47.24
48.16
47.45
46.76
46.19
48.62
46.52
47.63
47.61
47.18
46.59
45.68
40.12
42.26
41.72
40.89
41.76
41.54
42.26
40.42
42.51
41.42
41.22
41.87
41.80
42.55
40.60
41.71
42.12
40.50
41.69
41.90
42.96
17.75
17.69
17.66
17.52
17.26
17.01
16.80
17.60
17.85
17.84
17.80
17.42
16.85
16.61
2.74
2.73
2.72
2.70
2.66
2.74
2.71
2.82
2.60
2.48
2.85
2.80
2.55
2.61
La
CeO
Pr
Nd
Sm
2
O
3
Ce
2
3
2
O
2
Pr
2
3
2
O
6
O
11
3
Nd
2
3
2
O
2
O
Sm
2
3
2
O
2 3
O
Eu
2
3
2
O
Eu
2 3
O
Gd
2
3
2
O
Gd
2 3
O
2
-
4 4 6
Ln = Light lanthanides; L = C H O
1
23

Synthesis, characterization and thermal behavior
763
Table 2 Temperature ranges h, mass losses (%) and peak temperatures (°C) for each step of the TG-DTA curves of the compounds
Compound
Steps
First
Second
Third
Fourth
Fifth
La
2
(L)
3
Á5H
2
O
h (°C)
50–180
10.96
180–325
18.45
325–670
670–740
3.06
–
–
–
Loss (%)
Peak (%)
25.01
100 (en)
290 (en)
370/440/625 (ex)
710 (en)
Ce
2
(L)
h (°C)
Loss (%)
Peak (%)
(L)
Á5H
h (°C)
3
Á5H
2
O
50–180
10.97
180–350
47.63
–
–
–
–
–
–
–
–
–
111 (en)
343 (ex)
Pr
2
3
2
O
50–180
10.95
180–380
24.02
380–420
16.41
420–700
7.20
–
–
–
Loss (%)
Peak (%)
108 (en)
295 (en)
412 (ex)
550 (en)
Nd
2
(L)
3
Á5H
2
O
h (°C)
Loss (%)
50–180
11.17
180–385
22.61
385–465
7.94
465–590
13.89
590–700
3.17
Peak (%)
2
Sm (L) O
110 (en)
300 (en)
368/433 (ex)
567 (ex)
655 (en)
2
3
Á5H
h (°C)
Loss (%)
50–160
10.95
160–335
19.07
335–440
12.45
440–620
13.06
620–700
2.60
–
Peak (%)
110 (en)
300 (en)
372/418 (ex)
594 (ex)
Eu
2
(L)
3
Á5.5H
2
O
h (°C)
Loss (%)
50–160
11.61
160–325
19.85
325–570
25.91
570–670
2.83
–
–
–
–
Peak (%)
105 (en)
315 (ex)
530 (ex)
Gd
2
(L)
3
Á5.5H
2
O
h (°C)
Loss (%)
50–160
11.77
160–365
20.24
365–440
13.42
440–780
12.02
–
–
–
Peak (%)
105 (en)
305 (en)
420 (ex)
620 (ex)
2
6
-
L = C
4 4
H O
; en = endothermic; ex = exothermic
After dehydration the mass losses observed above 180 °C
for lanthanum to neodymium compounds (Fig. 1a–d) and
above 160 °C for samarium to gadolinium compounds
buted to the thermal decomposition being the exothermic
events due to the oxidation of the organic matter.
In the final step of the thermal decomposition only the
lanthanum, praseodymium and neodymium compounds
exhibit an endothermic peak at 710, 550 and 655 °C,
respectively, while the gadolinium compound shows an
exothermic event. For the samarium and europium com-
pounds no thermal event is observed probably because in
this step exothermic and endothermic reactions must occur
simultaneously; the resulting heat is insufficient to produce
a thermal event. Tests with hydrochloric acid solution on
samples heated up to 650 °C (La, Gd), 500 °C (Pr),
600 °C (Nd, Sm) and 550 °C (Eu) confirmed the elimi-
(
Fig. 1e–g) are due to the thermal decomposition of the
anhydrous compounds; these take place in consecutive and/
or overlapping steps with partial losses which are charac-
teristic for each compound.
For the cerium compound, the thermal decomposition
occurs up to 350 °C with the formation of cerium(IV),
CeO as final residue. The smaller final temperature of
2
thermal decomposition is due to the oxidation reaction of
Ce(III) to Ce(IV), together with the oxidation of the
organic matter. This behaviour had already been observed
for other cerium compounds [11, 12].
nation of CO and the presence of small quantity of car-
2
For the other compounds the mass loss up to 740 °C
La), 700 °C (Pr, Nd, Sm), 670 °C (Eu) and 780 °C (Gd)
corresponding to endothermic or exothermic peaks attri-
bonaceous residues showing that in this step occurs the
formation of an intermediate derivate of carbonate, prob-
ably the dioxycarbonate, as already observed during the
(
123

7
64
B. Ambrozini et al.
The DSC curves of the compounds are shown in Fig. 2.
These curves show endothermic and exothermic peaks that
all are in agreement with the mass losses observed in the
TG curves. The endothermic peak at 116–125 °C is assigned
to the dehydration, which occurs in single step. The dehy-
dration enthalpies found for the compounds (La to Gd) were:
-
1
1
45.8, 157.9, 102.9, 165.7, 159.6, 181.2, and 208.6 kJ mol ,
respectively.
Conclusions
From TG curves and from the results of elemental analysis
and complexometry a general formula could be established
for these compounds in the solid state.
The TG–DTA and DSC curves provided information on
the dehydration, thermal stability and thermal decomposi-
tion of these compounds.
Acknowledgements The authors thank FAPESP, CAPES and
CNPq Foundations (Brazil) for financial support.
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1
1
6
11
Ln O (L = La, Nd, Sm, Eu, Gd).
2
3
The mass losses, temperature ranges and the peak tem-
peratures observed for each step of the TG–DTA curves are
shown in Table 2. During the thermal decomposition of
these compounds, the formation of oxalate as intermediate
was not observed in disagreement with [2–5] even the
formation of Pr O as final residue.
1
2
3
1
23