Synthesis, characterization and thermal behaviour of heavy lanthanide and yttrium pyruvates in the solid state

Article abstract of DOI:10.1007/s10973-009-0537-y

Solid-state Ln-L compounds, where Ln stands for heavy trivalent lanthanides or yttrium (III) (Tb-Lu, Y) and where L is pyruvate, have been synthesized. Thermogravimetry and derivative thermogravimetry (TG/DTG), differential scanning calorimetry (DSC), X-R

Full text of DOI:10.1007/s10973-009-0537-y

J Therm Anal Calorim (2010) 100:95–100
DOI 10.1007/s10973-009-0537-y
Synthesis, characterization and thermal behaviour of heavy
lanthanide and yttrium pyruvates in the solid state
•
A. B. Siqueira C. T. de Carvalho E. C. Rodrigues
•
•
•
E. Y. Ionashiro G. Bannach M. Ionashiro
•
Received: 2 June 2009 / Accepted: 29 September 2009 / Published online: 1 November 2009
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract Solid-state Ln–L compounds, where Ln stands
for heavy trivalent lanthanides or yttrium (III) (Tb–Lu, Y)
and where L is pyruvate, have been synthesized. Thermo-
gravimetry and derivative thermogravimetry (TG/DTG),
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
behaviour, ligand denticity of the isolated complexes.
Introduction
Pyruvic acid is a substance present naturally in our
organisms, and it is a Krebs cycle base or citric acid cycle.
This cycle is the process from which the body converts the
glycogen and the glucose to energy. Pyruvic acid is the
result from the transformation of the glucose by aerobic
metabolism in a process known as glycolysis. Performing a
fundamental role in the Krebs cycle, the pyruvic acid has a
vital role in the conversion of food in energy.
Few investigations have been carried out on compound
derivatives of pyruvic acid (H3C–CO–COOH). In aqueous
solutions, the formation of some metal–ion complexes with
pyruvic acid in a ratio of metal to ligand of 1:1 and 1:2 has
been established by the spectroscopic method [1–3]. The
stability constants and thermodynamic functions of lan-
thanide-complex formation with pyruvic acid (DG, DH,
DS) have also been determined [4]. In the solid state,
preparation of europium pyruvate [5], as well as the
preparation and properties of lanthanides and yttrium
pyruvates have also been described [6–8].
Keywords Heavy lanthanides and yttrium ꢀ Pyruvate ꢀ
Characterization ꢀ Thermal behaviour
A. B. Siqueira
Instituto de Ciencias Exatas e da Terra, UFMT, Campus Pontal
ˆ
do Araguaia, 78698-000 Pontal do Araguaia, MT, Brazil
The aim of this work was to obtain heavy trivalent lan-
thanide pyruvates in the solid state and to investigate them by
means of complexometry, elemental analysis, X-Ray pow-
der diffractometry, infrared spectroscopy, thermogravimetry
(TG) and differential scanning calorimetry (DSC).
C. T. de Carvalho ꢀ M. Ionashiro (&)
´
Instituto de Quımica, UNESP, CP 355,
CEP 14801-970 Araraquara, SP, Brazil
e-mail: massaoi@yahoo.com.br
E. C. Rodrigues
Fundac¸a˜o Educacional de Barretos, CEP 14780-000 Barretos,
SP, Brazil
Experimental
E. Y. Ionashiro
´
Sodium pyruvate 99% pure was obtained from Sigma. An
aqueous solution of sodium pyruvate 0.30 mol L-1 was
made by direct weighing of the solid salt.
Instituto de Quımica, UFG, Campus II, Campus,
ˆ
74001–979 Goiania, GO, Brazil
G. Bannach
Faculdade de Ciencias de Bauru—UNESP,
Heavy lanthanide (III) and yttrium (III) chlorides were
prepared from the corresponding metal oxides by treating
ˆ
CEP 17033–360 Bauru, Brazil
123

96
A. B. Siqueira et al.
with concentrated hydrochloric acid. The resulting solu-
tions were evaporated to near dryness, the residues were
redissolved in distilled water and the solutions were again
evaporated to near dryness to eliminate the excess hydro-
chloric acid. The residues were again dissolved in distilled
water, transferred to a volumetric flask and diluted in order
to obtain 0.30 mol L-1 solutions whose pH were adjusted
to 5.0 by adding diluted sodium hydroxide or hydrochloric
acid solutions. The solid-state compounds were prepared
by adding equivalent quantities of hot solution of sodium
pyruvate to a hot solution of the respective metal chloride.
The solutions were maintained in a water bath until the
total precipitation of the metal pyruvates was achieved and
the precipitates were then washed with hot distilled water
to eliminate the chloride. These were then filtered through
and dried on Whatman no 42 filter paper and kept in a
desiccator over anhydrous calcium chloride.
compounds were recorded on a Nicolet model Impact 400
FTIR Instrument in the 4000–400 cm-1 range. The solid
samples were pressed into KBr pellets.
The TG and DTG curves were obtained using a Mettler
TA 4000 thermal analysis system with an air flow of
100 mL min-1, a heating rate of 5 K min-1 and samples
weighing about 7 mg. An alumina crucible was used for
the TG/DTG curves.
The DSC curves were obtained using a thermal analysis
system model DSCQ10 from TA Instruments. The purge
gas was an air flow of 50 mL min-1. A heating rate of
10 K min-1 was adopted for samples weighing about
5 mg. Aluminium crucibles along with perforated cover
were used for recording the DSC curves.
Results and discussion
After igniting the compounds to the respective oxides
(Tb4O7 and Ln2O3, Ln = Dy–Lu, Y) and dissolving them
in a hot solution of concentrated hydrochloric acid, their
lanthanide contents were determined by complexometric
titration with standard EDTA solution, using xylenol
orange as indicator [9]. The lanthanide contents were also
estimated from their corresponding TG curves. The dehy-
dration of the compounds was first indicated by their DTG
curves and subsequently confirmed by the broad endo-
thermic peaks centered at 348–448 K in the respective
DSC curves. The water content of the compounds was then
determined from the corresponding mass losses observed in
the TG curves. Next, the ligand content was also assessed
from the TG curves.
Table 1 presents the analytical, thermoanalytical (TG) and
elemental analysis (E.A) data for the prepared compounds
from which the general formula Ln(L)3ꢀnH2O can be
established, where Ln represents trivalent lanthanides L is
pyruvate and n = 4.5 (Tb); 3.5 (Dy, Ho); 3 (Tm - Lu, Y)
and 2.5 (Er).
The X-ray powder patterns showed that all compounds
are amorphous. The amorphous state is undoubtedly due to
the decreasing solubility with increasing temperature,
where the precipitation of these compounds occurs quickly
near the ebullition temperature.
The infrared spectroscopic data for sodium pyruvate 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 more informative in attempting to
assign coordination sites. For sodium pyruvate, a strong
X-ray powder patterns were obtained using a Siemens
D-5000 X-Ray diffractometer under CuKa radiation
˚
(k = 1.541 A) and set at 40 kV and 20 mA. The infrared
spectra for sodium pyruvate as well as for its metal–ion
Table 1 Analytical and thermoanalytical (TG) data for Ln(L)3ꢀnH2O, where Ln = heavy lanthanides or yttrium and L = pyruvate
Compound
Metal oxide/%
L, lost/%
Water/%
Carbon/%
Hidrogen/%
Calcd.
TG
EDTA
Calcd.
TG
Calcd.
TG
Calcd
E.A
Calcd
E.A
Tb(L)3ꢀ4.5H2O
Dy(L)3ꢀ3.5H2O
Ho(L)3ꢀ3.5H2O
Er(L)3ꢀ2.5H2O
Tm(L)3ꢀ3H2O
Yb(L)3ꢀ3H2O
Lu(L)3ꢀ3H2O
Y(L)3ꢀ3H2O
37.30
38.32
38.62
40.39
39.85
40.35
40.53
27.93
37.08
38.15
38.89
40.70
40.30
40.75
40.24
28.34
37.75
38.52
39.81
40.10
40.65
40.87
40.35
28.47
46.52
48.72
48.49
50.10
48.98
48.58
48.43
58.68
46.92
49.04
48.37
49.47
48.32
48.48
48.47
58.01
16.18
12.96
12.89
9.51
16.00
12.81
12.74
9.83
21.57
22.21
22.10
22.83
22.32
22.14
22.07
26.75
21.76
22.36
21.94
22.54
22.02
22.09
22.29
26.44
3.63
3.32
3.30
2.99
3.13
3.10
3.09
3.75
3.56
3.54
3.19
2.80
3.01
2.97
3.21
3.69
11.17
11.07
11.04
13.38
11.38
10.77
11.29
13.65
123

Synthesis, characterization and thermal behaviour of solid-state Ln–L compounds
97
Table 2 Spectroscopic data for sodium pyruvate and compounds with heavy trivalent lanthanides
msymðCOO =cmꢁ1
m
C=O/cm-1
ꢁ
ꢁÞ
ꢁÞ
Þ
Compound
mOH (H2O)
masymðCOO
DmasymðCOO
NaL
–
1640s
1603s
1601s
1605s
1595s
1597s
1601s
1599s
1605s
–
1406m
1411m
1411m
1412m
1406m
1398m
1396m
1400m
1410m
1709m
Tb(L)3ꢀ4.5H2O
Dy(L)3ꢀ3.5H2O
Ho(L)3ꢀ3.5H2O
Er(L)3ꢀ2.5H2O
Tm(L)3ꢀ3H2O
Yb(L)3ꢀ3H2O
Lu(L)3ꢀ3H2O
Y(L)3ꢀ3H2O
3370br
3373br
3387br
3381br
3387br
3412br
3400br
3350br
37
39
35
45
43
39
41
35
–
–
–
–
–
–
–
–
s strong, m medium, br broad
masymðCOO and msymðCOO Þ: symmetrical and anti-symmetrical vibrations of the COO- group, respectively
ꢁ
ꢁÞ
ꢁÞ
ꢁÞ
ꢁÞ
DmasymðCOO = masymðCOO NaL - masymðCOO (lanthanide complex)
m(C=O): ketonic carbonyl stretching frequency
m(O–H): hydroxyl group stretching frequency
band at 1640 cm-1 and a medium intensity band located at
1406 cm-1 are attributed to the anti-symmetrical and
symmetrical frequencies, respectively, of the carboxylate
group [10, 11]. The band centered at 1709 cm-1 is attrib-
uted to the stretching frequency of the ketonic carbonyl
group. For the prepared compounds, the infrared spectra
show a broad band in the 3350–3412 cm-1 range attributed
to hydration water. The anti-symmetrical and symmetrical
stretching frequencies of the carboxylate group are
observed between 1595–1605 and 1396–1412 cm-1
,
respectively. No band due to the stretching frequency of
the ketonic carbonyl group is observed in the spectrum of
these compounds, and its absence is undoubtedly due to the
overlapping bands of the anti-symmetrical stretching fre-
quency of the carboxylate and the stretching frequency of
the ketonic carbonyl group, as can be seen in Fig. 1. These
data show that the bands due to the anti-symmetrical
stretching frequency of the carboxylate and the stretching
frequency of the ketonic carbonyl group are moved to the
lower frequencies in comparison with the ligand frequen-
cies, suggesting that the metal ions are coordinated by
a-ketonic carbonyl and carboxylate groups [12, 13]. This
behaviour is in agreement with that observed for com-
pounds of lanthanides with phenyl-substituted derivatives
of benzylidenepyruvate [14–16].
(a)
(b)
The TG and DTG curves of the compounds are shown in
Fig. 2. These curves show mass losses in four (Tb, Yb, Lu)
and five (Dy, Ho, Er, Tm, Y) consecutive and/or overlap-
ping steps, without a plateau between the steps and without
evidence concerning the formation of stable anhydrous
compounds. As previously stressed, the temperatures cor-
responding to the mass losses due to dehydration were
depicted from the DTG curves. The mass losses beginning
at 303 K, observed in all the TG and DTG curves, were
undoubtedly provoked by the purge gas (air) flowing at a
rate of 100 mL min-1, as already observed for other
amorphous compounds [17].
(c)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber/cm–1
For all the compounds, the first mass loss up to 393 K
(Tm, Lu), 423 K (Er, Yb, Y), 408 K (Dy, Ho) and
413 K(Tb) is ascribed to dehydration, which occurs in a
Fig. 1 The IR spectra of: (a) NaL; (b) Dy(L)3.3.5H2O (m = 6.793 mg);
(c) Yb(L)3ꢀ3H2O. L = pyruvate
123

98
A. B. Siqueira et al.
Fig. 2 The TG-DTG curves of:
a Tb(L)3ꢀ4.5H2O
(m = 6.821 mg);
b Dy(L)3ꢀ3.5H2O
(m = 6.793 mg);
c Ho(L)3ꢀ3.5H2O
(m = 6.785 mg);
d Er(L)3ꢀ2.5H2O
(m = 6.662 mg);
e Tm(L)3ꢀ3H2O
(a)
(b)
DTG
TG
TG
DTG
(m = 6.670 mg);
f Yb(L)3ꢀ3H2O
473
673
873
1073
473
673
873
1073
(m = 6.863 mg);
g Lu(L)3ꢀ3H2O
Temperature/K
Temperature/K
(m = 6.876 mg);
h Y(L)3ꢀ3H2O
(d)
(c)
(m = 6.783 mg).
L = pyruvate
TG
DTG
TG
DTG
473
673
873
1073
473
673
873
1073
Temperature/K
Temperature/K
(e)
(f)
TG
DTG
TG
DTG
473
673
873
1073
473
673
873
1073
Temperature/ K
Temperature/ K
(h)
(g)
TG
DTG
TG
DTG
473
673
873
1073
473
673
873
1073
Temperature/ K
Temperature/ K
single step and via a slow process. This behaviour was also
observed during the dehydration of lanthanide and yttrium
compounds with phenyl-substituted derivatives of benzy-
lidenepyruvate, and it seems to be characteristic of com-
pounds obtained in the amorphous state [14–18].
After the dehydration, the thermal decomposition of
these compounds occurs in three (Tb, Yb, Lu) or four (Dy,
Ho, Er, Tm, Y) steps, with the mass losses in each step
being characteristic of each compound. After the last step
of thermal decomposition, the minimum oxide-level
123

Synthesis, characterization and thermal behaviour of solid-state Ln–L compounds
99
Table 3 Temperature ranges h/K, mass losses (%) for each step of the TG curves of the Ln(L)3ꢀnH2O compounds, where Ln = lanthanides or
and L = pyruvate
Compound
Steps
First
DmT
Second
Third
Fourth
Fifth
Calcd.
TG
Tb(L)3ꢀ4.5H2O
h/K
303–413
16.00
413–580
15.30
580–693
15.30
693–973
16.32
62.70
61.68
61.38
59.61
60.15
59.65
59.47
72.06
62.92
Loss/%
Dy(L)3ꢀ3.5H2O
h/K
303–408
12.81
408–580
17.83
580–733
19.57
733–833
7.18
833–1073
4.46
61.85
61.11
59.30
59.70
59.25
59.76
71.66
Loss/%
Ho(L)3ꢀ3.5H2O
h/K
303–408
12.74
408–583
16.61
583–723
21.01
723–833
6.35
833–820
4.40
Loss%
Er(L)3ꢀ2.5H2O
h/K
303–403
9.83
403–573
14.15
573–723
22.74
723–818
6.76
818–1153
5.82
Loss%
Tm(L)3ꢀ3H2O
h/K
303–393
11.38
410–563
13.18
563–683
25.26
683–823
5.22
823–1098
4.66
Loss%
Yb(L)3ꢀ3H2O
h/K
303–403
10.77
403–713
38.64
713–963
7.33
963–1153
2.51
Loss%
Lu(L)3ꢀ3H2O
h/K
303–393
11.29
393–733
39.31
733–983
7.00
983–1173
2.16
Loss%
Y(L)3ꢀ3H2O
h/K
303–403
13.65
403–583
18.96
583–723
21.22
723–823
11.88
823–1173
5.95
Loss%
DmT—Total mass losses calculated assuming that the find solid products of thermal decomposition of the obtained compounds are oxides: Tb4O7
and Ln2O3 (Ln = Dy–Lu and Y)
temperatures for the respective oxides were: 973 K(Tb),
1073 K(Dy), 1093 K(Ho), 1153 K (Er, Yb), 1098 K(Tm)
and 1173 K (Lu, Y). The less final thermal decomposition
temperature observed for the terbium compound must be
due to the oxidation reaction (exothermic) of Tb(III) to
Tb4O7.
For all the compounds, the final thermal decomposition
residues were the respective oxides: Tb4O7, Ln2O3
(Ln = Dy–Lu, Y). The temperature ranges (h/K) and mass
losses (%) observed for each step of the TG curve are
shown in Table 3.
The DSC curves of the compounds are shown in Fig. 3.
These curves show endothermic and exothermic peaks that
all agree with the mass losses observed in the TG curves.
The broad endothermic peak in the range of 348–448 K for
all compounds is attributed to the dehydration. The dehy-
dration enthalpies found for terbium to lutetium and
yttrium compounds were: 104.0; 87.3; 69.0; 57.0; 62.2;
43.4; 40.6 and 46.4 kJ mol-1, respectively.
For all the compounds, except terbium, the last mass
loss above 873 K (Dy–Tm, Y) and 923 K (Yb, Lu) that
occurs through a slow process is attributed to the thermal
decomposition of the carbonaceous residue and carbonate
to the respective oxide, Ln2O3 (Ln = Dy–Lu, Y). The
formation of carbonate and carbonaceous residue in this
step was confirmed by tests with hydrochloric acid solution
on samples heated up to the temperature as indicated by the
TG curves, and this is in agreement with the thermal
decomposition of the trivalent lanthanide compounds with
phenyl-substituted derivatives of benzylidendepyruvate
[14, 18, 19]. The formation of carbonate has already been
confirmed by the IR spectra [6, 7].
The exotherms observed for all compounds with evi-
dence of two (Tm, Yb, Lu); three (Ho–Er) or four (Tb)
peaks between 448 and 823 K are attributed to the thermal
decomposition of the anhydrous compounds, where the
oxidation of the organic matter takes place in consecutive
and/or overlapping steps.
123

100
A. B. Siqueira et al.
Acknowledgements The authors thank FAPESP (Procs. 90/2932-4
and 2005/00926-4), CNPQ and CAPES Foundations (Brazil) for
financial support.
DSC
exo up
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873
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Temperature/K
Fig. 3 The DSC curves of: (a) Tb(L)3ꢀ4.5H2O (m = 4.932 mg); (b)
Dy(L)3ꢀ3.5H2O (m = 4.822 mg); (c) Ho(L)3ꢀ3.5H2O (m = 5.005 mg);
(d) Er(L)3ꢀ2.5H2O (m = 5.115 mg); (e) Tm(L)3ꢀ3H2O (m = 5.008 mg);
(f)Yb(L)3ꢀ3H2O(m = 5.064 mg); (g)Lu(L)3ꢀ3H2O(m = 5.131 mg); (h)
Y(L)3ꢀ3H2O (m = 5.017 mg). L = pyruvate
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123