Synthesis, characterisation and thermal behaviour of solid stat compounds of 4-methylbenzylidenepyruvate with heavier trivalent lanthanides and yttrium(III)

Article abstract of DOI:10.1016/S0040-6031(02)00143-0

Solid state Ln-4-Me-BP compounds, where Ln stands for heavier trivalent lanthanides (gadolinium to lutetium) and yttrium(III) and 4-Me-BP is 4-methylbenzylidenepyruvate (CH₃-C6H₄-CH=CH-COCOO^-), have been synthesized. Eleme

Full text of DOI:10.1016/S0040-6031(02)00143-0

Thermochimica Acta 395 (2003) 145–150
Synthesis, characterisation and thermal behaviour of solid state
compounds of 4-methylbenzylidenepyruvate with heavier
trivalent lanthanides and yttrium(III)
R.N. Marques, C.B. Melios, M. Ionashiro*
´
Instituto de Quımica, UNESP, SP, CP 355, CEP 14801-970, Araraquara, SP, Brazil
Received 24 October 2001; received in revised form 28 February 2002; accepted 28 February 2002
Abstract
Solid state Ln-4-Me-BP compounds, where Ln stands for heavier trivalent lanthanides (gadolinium to lutetium) and
yttrium(III) and 4-Me-BP is 4-methylbenzylidenepyruvate (CH3–C6H4–CH=CH–COCOOꢀ), have been synthesized. Elemental
analysis, complexometry, X-ray powder diffractometry, infrared spectroscopy and simultaneous thermogravimetry-differential
thermal analysis (TG-DTA), have been used to characterise and to study the thermal behaviour of these compounds. The results
provided information concerning the stoichiometry, crystallinity, ligand’s denticity, thermal stability and thermal decomposition.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Heavier trivalent lanthanides; Yttrium(III); 4-Methylbenzylidenepyruvate; Complexes; Characterization; Thermal behaviour
1. Introduction
of the compounds by means of thermogravimetry,
derivative thermogravimetry (TG, DTG), differential
thermal analysis (DTA), differential scanning calori-
metry (DSC), X-ray powder diffractometry, and other
methods of analysis. Establishment of stoichiometry
and the details of the thermal decomposition were the
main purposes of these studies.
In this paper, the object of the present research
was to prepare solid state compounds of heavier
trivalent lanthanides (i.e. Gd, Tb, Dy, Ho, Er, Tm,
Yb and Lu) and yttrium(III) with 4-methylbenzylide-
nepyruvate (4-Me-BP) and to investigate by means
of complexometry, elemental analysis, X-ray powder
diffractometry, infrared spectroscopy 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 complexes of phenyl-substituted
derivatives of benzylidenepyruvate, C6H5–CH=CH–
COCOOꢀ (BP), have been investigated in aqueous
solutions [1–5] and in the solid state [6–12]. In aqu-
eous solutions these works reported the thermo-
dynamic stability (b1), and spectroscopic parameters
(e1max, lmax), associated with 1:1 complex species, as
well as analytical applications of sodium 4-dimethy-
lamino-BP for the gravimetric determination of
Cu(II), and as indicator in the complexometric titration
of Th(IV) and Al(III), with EDTA. In the solid state,
the works reported the synthesis and investigation
* Corresponding author. Tel. þ55-16-201-6617;
fax: þ55-16-222-7932.
E-mail address: rosemarq@posgrad.iq.unesp.br (M. Ionashiro).
0040-6031/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 0 2 ) 0 0 1 4 3 - 0

146
R.N. Marques et al. / Thermochimica Acta 395 (2003) 145–150
2. Experimental
hydrogen microanalysis were performed by using EA
1110, CHNS-O Elemental Analyser (CE Instruments).
X-ray powder patterns were obtained by using a
Siemens D-500 X-ray diffractometer, employing Cu
The sodium salt of 4-methylbenzylidenepyruvic
acid, was prepared following the same procedure
described in the literature [13]. Aqueous solutions
of 0.10 M Na-4-Me-BP were prepared by direct
weighing of the salt.
Lanthanide and yttrium chlorides were prepared
from the corresponding metal oxides by treatment
with concentrated hydrochloric acid. The resulting
solutions were evaporated to near dryness, the residues
dissolved in distilled water, and the solutions again
evaporated to near dryness to eliminate the excess of
hydrochloric acid. The residues were redissolved in
distilled water, transferred to a volummetric flask and
diluted in order to obtain ca. 0.10 M solutions, whose
pH were adjusted to 5.0 by adding diluted sodium
hydroxide or hydrochloric acid solutions.
˚
Ka radiation (l ¼ 1:541 A) and settings of 40 kV and
20 mA. Infrared spectra for 4-Me-BP (sodium salt) as
well as for its trivalent lanthanide and yttrium(III)
compounds, were run on a Nicolet mod. Impact
400 FT-IR instrument, within the 4000–400 cmꢀ1
range. The solid samples were pressed into KBr
pellets.
Simultaneous TG-DTA curves, were recorded on
a model SDT 2960 thermal analysis system from TA
Instruments. The purge gas was an air flow of 150 ml
minꢀ1. A heating rate of 20 8C minꢀ1 was adopted,
with samples weighing about 7–8 mg. Alumina cru-
cibles were used for recording the TG-DTA curves.
The solid state compounds were prepared by adding
slowly, with continuous stirring, the solution of the
ligand to the respective metal chloride solution, until
total precipitation of the metal ions. The precipitates
were washed with distilled water until elimination
of the chloride ion, filtered through and dried on
Whatman no. 42 filter paper, and kept in a desiccator
over anhydrous calcium chloride, under reduced pres-
sure, to constant mass.
In the solid state compounds, hydration water,
ligand and metal ion contents were determined from
the TG curves. The metal ions were also determined by
complexometric titrations with standard EDTA solu-
tion, using xylenol orange as indicator [14]. Carbon and
3. Results and discussion
The analytical results of the synthesised compounds
are shown in Table 1. These results permitted to
establish the stoichiometry of the compounds, which
isinagreementwiththegeneralformulaLn(4-Me-BP)3Á
1.5H2O, where Ln represents trivalents lanthanides
and yttrium and 4-Me-BP is 4-methylbenzyliden-
epyruvate.
The X-ray powder patterns showed that all the
compounds were obtained in amorphous state. The
amorphous state is undoubtedly related to the low
solubility of these compounds, as already observed for
Table 1
Analytical data for the LnL3Á1.5H2O compounds
Compound
Ln (%)
Ligand lost (%)
Calculated TG
Water (%)
Calculated
Carbon (%)
Calculated
Hydrogen (%)
Calculated
Calculated TG
EDTA
TG
EA
EA
GdL3Á1.5H2O 20.91
21.10
20.83
21.05
21.62
21.82
21.89
22.19
22.70
22.77
13.03
21.02
21.00
21.42
21.89
21.82
22.38
22.79
22.92
13.27
72.30
71.61
71.80
71.57
71.35
71.19
70.81
70.68
79.53
72.32
3.59
3.59
3.57
3.56
3.55
3.54
3.52
3.51
3.95
3.67
3.68
3.60
3.50
3.57
3.63
3.44
3.53
4.02
52.71
52.60
52.35
52.18
52.02
51.91
51.63
51.53
57.98
52.13 4.02
52.85 4.02
52.91 4.00
51.39 3.99
51.97 3.98
51.46 3.97
51.33 3.95
51.72 3.94
58.26 4.43
4.17
4.16
4.07
4.05
4.03
4.06
4.01
4.01
4.55
TbL3Á1.5H2O
71.56
71.59
71.50
71.40
71.03
70.70
70.57
79.44
DyL3Á1.5H2O 21.46
HoL3Á1.5H2O 21.71
ErL3Á1.5H2O
21.95
TmL3Á1.5H2O 22.12
YbL3Á1.5H2O 22.54
LuL3Á1.5H2O
YL3Á1.5H2O
22.68
13.01
Ln: trivalent lanthanides and yttrium(III); L: 4-methylbenzylidenepyruvate.

R.N. Marques et al. / Thermochimica Acta 395 (2003) 145–150
147
Table 2
Spectroscopic data for sodium 4-methylbenzylidenepyruvate and for its compounds with heavier trivalent lanthanides and yttrium(III)
ꢀÞ
nsðCOO
ꢀÞ
nasðCOO
Compounds
n
ðOꢀHÞ
(H2O)
n
ðC¼OÞ
4MeBP—NaÁ0.5H2O
Gd(4-MeBP)3Á1.5H2O
Tb(4-MeBP)3Á1.5H2O
Dy(4-MeBP)3Á1.5H2O
Ho(4-MeBP)3Á1.5H2O
Er(4-MeBP)3Á1.5H2O
Tm(4-MeBP)3Á1.5H2O
Yb(4-MeBP)3Á1.5H2O
Lu(4-MeBP)3Á1.5H2O
Y(4-MeBP)3Á1.5H2O
3425 m
3347 m
3352 m
3344 m
3361 m
3359 m
3344 m
3333 m
3355 m
3360 m
1406 m
1412 m
1407 m
1410 m
1415 m
1410 m
1403 m
1402 m
1410 m
1414 m
1635 s
1590 s
1589 s
1589 s
1590 s
1589 s
1587 s
1586 s
1588 s
1590 s
1670 s
1644 s
1631 s
1644 s
1643 s
1641 s
1640 s
1634 s
1645 s
1643 s
ꢀ
ꢀÞ
Strong: s; medium: m, 4-MeBP: 4-methylbenzylidenepyruvate;n
¼ hydroxyl group stretching frequence; nsðCOO and nasðCOO
¼
Þ
ðOꢀHÞ
symmetrical and anti-symmetrical vibrations of the COOꢀ structure; n
¼ ketonic carbonyl stretching frequency.
ðC¼OÞ
Fig. 1. Simultaneous TG-DTA curves of the compounds: (a) Gd(4-Me-BP)3Á1.5H2O (7.601 mg); (b) Tb(4-Me-BP)3Á1.5H2O (7.319 mg);
(c) Dy(4-Me-BP)3Á1.5H2O (8.032 mg); (d) Ho(4-Me-BP)3Á1.5H2O (8.573 mg); (e) Er(4-Me-BP)3Á1.5H2O (7.839 mg); (f) Tm(4-Me-BP)3Á1.5H2O
(7.391 mg); (g) Yb(4-Me-BP)3Á1.5H2O (7.612 mg); (h) Lu(4-Me-BP)3Á1.5H2O (7.335 mg); (i) Y(4-Me-BP)3Á1.5H2O (7.898 mg).

148
R.N. Marques et al. / Thermochimica Acta 395 (2003) 145–150
substances, also suggest the –COCOOꢀ moiety as the
bidentate metal binding site of 4-Me-BP [5].
Simultaneous TG-DTA curves of the compounds
are shown in Fig. 1. These curves exhibit mass losses
in three or four consecutive and/or overlapping steps
and thermal events corresponding to these losses.
Two patterns of thermal behaviour are observed up
to 400 8C. Firstly, a close similarity is noted concern-
ing the TG-DTA profiles of the gadolinium and ter-
bium compounds, Fig. 1a and b. On the other hand,
dysprosium to lutetium and yttrium compounds
display another set of very similar TG-DTA profiles,
Fig. 1c–i.
These curves also show that the first mass loss for all
the compounds occurs within the same temperature
range (i.e. 50–140 8C); the second mass loss also
begins at the same temperature (155 8C), showing that
the thermal behaviour up to this step is not dependent
on the nature of the lanthanide ion. However, the
features shown by the next steps of thermal decom-
position as well as the mass lost in each step are
characteristic of each compound, and no depend on the
lanthanide ion present. Probably this behaviour is
because all the compound was obtained in the amor-
phous state.
For all the compounds, the first mass loss (range:
55–140 8C), associated to endothermic peaks at 95–
100 8C, is ascribed to the dehydration, which occurs in
a single step and through a slow process. This beha-
viour was also observed during the dehydration of
lanthanides and yttrium compounds with other phe-
nyl-substituted derivatives of BP, and it seems to be
characteristic of compounds obtained in amorphous
state [6,7,12].
Fig. 1. (Continued ).
the lanthanides and yttrium compounds with other
phenyl-substituted derivatives of BP [6,7].
Infrared spectroscopic data on 4-methylbenzylide-
nepyruvate and its compounds with heavier trivalent
lanthanides and yttrium(III) are shown in Table 2.
The bands found for 4-Me-BP (sodium salt), centred
at 1670 cmꢀ1 (ketonic carbonyl stretching) and
1635 cmꢀ1 (anti-symmetrical carboxylate vibration)
are both shifted to lower frequencies in the complexes,
namely, 1645–1631 and 1590–1586 cmꢀ1, respec-
tively, suggesting lanthanides and yttrium co-ordina-
tion both by the a-ketonic carbonyl and carboxylate
groups of the ligand. This behaviour is in line with that
observed for the 1:1 complexes of the same ligand
with lanthanides in aqueous solution, where linear
free energy relationships, as applied to oxygen donor
Once dehydrated, the anhydrous compounds are
stable up to 155 8C, and above this temperature up
to 415 8C (Gd, Er, Yb); 455 8C (Tb); 410 8C (Dy);
490 8C (Ho); 420 8C (Tm, Y) and 430 8C (Lu), the
mass losses corresponding to exothermic events are
attributed to the oxidation of organic matter. For the
gadolinium and terbium compounds, the mass losses
occur in two consecutive steps through fast processes,
without a plateau between the steps. The similarity of
the TG-DTA curves up to this point suggests that the
decomposition mechanism is the same, for both com-
pounds. For the other compounds (Dy–Lu, Y), the
mass losses occur in a single step. The change in slope
that occurs in the TG curves above 320 8C, is due to

R.N. Marques et al. / Thermochimica Acta 395 (2003) 145–150
149
the increase of the reactions’ rates. The similarity
among these curves, also suggests that the decom-
position mechanism should be the same for the afore-
mentioned compounds.
confirmed, in all cases, evolution of CO2 and presence
of the carbonaceous residues.
For the Dy, Ho, Tm, Yb, Lu and Y compounds, the
thermal decomposition of the corresponding interme-
diates and of the carbonaceous residues occurs simul-
taneously and slowly in a single step; for the Gd, Tb and
Er compounds, two steps are observed. In corres-
pondence with the mass losses, the DTA curves show
small and broad exothermic events only for the Ho and
Er compounds, while for the other compounds these
thermal events are not observed. This is probably due to
the balance between in exothermic process (oxidation
of the carbonaceous residue) and an endothermic one
(decomposition of the metal dioxycarbonates); the
For each of the considered compounds, the oxida-
tion of the organic matter yields an intermediate
derivative, accompanied by a carbonaceous residue.
The intermediate is probably the corresponding diox-
ycarbonate, as already observed for the complexes of
other phenyl-substituted derivatives of BP with triva-
lent lanthanides and yttrium(III) [6,7]. Tests with
hydrochloric acid solution on samples heated up to
the temperatures of formation of these intermediates,
as indicated by the corresponding TG-DTA curves,
Table 3
Temperature ranges (Y), mass losses (%) and peak temperatures observed for each step of the TG-DTA curves of the compounds
LnL3Á1.5H2O where Ln ¼ trivalent lanthanides and yttrium(III); L ¼ 4-methylbenzylidenepyruvate
Compound
Steps
First
Second
Third
Fourth
GdL3Á1.5H2O
Y (8C)
Loss (%)
55–140
3.67
155–265
20.09
265–415
41.32
415–720
10.91
Peak (8C)
95 (endo)
260 (exo)
390 (exo)
545 (exo)
TbL3Á1.5H2O
DyL3Á1.5H2O
HoL3Á1.5H2O
ErL3Á1.5H2O
TmL3Á1.5H2O
YbL3Á1.5H2O
LuL3Á1.5H2O
YL3Á1.5H2O
Y (8C)
Loss (%)
55–140
3.68
155–290
21.10
290–455
50.47
455–710
1.99
–
Peak (8C)
100 (endo)
280 (exo)
435 (exo)
Y (8C)
Loss (%)
55–140
3.60
155–410
65.90
410–715
5.69
–
Peak (8C)
100 (endo)
390 (exo)
Y (8C)
Loss (%)
55–140
3.50
155–490
490–730
2.86
68.64
Peak (8C)
100 (endo)
385, 415 (exo)
620 (exo)
Y (8C)
Loss (%)
55–140
3.57
155–415
57.79
415–500
10.20
500–750
3.41
Peak (8C)
100 (endo)
400 (exo)
445 (exo)
635 (exo)
Y (8C)
Loss (%)
55–140
3.63
155–420
63.07
420–750
7.96
–
Peak (8C)
100 (endo)
385 (exo)
Y (8C)
Loss (%)
55–140
3.44
155–415
63.29
415–760
7.41
–
Peak (8C)
100 (endo)
380 (exo)
Y (8C)
Loss (%)
55–140
3.53
155–430
65.45
430–770
5.12
–
Peak (8C)
100 (endo)
400 (exo)
Y (8C)
Loss (%)
55–140
4.02
155–420
75.26
420–730
4.18
–
Peak (8C)
100 (endo)
370, 400, 440 (exo)

150
R.N. Marques et al. / Thermochimica Acta 395 (2003) 145–150
resulting net heats produce only small exothermic peak
or no thermal event at all.
References
[1] C.B. Melios, V.R. Torres, M.H.A. Mota, J.O. Tognolli, M.
Molina, Analyst 109 (1984) 385.
For all the compounds, the final thermal decom-
position residues were the respective oxides, Tb4O7
and Ln2O3 (Ln ¼ Gd, Dy–Lu, Y), as proven by X-ray
powder diffration analyses of these residues.
The mass losses, temperature ranges and the peak
temperatures observed for each step of the TG-DTA
curves are shown in Table 3.
[2] C.B. Melios, J.T.S. Campos, M.A.C. Mazzeu, L.L. Campos,
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4. Conclusions
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Thermochim. Acta 250 (1995) 151.
From the TG curves and elemental analysis, a
general formula could be established for these com-
pounds in the solid state. The infrared spectroscopic
data suggest that 4-Me-BP acts as a bidentate ligand
towards trivalent lanthanides and yttrium(III).
The TG-DTA curves and X-ray powder patterns
provided previously unreported information concern-
ing crystallinity, thermal stability and thermal decom-
position of these compounds.
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The authors thank FAPESP (Proc. 97/12646-8) and
CNPq Foundations (Brazil) for financial support.
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