R.N. Marques et al. / Journal of Alloys and Compounds 344 (2002) 88–91
89
ride (or nitrate) ions, filtered through and dried on What-
man no. 42 filter paper, and kept in a desiccator over
anhydrous calcium chloride, under reduced pressure 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 complex-
ometric titrations with standard EDTA solution, using
xylenol orange as indicator [14]. Carbon and hydrogen
microanalysis were performed using an EA 1110, CHNS-
O Elemental Analyser (CE Instruments).
yttrium compounds with other phenyl-substituted deriva-
tives of BP [6,7].
Infrared bands found for 4-Me-BP (sodium salt), cen-
tered at 1670 cm21 (ketonic carbonyl stretching) and 1635
cm21 (anti-symmetrical carboxylate vibration) are both
shifted to lower frequencies in the complexes, namely
1643–1635 and 1593–1585 cm21, respectively, suggesting
lanthanides coordination 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
substances, also suggest the –COCOO2 moiety as the
bidentate metal binding site of 4-Me-BP [5].
X-ray powder patterns were obtained by using a
Siemens D-500 X-ray diffractometer, employing Cu Ka
˚
radiation (l51.541 A) and settings of 40 kV and 20 mA.
The simultaneous TG-DTA curves of the compounds are
shown in Fig. 1. These curves show mass losses in two
(Ce), four (Eu), five (La, Pr, Sm) and six (Nd) steps
between 55 and 725 8C. The first mass loss in the range
70–125 8C (La-Sm) and 55–140 8C (Eu) is ascribed to
dehydration, which occurs in a single step.
Infrared spectra for 4-Me-BP (sodium salt) as well as for
its trivalent lanthanide compounds, were run on a Nicolet
mod. Impact 400 FT-IR instrument, within the 4000–400
cm21 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
min21. A heating rate of 20 8C min21 was adopted, with
samples weighing about 7–8 mg. Alumina crucibles were
used for recording the TG-DTA curves.
After dehydration, the mass losses observed above
145 8C for the cerium compound (Fig. 1b), above 155 8C
for the samarium and europium compounds (Fig. 1e,f) and
above 170 8C for the lanthanum, praseodymium and
neodymium compounds (Fig. 1a,c,d), are due to the
thermal decomposition of the anhydrous compounds; these
take place in consecutive and/or overlapping steps with
partial losses which are characteristic for each compound.
For the cerium compound, the thermal decomposition
occurs up to 375 8C, with the formation of cerium(IV)
oxide, CeO2, as the final residue. The smaller thermal
stability of the cerium compound is attributed to the
oxidation reaction of Ce(III) to Ce(IV), together with the
oxidation of the organic matter. This behaviour concerning
the thermal stability of the cerium compound, had already
been observed for other cerium compounds [6,7].
3. Results and discussion
The analytical results of the synthesized compounds are
shown in Table 1. These results permitted to establish the
stoichiometry of the compounds, which is in agreement
with the general formula Ln(4-Me-BP)3?nH2O, where Ln
represents
lanthanides,
4-Me-BP
is
4-
methylbenzylidenepyruvate and n51, except for Eu where
n51.5.
The X-ray powder patterns showed that all the com-
pounds were obtained in amorphous state. The amorphous
state is undoubtedly related to the low solubility of these
compounds, as already observed for the lanthanides and
For the other compounds, the mass losses up to 570 8C
(La, Sm), 445 8C (Pr, Eu) and 600 8C (Nd), corresponding
to exothermic peaks, are attributed to the oxidation of the
organic matter, with the probable formation of dioxycarbo-
nates, Ln2O2CO3, accompanied by small quantities of
Table 1
Analytical data for the LnL3?nH2O compounds
Compound
Lanthanides (%)
Ligand lost (%)
Water (%)
Calcd.
Carbon (%)
Calcd.
Hydrogen (%)
Calcd.
TG
EDTA
Calcd.
TG
TG
E.A.
Calcd.
E.A.
LaL3?H2O
CeL3?H2O
PrL3?H2O
NdL3?H2O
SmL3?H2O
EuL3?1.5H2O
19.17
19.31
19.39
19.76
20.43
20.35
19.32
19.54
19.29
19.75
20.33
20.22
19.38
19.54
19.29
20.04
20.58
20.59
75.03
73.80
74.09
74.47
73.86
72.81
74.80
73.70
74.16
74.48
73.91
72.86
2.49
2.48
2.48
2.47
2.45
3.62
2.55
2.30
2.54
2.50
2.51
3.73
54.70
54.61
54.58
54.30
53.85
53.08
53.96
54.80
54.59
53.88
53.33
53.98
4.04
4.04
4.03
4.01
3.98
4.05
4.17
4.13
4.11
4.17
4.15
4.12
Ln, lanthanides; L, 4-methylbenzylidenepyruvate.
Marques
