Synthesis, characterization and thermogravimetric study of the complexes [Eu(12-crown-4)·phen2]·X3 (phen=1,10-phenanthroline; X=F, Cl, Br, SCN, ClO4 and NO 3): Effect of the counter-ion on the thermal degradation profile

Article abstract of DOI:10.1016/j.tca.2005.06.020

The complexes [Eu(12-crown-4)·phen₂]·X₃ (phen = 1,10-phenanthroline; X = F, Cl, Br, SCN, ClO₄ and NO ₃) were synthesized and characterized by elemental analysis, UV-vis and IR spectroscopy. A thermogravimetric study was performed to evaluate the effect of the counter-ion on the thermal degradation profile of the [Eu(12-crown-4)·phen₂]⁺³ complex cation. In general, the 1,10-phenanthroline molecules are the first to be released, showing that the crown ether molecule forms more stable bonds with the +3 cation. The fluorine complex sublimes and thus could be employed as a precursor for preparation of luminescent films.

Full text of DOI:10.1016/j.tca.2005.06.020

Thermochimica Acta 437 (2005) 59–61
Synthesis, characterization and thermogravimetric study of the
complexes [Eu(12-crown-4)·phen ]·X (phen = 1,10-phenanthroline;
2
3
X = F, Cl, Br, SCN, ClO and NO ): Effect of the counter-ion
4
3
on the thermal degradation profile
a
a
a
M oˆ nica F. Belian , Severino Alves Jr. , Gilberto F. de S a´ ,
a
b,∗
Wagner E. Silva , Robson F. de Farias
a
Departamento de Qu ´ı mica Fundamental, Universidade Federal de Pernambuco, 50670-901 Recife, Pernambuco, Brazil
b
Programa de P o´ s-Gradua c¸ a˜ o em Qu ´ı mica, Universidade Federal do Rio Grande do Norte, Cx. Postal 1664,
59078-970 Natal, Rio Grande do Norte, Brazil
Received 3 March 2005; received in revised form 9 June 2005; accepted 16 June 2005
Available online 19 July 2005
Abstract
The complexes [Eu(12-crown-4)·phen
2
]·X
3 4 3
(phen = 1,10-phenanthroline; X = F, Cl, Br, SCN, ClO and NO ) were synthesized and charac-
terized by elemental analysis, UV–vis and IR spectroscopy. A thermogravimetric study was performed to evaluate the effect of the counter-ion
+
3
on the thermal degradation profile of the [Eu(12-crown-4)·phen
2
]
complex cation. In general, the 1,10-phenanthroline molecules are the
first to be released, showing that the crown ether molecule forms more stable bonds with the +3 cation. The fluorine complex sublimes and
thus could be employed as a precursor for preparation of luminescent films.
©
2005 Elsevier B.V. All rights reserved.
Keywords: Crown ether; Thermogravimetry; Counter-ion; Europium
1
. Introduction
2. Experimental
Thermogravimetry is a reliable tool to study the
All reagents were of analytical grade (Aldrich) and were
employed without further purification. With the exception of
EuF3, all europium salts were prepared from the respective
oxide: EuX3, were X = Cl, Br, NO3 and ClO4 were pre-
pared by reacting stoichiometric amounts of Eu2O3 and HCl,
HBr, HNO3 and HClO4, respectively. The europium content
was checked by EDTA titration. The Eu(SCN)3 was pre-
pared by reacting an ethanolic solution of EuCl3 with KSCN.
The secondary product (KCl) was removed by filtration and
the obtained solution of Eu(SCN)3 was used to prepare the
respective crown ether complex.
physico-chemical behavior of coordination compounds.
There is a very close relation between thermogravimetric,
reaction calorimetric and spectroscopic data for coor-
dination compounds [1]. The present work describes
the synthesis, characterization and thermogravimetry of
[
Eu(12-crown-4)·phen2]·X3 (phen = 1,10-phenanthroline;
X = F, Cl, Br, SCN, ClO4 and NO3) to evaluate the effect
of the anion on the thermal degradation of the complex
cation.
The complexes were synthesized as follows:
−
4
∗
5.0 × 10 mol of the europium salt and the same amount
Corresponding author. Tel.: +55 95 81118206; fax: +55 95 6213137.
E-mail address: robdefarias@yahoo.com.br (R.F. de Farias).
of 12-crown-4 were added to a 1:1 (v:v) mixture of acetone/
0
040-6031/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2005.06.020

6
0
M.F. Belian et al. / Thermochimica Acta 437 (2005) 59–61
ethanol with magnetic stirring. After precipitation of the
crown complexes (3 h), 1.0 mmol of 1,10-phenanthroline
was added. After evaporation of the solvent, the complex
was isolated, washed with cold acetone, and dried under
vacuum at room temperature.
AllcomplexeswerecharacterizedbyCHNelementalanal-
ysis (Carlo Erba model EA 1110), melting point (Isothermal
9
100), UV (Perkin-Elmer lambda 6, W lamp, 800–340 nm,
−
5
−6
−3
deuterium lamp, 350–190 nm, 10 to 10 mol dm in
ethanol) and IR spectroscopy (KBr discs, Bruker FTIR,
model IF66). Thermogravimetric curves were obtained
on a TGA 50/50H Shimadzu under N2 atmosphere at
◦
−1
.
1
0 C min
Fig. 1. Schematic representation for the supposed structure of the 12-crown-
/phen prepared complexes. The Eu(III) cation is coordinated to the four O
atoms in the crown ether ring, as shown in (a) as well as to four N atoms of
two phen molecules, as shown in (b).
4
3
. Results and discussion
The CHN elemental analysis are in good agreement with
the proposed formulas, as shown in Table 1. The measured
melting points are also summarized in Table 1.
With exception of the fluoride complex, the complexes
degrade without melting suggesting that the ionic bonds of
the crystal lattice are stronger than the intramolecular bonds.
The crown ether molecule is UV silent, hence the absorp-
tion is due to phenanthroline only. All absorptions are of the
*
␲
→ ␲ type, and the observed shifts, as well as the inversion
of the bands at 203 and 226 nm (comparing free phenanthro-
line and complexes) agree with coordination of phen to the
metal ion.
In all the complexes, negative shifts of the C–O–C (crown
ether) and C N (phenanthroline) IR absorption bands are
observed, in agreement with coordination through oxygen
and nitrogen, respectively. Despite the fact that a structural
study was not performed in this work, taking into account the
coordination features of 12-crown-4 and phen, we propose
the structure shown in Fig. 1.
The thermogravimetric curves are shown in Figs. 2 and 3.
Form the experimental mass loss percentages, as a gen-
eral behavior, the 1,10-phenathroline molecules are released
first. The crown ether molecule apparently forms more stable
bonds with the +3 cation.
Fig. 2. Thermogravimetric curves for the complexes: (a) [Eu(12-
crown-4)·phen2]F3, (b) [Eu(12-crown-4)·phen2]Cl3 and (c) [Eu(12-crown-
4)·phen2]Br3.
the fluoride complex, the ligand mass loss corresponds to
73.4%, with a final residue of 26.6%, due to EuF3 (calculated
value = 27.8%). This could be employed as a good precursor
for the preparation of luminescent films. For the chloride
In the halide complexes, a first mass loss step is associ-
ated with the release of physisorbed water molecules. For
Table 1
Elemental analysis results (calculated values are between parenthesis) and melting points for the synthesized Eu-(12-crown-4) complexes
◦
Complex
C
H
N
mp ( C)
[
[
[
[
[
[
Eu(12-crown-4)·phen2]F3
Eu(12-crown-4)·phen2]Cl3
Eu(12-crown-4)·phen2]Br3
Eu(12-crown-4)·phen2](ClO4)3
Eu(12-crown-4)·phen2](SCN)3
Eu(12-crown-4)·phen2](NO3)3
a
52.3 (52.0)
48.2 (48.0)
40.6 (41.0)
38.6 (38.9)
49.4 (49.0)
44.0 (43.9)
4.0 (4.2)
3.3 (4.0)
3.0 (3.4)
3.8 (3.3)
3.6 (3.7)
3.7 (3.7)
8.0 (7.5)
7.0 (7.1)
6.6 (6.1)
6.0 (5.7)
11.9 (11.4)
11.1 (11.2)
97
b
236a
171
240
259
a
a
a
The complex degrades at the reported temperature.
b
◦
This complex does not melt, and does not degrade until 300 C.

M.F. Belian et al. / Thermochimica Acta 437 (2005) 59–61
61
value = 32.4% = EuCl3). For the bromide complex, the final
residue is 34.2%, due to the formation of europium oxide
(
calculated value = 36.0%).
The SCN , ClO4 and NO3 complexes release phenan-
−
−
−
throline before the crown ether. In these three complexes,
the final residue is Eu2O3, within 2–10% of calculated val-
ues. The difference between the fluoride and chloride com-
−
◦
plexes (the F complex loses both ligands at 250 C, whereas
−
◦
the Cl complex releases the ligands above 300 C) is
remarkable.
Acknowledgement
The authors thanks the Conselho Nacional de Desenvolvi-
mento Cient ´ı fico e Tecnol o´ gico (CNPq) for fellowships and
financial support.
Fig. 3. Thermogravimetric curves for the complexes: (a) [Eu(12-crown-
4
)·phen2](SCN)3, (b) [Eu(12-crown-4)·phen2](ClO4)3 and (c) [Eu(12-
crown-4)·phen2](NO3)3.
complex, a total ligand mass loss of 67.9% is observed.
The first ligand mass loss is associated with the release
of phenanthroline molecules, and the second one with the
release of 12-crown-4. The final residue is 32.2% (calculated
Reference
[1] R.F. de Farias, C. Airoldi, H. Scatena Jr., Polyhedron 21 (2002)
1677.