YSZCZEK
ammonium trimellitate were poured over the gel in
different arms of U-tube. After several weeks com-
plexes in the form of the globules were separated
from the gel media and washed by distilled water.
The contents of C and H were obtained by means
of elemental analysis using a Perkin-Elmer CHN 2400
apparatus. The infrared spectra of the lanthanide(III)
complexes and 1,2,4-benzenetricarboxylic acid were
recorded in KBr discs on a SPECORD M80 spectro-
By diffusion of substracts in silica gel, three
complexes of the formulae: Nd(btc)·6H O, Gd(btc)·
4.5H O and Er(btc)·5H O (where btc=
(C H (COO) ) were obtained. The compounds were
2
2
2
3
–
6
3
3
crystallized in the form of globular crystallites of
color characteristic for lanthanide ions. The com-
plexes are isomorphous as arised from their X-ray
powder diffraction patterns.
The IR spectra of the complexes (Table 2) show
–1
sharp absorption band at 3640 cm assigned to
–1
photometer over the range 4000–400 cm . The X-ray
powder diffractions of the studied complexes were
recorded on a HZG 4 diffractometer, using Ni filtered
stretching vibrations nOH of coordination water
molecules [10]. The broad band with maximum at
–1
CuK
range of 2q= 5–70°.
Thermal analysis of prepared complexes was
carried out by the TG-DTA method using
SETSYS 16/18 analyser (Setaram). Samples (about
mg) were heated in ceramic crucible up to
a
radiations. Measurements were taken over the
3432 cm is due to stretching vibrations nOH of
hydrogen bonded water molecules. The complexation
process of lanthanide ions by trimellitate ligand is
confirmed by the IR spectra of the complexes. The
spectra of all compounds show intense bands with
–1
7
maximum at 1536 cm assigned to the asymmetric
–
00–800°C at a heating rate of 10°C min in dynamic
3 –1
air atmosphere (v=0.75 dm h ).
1
7
stretching vibrations of carboxylate groups nas(COO)
The symmetric stretching vibrations of carboxylate
.
groups n– 1s ym(COO) are located at 1408, 1412 and
1416 cm , respectively for complexes of Nd, Gd and
Results and discussion
Er complexes. The positions of these characteristic
bands indicate the existence of similar coordination
mode in the complexes. The application of magnitude
of Dn as spectral criterion for the prediction of the
mode of carboxylate bonding in the case of lanthanide
trimellitates is impossible because sodium salt of
1,2,4-benzenetricarboxylic acid do not has ionic char-
acter as can be clearly seen from the crystal struc-
ture [11]. For achieving the coordination number 9 or 8
(for heavier lanthanides) some water molecules and
carboxylate oxygen atoms form coordination environ-
ments of Ln(III) ions. Moreover, positions of carbo-
xylate groups in trimellitate molecule force the bridg-
ing or bridging–chelating character of COO groups.
The studied compounds have been investigated
by thermal methods in the temperature range
Complexes of lanthanide(III) with 1,2,4-benzene-
tricarboxylic acid were prepared by hydrothermal
method and crystallization in gel medium (Table 1).
Unfortunately, in spite of applications of two new
methods of synthesis, the obtaining of complexes in
the form of monocrystals was failed.
Table 1 Elemental analysis data of lanthanide(III)
1
,2,4-benzenetricarboxylates
C/%
H/%
Complex
calc.
found
calc. found
Nd(btc)·6H
2
O
23.52
26.78
25.69
29.16
33.43
31.31
31.02
29.88
29.75
30.48
28.92
28.73
28.55
28.43
28.13
27.98
23.10
26.22
25.10
28.80
32.98
30.86
30.77
29.55
29.31
30.80
28.08
28.43
28.50
28.05
28.51
26.67
3.27
2.96
3.09
1.75
0.93
1.74
1.75
1.94
1.93
1.41
1.87
1.86
1.85
1.84
1.83
1.81
3.19
3.10
2.94
1.65
0.90
1.60
1.85
1.82
1.83
1.35
1.77
1.80
1.71
1.77
1.69
1.75
Gd(btc)·4.5H
Er(btc)·5H
2
O
3
0–800°C. The results showed that their thermal be-
haviors are similar and the thermal data are summa-
rized in Table 3. Heating of the compounds above
0°C resulting in dehydration process, which as can
2
O
La(btc)·1.5H
Ce(btc)
2
O
4
Pr(btc)·1.5H
2
O
be seen from Figs 1–3 occurs in two stages. The first
mass loss accompanied by endothermic effect (at
171.3, 185.9, 172.7°C for complexes of Nd, Gd and
Er, respectively) corresponds to the release of weaker
bonding water molecules yielding the unstable hy-
drated lanthanide(III) trimellitate. The second step of
dehydration corresponds to loss of remaining water
molecules resulting in anhydrous complex formation.
Heating of anhydrous complexes causes decomposi-
tion. In oxidative air atmosphere degradation of
trimellitic ligand is accompanied by strong exother-
mic effect connected with burning of organic ligand.
The solid residues obtained during thermal decompo-
Nd(btc)·1.5H
2
O
Sm(btc)·2H
Eu(btc)·2H
Gd(btc)·H
2
O
2
O
2
O
Dy(btc)·2H
Ho(btc)·2H
2
2
O
O
Er(btc)·2H
2
O
Tm(btc)·2H
2
O
Yb(btc)·2H
Lu(btc)·2H
2
O
2
O
3–
btc=C H (COO)
6
3
3
834
J. Therm. Anal. Cal., 93, 2008