A.C. Gigante et al. / Thermochimica Acta 536 (2012) 6–14
7
Table 1
that the lanthanum to neodymium mandelates are more soluble
Theoretical geometry parameters of lanthanum(III) complex with mandelate.
than samarium to gadolinium ones.
˚
The precipitates were washed with distilled water until chlo-
ride (or nitrate) ions were eliminated, filtered and dried at 50 ◦C
in a forced circulation air oven during 12 h and maintained in a
desiccator over anhydrous calcium chloride.
dOwater La
dOCOO La
dCCOO OCOO
2.62 A
˚
2.52 A
˚
1.27 A
˚
1.52 A
dCR
CCOO
C
˚
dC C(ring)
1.39 A
<Hwater Owater La
<OCOO La OCOO
<C OCOO La
106.09◦
52.17◦
For the La to Nd compounds, due to a great loss during the wash-
ing of the precipitates, small quantity of these mandelates were
obtained. Thus, the same were also prepared by neutralization of
the respective lanthanide carbonates with mandelic acid.
The carbonates of lanthanum to neodymium were prepared by
adding slowly with continuous stirring saturated sodium hydrogen
carbonate solution to the corresponding metal chloride or nitrate
for cerium until total precipitation of the metal ions. The precip-
itates were washed with distilled water until the elimination of
chloride or nitrate ions (qualitative test with AgNO3/HNO3 solu-
tion for chloride ions or diphenylamine/H2SO4 solution for nitrate
ions) and maintained in aqueous suspension.
Solid-state La(III) to Nd(III) compounds were prepared by mix-
ing the corresponding metal carbonates maintained in aqueous
suspension with mandelic acid in slight excess. The aqueous sus-
pension was heated up to ebullition until total neutralization of the
carbonate. The solutions of the respective metal mandelates were
evaporated up to dryness in water bath, washed with ethanol to
eliminate the mandelic acid in excess, dried at 50 ◦C in a forced
circulation air oven during 12 h and kept in a desiccator over anhy-
drous calcium chloride.
contents were determined from TG curves. The metal ions were
also determined by complexometry with standard EDTA solution
after igniting the compounds to the respective oxides and their
dissolution in hydrochloric acid solution [12,13].
Carbon and hydrogen contents were determined by calculation
based on the mass losses observed in the TG curves, since the hydra-
tion water and ligand lost during the thermal decomposition occur
with the formation of the respective oxides with stoichiometry
known, as final residues.
93.66◦
118.48◦
<CR
C
d: distance; <: angle; COO: carboxylate group; R C: benzyl carbon.
atom (2D) were calculated according to the procedure described in
Ref. [16] and these values are: ˛s = 0.00669534, ˛p = 0.079333735,
˛d = 0.096432865.
Basis set for Na (2S) atom. The 22s13p [discretization param-
eters: ˝(s) = −0.620, ꢁ˝(s) = 0.136, N(s) = 6.0; ˝(p) = −0.268,
ꢁ˝(p) = 0.127, N(p) = 6.0]/10s6p.
(13,1,1,1,1,1,1,1,1,1/8,1,1,1,1,1) basis set were built with the
aid of the Generator Coordinate Hartree–Fock method. The polar-
function developed in this work for sodium mandelate are available
In order to better describe the properties of the compound in
the implementation of the calculations, it was necessary to include
polarization functions [16–18] for all atoms of the compound.
The polarization functions are: ˛p = 0.33353749 for H (2S),
˛d = 0.72760279, and ˛d = 0.36059494 for
C O
(3P), (3P),
˛d = 0.42912802 for Na (2S) respectively, and ˛f = 0.36935391
for La (2D) atoms. The role of a basis set is a crucial point in
configuration of the metal in the complex differs from the neutral
state. The performed molecular calculations in this study were
done using the Gaussian 09 routine [19].
The theoretical infrared spectrum was calculated using a har-
monic field [20] based on C1 symmetry (electronic state 1A).
description of vibrational modes are presented. The geometry opti-
mization was computed using the optimized algorithm of Berny
and the calculations of vibrational frequencies were also imple-
rithm of Berny can be seen in Fig. 1. It was also shown that the
compound in Fig. 1a is 5.74 kcal mol−1 more stable than the analo-
gous one in Fig. 1b. The structure parameters obtained for the most
stable compound are shown in Table 1.
X-ray powder patterns were obtained by using a Siemens D-
˚
5000 X-Ray Diffractometer employing CuK␣ radiation (ꢀ = 1.541 A)
and setting of 40 kV and 20 mA.
The attenuate total reflectance infrared spectra for sodium man-
delate and for its metal-ion compounds were run on a Nicolet iS10
FTIR spectrophotometer, using ATR accessory with Ge window.
Simultaneous TG–DTA and DSC curves were obtained with two
thermal analysis systems, model SDT 2960 and Q10, both from TA
Instruments. The purge gas was an air flow of 100 mL min−1. A
heating rate of 10 ◦C min−1 was adopted, with samples weighing
about 7 mg. Alumina and aluminum crucibles, the latter with per-
forated cover, were used for recording the TG–DTA and DSC curves,
respectively.
The measurements of the gaseous products were carried out
using a TG–DSC1 Mettler Toledo coupled to a FTIR spectrophotome-
ter Nicolet with gas cell and DTGS KBr detector. The furnace and the
heated gas cell (250 ◦C) were coupled through a heated (200 ◦C)
120 cm stainless steel line transfer with diameter of 3 mm, both
purged with dry air (50 mL min−1). The FTIR spectra were recorded
3. Results and discussion
The analytical and thermoanalytical (TG) data are shown in
these compounds, which are in agreement with the general formula
Ln(L)3·nH2O, where Ln represents lanthanides, L is mandelate and
n = 0 (Ce), 1 (La) or 2 (Pr to Gd).
with 16 scans per spectrum at a resolution of 4 cm−1
.
The X-ray powder patterns (Fig. 2) show that the lanthanum
compound was obtained in the amorphous state, while the other
compounds have a crystalline structure, evidencing the forma-
tion of two isomorphous series: being the praseodymium and
neodymium compounds the first one and samarium to gadolin-
ium compounds the other series. The X-ray powder patterns also
show that the crystallinity of these compounds follows the order:
hybrid theory [14] using the Lee–Yang–Par (LYP) correlation func-
tional [15], and the basis sets used for calculations were: 4s for H
(2S) [16], [5s4p] for C (3P) and O (3P) [16], [10s6p] for Na (2S) and
[17s11p7d] for La (2D) [17]. The diffuse functions for the lanthanum
∼
Gd > Sm > Eu > Ce > Nd Pr > La.
=
Gigante
