Thermal investigation by simultaneous TG/DTG-DTA and IR spectroscopy of new lanthanide complexes with salicylhydroxamic acid

Article abstract of DOI:10.1007/s10973-005-0795-2

The reaction of a hydrated nitrate salt of lanthanide (Ln=Pr, Nd, Gd, Dy, Er) with the polyfunctional ligand salicylhydroxamic acid (H₃sha), in the presence of base, afforded solid compounds, insoluble in common organic solvents and in water. The new complexes characterized by means of elemental analyses (C, H, N, Ln), magnetic moment determinations and spectroscopic data (IR, MS). It is proposed that they are neutral, with a possible polymeric structure of the general type: [Ln₂(Hsha)₂(H ₂sha)(DMF)_x(CH₃O)(H₂O)] _n×2H₂O Their thermal decomposition was studied in nitrogen and/or oxygen atmosphere, between 25-1000°C by using simultaneous TG/DTG-DTA technique. The IR spectroscopy used to determine the intermediates and the final products. The intermediates at 180°C suggest the formation of N-hydroxylactam complex, which upon further heating gives a carbonaceous residue of Ln₂O₃ at 1000°C in nitrogen, while in oxygen the stable oxides are formed at 600°C.

Full text of DOI:10.1007/s10973-005-0795-2

Journal of Thermal Analysis and Calorimetry, Vol. 81 (2005) 375–380
THERMAL INVESTIGATION BY SIMULTANEOUS TG/DTG-DTA AND
IR SPECTROSCOPY OF NEW LANTHANIDE COMPLEXES WITH
SALICYLHYDROXAMIC ACID
*
M. Lalia-Kantouri and Ch. Papadopoulos
Aristotle University of Thessaloniki, Department of Chemistry, Laboratory of Inorganic Chemistry, P.O. Box 135,
Thessaloniki 54124, Greece
The reaction of a hydrated nitrate salt of lanthanide (Ln=Pr, Nd, Gd, Dy, Er) with the polyfunctional ligand salicylhydroxamic acid
3
(H sha), in the presence of base, afforded solid compounds, insoluble in common organic solvents and in water. The new complexes
characterized by means of elemental analyses (C, H, N, Ln), magnetic moment determinations and spectroscopic data (IR, MS). It is
proposed that they are neutral, with a possible polymeric structure of the general type:
[
Ln
2
(Hsha)
2
(H
2
sha)(DMF)
x
(CH
3
O)(H
2
O)]
n
⋅2H
2
O
Their thermal decomposition was studied in nitrogen and/or oxygen atmosphere, between 25–1000°C by using simultaneous
TG/DTG-DTA technique. The IR spectroscopy used to determine the intermediates and the final products. The intermediates
at 180°C suggest the formation of N-hydroxylactam complex, which upon further heating gives a carbonaceous residue of Ln
at 1000°C in nitrogen, while in oxygen the stable oxides are formed at 600°C.
2 3
O
Keywords: IR, lanthanide(III) complexes, MS, salicylhydroxamic acid, TG/DTG-DTA
Introduction
ing hydroxamate oxygen atoms [9] but not with the
phenolic oxygen atom. When, however, the stoichio-
metric ratio M:L is 1:1, it may act as trianion, tetra-
dentate forming a metallacrown polymer in which the
metals take part in five- and six-membered chelating
ring [10, 11]. Recently, there is an increasing research
interest on the thermal properties of lanthanide com-
plexes with ligands having O and N donor ability, stud-
ied by TG-DTA techniques [12, 13].
The increasing interest in the chemistry of lanthanide
ions is due to their recent applications in therapeutic and
diagnostic pharmaceutical [1, 2], in catalysis and laser
technology [3, 4]. Their ability for high coordination
number, results in the preparation of complexes with
structural differences especially when polyfunctional
ligands are used. Such ligands can be the hydroxamic
acids which may act as bidentate, tridentate or
tetradentate ligands in a number of coordination modes
as mono- or dianions depending mostly on the metal in-
volved, the pH of the reaction solution [5] and the
stoichiometry of metal to ligand ratio. The knowledge of
the biological and medical importance of hydroxamic
acids is well recognized [6] and it has been proved that
the active sites of some biological enzymes include the
hydroxamic acids. In the chelates of simple hydroxamic
acids the ligands behave as bidentate O,O’ donors form-
ing five-membered ring complexes.
Scheme 1 Tautomeric configurations of the salicylhydroxamic
acid
However, in the chelates of salicylhydroxamic
acid (2-OH hydroxamic acid, H sha, Scheme 1), the
3
Survey in the literature revealed that no research
has been done with lanthanide ions and salicylhydrox-
amic acid. Herein we report the synthesis, spectro-
scopic (IR, MS) and thermal studies (TG/DTG-DTA)
of the reaction products of lanthanide nitrates and the
ligand salicylhydroxamic acid.
ligand contains a further coordination site adjacent to
the hydroxamate group. So, the salicylhydroxamic acid
may act as bidentate monoanion through the hydrox-
amic oxygens [7, 8] or in the same complex as bi-
dentate monoanionic or dianionic ligands with bridg-
*
Author for correspondence: lalia@chem.auth.gr
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2005 Akadémiai Kiadó, Budapest

LALIA-KANTOURI, PAPADOPOULOS
Experimental
forded immediately in good yield, insoluble solid com-
pounds, very stable in air in solid-state, but extremely
sensitive upon heating. For this reason, their thermal be-
haviour was studied by TG-DTA technique to explore
their thermal stability and decomposition mode under
controlled heating rate, as well as their fragmentation
pattern with the aim of mass spectroscopy.
The characterization of their molecular structure
was made by elemental analyses, magnetic moments
and infrared spectroscopy. A representative IR spectrum
for the Nd complex (compound 2) is given in Fig. 1.
Synthesis of the complexes
[Ln (Hsha) (H sha)DMF) (CH O)(H O)] 2H O
2 2 2 x 3 2 n 2
The hydrated nitrate salts of lanthanide (Ln(NO3)3
6H O, where Ln=Pr, Nd, Gd, Dy, Er) and the
salicylhydroxamic acid (H sha=C H NO ) were pur-
⋅
2
3
7
7
3
chased from Aldrich.
To a MeOH-DMF solution (5:1) of lanthanide
nitrate (0.65 mmol) was added dropwise a methanolic
solution of deprotonated by NaOH, salicylhydrox-
amic acid (1.0 mmol). Immediately a solid product
came out, filtrated and dried in air.
The compounds prepared are pale coloured, insol-
uble in common organic solvents and in water, indica-
tive of polynuclear species, and are stable in air in the
solid-state. Their physicochemical characteristics are
listed in Table 1. The results of elemental analyses are
consistent with metal-to-ligand ratio of 2:3, while the
magnetic moments (μeff) are characteristics of trivalent
lanthanide ions. Similar values have been observed with
substituted benzoate complexes of lanthanides [14, 15].
Physical measurements
Stoichiometric analyses (C, H, N) were performed on
a Perkin-Elmer 240B elemental analyzer. Metal con-
tent was determined by EDTA titration after decom-
position with nitric acid, using as indicator xylenol
orange and buffer hexamethylenetetramine [16].
Magnetic susceptibility measurements on pow-
dered samples were performed at 25°C employing the
Faraday method in instrument of Johnson Mathey,
Fig. 1 IR spectrum of the Nd complex
It is deduced that the ligand may act in the same
complex both as bidentate monoanion (H sha) and
2
dianion (Hsha) through the oxygens O,O’ of the
–
hydroxamato group (CONHO ), as well as from the N
atom, possibly coordinated to a second lanthanide
atom, while at least one phenolate hydroxyl is not
deprotonated and coordinated [17]. (IR bands:
type MSB-MKI, calibrated against Hg[Co(SCN)
Infrared spectra were recorded on a Perkin-Elmer
].
4
–1
–1
1
603 cm ν(CO) carbonyl oxamato, 1590 cm
–1
FT-IR 1650 spectrometer, in the region 4000–200 cm
–1
ν(C=N), 3410 cm ν(OH) phenolate hydroxyl,
using KBr pellets. Mass spectra were run on a
RMU-6L Hitachi Perkin-Elmer, double focusing mass
spectrometer, model TS 250 Fision, using direct probe
insertion for the samples, operating at 70 eV.
~
478 Ln–N, ~378 Ln–O.)
Based on the above mentioned, the prepared
compounds seem to be polymeric with possible struc-
ture of the type:
The simultaneous TG/DTG-DTA curves were ob-
tained on a Setaram instrument, model SETSYS-1200.
The samples were heated in platinum crucibles, in nitro-
gen and/or oxygen atmosphere, within the temperature
range 25–1000°C. The heating rate was 10°C min and
the sample size ranged in mass from 10–15 mg. The
stoichiometry of the residues checked with energy
dispersive spectrometry (EDS) of JSM-840A type with
analytical system Oxford ISIS-300.
[Ln
2
(Hsha)
2
(H
2
sha)(DMF)
x
(CH
3
O)(H
2
O)]
n
⋅2H
O
2
where x=2, 3, 4, 5 (Table 1). The existence of crystal
water and coordinated DMF molecules is inferred
–1
from the bands at 3440 and 1657 cm , respectively.
–1
Mass spectra
Mass spectra were obtained for the salicylhdroxamic
acid (Fig. 2a) and for its complex with praseodymium
(Fig. 2b). In the mass spectrum of the ligand detected
the molecular ion (m/e=153) and its fragments corre-
Results and discussion
sponding to the elimination of one hydroxylamine
(
The reactions of the lanthanide nitrate with the poly-
functional ligand salicylhydroxamic acid (H sha) af-
m/e=120) and one CO molecule (m/e=93). A second
3
376
J. Therm. Anal. Cal., 81, 2005

NEW LANTHANIDE COMPLEXES WITH SALICYLHYDROXAMIC ACID
fragmentation process of the ligand gives the daugh-
ter ion, salicylic acid (m/e=138), from which the
salicylaldehyde results (m/e=122) as the basic peak.
In the mass spectrum of the complex, neither the
molecular ion nor those corresponding to the elimina-
tion of one ligand from the parent ions are detected.
This was expected because of their high molecular
mass (967) and thermal instability, which makes it
difficult to give a complete fragmentation pattern.
The two mass spectra exhibit significant differ-
ences in their profiles. There are peaks beyond the
molecular mass of the ligand at m/e 219, 249, 262,
2
76, 389, 482, 491, which cause evidence for the
Pr-ligand bonds. More specifically, the fragments
49, 262 and 276 are assigned to intermediate frag-
ments which contain the metal and one ligand mole-
cule from which CO , NH OH and H O have respec-
tively been eliminated.
2
2
2
2
In the low mass-number region, the observed
peaks correspond to the released DMF molecule
(
m/e=73, base peak) and some fragments of the coordi-
nated ligand. The most prominent from these are CO2
m/e=44) benzaldehyde (m/e=105) and the ligand after
(
the release of a water molecule (m/e=135).
Thermal behaviour
The new lanthanide(III) complexes (1–5) and the
ligand H sha were subjected to TG-DTA analysis from
3
ambient temperature up to 1000°C in nitrogen and ox-
ygen atmospheres. The temperature ranges, the deter-
mined percentage mass losses and the thermal effects
accompanying the decomposition are given in Tables 2
and 3, respectively. Representative thermal curves
TG/DTG-DTA for the Pr and Dy complexes in nitro-
gen are depicted in Figs 3a and b, while in oxygen for
the same complexes in Figs 4a and b, respectively.
For all the investigated compounds, the thermal
decomposition mode in nitrogen seems to follow the
same model. The anhydrous studied compounds, after
3
Fig. 2 Mass spectra of the a – ligand H sha and b – Pr complex
Table 1 Analytical, physical and magnetic data for the complexes [Ln
2
(Hsha)
2
(H
2
sha)(DMF)
x
(CH
3
O)(H
2
O)]
n
⋅2H
2
O
Compound
Colour
green
Yield/%
72
C/%
4.2
N/%
7.4
H/%
Ln/%
μ
eff/MB
3
3.9
(4.00)
28.2
(29.14)
1
Pr x=2
Nd x=3
Gd x=5
Dy x=4
Er x=2
a
4.25
(
34.74)
5.3
35.56)
5.9
36.43)
4.9
35.32)
2.4
32.95)
(7.24)
3
8.3
(8.03)
3.9
(4.00)
27.0
(27.57)
2
3
4
pale violet
brownish
white
70
62
65
75
3.70
8.94
(
3
9.6
(9.19)
4.7
(4.59)
25.3
(25.81)
(
(
(
3
8.8
(8.4)
4.1
(4.2)
27.5
(28.13)
11.80
10.82
3
7.1
(6.86)
3.4
(3.43)
32.0
(32.81)
5
pink
a
calculated values in parenthesis
J. Therm. Anal. Cal., 81, 2005
377

LALIA-KANTOURI, PAPADOPOULOS
Fig. 3 Thermal curves TG/DTG-DTA for the a – Pr and
b – Dy complexes in nitrogen
the elimination of the crystal water molecules at
~
90°C, decompose in several stages followed by sev-
eral exothermic effects. The DTA curve shape indi-
cates that no melting takes place before decomposi-
tion. The endotherm at ~150°C, together with the
mass loss, is evidence for the elimination of the coor-
dinated water molecule.
Upon increasing the temperature, intramolecular
transformations in the coordinated ligands take place,
as it is deduced from the IR spectra of the intermedi-
Fig. 4 Thermal curves TG/DTG-DTA for the a – Pr and
b – Dy complexes in oxygen
–
1
ates at 180°C, where a new band at ~1758 cm ap-
peared (Fig. 5a). This can be attributed to the stretch-
ing mode of a carbonyl group ν(C=O) belonging to a
four-membered ring, such as a lactam.
This transformation may take place by elimina-
tion of a water molecule from one coordinated ligand
and a hydroxylamine from another one. This process
is in accordance with the thermal decomposition of
the ligand and their complexes with some transition
metals mentioned previously [18]. Beyond 200°C, the
continuous mass loss is due to successive elimination
of the DMF molecules and simultaneous degradation
of the derived N-hydroxylactam complex with
DTGmax at 230 and 290°C, as it is inferred from the
absence of the corresponding peaks in the IR spectra
–
1
–1
(1657 cm due to DMF and 1758 cm due to lactam)
of the intermediates at 400°C (Fig. 5b).
Fig. 5 Infrared spectra for the Pr complex: a – at 180°C and
b – at 400°C
378
J. Therm. Anal. Cal., 81, 2005

NEW LANTHANIDE COMPLEXES WITH SALICYLHYDROXAMIC ACID
Table 2 Thermoanalytical results (TG/DTG-DTA) for the complexes [Ln
2
(Hsha) (H
2
2
sha)(DMF)
x
3 2 n 2
(CH O)(H O)] ⋅2H O, in nitrogen
Compound Stage
Trange/°C
DTGmax/°C
DTA
Mass loss/% Evolved moiety formula Mass calc./%
1
2
3
40–130
130–180
180–320
320–600
600–980
>980
88
149
230, 285
570
88 endo
150 endo
240, 289 exo
570 exo
6.9
3.8
18.0
11.0
12.3
48.0
2H
2
O+CH
2H
2DMF+NH
3
OH
6.92
3.73
18.51
10.96
2
O
2
OH
1
4
7 6
C H O
5
residue
–
750 exo
unknown
Pr
6
O11+C
35.23+x
1
2
3
45–130
130–180
180–320
320–600
600–980
>980
74
120
232, 290
540
74 endo
120 endo
245, 290 exo
540 exo
6.5
3.4
24.0
10.1
9.0
2H O+CH
2H
3DMF+NH
2
3
OH
6.40
3.44
24.05
10.13
2
O
2
OH
2
4
7 6
C H O
5
residue
–
760 exo
unknown
Nd +C
47.0
2
O
3
32.16+x
1
2
3
60–200
200–320
320–600
600–980
>980
110
237, 297
100 endo
245, 297 exo
534 exo
8.4
32.0
8.7
10.9
40.0
4H O+CH OH
5DMF+NH OH
2
3
8.44
32.46
8.70
2
3
4
–
–
7 6
C H O
4
residue
750 exo
unknown
Gd +C
2
O
3
29.75+x
1
2
3
50–200
200–320
320–620
620–980
>980
105
245, 290
520
92 endo
256, 296 exo
520 exo
8.9
28.0
9.2
7.0
47.0
2H O+CH OH
4DMF+NH OH
2
3
8.90
28.14
9.18
2
7 6
C H O
4
residue
–
750 exo
unknown
Dy +C
2
O
3
32.29+x
1
2
3
4
50–140
140–180
180–310
310–600
600–980
>980
88
130
245, 295
520
88 endo
140 endo
265, 295 exo
530 exo
6.5
3.5
17.5
10.5
9.0
2H O+CH OH
2H
2DMF+NH
2
3
6.57
3.53
17.54
10.40
2
O
2
OH
5
7 6
C H O
5
residue
–
unknown
Er +C
53.0
2
O
3
37.46+x
Table 3 Thermoanalytical results (TG/DTG-DTA) for the complexes [Ln
2
(Hsha)
2
(H
2
sha)(DMF)
x
(CH
3
O)(H
2
O)]
n
⋅2H
2
O, in oxygen
Compound Stage
T
range/°C DTGmax/°C
DTA
Mass loss/%
Evolved moiety formula
2H O+CH OH
Mass calc./%
1
2
3
40–100
65, 90
130
240
410
490, 520
65, 90 endo
250 exo
410 exo
490, 519 exo
and 553 exo
6.9
3.8
18.0
11.0
25.3
2
3
6.92
3.72
18.51
10.96
25.26
100–180
180–320
320–450
450–580
2
2H O
2DMF+NH
2
OH
1
4
5
7 6
C H O
{2(L–O)–H
2
O}
residue
>580
35.0
Pr
6
O
11
35.23
1
2
3
45–120
120–320
320–470
470–580
>580
70
245
395
485
70 endo
250 exo
395 exo
485 exo
6.5
26.0
10.0
22.0
35.5
2H O+CH
2
2H O+3DMF+NH OH
2 2
3
OH
6.40
27.45
10.13
24.00
32.16
2
3
7 6
C H O
{2(L–O)–H
4
residue
2
O}
2 3
Nd O
1
2
3
60–200
200–320
320–420
420–600
>600
80, 110
240
390
80, 110 endo
265 exo
388 exo
8.5
32.5
8.5
21.50
29.00
4H
2
O+CH
5DMF+NH
3
OH
OH
8.44
32.46
8.70
21.00
29.75
2
7 6
C H O
4
residue
480
485, 582 exo
{2(L–O)–H
Gd
2
O}
2 3
O
1
2
3
4
50–120
120–350
350–440
440–460
460–560
>580
80
275
430
453
470
80 endo
275 exo
430 exo
453, 470 exo
and 525 exo
7.5
30.0
9.5
3H
2
O+CH
4DMF+NH
3
OH
OH+H O
2
7.41
29.70
9.18
2
7 6
C H O
4
5
21.0
{2(L–O)–H
2
O}
22.16
4
residue
a
32.0
Dy
O+CH
2DMF+NH
O
2 3
32.29
1
2
3
50–130
130–290
290–400
400–600
>600
110
280
330
465
90 endo
280 exo
335 exo
10.0
18.0
10.5
24.5
37.0
4H
2
3
OH
OH
10.36
17.54
10.40
24.64
37.46
2
7 6
C H O
4
residue
465, 560 exo
{2(L–O)–H
Er
2
O}
2 3
O
J. Therm. Anal. Cal., 81, 2005
379

LALIA-KANTOURI, PAPADOPOULOS
The intermediates at 400°C are thermally unsta-
ble and decompose further gradually until 1000°C,
giving a total mass loss of about 50% of the complex.
The residues at 1000°C for all the studied complexes
are carbonaceous solids consisting of the lanthanide
oxide Ln O plus carbon in a ratio of 20% of the com-
3 J. Arias, A. Cabera, P. Sharma, N. Rosas, J. Garea and
S. Hernandez, Inorg. Chim. Acta, 310 (2000) 261.
R. Reisfeld and C. Jorgensen, Laser and Excited States of
Rare Earths (1977), Springer.
4
5
F. Cotton, G. Wilkinson, C. Murillo and M. Bochman,
Advanced Inorganic Chemistry, Chapter 11, J. Wiley,
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2
3
6
Edition, 1999.
plex. Evidence for this arised from the IR peak
6
H. Kehl (Ed.), Chemistry and Biology of Hydroxamic Acids,
S. Karger, New York 1982.
–
1
at ~370 cm , attributable to Ln–O bond and from
EDS spectra. The formation of the oxide is accompa-
nied by a broad exotherm on DTA curve at ~750°C in
nitrogen, while in oxygen the stable oxides are
formed until 600°C [12, 19, 20].
Based on the initial decomposition temperatures,
the thermal stability of the complexes under investi-
gation follows the series: Gd>Dy=Er>Nd>Pr.
7 C. O’ Brion, S. Le Roy, J. Levaillain, D. G. Fitzgerald and
K. B. Nolan, Inorg. Chim. Acta, 266 (1997) 117.
8
Sh. Gao, Zhi-Q. Weng and Shi-X. Liu, Polyhedron,
7 (1998) 3595.
1
9
A. J. Stremmler, J. W. Kampf, M. L. Kirk and V. Pecoraro,
J. Am. Chem. Soc., 117 (1995) 6368.
1
1
0 M. S. Lah, M. L. Kirk, W. Hatfield and V. L. Pecoraro,
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1 D. P. Kessisoglou, J. J. Bodwin, J. Kampf,
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331 (2002) 73.
Conclusions
1
1
1
1
1
2 B. N. Sivasankar and J. R. Sharmila, J. Therm. Anal. Cal.,
73 (2003) 271.
The newly prepared salicylhydroxamate complexes
of lanthanides are thermally very unstable both in ni-
trogen and in oxygen atmosphere. They decompose
exothermally in several stages giving pure, stable
lanthanide oxide at ~600°C in oxygen, while in nitro-
gen the residue at 1000°C is carbonaceous lanthanide
oxide. It is proposed the thermal decomposition stud-
ies of this kind of complexes to be done in oxygen, in
order to obtain desirable products.
3 S. B. Jagtap, R. C. Chikate, O. S. Yemul, R. S. Ghadage
and B. A. Kulkarni, J. Therm. Anal. Cal., 78 (2004) 251.
4 W. Ferenc, B. Bocian and A. Walkow-Dziewulska,
J. Therm. Anal. Cal., 76 (2004) 179.
5 W. Ferenc, A. Walkow-Dziewulska and B. Bocian,
J. Therm. Anal. Cal., 79 (2005) 145.
6 S. Lyle and M. Rahman, Talanta, 10 (1963) 1177.
17 P. V. Khadikar, Bh. Pol and S. Mushtaq Ali,
Spectrochim. Acta, 42A (1986) 755.
1
1
2
8 F. Capitan, D. Gazquez, A. F. Gueto and
L. F. Caitan-Vallrey, Thermochim. Acta, 75 (1984) 313.
9 C. Duval, Inorganic Thermogravimetric Analysis,
Elsevier, New York 1963.
Acknowledgements
0 E. Y. Ionashiro, F. L. Fertonani, C. B. Melios and
M. Ionashiro, J. Therm. Anal. Cal., 79 (2005) 299.
The authors are thankful to Dr. Pavlidou Eleni, Laboratory of
Solid-state Physics, University of Thessaloniki, Greece, for
running the EDS spectra.
Received: June 21, 2004
In revised form: February 16, 2005
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