Novel lanthanide complexeswith di-2-pyridyl ketone-p-chloro- benzoylhydrazone : TTThermal investigation by simultaneous TG/DTG-DTA and IR spectroscopy

Article abstract of DOI:10.1007/s10973-007-8487-8

The reaction of a hydrated nitrate salt of lanthanide(III) (Ln=Er, Ho, Tb, Gd) or yttrium(III) (Y) with the ligand di-2-pyridyl ketone-p-Cl- benzoylhydrazone (DpkClBH), afforded air stable solid compounds. The new complexes characterized by means of elemental analysis (C, H, N, Ln), magnetic moment determinations and spectroscopic data (IR, MS). It is proposed that they are cationic of the general type: [Ln(DpkClBH)₂(NO₃) ₂]NO₃?nH₂O, (n=2, 1, 1, 1, 1.5 for Ln=Y, Gd, Tb, Ho, Er, respectively). Their thermal decomposition was studied in nitrogen atmosphere, between 25-980°C, by using simultaneous TG/DTG-DTA technique. The IR spectroscopy used to determine the intermediates and the final products. The anhydrous nitrate complexes decomposed to the intermediates Ln(DpkClBH)(NO₃)₂, which upon further heating give a carbonaceous residue of Ln₂O₃ at 980°C. The mass spectra revealed the molecular ions of the complexes and their possible fragmentation pattern.

Full text of DOI:10.1007/s10973-007-8487-8

Journal of Thermal Analysis and Calorimetry, Vol. 91 (2008) 3, 937–942
NOVEL LANTHANIDE COMPLEXES WITH DI-2-PYRIDYL
KETONE-p-CHLORO-BENZOYLHYDRAZONE
Thermal investigation by simultaneous TG/DTG-DTA and IR spectroscopy
Maria Lalia-Kantouri*, L. Tzavellas and D. Paschalidis
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(III) (Ln=Er, Ho, Tb, Gd) or yttrium(III) (Y) with the ligand di-2-pyridyl
ketone-p-Cl-benzoylhydrazone (DpkClBH), afforded air stable solid compounds. The new complexes characterized by means of el-
emental analysis (C, H, N, Ln), magnetic moment determinations and spectroscopic data (IR, MS). It is proposed that they are
cationic of the general type: [Ln(DpkClBH)2(NO3)2]NO3·nH2O, (n=2, 1, 1, 1, 1.5 for Ln=Y, Gd, Tb, Ho, Er, respectively).
Their thermal decomposition was studied in nitrogen atmosphere, between 25–980°C, by using simultaneous TG/DTG-DTA
technique. The IR spectroscopy used to determine the intermediates and the final products. The anhydrous nitrate complexes de-
composed to the intermediates Ln(DpkClBH)(NO3)2, which upon further heating give a carbonaceous residue of Ln2O3 at 980°C.
The mass spectra revealed the molecular ions of the complexes and their possible fragmentation pattern.
Keywords: hydrazone ligand, IR, lanthanide(III), MS, TG/DTG-DTA, yttrium complexes
Introduction
O
N
Lanthanide complexes are of continuing interest
N
N
mainly due to their structural and catalytic proper-
Cl
H
ties [1] and their applications in diagnostic pharma-
N
ceutical [2] and laser technology [3, 4]. Schiff-base
ligands like hydrazones, are considered privileged
ligands because they are easily prepared by a simple
one-pot condensation of a carbonyl compound and
primary amines in an alcohol solvent and are
associated with various interesting types of biological
effects, such as antiviral, antibacterial, and anti-
microbial activity [5]. In the lanthanide complexes
with various types of multidentate hydrazone ligands,
the metal can achieve high coordination number giving
structural differences responsible for their important
properties [6]. Recently, there is an increasing research
interest on the thermal properties of the lanthanide
complexes with ligands having O and N donor ability,
studied by TG-DTA techniques [7–9].
Fig. 1 Structural formula for the Schiff base ligand DpkClBH,
derived from di-2-pyridylketone and p-chloro-benzoyl-
hydrazide
Experimental
The hydrated nitrate salts of lanthanide
(Ln(NO3)3·xH2O, where Ln=Y, Er, Ho, Tb, Gd and
x=5 or 6) and the organic compounds p-Cl-benzo-
ylhydrazide (p-ClBH) and di-2-pyridyl ketone (Dpk)
were purchased from Aldrich and were used without
further purification. All solvents were distilled prior
to use.
In the course of our studies on the high coordina-
tion number lanthanide chemistry [10–12], we report
here the synthesis, spectral (IR, MS) and thermal
studies (TG/DTG-DTA) of five new lanthanide com-
plexes with the Schiff-base ligand di-2-pyridyl
ketone-p-Cl-benzoylhydrazone (DpkClBH) (Fig. 1).
As it is shown the ligand employs five potentially co-
ordinated sites, one secondary amine nitrogen, one
imine nitrogen, two pyridine nitrogens and one car-
bonyl oxygen to bind metal(III) ions.
Synthesis of the ligand DpkClBH
Preparation of the hydrazone ligand DpkClBH was
carried out according to literature method [13], by
refluxing a methanolic solution (500 mL) of p-chloro-
benzoylhydrazide (8.53 g, 50 mmol) and di-2-pyridyl
ketone (9.21 g, 50 mmol) for 48 h. After 24 h slow
cooling of the reaction mixture at room temperature, a
*
Author for correspondence: lalia@chem.auth.gr
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2008 Akadémiai Kiadó, Budapest

LALIA-KANTOURI et al.
crude yellow product was filtered off, washed with
SETSYS-1200. The samples were heated in platinum
crucibles, in nitrogen atmosphere, within the tempera-
ture range 25–980°C. The heating rate was
10°C min–1 and the samples, about 10 mg, were
weighted into a platinum crucible.
cold methanol and recrystallized twice from hot
methanol-water mixture.
Synthesis of the complexes
PXRD was performed using a Philips PW 1710
diffractometer with Ni-filtered CuKa radiation on
randomly oriented samples. The samples were
scanned within the range 2q=3–63°.
[Ln(DpkClBH)2(NO3)2]NO3·nH2O
[Ln(NO3)2(DpkClBH)2]NO3·nH2O complexes were
prepared by the following general procedure: To a
water solution (3 mL) of lanthanide nitrate (2 mmol)
was added drop-wise a methanolic solution (10 mL)
Results and discussion
of DpkClBH (4 mmol). After
4 h stirring,
microcrystalline products were obtained, filtered off,
washed with small portions of methanol, and dried in
vacuum over anhydrous calcium chloride.
The reaction of the lanthanide nitrate with the
Schiff-base ligand DpkClBH afforded in good yield
very stable in air solid compounds. The characteriza-
tion of their molecular structure was made by elemen-
tal analyses, conductivity and magnetic measure-
ments, as well as by infrared spectroscopy. Thermal
analysis by TG-DTA technique was proved very use-
ful in determining the crystal water content in the
complexes and their thermal stability and decomposi-
tion mode under controlled heating rate. The frag-
mentation pattern of the complexes was studied with
the aim of mass spectrometry.
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 [14].
Magnetic susceptibility measurements on pow-
dered samples were performed at 25°C employing the
Faraday method in instrument of Johnson Mathey,
type MSB-MKI, calibrated against Hg[Co(SCN)4].
Molar conductivities were measured in DMF solu-
tions, employing a WTW conductivity bridge and a
calibrated dip type cell.
The compounds prepared are pale colored, solu-
ble in methanol, ethanol, acetonitrile and
dimethylsulfoxide, but insoluble in chloroform, di-
chloromethane and diethylether. All the studied com-
plexes possess 1:2 metal-to-ligand composition, as it
is indicated from elemental analyses and exhibit cor-
responding conductivities (~80q S cm2 mol–1) in
DMF (Table 1), suggesting 1:1 electrolytic behavior.
The room temperature magnetic moments (meff) are
characteristics of trivalent lanthanide ions, showing
very close agreement with the theoretical values cal-
culated from Van Vleck formula indicating minor
participation of 4f electrons in the bond formation.
Infrared spectra were recorded on a Perkin-Elmer
FTIR 1650 spectrometer, in the region 4000-200 cm–1
using KBr pellets. Mass spectra were run on a RMU-6L
Hitachi PerkinElmer, double focusing mass spectrome-
ter, model TS 250 Fision, using direct probe insertion
for the samples, operating at 70 eV.
The simultaneous TG/DTG-DTA curves were
obtained on
a SETARAM instrument, model
Table 1 Analytical and physicochemical data for the complexes [Ln(DpkClBH)2(NO3)2]NO3·nH2O (n=2, 1, 1, 1, 1.5 for Ln=Y,
Gd, Tb, Ho, Er, respectively)
Complex Color
Yield/%
74
C/%
H/%
N/%
Ln/%
meff/MB
L/S cm2 mol–1
Y
white
white
yellow
yellow
pink
43.79
(43.94)*
41.53
3.08
(3.05)
2.46
15.53
(15.65)
14.99
9.01
(9.05)
15.06
D
67.5
Gd
Tb
Ho
Er
82
59
79
87
7.63
9.59
68.4
81.7
73.3
80.0
(41.78)
41.92
(2.71)
2.63
(14.89)
15.14
(15.28)
15.49
(41.74)
41.99
(2.70)
2.55
(14.88)
14.90
(15.36)
15.83
10.32
9.29
(41.49)
41.27
(2.69)
2.60
(14.79)
14.96
(15.85)
15.87
(41.10)
(2.76)
(14.65)
(15.79)
*calculated values in parenthesis; D=diamagnetic
938
J. Therm. Anal. Cal., 91, 2008

THERMAL INVESTIGATION OF NOVEL LANTHANIDE COMPLEXES
Similar values have been observed with substituted
benzoate complexes of lanthanides [15, 16]. The
complexes may be formulated as [Ln
bidentate bonding of nitrates [19]. This value is con-
firmed in absolutely related hydrazone–lanthanide
complexes with both spectral and structural data [11].
The existence of crystal water is inferred from the
bands at 3460 cm–1, while the bands due to the coordi-
nation bonds Ln–N and Ln–O at ~480 and 380 cm–1
respectively. A representative IR spectrum for the Ho
complex is given in Fig. 2.
(DpkClBH)2(NO3)2]NO3·nH2O, evidence also arisen
from the interpretation of the IR data of the ligand and
the complexes. Their physicochemical characteristics
are listed in Table 1.
Infrared spectra
70-
60-
50-
40-
30-
20-
10-
0-
The relevant infrared vibration bands of the free
ligand and the complexes, in the region
4000–250 cm–1, are given in Table 2. The broad band
at 3457 cm–1 of the free ligand DpkClBH, attributable
to v(N–H), is observed at the region 3234–3377 cm–1
for all the complexes. A strong band at 1675 cm–1 in
the DpClBH (due to v(C=O)), upon complexation is
shifted by ~50–60 cm–1 to lower frequencies due to
the coordination of the carbonyl oxygen with
lanthanide. The appearance of the v(N–H) and
v(C=O) bands, in the spectra of all complexes, is an
evidence for the coordination of the hydrazone with
the metal as neutral ligand [17]. For the complexes
the v(C=N) band appears at the region ~1560 cm–1,
which is ~25 cm–1 lower in frequency than the corre-
sponding band of the free DpkClBH. This indicates
that the azomethine nitrogen is coordinated to the
metal. The low energy pyridine ring in-plane and
out-of-plane vibrations observed in the spectrum of
the ligand at 613 and 403 cm–1 respectively, but the
corresponding bands for the complexes are shifted to
higher frequencies at 625–637 and 414–429 cm–1 re-
spectively, which is a indication of the coordination
of the heterocyclic nitrogen [18]. The appearance of a
strong band at ~1384 cm–1 in the spectra of all com-
plexes indicates the presence of ionic nitrates (D3h
Wavenumber/cm–1
Fig. 2 Infrared spectrum of the Ho complex
Mass spectra
The electron impact (EI) mass spectral data for four of
the investigated complexes are listed in Table 3. The
molecular ion [Ln(NO3)2L2]NO3¬+ is detected for the
complexes of Y(III), Er(III) and Tb(III) at m/e=947,
1024 and 1017 respectively, but not for the Ho(III)
one. The observed peaks due to the fragment
[Ln(NO3)2(L)2]+ are formed from the expulsion of the
radical –NO3 from the molecular ion. Further removal
of nitrate ion as HNO3 resulted in the formation of the
fragments [Ln(NO3)L2]+.
It is worthwhile to be mentioned that for the er-
bium complex, [Er(NO3)2(L)2]NO3·nH2O, a set of
four peaks was detected for each fragment containing
the metal, due to the different isotopes of erbium. For
example, there are four peaks at m/e 1024, 1025, 1026
and 1028 corresponding to the molecular ion
symmetry, free NO– ion). All the spectra demonstrate
3
also the presence of coordinated nitrates. Two strong
bands observed at 1288–1302 and 1488–1502 cm–1
assigned to the v4 and v1 vibrations modes of the ni-
trate group, respectively (C2V symmetry, coordinated
nitrate group). The magnitude of the splitting (v4–v1)
is ~180 cm–1 in all complexes and it is typical of
¬+
[Er(NO3)2L2]NO3 due to the 166Er, 167Er, 168Er and
170Er isotopes, respectively.
In the low mass-number region, an intense peak
at m/e 336, corresponding to the coordinated ligand
L+, is apparent for all the complexes. The elimination
Table 2 Selected IR bands/cm–1 for the ligand DpkClBH and its lanthanide complexes
v4 (NO3)
v3 (NO3)
v1 (NO3)
Pyridine ring
Comp.
v(N–H)
v(C=O)
v(C=N)
(C2v)
(D3h)
(C2)
in plane
out of plane
ligand
Y
3457
3365
3234
3234
3234
3377
1675
1616
1615
1623
1615
1615
1586
1561
1560
1560
1562
1561
–
–
–
613
625
636
637
636
625
403
429
428
428
420
414
1488
1485
1502
1488
1488
1384
1384
1384
1384
1384
1302
1293
1288
1300
1301
Gd
Tb
Ho
Er
J. Therm. Anal. Cal., 91, 2008
939

LALIA-KANTOURI et al.
Table 3 Relative abundances of the most significant ions in the mass spectra of the complexes
[Ln(DpkClBH)2(NO3)2]NO3·nH2O
m/e, Intensity/%
Chemical species
Ln=Y
Ln=Tb
Ln=Ho
Ln=Er
+
[Ln(NO3)2L2]NO3
[Ln(NO3)2L2]+
[Ln(NO3)L2]+
[LnL2]+
947 (6)
885 (4)
823 (5)
760 (7)
611 (5)
549 (3)
487 (7)
336 (9)
1017 (9)
955 (7)
893 (5)
830 (7)
681 (7)
619 (10)
557 (4)
336 (100)
–
1024 (9)
962 (8)
890 (8)
837 (5)
688 (5)
626 (6)
564 (6)
336 (11)
–
–
–
+
[Ln(NO3)2L]NO3
[Ln(NO3)2L]+
[LnNO3L]
L+
687 (8)
625 (11)
–
336 (15)
- NO3
- NO3
- NO3
given in Table 4. For all the investigated complexes,
the thermal decomposition mode seems to follow the
same model. Representative thermal curves are de-
+
+
+
+
[Ln(NO3)2L2]NO3
- L
[Ln(NO3)2L2]
- L
[LnNO3L2]
- L
[LnL2]
- NO3
- NO3
+
+
+
[LnNO3L]
[Ln(NO3)2L]
[Ln(NO3)2L]NO3
picted
for
the
yttrium
complex
[Y(DpkClBH)2(NO3)2]NO3·2H2O in Fig. 4.
Fig. 3 Fragmentation pattern of the lanthanide complexes
[Ln(NO3)2(DpkClBH)2]NO3
The elimination of the crystal water molecules at
~200°C suggests that these are strongly kept in the
crystal lattice of the complexes, due to the strong hy-
drogen bonds network, as it has been found in the
crystal structure of other analogous hydrazone
lanthanide complexes [11].
of a chloride ion of the ligand DpkClBH forms the
base peak at 301 m/e. A possible fragmentation pat-
tern for the lanthanide complexes under investigation,
is given in Fig. 3.
800-
700-
600-
500-
400-
300-
200-
100-
0-
Thermal behavior
The yttrium and the lanthanide complexes were sub-
jected to TG/DTA-DTA analysis from ambient up to
980°C in nitrogen atmosphere. The temperature
ranges, the determined percentage mass losses and the
thermal effects accompanying the decomposition are
-2000
-1500
-1000
-500
-0
0-
–20-
–40-
–60-
–80-
450-
400-
350-
300-
250-
200-
150-
100-
50-
DTA
TG
-–500
0-
–10-
–20-
–30-
–40-
–50-
DTG
0-
0 100 200 300 400 500 600 700 800 900 1000
Temperature/°C
Fig. 5 Powder XRD of the residues at 980°C for the a – Y and
Fig. 4 TG/DTG-DTA curves for the yttrium complex in
b – the Ho compounds
nitrogen
940
J. Therm. Anal. Cal., 91, 2008

THERMAL INVESTIGATION OF NOVEL LANTHANIDE COMPLEXES
Table 4 Thermoanalytical results (TG/DTG-DTA) for the complexes [Ln(DpkClBH)2(NO3)2]NO3·nH2O in nitrogen
Temp. range/ Evolved
DTGmax
°C
/
DTA/
°C
Mass loss/%
(calc./%)
Complex
°C
compounds
[Y(DpkClBH)2(NO3)2]NO3· 2H2O
175–210
210–300
300–495
495–850
Res.>900
179–197
197–310
310–450
450–830
Res.>900
175–195
195–305
305–442
495–850
Res.>900
182–195
195–320
320–495
495–840
Res.>900
2H2O
210
210 endo
3.3 (3.65)
DpkClBH+HNO3 230
230 exo
38.3 (34.20+6.41)
32.0 (34.20)
9.3 (9.84)
DpkClBH
2NO2+1/4O2
Y2O3+C
H2O
400
–
–
–
17.1 (11.48+x)
2.0 (1.70)
[Gd(DpkClBH)2(NO3)2]NO3·H2O
[Tb(DpClBH)2(NO3)2]NO3·H2O
[Ho(DpkClBH)2(NO3)2]NO3·H2O
197
197 endo
DpkClBH+HNO3 223
223 exo
37.0 (32.50+6.00)
31.20 (32.50)
9.5 (9.67)
–DpkClBH
2NO2+1/4O2
Gd2O3+C
H2O
415
–
–
–
20.3 (17.5+x)
2.0 (1.70)
194
194 endo
DpkClBH+HNO3 220
220 exo
37.7 (32.50+6.10)
31.3 (32.50)
9.3 (9.65)
DpkClBH
2NO2+1/4O2
Tb2O3+C
H2O
400
–
–
–
19.7 (17.66+x)
1.9 (1.70)
195
195 endo
DpkClBH+HNO3 250
250 exo
36.6 (32.30+6.00)
30.9 (32.30)
9.9 (9.59)
DpkClBH
2NO2+1/4O2
Ho2O3+C
1.5H2O
400
–
–
–
20.7 (18.14+x)
2.6 (2.60)
[Er(DpkClBH)2(NO3)2]NO3·1.5H2O 180–190
188
188 endo
190–330
330–497
497–830
Res.>900
DpkClBH+HNO3 240
240 exo
37.2 (31.90+5.90)
30.4 (31.90)
9.7 (9.50)
DpkClBH
2NO2+1/4O2
Er2O3+C
400
–
–
–
20.1 (18.14+x)
The anhydrous compounds are very unstable
upon heating, and decomposed suddenly with a mass
loss corresponding to the elimination of one HNO3
molecule and one hydrazone ligand. Fig. 4 shows that
the melting is accompanied by the decomposition.
The strong exothermic effect at 230°C on the DTA
curve causes evidence that an oxidation of the sample
takes place along with the decomposition. As it was
deduced from the TG findings and from the elemental
analysis and IR spectrum of the intermediate at
~300°C (the peak at 1384 cm–1, due to the uncoordi-
nated nitrate ion is absent), this compound could be
assigned as Ln(NO3)2(DpkClBH).
carbon in a ratio of ~10% of the complex, evidence
arisen from the TG/DTG curves and IR peak at
~370 cm–1, attributable to Ln–O bond, in agreement
with other analogous lanthanide compounds [7, 12].
The formation of the oxides Ln2O3 was observed at
~750°C as it was expected [21].
Powder XRD diagrams for the final residue of
the Y and Ho compounds are given in Figs 5a and b,
confirming the existence of Y2O3 and the lanthanide
oxide as Ho2O3 respectively.
Finally, from the thermoanalytical data
(TG/DTG-DTA) it is deduced that the thermal de-
composition mode of the titled complexes is in good
agreement with their fragmentation pattern derived
from mass spectral data.
Beyond 300°C, the continuous mass loss is pos-
sibly due to successive elimination of the second
hydrazone ligand, to be followed by degradation of
the nitrate groups with the evolution of 2NO2 plus 1/4
O2 [20]. This speculation can be enhanced from the
composition of the final residues. The residues at
980°C for all the studied complexes are carbonaceous
solids consisting of the lanthanide oxide Ln2O3 plus
Conclusions
The characterization of the newly synthesized
lanthanide complexes with the hydrazone ligand
DpkClBH was made by stoichiometric analysis, mo-
J. Therm. Anal. Cal., 91, 2008
941

LALIA-KANTOURI et al.
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A. G. Souza, J. Therm. Anal. Cal., 87 (2007) 433.
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2
Fig. 6 Proposed structure of the
[Ln(NO3)2(DpkClBH)2]NO3·nH2O complexes
Acknowledgements
We thank X. Sidiropoulos, Chemistry Department, Aristotle
University of Thessaloniki, for running the TG-DTA experi-
ments and N. Kantiranis, Geology Department, Aristotle Uni-
versity of Thessaloniki, for recording the XRD measurements.
Received: March 26, 2007
Accepted: June 3, 2007
DOI: 10.1007/s10973-007-8487-8
942
J. Therm. Anal. Cal., 91, 2008