Metal chelates of cerium(III), thorium(IV), and dioxouranium(VI); complexes with some derivatives of aryl schiff bases

Article abstract of DOI:10.1081/SIM-120019998

New Ce(III), Th(IV) and U(VI) complexes with the aryl Schiff bases 2-hydroxybenzylamine-2′-hydroxybenzylidene (HL¹), -2′-hydroxynaphthylidene (HL²), -2′-hydroxy-5′-bromobenzylidene (HL³), -2′-hydroxy-5′-chlorobenzylidene (HL⁴), 2′-hydroxy-3′,5′-dichlorobenzylidene (HL⁵) and 2′-hydroxy-3-methoxybenzylidene (HL⁶) have been synthesized and characterized by elemental and thermal analyses, molar conductance, magnetic susceptibility, IR, ¹H NMR and electronic spectra. Elemental analyses along with conductometric titrations showed the formation of 1:1 and 1:2 (M:L) complexes while IR, molar conductance and ¹H NMR data proved that these ligands act as monobasic, tridentates for the 1:1 and monobasic, bidentates for the 1:2 complexes with a coordination number of eight in both.

Full text of DOI:10.1081/SIM-120019998

This article was downloaded by: [McMaster University]
On: 01 September 2014, At: 23:38
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lsrt19
Metal Chelates of Cerium(III), Thorium(IV), and
Dioxouranium(VI); Complexes with Some Derivatives of
Aryl Schiff Bases
M. E. Moustafa a
a Chemistry Department , Faculty of Science , Benha University , Benha, Egypt
Published online: 15 Feb 2007.
To cite this article: M. E. Moustafa (2003) Metal Chelates of Cerium(III), Thorium(IV), and Dioxouranium(VI); Complexes with
Some Derivatives of Aryl Schiff Bases, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 33:3, 453-468, DOI:
10.1081/SIM-120019998
To link to this article: http://dx.doi.org/10.1081/SIM-120019998
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 33, No. 3, pp. 453–468, 2003
Metal Chelates of Cerium(III), Thorium(IV), and
Dioxouranium(VI); Complexes with Some
Derivatives of Aryl Schiff Bases
M. E. Moustafa*
Chemistry Department, Faculty of Science,
Benha University, Benha, Egypt
ABSTRACT
New Ce(III), Th(IV) and U(VI) complexes with the aryl Schiff bases 2-
hydroxybenzylamine-2’-hydroxybenzylidene (HL1), -2’-hydroxy-
naphthylidene (HL2), -2’-hydroxy-5’-bromobenzylidene (HL3), -2’-
hydroxy-5’-chlorobenzylidene (HL4), 2’-hydroxy-3’,5’-dichlorobenzyli-
dene (HL5) and 2’-hydroxy-3-methoxybenzylidene (HL6) have been
synthesized and characterized by elemental and thermal analyses, molar
conductance, magnetic susceptibility, IR, 1H NMR and electronic
spectra. Elemental analyses along with conductometric titrations showed
the formation of 1:1 and 1:2 (M:L) complexes while IR, molar
conductance and 1H NMR data proved that these ligands act as
monobasic, tridentates for the 1:1 and monobasic, bidentates for the 1:2
complexes with a coordination number of eight in both.
*
Correspondence: M. E. Moustafa, Chemistry Department, Faculty of Science, Benha
University, Benha, Egypt; E-mail: aliyoussy@hotmail.com.
453
DOI: 10.1081/SIM-120019998
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

454
Moustafa
INTRODUCTION
Although o,o’-dihydroxyaryl Schiff bases have been recognized as
forming stable complexes with transition metal ions[1–3] and found to have
wide applications in coordination chemistry,[4,5] little work has appeared on
their complex formation with rare earth metal ions.[6] The present paper
deals with the preparation and characterization of Ce(III), Th(IV) and U(VI)
complexes with some arylidene Schiff bases based of 2-hydroxybenzyla-
mine (shown in Figure 1). The new complexes were investigated by various
physico-chemical techniques.
EXPERIMENTAL
Preparation of the Schiff Bases
The Schiff bases included in this study were prepared according to our
previous work[7] by refluxing a mixture of o-hydroxybenzylamine and salicy-
laldehyde derivatives (1:1 molar ratio) in ethanol in the presence of piperidene.
o-Hydroxybenzylamine
o-Hydroxybenzylamine was prepared by dissolving 20 g (0.146 mol)
salicylaldoxime in 300 mL of 50% ethanol and reduced by 2.5% sodium
amalgam ( ꢀ 2.0 g). The temperature was kept below 55 °C and excess of
alkali was continuously neutralized by the addition of dilute HCl. The
reaction mixture must be slightly alkaline until the reaction has been
completed. The solution was then made slightly acidic, separated from the
mercury and evaporated under reduced pressure until sodium chloride
began to crystallize. The remaining solution was diluted with water to
ꢀ 300 mL and then transferred to an Erlenmeyer flask containing ꢀ 25 mL
Figure 1. Structure of the Schiff bases.

Cerium(III), Thorium(IV), and Dioxouranium(VI)
455
of diethyl ether. Ammonium hydroxide was added in small portions until a
slight excess was present. The mixture was vigorously shaken after each
addition for a few minutes whereby the amine began to crystallize on the
walls of the flask. The product was removed by filtration and recrystallized
from absolute alcohol-petroleum ether (60% v/v ethanol), m.p. 129 °C;
yield, 12.23 g (68%).
Salicylaldoxime
Salicylaldoxime was prepared by dissolving 20 g (0.164 mol) of
salicylaldehyde in 30 mL of ethanol, then added to a solution of 15 g
(0.216 mol) of hydroxylamine hydrochloride in 10% Na2CO3 solution
(100 ml) whilst cooling in ice. After standing overnight, the solution was
acidified with acetic acid, the alcohol was diluted off under reduced
pressure using a rotary evaporator. The distillate (salicylaldoxime) was
distilled with twice its volume of water and extracted with 50 mL of diethyl
ether. The product was crystallized from chloroform-light petroleum (60%
v/v chloroform); yield, 15.95 g (71%).
The purity and structures of the prepared Schiff bases were confirmed
by the melting point constancy, elemental analyses and various spectro-
scopic techniques.
Preparation of Complexes
The solid complexes of the stoichiometric ratios 1:1 and 1:2 (M:L) were
prepared by mixing a hot ethanolic solution (50 mL) of the metal salt (0.01
mol) [Ce(NO3)3, ThCl4 or UO2(OAc)2] with 0.01 or 0.02 mol of an ethanolic
ligand solution (50 mL). The mixture was refluxed for ꢀ 6 h and then allowed
to cool when the solid chelates separated. The complexes were crystallized
from pure ethanol (96%), dried and stored over dried silica gel. Analyses of
the solid complexes for C, H and N were performed at the Microanalytical
Centre, Cairo University, Giza, Egypt. The water content was determined by
the dehydration method while the metal contents were determined as metal
oxides[8] after ignition of the solid complexes at ꢀ 750 °C.
Instrumentation
IR spectra of the Schiff bases and their metal complexes were recorded
using a Beckman IR 4220 double-beam spectrophotometer within the range
1
4000–200 cmꢁ1 using KBr discs. H NMR spectra of some selected metal
complexes and their free ligands were recorded on a Varian EM 390–90

456
Moustafa
MHz NMR spectrometer using TMS as internal standard and DMSO-d6
as solvent. Electronic absorption spectra in the UV/Visible region of the
free ligands and their chelates were recorded both in DMF solution and in
the solid state by the Nujol mull technique using a Perkin–Elemer l3B
spectrophotometer with 1 cm matched silica cells. Magnetic susceptibilities
of some selected solid complexes were measured applying Gouy’s method
using HgCo(SCN)4 as calibrant. The experimental susceptibilities were
corrected for diamagnetism.
RESULTS AND DISCUSSION
The Schiff bases included in this study were prepared according to the
following scheme in Figure 2.
The general scheme for preparing the solid complexes is as shown in
Figure 3.
Figure 2. Synthesis of the ligands.

Cerium(III), Thorium(IV), and Dioxouranium(VI)
457
Figure 3. Synthesis of the complexes.
Elemental Analyses
Conductometric titration along with elemental analysis data for all the
newly prepared metal complexes, listed in Table 1, indicate that they have
1:1 or 1:2 (M:L) stoichiometric ratios. All the complexes are hygroscopic,
soluble in DMF but insoluble in other common organic solvents. The
insolubility of the solid complexes in common organic solvents indicates
either their non-electrolytic or polymeric nature. Molar conductance values
of the solubilized chelates in DMF lie within the range 76.6–189.2 ohmꢁ1
cm2 molꢁ1 indicating the presence of both 1:1 and 1:2 electrolytes. The
presence of Clꢁ outside the coordination sphere in case of the Th(IV)
complexes was confirmed by the precipitation of AgCl when AgNO3 was
added to the solubilized chelates in DMF.
Thermal Analyses
Thermogravimetric (TG) and differential thermogravimetric (DTA)
analyses of some chelates were measured up to 500 °C at a heating rate of
10 °C/min in air. From the TG curves, the weight loss corresponding to
each endo or exothermic peak on the DTA curve was calculated from
which the number of water molecules and the percent of metal ion content

458
Moustafa

Cerium(III), Thorium(IV), and Dioxouranium(VI)
459

460
Moustafa

Cerium(III), Thorium(IV), and Dioxouranium(VI)
461

462
Moustafa
in each chelate molecule were determined (cf. Table 2). Inspection of these
curves shows that the weight loss below 100 °C is attributed to the loss of
moisture and hygroscopic water while that within the range 130–180 °C is
due to dehydration of coordinated water molecules. The number of the
latter amounts to 5 or 4 per chelate molecule for the 1:1 and 1:2 (M:L)
complexes respectively, which are coordinated to the metal ion to fulfill the
coordination number of eight. The final residue is considered to be Ce2O3,
ThO2 or UO3 from which the metal contents may be calculated. The results
Table 2. TGA results of some Ce(III), Th(IV), and UO2(VI) complexes.
Weight loss (%)
Temp.
Complex
Ratio Calculated Found range (°C)
Assignment
[Th(L1)(H2O)5]Cl3
1:1
1:2
1:1
1:1
13.75
13.91
120–175
5H2O
(coordinated)
3HCl
16.71
40.35
17.01
41.66
300–375
480
Metal oxide
(ThO2)
4H2O
[Ce(L1)2(H2O)4]NO3
[UO2(L2)(H2O)4]OAc
[Th(L3)(H2O)5]Cl3
9.91
10.48
125–180
(coordinated)
HNO3
8.67
45.19
9.78
46.20
255–320
465
Metal oxide
(Ce2O3)
4H2O
10.22
11.34
130–180
(coordinated)
CH3COOH
Metal Oxide
(UO3)
8.38
40.62
9.21
42.01
215–245
445
12.27
14.10
140.200
5H2O
(coordinated)
3HCl
14.91
36.00
15.03
36.81
320–350
480
Metal oxide
(ThO2)
2H2O
[UO2(L4)2(H2O)2]
[Th(L5)2(H2O)4]Cl2
1:2
1:2
4.53
35.97
9.95
5.07
36.66
11.00
120–160
495
(coordinated)
Metal oxide
(UO3)
130–150
4H2O
(coordinated)
2HCl
10.08
36.5
11.64
37.24
235–265
435
Metal oxide
(ThO2)

Cerium(III), Thorium(IV), and Dioxouranium(VI)
463
obtained are in good agreement with the proposed values and with those
obtained from elemental analyses.
Magnetic Susceptibility
Magnetic data; showed the diamagnetic behaviour of the Th(IV) and
UO(VI) complexes as expected, whereas the magnetic moments of the
Ce(III) complexes are about 2.42 B.M. which deviates from the spin-only
value for metal ions with one unpaired electron. This is simply due to the
shielding of the 4f electrons in the lanthanide ions. In this case, according
to vanVleck,[9] the molar susceptibility is given by
XM ¼ NZ2b=3KT þ Na
where K is the Boltzman constant, N is Avogadro’s number, Zb is a low-
frequency part of the magnetic moment and a is a combination of the high-
frequency component and diamagnetic contribution. The magnitude of
separation between the energy levels so formed and the term KT determine
the magnitude of the spin-orbit coupling. For all tripositive lanthanide ions,
except for Gd(III), Sm(III) and Eu(III), the permanent magnetic moments
reflect a combination of spin and orbital effects.
It is worth to mention also that, in contrast to the first d-type transition
series, complexing groups have little effect upon the magnetic moments
of lanthanide ions. This is why the observed magnetic moments of the
Ce(III) complexes showed nearly no variation with changing the type of
ligand used.
1H NMR Spectra
1
The H NMR spectra of some UO2(VI) complexes in DMSO-d6 were
measured and compared to those of the ligands in the same solvent. The
various protons of the free ligands are numbered as shown in Figure 4.
Figure 4. Numbering of the various protons in the Schiff bases.

464
Moustafa
Table 3. 1H NMR signals of protons (ppm) of ligands HL1–HL6 and their
UO2(VI) complexes.
Ligand/complex
Ratio
H1
H2
H3
H4
HL1
–
8.35
8.60
8.35
8.45
8.40
8.50
8.25
8.35
8.35
8.70
8.30
8.60
8.40
10.35
–
10.62
6.70
6.78
7.07
6.75
6.70
6.80
6.65
6.80
6.60
6.73
6.60
6.80
6.70
4.53
4.51
4.57
4.54
4.52
4.54
4.48
4.5
[UO2(L1)(H2O)4]OAc
HL2
1:1
–
[UO2(L2)2(H2O)2]
HL3
1:2
–
–
10.30
[UO2(L3)2(H2O)2]
HL4
1:2
–
–
10.25
[UO2(L4)2(H2O)2]
HL5
1:2
–
–
10.20
4.5
[UO2(L5)(H2O)4]OAc
HL6
1:1
–
–
10.03
4.56
4.54
4.50
4.54
[UO2(L6)(H2O)4]OAc
[UO2(L6)2(H2O)2]
1:1
1:2
–
–
The 1H NMR signals of the free ligands compared to those of the
UO2(VI) complexes are listed in Table 3. This comparison showed the
disappearance of the signal at d 10.3 0.1 ppm due to the proton (2) of the
o–OH group of the salicylidene moiety of the ligand molecule, indicating
the elimination of hydrogen ion from this group on complex formation. On
the other hand, the signal at d 8.5 0.2 ppm in the spectra of the free
ligand, due to the proton (1) of the o–OH group of the arylidene moiety, is
shifted downfield by ꢀ 0.50 ppm for the 1:1 and by ꢀ 0.20 ppm for the
1:2 (M:L) complexes. This indicates coordination of the oxygen atom of
this group and the monobasic character of these ligands. The signals of the
aromatic protons of the free ligands present with in the range d 7.60–6.85
ppm are also shifted downfield with an obvious decrease and broaden-
ing in their envelopes. This is expected since the formation of M–O or M–
N bonds withdraws electrons from the aromatic rings resulting in a de-
shielding of the proton on the carbon atom adjacent to the azomethine
group. The new signal appearing at d ꢀ 3.4 ppm is due to the coordinated
H2O in the complexes.
IR Spectra
1
Substantial Support for the results obtained from H NMR spectra is
gained by considering the changes in the IR spectra of the solid chelates in
comparison with those of the free ligands. The absorption band at about
2900 cm-1 in the spectra of the free ligands is due to the stretching

Cerium(III), Thorium(IV), and Dioxouranium(VI)
465
Figure 5. Structure of 1:1 and 1:2 Th(IV) complexes (A = H2O).
vibration of the strongly intramolecularly hydrogen bonded o–OH (to the
nitrogen atom of the azomethine group) which is lost after complexation.
On the other hand, the two bands appearing at 3100–3150 and 1310–1350
cmꢁ1 in the IR spectra of the free ligands are due to the stretching and
bending vibrations of the o OH group, respectively. These two bands are
shifted to lower frequencies on complex formation, which can be taken as
another confirmation of the monobasicity of these ligands. The absorption
band around 1660–1640 cmꢁ1 originating from the in-plane stretching of
the –C=N-group is shifted to lower frequency by 10–30 cmꢁ1 on going
from the free ligands to the solid chelate spectra. This band also is sensitive
to environmental electronic changes because it is strongly influenced by
delocalization of the unpaired electrons of the nitrogen atom on com-
plexation and is mostly split. This is supported by the appearance of a
new band of varying intensity in the far-IR region at 450–430 cmꢁ1 due
to n(M–N) vibration. On the other hand, the absorption band of the –C–O–
bond observed at 1130–1105 cmꢁ1 in the free ligands is moved to 1060–
1040 cmꢁ1 and becomes less intense after metal–oxygen bond formation
since the mass of the bonding site is increased by substitution of metal with
hydrogen.[6] Thus, a new band in the far-IR region (360–330 cmꢁ1) has
appeared due to the n(M–O) vibration.
In light of these new finding, the structure of the solid complexes may
be represented by the formulas shown in Figure 5 for the Th(IV) complexes
as example.
Electronic Absorption Spectra
Electronic absorption spectra of the free ligands in DMF show broad
bands within the range 390–450 nm which disappear on adding a trace of

466
Moustafa
Figure 6. Electronic absorption spectra of the ligand HL4 and its complexes
in DMF.
an acid with the conversion of the orange colour of the solution into pale
yellow. This is most probably due to protonation of the C=N linkage of the
azomethine group. Therefore, the absence of this band in the spectra of the
complexes (Figure 6) can be taken as evidence for the participation of the
C =N group in a coordinate bond (C=N !M).[10]
The electronic absorption spectra in the visible region of the Ce(III),
Th(IV) and UO2(VI) chelates in the solid state (in Nujol mulls) exhibit
alterations in the intensity or shifts in the position of the absorption bands
or sometimes both. The value of Racah parameter (B) for a complex is
always less than that for the free aqueous ion. This reduction of B upon
complexation corresponds to a reduction of interelectronic repulsion, due
to delocalization of the metal electrons onto the ligands, and is known as
the nephelauxetic effect. The factor, b, by which B is reduced from the
free-ion is the average value of ncomplex/nequo. given by the equation[11]
shown below.
X
1
b ¼
ðncomplex=naquo:Þ
n
The wave lengths at which the various bands appear are red-shifted
compared to the aquo ion, a fact which had been ascribed to a nephel-
auxetic effect. The extent of the red-shift is related to the covalency in the

Cerium(III), Thorium(IV), and Dioxouranium(VI)
467
metal–ligand bond by the d scale, proposed by Sinha.[12] This covalency is
expressed as shown below.
d% ¼ ð1 ꢁ bÞ=b ꢂ 100
The spectral data of the Ce(III) complexes were used to calculate the
interelectronic repulsion parameter (b) and the percentage covalency (d%).
The values of the former lie within the range 0.9449–0.9896, while the
percentage covalency values are in the range 0.6441–0.3713.
REFERENCES
1. Xiang, M.Y.; Sui, S.H.; Song, J.P.; Sheny, H.G. Synthesis and
characterization of an organometallic Schiff base and its lanthanide
chelates. Transit. Met. Chem. 1991, 16, 308–310.
2. Sharada, L.N.; Ganorkar, M.C.; Ra, O.N.R. Structural study of metal
chelates derived from tridentate ligand. J. Indian Chem. Soc. 1995, 72
(7), 439–442.
3. Mohan, M.; Tandon, J.P.; Gupta, N.S. The synthesis and magnetic and
spectral studies of some lanthanide(III) chelates of 6-methylpyridine-2-
aldoxime. J. Inorg. Nucl. Chem. 1981, 43, 1223–1226.
4. Borel, M.; Rapp, M.; Pasqualini, R.; Madelmont, J.C.; Bodeneche,
D.; Veyre, A. Synthesis of potential super MTC nitrido tumor imag-
ing disposition in mice. Appl. Radiat. Isotopes 1992, 43 (3), 425–
436.
5. Khan, M.M.; Kureshy, R.I.; Khan, N.H. Synthesis and characterization
of ruthenium(III) chiral Schiff base complexes derived from salicyl-
aldehyde and L-amino acids. Tetrahedron: Asymmetry 1991, 2 (10),
1015–1020.
6. Bullita, E.; Querriero, P.; Tamburini, S.; Vigato, P.A. Synthesis and
properties of lanthanide and actinide complexes with new macrocyclic
and microacylic ligands containing long alipathic chains. J. Less-
Common Met. 1989, 153 (2), 211–218.
7. Moustafa, M.E.; Mabrouk, E.M.; Dessouki, H.A.; Amin, A.S. Spectro-
photometric microdetermination of copper(II), silver(I) and gold(III)
using azaztyrene Schiff bases. Microchem. J. 1991, 44, 311–317.
8. Kolthoff, I.M.; Elving, P.J.; Sandell, E.B. Treatise on Analytical
Chemistry; Interscience: New York, 1963; 8Part II.
9. Van Vleck, J.H.; Frank, N. The Chemistry of the Lanthanides; Chapman
& Hall Ltd.: London, 1965; 27.
10. Moustafa, M.E.; Issa, Y.M.; El-Hawary, W.F.; Refaat, M.R. Synthesis

468
Moustafa
and analytical application of the complexes of 4-methylesculetin azo
compounds with some transition metal ions. Spec. Lett. 1999, 32 (5),
829–840.
11. Jorgensen, C.K. Modern Aspects of Ligand Field Theory; American
Elsevier: New York, 1971; 347, 348.
12. Rajasekar, N.; Soundararajan, S. Complexes of lanthanide perchlorates
with 2-N-(pyridyl)benzamide. J. Inorg. Nucl. Chem. 1981, 43, 977–
980.
Received: August 21, 2000
Accepted: November 15, 2002
Referee I: R. P. Hotz
Referee II: T. H. Warren