Synthesis and characterization of some 3-phenyl-4-arylazo-5-pyrazolones with La(III), Ce(III), Th(IV), and UO2(VI) complexes

Article abstract of DOI:10.1081/SIM-100107203

La(III), Ce(III), Th(IV) and UO₂(VI) chelates with 3-phenyl-4-arylazo-5-pyrazolones have been synthesized and were characterized by several analytical tools such as elemental analyses, IR, NMR, TG and molar conductance techniques. The data obta

Full text of DOI:10.1081/SIM-100107203

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SYNTHESIS AND CHARACTERIZATION OF SOME 3-
PHENYL-4-ARYLAZO-5-PYRAZOLONES WITH La(III),
Ce(III), Th(IV), AND UO2(VI) COMPLEXES
S. A. Abdel-Latif a
a Chemistry Department, Faculty of Science , Helwan University , Cairo, Egypt
Published online: 09 Dec 2011.
To cite this article: S. A. Abdel-Latif (2001) SYNTHESIS AND CHARACTERIZATION OF SOME 3-PHENYL-4-ARYLAZO-5-
PYRAZOLONES WITH La(III), Ce(III), Th(IV), AND UO2(VI) COMPLEXES, Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry, 31:8, 1355-1374, DOI: 10.1081/SIM-100107203
To link to this article: http://dx.doi.org/10.1081/SIM-100107203
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(8), 1355±1374 (2001)
SYNTHESIS AND CHARACTERIZATION
OF SOME 3-PHENYL-4-ARYLAZO-5-
PYRAZOLONES WITH La(III), Ce(III),
Th(IV), AND UO2(VI) COMPLEXES
S. A. Abdel-Latif
Chemistry Department, Faculty of Science,
Helwan University, Cairo, Egypt
E-mail: saalatif@halpha.hun.eun.eg
ABSTRACT
La(III), Ce(III), Th(IV) and UO2(VI) chelates with 3-phenyl-
4-arylazo-5-pyrazolones have been synthesized and were
characterized by several analytical tools such as elemental
analyses, IR, NMR, TG and molar conductance techniques.
The data obtained show that all of the prepared complexes
contain water and=or alcohol molecules in their coordination
sphere and the ligands form 1:1 and 1:2 complexes which are
in good agreement with the proposed formulae. The NMR
data of the prepared ligands show the existence of the ketonic
structure rather than the enolic form. The TG data revealed
no crystal water outside the coordination sphere. The azo-
pyrazolone ligands act as neutral bidentate ligands bonded to
the metal ions through the oxygen atom of the carbonyl group
and the a nitrogen of the arylazo group. All solid chelates
prepared behave as non-electrolytes in DMF solution.
1355
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

1356
ABDEL-LATIF
The coordination numbers of the prepared chelates are ran-
ging from 6 to 12 for 1:1 and from 7 to 12 for 1:2 chelates.
INTRODUCTION
The importance of the pyrazolone azo dyes in industry as well as their
analytical applications and excellent ability to act as ligands attracted the
attention of coordination chemists to study their reactions with transition
metal ions1,2. Pyrazolones and pyrazol derivatives such as 5-pyrazolones are
formed by the reaction between hydrazines and b-ketonic esters e.g., 3-
methyl-1-phenyl pyrazolone was prepared from phenylhydrazine and ethyl
acetoacetate. This, on methylation gives antipyrine which is used in medi-
cine as an antipyretic3. Pyrazolin-5-ones have attracted much attention as
ligands for a large number of metal ions476. The metal chelates produced are
well known for their analytical and biological uses. The azo derivatives of
5-pyrazolones, as well as their metal complexes, have wide applications in
the dye industry and as analytical reagents for the micro determination of
metals7. Various methods were reported for the synthesis of 4-arylazo-5-
pyrazolone8. Dissociation constants of some azo pyrazolin-5-one derivatives
were obtained and the stability constants of their chelates with Th(IV),
Zr(IV), Ce(III), Y(III), La(III) and UO2(VI) were determined potentiome-
trically9. The order of stabilities were: Zr(IV) > Th(IV) > UO2(VI) >
Y(III) > Ce(III) > La(III). The reaction of La(III), Ce(III), Th(IV) and
UO2(VI) ions with some heterocyclic azo pyrazolones was studied spectro-
photometrically and by IR spectra10. All solid chelates prepared behave as
non-electrolytes in DMF solution. Metal chelates of pyridine azopyrazolin-
5-one derivatives with Zr(IV), La(III), Y(III) and UO2(VI) have
1
been prepared and characterized by electronic, IR, H NMR spectra and
thermogravimetric analyses1. The results revealed the possibility of both 1:1
and 1:2 metal ion to ligand adducts. Trivalent rare earth b-diketonate an-
tipyrine coordination compounds were synthesized11. Their properties were
1
studied by conductimetry, thermal, IR, UV and H NMR spectra. Pd(II)
complexes with some 1-phenyl-5-pyrazolone derivatives were prepared12.
The complexes were characterized by IR spectra and magnetic susceptibility
measurements. The structure of the ligands is shown in Fig. 1.
EXPERIMENTAL
All chemicals used were of the highest purity available from BDH.
These included La(NO3)3.6H2O, Ce(NO3)3.6H2O, Th(NO3)4.6H2O and

La(III), Ce(III), Th(IV), AND UO2(VI) COMPLEXES
1357
Figure 1. Structure of 3-phenyl-4-arylazo-5-pyrazolone derivatives.
UO2(NO3)2.6H2O. The solvents used were ethanol and deuterated dimethyl
sulfoxide (DMSO).
Preparation of 3-Phenyl-5-pyrazolone
A mixture of ethyl benzoylacetate (9.6 g, 49.94 mmole) and hydrazine
hydrate (1.6 g, 31.96 mmole) was heated at 120 ꢀC (oil-bath, temp.
1207130 ꢀC) for 1 h. The resulting oil was cooled and stirred with diethyl
ether (50 mL) until solidi®cation occurred and the crude product was then
®ltered o€. The ®nal product was crystallized from 50% ethanol water and
collected as white powder of 3-phenyl-5-pyrazolone13; yield 6.8 g (85%);
m.p. 250 ꢀC.
Preparation of 3-Phenyl-4-arylazo-5-pyrazolone Derivatives
A well-stirred solution of aniline, 4-chloroaniline, p-toluidine or
p-anisidine 0.01 mole in 40 mLethanol and 20 mL2 M HCl was cooled in
an ice salt bath and diazotized with an aqueous sodium nitrite solution
(20 mL, 0.01 mole). The cooled (075 ꢀC) diazonium solution was added
slowly to
a
well-stirred solution of 3-phenyl-5-pyrazolone (1.6 g,
0.01 mole) in ethanol (100 mL) containing sodium hydroxide (10 g). The
reaction mixture was stirred for 1 h at room temperature, then acidi®ed
with diluted HCl (100 mL, 2.5 M) to neutralize the reaction mixture and

1358
ABDEL-LATIF
precipitate the azopyrazolone derivatives. The products were recrystallized
from ethanol to give the 3-phenyl-4-arylazo-5-pyrazolone derivatives as
reddish orange crystals14.
Preparation of the Complexes
The 1:1 or 1:2 chelates were prepared by mixing hot alcoholic solutions
(100 mL) of the ligands (2 or 4 mmole) with the calculated amount of metal
salt (2 mmole) in 100 mLethanol. The pH of the solution was maintained at
5.076.0 by addition of 1:10 dilute ammonia solution. The reaction mixture
was then re¯uxed for 4 h on a water bath and evaporated on a steam bath,
with occasional stirring. The solid product was washed several times with
ethanol till a colorless ®ltrate was obtained. The solid was dried in vacuo and
®nally kept in a vacuum desiccator.
Measurements
The IR spectra were recorded on a Shimadzu FTIR 8201 PC spec-
trophotometer in KBr discs. The NMR spectra were measured using a
Varian-Mercury 300 MHz spectrometer. The solvent used was deutrated
dimethyl sulfoxide (DMSO) and the spectra were recorded from 0715 ppm
using TMS as internal standard. Thermal analyses (TG) were obtained using
a type TGA 50 Shimadzu Derivatograph. The molar conductivities were
carried out using a Jenway 4310 conductivity meter. Mass spectra were
obtained using a Shimadzu QP-5000 mass spectrometer coupled with a
Shimadzu GC-17A gas chromatograph.
RESULTS AND DISCUSSION
The elemental analyses of the ligands are given in Table I and were
1
con®rmed by H NMR, IR and mass spectra. The results of the elemental
analyses of the chelates derived from 3-phenyl-4-arylazo-5-pyrazolone deri-
vatives are recorded in Table II. The data obtained show that the ligands form
1:1 and 1:2 complexes and are in good agreement with the proposed formulae.
Infrared Spectra
The infrared spectra of the investigated ligands show the presence of
band at 319773186 cmÀ1 corresponding to n(NH). The strong
a

La(III), Ce(III), Th(IV), AND UO2(VI) COMPLEXES
1359

1360
ABDEL-LATIF

La(III), Ce(III), Th(IV), AND UO2(VI) COMPLEXES
1361

1362
ABDEL-LATIF

La(III), Ce(III), Th(IV), AND UO2(VI) COMPLEXES
1363
bands appearing at the range 166071650 cmÀ1 are assigned to n(CˆO). The
n(NˆN) bands are observed in the range 149671488 cmÀ1 and are con-
jugated with the aromatic ring skeletal vibrations15 [n(CˆC)] at
160471600 cmÀ1
.
The infrared spectra of the solid chelates display interesting changes
that may give a reasonable idea about the structure of these chelates. The
main IR bands of the solid chelates are given in Table III. A comparison of
the IR spectra of the ligands with those of their metal chelates indicates that
changes are occurring as a result of the involvement of the ligands with
various coordination sites with the metal ions. The absence of the CˆO
group indicates that it is a center of chelation as it loses its double bond
character (-C-O-M). The OH stretching frequency appears in the spectra of
all the complexes as a broad band within the range 320173570 cmÀ1 and is
due to the presence of water and=or alcohol and OHÀ which neutralizes the
charge on the metal ion. Most of the La(III), Ce(III), Th(IV) and UO2(VI)
complexes were characterized by four bands which may be assigned to the
nitrato ion C2v symmetry16: 151571552 (v1), 125971315 (v4), 100471051 (v2)
and 8007831 (v6) cmÀ1. The spectra of the metal chelates exhibit mainly
bands in the ranges 5207590 and 4307497 cmÀ1 which may be assigned to
n(M-N) and n(M-O) stretching frequencies, respectively. These bands are
possibly due to the formation of coordinate bonds between the donor atoms
(O and N) and the central metal ion17.
Nuclear Magnetic Resonance
Further support for the results obtained from the IR spectra is gained
by considering the changes in the NMR spectra of the investigated chelates
(Table IV). The 1H NMR spectra of the investigated ligands exhibit a singlet
at 2.5172.52 ppm which were assigned to the aliphatic proton H4. The sig-
nals observed at 8.177.4 ppm are assigned to the aromatic protons. The
integration curves show 9 protons for each ligand except for the ligand L1
which exhibits 10 protons. For the ligand L3 a singlet observed at 2.33 ppm
is assigned to the CH3 protons (the integration curve shows 3 protons). Also
for the ligand L4 a singlet observed at 3.81 ppm is assigned to the OCH3
protons. For all of the investigated ligands a singlet observed at
12.06712.15 ppm is assigned to the NH proton. The keto structure of the
free ligands was con®rmed by 1H NMR data which revealed that there is no
signal for the OH proton. Also this is con®rmed by the absence of a singlet
1
at 12.16712.15 ppm upon investigating the H NMR spectrum of 1,3-di-
phenyl-4-phenylazo-5-pyrazolone in which the signal at 12.14 ppm was not
observed. For the La chelates with the ligands L1, L2, L3 and L4 (1:1 and

1364
ABDEL-LATIF

La(III), Ce(III), Th(IV), AND UO2(VI) COMPLEXES
1365

1366
ABDEL-LATIF
Table IV. Proton NMR Spectral Data of the Azopyrazolone Ligands and Their
La(III) Complexes
Chemical
Shift
Ligands and Complexes
L1
M:L
Assignment
H1 (NH)
Aromatic C-H
H4 (aliphatic)
H1 (NH)
Aromatic C-H
H2O of coordination
H4 (aliphatic)
H1 (NH)
Aromatic C-H
H2O of coordination
H4 (aliphatic)
H1(NH)
12.14 s
8.177.2 m
2.51 s
12.14 s
8.177.2 m
3.35 s
[La(L1)(NO3)(OH)2(EtOH)2]
[La(L1)2(NO3)2(OH)(H2O)2]
1:1
1:2
2.52 s
12.14 s
8.177.2 m
3.35 s
2.52 s
L2
12.15 s
8.177.4 m
2.51 s
Aromatic C-H
H4(aliphatic)
H1 (NH)
[La(L2)(NO3)2(OH)(H2O)2(EtOH)3]
1:1
1:2
12.14 s
8.0977.5 m Aromatic C-H
3.35 s
2.52 s
12.14 s
8.0977.5 m Aromatic C-H
H2O of coordination
H4 (aliphatic)
H1 (NH)
[La(L2)2(NO3)(OH)2(H2O)2]
3.35 s
2.52 s
12.07 s
8.177.2 m
2.52 s
H2O of coordination
H4 (aliphatic)
H1(NH)
Aromatic C-H
H4(aliphatic)
CH3 protons
H1 (NH)
Aromatic C-H
H2O of coordination
H4 (aliphatic)
CH3 protons
Aromatic C-H
H2O of coordination
H4 (aliphatic)
CH3 protons
H1 (NH)
L3
2.33 s
[La(L3)(NO3)3(H2O)2(EtOH)2]
1:1
1:2
12.11 s
8.177.2 m
3.35 s
2.52 s
2.34 s
8.177.2 m
3.35 s
2.52 s
[La(L3)2(NO3)(OH)2]
2.34 s
L4
12.06 s
8.177.0 m
2.51 s
Aromatic C-H
H4 (aliphatic)
OCH3 protons
3.81 s

La(III), Ce(III), Th(IV), AND UO2(VI) COMPLEXES
1367
Table IV. Continued
Chemical
Shift
Ligands and Complexes
M:L
1:1
Assignment
H1 (NH)
[La(L4) (NO3)3(H2O)2(EtOH)]
12.06 s
8.177.06 m Aromatic C-H
3.8 s
3.35 s
2.51 s
12.06 s
OCH3 protons
H2O of coordination
H4 (aliphatic)
H1 (NH)
[La(L4)2(NO3)2(OH)(H2O)(EtOH)]
1:2
8.177.05 m Aromatic C-H
3.8 s
3.35 s
2.51 s
OCH3 protons
H2O of coordination
H4 (aliphatic)
1:2), coordinated water molecules were observed in the region at 3.35 ppm.
These signals obviously were not seen in the spectra of the free ligands. The
aromatic protons were observed at 8.177.05 ppm. The aliphatic H4 proton
was observed at 2.5272.51 ppm for the 1:1 and 1:2 chelates, respectively. For
the La-L3 (1:1 and 1:2) chelates, the singlet observed at 2.34 ppm corre-
sponds to the aliphatic CH3 protons. For the La-L4 (1:1 and 1:2) chelates, a
singlet observed at 3.8 ppm was assigned to the OCH3 protons. For all of the
investigated chelates a singlet observed at 12.14712.06 ppm was assigned to
the NH proton which means that NH at position 1 is not involved in che-
lation and the investigated ligands act as neutral bidentate ligands7.
The data obtained from the 1H NMR spectra con®rm the results
obtained from the IR spectra. The di€erence between the 1:1 and 1:2 che-
lates is that the integration curves show twice as many aromatic protons in
case of the 1:2 chelates. In addition, for the La-L3 1:2 and for the La-L4 1:2
chelates the integration curves show twice as many methyl protons, corre-
sponding to two methyl groups or two methoxy groups.
Mass Spectra
Mass spectra are a powerful tool in elucidating and con®rming the
structure of chemical compounds. It is known from the standard concepts of
physical organic chemistry that cyclic structures, double bonds, aromatic
and specially heteroaromatic rings, stabilize the parent ion and thus increase
the probability of its appearance in the mass spectra. The mass spectral
pattern of the ligand L1 shows a main peak of 264 (calcd. M. Wt. ˆ 264).

1368
ABDEL-LATIF
The fragmentation pattern of this ligand can be regarded as a general
scheme showing the main fragmentation paths involved. The di€erences in
the other ligands (L2, L3 and L4) results from the e€ects of the electro-
negativities of the substituent attached to the aromatic ring. For the ligand
L2, the main peak is observed at 298 (calcd. M. Wt. ˆ 298). As it is known
from the concepts of mass spectral analysis, a compound that contains one
chlorine atom will have a p‡2 peak approximately one-third the intensity of
the parent peak because of the presence of molecular ions containing the
37Cl isotope (relative abundance 34.8%). From the mass spectral pre-
sentation of the ligand L2, it is apparent that there is one chlorine atom in
the molecule, the intensity of the M‡2 peak (m=z 300, 34.8%) is almost one-
third the intensity of the parent peak (m=z 298, 100%). For the ligand L3,
the main peak is observed at 278 (calcd. M. Wt. ˆ 278). For the ligand L4,
the main peak is observed at 294 (calcd. M. Wt. ˆ 294). From the data
obtained we concluded that the molecular weights are in good agreement
with the calculated one.
Thermogravimetric Analyses (TG)
TG analyses of the La(III) complexes with the investigated ligands
(1:1) (Table V) were performed. The weight loss being measured from am-
bient temperature up to 800 ꢀC at a rate of 10 ꢀC minÀ1. The weight loss for
each chelate, obtained from the thermographs was used to calculate the
number of coordinated water and=or alcohol molecules present, since no
hygroscopic water or moisture was observed up to the 1357192 ꢀC range.
For the [La(L1)(NO3)(OH)2(EtOH)2] (1:1) chelate, two alcohol molecules
are coordinated to the metal ion; these are expelled within the temperature
range 1927293 ꢀC corresponding to a loss of 15.64% (calcd. 15.56%). In the
temperature range 2957438 ꢀC a weight loss of 22.86% (calcd. 22.44%) is
observed corresponding to the formation of an intermediate species through
the decomposition and combustion of the organic part with the loss of a
phenyl group and two hydroxy groups used for neutralization. Above this
temperature another loss occurred within the temperature range 4387597 ꢀC
which corresponds to a loss of 12.54% (calcd. 13.43%) corresponding to
two carbon and two nitrogen atoms followed by another loss at 5987749 ꢀC
corresponding to 4.52% (calcd. 4.77%) for an oxygen atom. At the end of
the thermogram the metal contents were calculated from the residual weight
of 23.33% (calcd. 23.52%), which is in good agreement with the calculated
values obtained by determination of the metal content after decomposition
of the chelate applying the method described by Macdonald18 and with the
result of elemental analysis (Table II).

La(III), Ce(III), Th(IV), AND UO2(VI) COMPLEXES
1369

1370
ABDEL-LATIF
For the [La(L2)(NO3)2(OH)(H2O)2(EtOH)3] (1:1) chelate, a weight
loss occurred within the temperature range 1467316 ꢀC corresponding to
the loss of 19.88% (calcd. 20.74%) for three coordinated alcohol molecules
and one water molecule. In the temperature range 3187471 ꢀC a loss of
19.71% (calcd. 18.46) that corresponds to one water molecule and two
nitrato groups is observed. At the higher temperature range 4737607 ꢀC a
loss of 15.97% (calcd. 16.05%) corresponds to the elimination of the
phenyl group. After this temperature another loss occurred within the
temperature range 6097802 ꢀC corresponding to 17.65% (calcd. 17.40) due
to the loss of chlorine and three carbon atoms which were oxidized by the
atmospheric oxygen to CO2. After this temperature a metal oxide residue
was obtained from which the metal content was calculated as 18.08%
(calcd. 18.48%).
For the [La(L3)(NO3)3(H2O)2(EtOH)2] (1:1) chelate, a loss of 40.57%
(calcd. 40.49%) occurs corresponding to the loss of two coordinated ethanol
molecules, one water molecule and three nitrato groups which are expelled
within the temperature range 1617331 ꢀC. By raising the temperature an-
other loss occurred within the temperature range 3317437 ꢀC corresponding
to 10.19% (calcd. 10.57%) due to the loss of one coordinated water and a
carbonyl group. In the temperature range 4407626 ꢀC decomposition and
combustion of the organic ligand starts followed by the loss of 30.51%
(calcd. 30.84%) which corresponds to the loss of -NˆN-C6H4-CH3. At the
®nal stage metal oxide as residue is obtained from which the metal content is
calculated to 19.00% (calcd. 19.01%).
For the [La(L4)(NO3)3(H2O)2(EtOH)] (1:1) chelate, a weight loss oc-
curred within the temperature range 1357298 ꢀC corresponding to the loss
of 14.64% (calcd. 15.40) for one coordinated ethanol and one nitrato group.
In the temperature range 2897398 ꢀC a loss of 12.71% (calcd. 12.14%)
occurs corresponding to the loss of two coordinated water molecules and
three carbon atoms which are oxidized by atmospheric oxygen to CO2. At
the higher temperature range of 4137661 ꢀC decomposition and combustion
of the organic ligand starts followed by a loss of 40.73% (calcd. 40.69%)
which corresponds to the phenyl group and -NˆNC6H4-OCH3. At the ®nal
stage metal oxide as residue is obtained from which the metal content is
calculated as 19.93% (calcd. 19.82%).
Molar Conductance
The molar conductivities of the solid chelates were measured in DMF
solution (10À3 M), the conductance values (LM) were found to be in the
range 30760 OÀ1 cm2 molÀ1
.
For [La(L1)(NO3)(OH)2(EtOH)2] (1:1),

La(III), Ce(III), Th(IV), AND UO2(VI) COMPLEXES
1371
[La(L2)(NO3)2-(OH)(H2O)2(EtOH)3] (1:1), for [La(L3)(NO3)3(H2O)2
(EtOH)2] (1:1) and for [La(L4)(NO3)3(H2O)2(EtOH)] (1:1) the conductivities
are 40, 60, 30 and 50 OÀ1 cm2 molÀ1, respectively. These values are small for
the ionic complexes of lanthanum metal ions and may be attributed to the
coordination of the nitrato ion in the above complexes rather than the ionic
association to the lanthanum ions during complex formation19. These molar
conductance values show that there are no anions present outside the co-
ordination sphere i.e., there are no nitrato groups outside this sphere and the
obtained chelates are neutral.
Figure 2. Suggested structure of the 1:1 complex formed by La(III) ions and
3-phenyl-4-(p-methoxyphenylazo)-5-pyrazolone.
Figure 3. Suggested structure of the 1:2 complex of La(III) ions with 3-phenyl-4-
(p-methoxyphenylazo)-5-pyrazolone.

1372
ABDEL-LATIF
CONCLUSION
Based on the results gained from the elemental analyses, IR, NMR,
molar conductance as well as TG analyses, a suggested structure of the
La(III) chelates with 3-phenyl-4-(p-methoxyphenylazo)-5-pyrazolone for 1:1
chelates is shown in Fig. 2 and for the 1:2 complexes in Fig. 3. The co-
ordination numbers of the prepared chelates (1:1) are 7, 1020, 921 and 822 for
La(III) ions, 7, 823, 6 and 7 for Ce(III) ions, 8, 12, 1219 and 10 for Th(IV)
ions and 9, 6, 1219 and 824 for UO2(VI) ions, respectively, while for the 1:2
chelates the coordination numbers are 9, 9, 7 and 9 for La(III) ions, 10, 11,
11 and 9 for Ce(III) ions, 11, 12, 12 and 11 for Th(IV) ions and 12, 7, 10 and
10 for UO2(VI) ions with the azopyrazolone ligands (L1), (L2), (L3) and (L4),
respectively.
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Received October 27, 2000
Accepted June 22, 2001
Referee I: J. G. Brennan
Referee II: M. M. Jones