Supramolecular and structural modification on conformational by mixed ligand

Article abstract of DOI:10.1016/j.saa.2012.09.016

A novel series of platinum(II) and palladium(II) complexes have been synthesized by template condensation of 4-methoxybenzaldehyde, benzaldehyde, 4-chlorobenzaldehyde and 4-nitrobenzaldehyde, with appropriate 4-aminoantipyrine (4-AAP) in the presence of K

Full text of DOI:10.1016/j.saa.2012.09.016

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 211–217
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
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Supramolecular and structural modification on conformational by mixed ligand
⇑
A.Z. El-Sonbati , M.A. Diab, A.A. El-Bindary, M.K. Abd El-Kader
Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
The formation of [Pd(Ln)(L)Cl] shows that upon the addition of [Pd(Ln)Cl2] to a solution of LH, the ligand
rearranges itself into the formation of an imine appended with Pd(II) and 4-derivatives benzaldehyde-4-
aminoantipyrine (Ln).
"
"
"
"
"
On the basis of these studies a
square planar geometry has been
proposed.
The infrared data indicate the
bidentate nature of ligands in all
complexes.
Molar conductance measurements
indicated the complexes to be
electrolytes.
Various ligand and nephelouxetic
parameter have been calculated for
the complexes.
The thermal decomposition for
complexes was studied.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 July 2012
Received in revised form 30 August 2012
Accepted 9 September 2012
Available online 21 September 2012
A novel series of platinum(II) and palladium(II) complexes have been synthesized by template condensa-
tion of 4-methoxybenzaldehyde, benzaldehyde, 4-chlorobenzaldehyde and 4-nitrobenzaldehyde, with
appropriate 4-aminoantipyrine (4-AAP) in the presence of K2PtCl4/PdCl2 to form complexes of the type
[M(Ln)Cl2](where M = Pt(II) or Pd(II)). The corresponding Schiff base complexes mixed ligand were pre-
pared by condensation of [M(Ln)Cl2] with ethanolamine (LH). The complexes have been characterized
with the help of elemental analysis, IR, 1H and 13C NMR, electronic spectra, conductance measurements,
magnetic susceptibilities and thermal analysis. On the basis of these studies, it is clear that ligands coor-
dinated to metal atom in a mononuclear (NO) in (1–6), Schiff base complexes (NNꢀ) in (7–9) and mono-
basic tridentate Schiff base complexes (NNꢀO) in (10–12). Thus, suitable square planar geometry for
tetradentated state has been suggested for the metal complexes. Various ligand and nephelouxetic
parameter have been calculated for the complexes. The thermal decomposition for complexes was
studied.
Keywords:
Pt(II)/Pd(II) supramolecular structure of
Schiff base
Spectral studies
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
and organometallic compounds has increased rapidly during the
past few years [2–4]. The field of pyrolozone chemistry of metals
Interest in coordination chemistry is increasing continuously
with the preparation of organic ligands containing a variety of do-
nor groups and it is multiplied manifold when the ligands have
biological importance [1]. The number and diversity of nitrogen
and oxygen chelating agents used to prepare new coordination
is developing very rapidly because of its importance in the area
of coordination chemistry [5]. Template condensation is one of
the most highlighted methods. Metal template condensation often
provides selective route towards the products that are not obtain-
able in absence of metal ion [6]. The preparation of Schiff bases
containing >C@O and >C@N groups with potential ligating ability
has drawn a lot of attention because of their use as chelating
agents, analytical reagents, metal indicators in complexometric
⇑
Corresponding author. Tel.: +20 1060081581; fax: +20 752403867.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.09.016

212
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 211–217
titrations and calorimetric reagents, in addition to biochemical re-
search [7]. The behavior of the >C@N bond is strongly dependent
on the structure of the amine moiety, which in turn controls the
efficiency of the conjugation and may incorporate structural ele-
ments able to modulate the steric crowding around the coordina-
tion [8].
Cisplatin, cis-[PtCl2(NH3)2], is one of the most effective chemo-
therapeutic agents currently used for the treatment of ovarian,
bladder, and testicular cancer [9,10]. The drug has to be adminis-
tered intravenously, however, and has dose-limiting side effects
such as severe renal toxicity, neurotoxicity, and emesis, arising,
in part, from the low solubility of cis-platin in water. These prob-
lems, along with the observation that cancer cells treated with
cis-platin acquire resistance to the drug, have provided an impetus
for research focused on the development of a more effective plati-
num drug that can be administered orally and with reduced side
effects.
solution of 4-aminoantipyrine (10 mmol) in the presence of
K2PtCl4/PdCl2 (10 mmol) in 1:1:1 molar ratio. After addition of all
the reagents, the contents were stirring for 6–7 h. The reaction
mixture was concentrated to half of its volume by removing the
solvent and kept in desiccators at room temperature. The com-
plexes obtained as solids, were washed with methanol and dried
under vacuo.
Preparation of cis-dichloro(4-derivatives benzaldehyde pyrazolone)
platinum(II) (1–3)/palladium(II) (4–6) (Scheme 1a)
The metal complexes were prepared by the addition of hot solu-
tion of the appropriate metal chloride (PdCl2, K2PtCl4) (10 mmol) in
ethanol (25 mL) to the hot solution of Ln (10 mmol) in the same
solvent (25 mL). The resulting mixture was stirred under reflux
for 1 h whereupon the complex precipitated. They were collected
by filtration, washed thoroughly with ethanol and dried in vacuum.
Our interest in this area is focused for a considerable time on
the investigation of coordination chemistry of transition metal
with using pyrazolone based ligand. To gain information about
the structure and stereochemistry of such type of complexes.
Therefore, in continuation of our earlier work on structural charac-
terization of mixed ligand transition metal complexes containing
rhodanine ligand [11–15], here we report the synthesis and charac-
terization of M(II) complexes and Schiff base complexes derived
from the condensation of 4-aminoantipyrine (4-AAP) with 4-deriv-
atives benzaldehyde (Ln). The complexes prepared were character-
ized particularly by elemental analysis, conductance, magnetic
measurements and spectral studies (IR, UV–vis and 1H NMR). Ther-
mal stabilities of the complexes have also been discussed.
In view of these facts and prosecute the research programs in
the field of template coordination chemistry, we report here the
synthesize cis-dichloro(pyrazolone derivatives) M(II) complexes
and Schiff bases complexes (Scheme 1).
Preparation of Schiff base complexes (1–6)
The Schiff base complexes were prepared by 1:1 interaction of
complexes (1–6) (Scheme 1a).
To the complexes of Pd(II)/Pt(II) (Scheme 1d) (1 mmol) 25 mL
methanol was added 4-derivatives benzaldehyde (R) (1 mmol).
Solution was allowed to stand for 10 min at room temperature
and then refluxed for 6–7 h on a water bath. The solution was re-
duced to 1/3 volume and kept in a desiccator as solids, were
washed with methanol and dried under vacuo.
Trans-Pt(II) Schiff base complexes (7–9) (Scheme 1b)
A solution of [Pt(Ln)Cl2] (1–3) (1 mmol) in DMF (10 mL) was
added to a solution of LH (ethanolamine) (1 mmol) in DMF/ethanol
(v/v%). The resulting mixture was stirred whilst heating on a water
bath for ꢁ5 h. The solid obtained after the addition of an aqueous
solution of ethanol was filtered, washed with distilled water and
followed by diethyl ether and dried in vacuo as [Pt(Ln)2(LH)2]Cl2
(Scheme 1b).
Experimental
Preparation of Pd(II) Schiff base complexes (10–12) (Scheme 1c)
Pd(II) Schiff base complexes (10–12) have also been prepared
using a method similar to that adopted for complexes (7–9) by
the addition of a solution of [Pd(Ln)Cl2] (4–6) (1 mmol) in DMF
(10 mL) to a solution of LH (1 mmol) in DMF. The product, after
heating on a sand bath for ꢁ4–5 h with stirring, was isolated after
the addition of H2O to the reaction mixture. It was then filtered and
washed with distilled water and methanol followed by diethyl
ether. The product was then dried in vacuo as [Pd(Ln)(L)Cl]
(Scheme 1c).
Materials
4-Aminoantipyrine, PdCl2, K2PtCl4 and various aldehydes were
purchased from Aldrich, and the other chemicals were of analytical
grade quality.
Preparation of ligands (Ln)
Ethanolic solutions of 4-aminoantipyrine (0.1 mol) and 4-deriv-
atives benzaldehyde (0.1 mol) were refluxed together for 4 h over a
steam bath. The excess solvent was removed by evaporation and
the concentrated solution was cooled in an ice bath with stirring.
The Schiff base (Ln) which separated out as a colored powder and
then recrystallized from ethanol. The purity of ligands was checked
by TLC. Our synthetic route of Schiff base ligands is shown in Fig. 1.
The color, yield %, M.P. °C and analytical data given in Table 1.
This indicates that the Pd(II) complex did not follow the same
reaction pattern as is followed by the Pt(II) complex.
All the complexes were recrystallization from 1:1 molar ratio
solution of methanol and benzene. The purity of the complexes
was checked by thin layer chromatography (TLC). The yield of com-
plexes = ꢁ55–75%.
The template synthesis of the complexes may be represented in
Scheme 1.
Preparation of Pt(II)/Pd(II) salt, complexes
Analytical and physical measurements
The complexes were prepared by the template condensation of
4-aminoantipyrine with 4-methoxybenzaldehyde, benzaldehyde,
4-chlorobenzaldehyde and 4-nitrobenzaldehyde in the presence
of K2PtCl4 and/or PdCl2.
Elemental microanalyses of the separated ligands and solid che-
lates for C, H, and N were performed in the Microanalytical Center,
Cairo University, Egypt. The analyses were repeated twice to check
the accuracy of the analyzed data. The 1H NMR spectrum was ob-
tained with a JEOL FX90 Fourier transform spectrometer with
DMSO-d6 as the solvent and TMS as an internal reference. Infrared
spectra were recorded as KBr pellets using a Pye Unicam SP 2000
spectrophotometer. Ultraviolet–visible (UV–vis) spectra of the
compounds were recorded in solution using a Unicom SP 8800
Preparation of cis-dichloro(4-derivatives benzaldehyde pyrazolone)
platinum(II) (1–3)/palladium(II) (4–6) (Scheme 1a)
A
weight amount of methanolic solution of 4-derivatives
benzaldehyde (10 mmol) 50 mL was mixed with the methanolic

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 211–217
213
NH2
O
H3C
Ethanol
N
Ln
O
+
X
N
K2PtCl4 / PdCl2
NH2
O
Cl
O
N
O
HC
Cl
N
K2PtCl4 / PdCl2
N
Pd
LH
X
+
M
x
N
N
O
Cl
Cis-Pd(II)
/
Pt(II)
(c) (10-12)
(a) (1-6)
LH
=
R
K2PtCl4 / PdCl2
Cl
/
LH
HO
H2N
O
HO
M
Cl
N
N
N
N
x
x
Pt
Pd
Cis-Pd(II)
/
Pt(II)
x
N
x
N
N
N
(d)
OH
OH
O
R =
HC
X
trans-bis (Pd(II))
trans-bis (Pt(II))
(b) (7-9)
X
=
OCH3 (1)
H
(2)
(3)
Cl
NO2 (4)
Scheme 1. The structures of the complexes.
H
C
N
X
NH2
OHC
X
N
N
+
N
O
N
O
Ln
X=OCH3 (1) , H (2), Cl (3), NO2 (4)
Fig. 1. Synthetic route of Schiff base ligands.
spectrophotometer. The magnetic moment of the prepared solid
complexes was determined at room temperature using the Gouy’s
method. Mercury(II) (tetrathiocyanato)cobalt(II), [Hg{Co(SCN)4}],
was used for the calibration of the Gouy tubes. Diamagnetic
corrections were calculated from the values given by Selwood
[16] and Pascal’s constants. Magnetic moments were calculated
flask in the presence of a KOHAH2O2 mixture. The halide content
was then determined by titration with a standard Hg(NO3)2 solu-
tion using diphenylcarbazone indicator. The conductance measure-
ment was achieved using Sargent Welch scientific Co., Skokie, IL,
USA.
using the equation,
leff.= 2.84 ½T
ꢂ
1=2. TG measurements were
v
Mcoor:
Results and discussion
made using a Du Pont 950 thermobalance. Ten milligram samples
were heated at a rate of 10 °C/min in a dynamic nitrogen atmo-
sphere (70 mL/min); the sample holder was boat-shaped, 10 ꢃ 5
ꢃ 2.5 mm deep; the temperature measuring thermocouple was
placed within 1 mm of the holder. The halogen content was deter-
mined by combustion of the solid complex (30 mg) in an oxygen
The ligand
In the present investigations, the ligands (Ln) were prepared by
stirring an appropriate amount of reactive 4-derivatives benzalde-
hyde with the corresponding 4-aminoantipyrine in ethanol. Schiff

214
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 211–217
Table 1
Table 3
Elemental analysis (C, H, N)a, color, yield (%) and melting point (°C) of derivatives (Ln).
Some selected bands of diagnostic importance from the IR spectra (cmꢄ1) of 4-AAP
and ligands (Ln).
Compounda
Color
Yield%
M.P. °C
Calc. (exp.)%
4-AAP
L1
L2
L3
L4
Assignment
C
H
N
3426
3315
3175
3087
2985
2918
1640
–
1405
1310
1200
–
–
–
–
–
–
–
–
–
t
t
t
t
t
t
(NH2)as
(NH2)s
(CH)as(Ar)
(CH)s(Ar)
(CH)as(CH3)
(CH)s(CH3)
L1
L2
L3
L4
Yellow
46.7
52.2
56.5
67
173
195
237
261
71.03
(71.17)
5.92
(5.99)
13.08
(13.37)
3085
3036
2935
2920
1644
1590
1416
1360
1179
1017
678
3085
3035
2930
2022
1648
1594
1418
1370
1181
1020
680
3086
3037
2928
2924
1650
1596
1420
1375
1183
1022
685
3088
3038
2928
2925
1653
1598
1423
1380
1185
1025
687
Pale yellow
Yellow
74.23
(74.42)
5.84
(5.93)
14.43
(14.59)
66.36
(66.45)
4.92
(5.13)
12.90
(13.21)
C@O
C@N
NACH3
CAN
d(CH3)
c
c
Pale yellow
64.29
(64.37)
4.76
(4.88)
16.67
(16.88)
a
The excellent agreement between calculated and experimental data suggests
the assignment suggested in the present work.
(C@N)
(CH)ring
730
base ligands (Ln) were light yellow in color and it is soluble in com-
mon organic solvents. The Schiff bases formed were characterized
with respect to its composition by elemental and spectral analysis.
The physical and analytical data given in Table 1, 1H NMR (Table 2)
and IR spectra (Table 3). Elemental analysis data of the ligand (Ln)
show good agreement with theoretical values.
For the four compounds (Ln) the yield %/M.P. °C of these com-
pounds were found to be sensitive to the nature of the substitu-
ents, X, on the ligand. In case of L4 with X = electron withdrawing
NO2, higher values (67/261) of the yield %/M.P. °C respectively
are observed, whereas lowers (46.7/173) is observed for L1
(X = OCH3), reflects the electron donating nature of the substituent
(Fig. 2).
70
60
P-NO
2
(a)
280
240
200
160
120
(b)
P-NO
P-Cl
P-Cl
2
P-H
50
P-OCH
P-H
3
P-OCH
3
Metal complexes and characterization
40
-0.5
0.0
0.5
1.0
R
Hammett's substituent coefficient (σ
)
The complexes are stable in air and atmosphere. All the com-
plexes are colored, stable at room temperature, high melting
points, soluble in DMSO and DMF, but they are insoluble in some
common organic solvents. Elemental analysis results for the metal
complexes (Table 4) were in good agreement with calculated val-
ues showing that the complexes (1–6), (7–9) and (10–12) had
the metal/ligand ratio of 1:1 [M(Ln)Cl2], 1:2:2 [Pt(Ln)2(LH)2]Cl2
and 1:1:1 [Pd(Ln)(L)Cl] respectively; where Ln = 4-derivatives benz-
aldehyde-4-aminoantipyrine; M = Pd(II) and/or Pt(II). The molar
conductivity of metal complexes in DMF solution (10ꢄ3 M) at room
temperature was measured to establish the charge of the metal
complexes. The molar conductivity of (1–6 and 10–12) complexes
indicates that they are non-electrolytes but complexes (7–9) indi-
cating that they are 1:2 electrolyte type [14,15,17].
-0.5
0.0
0.5
1.0
R
Hammett'ssubstituent coefficient (σ )
Fig. 2. The relation between Hammett’s substitution coefficient (
r
R) vs. (a) Yield%
and (b) melting point °C of ligand (Ln).
Table 4
Analytical dataa of complexesb.
Compoundc
Elemental analysis calc. (exp.)%
C
H
N
Cl
[Pt(L1)Cl2] (1)
[Pt(L2)Cl2] (2)
[Pt(L3)Cl2] (3)
[Pd(L1)Cl2] (4)
[Pd(L2)Cl2] (5)
[Pd(L3)Cl2] (6)
[Pt(L1)2(LH)2]Cl2
(7)
[Pt(L2)2(LH)2]Cl2
(8)
[Pt(L3)2(LH)2]Cl2
(9)
38.84(38.91) 3.24(3.21) 7.15(7.43)
38.77(38.90) 3.05(3.15) 7.54(7.77)
36.51(36.58) 2.71(2.82) 7.10(7.42)
45.74(45.82) 3.21(3.32) 8.43(8.54)
46.11(46.24) 3.63(3.73) 8.97(9.21)
42.95(43.12) 3.18(3.28) 8.35(8.47)
50.70(50.78) 4.83(4.94) 11.27(11.45) 7.14(7.44)
51.39(51.47) 4.71(4.89) 11.99(12.22) 7.60(7.78)
44.69(44.68) 3.91(3.99) 10.43(10.54) 19.83(19.89)
12.09(1223)
12.75(12.88)
18.00(18.33)
14.24(14.44)
15.16(15.35)
21.18(21.42)
Spectral studies
1H NMR and 13C NMR
The absence of protons signals of free NH2 groups in 1H NMR
indicates that condensation of NH2 (of 4-aminoantipyrine) with
4-derivatives benzaldehyde has taken place.
Table 2
1H NMR spectral data (d ppm) of 4-AAP and Schiff bases (Ln).
[Pd(L1)(L)Cl] (10)
[Pd(L2)(L)Cl] (11)
[Pd(L3)(L)Cl] (12)
49.91(50.05) 4.56(4.77) 11.09(11.38) 7.03(7.34)
50.54(50.66) 4.42(4.54) 11.79(11.94) 7.48(7.67)
47.11(47.23) 3.93(4.03) 10.99(11.23) 13.94(13.87)
Assignment
Compound
L1
L2
L3
L4
(4-AAP)
a
Microanalytical data as well as metal estimations are in good agreement with
the stoichiometry of the proposed complexes.
The excellent agreement between calculated and experimental data supports
the assignment suggested in the present work.
HL are the ligand as given in Scheme 1 and L is the anion; air-stable; no-
hygroscopic; insoluble in water; soluble in coordinating solvents such as DMF and
DMSO.
CACH3
NACH3
NH2
2.55
3.09
–
2.60
3.15
–
7.22–7.95
9.48
–
2.64
3.22
–
7.33–8.22
9.40
–
2.68
3.27
–
7.42–8.34
9.36
–
2.15
2.84
2.99
7.15–7.50
–
–
b
ArH
CH@N
OCH3
6.80–7.86
9.71
3.27
c

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 211–217
215
The 1H NMR spectra of the antipyrine and Schiff bases (Table 2)
were carried out at room temperature in DMSO-d6. The spectra dis-
play two sharp signals at 2.33–2.48 and 3.09–3.16 ppm with an
integration equivalent to three hydrogens corresponding to the
NACH3 and CACH3 groups. The aromatic rings give a group of mul-
ti signals at 6.80–7.86 ppm. The CH@N hydrogen for Ln resonates at
9.36–9.71 ppm as a sharp singlet. The Pd(II) complexes shows a
slight downfield shift of 0.3–0.6 ppm in the resonance peaks corre-
sponding to the phenyl ring and the azomethine proton, which
may be attributed to the coordination of the ligand to the Pt(II)/
Pd(II) ion. 13C NMR of L1–4 exhibited signals at 188–188.8 and
161–161.9 ppm corresponding to the carbon of C@O and C@N
groups. Methyl groups were observed between 18.4 and
19.8 ppm. Also, the spectra showed peaks at 19–131 ppm corre-
sponding to carbons of the phenyl ring. The downfield shift ob-
served indicates the coordination of oxygen and nitrogen to M(II)
ion.
The signal of OAH protons (in complexes 7–9) at ꢁ1.62 ppm
completely disappears in the spectra of Pd(II) complexes (10–12)
(Scheme 1c) indicating the involvement of the alcoholic oxygens
in the chelation through displacement of the OH proton.
In order to get further information about the ligand at its Pd(II)
complexes (10–12), the 13C NMR spectra were investigated. In the
Pd(II) complexes (10–12), exhibit signals at ꢁ191 ppm (C@Nꢀ). The
aliphatic carbon signals of ethyl groups showed peaks at ꢁ55.99
and 55.87 ppm. These observations are consequence of coordina-
tion of ligand via (C@N), (C@Nꢀ) and alcoholic oxygen atoms.
compounds display an intense band at 1645–1615 cmꢄ1 corre-
sponding to (C@O) of the antipyrine ring. The metal complexes
t
showed a strong absorption at 1660–1690 cmꢄ1
t(C@O) (D = 10–
20 cmꢄ1). Accordingly, all ligands act as bidentate chelating agents
bonded to the platinum(II)/palladium(II) ion via the azomethine
nitrogen and the pyrazolone ring oxygen atoms in all isolated com-
plexes. The appearance of t(CAH) and d(CAH) of the methylene
group at lower frequencies in the complexes compared to their
positions in the free ligands could also be taken as evidence for
the coordinating nature of the azomethine nitrogen.
In [Pt(L1)2(LH)2]Cl2 (Scheme 1b) (7–9), mixed ligand (Ln and LH)
behaves as a neutral bidentate coordinating via the
t(HC@N) and
new (HC@N) of Pt(II) mono-
t
(C@Nꢀ). This is confirmed by: (i) the
t
nuclear complexes (1–3), (ii) the disappearance of t(C@O) with
simultaneous appearance of new bands at ꢁ1648–1668 cmꢄ1 as-
signed to t
(C@Nꢀ), resulting from condensation between ethanol-
amine and carbonyl oxygen atom of pyrazolone and (iii) the
sharp band at ꢁ3447 cmꢄ1 show in ethanolamine complexes of
Pt(II) Schiff bases complexes correspond to free AOH of ethanol-
amine. This observation is further supported by its 1H NMR spectra,
which shows a peak at ꢁd 1.62 ppm assigned to OH protons.
In [Pd(L1)(L)Cl] (Structure 1c) (10–12), this mode of complexa-
tion is confirmed by the ligands (Ln and LH) behaves as NNꢀO
mononegative tridentate. The coordination takes place through
(CAO) and C@Nꢀ groups. The IR spectra of all complexes (10–12)
shows
t
t
(C@Nꢀ) peak at 1648–1668 cmꢄ1 and the absence of a
(C@O) peak at ꢁ1660–1690 cmꢄ1 is indicative of Schiff‘s base
complexes condensation. This phenomenon appears to be due to
the coordination of the azomethine nitrogen (C@Nꢀ) to the metal
IR spectra
ion [14,15,18]. Also, a broad
t(OH) band of ethanolamine at
Selected bands of diagnostic importance are discussed in this
part (Table 5).
ꢁ3435 cmꢄ1 disappears on complexation. This fact is further sup-
ported by the increase in CAO stretching frequency at ꢁ1288–
1280 cmꢄ1 in the complexes which indicates the other coordina-
tion of ligand to the Pd(II) ions through the charged alcoholic oxy-
gens. Thus the IR spectra of complexes (10–12) indicates that the
Schiff base ligands (Ln + L) (Scheme 1c) in all the complexes under
investigation is tridentate and the binding sites are two azome-
thine nitrogens (AC@NA and AC@NꢀA) and oxygen of alcoholic
OH atom. The square planar geometry of the palladium(II) complex
is completed by chlorine atom (Scheme 1c).
The IR spectra provide valuable information regarding the coor-
dinating sites of ligands. The IR spectra of the complexes were
compared with that of the free ligands to determine the changes
that might have taken place during the complexation. A compara-
tive study of the spectra of ligand and its metal complexes reveals
that certain peaks are common and therefore, only important
peaks, which have been either shifted or newly appeared, are
discussed.
In cis-[M(Ln)Cl2] (1–6) (Scheme 1a), spectra of free Schiff base
ligands (Ln) showed a band of the AC@NA group in the region of
1590–1598 cmꢄ1 which was shifted to lower frequencies in the
spectra of all complexes (1585–1565 cmꢄ1) indicating the involve-
ment of AC@NA nitrogen in coordination to the metal ion [14,18].
Coordination of the Schiff bases to the metal through the nitrogen
atom was expected to reduce the electron density in the azome-
The significant change in the complexing is the decrease in
t(C@N)Schiff. This shift in the spectra of the complexes suggests
coordination through both nitrogens groups [19]. Recent studies
[14,15,18] have shown that the s character of the nitrogen lone pair
in the C@N bond increases upon coordination; this change in
hybridization produces the shorter C@N bond length and greater
C@N stretching force constant, relative to the free neutral Schiff
bases. The variable magnitude of the shift reflects the variable Le-
wis acidity of the metal ions in the complexes under study.
These observations suggested that the ligand coordinate to the
Pd(II) ions through the charged alcoholic oxygens and the two
nitrogen atom of azomethin groups of bis-N2O compartments in
its complex. Moreover, the spectra of complexes exhibit band
due to (PdACl).
thine link and to lower the
t(C@N) vibration. All complexes
showed that bands in the 1090–1100 cmꢄ1 and 700–745 cmꢄ1 re-
gions which could be assigned to phenyl ring vibrations. All
Table 5
Important IR vibration frequencies (cmꢄ1) of complexes.
Complexa
t
(C@O)
t(C@N)
t(OH)
t
(CAH)
t(CAH)
Thus, the formation of [Pd(Ln)(L)Cl] (Scheme 1c) (10–12) shows
that upon the addition of [Pd(Ln)Cl2] (Scheme 1a) (1–6) to a solu-
tion of LH, the ligand rearranges itself into the formation of an
imine appended with Pd(II) and 4-derivatives benzaldehyde-4-
aminoantipyrine (Ln) as depicted in Scheme 1 .
As mentioned above, upon the complexation of [Pt(Ln)Cl2]
(Scheme 1a) (1–6) with LH, a (2 + 2) condensation between the
two components occurred and it resulted in the formation of a
metallopyrazolone.
1
2
3
4
5
6
7
8
9
1616
1612
1608
1617
1608
1606
–
–
–
–
–
1579
1587
1583
1553
1559
1563
1575, 1645
1585, 1658
1579, 1665
1550, 1660
1555, 1678
1580, 1688
–
–
–
–
–
–
1427, 1408
1426, 1409
1422, 1406
1440, 1410
1442, 1428
1441, 1417
1425, 1405
1424, 1406
1420, 1404
1436, 1408
1440, 1425
1438, 1415
1251
1253
1255
1219
1214
1214
1248
1250
1253
1217
1212
1213
3515
3516
3518
–
–
–
10
11
12
Although the reason for this difference in reactivity of Pd(II) and
Pt(II) with the Schiff base cannot be understood accurately, it may
be considered in view of the stronger PtAN@C bond as compared
–
a
Numbers as given in Table 4.

216
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 211–217
to the PdAN@C bond [20]. Theoretical calculations also support
that the relativistic bond stabilization is stronger for third row
transition metal complexes (Pt) than for second-row transition
metal complexes (Pd) [21].
assigning the stereochemistries of metal ions in the complexes
based on the positions and number of d–d transition peaks.
With the exception of a small number of palladium derivatives,
few six-coordinate complexes of these species are known. The
majority of complexes are four-coordinate and square planar. The
spectra of these complexes exhibit bands characteristic of square
planar palladium(II) complexes [11]. In the present studies all
the complexes are found to be diamagnetic as expected for square
planar d8 complexes [24]. The geometries are supported by their
electronic spectra.
All the complexes show bands at ꢁ1090–1100 and 700–
750 cmꢄ1, assigned to phenyl ring vibrations. In the far spectra,
various new bands observed are characteristic of
t(MAN) or
t
(MAO) frequencies. The new bands in palladium(II) complexes
at 435–460 cmꢄ1 may be assigned to
t
(PdAN) while those ob-
(PdAO) vibration
[14,22]. Similar bands in platinum(II) complexes observed at
345–415 cmꢄ1 are well within the assignable to
(PtAN) mode,
while those observed at 385–405 cmꢄ1 may be assigned to
(PtAO)
served at 410–465 cmꢄ1 may be assigned to
t
Electronic spectra of ligands and its complexes were recorded in
DMF solution, the wide range bands were observed due to either
t
t
the
transfer transition arising from
p–
pꢀ and n ? pꢀ of (C@N or C@O) chromophore or charge-
vibration [15,23]. These bands are consistent with the frequencies
observed for square planar complexes of these metal ions.
Therefore, it is clear from these results that the data obtained
from the elemental analyses, IR, and 1H NMR spectral measure-
ments are in agreement with each other.
p electron interactions between
the metal and ligand, which involved either a metal-to-ligand or li-
gand-to-metal electron transfer [25]. Despite the fact that the po-
sition of the CT band is influenced by the substituent on the
phenyl ring being shifted to longer wavelength with the increasing
donor character of the substituent. The electronic spectra of the
free ligand in DMF showed strong absorption bands in the ultravi-
olet region (23,530–37,460 cmꢄ1), that could be attributed to the
Geometry of the Pd2+APt2+ complexes
The electronic absorption spectra are often very helpful in the
evaluation of results furnished by other methods of structural
investigation. The electronic spectral measurements are used for
p
?
pꢀ and n ?
p
ꢀ transitions in the benzene ring or (AC@N or
C@O) groups for free ligand. The absorption bands between
37,460 and 23,530 cmꢄ1 in free ligands changed a bit in intensity
Table 6
Electronic absorption spectra (cmꢄ1) and ligand field parameters of complexes.
Complexa
1
Bands (cmꢄ1
)
Assignments
m2
/
m1
D1
D2
D3
20,615
23,920
27,320
d
d
xy ? dx2–y2
z2 ? dx2–y2
1.160
1.251
1.28
22,715
3300
4305
dxz, dyz ? dx2–y2
2
3
20,150
25,250
35,150
-do-
22,250
23,233
32,150
32,250
32,350
23,900
25,000
25,100
22,200
23,000
23,150
6300
7106
3390
3230
3230
4300
3100
3100
4600
2400
2450
9600
5848
6960
7020
7020
5800
5000
3900
4700
3250
2800
21,133
27,039
33,187
-do-
-do-
-do-
-do-
-do-
-do-
-do-
-do-
-do-
-do-
4
30,050
32,240
39,550
1.073
1.067
1.067
1.142
1.083
1.09
5
30,150
32,180
39,500
6
30,250
32,280
39,600
7
21,800
24,900
31,000
8
22,900
24,800
30,100
9
23,000
25,000
29,100
10
11
12
20,100
23,500
28,500
1.169
1.069
1.059
20,900
22,100
25,650
21,050
22,300
25,400
a
Numbers as given in Table 4.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 211–217
217
and remained slightly changed for metal complexes. The absorp-
Conclusions
tion shift and intensity change in the spectra of the metal com-
plexes most likely originated from the metallation, increased the
conjugation and delocalization of the whole electronic system
and resulted in the energy change of the
tions of the conjugated chromophore [26].
Based on the above observations of the elemental analysis, mo-
lar conductivity, UV–vis, magnetic, IR, 1H NMR spectral data it is
possible to determine the type of coordination of the ligands in
their metal complexes. The spectral data show that all the Schiff
bases exist as neutral bidentate in mononuclear (NO)/Schiff base
complexes (NNꢀ) and monobasic tridentate (NNꢀO) in Schiff bases
complexes. The analytical data show the presence of one metal
ion per one/two ligand molecules and suggest a mononuclear
structure for the complexes. The correlation of the experimental
data allows assigning a square planar stereochemistry to all the
above synthesized complexes as shown in Scheme 1. The present
study shows the construction of a Pt(II)-based metallopyrazolone
on the skeleton of a simple tridentate Schiff base which provides
an electron rich cavity. The space provided by the cavity is found
to be suitable for comparatively stronger binding of an electron
acceptor molecule. This study also allows the difference in the
reactivity of Pd(II) and Pt(II) complexes with tridentate Schiff base
to be understood.
p ?
pꢀ and n ? pꢀ transi-
The electronic spectra of patinum(II) and palladium(II) com-
plexes are indicative of square planar geometry (Structure 1). The
absorption bands for the platinum(II) and palladium(II) complexes
may be assigned to the three d–d forbidden transition expected
from the three lower lying d levels to empty dx2–y2 orbitals. The
1
ground state is A1g and the excited states corresponding to the
1
above transitions are A2g
,
1B1g and 1Eg in order of increasing en-
ergy. By assuming a value of F2 = 10F4 = 600 cmꢄ1 for a Slater–Con-
don interactions repulsion parameters and subsequently the
equations suggested by Cray and Ballhausen [27], it is possible to
calculate the single electron parameter D1, D2 and D3 (Table 6).
The t2 t1 value lies in the 1.059–1.251 range, comparable with
/
the values reported earlier for square planar complexes [14,15].
The values of D1 for Pt(II) complexes are much higher than those
observed for palladium(II) complexes but are in accordance with
those required for platinum(II) square planar complexes. The
values of D1 lie in between those observed for cyanide
(ꢁ30,000 cmꢄ1) and chloride complexes (ꢁ19,000 cmꢄ1) and are
consistent with intermediate ligand field strength [28,29]. The
crystal field stabilization energies for Pd(II) and Pt(II) complexes
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