Supramolecular structure and spectral studies on mixed-ligand complexes derived from β-diketone with azodye rhodanine derivatives

Article abstract of DOI:10.1016/j.saa.2012.08.059

A novel method to synthesize some mononuclear ternary palladium(II) complexes of the general formula [Pd(L_n)L] (where LH = diketone = acetylacetone, HL_n = azorhodanine) has been synthesize. The structure of the new mononuclear ternary palladium(II) complexes was characterized using elemental analysis, spectral (electronic, infrared and ¹H & ¹³C NMR) studies, magnetic susceptibility measurements and thermal studies. The IR showed that the ligands (HL_n & LH) act as monobasic bidentate through the azodye nitrogen, oxygen keto moiety and two enolato oxygen atoms. The molar conductivities show that all the complexes are non-electrolytes. Bidentate chelating nature of β-diketone and azorhodanine anions in the complexes was characterized by (electronic, infrared and ¹H & ¹³C NMR) spectra. Square planar geometry around palladium has been assigned in all complexes. Various ligand and nephelouxetic parameter have been calculated for the complexes. The thermal decomposition for complexes was studied.

Full text of DOI:10.1016/j.saa.2012.08.059

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 353–360
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Supramolecular structure and spectral studies on mixed-ligand complexes
derived from b-diketone with azodye rhodanine derivatives
a,
⇑
a
b
b,1
A.Z. El-Sonbati , M.A. Diab , A.A.M. Belal , Sh.M. Morgan
a
Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
Chemistry Department, Faculty of Science, Port Said University, Egypt
b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Both b-diketonate and azo compound act as bidentate chelating ligands and a square planar geometry
around palladium(II) is established forming stable six membered heterocyclic rings.
"
"
"
"
Structure of mononuclear ternary
palladium(II) complexes was
established.
Square planar geometry around
palladium has been assigned in all
complexes.
Various ligand and nephelouxetic
parameter have been calculated for
the complexes.
The thermal decomposition for
complexes were studied.
CH
3
CH3
CH3
O
O
O
O
O
O
H
2
C
H
C
H
H
C
H
CH
3
CH3
CH
3
(
a) keto form
(b) enol form
PdCl
2
Acetone
CH
3
O
O
O
C
O
O
HL
n
Pd
H
C
Pd
N
C
CH
3
2
(
d)
(c) metal complex
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 May 2012
Received in revised form 9 August 2012
Accepted 21 August 2012
Available online 7 September 2012
A novel method to synthesize some mononuclear ternary palladium(II) complexes of the general formula
Pd(L )L] (where LH = diketone = acetylacetone, HL = azorhodanine) has been synthesize. The structure
of the new mononuclear ternary palladium(II) complexes was characterized using elemental analysis,
[
n
n
1
13
spectral (electronic, infrared and H & C NMR) studies, magnetic susceptibility measurements and ther-
mal studies. The IR showed that the ligands (HL & LH) act as monobasic bidentate through the azodye
n
nitrogen, oxygen keto moiety and two enolato oxygen atoms. The molar conductivities show that all
Keywords:
the complexes are non-electrolytes. Bidentate chelating nature of b-diketone and azorhodanine anions
Pd(II) mixed-ligand complexes
Rhodanine azo ligand
b-Diketone
1
13
in the complexes was characterized by (electronic, infrared and H & C NMR) spectra. Square planar
geometry around palladium has been assigned in all complexes. Various ligand and nephelouxetic
parameter have been calculated for the complexes. The thermal decomposition for complexes was
studied.
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
[1]. In the last few decades, mixed ligand complexes have been
extensively studied in solution as well as in the solid [2]. Ternary
1
,3-Diketons constitute an important class of ligands in view of
complexes are found to be more stable than binary complexes. Ste-
ric effect and lack donation have also been invoked to account for
the preferred formation of mixed-ligand complexes [2].
their distinct structural properties and high synthetic utility. They
exist in two tautomeric forms which have been extensively studied
Current interest in the mononuclear metal b-diketonates
n
assemblies of the general composition [Pd(b-diketone)(L )] is
mainly because of these complexes possess anticancer and insulin
mimetic activity [3], specially with b-diketone ligands [4].
⇑
Corresponding author. Tel.: +20 1060081581; fax: +20 572403867.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
Abstracted from her M.Sc.
1
1
386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.08.059

3
54
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 353–360
The design and study of well arranged metal containing elec-
4-alkylaniline [12–18]. The resulting mixture was stirred and
cooled to 0 °C, a solution of 0.01 mol sodium nitrite in 20 ml of
water was added dropwise. The formed diazonium chloride was
consecutively coupled with an alkaline solution of 0.01 mol 2-thi-
oxo-4-thiazolidinone, in 10 ml of pyridine was filtered through sin-
tered glass crucible, washed several times with water. The formed
colored precipitate and ether. The crude product was purified by
recrystallization from hot ethanol, yield ꢁ35–65% then dried in
tron donors ligand is interesting field of chemistry and has at-
tracted the interest of both inorganic and bioinorganic chemists
in recent years [1]. The field of mixed-ligand chemistry of metal
is developing very rapidly because of its importance in the area
of coordination chemistry [5]. Finally design of the mixed-ligand
complexes depends upon the stereochemical requirements and
coordinating features of metal ion [1,5–8]. The coordination chem-
istry of square planar metal complexes involving nitrogen donor li-
gands has excited great interest among chemists in recent years
due to the applications of these in catalysis and their relavence
to bioinorganic system [1]. The studies of Pd(II) complexes have
been widely explored for the versatility of their coordination
geometries, technical application and their biochemical signifi-
vacuum desiccator over P
The resulting formed ligands are: 5-(4-methoxyphenylazo)-2-
thioxo-4-thiazolidinone (HL ), 5-(4-methyphenylazo)-2-thioxo-4-
thiazolidinone (HL ), 5-(4-phenylazo)-2-thioxo-4-thiazolidinone
(HL ), 5-(4-chlorophenylazo)-2-thioxo-4-thiazolidinone (HL ) and
5-(4-nitro phenylazo) -2-thioxo-4-thiazolidinone (HL ).
2 5
O .
1
2
3
4
5
2
NaNO2 HCl.H O
R
NH
2
HCl
+
-
R
N
N
Cl
O
O
HN
S
HN
alkaline solution
o
+
-
R
N
N
Cl
0-5 C
S
S
S
N
N
R
O
N
OH
HO
HN
HN
S
S
=
N
S
S
N
N
N
R
R
H
n = 1, R = OCH
3
1
(HL ); n = 2, CH
3
2 3 4 2 5
(HL ); n = 3, H (HL ); n = 4, Cl (HL ); and n = 5, NO (HL )
The formation mechanism of azodye ligands (HL )
n
cance. Square planar Pd(II) complexes of ligand containing mixed
electron donors have been studies extensive, due to their potential
applications as molecular materials [9–11].
The ligands were also characterized by elemental analysis
(Table 1), NMR and I.R. spectroscopy.
Our interest in this is focused for a considerable time on the inves-
tigation of coordination chemistry of transition metal with 1,3-dike-
tonate based ligand. To gain more information about the structure
and stereochemistry of such type of complex, a detailed investigation
on a novel palladium(II) complexes with a ligand involving nitrogen,
enolic oxygen as donors has been initiated on our part.
In the present study we report the synthesis of [Pd(L1ꢀ5)(L)]
n
complexes from mixed ligands (HL & LH). The synthesized com-
pounds have been characterized by analytical and spectral data.
General method of synthesis of complexes
Synthesis of bis(1,3-diketonato)palladium(II) complex [Pd(L)
The bis(1,3-diketonato)palladium(II) complex was prepared by
reacting a hot solution PdCl (0.05 mol) in acetone (20 mL) with
2
] (1)
2
a solution of 1,3-diketone (0.01 mol) in ethanol and then was stir-
red for 45 min. The resulting mixture was concentrated and the so-
lid thus obtained was filtered, dried and recrystallized from hexane
(Table 2).
Experimental
Synthesis of Pd(II) mixed-ligand complexes [Pd(L1ꢀ5)(L)] (2–6)
The novel solid complexes were prepared by the reaction of cal-
culated amount of (M:HL1ꢀ5:LH) 1:1:1 ratio of both metal salt and
ligands in methanol. The reaction mixture was refluxed for ꢁ10 h.
Synthesis of ligands
n
Synthesis of 5-(4-alkylphenylazo)-2-thioxo-4-thiazolidinone (HL )
In a typical preparation, 25 ml of distilled water containing
.01 mol hydrochloric acid were added to aniline (0.01 mol) or a
Another method as follows: To the [Pd(L)
2
] complex (1) (0.05 mol)
n
(0.05 mol). The solution was al-
0
(50 mL) ethanol was added HL

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 353–360
355
Table 1
a
o
n
Elemental analysis (C, H, N) , color, yield (%) and melting point ( C) of azorhodanine derivatives (HL ).
o
Compound
Color
Yield (%)
M.p. ( C)
Calc. (Exp.)%
C
H
N
HL
1
Red
37.45
47.81
42.19
51.37
66.09
221
231
237
248
245
44.93
(44.82)
47.79
(47.88)
45.55
(45.68)
39.78
(39.65)
38.29
3.39
(3.25)
3.61
(3.76)
2.97
(2.80)
2.23
(2.35)
2.14
(2.25)
15.72
(15.85)
16.72
(16.61)
17.71
(17.85)
15.46
(15.58)
19.85
(19.98)
C
10
H
9
N
N
3
O
2
S
2
HL
2
Dark orange
Pale yellow
Light orange
Dark yellow
C
10
H
9
3
OS
2
HL
3
C
9
H
7
6
6
N
3
N
3
N
4
OS
2
2
HL
4
C
9
H
OS
Cl
HL
5
C
9
H
O
3
S
2
(38.42)
a
The excellent agreement between calculated and experimental data suggests the assignment suggested in the present work.
Table 2
rate of 10 °C/min in a dynamic nitrogen atmosphere (70 ml/min);
the sample holder was boat-shaped, 10 ꢂ 5 ꢂ 2.5 mm deep; the
temperature measuring thermocouple was placed within 1 mm of
Method of preparation, elemental analysis and molar conductance data of Pd(II)
complexesa (for molecular structure see Fig. 1) .
b
Complexesc
Mol. ratio
Calc. (Exp.)%
K
d
M
the holder. Structural analysis of the powder HL
at room temperature by a Philips X-ray diffractometer equipped
with utilized monochromatic Cu K radiation (k = 1.5418 Å). The
2
was performed
C
H
N
S
a
[
[
[
[
[
[
Pd(L)
2
] (1)
1:2
1:1:1
1:1:1
1:1:1
1:1:1
1:1:1
34.44
5.20
(4.99)
3.33
(3.38)
3.51
(3.38)
3.41
(3.25)
2.34
(2.28)
2.85
–
–
12.60
8.80
X-ray tube voltage and current were 40 kV and 25 mA, respectively.
(34.24)
36.64
(36.57)
38.13
(37.89)
36.40
(36.25)
27.46
(27.31)
32.96
(32.82)
Pd(L
Pd(L
Pd(L
Pd(L
Pd(L
1
2
3
4
5
)(L)] (2)
)(L)] (3)
)(L)] (4)
)(L)] (5)
)(L)] (6)
9.55
14.32
(13.93)
14.82
(14.43)
15.25
(14.87)
11.65
(11.20)
13.84
(9.14)
9.83
(9.47)
10.10
(9.76)
7.65
(7.35)
12.20
(11.78)
9.35
Results and discussion
10.55
11.25
11.95
The azo group can act as a proton acceptor in hydrogen bonds
[
11,15,21]. The role of hydrogen bonding in azo aggregation has
been accepted for some time. Intramolecular hydrogen bonds
involving OH group with the –N@N– group increased their stabili-
ties through chelate ring structure [7,16,18]. The strength of the
hydrogen bond of compounds depends on the nature of substitu-
ents present in the coupling component from the aryl azo group.
Chelating rings formed by NH. . .N bonds are less stable than corre-
sponding rings formed by OH. . .N bonds [8,21]. The U.V. spectra of
acetylaminoazobenzene showed that the chelate ring is stable in di-
oxan and in methanol solvents, whereas the chelate ring in 2-hy-
droxy-4-methylazobenzene is stable in dioxan and hydroxylic
solvents. Chelate rings involving NH. . .N@N bonds in azo com-
pounds (e.g. 2-amino-4-dimethylaminoazo benzene) have been
treated theoretically and have been studied in the IR and UV. Spec-
tra where both five and six membered chelate rings with NH. . .N
bonds have been suggested [22]. The intramolecular hydrogen
bond in 1-phenylazo-2-naphthol was found to be stronger than in
the 2-hydroxyazobenzene, due to the attachment of the –OH group
to a larger resonance system thereby increasing the acidity [23].
In general, most of the azo compounds give spectral localized
bands in the wavelength range 47,620–34,480 and 31,250–
(2.74)
(13.46)
a
Microanalytical data as well as metal estimations are in good agreement with
the stoichiometries of the proposed complexes, air stable, non-hydroscopic, high
melting temperature and colored.
b
The excellent agreement between calculated and experimental data supports
the assignment suggested in the present work.
c
L
X
1 5 1 5
–L & L are the anions of the ligands HL –HL & LH as given in Fig. 1.
d
ꢀ1
2
ꢀ1
cm mol in DMF.
lowed to stain for 1 h at room temperature with stirring and then
refluxed for 12 h on a water bath. The resulting solution was con-
centrated to almost a quarter of its original volume and kept in
desiccator for ꢁ3 days. The color solid separated was filtered off,
washed with hot ethanol and dried in an oven at 110 °C; yield
5
8–68%. The analytical data are given in Table 2.
Measurements
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. Palladium was estimated gravi-
ꢀ1
27,000 cm . The first region is due to the absorption of the aro-
1
1
matic ring compared to
b b
B and L of mono substituted benzene
and the second region is due to the conjugation between the azo
group and the aromatic nuclei with intermolecular charge transfer
1
metrically [19]. The H NMR spectrum was obtained with a JEOL
FX90 Fourier transform spectrometer with DMSO-d
6
as the solvent
resulting from
tron donating substituents [24].
All five ligands HL –HL , gave satisfactory elemental analysis
(Table 1). The molecular structures of these ligands are such that
they can exist in three tautomeric forms as shown in Fig. 1.
Detailed solution and solid states studies of these ligands were
carried out to establish their geometry.
p-electron migration to the diazo group from elec-
and TMS as an internal reference. Infrared spectra were recorded as
KBr pellets using a Pye Unicam SP 2000 spectrophotometer. Ultra-
violet–Visible (UV–Vis) spectra of the compounds were recorded in
nuzol solution using a Unicom SP 8800 spectrophotometer. The
magnetic moment of the prepared solid complexes was determined
at room temperature using the Gouy’s method. Mercury(II) (tet-
1
5
rathiocyanato) cobalt(II), [Hg{Co(SCN)
4
}], was used for the
As shown in Table 1, the values of yield (%) and/or melting point
( C) is related to the nature of the p-substituent as they increase
o
calibration of the Gouy tubes. Diamagnetic corrections were calcu-
lated from the values given by Selwood [20] and Pascal’s constants.
Magnetic moments were calculated using the equation,
according to the following order p-(NO
This can be attributed to the fact that the effective charge increased
due to the electron withdrawing p-substituent (HL and HL ) while
it decreased by the electrons donating character of (HL and HL ).
2 3 3
> Cl > H > CH > OCH ).
Â
Ã
1
=2
coor:
M
leff: ¼ 2:84 T
v
. TG measurements were made using a Du
4
5
Pont 950 thermobalance. Ten milligram samples were heated at a
1
2

3
56
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 353–360
O
N
OH
O
HN
C
C
HN
C
C
C
HN
C
C
C
O
H
N
HN
C
C
C
H
N
CH
S
S
S
S
N
R
S
N
S
S
N
S
N
N
A
B
R
C
R
D
R
R
N
H
OH
O
N
HN
C
C
C
NH
OH
S
S
HN
C
C
C
C
C
or
C
C
C
S
N
S
NH
S
N
S
C
N
N
S
S
N
HO
N
R
R
R
R
E
F
N
O
N
H
S
S
HN
C
C
C
C
C
or
H
N
C
NH
S
O
S
N
R
G
n = 1
n = 2
n = 3
n = 4
n = 5
R = OCH
3
R = CH
3
R = H
R = Cl
R = NO
2
Structure of azo rhodanine (HLn)
CH3
CH
CH3
3
O
O
O
O
O
CH
CH
2
HC
OH
CH
3
CH3
CH
3
keto
Structure of β-diketone (LH)
enol
general form
Fig. 1. Schematic representation of the tautomeric form of the ligands.
70
60
50
40
5
a)
b)
2
60
4
4
5
240
220
2
2
3
1
3
1
-0.5
0.0
0.5
1.0
R
Hammett's substituent coefficient (σ )
-
0.5
0.0
0.5
1.0
R
Hammett's substituent coefficient (σ )
R
Fig. 2. The relation between Hammett’s substitution coefficient (
r
) vs. (a) Yield % and (b) Melting point °C of ligand (HL
n
).

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 353–360
357
ð1Þ
PdCl
2
2
þ LH ! ½PdðLÞ ꢃ þ 2HCl
2
PdCl
þ HL1ꢀ5 þ LH ! ½PdðL1ꢀ5ÞðLÞꢃ þ 2HCl
ð2-6Þ
½
PdðLÞ ꢃ þ HL1ꢀ5 ! ½PdðL1ꢀ5ÞðLÞꢃ
ð2-6Þ
and L = b-
ꢀ
2
1 2 3 4 5
where L1ꢀ5 = deprotonated HL , HL , HL , HL , HL
diketone.
The molar conductance values for the Pd(II) complexes (10 3 M)
are determined in DMF and these values are found to be low (8.75–
ꢀ1
2
ꢀ1
1
8.20
X
cm mol ) indicating non-electrolytic nature and there
is no counter ion present outside the coordination sphere of palla-
dium complexes [24–27]. The elemental analyses data concern
well with the planned formulae for the ligands and also recognized
2
the [Pd(L) ] and or [Pd(L1ꢀ5)(L) composition of the Pd(II) chelates].
b-Diketones and related derivatives are considered a class of
very important ligands in the growth of coordination chemistry.
Their complexes have been thoroughly studied. Due to the pres-
ence of two oxygen donor atoms and facile Keto-enol tautomerism
1
0
20
30
40
50
60
70
ο
θ
2
(Fig. 4a and b) they easily coordinate with metal ions after deprot-
2
Fig. 3. X-ray diffraction pattern for HL powder form.
onating the enolic hydrogen atom and provide stable metal com-
plex (Fig. 4c) with six-membered chelate ring.
Due to the weak metal–oxygen bond usually found in metal
acetylacetonates [28]. Diab and El-Sonbati et al. [1,5–8] discuss
and found that a relatively stronger ligand can replace the acetyl-
acetonato group to give a new and/or novel type of complex.
Replacement of one or both acetylacetonato groups depends upon
This is in accordance with that expected from Hammett’s constant
R
o
(
r
) as in Fig. 2, correlate the yield (%) and/or melting point ( C)
R
values with (
r
), it is clear that all these values increase with
R
increasing
Because of the high similarity of the X-ray diffraction, XRD, pat-
terns for all powders of HL ligands, we will suffice by mentioning
the XRD patterns of HL as representative results for the rest of the
ligands. The XRD patterns of the as-synthesized HL powder, mea-
r
.
2 2
the ligand to metal acetylacetonates (e.g. [MO (acac) ], M = V, Mo,
W, U) ratio taken, number of donating groups present in the ligand
and electronic as well as steric properties of the ligand replacing
acetylacetonato group. In this way metal acetylacetonates can acts
as starting materials to design various types of complexes with
varying structural and chemical properties [29,30].
n
2
2
sured at room temperature, are shown in Fig. 3. The XRD pattern of
the powder (Fig. 3) show many peaks which indicate the polycrys-
talline nature of the as-synthesized HL
2
ligand.
Spectral measurements
On the basis of elemental analysis, the Pd(II) ion complexes of li-
gand were assigned to posses the compositions and molecular for-
1
H NMR spectra
mulae listed in Table 2. The results reveal that the ligands (HL
LH behaves as monobasic bidentate towards the Pd(II) ion.
n
) and
The 1H NMR spectra of HL
n
shows signal for CH (ꢁ4.42 ppm),
favoring formation of an intramolecular hydrogen bond with the
N@N (azodye) group. Electron-withdrawing substituents reduce
the intramolecular hydrogen bond as indicated by the marked shift
The formation of the complexes may be represented by the fol-
lowing reactions:
CH3
CH3
CH3
O
O
O
O
O
H C
H
C
H
H
C
H
2
O
CH3
CH3
CH3
(
a) keto form
(
b) enol form
PdCl
2
Acetone
CH3
O
O
C
O
O
O
HLn
H
C
Pd
Pd
C
N
CH3
2
(
d)
(c) metal complex
Fig. 4. Proposed structure of keto (a), enol (b), bis(b-diketonato)Pd(II) (c), and its metal complex with electron donors mixed ligands (d).

3
58
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 353–360
Table 3
The infrared spectra of ligands shows a medium broad band lo-
1
H NMR spectral data (d ppm) for palladium(II) complexes.
ꢀ1
cated at ꢁ3460 cm due the stretching vibration of some sort of
*
1H NMR
Complex
hydrogen of hydrogen bonding. El-Sonbati et al. [12–17] made de-
tailed studies for the different types of hydrogen bonding which
are favorable to exist in the molecule under investigation:
1
2
5.44(s, 1H, CH acac), 2.28(s, 6H, acac)
7.09–7.49(m, 4H, arom), 5.54(s,1H, acac), 2.32(s,6H, acac), 3.9(s,
1
3H, L )
4
6
7.15–7.54(m, 5H, arom), 5.76(s, 1H, acac), 2.35(s,6H, acac)
7.18–7.63(m,4H, arom), 6.68(s, 1H, acac), 2.38(s, 6H, acac)
(
1) Intramolecular hydrogen bond between the nitrogen atom
of the –N@N- system and hydrogen atom of the hydroxy
hydrogen atom (Fig. 1-C). This is evident by the presence
*
Numbers as given in Table 2.
ꢀ1
of a broad band centered at 3460 cm
.
(
(
2) Hydrogen bonding of the OH. . .N type between the hydroxy
hydrogen atom and the N–Ph group (Fig. 1-C).
3) Intermolecular hydrogen bonding is possible forming a cyc-
lic dimer through NH. . .O@C (G), OH. . .N@N (F) or OH. . .OH
2
of the hydroxyl signal to higher field in the p-NO and p-Cl com-
pounds. Electron-donating substituents give the opposite effect,
arising from the increasing basicity of the azo-nitrogen. The broad
signals assigned to the OH protons at ꢁ11.36–11.88 ppm are not
affected by dilution. The previous two protons disappear in the
(
E) (Fig. 1).
presence of D
2
O. Absence of –CH proton signal of the ligand moiety
ꢀ1
The presence of a broad band located at ꢁ3200 cm is strong
indication of NH (Fig. 1-D). In general, the low frequency of such
indicated the existence of the ligand in the azo-enol form. Accord-
ing to Diab and El-Sonbati et al. [12–17], hydrogen bonding leads
t
region from its normal position is, again due to hydrogen bonding
property gathered with keto , enol tautomerism.
to a large deshielding of the protons. The shifts are in the sequence:
1
p-(NO
HL /HL
3.9(s,3H,OCH3)]. The aromatic protons have resonance at 7.10–
.45 ppm for the ligands. No signal was observed in the 1H NMR
spectra of the complexes (1–6) in the region 15.0–10.0 ppm
observed due to –OH proton) which indicated deprotonation
2
> Cl > H > OCH
3
> CH
3
). In the meantime, the H NMR of the
In general, hydrogen bonding involving both NH and OH groups
are proton donors and both –N and –O atoms are proton acceptors.
It is of interest since much multiplicity of proton donor and
acceptor sites are prevalent in biological systems. Both intra- and
intermolecular OH. . .N and NH. . .O may form leading to a number
of structures in simultaneous equilibrium.
1
2
exhibits
signals
at
d(ppm)
[3.3(s,3H,CH3)]/
[
7
D
(
and bonding of b-diketone and azo compounds to palladium. A
multiplet of phenyl protons was appeared in the region d 7.69–
2 n
IR spectra of [Pd(L) ] (1)and [Pd(L )(L)] (2–6) complexes
7
.15 ppm. A singlet at d = ꢁ2.28 ppm (6H) indicated the methyl
The bonding of the metal ion to the ligands can be clarified by
comparing the IR spectra of the complexes with those of the
ligands.
protons of acac while the methane proton of acac was observed
as a singlet at d = ꢁ5.44 ppm (1H) [31]. The signal positions ob-
served in the spectra for other complexes are given in Table 3.
(
1) In solution and in the presence of Pd(II) ions these com-
pounds exist in a tautomerism equilibrium [8,18] A , B , C
(Figs. 1 and 4). In infrared spectra of all the complexes O–H
stretching vibrations of b-diketone (LH) and azo compounds
1
3
C NMR spectra
The 13C NMR spectra of all the ligands contain signal in the
range of 153.3–167.2 ppm due to the presence of carbon which is
doubly bonded to nitrogen, a downfield shift in peak position is ob-
served in the ranges of 157–173 and 188–193 ppm in complexes
and this evidence confirms that the ligands coordinate through
ꢀ
1
(HL ) was found absent in the region 3600–3200 cm . No
n
ꢀ
1
band was found in 1600–1700 cm region indicating the
CO group of b-diketone and azorhodanine was not free in
the complexes. Two spitted new bands observed at 1597–
1565 cm
indicated the chelating nature of b-diketonate ion in the
complexes [33]. The (C–O)(phenolic) bands appeared in
the region 1285–1270 cm
n
nitrogen and oxygen (HL & LH) atoms. No appreciable change is
ꢀ1
. . .
ꢀ1
. . .
seen in the peak position corresponding to aromatic and CS proton
of rhodanine in the complexes. This also supports the CS is not
coordinate to the metal center in case of all the metal complexes
having the ligand as HL
due to the methoxy (OCH
NMR spectra, confirms the monobasic bidentate nature of the li-
gands, which has already been suggested by the IR spectral studies,
discussed above. On the basis of the above discussion, following
structures have been suggested for the metal complexes (Fig. 4).
[t
(C O)] and 1515–1495 cm
[t(C C)]
t
ꢀ1
n
. Also, the singlet peaks at 55.45 ppm is
in free azorhodanine were
13
ꢀ1
3
) carbon in HL
1
. Thus, the 1H and
C
shifted to higher wavenumber (ꢁ20 cm ) which may be
due to bond formation from oxygen to the metal after depro-
ꢀ
1
tonation. The absorption bands at ꢁ1500–1480 cm
are
Table 4
Electronic spectral data (cmꢀ1) of palladium(II) complexes.
Complexesa Spectral bands
Transitions D1
D2
D3
m2/m1
Hydrogen bonding
The infrared spectra of HL
sions. The ligands (HL
due to asymmetric and symmetric stretching vibrations of N–H
group and intramolecular hydrogen bonding NH. . .O systems
ꢀ
1
n
give interesting results and conclu-
) displays two bands at ꢁ3200–3040 cm
(cm )
ꢀ1
1
A1g ? 1A2g 19740 5160 6960 1.214
n
2
3
4
5
6
14540
22500
1
1
1
A
A
1g
?
?
B
1g
E
1g
1
34300
1g
18730
-do-
-do-
-do-
-do-
20830 5130 7180 1.210
21020 5120 5260 1.207
21480 5170 4910 1.205
21990 5460 4460 1.214
(Fig. 1-D), respectively. When the OH group (Fig. 1-C) is involved
2
3
2660
3900
in intramolecular hydrogen bonding, the O. . .N and N. . .O bond dis-
tances are the same. But, if such mechanism is happened in case of
intermolecular hydrogen bond, the O. . .O and O. . .N bond distances
are differ.
18920
2
3
2840
4800
19380
3350
ꢀ1
The broad absorption of a band located at ꢁ3400 cm is as-
2
signed to OH. The low frequency bands indicate that the hydroxy
m
35000
19890
hydrogen atom is involved in keto , enol (A , B) tautomerism
through hydrogen bonding (Fig. 1-C). Bellamy [32] made detailed
studies on some carbonyl compounds containing –NH-group. The
2
3
4150
5120
a
D
tNH values were used to study the phenomena of association.
Numbers as given in Table 2.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 353–360
359
(
n
5) Thus, this ligand (HL ) contains four potential donor sites
6
22000
21500
21000
20500
20000
19500
(Fig. 1): (i) the ring nitrogen NH, (ii) the ring CS, (iii) the car-
bonyl group, and (iv) the nitrogen of azo (N@N) group. How-
ever, considering the planarity of the ligand, it is unlikely
that this ligand could be a tetradentate on a single metal
center. Hence, this ligand is expected to be bidentate and
the three favorable possibilities of donor sites are: the car-
bonyl oxygen and the nitrogen atom of azo (N@N) group
or the carbonyl oxygen and the NH ring, and the third possi-
bility between NH ring and CS ring. The coordination of the
ring nitrogen (NH) is unlikely due to the zwitterions [34] for-
mation, thereby lowering the electron density on N. The ring
thion (CS) in this ligand is found to be inert towards coordi-
nation to palladium as revealed by the appearance of the
5
4
3
2
t
(C@S)(ring) mode at almost the same position here merged
with (C@O)(acac) compared with the (C@S)(ring) at
20 cm of the uncoordinated ligand after complexation.
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
t
t
Hammett's substituent coefficient (σR
)
ꢀ1
8
1
vs. Hammett‘s constant coefficient (r
R).
Fig. 5. The relation between
D
On the basis of all these data, the molecular structure of the
Pd(II) complexes could be suggested based on: (i) the absence of
anion, (ii) the disappearance of C@O, (iii) the coordination of azo-
group.
2
1
1
1
1
1
1
.214
.212
.210
.208
.206
.204
n
Under such condition the ligand (HL /LH) is behaving as a
monobasic bidentate [(O,N)(O,O)] with respect to the evidence
above, the structure for the novel complexes are tentatively pro-
posed as shown in Fig. 4d.
3
According to the structure shown in (Figs. 1 and 4) the HL
n
/LH
ligand takes its usual anionic form (L /L) to chelate Pd(II) through
n
N- of azo group with enol group (Fig. 1-C, Fig. 4) as the potential
binding sites.
4
Magnetic susceptibility measurement and electronic spectra
The magnetic susceptibility measurements show that all the
palladium(II) complexes are diamagnetic, as expected of square
5
8
planar d complexes system. The electronic absorption spectra of
-
0.5
0.0
0.5
1.0
the ligands exhibit mainly five bands (A–D, F). The band (A) located
ꢀ1
ꢄ
at 26360–26280 cm can be assigned to the n–
p transition of the
Hammett's substituent coefficient (σR)
ꢀ1
CS group. The band (B) within 30560–30260 cm ; can be assigned
ꢄ
R).
to n–
3
p
transition within the CO group. The band (C) within
Fig. 6. The relation between
2 1
m /m vs. Hammett‘s constant coefficient (r
ꢀ1
2980–33180 cm could be assigned to the H-bonding and asso-
ꢀ1
ciation. The band (D) located at 40250–3990 cm could be as-
ꢄ
ꢄ
attributed to the C@C stretching mode coupled slightly with
the C–H in-plane bending mode. The absorption band in the
region of 1412–1385 cm is assigned to the degenerate and
asymmetric deformation vibrations of the methyl group.
signed to Ph–Ph , p–p corresponding to the aromatic system. The
ꢀ1
band (F) located at 29620–29350 cm . These latter bands can be
ꢀ
1
ꢄ
assigned to phenyl rings overlapped by composite broad
p
–p
of
azo group which undergoes a blue shift in the complexes due to
the polarization within the N@N chromophore caused by the me-
tal–ligand electron interaction during the chelation. The shift of
this band in the spectra of the complexes suggest the coordination
of nitrogen to metal atom. The band B transition disappears with
ꢀ1
(
2) The appearance of
t
(N@N)(1440–1433 cm ) and the disap-
(C@O)(1710–
n
695 cm ) group in the free ligands (HL ) suggest that there
pearance of frequencly bands of the
t
ꢀ
1
1
is no hydrazo-keto transformation; this is similar to that
reported in the literature [1,7,15–20]. The N@N stretching
frequency of azo group is shifted to lower frequency by ca.
the simultaneous appearance of new bands, being attributed to
ꢄ
p–p
(C@C) as sequences of enolization. Furthermore, the band A
ꢀ
1
2
5–35 cm due to the involvement of one of the azo nitro-
transition shifts slightly to lower energy and remains almost con-
stant. In the electronic spectra of Pd(II) complexes, three spin-al-
lowed d–d transitions are expected, corresponding to transitions
from the three lower lying d-levels to the empty dx2 ꢀ y2 orbital;
gen atoms in coordination with metal ion [1,7,15–20]. This
lowering of frequency can be explained by the transfer of
electrons from nitrogen atom to the Pd(II) ion due to
coordination.
two-electron transitions would be very weak and can be neglected.
1
(
3) Far infrared spectra of the metal complexes show several
non-ligand bands of low intensity appearing in the region
The ground state is
these transitions are
A1g and the excited states, corresponding to
A , B1g and E in order of increasing en-
2g g
1
1
1
ꢀ
1
4
(
15–460, 435–455 cm
Pd–O) vibrations, respectively [1,5,15]. Absence of
can be assigned to (Pd–N) and
(Pd–S)
ergy. The electronic spectra of the Pd(II) complexes show four
bands are presented in Table 4. The spectra resemble the spectra
of four-coordinate square planar complexes of palladium reported
t
band in the far IR spectra gives added evidence for the
non-participation of ring sulfur atom in bond formation.
4) The variation in the spectral bands of the C–C, C@C, C–N and
C–H different modes of vibrations of the complexes lead to
that, probably, the aromaticity of the complex is differ from
one to other.
earlier [5,6,35,36]. The three orbital parameters,
1 2 3
D , D , and D
ꢀ
1
(
were calculated using a value of F = 10 F = 600 cm
2
4
for a
Slater–Condon interelectronic repulsion parameters and subse-
quently the equations suggested by Gray and Ballhausen [37,38].
The separation
1
D was the largest, which indicated that the

3
60
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 353–360
d
x2 ꢀ y2 was strongly antibonding. The
m
2
/
m
1
values were also calcu-
[2] D. Banerjea, Mixed Ligand Complexes in Coordination Chemistry, Tata
McGraw-Hill Publishing Company Limited, New Delhi, 1993.
lated (Table 4) and are in close agreement with data reported ear-
lier for square planar complexes [6,39].
[
3] C.R. Bhattacharijee, P. Goswami, M. Sengupta, J. Coord. Chem. 63 (2010) 3969–
980.
[4] S. Liang, D.V. Derveer, S.Y. Qian, B. Sturgeon, X.R. Bu, Polyhedron 21 (2002)
021–2025.
5] A.Z. El-Sonbati, A.A.M. Belal, M.A. Diab, R.H. Mohamed, Mol. Struct. 99 (2011)
6–31.
[6] A.Z. El-Sonbati, A.A. El-Bindary, M.A. Diab, Spectrochim. Acta A 59 (2003) 443–
54.
7] (a) A.Z. El-Sonbati, A.A. El-Bindary, R.M. Issa, H.M. Kera, Des. Monomers Polym.
(2004) 445–459;
(b) A.Z. El-Sonbati, R.M. Issa, A.M. Abd El-Gawad, Spectrochim. Acta A 68
2007) 134–138.
8] A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, S.G. Nozha, Spectrochim. Acta A 83
2011) 490–498.
3
The plot of
a linear relationship between
values are relatively insensitive to the inductive effect of the
phenyl ring substituents and chiefly depend on the stereochemical
factors as the redox properties. The values are weaker in the
compound (2) in agreement with the more electrondonating
D
1
vs.
r
[
r
= Hammett’s constant of R] (Fig. 5) shows
2
D
1
, and for each chromophore. The
r
[
D
1
2
4
D
1
[
[
7
character atom, while Fig. 6 is a plot of
inversely proportionality.
2 1
m /m (Table 4) vs. r shows
(
(
Thermal analyses
[9] D.P. Singh, R. Kumar, J. Singh, Eur. J. Med. Chem. 44 (2009) 1731–1736.
10] S. Lihan, H. Temel, Transition Met. Chem. 32 (2007) 1012–1017.
11] Iffat Masih, N. Fahmi, Spectrochim. Acta A 79 (2011) 940–947.
12] A.Z. El-Sonbati, M.A. Diab, Physico-Chemical Studies on the Complexes, LA
LAMBERT Academic Publishing GmbH, Leipzig & Co, KG, Germany, 2010 (ISBN:
978-3-8433-7229-9).
[
[
[
The thermal decomposition of the studied complexes presented
characteristic pathways, depending on the nature of the ligands, as
can been see from the TG/DTA curves. All TG and DTA figures of the
other compounds have the same trend. There is no loss in the range
[
[
[
[
[
[
[
13] A.Z. El-Sonbati, R.M. Issa, A.M. Abd El-Gawad, Spectrochim. Acta A 74 (2009)
643–647.
1
00–220 °C which indicates the absence of coordinated or uncoor-
14] N.A. El-Ghamaz, M.A. Diab, A.Z. El-Sonbati, O.L. Salem, Spectrochim. Acta A 83
(2011) 61–66.
15] A.Z. El-Sonbati, M.A. Diab, M.M. El-Halawany, N.E. Salam, Met. Chem. Phys.
dinated water molecule. DTA curves show no endothermic peaks
up to 200 °C confirming the absence of lattice or coordinated water
molecule in the complexes [40]. The sharp decomposition corre-
sponding to the loss of organic moiety in complexes can bee seen
in the DTA curves which contained one sharp exothermic peak fail-
ing in the range of 365–410 °C beyond which no decomposition
was observed indicating the formation of stable palladium oxide.
The final residue was analyzed by IR spectra and identified as me-
tal oxide corresponds to the calculated value.
123 (2010) 439–449.
16] A.Z. El-Sonbati, M.A. Diab, M.M. El-Halawany, N.E. Salam, Spectrochim. Acta A
77 (2010) 795–801.
17] A.Z. El-Sonbati, A.A. Belal, M.A. Diab, M.Z. Balboula, Spectrochim. Acta A 78
(
2011) 1119–1125.
18] M.A. Diab, A.A. El-Bindary, A.Z. El-Sonbati, O.L. Salem, Mol. Struct. 1007 (2012)
11–19.
19] A.I. Vogel, A Text Book of Quantitative Inorganic Analysis, Longman Green,
ELBS, London, 1962.
20] P.W. Selwood, Magnetic Chemistry, Interscience Pub. Inc., New York, 1956.
21] J. Ladik, A. Messumer, J. Redly, Acta Chim. Acad. Sci. Hung. 38 (1963) 393–397.
22] E. Sawicki, J. Org. Chem. 21 (1956) 605–609;
[
[
[
Conclusion
E. Sawicki, J. Org. Chem. 22 (1957) 915–919.
[
23] L.W. Reeves, Can. J. Chem. 38 (1960) 748–751.
In this work, 6 novel heterocyclic azo dyes were synthesized by
coupling diazotized rhodanine with p-derivatives aniline. Their
[24] O.Y. Elcl, J. Chem. Soc. D 1 (1971) 67.
[
25] E.V. Shchegolkove, O.G. Khudina, L.V. Anikina, Y.V. Burgatt, Pharm. Chem. J. 40
2006) 373–376.
26] A. Syamal, M.R. Maurya, Coord. Chem. Rev. 95 (1989) 183–238.
(
1
13
structures were confirmed by H and C NMR, IR and UV–Vis spec-
tra. The absorption data of the synthesized dyes revealed that all
dyes exist in the form of two tautomeric species. The present paper
reports on the synthesis, characterization and their electronic
absorption spectra of mixed ligand (azorhodanine and acetylace-
tone) and Pd(II) complexes. The synthetic procedure in this work
resulted in the formation of ternary complexes in the molar ratio
[
[27] S.B. Yu, R.H. Holm, Inorg. Chem. 28 (1989) 4385–4391.
[
[
28] S. Millifiori, G. Favini, Z. Phys. Chem. 75 (1971) 23–31.
29] J.A. Dean, Lange‘s Hand Book of Chemistry, 14th ed., MCGRAW-Hill, New York,
1992. pp. 35.
[30] L.K. Thompson, F.L. Lee, E.J. Gabe, Inorg. Chem. 27 (1988) 39–46.
[
[
31] R.M. Silverstein, G.C. Bassler, T.C. Morrill, Spectrometric Identification of
Organic Compounds, fifth ed., John Wiley & Sons Inc., Singapore, 1991.
32] F.C.L.J. Bellamy, The Infrared Spectra of Complex Molecules, Wiley, New York,
1958.
(
n
1:1:1)(M:L :L), respectively. Both b-diketonate and azo compound
act as monobasic bidentate chelating ligands and a square planar
geometry around palladium(II) is established (Fig. 4) forming sta-
ble six membered heterocyclic rings. From conductance measure-
ments Pd(II)-complexes are non-electrolytes. The values of ligand
field parameters orbital parameters were calculated.
[33] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds Part B, fifth ed., Wiley, New York, 1997.
[
[
34] A.Z. El-Sonbati, A.A. El-Bindary, Polish. J. Chem. 74 (2000) 621–630.
35] M. Mohan, P. Sharma, N.K. Jho, Inorg. Chim. Acta 106 (1985) 117–121.
[36] R.F. Fenske, D.S. Martin, K. Ruedenberg, Inorg. Chem. 1 (1962) 441–452.
[
[
[
37] D.H. Basch, C.J. Ballhausen, J. Am. Chem. Soc. 85 (1993) 260–267.
38] H.B. Gray, C.J. Ballhansen, J. Am. Chem. Soc. 85 (1963) 260–265.
39] B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amsterdam, 1968.
References
[40] A.V. Nikolaev, V.A. Log Vinenkova, L.I. Myachina, Thermal Analysis, Academic
Press, New York, 1969.
[
1] A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, Stoichiometry and research-the
importance of quantity in biomedicine’’ Pub. by In Tech, Janeza Trdine 9, 51000
Rijeka. Croatia, 2012, pp.. 147–194, P. Cm ISBN 978-953-51-0198-7.