Supramolecular coordination and antimicrobial activities of constructed mixed ligand complexes

Article abstract of DOI:10.1016/j.saa.2012.11.024

A novel series of copper(II) and palladium(II) with 4-derivatives benzaldehyde pyrazolone (L_n) were synthesized. The mixed ligand complexes were prepared by using 1,10-phenanthroline (Phen) as second ligand. The structure of these complexes was

Full text of DOI:10.1016/j.saa.2012.11.024

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 213–221
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Supramolecular coordination and antimicrobial activities of constructed mixed
ligand complexes
a
a
b
a,1
A.Z. El-Sonbati a, , M.A. Diab , A.A. El-Bindary , M.I. Abou-Dobara , H.A. Seyam
⇑
a Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
b Botany 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
Substituents effect on reactivities depend mainly on the rate controlling step and the nature of the tran-
sient specie, while Hammett’s relationship studies the reactivity trends in ligands and complexes with
the stability.
"
"
"
"
Ln behaves as bidentate ligand
bonding through azomethine
nitrogen and oxygen atoms.
Substituents effect on reactivities
depend mainly on the rate
controlling step.
The electron donating substituents
increase the electron density at the
metal.
Antimicrobial activity of ligands
depends on determined by the
values of clear zone.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 August 2012
Received in revised form 3 November 2012
Accepted 6 November 2012
Available online 29 November 2012
A novel series of copper(II) and palladium(II) with 4-derivatives benzaldehyde pyrazolone (Ln) were syn-
thesized. The mixed ligand complexes were prepared by using 1,10-phenanthroline (Phen) as second
ligand. The structure of these complexes was identified and confirm by elemental analysis, molar conduc-
tivity, UV–Vis, IR and 1H NMR spectroscopy and magnetic moment measurements as well as thermal
analysis. The ligand behaves as a neutral bidentate ligand through ON donor sites. ESR spectra show
the simultaneous presence of a planar trans and a nearly planar cis isomers in the 1:2 ratio for all N,O
complexes [Cu(Ln)2]Cl2ꢀ2H2O. Schiff bases (Ln) were tested against bacterial species; namely two Gram
positive bacteria (Staphylococcus aureus and Bacillus cereus) and two Gram negative bacteria (Escherichia
coli and Klebsiella pneumoniae) and fungal species (Aspergillus niger, Fusarium oxysporium, Penicillium
italicum and Alternaria alternata). The tested compounds have antibacterial activity against S. aureus,
B. cereus and K. pneumoniae.
Keywords:
Supramolecular structures
Cu(II), Pd(II) and mixed-ligand complexes
ESR Study
Antimicrobial activities
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
Ternary complexes are found to be more stable than binary
complexes [2,3]. Steric effect and back donation have also been
In the last few decades, mixed ligand complexes have been
extensively studied in solution as well as in the solid state [1].
invoked to account for the preferred formation of mixed-ligand
complexes [1].
Heterocyclic compounds such as pyridine (Py), 2,20-bipyridine
(bipy), 1,10-phenanthroline (Phen) and related molecules are good
ligands due to the presence of at least one ring nitrogen atom with
⇑
Corresponding author. Tel.: +20 1060081581; fax: +20 5702403868.
E-mail address: elsonbatisch@yahoo.com (A.Z. El-Sonbati).
1
Abstracted from her M.Sc.
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.11.024

214
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 213–221
a localized pair of electrons. The successful application of heterocy-
clic compounds has led to the formation of series of novel com-
pounds with a wide range of physical, chemical and biological
properties, spanning a broad spectrum of reactivity and stability
[2]. A large number of mixed-ligand complexes involving heterocy-
clic bases such as Py, bipy and Phen have been reported by many
workers [1–12] due to their bioinorganic applications and thermal
stability.
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
characterization of mixed ligand transition metal complexes con-
taining rhodanine ligand [9–13], here we report the synthesis
and characterization of mixed ligand Cu(II) complexes derived
from the condensation of 4-aminoantipyrine (4-AAP) with p-
derivatives benzaldehyde (Ln) as primary ligand and 1,10-phenan-
throline as co-ligands. The complexes prepared were characterized
by elemental analysis, conductance, magnetic measurements and
spectral studies (IR, UV–Vis and ESR). Thermal stabilities of the
complexes have also been discussed.
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
Scheme 1. The color, yield %, M.P. °C and analytical data given in
Table 1.
Preparation of copper(II) complexes
Preparation of [Cu(Ln)2]Cl2ꢀ2H2O(1–4) (A)
Method A: To a solution of the ligand (Ln) (1.00 mmol) in 25 mL
ethanol, an ethanolic (25 mL) solution of copper chloride
(0.5 mmol) was added slowly with constant stirring over a period
of 10 min in the molar ratio 2:1 (ligand:metal). The reaction
mixture was heated to reflux for 3–4 h, concentrated to a small
volume and allowed to cool. The formed solid product was re-
moved by filteration washed several times with ethanol, and dried
over CaCl2. The purity of the formed compounds was monitored by
TLC.
Antipyrine is an active moiety in pharmacological activity. Anti-
pyrine is used as antinflammatory agents for the treatment of
arthritis and analgesics [14–16]. Anticancer activity by antipyrine
has also been reported [17]. Antipyrine is a marker in the study of
transfer and biotransformations of drugs in the human body [18]
and antipyrine metabolites are reported to show a positive correla-
tion with plasma fibronectin level in monitoring patients with
chronic liver illness (HBC, HCV and alcohol-related disease) [19].
Preparation of [Cu(Ln)(L)Cl2] (5–8) (B)
Method B: A mixture of (5 mmol) (Ln) and (5 mmol) (Phen.) dis-
solved in 50 mL, ethanol was added to an solution of copper chlo-
ride (5 mmol). The reaction mixture was refluxed for 2–3 h with
constant stirring to ensure the complete formation of the metal
complexes. The precipitate was filtered and washed several times
with 50% (v/v) ethanol–water to remove any traces of unreacted
starting materials. Finally, the filtrate was dried in vacuum desicca-
tors over anhydrous CaCl2.
Experimental
Materials
4-Aminoantipyrine, CuCl2ꢀ2H2O, PdCl2 and various aldehydes
were purchased from Aldrich, and the other chemicals were of
analytical grade quality.
The obtain mixed ligand complexes are [Cu(Ln)(L)Cl2] (5–8) (B).
Fig. 3II represents the proposed chemical structure of mixed ligand
complexes.
H
N
C
X
NH2
OHC
X
+
N
N
O
N
N
O
Ln
X=OCH3 (1) , H (2), Cl (3), NO2 (4)
Scheme 1. Synthetic route of Schiff base ligands.
Table 1
Elemental analysis (C, H, N)a, color, yield (%) and melting point (°C) of ligands (Ln).
Compound
Color
Yield (%)
M.P. (°C)
Calc. (Exp.)%
C
H
N
L1
L2
L3
L4
Yellow
Pale yellow
Yellow
46.7
52.2
56.5
67.0
173
195
237
261
71.03 (71.17)
74.23 (74.42)
66.36 (66.45)
64.29 (64.37)
5.92 (5.99)
5.84 (5.93)
4.92 (5.13)
4.76 (4.88)
13.08 (13.37)
14.43 (14.59)
12.90 (13.21)
16.67 (16.88)
Pale yellow
a
The excellent agreement between calculated and experimental data suggests the assignment suggested in the present work.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 213–221
215
Preparation of [Pd(Ln)2]Cl2 (9–12) (C)
determination of crystal structure, phase diagram determination,
quantitative phase analysis, precise parameter measurements,
structure of polycrystalline aggregates, stress measurements,
orientation of crystals.
Phase analysis of L4 powder was performed at room tempera-
ture by a Philips X-ray diffractometer equipped with utilized
Method C: An ethanolic solution of 0.01 mol of PdCl2 was mixed
with the appropriate weight of the corresponding ligand (Ln) in
ethanol (25–40 ml). The reaction mixture was boiled with stirring
until the corresponding solid complex separated. On cooling the
crystalline product formed was filtered off, washed several times
with dry ethanol and dry diethyl ether and finally dried in a desic-
cator over fused CaCl2.
monochromatic Cu Ka radiation (k = 1.5418 Å). The X-ray tube
voltage and current were 40 kV and 25 mA, respectively.
Microbiological investigation
Results and discussion
For this investigation the agar well diffusion method was ap-
plied [20,21]. The antibacterial activities of the investigated com-
pounds were tested against two local Gram positive bacterial
isolates (Bacillus cereus and Staphylococcus aureus) and two local
Gram negative bacterial isolates (Escherichia coli and Klebsiella
pneumoniae) on nutrient agar medium. Also, the activities were
tested against four local fungal isolates (Aspergillus niger, Alternaria
alternata, Penicillium italicum and Fusarium oxysporium) on DOX
Synthesis and characterization of ligand
The ligands (Ln) were prepared by stirring an appropriate
amount of reactive p-derivatives benzaldehyde with the corre-
sponding 4-aminoantipyrine in ethanol. Schiff base ligands (Ln)
were light yellow in color and it is soluble in common organic sol-
vents. The Schiff bases formed were characterized with respect to
its composition by elemental and spectral analysis. Elemental anal-
ysis of the ligand (Ln) given in Table 1, IR spectra in Table 2 and 1H
NMR in Table 3. Elemental analysis of the ligand (Ln) show good
agreement with theoretical data.
agar medium. The concentrations of each solution were 50
100 g/ml and 150 g/ml. By using a sterile cork borer (10 mm
diameter), wells were made in agar medium plates previously
seeded with the test organism. 200 l of each compound was
lg/ml,
l
l
l
For the four compounds the yield %/M.P. °C of these compounds
were found to be sensitive to the nature of the substituents, 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 lower values (46.7/173) are observed for L1 (X = OCH3), re-
flects the electron donating nature of the substituent (Fig. 1).
Because of the high similarity of the X-ray diffraction, XRD, pat-
terns for all ligands (L1–4), we will suffice by mentioning the XRD
patterns of L4 as representative results for the rest of the ligands.
The X-ray diffraction (XRD) pattern for the L4 in powder form
shows many peaks superimposed with a broad peak at 2h ’ 8°
(as shown in Fig. 2). This indicates the polycrystalline nature of
the ligand under investigation in addition with some amorphous
domains.
applied in each well. The agar plates were kept at 4 °C for at least
30 min. to allow the diffusion of the compound to agar medium.
The plates were then incubated at 37 °C or 30 °C for bacteria and
fungi, respectively. The diameters of inhibition zone were
determined after 24 h for bacteria and 7 day for fungi.
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. The metal content in the
complexes was estimated by standard methods [22]. The 1H
NMR spectrum was obtained 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 nuzol solution using
a Unicom SP 8800 spectrophotometer. The magnetic moment of
the prepared solid complexes was determined at room tempera-
ture using the Gouy’s method. Mercury(II) (tetrathiocyanat-
o)cobalt(II), [Hg{Co(SCN)4}], was used for the calibration of the
Gouy tubes. Diamagnetic corrections were calculated from the val-
Table 2
Some selected bands of diagnostic importance from the IR spectra (cmꢃ1) of 4-AAP
and ligands (Ln).
4-AAP
L1
L2
L3
L4
Assignment
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)
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
ues given by Selwood [23] and Pascal’s constants. Magnetic mo-
C@O
C@N
NACH3
CAN
d(CH3)
c
c
1=2
ments were calculated using the equation, leff: ¼ 2:84½TvMcoor:
ꢁ
.
TG measurements were made using a Du Pont 950 thermobalance.
Ten milligram samples were heated at a rate of 10 °C/min in a dy-
namic 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 the holder. The halogen
content was determined by combustion of the solid complex
(30 mg) in an oxygen flask in the presence of a KOHAH2O2 mixture.
The halide content was then determined by titration with a
standard Hg(NO3)2 solution using diphenylcarbazone indicator.
ESR measurements of powdered samples were recorded at room
temperature (Tanta university, Egypt) using an X-band spectrome-
ter utilizing a 100 kHz magnetic field modulation with diphenyl
picrylhydrazyle (DPPH) as a reference material. The conductance
measurement was achieved using Sargent Welch scientific Co.,
Skokie, IL, USA. X-ray diffraction (XRD) is considered now as a pow-
erful technique in the following subjects: phase identification,
(C@N)
(CH)ring
730
Table 3
1H NMR spectral data (d ppm) of 4-AAP and ligands (Ln).
Assignment
Compound
L1
L2
L3
L4
(4-AAP)
CACH3
NACH3
NH2
2.55
3.09
–
2.60
3.15
–
2.64
3.22
–
2.68
3.27
–
2.15
2.84
2.99
ArH
CH@N
OCH3
6.80–7.86
9.71
3.27
7.22–7.95
9.48
–
7.33–8.22
9.40
–
7.42–8.34
9.36
–
7.15–7.50
–
–

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A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 213–221
70
60
Synthesis and characterization of metal complexes
The complexes are stable in air and atmosphere. All the com-
P-NO
(a)
2
plexes are soluble in DMF and DMSO, but they are insoluble in
some common organic solvents. The analytical data (Table 4) indi-
cate that the metal to ligand ratio is 1:2 [M(Ln)2]Cl2 (M:Ln) and
1:1:1[Cu(Ln)(L)Cl2](Ln:M:co.ligand) molar ratios in mixed-ligand
complexes as obtainable in the following reaction.
P-Cl
280
240
200
160
120
(b)
P-NO
P-Cl
2
P-H
MCl2 ꢀnH2O þ 2Ln ! ½MðLnÞ2ꢁCl2 ꢀ2H2O
50
P-OCH
P-H
CuCl2 ꢀ2H2O þ Ln þ L ! ½CuðLnÞðLÞCl2ꢁ þ nH2O
3
P-OCH
3
where Ln = primary ligands, L = co-ligand and M = Cu(II), n = 2 or
Pd(II), n = nil.
40
All these complexes are colored, air stable and insoluble in com-
mon organic solvents except DMF and DMSO. The molar conduc-
tivity values of the compounds 1–4 and 9–12 in 10ꢃ3 M solution
in DMF suggest that they are 1:2 electrolytes. But molar conductiv-
ity values of the compounds 5–8 shows that they are non-electro-
lyte indicating that the anions are coordinated to the central Cu(II)
ion values of the compounds.
-0.5
0.0
0.5
1.0
R
σ
-0.5
0.0
0.5
1.0
R
σ
Fig. 1. The relation between Hammett’s substitution coefficient (
and (b) melting point °C of ligand (Ln).
r
R) vs. (a) yield %
The ligand has two different bis-NO or N3O cores (nitrogen of
imine, keto O-atoms present in the pyrazolone ring and two azo-
methine nitrogen atoms in 1,10-phenanthroline to coordinate me-
tal ions. There are variable binding possibilities to metal ions for
ligand structural form (see Fig. 3). All binary complexes of Cu(II)
and Pd(II) ions (1–4 & 9–12) have 1:2 metal-to-ligand stoichiome-
try, as shown in Fig. 3I. Moreover, the analytical data of metal che-
lates (Table 4) indicates that the metal ion in case of all mixed
ligand complexes are coordinated to one mixed ligand molecule
(1,10-phenanthroline) in addition to Ln molecule (Fig. 3II).
400
300
200
100
0
IR spectra
The spectra of the free ligands (L1–4) display bands at 1645–
1655 and 1590–1600 cmꢃ1 due to
t(C@O) and t(C@N), respec-
tively. The spectra of complexes showed that these two bands of
the free ligands were not observed at the same frequencies and
the same intensities. They shift to lower frequencies and, at the
same time, their intensities are lowered. They results indicate that
the ligands act as neutral bidentate bonded to the metal through
the azomethine-nitrogen and the keto-oxygen atoms. Further
proof for the involvement of both azomethine-nitrogen and the
keto-oxygen atoms in complexation is the appearance of weak
bands in the far IR region of complexes at (400–450) and (475–
8
16
24
32
40
2θο
Fig. 2. X-ray diffraction patterns for ligands (L4).
Table 4
Analytical dataa of the complexes.b
Compoundc
Method of preparationd
Calc. (Exp.)%
C
H
N
M
Cl
[Cu(L1)2]Cl2.2H2O (1)
[Cu(L2)2]Cl22H2O (2)
[Cu(L3)2]Cl2.2H2O (3)
[Cu(L4)2]Cl2.2H2O (4)
[Cu(L1)(L)Cl2] (5)
[Cu(L2)(L)Cl2] (6)
[Cu(L3)(L)Cl2] (7)
Cu(L4)(L)Cl2] (8)
[Pd(L1)2]Cl2 (9)
[Pd(L2)2]Cl2 (10)
[Pd(L3)2]Cl2 (11)
[Pd(L4)2]Cl2 (12)
A
A
A
A
56.12 (56.34)
57.25 (57.36)
52.58 (52.42)
51.13 (51.24)
58.53 (58.63)
59.45 (59.56)
56.25 (56.42)
60.50 (60.65)
55.65 (55.73)
56.89 (56.98)
52.15 (52.24)
50.86 (50.94)
4.68 (4.87)
4.77 (4.86)
3.90 (4.02)
3.80 (3.87)
4.25 (4.40)
4.13 (4.23)
3.75 (3.67)
4.03 (4.21)
4.64 (4.74)
4.48 (4.57)
3.81 (3.93)
3.77 (3.88)
10.34 (10.52)
11.13 (11.53)
10.23 (10.44)
13.29 (13.18)
11.01 (11.42)
11.56 (11.87)
10.94 (11.59)
10.76 (10.87)
10.25 (10.46)
11.06 (11.25)
10.14 (10.35)
13.19 (13.35)
7.82 (8.07)
8.42 (8.68)
7.73 (7.82)
7.54 (7.68)
10.00 (10.23)
10.49 (11.66)
9.93 (10.34)
10.68 (10.78)
12.99 (13.24)
14.01 (14.42)
12.85 (12.96)
12.53 (12.65)
8.74 (8.44)
9.41 (9.52)
17.29 (17.32)
8.43 (8.03)
11.17 (11.38)
11.25 (11.45)
16.64 (16.86)
5.97 (6.09)
8.67 (8.87)
9.35 (9.55)
17.14 (17.34)
8.36 (8.55)
B
B
B
B
C
C
C
C
a
b
c
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.
Ln are the ligand as given in Scheme 1; air-stable; no-hygroscopic; insoluble in water; soluble in coordinating solvents such as DMF and DMSO.
See text.
d

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 213–221
217
R
R
CH
N
CH
N
Cl
H3C
H3C
H3C
H3C
CH3
N
N
N
O
N
M
Cu
,
Cl2.2X
N
N
O
O
N
N
N
CH3
Cl
HC
R
M = Cu(II), X= H2O
= Pd(II), X= nil
(I)
(II)
X
R =
X
=
OCH3
H
=
=
=
Cl
NO2
Fig. 3. Proposed structure of complexes.
505) cmꢃ1 due to
t
(MAN) and
t
(MAO) respectively [9–13] which
Electronic spectra and magnetic moments of copper(II) complexes (1–4)
are absent in the free ligands. In the spectra of mixed 1,10-phenan-
throline (L) complexes (5–8), the bands of L free ligand at 740 cmꢃ1
are shifted to higher frequencies ꢄ775 cmꢃ1. The OH stretching
frequency appears in the spectra of complexes around 3400 cmꢃ1
is attributed to the presence of water of hydration. Also, according
to Stefov et al. [24], coordinated water should exhibit frequencies
ꢄ830, 570 and 448 cmꢃ1. The absence of spectral bands in these re-
gions in the spectra of complexes indicates that the water mole-
cules in these complexes are not coordinated but are present as
lattice water. From the above mentioned, the ligands, act as neutral
bidentate chelating agents coordinated to the Cu(II) via the azome-
thine-nitrogen and keto-oxygen atoms forming the more stable
six-membered chelate rings.
Elemental analysis, IR and molar conductivity data were used to
prove the stoichiometry and formulation of the complexes. A
square planar geometry was assumed for all the complexes based
on their magnetic data and spectral studies.
Electronic spectra of ligand and its mononuclear copper(II)
complexes were recorded in DMF solution. In the electronic spectra
of the ligand and its mononuclear metal complexes, the wide range
bands were observed due to either the
chromophore or charge-transfer transition arising from
p
–
pꢅ and n ? pꢅ of C@N
electron
p
interactions between the metal and ligand, which involved either a
metal-to-ligand or ligand-to-metal electron transfer [25]. The elec-
tronic spectra of the free ligand in DMF showed strong absorption
bands in the ultraviolet region (23,530–37,460 cmꢃ1), that could be
attributed to the
p ?
pꢅ and n ? pꢅ transitions in the benzene ring
1H NMR spectra
or azomethine (AC@N) groups for free ligand. The absorption
bands between 37,460 and 23,530 cmꢃ1 in free ligand changed a
bit in intensity and remained slightly changed for metal com-
plexes. The absorption shift and intensity change in the spectra
of the metal complexes most likely originated from the metalla-
tion, increased the conjugation and delocalization of the whole
electronic system and resulted in the energy change of the
The 1H NMR spectra of the antipyrine Schiff bases (Table 3) 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
9.46–9.81 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 Pd(II)
ion. 13C NMR of L1–4 exhibited signals at 188–188.8 and 161–
161.9 ppm corresponding to the carbon of CAO and CAN groups.
Methyl groups were observed between 18.4 and 19.8 ppm. Also,
the spectra showed peaks at 19–131 ppm corresponding to car-
bons of the phenyl ring.
p
?
pꢅ and n ? pꢅ transitions of the conjugated chromophore
[26]. The electronic spectra of copper(II) complexes shows absorp-
tion band in the ranges 14,000–15,800 and 18,900–20,230 cmꢃ1
,
assignable respectively, to transitions 2B1g ? 2B2g and 2B1g ? 2Eg
of a square planar structure [27]. The copper(II) complexes para-
magnetic and the room temperature magnetic moments values
(1.80–2.10 B.M.) are indicative of one unpaired electron per Cu(II)
ion. These values are closer to or slightly higher than the spin-only

218
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 213–221
Table 5
vent molecules are in the inner or outer coordination sphere of
the central metal ion. The results of thermal analyses show good
agreement with the theoretical formula as suggested from the ele-
mental analyses. The thermograms of the complexes (1–4) can be
subdivided into three stages. The first stage extends up to 180 °C
and corresponds to the weight loss of the hydrated water mole-
cules during one exothermic process. The second stage extends
up to 345 °C and corresponds to the weight loss of the two HCl
molecules. The third stage above 345 °C with the formation of
the corresponding metal oxides.
ESR spectral assignments for Cu(II) complexes.
b
Complexa
gll
g
gl
All
gll/All
?
1
2
3
2.157
2.159
2.161
2.064
2.063
2.066
2.095
2.095
2.098
207
204
201
104
106
108
a
Numbers as given in Table 4.
Expressed in units of cmꢃ1 multiplied by a factor of 10ꢃ4
b
.
value, indicates absence of any magnetic exchange interactions be-
tween copper(II) ions.
Electronic spectra and magnetic moment of copper(II) mixed ligand
complexes (5–8)
ESR spectra of copper(II) complexes (1–4)
Electronic spectra of six-coordinate Cu(II) complexes (5–8) arise
from the electronic transition within a molecular or ion from a
lower to a higher electronic energy level. The transition metal ions
generally show a number of d-d transition bands depending on
their electronic configuration from d1 to d9 in UV–Vis regions.
ESR spectra of copper(II) complexes recorded in polycrystalline
state at room temperature also provides information about the
square planar geometry of the copper(II) complexes. The spectra
are typical for axial type complexes, from which gll, g\, g and All have
be calculated (Table 5). The ordering of g values gll > g\ > 2.0023 ob-
served for copper(II) complexes indicates that the unpaired electron
most likely resides in their dx2–y2 orbital [28] and 2B1g ground state
[29]. gll is a moderately sensitive function for indicating covalency
and gll > 2.3 and gll < 2.3 is characteristic of anionic and covalent
environments, respectively, in metal–ligand bonding. The fact that
the gll values are less than 2.3 is an indication of significant covalent
bonding in copper(II) complexes [29].
In axial symmetry G = gll ꢃ 2/g\ ꢃ 2 is a measure of the ex-
change interaction between Cu(II) centers in polycrystalline state.
The value of G > 4 indicates negligible exchange interaction in solid
complexes [30]. The G value in copper(II) complexes are less than 4
suggesting dx2ꢃy2 ground state with a small exchange coupling
[31]. The gll and |All| values indicate square planar coordination
geometry for the CuN2O2 moiety. All the spectra are almost super-
imposable. Whatever the electron withdrawing or donor power
and the para position of the substituent on the aromatic ring. In
fact, the ESR parameters which relate to electron density in CuN2-
O2 plan are relatively in sensitive to the substitution in these li-
gands aryl groups. Moreover the ratio gll/All is an indication of
the stereochemistry of the copper(II) complexes. Sagakachi and
Addison [32] have suggested that this ratio may be an empirical
indication of the tetrahedral distortion of a square planar geome-
try. The values lower than 135 cmꢃ1 are observed for square planar
structures and those higher than 150 cmꢃ1 for tetrahedrally dis-
torted complexes.
The copper(II) complexes generally show a broad band in the
2
13,000–18,000 cmꢃ1 region assigned to the envelop of B1g
?
2Eg + 2B2g + 2A1g transitions [33]. These bands are only slightly
shifted in DMSO solution and observed in the 15,200–
15,400 cmꢃ1, suggesting a distorted octahedral geometry for all
the complexes.
The magnetic moment of all the copper(II) complexes at room
temperature lie in the range of 1.90–2.20 B.M., corresponding to
one unpaired electron. This indicates that spin–spin coupling be-
tween unpaired electrons belonging to different copper ions is
absent.
ESR spectra of copper(II) mixed ligand complexes (5–8)
To obtain further information about the stereochemistry and
the site of the metal ligand bonding and to determine the magnetic
interaction in the metal complexes, the ESR spectra of all Cu(II)
complexes have been recorded. The spectra of the complexes show
typical axial behavior with slightly different gll and g values. The
geometric parameter G, which is measure of exchange coupling
interaction between two copper center explained by Hathaway
[34] expression G = (gll ꢃ 2)/(g\ ꢃ 2). Accordingly, if the value of
G is greater than four, the exchange interaction is negligible inter-
action, whereas when the value of G is less four a considerable
interaction is indicated in solid complex. The trend gll > g\ > ge
(2.0023) observed for these complexes shows that the unpaired
electron is localized in dx2ꢃy2 orbital of the Cu(II) ions and the spec-
tral features are characteristics of axial symmetry. For a Cu(II) com-
plex, gll is a parameter sensitive enough to indicate covalent. The gll
values for all the Cu(II) complexes (Table 6) are less than 2.3 is an
indication of significant covalent bonding in these complexes. The
complex under study may have six- coordinate tetragonal
geometry.
The lowest values of the ratio gll/All for the trans species are
indicative of a planar trans arrangement whereas the slightly high-
er values of the ratio gll/All for the cis compounds indicate only a
nearly planar cis arrangement.
Thermal gravimetric analyses of copper(II) complexes (1–4)
Thermal gravimetric analyses for [Cu(Ln)2]Cl2ꢀ2H2O (1–4) com-
plexes were obtained to give information concerning the thermal
stability of the complexes and decide whether the water and sol-
Molecular orbital coefficients, a
2 (a measure of the covalency of
the in-plane
r-bonding between a copper 3d orbital and the ligand
Table 6
ESR spectral assignments for Cu(II) mixed ligand complexes.
Complexa
gll
g?
ge
G
a2
b2
All
gll/All
b
K2ll
Kl2
5
6
7
2.221
2.224
2.239
2.047
2.096
2.060
2.105
2.138
2.119
4.9
2.4
4.1
0.48
0.63
0.54
1.054
0.813
1.011
72.77
118.13
85.89
0.506
0.512
0.546
0.414
0.866
0.533
305
188
260
a
Numbers as given in Table 4.
Expressed in units of cmꢃ1 multiplied by a factor of 10ꢃ4
b
.

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 213–221
219
Thermal gravimetric analyses of copper(II) mixed ligand complexes
(5–8)
b
a
208
206
204
202
3
2.165
2.160
2.155
The thermal decomposition process of mixed ligand complexes
(5–8) involves three decomposition steps. The complexes show no
mass lose up to 280 °C, respectively, revealing the absence of either
water or solvent molecules in these complexes. The first decompo-
sition step takes place in the temperature range 430–450 °C, corre-
sponding to the decomposition of half of the molecule (Ln). The
second take place in the 500–600 °C range may be attributed to
the decomposition of the remaining half of the molecule (Ln). The
third of decomposition which starts at 655 °C is a continuous
one. The steady mass loss observed in this step may be due to
the decomposition of 1,10-phenanthroline molecule (L) and leav-
ing anhydrous CuO.
2
1
1
3
2
103
104
105
106
107
108
109
g /A
ll ll
Fig. 4. The relation between gll/All vs. (a) gll and (b) All ꢂ 10ꢃ4 cmꢃ1
.
Electronic spectra and magnetic moments of palladium(II) complexes
(9–12)
The complexes (9–12) exhibit three spin allowed d-d transitions
from lower lying d-levels to the empty dx2ꢃy2 orbital. Although
other two electronic transitions are also observed but their inten-
sities are very weak and are neglected. The complexes show the
absorptions bands at 18,422–20,645 (1A1g ? A2g), 27,290–27,890
(1A1g ? 1B1g) and 31,120 (1A1g ? 1Eg) cmꢃ1 d–d transitions [36].
Moreover in the complexes, the high intensity charge transfer
absorption bands are also observed at 44,980 (1A1g ? 1A2u) and
36,670–37,140 (1A1g ? 1Eu) cmꢃ1 transitions. These absorption
bands suggest that the complexes possess D4h symmetry and
square planar geometry. The magnetic moment studies show that
all the complexes of Pd(II) are diamagnetic with spin-paired d8
system.
b
a
2.240
2.236
2.232
2.228
2.224
2.220
7
6
120
100
80
7
6
5
5
Structural interpretation
60
320
180
200
220
240
260
280
300
From all of the above observation and according to the data re-
ported in this paper based on the IR, molar conductivity, spectral
and magnetic susceptibility, the structure of these complexes is gi-
ven as shown in Fig. 3. The structure proposed for Cu(II) and Pd(II)
complexes (1–4 and 9–12) is square planar while for copper(II)
mixed ligand for complexes (5–8) is octahedral. This indicates that,
the ligand behaves as bidentate chelating ligand and both azome-
thine-nitrogen and keto-oxygen are the two sites of coordination.
g /A
ll
ll
Fig. 5. Plot of (a) gll and (b) All ꢂ 10ꢃ4 cmꢃ1 vs. gll/All.
orbitals) and b2 (covalent in-plane
p-bonding), were calculated by
using the following equations:
a2 ¼ ðAll=PÞ þ ðgll ꢃ 2:0023Þ þ 3=7ðg? ꢃ 2:0023Þ þ 0:04
b2 ¼ ðgll ꢃ 2:0023ÞE= ꢃ 8ka2
Microbiological investigation
The C@N linkage in azomethine derivatives is an essential struc-
tural requirement for biological activity [37]. Several Schiff bases
have been reported to possess remarkable antibacterial, antifungal,
anticancer and diuretic activities [38–41]. The antibacterial action
of Schiff base ligand may be significantly enhanced by the presence
of azomethine groups which have chelating properties. These
properties may be used in metal transport across the bacterial
membranes or to attach to the bacterial cells at a specific site from
which it can interfere with their growth [42].
The antimicrobial activity of L1, L2, L3 and L4 ligand was tested
against bacteria and fungi. More than one test organism used
tested to increase the chance of detection of their antimicrobial
activities. The used organisms in the present investigations in-
cluded two Gram positive bacteria (B. cereus and S. aureus) and
two Gram negative bacteria (E. coli and K. pneumoniae) in addition
to different kinds of fungi (A. niger, A. alternata, P. italicum and F.
oxysporium).
The observed values of
plexes have covalent character and there is interaction in the out-
of-plane -bonding. The lower values of
2 compared to b2 indicate
that the in-plane -bonding is more covalent than the in-plan
bonding. According to Hathaway [35], Kll ꢆ K\ ꢆ 0.77 for pure in-
plane -bonding and Kll < K\ for in-plane -bonding, while for out
of plane -bonding Kll > K\. In all the Cu(II) complexes, it is ob-
served that Kll < K\ which indicates the presence of significant in-
plane -bonding. Based on these observations, a distorted octahe-
a
2 and b2 parameters indicate that the com-
p
a
r
p-
r
p
p
p
dral geometry is proposed for Cu(II) complexes. The ESR study of
the Cu(II) complexes has provided supportive evidence to the con-
clusion obtained on the basis of electronic spectrum and magnetic
moment value.
The plot of gll and All ꢂ 10ꢃ4 cmꢃ1 vs. of f gives straight line with
increase the value of f decrease gll and increase the All ꢂ 10ꢃ4 cmꢃ1
(Figs. 4 and 5). It seems that the electron withdrawing p-substitu-
ent increase the positive charge on the metal ion leading to a in-
crease in f and All ꢂ 10ꢃ4 cmꢃ1 and subsequently a decrease in gll.
The results of the antibacterial activities of the synthesized
compounds were recorded in Table 7. Some of the used ligands
were found to have antibacterial activity against Gram positive

220
A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 213–221
Table 7
Antibacterial activities of some p-derivatives 4-aminoantipyrine against Staphylococcus aureus, Bacillus cereus, Escherichia coli and Klebsiella pneumoniae. Inhibition zone was
recorded as mm.
Compound
L1
Concentration (
lg/ml)
Gram positive bacteria
Gram negative bacteria
Bacillus cereus
Staphylococcus aureus
Escherichia coli
Klebsiella pneumoniae
50
100
150
ꢃve
3 mm
3 mm
5 mm
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
1 mm
1 mm
L2
L3
L4
50
100
150
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
7 mm
11 mm
11 mm
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
2 mm
7 mm
7 mm
1 mm
3 mm
50
100
150
ꢃve
ꢃve
ꢃve
3 mm
3 mm
1 mm
2 mm
2 mm
4 mm
50
100
150
ꢃve
ꢃve
8 mm
Table 8
Antifungal activities of some p-derivatives 4-aminoantipyrine against Aspergillus niger, Fusarium oxysporium, Penicillium italicum and Alternaria alternata. Inhibition zone was
recorded as mm.
Compound
L1
Concentration (
lg/ml)
Fusarium oxysporium
Penicillium italicum
Aspergillus niger
Alternaria alternata
50
100
150
1 mm
1 mm
1 mm
2 mm
2 mm
2 mm
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
L2
L3
L4
50
100
150
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
ꢃve
50
100
150
50
100
150
ꢃve
ꢃve
ꢃve
ꢃve
1 mm
1 mm
bacteria namely; B. cereus (inhibition zone of L4 = 7, 11 and 11 mm
at conc. = 50, 100 and 150 g/ml respectively) and S. aureus (inhi-
bition zone of L4 = 3 and 3 mm at conc. = 50 and 100 g/ml respec-
tively), (inhibition zone of L2 = 1 and 3 mm at conc. = 100 and
150 g/ml respectively) and (inhibition zone of L1 = 3 and 5 mm
at conc. = 50 and 150 g/ml respectively). Also some of these com-
l
l
l
l
pound have antibacterial activity against Gram negative bacterium
(K. pneumoniae) (inhibition zone of L2 = 2 and 7 mm at conc. = 50
and 150 lg/ml respectively) and inhibition zone of L3 = 2, 2 and
4 mm at conc. = 50, 100 and 150 lg/ml respectively, but no effect
was recorded against E. coli.
The results of the antifungal activities of the synthesized com-
pounds were recorded in Table 8. Some the used ligands were
found to have low antifungal activity against P. italicum and F. oxys-
porium, but no effect was observed against A. niger and A. alternata.
The screening data revealed that most of the tested compounds
showed good antimicrobial activity (see Fig. 6). The compound L4
exhibited good antibacterial activity, almost close to that of the
standard. Similar to other investigations, most of our compounds
moderately inhibited the growth of Gram positive bacteria [43].
The L4 is more active than L3, L2 and L1 against B. cereus, S. aureus
and K. pneumoniae). Whereas the L1 is more active than L2, L3
and L4 against P. italicum and F. oxysporium.
The values of clear zone for ligands are related to the nature of
the p-substituent as they increase according to the following order
p-(OCH3 < H < Cl < NO2) [29,44]. This can be attributed to the fact
that the effective charge experienced by the d-electrons increased
due to the electron withdrawing p-substituent (L3 and L4) while it
decreased by the electron donating character of L1. This is in
Fig. 6. Effect of L2 and L3 against Klebsiella pneumoniae. Inhibition zone was
recorded as mm as a result of L2 at conc. = 150
(b).
lg/ml (a) and L3 at conc. = 150 lg/ml
accordance with that expected from Hammett’s constant rR as
shown in Fig. 7 that correlates the values of inhibition zone
(mm) with r
R. It is clear that these values increase with increasing

A.Z. El-Sonbati et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 213–221
221
10
8
tant points and still many questions remain. Further studies with
the title ligands, using different metal ions, are in progress and will
be published in due course.
p-NO2
H
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The antimicrobial studies data reveal that the values of clear
zone for ligands are related to the nature of the p-substituent.
A series of studies in our laboratories, have been published
highlighting the chemistry, structural models and the chemical
equilibria of compounds and their complexes. The presentations
and discussions of these published papers explored many impor-