Synthesis, structural characterization, thermal studies, catalytic efficiency and antimicrobial activity of some M(II) complexes with ONO tridentate Schiff base N-salicylidene-o-aminophenol (saphH2)

Article abstract of DOI:10.1016/j.molstruc.2011.11.043

The reactions of acetate salts of M(II) (M = Mn, Co, Ni, Cu and Zn) with N-salicylidene-o-aminophenol (saphH₂) in ethyl alcohol afforded new four coordinated complexes with the general formula [M^(II)(saph) (H₂O)]. The complexes have been fully characterized by microanalysis, molar conductance, magnetic susceptibility, ¹H NMR, IR, UV-Vis, ESR, mass spectra and thermogravimetric analysis (TGA). The experimental data have been shown that all complexes are mononuclear with the M(II) being coordinated by a dianionic tridentate Schiff base ligand, through the deprotonated two enolic oxygen and the azomethine nitrogen atoms. UV-Vis spectra and magnetic moments have been suggested square planar stereochemistry for Co(II) and Cu(II) complexes, and tetrahedral geometry has been suggested for Mn(II), Ni(II) and Zn(II) complexes. The new complexes have been tested for their abilities to catalyze aerial oxidation of benzaldehyde to benzoic acid. Finally, in view of the biological activity, antibacterial and antifungal tests of the ligand and its complexes have been carried out and the results were compared with some known antibiotics.

Full text of DOI:10.1016/j.molstruc.2011.11.043

Journal of Molecular Structure 1010 (2012) 130–138
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structural characterization, thermal studies, catalytic efficiency and
antimicrobial activity of some M(II) complexes with ONO tridentate Schiff base
N-salicylidene-o-aminophenol (saphH2)
⇑
Ayman A. Abdel Aziz , Abdel Naby M. Salem, Mostafa A. Sayed, Mohamed M. Aboaly
Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of acetate salts of M(II) (M = Mn, Co, Ni, Cu and Zn) with N-salicylidene-o-aminophenol
Received 16 September 2011
Received in revised form 25 November 2011
Accepted 27 November 2011
Available online 7 December 2011
(
[
saphH
2
)
in ethyl alcohol afforded new four coordinated complexes with the general formula
(II)
M
(saph)(H O)]. The complexes have been fully characterized by microanalysis, molar conductance,
2
1
magnetic susceptibility, H NMR, IR, UV–Vis, ESR, mass spectra and thermogravimetric analysis (TGA).
The experimental data have been shown that all complexes are mononuclear with the M(II) being coor-
dinated by a dianionic tridentate Schiff base ligand, through the deprotonated two enolic oxygen and the
azomethine nitrogen atoms. UV–Vis spectra and magnetic moments have been suggested square planar
stereochemistry for Co(II) and Cu(II) complexes, and tetrahedral geometry has been suggested for Mn(II),
Ni(II) and Zn(II) complexes. The new complexes have been tested for their abilities to catalyze aerial oxi-
dation of benzaldehyde to benzoic acid. Finally, in view of the biological activity, antibacterial and anti-
fungal tests of the ligand and its complexes have been carried out and the results were compared with
some known antibiotics.
Keywords:
Synthesis
ONO donor
Complexes
Characterization
Catalytic activity
Microbial activities
Ó 2011 Elsevier B.V. All rights reserved.
1
. Introduction
sition metal acetate salts except the reaction of Ga(acac)
salicylidene-o-aminophenol [10]. Also the reactions of saphH
M(CO) , M = Cr, Mo and W under thermal and sunlight photolysis
was also reported [11,12].
Herein we report the synthesis and characterization of transi-
tion metals; Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of
N-salicylidene-o-aminophenol. Catalytic activities of the new syn-
thesized complexes were investigated for aerial oxidation of benz-
aldehyde to benzoic acid, which has a great importance in several
3
with N-
2
with
The coordination chemistry of nitrogen–oxygen donor ligands is
6
an interesting area of research. A great deal of attention in this area
has been focused on the complexes formed by transition metal ions
with Schiff bases because of the presence of both nitrogen and oxy-
gen donor atoms in the backbones of these ligands [1,2]
.
Schiff base ligands may act as bidentate N,O-, tridentate N,O,O-,
N,O,N-, and tetradentate N,N,O,O- which can be designed to yield
mononuclear, binuclear, one-dimensional (1D), two-dimensional
2
industrial processes. In addition saphH Schiff base and its com-
(
2D) and three-dimensional (3D) metal–organic frameworks [3,4].
The study of this diverse ligand system was linked with many of
plexes were tested for antibacterial and antifungal activities.
the key advances made in inorganic chemistry. Schiff base ligands
can also accommodate different metal centers involving various
coordination modes thereby allowing successful synthesis of homo
and hetero metallic complexes with varied stereochemistry [5].
Schiff base ligands have wide applications in biological field, as
antidepressants, antimicrobial, antitumor, antiphlogogistic, nema-
tocide, and other medicinal agents have been reported based on
these compounds [6,7]. Furthermore Schiff base metal complexes
have good catalytic role in many reactions [8,9]. A survey of the lit-
erature revealed that no work has been carried out on the reaction
2
. Experimental
2.1. Materials
Salicylaldehyde, 2-aminophenol, Mn(OAc)
2
ꢀ4H
ꢀ2H
plied from Aldrich. All solvents were of analytical grade.
2
O, Co(OAc)
2
ꢀ
4
2 2
H O, Ni(OAc) ꢀ4H
O, Cu(OAc) ꢀH
2 2 2
O and Zn(OAc)
2
2
O were sup-
2.2. Instruments
FTIR measurements in KBr Pellets (4000–400 cmꢁ1) were car-
2
between N-salicylidene-o-aminophenol (saphH ) and simple tran-
ried out on a Unicam-Mattson 1000 FT-IR. Elemental analyses were
1
⇑
Corresponding author. Tel.: +20 1001300155.
E-mail address: aymanaziz31@gmail.com (A.A. Abdel Aziz).
carried out on a JEOL JMS-AX500 MASS SPECTROMETER. H NMR
measurements were performed on a Spectrospin-Bruker AC
0
022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.11.043

A.A. Abdel Aziz et al. / Journal of Molecular Structure 1010 (2012) 130–138
131
3
00 MHz spectrometer using DMSO-d
6
as a solvent and TMS as an
rically by monitoring the increase in benzoic acid absorbance at
280 nm as a function of time. Under the same conditions, control
experiments showed that minor yield was detected in the absence
of catalyst.
internal reference. Mass spectra were recorded at 70 eV and 300 °C
on a GC MS-QP 100 Ex 5988 mass spectrometer. Molar conductiv-
ꢁ4
ities of 1 ꢂ 10 M DMSO complexes solutions were measured by
using Jenway 4010 conductivity meter. Electronic spectra were re-
ꢁ4
corded in DMSO solution with a concentration (1 ꢂ 10 M) for the
free ligand and its complexes using Shimadzu UV 1800 Spectro-
photometer in the range of 200–800 nm. The instrument is con-
trolled with a PC, using UVProbe software, version 2.34. Magnetic
moments were determined on a Sherwood Scientific magnetic mo-
ment balance (Model No.: MK1) at room temperature (25 °C) using
2.6. Screening for antimicrobial activity
2
The in vitro antimicrobial activity of saphH Schiff base ligand
and its complexes towards the bacteria: Staphylococcus aureus
(
gram +ve) and Escherichia coli (gram ꢁve) in Mueller Hinton-Agar
medium and fungi: Aspergillus flavus and Candida albicans in Doxs
medium were investigated. The antibacterial and antifungal activ-
ities were done at 20 mg/mL concentrations in DMSO solvent. Anti-
microbial activity of the tested samples was determined using a
modified Kirby-Bauer disc diffusion method [18]. At general proce-
4
Hg[Co(SCN) ] as a calibrant. Corrections for diamagnetism of the
constituents were made using Pascal constants [13]. Thermogravi-
metric analysis (TGA) was carried out using a Shimadzu DT-50
thermal analyzer under nitrogen atmosphere with a heating rate
1
0 °C/min. Electron spin resonance (ESR) measurements of solid
dure, 100
fresh media until they reached an account of approximately
08 cells/mL and 105 cells/mL for bacteria and fungi, respectively
19]. The microbial suspension was spread onto agar plates corre-
lL of the test bacteria/fungi were grown in 10 mL of
complexes were recorded at room temperature on Bruker EPR
spectrometer at 9.706 GHz (X-band), the microwave power was
1
[
(
1.0 mW) with 4.0 G modulation amplitude, using 2,2-diph-
enylpyridylhydrazone (DPPH) as standard (g = 2.0037).
sponding to the broth in which they were maintained. The bacte-
rial strains; S. aureus and E. coli were incubated for 24 h at 37 °C
and fungi strains; A. flavus and C. albicans were incubated at
2
2
.3. Syntheses
2
5 °C and 30 °C for 48 h respectively, then the diameters of the
inhibition zones were measured in millimeters. Blank paper discs
Schleicher & Schuell, Spain) with a diameter of 8.0 mm were
impregnated 10 L of tested concentration of the stock solutions.
.3.1. Synthesis of saphH
2
2
The Schiff base ligand (saphH ) was prepared as described in lit-
(
erature [14], according to the synthetic route shown in Scheme 1.
An ethanolic solution of 2-amiophenol (10 mmol) was magnet-
ically stirred in a round bottom flask followed by dropwise addi-
tion of salicylaldehyde (10 mmol). The reaction mixture was then
refluxed for 2 h. After cooling, the precipitated Schiff base was col-
lected by filtration and recrystallized from ethanol. The ligand was
dried in a desiccator over anhydrous CaCl under vacuum. The
2
resultant product was washed with ethanol and the purity of the
ligand was checked by TLC.
l
Standard antibacterial (Tetracycline) and antifungal drug (Ampho-
tericin B) were used as references to evaluate the potency of the
tested compounds under the same conditions. Activity was deter-
mined by measuring the diameter of the zone showing complete
inhibition (mm). 10 lL of solvent (DMSO) were used as a negative
control. Finally the activity results are calculated as a mean of
triplicates.
3
. Results and discussion
2.3.2. Synthesis of complexes
Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes were prepared
by using the following general procedure. Ethanolic solution
25 mL) of the Schiff base (1 mmol) and the metal salt (1 mmol)
in ethanol (25 mL) were mixed thoroughly and the resulting
solution was stirred and heated on a hot plate at 60 °C for 2 h.
The volume of the obtained solution was reduced to one-half by
evaporation 1 day later. The precipitated product was filtered,
washed with cold ethanol and hot petroleum ether 40–60 °C and
finally dried under vacuum.
2
N-salicylidene-o-aminophenol (saphH ) Schiff base and its me-
tal complexes were synthesized and characterized by elemental
(
1
analysis, molar conductance, magnetic susceptibility, H NMR, IR,
UV–Vis, ESR, mass spectra and thermogravimetric analysis (TGA).
All the metal complexes were colored, stable towards air, insoluble
in water and common solvents but soluble in DMF and DMSO, ex-
cept Zn(II) complex was soluble only in DMSO. The melting points
of the complexes were higher than that of the ligand, revealing that
the complexes are much more stable than the ligand. The molar
ꢁ4
conductivity (
DMSO falls in the range 0.0–4.0
indicated that all of the complexes have non-electrolytic nature
20]. Elemental analysis data (Table 1) of the complexes indicated
the formation of 1:1 [M:L] ratio. Elemental analyses and some
K
m
) of 1 ꢂ 10 M solutions of the complexes in
2
.4. Determination of the metal content of the complexes
ꢁ1 ꢁ1 2
X
mol cm . These low values
The metal content of the complexes was determined by analyt-
ical methods described in literature [15–17].
[
physical properties of saphH
in Table 1.
2
and its reported complexes are listed
2.5. Experimental set up for catalytic oxidation of benzaldehyde
Catalytic oxidation was carried out under air (atmospheric pres-
sure).
A
DMSO solution of the reported complexes (2 mL,
3.1. Spectroscopic studies
3.1.1. FT-IR spectra
ꢁ
4
ꢁ3
1
ꢂ 10 M) and 2 mL of 1 ꢂ 10 M freshly distilled benzaldehyde
in DMF were mixed in a 1 cm quartz cell at room temperature
(
25 °C). The course of the reaction was followed spectrophotomet-
2
In order to study the binding of saphH to the metal in the com-
plexes, the IR spectra of the metal complexes were compared with
that of the free Schiff base ligand. The characteristic IR data of
saphH Schiff base ligand and their metal complexes are listed in
2
HO
OH
OH
HO
N
Table 2. The IR spectra of the Schiff base ligand and a representa-
tive example of Co(II) complex are shown in Figs. 1 and 2. Charac-
teristic IR data are discussed in terms of the nature of bonding and
the structures of the complexes. Schiff bases are capable of forming
coordinate bonds with many metal ions through both azomethine
Ethnol
Reflux
C
H
N
C
H
O
+
H
2
saphH
2
Scheme 1. Synthetic route of N-salicylidene-o-aminophenol (saphH
2
).

1
32
A.A. Abdel Aziz et al. / Journal of Molecular Structure 1010 (2012) 130–138
Table 1
Elemental analyses and some physical properties of saphH
2
Schiff base ligand (H
2
L) and their reported complexes.
ꢁ
1
cm2 molꢁ1
)
Compounds
Yield (%)
MP (°C)
M. Wt.
Color
(Calculated) found (%)
K
m
(X
C
H
N
M
–
saphH
2
(H
2
L)
94
79
82
63
88
85
187
213.14
284.07
288.07
287.83
292.68
294.53
Orange
73.25
5.16
6.57
–
C
13
H
11NO
2
(73.40)
(5.05)
(6.50)
[
(
MnL(H O)]
11NO
CoL(H O)]
11NO
NiL(H O)]
11NO
CuL(H
11NO
ZnL(H O)]
11NO
2
>300
>300
>300
>300
>300
Yellow
54.96
(54.73)
3.87
(3.82)
4.93
(5.18)
19.33
(18.96)
3.4
1.9
1.1
4.0
0.0
C
13
H
3
)Mn (1)
)Co (2)
)Ni (3)
)Cu (4)
)Zn (5)
[
(
2
Brown
54.19
(54.05)
3.82
(3.77)
4.86
(5.17)
20.45
(19.98)
C
13
H
3
3
[
(
2
Reddish-brown
Green
54.24
(53.98)
3.82
(3.21)
4.86
(4.62)
20.39
(19.92)
C
13
H
[
(
2
O)]
53.34
(52.97)
3.76
(3.71)
4.79
(4.47)
21.71
(21.43)
C
13
H
3
[
(
2
Yellow
53.01
(53.03)
3.73
(3.50)
4.75
(5.06)
22.20
(21.87)
C
13
H
3
Table 2
Infrared (cmꢁ1, KBr) of saphH
(H
L) and its reported complexes.
d(OH) in-plane bending
2
2
Compound
m
(OH)
m(C@N)
m(CAO)
m(MAN)
m(MAO)
H
2
L
3430(w, br.)
3434(s, br.)
3433(s, br.)
3430(w, br.)
3442(s, br.)
3427(m, br.)
1413(m)
1441(m)
1440(m)
1440(m)
1440(m)
1442(m)
1631(s)
1604(s)
1605(s)
1607(s)
1611(s)
1612(s)
1274(m)
1296(m)
1292(m)
1287(m)
1298(m)
1294(m)
–
–
[
[
[
[
[
MnL(H
CoL(H
NiL(H
CuL(H
ZnL(H
2
O)] (1)
O)] (2)
O)] (3)
507(w)
517(w)
521(w)
537(w)
514(w)
445(w)
440(w)
451(w)
488(w)
446(w)
2
2
2
O)] (4)
2
O)] (5)
ꢃ
s: strong, m: medium, w: weak, br: broad.
Fig. 1. FTIR of saphH
2
(H
2
L) ligand.
group and phenolic group or via its azomethine or phenolic groups.
hydrogen bond becomes stronger, the bandwidth increases, and
this band sometimes is not detected [22]. Comparison of the IR
ꢁ1
The free ligand exhibited a broad band at 3430 cm , which may be
assigned to the (OH). The broadness of the band was attributed to
the presence of internal hydrogen bond OHꢀ ꢀ ꢀN@C [21]. As the
t
spectra of the metal complexes with that of the free saphH
2
re-
vealed that all complexes showed a broad band in the range

A.A. Abdel Aziz et al. / Journal of Molecular Structure 1010 (2012) 130–138
133
2
Fig. 2. FTIR of [CoL(H O)].
ꢁ
1
3
427–3442 cm
assignable to
t
(OH) of the coordinated water
the hydroxyl ions and the fourth site was occupied by a water
molecule.
molecule associated with the complexes. Besides, in the spectra
of these complexes, a narrow intense band was seen at 828–
36 cm , specific for coordinated water molecule [23]. Also the
participation of the OH group is apparent from the shift in position
of the d(OH) in-plane bending at 1413 cm in the free ligand by
7–29 cm in the reported complexes [24]. The presence of one
water molecule was indicated from the thermogravimetric studies
vide infra). The band at 1631 cm
in the free ligand, was shifted to lower frequency region (1604–
ꢁ1
8
1
3
.1.2. H NMR spectra
Evidence of the bonding mode of saphH
2
was also provided by
ꢁ1
1
the H NMR spectra of the Schiff base ligand and its diamagnetic
ꢁ1
2
1
Zn(II) complex. The H NMR spectra of the compounds were ob-
tained in d
6
-DMSO at room temperature using TMS as an internal
ꢁ1
(
characteristic of m(C@N)
standard. The chemical shifts of the different types of protons in
1
the H NMR spectra of saphH
complex are listed in Table 3. The H NMR spectrum of the parent
ligand saphH , Fig. 3, showed a singlet signal at very downfield at d
3.74 ppm, which was attributed to two phenolic AOH protons.
The OH signal disappeared with addition of the D O [27]. The li-
2
ligand and its diamagnetic Zn(II)
ꢁ1
1
612 cm ) after coordination between Schiff base ligand and me-
1
tal salts. This feature could be explained by the withdrawing of
electrons from the nitrogen atom to the metal ion due to coordina-
tion, indicating the involvement the azomethine nitrogen atom in
coordination and formation of metal–ligand bonds [23,24]. The
band at 1274 cm in the IR-spectrum of ligand is ascribed to the
phenolic CAO stretching vibration in the case of salicylideneani-
lines [25]. This band is found in the region 1287–1298 cm in
the IR-spectra of the complexes and the intensity of the band has
decreased showing the involvement of the phenolic oxygen in
coordination. Also this band was shifted to higher wave number
after complex formation. These changes can be interpreted as
proving the involvement of the phenolate oxygen atom in coordi-
nation [26]. The most obvious feature after the complexation were
found in the 400–600 cm range. More signals were observed for
metal complexes than that of corresponding Schiff base ligand. The
non-ligand bands at 507–537 cm and 440–488 cm were ob-
served due to MAO and MAN, which gave conclusive evidence
regarding the bonding of azomethine nitrogen and phenolic oxy-
gen of the Schiff base to the metal ion [21].
2
1
2
gand also showed one singlet at d 8.95 ppm which was attributed
ꢁ
1
to the azomethine (ACH@NA) proton, respectively [28]. The 1
H
NMR spectrum of the ligand revealed multiplets at 6.84–
ꢁ1
7
.62 ppm, corresponding to aromatic protons [29].
A comparison of H NMR spectrum of diamagnetic Zn(II) com-
1
plex with the spectrum of the corresponding saphH
2
Schiff base
(Table 3), showed that, the chemical shift observed for the OH pro-
tons in the ligand was not observed in the Zn(II) spectrum. The ab-
sence of AOH signals, indicated deprotonation of the hydroxyl
ꢁ1
Table 3
1
ꢁ
1
ꢁ1
H NMR spectral data (d, ppm) of saphH
2
(H
2
L) and its zinc(II) complex.
Compound
d (ppm)
Assignments
2
H L
13.74
8.95
(s, 2H, AOH)
(s, 1H, ACH@N)
(m, 8H, ArH)
6.84–7.62
From the above arguments together with the elemental anal-
yses, it is concluded that saphH
2
ligand behaves as a binegative
[ZnL(H
2
O)] (5)
–
8
6
–
.93
.53–7.58
(s, 1H, ACH@N)
(m, 8H), ArH)
tridentate ligand with ONO donor sites. In the complexes, three
of the four coordination sites of metal ions were occupied by
nitrogen atom of the azomethine group, two oxygen atoms of
ꢃ
s: singlet, m: multiplet.

1
34
A.A. Abdel Aziz et al. / Journal of Molecular Structure 1010 (2012) 130–138
Fig. 3. 1H NMR spectrum of saphH
(H L) Ligand.
2 2
group of the Schiff base ligand prior to coordination with Zn(II),
and confirmed the bonding of oxygen to the metal ions (CAOAM)
coordination of the ligand to the metal ions. The UV–Vis spectrum
of Cu(II) complex in DMSO solution displayed a broad band at
–
1
[
30]. Moreover, coordination of nitrogen atom of the ligand to
18,248 and a well-defined shoulder around 17,094 cm , attribut-
2
2
2
2
Zn(II) was indicated by a shift of the imine carbon proton signal
to downfield region 8.93 ppm in comparison with that of the free
ligand, inferring coordination through the azomethine nitrogen
atom of the ligand [30], suggesting deshielding of the azomethine
proton and proving its contribution to the covalent bond formed
with the metal. Besides, the displacement of chemicals shifts of
azomethine hydrogen, the aromatic protons multiplets were dis-
placed upper field region around d 6.53–7.58 ppm [31].
able to
B
1g ? A1g and
B1g ? B2g transitions which strongly
favored square-planar geometry around Cu(II) ion.[32]. The broad-
ness of the band can be taken as an indication of distortion from
perfect planar symmetry. The absence of band below 10,000
ꢁ1
cm excluded the possibility of tetrahedral geometry [32]. The
magnetic susceptibility value of Cu(II) complex (1.83 BM) was an
indicative of one unpaired electron per Cu(II) ion, suggesting that
the square-planar geometry [33]. The electronic spectrum of Ni(II)
complex displayed two absorption bands at 17,699 and
ꢁ1
3.1.3. UV–Vis spectra and magnetic susceptibility
14,880 cm , which were assigned to the spin allowed transitions
3
3
3
3
Magnetic measurements and electronic spectra were recorded
1 1 1 2
T (F) ? T (P) and T (F) ? A , respectively [33]. These transi-
in order to obtain information about the geometry of the com-
plexes. The electronic spectra of the Schiff base and the reported
tions are characteristic to the tetrahedral environment around
Ni(II) ion. The magnetic moment of Ni(II) complex (2.83 BM) was
close to that of 3.0–3.5 BM for the more distorted tetrahedral com-
ꢁ4
complexes were recorded in 1 ꢂ 10 M DMSO solution in the re-
gion 200–800 nm. The magnetic moments of the complexes deter-
mined at room temperature, the absorption region and the
assignment of the absorption bands are listed in Table 4. Within
the UV–Vis spectrum of the ligand, two high intensity absorption
–1
plexes [34]. The Co(II) complex showed a d–d band at 16,583 cm
,
1
1
assigned to A1g ? B1g transition, which confirmed square-planar
geometry. This was further confirmed by its magnetic susceptibil-
ity value (3.85 BM). In case of Mn(II) complex, there was no
allowed d–d transitions. The UV–Vis spectrum displayed a strong
ꢁ
1
bands were displayed at 36,630 and 27,855 cm
which were
ꢃ
ꢁ1
assignable to intra ligand
p–p/n–p
transitions [32]. These transi-
absorption band at 22,522 cm , which could be ascribed to the
tions were also observed in the spectra of the complexes, but they
shifted to longer wavelength (lower frequencies), confirming the
ligand-to-metal charge transfer (LMCT) transition [35]. Further-
more the magnetic moment value is found to be 5.21 BM. which
Table 4
Characteristics electronic transition bands and magnetic moments of saphH
2
and its reported complexes.
Assignments
Compound
UV–Vis (cmꢁ1, DMSO)
l
eff. (BM)
ꢃ
ꢃ
H
2
L
36,630, 27,855
p
p
p
p
p
p
?
p
, n ?
p
–
ꢃ
ꢃ
[
[
[
[
[
MnL(H
NiL(H O)] (2)
O)] (3)
2
O)] (1)
32,786, 25,510, 22,522
35,714, 27,700, 17,699, 14,880
36,101, 27,700, 16,583
35,714, 27,777, 18,248, 17,094
36,630, 27,777, 24,875
ꢁ
p
p
p
p
p
, nꢁ
, nꢁ
, nꢁ
, nꢁ
, nꢁ
p
p
p
p
p
, CT
T
A
B
5.21
2.83
3.85
1.83
Dia
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
3
(F) ? 3
(P), 3
(F) ? 3
2
ꢁ
ꢁ
ꢁ
ꢁ
,
,
,
1
T
1
T
1
A
2
(F)
1
2
1
CoL(H
CuL(H
2
1g
?
?
B
A
1g
2
1g, 2 1g ? 2
2
O)] (4)
O)] (5)
1g
B B
2g
ZnL(H
2
, CT

A.A. Abdel Aziz et al. / Journal of Molecular Structure 1010 (2012) 130–138
135
OH
2
OH
2
O
M
M
N
O
O
O
N
M= Co(II) and Cu(II)
M = Mn(II), Ni(II) and Zn(II)
Scheme 2. The proposed structure of salicylidene N-salicylidene-o-aminophenol
complexes.
ential thermal analysis (DTA). The sample was analyzed in a plat-
inum pan under N
2
and the temperature was linearly increased
2
Fig. 4. ESR spectrum of [CuL(H O)]) complex at 298 K.
ꢁ1
at 10 °C min
over a temperature range 20–1000 °C. Thermal
indicated the presence of Mn(II) complex in tetrahedral structure.
Finally, the spectrum of Zn(II) complex exhibited a moderately in-
analysis of the synthesized complexes confirmed the presence of
coordinated water molecule. The decomposition mass losses were
found in agreement with the formula weight of each complex pro-
posed from the elemental analysis. The decomposition patterns
were further confirmed from the mass spectral peaks, Table 5. A
representative mass spectrum of Ni(II) complex is given in Fig. 5.
ꢁ1
tense band at 24,875 cm , assigned to charge transfer from the li-
gand to the metal and vice versa. The Zn(II) complex is diamagnetic
1
0
as expected for d configuration. In analogy with those described
for Zn(II) complexes containing N–O donor Schiff bases [36] and
according to the empirical formulae of these complexes, a tetrahe-
dral geometry was proposed for the Zn(II) complex.
Table 5
3.1.4. ESR spectra
Selected mass spectral data of the reported complexes.
ESR studies of paramagnetic transition metal(II) complexes give
Complex
Molar mass
m/z values (relative intensity)
information about the distribution of the unpaired electrons and
hence about the nature of the bonding between the metal ion
and its ligands. The ESR spectrum of Cu(II) complex, recorded in
the solid state (Fig. 4) was consistent with the square-planar geom-
etry around each Cu(II) center in the complex [37]. The ‘‘g’’ tensor
values of the Cu(II) complexes could be used to obtain the ground
[
[
[
MnL(H
CoL(H
NiL(H
2
O)] (1)
O)] (2)
O)] (3)
284.17
288.16
287.92
292.78
294.62
+
284a (80.5%), 266b (40.5%), 87c (60.18%)
288a (91.2%), 270b (62.4%), 75d (70.3%)
288a (67.5%), 270b (60.1%), 74d (55.0%)
2
2
[CuL(H
2
O)] (4)
292a (75.3%), 274b (35.7%), 79d (74.7%)
295a (80.3%), 276b (50.5%), 81d (70.1%)
[
ZnL(H
2
O)] (5)
state [38]. In square planar complexes, the unpaired electron occu-
a
b
c
2
Molecular ion peak (P) .
pies the dx2ꢁy2 orbital with B1g ground state resulting in g|| > g
\
.
+
(
(
P-H
P-C13
2
O) .
O)+.
N + H
2
The ESR spectrum of Cu(II) complex exhibited anisotropic signal
with g|| = 2.20 and g = 2.04 and gaver. = 1/3(g + 2g||) = 2.14. The
trend in the observed ‘‘g’’ values g|| > g > g (2.0023) suggested
H
9
d
+
\
\
9 2
(P-C13H NO + H O) .
\
e
that the unpaired electron lies predominantly in the dx2ꢁy2 orbital
which is in agreement with the electronic absorption spectroscopic
assignments. Furthermore, for an ionic environment g|| is normally
2
.3 or larger, but for covalent environment g|| is less than 2.3 [39].
For the reported Cu(II) complex, g|| < 2.3 value, which have been
confirmed the covalent character of the metal–ligand bond. The ax-
ial symmetry parameter (anisotropic parameter) G value, which is
measure of exchange coupling interaction between two Cu(II) ions
has been calculated by Kneubuhl’s method [40], G = (g|| ꢁ 2)/
(g
\
ꢁ 2). According to Hathaway and Billing [41], if the G value
was greater than 4, the exchange interaction is negligible, while
a value of less than 4 indicated a considerable exchange interaction
in the complex. The anisotropic value, G (5.2) was greater than 4,
which suggests that the local tetragonal axis is aligned parallel or
slightly misaligned and consistent with dx2–y2 ground state. This re-
sult also indicates that the exchange coupling effects are not oper-
ative in the present complex [42,43]. The ESR spectra of the solid
Mn(II), Co(II) and Ni(II) complexes at room temperature do not
show ESR signal because the rapid spin lattice relaxation of the
Mn(II), Co(II) and Ni(II) broaden the lines at higher temperatures
Fig. 5. Mass spectrum of [NiL(H
2
O] complex.
Table 6
Thermogravimetric characteristics of complexes.
Complex
Temp. range
°C)
Mass loss
(%)
Assignment
Residue
(
(
calc.) found
[
MnL(H
1)
[CoL(H O)] (2) 431–644
2
O)]
320–499
69.42
(70.46)
74.02
C
13
H
9
N + H
2
O
MnO
2
(
[
44]. From the above arguments, the proposed structures of the re-
C13H NO + H O CoO
2
9
9
9
9
2
2
2
2
ported complexes is shown in Scheme 2.
(73.29)
74.08
[
NiL(H
[CuL(H
ZnL(H
2
O)] (3) 419–540
C
C
C
13
H
13
H
13
H
NO + H
NO + H
NO + H
O
O
O
NiO
CuO
ZnO
(
74.08)
72.85
71.85)
72.39
73.35)
3.2. Thermogravimetric and mass spectra analysis
2
O)] (4) 310–438
(
[
2
O)] (5) 466–647
The thermal behavior of complexes under investigation was
characterized using thermogravimetric analysis (TGA) and differ-
(

1
36
A.A. Abdel Aziz et al. / Journal of Molecular Structure 1010 (2012) 130–138
0
0
.0005
.0000
-
-
-
5.38
5.40
5.42
1
1
0
0
0
0
0
.2
.0
.8
.6
.4
.2
.0
-
-
0.0005
0.0010
-
5.44
-0.0015
-5.46
-5.48
-5.50
-5.52
-
-
-
0.0020
0.0025
0.0030
0.0035
-
5.54
-
0
100
200
300
400
o
500
600
700
800
-5.56
.300
Temp. ( C)
1
1.305
1.310
1.315
1.320
1000/T
Fig. 6. TGA and DTG of [NiL(H
2
O)] complex.
Fig. 7. Coats–Redfern linear plot for [NiL(H
2
O)] complex.
firmed a first order kinetics for the decomposition process. The acti-
o
up to T C
ꢃ
[M(C H NO (H O)]
13 9 2 2
MOx
vation entropy
(D
S ) was calculated using Eq. (2) [48], the
ꢃ
ꢃ
activation enthalpy (DH ), the free energy of activation (DG ) and
the specific rate constant (K) can be calculated using Eqs. (3)–(5):
;
x = 1 for Co, Ni, Cu, Zn and 2 for Mn
ꢀꢂ
ꢃꢁ
Ah
K T
B s
Sꢃ ¼ 2:303 R log
ð2Þ
T = 320 for Mn
T = 431 C for Co
T = 419 C for Ni
T = 310 C for Cu
D
o
ꢃ
o
D
D
H ¼ E
ꢁ RT
ð3Þ
ð4Þ
a
s
ꢃ
ꢃ
ꢃ
o
G ¼
D
ꢁ T
s
DS
o
ꢃ
T = 466 C for Zn
E
log K ¼ log A ꢁ
ð5Þ
2
:303RT
and T
peak temperature obtained from the DTA curve, respectively. The
s
Scheme 3. The thermal decomposition of N-salicylidene-o-aminophenol complexes.
where h, K
B
s
are Planck constant, Boltzmann constant and the
The reported complexes were found to be air stable and have high
thermal stability to use in catalytic reactions [45].
ꢃ
ꢃ
ꢃ
ꢃ
calculated values of E ,
DS , DH , DG and K for the decomposition
Inspection of the data revealed that the complexes start decom-
position at around 310–466 °C, in a very sharp endothermic step
with an inflection point in the range 387–564 °C, corresponding
to the elimination of coordinated water and organic ligand moiety,
leaving metallic oxide as the final decomposition product. The
residual metal oxide percentages were coincided fairly with the
theoretical values. Thermogravimetric characteristics of complexes
are listed in Table 6. An illustrative example is the TG thermogram
of Ni(II) complex is shown in Fig. 6. The thermal degradation of the
complexes have been be depicted in Scheme 3.
steps are given in Table 7. The activation energies of the decompo-
ꢁ1
sition were found to be in the range 59.89–229.10 kJ mol . The
high values of the activation energies reflected the thermal stability
of the complexes. According to data in Table 7, the order of thermal
stability was, Zn(II) > Co(II) > Ni(II) > Mn(II) > Cu(II). The positive
values of
D
H reflected the endothermic nature of thermal decompo-
ꢃ
sition. Furthermore the negative values of
D
S in the studied com-
plexes indicate that the reaction rates were slower than normal
ꢃ
and the positive values of
D
G indicated the non-spontaneous nat-
ure of process. The data clearly indicates similarity in the thermal
degradation of the complexes.
3.3. Kinetic and thermodynamic parameters
3.4. Catalytic activity
The thermogravimetric analysis had proved to be a useful ana-
Benzoic acid is used in the manufacture of benzoic acid esters,
lytical technique in evaluating thermodynamic parameters of
decomposition processes of complexes, namely, activation energy
which is used in the perfume industry. Moreover, in the food
industry benzoic acid (E 210) is used as a preservative especially
in pickled food. Because of increased solubility, it is rather used
for usual salts: sodium benzoate (E 211), potassium benzoate (E
ꢃ
ꢃ
ꢃ
(
(
E ), enthalpy (
D
H ), entropy (
D
S ), and Gibbs free energy change
ꢃ
D
G ),which could be evaluated graphically by employing the
Coats–Redfern method [46]. This method was reviewed by Johnson
and Gallagher [47] as an integral method assuming various orders
of reaction and comparing the linearity in each case to select the
correct order by using
2
12), calcium benzoate (E 213). In environmental application, it
is used in monitoring pitfall traps that are filled with saturated
benzoic acid to kill organisms such as insects and snails. Benzoic
acid is often used in perishable food such as in ketchup, sausage,
mustard and other sauces, margarine, fish, salads and many other
products as a preservative. The bacteriostatic and fungistatic effect
is based on the inhibitory effect against enzymes that break down
reactive oxygen species (catalase and peroxidase), which generates
a hydrogen peroxide accumulation in the cells of microorganisms.
This ultimately leads to their death. Benzoic acid in the human
organism is harmless, since the accumulation is prevented by the
conversion and retirement of the substance as hippuric acid. Cata-
lytic oxidation reactions are of great importance in industrial pro-
cess due to the wide variety of products synthesized by this route.
ꢀꢁ
Inð1=ð1 ꢁ
a
Þꢁ
ꢀ
AR
bE
ꢂ
2RT
E
ꢃꢁ
E
ꢃ
log
¼ log
1 ꢁ
ꢁ
ð1Þ
2
ꢃ
ꢃ
T
2:303RT
where
a is the fraction of sample decomposed at temperature T, A is
ꢃ
frequency factor, R is the gas constant, E is the activation energy in
ꢁ
1
ꢃ
kJ mol , b is the linear heating rate and the term (1–2RT/E ) ffi 1. A
2
plot of log [ꢁln1/(1 ꢁ
a)/T ] versus 1/T gives a straight line. The val-
ꢃ
ues E and A were calculated from the slope and intercept of the
straight lines, respectively. Fig. 7 represents the linear plot in case
of Ni(II) complex. The Coats and Redfern linearization plots, con-

A.A. Abdel Aziz et al. / Journal of Molecular Structure 1010 (2012) 130–138
137
Table 7
Thermodynamic parameters for the thermal degradation of the complexes.
a
ꢃ
ꢁ1
ꢁ1
ꢃ
ꢁ1
ꢃ
ꢁ1 ꢁ1
ꢃ
ꢁ1
ꢁ1
Complex
T
s
E
(kJ mol
)
A (s
)
D
H
(kJ mol
)
D
S
(J mol
K
)
D
G
(kJ mol
)
k (s )
2
8
7
2
1
ꢁ4
[
[
[
[
[
MnL(H
2
O)] (1)
O)] (2)
O)] (3)
O)] (4)
O)] (5)
394
564
489
387
562
68.76
0.72 ꢂ 10
1.85 ꢂ 10
6.40 ꢂ 10
0.12 ꢂ 10
1.85 ꢂ 10
67.22
175.70
154.14
54.40
ꢁ235.30
ꢁ95.25
224.27
255.47
232.87
206.34
253.73
2.98 ꢂ 10
7.42 ꢂ 10
6.43 ꢂ 10
2.39 ꢂ 10
8.91 ꢂ 10
ꢁ4
ꢁ4
ꢁ4
ꢁ4
CoL(H
2
182.67
160.48
59.89
NiL(H
CuL(H
2
ꢁ103.29
ꢁ230.17
ꢁ37.79
2
1
ZnL(H
2
229.10
222.15
T
s
a
: The derivative peak temperature.
Endothermic process.
Table 8
Antimicrobial activities of saphH
-
3
-1
-1
Mn( K = 8.322x10 Mol.L .min )
2
(H
2
L) and its reported complexes.
0
0
0
0
0
0
0
0
.7
.6
.5
.4
.3
.2
.1
.0
-3
-1
-1
Compounds
Diameter of inhibition zone (mm)
Antibacterial activity Antifungal activity
Cu( K = 6.227x10 Mol.L .min
)
-
3
-1
-1
Co ( K = 4.421x10 Mol.L .min
)
S. aureus
E. coli
A. flavus
C. albicans
-
3
-1
-1
Ni ( K = 3.730x10 Mol.L .min
)
H
2
L
13
27
12
10
13
12
28
–
13
25
11
10
14
11
30
–
13
12
12
0.0
0.0
0.0
–
13
17
0.0
0.0
0.0
0.0
–
[
[
[
[
MnL(H
CoL(H
NiL(H
CuL(H
2
O)] (1)
O)] (2)
O)] (3)
2
2
2
O)] (4)
2
O)] (5)
[ZnL(H
Tetracycline
Amphotericin B
DMSO
20
0.0
21
0.0
0.0
0.0
ion, (iv) the nature of the metal ion, (v) the nature of the counter
ions that neutralize the complex, and (vi) the geometrical structure
of the complex [50]. Furthermore, chelation reduces the polarity of
the metal ion because of partial sharing of its positive charge with
0
10
20
30
40
50
60
Time (min)
Fig. 8. The change in absorbance of benzoic acid versus time in presence of
the donor groups and possibly the
the whole chelate ring system that is formed during coordination
51]. These factors increase the lypophilic nature of the central
p-electron delocalization within
reported complexes.
[
metal atom and hence increasing the hydrophobic character and
liposolubility of the molecule favoring its permeation through
the lipid layer of the bacterial membrane. This enhances the rate
of uptake/entrance and thus the antibacterial activity of the testing
compounds.
Hence, studies on synthesis and catalytic activity of metal com-
plexes derived from Salen-type ligands with N and O donor atoms
type ligands have been gained greater momentum [49]. The cata-
lytic activities of complexes (1–5) were investigated for aerial oxi-
dation of benzaldehyde to benzoic acid. The course of the reaction
was followed spectrophotometrically by monitoring the increase
in benzoic acid absorbance at 280 nm as a function of time. Plots
of the absorbance versus time were linear (Fig. 8). The slope of
the line is equal to the reaction rate constant (K). In Absence of
the complexes, it was observed a negligible change in absorbance
at 280 nm, indicating the catalytic activity of the new complexes.
The catalytic activity was found to follow the order Mn(II) > -
Cu(II) > Co(II) > Ni(II), where no appreciable change was observed
in case of Zn(II) complex (5). Since the organic moiety was the
same in all complexes, the difference in catalytic activities of dif-
ferent complexes may be explained on the basis of change in nat-
ure of metal. According to European system Mn(II) has the greatest
2
The Schiff base saphH and its complexes (1–5) were tested for
their inhibitory effects on the growth of bacteria: S. aureus and
E. coli and fungi: A. flavus and C. albicans because such organisms
can achieve resistance to antibiotics through biochemical and mor-
phological modification [52]. The antibacterial and antifungal
activities of the new compounds are listed in Table 8, and repre-
sented graphically in Fig. 9. The results have been indicated that,
with regard to A. flavus, Ni(II), Cu(II) and Zn(II) complexes showed
no activity whereas Mn(II) and Co(II) complex showed moderate
activity. With C. albicans only Mn(II) complex showed high activity
and the other complexes showed no activity. The different com-
plexes exhibited weak to high activity against the bacterial strains
when compared with standard Tetracycline. The results of bacteri-
cidal screening showed that, Mn(II) complex also have been shown
the higher activity which was very close to standard Tetracycline.
The biological activity of the complexes follow the order Mn(II) > -
Cu(II) > Co(II) = Zn(II) > Ni(II). This would suggest that chelation
could facilitate the ability of the complex to cross a cell membrane
and can be explained by Tweedy’s chelation theory [53]. On chela-
tion, the polarity of the metal ion will be reduced to a greater ex-
tent due to the overlap of the ligand orbital and partial sharing
of the positive charge of the metal ion with donor groups. Further,
o
reduction potential (E = ꢁ1.18 V), which explained the highest
catalytic activity of its complex. With respect to other metals, the
trend in catalytic activity may be explained on the possibility of
fact that Mn has variable oxidation states, which enhanced elec-
tron transfer through oxidation reactions and this fact was sup-
ported by negligible activity of Zn complex, where Zn(II) is
limited to oxidation state (+2).
3.5. Antimicrobial activity
it increases the delocalization of
p-electrons over the whole
The biological activity of the metal complexes is governed by
the following factors: (i) the chelate effect of the ligands, (ii) the
nature of the donor atoms, (iii) the total charge on the complex
chelate ring and enhances the penetration of the complexes into
lipid membranes with blocking of the metal binding sites in the
enzymes of microorganisms. These complexes also disturb the

1
38
A.A. Abdel Aziz et al. / Journal of Molecular Structure 1010 (2012) 130–138
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0
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1
Fig. 9. Zone of inhibitions of reported compounds and antibiotics against two types
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[
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proteins, which restricts further growth of the organisms [54].
The variation in the effectiveness of different compounds against
different organisms depends on either the impermeability of the
cells of the microbes or on differences in ribosome of microbial
cells [51].
[
[
[
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condensation of salicylaldehyde with 2-aminophenol. Based on
the characterization data and keeping in mind the preferred geom-
etries, square planar was proposed for Co(II) and Cu(II) complexes,
whereas tetrahedral was proposed for Mn(II), Ni(II) and Zn(II) com-
plexes. The newly synthesized complexes were found to be acting
as efficient catalysts for the aerial oxidation of the aerial oxidation
of benzaldehyde to benzoic acid that has a great importance, espe-
cially in food industry. The new complexes can be used as low cost,
reliable and highly efficient catalyst for oxidation of aldehydes. The
in vitro antimicrobial activities of the new complexes were studied
against the bacteria: S. aureus (gram +ve) and E. coli (gram ꢁve)
and fungi: A. flavus and C. albicans. The data has shown that Mn(II)
complex show the higher antibacterial and antifungal activity,
while other complexes showed no to moderate activity. The results
have been compared with some known antibiotics.
[
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[
[
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[
[
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