Spectroscopic study of molecular structures of novel Schiff base derived from o-phthaldehyde and 2-aminophenol and its coordination compounds together with their biological activity

Article abstract of DOI:10.1016/j.saa.2009.04.005

New Schiff base (H₂L) ligand is prepared via condensation of o-phthaldehyde and 2-aminophenol. The metal complexes of Cr(III), Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) with the ligand are prepared in good yield from the reacti

Full text of DOI:10.1016/j.saa.2009.04.005

Spectrochimica Acta Part A 73 (2009) 833–840
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Spectroscopic study of molecular structures of novel Schiff base derived from
o-phthaldehyde and 2-aminophenol and its coordination compounds
together with their biological activity
Sayed M. Abdallaha, Gehad G. Mohamedb,∗, M.A. Zayedb, Mohsen S. Abou El-Elac
a Works University, Aswan, Egypt
b Botany Department, Faculty of Science, Cairo University, 12613, Giza, Egypt
c Chemistry Department, Faculty of Science, Cairo University, 12613, Giza, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
New Schiff base (H2L) ligand is prepared via condensation of o-phthaldehyde and 2-aminophenol. The
metal complexes of Cr(III), Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) with the ligand are prepared
in good yield from the reaction of the ligand with the corresponding metal salts. They are characterized
based on elemental analyses, IR, solid reflectance, magnetic moment, electron spin resonance (ESR), molar
conductance, 1H NMR and thermal analysis (TGA). From the elemental analyses data, the complexes are
proposed to have the general formulae [M(L)(H2O)n]·yH2O (where M = Mn(II) (n = 0, y = 1), Fe(II) (n = y = 0),
Co(II) (n = 2, y = 0), Ni(II) (n = y = 2), Cu(II) (n = 0, y = 2) and Zn(II) (n = y = 0), and [MCl(L)(H2O)]·yH2O (where
M = Cr(III) and Fe(III), y = 1–2). The molar conductance data reveal that all the metal chelates are non-
electrolytes. IR spectra show that H2L is coordinated to the metal ions in a bi-negatively tetradentate
manner with ONNO donor sites of the azomethine N and deprotonated phenolic-OH. This is supported by
the 1H NMR and ESR data. From the magnetic and solid reflectance spectra, it is found that the geometrical
structures of these complexes are octahedral (Cr(III), Fe(III), Co(II) and Ni(II) complexes), tetrahedral
(Mn(II), Fe(II) and Zn(II) complexes) and square planar (Cu(II) complex). The thermal behaviour of these
chelates is studied and the activation thermodynamic parameters, such as, E*, ꢀH*, ꢀS* and ꢀG* are
calculated from the DrTGA curves using Coats-Redfern method. The parent Schiff base and its eight metal
complexes are assayed against two fungal and two bacterial species. With respect to antifungal activity,
the parent Schiff base and four metal complexes inhibited the growth of the tested fungi at different rates.
Ni(II) complex is the most inhibitory metal complex, followed by Cr(III) complex, parent Schiff base then
Co(II) complex. With regard to bacteria, only two of the tested metal complexes (Mn(II) and Fe(II)) weakly
inhibit the growth of the two tested bacteria.
Received 27 November 2008
Received in revised form 18 March 2009
Accepted 14 April 2009
Keywords:
Schiff base
Transition metal complexes
IR
1H NMR
ESR
Solid reflectance
Magnetic moment
Molar conductance
Thermal analysis
Biological activity
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
furthermore complexes of Schiff bases showed promising appli-
cations in biological activity and biological modeling applications
Schiff bases have been used extensively as ligands in the
field of coordination chemistry, some of the reasons are that the
intramolecular hydrogen bonds between the (O) and the (N) atoms
which play an important role in the formation of metal complexes
and that Schiff base compounds show photochromism and ther-
mochromism in the solid state by proton transfer from the hydroxyl
(O) to the imine (N) atoms [1]. A large number of Schiff bases and
their complexes have been investigated for their interesting and
important properties, such as their ability to reversibly bind oxy-
gen, catalytic activity in the hydrogenation of olefins, photochromic
properties and complexing ability towards some toxic metals,
[2–4].
Schiff bases are important class of compounds in medicinal
and pharmaceutical field. They show biological applications includ-
ing antibacterial [5,6], antifungal [7] and antitumor activity [8].
Microbes encounter a variety of metal ions in the environment and
interact with them, which is sometimes beneficial or detrimental
depending on the chemical/physical nature and oxidation state of
the metal ion. Of particular interest are those metal ions, which exist
mostly as cations (or cationic complexes), oxyanions, as salts or
oxides in crystalline form or as amorphous precipitates in insoluble
form. The microbes have the ability to bind to metal ions present in
the external environment at the cell surface and to transport them
into the cell for various intracellular functions [9]. The incidence of
life-threatening Aspergillus infections has risen in recent years [10].
Although Aspergillus fumigatus accounts for the majority of cases
∗
Corresponding author.
E-mail address: ggenidy@hotmail.com (G.G. Mohamed).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.04.005

834
S.M. Abdallah et al. / Spectrochimica Acta Part A 73 (2009) 833–840
of human aspergillosis, the number of infections caused by other
Aspergillus species has increased [11]. The emerging threat posed
by these species is especially important to understand because of
their inherent reduced susceptibility to many antifungal agents
[12]. Few reports describe Aspergillus species as a possible cause
of sternal wound infection [13].
As an extension of our work on the structural characterization
of Schiff base ligands and their metal complexes [14–17], the main
target of the present article is to study the coordination behaviour
of H2L Schiff base that incorporate several binding sites towards
Cr(III), Mn(II), Fe(III), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) ions, also to
evaluate the relative thermal stability of the synthesized complexes
and to examine their antimicrobial activity against different species
of bacteria and fungi.
2.3. Synthesis of Schiff base (H2L)
Hot solution (60 ◦C) of 2-aminophenol (2.18 g, 20 mmol) was
mixed with hot solution (60 ◦C) of o-phthaldehyde (1.34 g, 10 mmol)
in 50 mL ethanol. The resulting mixture was left under reflux for 4 h
and the solvent was evaporated till deep yellow oil product is sep-
arated. This oil is poured on ice cold HCl whereupon the yellow
crystalline product is separated. The formed solid product was sep-
arated by filtration, purified by crystallization from ethanol, washed
with diethyl ether and dried under vacuum. The yellow product is
produced in 80% yield.
2.4. Synthesis of metal complexes
The metal complexes were prepared by adding equimolar
amounts of hot solution (60 ◦C) of the appropriate metal chlo-
ride (1 mmol) in an ethanol–water mixture (1:1, 25 mL) to the hot
solution (60 ◦C) of the Schiff base (0.316 g, 1 mmol) in the same sol-
vent (25 mL). The resulting mixture was stirred under reflux for 1 h
whereupon the complexes precipitated. The resulting precipitates
were filtered off, washed several times with a 1:1 ethanol:water
mixture and diethyl ether and dried under vacuum. The analytical
data for C, H and N were repeated twice.
2. Experimental
2.1. Materials and reagents
All chemicals used were of the analytical reagent grade (AR), and
of highest purity available. They included o-phthaldehyde (Sigma);
2-aminophenol (Sigma); Cu(II) chloride dihydrate (Prolabo); Co(II)
and Ni(II) chlorides hexahydrates (BDH); ferrous chloride dihy-
drate (Sigma), Zn(II) chloride dihydrate (Ubichem), Cr(III) chloride
hexahydrate (Sigma); Mn(II) chloride and Fe(III) chloride hexahy-
drate (Prolabo). Zinc oxide and EDTA (Analar), ammonia solution
(33% v/v) and ammonium chloride were supplied from El-Nasr
pharm. Chem. Co., Egypt. Organic solvents used included absolute
ethyl alcohol, diethylether, and dimethylformamide (DMF). These
solvents were spectroscopic pure from BDH. Hydrogen peroxide,
hydrochloric and nitric acids (MERCK) were used. De-ionized water
collected from all glass equipments was usually used in all prepa-
rations.
2.5. Biological activity
2.5.1. Disc diffusion assay for Aspergillus spp.
The in vitro activity of H2L and its metal complexes was tested
against two Aspergillus spp. (Aspergillus flavus and Aspergillus niger).
The test organisms were identified to the species level by standard
methods [18] and maintained at −70 ◦C on Sabouraud dextrose agar
slant until tested. This assay employed an investigational method
that used the reference RPMI 1640 agar supplemented with 2% glu-
cose as the test medium [19]. Ten ␮g/ml of the tested compounds
were prepared by using blank paper disks (6.3 mm in diameter),
the disks were allowed to dry at room temperature prior to their
use in disk diffusion assays. The inoculum density to be used in the
test was adjusted spectrophotometrically to 106 CFU/ml. The previ-
ously prepared Schiff base and its metal complexes disks were then
placed on the inoculated plates, and the plates were incubated at
35 ◦C. The results were examined after 5 days of incubation and the
% of inhibition zone was compared to that of control.
Two Aspergillus species: A. flavus Link and A. niger V. Tiegh and
two Bacteria: Escherichia coli and Staphyllococcus aureus were used
for this study. All isolates were from Microanalytical Center, Faculty
of Science, Cairo University.
2.2. Instruments
The molar conductance of solid complexes in DMF was
measured using Sybron-Barnstead conductometer (Meter-PM.6,
E = 3406). Elemental microanalyses of the separated solid chelates
for C, H and N were performed in the Microanalytical Cen-
ter, Cairo University. The analyses were repeated twice to check
the accuracy of the data. Infrared spectra were recorded on a
PerkinElmer FT-IR type 1650 spectrophotometer in wave number
region 4000–400 cm−1. The spectra were recorded as KBr pel-
lets. The 1H NMR spectra were recorded with a JEOL EX-270 MHz
in d6-DMSO as solvent, where the chemical shifts were deter-
mined relative to the solvent peaks. The solid ESR spectra of
the complexes were recorded with ELEXSYS E500 Bruker spec-
trometer in 3 mm pyrex tubes at 298 K. Diphenylpicrydrazide
(DPPH) was used as a g-marker for the calibration of the spec-
tra. The solid reflectance spectra were measured on a Shimadzu
3101pc spectrophotometer. The molar magnetic susceptibility was
measured on powdered samples using the Faraday method. The
diamagnetic corrections were made by Pascal’s constant and
Hg[Co(SCN)4] was used as a calibrant. The thermogravimetric
analysis (TGA and DrTGA) was carried out in dynamic nitro-
gen atmosphere (20 mL min−1) with a heating rate of 10 ◦C min−1
using Shimadzu TGA-50H thermal analyzer. The mass spectra were
recorded by the EI technique at 70 eV using MS-5988 GC–MS
Hewlett-Packard instrument in the Microanalytical Center, Cairo
University.
2.5.2. Disc diffusion assay for bacteria
Disk diffusion testing was by standard NCCLS methods[20] using
Mueller–Hinton plates supplemented with sheep blood and inoc-
ulated with 0.5 McFarland standard. Disks with 10 ␮g of the tested
compounds were applied. After overnight incubation at 35 ◦C, the
inhibition zone diameters were measured.
2.5.3. Determination of MIC
Antimicrobial activities of the compounds were estimated by
a minimum inhibitory concentration (MIC, ␮g/ml) in the usual
fashion [21].The evaluation of the inhibitory effect of the Schiff
base and their complexes on the microbial growth was carried
out by the twofold serial dilution method. Mueller–Hinton broth
and Sabouraud liquid medium were employed as culture media
for bacteria and fungi, respectively. The compounds were dissolved
in dimethylsulfoxide (DMSO). Test inoculums of 5 × 104 M bacteria
ml−1 and 103 M spores ml−1 were applied. The absence of micro-
bial growth after an incubation period of 24 h at 37 ◦C for bacteria
or of 5 days at 30 ◦C for fungi was taken to be a criterion of effec-
tiveness. In every case, MIC was determined. The MIC was defined
as the lowest drug concentration that inhibits growth by 50%. The
amount of DMSO in the medium was 1% and did not affect the
growth of the microorganisms tested. There were three replicates

S.M. Abdallah et al. / Spectrochimica Acta Part A 73 (2009) 833–840
835
for each dilution. Results were always verified in three separate
experiments.
3. Results and discussion
3.1. Schiff base characterization
The Schiff base, H2L, is subjected to elemental analyses. The
results of elemental analyses (C, H and N) with molecular formula
and the melting point are presented in Table 1. The results obtained
are in good agreement with those calculated for the suggested for-
mula and the melting point is sharp indicating the purity of the
prepared Schiff base. The structure of the Schiff base under study is
given below in Fig. 1.
Fig. 1. Preparation of H2L ligand.
The structure of this Schiff base is also confirmed by IR and 1
H
3.4. IR spectra and mode of bonding
NMR spectra, which will be discussed in detailed manner together
with its metal complexes later. It takes the following IUPAC name:
2-((1))-2-{2-[(1)-2-aza-2-2-(2-hydroxyphenyl)vinyl]phenyl}-1-
azavinyl)phenol.
The IR data of the spectra of H2L Schiff base and its complexes
are listed in Table 2. Upon comparison it was found that the azome-
thine ꢂ(C = N) stretching vibration is found in the free ligand at
1642 cm−1. This band is shifted to 1654–1657 cm−1 in the com-
plexes indicating the participation of the azomethine nitrogen in
coordination (M–N) [15]. The ꢂ(OH), ꢂ(C–O) and ı(OH) vibrations
are observed at 3068, 1243 and 1456 cm−1 for H2L. The existence
of water of hydration and/or water of coordination in the spec-
tra of the complexes render it difficult to get conclusion from the
ꢂ(OH) group of the H2L ligand, which will be overlapped by those
of the water molecules. The participation of the OH group is further
confirmed by clarifying the effect of chelation on the ꢂ(C–O) and
in-plane bending, ı(OH) vibrations. The participation of the phe-
nolic O atom in the complex formation was proved by the shift in
position of these bands to 1239–1246 and 1450–1452 cm−1 [22].
New bands are found in the spectra of the complexes in the regions
468–530, which are assigned to ꢂ(M–O) stretching vibrations. The
bands at 417–472 have been assigned to ꢂ(M–N) mode.
3.2. Composition and structure of Schiff base complexes
The isolated solid complexes of Cr(III), Mn(II), Fe(II), Fe(III),
Co(II), Ni(II), Cu(II) and Zn(II) ions with the Schiff base H2L lig-
and were subjected to elemental analyses (C, H, N and metal
content), IR, magnetic studies, ESR, 1H NMR, molar conductance
and thermal analysis (TGA), to identify their tentative formulae
in a trial to elucidate their molecular structures. The elemen-
tal analyses confirm that the complexes have 1:1 molar ratio
between the metal ions and the ligand. The results of elemental
analyses listed in Table 1 suggest the proposed general formu-
lae of the prepared complexes as: [MCl(L)(H2O)]·yH2O (M = Cr(III),
Fe(III); y = 1–2), [M(L)(H2O)2]·yH2O (M = Co(II), Ni(II); y = 0–2) and
[M(L)]·yH2O (M = Mn(II), Fe(II), Cu(II), Zn(II); y = 0–2). The com-
plexes are found to be insoluble in common organic solvents such
as ethanol, methanol, acetone, 1,4-dioxane, water and chloroform
but soluble in DMF and DMSO.
Therefore, the above arguments together with the elemental
analyses indicated that H2L ligand behaves as a dibasic tetraden-
tate ligand coordinated to the metal ions via the azomethine N and
deprotonated phenolic O.
3.3. Molar conductivity measurements
The molar conductivities of 10−3 M solutions of the dis-
solved chelates in DMF are measured at 25 ◦C and listed
in Table 1. The molar conductance values are found to be
9.21–14.55 ꢁ−1 mol−1 cm2 indicating that, these chelates are non-
electrolytes.
3.5. 1H NMR spectra
The chemical shifts of the different types of protons in the 1H
NMR spectra of the H2L ligand and its diamagnetic Zn(II) complex
are listed in Table 3. Upon examinations it is found that the phe-
Table 1
Analytical and Physical data of H2L ligand and its metal complexes.
−1
mol−1 cm2
Compound
m.p. (◦C)
Colour (% yield)
% Found (calcd.)
ꢃeff. (B.M.)
ꢄm
˝
C
H
N
M
–
H2L
100
>300
>300
>300
>300
>300
>300
>300
>300
Yellow
(80)
Brown
(69)
Brown
(68)
Yellowish brown
(63)
Yellowish brown
(63)
Reddish brown
(59)
Brown
(66)
Green
68.09
4.41
6.94
–
–
(C20H16 N2O2)
[CrCl(L)(H2O)]·H2O
C20H18 ClCrN2O4
[Mn(L)]·H2O
(67.97)
54.87
(54.61)
61.77
(62.18)
64.90
(64.87)
51.97
(52.23)
58.86
(58.68)
53.60
(53.90)
57.77
(58.04)
63.52
(4.01)
3.79
(4.10)
4.22
(4.15)
3.39
(3.78)
4.56
(4.35)
4.80
(4.40)
4.72
(4.94)
4.22
(4.35)
3.36
(6.60)
6.58
(6.37)
7.45
(7.25)
7.98
(7.57)
6.19
(6.09)
7.00
(6.85)
6.41
(6.29)
6.76
(6.77)
7.55
11.99
(12.29)
14.05
(13.99)
15.08
(15.14)
12.48
(12.19)
14.62
(14.43)
13.56
(13.26)
15.23
(15.36)
17.07
4.15
10.96
14.55
9.21
C20H16 MnN2O3
4.69
4.89
5.69
5.72
3.44
1.98
Diam.
[Fe(L)]
C20H14 FeN2O2
[FeCl(L)(H2O)]·2H2O
C20H20ClFeN2O5
[Co(L)(H2O)2]
C20H18 CoN2O4
[Ni(L)(H2O)2]·2H2O
C20H22NiN2O6
[Cu(L)]·2H2O
C20H18 CuN2O4
[Zn(L)]
11.33
11.75
12.45
14.16
13.11
(60)
Brown
(58)
C20H14 N2O2Zn
(63.32)
(3.69)
(7.39)
(17.15)

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S.M. Abdallah et al. / Spectrochimica Acta Part A 73 (2009) 833–840
Table 2
Table 4
IR spectra (4000-400 cm−1) of the H2L ligand and its metal complexes.
ESR parameters for H2L metal complexes.
Compound
ꢅ(OH)
ꢅ(C–O) ı(OH)
ꢅ(CH N) ꢅ(M–O) ꢅ(M–N)
Complex
g
||
g
⊥
agiso/av
bG
H2L
3068br 1243m 1456m 1642sh
3179br 1240m 1452m 1656sh
–
–
[Mn(L)]·H2O
[Fe(L)]
4.751
2.346
2.202
2.44
2.296
4.765
3.295
2.261
3.114
3.959
2.931
2.321
9.294
0.125
0.156
1.686
[CrCl(L)(H2O)]·H2O
[Mn(L)]·H2O
[Fe(L)]
530s
545s
478s
472s
471m
468m
515w
472s
460w
472s
430w
430w
421s
417w
472s
421s
3176br
1240m 1452m 1655sh
[FeCl(L)(H2O)]·2H2O
3139br 1240m 1451m 1655sh
[Cu(L)]·2H2O
[FeCl(L)(H2O)]·2H2O 3152br 1239m 1451sh 1654sh
a3giso = (g + g + 2).
⊥
||
[Co(L)(H2O)2]
[Ni(L)(H2O)2]·2H2O
[Cu(L)]·2H2O
[Zn(L)]
3142br 1246m 1453m 1657sh
3140br 1240m 1451m 1655sh
3139br 1246m 1450m 1657sh
3199br 1240m 1451m 1655sh
bG = (g − 2)/(g⊥ − 2).
|
The Ni(II) complex reported herein has a room temperature
magnetic moment value of 3.44 B.M.; which is in the normal
range observed for octahedral Ni(II) complexes [23]. This indi-
cates that, the complexes of Ni(II) are six coordinate and probably
sh = sharp, m = medium, s = small, w = weak, br = broad.
nolic OH signal is found at 9.80 ppm in the spectrum of H2L ligand.
This signal is disappeared in case of [Zn(L)] complex indicating the
participation of the phenolic OH group in chelation with proton
displacement.
octahedral [23]. The electronic spectrum displays three bands,
in the solid reflectance spectrum at ꢅ1:15,700 cm−1:3A2g → T2g
;
3
ꢅ2:17,655 cm−1:3A2g → T1g (F) and ꢅ3:21,202 cm−1:3A2g→ T1g (P).
The spectrum shows also a band at 23,870 cm−1 which may be
attributed to ligand-metal charge transfer. The ꢃeff = 1.98 B.M. of
the Cu(II) complex indicates the square planar geometry. The con-
firmation of this structure is obtained by the appearance of a band
at 14,875 cm−1 and two shoulders at 18,962 and 12,085 cm−1. These
3
3
3.6. Magnetic susceptibility and electronic spectra measurements
The diffused reflectance spectrum of the Cr(III) chelate shows
three absorption bands at 18,975 (ꢅ1), 27,240 (ꢅ2), and 28,860 cm−1
(ꢅ3) which are assigned to the three spin allowed transitions in
2
2
2
2
2
are assigned to B1g → A1g
,
2B1g → B2g and B1g → E2g transi-
the electronic spectrum, ꢅ1:4A2g → T2g, ꢅ2:4A2g → T2g (F), and
4
4
tions, respectively [23]. A moderately intense peak observed at
24,895 cm−1 is due to ligand-metal charge transfer.
ꢅ3:4A2g → T1g (P) [23]. The electronic spectrum of this Cr(III)
4
The Zn(II) complex is diamagnetic and according to the empirical
formula, it is proposed to have a tetrahedral geometry.
chelate is in reasonable agreement with those reported in the liter-
ature [23]. The magnetic moment of this chelate measured at room
temperature is 4.15 B.M., and corresponds to the expected value
for octahedral Cr(III) complexes [23]. The diffused reflectance spec-
trum of the Mn(II) complex shows three bands at 16,645, 22,765 and
3.7. Electron spin resonance spectra (ESR)
27,765 cm−1 assignable to A1g → T1g
,
6A1g → T2g (G) and 6A1 →
6
4
4
The ESR data are listed in Table 4. The ESR spectra of the Cu(II)
complex at room temperature exhibits anisotropic signals with g
value g = 2.44 and g = 2.261 (Fig. 2 and Table 4) which is charac-
4T2g (D) transitions, respectively [23]. The magnetic moment value
is4.69 B.M., whichindicatesthepresenceofMn(II)complexin tetra-
hedral structure.
||
⊥
teristic for axial symmetry [25]. Since the g and g values are closer
||
⊥
to 2 and g > g suggesting a tetragonal distortion around Cu(II) ion
From the diffused reflectance spectrum, it is observed that,
||
⊥
the Fe(III) chelate exhibit a band at 20,750 cm−1, which may be
corresponding to elongation along the fourfold symmetry Z-axis
assigned to the 6A1g → T2g (G) transition in octahedral geometry of
[26]. The trend g > g > ge (2.0023) shows that the unpaired elec-
tron in localized in the dx2-y2 orbital of the Cu(II) ion in complexes
[27]. In addition, exchange coupling interaction between two Cu(II)
||
⊥
6
the Fe(III) complexes [24]. The A1g
→
5T1g transition appears to
be split into two bands at 17,876 and 14,980 cm−1. The observed
magnetic moment of Fe(III) complex is 5.69 B.M. Thus, the com-
plexes formed have the octahedral geometry [23]. The spectrum
shows also a band at 28,331 cm−1 which may attribute to ligand to
metal charge transfer. The electronic spectrum of the Fe(II) com-
plex displays two absorption bands at 16,540 and 18,670 cm−1 that
ions is explained by Hathaway expression G = (g − 2)/(g⊥ − 2).
||
When the value G < 4.0, a considerable exchange coupling is present
in solid complex (G = 1.686) [25]. Kivelson and Neiman showed that
for an ionic environment g is normally 2.3 or larger, but for cova-
lent environment g are less than 2.3. The g value for the Cu(II)
complex is 2.44, consequently the environment is essentially ionic.
The ESR spectra of the solid Co(II), Ni(II) and Zn(II) complexes at
room temperature do not show ESR signal because the rapid spin
lattice relaxation of the Co(II), Ni(II) and Zn(II) (Fig. 3) broadness
||
||
||
5
are assigned to 5Eg → T2g (D) transition [17]. In addition, the band
at 24,495 cm−1 is assigned to L → M charge transfer. The observed
magnetic moment of 4.89 B.M. is assigned to tetrahedral geometry
[17].
The electronic spectrum of the Co(II) complex gives three bands
at 16,666, 18,785 and 22,330 cm−1. The bands observed are assigned
4
4
4
4
to the transitions T1g (F) → T2g (F) (ꢅ1), T1g (F) → A2g (F) (ꢅ2)
4
4
and T1g (F) → T2g (P) (ꢅ3), respectively, suggesting that there is
an octahedral geometry around Co(II) ion [23,22]. The magnetic
susceptibility value of 5.72 B.M. indicates an octahedral geome-
try [23,22]. The band at 24,680 cm−1 refers to the charge transfer
occurring in this complex.
Table 3
1H NMR data of H2L and its Zn(II) complexs.
Compound
H2L
␦ (ppm)
Assignments
9.80
8.089
6.386–7.779
8.12
6.42–7.775
(br, 2H, Phenolic OH)
(s, 2H, –CH N)
(m, 12H, ArH)
(s, 2H, –CH N)
(m, 12H, ArH)
[Zn(L)]
Fig. 2. ESR of Cu(II)-H2L complex.

S.M. Abdallah et al. / Spectrochimica Acta Part A 73 (2009) 833–840
837
The TGA curves of the Co(II) and Ni(II)-chelates show three to
four stages of decomposition within the temperature ranges of
30–1000 and 30–900 ◦C, respectively. For Ni(II) complex, the first
stage at 30–130 ◦C corresponds to the loss of water molecules of
hydration. The value of energy of activation for this dehydration
step was found to be = 49.75 kJ mol−1. While the subsequent stages
involved the loss of coordinated H2O and ligand molecules with a
mass loss of 81.91% (calcd. 81.66%) and 75.71% (calcd. 75.06%) for
Co(II) and Ni(II) complexes, respectively. The overall weight loss
amounts to 81.91% (calcd. 81.66%) and 84.17% (calcd. 83.15%) for
Co(II) and Ni(II) chelates, respectively.
On the other hand, [M(L)] (M = Fe(II) and Zn(II)) chelates
exhibit three decomposition steps within the temperature range
70–1000 ◦C (mass loss = 79.99%; calcd. 80.54%) and 120–1000 ◦C
(mass loss = 78.95%; calcd. 78.63%) which may accounted for the
thermal decomposition of H2L molecule in three steps in each
complex leaving metal oxides as a residue for Fe(II) and Zn(II) com-
plexes, respectively. The energies of activation for these six steps
(three in each complex) were found to be = 60.55, 117.6 and 176.9
and 60.88, 82.99 and 162.5 kJ mol−1 for Fe(II) and Zn(II) complexes,
respectively.
Each of [Mn(L)]·H2O and [Cu(L)]·2H2O complexes were ther-
mally decomposed in four steps within the temperature range from
40 to 1000 and 30 to 700 ◦C, respectively. The first decomposi-
tion step with an estimated mass loss of 4.95% (calcd. 4.66%) and
8.85% (calcd. 8.71%) occurred within the temperature range from
40 to 110 and 30 to 130 ◦C for Mn(II) and Cu(II) complexes, respec-
tively. This step may be attributed to the liberation of the hydrated
water molecules. The activation energy values for these losses
were = 30.46 and 53.65 kJ mol−1 for Mn(II) and Cu(II) complexes,
respectively. The remaining three decomposition steps of each com-
plex were observed within the temperature ranges from 110 to 1000
and 140 to 700 ◦C for Mn(II) and Cu(II) complexes, respectively. The
estimated mass losses of 77.06% (calcd. 77.20%) and 73.08% (calcd.
72.07%) are reasonably accounted for the removal of H2L ligand in
three steps for each complex as gases, for Mn(II) and Cu(II) com-
plexes, respectively. Theactivation energies for these six losseswere
78.64, 169.8 and 233.4 and 95.99, 147.6 and201.5 kJ mol−1 for the
second, third and fourth steps, respectively.
Fig. 3. ESR of Zn(II)-H2L complex.
the lines at higher temperatures [25]. The ESR spectra only show
signals that may be accounted for the presence of free radicals that
can resulted from the cleavage of any double bond and distribution
of the charge on the two neighbor atoms.
The ESR spectrum of the Mn(II) complex (Table 3) at room tem-
perature give two signals with g = 4.751 and g = 2.296. This finding
||
⊥
indicates that the complex is tetrahedral which is in agreement with
the data of solid reflectance and magnetic moment measurements
[25]. The ESR spectrum of the [FeCl(L)(H2O)]·2H2O complex showed
two signals observed at g values 2.202 and 3.295. These values can
be respected as the signal of high spin state of the Fe(III) (S = 5/2)
[25].
3.8. Thermal analyses (TGA and DrTGA)
The thermal analysis data are listed in Table 5 and the calculated
thermodynamic parameters from DrTGA are listed in Table 6.
The thermograms of [MCl(L)(H2O)3]·xH2O chelates (M = Cr(III)
(x = 1) and Fe(III) (x = 2)) show four decomposition steps within
the temperature range 30–1000 ◦C. The first step of decomposition
within the temperature ranges 30–120 and 30–250 ◦C corresponds
to the loss of hydrated and coordinated water molecules with a
mass loss of 4.65% (calcd. 4.10%) and 11.51% (calcd. 11.75%) for Cr(III)
and Fe(III) complexes, respectively. The energy of activation val-
ues were 43.65 and 52.15 kJ mol−1 for Cr(III) and Fe(III) complexes,
respectively. The subsequent weight loss steps (120–1000 or
250–1000 ◦C) correspond to the removal of HCl, coordinated H2O
and the organic part of the ligand leaving metal oxide as a residue.
The overall weight losses are found to be 83.35% (calcd. 82.71%) and
82.52% (calcd. 82.59%) for Cr(III) and Fe(III) complexes, respectively.
3.9. Kinetic data
The thermodynamic activation parameters of decomposition
processes of dehydrated complexes namely activation energy (E*),
enthalpy (ꢀH*), entropy (ꢀS*) and Gibbs free energy change of
the decomposition (ꢀG*) were evaluated graphically by employ-
ing the Coats-Redfern relation [28]. The entropy of activation (ꢀS*),
enthalpy of activation (ꢀH*) and the free energy change of activa-
tion (ꢀG*) were calculated and the data are summarized in Table 6.
Table 5
Thermal analyses (TGA) results of H2L and its chelates.
Complex
Temp. range (◦C)
n#
Mass loss total mass loss % found (calcd)
Assignment
Metallic residue
1/2Cr2O3
[CrCl(L)(H2O)]
H2O
[Mn(L)]·H2O
30–120
120–1000
40–110
110–1000
70–1000
30–250
250–1000
100–1000
30–130
130–900
30–150
1.0
3.0
1.0
3.0
3.0
1.0
3.0
3.0
1.0
3.0
1.0
3.0
3.0
4.65 (4.10)
78.70 (78.61) 83.35 (82.71)
4.95 (4.66)
77.06 (77.20) 82.01 (81.86)
79.99 (80.54)
11.51 (11.75)
71.01 (70.84) 82.52 (82.59)
81.91 (81.66)
8.46 (8.09)
75.71 (75.06) 84.17 (83.15)
8.85 (8.71)
73.08 (72.07) 81.93 (80.78)
78.95 (78.63)
Loss of H2O.
Loss of HCl, H2O and L
Loss of H2O.
Loss of L.
Loss of L.
Loss of 3H2O.
Loss of HCl and L.
Loss of 2H2O and L
Loss of 2H2O.
Loss of 2H2O and L.
Loss of 2H2O.
Loss of L.
MnO
FeO
1/2Fe2O3
[Fe(L)]
[FeCl(L)(H2O)]
2H2O
[Co(L)(H2O)2]
[Ni(L)(H2O)2]
2H2O
[Cu(L)]·2H2O
CoO
NiO
150–700
120–1000
CuO
ZnO
[Zn(L)]
Loss of L.
n
# = number of decomposition steps.

838
S.M. Abdallah et al. / Spectrochimica Acta Part A 73 (2009) 833–840
Table 6
The calculated thermodynamic parameters for the thermal decomposition data of H2L metal complexes.
Complex
TG range (◦C)
E* (kJ mol−1
)
A (S−1
)
ꢀS* (JK−1 mol−1
)
ꢀH* (kJ mol−1
)
ꢀG* (kJ mol−1
)
[CrCl(L)(H2O)]
H2O
30–120
120–380
380–670
670–1000
43.65
92.86
192.5
115.7
4.32 × 107
2.95 × 1011
5.42 × 108
3.66 × 109
−44.63
−82.67
−126.3
−174.2
54.35
127.2
145.4
197.4
77.43
156.2
189.3
235.6
[Mn(L)]·H2O
40–110
110–300
300–650
650–1000
30.46
78.64
169.8
233.4
4.07 × 106
6.59 × 1010
6.09 × 1011
5.23 × 108
−34.99
−95.83
−152.4
−166.8
42.88
109.7
162.5
201.1
54.56
138.7
182.7
243.3
[Fe(L)]
70–320
320–700
700–1000
60.55
117.6
176.9
3.18 × 109
4.50 × 1010
6.75 × 107
−49.84
−80.95
−143.7
73.62
145.2
186.7
86.26
187.1
223.6
[FeCl(L)(H2O)]
2H2O
30–250
250–520
520–730
730–1000
52.15
105.9
182.4
256.3
5.16 × 108
4.08 × 109
6.56 × 1011
7.56 × 107
−60.38
−108.3
−157.6
−196.2
66.42
126.3
192.4
260.5
73.39
139.3
203.9
269.8
[Co(L)(H2O)2]
100–240
240–640
640–1000
63.95
95.19
127.9
3.09 × 1010
7.92 × 107
4.69 × 1013
−53.46
−109.2
−152.9
72.76
147.6
198.9
96.86
175.7
230.4
[Ni(L)(H2O)2]
2H2O
30–130
130–320
320–750
750–900
49.75
75.97
147.2
199.2
3.13 × 107
4.17 × 1010
3.75 × 1012
6.97 × 108
−50.33
−89.77
−140.3
−176.5
77.72
133.2
186.7
250.1
95.53
140.2
222.4
260.5
[Cu(L)]·2H2O
30–150
150–330
330–520
520–700
53.65
95.99
147.6
201.5
1.43 × 1013
6.37 × 1011
4.22 × 106
7.32 × 1084
−33.66
−90.97
−142.3
−172.3
48.97
116.2
176.4
205.3
69.86
138.86
189.7
250.3
[Zn(L)]
120–330
330–640
640–1000
60.88
82.99
162.5
7.85 × 109
4.99 × 108
5.96 × 1010
−40.75
−80.08
−136.6
59.66
109.7
158.8
73.36
121.99
192.4
The activation energies of decomposition were found to be in the
range 22.95–243.4 kJ mol−1. The high values of the activation ener-
gies reflect the thermal stability of the complexes. The entropy of
activation was found to have negative values in all the complexes,
which indicates that the decomposition reactions proceed with a
lower rate than the normal ones.
conclusion, the investigated Schiff base behaves as a tetradentate
and its metal complexes structurs can be given as shown below
(Fig. 4).
3.11. Biological activity
In testing the antimicrobial activity of these compounds, we
used more than one test organism to increase the chance of detect-
ing antibiotic principles in the tested materials. The sensitivity
of a microorganism to antibiotics and other antimicrobial agents
was determined by the assay plates. Metal complexes: Mn(II),
Fe(II), Fe(III), Cu(II) and Zn(II) virtually lack any noticeable anti-
fungal activities. A detectable antifungal activity was observed in
case of using H2L, Cr(III), Co(II) and Ni(II) at concentrations above
3.10. Structural interpretation
The structures of the complexes of Schiff base with Cr(III), Mn(II),
Fe(III), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) ions were confirmed
by the elemental analyses, IR, molar conductance, magnetic, solid
reflectance and thermal analysis data. Therefore, from the IR spec-
tra, it is concluded that H2L behaves as a bi-negatively tetradentate
ligand coordinated to the metal ions via the azomethine N and
deprotonated phenolic-O. From the molar conductance data, it is
found that the complexes are non-electrolytes. On the basis of the
above observations and from the magnetic and solid reflectance
measurements, octahedral, terahderal and square planar geome-
tries are suggested for the investigated complexes. As a general
50 ␮g ml−1
.
With regard to A. flavus, Table 7 shows that the parent Schiff base
and four of its metal complexes could inhibit the growth where the
inhibition zone diameter follow the order Ni(II) (31 mm) > Cr(III)
(26 mm) > Co(II) (17 mm) > parent Schiff base (16 mm) > cefepime
standard (12 mm). With respect to A. niger, the parent schiff
Fig. 4. Proposed structures of metal complexes.

S.M. Abdallah et al. / Spectrochimica Acta Part A 73 (2009) 833–840
839
Table 7
Antifungal assay of H2L and its metal complexes.
Aspergillus flavus
Aspergillus niger
Compounds
Inhibition zone diameter (mm)
Inhibition (%)
Inhibition zone diameter (mm)
Inhibition (%)
Control
H2L
[CrCl(L)(H2O)]·H2O
[Mn(L)]·H2O
[Fe(L)]
0
16
26
0
0
17.7
28.8
0
0
15
24
0
0
16.6
26.6
0
0
0
0
0
[FeCl(L)(H2O)]·2H2O
[Co(L)(H2O)2]
[Ni(L)(H2O)2]·2H2O
[Cu(L)]·2H2O
[Zn(L)]
0
0
0
19
28
0
0
17
31
0
18.8
34.4
0
21.1
31.1
0
0
0
0
0
Cefepime
12
13.3
10
11
L.S.D. 1% 5%
2.471.52
2.251.29
Table 8
Antibacterial assay of H2L and its metal complexes.
Escherichia coli
Staphylococcus aureus
Compounds
Inhibition zone diameter (mm)
Inhibition (%)
Inhibition zone diameter (mm)
Inhibition (%)
Control
H2L
0
0
0
0
0
0
0
0
[CrCl(L)(H2O)]·H2O
[Mn(L)]·H2O
[Fe(L)]
14
12
0
15.5
13.3
0
11
10
0
12.2
11.1
0
[FeCl(L)(H2O)]·2H2O
[Co(L)(H2O)2]
[Ni(L)(H2O)2]·2H2O
[Cu(L)]·2H2O
[Zn(L)]
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Cefepime
10
11
8
8.87
Fig. 5. Determination of MIC of H2L and its metal complexes on the growth of
Aspergillus flavus by disk diffusion method.
Fig. 6. Determination of MIC of H2L and its metal complexes on the growth of
Aspergillus niger by disk diffusion method.
Table 9
Antimicrobial activities of the compounds tested as evaluated by the minimum
inhibitory concentration (MIC, ␮g/ml).
base and four of its metal complexes inhibited the growth. The
inhibition was attained in the order Ni(II) > Cr(III) > Co(II) > Schif
base > cefepime standard where the inhibition zones were 28, 24,
19, 15 and 10 mm in diameter, respectively.
H2L and some metal complexes: Fe(II), Fe(III), Cu(II), Co(II)
and Zn(II) virtually lack any noticeable antibacterial activities. The
antibacterial activity of H2L ligand and its metal complexes was car-
ried out and the data obtained are shown in Table 8. With regard
to S. aureus (Gram-positive), the data show that only two metal
complexes inhibited the growth where the inhibition zone diame-
ters reached 11 and 10 mm in case of Cr(III) and Mn(II) complexes,
respectively. Their biological activities are higher that of cefepime
standard (inhibition zone is found to be 8 mm).
Test organism
H2L
Cr(II)
Mn(II)
Co(II)
Ni(II)
Aspergillus flavus
Aspergillus niger
Escherichia coli
120
150
0
55
65
120
100
0
0
130
105
110
140
0
70
80
0
Staphyllococcus aureus
0
0
0
3.12. Determination of MIC
Regression analysis was carried out for data. The correlation
coefficient (r2) was calculated to measure the strength of the rela-
tion between two variables x and y. The equation of the regression
line was given. Figs. 5 and 6 show determination of MIC of H2L and
its metal complexes on the growth of A. flavus (Fig. 5) and A. niger
(Fig. 6) by disk diffusion method.
With regard to E. coli (Gram-negative), the data in Table 8 shows
that only two metal complexes together with the cefipime standard
inhibited the growth where the inhibition zone diameters reached
14, 12 and 10 mm in case of Cr(III), Mn(II) complexes and cefepime
standard, respectively.
In case of A. flavus, Table 9 shows that Cr(III) showed the least
MIC (55 ␮g/ml), followed by Ni(II) (70 ␮g ml−1), Co(II) (110 ␮g ml−1
)
and H2L (120 ␮g ml−1). In case of A. niger, Table 9 shows that Cr(III)

840
S.M. Abdallah et al. / Spectrochimica Acta Part A 73 (2009) 833–840
showed the least MIC (65 ␮g ml−1), followed by Ni(II) (80 ␮g ml−1),
Co(II) (140 ␮g ml−1) and H2L (150 ␮g ml−1). The complexation with
Cr(III) and Ni(II) ions can somewhat increase the activities of H2L
against the tested fungal species.
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