Spectroscopic characterization of metal complexes of novel Schiff base. Synthesis, thermal and biological activity studies

Article abstract of DOI:10.1016/j.saa.2009.02.043

Novel Schiff base (HL) ligand is prepared via condensation of 4-aminoantipyrine and 2-aminobenzoic acid. The ligand is characterized based on elemental analysis, mass, IR and ¹H NMR spectra. Metal complexes are reported and characterized based

Full text of DOI:10.1016/j.saa.2009.02.043

Spectrochimica Acta Part A 73 (2009) 358–369
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Spectroscopic characterization of metal complexes of novel Schiff base.
Synthesis, thermal and biological activity studies
M.M. Omar∗, Gehad G. Mohamed, Amr A. Ibrahim
Chemistry Department, Faculty of Science, Cairo University, Giza 12613, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel Schiff base (HL) ligand is prepared via condensation of 4-aminoantipyrine and 2-aminobenzoic acid.
The ligand is characterized based on elemental analysis, mass, IR and 1H NMR spectra. Metal complexes are
reported and characterized based on elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment,
molar conductance and thermal analyses (TGA, DrTGA and DTA). The molar conductance data reveal that
all the metal chelates are non-electrolytes. IR spectra show that HL is coordinated to the metal ions in a
uninegatively tridentate manner with NNO donor sites of the azomethine N, amino N and deprotonated
caroxylic-O. From the magnetic and solid reflectance spectra, it is found that the geometrical structures
of these complexes are octahedral. The thermal behaviour of these chelates shows that the hydrated
complexes losses water molecules of hydration in the first step followed immediately by decomposition
of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters,
such as, E*, ꢀH*, ꢀS* and ꢀG* are calculated from the DrTG curves using Coats–Redfern method. The
synthesized ligands, in comparison to their metal complexes also were screened for their antibacterial
activity against bacterial species, Escherichia Coli, Pseudomonas aeruginosa, Staphylococcus Pyogones and
Fungi (Candida). The activity data show that the metal complexes to be more potent/antibacterial than
the parent Shciff base ligand against one or more bacterial species.
Received 28 September 2008
Received in revised form 17 February 2009
Accepted 20 February 2009
Keywords:
4-Aminoantipyrine
2-Aminobenzoic acid
Transition metal complexes
IR
Molar conductance
Solid reflectance
Magnetic moment
Thermal analyses
Biological activity
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
metallocenters in order to elucidate the factors that determine
the reversible binding and activation of O2 in various natural oxy-
The Schiff base ligands with sulphur and nitrogen donor atoms
in their structures act as good chelating agents for the transition and
non-transition metal ions [1–4]. Coordination of such compounds
with metal ions, such as copper, nickel and iron, often enhance
their activities [5], as has been reported for pathogenic fungi [6].
There is a continuing interest in metal complexes of Schiff bases.
Because of the presence of both hard nitrogen or oxygen and soft
sulphur donor atoms in the backbones of these ligands, they readily
coordinate with a wide range of transition metal ions yielding sta-
ble and intensely coloured metal complexes, some of which have
been shown to exhibit interesting physical and chemical proper-
ties [7] and potentially useful biological activities [8]. Many reports
are available for the preparation and properties of model copper
complexes which mimic copper-containing metalloproteins such
as hemocyanine and tyrosinase. Two noticeable properties of cop-
per proteins are an intense absorption band [9] near 600 nm and
relatively high copper(II)/copper(I) reduction potentials [7]. Atten-
tion was particularly focused on their correlation with the active
site of metalloenzymes and metalloproteins containing dinuclear
gen transport systems and mono- and dioxygenases and to mimic
their activity [9]. Schiff bases [10] were still regarded as one of the
most potential group of chelators for facile preparations of metallo-
organic hybrid materials. In the past two decades, the properties
of Schiff base metal complexes stimulated much interest for their
noteworthy contributions to single molecule-based magnetism,
material science [11], catalysis of many reactions like carbonyla-
tion, hydroformylation, oxidation, reduction and epoxidation [12],
their industrial applications [13], complexing ability towards some
toxic metals [14]. The interest in Schiff base compounds as analyti-
cal reagents is increasing since they enable simple and unexpensive
determinations of different organic and inorganic substances [15].
The high affinity for the chelation of the Schiff bases towards the
transition metal ions is utilized in preparing their solid complexes.
The present study describes the chelation behaviour of Schiff
base derived from the condensation of 4-aminoantipyrine with 2-
aminobenzoic acid (HL) towards some transition elements, which
may help in more understanding of the mode of chelation of HL
towards metals. For this purpose the complexes of Fe(III), Co(II),
Ni(II), Cu(II), Zn(II), UO2(II), Mn(II) and Th(IV) ions with HL are
studied in solution and in the solid state. The stability constants
are evaluated and structure of the studied complexes is elucidated
using elemental analyses, IR, 1H NMR, solid reflectance, magnetic
∗
Corresponding author. Tel.: +2 0109174425; fax: +2 0235727556.
E-mail address: mmomar27@yahoo.com (M.M. Omar).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.02.043

M.M. Omar et al. / Spectrochimica Acta Part A 73 (2009) 358–369
359
Center, Cairo University. The 1H NMR spectra were recorded using
300 MHz Varian-Oxford Mercury. The deuterated solvent used was
dimethylsulphoxide (DMSO) and the spectra extended from 0 to
15 ppm. The thermal analyses (TGA and DTA) were carried out in
dynamic nitrogen atmosphere (20 mL min−1) with a heating rate of
10 ◦C min−1 using Shimadzu TGA-50H and DTA-50H thermal ana-
lyzers.
moment, molar conductance, and thermal analyses (TGA, DrTGA
and DTA) measurements. The biological activity of the parent Schiff
base and its metal complexes is reported.
2. Experimental
2.1. Materials and reagents
All chemicals used were of the analytical reagent (AR) grade,
and of highest purity available. They included 4-aminoantipyrine
(Sigma) and 2-aminobenzoic acid (Aldrich). Cu(II)Cl2·2H2O
(Sigma), Co(II)Cl2·6H2O and Ni(II)Cl2·6H2O (BDH); MnCl2 (sigma),
ThCl4 (Aldrich), ZnCl2·2H2O (Ubichem), UO2(AcO)2·2H2O (Sigma)
and FeCl3·6H2O (Prolabo) were used. Organic solvents used
included absolute ethyl alcohol, diethylether and dimethylfor-
mamide (DMF). These solvents were spectroscopic pure from BDH.
Hydrogen peroxide and chloride, carbonate and hydroxide salts
of sodium (A.R.) were used. Hydrochloric and nitric acids (Merck)
were used. De-ionized water collected from all glass equipments
was usually used in all preparations.
2.4. Procedures
2.4.1. Potentiometric measurements
The potentiometric measurements were carried out at 25 ◦C and
ionic strength ꢁ = 0.1 M by the addition of appropriate amounts of
1 M sodium chloride solution. The pH-meter was calibrated before
each titration using standard buffers. The ionization constants of
the investigated Schiff base and the stability constants of their metal
chelates with Fe(III), Co(II), Ni(II), Cu(II), Zn(II), UO2(II), Mn(II) and
Th(IV) ions were determined potentiometrically using the tech-
nique of Sarin and Munshi [17]. For this purpose three solution
mixtures of total volume 50 mL were prepared. Thus,
2.2. Solutions
(A) 3 mL of standard HCl (0.10 M) + 5 mL 1 M NaCl + 25 mL ethanol
and the volume was completed up to 50 mL with distilled water.
(B) 3 mL of 0.10 M HCl + 5 mL 1 M NaCl + 25 mL 0.001 M of ethanolic
solution of the Schiff base (HL) and the volume was completed
to 50 mL with distilled water.
(C) 3 mL of 0.10 M HCl + 5 mL 1 M NaCl + 25 mL 0.001 M of ethanolic
solution of the Schiff base + 5 mL 0.001 M metal ion solution and
the volume was completed to 50 mL with distilled water.
Fresh stock solution of 5 × 10−3 M ligand was prepared by
dissolving the accurately weighed amount of 0.161 g/L in the appro-
priate volume of absolute ethanol. 5 × 10−3 M Stock solutions of
the metal salts (Fe(III), 0.271 g/L; Co(II), 0.238 g/L; Ni(II), 0.238 g/L;
Cu(II), 0.218 g/L; Zn(II), 0.219 g/L; UO2(II), 0.50 g/L, Mn(II), 0.170 g/L
and Th(IV), 0.316 g/L) were prepared by dissolving the accurately
weighed amounts of the metal salts in the appropriate volume of
de-ionized water. The metal salt solutions were acidified and stan-
dardized by the recommended procedures [16].
Dilute solutions of the metal ions and Schiff base under study of
2.5 × 10−6 M, 1 × 10−6 M, 2.5 × 10−5 M, 1 × 10−5 M, and 1 × 10−4 M
were prepared by accurate dilution. For potentiometric studies, all
solutions of metal ions were prepared by dissolving the calculated
amount of their salts in the least amount of water, then ethanol
was added to the appropriate volume. Standard 0.1N sodium car-
bonate solution was prepared from dried sodium carbonate. 0.1N
hydrochloric acid was prepared and standardized using sodium car-
bonate. 1.00 M sodium chloride solution was also prepared. A 1:1
sodium hydroxide solution was prepared from A.R. product and
stored in a well steamed waxed tall glass cylinder for some days
with occasional shaking to obtain a carbonate free sodium hydrox-
ide solution. The clear solution was filtered through a sintered glass
funnel G4. Solutions of the required molarity were prepared by
dilution and then standardized by recommended procedure [16].
The above three mixtures were titrated potentiometrically
against standard sodium hydroxide solution (0.10 M). The molar-
ities of HCl and NaOH were checked every day before the titrations.
The appropriate volume of ethanol was added so as to keep the ratio
50% (v/v) ethanol/water, constant to ensure the complete solubili-
ties of the Schiff base during the titration. The three curves obtained
were referred to as: (A) acid titration curve, (B) ligand titration curve
and (C) complex titration curve.
2.4.2. Synthesis of Schiff base (HL)
Hot solution (60 ◦C) of 4-aminoantipyrine (5 g, 24.88 mmol) was
mixed with hot solution (60 ◦C) of 2-aminobenzoic acid (3.41 g,
24.88 mmol) in 50 mL ethanol. The resulting mixture was left under
reflux for 2 h and the formed solid product was separated by filtra-
tion, purified by crystallization from ethanol, washed with diethyl
ether and dried in a vacuum over anhydrous calcium chloride. The
brownish yellow products were produced in 88% yield.
2.3. Instruments
2.4.3. Synthesis of metal complexes
The metal complexes of the Schiff base, HL were prepared by the
addition of hot solution (60 ◦C) of the appropriate metal chloride or
acetate (1 mmol) in an ethanol–water mixture (1:1, 25 mL) to the
hot solution (60 ◦C) of the Schiff base (0.203 g, 1 mmol) in the same
solvent (25 mL). The resulting mixture was stirred under reflux for
1 h whereupon the complexes precipitated. They were collected by
filtration and purified by washing with an ethanol–water mixture
(1:1) and diethyl ether. The analytical data for C, H and N were
repeated twice.
pH measurements were carried out using 716 DMS Titrino
Metrohm connected with 728 Metrohm Stirrer. Elemental micro-
analyses of the separated solid chelates for C, H and N were
performed in the Microanalytical Center, Cairo University. The anal-
yses were repeated twice to check the accuracy of the analyzed
data. The molar conductance of solid chelates in DMF was measured
using Sybron-Barnstead conductometer (Meter-PM.6, E = 3406).
Infrared spectra were recorded on a PerkinElmer FT-IR type 1650
spectrophotometer in wave number region 4000–200 cm−1. The
spectra were recorded as KBr pellets. The solid reflectance spec-
tra 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
mass spectra were recorded by the EI technique at 70 eV using MS-
5988 GS–MS Hewlett-Packard instrument in the Microanalytical
2.5. Determination of the metal content of the chelates
An accurately weighed portion of the different chelates ranged
from 10 to 30 mg was placed in Kjeldahl flask. A measured volume of
concentrated nitric acid ranged from 5 to 10 mL was added initially
to the powdered chelates, to start the fast wet oxidation digestion.
This mixture had been digested by a gradual heating with dropping

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M.M. Omar et al. / Spectrochimica Acta Part A 73 (2009) 358–369
of H2O2 solution. This treatment was conducted until most of the
powdered complexes were diminished and the remained solution
had the colour of the corresponding metal salt. This solution was
diluted up to 50 mL with bidistilled water and the metal content
was determined by titration against standard EDTA solution at a
suitable pH value using the suitable indicator.
2.6. Biological activity
Fig. 1. Structure of Schiff base.
5 mm disk of filter paper was transferred into 250 flasks con-
taining 20 ml of working volume of tested solution. All flasks were
autoclaved for 20 min at 121 ◦C.
spectrum of HL shows a well-defined parent peak at m/z = 323
(M+) with a relative intensity = 1%. The parent ion and the frag-
ments obtained by cleavage in different positions in HL molecule
are shown in Scheme 1.
•
LB agar media surfaces were inoculated with 4 investigated bac-
teria (2 Gram-positive and 2 Gram-negative) then, transferred to
a saturated disk with a tested solution in the center of Petri dish
(agar plates).
3.2. Potentiometric determination of the ionization constants of
Schiff base
Finally, all these Petri dishes were incubated at 25 ◦C for 48 h
where clear or inhibition zones were detected around each disk.
Control flask of the experiment was designed to perform under
the same condition described previously for each microorganism
but with DMF solution only and by subtracting the diameter of
inhibition zone resulting with DMF from that obtained in each
case, so antibacterial activity could be calculated [18].
All experiments were performed as triplicate and data plotted
were the mean value.
•
•
The ionization constants of the ionizable groups in Schiff base
under investigation are determined by a method similar to that
described by Sarin and Munshi [17]. The average of protons associ-
ated with the ligand (n¯ A) at different pH values is calculated utilizing
acid and ligand titration curves. The pKa values can be calculated
from the curves obtained by plotting n¯ A versus pH. The formation
curves are found between 0 and 1. This indicates that the ligand
have one dissociable proton from COOH group. The pKa values can
be calculated also by plotting log n¯ A/(1 − n¯ A) versus pH whereby
a straight line is obtained intersecting the x-axis at the pKa value.
The pKa value of 6.55 can be attributed to the ionization of COOH
proton from HL ligand. The free energy change, ꢀG◦, was also cal-
culated and was found to be −45.54 kJ mol−1. The negative value
indicates the spontaneous character of association reaction.
•
3. Results and discussion
3.1. Characterization of Schiff base
The Schiff base is prepared as described in the experimental part,
crystallized and dried under vacuum and subjected to elemental
analyses, mass and IR spectral analysis. 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 formula 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 as shown in
Fig. 1.
3.3. Potentiometric determination of the stability constants
The stability constants of the Mn(II), Fe(III), Co(II), Ni(II), Cu(II),
Zn(II), Cd(II) and Th(IV) complexes with HL ligand is determined
potentiometrically using the method described by Sarin [17] and
Bjerrum [19]. The formation curves of the investigated complexes
are obtained by plotting a graph between average number of ligands
attached per metal ion (n¯ ) and free ligand exponent (pL), (Fig. 2).
Values of n¯ and pL are calculated. The maximum n¯ values calculated
for metal–ligand system are found to be not exceed two indicating
the possibilities of formation of 1:1 and 1:2 (metal: ligand) com-
plexes. The mean log ˇ1 and log ˇ2 values for complexes of Mn(II),
Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Th(IV) ions and HL are
listed in Table 2.
The structure of the Schiff base is also confirmed by IR and 1H
NMR spectra, which will be discussed in detailed manner with
metal complexes later.
3.1.1. Mass spectra of the Schiff base
The electron impact mass spectra of HL ligand is recorded and
investigated at 70 eV of electron energy. The mass spectra of the
studied Schiff base is characterized by moderate to high relative
intensity molecular ions peaks at 70 eV. It is obvious that, the molec-
ular ion peaks are in good agreement with their suggested empirical
formula as indicated from elemental analyses (Table 1). The mass
The complex-forming abilities of the transition metal ions are
frequently characterized by stability orders. The order of stabil-
ity constants is found to be: Mn(II) < Co(II) < Ni(II) < Cu(II) >Zn(II)
in accordance with Irving and Williams order [20,21] for divalent
Table 1
Analytical and physical data of HL ligand and its metal complexes.
Compound
Colour (yield) M.p. (◦C) % found (calcd)
ꢁeff. (B.M.) ꢂm (ꢃ−1mol−1cm2)
C
H
N
M
HL C18 H18 N4O2
Yellow (88)
Brown (75)
Black (65)
Green (55)
Yellow (73)
Blue (67)
Yellow (69)
Brown (63)
Brown (67)
Yellow (71)
78
2
67.43 (67.08)
45.99 (46.41)
42.83 (43.04) 3.95 (3.98)
45.84 (46.01)
47.13 (46.99)
42.62 (42.35) 5.31 (5.29)
45.67 (45.39) 4.73 (4.83)
39.75 (39.93) 4.90 (4.62)
5.95 (5.59)
4.97 (4.94)
17.33 (17.39)
12.21 (12.03)
10.99 (11.15)
11.38 (11.93)
11.56 (11.93)
10.74 (10.98)
11.52 (11.77)
10.09 (10.35)
7.65 (7.66)
–
–
–
[Mn(L1)Cl(H2O)2]·H2O C18 H23Mn Cl N4O5
[Fe(L1)Cl2(H2O)]·2H2O C18 H23Cl2FeN4O5
[Co(L1)Cl(H2O)2]·H2O C18 H23CoClN4O5
[Ni(L1)Cl(H2O)2]·H2O C18 H23ClNiN4O5
[Cu(L1)Cl(H2O)2]·3H2O C18 H27CuClN4O7
[Zn(L1)Cl(H2O)2]·H2O C18 H23ClN4O5Zn
[Cd(L1)Cl(H2O)2]·2H2O C18 H25CdClN4O6
[Th(L1)Cl(H2O)2]Cl2·2H2O C18 H25Cl3N4O6Th
[UO2(L1)(CH3COO)(H2O)2]·2H2O C20H28N4O10
>300
>300
>300
>300
>300
>300
>300
>300
>300
11.65 (11.82)
10.92 (11.15)
12.86 (12.57)
12.22 (12.51)
12.74 (12.45)
13.96 (13.66)
21.00 (20.71) Diam.
31.37 (31.72)
33.35 (33.52)
5.35
5.64
5.51
3.95
2.01
Diam.
10.11
13.22
10.76
12.95
9.35
8.75
7.99
162.9
8.99
4.87 (4.90)
4.94 (4.90)
29.21 (29.52)
31.99 (32.11)
3.38 (3.42)
3.90 (3.94)
Diam.
Diam.
U
7.91 (7.89)

M.M. Omar et al. / Spectrochimica Acta Part A 73 (2009) 358–369
361
Scheme 1. Mass fragmentation pattern of HL.
One would expect a bigger difference between log K1 and log K2
values in such a ligand because of possible steric hindrance to the
linking of the second ligand to the metal ion. The small difference
may be due to trans-structure.
The free energy of formation, ꢀG◦, accompanying the complex-
ation reaction has been determined at 25 ◦C. The results are given
in Table 2. From the table, it is apparent that the negative val-
ues of ꢀG◦ show that the driving tendency of the complexation
reaction is from left to right and the reaction proceeds sponta-
neously.
3.4. Composition and structures of Schiff base complexes
The novel Schiff base ligand HL is not previously prepared and
no studies concerning metals complexes are reported. Hence these
complexes are prepared and completely characterized. The solid
complexes of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), UO2(II)
and Th(IV) ions with the Schiff bases HL ligand are subjected to
elemental analyses (C, H and N, metal content), IR, 1H NMR, solid
reflectance, magnetic studies, molar conductance and thermal anal-
yses (TGA, DrTGA and DTA), to identify their tentative formulae in a
trial to elucidate their molecular structures. The biological activity
of the Schiff base ligand and its metal chelates are studied against
antibacterial organisms.
Fig. 2. Formation curves of HL complexes.
metal ions of the 3d series. It is clear from Table 2 that the stability
of Cu(II) complexes are larger as compared to the other metal ions
of 3d series. Under influence of the ligand field, Cu(II) (3d9) will
receive some extra stabilization [22] due to tetragonal distortion of
octahedral symmetry in their complexes. The Cu(II) complexes will
be further stabilized due to Jhan-Tellar effect [23].
Table 2
Cumulative data of log ˇ1 and log ˇ2 values for complexes of HL ligand with Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Th(IV).
Ion
HL
log ˇ1
A
log ˇ2
A
B
M
−ꢀG◦ (kJ mol−1
)
B
C
M
−ꢀG◦ (kJ mol−1
)
Mn(II)
Fe(III)
Co(II)
Ni(II)
Cu(II)
Zn(II)
Cd(II)
Th(IV)
6.88
7.50
6.95
7.00
7.20
7.10
7.15
7.40
6.75
7.10
6.87
6.89
6.96
6.91
6.95
7.06
6.82
7.30
6.91
6.95
7.08
7.01
7.05
7.23
46.5
48.2
46.8
47.0
47.4
47.2
47.3
47.9
12.76
13.79
12.90
13.24
13.98
13.10
13.17
13.66
12.53
13.26
12.74
13.07
12.86
13.31
13.01
13.58
12.58
13.20
12.76
13.04
12.86
12.90
13.00
13.08
12.62
13.42
12.80
13.12
13.23
13.10
13.06
13.44
61.4
62.9
61.8
62.4
62.6
62.3
62.3
63.0
Where (A) interpolation at half values method; (B) correction-term method; (C) mid-point method; (M) mean.

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M.M. Omar et al. / Spectrochimica Acta Part A 73 (2009) 358–369
3.4.1. Elemental analyses of the complexes
The results of elemental analyses, Table 1 is in good agreement
with those required by the proposed formulae. The formation of
these complexes may proceed according to the following equations
given below.
MX2 + HL + 2H2O + yH2O → [M(L)X(H2O)2]·yH2O
M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)andUO2(II);
y = 1–3, X = ClorAcO
FeCl3 + HL + H2O + 2H2O → [Fe(L)Cl2(H2O)]·2H2O
ThCl4 + HL + 2H2O + 2H2O → [Th(L)Cl(H2O)2]Cl2·2H2O
3.4.2. Molar conductance measurements
The chelates are dissolved in DMF and the molar conductivities
of 10−3 M of their solutions at 25 2 ◦C are measured. Table 1 shows
the molar conductance values of the complexes. It is concluded from
the results that the Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and
Cd(II) complexes of HL ligand has a molar conductivity values in the
range from 7.99 to 13.22 ꢃ−1 mol−1 cm2 (Table 1) which indicates
the non-ionic nature of these complexes and they are considered as
non-electrolytes. Th(IV) complex is found to has molar conductance
value of 162.9 mol−1 cm2, indicating its ionic character and that it
is 2:1 electrolyte [24].
3.4.3. IR spectra and mode of bonding
The data of the IR spectra of Schiff base ligand (HL) and its
complexes is listed in Table 3. The IR spectra of the complexes are
compared with those of the free ligand in order to determine the
coordination sites that may involved in chelation. There are some
guide peaks, in the spectra of the ligand, which are of good help
for achieving this goal. These peaks are expected to be involved in
chelation such as those of OH, NH, C O, COOH and azomethine N.
The position and/or the intensities of these peaks are expected to
be changed upon chelation. New peaks are also guide peaks as well
as water in chelation. These guide peaks are listed in Table 3. Upon
comparison it is found that:
(1) The ꢄ(C N) stretching vibration of the azomethine is found in
the free ligand at 1638 cm−1. This band is shifted to higher or
lower wavenumbers in the complexes indicating the participa-
tion of the azomethine nitrogen in coordination (M N) [25].
(2) The ꢄ(OH), ꢄ(C O), ꢄasym(COO) and ꢄsym(COO) stretching
vibrations are observed at 3443, 1685, 1490 and 1355 cm−1
for HL, respectively. The participation of the carboxylate O
atom in the complexes formation is evidenced from the dis-
appearance or shift in position of these bands to 3424–3470,
disappear–1670, 1492–1489 and 1407–1302 cm−1 for HL metal
complexes.
(3) The IR spectrum of HL showed a medium broad band at (3374
and 3319) cm−1 which attributed to NH2 of the amino acid
group. The existence of water of hydration and/or water of coor-
dination in the spectra of the complexes render it difficult to get
conclusion from the NH2 group of the HL which will be over-
lapped by those of the water molecules. The participation of
the NH2 group is further confirmed by clearifying the effect of
chelation on the in-plane bending, ı(NH2) vibration. The shift
of this band, from 1577 cm−1 in the free HL to 1545–1599 cm−1
in the complexes indicates the participation of the NH2 group
in complex formation [26].
(4) New bands are found in the spectra of the complexes in the
regions 566–590 (carboxylate O) which are assigned to ꢄ(M O)

M.M. Omar et al. / Spectrochimica Acta Part A 73 (2009) 358–369
363
ion [28]. The spectrum shows also a band at 23,529 cm−1 which may
be attributed to ligand to metal charge transfer.
Table 4
1H NMR spectral data of the Schiff base and its metal chelates.
Compound
HL
Chemical shift (ı), ppm
Assignment
The Ni(II) complex reported herein is high spin with a room
temperature magnetic moment value of 3.71 B.M.; which is
in the normal range observed for octahedral Ni(II) complexes
(ꢁeff = 2.9–3.3 B.M.) [28]. This indicates that, the complex of Ni(II) is
six coordinate and probably octahedral [29]. Its electronic spectra,
in addition to show the ␲–␲* and n–␲* bands of the free ligand, dis-
13.30
6.481–7.693
(S, 1H, COOH)
(m, 9H, 5ArH and 4
anthranilic-H)
(br, 2H, NH2)
(S, 3H, N-CH3)
(S, 3H, C-CH3)
3.879
2.733
2.096
play three bands, in the solid reflectance spectra at ꢅ1: 12,635 cm−1
:
:
[Cd(L)Cl(H2O)2]·2H2O
6.466–7.70
(m, 9H, 5ArH and 4
anthranilic-H)
(br, 2H, NH2)
(S, 3H, N-CH3)
(S, 3H, C-CH3)
3A2g → T2g, ꢅ2: 15,595 cm−1
:
3A2g → T1g (F) and ꢅ3: 21,172 cm−1
3
3
3
3A2g → T1g (P). The Racah parameters are calculated according to
3.326
2.764
2.108
the following equations:
ꢅ2 + ꢅ3 − 3ꢅ1
B =
15
B =
{3ꢅ2[25(ꢅ3 − ꢅ2)2 − 16ꢅ1]2}1/2
1
75
stretching vibrations for HL metal complexes. The bands at
414–475 in HL metal complexes have been assigned to ꢄ(M N)
of the azomethine mode. The ꢄ(M N) bands due to amino
group are appeared at 464–520 cm−1 for HL metal complexes
[27].
10 Dq = ꢅ1
The 10Dq values lie in the 12,711 cm−1, again confirming the octa-
hedral configuration of the chelate [30]. The spectrum shows also a
band at 25,651 cm−1 which may attribute to ligand to metal charge
transfer.
Therefore, from the IR spectra, it is concluded that: HL behaves
as a uninegatively tridentate ligand with NNO donor sites and
coordinated to the metal ions via the azomethine N, deprotonated
carboxylic O and amino N atoms.
The electronic spectrum of the Co(II) complex gives three bands
at 12,799, 16,771 and 20,985 cm−1. The band at 25,445 cm−1 refers
to the charge transfer band. The bands observed are assigned to the
4
4
transitions 4T1g (F) → T2g (F) (ꢅ1), 4T1g (F) → A2g (F) (ꢅ2) and 4T1g
4
(F) → T2g (P) (ꢅ3), respectively, suggesting that there is an octa-
3.4.4. 1H NMR spectra
hedral geometry around Co(II) ion [31]. For calculating the Racah
parameters, the following equations are used [30].
The 1H NMR spectra of Schiff base (HL) was recorded in d6-
dimethylsulfoxide (DMSO) solution using tetramethylsilane (TMS)
as internal standard. The chemical shifts of the different types of
protons in the 1H NMR spectra of the Schiff base HL and its diamag-
netic Cd(II) complex are listed in Table 4. The spectra of the complex
are examined in comparison with those of the parent Schiff base.
Upon examinations it is found that:
10 Dq = 2ꢅ1 − ꢅ3 + 15B
ꢀ
ꢁ
1
B =
−(ꢅ1 − ꢅ3) (−ꢅ12 + ꢅ32 + ꢅ1ꢅ3)1/2
30
1
10 Dq = (2ꢅ2 − ꢅ3) + 5B
2
ꢀ
ꢁ
1
510
B =
7(ꢅ3 − 2ꢅ2) 3[81ꢅ32 − 16ꢅ2(ꢅ2 − ꢅ3)1/2
(1) The COOH signal is found at 13.30 ppm in the spectrum of HL
ligand. This signal is completely disappeared in the spectrum
of the Cd(II) complex indicating the involvement of the COOH
group in chelation through displacement of the COOH proton.
(2) The signals observed at 3.879 ppm for HL ligand, is assigned to
NH2 protons. These signal is found at 3.326 Cd(II) complex with
HL. This indicates that the NH2 group is coordinated to the Cd(II)
ion without proton displacement.
From the position of the bands and the calculated Racah parameters,
the chelate is octahedral with largely covalent bonds between the
organic ligand and the metal ion [30]. The magnetic susceptibility
measurement is found to be 5.51 B.M. (normal range for octahe-
dral Co(II) complex is 4.3–5.2 B.M.), is an indicative of octahedral
geometry [32].
The reflectance spectrum of the Cu(II) chelate consist of a broad,
low intensity shoulder band centered at 14,777 and 17,493 cm−1
.
The 2Eg and 2T2g states of the octahedral Cu(II) ion (d9) split under
the influence of the tetragonal distortion and the distortion can be
Therefore, it is clear from these results that the data obtained
from the elemental analyses, IR and 1H NMR spectral measure-
ments are in agreement with each other.
such as to cause the three transitions 2B1g → B2g
;
2B1g → Eg and
2
2
2
2B1g → A1g to remain unresolved in the spectrum [33]. It is con-
cluded that, all three transitions lie within the single broad envelope
centered at the same range previously mentioned. This assignment
is in agreement with the general observation that Cu(II) d–d tran-
sitions are normally close in energy [33]. The magnetic moment
of 1.97 B.M. falls within the range normally observed for octahe-
dral Cu(II) complexes [28]. A moderately intense peak observed at
21,555 cm−1 is due to ligand–metal charge transfer transition [34].
The complexes of Zn(II) and UO2(II) are diamagnetic. In analogy
with those described for Zn(II) complexes containing N–O donor
Schiff bases [35,36] and according to the empirical formulae of these
complexes, we proposed an octahedral geometry for the Zn(II) and
UO2(II) complexes.
3.4.5. Magnetic susceptibility and electronic spectra
measurements
In this part, we would like to elucidate the important role played
by magnetic and electronic spectra in determining the geometrical
structures of the above investigated metal chelates.
The diffuse reflectance spectrum of the Mn(II) complex shows
three bands from 15,873 to 16,150 cm−1 assignable to 4T1g → A1g
,
6
4T2g (G) → A1g and T1g (D) → A1g transitions, respectively [28].
The magnetic moment value is found to be 5.35 B.M., which indi-
cates the presence of Mn(II) complex in octahedral structure.
From the diffuse reflectance spectrum it is observed that, the
Fe(III) chelate exhibit a band at 20,691 cm−1, which may be assigned
to the 6A1g → T2g (G) transition in octahedral geometry of the com-
6
4
6
5
plexes [28]. The 6A1g → T1g transition appears to be split into two
3.4.6. Thermal analyses (TGA, DrTGA and DTA)
bands at 16,135 and 12,657 cm−1. The observed magnetic moment
of Fe(III) complex is found to be 5.43 B.M. Thus, the complex formed
has the octahedral geometry involving d2sp3 hybridization in Fe(III)
Thermogravimetry (TGA) is a technique in which the change in
the weight of a substance is recorded as a function of temperature
or time. The basic instrumental requirement for thermogravime-

364
M.M. Omar et al. / Spectrochimica Acta Part A 73 (2009) 358–369
try is a precision balance with a furnace programmed for a linear
rise of temperature with time. The results may be presented as (i)
a thermogravimetric (TGA) curve; in which the weight change is
recorded as a function of temperature or time, or (ii) as a derivative
thermogravimetric (DrTGA) curve where the first derivative of the
TGA curve is plotted with respect to either temperature or time.
Thermogravimetric analyses (TGA, DrTGA and DTA) of the Schiff
base ligand; HL and its chelates are used to (i) get information about
the thermal stability of these new complexes, (ii) decide whether
the water molecules (if present) are inside or outside the inner coor-
dination sphere of the central metal ion and (iii) suggest a general
scheme for thermal decomposition of these chelates. The TGA (and
DrTGA) and DTA curves are given in Fig. 3 and the data are listed
in Table 5. The weight losses for each chelate are calculated within
the corresponding temperature ranges.
3.4.6.1. Thermal analyses (TGA, DrTGA and DTA) of Schiff base. The
TGA curve of Schiff base HL, (Fig. 3a), exhibits a first estimated
mass loss of 52.02% (calcd. 51.25%) at 140–275 ◦C, which may be
attributed to the liberation of C9H11 NO2 molecule as gases. In the
2nd and 3rd stages within the temperature range of 275–950 ◦C, HL
losses the remaining part with an estimated mass loss of 48.76%
(calcd. 48.76%) with a complete decomposition as CO, CO2, NO,
NO2, etc. gases (Table 5). These losses appear in the DTA curves as
exothermic and endothermic peaks within the temperature range
of decomposition from 125 to 950 ◦C as three endothermic peaks
at 125, 450 and 950 ◦C and six exothermic peaks at 240, 275, 400,
440, 460 and 575 ◦C.
The thermogram of Fe(III) chelate shows three decomposition
steps within the temperature range from 30 to 1000 ◦C. The first two
steps of decompositions within the temperature range of 29–400 ◦C
corresponds to the loss of water molecules of hydration, the coordi-
nated water, HCl, two methyl groups and amino group for HL with
a mass loss of 3.59% (calcd. 3.33%) and 30.89% (calcd 31.27%) for
Fe(III) complex. The subsequent step (275–1000 ◦C) corresponds to
the removal of the organic part of the ligand leaving metal oxide as a
residue. The overall weight loss amounts to 84.10% (calcd. 84.34%)
for Fe(III) complex. The DTA data are listed in Table 5 and repre-
sented graphically in Fig. 3b. It is clear from these data that these
mass losses are accompanied by exothermic peaks at 40, 175, 350
and 475 ◦C and endothermic peaks at 60 and 400 ◦C.
The TGA curve of the Co(II) chelate is shown in Fig. 3c and listed
in Table 5. It decomposes in three steps in the temperature range
from 30 to 1000 ◦C. The first step is the loss of the hydrated water
and one HCl molecules with mass loss of 3.83% (calcd. 3.29%). The
2nd and 3rd steps correspond to the removal of coordinated water,
HCl molecules and the residue of ligand as gases with mass loss of
80.41% (calcd. 80.06%). These steps are accompanied by exothermic
peaks at 30, 120, 225, 375, 450, 550 and 605 ◦C and endothermic
peaks at 60, 200, 415, 475 and 900 ◦C.
The TGA curve of the Ni(II) chelate shows three stages of decom-
position within the temperature range of 30–1000 ◦C. The first step
corresponds to the loss of water of hydration and coordinated water
while the subsequent (2nd and 3rd) stages involve the loss of HCl
and ligand molecules. The overall weight loss amounts to 84.07%
(calcd. 84.02%). The DTA data are listed in Table 5 and represented
graphically in Fig. 3d. It is clear from these data that these mass
losses are accompanied by exothermic peaks at 115, 155, 275, 450
and 550 ◦C and endothermic peaks at 75, 135, 325 and 510 ◦C.
On the other hand, [Cu(L)Cl(H2O)2]·H2O chelate exhibits three
decomposition steps (Fig. 3e). The first step in the temperature
range from 30 to 170 ◦C corresponds to the loss of the hydrated
water with estimated mass loss = 10.59% (calcd. 10.34%). The total
mass losses of the decomposition steps is found to be 84.41% (calcd.
84.63%), leaving CuO as a residue. The DTA data are listed in Table 5
and represented graphically in Fig. 3e. It is clear from these data that

M.M. Omar et al. / Spectrochimica Acta Part A 73 (2009) 358–369
365
Fig. 3. Thermal analysis of HL ligand and its complexes. (a) HL ligand, (b) Fe(III), (c) Co(II), (d) Ni(II) and (e) Cu(II) complexes.
these mass losses are accompanied by eight exothermic and five
ꢀH∗ = E∗ − RT
(3)
(4)
endothermic peaks at 50, 160, 190, 300, 350, 575, 640 and 910 ◦C
and 105, 170, 410, 480 and 610 ◦C, respectively.
ꢀG∗ = ꢀH∗ − TꢀS∗
3.4.7. Calculation of activation thermodynamic parameters
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*) are evaluated graphically by employing the
Coats–Redfern relation [37]:
The data are summarized in Table 6.
The activation energies of decomposition are found to be in the
range of 41.47–299.7 kJ mol−1. The high values of the activation
energies reflect the thermal stability of the complexes. The entropy
of activation is found to have negative values in all the complexes
which indicate that the decomposition reactions proceed with a
lower rate than the normal ones.
ꢀ
ꢁ
ꢀ
ꢂ
ꢃꢁ
log {Wf/(Wf − W)}
AR
ꢆE∗
2RT
E∗
log
=log
1−
−
(1)
E∗
2.303 RT
T2
3.4.8. Structural interpretation
where Wf is the mass loss at the completion of the reaction, W is the
mass loss up to temperature T; R is the gas constant, E* is the activa-
The structures of the complexes of Schiff base; HL, with Mn(II),
Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), UO2(II) and Th(IV) ions are
confirmed by the elemental analyses, IR, 1H NMR, molar conduc-
tance, magnetic moment, solid reflectance and thermal analyses
data. Therefore, from the IR spectra, it is concluded that HL behaves
as a uninegatively tridentate ligand with NNO sites and coordinated
to the metal ions via the azomethine N, deprotonated carboxylic
O and amino N. From the molar conductance data of the com-
plexes (ꢂm), it is concluded that the complexes are considered
as non-electrolytes and Th(IV) complex is 2:1 electrolyte. The 1H
tion energy in kJ mol−1, ꢆ is the heating rate and (1 − (2RT/E*)) 1.
∼
=
A plot of the left-hand side of Eq. (1) against 1/T gives a slope from
which E* is calculated and A (Arrhenius factor) is determined from
the intercept. The entropy of activation (ꢀS*), enthalpy of activation
(ꢀH*) and the free energy change of activation (ꢀG*) are calculated
using the following equations:
ꢀ
ꢂ
ꢃ ꢁ
Ah
kT
ꢀS∗ = 2.303 log
R
(2)

366
M.M. Omar et al. / Spectrochimica Acta Part A 73 (2009) 358–369
Table 6
Thermodynamic data of the thermal decomposition of HL ligand and its metal complexes.
Complex
HL
Decomposition temperature (◦C)
E* (kJ mol−1
)
A (s−1
)
ꢀS* (kJ mol−1
)
ꢀH* (kJ mol−1
)
ꢀG* (kJ mol−1
)
50–300
300–500
500–1000
41.47
96.48
286.30
3.11 × 106
5.89 × 106
2.15 × 1016
−119.2
−117.0
−61.93
39.38
93.44
281.30
69.31
136.3
244.1
30–105
105–350
350–600
600–900
48.53
46.46
96.14
3.74 × 106
4.12 × 105
1.28 × 107
1.29 × 107
3.02 × 1010
3.03 × 106
1.22 × 106
1.03 × 1020
6.57 × 107
−105.8
−134.8
−110.4
−112.3
48.03
44.65
93.17
54.42
73.93
132.6
168.7
(1)
(2)
121.60
117.80
30–100
100–210
210–280
2800–430
430–1000
42.23
68.98
85.81
287.40
143.10
−31.2
−117.0
−130.0
−134.8
−100.6
41.72
67.26
82.65
283.7
138.40
43.64
91.53
132.3
222.8
195.6
30–120
120–210
210–350
350–450
450–600
600–900
65.98
144.2
99.30
171.5
299.7
230.0
1.40 × 109
5.25 × 1017
3.09 × 108
2.72 × 1012
1.45 × 1020
4.85 × 1013
5.12 × 104
1.33 × 105
1.12 × 1011
−58.01
−100.9
−81.9
65.39
143.1
96.96
168.1
295.7
225.4
69.55
129.4
120.0
171.9
229.4
218.8
(3)
(4)
−9.3
−137.1
−11.98
60–110
110–360
360–900
42.30
56.62
113.2
−146.0
−145.0
−169.1
41.42
54.53
94.2
56.79
91.09
121.4
(1) [Fe(L)Cl(H2O)2]Cl·2H2O; (2) [Co(L)Cl(H2O)2]·H2O; (3) [Ni(L)Cl(H2O)2]·H2O; (4) [Cu(L)Cl(H2O)2]·3H2O.
NMR spectra of the free ligand and its diamagnetic Cd(II) complex
shows that the COOH signal of HL ligand participate in chelation
with proton displacement. While NH2 signal of HL appeared in the
spectrum of HL and its Cd(II) complex show that NH2 involved in
chelation without proton displacement. On the basis of the above
observations and from the magnetic and solid reflectance measure-
ments, octahedral and tetrahedral geometry is suggested for the
investigated complexes.
3.5. Biological activity
The main aim of the production and synthesis of any antimi-
crobial compound is to inhibit the causal microbe without any side
effects on the patients. In addition, it is worthy to stress here on the
basic idea of applying any chemotherapeutic agent which depends
essentially on the specific control of only one biological function
and not multiple ones.
On the basis of the above observations and from the magnetic
and solid reflectance measurements, octahedral and tetrahedral
geometry is suggested for the investigated complexes. The structure
of the complexes are shown in Fig. 4.
The chemotherapeutic agent affecting only one function has
a highly sounding application in the field of treatment by anti-
cancer, since most anticancer used in the present time affect both
cancerous diseased cells and healthy ones which in turns affect
Fig. 4. Structural formulas of HL metal complexes.

M.M. Omar et al. / Spectrochimica Acta Part A 73 (2009) 358–369
367
the general health of the patients. Therefore, there is a real need
for having a chemotherapeutic agent which controls only one
function.
bases and their metal complexes with the standard (Cefepime), the
following results are obtained:
In testing the antibacterial activity of these compounds we used
more than one test organism to increase the chance of detect-
ing antibiotic principles in tested materials. The sensitivity of a
microorganism to antibiotics and other antimicrobial agents is
determined by the assay plates which incubated at 37 ◦C for 2 days
for bacteria. All of the tested compounds show a remarkable bio-
logical activity against different types of Gram-positive (G+) and
Gram-negative (G−) bacteria. The data are listed in Table 7 and
shown in Fig. 5. On comparing the biological activity of the Schiff
(a) Using Bacillus simplex bacteria (G+):
The data listed in Table 7 show that Cd(II) complex has the
higher biological activity than that of the free HL ligand and
both of them are higher than cefepime standard. The biological
activity of Mn(II), Zn(II) and UO2(II) complexes is equal to that
of the ligand and higher than that of the standard. Therefore,
the biological activity of the complexes follow the order
Cd(II) > HL = Mn(II) = Zn(II) = UO2(II) > Cu(II) > Fe(III) = Co(II) =
Ni(II) = Th(IV) > cefepime.
Fig. 5. Biological activity of HL and its complexes at (a) 5 ppm, (b) 2.5 ppm and (c) 1 ppm.

368
M.M. Omar et al. / Spectrochimica Acta Part A 73 (2009) 358–369
Table 7
Biological activity of HL and its metal complexes.
Sample
Bacillus simplex
Exiguobacterium acetylicum
Pseudomonas putida
E. coli bacteria
C, mg/l
HL
5
2.5
++
++
++
++
++
++
++
+++
++
++
+
1
++
+
+
+
+
++
+
+
+
5
2.5
++
++
++
++
++
++
+
++
+
++
++
1
5
2.5
++
++
++
++
++
++
++
++
++
++
++
1
5
++
+
+
+
+
+
+
+
2.5
+
+
+
+
+
+
+
+
1
+
+
+
+
+
+
+
+
+
+
++
++
++
++
++
++
++
++
+++
++
++
+
++
++
++
++
++
++
++
++
++
++
++
++
++
+
+
+
++
++
+
+
+
++
++
++
++
++
++
+++
+++
++
++
++
++
++
+
+
+
++
+
+
+
++
++
[Mn(L)Cl(H2O)2]·H2O
[Fe(L)Cl(H2O)2]Cl·2H2O
[Co(L)Cl(H2O)2]·H2O
[Ni(L)Cl(H2O)2]·H2O
[Cu(L)Cl(H2O)2]·3H2O
[Zn(L)Cl(H2O)2]·H2O
[Cd(L1)Cl(H2O)2]·2H2O
[Th(L)Cl(H2O)2]Cl2·2H2O
[UO2(L)(CH3COO)(H2O)2]·2H2O
Cefepime
+
++
++
+
+
++
+
+
++
The test was done using the diffusion agar technique.
Inhibition values = 0.1–0.6 cm beyond control = +.
Inhibition values = 0.65–1.0 cm beyond control = ++.
Inhibition values = 1.1–1.5 cm beyond control = +++.
(b) Exiguobacterium acetylicum bacteria (G+)
plexes might be recommended and/or established a new line for
search to new antitumour particularly when one knows that many
workers studied the possible antitumour action of many synthetic
and semisynthetic compounds, e.g., Hodnett et al. [42] and Hick-
man [43]. Such compounds may have a possible antitumour effect
since Gram-negative bacteria are considered a quantitative micro-
biological method testing beneficial and important drugs in both
clinical and experimental tumour chemotherapy [44].
The biological activity of the HL ligand is higher than that of
standard cefepime and less than Cd(II) and Zn(II) complexes. All
the complexes have higher activity than the standard cefepime.
The biological activity of the complexes follow the order
Cd(II) > Zn(II) > HL = Mn(II) = Ni(II) = Cu(II) = UO2(II) > Fe(III) =
Co(III) = Th(IV) = cefepime.
(c) Using Pseudomonas putida bacteria (G−)
The biological activity of the ligand HL equals to that of the
standard cefepime and Cu(II), Mn(II) and Zn(II) complexes
and higher than that of the rest of complexes. The biolog-
ical activity of the complexes are found to follow the order
HL = cefepime = Cu(II) = Mn(II) = Zn(II) > Cd(II) > Ni(II) > Fe(III) =
Co(II) = Th(IV) = UO2(II).
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