Preparation, characterization and biological activity of novel metal-NNNN donor Schiff base complexes

Article abstract of DOI:10.1016/j.saa.2009.11.039

Novel Schiff base (H₂L) ligand is prepared via condensation of benzil and triethylenetetraamine. 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 (TG, DTG and DTA). 1:1 [M]:[H₂L] complexes are found from the elemental analyses data having the formulae [M(H₂L)Cl₂]·yH₂O (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)), [Fe(H₂L)Cl₂]Cl·H₂O, [Th(H₂L)Cl₂]Cl₂·3H₂O and [UO₂(H₂L)](CH₃COO)₂·2H₂O. The metal chelates are found to be non-electrolytes except Fe(III), Th(IV) and UO₂(II) complexes are electrolytes. IR spectra show that H₂L is coordinated to the metal ions in a neutral tetradentate manner with 4Ns donor sites of the two azomethine N and two NH groups. The geometrical structures of these complexes are found to be octahedral. The thermal behaviour of these chelates is studied where the hydrated complexes lose 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 are calculated using Coats-Redfern method. The ligand (H₂L), in comparison to its metal complexes, is screened for its antibacterial activity. The activity data show that the metal complexes have antibacterial activity more than the parent Schiff base ligand and cefepime standard against one or more bacterial species.

Full text of DOI:10.1016/j.saa.2009.11.039

Spectrochimica Acta Part A 75 (2010) 678–685
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Preparation, characterization and biological activity of novel
metal-NNNN donor Schiff base complexes
∗
Gehad G. Mohamed , M.M. Omar, Amr A. Ibrahim
Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 August 2009
Received in revised form
Novel Schiff base (H L) ligand is prepared via condensation of benzil and triethylenetetraamine. The
2
1
ligand is characterized based on elemental analysis, mass, IR and H NMR spectra. Metal complexes are
1
reported and characterized based on elemental analyses, IR, H NMR, solid reflectance, magnetic moment,
1
4 November 2009
molar conductance, and thermal analyses (TG, DTG and DTA). 1:1 [M]:[H2L] complexes are found from
the elemental analyses data having the formulae [M(H2L)Cl2]·yH2O (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II),
Cd(II)), [Fe(H2L)Cl2]Cl·H2O, [Th(H2L)Cl2]Cl2·3H2O and [UO2(H2L)](CH3COO)2·2H2O. The metal chelates
are found to be non-electrolytes except Fe(III), Th(IV) and UO2(II) complexes are electrolytes. IR spectra
show that H2L is coordinated to the metal ions in a neutral tetradentate manner with 4Ns donor sites
of the two azomethine N and two NH groups. The geometrical structures of these complexes are found
to be octahedral. The thermal behaviour of these chelates is studied where the hydrated complexes lose
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 are calculated
using Coats–Redfern method. The ligand (H2L), in comparison to its metal complexes, is screened for its
antibacterial activity. The activity data show that the metal complexes have antibacterial activity more
than the parent Schiff base ligand and cefepime standard against one or more bacterial species.
Accepted 17 November 2009
Keywords:
Schiff base
Transition metal complexes
Spectroscopy
Thermal analyses
Biological activity
©
2009 Elsevier B.V. All rights reserved.
1
. Introduction
with triethylenetetraamine and their complexes were reported
11–14].
In continuation to our interest in metal complexes of Schiff bases
[
There is a continuing interest in transition 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, some of these complexes have been exhibit inter-
esting physical and chemical properties [1] and potentially useful
biological activities [2]. Many reports were available for the prepa-
ration and properties of model copper complexes which mimic
copper-containing metalloproteins [3]. 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 [4], catalysis of many reactions
[15–18], the present study describes the coordination behaviour
of novel Schiff base derived from the condensation of benzil
with triethylenetetraamine (H L) towards some transition ele-
2
ments namely Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II),
UO (II) and Th(IV). The 4Ns coordination sites are helpful as they
2
will do a cavity around the metal ions and hence they can be
used as analytical reagents for determination of metal ions. The
structure of the studied complexes is elucidated using elemental
analyses, IR, solid reflectance, magnetic moment, 1H NMR, molar
conductance, and thermal analyses measurements. The biologi-
cal activities of the parent Schiff base and its metal complexes
are reported and compared with a reference standard antibiotic
drug.
[
5] and their industrial applications [6]. The interest in Schiff
base compounds as analytical reagents was increasing since they
enabled simple determinations of different organic and inor-
ganic substances [7]. Transition metal complexes of Schiff bases
derived from benzil with different amines had been prepared
and characterized by physical and chemical techniques [8–10].
Schiff bases derived from condensation of various aldehydes
2. Experimental
2.1. Materials and reagents
The chemicals used included triethylenetetraamine (Sigma) and
∗ Corresponding author.
E-mail address: ggenidy@hotmail.com (G.G. Mohamed).
benzil (Aldrich). CuCl ·2H O (Sigma), CoCl ·6H O and NiCl ·6H O
2
2
2
2
2
2
(BDH); MnCl2 (Sigma), ThCl4 (Aldrich), ZnCl ·2H O (Ubichem),
2
2
1
386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.11.039

G.G. Mohamed et al. / Spectrochimica Acta Part A 75 (2010) 678–685
679
Table 1
Analytical and physical data of H2L ligand and its metal complexes.
◦
Compound
Colour (yield) % M.P. ( C)
% Found (calcd.)
ꢀeff. (B.M.)
ꢁm
(ꢂ
mol cm2)
−1 −1
C
H
N
M
H2L C20H24N4
Brown (81)
Brown (75)
124–126
>300
75.00 (74.75)
49.49 (49.79)
17.50 (17.65)
5.95 (5.81)
7.50 (7.85)
–
–
5.72
–
[
Mn(H2L)Cl2]·2H2O
C20H28Cl2MnN4O2
Fe(H2L)Cl2]Cl·1.5H2O
C20H27Cl3FeN4O1.5
Co(H2L)Cl2]·2.5H2O
C20H29Cl2CoN4O2.5
Ni(H2L)Cl2]·2.5H2O
C20H29Cl2NiN4O2.5
Cu(H2L)Cl2]·3H2O
C20H30Cl2CuN4O3
Zn(H2L)Cl2]·3H2O
C20H30Cl2N4O3Zn
Cd(H2L)Cl2]·1.5H2O
C20H27Cl2CdN4O1.5
Th(H2L)Cl2]Cl2·3H2O
C20H30Cl4N4O3Th
UO2(H2L)](CH3COO)2·2H2O Brown (76)
C22H34N4O8U
11.32 (11.62)
11.05 (10.99)
11.76 (11.31)
11.68 (11.31)
11.13 (11.01)
11.13 (10.97)
10.76 (10.56)
7.47 (7.49)
11.35 (11.41)
10.35
[
Brown (77)
Black (65)
Green (79)
Green (83)
Brown (64)
Brown (74)
Black (71)
>300
>300
>300
>300
>300
>300
>300
>300
47.32 (47.11)
48.26 (48.48)
48.30 (48.48)
47.35 (47.20)
47.22 (47.02)
45.55 (45.25)
32.35 (32.09)
36.93 (36.67)
5.17 (5.30)
5.97 (5.86)
5.30 (5.86)
5.80 (5.90)
6.01 (5.88)
5.19 (5.09)
3.97 (4.01)
4.89 (4.72)
11.17 (10.99)
12.03 11.92
5.82
92.0
[
5.55
11.33
7.75
[
12.25 11.92
3.71
[
12.55 (12.49)
12.95 (12.81)
21.39 (21.19)
31.49 (31.02)
33.33 (33.06)
1.97
9.85
[
Diam.
Diam.
Diam.
Diam.
6.30
[
10.50
[
143.6
120.5
[
7.50 (7.78)
UO (AcO) ·2H O (Sigma) and FeCl ·6H O (Prolabo). Organic sol-
2.4. Synthesis of metal complexes
2
2
2
3
2
vents (spectroscopic pure from BDH) used included ethanol,
diethyl ether and dimethylformamide. Hydrogen peroxide and
sodium chloride, sodium carbonate and sodium hydroxide
The metal complexes of the Schiff base, H L, were prepared
by the addition of hot solution (60 C) of the appropriate metal
2
◦
(
A.R.) were used. Hydrochloric and nitric acids (Merck) were
chloride or acetate (1 mmol) in an ethanol–water mixture (1:1,
◦
used.
25 mL) to the hot solution (60 C) of the Schiff base (0.320 g H L,
2
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.
2
.2. Instruments
Elemental microanalyses of the separated solid chelates for C,
H, N and Cl were performed at the Microanalytical Center, Cairo
University using CHNS-932 (LECO) Vario Elemental analyzers. 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 spec-
trophotometer in wavenumber region 4000–200 cm . The spectra
were recorded as KBr pellets. 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
2
.5. Determination of the metal content of the chelates
The metal content of the complexes were analyzed complexo-
metrically.
.6. Biological activity
filter paper disk (5 mm) was transferred into 250 mL
−
1
2
A
flasks containing 20 mL of working volume of tested solution
◦
(100 ␮g/mL). All flasks were autoclaved for 20 min at 121 C:
Pascal’s constant and Hg[Co(SCN) ] was used as a calibrant. The
4
biological activity is carried out at the Microanalytical Center, Cairo
University.
-
LB agar media surfaces were inoculated with four investigated
bacteria (2 g positive and 2 g negative) then, transferred to a sat-
urated disk with a tested solution in the center of Petri dish (agar
plates).
The mass spectrum was recorded by the EI technique at 70 eV
using MS-5988 GS–MS Hewlett-Packard instrument. 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
◦
-
-
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 dimethylformamide solution only and by subtracting the
diameter of inhibition zone resulting with dimethylformamide
from that obtained in each case, so antibacterial activity could be
calculated [19].
(
(
TG and DTA) were carried out in dynamic nitrogen atmosphere
20 mL min ) with a heating rate of 10 C min using Shimadzu
−1
◦
−1
TG-60H and DTA-60H thermal analyzers.
2
.3. Synthesis of Schiff base (H L)
2
-
All experiments were performed as triplicate and data plotted
were the mean value.
◦
Hot solution (60 C) of triethylenetetraamine (5 g, 34.19 mmol)
◦
in 25 mL ethanol was mixed with hot solution (60 C) of benzil
(
7.18 g, 34.19 mmol) in the same solvent and the reaction mixture
3. Results and discussion
was left under reflux for 2 h. The formed solid product was sepa-
rated by filtration, purified by crystallization from ethanol, washed
with diethyl ether and dried in a vacuum over anhydrous calcium
3.1. Characterization of Schiff base
chloride. The yellow Schiff base product; H L was produced in 81%
yield.
The preparation of the Schiff base under study is given below
as shown in reaction (1). The Schiff base is prepared and subjected
2

6
80
G.G. Mohamed et al. / Spectrochimica Acta Part A 75 (2010) 678–685
m/z = 320 (R.I. = 1%). Fragment at m/z = 165 (R.I. = 100%, base peak)
is attributed to C H12N4 ion as shown in Scheme 1.
8
3.2. Elemental analyses of the complexes
The results of elemental analyses are in good agreement with
those required by the proposed formulae given in Table 1.
3.3. Molar conductance measurements
The chelates are dissolved in DMF and the molar conduc-
−
3
◦
tivities of 10 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 Co(II), Ni(II), Cu(II), Zn(II)
and Cd(II) complexes have a molar conductivity values in the
−
1
−1
2
range 6.30–11.33 ꢂ mol cm (Table 1) which indicates the
non-ionic nature of these complexes and they are considered as
non-electrolytes. Th(IV) complex has a molar conductance value
−
1
−1
2
of 143.6 ꢂ mol cm , indicating that it is 2:1 electrolyte [20]. In
addition, the results listed in Table 1 indicate that the UO (II) and
2
−
1
−1
2
Fe(III) complexes are of the types 2:1 (ꢁm = 120.5 ꢂ mol cm )
and 1:1 (ꢁm = 92.0 ꢂ mol cm ) electrolytes, respectively [20].
−
1
−1
2
3.4. IR spectral studies
The data of the IR spectra of Schiff base ligand (H L) and its
2
complexes are listed in Table 2. The IR spectra of the complexes
are compared with the free ligand in order to determine the coor-
dination sites that may involved in chelation. New peaks are also
guide peaks as well as water in chelation. These characteristic peaks
are listed in Table 2. Upon comparison it is found that the ꢃ(C N)
stretching vibration of the azomethine is found in the free lig-
−
1
and at 1655 cm for H L. This band is shifted to higher or lower
2
wavenumbers in the complexes indicating the participation of the
azomethine nitrogen in coordination (M–N) [21].
−
1
The NH stretching vibration; ꢃ(NH), is found at 3057 cm in the
spectrum of free H L ligand. However, the participation of the NH
2
group in chelation is ascertained from the shift of the band to lower
or higher wavenumbers or its disappearance in the spectra of the
complexes [22]. The bands at 419–455 cm in the spectra of metal
Scheme 1. Mass fragmentation pattern of H2L.
−1
complexes, have been assigned to ꢃ(M–N) of the azomethine mode
[
18]. Two bands are found in the spectrum of the UO (II) complex
2
−
1
at 1540 and 1330 cm which are assigned to stretching vibrations
to elemental analyses, mass, 1H NMR and IR spectral analyses. The
results of elemental analyses with molecular formula and the melt-
ing 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:
of ꢃasym(COO) and ꢃsym(COO) of the acetate group.
Therefore, from the IR spectra, it is concluded that H L behaves
2
as neutral tetradentate ligand with 4Ns donor sites and binds to the
metal ions through two azomethine N and two secondary amine
NH.
(1)
3.1.1. Mass spectrum of the Schiff base
3.5. 1H NMR spectra
The electron impact mass spectrum of H L ligand is recorded
2
and investigated at 70 eV of electron energy. The important peaks
and their relative intensities for the molecular ions are shown in
Scheme 1. Mass spectrum of the studied Schiff base is character-
ized by moderate to high relative intensity molecular ion peaks
The 1H NMR spectrum of Schiff base (H L) is recorded in d -
2
6
dimethylsulphoxide (DMSO-d ) solution using tetramethylsilane
6
(TMS) as internal standard. The chemical shifts of the different
types of protons found in the 1H NMR spectra of the Schiff base;
at 70 eV. Scheme 1 shows a well-defined parent peak of H L at
H L, and its diamagnetic Cd(II) complex are listed in Table 3. The
2
2

G.G. Mohamed et al. / Spectrochimica Acta Part A 75 (2010) 678–685
681
Table 2
R data (4000–400 cm 1) of H2L ligand and its metal complexes.
−
1
Compound
H2L
ꢃ(NH)
ꢃ(C N) (azomethine)
ꢃ(C N) (azomethine)
ꢃ(M–N)
ꢃ(M–N)
3057s
3060w
1655m
1651m
1651s
1657m
1657m
1676s
1630m
1597m
1603s
1622m
1598s
1652sh
1613s
1594m
1623s
1627s
–
521w
472w
494w
515w
470w
485w
521s
–
424w
425w
419w
421w
420w
421w
422w
455s
[
[
[
[
[
[
[
[
[
Mn(H2L)Cl2]·2H2O
Fe(H2L)Cl2]Cl·1.5H2O
Co(H2L)Cl2]·2.5H2O
Ni(H2L)Cl2]·2.5H2O
Cu(H2L)Cl2]·3H2O
Disappear
3102br
Disappear
Disappear
Disappear
3058s
Zn(H2L)Cl2]·3H2O
1655s
Cd(H2L)Cl2]·1.5H2O
Th(H2L)Cl2]Cl2·3H2O
UO2(H2L)](CH3COO)2·2H2O
1652m
Disappear
Disappear
Disappear
Disappear
503w
545br
419w
sh = sharp, m = medium, br = broad, s = small, and w = weak.
1H NMR spectrum of the ligand reveals the following signals at
(P). The spectrum shows also a band at 26,773 cm which may be
attributed to ligand to metal charge transfer. The electronic spec-
trum of the Co(II) complex gives three bands at 12,990, 16,665
−1
ı = 7.34–7.99 (m, 10H, ArH), 2.10–2.14 (t, 4H, 2CH ), 2.67–3.10 (t,
2
4
H, 2CH ), 3.21 (s, 4H, 2CH ) and 3.52 ppm (s, 2H, 2NH). While,
2
2
1
−1
−1
the H NMR spectrum of the Cd(II) complex reveals the follow-
and 20,798 cm . The region at 26,544 cm refers to the charge
transfer band. The bands observed are assigned to the transitions
ing signals at ı = 7.15–8.12 (m, 10H, ArH), 2.41–2.75 (t, 4H, 2CH ),
2
4
4
4
4
4
4
2
.80–3.11 (t, 4H, 2CH ), 3.20 (s, 4H, 2CH ) and 3.34 ppm (s, 2H,
T1g(F) → T (F) (ꢄ ), T1g(F) → A (F) (ꢄ ) and T1g(F) → T2g(P)
2
2
2g
1
2g
2
2
NH). The spectrum of the Cd(II) complex is examined in compari-
(ꢄ ), respectively, suggesting that there is an octahedral geometry
3
son with the parent Schiff base. Upon examinations it is found that
around Co(II) ion [24,25]. The magnetic moment value is found to
be 5.55 B.M. is an indicative of octahedral geometry [24].
The reflectance spectrum of the Cu(II) chelate consists of a broad
the signal observed at 3.52 ppm for H L ligand is assigned to NH
2
protons [23]. This signal is found at 3.74 ppm for its Cd(II) complex.
This indicates that the NH group is coordinated to the Cd(II) ion
without proton displacement [23].
band centered at 15,670 and 19,556 cm . The 2Eg and 2T2g states
−
1
9
of the octahedral Cu(II) ion (d ) split under the influence of the
tetragonal distortion and the distortion can be such as to cause
the three transitions 2B1g → B2g; B1g → Eg and B1g → A to
2
2
2
2
2
1g
3
.6. Magnetic susceptibility and electronic spectral studies
remain unresolved in the spectrum [24,26]. It is concluded 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 transi-
tions are normally close in energy [24]. The magnetic moment of
The diffused reflectance spectrum of the Mn(II) complex shows
−
1
three bands at 15,975, 21,850 and 27,780 cm
assignable to
4
6
4
6
4
6
T1g → A , T (G) → A and T (D) → A transitions, respec-
1g
2g
1g
1g
1g
tively [24]. The magnetic moment value is found to be 5.72 B.M.
which indicates the presence of Mn(II) complex in octahedral struc-
ture.
1
.97 B.M. falls within the range normally observed for octahedral
Cu(II) complexes [27]. A moderately intense peak observed in the
−
1
range 25,655 cm is due to ligand to metal charge transfer transi-
tion [24].
The Zn(II), UO2(II) and Th(IV) complexes are diamagnetic. By
analogy with those described for the complexes containing N–O
donor Schiff bases and according to the empirical formulae of these
complexes, an octahedral geometry is proposed.
From the diffused reflectance spectrum, it is observed that,
−
1
the Fe(III) chelate exhibits a band at 20,890 cm , which may
be assigned to the 6A1g → T (G) transition in octahedral geom-
2g
6
5
etry of the complex [21]. The A1g → T g transition appears
1
−
1
to be split into two bands at 16,635 and 12,850 cm . The
observed magnetic moment value of Fe(III) complex is found
2
3
to be 5.82 B.M., indicating octahedral geometry involving d sp
hybridization in Fe(III) ion [24]. The spectrum shows also a band
at 24,690 cm which may be attributed to ligand to metal charge
transfer.
The Ni(II) complex reported herein is high spin with a room
temperature magnetic moment value of 3.71 B.M. indicating that
the Ni(II) complex is octahedral [24,22]. The diffused reflectance
spectrum shows the ␲–␲* and n–␲* bands of the free ligand
3
.7. Thermal analyses (TG, DTG and DTA) studies
−1
Fig. 1a–c and Table 4 show the TG, DTG and DTA results of ther-
mal decomposition of metal chelates.
The TG curve of the Co(II) chelate is shown in Fig. 1a and data
obtained are listed in Table 4. It decomposes in three steps in the
temperature range 30–700 C. The first step is accounted to the loss
of H O molecule of the hydrated water and one HCl molecule with
mass loss of 12.83% (calcd. 11.21%). The mass losses of the 2nd and
rd steps (T = 200–700 C) correspond to the removal of HCl and the
◦
−
1
3
3
and displays three bands at ꢄ : (13,488) cm
:
A
→ T , ꢄ :
1
2g
−1
2g
2
2
−1
3
3
3
3
(
15,957) cm
:
A2g → T (F) and ꢄ : (21,852) cm
:
A
→ T
1g
3
2g
1g
◦
3
ligand molecules (estimated mass loss = 72.02%; calcd. = 73.07%).
Table 3
1
These steps are accompanied by exothermic peaks (175, 550, 650,
H NMR spectral data of the Schiff base and its Cd(II) chelate.
◦
7
50, 800, 875 and 950 C) and endothermic peaks (65, 260, 700, 825
Compound
H2L
Chemical shift, ı (ppm)
Assignment
◦
and 975 C) peaks. On the other hand, [Cu(H L)Cl ]·3H O chelate
2
2
2
7.34–7.99
(m, 10H, ArH)
(t, 4H, 2CH2)
(t, 4H, 2CH2)
(s, 4H, 2CH2)
(s, 2H, 2NH)
exhibits three decomposition steps (Fig. 1b) within the tempera-
2
2
3
3
.10–2.14,
.67–3.10
.21
◦
ture range from 30 to 760 C. The estimated weight loss of 7.08%
(
calcd. 7.73%) for the first step within the temperature range from
◦
.52
30 to 130 C can be attributed to the loss of two hydrated water
molecules. According to the data listed in Table 4, the total weight
losses of the decomposition steps are found to be 84.36% (calcd.
84.19%) and CuO is suggested as a residue. The DTA data are listed
in Table 4 and represented graphically in Fig. 1b. It is clear from
these data that these mass losses have ten exothermic (185, 275,
[Cd(H2L)Cl2] 1.5H2O
7.15–8.12
(m, 10H, ArH)
(t, 4H, 2CH2)
(t, 4H, 2CH2)
(s, 4H, 2CH2)
(s, 2H, 2NH)
2
2
3
3
.41–2.75
.80–3.11
.20
.74

Table 4
Thermoanalytical results (TG, DTG and DTA) of metal complexes.
◦
◦
Complex
TG range ( C)
DTGmax ( C)
n*
Mass loss
Estim. (calcd.) %
Total mass loss
84.85 (85.65)
Assignment
Metallic residue
DT
[
Co(H2L)Cl2]·2.5H2O
Cu(H2L)Cl2]·3H2O
30–200
60, 155
1
12.83 (11.21)
Loss of H2O and HCl.
65(+), 175(−), 260(+), 550(−),
6
8
50(−), 700(+), 750(−), 800(−),
25(+), 875(−), 950(−), 975(+).
2
5
00–515
15–700
325
640
1
1
33.84 (34.43)
38.18 (38.64)
Loss of HCl and C9H9N.
Loss of C11H15N3.
CoO
[
30–130
65
1
7.08 (7.73)
Loss of 2H2O.
65(+), 185(−), 275(−), 315(+),
375(−), 400(+), 450(−), 500(+),
550(−), 575(+), 635(−), 700(−),
900(−), 915(+), 925(−), 955(+),
965(−), 975(+).
1
3
30–390
90–760
160–320
655
1
2
34.61 (34.89)
42.67 (41.57)
Loss of 2HCl and C7H5N.
Loss of C13H19N3.
CuO
84.36 (84.19)
45.82 (45.50)
[UO2(H2L)](CH3COO)2·2H2O
20–135
80
1
4.44 (4.32)
Loss of C2H4.
UO2(NO3)2
40(−), 75(+), 175(−), 200(+),
2
4
25(−), 300(+), 350(−), 425(+),
90(−).
1
4
35–425
235,370
490
2
1
23.19 (23.36)
18.19 (17.82)
Loss of C12H23.
Loss of C8H7N2.
25–1000
n* = number of decomposition steps. (−) = endothermic, (+) = exothermic.

G.G. Mohamed et al. / Spectrochimica Acta Part A 75 (2010) 678–685
683
Table 5
Thermodynamic data of the thermal decomposition of H2L ligand and its metal complexes.
◦
−1
−1
−1
−1
−1
Complex
Decomp. temp. ( C)
E* (kJ mol
)
A (s
)
ꢅS* (kJ mol
)
ꢅH* (kJ mol
)
ꢅG* (kJ mol
)
6
7
1
6
6
[Co(H2L)Cl2]·2.5H2O
30–120
50.36
72.00
136.1
57.02
142.7
3.87 × 10
5.63 × 10
3.13 × 10
3.42 × 10
7.37 × 10
−105.9
−91.09
−4.72
49.84
70.71
133.9
54.30
137.3
56.49
84.79
135.1
93.62
214.6
120–200
200–300
300–500
500–850
2
−120.6
−119.9
6
6
8
[
[
Cu(H2L)Cl2]·3H2O
30–210
10–400
00–900
0.90
86.15
177.3
2.18 × 10
2.63 × 10
6.75 × 10
−111.0
−122.7
−82.49
00.35
83.47
171.8
7.62
122.9
226.2
2
4
4
5
1
UO2(H2L)](CH3COO)2·2H2O
20–150
50–425
25–1000
40.52
65.23
265.1
8.63 × 10
3.96 × 10
1.88 × 10
−139.59
−135.93
−81.56
39.8
63.24
261.0
51.12
95.69
220.56
1
4
7
Fig. 2. Structural formulas of H2L metal complexes.
3.8. Calculation of activation thermodynamic parameters
decomposition (ꢅG*) are evaluated graphically by employing the
Coats–Redfern relation [28]:
ꢀ
ꢁ
The thermodynamic activation parameters of decomposition
processes of dehydrated complexes namely activation energy (E*),
enthalpy (ꢅH*), entropy (ꢅS*) and Gibbs free energy change of the
ꢂ
ꢃ
ꢄꢅ
log{W /(W − W)}
AR
2RT
E∗
E
f
f
log
= log
1 −
−
(1)
2
T
ꢆE∗
2.303RT
Table 6
Biological activity of H2L and its metal complexes.
Sample
Bacillus simplex
Exiguobacterium acetylicum
Pseudomonas putida
E. coli bacteria
C (mg/l)
5
2.5
1
5
2.5
1
5
2.5
1
+
5
2.5
1
H2L
++
++
++
++
++
++
++
++
++
++
+
++
++
++
+
+
+
+
+
+
+
++
+
+
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
+
++
+
+
++
+
+
+
+
+
+
+
+
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
++
+
++
+
+
+
+
++
+
+
+
++
++
+
+
+
+
+
+
+
+
+
+
++
+
+
+
+
+
+
+
+
+
+
++
[
[
[
[
[
[
[
[
[
Mn(H2L)Cl2]·2H2O
Fe(H2L)Cl2]Cl·1.5H2O
Co(H2L)Cl2]·2.5H2O
Ni(H2L)Cl2]·2.5H2O
Cu(H2L)Cl2]·3H2O
++
+
+
+
++
+
+
+
++
++
+
++
++
++
++
+
Zn(H2L)Cl2]·3H2O
Cd(H2L)Cl2]·1.5H2O
Th(H2L)Cl2]Cl2·3H2O
UO2(H2L)](CH3COO)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 = +++.

6
84
G.G. Mohamed et al. / Spectrochimica Acta Part A 75 (2010) 678–685
where W is the mass loss at the completion of the reaction, W is the
f
mass loss up to temperature T; R is the gas constant, E* is the activa-
−
1
∼
tion energy in kJ mol , ꢆ is the heating rate and (1 − (2RT/E*)) = 1. A
2
plot of lg[log(W /(W − W))/T ] against 1/T gives a slope from which
f
f
E* is calculated and A (Arrhenius factor) is determined from the
intercept. The entropy of activation (ꢅS*), enthalpy of activation
(
ꢅH*) and the free energy change of activation (ꢅG*) are calculated
and the data are summarized in Table 5. The activation energies of
−
1
decomposition are found to be in the range 55.42–350.6 kJ mol
.
The high values of the activation energies reflect the thermal sta-
bility of the complexes. The entropy of activation is found to have
negative values in all the complexes which indicate that the decom-
position reactions proceed spontaneously.
3.9. Structural interpretation
From the IR spectra, it is concluded that H L behaves as neutral
2
tetradentate ligand with 4Ns donor sites and binds to the metal
ions thorough two azomethine N and two secondary amine NH.
From the molar conductance data of the complexes (ꢁm), it is
concluded that the complexes of H L ligand are considered as non-
2
electrolytes. Th(IV) complex with H L ligand is 2:1 electrolyte, in
2
addition, the results indicate also that the UO (II) and Fe(III) com-
2
plexes with H L ligand are of the type 2:1 and 1:1 electrolytes,
2
respectively.
On the basis of the above observations and from the mag-
netic and solid reflectance measurements, octahedral geometry is
suggested for the investigated complexes. The strucutres of the
complexes are shown in Fig. 2.
3.10. Biological activity
The main aim of the production and synthesis of any antimicro-
bial 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. The chemotherapeutic agent affecting only
one function has a highly sounding application in the field of treat-
ment by anticancer, since most anticancers used in the present time
affect both cancerous diseased cells and healthy ones which in turns
affect the general health of the patients. Therefore, there is a real
need for having a chemotherapeutic agent which controls only one
function [29].
In testing the antibacterial activity of these compounds more
than one test organism was used to increase the chance of detecting
antibiotic principles in tested materials. All of the tested com-
pounds show a remarkable biological activity against different
types of Gram-positive (G ) and Gram-negative (G ) bacteria. The
data are listed in Table 6 and shown in Fig. 3. On comparing the
biological activity of the Schiff base and its metal complexes with
the standard (cefepime), the following results are obtained:
Fig. 3. Biological activity of H L and its complexes at (a) 5 ppm, (b) 2.5 ppm and (c)
1 ppm.
2
+
−
The activity of H L free ligand is found to be equal to
2
that of the standard (cefepime). The biological activ-
ity of the complexes is found to follow the order:
Cd(II) > Mn(II) = Co(II) = Ni(II) = Zn(II) = UO (II) > H L = cefepime >
+
(
a) Using Bacillus simplex bacteria (G ):
2
2
The biological activity of Mn(II), Fe(III), Co(II), Ni(II), Cu(II),
Fe(III) = Cu(II) > Th(IV).
a. Using Pseudomonas putida bacteria (G ).
−
Zn(II), Cd(II), Th(IV) and UO (II) complexes are higher than that
2
of the standard cefepime. In addition, the biological activity of
Cd(II) and Mn(II) complexes are higher than that of the free lig-
It is found that cefepime, Mn(II) and Cu(II) com-
plexes have the higher activity than that of the H2L
ligand and the remaining complexes. The biological
activity of the complexes is found to follow the order:
and. For Cu(II) and UO (II) complexes, their biological activities
2
are nearly the same like that of the free ligand. The biolog-
ical activity of the complexes therefore, follows the order:
cefepime > Mn(II) = Cu(II) > H L = Co(II) = Cd(II) = Th(IV) > Ni(II) =
2
Cd(II) > Mn(II) > H L = Cu(II) = UO (II) > Zn(II) = Th(IV) > Fe(III) =
UO (II) > Fe(III) = Zn(II).
(c) Using Escherichia coli bacteria (G )
2
2
2
−
Co(II) = Ni(II) > cefepime.
+
(
b) Using Exiguobacterium acetylicum bacteria (G )
It is found that the standard cefepime and UO (II)
2
The biological activity of Cd(II) complex is found to
be higher than that of the free ligand and standard.
complex have higher biological activity than that of
the H2L ligand and its remaining complexes. The bio-

G.G. Mohamed et al. / Spectrochimica Acta Part A 75 (2010) 678–685
685
logical activity of the complexes follows the order:
cefepime > UO (II) > H L > Mn(II) = Fe(III) = Co(II) = Ni(II) = Cu(II) =
Zn(II) = Cd(II) = Th(IV).
[4] M.M.T. Khan, S.B. Halligudi, S. Shukla, Z.A. Shaikh, J. Mol. Catal. 57 (1990)
01–305.
3
2
2
[
5] D. Bose, J. Banerjee, S.K.H. Rahaman, G. Mostafa, H.K. Fun, W.R.D. Bailey, M.J.
Zaworotko, B.K. Ghosh, Polyhedron 23 (2004) 2045–2051.
[
[
6] H.A. El-Boraey, J. Therm. Anal. Calorim. 81 (2005) 339–346.
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Also, it is found that E. coli is inhibited by UO (II), Co(II) and
2
(
2003) 243–348.
Cd(II) complexes. The importance of this lies in the fact that these
complexes could be applied fairly in the treatment of some common
diseases caused by E. coli e.g. Septicaemia, Gastroenteritis, Urinary
tract infections and hospital acquired infections [30].
[
8] A. Arquero, M. Canadas, M. Martinez-Ripoll, M.A. Mendiola, A. Rodriguez, Tetra-
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[
1551–1561.
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[11] U. Mukhopadhay, L. Govindassamy, K. Ravikumar, D. Velmurugan, D. Ray, Inorg.
Chem. 1 (1998) 152–154.
2
and Th(IV) complexes are inhibiting Gram-positive and Gram-
negative bacterial strains (B. simplex, P. putida and E. acetylicum).
The importance of this unique property of the investigated Schiff
base complexes lies in the fact that, it can be applied safely in the
treatment of infections caused by any of these particular strains.
Since almost all scientists working in the field of search for
new antitumour depend basically on the line of antibiotics affect-
ing Gram-negative bacteria [31,32], and since there are certain
organisms which have proved difficult to treat and most of them
are Gram-negative rods, it is therefore believed that all the com-
plexes which are biologically active against both the Gram-negative
strains may has something to do with the barrier function of the
envelope of these Gram-negative strains activity, acting in a way
similar to that described by Brown [32] and Nikaido and Nakae [31].
Therefore, it is claimed here that the synthesis of these complexes
might be recommended and/or established a new line for search
to new antitumour particularly when one knows that many work-
ers studied the possible antitumour action of many synthetic and
semisynthetic compounds e.g., Hickman and co-workers [33]. Such
compounds may have a possible antitumour effect since Gram-
negative bacteria are considered a quantitative microbiological
method testing benificial and important drugs in both clinical and
experimental tumour chemotherapy [29].
[
12] M. Boca, M. Valko, G. Kickelbick, M. DurÃ-ka, W. Linert, Inorg. Chim. Acta 349
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(
[
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Inorg. Chem. 39 (2000) 3205–3212.
[
[
15] G.G. Mohamed, C.M. Sharaby, Spectrochim. Acta (Part A) 4 (2007) 949–958.
16] M.M. Omar, G.G. Mohamed, A.M.M. Hindy, J. Therm. Anal. Calorim. 86 (2006)
315–325.
17] G.G. Mohamed, Spectrochim. Acta (Part A) 64 (2006) 188–195.
18] G.G. Mohamed, M.M. Omar, A.M.M. Hindy, Spectrochim. Acta (Part A) 62 (2005)
[
[
1140–1150.
[19] I. Sakiyan, E. Logoglu, S. Arslan, N. Sari, Bio. Met. 17 (2004) 115–120.
[
[
20] J.A. Dean, S. Lange, Hand Book of Chemsitry, 14th edn., Megraw-Hill, New York,
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1
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358–369.
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141–3151;
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[23] G.G. Mohamed, F.A. Nour EL-Dien, S.M. Khalil, A.S. Mohammad, J. Coord. Chem.
62 (2009) 645–654.
[
[
[
[
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