Spectral characterization, thermal and biological activity studies of Schiff base complexes derived from 4,4′-Methylenedianiline, ethanol amine and benzil

Article abstract of DOI:10.1016/j.molstruc.2016.12.071

Some new metal(II) complexes of asymmetric Schiff base ligand were prepared by template technique. The shaped complexes are in binuclear structures and were explained through elemental analysis, molar conductivity, various spectroscopic methods (IR, U.V–V

Full text of DOI:10.1016/j.molstruc.2016.12.071

Accepted Manuscript
Spectral Characterization, Thermal and Biological Activity Studies of Schiff Base
Complexes Derived from 4,4′-Methylenedianiline, Ethanol Amine and Benzil
Sanaa Moustafa Emam
PII:
S0022-2860(16)31390-4
10.1016/j.molstruc.2016.12.071
MOLSTR 23269
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
24 June 2016
22 December 2016
24 December 2016
Please cite this article as: Sanaa Moustafa Emam, Spectral Characterization, Thermal and
Biological Activity Studies of Schiff Base Complexes Derived from 4,4′-Methylenedianiline, Ethanol
Amine and Benzil, Journal of Molecular Structure (2016), doi: 10.1016/j.molstruc.2016.12.071
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Highlights
 Preparation of new metal complexes using in situ reaction.
 Comparing the IR spectra of metal oxides resulted from thermal
decomposition of metal complexes with that of their metal complexes.
 XRD spectra of metal complexes and their final product were also carried
out to calculate their crystallite size.

Biological activity of metal complexes against Land Snails and
Hepatocellular Carcinoma cell (Hep-G2).

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Spectral Characterization, Thermal and Biological Activity Studies of Schiff Base
Complexes Derived from 4,4′-Methylenedianiline, Ethanol Amine and Benzil
Sanaa Moustafa Emam*
Chemistry Department, Faculty of Science, Menoufia University, Shebin El-Kom, Egypt
Abstract
Some new metal(II) complexes of asymmetric Schiff base ligand were prepared by
template technique. The shaped complexes are in binuclear structures and were
explained through elemental analysis, molar conductivity, various spectroscopic
methods (IR, U.V-Vis, XRD, ESR), thermal (TG) and magnetic moment measurements.
The IR spectra were done demonstrating that the Schiff base ligand acts as neutral
tetradentate moiety in all metal complexes. The electronic absorption spectra
represented octahedral geometry for all complexes, while, the ESR spectra for Cu(II)
complex showed axially symmetric g-tensor parameter with g׀׀ > g┴ > 2.0023 indicating
to 2B1g ground state with (dx2-y2)1 configuration. The nature of the solid residue created
from TG estimations was affirmed utilizing IR and XRD spectra. The biological activity
of the prepared complexes was studied against Land Snails. Additionally, the in vitro
antitumor activity of the synthesized complexes with Hepatocellular Carcinoma cell
(Hep-G2) was examined. It was observed that Zn(II) complex (5), exhibits a high
inhibition of growth of the cell line with IC50 of 7.09 μg/ml.
Key words: Metal complexes; IR spectra; Thermogravimeteric analysis; powder X-ray
diffraction; Biological activity
1. Introduction
Metal coordination compounds have wide assorted qualities of technological and
modern applications ranging from catalysis to anti-tumor drugs. Schiff base complexes
have numerous applications in modern and biological systems [1-10]. Chelate metal
complexes having high-luminance blue transmitting nature find use as materials for
RGB (red, green, and blue) emission. The complexes containing oxygen and nitrogen
*Corresponding author mail: sanaa.mostafa74@yahoo.com
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atoms go about as models for metalloproteins, metalloenzymes which catalyze the
reduction of nitrogen and oxygen [11]. Likewise, this kind of complexes assumed an
important role in life; they demonstrated high catalytic activity, antiviral, threatening to
tumor, and anti-inflammatory agents [12].
Multifunctional ligands represent one of the most important compounds because of
their applications in catalysis, supramolecular chemistry, medicinal inorganic chemistry
research, numerous new and exciting difficulties lie ahead [13]. Metal complexes of
multifunctional ligands assume an imperative part in muting the potential toxicity of a
metallodrug to have a positive impact in fields of diagnosis and therapy [14].
4,4`-Methylenedianiline (MDA) is utilized as intermediate in synthesis of
polyurethane froths, thermoplastics, preparation of azodyes [15] and used as antioxidant
agent for lubricating oils, elastic preparing and curing specialists for epoxy resins,
urethane elastomers, a corrosion safeguard for iron. MDA has possibly unsafe
consequences for animals and human wellbeing. While, in people, oral or dermal
exposure or inhalation of MDA has prompted inconveniences in liver digestion system
with altogether expanded action of liver proteins [16]. The high flexibility of MDA is a
decent candidate in the effort to prepare flexible multifunctional Schiff bases by
coordination with an assortment of aldehydes and ketones. This kind of ligands can react
with metal ions giving complexes with suitable properties for practical and biological
applications [17]. The most well-known rout for preparation of the multifunctional
Schiff base ligands is the condensation of primary diamines with dicarbonyl compounds.
A carful literature study demonstrated that the metal complexes of multifunctional
Schiff bases containing MDA, benzil and ethanolamine were not beforehand reported
so, this kind of ligands must be prepared in two stages. The first is the synthesis of (bis-
((E)- 2-(4-ethylphenylimino)-1,2-diphenylethanone) obtained from the reaction of
MDA with benzil with (1:2) molar ratio in ethanol. The got ligand contains two free
carbonyl groups accessible for the condensation with ethanolamine with (1:2) molar
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ratio in the second step. While, in this stage numerous endeavors have been done to
separate this ligand, yet all endeavors were unsuccessful even under various conditions.
Henceforth, template reactions have been broadly used for the preparation of Mn(II),
Co(II), Ni(II), Cu(II) and Zn(II) complexes of Schiff base ligand isolated from MDA,
benzil and ethanolamine in which the metal ions are largely utilized as template agent
1
[18,19]. These complexes were described by a few physicochemical methods as IR, H
NMR, ESR, electronic spectra, elemental analysis, thermal studies, X-ray diffraction,
magnetic susceptibilities and conductance estimations. Besides, the biological screening
of metal(II) complexes against Land Snails and Hepatocellular Carcinoma cell (Hep-G2)
was assessed.
2. Experimental
2.1. Analytical and Physical Measurements
All chemicals were of analytical grade (BDH, Sigma or Aldrich) and were utilized
as got without further purification.
Elemental analyses (C, H, and N) have been performed on a Perkin Elmer-2400
elemental analyzer at Main Defense Chemical Laboratory. Manganese(II), cobalt(II),
nickel(II) and copper(II) ions of metal complexes were estimated by complexometric
titration, while, zinc(II) ion was determined by means of gravimetric analyses [20].
Additionally, the chloride ions were evaluated by utilizing Mohr's technique [20].
The infrared spectra were recorded as KBr plates on a Nicolet FT-IR spectrophotometer
in the reach 4000-400cm-1. Molar conductivity estimations were made in DMSO
solution (10-3 M) using a type CD6N Tacussel conductimeter. Magnetic susceptibilities
were measured at room temperature by an modified Gouy method by utilizing a Johnson
Matthey magnetic susceptibility balance. Diamagnetic corrections were determined
using Pascal's constants [21]. The effective magnetic moments were ascertained from
the mathematical statement µeff =2.84(XMcorrt T)1/2 where, XMcorrt is the molar magnetic
susceptibility corrected for diamagnetism of all atoms in the compounds. The 1H NMR
spectra were done in DMSO-d6 on a Varian Gemini 200 NMR spectrophotometer at 300
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MHz. The electron spin resonance (ESR) spectrum for Cu(II) complex was performed
utilizing a Varian E-109C model spectrometer outfitted with a field modulation unit at
frequency 100 kHz. Estimations were affected in the X-band on a microcrystalline
powder at room temperature; the microwave force was around 10 mW. The absorption
electronic spectra were measured in Nujol mulls on a Perkin Elmer Lambda 4B
spectrophotometer. The thermal analysis (TG) was done by using a Shimadzu DAT/TG-
50 thermal analyzer with a heating rate of 10οC/min under N2 environment with a
streaming rate of 20 mL/min from the room temperature up to 900°C utilizing platinum
crucibles. Powder X-ray diffraction designs for complexes (1-5) and their final products
acquired from TG examination were measured utilizing X-ray diffractometer equipped
with a graphite monochromator in the range (2θ=4-80◦) by nickel separated CuKα
radiation (λ= 1.5418 A◦). The average crystallite size of complexes (1-5) and their final
products obtained from TG analysis was estimated using Debeys-Scherrer equation
[22]. Melting points were measured by using Stuart melting point apparatus.
Biochemical measurements were carried out at Plant Protection Researches Institute,
Giza, Egypt and the Regional Center for Mycology and Biotechnology, Egypt.
2.2. Cytotoxicity assay
Anticancer activity was carried out in Regional Center for Mycology and
Biotechnology, Al-Azhar University, Cairo, Egypt. The metal complexes (1-5), MDA,
benzil were screened for their cytotoxicity in vitro, in comparison with doxorubicin
(DOX) as a reference drug against human-hepatic carcinoma cell line, Hep-G2. The
tumor cell lines were kept up in Dulbecco's modified Eagle's medium (DMEM)
supplemented with 10% heat inactivated fetal calf serum (GIBCO). Cells (104 cells/
well) were incubated at 37°C for 48 h in humidified atmosphere containing 5% CO2
before treatment with the tested compounds to allow attachment of cell to the wall of the
plate. Six concentrations (1.56, 3.125, 6.25, 12.50, 25.0 and 50.0 μg/mL) of complexes
(1-5) were prepared by using DMSO as a diluent, at that point, 0.2 mL of each
concentration of test compounds and the standard drug (doxorubicin) was added to every
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cell line and incubated at 37 °C for 24 h, in a humidified 5% CO2 atmosphere. Cells
survival was estimated at the end of the incubation period. Viable cells yield was
determined by colorimetric method [23]. The viable cell number is inversely
proportional to the concentration of each complex. The compound concentrations which
give 50% growth inhibition are referred to as the IC50 and values were obtained
mathematically from the concentration response curve using a computer program for
probity analysis.
2.3. Biological Activity
Two sorts of land snail were gathered from untreated fields and decorative plants at
Menoufia governorate, Egypt; they are the glassy clover snail, Monacha obstructa and
the brown garden snail, Eobania vermiculata. Muslin sacks were utilized to transfer the
snails straightforwardly to the laboratory. At that point, they are kept for two weeks in
little plastic boxes that contain 8-10 cm moist optimal soil supplied with fresh green
lettuce leaves. At first, healthy adult snails with the same shell width were chosen for
every treatment and incubated for 24 h. Based on the thin layer film system [24], five
concentrations of the tested compounds were readied utilizing refined water and DMSO,
then 2 mL of every concentration were stored and dispersed on the base of a petri dish
by moving the dish delicately in circles. Under room conditions, solvents were
evaporated leaving a thin layer of the applied concentration of the tested compounds.
Five snails of the tried species were taken and exposed to the candidate concentration of
the tested compounds for 72 h, then exchanged to another plastic box (24× 10 ×12 cm),
shut with muslin material containing ideal soil (3-5 cm). The last experiment must be
repeated with a parallel control test utilizing water and DMSO. Dead snails were
numbered and expelled from the containers each 24 h. Probity analysis was used to
compute LC50 values [25].
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2.4. Synthesis of Schiff base metal complexes obtained by template reaction of MDA,
benzil and ethanolamine
A few endeavors to synthesize the free Schiff base ligand were unsuccessful.
Subsequently, all the complexes were synthesized by template reaction with molar ratio
(1MDA: 2Benzil: 2Ethanol amine: 2M). 0.02 mol of a hot ethanolic solution of benzil
was added to 0.01 mol of MDA in 25 mL ethanol. The reaction mixture was refluxed for
2 h at 50°C, then, 0.02 mol of ethanolamine was added to the mixture followed by reflux
for 60 minutes. 0.02 mol of proper metal(II) chloride in 20 mL ethanol was added
dropwise to the reactants and few drops of concentrated H2SO4 were added to the
reaction mixture. It was refluxed for 3 h at 70°C. The formed complex was filtered off,
washed a few times with ethanol and dried in a vacuum desiccator anhydrous CaCl2 and
P2O5.
3. Results and Discussion
3.1. Chemistry
A few trials to synthesize the free Schiff base ligand derived from the condensation
of 4,4’-methylenedianiline, ethanolamine with benzil, were unsuccessful. But, the metal
complexes were prepared by tempelate reaction using the chloride salts of Mn(II),
Co(II), Ni(II), Cu(II) and Zn(II) ions with molar ratio (1MDA: 2Benzil: 2Ethanol amine:
2M) affording metal complexes (1-5). The suggested structures for the prepared
complexes were presented in Scheme (1). The structure of these complexes was
identified using analytical and spectral methods.
Insert Scheme (1) and its caption here
3.2. Analytical data
Table (1) demonstrates the colors, elemental analyses, stoichiometry, melting points
and molar conductivity of the metal complexes separated by template reaction. We
report that few endeavors to incorporate the hexadentate Schiff base ligand from the
direct reaction of 4,4΄-methylenedianiline, benzile and ethanolamine, failed, resulting
instead in tetradentate Schiff base through the metal template reaction. The analytical
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data of metal complexes are given in Table (1) which show that template reactions of
(MDA: benzil: ethanolamine: metal) (1:2:2:2) molar ratio might be represented by the
chemical formula:
 [M2(L)Cl4(H2O)2].nH2O.mEtOH, where M=Mn(II), Co(II), Ni(II), Zn(II); n=(7.5,
8.5, 5, 7) and m= (0.5, 0, 0, 0) for complexes, (1), (2), (3) and (5), respectively.
 [Cu2(L)Cl3(H2O)3].Cl.11H2O, complex (4).
The complexes are steady, non-hygroscopic and partially dissolvable in most organic
solvents, for example, methanol, ethanol, acetonitrile, DMF and freely soluble in
DMSO. The molar conductivity estimations of (10-3 M) DMSO solutions of metal
complexes revealed that all complexes (except 4) are non-electrolytes, demonstrating
that the chloride ions are directly bonded to the metal ions [15,26-30]. The molar
conductance value (54 ohm-1cm2mol-1) for complex (4) typified (1:1) electrolytes [26-
30].
Insert Table 1 and its caption here
3.3. Infrared Spectra
The fundamental infrared spectral bands of the metal complexes are listed and
shown in Table (2) and Figs (1a, 2a, 3a, 4a). The spectra of all metal complexes were
compared to the spectra of parent reactants. The IR spectra confirm the presence of
MDA in the complexes with the existence of absorption bands at 3027-3080; 2929-
2943, 2840-2864; 1438-1444, 1226-1271 and 1147-1170 cm-1 ascribed to aromatic,
aliphatic stretching vibrations of (CH) group; asymmetric, symmetric stretching
vibrations, scissoring, wagging and twisting bending vibrations of (CH2) group,
respectively [31]. The spectra of all metal complexes lack absorptions bands at 1600-
1700 cm-1 which could be ascribed to ν(C=O) of benzil [11,16,50], but show another
absorption band at 1566-1586 cm-1 range, may be assigned to ν(C=N) of azomethine
group [31-33]. This is indicative of the involvement of benzil carbonyl groups in
condensation with MDA. Furthermore, the appearance of medium bands in the spectra
of all metal complexes situated at 3274-3337 and 3232-3273 cm-1 range, attributed to
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υas and υs of coordinated NH2 group [34,35]. In addition, the existence of NH2 group in
structure of complexes is supported by the presence of extra absorption bands at (1610-
1625) and (1100-1180 cm-1), due to δ(NH2) of MDA [28] and that of EA ν(-C-NH2),
respectively [36]. Another evidence to the coexistence of NH2 group is the overtone
band at ca.(505-551 cm-1) [31] which undergoes blue/red shift frequency upon chelation
(517-538 cm-1) suggesting ν(M-N) of NH2 group. Likewise, the spectra showed bands
at (466-499 cm-1), due to ν(M-N) of azomethine group [37,38]. On the otherhand, the
frequency band ν(-CH2-OH) of ethanolamine (EA) which is observed at 1080 cm-1
exhibits low/high shift frequency upon chelation and appeared in extent 1067-1096
cm-1 [31,32,37,39]. Also, the spectra of complexes displayed peaks at at (1100-1156
cm-1) and (1301-1327 cm-1) range, attributed to ν(M-OH), and δ(OH) of EA [36],
respectively. A broad intense absorption band in the region (3388-3427 cm-1) present in
all metal complexes is probably ascribed to the presence of coordinated OH group of
EA together with lattice and/or coordinated water molecules. The coordination of water
with the metal ion is supported by appearance of weak to medium band at ca (655-682
cm-1) due to wagging mode [40].
The results mentioned above and the stoichiometry together with IR spectral data of
isolated binuclear complexes reveal that the formed Schiff base ligand acts as
tetradentate moiety where it is coordinated to the metal ion via two imine nitrogens, one
NH2 nitrogen (MDA) and one OH oxygen atom of EA as shown in Scheme (1). This is
indicative of the involvement of only one mole of benzil in condensation with only one
NH2 group of MDA and NH2 group of EA leading to the formation of monoanil
asymmetric Schiff base, while, the other mole of ethanol amine used as adduct in metal
complexes and the other mole of benzil is hydrolysed. This was supported also by
elemental analyses and thermal studies.
Insert Table 2 and its caption here
Insert Figurees (1-4) and their captions here
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3.3. 1H NMR
The 1H NMR spectrum of complex (5) in DMSO displays multiple signals at δ
(6.81-6.33ppm) range assignable to protons of aromatic rings [38,41]. The spectra of
complexes (5) show multiple bands at (4.32, 3.55, 3.40, 3.31 and 3.20 ppm), attributed
to OH, CH2-phenyl, CH2-OH, NH2 and CH2-NH2 protons [41], respectively. Also, the
spectrum depicts singlet signal at δ 4.78ppm, due to NH2-phenyl [31,32,42].
3.4. Molecular modeling study of Mn(II) complex
Molecular modeling studies using (MM+) calculations [43,44] are performed to
determine a better understanding of the geometry of the investigated compound. The
molecular mechanisms (MM+) has wide applications in the field of coordination
chemistry [44]. The molecular modeling of Mn(II) complex, Table (3) and Figure (5)
demonstrated some of the important bond lengths and numbering of the complex
Skelton. It was watched that the stability order diminishes in this way:
N(18)ethanol=C(17)benzil ≈ C(4)ring–N(14) > C(16)–C(17) ≈ C(17)–C(42) ≈ C(16)–
C(36) > N(18)ethanol-C(22)ethanol > Mn(21)–O(24)ethanol≈ Mn(28)–O(30)ethanol
> Mn(21)–N(18) ethanol ≈ Mn(21)–N(14)MDA > Mn(21)–Cl(26) ≈ Mn(21)–Cl(25)
Insert Table 3 and its caption here
Insert Figure 5 and its caption here
3.5. Electronic Spectra and Magnetic Moments
Electronic spectral data and magnetic moment measurements provide sufficient data
to establish the geometry of metal complexes. The magnetic moment values per metal
ion at room temperature and the Nujol mulls electronic absorptions are given in Table
(4). The spectra of the complexes show bands at (252-296), (319-324) and (438-516 nm)
ranges, ascribed to π-π* electronic transitions of benzenoide system and (C=N) group; n-
π* transition due to localized lone pair of electrons on nitrogen atom of azomethine
group and ligand to metal charge transfer (LMCT) [45-47].
The electronic spectrum of Mn(II) complex [Mn2(L)Cl4(H2O)2].7.5H2O.0.5EtOH (1)
6
4
6
displays bands near 662, 584 and 524 nm, assignable to A1g → T1g (G4) (υ1), A1g →
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6
4
4Eg (G4) (υ2) and A1g → Eg (D4) (υ3) transitions, respectively. These bands suggest an
octahedral geometry around Mn(II) ion [48,49].
The electronic spectrum of Co(II) complex [Co2(L)Cl4(H2O)2].8.5H2O (2) exhibits
4
4
bands at 657 and 580 nm, corresponding to T1g(F)→4A2g(P) (υ2) and T1g(F)→4T2g(P)
(υ3), respectively. These transitions are consistent with an octahedral Co(II) complex
[50,51]. While, the electronic spectrum of Ni(II) complex [Ni2(L)Cl4(H2O)2].5H2O (3)
3
3
shows bands at 725, 620 and 526 nm, assigned to A2g(F) → T2g(F) (υ1),3A2g(F) →
3
3T1g(F) (υ2) and A2g(F) → 3T1g(P) (υ3), respectively. These bands suggest an octahedral
geometry for Ni(II) complex [41,48-50,52]. Moreover, the electronic spectrum of Cu(II)
complex [Cu2(L)Cl3(H2O)3].Cl.11H2O (4) displays bands at 662 and 541 nm,
2
2
corresponding to B1g→2B2g (υ2) and B1g→2Eg (υ3) transitions, respectively indicating
distorted octahedral geometry for Cu(II) complex [45,47,50]. Table (4) showed that the
experimental values of magnetic moment are not high as μ(S+L), this is may be due to the
effect of electric field of other atoms, where the molecules surrounding the metal ion
restrict the orbital motion of electrons and the orbital contribution to the magnetic
moment is partially quenched. The magnetic moment values for complexes (1,2, 3, 4)
are 1.61, 4.06, 3.11 and 1.59 B.M., respectively, and convenient with electronic
transitions to propose the octahedral geometry for those complexes [53-55].
Furthermore, the slightly low values of magnetic moment of complexes (1-4) may be
attributed to anti-ferromagnetic interactions [56,57]. The spectra of Zn(II) complex (5)
do not show any d-d transitions, as well as, it is a diamagnetic complex.
The proposed chemical structures for the synthesized metal complexes (based on
elemental analyses and spectral methods), are represented in Scheme 1.
Insert Table 4 and its caption here
3.6. Thermal Studies
Thermal analysis is a very useful technique in order to assess the thermal stability of
materials, confirm molecular structures and identify the different types of solvent of
crystallization. Figure (6) represents TG/DTG curves of complexes (1-5). The observed
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and the calculated data with DTG peaks are summarized in Table 5. The DTG curves of
the metal complexes can be used to be analyzed using the rate equation [58-60]:
dα/dt=K(1–α)n
In the last equation, (α) and (n) pointed to the decomposed fraction and the reaction
order, respectively while, K represents the rate constant which is given by Arrhenius
equation: K=Ae–E*/RT, where E*, A, R and T are the activation energy, frequency factor,
the gas constant and the temperature in kelvin. The initial rate method, in which
(I is
푙푛퐼
the intensity of the DTG or DTA curve) is plotted versus (1000/T) can be applied to
calculate the activation energy (∆E*) [58-60]. This should give a straight line, its slope
푑훼
is (-E*/R). The intensity (I) represents (
) in DTG curve and ΔT in DTA curve
푑푡
[59,60] Also, the kinetic parameters (ΔH, ΔS* and ΔG) were calculated using these
relations:
ΔH= ΔE*–R∆T; ΔS*=RTln(Ah/KT); ΔG=ΔH–TΔS*, where K, h, R, A and T are
Boltzmann’s, Planck’s and gas constants, frequency factor and absolute temperature,
respectively. So, the thermodynamic and kinetic parameters of the metal complexes are
given in Table 6.
The thermogravimeteric curves indicate that the complexes loss their solvent of
crystallization in one step (complexes 1, 3) or more steps (complexes 2, 4, 5). The
desolvation step is extended over 26-398°C temperature range. Sometimes, this process
interacts with the ligand pyrolysis (complex 2), or with the dehalogenation
process/removal of coordinated water as observed in complexes (5) and (4),
respectively, Table (5). After that, the desolvation stage is followed by a number of
decomposition peaks in the temperature range 398-900°C producing metal oxides [41]
as final residue. The nature of the solid products was established on the basis of the TG
curves and confirmed by IR and XRD spectroscopy.
The correlations between the different decomposition steps of the compounds
corresponding to the weight losses are discussed in terms of the proposed formula of the
complexes.
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Insert Figure (6) and its caption here
The TG curves of metal complexes exhibit mass losses in three steps for
[Mn2(L)Cl4(H2O)2].7.5H2O.0.5EtOH (1), [Co2(L)Cl4(H2O)2].8.5H2O (2),
[Ni2(L)Cl4(H2O)2].5H2O (3), [Zn2(L)Cl4(H2O)2].7H2O (5) and five steps for
[Cu2(L)Cl3(H2O)3].Cl. 11H2O (4) between 25 and 900°C.
The thermal behavior of Mn(II) complex [Mn2(L)Cl4(H2O)2].7.5H2O.0.5EtOH (1)
and Co(II) complex [Co2(L)Cl4(H2O)2].8.5H2O (2) is almost similar. The thermal
decomposition of complexes (1,2) proceeds with three main degradation stages within
the temperature range (26-900°C) and (27-900°C) for complexes (1) and (2). The first
one occurs within the temperature range (26-391°C) and (27-361°C); and corresponded
to the removal of solvent of crystallization (0.5 EtOH+7.5H2O) and (5H2O) with an
estimated weight losses 16.81and 9.66% for complexes (1) and (2), respectively. This
step is associated with weak DTG peaks at (Tmax.= 43,349 οC) and (51, 345οC) and
follows a first order and kinetic activation energy values (58.02, 252.88 KJmol-1) for
complex (1) and (44.54, 94.81 KJmol-1) for complex (2). Considering the IR spectra
of complex (1), Fig. (1a,b) represents the IR spectra of complex (1) before and after
heating up to 391°C, they are quite similar, but some changes observed in intensity and
the shape of some peaks accompanied with the disappearance of bands characteristic for
EtOH and hydrated water, this confirms the removal of solvent of crystallization.
Furthermore, the X-ray patterns of both solvated and desolvated forms of complex (1)
(Fig. 7a,b) are similar but the crystalinity increases after heating due to the higher
number of reflections. After desolvation, the second stage appears at (391-538°C) and
(361-582°C) assigned to the ligand pyrolysis, along with dehalogenation and elimination
of the rest outersphere water molecules, with estimated weight losses of 48.68 and
59.27%. This step is accompanied by weak to strong DTG peaks at (Tmax.= 484 οC and
449οC) and follows a first order and kinetic activation energy values (367.57 and 264.24
KJmol-1) for Mn(II) and Co(II) complexes, respectively. The modeling structure of the
Mn(II) complex (Fig, 5 and Table 3) shows that the Mn–Cl and Mn–N bonds are more
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lengthen than the other bonds, this is an evidence for the proposed mechanism for the
thermal decomposition pathway for complex (1) (Scheme 2). The second decomposition
stage for complex (1) led to isolation of intermediate (C6.5H12NO4Mn2Cl) which is stable
over a large temperature range (538-706°C) as shown in Fig. 6. Its structure was
confirmed by IR spectra (Fig. 8a), elemental analysis and energy dispersive X-ray
spectroscopy (EDX) spectra, Fig. 9.The IR spectrum, (Fig. 8b) showed the lack of
absorption bands characteristic to monosubstituted, paradisubstituted phenyl rings but
new peaks appeared at 3482, 2925, 1629, 1445, 1125, 1000, 877, 610 and 520 cm-1.
These bands may be attributed to coordinated OH (hydroxyl group); υ(C–H) of
CH3/CH2 group; stretching frequency of coordinated (C=O) that overlapped with other
peaks like υ(C=N) which falls within this region; δ(CH2) [15]; {υ(C–N)+ υ(C–OH)} of
primary amine and ethanol amine [31,32,39]; υ(Mn–OH) [40]; δr(CH2) [15]; and υ(Mn–
O) vibrations [40], respectively. Again, the last decomposition step observed in the
temperature range (706-900°C) and (582-900°C) indicating to further ligand pyrolysis
with the formation of (Mn3O4) and (Co3O4) as final products for Mn(II) and Co(II)
complexes [56,60], individually, (Table 5). The final residue of the thermal
decomposition of complexes (1) and (2) were explored by IR and XRD spectra. The IR
spectra of the final products (Mn3O4) and (Co3O4) (Figs. 8b and 2b) show two bands at
(614, 517cm-1) and (649, 549 cm-1) represented to 훎(Mn–O) and 훎(Co–O), respectively
[61-65]. In Co3O4 residue, the band observed at 649 cm-1 may be related to υ(Co–O)
where Co2+ is tetrahedrally coordinated, while, the band observed at 549 cm-1 is
assigned to the υ(Co–O) where Co3+ is octahedrally coordinated. It is clear that the
XRD diffractogram peaks of the final products for Mn(II) and Co(II) complexes are
consistent with the data of the JCPDS cards number (24-0734) for (Mn3O4), (Fig. 7c)
[66] and (01-076-1802) for Co3O4 (Fig. 10b), respectively. The X-ray patterns
demonstrate that these oxides have a lower degree of crystallinity than their metal
complexes. Figure (7c) showed broad and weak diffraction peaks for Mn3O4 residue due
to its poor crystallinity or its small crystal particles. Its diffraction peaks are seen at 2θ
13

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values of 33.84, 37.91, 42.35 and 71.08° indicating to the crystal planes of (103),
(211), (400) and (321) of the tetragonal phase of Mn3O4 oxide, respectively, and they
were similar to husmannite moiety Mn3O4 [63]. Also, Fig. 10b showed peaks at 2θ
values of 22.01, 36.38, 43.05 and 65.69° correspond to the crystal planes of (111),
(311), (400) and (440) of the cubic phase of Co3O4 oxide, respectively [64,65]. The
average crystallite size of the final products was calculated using Debeys-Scherrer
equation [22] to give diameters of 29.4, 42.05nm for Mn3O4 and Co3O4 oxides,
respectively, indicating to nanonature for these oxides [63-65].
D=Kλ/βCosθ
where D is the crystallite size, K= shape factor, with a value close to unity. The shape
factor has a typical value of about 0.9, but varies with the actual shape of the crystallite;
λ is the wavelength of X-ray, θ-angle diffraction and β-Full width at Half Maximum.
Insert Figures (7-10) and their captions here
[Ni2(L)Cl4(H2O)2].5H2O (3), [Zn2(L)Cl4(H2O)2].7H2O (5) complexes decompose in
three stages but the decomposition of [Cu2(L)Cl3(H2O)3].Cl.11H2O (4) occurs in five
steps. The first decomposition step within the temperature range (31-398οC), (26-251οC)
and (25-333οC) points to the elimination of outersphere water molecules (5, 7 and 3.5
H2O); associated with TG weight losses (10.55, 12.58 and 6.69 %) for complexes (3),
(4) and (5), respectively. This step is accompanied with weak to medium DTG peaks at
Tmax.= (52,306 οC); (48,73,176 οC) and (36οC) for complexes (3), (4) and (5),
respectively. This step follows first order of reaction for complexes (3), (4) and second
order of reaction for complex (5) but, the calculated activation energy are (92.57,
225.23 KJmol-1); (26.81, 123.71, 268.54 KJmol-1) and (120.8 KJmol-1) for complexes
(3), (4) and (5), respectively. After that, the thermal decomposition process of complexes
(3) and (5) occurs in the second and third steps at temperature ranges; (333-538°C) and
(394-798οC). The second one depicts TG weight losses (32.65 and 14.61%)
corresponding to the partial ligand pyrolysis and partial dehalogenation along with
release of the rest lattice water molecules associated with first and second kinetic order
14

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for complexes (3) and (5), respectively, Tables (5 and 6). The third step at temperature
range (394-798οC) may be assigned to complete delegation together with dehalogenation
and removal of coordinated water leading to the formation of 2NiO and 2ZnO as final
products [11,12,67,68]. On the other hand, the TG curve of complex (4) displays weight
loss (36.56, 10.51%) in the temperature range (251-445°C) corresponding to the removal
of (C21H22N2+Cl2) with strong DTG peak at (Tmax=307°C) in the second stage and
release of two mole of coordinated H2O gathered with the rest of hydrated H2O in the
third stage. The calculated order of reaction and activation energies were found (1.53,
146.23; 1.61, 317.46 KJmol-1) for these steps. Then, complete delegation associated with
the removal of chlorine gas takes place in the temperature range (445-630°C) resulting
in 2CuO as a final product [68], Table 5. The nature of the solid products characteristic
to complexes (3) and (4) was determined on the basis of the TG graphs and confirmed
by their IR spectra (Figs. 3b and 4b) and X-ray diffraction (Figs. 11b and 12b). The
diffractogram related to the final product NiO shows diffraction peaks at 2θ values of
37.45, 43.51, 58.59 and 74.7 indicating to the crystal planes of (111), (200), (220) and
(311) matching with the standard values characteristic to pure cubic phase of NiO [69].
Also, this is consistent with JCPDS card number (00-78-0429) [69]. But, the XRD
diffraction pattern of the final residue CuO demonstrates peaks at 2θ values of 35.12,
41.44, 45.35, 62.99 and 74.17° indicating to the crystal planes of (002), (1–11), (200),
(020) and (1–13) of the monoclinic phase of CuO oxide, respectively [70,71]; this is
confirmed with ASTM card number (01-089-5907) [70,71]. The average crystallite size
of the final products was calculated using Debeys-Scherrer equation [22] to give
diameters of 37.5 and 60.2 nm for NiO and CuO oxides, respectively. Moreover, Figs
3b and 4b showed peaks at 674, 491, 435 and 660, 520 cm-1 assigned to υ(Ni–O) and
υ(Cu–O) of NiO and CuO [69-71], respectively.
Insert Figures (11-13) and their captions here
15

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In order to demonstrate the effects of the structural properties of the metal
complexes and the type of the metal ion on the thermal behavior of them, the values of
activation energy ΔE* and the order of the reaction for the various decomposition stages
were calculated and discussed through the analysis of the DTG curves. Some remarks
and conclusions were obtained using the TG/DTG curves and kinetic parameters, as
follows:
 Ni(II) complex (3) has higher thermal stability (369°C) than the corresponding for
Mn(II), Co(II) and Zn(II) complexes, this is may be due to the lower ionic radii of
Ni(II) ion than the others [47,72]. Moreover, the activation energy value of complexes
increases as the thermal stability increases. So, ΔE* value for the initial
decomposition for Ni(II) complex (3) is higher than that the corresponding ΔE* for
complex (1, 2, 5), Table (6).
 All the decomposition processes of all metal complexes proceed through first order
reaction except Zn(II) complex where its decomposition processes proceeds through
first and second order reaction, (Table 6). Also, the fraction appeared in the
calculated order of the thermal reactions (n), confirmed that the reactions proceeded in
complicated mechanisms [73,74].
 The change of entropy values (ΔS*) of complexes (1-5) for the thermal
decompositions stages (Table 6), illustrated that the transition states are more ordered,
than the reacting complexes [73,74].
3.7. Powder XRD studies
The X-ray diffraction patterns of metal complexes (1-5) are shown in Figs. (7a, 10a,
11a, 12a and 13). The spectra showed sharp crystalline peaks indicating to their
crystalline nature. The average crystallite size of the complexes was calculated using
Debeys-Scherrer equation [22]. Using the full width at half maximum intensity of the
peaks, the average sizes are found to be 34.68, 31.31, 21.73, 18.66 and 27.99 nm for
complexes (1), (2), (3), (4) and (5), respectively, indicating to nanostructure for these
compounds.
16

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Insert Table 5 and its caption here
Insert Table 6 and its caption here
3.8. Electronic Spin Resonance (ESR) Spectral Studies
ESR spectra of Cu(II) complex (4) were recorded at room temperature as
polycrystalline samples, on X-band at frequency of 9.71 GHz. The spectral analyses of
complex (4) give g׀׀ = 2.269, g┴ = 2.073 and G = 3.77. The observed g׀׀ value for
complex (4) is less than 2.3 in agreement with the covalent character of the metal ligand
bond. The trend g׀׀ > g┴ > 2.0023 observed for this complex, indicates that unpaired
electron is localized in dx2-y2 orbital of the Cu(II) ion and the spectral features are
characteristic of axial symmetry [68,75]. Thus, a tetragonal geometry is confirmed for
the aforesaid complex [15,76]. G = (g׀׀ – 2.0023) / ( g┴ – 2.0023), which measures the
exchange interaction between the metal centers in a polycrystalline solid, has been
calculated. According to Hathaway, if G > 4, the exchange interaction is negligible, but
G < 4 indicates considerable exchange interaction in the solid complexes [77]. The G
value for complex (4) is slightly less than 4, indicating the exchange interaction in solid
complex.
3.9.1. Biological Activity
The present results revealed that Eobania vermiculata was comparatively less
susceptible to MDA and complexes (1-4) than Monacha obstructa which was less
susceptible to complex (5) than Eobania vermiculata. Reviewing the above mentioned
results, it is obvious that there are different susceptibility levels between the two tested
snail species according to type of tested compound. These differences in the sensitivity
levels may be due to the physiological state of the snail which changes from species to
another [15,78]. The data represented in Table (7) concluded that:
1- MDA has higher toxicity than the metal complexes against the two land snail
species. This is may be attributed to the presence of free amino groups in the former
which can react in cells leading to the initiation of carcinogenic process [79].
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2- Copper(II) complex (4) has higher toxicity against the two land snails than other
complexes. This is may be ascribed to the higher toxicity of Cu(II) ions [80] which
facilitate the entrance into the snail cell wall and exert metal toxic action on the
metabolic activity of snails.
Insert Table 7 and its caption here
3.9.2. Cytotoxicity assay
The synthesized compounds (1-5) were screened in vitro against human-hepatic
carcinoma cell line, Hep-G2 using doxorubicin (DOX) as a reference drug. Cytotoxicity
of doxorubicin on Hep-G2 was assessed using calorimetric method. The results were
compared to the antiproliferative effects of the reference control doxorubicin as shown
in Table 8, plotted in Figure 14. Responses of Hep-G2 cells toward increase
concentrations of metal complexes were exponential. Hep-G2 cells experienced a
significant increase in viability at low concentrations of metal complexes, with an
eventual decline at the highest concentrations tested. The estimated IC50 values ranged
between 41.9 and 7.09 μg/ml after 24 hours. From the results (Table 8), it is evident that
all the tested complexes displayed moderate growth inhibitory activity, in particular
compounds (5), (3) and (2) (IC50 7.09, 9.11 and 10.7 μg/ml), respectively. The
antiproliferative activity of the test compounds against HepG2 cell line may be arranged
in order Zn, Ni, Co, Mn, Cu {i.e. (5) > (3) > (2) > (1) > (4)} which corresponds to the
concentration required for 50% inhibition of cell viability.
Insert Figure (13) and its caption here
Insert Table (8) and its caption here
4. Conclusion
In this work, the newly Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with Schiff
base were prepared by template condensation reaction of 4,4’-methylenediamine,
benzile and ethanolamine. They are confirmed via various methods of analysis. The
results obtained can be summarized as following:
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(1)This work suggested that the formed HL behaves as monoanil asymmetric moiety
and chelating neutral tetradentate ligand in all metal complexes, bonding with the
metal ion occurs through azomethine nitrogen, NH2 group nitrogen atoms and
oxygen atom of ethanolamine OH group. All complexes were found to be binuclear.
(2)The IR spectra elucidated that one mole of benzile and one mole of ethanolamine are
involved in condensation with only one NH2 group of MDA but the other mole of
EA used as adduct in metal complexes.
(3)The data showed that all complexes are non-electrolytes except Cu(II) complex.
Electronic spectra, of metal complexes display octahedral stereochemistry which is
confirmed by magnetic moments at room temperature.
(4) The ESR spectra for Cu(II) complex showed axially symmetric g-tensor parameter
with g׀׀ > g┴ > 2.0023 demonstrating to 2B1g ground state with (dx2-y2)1 configuration.
(5)The thermal decomposition of metal complexes was investigated by TG analysis
within temperature range 26-900°C, resulting in the formation of metal oxide as end
products as both IR spectra and X-ray diffraction indicates. In addition, the
thermodynamic parameters of the dissociation steps were calculated from DTG
curves.
(6)The powder X-ray diffraction patterns indicate that all metal complexes have a
nanostructure.
(7)The biological activity of the synthesized metal complexes was studied against two
Land Snails, the glassy clover snail Monacha obstructa and the brown garden snail,
Eobania vermiculata and also, against human-hepatic carcinoma cell line, Hep-G2.
It was found that Cu(II) complex has higher toxicity against the two land snails than
other complexes. Additionally, Zn(II) complex (5), exhibits a high inhibition of
growth of the cell line with MIC50 of 7.09 μg/mL.
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