Mononuclear, homo- and hetero-binuclear complexes of 1-(5-(1-(2-aminophenylimino)ethyl)-2,4-dihydroxyphenyl)ethanone: Synthesis, magnetic, spectral, antimicrobial, antioxidant, and antitumor studies

Article abstract of DOI:10.1080/00958972.2015.1116688

A new Schiff base, H₂L, was prepared by condensation of 4,6-diacetylresorcinol with o-phenylenediamine in molar ratio 1: 1. The ligand reacted with copper(II), nickel(II), cobalt(II), iron(III), zinc(II), oxovanadium(IV), and dioxouranium(VI) i

Full text of DOI:10.1080/00958972.2015.1116688

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Mononuclear, homo- and hetero-
binuclear complexes of 1-(5-(1-
(2-aminophenylimino)ethyl)-2,4-
dihydroxyphenyl)ethanone: synthesis, magnetic,
spectral, antimicrobial, antioxidant, and antitumor
studies
Magdy Shebl
To cite this article: Magdy Shebl (2016) Mononuclear, homo- and hetero-binuclear complexes
of 1-(5-(1-(2-aminophenylimino)ethyl)-2,4-dihydroxyphenyl)ethanone: synthesis, magnetic,
spectral, antimicrobial, antioxidant, and antitumor studies, Journal of Coordination Chemistry,
69:2, 199-214, DOI: 10.1080/00958972.2015.1116688
To link to this article: http://dx.doi.org/10.1080/00958972.2015.1116688
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Nov 2015.
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Date: 23 January 2016, At: 01:06

Journal of Coordination Chemistry, 2016
Vol. 69, no. 2, 199–214
http://dx.doi.org/10.1080/00958972.2015.1116688
Mononuclear, homo- and hetero-binuclear complexes of
1-(5-(1-(2-aminophenylimino)ethyl)-2,4-dihydroxyphenyl)
ethanone: synthesis, magnetic, spectral, antimicrobial,
antioxidant, and antitumor studies
Magdy Shebl
faculty of education, department of Chemistry, ain shams university, Cairo, egypt
ARTICLE HISTORY
ABSTRACT
received 29 January 2015
accepted 15 october 2015
AnewSchiffbase, H2L, waspreparedbycondensationof4,6-diacetylresorcinol
witho-phenylenediamineinmolarratio1:1.Theligandreactedwithcopper(II),
nickel(II), cobalt(II), iron(III), zinc(II), oxovanadium(IV), and dioxouranium(VI)
ions in the absence and presence of LiOH to yield mononuclear and
homobinuclear complexes. The mononuclear dioxouranium(VI) complex
[(HL)(UO2)(OAc)(H2O)]·5H2O was used to synthesize heterobinuclear
complexes. The ligand and its metal complexes were characterized by
elemental analyses, IR, 1H-, and 13C-NMR, electronic, ESR and mass spectra,
conductivity, and magnetic susceptibility measurements as well as thermal
analysis. In the absence of LiOH, mononuclear complexes (1, 4, and 9)
were obtained; in the presence of LiOH, binuclear complexes (3, 5, 7, and
10) as well as mononuclear complexes (2, 6, and 8) were obtained. In the
mononuclear complexes, the coordinating sites are the phenolic oxygen,
azomethine nitrogen, and amino nitrogen. In addition to these coordinating
sites, the free carbonyl and phenolic OH are involved in coordination in
binuclear complexes. The metal complexes exhibited octahedral, tetrahedral,
and square planar geometries while the uranium is seven-coordinate. The
antimicrobial and antioxidant activities of the ligand and its complexes were
investigated. The ligand and the metal complexes showed antitumor activity
against Ehrlich Acites Carcinoma.
KEYWORDS
schiff base ligand; mono-
and binuclear complexes;
4,6-diacetylresorcinol;
13C-nmr spectra; esr
spectra; antimicrobial;
antioxidant and antitumor
activities
CH3
CH3
N
O
Y
O
O
OH2
O
.nX
NH2
O
Y
X
M
U
OAc
Cl
M = Cu, Ni or Co
CONTACT magdy shebl
magdy_shebl@hotmail.com
supplemental data for this article can be accessed at http://dx.doi.org/10.1080/00958972.2015.1116688.
© 2015 taylor & francis

200
M. SHEbL
1. Introduction
Coordination chemistry of Schiff base ligands has been the subject of interest with various applications
as antibacterial, antifungal, antioxidant and antitumor agents [1–3], and oxygen carriers [4, 5]. Due to
their important role in catalysis and magnetism [6–9], many complexes have been given attention [10].
binuclear complexes particularly heterobinuclear systems [11, 12] are of special interest due to their
relevance to molecular magnetism, material sciences, industrial catalysis, and bioinorganic chemistry
[13], and they are ubiquitous in nature as active sites in a variety of metalloenzymes [14–17].
4,6-Diacetylresorcinol (DAR) is a starting material for construction of polydentate ligands [18–24].
In our previous studies, metal complexes of different polydentate ligands derived from 4,6-diacetylre-
sorcinol [25–29] were synthesized and characterized. These ligands were used to synthesize homopol-
ynuclear complexes with different modes of bonding. However, no heterobinuclear complexes have
been synthesized or studied biologically.
The present work is an extension to our work and is devoted to the synthesis of the new Schiff
base ligand 1-(5-(1-(2-aminophenylimino)ethyl)-2,4-dihydroxyphenyl)ethanone by condensation of
4,6-diacetylresorcinol with o-phenylenediamine in the molar ratio 1:1. Reactions of the Schiff base
with copper(II), nickel(II), cobalt(II), iron(III), zinc(II), oxovanadium(IV), and dioxouranium(VI) ions in the
absence and presence of LiOH were studied. The dioxouranium(VI) complex (9) was used as a ligand
towards copper(II), nickel(II), cobalt(II), and iron(III) ions, yielding heterobinuclear complexes. The ligand
and its metal complexes were characterized by elemental analyses, IR, 1H-, and 13C-NMR, electronic, ESR
and mass spectra, conductivity, and magnetic susceptibility measurements as well as thermal analysis.
The biological activity of the ligand and its complexes was screened against selected bacteria and
fungi. The antioxidant and antitumor activities of the ligand and its metal complexes were investigated.
2. Experimental
2.1. Reagents and materials
4,6-Diacetylresorcinol was prepared as cited in the literature [19]. Copper(II), nickel(II), cobalt(II), and
iron(III) were used as nitrate salts and obtained from Merck or bDH. Zinc(II) and dioxouranium(VI) ions
were used as acetate salts, while the oxovanadium(IV) was used as the sulfate and were from Merck or
Analar. o-Phenylenediamine, lithium hydroxide, nitric acid, ammonium hydroxide, metal indicators, and
EDTA disodium salt were from bDH or Merck. Organic solvents (ethanol, absolute ethanol, methanol,
diethylether, dimethylformamide (DMF), and dimethylsulfoxide (DMSO)) were reagent grade chemicals
and were used without purification.
2.2. Synthesis of the Schiff base H2L
The Schiff base H2L was synthesized by adding 4,6-diacetylresorcinol (1.94 g, 10.0 mmol) dissolved in
hot absolute ethanol (30 mL) to o-phenylenediamine (1.08 g, 10.0 mmol) in absolute ethanol (30 mL).
The reaction mixture was heated to reflux for 6 h. The obtained yellow product was filtered and washed
with ethanol then diethylether, air dried and recrystallized from ethanol. The crystalline ligand was kept
in a desiccator until used. The yield was 2.14 g (75%). The melting point for H2L was 206 °C. The reaction
for the formation of H2L is illustrated in Scheme 1.
2.3. Synthesis of the metal complexes
An ethanolic solution of the metal salt (30 mL) was added gradually to ethanolic solution of H2L (40 mL)
in molar ratio 1:1 (without using LiOH) and 2:1; M:L (in the presence of LiOH). The dioxouranium(VI)
complexes were prepared in methanol as uranyl acetate is more soluble in this solvent; water was
added to ensure complete dissolution of the metal salt in case of oxovanadium(IV) complex. Nickel(II),
iron(III), zinc(II), and oxovanadium(IV) complexes were prepared successfully only in the presence of

JOURNAL OF COORDINATION CHEMISTRy
201
LiOH. The reaction mixture was heated to reflux for 8 h. The resulting precipitates were filtered, washed
with ethanol or methanol then diethylether, and finally air dried. The following detailed preparations
are given as examples and the other complexes were obtained similarly.
2.3.1. Synthesis of [(HL)Cu(EtOH)](NO3) (1)
About 0.328 g (1.41 mmol) of Cu(NO3)2·2.5H2O dissolved in 30 mL ethanol was added gradually with
constant stirring to the solution of H2L (0.4 g, 1.41 mmol) in ethanol (30 mL). The reaction mixture
was heated to reflux for 8 h giving a brown precipitate which was filtered, washed several times
with small amounts of ethanol then diethylether and finally air dried. The yield was 0.258 g (40%),
m.p. >300 °C.
2.3.2. Synthesis of [(HL)Cu(NO3)(H2O)2]·EtOH (2)
About 0.118 g (2.81 mmol) of LiOH·H2O dissolved in minimum distilled water (5 mL) was added gradually
with constant stirring to solution of H2L (0.4 g, 1.41 mmol) in ethanol (30 mL), then 0.656 g (2.82 mmol)
of Cu(NO3)2·2.5H2O dissolved in 30 mL ethanol was added to the mixture. The reaction mixture was
heated to reflux for 8 h giving a dark brown precipitate which was filtered, washed several times with
small amounts of distilled water, ethanol then diethylether, and finally air dried. The yield was 0.52 g
(75%), m.p. 230 °C.
2.3.3. Synthesis of [(L)(UO2)Cu(OAc)Cl(H2O)(MeOH)]·MeOH (11)
About 0.07 g (1.67 mmol) of LiOH·H2O dissolved in minimum distilled water (5 mL) was added gradually
with constant stirring to 9 (1.2 g, 1.67 mmol), suspended in methanol (40 mL) and 0.225 g (1.67 mmol)
of CuCl2 dissolved in 30 mL methanol was added to the mixture. The reaction mixture was heated to
reflux for 12 h giving a dark olive green precipitate which was filtered, washed several times with small
amounts of distilled water, methanol then diethylether, and finally air dried. The yield was 0.75 g (57%),
m.p. >300 °C.
2.4. Analytical and physical measurements
Elemental analyses were carried out using a Vario El-Elementar at the Ministry of Defense, Chemical
War Department. Melting points of the ligand and its metal complexes were determined using a
Stuart melting point instrument. Analyses of the metals followed dissolution of the solid complex
in concentrated HNO3, neutralizing the diluted aqueous solutions with ammonia (except iron(III)
complex) and titrating the metal solutions with EDTA. IR spectra were recorded using Kbr disks on
a FT IR Nicolet IS10 spectrometer. Electronic spectra were recorded as solutions in DMF or Nujol
1
mulls on a Jasco UV–vis spectrophotometer model V-550 UV–Vis. H- and 13C-NMR spectra were
recorded at room temperature using a bruker WP 200 Sy spectrometer. Deuterated dimethylsulfoxide
(DMSO-d6) was used as a solvent and tetramethylsilane (TMS) as an internal reference. The chemical
shifts (δ) are given downfield relative to TMS. D2O was added to test for deuteration of the samples.
ESR spectra were recorded at an Elexsys, E500, bruker company. The magnetic field was calibrated
with 2,2′-diphenyl-1-picrylhydrazyl (DPPH) purchased from Aldrich. Mass spectra were recorded at
70 eV on a Gas chromatographic GCMSqp 1000 ex Shimadzu instrument. The magnetic susceptibil-
ity measurements were carried out at room temperature using a magnetic susceptibility balance,
Johnson Matthey, Alfa product, Model No (MKI). Effective magnetic moments were calculated from
the expression μeff = 2.828 (χM.T)1/2 (bM), where χM is the molar susceptibility corrected using Pascal’s
constants for the diamagnetism of all atoms in the compounds [30]. Molar conductivities of 10−3
M
solutions of the solid complexes in DMF were measured on a Corning conductivity meter Ny 14831
model 441. TGA-measurements were carried out from room temperature to 800 °C at a heating rate
of 10 °C min−1 on a Shimadzu-50 thermal analyzer.

202
M. SHEbL
2.5. Antimicrobial activity
The standardized disk-agar diffusion method [31, 32] was followed to determine the activity of the
synthesized compounds against Staphylococcus aureus (ATCC 25923) and Bacillus subtilis (ATCC 6635)
as Gram-positive bacteria, Salmonella typhimurium (ATCC 14028) and Escherichia coli (ATCC 25922) as
Gram-negative bacteria and Candida albicans (ATCC 10231) and Aspergillus fumigatus as fungi. The
antibiotic chloramphenicol was used as reference in the case of Gram-positive bacteria, cephalothin
in the case of Gram-negative bacteria, and cycloheximide in the case of fungi.
2.5.1. Preparation of the tested compound
The tested compounds were dissolved in DMF and prepared in two concentrations; 100 and 50 mg mL−1
and then 10 μL of each preparation was dropped on a 6 mm disk and the concentrations became 1
and 0.5 mg disk−1, respectively. In the case of insoluble compounds, the compounds were suspended
in DMF and vortexed then processed.
2.5.2. Testing for antibacterial and yeasts activity
bacterial cultures were grown in nutrient broth medium at 30 °C. After 16 h of growth, each micro-or-
ganism, at a concentration of 108 cells mL−1, was inoculated on the surface of Mueller-Hinton agar
plates using a sterile cotton swab. Subsequently, uniform size filter paper disks (6-mm in diameter)
were impregnated by equal volume (10 µL) from the specific concentration of dissolved compounds
and carefully placed on the surface of each inoculated plate. The plates were incubated in the upright
position at 36 °C for 24 h. Three replicates were carried out for each extract against each test organism.
Simultaneously, addition of the respective solvent instead of dissolved compound was carried out as
negative controls. After incubation, the diameters of the growth inhibition zones formed around the
disk were measured with transparent ruler in millimeter, averaged and the mean values were tabulated.
2.5.3. Testing for antifungal activity
Active inoculum for experiments was prepared by transferring many loopfuls of spores from the stock
cultures to test tubes of sterile distilled water that were agitated and diluted with sterile distilled water
to achieve optical density corresponding to 2.0 × 105 spore mL−1. Inoculum of 0.1% suspension was
swabbed uniformly and the inoculum was allowed to dry for 5 min; then the same procedure was
followed as described above.
2.5.4. Determination of minimum inhibitory concentration (MIC)
MIC is the lowest concentration of an antimicrobial compound that will inhibit the visible growth of
a micro-organism after overnight incubation. MIC values of the synthesized compounds were deter-
mined using agar dilution technique [33]. Each compound with an antimicrobial effect shown in the
disk diffusion test was further diluted with DMF to 25.6, 12.8, 6.4, 3.2, 1.6, 0.8, 0.4, 0.2, and 0.1 mg mL−1
respectively. The concentrations of the compounds became 256, 128, 64, 32, 16, 8, 4, 2, and 1 μg mL−1
,
,
respectively. Then 100 μL of each diluted compound was mixed with 10 ml of cooled (50 °C) melted
Mueller-Hinton agar and 10 μL of specific microbial culture (at concentration of 108 cells mL−1), which
were grown in nutrient broth medium for 16 h at 30 °C then plated into a 6-cm sterile Petri dish. Each
dilution was prepared in duplicate. Each concentration was prepared for two dishes. All plates were
incubated at 33 °C for 24 h. MIC of each compound was measured from the plate with the lowest con-
centration with no visible growth of specific organism.
2.6. Antioxidant activity
The method used by Takao et al. [34] was adopted with suitable modifications. DPPH (8 mg) was
dissolved in methanol (100 mL) to obtain a concentration of 80 μg mL−1. Serial dilutions were car-
ried out with the stock solutions (4 mM) of the compounds in methanol to obtain concentrations of

JOURNAL OF COORDINATION CHEMISTRy
203
2 × 10−4–0.25 × 10−4 M. Diluted solutions (2 mL each) were mixed with DPPH (2 mL) and allowed to
stand for 30 and 60 min for any reaction to occur. The absorbance was recorded at 517 nm. The exper-
iment was performed in triplicate and the average absorbance was noted for each concentration. The
IC50 value, which is the concentration of the test compound that reduces 50% of the initial free radical
concentration, was calculated as μM. Ascorbic acid was used as reference standard. Control sample
was prepared containing the same volume without test compounds and reference compounds. The
radical-scavenging activity of the tested samples, expressed as percentage inhibition of DPPH, was
calculated according to the formula IC (%) = [(A0−At)/A0] × 100, where At is the absorbance value of the
tested sample and A0 is the absorbance value of blank sample, at a particular time. Percent inhibitions
after 30 and 60 min were plotted against concentration, and the equation for the line was used to obtain
the IC50 value. A lower IC50 value indicates greater antioxidant activity.
2.7. Cytotoxicity assay
The antitumor activity of the Schiff base and its complexes was tested on Ehrlich Ascites Carcinoma
(E.A.C.) according to the literature method [35]. A set of sterile test tubes was used, where 2.5 × 105 tumor
cells per mL were suspended in phosphate buffer saline. Three tubes with three different concentrations
for each compound (25, 50, and 100 μg mL−1 DMSO) were made and 2.5 × 105 tumor cells were added
for each tube. The tubes were kept for 2 h at 37 °C. The samples were taken volume by volume with
trypan blue on slides and were covered and examined under the microscope. Dead cells were stained
blue and live cells were not stained. Then the percentage of non-viable cells was calculated.
3. Results and discussion
3.1. The Schiff base H2L
The Schiff base H2L was prepared by condensation of 4,6-diacetylresorcinol with o-phenylenediamine
in the molar ratio 1:1. The analytical and physical data of H2L and its metal complexes are listed in
Table S1. The results of the elemental analyses are in agreement with the proposed formulas.
The characteristic infrared spectral data of H2L and its metal complexes are listed in Table S2. The
IR spectrum of H2L showed a broad band at 3426 cm−1 assigned to ν(OH) and two bands at 3372 and
3215 cm−1 assigned to νas and νs of the amino group, respectively; strong bands at 1629 and 1595 cm−1
may be attributed to ν(C=O) and ν(C=N), respectively.
Electronic spectral data of H2L (Table S3) were recorded in DMF solution. Four absorption bands
1
1
at 268 nm, 312 nm, 350 nm, and 402 nm were observed. The first two bands correspond to La→ A1
1
and 1Lb→ A1 transitions of the phenyl ring [36]. The third band corresponds to the π→π* transition of
the azomethine and carbonyl groups while the last band corresponds to the n→π* transition which is
overlapped with the intermolecular charge-transfer (CT) from the phenyl ring [37, 38].
1H-NMR spectral data (δ ppm) of the ligand relative to TMS (0 ppm) in DMSO-d6 are listed in Table S4.
The signals observed at 16.94 and 12.72 ppm may be assigned to the hydrogen-bonded phenolic –OH
[1, 26, 27, 29] with two different environments around the phenolic –OH [39]. Signals at 4.92 ppm and
in the range of 2.4–2.65 ppm may be assigned to the –NH2 and CH3 protons, respectively. Finally, the
signals due to aromatic protons are 6.26–8.42 ppm. Assignment of the 13C-NMR spectral data of H2L
(Figure S1) is based on 13C shifts in similar Schiff bases [23]. The signals at 203.2 ppm, 174.1 ppm,
166 ppm, and 141.2 ppm may be assigned to (C=O), (C=N) and the two (C–OH) phenolic carbons, respec-
tively. The methyl groups were between 27.9 and 17 ppm. Finally, aromatic carbons were observed
between 103.9 and 137.9 ppm.
The mass spectrum of H2L (Figure S2) showed the molecular ion peak at m/e 284, confirming its
formula weight (F.W. 284.32). The mass fragmentation pattern shown in Scheme S1 supported the
suggested structure of the ligand.

204
M. SHEbL
CH3
CH3
H2N
O
O
+
H2N
HO
OH
-Diacetylresorcinol (DAR)
o-phenylenediamine
4 6
,
CH3
CH3
N
O
NH2
HO
OH
Scheme 1. synthesis of h2l.
-EtOH
30-146
[(HL)Cu(NO3)(H2O2)]
- 2H2O
[(HL)Cu(NO3)(H2O)2].EtOH
- HNO3
o
C
[(L)Cu]
[(HL)Cu(NO3)]
o
o
289-412
146-289
C
C
Scheme 2. thermal degradation pattern of [(hl)Cu(no3)(h2o)2]·etoh (2) from 30 to 412 °C.
3.2. Characterization of the metal complexes
H2L was allowed to react with copper(II), nickel(II), cobalt(II), iron(III), zinc(II), oxovanadium(IV), and
dioxouranium(VI) ions. These reactions were repeated in the presence of LiOH to affect deprotonation
of the ligand. The prepared complexes are stable at room temperature, non-hygroscopic, and insoluble
in water and most common organic solvents. The analytical and physical data of the metal complexes
are listed in Table S1.
3.2.1. IR spectra
IR spectral data of the metal complexes (Table S2) exhibit changes in the frequencies of the functional
groups when compared to the spectrum of the ligand. These can be correlated to the specific coordina-
tion positions of the ligand. Some additional bands that appear in the spectra of the metal complexes
can be correlated to metal coordinated positions.
There are four features in the IR spectra of the complexes. The first is the shift of the stretching fre-
quencies of the azomethine ν(C=N) group of the metal complexes to lower frequencies compared with
the free ligand band at 1595 cm−1, which may be due to coordination of the azomethine group to metal
ions. Similarly, bands assigned to ν(NH2) were shifted to lower frequencies in the complexes, indicating
involvement of the amino group in chelation [40]. The ν(C=O) of the free ligand at 1629 cm−1 shifted to
lower frequencies in the binuclear complexes, suggesting participation of the carbonyl group in chela-
tion [41–43]. However, in the mononuclear complexes, no lowering of the ν(C=O) band was observed,
suggesting that metal carbonyl oxygen linkage is absent [29]. The second feature is the broad bands at

JOURNAL OF COORDINATION CHEMISTRy
205
3335–3446 cm−1 which can be assigned to the stretching frequencies of ν(OH) of alcohol, OH-phenolic,
and/or water molecules associated to the complexes which are also confirmed by elemental and thermal
analyses. The third feature is about nitrate and acetate anions as they are either coordinated or unco-
ordinated in their complexes. Complexes 1 and 4 showed new bands at 1369–1384 and 903–904 cm−1
which can be assigned to ionic NO3− [18], indicating the ionic nature of these complexes. Complex 2
showed new bands at 1299 and 1055 cm−1 which can be assigned to monodentate NO3− [44]. These IR
spectral data were supported by conductance data. For 7, 9, and 11–14, new bands characteristic for
ν
asym(COO−) and νsym(COO−) of acetate were observed at 1638–1669 and 1392–1415 cm−1, respectively
[1, 45, 46]. The higher difference (223–267 cm−1) between the two bands indicates monodentate acetate
[1, 45, 46]. The fourth feature includes bands related to metal ions where the characteristic ν(V=O) is
observed in the IR spectrum of the oxovanadium(IV) complex (8) at 952 cm−1 [47, 48]. Also, the diox-
ouranium(VI) complexes (9–14) showed strong absorptions at 903–914 cm−1 which can be assigned
to the antisymmetric ν3(O=U=O) vibration [26, 49, 50]. The values of ν(V=O) and ν(O=U=O) are used
to calculate the force constant (F) of (V=O) and (O=U=O) by the method of McGlynn and Smith [51]:
(ν)2 = (1307)2(FM–O)/14.103. The calculated force constant for the oxovanadium(IV) and dioxouranium(VI)
complexes are 7.482 and 6.732–6.897 mdyn Å−1, respectively. The M–O distance is also calculated by
substitution in Jones relation [52]: RM–O = 1.08(FM–O)
−1/3 +1.17. The values of RM–O for oxovanadium(IV)
and dioxouranium(VI) complexes are 1.722 and 1.737–1.742 Å, respectively. The calculated FM–O and
RM–O values fall in the usual range for the oxovanadium(IV) and dioxouranium(VI) complexes [1, 47].
New bands at 592–615 and 412–486 cm−1 may be assigned to stretching frequencies of ν(M–O) and
ν(M–N), respectively [25, 27, 29, 47, 53].
3.2.2. Conductivity measurements
The molar conductivities of the complexes (Table S3) showed that all complexes have non-electrolytic
nature except 1 and 4 which gave molar conductance values of 90 and 77 Ω−1 cm2 mol−1, respectively,
suggesting their 1:1 electrolytic nature [54]. This is consistent with the infrared data that showed the
presence of an ionic nitrate.
3.2.3. Magnetic measurements, electronic, and ESR spectra
The magnetic properties of the complexes, in addition to electronic spectral data, provide valuable
information for distinguishing their stereochemistry. The electronic spectral measurements of all metal
complexes (Table S3) were carried out as DMF solutions and Nujol mulls. The spectra and position of
the bands of all complexes in DMF solutions are approximately the same as those recorded as Nujol
mulls, reflecting insignificant effect of DMF on the complex configuration. This also proves that the
same species is present both in the solid and the solution states, indicating that the complexes retain
their integrity in solutions [55, 56]. Comparison of the spectrum of the free ligand with its complexes
showed that bands of the free ligand were slightly shifted to blue or red regions of the spectrum in all
complexes which may be considered as evidence for the complex formation. Also, new bands were
observed in the spectra of the complexes which are listed in Table S3.
3.2.3.1. Mono- and homo-binuclear complexes. The effective magnetic moment values of the
copper(II) complexes (1 and 2) are in the range of 1.82–1.97 bM [29, 43]. The electronic spectrum of
2
2
1 showed a band at 472 nm, which may be assigned to the b1g→ b2g transition in a square planar
geometry [57]. Complex 2 showed two absorption bands at 440 and 558 nm, which may be assigned to
2
2
the 2b1g→ Eg and 2b1g→ b2g transitions, respectively, corresponding to a distorted octahedral geometry
[29, 58]. X-band ESR spectrum of [(HL)Cu(NO3)(H2O)2]·EtOH (2) (Figure S3) was recorded in the solid
state at 25 °C. The spectrum of the complex exhibits two signals at g = 2.18 and g = 2.07. The shape
of the spectrum is consistent with octahedral geometry around Cu(II) in the complex [26, 29, 43]. The
spin Hamiltonian parameters of the complex were calculated and are summarized in Table 1. The ESR
spectrum of the complex exhibited axial g-tensor parameters with gǁ > g⊥ > 2.0023. The exchange

206
M. SHEbL
Table 1. esr data of copper(ii) and oxovanadium(iV) complexes at room temperature.
Complex
gǁ
g⊥
Aǁ × 10−4 (cm−1
)
A⊥ × 10−4 (cm−1
)
α2
β2
[(hl)Cu(no3)(h2o)2]·etoh (2)
[(hl)Vo(oh)(etoh)] (8)
2.18
1.97
2.07
1.99
140
160
70
75
0.64
0.61
0.75
0.94
interaction parameter term G, estimated from the expression G = (gǁ −2.0023)/(g⊥ −2.0023) [59] is 2.62,
indicating a Cu…Cu exchange interaction [58].
Molecular orbital coefficients, α2 (a measure of the covalency of the in-plane σ-bonding between
copper 3d orbital and the ligand orbitals) and β2 (covalent in-plane π-bonding), were calculated [60].
The lower value of α2 compared to β2 indicates that the in-plane σ–bonding is more covalent than the
in-plane π–bonding. These data are in agreement with the data reported earlier [1, 29, 58].
The effective magnetic moment of the nickel(II) complex (3) is 3.4 bM which lies in the range (3.2–
4.1 bM) reported for tetrahedral geometry [61]. The electronic spectrum of 3 showed one band at
3
784 nm which may be assigned to the 3T1(F)→ T1(P) transition in a tetrahedral geometry [19, 39].
The effective magnetic moment values of the cobalt(II) complexes (4 and 5) are 3.5–3.6 bM, lower
than expected for tetrahedral complexes (4.4–4.8 bM). The lower values of magnetic moments may
point to a not purely tetrahedral geometry of Co(II) and a tendency towards square-planar geometry
[62], which is characterized by lower magnetic moments (2.1–2.8 bM) [63]. The tetrahedral geometry is
supported by the electronic spectra of the complexes that showed bands in the range of 530–575 nm,
4
which may be assigned to the 4A2(F)→ T1(P) electronic transition in a tetrahedral geometry [64].
The effective magnetic moment of the iron(III) complex (6) is 5.9 bM which is consistent with the
presence of five unpaired electrons in the Fe(III) ion in an octahedral geometry [61]. The electronic
spectrum of 6 showed one band at 492 nm, within the range reported for octahedral complexes [49].
It was not possible to identify the type of the d–d transition. This is due to a strong charge transfer (CT)
band tailing from UV-region to the visible region [18, 26].
Zinc(II) complex 7 is diamagnetic as expected. The electronic spectrum of the complex showed one
band at 440 nm, which may be attributed to CT transitions.
The effective magnetic moment value of the oxovanadium(IV) complex (8) is 1.4 bM. The value is
lower than reported values (1.74–2.10 bM), indicating an interaction of the oxovanadium(IV) ion with
neighboring ions [65]. The electronic spectrum of the complex (8) showed new bands at 449 and
2
2
525 nm that may be assigned to the 2b2→ E and 2b2g → b1 transitions, respectively, in an octahedral
geometry [64]. In addition, the V=O stretching frequency for the complex at 952 cm−1 supports octa-
hedral geometry of the complex [47, 66, 67]. The X-band ESR spectrum of a powdered sample of 8 at
room temperature (Figure S3) showed a broad band without resolved hyperfine structure. In particular,
the hyperfine coupling with the nearby 51V (I = 7/2) nucleus is not observed. The absence of vanadium
hyperfine coupling is common in solid state samples [68] and may be attributed to the simultaneous
flipping of neighboring electron spins [69] or to strong exchange interactions, which average out the
interaction with the nuclei. The g and A values (Table 1) in addition to the energy of d–d transition
were used to evaluate the molecular orbital coefficients α2, β2 for the complex [70]. The calculated
values α2 = 0.62 and β2 = 0.90 agree well with those reported for octahedral configuration around
oxovanadium(IV) [65]. The lower value of α2 compared to β2 indicates that the in-plane σ–bonding is
more covalent than the in-plane π–bonding [47].
The dioxouranium(VI) complexes (9 and 10) are diamagnetic as expected. The electronic spectra
of the complexes showed new absorptions at 441–473 nm, which may be attributed to an electronic
transition from the apical oxygens to f-orbitals of the uranium(VI) or due to a CT transition from the
ligand to uranium(VI) [25, 26, 28].
3.2.3.2. Heterobinuclear complexes. Since the mononuclear dioxouranium(VI) complex [(HL)-
(UO2)(OAc)(H2O)]·5H2O (9) has free coordinating sites, it can be used as a chelating agent towards
copper(II), nickel(II), cobalt(II), and iron(III) to yield heterobinuclear complexes. The complex ligand

JOURNAL OF COORDINATION CHEMISTRy
207
(9) is diamagnetic, so any magnetic moments of the heteronuclear complexes can be attributed to
introduction of metal cations.
The reactions of 9 with CuCl2, NiCl2·6H2O, CoCl2.6H2O, and FeCl3·6H2O in a 1 : 1 molar ratio in the
presence of LiOH yielded the heterobinuclear complexes, [(L)(UO2)Cu(OAc)Cl(H2O)(MeOH)]·MeOH (11),
[(L)(UO2)Ni(OAc)Cl(H2O)4]·3H2O (12), [(L)(UO2)Co(OAc)Cl(H2O)2]·2.5H2O (13) and [(L)(UO2)Fe(OAc)Cl2(H2O)-
(MeOH)2] (14).
Electronic spectra of the heterobinuclear complexes showed two absorptions. The first is similar
to that observed in 9. The second is related to d–d transition of the introduced metal ions which was
supported by magnetic moment measurements. The magnetic moment of 11 is 1.8 bM [29, 43]. The
electronic spectrum of the complex showed a new band at 573 nm which may be assigned to the
2
2b1g→ A1g transition in a square planar geometry [25, 58].
The magnetic moment of 12 is 2.8 bM which indicates the presence of two unpaired electrons per
Ni(II), also confirming its octahedral geometry [1]. The electronic spectrum of the complex showed a
3
band at 530 nm which may be assigned to the 3A2g(F)→ T1g(P) transition in an octahedral geometry [71].
The magnetic moment of 13 is 2.56 bM which indicates a square-planar geometry [49]. The elec-
2
tronic spectrum of the complex showed one band at 545 nm which may be assigned to the 2A1g→ b2g
transition in a square-planar geometry [49, 72].
The magnetic moment of 14 is 5.3 bM indicating octahedral arrangement with a slight antiferro-
magnetic interaction [27]. The electronic spectrum of the complex showed one band at 452 nm which
indicates octahedral geometry [62].
3.2.4. Thermal analysis
Thermal gravimetric analysis indicates whether the water and solvent molecules are in the inner or
outer coordination sphere of the central metal ion [1, 27]. Complexes 2, 10, 11, 12, and 13 were taken
as representative examples for thermal analysis. Figure S4 shows the thermogram of 11. The thermal
analyses of the complexes (Table S5) are in agreement with the formulas as suggested from elemental
analyses. The first stage of decomposition of the complexes extends up to 146 °C corresponding to
loss of non-coordinated water or solvated ethanol or methanol. The second stage of decomposition
extends up to 289 °C corresponding to loss of coordinated water and/or methanol molecules which is
accompanied with the elimination of HCl (12). The third stage of decomposition extends up to 412 °C
corresponding to loss of the coordinated anions as HCl, HNO3, or AcOH. The decomposition pattern of
2 is shown in Scheme 2.
3.2.5. Mass spectra
Complexes 1, 3, 6, 9, 10, and 12 were chosen as representative complexes for mass spectral studies
as they include all types of the synthesized complexes [mononuclear (1, 6, and 9), homo-binuclear
complexes (3 and 10) and hetero-binuclear complex (12)]. The mass spectra of 1, 6, 9, and 12 are
depicted in Figure S2.
The mass spectrum of 1 showed the molecular ion peak at m/e = 455 (Calcd = 454.93) with 15.57%
abundance. The peaks observed at m/e = 456 [M + 1] and 457 [M + 2] may be due to isotopic species.
The fragments observed at m/e = 409 (15.57%), 392 (14.21%) and 363 (16.39) correspond to [M–EtOH],
[M–HNO3] and [M–C6H4NH2], respectively. The peak at m/e = 79 (20.22%) represents CuO. Finally, the
peak at m/e = 65 (31.69%) is due to Cu. Proposal degradation steps of 1 are shown in Scheme S2.
The mass spectrum of 3 showed the molecular ion peak at m/e = 452 (Calcd = 451.78) with 32.83%
abundance which corresponds to [M–2H2O]. The peak observed at m/e = 453 may be due to isotopic
species. The fragments observed at m/e = 437 (38.38%) and 400 (402; 28.79%) correspond to [M–CH3]
and [M–H2O,–2OH], respectively. The peak at m/e = 76 (28.79%) represents NiO. Finally, the peak at
m/e = 59 (27.78%) is due to Ni.
The mass spectrum of 6 showed the molecular ion peak at m/e = 428 (Calcd = 428.08) with 37.25%
abundance. The peaks observed at m/e = 429 [M + 1] and 430 [M + 2] may be due to isotopic species.
The fragments observed at m/e = 411 (37.25%), 410 (58.17%), 393 (52.94%), 357 (356; 37.25%) and 336

208
M. SHEbL
(337; 47.71%) correspond to [M–OH], [M–H2O], [M–Cl], [M–Cl2] and [M–C6H4NH2], respectively. The peak
at m/e = 72 (47.71%) represents FeO. Finally, the peak at m/e = 56 (50.98%) is due to Fe.
The mass spectrum of 9 showed the molecular ion peak at m/e = 631 (Calcd = 630.48) with 23.8%
abundance which corresponds to [M–5H2O]. The peaks observed at m/e = 632 and 633 may be due to
isotopic species. The fragments observed at m/e = 616 (16.57%), 588 (589; 18.98%), 553 (18.07%) and
539 (26.2%) correspond to [M–CH3], [M–COCH3], [M-H2O,–AcOH], and [M–C6H4NH2], respectively. The
peaks at m/e = 270 (21.99%) and 238 (25.9%) represent UO2 and U, respectively.
Similarly, the mass spectra of 10 and 12 showed the molecular ion peaks at m/e = 911; 44.29%
(Calcd = 910.5) and 779; 63.79% (Calcd = 778.65), which correspond to [M-5H2O] and [M–3H2O], respec-
tively. The peaks observed at m/e = 912 and 913 (10) and at m/e = 780 and 781 (12) may be due to iso-
topic species. In 10, the fragments observed at m/e = 877 (878; 73.57%), 857 (38.57%), 819 (4.29%), 270
(12.14%), and 239 (18.57%) correspond to [M–2OH], [M–3H2O], [M–C6H4NH2], UO2, and U, respectively.
In 12, the fragments observed at m/e = 764 (50%), 749 (750; 62.93%), 744 (67.24%), 719 (718; 46.55%),
687 (56.03%), and 648 (44.83%) correspond to [M–CH3], [M–2CH3], [M–Cl], [M-AcOH], [M–C6H4NH2], and
[M–4H2O,–AcOH], respectively. Thus, we can conclude that mass spectral data reinforce the conclusions
drawn from analytical and spectral data.
based on the above interpretation of elemental and thermal analyses and spectral data (infrared,
electronic, mass, and ESR) as well as magnetic susceptibility measurements at room temperature
and conductivity measurements, it is possible to draw tentative structures of the metal complexes.
Figures 1–3 represent the proposed structures of the metal complexes.
3.3. Antimicrobial activity
The antimicrobial activities of the ligand and its metal complexes were investigated against S. aureus
(ATCC 25923) and B. subtilis (ATCC 6635) as Gram-positive bacteria, E. coli (ATCC 25922) and S. typhimu-
rium (ATCC 14028) as Gram-negative bacteria, yeast: C. albicans (ATCC 10231), and fungus: A. fumigatus.
The results are listed in Table S6. The data in Table S6 reveal that the ligand and is metal complexes are
inactive against S. aureus and E. coli. Against S. typhimurium, the ligand showed low activity while its
oxovanadium(IV) complex showed moderate activity. Against B. subtilis, the ligand showed low activity.
This activity is enhanced upon complexation with copper(II), nickel(II), iron(III), zinc(II), and oxovana-
dium(IV) and the order of activity is Fe(III) > VO(IV) > Ni(II) > Cu(II); cationic complex 1 > Zn(II) > Cu(II);
neutral complex 2. Generally, it can be concluded that chelation tends to make the ligand a more
powerful bacterial agent. A possible explanation for this increase in the activity upon chelation is that,
in chelated complex, the positive charge of the metal is partially shared with donors present on the
ligands [20]. Generally, chelated complexes deactivate various cellular enzymes, which play a vital role
in various metabolic pathways of these micro-organisms. Other factors such as solubility, conductivity
and dipole moment, affected by the presence of metal ions, may also be reasons for increasing the
biological activity of the metal complexes as compared to the ligand from which they are derived [20].
Against C. albicans, the ligand and all metal complexes showed high activity and most of the com-
plexes are more active than the ligand. The order of activity for mono- and homo-binuclear complexes is
Cu(II) > UO(VI) > VO(IV) > Fe(III) > Ni(II) > Zn(II) > Co(II) while for heterobinuclear complexes Cu(II)≈Co(II)
> Ni(II) > Fe(III).
Against A. fumigatus, the ligand and most of its metal complexes have high activity and most com-
plexes are more active than the ligand. The increased activity against C. albicans and A. fumigatus may
be due to the formation of hydrogen bonds between the azomethine nitrogen or carbonyl oxygen
with active centers of the cell constituents, resulting in interference with the normal cell process [24].
The minimum inhibitory concentration (MIC) was determined for the synthesized compounds
and the results are listed in Table 2. Against B. subtilis, the ligand and 12 showed lower activity
(MIC = 62–75 μg mL−1), while 1–3 and 6–8 showed an intermediate activity (MIC = 39–50 μg mL−1).
Against S. typhimurium, the ligand showed a low activity (MIC = 88 μg mL−1) and 8 showed intermediate
activity (MIC = 66 μg mL−1). Against C. albicans, the ligand and most of its complexes showed promising

JOURNAL OF COORDINATION CHEMISTRy
209
CH3
O
CH3OC
HO
N
NO3.nEtOH
NH2
M
EtOH
M
Cu
Co
n
--
1
Complex
1
4
CH3
CH3OC
HO
N
OH2
.EtOH
O
NH2
Cu
OH2
NO3
(2)
CH3
CH3OC
HO
N
Cl
O
NH2
Fe
OH2
Cl
(6)
CH3
CH3OC
HO
N
OH
O
O
NH2
V
EtOH
(8)
CH3
CH3OC
HO
N
O
OH2
O
.5H2O
O
NH2
U
OAc
(9)
Figure 1. Proposed structures of the mononuclear complexes of h2l.

210
M. SHEbL
CH3
CH3
O
O
N
.nZ
NH2
H2O
O
M
M
X
X
M
X
n
2
1
Z
Complex
Ni
Co
Zn
OH
OH
H2O
3
5
7
EtOH
OAc 0.5 H2O
CH3
CH3
N
O
O
O
O
H2O
OH
O
OH
O
.5H2O
NH2
U
U
O
OH2
OH2
(10)
Figure 2. Proposed structures of the homo-binuclear complexes of h2l.
activity, especially 1 and 2 (MIC = 4–5 μg mL−1). The other complexes showed intermediate to higher
activity (MIC = 6–22 μg mL−1). Finally, against A. fumigatus, the ligand showed an intermediate activity
(MIC = 30 μg mL−1) and the complexes showed moderate to high activity (MIC = 8–40 μg mL−1).
1, 2, and 12 seem to be promising as they showed antimicrobial activity and MIC values that are
comparable to that of cycloheximide and, thus, can be further explored as specific antimicrobial drugs.
The obtained results are consistent with the previously reported metal complexes of similar Schiff
bases which were tested in vitro for their antibacterial activities against bacteria or fungi (using disk
diffusion method [20, 59, 73] or MIC method [21, 24, 74, 75]).
3.4. Antioxidant activity
DPPH is a stable free radical used for studying radical scavenging activity in chemical analysis [76],
which is measured as IC50 values. The antioxidant activity of the Schiff base and its complexes against
DPPH radical was carried out with the hope to develop potential antioxidants and therapeutic agents.
The DPPH radical shows a strong absorption at 517 nm in the visible spectrum due to the presence of
an odd electron. As this electron becomes paired-off in the presence of a free radical scavenger, this
absorption vanishes with respect to the number of electrons taken up. The DPPH scavenging ability of
the synthesized compounds was compared with that of the well-known natural antioxidant ascorbic
acid under the same experimental conditions. The results of the in vitro radical scavenging assay (Table 3)
strongly support that the synthesized compounds exhibit antioxidant activity against DPPH radical.
H2L showed promising antioxidant activity (IC50 = 118.1 μM) which is the highest among the complexes
and higher than that of ascorbic acid. The IC50 values for mononuclear and binuclear complexes are
151.3–175.4 and 208.2–240 μM, respectively. The order of antioxidant activity was H2L > mononuclear

JOURNAL OF COORDINATION CHEMISTRy
211
CH3
CH3
N
O
Y
O
O
OH2
.nX
NH2
O
O
Y
X
M
U
OAc
Cl
M
X
Y
n
Complex
Cu
Ni
Co
MeOH --
1
11
12
13
H2O
H2O
H2O
3
--
2.5
CH3
CH3
MeOH
Cl
N
O
O
O
OH2
O
NH2
O
U
Fe
HOMe
OAc
Cl
(14)
Figure 3. Proposed structures of the hetero-binuclear complexes of h2l.
Table 2. minimum inhibitory concentration (miC) (μg ml−1) of h2l and its complexes.
Gram-(+) bacteria
Gram-(−) bacteria
yeasts and fungi
C. albicans A. fumigatus
10 30
Compound
B. subtilis
S. typhimurium
h2l
75
44
50
42
nd
nd
39
47
40
nd
nd
nd
62
nd
nd
1
88
ndb
nd
nd
nd
nd
nd
nd
66
nd
nd
nd
nd
nd
nd
13
[(hl)Cu(etoh)]no3 (1)
4
5
36
nd
36
nd
nd
20
20
40
25
24
20
8
[(hl)Cu(no3)(h2o)2]·etoh (2)
[(l)ni2(oh)2(h2o)]·2h2o (3)
[(hl)Co(etoh)]no3·etoh (4)
[(l)Co2(oh)2(h2o)]·etoh (5)
[(hl)feCl2(h2o)] (6)
13
22
21
10
16
7
6
7
9
11
9
[(l)Zn2(oac)2(h2o)]·0.5h2o (7)
[(hl)Vo(oh)(etoh)] (8)
[(hl)(uo2)(oac)(h2o)]·5h2o (9)
[(l)(uo2)2(oh)2(h2o)3]·5h2o (10)
[(l)(uo2)Cu(oac)Cl(h2o)(meoh)]·meoh (11)
[(l)(uo2)ni(oac)Cl(h2o)4]·3h2o (12)
[(l)(uo2)Co(oac)Cl(h2o)2]·2.5h2o (13)
[(l)(uo2)fe(oac)Cl2(h2o)(meoh)2] (14)
Controla
21
20
2
14
3
aChloramphenicol in the case of Gram-positive bacteria, cephalothin in the case of Gram-negative bacteria and cycloheximide in
the case of yeasts and fungi.
bnd = not determined.
complexes > binuclear complexes. This order may be due to the presence of two phenolic OH groups
in the ligand which donate a proton to DPPH and converts into the stable free radical [24]. Upon com-
plexation, deprotonation occurs (for one OH group in mononuclear and two OH groups in binuclear
complexes), lowering the antioxidant activity. The obtained results are consistent with those obtained by
Raj et al. [24] in a previous study including Cu(II), Co(II), Ni(II), and Zn(II) complexes of bicompartmental

212
M. SHEbL
Table 3. antioxidant activity of h2l and its complexes.
DPPH assay IC50 (μM)a
Compound
30 min
60 min
h2l
118.1 3.51
151.3 2.5
160.5 3.1
240 0.4
162.5 0.25
220.1 1.3
170 1.3
175.4 4.2
230.2 2.1
216.2 1.2
208.2 1.5
235 0.05
126.4 11.3
105.3 6.41
133.4 1.4
142 4.2
216 1.2
145.3 0.07
200 1.4
158.3 2.4
162.6 4.1
205.4 4.3
198.4 3.05
190.1 3.5
204.1 4.2
122.5 10.4
[(hl)Cu(etoh)]no3 (1)
[(hl)Cu(no3)(h2o)2]·etoh (2)
[(l)ni2(oh)2(h2o)]·2h2o (3)
[(hl)Co(etoh)]no3·etoh (4)
[(l)Co2(oh)2(h2o)]·etoh (5)
[(hl)feCl2(h2o)] (6)
[(hl)Vo(oh)(etoh)] (8)
[(l)(uo2)Cu(oac)Cl(h2o)(meoh)]·meoh (11)
[(l)(uo2)ni(oac)Cl(h2o)4]·3h2o (12)
[(l)(uo2)Co(oac)Cl(h2o)2]·2.5h2o (13)
[(l)(uo2)fe(oac)Cl2(h2o)(meoh)2] (14)
ascorbic acid
aiC50 values were determined by linear regression analysis.
Table 4. in vitro cytotoxicity of h2l and its complexes on ehrlich ascites Carcinoma cell line.
Compound
IC50 (mg mL−1
)
h2l
85.36
21.34
25.05
18.48
20.33
15.73
27.46
22.06
16.22
15.38
17.4
19.65
22.01
24.39
27.33
5
[(hl)Cu(etoh)]no3 (1)
[(hl)Cu(no3)(h2o)2]·etoh (2)
[(l)ni2(oh)2(h2o)]·2h2o (3)
[(hl)Co(etoh)]no3·etoh (4)
[(l)Co2(oh)2(h2o)]·etoh (5)
[(hl)feCl2(h2o)] (6)
[(l)Zn2(oac)2(h2o)]·0.5h2o (7)
[(hl)Vo(oh)(etoh)] (8)
[(hl)(uo2) (oac)(h2o)]·5h2o (9)
[(l)(uo2)2(oh)2(h2o)3]·5h2o (10)
[(l)(uo2)Cu(oac)Cl(h2o)(meoh)]·meoh (11)
[(l)(uo2)ni(oac)Cl(h2o)4]·3h2o (12)
[(l)(uo2)Co(oac)Cl(h2o)2]·2.5h2o (13)
[(l)(uo2)fe(oac)Cl2(h2o)(meoh)2] (14)
Cisplatin
note: iC50 = inhibition concentration 50%.
Schiff bases derived from 4,6-diacetylresorcinol. Finally, the difference in the activity of the metal com-
plexes may be due to the coordination environment and the redox properties. In general, the redox
properties of the complex depend on chelate ring size, axial ligation, and degree of unsaturation in
the chelate ring [77].
3.5. Antitumor activity
The antitumor activities of the Schiff base and its complexes were tested on Ehrlich Ascites Carcinoma
and the results are listed in Table 4. The ligand showed moderate activity (IC50 = 85.36 mg mL−1), while
complexes showed higher activity (IC50 = 15.38–27.46 mg mL−1).
The activity of the complexes is due to the metal ions which enhance the anticancer behavior as
it is evidenced by the lower IC50 values of the complexes compared with free H2L. The higher activity
of the complexes than H2L may be attributed to the extended planar structure induced by the π–π*
conjugation resulting from chelation of the metal ion with the ligand [78, 79]. In addition, enhanced
activity of metal complexes may also be due to higher lipophilic nature of the complexes, increased
due to chelation with faster diffusion of the chelates through the cell membrane [80]. Complexes 5, 8,
and 9 are promising as they showed low toxicity in relation to cis-platin.

JOURNAL OF COORDINATION CHEMISTRy
213
4. Conclusion
The condensation of 4,6-diacetylresorcinol with o-phenylenediamine in molar ratio 1 :1 afforded the
new Schiff base H2L. The reactions of the Schiff base with copper(II), nickel(II), cobalt(II), iron(III), zinc(II),
oxovanadium(IV), and dioxouranium(VI) in the absence and presence of LiOH yielded mono- and bi-nu-
clear complexes with different coordination sites. The mononuclear dioxouranium(VI) complex [(HL)-
(UO2)(OAc)(H2O)]·5H2O was used to synthesize heterobinuclear complexes. The ligand and its metal
complexes were characterized by elemental analyses, IR, 1H-, and 13C-NMR, electronic, ESR, and mass
spectra, conductivity and magnetic susceptibility measurements as well as thermal analysis. The ligand
and its metal complexes showed promising antimicrobial and antioxidant activities. The ligand and
metal complexes showed antitumor activity against Ehrlich Acites Carcinoma.
Disclosure statement
No potential conflict of interest was reported by the author.
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