Synthesis and spectral investigation (1H and 13C) of Tetradentate schiff base Ligands for the preparation of post transition bimetallic complexes of antimicrobial importance

Article abstract of DOI:10.14233/ajchem.2014.15834

A tetradentate Schiff base ligand 2-(bis-2-hydroxylphenylidene)-1,2- diiminoethanne (L) was synthesized and then its structure was investigated by 1H NMR and ¹³C NMR techniques. The ligand and its bimetallic complexes were screened in vitro for

Full text of DOI:10.14233/ajchem.2014.15834

Asian Journal of Chemistry; Vol. 26, No. 3 (2014), 841-845
http://dx.doi.org/10.14233/ajchem.2014.15834
Synthesis and Spectral Investigation (1H and 13C) of Tetradentate Schiff Base Ligands for the
Preparation of Post Transition Bimetallic Complexes of Antimicrobial Importance
1
1,*
1
2
1
AMEER FAWAD ZAHOOR , MUHAMMAD YOUSAF , MUHAMMAD PERVAIZ , ANBREEN ANJUM , KULSOOM GHULAM ALI ,
3
4
2
1
FAISAL MAQBOOL ZAHID , SAJJAD AHMAD , SHAZIA ANWER BUKHARI and BUSHRA PARVEEN
1Department of Chemistry, Government College University, Faisalabad, Pakistan
2Department of Applied Chemistry and Biochemistry, Government College University, Faisalabad, Pakistan
3Department of Statistics, Government College University, Faisalabad, Pakistan
4University of Engineering and Technology Lahore, Faisalabad Campus, Faisalabad, Pakistan
*Corresponding author: E-mail: dryousafsmor@gmail.com
Received: 27 May 2013;
Accepted: 19 August 2013;
Published online: 30 January 2014;
AJC-14650
A tetradentate Schiff base ligand 2-(bis-2-hydroxylphenylidene)-1,2-diiminoethanne (L) was synthesized and then its structure was
investigated by 1H NMR and 13C NMR techniques. The ligand and its bimetallic complexes were screened in vitro for antibacterial and
antifungal activities by using disc diffusion method. The results showed that in case of antibacterial activity the Co2L2 exhibited better
efficiency (9 0.816) against E. coli while binuclear complex of Mn2L2 showed better potential against all the three strains (E. coli, S.
aureus and A. alternate) as compared with other attempted bimetallic (Cu, Mn and Zn) complexes when compared with standard one.
Similarly the antifungal potential of binuclear (Co2L2) complex was satisfactory (12.25 0.062) for A. alternate while the binuclear Cu2L2
complex exhibited good effect (7.75 0.957) against A. niger. Similarly binuclear Mn2L2 complex showed better efficiency (10.25 0.5)
against A. flavous. The biological activity data justified that binuclear post transition metal complexes with Schiff base can be successfully
used against fungal as well as bacterial infections.
Keywords: Tetradentate Schiff base, Binuclear complexes, Bacterial strains, Fungal strains.
be enhanced by coordination with transition metals. Complex
formation promotes dissolving power of different drugs in lipid
containing organisms and ultimately enhances the drugs effect
against different diseases. The activities of anticancer, antitumor,
antianalgesic and antibiotic drugs can be increased by
complexing them with transition metals5. Metallo-elements
specially zinc and copper play significant role in the viral
growth and restrict virus to enter into the host cell, for example
sulfur and zinc occur in viruses and bacteria respectively. Zinc
quickly coordinates with sulfur present at the outer layer of
virus and can transfer virus into the host cell, so to break this
coordination, transition metals were considered to be very
important to arrest the sulfur. So viral growth depends on these
metals and can be controlled by varying concentrations of
metallo-elements6. Literature justifies that much more
interest is being focused on the effect of ligands and their
mono-transition metal complexes for their biological poten-
tial. Keeping in mind the importance of the transition metal
complexes, the present study was carried out to see the effect
of binuclear post transition metal complexes for antimicrobial
activities.
INTRODUCTION
The Schiff bases and their metal complexes are consi-
dered to be very important due to their interest in a variety of
biological mechanisms1. Many transition metal complexes
were found to exhibit greater stability and are very active
against different diseases. Depending upon the stability, the
transition metals and their complexes were used against tumor
and cancer treatments2. The stability of complexes mainly
depends on the chelating and donating powers of the ligand
which ultimately facilitates oxidizing and electrophilic reactions.
The less stability of metal complexes restricts their applications
in some biological processes3. Ligands made from salicylalde-
hyde exhibit higher values of antibacterial activities against
different species including S. aureus, P. mirabilis, H. influenza
and Salmonella spp4.Apart from ligands and metal complexes,
salicylaldehyde is more frequently used as larvicide and fungi-
cides.
A number of biological components such as glucose,
vitamins, drugs, nitrogenous bases and some heterocyclic
compounds containing nitrogen atom act as bioligands. These
bioligands exhibit average antimicrobial activities which can

842 Zahoor et al.
Asian J. Chem.
discs were cited on growth medium. Appropriate fungal strain
was transferred on the filter paper disc present in the growth
medium containing Petri plate. The bimetallic complexes and
ligand were applied (100 µL) separately on each disc and then
the Petri plates were incubated for 48 h at 28 °C for fungus
growth. The binuclear complexes as well as ligand itself success-
fully inhibited the fungal growth. The results of the complexes
were compared antifungal drug fluconazol10.
EXPERIMENTAL
All solvents and reagents including ethylenediamine,
cobalt acetate, copper acetate, manganese acetate, zinc acetate,
ethanol, salicylaldehyde, acetic acid, toluene and ethyl acetate
ofAR grade were purchased from Sigma-Aldrich (Germany).
Synthesis of ligand: This ligand (tetradentate Schiff base)
was synthesized by condensation reaction of equimolar
quantities of salicylaldehyde (23.4 g, 0.1 mol) and ethylene-
diammine (6 g, 0.1 mol). The reactants along with glacial
acetic acid (1 mL) were refluxed in 40 mL of ethanol for 7 h7.
After refluxing, the progress of the reaction was checked by
TLC test in a pet ether-ethyl acetate (1:1) solvent system. The
crude product was then subjected to column chromatography
by using silica gel and pet ether-ethyl acetate (1:1) solvent
system. The eluent of the column chromatography was then
concentrated up to dryness by rotary evaporator. After drying
well the productivity was calculated to be 72 %. The ligand
was subjected to spectral investigation (1H, 13C) after dissolving
the sample in CDCl3 and calibration was achieved with TMS.
Synthesis of bimetallic complexes: In order to prepare
four binuclear (Cu, Co, Mn & Zn) complexes with Schiff base
(L), the equi-molar quantities of metal acetates (Co, Cu, Mn,
Zn) were dissolved seperately in ethanol/ toluene and were
reacted with ligand dissolved in toluene. Reaction mixture in
250 mL flask was refluxed along with stirring for 4-5 h to
complete the reaction. The success of each reaction was
checked by TLC test. After the reaction the solvent was
removed by the rotary evaporator, washed with pet ether-ethyl
acetate (1:1) solvent. All the complexes were recrystallized
from toluene/pet-ether system. After filtration each pure
product was dried well under vacuum and productivity was
calculated. These newly synthesized binuclear complexes
along with the ligand were tested for their antibacterial as well
as antifungal activities.
RESULTS AND DISCUSSION
The tetradentate Schiff base, 2-(bis-2-hydroxylphenyli-
dene)-1,2-diiminoethanne (L) and its the binuclear complexes
were prepared Schemes I and II.
OH
OH
CHO
H2N
N
Ethanol/CH3COOH
N
+
Reflux
Room temp
,
NH2
HO
7 hours
L= C16H16N2O2
Scheme-I: Synthesis of tetradentate Schiff base, 2-(bis-2-hydroxylphenyli-
dene)-1,2-diiminoethane (L)
OH
N
N
+
M(O CCH )
2
3 2
HO
N
N
Antimicrobial activity: Disc diffusion method was used
to test the antibacterial and antifungal activity. Different strains
(bacterial and fungal strains) were engaged to check the anti-
bacterial and antifungal activities.
O
O
M
N
O
O
M
Antibacterial activity: Different strains were used to test
the antibacterial activity. The selected strains were Escherichia
coli, Staphylococcus aureus and Bacillus Subtilis8. The ligand
and bimetallic complexes were employed for antibacterial
activity under Disc diffusion method. Nutrient agar was mixed
in distilled water and dispersed homogenously. Sterilization
of the medium was carried out by means of autoclave at 121 °C
for 20 min. Medium was treated with inoculums before it was
transferred to petri plates. The filter paper discs were placed
parallel on growth medium (100 µL) containing bimetallic
complexes and ligand separately. The incubation of petri plates
was taken for 24 h at 37 °C for bacterial growth. The comp-
lexes as well as ligand successfully inhibited the growth of
bacteria and formed clear zones. Zone reader was employed
to measure the inhibition zones in mm. The results of the comp-
lexes and ligand were compared with drug rifamipicin9.
Antifungal activity: Fungal strains were used to test the
antifungal activity. The selected strains were A. flavus, A.
alternate and A. niger8. The growth medium was synthesized,
sterilized and then transferred to the petri plates. Filter paper
N
(M= Co, Cu, Mn, Zn)
Scheme-II: Synthesis of teradentate Schiff base derivatives of binuclear
complexes
The Ligand (L) and it binuclear complexes showed sharp
melting points and were soluble in most of the organic solvents
(Tables 1 and 2).
TABLE-1
PHYSICAL PROPERTIES OF LIGANDS
AND ITS METAL COMPLEXES
S.
No.
Compound
nature
m.w.
m.f.
m.p. (°C)
1
2
3
4
5
L
268
659
650
642
662
C16H16O2N2
116
Cu2L2
Co2L2
Mn2L2
Zn2L2
Cu2(C16H14O2N2)2
Co2(C16H14O2N2)2
Mn2(C16H14O2N2)2
Zn2(C16H14O2N2)2
> 350
> 350
> 350
> 350

Vol. 26, No. 3 (2014)
Synthesis of Tetradentate Schiff Base Ligands for the Preparation of Post Transition Bimetallic Complexes 843
TABLE-2
SOLUBILITY OF LIGAND AND ITS BINUCLEAR COMPLEXES
Solubility
S. No.
Compound
Chlorofom
Mixed solvent system (Ethanol.
Toluene. Ethyl acetate)
DMSO
Ethyl alcohol
1
2
3
4
5
C16H16N2O2
+
+
+
+
+
+
+
+
Cu2(C16H14N2O2)2
Co2(C16H14N2O2)2
Mn2(C16H14N2O2)2
Zn2(C16H14N2O2)2
Slightly soluble
Slightly soluble
Slightly soluble
Slightly soluble
Slightly soluble
Slightly soluble
Slightly soluble
Slightly soluble
Slightly soluble
Slightly soluble
Slightly soluble
Slightly soluble
1H NMR analysis of ligand: The singlet peak at 3.95
ppm is exhibited by protons of ethylene. Each aryl group has
four protons in the molecule. Different environment of these
protons is found (Table-3) with labeling from C1-C4. C1, C2,
C3 and C4 protons showed doublet, triplet, triplet and doublet
at 7.02, 7.52, 7.08 and 7.66 ppm correspondingly. Imines
protons showed singlet at 8.54 ppm. Imine group have π electrons
which are deshielded and showed high value.A singlet at 11.26
ppm is exhibited by phenolic a proton which is probably due
to the strong effect of deshielded oxygen atom. The results
can be visualized from the spectrum (Fig. 1).
carbons of the molecule showed peak at 161.1 ppm. This is
perhaps due to the presence of more electronegative oxygen
atom (O) which is bonded to carbon and described the
downfield shift. On the contrary oxygen atoms also contain
lone pair which is correlated with the ortho and para carbons
of the phenols which exhibit up field shift by mesomeric
effect. The meta carbon of phenol remained unchanged (Table-
4). The results can be visualized from the respective spectrum
(Fig. 2).
TABLE-4
13C NMR DATA OF LIGAND (L)
Position of Carbon
Observed Value in
ppm
Peak area equivalent
to No of carbon
TABLE-3
1HNMR DATA OF LIGAND (L)
1 and 1'
2 and 2'
3 and 3'
4 and 4'
5 and 5'
6 and 6
7 and 7'
8 and 8'
61.9
Two
Two
Two
Two
Two
Two
Two
Two
Position of Protons
Type of Peak
Doublet
Triplet
Value in ppm
7.02
157.5
124.6
161.1
117.8
132.4
121.4
132.1
C1
C2
C3
C4
7.08
Triplet
7.52
Doublet
7.66
OH
N
N
OH
HO
N
N
HO
16
14
12
10
8
ppm
2
0
6
4
Fig. 1. 1H NMR spectrum of Ligand
13C NMR analysis of ligand: The environment of the
ligand molecule containing different carbon atoms is supported
easily by 13C NMR spectrum. Two carbon atoms correspond
to each peak in the molecule. First peak at 61.9 ppm is due to
the CH2-CH2 group. The signals of sp3 hybridized carbon atom
present in the middle of the molecule mostly appears at about
30 ppm but due to the presence of electronegative atom (N)
and the presence of π bonds adjacent to CH2-CH2 group
resulted the signals at downfield (61.9 ppm). The CH carbon
exhibits sp2 hybridization which is not terminal and is found
at 140 ppm. The presence of electronegative nitrogen (N) is
correlated with the observed value of carbon which showed
some deviation. Also the aryl group contains carbon atoms
which are observed from 120-130 ppm whereas the phenolic
200 180 160 140 120 100
80
60
40
20
.0
Fig. 2. 13C NMR spectrum of Ligand(L)
Antimicrobial activity: The antimicrobial activity was
determined by using disc diffusion method against different
species of fungus and bacteria and the results were compared
with standard drugs. The results confirmed that the activity of
bimetallic complexes is considerable high against bacteria and
fungus as compared to ligand.
Antibacterial activity: The tetradentate Schiff base (2-
(bis-2-hydroxylphenylidene)-1,2-diiminoethane (L) ligand and
its binuclear complexes were tested for their antibacterial

844 Zahoor et al.
Asian J. Chem.
activity against B. subtilis, S.aureus and E. coli along with
rifamipicin as a standard one8. The results are explained as
mean SD (Table-5). The ligand showed less activity as
compared to bimetallic complexes. The Mn2L2 exhibited best
activity (10.5 0.577) against S. aureus. while Mn2L2 and
Co2L2 expressed better antibacterial potential (9.75 0.5* and
Fig. 4. The antibacterial as well as antifungal results of
attempted complexes explained that antimicrobial potential
of Mn2L2 is the best while the Zn2L2 exhibited the least one.
This may be due to the least chelating ability of Zn (having
greater number of outer d electrons and hence smaller vacancies
are available for chelation) and good chelating capacity of
Mn is due to less number of electrons and hence greater vacancies
for available for for chelation. Earlier in a similar type of the
study Schiff base and its post transition metal complexes were
attempted for antimicrobial study. The results showed that
metallation can increase the antibacterial activity rather than
free ligand. Further it was observed that complexes exhibited
variable antimicrobial potential due to different metals involved
for metallatic11. Similarly the results of most studies showed
that the antimicrobial activity of the complexes was observed
higher than related ligand. The increased activity of the metal
complexes was explained on the basis of chelating theory.
Chelating reduces the polarity of the metal ion, because positive
charges of the metal are partially shared with the donor atoms
present in the ligands and there may be π-electron delocalization
over the whole chelation. This phenomenon increases the
lipophilic character of the metal chelate and favors its perme-
ation more efficiently through the lipoid layer of the microorga-
nism, thus destroying them more forcefully. The other factors
like solubility, conductivity and bond length between the metal
and ligand also increase the activity12.
9
0.816) against B. subtilus and E. coli, respectively. The
results of the Mn2L2 against S. aureus and B. subtilus are
statistically significant (p < 0.05) with zone 10.5 0.577 mm
and 9.75 0.5 respectively. Similarly the activity Co2L2 against
E. coli were also found statistically significant (p < 0.05) with
zones 9.75 0.5 mm. All results are given in comparison with
standard drug (rifamipicin) which gave the zone 24.5 0.577
mm. The anti bacterial potential of the titled complexes along
with ligand can be verified (Fig. 3).
TABLE-5
ANTIBACTERIAL ACTIVITY DATA OF LIGAND (L)
AND ITS BINUCLEAR COMPLEXES
Tested microorganism
diameter of inhibition zone
E. coli S. aureus B. subtilus
0.816 0.816 4.25 0.957
0.816*
Sr.No.
Comps.
1
2
3
4
5
6
(L)
4
6
Co2L2
Cu2L2
Mn2L2
Zn2L2
9
5.25 0.957
6.25 0.957
10.5 0.577*
5.75 0.5
8
6
0.816
1.154
5.25 0.957
8.75 0.5*
6.5 0.577
9.75 0.5*
6.5 0.577
23 0.816
Standard 23.25 2.061
24.5 0.577
Values shown are mean SD.
TABLE-6
ANTIFUNGAL ACTIVITY DATA OF LIGAND (L)
AND ITS BINUCLEAR COMPLEXES
*represents the significant difference at p < 0.05.
30
Tested microorganism diameter of inhibition zone
Sr.
No.
Comps.
A. niger
A. flavous
A. alternate
E. coli
S. aureus
B. subtilus
25
20
15
10
5
1
2
3
4
5
6
(L)
Nil
4
4.25 0.577
4
1.825
Co2L2
Cu2L2
Mn2L2
Zn2L2
1.825
7.75 0.957 12.25 0.062*
6.25 0.957 1.154
10.25 0.5* 8.5 0.577
5.75 0.5 Nil
23.25 2.061 23 0.816
7.75 0.957*
0.816
6.5 0.577
6
6
Standard 24.5 0.577
Values shown are mean SD.
*Represents the significant difference at p < 0.
0
(L)
Co2L2
Cu2L2
Mn2L2
Zn2L2
Standard
30
Fig. 3. Antibacterial activity data of Ligand (L) and its binuclear complexes
A. niger
A. flavous
A. alternata
25
20
15
10
5
Antifungal activity: Similarly the antifungal potential of
Schiff base and its bimetallic complexes were evaluated against
various fungal strains (A. alternata, A. niger, A. flavis) along
with fluconazol drug as a standard one by using disc diffusion
method. (Table-6). Results are shown as mean SD. The
results showed that Co2L2 exhibited highest activity against
A. alternate (12.25 0.062) while Cu2L2 and Mn2L2 expressed
better antifungal potential against A. niger (7.75 0.957) and
A. flavous (10.25 0.5), respectively. The antifungal activity
of Co2L2 against A. alternata and Cu2L2 against A. niger was
found statistically significant with zone 12.25 0.062 mm
and 7.75 0.957 mm respectively (p < 0.05). Similarly the
activity of Mn2L2 against A. flavus with zones 10.25 0.5 was
observed statistically significant (p < 0.05). All above results
are in comparison with standard drug (fluconazol) which gave
the zone 24 0.577 mm. The results can further be verified
0
(L)
Co2L2
Cu2L2
Mn2L2
Zn2L2 Standard
Fig. 4. Antifungal activity data of Ligand (L) and its binuclear complexes
ACKNOWLEDGEMENTS
The financial support for research from GC University
Faisalabad Pakistan is highly appreciated.

Vol. 26, No. 3 (2014)
Synthesis of Tetradentate Schiff Base Ligands for the Preparation of Post Transition Bimetallic Complexes 845
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