Preparation and antibacterial activity of mixed ligand complexes of Co(II), Ni(II), Cu(II) and Cd(II) derived from 1-phenylazo-2-naphthol and salicylaldehyde

Article abstract of DOI:10.1155/2011/519273

The mixed ligand complexes of Co(II), Ni(II), Cu(II) and Cd(II) have been synthesized by using 1-phenylazo-2-naphthol as primary ligand and salicylaldehyde as secondary ligand. All the prepared complexes were identified and confirmed by elemental analyses (C, H and N), molar conductance measurements, infrared, electronic absorption and electron paramagnetic resonance. The elemental analysis data suggest that the stoichiometry of the complexes to be 1:1:1[M: L¹: L²] ratio. The molar conductance measurements of the complexes indicate their non-electrolytic nature. The infrared spectral data showed the coordination sites of the free ligand with the central metal ion. The electronic absorption spectral data revealed the existence of an octahedral geometry for Co(II) and Cd(II) complexes and a square planar geometry for Ni(II) and Cu(II) complexes. The electron paramagnetic resonance spectra of the Co(II) and Cu(II) complexes showed the existence a paramagnetic phenomenon and supported their geometrical structures which confirmed by the electronic absorption spectra. The ligands and mixed ligand complexes have been tested on antibacterial activity against three strains of pathogenic bacteria such as Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa.

Full text of DOI:10.1155/2011/519273

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(1), 43-48
http://www.e-journals.net
Preparation and Antibacterial
Activity of Mixed Ligand Complexes of Co(II),
Ni(II), Cu(II) and Cd(II) Derived from
1-Phenylazo-2-naphthol and Salicylaldehyde
S. A. I. SHARIF, A. N. EL-TAJOURY* and A. A. ELAMARI#
Life Science Department, Faculty of Education
Garyounis University, Qemeenes, Libya
*Chemistry Department, Sci ence Faculty
Omar Al-mukhtar University, Derna, Libya
#Botany Department, Faculty of Science
Garyounis University, Benghazi, Libya
anh_chem2005@yahoo.com
Received 11 November 2009; Accepted 5 January 2010
Abstract: The mixed ligand complexes of Co(II), Ni(II), Cu(II) and Cd(II) have
been synthesized by using 1-phenylazo-2-naphthol as primary ligand and
salicylaldehyde as secondary ligand. All the prepared complexes were identified
and confirmed by elemental analyses (C, H and N), molar conductance
measurements, infrared, electronic absorption and electron paramagnetic
resonance. The elemental analysis data suggest that the stoichiometry of the
complexes to be 1:1:1[M: L1: L2] ratio. The molar conductance measurements of
the complexes indicate their non-electrolytic nature. The infrared spectral data
showed the coordination sites of the free ligand with the central metal ion. The
electronic absorption spectral data revealed the existence of an octahedral
geometry for Co(II) and Cd(II) complexes and a square planar geometry for
Ni(II) and Cu(II) complexes. The electron paramagnetic resonance spectra of the
Co(II) and Cu(II) complexes showed the existence a paramagnetic phenomenon
and supported their geometrical structures which confirmed by the electronic
absorption spectra. The ligands and mixed ligand complexes have been tested on
antibacterial activity against three strains of pathogenic bacteria such as
Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa.
Keywords: Mixed ligand, 1-Phenylazo-2-naphthol, Salicylaldehyde, Antibacterial activity.
Introduction
1-Phenylazo-2-naphthol and salicylaldehyde are bidentate ligands and have a good ability to
form many transition metal ion complexes1. Some mixed ligand complexes of divalent metal

44
A. N. EL-TAJOURY et al.
ions with salicylaldehyde, phathalic acid and L-alanine have been prepared and the investigation
was done by using different physical techniques, in particular; elemental analysis, molar
conductivity, infrared and electron paramagnetic resonance spectra2. Antibacterial activity studies of
the mixed ligand complexes of transition metal with maleic acid and heterocyclic amine bases have
been synthesized and identified on the basis of their chemical analyses and spectral characteristics.
All the complexes have been evaluated to possess octahedral structures and their biological
activities3. Synthesis and characterization of Co(II), Ni(II), Cu(II) and Zn(II) complexes with
3-salicylienehydrazono-2-indolinone was carried out by Konstantininovic et al.4. They found that
Ni(II) and Cu(II) complexes have a square planar geometry and a tetrahedral one for the Co(II) and
Zn(II) complexes and were found to exhibit antibacterial activity against Staphylococcus aureus,
Enterococcus D, Proteus mirabilis, Escherichia coli, Bacillus anthracis, Pseudomonas aeruginosa
and Candida albicans. The aim of the present paper was to synthesis some mixed ligand complexes
derived from 1-phenylazo-2-naphthol and salicylaldehyde and to elucidate their geometrical
structures, then to study their biological activities on some pathogenic bacteria
Experimental
All chemicals were reagent grade and purchased from BDH or Aldrich
including CoCl2.6H2O, NiCl2.6H2O, CuCl2.H2O, Cd(CH3COO)2.2H2O, salicylaldehyde,
NH4OH, C2H5OH, CHCl3, DMSO and nutrient agar (OXID). The ligands under
investigation have the following structures:
HO
HO
N
N
O
salicylaldehyde
Salicylaldehyde
1-phenylazo-2-naphthol
1-Phenylazo-2-naphthol
L2
L1
Measurements
The prepared mixed ligand complexes were subjected to (C, H and N) elemental analyses
using 2400 CH elemental analyzer. The molar conductance measurements were carried out
in DMSO using conductivity meter model CMD650 digital, were preformed in chemistry
department, Garyounis University, Benghazi, Libya.
The Infrared spectra were obtained by using KBr disk technique on IFS-25 DPUS/IR
spectrometer (Bruker) in the range of 4000-500 cm-1. The electronic absorption spectra of the
complexes were measured in DMSO using UV Vis-NIR3101PC Schimadzu (Japan). The electron
paramagnetic resonance spectra were recorded by using EMX ESR spectrometer (Bruker) 1998Y.
All the previous chemical analyses were done at the Advanced Laboratory of Chemical Analyses,
National Office for Research and Development, Tripoli, Libya.
Preparation of 1-phenylazo-2-naphthol
A (0.054 mol, 5.0 g) of aniline was dissolved in 16 mL of conc. HCl and 16 mL of water in
a 250 mL 3-necked flask and cooled in ice bath. Then 20 mL of (0.058 mol, 4.0 g) sodium
nitrite solution was added drop wise to the above solution with stirring and the resulting
o
mixture was left for 1 h at 0 C. A cooled solution (45 mL) 10% NaOH solution of 2-
naphthol (0.054 mol, 7.8 g) was added drop wise to the resulting solution with stirring and
o
the mixture was left for 1 h at 0 C. 1-Phenylazo-2-naphthol was precipitated as red solids.
The reaction mixture was filtered. The crude product was recrystallised from acetic acid and
washed with ethanol. The yield of deep red crystals is about 3 g, m.p. 131 oC.

Preparation and Antibacterial Activity of Mixed Ligand
45
Preparation of mixed ligand complexes
The present mixed ligand complexes were prepared by mixing equal amounts (0.01 mol) of
hot saturated ethanolic solutions of the first ligand (1-phenylazo-2-naphthol; 2.72 g) with the
same ratio of CoCl2.6H2O, NiCl2.6H2O CuCl2.2H2O and Cd(CH3COO)2.2H2O salts. The
mixtures were refluxed for one hour and then the second ligand (salicylaldehyde; 1.22 g) was
added in the same ratio to the previous mixtures and refluxed for three extra hours. Few drops
of ammonia solution were added to adjust the pH at which the mixed ligand complexes even
separated. The resulting complexes were washed several times with hot ethanol until the
filtrate becomes clear, dried in air and then in vaccum over anhydrous CaCl2. The yield was
ranged from 65-83%. The prepared mixed ligand complexes were subjected to elemental and
spectroscopic analyses. The obtained complexes are insoluble in C2H5OH but soluble in
DMSO. The purity of the mixed ligand complexes were tested by TLC technique.
Antibacterial assay
The antibacterial tests were assayed according to the diffusion method. The strains of bacteria
used were Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. All strains
were isolated from patients in Al-Jamahiriya hospital, Benghazi, Libya. The identity of all the
strains was confirmed. A bacterial suspension was prepared and added to the sterilized nutrient
agar (OXID/England) medium before solidification. The medium with bacteria was poured into
sterilized Petri dishes under aseptic condition. Different weights of ligands and mixed ligand
complexes (0.5 mg, 1 mg and 2 mg) were placed on the surface of the culture and incubated at
37 oC for 24 h. After incubation, the average of inhibition zones was recorded (mm).
Antibacterial activity was indicated by the presence of clear inhibition zones around the samples.
Results and Discussion
Microanalysis
The elemental analysis data of the mixed ligand complexes shown in Table 1 show the
formation of 1: 1: 1 [M: L1: L2] ratio. It has been found that the theoretical values are in a
good agreement with the found values.
Molar conductance measurements
The molar conductance values of the synthesized mixed ligand complexes with the
mentioned metal ions under investigation were determined using 10-3 M DMF solvent, as
shown in Table 1 are in the range of 0.83 - 1.65 Ω-1 cm2 mol.-1. These values suggest the
presence of a non-electrolyte nature5.
Table 1. Some physical properties of mixed ligand complexes
Chelates
[CoL1L2.2H2O].3H2O
[Ni L1L2].2H2O
M.Wt
C%
H%
N%
M.C*
540.9 55.20(55.46) 4.02(4.81) 4.93(5.18) 1.52
486.7 61.12(61.64) 4.17(4.11) 5.63(5.75) 1.33
509.5 58.27(58.88) 4.53(4.32) 5.81(5.49) 0.83
576.4 52.17(52.05) 3.98(4.16) 4.93(4.86) 1.65
[Cu L1L2].3H2O
[ Cd L1L2.2H2O]2H2O
*Unit of molar conductance Ω -1 cm 2 mol-1, Calculated values in parentheses
Infrared spectra
The infrared spectral data of Co(II), Ni(II), Cu(II) and Cd(II) complexes shown in Table 2
reveal broad bands in the range of 3306-3400 cm-1 attributed to the existence of coordinated
and crystallized water molecules6. Meanwhile, the same spectra display the bands which can be

46
A. N. EL-TAJOURY et al.
observed in the range 1575-1620 cm-1 due to the υ(C=O) group of the salicylaldehyde ring
moiety (1650 cm-1) and the υ(N=N) group of the1-phenylazo-2-naphthol ring moiety (1575 cm-1).
These bands are shifted to lower region during the complex formation indicating its
participation in coordination with the mentioned metal ions. Another bands in the range of
532-698 cm-1 and 432 - 469 cm-1 which are not present in the free ligands assigned to υ(M-O)
and υ(M-N) vibrations. The appearance of this vibration supports the involvement of –OH, –
CHO and –N=N– group in chelation7.
Electronic spectra
The electronic absorption spectra of the prepared complexes were recorded in DMSO
solvent as shown in Table 2. The absorption spectral data of [CoL1L2.2H2O].3H2O complex
show several bands shown in Table 2 attributed to the intra-ligand of the π-π* (phenyl ring),
4
4
4
charge transfer, 4T1g(F)→ T2g(F), 4T1g(F)→ A2g(F) and 4T1g(F)→ T1g(P) transitions,
which propose octahedral structure8-10. The electronic absorption spectrum of [NiL1L2].
2H2O complex reveals several bands which can be observed in the range12903 and
14771 cm-1 due to the presence of π-π*, n-π* transitions in the free ligands, charge transfer
(M→L) and 1A1(G)→ B1(G) transitions. The intensity of these bands indicates square planar
1
geometry. The electronic spectrum of the Cu(II) complex exhibits different bands Table 2
2
2
assigned due to charge transfer and B1(G)→ E(G) transitions. A square planar geometry
was proposed11. The obtained absorption bands of the [Cd L1L2.2H2O]2H2O complex which
appeared at 13831, 22573 and 26525 cm-1 are attributed to a charge transfer transition. This
observation supports the existence of an octahedral configuration around Cd(II) ion12.
Electron paramagnetic resonance spectra
The electron paramagnetic resonance spectral data of [CoL1L2.2H2O].3H2O and [CuL1L2].
3H2O complexes shown in Table 2 display geff values in the range of 1.898 - 2.135. These
values are deviated from the ideal free electron value. The observed deviation is attributed to
the presence of a partial ionic character of the covalent bond between the Co(II) and Cu(II)
ions with the mentioned ligands. Meanwhile, the obtained geff values suggest the existence
of an octahedral geometry13,14 except Cu(II) complex which has a square planar structure15.
Table 2. Electron paramagnetic resonance spectra of the complexes, infrared assignments
(cm-1) and electronic spectral data (nm, cm-1) of the ligands and complexes
Ligands/
Complexes
L1
ν(OH) νC=O
H2O (CHO) (N=N) (M-N)(M-O)
ν
ν
ν
Expected
geometry
λ
max nm, cm-1 geff
-
-
-
1650
1575
-
-
-
-
-
-
-
-
-
-
-
L2
[CoL1L2.2H2O]
.3H2O
324 (30864)
391 (25575)
775 (12903)
3400
1600
1540 432 532
1.898 Octahedral
[Ni L1L2].2H2O 3379
[Cu L1L2].3H2O 3309
1620
1538 478 698 736 (13587)
677 (14771)
723 (13831)
-
Square
planar
1620
1616
1541 461 555 360 (27777) 2.135 Square
287 (34843)
443 (22573)
1544 469 598 377 (26525)
359 (13831)
planar
[ Cd L1L2.2H2O]
3400
-
Octahedral
. 2H2O

Preparation and Antibacterial Activity of Mixed Ligand
47
Antibacterial activities
Table 3 shows the mean of inhibition zone of the ligands and mixed ligand complexes
Co(III), Ni(II), Cu(II) and Cd(II) ions which tested at different concentrations of 0.5, 1 and 2 mg
against several species of human pathogenic bacteria. The moderate effect was observed
with Cu(II) complex against Staphylococcus aureus and Pseudomonas aeruginosa; which
known as a resistant to most commercial antibiotic. However, no effect was observed
against Escherichia coli with all concentrations used. Compartively, Cd(II) complex showed
significant effect against Staphylococcus aureus with all concentration used. In contrast no
effect was observed against Escherichia coli and Pseudomonas aeruginosa. And Ni(II) did
not had any effect against all bacterial tested.
Table 3. The effect of ligands and the complexes on bacteria growth
Mean of inhibition zone, mm
Staphlococcus aureus Pseudomonas aeruginosa
Species of
bacteria
Samples
L1
Escherichia coli
0.5 mg 1 mg 2 mg 0.5 mg 1 mg 2 mg
0.5 mg 1 mg 2 mg
13
13
21
16
21
-
22
19
26
-
12
7
15
9
21
27
13
-
11
7
13
13
15
-
21
16
26
-
L2
Co(III) complex 17
13
-
13
-
12
-
Ni(II) complex
Cu(II) complex
Cd(II) complex
-
-
-
-
-
-
-
-
17
14
13
16
21
26
27
-
-
-
-
The 1-phenylazo-2-naphthol had more antibacterial activity than other ligand used. This
effect may be due to the presence of –Ph, –OH and –N=N– groups which are electron-releasing.
The antibacterial results evidently showed that the activity of the ligand compounds became
more pronounced when coordination to the metal ions. However, Co(II) complex has the best
results and presented antibacterial activity of Gram(positive) and Gram(negative) bacteria
compared to other complexes and it is definitive that metal ions do play a significant role in
enhancing the antibacterial activity of antibacterial agents on chelation. It is suggested that in the
chelated complex, the positive charge of the metal ion is partially shared with the donor atoms
and there is π-electron delocalization over the completely complex ring. This increases the
lipophilic character of the metal complex and favors its permeation through lipoid layers of the
bacterial membranes. It is also suspected that factors such as solubility, dipole moment and cell
permeability mechanisms are also influenced by presence of the metal ions16. The result showed
a significant reduction of inhibition zone as the concentration of chelates decreased.
Conclusion
From the previous data [elemental analysis, molar conductance measurements infrared,
electronic absorption and electron paramagnetic resonance] we can propose the following
chemical formulae for the synthesized mixed ligand complexes.
O
Cu
N
O
O
O
O
Ni
O
.3 H2O
.2 H2O
N
N
N

48
A. N. EL-TAJOURY et al.
O
O
OH2
O
OH
2
O
O
Cd
N
Co
N
O
H2
O
H
O
2
.2 H2O
.3 H2O
N
N
Acknowledgment
We are thankful to Wedad Al-Akrash and Khadeja Essaga from the Advanced Laboratory of
Chemical Analyses, National Office for Research and Development, Tripoli, Libya for their
help for us and for analysis of samples in this work.
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