Co (II) and Zn (II) metal complexes of heterocyclic Schiff bases: A synthesis, spectral and antimicrobial study

Article abstract of DOI:10.13005/ojc/300353

The Schiff bases have been synthesised by the reaction of Benzoinoxime primary ligand with heterocyclic compounds such as 2-aminothiazole (SL₁) and 8-hydroxyquinoline (SL₂) to form the secondary ligand, which than react with the metal halides to form complexes of Co (II) and Zn (II). The elemental analysis data shows that the metal to ligand ratio in all Co (II) simple is 1:2 for simple complexes and 1:2:2 for metal complex with oxime as a primary ligand and SL₁as a secondary ligand while it is 1:2:1 for metal complex with oxime as a primary ligand and SL₃ as a secondary ligand whereas Zn (II) complexes of mixed ligand exhibit the stoichiometry 1:2:2. The structural features have been determined from IR, UV-Vis, and XRD data. All the complex shows a distorted octahedral geometry to mononuclear Co (II) complexes of mixed ligands, while square planner geometry to mononuclear Co (II) complexes of oximes. Zn (II) complexes of mixed ligands shows a distorted octahedral geometry, while square planner geometry to mononuclear Zn (II) complexes of oximes. All the synthesised compounds were screened for antimicrobial activity.

Full text of DOI:10.13005/ojc/300353

ISSN: 0970-020 X
CODEN: OJCHEG
014, Vol. 30, No. (3):
Pg. 1343-1348
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
2
www.orientjchem.org
Co (II) and Zn (II) Metal Complexes of Heterocyclic
Schiff Bases: A Synthesis, Spectral and Antimicrobial Study
1
2
SACHIN R. JOSHI and SEEMA I. HABIB
1
Department of Chemistry, Shankarrao Chavan Mahavidyalaya, Ardhapur, India.
2
Department of Chemistry, NSB College. Nanded (M.S.), India.
*
Corresponding author E-mail: seemahabib12@gmail.com
http://dx.doi.org/10.13005/ojc/300353
(
Received: May 29, 2014; Accepted: July 01, 2014)
ABSTRACT
The Schiff bases have been synthesised by the reaction of Benzoinoxime primary ligand with
heterocyclic compounds such as 2-aminothiazole (SL ) and 8-hydroxyquinoline (SL ) to form the
1
2
secondary ligand, which than react with the metal halides to form complexes of Co (II) and Zn (II).
The elemental analysis data shows that the metal to ligand ratio in all Co (II) simple is 1:2 for simple
complexes and 1:2:2 for metal complex with oxime as a primary ligand and SL as a secondary ligand
1
while it is 1:2:1 for metal complex with oxime as a primary ligand and SL as a secondary ligand
3
whereas Zn (II) complexes of mixed ligand exhibit the stoichiometry 1:2:2. The structural features
have been determined from IR, UV-Vis, and XRD data. All the complex shows a distorted octahedral
geometry to mononuclear Co (II) complexes of mixed ligands, while square planner geometry to
mononuclear Co (II) complexes of oximes. Zn (II) complexes of mixed ligands shows a distorted
octahedral geometry, while square planner geometry to mononuclear Zn (II) complexes of oximes.
All the synthesised compounds were screened for antimicrobial activity.
Key words: Schiff base, Antimicrobial activity, heterocyclic compounds.
INTRODUCTION
The metal complexes of Schiff bases derived from
heterocyclic compounds have been the centre
of attraction for many workers in recent years .
A study through the literature revealed that no
work has been realized on the preparation and
characterization of metal complexes of mixed
heterocyclic Schiff bases derived by the reaction of
Co (II) and Ni (II) Benzoinoxime primary ligand with
heterocyclic compounds such as 2-aminothiazole
and 8-hydroxyquinoline to form the secondary
4
-8
Metal complexes of Schiff bases are
extensively studied due to synthetic flexibility,
selectivity and sensitivity towards a variety of
metal atoms . Schiff bases are most widely used
as chelating ligands in coordination chemistry .
1
2
They are also useful in catalysis and in medicine
as antibiotics, antiallergic and antitumor agents .
3

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JOSHI & HABIB, Orient. J. Chem., Vol. 30(3), 1343-1348 (2014)
ligand, an attempt has been made to synthesize and an aqueous solution of 8.0 gm (0.087 mol) of
characterize some novel metal complexes of these hydroxylamine was taken together in a 250 ml
Schiff base ligands.The prepared ligands as well as round bottom flask. Before using hydroxylamine
their metal complexes were also investigated for their hydrochloride was neutralized with 4.4 gm (0.091
in vitro activity against some bacterial and fungal mol) of sodium hydroxide.The mixture was refluxed
species.The purpose of the work was to understand for 60 min. Then water was added to precipitate
the coordination as well as the biological chemistry benzoinoxime. It was cooled in ice bath. The solid
of these novel synthesized compounds.
was filtered with solution at pump and it was washed
with water finally the product was recrystallised by
using ethanol.
MATERIAL AND METHOD
Synthesis of Benzoinoxime
The purity of the product was checked by
Benzoinoxime was prepared by standard TLC and Melting point. Melting point of Benzoin
9
0
procedure in which 10 gm (0.047 mol) of benzoin Oxime is 151 C.
and 20 gm (25 ml) of rectified spirit together with
C
H N OH
2
O
C
N
OH
Refluxin
EtOH -H O
2
C
H
OH
C
H
OH
Scheme
PreparationofsimplecomplexesofBenzoinoxime hrs on cooling the coloured precipitate separate that
The following complexes of CO- was filtered, washed with cold hexane solvent and
Benzoinoxime and Zn- Benzoinoxime have been dried under vacuum over night.
10-14
synthesized as follows
.
RESULTS AND DISCUSSION
The above metal complexes were prepared
by mixing the solution of the primary ligand [(PL2 Elemental analysis and magnetic moment
Benzoinoxime) ( 0.06 mole)] in 80 ml of boiling
Elemental analysis data reveals that the
ethanol with 0.03 mole of metal(II) chloride solution in observed values of percentage of C, H, N, halogen
0 ml of distilled water.The mixture was magnetically and metal ion are in good agreement with values
stirred for about one hour.Then coloured precipitate predicted and calculated for Co(II) complexes with
except Zn) were formed which was filtered out and 1:2 metal to ligand ratio for simple complexes and
washed with hot water or methanol then dried over 1:2:2 for metal complex with oxime as a primary
2
(
vacuum. The purity was checked by using TLC.
ligand and SL as a secondary ligand while it is 1:2:1
1
for metal complex with oxime as a primary ligand and
Preparation of mixed ligand complexes of Co (II), SL as a secondary ligand. The elemental analysis
3
Zn (II) Benzoinoxime with S-L and S-L3
indicates that Zn(II) complexes of mixed ligand
1
Co(II),Zn(II)Benzoinoximecomplexsolution exhibit the stoichiometry 1:2:2.The Zn (II) complexes
(
0.01 mol) in ethanol and solution of S-L and S-L3 undergo decomposition at high temperature.
1
were dissolved in 25 ml ethanol or 25 ml CH Cl were
2
2
mixed separately in 250 ml round bottom flask. The
The magnetic moment values are in the
reaction mixture was refluxed on a water bath for 2-4 range of 2.74 to 3.25 B.M.of mixed ligand complexes

JOSHI & HABIB, Orient. J. Chem., Vol. 30(3), 1343-1348 (2014)
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JOSHI & HABIB, Orient. J. Chem., Vol. 30(3), 1343-1348 (2014)
1
5
in present work indicates octahedral geometry .Due
to completely filled‘d’shell as expected for Zn(II) ion it
exhibits diamagnetic nature.The present complexes
are found to be diamagnetic in nature for the square
43.445 kcal/mole for simple complexes are in good
agreement with octahedral CO (II) complexes and
square planner complexes respectively. In present
work the electronic absorption spectrum of Zn (II)
complexes shows only one absorption band in UV-
1
6
plannear geometry.
-
1
visible spectrum in the range 357 nm (2800 cm
)
-
1
The electronic spectra of Co (II) complexes
exhibit absorption bands at 10661-10870 cm (D ),
to 372 nm ( 26882 cm ). This is due to absence
of d-d transition. This observed peak is because of
metal to ligand charge transfer spectra. The values
are in agreement with octahedral geometry of these
-
1
1
-
1
1
6694-18149 cm (D ) and 20661-25189(D ) from
2
3
lower energy level to higher energy level, which also
clearly indicate the square planer and octahedral
17, 18, 19
complexes
.
15
stereochemistry of Co (II) complexes .
The ligand field parameter values i.e. LFSE
observed in the range 30.383 to 30.979 Kcal/
mole for mixed ligand complexes and 42.986 to
IR Spectroscopy
The azomethine C=N stretching is found
at 1650 cm for benzoinoxime . For Co(II) and
-
1
20
-
1
Table 2: Selected IR bands (cm ) of Co (II) and Zn (II) BO with SL SL (mixed ligand) complexes
1,
3
Complex
C=N
C=C
Aromatic Oximino M-N
M-O
Prim.
Lig.
M-O / M-N -NH
C-O
O-H
Prim.
Lig.
Sec. Lig.
Sec.
Lig.
Co(BO) + SL1 1579
Co(BO) + SL3 1578
Zn(BO) + SL1 1578
Zn(BO) + SL3 1571
1416-1600
1414-1610
1425-1600
1422-1600
1084
1090
1106
1109
3312
3308
3367
3369
494
491
484
487
509
508
544
547
/426
430 /
/ 428
429/
3450
- -
3452
- -
Table 3: Antimcrobial Activity
S.
Ligand / Complex
Bacterial Strain
Fungal Strain
No.
E. coli
S.aureus
A. niger
A. flavus
1
2
3
4
5
6
7
8
9
PL2
SL1
SL3
8
5
0
0
0
0
0
0
0
9
0
12
0
0
14
0
8
0
0
0
2
0
0
3
0
9
6
0
0
6
0
0
5
0
Co(II) PL2
Co(II) PL2 + SL1
Co(II) PL2 + SL3
Zn(II) PL2
Zn(II) PL2 + SL1
Zn(II) PL2 + SL3
0
9
Zn(II) Benzoinoxime the same band shifted to lower
The ligand benzoinoxime exhibit four peaks
-
1
-1
-1
-1
frequency and appears at 1623 cm , 1647 cm , in the range of 1430 cm to 1575 cm attributed to
for their adducts it is again to lower frequency and aromatic C=C stretch for two aromatic ring while its
-
1
appear in the range of 1576-1580 cm and 1571- Co(II) and Zn(II) complexes exhibits the same stretch
-
1
-
1
578 cm .This indicates that the azomethine group at 1415-1600 cm 1 and at 1446-1601 cm-1and the
of the ligand is coordinated to metal ion via nitrogen mixed ligand complexes exhibit it in the range of
2
1
-1
-1
atom .
1414-1600 cm , 1418-1600 cm .

JOSHI & HABIB, Orient. J. Chem., Vol. 30(3), 1343-1348 (2014)
1347
In the case of mixed ligand complex of and calculated density is 1.4220. The porosity
-aminothiazole and 8-hydroxyquinoline frequency of percentage was calculated from the observed and
OH is shifted to 3389-3398 cm showing weakening calculated density which is found to be 21.004 %.The
2
-
1
of intramolecular hydrogen bonding.
crystallographic data of the complexes fit perfectly
in monoclinic crystal system with four molecules per
The ligand band at 1403 cm is due to the unit cell. The probable spaces group is P /m.
O-H deformation mode of the oximino hydroxyl group
-
1
2
-
1
it identified at 1640-1645 cm for Co(II) and Zn(II) Antimicrobial activity
adducts ( mixed ligand complexes) indicating that Antibacterial activity by ditch-plate method
22
the oximino hydroxyl group remains intact in the
Nutrient agar of 20ml. was placed in a flat
complex of Co(II) with all heterocylic ligands used bottomed Petri dish.When solidified, 4 ml of second
in present work. However the O-H deformation band nutrient sol., Seed with test bacteria was poured
-
1
0
of the phenolic oxygen appears at the 1315 cm in evenly onto the first layer (at 48 c). As soon as the
the ligands disappears in the complexes showing second layer was solidified, in six sterile stainless
co-ordination through phenolic oxygen.
steel cylinders were added an equal amount of a
standard penicillin solution of concentrations 2.0,
Co (II), Zn (II) of Benzoine oxime complexes 1.5, 1.0, 0.5 and 0.25 mg/ml. Sample of the test
-
1
shows at 486 cm due to metal-nitrogen stretching solutions were deposited analogously on the other
-
1
-1
0
and at 492 cm , 539 cm due to metal-oxygen Petri dishes. The dishes were incubated at 37 c for
stretching. The metal oxygen bond shifted to higher 16-18 hours. During this time the penicillin diffuses
value in case of mixed ligand complex of Co(II), out of the cylinder into the surrounding agar and
Zn(II) of Benzoineoxime and appears in the range suppresses the growth of the test organism. Thus
-
1
-1
5
04-511cm , 544-547 cm .
the cylinder was surrounded by clear zone, free of
bacteria. The diameter of each zone provides an
A metal nitrogen weak band appears for all index of activity of the penicillin preparation. The
-
1
mixed ligand complexes in the range 491-495 cm
mean values obtained from 10-20 standard plates
this is due to formation of a bond between nitrogen are used to draw a curve and the biological activity
atom of secondary ligand and central metal cobalt of the test solution in international unit is determined
ion. In case of mixed ligand complex of Co (II), Zn using conversion table.
(
II) Benzoineoxime and 8-hydroxyquinoline one more
-
1
-1
band is observed at 430 cm , 429 cm .This clearly Antifungal activity by paper disc diffusion
indicates that the phenolic oxygen bonded to Co (II). method
Whatman No. 1 filter paper disc of 5mm
Inmixedligandcomplexesof2-aminothiazole diameter were sterilized by autoclaving for 15 min.
-
1
0
and 2-aminopyridine the bands appears at 3450 cm
at 121 C. The sterile disks were impregnated with
-1
and 3248 cm .This is due to free N-H- stretch proves different compounds. Agar plates were surface
that the –NH group do not participate in complex inoculated uniformly from the both culture of the
2
formation.
tested microorganisms. The impregnated disks
were placed on the medium suitably spaced apart
and plates were incubated at 28 C for 72 hours.The
0
X-ray Diffraction Study of Co (II) Complexes
The X-ray power diffractogram of [Co(II) inhibition zones caused by various compounds on
PL +(SL )] complex was selected for the study and the microorganisms were examined.
(
1
3
is reported in (Fig.5.74). The XRD data was fed to
computer to get the values of h, k, l, d, for various
refluxes using 1/d values.The indexing of data with
CONCLUSION
2
respect to prominent peaks was done independently
All the Co(II) complexes are pinkish, brown
by trial and error method. The standard deviation in coloured, whereas Zn(II) complexes are faint yellow,
crystal parameter found is within permissible limit. lemon yellow and white in colour, stable to air
The observed density of [Co(II)(PL +(SL )]is 1.1234 and moisture but decompose at high temperature
1
3

1
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JOSHI & HABIB, Orient. J. Chem., Vol. 30(3), 1343-1348 (2014)
In the present investigation, on the
rather than showing sharp melting points. They are
insoluble in water and soluble in DMSO, DMF and basis of elemental analysis, magnetic moment,
dioxane. In the present investigation, on the basis electronic absorption spectral data, shows a
of elemental analysis, magnetic moment, electronic distorted octahedral geometry to mononuclear Zn(II)
absorption spectral data, LFSE values shows a complexes of mixed ligands, while square planner
distorted octahedral geometry to mononuclear Co(II) geometry to mononuclear Zn(II) complexes of oximes
complexes of mixed ligands, while square planner
geometry to mononuclear Co(II) complexes of
oximes.The higher LFSE values of Co(II) complexes
shows that these complexes are less stabilized
ACKNOWLEDGEMENTS
The authors are thankful to the principal
than Cu(II) and Ni(II) complexes of oximes and NSB College Nanded for providing laboratory
heterocyclic ligands.
facilities. The authors are also thankful to the Head
IICT Hyderabad, for providing spectral data.
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