Synthesis, physical characterization and biological evaluation of schiff base Cr(III), Mn(III) and Fe(III) complexes

Article abstract of DOI:10.1155/2010/623915

M(III) complexes with Cr, Mn and Fe with Schiff base derived from 2-amino-4-ethyl-5-hydroxy benzaldehyde and oxocarbohydrazide were synthesized and characterized by several techniques using elemental analysis (C, H, N), molar conductance measurements, magnetic measurements, electronic, mass and IR spectral studies. On the bases of these studies, a five coordinated square pyramidal geometry for all these complexes has been proposed and found to be potential antimicrobial agent. The Schiff base ligand and complexes were also tested for their antimicrobial activity (against the bacteria Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus megaterium and the fungi Kluyveromyces fragilis, Rhodotorula rubra, Candida albicans and Trichoderma reesei) to assess their inhibiting potential. An attempt is also made to correlate the antimicrobial activity with geometry of the complexes. All complexes were found to be less active against the pathogens E.coli, S.aureus and P.aeruginosa. Cr(III) complex showed the best antimicrobial activity, but ligand alone was found to be active against the fungus T.reesei.

Full text of DOI:10.1155/2010/623915

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2010, 7(3), 813-820
http://www.e-journals.net
Synthesis, Physical Characterization and
Biological Evaluation of Schiff Base
Cr(III), Mn(III) and Fe(III) Complexes
GAJENDRA KUMAR, DHARMENDRA KUMAR§,
SHOMA DEVI#, AMIT KUMAR and RAJEEV JOHARI*§
Department of Chemistry, Meerut College, Meerut, (U.P)- 250001, India.
§Department of Chemistry, Vardhaman College, Bijnor (UP)- 246701, India.
#Department of Life Science, Vardhaman College, Bijnor (UP) -246701, India.
gaj25chem@gmail.com
Received 11 December 2009; Accepted 7 February 2010
Abstract: M(III) complexes with Cr, Mn and Fe with Schiff base derived
from 2-amino-4-ethyl-5-hydroxy benzaldehyde and oxocarbohydrazide were
synthesized and characterized by several techniques using elemental analysis
(C, H, N), molar conductance measurements, magnetic measurements,
electronic, mass and IR spectral studies. On the bases of these studies, a five
coordinated square pyramidal geometry for all these complexes has been
proposed and found to be potential antimicrobial agent. The Schiff base
ligand and complexes were also tested for their antimicrobial activity (against
the bacteria Escherichia coli, Staphylococcus aureus, Pseudomonas
aeruginosa and Bacillus megaterium and the fungi Kluyveromyces fragilis,
Rhodotorula rubra, Candida albicans and Trichoderma reesei) to assess their
inhibiting potential. An attempt is also made to correlate the antimicrobial
activity with geometry of the complexes. All complexes were found to be less
active against the pathogens E.coli, S.aureus and P.aeruginosa. Cr(III)
complex showed the best antimicrobial activity, but ligand alone was found to
be active against the fungus T.reesei.
Keywords: Co(III), Cr(III) and Fe(III) Complexes, Schiff base, 2-Amino-4-ethyl-5-hydroxy
benzaldehyde, Oxocarbohydrazide, Antimicrobial activity
Introduction
The field of Schiff base complexes was fast developing on account of the wide variety of
possible structure for the ligands depending up on the aldehydes and amines. Many Schiff base

814
RAJEEV JOHARI et al.
and their complexes have been widely studied because of their industrial and biological
applications1,2. Some Schiff base was tested for fungicidal activity which is related to
their chemical structure3. Schiff base compound containing an amine group (–RC=N–)
are usually formed by the condensation of a primary amine with an active carbonyl. The
cross linking agents can also be derived from metal complexes with O–N– or –S ligands
for example, the intra coordination salt such as salicylates, anthranilates and the aliphatic
or aromatic amines can form strong five or six membered chelates rings which are able to
produce the metal containing crosslinking agents with required properties4-7. Synthesis of
oxovanadium(IV) complexes of the Schiff base derived by the condensation of 2-
aminobenzaldehyde with various diamines (1, 2-diaminoethane, 1, 2-diaminopropane, 1,
3-diaminopropane) and characterized by elemental analysis, spectral data and
electrochemical studies8. The complexes of Co(II), Ni(II) and Cu(II) ions with the Schiff
base derived from the condensation of salicylaldehyde and o-aminophenol or
2-aminobenzoic acid were synthesized and characterized by using different techniques, in
particular the elemental analysis, molar conductance measurements, IR and electronic
spectra9-10
.
The aim of the present paper is to prepare, characterize and study the antimicrobial
activity of the Schiff base complexes derived from oxocarbohydrazide and 2-amino-4-ethyl-
5-hydroxy benzaldehyde.
Experimental
All chemicals used in this work were analytical reagent grade (anhydrous). CrCl3, MnCl3
and FeCl3 were purchase from Aldrich (New Delhi, India) DMSO, DMF, ethanol were
purchase from sigma (New Delhi, India) and 2-amino-4-ethyl-5-hydroxy benzaldehyde and
oxocarbohydazide from Fluka (Mumbai, India).
Synthesis of Schiff base
The Schiff base (ligand) was prepared by mixing a warm dilute ethanol solution of
oxocarbohydrazide (5 mmol) with 2-aminobenzaldehyde (10 mmol) under reflux for two
hours. The precipitate was then removed from the reaction mixture by filtration10,11, washed
with ethanol and dried in desiccator over anhydrous CaCl2. The colour of the solid product
was yellow (yield 65%).
Scheme 1. Synthesis of Schiff base ligand.
Synthesis of complexes
The Schiff base was taken in ethanol (50 cm3) and stirred gently for one hour to give
homogeneous solution and added trivalent chromium, manganese or iron chlorides salts
(25 cm3). The resulting solution was refluxed for 6-8 hours. The mixture was concentrated
to half of its initial volume and kept in a desiccator for two days over anhydrous CaCl2.

Synthesis, Physical Characterization and Biological Evaluation
815
The complexes were then filtered, washed with ethanol and dried. The complexes are
soluble in DMF and DMSO but are insoluble in other common organic solvent and water.
They were thermally stable up to 523-553K and then decompose.
Scheme 2. Synthesis of the M(III) Schiff base complexes.
Methods
The microanalysis of C, H and N were estimated by elemental analyzer (Perkin Elmer
2400), at SAIF, CDRI, Lucknow, India and the metal contents of Mn(III), Co(III) and
Cu(III) was determined using atomic absorption spectrophotometer Perkin Elmer 5000.
(See Table 1 containing also some physical properties of the prepared compounds). The
conductivity was measured on digital conductivity meter (HPG system, G-3001) in
DMSO at room temperature. The magnetic susceptibility measurements were carried out
on vibrating sample magnetometer (Model PAR 155) at room temperature. Electronic
spectra (in DMSO) were recorded on a Hitachi 330 spectrophotometer (5815-32573 cm-1).
The IR spectra were performed using a FT-IR spectrophotometer Perkin Elmer 1650 in
the range 4000–200 cm-1 using Nujol Mull (In Tables 1 and 2 molar conductivities,
magnetic moments and spectral data are given). The FAB mass spectra (at room
temperature) were recorded on VG-70-S mass spectrometer. The purity of the Schiff
base and its complexes were confirmed also by TLC [microcrystalline cellulose (E. Merck)
was used for the preparation of thin layer, complete separation was achieved with the
solvent system acetone/conc. HCl/water (86:8:7). RF values increase in the following
order of M(II) complexes: Mn, Co, Cu (0.20, 0.34, 0.60)] and HPLC. The HPLC
chromatographic apparatus consisted of a model waters 600 pump with waters 600
controller, waters 2996 photodiode array detector with UV detection 254 nm, flow rate 1 mL/min
a discovery C8, 15 cm x 4.6 mm I.D, 5 µm particles and mobile phase methanol:25 mm
KH2PO4 (20:80) PH=3 techniques.

816
RAJEEV JOHARI et al.
Table 1. Elemental analysis in %, molar conductance (ΛM in DMSO) in S cm2 mol-1 and
magnetic moment (µeff) in µB of the Schiff base ligand and its metal complexes.
C
H
N
M
µeff ΛM
Compoundsa Molecular formula
FW
Colour
Calcu Calcu Calcu Calcu
(Found) (Found) (Found) (Found)
59.39
(58.84) (6.50) (21.87)
greenish 42.06 4.42 15.48
yellow (42.12) (4.45) (15.45) (9.49)
41.83 4.39 15.39 10.07
(41.75) (4.41) (15.35) (10.15)
orange 41.76 4.39 15.37 10.22
(41.75) (4.35) (15.40) (10.25)
6.2
21.84
Ligand (HL)
C19H24N6O3
384.209 yellow
9.57
Cr complex [Cr(C19H24N6O3)X]X2 542.56
4.35 58.8
4.85 40.00
5.78 32.50
Mn complex [Mn(C19H24N6O3)X]X2 545.50 dark
Fe complex [Fe(C19H24N6O3)X]X2 546.41
a HL = free Schiff base C19H24N6O2S.
Red
Table 2. IR spectral bands position/cm¯ 1 and electronic spectral data (in DMSO) cm¯ 1 of the
Schiff base ligand and its metal complexes.
Compoundsa
maxima
-OH str -OH ben
UV-Vis
27027
(NH2) (C=N) (C=O) (M–Cl) (M–N)
υ
υ
υ
υ
υ
Ligand (HL) 3250 1560 1696
Cr(III)
295
310
410
400
3327
3292
1350
1352
3280 1530 1715
complex
Mn(III)
8950-9300
3260 1560 1705
complex
Fe(III)
290
391
440
450
3375
3438
1380 22200-22575
1332 9540-9830
3310 1520 1699
complex
aHL = free Schiff base C19H24N6O2S, UV-vis ( extinction coefficients are given in parentheses, dm3
mol-1 cm-1) for HL (35800), Cr(III) complex (24500, 8200), Mn(III) complex (32400, 12600) and
Fe(III) complex (18300, 8900).
Antimicrobial activity
The antibacterial and antifungal activities of the newly synthesized compounds were
evaluated by agar well diffusion method12. All the microbial cultures were adjusted to 0.5
McFarland standards, which is visually comparable to a microbial suspension containing
approximately 1.5x108 cfu/mL13. 20 mL of agar media was poured into each Petri plate and
plates were swabbed with 100 µL inocula of the test microorganisms and kept 15 min for
adsorption. Using sterile cork borer of 8 mm diameter, wells were bored into the seeded agar
plates and these were loaded with a 100 mL volume with concentration of 1.0 mg/mL of each
compound dissolved in the dimethylsulphoxide (DMSO). All the plates were incubated at 300K
for 24 h. Antimicrobial activity of all the synthesized compounds was evaluated by measuring
the zone of growth inhibition against the test organisms with zone reader (Hi antibiotic zone
scale). The medium with dimethylsulphoxide (DMSO) as solvent was used as a negative control
whereas media with Ciprofloxacin (standard antibiotic) and Griseofulvin (standard antifungal
drug) were used as positive control. The experiments were performed in triplicates.
The ligand HL and its Cr(III), Mn(III) and Fe(III) complexes were tested for their
antibacterial and antifungal activity against the bacteria: Escherichia coli, Staphylococcus aureus,
Pseudomonas aeruginosa and Bacillus megaterium and the fungi: Kluyveromyces fragilis,
Rhodotorula rubra, Candida albicans and Trichoderma reesei procured from Microbial Type
Collection and Gene Bank, Institute of Microbial Technology (IMTECH), Chandigarh, India.

Synthesis, Physical Characterization and Biological Evaluation
817
Results and Discussion
The elemental analysis (C, H, N, M) data of the metal chelates showed that they may be
represented by the formula [M(C19H24N6O3)X]X2, (M(III) = Cr, Mn and Fe; X=Cl). The
purity of the Schiff base and its complexes was also confirmed by TLC and HPLC
techniques.
The measurements of molar conductance in DMSO show that these chelates are 1:2 type
of electrolytes (conductance values were 30-60 S cm2 mol-1, whereas the literature range was
30-180 Scm2 mol-1)14. The tests for anions are positive before decomposing and after
decomposing the chelates with concentrated HNO3 showing their presence outside as well as
inside the coordination sphere. Several attempts failed to obtain a single crystal suitable for
x-ray crystallography. However, the analytical, spectroscopic and magnetic data enable us to
predict the possible structure of the synthesized complexes. The low molar conductance of
the complexes might arise due to large size of the cation coordination sphere, which might
have low ionic mobility, the value of molar conductance’s suggest that complexes are
electrolytes and that chloride is present as the counter ion.
The IR spectra provide valuable information regarding the nature of functional group
attached to the metal atom. The presence of a single medium band in the region 3250-3330 cm-
1 in the complexes may be assigned to N-H stretching vibrations15,16. It was noted that a pair of
1
bands corresponding to (NH2) at 3245 cm¯1 and 3309 cm¯ are present in the spectra of the
υ
thiocarbohydrazide . The value of (C=N) stretching vibration is found lower (1520–1560
υ
cm¯ 1) than the expected value (1580 -1650 cm¯1). This may be explained on the basis of a drift
18
of lone pair density of azomethine nitrogen towards the metal atom17,
indicating that
coordination takes place through nitrogen of (C=N) groups. The bands present in the range
3020-3040 cm¯1 may be assigned due to (C–H) stretching vibrations of benzil and naphthalene
rings19. The C–N stretching was in the range 1000-1300 cm¯1. The band near 1700 cm¯1 in
oxocarbohydrazide may be assigned to free υ(C=O). The band at 3292-3438 cm¯1 is due to the
presence of -OH group in the complexes. This band is also present in the spectra of all the
complexes, which indicate that oxygen is not coordinating to the metal atom20,21. The far IR
spectra show bands in the region 420-450 cm¯1 corresponding to (M–N) vibrations22-24. The
υ
presence of bands in all complexes in the region 420-450 cm¯ 1 originates from the (M–N)
azomethine vibrational modes and identifies coordination of azomethine nitrogen25. The bands
present at 290-310 cm¯1 may be assigned toυ(M–Cl) vibrations26,27
.
The FAB mass spectra of ligand, Cr(III), Mn(III) and Fe(III) complexes have been
recorded. All the spectra exhibit parent peaks due to molecular ions (M+). The proposed
molecular formula of these complexes was confirmed by comparing their molecular formula
weights with m/z values. The molecular ion (M+) peaks obtained for various complexes are
as follows: m/z 384 (ligand), m/z 542 (Cr(III) complex), m/z 545 (Mn(III) complex), m/z 546
(Fe(III) complex) These data are in good agreement with the proposed molecular formula
for these complexes i.e. [M(C19H24N6O3)X]X2. Where M = Cr(III), Mn(III) and Fe(III) and
X = Cl¯ . In addition to the peaks due to the molecular ions, the spectra exhibit peaks
assignable to various fragments arising from the thermal cleavage of the complexes. The
peak intensity suggested the stability of the fragments.
The electronic spectra of the Schiff base and its complexes were recorded in DMSO.
The absorption spectra of free ligand consist of an intense bands centered at 370 nm (27027 cm-1)
attributed to n → π* transition of the oxo group. Another intense band in higher energy
region of the spectra of the free ligand was related to n → π* transition of benzene rings21.

818
RAJEEV JOHARI et al.
Magnetic moments of Cr(III) complex was found 4.35 µB at room temperature which is
close to the predicted values for three unpaired electrons in the metal ion28. The electronic
1
spectrum of Cr(III) complex showed bands in the range 8950-9310 cm¯ . The spectral bands
are consistent with that of five-coordinated Cr(III) complex, whose structure has been
confirmed with the help of x-ray measurements29. On the basis of the analytical data,
spectral studies and electrolytic nature of the complex, a square-pyramidal geometry may be
4
assigned for this complex30. The spectral bands may be assigned as: B1→4Ea 4B1→4B2,
4B1→4A1 and 4B1→4Eb.
The magnetic moment of Mn(III) complex was 4.85 µB which indicates the high spin d4
system28. The electronic spectra of manganese complex show three d-d band which lays in
the range 12250-12590 cm¯ 1 and may be assigned to charge transfer transitions. The spectra
resemble to those reported for five coordinate square pyramidal manganese(III) complexes30.
1
This is further supported by the presence of the broad ligand field band at 20400 cm¯ . The
5
5
4
various bands may be assigned as follows: B1→5A1, B1→5B2 and B1→5E. The band
assignment in single electron transition may be made as: dz2→dx2_ 2, dxy→dx
and dxy,
2_ 2
y
y
dyz→dx2_ 2, respectively, in order of increasing energy. However, the complexes do not have
idealized C4V symmetry.
y
The magnetic moment of Fe(III) complex was 5.78 µB corresponding to the five
unpaired electrons and is close to the predicted high spin values for this metal ion28. The
1
electronic spectra of Fe(III) complex show various bands in the range 9820-9970 cm¯ and
are consistent with the range of spectral bands reported for five coordinate square pyramidal
Fe(III) complex31. The various bands can be assigned as: dxy→dxz, dyz and dxy→dz2. Any
attempt to make accurate assignment is difficult due to interactions of the metal-ligand
π-bond systems lifting the degeneracy of the dxz and dyz pair.
Based on various studies like elemental analysis, conductance measurements, magnetic
susceptibilities, IR, electronic and mass spectral studies the structure shown in Scheme 2
may be proposed for all of the complexes.
The results showed (Table 3) that HL (ligand) exhibits moderate activity against all tested
bacteria and Candida albicans fungus. HL showed high antifungal activity against
Kluyveromyces fragilis and Trichoderma reesei but no activity against Rhodotorula rubra.
Cr(III) complex showed high antibacterial and antifungal activity against Bacillus megaterium,
Kluyveromyces fragilis, Rhodotorula rubra and Candida albicans, moderate activity against
Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa, but no activity against
the Trichoderma reesei. Mn(III) complex exhibited moderate activity against Pseudomonas
aeruginosa and Bacillus megaterium, was highly effective against the Kluyveromyces fragilis,
Candida albicans and Trichoderma reesei but showed no activity against the Escherichia coli,
Staphylococcus aureus and Rhodotorula rubra. Fe(III) complex exhibited moderate activity
against Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus megaterium and
Trichoderma reesei, higher effect against Kluyveromyces fragilis and Candida albicans, but no
activity against Escherichia coli and Rhodotorula rubra microorganisms.
Antibacterial and antifungal activity of the ligand and its metal complexes is compared
with the standard drug Ciprofloxacin and Griseofulvin. The variation in the activity of
different metal complexes against different microorganisms depends on their impermeability
of the cell or the differences in ribosomes in microbial cell32. The lipid membrane
surrounding the cell favors the passage of any lipid soluble materials and it is known that
liposolubility is an important factor controlling antimicrobial activity33,34
.

Synthesis, Physical Characterization and Biological Evaluation
819
In the present study low activity of the some metal complexes is may be due to their low
lipophilicity, because of which penetration of the complex through the lipid membrane was
decreased and hence, they could neither block nor inhibit the growth of the microorganism.
Table 3. Antibacterial and antifungal activity of the standards, solvent, ligand and its metal
complexes.
Bacterial inhibition zone/mm
Fungi inhibition zone/mm
Compoundsa
7
9
7
8
7
7
8
16
7
12
18
10
15
-
0
16
0
9
12
15
12
-
14
0
Ligand (HL)
Cr Complex
Mn Complex
Fe Complex
Ciprofloxacin
Griseofulvin
DMSO (Control)
0
0
9
12
7
0
8
9
7
0
24
-
20
-
22
-
24
-
-
1
24
0
24
0
24
0
23
0
0
0
0
0
a HL = free Schiff base C19H24N6O2S.
Conclusion
The analytical data show the presence of one metal ion per ligand molecule and suggest a
mononuclear structure for the complexes [M (C19H24N6O3)X]X2. The electronic spectral data
is in the favor of square pyramidal geometry of the complexes. The ligand and its Cr(III),
Mn(III) and Fe(III) complexes were tested for antimicrobial activity against some pathogens.
All the complexes were found to be less active against the bacteria E.coli, S.aureus and
P.aeruginosa, whereas Cr(III) complex showed the best antimicrobial activity against the
bacterium B.megaterium and the fungi K.fragilis and R.rubra. The free ligand (C19H24N6O3)
was found to be active against the fungus T.reesei.
Acknowledgment
The authors express their sincere thank to the head from Department of Chemistry, Principal
and College Managing Board of Vardhaman College, Bijnor, India for their encouragement
and providing research facilities and to CDRI Lucknow and IIT Roorkee for providing mass,
electronic and IR spectral data.
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