Synthesis, Characterization and
Antimicrobial Activity of Novel Schiff’s Base Complexes of some Transition
Metal Ions.
A.K. Ibrahim Sheriff1 and S.
Syed Shafi2*
1PG and Research Dept. of Chemistry, C. Abdul Hakeem
College, Melvisharam-632 509, India.
2Dept. of Chemistry, Thiruvalluvar University, Serkadu,
Vellore-632 004, India.
*Corresponding Author E-mail: suban_shafi@yahoo.com
ABSTRACT:
Condensation of p-methyl thioaniline with
salicylaldehyde gives a novel Schiff base which gives trischelate octahedral
complexes with Fe(II), Co(II), Ni(II) and Ru(III) metal ions and bis chelate
diaqua octahedral complex with Cu(II) ion. They have been characterized by magnetic
susceptibility measurements, electronic spectroscopy, IR,1H NMR and 13C
NMR techniques. Their electrochemical properties have been studied. Some of
these complexes have been found to be effective antimicrobials against some
selected Gram (+) and Gram (-) bacteria and fungi. Their ligand field
parameters such a 10Dq, LFSE, Racah parameter β have been calculated to
assess the strength and covalency of M-L bond.
KEYWORDS: Tris chelate, spectral studies, cyclic voltammetry,
ligand field parameters, antimicrobial.
INTRODUCTION:
Schiff bases and their complexes are widely studied
because of the simple and easy methods of their preparation. Their biological
activities and considerable commercial importance coupled with intriguing
structures similar to biomolecules have stimulated intense efforts for an
avalanche of research in this field.
They have been reported to have antibacterial, ant
tubercular, anticancer and antiviral properties. Many biological
transformations taking place in living organisms involve complexes of
transition metal ions. The antimicrobial activity increases with the presence
of sulphur in the compounds. In this present study a sulphur containing Schiff
base and its complexes have been synthesized, characterized and their
antimicrobial activity studied.
MATERIALS AND METHODS:
The chemicals employed for the synthesis of Schiff base
and its metal complexes are of AR grade. Standard methods were used to purify
all the solvents. All the
reagents were of analar grade and the solvents were purified by standard
methods. Elemental analyzer and standard methods were employed to estimate the
amount of elements.
Electrical conductance was determined on a Systronics conductivity meter type 304 with a dip type cell
having platinum electrode. Magnetic susceptibility measurements of the
complexes were made by Vibrating Sample Magnetometer EG&G Model: 155.The
UV-Visible spectra of the ligands and complexes were run on Cary -5E
spectrometer. Infrared spectra (4000-450 cm-1)
were studied on KBr disc using a Perkin Elmer spectrum ONE-N0174-1159. The
magnetic resonance of the 1H and 13C nuclei were recorded
using the instrument Brucker 300 FT NMR. The
electrochemical behavior of the complexes was inferred using the instrument
CH1660B Electrochemical Workstation using tetra butyl
ammonium per chlorate as background electrolyte, glassy carbon as working
electrode, Ag/Ag+ electrode as reference electrode and platinum wire as
auxiliary electrode.TGA and DTA thermogram were recorded using the instrument
NETZSCH STA 409-C/CD in the temperature range 25 to 1400°C at the rate of 10.0
k/min.
EXPERIMENTAL:
Synthesis of Schiff base HL1, (C14
H12 NSO):
A mixture of p-methylthioaniline and salicylaldehyde in
1:1 molar ratio in methanol on reflux yields the Schiff base HL1.
Synthesis of complexes:
A methanolic solution of the ligand on reflux with
suitable metal salt of Fe(II), Co(II), N(II)i and Ru(III) ions in 3:1 molar
ratio gives the corresponding tris chelate metal complexes1.
Similarly the Cu(II) complex is obtained by the above procedure when the molar
ratio of metal and Schiff base is 2:1. The amorphous complexes were filtered,
dried and recrystalized.
RESULTS AND DISCUSSION:
The molar conductivity of these complexes was measured
in 10-3M DMSO solvent. The complexes of Fe(II), Co(II) and Ni(II)
have been found to be 1:1 electrolytes but those Cu(II) and Ru(III) are non
ionic2. The analytical data (Table-1) shows that the Schiff base
behaves as a bidentate chelate.
Magnetic Susceptibility measurements:
Their magnetic susceptibility measurements show that
the complexes of Fe(II), Co(II), Ni(II), Cu(II) and Ru(III) are all
paramagnetic with 4,3,2, 1 and 1 unpaired electrons respectively due to the
electronic configuration t2g4 eg2,
t2g5 eg2, t2g6 eg2,
t2g6 eg3and t2g5 eg0.
Electronic Spectra:
The values of 10Dq, LESE and Racah’s interelectronic
repulsion parameter β have been calculated from the electronic
spectral data of these complexes (Table-2). Fe(II) complex shows only one band
due to the transition 5T2g (D) 
5Eg. The Co(II)
complex shows three bands due to the transitions 4T1g(F)4T2g
(F) (υ1) ,4T1g (F)4T1g(P) (υ2)
and 4T1g (F)4A2g (F) (υ3).The
Ni(II) complex also shows three bands due to the transitions 3A2g
(F) 3T2g
(F), 3A2g (F) 3T1g (P) and 3A2g
(F) 
3T1g
(F). The Cu(II) and Ru(III) complexes show only one band respectively
due to the transitions 2Eg 2 T2g and 2 T2g
2A2g.
The Cu(II) complex shows a broad band due to Jahn -Teller effect indicating the
presence of distorted octahedral geometry. The value of LFSE increases in the
order Fe(II) < Co(II) <Ni(II) < Cu(II) < Ru (III) which is in
accordance with Irving-William order of stability3-7.
IR Spectra:
The infrared spectral studies reveal the nature of the
ligating atom which forms bond with the central metal ions. The ligand HL1
shows an absorption band at1610 cm-1indicating the presence of
azomethine (-CH=N-) moiety. The decrease in its absorption frequency in all
these complexes indicate the coordination of the nitrogen in the ligand with
these metal ions. The absence of the VO-H in these complexes confirms the
coordination of the deprotonated ligand in these complexes. Thus the ligand
acts as a (N,O) bidentate donor. The presence of a broad band at 3282 cm-1
is attributed to H2O in the Cu(II) complex which confirms the
presence of coordinated water molecules. The appearance of new bands in the
region 520-565 cm-1and 460-520 cm-1 due to the stretching
of M—O and M---N bonds respectively give further evidence for the coordination
of phenoxy oxygen and azomethine nitrogen with these metal ions8-11.The
IR spectral data is given in Table-3.
1H NMR and 13C NMR STUDIES:
The proton NMR spectrum of the Schiff base shows a
multiplet at δ (in ppm)
6.84-7.46 due to the aromatic protons of the two phenyl rings (8H), a singlet
at δ 2.40due to S-CH3 (3H), a singlet at δ 8.34due to the
methine(-N=CH-) proton (1H) and a singlet at δ 5.13due to
phenolic proton (1H).
The 13C NMR spectrum of the Schiff base
ligand HL1 was recorded in D2O at room temperature. The
data is given in Table-4 . Its spectrum exhibits 12 lines indicating the
presence of 12 types of chemically different carbon atoms. The lines at 17.26,
163.2 and 164.8 ppm are due to the methyl, methine and phenoxy carbons
respectively12,13.
Cyclic Voltammetry Studies:
The cyclic voltammogram of Fe(II) complex(0.01M) with
Et4NClO4 as supporting electrolyte, glassy carbon as
working electrode and platinum wire as auxiliary electrode was recorded in DMSO
solvent in the potential range 1.0 V to 0 V at scan rate 100 mVs-1.
It shows an anodic peak due to oxidation of Fe(II) to Fe(III) during the
backward scan and a cathodic peak due to reduction of Fe(III) to Fe(II) during
forward scan. The ratio of intensity of current of the anodic peak with that of
the cathodic peak shows that the redox process is quasi reversible with
transfer of one electron. The CV of the Cu(II) complex showed two quasi
reversible redox waves. In the forward scan it showed two cathodic reduction
peaks at 0.22V and – 0.80V respectively due to the reduction of Cu(II) Cu(I) and Cu(I) Cu(0). In the
backward scan it showed two anodic oxidation peaks at - 0.72Vand 0.29V
respectively corresponding to the oxidation of Cu(0) Cu(I) and Cu(I) Cu(II).In the case of the
Ru(III) complex the reduction of Ru (IV) Ru(III) and Ru(III) Ru(II) takes place in the
forward scan at the potential + 0.48V and - 0.32V respectively. The oxidation
of Ru(II) Ru(III)
and Ru(III) Ru(IV)
takes place in the backward scan at - 0.25V and + 0.56V respectively. The redox
processes with peak to peak separation (∆E) values for oxidation RuIII/RuIV
and (RuII/RuIII) have been found to be 60 to 80 mV. This
suggests one step electron transfer process14,15.
Thermal studies:
The TGA and DTA studies of the complex [Cu(L1)2(H20)2]
show an endothermic peak at 148.2 ºC with a mass loss corresponding to two
coordinated water molecules. No such peaks are observed in the thermograms of
the other complexes16,17.
ANTIMICROBIAL ACTIVITY STUDIES:
The complexes were subjected to in vitro biological
screening effects by using the well diffusion method. Their antibacterial activity was studied against the Gram positive bacteria Staphylococcus
aureus, Micrococcus leteus, Bacillus cereus and Gram negative bacteria Escherichia
coli, Salmonella typhi and Pseudomonas aeruginosa using
chloroamphenicol as standard antimicrobial agent. The antifungal nature of the
ligands and their complexes was studied by well diffusion method against the
fungi Aspergillus niger, Candida albicans and Cryptococcus neoforman
using Ketoconazole as standard antimicrobial agent. The results showed that they posses weak to moderate
activity18,19. The
metal complexes are more effective in curbing the growth of these
microorganisms than the respective free ligands (Table-5).
CONCLUSIONS:
1H
nmr, 13C nmr and ir spectra of the ligand show that it posses a
methine moiety and phenolic –OH group. The IR spectra of its complexes reveal
that it acts a (N,O) bidentate chelate. Magnetic susceptibility and electronic
spectral studies disclose that all the complexes are paramagnetic and tris
chelate octahedral ones except that of Cu(ll) which is bis chelate with two
coordinated water molecules as it is evidenced from its thermogram. All these
complexes exhibit appreciable activity against the selected bacteria and fungi.
REFERENCES:
1
Dhar S. Nethaji M and
Chakravarty AR, Inorg Chim Acta, 358 (2004) 2437.
2
M.M Taquikhan, R.I.
Kurshey and N.H.Khan, Tetrahedron 2(1991) 1015.
3
Lewis J and Walton RA, J
chem Soc, 5(1966) 1557.
4
Lever ABP, Inorganic
Electronic Spectroscopy (Elsevier Amsterdam), 1984.
5
J.T. Makode and A S
Aswar, Indian J chem. 43A (2004) 2120.
6
Reddy KH, Indian J chem,
29A(1990) 497.
7
Hankare P P and Chavan S
S, Indian J chem. 42A(2003) 540
8
Nakamoto K,Infrared
Spectra of Inorganic and coordination compounds (Wiley, New York)
1970.
9
Kimberly J.Miller, Jun
Ho Baag and Mahdi M.Abu Omar, Inorg chem. 1999, 38,4510-4514.
10 Dnato Attanasio, Giulia Dessy and Vincenzo
Fares, Inorganica Chimica Acta, 104(1985) 99-107.
11 Yudhvir S.Sharma,H.N.Pandey and Pavan
Mathur, Polyhedron, 13,22(1994), 3111-3117.
12 Williams D and Flaming I, Spectroscopic
methods in Organic Chemistry, 4th Edn (Tata Mc Graw – Hill,New
Delhi), 1988.
13 Sayaji Rao M and Hussain Reddy K, Indian J
chem, 38A(1992) 262.
14 Bu X H, Zhang Z H, CaoX, Ma S and Ticlen Y,
Polyhedron, 15(1996) 410.
15 K . Hussain Reddy, M.Surendra Babu, P.Suresh
Babu and S.Dayananda, Indian J chem, 43A (2004) 1223.
16 S.M.Abu-el-Wafa, R.M.Issa and C.A.Mc
Auliffe, Inorganica Chimica Acta, 99 (1985) 103-106.
17 R.L.Dutta and R.K.Ray J.Inorg nucl
chem,39(1997) 1848-1850.
18 Pahmi N, Jodan SCS and singh R V,
Phosphorous, Sulphur, Silicon, 81(1993) 133.
19 Chohan Z B, Praveen M and Ghaffar A, Synth
React Inorg Met-Org Chem, 28(1988) 1673.