Synthesis, characterization and antimicrobial properties of some transition metal complexes with NS-chelating Schiff base ligand incorporating thiophene and sulfonamide moieties

Article abstract of DOI:10.14233/ajchem.2015.17627

Schiff base namely 4-[(thiophene-2-yl)methyleneamino]phenyl sulfonamide (L) and its Co(II), Ni(II), Cu(II) and Zn(II) complexes were synthesized and characterized by UV-visible, IR, 1H NMR, MS-EI, elemental analysis and TGA. Molar conductance and magnetic susceptibility of the complexes were also analyzed. Elemental analyses confirmed a 2:1 molar ratio of ligand to metal ion of the complexes. IR spectra revealed that the ligand is coordinated to the metal ions through azomethine-N and thiophene-S. On the basis of experimental data octahedral geometry was proposed for all complexes. Thermal studies together with IR showed the presence of lattice and coordinated water molecules in all complexes. The in vitro antimicrobial activities of the compounds were tested against S. aureus, K. pneumoniae, C. albicans and C. krusei by the agar well diffusion assay. The result indicated that the ligand become antimicrobially active on chelation with metal ions. It was found that Cu(II) complex showed the highest antibacterial activity among all complexes.

Full text of DOI:10.14233/ajchem.2015.17627

Asian Journal of Chemistry; Vol. 27, No. 3 (2015), 941-948
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.17627
Synthesis, Characterization and Antimicrobial Properties of Some Transition Metal Complexes
with NS-Chelating Schiff Base Ligand Incorporating Thiophene and Sulfonamide Moieties
1
2
1,*
YIHEYIS BOGALE ZEMEDE , D. NITHYAKALYANI and S. ANANDA KUMAR
1
2
Department of Chemistry, Faculty of Science and Humanity, Anna University Chennai-600 025, India
Centre for Biotechnology, Alagappa College of Technology, Anna University, Chennai-600 025, India
*
Corresponding author: E-mail: sri_anand_72@yahoo.com
Received: 19 March 2014; Accepted: 25 May 2014;
Published online: 19 January 2015;
AJC-16701
Schiff base namely 4-[(thiophene-2-yl)methyleneamino]phenyl sulfonamide (L) and its Co(II), Ni(II), Cu(II) and Zn(II) complexes were
1
synthesized and characterized by UV-visible, IR, H NMR, MS-EI, elemental analysis and TGA. Molar conductance and magnetic
susceptibility of the complexes were also analyzed. Elemental analyses confirmed a 2:1 molar ratio of ligand to metal ion of the complexes.
IR spectra revealed that the ligand is coordinated to the metal ions through azomethine-N and thiophene-S. On the basis of experimental
data octahedral geometry was proposed for all complexes. Thermal studies together with IR showed the presence of lattice and coordinated
water molecules in all complexes. The in vitro antimicrobial activities of the compounds were tested against S. aureus, K. pneumoniae, C.
albicans and C. krusei by the agar well diffusion assay. The result indicated that the ligand become antimicrobially active on chelation
with metal ions. It was found that Cu(II) complex showed the highest antibacterial activity among all complexes.
Keywords: Transition metal(II) complexes, 4-[(Thiophene-2-yl)methyleneamino]phenyl sulphonamide, Octahedral geometry.
complexes have been synthesized and tested for their anti-
microbial activities against different disease causing bacteria
and fungi, they however not satisfactory in acting against the
INTRODUCTION
In recent years, different families of organic-inorganic
chemicals are being investigated extensively because of their
medicinal applications. Sulfonamides and their derivatives are
one of those families. They were the first effective drugs found
to act selectively and could be used systematically as preventive
22-25
same effectively . To design effective chemotherapeutic
agents and better antimicrobial drugs, it is essential to explore
the interactions of metal with different Schiff bases. Hence, in
the present work, we report the synthesis and characterization
of a Schiff base derived from 2-thiophenecarboxaldehyde and
sulfanilamide and it's Co(II), Ni(II) Cu(II) and Zn(II) comp-
lexes to gain more information about related structural and
spectral properties. They were thoroughly characterized on the
1
-7
and therapeutic agents against various diseases . The deve-
lopment of sulfonamides is a fascinating and informative area
8
-10
in medicinal chemistry . Many chemotherapeutically
important sulpha drugs, like sulphadia-zine, sulphathiazole and
sulphamerazine possess -SO
toxophoric functional group.
2
NH- moiety as an important
1
basis of their melting point, TLC, FT-IR, H NMR, elemental
analysis, UV-visible, MS, TGA, Magnetic moment and molar
conductivity. Based on the spectral and analytical data geo-
metry of the complexes was proposed. Furthermore, anti-
microbial activity of the sulfonamide-imine and its M(II)
complexes were evaluated against two pathogenic bacterial
and two fungal strains by the agar well diffusion assay.
Amino substituted sulfonamide undergoes condensation
reaction with carbonyl compounds to form sulfonamide Schiff
11-13
bases . These schiff bases have been reported to posses anti-
1
4-17
18
19,20
microbial , anticancer cell , antimalarial
and antihel-
21
mintic activities . The presences of azomethine and sulfonyl
functional group are responsible for antimicrobial activity.
Sulfonamide containing Schiff bases and their transition
metal complexes had been previously prepared, characterized
with different analytical and spectroscopic techniques and
tested for their antimicrobial activities. It has been reported
that the biological activities of Schiff bases get enhanced
on coordination with metals. Though many schiff base metal
EXPERIMENTAL
All chemicals used in this investigation were of the analy-
tical reagent grade (AR) and of highest purity available. They
included 2-thiophenecarboxaldehyde (spectrochem), sulfanil-
amide (LOBA Chemie), copper(II) chloride (Fisher Scientific),

942 Zemede et al.
Asian J. Chem.
cobalt(II) chloride (Fisher Scientific), nickel(II) chloride
Fisher Scientific), zinc chloride (Fisher Scientific), absolute
ethanol (Hayman), dimethyl formamaide (SRLA), tetrahydro-
furan (Fisher), dichloromethane (Fisher), dimethyl sulphoxide
N NaOH and further refluxed with stirring for about 8-16 h.
The completion of the reaction was monitored by TLC. The
resulting solution was reduced to 1/3 of its volume and kept
(
rd
aside for one day. On standing, solid metal complexes were
obtained and collected by vacuum filtration, washed with
water, diethyl ether followed by ethanol. The final products
were kept in an oven for drying. All complexes were stable up
to 300 °C.
Determination of metal content of the chelates: 10 mg
of each of the synthesized chelates was accurately weighed
and placed in Kjeldahl flask. 10 mL of concentrated nitric
acid was added initially to the powdered chelates, to start the
fast wet oxidation digestion. This mixture had been digested
(
SRLA), glacial acetic acid (Fisher), acetonitrile (Fisher) and
chloroform (Fisher).
Physical measurements: The purity of the compounds
was checked using precoated TLC plates using hexane:ethyl
acetate (3:1) solvent system. The developed chromatographic
plates were visualized under ultraviolet light. Melting point
of the ligand and decomposition temperature of complexes
were determined by open capillary on Stuart Melting point,
SMP10, instrument. IR spectra of the ligand and complexes
-1
were recorded using KBr pellets in the range (4000-400 cm )
on FT-IR spectrometer Perkin-Elmer Infrared model 337.
by a gradual heating with dropping of H
2
2
O solution. This
treatment was conducted until most of the powdered complexes
were diminished and the remained solution had the colour of
the corresponding metal salt. This solution was diluted up to 35
mL with distilled water and the metal content was determined
by complexometric titration against standard EDTA solution
at a suitable pH value using the suitable indicator.
Elemental analyses were performed on a Perkin Elmer Model
1
2
40C Elemental Analyzer. H NMR spectrum of the ligand in
DMSO-d was recorded on a 500 MHz FT NMR Spectrometer
6
using TMS as internal standard. Electronic absorption spectra
were obtained on a Perkin-Elmer Lambda 35 UV-visible spectro-
-
5
photometer using a prepared CH
3
CN solution (10 mol/L).
Chloride ion test in the complexes: The test for ionizable
chloride (s) in each of the metal complexes was determined
by the titration of the samples, whose concentrations are un-
known, with standard solution of silver nitrate in the presence
The EI mass spectrum of the ligand was recorded on waters
ESI mass spectrometer. Metal estimation in the complexes and
consequently molar ratio of metal to ligand of the complexes
were obtained from complexometric titration against standard
EDTA solution at a suitable pH value using the suitable indi-
cators. The conductivity measurements were measured in
acetonitrile solutions (0.001 M) using digital conductivity
meter-611. Room magnetic susceptibilities of the complexes
were determined on well ground solid samples by using MSB-
AUTO, Sherwood scientific magnetic susceptibility balance
26
of 1 mL of potassium chromate as an indicator . The end point
of the titration was determined by the formation of a red preci-
pitate. The number of moles of chloride was thus calculated
based on titration value.
Biological activity: The antimicrobial activity of the
synthesized Schiff base ligand, L and its Co(II), Ni(II), Cu(II)
and Zn(II) complexes were determined by the agar well
27
4
using Hg [Co (NCS) ] as standard. Thermogravimetric analysis
diffusion assay . The bacteria strains: Klebsiella pnuemonia
and Staphylococcus aureus and the fungal strains: Candida
albicans and Candida krusei were selected because of their
clinical relevance. The bacterial and fungal strains used for the
assay were maintained on Nutrient agar and Sabouard dextrose
agar, respectively. In the agar diffusion method, Muller-Hinton
agar and Sabouard dextrose agar were sterilized in flasks and
poured into sterile petriplates and allowed to solidify. The
inoculum was prepared by suspending the colonies of the
organisms to be tested in 0.9 % sterile saline and turbidity
of complexes has been carried on SDT Q600 V8.0 Build 95
instrument in the temperature range of 30-800 °C.
Synthesis of Schiff base (L): Sulfanilamide (1.84 g,
0
.0107 mol) dissolved in a 40 mL of mixture of THF/EtOH in
a ratio of 1:4, v/v was mixed with 2-thiophenecarboxaldehyde
1 mL, 0.0107 mol), which was dissolved in 30 mL of a mixture
of same solvent followed by addition of glacial acetic acid
2.5 mL) to prepare a Schiff base 4-[(thiophene-2-yl)methy-
(
(
leneamino]phenyl sulphonamide. The reaction mixture was
refluxed on oil bath at 75 °C for 6 h with continuous stirring.
The progress of the reaction was monitored by TLC. The mix-
ture was cooled and poured into ice-cooled water to precipitate
Schiff base. The resulting coloured precipitate was filtered and
dried in vacuum oven at 80 °C. The dried solid product was
recrystallized twice from hot ethanol and then dried under
8
adjusted to 0.5 McFarland standard (10 UFC/mL). Sterile
swabs were used for inoculating the surface of the petriplates
and wells of 7 mm diameter were aseptically bored into the
culture medium and 50 µL of compounds dissolved in DMSO
were added to these wells. DMSO alone was used as negative
control along with the antimicrobials. Voriconazole and
ampicillin were used as positive controls for fungi and bacteria,
respectively. The plates were incubated aerobically at 37 °C
for 24 h and the antimicrobial activity was assessed by
measuring the inhibition halo of microbial growth around the
well.
reduced pressure over anhydrous CaCl in a desiccator. The
2
product isolated as shiny yellow powder in 92 % yield. The
melting point of the product was found to be 217 °C.
Synthesis of metal complexes: All the Schiff base metal
complexes were prepared by the same general procedure with
stoichiometric amount of ligand and metal salts in a 2:1 mole
ratio. To a 40 mL of CH
0.05012 g, 0.000188 mole), 20 mL of methanolic solution
of corresponding Co(II), Ni(II), Cu(II) and Zn(II) chlorides
0.000188 mole) was added drop wise. Then the mixture was
refluxed with continuous stirring for 2 h and then pH of the
solution was adjusted to 7-7.5 using aqueous solution of 0.1
2
Cl
2
solution of Schiff base ligand
RESULTS AND DISCUSSION
(
Schiff base characterization: The structure of the synthe-
sized ligand was confirmed on the basis of its elemental analysis
and spectral data. The result of elemental analyses (C, H, N)
with molecular formula and melting point are presented in
(

Vol. 27, No. 3 (2015)
Synthesis, Characterization and Antimicrobial Properties of Some Transition Metal Complexes 943
Table-1. The elemental analysis of the prepared ligand is
consistent with the calculated results from the empirical
formula of the ligand and the melting point is sharp indicating
the purity of the prepared Schiff base. The structure of the
Schiff base under study is given in Fig. 1.
attributed to the fragmentation of L molecule obtained from
the rupture of different bonds inside the molecule as shown
in Fig. 3. The fragments were in good agreement with the
proposed formula of the Schiff base ligand.
H
NH2
C
N
SO2 NH2
SO
2
S
m/z=266.35 (R.I.=100%)
O
+
2
H N
S
H
C
N
SO
2
C
N
Reflux at 75oC
H
SO
2
NH
2
S
S
THF/EtOH
m/z=186 (R.I.=76%)
6
hrs
m/z=250.35 (R.I.=15%)
m/z=156 (R.I.=10%)
C
N
SO
2
NH2
H
H
C
N
S
C
N
SO
H
S
S
m/z=110 (R.I.=10%)
Fig. 1. General scheme for the synthesis of Schiff base (L)
m/z=234.35 (R.I.=10%)
m/z=76 (R.I.=34%)
The mass spectrum of the Schiff base ligand (Fig. 2)
showed a signal with m/z ratio of 266.35 (R.I.100 %, base
peak) which is same as the calculated formula m/z = 266.35.
S
m/z=83 (R.I.=10%)
Fig. 3. Suggested mass fragmentation of the ligand
1
00
The structure of the Schiff base is also confirmed by IR,
UV-visible and H NMR spectra.
1
80
60
40
20
Composition and structure of metal complexes: The
isolated solid metal complexes of Co(II), Ni(II), Cu(II) and
Zn(II) ions with Schiff base ligand (L) were subjected to
elemental analyses (C, H, N and metal), IR, magnetic studies,
1
thermal analyses, electronic spectra, H NMR and molar
conductance to identify their tentative formulae in a trial to
elucidate their molecular structures. The elemental analyses
of the complexes are consistent with the calculated results
from the empirical formula of each compound. The elemental
analyses confirmed that the complexes have 2:1 molar ratio
of the ligand to metal ion. The results of elemental analyses
listed in Table-1 suggest the proposed general formulae of the
6
0
80
100
120 140
160 180
200 220
240
260 280
m/z
Fig. 2. Mass spectrum of the ligand
This m/z ratio of 266.35 confirms its molecular formula
. It is obvious that, the molecular ion peak is in
C
11
H
10
N
2
O
2
S
2
prepared complexes as:[M(L)
2
(H
2
O)
2
]Cl
2
.nH O (n = 0.5 for
2
good agreement with its suggested empirical formula as
indicated from elemental analyses (Table-1). Peaks of m/z
ration at 250.35 (15 %), 234.35 (10 %), 186 (76 %), 156 (10 %)
and 76 (34 %) confirm the suggested structure illustrated in
Fig. 1. The other peaks appeared in the mass spectrum are
M = Ni(II), Co(II), Cu(II) and n = 1 for M = Zn(II)).
Colour change of the complexes along with decompo-
sition point show characteristic differences between Schiff base
and metal complexes. The melting points of the complexes
are higher than the ligand revealing that the complexes are
TABLE-1
ANALYTICAL AND PHYSICAL DATA OF THE LIGAND AND ITS METAL COMPLEXES
Elemental analysis (%): Found (calcd.)
o
Compound {Empirical formula}
C H O N S
Color
Yeld: (%)
(92)
m.p. ( C)
C
H
N
M
-
Λm
-
L
Shiny yellow
217
49.52
49.56)
37.29
(37.33)
37.30
(37.34)
37.12
(37.09)
36.51
3.77
(3.75)
3.58
(3.54)
3.55
10.48
(10.51)
7.97
(7.92)
7.91
11
10
2
2 2
(
1
2
3
4
[Co(L) (H O) ]Cl ·0.5H O
Black
Black
(66)
(64)
(72)
(66)
> 300
> 300
> 300
> 300
8.31
(8.33)
8.27
269
2
2
2
2
2
{
C H CoCl N S O }
2
2
25
2
4
4
6.5
[Ni(L)
2
2
(H O)
2 2 2
]Cl ·0.5H O
{
C H NiCl N S O }
(3.54)
3.53
(7.92)
7.82
(8.30)
8.94
287
255
231
2
2
25
2
4
4
6.5
[Cu(L) (H O) ]Cl ·0.5H O
Black
2
2
2
2
2
{
C H CuCl N S O }
(3.51)
3.58
(7.87)
7.77
(8.92)
9.11
2
2
25
2
4
4
6.5
[Zn(L) (H O) ]Cl ·H O
Dark green
2
2
2
2
2
{
C H ZnCl N S O }
(36.53)
(3.60)
(7.75)
(9.05)
2
2
26
2
4
4
7
2
- 1
-1
Λ = Molar conductance (cm Ω mol )
m

944 Zemede et al.
Asian J. Chem.
much more stable than the ligand. All compounds are stable
in air. The chemical equations concerning the formation of
the Schiff base and its metal complexes are represented in
Figs. 1 and 4, respectively. The interaction of the ligand with
be changed upon chelation. The new peaks in the IR spectra of
the complexes are also guide peaks in chelation. These guide/
characteristic peaks are listed in Table-2 together with the
assignments for most of the major peaks. The ligand used in
this investigation is a neutral one having two coordination sites,
N of azomethine and S of thiophene, that can bind to the metal
ion.
the appropriate metal chlorides in a mixture of CH
2
Cl
2
/CH OH
3
solvents in a molar ratio of 2:1 under reflux conditions gave
the products presented in Table-1.
In the IR spectrum of the ligand, N-H (primary amine)
and C=N (azomethine) stretching vibrations and N-H bending;
H
2
C
N
SO
2
NH2
+
M
IICl .nH O
-1
2
2
NH
2
were observed at 3290, 1607 and 1579 cm , respectively.
S
These values are in agreement with those observed for similar
CH
2
Cl
2
/CH
3
OH
11,12,22
compounds
. The azomethine vibration of the ligand at
o
Refrlux at 50-55 C
-1
1
607 cm was shifted to lower or higher frequencies after
8-16hrs
-1
complexation, 1630, 1624, 1628 and 1602 cm for Co(II),
Ni(II), Cu(II) and Zn(II) complexes, respectively. This clearly
indicates coordination of the Schiff bases through the
C
N
SO
2
NH2
H
S
26,29-32
azomethine nitrogen
.
M
OH
2
2
H O
Cl
2
2
mH O
In addition, the free ligand exhibits two bands at 1335 and
S
-1
1
314 cm due to νasym(S=O) and νsym(S=O) stretching vibration
of -SO - moiety, respectively. These bands remain unchanged
in all complexes up on complexation. This indicates the non
participation of O of sulfonyl group of sulfonamide,-SO -NH
H
2
N
O
2
S
N
C
H
2
2
,
m=0.5 for M= Ni(II),Co(II),Cu(II) and m=1 for M= Zn(II)
Fig. 4. General scheme for the synthesis of M(II) complexes
2
33
in coordination of the complexes .
-1
The band at 1153 cm in the free ligand is observed at
almost the same region in complexes spectra. These bands
can be attributed to the ν(ph-N) and the slight change in wave
numbers may be understood as a result of changing the electron
Molar conductance measurements: Table-1 shows the
molar conductance values of metal complexes. The molar
conductance values of the synthesized complexes were deter-
mined at room temperature using 1 × 10 M concentration in
acetonitrile as solvent, are in the range of 220-300 Ω cm
mol . These values suggested electrolytic nature of the comp-
lexes with a cation to anion ratio of 1:2 and the anions present
are not coordinated to the metal ions. This is in accordance
with the fact that conductivity values for an electrolytes are
2
0, 23,25
-3
density of the aromatic system due to complexation
. The
-1
-1
2
free ligand also exhibits two bands at 846 and 721 cm due to
ν(C-S-C) asymmetric and symmetric stretching vibration of
thiophene moiety, respectively. These bands shifted to higher
-
1
-1
or lower stretching frequency, 831-826 and 765-710 cm , in
the complexes. This indicates the involvement of thiophene
3
4,35
-1
2
-1
28
sulfur in coordination using its lone pair electrons
.
above 220 Ω cm mol in acetonitrile solution .
Appearance of a broad and strong band in the region 3480-
IR spectra and mode of bonding: The IR spectra of the
complexes are compared with that of the free ligand in order
to determine the coordination sites that may be involved in
chelation. There are some guide peaks, in the spectra of the
ligand, which are of good help for achieving this goal. The
position and/or the intensities of these peaks are expected to
-1
3
463 cm in the spectra of all complexes considerably supports
the presence of coordinated water molecules. The coordination
of water in Co(II), Ni(II), Cu(II) and Zn(II) complexes is further
confirmed by the strong broad absorption band at 3462, 3478,
-1
3
480 and 3464 cm and the medium sharp band at 900, 892,
TABLE-2
a
–1
CHARACTERISTIC INFRARED FREQUENCIES (cm ) AND TENTATIVE
ASSIGNMENTS FOR THE SCHIFF BASE WITH ITS METAL COMPLEXES
b
L
1
2
3
4
Assignments
3
290s,sh
-
-
-
-
-
ν(N-H) ;-NH2
3462s,br
3478s,br
3480s,br
3464s,br
ν(O-H) ;H O
2
1607s,sh
1630s,sh
1335m,sh
1314m,sh
1624s,sh
1334m,sh
1312m,sh
1628m,sh
1335m,sh
1311s,sh
1602s,sh
1334s,sh
1314m,sh
C=N stre
νasym(S=O)
νsym(S=O)
1
1
335m,sh
314m,sh
1
8
7
153s,sh
46m,sh
21m,sh
-
1151s,sh
829m,sh
710m,sh
1152s,sh
826m,sh
758m,sh
1150s,sh
831m,sh
765m,sh
1151s,sh
829m,sh
712m,sh
ν(C-N); aromatic
ν(C-S-C) asym
ν(C-S-C) sym
1
9
466w,sh
00m,sh
1482w,sh
892w,sh
560w,sh
540m,sh
568w,sh
1466m,sh
901m,sh
555vw,sh
538vw,sh
1499m,sh
902m,sh
563w,sh
542m,sh
596vw,sh
δ(H O) in plane bending of coo.H O
2
2
-
-
-
-
δr (H O) of coo.H O
2
2
5
5
5
62w,sh
42w,sh
99w,sh
ν(M-N)
ν(M-S)
ν(M-O); O of coord.H O
565vw,sh
2
a
b
s, strong; m, medium; w, weak; vw, very weak; br, broad; s, sharp ; ν, stretching; δ,deformation, 1. [Co(L) (H O) ]Cl ·0.5H O;
. [Ni(L) (H O) ]Cl ·0.5H O; 3. [Cu(L) (H O) ]Cl ·0.5H O, 4. [Zn(L) (H O) ]Cl ·H O
2
2
2
2
2
2
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

Vol. 27, No. 3 (2015)
Synthesis, Characterization and Antimicrobial Properties of Some Transition Metal Complexes 945
-
1
9
01, and 902 cm , respectivelly. These bands are attributed to
The electronic spectrum of Co(II) complex gave three
-
1
4
the stretching and rocking vibrations of coordinated water
molecules of the complexes, respectively . In addition to
these bands in the spectra of the complexes, a band around
500 cm is appeared due to OH stretching frequency of
uncoordinated water molecule. This is attributed to the presence
of water of hydration.
bands in the visible region at 16, 207 cm : T1g(F) →
36, 37
4
-1
4
4
T
2g(F)(ν
1
), 19, 531 cm : T1g(F) → A2g(F) (ν
2
) and 22, 883
-
1
4
4
cm ; T1g(F) → T1g(P) (ν
3
). These data along with room
-
1
3
temperature magnetic moment value, 4.58 B.M., (normal range
for octahedral Co(II) complexes is 4.30-5.20 B.M.), is an
indicative of octahedral geometry.
The band due to N-H stretching of -NH
complexes was difficult to be interpreted due to overlapping of
its band with the more intense O-H stretch of coordinated H
molecule that absorbed and appeared in the same region.
Apart from these bands, the far IR spectra of Co(II), Ni(II),
Cu(II) and Zn(II) complexes showed non-ligand bands of low
intensity in the region 599-560, 563-555 and 542-538 cm
can be assigned to ν(M-O) (coordinated water-O), ν(M-N)
imine-N) and ν(M-S) (Thiophene-S) vibrations, respectively.
The IR spectra revealed that L coordinated to the metal ions
via azomethin-N and thiophene-S. Therefore, the above argu-
ments together with the elemental analyses indicated that the
behaviour of Schiff base ligand as neutral NS type bidentate
ligand.
2
of the ligand in the
The electronic spectrum of Ni (II) complex also displayed
three bands in the visible region. These bands at 16, 393, 19,841
-1
3
3
2
O
and 21, 368 cm are assigned to octahedral A2g → T2g(F),
3 3 3 3
A
2g → T1g(F) and A2g → T1g(p) transitions, respectively. The
-
band at 27, 174 cm is due to charge transfer. These data along
with room temperature magnetic moment value of 3.31 B.M,
µeff = 3.33 B.M., are compatible and considered as an evidence
for octahedral geometry around nickel(II) ion.
-1
(
The electronic spectrum of Cu(II) chelate consists of a
-
1
broad, low intensity shoulder band centered at 23,980 cm
-1
2
2
and another band at 15,625 cm . The E and T2g states of the
octahedral Cu(II) ion (d ) split under the influence of the
tetragonal distortion and the distortion can be such as to cause
g
9
2
2
2
2
2
2
the three transitions B1g → B2g ; B1g → E and B1g→ A1g to
g
Electronic spectra and magnetic susceptibility measure-
ments: The electronic spectral data along with magnetic suscep-
tibility measurements gave adequate support in establishing
the geometry of the metal complexes. The electronic absorption
remain unresolved in the spectra. This assignment is in
agreement with the general observation that Cu(II) d-d transi-
tions are normally close in energy. The magnetic moment value
of 2.11 B.M. falls within the range normally observed for
octahedral Cu(II) complexes.
-5
spectra for 10 M solution of the ligand and its metal complexes
in acetonitrile at λ ranging from 200 to 800 nm, against the
same solvent as a blank, were recorded at room temperature.
These electronic absorption spectra of the ligand and its metal
complexes are presented in Fig. 5. The ligand showed two
bands at 269 and 328 nm which may be assigned to the
The electronic absorption spectrum of Zn(II) complex
showed only intraligand transition and no d-d transition is
10
-1
expected for a d configuration. The band at 28,090 cm is
due to charge transfer. The colour the complex is due to this
charge transfer. According to the empirical formula and in
analogy with those described for Zn(II) complexes containing
*
aromatic and C=N chromophore π → π and non-bonding
6,7,13,26
29-31
electrons n → π* transitions, respectively
.
N-S donor Schiff bases , the diamagnetic Zinc(II) complex
is likely to be Octahedral. Therefore we proposed an octahedral
geometry for Zn(II) complex.
0
0
0
0
0
0
0
.6
.5
.4
.3
.2
.1
.0
1
H NMR spectra: The chemical shift of the different types
1
of protons in the H NMR spectra of the L was recorded in
DMSO-d using TMS as internal standard.
6
L
1
2
3
4
1
The H NMR spectrum of the Schiff base ligand revealed
its formation by the presence of azomethine, -CH=N, proton
signal at δ = 8.82 ppm. This is further supported by the appea-
rance of stretching vibration band ν(CH =N) azomethine at
-1
1607 cm . The resonance of amine proton downfield shifted
to 10.3 ppm due to the strong electron withdrawing effect of
the sulphonyl group. Also the multiple signals lying in range
7.255-7.895 and 7.757-7.895 ppm were attributed to resonance
6,7,13,26
of Thiophene and benzene protons
.
Thermal analysis: Fig. 6 shows the TGA of Schiff base
L and its metal chelates. The TGA was recorded from 30 to
800 ºC. In all samples of the metal complexes there was a
rapid initial mass loss between temperatures of 30-100 ºC.
This lower dehydration temperature suggests the presence of
non coordinated water molecule to the metal ions. This is
characteristics of desorption or drying, usually moisture,
amounts to 7.0, 8.86, 10.61 and 19.45 % for Co(II), Ni(II),
Cu(II) and Zn(II) complexes, respectively.
300
400
500
600
700
Wavelength (nm)
Fig. 5. Electronic absorption spectra of L and its complexes
Up on complexation, shift of the ligand bands and appea-
rance of new bands in the visible region are expected. The
band at 328 nm due to n → π transition of the non-bonding
*
electrons on the N of the azomethine group in the free ligand
shifted to shorter wavelength, indicating the involvement of
The ligand is stable up to 200 ºC. The TGA curve of the
Schiff base refers to two stages of mass losses at temperature
range 200-780 ºC. These stages involved an experimental and
11,12,22
the imine group in metal complexation
.

946 Zemede et al.
Asian J. Chem.
1
10
The third, fourth and fifth steps of decomposition within the
temperature range 218-429, 429-586 and 586-800 ºC
100
correspond to the removal of the chelates as SO
2
, SO, 2HCl
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
and N and 2CN and 2C S with mass loss of 29.44 % (calcd.
2
H
4 3
29.47 %), 7.11 % (calcd 7.2 %) and 23.13 % (calcd. 23.10 %),
respectively. The total mass losses of the decomposition steps
within the temperature range 100-800 ºC were 67.23 % (calcd.
6
7.25 %).
From the TGA, it was interesting to observe that the
3
2
complexes of the present study illustrated different thermal
degradation patterns. The weight loss amounts 49.21, 49.33
and 32.77 % occurred above 800 ºC for Ni (II), Cu(II) and
Zn(II) complexes, respectively. While no weight loss was
occurred above 800 ºC for Co(II) complex. Weight loss
amounts 82.14 % (calcd. 82.39 %) of Co(II) complex decom-
poses below 800 ºC leaving CoO as a residue. Among all the
complexes under study, Cu(II) complex showed the highest
and Co(II) complex showed the least thermal stability with
delayed and fast degradations, respectively. Nickel(II) complex
exhibited comparable thermal stability with that of Cu(II)
complex. This is in accordance to Irving-William's series of
L
4
1
0
100 200 300
Temperature (°C)
Fig. 6. Thermograms of L and its metal complexes
400 500
600
700 800
calculated mass loss of 71.11 and 70.9 %, respectively. These
mass losses are due to the successive losses of part of
38
stability . For a given ligand, the stability of the complexes
with dispositive metal ions follows the order; Co(II) < Ni(II)
C
11
H
10
O
2
N
2
S
2
molecule (NH
2
, SO
2
, CN and C
6
H
5
-) as gases at
the given temperature range. The remaining part, 28.89 % (calc.
9.1 %) of the ligand decomposes above 800 ºC.
<
Cu(II) > Zn(II). This order arises in part from a decrease in
2
size across the series and in part from ligand field effect. The
smaller the size of the metal ion the greater electro negativity
will be.An increase in electro negativity of the metal ions will
decrease electro negativity difference between the metal ions
and the donor atom of the ligand. Thus, the M-L bond would
be having more covalent character, which may lead to greater
stability of metal chelates. Hence Cu(II) complex can be used
for applications which involve higher thermal stability.
Chloride ion test in the complexes: The test for chloride
ion was positive for all metal complexes under study indicating
that chloride ion was outside the coordination sphere of the
central metal. The result confirmed the presence of two moles
of chloride ions outside the coordination sphere for charge
balance. This indicated the chlorides in metal complexes were
ionizable, which remain uncoordinated to the metal ions.
Metal content of the chelates: The metal content in each
of the metal complexes was determined by complexometric
titration against standard EDTA solution at a suitable pH value
using the suitable indicator. The result indicated that molar
ratio of metal to ligand of the complexes was 1:2.
Biological activity: The Schiff base ligand and its comp-
lexes (1-4) were tested for their inhibitory effects against
growth of bacteria: S. aureus and K. pneumoniae and fungi:
C. albicans and C. krusei by the agar well diffusion assay.
The results of antibacterial and antifungal activities of the
ligand and its coordinated compounds are listed in Table-3
and are represented graphically in Fig. 7. Photograph as well
showing the antifungal behaviour of L and its metal complexes
against C. krusei was also shown in Fig. 8.
The complexes of the present study illustrated different
thermal degradation patterns. The thermograms of Co(II),
Ni(II) and Cu(II) chelates showed four decomposition steps
within the temperature range 100-800 ºC. The first step of
decomposition within the temperature range 100-130 ºC corres-
ponds to the loss of lattice water molecule (1/2H
mass loss of 1.33 % (calcd.1.30 %), 1.26 % (calc.1.27 %) and
.29 % (calcd.1.26 %), respectively. The second step of decom-
position occurred for Co(II), Ni(II) and Cu(II) complexes at
30-210, 130-202 and 130-250 ºC corresponds to the loss of
two moles of coordinated water molecules with a mass loss of
2
O) with a
1
1
5
5
4
.05 % (calc. 5.08 %), 5 % (calc. 5.08 %) and 5.03 (calc.
.05 %), respectively. The third step occurred at 210-387, 202-
62 and 250-392 ºC corresponds to the removal part of Co(II)
complex as SO
complex as N , 2HCl, SO
and 2HCl with a mass loss of 60.78 % (calc. 60.91 %), 29.98 %
calc. 30.11 %) and 14.17 % (calcd.14.18 %), respectively. In
2
, SO, N
2
, 2HCl, 2CN and 2C
4
3
H S, Ni(II)
2
2
and SO and Cu(II) complex as N
2
(
a similar way, the fourth step of decomposition occurred for
the same complexes at 387-572, 462-800 and 392-800 ºC
involved the loss of Co(II) complex as 2C
6
H
5
-, Ni(II) complex
CN with
as C CN and Cu(II) complex as SO , SO and C
H
6 5
2
6
H
5
mass loss of 14.98 % (calc. 15.10 %), 14.55 % (calc. 14.56 %)
and 30.18 % (calcd. 30.20 %), respectively. The overall weight
losses that occurred between temperature range of 100-800 ºC
for Co(II), Ni(II) and Cu(II) complexes amount to 82.14 %
calcd. 82.39 %), 50.79 % (calcd. 51.00 %) and 50.67 % (calcd.
0.69 %), respectively.
(
5
Unlike others, the TGA curves of the Zn (II) chelate gave
The results indicated that all the compounds have showed
weak to strong antimicrobial activities against all organisms
used in this study except L, 2 and 4 compounds that showed
no antimicrobial activity against K. pneumoniae. Complex 3
and L have, respectively shown the best antibacterial and
antifungal activities among all. The bacteria S. aureus and the
five decomposition steps as illustrated in Fig. 6. The first and
second steps of decomposition correspond to the loss of one
mole of lattice and two coordinated water molecules within
the temperature range 100-135 and 135-218 ºC with mass loss
of 2.55 % (calcd. 2.50 %) and 5 % (calcd. 4.98 %), respectively.

Vol. 27, No. 3 (2015)
Synthesis, Characterization and Antimicrobial Properties of Some Transition Metal Complexes 947
the ability of the complexes to cross a cell membrane. On
TABLE-3
ANTIMICROBIAL ACTIVITY OF SCHIFF BASE LIGAND
chelation or coordination, the polarity of the metal ion will be
reduced to a greater extent due to the overlap of the ligand
orbital and partial sharing of the positive charge of the metal
ion with donor groups. Further, it increases the delocalization
of π-electrons over the whole chelate ring. This process thus
increases the lipophilic nature of the compound which, in turn,
favors penetration through the bacterial and fungal wall of the
microorganisms. These complexes also disturb the respiration
process of the cell and thus block the synthesis of proteins,
which restricts further growth of the organisms. Complex 3
showed the best effective antibacterial activity among all due
to a highest stability constant and this appears to be an ideal
antibacterial complex providing non-conducive environment
for the growth of bacteria. On the other hand, the difference in
the magnitude of antimicrobial activity came from other
factors, such as solubility and the charge of the complexes.
Thus, it was apparent that the antimicrobial activity of
complexes of the Schiff base was not only dependent on the
charge, but also on the nature of the counter ions that neutralize
the complex, the geometrical structure of the complex and
AND ITS COMPLEXES (CONCENTRATION 50 µg/mL)
Diameter of inhibition zone (in mm)
Compounds
S. aureus K. pneumoniae C. albicans C. krusei
Ligand
1
2
3
4
16
15
18
20
17
-
-
11
-
15
-
40
38
39
32
35
-
15
14
24
15
13
-
DMSO
-
Ampicillin
Voriconazole
40
-
12
-
-
56
-
36
6
5
5
4
4
3
3
2
2
1
1
0
5
0
5
0
5
0
5
0
5
0
5
0
S. aureus
K. pneumoniae
C. albicans
C. krusei
4
0-42
nature of metal ions
.
Conclusion
The present study reports on the synthesis, characterization
and antimicrobial evaluation of Schiff base ligand (L) and its
Co(II), Ni(II), Cu(II) and Zn(II) complexes. The synthetic
procedure in this work resulted in the formation of complexes
in molar ratio (2:1) (L:M), respectively. The IR spectra revealed
that L coordinated to the metal ions via azomethine-N and
thiophene-S. The synthesized schiff base acts as a neutral NS
type bidentate ligand. On the basis of elemental analyses data,
UV-visible spectra and magnetic susceptibility measurements
octahedral geometry was proposed for all complexes where
the fifth and sixth coordination sites were occupied by water
molecules. The molar conductance studies indicated the elec-
trolytic nature of the complexes with a cation to anion ratio of
Compounds and drugs
Fig. 7. Zone of inhibitions of reported compounds and standards against
four types of microorganisms (two bacteria and two fungi
1:2, respectively.Among all the complexes under study, Cu(II)
complex showed the highest and Co(II) complex showed the
least thermal stability with delayed and fast degradations,
respectively. Nickel(II) complex exhibited comparable thermal
stability with that of Cu(II) complex. Hence Cu(II) complex
can be used for applications which involve higher thermal
stability. The in vitro biological activities result showed that
the ligand become antimicrobially active on chelation with
metal ions and the antibacterial activity of 3 and the antifungal
activities of 1 and 2 could be further studied for the treatment
of infections caused by any of the above organisms.
Fig. 8. Photograph showing antifungal studies of L and its metal complexes
against C. krusei
fungi C. albicans were more sensitive than K. pneumoniae
and C. krusei to the synthesized compounds due to the different
components of the bacterial and fungal cell wall. In general
the biological activity of the synthesized compounds follow
the order 2 > 3 > 1 > L > 4. It is evident from the data that
there is a considerable increase in toxicity of complexes as
compared to the ligand.A possible mode of enhancing toxicity
of complexes could be speculated in the light of "Chelation
ACKNOWLEDGEMENTS
Financial support from the Indian Council for Cultural
Relation (ICCR) is gratefully acknowledged. The authors are
also thankful to Department of Chemistry and SAIF, IIT Madras,
1
India for recording elemental analyses, H NMR and MS. Other
Instrumentation facility provided by DST-FIST sponsored
Department of Chemistry, Anna University, Chennai, India is
acknowledged with thanks.
39
Theory" . This would suggest that chelation could facilitate

948 Zemede et al.
Asian J. Chem.
2
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