Synthesis, spectroscopic characterization, antibacterial and corrosion inhibitory activities of some 3d-metal complexes of [(2-pyrrole-2-carboxaldehyde)-3-isatin]bishydrazone

Article abstract of DOI:10.14233/ajchem.2015.19346

A novel bishydrazone was synthesized by the condensation of isatin monohydrazone with pyrrole-2-carboxaldehyde, which formed a series of complexes with manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II). The ligand and the metal complexes were characterized on the basis of elemental analysis, molar conductance, magnetic moment, IR, UV-visible, 1H NMR, EPR and thermal analysis. Spectral studies revealed that the ligand acted as neutral bidentate, coordinating to the metal ion through the aldimine nitrogen and carbonyl oxygen atom of the isatin moiety. The low molar conductance values indicate that all complexes are non-electrolytes. Based on the spectral results and magnetic susceptibility measurements, suitable geometry was proposed for each metal complex. The EPR spectral data of copper(II) complex indicated that metal-ligand bond had considerable covalent character. The ligand and its nickel(II) complex were subjected to XRD studies. In vitro biological screening effects of the compounds were tested against the some selected bacteria by the agar disc diffusion method. The corrosion inhibitory activity of the ligand and its nickel(II) complex used in acid (H2SO4) media was examined by open circuit potential measurements.

Full text of DOI:10.14233/ajchem.2015.19346

Asian Journal of Chemistry; Vol. 27, No. 12 (2015), 4679-4685
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.19346
Synthesis, Spectroscopic Characterization, Antibacterial and Corrosion Inhibitory Activities of
Some 3d-Metal Complexes of [(2-Pyrrole-2-carboxaldehyde)-3-isatin]bishydrazone
1,*
1
2
S.S. SWATHY , R. BIJU and K. MOHANAN
1
2
Department of Chemistry, Sree Narayana College, Varkala, Trivandrum-695 145, India
Department of Chemistry, University of Kerala, Kariavattom Campus, Trivandrum-695 581, India
Corresponding author: E-mail: rajendran.biju@gmail.com
Received: 15 May 2015; Accepted: 27 June 2015;
*
Published online: 29 August 2015;
AJC-17528
A novel bishydrazone was synthesized by the condensation of isatin monohydrazone with pyrrole-2-carboxaldehyde, which formed a
series of complexes with manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II). The ligand and the metal complexes were characterized
1
on the basis of elemental analysis, molar conductance, magnetic moment, IR, UV-visible, H NMR, EPR and thermal analysis. Spectral
studies revealed that the ligand acted as neutral bidentate, coordinating to the metal ion through the aldimine nitrogen and carbonyl
oxygen atom of the isatin moiety. The low molar conductance values indicate that all complexes are non-electrolytes. Based on the
spectral results and magnetic susceptibility measurements, suitable geometry was proposed for each metal complex. The EPR spectral
data of copper(II) complex indicated that metal-ligand bond had considerable covalent character. The ligand and its nickel(II) complex
were subjected to XRD studies. In vitro biological screening effects of the compounds were tested against the some selected bacteria by
the agar disc diffusion method. The corrosion inhibitory activity of the ligand and its nickel(II) complex used in acid (H
2
SO ) media was
4
examined by open circuit potential measurements.
Keywords: Hydrazone, Spectral studies, Cyclic voltammetry, Antibacterial activity.
INTRODUCTION
EXPERIMENTAL
Hydrazones form an interesting class of chelating ligands
which contain an azomethine group linked to a nitrogen atom
All chemicals used were of analytical grade. Isatin,
hydrazine hydrate (99 %) and pyrrole-2-carboxaldehyde were
obtained from Fluka and Sisco Chemicals.
1
-6
and find extensive application in various fields .The interest
in the study of hydrazones possessing potential donor sites
have been intensively increasing because of their coordination
capability, their pharmacological activity and their use in analy-
Synthesis of isatin monohydrazone: A solution of hydra-
zine hydrate (0.5 mL, 10 mmol) dissolved in hot methanol (10
mL) was added to isatin (1.47 g, 10 mmol) dissolved in methanol
(40 mL). The resulting solution was refluxed for 3 h on a water-
bath and the yellow coloured compound was separated out on
cooling. It was filtered, dried in vacuum and further purified by
recrystallization from methanol (m.p. 226 °C; yield 95 %).
Synthesisofbishydrazone([2-(pyrrole-2-carboxaldehyde)-
3-isatin]bishydrazone): A solution of pyrrole-2-carboxal-
dehyde (0.01 mol) in methanol (10 mL) was added to a solution
of isatin monohydrazone (0.01 mol) in hot methanol (50 mL).
The reaction mixture was boiled under reflux for 4 h. It was
reduced to half of its volume, cooled and allowed to crystallize.
Orange crystals formed was filtered, washed several times with
7
-9
tical chemistry as metal extracting agents . The coordination
behaviour of hydrazones depends on several factors such as
pH of the medium, nature of the substituent and position of
hydrazone group relative to other nucleus.
A thorough survey of literature on pyrrole-2-carboxalde-
hyde complexes reveals that metal complexes of bishydrazones
derived from pyrrole-2 carboxaldehyde have been largely
neglected. The compounds containing isatin moiety possess
1
0-13
interesting biological and pharmacological activities . This
paper is devoted to the synthesis, characterization, X-ray
diffraction and cyclic voltammetric studies on some 3d metal
complexes in their +2 oxidation states with a bishydrazone
formed from isatin monohydrazone and pyrrole-2-carboxal-
dehyde to form a potentially neutral bidentate bishydrazone
viz. [2-(pyrrole-2-carboxaldehyde)-3-isatin]bishydrazone (IPB).
methanol and dried in vacuum over P O10 (m.p. 219 °C).
4
Synthesis of metal complexes
Manganese(II) complex: Manganese(II) acetate (0.001
mol) dissolved in minimum quantity of methanol was added

4
680 Swathy et al.
Asian J. Chem.
to a hot solution of the ligand (0.002 mol) in methanol (60 mL)
with constant stirring. The pH of the solution was maintained
between 6.5 and 7.5 by adding alcoholic ammonia solution.
The reaction mixture was then refluxed on a water-bath for
FTIR-410 spectrometer using KBr pellets and far infrared in
the 500-100 cm region using CsI-discs on a polytech FIR 30
Fourier spectrometer. Proton NMR spectra of the ligand and
-1
its zinc(II) complex were recorded in DMSO-d
6
on a JEOL
5
h. Then it was concentrated to half of its initial volume by
GSX 400 NB 400 MHz FT-NMR spectrometer. Molar conduc-
-3
evaporation. On cooling the solution, the separated complex
was filtered off, washed with methanol and then dried in
vacuum.
Cobalt(II) complex: Cobalt(II) complex was prepared
according to the procedure similar to that followed for the
synthesis of manganese(II) complex, except the refluxing time
was about for 4 h and the pH was adjusted to about 6.0. The
reddish brown solid product was filtered off, washed several
times with methanol and dried in vacuum.
tance measurements were conducted using 10 M solution of
the complexes in DMSO at room temperature with a Systronics
model 304 digital conductivity meter. Magnetic measurements
of the metal complexes were performed on a Magway MSB
Mk1 magnetic susceptibility balance. The EPR spectrum of
the copper(II) complex was recorded using a Varian E-112
EPR spectrometer. The XRD patterns of the ligand and its
nickel(II) complex were recorded on a Rigaku Dmax X-ray
diffractometer using CuK radiation (λ = 1.5404 Å).
α
Nickel(II) complex: Nickel(II) complex was prepared
by employing the same procedure for the preparation of
manganese(II) complex, except that the pH was maintained at
about 6.5. On adding the nickel(II) chloride, the ligand solution
turned to light brown colour.The metal-ligand ratio was
maintained to be 1:2 and the reaction mixture was refluxed
for 3-4 h. The final solution was concentrated to half of its
initial volume by evaporation and then cooled. The product
formed was filtered, washed successively with methanol and
dried in vacuum.
Copper(II) complex: Copper(II) chloride (0.002 mol)
dissolved in minimum quantity of methanol was added to a
hot solution of the ligand (0.002 mol) in methanol (60 mL).
The pH of the solution was maintained between 6.5 and 7.5,
by adding alcoholic ammonia solution and heated under reflux
for 2-3 h. The reaction mixture was then reduced to half of its
original volume by evaporation and was allowed to cool. The
complex separated out was filtered, washed with methanol,
ether and finally dried in vacuum.
In vitro antibacterial activity: The in vitro antibacterial
activity of the ligand and its complexes were tested against
the bacterial species, Staphylococcus aureus, Escherichia coli
14
and Salmonella typhi by agar disc diffusion method . Strepto-
mycin was used as standard for antibacterial agents. The
standard samples of antibacterial activity are done at 100 µg/
mL concentration in DMSO. The test organisms were grown
on nutrient agar medium in petri plates. The antibacterial
activities of the ligand and its metal complexes were done at
50, 100 and 200 µg/mL concentration in DMSO solvent by
the minimum inhibitory concentration (MIC) method. The
discs were placed on the previously seeded plates and incubated
at 37 °C. The diameter of inhibition zone around each disc
was measured after 24 h for bacterial species. Activity was
determined by measuring the diameter of the zone showing
complete inhibition (mm).
Open circuit potential (OCP) measurements: The
pretreated coupons were weighed and suspended vertically
for 15 days in 100 mL aerated, unstirred 1 M H
2
SO with and
4
Zinc(II) complex: Zinc(II) chloride complex was prepared
by the same method explained for the synthesis of copper(II)
complex. The metal-ligand ratio was maintained to be 1:1 and
the pH of solution was adjusted to about 7.5 by adding
alcoholic ammonia solution. The reaction mixture was then
refluxed for about 6 h. On cooling the final solution after
evaporation to half of its orginal volume, the complex obtained
was filtered, washed with methanol and then dried in vacuum
Physical measurements: Elemental analysis (C, H and
N) was carried out using a Heracus Carlo Erba 1108-CHN
Analyzer. The metal contents in the complexes were analyzed
using an atomic absorption spectrometer (GBC Avanta). The
electronic spectra were recorded on Hitachi 320 UV-visible
spectrometer in the range 200-900 nm. Infrared spectra of the
ligand and the metal complexes were recorded on a Jasco
without the corrodent-inhibitor of different concentrations
-3
-3
varying from 10 to 5 × 10 g. The coupons were then removed
-1
and washed with 20 % NaOH solution containing 200 g L of
zinc dust in order to remove the corrosion products, dried in
acetone. The electrolytes were kept under stagnant condition.
The potential were measured for 15 days under open circuit
condition as a function of time against a saturated calomel
electrode.
RESULTS AND DISCUSSION
Structure of ligand: The bishydrazone was characterized
through elemental analysis and various spectral studies.
Analytical data and other details of the ligand are given in
Table-1. The purity of the ligand was checked byTLC technique
(silica gel).
TABLE-1
ANALYTICAL DATA OF THE LIGAND (IPB) AND ITS DIVALENT METAL COMPLEXES
Yield
Elemental analysis (%): Found (calcd.)
Molar conductance
Compound
IPB
µeff (BM)
-1
2
-1
(
%)
(Ω cm mol ) DMSO
C
H
N
M
77
78
85
88
82
80
65.27 (65.54)
55.61 (55.48)
51.38 (51.49)
51.64 (51.51)
41.88 (41.87)
41.59 (41.67)
4.12 (4.20)
4.12 (4.01)
3.21 (3.30)
3.28 (3.30)
2.64 (2.68)
2.62 (2.67)
23.45 (23.53)
17.25 (17.26)
18.58 (18.48)
18.53 (18.49)
15.01 (15.03)
14.88 (14.96)
–
–
–
5.78
4.84
3.12
1.81
[
[
[
[
[
Mn(IPB) (OAc) ]
8.24 (8.46)
9.74 (9.72)
9.56 (9.68)
17.16 (17.06)
17.48 (17.47)
5.9
9.0
9.2
7.4
8.3
2
2
Co(IPB) Cl ]
2
2
Ni(IPB) Cl ]
2
2
Cu(IPB)Cl2]
Zn(IPB)Cl2]
Diamagnetic

Vol. 27, No. 12 (2015)
Synthesis of Some 3d-Metal Complexes of [(2-Pyrrole-2-carboxaldehyde)-3-isatin]bishydrazone 4681
The electronic spectrum of the bishydrazone ligand show
Formation of divalent metal complexes: Formation of
metal complexes can be represented by the following general
formulas (1) and (2).
-1
-1
absorption bands at 30303 cm and 35842 cm assignable to
n → π* transitions of the ketimine and aldimine moieties,
respectively. Infrared spectrum of the bishydrazone exhibit a
MX
2
+ IPB → [M(IPB)X
2
]
(1)
-1
absorption peak at 3358 cm , which can be attributed to N-H
group of the pyrrole moiety. Another band observed at 3157
–
M = Cu(II) and Zn(II), X = Cl
-
1
cm of medium intensity, can be assignable to (N-H) vibrations
of the indole ring system. A sharp band appearing at 1686
MX
2
+ 2 IPB → [M(IPB)
2 2
X ]
(2)
-
1
15
–
–
cm is assigned to the >C=O group of the isatin moiety .
Vibrational characteristics of ketimine and aldimine groups
M = Ni(II), Co(II) and Mn(II); X = Cl , CH COO
3
All the complexes are stable in ambient condition. The
analytical results obtained are in good agreement with the
calculated values for the suggested formula. The ligand is
soluble in common organic solvents, but the complexes are
found to be insoluble except in DMSO and DMF. The low
molar conductance values of the metal complexes in DMSO
indicate their non-electrolytic nature.
-1
are observed at 1588 and 1551 cm respectively. The band
-1
observed at 981 cm corresponds to the hydrazinic ν(N-N)
stretching vibration.
1
H NMR spectrum of the ligand (Fig. 1) gave a signal at
1
0.67 δ characteristic of pyrrole ring (NH). Signals appearing
at 8.75 δ and 9.56 δ can be attributed to the azomethine proton
and NH protons of the indole ring, respectively. Signals due
to aromatic proton are observed as multiplet in the range 6.82
to 7.36 δ. On the basis of the above spectral data, the structure
as in Fig. 2 has been assigned for the ligand.
Infrared spectra: Infrared spectral data of the complexes
are presented in Table-2 along with their tentative assignments.
-1
The band at 3358 cm for pyrrole N-H in the free ligand
remains more or less at the same position, indicating that this
group did not take part in complexation. The ν(C=N) vibration
-1
of the ligand undergoes a bathochromic shift about 25 cm in
the complexes due to the conjugation of the p-orbital on the
double bond with the d-orbital on metal ion with reduction of
the force constant, indicating involvement of the azomethine
nitrogen in chelation with the metal ion. The band observed
-1
due to ν(C=O) at 1686 cm is shifted to a lower frequency by
-1
about 25-35 cm , supporting the coordination of the carbonyl
oxygen. The ν(N-N) band exhibited a higher frequency shift
-1
of 12-14 cm , which is attributed to the electron attracting
1
6
inductive effect, when forming the conjugated system .
However, the bands assignable to ν(N-H) of the indole ring
remain more or less at the same position, indicating that this
group did not take part in chelation. In the far-IR region, the
appearance of new band in the regions 538-529, 490-479 and
1
Fig. 1. H NMR spectrum of the ligand (IPB)
-1
3
25-319 cm can be assigned to ν(M-O), ν(M-N) and ν(M-Cl)
17-19
H
vibrations respectively . For the manganese(II) complex,
characteristic vibrations for acetate have been observed at 1560
and 1416 cm due to ν
N
N
-1
20
a
(COO) and ν (COO), respectively .
s
These observations reveal that the ligand binds the metal
ion in a bidentate manner coordinating through aldimine
nitrogen and the carbonyl oxygen(C=O) of the isatin moiety.
N
N
H
O
H
1
H NMR spectrum: The proton NMR spectrum of the
zinc(II) complex recorded in DMSO-d is shown in Fig. 3.
6
1
The signal at 10.67 δ in the H NMR spectrum of the ligand
Fig. 2. Structure of the ligand
due to NH proton of the pyrrole ring appeared at the same
TABLE-2
KEY IR SPECTRAL BANDS (cm ) OF THE LIGAND (IPB) AND ITS DIVALENT METAL COMPLEXES
–
1
IPB
[Mn(IPB) (OAc) ]
[Co(IPB) Cl ]
[Ni(IPB) Cl ]
[Cu(IPB)Cl2]
3359
3157
1657
1584
1525
993
[Zn(IPB)Cl2]
3356
3154
1661
1587
1523
993
Tentative assignments
Pyrrole ring N-H
Indole ring N-H
ν(C=O) ring
ν(C=N) ring
ν(C=N) aldimine
ν(N-N)
2
2
2
2
2
2
3
358
157
686
588
552
3359
3158
1652
1588
1526
995
3360
3357
3
1
1
1
3155
1656
1586
1527
994
3156
1653
1582
1524
995
981
–
479
481
490
485
489
ν(M-N)
–
536
538
537
529
534
ν(M-O)
–
323
325
319
320
322
ν(M-Cl)

4
682 Swathy et al.
Asian J. Chem.
position in the spectrum of the complex. This is a clear indi-
cation that the NH proton of the pyrrole ring did not take part
adopt in its coordination shell. It is reported that tetrahedral
geometry is the most preferred structure for four coordinated
zinc(II) complex .
From the above spectral data, the structures as in Figs. 4
and 5 have been assigned for the metal complexes.
21
26
in complexation . Also in the ligand spectrum, a peak at 8.75
δ has been assigned for the hydrogen of the azomethine moiety
and is shifted to 8.59 δ in the complex indicating the involve-
ment of azomethine group [CH=N-] in complex formation.
The protons due to benzene and indole rings are found to be
in the expected region and shifted slightly by about 0.10-0.20
δ due to the coordination of the ligand to the metal ion.
N
N
O
N
H
H
Cl
M
N
H
Cl
M = Cu(II) and Zn(II)
Fig. 4. Structure of 1:1 metal complexes
N
N
O
N
H
H
Cl
H
N
N
M
O
10
9
8
7
6
5
4
3
2
1
ppm
H
1
Fig. 3. H NMR spectrum of zinc(II) complex
Cl
H
Electronic spectra and magnetic susceptibity measure-
N
N
H
ments: The electronic spectra of manganese(II) complex shows
N
-1
absorption bands at 14,100, 16,500 and 19,650 cm , which
6
4
6
4
are due to charge transfer and A
1
g → T
1
22
g, A
1
g → T
2
g and
6
4
4
A
1
g → Eg, A g transitions, respectively . These data along
1
M = Ni(II), Co(II), Mn(II)
Fig. 5. Structure of 1:2 metal complexes
with magnetic moment value of manganese(II) complex
indicates an octahedral environment around the metal ion.
Cobalt(II) complex exhibits bands at 7,300, 17,241 and
EPR spectrum:The X-band EPR spectra of the copper(II)
complex provides information of the metal ion environment.
It has been recorded in solid state room temperature. The
spectrum at room temperature itself shows axial spectrum. The
values have been found to be 2.2350 and 2.0601,
respectively. The gav value is 2.1184. The trend g|| > g > 2.0027
observed for the complexes indicate that the unpaired electron
is localized in the dx2-y2 orbital of the copper(II) ion and are
characteristic for the axial symmetry. The fact that the unpaired
electron lies predominately in the dx2-y2 orbital is also supported
-
1
4
4
4
4
2
0,449 cm assignable to T1g(F) → T g(F), T1g(F) → A2g(F)
2
4
4
23,24
and T1g(F) → T g(P) transitions, respectively . Tetrahedral
2
cobalt(II) complexes have generally lower magnetic moment
values of the range 4.20-4.58 BM. But the magnetic moment
values for the corresponding octahedral complexes are around
.8 BM and also the observed electronic spectral data for the
present cobalt(II) complex is comparable with an octahedral
geometry around the metal ion.
g
|| and g
⊥
⊥
4
The electronic spectra of nickel(II) complex show three
-1
peaks at 25,500, 17,200 and 9,750 cm which are assigned to
by the value of exchange interaction term G estimated from
3
3
3
3
3
3
A
2g(F) → T1g(P), A2g(F) → T1g(F) and A2g(F) → T2g(P)
27
the expression .
transitions, respectively. These transitions along with magnetic
moment value suggest an octahedral geometry for the nickel(II)
⊥
G = (g|| - 2.0027)/(g - 2.0027)
2
5
complex . The copper(II) complex exhibits a broad band
If G > 4.0, the local axes are aligned parallel or only
slightly misaligned. If G < 4.0, significant exchange coupling
is present and the misalignment is appreciable. The observed
value for the exchange interaction parameter for the copper(II)
complex (G = 4.0470) suggests that the local tetragonal axes
are aligned parallel or slightly misaligned and that the unpaired
-1
2
2
centered at 13,500 cm due to B1g → A1g transitions of a distorted
square planar geometry. These observations together with the
magnetic moment value of 1.81 BM, support a distorted square
planar geometry for the copper(II) complex.
Analytical data, molar conductance values and diamagnetic
nature, adequately support a tetrahedral geometry for the
zinc(II) complex. The completely filled d-orbitals in zinc(II)
and the absence of LFSE seem largely responsible for the much
less extensive coordination chemistry of zinc(II). The zinc(II)
ion is flexible with respect to the number of ligands it can
electron is present in the dx2-y2
orbital.
XRD studies: The X-ray diffraction pattern of the ligand
(Fig. 6) indicates its high crystallinity. The diffractogram shows
10 reflections for 2θ value ranging from 12° to 33° with
maxima at 2θ = 13.29403 which corresponds to interplanar

Vol. 27, No. 12 (2015)
Synthesis of Some 3d-Metal Complexes of [(2-Pyrrole-2-carboxaldehyde)-3-isatin]bishydrazone 4683
1.0
0.5
0.0
10000
8
000
-
0.5
1.0
1.5
2.0
2.5
3.0
3.5
-4.0
-
6000
-
-
4000
-
-
2000
-
0
1
0
20
30
40
2θ
50
60
70
0.00
0.25
0.50 0.75
Potential (V)
Fig. 7. Cyclic voltammogram of copper(II) complex
1.00 1.25
1.50
1.75 2.00
(°)
Fig. 6. XRD pattern of the ligand (IPB)
-
3
-3
distance d = 6.6546 Å. The main peaks have been indexed
using the XRDA software and the data obtained are tabulated
varying concentration from 1 × 10 to 5 × 10 g is measured
and compared. Apart from this, the ligand is found to possess
more inhibitory action than the metal complex. The inhibition
efficiency increases with increase in concentration of the
additives. The lone pair of electrons of nitrogen and oxygen
atoms along with the delocalized p-electron can be the reason
2
in Table-3. The observed sin θ and 2θ values obtained have
28
been compared with the calculated values .
A comparison of these values shows good agreement
between observed and calculated values. Hence the ligand is
successfully indexed to orthorhombic crystal system with the
lattice constant unit cell parameters are; a =16.16492 Å, b =
32
for higher inhibition efficiency . These factors play the vital
role in the adsorption of the inhibitor and the formation of
coordinate bond with metal. The adsorption of inhibitor on
the mild steel surface can occur either directly by the inter-
actions between the π-electrons of the inhibitor and the vacant
d-orbitals of metal surface atoms. The adsorption of inhibitor
on mild steel may also be due to the interaction of nitrogen
and oxygen with the surface atoms of metal. As inhibitor
concentration increases, it covers more and more surface area
and results in the reduction of corrosion rate . Fig. 8 shows
the trend of open circuit potential decay with and without the
corrodent inhibitor (Table-4) of varying concentration from
10 to 5 × 10 g for 15 days. The open circuit potential decay
of a mild steel coupon kept in a blank cell i.e. without inhibitor
1
1.73966 Å and c = 8.68687 Å. The unit cell volume is found
3
to be 1,648.5 Å . On complexation, crystallinity of the ligand
has been lost and the complex becomes amorphous in nature.
Cyclic voltammetric studies: The copper(II) complex
of IPB has been subjected to cyclic voltammetric study. The
CV profile (Fig. 7) of [Cu(IPB)Cl ] complex, has displayed a
2
wave at Epa value +0.60V, due to the oxidation of Cu(I) to Cu(II)
and Epc value at +0.67 V, which is attributed to the reduction
33
of Cu(II). The peak separation (∆E
∆E greater than 59 indicates irreversible reaction) indicating
one electron transfer in the electrode reaction. The ratio of the
p
) is found to be 75 mV
(
p
-3
-3
2
9,30
anodic to cathodic peak current (Ipa/Ipc) approaches to one
.
Thus from the above voltammetric data electrochemical
(1 M H
2
SO ) is also given in Fig. 8 to understand the extent of
4
II
-
I
–
2
process is [Cu (IPB)Cl ] + 1e → [Cu (IPB)Cl] + Cl . Here,
open circuit potential deviation due to the presence of the
inhibitor. In the case of blank solution the initial open circuit
potential value instantly changes to a negative value as high
as -0.925 mV which shows severe corrosion attack. However
the addition of different concentration of the ligand and
complex to the solution is able to bring the potential values
towards positive region. This is due to the ability of the ligand
complex solution to form a passive film on the surface of mild
the electrochemical process is diffusion controlled. The
decomplexation and copper metal deposition on the electrode
31
have not been observed .
Corrosion inhibition activity: Corrosion inhibition is
attributed to the adsorption of inhibitors on mild steel. The
open circuit decay of mild steel coupon immersed in 1 M
H
2
SO for 15 days with and without the corrodent-inhibitor of
4
TABLE-3
X-RAY DIFFRACTION DATA OF LIGAND
2
2
Peak No.
d (Å)
Observed (2θ)
13.29403
14.43433
16.35104
20.43184
21.40192
23.78932
24.36926
24.99258
27.56247
31.25268
Calculated (2θ)
13.28376
14.53374
16.43162
20.42266
21.29546
23.79427
24.44097
24.94269
27.80000
31.34682
Observed (sin θ) Calculated (sin θ)
hkl
1
2
3
4
5
6
7
8
9
6.65460
6.13132
5.41665
4.34307
4.14836
3.73717
3.64953
3.55991
3.23354
2.85964
0.013385
0.015767
0.020202
0.031424
0.034440
0.042440
0.044503
0.046772
0.056690
0.072484
0.013378
0.016000
0.020421
0.031428
0.034140
0.042500
0.044806
0.046635
0.057711
0.072983
210
120
003
002
221
220
122
202
222
103
10

4
684 Swathy et al.
Asian J. Chem.
TABLE-4
VARIATION OF OPEN CIRCUIT POTENTIAL DECAY FOR MILD STEEL IMMERSED IN
BLANK AND INHIBITOR SOLUTIONS OF IPB AND [Ni(IPB) Cl ] COMPLEX
2
2
Potential blank
mV)
Potential (mV) of ligand in various concentration
Potential (mV) of complex in various concentration
No. of days
-
3
-3
-3
-3
-3
-3
(
1 × 10 (g)
-0.592
-0.583
-0.572
-0.568
-0.553
-0.544
3 × 10 (g)
5 × 10 (g)
1 × 10 (g)
3 × 10 (g)
5 × 10 (g)
3
6
9
-0.496
-0.545
-0.623
-0.715
-0.880
-0.925
-0.582
-0.575
-0.565
-0.555
-0.548
-0.540
-0.608
-0.570
-0.561
-0.552
-0.545
-0.536
-0.720
-0.709
-0.682
-0.670
-0.652
-0.621
-0.712
-0.705
-0.681
-0.665
-0.645
-0.612
-0.707
-0.692
-0.670
-0.658
-0.639
-0.611
12
15
18
-
-
-
-
-
-
-
-
-
-
0.45
TABLE-5
ANTIBACTERIAL RESULTS OF THE
INVESTIGATED COMPOUNDS OF IPB
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
Diameter of zones showing complete
inhibition of growth (mm)
Conc.
µg/mL)
IPB
Compound
(
Blank–
3
E. coli
S. typhi
S. aureus
1
3
5
1
3
×10–
3
50
100
4.8
5.9
7.6
8.2
10.6
14.8
6.2
11.2
16.0
–
4.0
5.1
6.8
6.0
9.0
13.6
8.3
14.3
14.0
–
3.2
5.6
7.1
×10–3
Ni(IBP)2
×10–
IPB
3
200
×10–3
×10–
50
100
7.8
3
5×10
[
Mn(IPB) (OAc) ]
2
2
10.9
14.2
5.6
10.5
12.4
8.1
12.5
14.1
7.0
200
50
0
2
4
6
8
10
12
14
16
[
Co(IPB) Cl ]
100
00
2
2
No. of days
2
Fig. 8. Trend of open circuit potential decay for mild steel immersed in
blank and inhibitor solutions of IPB and [Ni(IPB) Cl ] complex
50
100
2
2
[Ni(IPB) Cl ]
–
8.6
–
–
6.2
4.2
2
2
200
50
steel coupons. Extend of film formation is more prominent in
the ligand when compared to the complexes because the ligand
is more chemical adsorptive than complexes. It can be explained
on the basis of the effect of chemical structure. In this respect,
the isatin ring, benzene ring, N-H, C=N and C=O of bishydrazone
can form a big π bond accordingly, not only the π of benzene,
C=O enter the unoccupied orbital of iron, but also the π* orbital
can accept the electron of d orbital of iron to form back bonds.
These back bonds produce more than one centre of chemical
adsorption on the mild steel surfaces . In case of the metal
complexes the chemical adsorption is less because the ligand
shares its lone pair to the metal ion that will reduce the effective
adsorption of mild steel surface.
[
Cu(IPB)Cl]
100
200
50
–
10.2
15.0
9.2
12.5
14.0
31.0
12.0
13.2
7.0
12.2
15.2
32.0
12.0
8.7
12.5
14.6
30.0
[
Zn(IPB)Cl]
100
200
a
Streptomycin
Standards
100
a
Antibacterial activity: >15 mm, significant; 10-14 mm, moderate
activity; <10, weak activity.
34
the lipid membrane surrounding the cell favours the passage
of only lipid-soluble materials, due to which liposolubility is
an important factor controlling the antibacterial activity. On
chelation, 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. Furthermore, the mode of action of the compound may
involve formation of a hydrogen bond through the azomethine
group with the active centre of cell constituents, resulting in
interference with normal cell processes.
Antibacterial activity: The in vitro antibacterial activity
value of the compounds against the growth of micro-organisms
is summarized in Table-5. Inhibition is found to increase with
increase in concentration of metal complex. The results show
that the metal complexes exhibit higher activity against each
class of organism. The activity is related to the nature and
structure of the complexes. The relation between chelation
and toxicity is very complex, expected to be a function of
steric, electronic and pharmacokinetic factors along with
mechanistic pathways. The MIC values of some compounds,
show significant activity against selected bacterial species. The
results indicate that, these compounds are active in inhibiting
the growth of the bacterial species. A comparative study of
the ligand and its complexes indicate that the metal complex
exhibit higher antibacterial activity than the free ligand. Such
increased activity of the complexes can be explained on the
basis of the Overtone concept and the Tweedy’s chelation
Conclusion
A novel bishydrazone viz. [(2-pyrrole-2-carboxaldehyde)-
3-isatin]bishydrazone and its metal complexes were synthe-
sized and characterized on the basis of various physico-
chemical and spectral studies. The ligand behaved as neutral
bidentate coordinating to the metal ion through the aldimine
nitrogen and carbonyl oxygen atom of the isatin moiety. On
the basis of all the spectral data, it is observed that manganese(II),
cobalt(II) and nickel(II) complexes possess an octahedral
geometry, copper(II) complex possess a distorted square planar
geometry whereas zinc(II) complex possess a tetrahedral
24,35
theory .According to the Overtone concept of cell permeability,

Vol. 27, No. 12 (2015)
Synthesis of Some 3d-Metal Complexes of [(2-Pyrrole-2-carboxaldehyde)-3-isatin]bishydrazone 4685
1
1
2. S.K. Sridhar, S.N. Pandeya, J.P. Stables andA. Ramesh, Eur. J. Pharm.,
6, 129 (2002).
3. L.P. Nitha, R. Aswathy, N.E. Mathews, B.S. Kumari and K. Mohanan,
geometry. The XRD studies show that ligand possess crystalline
nature with orthorhombic crystal lattice and but its nickel(II)
complex is amorphous in nature. In view of antibacterial activity
observations of hydrazone derivatives, metal complexes are
found to be more potent bactericides than the ligand. Corrosion
inhibition efficiency of the ligand and its nickel(II) complex
reveal that the ligand possess greater activity than the metal
complex.
1
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ACKNOWLEDGEMENTS
The authors express their sincere thanks to Prof. and Head,
Department of Chemistry, University of Kerala, Kariavattom
Campus, Trivandrum, India for providing the necessary
facilities for carrying out this work. Instrumental facilities
provided by SAIF, Cochin, IIT, Bombay, CDRI, Lucknow and
NIIST, Trivandrum are also gratefully acknowledged.
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