Phenoxide bridged tetranuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes: Electrochemical, magnetic and antimicrobial studies

Article abstract of DOI:10.1016/j.saa.2011.04.079

Phenoxide bridged later first row transition metal(II) complexes have been prepared by the interaction of later 3d transition metal(II) chlorides with tetranucleating compartmental Schiff base ligand system derived from 2,6-diformyl-4-methylphenol, p-phenylenediamine and 2-hydrazinobenzothiazole. Ligand and complexes were characterized by analytical, spectral (IR, UV-visible, ESR, FAB-mass and fluorescence), magnetic and thermal studies. All complexes are found to have octahedral geometry. The mutual influence of metal centres in terms of cooperative effect on the electronic, magnetic, electrochemical and structural properties was investigated. The Schiff base and its complexes have been screened for their antibacterial (against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa) and antifungal activities (against Aspergillus niger, and Candida albicans).

Full text of DOI:10.1016/j.saa.2011.04.079

Spectrochimica Acta Part A 79 (2011) 1418–1424
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Phenoxide bridged tetranuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes:
Electrochemical, magnetic and antimicrobial studies
Anupama Kamatha, Naveen V. Kulkarnia,b, Priya P. Netalkara, Vidyanand K. Revankara,∗
a Department of Chemistry, Karnatak University, Pavate Nagar, Dharwad 580 003, Karnataka, India
b Department of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel
a r t i c l e i n f o
a b s t r a c t
Article history:
Phenoxide bridged later first row transition metal(II) complexes have been prepared by the interaction
of later 3d transition metal(II) chlorides with tetranucleating compartmental Schiff base ligand system
derived from 2,6-diformyl-4-methylphenol, p-phenylenediamine and 2-hydrazinobenzothiazole. Ligand
and complexes were characterized by analytical, spectral (IR, UV–visible, ESR, FAB-mass and fluores-
cence), magnetic and thermal studies. All complexes are found to have octahedral geometry. The mutual
influence of metal centres in terms of cooperative effect on the electronic, magnetic, electrochemical
and structural properties was investigated. The Schiff base and its complexes have been screened for
their antibacterial (against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa) and antifungal
activities (against Aspergillus niger, and Candida albicans).
Received 29 September 2010
Received in revised form 28 April 2011
Accepted 29 April 2011
Keywords:
2,6-Diformyl-4-methylphenol
2-Hydrazinobenzothiazole
Antimicrobial activity
Tetranuclear
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
ing 2,6-diformyl-4-methylphenol and 2-substituted benzothiazole
moiety do fluoresce and act as fluorescence sensor for zinc and
Schiff-base compounds have a great importance in coordina-
tion chemistry, due to their ability to form a range of complexes
which have applications in different fields. One approach in the
field of coordination chemistry has been to investigate the use of
Schiff-base ligands to develop phenoxo-bridged transition metal
complexes that have applications in biomedical [1–4], biomimetic
and catalytic systems [5]. Planar ligands with amine or imine donor
groups and bridging phenol oxygens are referred to as Robson-type
ligands [6]. The donor groups of these compartmental ligands pro-
vide a significant diversification of the coordination sites making
them good candidates for metal ion complexation and for mim-
icking biological systems. Recently, the design and synthesis of
polynuclear metal complexes has been a topic of growing interest
[7–9] for the reason that such supramolecular materials not only
display interesting structures, but also occasionally exhibit novel
properties such as porosity, magnetism and non-linear optical
behaviour [10]. The chemistry of 2,6-diformyl-4-methylphenol and
its derivatives is of a great interest in designing the compartmental
ligands which can form polynuclear complex systems having mag-
netic communication between the metal centres. The study of their
stereochemical, electronic, magnetic, catalytic spectroscopic and
also biological properties have allowed the proposal of probes for
some important applications [11,12]. Some compounds contain-
can be used as zinc ion-selective luminescent probe for biological
application under physiological conditions [13–15].
Benzothiazole finds use in research as a starting material for
the synthesis of larger, usually bioactive structures. Its aromaticity
makes it relatively stable. From the literature survey, it has been
found that extensive work has been reported on 2-substituted ben-
zothiazole derivatives in past and evaluated for different activities
like antibacterial, anticancer, antiviral, antitumor [4], antifun-
gal, anti-inflammatory, antioxidative, radioprotective, antidiabetic,
anthelmintic, anti-leishmanial, anticonvulsant and neuroprotec-
tive [16–19].
In this paper we describe the preparation, characterization and
antimicrobial activity of cobalt(II), nickel(II), copper(II) and zinc(II)
complexes with a new Schiff base, LH2 (Fig. 1), derived by con-
densing 2,6-diformyl-4-methylphenol, p-phenylene diamine and
2-hydrazinobenzothiazole. The complexes have the general com-
position [M4L(␮-Cl2)Cl4(H2O)6].
2. Experimental
2.1. Materials and methods
Estimation of the metal(II) ions was done according to the stan-
dard methods. The molar conductivity measurements were made
on ELICO-CM-82 conductivity bridge. The magnetic susceptibility
measurements were made on Faraday balance at room temperature
using Hg[Co(SCN)4] as calibrant. The 1H NMR spectra were recorded
∗
Corresponding author. Tel.: +91 836 4250821; mobile: +91 9900485652.
E-mail address: vkrevankar@rediffmail.com (V.K. Revankar).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.04.079

A. Kamath et al. / Spectrochimica Acta Part A 79 (2011) 1418–1424
1419
CH3
CH3
NH2
O
OH
N
Absolute ethanol
Reflux
2
+
N
OH
O
O
OH
O
NH2
A
p-phenylenediamine
2,6-Diformyl-4-methylphenol
CH3
CH3
S
N
N
S
NH
NH2
2
N
N
OH
N
HN
N
NH
Absolute ethanol, Reflux
N
OH
S
CH3
LH2
Fig. 1. Preparation of the ligand LH2.
in CDCl3 and DMSO-d6 solvent on Bruker-300 MHz spectrometer at
room temperature using TMS as internal reference. IR spectra were
recorded in a KBr matrix using an Impact-410 Nicolet (USA) FT-
IR spectrometer in 4000–400 cm−1 range. The electronic spectra
of the complexes were recorded on a Hitachi 150-20 spectropho-
tometer in the range of 1000–200 nm. The cyclic voltametric studies
were performed at room temperature in DMSO under O2 free con-
dition using CH instruments Electrochemical analyzer, CHI-1110A
(USA). The ESR spectra of the copper complexes were scanned (at
room temperature and liquid nitrogen temperature) on a Varian
E-4X-band EPR spectrometer, using TCNE as the g-marker. TG and
DTA measurements of the complexes were recorded in nitrogen
atmosphere on Universal V2.4F TA instrument keeping final tem-
perature at 800 ◦C and heating rate 10 ◦C/min. The FAB mass spectra
were drawn from JEOL SX 102/DA-6000 mass spectrometer using
Argon/Xenon (6 kV, 10 mA) as the FAB gas.
Diformyl-4-methylphenol was prepared according to the method
reported by Denton and Suschitzky [21] but with slight modi-
fication. 2-Mercaptobenzothiazole was purchased from SD Fine
Chemicals. The zinc chloride used was anhydrous whereas the
other metal salts were in their hydrated form, i.e., CoCl2·6H2O,
NiCl2·6H2O and CuCl2·2H2O.
2.2.1. 2-Hydrazinobenzothiazole
A
mixture
of
hydrazinehydrate
(0.01 mol),
2-
mercaptobenzothiazole (0.01 mol) and EtOH (ca. 50 cm3) was
placed in a round-bottomed flask and boiled under reflux for
8–10 h, i.e., until H2S evolution had ceased. The reaction mixture
was then left overnight and, on cooling, a white crystalline solid
mass separated. This was filtered off, air dried and recrystallized
from EtOH [4]. m.p.: 193–194 ◦C (Lit. 197–199 ◦C), yield: 80%.
2.2.2. Synthesis of ligand LH2
2.2. Synthesis
2,6-Diformyl-4-methylphenol (0.1 mol) was taken in 50 ml of
absolute ethanol, to which p-phenylenediamine (0.05 mol) in abso-
lute alcohol was added dropwise with constant stirring. Further the
mixture was stirred at room temperature for 30 min. The reaction
All chemicals used were of reagent grade. Solvents were dried
and distilled before use according to standard procedures [20]. 2,6-

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A. Kamath et al. / Spectrochimica Acta Part A 79 (2011) 1418–1424
Table 1
Analytical and conductance data of complexes.
Compound
Yield in %
Elemental analysis (%)
Found (calculated)
Molar cond.
ꢀM ꢁ−1 cm2 mol−1
C
H
N
S
M
Cl
A
LH2
90
78
74
73
76
72
71.83 (72.00)
65.43(65.76)
36.70 (36.02)
35.73 (35.45)
34.08 (34.00)
35.86 (35.79)
5.02 (4.96)
4.55 (4.34)
3.48 (3.31)
3.48 (3.42)
3.07 (3.57)
3.25 (3.13)
7.06 (6.99)
–
–
–
–
–
–
–
38.7
23.8
34.2
15.9
16.70 (16.14)
8.45 (8.84)
8.86 (8.72)
8.96 (8.35)
8.88 (8.79)
9.14 (9.22)
5.25 (5.06)
4.76 (4.99)
4.55 (4.77)
5.50 (5.02)
[Co4L(␮-Cl2)Cl4(H2O)6].H2O
[Ni4L(␮-Cl2)Cl4(H2O)6].2H2O
[Cu4L(␮-Cl2)Cl4(H2O)6].4H2O
[Zn4L(␮-Cl2)Cl4(H2O)6]
18.87 (18.66)
18.40 (18.28)
18.96 (18.93)
20.60(20.51)
16.97 (16.78)
16.75 (16.56)
15.92 (15.84)
16.76 (16.68)
mixture was refluxed on water bath temperature for 4 h. The red-
dish solid that formed (precursor A) was filtered off and washed
with hot ethanol (m.p.: 260 ◦C, yield: 90%).
ing with the metal ions [3]. Further, the bands in the region
520–570 cm−1 and 400–480 cm−1, are probably due to the forma-
tion of M–O and M–N bonds respectively [23]. Also, the presence
of coordinated water molecules in the complexes is supported by
the two bands in the ranges 820–850 and 737–756 cm−1 which are
due to (–OH) rocking and wagging mode of vibrations, respectively
[24].
The ethanolic solution of 2-hydrazinobenzothiazole (0.2 mol) is
added slowly to the above obtained compound (0.1 mol) in 70 ml of
ethanol with constant stirring. After completion of the addition the
mixture was stirred at room temperature for 15 min and refluxed
on water bath temperature for 4 h. Catalytical amount of acetic acid
is added while refluxing. The dirty-yellow solid that formed was
filtered off and washed with hot ethanol (m.p.: 340 ◦C, yield: 78%).
The reaction pathway is given in Fig. 1.
3.2. 1H NMR studies
NMR studies provide significant conclusion regarding the nature
of bonding and coordination. Precursor A, ligand LH2 and zinc com-
plex were scanned in the region of 0–16 ppm for proton NMR
studies. The spectrum of precursor A show signals at 13.98, 10.56
and 8.73 ppm corresponding to phenolic, azomethine and aldehy-
dic protons respectively. Aromatic protons resonate in the range
6.75–7.78 ppm. NMR spectrum of ligand LH2 showed broad peak
at 12.31 ppm due to phenolic –OH protons and are exchangeable
with D2O. Absence of this peak in the spectrum of zinc complex
indicates the coordination of phenolic oxygen after deprotonation.
The signal at 8.49 ppm is due to azomethine protons attached to
hydrazide part, 7.78 ppm is due to azomethine protons attached
to p-phenylenediamine and are shifted to little downfield in zinc
complex, i.e., to 8.71, 8.24 ppm respectively owing to the coordina-
tion through nitrogen. The –NH– of hydrazide resonated at 6.65 and
6.41 ppm in ligand and complex respectively. The aromatic protons
resonated in the region 7.12–7.61 ppm and 6.87–7.50 ppm in lig-
and and complexes respectively. Ar–CH3 protons resonated around
2.33 ppm for all above compounds. The absence of OH protons
(coordinated H2O) may be due to their replacement by DMSO-d6
molecules [25].
2.2.3. Preparation of complexes
The CoII, NiII, CuII and ZnII complexes were prepared by refluxing
the respective hydrated metal chloride (0.04 mol) in EtOH (30 cm3)
with ligand (0.01 mol) for 4 h, during this little ammonia was added
to separate the complexes in solid form. So obtained solids were
filtered off, washed with hot ethanol and dried over fused CaCl2.
3. Results and discussion
The phenoxo bridged binuclear complexes obtained in the
present investigation were non-hygroscopic and in the form
of amorphous solids. They are insoluble in ethanol, water and
chloro-hydrocarbons, but partially soluble in DMF and DMSO. The
analytical and physicochemical data of the complexes are summa-
rized in Table 1.
3.1. Infrared spectral studies
The key IR absorption bands are summarized in Table 2.
The FT-IR spectrum of free ligand shows a band in the region
3395–3407 cm−1, assigned to the phenolic ꢂ(OH) group. The peaks
at 1676 and 1619 cm−1 in precursor A are due to aldehydic
ꢂ(C O) and azomethine ꢂ(>C N) respectively [3]. The azomethine
ꢂ(>C N), which is observed at 1619 cm−1 in ligand has shifted
to higher frequency in all complexes due to its participation in
the coordination. ꢂ(C N) of benzothiazole ring is observed at
1570 cm−1 in ligand and has shifted to lower frequency region
in all complexes indicating the coordination of nitrogen [4]. Phe-
nolic ꢂ(C–O) in ligand observed at 1274 cm−1 shifted to higher
frequency in all complexes due to coordination of oxygen upon
deprotonation [22]. The appearance of bands in the region of
1530–1545 cm−1 in all the complexes suggests phenoxide bridg-
3.3. Magnetic susceptibility and absorption spectral studies
The magnetic susceptibility of metal ions, encapsulated by the
organic ligand field, is one of the most important properties of coor-
dination compounds, which focuses the electronic structure [26].
The magnetic moments of the complexes were recorded at room
temperature and the observed magnetic moment value for the
Co(II), Ni(II) and Cu(II) complexes are 5.33, 3.49 and 1.68 BM respec-
tively. The magnetic moment value for copper complex is less than
the spin only value of free metal ion. Hence the antiferromagnetic
exchange interaction exists through endogenous phenoxide bridge.
The common entity measured for these ions from the magnetism
Table 2
Infrared spectral data in cm−1
.
Compound
LH2
[Co4L(␮-Cl2)Cl4(H2O)6]·H2O
[Ni4L(␮-Cl2)Cl4(H2O)6]·2H2O
[Cu4L(␮-Cl2)Cl4(H2O)6]·4H2O
[Zn4L(␮-Cl2)Cl4(H2O)6]
ꢂ(C N) (azomethine)
ꢂ(C N) (benzothiazole)
ꢂ(C–O) (phenolic)
ꢂ(M–N)
ꢂ(M–O)
1619
1626
1632
1627
1621
1570
1542
1556
1562
1543
1274
1280
1276
1282
1278
–
468
471
474
473
–
551
530
512
520

A. Kamath et al. / Spectrochimica Acta Part A 79 (2011) 1418–1424
1421
Table 3
coordination of nitrogen of benzothiazole unit. The n → ␲* tran-
sition associated with azomethine linkage. This band in complex
has shown bathochromic shift due to the donation of a lone pair
of electrons to the metal and hence the coordination of azome-
thine [27]. The medium absorption bands at 415–440 nm range in
all complexes are charge transfer transitions from the ligand phe-
noxide to metal ions (LMCT). The d–d transitions have observed
for all complexes in the visible region except for zinc(II) complex.
Copper complex exhibits the broad band at 605 nm corresponding
The electronic spectra and magnetic moment data.
Compound
ꢃmax (nm)
ꢄeff (BM)
LH2
340, 387
–
5.33
3.49
1.68
[Co4L(␮-Cl2)Cl4(H2O)6]·H2O
[Ni4L(␮-Cl2)Cl4(H2O)6]·2H2O
[Cu4L(␮-Cl2)Cl4(H2O)6]·4H2O
[Zn4L(␮-Cl2)Cl4(H2O)6]
268, 419, 450, 583, 678
266, 399, 440, 617, 679
268, 415, 430, 605
265, 386, 440
Diamagnetic
2
to the 2Eg → T2g transition which is in agreement with the cop-
per complexes of octahedral geometry [28]. CoII complex shows
4
two bands at 583 and 678 nm, because of the 4T1g(F) → T1g(P) and
4
4T1g(F) → A2g(F) transitions concordant with octahedral structure.
3
NiII complex exhibit bands at 617 and 679 nm due to 3A2g → T1g(P)
3
3
and A2g → T1g(F) transitions which shows its octahedral nature
[29].
3.4. Fluorescence studies
Fluorescence studies have been performed by using a Spec-
trofluorimeter model F-7000 (Hitachi, Japan) equipped with 150 W
Xenon lamp and a slit width of 3 nm. Schiff-base systems exhibit
fluorescence due to intraligand ␲ → ␲* transitions. Fluorescence
spectra of the ligand and complexes show (Fig. 3) an emission
band at 519 nm when excited with 440 nm radiation, at room tem-
perature with sample concentration of 0.1 mmol in DMF. Almost
double enhancement in fluorescence intensity was observed in zinc
complex. The emission is neither MLCT (metal-to-ligand charge
transfer) nor LMCT in nature, since a similar emission is also
observed for the free ligand with reduced intensity. Hence we ten-
tatively assign it to the intraligand (␲ → ␲*) fluorescence. After
complexation with zinc, the free rotation of the flexible bonds of
the ligand is reduced and energy dissipation through non-radiative
channels is reduced [30]. As ligand LH2 acts as fluorescence sen-
sor for Zn and can be used as zinc ion-selective luminescent probe
for biological application under physiological conditions [13,14].
The fluorescence property of ligand was quenched with copper and
vanished completely with cobalt and nickel after complexation.
Fig. 2. UV–visible spectra of ligand and complexes in the range 275–500 nm.
point of view is that, they have surrounded by the octahedral ligand
field.
The electronic absorption spectra of the complexes were
recorded in DMF solution over the range 200–1000 nm and the
spectral data are listed in Table 3. Ligand exhibits absorption bands
at 340 and 387 nm, which are due to the intra ligand ␲ → ␲* tran-
sition and n → ␲* transitions respectively. In all complexes ␲ → ␲*
transition has suffered blue shift (Fig. 2) which internally supports
the enough stability of bonding molecular orbitals and indicates the
Fig. 3. Emission spectra of ligand and complexes.

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A. Kamath et al. / Spectrochimica Acta Part A 79 (2011) 1418–1424
Table 4
Antimicrobial data of ligand and metal complexes.
Compound
Concentration (␮g ml−1
)
% inhibition against bacteria
% inhibition against fungi
Pseudomonas aeruginosa
Staphylococcus aureus
Aspergillus niger
Candida albicans
5
10
25
50
100
36.15
36.15
41.54
48.46
51.54
5.71
6.67
8.10
8.57
42.86
0
0.36
1.35
6.76
17.57
29.73
7.55
37.74
39.62
50.94
Ligand (LH2)
5
10
25
50
100
15.38
40.00
46.15
50.77
52.31
3.81
6.19
6.67
8.57
9.52
16.98
33.96
39.62
50.94
64.15
0
4.05
8.11
24.32
44.89
[Co4L(␮-Cl2)Cl4(H2O)6]·H2O
[Ni4L(␮-Cl2)Cl4(H2O)6]·2H2O
[Cu4L(␮-Cl2)Cl4(H2O)6]·4H2O
[Zn4L(␮-Cl2)Cl4(H2O)6]
Gentamycin
5
10
25
50
100
36.92
40.00
48.46
56.15
63.08
4.29
5.71
7.62
19.52
24.29
16.98
20.75
32.08
37.74
39.62
1.35
4.05
8.11
16.22
21.62
5
10
25
50
100
36.92
38.46
44.62
55.38
64.62
2.86
8.10
10.48
17.62
18.10
20.75
33.96
35.85
43.40
73.58
2.70
10.81
21.62
44.59
55.41
5
10
25
50
100
38.46
39.23
46.15
54.62
57.69
1.43
7.62
8.10
10.95
11.90
0
0
0
0
0
12.16
21.32
29.73
16.98
28.30
5
10
25
50
100
60.00
68.46
80.00
86.15
90.77
27.62
54.29
76.67
95.71
–
–
100
5
10
25
–
–
41.51
53.49
67.93
100
19.57
27.38
44.60
78.38
Amphotericin
50
100
100
100
3.5. Molar conductivity measurements
erable change in the geometry of ligand field around the metal ion
when temperature is lowered.
The molar conductance values of all the complexes measured
at room temperature in DMF solution with 10−3 mol dm−3 concen-
tration fall in the range 15.9–38.7 ꢁ−1 cm2 mol−1, which indicates
the non-electrolytic nature of the complexes [31].
3.7. FAB mass spectral studies
In the mass spectrum of the copper complex shows m/z ion peak
at 1342 corresponding to molecular weight of the complex. The
molecular ion observed in the spectrum corresponds to the mass of
3.6. Electron spin resonance spectral study
The X-band ESR spectrum of copper(II) complex in solid form
was scanned in the region of 9000 MHz with corresponding field
intensity at ∼3000 Gauss, at room temperature as well as liquid
nitrogen temperature. The spectrum is characteristically a tetrago-
nally distorted octahedral, which shows slight broadened features
with g⊥ and g|| values of 2.079 and 2.253. The spectrum at liquid
nitrogen temperature is slightly broadened. In general, chloro-
bridged binuclear copper(II) complexes give broad ESR signals [4] in
which the broadening is assigned to a dipolar interaction. The exis-
tences of g|| > g⊥ suggests that dx2 − y2 is in the ground state with
the d9 (CuII) configuration [32]. The g values are related to the axial
symmetry parameter, G, by the expression G = (g|| − 2)/(g⊥ − 2). The
G values measure the extent of the exchange interaction between
copper centres in the polycrystalline solid. In the present case,
G = 3.19, which indicates the presence of a weak exchange interac-
tion in the complex. The ESR spectra at room temperature and liquid
nitrogen temperature have similar nature, which shows no consid-
Fig. 4. Cyclic voltammogram of CuII complex at the scan rate of 0.05 V/s.

A. Kamath et al. / Spectrochimica Acta Part A 79 (2011) 1418–1424
1423
Fig. 5. Graphical representation of antimicrobial studies (% inhibition V/s ␮g ml−1).
entire complex including bridging chloride, lattice held and coor-
dinated water molecules. The spectrum also contains peaks due
to molecular cations of the various fragments of the complex. The
information gathered from FAB mass data agrees well with elemen-
tal analysis data. The tentative structures of complexes are given in
Fig. 6.
sphere over the temperature range of 30–800 ◦C with heating rate
of 10 ◦C/min. All complexes show similar decomposition pattern
with weight losses in three stages. In the first stage 9.9%, 10.9%,
12.5% and 7.8% in the temperature range 40–180 ◦C is attributed
to the weight loss of coordinated water molecules along with lat-
tice held water for CoII, NiII, CuII and ZnII complexes respectively.
The corresponding DTA curve indicates the endothermic nature
of the process. In the next stage the weight loss around 16% in
all complexes correspond to coordinated chlorides in the temper-
ature range 180–400 ◦C. In the third stage weight loss is due to
the decomposition of ligand part. The final decomposition prod-
ucts were found to be stable metal oxides. The weights of the
3.8. Thermogravimetric analysis
The thermal stability and decomposition pattern of the com-
plexes was analyzed by TG and DTA studies. Thermo gravimetric
analysis of the complexes has been carried out in nitrogen atmo-
CH3
OH2
M
Cl
OH2
Cl
Cl
O
N
N
S
N
N
O
N
H2O
HN
. n H2O
M
M
M
Cl
NH
OH2
N
S
Cl
Cl
OH2
OH2
M= Co, n=1
M= Ni, n=2
M=Cu, n=4
M=Zn, n=0
CH3
Fig. 6. Proposed structures of the complexes.

1424
A. Kamath et al. / Spectrochimica Acta Part A 79 (2011) 1418–1424
final decomposition products left are 32%, 31%, 40% and 41% for
cobalt, nickel, copper and zinc complexes respectively. The frag-
mentation patterns of the thermograms agree well with theoretical
calculations and support the stereochemical and stoichiometrical
assignments.
Acknowledgments
The authors thank the USIC and Department of Chemistry, Kar-
natak University, Dharwad for providing spectral facility. Recording
of FAB mass spectra (CDRI Lucknow) and ESR spectra (IIT Bom-
bay) are gratefully acknowledged. One of the authors (AK) thanks
UGC for providing Research Fellowship in Science for Meritorious
Students.
3.9. Electrochemistry
The redox behaviour of ligands and their complexes were
scanned at room temperature in DMF solution using cyclic voltam-
meter in the working potential range of −1 to +1 V at three different
scan rates viz., 0.05, 0.1 and 0.15 V/s under the nitrogen atmo-
sphere. The voltammograms of the copper complex is shown in
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3.10. Antimicrobial analysis
The ligand and its complexes were screened for antibacterial
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domonas aeruginosa and antifungal activity against Aspergillus
niger, Candida albicans by turbidity method at 100 ␮g ml−1 using
Gentamycin (for bacteria) and Amphotericin (for fungi) as stan-
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5–50 ␮g ml−1 accordingly. Schiff base is highly active against P.
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activity is may be due to the metal chelation which makes com-
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Ligand showed good activity against C. albicans and A. niger, which
has been increased on complexation with cobalt and copper. Lig-
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have not shown any activity against E. coli. The data is sum-
marized in Table 4 and the same is represented graphically
in Fig. 5.
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Ligand reported in this article is tetranucleating towards the
later first row transition metal ions. All synthesized complexes have
[M4L(␮-Cl2)Cl4(H2O)6]·nH2O composition and octahedral geome-
try. All complexes are monomers and non-electrolytic in nature.
Antiferromagnetic interaction is present between the metal ions
in copper complex via phenoxide bridge. Ligand is fluorescence
active and can act as fluorescence sensor for zinc. The copper com-
plex has shown quasireversible redox responses over the applied
potential range, whereas ligand and other complexes are found to
be electrochemically innocent. All compounds have shown good
antimicrobial activity.
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