Synthesis, physico-chemical characterization and antimicrobial activities of 3-methoxysalicylaldehyde-2-aminobenzoylhydrazone and its transition metal complexes

Article abstract of DOI:10.1016/j.molstruc.2012.02.062

The transition metal complexes of 3-methoxysalicylaldehyde-2- aminobenzhydrazone (H₂L) were synthesized and characterized by various spectroscopic (IR, NMR, UV-Vis, mass), thermal and other physicochemical methods. The ligand acts both in monob

Full text of DOI:10.1016/j.molstruc.2012.02.062

Journal of Molecular Structure 1019 (2012) 159–165
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, physico-chemical characterization and antimicrobial activities
of 3-methoxysalicylaldehyde-2-aminobenzoylhydrazone and its transition
metal complexes
Dayananda S. Badiger a, Rekha S. Hunoor a, Basavaraj R. Patil a, Ramesh S. Vadavi a,
Chandrashekhar V. Mangannavar b, Iranna S. Muchchandi b, Kalagouda B. Gudasi a,
⇑
a Department of Chemistry, Karnatak University, Pavate Nagar, Dharwad 580 003, Karnataka, India
b H.S.K. College of Pharmacy, Bagalkot 587 101, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The transition metal complexes of 3-methoxysalicylaldehyde-2-aminobenzhydrazone (H2L) were syn-
thesized and characterized by various spectroscopic (IR, NMR, UV–Vis, Mass), thermal and other physi-
cochemical methods. The ligand acts both in monobasic as well as dibasic manner and coordinates in
tridentate fashion with carbonyl oxygen, azomethine nitrogen and phenolic oxygen via deprotonation
except in Cu(II) complex where the ligand coordinates via enolization and deprotonation of amide proton.
An octahedral geometry was assigned for Mn(II), Co(II), Ni(II) and Zn(II) complexes and square planar for
Cu(II) complex. The ligand and its metal complexes have been screened for their in vitro antimicrobial
activities using serial dilution method. Metal complexes in general have exhibited better antibacterial
and antifungal activity than the free ligand. The Cu(II) complex exhibited highest antimicrobial activity
among the compounds tested.
Received 27 December 2011
Received in revised form 22 February 2012
Accepted 24 February 2012
Available online 3 March 2012
Keywords:
Hydrazone
2-Aminobenzoylhydrazide
3-Methoxysalicylaldehyde
Metal complex
Ó 2012 Elsevier B.V. All rights reserved.
Antimicrobial activity
1. Introduction
proceeds through an intermediate hydrazone formation step,
hence it is appealing to isolate 2-aminobenzoylhydrazone derived
The hydrazone compounds along with their metal complexes
have been extensively investigated for their versatile coordination
modes [1–3] with prospective biological activities [4–6]. The
promising antimicrobial activities of hydrazone Schiff bases have
been recently reviewed [7]. The hydrazone Schiff bases and their
transition metal complexes derived from the salicylaldehyde have
attracted much attention in recent years [8–14], on the other hand,
the complexes derived from the 3-methoxysalicylaldehyde have
rarely been reported and shows promising applications [15]. The
facile syntheses of hydrazones have been achieved by the conden-
sation reaction of aldehydes with primary amines of substituted
benzhydrazides [16–19].
from 2-ABH in which the NH2 at second position remains free
when reacted with aromatic aldehyde.
In our earlier communication, it has been reported that the
reaction of 2-ABH and 3-methoxysalicylaldehyde at refluxing tem-
perature yielded 1,2-dihydroquinazolinone [27]. In the present
work, we describe a simple temperature controlled condensation
of 2-ABH and 3-methoxysalicylaldehyde to yield the title
compound 3-methoxysalicylaldehyde-2-aminobenzoylhydrazone
(H2L). The transition metal complexes of H2L were synthesized,
characterized and evaluated for their anti-microbial activities.
2. Experimental details
Many workers have reported [20–22] the chelating behavior of
hydrazone Schiff bases obtained by the reaction of aldehydes and
2-aminobenzoylhydrazide [2-ABH]. However recently it has been
shown that the condensation of 2-ABH with aromatic and hetero-
cyclic aldehydes yielded 1,2-dihydroquinazolinone instead of the
Schiff base product [23–26]. It is remarkable to note that the reac-
tions at room temperature even with a 1:1 equivalent of 2-ABH
and aldehyde lead to the formation of 1,2-dihydroquinazolinone.
It was suggested that the formation of 1,2-dihydroquinazolinone
2.1. Materials and methods
Analytical reagent grade 3-methoxysalicylaldehyde, methyl
anthranilate, hydrazine hydrate and metal(II) chlorides are pur-
chased from s.d. Fine chemicals and Spectrochem, India and are
used as received. Solvents were distilled before use [28]. Melting
points (uncorrected) are determined using the Gallenkamp melting
point apparatus. Conductance measurements were made in DMF
(10À3 M) solution using an ELICO-CM-82 conductivity meter with
cell type CC-01 and cell constant 0.53. Metal complexes were ana-
lyzed for their metal content after decomposition with a mixture of
⇑
Corresponding author. Tel.: +91 836 2215286x28; fax: +91 836 2771275.
E-mail address: kbgudasi@gmail.com (K.B. Gudasi).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2012.02.062

160
D.S. Badiger et al. / Journal of Molecular Structure 1019 (2012) 159–165
HCl and HClO4. The presence/absence of chlorides in the complexes
was tested by reacting them with AgNO3 as precipitating agent
after decomposition of complexes with conc. HNO3. The C, H, and
N elemental analyses were recorded on a Thermoquest CHN
analyzer. IR spectra were recorded as KBr disks on a Nicolet 170
SX FT-IR spectrometer in the range 4000–400 cmÀ1. NMR spectra
were recorded on a Bruker Avance 400 MHz spectrometer operat-
ing at 400.23 MHz in DMSO-d6 solvent. UV–visible spectra were
recorded in DMF solutions on a CARY-50 Bio UV–visible spectro-
photometer in the range 200–1100 nm. Magnetic susceptibilities
were carried out on a Gouy Balance using Hg[Co(SCN)4] as the cal-
ibrant and diamagnetic corrections are calculated using Pascal’s
constants [29]. Thermogravimetric analyses were carried out using
a TGA7 ANALYSER, Perkin–Elmer, US, at a heating rate of 10 °C per
min in 25–1000 °C temperature range. The mass spectra were
recorded on QTOF (Quadrupole Time-of-Flight) and FAB mass
spectrometer.
Cu(II)] (1 mmol) and anhydrous ZnCl2 (1 mmol) in methanol
(5 mL) to the methanolic solution (20 mL) of H2L (1 mmol) with
constant stirring at room temperature for 2 h. The precipitated
complexes were filtered, washed several times with methanol,
ether and dried under vacuo. The isolation of crystals suitable for
X-ray diffraction study was unsuccessful. Yield 60–75%.
[Zn(HL)2]: 1H NMR (DMSO-d6, d ppm): 12.12 (s, 1H, NH), 8.57 (s,
1H, NC@H), 6.27 (s, 2H, NH2), 7.69–6.53 (m, 7H, Ar-CH), 3.83 (s, 3H,
OCH3); 13C NMR (DMSO-d6, d ppm): 164.17 (C@O), 156.34 (C@N),
149.08 (CAOH), 147.14, 134.11, 132.46, 128.18, 121.92, 120.93,
118.94, 117.53, 116.41, 113.60, 111.93, 55.74.
2.4. Antimicrobial studies
Micro-dilution broth susceptibility method was adopted for the
evaluation of in vitro antimicrobial activity as described in our
earlier report [30].
2.2. Preparation of H2L
3. Results and discussion
A solution of 3-methoxysalicylaldehyde (1.52 g, 10 mmol) in
methanol (10 mL) was added drop wise to a cold (À5 to 0 °C) solu-
tion of 2-aminobenzoylhydrazide (1.51 g, 10 mmol) in methanol
(20 mL) with constant stirring. The resulting yellow solution was
kept stirring at À5 to 0 °C for 4 h. The yellowish product separated
was filtered, washed with cold methanol and dried in vacuo. Yield
90%. m.p. 143 °C.
3.1. Synthesis
In our earlier communication, we have reported that the reaction
of 2-ABH with 3-methoxysalicylaldehyde leads to the formation of
1,2-dihydroquinazolinone [27] at elevated temperature (Scheme
1). It was assumed that the formation of quinazolinone product pro-
ceeds through an intermediate hydrazone formation step. Thus, in
the present work, we have adopted the simple methodology for
the isolation of hydrazone, H2L as shown in Scheme 1. The synthesis
of H2L was achieved by the condensation of 1:1 equivalent of 2-ABH
and 3-methoxysalicylaldehyde at À5 to 0 °C. To validate the utility
of this methodology the reaction was also performed with different
stoichiometric ratios of the reactants. It is momentous to note that
the reactions at À5 to 0 °C even with 1:2 equivalent of 2-ABH and
3-methoxysalicylaldehyde lead to the formation of H2L rather than
1,2-dihydroquinazolinone product.
H2L: 1H NMR (DMSO-d6, d ppm): 11.84 (s, 1H, OH), 11.24 (s, 1H,
NH), 8.58 (s, 1H, NC@H), 6.43 (s, 2H, NH2), 7.60–6.67 (m, 7H, Ar-CH),
3.81 (s, 3H, OCH3); 13C NMR (DMSO-d6, d ppm): 163.12 (C@O),
154.31 (C@N), 149.12 (CAOH), 147.51, 134.15, 132.44, 128.15,
121.87, 120.99, 118.95, 117.50, 116.39, 113.62, 111.95, 55.75.
2.3. Preparation of metal (II) complexes
The transition metal complexes were prepared by drop wise
addition of hydrated metal chloride salts [Mn(II), Co(II), Ni(II),
OCH3
HO
O
O
HO
OCH3
NH2
N
O
H
N
H
N
H
CH3OH
+
Stirr, -5 to 0 o
4 h
C
H
NH2
NH2
2-ABH
3-methoxysalicylaldehyde
Hydrazone (H2L)
OCH3
HO
O
N
N
CH
O
H
3
H
Reflux, 3-4 h
N
H
H
OH
OCH3
1,2-dihydroquinazolinone [Ref. 27]
Scheme 1.

D.S. Badiger et al. / Journal of Molecular Structure 1019 (2012) 159–165
161
Transition metal complexes of H2L ligand were prepared by
treating methanolic solution of the ligand and an equimolar
amount of MCl2ÁnH2O. The complexes are stable and soluble in
DMF and DMSO solvents. Molar conductance values (Table 1) of
the complexes measured in DMF (10À3 M solutions) adequately
confirm the non-electrolytic nature of the complexes.
coordinating sites. Thus, the IR spectral data clearly reveals that
the ligand acts in both monobasic and dibasic tridentate nature.
3.3. NMR spectral studies
In order to validate the formation of H2L and to correlate the
chemical shifts of directly attached protons and carbon, we have
undertaken CAH COSY (HMQC) NMR spectral studies (Fig. 1). The
absence of contour around 65–75 ppm in the CAH COSY (HMQC)
NMR spectrum, which is characteristic for the sp3 hybridized car-
bon confirms the ligand to be a hydrazone product rather than
the cyclized 1,2-dihydroquinazolinone. 1H NMR spectrum of H2L
shows D2O exchangeable broad singlet’s at 11.84, 11.24 ppm inte-
grating for one proton each and 6.43 ppm integrating for two pro-
tons assigned to OH, NH and NH2 respectively. Appearance of NH2
protons, downfield to TMS, may be due to the presence of intra
molecular hydrogen bonding between NH2 proton and carbonyl
oxygen. Aromatic protons appear between 7.60–6.67 ppm inte-
grating for seven protons. The protons due to AOCH3 and AN@CH
have appeared as singlets at 3.81 and 8.58 ppm respectively. The
13C NMR spectrum of H2L shows fifteen signals corresponding to
the total number of carbon atoms present in H2L. Carbon signals
due to carbonyl carbon, azomethine carbon, methoxy carbon and
carbon attached to hydroxy group are observed at 163.12,
154.31, 55.75 and 149.12 ppm respectively. Thus, the 1H, 13C and
CAH COSY (HMQC) NMR prove the formation of ligand. The 1H
and 13C NMR spectra of H2L are given in Supplementary material
as S-1 and S-2 respectively.
3.2. Infrared spectral studies
The infrared spectrum of the ligand H2L is consistent with the
formation of hydrazone (Table 2). The band at 1645 cmÀ1 is due
to amide carbonyl and a sharp band at 1612 cmÀ1 corresponds to
an azomethine stretching frequency. This suggests the existence
of ligand in keto form in the solid state. The phenolic AOH and
ANH stretching vibrations appear as a strong envelope in the
range 3413–3273 cmÀ1. The OAH bending and CAO stretching
vibrations are found around 1352 and 1249 cmÀ1, respectively.
The absence of AOH stretching bands in IR spectra of all com-
plexes, clearly indicates the coordination of ligand in its deproto-
nated form. The decrease in
m(C@O) stretching band vibrations
upon coordination with Mn(II), Co(II), Ni(II), Zn(II) complexes in
the range 1631–1638 cmÀ1 clearly indicates its coordination in
keto form. This band is absent in Cu(II) complex and the appear-
ance of new band around 1589 cmÀ1, assigned to AC@NAN@CA
stretching vibration indicates that the ligand coordinates to Cu(II)
metal ion via enolization and deprotonation. The other non li-
gand band d(OH)Water appeared around 811 cmÀ1 in Cu(II) com-
plex suggests the coordination of water molecule to the metal
ion. Strong bands in the range 1577–1598 cmÀ1 for complexes
The absence of OH resonance in 1H NMR spectrum of Zn(II)
complex indicates the coordination of H2L via deprotonation of
phenolic OH. The resonance due to NH2 protons has shifted up
field, indicating the breakdown of intra molecular bonding be-
tween NH2 proton and carbonyl oxygen on complexation. Absence
of these NH2 protons after the D2O exchange in 1H NMR spectrum
of Zn(II) complex confirms the noninvolvement of NH2 protons in
coordination. In the 13C NMR spectrum of Zn(II) complex, signals
corresponding to carbonyl carbon and azomethine carbon have
shifted downfield by 1.05 and 2.03 ppm and thus confirms the
coordination of carbonyl oxygen and azomethine nitrogen to metal
ion.
are assigned to
the ligand revealing its coordination to the metal ion. The bands
due to
(NH2) remain unchanged at 3400 cmÀl (asymmetric) and
m(C@N) stretching which is low as compared with
m
3310 cmÀl (symmetric) in the ligand and complexes, showing its
non-participation in the coordination. The stretching vibrations
for AOCH3 groups appear at 2927–2838 cmÀ1. The above assign-
ments suggest that, in Mn(II), Co(II), Ni(II), Zn(II) complexes the
ligand has coordinated through carbonyl oxygen, azomethine
nitrogen and phenolic oxygen via deprotonation. For Cu(II) com-
plex, imino nitrogen and deprotonated enolic oxygens are the
Table 1
Analytical and physicochemical data of H2L and its metal complexes.
a
Compound (empirical formula)
M.W
Elemental analysis (%) found (calculated)
kmax (nm)
leff (BM)
(
KM
)
C
H
N
M
H2L (C15H15N3O3)
285.11
623.14
627.14
626.14
364.03
632.13
63.23 (63.15)
57.73 (57.79)
57.28 (57.42)
57.41 (57.44)
49.33 (49.38)
56.83 (56.84)
5.27 (5.30)
4.57 (4.53)
4.46 (4.50)
4.42 (4.50)
4.09 (4.14)
4.42 (4.45)
14.71 (14.73)
13.54 (13.48)
13.43 (13.39)
13.46 (13.40)
11.54 (11.52)
13.30 (13.26)
–
398, 690
343
364, 435, 538, 466
373, 447, 789, 634
380, 463, 600–840
468
–
–
[Mn(HL)2] (C30H28MnN6O6)
[Co(HL)2] (C30H28CoN6O6)
[Ni(HL)2] (C30H28N6NiO6)
[Cu(L)H2O] (C15H15CuN3O4)
[Zn(HL)2] (C30H28N6O6Zn)
8.78 (8.81)
9.37 (9.39)
9.31 (9.36)
17.37 (17.42)
10.37 (10.31)
5.89
4.78
2.89
1.66
–
1.61
0.35
2.48
3.63
0.55
a
X
À1 cm2 molÀ1
.
Table 2
Diagnostic IR bands (cmÀ1) in H2L and its metal complexes.
Compound
m(NH2)
m(NH)
m(OH)
m(OCH3)
m
(C@O)
m(C@N)
m(CAO)
d(OH)Water
m(AC@NAN@CA)
H2L
3403–3305s
3407–3304sh
3410b
3408–3305w
3400–3306w
3401–3310sh
3273w
3225w
n.o.
3213b
3185b
3228b
3413s
2927–2838s
2931–2840w
2937–2842s
2925–2833s
2928–2849w
2939–2845w
1645s
1631s
1634s
1638s
–
1612sh
1587sh
1590w
1598sh
1592w
1577sh
1249s
1243s
1253w
1257s
1251s
1259s
–
–
–
–
–
–
–
–
[Mn(HL)2]
[Co(HL)2]
[Ni(HL)2]
[Cu(L)H2O]
[Zn(HL)2]
–
–
–
–
–
811w
–
1589sh
–
1637s
b = broad, sh = sharp, s = strong, w = weak, n.o. = not observed.

162
D.S. Badiger et al. / Journal of Molecular Structure 1019 (2012) 159–165
Fig. 1. CAH COSY (HMQC) NMR spectrum of H2L.
3.4. Electronic spectral and magnetic moment studies
3.5. Mass spectral studies
Electronic spectrum of the ligand shows two prominent
absorptions at 398 and 690 nm. The band at 398 nm correspond
to the azomethine group and a broad band at 690 nm corre-
sponds to the n ? pà transition [31,32]. All the complexes show
The molecular ion peak, m/z = 308 (M + Na+) corresponds to the
molecular weight of the ligand H2L (Fig. 2). The FAB mass spectra of
Mn(II) and Cu(II) complex show molecular ion peaks with m/z val-
ues 623 and 364 corresponding to the molecular weight of the
respective complexes. These values are in good agreement with
the proposed composition for the complexes. Representative FAB
mass spectra of Cu(II) and Mn(II) complexes are shown in Figs. 3
and 4.
p
?
pà transition in the range 343–380 nm. In addition, they also
display bands at 435, 447, 463 and 468 nm in case of Co(II), Ni(II),
Cu(II) and Zn(II) complexes respectively and were assigned to
charge transfer transitions. A broad band around 600–840 nm
appearing as an envelope in the Cu(II) complex, was assigned to
E2g ? T2g transition. This may be due to the compression of the
3.6. Thermal studies
tetrahedron towards square planar geometry [33]. Ni(II) complex
exhibits two bands at 789 and 634 nm and are due to
Thermal studies of complexes have been undertaken to know
the presence/absence of coordinated/lattice held water molecules
and to confirm the composition as well. The thermogram of Cu(II)
complex show a weight loss of 4.93% (Calc. 4.95%) between the
temperature 50 and 250 °C indicating the presence of one coordi-
nated water molecule. Weight loss of 77.71% (Calc. 77.76%) around
250–510 °C corresponds to the loss of a ligand molecule. The pla-
teau obtained after heating above 510 °C corresponds to the forma-
tion of stable metal oxide, and the metal content calculated from
this residue (17.28%) tallies with the metal analysis (17.37%). In
case of Mn(II), Co(II), Ni(II) and Zn(II) complexes, no weight loss
was observed up to the temperature 260 °C and indicates the ab-
sence of any lattice held/coordinated solvent molecules. The
weight loss of 91.13%, 90.57%, 90.63% and 89.81% (Calc. 91.18%,
90.60%, 90.74% and 89.88%) respectively around 360–390 °C corre-
spond to the loss of two ligand molecules. Weight of the residue
obtained after heating the complex above 390 °C corresponds to
the formation of stable metal oxides. Thus, thermal studies support
the suggested composition for the complexes. As representatives,
thermograms of Cu(II) and Ni(II) complexes are given in Figs. 5
and 6 respectively.
3
3A2g(F) ? 3T2g(F)(
m
1) and A2g(F) ? 3T1g(F)(
m
2) transitions indicat-
ing an octahedral geometry [34]. The two distinct bands in re-
gions 538 and 466 for the Co(II) complex are assignable to spin
allowed transitions and are consistent with an octahedral geom-
etry [31].
Magnetic moments of paramagnetic complexes were recorded
in order to obtain the structural information of these complexes.
The magnetic moment value observed for Co(II) complex is 4.78
BM indicating that it has three unpaired electrons reveals an
high-spin octahedral geometry around Co(II) metal center. Higher
magnetic moment value observed for octahedral Co(II) complexes,
may be due to large orbital contribution of 4Tg ground term and
exhibit leff value in the range 4.6–5.6 BM [35,36]. The leff value
of 2.89 BM for Ni(II) complex also suggest an octahedral geometry
around the metal ion [37]. The magnetic moment value for Cu(II)
complex (1.66 BM) is well within the range corresponding to
spin-only value for one unpaired electron with a square planar
geometry. An effective magnetic moment of 5.89 was observed
for Mn(II) complex and is within the range for high spin octahedral
complexes [37].

D.S. Badiger et al. / Journal of Molecular Structure 1019 (2012) 159–165
163
Fig. 2. Mass spectrum of H2L.
Fig. 3. FAB Mass spectrum of Cu(II) complex.
Fig. 4. FAB Mass spectrum of Mn(II) complex.
3.7. EPR Spectral studies
3.8. Antimicrobial studies
The EPR spectra of the Cu(II) complex show a broad absorption
band, both at 300 and 77 K, which is isotropic due to the tumbling
motion of the molecules. The ‘giso’ values at 300 and 77 K are 2.016
and 2.012 respectively.
The in vitro antimicrobial activity of synthesized derivatives
was measured in comparison with ciprofloxacin and Fluconozole
(Table 3) as standards to reveal the potency of synthesized
derivatives. All the selected strains of bacteria and fungi namely

164
D.S. Badiger et al. / Journal of Molecular Structure 1019 (2012) 159–165
Fig. 5. Thermogram of Cu(II) complex.
Fig. 6. Thermogram of Ni(II) complex.
Table 3
H2N
In vitro antimicrobial activities of H2L and its metal complexes (MIC in
l
g/mL).
H
H2O
Cu
H
N
Compound
Bacteria
Fungi
OCH3
N
Gram positive
Gram negative
O
H
O
O
O
OCH3
SA
EF
EC
SM
CA
AN
M
N
H2L
50
25
100
50
25
25
50
25
12.5
3.125
12.5
6.25
1.6
6.25
–
0.006
OCH3
O
N
O
[Mn(HL)2]
[Co(HL)2]
[Ni(HL)2]
[Cu(L)H2O]
[Zn(HL)2]
Ciprofloxacin
Fluconozole
25
12.5
25
6.25
3.125
12.5
1.6
12.5
–
12.5
12.5
6.25
25
0.006
–
12.5
6.25
3.125
3.125
0.0125
–
N
NH2
25
3.125
12.5
6.25
0.0125
–
N
H
3.125
12.5
0.006
–
H
NH2
(a)
M = Mn(II), Co(II), Ni(II), Zn(II)
(b)
0.05
SA – Staphylococcus aureus; EF – Enterococcus faecalis; EC – Escherichia coli;
SM – Streptococcus mutans; CA – Candida albicans; AN – Aspergillus niger.
Fig. 7. Tentative structures for complexes.
Staphylococcus aureus (SA), Enterococcus faecalis (EF) (Gram posi-
tive), Escherichia coli (EC), Streptococcus mutans (SM) (Gram nega-
tive) and the fungal strains Candida albicans (CA) and Aspergillus
niger (AN) showed sensitivity to all the derivatives comparatively
at lower concentration (MIC 1.6–100 g/mL). Among the prepared
compounds, complexes (MIC 1.6–50 g/mL) have shown enhanced
l
l

D.S. Badiger et al. / Journal of Molecular Structure 1019 (2012) 159–165
165
activity compared to the ligand (MIC 12.5–100
quite comparable with standard drugs used.
In general, the activity shown by the compounds against all the
strains varies in the order CA, AN > EC, SM > SA, EF strains. Among
the complexes, Cu(II) complex has shown the maximum activity
against the tested bacterial strains and significant activity against
fungal strains (CA and AN) with an MIC value of 1.6 lg/mL. For
the other complexes, the activity is in the following order
Ni > Co > Zn > Mn complexes.
lg/mL) and are
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Methoxysalicylaldehyde-2-aminobenzoylhydrazone (H2L) was
isolated by the condensation of 2-ABH and 3-methoxysalicylalde-
hyde at À5 to 0 °C. The structure of H2L was confirmed by various
spectroscopic techniques. The coordination mode of H2L is well
established from elemental analysis, molar conductivity, IR, NMR,
mass, electronic spectral and thermal studies. These studies indi-
cate that the ligand essentially coordinates in tridentate fashion
with carbonyl oxygen, azomethine nitrogen and phenolic oxygen
via deprotonation except in Cu(II) complex where the ligand coor-
dinates via enolization and deprotonation of amide proton. The
octahedral geometry was assigned for Mn(II), Co(II), Ni(II) and
Zn(II) complexes and square planar for Cu(II) complex. Thus, the li-
gand acts both in monobasic as well as dibasic manner. The tenta-
tive structures for complexes are depicted in Fig. 7a and b.
The H2L and their complexes have been screened for their
in vitro antimicrobial activities. The activity of ligand was en-
hanced on complexation. The increase in activity of the metal com-
plexes was probably due to the greater lipophilic nature of the
complexes. Among the complexes Cu(II) complex has shown high-
est activity. The difference in activity among the tested compounds
may be attributed to the electrostatic nature of ligand and central
metal ion.
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Authors thank USIC, Karnatak University, Dharwad for spectral
facilities. Thanks are due to Department of Physics, Karnatak
University, Dharwad for magnetic moment measurements and
CDRI, Lucknow for providing FAB mass spectra.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2012.02.062.