Synthesis, spectroscopic properties and biological evaluation of transition metal complexes of salicylhydrazone of anthranilhydrazide: X-ray crystal structure of copper complex

Article abstract of DOI:10.1016/j.ica.2011.11.063

The transition metal complexes of salicylhydrazone of anthranilhydrazide (H₂L) were synthesised. The structures of metal complexes were characterized by various spectroscopic [IR, NMR, UV-Vis, EPR], thermal and other physicochemical methods. Th

Full text of DOI:10.1016/j.ica.2011.11.063

Inorganica Chimica Acta 384 (2012) 197–203
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Synthesis, spectroscopic properties and biological evaluation of transition
metal complexes of salicylhydrazone of anthranilhydrazide: X-ray
crystal structure of copper complex
Dayananda S. Badiger a, Rekha S. Hunoor a, Basavaraj R. Patil a, Ramesh S. Vadavi a,
Chandrashekhar V. Mangannavar b, Iranna S. Muchchandi b, Yogesh P. Patil c,
Munirathinam Nethaji c, Kalagouda B. Gudasi a,
⇑
a Department of Chemistry, Karnatak University, Pavate Nagar, Dharwad 580003, Karnataka, India
b H.S.K. College of Pharmacy, Bagalkot 587101, Karnataka, India
c Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, 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 salicylhydrazone of anthranilhydrazide (H2L) were synthesised. The
structures of metal complexes were characterized by various spectroscopic [IR, NMR, UV–Vis, EPR], ther-
mal and other physicochemical methods. The single-crystal X-ray diffraction study of [Cu(HL)Cl]ꢀH2O
reveal its orthorhombic system with space group P2(1)2(1)2 and Z = 4. The copper center has a distorted
square planar geometry with ONO and Cl as the donor atoms. The ligand and its metal chelates have been
screened for their antimicrobial and anti-tubercular activities using serial dilution method. Metal com-
plexes in general have exhibited better antibacterial and antifungal activity than the free ligand and in
few cases better than the standard used. Among the bacterial strains used, the complexes are highly
potent against Gram-positive strains compared to Gram-negative. Anti-tubercular activity exhibited by
the Co(II) complex is comparable with the standard used.
Received 6 September 2011
Received in revised form 24 November 2011
Accepted 30 November 2011
Available online 8 December 2011
Keywords:
Hydrazone
Crystal structure
Metal complex
Anti-tubercular activity
Antimicrobial activity
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Schiff base ligands are well known for their wide range
of applications in pharmaceutical and industrial fields [1–3].
Moreover, the hydrazone group plays an important role for the
antimicrobial activity and possesses interesting antibacterial,
antifungal [4–6], anti-tubercular activities [7–12]. In addition,
their varied coordinating behavior makes them interesting
candidates towards metal-based drugs. Generally, the ligands
act synergistically with metals towards their biological activity
[12].
In the present work, an attempt is made to merge the comple-
mentary properties of salicylhydrazone of anthranilhydrazide
(H2L) [13] and transition metals. Here we report the synthesis,
characterization and comparative antimicrobial and anti-tubercu-
lar activities of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of
the title ligand. The structure of Cu(II) complex is further con-
firmed by single crystal X-ray diffractometry.
2.1. Physical measurements
Methyl anthranilate, hydrazine hydrate and salicylaldehyde
(s.d. Fine Chemicals, India) were of A.R. grade and used without
further purification. Solvents were distilled before use [14] and
hydrated metal chloride salts and anhydrous ZnCl2 were used as
received.
Elemental analyses were carried out on a Thermoquest CHN
analyser and metal complexes were analyzed for their metal con-
tent gravimetrically and volumetrically after decomposition with
a mixture of HCl and HClO4. The chloride content of the complexes
was determined gravimetrically as AgCl after decomposing the
complexes with conc. HNO3. The IR spectra were recorded on a
Nicolet 170 SX FT-IR spectrometer in 4000–400 cmꢁ1 region using
KBr discs. The NMR spectra were recorded on a Bruker Avance
400 MHz spectrometer operating at 400.23 MHz. Electronic spectra
were recorded on a CARY 50 Bio UV–Vis spectrophotometer in 200–
1100 nm range in DMF solutions. Magnetic susceptibility measure-
ments were carried out on a Gouy Balance using Hg[Co(SCN)4] as
the calibrant. Conductance measurements were made in DMF
⇑
Corresponding author. Tel.: +91 836 2215286x28; fax: +91 836 2771275.
E-mail address: kbgudasi@gmail.com (K.B. Gudasi).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.11.063

198
D.S. Badiger et al. / Inorganica Chimica Acta 384 (2012) 197–203
(10ꢁ3 M) solution using an ELICO-CM-82 conductivity bridge with
cell type CC-01 and cell constant 0.53. Thermal studies were carried
out in the temperature range 25–1000 °C using a TGA7 ANALYSER,
Perkin–Elmer, US, with a heating rate of 10 °C per min. The mass
spectrum was recorded on QTOF (Quadrupole Time-of-Flight) Mass
Spectrometer. The EPR spectrum of a polycrystalline Cu(II) complex
was recorded at room temperature and liquid nitrogen temperature
on a Varian E-4 X-band spectrometer using TCNE (tetracyanoethyl-
ene) as the calibrant. Melting points were determined in an open
capillary on a Gallenkamp melting point apparatus and are
uncorrected.
2.2. Synthesis of H2L
The H2L was prepared by condensation of salicylaldehyde and
anthranilhydrazide with a slight modification of the known litera-
ture procedure [13] (Scheme 1). Salicylaldehyde (3.05 g,
25.00 mmol) was gradually added over a cooled (ꢁ5 to 0 °C) solution
of anthranilhydrazide (3.83 g, 25.33 mmol) in methanol (15 mL).
The yellow solution was kept stirring at ꢁ5 to 0 °C for 3 h. The bright
yellow solid formed was filtered, washed thoroughly with cold
methanol and diethyl ether and dried in vacuo. Yield 85%. m.p.
165 °C.
Fig. 1. ORTEP of [Cu(HL)Cl]ꢀH2O with atom labeling scheme. The thermal ellipsoids
are drawn at 45% probability.
(k = 0.71073 Å) and scan mode in the range of 1.82 < h < 28.00°. A
total of 9366 (3501 independent, Rint = 0.0490) reflections were
measured. The structure was solved by direct methods and refined
by full-matrix least squares on F2. All of the non-hydrogen atoms
were refined with anisotropic temperature factors. The calculations
were performed with the SHELXL programme [15]. Structure solution
and refinement were based on 3501 independent reflections with
H2L: mass: 278; 1H NMR (DMSO-d6, d ppm): 6.46 (s, 2H, NH2),
6.57–7.58 (m, 8H, Ar–CH), 8.56 (s, 1H, CH@N), 10.18 (s, OH),
11.85 (s, 1H, NH); 13C NMR (DMSO-d6, d ppm): 165.89 (C@O),
158.47 (C@N), 155.59 (C–OH), 147.23, 133.45, 131.99, 130.61,
129.13, 120.15, 119.52, 119.18, 117.40, 115.51, 114.04.
I > 2r(I) and on 215 parameters gave R2 = 0.0401 (wR2 = 0.0864).
2.5. Antimicrobial activity
Peptone (5 g), sodium chloride (5 g), beef extract (1.5 g) were
suspended in 1000 mL distilled water and boiled to dissolve all
the ingredients. The pH of the solution at 25 °C was adjusted to
7.4 0.2 and sterilized by autoclaving at 15 lb pressure (121 °C)
for 15 min. One day prior to the test, bacterial and fungal strains
were made in the sterile nutrient broth and incubated at 37 °C
overnight. Sample solutions were prepared by dissolving 1 mg of
sample in 10 mL of 2% DMSO to give the concentration of
2.3. Synthesis of transition metal complexes [Mn(II), Co(II), Ni(II),
Cu(II), Zn(II)]
Hydrated metal chloride salts and anhydrous ZnCl2 (1 mmol)
were dissolved in a minimum amount of methanol and added
slowly to the methanolic solution (20 mL) of H2L (1 mmol) with
constant stirring at room temperature. The complexes of Mn(II),
Co(II), Ni(II) and Zn(II) got precipitated immediately on mixing
the two reactants. The products were filtered, washed several
times with methanol, ether and dried under vacuo. The Cu(II) com-
plex was obtained by reducing the volume of the reaction mixture.
The crystals suitable for X-ray diffraction study were obtained for
Cu(II) complex by slow evaporation of its methanolic solution.
Yield 65–88%.
100
drug) and Ketoconazole (antifungal drug) were prepared in 2%
DMSO to give a concentration of 100 g/mL. Serial broth microdi-
lg/mL. The standard solutions of Ciprofloxacin (antibacterial
l
lution was adopted as a reference method. Serial dilutions of test
compounds were made in broth, after which a standardized micro-
organism suspension was added (10 test tubes). Quantities of test
compounds were serially diluted to attain the final concentrations
[Zn(HL)Cl.H2O]: 1H NMR (DMSO-d6, d ppm): 6.43 (s, 2H, NH2),
6.56–7.81 (m, 8H, Ar–CH), 8.60 (s, 1H, CH@N), 11.89 (s, 1H, NH);
13C NMR (DMSO-d6, d ppm): 169.09 (C@O), 159.23 (C@N), 155.27
(C–OH), 147.22, 132.47, 131.34, 130.59, 128.93, 120.02, 119.88,
119.19, 117.43, 115.83, 114.37.
of 100–0.2 lg/mL. One of the test tubes was kept as control. Each of
the 10 test tubes was inoculated with a suspension of microorgan-
ism to be tested and incubated at 35 °C for 18 h. At the end of incu-
bation period, the tubes were visually examined for the turbidity.
Cloudiness in the test tubes indicated that microorganism growth
has not inhibited by the antibiotic contained in the medium at the
test concentration. The tests were run in triplicate.
2.4. The structure of [Cu(HL)Cl]ꢀH2O
The crystal structure of Cu(II) complex (Fig. 1) was determined
by X-ray diffraction studies using a single crystal having dimen-
sions of 0.45 ꢂ 0.33 ꢂ 0.32 mm3. Data were collected at 293 K on
2.6. Anti-tubercular activity
Test compounds were evaluated in triplicate for in vitro anti-
tubercular activity. The MIC’s were determined and interpreted
a ‘BRUKER SMART APEX CCD’ diffractometer with Mo K
a
radiation
O
HO
O
HO
NH2
H
O
N
N
H
N
H
CH3OH
+
Stirr, -5 to 0 °C, 3h
NH2
Anthranilhydrazide
H
1:1
NH2
Salicylhydrazone of anthranilhydrazide (H2L)
Salicylaldehyde
Scheme 1. Synthesis of H2L.

D.S. Badiger et al. / Inorganica Chimica Acta 384 (2012) 197–203
199
for Mycobacterium tuberculosis H37Rv according to the procedure of
the approved microdilution reference method of antimicrobial sus-
ceptibility testing [16]. Compounds were taken at concentrations
held water molecule is also present within the crystal unit. The
metal ion has square planer co-ordination with O(1), N(1) and
O(2) of the ligand and one chlorine as the coordinating sites. The
O(1)ꢁC(7) bond distance of 1.252(4) Å, corresponds to a carbon–
oxygen double bond [17] and confirms the existence of the ligand
in keto form in solid state.
On comparison with the free ligand [13], lengthening of
O(1)ꢁC(7) = 1.252(4), N(1)–C(8) = 1.287(4) Å and shortening of
O(2)–C(14) = 1.317(4) Å bond distance (Table 3) is observed on
coordination (Ligand: 1.223(6), 1.276(7) and 1.360(6), respec-
tively). The coordinating atoms, i.e., carbonyl oxygen, imine nitro-
gen, phenolic oxygen and chlorine are at distance of 1.968(2),
1.934(2), 1.891(2) and 2.226(1) Å respectively from the Cu(II)
metal center. These are well within the range of the similar re-
ported structures [18].
The square-planar geometry around the Cu(II) metal ion is
slightly distorted since the bond angles; N(1)–Cu(1)–O(1) =
80.3(1), N(1)–Cu(1)–O(2) = 92.1(1), Cl(1)–Cu(1)–O(1) = 92.84(7)
and Cl(1)–Cu(1)–O(2) = 94.56(8) are deviated from 90°. The related
trans angles, Cl(1)–Cu(1)–N(1) and O(1)–Cu(1)–O(2), i.e., 172.18
(8)°, 172.3(1)°, respectively which also deviate from the ideal bond
angle 180°, make a overall deviation from planarity.
The N(2) and N(3) form hydrogen bonds with O(3) of lattice
held water and O(1) of carbonyl oxygen respectively. The distances
N(2)–H(20)ꢀ ꢀ ꢀO(3) = 2.792 and N(3)–H(3B)ꢀ ꢀ ꢀO(1) = 2.073 Å indi-
cate the existence of strong intramolecular hydrogen bonding.
The molecular packing diagram (Fig. 3) reveals that Cl(1) and
O(2) of the molecule are involved in inter molecular hydrogen
bonding with O(3)–H (lattice held water) of other molecules in
the unit cell.
of 200, 100, 50, 25, 12.5 and 6.25
lg/mL in 2% DMF. M. tuberculosis
H
37Rv strain was used in Middle brook 7H-9 broth which was inoc-
ulated with standard as well as test compounds and incubated at
37 °C for 4 weeks. The bottles were inspected for growth twice a
week for a period of 3 weeks. Readings were taken at the end of
fourth week. The appearance of turbidity was considered as bacte-
rial growth and indicates resistance to the test compound. The
growth was confirmed by making a smear from each bottle and
performing a Ziehl-Neelsen staining. Test compounds were com-
pared to the reference drug Isoniazid.
As the compounds differ in their molecular weights, antimicro-
bial and anti-tubercular activity results are presented in
liter.
lM per
3. Results and discussion
3.1. Synthesis
The monobasic tridentate Schiff base was prepared as reported
earlier[13]. TheformationofH2LwasconfirmedbyIR,NMRandMass
spectral analysis (Molecular ion peak, m/z = 278 (M + Na)+) (Fig. 2).
All the complexes have been synthesized in moderate to good yields
(65–88%) by reacting the H2L and the hydrated metal(II) chlorides
(Mn, Co, Ni, Cu) and anhydrous ZnCl2 in methanol in 1:1 M ratio.
Complexes are insoluble in ethanol, methanol and dichloromethane
(except copper complex, which is soluble in methanol, chloroform
and dichloromethane), but soluble in DMF and DMSO. The analytical
data (Table 1) is satisfactory with the molecular formulae given. The
complexes are electrically non-conducting in DMF solution.
The planes of six (O(2), C(14), C(9), C(8), N(1) and Cu(1)) and five
(O(1), C(7), N(2), N(1) and Cu(1)) membered chelate rings form a
dihedral angle of 3.25° reveals that they are almost coplanar with
each other. However both chelate rings show a twisted conforma-
3.2. Description of [Cu(HL)Cl]ꢀH2O crystal structure
tion, with puckering parameters q2 = 0.0605 Å, q3 = 0.0198 Å, U2
=
8.48°, QT = 0.0637, spherical polar angles h2 = 71.86° for six mem-
bered ring and q2 = 0.0474 Å, U2 = ꢁ4.03° for five membered ring.
The ORTEP view of the [Cu(HL)Cl]ꢀH2O complex together with
atom numbering scheme is shown in Fig. 1 and the relevant crystal
parameters, bond distances and angles are collected in Tables 2
and 3.
3.3. IR spectral data
From the crystal structure, it is clear that the ligand H2L behaves
in a monobasic tridentate manner forming a six membered and an-
other five membered chelate ring involving Cu(II) Ion. A lattice
The comparison of IR spectra of ligand and its metal complexes
imply that the ligand, H2L, is monobasic tridentate in nature with
Fig. 2. Mass spectrum of H2L.

200
D.S. Badiger et al. / Inorganica Chimica Acta 384 (2012) 197–203
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
Cl
H2L (C14H13N3O2)
[Mn(HL)Cl.H2O] (C14H14ClN3O3Mn)
[Co(HL)2] (C28H24N6O4Co)
[Ni(HL)Cl.H2O] (C14H14ClN3O3Ni)
[Cu(HL)Cl].H2O (C14H14ClN3O3Cu)
[Zn(HL)Cl.H2O] (C14H14ClN3O3Zn)
255.27
362.67
567.46
366.42
371.27
373.12
65.83 (65.87)
46.39 (46.36)
59.23 (59.26)
45.85 (45.89)
45.24 (45.29)
45.13 (45.07)
5.03 (5.13)
3.82 (3.89)
4.28 (4.26)
3.86 (3.85)
3.77 (3.80)
3.76 (3.78)
16.41 (16.46)
11.54 (11.59)
14.87 (14.81)
14.54 (11.47)
11.36 (11.32)
11.30 (11.26)
–
–
230, 291, 336
–
513, 453
810, 520
555, 369
–
–
–
15.10 (15.15)
10.37 (10.39)
16.03 (16.02)
17.17 (17.12)
17.45 (17.53)
9.73 (9.78)
–
9.63 (9.68)
9.59 (9.55)
9.47 (9.50)
5.78
4.90
2.35
1.69
–
0.61
0.35
0.48
0.63
0.55
a
X
ꢁ1 cm2 molꢁ1
.
Table 2
Crystal structure refinement data of [Cu(HL)Cl]ꢀH2O.
Formula
Formula weight
T (K)
C14H14ClN3O3Cu
371.27
293
K
(Mo K
a
) (Å)
0.71073
System
Space group
orthorhombic
P2(1)2(1)2
Unit cell dimensions
a (Å)
b (Å)
c (Å)
15.850(3)
15.870(3)
5.9100(12)
90
a
(°)
b (°)
90
c
(°)
90
1486.6(5)
4
1.659
1.664
V (Å3)
Z
Dx (g cmꢁ3
)
Absorption coefficient (mmꢁ1
F(000)
)
756.0
Crystal size (mm)
h Range for data collection (°)
Index ranges
0.45 ꢂ 0.33 ꢂ 0.32
1.82–28.00
ꢁ20 6 h 6 20
ꢁ20 6 k 6 12
ꢁ7 6 l 6 7
9366
Fig. 3. Molecular packing diagram of [Cu(HL)Cl]ꢀH2O.
Reflections collected
3273 cmꢁ1 were assigned to phenolic OH and amide NH stretching
vibrations respectively.
The absence of band due to phenolic OH group in the spectra of
all metal complexes suggests the coordination of ligand to the
Independent reflections (Rint
Data/restraints/parameters
Goodness-of-fit on F2
)
3501 (0.0490)
3501/1/215
1.049
R1 = 0.0490
R2 = 0.0401
wR1 = 0.0896
wR2 = 0.0864
Final R indices [I > 2
r(I)]
metal via deprotonation. The bands due to m(C@N) and m(C@O) of
the free ligand have shifted to lower frequency on complexation,
indicating the involvement of azomethine nitrogen and carbonyl
oxygen in coordination [19]. The presence of asymmetric and
Table 3
symmetric modes of the m(NH2) bands in all the complexes clearly
Selected bond lengths (Å) and bond angles (°) for [Cu(HL)Cl]ꢀH2O.
indicates the noninvolvement of -NH2 in coordination [20]. The
appearance of non ligand band around 818, 811 and 819 cmꢁ1 in
Mn(II), Ni(II) and Zn(II) complexes respectively was assigned to
the d(O–H)Water which indicates the presence of coordinated water
molecule in respective complexes [21]. The stretching frequencies
of (O–H)Water could not be assigned due to their overlapping with
Bond lengths (Å)
Cu(1)–Cl(1)
Cu(1)–N(1)
Cu(1)–O(1)
Cu(1)–O(2)
N(1)–C(8)
2.226(1)
1.934(2)
1.968(2)
1.891(2)
1.287(4)
N(1)–N(2)
N(2)–C(7)
O(1)–C(7)
N(3)–C(2)
O(2)–C(14)
1.381(3)
1.342(4)
1.252(4)
1.338(5)
1.317(4)
m(N–H) band.
Bond angles (°)
Cu(1)–O(1)–C(7)
Cu(1)–O(2)–C(14)
N(1)–Cu(1)–O(1)
N(1)–Cu(1)–O(2)
O(1)–Cu(1)–O(2)
Cu(1)–N(1)–N(2)
Cu(1)–N(1)–C(8)
Cl(1)–Cu(1)–N(1)
Cl(1)–Cu1–O(1)
114.3(2)
127.8(2)
80.3(1)
Cl(1)–Cu(1)–O(2)
O(2)–C(14)–C(9)
N(1)–C(8)–C(9)
N(1)–N(2)–C(7)
N(2)–C(7)–O(1)
O(1)–C(7)–C(1)
N(3)–C(2)–C(1)
O(2)–C(14)–C(13)
N(3)–C(2)–C(3)
94.56(8)
124.6(3)
123.2(3)
114.5(2)
118.4(3)
122.2(3)
124.4(3)
118.8(3)
118.7(3)
3.4. Electronic spectra and magnetic moments
92.1(1)
172.3(1)
112.2(2)
129.1(2)
172.18(8)
92.84(7)
The electronic spectral data of the ligand exhibit three peaks in
the UV region. A peak appearing in the range of 230 nm is attrib-
uted to
The peak around 291 nm can be assigned to intra ligand
p ?
p⁄ transition of the benzenoid moiety of the ligand.
p
?
p⁄
transition. The other peak observed in the region of 336 nm is
attributed to n ? p⁄ electronic transitions [22,23].
carbonyl-oxygen, azomethine-nitrogen and phenolic-oxygen as
the coordination sites. The diagnostic IR-data is presented in Table
The appearance of two peaks at 555 and 369 nm in the elec-
tronic spectrum of Cu(II) complex is consistent with the square
planar geometry [24]. The electronic spectrum of Ni(II) complex
exhibits two peaks in the region at 810 and 520 nm. These transi-
tions indicate trigonal bipyramidal geometry around the Ni(II) ion
4. In the IR spectrum of H2L, the characteristic
(C@N) bands appear at 1657, 1614 and 1581 cmꢁ1, respectively.
A strong band at 3413 cmꢁ1 and comparatively weak band at
m(C@O), d(N–H),
m

D.S. Badiger et al. / Inorganica Chimica Acta 384 (2012) 197–203
201
Table 4
Diagnostic IR bands (cmꢁ1) in H2L and its metal complexes.
Compound
m(NH2)
m
(NH)
d(NH)
m
(OH)
m
(C@O)
m(C@N)
m
(C–O)
d(OH)Water
H2L
3371w, 3325sh
3372sh
3380b
3378b, 3335w
3456b, 3336w
3478w, 3372sh
3273w
3225w
n.o.
3213b
3185b
3228b
1614sh
1616sh
1619sh
1617b
1615sh
1617sh
3413s
1657s
1643s
1647s
1638s
1635s
1644s
1581sh
1546sh
1570w
1548sh
1574w
1547sh
1153s
1156s
1160w
1159s
1152s
1156s
–
[Mn(HL)ClꢀH2O]
–
–
–
–
–
818w
–
811w
–
[Co(HL)2]
[Ni(HL)ClꢀH2O]
[Cu(HL)Cl]ꢀH2O
[Zn(HL)ClꢀH2O]
819w
b = broad, sh = sharp, s = strong, w = weak, n.o. = not observed.
[25]. In the electronic spectrum of the Co(II) complex, two spin
allowed transitions at 513 and 453 nm were observed. These tran-
sitions are in consistent with an octahedral geometry around the
Co(II) ion [26]. The Mn(II) and Zn(II) complexes did not show any
d–d transitions.
experimental section. The carbonyl carbon and imine carbons in
Zn(II) complex have shifted downfield compared to its ligand,
confirming the coordination through carbonyl oxygen and imine
nitrogen.
The effective magnetic moments of 5.78 and 2.35 BM were
observed for Mn(II), Ni(II) complexes, respectively. These values
are in consistent with trigonal bipyramidal geometry [27,28]. An
effective magnetic moment of 1.69 BM is observed for Cu(II) com-
plex which is close to 1.73 BM as expected for discrete magneti-
cally non-coupled spin only value for Cu(II) ion [29]. The leff
value for both tetrahedral and high-spin octahedral Co(II) com-
plexes possess three unpaired electrons, but may be distinguished
by the magnitude of the deviation of leff value from the spin-only
value. The magnetic moment of tetrahedral Co(II) complex with an
orbitally non-generate ground term is increased above the spin
only value via contribution from higher orbitally degenerate terms
and occurs in the range 4.2–4.7 B.M. [30,31]. Octahedral Co(II)
complexes, however, maintain a large contribution due to 4Tg
ground term and exhibit leff value in the range 4.8–5.6 B.M.
[30,31]. The magnetic measurement on the complex reported here-
in is 4.90 B.M showing that it has three unpaired electrons indicat-
ing a high-spin octahedral configuration. From the electronic and
magnetic moment results, the trigonal bipyramidal geometry
was assined to Mn(II) and Ni(II) (Fig. 4a) complexes and octahedral
geometry was assigned for Co(II) complex (Fig. 4b).
3.6. EPR spectra
The EPR spectra of the Cu(II) complex both at 300 and 77 K
show a broad absorption band, which is isotropic due to the tum-
bling motion of the molecules. The ‘giso’ values at 300 and 77 K are
2.11 and 2.12, respectively.
3.7. Thermogravimetric analyses
The thermal decomposition pattern for Mn(II), Ni(II), and Zn(II)
complexes is almost same and have decomposed in three stages.
The first weight loss of 4.91%, 4.87% and 4.84% (calc. 4.96%, 4.91%
and 4.82%), respectively between 183 and 210 °C corresponds to
the loss of one coordinated water molecule. In the second stage be-
tween 211 and 470 °C, weight loss of about 79.85%, 79.13% and
77.60% (calc. 79.88%, 79.06% and 77.64%) corresponds to the com-
bined loss of one chlorine and the ligand molecule, respectively. A
plateau obtained above 470 °C, corresponds to the stable metal
oxides. In case of Cu(II) complex, the weight loss of 4.83% (calc.
4.85%) at about 90 °C corresponds to the loss of lattice held water
molecule while the 2nd and 3rd decomposition stages resembles
the previous complexes. In Co(II) complex, there was no weight
loss up to 310 °C which suggests the absence of water molecule
as well as chlorine atom. Decomposition occurs between 310 and
513 °C and corresponds to the weight loss of two ligand molecules
89.57% (calc. 89.61%). Above this temperature the formation of the
stable metal oxide occurs.
3.5. NMR spectra
The 1H NMR spectrum of the free ligand exhibit an OH (phenolic)
proton resonance at 10.18 ppm, an imine proton resonance at
8.56 ppm and aromatic proton resonances in the range 6.57–
7.58 ppm, respectively. On coordination, the signal due to OH pro-
ton disappears, indicating deprotonation of the phenolic OH and
subsequent coordination of the phenoxide oxygen to the Zn(II) me-
tal ion. Involvement of the imine nitrogen in coordination has
shifted the resonance signal of the imine proton by about 0.4 ppm
downfield. The peaks observed in 13C NMR spectra of ligand and
Zn(II) complex are in expected range and values are given in
3.8. Biological studies
3.8.1. Antimicrobial activity
All the synthesized compounds were screened for their in vitro
antimicrobial activity against three Gram-positive, three Gram-
negative bacterial strains and three fungal strains.
A comparative study of MIC (Minimum Inhibitory Concentra-
tions) values of the H2L and its complexes (Table 5) indicates that
the metal complexes generally have a better activity than the free
ligand. Such an increased activity of the metal complexes can be ex-
plained based on chelating theory [32] probably due to the greater
lipophilic nature of the complexes. The antimicrobial results evi-
dently show that the activity of the H2L has enhanced on coordina-
tion to the metal ions. This general trend is not observed in case of
Aspergillus fumigatus (AF) and Aspergillus niger (AN) strains.
The antimicrobial activity reveals that the compounds exhibited
better activity against the bacterial strains tested. The bacterium,
Staphylococcus aureus (SA) is found to be most susceptible one
while Klebsiella pneumoniae (KP) least susceptible against all the
compounds. Similarly, Candida albicans (CA) is most susceptible
among the fungal strains. From the in vitro antimicrobial assay, it
H2N
H
(a)
(b)
H
N
OH2
Cl
N
M
O
O
O
H
O
Co
N
O
H
N
O
N
H
N
H
NH2
M = Mn(II), Ni(II), Zn(II)
NH2
Fig. 4. Tentative structures for metal complexes.

202
D.S. Badiger et al. / Inorganica Chimica Acta 384 (2012) 197–203
Table 5
In vitro antimicrobial and anti-tubercular activities of the compounds.
Compound
MIC(lM)
Bacteria
Fungi
Mycobacterium tuberculosis
Gram Positive
Gram Negative
EF
PA
SA
EC
SM
KP
CA
AF
1.5
2.2
5.5
17.0
8.4
33.5
AN
6.2
34.4
2.8
4.3
67.3
4.2
H37Rv
H2L
6.2
2.2
0.3
1.0
0.5
0.5
0.7
48.9
2.2
1.4
2.1
67.3
1.0
6.2
2.2
0.3
8.5
4.3
0.5
9.4
48.9
1.1
0.7
4.3
4.3
1.0
1.2
12.2
0.5
22.0
34.1
1.0
195.8
68.9
88.1
136.4
269.3
134.0
2.4
24.4
4.4
0.3
0.5
0.5
1.0
391.7
137.8
44.0
136.4
134.6
67.0
[Mn(HL)ClꢀH2O]
[Co(HL)2]
[Ni(HL)ClꢀH2O]
[Cu(HL)Cl]ꢀH2O
[Zn(HL)ClꢀH2O]
Ciprofloxacin
Ketoconazole
Isoniazid
33.5
0.7
4.8
0.7
0.4
0.7
45.5
EF, Enterococcus faecalis; PA, Pseudomonas aerugenosa; SA, Staphylococcus aureus; EC, Escherichia coli; SM, Streptococcus mutans; KP, Klebsiella pneumoniae; CA, Candida albicans;
AF, Aspergillus fumigatus; AN, Aspergillus niger.
is thus found that the tested compounds possess excellent antimi-
crobial activities even when compared with the standards used.
susceptible strains. The activity of metal complexes are comparable
with the standard used and have shown comparatively good activ-
ity against Gram-positive bacteria. The anti-tubercular activity of
Co(II) complex against the M. tuberculosis H37Rv is equipotent to
the standard drug Isoniazid. From the results, it must be empha-
sized that the studied metal complexes were more active than the
free ligand. The difference in activity among the tested compounds
may be attributed to the electrostatic nature of ligand and central
metal ion and the lipophilicity of compounds.
3.8.2. Anti-tubercular activity
It is well known that hydroxy substituted Schiff bases [11] and
o-aminobezoic acid hydrazides have shown good anti-tubercular
activities [12]. Prompted by the promising antibacterial activity
exhibited by compounds in the present study, we have also under-
taken their anti-tubercular study against the M. tuberculosis H37Rv.
The MIC values of compounds were compared with Isoniazid, the
standard anti-tubercular drug and the results are summarized in
Table 5. The results show that the ligand has MIC value
Acknowledgments
391.7 lM/L, which is much higher than anticipated. This indicates
Authors thank USIC, Karnatak University, Dharwad for spectral
facilities. CCD-X-ray facility at the Department of Inorganic and
Physical Chemistry, Indian Institute of Science, Bangalore, India,
is gratefully acknowledged. Thanks are due to Department of Phys-
ics, Karnatak University, Dharwad for magnetic moment measure-
ments and IIT Bombay for EPR spectra.
its poor activity towards M. tuberculosis H37Rv. However, metal
conjugation has synergistically enhanced the anti-tubercular activ-
ity of the parent ligand [33,34]. The activity exhibited by the Co(II)
complex is equipotent to the standard used.
The results of biological study indicate that tested compounds
exhibit higher activity against Gram-positive bacteria than
Gram-negative bacteria and fungal strains. The nature of the cen-
tral metal ion and the ligand to metal stoichiometry affect the
MIC values. The activity of the complexes is found to be different
against different strains.
In conclusion, the antimicrobial and anti-tubercular results re-
veal that complexes possess higher activity compared to parent li-
gand. The MIC values obtained for anti-tubercular activity shows
that the Co(II) complex is more active among the tested com-
pounds against H37Rv.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2011.11.063.
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