Synthesis, spectroscopic evaluation, molecular modelling, thermal study and biological evaluation of manganese(II) complexes derived from bidentate N,O and N,S donor Schiff base ligands

Article abstract of DOI:10.1002/aoc.4149

Manganese(II) complexes having the general composition Mn(L)₂X₂ (where L?=?3-bromoacetophenone semicarbazone, 3-bromoacetophenone thiosemicarbazone, 1-tetralone semicarbazone, 1-tetralone thiosemicarbazone, flavanone semicarbazone or

Full text of DOI:10.1002/aoc.4149

Received: 12 July 2017
DOI: 10.1002/aoc.4149
Revised: 25 September 2017
Accepted: 26 September 2017
F U L L P A P E R
Synthesis, spectroscopic evaluation, molecular modelling,
thermal study and biological evaluation of manganese(II)
complexes derived from bidentate N,O and N,S donor Schiff
base ligands
1
2
2
1
3
Savita Bargujar
| Sulekh Chandra
| Reeta Chauhan | Hament K. Rajor | Jyoti Bhardwaj
1
Department of Chemistry, Ramjas
Manganese(II) complexes having the general composition Mn(L) X (where
2 2
College, University of Delhi, Delhi 110
0
2
07, India
L = 3‐bromoacetophenone semicarbazone, 3‐bromoacetophenone thiosemicar-
bazone, 1‐tetralone semicarbazone, 1‐tetralone thiosemicarbazone, flavanone
Department of Chemistry, Zakir Husain
Delhi College (Delhi University), JLN
Marg, New Delhi 110 002, India
−
2−
semicarbazone or flavanone thiosemicarbazone and X = Cl or ½SO4 ) were
3
synthesized. All the complexes were characterized using elemental analyses,
Division of Plant Exploration and
1
Germplasm Collection, NBPGR, Pusa,
New Delhi 110012, India
molar conductance and magnetic moment measurements, and mass,
H
NMR, infrared, electron paramagnetic resonance and electronic spectral stud-
ies. The molar conductance of the complexes in dimethylsulfoxide lies in the
Correspondence
Sulekh Chandra, Department of
Chemistry, Zakir Husain Delhi College
−
1
2
−1
range 10–20 Ω cm mol indicating their non‐electrolytic nature. All the
complexes show magnetic moments corresponding to five unpaired electrons.
The possible geometries of the complexes were assigned on the basis of electron
paramagnetic resonance, electronic and infrared spectral studies. Some of the
synthesized ligands and their complexes were screened for their antifungal
activities against fungi Macrophomina phaseolina, Botrytis cinerea and Phoma
glomerata using the food poison technique and their antibacterial activities
against Xanthomonas campestris pv. campestris and Ralstonia solanacearum
using the paper disc diffusion method. They showed appreciable activities.
(
Delhi University), JLN Marg, New Delhi
10 002, India.
1
Email: schandra_00@yahoo.com
Funding information
University Grants Commission, Grant/
Award Number: 8‐3(19)/2011 (MRP/
NRCB) dated 20/12/2011
KEYWORDS
antifungal and antibacterial activities, bidentate, manganese(II) complexes, semicarbazone,
thiosemicarbazone
[
4]
1
| INTRODUCTION
dyes, polymeric stabilizers and corrosion inhibitors. It
is also known that N and S donor atoms of Schiff bases
play an important role in coordination of metals at the
Schiff base ligands are known for their excellent
coordinating properties and hence exhibit variety in the
structure of their metal complexes. Schiff bases derived
from thiosemicarbazide and semicarbazide moieties are
an important class of compounds which have long
attracted attention, owing to their notable biological and
[5]
active sites of numerous metallobiomolecules. Com-
plexes of thiosemicarbazones with transition metals have
received considerable attention because of their wide
range of biological activities that include anti‐tumour,
[1]
antibacterial, fungicidal and anti‐carcinogenic proper-
[2,3]
[6–12]
pharmacological properties.
Schiff bases are also used
ties.
The well‐documented biological activities of
as catalysts, intermediates in organic synthesis, pigments,
several thiosemicarbazones often have been attributed to
Appl Organometal Chem. 2017;e4149.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 14
https://doi.org/10.1002/aoc.4149

2
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BARGUJAR ET AL.
their ability to form chelates with transition metal
[13,14]
ions.
Mn(II) coordination compounds are very abundant in
[
15,16]
soil
are formed by biodegradation of lignin.
found to be important for enzymatic systems with DNA.
and are essential for plant growth. In soil, these
[17]
Mn(II) was
[18]
DNA and RNA polymerases
catalyse the replication
and transcription of DNA and have a specific require-
[
19]
ments for Mn(II).
The complexes of Mn(II) play an
[20]
important role in catalytic properties.
In view of these applications, we have synthesized a
series Schiff bases derived from semicarbazide and
thiosemicarbazide moieties. These Schiff bases are further
complexed with Mn(II) metal ion. Further structure eluci-
dation and investigation of biological activities have been
performed. In this paper we report the synthesis, charac-
terization and biological evaluation of Mn(II) complexes
with six bidentate N,O and N,S donor Schiff base ligands
(Figure 1).
2
2
| EXPERIMENTAL
.1 | Materials and methods
All the chemicals used were of AR grade and procured
from Sigma Aldrich. Metal salts were purchased from E.
Merck and were used as received. Fungal species were
obtained from ITCC, Indian Agricultural Research
Institute, New Delhi, and Plant Quarantine Division of
National Bureau of Plant Genetic Resources, Pusa, New
Delhi. Antifungal activities and antibacterial activities
were evaluated using the food poison technique and disc
diffusion method, respectively.
FIGURE 1 Structures of ligands
2.2 | Synthesis of ligands
3 | ANALYSIS
All the ligands were prepared using methods reported
[21a]
3.1 | Physical measurements (Table 2)
earlier
and thiosemicarbazide with the corresponding ketones
Table 1).
by coupling of semicarbazide hydrochloride
Contents of C and H were analysed with a Carlo‐Erba
1106 elemental analyser. The nitrogen content of the
complexes was determined using Kjeldahl's method.
Molar conductance was measured with an ELICO
(
(
CM82T) conductivity bridge. Magnetic susceptibilities
2.3 | Preparation of complexes
were measured at room temperature with a Gouy bal-
A hot ethanolic (20 ml) solution of corresponding metal
salt (0.001 mol) was mixed with a hot ethanolic solution
ance using CuSO ⋅5H O as calibrant. Electron impact
4
2
mass spectra were recorded with a JEOL JMS‐DX‐303
[21b]
1
of the corresponding ligands (0.002 mol).
The mixture
mass spectrometer. Proton ( H) NMR spectra were
was refluxed at 80 ± 5 °C for 3–36 h. On cooling the
contents, the complexes were precipitated out. These were
filtered, washed with 50% ethanol and dried in vacuum
over P O .
recorded with a Hitachi FT‐NMR model R‐600 spec-
trometer using deuterated dimethylsulfoxide (DMSO‐
d6) as a solvent at 300 MHz. Chemical shifts were
measured relative to tetramethylesilane. Fourier
4
10

BARGUJAR ET AL.
3 of 14
1 6
TABLE 1 Schematic representation of synthesis of ligands L –L from respective ketones and semicarbazide and thiosemicarbazide
transform infrared (FT‐IR) spectra (CsI) were recorded
with an FT‐IR spectrum BX‐II spectrophotometer. The
electronic spectra were recorded in DMSO with a
Shimadzu UV mini‐1240 spectrophotometer. Electron
paramagnetic resonance (EPR) spectra of the Mn(II)
complexes were recorded as polycrystalline samples
All the characterization work was done at the
University Science Instrumentation Centre (USIC),
University of Delhi, except EPR and NMR studies which
were carried out at SAIF, IIT Bombay, Powai, Mumbai.
NMR studies were carried out at IIT Delhi.
at room temperature with an E ‐EPR spectrometer
4
3
.2 | Molecular modelling
using DPPH as the g‐marker. The molecular weights
of complexes were determined cryoscopically in
benzene.
HyperChem version 7.51 was used to perform molecular
modelling of the ligands and their corresponding metal

4
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BARGUJAR ET AL.
complexes. It was used to determine energy values and
other parameters like bond lengths and bond angles by
first molecular mechanics MM plus force field and then
semi‐empirical method PM3 (parametric 3). Each time, a
convergence limit was reached to 0.010 by setting up a
criterion of RMS gradient of 0.100 kcal Å mol and
Polak–Ribiere optimization algorithm. Hydrogen atoms
were omitted for clarity. Several cycles of energy minimi-
zation had to be carried out for each complex.
4 | RESULTS AND DISCUSSION
The molar conductance data (Table 2) of these complexes
in DMSO indicated that they are non‐electrolyte in
[
23]
nature.
Therefore, the complexes may be formulated
−
1
−1
2−
as [Mn(L) X ] (X = Clˉ or ½SO ), where L = L , L ,
2
2
4
1
2
L , L , L or L .
3
4
5
6
4.1 | FT‐IR spectra of ligands
The FT‐IR spectra of all the ligands showed bands in the
−
1
range 3292–3499 and 3142–3197 cm corresponding to
the ν (NH ) and ν (NH) stretching vibrations, respec-
3
.3 | In Vitro screening for antifungal
activity
as
2
as
tively, showing the presence of NH and NH groups in
2
The preliminary fungitoxicity screening of the compounds
at various concentrations was performed in vitro against
the fungi Macrophomina phaseolina, Botrytis cinerea and
the ligands.
The FT‐IR spectra of the semicarbazide‐based ligands
(
L , L and L ) also showed bands in the range 1690–1708
1
3
5
[
22]
Phoma glomerata using the food poison technique.
−1
and 1571–1583 cm which may be assigned to ν(C¼O)
Fungal culture of B. cinerea was obtained from Indian
Type Culture Collection, Indian Agricultural Research
Institute, New Delhi (ITCC no. 6192) and P. glomerata
was isolated from seeds of Impatiens glandulifera received
from the UK in the Plant Quarantine Division of National
Bureau of Plant Genetic Resources, New Delhi, by incuba-
tion on blotter. The mycelial growth of fungi (mm) in
each Petri plate was measured diametrically and growth
inhibition (I) was calculated using the formula
and ν(C¼N) stretching vibrations, respectively, while the
FT‐IR spectra of the thiosemicarbazide‐based ligands (L ,
2
L and L ) showed bands in the range 1585–1601 and
4
6
−1
7
62–852 cm which may be assigned to ν(C¼N) and
ν(C¼S) stretching vibrations, respectively. On complexa-
tion, the positions of bands due to ν(>C¼N) and
ν(>C¼O) in L , L and L and due to ν(>C¼N) and
1
3
5
−1
ν(>C¼S) in L , L and L are shifted by 10–60 cm . This
2
4
6
indicated that in the case of semicarbazone complexes the
coordination takes place through the nitrogen atoms of
imine group and oxygen atom of the >C¼O group, while
in the case of thiosemicarbazone complexes the coordina-
tion takes place through nitrogen atoms of the imine group
and sulfur atom of the >C¼S group. Hence all the ligands
C−T
I ð%Þ ¼
×100
C
where C is the radial diameter of colony of control and T
the radial diameter of colony of test compound.
[24,25]
behave as bidentate ones.
1
4
.2 | H NMR spectra of ligands
1
3
.4 | In Vitro screening for antibacterial
H NMR spectra of the ligands were recorded in DMSO‐d6
at 300 MHz (Figure 2). The non‐equivalent protons were
found to resonate at different values of applied field.
activity
The antibacterial activities of the ligands and their metal
complexes were evaluated against Xanthomonas
campestris pv. campestris and Ralstonia solanacearum
4
.2.1 | Ligand L1
[6]
using the paper disc diffusion method. Cultures of these
bacteria were obtained from the Indian Agricultural
Research Institute, New Delhi. Nutrient agar medium
was used. Filter paper disc treated with DMSO served as
control and with streptomycin used as a standard antibi-
otic. All determinations were made in duplicate for each
of the compounds. An average of two independent
readings for each compound was recorded. The Petri
plates were kept in a refrigerator for 24 h for pre‐diffusion.
Finally, Petri plates were incubated for 26–30 h at 28 ±
A singlet appeared at 9.415 ppm attributed to one proton
of NH, a singlet at 6.590 ppm was observed for two
protons of NH , a singlet at 2.173 ppm was due to 3H of
2
CH group and a multiplet observed between 7.305 and
3
8.072 ppm was attributed to aromatic protons.
4.2.2 | Ligand L2
A singlet appeared at 8.760 ppm for one proton of NH, a
singlet at 6.461 ppm was observed for two protons of
2
°C. The zone of inhibition was measured carefully.

BARGUJAR ET AL.
5 of 14
TABLE 2 Colour, molar conductance and elemental analyses of Mn(II) complexes
Elemental analysis: found (calcd)
Molecular
weight
Molar
conductance
Yield
(%)
Complex
Mn(L Cl
MnC18
Mn(L
MnC18
Mn(L
MnC18
Mn(L
MnC18
Mn(L
MnC22
Mn(L
MnC22
Mn(L
MnC22
Mn(L
MnC22
Mn(L
MnC32
Mn(L
MnC32
Mn(L
MnC32
Mn(L
MnC32
Color
M (%)
C (%)
H (%)
N (%)
[
1
)
2
2
]
Pink
635.9
660.9
667.9
692.9
531.9
556.9
563.9
588.9
687.9
712.9
719.9
744.9
10.7
12.1
10.8
10.1
12.5
13.1
11.3
15.4
14.8
15.2
13.6
14.9
62
61
57
59
52
54
53
56
52
54
54
55
8.57
33.90
3.08
13.09
(13.21)
12.67
H
20
N
6
O
2
Br
Br
2
2
Cl
S
2
(8.63)
8.27
(33.97)
32.59
(3.15)
2.94
[
1
)
2
SO
4
]
Pink
H
20
N
6
O
6
(8.31)
8.17
(32.68)
32.29
(3.03)
2.92
(12.71)
12.78
[
2
)
2
Cl
2
]
White
White
White
White
White
White
Yellow
White
White
White
H
20
N
6
Br
2
S
2
Cl
2
(8.22)
7.87
(32.34)
31.13
(2.99)
2.89
(12.86)
12.07
[
2
)
2
4
SO ]
H
20
N
6
O
4
2
6
Br
2
S
3
(7.92)
10.26
(10.32)
9.78
(31.17)
49.52
(2.81)
4.81
(12.12)
15.72
[
3
)
2
Cl
2
]
H
26
N
6
O
Cl
S
2
(49.63)
47.33
(4.89)
4.61
(15.79)
15.01
[
3
)
2
4
SO ]
H
26
N
6
O
(9.86)
9.71
(47.41)
46.78
(4.67)
4.54
(15.08)
14.87
[
4
)
2
Cl
2
]
H
26
N
6
S
2
Cl
2
(9.74)
9.25
(46.82)
44.79
(4.61)
4.37
(14.90)
14.23
[
4
)
2
4
SO ]
H
26
N
6
O
4
S
3
(9.32)
7.93
(44.83)
55.74
(4.42)
4.31
(14.26)
12.14
[
5
)
2
Cl
2
]
H
30
N
6
O
4
8
2
6
Cl
S
2
(7.98)
7.74
(55.82)
53.81
(4.36)
4.18
(12.21)
11.71
[
5
)
2
4
SO ]
H
30
N
6
O
(7.70)
7.59
(53.86)
53.31
(4.21)
4.13
(11.78)
11.62
[
6
)
2
Cl
2
]
H
30
N
6
O
S
S
2
3
Cl
2
(7.63)
7.32
(53.34)
51.58
(4.17)
4.07
(11.67)
11.21
[
6
)
2
4
SO ]
H
30
N
6
O
(7.37)
(51.55)
(4.03)
(11.28)
NH , a singlet at 1.650 ppm was due to 3H of CH group
and a multiplet observed between 7.266 and 7.860 ppm
was attributed to aromatic protons.
4.2.5 | Ligand L5
2
3
A singlet appeared at 9.511 ppm for one proton of NH, a
singlet at 6.616 ppm was observed for two protons of
NH2 and a multiplet observed between 6.950 and
8.226 ppm was attributed to aromatic protons.
4.2.3 | Ligand L3
A singlet appeared at 9.280 ppm for one proton of NH, a
singlet at 6.527 ppm was observed for two protons of
NH2 and a multiplet observed between 7.132 and
4
.2.6 | Ligand L6
A singlet appeared at 8.658 ppm for one proton of NH, a
singlet at 6.369 ppm was observed for two protons of
NH2 and a multiplet observed between 7.008 and
7
.244 ppm was attributed to aromatic protons.
7.975 ppm was attributed to aromatic protons.
4
.2.4 | Ligand L4
4
.3 | Electron impact mass spectra of
A singlet appeared at 10.139 ppm for one proton of NH, a
singlet at 6.005 ppm was observed for two protons of NH2
and a multiplet observed between 7.169 and 7.283 ppm
was attributed to aromatic protons.
ligands
The electron impact mass spectra of the ligands showed
molecular ion peaks at m/z = 255, 271, 203, 219, 281

6
of 14
BARGUJAR ET AL.
1
FIGURE 2 H NMR spectra of ligands
in DMSO‐d
6

BARGUJAR ET AL.
7 of 14
+
[23]
and 297 amu corresponding to species [C H N OBr] ,
non‐electrolyte behaviour.
The electronic spectra of
9
10 3
+
+
+
[
[
C H N SBr] ,
[C H N O] ,
[C H N S] ,
the complexes (Table 3) recorded at room temperature
in DMSO solution showed three bands in the range
9785–18 416 cm (ε = 38–44 l mol cm ), 17 825–23
9
10
3
11 13
3
11 13 3
+
+
C H N O ] and [C H N OS] , respectively, which
16
15
3
2
16 15 3
−1
−1
−1
confirmed the proposed formula of the ligands. These
ligands also showed peaks corresponding to various frag-
ments. The intensities of these peaks gave an indication
of the stabilities of the fragments.
−
1
−1
−1
052 cm
(ε = 73–86 l mol
cm ) and 22 272–27
−1
−1
−1
248 cm (ε = 136–149 l mol cm ), which may be
6
4
6
4
assigned to the transitions A → T (4G), A → T
1
g
2g
1g
2g
6
4
[29,30]
(
4D) and A1g → A (4F), respectively.
These bands
2g
are characteristic for six‐coordinated octahedral geometry
for these complexes.
4
.4 | Chloro complexes: [Mn(L) Cl ]
2 2
Magnetic moments of these complexes lie in the range
All the Mn(II) complexes show isotropic EPR spectra
(Figure 4), when recorded as polycrystalline samples.
The g‐tensor values were calculated using the Kneubuhl
method and the results are presented in Table 3. The
parameters B and C were calculated from the second
and third transitions because these transitions are free
5
.81–5.97 BM corresponding to five unpaired elec-
[26]
trons.
The electronic spectra of the complexes
(
9
9
(
(
Table 3) show four weak‐intensity bands in the range
−
1
−1
−1
681–19 201 cm (ε = 32–38 l mol cm ), 16 920–27
−
1
−1
−1
−1
−1
32 cm (ε = 41–45 l mol cm ), 21 413–30 487 cm
−
1
−1
ε = 75–88 l mo−l 1 cm ) and 27 173–34 965 cm
from the crystal field splitting and depend on B and C
−1
[31]
ε = 138–149 l mol cm ). These bands may be assigned
parameters.
The values of Dq were obtained with the
6
4
6
4
to A → T (4G), A → E , 4A (4G) (10B + 5C),
help of a curve of transition energies versus Dq, as given
1g
1g
1g
g
1g
6
4
6
4
[32]
A1g
→
Eg (4D) (17B + 5C) and A1g
→
T1g (4P)
by Orgel
using the energy due to the transition
[27]
6
4
(7B + 7C) transitions, respectively.
A1g → T (4G). Parameters B and C are linear combina-
1g
tions of certain Coulomb and exchange integral and are
generally treated as empirical parameters obtained from
the spectra of the free ions. Slater–Condon–Shortley
4
.5 | Sulfato complexes: [Mn(L) SO ]
2 4
Room temperature magnetic moments of these
complexes lie in the range 5.84–5.96 BM, these values
being in tune with a high‐spin configuration. The FT‐IR
spectra of the sulfato complexes show bands
repulsion parameters F and F4 are related to Racah
2
parameters B and C as: B = F − 5F and C = 35F .
2
4
4
The electron–electron repulsion in the complexes is
more than in the free ion, resulting in an increased
distance between electrons, and thus affecting the size of
the orbital. On increasing delocalization, the value of β
decreases to less than one for the complexes. The value
of β can be calculated from the nephelauxetic parameter
for the ligand (hx) and the nephelauxetic parameter for
characteristic of bidentate sulfate group where ν split
3
−
1
at 1113–1194, 1054–1089 and 1021–1031 cm while ν1
−
1
[28]
at 903–990 cm (Figure 3).
The molar conductance
measurements of the sulfato complexes recorded at room
temperature in DMSO solution were indicative of
TABLE 3 Magnetic moments, electronic spectral data and EPR spectral data of Mn(II) complexes
μ
eff
λ
max
Dq
(cm
B
(cm
C
(cm
F
(cm
2
F
4
−
1
−1
−1
−1
−1
−1
Complex
(BM) (cm
)
)
)
)
Β
)
(cm
)
hx
g
iso
[
[
[
[
[
[
[
[
[
[
[
[
Mn(L
Mn(L
Mn(L
Mn(L
Mn(L
Mn(L
Mn(L
Mn(L
Mn(L
Mn(L
Mn(L
Mn(L
1
1
2
2
3
3
4
4
5
5
6
6
)
)
)
)
)
)
)
)
)
)
)
)
2
2
2
2
2
2
2
2
2
2
2
2
Cl
2
]
5.91
5.84
5.81
5.92
5.97
5.93
5.96
5.87
5.89
5.92
5.99
5.96
10 121, 18 622, 23 095, 32 573
10 000, 17 825, 22 272, 30 864
18 622, 22 523, 26 525, 28 902
703
699
629
639
635
572
601
610
579
642
686
588
301
365
661
2446
2295
3361
2481
2371
2566
2100
2373
2662
4009
4856
3204
0.8
988
963
70
2.67 2.0018
2.74 2.0014
3.89 2.0019
3.36 2.0017
SO
4
]
0.8
66
96
Cl
2
]
0.7 1052
SO
4
]
9785, 18 418, 22 626, 29 674, 32 258 661
0.8
0.8
0.7
0.8
956
949
946
942
71
Cl
2
]
9980, 17 953, 22 222, 34 843
10 081, 18 622, 22 676, 34 602
9681, 16 920, 21 413, 34 965
10 021, 18 727, 23 529, 28 653
671
637
706
755
68
3.2
2.0021
SO
4
]
73
3.76 2.0022
2.62 2.0015
1.82 2.0018
Cl
2
]
60
SO
4
]
0.9 1025
68
Cl
2
]
9709, 19 193, 23 310, 27 173, 28 248 647
0.8
0.4
968
873
76
3.6
2.002
SO
4
]
18 330, 23 052, 25 157, 28 854
19 201, 27 932, 30 487, 28 916
18 416, 22 624, 27 248, 32 258
331
402
727
115
139
92
8.82 2.0015
7.65 2.0014
2.28 2.0016
Cl
2
]
0.5 1059
0.8 1118
4
SO ]

8
of 14
BARGUJAR ET AL.
1 2 4
FIGURE 3 FT‐IR spectrum of [Mn(L ) SO ]
2 2 4
FIGURE 4 EPR spectrum of [Mn(L ) SO ]
the metal ion (km) as (1 − β) = hx × km. The value of the
parameter hx for Mn(II) complexes was calculated using
the covalency contribution of Mn(II), while for the calcu-
lation of β, we used the numerical value of B for Mn(II)
free ion which is 786 cm . The observed values for β
and hx suggest that the complexes, reported here, have
FIGURE 5 Energy minimized structures of (a) Mn(L
b) Mn(L SO , (c) Mn(L Cl , (d) Mn(L SO , (e) Mn(L Cl
and (f) Mn(L SO . Cyan, carbon; blue, nitrogen; orange,
1 2 2
) Cl ,
(
1
)
2
4
2
)
2
2
2
)
2
4
3
)
2
2
3
)
2
4
−
1
manganese; yellow, sulfur; yellow in phenyl ring, bromine; red,
oxygen; grey, chlorine

BARGUJAR ET AL.
9 of 14

10 of 14
BARGUJAR ET AL.
FIGURE 6 Proposed structures of
complexes: (a) [Mn(L Cl ];
]; (c) [Mn(L
]; (e) [Mn(L
1
)
2
2
(
(
(
(
(
(
b) [Mn(L
1
)
)
2
SO
SO
4
2
)
2
Cl
Cl
Cl
Cl
Cl
2
];
];
];
d) [Mn(L
2
2
4
3
)
2
2
f) [Mn(L
h) [Mn(L
3
)
2
SO
SO
SO
SO
4
]; (g) [Mn(L
]; (i) [Mn(L
]; (k) [Mn(L
4
)
2
2
4
)
2
4
5
)
2
2
];
];
j) [Mn(L
l) [Mn(L
5
)
2
4
6
)
2
2
6
)
2
4
]

BARGUJAR ET AL.
11 of 14
[
33,34]
appreciable ionic character.
The calculated values of
coordinated water. Generally in lattice water is lost at
low temperature between 60 and 120 °C, whereas coordi-
nated water requires 120–250 °C. Absence of water mol-
ecules in the Mn(II) complexes was supported by the
differential thermal analysis (DTA) curves, which repre-
sented weight loss by endothermic bands. The DTA
curves of Mn(II) complexes have no endothermic bands
in the range 60–250 °C. Endothermic bands present at
high temperature in DTA curves of Mn(II) complexes
were due to loss of organic molecules and finally metal
the ligand field parameters are given in Table 3.
4
.6 | Molecular modelling
As single crystals of the metal complexes could not be
obtained, molecular modelling was done to obtain much
structural information. Geometry optimization was done
using HyperChem version 7.51
ligands and their complexes, i.e. [Mn(L )Cl ], [Mn(L )
[35]
for L , L3 and L5
1
1
2
1
[
36,37]
SO4], [Mn(L )Cl ], [Mn(L )SO ], [Mn(L )Cl ] and
may convert into its oxide.
In addition to endother-
3
2
3
4
5
2
[
Mn(L )SO ], while L , L and L complexes are not pre-
mic bands, the DTA curves of the complexes also show
exothermic bands. These bands appeared at high temper-
ature and represent phase transition, oxidation and/or
decomposition of the complex. For the thermograms of
the Mn(II) complexes attempts were not made to
characterize the products formed at the end of the first
stage. At the end of the second step, i.e. at 750 °C, stable
manganese oxide was formed. The complexes are found
to be thermally more stable than the corresponding
Schiff base ligands.
5
4
2
4
6
sented here as there is a sulfur atom in place of an
oxygen atom of the ligands.
In order to obtain energy values and other structural
details for these complexes we optimized the molecular
structure of the complexes. Energy minimization was
repeated several times by constraining the octahedral
geometry to determine the global minimum. The energy
minimized structures along with bond lengths are pre-
sented in Figure 5. The energy values and bond angles
are presented in Table 4.
On the basis of the above discussion, structures can be
proposed for the synthesized complexes, as shown in
Figure 6.
4
.7 | Thermal study
The thermal stability of the Mn(II) complexes was
4
.8 | In Vitro screening for antifungal
−
1
studied by controlling heating rates at 10 °C min under
nitrogen atmosphere. Thermograms of Mn(II) complexes
show two steps of decomposition and stable up to 250 °C,
indicating the absence of lattice water as well as
activity
The antifungal screening data showed that the
compounds exhibit antifungal properties, and it is also
TABLE 5 Fungal inhibition (%)
M. phaseolina
B. cinerea
P. glomerata
5
00 μg 800 μg 1000 μg 1500 μg 500 μg 800 μg 1000 μg 1500 μg 500 μg 800 μg 1000 μg 1500 μg
−
1
−1
−1
−1
−1
−1
−1
−1
−1
−1
−1
−1
Compound ml
ml
ml
ml
ml
ml
ml
ml
ml
ml
ml
ml
L
1
39
43
48
52
67
54
74
78
55
61
66
62.9
68
71
56
59
80
61
81
92
60
68
73
64
76
83
100
62
72
90
75
93
97
71
77
84
—
84
95
100
3.7
68
71
83
85
90
33
38
57
65
48
63
72
64
75
83
70.6
77
85
52
75
84
63
82
94
67
81
88
74
80
93
100
64
86
91
69
90
97
80
87
96
—
90
98
100
[
Mn(L
1
1
)
)
2
2
Cl
2
]
28
49
75
83
51
57
[
Mn(L
SO
4
] 62
94
100
70
a
L
2
45.83
67
5.4
74.7
88
—
39.04
59
[
Mn(L
Mn(L
2
)
)
2
2
Cl
2
]
34
55
51
62
68
—
70
81
26
95
100
72
100
100
84
[
2
SO
4
] 70
91
65
L
3
34
48
65
53
[
Mn(L
3
3
)
)
2
2
Cl
2
]
70
80
92
60
[
Mn(L
SO
4
] 55
77
89
99
69
L
4
—
74.7
81
76
—
—
[
Mn(L
4
4
)
)
2
2
Cl
2
]
53
84
88
67
[
Mn(L
SO
4
] 58
96
100
62
100
71
76
Bavistin
90
100
51
86
100
a
Not tested.

12 of 14
BARGUJAR ET AL.
FIGURE 7 Plates showing antifungal activities
FIGURE 8 Activities of various ligands
and complexes at different concentrations
against the fungus B. cinerea
2 4
TABLE 6 Antibacterial screening data for ligands L and L their chloro and sulfato complexes
Diameter of inhibition zone (mm)
X. campestris pv. campestris
R. solanacearum
−1
−1
−1
−1
−1
−1
Compound
250 μg ml
500 μg ml
1000 μg ml
250 μg ml
500 μg ml
1000 μg ml
s
0
0
0
0
0
0
[
Mn(L
2
2
)
)
2
2
Cl
2
]
0
18
0
0
20
0
0
24
0
0
17
0
0
19
0
0
[
Mn(L
SO
4
]
25.3
0
L
4
[
Mn(L
4
4
)
)
2
2
Cl
2
]
0
0
0
0
0
11
[
Mn(L
SO
4
]
17.5
19
0
20
22
0
22
26
0
14
26
0
16.5
30
0
19.05
a
Streptomycin (standard)
Solvent (DMSO)
—
0
a
Not tested.

BARGUJAR ET AL.
13 of 14
2
FIGURE 9 Activities of ligands L and
L and their chloride and sulfato
4
complexes against bacteria X. campestris
pv. campestris (Xc) and R. solanacearum
(
Rs)
important to note that some of the metal chelates exhibit
greater inhibitory effects than the parent ligands
[Mn(L ) SO ]>[Mn(L ) SO ]=[Mn(L ) Cl ]=[Mn(L ) C-
3
2
4
1 2
4
2 2
2
4 2
l ] > [Mn(L ) Cl ] ≈ [Mn(L ) Cl ] > L > L > L . In this
2
1 2
2
3 2
2
3
2
1
(
Table 5). The increased activity of the metal chelates
case the sulfato complexes with ligands L , L and L were
2 3 4
[38]
can be explained on the basis of chelation theory. Some
of the metal complexes exhibited greater activity than the
commercial fungicide Bavistin (Figure 7). The data also
indicated that the sulfato complexes of Mn(II) showed
better activities than the chloro complexes. Further, the
activities increased with increasing concentration of the
compounds under investigation.
found to be equally active as the other complexes and
ligands but all the test compounds showed less activity
than the commercial fungicide Bavistin.
4.9 | In Vitro screening for antibacterial
activity
For fungus M. phaseolena (at a concentration of
500 ppm) the activity order was: Bavistin (stan-
The data presented in Table 6 indicated that the sulfato
complexes of Mn(II) with ligands L2 and L4 showed
better activities against bacteria X. campestris pv.
campestris as well as R. solanacearum than the parent
ligands. The other ligands and complexes except
1
dard)>[Mn(L ) SO ]>[Mn(L ) SO ]>[Mn(L ) Cl ]>[M-
2
2
4
4 2
4
2 2
2
n(L ) SO ]>[Mn(L ) SO ]>[Mn(L ) Cl ]>L >[Mn(L ) C-
1
2
4
3 2
4
3 2
2
2
1 2
l ] > L > L . Here the sulfato complexes with ligand L
2
2
3
1
and L were found to be more active than the other com-
4
[
Mn(L ) Cl ] did not show any activity against these two
4 2 2
plexes and ligands, while all the test compounds showed
less activity than the commercial fungicide Bavistin.
The activity order for fungus B. cinerea (at a concen-
tration of 1500 ppm) was found to be:
bacterial pathogens. The complex [Mn(L ) SO ] was found
4
2
4
to be more active than [Mn(L ) SO ] against X. campestris
2
2
4
pv. campestris at all concentrations, i.e. 250, 500 and 1000
−1
μg ml , but streptomycin (standard) showed better activi-
[
Mn(L ) SO ]=[Mn(L ) Cl ]=[Mn(L ) SO ]=[Mn(L ) S-
1 2 4 2 2 2 2 2 4 4 2
ties than the complexes at all concentrations (Figure 9).
O ]≈[Mn(L ) SO ]>[Mn(L ) Cl ]>[Mn(L ) Cl ]>[Mn(-
4
3 2
4
3 2
2
1 2
2
L ) Cl ] > L > Bavistin (standard) ≈ L . Here all the test
4
2
2
1
2
compounds showed more activity than the commercial
fungicide Bavistin (Figure 8).
5 | CONCLUSIONS
The activity order for fungus P. glomerata (at a
concentration of 1500 ppm) was found to be: Bavistin
Different Mn(II) complexes having the general composition
Mn(L) X were synthesized and characterized using elemen-
2
2
(standard)
>
[Mn(L ) SO ]
≈
[Mn(L ) SO ]
≈
tal analyses, molar conductance and magnetic moment
4
2
4
2 2
4

14 of 14
BARGUJAR ET AL.
1
measurements, and mass, H NMR, FT‐IR, EPR and elec-
tronic spectral studies. The possible geometries of the com-
plexes were assigned on the basis of EPR, electronic and
FT‐IR spectral data. The synthesized ligands and their com-
plexes were screened for their antifungal activities against
the fungi M. phaseolina, B. cinerea and P. glomerata and
showed better results than the commercial fungicide Bavistin
against B. cinerea. The sulfato complexes of Mn(II) with
[15] Y. K. Sharma, M. Karkwal, S. Uma, R. Nagarajan, Polyhedron
2
009, 28, 205.
[16] M. Singh, V. Aggarwal, U. P. Singh, N. K. Singh, Polyhedron
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[18] A. S. Mildwan, L. A. Loeb, Adv. Inorg. Biochem. 1981, 3, 103.
[19] H. A. Ewais, J. Coord. Chem. 2009, 62, 940.
ligands L and L showed better activities against bacteria
2
4
[20] R. I. Kureshy, N. H. Khan, S. H. R. Abdi, P. Iyer, S. T. Patel,
X. campestris pv. campestris and R. solanacearum than the
Polyhedron 1999, 18, 177.
parent ligands.
[
[
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ACKNOWLEDGEMENTS
Spectrochim. Acta A 2013, 113, 164.
The authors are grateful to UGC, New Delhi for financial assis-
tance, IIT Bombay for recording EPR spectra and IIT Delhi for
recording NMR spectra. We are also grateful to Director,
NBPGR, Pusa campus, New Delhi for providing facilities to
conduct experiments for evaluating antimicrobial activities.
23] S. Chandra, S. Bargujar, R. Nirwal, N. Yadav, Spectrochim. Acta
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2005, 35, 391.
26] M. Tyagi, S. Chandra, P. Tyagi, Spectrochim. Acta A 2014, 117,
ORCID
1.
Savita Bargujar http://orcid.org/0000-0002-1224-8391
Sulekh Chandra http://orcid.org/0000-0002-5439-5330
27] A. B. P. Lever, Inorganic Electronic Spectroscopy, 1st ed.,
Elsevier, Amsterdam 1968 249.
28] A. B. P. Lever, Inorganic Electronic Spectroscopy, Elsevier,
Amsterdam 1984.
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