Synthesis, crystal structure and antibacterial activity of a group of mononuclear manganese(II) Schiff base complexes

Article abstract of DOI:10.1016/j.poly.2010.12.012

Five mononuclear complexes of manganese(II) of a group of the general formula, [MnL(NCS)₂] where the Schiff base L = N,N′- bis[(pyridin-2-yl)ethylidene]ethane-1,2-diamine (L¹), (1); N,N′-bis[(pyridin-2-yl)benzylidene]ethane-1,2-diamine (L²), (2); N,N′-bis[(pyridin-2-yl)methylidene]propane-1,2-diamine (L ³), (3); N,N′-bis[(pyridin-2-yl)ethylidene]propane-1,2-diamine (L⁴), (4) and N,N′-bis[(pyridin-2-yl)benzylidene]propane-1,2- diamine (L⁵), (5) have been prepared. The syntheses have been achieved by reacting manganese chloride with the corresponding tetradentate Schiff bases in presence of thiocyanate in the molar ratio of 1:1:2. The complexes have been characterized by IR spectroscopy, elemental analysis and other physicochemical studies, including crystal structure determination of 1, 2 and 4. Structural studies reveal that the complexes 1, 2 and 4 adopt highly distorted octahedral geometry. The antibacterial activity of all the complexes and their respective Schiff bases has been tested against Gram(+) and Gram(-) bacteria.

Full text of DOI:10.1016/j.poly.2010.12.012

Polyhedron 30 (2011) 790–795
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, crystal structure and antibacterial activity of a group
of mononuclear manganese(II) Schiff base complexes
Santanu Mandal a, Tapan Kumar Karmakar b, Anupam Ghosh c, Michel Fleck d, Debasis Bandyopadhyay a,
⇑
a Department of Chemistry, Bankura Christian College, Bankura, West Bengal, India
b Department of Chemistry, D.N. College, Aurangabad, Murshidabad, West Bengal, India
c Department of Zoology, Bankura Christian College, Bankura, West Bengal, India
d Institute of Mineralogy and Crystallography Geozentrum, University of Vienna, Althanstrasse 14 A-1090 Vienna, Austria
a r t i c l e i n f o
a b s t r a c t
Article history:
Five mononuclear complexes of manganese(II) of a group of the general formula, [MnL(NCS)2] where the
Schiff base L = N,N0-bis[(pyridin-2-yl)ethylidene]ethane-1,2-diamine (L1), (1); N,N0-bis[(pyridin-2-yl)ben-
zylidene]ethane-1,2-diamine (L2), (2); N,N0-bis[(pyridin-2-yl)methylidene]propane-1,2-diamine (L3), (3);
N,N0-bis[(pyridin-2-yl)ethylidene]propane-1,2-diamine (L4), (4) and N,N0-bis[(pyridin-2-yl)benzyli-
dene]propane-1,2-diamine (L5), (5) have been prepared. The syntheses have been achieved by reacting
manganese chloride with the corresponding tetradentate Schiff bases in presence of thiocyanate in the
molar ratio of 1:1:2. The complexes have been characterized by IR spectroscopy, elemental analysis
and other physicochemical studies, including crystal structure determination of 1, 2 and 4. Structural
studies reveal that the complexes 1, 2 and 4 adopt highly distorted octahedral geometry. The antibacte-
rial activity of all the complexes and their respective Schiff bases has been tested against Gram(+) and
Gram(ꢀ) bacteria.
Received 17 September 2010
Accepted 10 December 2010
Available online 22 December 2010
Keywords:
Manganese(II)
Schiff base
Crystal structure
Antibacterial activity
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
In the present work, we describe the synthesis of a group of five
new mononuclear complexes of manganese(II), viz. [MnL1(NCS)2]
The coordination chemistry of manganese has long been a sub-
ject of considerable interest in inorganic biochemistry [1]. En-
hanced interest in synthesis and characterization of Schiff base
complexes of manganese in various oxidation states is due to their
important roles in metalloenzymes, redox and non-redox proteins
[2,3]. In addition to the biological importance, diverse catalytic and
magnetic properties of such compounds are now being explored
[4–6]. Designing a suitable polydentate Schiff base ligand to com-
bine with a metal ion along with pseudohalide anions has opened a
new era of synthesizing metal complexes of particular choice [7].
Although a plenty of Schiff bases have been extensively used to
synthesize complexes of manganese(II), simple mononuclear com-
plexes with Schiff bases derived from diamines like ethane-1,2-
diamine or propane-1,2-diamine and pyridine-2-al or its deriva-
tives are lacking. A report on the preparation and characterization
of two such complexes containing Schiff base of 1,3-diaminopro-
pane as the amine counterpart along with thiocyanate anion has
appeared earlier [8]. However, the investigation of biological prop-
erties of such Schiff bases or their complexes of Mn(II) have not re-
ceived adequate attention. Only a few reports on the antimicrobial
activity of Mn(II) complexes have been reported recently [9–13].
(1), [MnL2(NCS)2] (2), [MnL3(NCS)2] (3), [MnL4(NCS)2] (4) and
[MnL5(NCS)2] (5) containing the corresponding N-donor Schiff base
ligand (L = L1–L5). These ligands were prepared by the condensa-
tion of ethylenediamine with 2-acetyl pyridine (L1) or 2-benzoyl
pyridine (L2), 1,2-diaminopropane with pyridine 2-carboxaldehyde
(L3) or 2-acetyl pyridine (L4) or 2-benzoyl pyridine (L5). All the
complexes have been characterized by microanalytical, spectro-
scopic, magnetic and other physicochemical studies, including sin-
gle crystal X-ray structural analysis of 1, 2 and 4. The complexes
and the constituent Schiff base ligands have also been tested
in vitro to assess their antibacterial activities against some common
reference bacteria and the results were compared with similar
doses of commercial antibiotics viz. Gattifloxacin and Ciprofloxacin.
2. Experimental
2.1. Physical measurements
Elemental analyses for carbon, hydrogen and nitrogen were
carried out using a Perkin–Elmer 2400-II elemental analyzer.
Manganese content was determined using the titrimetric method.
Sulphur contents of 3 and 5 were determined gravimetrically
by converting it to barium sulphate. The infrared spectra were
⇑
Corresponding author. Tel.: +91 3242 250924.
E-mail address: dbbccchem@yahoo.co.in (D. Bandyopadhyay).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.12.012

S. Mandal et al. / Polyhedron 30 (2011) 790–795
791
recorded on a Perkin–Elmer FT-IR spectrophotometer with KBr
discs (4000–300 cmꢀ1). Room temperature solid phase magnetic
susceptibilities were measured at 298 K with a PAR 155 vibrating
sample magnetometer with Hg[Co(NCS)4] as the calibrant. The dia-
magnetic corrections were calculated from Pascal’s constants. Mo-
lar conductances of the complexes in dry DMF were measured
using a direct reading conductivity meter of Systronics (Type 304).
2934(m), 2058(s), 1643(s), 1590(s), 1442(m), 1348(m), 1318(m),
1258(w), 1105(m), 1008(m), 955(w), 804(m), 705(m), 632(w). KM
(DMF, Oꢀ1 cm2 molꢀ1): 7. leff (RT, BM): 5.92. Anal. Calc. for
C17H16MnN6S2 (3): C, 48.22; H, 3.81; N, 19.85; Mn, 12.97; S, 15.15.
Found: C, 48.35; H, 3.85; N, 19.82; Mn, 12.95; S, 15.22%. FTIR (KBr,
cmꢀ1): 2959(s), 2066(s), 1651(s), 1593(s), 1474(w), 1441(w),
1383(w), 1297(w), 1153(w), 1090(w), 1005(m), 889(w), 776(m),
703(s), 627(w). KM (DMF, Oꢀ1 cm2 molꢀ1): 6. leff (RT, BM): 5.93.
Anal. Calc. for C19H20MnN6S2 (4): C, 50.55; H, 4.47; N, 18.61; Mn,
12.17. Found: C, 50.35; H, 4.29; N, 18.62; Mn, 12.12%. FTIR (KBr,
cmꢀ1): 2917(m), 2339(m), 2067(s), 1642(s), 1590(s), 1476(w),
1434(s), 1379(s), 1248(w), 1139(w), 1007(m), 802(w), 781(s),
2.2. Materials
Reagent grade ethylenediamine, 1,2-diaminopropane, pyridine
2-carboxaldehyde, 2-acetyl pyridine, 2-benzoyl pyridine, ammo-
nium thiocyanate and manganese(II) chloride tetrahydrate were
purchased from reputed manufacturers and used as received. All
other chemicals and solvents were of analytical grade. The tetra-
dentate ligands N,N0-bis[(pyridin-2-yl)ethylidene]ethane-1,2-dia-
mine (L1), N,N0-bis[(pyridin-2-yl)benzylidene]ethane-1,2-diamine
(L2), N,N0-bis[(pyridin-2-yl)methylidene]propane-1,2-diamine (L3),
N,N0-bis[(pyridin-2-yl)ethylidene]propane-1,2-diamine (L4) and
N,N0-bis[(pyridin-2-yl)benzylidene]propane-1,2-diamine (L5) were
prepared by the condensation of the respective carbonyl com-
pounds and amines using similar methods as described earlier [14].
631(w). KM (DMF, Oꢀ1 cm2 molꢀ1): 5.
leff (RT, BM): 5.87. Anal. Calc.
for C29H24MnN6S2 (5): C, 60.51; H, 4.20; N, 14.60; Mn, 9.54; S, 11.14.
Found: C, 60.65; H, 4.15; N, 14.72; Mn, 9.59; S, 11.02%. FTIR (KBr,
cmꢀ1): 2971(s), 2350(m), 2063(s), 1628(s), 1589(s), 1466(w),
1440(s), 1328(m), 1256(m), 1155(w), 1007(m), 803(m), 751(m),
703(s), 664(w). KM (DMF, Oꢀ1 cm2 molꢀ1): 6.
leff (RT, BM): 5.91.
2.4. Crystal structure determination and refinement
Suitable single crystals of 1, 2 and 4 with dimensions of
0.06 ꢂ 0.04 ꢂ 0.03, 0.06 ꢂ 0.05 ꢂ 0.04 and 0.04 ꢂ 0.04 ꢂ 0.04
mm3, respectively, were collected on a Bruker APEX-II diffractom-
eter, equipped with CCD area detector and graphite-monochro-
R1
mated Mo K
the Bruker-Nonius program suite SAINT
a
radiation. The intensity data were processed with
PLUS and corrected for
N
N
-
R2
R2
Lorentz, polarization, background and absorption effects [15,16].
The structures were solved by direct methods and subsequent
Fourier and difference Fourier syntheses, followed by full-matrix
least-square refinements on F2 using the program SHELX [17]. Scat-
tering factors for neutral atoms were employed in the refinements.
In the refinement process of 1 and 2, all hydrogen atoms were
located from the difference Fourier maps and refined freely, except
for the methyl hydrogen atoms in 1 where displacement parame-
ters were constrained to 1.2 times that of the parent atoms. For
4, the hydrogen atoms were placed at geometrically calculated
positions and then treated as riding on their parent atoms, with
free refinement of the isotropic displacement parameters (except
for H atoms attached to C7, C9, C10 and C12 which were con-
strained like that in 1). All non-hydrogen atoms were refined
anisotropically and all hydrogen atoms isotropically. The final R-
N
N
Structure of L: R1 = H, R2 = CH3 for 1; R1 = H, R2 = C6H5 for 2;
R1 = CH3, R2 = H for 3; R1 = CH3, R2 = CH3 for 4 and R1 = CH3,
R2 = C6H5 for 5.
2.3. Synthesis of compounds 1–5
All the complexes 1–5 were prepared by a general method viz.
mixing MnCl2ꢁ4H2O, the respective Schiff base ligand and ammo-
nium thiocyanate in a 1:1:2 M ratio in methanol solvent followed
by slow evaporation. In case of compound 1, a methanolic solution
(10 ml) of Schiff base ligand, L1 (0.13 g, 0.5 mmol) was added drop-
values of the refinements for Fo > 4r(Fo) were 0.046, 0.047 and
0.064 respectively for 1, 2 and 4. A summary of the crystallographic
data, structural parameters and refinement details is presented in
Table 1.
wise to
a
methanolic solution (5 ml) of MnCl2ꢁ4H2O (0.1 g,
0.5 mmol) with constant stirring at room temperature. To the result-
ing light yellow solution, a methanolic solution (5 ml) of ammonium
thiocyanate (0.08 g, 1.0 mmol) was added slowly. Stirring was con-
tinued for 15 min and the solution was left for slow evaporation at
room temperature in a beaker open to the atmosphere. After 3–
5 days, yellow brown crystals of compound 1 appeared. The crystals
were collected by filtration, washed with methanol and finally dried.
Yield: 0.15 g (68%). The synthetic route described for 1 was followed
in the preparation of other four compounds 2, 3, 4 and 5, except that
10 ml methanolic solution of the Schiff base ligand, L2 (0.2 g,
0.5 mmol), L3 (0.13 g, 0.5 mmol), L4 (0.14 g, 0.5 mmol) and L5
(0.20 g, 0.5 mmol) respectively was used instead of L1 in each case.
Yields of 2, 3, 4 and 5 starting from 0.1 g of MnCl2ꢁ4H2O are 0.16 g
(57%), 0.13 g (61%), 0.15 g (66%) and 0.18 g (62%), respectively.
Although all the complexes are crystalline in nature, crystals suit-
able for X-ray structural analysis could only be collected for 1, 2
and 4. Anal. Calc. for C18H18MnN6S2 (1): C, 49.42; H, 4.15; N, 19.21;
Mn, 12.56. Found: C, 49.98; H, 4.18; N, 18.92; Mn, 12.44%. FTIR
2.5. Antimicrobial activity – minimum inhibitory concentration
Antibiograms of the compounds 1–5 and two reference com-
mercial antibiotics viz. Gattifloxacin and Ciprofloxacin (purchased
in powder form from Span Diagnostic Limited, Surat, India) were
prepared against two Gram positive bacteria, viz. Staphylococcus
aureus MTCC 2940 and Bacillus subtilis MTCC 441 and two Gram
negative bacteria viz. Pseudomonas aeruginosa MTCC 2453 and
Escherichia coli MTCC 739 using the agar well diffusion method
on nutrient agar medium with necessary modifications [18]. Dur-
ing the experiment, the test microbes were removed from the slant
aseptically with inoculating loops and transferred to separate test
tubes containing 5.0 ml of saline solution (0.85% NaCl). Sufficient
inoculum was then added to adjust the turbidity to 0.5 McFarland
(108 CFU mlꢀ1), as recorded in a digital colony counter. For each
bacterium, 1.0 ml of the suspension was added to 15–20 ml of
nutrient agar and transferred to an agar plate of 9.0 cm diameter.
The antibacterial activities of the compounds were tested after
cooling the inoculated agars at room temperature for 25 min. The
(KBr, cmꢀ1): KM (DMF, Oꢀ1 cm2 molꢀ1): 5.
leff (RT, BM): 5.88. Anal.
Calc. for C28H22MnN6S2 (2): C, 59.88; H, 3.95; N, 14.96; Mn, 9.78.
Found: C, 59.75; H, 4.02; N, 14.92; Mn, 9.69%. FTIR (KBr, cmꢀ1):

792
S. Mandal et al. / Polyhedron 30 (2011) 790–795
Table 1
Crystal data and structure refinement for 1, 2 and 4.
Parameters
Formula
1
2
4
C
18H18MnN6S2
C28H22MnN6S2
561.58
0.06 ꢂ 0.05 ꢂ 0.04
monoclinic
P21/c
8.1917(3)
16.7332(6)
20.6123(7)
90
98.252(2)
90
C19H20MnN6S2
451.47
Formula weight (g molꢀ1
Crystal size (mm3)
Crystal system
Space group
a (Å)
)
437.44
0.06 ꢂ 0.04 ꢂ 0.03
monoclinic
C2/c
12.549(1)
16.370(2)
9.944(1)
90
90.805(5)
90
2042.7(4)
4
0.05 ꢂ 0.04 ꢂ 0.04
triclinic
ꢀ
P1
8.658(1)
9.142(2)
14.582(3)
84.481(7)
79.330(6)
70.642(5)
1069.4(3)
1
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
2796.1(2)
4
1.334
Z
Dcalc (g cmꢀ3
)
1.422
0.865
1.402
0.829
l
(mmꢀ1
)
0.649
F(0 0 0)
900
1156
466
hkl range
T (K)
Reflections measured
Reflections unique
ꢀ18/17, 24, 14
293(2)
12580
ꢀ10/12, ꢀ24/21, ꢀ30/23
12, ꢀ13/12, ꢀ18/21
293(2)
293(2)
34740
9361
12416
6906
3432
Data with Fo > 4
r
(Fo)
2254
7285
4842
Rint
0.045
0.016
0.014
Parameters refined
147
422
0.0472
0.1344
0.057/1.117
1.05
289
0.0635
0.1847
0.071/0.882
1.021
Ra, Fo > 4
r
(Fo)
0.0459
0.1396
0.050/1.775
1.06
wRb
Weighting parameters a/b
S
D
q
/
max Dqmin (e Åꢀ3
)
0.42/ꢀ0.54
0.72/ꢀ0.62
0.65/ꢀ0.37
a
R =
wR = [
R
||Fo| ꢀ |Fc||
R|Fo|.
b
2
4
R
w(Fo ꢀ Fc2)2/
RwFo ] r
1/2, w = 1/[ 2(Fo2) + (a ꢂ P)2 + b ꢂ P], P = (Fo2 + 2Fc2)/3.
antibacterial activities of the five constituent Schiff bases L1–L5
were also evaluated during the same experiment. All the com-
pounds including the antibiotics were dissolved in dimethylsulph-
oxide (DMSO) to prepare five different concentrations (0.5, 1.0, 2.0,
3.0 and 4.0 mg mlꢀ1) for evaluation of limiting doses. Wells of
0.6 cm diameter were punched in the agar and filled with the test
compounds of varied concentrations and incubated for 24 h at
303 K for B. subtilis and at 310 K for all other bacteria. Antibacterial
activities were evaluated by measuring the inhibition zone diame-
ters (IZD) and their minimum inhibitory concentrations (MIC). The
MIC values of the test compounds were determined by serial dilu-
tion technique adopted by the National Committee for Clinical Lab-
oratory Standards [19]. Each of the above experiments was
repeated thrice along with a control set using DMSO.
the Mn(II) complexes. Although determination of structures of 3
and 5 was not possible due to non-availability of good quality sin-
gle crystals, all other studies support that these two complexes
also belong to the same series of Mn(II) complexes.
3.2. FTIR spectra
The infrared spectra of the compounds 1–5 are similar in some
respects as expected. They all show sharp and distinct absorption
bands in the region 2058–2070 cmꢀ1, assignable to the asymmetric
stretching vibrations of N-bonded terminal thiocyanate. Strong
absorption bands in the regions 1628–1651 and 1589–1593 exhib-
ited by 1–5 correspond to the mCN stretches of the ligands. Few
other characteristic vibrations of the metal-bound Schiff bases
are located in the range 600–1600 cmꢀ1. Thus, the infrared spectra
of the compounds are in good agreement [20] with their respective
structural features.
3. Results and discussion
3.1. Synthesis
3.3. Crystal structure of the complexes 1, 2 and 4
The one-pot reaction of the respective tetradentate Schiff base
ligand with manganese chloride and thiocyanate in the mole ratio
Mn(II):L:SCNꢀ = 1:1:2 in methanol solvent resulted in the forma-
tion of the complexes 1–5. All the complexes have been character-
ized by elemental analysis, IR spectroscopy, electrical conductivity
and magnetic susceptibility measurements as well as by single
crystal X-ray structural analysis for 1, 2 and 4. In DMF solvent,
all of these compounds behave as non-electrolytes as is evident
from their KM values (ca. 5–7 Oꢀ1 cm2 molꢀ1 respectively). Room
temperature magnetic susceptibility measurements indicate that
the complexes have magnetic moments (5.87–5.93 B.M.) close to
the spin-only value of Mn(II). This is indicative of the presence in
each, a high spin idealized t32ge2g, S = 5/2 electronic configuration
with five unpaired electrons as expected for a Mn(II) species [3].
All these results along with the X-ray structural analysis of 1, 2
and 4 are consistent with the proposed mononuclear formulae of
The molecular structures of the complexes 1, 2 and 4 are dis-
played in Fig. 1 and some selected bond lengths and angles are
listed in Table 2. These three compounds are structurally similar
as is evident from insignificant variations in their bond lengths
and angles. In each of these complexes, the central Mn(II) ion is a
member of three five-membered rings and adopts a highly dis-
torted octahedral (MnN6) geometry. The irregular hexacoordina-
tion environment around Mn(II) comprises four nitrogen atoms
(N1, N1, N2, N2 in 1 and N1, N2, N3, N4 in 2 and 4, respectively)
from the tetradentate Schiff base ligand and two nitrogen atoms
(N1A, N1A in 1 and N1A, N1B in 2 and 4 respectively) from the
thiocyanate anion.
The Mn–N distances ranging from 2.116 to 2.379 Å in 1, 2 and 4
are comparable to each other and with other analogous complexes
containing MnN6 chromophores [8]. The two Mn–NCS distances in

S. Mandal et al. / Polyhedron 30 (2011) 790–795
793
Fig. 1. Molecular structures of 1, 2 and 4 with atom numbering scheme [21] and 30% probability ellipsoids. For clarity, hydrogen labels are omitted.
each complex are considerably shorter than the Mn–N(L) counter-
parts due to the stronger ability of thiocyanate ion to bind the
Mn(II) ion in comparison to the neutral polydentate ligand [22].
In these molecules, the distortions in the coordination spheres
are too large as is evident from the wider ranges of the cisoid
and transoid angles. As noted earlier [23–25], these substantial dis-
tortions are due to the structural constraints imposed by the poly-
dentate ligand framework around the Mn(II) ion. In each of 1, 2 and
4, the Schiff base nitrogen atoms form a non-planar trapezoid
around the central Mn(II) ion and therefore, the thiocyanato nitro-
gens move far away from the apical positions to give rise to an
irregular coordination polyhedron.
Table 2
Selected bond lengths [Å] and bond angles [°] for compounds 1, 2 and 4.
1
2
4
Mn1–N1A 2.121(2)
Mn1–N1A 2.121(2)
Mn1–N2 2.266(2)
Mn1–N2 2.266(2)
Mn1–N1 2.379(2)
Mn1–N1 2.379(2)
Mn1–N1B 2.116(4)
Mn1–N1A 2.135(4)
Mn1–N3 2.268(5)
Mn1–N2 2.290(3)
Mn1–N4 2.364(3)
Mn1–N1 2.378(3)
Mn1–N1B 2.119(3)
Mn1–N1A 2.138(4)
Mn1–N3 2.262(3)
Mn1–N2 2.267(3)
Mn1–N4 2.346(2)
Mn1–N1 2.355(2)
3.4. Antibacterial activity
N1A–Mn1–N1A 128.30(9) N1B–Mn1–N1A 122.91(8) N1B–Mn1–N1A 152.23(1)
N1A–Mn1–N2 114.15(8) N1B–Mn1–N3 110.60(7) N1B–Mn1–N3 98.55(1)
N1A–Mn1–N2 106.84(8) N1A–Mn1–N3 117.42(7) N1A–Mn1–N3 103.67(1)
N1A–Mn1–N2 106.84(8) N1B–Mn1–N2 129.29(7) N1B–Mn1–N2 102.09(1)
N1A–Mn1–N2 114.15(8) N1A–Mn1–N2 94.44(7) N1A–Mn1–N2 100.18(1)
The antibacterial potentiality of all the tested compounds and
their MIC values against the four chosen bacteria are presented
in Tables 3 and 4, respectively. The results of the antibacterial
screening indicate that all the compounds exhibit broad spectrum
antibacterial activity against the reference bacteria. However, they
possess rather high MIC and low IZD values. The antibacterial
activity was found to be highest at a concentration of 4 mg mlꢀ1
for each of the tested compounds. Among all of the tested com-
pounds, the highest IZD and lowest MIC values of similar magni-
tude are observed in compounds 2 and 5. This suggests that
these two compounds are the most active against all the reference
bacteria. In this case, the corresponding Schiff bases L2 and L5,
however, lack any bacterial growth retardation activity. For the
N2–Mn1–N2 73.48(7)
N3–Mn1–N2 72.28(5)
N3–Mn1–N2 73.01(1)
N1A–Mn1–N1 84.53(8) N1B–Mn1–N4 83.50(7) N1B–Mn1–N4 86.27(1)
N1A–Mn1–N1 82.04(8) N1A–Mn1–N4 86.02(6) N1A–Mn1–N4 85.93(1)
N2–Mn1–N1 141.80(7) N2–Mn1–N4 136.72(5) N2–Mn1–N4 142.84(1)
N2–Mn1–N1 69.14(7)
N3–Mn1–N4 69.36(5)
N3–Mn1–N4 69.94(1)
N1A–Mn1–N1 82.04(8) N1B–Mn1–N1 82.91(7) N1B–Mn1–N1 83.32(1)
N1A–Mn1–N1 84.53(8) N1A–Mn1–N1 82.05(6) N1A–Mn1–N1 89.13(1)
N2–Mn1–N1 141.80(7) N3–Mn1–N1 137.43(5) N3–Mn1–N1 142.09(1)
N2–Mn1–N1 69.14(7)
N2–Mn1–N1 68.56(5)
N2–Mn1–N1 69.63(9)
N1–Mn1–N1 148.89(7) N4–Mn1–N1 153.07(5) N4–Mn1–N1 147.49(9)

794
S. Mandal et al. / Polyhedron 30 (2011) 790–795
Table 3
Antibacterial activities of 1–5 and their constituent Schiff bases compared to control (DMSO) and standard antibiotics.
Compounds
Dose (mg mlꢀ1
)
Inhibition zone diameter (mean standard error) in cm
Gram positive bacteria
Gram negative bacteria
S. aureus MTCC 2940
B. subtilis MTCC 441
P. aeruginosa MTCC 2453
E. coli MTCC 739
1
2
4
3
1.267 0.333
–
–
2.100 0.000
1.533 0.333
1.233 0.333
1.033 0.333
–
1.267 0.333
–
–
2.267 0.333
1.633 0.333
1.300 0.577
1.067 0.333
–
1.400 0.577
1.133 0.333
–
2.533 0.333
2.133 0.333
1.667 0.333
1.433 0.333
1.133 0.333
1.133 0.333
–
1.367 0.333
1.067 0.333
–
2.267 0.333
1.600 0.000
1.300 0.577
1.100 0.000
–
1.633 0.333
1.233 0.333
1.033 0.333
–
2, 1, 0.5
4
3
2
1
0.5
4
3
3
1.000 0.000
–
–
1.233 0.333
–
–
2
–
–
1, 0.5
–
–
4
5
4
3
1.133 0.333
1.067 0.333
–
2.400 0.577
1.700 0.577
1.433 0.333
1.167 0.333
–
1.367 0.333
1.133 0.333
–
1.000 0.000
–
1.967 0.333
1.667 0.333
1.300 0.577
1.033 0.333
–
1.633 0.333
1.133 0.333
–
1.167 0.333
1.000 0.000
–
2.233 0.333
1.633 0.333
1.433 0.333
1.133 0.333
–
1.533 0.333
1.133 0.333
–
1.067 0.333
–
1.267 0.333
1.167 0.333
–
1.233 0.333
1.033 0.333
–
2, 1, 0.5
4
3
2
1
0.5
4
3
2, 1, 0.5
4
3, 2, 1, 0.5
4
3
2
1
0.5
2.633 0.333
2.233 0.333
1.700 0.577
1.433 0.333
1.133 0.333
1.533 0.333
1.000 0.000
–
1.033 0.333
–
1.767 0.333
1.433 0.333
1.133 0.333
–
2.433 0.333
1.767 0.667
1.633 0.333
1.367 0.333
1.067 0.333
1.433 0.333
1.167 0.333
–
L1
L2
L3
1.033 0.333
–
1.667 0.333
1.200 0.577
0.967 0.667
–
1.967 0.667
1.667 0.333
1.200 0.577
1.033 0.333
–
1.533 0.333
1.167 0.333
–
–
–
L4
4
3
1.967 0.667
1.033 0.333
–
1.066 0.333
–
1.767 0.667
1.067 0.333
–
–
–
2, 1, 0.5
4
3, 2, 1, 0.5
L5
–
–
–
–
Gattifloxacin
4
3
2
1
0.5
4
3
2
1
3.133 0.333
2.633 0.577
2.233 0.333
1.867 0.667
1.433 0.667
2.667 0.577
2.433 0.577
2.133 0.667
1.833 0.667
1.533 0.333
–
3.433 0.333
3.133 0.333
2.333 0.333
2.167 0.667
1.333 0.333
2.833 0.333
2.333 0.333
2.167 0.333
1.833 0.333
1.433 0.667
–
3.333 0.333
3.233 0.577
2.433 0.667
1.933 0.667
1.433 0.333
2.333 0.333
1.967 0.667
1.633 0.333
1.433 0.333
1.133 0.667
–
3.667 0.333
3.133 0.577
2.633 0.333
2.433 0.667
1.633 0.333
2.667 0.333
2.133 0.333
1.967 0.333
1.433 0.667
1.133 0.333
–
Ciprofloxacin
0.5
4–0.5
Control (DMSO)
Table 4
MICa values (mg mlꢀ1) of 1–5, related Schiff bases and antibiotics.
4. Conclusion
Compounds
S. aureus
B. subtilis
P. aeruginosa
E. coli
Synthesis and characterization of a series of five new mononu-
clear Mn(II) complexes containing N-donor tetradentate Schiff
base ligands and terminal thiocyanate anion have been described
in this paper. Three representative complexes of the series have
been studied by X-ray diffraction and found to possess severely
distorted hexacoordination around the Mn(II) ions. The results of
the antibacterial screening of the test compounds indicate mild
to moderate bactericidal activities. In addition to the synthetic
and structural investigations, this study helps to evaluate the
potentiality and effectiveness of newer Schiff base complexes of
Mn(II) to use as antibacterial agents.
1 (L1)
<4 (<3)
<1 (<4)
<4 (<1)
<3 (<3)
<1 (>4)
<0.5
<4 (<3)
<1 (<4)
<4 (<2)
<3 (<3)
<1 (<4)
<0.5
<3 (<3)
<0.5 (<4)
<4 (<2)
<3 (<3)
<0.5 (>4)
<0.5
<3 (<3)
<1 (<4)
<2 (<1)
<3 (<3)
<0.5 (>4)
<0.5
2 (L2)
3 (L3)
4 (L4)
5 (L5)
Gattifloxacin
Ciprofloxacin
<0.5
<0.5
<0.5
<0.5
a
MIC was the lowest concentration of a compound extracted in DMSO that
exhibited no visual growth of the organisms during culture.
complexes 1, 3 and 4, the MIC values are higher and the metal
complexes exhibit less antibacterial activity than their respective
Schiff bases unlike 2 and 5. Among all the bacteria, P. aeruginosa
is found to be the most susceptible one against all the compounds
except 3. From the in vitro antibacterial assay, it is thus found that
all the tested compounds possess antibacterial activities to some
extent, but the activities are much lower than those of the tested
commercial antibiotics at similar concentrations.
Acknowledgements
Our thanks are extended to Rt. Revd. Dr. P.K. Dutta (Chairman of
Governing Body), Dr. R.N. Bajpai (Principal) and Dr. S.K. Roy (Head,
Chemistry Department) of Bankura Christian College for their

S. Mandal et al. / Polyhedron 30 (2011) 790–795
795
[7] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic
Chemistry, sixth ed., John Wiley and Sons, Inc., New York, 1999.
[8] T.K. Karmakar, B.K. Ghosh, S.K. Chandra, Ind. J. Chem. 45A (2006) 1121.
[9] P. Dorkov, I.N. Pantcheva, W.S. Sheldrick, H. Mayer-Figge, R. Petrova, M.
Mitewa, J. Inorg. Biochem. 102 (2008) 26.
[10] M. Geraghty, J.F. Cronin, M. Devereux, M. McCann, BioMetals 13 (2000) 1.
[11] M. Patil, R. Hunoor, K. Gudasi, Eur. J. Med. Chem. 45 (2010) 2981.
[12] G.G. Mohamed, M.M. Omar, A.A. Ibrahim, Spectrochim. Acta A, Mol. Biomol.
Spectrosc. 75 (2010) 678.
constant encouragement and valuable suggestions in doing the
work. We also thank Mr. Kalyan Dana for his assistance.
Appendix A. Supplementary data
CCDC 763039, 763038 and 781567 contains the supplementary
crystallographic data for 1, 2 and 4. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
[13] N. Nishat, Rahis-Ud-Din, S. Dhyani, J. Coord. Chem. 62 (2009) 996.
[14] T.K. Karmakar, B.K. Ghosh, A. Usman, H.-K. Fun, E. Rivière, T. Mallah, G. Aromi,
S.K. Chandra, Inorg. Chem. 44 (2005) 2391.
[15] Bruker-Nonius, Apex-II and SAINT
Madison, Wisconsin, USA, 2004.
-PLUS (Version 7.06a), Bruker AXS Inc.,
[16] Z. Otwinowski, W. Minor, Methods Enzymol. A 276 (1997) 307.
[17] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[18] C. Perez, M. Paul, P. Bazerque, Acta Biol. Med. Exp. 15 (1990) 113.
[19] National Committee for Clinical Laboratory Standards, Performance Standards
for Antimicrobial Disc Susceptibility Tests. Approved Standard NCCLS
Publications. M2-A5, Villanova, 1993.
[20] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, fourth ed., Wiley Interscience, New York, 1986.
[21] G. Bergerhoff, M. Berndt, K. Brandenburg, J. Res. NIST 101 (1997) 221.
[22] S. Deoghoria, G. Mostafa, T.H. Lu, S.K. Chandra, Ind. J. Chem. 43A (2004) 329.
[23] S. Collinson, N.W. Alcock, A. Raghunathan, P.K. Kahol, D.H. Busch, Inorg. Chem.
39 (2000) 757.
[24] M.G. Barandika, M.L. Hernandez-Pino, M.K. Urtiaga, R. Cortes, L. Lezama, M.I.
Arriortua, T. Rojo, J. Chem. Soc., Dalton Trans. (2000) 1469.
References
[1] V.L. Pecoraro, W.-Y. Hsieh, in: A. Sigel, H. Sigel (Eds.), Metal Ions in Biological
Systems: Manganese and its Role in Biological Processes, vol. 37, Marcel
Dekker, New York, 2000, pp. 431–444.
[2] J.J.R. Fraústo da Silva, R.J.P. Williams, The Biological Chemistry of the Elements,
Oxford University Press, 2001.
[3] V.L. Pecoraro (Ed.), Manganese Redox Enzymes, VCH, New York, 1992.
[4] E.M. McGarrigle, D.G. Gilheany, Chem. Rev. 105 (5) (2005) 1563.
[5] Reviews: O. Kahn, Molecular Magnetism, VCH, Weinheim, Germany, 1993.
[6] S. Mandal, A.K. Rout, M. Fleck, G. Pilet, J. Ribas, D. Bandyopadhyay, Inorg. Chim.
Acta 363 (2010) 2250.
[25] E.V. Rybak-Akimova, N.W. Alcock, D.H. Busch, Inorg. Chem. 37 (1998) 1563.