Synthesis, Crystal Structures, and Antibacterial Activity of Manganese(III) Complexes with Schiff Bases

Article abstract of DOI:10.1134/S1070328419080104

Abstract: Two new manganese(III) complexes, [MnL¹(EtOH)(Acac)] (I) and [MnL²(DMF)(Esal)] · H₂O (II), where L¹ and L² are the dianionic form of 2-[(2-hydroxyphenylimino)methyl]-6-methoxyphenol (H₂

Full text of DOI:10.1134/S1070328419080104

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2019, Vol. 45, No. 8, pp. 608–614. © Pleiades Publishing, Ltd., 2019.
Synthesis, Crystal Structures, and Antibacterial Activity
of Manganese(III) Complexes with Schiff Bases
X. W. Zhu*
Key Laboratory of Surface and Interface Science of Henan, School of Material and Chemical Engineering,
Zhengzhou University of Light Industry, Zhengzhou, 450002 P.R. China
*
e-mail: zhuxuewen2017@126.com
Received June 17, 2018; revised January 24, 2019; accepted January 28, 2019
1
2
Abstract—Two new manganese(III) complexes, [MnL (EtOH)(Acac)] (I) and [MnL (DMF)(Esal)] · H O
2
1
2
(
II), where L and L are the dianionic form of 2-[(2-hydroxyphenylimino)methyl]-6-methoxyphenol
1
2
(
H L ) and 4-chloro-2-[(3-ethoxy-2-hydroxybenzylidene)amino]phenol (H L ), respectively, Acac is
2
2
acetylacetone, Esal is 3-ethoxysalicylaldehyde, were prepared and characterized by IR and UV-Vis spectra,
as well as single crystal X-ray diffraction (CIF files CCDC nos. 1849854 (I) and 1849855 (II)). Complex I
crystallizes as the hexagonal space group P3 with unit cell dimensions a = b = 20.4482(9), c = 8.6952(7) Å,
3
V = 3148.6(3) Å , Z = 6, R = 0.0375, wR = 0.0957, GOOF = 1.050. Complex II crystallizes as the triclinic
1
2
space group P ¯1 with unit cell dimensions a = 8.1602(12), b = 11.5960(15), c = 15.3859(13) Å, α = 78.873(2)°,
3
β = 83.766(2)°, γ = 84.964(2)°, V = 1416.7(3) Å , Z = 2, R = 0.0733, wR = 0.1795, GOOF = 1.029. X-ray
1
2
analyses indicate that the complexes are manganese(III) species, with the Mn atoms in octahedral coordina-
tion. The Schiff bases and the complexes were evaluated for their antibacterial (Bacillus subtilis, Staphylococ-
cus aureus, Escherichia coli, and Pseudomonas fluorescence) activities.
Keywords: Schiff base, manganese complex, mononuclear complex, crystal structure, antibacterial activity
DOI: 10.1134/S1070328419080104
INTRODUCTION
described in [10]. Manganese complexes with Schiff
bases have been reported to have interesting antibacterial
Schiff bases are a kind of biological active com-
pound, which can be prepared by the condensation
activities [11–14]. In the present work, two new manga-
1
reaction of carbonyl-containing compounds with various nese(III) complexes, [MnL (EtOH)(Acac)] (I) and
2
1
2
amines. The compounds have attracted considerable
attention for their wide range of biological activities [1–
[
MnL (DMF)(Esal)] · H O (II), where L and L are the
2
dianionic form of 2-[(2-hydroxyphenylimino)methyl]-
7
]. It was reported that compounds bearing electron-
1
6
-methoxyphenol (H L ) and 4-chloro-2-[(3-ethoxy-2-
2
withdrawing groups such as halide can improve their
antimicrobial activities [8, 9]. Series of fluoro, chloro,
2
hydroxybenzylidene)amino]phenol (H L ), respectively,
2
bromo, and iodo-substituted compounds, and found Acac is acetylacetone, Esal is 3-ethoxysalicylaldehyde,
that they have significant antimicrobial activities were are reported.
Cl
N
N
OH
OH
OH
OH
OMe
OEt
1
2
(
H L )
(H L )
2
2
608

SYNTHESIS, CRYSTAL STRUCTURES, AND ANTIBACTERIAL ACTIVITY
609
EXPERIMENTAL
150.11, 147.17, 135.84, 127.30, 124.13, 123.08, 119.33,
119.10, 118.18, 117.76, 116.99, 64.09, 14.77.
Materials and methods. 3-Methoxysalicylalde-
hyde, 3-ethoxysalicylaldehyde, 2-aminophenol and For C H ClNO
15
14
3
MoO (Acac) were purchased from Sigma-Aldrich
2
2
Anal. calcd., %
Found, %
C, 61.76
C, 61.57
H, 4.84
H, 4.93
N, 4.80
N, 4.71
and used as received. All other reagents were of analyt-
ical reagent grade. Elemental analyses of C, H and N
were carried out in a Perkin-Elmer automated model
1
Synthesis of complex I. H L (0.01 mol, 2.43 g) and
2
2
400 Series II CHNS/O analyzer. FT-IR spectra were
Mn(Acac) (0.01 mol, 2.53 g) were mixed and dis-
obtained on a Perkin-Elmer 377 FT-IR spectrometer
2
solved in ethanol (50 mL). The mixture was stirred for
1 h to give brown solution. Single crystals of the com-
plex, suitable for X-ray diffraction, were grown from
the solution upon slowly evaporation for a few days.
The yield was 2.03 g (45%).
with samples prepared as KBr pellets. UV-Vis spectra
1
were obtained on a Lambda 900 spectrometer. H
13
NMR and C NMR data was recorded on a Bruker
5
00 MHz spectrometer. X-ray diffraction was carried
out on a Bruker APEX II CCD diffractometer.
–1
IR data (ν, cm ): 3434 (O–H), 1658 (C=O), 1596
1
Synthesis of H L . 3-Methoxysalicylaldehyde (C=N), 1257 (Ar–O). UV-Vis data (CH OH; λ
,
max
2
3
nm): 250, 430.
(
1
0.01 mol, 1.52 g) and 2-aminophenol (0.01 mol,
.10 g) were dissolved in ethanol (50 mL). The mixture
was stirred for 30 min to give red solution. Then, the
solvent was removed by distillation. The red solid was
recrystallized from ethanol to give the Schiff base Found, %
For C H NO Mn
21
24
6
Anal. calcd., %
C, 57.15
C, 57.33
H, 5.48
H, 5.57
N, 3.17
N, 3.08
1
H L . The yield was 2.12 g (87%).
2
2
Synthesis of complex II. H L (0.01 mol, 2.91 g) and
2
–1
IR data (ν, cm ): 3432 (O–H), 1628 (C=N), 1277
Mn(CH COO) · 4H O (0.01 mol, 2.45 g) were mixed
3
2
2
(
Ar–O). UV-Vis data (CH OH; λmax, nm): 267, 346,
3
and dissolved in ethanol (50 mL) and DMF (10 mL).
The mixture was stirred for 1 h to give yellow solution.
Single crystals of the complex, suitable for X-ray dif-
fraction, were grown from the solution upon slowly
evaporation for a few days. The yield was 2.33 g (38%).
1
4
51. H NMR (500 MHz; DMSO; δ, ppm): 14.02 (s.,
1
H, OH), 9.74 (s., 1H, OH), 8.95 (s., 1H, CH=N),
7
.37 (d., 1H, ArH), 7.20–7.07 (m., 3H, ArH), 6.98–
13
6
.84 (m., 3H, ArH), 3.81 (s., 3H, CH ). C NMR
3
–1
IR data (ν, cm ): 3357 (O–H), 1655 (C=O), 1598
(
126 MHz; DMSO; δ, ppm): 161.54, 151.80, 150.95,
48.15, 134.47, 127.98, 123.78, 119.57, 119.48, 119.22,
17.89, 116.49, 115.22, 55.85.
(
C=N), 1261 (Ar–O). UV-Vis data (CH OH; λ
,
max
3
1
nm): 245, 435.
1
For C H N O ClMn
27
30
2
8
For C H NO
3
14
13
Anal. calcd., %
Found, %
C, 53.96
C, 54.21
H, 5.03
H, 5.12
N, 4.66
N, 4.57
Anal. calcd., %
Found, %
C, 69.12
C, 68.95
H, 5.39
H, 5.50
N, 5.76
N, 5.83
X-ray crystallography. X-ray diffraction was carried
2
Synthesis of H L . 3-Ethoxysalicylaldehyde out at a Bruker APEX II CCD area diffractometer
2
equipped with MoK radiation (λ = 0.71073 Å). The
(
0.01 mol, 1.66 g) and 2-amino-4-chlorophenol
α
(
0.01 mol, 1.45 g) were dissolved in ethanol (50 mL). collected data were reduced with SAINT [15], and
multi-scan absorption correction was performed using
SADABS [16]. The structures of the complexes were
The mixture was stirred for 30 min to give red solution.
Then, the solvent was removed by distillation. The red
solid was recrystallized from ethanol to give the Schiff
2
solved by direct method and refined against F by full-
2
matrix least-squares method using SHELXTL [17].
All of the non-hydrogen atoms were refined aniso-
tropically. The ethanol hydrogen atom in complex I
was located from an electronic density map and
refined isotropically with O–H distance restrained to
base H L . The yield was 2.52 g (86%).
2
–1
IR data (ν, cm ): 3439 (O–H), 1625 (C=N), 1289
Ar–O). UV-Vis data (CH OH; λ , nm): 265, 300,
(
3
(
3
max
1
45, 450. H NMR (500 MHz; DMSO; δ, ppm): 13.70
0
.85(1) Å. The remaining hydrogen atoms were placed
s., 1H, OH), 10.01 (s., 1H, OH), 8.98 (s., 1H,
in calculated positions and constrained to ride on their
parent atoms. The crystallographic data and refine-
ment parameters for the complexes are listed in
Table 1. Selected bond lengths and angles are listed in
CH=N), 7.49 (s., 1H, ArH), 7.20–7.15 (m., 2H,
ArH), 7.09 (d., 1H, ArH), 6.97 (d., 1H, ArH), 6.86 (t.,
13
1
H, ArH), 4.07 (q., 2H, CH ), 1.34 (t., 3H, CH ). C
2 3
NMR (126 MHz; DMSO; δ, ppm): 162.96, 151.68, Table 2.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 45 No. 8 2019

6
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Table 1. Crystallographic data and structure refinement for I and II
Value
Parameter
I
II
Formula weight
441.35
Block/brown
298(2)
600.92
Block/brown
298(2)
Crystal shape/color
T, K
Crystal dimensions, mm
0.26 × 0.23 × 0.20
Hexagonal
P3
0.20 × 0.18 × 0.15
Triclinic
Crystal system
Space group
a, Å
P1
20.4482(9)
20.4482(9)
8.6952(7)
90
8.1602(12)
11.5960(15)
15.3859(13)
78.873(2)
83.766(2)
84.964(2)
1416.7(3)
b, Å
c, Å
α, deg
β, deg
90
γ, deg
V, Å3
120
3148.6(3)
Z
6
2
ρcalcd, g cm–3
1.397
1.409
μ (MoK ), mm–1
0.665
0.611
α
F(000)
1380
18857
624
8300
Measured reflections
Unique reflections (Rint)
Observed reflections
3909 (0.0415)
3001
5244 (0.0468)
2957
(I ≥ 2σ(I))
Min and max transmission
Parameters
0.8460 and 0.8784
0.8876 and 0.9140
267
1
359
0
Restraints
Goodness of fit on F2
R , wR (I ≥ 2σ(I))*
1
.050
1.029
0.0375, 0.0957
0.0549, 0.1127
0.0733, 0.1795
0.1389, 0.2147
1
2
R , wR (all data)*
1
2
2
2
2 2 1/2
*
R = F – F /F , wR = [∑ w(F – F )/∑ w(F ) ]
.
1
o
c
o
2
o
c
o
Supplementary material for structures has been method using the dye MTT [18]. A stock solution of
–
1
deposited with the Cambridge Crystallographic Data
Centre (CCDC nos. 1849854 (I) and 1849855 (II);
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk).
the compound (150 μg mL ) in DMSO was prepared
and graded quantities (75, 37.5, 18.8, 9.4, 4.7, 2.3, 1.2,
.59 μg mL ) were incorporated in specified quantity
of the corresponding sterilized liquid medium. A spec-
ified quantity of the medium containing the com-
pound was poured into micro-titration plates. Suspen-
sion of the microorganism was prepared to contain
–1
0
Antimicrobial assay. The antibacterial activities of
the compounds were tested against B. subtilis,
S. aureus, E. coli, and P. f luorescence using MH
5
–1
(
Mueller–Hinton) medium. The MIC values of the approximately 1.0 × 10 cfu mL and applied to
tested compounds were determined by a colorimetric microtitration plates with serially diluted compounds
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
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SYNTHESIS, CRYSTAL STRUCTURES, AND ANTIBACTERIAL ACTIVITY
611
Table 2. Selected bond distances (Å) and angles (deg) for complexes I and II
Bond
d, Å
Bond
d, Å
I
Mn(1)–O(1)
1.8949(18)
1.9217(17)
2.287(2)
Mn(1)–O(2)
1.9068(18)
2.1369(19)
1.993(2)
Mn(1)–O(4)
Mn(1)–O(6)
Mn(1)–O(5)
Mn(1)–N(1)
II
Mn(1)–O(1)
Mn(1)–O(4)
Mn(1)–O(7)
1.888(4)
2.245(4)
2.189(4)
Mn(1)–O(3)
Mn(1)–O(6)
Mn(1)–N(1)
1.912(3)
1.885(4)
1.994(4)
Angle
ω, deg
Angle
ω, deg
I
O(1)Mn(1)O(2)
O(2)Mn(1)O(4)
O(2)Mn(1)N(1)
O(1)Mn(1)O(5)
O(4)Mn(1)O(5)
O(1)Mn(1)O(6)
O(4)Mn(1)O(6)
O(5)Mn(1)O(6)
174.13(7)
90.75(8)
83.45(8)
90.36(9)
87.72(8)
93.89(8)
86.51(8)
173.10(7)
O(1)Mn(1)O(4)
O(1)Mn(1)N(1)
O(4)Mn(1)N(1)
O(2)Mn(1)O(5)
N(1)Mn(1)O(5)
O(2)Mn(1)O(6)
N(1)Mn(1)O(6)
94.89(8)
90.90(8)
174.19(9)
91.50(8)
92.78(8)
84.81(8)
92.59(8)
II
O(6)Mn(1)O(1)
O(1)Mn(1)O(3)
O(1)Mn(1)N(1)
O(6)Mn(1)O(7)
O(3)Mn(1)O(7)
O(6)Mn(1)O(4)
O(3)Mn(1)O(4)
O(7)Mn(1)O(4)
174.35(15)
92.53(16)
90.91(16)
90.51(17)
91.24(15)
87.98(17)
86.33(15)
177.06(16)
O(6)Mn(1)O(3)
O(6)Mn(1)N(1)
O(3)Mn(1)N(1)
O(1)Mn(1)O(7)
N(1)Mn(1)O(7)
O(1)Mn(1)O(4)
N(1)Mn(1)O(4)
93.09(16)
83.45(16)
175.45(16)
89.93(17)
91.73(15)
91.83(17)
90.59(15)
in DMSO to be tested and incubated at 37°C for 24 dye. After 12 h of incubation at room temperature, the
and 48 h for bacterial and fungi, respectively. Then the optical density was measured with a microplate reader
at 550 nm.
MIC values were visually determined on each of the
microtitration plates, 50 μL of PBS (phosphate buff-
–1
ered saline 0.01 mol L , pH 7.4) containing 2 mg of
MTT mL–1 was added to each well. Incubation was
continued at room temperature for 4–5 h. The content
of each well was removed and 100 μL of isopropanol
RESULTS AND DISCUSSION
1
2
The Schiff bases H L and H L were readily pre-
2
2
pared by the condensation reaction of 2-aminophenol
–1
containing 5% 1 mol L HCl was added to extract the with 3-methoxysalicylaldehyde and 2-amino-4-chlo-
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 45 No. 8 2019

6
12
ZHU
rophenol with 3-ethoxysalicylaldehyde, respectively. Table 3. Antibacterial activities of the Schiff bases and the
–
1
complexes (MIC, μg mL )
The manganese(III) complexes I and II were synthe-
sized by stirring equimolar quantities of the Schiff
bases with manganese salts and other materials at
room temperature. Single crystals of the complexes are
stable in air at ambient condition. The complexes are
soluble in methanol, ethanol, acetonitrile, DMSO,
DMF, but insoluble in water. The chemical formulae
Tested material B. subtilis S. aureus E. coli P. fluoresence
H2L1
18.8
37.5
18.8
>75
18.8
>75
>75
of the complexes have been confirmed by elemental H2L2
analyses, IR spectra, and single crystal X-ray diffrac-
9.4
tion.
I
4.7
1.2
2.3
9.4
4.7
4.7
37.5
9.4
>75
37.5
>75
In the spectra of the Schiff bases and the com-
plexes, the weak and broad bands in the range 3300–
II
–
1
3
500 cm are assigned to the vibration of O–H bonds.
–1
The bands at 1628 and 1625 cm characteristic of the
azomethine groups presented in the free Schiff bases,
Penicillin G
>75
–1
were shifted to lower wave numbers at 1596 cm for I
–1
and 1598 cm for II and indicated involvement of the
i
i
azomethine nitrogen atoms in coordination [19]. The O(6)···O(2) 2.749(2) Å, O(6)–H(6)···O(2) 169(4)°;
bands at 1277–12891 cm in the spectra of the symmetry code: 1 – x, 2 – y, 1 – z) to form dimers
–1
i
Schiff bases are ascribed to the phenolic C–O stretch- (Fig. 2a).
ing vibration. These bands are found at 1257 and
The molecular structure of complex II is shown in
–1
1
261 cm in the spectra of the complexes. These Fig. 1b. The asymmetric unit of the compound con-
changes suggest that the hydroxyl groups of the Schiff tains a mononuclear manganese(III) complex mole-
bases took part in the complex formation. Further evi- cule and a water molecule of crystallization. The Mn
dence of the bonding is also shown by the observation atom in the complex is in an octahedral coordination
that new bands in the IR spectra of the metal com- with the phenolate O and imine N atoms of the Schiff
–1
plexes appear at 430–680 cm assigned to Mn–N and base ligand and the phenolate O atom of Esal ligand
Mn–O stretching vibrations.
defining the equatorial plane and with the carbonyl O
atoms of the Esal ligand and DMF ligand occupying
the two axial positions. The Mn atom deviates from
the least-squares plane defined by the four equatorial
donor atoms by 0.029(3) Å. The Mn–O and Mn–N
coordinate bond lengths in the complex are compara-
ble to the corresponding values observed in other sim-
ilar manganese(III) complexes with Schiff bases [20–
Electronic absorption spectra of the Schiff bases
and the complexes were obtained in methanol solu-
tions. The electronic absorption spectra of the free
Schiff bases displayed three bands at about 265, 345
and 450 nm, which are assigned for the π → π* and
n → π* transitions, respectively. In the electronic
spectra of the complexes, the strong bands centered at
about 250 nm are attributed to the intra-ligand π → π*
absorption peak of the Schiff base ligands. The LMCT
and to some extent π → π* bands appear at about
2
4]. The dihedral angle between the two benzene rings
of the Schiff base ligand is 7.0(6)°. In the crystal struc-
ture of the complex, the water molecules are linked to
the manganese complex molecules through O–H···O
hydrogen bonds (O(8)–H(8B) 0.85, H(8B)···O(1)
430 nm.
The molecular structure of complex I is shown in
2
1
.53, O(8)···O(1) 3.106(7) Å, O(8)–H(8B)···O(1)
Fig. 1a. The Mn atom in the complex is in an octahe-
dral coordination with the phenolate O and imine N
atoms of the Schiff base ligand and one O atom of acac
ligand defining the equatorial plane, and with the
other O atom of Acac ligand and one ethanol O atom
occupying the two axial positions. The Mn atom devi-
ates from the least-squares plane defined by the four
equatorial donor atoms by 0.017(3) Å. The Mn–O and
Mn–N coordinate bond lengths in the complex are
comparable to the corresponding values observed in
other similar manganese(III) complexes with Schiff
bases [20–24]. The dihedral angle between the two
benzene rings of the Schiff base ligand is 8.1(5)°. In
the crystal structure of the complex, adjacent two
26(5)°; O(8)–H(8B) 0.85, H(8B)···O(2) 2.50,
O(8)···O(2) 2.991(9) Å, O(8)–H(8B)···O(2) 118(5)°;
O(8)–H(8A) 0.85, H(8A)···O(3) 2.50, O(8)···O(3)
2
.920(8) Å, O(8)–H(8A)···O(3) 112(5)°) (Fig. 2b).
The Schiff bases and the two manganese complexes
were screened for antibacterial activities against two
Gram (+) bacterial strains (Bacillus subtilis and Staph-
ylococcus aureus) and two Gram (–) bacterial strains
(
Escherichia coli and Pseudomonas fluorescence) by
MTT method. The MIC (minimum inhibitory con-
–1
centration, μg mL ) values of the compounds against
four bacteria are listed in Table 3. Penicillin G was
1
used as the standard drug. The Schiff base H L shows
2
complex molecules are linked by ethanol ligands medium activity against B. subtilis and S. aureus and
through intermolecular O–H···O hydrogen bonds no activity against E. coli and P. f luorescence. The
i
2
(
O(6)–H(6) 0.85(1), H(6)···O(2) 1.91(1) Å, Schiff base H L shows strong activity against B. subti-
2
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
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SYNTHESIS, CRYSTAL STRUCTURES, AND ANTIBACTERIAL ACTIVITY
а)
C(17)
613
(
C(19)
C(15)
C(18)
O(4)
Mn
C(16)
O(5)
O(2)
C(9)
O(3)
O(6)
C(14)
C(4)
C(10)
C(3)
O(1)
N(1)
C(2)
C(8)
C(11)
C(12)
C(20)
C(1)
C(7)
C(13)
C(6)
C(5)
C(21)
b)
(
C(25)
C(26)
C(4)
N(2)
C(3) C(2) O(6)
O(5)
C(24)
C(23)
O(7)
C(18)
O(3) C(17)
C(27)
Cl(1) C(5)
C(1)
Mn(1)
C(6)
C(19)
C(20)
C(22)
C(16)
O(1)
C(9)
N(1)
C(8)
C(21)
O(4)
C(7)
O(8)
O(2)
C(13)
C(10)
C(11)
C(15)
C(12)
C(14)
Fig. 1. A perspective view of the complex I (a) and II (b) with the atom labeling scheme. Thermal ellipsoids are drawn at the 30%
probability level.
lis, medium activity against S. aureus and E. coli and against E. coli and no activity against P. f luorescence.
2
no activity against P. f luorescence. In general, H L has Complex II has strong activity against B. subtilis,
2
1
stronger activities than H L . Complex I has strong S. aureus, and E. coli and weak activity against P. f luo-
2
activity against B. subtilis and S. aureus, weak activity rescence. Like the Schiff bases, complex II has stronger
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RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
Vol. 45
No. 8
2019