Synthesis, Crystal Structure, and Antimicrobial Activity of Manganese(III) and Iron(III) Complexes Derived from Similar bis-Schiff Bases

Article abstract of DOI:10.1080/15533174.2015.1137068

A new manganese(III) complex, [Mn(L¹)(CH₃OH)(dca)] 1, and a new iron(III) complex, [Fe(L²)(CH₃OH)(NCS)] 2, for which dca is dicyanoamide anion, and L¹ and L² are the dianionic form of N,N′-

Full text of DOI:10.1080/15533174.2015.1137068

Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry
ISSN: 1553-3174 (Print) 1553-3182 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt20
Synthesis, Crystal Structure and Antimicrobial
Activity of Manganese(III) And Iron(III) Complexes
Derived from Similar Bis-Schiff Bases
Zi-Hong Pan, Gan-Qing Zhao, Ling-Wei Xue & Wei-Chun Yang
To cite this article: Zi-Hong Pan, Gan-Qing Zhao, Ling-Wei Xue & Wei-Chun Yang (2016):
Synthesis, Crystal Structure and Antimicrobial Activity of Manganese(III) And Iron(III) Complexes
Derived from Similar Bis-Schiff Bases, Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry, DOI: 10.1080/15533174.2015.1137068
To link to this article: http://dx.doi.org/10.1080/15533174.2015.1137068
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Published online: 16 May 2016.
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Synthesis, Crystal Structure and Antimicrobial Activity of Manganese(III) And Iron(III)
Complexes Derived from Similar Bis-Schiff Bases
*
ZI-HONG PAN, GAN-QING ZHAO, LING-WEI XUE , AND WEI-CHUN YANG
College of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan Henan,
4
67000 P.R. China
*
Corresponding author. E-mail: pdsuchemistry@163.com
Abstract
1
A new manganese(III) complex, [Mn(L )(CH OH)(dca)] (1), and a new iron(III) complex,
3
2
1
2
[
Fe(L )(CH OH)(NCS)] (2), which dca is dicyanoamide anion, and L and L are the dianionic
3
form of N,N’-3,4-methylphenylenebis(5-methylsalicylaldimine) and
N,N’-bis(5-methylsalicylidene)-o-phenylenediamine, respectively, have been prepared and
characterized by elemental analyses, IR, and single crystal X-ray crystallographic determination.
The crystal of complex (1) is orthorhombic: space group Pna2 , a = 14.6557(6), b = 10.8906(5),
1
3
c = 15.0536(7) Å, V = 2402.7(2) Å , Z = 4, R = 0.0321, wR = 0.0715. The crystal of complex
1
2
(2) is monoclinic: space group C2/c, a = 14.6798(9), b = 11.1306(7), c = 27.831(1) Å, β =
3
9
3.782(2)°, V = 4537.6(5) Å , Z = 8, R = 0.0423, wR = 0.1027. The bis-Schiff base ligands
1
2
coordinate to the metal center through phenolate O and imine N atoms. Both the Mn and Fe
atoms in the complexes are in octahedral coordination, with the equatorial donor atoms come
from the Schiff base ligands, and with the axial donor atoms come from a methanol O atom and
1
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a pseudohalide N atom. The effects of the complexes on the antimicrobial activity against
Staphylococcus aureus, Escherichia coli, and Candida albicans were studied.
Keywords
Schiff base, manganese complex, iron complex, crystal structure, antimicrobial activity
2
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Introduction
Schiff bases are a kind of important ligands in coordination chemistry and have extensive
[1--3]
application in many fields.
Schiff bases derived from aromatic carbonyl compounds have
been widely studied in connection with metalloprotein models and asymmetric catalysis, due to
the versatility of their steric and electronic properties. Schiff bases and their biologically active
complexes have been often used as chelating ligands in the coordination chemistry of transition
metals as radiopharmaceuticals for cancer targeting, agrochemicals, as model systems for
[
4--7]
biological macromolecules, as catalysts and as dioxygen carriers.
In recent years, metal
complexes of Schiff bases have attracted dramatically attention due to their versatile biological
[
8--10]
activity, such as antifungal, antibacterial and antitumor.
It has been shown that the Schiff
base complexes derived from salicylaldehyde and its derivatives with primary amines, bearing
[
11--14]
the N O, N S, NO or NSO donor sets, have interesting biological activity.
In the present
2
2
2
paper, the preparation, characterization and antimicrobial activity of a new manganese(III)
1
2
complex, [Mn(L )(CH OH)(dca)] (1), and a new iron(III) complex, [Fe(L )(CH OH)(NCS)] (2),
3
3
1
2
which dca is dicyanoamide anion, and L and L are the dianionic form of
N,N’-3,4-methylphenylenebis(5-methylsalicylaldimine) and
N,N’-bis(5-methylsalicylidene)-o-phenylenediamine, respectively, are reported.
Experimental
Material and Methods
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5
-Methylsalicylaldehyde, 1,2-diaminobenzene, and 1,2-diamino-4-methylbenzene were
purchased from Fluka. Other reagents and solvents were analytical grade and used without
further purification. Elemental (C, H, and N) analyses were made on a Perkin-Elmer Model
2
40B automatic analyser. Infrared (IR) spectra were recorded on an IR-408 Shimadzu 568
spectrophotometer. X-ray diffraction was carried out on a Bruker SMART 1000 CCD area
diffractometer.
Synthesis of Complex (1)
5
-Methylsalicylaldehyde (0.272 g, 2 mmol) and 1,2-diamino-4-methylbenzene (0.122 g, 1
mmol) were reacted in methanol (30 mL) at ambient temperature for 1 h. Then, manganese
perchlorate hexahydrate (0.362 g, 1 mmol) and sodium dicyanoamide (0.089 g, 1 mmol) were
added to the mixture. The mixture was further stirred at room temperature for 30 min to give a
deep brown solution. The solution was kept still in air for a few days, generating deep brown
single crystals. Yield, 287 mg. Analysis Calc. (%) for C H MnN O : C, 61.30; H, 4.75; N,
2
6
24
5
3
--1
1
3.75. Found (%): C, 61.17; H, 4.82; N, 13.62. Selected IR data (ν, cm ): 2283 s, 2228 s, 2181
s, ν(dca), 1607 s, ν(C = N).
Synthesis of Complex (2)
5
-Methylsalicylaldehyde (0.272 g, 2 mmol) and 1,2-diaminobenzene (0.108 g, 1 mmol) were
reacted in methanol (30 mL) at ambient temperature for 1 h. Then, iron perchlorate hexahydrate
(0.462 g, 1 mmol) and ammonium thiocyanate (0.065 g, 1 mmol) were added to the mixture. The
4
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mixture was further stirred at room temperature for 30 min to give a red solution. The solution
was kept still in air for a few days, generating red single crystals. Yield, 216 mg. Analysis Calc.
(
%) for C H FeN O S: C, 59.03; H, 4.54; N, 8.60. Found (%): C, 59.18; H, 4.62; N, 8.45.
24 22 3 3
--1
Selected IR data (ν, cm ): 2107 s, ν(N ), 1605 s, ν(C = N).
3
X-Ray Diffraction
Data were collected from selected crystals mounted on thin glass fibers. The data for the
[
15]
[16]
complexes were processed with SAINT and corrected for absorption using SADABS.
[
17]
Multi-scan absorption corrections were applied with ψ-scans. The structures were solved by
2
direct method using SHELXS-97 and refined by full-matrix least-squares techniques on F using
[
18]
anisotropic displacement parameters. The methanol hydrogen atoms were located from
difference Fourier maps and refined isotropically, with O‒H distances restrained to 0.85(1) Å.
The remaining hydrogen atoms were placed at calculated positions. Idealized H atoms were
refined with isotropic displacement parameters set to 1.2 (1.5 for methyl groups) times the
equivalent isotropic U values of the parent carbon atoms. The crystallographic data for the
complexes are listed Table 1.
Results and Discussion
The Schiff bases were readily prepared by the condensation of 2:1 molar ratio of
5
-methylsalicylaldehyde with 1,2-diamino-4-methylbenzene and 1,2-diaminobenzene,
respectively, in methanol at ambient temperature. The Schiff bases were not isolated and used
directly to the synthesis of the complexes. Crystals of the complexes are very stable at room
5
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temperature. The results of the elemental analyses are in accord with the composition suggested
for the complexes.
Infrared Spectra
In order to compare the IR spectrum of the complexes with the free Schiff bases, small
quantity of the Schiff bases was prepared. The IR spectra of the Schiff bases contain medium

1
C--O absorption bands at about 1235 cm . The bands disappeared on complexation, and new

1
C--O absorption bands appeared at about 1090 cm in the spectra of the complexes, indicating
that the Schiff bases coordinate to the metal atoms through deprotonated form. The infrared

1
spectra of the complexes displays intense absorption bands at 1607 cm for complex (1) and

1
1
605 cm for complex (2), which can be assigned to the C = N stretching frequencies of the
Schiff base ligands, whereas for the free Schiff bases the corresponding absorption bands are
observed at higher wave numbers. The shift of the bands on complexation indicates the
[
19]
coordination of the imine nitrogen to the metal centers. In the spectrum of complex (1), strong

1
[20]
bands observed at 2283, 2228, and 2181 cm are assigned to the absorption of the dca ligand,

1
and in the spectrum of complex (2), strong band observed at 2107 cm is assigned to the
[
21]
absorption of the thiocyanate ligand.
Crystal Structure Description
The molecular structures of the complexes are shown in Figures 1 and 2. Selected bond
distances and angles are listed in Table 2. The complexes are structurally similar mononuclear
compounds. The Mn atom in complex (1) is coordinated by two phenolate O and two imine N
6
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1
atoms of the Schiff base ligand L , defining the equatorial plane, and by one methanol O atom
and one dicyanoamide N atom, occupying the two axial positions, generating an octahedral
geometry. The Fe atom in complex (2) is coordinated by two phenolate O and two imine N
2
atoms of the Schiff base ligand L , defining the equatorial plane, and by one methanol O atom
and one thiocyanate N atom, occupying the two axial positions, generating an octahedral
geometry. The axial bonds are much longer than the basal bonds, which is caused by the
Jahn--Teller effects. The equatorial bond distances subtended at the Mn atoms in complex (1) are
shorter than those subtended at the Fe atoms in complex (2), while the axial bond distances
related to the Mn atom in complex (1) are longer than those related the Fe atom in complex (2).
The coordinate bond lengths in both structures are comparable to those observed in similar
[
22--26]
manganese (III) or iron(III) complexes with Schiff bases.
The dihedral angles between the
two benzene rings of the Schiff base ligands are 14.6(3)º for complex (1) and 21.6(3)º for
complex (2).
In the crystal structure of complex (1), the complex molecules are linked through
intermolecular O--H···N hydrogen bonds (Table 3), generating 1D chains along the axis-a
direction (Figure 3). In the crystal structure of complex (2), the complex molecules are linked
through intermolecular O--H···O hydrogen bonds (Table 3), generating dimers (Figure 4).
Antimicrobial Activity
Qualitative determination of antimicrobial activity was done using the disk diffusion
[
27--29]
method.
The results are summarized in Table 4. A comparative study of minimum
inhibitory concentration (MIC) values of the free Schiff bases and the complexes indicated that
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the complexes have more effective activity than the free Schiff bases. Generally, this is caused
by the greater lipophilic nature of the complexes than the ligands. Such increased activity of the
[
30]
metal chelates can be explained on the basis of chelating theory. On chelating, the polarity of
the metal atoms will be reduced to a greater extent due to the overlap of the ligand orbital and
partial sharing of positive charge of the metal atoms with donor atoms. Further, it increases the
delocalization of p-electrons over the whole chelate ring and enhances the lipophilicity of the
complexes. This increased lipophilicity enhances the penetration of the complexes into lipid
membrane and blocks the metal binding sites on enzymes of micro-organisms.
From Table 4, it can be seen that complex (1) has greater antibacterial and antifungi activities
against the bacteria than complex (2). Complex (1) has a similar activity against Escherichia coli
to the reference drug Tetracycline. Both complexes are more effective against Candida albicans
than Tetracycline, however, for Staphylococcus aureus, the activities of the complexes are much
weak.
Conclusion
In summary, a new manganese(III) complex and a new iron(III) complex derived from bis-Schiff
bases have been prepared and characterized. The crystal structures of the complexes were
confirmed by X-ray single crystal structure determination. The Mn and Fe atoms in the
complexes are in octahedral coordination. The biological test showed that the complexes have
effective activities against Escherichia coli and Candida albicans.
Supplementary Material
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A full detail of data collections and structure determinations has been deposited with the
Cambridge Crystallographic Data Centre (no. 1424596 (1) and 1424568 (2);
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Acknowledgments
This research was supported by the National Sciences Foundation of China (No. 20676057
and 20877036) and Top-class foundation of Pingdingshan University (No. 2008010).
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Table 1. Crystallographic data and experimental details for the complexes
Parameter
Value
(1)
(2)
Habit; color
Formula
Block; deep brown
C H MnN O
Block; red
C H FeN O S
26
24
5
3
24 22
3
3
Formula weight
Temperature, K
Crystal size, mm
Radiation (λ, Å)
Crystal system
Space group
Unit cell dimensions:
a, Å
509.4
488.4
298(2)
298(2)
0.30 × 0.29 × 0.26
0.27 × 0.27 × 0.23
MoK (0.71073)
MoK (0.71073)
α
α
Orthorhombic
Monoclinic
Pna21
C2/c
14.6557(6)
10.8906(5)
15.0536(7)
14.6798(9)
11.1306(7)
27.831(1)
b, Å
c, Å
1
5
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β, deg
93.782(2)
4537.6(5)
8
3
V, Å
2402.7(2)
4
Z
-
-3
ρcalcd, g cm
F(000)
1.408
1056
0.588
1.430
2024
Absorption coefficient,
0.788
--1
mm
θ Range for data collection, 3.09--25.50
2.93--25.49
deg
Index ranges, h, k, l
--15 ≤ h ≤ 17; --12 ≤ k ≤ --17 ≤ h ≤ 15; --13 ≤ k ≤
1
3; --17 ≤ l ≤ 18
11; --33 ≤ l ≤ 32
13129
Reflections collected
8133
Independent reflections
3962 (0.0233)
4207 (0.0312)
(
R )
int
Reflections with I > 2σ(I)
Parameters
3453
322
2
3362
294
1
Restraints
1
6
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2
Goodness-of-fit on F
1.061
1.050
Final R indices (I > 2σ(I))
R
1
= 0.0321, wR
2
2
=
=
R
1
= 0.0423, wR
2
2
=
=
0
.0715
0.1027
R indices (all data)
R
1
= 0.0424, wR
R = 0.0576, wR
1
0
.0778
0.1133
Largest difference peak and 0.195, --0.233
0.712, --0.481
--3
hole, e Å
1
7
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Table 2. Selected bond distances (Å) and angles (deg) for the complexes
(1)
Bond lengths
Mn1--O1
1.8748(18)
1.992(3)
2.347(2)
Mn1--O2
Mn1--N2
Mn1--N3
1.870(3)
1.994(2)
2.271(3)
Mn1--N1
Mn1--O3
Bond angles
O2--Mn1--O1
O1--Mn1--N1
O1--Mn1--N2
O2--Mn1--N3
N1--Mn1--N3
O2--Mn1--O3
N1--Mn1--O3
N3--Mn1--O3
93.56(10)
91.80(10)
170.61(10)
90.46(11)
89.69(11)
87.93(11)
91.50(10)
175.21(8)
O2--Mn1--N1
O2--Mn1--N2
N1--Mn1--N2
O1--Mn1--N3
N2--Mn1--N3
O1--Mn1--O3
N2--Mn1--O3
174.62(10)
92.92(9)
81.70(10)
93.88(10)
92.86(9)
90.72(9)
82.73(8)
(2)
1
8
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Bond lengths
Fe1--O1
1.888(2)
2.123(2)
2.146(2)
Fe1--O2
Fe1--N2
Fe1--N3
1.9326(17)
2.118(2)
2.033(3)
Fe1--N1
Fe1--O3
Bond angles
O1--Fe1--O2
O2--Fe1--N3
O2--Fe1--N2
O1--Fe1--N1
N3--Fe1--N1
O1--Fe1--O3
N3--Fe1--O3
N1--Fe1--O3
104.52(8)
95.20(9)
89.05(8)
88.85(9)
92.60(9)
90.04(9)
176.29(11)
87.52(8)
O1--Fe1--N3
O1--Fe1--N2
N3--Fe1--N2
O2--Fe1--N1
N2--Fe1--N1
O2--Fe1--O3
N2--Fe1--O3
93.66(11)
165.71(8)
89.47(11)
164.01(9)
77.08(9)
83.80(8)
86.94(9)
1
9
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Table 3. Hydrogen geometries for the complexes
D--H∙∙∙A
d(D--H, Å) d(H∙∙∙A, Å) d(D∙∙∙A, Å) ω(D--H∙∙∙A, deg)
(1)
i
O3--H3∙∙∙N5
0.85(1)
1.97(1)
2.800(4)
170(4)
169(4)
(2)
ii
O3--H3∙∙∙O2
0.85(1)
1.90(1)
2.732(3)
Symmetry codes : (i) 1/2 + x, 1/2 -- y, z; (ii) -- x, y, 1/2 -- z.
2
0
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Table 4. MIC values (μg/mL) for the antimicrobial activities of the tested compounds
Compound
Staphylococcus
aureus
Escherichia coli
Candida albicans
1
H2L
128
128
8.0
256
512
2.0
> 1024
> 1024
256
2
H2L
Complex (1)
Complex (2)
Tetracycline
32
16
512
0.30
2.15
> 1024
2
1
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Figure 1. Perspective view of complex (1) with 30% probability thermal ellipsoids.
2
2
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Figure 2. Perspective view of complex (2) with 30% probability thermal ellipsoids.
2
3
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Figure 3. Molecular packing structure of complex (1). Hydrogen bonds are drawn as dashed
lines.
2
4
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Figure 4. Molecular packing structure of complex (2). Hydrogen bonds are drawn as dashed
lines.
2
5
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