Synthesis, crystal structure and antimicrobial activity of a hetero trinuclear manganese(III)-iron(II) complex derived from N,N'-bis(5-methylsalicylidene)-1,2-diaminoethane

Article abstract of DOI:10.4314/bcse.v29i3.8

A new hetero trinuclear manganese(III)-iron(II) complex, [Mn(salen)(H₂O)]₂[Fe(CN)₆], in which salen is the dianionic form of N,N'-bis(5-methylsalicylidene)-1,2-diaminoethane, has been prepared and characterized by elementa

Full text of DOI:10.4314/bcse.v29i3.8

Bull. Chem. Soc. Ethiop. 2015, 29(3), 407-413.
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v29i3.8
ISSN 1011-3924
 2015 Chemical Society of Ethiopia
SYNTHESIS, CRYSTAL STRUCTURE AND ANTIMICROBIAL ACTIVITY OF A
HETERO TRINUCLEAR MANGANESE(III)-IRON(II) COMPLEX DERIVED FROM
N,N’-BIS(5-METHYLSALICYLIDENE)-1,2-DIAMINOETHANE
*
Xiao-Ming Hu, Ling-Wei Xue , Gan-Qing Zhao and Wei-Chun Yang
College of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan
Henan, 467000, China
(
Received October 22, 2014; revised September 5, 2015)
2 2 6
ABSTRACT. A new hetero trinuclear manganese(III)-iron(II) complex, [Mn(salen)(H O)] [Fe(CN) ], in which
salen is the dianionic form of N,N’-bis(5-methylsalicylidene)-1,2-diaminoethane, has been prepared and
characterized by elemental analyses, IR, and single crystal X-ray crystallographic determination. The crystal of the
complex is monoclinic: space group P2
1
/c, a = 10.768(2), b = 14.248(3), c = 15.222(3) Å, β = 95.394(2)º, V =
3
2
325.0(8) Å , Z = 2, R = 0.0754, wR = 0.2366. The bis-Schiff base ligand coordinates to the Mn atom through
1
2
phenolate O and imine N atoms. Each Mn atom in the complex is in octahedral coordination, with the equatorial
donor atoms come from the Schiff base ligand, and with the axial donor atoms come from a water O atom and a
cyanide N atom. The effects of the complex on the antimicrobial activity against Staphylococcus aureus,
Escherichia coli, and Candida albicans were studied.
KEY WORDS: Schiff base, Manganese(III) complex, Iron(II) complex, Heteronuclear, Crystal structure
INTRODUCTION
Schiff bases are a kind of important ligands in coordination chemistry and have extensive
application in many fields [1-3]. 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
biological macromolecules, as catalysts and as dioxygen carriers [4–7]. In recent years, metal
complexes of Schiff bases have attracted dramatically attention due to their versatile biological
activity, such as antifungal, antibacterial and antitumor [8–10]. It has been shown that the Schiff
base complexes derived from salicylaldehyde and its derivatives with primary amines, bearing
2 2 2
the N O, N S, NO or NSO donor sets, have interesting biological activity [11–14]. In addition,
the molecular design of extended structures starting from molecular precursors is of great
interest. A preferred way to construct such materials is to use ionic building blocks in which one
unit contains a potential bridging ligand and another contains a potential coordination site [15].
In the present paper, the preparation, characterization and antimicrobial activity of a new hetero
trinuclear manganese(III)-iron(II) complex, [Mn(salen)(H
dianionic form of N,N’-bis(5-methylsalicylidene)-1,2-diaminoethane (H
2
O)]
2
[Fe(CN)
6
], in which salen is the
2
salen), is reported.
EXPERIMENTAL
Material and methods
5
-Methylsalicylaldehyde and ethane-1,2-diamine were purchased from Fluka. Other reagents
and solvents were analytical grade and used without further purification. Elemental (C, H, and
_
*
_________
Corresponding author. E-mail: pdsuchemistry@163.com

408
Xiao-Ming Hu et al.
N) analyses were made on a PerkinElmer Model 240B 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 the complex
5
-Methylsalicylaldehyde (0.272 g, 2 mmol) and ethane-1,2-diamine (0.060 g, 1 mmol) were
reacted in methanol (30 mL) at ambient temperature for 1 h. Then, manganese perchlorate
hexahydrate (0.362 g, 1 mmol) was added to the mixture. The mixture was further stirred at
room temperature for 30 min to give a deep brown solution. The methanol solution was
carefully layered on the top of an aqueous solution (20 mL) of K [Fe(CN) ]·3H O (0.422 g, 1
4 6 2
mmol) in a test tube. Deep brown single crystals of the complex, suitable for single crystal X-
ray diffraction, were formed after a few days. Yield, 323 mg. Analysis calc. (%) for
C H40FeMn N O : C, 53.29; H, 4.26; N, 14.80. Found (%): C, 53.03; H, 4.41; N, 14.66.
42 2 10 6
–1
Selected IR data (ν, cm ): 2027 s, ν(N
3
), 1632 s, ν(C=N).
Table 1. Crystallographic data and experimental details for the complex.
Parameter
Value
Habit; color
Formula
Block; deep brown
C H40FeMn N O
42 2 10 6
Formula weight
Temperature, K
Crystal size, mm
Radiation (λ, Å)
Crystal system
Space group
Unit cell dimensions:
a, Å
946.6
298(2)
0.17 × 0.17 × 0.13
MoK (0.71073)
Monoclinic
P2 /c
α
1
10.768(2)
14.248(3)
15.222(3)
95.394(2)
2325.0(8)
2
b, Å
c, Å
β, deg
3
V, Å
Z
–3
ρcalcd, g cm
1.352
F(000)
Absorption coefficient, mm
972
0.897
–1
θ Range for data collection, deg
Index ranges, h, k, l
2.38–25.20
–12 ≤ h ≤ 12; –17 ≤ k ≤ 17; –18 ≤ l ≤ 17
Reflections collected
21089
Independent reflections (Rint
Reflections with I > 2σ(I)
Parameters
)
4169 (0.0607)
2798
285
3
Restraints
2
Goodness-of-fit on F
1.090
Final R indices (I > 2σ(I))
R indices (all data)
Largest difference peak and hole, e Å
R
R
1
= 0.0754, wR
= 0.1207, wR
2
= 0.2366
= 0.2674
1
2
–3
1.054, –0.332
X-ray diffraction
Data were collected from a selected crystal mounted on a thin glass fiber. The data for the
complex were processed with SAINT [16] and corrected for absorption using SADABS [17].
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Hetero trinuclear manganese(III)-iron(II) complex
409
Multi-scan absorption corrections were applied with ψ-scans [18]. The structure was solved by
direct method using the program SHELXS-97 and refined by full-matrix least-squares
2
techniques on F using anisotropic displacement parameters [19]. The water hydrogen atoms
were located from a difference Fourier map and refined isotropically, with O‒H and H···H
distances restrained to 0.85(1) and 1.37(2) Å, respectively. The remaining hydrogen atoms were
placed at the 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 in Table 1.
Supplementary material has been deposited with the Cambridge Crystallographic Data
Centre (no. 1024665; deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
The Schiff base H
,2-diamine with 5-methylsalicylaldehyde in methanol at ambient temperature. The Schiff base
was not isolated and used directly to the synthesis of the complex with K [Fe(CN) ]·3H O.
2
salen was readily prepared by the condensation of 1:2 molar ratio of ethane-
1
4
6
2
Crystals of the complex are very stable at room temperature. The results of the elemental
analyses are in accord with the composition suggested for the complex.
Infrared spectra
In order to compare the IR spectrum of the complex with the free Schiff base, small quantity of
H salen was prepared. The IR spectrum of the Schiff base contains medium C–O absorption
2
-1
band at 1237 cm . The band disappeared on complexation, and new C–O absorption band
-1
appeared at 1086 cm in the spectrum of the complex, indicating that the Schiff base
coordinates to the metal atom through deprotonated form. The infrared spectrum of the complex
-
1
displays intense absorption band at 1615 cm , which can be assigned to the C=N stretching
frequencies of the Schiff base ligand, whereas for the free Schiff base the corresponding
-1
absorption band is observed at higher wavenumber, 1632 cm . The shift of the band on
complexation indicates the coordination of the imine nitrogen to the metal center [20]. In the
-1
spectrum of the complex, strong bands observed at 2155 and 2143 cm are assigned to the
absorptions of the non-bridging and bridging cyanide groups [21], and weak and broad band
-1
centered at 3318 cm is assigned to the water O-H vibration.
Crystal structure description
The molecular structure of the complex is shown in Figure 1. Selected bond distances and
angles are listed in Table 2. The complex is a cyano-bridged heteronuclear manganese (III)-
iron(II) species, with Mn···Fe separation of 5.210(2) Å. The Mn atom in the complex is
coordinated by two phenolate O and two imine N atoms of the Schiff base ligand, defining the
equatorial plane, and by one water O atom and one cyanide N atom, occupying the two axial
positions, generating an octahedral geometry. The two axial bonds are much longer than the
basal bonds, which is caused by the Jahn–Teller effects. The bond distances subtended at the
Mn atoms are comparable to those observed in similar manganese (III) complexes with Schiff
bases [22–24]. The dihedral angle between the two benzene rings of the Schiff base ligand is
7
.0(3)º. The Fe atom in the complex is coordinated by six C atoms from cyanide ligands,
generating an octahedral geometry. The bond distances subtended at the Fe atom are comparable
to those observed in similar complexes with Fe-C bonds [22–24].
In the crystal structure of the complex, the [Mn(salen)(H
2
O)] moieties are linked by a
[
Fe(CN) ] core. The hetero trinuclear complex molecules are further linked through
6
intermolecular O–H···O and O–H···N hydrogen bonds (Table 3), generating 1D chains along
Bull. Chem. Soc. Ethiop. 2015, 29(3)

410
Xiao-Ming Hu et al.
the axis-c direction (Figure 2). There are π···π interactions among the chains in the axis-b
direction, with a centroid (C1-C6) – centroid (C11-C16) distance of 3.799(2) Å.
Figure 1. Perspective view of the complex with 30% probability thermal ellipsoids. Atoms
labelled with the suffix A are at the symmetry position 2 – x, 1 – y, 1 – z.
*
Table 2. Selected bond distances (Å) and angles (deg) for the complex .
Bond lengths
Fe(1)–C(20)
Fe(1)–C(19)
Mn(1)–O(2)
Mn(1)–N(2)
1.801(8)
1.939(7)
1.878(4)
1.986(5)
2.273(5)
Fe(1)–C(21)
Mn(1)–O(1)
Mn(1)–N(1)
Mn(1)–N(3)
1.930(8)
1.858(5)
1.972(5)
2.363(6)
Mn(1)–O(3)
Bond angles
C(20)–Fe(1)–C(20A)
C(20)–Fe(1)–C(21)
C(20)–Fe(1)–C(19)
C(21)–Fe(1)–C(19A)
C(19)–Fe(1)–C(19A)
O(1)–Mn(1)–N(1)
O(1)–Mn(1)–N(2)
N(1)–Mn(1)–N(2)
O(2)–Mn(1)–O(3)
N(2)–Mn(1)–O(3)
O(2)–Mn(1)–N(3)
N(2)–Mn(1)–N(3)
180
C(20)–Fe(1)–C(21A)
C(21)–Fe(1)–C(21A)
C(20)–Fe(1)–C(19A)
C(21)–Fe(1)–C(19)
O(1)–Mn(1)–O(2)
O(2)–Mn(1)–N(1)
O(2)–Mn(1)–N(2)
O(1)–Mn(1)–O(3)
N(1)–Mn(1)–O(3)
O(1)–Mn(1)–N(3)
N(1)–Mn(1)–N(3)
O(3)–Mn(1)–N(3)
89.5(3)
180
90.5(3)
89.2(3)
90.1(3)
180
92.8(2)
174.6(2)
82.2(2)
94.05(19)
88.87(19)
96.0(2)
89.5(2)
90.8(3)
89.9(3)
92.5(2)
174.6(2)
92.5(2)
88.74(19)
87.2(2)
92.0(2)
82.7(2)
169.9(2)
*
Symmetry code for A: 2 – x, 1 – y, 1 – z.
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Hetero trinuclear manganese(III)-iron(II) complex
Table 3. Hydrogen geometries for the complex.
411
D–H···A
O(3)–H(3A)···O(2)
O(3)–H(3B)···N(5)
d(D–H, Å)
0.85(1)
0.85(1)
d(H···A, Å)
2.03(2)
2.00(2)
d(D···A, Å)
2.854(6)
2.830(8)
ω(D–H···A, deg)
i
165(8)
167(8)
ii
Symmetry codes : (i) 2 – x, 1 – y, – z; (ii) 2 – x, –1/2 + y, 1/2 – z.
Figure 2. Molecular packing structure of the complex.
Antimicrobial activity
Qualitative determination of antimicrobial activity was done using the disk diffusion method
25-27]. The results are summarized in Table 4. A comparative study of minimum inhibitory
[
concentration (MIC) values of the free Schiff base and the complex indicated that the complex
has more effective activity than the free Schiff base. Generally, this is caused by the greater
lipophilic nature of the complexes than the ligands. Such increased activity of the metal chelates
can be explained on the basis of chelating theory [28, 29]. 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 the complex has greater antibacterial and antifungal
activities against Escherichia coli and Candida albicans when compared to the reference drug
tetracycline. But, for Staphylococcus aureus, the activity of the complex is much weak.
Table 4. MIC values (μg/mL) for the antimicrobial activities of the tested compounds.
Compound
salen
The complex
Tetracycline
Staphylococcus aureus
Escherichia coli
Candida albicans
> 1024
H
2
128
16.0
0.30
512
2.0
2.15
128
> 1024
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Xiao-Ming Hu et al.
CONCLUSION
In summary, a new hetero trinuclear manganese(III)-iron(II) complex derived from the bis-
Schiff base ligand N,N’-bis(5-methylsalicylidene)-1,2-diaminoethane has been prepared and
characterized. The crystal structure of the complex was confirmed by X-ray single crystal
structure determination. The Mn and Fe atoms in the complex are in octahedral coordination.
The biological test showed that the complex has effective activities against Escherichia coli and
Candida albicans.
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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