Synthesis and crystal structures of N,N'-bis(5-fluoro-2-hydroxybenzylidene) ethane-1,2-diamine and its dinuclear manganese(III) complex with antibacterial activities

Article abstract of DOI:10.1080/00958972.2013.859253

A new dinuclear manganese complex, [Mn₂L₂(N ₃)₂], was prepared by reaction of bis-Schiff base N,N'-bis(5-fluoro-2-hydroxybenzylidene)ethane-1,2-diamine (H₂L) with manganese acetate and sodium azide in methanol. Both the Schiff base and the complex were characterized by physico-chemical methods and single crystal X-ray determination. The Schiff base crystallized in the orthorhombic space group Pbca with unit cell dimensions a = 7.3191(7) A, b = 6.0948(6) A, c = 35.382(3) A, V = 1578.3(3) A³, Z = 4, R₁ = 0.0481, wR₂ = 0.1488. The manganese complex crystallized in the monoclinic space group P2₁/c with unit cell dimensions a = 8.802(1) A, b = 14.928(2) A, c = 14.478(2) A, β = 105.517(2)°, V = 1833.0(4)A³, Z = 2, R₁ = 0.0768, wR₂ = 0.1640. There are crystallographic inversion centers in both the ligand and the complex. The ligand coordinates to Mn through all the phenolate oxygens and imino nitrogens. The two Mn in the complex are bridged by two phenolate oxygens with separation of 3.549(1) A. Each Mn is octahedral with four donors of the Schiff base ligand defining the equatorial plane, and with one azido nitrogen and one phenolate oxygen of an adjacent Schiff base ligand occupying the axial positions. The Schiff base and the complex were tested in vitro for their antibacterial activities.

Full text of DOI:10.1080/00958972.2013.859253

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Synthesis and crystal structures
of N,N'-bis(5-fluoro-2-
hydroxybenzylidene)ethane-1,2-
diamine and its dinuclear
manganese(III) complex with
antibacterial activities
Ya-Li Sanga, Xiao-Chun Lia & Wen-Min Xiaoa
a Department of Chemistry and Chemical Engineering, Chifeng
University, Chifeng, P.R. China
Accepted author version posted online: 28 Oct 2013.Published
online: 26 Nov 2013.
To cite this article: Ya-Li Sang, Xiao-Chun Li & Wen-Min Xiao (2013) Synthesis and crystal structures
of N,N'-bis(5-fluoro-2-hydroxybenzylidene)ethane-1,2-diamine and its dinuclear manganese(III)
complex with antibacterial activities, Journal of Coordination Chemistry, 66:22, 4015-4022, DOI:
10.1080/00958972.2013.859253
To link to this article: http://dx.doi.org/10.1080/00958972.2013.859253
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Journal of Coordination Chemistry, 2013
Vol. 66, No. 22, 4015–4022, http://dx.doi.org/10.1080/00958972.2013.859253
Synthesis and crystal structures of N,N'-bis(5-fluoro-
2-hydroxybenzylidene)ethane-1,2-diamine and its dinuclear
manganese(III) complex with antibacterial activities
YA-LI SANG*, XIAO-CHUN LI and WEN-MIN XIAO
Department of Chemistry and Chemical Engineering, Chifeng University, Chifeng, P.R. China
(Received 5 June 2013; accepted 8 October 2013)
A new dinuclear manganese complex, [Mn2L2(N3)2], was prepared by reaction of bis-Schiff base
N,N'-bis(5-fluoro-2-hydroxybenzylidene)ethane-1,2-diamine (H2L) with manganese acetate and
sodium azide in methanol. Both the Schiff base and the complex were characterized by
physico-chemical methods and single crystal X-ray determination. The Schiff base crystallized in
the orthorhombic space group Pbca with unit cell dimensions a = 7.3191(7) Å, b = 6.0948(6) Å,
c = 35.382(3) Å, V = 1578.3(3) Å3, Z = 4, R1 = 0.0481, wR2 = 0.1488. The manganese complex crys-
tallized in the monoclinic space group P21/c with unit cell dimensions a = 8.802(1) Å, b = 14.928(2)
Å, c = 14.478(2) Å, β = 105.517(2)°, V = 1833.0(4) Å3, Z = 2, R1 = 0.0768, wR2 = 0.1640. There are
crystallographic inversion centers in both the ligand and the complex. The ligand coordinates to Mn
through all the phenolate oxygens and imino nitrogens. The two Mn in the complex are bridged by
two phenolate oxygens with separation of 3.549(1) Å. Each Mn is octahedral with four donors of
the Schiff base ligand defining the equatorial plane, and with one azido nitrogen and one phenolate
oxygen of an adjacent Schiff base ligand occupying the axial positions. The Schiff base and the
complex were tested in vitro for their antibacterial activities.
Keywords: Schiff base; Manganese; Synthesis; Crystal structure; Antibacterial activity
1. Introduction
Schiff bases are readily synthesized by condensation reaction of carbonyl compounds with
primary amines [1, 2]. Schiff bases have been widely investigated for biological activities,
such as antibacterial and antitumor activities [3, 4], biomimetic catalytic properties [5], etc.
Metal complexes of Schiff bases have also received attention. These complexes play an
important role in the development of coordination chemistry related to catalysis and enzy-
matic reactions, magnetism and molecular architectures [6–8], and also exhibit interesting
biological activities [9–11].
A number of Schiff bases derived from salicylaldehyde and ethane-1,2-diamine and their
complexes have been reported [12–14]. Most show versatile biological properties, espe-
cially antibacterial activities [15, 16]. It was reported that compounds bearing one or more
halogens on the aromatic ring have improved antibacterial and antifungal activities [17].
*Corresponding author. Email: sangyali0814@126.com
© 2013 Taylor & Francis

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Y.-L. Sang et al.
Azide is a versatile ligand for preparation of complexes with terminal or bridging
coordination [18–20]. In the present work, we choose a fluoro-containing bis-Schiff base,
N,N'-bis(5-fluoro-2-hydroxybenzylidene)ethane-1,2-diamine (H2L), as ligand to prepare
[Mn2L2(N3)2]. Only five complexes derived from H2L have been reported [21–23]. The
antibacterial activities against Bacillus subtilis, Staphylococcus aureus, Escherichia coli,
and Pseudomonas fluorescens were evaluated for the Schiff base and the manganese
complex (scheme 1).
2. Experimental
2.1. Materials and measurements
5-Fluoro-2-hydroxybenzaldehyde, ethane-1,2-diamine, and sodium azide of AR grade were
obtained from Aldrich and used as received. Elemental analyzes were performed using a
Perkin–Elmer 240C analytical instrument. Infrared spectra were recorded on a Nicolet 5DX
1
FT-IR spectrophotometer with KBr pellets. H NMR spectra were recorded on a Bruker
instrument at 400 MHz. UV–vis spectra were recorded on a JASCO V-570 spectrophotome-
ter. Molar conductance was measured with a Shanghai DDS-11A conductometer.
Caution! Although no problems were encountered in our work, compounds containing
azide are potentially explosive. Therefore, only a small amount of the materials should be
used and they should be handled with care.
2.2. Synthesis of H2L
H2L was prepared by refluxing 5-fluoro-2-hydroxybenzaldehyde (2.80 g, 0.02 M) and eth-
ane-1,2-diamine (0.60 g, 0.01 M) in 30 mL methanol for half an hour. The solution was
evaporated to give yellow powder, which was washed three times with methanol and dried
in air. Yield: 93%. Anal. Calcd for C16H14F2N2O2 (%): C, 63.2; H, 4.6; N, 9.2. Found: C,
1
63.0; H, 4.7; N, 9.3. H NMR (d6-DMSO): δ: 2.32 (s, 6H), 3.93 (m, 4H), 6.87 (d, 2H),
7.13 (d, 2H), 7.51 (s, 2H), 8.57 (s, 2H), 11.83 (s, 2H). 13C NMR (d6-DMSO): δ: 21.2, 61.5,
116.8, 124.5, 130.9, 131.4, 132.5, 158.1, 158.5. Single crystals of the compound, suitable
for X-ray diffraction, were obtained by slow evaporation of methanolic solution of the
compound in air.
Scheme 1. The Schiff base ligand and the complex.

Dinuclear manganese(III) complex
2.3. Synthesis of [Mn2L2(N3)2]
4017
To a methanolic solution (10 mL) of H2L (91.3 mg, 0.3 mM) and sodium azide (19.5 mg,
0.3 mM) in methanol (20 mL), solid manganese acetate (73.5 mg, 0.3 mM) was added with
stirring. The mixture was stirred for half an hour and filtered. The filtrate was kept undis-
turbed at room temperature to slowly evaporate for a few days, generating deep brown crys-
tals suitable for X-ray diffraction. Crystals were isolated by filtration and dried in air. Yield
45% with respect to H2L. Anal. Calcd for C36H36Mn2N10O4 (%): C, 55.2; H, 4.6; N, 17.9.
Found: C, 55.3; H, 4.7; N, 17.8.
2.4. X-ray crystallography
Suitable single crystals with high quality of the Schiff base and the complex were selected
and mounted on a Bruker Smart 1000 CCD area-detector diffractometer with graphite
monochromated Mo-Kα radiation (λ = 0.71073 Å). Diffraction data for the compounds were
collected by ω scan at 298(2) K. Data reduction and cell refinement were performed by
SMART and SAINT [24]. Empirical absorption correction was applied by using SADABS
[25]. The structures were solved by direct methods and refined with full-matrix least-
squares using the SHELXL97 package [26]. The non-H atoms in the structures were
subjected to anisotropic refinement. Hydrogens were located geometrically and treated with
riding mode. Crystallographic data and experimental details for the complexes are summa-
rized in table 1. Selected bond lengths and angles for the complexes are listed in table 2.
2.5. Antibacterial test
Antibacterial activities of the Schiff base and the complex were tested in vitro against
B. subtilis, S. aureus, E. coli, and P. fluorescens using MH medium (Mueller–Hinton med-
ium: casein hydrolysate 17.5 g, soluble starch 1.5 g, beef extract 1000 mL). The minimum
inhibitory concentrations (MIC) of the test compounds were determined by a colorimetric
method using the dye MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)
[27]. A solution of the compound (50 μg mL−1) in DMSO was prepared and graded quanti-
ties of the test compounds were incorporated in specified quantity of sterilized liquid MH
medium. A specified quantity of the medium containing the compound was poured into
microtitration plates. Suspension of the microorganism was prepared to contain about 105
colony forming units cfu mL−1 and applied to microtitration plates with serially diluted
compounds in DMSO to be tested and incubated at 37 °C for 24 h. After MICs were visu-
ally determined on each of the microtitration plates, 50 μL of PBS (Phosphate Buffered Sal-
ine 0.01 M L−1, pH 7.4: Na2HPO4·12H2O 2.9 g, KH2PO4 0.2 g, NaCl 8.0 g, KCl 0.2 g,
distilled water 1000 mL) containing 2 mg of MTT 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 isopropyl alcohol containing 5% 1.0 M L−1 HCl was added to extract the dye.
After 12 h of incubation at room temperature, the optical density was measured with a
microplate reader at 550 nm. The observed MICs are presented in table 3.
3. Results and discussion
The manganese(III) complex was prepared by reaction of equimolar quantities of the Schiff
base ligand, manganese acetate, and sodium azide in methanol. As usually observed for

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Y.-L. Sang et al.
Table 1. Crystallographic and experimental data for H2L and [Mn2L2(N3)2].
Complex
Chemical formula
Formula weight
T (K)
H2L
C18H20N2O2
296.4
[Mn2L2(N3)2]
C36H36Mn2N10O4
782.6
298(2)
298(2)
λ(Mo-Kα) (Å)
Color; shape
Crystal size (mm3)
Crystal system
Space group
a (Å)
0.71073
Yellow; block
0.27 × 0.23 × 0.23
Orthorhombic
Pbca
7.3191(7)
6.0948(6)
35.382(3)
90
1578.3(3)
4
1.247
0.082
1.15–25.50
632
0.71073
Blue; block
0.15 × 0.13 × 0.10
Monoclinic
P21/c
8.802(1)
14.928(2)
14.478(2)
105.517(2)
1833.0(4)
2
b (Å)
c (Å)
β (°)
V (Å3)
Z
ρ (g/cm3)
1.418
0.742
2.00–25.49
808
μ (Mo-Kα) (mm−1
θ Range (°)
)
F (0 0 0)
Tmin and Tmax
0.9782 and 0.9814
7437
1472
1084
102/0
0.0265
1.107
0.0481, 0.1488
0.0733, 0.1779
0.8968 and 0.9295
9103
3335
1623
237/0
0.0821
0.970
0.0768, 0.1640
0.1673, 0.2053
No. of measured reflections
No. of unique reflections
No. of observed reflections
Parameters/restraints
Rint
Goodness of fit on F2
R1, wR2 [I ≥ 2σ(I)]a
R1, wR2 (all data)a
aR1 = ∑|Fo| – |Fc|/∑|Fo|, wR2 = [∑w(Fo2 – Fc2)2/∑w(Fo2)2]1/2
.
Table 2. Selected bond lengths (Å) and angles (°) for H2L and [Mn2L2(N3)2].
H2L
Bond lengths
C8–N1
1.274(3)
122.7(2)
C9–N1
1.452(3)
118.5(2)
Bond angles
C1–C8–N1
[Mn2L2(N3)2]
Bond lengths
C8–N1
C11–N2
Mn1–O1
Mn1–N1
Mn1–N3
C8–N1–C9
1.258(7)
1.276(7)
1.859(4)
1.978(5)
2.136(7)
C9–N1
1.498(8)
1.476(9)
1.900(4)
1.979(5)
C10–N2
Mn1–O2
Mn1–N2
Bond angles
C1–C8–N1
C12–C11–N2
O1–Mn1–O2
O2–Mn1–N1
O2–Mn1–N2
O1–Mn1–N3
N1–Mn1–N3
126.6(6)
C8–N1–C9
122.1(6)
123.5(6)
94.12(17)
161.2(2)
88.6(2)
97.8(2)
99.3(2)
C10–N2–C11
O1–Mn1–N1
O1–Mn1–N2
N1–Mn1–N2
O2–Mn1–N3
N2–Mn1–N3
123.0(6)
92.22(19)
170.4(2)
82.5(2)
97.3(2)
90.9(2)
manganese complexes, MnII underwent aerial oxidation to MnIII in the synthetic route. The
molar conductivity of the complex measured in methanol at concentration of 10−3 M is
21 Ω−1 cm2 M−1, indicating the non-electrolytic nature of the complex in solution [28].

Dinuclear manganese(III) complex
4019
Table 3. Antibacterial activities.
MIC (μg mL−1
)
B. subtilis
E. coli
P. fluorescens
S. aureus
H2L
[Mn2L2(N3)2]
Penicillin
50
12.5
1.3
25
3.12
>100
50
12.5
>100
25
6.25
2.1
3.1. Crystal structure description
Figures 1 and 2 give perspective views of H2L and the manganese complex, respectively.
The Schiff base possesses crystallographic inversion center symmetry, with the inversion
center located at the midpoint of C9 and C9A. There are two intramolecular O–H⋯N
hydrogen bonds in the free Schiff base, which are absent in the complex. The dihedral
angles between the two benzene rings are 0° for H2L and 9.0(3)° for the complex. The tor-
sion angle of N1–C9–C9A–C8A in H2L is 0°, yet, in the complex, the corresponding tor-
sion angle of N1–C9–C10–N2 is –47.9(3)°. The bond values of H2L are within normal
ranges when compared to other similar bis-Schiff bases [29, 30].
The complex is a centrosymmetric dinuclear manganese(III) compound, with the inver-
sion center located at the midpoint of the two Mn ions. The Mn are bridged by two pheno-
late oxygens, with separation of 3.549(1) Å. The Schiff base ligand forms one five- and two
six-membered chelate rings with bite angles of 82.5(2)°, 92.2(2)°, and 88.6(2)°. Each Mn is
octahedral with the four donors of the Schiff base defining the equatorial plane, and with
one azido nitrogen and one phenolate oxygen of an adjacent Schiff base occupying the axial
positions. The displacement of Mn from the equatorial plane towards the axial azide ligand
is 0.217(2) Å. The axial Mn–O and Mn–N bonds are much longer than those in the equato-
rial plane, caused by Jahn–Teller distortion. The cis bond angles are 80.6(2)–99.3(2)° and
the trans bond angles are 161.2(2)–170.4(2)°. The Mn–O and Mn–N bond lengths in the
complex are comparable to the values observed in Schiff base manganese(III) complexes
[31, 32].
Coordination of the Schiff base to Mn is shown by the change of related bond lengths
and angles. The bond length of C8–N1 [1.258(7) Å] is much shorter than that of 1.274(3) Å
in H2L, but the bond length of C11–N2 [1.276(7) Å] is equal to that of H2L. The bond
lengths of C2–O1 [1.338(6) Å] and C13–O2 [1.335(6) Å] in the complex are slightly shorter
than that of C2–O1 [1.345(2) Å] in H2L.
Figure 1. Molecular structure of H2L. Displacement is drawn at the 30% probability level. Unlabeled atoms are at
the symmetry position 1 − x, 1 − y, 1 − z.

4020
Y.-L. Sang et al.
Figure 2. Molecular structure of [Mn2L2(N3)2]. Displacement is drawn at the 30% probability level. Atoms
labeled with the suffix A or unlabeled are at the symmetry position 1 – x, 2 – y, 1 – z.
3.2. IR and electronic spectra
IR spectra of H2L and the manganese complex also provide information about the metal-
ligand bonding. The weak and broad absorption centered at 3450 cm−1 is assigned to
stretch of the phenolic O–H of the free Schiff base, absent in the spectrum of the complex,
indicating coordination through deprotonated phenolate oxygen. Several other bands from
2900 to 3150 cm−1 are assigned to absorption of CH. The phenolic ν(C–O) in the spectrum
of the Schiff base is a medium band at 1277 cm−1. However, in the spectrum of the com-
plex, the absorption appears at 1290 cm−1. The strong band at 1637 cm−1 of the free Schiff
base is assigned to the azomethine group, νC=N [33], which is observed at 1623 cm−1 for
the complex, indicating coordination of the imino nitrogen. The spectrum of the complex
exhibits a very strong and sharp absorption at 2034 cm−1, corresponding to the asymmetric
stretch of terminal azide. The newly observed bands in the region 450–620 cm−1 can be
assigned to the Mn–O and Mn–N bonds.
The electronic spectra of the compounds in acetonitrile were recorded from 200 to
800 nm. The intense absorption bands at 232 and 278 nm may be assigned to intra-ligand
π–π transitions. The weak absorptions centered at 312 and 413 nm may be assigned to the
phenolate of Schiff base ligand to Mn center charge transfer band (LMCT).
3.3. Antibacterial activities
The Schiff base H2L and the complex were screened in vitro for antibacterial activities
against B. subtilis, S. aureus, E. coli, and P. fluorescens by the MTT method. The MICs of
the compounds against the bacteria are presented in table 3. Penicillin was used as a
reference.
The Schiff base H2L shows moderate antibacterial activities against all four bacteria; the
complex has stronger activities against the bacteria than the free Schiff base. Even though
the complex has from moderate to strong activities against B. subtilis and S. aureus, it is
much weaker than Penicillin. But, for E. coli and P. fluorescens the complex is superior to

Dinuclear manganese(III) complex
4021
Penicillin. The trends in the present work accord with those in the literatures that metal
complexes usually have stronger antibacterial activities than their corresponding Schiff base
ligands [34–38].
4. Conclusions
A new dinuclear manganese complex has been prepared and characterized. Coordination of
the bis-Schiff base N,N'-bis(5-fluoro-2-hydroxybenzylidene)ethane-1,2-diamine to Mn was
investigated by infrared spectra and single crystal X-ray determination. The Schiff base
coordinates to Mn through phenolate oxygen and imino nitrogen with azide coordinating to
Mn terminal. The antibacterial activities of the Schiff base and the complex were assayed.
The results indicate that the complex is a potential antibacterial material.
Supplementary material
CCDC reference numbers 942635 for H2L and 942636 for the manganese complex contain the
supplementary crystallographic data for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk, or from the Cambridge Crystallographic Data Center, 12 Union Road,
Cambridge CB2 1EZ, UK; Fax: +44 1223 336 033; E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgement
The authors gratefully acknowledge the financial support by the Research Program of
Universities of Inner Mongolia Autonomous Region (NJ10245).
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