Synthesis, structures, and antibacterial activities of two iron(III) complexes with Schiff bases

Article abstract of DOI:10.1134/S1070328414040113

Two Schiff base iron(III) complexes, [FeL¹(AHA)] · H ₂O (I) and [Fe(L²)₂] · ClO₄ (II), where AHA is the deprotonated form of acetohydroxamic acid, and L ¹ and L² are the anionic

Full text of DOI:10.1134/S1070328414040113

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2014, Vol. 40, No. 5, pp. 289–296. © Pleiades Publishing, Ltd., 2014.
Synthesis, Structures, and Antibacterial Activities of Two Iron(III)
Complexes with Schiff Bases1
F. Y. Wei* and P. H. Wen
Department of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences, Baoji, 721013 P.R. China
*eꢀmail: weifenyan78@163.com
Received July 25, 2013
Abstract
AHA is the deprotonated form of acetohydroxamic acid, and L1 and L2 are the anionic form of
ethoxysalicylidene)propaneꢀ1,2ꢀdiamine and 2ꢀ[1ꢀ(2ꢀaminopropylimino)ethyl]phenol, respectively, have
been synthesized and characterized by physical chemical methods and single crystal Xꢀray diffraction. Crysꢀ
—
Two Schiff base iron(III) complexes, [FeL1(AHA)]
·
H2O (
I
) and [Fe(L2)2]
·
ClO4 (II), where
N,N'ꢀbis(3ꢀ
tallographic data for
4923.7(12) Å3
= 8,
12.748(1), = 13.401(1),
2784.9(4) Å3
= 4,
I
: orthorhombic, space group Iba2,
a
= 20.781(3),
b
= 23.527(3),
c
= 10.071(2)
P1,
= 112.543(2)°, V
Å
,
V
a
=
=
=
,
Z
R
1 = 0.0374, wR2 = 0.0900. Crystallographic data for II: triclinic, space group
b
c
= 19.007(1)
Å,
α
= 106.623(2) β = 97.462(2)
°,
°,
γ
,
Z
R
1 = 0.0892, wR2 = 0.2434. Xꢀray crystal structural study indicated that the coordination
environment around each Fe atom in the complexes is a sixꢀcoordinated distorted octahedron. The antibacꢀ
terial activities of the complexes were assayed.
DOI: 10.1134/S1070328414040113
1
INTRODUCTION
spectra were recorded on a PerkinElmer RX I FTꢀIR
spectrophotometer with KBr discs. TG–DTA analysis
was carried out under nitrogen with a heating rate of
Iron is an important element for biological proꢀ
cesses of human beings [1–3]. Iron is also an essential
cofactor in metalloenzymes [4]. Its importance in
DNA synthesis, control of gene expression, and inꢀ
duction of cell apoptosis is becoming better underꢀ
stood [5]. Schiff bases derived from benzaldehydes
with various organic amines are important ligands in the
coordination of transition metal atoms. Iron complexes
with Schiff bases have been received particular interest
for their biological effects, especially antibacterial and
antitumor activities [6–10]. However, when compared
to other transition metal ions, the number of complexes
bearing iron centers is much less. In the present work,
10°
C min–1 using a Perkin Elmer Pyris Diamond
TG/DTA analyzer.
Iron perchlorate is potentially explosive, only small
quantity should be used and handled with great care.
Synthesis of the Schiff bases. The Schiff bases H2L1
and HL2 were synthesized by refluxing hot ethanolic
solution (30 mL) of propaneꢀ1,2ꢀdiamine (0.01 mol)
with 3ꢀethoxysalicylaldehyde (0.02 mol) and 2ꢀaceꢀ
tylphenol (0.02 mol), respectively for about 1 h. The
precipitates formed during reflux were filtered, washed
with cold EtOH, and recrystallized from hot EtOH.
The yields were 83 and 77% for H2L1and HL2, respecꢀ
tively.
two new iron(III) complexes, [FeL1(AHA)]
and [Fe(L2)2]
ClO4 (II), where AHA is the deprotoꢀ
nated form of acetohydroxamic acid, and L1 and L2
· H2O (I)
·
are the anionic form of
N,N'ꢀbis(3ꢀethoxysaliꢀ
For C21H26N2O4 (H2L1)
cylidene)propaneꢀ1,2ꢀdiamine (H2L1) and 2ꢀ[1ꢀ(2ꢀ
anal. calcd., %: C, 68.1;
Found, %: C, 67.9;
H, 7.1;
H, 7.2;
N, 7.6.
N, 7.5.
aminopropylimino)ethyl]phenol (HL2), respectively,
have been synthesized, characterized, and investigated
for their antibacterial activities.
For C11H16N2O (HL2)
anal. calcd., %: C, 68.7;
H, 8.4;
H, 8.3;
N, 14.6.
N, 14.4.
EXPERIMENTAL
Found, %:
C, 68.6;
All chemical reagents and solvents were of analytiꢀ
cal grade and were obtained from SigmaꢀAldrich.
Methanol was dried over molecular sieves (4 N)
prior to use. Elemental analyses were performed on a
PerkinElmer 2400 II elemental analyzer. Infrared
Synthesis of complex I. A methanolic solution
(10 mL) of H2L1 (0.1 mmol, 37.0 mg) was mixed with
a methanolic solution (10 mL) of Fe(ClO4)3
(0.1 mmol, 37.2 mg) and acetohydroxamic acid
(0.1 mmol, 7.5 mg), and refluxed in a water bath for
1
The article is published in the original.
289

290
WEI, WEN
1 h. Single crystals suitable for Xꢀray diffraction were showed no inhibition in a preliminary test. The macꢀ
obtained by slow evaporation of the solution in air for roꢀdilution broth susceptibility assay was used for the
a few days. The yield was 43%.
evaluation of minimal inhibitory concentration
(MIC). By including 1 mL Muller–Hinton broth in
each test, and then adding 1 mL extract with concenꢀ
tration 100 mg/mL in the first tube, we made serial diꢀ
lution of this extract from first tube to last tube. Bacteꢀ
rial suspension prepared to match the turbidity of
0.5 Mcfarland turbidity standards. Matching this turꢀ
bidity provides a bacterial inoculum concentration of
For C23H30N3O7Fe
anal. calcd., %: C, 53.5;
H, 5.9;
H, 6.0;
N, 8.1.
N, 8.1.
Found, %:
C, 53.7;
Synthesis of complex II. A methanolic solution
(10 mL) of HL2 (0.1 mmol, 19.2 mg) was mixed with a
methanolic solution (10 mL) of Fe(ClO4)3 (0.1 mmol,
37.2 mg), and refluxed in a water bath for 1 h. Single
crystals suitable for Xꢀray diffraction were obtained by
slow evaporation of the solution in air for a few days.
The yield was 65%.
1.5
was added to each test tube. After incubation at 37
×
108 cfu/mL. Then 1 mL of bacterial suspension
°C
for 24 h, the last tube was determined as the minimal
inhibitory concentration (MIC) without turbidity.
RESULTS AND DISCUSSION
For C22H30N4O6ClFe
Two new mononuclear iron(III) complexes were
synthesized by reaction of Schiff bases, acetohydroxꢀ
amic acid, with iron perchlorate in methanol. For
anal. calcd., %: C, 49.1;
Found, %: C, 49.0;
H, 5.6;
H, 5.7;
N, 10.4.
N, 10.2.
complex I, acetohydroxamic acid was coordinated to
the Fe atom, while for complex II, even though we had
added the material, it has not participated in coordiꢀ
nation.
Single crystal Xꢀray diffraction. Xꢀray data for the
complexes were collected on a Bruker SMART
APEXII diffractometer equipped with graphiteꢀ
monochromated Mo
K
radiation (
λ
= 0.71073
preliminary orientation matrix and cell parameters
were determined from three sets of scans at different
starting angles. Data frames were obtained at scan inꢀ
tervals of 0.5
Å). A
The asymmetric unit of compound
I contains a
α
mononuclear iron complex molecule and a water molꢀ
ecule of crystallization (Fig. 1a). The Fe atom in the
complex shows distorted octahedral coordination geꢀ
ω
°
with an exposure time of 10 s frame–1. ometry, with O(1), N(2) atoms of the Schiff base
The reflection data were corrected for Lorentz and poꢀ ligand, and O(5) and O(6) atoms of the AHA ligand
larization factors. Absorption corrections were carried defining the equatorial coordination sites, and N(1)
out using SADABS. The structures were solved by diꢀ and O(2) atoms of the Schiff base ligand occupying the
rect methods and refined by fullꢀmatrix leastꢀsquares axial positions. The Fe atom deviates from the best coꢀ
analysis using anisotropic thermal parameters for nonꢀ ordination plane defined by the equatorial atoms by
H atoms with the SHELXTL program [11]. All H atꢀ 0.145(1)
oms were calculated at idealized positions and refined bond lengths and angles (Table 2) are in line with the
with the riding models. Crystallographic data for the corresponding values found in related sixꢀcoordinated
Å in direction of O(2) atom. The coordinate
complexes are summarized in Table 1.
iron(III) complexes with Schiff bases [13, 14]. The
distortion of the octahedral coordination may be
caused by the strain created by the fiveꢀmembered
chelate rings Fe(1)–N(1)–C(8)–C(9)–N(2) and
Fe(1)–O(5)–C(22)–N(3)–O(6). The three trans anꢀ
Supplementary material has been deposited with
the Cambridge Crystallographic Data Centre
(nos. 950909
ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
(
I
)
and 950910
(II); deposit@
gles are much deviated from the ideal value of 180
ranging from 155.9(1) to 161.7(1) . The remaining
bond angles are also deviated from the ideal value of
90 , ranging from 74.4(1) to 112.4(1) . The dihedral
angle between the two benzene rings of the Schiff base
ligand is 33.5(3)
°,
Antibacterial activity test. The in vitro activity test
was carried out using the growth inhibitory zone (well
method) [12]. The potency of components was deterꢀ
mined against the Gramꢀpositive bacteria: S. agalactiae
and S. aureus and the Gramꢀnegative bacteria:
K. pneumoniae and P. aeruginosa. Microorganisms
were cultured on Muller–Hinton agar medium. The
inhibitory activity was compared with that of standard
°
°
°
°
°
°.
In the crystal structure of complex I, the iron comꢀ
plex molecules and the water molecules are linked toꢀ
gether by O–H···O and N–H···O hydrogen bonds (Taꢀ
ble 3), to form 2D layers parallel to the yz plane (Fig. 2a).
antibiotics, such as gentamicine (10
wells on medium using a 6 mm cork borer, 100
solution from different compounds were poured into
each well. The plates were incubated at 37
μg). After drilling
μL of
The asymmetric unit of compound II contains two
C overꢀ mononuclear iron complex cations and two perchlorꢀ
°
night. The diameter of the inhibition zone was meaꢀ ate anions (Fig. 1b). The Fe atom in the complex
sured to the nearest. Each test was carried out in tripꢀ shows distorted octahedral coordination geometry,
licate and the average was calculated for inhibition with the three donor atoms of one Schiff base ligand
zone diameters. A blank containing only methanol and the imino N atom of the other Schiff base ligand
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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SYNTHESIS, STRUCTURES, AND ANTIBACTERIAL ACTIVITIES
291
Table 1. Crystallographic data and experimental details for structures
I
and II
Value
Parameter
I
II
Formula weight
Crystal size, mm
Temperature, K
Crystal system
Space group
516.35
537.80
0.30
×
0.27
×
0.27
0.30
×
0.27
×
0.27
298(2)
298(2)
Triclinic
Orthorhombic
Iba
2
P1
a
, Å
, Å
20.781(3)
23.527(3)
10.071(2)
90
12.748(1)
13.491(1)
19.007(1)
b
c
, Å
, deg
, deg
, deg
α
106.623(2)
97.462(2)
112.543(2)
2784.9(4)
4
β
90
γ
90
V
Z
, Å3
4923.7(12)
8
ρcalcd, mg cm–3
), mm–1
1.393
1.283
μ
(Mo
K
0.660
0.677
α
F(000)
2168
1124
Number of measured reflections
24588
5071
26141
10319
5591
Number of observations (
Unique reflections
Parameters
I
> 2σ(
I
))
4132
320
616
Number of restraints
5
48
R1
,
,
wR2
(
I
> 2
σ
(
I
))*
0.0374, 0.0900
0.0534, 0.0999
1.043
0.0892, 0.2434
0.1632, 0.2942
1.020
R1
wR2 (all data)*
Goodness of fit of F 2
Largest difference peak and hole,
e
Å–3
0.280, –0.271
0.799, –0.572
*
R
=
∑
||F
| – |F
||/
∑
|F
|, wR = [
∑
w
(Fo2 − 2Fc2)2
/
∑
w
(Fo2)2]1 2
.
1
o
c
o
2
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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292
WEI, WEN
(a)
C(19)
C(15)
C(14)
C(20)
O(4)
C(22)
C(13)
C(21)
N(3)
C(16)
O(2)
C(12)
C(11)
O(5)
C(10)
O(6)
N(2)
C(9)
Fe(1)
O(1)
C(2)
C(18)
O(3)
C(8)
N(1)
C(7)
C(17)
C(3)
O(7)
C(23)
C(4)
C(1)
C(6)
C(5)
(b)
O(5)
O(6)
Cl(1)
C(11)
O(8)
O(7)
C(10)
N(2)
C(22)
N(4)
C(21)
C(9)
C(20)
N(1)
C(19)
Fe(1)
O(2)
C(8)
C(6)
N(3)
C(13)
C(18)
C(17)
C(7)
C(1)
C(12)
C(14)
C(16)
O(1)
C(15)
C(2)
C(3)
C(5)
C(4)
Fig. 1. ORTEP diagram of complexes I (a) and II (b) with 30% thermal ellipsoids for all nonꢀhydrogen atoms.
defining the equatorial coordination sites, and the reꢀ defined by the equatorial atoms by 0.095(1)
maining two donor atoms of the second Schiff base 0.116(1) , respectively. The coordinate bond lengths
ligand occupying the axial positions. The Fe(1) and and angles (Table 2) are comparable to those observed
Fe(2) atoms deviate from the best coordination planes in complex , and also in line with the corresponding
Å and
Å
I
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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SYNTHESIS, STRUCTURES, AND ANTIBACTERIAL ACTIVITIES
Table 2. Selected bond lengths (Å) and angles (deg) for
293
I
and II
values found in related sixꢀcoordinated iron(III)
complexes with Schiff bases [15, 16]. The distortion
of the octahedral coordination may be caused by the
strain created by the fiveꢀmembered chelate rings
Bond
d
, Å
Bond
d, Å
I
Fe(1)–N(1)–C(9)–C(10)–N(2),
Fe(1)–N(3)–
C(20)–C(21)–N(4), Fe(2)–N(5)–C(31)–C(2)–N(6),
and Fe(2)–N(7)–C(42)–C(43)–N(8). The three
trans angles are much deviated from the ideal value of
Fe(1)–O(1)
Fe(1)–O(5)
Fe(1)–N(1)
1.969(2) Fe(1)–O(2)
2.084(2) Fe(1)–O(6)
2.113(3) Fe(1)–N(2)
II
1.933(2)
1.9657(18)
2.189(3)
180
and from 162.7(2)o to 168.9(2)
maining bond angles are also deviated from the ideal
value of 90 , ranging from 78.5(2) to 100.1(2) for
Fe(1) and from 77.8(2) to 100.8(2) for Fe(2). The
two Schiff base ligands in the complex are also vertical
to each other, with dihedral angles of 99.6(3) for
Fe(1) complex molecule, and 108.0(3) for Fe(2)
complex molecule.
In the crystal structure of complex II, the complex
°
, ranging from 164.7(2)o to 170.4(2)
°
for Fe(1)
°
for Fe(2). The reꢀ
Fe(1)–O(1)
Fe(1)–N(1)
Fe(1)–N(3)
Fe(2)–O(3)
Fe(2)–N(5)
1.881(5) Fe(1)–O(2)
2.143(5) Fe(1)–N(2)
2.133(5) Fe(1)–N(4)
1.899(5) Fe(2)–O(4)
2.136(5) Fe(2)–N(6)
2.144(5) Fe(2)–N(8)
1.888(5)
2.176(6)
2.148(6)
1.882(5)
2.161(6)
2.163(5)
°
°
°
°
°
°
°
cations and the perchlorate anions are linked together Fe(2)–N(7)
by N–H···O hydrogen bonds (Table 3), to form dimers
(Fig. 2b).
Angle
ω
, deg
Angle
ω
, deg
The infrared spectra of the Schiff bases and their
complexes provide information about the metal–
ligand bonding. The medium and broad absorptions in
I
O(2)Fe(1)O(6) 103.3(1) O(2)Fe(1)O(1) 94.0(1)
the 3200–3500 cm–1 region for the Schiff bases and
O(6)Fe(1)O(1)
O(6)Fe(1)O(5)
86.0(1) O(2)Fe(1)O(5) 98.4(1)
78.2(1) O(1)Fe(1)O(5) 161.7(1)
complex
I substantiate the presence of O–H groups.
The sharp and weak absorptions at 3227 and 3258 cm–1
O(2)Fe(1)N(1) 155.9(1) O(6)Fe(1)N(1) 100.6(1)
for complexes
I and II are assigned to N–H groups.
Strong absorptions at 1645 cm–1 for H2L1 and
1639 cm–1 for HL2 are assigned to the azomethine
O(1)Fe(1)N(1)
O(2)Fe(1)N(2)
84.6(1) O(5)Fe(1)N(1) 89.4(1)
84.1(1) O(6)Fe(1)N(2) 159.9(1)
groups,
1633 cm–1 for
tributed to donation of the nitrogen atom lone pair of
the azomethine groups to the metal ions. The phenolic
ν
(C=N) [17]. The bands appeared at
I
and 1636 cm–1 for II, which can be atꢀ
O(1)Fe(1)N(2) 112.4(1) O(5)Fe(1)N(2) 82.3(1)
N(1)Fe(1)N(2)
74.4(1)
ν
(C–O) in the free Schiff base ligands exhibit strong
II
bands at 1262 cm–1 for H2L1 and 1253 cm–1 for HL2.
In the complexes, the bands appear at lower wave
1243 cm–1 for and 1235 cm–1 for II
numbers, viz. I ,
when compared to those of the free Schiff bases. In the
spectrum of II, the intense band centered at 1115 cm–1
is attributed to the perchlorate anions. Conclusive evꢀ
idence of the bonding is also shown by the presence of
new bands in the spectra of the complexes at about
520–570 and 410–490 cm–1, which can be attributed
O(1)Fe(1)O(2)
O(2)Fe(1)N(3)
O(2)Fe(1)N(1)
O(1)Fe(1)N(4)
N(3)Fe(1)N(4)
96.2(3) O(1)Fe(1)N(3) 100.1(2)
86.7(2) O(1)Fe(1)N(1) 86.3(2)
99.8(2) N(3)Fe(1)N(1) 170.4(2)
90.4(2) O(2)Fe(1)N(4) 164.7(2)
78.5(2) N(1)Fe(1)N(4) 94.3(2)
O(1)Fe(1)N(2) 165.6(2) O(2)Fe(1)N(2) 88.8(2)
to
ν
(Fe–O) and (Fe–N) stretching vibrations, reꢀ
ν
N(3)Fe(1)N(2)
N(4)Fe(1)N(2)
93.7(2) N(1)Fe(1)N(2) 79.5(2)
88.2(2) O(4)Fe(2)O(3) 96.7(3)
spectively [18].
TG–DTA curves of complex
The mass loss corresponding to one lattice water molꢀ
ecule is observed at 100–170 C. The organic part of
the complex decomposes into roughly two steps, the
first lies in the range 170–218 C with a DTG peak at
222 C. The mass loss (14.0%) corresponds to loss of
the AHA ligand. The next stage of decomposition
starts at 220 C and ends at 450 C. Since the TG curve
I are shown in Fig. 3a.
O(4)Fe(2)N(5) 100.8(2) O(3)Fe(2)N(5) 85.2(2)
O(4)Fe(2)N(7) 86.2(2) O(3)Fe(2)N(7) 102.7(2)
°
N(5)Fe(2)N(7) 168.9(2) O(4)Fe(2)N(6) 89.3(3)
O(3)Fe(2)N(6) 162.7(2) N(5)Fe(2)N(6) 77.8(2)
°
°
N(7)Fe(2)N(6)
O(3)Fe(2)N(8)
N(7)Fe(2)N(8)
93.8(2) O(4)Fe(2)N(8) 164.6(2)
89.8(2) N(5)Fe(2)N(8) 93.5(2)
78.8(2) N(6)Fe(2)N(8) 88.4(2)
°
°
of the complex showed continuous degradation at this
stage, we were not able to isolate the intermediates.
The steady mass loss observed at this stage may be due
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WEI, WEN
Table 3. Geometric parameters of hydrogen bonds for
I
and II
*
Distance, Å
D–H⋅⋅⋅
A
Angle DHA, deg
D–H
H⋅⋅⋅
A
D⋅⋅⋅A
I
O(7)–H(7B)⋅⋅⋅O(3)i
O(7)–H(7B)⋅⋅⋅O(1)i
N(3)–H(3)⋅⋅⋅O(7)ii
0.85(1)
0.85(1)
0.90(1)
2.31(2)
2.31(2)
1.92(1)
II
3.026(4)
3.044(3)
2.810(4)
144(3)
147(3)
171(4)
N(8)–H(8B)⋅⋅⋅O(6)
N(8)–H(8A)⋅⋅⋅O(11)iii
N(6)–H(6B)⋅⋅⋅O(9)iv
N(6)–H(6A)⋅⋅⋅O(9)iii
N(4)–H(4B)⋅⋅⋅O(8)iii
N(4)–H(4A)⋅⋅⋅O(8)
N(2)–H(2A)⋅⋅⋅O(6)
0.90
0.90
0.90
0.90
0.90
0.90
0.90
2.41
3.28(2)
3.04(1)
3.15(1)
3.21(2)
3.06(1)
3.23(1)
3.27(2)
3.16(1)
160
167
146
158
140
168
142
138
2.16
2.37
2.35
2.31
2.34
2.52
N(2)–H(2A)⋅⋅⋅O(7)
0.90
2.44
i
ii
iii
iv
* Symmetry codes:
x, 1 –
y, –1/2 +
z;
x, –1 +
y,
z;
1 – x, 2 – y, 1 – z; x, y, –1 + z.
to the removal of the Schiff base ligand, and the forꢀ
mation of final product (Fe2O3).
Antibacterial activities of the Schiff bases and the
two complexes as well as the reference drug gentamiꢀ
cine are summarized in Table 4 (zone of growth inhiꢀ
bition and minimal inhibitory concentrations). The
results indicate strong activity of the free Schiff bases
against Gramꢀpositive bacteria, S. agalactiae, and
moderate activities of them toward Gramꢀpositive
bacteria S. aureus and Gramꢀnegative bacteria
K. pneumoniae and P. aeruginosa. In comparison, the
iron complexes have stronger activities against all the
bacteria than the free Schiff bases. The increased acꢀ
tivity of the complexes may be explained on the basis
of chelation theory; chelation reduces the polarity of
the metal atom mainly because of partial sharing of
its positive charge with the donor groups and possible
TG–DTA curves of complex II are shown in
Fig. 3b. The mass loss corresponding to one perchlorꢀ
ate anion is observed at 110–160
of the complex decomposes into roughly two steps, the
first lies in the range 208–240 C with a DTG peak at
218 C. The mass loss (50.0%) corresponds to loss of
the four outer atoms of the benzene rings and the meꢀ
thyl atoms of the Schiff base ligands. The next stage of
decomposition starts at 240 C and ends at 460 C. The
°C. The organic part
°
°
°
°
steady mass loss observed at this stage may be due to
the removal of the remaining parts of the Schiff base
ligands, and the formation of final product (Fe2O3).
Table 4. Growth inhibition zone (mm) and MIC (mg/mL) values (in brackets) of compounds H2L1, HL2,
I, and II
Gramꢀpositive
and ꢀnegative bacteria
Gentamicine
H2L1
HL2
I
II
S. agalactiae
S. aureus
20 (25)
10 (25)
20 (12.5)
10 (50)
10 (50)
10 (25)
20 (12.5)
10 (25)
30 (6.25)
40 (3.125)
30 (6.25)
30 (12.5)
30 (12.5)
30 (6.25)
40 (3.125)
20 (12.5)
20
20
15
K. pneumoniae
P. aeruginosa
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2014

SYNTHESIS, STRUCTURES, AND ANTIBACTERIAL ACTIVITIES
295
(a)
x
0
z
y
(b)
z
y
0
x
Fig. 2. Molecular packing structure of complexes I (a) and II (b), viewed along the y and z axes, respectively. Hydrogen bonds are
drawn as dotted lines.
p
ꢀelectron delocalization within the whole chelation.
In summary, the present paper reports the syntheꢀ
sis, characterization and crystal structures of two new
iron(III) complexes with Schiff bases. The complexes
show effective antibacterial activities against Gramꢀ
positive bacteria S. agalactiae and S. aureus and
Gramꢀnegative bacteria K. pneumoniae and P. aerugiꢀ
nosa. Further work might be carried out to explore
Also, chelation increases the lipophilic nature of the
central atom which subsequently favors its permeation
through the lipid layer of the cell membrane [19]. The
quantitative assays gave MIC values in the range
3.125–50 mg mL–1, that confirmed the above obꢀ
tained results.
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2014

296
WEI, WEN
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We acknowledge the Education Office of Shanxi
Province (project no. 11JK0601) and the Natural Sciꢀ
ence Foundation of China (project no. 21173003) for
supporting this work.
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2014