Synthesis, crystal structures, and antibacterial activity of cobalt and copper complexes with tridentate schiff bases

Article abstract of DOI:10.1080/15533174.2012.680155

Three mononuclear cobalt and copper complexes, [Co(HL¹) ₂]·[Co(L¹)₂] (1), [Cu(HL ²)₂] (2), and [CoL²(HL²)] ₂ (3), where HL¹ and HL² ar

Full text of DOI:10.1080/15533174.2012.680155

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Synthesis, Crystal Structures, and Antibacterial Activity
of Cobalt and Copper Complexes With Tridentate Schiff
Bases
a
Juan Du
a
Zhengzhou College of Animal Husbandry Engineering, Department of Pharmacy
Engineering, Zhengzhou, P. R. China
Accepted author version posted online: 27 Jul 2012.Version of record first published: 05 Oct
2012.
To cite this article: Juan Du (2012): Synthesis, Crystal Structures, and Antibacterial Activity of Cobalt and Copper Complexes
With Tridentate Schiff Bases, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:10,
1410-1414
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:1410–1414, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.680155
Synthesis, Crystal Structures, and Antibacterial Activity of
Cobalt and Copper Complexes With Tridentate Schiff Bases
Juan Du
Zhengzhou College of Animal Husbandry Engineering, Department of Pharmacy Engineering,
Zhengzhou, P. R. China
liminary antibacterial activity of the complexes on the bacteria
Three mononuclear cobalt and copper complexes, S. aureus, E. coli, P. aeruginosa, and S. typhi was evaluated.
1
1
2
2
2
[
(
Co(HL )
2
]·[Co(L )
2
] (1), [Cu(HL )
2
] (2), and [CoL (HL )]
2
1
2
3), where HL and HL are the monoanionic form of 2-
ethoxy-6-[(2-hydroxyethylimino)methyl]phenol
OH
1
(H
2
2
2
L )
and
N
2
1
Br
OH
4
-bromo-2-[(2-hydroxyethylimino)methyl]phenol (H
L ), and L
L , have been
N
2
1
and L are the dianionic form of H
2
L
and H
2
OH
synthesized and characterized by elemental analysis, FT-IR
spectra, and single-crystal X-ray determination. The Co atoms in
OEt
OH
(
1) and (3) are in octahedral coordination, and the Cu atom in (2)
1
2
SCH. 1. The Schiff bases HL and HL .
is in square planar coordination. The preliminary antibacterial
activity of the complexes on the bacteria S. aureus, E. coli, P.
aeruginosa, and S. typhi was evaluated.
EXPERIMENTAL
Keywords antibacterial activity, cobalt, copper, crystal structure, Materials and Measurements
Schiff base
3-Ethoxysalicylaldehyde, 5-bromosalicylaldehyde, and 2-
aminoethanol were obtained from Lancaster (England). Other
chemicals were obtained commercially and were used as re-
ceived. Carbon, hydrogen, and nitrogen analyses were obtained
INTRODUCTION
The coordination chemistry of cobalt and copper complexes on an Eager 300 NCH System Elemental Analyzer (Zhengzhou,
with multidentate ligands has received considerable attention in College of Animal Husbandry, China). IR spectra of the com-
recent years for their biological and medicinal applications.[
1–3]
plexes were recorded as KBr pellets on a Nicolet-5700 FT-IR
Among the multidentate ligands, Schiff bases are considered as spectrophotometer (Zhengzhou, College of Animal Husbandry,
a very important class of organic compounds that have wide China).
applications in many biological aspects. Some Schiff bases
1
1
Synthesis of [Co(HL )2]·[Co(L )2] (1)
were reported to possess antibacterial, antifungal, and antitu-
1
mor activities.[4–7] Schiff base complexes have widely been
H L (1.0 mmol, 0.21 g) in methanol (30 mL) was added
with stirring to cobalt nitrate hexahydrate (0.5 mmol, 0.15 g)
in methanol (20 mL). The mixture was stirred at refluxed for
30 min to give a brown solution. The solution was left still
at room temperature in air to give brown block-shaped single
crystals, which were collected by filtration and dried in vacuum
containing anhydrous CaCl . The yield is 0.16 g (67.5%). Anal.
2
44 54 2 4 12
Calcd. for C H Co N O (%): C, 55.7; H, 5.7; N, 5.9. Found
(%): C, 55.5; H, 5.8; N, 5.8.
2
used as drugs. Moreover, it is well known that some biologi-
cal activities, when administered as metal complexes, are be-
ing increased.[
8,9]
We report herein the synthesis and charac-
terization of three mononuclear cobalt and copper complexes,
1
1
2
2
2
[
(
6
2
Co(HL )2]·[Co(L )2] (1), [Cu(HL )2] (2), and [CoL (HL )]2
1 2
3), where HL and HL are the monoanionic form of 2-ethoxy-
-[(2-hydroxyethylimino)methyl]phenol (H2L ) and 4-bromo-
-[(2-hydroxyethylimino)methyl]phenol (H2L ; Scheme 1), and
L and L are the dianionic form of H2L and H2L . The pre-
1
2
1
2
1
2
2
Synthesis of [Cu(HL )2] (2)
2
H2L (1.0 mmol, 0.24 g) in methanol (30 mL) was added
with stirring to copper acetate monohydrate (0.5 mmol, 0.10 g)
in methanol (20 mL). The mixture was stirred at refluxed for
Received 2 October 2011; accepted 24 March 2012.
30 min to give a blue solution. The solution was left still at
Address correspondence to Juan Du, Zhengzhou College of An-
imal Husbandry Engineering, Department of Pharmacy Engineering,
Zhengzhou 450011, P. R. China. E-mail: dujuan zz@126.com
room temperature in air to give blue block-shaped single crys-
tals, which were collected by filtration and dried in vacuum
1410

COBALT AND COPPER COMPLEXES WITH SCHIFF BASES
1411
TABLE 1
Crystal data and structural refinement details for the complexes
Complex
(1)
(2)
(3)
Chemical formula
Formula weight
Color and habit
T (K)
radiation (λ, Å)
Crystal system
Space group
a (Å)
C44H54Co2N4O12
948.8
C18H18Br2CuN2O4
549.7
C18H17Br2CoN2O4
544.1
brown, block
298(2)
Mo Kα (0.71073)
Orthorhombic
Pbca
blue, block
298(2)
Mo Kα (0.71073)
Monoclinic
P21/n
brown, block
298(2)
Mo Kα (0.71073)
Hexagonal
R-3
14.343(12)
16.019(13)
38.11(3)
90
90
90
8756(12)
8
1.439
4.9943(11)
17.1869(18)
10.9889(13)
90
94.513(2)
90
940.3(3)
2
1.941
19.096(2)
19.096(2)
27.402(3)
90
90
120
8653.7(16)
18
b (Å)
c (Å)
◦
α ( )
◦
β ( )
◦
γ ( )
V (Å )
3
Z
–
3
dcalcd (g cm )
µ (mm )
1.879
5.075
–1
0.825
5.438
F(000)
3968
542
4824
Reflections collected
Unique reflections
Observed reflections [I ≥ 2σ(I)]
No. of parameters
No. of restraints
45457
10762
4069
569
21
0.965
7548
2039
1475
125
17825
4203
2193
287
11
1.009
0.0422
0.0720
0.1192
0.0917
0
2
Goodness of fit on F
1.021
a
R1 [I ≥ 2σ(I)]
0.0733
0.1362
0.2188
0.1882
ꢀ
0.0353
0.0673
0.0599
0.0751
a
R1 (all data)
b
wR2 [I ≥ 2σ(I)]
b
wR2 (all data)
ꢀ
||Fo| – |Fc||/
ꢀ|Fo|, b
= [ꢀ
aR
2
2 2
2 2 1/2
1
=
wR
2
w(Fo – Fc ) / w(Fo ) ]
.
containing anhydrous CaCl2. The yield is 0.14 g (50.9%). Anal. absorption corrections were applied using the SADABS pro-
Calcd. for C18H18Br2CuN2O4 (%): C, 39.3; H, 3.3; N, 5.1. Found gram (Bruker, Germany).[ The structures of the complexes
10]
(
%): C, 39.5; H, 3.3; N, 5.2.
were solved by direct method and were refined by full-matrix
2
least-squares technique based on F using the SHELXL97 pack-
2
2
age (Bruker, Germany).[ All non-hydrogenatoms were refined
11]
Synthesis of [CoL (HL )]2 (3)
2
H2L (1.0 mmol, 0.24 g) in methanol (30 mL) was added anisotropically. The hydroxyl H atoms in the complexes (1)
with stirring to cobalt nitrate hexahydrate (0.5 mmol, 0.15 g) and (3) were located from difference Fourier maps and refined
in methanol (20 mL). The mixture was stirred at refluxed for isotropically, with O−H distances restrained to 0.85(1) Å. The
3
0 min to give a brown solution. The solution was left still remaining hydrogen atoms were refined as riding model. One
at room temperature in air to give brown block-shaped single ethylene group of (3) is disordered over two sites with occu-
crystals, which were collected by filtration and dried in vacuum pancies of 0.652(3) and 0.348(3). The crystallographic data and
containing anhydrous CaCl2. The yield is 0.19 g (69.9%). Anal. structure determination parameters for the complexes are given
Calcd. for C18H17Br2CoN2O4 (%): C, 39.7; H, 3.1; N, 5.1. Found in Table 1. Selected bond lengths and angles are summarized in
(%): C, 39.6; H, 3.2; N, 5.2.
Table 2.
Crystal Structure Determination
Antibacterial Test
Single crystals of the complexes were selected and mounted
The complexes and the free Schiff bases were determined
on glass fibers. The data were collected at 298(2) K on a against the bacteria S. aureus, E. coli, P. aeruginosa, and S.
Bruker SMART 1000 CCD area-detector (Liaocheng Univer- typhi. Microorganisms were cultured on M u¨ ller–Hinton agar
sity, China) with MoKα radiation (λ = 0.71073 Å). Multiscan medium. After drilling wells on medium using a 6 mm cork

1412
J. DU
TABLE 2
Selected bond lengths (Å) and angles ( ) for the complexes
◦
(
1)
Bond lengths
Co1-N1
Co1-O1
Co1-O4
Co2-N3
Co2-O7
Co2-O10
1.877 (5)
Co1-N2
Co1-O2
Co1-O5
Co2-N4
Co2-O8
Co2-O11
1.880 (5)
1.934 (4)
1.917 (4)
1.884 (5)
1.900 (4)
1.929 (4)
1.880 (4)
1.879 (4)
1.883 (4)
1.884 (4)
1.869 (4)
Bond angles
N1-Co1-O4
O4-Co1-N2
O4-Co1-O1
N1-Co1-O5
N2-Co1-O5
N1-Co1-O2
N2-Co1-O2
O5-Co1-O2
O10-Co2-N4
O10-Co2-O7
N4-Co2-O7
N3-Co2-O8
O7-Co2-O8
N3-Co2-O11
O7-Co2-O11
87.76 (18)
95.0 (2)
N1-Co1-N2
N1-Co1-O1
N2-Co1-O1
O4-Co1-O5
O1-Co1-O5
O4-Co1-O2
O1-Co1-O2
O10-Co2-N3
N3-Co2-N4
N3-Co2-O7
O10-Co2-O8
N4-Co2-O8
174.8 (2)
94.22 (19)
90.21 (18)
177.64 (16)
87.61 (16)
90.52 (16)
179.35 (17)
89.28 (18)
174.0 (2)
94.47 (19)
91.64 (17)
89.30 (19)
178.78 (17)
84.49 (19)
89.03 (17)
FIG. 1. Molecular structure of (1) at 30% probability displacement.
90.11 (16)
91.78 (18)
85.67 (19)
85.71 (19)
89.84 (18)
91.75 (15)
94.5 (2)
89.16 (17)
90.20 (19)
85.98 (19)
only methanol showed no inhibition in a preliminary test. The
macrodilution broth susceptibility assay was used for the evalu-
ation of minimal inhibitory concentration (MIC). By including
1 mL M u¨ ller-Hinton broth in each test, and then adding 1 mL
–
1
extract with concentration 100 µg mL in the first tube, we
made serial dilution of this extract from first tube to last tube.
Bacterial suspension prepared to match the turbidity of 0.5 Mc-
Farland turbidity standards. Matching this turbidity provides a
8
–1
179.09 (18) O10-Co2-O11
91.78 (17)
90.16 (17)
bacterial inoculum concentration of 1.5 × 10 cfu mL . Then
N4-Co2-O11
O8-Co2-O11
1 mL of bacterial suspension was added to each test tube. After
◦
incubation at 37 C for 24 h, the last tube was determined as the
MIC without turbidity.
(
2)
Bond lengths
1.943 (2) Cu1-N1
Bond angles
O1-Cu1-N1A
89.14 (11) N1-Cu1-N1A
3)
Bond lengths
Cu1-O1
1.997 (3)
RESULTS AND DISCUSSION
The Schiff bases were prepared by the reaction of equimolar
quantities of 2-aminoethanol with 3-ethoxysalicylaldehyde and
O1-Cu1-O1A
O1-Cu1-N1
180
90.86 (11)
180
5-bromosalicylaldehyde in methanol. The cobalt and copper
(
complexes were simply prepared by the reaction of the Schiff
bases with cobalt nitrate and copper acetate in methanol at open
air. The Co atom with +2 oxidation number in cobalt nitrate
was oxidized to +3 in the complexes (1) and (3).
Co1-O1
Co1-O3
Co1-N1
1.878 (3)
Co1-O2
Co1-O4
Co1-N2
1.924 (3)
1.921 (3)
1.890 (4)
1.869 (3)
1.881 (4)
Bond angles
O3-Co1-O1
O1-Co1-N1
O1-Co1-N2
O3-Co1-O4
N1-Co1-O4
O3-Co1-O2
N1-Co1-O2
O4-Co1-O2
90.82 (14)
94.58 (14)
87.84 (13)
178.48 (14)
92.83 (15)
88.27 (14)
86.18 (15)
90.57 (14)
O3-Co1-N1
O3-Co1-N2
N1-Co1-N2
O1-Co1-O4
N2-Co1-O4
O1-Co1-O2
N2-Co1-O2
86.11 (14)
94.83 (15)
177.39 (15)
90.35 (14)
86.18 (15)
178.77 (14)
91.41 (14)
borer, 100 µL of solution from different compounds was poured
◦
into each well. The plates were incubated at 37 C overnight.
The diameter of the inhibition zone was measured to the near-
est. Each test was carried out in triplicate and the average was
calculated for inhibition zone diameters. A blank containing
FIG. 2. Molecular structure of (2) at 30% probability displacement.

COBALT AND COPPER COMPLEXES WITH SCHIFF BASES
1413
TABLE 4
MIC values (µg mL )
–
1
Tested material S. aureus E. coli P. aeruginosa S. typhi
1
HL
HL
> 50
38.2
18.9
5.3
14.0
8.2
43.5
27.3
12.3
15.2
19.0
3.7
> 50
> 50
15.5
2.7
10.1
5.1
32.1
40.3
21.0
17.9
15.3
8.5
2
(
(
(
1)
2)
3)
Imipenum
(
2), and 1628 cm–1 for (3), indicating that the Schiff bases are
FIG. 3. Molecular structure of (3) at 30% probability displacement.
coordinated to the V atoms through the azomethine N atoms.
The middle ν(C-O) bands in the spectra of the complexes are
Structure Description of the Complexes
The molecular structures of the complexes (1), (2), and (3) are
presented in Figures 1, 2, and 3, respectively. The asymmetric
–
1
located at 1170–1183 cm . The weak bands in the low wave
–
1
numbers 400–570 cm can be assigned to the vibration of the
M-O and M-N bonds.
1
+
unit of the mononuclear complex (1) contains a [Co(HL )2]
1
–
cation and a [Co(L )2] anion. The mononuclear complex (2)
possesses a crystallographic inversion center symmetry, with
the Cu atom located at the inversion center. The Co atoms in
complexes (1) and (3) are coordinated by two phenolate O, two
hydroxy O, and two imine N atoms from two Schiff base ligands,
forming octahedral coordination. The Cu atom in complex (2)
is coordinated by two phenolate O and two imine N atoms
from two Schiff bases, forming square planar coordination. The
Co-O and Co-N coordinate bond lengths in the complexes (1)
and (3) are comparable to each other, and are also comparable
to the corresponding values observed in other similar cobalt
Antibacterial Activity
Transition metal complexes, in particular biometals contain-
ing biologically important ligands, have significance as potential
biologically relevant agents. The free Schiff bases and the three
complexes were tested in vitro for their antibacterial activities
against the bacteria S. aureus, E. coli, P. aeruginosa, and S. typhi
(Tables 3 and 4). The results were compared with the positive
control Imipenum.
From the results, we can found that the antibacterial activities
of the complexes are much more stronger than the free Schiff
bases. The copper complex (2) is in general more effective than
the cobalt complexes (1) and (3). It is interesting that complex (2)
show stronger activities against S. aureus and P. aeruginosa than
the reference drug Imipenum. The enhancement in the activity
of the complexes in comparison to the free ligands may be due
to the coordination of the Schiff bases to metal and an efficient
diffusion of the metal complexes into bacterial cell.[
[
12–14]
complexes with Schiff bases.
The Cu-O and Cu-N bond
lengths in complex (2) are comparable to the corresponding
values observed in other similar copper complexes with Schiff
bases.[
15–17]
Infrared Spectra
18,19]
The weak and broad bands in the region 3250–3470 cm–1
are assigned to the streching vibration of the O-H groups of
the Schiff bases and the complexes. In the IR spectra of the CONCLUSION
–
1
free Schiff bases, the ν(C N) bands are at about 1637 cm for
Three mononuclear cobalt and copper complexes have been
prepared by the reaction of the tridentate Schiff bases 2-
ethoxy-6-[(2-hydroxyethylimino)methyl]phenol and 4-bromo-
1
–1
2
HL and 1651 cm for HL , which are located at lower wave
–
1
–1
numbers for the complexes, 1619 cm for (1), 1625 cm for
2
-[(2-hydroxyethylimino)methyl]phenol with cobalt nitrate and
TABLE 3
Zone of growth inhibition (mm)
copper acetate, respectively. The structures of the complexes
have been characterized by elemental analysis, IR spectra, and
single-crystal X-ray diffraction. The Schiff bases coordinate to
the Co and Cu atoms through the NNO donor atoms. The com-
plexes show effective antibacterial activities against the bacteria
S. aureus, E. coli, P. aeruginosa, and S. typhi.
Tested material S. aureus E. coli P. aeruginosa S. typhi
HL1
HL
7
11
15
27
21
26
10
15
23
21
18
29
6
8
16
35
12
30
8
7
13
24
15
29
2
(
(
(
1)
2)
3)
SUPPLEMENTARY MATERIALS
X-ray crystallographic data for the complexes have been de-
posited with the Cambridge Crystallographic Data Centre (The
Imipenum

1414
J. DU
Director, CCDC, 12 Union Road, Cambridge, CB2 1 EZ, UK;
e-mail: deposit@ccdc.cam.ac.uk; http://www.ccdc.cam.ac.uk;
fax: +44-(0)1223–336033) and are available free of charge on
request, quoting the deposition number CCDC 846540 for (1),
Co(II), Ni(II) and Cu(II) complexes with 1,2,4-triazole Schiff bases. Eur. J.
Med. Chem. 2008, 43, 2639–2649.
. Sun, Y.-X. Synthesis, crystal structures and antibacterial activities of two
Schiff base copper(II) complexes. Synth. React. Inorg. Met.-Org. Nano-Met.
Chem. 2006, 36, 621–625.
0. Sheldrick, G. M. SADABS. Program for Empirical Absorption Correction
of Area Detector; G o¨ ttingen, Germany: University of G o¨ ttingen, 1996.
1. Sheldrick, G. M.; SHELXTL Version 5.1, Software Reference Manual,
Madison (WI, USA): Bruker AXS, 1997.
9
846541 for (2), and 846542 for (3).
1
1
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