Synthesis, structures, and antimicrobial activities of dimeric oxovanadium(V) complexes with tridentate schiff bases

Article abstract of DOI:10.1080/15533174.2012.751420

Two new dimeric oxovanadium(V) complexes, [VO₂L ¹]₂ (1) and [VO₂L²]₂ (2), where L¹ and L² are the monoanionic form of 2-{1-[2-(2-hydroxyethylamino)ethylimino]ethyl}phe

Full text of DOI:10.1080/15533174.2012.751420

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Synthesis, Structures, and Antimicrobial Activities of
Dimeric Oxovanadium(V) Complexes with Tridentate
Schiff Bases
a
a
a
Xiao-Jun Zhao , Ling-Wei Xue & Gan-Qing Zhao
a
College of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan
Henan, 467000, P.R. China
Accepted author version posted online: 07 Mar 2013.
To cite this article: Xiao-Jun Zhao , Ling-Wei Xue & Gan-Qing Zhao (2013): Synthesis, Structures, and Antimicrobial Activities
of Dimeric Oxovanadium(V) Complexes with Tridentate Schiff Bases, Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry, DOI:10.1080/15533174.2012.751420
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ACCEPTED MANUSCRIPT
Synthesis, Structures, and Antimicrobial Activities of Dimeric Oxovanadium(V) Complexes
with Tridentate Schiff Bases
Xiao-Jun Zhao, Ling-Wei Xue*, Gan-Qing Zhao
College of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan Henan
4
*
67000, P.R. China
Corresponding author. E-mail: pdsuchemistry@163.com
Abstract
1
2
1
2
Two new dimeric oxovanadium(V) complexes, [VO
2
L ]
2
(1) and [VO
2
L ]
2
(2), where L and L
1
are the mono-anionic form of 2-{1-[2-(2-hydroxyethylamino)ethylimino]ethyl}phenol (HL ) and
2
2
-[1-(2-ethylaminoethylimino)ethyl]phenol (HL ), respectively, have been synthesized and
characterized by elemental analysis, FT-IR spectra, and single crystal X-ray determination. The
crystal of complex (1) is orthorhombic: space group Pbca, a = 9.284(1), b = 12.733(2), c =
3
2
1.626(3) Å, V = 2556.5(7) Å , Z = 4. The crystal of complex (2) is orthorhombic: space group
3
Pbca, a = 9.618(2), b = 12.416(3), c = 21.370(3) Å, V = 2552.0(9) Å , Z = 4. The V···V distances
are 3.138(1) Å in complex (1) and 3.141(1) Å in complex (2). The V atoms in the complexes are
octahedrally coordinated. The antimicrobial activity of the free Schiff bases and the complexes
were studied. The complexes have potential activities against Staphylococcus aureus,
Escherichia coli, and Candida albicans.
Keywords oxovanadium, Schiff base, crystal structure, dimeric complex, antimicrobial activity
1
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INTRODUCTION
Coordination chemistry of oxovanadium complexes with multi-dentate ligands has received
[1-4]
considerable attention in recent years for their biological and medicinal applications.
Among
the multi-dentate ligands, Schiff bases are considered as a very important class of organic
compounds which have wide applications in many biological aspects. Some Schiff bases were
[5-7]
reported to possess antibacterial, antifungal and antitumor activities.
Schiff base complexes
have been used as drugs. Moreover, it is well known that some biological activities, when
[8,9]
administered as metal complexes, are being increased.
The literature reveals that
oxovanadium complexes with Schiff bases have been less studied. We report herein the
synthesis, characterization, and antimicrobial activities of two new dimeric oxovanadium(V)
1
2
1
2
complexes, [VO
2
L ]
2
(1) and [VO
2
L ]
2
(2), where L and L are the deprotonated form of 2-{1-
1
[
2-(2-hydroxyethylamino)ethylimino]ethyl}phenol (HL ; Chart 1) and 2-[1-(2-
2
ethylaminoethylimino)ethyl]phenol (HL ; Chart 1), respectively.
EXPERIMENTAL
Materials and methods
2
-Acetylphenol, 2-(2-aminoethylamino)ethanol, and N-ethylethane-1,2-diamine 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 240B
automatic analyzer. Vanadium content of the complexes was determined as V
were recorded on an IR-408 Shimadzu 568 spectrophotometer.
2
5
O . IR spectra
1
Synthesis of L
2
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2
-Acetylphenol (1.36 g, 0.01 mmol) and 2-(2-aminoethylamino)ethanol (1.04 g, 0.01 mol) were
mixed in methanol (60 mL). The mixture was stirred at reflux for 30 min and three quarter of the
1
solvent was evaporated, to give yellow solid product of L , which was collected by filtration and
dried in vacuum containing anhydrous CaCl
2
. The yield is 1.89 g (85.1%). Analysis calculated
for C12
H
18
N
2
O
2
: C, 64.8; H, 8.2; N, 12.6%; found: C, 64.5; H, 8.2; N, 12.7%.
2
Synthesis of L
2
-Acetylphenol (1.36 g, 0.01 mmol) and N-ethylethane-1,2-diamine (0.88 g, 0.01 mol) were
mixed in methanol (60 mL). The mixture was stirred at reflux for 30 min and three quarter of the
2
solvent was evaporated, to give yellow solid product of L , which was collected by filtration and
dried in vacuum containing anhydrous CaCl
2
. The yield is 1.21 g (58.8%). Analysis calculated
for C12
H
18
N
2
O: C, 69.9; H, 8.8; N, 13.6%; found: C, 69.7; H, 8.9; N, 13.7%.
Synthesis of complex (1)
1
L (0.5 mmol, 0.11 g) in methanol (20 mL) was added with stirring to VO(acac)
2
(0.5 mmol,
0
.13 mg) in methanol (10 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 0.11 g (72.4%). Analysis calculated for C24 : C, 47.4; H, 5.6; N, 9.2; V,
6.7%; found: C, 47.6; H, 5.7; N, 9.3; V, 16.9%.
2
.
H
34
N
4
O
8
V
2
1
Synthesis of complex (2)
2
L (0.5 mmol, 0.10 g) in methanol (20 mL) was added with stirring to VO(acac)
2
(0.5 mmol,
0
.13 mg) in methanol (10 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
3
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crystals, which were collected by filtration and dried in vacuum containing anhydrous CaCl .
2
The yield is 0.09 g (62.5%). Analysis calculated for C24
7.7%; found: C, 49.7; H, 5.9; N, 9.6; V, 17.9%.
X-ray crystal determination
Data were collected from selected crystals mounted on glass fibers. The data for the complexes
H
34
N
4
O
6
2
V : C, 50.0; H, 5.9; N, 9.7; V,
1
[10]
[11]
were processed with SAINT and corrected for absorption using SADABS. Semi-empirical
[12]
absorption corrections were applied with ψ scans. The structures of the complexes were
solved by direct method using the SHELXS-97 program and refined by full-matrix least-squares
2
[13]
techniques on F using anisotropic displacement parameters. All non-hydrogen atoms were
refined anisotropically. Amino H atoms in the complexes were located from difference Fourier
maps and refined isotropically, with NH distances restrained to 0.90(1) Å. The remaining
hydrogen atoms were placed at the calculated positions. Crystallographic data for the complexes
are listed in Table 1. Selected bond lengths and angles are given in Table 2. Hydrogen bonding
information is listed in Table 3.
RESULTS AND DISCUSSION
The synthesis of the complexes is shown as Chart 2.
Crystal structure description of the complexes
The molecular structures of complexes (1) and (2) are shown in Figs. 1 and 2, respectively. The
two complexes crystallize as centrosymmetric dimeric structures, with the inversion center
located at the midpoint of the two V atoms. The V···V distances are 3.138(1) Å in complex (1)
and 3.141(1) Å in complex (2). The V atom in each complex is octahedrally coordinated, with
4
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phenolic O, imino N, and amine N atoms of the Schiff base ligand and one oxo O atom defining
the equatorial plane, and two oxo O atoms occupying the two axial positions. The V atoms
deviate from the least-squares planes defined by the four equatorial donor atoms are 0.332(1) Å
in complex (1), and 0.354(1) Å in complex (2). The V–O and V–N coordinate bond lengths in
the complexes are comparable to each other, as well as the corresponding values observed in
[14-17]
other similar oxovanadium(V) complexes with Schiff bases.
There exist two N−H···O
hydrogen bonds between the two [VO
2
L] units, which might contribute to the formation of
dimeric structures.
Infrared spectra
In the infrared spectra of the free Schiff bases, weak ν(O–H) bands were observed at about
-1
3
420–3450 cm . The bands are absent after chelation, suggesting coordination through the
deprotonated form. In the infrared spectra of the free Schiff bases, ν(C=N) bands are at about
-1
–1
1
643 cm , which are located at lower wave numbers for the complexes, 1612–1615 cm ,
indicating that the Schiff bases are coordinated to the V atoms through azomethine N atoms. The
-1
middle ν(C–O) bands in the spectra of the complexes are located at 1125–1129 cm . The
-1
characteristic ν(V=O) and ν(V–O) bands can be monitored at 985 and 435-470 cm ,
respectively.
Antimicrobial activity
Qualitative determination of antimicrobial activity was done using the disk diffusion
[18,19]
method.
The results are summarized in Table 4. A comparative study of minimum
inhibitory concentration (MIC) values of the Schiff bases and the two complexes indicate that the
cobalt complexes have better activity than the free Schiff bases. Generally, this is caused by the
5
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greater lipophilic nature of the complexes than the ligand. Such increased activity of the metal
[20]
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 is obvious that the complexes showed greater antimicrobial and antifungi
activities against Staphylococcus aureus, Escherichia coli, and Candida albicans when
compared to the free Schiff bases. The structures of the tested compounds seem to be the
principal factor influencing the antimicrobial activity. For Staphylococcus aureus and
Escherichia coli, the activities of complex (1) are stronger than complex (2). And for Candida
albicans, both complexes have similar activities. It is somewhat disappointed that even though
the activities for Staphylococcus aureus and Escherichia coli of the complexes are stronger than
those of the free Schiff bases, they are still much less than the control drug Tetracycline. But for
Candida albicans, both complexes showed stronger activities than the Schiff bases and
Tetracycline.
CONCLUSION
In summary, two new centrosymmetric dimeric oxovanadium(V) complexes have been
prepared by reaction of the tridentate Schiff bases 2-{1-[2-(2-
hydroxyethylamino)ethylimino]ethyl}phenol and 2-[1-(2-ethylaminoethylimino)ethyl]phenol
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with VO(acac)
infrared spectra and single crystal X-ray diffraction. The Schiff bases coordinate to the V atoms
through the NNO donor atoms. The existence of N−H···O hydrogen bonds between two [VO L]
2
. The structures of the complexes have been characterized by elemental analysis,
2
units might contributes to the formation of dimeric structures. Antimicrobial test shows that both
complexes have potential activities against Staphylococcus aureus, Escherichia coli, and
Candida albicans.
SUPPLEMENTARY MATERIAL
CCDC-846536 for complex (1) and 846537 for complex (2) contain the supplementary
crystallographic data for this paper. These data can be obtained free of charge at
http://www.ccdc.cam.ac.uk/const/retrieving.html or from the Cambridge Crystallographic Data
Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk.
ACKNOWLEDGMENTS
This research was supported by the National Sciences Foundation of China (No. 20676057 and
2
0877036) and Top-class foundation of Pingdingshan University (No. 2008010).
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0
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FIG. 1. Molecular structure of (1) at 30% probability displacement. Symmetry code for A: 2 – x,
–
y, – z.
FIG. 2. Molecular structure of (2) at 30% probability displacement. Symmetry code for A: 2 – x,
– y, – z.
1
H
H
N
N
N
OH
N
OH
OH
1
2
Chart 1. The Schiff bases HL and HL
1
1
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N
O
O
H
N
H
R
N
R
O
V
N
methanol
reflux
+ VO(acac)
2
O
OH
H
N
V
O
R
O
N
Chart 2. The preparation of the complexes [R = CH
2)]
2
OH for complex (1) and CH
3
for complex
(
TABLE 1 Crystal and structure refinement data for (1) and (2)
Compound
CCDC
(1)
(2)
846536
846537
Molecular formula
Molecular weight
Crystal system
Space group
a /Å
C
24
H
34
N
4
O
8
V
2
C
24
H
34
N
4
O
6
V
2
608.4
576.4
Orthorhombic
Pbca
Orthorhombic
Pbca
9.284(1)
12.733(2)
21.626(3)
2556.5(7)
4
9.618(2)
12.416(3)
21.370(3)
2552.0(9)
4
b /Å
c /Å
3
V /Å
Z
1
2
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-3
D
calc (g cm )
1.581
1.500
Crystal dimensions (mm)
0.20 × 0.20 × 0.17
0.788
0.17 × 0.15 × 0.15
0.779
-
1
µ (mm )
Radiation λ
Mo Kα (0.71073 Ǻ)
0.8583/0.8777
12786
Mo Kα (0.71073 Ǻ)
0.8789/0.8921
14239
T
min/Tmax
Reflections measured
Range/indices (h, k, l)
θ limit (°)
-11, 11; -16, 10; -27, 23 -12, 12; -13, 15; -27, 18
2.87–27.00
2778 [Rint = 0.0408]
2104
2.84-27.00
Unique reflections
Observed reflections (I >
2771 [Rint = 0.0342]
2240
2
σ(I))
Parameters
Restraints
178
168
1
1
2
Goodness of fit on F
1.046
1.050
a
R
1
1
, wR
, wR
2
2
[I  2(I)]
0.0364, 0.0893
0.0542, 0.0982
0.0341, 0.0824
0.0458, 0.0883
a
R
(all data)
a
2
2 2
2 2 1/2
R
1
= F
o
-F
c
/F
o
, wR
2
= [w(F
o
-F
c
) /w(F ) ]
o
TABLE 2 Selected bond lengths (Å) and angles (°) for (1) and (2)
(
1)
1
3
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Bond lengths
V1-O1
1.889(2)
1.683(2)
2.179(2)
V1-O3
V1-O4
V1-N2
2.347(2)
1.603(2)
2.169(2)
V1-O3A
V1-N1
Bond angles
O4-V1-O3A
O3-V1-O1A
O3-V1-N2A
O4-V1-N1
O1-V1-N1
O4-V1-O3
O1-V1-O3
N1-V1-O3
107.1(1)
99.8(1)
92.7(1)
95.3(1)
82.8(1)
170.9(1)
83.5(1)
77.8(1)
O4-V1-O1
O4-V1-N2
O1-V1-N2
O3-V1-N1A
N2-V1-N1
O3-V1-O3A
N2-V1-O3
101.8(1)
93.3(1)
156.6(1)
156.3(1)
78.0(1)
79.0(1)
79.5(1)
Symmetry code for A: 2 – x, – y, – z
2)
(
Bond lengths
V1-O1
1.907(2)
1.669(1)
2.188(2)
V1-O2
V1-O3
V1-N2
1.614(2)
2.364(2)
2.161(2)
V1-O3A
V1-N1
Bond angles
O2-V1-O3A
O3-V1-O1A
107.7(1)
99.5(1)
O2-V1-O1
O2-V1-N2
101.8(1)
94.8(1)
1
4
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O3-V1-N2A
O2-V1-N1
O1-V1-N1
O2-V1-O3
O1-V1-O3
N1-V1-O3
91.8(1)
95.9(1)
82.9(1)
170.4(1)
83.3(1)
76.6(1)
O1-V1-N2
O3-V1-N1A
N2-V1-N1
O3-V1-O3A
N2-V1-O3
155.9(1)
155.1(1)
78.0(1)
79.1(1)
78.0(1)
Symmetry code for A: 2 – x, 1 – y, – z
TABLE 3 Hydrogen geometries for (1) and (2)
D–H···A
1)
d(D–H) (Å) d(H···A) (Å) d(D···A) (Å) Angle(D–H···A) (°)
(
i
N2–H2A···O1
0.88(1)
0.82
2.33(2)
2.05
3.027(2)
2.841(3)
136(2)
161
ii
O2–H2···O3
(
2)
iii
N2–H2···O1
0.89(1)
2.21(2)
2.959(2)
142(3)
Symmetry codes: i) 2 – x, – y, – z; ii) 3/2 – x, 1/2 + y, z; iii) 2 – x, 1 – y, – z.
TABLE 4 MIC values (µg/mL) for the antimicrobial activities of the tested compounds
Staphylococcus
Escherichia coli
Candida albicans
1
5
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aureus
1
HL
64
256
2
256
128
16
> 1024
> 1024
256
2
HL
(
(
1)
2)
8
32
128
Tetracycline
0.32
2.12
> 1024
1
6
ACCEPTED MANUSCRIPT