Synthesis, crystal structures, and biological property of dinuclear oxovanadium(V) complexes derived from tridentate Schiff bases

Article abstract of DOI:10.1134/S1070328414060116

A pair of structurally similar dinuclear oxovanadium(V) complexes, [VO ₂L¹]₂ (I) and [VO₂L ²]₂ (II), where L¹ and L² are the mono-anionic form of 2-[(2-isopropylaminoethylimino)methyl]-4-methylphenol (HL¹) and 4-fluoro-2-[(2-isopropylaminoethylimino)methyl]phenol (HL²), respectively, have been synthesized and characterized by elemental analysis, FT-IR spectra, and single crystal X-ray determination. The crystal of I is monoclinic: space group P2₁/c, a = 12.528(1), b = 12.266(1), c = 9.432(1) A, β = 104.814(3)°, V = 1401.2(3) A³, Z = 2. The crystal of I is monoclinic: space group P2 ₁/n, a = 12.3128(5), b = 6.5124(3), c = 17.1272(7) A, β = 105.863(1)°, V = 1321.1(1) A³, Z = 2. The V...V distances are 3.210(1) A in I and 3.219(1) A in II. The V atoms in the complexes are in octahedral coordination. Biological assay indicates that complex II, bearing fluoro-substitute groups, has stronger antimicrobial activity against most bacteria than complex I which bearing methyl-substitute groups.

Full text of DOI:10.1134/S1070328414060116

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2014, Vol. 40, No. 6, pp. 407–412. © Pleiades Publishing, Ltd., 2014.
Synthesis, Crystal Structures, and Biological Property of Dinuclear
Oxovanadium(V) Complexes Derived from Tridentate Schiff Bases1
,
X. J. Zhaoa, Q. Pengb, and L. W. Xuea *
aCollege of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan Henan, 467000 P.R. China
bCollege of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang Henan, 464000 P.R. China
*eꢀmail: pdsuchemistry@163.com
Received January 27, 2014
Abstract—A pair of structurally similar dinuclear oxovanadium(V) complexes, [VO2L1]2 ( ) and [VO2L2]2
I
(
II), where L1 and L2 are the monoꢀanionic form of 2ꢀ[(2ꢀisopropylaminoethylimino)methyl]ꢀ4ꢀmethylpheꢀ
nol (HL1) and 4ꢀfluoroꢀ2ꢀ[(2ꢀisopropylaminoethylimino)methyl]phenol (HL2), respectively, have been synꢀ
thesized and characterized by elemental analysis, FTꢀIR spectra, and single crystal Xꢀray determination. The
crystal of
V
c
I
is monoclinic: space group
= 1401.2(3) Å3,
= 2. The crystal of
= 17.1272(7) Å, = 105.863(1)
= 1321.1(1) Å3,
P
21/
c
,
a
= 12.528(1),
b
= 12.266(1),
21/
c
β
= 104.814(3)
= 6.5124(3),
and
°
,
Z
I
is monoclinic: space group
P
n
,
β
°
,
V
Z
= 2. The V···V distances are 3.210(1) Å in
I
3.219(1) Å in II. The V atoms in the complexes are in octahedral coordination. Biological assay indicates that
complex II, bearing fluoroꢀsubstitute groups, has stronger antimicrobial activity against most bacteria than
complex I which bearing methylꢀsubstitute groups.
DOI: 10.1134/S1070328414060116
INTRODUCTION
increased [8, 9]. The literature reveals that oxovanaꢀ
dium complexes with Schiff bases have been less studꢀ
ied. Zhang and coworkers have reported that haloꢀ
subsituted compounds usually have effective biological
properties [10]. We report herein two new dimeric
Vanadium complexes with various types of organic
ligands have received remarkable attention in recent
years for their biological and medicinal applications
[1–4]. Among the 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 reported to possess antibacteꢀ
rial, antifungal and antitumor activities [5–7]. Moreꢀ
over, it is well known that some biological activities,
oxovanadium(V) complexes, [VO2L1]2
(
I)
and
[VO2L2]2 (II), where L1 and L2 are the monoꢀanionic
form of 2ꢀ[(2ꢀisopropylaminoethylimino)methyl]ꢀ4ꢀ
methylphenol (HL1) and 4ꢀfluoroꢀ2ꢀ[(2ꢀisopropyꢀ
when administered as metal complexes, are being laminoethylimino)methyl]phenol (HL2), respectively.
H
H
N
F
N
N
N
OH
(HL1)
OH
(HL2)
EXPERIMENTAL
Materials and methods. 5ꢀMethylsalicylaldehyde,
5ꢀfluorosalicylaldehyde, and ꢀisopropylethaneꢀ1,2ꢀ
and solvents were analytical grade and used without
further purification. Elemental (C, H, and N) analyses
were made on a PerkinElmer Model 240B automatic
N
diamine were purchased from Fluka. Other reagents analyzer. The vanadium content was determined as
1
The article is published in the original.
407

408
ZHAO et al.
V2O5. IR spectra were recorded on an IRꢀ408 Shiꢀ
madzu 568 spectrophotometer.
For C24H32F2N4O6V2 (II
anal. calcd., %: C, 47.07; H, 5.27; N, 9.15; V, 16.64.
Found, %: C, 47.21; H, 5.33; N, 9.06; V, 16.83.
)
Synthesis of HL1 and HL2.
NꢀIsopropylethaneꢀ
1,2ꢀdiamine (1.02 g, 0.01 mol) and 5ꢀmethylsalicylalꢀ
dehyde (1.36 g, 0.01 mmol) for HL1 or 5ꢀfluorosalicyꢀ
laldehyde (1.40 g, 0.01 mmol) for HL2 were mixed in
methanol (30 mL). The mixtures were stirred at reflux
for 30 min and the solvent was evaporated to give yelꢀ
low oily products of HL1 and HL2.
Xꢀray crystal determination. Data were collected
from selected crystals mounted on glass fibers. The
data for the complexes were processed with SAINT
[11] and corrected for absorption using SADABS [12].
Multiꢀscan absorption corrections were applied with
ψ
scans [13]. The structures were solved by direct
For C13H20N2O (HL1)
method using the SHELXSꢀ97 program and refined
by fullꢀmatrix leastꢀsquares techniques on F2 using
anisotropic displacement parameters [14]. All nonꢀ
hydrogen atoms were refined anisotropically. The
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 posiꢀ
tions. The 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. Supplementary materials have been
deposited with the Cambridge Crystallographic Data
anal. calcd., %: C, 70.87;
Found, %: C, 70.62;
H, 9.15;
H, 9.23;
N, 12.72.
N, 12.85.
For C12H17FN2O (HL2)
anal. calcd., %: C, 64.26;
H, 7.64;
H, 7.55;
N, 12.49.
N, 12.60.
Found, %:
C, 64.37;
Synthesis of the complexes. The Schiff bases
(0.5 mmol each) in methanol (20 mL) was added with
stirring to VOAacac)2 (0.5 mmol, 0.13 g) in methanol
(10 mL). The mixtures were stirred at refluxed for
30 min to give yellow solution. The solution was left
still at room temperature in air to give yellow blockꢀ
shaped single crystals, which were collected by filtraꢀ
tion and dried in vacuum containing anhydrous
CaCl2. The yields were over 70%.
Centre (nos. 960528 (I) and 960527 (II); deposit@
ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
For C26H38N4O6V2 (
anal. calcd., %: C, 51.66; H, 6.34; N, 9.27; V, 16.85.
Found, %: C, 51.51; H, 6.40; N, 9.18; V, 17.02.
I)
The synthesis of the complexes is shown in
Scheme:
R
N
O
N
V
H
O
H
R
N
Methanol
reflux
N
O
+ VO(Acac)2
O
O
H
N
O
V
OH
N
R
R = CH3 (I), F (II)
Scheme.
The molecular structures of the complexes I and II defining the equatorial plane, and with two oxo O
are shown in Fig. 1. Both complexes crystallize as cenꢀ atoms occupying the two axial positions. The V atoms
trosymmetric dinuclear structures, with the inversion deviate from the leastꢀsquares planes defined by the
center located at the midpoint of the two V atoms. The four equatorial donor atoms by 0.357(1) Å in
I and
V
⋅⋅⋅V distances are 3.210(1) Å in and 3.219(1) Å in II 0.350(1) Å in II. The V–O and V–N coordinate bond
I
.
The V atom in each complex is in an octahedral coorꢀ lengths in the complexes are comparable to each other
dination with the phenolate O, imine N, and amine N and also comparable to the corresponding values
atoms of the Schiff base ligand and one oxo O atom observed in other similar oxovanadium(V) complexes
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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2014

SYNTHESIS, CRYSTAL STRUCTURES, AND BIOLOGICAL PROPERTY
Table 1. Crystallographic data and structure refinement summary for complexes and II
Value
409
I
Parameter
I
II
Habit, colour
Block, yellow
604.48
Block, yellow
612.42
Formula weight
Temperature, K
Crystal size, mm
298(2)
298(2)
0.27
Mo
×
0.23
×
0.23
0.20
×
0.20
×
0.17
Radiation,
λ
, Å
K
(0.71073)
Mo
K (0.71073)
α
α
Crystal system
Monoclinic
21/
Monoclinic
21/
Space group
P
c
P
n
Unit cell dimensions:
a
, Å
, Å
12.528(1)
12.266(1)
9.432(1)
104.814(3)
1401.2(3)
2
12.3128(5)
6.5124(3)
17.1272(7)
105.863(1)
1321.1(1)
2
b
c
, Å
β
V
Z
, deg
, Å3
ρcalcd, mg cm–3
1.433
1.540
F
(000)
632
632
Absorption coefficient, mm–1
0.713
0.768
θ
Range for data collection, deg
2.36–25.50
2.47–25.50
Index ranges
⎯
13
≤
h
≤
15,
⎯14
≤
k
≤
12,
⎯11
≤
l
≤
11
⎯
14
≤
h
≤
14,
⎯
7
≤
k
≤
7,
⎯
20
≤
l ≤ 20
Reflections collected
Independent reflections
Data/restraints/parameters
12454
2605
12092
2443
2008/1/179
0.0342
2173/1/178
0.0289
Final
R
indices (
I
> 2σ(I))
R
indices (all data)
0.0839
0.0768
Goodnessꢀofꢀfit
Å–3
1.047
1.070
Δρmax
,
Δρmin
,
e
0.255, –0.236
0.218, –0.204
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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410
ZHAO et al.
Table 2. Coordinate bond distances (Å) and angles (deg) for Table 3. Hydrogen bond distances (Å) and bond angles
complexes
I
and II
*
(deg) for complexes
I
and II
*
Distance, Å
Bond
d
, Å
Bond
d, Å
Angle
D–H⋅⋅⋅A,
deg
D–H⋅⋅⋅
A
D–H
H⋅⋅⋅A
D⋅⋅⋅A
I
V(1)–O(1)
V(1)–O(3)
V(1)–N(2)
1.919(2) V(1)–O(2)
1.660(2) V(1)–N(1)
1.607(2)
2.157(2)
2.408(2)
I
N(2)–H(2)⋅⋅⋅O(1)i 0.90(1) 2.34(2) 3.072(2) 139(2)
N(2)–H(2)⋅⋅⋅O(3)i 0.90(1) 2.33(2) 2.871(2) 119(2)
II
2.184(2) V(1)–O(3
A)
II
N(2)–H(2)⋅⋅⋅O(1)ii 0.90(1) 2.36(2) 3.062(2) 135(2)
N(2)–H(2)⋅⋅⋅O(3) 0.90(1) 2.36(2) 2.897(2) 118(2)
V(1)–O(1)
V(1)–O(3)
V(1)–N(2)
1.926(1) V(1)–O(2)
2.445(1) V(1)–N(1)
1.612(1)
2.155(2)
1.658(1)
i
ii
2.155(2) V(1)–O(3
B)
* Symmetry codes for: 2 – x, 1 – y, ⎯z; –x, 2 – y, –z.
Angle
ω
, deg Angle
ω
, deg
Table 4. MIC values (
the compounds
μg/mL) for antimicrobial activities of
I
Staphylococꢀ Escherichia
Candida
albicans
O(2)V(1)O(3)
O(3)V(1)O(1)
107.00(8) O(2)V(1)O(1) 100.67(8)
Compound
cus aureus
coli
99.13(7) O(2)V(1)N(1)
99.72(8)
84.52(7)
92.37(7)
76.44(7)
77.36(7)
74.89(6)
HL1
32
16
8
128
32
16
8
>512
128
64
O(3)V(1)N(1) 151.74(7) O(1)V(1)N(1)
O(2)V(1)N(2) 94.20(8) O(3)V(1)N(2)
O(1)V(1)N(2) 157.58(7) N(1)V(1)N(2)
HL2
I
O(2)V(1)O(3
A
)
)
170.67(7) O(3)V(1)O(3A)
II
2
64
O(1)V(1)O(3
A
86.55(6) N(1)V(1)O(3A)
N(2)V(1)O(3
A
)
77.22(6)
Tetracycline
0.32
2.12
>512
II
with Schiff bases [15–18]. There exist two N–H⋅⋅⋅
O
O(2)V(1)O(3
B
)
108.85(7) O(2)V(1)O(1) 100.13(6)
hydrogen bonds between the two [VO2L] units, which
might contribute to the formation of dimeric strucꢀ
tures. Crystal structures of the complexes are stabilized
by hydrogen bonds, as shown in Fig. 2.
O(3
B
B
)V(1)O(1) 98.83(6) O(2)V(1)N(1)
)V(1)N(1) 153.48(6) O(1)V(1)N(1)
96.42(6)
84.10(6)
O(3
O(2)V(1)N(2)
94.66(6) O(3B)V(1)N(2) 92.67(6)
In the infrared spectra of the free Schiff bases, the
weak (O–H) bands were observed at about 3350–
ν
O(3)V(1)N(2) 157.16(6) N(1)V(1)N(2)
76.98(6)
78.35(6)
75.63(5)
3480 cm–1. The bands are absent after chelation, sugꢀ
gesting the coordination through the deprotonated
form. In the infrared spectra of the free Schiff bases,
O(2)V(1)O(3)
O(1)V(1)O(3)
N(2)V(1)O(3)
* Symmetry codes: (
169.99(6) O(3)V(1)O(3B)
the
which are located at lower wave numbers for the comꢀ
plexes, 1637 cm–1 for and 1639 cm–1 for II, indicatꢀ
ν
(C=N) bands are at about 1647–1651 cm–1,
85.27(5) N(1)V(1)O(3)
77.78(5)
I
ing that the Schiff bases are coordinated to the
Vatoms through the azomethine N atoms. The midꢀ
A) 2 – x, 1 – y, –z; (B) –x, 2 – y, –z.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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SYNTHESIS, CRYSTAL STRUCTURES, AND BIOLOGICAL PROPERTY
411
(a)
C(12)
C(10)
C(9)
C(13)
C(9)
N(1)
C(11)
O(2)
C(1)
C(6)
C(5)
N(2)
O(3)
C(3
A
)
)
C(7)
O(1
A
)
V(1)
O(3
C(4A)
C(2
A
)
C(2)
C(4)
A
)
O(1)
C(1
A
)
C(7A)
C(3)
C(5A)
V(1A
)
C(8A)
C(6A
O(2A)
N(1A
)
N(2A)
C(11A)
C(9A)
C(13A)
C(12A)
C(10
A)
(b)
C(9B)
C(11B)
C(12B)
C(8B
)
N(1
B
)
C(6B)
C(1B)
O(2B)
N(2B)
C(10B)
C(7B)
C(5B)
V(1B)
F(1B)
O(3)
C(3)
C(2)
C(4)
C(5)
C(4B)
C(2B)
O(1B)
O(3B)
C(3B)
O(1)
C(7)
V(1)
O(2)
C(8)
C(1)
F(1)
C(10)
C(6)
N(2)
N(1)
C(12)
C(9)
C(11)
Fig. 1. Molecular structure of I (a) and II (b) at 30% probability displacement. Hydrogen bonds are drawn as dotted lines.
dle
ν
(C–O) bands in the spectra of the complexes are the metal atoms will be reduced to a greater extent
located at 1123 cm–1 for
I
and 1127 cm–1 for II. The
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 derealization
characteristic
ν
(V=O) and
ν
(V–O) bands can be
monitored at about 940 and 450 cm–1, respectively.
of
pꢀelectrons over the whole chelate ring and
Qualitative determination of antimicrobial
activity was done using the disk diffusion method
[19, 20]. The results are summarized in Table 4.
Generally, the complexes show greater antimicroꢀ
bial activities against Staphylococcus aureus,
Escherichia coli, and Candida albicans, when comꢀ
pared to the free Schiff bases. Generally, this is
caused by the greater lipophilic nature of the comꢀ
plex than the ligand. Such increased activity of the
metal chelates can be explained on the basis of
enhances the lipophilicity of the complex. This
increased lipophilicity enhances the penetration of
the complex into the lipid membrane and blocks the
metal binding sites on enzymes of microorganisms.
In addition, it is obvious that complex II has stronꢀ
ger activities than complex I. Detailed study on the
relationship between the structures of the Schiff
bases and complexes with their activities can conꢀ
clude that the fluoroꢀsubstitute groups can increase
chelating theory [21]. On chelating, the polarity of the biological properties.
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ZHAO et al.
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