Oxovanadium(V) complexes incorporating tridentate aroylhydrazoneoximes: Synthesis, characterizations and antibacterial activity

Article abstract of DOI:10.1016/j.poly.2011.10.017

Some new oxovanadium(V) complexes, [VOL^1-3(OEt)(EtOH)] (1-3), have been reported, which were obtained from the reaction of the Schiff bases H₂L^1-3 (where H₂L¹ = the salicylhydrazone of diacetyl monoxi

Full text of DOI:10.1016/j.poly.2011.10.017

Polyhedron 31 (2012) 524–529
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Oxovanadium(V) complexes incorporating tridentate aroylhydrazoneoximes:
Synthesis, characterizations and antibacterial activity
Subhashree P. Dash a, Sagarika Pasayat a, Saswati a, Hirak R. Dash b, Surajit Das b, Ray J. Butcher c,
Rupam Dinda a,
⇑
a Department of Chemistry, National Institute of Technology, Rourkela 769008, Orissa, India
b Department of Life Science, National Institute of Technology, Rourkela 769008, Orissa, India
c Department of Chemistry, Howard University, Washington, DC 20059, USA
a r t i c l e i n f o
a b s t r a c t
Some new oxovanadium(V) complexes, [VOL1–3(OEt)(EtOH)] (1–3), have been reported, which were
obtained from the reaction of the Schiff bases H2L1–3 (where H2L1 = the salicylhydrazone of diacetyl
monoxime; H2L2 = the 4-methoxy salicylhydrazone of diacetyl monoxime and H2L3 = the 4-hydroxy sal-
icylhydrazone of diacetyl monoxime) with VO(acac)2 in a 1:1 molar ratio. Three 4-R-aroylhydrazoneox-
imes (V) have been used as ligands in the present study, differing in the inductive effect of the substituent
R (R = H, OCH3 and OH), in order to observe their influence, if any, on the redox potentials and biological
activity of the complexes. All the synthesized ligands and metal complexes were successfully character-
ized by elemental analysis, IR, UV–Vis and NMR spectroscopy. An X-ray diffraction study of [VOL1(OEt)-
(EtOH)] (1) reveals that the metal center has a distorted octahedral O5N coordination sphere, where the
O,N,O donor ligand and the ethoxo group constitute a satisfactory O3N basal plane. Cyclic voltammetry of
the complexes show a quasi-reversible cyclic voltammetric response in the potential range 0.29–0.36 V
involving a single electron V(V)–V(IV) reduction. The complexes have also been screened for their
antibacterial activity against Escherichia coli, Bacillus, Proteus and Klebsiella. Minimum inhibitory concen-
trations of these complexes and the antibacterial activities indicate compound 1 as the potential lead
molecule for drug design.
Article history:
Received 24 June 2011
Accepted 5 October 2011
Available online 18 October 2011
Keywords:
Aroylhydrazoneoxime ligand
Oxovanadium(V) complexes
X-ray crystal structure
Antibacterial study
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
perfusion imaging agents [30]. As a ligand, the oxime moiety is
potentially ambidentate [16] and can coordinate either through
The chemistry of vanadium has become a fascinating area of re-
search in recent time because of the presence of vanadium in
metalloenzymes and its medicinal as well as catalytic importance
[1–13]. The expanding knowledge of the role of vanadium in bio-
logical systems as a therapeutic agent, for example in antitumor
and anticancer drugs [14,15], has led to a continuously increasing
interest in the coordination chemistry and solution chemistry of
this element.
Over the years, oximes have been widely used as very efficient
complexing agents in analytical chemistry for the isolation, separa-
tion and extraction of different metal ions [16–26]. Metal com-
plexes of oxime also have various interesting features [27,28],
which include short intramolecular hydrogen bonding and packing
configurations that give rise to unusual optical properties. From a
medicinal chemistry point of view, it is found that they serve as
models for biosystems such as vitamin B12 [29] and myocardial
the nitrogen (I, Chart 1) [23–26] or the oxygen atom (II) [31].
The vast literature on structural studies of oxime complexes re-
veals some interesting features of its coordination behavior. It
may coordinate to one metal ion through the nitrogen atom and
another metal ion through the oxygen atom (III). Thus it can form
a
l1,2 (N,O) oximato-bridged extended network [19–22]. In the
majority of complexes, only the nitrogen atom (I) coordinates to
the metal center, and the oxygen atom does not take part in coor-
dination, although there are quite few examples where both the
atoms (oximato nitrogen and oxygen, IV) do take part in coordina-
tion [32,33].
On the other hand, hydrazones –NH–N@CRR’ (R and R0 = H,
alkyl, aryl) are versatile ligands due to their applications in the field
of analytical [34] and medicinal chemistry [35]. Hydrazone moie-
ties are the most important pharmacophoric cores of several
anti-inflammatory, antinociceptive and antiplatelet drugs [36]. It
may be relevant to mention here that although the chemistry of
aroylhydrazones complexes of many transition metals has been
extensively studied [37–40], that of aroylhydrazoneoximes (V)
appears to have remained practically unexplored [41,42].
⇑
Corresponding author. Tel.: +91 661 246 2657; fax: +91 661 246 2022.
E-mail address: rupamdinda@nitrkl.ac.in (R. Dinda).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.10.017

S.P. Dash et al. / Polyhedron 31 (2012) 524–529
525
M
N
M1
M
M
OH
N OH
N
OH
N
OH
R1
R1
R1
R1
R2
R2
IV
R2
R2
II
M2
I
III
H3C
CH3
H2L1 (R = H)
H3C
CH3
H3C
CH3
C
C
C
C
H2L2 (R = OCH3)
H2L3 (R = OH)
C
C
O
N
O
N
N
O-
N
N
N
N
C
HN
N
C
V
OH
C
O-
O
O
OEt
EtOH
OH
OH
R
OH
R
R
VI
V
Chart 1. Structures I–VI.
Keeping this observation in mind and in continuation of our
studies on oxovanadium complexes of hydrazone Schiff base li-
gands [43–44], the oxime functionality is incorporated into the li-
gand moiety. In this paper we report the syntheses, X-ray structure
and physical properties of some oxovanadium(V) complexes of
aroylhydrazoneoximes, with special reference to their antibacterial
activity. It is worth mentioning here that, to the best of our knowl-
edge, this report is a rare example [31] of aroylhydrazoneoxime
complexes where the oximato oxygen atom coordinates to the
metal center, while the nitrogen atom does not take part in
coordination.
salicylhydrazine with diacetyl monoxime in methanol media by
standard procedures [46]. The resulting white compound was
filtered, washed thoroughly with ethanol and dried over fused
CaCl2.
2.4. Synthesis of the complexes [VO(L1–3)(OEt)(EtOH)] (1–3)
To a stirring solution of the ligand H2L1–3 (1.0 mmol) in 20 mL of
ethanol, VO(acac)2 (1.0 mmol) was added. The color changed to
brownish red. After 3 h of stirring, the solution was filtered. The fil-
trate was allowed to stand at room temperature for 4 days, during
which crystals, suitable for X-ray analysis, were isolated. [VO(L1
)(OEt)(EtOH)] (1): Yield: 58%. Anal. Calc. for C15H22N3O6V: C,
46.03; H, 5.62; N, 10.74. Found: C, 46.07; H, 5.65; N, 10.79%. 1H
NMR (DMSO-d6, d): 2.63 (s, 3H, CH3C@NN), 2.52 (s, 3H, CH3C@NO),
7.86–6.93 (m, 4H, C6H4), 11.42 (s, 1H, OH). 51V NMR (DMSO-d6, d):
ꢀ513. [VO(L2)(OEt)(EtOH)] (2): Yield: 54%. Anal. Calc. for
2. Experimental
2.1. Materials
[VO(acac)2] was prepared as described in the literature [45]. Re-
agent grade solvents were dried and distilled prior to use. All other
chemicals were reagent grade, available commercially and used as
received. Commercially available TBAP (tetra butyl ammonium
perchlorate) was properly dried and used as a supporting electro-
lyte for recording the cyclic voltammograms of the complexes.
C
16H24N3O7V: C, 45.60; H, 5.70; N, 9.97. Found: C, 45.65; H, 5.73;
N, 9.94%. 1H NMR (DMSO-d6, d): 2.68 (s, 3H, CH3C@NN), 2.53 (s,
3H, CH3C@NO), 3.71 (s, 3H, CH3O), 7.94–6.83 (m, 3H, C6H4),
11.46 (s, 1H, OH). 51V NMR (DMSO-d6, d): ꢀ518. [VO(L3)(OEt)(E-
tOH)] (3): Yield: 61%. Anal. Calc. for C15H22N3O7V: C, 44.22; H,
5.40; N, 10.31. Found: C, 44.27; H, 5.36; N, 10.27%. 1H NMR
(DMSO-d6, d): 2.61 (s, 3H, CH3C@NN), 2.48 (s, 3H, CH3C@NO),
7.74–6.87 (m, 3H, C6H4), 9.76 (s, 1H, p-Ar–OH), 11.48 (s, 1H, o-
Ar–OH). 51V NMR (DMSO-d6, d): ꢀ529.
2.2. Physical measurements
Elemental analyses were performed on a Vario ELcube CHNS
Elemental analyzer. IR spectra were recorded on a Perkin-Elmer
Spectrum RXI spectrometer. 1H NMR spectra were recorded with
a Bruker Ultrashield 400 MHz spectrometer using SiMe4 as an
internal standard. Electronic spectra were recorded on a Lamda25,
Perkin-Elmer spectrophotometer. Magnetic susceptibility was
measured with a Sherwood Scientific AUTOMSB sample magne-
tometer. Electrochemical data were collected using a PAR electro-
chemical analyzer and a PC-controlled Potentiostat/Galvanostat
(PAR 273A) at 298 K in a dry nitrogen atmosphere. Cyclic voltam-
metry experiments were carried out with a glassy carbon working
electrode, platinum counter electrode and Ag/AgCl as reference
electrode, and TBAP as the supporting electrolyte. Antibacterial
activity was measured with a Perkin-Elmer (2030 VICTOR X3)
microtitre plate optical colorimeter (OD600).
2.5. Crystallography
A suitable single crystal of 1 was chosen for the X-ray diffrac-
tion studies. This compound crystallized in the monoclinic space
group P 121/n1. The diffraction data for 1 were collected at
295 K with a Bruker AXS Smart CCD diffractometer using graphite
monochromated Mo K
a radiation (k = 0.71073 Å). The following
Bruker software packages were used: SMART for collecting frames
of data, indexing and determination of lattice parameters, SAINT
for integration of intensity of reflections and scaling, SADABS for
absorption correction, and SHELXTL for space group and structure
determination, and for refinement. The structures were solved
by direct methods with SHELX-86 and refined by full-matrix
least-squares analysis with SHELXL-97 [47]. All the hydrogen atoms
were added in their calculated positions using riding models,
whereas non-hydrogen atoms were refined with anisotropic ther-
mal parameters. Crystallographic data and details of refinement
are given in Table 1.
2.3. Synthesis of the ligands (H2L1, H2L2, H2L3)
The Schiff base ligands H2L1–3 were prepared in 80–90% yield by
the condensation of an equimolar ratio of 4-substituted

526
S.P. Dash et al. / Polyhedron 31 (2012) 524–529
Table 1
R (R = H, OCH3 and OH), in order to observe their influence, if
any, on the redox potentials and biological activities of the com-
plexes. The reactions of the selected aroylhydrazoneoximes (V)
with VO(acac)2 proceeded in stirring ethanol and each of these
reactions afforded reddish black colored products in decent yields.
During this reaction, vanadium is oxidized from its initial +IV state
to the +V state. These compounds are highly soluble in aprotic sol-
vents, viz. CH3CN, DMF or DMSO.
Crystallographic data and details of refinement for [VO(L1)(OEt)(EtOH)] (1).
Identification code
Empirical formula
Formula weight
T (K)
rd-sd4
15H22N3O6V
C
391.30
295(2)
1.54184
monoclinic
P121/n1
k (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
7.06518(10)
21.9429(3)
3.2. Spectral characteristics
b (Å)
c (Å)
11.80060(13)
90
96.5499(12)
90
1817.51(4)
4
1.430
4.887
The spectral characteristics of 1–3 are listed in Table 2. The
infrared spectra of the complexes display a broad band centered
at around 3400 cmꢀ1. This band is possibly due to the O–H stretch
of the hydrazine fragment of the ligand. The C@O stretch
(1654 cmꢀ1) of the amide functionality [49] in the free ligand is
found to be absent in the spectra of the complexes, which indicates
that the Schiff base is completely deprotonated and acts as a diba-
sic enolate. The strong and sharp peak displayed by the complexes
in the range 1592–1603 cmꢀ1 is likely to be associated with the
C@N–N@C moiety [43,44,50]. The presence of a strong band in
the range 976–985 cmꢀ1 is assigned to V@O stretching [43,44].
The electronic spectra of the complexes were recorded using
acetonitrile solutions. The main features of all the spectra are quite
similar. Three strong absorptions are observed in the wavelength
range 403–207 nm. The lower energy absorption at around
390 nm is ascribable to ligand-to-metal charge transfer transitions,
whereas the higher energy absorptions are likely to be due to li-
gand centered transitions [43,44].
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (mg/m3)
Absorption coefficient (mmꢀ1
F(000)
)
816
Crystal size (mm3)
0.54 ꢁ 0.24 ꢁ 0.17
Theta range for data collection (°)
Index ranges
5.52–77.38
ꢀ8 6 h 6 8,
ꢀ27 6 k 6 26,
ꢀ14 6 l 6 10
8227
Reflections collected
Independent reflections (Rint
Completeness to theta = 67.50°
Absorption correction
Maximum and minimum transmission
Refinement method
)
3776 (0.0201)
99.6%
semi-empirical from equivalents
1.00000 and 0.19723
Full-matrix least-squares on F2
3776/10/250
1.042
R1 = 0.0541, wR2 = 0.1500
R1 = 0.0604, wR2 = 0.1563
0.535 and ꢀ0.399
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r(I)]
The 1H NMR spectral data of the free ligands and the corre-
sponding oxovanadium(V) complexes (1–3) were recorded using
DMSO-d6. The spectra of the free ligands exhibit two close but sep-
arate singlets in the range 11.74–11.53 ppm due to NH and OH
(@N–OH) groups, which are absent in the spectra of the complexes
indicating coordination of these groups to the metal center. How-
ever all the spectra display a singlet in the range 11.42–11.48 ppm,
which corresponds to the OH (phenolic) group of the ligand frag-
ment, showing it remains uncoordinated in the complexes. Signals
for the aromatic protons are found as multiplets in the 7.94–
6.83 ppm range [46]. The protons of the methyl group of the meth-
oxy substituent in [VO(L2)(OEt)(EtOH)] (2) resonate as a singlet at
3.71 ppm and the proton of the hydroxyl substituent at the 4-posi-
tion in [VO(L3)(OEt)(EtOH)] (3) resonates as a singlet at 9.76 ppm
[51]. The two methyl groups of the diacetyl monoxime moiety ap-
pear as singlets in the range 2.48–2.68 ppm. The 51V NMR spectra
of 1–3 display a singlet at ꢀ513, ꢀ518 and ꢀ529 ppm, respectively.
These chemical shifts are usual for complexes containing the
mono-oxovanadium(V) unit [52].
Largest difference in peak and hole (eÅꢀ3
)
2.6. Antibacterial activity
The antibacterial activity of the compounds (ligands and com-
plexes) was studied against Escherichia coli (E. coli), Bacillus, Proteus
and Klebsiella by determining the minimum inhibitory concentra-
tion (MIC) values, following CLSI guidelines for the broth micro-
dilution method [48]. Briefly, bacterial strains were cultured onto
Luria Bertani Agar medium [containing 0.5% peptone, 0.5% yeast
extract, 1% NaCl and 1.5% Agar, at pH 7.5 0.2]. The stock solution
was prepared by dissolving the tested compounds in dimethyl sulf-
oxide (DMSO). Chloramphenicol, a common antibiotic, was used as
the positive control and DMSO was used as the negative control.
Bacterial cultures were added to the sterilized Mueller Hinton
Broth (MHB) [containing 30% beef extract, 1.75% casein acid hydro-
lysate and 0.15% starch, pH 7.4 0.2]. The MIC was determined by
using 2-fold serial dilutions in the medium (MHB) containing 1.95–
3.3. Electrochemical properties
1000
lg/ml of the test compounds. To each well of a 96 well micro-
titre plate, 150
l
l of medium (MHB) was taken in duplicate, to
l of 0.5 McFarland standard (1.5 ꢁ 108 CFU/ml) culture
The electrochemical properties of all the oxovanadium(V) com-
plexes have been examined in CH3CN solution (0.1 M TBAP) by cyc-
lic voltammetry. All the complexes show a quasi-reversible cyclic
voltammetric response in the potential range 0.29–0.36 V involv-
ing single electron V(V)–V(IV) reduction [44]. The one-electron
nature of this reduction has been tentatively established by
comparing its current height with that of the standard ferrocene/
ferrocenium couple under the same experimental conditions. The
potential data of 1–3 are listed in Table 3, and a selected voltam-
mogram is shown in Fig. 1. The potential of the V(V)–V(IV) reduc-
tion in the 4-R-aroylhydrazoneoxime complexes (VI) has been
found to be sensitive to the nature of the substituent R in the aro-
ylhydrazone fragment. The potential decreases with increasing
electron-releasing character of the substituent R, as expected
[53,54].
which 10
l
pathogens from MHB was added. The inoculated plates were incu-
bated at 37 °C for 24 h. After incubation, the bacterial growth was
monitored by measuring the turbidity of the culture by a microtitre
plate optical colorimeter (OD600). The MIC was determined as the
lowest concentration of compound at which the visible growth of
the organisms was completely inhibited.
3. Results and discussion
3.1. Synthesis
Three 4-R-aroylhydrazoneoximes (V) have been used in the
present study, differing in the inductive effect of the substituent

S.P. Dash et al. / Polyhedron 31 (2012) 524–529
527
Table 2
Characteristics IRa bands (cmꢀ1) and electronic spectralb data [nm (dm3 mol-1 cmꢀ1)] for complexes 1–3.
Complex
m
(OH)
m(C@N)
m(V@O)
kmax (e)
[VO(L1)(OEt)(EtOH)] (1)
[VO(L2)(OEt)(EtOH)] (2)
[VO(L3)(OEt)(EtOH)] (3)
3434
3381
3402
1592
1603
1598
977
985
976
383 (4324); 263 (11190); 221 (14423)
395 (5212); 278 (13654); 216 (15709)
403 (4931); 265 (12654); 207 (17809)
a
KBr pellet.
In CH3CN.
b
Table 3
Cyclic voltammetric resultsa for oxovanadium(V) complexes 1–3 at 298 K.
Complex
E1/2 (V)
DEP (mV)
[VO(L1)(OEt)(EtOH)] (1)
[VO(L2)(OEt)(EtOH)] (2)
[VO(L3)(OEt)(EtOH)] (3)
0.36
0.31
0.29
91
86
79
a
In acetonitrile at a scan rate of 50 mV sꢀ1. E1/2 = (Epa + Epc)/2, where Epa and Epc
are the anodic and cathodic peak potentials vs. Ag/AgCl, respectively.
D
EP = Epa ꢀ Epc
.
Fig. 2. ORTEP diagram of [VO(L1)(OEt)(EtOH)], 1 with the atom labeling scheme.
Table 4
0. 2 µ
A
Selected bond distances (Å) and angles (°) for [VO(L1)(OEt)(EtOH)] (1). The estimated
standard deviations are shown in parentheses.
V–O(4)
1.580(3)
V–O(2)
1.984(2)
V–O(5A)
1.774(2)
V–N(2)
2.116(2)
V–O(3)
1.839(2)
V–O(6A)
2.366(2)
O(3)–V–N(2)
O(3)–V–O(2)
O(3)–V–O(5A)
O(3)–V–O(4)
O(3)–V–O(6A)
N(2)–V–O(2)
N(2)–V–O(5A)
N(2)–V–O(4)
81.08(8)
N(2)–V–O(6A)
O(2)–V–O(5A)
O(2)–V–O(4)
O(2)–V–O(6A)
O(5A)–V–O(3)
O(5A)–V–O(6A)
O(4)–V–O(6A)
O(4)–V–O(5A)
81.43(9)
149.44(9)
103.71(11)
100.03(13)
79.20(11)
4.44(8)
94.02(10)
99.68(12)
79.30(10)
103.71(11)
80.86(11)
175.46(11)
103.64(12)
0.1
0.2
0.3
0.4
0.5
0.6
E(V)
160.40(10)
94.04(10)
Fig. 1. Cyclic voltammogram of complex 1 in CH3CN (0.1 M TBAP); scan rate 50 mV/
s, and potentials recorded vs. Ag/AgCl.
3.4. Description of the crystal structure of [VO(L1)(OEt)(EtOH)] (1)
coordination of the ethanol molecule [54]. The short V–O(4) dis-
tance of 1.580(3) Å indicates the presence of a vanadium–oxygen
double-bond (V@O), which is commonly found in five- and six-
coordinated octahedral complexes of vanadium(IV) and vana-
dium(V) [43,44,54–57]. The five V–O bond lengths are unequal;
the V@O bond being the shortest and the V–O [ethanolic oxygen
O(6A)] being the longest due to the trans influence of the oxo atom.
The V–O bond lengths follow the order V–O (oxo) < V–O (ethox-
ide) < V–O (oxime) < V–O (enolate) < V–O (ethanolic). This data
indicates stronger binding of the alkoxo group compared to the
other bonded oxygen atoms. The V–O bond distance (av. 1.908 Å)
is similar to those reported for V–O bonds in somewhat related
systems [54]. The cis bond angles are in the range 74.44(8)–
103.71(11)°, while the trans O@V–O (ethanol) bond angle of
175.46(11)° is almost linear as compared to the other two trans an-
gles (149.44(9)° and 160.40(10)°) (Table 4). The orientation of the
ethoxo ethyl in complex 1 is towards the oxo group side, perhaps
due to steric constraints imposed by the metal coordinated etha-
nol, Fig. 2.
Although the preliminary characterization data (microanalyti-
cal and spectroscopic) of the complexes gave some idea about their
composition and the donor points through which the ligands were
attached to the oxovanadium(V) center, they could not definitely
reveal the actual structures, which could only be provided by a
structure determination using the single-crystal X-ray diffraction
technique. To determine the coordination mode of the aro-
ylhydrazoneoxime ligands in these complexes (1–3), the structure
of a representative member of this family, viz. [VO(L1)(OEt)(EtOH)]
(1), was determined. The molecular structure of 1 is shown in Fig. 2
and some relevant bond parameters are listed in Table 4. In the
structure the metal center is in a distorted octahedral O5N coordi-
nation sphere. The O,N,O donor ligand and the ethoxo group
constitute a satisfactory O3N basal plane, and the oxo group occu-
pies an apical position. Essentially the same arrangement around
vanadium has been seen in related systems [31,44,54]. The
displacement of the metal center from the basal plane toward
the apical oxo group is 0.2570(5) Å, though this displacement is
noticeably small. This small displacement is possibly due to the
The one-dimensional self-assembling of the molecule [VO
(L1)(OEt)(EtOH)] is shown in Fig. 3. The molecule is found to show

528
S.P. Dash et al. / Polyhedron 31 (2012) 524–529
Fig. 3. Hydrogen bonding diagram of complex 1 with the atom labeling scheme.
(62.5–250 lg/mL) as reported by Sharma et al. [58] following the
Table 5
Hydrogen bond distances (Å) and angles (°) for [VO(L1)(OEt)(EtOH)] (1).
broth micro-dilution method. However, the corresponding oxova-
nadium(V) complexes (1–3) showed much better results with re-
spect to the individual ligands. A possible explanation is that by
coordination, the polarity of the ligand and the central metal ion
are reduced through the charge equilibration, which favors perme-
ation of the complexes through the lipid layer of the bacterial cell
membrane [59,60]. Complex 1 showed the most promising results
as compared to the other compounds (2 and 3) of this study and
similar compounds against the same and other pathogens, as re-
ported by Sharma et al. [58]. The antibacterial activity of similar
type compounds has also been reported by Chohan et al. [61]
and Tahira et al. [62] using the agar well diffusion technique
against E. coli, Shigella, Pseudomonas, Salmonella, Staphylococcus
and Bacillus, and the present results are in accordance with the re-
ported values. However, the difference in value may be attributed
to the nature of the compounds synthesized with different
ligands.
Vanadium is a trace element which is essential for higher
organisms for their survival, whereas vanadium(V) complexes are
known as potential inhibitors of various enzymes [63]. There are
reports of vanadium complexes showing antibacterial, antifungal
and anticancerous properties [58,61–63]. Hence, the currently syn-
thesized compounds have the potential to be used as an antimicro-
bial as well as an antidiabetic drug. There are also certain
drawbacks in using vanadium complexes as a therapeutic agent
as its toxicity varies with the route of administration and duration;
however, there is no report yet available about its chronic toxicity
[64].
D–H. . .A
d(D–H)
d(H. . .A)
d(D. . .A)
\(DHA)
O(1)–H(1). . .N(1)
O(6A)–H(6A). . .O(1)#1
0.82
0.82
1.84
2.35
2.562(3)
2.847(3)
146.3
119.8
both inter and intra molecular hydrogen bonding. Two [VO(L1)(OE-
t)(EtOH)] molecules form a dimeric unit via a pair of reciprocal
hydrogen bonds between the phenolic oxygen of one molecule
with the ethanolic proton of the other moiety, forming intermolec-
ular hydrogen bonding. Another hydrogen bonding between N(1)
and the phenolic hydrogen, H(1), is also observed, constituting an
intramolecular hydrogen bond. The H-bonding parameters are
listed in Table 5.
Structural characterization of complexes 2 and 3 by X-ray crys-
tallography has not been possible, as their single crystals could not
be grown. As all three complexes have been synthesized similarly
and display similar properties, the other two [VO(L2–3)(OEt)(EtOH)]
complexes (2–3) are assumed to have the same structure as [VO(-
L1)(OEt)(EtOH)] (1). The results of the 1H NMR in DMSO-d6 and IR
in CH2Cl2 solution indicate that the structures of complexes 1–3 in
solution remain the same as those in the solid state.
3.5. Antimicrobial activity
In the present study, the synthesized compounds (1–3) showed
potential antibacterial activity against all the pathogens tested (E.
coli, Bacillus, Proteus and Klebsiella), and in some cases they showed
more promising results by giving MIC values that are lower than
the standard drug examined. The biological data (Table 6) of the
MIC of the free ligands showed poor activity (MIC = ꢂ15.62–
4. Conclusion
500 lg/mL), which is in agreement with the previous results
The present study shows that the 4-R-aroylhydrazoneoximes li-
gands (H2L1–3, V) can bind to vanadium upon reaction with [VO(a-
cac)2], affording complexes of the type [VO(L)(OEt)(EtOH)], where
the oxime oxygen atom coordinates to the metal center and the
nitrogen atom does not take part in coordination (VI). All the com-
plexes have been characterized with the help of various spectro-
scopic techniques and electrochemical measurements. X-ray
diffraction measurements of 1, [VO(L1)(OEt)(EtOH)], have been car-
ried out. The complexes 1–3 have also been screened for their anti-
bacterial activity against E. coli, Bacillus, Proteus and Klebsiella. The
minimum inhibitory concentration of these complexes and their
antibacterial activity indicates compound 1 as the potential lead
molecule for drug design.
Table 6
Antibacterial activity of all the ligands and oxovanadium(V) complexes, in vitro MIC in
l
g mLꢀ1
.
E. coli
Bacillus
Proteus
Klebsiella
H2L1
H2L2
H2L3
15.62
125
125
7.81
62.50
62.50
2.00
31.25
–
–
15.62
62.50
31.25
2.00
–
125
–
15.62
31.25
125
16.00
–
500
125
7.81
125
62.50
16.00
[VO(L1)(OEt)(EtOH)] (1)
[VO(L2)(OEt)(EtOH)] (2)
[VO(L3)(OEt)(EtOH)] (3)
Chloramphenicol

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Appendix A. Supplementary data
CCDC 822842 contains the supplementary crystallographic data
for complex 1. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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