Synthesis and spectral characterization of ternary complexes of oxovanadium(IV) containing some acid hydrazones and 2,2′-bipyridine

Article abstract of DOI:10.1016/j.saa.2004.04.001

An interesting series of heterocyclic base adducts of oxovanadium(IV) complexes have been synthesized by the reaction of vanadium(IV) oxide acetylacetonate with some hydrazones (H₂L) in the presence of a heterocyclic base 2,2′-bipyridine. The c

Full text of DOI:10.1016/j.saa.2004.04.001

Spectrochimica Acta Part A 61 (2005) 331–336
Synthesis and spectral characterization of ternary complexes
of oxovanadium(IV) containing some acid
hydrazones and 2,2ꢀ-bipyridine
P.B. Sreeja, M.R. Prathapachandra Kurup∗
Department of Applied Chemistry, Cochin University of Science & Technology, Kochi 682 022, India
Received 4 January 2004; received in revised form 1 April 2004; accepted 1 April 2004
Abstract
An interesting series of heterocyclic base adducts of oxovanadium(IV) complexes have been synthesized by the reaction of vanadium(IV)
oxide acetylacetonate with some hydrazones (H2L) in the presence of a heterocyclic base 2,2ꢀ-bipyridine. The compounds were characterized
by analytical and different physico-chemical techniques like IR, electron paramagnetic resonance (EPR) and UV-Vis spectral studies and
magnetic studies. The EPR spectra indicate that the free electron is in the dxy orbital. The coordination geometry around oxovanadium(IV) in all
complexes is octahedral, with one dibasic tridentate ligand L2−, and one bidentate heterocyclic base. The IR spectra suggest that coordination
takes place through azomethine nitrogen and enolate oxygen from the hydrazide moiety and phenolate oxygen. The pyridyl nitrogens of the
hydrazones, H2L2 and H2L4 are not involved in the coordination. The molar conductivities show that all the complexes are non-electrolytes.
All electronic transitions were assigned. All the compounds are paramagnetic. EPR studies of all compounds suggest axial symmetry. The
calculated bonding parameters indicate that in-plane ␴ bonding is more covalent than in-plane ␲ bonding.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Hydrazones; Oxovanadium(IV); Hydrazonate complexes; 2,2ꢀ-Bipyridine; EPR
1. Introduction
The coordination chemistry of vanadium has received
considerable attention since the discovery of vanadium in en-
zymes like bromoperoxide and azetobactorvinelandii [4]. Its
biological significance is further exemplified by its incorpo-
ration in natural products (amavadin in mushroom), in blood
of sessile marine organism and enzyme in potent inhibitor of
phosphoryl transfer [5]. Several vanadium compounds have
recently been investigated in animal model systems as treat-
ment for diabetes [6]. Studies are ongoing in clinical trial in
human beings with transition metal complexes [7]. In addi-
tion, studies with vanadate in human beings have recently
been reported [8].
In this paper, we report syntheses, analytical and spec-
tral characterizations of some oxovanadium(IV) com-
plexes with four different aroyl hydrazones, derived
from acid hydrazides namely, benzoic acid hydrazide,
nicotinic acid hydrazide and 4-hydroxybenzoic acid hy-
drazide. The aldehyde/ketone used are salicylaldehyde and
2-hydroxyacetophenone. A bidentate base 2,2ꢀ-bipyridine
was used as auxiliary ligand for coordination with oxovana-
dium(IV).
The synthesis and structural investigation and reaction of
transition metal Schiff’s bases have received a renewed at-
tention in recent years, because of their biological activi-
ties as antitumoral, antifungal and antiviral activities. A lot
of Schiff’s bases such as thiosemicarbazones have been re-
ported [1,2]. Most of the thiosemicarbazones contain NNS
donor atoms. However, very little information is available
for hydrazones containing ONO or NNO donor atoms. Cop-
per(II) complex of salicylaldehyde benzoylhydrazone was
shown to be a potent inhibitor of DNA synthesis and cell
growth. This hydrazone also has mild bacteriostatic activity
and a range of analogues has been investigated as potential
oral iron chelating drugs for genetic disorders such as tha-
lassemia [3].
∗
Corresponding author. Tel.: +91-484-2575804;
fax: +91-484-2577595.
E-mail address: mrp@cusat.ac.in (M.R.P. Kurup).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.04.001

332
P.B. Sreeja, M.R.P. Kurup / Spectrochimica Acta Part A 61 (2005) 331–336
2. Experimental
2.1. Materials
Salicylaldehyde (BDH), 2-hydroxyacetophenone (BDH),
benzoic acid hydrazide (Fluka), 4-hydroxybenzoic acid
hydrazide (Fluka), nicotinic acid hydrazide (Fluka),
2,2ꢀ-bipyridine (S.D. Fine Chem. Ltd.) and vanadium(IV)
oxide acetylacetonate (Merk) were of Analar grade and
used without further purification. All the solvents were
dried using standard methods before use.
2.2. Physical measurements
Elemental analyses were carried out using a Heraeus Ele-
mental Analyzer at Regional Sophisticated Instrumentation
Center, Center Drug Research Institute, Lucknow, India. IR
spectra in the range of 4000–400 cm−1 were recorded on a
Shimadzu DR 8001 series FTIR instrument as KBr pellets.
Far IR spectra were recorded in polyethylene matrix on IFS
66 V FT-IR spectrometer in the range of 500–50 cm−1. The
1H NMR spectra were recorded by using Bruker DRX500,
using DMSO-d6 as solvent and TMS as standard at So-
phisticated Instruments Facility, Indian Institute of Science,
Bangalore, India. Magnetic studies were done using vibrat-
ing sample magnetometer at IIT, Roorkee, India. Electron
paramagnetic resonance (EPR) spectra were recorded in a
Varian E-112 spectrometer at X-band, using TCNE as the
standard at Regional Sophisticated Instrumentation Center,
Indian Institute of Technology, Bombay, India. Frozen solu-
tion spectra were simulated with computer programs. Solid
state reflectance were measured using Ocean Optics Inc.,
SD-2000 Fiber Optic Spectrometer.
Fig. 2. Structures of acid hydrazones.
2.3. Syntheses of ligands
Acid hydrazides (1 mmol) dissolved in methanol was
refluxed with methanolic solutions of salicylaldehyde or
2-hydroxyacetophenone (1 mmol), in presence of a few
drops of glacial acetic acid for 6 h (Fig. 1). On cooling
the reactant media, crystals of hydrazones were separated
out. All the compounds (Fig. 2) were recrystallised from
methanol and characterized by analytical and different
spectral methods.
Fig. 3. Scheme of the synthesis of the complexes.
(1 mmol) was dissolved in dichloromethane. To a stirred
ethanolic solution of hydrazone (1 mmol) and 2,2ꢀ-bipyridine
(1 mmol), under dinitrogen atmosphere vanadyl solution
was added. Resultant homogeneous brown solution was
stirred for 3 h (Fig. 3). Reddish orange products formed
were filtered and washed with cold ethanol, followed by
2.4. Syntheses of complexes
All the complexes were synthesized using the follow-
ing general method. Vanadium(IV) oxide acetylacetonate
Fig. 1. Scheme of synthesis of H2L4.

P.B. Sreeja, M.R.P. Kurup / Spectrochimica Acta Part A 61 (2005) 331–336
333
2E
Table 2
ether, and dried in vacuo. Unfortunately, we are unable to
grow single crystals suitable for single crystal XRD for any
of these complexes.
Electronic spectral assignments (cm−1
)
2B2
→
2B1 2B2
→
2A1 LMCT n–␲
2B2
→
∗
Compound
(VO)L1(bipy) 18,518
(VO)L2(bipy) 18,450
20,560
20,408
25,125 33,333 14,705
23,809 34,722, 14,306
31,520
25,120 30,769 14,520
24,390 34,482 14,285
3. Results and discussion
(VO)L3(bipy) 18,398
(VO)L4(bipy) 18,248
20,320
19,230
3.1. Syntheses of the ligand and oxovanadium(IV)
complexes
The 1H NMR spectral assignments of all the ligands
were made on the basis of previous reports [9–12]. All the
spectra show two singlets corresponding to phenolic –OH
and –NH. The singlet at δ =∼ 13 ppm and δ =∼ 11 ppm
represent –OH and –NH, respectively. The signal for –OH is
obtained at a down field due to possibility of the formation
of intramolecular hydrogen bonding with azomethine nitro-
gen. The ligands do not show any peak attributed to enolic
–OH proton indicating that they exist in keto forms. Upon
addition of D2O the intensities of both OH and NH protons
significantly decrease. This supports the assignment. The
aromatic protons appear as multiplets at 6.9–7.9 ppm.
The ligands were found to coordinate as dianionic L2−
on complexation to oxovanadium(IV). The complexes
were found to be readily formed from vanadium(IV) ox-
ide acetylacetonate solution in ethanol by H2L in presence
of heterocyclic base, 2,2ꢀ-bipyridine. The elemental anal-
yses (Table 1) of the complexes are in agreement with the
formula (VO)L(bipy). All compounds are found to be spar-
ingly soluble in water, ethanol and methanol and soluble
in DMF and DMSO. Conductivity measurements in DMF
show the complexes to be nonconductors.
Fig. 4. Solution state EPR spectrum of (VO)L1(bipy) at 77 K.
terms of Ballhausen and Gray model for the one electron
transitions [14]. Accordingly, the first absorption band at
∼14,300 cm−1 region can be assigned to the electronic
2
transition B2
→
2E (dxy → dxz, dyz), the second signal
The magnetic moment obtained at 298 K for the com-
plexes are in the range of 1.57–1.91 BM The values corre-
spond to spin only value of systems having one electron.
These are magnetically diluted complexes in which metal
ion is not involved in magnetic exchange with the neighbor-
ing metal ion [13].
∼18,200 cm−1 due to B2 → B1 → B1 (dxy → dx2−y2
)
2
2
2
and the third one due to 2B2 → A1 (dxy → dz2 ) (Table 2).
These values are consistent with distorted octahedral struc-
ture for oxovanadium(IV) [15].
2
3.3. Electron paramagnetic resonance spectral studies
3.2. Electronic spectral analysis
The EPR spectra (Table 3) of the all the complexes were
recorded in DMF solution at 77 K and the representative
spectrum is presented in the Fig. 4.
The solid state visible spectra show the characteristic
series of absorption bands common to vanadyl systems in
Table 1
Colors and elemental analyses the ligands and complexes
Compound
Color
Analytical data found (calculated)
C (%)
H (%)
N (%)
H2L1
(VO)L1(bipy)
Pale yellow
Reddish orange
69.74 (70.00)
63.17 (62.58)
5.19 (5.00)
4.06 (3.93)
11.51 (11.66)
12.19 (12.14)
H2L2
(VO)L2(bipy)
Pale yellow
Reddish orange
66.12 (65.85)
60.47 (60.51)
5.24 (5.13)
4.13 (4.02)
16.95 (16.46)
14.55 (14.70)
H2L3
(VO) L3(bipy)
Pale yellow
Reddish orange
66.66 (66.70)
61.34 (61.11)
5.22 (5.26)
4.23 (4.10)
10.36 (10.43)
11.24 (11.4)
H2L4
(VO)L4(bipy)
Pale yellow
Reddish orange
60.70 (60.23)
59.19 (59.79)
4.83 (4.60)
3.84 (3.71)
16.55 (16.21)
14.64 (15.15)

334
P.B. Sreeja, M.R.P. Kurup / Spectrochimica Acta Part A 61 (2005) 331–336
Table 3
EPR and bonding parameters of the complexes
(VO)L1(bipy)
(VO)L2(bipy)
(VO)L3(bipy)
(VO)L4(bipy)
µ (BM)
1.90
1.67
1.60
1.61
g
g
1.960
1.992
1.981
145.99 × 10−4
46.38 × 10−4
79.96 × 10−4
0.616
1.963
1.994
1.981
147.65 × 10−4
49.13 × 10−4
82.2 × 10−4
0.589
1.964
1.998
1.986
146.97 × 10−4
52.51 × 10−4
84.34 × 10−4
0.578
1.956
1.986
1.979
141.54 × 10−4
50.99 × 10−4
82.00 × 10−4
0.704
||
⊥
gav/iso
A
A
(cm−1
)
)
||
⊥
(cm−1
Aav/iso (cm−1
)
α2
β2
0.947
0.939
0.902
0.869
Fig. 5. IR Spectra of H2L2 (a) and (VO)L2(bipy) (b) (cm−1).

P.B. Sreeja, M.R.P. Kurup / Spectrochimica Acta Part A 61 (2005) 331–336
335
Table 4
Selected IR frequencies (cm−1) of ligands and complexes
Compound
vC
vN–C
vC–O
vV
vV–O
vV–N
vbipy
=
=
O
N
H2L1
(VO)L1(bipy)
1620
1600
–
–
–
955
–
518
–
–
1536
1344, 1469
455, 419
1438, 712, 616
H2L2
(VO)L2(bipy)
1603
1589
–
–
–
963
–
510
–
–
1528
1366, 1471
443, 417
1436, 722, 628
H2L3
(VO)L3(bipy)
1610
–
–
–
–
470
–
–
–
–
1535
1347, 1458
451, 418
1440, 718, 619
H2L4
(VO)L4(bipy)
1609
1595
-
–
–
957
–
520
–
–
1522
1352, 1469
458, 418
1439, 722, 621
Axially anisotropic spectra are obtained with two sets of
dium coordination environment and may be used to distin-
guish between the species with different coordination envi-
ronment. In the present case, A and g values for all the com-
plexes are almost same and therefore no appreciable change
in the coordination environment.
eight line pattern with g < g and A ꢁ A relationship
||
⊥
||
⊥
is characteristics of an axially compressed dxy1 configuration
[16,17].
The spectra show two type of resonance components, one
set is due to parallel features and other set due to perpendic-
ular features, which indicate axially symmetric anisotropy
with sixteen line hyperfine splitting, characteristic of inter-
action between the electron and vanadium nuclear spins. The
g0 and A0 values are remarkably constant for all complexes.
Ligand nitrogen or hydrogen superhyperfine splittings are
not observed on vanadium line. This indicates the unpaired
The molecular orbital coefficient α2 and β2 were also cal-
culated for the complexes by using the following equations.
(2.0023 − g )E
||
α2 =
β2 =
8λβ2
ꢀꢁ
ꢂ
ꢁ
ꢂ
ꢁ
ꢂ
ꢃ
7
6
A
A
5
9
||
⊥
−
+
+
g −
||
g
−
ge
⊥
P
P
14
14
2
electrons to be in b2g orbital (dxy, B2 ground state) local-
where P = 128 × 10−4 cm−1, λ = 135 cm−1 and E is the
ized in metal, thus excluding the possibility of its interaction
with ligands [18–22].
electronic transition energy of 2B2 → E. The lower values
2
for α2 compared to β2 indicated that in-plane ␴ bonding is
more covalent than in-plane ␲ bonding [26].
The spectra show signals characteristic of mononuclear
VO2+ species. The isotropic parameters g0 and A0 are ∼1.98
and ∼ 88 G, respectively. These values are in range of typi-
cal for VO2+ distorted octahedral complexes [23–25]. It is
reported the g and A values are very sensitive to the vana-
The in-plane ␲ bonding parameter β2 observed are con-
sistent with those observed for McGarvey and Kilvelson for
vanadyl complexes of acetylacetone.
Fig. 6. Far IR spectrum of the of (VO)L4(bipy).

336
P.B. Sreeja, M.R.P. Kurup / Spectrochimica Acta Part A 61 (2005) 331–336
3.4. Infrared spectral studies
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3400 and 3200 cm−1, which are due to OH streching mode
and NH streching mode of free OH and NH groups, re-
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suggests deprotonation of the phenolic group indicating the
coordination though phenolic oxygen, and enolisation of
the carbonyl group, followed by deprotonation. IR spectra
of complexes show sharp band at 1536–1510 cm−1 due
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One of the authors S.P.B. is thankful to Cochin University
of Science and Technology, Kochi-22, India and University
Grants Commission, New Delhi, India, for the financial
assistance in the form of Junior Research Fellowship, So-
phisticated Instruments Facility, Indian Institute of Science,
Bangalore, India, for NMR data and Regional Sophisticated
Instrumentation Center, Central Drug Research Institute,
Lucknow for elemental analysis and M.R.P. K is thankful to
STED, Government of Kerala, India for financial support.
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