Oxovanadium(IV) complexes of bioinorganic and medicinal relevance: Synthesis, characterization and 3D molecular modeling and analysis of some oxovanadium(IV) complexes involving the O, N-donor environment of pyrazolone-based sulfa drug Schiff bases

Article abstract of DOI:10.1016/j.molstruc.2006.01.031

Four new oxovanadium(IV) complexes, formed by the interaction of vanadyl sulfate pentahydrate and the Schiff bases derived from 3-methyl-1-phenyl-4-valeryl-2-pyrazolin-5-one and the sulfa drugs, N-(3′-methyl-1′-phenyl-4′-valerylidene-2′-pyrazolin-5′-one)s

Full text of DOI:10.1016/j.molstruc.2006.01.031

Journal of Molecular Structure 794 (2006) 24–34
www.elsevier.com/locate/molstruc
Oxovanadium(IV) complexes of bioinorganic and medicinal relevance:
Synthesis, characterization and 3D molecular modeling and analysis
of some oxovanadium(IV) complexes involving the O, N-donor
environment of pyrazolone-based sulfa drug Schiff bases
*
R.C. Maurya , S. Rajput
Coordination Chemistry Laboratory, Department of P.G. Studies and Research in Chemistry, R.D. University, Jabalpur 482 001, India
Received 7 October 2005; received in revised form 23 December 2005; accepted 23 January 2006
Available online 28 February 2006
Abstract
Four new oxovanadium(IV) complexes, formed by the interaction of vanadyl sulfate pentahydrate and the Schiff bases derived from 3-methyl-
1-phenyl-4-valeryl-2-pyrazolin-5-one and the sulfa drugs, N-(30-methyl-10-phenyl-40-valerylidene-20-pyrazolin-50-one)sulfadiazine (L1H), N-(30-
methyl-10-phenyl-40-valerylidene-20-pyrazolin-50-)sulfaguanidine (L2H), N-(30-methyl-10-phenyl-40-valerylidene-20-pyrazolin-50-one)sulphani-
lamide (L3H) and N0(-30-methyl-10-phenyl-40-valerylidene-20-pyrazolin-50-one)sulphamethoxazole (L4H) in aqueous ethanol are described. The
resulting complexes were characterized by elemental analyses, molar conductances, magnetic and decomposition temperature measurements,
cyclic voltammetry, electron spin resonance, infrared and electronic spectral studies. They have the composition [VO(L)2]$H2O, where
LHZSchiff base L1H, L2H, L3H or L4H mentioned above. A square–pyramidal structure having a slight /VaO/VaO/ type interaction has
been proposed for these complexes.
q 2006 Published by Elsevier B.V.
Keywords: Oxovanadium(IV) complexes; Sulfa drug based ligands; Bioinorganic; Medicinal relevance; 3D molecular modeling
1. Introduction
Tunicates accumulate vanadium(V) from the marine environ-
ment and store it in their blood cells in the reduced tetra- and
trivalent state [9]. However, the vanadium metabolism of the
tunicates remains unclear [9] as tunichromes present in
tunicates in vitro are able to reduce V(V)–V(IV) only, and
not further to V(III). The mushroom accumulates vanadium to
produce amavadin [8,9]. Spectroscopic investigations have
shown a distinct preference of this metal center for N- and/or
O-coordinated environments [13–16]. This is consistent with
combination of hard acid (VO2C) and hard (N and O ligands)
bases [17]. There is heightened interest in the biological
chemistry due to the recent discovery of two types of
vanadium-dependent enzymes: vanadium nitrogenase [18]
and vanadium haloperoxidases [19]. Although in recent years
a number of vanadium complexes have been synthesized and
characterized as models of amavadin and vanadium-dependent
metalloenzymes, the biological role of vanadium in living
organisms and also in both reductive and oxidative catalytic
transformations is still obscure and debatable [20].
Pyrazolone derivatives have been extensively investigated
on account of their wide range of pharmacological activities
[1]. 4-Acyl-3-methyl-1-phenyl-2-pyrazolin-5-ones have been
investigated as extractants for metals from acidic solutions
[2]. The metal complexes of Schiff bases derived from sulfa
drugs have gained considerable importance due to their
pronounced biological activity [3]. There are several reports
on the Schiff base complexes of metal derived from sulfa
drugs [4–7]. They have been found to possess effective
fungicidal activity [4].
Recognition of vanadium as an essential trace element
found in living organisms [8–12] has generated increasing
interest in the structure and function of its complexes.
*
Corresponding author. Fax: C91 761 2392120.
E-mail addresses: rcmaurya@sancharnet.in, rcmauryajb@dataone.in
(R.C. Maurya).
The last decade is characterized by a continuing increase in
interest in the bioinorganic chemistry of vanadium as
documented by the appearance of four monographs [21–24].
0022-2860/$ - see front matter q 2006 Published by Elsevier B.V.
doi:10.1016/j.molstruc.2006.01.031

R.C. Maurya, S. Rajput / Journal of Molecular Structure 794 (2006) 24–34
25
Studies on the interaction of vanadium with biologically
2. Experimental
important ligands aimed at finding structural and/or functional
models of biogenic compounds are numerous and have been
the subject of several reviews [8–12,18,19,25–28].
2.1. Materials
Vanadyl sulfate pentahydrate (Thomas Baker Co., Ltd,
Mumbai), 3-methyl-1-phenyl-2-pyrazolin-5-one (Johnson
Chemicals Co., Mumbai), sulpha drugs (sulfadiazine, sulfa-
guanidine, sulfanilamide and sulfamethoxazole, Sigma Chemi-
cals Co., USA) and valeryl chloride (Fluka Chemie A.G,
Switzerland), were used as supplied. All other chemicals used
were of analytical reagent grade.
There has been great interest in the past two decades in
the mechanism of the insulin-like function of vanadium and
in developing new vanadium compounds as potential insulin
adjuvants [29] or replacement in the treatment of diabetes,
most notably when administered orally. Still, gastrointestinal
absorption (by passive diffusion) of vanadium is usually poor
and depends on the chemical nature, solubility, and
speciation of the metal ion complex. Great efforts have
therefore been made to synthesize oxovanadium(IV)
complexes of high biological activity and low toxicity
which are readily absorbed. Many oxovanadium(IV)
complexes with various coordination modes [30,31] have
been prepared, viz. VO(O4), VO(S2N2), VO(S4), VO(N3O),
and VO(N2O2), and the relationship between their structures
and insulin-mimetic activities has been examined by
evaluating both in vivo and in vitro results. Among others,
bis (maltolato) oxovanadium(IV) (BMOV) [VO (O4) type]
proved to be potent in decreasing the blood glucose level
with high efficiency without any overt toxic [31] side effect.
Vanadium compounds as insulin mimics have been recently
reviewed [32–34].
2.2. Preparation of 3-methyl-1-phenyl-4-valeryl-2-pyrazolin-
5-one (mpvpH)
This compound was prepared by the acylation of 3-methyl-
1-phenyl-2-pyrazolin-5-one with valeryl chloride in dimethyl-
formamide by the method reported by Jensen [35].
2.3. Synthesis of sulfa drug Schiff bases
The Schiff bases of sulfa drugs were prepared as follows: an
ethanolic solution (15 mL) of mpvpH (2.58 g, 1 mmol), was
added to the solution (w20 mL) of sulphadiazine (2.50 g,
1 mmol), sulfaguanidine (2.14 g, 1 mmol), sulfamethoxazol
(2.53 g, 1 mmol) in ethanol or sulphanilamide (1.72 g, 1 mmol)
in acetone. The resulting solution was refluxed with stirring for
6–7 h and then filtered to remove insoluble sulpha drug if any.
The filtrate so obtained was concentrated on a water bath and
left overnight at room temperature when colored crystals of the
Schiff bases separated out from their respective solutions. The
crystals thus obtained were washed with ethanol–water (1:1)
and dried in vacuo. They were recrystallised from ethanol. The
characterization data of Schiff bases are given in Table 1.
Considering the pronounced biological activity of sulfa drug
Schiff base complexes, in view of the importance of vanadium
compounds, and also extending the search for more efficacious
vanadium compounds, a study was undertaken of the
coordination chemistry of oxovanadium(IV) complexes
{[VO(N2O2)] type} involving pyrazolone-based sulfa drug
Schiff bases, viz. N-(30-methyl-10-phenyl-40-valerylidene-20-
pyrazolin-50-one)sulfadiazine (L1H), N-(30-methyl-10-phenyl-
40-valerylidene-20-pyrazolin-50-one)sulfaguanidine (L2H),
N-(30-methyl-10-phenyl-40-valerylidene-20-pyrazolin-50-one)-
sulphanilamide (L3H) and N0(-30-methyl-10-phenyl-40-valery-
lidene-20-pyrazolin-50-one)sulphamethoxazole (L4H) (Fig. 1).
2.4. Synthesis of complexes
The following general procedure was used in the synthesis
of all of the complexes. The salt VOSO4$5H2O (0.253 g,
1 mmol) was dissolved in water (5 mL) and the solution was
added to a warmed, stirred ethanolic solution (w25 mL) of the
corresponding Schiff bases L1H (0.980 g, 2 mmol), L2H
(0.908 g, 2 mmol), L3H (0.824 g, 2 mmol), or L4H (0.986 g,
2 mmol). The resulting solution was refluxed for 10–12 h and
then concentrated to half of its volume. The resulting colored
precipitate was filtered and washed several times with ethanol
to remove any unreacted ligand and the metal salt. The product
was dried in vacuo. The analytical data of the complexes are
given in Table 2.
O
O
X
X
S
S
O
O
H9C4
H9C4
H3C
H3C
N
N
3
3
4
4
5
5
2
2
1
N
N
1
OH
O
N
N
NH2
N
2.5. Analyses
X = NH
(L1H)
N
C
(L2H)
(L4H)
;
N
NH2
O
Carbon, hydrogen and nitrogen were determined micro-
analytically at the Central Drug Research Institute, Lucknow.
A 100 mg sample of the compound was placed in a silica
crucible, decomposed by gentle heating and then adding
1–2 mL of concentrated HNO3, 2–3 times. An orange colored
N
(L3H)
;
NH
NH2
CH3
Fig. 1. Structures of sulfa drug Schiff bases.

Table 1
Characterization data of the synthesized Schiff bases
Ligand Empirical formula (for-
mula wt.)
Mp (8C)
Yield (%)
Color
Found (calcd, %)
C
n(CaN)
(Azometh)
n(C–O)
n(NH)/NH2
n(OH)
n(CaN2)
(cyclic)
(Enolic)
H
N
L1H
L2H
L3H
C25H26N6O3S (490)
C22H26N6O3S (454.00)
C21H24N4O3S (412)
180
175
165
65
62
60
Middle buff 61.22 (61.22)
5.10 (5.31)
5.62 (5.73)
5.65 (5.83)
17.14 (17.14)
18.28 (18.50)
13.71 (13.59)
1628s
1645s
1614s
1228m
1145m
1241m
3250w
3344w
3366w;
3260w
3233w
3410br
3410br
3450br
1580s
1588s
1590s
Sand stone
Light
58.34 (58.15)
60.92 (61.17)
yellow
Ivory
L4H
C25H27N5O4S (493)
170
65
60.72 (60.85)
5.62 (5.48)
14.32 (14.20)
1620s
1178m
3433br
1584s
L1H, N-(30-methyl-10-phenyl-40-valerylidene-20-pyrazolin-50-one)sulfadiazine; L2H, N-(30-methyl-10-phenyl-40-valerylidene-20-pyrazolin-50-one)sulfaguanidine; L3H, N-(30-methyl-10-phenyl-40-valerylidene-20-
pyrazolin-50-one)sulphanilamide and L4H, N0(-30-methyl-10-phenyl-40-valerylidene-20-pyrazolin-50-one)sulphamethoxazole.
Table 2
Elemental analysis and some physical properties of the synthesized complexes
Sr. no. Complex (empirical formula) (mol. wt.)
Found (calcd, %)
Colour
Decomp.
LM
(UK1 cm2–molK1
)
Yield (%)
meff (BM)
temp. (8C)
C
H
N
V
(1)
(2)
(3)
(4)
[VO(L1)2]$H2O (C50H52N12O8S2V) (1062.94) 56.14 (56.45) 4.76 (4.89)
15.64 (15.81) 4.58 (4.79)
16.64 (16.95) 5.37 (5.14)
12.19 (12.35) 5.31 (5.62)
13.28 (13.10) 4.89 (4.77)
Daffodil yellow
Golden green
Greenish yellow
Golden green
110
105
115
110
28.7
22.6
31.5
20.4
45
50
55
55
1.64
1.58
1.65
1.61
[VO(L2)2]$H2O (C44H52N12O8S2V) (990.94)
[VO(L3)2]$H2O (C42H48N8O8S2V) (906.94)
53.47 (53.28) 5.14 (5.25)
55.29 (55.57) 5.40 (5.29)
[VO(L4)2]$H2O (C50H54N10O10S2V) (1068.94) 56.41 (56.13) 5.14 (5.05)

R.C. Maurya, S. Rajput / Journal of Molecular Structure 794 (2006) 24–34
27
Table 3
Important IR spectral bands (cmK1) of the synthesized complexes
Sr. no.
Complex
n(CaN)
azomethine (s)
n(C–O) enolic
n(OH)
n(VaO)
n(CaN2) cyclic
n(NH)/NH2
(1)
(2)
(3)
(4)
[VO(L1)2]$H2O
[VO(L2)2]$H2O
[VO(L3)2]$H2O
[VO(L4)2]$H2O
1603s
1612s
1606s
1607s
1258m
1156m
1293m
1224m
3410br
3416br
3413br
3400br
913m
903m
904m
903m
1583s
1585s
1586s
1585s
3258w
3336, 3245w
3350w; 3283w
3293w
mass (V2O5) was obtained after decomposition and complete
drying. It was dissolved in the minimum amount of dilute
H2SO4, and the solution so obtained was diluted with distilled
water to 100 mL in a measuring flask. The vanadium content of
each of the complexes was determined volumetrically [36]
using 0.02 M KMnO4 solution as an oxidizing agent in the
presence of sulfurous acid. Based on the following redox
reactions, the amount of vanadium in the sample solution was
calculated using the standard [36] relationship: 1 mL of 0.02 M
KMnO4Z0.0051 g vanadium
system. A three-electrode system consisting of (i) a platinum
disk working electrode, (ii) a platinum wire counter electrode
and (iii) an Ag/AgCl reference electrode, was used. A 10 mL
glass cell with a Teflon cell cover holding working, counter and
reference electrodes and deoxygenating purge tube formed the
sample cell. Prior to each run, the working electrode was
polished using polishing nylon cloth over a glass plate. The
sample solution was deoxygenated by passing purified nitrogen
gas through the solution. The X-Band and EPR spectra of the
complexes were measured on a Bruker ESP X-band EPR
spectrometer using powdered samples at the Regional
Sophisticated Instrumentation Centre, Indian Institute of
Technology, Chennai.
2VOK3ꢀ CH2SO3 C4HC/2VO2C CSO42KC3H2O
MnOK4 C5VO2C C6H2O/5VOK3 CMn2C C12HC
*in aqueous solution V2O5 exists as vanadate (VOK3 ) [36].
2.7. Molecular modeling studies
The 3D molecular modeling of a representative compound
was carried out on a CS Chem 3D Ultra Molecular Modeling
and Analysis Program [37]. It an interactive graphics program
that allows rapid structure building, geometry optimization
with minimum energy and molecular display. It has ability to
handle transition metal compounds.
2.6. Physical methods
Solid state infrared spectra were obtained using KBr pellets
with a Perkin–Elmer model 1620 FT-IR spectrophotometer at
the Central Drug Research Institute, Lucknow. Electronic
spectra were recorded on an ATI Unicam UV-1-100
UV/visible spectrophotometer in our laboratory. Conductance
measurements were made in DMF solution using a Toshniwal
conductivity bridge and dip-type cell with a smooth platinum
electrode of cell constant 1.02. Magnetic measurements were
performed by a vibrating sample magnetometer at the Regional
Sophisticated Instrumentation Centre, Indian Institute of
Technology, Chennai. The decomposition temperatures of the
complexes were recorded by an electrically operated melting
point apparatus (Kumar Industries, Mumbai) of heating
capacity up to 360 8C. Cyclic voltammetric measurements
were carried out on an ECDA-001 basic electrochemistry
3. Results and discussion
The oxovanadium(IV) sulfa drug complexes were prepared
according to the following equation
Fig. 2. IR spectrum of L4H.
Fig. 3. IR spectrum of [VO(L4)2]$H2O.

28
R.C. Maurya, S. Rajput / Journal of Molecular Structure 794 (2006) 24–34
Table 4
Electronic spectral data of the synthesized complexes
Compound no.
Compound
lMax (nm)
n (cmK1
)
3, (L cmK1 molK1
)
Peak assignment
(1)
[VO(L1)2]$H2O
284
307
460
295
314
475
285
302
327
448
310
335
350
560
35211
32573
21739
33898
31847
21052
35087
33112
30581
23364
32258
29850
28571
17857
2993
3176
177
Charge transfer transition
Charge transfer transition
1
b2/ aꢀ1
Charge transfer transition
(2)
(3)
[VO(L2)2]$H2O
[VO(L3)2]$H2O
3033
2919
133
Charge transfer transition
1
b2/ aꢀ1
3862
4546
4004
342
Charge transfer transition
Charge transfer transition
Charge transfer transition
1
b2/ aꢀ1
(4)
[VO(L4)2]$H2O
4720
3945
3880
135
Charge transfer transition
Charge transfer transition
Charge transfer transition
1
b2/ aꢀ1
The Schiff base ligands, L1H to L4H contain six potential
VOSO4$5H2O C2LH H O$;$C%H OH½VOðLÞ2ꢁ$H2O CH2SO4
2
2
5
donor sites: (i) the enolic oxygen; (ii) the cyclic nitrogen N1;
(iii) the cyclic nitrogen N2; (iv) the azomethine nitrogen; (v)
the sulfonamide (SO2NH) oxygen or nitrogen and; (vi) the ring
nitrogen of sulfa drug. All the Schiff base ligands show a sharp
and strong band due to n(CaN) of the azomethine group at
1614–1645 cmK1. The observed low-energy shift of this band
in the chelates and appearing at 1603–1612 cmK1 suggests the
coordination of the azomethine nitrogen [16].
Reflux
where LHZL1H, L2H, L3H or L4H.
The complexes obtained in this investigation are colored
solids (see Table 2 for colors). Their decomposition tempera-
tures are given in Table 2. The complexes are soluble in DMF,
DMSO and acetonitrile but insoluble in ethanol, methanol and
chloroform. The following physical studies have been
employed in the characterization of these complexes.
The n(CaN2) (cyclic) band arising from the pyrazolone
moiety of the ligands appears at 1580–1590 cmK1 and does not
show any appreciable change in their position in the
complexes. This observation indicates the non-participation
of the ring nitrogen N2 in coordination. The coordination of the
ring nitrogen N1 is unfavorable due to the presence of the bulky
phenyl ring attached to it.
3.1. Infrared spectral studies
The important spectral bands of the synthesized ligands as
well as the complexes are presented in Tables 1 and 3,
respectively. All of the Schiff base ligands in the present
nvestigation exhibit a broad band centered at 3410–3450 cmK1
The n(NH) mode of the sulfonamide group/amino group in the
uncoordinated Schiff bases remains unchanged in the spectra of
their complexes (see Tables 1 and 3). This suggests that the
sulfonamide nitrogen/amino group is not taking part in
coordination. The bandatw1386 cmK1 in the ligandsisassigned
to nas(OaSaO). This band remains almost at the same position in
the complexes and hence suggests that the sulfonamide oxygen is
not taking part in coordination with the metal center.
.
This suggests the presence of a strongly hydrogen-bonded OH
group [38]. This indicates the involvement of the 5-OH group
in intramolecular hydrogen bonding with the lone pair of
azomethine nitrogen. It also suggests that the ligands exist in
enol form in the solid state [16].
Fig. 4. Electron spectrum of [VO(L3)2]$H2O.
Fig. 5. ESR spectrum of [VO(L3)2]$H2O.

R.C. Maurya, S. Rajput / Journal of Molecular Structure 794 (2006) 24–34
29
Table 5
Cyclic voltammetric data of some oxovanadium(IV) complexes
Compound
no.
Compound
V(IV)/V(V)
V(IV)/V(III)
Epc(mV)
Epa(mV)
Er(mV)
DEp(mV)
Epa(mV)
Epc(mV)
Er(mV)
DEp(mV)
(1)
(4)
[VO(L1)2]$H2O
[VO(L4)2]$H2O
462
425
373
340
417.5
382.5
89
85
K760
K675
K680
K580
K720
K627.5
80
95
Supporting electrolyte: tetrabutylammonium tetrafluoroborate, [CH3(CH2)3]4NBF4 (50 mmol); concentration of complexes: 1 mmol; all the potentials are
referenced to the Ag/AgCl electrode; ErZ0.5(EpaCEpc), where Epa and Epc are anodic and cathodic potentials.
The reaction of the enolic Schiff bases with VO2C ion with
elimination of a proton is revealed by the presence of a new
band in the complexes at 1156–1293 cmK1 as compared to that
of the Schiff bases at 1145–1241 cmK1 due to the n(C–O)
(enolic) [39]. The appearance of a broad band due to n(OH) at
3400–3416 cmK1 in the complexes may be due to a lattice
water molecule attached with the complexes. The low
decomposition temperatures of the complexes (105–115 8C)
(see Table 2) also support the presence of lattice water in these
complexes.
been reported by Maurya et al. [41] in some oxovanadium(IV)
complexes involving Schiff bases derived from 4-butyryl-3-
methyl-1-phenyl-2-pyrazolin-5-one and certain aromatic
amines.
3.4. Electronic spectral studies
The electronic spectra of these compounds were recorded
in 10K3 molar dimethylformamide solutions in the range
200–800 nm. The lmax of electronic spectral peaks and
respective molar extinction coefficients along with their
tentative assignments are given in Table 4. Besides high
intensity charge transfer transitions, all these complexes
displayed one low intensity d–d transition which may be
Most of the oxovanadiun(IV) complexes exhibit a strong
band near 1000 cmK1, which has been assigned to n(VaO)
[40]. In contrast, several oxovanadium(IV) complexes have
been reported in which this stretching mode appears at quite
lower [41] wave numbers, around 900 cmK1. The shift of
n(VaO) band to lower wave numbers has been suggested due
to the presence of a slight /VaO/VaO/ type interaction
occurring between vanadyl oxygen of one molecule with a
vanadium metal in another molecule [42]. In the present work,
the n(VaO) mode is found at 903–913 cmK1. This shift of
n(VaO) mode to lower wave numbers suggests the presence of
a slight /VaO/VaO/ type interaction in these complexes.
The IR spectra of the Schiff base L4H and its complex,
[VO(L4)2]$H2O are given in Figs. 2 and 3, respectively.
1
1
assigned to b2/ aꢀ1 [44] transition. The assignment of b2/ aꢀ1
transition in each case assumes idealized C2v symmetry. These
spectra are typical of oxovanadium(IV) complexes [15,45].
The electronic spectrum of compound (3) is shown in Fig. 4.
3.5. ESR spectral studies
The liquid nitrogen temperature X-Band EPR Spectrum
(Fig. 5) of a representative compound, [VO(L3)]$H2O, was
recorded in frozen DMF solution, without DPPH using the
microwave frequency 9.17 GHz. The spectrum shows an eight-
line pattern, characteristic of an unpaired electron being
coupled with a vanadium nuclear spin (IZ7/2). The
oxovanadium(IV) ion belongs to the 3d1 system and the
vanadium nucleus has IZ7/2. This means that the unpaired
electron is in the vicinity of IZ7/2 of its own mother nucleus.
Thus, the isotropic ESR Spectrum of a magnetically dilute
oxovanadium(IV) complex gives 2!7/2C1Z8 lines.
The observed spectral parameters for this compound are:
gtZ2.003, gsZ1.974, gavZ1.993. The observed gav value
deviates from the free ion value 2.0036, and this suggests that
3.2. Conductance measurements
The observed molar conductances of these complexes in 10K3
molar DMF solutions are in the range 20.4–31.5 UK1 cm2 molK1
(Table 2) and are consistent with the non-electrolytic nature of
these complexes [43]. Such a non-zero molar conductance
value for each of the complex in the present study is most
probably due to the strong donor capacity of DMF, which may
lead to the displacement of anionic ligand and change of
electrolyte [43] type.
3.3. Magnetic measurements
The oxovanadium(IV) ion belongs to the SZ1/2 system.
The magnetically dilute oxovanadium(IV) complexes usually
exhibit magnetic moments to their spin-only value of 1.73 BM.
The observed magnetic moments of the complexes under study
are found in the range 1.61–1.65 BM. These results suggest
that an interaction [42] of the of the type /VaO/VaO/ is
taking place in these complexes. Such a result has recently
O
V
N
O
O
N
O
O
Fig. 6. Structure of bis(picolinato) oxovanadium(IV).

30
R.C. Maurya, S. Rajput / Journal of Molecular Structure 794 (2006) 24–34
Fig. 7. 3D Structure of [VO(L3)2] (3).
the complex is appreciably covalent [46]. The ‘g’-value so
obtained is comparable with the g values reported earlier for
oxovanadium(IV) complexes [16,45].
from 382.5 to 417.5 mV (oxidation) and from K627.5 to
K720 mV (reduction) against the saturated Ag/AgCl electrode
(Table5).Thesetwocomplexesshowedredoxcoupleswithpeak-
to-peak separation values (DEp) ranging from 80 to 95 mV,
indicating a single-step one-electron transfer process [47]. Thus,
the positive Er values (382.5–417.5 mV) may be assigned to the
metal centered oxidation [48] of V(IV)–V(V) in which the stereo
structures of parent and oxidized species are expected to be
similar. The negative Er potentials (K627.5 to K720 mV) may
be assigned to the conversion [48] of V(IV)–V(III). Besides
establishing (CIV) oxidation state, these observations conclude
that the ligand environments present in these two complexes
facilitate electron transfer reactions. This study gives some
insight in the vanadium metabolism of the tunicates (9) that
3.6. Cyclic voltammetric studies
Cyclic voltammetric measurements of two representative
complexes, (1) and (4), were carried out on an ECDA-001 basic
electrochemistry system in order to assess the suitability of ligand
environments in the present complexes to facilitate electron
transfer reactions. The complexes were dissolved in acetonitrile
and the cyclic voltammogram were recorded in the scan range
1500 to K1000 mV. The oxidations and reductions of these
complexes were achieved by waves with Er values in the range

R.C. Maurya, S. Rajput / Journal of Molecular Structure 794 (2006) 24–34
31
Table 6
Various bond lengths of compound [VO(L3)2] (3)
S. no.
Atoms
Actual bond
length
Optimal bond
length
S. no.
Atoms
Actual bond
length
Optimal bond
length
1
H(79)–C(25)
C(25)–C(24)
C(23)–S(20)
C(58)–C(57)
C(5)–N(1)
1.1
1.1
58
59
H(77)–C(19)
H(91)–C(41)
H(78)–C(24)
H(90)–C(41)
C(40)–H(89)
C(18)–C(13)
C(10)–H(64)
C(11)–H(65)
C(52)–C(53)
H(70)–C(14)
N(27)–H(80)
C(48)–H(98)
C(23)–C(29)
C(54)–H(102)
S(20)–O(21)
H(82)–C(28)
C(32)–C(33)
C(40)–H(88)
C(33)–C(36)
C(41)–H(92)
C(26)–C(28)
C(23)–C(24)
N(1)–N(2)
1.113
1.113
1.1
1.113
1.113
1.1
2
1.337
1.79
1.42
–
3
60
4
1.337
1.266
1.696
1.1
1.42
1.462
–
61
1.113
1.113
1.337
1.113
1.113
1.337
1.1
1.113
1.113
1.42
1.113
1.113
1.42
1.1
5
62
6
N(8)–S(20)
63
7
H(96)–C(46)
H(94)–C(44)
C(48)–H(99)
H(101)–C(53)
C(34)–N(30)
C(15)–C(14)
H(85)–C(38)
S(49)–O(51)
H(86)–C(39)
C(28)–C(29)
O(60)–V(59)
H(62)–C(9)
C(32)–C(48)
C(10)–H(63)
C(55)–C(57)
H(71)–C(15)
S(49)–N(37)
C(47)–C(46)
C(58)–C(52)
C(12)–H(69)
C(55)–C(54)
N(8)–V(59)
C(7)–C(9)
1.1
64
8
1.1
1.1
65
9
1.113
1.1
1.113
1.1
66
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
67
1.266
1.337
1.113
1.45
1.462
1.42
1.113
1.45
1.113
1.42
–
68
1.05
1.05
1.113
1.42
1.1
69
1.113
1.337
1.1
70
71
1.113
1.337
1.5996
1.113
1.497
1.113
1.337
1.1
72
1.45
1.45
1.1
73
1.1
74
1.337
1.113
1.337
1.113
1.337
1.337
1.614
1.26
1.503
1.113
1.503
1.113
1.42
1.42
1.426
1.26
1.426
1.523
1.523
1.462
1.1
1.113
1.497
1.113
1.42
1.1
75
76
77
78
79
1.696
1.337
1.337
1.113
1.337
1.9264
1.497
1.377
1.113
1.86
–
80
1.42
1.42
1.113
1.42
–
81
C(3)–N(2)
82
N(30)–N(31)
C(10)–C(9)
C(10)–C(11)
C(26)–N(27)
C(58)–H(106)
C(18)–C(17)
C(45)–C(46)
C(34)–O(35)
C(40)–C(39)
C(16)–C(15)
C(17)–C(16)
C(3)–C(4)
1.23
83
1.523
1.523
1.266
1.1
84
85
1.497
–
86
C(36)–N(37)
H(87)–C(39)
V(59)–O(6)
C(13)–N(1)
C(17)–H(73)
C(47)–H(97)
H(104)–N(56)
C(5)–C(4)
87
1.337
1.337
1.355
1.523
1.337
1.337
1.337
1.497
1.113
1.113
1.337
1.377
1.113
2.0946
1.1
1.42
1.42
1.355
1.523
1.42
1.42
1.503
1.497
1.113
1.113
1.503
–
1.113
–
88
89
1.266
1.1
1.462
1.1
90
91
1.1
1.1
92
1.05
1.05
1.337
1.355
1.113
1.113
1.113
1.523
1.42
1.1
93
1.337
1.355
1.113
1.113
1.113
1.523
1.337
1.1
94
C(19)–C(3)
C(12)–H(68)
C(12)–H(67)
C(7)–C(4)
C(5)–O(6)
95
C(48)–H(100)
H(76)–C(19)
H(75)–C(19)
C(12)–C(11)
C(13)–C(14)
C(18)–H(74)
C(47)–C(42)
C(52)–S(49)
H(84)–C(38)
N(27)–H(81)
H(103)–N(56)
H(61)–C(9)
O(35)–V(59)
H(105)–C(57)
C(16)–H(72)
C(55)–N(56)
C(54)–C(53)
C(32)–N(31)
C(26)–C(25)
96
97
98
N(8)–C(7)
99
C(11)–H(66)
V(59)–N(37)
H(95)–C(45)
C(43)–H(93)
C(43)–C(44)
H(83)–C(29)
N(30)–C(42)
C(43)–C(42)
S(49)–O(50)
C(40)–C(41)
C(38)–C(39)
S(20)–O(22)
C(36)–C(38)
C(44)–C(45)
C(33)–C(34)
1.113
–
100
101
102
103
104
105
106
107
108
109
110
111
112
113
1.1
1.337
1.79
1.42
–
1.1
1.1
1.337
1.1
1.42
1.1
1.113
1.05
1.113
1.05
1.05
1.113
–
1.266
1.337
1.45
1.462
1.42
1.45
1.523
1.523
1.45
1.497
1.42
1.337
1.05
1.113
1.86
1.523
1.523
1.45
1.1
1.1
1.1
1.1
1.266
1.337
1.5526
1.337
1.462
1.42
1.26
1.42
1.497
1.337
1.337
the vanadium(IV) formed from vanadium(V) of the marine
environment in the initial reduction could become ligated in such
a way as to lower its reduction potential to the required trivalent
state.
3.7. 3D molecular modeling and analysis
In view the penta-coordination of all the complexes (vide
infra), and also taking into account of the well established

32
R.C. Maurya, S. Rajput / Journal of Molecular Structure 794 (2006) 24–34
Table 7
Various bond angles of compound [VO(L3)2] (3)
S. no.
Atoms
Actual bond
angles
Optimal bond
angles
S. no.
Atoms
Actual bond
angles
Optimal bond
angles
1
H(90)–C(41)–H(91)
H(91)–C(41)–H(92)
C(40)–C(41)–H(91)
H(90)–C(41)–H(92)
C(40)–C(41)–H(90)
C(40)–C(41)–H(92)
H(88)–C(40)–H(89)
H(89)–C(40)–C(39)
C(41)–C(40)–H(89)
H(88)–C(40)–C(39)
C(41)–C(40)–H(88)
C(41)–C(40)–C(39)
H(86)–C(39)–H(87)
C(40)–C(39)–H(86)
H(86)–C(39)–C(38)
C(40)–C(39)–H(87)
H(87)–C(39)–C(38)
C(40)–C(39)–C(38)
H(69)–C(12)–C(11)
H(69)–C(12)–H(68)
H(67)–C(12)–H(69)
C(11)–C(12)–H(68)
H(67)–C(12)–C(11)
H(67)–C(12)–H(68)
C(12)–C(11)–H(65)
C(12)–C(11)–C(10)
C(12)–C(11)–H(66)
C(10)–C(11)–H(65)
H(65)–C(11)–H(66)
C(10)–C(11)–H(66)
H(64)–C(10)–H(63)
C(9)–C(10)–H(63)
C(11)–C(10)–H(63)
H(64)–C(10)–C(9)
C(11)–C(10)–H(64)
C(11)–C(10)–C(9)
C(55)–C(57)–C(58)
C(58)–C(57)–H(105)
C(55)–C(57)–H(105)
H(104)–N(56)–H(103)
C(55)–N(56)–H(104)
C(55)–N(56)–H(103)
C(54)–C(55)–C(57)
N(56)–C(55)–C(57)
C(54)–C(55)–N(56)
C(55)–C(54)–C(53)
C(55)–C(54)–H(102)
H(102)–C(54)–C(53)
C(52)–C(58)–C(57)
H(106)–C(58)–C(57)
C(52)–C(58)–H(106)
C(54)–C(53)–H(101)
C(52)–C(53)–H(101)
C(54)–C(53)–C(52)
C(58)–C(52)–S(49)
C(58)–C(52)–C(53)
S(49)–C(52)–C(53)
C(47)–C(46)–H(96)
H(96)–C(46)–C(45)
C(47)–C(46)–C(45)
H(95)–C(45)–C(46)
C(44)–C(45)–C(46)
109.442
109.52
109.442
109.462
109.5
109
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
C(34)–N(30)–N(31)
C(34)–N(30)–C(42)
C(42)–N(30)–N(31)
C(32)–C(33)–C(36)
C(32)–C(33)–C(34)
C(34)–C(33)–C(36)
O(35)–C(34)–N(30)
C(33)–C(34)–N(30)
C(33)–C(34)–O(35)
H(82)–C(28)–C(29)
C(26)–C(28)–C(29)
C(26)–C(28)–H(82)
111
124
124
124
120
120
120
–
2
109
124.5
124.5
128.998
111
3
110
4
109
5
110
6
109.462
109.52
109.462
109.462
109.442
109.442
109.5
110
119.998
124.698
110.999
124.3
120
7
109.4
109.41
109.41
109.41
109.41
109.5
109.4
109.41
109.41
109.41
109.41
109.5
110
8
120
124.3
120
–
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
120
120
120
118.8
–
109.52
109.442
109.442
109.462
109.462
109.5
H(80)–N(27)–H(81) 120
C(26)–N(27)–H(81)
C(26)–N(27)–H(80)
C(25)–C(26)–C(28)
C(25)–C(26)–N(27)
N(27)–C(26)–C(28)
H(79)–C(25)–C(24)
H(79)–C(25)–C(26)
C(26)–C(25)–C(24)
C(23)–C(29)–C(28)
H(83)–C(29)–C(28)
C(23)–C(29)–H(83)
H(78)–C(24)–C(25)
C(23)–C(24)–C(25)
H(78)–C(24)–C(23)
S(20)–C(23)–C(29)
S(20)–C(23)–C(24)
C(24)–C(23)–C(29)
C(18)–C(17)–H(73)
C(16)–C(17)–H(73)
C(18)–C(17)–C(16)
H(72)–C(16)–C(15)
C(17)–C(16)–H(72)
C(17)–C(16)–C(15)
H(71)–C(15)–C(14)
C(16)–C(15)–C(14)
H(71)–C(15)–C(16)
C(13)–C(18)–H(74)
C(17)–C(18)–H(74)
C(13)–C(18)–C(17)
C(13)–C(14)–C(15)
H(70)–C(14)–C(15)
C(13)–C(14)–H(70)
S(49)–N(37)–C(36)
S(49)–N(37)–V(59)
V(59)–N(37)–C(36)
C(34)–O(35)–V(59)
N(8)–V(59)–O(60)
O(60)–V(59)–O(6)
120
120
–
120
120
120
120
120
120
–
120
120
109.462
109.52
109.462
109.442
109.5
120
109
120
109
120
110
120
–
110
119.999
120.001
119.999
120
120
120
120
–
109.442
109.442
109.5
109
109.41
109.5
109.41
109.41
109.4
109.41
109.4
109.41
109.41
109.41
109.41
109.5
–
109.462
109.442
109.52
109.462
109.52
109.442
109.442
109.462
109.462
109.5
120.001
120
120
–
120
–
120
120
120
120
–
120
120
120
120
120
120
–
120
120
120
120
120
–
120
120
120
120.001
120
120
120
120
120
120
–
118.8
–
120
120
120
120.001
120.001
119.999
120
–
120
120
120
–
120
120
120
120
–
120
120
120
–
110.267
110.267
106.168
109.5
19.5526
90
120.001
120
120
–
120
–
120
–
–
120
120
–
120
120
–
120
120
O(60)–V(59)–O(35) 89.9999
O(60)–V(59)–N(37) 100.509
–
120
120
–
120
–
N(8)–V(59)–O(6)
N(8)–V(59)–O(35)
N(8)–V(59)–N(37)
O(35)–V(59)–O(6)
N(37)–V(59)–O(6)
82.2944
109.5
–
120
–
–
120
120
102.675
109.5
–
120
–
–
120
120
33.4368
–
120
120
O(35)–V(59)–N(37) 77.7856
–
120
–
C(23)–S(20)–N(8)
C(23)–S(20)–O(21)
C(23)–S(20)–O(22)
109.52
–
120
120
109.462
109.462
–
120
–
–

R.C. Maurya, S. Rajput / Journal of Molecular Structure 794 (2006) 24–34
33
Table 7 (continued)
S. no.
Atoms
Actual bond
angles
Optimal bond
angles
S. no.
Atoms
Actual bond
angles
Optimal bond
angles
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
H(95)–C(45)–C(44)
C(43)–C(44)–H(94)
H(94)–C(44)–C(45)
C(43)–C(44)–C(45)
H(97)–C(47)–C(46)
C(42)–C(47)–C(46)
H(97)–C(47)–C(42)
H(93)–C(43)–C(44)
C(42)–C(43)–H(93)
C(42)–C(43)–C(44)
C(47)–C(42)–N(30)
C(47)–C(42)–C(43)
N(30)–C(42)–C(43)
C(32)–C(48)–H(99)
H(99)–C(48)–H(100)
H(98)–C(48)–H(99)
C(32)–C(48)–H(100)
C(32)–C(48)–H(98)
H(98)–C(48)–H(100)
C(32)–N(31)–N(30)
N(37)–S(49)–O(51)
C(52)–S(49)–O(51)
O(50)–S(49)–O(51)
C(52)–S(49)–N(37)
O(50)–S(49)–N(37)
C(52)–S(49)–O(50)
H(84)–C(38)–H(85)
H(85)–C(38)–C(39)
C(36)–C(38)–H(85)
H(84)–C(38)–C(39)
C(36)–C(38)–H(84)
C(36)–C(38)–C(39)
C(33)–C(36)–N(37)
N(37)–C(36)–C(38)
C(33)–C(36)–C(38)
C(48)–C(32)–N(31)
C(33)–C(32)–C(48)
C(33)–C(32)–N(31)
120
120
120
120
–
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
N(8)–S(20)–O(21)
N(8)–S(20)–O(22)
O(21)–S(20)–O(22)
H(62)–C(9)–C(7)
H(62)–C(9)–H(61)
H(62)–C(9)–C(10)
H(61)–C(9)–C(7)
C(10)–C(9)–C(7)
C(10)–C(9)–H(61)
S(20)–N(8)–V(59)
S(20)–N(8)–C(7)
C(7)–N(8)–V(59)
N(1)–C(13)–C(14)
C(18)–C(13)–N(1)
C(18)–C(13)–C(14)
C(9)–C(7)–C(4)
109.442
109.442
109.5
–
120
–
120
–
120
109.462
109.52
109.462
109.442
109.5
109.41
109.4
109.41
109.41
109.5
109.41
–
120
120
–
120
120
120
120
120
–
120
120
109.442
110.042
110.041
107.085
120
120
120
120
120
120
110
109
109
110
110
109
115
–
–
120
–
120
120
120
120
121.4
–
109.442
109.52
109.442
109.462
109.5
109.462
108.832
109.442
109.462
109.5
109.52
109.442
109.462
109.52
109.462
109.462
109.441
109.442
109.5
123
120
120
118.5
N(8)–C(7)–C(9)
N(8)–C(7)–C(4)
C(5)–O(6)–V(59)
N(1)–C(5)–C(4)
N(1)–C(5)–O(6)
C(4)–C(5)–O(6)
H(75)–C(19)–H(76)
H(77)–C(19)–H(76)
H(76)–C(19)–C(3)
H(77)–C(19)–H(75)
H(75)–C(19)–C(3)
H(77)–C(19)–C(3)
C(5)–C(4)–C(3)
118.5
123
–
109.5
–
111
120
–
124.698
124.298
109.442
109.52
109.442
109.462
109.5
–
124.3
109
109
110
109
110
110
120
120
120
124
124
124
120
115.1
121.4
115
116.6
–
–
–
109.4
109.41
109.41
109.41
109.41
109.5
–
109.462
111
C(5)–C(4)–C(7)
119.999
128.998
128.353
103.293
128.353
111
C(7)–C(4)–C(3)
C(13)–N(1)–C(5)
C(5)–N(1)–N(2)
C(13)–N(1)–N(2)
N(2)–C(3)–C(4)
C(19)–C(3)–N(2)
C(19)–C(3)–C(4)
N(1)–N(2)–C(3)
118.5
118.5
130.916
130.915
98.169
–
121.4
115.1
121.4
120
124.5
124.5
103.707
square pyramidal structure [49] of bis(picolinato)oxovanadiu-
m(IV) (Fig. 6) [having a monoprotic bidentate (O, N-donor)
picolinate ligand, similar to monoprotic (O, N-donor) L1H,
L2H, L3H or L4H ligand in the present investigation], the
molecular modeling of a representative compound, [VO(L3)2]
(3), is based on its square pyramidal structure. The details of
bond lengths and bond angles as per the 3D structure (Fig. 7)
are given in Tables 6 and 7, respectively. For convenience of
looking over the different bond lengths and bond angles, the
various atoms in the compound in question are numbered in
Arabic numerals. In all, 313 measurements of the bond lengths,
plus the bond angles are listed in the Tables 6 and 7. Except few
cases, optimal values (most favorable) of both the bond lengths
and the bond angles are given in the tables along with the actual
ones. In most of the cases, the actual bond lengths and bond
angles are close to the optimal values, and thus the proposed
structure of the compound (3) as well as of the others, are
acceptable.
4. Conclusion
The satisfactory analytical data and all the studies
presented above suggests that the present complexes may
be formulated as [VO(L)2]$H2O, where LHZL1H, L2H, L3H
or L4H. Keeping in view of the n(VaO) mode at quite lower
values around 900 cmK1 and the observed magnetic
moments of the complexes in the range 1.61–1.65 BM, and
considering the well established square pyramidal structure
[49] of bis(picolinato)oxovanadium(IV) (Fig. 6) in the solid
state [involving a monoprotic bidentate (O, N-donor)
picolinate ligand, similar to monoprotic bidentate (O,
N-donor) LH ligands in the present investigation], a square
based pyramidal structure (Fig. 8) having a slight /VaO/
VaO/ type interaction has been proposed for these
complexes. X-ray crystallographic studies, which might
confirm the proposed structures, could not be carried out as
suitable crystals were not obtained.

34
R.C. Maurya, S. Rajput / Journal of Molecular Structure 794 (2006) 24–34
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X
S
Soc. Dalton Tans. (1995) 2459.
O
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O
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Inorg. Chim. Acta 283 (1998) 175.
C4H9
CH3
N
O
V
N
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N
O
N
H3C
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N
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H9C4
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Life, vol. 31, Marcel Dekker, New York, 1995.
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[23] A.S. Tracey, D.C. Crans (Eds.), Vanadium Compounds: Chemistry,
Biochemistry and Therapeutic Applications, American Chemical Society,
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X
NH2
N
N
;
C
X = NH
(1)
N
(2)
(4)
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1998.
NH2
O
N
;
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(2003) 89.
NH
(3)
NH2
CH3
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Fig. 8. Suggested structure of complexes.
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references therein).
Acknowledgements
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The authors are thankful to Dr S.M. Paul Khurana, Vice-
chancellor of this University, for encouragement, and Professor
K.K. Verma, Head, Department of Chemistry, for laboratory
facilities and helpful discussion. We are grateful to the
Department of Science and Technology, New Delhi, India,
for financial assistance. Analytical facilities provided by the
Central Drug Research Institute, Lucknow, India, and the
Regional Sophisticated Instrumentation Centre, Indian Insti-
tute of Technology, Chennai, India, are gratefully
acknowledged.
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