Synthesis, structural characterization and electrochemical activity of oxidovanadium(IV/V) complexes of a diprotic ONS chelating ligand

Article abstract of DOI:10.1016/j.ica.2010.06.025

The present work reports the chemistry of a few oxidovanadium(IV) and (V) complexes of the ONS chelating ligand S-benzyl-β-N-(2- hydroxyphenylethylidine) dithiocarbazate (H₂L). Major objective of this work is to arrive at some general conclusions about the influence of binding environment generated by the replacement of an O-donor center by a S-donor point in a ligand (of a similar arrangement of the other O- and N-donor points) on the redox behavior and on the structural features of comparable [VO(OEt)(ONS)] and [VO(OEt)(ONO)] complexes. Synthesis, characterization by various physicochemical techniques (UV-Vis, IR, EPR and elemental analysis), exploration of electrochemical activity of the oxidovanadium(V) complex [V ^VO(OEt)L] (1), the mixed ligand complex [V^VO(N-O)L] (3) (where N-O is the mono anion of 8-hydroxyquinoline) and a binuclear complex [V^VO(OEt)L]₂(μ-4,4′-bipy) (2) are reported. Similar studies on of mixed ligand oxidovanadium(IV) complexes of the formula [V^VO(N-N)L] (4,5) (where N-N = 2,2′-bipy and o-phen) are also presented here. The [V^VO(OEt)L] complex is pentacoordinated and distorted square pyramidal, while the [V^IV(N-N)L] complexes are hexacoordinated and octahedral. Structural features of the complex 1 were compared with the corresponding aspects of the previously reported analogous complex [V^VO(OEt)(ONO)] (1′).

Full text of DOI:10.1016/j.ica.2010.06.025

Inorganica Chimica Acta 363 (2010) 3376–3383
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, structural characterization and electrochemical activity of
oxidovanadium(IV/V) complexes of a diprotic ONS chelating ligand
Manas Sutradhar a,b, Tannistha Roy Barman , Gurunath Mukherjee , Michael G.B. Drew ,
Saktiprosad Ghosh
a
a
a
c
a,
*
Department of Chemistry, University of Calcutta, University College of Science, 92, Acharya Prafulla Chandra Road, Kolkata 700009, India
Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University of Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany
School of Chemistry, The University of Reading, P.O. Box 224 Whiteknights, Reading RG6 6AD, UK
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
The present work reports the chemistry of a few oxidovanadium(IV) and (V) complexes of the ONS che-
lating ligand S-benzyl-b-N-(2-hydroxyphenylethylidine) dithiocarbazate (H L). Major objective of this
2
work is to arrive at some general conclusions about the influence of binding environment generated
by the replacement of an O-donor center by a S-donor point in a ligand (of a similar arrangement of
the other O- and N-donor points) on the redox behavior and on the structural features of comparable
Received 2 February 2010
Received in revised form 8 June 2010
Accepted 15 June 2010
Available online 22 June 2010
[
VO(OEt)(ONS)] and [VO(OEt)(ONO)] complexes. Synthesis, characterization by various physicochemical
Keywords:
techniques (UV–Vis, IR, EPR and elemental analysis), exploration of electrochemical activity of the oxido-
vanadium(V) complex [V O(OEt)L] (1), the mixed ligand complex [V O(N–O)L] (3) (where N–O is the
mono anion of 8-hydroxyquinoline) and a binuclear complex [V O(OEt)L]
Similar studies on of mixed ligand oxidovanadium(IV) complexes of the formula [V O(N–N)L] (4,5) (where
N–N = 2,2 -bipy and o-phen) are also presented here. The [V O(OEt)L] complex is pentacoordinated and dis-
torted square pyramidal, while the [V (N–N)L] complexes are hexacoordinated and octahedral. Structural
Oxidovanadium(IV/V) complexes
ONS chelating ligand
Electrochemical activity
Binuclear complex
V
V
V
0
2
(
l
-4,4 -bipy) (2) are reported.
V
0
V
X-ray crystallography
IV
features of the complex 1 were compared with the corresponding aspects of the previously reported
V
0
analogous complex [V O(OEt)(ONO)] (1 ).
Ó 2010 Elsevier B.V. All rights reserved.
1
. Introduction
plexes involving a series of tridentate ONS donor ligands [51–57].
In this backdrop and in continuation of our work in the complex
chemistry of vanadium in +3, +4 and +5 oxidation states
[3,10,27,28,30–33], specially in the form of oxidovanadium species,
the present study of oxidoalkoxido containing vanadium com-
plexes involving a ONS donor ligand are under taken. The complex
Compared to chemistry of vanadium ligated to various types of
N–O donor ligands [1–33] vanadium complexes in total or partial
sulfur coordination have received much less attention. It is rather
surprising because some vanadium complexes in total or partial
sulfur environment were known for the last three decades. Such
vanadium complexes are found to be involved in conducting vana-
dium–sulfur materials [34], in the removal of vanadium from crude
oils [35], as catalysts for oxidizing sulfides to sulfoxides [36]. The
thiolato complexes containing vanadium(III) [37], vanadium(IV)
2
[VO(OEt)L] (1) [where H L is a diprotic tridentate ONS ligand,
S-benzyl-b-N-(2-hydroxyphenylethylidine) dithiocarbazate] is
pentacoordinate and so has one position vacant in the coordina-
tion octahedron which can be utilized as a substrate binding site
for neutral monodentate N-heterocyclic bases and are also ame-
nable to the formation of binuclear complexes utilizing suitable
[
38], oxidovanadium(IV) [38,39] and vanadium(V) [40] cores are
0
also reported along with a structurally characterized V(V) thiolate
neutral exobidentate ligands like 4,4 -bipyridine. The present
complex [40] and the VO3 complex [VO(SCH
other vanadium–sulfur systems also received limited attention
42–50]. From 1997 onwards Chaudhury and his group explored
+
–CH
)
3
N] [41]. A few
work reports the findings enumerated below: (a) synthesis, struc-
tural characterization, examination of chemical and electrochem-
ical properties of the monooxidoalkoxidovanadium(V) complex
2
2
[
synthesis, structural characterization, magnetic, chemical, electro-
chemical and photochemical properties of oxidovanadium com-
[VO(OEt)L] (1), the mixed ligand oxidovanadium(V) complex
0
[VO(N–O)L] (3), a binuclear complex [VO(OEt)L]
2
(l-4,4 -bipy) (2)
and the mixed ligand oxidovanadium(IV) complexes of the type
[
VO(N–N)L] (4,5) where H
2
L is a diprotic tridentate ONS donor
0
ligand, N–O = 8-hydroxy quinoline and N–N = 2,2 -bipyridine,
*
Corresponding author. Tel.: +91 3324647702.
E-mail address: ghosh_sakti@vsnl.net (S. Ghosh).
1
,10-phenanthroline.
0
020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.06.025

M. Sutradhar et al. / Inorganica Chimica Acta 363 (2010) 3376–3383
3377
ꢁ
1
ꢁ1
m H
(V@O). 1
2
. Experimental
.1. Materials
2
VO(acac) ] was prepared as described in literature [58] and
m
(C–O enolic), 1046 cm
for
m
(N–N), 960 cm
for
Si): 7.89–6.57 (15H, m, C
C@N–).
NMR d
4.56 (2H, s, –CH
H
(300 MHz; DMSO d
6
; Me
4
6 4
H ),
2
2
–), 2.74 (3H, s, –CH
3
[
2
(
.2.5. Synthesis of the oxidovanadium(IV) complexes [VO(o-phen)L]
4) and [VO(2,2 - bipy)L] (5)
These two complexes were obtained as orange red crystalline
solids utilizing the same method mentioned in the preparation of
complex 3 using o-phenanthroline for 4 and 2,2 -bipyridine for 5
in place of 8-hydroxyquinoline and acetonitrile as the reaction
medium.
was used as the source of vanadium. Reagent grade solvents were
dried and distilled prior to use. All other chemicals were reagent
grade, obtained from commercial sources and used without further
purification. Spectroscopic grade solvents were used for spectral
measurements.
0
0
2.2. Preparations
22 4 2 2
Complex 4: Yield: 70%. Anal. Calc. for C28H N O S V: C, 59.89;
H, 3.92; N, 9.98; V, 9.09. Found: C, 59.86; H, 3.94; N, 9.96; V,
2
.2.1. Synthesis of the ligand H
2
L
ꢁ1
ꢁ1
ꢁ1
9
for
9
.07%. IR (KBr pellet, cm ): 3423 cm
for
m
(O–H), 1597 cm
The Schiff base ligand, S-benzyl-b-N-(2-hydroxyphenylethyli-
dine) dithiocarbazate (H L) was prepared by using a reported proce-
dure [59]. Yield ꢀ80%, m. p. ꢀ148 °C. Anal. Calc. for C16 OS : C,
ꢁ1
ꢁ1
m
(C@N), 1238 cm for
m(C–O enolic), 1062 cm for
m(N–N),
2
ꢁ1
57 cm for
m
(V@O).
H
16
N
2
2
22 4 2 2
Complex 5: Yield: 73%. Anal. Calc. for C26H N O S V: C, 58.10;
6
0.76; H, 5.06; N, 8.86. Found: C; 60.71, H, 5.63; N, 8.82%. IR (KBr pel-
H, 4.09; N, 10.43; V, 9.49. Found: C, 58.08; H, 4.11; N, 10.43; V,
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
let, cm ): 3436 cm for
for
Me
4
m
(O–H), 3171 cm for
m
(N–H), 1600 cm
(300 MHz; DMSO d
ꢁ1
ꢁ1
ꢁ1
9
for
9
.46%. IR (KBr pellet, cm ): 3436 cm
for
m
(O–H), 1595 cm
ꢁ
1
1
m
(C@N), 1309 for cm
m
(C@S). H NMR d
H
6
;
ꢁ1
ꢁ1
m
(C@N), 1242 cm for
m
(C–O enolic), 1068 cm for
m
(N–N),
4
Si): 11.26 (1H, s, OH), 11.25 (1H, s, NH), 7.41–6.82 (9H, m, C
–), 2.47 (3H, s, –CH @CN–).
6
H
4
),
ꢁ1
58 cm for
m
(V@O).
.51 (2H, s, –CH
2
3
2.3. Physical measurements
2.2.2. Synthesis of the oxidovanadium(V) complex [VO(OEt)L] (1)
The ligand H L (0.32 g, 1.02 mmol) was dissolved in 30 ml of
2
Elemental analyses (C, H and N) were done with a Perkin–Elmer
400 CHNS/O analyzer and vanadium contents (%) of the com-
plexes were determined gravimetrically [60] as V O . Electronic
2 5
ethanol and 0.27 g (1.02 mmol) of vanadium(IV) acetylacetonate
was added to this solution and the mixture was refluxed for 4 h
on a steam bath. The color of the solution changed from yellow-
green to dark brown. The solution was filtered and allowed to
evaporate slowly at room temperature. After 2–3 days yellowish
brown single crystals, suitable for X-ray diffraction analysis sepa-
2
spectra of the complexes in acetonitrile were recorded on a Hitachi
U-3501 spectrophotometer and IR spectra (as KBr pellets) were re-
1
corded using a Perkin Elmer RXI FT-IR spectrophotometer. The H
NMR Spectra were recorded on a Bruker Model Advance DPX300
Spectrometer. Electrochemical measurements were performed
with a PAR model 362 scanning potentiostat and cyclic voltammo-
grams were recorded at 25 °C in the designated solvent under dry
rated out. Yield: 70%. Anal. Calc. for C18
19
H N
2
O
S
3 2
V: C, 50.70; H,
4
1
for
9
1
(
.46; N, 6.57; V, 11.97. Found: C, 50.68; H, 4.54; N, 6.54; V,
ꢁ
1
ꢁ1
ꢁ1
1.94%. IR (KBr pellet, cm ): 3435 cm for
m
(O–H), 1595 cm
ꢁ1
ꢁ1
m
(C@N), 1237 cm for
m
(C–O enolic), 1042 cm for
m
(N–N),
; Me Si):
ꢁ3
ꢁ1
(V@O). 1H NMR d
dintrogen with the electroactive component at ca 10 M. Tetra-
93 cm for
0.92 (1H, s, OH), 10.09 (1H, s, NH), 7.43–6.92 (9H, m,C
–), 2.73 (3H, s, –CH C@N–).
m
H
(300 MHz; DMSO d
6
4
ethyl ammonium perchlorate (NEt ClO , 0.1 M) was used as the
4
4
6
H
4
), 4.54
supporting electrolyte. EPR spectra were obtained at X-band fre-
quencies on a Varian E-109C spectrometer around 110 K. The
experiments were carried out using a Varian variable temperature
accessory. This accessory utilizes open gas-flow system and uses
liquid nitrogen as coolant. Nitrogen gas is used to cool the sample.
The calibrant was TCNE (g = 2.00277). For electrochemical investi-
gations a three-electrode configuration was employed with plati-
num working electrode, a calomel reference electrode, and a
2H, s, –CH
2
3
0
2
.2.3. Synthesis of the oxidovanadium(V) complex [VO(OEt)L]
2
(l
-4,4 -
bipy) (2)
To 30 ml ethanolic solution of complex 1 (0.412 g, 1.0 mmol),
0
4
,4 - bipyridine (0.078 g, 0.50 mmol) was added and the mixture
was refluxed for 5 h on a steam bath. The mixture was cooled, fil-
tered and the filtrate allowed to evaporate slowly in a refrigerator.
After 5–6 days reddish brown solid separated out. Yield: 68%. Anal.
+
platinum auxiliary electrode. The Ferrocene/Ferrocenium (Fc/Fc )
couple was used as the internal standard [61]. Room temperature
magnetic susceptibilities of complexes were measured in polycrys-
talline state on a PAR 155 vibrating sample magnetometer using
Calc. for C46
46 6 6 4 2
H N O S V : C, 54.76; H, 4.56; N, 8.33; V, 10.12.
Found: C, 54.76; H, 4.56; N, 8.30; V, 10.12%. IR (KBr pellet,
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
cm ): 3437 cm for
m
(O–H), 1589 cm for
m
(C@N), 1239 cm
ꢁ
1
ꢁ1
Hg[Co(SCN) ] as the calibrant.
4
for (C–O enolic), 1072 cm for
m
m
(N–N), 967 cm for
m
(V@O).
1
H NMR d
), 5.44 (4H, q, CH
C@N–), 1.71 (6H, t, CH
3
H
(300 MHz; DMSO d
, OEt), 4.56 (4H, s, –CH
, OEt).
6
; Me
4
Si): 7.92–6.64 (26H, m,
C
–
6
H
4
2
2
–), 2.74 (6H, s,
2.4. X-ray crystallography
CH
3
Diffraction data for suitable single crystals of complexes 1 and 5
2.2.4. Synthesis of the oxidovanadium(V) complex [VO(8-HQ)L] (3)
were measured with Mo Ka radiation using the MARresearch Im-
The ligand H L (0.32 g, 1.02 mmol) was dissolved in 30 ml of
2
age Plate System. The crystals were positioned at 70 mm from
the Image Plate. A total of 95 frames were measured at 2° intervals
with a counting time of 2 min. Data analyses were carried out with
the XDS program [62]. The structures were solved using direct
methods with the SHELX-86 program [63]. The non-hydrogen atoms
were refined with anisotropic thermal parameters. The hydrogen
atoms bonded to carbon and nitrogen were included in geometric
positions and given thermal parameters equivalent to 1.2 times
those of the atom to which they were attached. Absorption correc-
tions were carried out using the DIFABS program [64]. The structures
ethanol, 0.27 g (1.02 mmol) of vanadium(IV) acetylacetonate was
added to it and the mixture was refluxed for 1 h on a steam bath.
The color of the solution changed from yellow-green to brown. To
this brown solution 0.15 g (1.03 mmol) 8-hydroxy quinoline was
added and refluxing was continued for 5 h. The solution was fil-
tered and allowed to evaporate slowly at room temperature. After
2
–3 days bluish brown solid separated out. Yield: 76%. Anal. Calc.
for C25
H
20
N
3
O
3
S
2
V: C, 57.03; H, 3.99; N, 7.98; V, 9.96. Found: C,
ꢁ1
5
3
7.01; H, 3.95; N, 7.93; V, 9.64%. IR (KBr pellet, cm ):
373 cm
ꢁ
1
ꢁ1
ꢁ1
2
for
m(O–H), 1601 cm
for
m(C@N), 1252 cm
for
were refined on F using SHELXL [65]. The structures were generated

3
378
M. Sutradhar et al. / Inorganica Chimica Acta 363 (2010) 3376–3383
using ORTEP-3 [66]. Crystallographic data are summarized in
Tables 1 and 2.
Table 2
0
Selected dimensions in complexes 1, 1 and 5 (distances, Å, angles °).
0
1
1
5
Bond distances
V(1)–O(2)
3
. Results and discussion
1.802(2)
1.591(2)
1.7706(18)
2.3310(11)
2.159(2)
–
1.8547(16)
1.5809(17)
1.7430(16)
1.9477(16)
2.1331(19)
–
1.942(4)
1.595(3)
–
2.4563(16)
2.090(4)
2.343(4)
2.138(4)
V(1)–O(35)
V(1)–O(23)
V(1)–S(14)
V(1)–N(11)
V(1)–N(23)
V(1)–N(30)
The monooxidoethoxidovanadium(V) complex [VO(OEt)L] (1)
*
was obtained as yellowish brown crystalline solid by refluxing an
equimolar solution of [VO(acac) ] and the ligand H L in ethanol
2
2
2ꢁ
medium [(L) = dianion of the ONS donor ligand ] in ꢀ70% yield.
V(IV) was found to be oxidized to V(V) during the reaction period.
Similar complexes containing other coordinated alkoxides could
also be prepared easily using appropriate alcohols. However, de-
tailed characterization of the other alkoxido complexes are not re-
ported because of their very similar properties. Complex (1) was
–
–
Bond angles
*
S14–V1–O2
S14–V1–O23
S14–V1–O35
S14–V1–N11
O2–V1–O23
O2–V1–O35
O2–V1–N11
O23–V1–O35
O23–V1–N11
O35–V1–N11
S14–V1–N23
S14–V1–N30
O2–V1–N23
O2–V1–N30
O35–V1–N23
O35–V1–N30
N11–V1–N23
N11–V1–N30
N23–V1–N30
134.36(8)
84.18(7)
110.34(8)
78.74(7)
101.24(9)
111.61(10)
82.31(9)
105.31(10)
158.79(9)
92.46(10)
147.77(6)
92.82(7)
158.92(11)
*
*
102.15(7)
97.14(14)
80.58(11)
*
73.89(6)
used as the precursor for preparing the binuclear oxidovanadi-
um(V) complex [VO(OEt)L]
101.24(9)
111.61(10)
82.31(9)
105.31(10)
158.79(9)
92.46(10)
0
2
(
l
-4,4 -bipy) (2) by refluxing
101.95(17)
85.82(15)
0
[
VO(OEt)L] and 4,4 -bipy in 2:1 molar ratio in ethanol in 65–70%
yield. However, as single crystals of proper quality could not be ob-
tained, structure of this compound could not be solved. The mixed
ligand oxidovanadium(V) complex [VO(8-HQ)L] (3) was isolated as
bluish brown microcrystals in 76% yield by refluxing [VO(acac)
and H L in 1:1 molar proportion in ethanol for 1 hour followed
by addition of 1 mole 8-hydroxyquinoline (8-HQH) and further
refluxing for 5 h. Single crystals fit for X-ray diffraction study could
not be obtained. Mixed ligand oxidovanadium(IV) complexes
105.19(17)
81.04(11)
97.15(11)
82.45(15)
90.13(15)
166.35(18)
94.84(17)
87.92(15)
159.97(15)
72.09(14)
2
]
2
0
[
VO(o-phen)L] (4) and [VO(2,2 -bipy)L] (5) were obtained as orange
red solids in 70–75% yield following the same method as in the
case of complex 3 using acetonitrile in place of ethanol as the reac-
tion medium and 1,10-phenanthroline (o-phen) or 2,2 -bipyridine
*
0
Consider O(14) instead of S(14) for 1 .
0
(
bipy) instead of 8-hydroxyquinoline. Single crystals of 5 were ob-
tained and its crystal and molecular structure was determined. The
synthetic route to all the complexes are summarized in Scheme 1.
2
. On careful inspection of the data presented in Table 2 it is found
that the V1–O2 distance [1.942(4) Å] in 5 is a bit longer than the
corresponding distance [1.802(2) Å] in 1. Also, the V1-S14 distance
[2.4563(16) Å] in 5 is longer than that of the corresponding bond
3.1. Crystal structure of the complexes
[
2.3310(11) Å] in 1. When we focus our attention on the length
Structure determination of 1 and 5 by X-ray crystallography
showed that the coordination mode of the ligand H L remained
2
same in both V(V) and V(IV) complexes though 1 is pentacoordi-
nated and has a distorted square pyramidal structure, while 5 is
hexacordinated and is distorted octahedral. Metric dimensions of
the corresponding bond lengths and bond angles are given in Table
of the V@O bonds we notice the same trend but the magnitude
of difference is lower. However, in case of the V1–N11 bonds,
V1–N11 in 1 is slightly longer than that in 5 indicating that this
bond is stronger in 5 which may be attributed to the effect of coor-
0
dination of the chelating secondary ligand 2,2 -bipyridine. Thus,
the presence of a secondary chelating ligand in the coordination
environment of the central vanadium atom leads to noticeable
changes in the lengths of the bonds that the ligand makes with
the vanadium center. It is also noted that the deviation of vana-
dium acceptor center in 5 from the equatorial plane [0.5211 Å] is
higher than that of the vanadium center in 1, both being displaced
towards the axial vanadyl oxygen (O35).
Table 1
Crystal data and structure determination summery of complexes 1 and 5.
1
5
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
18
H
19
N
2
O
3
S
2
V
C
26 22 4 2 2
H N O S V
426.43
monoclinic
P2 /a (No. 14)
7.3241(12)
22.633(4)
11.705(2)
(90)
98.828(15)
(90)
1917.3(6)
4
537.56
monoclinic
P2 /c (No. 14)
9.1267(11)
12.4132(13)
21.842(2)
(90)
95.322(9)
(90)
2463.9(5)
4
3.1.1. Description of crystal structure [VO(OEt)L] (1)
1
1
The yellow-brown complex [VO(OEt)L] (1) crystallizes in the
monoclinic system with the space group P2 /a. A perspective view
1
of this complex is shown in Fig. 1 and important bond parameters
are presented in Tables 1 and 2. The vanadium(V) center is present
3
in a distorted square pyramidal VO NS coordination with the four
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
3
basal positions occupied by the three donor points O2 (phenoxide
oxygen), N11 (imine nitrogen), S14 (thioenolate sulfur)of the tri-
dentate ligand and O23 of the coordinated alkoxide moiety. The ax-
ial site is occupied by the vanadyl oxygen O35 which forms angles
in the range 92.46°(10)–111.61°(10) with the previously defined
basl plane. The deviation of these four points from the least-
squares plane O2, N11, S14, and O23 are 0.2402, ꢁ0.2323,
V (Å )
Z
D
calc (g cm 3
ꢁ
)
1.477
1.449
Data/restraints/param
Number of observed reflections [I > 2
5633/0/235
(I)] 1512
7042/0/316
3752
r
a
R(F), wR(F) (obsd data)
0.0448, 0.0821 0.1026, 0.1864
0.1463, 0.0909 0.1799, 0.2087
2
2
b
R(F ), wR(F ) (all data)
R
int
0.087
0.083
Peaks in final difference map (e Aꢁ3)
0. 68, ꢁ0.43
0.93, ꢁ0.47
0
.2178, ꢁ0.2257 Å, respectively. Magnitude of the trans angle
Goodness-of-fit on F2
0.515
1.095
O23–V1–N11 [158.79°(9)] indicates that the V1 center is displaced
towards the apical oxido-oxygen atom O35 and lies 0.5211 Å out of
the plane. The V@O distance of 1.591(2) Å is not uncommon.
a
R =
R
||F
o
| ꢁ |F
c
||/
R
|
|F
ꢁ |F
o
|.
b
2
2
2
2
|4]1/2.
wR(F ) = [ w(|F
R
o
c o
| ) /Rw|F

M. Sutradhar et al. / Inorganica Chimica Acta 363 (2010) 3376–3383
3379
CH3
S
NH2
O
N
+
S
N
H
HO
EtOH,
Stirr
H+
HO
S
S
N
H
CH3
7
(
H L )
2
VO(acac)2
N
EtOH, reflux
4hrs
O
VO(acac)2
VO(acac)2 reflux
N
EtOH
4hrs
N
CH CN , reflux
3
O
4hrs
O
N
N
O
O
O
S
O
V
O
VIV
OEt
V
V
V
S
N
N
S
N
N
(
1)
N
(
4,5)
(3)
N
reflux
EtOH
4
hrs
O
V
O
OEt
V
N
O
S
N
N
N
V
V
O
EtO
S
(
2)
Scheme 1. Synthesis of the complexes 1–5.
0
3
.1.2. Description of crystal structure [VO(2,2 -bipy)L] (5)
vanadium thioenolate bond distance usually found in five and six
coordinated V(IV) and V(V) complexes of ONS donor ligands
[47,49,50]. It was noted that oxidation of vanadium(IV) to vana-
dium(V) in complexes 1, 2 and 3 took place in ethanol medium
while in acetonitrile medium vanadium(IV) did not get oxidized
to vanadium(V).
The brown complex 5 crystallizes in monoclinic system with
space group P2 /c. Molecular structure and atom labeling scheme
1
of 5 is illustrated in Fig. 2 and metric dimensions are presented
in Tables 1 and 2. In contrast to the complex 1, the vanadium
IV) center of 2 is hexacoordinated and is present in a distorted
(
octahedral VO S coordination with the O2, N11, S14 atoms of
2 3
N
the ligand and N30 of the bipyridine molecule constituting the
equatorial plane. Vanadyl oxygen O35 occupies the axial position
which forms angle in the 94.84(17)–105.19(17) range with the ba-
sal plane defined previously. The second nitrogen atom N23 of the
bipyridine moiety is situated trans to the vanadyl oxygen O35 and
the trans angle O35–V1–N23 is 166.35°(18). The V1–N23 bond
3.1.3. Structural comparison of [VO(OEt)(ONS)] (1) versus
[VO(OEt)(ONO)] (1 )
0
It is expected that substitution of an ‘O’ donor point by an ‘S’ do-
nor center in a similar chelating ligand would generate significant
alteration in structure and properties of comparable complexes of
the same metal ion in the same oxidation state. From this point of
view, it appears worthwhile to compare the structures of the two
[
2.343(4) Å] is considerably longer than the V1–N30 bond
0
[
2.138(4) Å] due to trans influence of the V@O moiety.
complexes [VO(OEt)(ONS)] (1) and [VO(OEt)(ONO)] (1 ). ORTEP
0
Unequal lengths of all bonds involving the vanadium(V) center
diagram of 1 and 1 are shown side by side in Fig. 1 and metric val-
and the six donor points signify distortion of coordination octahe-
dron. The tridentate ONS ligand forms one six membered and one
five membered chelate ring at the vanadium(V) acceptor center,
the corresponding bite angles being 82.31°(9) and 80.58°(11),
respectively the two axial positions are occupied by the oxido oxy-
gen atom O35 and nitrogen atom N23 of the secondary ligand
bipyridine. The short V1–O35 distance of 1.595(3) Å indicate the
presence of vanadium oxygen double bond commonly found in five
and six coordinated complexes of V(IV) and V(V). The V1–S14 bond
length of 2.4563(16) Å is slightly longer than the corresponding
ues of the bond lengths and bond angles are presented in Table 2. A
careful inspection of the structural data of 1 and 1 reveals that ma-
jor structural features as well as the values of the corresponding
bond distances and bond angles are fairly close. The coordination
geometry of both the complexes are also very similar, both having
0
distorted square pyramidal structure. Calculated
(1) and 0.183 (1 ) also quantify distortion of 1 and 1 from perfect
s
values are 0.407
0
0
square pyramidal geometry. Similarity in redox behavior is clearly
reflected in the irreversible one electron reduction step at 0.43 V
0
for (1) and at 0.42 V for (1 ). In their IR spectra the
m(V@O) mode

3
380
M. Sutradhar et al. / Inorganica Chimica Acta 363 (2010) 3376–3383
0
Fig. 1. Molecular structure and atom-numbering scheme for the complex 1 and complex 1 with thermal ellipsoids drawn at the 30% probability level.
is observed at the same frequency [30] of 993 cmꢁ1. Therefore, one
is tempted to comment that in these two cases substitution of an
oxygen donor point by a sulfur donor point in a multidentate che-
lating ligand forming similar metallocycles with an identical
acceptor center may not always lead to major change of structural,
electrochemical and spectroscopic properties.
1
3
.2. IR and H NMR spectroscopy
IR spectra of the complexes 1–5 display features characteristic
of the dianionic tridentate ONS mode of ligation through the phe-
nolate oxygen, imine nitrogen and the thioenolate sulfur. Com-
ꢁ1
pound 1, 2 and 3 also display a strong band in the 954–993 cm
range due to the terminal (V=O) mode. In the two vanadium(IV)
complexes 4 and 5 the (V@O) is found at slightly lower frequen-
t
t
ꢁ1
cies (954 and 958 cm ).
1
2 6
The H NMR data of the free ligand H L in d -DMSO and its oxi-
dovanadium(V) complexes 1, 2 and 3 are given in the experimental
section. The free ligand displays two characteristic resonances, one
with a sharp feature at 10.92 ppm and the other with a broad peak
at 10.09 ppm due to phenolic OH and NH functionalities, respec-
tively, which are missing in the spectra of the complexes indicating
that the coordinated ligand is dianionic. Besides having all the
Fig. 2. Molecular structure and atom-numbering scheme for the complex 5 with
thermal ellipsoids drawn at the 30% probability level.

M. Sutradhar et al. / Inorganica Chimica Acta 363 (2010) 3376–3383
3381
Table 3
Cyclic voltammetric dataa and UV–Vis spectral dataa of the vanadium(V) complexes
–5.
1
ꢁ
1
ꢁ1
Compound
E
1/2, V
kmax (nm) (e, L M cm )
(D
E
p
b, mV)
0.432(102) 392 (10,744), 300 (40,844)
[
VO(OEt)L] (1)
VO(OEt)L] -4,4 - bipy) 0.424(96)
2)
0
[
2
(l
396 (9,886), 306 (11,328)
(
[
[
[
VO(8-HQ)L] (3)
0.461(136) 396 (10,375), 315 (18,427), 243
(
49,948)
0.418(123) 800 (147), 402 (11,054), 306
34,637)
0.421(127) 800 (130.7), 404 (10,251), 306
32,517)
VO(o-phen)L] (4)
(
0
VO(2,2 -bipy)L] (5)
(
a
ꢁ1
In acetonitrile; scan rate 50 mV s , E1/2 is calculated as the average of anodic
Epa) and cathodic (Epc) peak potentials.
(
b
D
E
p
= Epa ꢁ Epc
.
remaining peaks of the coordinated ONS ligand, the spectrum of 1
displays a quartet at 5.42 ppm (J = 7.2 Hz) and a triplet at 1.69 ppm
3
Fig. 4. Cyclic voltammogram of complex 5 in CH CN.
(J = 7.0 Hz) due to the methylene and methyl protons, respectively,
of the coordinated ethoxy group.
complexes 4 and 5 (Fig. 4) one-electron oxidation is observed at
.418 and 0.421 v, respectively. One-electron nature is inferred
3.3. Electronic spectra
0
+
by comparison with the authentic one-electron system [Fc /Fc] un-
der identical conditions. It is to be noted that the binuclear com-
plex 2 undergo one-step two-electron reduction at +0.424 v
probably due to the centrosymmetric character of the complex,
which is observed in similar type complexes involving ONO chelat-
ing ligand [32].
Electronic spectral data of the vanadium(V) complexes 1, 2 and
are presented in Table 3 along with those of vanadium(IV) com-
3
plexes 4 and 5. The V(V) complexes in acetonitrile solution display
ꢁ
a strong absorption around 400 nm which is due to PhO ? V(d
p)
LMCT transition and two other absorption band in 300–243 nm re-
gion corresponding to intraligand transitions. The vanadium(IV)
complexes 4 and 5 exhibit an additional low intensity band at ca
2
+
3.5. Magnetic moment and EPR studies
8
00 nm due to ligand field transition dxz, dyz ? dxy of the VO cen-
ter. The strong band observed at ꢀ400 is due to enolate oxygen to
vanadium(IV) transition. Bands observed around 300 nm and be-
low are due to intraligand transitions.
The two oxidovanadium(IV) complexes, 4 and 5, exhibit room
temperature magnetic moment values of 1.71 B.M. and 1.68 B.M.,
respectively (Table 4) as expected for spin only value of a d1
system.
3.4. Electrochemistry
EPR spectral parameters of 4 and 5 are practically identical
(
Table 4). EPR spectrum is recorded of 5 in dichloromethane at
Cyclic voltammograms of all the reported complexes are re-
corded in acetonitrile solution with Et NClO as the supporting
4 4
electrolyte at a platinum working electrode. The corresponding
data are presented in Table 3. All the three vanadium(V) complexes
exhibit identical one-electron response corresponding to the V(V)/
room temperature and at ꢀ110 K. The room temperature spectrum
exhibits eight line pattern [gav = 1.983 for 4 and 1.985 for 5;
ꢁ4
ꢁ1
ꢁ4
ꢁ1
51
A
av = 81.3 ꢂ 10 cm for 4 and 84.0 ꢂ 10 cm for 5] typical
of one unpaired electron being coupled to a single V (I = 7/2) nu-
cleus. The spectrum at ꢀ110 K displays axial anisotropy with two
sets of eight line pattern corresponding to resonance parameters:
g
for
4
A
(
V(IV) reduction process in the 0.42–0.46 v range versus SCE.
DE
p
values indicate quasireversible nature of the reduction process in
case of 1 (Fig. 3), 2 and 3. In case of the two vanadium(IV)
-4
ꢁ1
ꢁ4
ꢁ1
|| 1.953, A|| 152 ꢂ 10 cm and g
\
1.999, A
\
45.8 ꢂ 10 cm
ꢁ4
ꢁ1
4
and
g
|| 1.974,
A
|| 154 ꢂ 10 cm
\ \
and g 1.990, A
ꢁ4
ꢁ1
8.7 ꢂ 10 cm for 5. It may be mentioned that the experimental
|| are in accord with the calculated coupling constants
ꢁ4
ꢁ1
153 ꢂ 10 cm ), calculated from the additivity rule with the
equatorial ligand set found in the solid state crystal structure.
4
. Conclusion
This work reports synthesis and characterization of three five
coordinated distorted square planar oxidovanadium(V) complexes
[
(
[
VO(OEt)L] (1), the binuclear V(V)–V(V) complex [VO(OEt)L]
4,4 -bipy) (2) and the six coordinate mixed ligand complex
2
-
l
-
0
VO(8-HQ)L] (3). Two six coordinate oxidovanadium(IV) com-
0
plexes [VO(o-phen)L] (4) and [VO(2,2 -bipy)L] (5) are also dis-
cussed. Of these five complexes,
1 and 5 are structurally
characterized by single crystal X-ray crystallography. We have re-
cently reported preparation, structural characterization and chem-
ical reactivity of binuclear complexes of the type [VO(OEt)L]
2
-
l
-
0
(
2
4,4 -bipy) (where H L = a diprotic tridentate ONO donor ligand)
Fig. 3. Cyclic voltammogram of complex 1 in CH
3
CN.
which is similar to 2 which is expected to have a similar structure.

3
382
M. Sutradhar et al. / Inorganica Chimica Acta 363 (2010) 3376–3383
Table 4
Magnetic moment dataa and EPRb data for the complexes (4) and (5).
Compound
r. t.
r. t.
av (10 cm
ꢀ110 K
a
ꢁ4
ꢁ1
ꢁ4
ꢁ1
ꢁ4
ꢁ1
ꢁ4
ꢁ1
c
ꢁ4
ꢁ1
d
ꢁ4
ꢁ1
leff (B.M.)
g
)
A
av (10 cm
)
g
|| (10 cm
)
A
|| (10 cm
)
g
\
(10 cm
)
\
A (10 cm )
[
[
VO(o-phen)L] (4)
VO(2,2 -bipy)L] (5)
1.71
1.68
1.983
1.985
81.3
84.0
1.953
1.974
152
154
1.999
1.990
45.8
48.7
0
a
b
c
In solid state.
In dichloromethane (at room temperature and ꢀ110 K).
av = (g|| + 2g )/3.
av = (A|| + 2A )/3.
g
\
d
A
\
Cyclic voltametric study of 2 reveals only a single two-electron
reductive response suggesting a centrosymmetric structure just
like the corresponding structurally characterized and previously
reported binuclear complex involving the ONO donor ligand. To
our knowledge, complex 2 is the first report of a bipyridine bridged
binuclear oxidovanadium(V) complex of a diprotic tridentate ONS
donor ligand.
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[
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[
[
It is noted that the use of acetonitrile in place of ethanol (which
ꢁ
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[
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[
[
5
1
interacting with one V center. Comparison of the structural fea-
[
[
[
[
tures of the complex 1 (involving a ONS donor ligand) with that
0
of the previously reported complex 1 (involving a ONO donor li-
gand) indicates that contrary to the established belief that pres-
ence of one or more sulfur donor centers in the coordination
zone of a metal accepter center exert significant influence on spec-
troscopic, electrochemical and structural characteristics of the
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chemical and spectroscopic properties of the corresponding
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