Synthesis, X-ray structure, DFT studies, and catalytic activity of a vanadium(V) complex containing a tridentate Schiff base

Article abstract of DOI:10.1080/00958972.2013.851789

Reactions of a solution of NH₄VO₃ in H ₂O₂ and water and salicylidene benzoyl hydrazine as a tridentate Schiff base (ONO) afford a six-coordinate V(V) complex [VO(ONO)(OCH₃)(CH₃OH)] with a distorted octahedral configuration. The complexes [VO(ONO)(OCH₃)(CH₃OH)] were isolated as air-stable crystalline solids and fully characterized, including by single-crystal X-ray structure analysis. DFT calculations have been performed to understand the electronic structure of the complex. Vibrational frequencies and maximum absorption wavelengths of the complex theoretically calculated are in good agreement with experimental values. [VO(ONO)(OCH₃)(CH ₃OH)] shows efficient oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the oxidant at room temperature under air.

Full text of DOI:10.1080/00958972.2013.851789

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Synthesis, X-ray structure, DFT studies,
and catalytic activity of a vanadium(V)
complex containing a tridentate Schiff
base
Mojtaba Aminia, Ali Arabb, Rouhollah Soleymanc, Arkady Ellernd &
L. Keith Wood
a Department of Chemistry, Faculty of Science, University of
Maragheh, Maragheh, Iran
b Department of Chemistry, Semnan University, Semnan, Iran
c Polymer Science and Technology Division, Research Institute of
Petroleum Industry (RIPI), Tehran, Iran
d Chemistry Department, Iowa State University, Ames, IA, USA
Accepted author version posted online: 09 Oct 2013.Published
online: 15 Nov 2013.
To cite this article: Mojtaba Amini, Ali Arab, Rouhollah Soleyman, Arkady Ellern & L. Keith Woo
(2013) Synthesis, X-ray structure, DFT studies, and catalytic activity of a vanadium(V) complex
containing a tridentate Schiff base, Journal of Coordination Chemistry, 66:21, 3770-3781, DOI:
10.1080/00958972.2013.851789
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Journal of Coordination Chemistry, 2013
Vol. 66, No. 21, 3770–3781, http://dx.doi.org/10.1080/00958972.2013.851789
Synthesis, X-ray structure, DFT studies, and catalytic activity
of a vanadium(V) complex containing a tridentate Schiff base
MOJTABA AMINI*†, ALI ARAB*‡, ROUHOLLAH SOLEYMAN§, ARKADY
ELLERN¶ and L. KEITH WOO¶
†Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Iran
‡Department of Chemistry, Semnan University, Semnan, Iran
§Polymer Science and Technology Division, Research Institute of Petroleum Industry (RIPI),
Tehran, Iran
¶Chemistry Department, Iowa State University, Ames, IA, USA
(Received 30 May 2013; accepted 28 August 2013)
Reactions of a solution of NH4VO3 in H2O2 and water and salicylidene benzoyl hydrazine as a
tridentate Schiff base (ONO) afford a six-coordinate V(V) complex [VO(ONO)(OCH3)(CH3OH)]
with a distorted octahedral configuration. The complexes [VO(ONO)(OCH3)(CH3OH)] were isolated
as air-stable crystalline solids and fully characterized, including by single-crystal X-ray structure
analysis. DFT calculations have been performed to understand the electronic structure of the
complex. Vibrational frequencies and maximum absorption wavelengths of the complex theoretically
calculated are in good agreement with experimental values. [VO(ONO)(OCH3)(CH3OH)] shows
efficient oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the
oxidant at room temperature under air.
Keywords: Vanadium(V) complex; Schiff base; Crystal structure; Sulfide oxidation; DFT
calculations
1. Introduction
Selective oxidation of sulfides to sulfoxides is an attractive method for production of
sulfoxides, which are useful building blocks as chiral auxiliaries in organic synthesis and as
bioactive ingredients in the pharmaceutical industry [1–4]. A number of methods and
procedures have been devoted to the development of effective catalysts for oxidation of
sulfides [5–7]. Transition metal complexes as catalytic systems based on readily available,
inexpensive, and environmentally benign “green oxidants” like hydrogen peroxide is very
attractive [8–10].
Metal complexes with Schiff bases have played an important part in the development
of coordination chemistry with many reports on their applications in homogeneous and
heterogeneous catalysis [11, 12]. Among various transition metal complexes, Schiff
base oxovanadium(V) complexes are the most efficient catalysts for oxidation reactions
[13–16].
*Corresponding authors. Emails: mamini@maragheh.ac.ir (M. Amini); a.arab@profs.semnan.ac.ir (A. Arab)
© 2013 Taylor & Francis

Vanadium(V) tridentate Schiff base
3771
Density functional theory (DFT) has been accepted as a powerful tool in prediction of
molecular properties of inorganic compounds [17, 18]. There is a lot of information in the
literature about structures, electronic properties, chemical reaction kinetics and mechanism,
thermodynamic properties, vibrational, absorption, Raman, and NMR spectra of metallic
complexes predicted by DFT [19–25]. Vanadium complexes are also the subject of many
theoretical studies [23–25]. For example, DFT computations were used to investigate
nucleophilic and electrophilic centers of some vanadium complexes by calculating global
hardness and global softness [23]. Another DFT study [24], investigated the correlation
between catalytic activities of vanadium complexes toward sulfide oxidation and the
electronic character of the vanadium center.
Herein, we describe the synthesis, X-ray analysis, and DFT results of a new V(V)
complex [VO(ONO)(OCH3)(CH3OH)] (ONO = salicylidene benzoyl hydrazine). The use of
this complex as a catalyst in the oxidation of sulfides in the presence of urea hydrogen
peroxide (UHP) as an oxidant under air at room temperature was also studied (scheme 1).
2. Experimental
Chemicals and solvents were purchased from Fluka and Merck Chemical companies.
Salicylidene benzoyl hydrazine (ONO) was synthesized according to a published procedure
[26].
Elemental analysis (carbon, hydrogen, and nitrogen) of the compound was obtained from
a Carlo ERBA Model EA 1108 analyzer. Molar conductance of the complex was
determined in methanol (ca. 10−3 M) at room temperature using a Toa CM 405 conductivity
meter. FT-IR spectrum was obtained by using an Unicam Matson 1000 FT-IR spectropho-
tometer using KBr disks at room temperature. The products of oxidation reactions were
determined and analyzed by an HP Agilent 6890 gas chromatograph equipped with a HP-5
capillary column (phenyl methyl siloxane 30 m 320 lm 0.25 lm), and a flame ionization
detector.
2.1. Synthesis of [VO(ONO)(OCH3)(CH3OH)]
2.0 mM of H2O2 (w = 30%) was added to 1.0 mM of NH4VO3, dissolved in H2O (2 mL),
and then an ethanolic solution of salicylidene benzoyl hydrazine (1.0 mM) was added. After
2 h of stirring at room temperature, the solution was filtered, and evaporated under reduced
Scheme 1. Oxidation of sulfides in the presence of [VO(ONO)(OCH3)(CH3OH)].

3772
M. Amini et al.
pressure to give the complex. Recrystallization from methanol yielded the complex as
red-brown crystals. Yield: 0.289 g, 79%. Anal. Calcd for C18H16N2O5V: C, 54.97; H, 4.61;
N, 7.12. Found: C, 54.89; H, 4.57; N, 7.21. Selected IR frequency (KBr disk, cm−1): 1612
1
(νC=N); H NMR(d6-DMSO): δ 3.18 (s, 3 H), 4.09 (s, 1 H), 5.29 (s, 3 H), 6.90 (d, 1H),
7.04 (dt, 1H), 7.44 (t, 1H), 7.51 (t, 2H), 7.57 (t, 1H), 7.72 (dd, 1H), 8.06 (t, 2H), 9.01
(s, 1H).
2.2. General procedure for sulfide oxidation
To a solution of sulfide (0.2 mM), chlorobenzene (0.2 mM) as internal standard, and [VO
(ONO)(OCH3)(CH3OH)] (0.01 mM) in a 1 : 1 mixture of CH3OH/CH2Cl2 (1 mL) was
added 0.4 mM UHP as oxidant. The mixture was stirred at room temperature and the
reaction progress was monitored by GC. Assignments of products were made by
comparison with authentic samples.
2.3. Computational details
The ground-state structure of the complex was optimized by B3LYP hybrid density
functional method using the 6-31G* basis set. This hybrid functional exploits a combination
of B3 exchange functional [27] and LYP correlation functional [28]. B3LYP functional is
accepted as a reliable method for investigation of metal complexes and there is abundant
evidence in the literature that persuaded us to use this method. Back et al. [23] used the
B3LYP functional to calculate the HOMO-LUMO gap, electron affinity, ionization poten-
tial, global hardness, and global softness of vanadium complexes. The mechanistic aspects
of sulfide oxidation on different complexes of vanadium were also investigated by B3LYP
functional [24]. Magnetic properties of vanadium-based complexes were studied by B3LYP
functional too [29]. Frequency calculations are also performed on the optimized structure to
confirm that the structure belongs to the local minima on the potential energy surface.
3. Results and discussion
3.1. Complex characterization
[VO(ONO)(OCH3)(CH3OH)] was obtained by reaction of an ethanolic solution of salicylid-
ene benzoyl hydrazine (ONO) with NH4VO3 and H2O2.
The molar conductance of the complex is 4 Ohm−1 cm2 M−1, indicating that the complex
is a nonelectrolyte. The C=N stretching frequency for the ligand occurs at 1639 cm−1 and
for the complex it is expected to appear at lower frequencies (1612 cm−1). This shift by at
least 29 cm−1 to lower frequency compared to that of free ligand indicates a decrease in the
bond order due to coordination of the metal with the azomethine nitrogen of ligand [30,
31]. The characteristic V=O stretch of the complex is at 960 cm−1, i.e. within the range
950–1000 cm−1 reported for similar oxovanadium complexes [32, 33].
1
The coordination of the ligand was confirmed by comparing H NMR patterns of the
ligands and the complex. The signal at δ = 12.11 ppm, due to phenolic OH, disappears in

Vanadium(V) tridentate Schiff base
3773
spectra of the complex [3, 30]. A significant downfield shift (Δδ = 1.94 ppm) of the signal
for the azomethine (–CH=N–) proton in the complex relative to the corresponding ligand
demonstrates coordination of azomethine nitrogen. Aromatic protons appear in the expected
regions with minor variations in their positions (δ = 6.90–8.06 ppm). The methyl protons of
methoxy resonate at δ = 5.29 ppm and two signals appear at δ = 3.18 and 4.09 ppm due to
coordinated methanol [3, 30].
To confirm coordination of salicylidene benzoyl hydrazine in this complex as well as the
stereochemistry of the complex, the structure of complex has been determined by X-ray
crystallography, and an ORTEP view of the complex is shown in figure 1.
The complex crystallizes in the monoclinic crystal system, space group P21/c. The crystal
data are given in table 1. The molecular view of complex containing [VO(ONO)(OCH3)
(CH3OH)] is shown in figure 1. The structure of the complex is mononuclear, consisting of
discrete monomeric units of [VO(ONO)(OCH3)(CH3OH)], in which V is surrounded by
two O and one N of the tridentate Schiff base in a distorted octahedral configuration. The
V–O distances of the oxo (O5) are significantly shorter [1.5936(14) Å] than the correspond-
ing distances to O of the tridentate ligands (O1 and O2) [1.9610(13), 1.8544(14) Å]. The
V–N distance is longer [2.1284(15) Å]. The V–O3 and V–O4 distances are 2.334(13) and
1.769(13) Å, respectively, which are typical for the methanol and the methoxy group,
respectively.
The crystal lattice is stabilized by intermolecular hydrogen bonds O–H⋯N between
hydrogen of coordinated methanol and N of the Schiff base belonging to two neighboring
complexes to form an infinite one-dimensional polymeric array along the a-axis (figure 2).
3.2. DFT computations
The structure of the vanadium complex was optimized by B3LYP level of theory using the
6-31G* basis set. The calculation involves determination of vibrational frequencies for
validation of the local energy minima of the optimized structure. The optimized structure of
the complex has a distorted octahedral configuration as predicted by X-ray analysis. Table 2
presents some selected optimized and X-ray experimental values of bond lengths and
bond angles around vanadium. The difference between experimental and optimized values
Figure 1. ORTEP diagram of [VO(ONO)(OCH3)(CH3OH)] with thermal ellipsoids drawn at 50% probability.

3774
M. Amini et al.
Table 1. Crystal data and structure refinement for [VO(ONO)(OCH3)(CH3OH)].
Empirical formula
C16H16N2O5V
Formula weight
Temperature
367.25
173(2) K
Wavelength
0.71073 Å
Crystal system
Space group
Monoclinic
P 1 21/c 1
Unit cell dimensions
a = 8.0974(6) Å
α = 90°
b = 16.9355(12) Å
β = 103.7170(10)°
c = 12.1217(9) Å
γ = 90°
Volume
1614.9(2) Å3
Z
4
Density (Calcd)
Absorption coefficient
F (0 0 0)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta = 28.70°
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2 sigma(I)]
R indices (all data)
Largest diff. peak and hole
1.511 Mg/cm3
0.643 mm−1
756
0.13 × 0.22 × 0.26 mm3
2.11–28.79°
−10<=h<=10, −22<=k<=22, −16<=l<=16
16,826
4177 [R(int) = 0.0352]
99.4%
Multi-scan
0.9211 and 0.8506
Full-matrix least-squares on F2
4177/0/219
1.045
R1 = 0.0363, wR2 = 0.0890
R1 = 0.0519, wR2 = 0.0976
0.770 and −0.389 eÅ−3
Rint = Σ|Fo2–Fo2(mean)|/Σ[Fo2].
R
1 = Σ||Fo|−|Fc||/Σ|Fo|.
GOOF = S = {Σ[w(Fo2−Fc2)2]/(n−p)}1/2
wR2 = {Σ[w(Fo2−Fc2)2]/Σ[w(Fo2)2]}1/2
w = 1/[σ(Fo2) + (aP)2 + bP] where P is [2Fc2 + Max(Fo2, 0)]/3.
.
.
(Error %) are also reported in table 2. Very good agreement between optimized and experi-
mental values is observed and the error % values are acceptable because we note that the
experimental results are for the solid phase while the computational results are for the gas
phase. The optimized values of V–N and V–O bond lengths are acceptable according to
data in the literature [34]. Among the optimized V–O bonds (see table 2 and figure 1), the
V1–O5 (double bond character) bond length is shorter than the others, in accord with the
experimental results. The V1–O3 bond length as obtained by both computational and exper-
imental methods is longer than the other V1–O bond lengths. As can be seen in table 2, the
optimized angles are in very good agreement with the experimental values. The highest
error (3.97%) is for O1–V1–O3. The other bond lengths and angles of the complex (not
shown in table 2) differed from the X-ray values with lower than 3% error.
The calculated Mulliken atomic charges of V1, O1, O2, O3, O4, O5, N1, and N2 (see
figure 1) are +1.32, −0.63, −0.65, −0.61, −0.54, −0.42, −0.40, and −0.37, respectively.
The charge on vanadium (+1.32) is significantly lower than the formal charge of +5, which
indicates charge donation from the ligands to the metal center. The charge on C15 (carbon
of methanol group) and C16 (carbon of methoxy) is negative (−0.23 and −0.20,

Vanadium(V) tridentate Schiff base
3775
Figure 2. Depicting intermolecular hydrogen bonded 1D polymeric array along the a axis for [VO(ONO)(OCH3)
(CH3OH)].
Table 2. Experimental X-ray and optimized geometrical parameters of the vanadium complex.
Selected bond Optimized (Å) X-ray (Å) Error (%) Selected angle Optimized (°) X-ray (°) Error (%)
V1–O1
V1–O2
V1–O3
V1–O4
V1–O5
V1–N1
1.9523
1.8491
2.5321
1.7678
1.5656
2.1585
1.9610(13)
1.8544(14)
2.3441(13)
1.7691(13)
1.5936(14)
2.1284(15)
0.45
0.29
8.02
0.07
1.76
1.41
N1–V1–O5
N1–V1–O1
N1–V1–O3
N1–V1–O2
O5–V1–O4
O1–V1–O4
O3–V1–O4
O2–V1–O4
O5–V1–O1
O1–V1–O3
O3–V1–O2
O2–V1–O5
O4–V1–N1
97.22
73.44
77.18
82.55
104.24
93.25
81.00
102.08
99.67
77.11
96.08(6)
73.91(5)
79.44(5)
83.58(5)
103.25(7)
94.44(6)
80.91(5)
101.85(6)
96.93(7)
80.30(5)
81.38(6)
99.86(7)
158.58(6)
1.18
0.64
2.84
1.23
0.95
1.26
0.11
0.22
2.83
3.97
2.49
2.05
1.34
79.35
101.91
156.46
respectively) while the charge on C1, C8, and C14 (carbons of Schiff base) is positive
(+0.55, +0.07, and +0.40, respectively). Such a charge distribution produces a total dipole
moment of 2.39 Debye for the complex that is directed toward the coordinated methoxy
and methanol. The charge on hydrogen (H–OCH3) of the coordinated methanol is +0.43.
Therefore, an intermolecular hydrogen bond can easily form between this positive hydrogen
of one complex and negative nitrogens (charges −0.40, −0.37) of another complex.
Frontier molecular orbitals are very important to clarify optical properties and chemical
activity. Figure 3 shows HOMO-1 (−6.31 eV), HOMO (−5.72 eV), LUMO (−2.48 eV),
and LUMO + 1 (−2.03 eV) molecular orbitals of the vanadium complex computed at the
B3LYP/6-31G* level of theory. While the HOMO-1 and HOMO show greater contributions
at the benzene rings (π-like orbitals) at both sides of the complex center, the LUMO and
LUMO + 1 show greater contributions in the center of the complex on the vanadium,
oxygen, and nitrogen. The calculated HOMO-LUMO and HOMO-1–LUMO + 1 energy
gaps are 3.24 and 4.28 eV, respectively. These large energy gaps indicate high excitation

3776
M. Amini et al.
Figure 3. Presentation of HOMO-1, HOMO, LUMO, and LUMO + 1 molecular orbitals of the vanadium
complex.
energies (in the UV region), good stability, and chemical hardness. Ultraviolet spectrum of
vanadium complex in the gas phase has been calculated. Time-dependent DFT (TD-DFT)
through B3LYP functional and 6-31G* basis set was employed to predict the electronic
excitation of the vanadium complex. The calculated maximum absorption wavelengths
obtained, viz. 383, 323, and 270 nm, are in good agreement with the experimental values of
393, 320, and 260 nm, attributed to the excitation from HOMO to LUMO, HOMO-1 to
LUMO, and HOMO-1 to LUMO + 1 or LUMO + 2 (not shown in figure 3), respectively.
Frequency calculation of the complex has been performed at the B3LYP/6-31G* level of
theory, confirming that the optimized structure is a minimum on the potential energy
surface. The experimental and theoretical FTIR spectra are presented in figure 4. Some of
the experimental and corresponding calculated vibrational wavenumbers along with their
intensities and assignments are reported in table 3. The vibrational wavenumbers of the
complex were scaled by a scaling factor of 0.9613 [35] in order to correct the theoretical
errors, such as electron correlation and basis set deficiencies. According to figure 4 and
table 3, good agreement between experimental and calculated values in the main spectral
features is observed.
The observed peaks with medium intensities between 3100–3000 cm−1 in the theoretical
FTIR spectrum are related to aromatic C–H stretches [36]. The aromatic C–H in-plane
bending and C–H out-of-plane bending modes of benzene and its derivatives are at
1300–1000 and 1000–675 cm−1, respectively [37]. Our calculated wavenumbers of the
aromatic C–H in-plane bending are 1235, 1147, and 1110 cm−1 and C–H out-of-plane
bending are 966, 740, and 686 cm−1, in agreement with reported values. Some of the
aromatic C–H in-plane bending modes overlap with other vibrational modes. The expected

Vanadium(V) tridentate Schiff base
3777
Figure 4. Experimental (top) and theoretical (bottom) FTIR spectra of the vanadium complex.
values of the C–C stretch of benzene and its derivatives are 1650–1200 cm−1 [38]. Our
calculated values of 1605, 1537, and 1504 cm−1 for C–C stretches of benzene are in
agreement. Our calculated value of the V=O stretching frequency is 982 cm−1, i.e. within
the 950–1000 cm−1 range reported for similar oxovanadium complexes [32, 33].
3.3. Catalytic reaction
Figure 5 illustrates the effect of amount of catalyst on the conversion and the selectivity of
methylphenyl sulfide oxidation, at room temperature for 60 min in a 1 : 1 mixture of
CH3OH/CH2Cl2 (1 mL). The conversion of methylphenyl sulfide increases with the addi-
tion of catalyst of 0.004–0.01 mM. When the amount of catalyst is increased to 0.012 mM,
the selectivity of methylphenyl sulfide oxidation reduces from 83 to 69%. The reaction
without catalyst proceeds very slightly. Hence, the amount of catalyst can enhance the
reaction rate for selective oxidation of methylphenyl sulfide.
The amount of UHP could also significantly affect the conversion and methylphenyl sulf-
oxide selectivity (figure 6). When the amount of UHP was increased from 0.1 to 0.4 mM,
the conversion of methylphenyl sulfide increased from 33 to 96%. With a further increase
of UHP to 0.5 mM, the selectivity to sulfoxide decreases from 83 to 71%, where the
conversion of methylphenyl sulfide increased from 96 to 100%.
A series of structurally diverse sulfides were subjected to oxidation using [VO(ONO)
(OCH3)(CH3OH)] as catalyst and UHP as oxidant (table 4). Arylalkyl (table 4, entries

3778
M. Amini et al.
Table 3. Comparison of the experimental and calculated vibrational frequencies of the vanadium complex.
Theoretically calculated IR
Experimental IR
wavenumber
Unscaled
Scaled
wavenumber
wavenumber
Assignment
(cm−1
)
(cm−1
)
(cm−1
)
Intensity
α (O3–H)
α (C8–N1) + aasymm (C–C)rings
aasymm (C–C)rings
α (C1–N2) + aasymm (C–C)rings
α (C1–C2) + β (C8–H) + β (C–H)rings
β (C15–O3–H) + β (C–H)rings
aasymm [C16–O4, V1–O5]
α (C15–O3)
aasymm [C16–O4, V1–O5]
β (C–C–C)ring
γ (C–H)rings
γ (C–H)rings
α (V1–O4)
3438
1612
1548
–
1400
1311
1094
–
960
888
759
701
623
578
466
3756
1670
1599
1565
1421
1386
1118
1050
1022
917
3611
1605
1537
1504
1366
1332
1075
1009
982
882
740
686
630
19.5
315.7
141.7
191.2
125.8
82.6
368.4
137.1
147.2
48.9
51.6
47.2
172.2
100.1
56.7
770
714
655
592
α (V1–O1) + β (C–C–C)rings
γ (O3–H) + γ (C–C–C)rings
569
461
480
α: stretching, β: in-plane bending, γ: out-of-plane bending.
Figure 5. The effect of the amount of catalyst on the oxidation of methylphenyl sulfide by the [VO(ONO)(OCH3)
(CH3OH)]/UHP catalytic system.
1 and 2), arylbenzyl (table 4, entry 3), dibenzyl (table 4, entry 4), diaryl (table 4, entry 5),
and dialkyl (table 4, entries 6–8) sulfides underwent clean and selective oxidation to the
corresponding sulfoxide under air, with impressive selectivity (78–100%). Very good con-
versions of substrates depending on the nature of the sulfide, 62–100% (TON = 12.4–20),
were obtained for all cases. Aromatic sulfides undergo oxidation reactions more easily than
aliphatic substrates. The highest and lowest conversions were obtained for dibenzyl sulfide
(100%) and dioctyl sulfide (62%), respectively (table 4, entries 4 and 8).

Vanadium(V) tridentate Schiff base
3779
Figure 6. The effect of the amount of UHP on the oxidation of methylphenyl sulfide by the [VO(ONO)(OCH3)
(CH3OH)]/UHP catalytic system.
Table 4. Oxidation of sulfides catalyzed by [VO(ONO)(OCH3)(CH3OH)]/UHPa.
Entry
1
Substrate
Conversion (%)b (TON)c
Selectivity (%)d
83
96 (19.2)
S CH2CH3
S CH2CH3
2
3
91 (18.2)
99 (19.8)
85
85
S C
H2
4
5
100 (20)
94 (18.8)
78
81
C S C
H2 H2
S
6
7
8
CH3 CH2–S–CH2 CH3
CH3 (CH2)2–S–(CH2)2 CH3
CH3 (CH2)7–S–(CH2)7 CH3
73 (14.6)
68 (13.6)
62 (12.4)
99
100
100
aThe molar ratios for [VO(ONO)(OCH3)(CH3OH)]: substrate: oxidant are 1 : 20 : 40. The reactions were performed in (1 : 1)
mixture of CH2Cl2/CH3OH (1 mL) under air at room temperature within 60 min.
bThe GC yield (%) are measured relative to the starting sulfide.
cTON = (mM of sulfoxide + mM of sulfone)/mM of catalyst.
dSelectivity to sulfoxide = (sulfoxide %/(sulfoxide % + sulfone %)) × 100.
4. Conclusion
The six-coordinate V(V) complex [VO(ONO)(OCH3)(CH3OH)] has been synthesized and
characterized. X-ray diffraction studies revealed coordination of the tridentate salicylidene
benzoyl hydrazine to vanadium via two O and one N. The complex has distorted octahedral
configuration around V. The complex has been theoretically analyzed through the B3LYP
level of theory using the 6-31G* basis set. Very good agreement between the X-ray and
optimized geometrical parameters has been observed. Distributions of electron density,

3780
M. Amini et al.
dipole moment, and HOMO-LUMO energy gap of complex have been addressed. The IR
spectrum of the complex was calculated and different modes of vibration assigned. We have
demonstrated the effectiveness of this complex as a catalyst for oxidation of sulfides to their
corresponding sulfoxides. Easy preparation, mild reaction condition, the use of UHP as a
green oxidant, high yields of the products, short reaction time, high selectivity, and low cost
make [VO(ONO)(OCH3)(CH3OH)]/UHP an useful catalytic system for oxidation of
sulfides.
Supplementary material
The CIF file of crystal structure complex [VO(ONO)(OCH3)(CH3OH)] has been
deposited with the CCDC, No. 940784. This data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223-336-033; or
E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
Mojtaba Amini, Ali Arab, and L. Keithi Woo, thank respectively, the Research Council of
University of Maragheh, Research Council of Semnan University, and the National Science
Foundation for funding of this work.
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