Complexes of cis-dioxomolybdenum(VI) and oxovanadium(IV) with a tridentate ONS donor ligand: Synthesis, spectroscopic properties, X-ray crystal structure and catalytic activity

Article abstract of DOI:10.1016/j.saa.2014.03.064

New cis-dioxomolybdenum(VI) and oxovanadium(IV) complexes of the Schiff base, derived from S-methyl dithiocarbazate and 2,3-dihydroxybenzaldehyde (H₂dhsm), have been synthesized. The complexes of the type cis-[MoO₂(dhsm)] (1a), cis-[MoO₂(dhsm)(D)] (1b-1d) [D = neutral monodentate ligand; EtOH, pyridine (py) or imidazole (imz)], [VO(dhsm)(NN)] (2a, 2b) [NN = 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen)] and [VO(dhsm)] (2c) have been isolated, characterized by ¹H NMR, IR, UV-Vis and EPR spectral studies and investigated by cyclic voltammetry. The X-ray crystal structure of cis-[MoO ₂(dhsm)(EtOH)] (1b) has been determined and shows that the complex has a distorted octahedral geometry in which the H₂dhsm behaves as a dianionic ONS tridentate ligand coordinating via phenoxide oxygen, hydrazinic nitrogen and thiolate sulfur. The oxomolybdenum(IV) complex [MoO(dhsm)] (1e) has obtained from dioxomolybdenum(VI) complex (1b) by oxo abstraction with PPh ₃. The reactivity of the complexes toward catalytic oxidation of alcohols in the presence of H₂O₂ and t-BuOOH as co-oxidants under solvent free conditions is reported.

Full text of DOI:10.1016/j.saa.2014.03.064

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 293–302
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Complexes of cis-dioxomolybdenum(VI) and oxovanadium(IV)
with a tridentate ONS donor ligand: Synthesis, spectroscopic properties,
X-ray crystal structure and catalytic activity
⇑
Ahmed M. Fayed, Shadia A. Elsayed, Ahmed M. El-Hendawy , Mohamed R. Mostafa
Department of Chemistry, Faculty of Science, Damietta University, Damietta, Egypt
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Cis-dioxomolybdenum(VI) and oxovanadium(VI) complexes with the Schiff base ligand, H2dhsm have
been prepared and characterized by spectroscopic and electrochemical studies. The X-ray structure of
cis-[MoO2(dhsm)(EtOH)] (shown below) indicates that the (dhsm)2ꢁ behaves as a dianionic ONS triden-
tate ligand. Some of the complexes act as catalysts toward alcohol oxidations in the presence of H2O2 or
t-BuOOH.
ꢀ
Synthesis of new cis-
dioxomolybdenum(VI) and
oxovanadium(IV) complexes with a
tridentate ONS-donor ligand.
Spectral and electrochemical
characterization of the synthesized
compounds.
ꢀ
ꢀ
ꢀ
X-ray crystal structure for one of the
complexes as a typical example.
Reactivity of some complexes as
catalytic oxidants for alcohols.
a r t i c l e i n f o
a b s t r a c t
Article history:
New cis-dioxomolybdenum(VI) and oxovanadium(IV) complexes of the Schiff base, derived from
S-methyl dithiocarbazate and 2,3-dihydroxybenzaldehyde (H2dhsm), have been synthesized. The com-
plexes of the type cis-[MoO2(dhsm)] (1a), cis-[MoO2(dhsm)(D)] (1b–1d) [D = neutral monodentate ligand;
EtOH, pyridine (py) or imidazole (imz)], [VO(dhsm)(NAN)] (2a, 2b) [NAN = 2,20-bipyridine (bipy) or 1,10-
phenanthroline (phen)] and [VO(dhsm)] (2c) have been isolated, characterized by 1H NMR, IR, UV–Vis
and EPR spectral studies and investigated by cyclic voltammetry. The X-ray crystal structure of cis-
[MoO2(dhsm)(EtOH)] (1b) has been determined and shows that the complex has a distorted octahedral
geometry in which the H2dhsm behaves as a dianionic ONS tridentate ligand coordinating via phenoxide
oxygen, hydrazinic nitrogen and thiolate sulfur. The oxomolybdenum(IV) complex [MoO(dhsm)] (1e) has
obtained from dioxomolybdenum(VI) complex (1b) by oxo abstraction with PPh3. The reactivity of the
complexes toward catalytic oxidation of alcohols in the presence of H2O2 and t-BuOOH as co-oxidants
under solvent free conditions is reported.
Received 13 January 2014
Received in revised form 13 March 2014
Accepted 21 March 2014
Available online 2 April 2014
Keywords:
Dioxomolybdenum(VI) complexes
Oxovanadium(IV) complexes
ONS-donor ligand
X-ray crystal structure
Catalytic oxidations
Ó 2014 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel.: +20 1006869447.
E-mail address: amelhendawy@yahoo.com (A.M. El-Hendawy).
http://dx.doi.org/10.1016/j.saa.2014.03.064
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

294
A.M. Fayed et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 293–302
anisotropic thermal parameters. Crystallographic data for the com-
Introduction
plex (1b) are summarized in Table 1.
The transition metal complexes of S-methyl- and S-benzyl dith-
iocarbazate Schiff bases derived from o-hydroxy aldehydes and ke-
tones have been widely studied [1–5]. Interest in metal complexes
of these ligands is simulated by their interesting physico-chemical
properties and significant biological activities [6,7]. EXAFS spectro-
scopic studies have implicated the presence of a sulfur atom, be-
sides oxygen and nitrogen, at the active sites of oxo transfer
molybdoenzymes whose catalytic reactions are known to involve
oxidation states Mo(VI) and Mo(IV) [8,9]. Thus, mixed hard-soft
donor sets in ONS tridentate ligands and their related complexes
of high valent oxo moieties is of current interest as model systems
for the active sites of molybdoenzymes such as xanthine oxidase
and sulfite oxidase [3,10,11]. Vanadium complexes having sulfur
functionality have been found to be orally active insulin-mimetic
agent in the treatment of diabetic model animals [12,13]. Dioxo-
and oxovanadium(V) complexes of ONS donor ligands derived
from S-benzyl/S-methyl dithiocarbazate with pyridoxal have been
found more effective than metronidazole, a commonly used drug
against amoebiasis [2].
Synthesis of the ligand (H2dhsm)
A solution of S-methyldithiocarbazate [22] (1.22 g, 10 mmol) in
ethanol (10 mL) was added to an ethanolic solution (10 mL) of 2,3-
dihydroxybenzaldehyde (1.38 g, 10 mmol). The reaction mixture
was heated under reflux for 30 min, during which a yellow precip-
itate was formed after cooling to room temperature. The crystalline
solid product was isolated by filtration and recrystallized from eth-
anol, then dried in vacuo. Yield, 2.1 g (ꢂ88%); m.p. 225 °C. Anal.
Calcd. for C9H10N2O2S2: C, 44.6; H, 4.1; N, 11.6. Found: C, 44.5; H,
4.0; N, 11.5. IR, cmꢁ1
3109(s), (C@N) 1620(m), 1600(s), d(OH) 1365(s),
1280(s), 1260(s),
(C@S) 1323(vs). 1H NMR (d6-Me2SO, d/ppm):
:
m(OAH) 3350(s,b), 3220(b),
m
(NAH)
m
m(CAO)
m
2.47 (s, 3H, SCH3); aromatic protons: 6.68 (t, 1H), 6.84(d, 1H),
7.08 (d, 1H); 8.48 (s, 1H, ACH@N); 9.51 (S, 1H, NH); 9.57 (S, 1H,
3-OH); 13.33 (S, 1H, 2-OH).
As a continuation of our research on tridentate ligands contain-
ing sulfur atom with different transition metals [14–16], we de-
scribe herein the preparation, spectroscopic characterization and
redox properties of Mo(VI), Mo(IV) and V(IV) complexes of 2,3-
dihydroxybenzaldhyde Schiff base of S-methyldithiocarbazate
(H2dhsm). We also report the X-ray crystal structure of the com-
plex [MoO2(dhsm)(EtOH)] which exhibits oxo transfer to PPh3 in
acetonitrile medium leading to the formation of [MoIVO(dhsm)].
The catalytic activity of these complexes toward oxidation of
alcohols in the presence of t-BuOOH and H2O2 as co-oxidants in
comparison with the previous work on catalytic oxidants by dioxo-
molybdenum(VI) [17] and oxovanadium(IV) complexes [14,18] has
been studied.
Synthesis of [MoO2 (dhsm)] (1a)
To dry acetonitrile solution (20 mL) of [MoO2 (acac)2] [23]
(0.16 g, 0.5 mmol), the ligand, H2dhsm (0.12 g, 0.5 mmol) was
added. The mixture was refluxed for 1 h, during which a brown
precipitate was formed. This was filtered off, washed with acetoni-
trile and then dried in vacuo. Yield, 0.12 g (ꢂ75%); diamagnetic.
Anal. Calcd. for C9H8N2O4S2Mo: C, 29.4; H, 2.2; N, 7.6. Found: C,
29.3; H, 2.1; N, 7.5. IR, cmꢁ1
1563(vs), d(OH) 1363(s),
931(s),
as(MoO2) 891(s)
:
m
m
(OAH) 3359(vs),
m
(C@N) 1593(vs),
s(MoO2)
(MoAN)
(CAO) 1271(s), 1232(s),
m
m
m
m(Mo@Oꢃ ꢃ ꢃMo) 793(vs),
499(m). 1H NMR (d6-Me2SO, d/ppm): 2.49 (s, 3H, SCH3); aromatic
protons: 6.88 (t, 1H), 7.08 (d, 1H), 7.21 (d, 1H); 8.85 (s, 1H,
ACH@N); 9.41 (S, 1H, 3-OH).
Experimental
Table 1
Analytical and physical measurements
Crystal data and structure refinement parameters for cis-[MoO2(dhsm)2(EtOH)] (1b).
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit cell dimensions
a
b
c
a
b
C11H14 Mo N2 O5S2
414.31
298 K
IR spectra were measured on a JASCO 4100 FTIR spectrometer
(4000–400 cmꢁ1) as KBr disks. 1H NMR spectra were measured
on a Varian Gemini WM-200 spectrometer (Laser Centre, Cairo
University). Electronic spectra in CH2Cl2 were recorded using a Per-
kin–Elmer Lambda 2S spectrophotometer. ESR spectra were re-
corded with a Bruker EMX spectrometer (Radiation Technology
Centre, Cairo). Cyclic voltammetric studies were carried out on
an electroanalyzer CHI 610A, the three electrode cell comprised a
reference Ag wire, Pt auxiliary, and working electrodes, solutions
of the complexes (10ꢁ3 M) in 0.1 M (n-Bu4N)PF6 as supporting elec-
trolyte were used. Magnetic measurements were taken on a
Johnson Matthey magnetic susceptibility balance.
0.71073
Triclinic
ꢀ
P1
8.4588(2) Å
9.7139(2) Å
11.3107(4) Å
110.6334(12)°
100.6194(14)°
c
109.6044(14)°
Volume
Z
Density
Absorption coefficient
Theta range for data collection
Index ranges
Independent reflections
Observed reflections
Absorption correction
Reflections collected
769.59(4) Å3
2
1.788 Mg mꢁ3
1.14 mmꢁ1
2.91–28.70o
X-ray crystallography
ꢁ11 6 h 6 11, ꢁ13 6 k 6 13, ꢁ15 6 l 6 15
4053
2833
None
2833
Orange triclinic crystals of [MoO2(dhsm)(EtOH)] (1b) having
appropriate dimensions were measured on Bruker Kappa CCD dif-
fractometer equipped with graphite-monochromated Mo Ka radi-
ation (k = 0.71073 Å), the unit cell dimensions and intensity data
were measured at 298 K. The structure was solved by least square
fit of the angular setting of strong reflection based on F2. Program
used to solve structure was SIR92 [19], while the program used to
refine structure was maXus [20]. Integration and scaling of the
reflections were performed with the HKL Denzo-scale pack system
of programs [21]. The non-hydrogen atoms were refined with
[I > 3r(I)]
Refinement method
Reflections/restraints/
parameters
Full-matrix least squares on F2
4053/0/190
D
qmax,
D
q
min (e Åꢁ3
)
0.55, ꢁ0.69
Goodness of fit
Final R indices
R indices (all data)
0.943
R1 = 0.033, wR2 = 0.064
R1 = 0.052, wR2 = 0.069

A.M. Fayed et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 293–302
295
Synthesis of [MoO2(dhsm)(EtOH)] (1b)
Reaction of [MoIVO(dhsm)] (1e) and Me2SO
To a solution of [MoO2 (acac)2] (0.16 g, 0.5 mmol) in ethanol
(10 mL), H2dhsm (0.12 g, 0.5 mmol) was added. The mixture was
stirred at room temperature for 1 h, during which an orange solu-
tion was obtained. This was then left for slow evaporation at room
temperature. The orange crystals so formed were suitable for X-ray
diffraction; they were filtered off, washed carefully with little eth-
anol, followed by ether, and dried in vacuo. Yield, 0.15 g (ꢂ80%);
diamagnetic. Anal. Calcd. for C11H14N2O5S2Mo: C, 31.9; H, 3.4; N,
To a solution of the complex [MoIVO(dhsm)] (0.1 g, 0.28 mmol)
in deoxygenated Me2SO (2 mL) and DMF (0.5 mL), pyridine
(0.1 mL, 1.2 mmol) was added. The reaction mixture was stirred
and heated at 70 °C for 7 h, then the solvents were evaporated at
ca. 90 °C with passing vigorous N2 gas. Addition of excess Et2O
afforded
a reddish brown precipitate which was thoroughly
washed with solvent, filtered off and dried in vacuo. IR and
UV–Vis spectra identified the product and found typically as
[MoVIO2(dhsm)(py)] (1c) above. Yield: 0.09 g (ꢂ71%).
6.8. Found: C, 31.7; H, 3.3; N, 6.7. IR, cmꢁ1
(C@N) 1590(s), 1556(s), d(OH) 1365(m),
1224(s),
s(MoO2) 939(s), as(MoO2) 904(vs),
(MoAN) 507(m). 1H NMR (d6-Me2SO, d/ppm): 1.03 (t, 3H, CH3);
:
m
m
(OAH) 3382(s,b),
(CAO) 1277(s),
(CAS) 783(m),
m
m
m
m
Synthesis of [VO (dhsm)(bipy)] (2a)
m
2.47 (s, 3H, SCH3); 3.41 (q, 2H, CH2); 4.35 (b, 1H, OH); aromatic
protons: 6.85 (t, 1H), 7.05 (d, 1H), 7.18 (d, 1H); 8.85 (s, 1H,
ACH@N); 9.41 (S, 1H, 3-OH).
To a solution of [VO (acac)2] [24] (0.13 g, 0.5 mmol) in ethanol
(10 mL), H2dhsm (0.12 g, 0.5 mmol) was added. The mixture was
stirred at room temperature for 30 min, then 2,20-bipyridyl
(0.078 g, 0.5 mmol) was added. This mixture was then refluxed
for 1 h and the resulting brown solution was concentrated to
one-third volume and cooled to room temperature. A brown pre-
cipitate was formed, filtered off, washed carefully with little etha-
nol, followed by ether, and dried in vacuo. Yield: 0.17 g (75%);
Synthesis of [MoO2(dhsm)(py)] (1c)
To a solution of [MoO2 (acac)2] (0.16 g, 0.5 mmol) in ethanol
(10 mL), H2dhsm (0.12 g, 0.5 mmol) was added. The mixture was
stirred at room temperature for 30 min, during which an orange
solution was obtained, and then pyridine (0.04 g, 0.5 mmol) was
added. This mixture was refluxed for 1 h and the resulting solution
was concentrated to one-third volume and cooled to room temper-
ature. A brown precipitate was formed, filtered off, washed with
little ethanol, and then ether, and dried in vacuo. Yield, 0.11 g
(ꢂ70%); diamagnetic. Anal. Calcd. for C14H13N3O4S2Mo: C, 37.6;
l
eff = 1.72 BM. Anal. Calcd. for C19H16N4O3S2V: C, 49.3; H, 3.5; N,
12.1. Found: C, 49.1; H, 3.4; N, 12.0. IR, cmꢁ1
(OAH) 3420(b),
(C@N) 1610(s), 1585(s), d(OH) 1362(m), (CAO) 1309(m),
1223(s), (V@O) 957(s), (CAS) 765(s), (VAN) 499(w), bipy vibra-
:
m
m
m
m
m
m
tions: 1485(s), 868(m). EPR (CH2Cl2, 298 K): Experimental gav
1.976, Aav 82.6 ꢄ 10ꢁ4 cmꢁ1; Calcd. g ? 1.983, g// 1.935, gav 1.967.
Synthesis of [VO (dhsm)(phen)] (2b)
H, 2.9; N, 9.4. Found: C, 37.4; H, 2.7; N, 9.2. IR, cmꢁ1
:
m
m
m
(OAH)
(CAO)
(CAS)
(MoAN) 499(m). 1H NMR (d6-Me2SO, d/ppm): 2.50 (s,
3420(s,b),
1261(vs), 1210(m),
781(m),
m
(C@N) 1630(m), 1593(vs), d(OH) 1363(m),
This complex was prepared by a similar procedure to that for
complex 2a, using 1,10-phenanthroline (0.1 g, 0.5 mmol) instead
m
s(MoO2) 930(s), as(MoO2) 887(vs),
m
m
of 2,20-bipyridyl. Yield: 0.194 g (80%);
l
eff = 1.75 BM. Anal. Calc.
for C21H16N4O3S2V: C, 51.8; H, 3.3; N, 11.5. Found: C, 51.7; H,
3.2; N, 11.4. IR, cmꢁ1
(OAH) 3420(b), (C@N) 1610(m),
1581(m), d(OH) 1365(m), (CAO) 1304(m), 1226(vs), (V@O)
957(vs), (CAS) 779(s), (VAN) 497(m), phen vibrations: 1480(s),
3H, SCH3); aromatic protons: 6.90 (t, 1H), 7.06 (d, 1H), 7.20 (m,
1H); pyridine protons: 7.50 (t, 2H), 7.90 (t, 1H), 8.60 (d, 2H); 8.87
(s, 1H, ACH@N); 9.37 (S, 1H, 3-OH).
:
m
m
m
m
m
m
839(s). EPR (CH2Cl2, 298 K): Experimental gav 1.973, Aav
Synthesis of [MoO2(dhsm)(imz)] (1d)
82.4 ꢄ 10ꢁ4 cmꢁ1; Calcd. g ? 1.982, g// 1.936, gav 1.967.
This reddish brown complex was prepared by a similar proce-
dure to that for complex 1c, using imidazole (0.04 g, 0.5 mmol) in-
stead of pyridine. Yield, 0.15 g (ꢂ74%); diamagnetic. Anal. Calcd.
for C12H12N4O4S2Mo: C, 33.0; H, 2.8; N, 12.8. Found: C, 32.8; H,
Synthesis of [VO (dhsm)] (2c)
To a solution of [VO(acac)2] (0.13 g, 0.5 mmol) in ethanol
(10 mL), H2dhsm (0.12 g, 0.5 mmol) was added. The mixture was
reflux and stirred at 70 °C for 2 h, during which a violet precipitate
was obtained. This precipitate was filtered off, washed with little
ethanol, followed by ether, and dried in vacuo. Yield, 0.2 g (72%);
2.6; N, 12.6. IR, cmꢁ1
:
m
(OAH) 3430(s,b),
m
m
(NAH) 3143(vs),
(CAO) 1260(vs),
s(MoO2) 930(s), as(MoO2) 899(vs),
m m m(CAS) 780(m),
m
(C@N) 1620(m), 1587(s), d(OH) 1365(w),
1219(m),
m
(MoAN) 499(m), other imidazole bands: 3143(vs), 2974(s),
2895(s). 1H NMR (d6-Me2SO, d/ppm): 2.48 (s, 3H, SCH3); aromatic
protons: 6.90 (t, 1H), 7.06 (d, 1H), 7.20 (m, 1H); imidazole protons:
6.10 (b, 1H, NH), 7.20 (m, 2H, CH), 7.95 (s, 1H, ACH@N); 8.85 (s, 1H,
ACH@N); 9.46 (b, 1H, 3-OH).
l
eff = 1.10 BM. Anal. Calcd. for C9H8N2O3S2V: C, 35.2; H, 2.6; N,
9.1. Found: C, 35.3; H, 2.4; N, 9.0. IR, cmꢁ1
(OAH) 3442(b),
(CAO) 1290(s),
(CAS) 780(m), (VAN)
:
m
m
m(C@N) 1585(vs), 1530(vs), d(OH) 1360(w),
(V@O) 995(vs),
(VAOꢃ ꢃ ꢃV) 823(m),
m
m
m
m
500(m).
Synthesis of [MoO(dhsm)] (1e)
Catalytic oxidations with t-BuOOH or H2O2
To an acetonitrile solution (20 mL) of [MoO2 (dhsm)(EtOH)]
(0.21 g, 0.5 mmol), PPh3 (0.2 g, 0.75 mmol) was added. The orange
solution mixture was refluxed for 2 h, where a reddish brown pre-
cipitate was obtained, filtered off washed with MeCN, followed by
ether and then dried in vacuo. Yield, 0.15 g (ꢂ80%); diamagnetic.
Anal. Calcd. for C9H8N2O3S2Mo: C, 30.7; H, 2.3; N, 8.0. Found: C,
The oxidation of benzyl alcohol by [MoO2 (dhsm)(EtOH)] (1b) is
typical. To the alcohol (2.5 mmol), complex (1b) (0.01 mmol) and
70% in water t-BuOOH (5 mmol) were added. The reaction mixture
was stirred at 70 °C for 3 h, extracted with CH2Cl2 (3 ꢄ 10 mL). The
extracts were combined, dried over anhydrous Na2SO4, evaporated
to dryness and aldehyde product was quantified as its 2,4-dini-
trophenylhydrazone derivative [8,9] (equivalent to 1 mmol of
benzaldehyde product was obtained). The absence of benzoic
product was detected by TLC techniques. The same experiment
30.6; H, 2.2; N, 7.9. IR, cmꢁ1
1577(s), d(OH) 1358(m),
962(vs), 868(m), (CAS) 773(m),
:
m
m
(OAH) 3464(m),
(CAO) 1274(s), 1218(s),
(MoAN) 503(m).
m
(C@N) 1608(m),
m(Mo@O)
m
m

296
A.M. Fayed et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 293–302
were carried out using 30% H2O2 (5 mmol) instead of 70% t-BuOOH
where 0.25 mmol benzaldehyde was produced.
O15, N6, S3 from the tridentate ligand (H2dhsm), and the terminal
oxo atom O17, occupy the meridional plane. Both the other oxo
terminal atom O21 and O16 from the coordinated ethanol mole-
cule, define the axial positions. The O17@Mo@O21 bond angle is
105.90(11)° and the bond lengths; Mo1@O17@1.707(2) Å and
Mo1@O21@1.691(2) Å are usual for cis-dioxomolybdenum(VI)
complexes [27,28].
The MoAO16 bond trans to the terminal oxygen atom O21 has
been significantly lengthened [2.331(2) Å], compared to the
Mo1AO15 distance [1.936(2) Å] occupying cis-position indicating
that EtOH molecule is weakly coordinated to the metal center.
Also, the imine nitrogen N6 is trans to the oxo terminal atom
O17 and the MoAN6 bond length of 2.283(2) Å is rather long due
to trans effect. The C4AN5 length [1.293(4) Å] is close to usual
C@N bond length [3,29]. This thiol form is also identified by the
fact that the hydrazinic nitrogen N5 is not covalently bonded to
any hydrogen atom.
Results and discussion
The free ligand, H2dhsm (Scheme 1) was prepared by condensa-
tion of equimolecular amounts of 2,3-dihydroxybenzaldehyde and
S-methyldithiocarbazate in ethanol. The 1HNMR spectrum of
H2dhsm in (CD3)2SO shows singlet at d 9.51, 9.57 and 13.33 ppm
which are absent when using (CD3)2SO/D2O as solvent, these
attributed to protons of NH, free and hydrogen-bond hydroxyl
groups (3-OH, 2-OH), respectively. The azomethine hydrogen ap-
pears at d 8.48 ppm, aromatic protons shifts are found within the
range d 6.68–7.08 ppm (3 protons), while methyl protons of SCH3
resonate as singlet at 2.47 ppm. Similar 1H NMR spectra have been
reported for related Schiff base ligands [3,25] and these data indi-
cate that the free ligand is in the thione form (a).
Fig. 2 shows the intermolecular hydrogen bonding for Hꢃ ꢃ ꢃO and
Hꢃ ꢃ ꢃN interactions characterized in the lattice for the complex 1b.
Each molecule is interconnected with the other neighboring mole-
cules via hydrogen bonds between dioxo atoms (O17, O21), hydra-
zinic nitrogen N5 and hydroxyl oxygen O14 of the aromatic ring.
The Hꢃ ꢃ ꢃO bonding is defined by strong interaction
O14AH14ꢃ ꢃ ꢃO17 [dH (H14ꢃ ꢃ ꢃO17 = 1.971(2) Å] and a weaker one
C13AH13ꢃ ꢃ ꢃO21 [dH (H13ꢃ ꢃ ꢃO21) = 2.596(2) Å] or C18AH18ꢃ ꢃ ꢃO14
[dH (H18ꢃ ꢃ ꢃO14) = 2.393 Å]. The dH (Hꢃ ꢃ ꢃO) distances are shorter
than the maximum values 2.72 Å for the Van der Waals radii of
hydrogen and oxygen atoms and considered for any contacts
[30]. However, such the latter CAHꢃ ꢃ ꢃO interaction is somewhat
scarce in coordination compounds; it has been recognized to play
an important in protein structure and stability [31]. The theoretical
calculations showed that the CAHꢃ ꢃ ꢃO association energy
ꢂ2.1 kcal molꢁ1 essentially contribute to the structure stabilization
[32]. It is noteworthy to find that the coordinated ethanolic mole-
cule in the complex 1b participates in a more strong interaction
through the alcoholic hydroxyl hydrogen H16 and the hydrazinic
nitrogen N5 in O16AH16ꢃ ꢃ ꢃN5 [dH (H16ꢃ ꢃ ꢃN5) = 1.853(2) Å].
Table 3 lists the different hydrogen bonding in structure 1b.
Dioxomolybdenum(VI) complex (1a) of the formula [MoO2
(dhsm)] was prepared by refluxing [MoO2(acac)] with the ligand
(H2dhsm) in 1:1 M proportion using CH3CN as a solvent, while
the complex [MoO2(dhsm)(EtOH)] (1b) was isolated as orange
crystals when EtOH used. The complexes [MoO2(dhsm)D] [D =
pyridine (1c), imidazole (1d)] were similarly prepared as the com-
plex (1b), but in the presence of added equivalent amounts from
pyridine or imidazole. The reddish brown oxomolybdenum(IV)
complex [MoO(dhsm)] (1e) was prepared by oxo-abstraction reac-
tion of (1b) with PPh3 in MeCN medium, as similarly obtained for
related molybdenum(IV) complexes of ONS-donor ligands [26,27].
The complex [MoO2(dhsm)(py)] (1c) has been also obtained from
reaction of [MoIVO(dhsm)] (1e) and Me2SO in the presence of pyr-
idine indicating oxo-accepting behavior of MoIVO22+ core with a
consequent oxidation to MoVIO22+ complex. This is similarly related
to other molybdenum(IV) complexes and to the behavior of oxido-
reductase enzymes, through two electron reduction of the sub-
strate by removing an oxo ligand [26]. Vanadium complexes of
the formula [VO(dhsm)bipy/phen] (2a, 2b) were isolated by reflux
of equimolar quantities of [VO(acac)2], H2dhsm and bipy/phen in
MeOH, while the complex [VO(dhsm)] (2c) was obtained simply
by a similar way in absence of bipy/phen. All the compounds are
readily soluble in CH2Cl2, MeCN and DMF and their molar conduc-
tivities in CH2Cl2 are very low. They are also soluble in diluted
aqueous NaOH.
Infrared spectra
The IR spectrum of the ligand (H2dhsm) shows two medium
broad bands near 3350 and 3220 cmꢁ1 due to the
m
(OH) vibrations
of the free and hydrogen-bonded hydroxyl groups, respectively
[25]. The low wavenumber (OH) vibration disappears in the com-
plexes while the other band is still present. The medium band at
1620 cmꢁ1, attributed to
(C@N) in the free ligand is shifted in
Crystal Structure of cis-[MoO2(dhsm)(EtOH)] (1b)
m
The perspective view of the complex 1b is shown in Fig. 1. As
indicated by the bond angles in Table 2, this six coordinate
complex is appreciably distorted from ideal octahedral geometry.
In particular, the angles, O16AMo1AO21 [169.65(9)°], O17A
Mo1AN6 [157.93(9)°] and S3AMo1AO15 [153.96(7)°], are less
than the ideal value of 180°, similarly typical to that found for
the related bond angles in the complex cis-[MoO2(ONS)(H2O)]
(ONS = dianione of the tridentate Schiff base ligand of salicyalde-
hyde with S-methyl dithiocarbazate) [3,27]. The donor atoms
m
complexes to lower wavenumbers. The observed band at
1365 cmꢁ1 in the ligand, which by analogy with catechol and
2,3-dihydroxynaphthalene is assigned to d(OH), does appear [25]
in our complexes, while its absence was noted in catecholato
[33] and naphthalene-2,3-diolato [34] complexes. Shifted
strong bands comparable to the ligand (H2dhsm), lie in the range
1277–1210 cmꢁ1 for the complexes, consistent with the phenolic
Scheme 1.

A.M. Fayed et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 293–302
297
Fig. 1. ORTEP diagram of the compound [MoO2 (dhsm)(EtOH)] (1b), with 50% ellipsoidal probability. Hydrogen atoms are shown as smaller spheres of arbitrary radii.
Table 2
Selected bond lengths and angles for cis-[MoO2(dhsm)(EtOH)] (1b).
Bond lengths (Å)
Mo1AO17
Mo1AO21
Mo1AO16
Mo1AO15
Mo1AN6
1.707(2)
1.691(2)
2.331(2)
1.936(2)
2.283(2)
C4AN5
Mo1AS3
S3AC4
S2AC4
S2AC18
1.293(4)
2.458(8)
1.722(3)
1.758(3)
1.787(4)
Bond angles (°)
O16AMo1AO21
O17AMo1AN6
S3AMo1AO15
O17AMo1AO21
S3AMo1AO17
S3AMo1AO16
O15AMo1AO17
O15AMo1AN6
169.65(9)
157.93(9)
153.96(7)
105.90(11)
91.73(7)
81.98(6)
105.41(9)
81.67(8)
O16AMo1AO17
O15AMo1AO21
O16AMo1AN6
S3AMo1AN6
S3AMo1AO21
O15AMo1AO16
N6AMo1AO21
84.34(9)
97.91(11)
76.15(7)
75.57(6)
95.97(9)
80.42(8)
93.50(9)
m(CAO) vibrations [25,33–36]. This confirms the participation of
the azomethine nitrogen and the hydroxyl oxygen atom in coordi-
nation. The free ligand exhibits two strong distinct bands at 3109
and 1323 cmꢁ1 due to
m
(NAH) and
peared upon complex formation with the presence of a new med-
ium band near 780 cmꢁ1 arising from
(CAS) vibration, suggesting
m(C@S) modes [1,3], both disap-
m
deprotonation and coordination through thiolate sulfur [2,5,14].
Two strong bands near 935 and 900 cmꢁ1 assigned to symmet-
ric and asymmetric stretches of the cis-MoO2 unit similar to those
found for most of the cis-dioxomolybdenum(VI) complexes [25,33–
36]. A strong broad band at 793 cmꢁ1 was only observed in the
complex [MoO2(dhsm)] (1a), which can be assigned to Mo@Oꢃ ꢃ ꢃMo
grouping and suggesting a weak polymeric interaction [37,38]
(Structure 1a). In oxovanadium complexes, a strong band at 995
1H NMR spectra
The 1H NMR spectra for the diamagnetic molybdenum(VI) com-
plexes recorded in (CD3)2SO (Scheme 1, for atom numbering)
showed absence of the ligand proton resonances for NH and hydro-
gen bonded 2-OH, while the proton of free hydroxyl group (3-OH),
still appears as singlet but shifted up field by 0.11–0.20 ppm. The
resonance arising from the azomethine nitrogen (CH@N) and aro-
matic protons (H4, H5 and H6) are shifted down field. This feature
is indicative of a decrease in the electron density caused by elec-
tron withdrawal by the molybdenum ion [15]. These refer to com-
plex formation and participation of hydroxyl oxygen (2-OH group),
azomethine nitrogen and thiolate sulfur in coordination as con-
firmed by single crystal X-ray for cis-dioxomolybdenum(VI) com-
plex (1b). For the complexes cis-[MoO2(dhsm)D] (D = EtOH, py,
or 957 cmꢁ1 was observed, due to
m(V@O) vibrations and the addi-
tional new medium band at 823 cmꢁ1 found in complex (2c) is
attributed to VAOꢃ ꢃ ꢃV bridging vibration of its dimeric nature
[39]. The molybdenum and vanadium complexes exhibit also char-
acteristic bands corresponding to the bound monodentate (etha-
nol, pyridine, imidazole), or bidentate donor (bipy, phen) [39] to
complete six-coordination around molybdenum or vanadium
atom. A new band near 500 cmꢁ1 was observed for complexes,
assigned to m(MAN) [1,3,39].

298
A.M. Fayed et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 293–302
Fig. 2. The main intermolecular hydrogen bonding characterized in the lattice for the complex [MoO2 (dhsm)(EtOH)] (1b).
Table 3
Hydrogen bonding parameters (Å, °) for cis-[MoO2 (dhsm) (EtOH)] (1b).
DAHꢃ ꢃ ꢃA
Symmetry
DAH (Å)
Hꢃ ꢃ ꢃA (Å)
Dꢃ ꢃ ꢃA (Å)
DAHꢃ ꢃ ꢃA (°)
O14AH14ꢃ ꢃ ꢃO17
C13AH13ꢃ ꢃ ꢃO21
C18AH18ꢃ ꢃ ꢃO14
O16AH16ꢃ ꢃ ꢃN5
1 ꢁ x, ꢁy, 1 ꢁ z
1 ꢁ x, ꢁy, ꢁz
1 + x, y, 1 + z
ꢁx, ꢁy, ꢁz
0.983(2)
0.960(3)
0.960(3)
0.936(2)
1.971(2)
2.596(2)
2.393(2)
1.853(2)
2.866(3)
3.478(4)
3.291(4)
2.779(3)
150.2(2)
152.9(2)
155.6(3)
170.1(2)
imz), distinct resonances for the coordinated monodentate ligand
D have been displayed.
containing PPh3. The parent complex has a band near 400 nm
due to a S(p ) ? Mo(d ) LMCT transition. When the complex,
p
p
e.g. cis-[MoO2(dhsm)(EtOH)] (1b) is reacted with PPh3, this band
is found to be shifted to lower energy (476 nm) and a new band ap-
pears at 660 nm. The isolated complex [MoIVO(dhsm)] (1e) has the
same spectral feature and the oxo-transfer reaction may be repre-
sented as:
Electronic spectra
Electronic spectra of the complexes and the ligand (H2dhsm)
were recorded in CH2Cl2 and the results are summarized in Table 4.
Dioxomolybdenum complexes (1a–1d) with 4d0 configuration
showed the lowest energy absorption maxima located in the
MoVIO2L þ PPh3 ! MoIVOL þ OPPh3
390–402 nm range and may be assigned to S(pp)-Mo(dp) LMCT
This oxo-transfer reaction may be visualized as a simple bimo-
lecular reaction that involves the interaction between one MoO2L
and one PPh3 molecule in the activated complex, leading to the
transfer of an oxygen atom by the donation of the lone pair of elec-
trons of the phosphorous atom into the antibonding Mo@O pꢅ
orbital. This leads to the formation of the PAO bond and Mo(IV)
– oxo complex with a 4d2xy configuration. We could isolate OPPh3
which ascertained by identifying its characteristic peak at
1180 cmꢁ1 in the IR spectrum. So, the reaction may be considered
as a two-electron redox/oxygen atom transfer process.
The oxygen atom transfer from the substrate (Me2SO) to
[MoIVO(dhsm)] (1e) has been studied spectrophotometrically in
DMF solution. When a drop of Me2SO is added to the reddish
brown solution of (1e), the bands at 476 and 660 nm disappear
within 15 min, and the band near 400 nm characteristic to Mo(VI)
complex (1a–1d) makes its appearance with a predomination of an
orange color solution. This observation clearly indicates the trans-
fer of an oxygen atom from Me2SO to the MoIVO2+ core, leading to
the formation of MoO22+ species and Me2S [3,26,27]. The reaction
may be shown as
transitions [3,40]. Other LMCT bands are observed in the region
390–285 nm [3,41], which may be assigned to transitions from
nitrogen or oxygen to molybdenum [3,40]. The oxomolybde-
num(IV) (1e) in DMF gives brown solution and exhibits one low-
energy charge transfer band at 660 nm (e
= 350 Mꢁ1 cmꢁ1), similar
to that found for related molybdenum complexes [3,37]. In the
oxovanadium(IV) complexes (2a–2c) which are 3d1 system, med-
ium to intense bands are found in the range 352–550 nm, attrib-
uted to LMCT arising from the ONS-donor ligand [14,42,43]. The
weak broad bands
(e ) lie in the region
= 310–540 Mꢁ1 cmꢁ1
660–780 nm, are as expected due to 2B2(dxy) ? 2E(dxz, dyz) and
2B2(dxy) ? 2B1(dx2ꢁy2) transitions while the other weak d–d transi-
tion of higher energy may be obscured by such LMCT bands [43].
The bands at or below 325 nm are of the intraligand transitions.
Oxo transfer reactivity of dioxomolybdenum(VI) complexes
The property of the complexes MoVIO2L (1a–1d) to transfer an
oxygen atom to the substrate has been examined in CH3CN

A.M. Fayed et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 293–302
299
Table 4
Electronic spectral and cyclic voltammetric data for complexes.
a
Compounda
kmax nm (
e
, Mꢁ1 cmꢁ1
)
Epa
Epc
V
[MoO2(dhsm)]
(1a)
(1b)
(1c)
(1d)
(1e)
(2a)
(2b)
(2c)
290(35,025); 330(67,800); 402(19,150)
285(33,600); 312(39,900); 395(14,700)
290(23,600); 330(47,270); 390(17,700)
292(13,980); 340(44,550); 420(12,820)
ꢁ0.67b
ꢁ1.12b
[MoO2(dhsm)(EtOH)]
[MoO2(dhsm)(py)]
[MoO2(dhsm)(imz)]
[MoO (dhsm)]
[VO(dhsm)(bipy)]
[VO(dhsm)(phen)]
[VO(dhsm)]
–
ꢁ0.65, ꢁ0.95
–
–
ꢁ0.85, ꢁ1.25
ꢁ0.81, ꢁ1.23
294(7510); 328(12,690); 398(5520); 476(1470); 660(350)c
310(36,040); 360(31,330); 418(13,270); 675(360)d, 780(300)d
310(38,020); 352(39,350); 405(17,980); 660(310)d, 760(200)d
312(23,900); 325(24,170); 397(12,450); 550(5900); 740(540)
+0.68c
+0.70
+0.80
–
–
–
–
–
a
b
c
UV/Vis data of the ligand (H2dhsm): 295(24,800), 320(57,100), 334(65,800).
C.V. data obtained in CH3CN.
UV/Vis and C.V. data recorded in DMF.
d
d–d transition bands used for calculated g-values.
MoOL þ Me2SO ! MoO2L þ Me2S
It is worthwhile to note that the reaction of MoIVO complexes with
Me2SO in DMF solvent has a high reaction velocity of more than 13-
fold times than that in the absence of DMF [26c], and the identity of
Me2S formed was confirmed by GC/MS-head space analysis for sim-
ilar molybdenum reactions to oxidize PPh3 catalytically [26d].
Magnetic and EPR spectra
Magnetic susceptibility of the solid complexes were measured
at 298 K. Oxovanadium complexes (2a) and (2b) are paramagnetic
corresponding to one unpaired electron, with leff values of 1.70
and 1.75 BM close to the spin only value (1.73 BM), as expected
for a simple S = 1/2 with dxy based ground state mononuclear com-
plexes [43]. EPR spectra at 298 K in CH2Cl2 exhibit a set of eight
hyperfine lines arising from interaction of the unpaired electron
of the oxovanadium(IV) center with the single vanadium nucleus
Fig. 3. X-band EPR spectra of [VO (dhsm)(bipy)] (2a) at 298 K in 5 ꢄ 10ꢁ3 M CH2Cl2
(
51V, I = 7/2). A typical spectrum (Fig. 3) for [VO(dhsm)(bipy)]
solution.
(2a) shows an eight line pattern: gav, 1.976 and Aav, 82.6 ꢄ 10ꢁ4
cmꢁ1. Using both energies of our corresponding electronic spectral
data (Table 4.) for the d–d transitions of complexes (2a) and (2b)
and the Eqs. (1) and (2) [44], we have got values (gav) in a good
agreement with the experimental results.
2
2
g ?¼ 2½1 ꢁ ðcꢅ1Þ k=Eð B2 ! 2EÞꢆ
ð1Þ
2
2
2
g== ¼ 2½1 ꢁ ðcꢅ1Þ 4k=Eð B2 ! B1Þꢆ
ð2Þ
where the c⁄1 are 0.907 and 0.946 for the first and second excited
states, respectively; k is the spin–orbit coupling parameter, taken
to be 135 cmꢁ1. The gav-value, corrupted from g ? and g// compo-
nents above is given by: ga ¼ 1=3ðg== þ 2g ?Þ. It is worthwhile to
v
note that calculated g ? > g// as expected and g ? has a relatively
larger values when compared with those for related oxovana-
dium(IV) complexes in N/O donor environments [45]. This indicates
Electrochemical properties
moderate
leading to increased delocalization of the vanadium unpaired elec-
tron [43]. For the oxovanadium complex (2c), the eff (at 298 K) has
a lower value of 1.10 BM, as similarly found for oxovanadium(IV)
complexes with tridentate Schiff base ligands having subnormal
magnetic moments [46], and arise from the antiferromagnetic
spin–spin interaction between neighboring oxovanadium(IV) cen-
ters [47]. The EPR spectra at room temperature for complex (2c)
in both CH2Cl2 and powdered sample shows a 15-line spectrum
p-interaction of sulfur in the present ONS ligand system,
Cyclic voltammograms of the complexes at Pt-electrode were
recorded in dry degassed CH2Cl2 containing 0.1 M (n-Bu4N)PF6 as
supporting electrolyte. Voltammetric data versus a silver electrode
are shown in Fig. 4a and c and Table 4. The E1/2 for ferrocene/ferro-
cenium couple under the experimental conditions was 0.4 V
l
(D
E = 65 mV) [49]. The complex [MoVIO2(dhsm)] (1a) showed an
irreversible reductive peak (Epc = ꢁ1.12 V) and another one for oxi-
dative response (Epa = ꢁ0.67 V), each peak of current height twice
that observed in the other complexes (1b–1d). This is assigned to
a metal center 2eꢁ process [3,5,29], MoVI/MoIV reduction and MoIV/
MoVI oxidation. Two irreversible one electron reductive responses
are found in molybdenum(VI) complexes (1b–1d) due to MoVI/
MoV and MoV/MoIV reductions. The complex [MoIVO(dhsm)] (1e)
which is characteristic of
a tentative dimeric structure (2c)
[39,47] and confirmed by IR data before, with a proposed square-
pyramidal geometry [47]. This is due to spin–spin coupling between
the two adjacent vanadium atoms, as the case for similar related
vanadium(IV) complexes [47,48].

300
A.M. Fayed et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 293–302
showed a high current anodic peak (Epa = +0.68 V), arising from
MoIV/MoVI oxidation [3]. For oxovanadium(IV) complexes (2a)
and (2b) an anodic oxidation peak has been observed which is
attributed to VIV/VV oxidation, while the complex (2c) shows elec-
tro inactive behavior.
Catalytic oxidation
Many oxoperoxo-molybdenum(VI) complexes are commonly
known to catalyze the oxidation of alcohols to aldehyde/ketones
[50], but dioxomolybdenum(VI) complexes are scarce for such
Fig. 4. Cyclic voltammogram with scan rate 50 mV sꢁ1 for 10ꢁ3 M of: (a) [MoO2(dhsm)] (1a) in CH3CN (b) [MoO2(dhsm)(EtOH)] (1b) in CH2Cl2 (c) [VO(dhsm)(bipy)] (2a) in
CH2Cl2.

A.M. Fayed et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 293–302
301
Table 5
selective oxidation of primary alcohol into the corresponding alde-
hyde under solvent free conditions.
Catalytic oxidation by molybdenum(VI)/(IV) and vanadium(IV) complexes.
Catalyst
(1b)
Substrate
Producta
Time
t-BuOOH
Turnover
H2O2
Supplementary data
Benzyl alcohol
Cinnamyl alcohol
Cyclohexanol
Benzyl alcohol
Cinnamyl alcohol
Cyclohexanol
Benzyl alcohol
Cinnamyl alcohol
Cyclohexanol
A
A
K
A
A
K
A
A
K
3
3
4
3
3
4
3
3
4
40
15
20
22
10
20
80
10
30
10
35
0
12
20
7
50
17
0
Crystallographic data for the structure analysis have been
deposited with the Cambridge Crystallographic Data Center, CCDC
No. 873349 for [MoO2(dhsm)(EtOH)]. Copy of information can be
obtained free of charge from The Director, CCDC, 12 Union Road,
Cambridge, CB21EZ, UK (fax: +44 1223 336 033; e-mail: depos-
it@ccd.com.ac.uk https://www.ccdc.cam.ac.uk.
(1e)
(2b)
a
A = corresponding aldehyde, K = corresponding ketone.
Acknowledgments
We thank Ministry of Higher Education for CIQAP project to
cover research equipment funds, and also National Research Centre
in Cairo for the X-ray crystallographic facility.
catalytic oxidation [17]. Oxovanadium(IV) complexes catalyzed
oxidations of several alcohols have been reported with high selec-
tivity but low turnovers [51,52]. We have investigated the use of t-
butyl hydroperoxide (t-BuOOH) and H2O2 as co-oxidants with the
present metal complexes (1b, 1e and 2b) as typical examples in the
catalytic oxidations of alcohols. Table 5 summarizes the results of
these experiments. Using t-BuOOH under solvent-free conditions
at 70 °C for 3–4 h, benzyl alcohol and cyclohexanol were oxidized.
Selectivity to benzaldehyde and cyclohexanone (turnovers, 80–10).
Unsaturated alcohol, e.g. cinnamyl alcohol is oxidized without
competing double bond attack. Under similar reaction conditions
with H2O2 as co-oxidant, the complexes were ineffective towards
cyclohexanol oxidation and lower turnovers (ca. 50–7) achieved
in oxidation of other alcohols. This reflects better catalytic oxida-
tions obtained with t-BuOOH than H2O2, due to more solubility
of alcohols and catalysts in the former co-oxidant. The oxovana-
dium(IV) complex (2b) shows higher turnovers compared to those
for molybdenum complexes (1b and 1e). Oxidation products ob-
tained under similar reaction conditions and in the absence of
these metal complexes. Oxidations of benzyl alcohol to the corre-
sponding benzoic acid with the systems of dioxomolybdenum(VI)
Schiff base complexes/H2O2 in THF at 90 °C for 24 h have achieved
modest turnovers (40–26) [17], while oxovanadium(IV) com-
plexes/t-BuOOH in dry toluene at RT (24–48 h) have oxidized
allylic alcohols to their corresponding aldehydes or ketones with
20 turnovers [18].
In the presence of excess peroxide, either molybdenum trioxide
with different donor ligands or oxovanadium(IV) are readily con-
verted to their corresponding oxoperoxo-molybdenum(VI) or
vanadium(V) species [50,53]. So, we suggest that oxidation by
molybdenum and vanadium catalysts in the presence of excess
H2O2 or t-BuOOH as co-oxidants proceeds via oxoperoxo molybde-
num or vanadium intermediates. Vanadium monoperoxo com-
plexes can function as a ‘‘catalytic pump’’ for generation of
hydroxyl radicals [54], which are very reactive and strong oxidants
and promote other radical chains, e.g. by abstracting H from an
organic substrate [55].
References
[1] N.R. Pramanik, S. Ghosh, T.K. Raychaudhuri, S.S. Chauduri, M.G.B. Drew, S.S.
Mandal, J. Coord. Chem. 60 (2007) 2177–2190.
[2] M.R. Maurya, A. Kumar, A.R. Bahat, A. Azam, C. Bader, D. Rehder, Inorg. Chem.
45 (2006) 1260–1269.
[3] N.R. Pramanik, S. Ghosh, T.K. Raychaudhuri, S. Ray, R.J. Butcher, S.S. Mandal,
Polyhedron 23 (2004) 1595–1603.
[4] M. Sutradhar, T.R. Barman, G. Mukherjee, M.G.B. Drew, Inorg. Chim. Acta 363
(2010) 3376–3383.
[5] M. Chakraborty, S. Roychowdhury, N.R. Pramanik, T.K. Raychaudhuri, T.K.
Mondal, S. Kundu, M.G. Drew, S. Gosh, S.S. Mandal, Polyhedron 50 (2013) 602–
611.
[6] M.B. Ferrari, F. Bisceglie, G.G. Fava, G. Pelosi, P. Tarasconi, R. Albertini, S. Pinelli,
J. Inorg. Biochem. 89 (2002) 36–44.
[7] I.H. Hall, B.J. Barnes, J.E. Roswell, K.A. Shaffer, S.E. Cho, D.X. West, A.M. Stark,
Pharmazie 56 (2001) 648–653.
[8] F.J. Hine, A.J. Taylor, C.D. Garner, Coord. Chem. Rev. 254 (2010) 1570–1579.
[9] R.C. Bray, S.P. Vincent, D.J. Lowe, R.A. Clegg, P.B. Garland, J. Biochem. 155
(1976) 201–203.
[10] D. Eierhoff, W.C. Tung, A. Hammerschmidt, B. Krebs, Inorg. Chim. Acta 362
(2009) 915–928.
[11] Z.M. Shoeili, D.M. Boghaei, M. Amini, M. Bagherzadeh, B. Notash, Inorg. Chem.
Commun. 27 (2013) 26–30.
[12] E. Kiss, K. Kawabe, A. Tamura, T. Jakusch, H. Sakurai, T. Kiss, J. Inorg. Biochem.
95 (2003) 69–76.
[13] A. Katoh, M. Yamaguchi, R. Saito, Y. Adachi, H. Sakurai, Chem. Lett. 30 (2004)
1274–1275.
[14] A.M. El-Hendawy, A.M. Fayed, M.R. Mostafa, Transition Met. Chem. 36 (2011)
351–361.
[15] S.A. Elsayed, A.M. El-Hendawy, S.I. Mostafa, I.S. Butler, Inorg. Chim. Acta 363
(2010) 2526–2532.
[16] S.A. Elsayed, A.M. El-Hendawy, S.I. Mostafa, B.J. Jean-Claude, M. Todorova, I.S.
Butler, Bioinorg. Chem. Appl. 149 (2010) 149–159.
[17] N.K. Ngan, K.M. Lo, C.S.R. Wong, Polyhedron 33 (2012) 235–251.
[18] W. Zeng, T.E. Ballard, C. Melander, Tetrahedron Lett. 47 (2006) 5923–5926.
[19] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C. Burla, G. Polidori,
M. Camalli, J. Appl. Cryst. 27 (1994) 435–436.
[20] S. Mackay, C. Gilmore, C.J. Edwards, N. Stewart, K. Shankland, maXus Computer
Program for the Solution and Refinement of Crystal Structures, Bruker Nonius,
the Netherlands, MacScience, Japan and the University of Glasgow, 1999.
[21] Z. Otwinowski, W. Minor, in: C.W. Carter Jr., R.M. Sweet (Eds.), Methods in
Enzymology, vol. 276, Academic Press, New York, 1997, pp. 307–326.
[22] M. Das, S.E. Livingstone, Inorg. Chim. Acta 19 (1976) 5–10.
[23] G.J.J. Chen, J.W. McDonald, W.E. Newton, Inorg. Chem. 15 (1976) 2612–2615.
[24] R.A. Rowe, M.M. Jones, Inorg. Synth. 5 (1957) 113–116.
[25] A.M. El-Hendawy, A.E. El-Kourashy, M.M. Shanab, Polyhedron 11 (1992) 523–
530.
Conclusion
[26] (a) N.R. Pramanik, S. Ghosh, T.K. Raychaudhuri, S.S. Mandal, J. Coord. Chem. 62
(2009) 3845–3852;
The Schiff base ligand derived from S-methyl dithiocarbazate
and 2,3-dihydroxybenzaldhyde has been used to prepare the new
cis-dioxomolybdenum(VI) and oxovanadium(IV) complexes in
high yields. The oxomolybdenum(IV) has been obtained from
dioxomolybdenium(VI) species by oxo abstraction with PPh3. The
redox properties have been studied by cyclic voltammetry. Analyt-
ical and spectroscopic data together with the X-ray crystal struc-
ture for one of the dioxomolybdenum(VI) complexes showed that
the Schiff base behaves as a dianionic ONS tridentate ligand in its
thiolate form. The complexes showed catalytic reactivity towards
(b) Z. Xiao, M.A. Bruck, J.H. Enemark, C.G. Young, A.G. Wedd, Inorg. Chem. 35
(1996) 7508–7515;
(c) L.J. Laughlin, C.G. Young, Inorg. Chem. 35 (1996) 1050–1058;
(d) S.A. Roberts, C.G. Young, W.E. Cleland, J.R.B. Ortega, J.H. Enemark, Inorg.
Chem. 27 (1988) 3044–3051;
(e) J.H. Enemark, J.J.A. Cooney, J.J. Wang, R.H. Holm, Chem. Rev. 104 (2004)
1175–1200.
[27] S.K. Dutta, D.B. McConville, W.I. Youngs, M. Chandhury, Inorg. Chem. 36 (1997)
2517–2522.
[28] M. Cindric, V. Vrdoljak, N. Strukan, B. Kamenar, Polyhedron 24 (2005) 369–
376.

302
A.M. Fayed et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 293–302
[29] C. Bustos, O. Burckhardt, R. Schrebler, D. Carrillo, A.M. Arif, A.H. Cowley, C.M.
Nunn, Inorg. Chem. 29 (1990) 3996–4001.
[42] M.R. Maurya, S. Khurana, W. Zhang, D. Rehder, Eur. J. Inorg. Chem. (2002)
1749–1760.
[30] S. Pacigova, R. Gyepes, J. Tatiersky, M. Sivak, Dalton Trans. (2008) 121–130
(and references therein).
[31] G. Desiraju, R. Steiner, The Weak Hydrogen Bond in Structural Chemistry and
Biology, Oxford University Press, Oxford, 1999.
[43] S.K. Dutta, E.R. Tiekink, M. Chandhury, Polyhedron 16 (1997) 1863–1871.
[44] I. Bernal, P.H. Rieger, Inorg. Chem. 2 (1963) 256–260.
[45] C.R. Cornman, J. Kampf, M.S. Lah, V.L. Pecoraro, Inorg. Chem. 31 (1992) 2035–
2043.
[32] R. Vargas, J. Garza, D.A. Dixon, B.P. Hay, J. Am. Chem. Soc. 122 (2000) 4750–
4755.
[33] W.P. Griffith, C.A. Pumphrey, T.A. Rainey, J. Chem. Soc. Dalton Trans. (1986)
1125–1128.
[34] A.M. El-Hendawy, W.P. Griffith, C.A. O’Mahoney, D.J. Williams, Polyhedron 8
(1989) 519–525.
[35] A.M. El-Hendawy, W.P. Griffith, C.A. Pumphrey, J. Chem. Soc. Dalton Trans.
(1988) 1817–1821.
[46] L.V. Boas, J.C. Pessoa, in: Sir G. Wilkinson (Ed.), Comprehensive Coordination
Chemistry, vol. 3, Pergamon Press, Oxford, 1987, p. 484 (and references
therein).
[47] S.N. Rao, D.D. Mishra, R.C. Maurya, N.N. Rao, Polyhedron 16 (1997) 1825–
1829.
[48] B.R. Havinale, I.B. Pujar, J. Inorg. Nucl. Chem. 43 (1981) 2689–2694.
[49] B. Mondal, M.G.B. Drew, T. Gosh, Inorg. Chim. Acta 362 (2009) 3303–3308.
[50] M. Amini, Coord. Chem. Rev. 257 (2013) 1093–1121.
[51] M. Bagherzadeh, M. Amini, J. Coord. Chem. 63 (2010) 3849–3858.
[52] J.A.L. da Silva, J.J.R. Frausto da Silva, A.J.L. Pombeiro, Coord. Chem. Rev. 255
(2011) 2232–2248.
[36] A.M. El-Hendawy, W.P. Griffith, Inorg. Chim. Acta 160 (1989) 67–70.
[37] S. Purohit, A.P. Koley, L.S. Prasad, P.T. Mansharan, S. Gosh, Inorg. Chem. 28
(1989) 3735–3742.
[38] V. Vardoljak, D. Milic, M. Cindric, D.M. Carlogovic, J. Pisk, M. Markovic, P.
Novac, Z. Anorg, Allg. Chem. 635 (2009) 1242–1248.
[39] N.A. Mangalam, M.R.P. Kurup, Spectrochim. Acta A71 (2009) 2040–2044.
[40] M. Chandhury, Inorg. Chem. 24 (1985) 3011–3017.
[41] H. Adams, C. Allott, M.N. Bancroft, M.J. Morris, J. Chem. Soc. Dalton Trans.
(1998) 2607–2610.
[53] M.R. Maurya, S. Khurana, W. Zhang, D. Rehder, J. Chem. Soc. Dalton Trans.
(2002) 3015–3023.
[54] G. Suss-Fink, S. Stanis, G.B. Las, G.V. Shulpin, G.V. Nizova, Appl. Organomet.
Chem. 14 (2000) 623–628.
[55] P.J. Figiel, J.M. Sobaczak, J. Catal. 263 (2009) 167–172.