Synthetic, characterization and catalytic studies of some coordination compounds derived from unsymmetrical quadridentate Schiff base ligand

Article abstract of DOI:10.1134/S1070363211110144

The stable complexes of VO(IV), Cr(III), Mn(III), Fe(III), MoO ₂(VI), and WO₂(VI), with an unsymmetrical tetradentate Schiff base ligand derived from 2-hydroxy-5-methylacetophenone, 2-hydroxy-5-chloroacetophenone and carbohydrazide were synthesized and characterized by the elemental analysis, UV-Vis and IR spectroscopy, magnetic measurements and thermal analysis. The VO(IV) and Mn(III) complexes were tested for the catalytic oxidation of styrene. The conversion of styrene increases with use of VO(IV) catalyst and decreases with use of Mn(III) catalyst.

Full text of DOI:10.1134/S1070363211110144

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 11, pp. 2304–2309. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © G.B. Pethe, A.R. Yaul, A.S. Aswar, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 11, pp. 1853–1858.
Synthetic, Characterization and Catalytic Studies
of Some Coordination Compounds
Derived from Unsymmetrical Quadridentate
Schiff Base Ligand
G. B. Pethe, A. R. Yaul, and A. S. Aswar
Department of Chemistry, St. Gadge Baba Amravati University, Amravati-444 602, M.S. India
e-mail: aswar2341@rediffmail.com
Received May 25, 2010
Abstract—The stable complexes of VO(IV), Cr(III), Mn(III), Fe(III), MoO2(VI), and WO2(VI), with an
unsymmetrical tetradentate Schiff base ligand derived from 2-hydroxy-5-methylacetophenone, 2-hydroxy-5-
chloroacetophenone and carbohydrazide were synthesized and characterized by the elemental analysis, UV-Vis
and IR spectroscopy, magnetic measurements and thermal analysis. The VO(IV) and Mn(III) complexes were
tested for the catalytic oxidation of styrene. The conversion of styrene increases with use of VO(IV) catalyst
and decreases with use of Mn(III) catalyst.
DOI: 10.1134/S1070363211110144
Schiff bases are an important class of ligands in
coordination chemistry due to their synthetic
flexibility, selectivity and sensitivity towards a variety
of metal atoms [1]. They are found useful in catalysis,
in medicine as antibiotics and anti-inflammatory
agents [2, 3]. The metal complexes of Schiff bases
derived from heterocyclic compounds have been the
centres of attraction for many researches in recent
years. Tetradentate Schiff bases are well known for
their coordination with various metal ions to give the
stable compounds. Several symmetrical Schiff bases
and their complexes have been studied while
comparatively unsymmetrical tetradentate Schiff base
complexes were less studied then symmetrical ones.
These metal complexes find wide spread applications
as heterogeneous and homogeneous catalysts for the
epoxidation of styrene [4].
The aim of the present work is to synthesize and
characterize unsymmetrical Schiff base ligand derived
from the 2-hydroxy 4-methylacetophenone, 2-
hydroxy-4-chloroacetophenone, and carbohydrazide
and its complexes.
The reaction of 2-hydroxy-5-metylacetophenone, 2-
hydroxy-5-chloroacetophenone with carbohydrazide in
hot DMF–ethanol yields the Schiff base (H2L). The
reaction of H2L in DMF and appropriate metal salts in
ethanol yields the complexes.
OH
HO
H
N
H
N
+
+
H2N
NH2
O
O
H3C
Cl
O
CH3
CH3
H3C
Cl
H2O
OH
HO
NH NH
H3C
N
CH3
N
O
2304

SYNTHETIC, CHARACTERIZATION AND CATALYTIC STUDIES
Table 1. Analytical and physical data of the ligand and its complexes
2305
Found, %
Calculated, %
М,
σ, Ω–1 cm–1
Compound
Еа, eV
g mol–1
at 373 K
C
H
N
M
–
C
H
N
M
–
H2L
[VOL]
374.82
439.74
57.32
5.02
14.12
57.68
5.11
14.95
1.68×10–11 0.9961
48.88
43.18
48.83
43.10
42.98
34.99
3.79
4.19
4.08
4.19
3.11
2.55
12.10
10.87
11.21
10.93
10.91
10.69
11.14
9.92
49.16
43.56
49.35
43.23
43.17
35.29
3.90
4.27
4.14
4.23
3.42
2.65
12.74
11.29
11.51
11.20
11.19
10.83
11.58
10.48
11.51
11.17
19.16
28.43
3.44×10–6
6.85×10–8
2.31×10–5
0.8917
0.8325
0.7288
[CrL(H2O)Cl]·H2O 496.28
[MnLOAc] 486.78
[FeL(H2O)Cl]·H2O 500.13
11.03
11.08
18.91
28.17
4.32×10–10 0.6658
[MoO2L]
500.74
646.72
2.73×10–9
4.87×10–7
0.6029
0.5417
[WO2LNCS]
Table 2. The IR data (ν, cm–1) of the ligand and its complexes
O–H
Compound
N–H
3270
C=N
1633
C=O
1702
C–O
N–N
M–O
–
M–N
–
H2O
phenol
2982
H2L
1246
1265
1260
1263
1260
1257
1269
995
1012
1024
1018
1027
1013
1005
–
–
[VOL]
–
–
–
–
–
–
3284
3263
3261
3278
3288
3268
1628
1620
1609
1591
1618
1597
1681
1685
1720
1693
1683
1698
549
511
535
509
552
527
443
455
435
439
424
412
[CrL(H2O)Cl]·H2O
[Mn LOAc]
3392, 1614, 892,732
–
[FeL(H2O)Cl]·H2O
[MoO2L]
3361, 1609, 838, 751
–
–
[WO2LNCS]
The analytical data for the ligand and complexes
are given in Table 1. All the complexes are coloured
solids, non-hygroscopic, air stable and insoluble in
common organic solvents, but sparingly soluble in
DMSO. The elemental analysis shows 1:1 metal to
ligand stoichiometry for all the complexes.
ligand and which get shifted to higher region 1257–
1269 cm–1 in complexes, also suggest the coordination
of ligand through phenolic oxygen via deprotonation
[6]. The IR spectrum of ligand shows a strong band at
1633 cm–1 due to the C=N stretching vibrations. On
complexation this shows negative shift by 5–40 cm–1,
which indicates the coordination of azomethyne
nitrogen atom to the metal ions in the complexes [7–9].
The ν(N–H) and ν(C=O) bands of the ligand at 3270
and 1702 cm–1 do not change their position after
complexation, indicating that ligand exist in keto-form
in free state as well as in all the complexes [10]. Non
involvement of amido oxygen in coordination of the
acetate group in Mn(III) complexes is confirmed due
to the difference between the two bands (Δν > 193 cm–1)
appeared at 1619 and 1426 cm–1, belonging to
νas(OCO) and νs(OCO). A band at 671 cm–1 [δ(O–C–O)]
confirms a monodendate ligand formation [11, 12].
IR spectroscopy. The IR spectra of the complexes
(Table 2) were interpreted by comparing the spectra
with that of the free ligand. The IR spectrum of the
free ligand exhibits a band at 2982 cm–1 due to the
intramolecular hydrogen bonded OH-group. The
disappearance of this band upon complexation
indicates the breakdown of the H-bonding followed by
the deprotonation of phenolic OH-group and the
subsequent involvement of phenolic oxygen atoms
towards coordination [5]. The phenolic stretching
vibrations bands ν(C–O) appear at 1246 cm–1 in the
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2306
PETHE et al.
Table 3. Thermal decomposition, magnetic properties and electronic spectral data of the ligand and its complexes
Еа,
Compound
Т1/2, °C
μef, BM
λ, nm
kJ mol–1
H2L
292
348
31.02
–
–
[VOL]
48.31
1.58
920 [dxy(b2)→dxydyz(e*)], 516 [dxy(b2)→dx2–y2(b1*)], 382 [dxy(b2)→dz2(a1*)]
[CrL(H2O)Cl]·H2O
[Mn LOAc]
412
427
366
409
420
37.73
50.99
49.92
31.01
34.45
3.81
4.87
618 [4A2g(F)→4T2g(F)], 471 [4A2g(F)→4T1g(F)], 270 [4A2g(F)→4T1g(P)]
742 (5B1→5B2), 609 (5B1→5A1), 511 (5B1→5E), 352 (ligand–metal transition)
[FeL(H2O)Cl]·H2O
[MoO2L]
5.69
760 (6A1g→4T1g), 639 (6A1g→4T2g), 435 (6A1g→4Eg)
Diamagnetic
''
–
–
[WO2LNCS]
The coordination of water in Cr(III) and Fe(III)
complexes is indicated by the appearance of the bands
at 3392–3361, 1609–1614, 838–892 and 732–751 cm–1
assignable to γ(O–H) , δ(O–H), ρr(H2O), and ρw(H2O)
vibrations respectively [13]. The MoO2(VI) and WO2
(VI) complexes show new bands at 944 and 930 cm–1
belonging to νas(O=Mo=O) and νas(O=W=O) vibra-
tions [14]. In the spectrum of WO2(VI) complex there
is the bands at 2075 (CN), 778 (CS), and 487 cm–1
(NCS) suggesting that the thiocyanate group act as a
ligand, in which bonding through nitrogen takes place
[15].
Magnetic properties. The molar magnetic
susceptibility of the VO(IV), Cr(III), Mn(III), and
Fe(III) complexes at room temperature is given in
Table 3. The μef value of VO(IV), Cr(III), Mn(III), and
Fe(III) complexes at room temperature is found to be
1.58, 3.81, 4.87 and 5.69 B.M., respectively. These
values support to those reported earlier. The MoO2(VI)
and WO2(VI) complexes are diamagnetic as
considered with their electronic configuration.
Electrical conductivity. The solid state electrical
conductivity of the ligand and its complexes is given in
Table 1. The solid state electrical conductivity was
measured in compressed pellet from room temperature
to 403 K. The solid state electrical conductivity
increases with increasing the temperature [20]. The
electrical conductivity (σ) varies experimentally with
the absolute temperature according to the relation σ =
σ0 exp (Ea/kT), where σ0 is constant, Ea is the
activation energy of electrical conduction, T is the
absolute temperature and k is the Boltzmann constant.
The dependence logσ–1/T was found to be linear over
the studied temperature range indicating the
semiconducting behaviour for the obtained complexes
[21]. The values of electrical conductivity lies in the
range of 1.68×10–11–2.31×10–5 eV, in which ac-
cordance the obtained complexes can be arranged as
follows: H2L < Fe(III) < MoO2(VI) < Cr(III) <
WO2(VI) < VO(IV) < Mn(III).
Electronic Spectra. The electronic spectral data for
the obtained complexes are given in Table 3. The
electronic spectrum of VO(IV) complex contains
absorption bands at 920, 516 and 382 nm correspond-
ing to square pyramidal geometry [16]. These bands
may be assigned to dxy(b2) → dxydyz(e*), dxy(b2) →
d
x2–y2(b1*) and dxy(b2)
→
dz2(a1*) transitions
respectively. The Cr(III) complex shows absorption
band at 618, 471 and 270 nm owing to 4A2g(F) → 4T2g (F),
4
4
4
4A2g(F) → T1g(F), and A2g(F) → T1g(P) transitions
indicating an octahedral geometry of the Cr(III) ion
[17]. The spectrum of the Mn(III) complex contains
the absorption bands at 742, 609, 511 and 352 nm
originating from 5B1 → B2, B1 → A1, and B1 → E
and LMCT transitions, which corresponds to the
square pyramidal geometry of the complex [18]. In the
spectrum of the Fe(III) complex there are the
absorption bands at 760, 639, and 435 nm due to
5
5
5
5
5
Thermogravimetric study. In order to know the
presence of water molecules and decomposition
pattern of the ligand and its complexes TG analysis
was carried out. The thermogram reveals three stage
6A1g → T1g, A1g → T2g, and A1g → Eg transitions,
respectively, indicating the octahedral geometry for the
complex [19].
4
6
4
6
4
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SYNTHETIC, CHARACTERIZATION AND CATALYTIC STUDIES
2307
2θ, deg
Fig. 1. X-ray Diffraction Spectrum of the VO(IV) complex.
decomposition pattern for Cr(III) and Fe(III)
complexes and two stage for VO(IV), MoO2(VI), and
WO2(VI) complexes. The TG curve of Cr(III) and
Fe(III) complexes elimination of an water molecule
takes place between 70–120°C, indicating the presence
of lattice water molecule, and 145–225°C, indicating
the presence of an coordinated water molecule [22].
The Mn(III) complexes is almost stable up to 200°C
and then after the thermogram shows gradual weight
loss up to ~280°C corresponding to loss of one acetate
group. The MoO2(VI) and WO2 complexes are almost
stable up to 160°C indicating the absence of lattice or
coordinated water molecule. The thermogram of the
WO2 complex shows weight loss in the range of 175–
225°C, which corresponds to loss of one thiocyanate
group [15]. The half decomposition temperature and
activation energy values were calculated by the
Broido’s method and are given in Table 3 [23]. The
final stage ends with aerial oxidation of the complexes
that includes the decomposition of organic part with
increasing temperature and formation of the stable
metal oxides.
Time, h
Fig. 2. Effect of [VOL] catalyst on styrene conversion: (1)
0.020, (2) 0.030, and (3) 0.040 g.
benzaldehyde, benzoic acid, phenyl acetic acid and 1-
phenylethan-1,2-diol and other side products [24]. In
the present work the oxidation of styrene catalysed by
the VO(IV) and Mn(III) complexes was carried out.
The catalytic activity of these complexes was checked
as a function of the amount of catalyst and H2O2 used
as oxidant. The amount of catalyst is used like 0.020,
0.030 and 0.040 g, respectively; amount of styrene and
H2O2 (1:2) was fixed in the presence of acetonitrile at
80°C. The conversion of styrene using the VO(IV) and
Mn(III) complexes was 25–36 and 42–45%,
respectively, as shown in Figs 2, 3. The styrene
conversion increases with increase in amount of
catalyst in presence of fixed amount of H2O2 and
styrene in case of the VO(IV) complex catalyst, but it
decreases as the amount of Mn(III) complex catalyst
increases.
Powder XRD study of the VO(IV) complex. The X-
ray diffraction spectrum of the VO(IV) complex is
shown in Fig. 1. The X-ray diffraction spectrum of the
VO(IV) complex exhibits sharp peaks indicating the
crystalline nature of the complex. The XRD spectrum
was recorded with CuKα-irradiation in the range 2θ 4°–
35° with λ 1.5406 Å. All the main peaks were indexed
by using the appropriate methodology and PowdMult,
Version 2.3 program package. The unit cell lattice
parameter of the VO(IV) complex are: a 7.5711, b
19.6694, c 6.4079 Å; α 106.665°, β 101.406°,
γ 98.264°, V 875.48 Å3; triclinic system.
EXPERIMENTAL
All the chemicals and solvents were of analytical
grade and purchased from commercial sources.
Vanadyl sulphate petahydrate, chromium chloride
hexahydrate, anhydrous ferric chloride, dioxotungsten
tetrathiocyanate and carbohydrazide were of Rankem
and SD fine chemicals and use as supplied. Mn(OAc)3·
2H2O was prepared by the oxidation of Mn(OAc)2·
4H2O using Christensen’s method [25]. Bis(acetyl-
Catalytic activity of the complexes obtained in
styrene oxidation. In generally, the catalytic oxidation
of styrene gives the products like styrene oxide,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 11 2011

2308
PETHE et al.
chromatography was recorded on a Shimandzu 14B
gas chromatograph with SE-30 column and FID
detector (School of Chemical Science, Devi Ahilya
University, Indore).
Synthesis of N''-[1-(5-chloro-2-hydroxyphenyl)
ethylidene]-N'''-[(1-(2-hydroxy-5-methylphenyl)-
ethylidene]carbonohydrazide (H2L). To a mixture of
ethanolic solutions of 2-hydroxy-5-methylaceto-
phenone (2.4 g, 0.016 M) and 2-hydroxy-5-chloro-
acetophenone (2.72 g, 0.016 M.) was added dropwise a
hot ethanol–DMF solution (60:40 v/v, 25 ml) of
carbohydrazide (1.44 g., 0.016 M.) with stirring. The
mixture was refluxed on sand bath for about 7 h. The
solvent was then partially evaporated under air and
yellow coloured compound formed was filtered off,
washed with ethanol, petroleum ether and then dried in
vacuum. Yield 72%, mp 292ºC.
1H NMR spectrum, δ, ppm: 12.78 s (1H, OH,
phenolic), 12.48 s (1H, OH, phenolic), 11.16–11.41 s
(2H, NH-imino), 2.21 s (6H, CH3), 2.15 s (3H, Ph–
CH3), 6.77–7.94 m (6H, HPh).
Time, h
Fig. 3. Effect of [MnLOAc] catalyst on styrene conversion:
(1) 0.020, (2) 0.030, and (3) 0.040 g.
Synthesis of VO(IV), Cr(III), Mn(III), Fe(III),
and MoO2 complexes. To a hot DMF solution (25 ml)
of the organic ligand (1.0 mmol) was added a hot
ethanolic solution of the appropriate metal salt
(1.0 mmol) solution under continuous stirring. The
resulting mixture was refluxed for 4–5 h. On cooling to
room temperature the precipitate solid metal com-
plexes was filtered off, washed thoroughly with
ethanol, DMF and petroleum ether to remove the
unreacted ligand and metal salts. Finally all the
complexes were dried under vacuum at room
temperature. Yield 65–70%.
acetonato)dioxomolybdenum(VI) was synthesized ac-
cording to the literature method [26].
The elemental analysis was performed on a Carlo
Erba 1108 analyser in micro analytical laboratory
(CDRI, Lucknow). The IR spectra were recorded on a
Perkin-Elmer 597 spectrophotometer from KBr pellets
1
(SAIF Punjab University, Chandigarh). The H NMR
spectrum of ligand was obtained on a Bruker Auance-
II 400 NMR spectrophotometer in DMSO-d6 (SAIF
Punjab University, Chandigarh). The electronic spectra
of the complexes were recorded on Varian SE UV–
NIR spectrophotometer using MgO as reference. The
magnetic susceptibility was measured at room
temperature by Gouy’s method using Hg[CO(NCS)4]
as a calibrant and the diamagnetic corrections were
made using Pascal’s constants. The solid state d.c.
electrical conductivity of compounds was measured by
Zentech Electrometer in their compressed pellet form
over 313–403 K temperature range. The TG analysis
of the complexes was carried out on a Perkin Elmer
TG-2 thermobalance in ambient air with a heating rate
of 10°C per minute. Metal contents of the complexes
were analysed gravimetrically after decomposing the
complexes with a mixture of HClO4, H2SO4 and HNO3
and then igniting to metal oxide. The XRD
measurement of the complexes was recorded with a
Bruker AXS, D8-Avance instrument equipped with θ/θ
gonimeter and a Lynv Eye detector. The gas
Synthesis of the WO2 complex. To a mixture of
aqueous solutions of sodium tungstate dihydrate (1.2 g,
0.00363 mol) and ammonium thiocyanate (2.9 g,
0.038 mol) at room temperature was added 7.5 ml of
11 M HCl. The resulting yellow solution was cooled in
an ice bath and DMF solution (10 ml) of ligand
(0.00363 M.) was added to it. The precipitate formed
was filtered off, washed 3–4 times with water
containing few drops of HCl and dried in vacuum.
Catalytic oxidation of styrene. The catalytic
reactions were carried out in 250 ml reaction flask
fitted with water condenser. To a mixture of styrene
(1.04 g, 10 mmol) and 30% H2O2 (2.27 g, 20 mmol) in
10 ml of MeCN was added and the catalyst tested
(0.020 g) and the reaction mixture was heated in an oil
bath with continuous stirring at 80°C for 8 h. The
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SYNTHETIC, CHARACTERIZATION AND CATALYTIC STUDIES
2309
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