Exploring microwave synthesis for co-ordination: Synthesis, spectral characterization and comparative study of transition metal complexes with binuclear core derived from 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one

Article abstract of DOI:10.1080/00958970903305437

A series of transition metal complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Hg(II), and Sn(II) has been synthesized from the Schiff base (L) derived from 4-aminoantipyrine and 4-fluoro-benzaldehyde using traditional synthetic methodology and microwa

Full text of DOI:10.1080/00958970903305437

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Exploring microwave synthesis for
co-ordination: synthesis, spectral
characterization and comparative
study of transition metal complexes
with binuclear core derived from
4-amino-2,3-dimethyl-1-phenyl-3-
pyrazolin-5-one
Parvez Ali a , P. Ramakanth a & Jyotsna Meshram a
a Department of Chemistry, Rashtrasant Tukadoji Maharaj Nagpur
University, Nagpur 440033, India
Version of record first published: 05 Oct 2009.
To cite this article: Parvez Ali, P. Ramakanth & Jyotsna Meshram (2010): Exploring microwave
synthesis for co-ordination: synthesis, spectral characterization and comparative study of transition
metal complexes with binuclear core derived from 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-
one, Journal of Coordination Chemistry, 63:2, 323-329
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Journal of Coordination Chemistry
Vol. 63, No. 2, 20 January 2010, 323–329
Exploring microwave synthesis for co-ordination: synthesis,
spectral characterization and comparative study of
transition metal complexes with binuclear core derived from
4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one
PARVEZ ALI, P. RAMAKANTH and JYOTSNA MESHRAM*
Department of Chemistry, Rashtrasant Tukadoji Maharaj
Nagpur University, Nagpur 440033, India
(Received 16 April 2009; in final form 16 July 2009)
A series of transition metal complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Hg(II), and
Sn(II) has been synthesized from the Schiff base (L) derived from 4-aminoantipyrine and
4-fluoro-benzaldehyde using traditional synthetic methodology and microwave-induced
organic reaction enhancement (MORE) technique. A benign, simple, and versatile route to a
Schiff-base ligand and its metal complexes has been explored. Neat reactants were subjected to
microwave irradiation giving the required products more quickly and in better yield compared
to the classical methodology. Structural features were obtained from elemental analysis, molar
conductivity, 1H-NMR, mass, UV-Vis, and FTIR spectroscopy and X-ray diffraction. The data
show that these complexes are ML2. The MORE method for synthesis is easy, convenient, and
ecofriendly as compared to the traditional synthetic method.
Keywords: Ligand; Complexes; MORE; Characterization
1. Introduction
Microwave irradiation on homogenous reaction mixtures and solid surfaces has
emerged as a useful methodology for achieving better yields of product, significant
reduction in reaction time, and reduction or elimination of environmentally detrimental
solvents. For these reasons, microwave-assisted synthesis has become a rapidly growing
field of study especially for various organic transformations [1]. Acceleration of
reactions under microwave radiation can result from material–wave interactions leading
to thermal effects [2, 3] or nonthermal effects [2]. The salient features of these high-yield
protocols deal with enhanced reaction rates and ease of manipulation [4], advantageous
for environmental reasons [5].
Schiff bases containing an azomethine group (–CH¼N–) are formed by the
condensation of a primary amine with a carbonyl compound. These bases are active,
well designed and stable under a variety of oxidative and reductive conditions [6]. The
Schiff base of 4-aminoantipyrine having a pyrazoline skeleton and its complexes have a
*Corresponding author. Email: drjsmeshram@rediffmail.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958970903305437

324
P. Ali et al.
variety of applications in biological, clinical, analytical, and pharmacological areas
[7–9]. Coordination chemistry of pyrazoline has also received attention, primarily due
to biological implications. Much work has been done [10–14] on the complexation of
pyrazoline skeleton with iron, cobalt, nickel, and copper.
Studies of Schiff bases used in chemotherapy are now attracting the attention of
biochemists [15, 16]; some drugs showed increased activity when administered as metal
complexes rather than as organic compounds [17, 18].
Traditionally, Schiff bases are prepared by refluxing mixtures of the amine and the
carbonyl compound in an organic solvent, for example, ethanol or methanol [19] and
metal complexes by refluxing Schiff bases and metal salt in ethanol or methanol for
several hours. Herein, benign, simple, cost-effective, and versatile routes to a Schiff base
and its metal complexes are demonstrated. We investigate the synthesis, characteriza-
tion, and comparison of the Schiff base derived from 4-aminoantipyrine as shown in
figure 1 and its complexes by traditional and microwave-induced organic reaction
enhancement (MORE) synthesis. In general, the reactions are very clean, without any
side product. In fact, the crude products obtained are of high purity with remarkable
yields and do not require chromatographic separation.
2. Results and discussion
The Schiff base 1-(2-furyl)-3-(4-aminophenyl)-2-propene-1-one (FAPPO) was prepared
by the condensation of 4-fluoro benzaldehyde and 4-aminoantipyrine in ethanol
classically and without using solvent ethanol under MORE technique as shown in
scheme 1. The transition metal complexes were then synthesized by the reaction of
N
C
H
F
N
O
N
Figure 1. Ligand (FAPPO).
H
NH2
O
C
N
F
EtOH, Reflux
N
OHC
F
N
O
N
30 min
N
or
MWI (200 W)
5 s
(I)
(II)
(III)
Scheme 1. Ligand synthesis.

Microwave synthesis
325
appropriate metal(II) salts with ligand traditionally and by MORE as shown in
scheme 2. The newly synthesized compounds were characterized by elemental analysis,
1H-NMR, mass, UV-Vis and FTIR spectroscopy and X-ray diffraction studies. The
data show that these complexes, ML2, are air-stable, nonhygroscopic, colored solids,
insoluble in water, and common organic solvents (alcohol, ethyl acetate, hexane, ether,
and toluene) and soluble in dimethyl sulfoxide (DMSO) and dimethylformamide
(DMF). Physical characterization and comparative yield data of ligand and complexes
together with some physical properties are summarized in table 1. It is clear from the
data that the MORE technique for the synthesis of the complexes is high yielding, easy,
convenient, and ecofriendly as compared with the traditional method.
2.1. Mass spectra
The mass spectra of the ligand (FAPPO) and its metal complexes recorded at room
temperature were used to compare their stoichiometry composition. The Schiff base
showed a molecular ion peak at 309. The molecular ion peak for the nickel complex
observed at m/z 676 confirms the stoichiometry of metal chelates as ML2 type, also
supported by mass spectra of other complexes.
F
H
N
C
F
HC
N
N
O
EtOH, Reflux
5 hrs.
N
N
O
N
M
M(OAc)2
(IV)
N
N
O
or
N
CH
EtOH, MWI
600 W 1–2 min
(III)
(V)
F
M = Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Hg(II), and Sn(II)
Scheme 2. Complex synthesis.
Table 1. Physical characterization and comparative yield of ligand and complexes.
TM
MT
Compound
Molecular formula
Color
M.P
Time (h)
% Yield
Time (s)
% Yield
FAPPO
C18H16FN3O
Orange
Orange
Red
Orange
Green
Orange
Yellow
Yellow
120
4250
4250
4250
4250
4250
4250
4250
1.0
5.0
5.0
5.5
5.0
5.0
5.0
5.5
85
80
83
81
76
83
85
78
5.0
15.0
25.0
18.0
20.0
25.0
35.0
25.0
95
90
95
92
90
94
95
88
Zn(FAPPO)2
Co(FAPPO)2
Cu(FAPPO)2
Ni(FAPPO)2
Hg(FAPPO)2
Sn(FAPPO)2
Mn(FAPPO)2
C36H32F2N6ZnO2
C36H32F2N6CoO2
C36H32F2N6CuO2
C36H32F2N6NiO2
C36H32F2N6HgO2
C36H32F2N6SnO2
C36H32F2N6MnO2

326
P. Ali et al.
Table 2. Infrared spectral data (cmꢀ1) of ligand and complexes.
Compound
(C¼O) pyrazolone
(C¼N) azomethine
M–O
M–N
FAPPO
1650
1602
1600
1600
1600
1600
1600
1602
1590
1550
1552
1565
1562
1550
1550
1552
–
–
Zn(FAPPO)2
Co(FAPPO)2
Cu(FAPPO)2
Ni(FAPPO)2
Hg(FAPPO)2
Sn(FAPPO)2
Mn(FAPPO)2
455
450
455
472
460
465
445
392
382
390
365
360
365
350
2.2. IR spectra
The IR spectra provide valuable information regarding the nature of functional group
attached to the metal (table 2). Infrared absorptions of FAPPO have been assigned by
comparison of its spectra with those of the pyrazole ring system [20], the
monosubstituted benzene ring system [21], antipyrine, and 4-aminoantipyrine [22, 23],
substituted 4-aminoantipyrine [24] and other Schiff bases of 4-aminoantipyrine [25, 26].
The infrared spectra of all the complexes show a considerable negative shift in carbonyl
(pyrazolone) absorption (C¼O) 45–50 cmꢀ1, indicating coordination through the
oxygen. Another important band at 1590–1550 cmꢀ1 attributed to (C¼N) mode [27, 28]
is shifted to lower frequencies in the spectra of the complexes (1570–1520 cmꢀ1
)
indicating –C¼N coordination to the metal. Strong bands at 1510–1490 cmꢀ1 assigned
to ring stretching of the five-membered ring and several other absorptions associated
with C–H out-of-plane deformation modes at 920–720 cmꢀ1 undergo a slight positive
shift due to decrease in electron density on the aromatic ring on complexation. Bands in
the 460–360 cmꢀ1 range are assigned to (M–O) and (M–N) modes (table 2).
2.3. 1H-NMR spectra
1
The H-NMR spectrum of the ligand recorded in CDCl3 are listed in section 3 and a
table in ‘‘Supplementary material’’.
2.4. UV-Vis spectra
The UV-Vis spectra of FAPPO and complexes were recorded at room temperature
in DMF. The electronic spectral data of ligand and complexes are given in
‘‘Supplementary material’’. The spectrum of FAPPO exhibits three main peaks at
370, 325, and 270 nm. The first and second peaks are attributed to aromatic ꢀ–ꢀ* and
imino ꢀ–ꢀ* transitions, respectively. In the complexes blue-shift is observed in the
bands indicating coordination of the imino nitrogen to metal. Further d–d transition of
the complexes showed a broad band centered at 550–600 nm suggesting an approximate
square planar geometry of the ligand around the metal ion. In the Ni-complex the main
1
1
peaks are at 395, 340, 255, and 535 nm due to d–d transition assigned to A1g ! B1g
1
1
and A1g ! B2g characteristic of square planar complexes.

Microwave synthesis
n+
327
F
CH
N
N
O
.n (CH3COO)–
N
M
N
N
O
N
CH
F
Figure 2. Proposed structure of complexes, where M ¼ Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Hg(II),
and Sn(II).
2.5. Molar conductivities of the complexes
Conductivity measurements in DMF for 10ꢀ3 M solution, table 3, show that the
complexes are electrolytes. Thus, CH3COOꢀ is present and completes the coordination
sphere. On the basis of physical and spectral data, the structure in figure 2 is proposed
for the complexes.
2.6. X-ray diffraction studies
The X-ray diffractograms of FAPPO and its metal complexes support that FAPPO has
higher crystallinity than its complexes.
3. Experimental
Reagents such as 4-aminoantipyrine, 4-fluoro benzaldehyde, and various metal(II)
acetates from Merck (USA) were used without purification. Anhydrous grade ethanol
and DMF were purified according to standard procedures. FTIR spectra were recorded
using KBr pellets on a Shimadzu spectrophotometer from 400 to 4000 cmꢀ1. A Perkin–
Elmer Lambda 7 (UV-Vis) spectrophotometer was used to determine electronic spectra
from 200 to 800 nm in DMSO. 1H-NMR spectra of the Schiff base and metal complexes
were recorded in DMSO-d6 using a Varian XL-200 NMR spectrophotometer with
tetramethylsilane as an internal standard. Mass spectra were recorded on a Varian
MAT CH-5 spectrometer. Elemental analyses were carried out using a Perkin–Elmer,
CHNS/O elemental analyzer model 2400. X-ray diffraction data were collected on PAN
analytical Xpert-pro.
3.1. Synthesis of the Schiff base ligand 4-(4-fluorobenzylidineamino)-1,2-dihydro-2,
3-dimethyl-1-phenylpyrazol-5-one by classical method
Schiff base was prepared from the reaction of 4-aminoantipyrine and 4-fluorobenzal-
dehyde using a standard condensation protocol [22]. In the process, ethanol solution of

328
P. Ali et al.
4-fluorobenzaldehyde 1.0 mm was added to the well-stirred solution of 4-aminoanti-
pyrine 1.0 mm in ethanol. The reaction mixture thus obtained was refluxed for 30 min.
The resulting reaction mass was allowed to attain room temperature. The yellow
crystalline solid obtained was then filtered and washed with cold ethanol. It was dried
and recrystallization was afforded by methanol.
3.2. Synthesis of the Schiff base ligand 4-(4-fluorobenzylidineamino)-1,2-dihydro-2,
3-dimethyl-1-phenylpyrazol-5-one by MORE method
4-(4-Fluorobenzylidineamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one
was
obtained by the condensation of 1.0 mm of 4-aminoantipyrine and 1.0 mm of
4-fluorobenzaldehyde without solvent. In a typical preparation, the mixture of amine
and 4-fluorobenzaldehyde were taken in a flask capped with a funnel, placed in a
microwave oven and irradiated at 200 W for 5 s. The reaction was monitored by TLC.
After completion of the reaction, the reaction mixture was allowed to attain room
temperature. After cooling, the resulting solid was crushed, washed with cold ethanol,
filtered, and dried under vacuum to give the crude product which was recrystallized
using hot methanol.
3.3. Synthesis of metal complexes [M (FAPPO)2] by classical method
Metal(II) complexes were prepared by addition of 1 mm of hot ethanol solution of
Zn(CH3COO)2 Á 2H2O, Cu(CH3COO)2 Á H2O, Hg(CH3COO)2, Mn(CH3COO)2,
Sn(CH3COO)2, Ni(CH3COO)2 Á 4H2O, or Co(CH3COO)2 Á H2O into a hot ethanolic
solution of 1 mmol of FAPPO. The mixture was then refluxed for about 5 h. The
precipitated solids were filtered from the hot ethanol reaction mixture, washed with hot
ethanol and then with diethyl ether, followed by drying in an oven.
3.4. Synthesis of metal complexes [M (FAPPO)2] by MORE method
Slurry of ligand (FAPPO) was prepared in aqueous ethanol. To this, a solution of metal
acetates in ethanol was added. The resulting mixture was irradiated in a microwave
oven for 1.0–2.0 min at medium power level (600 W) maintaining the occasional
shaking. The hot reaction mixture was filtered, washed with hot ethanol and ether,
followed by drying in an oven.
4. Conclusion
Coordination chemistry of a Schiff base obtained from the reaction of 4-aminoanti-
pyrine and 4-fluoro benzaldehyde with Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Hg(II),
and Sn(II) is described by traditional and MORE methods. The observed yields and
improvement in reaction rates for this greener approach is attributed to the reaction
conditions coupled with the use of microwave radiation. MORE method for the

Microwave synthesis
329
synthesis of complexes is convenient, high yielding, and ecofriendly as compared to the
traditional method.
Acknowledgement
Financial support from University Grant Commission, New Delhi, is highly
acknowledged.
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