Spectral and thermal characterization of 3-acetyl-5-azophenyl-4-hydroxy-6- methyl-pyran-2-one and its metal complexes

Article abstract of DOI:10.1016/j.saa.2013.04.046

Five chelates of 3-acetyl-5-azophenyl-4-hydroxy-6-methyl-pyran-2-one (phenylazo dehydroacetic acid) with Cr(III), Fe(III), Ni(II), Cu(II) and Zn(II) have been synthesized and characterized by elemental analysis, magnetic susceptibility measurements, elect

Full text of DOI:10.1016/j.saa.2013.04.046

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 276–279
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Spectral and thermal characterization of 3-acetyl-5-azophenyl-
4-hydroxy-6-methyl-pyran-2-one and its metal complexes
b
Susannah Seth a, , K.K. Aravindakshan
⇑
a P.G. and Research Department of Chemistry, Malabar Christian College, Kozhikode 673 001, Kerala, India
b Department of Chemistry, University of Calicut, Kozhikode 673 635, Kerala, India
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
ꢀ
ꢀ
ꢀ
ꢀ
A novel diazo-coupled compound
with phenylazo group at a rather
unusual position.
The synthesized compound was
found to be acting as a potential
ligand.
Five chelates of phenylazo
dehydroacetic acid were synthesized
and characterized.
Analytical, spectral and thermal data
confirm the structure of the
compounds.
a r t i c l e i n f o
a b s t r a c t
Article history:
Five chelates of 3-acetyl-5-azophenyl-4-hydroxy-6-methyl-pyran-2-one (phenylazo dehydroacetic acid)
with Cr(III), Fe(III), Ni(II), Cu(II) and Zn(II) have been synthesized and characterized by elemental analysis,
magnetic susceptibility measurements, electronic, 1H NMR, FAB mass, IR-spectral and thermal (TG/DTG)
analytical techniques. In the present work it has been found that oxygen of the deprotonated AOH group
and one of the azo-nitrogens of the ligand take part in coordination. The Cr(III), Fe(III) and Ni(II) com-
plexes were found to be having octahedral geometry and the Cu(II) and Zn(II) tetrahedral.
Ó 2013 Elsevier B.V. All rights reserved.
Received 30 September 2012
Received in revised form 5 April 2013
Accepted 10 April 2013
Available online 23 April 2013
Keywords:
Phenylazo dehydroacetic acid
Complexes
Mass spectrum
Thermogravimetry
Introduction
this compound has several reactive functional groups and can
serve as a reagent in organic synthesis. The synthesis and charac-
Dehydroacetic acid, 3-acetyl-4-hydroxy-6-methyl-2Hpyran-2-
one (DAA) is found to be occurring in anthers of Solandra nitida
(solanaceae). It possesses interesting biological properties such as
fungicidal and antibacterial activity and is used as a cosmetic pre-
servative too. It can also act as a complexing ligand. Furthermore,
terization of two macrocyclic ligands, by the condensation of
dehydroacetic acid with 1,2-phenylenediamine and 1,3-propylene-
diamine [1] have also been reported. DAA in solution exists as a
completely enolised species [2]. Like phenols, it can couple with
diazonium salts at C-5 and some reports [3,4] are available on
the condensation of DAA with diazotised derivatives of aniline,
substituted anilines, benzidine, etc. Even though some studies
are available on metal chelate of DAA [5], no work has so far been
⇑
Corresponding author. Tel.: +91 8086733577; fax: +91 4952768219.
E-mail address: susannahseth@yahoo.co.in (S. Seth).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.04.046

S. Seth, K.K. Aravindakshan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 276–279
277
reported on chelates of azo dehydroacetic acid (ADAA). ADAA
formed stable complexes with Cr(III), Fe(III), Ni(II), Cu(II) and Zn(II).
In all the complexes one of the azo nitrogens took part in coordina-
tion together with oxygen of the enolic OH. The Zn(II) complex was
diamagnetic and all others showed expected magnetic moment
values. All complexes were deep red/brown in color.
of the compounds were recorded by their thin KBr discs. The FAB
mass spectra were obtained using argon as the FAB gas, accelerat-
ing voltage, 10 kV and m-nitrobenzyl alcohol (NBA) as matrix. The
metal percentage analyses in some cases were conducted using
ICP-AES spectrometer using argon as the conductor gas for plasma
state at a core temperature of 9000 K. The other metal percentages
were determined by adopting standard procedure. The NMR spec-
tra were obtained using CDCl3 as solvent and TMS as internal stan-
dard. Magnetic susceptibility was determined at room temperature
on Sherwood Magway susceptibility instrument which was cali-
brated using Hg[Co(NCS)4]. Thermogravimetric studies, TG/DTG
were carried out in nitrogen atmosphere with a heating rate of
10 °C/min.
Experimental
Materials and methods
All the chemicals used for synthetic purposes were of Analar
grade. Solvents like methanol, acetic acid, acetone, dichlorometh-
ane and chloroform were purchased from E Merck and used as
received. Commercial ethanol was purified by distillation and used.
The metal salts used for the synthesis of complexes were acetate of
Ni(II) and Cu(II) and chlorides of Cr(III), Fe(III) and Zn(II).
Results and discussion
The elemental percentages of the ligand, ADAA were found to
be in fine agreement with molecular formula C14N2O3H12. ADAA
formed stable complexes with Cr(III), Fe(III), Ni(II), Cu(II) and Zn(II).
In all the complexes one of the azo nitrogens took part in coordina-
tion together with oxygen of the enolic OH. The Zn(II) complex was
diamagnetic and all others showed expected magnetic moment
values. All complexes were deep red/brown in color. The molar
conductivity of the complexes in DMF solutions (10À3 M) at room
temperature indicated that these are non-electrolytes. The analyt-
ical data are entered in Table 1.
Synthesis of phenylazo dehydroacetic acid (ADAA)
Aniline (0.01 mol) was diazotised and this solution of diazo-
nium salt was added slowly drop wise to a well cooled alkaline
solution of DAA (0.02 M). The mixture was allowed to stand for
0.5 h. The product, phenylazo dehydroacetic acid, (ADAA) was fil-
tered, washed successively with very dilute HCl and water, recrys-
tallized from methanol and stored over anhydrous MgSO4 in a
desiccator.
Spectral studies
Synthesis of metal complexes
Electronic spectra and magnetic moment interpretation
To a methanolic solution of ADAA, the metal salt solution, also in
methanol was added drop wise with stirring. The mixture was re-
fluxed on a steam bath for about 1 h. The metal salt to ligand ratio
was kept at 1:2/1:3 for bivalent/trivalent metals, respectively. The
precipitated complexes were filtered, washed with water, methanol
and dried. These were recrystallized from CH2Cl2ACH3OH mixture
and stored over anhydrous MgSO4 in a desiccator.
The electronic spectrum of ADAA was conspicuous with the
band at 278 nm which is characteristic of an azo form. The other
bands of importance were at 260 nm (carbonyl) and 370 nm
(N@NA). The magnetic moment value of 3.76 B.M. for the
Chromium(III) complex suggested [7] an octahedral geometry.
The prominent electronic spectral bands include 380 nm
(4T1g(F) ? A2g(F)) and 570 nm (4A2g(F) ? 4T2g(F)) which also
pointed to an octahedral geometry Fe(III) complex spectrum was
difficult to interpret due to CT bands. The magnetic moment value
of 5.85 B.M. indicated an octahedral geometry. The spectrum of
Ni(II) complex had almost all of the peaks expected for an octahe-
dral geometry. The bands at 376 nm (3A2g ? 3T1g(P)) and 680 nm
(3A2g ? 3T1g(F)) were very conspicuous. The magnetic moment va-
lue of 2.92 B.M. also confirmed the octahedral geometry. The cop-
per(II) complex exhibited bands at 316 nm and 682 nm which
were characteristic overlapped bands of copper complexes. The
band at 420 nm was typical [8] of a tetrahedral geometry. The
Physical measurements
The elemental percentage analyses of C, H and N were carried
out using Vario EL III CHN analyzer. Some of the metal percentage
analyses were conducted using ICP-AES spectrometer using argon
as the conductor gas for plasma state at a core temperature of
9000 K. The other metal percentages were determined by adopting
standard [6] procedure. UV–visible spectra were recorded using
10À3 M solutions of ligands and complexes in methanol. IR spectra
Table 1
Analytical and physical data of the ligand (LH) and its metal complexes.
Sl.
No.
Compound
Color
Yield
(%)
MP
(°C)
Elemental analysis found (calc.)%
Magnetic
Electronic spectral
data kmax (nm)
moment
l
B.M.
C
H
N
M
Cl
1
2
3
4
5
6
C
14N2O4H12 (LH) Brick
60
65
65
70
70
50
61.70 (61.77) 4.26 (4.41) 9.95 (10.29)
51.53 (51.89) 4.10 (4.32) 8.98 (8.65)
51.15 (51.58) 4.26 (4.29) 8.14 (8.59)
52.72 (52.75) 4.82 (4.71) 8.84 (8.79)
260, 278, 370
red
Dark
brown
Dark
brown
Dark
[Cr(L)2Cl(H2O)]
[Fe(L)2Cl(H2O)]
[Ni(L)2(H2O)2]
80
8.65 (8.03)
5.69
(5.48)
5.71
(5.45)
–
3.76
5.85
2.82
2.10
Da
276, 314, 380, 570
278, 310, 370, 514
278, 312, 376, 680
140
160
8.13 (8.58)
9.74 (9.22)
brown
[Cu(L)(OAc)H2O] Dark
brown
Maroon 65
>300 46.64 (46.60) 4.12 (3.88) 6.79 (6.90)
210 55.01 (55.32) 3.55 (3.62) 9.76 (9.22)
15.38 (15.42)
10.25 (10.76)
–
278, 316, 377,420,
682
278, 310, 370,445,
512
[Zn(L)2]
a
Diamagnetic.

278
S. Seth, K.K. Aravindakshan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 276–279
Fig. 1. 1H NMR Spectrum of phenylazo dehydroacetic acid.
magnetic moment value of the Cu(II) complex 2.10 B.M was an
additional support to the tetrahedral geometry. The Zn(II) complex
exhibited conspicuous bands at 375 nm and 445 nm which sug-
gested [9] the tetrahedral nature of the complex.
exhibited all the peaks of the ligand except the enolic OH peak at
ꢁ15.58 ppm. This indicated the coordination through enolic oxy-
gen where the metal has replaced H leading to the formation of a
six membered chelate. Other peaks of importance were at 2.48
(s) (acetyl proton) and 2.62 ppm (s) (methyl protons).
FTIR spectra
Mass spectra
In FTIR spectra, the broad band at 3445 cmÀ1 in the ligand
showed the presence of hydrogen bonded OH. The band at
1599 cmÀ1 is typical of an AN@NA group. The free acetyl carbonyl
absorption was found at ꢁ720 cmÀ1 and the ring C@O at
1657 cmÀ1. The band due to CAOAC stretch of the pyrone was
observed at 1125 cmÀ1. The FTIR spectra of all complexes showed
the acetyl carbonyl stretch more or less at the same position indi-
cating the absence of coordination through this carbonyl oxygen.
The N@N stretch also has lowered from ꢁ1600 to 1570 cmÀ1 point-
ing to coordination through azo nitrogen. The appearance of two
new bands at lower wave numbers around 580 and 440 cmÀ1
may be an indication of MAN and MAO bonds, respectively.
The mass spectrum of ADAA showed the M+ peaks at m/z 272.
The peaks at 244 pertained to (MAN2)+ which is very characteristic
of an azo group. The base peak at m/z 149 indicated the fragment
[MA(C6H5N2 + OH)]+. So, based on the above evidences the proba-
ble structure of ADAA was found to be as depicted in Fig. 1, which
is in conformity with other findings. The mass spectrum of the
Cu(II) complex showed M + 1 peak at 413 which confirmed the for-
mula [CuL(OAc)(H2O)]. Other prominent peaks were 394 (MAH2O),
375 [MA(H2O + N2)] which supports the azo structure. The peaks
at 244, 168, 149 were the same as those in the spectrum of the
ligand.
1H NMR spectra
Thermal data
1H NMR spectrum of ADAA (Fig. 1) showed all the peaks ex-
pected of dehydroacetic acid [10] except the peaks at C-5 where
the proton has been substituted by a phenylazo group. The peak
at 15.68 ppm belonged unmistakably to the acidic proton of OH
at C-4 and other prominent peaks were 7.48 nm (unsymmetrical
pattern, aromatic), 2.7 ppm for HS on C-8 and 2.4 ppm for HS on
C-9.The 1H NMR spectrum of the diamagnetic Zn(II) complex
The thermal decomposition curves of the complexes
[Cu(L)(OAc)(H2O)] and [Ni(L)2(H2O)2] were in conformity with
the formulae. The decomposition pattern is summarized in Table
2. It can be observed from the data that both of the complexes
are stable up to 150 °C. Above this temperature, decomposition be-
gins slowly. After the loss of coordinated OAc/H2O, the final stage is
attained at a very high temperature of ꢁ1000 °C. This is a clear
Table 2
Thermal decomposition data of copper and nickel complexes from TG/DTG.
Complex
F.W.
Decomposition stage
Decomposition temperature (°C)
Mass loss% TG (calc.)
Decomposition pattern
Stage 1
Stage 2
Stage 3
Stage 1
Stage 2
181.9
281.5
1000.1
160.6
3.8 (4.4)
18.5 (18.6)
86.1 (80.7)
9.2 (5.7)
Loss of H2O
[Cu(L)(OAc)(H2O)]
[Ni(L)2(H2O)2]
412
636
Loss of (H2O + OAc)
Final residue CuO
Loss of two H2O
Final residue NiO
1001.2
88.2 (88.3)

S. Seth, K.K. Aravindakshan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 276–279
279
indication of the strong binding nature of the ligand ADAA. The
Appendix A. Supplementary material
degradation pattern strongly supports the proposed molecular for-
mulae as the percentages of mass loss at different stages are very
close to the calculated values.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.04.046.
References
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be attached to two ligand moieties, thus satisfying both primary
and secondary valencies. The Cr(III), Fe(III) and Ni(II) complexes
were found to assume octahedral geometry and the Cu(II) and
Zn(II) complexes, tetrahedral geometry.
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This work was supported by the Teacher fellowship of the Uni-
versity Grants Commission of India.