Chelating competency and electrochemical response of a heterocyclic phenylhydrazone and its copper chelate

Article abstract of DOI:10.13005/ojc/300479

Heterocyclic compound 3-acetylpyridine phenylhydrazone (APPH) and its copper chelate were synthesized and characterized by spectral, elemental, magnetic and conductance measurements. Investigations showed that APPH behaved as bidentate ligand during chela

Full text of DOI:10.13005/ojc/300479

ISSN: 0970-020 X
CODEN: OJCHEG
2014, Vol. 30, No. (4):
Pg. 2099-2104
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Chelating Competency and Electrochemical Response of a
Heterocyclic Phenylhydrazone and its Copper Chelate
VINOD P RAPHAEL, JOBY THOMAS K*, K.S. SHAJU and NIMMY KURIAKOSE
Department of Chemistry, St. Thomas’ College (University of Calicut),
Thrissur, Kerala - 680001, India.
*Corresponding author E-mail: drjobythomask@gmail.com
http://dx.doi.org/10.13005/ojc/300479
(Received: August 26, 2014; Accepted: October 15, 2014)
ABSTRACT
Heterocyclic compound 3-acetylpyridine phenylhydrazone (APPH) and its copper chelate
were synthesized and characterized by spectral, elemental, magnetic and conductance
measurements. Investigations showed that APPH behaved as bidentate ligand during chelation.
The square planar geometry of the chelate was confirmed by magnetic and optical spectral
studies. The detailed electrochemical response of the ligand and chelate were evaluated and
reported.
Key words: Phenylhydrazone, chelate, square planar, cyclic voltammetry.
INTRODUCTION
MATERIALSAND METHOD
The compounds which possess
azomethine linkage or Schiff bases are well-known
for its chelating competency. Such molecules and
their metal chelates are having wide variety of
applications in the pharmaceutical, catalysis,
analytical and corrosion field1-15. In the present
investigation we explored the structure of the 3-
acetylpyridine phenylhydrazone and its copper
chelate using various spectroscopic methods. The
electrochemical response of these synthesized
compounds was also studied using cyclic
voltammetry.
3-acetyl pyridine was purchased from
Fluka. Phenylhydrazine hydrochloride and cupric
acetate were obtained from E. merck. Shimadzu
model FT-IR Spectrometer (Model: IR affinity) and
Shimadzu UV-visible-1800 spectrophotometer
were used for recording infrared and electronic
spectra. Mass spectrum of the hydrazone was
recorded using QP 2010 model Shimadzu GCMS.
1Hnmr and 13Cnmr spectral studies were carried
out on Bruker Avance III HD.

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APPH was synthesized by condensing weak but broad signal appeared at 9.86 was
equimolar mixture of 3-acetylpyridine in ethanol and assignable to the NH proton of phenylhydrazine
1
phenylhydrazine hydrochloride in ethanol water part. Two dimensional H-1Hnmr spectrum (COSY)
mixture (3:1). The reaction mixture was refluxed for was very helpful in identifying different hydrogen
four hours, evaporated nearly to dryness and atoms (Figure 1). Nine diagonal contours were
allowed to cool slowly. The precipitated yellow appeared in the COSY spectrum, for nine different
coloured phenylhydrazone was filtered, washed protons of the molecule. Strong off diagonal peaks
with ethanol and dried.
for H1-H2 & H1-H3 interactions were emerged in
the COSY spectrum, which were originated by the
The phenylhydrazone APPH (3mmol) in strong ortho coupling. Due to the meta coupling
ethanol was heated to reflux, hot ethanolic solution between the protons H5 and H4 in the pyridine ring,
(3mmol) of metal salt was added and the resulting weak contours were seen in the spectrum. H6-H7
mixture was refluxed for 5 hours, evaporated, cooled and H5-H6 ortho coupling was confirmed by the
and the chelate separated was filtered.
strong off diagonal contours.
RESULTSAND DISCUSSION
The signals appeared in 13Cnmr spectrum
of APPH were assigned for 11 labelled carbon atoms
and given in Table 1. The signal of the azomethine
Characterization of phenylhydrazone
In the mass spectrum of APPH, the carbon appeared at 137.99ppm. A peak observed
molecular ion peak was observed at m/z=211. at 12.53ppm was assignable to methyl carbon atom.
1Hnmr spectrum displayed nine signals for nine The quaternary carbon atoms labelled 6 and 4 gave
distinguished hydrogen atoms.The signal appeared their signals 134.88 and 145.07ppm respectively.
at 2.28  was due to the methyl protons (Table 1). A On close observation of the molecular structure it is
Table 1: 1Hnmr and 13Cnmr spectral data of APPH
1Hnmr
13Cnmr
 value
Assignment/
Labelled No.
value
Assignment/
Labelled No.
9
8
9.86(sbr,1H)
9.05(d,1H)
8.72(dd,1H)
8.66(dd,1H)
7.80(m,1H)
7.28(d,1H)
7.19(m,1H)
6.76(m,1H)
2.28(s,3H)
8 (NH)
145.07
139.92
139.82
138.63
137.99
134.88
128.96
126.47
120.02
113.34
12.53
4
7
9
10
5
6
2
8
1
7
6
4
5
7
6
3
2
1
9
7
N
N
5
10
6
5
4
CH3
11
CH3
9
N
N
NH
NH
8
3
1
4
3
2
2
3
11
1
Table 2: Cyclic voltammetric data of APPH
(mV/s)
Epc (mV)
ipc(µA)
Epa(mV)
ipa(µA)
ipa/ipc
ipc/õ1/2
ipa/ 1/2
Ep (mV)
40
60
80
100
578
580
579
580
0.62
0.79
0.78
0.75
736
740
740
735
0.96
1.35
1.88
2.28
1.55
1.71
2.41
3.04
0.098
0.10
0.087
0.075
0.15
0.17
0.21
0.22
158
160
161
155

RAPHAEL et al., Orient. J. Chem., Vol. 30(4), 2099-2104 (2014)
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Table 3: Cyclic voltammetric data of Cu(II)-APPH chelate

Epc1
ipc1
Epc2
ipc2
Epa1
ipa1
Epa2
ipa2
ipa1/ipc1 ipa2/ipc2 Ep1
Ep1
(mV/s)
(mV) (µA) (mV) (µA) (mV) (µA) (mV) (µA)
20
40
60
80
-737
-2.0
-197 -0.58
-58
-43
-29
2.79
4.07
4.92
5.08
577
599
606
628
0.64
0.81
0.89
0.91
1.4
1.8
2.5
-
1.1
0.94
1.14
2.4
679
767
847
-
774
826
869
-810 2.24 -227 -0.91
-876 1.95 -263 -0.78
-
-
-591 0.367 -14
1219
evident that the molecule APPH bear three
quaternary carbon atoms, labelled as 4, 5 and 6. In
the DEPT-135 spectrum of the molecule, the signals
corresponds to these carbon atoms were totally
absent, confirming that these peaks are definitely
due to quaternary carbons. Since there were no
methylene groups in the molecule, the DEPT 135
spectrum not displayed any inverse signals. In the
667cm-1 can be considered as in-plane deformation
mode of the pyridine ring. The important electronic
transitions occurred in the molecules were
observed at 32679cm-1 and 29239cm-1 which are
attributed to * and n* transitions respectively.
Characterization of Cu(II) chelate
Elemental analysis of the metal chelate:
1
HMQC spectrum of APPH (Figure 2), the Hnmr
Metal %16.82 (16.21); C% 50.99 (51.96); H% 4.33
(4.84); N% 10.44 (10.69). Calculated values are
represented in brackets. A square planar geometry
was assigned to the Cu(II) chelate (Figure 3) since
it displayed µeff of 1.97BM (d9 system)16-18, which
was further confirmed by electronic spectroscopic
studies. In the optical absorption spectrum, the
chelate gave two bands at 27310 and 28998cm-1
signal was absent corresponds to the C4 (observed
at 145.07ppm), since this carbon atom is not bearing
a proton. Similarly the corresponding 1Hnmr signal
was not appeared for C6 signal at 13Cnmr axis. The
corresponding 13C contours for the proton signal
appeared at 9.86 was not present in the HMQC
spectrum.This evidently establishes that this proton
is not bearing a carbon atom and it is assigned for
NH proton signal.
2
2
which are due to B12A1 and B12B2 transitions
respectively in addition to intra ligand transitions.
Non-electrolytic nature of the chelate was
established by the molar conductance data in
DMSO (15 -1cm2mol-1).
An intense IR peak appeared at 1593cm-
1 can be assigned to the C=N stretching vibration. A
broad band displayed at 3265cm-1 is due to N-H
frequency. C=N was appeared at 1465cm-1 and C-H
stretching frequencies was shown between 3030-
3100cm-1 and the bands appeared at 621 and
Interpretation of the IR spectral data was
very helpful for the assignment of the correct probe
of the ligand which will make coordinate bonds with
Fig. 1: COSY spectrum of APPH
Fig. 2: HMQC spectrum of APPH

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the central metal ion in a chelate. The IR spectrum evidence for the coordination of heterocyclic
of the phenylhydrazone exhibited a peak at 1593cm- nitrogen was also obtained from the IR spectral data.
1, which was due to the stretching vibration of The in-plane deformation modes of pyridine ring
azomethine group. The C=N of chelate was lowered shown by the ligand at 621 and 667cm-1 respectively
to 1579cm-1 which is an indication of the shifted to 625 and 687cm-1 in chelate, suggesting
coordination of azomethine nitrogen. A confirmatory the coordination of the hetero aromatic nitrogen to
the metal19-20. Appearance of new bands at 434
and 411cm-1 respectively, is an indication of
CH3
O
coordination of the heteroaromatic nitrogen and
azomethine nitrogen of the ligand APPH to the
central metal ion. The IR spectrum of Cu(II) chelate
displayed asymmetric and symmetric stretching
frequencies C-O bond of acetate ion at around 1597
and 1423cm-1, respectively showing a difference of
about 150cm-1, which indicates the monodentate
behaviour of acetate.
N
O
O
Cu
H3C
CH3
N
NH
O
Cyclic voltammetric studies on 3-acetylpyridine
phenylhydrazone
Fig. 3: Structure of Cu(II) chelate
Figure 4a and 4b display the cyclic
Fig. 4: Cyclic voltammogram of APPH a) at scan rate of 40mV/s b) at scan rates 40-100mV/s
voltammogram of the phenylhydrazone APPH at
scan rate 40mV/s and overlay contours of the
voltammograms at various scan rates respectively.
The CV diagram of APPH exhibited one reduction
and oxidation peak and the redox couple behaved
more close to a reversible system. The peak
potentials (Ep) were independent of the scan rate,
suggesting the behaviour of the reversible system.
The peak separation (Epa-Epc) was comparable with
the values of reversible redox couples and was
independent on the rate of sweep. But the ratio of
peak heights was greater than one and showed
gradual rise with the scan rate. The cathodic peak
current was not strictly proportional to the square
Fig. 5: The ipa- 1/2 curves of Phenyl hydrazone APPH

RAPHAEL et al., Orient. J. Chem., Vol. 30(4), 2099-2104 (2014)
2103
root of sweep rate, but the anodic current exhibited On reverse scan, two oxidation peaks were
fair proportionality to 1/2 (Figure 5). Even though, exhibited in the cyclic voltammogram, whose
some parameters emphasize the reversibility of the potentials are designated as Epa1 and Epa2. Epa1 and
redox process, the actual electrochemical response Epa2 are the genuine counter peaks of cathodic
of this system fall in the quasi reversible spectrum peaks Epc1 and Epc2 respectively.Both counter peaks
of compounds. The voltammetric data of the were shifted to more positive potential as the scan
compound APPH is provided in Table 2.
rate was increased. The peak separation values of
cathodic and anodic peaks suggest the quasi
Cyclic voltammetric studies on Cu(II)-APPH reversible nature of the redox system. Cyclic
chelate
voltammetric data of Cu(II)-APPH chelate is given
Cyclic voltammogram of Cu(II)-APPH in Table 3. Taking into consideration the cyclic
chelate at scan rate 20mV/s is provided in Figure 6. voltammetric response of Cu(II)-APPH chelate, one
In the forward scan, the voltammogram has two well can propose the mechanism of electrochemical
defined cathodic waves with first peak (Epc1) situated reactions as follows.The first cathodic curve can be
at more negative cathodic potential and the second assigned to the cathodic reduction of Cu(II)-chelate
peak appeared at a less cathodic potential.
to the Cu(I)-chelate in a quasi reversible
mechanism, since there is a negative shift to
As the sweep increased both cathodic cathodic peak potential with increase in the scan
peaks were shifted to more negative potentials and rate.
at higher scan rates the Epc1 peak was disappeared.
Fig. 6: Cyclic voltammogram of Cu(II)-APPH chelate a) at scan rate of 20mV/s b) at scan rates 20-80mV/s
Fig. 7: The ipa1- 1/2 curves of Cu(II)- APPH chelate
Fig. 8: The ipa2- 1/2 curves of Cu(II)- APPH chelate

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RAPHAEL et al., Orient. J. Chem., Vol. 30(4), 2099-2104 (2014)
The second cathodic peak, which arise in the scan rate and the anodic current was
the more negative potential to that of the first proportional to 1/2 (Figure 8). The overall
reduction peak is assignable to the reduction of mechanism can be represented as follows.
Cu(I)-chelate to the Cu(0)-chelate. Since the Epc2
was also moved to the higher negative potentials
with the scan rate, quasi reversible nature of the
CONCLUSIONS
electrode process can be assumed.The peak height
was not proportional to the square root of scan rate.
The stability of Cu(0)–chelate is very low and the
ligand molecules may or may not detach
(decomplexation) from the metal atom within a short
span. So the concentration of Cu(0)-chelate in the
immediate vicinity of the carbon electrode will be
very low.The first anodic peak in CV can be attributed
to the anodic oxidation of Cu(0)-chelate, which is
the counter peak of Epc1. The height of this anodic
peak was high and showed proportionality with 1/
´
´
Novel heterocyclic phenylhydrazone (APPH)
and its copper chelate were synthesized.
Structure of the ligand and chelate were
established by various analytical methods
and it was proved that a 1:1 stoichiometry
exist between the ligand and the metal ion.
Square planar geometry was suggested for
the chelate.
The electrochemical behaviour of the ligand
and chelate were studied using cyclic
voltammetry. One redox couple was shown
by APPH, while the chelate displayed two
redox couples in the voltammogram.
The quasi reversible nature of the redox
process was observed in both APPH and its
Cu(II) chelate
´
´
2
(Figure 7) which may be due to the combined
oxidation of unstable Cu(0)-chelate and free Cu
atoms adjacent to the electrode.The second anodic
peak appeared at high positive potential can be
assigned to the anodic oxidation of Cu(I)-chelate to
Cu(II)-chelate in a quasi reversible manner. This
peak was shifted to more positive potentials with
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