Synthesis, characterization and biological activity of complexes of 2-hydroxy-3,5-dimethylacetophenoneoxime (HDMAOX) with copper(II), cobalt(II), nickel(II) and palladium(II)

Article abstract of DOI:10.1016/j.saa.2006.11.001

A new series of complexes of 2-hydroxy-3,5-dimethyl acetophenone oxime (HDMAOX) with Cu(II), Co(II), Ni(II) and Pd(II) have been prepared and characterized by different physical techniques. Infrared spectra of the complexes indicate deprotonation and coordination of the phenolic OH. It also confirms that nitrogen atom of the oximino group contributes to the complexation. Electronic spectra and magnetic susceptibility measurements reveal square planar geometry for Cu(II), Ni(II) and Pd(II) complexes and tetrahedral geometry for Co(II) complex. The elemental analyses and mass spectral data have justified the ML₂ composition of complexes. Kinetic and thermodynamic parameters were computed from the thermal decomposition data using Coats and Redfern method. The geometry of the metal complexes has been optimized with the help of molecular modeling. The free ligand (HDMAOX) and its metal complexes have been tested in vitro against Alternarie alternate, Aspergillus flavus, Aspergillus nidulans and Aspergillus niger fungi and Streptococcus, Staph, Staphylococcus and Escherchia coli bacteria in order to assess their antimicrobial potential. The results indicate that the ligand and its metal complexes possess antimicrobial properties.

Full text of DOI:10.1016/j.saa.2006.11.001

Spectrochimica Acta Part A 68 (2007) 63–73
Synthesis, characterization and biological activity of complexes of
2-hydroxy-3,5-dimethylacetophenoneoxime (HDMAOX) with
copper(II), cobalt(II), nickel(II) and palladium(II)
Bibhesh K. Singha, Umesh K. Jetleyb, Rakesh K. Sharmaa, Bhagwan S. Garga,∗
a Department of Chemistry, University of Delhi, Delhi 110007, India
b Department of Chemistry, R.S.S. (P.G.) College, Ghaziabad, NCR, Delhi, India
Received 21 September 2006; accepted 1 November 2006
Abstract
A new series of complexes of 2-hydroxy-3,5-dimethyl acetophenone oxime (HDMAOX) with Cu(II), Co(II), Ni(II) and Pd(II) have been prepared
and characterized by different physical techniques. Infrared spectra of the complexes indicate deprotonation and coordination of the phenolic OH. It
also confirms that nitrogen atom of the oximino group contributes to the complexation. Electronic spectra and magnetic susceptibility measurements
reveal square planar geometry for Cu(II), Ni(II) and Pd(II) complexes and tetrahedral geometry for Co(II) complex. The elemental analyses and
mass spectral data have justified the ML2 composition of complexes. Kinetic and thermodynamic parameters were computed from the thermal
decomposition data using Coats and Redfern method. The geometry of the metal complexes has been optimized with the help of molecular modeling.
The free ligand (HDMAOX) and its metal complexes have been tested in vitro against Alternarie alternate, Aspergillus flavus, Aspergillus nidulans
and Aspergillus niger fungi and Streptococcus, Staph, Staphylococcus and Escherchia coli bacteria in order to assess their antimicrobial potential.
The results indicate that the ligand and its metal complexes possess antimicrobial properties.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Bioactivity; Kinetics; Metal complexes; Molecular modeling; Spectra
1. Introduction
against the mycobacteria [3]. Some acetophenone derivatives
have antimicrobial activity against gram-positive bacteria and
fungi [4] while others are used as herbicides [5]. Certain ace-
tophenonescarryingahydroxylgroupatC-2haveantimutagenic
activity in salmonella typhimurium [6]. Many acetophenones
occur as natural products in plants [7] and fungi [8]. Paeonol
(2-hydroxy-4-methoxy acetophenone) an oral administration to
rats is rapidly excreted in the urine as sulphated derivative [9].
Ortho-hydroxyacetophenoneoxime acts as an important analyt-
ical reagent for the gravimetric and colorimetric estimation of
transition metals [10].
Spectral characterization and the kinetic calculations of ther-
mal decomposition reactions serve as important tools for the
interpretation of structures of molecules of biological and ana-
lytical importance. Therefore, we report herein the synthesis,
spectral characterization (infrared, electronic, mass and 1H
NMR), magnetic susceptibility measurements and thermal stud-
ies of the complexes of HDMAOX with selected transition
metal (II) ions. The geometry of the metal complexes has
been optimized through molecular modeling studies, which
involve energy minimization calculations. The present works
Presently, there is a growing interest in the coordination
chemistry of structurally modified bio-ligands. Transition metal
complexes with potential biological activity are the focus of
extensive investigations. Acetophenoneoxime is an important
bioactive ligand for a wide variety of applications. Different
oximes and their metal complexes have shown notable bioactiv-
ity as chelating therapeutics, as drugs, as inhibitors of enzymes
and as intermediates in the biosynthesis of nitrogen oxides [1].
However, with increasing use of oximes as drugs and pesticides,
the intake of these chemicals followed by enzymatic oxidation
may result in the formation of a variety of reactive intermediates,
which may lead to cell and tissue damage [2].
Acetophenone (AP, phenylmethylketone or hypnone) is used
in consumer fragrances and as an industrial solvent. In general,
acetophenones may serve as a novel group of useful therapeutics
∗
Corresponding author. Tel.: +91 27677525; fax: +91 27666250.
E-mail address: bibheshksingh@yahoo.co.in (B.K. Singh).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.11.001

64
B.K. Singh et al. / Spectrochimica Acta Part A 68 (2007) 63–73
2.2. Synthesis of the complexes
To 50 ml of 0.2 M aqueous solution of the salts of respective
metal chlorides, 100 ml of 0.4 M solution of 2-hydroxy-3,5-
dimethylacetophenoneoxime (HDMAOX) [11] in 50% ethanol
was added. Cu(II), Co(II), Ni(II) and Pd(II) formed buff, brown,
green and yellow colored precipitates in the pH range 2.5–9.0,
6.0–9.0, 5.0–9.0 and 1.5–6.5, respectively. The precipitated
complexes were digested, filtered, washed first with hot water
and then with 20% ethanol and finally dried at 105–110 ◦C in
an air oven. The yields of the respective complexes were in the
range of 75–85%.
Fig. 1. Structure of 2-hydroxy-3,5-dimethylacetophenoneoxime (HDMAOX).
deals specifically the coordination properties of 2-hydroxy-3,5-
dimethylacetophenoneoxime (HDMAOX) (Fig. 1) concerning
its interactions with Cu(II), Co(II), Ni(II) and Pd(II). The bio-
efficacy of these complexes has also been examined against the
growth of bacteria and pathogenic fungi in vitro to evaluate their
anti-microbial potential.
2.3. Biological activity
2.3.1. Antibacterial screening
In vitro anti-microbial (anti-bacterial) activities of the syn-
thesized ligand and its metal complexes were tested using paper
disc diffusion method [12]. The nutrient agar medium (peptone,
beef extract, NaCl and agar-agar) and 5 mm diameter paper discs
of Whatman No. 1 were used. The test compound was dissolved
in methanol in 0.05–0.40% concentrations. The filter paper discs
were soaked in different solutions of the compound, dried and
thenplacedinthePetriplates(9 mmdiameter)previouslyseeded
with the test organisms Streptococcus, Staph, Staphylococcus
and Escherchia coli. The plates were incubated for 24–30 h at
27 1 ◦C and the inhibition zone (mm) was measured around
each disc. As the organism grows, it forms a turbid layer, except
in the region where the concentration of antibacterial agent is
above the minimum inhibitory concentration and a zone of inhi-
bition is seen. The size of the inhibition zone depends upon the
culture medium, incubation conditions, rate of diffusion and the
concentration of the antibacterial agent.
2. Experimental
2.1. Physiochemical studies
The stoichiometric analyses (C, H and N) of the complexes
were performed using Elementar vario EL III (Germany) model.
Metal contents were estimated on an AA-640-13 Shimadzu
flame atomic absorption spectrophotometer in solution prepared
by decomposing the respective complex in hot concentrated
HNO3. Their IR spectra were recorded on Perkin-Elmer FT-IR
spectrophotometer in nujol mull and polyethylene pellets. The
UV–vis spectra were recorded in CDCl3 on Beckman DU-64
spectrophotometer and mass spectra (TOF-MS) were recorded
on Waters (USA) KC-455 model with ES+ mode.1H NMR
was recorded on a Bruker Advance 300 instrument. Magnetic
susceptibility measurements were carried out at room temper-
ature in powder form on a vibrating sample magnetometer
PAR 155 with 5000G-field strength, using Co [Hg (SCN)4] as
the calibrant (magnetic susceptibility ≈ 1.644 × 10−5 cm3 g−1).
Rigaku model 8150 thermoanalyser (Thermaflex) was used for
simultaneous recording of TG–DTA curves at a heating rate of
5 ◦C min−1. For TG, the instrument was calibrated using cal-
cium oxalate while for DTA, calibration was done using indium
metal, both of which were supplied along with the instrument
in ambient condition. A flat bed type aluminium crucible was
used with ␣-alumina (99% pure) as the reference material for
DTA. The number of decomposition steps was identified using
TG. The activation energy (E) and Arrhenius constant of the
degradation process was obtained by Coats and Redfern method.
The initial 3D structure related to the probable geometry of
each metal complex was drawn through constrain geometry
and model builder option of the computer program, Hyperchem
release 7.51 professional version and related minimum strain
energy was calculated. The geometry of the complex was ener-
getically optimized through molecular mechanics. Metal salts
were procured from Aldrich and were used as received. Sol-
ventsused wereof analyticalgradeand werepurified by standard
procedures.
2.3.2. Antifungal screening
The antifungal activity of the complexes was checked by dry
weight method for the Alternarie alternate, Aspergillus flavus,
AspergillusnidulansandAspergillusnigerfungi. Thecomplexes
were directly added to the growth medium in varying concentra-
tion (0.05–0.40% (w/v)). The actively growing mycelia (of the
test fungi) were placed on the medium with the help of inocu-
lum needle and incubated at 27 1 ◦C for 7 days. The medium
with the test solutions served as ‘treated’ while without them as
‘control’ or check’. The resulting mycelia mats in each set were
carefully removed, washed, dried and then weighed separately.
The fungal growth was calculated from the following relation:
Cg − Tg
fungal growth inhibition (%) =
× 100
Cg
where Cg is the average growth in the ‘control’ or ‘check’ set
and Tg is the average growth in the treated set.
3. Results and discussion
On the basis of elemental analysis data (Table 1), all
the complexes have the general composition ML2, where

B.K. Singh et al. / Spectrochimica Acta Part A 68 (2007) 63–73
65
M = Cu(II), Co(II), Ni(II) and Pd(II); L = 2-hydroxy-3,5-
dimethylacetophenoneoxime(HDMAOX). Thecomplexeswere
obtained in powder form. These were found to be sufficiently
soluble in chloroform and DMSO for spectral measurements.
Various attempts to obtain the single crystals of the complexes
have so far been unsuccessful.
3.1. IR spectra and mode of bonding
In the absence of a powerful technique such as X-ray crys-
tallography, IR spectra have proven to be the most suitable
technique to give enough information’s to elucidate the nature
of bonding of the ligand to the metal ion. The IR spectra of
the free ligand and metal complexes (Fig. 2a–d) were carried
out in the range 4000–400 cm−1 and 400–100 cm−1 (Table 2).
The IR spectrum of the ligand shows a broad band between
3200 and 3450 cm−1, which can be attributed to phenolic OH
group. This band disappears in all complexes, which can be
attributed to the involvement of phenolic OH in coordination.
The involvement of deprotonated phenolic moiety in complexes
is confirmed by the shift of ν(C O) stretching band observed at
1212 cm−1 in the free ligand to a lower frequency to the extent
of 10–20 cm−1 [13]. The shift of ν(C O) band at 1212 cm−1
to a lower frequency suggests the weakening of ν(C O) and
formation of stronger M O bond. The broad and low inten-
sity bands due to ν(O H) modes of N OH groups in the
4000–3000 cm−1 frequency range shifted to the lower frequency
region (3136–3188 cm−1) which suggests the weakening of
N OHbondandformationofM Nbond[1]. Themediumbands
observed in the 1646–1620 cm−1 frequency ranges in complexes
were assigned to ν(C N) mode. The shift of ν(C N) vibra-
tion in all the complexes to a lower frequency suggests that the
nitrogen atom of the ring contributes to the complexation. The
lower ν(C N) frequency also indicates stronger M N bonding
[14,15].
The IR spectrum of the ligand showed that the ν(N O)
band appears at 860 cm−1. So, on M N interaction, ν(N O)
appeared at higher frequencies, indicating that N O bond length
decreases. The positive ν(N O) shift indicates strengthening of
the M N bond. In the IR spectra of the complexes, a band is
observed between 430 and 460 cm−1 that is attributed to the
ν(M N) stretching vibrations. Another band appeared between
660 and 672 cm−1, which is assigned to the interaction of phe-
nolic oxygen to the metal atom, i.e., the stretching vibrations
ν(M O) [13]. The band at 1374–1376 cm−1 in all the complexes
is due to the ν(CH3) frequency, is not affected upon complexa-
tion. Furthermore, the aliphatic protons are not greatly affected
upon complexation [16].
3.2. Magnetic moments and electronic spectra
Magnetic susceptibility measurements were carried out in
the solid state at room temperature (25 ◦C) and the results are
presented in Table 1. The magnetic moments of the copper(II)
and cobalt(II) complexes are 1.74 and 4.32 BM, respectively,
which suggests square planar geometry for copper(II) complex
and tetrahedral geometry for cobalt(II) complex. For tetrahedral

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B.K. Singh et al. / Spectrochimica Acta Part A 68 (2007) 63–73
Fig. 2. (a) IR spectrum of Cu–HDMAOX complex, (b) IR spectrum of Co–HDMAOX complex, (c) IR spectrum of Ni–HDMAOX complex, and (d) IR spectrum of
Pd–HDMAOX complex.
cobalt(II) complex, the state acquires orbital angular momentum
onlyindirectlythroughthemixingofthe4T2 statebyaspin–orbit
coupling perturbation. The nickel(II) and palladium(II) com-
plexes are diamagnetic at room temperature revealing the square
planar geometry around the metal (II) ion [17]. The electronic
spectra of the complexes are presented in Table 1. Two very
strong bands in the region 242–252 and 345–370 nm in the
spectra of the complexes, are attributed to n → ␲* and ␲ → ␲*
transitions in aromatic ring and C N chromophore [18]. The
visible spectrum of copper complex (Fig. 3a), shows two absorp-
2
2
tion bands at 660 nm and 510 nm assignable to B1g → B2g
2
2
and B1g → Eg transitions respectively, which indicates the
possibility of square planar geometry of the metal complex
[19]. Cobalt (II) complex (Fig. 3b) shows absorption bands at
Table 2
IR spectral data (cm−1) of metal complexes
Frequency
[Cu (HDMAOX)2]
[Co (HDMAOX)2]
[Ni (HDMAOX)2]
[Pd (HDMAOX)2]
ν(OH)NOH
ν(C N)
δ(NOH)
ν(CH)
3175 (w)
1641 (s)
1467 (s)
2924 (s), 2854 (m)
975
3188 (w)
1630 (s)
1463 (s)
2924 (s), 2855 (m)
971
3142 (w)
1639 (s)
1463 (s)
2923 (s), 2855 (m)
977
3136 (w)
1646 (s)
1464 (s)
2924 (s), 2855 (m)
978
ν(NO)
δ(O M−O)
186
214
193
233
191
236
194
237
δ(O
M
N)
ν(M O)
ν(M N)
ν(CH3)
340 (m)
272 (m)
1376
317 (m)
285 (m)
1377
329 (m)
293 (m)
1375
334(m)
287 (m)
1376
ν(C O)
1201
1204
1203
1202

B.K. Singh et al. / Spectrochimica Acta Part A 68 (2007) 63–73
67
Fig. 3. (a) Electronic spectra of Cu–HDMAOX complex, (b) electronic spectra of Co–HDMAOX complex, (c) electronic spectra of Ni–HDMAOX complex, and (d)
electronic spectra of Pd–HDMAOX complex.
4
4
(413 nm) [20,22]. These transitions are from the lower lying d
orbital to the empty dx2−y2 orbital. The strong band at 373 nm
is assignable to a combination of M → L (charge transfer) and
d–d bands.
668 nm assigned to A2 → T1 (P) transition. The existence
of spin - orbit coupling also allows some quartet → doublet
spin transition to occur. Another band at 705 nm is assigned
to4A2 → T1 (F). The expected 4A2 → T1 transition appearing
at a 4500 cm−1 is overlapped by ligand vibration transitions (i.e.,
the infrared bands) suggests tetrahedral geometry of the complex
[20,21], which is also corroborated by magnetic moment value
of the complex. Spectra of the nickel complex (Fig. 3c) shows an
4
4
3.3. Mass spectra
The recorded mass spectra of the complexes (Fig. 4a–d) and
the molecular ion peaks have been used to confirm the proposed
formula. Calculated and found molecular weights correspond-
ing to the important mass peaks for the studied compounds are
given in Table 3. The multi-peaks pattern of the mass spec-
trum gives an impression of the successive degradation of the
target compound with the series of peaks corresponding to the
absorption band at 650 nm, assignable to a 1A1g → A2g transi-
1
tion and a shoulder at 552 nm corresponding to a 1A1g → B1g
1
transition which are consistent with square planar stereochem-
istry about the nickel(II) ion. Palladium complex (Fig. 3d) has
three spin allowed singlet–singlet d–d transitions, which are
1A1g → A2g (715 nm), 1A1g → B1g (498 nm) and 1A1g → Eg
1
1
1

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B.K. Singh et al. / Spectrochimica Acta Part A 68 (2007) 63–73
Fig. 4. (a) Mass spectra of Cu–HDMAOX complex, (b) mass spectra of Co–HDMAOX complex, (c) mass spectra of Ni–HDMAOX complex, and (d) mass spectra
of Pd–HDMAOX complex.
various fragments. Their intensity gives an idea of stability of
fragments. The last two fragments in all the complexes appear
at positions (m/z value) 212 (100%) and 158 (<100%). These
values correspond to the [C16H20]+ and [C12H14]+ fragments,
respectively.
3.5. Kinetics of thermal decomposition
Recently, there has been increasing interest in determin-
ing the rate-dependent parameters of solid-state non-isothermal
decomposition reactions by analysis of TG curves [23,24].
Thermogravimetric (TG) and differential thermogravimetric
(DTG) analyses were carried out for Cu(II), Co(II), Ni(II)
and Pd(II)–HDMAOX complexes in ambient conditions. The
correlations between the different decomposition steps of
the complexes with the corresponding weight losses are
discussed in terms of the proposed formula of the com-
plexes.
The complex [Cu (HDMAOX)2] with the molecular formula
[C20H24N2O4Cu] is thermally decomposed in two successive
decomposition steps (Fig. 6a). The first estimated mass loss of
38.60% (calculated mass loss = 38.62%) within the temperature
range 540–590 K may be attributed to the loss of (C10H12NO)
fragment. The DTG curve gives an exothermic peak at 553 K
(the maximum peak temperature). The second step occurs within
the temperature range 661–853 K with the estimated mass loss
42.40% (calculated mass loss = 42.43%) which corresponds to
the loss of C10H12NO2 fragment leaving CuO as residue. The
DTG curve gives an exothermic peak at 770 K (the maximum
3.4. 1H nuclear magnetic resonance spectra
The 1H NMR spectra of a DMSO-d6 solution of the oxime
ligand (HDMAOX) and Ni(II), Pd(II) complexes show well-
resolved signals as expected. The solvent impurity resonates
near 3.0. The spectrum of the oxime shows a singlet at 1.2 ppm
(3H), singlet at 2.2 ppm (6H), singlet at 7.60–7.90 ppm (2H), sin-
1
glet at 11.4 ppm (1H), singlet at 12.6 ppm (1H). The H NMR
spectra of both the complexes (Fig. 5a and b) show the resonance
with expected integrated intensities. In both complexes, no sig-
nal is recorded for phenolic hydrogen in the 12–13.5 ppm region,
as in the case of ligand (HDMAOX). This indicates deprotona-
tion of the ortho-hydroxyl group on complexation. The other
resonances were observed at 0.8–1.3 ppm (6H), 2.0–2.7 ppm
(12H), 6.7–8.1 ppm (4H) and 11.53 ppm (2H) corresponding
to CH3-a, CH3-b, aromatic protons and oxime OH proton
resonances.

B.K. Singh et al. / Spectrochimica Acta Part A 68 (2007) 63–73
69
Table 3
Important mass peaks for the compounds studied
Mass assignments
M
m/z
(1)
(2)
[C20H24N2O4Cu]+
[C17H23NO3Cu]+
419.5
352.5
255.0
212.0
158.0
419.36
353.11
252.06
214.13
158.05
[C17H21NO]+
+
[C16H20
[C12H14
]
]
+
[C20H24N2O4Co]+
[C20H24NO3Co]+
[C20H24O2Co]+
[C20H22O2]+
415.1
384.9
354.9
294.0
278.0
212.0
158.0
415.15
385.14
356.11
295.08
279.09
214.13
158.02
[C20H22O]+
+
[C16H20
[C12H14
]
]
+
(3)
(4)
[C20H24N2O4Ni]+
[C20H24O2Ni]+
414.9
354.7
300.9
212.0
158.0
415.19
355.18
301.19
212.15
158.01
[C17H22ONi]+
+
[C16H20
[C12H14
]
]
+
[C20H24N2O4Pd]+
[C19H23NO3Pd]+
[C18H22O2Pd]+
[C17H20O2Pd]+
462.4
419.4
376.4
362.4
319.23
212.0
158.0
463.21
421.30
377.27
363.25
318.4
[C16H20Pd]+
+
[C16H20
[C12H14
]
]
212.01
158.56
+
peak temperature). Total estimated mass loss is 81.00% (calcu-
lated mass loss = 81.05%).
The thermal decomposition of [Co (HDMAOX)2] complex
(Fig. 6b) with the molecular formula [C20H24N2O4Co] proceeds
with two main degradation steps. The first step occurs within
the temperature range 485–590 K with an estimated mass loss
31.95% (calculated mass loss = 32.00%) which is reasonably
accounted for the loss of C8H7NO fragment. The DTG curve
gives an exothermic peak at 638 K (the maximum peak tem-
perature). The second step occurs within the temperature range
595–795 K with an estimated mass loss 50.25% (calculated mass
loss = 50.00%), which is reasonably accounted for the loss of
rest of the ligand molecule, leaving CoO as residue. The DTG
curve gives an exothermic peak at 705 K (the maximum peak
temperature). Total estimated mass loss is 82.20% (calculated
mass loss = 82.00%).
The thermal decomposition of [Ni (HDMAOX)2] complex
(Fig. 6c) with the molecular formula [C20H24N2O4Ni] also pro-
ceeds with two main degradation steps. The first estimated mass
loss of 19.90% (calculated mass loss = 20.00%) within the tem-
perature range 592–625 K could be attributed to the liberation of
C4H5NO fragment. The DTG curve gives an exothermic peak at
596 K (the maximum peak temperature). The second step occurs
within the temperature range 650–815 K with an estimated mass
loss 61.50% (calculated mass loss = 61.95%), which is reason-
ably accounted for the decomposition of remaining part of the
ligand molecule (C16H19NO2) leaving NiO as residue. The DTG
curve gives an exothermic peak at 760 K (the maximum peak
temperature). Total estimated mass loss is 81.40% (calculated
mass loss = 81.95).
Fig. 5. (a) NMR spectra of Ni–HDMAOX complex and (b) NMR spectra of
Pd–HDMAOX complex.
The [Pd (HDMAOX)2] complex (Fig. 6d) with the molecular
formula [C20H24N2O4Pd] is thermally decomposed in two suc-
cessive steps. The first estimated mass loss 35.00% (calculated
mass loss = 35.03%) within the temperature range 558–579 K
can be attributed to the loss of (C10H12NO) fragment. The DTG
curve gives an exothermic peak at 568 K (the maximum peak
temperature). The second step occurs within the temperature
range 593–698 K with an estimated mass loss 38.48% (calcu-
lated mass loss = 38.53%), which is reasonably accounted for the
loss of rest of the ligand molecule (C10H12NO2), leaving PdO
as residue with total estimated mass loss of 73.48% (calculated
mass loss = 73.53%). The DTG curve gives an exothermic peak
at 659 K (the maximum peak temperature).
The final product of decomposition at 875 K corresponds to
the formation of metal oxide as the end product, which was con-
firmed by comparing the observed/estimated and the calculated
mass of the pyrolysis product.
The kinetic analysis parameters such as activation energy
(ꢀE*), enthalpy of activation (ꢀH*), entropy of activation
(ꢀS*), free energy change of decomposition (ꢀG*) were evalu-

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B.K. Singh et al. / Spectrochimica Acta Part A 68 (2007) 63–73
Fig. 6. (a) TG–DTG curves of the Cu–HDMAOX complex, (b) TG–DTG curves of the Co–HDMAOX complex, (c) TG–DTG curves of the Ni–HDMAOX complex,
and (d) TG–DTG curves of the Pd–HDMAOX complex.
ated graphically by employing the Coats–Redfern relation [25]:
from the DTA curves was done by using the relation:
ꢀ
ꢁ
ꢀ
ꢁ
log(1 − α)
AR
θE∗(1 − 2RT/E∗)
E∗
ꢀH∗ = ꢀH(muv) 60 × 10−6 (MJ mol−1
)
(2)
log −
= log
−
T2
2.303RT
(1)
where M is the molar mass of the complex and muv = micro unit
volt. The entropy of activation (ꢀS*) and the free energy change
of activation (ꢀG*) were calculated using Eqs. (2) and (3):
where α is the mass loss up to the temperature T, R the gas con-
stant, E* theactivationenergyinJ mol−1, θ thelinearheatingrate
*
∼
and the term (1 − 2RT/E ) 1. A straight line plot of left-hand
ꢀ
ꢂ
ꢃꢁ
=
Ah
kT
side of Eq. (1) against 1/T gives the value of E* while its intercept
corresponds to A (Arrhenius constant). The linearization plots
(Fig. 7(a–d)), confirms thefirst-orderkineticsforthe decomposi-
tion process. The calculation of heat of reaction (ꢀH*) (Table 4)
ꢀS∗ = 2.303R log
(JK−1 mol−1
)
(3)
(4)
ꢀG∗ = ꢀH∗ − TꢀS∗ (J mol−1
)

B.K. Singh et al. / Spectrochimica Acta Part A 68 (2007) 63–73
71
Fig. 7. Linearization plot of (a) (ꢀ) Cu-HDMAOX complex, (b) (ꢀ)
Co–HDMAOX complex, (c) (᭹) Ni–HDMAOX complex, and (d) (♦)
Pd–HDMAOX complex.
where k and h are the Boltzman and Plank constants respec-
tively. The calculated values of E*, A, ꢀS*, ꢀH* and ꢀG* for the
decomposition steps of the complexes are appended in Table 4.
AccordingtothekineticdataobtainedfromtheTGcurves, allthe
complexes have a negative entropy which indicates that the com-
plexes are formed spontaneously. The negative value of entropy
also indicates a more ordered activated state that may be possible
through the chemisorption of oxygen and other decomposition
products. The negative values of the entropies of activation are
compensated by the values of the enthalpies of activation, lead-
ing to almost the same values for the free energy of activation
[26].
Fig. 8. (a) Optimized structure of Cu–HDMAOX complex and (b) optimized
structure of Co–HDMAOX complex.
complexation. Energy minimization was repeated several times
to find the global minimum. The computational strategy in this
study is to determine the minimum strain energy for Cu(II),
Ni(II) and Pd(II)–HDMAOX complexes, the energy minimiza-
tion values for square planar and without restricting the structure
are almost equal i.e., 4.91, 4.44 and 34.06 kcal/mol, respectively,
whereas for Co(II)–HDMAOX complex, the energy minimiza-
tion values for tetrahedral and without restricting the structure
are almost equal, i.e., 4.98 kcal/mol. This supports square planar
geometry for Cu(II), Ni(II) and Pd(II)–HDMAOX complexes
and tetrahedral geometry for Co(II)–HDMAOX complex. Some
important calculated bond length for Cu (HDMAOX)2 is Cu N,
3.6. Molecular modeling
The molecular modeling calculations for Cu(II), Co(II),
Ni(II) and Pd(II)–HDMAOX complexes were carried out using
a Hyperchem program that allows for rapid structure building,
geometry optimization and molecular display [27]. Molecu-
lar mechanics calculate the steric energy, which partition into
stretching, bending, torsion and non-bonded interactions for the
molecules and gives a stable structure with least strain energy.
It provides an ideal, computationally efficient tool to evaluate
the degree to which a ligand is structurally organized for metal
˚
˚
˚
1.831 A; Cu O, 1.769 A; N O (oxime), 1.298 A and for Co
˚
˚
(HDMAOX)2 is Co N, 1.832 A; Co O, 1.769 A; N O (oxime),
˚
1.300 A. Fig. 8(a) and (b) shows the energy-minimized structure
of Cu(II) and Co(II)–HDMAOX complex.
Table 4
Thermodynamic activation parameters of metal complexes
Complex
Order (n)
Steps
E* (J mol−1
)
A (×105 s−1
)
ꢀS* (J K−1 mol−1
)
ꢀH* (J mol−1
)
ꢀG* (kJ mol−1
)
1
I
II
22.97
24.88
0.27
0.25
−184.13
−168.33
185.93
1245.84
102.07
130.93
[Cu (HDMAOX)2]
1
1
1
I
II
45.03
45.11
0.26
0.20
−165.03
−169.45
95.55
1967.98
88.93
121.38
[Co (HDMAOX)2]
[Ni(HDMAOX)2]
[Pd (HDMAOX)2]
I
II
33.86
32.65
0.64
0.47
−158.57
−162.98
132.27
2582.03
96.57
126.45
I
II
45.93
46.78
0.20
0.19
−168.01
−169.31
272.01
2834.81
99.90
114.34

72
B.K. Singh et al. / Spectrochimica Acta Part A 68 (2007) 63–73
Fig. 9. (a) Anti-fungal screening and (b) anti-bacterial screening.
3.7. Antimicrobial activities
The free ligand and its respective metal chelates were
screened against A. alternate, A. flavus, A. nidulence and A.
niger fungi and Streproproteus, Staph, Staphylococcus and E.
coli bacteria to asses their potential antimicrobial agents. The
results are quite promising. It is clear from the antifungal screen-
ing data (Fig. 9a), that the metal complexes are more fungitoxic
than the chelating agent itself. The bacterial screening results
(Fig. 9b) reveal that the free ligand (HDMAOX) showed the
maximum activity against Streproproteus bacteria. Its copper,
cobalt and palladium complexes also showed the maximum
activity against Streproproteus bacteria whereas the nickel com-
plex showed the maximum activity against Staphylococcus
bacteria. In general, the activity was the least against Staph
bacteria.
The antimicrobial data reveal that the complexes are more
bioactive than the free ligand. The enhanced activity of the metal
complexes may be ascribed to the increased lipophilic nature of
these complexes arising due to chelation [28]. It was also noted
that the toxicity of the metal chelates increases on increasing the
metal ion concentration. It is probably due to faster diffusion of
the chelates as a whole through the cell membrane or due to
the chelation theory. The bounded metal may block enzymatic
activity of the cell or else it may catalyze toxic reactions among
cellular constituents.
Fig. 10. Proposed structure of metal–HDMAOX complexes, where M = Cu(II),
Co(II), Ni(II) and Pd(II).
It can be concluded from all the results given above that the
ligand acts as bidentate chelating agent, coordinates with transi-
tion metal ions to give square planar/tetrahedral environments,
around the metal ion anchor. The metal chelates of HDMAOX
possess reasonable antimicrobial potential. The proposed struc-
ture of the complexes (Fig. 10).
Acknowledgements
One of the authors (B.K. Singh) is thankful to University
Grants Commission, New Delhi, India for financial assistance
under research award scheme. The author UKJ is thankful to
the Principal, R.S.S. (P.G.) College, Ghaziabad (NCR, Delhi),
India, for providing necessary lab facilities.

B.K. Singh et al. / Spectrochimica Acta Part A 68 (2007) 63–73
73
References
[14] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Wiley, New York, 1978.
[15] R.M. Silverstein, O.G. Bassler, T.C. Morrill, Spectrophotometic Identifi-
cation of Organic Compounds, Wiley, New York, 1974.
[16] N.M. Shauib, A.-Z.A. Elassar, A. El-Dissouky, Spectrochim. Acta A 63
(2006) 714.
[17] B.N. Figgs, Introduction to Ligand Fields, 1st ed., 1966.
[18] D.H. Williams, I. Flemings, Spectrophotomtric Methods in Organic Chem-
istry, 4th ed., McGraw-Hill, London, 1989.
[19] T.P. Chessman, D. Hall, T.N. Waters, J. Chem. Soc. A (1966) 694.
[20] M. Ciampolini, Struct. Bonding 6 (1969) 52.
[21] K. Nakamoto, S.J. McCarthy, Spectroscopy & Structure of Metal Chelate
Compounds, John Wiley & Sons, USA, 1968.
[1] I. Georgieva, N. Tredafilova, G. Bauer, Spectrochim. Acta A 63 (2006) 403.
[2] A. Park, N.M. Kosareff, J.S. Kim, H.J. Peter de Lijser, Photochem. Photo-
biol. 82 (2006) 110.
[3] L. Rajabi, C. Courreges, J. Montoya, R.J. Aguilera, T.P. Primm, Lett. Appl.
Microbiol. 40 (2005) 212.
[4] H.I. Gul, A.A. Denizci, E. Erciyas, Arzneimittel Forschung 52 (2002) 773.
[5] M. Teruyuki, H. Yoshiharu, Y. Ka, Oxime derivative thereof, Process for
preparing thereof, Herbicidal composition and methods for the destruction
of undesirable weeds, Asahi Chemical Ind., Japan, 1986.
[6] M. Miyazawa, H. Shimamura, S. Nakamura, J. Agric. Food Chem. 48
(2000) 4377.
[22] K.I. Goldberg, J.V. Martinez, G.E. Perez, L.A. Ackerman, D.X. West,
Polyhedron 18 (1999) 1177.
[7] C. Guyot, A. Bouseta, V.V. Scheirman, J. Agric. Food Chem. 46 (1998)
625.
[23] B.K. Singh, R.K. Sharma, B.S. Garg, J. Therm. Anal. Catal. 84 (2006) 593.
[24] B.K. Singh, P. Mishra, B.S. Garg, Spectrochim. Acta A (2006) (on line
available).
[8] C.K. Wilkins, S. Scholl, Int. J. Food Microbiol. 8 (1989) 11.
[9] T. Yasuda, R. Kon, T. Nakazawa, K. Ohsawa, J. Nat. Product 62 (1999)
1142.
[10] S.N. Poddar, Analyt. Bioanalyt. Chem. 154 (1957) 254.
[11] W. Nogami, J. Pharm. Soc. Jpn. 61 (1941) 46.
[12] C. Saxena, D.K. Sharma, R.V. Singh, Phosphorus Sulfur Silicon 85 (1993)
9.
[25] A.W. Coats, J.P. Redfern, Nature 68 (1964) 201.
[26] B.K. Singh, R.K. Sharma, B.S. Garg, Spectrochim. Acta A 63 (2006) 96.
[27] Hyperchem Release 7.51 Professional Version for Windows, Molecular
Modeling System, Hyperchem Inc. Canada, 2005.
[28] L.D.S. Yadav, S. Singh, Ind. J. Chem. B 40 (2001) 440.
[13] M.M. Omar, G.G. Mohamed, Spectrochim. Acta A 61 (2005) 929.