Bivalent transition metal complexes of o-hydroxyacetophenone [N-(3-hydroxy-2-naphthoyl)] hydrazone: Spectroscopic, antibacterial, antifungal activity and thermogravimetric studies

Article abstract of DOI:10.1016/j.saa.2011.05.028

Schiff base complexes of Cu(II), Ni(II) and Zn(II) with the o-hydroxyacetophenone [N-(3-hydroxy-2-naphthoyl)] hydrazone (H ₂o-HAHNH) containing N and O donor sites have been synthesized. Both ligand and its metal complexes were characterized by different physicochemical methods, elemental analysis, molar conductivity (¹H NMR, ¹³C NMR, IR, UV-visible, ESR, MS spectra) and also thermal analysis (TG and DTG) techniques. The discussion of the outcome data of the prepared complexes indicates that the ligand behave as a bidentate and/or tridentate ligand. The electronic spectra of the complexes as well as their magnetic moments suggest octahedral geometries for all isolated complexes. The room temperature solid state ESR spectrum of the Cu(II) complex shows d _x2-y2 as a ground state, suggesting tetragonally distorted octahedral geometry around Cu(II) centre. The molar conductance measurements proved that the complexes are non-electrolytes. The kinetic thermodynamic parameters such as: E^#, ΔH^#, ΔG^#, ΔS ^# are calculated from the DTG curves, for the [Ni(H _O-HAHNH)₂] and [Zn(H_2O-HAHNH)(OAc) ₂]·H₂O complexes using the Coats-Redfern equation. Also, the antimicrobial properties of all compounds were studied using a wide spectrum of bacterial and fungal strains. The [Cu(Ho-HAHNH)(OAc)(H ₂O)₂] complex was the most active against all strains, including Aspergillus sp., Stemphylium sp. and Trichoderma sp. Fungi; E. coli and Clostridium sp. Bacteria.

Full text of DOI:10.1016/j.saa.2011.05.028

Spectrochimica Acta Part A 81 (2011) 28–34
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Bivalent transition metal complexes of o-hydroxyacetophenone
[N-(3-hydroxy-2-naphthoyl)] hydrazone: Spectroscopic, antibacterial, antifungal
activity and thermogravimetric studies
R.R. Zaky∗, K.M. Ibrahim, I.M. Gabr
Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Schiff base complexes of Cu(II), Ni(II) and Zn(II) with the o-hydroxyacetophenone [N-(3-hydroxy-2-
naphthoyl)] hydrazone (H2o-HAHNH) containing N and O donor sites have been synthesized. Both ligand
and its metal complexes were characterized by different physicochemical methods, elemental analysis,
molar conductivity (1H NMR, 13C NMR, IR, UV–visible, ESR, MS spectra) and also thermal analysis (TG
and DTG) techniques. The discussion of the outcome data of the prepared complexes indicates that the
ligand behave as a bidentate and/or tridentate ligand. The electronic spectra of the complexes as well as
their magnetic moments suggest octahedral geometries for all isolated complexes. The room temperature
solid state ESR spectrum of the Cu(II) complex shows dx2−y2 as a ground state, suggesting tetragonally dis-
torted octahedral geometry around Cu(II) centre. The molar conductance measurements proved that the
complexes are non-electrolytes. The kinetic thermodynamic parameters such as: E#, ꢀH#, ꢀG#, ꢀS# are
calculated from the DTG curves, for the [Ni(HO-HAHNH)2] and [Zn(H2O-HAHNH)(OAc)2]·H2O complexes
using the Coats–Redfern equation. Also, the antimicrobial properties of all compounds were studied using
a wide spectrum of bacterial and fungal strains. The [Cu(Ho-HAHNH)(OAc)(H2O)2] complex was the most
active against all strains, including Aspergillus sp., Stemphylium sp. and Trichoderma sp. Fungi; E. coli and
Clostridium sp. Bacteria.
Received 3 October 2010
Received in revised form 19 April 2011
Accepted 16 May 2011
Keywords:
Hydrazone complexes
1H and 13C NMR
ESR
Thermal analysis
Antimicrobial activity
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
carbonic anhydrase, carboxy peptidase, alcohol dehydrogenases,
aldoses, proteases, phosphatases, DNA- and RNA-polymerases, etc.
Transition metal ions with different oxidation state have a
strong role in bio-inorganic chemistry and redox enzyme systems
and may provide the basis of models for active sites of biological
systems [1]. Copper is the third most abundant metallic element in
the human body, following iron and zinc. It also occurs in all other
form of life and plays a role in the action of a multitude of enzymes
that catalyze a great variety of reactions [2–4]. Superoxide dismu-
tase has normal Cu(II) enzyme active sites containing tetragonally
coordinated Cu(II) ion. The “blue” copper sites [5] seem gener-
ally to be involved in electron transfer, with the copper cycling
between +1 and +2 oxidation states [6]. Nickel is an essential com-
ponent in at least 4 types of enzymes viz. urease, carbon monoxide
dehydrogenase (CODH) or acetyl coenzyme A synthase, hydroge-
nase and methyl-S-coenzyme M reductase. There is spectroscopic
evidence for nickel–methyl complexes in CODH of anaerobic bac-
teria [7,8]. Zinc is essential to all forms of life [9] and a large
number of diseases and congenital disorders have been traced
to zinc deficiency. Several zinc enzymes have been reported viz.
The metal complexes formed by the combination of transition
metal ion with a potent acylhydrazone ligand should be more
biologically active than the metal salts or the ligand individually.
Therefore, we report here the synthesis and characterization of
Ni(II), Cu(II) and Zn(II) complexes with o-hydroxyacetophenone
[N-(3-hydroxy-2-naphthoyl)] hydrazone (H2o-HAHNH). The anti-
fungal and antibacterial properties of the ligand and its complexes
were also tested.
2. Experiment
2.1. Material
All manipulations were performed under aerobic conditions. All
metal salts and other reagents used were pure (Fluka, Aldrich, or
Merck).
2.2. Preparation of o-hydroxy acetophenone [N-(3-hydroxy-2-
naphthoyl)] hydrazone (H2o-HAHNH, 1, C19H16O3N2)
∗
H2o-HAHNH (Scheme 1) was prepared by heating a mixture of 3-
hydroxy naphthoic acid hydrazide (0.01 mol; 2.02 g) and o-hydroxy
Corresponding author. Tel.: +20 105193223; fax: +20 502219214.
E-mail address: rania.zaky@yahoo.com (R.R. Zaky).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.05.028

R.R. Zaky et al. / Spectrochimica Acta Part A 81 (2011) 28–34
29
Hg[Co(SCN)4] as calibrant. The electronic spectra of the complexes
were recorded in DMSO solution on a Unicam UV2-UV–visible
spectrometer, in the range 200–900 nm. Infrared spectra of the
complexes and parent ligand were recorded on Mattson 5000 FTIR
spectrophotometer, in the range 500–4000 cm−1 in KBr disk. Mass
spectra were recorded on a Mattson 5000 FTIR spectrophotometer.
1H and 13C NMR spectra of the ligand and Zn(II) complex were
recorded in DMSO on an EM-390 (200 MHz) Spectrometer. ESR
spectra were obtained on a Bruker EMX Spectrometer working in
the X-band (9.78 GHz) with 100 kHz modulation frequency. The
microwave power was set at 1 mW and modulation amplitude was
set at 4 Gauss. The low-field signal was obtained after four scans
with a tenfold increase in the receiver gain. A powder spectrum
was obtained in a 2 mm quartz capillary at room temperature.
2.5. Biological activity
2.5.1. Antifungal activity
The ligand as well as its complexes was screened for their
antifungal activity against various fungi viz. Aspergillus sp., Tricho-
derma sp. and Stemphylium sp. These species were isolated from the
infected organs of the host plants on potato dextrose agar (potato
250 g + dextrose 20 g + agar 20 g) medium. The cultures of the fungi
were purified by single spore isolation technique. The solution in
different concentrations 0.5, 1 and 1.5 mg/ml of each compound in
DMSO were prepared for testing against spore germination. A drop
of the solution of each concentration was kept separately on glass
slides. The conidia, fungal reproducing spores (approximately 200)
lifted with the help of an inoculating needle, were mixed in every
drop of each compound separately. Each treatment was replicated
thrice and a parallel DMSO solvent control set was run concurrently
on separate glass slides. All the slides were incubated in humid
chambers at 25 2 ◦C for 24 h. Each slide was observed under the
microscope for spore germination and percent germination was
finally calculated. The results were also compared with a standard
antifungal drug Miconazole at the same concentrations.
Scheme 1. The outline of the synthesis of ligand and its complexes.
acetophenone (0.01 mol; 1.36 g) under reflux in absolute ethanol
for 2 h. On heating, pale yellow crystals were formed, filtered off,
washed with EtOH and Et2O and recrystallized from EtOH (M.p.:
290 ◦C; yield 90%). The purity of the compound was checked by
TLC.
2.3. Synthesis of metal complexes
The metal complexes were synthesized by taking 50 ml solu-
tions of each Ni(II), Cu(II) and Zn(II) acetate (10 mmol) in distilled
water and 50 ml hot ethanolic solution of the ligand H2O-HAHNH
(10 mmol, 3.20 g) in a round bottom flask. After refluxing the reac-
tants for 2–3 h and cooling to room temperature, the complexes
precipitated and were filtered in a glass crucible. The products were
washed several times with water, ethanol and finally with diethyl
ether and the pure complexes thus obtained were dried in a desicca-
tor over anhydrous CaCl2. The isolated complexes are powder-like,
stable in the normal laboratory atmosphere, and soluble in DMF or
DMSO. The characterization of these complexes was based on the
physical and spectroscopic techniques.
2.5.2. Antibacterial activity
The antibacterial activity of the ligand and its complexes were
studied against Clostridium sp. and E. coli bacteria. Each of the
compounds was dissolved in DMSO and solutions of the concentra-
tion 2 mg/ml and 1 mg/ml were prepared separately. Paper discs of
Whatman filter paper (No. 42) of uniform diameter (2 cm) were cut
and sterilized in an autoclave. The paper discs soaked in the desired
concentration of the complex solutions were placed aseptically in
the petridishes containing nutrient agar media (agar 20 g + beef
extract 3 g + peptone 5 g) seeded with Clostridium sp. and E. coli
bacteria separately. The petridishes were incubated at 37 ◦C and
the inhibition zones were recorded after 24 h of incubation. Each
treatment was replicated 9 times. The antibacterial activity of a
common standard antibiotic Ampicillin was also recorded using
the same procedure as above at the same concentrations and sol-
vent. The % Activity Index for the complex was calculated by the
formula as under:
2.4. Analyses of the complexes
2.4.1. Elemental analyses
The complexes were analyzed for metal content gravimetrically
by literature procedures [10] after decomposing the organic mat-
ter with a mixture of HNO3 and HCl and evaporating the residue
to dryness with concentrated H2SO4. Carbon and hydrogen were
determined microanalytically at the Microanalytical Unit of Cairo
University.
Activity Index
Zone of inhibition by test compound (diametre)
=
× 100
2.4.2. Physico-chemical measurements
Zone of inhibition by standard (diametre)
The molar conductance of the complexes were determined by
preparing 10−3 M solutions of the complexes in DMSO at room
temperature and measured on a YSI Model 32 conductivity bridge.
Thermogravimetric analysis was performed using an automatic
recording thermobalance type (DuPont 951 Instrument). Ther-
mal Analyzer between room temperature and 800 ◦C. Magnetic
moment values were evaluated at room temperature (25 1 ◦C)
using a Johnson Matthey magnetic susceptibility balance using
Determination of minimum inhibitory concentration (MIC)
value: the antibacterial screening concentrations of the compounds
to be used were estimated from the minimum inhibitory con-
centration (MIC) value. The MIC was determined using the disc
diffusion technique by preparing discs containing 0.1–1.0 mg/ml
of each compound against both the bacteria and applying the pro-
tocol. All the compounds were more effective at 1.0 and 2.0 mg/ml

30
R.R. Zaky et al. / Spectrochimica Acta Part A 81 (2011) 28–34
Table 1
Analytical and physical data of H2O-HAHNH and its metal complexes.
a
Compound
Empirical formula
F.W. Found (Calcd.)
Colour
MP (◦C)
Yield (%)
% found (Calcd)
C
ꢁm
H
M
H2O-HAHNH
C19H16O3N2
320.212 (320.350)
[Ni(Ho-HAHNH)2]
Yellow
290
>300
>300
>300
90
85
75
80
71.24
(71.27)
5.08
(5.03)
–
–
–
4
5
3
Green
65.54
(65.44)
4.45
(4.33)
8.37
(8.42)
NiC38
H30O6N4
696.914 (697.397)
[Cu(Ho-HAHNH)(OAc)(H2O)2]
CuC21H22O7N2
Green
52.93
(52.77)
4.56
(4.63)
13.17
(13.29)
477.636 (477.955)
[Zn(H2o-HAHNH)(OAc)2]·H2O
Yellowish-white
52.99
(52.94)
4.70
(4.64)
12.65
(12.53)
ZnC23H24O8N2
521.341 (521.827)
a
In DMSO (ꢂ−1 cm2 mol−1).
concentrations. Consequently all the compounds were screened at
these concentrations against both the bacteria. The results of MIC
values (mg/ml) are given in Table 7.
Comparison of the infrared spectrum of the ligand with those of
its metal complexes reveals that H2O-HAHNH behaves as a biden-
tate and/or tridentate ligand depending on the metal salt and the
reaction conditions (see Table 2).
In [Zn(H2O-HAHNH)(OAc)2]·H2O, complex, H2O-HAHNH acts as
a neutral bidentate ligand coordinating via carbonyl oxygen (C O)
and azomethine nitrogen (C N). This mode of chelation is sup-
ported by shift of both ꢃ(C N) and ꢃ(C O) vibrations to lower
wavenumber. The ꢃ(NH) vibration remains more or less at the same
position. The ꢃ(OH)naphthoic is shifted to higher wavenumber. Also,
the infrared spectra of these complexes show new bands at the
525 and 432 cm−1 assignable to ꢃ(Zn–O) and ꢃ(Zn–N), respectively
[16]. In addition, the Zn(II) complex shows two bands at 1380 and
1578 cm−1 which can be assigned to ꢃas(O–C–O) and ꢃs(O–C–O) of
the acetate group with a difference (198 cm−1) between those two
bands indicates a monodentate acetate [17].
Also, H2O-HAHNH behaves as a mononegative tridentate lig-
and coordinating through the azomethine nitrogen (C N), carbonyl
oxygen (C O) and (OH)naphthoic with the displacement of the hydro-
gen atom from the latter group. This behavior is observed in
[Ni(HO-HAHNH)2] complex. This mode of chelation is based on the
disappearance of the (OH)naphthoic and the shift of both ꢃ(C O) and
ꢃ(C N) to lower wavenumbers. Also, the new bands were observed
at the 520 and 430 cm−1 tentatively attributed to ꢃ(Ni–O) and
ꢃ(Ni–N), respectively.
3. Results and discussion
The ligand and its complexes are stable in air, the ligand is
soluble in common organic solvents but its complexes are solu-
ble only in DMF and DMSO. Elemental analysis of the ligand and
its complexes are in agreement with the presented formula (see
Table 1). Molar conductivity values indicate that complexes are
non-electrolytes.
3.1. IR spectral studies
The infrared spectrum of H2O-HAHNH displays five bands at
1647, 1618, 3125, 3240 and 3419 cm−1 assigned to ꢃ(C O) [11] and
ꢃ(C N)hydrazone [12], ꢃ(NH) [13], (OH)naphthoic and (OH)phenolic [14]
vibrations, respectively (see Table 2). The two bands at 1273 and
1365 cm−1 are attributed to ı(OH)phenolic and ı(OH)naphthoic. The
appearance of (OH)naphthoic and(OH)phenolic as a broad band at lower
wavenumbers and the two weak broad bands in the 1900–2080 and
2150–2230 cm−1 regions suggest intramolecular hydrogen bond-
ing (O–H· · ·O) [15] as shown in Fig. 1.
Moreover, in [Cu(HO-HAHNH)(OAc)(H2O)2] complex H2O
-
HAHNH acts as a mononegative bidentate ligand coordinating via
azomethine nitrogen (C N) and deprotonated enolized carbonyl
group forming five membered ring including the metal atom. This
mode of complexation is supported by the disappearance of both
ꢃ(C O) and ꢃ(NH) with simultaneous appearance of new bands
at 1638 and 1148 cm−1 regions assignable to ꢃ(C N*) and enolic
ꢃ(C–O) [18]; the negative shift of ꢃ(C N) and the appearance of
new bands at 530 and 424 cm−1 assigned to ꢃ(M–O) and ꢃ(M–N),
respectively [16]. The Cu(II) complex shows two bands at 1444
and 1539 cm−1 attributable to the ꢃas(O–C–O) and ꢃs(O–C–O) of
the acetate group. The difference (95 cm−1) between those two
bands indicating the bidentate bonding for the acetate group
[19]. Also, the bands of coordinated water observed at 821and
537 cm−1 are assigned to ꢄr(H2O) and ꢄw(H2O), respectively [19].
Moreover, strong evidence for the presence or absence of water
of crystallization and/or coordinated water supported by the
thermogram of all complexes.
(d)
(c)
(b)
(a)
4000
3000
2000
1000
Wavenumber (cm-1)
3.2. Nuclear magnetic resonance spectral studies
The 1H NMR and 13C NMR spectra of H2O-HAHNH and its zinc
complex (Scheme 2) were recorded in DMSO. The 1H NMR spec-
Fig. 1. IR spectra of (a) H2O-HAHNH, (b) [Cu(H2O-HAHNH)(OAc)(H2O)2], (c) [Ni(HO-
HAHNH)2] and (d) [Zn(H2O-HAHNH)(OAc)2]·H2O complexes.

R.R. Zaky et al. / Spectrochimica Acta Part A 81 (2011) 28–34
31
Table 2
Most important IR spectral bands of H2O-HAHNH, its metal complexes in cm−1
.
Compound
ꢃ(OH)naphthoic
ꢃ(OH)phenolic
ꢃ(NH)
ꢃ(C O)
ꢃ(C N)
ꢃ(C–O)naphthoic
ꢃ(M–O)
ꢃ(M–N)
H2o-HAHNH
[Ni(Ho-HAHNH)2]
[Cu(Ho-HAHNH)(OAc)(H2O) 2
[Zn(H2o-HAHNH) (OAc)2]·H2O
3240
–
3506
3440
3419
3442
3459
3434
3125
3185
–
1647
1630
–
1618
1604
1593
1600
1219
1223
1239
1222
–
520
530
525
–
430
424
432
]
3245
1630
trum of H2O-HAHNH in DMSO shows three signals at 11.24, 12.19
and 11.32 ppm assignable to the protons of (NH), (OH)naphthoic and
(OH)phenolic, respectively. The appearance of the signal attributed to
the proton of OH group at a high value downfield from TMS suggests
the presence of intramolecular hydrogen bonding. The multiplet
signals observed in the 6.92–8.67 ppm region are assigned to the
aromatic protons. Also, the 1H NMR spectrum of the Zn(II) com-
plex shows the signals attributed to the NH and OH protons remain
more or less at the same positions indicating that these groups play
no part in coordination. From 13C NMR spectral data (Table 3), for
the zinc complex, the signals for the C–O carbon and C–N carbon
showed an upfield shift on complexation [20] compared with the
free ligand. Also, the appearance of new signals at ı = 174 ppm and
ı = 51 ppm give strong evidence for the presence of acetate group.
The other ring carbon atoms did not show significant shifts.
3.4. ESR studies
The solid-state ESR spectrum (Fig. 2) of [Cu(HO-
HAHNH)(OAc)(H2O)2] exhibits axially symmetric g-tensor
parameters with
g
(2.27) > g (2.06) > 2.0023 indicating that
||
⊥
2
the copper site has a dx − y2 ground-state characteristic of tetra-
hedral, square planar or octahedral stereochemistry [22]. The
spin-Hamiltonian parameters of this complex was calculated.
In axial symmetry the g-values are related by the expression,
G = (g − 2)/(g⊥ − 2) = 4, where
G is the exchange interaction
||
parameter. According to Hathaway [23], if the value of G is greater
than 4, the exchange interaction between Cu(II) centres in the solid
state is negligible, whereas when is less than 4, a considerable
exchange interaction is indicated in the solid complex. The calcu-
lated G value was 4.5 suggesting that there are no copper–copper
exchange interactions.
The tendency of A (160 × 10−4 cm−1) to decrease with increas-
||
ing of g is an index of an increase of the tetrahedral distortion
||
3.3. Electronic spectra
in the coordination sphere of copper [24,25]. In order to quan-
tify the degree of distortion of the Cu(II) complexes, we selected
The electronic spectrum of [Ni(HO-HAHNH)2] complex con-
tains two bands at 14,084 and 23,812 cm−1 assigned to
the f factor g /A obtained from the ESR spectra. Where, the f
|| ||
factor is regarded as an empirical index of tetrahedral distortion.
Its value ranges between 105 and 135 for square planar com-
plexes, depending on the nature of the coordinated atoms. In the
presence of a tetrahedrally distorted structure the values can be
3
3
3A2¯g(F) → T1¯g(F) and 3A2¯g(F) → T1g(P) transitions, respectively,
in an octahedral geometry [21]. The calculated values of 10Dq
(870 cm−1), B (791 cm−1), ˇ (0.76 cm−1) and ꢃ2/ꢃ1 (1.63 cm−1) val-
ues lie in the range reported for octahedral structure. The position of
ꢃ1 (8640 cm−1) is calculated theoretically. The magnetic moments
(ꢅeff = 3.20 BM), can be taken as an additional evidence for an octa-
hedral geometry.
much larger. For this complex, the g /A quotient is 141, demon-
|| ||
strating the presence of significant dihedral angle distortion in
the dxy-plane and indicating a tetrahedral distortion from square-
planar geometry. Superhyperfine structure for this complex was
not seen at higher fields, excluding any interaction of the nuclear
spins of nitrogen (I = 1) with the unpaired electron density on
Cu(II) [13].
The Cu(II) complex has magnetic (1.83 BM), which is close
to the spin value for one unpaired electron and within the
general range for Cu(II) complexes. The electronic spectrum of
[Cu(HO-HAHNH)(OAc)(H2O)2] complex contains a broad band at
16,667 cm−1 with a shoulder at 14,285 cm−1 which assigns to
2
2
2B1¯g → Eg and 2E1¯g → A1¯g transitions, respectively, as reported
for tetragonally distorted octahedral configuration [21].
2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4600
G (Gauss)
Scheme 2. 13C NMR spectra of (A) H2O-HAHNH and (B) [Zn(H2o-
HAHNH)(OAc)2]·H2O complex.
Fig. 2. Room temperature solid state X-band ESR spectrum of [Cu(HO-
HAHNH)(OAc)(H2O)2] complex.

32
R.R. Zaky et al. / Spectrochimica Acta Part A 81 (2011) 28–34
Table 3
13C NMR chemical shift in (ppm) assignments for H2OHAHNH and [Zn(H2O-HAHNH) (OAc)2]·H2O.
Assignment
H2o-HAHNH
[Zn(H2o-HAHNH) (OAc)2]·H2O
118
131
164
119
163C1
HO
C1
O
135
133
122
H
170
C3
48
H3C
Zn
123
N
C
C2
135
C2
HN
178C3
120
120
128
N
129
170
124
130
C1520
NH
O
O
C4
45
165
174
131
113
130
131
138
127
C4
O
O
C
127
O
126
131
51
C5
H
174
127
C6
136
O
O
157
51
128
C6
HO
156
111
C1
C2
C3
C4
C5
C6
163
120
178
170
120
157
164
120
170
165
127
156
Molecular orbital coefficients, ˛2 (covalent in-plane ␴-bonding)
and ˇ2 (covalent in-plane ␲-bonding) were calculated:
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
ꢀ
ꢁ
A
3(g⊥ − 2.0023)
||
2
˛
=
+ (g|| − 2.0023) +
+ 0.04
0.000
0.036
7
(g|| − 2.0023)E
ˇ2
=
−8ꢆ˛2
ꢆ = 828 cm−1 for the free ion and E is the 2B1¯g → A1¯g transition.
2
As a measure of the covalency of the in-plane ␴-bonding ˛2 = 1
indicates complete ionic character, whereas ˛2 = 0.5 indicates 100%
covalent bonding, with the assumption of negligibly small values
of the overlap integral. The ˇ2 parameter gives an indication of the
covalency of the in-plane ␲-bonding. The smaller ˇ2, indicates the
larger covalency of the bonding.
-0.005
0
100
200
300
400
500
600
700
800
The values of ˛2 (0.77) and ˇ2 (0.87) for the complex indi-
cate that the in-plane ␴-bonding and in-plane ␲-bonding are
appreciably covalent and are consistent with very strong in-plane
␲-bonding in this complex. These results are anticipated because
there are appropriate ligand orbitals to combine with the dxy
Temp C
Fig. 3. TG, DTG of [Ni(HO-HAHNH)2] complex.
orbital of the Cu(II) ion. The higher values of ˇ2 compared with
decomposition of the complex begins. In the temperature range
380–575 ◦C (see Table 4), the TG curve is indicative of 73.9% weight
loss (Fig. 3) which could be ascribed to the elimination of the two
loosely bound (C19H15O) moieties. The final weight loss of 14.6%
ending at 772 ◦C, is attributed to complete decomposition of the
remaining more tightly bound fragment of the organic molecule,
alongside rupture of the chelate bond, leaving NiO comprising
11.5% of the initial mass of the complex.
2
˛
indicate that the in-plane ␲-bonding is less covalent than the
in-plane ␴-bonding. These data are highly consistent with other
reported values.
3.5. Thermal analysis
The TG and DTG curves of [Ni(HO-HAHNH)2] complex show
that it is thermally stable up to 380 ◦C, above which point partial
Table 4
Thermal behavior of metal complexes of H2O-HAHNH.
Complex (Mol. wt.)
Temp. range (◦C)
Decomp. prod (formula wt.)
Wt. loss (%)
Found
73.9
Calcd
74.4
[Ni(HO-HAHNH)2]
(697.397)
380–575
2C19H15O
(518.661)
O3N4
(104.268)
Residue, NiO
(74.710)
H2O
575–772
>772
14.6
11.5
3.5
14.9
10.7
3.5
[Zn(H2O-HAHNH)(OAc)2]·H2O
62–151
(521.827)
(18.016)
297–410
C6H5O
17.9
17.8
(93.106)
410–659
>659
C13H11N2O + 2C2H3O2 (329.335)
Residue, ZnO
63.0
15.6
63.1
15.6
(81.369)

R.R. Zaky et al. / Spectrochimica Acta Part A 81 (2011) 28–34
33
Table 5
Kinetic and thermodynamic parameters for some decomposition steps of Ni(II) and Zn(II) complexes of H2O-HAHNH.
Complex
Step
r
A (S−1
)
E# (kJ mol−1
)
ꢀS# (J mol−1 K−1
)
ꢀH# (kJ mol−1
)
ꢀG# (kJ mol−1
)
[Ni(HO-HAHNH)2]
[Zn(H2O-HAHNH)(OAc)2] H2O
1st
2nd
3th
0.874
0.999
0.994
299
31.0
9106.1
124
50.9
137.1
−118
134
46.2
130.4
227
172
273.6
−221.7
−177.3
The [Zn(H2O-HAHNH)(OAc)2]·H2O complex is thermally stable
up to 62 ◦C above which the dehydration begins. This relative low
temperature suggests that the water molecule is out of coordina-
tion sphere of the zinc ion. Thermal degradation of the organic
molecule starts above 297 ◦C. Over the temperature 297–410 ◦C,
the weight loss 17.9% in the TG curve is most probably ascribed to
the partial decomposition of the chelating agent with the elimina-
tion of the (C6H5O) moiety. The final weight loss of 63.0% ending
at 659 ◦C, is largely attributed to complete decomposition of the
remaining organic molecule (C13H11N2O) as well as two acetate
groups (2C2H3O2), alongside rupture of the chelate bond, leaving
ZnO comprising 15.6% of the initial mass of the complex.
For more information about the effects of anions, the structural
properties and the bonding coefficients on the thermal behavior of
the complexes, the order, n, and the heat of activation E# of the
decomposition steps were determined from the TG and DTG ther-
mogramms for some steps of decomposition of Ni(II) and Zn(II)
complexes of HO-HAHNH using the Coats–Redfern equations [26]:
fragments which require more energy for its rearrangement before
final decomposition (Table 5).
3.6. Antifungal activity
The experimental antifungal activity data (Table 6) indicate that
the ligand as well as its complexes shows an appreciable activity
against Aspergillus sp., Stemphylium sp. and Trichoderma sp. at 0.5,
1.0 and 1.5 mg/ml concentration. Their activity generally increases
with increasing the concentration of the compounds. DMSO con-
trol has shown a negligible activity as compare to the ligand and
its metal complexes. The experimental results of the compounds
were compared against DMSO as the control and are expressed
as percentage inhibition versus control. The complexes are more
effective against Aspergillus sp. than Stemphylium sp. and Tricho-
derma sp. [Cu(HO-HAHNH)(OAc)(H2O)2] shows the highest activity
(96%) against Aspergillus sp. at the concentration of 1.5 mg/ml
among all the metal complexes. The same complex also shows
the highest activity (94%) against Stemphylium sp. The antifungal
activity varies in the following order of fungal species:
ꢂ
ꢄ
ꢃ
1 − (1 − ˛)1−n
(1 − n)T2
M
T
In
In
=
+ B for n =/ 1
(1)
(2)
Aspergillus sp. > Stemphylium sp. > Trichoderma sp.
All the metal complexes exhibited greater antifungal activity
against Aspergillus sp. as compare to the standard drug Miconazole.
The Ni(II), Cu(II) and Zn(II) complexes show better activity against
Stemphylium sp. than the standard, whereas, Zn(II) complex is more
effective against Trichoderma sp. From the data it has also been
observed that the complexes are more active than the ligand [28].
The toxicity of the complexes can be related to the strength of the
metal–ligand bond, besides other factors such as size of the cation
[29]. Where, the higher the size of metal ion, the higher the anti-
fungal activity of the complex. Also, the study exhibited that any
metal salt alone has higher activity than its investigated complex.
However, metal salts alone cannot be used as antibacterial agents
because of their natural toxicities and the probability of binding to
the free ligand [30] presented in the biological systems such as the
nitrogen bases of nucleic acids and/or proteins.
ꢅ
−In(1 − ˛)
M
=
+ B for n = 1
T2
T
where M = −E#/R and B = ln AR/˚E#; E#, R, A and ˚ are the heat
of activation, the universal gas constant, pre-exponential factor
and heating rate, respectively. The correlation coefficient, r, was
computed using the least squares method for different values of
n, by plotting the left-hand side of the Eqs. (1) and (2) versus
1000/T. The n value which gave the best fit (r ≈ 1) was chosen as the
order parameter for the decomposition step of interest. From the
intercept and linear slope of each step, the A and E# values were
determined. The other thermodynamic parameters, ꢀH#, ꢀG#
and ꢀS# were computed using the relationships: ꢀH# = E# − RT,
ꢀS# = R[ln(Ah/kT) − 1] and ꢀG# = ꢀH# − TꢀS, where k is the Boltz-
mann’s constant and h is Planck’s constant. The thermodynamic
parameters are listed in Table 4.
3.7. Antibacterial activity
It has been found that, most of the activation entropies ꢀS#
are negative, indicating that the reactions are slow or the acti-
vated complex is more ordered than the reactants [27]. The
positive values of ꢀH# mean that the decomposition processes are
endothermic. The values of ꢀG# increase significantly for the sub-
sequent decomposition stages of a given complex due to increasing
of TꢀS. Increasing the values of ꢀG# reflects the structural rigidity
of the remaining fragments after the expulsion of one and more
The metal complexes, ligand, standard drug Ampicillin and
DMSO solvent control were screened separately for their antibac-
terial activity against E. coli and Clostridium sp. at 1.0 and 2.0 mg/ml
concentration. Their activity is greatly enhanced at the higher con-
centration [31]. The activity of the complexes has been compared
with the activity of a common standard antibiotic Ampicillin and %
Activity Index for the complexes has been calculated. The antibac-
terial results suggest that the ligands and their complexes (Table 7)
Table 6
Antifungal activity of the ligand and its complexes.
Compound
% inhibition of spore germination
Aspergillus sp. (mg/ml)
Stemphylium sp. (mg/ml)
Trichoderma sp. (mg/ml)
0.5
1.0
1.5
0.5
1.0
1.5
0.5
1.0
1.5
Miconazole (standard)
H2o-HAHNH
[Ni(Ho-HAHNH)2]
[Cu(Ho-HAHNH)(OAc)(H2O)2]
[Zn(H2o-HAHNH)(OAc)2]·H2O
62
34
55
58
52
80
45
76
88
70
90
60
90
96
90
52
41
59
54
49
70
55
75
76
69
90
62
88
94
86
55
43
49
54
47
70
56
68
69
60
92
59
85
83
90

34
R.R. Zaky et al. / Spectrochimica Acta Part A 81 (2011) 28–34
Table 7
Antibacterial activity of the ligand and its complexes.
Compound
E. coli (mg/ml)
Clostridium sp. (mg/ml)
MIC Diameter of inhibition % Activity Index
MIC
(mg/ml)
Diameter of inhibition % Activity Index
zone (in mm)
(mg/ml)
zone (in mm)
1.0
2.0
1.0
2.0
1.0
2.0
1.0
2.0
Ampicillin (standard)
H2o-HAHNH
[Ni(Ho-HAHNH)2]
[Cu(Ho-HAHNH)(OAc)(H2O)2]
[Zn(H2o-HAHNH)(OAc)2]·H2O
0.2
0.8
0.4
0.4
0.3
16
3
13
13
10
19
4
16
16
13
100
19
81
81
63
100
21
84
90
0.3
0.7
0.4
0.4
0.5
14
5
12
12
9
17
7
14
16
12
100
36
86
86
64
100
41
88
94
71
68
show a moderate activity against both the bacteria [32,33] as com-
pared to the standard drug (Ampicillin). The metal complexes show
higher antibacterial activity than the ligand. The DMSO control
showed no activity against any bacterial strain. The % Activity Index
data show the highest activity for [Cu(HO-HAHNH)(OAc)(H2O)2]
against E. coli and Clostridium sp. at the concentration of 2.0 mg/ml.
The complexes are more effective against Clostridium sp. than E. coli
and show better antibacterial activity than the ligand.
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