Synthesis, characterization, biological activity and equilibrium studies of metal(II) ion complexes with tridentate hydrazone ligand derived from hydralazine

Article abstract of DOI:10.1016/j.saa.2012.08.034

In the present study, a new hydrazone ligand (2-((2-phthalazin-1-yl) hydrazono)methyl)phenol) prepared by condensation of hydralazine (1-Hydralazinophthalazine) with salicylaldehyde (SAH). The synthesized SAH-hydrazone and its metal complexes have been characterized by elemental analyses, IR, ¹H NMR, solid reflectance, magnetic moment, molar conductance, mass spectra, UV-vis and thermal analysis (TGA). The analytical data of the complexes show the formation of 1:1 [M:L] ratio, where M represents Ni(II), Co(II) and Cu(II) ions, while L represents the deprotonated hydrazone ligand. IR spectra show that SAH is coordinated to the metal ions in a tridentate manner through phthalazine-N, azomethine-N and phenolic-oxygen groups. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria and fungi. Proton-ligand association constants of (SAH) and the stepwise stability constants of its metal complexes are determined potentiometrically in 0.1 M NaNO₃ at different temperatures and the corresponding thermodynamic parameters were derived and discussed. The order of -ΔG° and -ΔH° were found to obey Mn²⁺ < Co²⁺ < Ni²⁺ < Cu²⁺, in accordance with the Irving-Williams order. The complexes were stabilized by enthalpy changes and the results suggest that the complexation is an enthalpy-driven process. The concentration distribution diagrams of the complexes are evaluated.

Full text of DOI:10.1016/j.saa.2012.08.034

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization, biological activity and equilibrium studies
of metal(II) ion complexes with tridentate hydrazone ligand derived from
hydralazine
⇑
Ahmed A. El-Sherif, Mohamed M. Shoukry , Mohamed M.A. Abd-Elgawad
Department of Chemistry, Faculty of Science, Cairo University, Cairo, Egypt
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
A new hydrazone ligand derived
from the biologically active
hydralazine was synthesised and
characterized.
"
"
Metal complexes were synthesised
and characterized and showed
promising biological activity.
Stability and structural
characterization of the complexes
are supporting the biological activity
of this class of complexes.
"
Stability constant data is used to
calculate the equilibrium
distribution of the metal complexes
in biological fluids.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 June 2012
Received in revised form 10 August 2012
Accepted 14 August 2012
Available online 1 September 2012
In the present study, a new hydrazone ligand (2-((2-phthalazin-1-yl)hydrazono)methyl)phenol) prepared
by condensation of hydralazine (1-Hydralazinophthalazine) with salicylaldehyde (SAH). The synthesized
SAH-hydrazone and its metal complexes have been characterized by elemental analyses, IR, 1H NMR,
solid reflectance, magnetic moment, molar conductance, mass spectra, UV–vis and thermal analysis
(TGA). The analytical data of the complexes show the formation of 1:1 [M:L] ratio, where M represents
Ni(II), Co(II) and Cu(II) ions, while L represents the deprotonated hydrazone ligand. IR spectra show that
SAH is coordinated to the metal ions in a tridentate manner through phthalazine-N, azomethine-N and
phenolic-oxygen groups. The ligand and their metal chelates have been screened for their antimicrobial
activities using the disc diffusion method against the selected bacteria and fungi. Proton-ligand associa-
tion constants of (SAH) and the stepwise stability constants of its metal complexes are determined poten-
tiometrically in 0.1 M NaNO3 at different temperatures and the corresponding thermodynamic
Keywords:
Hydrazones
Metal(II)
Hydralazine
Electronic spectra
Stability constants
Biological activity
parameters were derived and discussed. The order of ꢀ
DG° and ꢀ
D
H° were found to obey Mn2+ < Co2+
< Ni2+ < Cu2+, in accordance with the Irving–Williams order. The complexes were stabilized by enthalpy
changes and the results suggest that the complexation is an enthalpy-driven process. The concentration
distribution diagrams of the complexes are evaluated.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
effectively controlling a specific reaction. Without the appropriate
metal ion, a biochemical reaction would proceed very slowly, if at
Metal ions play essential roles in most of biochemical processes
[1]. These ions can modify electron flow in a substrate, then
all. The interest in the study of hydralazine compounds has
recently been grown up due to their biological activity and coordi-
nation capacity [2,3]. They find wide applications in the treatment
of diseases such as tuberculosis, leprosy, and mental disorder. Also,
they can be used as antihypertensive, antimicrobial, antimalarial
⇑
Corresponding author. Tel.: +21 001834458; fax: +20 2 35728843.
E-mail address: shoukrymm@hotmail.com (M.M. Shoukry).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.08.034

308
A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
and antitumor [4]. The preparation of a new ligand was perhaps
the most important step in the development of metal complexes
which exhibit unique properties and novel reactivity. Since the
electron donor and electron acceptor properties of the ligands,
structural functional groups and the position of the ligand in the
coordination sphere together with the reactivity of coordination
compounds may be the factor for different studies [5,6]. Hydra-
zones were important class of ligands, such ligands have interest-
ing ligation properties due to presence of several coordination sites
[7]. Hydrazone ligands create an environment similar to biological
systems by usually making coordination through oxygen and nitro-
gen atoms. Coordination chemistry of metal complexes of hydra-
zones [8] has gained a special attraction due to their biological
activity and their ability to act as potential inhibitors for many en-
zymes [9]. Hydrazone derivatives possessing anti-inflammatory,
analgesic [10], antipyretic [11], antibacterial [12] and antitumor
[13] activities are also reported in the literature. With the above
in mind, and in conjunction with our studies of metal complexes
of biological significance [14–19], the present work is devoted to
the preparation of hydrazone ligand derived from hydralazine with
salicylaldehyde and its metal complexes. The study also includes
biological activity of the synthesized complexes.
of ethanol and sodium acetate (3.46 g, 0.01 mmol) in 10 ml water
as a buffering agent. The mixture then refluxed with stirring for
3 h. The product was left overnight then removed by vacuum filtra-
tion, washed several times by water, EtOH and Et2O, and finally
crystallized from EtOH. The ligand (HL) formed yellow crystals
and yield 85%.
2.3. Preparation of the solid complexes
Copper(II), Nickel(II) and Cobalt(II) complexes of the SAH were
prepared by direct mixing of 0.5 mmol of metal salt and the corre-
sponding amount of SAH-hydrazone ligand and sodium acetate.
The metal chloride was dissolved in water and ligand was dis-
solved in ethanol and sodium acetate in the smallest possible vol-
ume of water. The mixture was refluxed for 1–3 h. The formed
solid complexes were separated by filtration and then washed sev-
eral times with acetone and then diethyl ether. The solid com-
plexes were dried in vacuum desiccator. The yield ranged from
79% to 82%. The complexes are soluble in ethanol, methanol,
DMF and DMSO. The dried complexes were subjected to elemental
and spectroscopic analysis.
2.4. Biological activity
2. Experimental
Antimicrobial activity of the tested samples was determined
using a modified Kirby-Bauer disc diffusion method [21]. Briefly,
2.1. Materials
100
ia until they reached a count of approximately 108 cells/ml or
105 cells/ml for fungi [22]. 100 l of microbial suspension was
ll of the test bacteria/fungi were grown in 10 ml of fresh med-
All chemicals used in this investigation were laboratory
pure including hydralazine, CuCl2ꢁ2H2O, NiCl2ꢁ6H2O, CoCl2ꢁ6H2O,
MnCl2ꢁ4H2O, DMSO and salicylaldehyde were obtained from Sigma
Chem. Co. Metal salt solutions were prepared and standardized as
described previously [20]. NaOH solution (titrant) was prepared
and standardized against potassium hydrogen phthalate solution.
All solutions were prepared in deionized water.
l
spread onto agar plates corresponding to the broth in which they
were maintained. Isolated colonies of each organism that might
be playing a pathogenic role should be selected from primary agar
plates and tested for susceptibility by disc diffusion method of the
National Committee for Clinical Laboratory Standards (NCCLS)
[23]. Among the available media available, NCCLS recommends
Mueller–Hinton agar due to: it results in good batch-to-batch
reproducibility. Disc diffusion method for filamentous fungi tested
by using approved standard method (M38-A) developed by the
NCCLS [24] for evaluating the susceptibilities of filamentous fungi
to antifungal agents. Disc diffusion method for yeasts developed by
2.2. Preparation of hydrazone ligand
The hydrazone ligand abbreviated as SAH was prepared by
mixing an ethanolic solution (20 ml) of 2.01 g (0.01 mol) of salicyl-
aldehyde with 1.13 g (0.01 mol) of hydralazine in the same volume
NH2
NH
OH
CHO
N
N
EtOH
+
H
N
N
OH
N
N
M2+/EtOH/H2 O/Reflux
H
N
N
M
.nH2O
O
Cl
N
N
M = Cu(II); n = H2 O
= Ni(II), n = H
2 O
= Co(II); n = 2H 2 O
Scheme 1. The general proposed structure for MII-SAH complexes.

A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
309
Table 1
Analytical and physical data of compounds.
Compound
M wt.
% Yield
Color
% Found (Calc.)
C
H
N
Cl
M
SAH
264.3
85%
79%
82%
81%
Yellow
48.49 (48.17)
47.45 (47.37)
47.85 (47.99)
45.88 (45.76)
3.39 (4.58)
3.72 (3.45)
3.38 (3.49)
3.78 (3.84)
4.80 (21.20)
–
–
[Cu(SAH)Cl]ꢁH2O (1)
[Ni(SAH)Cl]ꢁH2O (2)
[Co(SAH)Cl]ꢁ2H2O (3)
380.29
375.44
393.69
Pale green
Dark green
Reddish brown
14.47 (14.73)
14.98 (14.92)
14.12 (14.23)
9.19 (9.32)
9.25 (9.44)
8.95 (9.01)
16.81 (16.71)
15.59 (15.63)
14.86 (14.97)
Table 2
Tentative assignment of the important infrared bands of the synthesized complexes.
Compound
t
t
–
3365
3400
3410
(cmꢀ1
(H2O)
)
t
(OH)
t
(C@N)
d(O–H)
t
(C–O)phenolic
d(NH)
t
(NH)
Ar-ring
t
(M–N)
t
(M–O)
–
t(M–Cl)
SAH
(1)
(2)
3387
1607
1597
1602
1597
1471
1462
1445
1454
1263
1246
1249
1247
1527
1548
1530
1535
3315
3054
3016
3046
960, 912, 786, 750
965, 909, 812, 758
943, 911, 841, 736
955, 918, 860, 747
–
–
–
–
520
498
594
467
444
457
345
348
352
(3)
using approved standard method (M44-P) by the NCCLS [25].
Plates inoculated with filamentous fungi as Aspergillus flavus at
25 °C for 48 h; Gram (+) bacteria as Staphylococcus aureus, Bacillus
subtilis; Gram (ꢀ) bacteria as Escherichia coli, Pseudomonas aeuro-
ginosa, they were incubated at 35–37 °C for 24–48 h and fungi as
A. flavus and Candida albicans incubated at 30 °C for 24–48 h and
then the diameters of inhibition zones were measured in millime-
ters [21]. Standard discs of Ampicillin (Antibacterial agent), Ampho-
solvent were used as a negative control. The agar used is Meul-
ler–Hinton agar that is rigorously tested for composition and pH.
Further the depth of the agar in the plate is a factor to be consid-
ered in the disc diffusion method. This method is well documented
and standard zones of inhibition have been determined for suscep-
tible and resistant values. Blank paper disks (Schleicher and Schu-
ell, Spain) with a diameter of 8.0 mm were impregnated with 10 ll
of tested concentration of the stock solutions. When a filter paper
disc impregnated with a tested chemical is placed on agar, the
chemical will diffuse from the disc into the agar. This diffusion will
tericin
B (Antifungal agent) served as positive controls for
antimicrobial activity but filter discs impregnated with 10 ll of
110
100
90
SAH
80
70
60
50
3900
3400
2900
2400
1900
1400
900
400
-1
Wave number (cm )
120
110
100
90
[Cu(SAH)Cl]
80
70
60
50
40
30
4000
3500
3000
2500
2000
1500
1000
500
-1
Wave number (cm )
Fig. 1. FTIR of SAH-Schiff base ligand and [Cu(SAH)Cl] complex.

310
A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
Table 3
place the chemical in the agar only around the disc. The solubility
of the chemical and its molecular size will determine the size of the
area of chemical infiltration around the disc. If an organism is
placed on the agar, it will not grow in the area around the disc if
it is susceptible to the chemical. This area of no growth around
the disc is known as a ‘‘Zone of inhibition’’ or ‘‘Clear Zone’’. For
the disc diffusion, the zone diameters were measured with slipping
calipers of the (NCCLS) [23]. Agar-based methods such as E-test
and disk diffusion can be good alternatives because they are sim-
pler and faster the broth-based methods [26,27].
Molar conductance, magnetic moment and electronic spectral data of Cu-SAH
complexes.
kmax (cmꢀ1
)
a
Complex
KM
leff (BM)
SAH
–
–
1.85
0
25,974, 34,722
27,100, 17,094
22,222, 15,552
19,417
[Cu(SAH)Cl]ꢁH2O (1)
[Ni(SAH)Cl]ꢁH2O (2)
[Co(SAH)Cl]ꢁ2H2O (3)
12.9
10.5
11.2
2.55
a
Molar conductance measured for 10ꢀ3 M DMSO solution,
X .
ꢀ1 cm2 molꢀ1
determined potentiometrically by titrating mixture (b). The forma-
tion constants of M(II)-SAH were determined by titrating mixture
(c). All titrations were performed in a purified N2 atmosphere,
using aqueous 0.05 M NaOH as titrant.
2.5. Instruments
The microchemical analysis of the separated solid chelates for C,
H and N were performed in the microanalytical Center, Cairo Uni-
versity. The analyses were performed twice to check the accuracy
of the analyses data. Infrared spectra were recorded on a 8001-
PC FTIR Shimadzu spectrophotometer using KBr pellets. The solid
reflectance spectra were measured on a Schimadzu 3101 pc spec-
trophotometer. The molar conductance of the complexes was
measured for 1.00 ꢂ 10ꢀ3 M DMSO solutions at 25 1 °C using a
systronic conductivity bridge type 305. The room temperature
magnetic susceptibility measurements for the complexes were
determined by the Gouy balance using Hg[Co(SCN)4] as a calibrant.
A Shimadzu TGA-50H thermal analyzer was used to record simul-
taneously TG and DTG curves. The measurements were carried out
in N2 atmosphere (20 ml minꢀ1) with a heating rate of 10 °C minꢀ1
in the temperature range 20–1200 °C using platinum crucibles,
with a TGA-50 Shimadzu instrument.
PðMÞ þ qðSAHÞ þ rðHÞꢀðMÞpðSAHÞqðHÞr
½ðMÞpðSAHÞqðHÞrꢃ
ð1Þ
bpqr
¼
ð2Þ
p
q
r
½Mꢃ ½SAHꢃ ½Hꢃ
Caution!
Although no problems were encountered in this work, but it
should be pointed out that for DMSO solutions only glass equip-
ment and Hamilton Teflon valves can be used!
2.7. Data processing
The calculations were obtained from ca. 100 data points in each
titration using the computer program MINIQUAD-75 [30]. The
Potentiometric measurements were made using a Metrohm 686
titroprocessor equipped with
a 665 Dosimat (Switzerland-
Herisau). A thermostated glass-cell was used equipped with a
magnetic stirring system, a Metrohm glass electrode, a thermometric
probe, a microburette delivery tube and a salt bridge connected with
the reference cell filled with 0.1 M KCl solution in which saturated
calomel electrode was dipped. Temperature was maintained con-
stant inside the cell at 25.0 0.02 °C, by the circulating water by a
thermostated bath (precision 0.02). All potentiometric measure-
ments in this study were carried out in Dimethylsulphoxide (DMSO)-
water mixture containing 70% DMSO because of low solubility of
hydrazone ligand and possible hydrolysis in aqueous solution.
1.4
1.2
1
2.6. Potentiometric titrations
The potentiometric cell was calibrated before each experiment
to convert the pH meter readings into hydrogen ion concentration
as reported in literature [28]. The ionic product ðKw ¼ ½Hþꢃ½OHꢀꢃÞ
were calculated at a constant ionic strength of 0.10 mol-dmꢀ3 with
NaNO3 in 70% aqueous DMSO solutions based on measurements of
[OHꢀ] and pH in several series of experiments. We calculated the
reproducible values of pKw for the examined 70% aqueous di-
methyl sulfoxide solution [29]. The pKw value obtained is 15.75
in this medium. The following mixtures were prepared and titrated
potentiometrically with 0.05 M NaOH solution.
0.8
0.6
0.4
0.2
0
(a) 50 ml of solution containing 8.0 ꢂ 10ꢀ4 M Metal(II) ion of
constant ionic strength 0.1 M NaNO3.
(b) 50 ml of solution containing 8.0 ꢂ 10ꢀ4 M SAH ligand + 1.6 ꢂ
10ꢀ3 M HNO3 of constant ionic strength 0.1 M (adjusted with
NaNO3);
(c) 50 ml of solution containing 8.0 ꢂ 10ꢀ4 M Metal(II) ion, 1.6 ꢂ
10ꢀ3 M SAH ligand + 1.6 ꢂ 10ꢀ3 M HNO3 of constant ionic
strength 0.1 M NaNO3.
340
390
440
490
540
590
640
690
740
Wave length (nm)
The hydrolysis constants of metal(II) were determined by
titrating mixture (a). The protonation constants of SAH were
Fig. 2. Electronic spectra of Cu-SAH complex.

A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
311
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
3. Results and discussion
The condensation of salicylaldehyde with hydralazine in boiling
ethanol yields a hydrazone compound (SAH). The chemical equa-
tions concerning the formation of the hydrazone and the com-
plexes represented in Scheme 1. The interaction of SAH ligand
and metal(II) salts in EtOH under reflux conditions gave the prod-
ucts presented in Table 1.
3.1. Elemental analysis
The elemental analysis data of the SAH ligand and its complexes
are given in Table 1. The data show the formation of [M(SAH)Cl] in
the complexes (where SAH represents the deprotonated hydrazone
ligand). We found that the theoretical values are in a good agree-
ment with the found values.
3.2. Molar conductance measurements
By using the relation: KM = K/C, the molar conductance values
of the prepared complexes with the mentioned metal ions under
investigation were determined using 1 ꢂ 10ꢀ3 M DMSO solution,
are in the range of 10.5–12.9
X
ꢀ1 cm2 molꢀ1. These values indi-
cated that, all synthesized complexes are nonelectrolytes. This is
in accordance with the fact that conductivity values for a nonelec-
trolytes are below 50
X
ꢀ1 cm2 molꢀ1 in DMSO solution [32,33].
Conductivity measurements are in a good agreement with the ele-
mental analysis data, where Clꢀ1 ions are detected by addition of
AgNO3 solution, inside the coordination sphere of the complexes
by the dissolving of the all complexes using nitric acid.
3.3. IR spectra and mode of bonding
350
400
450
500
550
600
650
700
750
Wave length (nm)
The IR spectra in the (4000–400 cmꢀ1) region provide informa-
tion regarding the coordination mode in the complexes were ana-
lyzed by comparison with the data for the free ligand. The most
relevant bands and proposed assignments for all complexes along
with the hydrazone ligand (SAH) ligand are given in Table 2. The
IR-spectra of free hydrazone ligand and its Cu(II)-complex are
shown in Fig. 1.
Fig. 3. Electronic spectra of Co-SAH complex.
stoichiometry and stability constants of the complexes formed
were determined by trying various possible composition models.
The model selected gave the best statistical fit and was chemically
consistent with the titration data without giving any systematic
drifts in the magnitudes of various residuals, as described
elsewhere [30]. The fitted model was tested by comparing the
experimental titration data points and the theoretical curve
calculated from the values of the acid dissociation constant of
the ligand and the formation constants of the corresponding com-
plexes. The species distribution diagrams were obtained using the
program SPECIES [31] under the experimental condition employed.
All measurements were carried out in our laboratory in Cairo
University.
The IR spectrum of the free hydrazone ligand (SAH) reveals bands
at 3387 cmꢀ1 may be assigned to
t(OH) and
t(NH) respectively. The
t(OH) band is absent in the spectra of metal complexes, indicating
coordination through the deprotonated phenolic OH group [34,
35]. Also, the participation of the OH group in coordination is appar-
ent from the shift in position of the d(OH) in-plane bending at
1471 cmꢀ1 [36] in the free ligand by 11–24 cmꢀ1 in the complexes
and formation of M–O bond via deprotonation. Moreover, it was
evidenced from the shift in the position of
[37] to the lower frequency region in the spectra of complexes
t
(C–O) at 1263 cmꢀ1
Fig. 4. Mass Spectrum of SAH-Schiff base.

312
A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
[38]. However, the strong band observed at 1607 cmꢀ1 in the free
SAH ligand due to azomethine group vibration is shifted towards
lower frequencies in the complexes, suggesting that azomethine
group is involved in coordination [39–42]. Bands appearing at 960,
912, 786, 750 cmꢀ1 are the usual modes of aromatic ring vibrations.
The previously bands corresponding to aromatic moiety reveal
small shifts in the resulted complexes than free ligand, this is usual
due to the expected electronic structure changes upon
complexation. The appearance of new bands in the low frequency
vibrations [43] respectively, support the participation of the nitro-
gen atom of the azomethine group and oxygen of the OH group of
the ligand in the complexation with metal ions [43] as shown in
Scheme 1.
All the complexes exhibit a band at 345–352 cmꢀ1 originating
from a t(M–Cl) vibration indicating the presence of chloride coor-
dination thus completing the square-planar geometry for the
present series of complexes [44].
As a general conclusion, the hydrazone ligand (SAH) partici-
pated in bonding to metal(II) as monobasic tridentate (N,N,O
ranges at 498–594 and 444–476 cmꢀ1 due to
t(M–O) and t(M–N)
H
C
N
N
H
OH
N
N
m/z = 264
H
C
N
N
+
+
H
m/z = 51
N
N
m/z = 247
+
+
N
H2C
m/z = 63
N
H
N
N
m/z = 171
+
m/z = 77
+
NH2
N
N
+
m/z = 145
m/z = 89
+
N
N
N
N
+
+
N
m/z = 129
m/z = 117
m/z = 103
Scheme 2. Mass fragmentation pattern of SAH hydrazone ligand.

A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
313
reflectance spectra and magnetic moment measurements are used
for this purpose. The solid reflectance spectra of metal complexes
show different bands at different wavelengths, each one is corre-
sponding to certain transition which suggests the geometry of
the complex compounds. In general, the d–d bands of copper(II)
complexes for which a square planar structure has been proposed
to occur in the range 16,000–20,000 cmꢀ1 [45]. The electronic
spectra of the [Cu(SAH)Cl] complex (Fig. 2) showed d–d absorption
band centered at 17,094 cmꢀ1 due to B1g
!
2A1g as reported for
2
square planner Cu(II) complex [46,47]. As is known, magnetic sus-
ceptibility measurements provide information to characterize the
structure of the complexes. The magnetic moments of the com-
plexes were measured at room temperature and are listed in Table
3. The room temperature magnetic moment for [Cu(SAH)(Cl)] com-
plex (leff = 1.85 BM) falls in the normal range for copper(II) species
with S = 1/2 and this confirms that the copper(II) complex has
square-planar geometry [48] with dx2ꢀy2 ground state [49].
Theelectronic spectrum of the diamagneticnickel(II) complex (2)
(Table 3) showed two absorption bands at 15,552 and 22,222 cmꢀ1
Fig. 5. 1H NMR of SAH-Schiff base.
1
1
which may be assigned to the A1g
!
1B2g,1A1g ! B1g transitions,
respectively, around Ni(II) in a square-planar geometry [50]. The as-
sumed square planar geometry for this complex is confirmed from
the value of its room temperature magnetic moment of zero [51].
The room temperature magnetic moment of [CoSAH)Cl] of
2.55 BM is more than that of low spin octahedral and lower than
the values characteristic of tetrahedral cobalt(II) complexes. Fur-
thermore, these values are similar to that reported for the square
planar cobalt(II) complexes [52–54]. The electronic spectrum of
donor) ligand (Scheme 1). The nonelectrolytic nature of the
complexes was evidenced from the low values of the molar con-
ductance of the complexes measured in DMSO (Table 3).
3.4. Electronic spectra and magnetic properties
As the result of failure to obtain a single crystal for X-ray anal-
yses to confirm the geometric structure for these complexes, solid
3.000
2.500
2.000
1.500
1.000
0.500
0.000
0.0009
0.0004
-0.0001
-0.0006
-0.0011
-0.0016
-0.0021
-0.0026
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
Temperature, 0C
Fig. 6. TG and DTG of [Cu(SAH)Cl)ꢁH2O complex.
Table 4
Stepwise thermal degradation data obtained from TGA curves for MII-SAH complexes.
Complex
Molar mass
TG
(°C)
DTGmax (K)
Weight loss
Predicated intermediates and final products
Metallic residue found (calcd.%)
range
Found
Calcd.
(1)
380.29
48–104
104–270
474–510
510–675
43–180
259–532
532–776
41–120
73
246
487
639
90
436
673
76
4.58
9.56
18.35
46.4
4.73
9.33
18.93
46.1
H2O
1/2Cl2
2N2 + CH4
C14H6
H2O
2N2+ 1/2Cl2 + CH4
C14H6
2H2O
CuO
20.84
(20.91)
(2)
(3)
374.54
393.69
4.31
4.80
NiO
28.85
46.58
9.43
28.75
46.45
9.14
20.26
(20.03)
CoO
228–367
367–402
402–659
355
379
459
9.17
7.21
56.05
9.01
7.11
55.62
1/2Cl2
N2
Phthalazine + C7H5
18.14
(19.12)

314
A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
Table 5
The kinetic parameters for the non-isothermal decomposition of the complexes.
Range (°C)
Ta
Ea (kJ molꢀ1
)
D
H⁄ (kJ molꢀ1
)
D
S⁄ (JKꢀ1 molꢀ1
)
D )
G⁄(kJ molꢀ1
[Cu(SAH)Cl]ꢁH2O(1)
48–104
104–270
474–510
510–675
73
42.36 2.54
12.82 0.76
7.81 0.46
37.60 2.25
ꢀ38.05 3.80
ꢀ6.50 3.20
ꢀ0.233 0.02
ꢀ37.60 6.89
ꢀ205.35 35.22
ꢀ328.41 46.41
ꢀ347.20 52.78
ꢀ319.15 44.29
33.00 18.30
163.94 73.07
263.64 103.64
253.46 101.8
246
487
639
[Ni(SAH)Cl]ꢁH2O(2)
43–180
259–532
90
436
673
17.30 1.04
66.09 3.96
21.10 1.27
ꢀ11.41 1.84
ꢀ58.23 7.98
ꢀ21.10 2.94
ꢀ298.52 41.20
ꢀ259.96 37.31
ꢀ347.10 55.23
96.95 62.23
126.09 71.35
307.25 109.21
533–776
[Co(SAH)Cl]ꢁ2H2O(3)
41–120
228–367
367–402
404–659
76
355
379
459
28.37 1.70
16.20 0.97
16.12 0.96
44.51 2.67
ꢀ23.16 3.11
ꢀ10.79 4.32
ꢀ10.04 4.11
ꢀ44.52 8.02
ꢀ253.88 63.32
ꢀ330.94 50.21
ꢀ308.16 44.98
ꢀ299.35 42.02
65.45 24.22
197.05 89.11
190.88 88.78
174.61 81.45
a
The peak temperature from the DTG curve (°C).
1000/T
-16
2.84
2.85
2.86
2.87
2.88
2.89
2.90
2.91
2.92
2.93
2.94
2.95
2.96
-16.2
-16.4
-16.6
-16.8
-17
-17.2
-17.4
Fig. 7. Coats-Redfern linear plot for [Cu(SAH)Cl]ꢁH2O complex.
the complex, Fig. 3, exhibits a band at 19,417 cmꢀ1 characteristic of
square planar cobalt(II) complexes [55].
Table 6
Association constants of (SAH) at different temperatures at (70% DMSO-30% H2O).
System
Temp. (°C)
logba
Sb
3.5. Mass spectra
SAH
(1) Lꢀ þ HþꢀHL
20
11.11 0.05
15.46 0.02
1.1E ꢀ 7
(2) Lꢀ þ 2HþꢀH2Lþ
The electron impact mass spectra of SAH- hydrazone ligand are
recorded and investigated recorded and investigated at 70 eV of
electron energy. The mass spectra of the studied hydrazone ligand
are characterized by moderate to high relative intensity molecular
ion peaks. The mass spectrum of SAH, and the possible molecular
ion peaks with their respective relative intensities are shown in
Fig. 4. The mass spectra of SAH and the molecular ion peaks of
the different suggested fragments are shown in Scheme 2. Their
signals give an idea about the construction of ligand. Scheme 2
demonstrates the proposed path of the decomposition steps for
the investigated hydrazone ligand. SAH shows a parent peak at
m/z = 264 with a relative intensity = 54% (C15H12N4O, calculated
atomic mass 264 amu) represents the molecular ion peak of the
SAH hydrazone ligand. The other molecular ion peaks (171
(100%), 145 (13.5%), 129 (9%), 117 (18%), 103 (21%), 89 (16%),
77(17%), 63 (9%) and 51 (11%)) appeared in the mass spectra are
attributed to the fragmentation of SAH molecule obtained from
SAH
(1) Lꢀ þ HþꢀHL
25
30
35
10.87 0.03
15.10 0.04
5.8E ꢀ 7
6.2E ꢀ 7
1.9E ꢀ 7
(2) Lꢀ þ 2HþꢀH2Lþ
SAH
(1) Lꢀ þ HþꢀHL
10.52 0.03
14.61 0.04
(2) Lꢀ þ 2HþꢀH2Lþ
SAH
(1) Lꢀ þ HþꢀHL
10.32 0.04
14.29 0.01
(2) Lꢀ þ 2HþꢀH2Lþ
the rupture of different bonds inside the molecule [56]. From the
data obtained we concluded that the molecular weight was in good
agreement with this of the calculated molecular weight of the
investigated ligand.

A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
315
H
H
N
N
N
N
O
-
OH
KOH
N
+
N
+
H
N
N
-
L
HL
H
N
N
OH
H
N
N
Kphthalazine
N
+
OH
+
H
N
N
H
+
N
HL
+
H2L
Scheme 3. Protonation of SAH hydrazone ligand.
3.6. 1H NMR spectra
mass loss 28.9% (calcd. 28.8%). The third step (532–776 °C) corre-
sponds to the loss of C14H6 molecule with mass loss 46.6% (calcd.
46.5%). The energies of activation were 17.3, 66.1 and 21.1 kJ molꢀ1
for the first, second and third steps respectively. The total mass loss
up to 776 °C is in agreement with the formation of NiO as the final
residue (TG 20.2%, calcd. 20.0%).
The TGA curve of the [Cu(SAH)Cl]ꢁH2O complex shows four
stages of decomposition within the temperature range (41–
659 °C). The first step of decomposition within the temperature
range (41–120 °C) corresponds to the loss of two water molecules
1H NMR spectra of SAH (Fig. 5) were recorded in DMSO-d6
solvent. The 1H NMR spectra of SAH hydrazone ligand showed
one singlet at 12.14 ppm corresponding to phenolic –OH proton
and one singlet at 10.31 ppm corresponding to NH proton (@N–
NH–). The signal respect of the proton of (@N–CH) group of Phthal-
azine was observed at 8.67 ppm. The signal observed at 8.31 ppm
is due to azomethine proton (–CH@N–) [57,58]. Also, the 1H
NMR spectra of SAH- hydrazone ligand revealed a multiplet at
6.86–7.87 ppm corresponding to aromatic protons [59,60].
12
10
8
3.7. Thermogravimetric analysis
The thermogravimetric (TG) and the derivative thermogravi-
metric (DTG) plots of CuII-complex as an illustrative example were
given in Fig. 6. The correlations between the different decomposi-
tion steps of the complexes with the corresponding weight losses
are discussed in terms of the proposed formulae of the complexes.
The predicated intermediates and final products were given in
Table 4.
The TG and DTG curves of [Cu(SAH)Cl]ꢁH2O are shown in Fig. 6.
The TGA curve of the [Cu(SAH)Cl]ꢁH2O complex shows four stages
of decomposition within the temperature range (48–675 °C). The
first step of decomposition within the temperature range (48–
104 °C) corresponds to the loss of water molecule of hydration
with a mass loss 4.6% (calcd. 4.7%). The second step (104–270 °C)
corresponds to the loss of half Cl2 with mass loss 9.5% (calcd.
9.3%). The third step (474–510 °C) corresponds to the loss of
2N2 + CH4 molecules with mass loss 18.4% (calcd. 18.9%). The
fourth step (510–675 °C) corresponds to the loss of C14H6 molecule
with mass loss 46.6% (calcd. 46.1%). The energies of activation were
42.3, 12.8, 7.8 and 37.6 kJ molꢀ1 for the first, second, third and
fourth steps respectively. The total mass loss up to 670 °C is in
agreement with the formation of CuO as the final residue (TG
20.84%, calcd. 20.91%).
The TGA curve of the [Ni(SAH)Cl]ꢁH2O complex shows three
stages of decomposition within the temperature range (48–
776 °C). The first step of decomposition within the temperature
range (43–180 °C) corresponds to the loss of water molecule of
hydration with a mass loss 4.3% (calcd. 4.8%). The second step
(259–532 °C) corresponds to the loss of 2N2 + 1/2Cl2 + CH4 with
6
4
2
SAH
Co-SAH
0
0
0.5
1
1.5
2
2.5
3
3.5
4
Moles of base added per mole of ligand
Fig. 8. Potentiometric titration curve for Co-SAH system.

316
A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
of hydration with a mass loss 9.4% (calcd. 9.1%). The second step
(228–367 °C) corresponds to the loss of half Cl2 with mass loss
9.1% (calcd. 9.0%). The third step (367–402 °C) corresponds to the
loss of N2 molecule with mass loss 7.2% (calcd. 7.1%). The fourth
step (402–659 °C) corresponds to the loss of Phthalazine + C7H5
molecules with mass loss 56.0% (calcd. 55.6%). The energies of acti-
vation were 28.4, 16.2, 16.1 and 44.5 kJ molꢀ1 for the first, second
and third steps respectively. The total mass loss up to 659 °C is in
agreement with the formation of CoO as the final residue (TG
18.1%, calcd. 19.1%).
DMSO-water mixture at 25 °C and these constants are tabulated
in Table 6. Upon addition of NaOH deprotonation of SAH ligand
occurs, representation of the acid dissociation constants (Ka) in
stability study expressed in terms of proton-ligand formation con-
stant or protonation constant Eq. (7), and also used in the present
investigation. Analysis of the potentiometric titration curve of
SAH- hydrazone ligand using the program Miniquad-75 gave best
fit for two protonation constants as proposed by the Eq. (7)
(charges are omitted for clarity).
½LHnꢃ
LHnꢀ1 þ H ꢀ LHn; K1n
¼
ð4Þ
The thermodynamic activation parameters of decomposition
processes of complexes namely activation energy (Ea), enthalpy
½LHnꢀ1ꢃ½Hꢃ
(D
H⁄), entropy (
position (
Coats–Redfern relation as follows [61]:
D
S⁄) and Gibbs free energy change of the decom-
D
G⁄) were evaluated graphically by employing the
Table 7
Formation constants for binary complexes of (SAH) with metal(II) ions at different
temperatures at 70% DMSO-3% H2O mixture.
ꢂ
ꢀ
ꢁꢃ
ꢀ
ꢄ
ꢅꢁ
1 ꢀ
a
AR
hEa
2RT
Ea
Ea
log ꢀ log
¼ log
1 ꢀ
ꢀ
ð3Þ
T2
2:303RT
System
Temp. (°C)
logba
Sb
Cu-SAH
20
where a is the fraction of sample decomposed at time t, T is the deriv-
ative peak temperature, A the frequency factor, Ea the activation en-
(1) Cu2þ þ LꢀꢀCuLþ
12.45 0.02
22.65 0.04
1.1E ꢀ 7
(2) Cu2þ þ 2LꢀꢀCuL2
ergy, R the gas constant h is the heating rate and (1-(2RT/Ea)) ffi 1. A
Ni-SAH
plot of logfꢀ logð1 ꢀ
a
Þ=T2g versus 1/T gives a slope from which
(1) Ni2þ þ LꢀꢀNiLþ
11.50 0.03
20.18 0.01
2.3E ꢀ 7
3.8E ꢀ 7
8.1E ꢀ 7
the Ea was calculated and A (Arrhenius factor) was determined from
the intercept. The entropy of activation was calculated [62]. Fig. 5
represents the linear plots of the thermal decomposition steps of
Cu(II)-complex as a representative example of the synthesized com-
(2) Ni2þ þ 2LꢀꢀNiL2
Co-SAH
(1) Co2þ þ LꢀꢀCoLþ
10.98 0.04
18.95 0.05
(2) Co2þ þ 2LꢀꢀCoL2
plexes. The free energy of activation
D
G⁄ and the enthalpy of activa-
Mn-SAH
tion
D
H⁄ were calculated [62]. The kinetic data obtained from the
(1) Mn2þ þ LꢀꢀMnLþ
9.20 0.02
(2) Mn2þ þ 2LꢀꢀMnL2
15.90 0.04
non-isothermal decomposition of the complexes using the appropri-
ate calculation method are cited in Table 5. The negative values of
Cu-SAH
25
30
35
D
S⁄ indicate that the reaction rates are slower than normal which
11.96 0.01
21.87 0.02
4.0E ꢀ 7
4.5E ꢀ 7
9.3E ꢀ 7
3.9E ꢀ 6
(1) Cu2þ þ LꢀꢀCuLþ
(2) Cu2þ þ 2LꢀꢀCuL2
is consistent with the results reported previously [63,64] and the
positive values of
D
G⁄ reflected the non-spontaneous nature of pro-
Ni-SAH
(1) Ni2þ þ LꢀꢀNiLþ
11.08 0.01
19.58 0.08
cess. The correlation coefficients of the thermal decomposition plots
were found to lie in the range 0.97–0.99, showing a good fit with lin-
ear function. The linear plot of [Cu(SAH)Cl]ꢁH2O complex as a repre-
sentation example of MII-SAH complexes was given in Fig. 7. It is
clear that the thermal decomposition process of all SAH complexes
is non-spontaneous, i.e., the complexes are thermally stable.
(2) Ni2þ þ 2LꢀꢀNiL2
Co-SAH
(1) Co2þ þ LꢀꢀCoLþ
10.75 0.02
18.21 0.02
(2) Co2þ þ 2LꢀꢀCoL2
Mn-SAH
(1) Mn2þ þ LꢀꢀMnLþ
8.20 0.1
(2) Mn2þ þ 2LꢀꢀMnL2
14.26 0.1
3.8. Solution equilibrium studies
Cu-SAH
(1) Cu2þ þ LꢀꢀCuLþ
11.35 0.01
20.71 0.02
4.8E ꢀ 7
3.3E ꢀ 7
7.6E ꢀ 7
5.2E ꢀ 7
(2) Cu2þ þ 2LꢀꢀCuL2
3.8.1. Protonation constants of hydrazone ligand (SAH)
Ni-SAH
(1) Ni2þ þ LꢀꢀNiLþ
10.75 0.01
19.01 0.06
Equilibrium studies of SAH hydrazone ligand and its complex
formation can not be carried out in aqueous solution because of
the nature of the compound involved. These metal complexes as
well as SAH hydrazone ligand are insoluble in water. This solvent
has been widely used for potentiometric determination of stability
constants. The mixture DMSO-water was the chosen solvent for
our study. In such a medium, the studied hydrazone ligand and
its metal complexes are soluble giving stable solutions. The use
of this mixed solvent has some advantages over pure DMSO. Thus,
pure DMSO is very hygroscopic and controlling its water content is
difficult [65]. This fact would affect reproducibility of our experi-
ment. However, DMSO-water 70:30% mixture has only small
hygroscopic character. A further advantage is its compatibility with
the standard glass electrode, so that the pH measurements may be
carried out in a similar way to that employed in a purely aqueous
solution. In contrast, the use of pure DMSO is not recommended for
potentiometry. Another advantage of the DMSO-water mixture is
its large acidity range (pKw = 15.75) which allows the investigation
of deprotonation equilibria of weak acids which could be hardly
studied in water [66,67]. The stoichiometric protonation constants
of the investigated hydrazone ligand were determined in 70%
(2) Ni2þ þ 2LꢀꢀNiL2
Co-SAH
(1) Co2þ þ LꢀꢀCoLþ
10.45 0.01
17.66 0.02
(2) Co2þ þ 2LꢀꢀCoL2
Mn-SAH
(1) Mn2þ þ LꢀꢀMnLþ
6.89 0.06
(2) Mn2þ þ 2LꢀꢀMnL2
12.18 0.07
Cu-SAH
(1) Cu2þ þ LꢀꢀCuLþ
10.85 0.05
19.66 0.07
6.3E ꢀ 7
1.7E ꢀ 7
8.2E ꢀ 7
5.3E ꢀ 7
(2) Cu2þ þ 2LꢀꢀCuL2
Ni-SAH
(1) Ni2þ þ LꢀꢀNiLþ
10.30 0.03
18.39 0.02
(2) Ni2þ þ 2LꢀꢀNiL2
Co-SAH
(1) Co2þ þ LꢀꢀCoLþ
10.10 0.04
17.09 0.04
(2) Co2þ þ 2LꢀꢀCoL2
Mn-SAH
(1) Mn2þ þ LꢀꢀMnLþ
6.02 0.07
(2) Mn2þ þ 2LꢀꢀMnL2
11.02 0.08
a
Standard deviation is given in parenthesis.
Sum of square of residuals.
b

A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
317
(Mn2+(1.55) < Co2+(1.88) < Ni2+ (1.91) < Cu2+ (2.0)) will decrease
the electronegativity difference between the metal atom and the do-
nor atom of the ligand. Thus, the metal–ligand bond would have
more covalent character, which may lead to greater stability of the
metal chelates. A good linear relationship has been obtained be-
tween logKML and the second ionization potential of the bivalent
metal ions under study. In general, it is noted that the stability con-
stant of the Cu2+ complex is quite large compared to the other met-
als. The ligand field will give Cu2+ some extra stabilization due to
tetragonal distortion of the octahedral symmetry [70,71]. Thus, logK
value for the Cu2+-complex deviates significantly when logK values
of metal chelates are plotted against properties of the metal ions. The
lower stability of Mn(II) chelates may be due to its larger radius (80).
The two protonation constants are related to the protonation of
phenolate, and phthalazine nitrogen atoms, respectively as shown
in Scheme 3. Titration with a base produces, in a first stage depro-
tonation of the protonated phthalazine proton is deprotonated with
pKa1 value of 4.35 (pKa1 = logb012 ꢀ logb011). By further increase of
pH, the phenolic proton is deprotonated with pKa2 value of 11.11
(pKa2 = logb011).
3.8.2. MetalII complex formation equilibria
Potentiometric titrations of SAH with Cu2+, Ni2+, Co2+ and Mn2+
ions were carried out in 1:1 and 1:2 metal–ligand molar ratios at
l
= 0.1 M NaNO3 and 25 °C in DMSO-water 70:30% mixture. The
deviation in the metal–ligand titration curves from the ligand titra-
tion curve implies the formation of metal complexes. The potenti-
ometric titration curve of Co(II)-SAH as a representative example of
metal(II)-complexes was given in Fig. 8. The overall formation con-
stants (logb) of the species were calculated using Miniquad-75
program. The derived protonation constants of SAH and stepwise
formation constants (logK) of complexes are summarized in Tables
6 and 7.
3.10. Effect of temperature
The values obtained for the thermodynamic parameters
S° and G°, associated with the protonation of SAH and its com-
plex formation with Cu(II) species were calculated from the tem-
DH°,
D
D
perature dependence of the data in Table 6
obtained by linear least square fit of ln
DH° and DS° were
K
versus 1/T (ln
K = ꢀ
D
H°/RT +
D
S°/R) leading to an intercept
D
S°/R and a slope
3.9. Correlation of the properties of metal ions with the formation
constants of mixed ligand complexes
ꢀ
DH°/R, where K is the equilibrium constant, Figs. 9 and 10, The
main conclusions from the data can be summarized as follows.
(I) The protonation reactions of the SAH are exothermic and of
In an attempt to explain why a given ligand prefers binding to
one metal rather than another, it is necessary to correlate the sta-
bility constants with the characteristic properties of the metal ions,
such as the ionic radius, ionization energy, electronegativity and
the atomic number were investigated. Here we have discussed
relationships between the properties of central metal ions reported
in literature [60,68] and the stability constants of complexes.
The formation constants of MII-complexes of bivalent 3d transi-
tion metal ions with SAH are in the order: Cu2+ > Ni2+ > Co2+ > Mn2+
in accordance with Irving and Williams order [69]. The correlation
between the logKML and the reciprocal ionic radii (1/r) of the studied
bivalent transition metal ions was found to be almost linear. Also, a
good linear correlation has been obtained between logKML and the
electronegativities of the metal ions under study. This in accordance
with the fact that increasing electronegativity of the metal ions
comparable
fect the protonation reactions in Table 6:
DH° and DS° with a net negative DG°. Three factors af-
(i) The neutralization reaction, which is an exothermic reaction
process.
(ii) Desolvation of ions, which is an endothermic process.
(iii) The change of the configuration and the arrangements of the
hydrogen bonds around the free and the protonated ligands.
The negative
DS° indicates that the total number of solvent
molecules bound with the dissociated ligand is greater than that
originally accompanying the undissociated form.
The stability constants of the complexes formed at different
temperatures were calculated and the average values are included
in Table 7. From these results the following conclusions can be
12
10
8
6
4
2
logk1
log k2
log k3
0
0.00322 0.00324 0.00326 0.00328
0.0033
0.00332 0.00334 0.00336 0.00338
1/T
0.0034
0.00342 0.00344
Fig. 9. Effect of temperature on stepwise protonation constant of SAH.

318
A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
14
12
10
8
6
4
Mn(SAH)
Co(SAH)
Ni(SAH)
Cu(SAH)
2
0
0.00322
0.00324
0.00326
0.00328
0.0033
0.00332
0.00334
0.00336
0.00338
0.0034
0.00342
0.00344
1/T
12
10
8
6
4
Mn(SAH)2
Co(SAH)2
Ni(SAH)2
Cu(SAH)2
2
0
0.00322
0.00324
0.00326
0.00328
0.0033
0.00332
0.00334
0.00336
0.00338
0.0034
0.00342
0.00344
1/T
Fig. 10. Effect of temperature on lnK of M(II)-complexes with SAH-Schiff base.
reached. These values decrease with increasing temperature, con-
firming that the complexation process is more favorable at lower
temperatures. It is known that the divalent metal ions exist in solu-
tion as octahedrally hydrated species [72] and the obtained values
3. All values of
cating that the chelation process proceeds spontaneously.
4. The negative values of H° show that the chelation process is
DG° for complexation are negative (Table 8), indi-
D
exothermic, indicating that the complexation reactions are
of
DH and DS can then be considered as sum of two contributions:
favored at low temperatures.
(a) release of H2O molecules and (b) metal–ligand bond formation.
From these results the following conclusions can be made.
5. The entropy term (DS°) for the complexation reactions is
negative, which is in consistency with the protonation reac-
tion of the ligand. The negative entropy changes together
with the high negative enthalpy change contribute to the
favorable free energy change of the complex formation
reactions.
1. Table 7 shows that (logK1 ꢀ logK2) values are usually positive,
since the coordination sites of the metal ions are more freely
available for binding of the first molecule than the second one.
2. For the same ligand at constant temperature, the stability of the
chelates increases in the order Cu2+ > Ni2+ > Co2+ > Mn2+ [69].
This order largely reflect the changes in the heat of complex for-
mation across the series from a combination of the influence of
both the crystal field stabilization energies [72] and the polariz-
ing ability of the metal ion [73].
3.11. Species distribution curves of metal(II)-SAH complexes
Estimation of equilibrium concentrations of metal(II) com-
plexes as a function of pH provides a useful picture of metal ion
binding in solutions. All of the species distributions were calcu-

A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
319
100
90
80
70
60
50
40
30
20
10
0
lated with the aid of the Species computer program [31]. The
concentrations of metal ligand complexes increase with increasing
of pH. The species distribution pattern for Cu-(SAH), taken as a rep-
resentative of metal ligand complexes, is given in Fig. 11. Cu(SAH)
complex starts to form at pH ꢄ 2.6 and reaches its maximum
concentration 84% at pH ꢄ 3.8. Also, Cu(SAH)2 complex starts to
form at pH ꢄ 3.6 and reaches its maximum concentration 97% at
pH ꢄ 7.4.
100
120
110
3.12. Biological activity
The biological activity of the metal complexes is governed by
the following factors: (i) the chelate effect of the ligands, (ii) the
nature of the donor atoms, (iii) the total charge on the complex
ion, (iv) the nature of the metal ion, (v) the nature of the counter
ions that neutralize the complex, and (vi) the geometrical structure
of the complex [74]. Furthermore, chelation reduces the polarity of
the metal ion because of partial sharing of its positive charge with
2
3
4
5
6
7
8
9
pH
Fig. 11. Concentration distribution of various species as a function of pH in the
Cu-SAH system.
the donor groups and possibly the p-electron delocalization within
(2) The synthesized compounds were found to be more toxic
compared with their parent hydrazone ligand against the
same micro-organism and under the identical experimental
conditions. The increase in biological activity of the metal
chelates may be due to the effect of the metal ion on the nor-
mal cell process. A possible mode of toxicity increase may be
considered in the light of Tweedy’s chelation theory [79].
Chelation considerably reduce the polarity of the metal ion
because of partial sharing of its positive charge with the
the whole chelate ring system that is formed during coordination
[75]. These factors increase the lypophilic nature of the central me-
tal atom and hence increasing the hydrophobic character and lipo-
solubility of the molecule favoring its permeation through the lipid
layer of the bacterial membrane. This enhances the rate of uptake/
entrance and thus the antibacterial activity of the testing com-
pounds. The hydrazone SAH ligand and its chelates (1–3) were
tested for their inhibitory effects on the growth of two Gram posi-
tive (S. aureus, Bacillus subtillis) and two Gram negative (E. coli,
Pseudomonas aeruginosa) bacteria at concentration of 20 mg/ml in
DMSO as solvent using Ampicillin as standard material and fungi:
A. flavus and C. albicans using Amphotericin as standard material be-
cause such organisms can achieve resistance to antibiotics through
biochemical and morphological modification [76]. The antibacte-
rial and antifungal activities of the new compounds are listed in
Tables 9 and 10 and represented graphically in Fig. 12. The antibac-
terial activity was tested by using the disc diffusion method. The
antimicrobial results showed that:
donor group and possible
p-electron delocalization within
the whole chelate ring system that is formed during coordi-
nation. Such chelation could enhance the lipophilic charac-
ter of the central metal atom and hence increasing the
hydrophobic character and liposolubility of the complex
favoring its permeation through the lipid layers of the cell
membrane. This enhances the rate of uptake/entrance and
thus the antimicrobial activity of the testing compounds.
Accordingly, the antimicrobial activity of the isolated com-
plexes can be referred to the increase of their lipophilic char-
(1) The hydrazone SAH ligand is biologically active and its activ-
ity may be arise from the hydroxyl groups which may play
an important role in the antibacterial activity [77], as well
as the presence of imine group which imports in elucidating
the mechanism of transformation reaction in biological sys-
tems [78].
Table 9
Antibacterial activity of M(II)-SAH complexes.
Compounds
Parameters Diameter of inhibition Diameter of inhibition
zone (in mm) (Gꢀ) zone (in mm) (G+)
P. aeuroginosa E. coli B. subtillis S. aureus
Conc. (mg/ml)
SAH
20.0
10.87 11
4.23
20.0
11
20.0
12
20.0
12
logKH1
logKH2
Table 8
CuII
logK 11.96 15
logK 11.08 13
14
13
12
22
0
15
12
0
20
0
14
13
0
18
0
Thermodynamic parameters for the protonation equilibria of SAH and formation
equilibria of metal(II)-SAH complexes.
NiII
CoII
logK 10.75
–
0
17
0
Equilibrium
D
H kJ molꢀ1
D
S JKꢀ1 molꢀ1
D
G kJ molꢀ1
Ampicillin
DMSO (control) –
SAH
(1) Lꢀ þ HþꢀHL
ꢀ94.03
ꢀ44.23
ꢀ108
ꢀ61.83
ꢀ24.09
(2) HL þ HþꢀH2Lþ
ꢀ67.58
Cu-SAH
Table 10
Antifungal activity of M(II)-SAH complexes.
(2) Cu2þ þ LꢀꢀCuLþ
ꢀ186.9
ꢀ162.7
ꢀ399
ꢀ358.6
ꢀ68.01
ꢀ55.92
(3) CuLþ þ LꢀꢀCuL2
Compounds
Parameters
Diameter of inhibition zone (in mm)
Ni-SAH
(2) Ni2þ þ LꢀꢀNiLþ
A. flavus
C. albicans
ꢀ135.8
ꢀ69.46
ꢀ242.6
ꢀ70.69
ꢀ63.47
ꢀ48.41
(3) NiLþ þ LꢀꢀNiL2
Conc. (mg/ml)
SAH
20.0
10
20.0
10
logKH1
10.87
Co-SAH
logKH2
logK
logK
logK
–
4.23
(2) Co2þ þ LꢀꢀCoLþ
ꢀ101.5
ꢀ79.11
ꢀ135.2
ꢀ122.9
ꢀ61.16
ꢀ42.48
CuII
11.96
11.08
10.75
13
11
10
17
0
14
12
11
17
0
(3) CoLþ þ LꢀꢀCoL2
NiII
CoII
Mn-SAH
(2) Mn2þ þ LꢀꢀMnLþ
ꢀ375
ꢀ375
ꢀ1103
ꢀ566.2
ꢀ46.26
ꢀ34.51
Amphotericin (B)
DMSO (control)
(3) MnLþ þ LꢀꢀMnL2
–

320
A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
18
16
14
12
10
8
25
Pseudomonas Aeuroginosa
Bacillus subtillis
20
15
10
5
6
4
2
0
0
20
18
16
14
12
10
8
25
Staphylococcus aureus
E. Coli
20
15
10
5
6
4
2
0
0
Fig. 12. Biological activity of metal complexes towards different types of bacterial strains.
acter which in turn deactivates enzymes responsible for res-
piration processes and probably other cellular enzymes,
which play a vital role in various metabolic pathways of
the tested micro-organisms. Furthermore, the mode of
action of the compounds may involve the formation of a
hydrogen bond through the azomethine nitrogen atom
(>C@N) with the active centers of cell constituents, resulting
in interference with the normal cell process [80].
(5) The antibacterial activity can be ordered as [Cu(SAH)] > [Ni
(SAH] > [Co(SAH)], suggesting that the lipophilic behaviour
increases in the same order. This in accordance also with the
stability constants order logKCu-SAH = 11.96 > logKNi-SAH
11.08 > logKCo-SAH = 10.75.
=
(6) The results indicate that, the three complexes exhibited
moderate activity against the fungal strains when compared
with standard Amphotericin.
(3) From the above mentioned points, structure activity relation-
ships evidence that the complexation with copper enhances
the antimicrobial activity of the ligands against some of the
tested organisms. Since copper chelates have an enhanced
antimicrobial activity, in comparison to their analogous con-
taining metal(II) and nickel(II) ions, the metal seems to play a
relevant role in the activity of these compounds. A similar
behavior of the increased antibacterial activity was also
exhibited by copper derivatives of 2,6-diacetylpyridine bis
(2-thenoylhydrazone) in comparison to the corresponding
Co(II) and Ni(II) chelates [81,82].
(7) The variation in the effectiveness of different compounds
against different organisms depends on either the imperme-
ability of the cells of the microbes or on differences in ribo-
some of microbial cells [74].
(8) The importance of such work lies in the possibility that the
new compounds might be more effective drugs against
bacteria for which a thorough investigation regarding the
structure–activity relationship, toxicity and in their biologi-
cal effects which could be helpful in designing more potent
antibacterial agents for therapeutic use.
(4) The tested complexes were more active against Gram-posi-
tive than Gram-negative bacteria, it may be concluded that
the antimicrobial activity of the compounds is related to cell
wall structure of the bacteria. It is possible because the cell
wall is essential to the survival of bacteria and some antibiot-
ics are able to kill bacteria by inhibiting a step in the synthesis
of peptidoglycan. Gram-positive bacteria possess a thick cell
wall containing many layers of peptidoglycan and teichoic
acids, but in contrast, Gram negative bacteria have a relatively
thin cell wall consisting of a few layers of peptidoglycan
surrounded by a second lipid membrane containing lipopoly-
saccharides and lipoproteins. These differences in cell wall
structure can produce differences in antibacterial susceptibil-
ity and some antibiotics can kill only Gram-positive bacteria
and is infective against Gram-negative pathogens [83].
Conclusions
A series of three coordinated transition metal(II) complexes
have been synthesized by the reaction of metal chloride with the
tridentate NNO hydrazone (SAH), which was prepared by the con-
densation of salicylaldehyde with hydralazine. The synthetic pro-
cedure in this work resulted in the formation of complexes in the
molar ratio (1:1) (Cu:SAH). The newly synthesized hydrazone par-
ticipated in bonding to copper as monobasic tridentate ligand
through the azomethine-N, phthalazine-N and phenolic oxygen
atom via deprotonation forming stable six and five membered
rings. The ionization constants of the investigated ligands have
been determined potentiometrically. The complex formation
equilibria were investigated to ascertain the composition and
stability constants of the complexes. The concentration distribu-

A.A. El-Sherif et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 307–321
321
[35] L.J. Bellamy, The Infrared Spectra of Complex Molecules, second ed., J. Wiley,
New York, 1964.
tion diagrams of the complexes were evaluated. The antibacterial
activity results indicated that tested complexes were more active
against Gram-positive than Gram-negative bacteria. It may be con-
cluded that antibacterial activity of the compounds is related to
cell wall structure of the bacteria. It is possible because the cell
wall is essential to the survival of many bacteria and some antibi-
otics are able to kill bacteria by inhibiting a step in the synthesis of
peptidoglycan. The antibacterial activity of the isolated metal
chelates obeyed this order [Cu(SAH)] > [Ni (SAH)] > [Co(SAH)]
which is in accordance with the stability constants order
logKCu-SAH = 11.96 > logKNi-SAH = 11.08 > logKCo-SAH = 10.75.
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