Synthesis, spectroscopic characterization and thermal behavior of metal complexes formed with N′-(1-(4-hydroxyphenyl) ethylidene)-2-oxo-2- (phenylamino) acetohydrazide (H3OPAH)

Article abstract of DOI:10.1016/j.saa.2011.04.055

Complexes of Co(II), Ni(II), Cu(II), Mn(II), Cd(II), Zn(II), Hg(II) and U(IV)O₂²⁺ with N′-(1-(4-hydroxyphenyl) ethylidene)-2-oxo-2-(phenylamino) acetohydrazide (H₃OPAH) are reported and have been characterized by various s

Full text of DOI:10.1016/j.saa.2011.04.055

Spectrochimica Acta Part A 83 (2011) 17–27
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectroscopic characterization and thermal behavior of metal
complexes formed with Nꢀ-(1-(4-hydroxyphenyl)
ethylidene)-2-oxo-2-(phenylamino) acetohydrazide (H3OPAH)
Sara F. Ahmed, Ola A. El-Gammal, Gaber Abu El-Reash∗
Department of Chemistry, Faculty of Science, Mansoura University, P.O. Box 70, Mansoura, Egypt
a r t i c l e i n f o
a b s t r a c t
Complexes of Co(II), Ni(II), Cu(II), Mn(II), Cd(II), Zn(II), Hg(II) and U(IV)O22+ with Nꢀ-(1-(4-hydroxyphenyl)
ethylidene)-2-oxo-2-(phenylamino) acetohydrazide (H3OPAH) are reported and have been characterized
by various spectroscopic techniques like IR, UV–visible, 1H NMR and ESR as well as magnetic and ther-
mal (TG and DTA) measurements. It is found that the ligand behaves as a neutral bidentate, monoanionic
tridentate or tetradentate and dianionic tetradentate. An octahedral geometry for [Mn(H3OPAH)2Cl2],
[Co2(H2OPAH)2Cl2(H2O)4] and [(UO2)2(HOPAH)(OAc)2(H2O)2] complexes, a square planar geometry for
[Cu2(H2OPAH)Cl3(H2O)]H2O complex, a tetrahedral structure for [Cd(H3OPAH)Cl2], [Zn(H3OPAH)(OAc)2]
and [Hg(H3OPAH)Cl2]H2O complexes. The binuclear [Ni2(HOPAH)Cl2(H2O)2]H2O complex contains a
mixed geometry of both tetrahedral and square planar structures. The protonation constants of ligand
and stepwise stability constants of its complexes at 298, 308 and 318 K as well as the thermodynamic
parameters are being calculated. The bond lengths, bond angles, HOMO, LUMO and dipole moments have
been calculated to confirm the geometry of the ligand and the investigated complexes. Also, thermal prop-
erties and decomposition kinetics of all compounds are investigated. The interpretation, mathematical
analysis and evaluation of kinetic parameters (Ea, A, ꢀH, ꢀS and ꢀG) of all thermal decomposition stages
have been evaluated using Coats–Redfern and Horowitz–Metzger methods.
Article history:
Received 16 January 2011
Received in revised form 8 March 2011
Accepted 26 April 2011
Keywords:
Hydrazone derivatives
Coats–Redfern
Heterocyclic schiff base
Horowitz–Metzger
pH-metry
© 2011 Published by Elsevier B.V.
1. Introduction
2. Experimental
Hydrazones are an important class of ligands which present
in numerous physiological and biological applications as antimi-
crobial, antitumour agents, insecticides, anticoagulants, anticon-
vulsant, analgesic, antioxidants, anti-inflammatory, antiplatelet,
antitubercular and plant growth regulators [1–4].
Metal complexes of hydrazones have found applications as cat-
alysts [5], luminescent probes [6], nonlinear optics and molecular
sensors [7]. Moreover, it has been recently shown that pyridoxal
isonicotinyl hydrazone can be used in the treatment of iron over-
load [8].
2.1. Physical measurements
All the chemicals were purchased from Aldrich and Fluka and
used without further purification. Elemental analyses (C, H, and
N) were performed with a Perkin-Elmer 2400 series II analyzer.
IR spectra (4000–400 cm−1) for KBr discs were recorded on a
Mattson 5000 FTIR spectrophotometer. Electronic spectra were
recorded on a Unicam UV–Vis spectrophotometer UV2. Magnetic
susceptibilities were measured with a Sherwood scientific mag-
netic susceptibility balance at 298 K. 1H NMR measurements in
d6-DMSO at room temperature were carried out on a Varian Gemini
WM-200 MHz spectrometer at the Microanalytical Unit, Cairo Uni-
versity. Thermogravimetric measurements (TGA, DTA, 20–1000 ◦C)
were recorded on a DTG-50 Shimadzu thermogravimetric analyzer
at a heating rate of 10 ◦C/min and nitrogen flow rate of 20 ml/min.
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 and modulation amplitudes were set at 1 mW
and 4 gauss, respectively. The low field signal was obtained after 4
scans with 10-fold increase in the receiver again. A powder spec-
trum was obtained in a 2 mm quartz capillary at room temperature.
We were thus motivated to undertake a systematic study
of preparation and characterization of a new transition metal
complex formed with Nꢀ-(1-(4-hydroxyphenyl) ethylidene)-2-oxo-
2-(phenylamino) acetohydrazide (H3OPAH) and Cu(II), Co(II), Ni(II),
2+
Mn(II), Cd(II), Zn(II), Hg(II) and U(IV)O2 ions.
∗
Corresponding author. Tel.: +20 100373155.
E-mail address: gaelreash@mans.edu.eg (G.A. El-Reash).
1386-1425/$ – see front matter © 2011 Published by Elsevier B.V.
doi:10.1016/j.saa.2011.04.055

18
S.F. Ahmed et al. / Spectrochimica Acta Part A 83 (2011) 17–27
2.2. Procedure for the pH-metric titration
insoluble in common organic solvents, partially soluble in DMSO
and DMF and found to be non-electrolytes.
The pH-metric measurements were carried out with Hanna
Instrument 8519 digital pH meter. The titrations were preformed at
different temperatures (298, 308 and 318 K). The experimental pro-
cedure involves the pH-metric titration of the following solutions
against standardized free carbonate sodium hydroxide solution
(11.1 mM) in 50% (v/v) dioxane–water at constant ionic strength
KCl (1 M) which is shown in Figs. 1S–3S (Supplementary Materials).
The solution mixtures (i–iii) were prepared as follows:
Type I (the ligand reacts in a neutral manner):
MCl2 · 2H2O + H3OPAHEtOH, NaOAc
[M(H3OPAH)Cl2] · mH2O
reflux,3 h
−→
where m = 1 for M = Hg and m = 0 for M = Cd.
EtOH
Zn(CH3COO)2 · 2H2O + H3OPAH −→ [Zn(H3OPAH)(OAc)2]
reflux,3 h
(i) 1.25 ml HCl (12.1 mM) + 1.25 ml KCl (1 M) + 12.5 ml diox-
ane + 10 ml bidistilled H2O.
(ii) 1.25 ml HCl (12.1 mM) + 1.25 ml KCl (1 M) + 2.5 ml (5 mM)
H3OPAH + 10 ml dioxane + 10 ml bidistilled H2O.
MnCl2 · 4H2O + H3OPAHEtOH−,→NaOAc[Mn(H3OPAH) Cl2]
2
reflux,3 h
(iii) 1.25 ml HCl (12.1 mM) + 1.25 ml KCl (1 M) + 2.5 ml H3OPAH
(5 mM) + 10 ml dioxane + 0.5 ml metal ion (Mn+) (5 mM) [where
Mn+ = Cu(II), Mn(II), Ni(II), Cd(II), Hg(II), Co(II), U(IV)O2 and
Zn(II)] + 9.5 ml bidistilled H2O.
Type II (the ligand reacts in a monoanionic manner):
CoCl2 · 6H2O + H3OPAH
−→
EtOH, NaOAc[Co2(H2OPAH) Cl2(H2O) ]
2 4
reflux,3 h
The total volume was adjusted to 25 ml by adding dioxane in each
case.
CuCl2 · 2H2O + H3OPAHEtOH, NaOAc
−→
[Cu2(H2OPAH)Cl3(H2O)]H2O
reflux,3 h
2.3. Synthesis of Nꢀ-(1-(4-hydroxyphenyl)
ethylidene)-2-oxo-2-(phenylamino) acetohydrazide (H3OPAH)
Type III (the ligand reacts in a dianionic manner):
UO2(CH3COO)2 · 2H2O
EtOH
2-Hydrazino-2-oxo-N-phenyl-acetamide was synthesized
according to the general literature method [9]. H3OPAH was
synthesized according to the following scheme:
O
+ H3OPAH −→ [(UO2)2(HOPAH)(OAc)2(H2O)2]
reflux,3 h
H
N
NH2
N
H
O
+
EtOH
O
Refulx, 4h
OH
2-hydrazino-2-oxo-N-phenyl-acetamide
p-hydroxy acetophenone
OH
O
H
N
N
N
H
O
N'-(1-(4-hydroxyphenyl) ethylidene)-2-oxo-2-(phenylamino) acetohydrazide (H3OPAH)
The pale yellow precipitate (H3OPAH) was filtered off, washed
several times with ethanol and recrystallized from hot ethanol and
NiCl2 · 6H2O + H3OPAH
−→
EtOH, NaOAc[Ni2(HOPAH)Cl2(H2O) ]H2O
2
finally dried in vacuum desiccators over anhydrous CaCl2 (m.p.
reflux,3 h
270 ◦C).
2.5. Molecular modeling
2.4. Synthesis of metal complexes
An attempt to gain a better insight on the molecular structure of
the ligand and its complexes, geometry optimization and confor-
mational analysis has been performed by the use of MM+ force-field
as implemented in hyperchem 8.0 [10]. The low lying obtained from
MM+ was then optimized at PM3 using the Polak–Ribiere algorithm
in RHF-SCF, set to terminate at an RMS gradient of 0.01 kcal/mol.
A hot ethanolic solution of the respective metal chlorides (Co(II),
Ni(II), Cu(II), Mn(II), Cd(II), Hg(II)) or acetates (Zn(II) and U(VI)O2)
(1.0 mmol) was added to hot ethanolic solution of H3OPAH (0.297 g,
1.0 mmol). The resultant mixture was heated under reflux for 2–3 h.
0.5 g of sodium acetate in 30 ml bidistilled water was added as a
buffering agent except in case of zinc and uranyl complexes. The
formed precipitates were filtered off, washed with ethanol followed
by diethyl ether and dried in a vacuum desiccator over anhydrous
CaCl2. The physical and analytical data of the isolated complexes
are listed in Table 1. The complexes have high melting points and
3. Results and discussion
The data of elemental analysis together with some physical
properties of the complexes are summarized in Table 1.

S.F. Ahmed et al. / Spectrochimica Acta Part A 83 (2011) 17–27
19
Table 1
Analytical and physical data of H3OPAH and its metal complexes.
Compound empirical formula (F. Wt.)
Colour
m.p. (◦C)
% Found (Calcd.)
M
Yield (%)
Cl
C
H
H3OPAH, C16H15N3O3 (297.31)
Pale yellow
Deep green
Reddish brown
Pale green
Brown
White
White
Pale brown
Orange
290
>300
>300
>300
>300
>300
>300
>300
>300
–
–
64.10 (64.64)
34.86 (35.09)
45.09 (45.03)
35.33 (35.74)
53.33 (53.35)
39.80 (39.98)
50.01 (49.96)
32.87 (32.75)
24.23 (24.28)
5.19 (5.09)
3.62 (3.81)
4.28 (4.25)
3.49 (3.56)
4.39 (4.20)
3.25 (3.15)
4.41 (4.40)
2.81 (2.92)
2.86 (2.84)
92
81
72
88
75
80
89
76
80
[Cu2(H2OPAH)Cl3(H2O)]H2O, C17H22Cl3Cu2N3O5 (581.82)
[Co2(H2OPAH)2Cl2(H2O)4], C32H36Cl2Co2N6O10 (853.43)
[Ni2(HOPAH)Cl2(H2O)2]H2O, C16H19Cl2N3Ni2O6 (537.63)
[Mn(H3OPAH)2Cl2], C32H30Cl2MnN6O6 (720.46)
[Cd(H3OPAH)Cl2], C16H15CdCl2N3O3 (480.63)
[Zn(H3OPAH)(OAc)2], C20H21N3O7Zn (480.79)
[Hg(H3OPAH)Cl2]H2O, C16H17Cl2HgN3O4 (586.82)
[(UO2)2(HOPAH)(OAc)2(H2O)2], C20H23N3O13U2 (989.47)
21.10 (21.84)
13.85 (13.81)
21.65 (21.83)
7.65 (7.63)
23.28 (23.39)
13.55 (13.60)
34.80 (34.18)
48.01 (48.11)
18.31 (18.28)
8.29 (8.31)
13.33 (13.19)
9.63 (9.84)
14.88 (14.75)
–
12.01 (12.08)
–
Scheme 1. H3OPAH.
3.1. IR and 1H NMR spectra
1174 cm−1 are attributed to ꢁ(N–N) [15] and ꢁ(C–O) [16] vibrations,
respectively. No bands at 1800–1960 cm−1 and 2300–2400 cm−1
are observed so intramolecular hydrogen bonding (N–H· · ·O)
[17] is ruled out suggesting the presence of the ligand in keto
form.
The most important IR bands of H3OPAH (Structure 1) and its
complexes with probable assignments are given in Table 2. The lig-
and has multi-coordination sites which gave variable coordination
modes. A comparison of the spectrum of H3OPAH and its com-
plexes revealed that the ligand coordinates in the ketone and enol
forms. H3OPAH (in KBr) shows two bands at 1596 and 1606 cm−1
assignable to ꢁ(C N) (azomethine) and ꢁ(C C) phenyl vibrations,
respectively [11]. The sharp band located at 1655 cm−1 is attributed
to ꢁ[(C O)2 + (C O)3] vibrations. The medium band observed at
3304 cm−1 is attributable to ꢁ(N4H) [12] and ꢁ(N1H) [13] vibrations,
respectively. The bands at 3386 and 1262 cm−1 are due to ꢁ(OH)
and ı(OH) vibrations [14]. The medium intensity bands at 1066 and
The 1H NMR spectrum of H3OPAH in d6-DMSO shows three sig-
nals at ı = 10.98, 10.81 and 9.92 ppm relative to TMS assignable to
N4H, N1H [12] and OH [17] protons, respectively. The multiplets at
6.50–8.00 ppm are assigned to phenyl ring protons [17], while the
signal at 3.41 is due to –CH3 proton [17].
H3OPAH behaves as a neutral OO bidentate ligand via the
oxygen atoms of the two carbonyl groups. This behavior is
found in [Cd(H3OPAH)Cl2] (Structure 2), [Hg(H3OPAH)Cl2]H2O and
[Mn(H3OPAH)2Cl2] complexes and revealed by: (i) the shift of
Table 2
Principle infrared bands of H3OPAH and its metal complexes.
Compound
ꢁ(C N) ꢁ(C O)2 ꢁ(C O)3 ꢁ(N1H) ꢁ(N4H) ꢁ(C–O) ꢁ(O–H) ı(O–H) ꢁ(C N)*
ꢁ(C–O)* ꢁ(N–N) ꢁ(M–O) ꢁ(M–N)
H3OPAH
1596
1579
1583
1582
1600
1599
1596
1587
1655
1646
–
1655
1633
–
1675
1648
1671
1652
1656
–
3304
Broad
–
3304
Broad
–
3310
3361
3337
3260
3217
–
1174
1180
1174
1168
1174
1167
1174
1176
1170
3386
–
1262
–
–
–
–
–
1060
1074
1074
1073
1074
1074
1074
1074
1074
–
501
503
509
501
506
516
501
524
–
434
447
446
–
–
–
446
447
[Co2(H2OPAH)2Cl2(H2O)4]
[Ni2(HOPAH)Cl2(H2O)2]H2O
[Cu2(H2OPAH)Cl3(H2O)]H2O
[Mn(H3OPAH)2Cl2]
[Cd(H3OPAH)Cl2]
[Hg(H3OPAH)Cl2]H2O
[Zn(H3OPAH)(OAc)2]
Broad
3383
Broad
3362
3384
3378
3380
1267
1255
1267
1260
1265
1260
1257
16321622 1166
1615
–
–
–
–
–
–
1113
1657
1707
1652
1666
–
3361
3280
3286
3264
–
–
–
–
–
[(UO2)2(HOPAH)(OAc)2(H2O)2] 1580
16351620 1127

20
S.F. Ahmed et al. / Spectrochimica Acta Part A 83 (2011) 17–27
In [Co2(H2OPAH)2Cl2(H2O)4] complex (Structure 4), H3OPAH
behaves as a monoanionic ONO tridentate ligand through the
deprotonated OH, (C O)2 groups and the N of the azomethine
group. This behavior is supported by: (i) the disappearance of ꢁ(OH)
band, (ii) the shift of ꢁ(C N) (azomethine) to lower wavenumber
and ꢁ(N–N) to higher wavenumber (iii) the shift of ꢁ(C O)2 band
to lower frequency and ꢁ(C–O) band to higher frequency.
H3OPAH behaves as monoanionic tetradentate ligand coordi-
nating through the oxygen atom (C O)3 and new azomethine
group from one side, and the deprotonated enolic oxygen atom
(
C–O−)2 and C N (azomethine) group from the other one. This
mode of chelation is found in [Cu2(H2OPAH)Cl3(H2O)]H2O com-
plex (Structure 5). This behavior is supported by: (i) the absence
of (C O)3 with simultaneous appearance of new broad bands at
1615 cm−1 assignable to the conjugation (–C N–N C–) system
[18] and band at 1113 cm−1 assignable to ꢁ(C–O) [16] and (ii) the
shift of ꢁ(N–N) to higher wavenumber.
Scheme 2.
two ꢁ(C O) to lower and higher wavenumber depending upon
the metal salt used and (ii) the ꢁ(C N) (azomethine) and ꢁ(N–N)
bands remain practically unaltered indicating that the azomethine
group is not participated in bonding. The 1H NMR spectrum of
[Cd(H3OPAH)Cl2] in d6-DMSO shows three signals at ı = 13.62,
11.29 and 10.986 ppm relative to TMS which may be assigned to
OH, N4H and N1H protons, respectively, confirming the neutral
behavior of the ligand.
The IR spectrum of [Zn(H3OPAH)(OAc)2] complex (Structure
3) shows that H3OPAH coordinates in neutral NO bidentate lig-
and through C N (azomethine) and C O2 groups. This behavior
is suggested by: (i) the shift of ꢁ(C N) (azomethine) to lower
wavenumber and ꢁ(C O)2 to higher wavenumber, (ii) the position
of ꢁ(C O)3 band remains practically unaltered indicating that this
group is not participated in bonding and (iii) the shift of ꢁ(N–N) to
higher wavenumber.
Finally, H3OPAH behaves as dianionic tetradentate ligand coor-
dinating through the deprotonated enolic oxygen atom ( C–O−)2
and C N (azomethine) from one side, and the deprotonated enolic
oxygen atom ( C–O−)3 and new azomethine group from the other
one. This mode of chelation is found in [Ni2(HOPAH)Cl2(H2O)2]H2O
(Structure 6) and [(UO2)2(HOPAH)(OAc)2(H2O)2] complexes. This
behavior is supported by: (i) the absence of both (C O) with simul-
taneous appearance of new broad bands at 1620, 1635 cm−1 for
Ni(II) and 1622, 1632 cm−1 for U(VI) assignable to the conjugation
(–C N–N C–) system [18] and band at 1113, 1127 cm−1 assignable
to ꢁ(C–O) [16] and (ii) the shift of ꢁ(N–N) to higher wavenumber.
The absorption bands of the coordinated acetate groups were
observed at 1454 and 1322 cm−1 indicating a monodentate acetate
anion character [19,20]. Moreover, the IR spectrum exhibits two
bands at 931 and 860 cm−1, assigned to the asymmetric stretch-
Scheme 3.
Scheme 4.

S.F. Ahmed et al. / Spectrochimica Acta Part A 83 (2011) 17–27
21
Scheme 5.
coordinated and hydrated water, TGA measurement was carried
out.
3.2. Spectral and magnetic studies
Electronic spectra were measured in dimethylsulfoxide (DMSO)
solution for H3OPAH and its metal complexes. The tentative
assignments of the significant spectral absorption bands, magnetic
moments and ligand field parameters of metal complexes are given
in Table 3.
The electronic spectrum of the ligand shows two bands at
33,112 and 28,735 cm−1. The strong band at 33,112 cm−1 is due
to ␲ → ␲* transition of the benzene ring [27]. The n → ␲* transi-
tions associated to the azomethine and carbonyl function overlap
at 28,735 cm−1 [28]. These bands undergo a shift to higher energy in
the spectra of complexes [27], suggesting the coordination of imino
nitrogen atom and oxygen atom of carbonyl group with the central
metal ion [29]. The Cl → M2+ (M2+ = Cu2+, Ni2+ and Mn2+) transition
is generally found in the 28,735 cm−1 region and would contribute
to the higher energy n → ␲* band [30].
Scheme 6.
ing frequency (ꢁ3) and the symmetric stretching frequency (ꢁ1),
respectively, of the dioxouranium ion [17,21]. The force constant
(F) for the bonding sites of ꢁ(U O) is calculated by the method of
McGlynn et al. [22]; FU–O value is found to be 7.15 mdynes A−1. Also,
˚
the U–O bond distance is calculated by the method of Jones [23];
RU–O value is 1.73 A. The U–O bond distance falls in usual range as
˚
reported earlier [24] and extremely in accordance with the bond
length calculated by the use of MM+ force field (as implemented in
hyperchem 8.0 [10]).
New bands observed in all complexes at 501–524 and
434–447 cm−1 are tentatively assigned to the ꢁ(M–O) [25] and
ꢁ(M–N) [26], respectively.
The electronic spectrum of [Co2(H2OPAH)2Cl2(H2O)4] com-
plex shows two bands at 15,974 and 18,382 cm−1 assignable to
4
4
4
4T1g(F) → A2g(F) and T1g(F) → T1g(p) transitions [30], respec-
tively, in a octahedral configuration. The calculated values of ligand
field parameters (Dq = 743 cm−1, B = 774 cm−1 and ˇ = 0.79) are in
good agreement with those reported for octahedral Co(II) com-
plexes. Also, the value of ꢃeff (5.06 B.M.) is an additional evidence
for an octahedral structure.
The broad bands at ≈3399–3454, 868–850, and at ≈567 cm−1 in
the IR spectra of the investigated complexes are referred to ꢁ(OH),
ꢂ(H2O), pr(H2O) and Pw(H2O) vibrations for the coordinated water.
The broad band centered at 3500 cm−1 in the spectra of the studied
complexes may be due to hydrated water. To verify between the
The
complex
[Ni2(HOPAH)
Cl2(H2O)2]H2O has a magnetic moment value (3.14 B.M.) which is
lower than the measured value per one nickel atom which is in
Table 3
Spectral absorption bands, magnetic moments and ligand field parameters of H3OPAH metal complexes.
Compound
H3OPAH
Band position (cm−1
)
Assignment
ꢃeff (B.M.)
33,446
28,735
␲ → ␲*
n → ␲*
–
4
15,974
18,382
4T1g(F) → A2g(F)
[Co2(H2OPAH)2Cl2(H2O)4]
[Ni2(HOPAH)Cl2(H2O)2]H2O
[Cu2(H2OPAH)Cl3(H2O)]H2O
[Mn(H3OPAH)2Cl2]
5.06
3.14
1.91
6.50
Diam.
4
4T1g(F) → T1g(p)
17,667
21,929
3T1(F) → 3T1(P)
1A1g
2T2g
→
→
1A2g
2Eg
14,326
25,906
LMCT
24,630
27,932
6A1g
6A1g
→
4T1g(G)
4T2g(G)
→
1ꢄ+
→
␲
4
2
23,696
27,932
n →g␲*
[(UO2)2(HOPAH)(OAc)2(H2O)2]
Diam., diamagnetic.
LMCT, ligand to metal charge transfer.

22
S.F. Ahmed et al. / Spectrochimica Acta Part A 83 (2011) 17–27
Fig. 1. ESR spectra of [Cu2(H2OPAH)Cl3(H2O)]H2O.
Fig. 2. ESR spectra of [Cu2(H2OPAH)Cl3(H2O)]H2O.
Table 4
Kinetic parameters evaluated by Coats–Redfern equation for H3OPAH complexes.
Complex
Peak
Mid temp (K)
Ea (kJ/mol)
A (s−1
)
ꢀH* (kJ/mol)
ꢀS* (kJ/mol K)
ꢀG* (kJ/mol)
1st
2nd
3rd
355
651
736
28.55
109.51
84.48
2.84 × 104
1.95 × 105
4.13 × 105
25.60
104.09
78.36
−0.161
−0.150
−0.144
82.86
201.97
185.04
[Co2(H2OPAH)2Cl2(H2O)4]
1st
354
576
708
1029
28.86
2.26 × 104
2.75 × 105
4.62 × 105
3.56 × 106
4.15 × 104
1.51 × 105
1.02 × 105
1.92 × 106
3.92 × 105
3.31 × 106
25.91
124.10
99.55
−0.162
−0.146
−0.143
−0.129
83.63
[Ni2(HOPAH)Cl2(H2O)2]H2O
[Cu2(H2OPAH)Cl3(H2O)]H2O
2nd
3rd
4th
128.89
105.44
528.45
208.38
201.37
653.47
519.89
1st
335
492
576
665
846
1027
48.86
46.07
121.22
121.42
171.29
65.53
−0.157
−0.149
−0.154
−0.131
−0.146
−0.130
98.82
2nd
3rd
4th
5th
6th
125.31
126.21
176.82
72.57
194.98
210.41
258.58
189.47
626.73
501.37
492.84
1st
2nd
3rd
656
839
983
94.33
163.89
285.65
1.13 × 106
1.08 × 106
6.94 × 105
88.88
156.92
277.48
−0.135
−0.137
−0.143
177.80
272.75
418.05
[Mn(H3OPAH)2Cl2]
[Zn(H3OPAH)(OAc)2]
1st
2nd
576
717
163.17
108.87
7.90 × 105
158.38
102.91
−0.137
−0.150
237.57
210.62
2.12 × 105
Table 5
Kinetic parameters evaluated by Horowitz–Metzger equation for H3OPAH complexes.
Complex
Peak
Mid temp (K)
Ea (kJ/mol)
A (s−1
)
ꢀH* (kJ/mol)
ꢀS* (kJ/mol K)
ꢀG* (kJ/mol)
1st
2nd
3rd
355
651
736
28.42
109.88
84.79
2.75 × 104
1.98 × 105
4.06 × 105
25.46
104.46
78.67
−0.161
−0.150
−0.145
82.82
202.25
185.45
[Co2(H2OPAH)2Cl2(H2O)4]
1st
354
576
709
1030
28.88
2.36 × 104
2.76 × 105
4.81 × 105
3.52 × 106
4.13 × 104
1.52 × 105
1.00 × 105
1.95 × 106
4.55 × 105
3.25 × 106
25.93
123.58
99.33
−0.162
−0.146
−0.143
−0.129
83.52
[Ni2(HOPAH)Cl2(H2O)2]H2O
[Cu2(H2OPAH)Cl3(H2O)]H2O
2nd
3rd
4th
128.37
105.23
528.32
207.84
201.02
653.54
519.76
1st
335
492
576
665
846
1027
48.65
45.87
122.25
121.57
171.42
65.56
−0.157
−0.149
−0.154
−0.131
−0.145
−0.130
98.63
2nd
3rd
4th
5th
6th
126.34
126.36
176.95
72.59
195.98
210.64
258.63
188.45
627.08
501.58
493.04
1st
2nd
3rd
656
839
983
94.34
163.28
285.19
1.17 × 106
1.25 × 106
6.41 × 105
88.89
156.30
277.02
−0.135
−0.136
−0.143
177.62
271.05
418.23
[Mn(H3OPAH)2Cl2]
[Zn(H3OPAH)(OAc)2]
1st
2nd
576
717
162.63
107.42
9.30 × 105
157.84
101.46
−0.136
−0.150
236.25
209.26
2.09 × 105

S.F. Ahmed et al. / Spectrochimica Acta Part A 83 (2011) 17–27
23
(A)
-11.0
(B)
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n = 0.5
-11.0
-11.5
-12.0
-12.5
-13.0
-11.5
-12.0
-12.5
-13.0
Linear Fit of Data1_J
lnX n = 0.5
Linear Fit of Data1_J
0.0026
0.0028
0.0030
0.0032
0.0026
0.0028
0.0030
1/T
1000/T
(D)
(C)
lnX n=1
lnX n=1
lnX n=0.66
lnX n=0.66
lnX n=0.33
lnX n=0
-12.5
-13.0
-13.5
-14.0
-14.5
lnX n=0.33
lnX n=0
-11
-12
-13
lnX n = 0.5
lnX n = 0.5
Linear Fit of Data1_J
Linear Fit of Data1_J
0.0015
0.0016
0.0028
0.0030
1000/T
0.0032
1/T
lnX n=1
(E)
lnX n=0.66
lnX n=0.33
lnX n=0
-13.0
lnX n = 0.5
Linear Fit of Data1_J
-13.5
-14.0
-14.5
0.00175
0.00180
1/T
Fig. 3. Coats–Redfern plot of first degradation step for (A) [Co2(H2OPAH)2Cl2(H2O)4], (B) [Ni2(HOPAH)Cl2(H2O)2]H2O, (C) [Cu2(H2OPAH)Cl3(H2O)]H2O, (D) [Mn(H3OPAH)2Cl2]
and (E) [Zn(H3OPAH)(OAc)2] complex.
turn less than that reported for d8-octahedral and/or tetrahedral
complexes and higher than that for diamagnetic square-planar
complexes. The values may suggest the existence of the complexes
in a mixed stereochemistry [31]. Such assumption is also con-
and the magnetic moment value (1.91 B.M.) can be taken as an
evidence for the square-planar configuration [17,25].
The [Mn(H3OPAH)2Cl2] complex shows a band at 24,630
6
4
and at 27,932 cm−1 which may be due to A1g → T1g(G) and
6A1g → T2g(G) transitions, respectively, in an octahedral config-
4
3
firmed by one band at 17,667 cm−1 assignable to 3T1(F) → T1(P)
uration [33] around the metal ion. Also, the value of magnetic
moment (6.5 B.M.) is in the range measured for high spin d5
system.
transition consistent with a tetrahedral configuration in addition
to another band at 21,929 cm−1, respectively, referring to a square
planar geometry [32].
Finally, the [(UO2)2(HOPAH)(OAc)2(H2O)2] complex shows two
The electronic spectrum of [Cu2(H2OPAH)Cl3(H2O)]H2O
exhibits two bands: an asymmetric broad band at 14,326 cm−1
and a more intense band at 25,906 cm−1. The latter band may be
assigned to ligand metal charge transfer transition. The asymmet-
bands in its spectrum, the first at 27,932 cm−1 is due to charge
transfer, probably H3OPAH → O
U
O, while the second band at
2
23,696 cm−1 can be definitely assigned to the 1ꢄ+g → ␲ transi-
4
2
2
tion [34].
ric band is assigned to T2g → Eg transition. The band position

24
S.F. Ahmed et al. / Spectrochimica Acta Part A 83 (2011) 17–27
(A)
(B)2
lnX n=1
lnX n=0.66
lnX n=1
2
1
lnX n=0.33
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0
lnX n = 0.5
lnX n = 0.5
Linear Fit of D ata1_J
Linear Fit of Data1_J
1
0
0
-1
-2
-1
-40
-30
-20
-10
0
10
20
30
40
-40
-30
-20
-10
0
10
20
30
40
50
T-Ts
T-Ts
(C)
(D)
lnX n=1
1.5
1.0
0.5
0.0
lnX n=1
1.5
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n=0.66
lnX n=0.33
lnX n=0
lnX n = 0.5
1.0
lnX n = 0.5
Linear Fit of Data1_J
Linear Fit of Data1_J
0.5
0.0
-0.5
-1.0
-0.5
-1.0
-10
0
10
20
30
-40
-20
0
20
T-Ts
40
60
80
T-Ts
(E)0.0
lnX n=1
lnX n=0.66
lnX n=0.33
lnX n=0
-0.5
-1.0
-1.5
-2.0
-2.5
lnX n = 0.5
Linear Fit of Data1_J
-30
-25
-20
-15
-10
-5
T-Ts
Fig. 4. Horowitz–Metzger plot of first degradation step for (A) [Co2(H2OPAH)2Cl2(H2O)4], (B) [Ni2(HOPAH)Cl2(H2O)2]H2O, (C) [Cu2(H2OPAH)Cl3(H2O)]H2O, (D)
[Mn(H3OPAH)2Cl2] and (E) [Zn(H3OPAH)(OAc)2] complex.
3.3. ESR spectra
narrowing toward the coalescence of four copper hyberfine lines
to a single line.
The copper complex displays an axial ESR powder spectrum
(Fig. 1) with g = 2.21 and g = 2.08 indicating that the d
ground state. In axial symmetry, the g-values are related to the G
is the
2
2
||
⊥
x
−y
3.4. Thermogravimetric studies
factor by the expression, G = (g − 2)/(g⊥ − 2). The value of G which
Thermal data showed that the crystal water molecules are
volatilized within the temperature range 75–125 ◦C, while the coor-
dinated water molecules are removed in the temperature range
120–200 ◦C. The TGA of [Cu2(H2OPAH)Cl3(H2O)]H2O complex was
discussed in detail as a representative example. In TG thermogram
||
||
is 2.86 and also the value of g > g > 2.0023 are consistent with a
⊥
square-planar geometry [35,36]. The ESR spectrum (Fig. 2) is sim-
ilar to the ESR spectra of the binuclear Cu(II) complexes [37,38].
The line broadening is probably due to insufficient spin-exchange

S.F. Ahmed et al. / Spectrochimica Acta Part A 83 (2011) 17–27
25
of this complex, the first stage at 32–91 ◦C with weight loss of 3.05
(Calcd. 3.18%) is corresponding to the loss of the one lattice water
molecule. The second step with weight loss of 3.11 (Calcd. 3.18%) at
183–255 ◦C is attributed to the elimination of H2O. It is clear that,
the TG thermograms for the investigated complexes displayed
high residual part indicating high stability of the formed chelates.
3.5. Kinetic data
The kinetic and thermodynamic parameters of thermal degra-
dation process have been calculated using Coats–Redfern and
Horowitz–Metzger models [39,40].
A number of pyrolysis processes can be represented as a first
order reaction. Particularly, the degradation of a series of H3OPAH
complexes was suggested to be first order [41], therefore we
assume n = 1 for the remainder of the present text. The other ther-
modynamic parameters of activation can be calculated by Eyring
equation [42]:
ꢀH = Ea − RT
hA
ꢀS = R ln
kBT
(3)
(4)
(5)
ꢀG = ꢀH − TꢀS
Thermodynamic parameters such as activation energy (Ea), pre-
exponential factor (A), entropy of activation (ꢀS), enthalpy of
activation (ꢀH) and free energy of activation (ꢀG) of decom-
position steps were calculated using Coats–Redfern [39] and
Horowitz–Metzger [40] methods (Tables 4 and 5). In both meth-
ods, the lift side of Eqs. (3) and (4) are plotted against 1/T and ꢅ,
respectively (Figs. 3 and 4). From the results, the following remarks
can be pointed out:
- The high values of the energy of activation, Ea of the complexes
reveal the high stability of such chelates due to their covalent
bond character [43].
- The positive sign of ꢀG for the investigated complexes reveals
that the free energy of the final residue is higher than that of
the initial compound, and all the decomposition steps are non-
spontaneous processes. Also, the values of the activation, ꢀG
increases significantly for the subsequent decomposition stages
of a given complex. This is due to increasing the values of TꢀS
significantly from one step to another which overrides the values
of ꢀH [44–46].
- The negative values of ꢀS for the degradation process indicate
that more ordered activated complex than the reactants or the
reaction is slow [42].
3.6. pH-metric studies
The proton–ligand formation constants and the stability con-
stants of its metal complexes at 298, 308 and 318 K were
determined. The values of the average number of protons n¯ A, the
average number of ligand molecules attached per metal ion and the
free ligand exponent (pL) were calculated at different pH values by
applying Irving and Rossotti equation [47]. Plotting of n¯ A versus pH
(Fig. 4S, Supplementary Materials) gives a curve which is suitable to
calculate the ligand constants (log K1, log K2 and log K3) (Table 6).
The first value is due to the OH proton while the second and the
third are due to the amide (NHCO) protons. The stability constants
of the complexes were calculated by half method. The titration
curves of the complexes were drawn as in Figs. 5S–10S (Supplemen-
tary Materials) (Table 7). The data reveal that, log K1 is higher than
log K2 or log K3 for the same complex because the vacant sites of
the metal ions are more freely available for binding the first ligand
more than the second or the third.

26
S.F. Ahmed et al. / Spectrochimica Acta Part A 83 (2011) 17–27
Table 7
Stability constants of metal ions–H3OPAH complexes in 50% (v/v) dioxane–water and KCl at different temperatures.
Cation
Dissociation constant
298 K
308 K
318 K
log K1
log K2
log K1
log K2
log K1
log K2
Ni(II)
Co(II)
Cu(II)
Mn(II)
Cd(II)
Hg(II)
Zn(II)
U(VI)
14.29
17.05
26.09
9.97
9.84
7.63
7.16
9.05
11.28
6.51
6.80
5.29
7.47
5.79
13.46
15.43
22.34
7.45
6.37
6.44
6.62
8.24
9.11
4.98
5.21
4.48
5.67
5.61
12.06
13.04
17.22
5.94
5.37
5.45
6.10
8.03
7.17
1.97
2.05
4.13
4.20
5.45
16.69
17.49
14.76
16.59
11.45
16.00
Table 8
Thermodynamic parameters of metal ions–H3OPAH complexes in 50% (v/v) dioxane–water, 1 M KCl at different temperatures.
Ligand
Free energy change (ꢀG, kJ/mol)
Enthalpychange(ꢀH, kJ/mol)
Entropy change (ꢀS, kJ/mol K)
298 K
308 K
318 K
Co(II)
Ni(II)
−100.58
−82.42
−150.26
−56.46
−56.09
−42.92
−98.26
−99.64
−51.33
−42.48
−65.85
−39.79
−41.73
−31.13
−44.19
−32.94
−91.78
−78.42
−128.36
−46.06
−44.29
−37.72
−85.66
−98.44
−49.93
−40.68
−55.55
−27.19
−28.73
−28.63
−34.79
−33.01
−82.98
−74.42
−106.46
−35.66
−32.49
−32.52
−73.06
−97.24
−48.53
−38.88
−45.25
−14.59
−15.73
−26.13
−25.39
−33.08
−362.82
−201.62
−802.88
−366.38
−407.73
−197.88
−473.74
−135.40
−93.05
−96.12
−0.88
−0.40
−2.19
−1.04
−1.18
−0.52
−1.26
−0.12
−0.14
−0.18
−1.03
−1.26
−1.30
−0.25
−0.94
0.007
Cu(II)
Mn(II)
Cd(II)
Hg(II)
Zn(II)
UO2(VI)
−372.79
−415.27
−429.13
−105.63
−324.31
−30.85
Furthermore, the thermodynamic parameters, ꢀH◦ and ꢀS◦
were obtained by linear least square fit of pK against 1/T with
for the bond lengths and angles for the bond, one can conclude the
following remarks:
an intercept equals ꢀS◦/2.303R and
a
slope of ꢀH◦/2.303R
(Figs. 11S–15S, Supplementary Figures). The free energy (ꢀG◦)
change can be estimated using the relationships:
(1) The N(10)–N(11) bond length becomes slightly longer
in complexes as the coordination takes place via
N
atoms of –C N–N C– group that is formed on deproto-
nation of OH group in [Ni2(HOPAH)Cl2(H2O)2]H2O and
[(UO2)2(HOPAH)(OAc)2(H2O)2] complexes [12].
ꢀG◦ = ꢀH◦ − TꢀS◦
The data of the thermodynamic functions are recorded in Table 8
and the data reveal the following remarks:
(2) The C(8)–O(12) bond distance in [Cu2(H2OPAH)Cl3(H2O)]H2O,
[Ni2(HOPAH)Cl2(H2O)2]H2O,
[Cd(H3OPAH)Cl2],
[Mn(H3OPAH)2Cl2],
[Hg(H3OPAH)Cl2]H2O and
(1) The stepwise stability constants decrease with increasing
temperature indicating that the complexation processes are
unfavorable with increasing temperature.
[(UO2)2(HOPAH)(OAc)2(H2O)2] complexes becomes longer
due to the formation of the M–O bond which makes the
C–O bond weaker except [Co2(H2OPAH)2Cl2(H2O)4] and
[Zn(H3OPAH)(OAc)2] complexes in which this bond distance
remains practically unaltered indicating that this group is not
participated in bonding. The C(9)–O(13) bond distance in all
complexes becomes longer due to the formation of the M–O
bond [28].
(2) All ꢀG◦ values are negative indication of spontaneous character
of chelation.
(3) The negative values of ꢀS◦ indicate that the complexation pro-
cesses are entropically unfavorable.
(4) The negative values of ꢀH◦ suggest that the chelation processes
are accompanied by generation of heat (i.e. the processes are
exothermic).
(3) In
[Ni2(HOPAH)Cl2(H2O)2]H2O
complexes,
and
[(UO2)2(HOPAH)(OAc)2(H2O)2]
C(8)–O(12)
3.7. Molecular modeling
bond distance is more longer due to the deproto-
nation at N(7) which leads to higher single bond
character for C(8)–O(12). On the other hand, in
[Cu2(H2OPAH)Cl3(H2O)]H2O, [Ni2(HOPAH)Cl2(H2O)2]H2O
and [(UO2)2(HOPAH)(OAc)2(H2O)2] complexes, C(9)–O(13)
bond distance is more longer due to the deprotonation at N(10)
a
The molecular structure along with atom numbering of H3OPAH
and its metal complexes are shown in Structures 1–9 where
Structures 7–9 are in Supplementary Materials. From the analysis
of the data in Tables 1S–18S (Supplementary Materials) calculated
Table 9
Some energetic properties of H3OPAH and its complexes calculated by PM3 method.
Compound
Total energy
(kcal/mol)
Binding energy
(kcal/mol)
Electronic energy
(kcal/mol)
Heat of formation
(kcal/mol)
Dipole
moment (D)
HOMO (eV)
LUMO (eV)
H3OPAH
−8.05 × 104
−1.57 × 105
−2.41 × 105
−1.64 × 105
−1.84 × 105
−1.21 × 105
−9.58 × 105
−4067.57
−5046.37
−9774.73
−4625.05
−8320.55
−5458.11
−4193.73
−5.33 × 105
−1.11 × 106
−2.59 × 106
−1.11 × 106
−2.02 × 106
−9.81 × 105
−6.65 × 105
−34.123
−526.02
−894.21
−231.57
−127.98
−159.09
−87.61
1.74
7.97
15.72
4.83
4.60
5.28
−8.90
−8.60
−7.64
−8.63
−4.34
−9.20
−9.31
−0.43
−1.70
−1.93
−1.80
−0.97
−1.29
−1.65
[Ni2(HOPAH)Cl2(H2O)2]H2O
[Co2(H2OPAH)2Cl2(H2O)4]
[Cu2(H2OPAH)Cl3(H2O)]H2O
[Mn(H3OPAH)2Cl2]
[Zn(H3OPAH)(OAc)2]
[Hg(H3OPAH)Cl2]H2O
12.99

S.F. Ahmed et al. / Spectrochimica Acta Part A 83 (2011) 17–27
27
which leads to a higher single bond character for C(9)–O(13)
[28].
(4) In [Cu2(H2OPAH)Cl3(H2O)]H2O, [Ni2(HOPAH)Cl2(H2O)2]H2O
and [(UO2)2(HOPAH)(OAc)2(H2O)2] complexes, C(9)–N(10)
and N(7)–C(8) bond distances are shortened due to the forma-
tion of a double bond character.
(5) The bond angles of the hydrazone moiety of H3OPAH are altered
somewhat upon coordination but the angles around the metal
undergo appreciable variations upon changing the metal
center [48]. The largest change affects C(9)–N(10)–N(11),
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C(9)–C(8)–O(12),
N(7)–C(8)–C(9),
N(10)–C(9)–O(13),
O(12)–C(8)–N(7) and N(10)–C(9)–C(8) angles which are
reduced or increased on complex formation as a consequence
of bonding [12].
(6) The bond angles in complexes namely, [Cd(H3OPAH)Cl2],
[Zn(H3OPAH)(OAc)2] and [Hg(H3OPAH)Cl2]H2O are quite
near to a tetrahedral geometry predicting sp3 hybridiza-
tion. On the other hand, [Cu2(H2OPAH)Cl3(H2O)]H2O and
[Ni2(HOPAH)Cl2(H2O)2]H2O complex afforded
planar geometry with dsp2 hybridization and quite near
to
tetrahedral geometry predicting sp3 hybridization.
a
square
a
Also, [Mn(H3OPAH)2Cl2], [Co2(H2OPAH)2Cl2(H2O)4] and
[(UO2)2(HOPAH)(OAc)2(H2O)2] complexes afforded octahedral
geometry.
(7) The lower HOMO energy values show that molecule donat-
ing electron ability is weaker. On contrary, the higher HOMO
energy implies that the molecule is a good electron donor.
LUMO energy represents the ability of a molecule receiving
electron as in Table 9 [49].
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A new series of complexes, Structures 2–9, were prepared from
the novel ligand Nꢀ-(1-(4-hydroxyphenyl) ethylidene)-2-oxo-2-
(phenylamino) acetohydrazide (H3OPAH). Geometry optimization
and conformational analysis have been performed and the per-
fect agreement with spectral studies allows for suggesting the
exact structure of all studies complexes. The stability of complexes
was explained and kinetic parameters (Ea, A, ꢀH, ꢀS and ꢀG) of
all the thermal decomposition stages have been evaluated using
Coats–Redfern and Horowitz–Metzger methods.
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Supplementary data
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Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.04.055.
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