Cu(II), Co(II) and Ni(II) complexes of new Schiff base ligand: Synthesis, thermal and spectroscopic characterizations

Article abstract of DOI:10.1016/j.molstruc.2013.01.059

Cu(II), Co(II), and Ni(II) complexes were synthesized from 2-[(5-o-chlorophenylazo-2-hydroxybenzylidin)amino]-phenol Schiff base (H ₂L). Metal ions coordinate in a tetradentate or hexadentate features with these O₂N donor ligand, which are characterized by elemental analyses, magnetic moments, infrared, Raman laser, electronic, and ¹H NMR spectral studies. The elemental analysis suggests the stoichiometry to be 1:1 (metal:ligand). Reactions with Cu(II), Co(II) and Ni(II), resulted [Cu(H₂L)(H₂O)₂(Cl)]Cl, [Co(H ₂L)(H₂O)₃]Cl₂?3H₂O and [Ni(H₂L)(H₂O)₂]Cl₂?6H ₂O. The thermal decomposition behavior of H₂L complexes has been investigated by thermogravimetric analysis (TG/DTG) at a heating rate of 10 °C min^-1 under nitrogen atmosphere. The brightness side in this study is to take advantage for the preparation and characterizations of single phases of CuO, CoO and NiO nanoparticles using H₂L complexes as precursors via a solid-state decomposition procedure. The crystalline structures of products using X-ray diffractometer (XRD), morphology of particles by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) were investigated.

Full text of DOI:10.1016/j.molstruc.2013.01.059

Journal of Molecular Structure 1038 (2013) 62–72
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Cu(II), Co(II) and Ni(II) complexes of new Schiff base ligand: Synthesis, thermal
and spectroscopic characterizations
c
b
Moamen S. Refat a,b, , Mohamed Y. El-Sayed , Abdel Majid A. Adam
⇑
a Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt
b Department of Chemistry, Faculty of Science, Taif University, 888 Taif, Saudi Arabia
c Department of Chemistry, Faculty of Science, Zagazig University, Egypt
h i g h l i g h t s
"
"
"
Three novel bi- or tridentate Schiff base complexes of Cu(II), Co(II) and Ni(II) have synthesized.
The calcinations of the Cu(II), Co(II) and Ni(II)AH2L at 600 °C have succeeded in synthesized nano-structured oxides.
The particles deposited at calcinations temperature is in the region of 250–480 nm.
a r t i c l e i n f o
a b s t r a c t
Article history:
Cu(II), Co(II), and Ni(II) complexes were synthesized from 2-[(5-o-chlorophenylazo-2-hydroxybenzyli-
din)amino]-phenol Schiff base (H2L). Metal ions coordinate in a tetradentate or hexadentate features with
these O2N donor ligand, which are characterized by elemental analyses, magnetic moments, infrared,
Raman laser, electronic, and 1H NMR spectral studies. The elemental analysis suggests the stoichiometry
to be 1:1 (metal:ligand). Reactions with Cu(II), Co(II) and Ni(II), resulted [Cu(H2L)(H2O)2(Cl)]Cl,
[Co(H2L)(H2O)3]Cl2ꢀ3H2O and [Ni(H2L)(H2O)2]Cl2ꢀ6H2O. The thermal decomposition behavior of H2L
Received 9 November 2012
Received in revised form 22 January 2013
Accepted 24 January 2013
Available online 31 January 2013
Keywords:
Schiff base
Nano-particles
Transition metals
Thermal analysis
complexes has been investigated by thermogravimetric analysis (TG/DTG) at
a heating rate of
10 °C minꢁ1 under nitrogen atmosphere. The brightness side in this study is to take advantage for the
preparation and characterizations of single phases of CuO, CoO and NiO nanoparticles using H2L com-
plexes as precursors via a solid-state decomposition procedure. The crystalline structures of products
using X-ray diffractometer (XRD), morphology of particles by scanning electron microscopy (SEM),
energy-dispersive X-ray spectroscopy (EDX) were investigated.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
no benzoic acid. Azo compounds have been studied widely because
of their excellent thermal, antibacterial activity and optical proper-
Schiff base compounds with the azomethine group (ARC@NA)
are usually formed by the condensation of amine ANH2 group with
active AC@O carbonyl group [1]. The field of Schiff bases is fast
developing because of the wide variety and potential applications
of their industrial, biological, analytical, medicinal, pharmaceutical
and catalytical applications [2–7]. Complexes of Schiff bases with
some transition metals show significant biological notification
including antimicrobial, antibacterial, antifungal and anticancer
activities [7–10]. In recent years [11–15] a number of research
articles have been published on transition metal complexes of
Cu(II), Co(II), Ni(II), Fe(III), Zn(II) with Schiff bases derived from
the condensation of salicyladehyde and o-amino phenol or 2-ami-
ties in applications such as optical recording medium, toner, ink-jet
printing and oil-soluble lightfast dyes [16–19].
Based on the previous considerations, we are initiating a line of
investigation on the coordination chemistry of Schiff base com-
pounds containing azo group attached with organic moieties. In
this paper, we report the characterization by elemental analysis,
magnetic properties, infrared spectra (IR), Raman laser, ultraviolet
and visible spectra (UV–Vis), X-ray diffraction, scanning electron
microscopy, proton nuclear magnetic resonance (1H NMR), and
mass spectra of 2-[(5-o-chlorophenylazo-2-hydroxybenzylidin)
amino]-phenol Schiff base (H2L) and its Cu(II), Co(II) and Ni(II)
complexes. Thus, the complexes have been isolated and there are
well characterized. The ligand H2L acts as tridentate through two
oxygen atoms and nitrogen atom of o-aminophenol and salicylade-
hyde rings, respectively, for Cu(II) and Co(II) complexes. On the
other hand, H2L acts as bidentate through two oxygen atoms for
⇑
Corresponding author at: Department of Chemistry, Faculty of Science, Port Said
University, Port Said, Egypt. Tel.: +966 561926288.
E-mail address: msrefat@yahoo.com (M.S. Refat).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.01.059

M.S. Refat et al. / Journal of Molecular Structure 1038 (2013) 62–72
63
N
N
HC
N
Cl
OH
HO
Fig. 1. The structural formula of H2L Schiff base ligand.
Table 1
Analytical and physical data for H2L Schiff base and their metal complexes.
Compound
Color
Km (
X
ꢁ1 cm2 molꢁ1
)
Elemental analysis (%) found (Calcd.)
Empirical formula (M. Wt.)
C
H
N
Cl
M
H2L[C19H14N3O2Cl] (351.5)
Dark red
30
75
146
163
64.80(64.86)
43.14(43.67)
38.54(38.68)
36.45(36.47)
3.95(3.98)
3.38(3.45)
4.36(4.41)
4.78(4.80)
11.92(11.95)
8.00(8.04)
7.09(7.13)
6.65(6.72)
10.08(10.10)
20.09(20.11)
17.87(18.07)
16.97(17.03)
–
[Cu(H2L)(H2O)2(Cl)]Cl (522.05)
[Co(H2L)(H2O)3]Cl2ꢀ3H2O (589.43)
[Ni(H2L)(H2O)2]Cl2ꢀ6H2O (625.2)
Dark green
Dark brown
Orange yellow
12.13(12.17)
9.80(10.00)
9.28(9.39)
Ni(II) complex. The Cu(II), Co(II) and Ni(II) oxides nanostructures
are collected through thermal decomposition process of H2L com-
plexes which has many advantages like controlling on the process
conditions, particle size, particle crystal structure, decreasing the
calcinations temperature, and purity.
2. Experimental
2.1. Reagents
o-Chloroaniline, o-aminophenol, and salicyladehyde were ob-
tained from Porlabo. All chemicals used for the study were of ana-
lytically reagent grade and used without previous purification as
transition metal salts NiCl2ꢀ6H2O, CoCl2ꢀ6H2O, CuCl2ꢀ2H2O and
other chemicals. Double distilled water, methanol and diethyl
ether solvents were used.
Fig. 2. Mass spectrum of H2L Schiff base ligand.
diazonium solution was coupled with salicyladehyde in alkaline
media at the para position to the hydroxyl group. During the pro-
cedure the pH value was maintained within 7–9, and the temper-
ature at 0–5 °C [20]. The mixture was recrystallized several times;
the pH value was decreased to ꢂ3, and then left overnight. The pre-
cipitate was collected by filtration, washed with small portion of
diethyl ether to extract all organic impurities, and then dried under
vacuum at 70 °C. The purity of the diazo compound was evaluated
by thin layer chromatography.
2.2. Synthesis of Schiff base ligands
The ligand, 2-[(5-o-chlorophenylazo-2-hydroxybenzylidin)
amino]-phenol Schiff base (H2L) (Fig. 1) was obtained by a proce-
dure in two steps as follows.
2.2.2. Synthesis of the H2L Schiff base ligand
2.2.1. Synthesis of 5-arylazo-salicyladehyde compound (diazotization
and coupling processes)
The Schiff base (H2L) was prepared by mixing 50 mL methanol
solution of o-aminophenol (50 mmol) with a solution of 5-ary-
lazo-salicyladehyde (50 mmol) in water (100 mL) under reflux for
2 h. at 70 °C on a hot plate [21]. After cooling, the precipitate was
filtered, washed several times with methanol and diethyl ether
to remove all organic impurities, dried in vacuo over calcium chlo-
ride. The purity of the ligand was evaluated by thin layer
chromatography and the composition was confirmed by elemental
analysis CHN, and (IR, mass, and 1H NMR) spectra.
5-Arylazo-salicyladehyde compound was prepared by dissolv-
ing o-chloroaniline (50 mmol) in 6.0 mL of hydrochloric acid with
concentration 37% and distilled water (30 mL). The solution was
then cooled to 0–5 °C in ice-bath and maintained at this tempera-
ture. Sodium nitrite (40 mmol, 2.8 g) solution in distilled water
(30 mL) was then added dropwise. Stirring was continued for
30 min to produce diazonium salt at the same temperature. The

64
M.S. Refat et al. / Journal of Molecular Structure 1038 (2013) 62–72
Scheme 1. The fragmentation pattern proposed for 2-[(5-o-chlorophenylazo-2-hydroxy benzylidin)amino]-phenol Schiff base (H2L).
Table 2
Assignments of the IR and Raman Spectral bands (cmꢁ1) for H2L Schiff base and their metal complexes.
Compound
m(OH)
IR
mC@N
IR
mN@N
IR
mCAO
IR
mMAN
IR
mMAO
IR
Raman
–
Raman
1591
–
Raman
1415
Raman
1256
Raman
–
Raman
–
H2L
3420
3162
1620
1603
1464
1468
1205
1179
–
–
[Cu(H2L)(H2O)2(Cl)]Cl
3249
1424
1161
678
536
573
506
455
458
[Co(H2L)(H2O)3]Cl2ꢀ3H2O
[Ni(H2L)(H2O)2]Cl2ꢀ6H2O
3180
3065
3319
3073
1601
1618
–
1466
1465
1407
1424
1151
1152
1205
1186
666
581
573
586
542
511
511
1591
672
552
517
480
2.3. Synthesis of complexes
70 °C for 2 h, and then concentrated to half its initial volume. After
cooling for the mixtures overnight, the solid complexes are precip-
itated and separated, washed with methanol and diethyl ether. The
synthesized complexes was recrystallized from methanol and dried
under vacuum over anhydrous CaCl2. The purity was checked by
thin layer chromatography.
To a hot solution (1 mmol) of H2L Schiff base ligand in (30 mL)
methanol, a hot solution of corresponding metal(II) salts (Ni2+
,
Co2+, Cu2+) (1 mmol, in 30 mL methanol) were added slowly. The
resulting mixtures were stirred and refluxed on a hot plate at

M.S. Refat et al. / Journal of Molecular Structure 1038 (2013) 62–72
65
355 nm
A
3.0
A
2.5
278 nm
6
5
4
3
2
1
0
2.0
1.5
230 nm
1.0
0.5
0.0
475 nm
200
300
400
500
600
700
800
Wavelength (nm)
4000 3500 3000 2500 2000 1500 1000 500
-1
0
Wavenumbers
(cm )
275 nm
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
B
372 nm
440 nm
B
0.020
0.015
0.010
0.005
0.000
260 nm
200
300
400
500
600
700
800
4000 3500 3000 2500 2000 1500 1000 500
0
Wavelength (nm)
-1
Wavenumbers (cm )
2.5
2.0
1.5
1.0
0.5
0.0
355 nm
C
C
0.12
280 nm
0.10
0.08
0.06
0.04
0.02
0.00
450 nm
200
300
400
500
600
700
800
4000 3500 3000 2500 2000 1500 1000 500
0
Wavelength (nm)
Wavenumbers(cm-1)
350 nm
3
2
1
0
D
0.10
0.08
0.06
0.04
0.02
0.00
D
280 nm
445 nm
4000 3500 3000 2500 2000 1500 1000 500
-1
0
200
300
400
500
600
700
800
)
Wavenumbers(cm
Wavelength (nm)
Fig. 3. Raman spectra of H2L, Cu(II), Co(II) and Ni(III) H2L complexes (A, B, C and D,
Fig. 4. Electronic spectra of H2L, Cu(II), Co(II) and Ni(III) H2L complexes (A, B, C and
respectively).
D, respectively).

66
M.S. Refat et al. / Journal of Molecular Structure 1038 (2013) 62–72
Table 3
Electronic spectral bands (cmꢁ1) and magnetic moments of the H2L ligand and their complexes.
Compound
Magnetic moments leff
Electronic spectral values (cmꢁ1
)
Proposed geometry
H2L
–
21,052, 28,169, 35,971, 43,478
–
[Cu(H2L)(H2O)2(Cl)]Cl
[Co(H2L)(H2O)3]Cl2ꢀ3H2O
[Ni(H2L)(H2O)2]Cl2ꢀ6H2O
1.76
3.89
–
22,727, 26,881, 36,363, 38,461, 44,444
22,222, 28,169, 35,714
22,472, 28,571, 35,714
Octahedral
Octahedral
Square planar
Fig. 8. 1H NMR spectrum of H2L Schiff base ligand.
Fig. 5. Suggestion structure of [Cu(H2L)(H2O)2(Cl)]Cl complex.
cisely Lambda 25 UV/Vis double beam Spectrometer fitted with a
quartz cell of 1.0 cm path length, and a Varian Gemini Spectropho-
tometers, respectively at Taif (Saudi Arabia) and Cairo universities.
The thermal studies were carried out on a Shimadzu thermogravi-
metric analyzer at a heating rate of 10 °C minꢁ1 under nitrogen till
600 °C in Cairo University. The purity of H2L Schiff base ligand was
checked via mass spectra at 70 eV by using AEI MS 30 mass spec-
trometer at room temperature. The X-ray diffraction patterns for
the three final decomposition products were recorded on Bruker
AXS configuration X-ray powder diffraction. Scanning electron
microscopy (SEM) images and Energy Dispersive X-ray Detection
(EDX) were taken in Joel JSM-639OLA equipment, with an acceler-
ating voltage of 20 kV.
Fig. 6. Suggestion structure of [Co(H2L)(H2O)3]Cl2ꢀ3H2O complex.
3. Results and discussion
The percentage (%) of carbon, hydrogen, nitrogen and chloride
contents as well as some physical values is tabulated in Table 1.
All the isolated of H2L complexes are stable in air, having high
melting points (>300 °C), insoluble in H2O and most organic sol-
vents except DMSO and DMF soluble with gently heating. The mo-
lar conductivity measurements for (1.0 ꢃ 10ꢁ3 mol) in DMSO
solvent are found within the highly conducting feature for cobal-
t(II) and nickel(II) H2L complexes but the copper(II) complex is
slightly conducting [23]. The conductivity feature of MAH2L com-
plexes belongs to positively charged coordination sphere ionically
attached with two (for Co(II) and Ni(II)) or one (for Cu(II)) conju-
gated chloride anion in the investigated complexes. This phenom-
enon in agreement with the analytical data which suggest the
presence of chloride anion covalently or ionically attached with
the central metal ions in MAH2L complexes.
Fig. 7. Suggestion structure of [Ni(H2L)(H2O)2]Cl2ꢀ6H2O complex.
2.4. Equipments
Carbon, hydrogen and nitrogen were analyzed at the Microana-
lytical unit of Cairo University by a Perkin–Elmer CHN 2400 ele-
mental analyzer. The metal contents were determined
gravimetrically by converting the compounds to its corresponding
oxides. The chloride ions were gravimetrically determined using a
standard method [22] and the data reflect the high conformity
with that theoretically proposed. The molar conductivities of
freshly prepared 1.0 ꢃ 10ꢁ3 mol/cm3 dimethylsulfoxide solutions
were measured for the soluble complexes using Jenway 4010 con-
ductivity meter. The magnetic measurements were performed
using magnetic susceptibility balance Sherwood Scientific Cam-
bridge, England. The infrared spectra, as KBr discs, were recorded
on a Bruker FT-IR Spectrophotometer (4000–400 cmꢁ1) at Cairo
University, while Raman laser spectra of samples were measured
on the Bruker FT-Raman with laser 50 mW. The electronic and
1H NMR (200 MHz) spectra were recorded on Perkin–Elmer Pre-
3.1. Mass spectral analysis
Mass spectrometry has been successfully used to confirm the
molecular ion peaks of H2L Schiff base and investigate the fragment
species. The fragment pattern of mass spectrum gives an impres-
sion for the successive degradation of the target compound with
the series of peaks corresponding to various fragments. Also, the
peaks intensity gives an idea about the stability of fragments espe-
cially with the base peak. The recorded mass spectrum of H2L
ligand (Fig. 2) reveals molecular ion peak confirms strongly the
proposed formula. The spectrum of the ligand having peak at

M.S. Refat et al. / Journal of Molecular Structure 1038 (2013) 62–72
67
C l (2 7 )
H (2 9 )
H (3 4 )
H (3 5 )
C (1 3 )
C (2 5 )
C (2 6 )
C (1 2 )
N (1 9 )
H (1 0 )
H (3 9 )
C (3 )
H (3 0 )
C (2 4 )
C (2 1 )
C (1 4 )
N (2 0 )
H (3 6 )
C (1 1 )
C (9 )
C (2 )
C (2 3 )
C (2 2 )
C (1 5 )
C (1 6 )
N (7 )
C (4 )
H (3 1 )
H (3 2 )
H (3 3 )
C (1 )
H (3 7 )
H (2 8 )
O (1 7 )
H (1 8 )
C (5 )
C (6 )
O (8 )
H (3 8 )
Fig. 9. Hydrogen bonding between OH and nitrogen of azomethine group.
m/z = 351 (27%) which is referring to the molecular ion peak (M+)
and confirming the purity of the ligand prepared. The degradation
pattern have prominent peaks at m/z = 212(39%), 154(22%),
120(80%) and 65(100%) as displayed in degradation Scheme 1.
complexes exhibited a broad band around 3414–3365 cmꢁ1, which
is assigned to water molecules, (OH), associated with the com-
m
plexes. In addition to these modes, coordinated water exhibited
dr(H2O) rocking near 831–893 cmꢁ1 and dw(H2O) wagging near
550–530 cmꢁ1 [26]. In the copper(II) complex, the
m(CuACl) band
cannot easily detected due to the wavenumber scanning range
ended at ꢂ400 cmꢁ1 which do not includes the value of terminal
CuACl band rather than bridging chlorine [26].
Fig. 3 shows that the most intense Raman lines in the spectra of
H2L and its Cu(II), Co(II) and Ni(II) complexes were observed at re-
gion 3070–3320 cmꢁ1, these lines were assigned to vibrational
3.2. IR and Raman spectral analyses
The distinguish IR spectra (Table 2) provide valuable informa-
tion regarding the nature of the functional group attached to the
metal atom [14,15]. The IR spectra of ligand and its complexes
are found to be quite complex as they in general exhibit large num-
ber of bands of varying intensities. The spectrum of the free Schiff
base ligand shows the peak of azomethine group ACH@N at
1620 cmꢁ1, which is shifted to lower frequencies in the spectra
of both copper(II) and cobalt(II) complexes at 1603 and
1601 cmꢁ1, respectively, indication the involvement of the ACH@N
nitrogen in the coordination to metal ion [14]. Concerning nicke-
l(II) complex, the azomethine group located at the same place of
H2L Schiff base ligand (1618 cmꢁ1), this ascribe to the non-partic-
ipation of azomethine group in the chelation process. Coordination
of the Schiff base to the metal ions through the nitrogen atom is ex-
pected to reduce the electron density in the azomethine link and
modes of m(OH) Table 2. Furthermore, the other very-medium in-
tense Raman lines observed at (1161, 1205, 1186 cmꢁ1), (573,
581, 573 cmꢁ1), (458, 511, 511 cmꢁ1) in the spectra of Cu(II), Co(II)
and Ni(II) complexes, respectively, were assigned to that
m(CAO),
m
(MAN) and (MAO). These show the effect of complexation via
m
phenolic oxygen and azomethine nitrogen in shifting a number
of stretching modes to lower frequencies comparable to free
ligand. The Raman line observed at 371 cmꢁ1 in case of copper(II)
complex was assigned to the stretching vibration of m(CuACl).
3.3. Electronic spectral analysis and magnetic measurements
lowers the stretching vibrational motion of
m(C@N). In the IR spec-
trum of ligand (H2L),
m
(OH) band appeared at 3420 cmꢁ1. This band
The data of electronic spectrum of free H2L Schiff base ligand
(Fig. 4, Table 3) was collected in DMSO solvent with four absorp-
tion bands at 475, 355, 278 and 230 nm. The spectral bands at
230 and 278 nm were assigned to transition motions of phenyl
rings [27,28]. The transition band at 355 nm corresponded to
n ? pꢄ transition of azomethine group ACH@N, while, the band
at 475 nm assigned to n ? pꢄ transitions of donating atoms like
oxygen and nitrogen which are overlapped with the intermolecular
is shifted to lower frequency at 3162, 3180, and 3065 cmꢁ1, respec-
tively, in the Cu(II), Co(II) and Ni(II) complexes. The band appearing
at the frequency of 1464 cmꢁ1 in the spectrum of ligand assigned
to AN@NA group not affected in the complexes indicates non-par-
ticipation of azo nitrogen in coordination with metal ions. The phe-
nolic CAO stretching vibrations appeared at ꢂ1204 cmꢁ1 in the
Schiff base under a shift towards lower frequencies (25–53 cmꢁ1
)
in the complexes (Table 2). This shift confirms the participation
of oxygen in the CAOAM bond [24,25]. The weak-to-very weak
bands in the two ranges (678–536 cmꢁ1) and (586–455 cmꢁ1),
respectively, are assigned to the stretching frequencies of the
LCT from aromatic rings. The peaks within the transition motions of
phenyl rings have been relatively unaffected in the spectra of the
complexes; this is expected for the relatively unshared of aromatic
ring in chelation. The transition bands up to 350 nm which
assigned to n ? pꢄ transition due to involving molecular orbitals
of the ACH@N chromophore. The bands of n ? pꢄ transition have
been shifted upon complexation of H2L ligand towards all metal
m(MAO) [26] and m(MAN) [26] bands, which confirmed the
attached of H2L ligand to the center metal ions through the pheno-
lic oxygen atoms and the azomethine nitrogen. The spectra of H2L

68
M.S. Refat et al. / Journal of Molecular Structure 1038 (2013) 62–72
Table 4
0.2
Thermogravimetric data of Cu(II), Co(II) and Ni(II)/H2L complexes.
A
Complexes
Steps
Temp.
range
(°C)
Decomposed
assignments
Weight loss
found
(Calcd. %)
100
80
0.1
[Cu(H2L)(H2O)2(Cl)]Cl
1st
25–
120
120–
245
245–
370
AH2O
3.19 (3.45)
10.75(10.25)
13.49(13.60)
16.00(16.09)
CuO
DTG
0.0
2nd
3rd
4th
AH2O + 1/
2Cl2
ACl2
TGA
-0.1
-0.2
60
370–
600
Dec. H2L
–
Residue 600
[Co(H2L)(H2O)3]Cl2.3H2O 1st
2nd
25–75
75–
165
165–
270
A3H2O
A2H2O
9.31(9.16)
6.77(6.12)
0
100
200
300
400
C]
500
600
Temp [o
3rd
A½Cl2 + H2O
9.00(9.08)
21.89(22.26)
CoO
4th and 270–
5th
Residue
ACl2 + Dec.
H2L
–
B
100
90
80
70
60
50
600
0.0
DTG
[Ni(H2L)(H2O)2]Cl2.6H2O 1st
25–70
70–
180
180–
270
270–
375
A2H2O
A3H2O
5.69(5.76)
9.08(8.64)
2nd
-0.5
-1.0
3rd
A3H2O
A½Cl2
9.19(8.64)
6.24(5.68)
4th
TGA
5th
375–
600
Cl2 + Dec. H2L 21.80(22.87)
– NiO
Residue
0
100
200
300
400
500
600
Temp [oC]
this complex has an octahedral feature. There are two detectable
bands were observed at 22,222 cmꢁ1 (strong intensity) nm and
28,169 cmꢁ1 (very strong intensity) due to 4T1g ? 4A2g and
4T1g ? 4T1g(P) transition, respectively. The magnetic moment of
Co(II) complex was found at 3.89 B.M. at room temperature which
supported the octahedral geometry (Fig. 6).
0.2
0.1
0.0
-0.1
-0.2
C
100
50
0
The electronic spectrum of the orange yellow color complex of
TGA
DTG
nickel(II) ion, [Ni(H2L)(H2O)2]Cl2ꢀ6H2O, has
a strong band at
22,472 cmꢁ1 located inside the experimental value at (15,000–
25,000 cmꢁ1) of square planar geometry. This band ascribe to
1A1g ? 1A2g transition [29]. In literature survey the square planar
complexes of nickel have been a color ranged from orange to red,
this information matched with our nickel(II) complex. The
magnetic measurements come also to confirm the square planar
structure with a diamagnetic value. The structure of Ni(II) complex
according to elemental analysis, infrared/Raman spectra and elec-
tronic spectra as well as magnetic moments can be designed as
follows in Fig. 7.
0
200
400
C]
600
Temp [o
Fig. 10. TG curves of Cu(II), Co(II) and Ni(II)A H2L complexes (A, B and C).
ions. This is indicating that, the azomethine group nitrogen atom
appears to be coordinated to the metal ions [14].
3.4. 1H NMR Spectral analysis
The electronic spectrum of the dark green copper(II) complex,
[Cu(H2L)(H2O)2(Cl)]Cl, in DMSO solvent (Fig. 5) showed mainly
transition bands at 22,727 cmꢁ1 ascribe to 2Eg ? 2T2g transition
in distorted octahedral geometry [28]. The other detectable band
at 26,881 cmꢁ1 was assigned to L ? M charge transfer. The found
value of the magnetic moment of Cu(II) complex was 1.76 B.M.,
which supported the octahedral feature [28].
Undertaken the phenomena that octahedral cobalt(II) com-
plexes have a pink or reddish brown [28] but most tetrahedral
Co(II) complexes have an intense blue or green color, herein the
electronic spectrum of the dark brown, [Co(H2L)(H2O)3]Cl2ꢀ3H2O,
complex in DMSO solvent with 1.0 ꢃ 10ꢁ3 mol/cm3 showed that
The 1H NMR spectrum of H2L Schiff base ligand was recorded to
confirm the structural. The spectrum of H2L ligand (Fig. 8) showed
a (s, 1H) at d = 15.284 ppm for NH proton, its down field appear-
ance may be due to the participation of NH group in H-bonding
with its neighboring nitrogen of azomethine group, (s, 1H) at
d = 10.220 ppm for OH group attached to C16 (Fig. 9), (s, 1H) at
d = 9.309 ppm for C9AH10 of azomethine group, (m, 11H) at
d = 6.994–8.322 ppm range for aromatic protons of the three aro-
matic rings and (s, 2H) at d = 2.559 and 3.414 ppm for DMSO and
H2O/DMSO, respectively. The assignment for the spectrum peaks
proposed the presence of free ligand in its hydrogen bonding
between H(28)AN(7) (Fig. 9).

M.S. Refat et al. / Journal of Molecular Structure 1038 (2013) 62–72
69
Scheme 2. Thermal decomposition steps of Cu(II), Co(II) and Ni(II) complexes.
losses obtained from TG curves are in a good agreement with the
calculated values. The first decomposition step of the [Cu(H2L)-
(H2O)2(Cl)]Cl complex occurs at the 25–120 °C range (Fig. 10) with
a weak DTG maximum peak at 75 °C. This step is accompanied by
weight loss (Obs. = 3.19%, Calc. = 3.45%) which assigned to the loss
of one water molecules. The second step at 120–245 °C range with
a weak DTG peak at 193 °C due to weight loss of (Obs. = 10.75%,
Calc. = 10.25%) corresponds to the elimination of H2O + 0.5Cl2.
The third decomposition step (DTGmax = 320 °C) located within
the range of 245–370 °C with mass loss (Obs. = 13.49%,
Calc. = 13.60%) and assigned to the evolved half chlorine molecule.
The decomposition of H2L ligand started above 370 °C with mass
loss (Obs. = 16.00%, Calc. = 16.09%) and left CuO contaminated with
carbon atoms.
Fig. 11. SEM images of Cu(II), Co(II) and Ni(II)AH2L complexes at 600 °C.
3.5. Thermal analysis
The TG/DTG curve of [Co(H2L)(H2O)3]Cl2ꢀ3H2O complex, a five
decomposition steps were observed. The first and second steps in
the range of 25–165 °C with DTG peaks at 45 and 125 °C, respec-
tively, have a total weight loss (Obs. = 16.08%, Calc. = 15.28%). This
temperature range is within the normal limit to that reported for
the release of uncoordinated and coordinated of water molecules.
The third step within the range of (165–270 °C) with a medium
strong DTG peak at 211 °C was assigned to the loss of (0.5Cl2 + H2-
O) molecules and the weight loss (Obs. = 9.00%, Calc. = 9.08%). In
case of the fourth and fifth decomposition steps the total mass loss
up to 270 °C is in agreement with the calculated values
The TGA and DTG thermal curves of Cu(II), Co(II) and Ni(II) com-
plexes of 2-[(5-o-chlorophenylazo-2-hydroxybenzylidin)amino]-
phenol Schiff base (H2L) in nitrogen environment with a heating
rate 10 °C/min are given in Fig. 10 and the decomposition steps
are assigned in Table 4. The pathway of these complexes is the
same sequences with overlapping steps vary from one complex
to another as designed in the following Scheme 2.
Table 4 illustrated to the behavior of the thermal degradation
according to TG curves for each step in the decomposition
sequence of the Cu(II), Co(II) and Ni(II)AH2L complexes. The mass

70
M.S. Refat et al. / Journal of Molecular Structure 1038 (2013) 62–72
Fig. 12. The EDX analysis of (A) Cu(II) and (B) Co(II)AH2L complexes at 600 °C.
Table 5
Intensity
2000
XRD spectral data of the highest value of intensity of the cobalt and nickel residuals at
600 °C.
Residuals
2h
FWHM
Relative intensity
Particle size
Cobalt
Nickel
37
43
0.170
0.305
100
100
51
29
1600
1200
800
400
0
(Obs. = 21.89%, Calc. = 22.26%). The CoO as a final residual at 600 °C
was checked using X-ray powder diffraction technique.
Concerning to [Ni(H2L)(H2O)2]Cl2ꢀ6H2O complex the first-to-
fifth steps of decomposition in TG curve occurs at 25–70 °C,
70–180 °C, 180–270 °C, 270–375 °C and 375–600 °C ranges with
different temperatures of maximum DTG at 43, 152, 258, 362
and 527 °C, respectively. The weight loss of 1st (Obs. = 5.69%,
Calc. = 5.76%), 2nd (Obs. = 9.08%, Calc. = 8.64%), 3rd (Obs. = 9.19%,
Calc. = 8.64%), 4th (Obs. = 6.24%, Calc. = 5.68%), and 5th
(Obs. = 21.80%, Calc. = 22.87%) were assigned to the loss of 2H2O,
3H2O, 3H2O, 0.5Cl2 and (0.5Cl2 + decomposition of H2L),
respectively.
10
20
30
40
50
60
70
80
90
2θ
Fig. 13. The XRD spectrum of Ni(II)AH2L complex at 600 °C.

M.S. Refat et al. / Journal of Molecular Structure 1038 (2013) 62–72
71
Table 6
Kinetic parameters using the Coats–Redfern (CR) and Horowitz–Metzger (HM) equations for the Cu(II), Co(II) and Ni(II)AH2L complexes.
Complex
Stage
Method
Parameter
r
E (J molꢁ1
)
A (sꢁ1
)
D
S (J molꢁ1 Kꢁ1
)
D
H (J molꢁ1
)
D )
G (J molꢁ1
Cu(II)
Co(II)
Ni(II)
3rd
3rd
3rd
CR
HM
7.39 ꢃ 104
1.60 ꢃ 104
ꢁ1.70 ꢃ 102
6.90 ꢃ 104
1.70 ꢃ 105
0.9951
0.9934
8.49 ꢃ 104
2.26 ꢃ 105
ꢁ1.48 ꢃ 102
8.00 ꢃ 104
1.68 ꢃ 105
CR
HM
1.03 ꢃ 105
1.09 ꢃ 105
1.20 ꢃ 109
9.63 ꢃ 109
ꢁ7.51 ꢃ 101
ꢁ5.78 ꢃ 101
9.95 ꢃ 104
10.5 ꢃ 10
1.36 ꢃ 104
1.33 ꢃ 104
0.9977
0.9957
CR
HM
8.34 ꢃ 104
9.88 ꢃ 105
ꢁ1.35 ꢃ 102
7.90 ꢃ 104
1.51 ꢃ 105
0.9825
0.9791
9.26 ꢃ 104
1.32 ꢃ 107
ꢁ1.13 ꢃ 102
8.82 ꢃ 104
1.48 ꢃ 105
3.6. XRD and SEM/EDX studies
kinetic parameters. The data was summarized and tabulated in
Table 6. In fact the increasing in (A) value led to decreasing in
(Eꢄ), so, when the activation energy has a higher value the thermal
stability increased. The higher values of (Eꢄ) and lower values of (A)
are supported the reaction to proceed slower than normal [35,36].
This fact has been applicable for the H2L complexes studied in the
present paper. So, the following order of thermal stability has been
sequences as follows:
The aim of this paper beside the synthesis and characterization
of the novel Schiff base and its Cu(II), Co(II) and Ni(II) complexes is
to study of the final thermal decomposition products at 600 °C.
These residuals were checked using scanning electron microscopy
(SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray dif-
fraction (XRD) techniques.
SEM is a simple method can be used to check the deposited
samples which clearly indicated that the nanoparticles have been
formed. According to the images of SEM, the diameters of the
residual samples for Cu(II), Co(II) and Ni(II) are about 400, 250
and 480 nm, respectively. Fig. 11 shows the scanning electron
microscopy pictures of Cu(II), Co(II) and Ni(II)AH2L particles at
600 °C. By comparison between the residual products in this study
and the copper(II), cobalt(II) and nickel(II) oxides nanoparticles in
the literature [30,31], it is obvious that the particles (250–
480 nm diameters) are smaller and the Schiff base ligands can be
used as a good precursors.
½NiðH2LÞðH2OÞ2ꢅCl2 ꢀ 6H2O > ½CuðH2LÞðH2OÞ2ðClÞꢅCl
> ½CoðH2LÞðH2OÞ3ꢅCl2 ꢀ 3H2O
The negative values of (Sꢄ) indicate that the activated complex has a
more ordered [37] than that of either the reactants. The values of
both Eꢄ and Hꢄ are equivalent.
4. Conclusion
A novel tridentate Schiff base ligand derived from condensation
of aminophenol and 5-arylazo-salicyladehyde and its copper(II),
cobalt(II) and nickel(II) complexes have been characterized by
spectroscopic techniques. The calcinations of the Cu(II), Co(II)
and Ni(II)AH2L at 600 °C have succeeded in synthesized nano-
structured of Ni and Co oxides nanoparticles. The micro/nano-
structures and the composition of the residuals nanoparticles have
been studied using SEM, EDX and XRD. The particles deposited at
calcinations temperature (600 °C) which is in the region of 250–
480 nm in diameters.
The results by energy dispersive X-ray analysis (EDX) have indi-
cated that there are copper, cobalt and oxygen peaks, which meant
there were oxygen contamination or the deposited products were
copper or cobalt oxides as shown in Fig. 12.
The X-ray powder diffraction patterns in the range of
10° < 2h < 90° for the residual products at 600 °C were carried in
order to obtain an idea about the lattice dynamics of the resulted
oxides of cobalt and nickel. X-ray diffraction of the residual prod-
ucts of cobalt and nickel H2L complexes were recorded between
10o and 90o 2h and are given in Fig. 13. The values of 2h, full width
at half maximum (FWHM) of prominent intensity peak, relative
intensity and particle size of cobalt and nickel residual products
were compiled in Table 5. The crystallite size of the cobalt and
nickel residuals at 600 °C could be estimated from XRD patterns
by applying FWHM of the characteristic peaks using Deby–Scher-
rer equation (1) [32].
Acknowledgement
The author express a lot of thanks for prof. I.M. El-Deen, Depart-
ment of Chemistry, Faculty of Science, Port Said University for his
assistance in saving the Schiff base compound used in this study.
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D ¼ Kk=bCos h
ð1Þ
where D is the particle size of the crystal gain, K is a constant (0.94
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estimated according to the highest value of intensity compared
with the other peaks. The particle size for the cobalt and nickel thus
obtained were 51 and 29 nm, respectively. These data gave an
impression that the particle size located within nano-scale range.
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