Synthesis, spectroscopic, coordination and biological activities of some transition metal complexes containing ONO tridentate Schiff base ligand

Article abstract of DOI:10.1016/j.saa.2015.05.005

The main target of this paper is to get an interesting data for the preparation and characterizations of metal oxide (MO) nanoparticles using H₂L Schiff base complexes as precursors through the thermal decomposition procedure. Five Schiff base complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions were synthesized from 2-[(2-hydroxy-naphthalen-1-ylmethylene)-amino]-benzoic acid new adduct (H₂L). Theses complexes were characterized using infrared, electronic, mass and ¹H NMR spectroscopic techniques. The elemental analysis data was confirmed that the stoichiometry of (metal:H₂L) is 1:1 molar ratio. The molar conductance indicates that all of complexes are non electrolytic. The general chemical formulas of these complexes is [M(L)(NH₃)]·nH₂O. All complexes are tetrahedral geometry. The thermal decomposition behavior of H₂L hydrated and anhydrous complexes has been discussed using thermogravimetric analysis (TG/DTG) and differential thermal analyses (DTA) under nitrogen atmosphere. The crystalline phases of the reaction products were checked using X-ray diffractometer (XRD) and scanning electron microscopy (SEM).

Full text of DOI:10.1016/j.saa.2015.05.005

Accepted Manuscript
Synthesis, spectroscopic, coordination and biological activities of some transi-
tion metal complexes containing ONO tridentate Schiff base ligand
A.A.M. Belal, I.M. El-Deen, N.Y. Farid, Rosan Zakaria, Moamen S. Refat
PII:
S1386-1425(15)00593-4
http://dx.doi.org/10.1016/j.saa.2015.05.005
SAA 13672
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
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Revised Date:
Accepted Date:
4 November 2014
21 April 2015
4 May 2015
Please cite this article as: A.A.M. Belal, I.M. El-Deen, N.Y. Farid, R. Zakaria, M.S. Refat, Synthesis, spectroscopic,
coordination and biological activities of some transition metal complexes containing ONO tridentate Schiff base
ligand, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/
10.1016/j.saa.2015.05.005
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Synthesis, spectroscopic, coordination and biological activities of some transition
metal complexes containing ONO tridentate Schiff base ligand
A.A.M. Belal1, I.M. El-Deen1, N.Y. Farid 1, Rosan Zakaria1 and Moamen S. Refat1,2*
1 Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt
2
Department of Chemistry, Faculty of Science, Taif University, Al-Hawiah, Taif, P.O.
Box 888 Zip Code 21974, Saudi Arabia
Email: msrefat@yahoo.com
Abstract
The main target of this paper is to get an interesting data for the preparation and
characterizations of metal oxide (MO) nanoparticles using H2L Schiff base complexes as
precursors through the thermal decomposition procedure. Five Schiff base complexes of
Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions were synthesized from 2-[(2-hydroxy-
naphthalen-1-ylmethylene)-amino]-benzoic acid new adduct (H2L). Theses complexes
were characterized using infrared, electronic, mass and 1HNMR spectroscopic
techniques. The elemental analysis data was confirmed that the stoichiometry of (metal:
H2L) is 1:1 molar ratio. The molar conductance indicates that all of complexes are non
electrolytic. The general chemical formulas of these complexes is [M(L)(NH3)].nH2O.
All complexes are tetrahedral geometry. The thermal decomposition behavior of H2L
hydrated and anhydrous complexes has been discussed using thermogravimetric analysis
(TG/DTG) and differential thermal analyses (DTA) under nitrogen atmosphere. The
crystalline phases of the reaction products were checked using X-ray diffractometer
(XRD) and scanning electron microscopy (SEM).
Keywords: Schiff base; transition metals; nano-particles; XRD; SEM; thermal analysis.
1- Introduction
Schiff base compounds with the azomethine group (-RC=N-) were usually
formed by the condensation of amine –NH2 group with active –C=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 literature survey [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-amino benzoic acid. Azo compounds have been studied widely because of
their excellent thermal, antibacterial activity and optical properties 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 compounds containing azo group attached with
organic moieties. In this paper, we report the characterization by elemental analysis,
magnetic properties, infrared spectra (IR), ultraviolet and visible spectra (UV–Vis),
X-ray diffraction, scanning electron microscopy, proton nuclear magnetic resonance (1H-
NMR), and mass spectra of 2-[(2-hydroxy-naphthalen-1-ylmethylene)-amino]-benzoic
acid Schiff base (H2L) and its Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes. Thus,
the complexes have been isolated and there are well characterized. The ligand H2L acts
1

as tridentate through two oxygen atoms (–OH phenolic and carboxylic acid) and nitrogen
atom of azomethine group deduced from the chemical interaction between anthranilic
acid and 2-hydroxy-naphthalene-1-carbaldehyde moieties. The Cu(II) and Zn(II) oxides
nano-particles are collected through thermal decomposition process of copper(II) and
zinc(II) H2L complexes which has many advantages like controlling on the process
conditions, particle size, particle crystal structure, decreasing the calcinations
temperature, and high purity.
2- Experimental
2-1- Reagents
All chemicals used in this paper were of analytical grade and used without further
purification as transition metal salts MnCl2.4H2O, CoCl2.6H2O, NiCl2.6H2O,
CuCl2.2H2O, and ZnCl2. Organic compounds like anthranilic acid and 2-hydroxy-
naphthalene-1-carbaldehyde were obtained from BDH chemical company. The distilled
water, methanol and diethyl ether solvents were used without distillation.
2-2- Synthesis of new H2L Schiff base ligand
New 2-[(2-hydroxy-naphthalen-1-ylmethylene)-amino]-benzoic acid Schiff base
(H2L) chelat (Fig. 1) was obtained by a procedure in two steps as follows.
The Schiff base (H2L) was prepared by mixing 50 mL methanol solution of 2-
hydroxy-naphthalene-1-carbaldehyde (50 mmol) with a solution of anthranilic acid (50
mmol) in methanol (50 mL) under reflux for 3 h. at 70 ºC on a hot plate [20, 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 chloride. 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.
H
C
N
C
OH
HO
O
C18H13NO3
Mol. Wt.: 291.30
m/e: 291.09 (100.0%)
C, 74.22; H, 4.50; N, 4.81; O, 16.48
Fig. 1: The structural formula of H2L 2-[(2-hydroxy-naphthalen-1-ylmethylene)-amino]-
benzoic acid Schiff base ligand
2-3- Synthesis of complexes
To a hot solution (1 mmol) of H2L Schiff base ligand in (50 mL) methanol, a hot
solution of corresponding metal(II) salts (MnCl2.4H2O, CoCl2.6H2O, NiCl2.6H2O,
CuCl2.2H2O, and ZnCl2) (1 mmol, in 50 mL methanol) were added slowly. The resulting
mixtures were neutralized at pH= 7-8 using ammonia solution, stirred and refluxed on a
2

hot plate at 70 ºC for 1 hr, and then concentrated to half its initial volume. After cooling
for the mixtures overnight, the solid complexes are precipitated and separated, washed
with methanol and diethyl ether. The synthesized complexes was re-crystallized from
methanol and dried under vacuum over anhydrous CaCl2. The purity was checked by thin
layer chromatography.
2-4- Instruments
The elemental analyses (e.g., carbon, hydrogen and nitrogen) were collected at
the Microanalytical unit of Ain Shams, University Egypt, by a Perkin-Elmer CHN 2400
elemental analyzer. The metal contents were determined gravimetrically by converting
the compounds to its corresponding stable 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 1.0×10-3
mol/cm3 dimethylsulfoxide solutions were measured for the soluble complexes using
Jenway 4010 conductivity meter. The magnetic measurements were performed using
magnetic susceptibility balance Sherwood Scientific Cambridge, England. The infrared
spectra, as KBr discs, were recorded on a Bruker FT-IR Spectrophotometer (4000 – 400
cm-1) at Cairo University. The electronic and 1H-NMR (200 MHz) spectra were recorded
on Perkin-Elmer Precisely Lambda 25 UV/Vis double beam Spectrometer fitted with a
quartz cell of 1.0 cm path length, and a Varian Gemini Spectrophotometers, respectively
at Cairo universities. The thermal studies were carried out on a Shimadzu thermo
o
gravimetric analyzer at a heating rate of 10 C min-1 under nitrogen till 800 oC in Cairo
University. The purity of H2L Schiff base ligand was checked via mass spectra at 70 eV
by using AEI MS 30 mass spectrometer at room temperature. The X-ray diffraction
patterns were recorded on Bruker AXS configuration X-ray powder diffraction. Scanning
electron microscopy (SEM) images were taken in Joel JSM-639OLA equipment, with an
accelerating voltage of 20 KV.
3. Results and discussion
3-1- Elemental analyses and physical properties
The %carbon, %hydrogen, %nitrogen and %chloride percentages with some
physicochemical data are listed in Table 1. The colored solid isolated Mn(II), Co(II),
Ni(II), Cu(II) and Zn(II) H2L complexes are stable in air, having high melting points
o
>250 C, insoluble in H2O and most organic solvents except DMSO and DMF soluble
with gently heating.
3-2- Conductance measurements
The molar conductivities measurements of H2L divalent complexes were
measured in DMSO solvent with 1.0×10-3 mol concentration. The magnitudes of Λm
(Ω-1cm2mol-1) recorded in Table 1 found that all of complexes are non-electrolytic nature
[23]. The very low conductivity values indicate no any conjugated chloride anion existed
in the discussed complexes. This result agreement with the analytical data assigned to the
absence of any chloride anion covalently or ionically attached with the central metal ions
in M–H2L complexes.
3

Table1: Physicochemical data of H2L Schiff base and its metal complexes
Elemental analysis, % Found % (Calcd.)
Λm
Color
Empirical formula
(µS)
C
H
N
Cl
--
M
--
74.06
4.43
4.77
H2L
Yellow
9.28
5.59
2.76
2.45
2.17
2.72
(74.22) (4.50) (4.81)
59.22 4.23 7.70
(59.85) (3.91) (7.75)
57.16 3.80 7.51
(56.41) (4.21) (7.31)
58.22 3.57 7.58
(59.23) (3.87) (7.67)
56.90 3.72 7.44
(55.74) (4.16) (7.22)
55.91 3.45 7.51
(55.47) (4.14) (7.19)
15.10
(15.21)
15.21
(15.38)
15.77
(16.08)
16.09
(16.38)
16.44
(16.78)
[Mn(L)(NH3)]
[Co(L)(NH3)].H2O
[Ni(L)(NH3)]
Reddish brown
Light brown
Greenish brown
Dark green
--
--
--
--
--
[Cu(L)(NH3)].H2O
[Zn(L)(NH3)].H2O
Dark brown
3-3- Mass spectral analysis
Mass spectrometry an interesting technique 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 impression 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 especially 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/z =
291 (85 %) 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=
231(100%) base peak, 207(83%), 181(60%), 159(80%), 78(7%) and 29(52%) as
displayed in degradation scheme 1.
FAB mass spectra of the [Ni(L)(NH3)] and [Cu(L)(NH3)].H2O complexes have
been performed. The peaks revealed a distinctive set of ions with masses corresponding
to the cation and fragments of parent ions derived by loss of the ligand.
Fig. 2: Mass spectrum of H2L Schiff base ligand
4

H
C
H
C
- CO3
N
N
C
C17H13N
Mol. Wt.: 231.29
m/e: 231.10 (100 %)
OH
HO
O
C18H13NO3
Mol. Wt.: 291.30
m/e: 291.09 (85 %)
- 2C
H
C
H
- C2H2
N
C
N
C15H13N
Mol. Wt.: 207.27
m/e: 207.10 (83 %)
C13H11N
Mol. Wt.: 181.23
m/e: 181.09 (60%)
- 2C
H
C
- C2H2
- C5H10N
N
C4H4
Mol. Wt.: 52.07
m/e: 52.03 (29 %)
C6H6
Mol. Wt.: 78.11
m/e: 78.05 (7 %)
C11H13N
Mol. Wt.: 159.23
m/e: 159.10 (80%)
Scheme 1: The fragmentation pattern proposed for H2L Schiff base ligand
5

3-4- Infrared spectral data
The characteristic infrared spectra of H2L and its complexes are shown in Fig. 3
as well as their bands assignments are listed in Table 2. These bands give essential
information about the nature of the functional group attached to the metal atom [14, 15].
The IR spectra of H2L ligand and its complexes are found to be quite complex as they in
general exhibit large number of bands of varying intensities.
i- The spectrum of the free Schiff base ligand shows the peak of azomethine
group –CH=N at 1589 cm–1, which is shifted to lower frequencies in the spectra of all
complexes within the range 1542-1537 cm–1. This result indicate that the nitrogen atom
of –CH=N sharing in the coordination with metal ions [14].
ii- The stretching vibration motion of ν(C=O) of carboxylic group in H2L free
ligand located at 1709 cm–1 is disappeared in all complexes, this ascribe to the
deprotonation of carboxylic group and participate in the chelation process.
iii- Two essential strong-to-medium strong bands were found in the range 1626–
1587 and 1428–1384 cm-1 which could be assigned to (νasCOO) (antisymmetric) and
(νsCOO) (symmetric) vibrations of the carboxylate ions, respectively [26]. The
differences between the asymmetric and symmetric stretching vibration motions,
∆[νas(COO)- νs(COO)] were in the range 213–198 cm-1, which were matched with
monodentate ligational [22]. These values confirm that the carboxylate group was
coordinated to Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) ions in a monodentate mode
involving coordination of the oxygen atom of the ligand [26].
iv- In the IR spectrum of ligand (H2L), ν(OH) band appeared at 3425 cm–1. This
band is absence in the complexes but alternated in the same place by other bands within
3450-3420 cm-1 which assigned to the stretching motions of uncoordinated water
molecules.
Table 2: Assignments of the IR and Raman Spectral bands (cm-1) for H2L Schiff base
and its metal complexes
ν(NH);
NH3
Compound
ν(OH)
ν(C=N)
νs(COO)
νas(COO)
ν(C-O)
ν(M-O) ν(M-N)
H2L
3425
-
-
1589
1539
1537
1539
1615
1587
1614
1612
1483
1384
1404
1405
1277
1210
1244
1242
-
-
572
530
516
551
521
575
538
561
509
494
448
419
478
431
486
439
457
410
[Mn(L)(NH3)]
[Co(L)(NH3)].H2O
[Ni(L)(NH3)]
3260
3306
3304
3426
3420
[Cu(L)(NH3)].H2O
[Zn(L)(NH3)].H2O
3440
3450
3275
3298
1546
1542
1626
1615
1428
1402
1242
1211
v- The new bands exhibit at the frequency of 3306-3260 cm–1 in the spectra of
Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes are assigned to ν(NH) of –NH3
group, which indicate the participation of nitrogen atom of –NH3 group in coordination
with metal ions.
vi- The phenolic C–O stretching vibrations appeared at 1277 cm–1 in the Schiff
base free ligand is shifted towards lower frequencies (1244–1210 cm–1) in the complexes
6

(Table 2). This shift confirms the participation of oxygen atom of phenolic group in the
chelation with C–O–M bond [24, 25].
vii- In case of H2L complexes, there are number of medium-to-weak bands in the
two ranges (572–509 cm–1) and (494–410 cm–1) are assigned to the stretching frequencies
of the ν(M–O) and ν(M–N) [26] bands, respectively, which confirmed the attached of
H2L ligand to the center metal ions through the phenolic oxygen atoms and the
azomethine nitrogen.
viii- The spectra of H2L complexes exhibited a broad band around 3450–33420
cm–1, which is assigned to water molecules, ν(OH), associated with the complexes.
Fig. 3A
7

Fig. 3B
Fig. 3: Infrared spectra of A-H2L, and its B-Mn(II) Schiff base complex
3-5- Electronic spectra and magnetic measurements
The electronic spectral data of the free H2L Schiff base ligand (Table 3) was
collected in DMSO solvent with four absorption bands at 295, 320, 355 and 420 nm. The
spectral bands at 295 and 320 nm were assigned to transition motions of phenyl rings
[27-29]. The transition band at 355 nm corresponded to n→π* transition of azomethine
group –CH=N, while, the band at 420 nm assigned to n→π* transitions of donating atoms
like oxygen and nitrogen which are overlapped with the intermolecular 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→π* transition due to involving molecular orbitals of the –CH=N chromophore. The
bands of n→π* transition have been shifted upon complexation of H2L ligand towards all
metal ions. This is indicating that, the azomethine group nitrogen atom appears to be
coordinated to the metal ions [14].
8

The tetrahedral manganese(II) complex was reddish brown. This color is a guide
to confirm that the formed Mn(II) complex has tetrahedral geometry rather than
octahedral [30]. The Mn[(L)(NH3)] complex in DMSO solvent shows absorption bands
6
at 27777 cm−1 assigned to A1g→4T1g transition. Moreover, there are two charge transfer
bands at 33898 and 31250 cm−1. The tetrahedral Mn(II) complex gives an essentially
spin-only magnetic moment value of 5.92 B.M., which does not vary much since the
magnetic moment is temperature independent. The observed magnetic moment value
5.92 B.M. in Mn(II) complex is appreciably close to the calculated spin value only. The
observed magnetic moment value and electronic spectrum suggest a tetrahedral geometry
[31] for the Mn(II) complex.
For the cobalt(II) tetrahedral complex, there are two orbital forbidden
absorptions, which are rarely observed [32]. There is a complex absorption in the visible
region and the intensity of the band is due to spin-orbit coupling [33]. For Co(II)
4
4
complex, two bands at 20618 and 25000 cm−1 assigned to A2(F)→4T2(F) and A2(F)
→4T1(F) transitions, respectively. There are another two charge transfer bands at 31250
cm−1 and 33898 cm−1, were recorded. The effective magnetic moment for a tetrahedral
Co(II) species is 4.06 B.M., while the calculated value is 3.89 B.M., this give a close
matching data between experimental and theoretical data.
The greenish brown tetrahedral nickel(II) complex has three absorption bands at
3
3
3
23809, 28571 and 32258 cm−1, assigned to T1(F)→3T2(F), T1(F)→3A2(F) and T1(F)
→3T1(P) transitions, respectively. There is one bands at 33898 cm−1 due to charge
transfer complexation [34]. The magnetic moment of a common tetrahedral nickel(II)
should be approximately 3.52 B.M. (calculated magnetic moment of tetrahedral Ni(II)
ion is lies between 3.5-3.2 B.M), so, the experimental magnetic moment value was
existed within the logical limits [35].
Concerning the copper(II) complex, only one band at 19047 cm−1 of lower energy
was assigned to the d-d transition, which is considered sensitive to the ligand field
2
strength and changes in the molecular geometry and corresponds to the B1g →2A1g
transition [28, 36]. On the basis of d-d transitions, it is difficult to distinguish between a
square-planar and a tetrahedral Cu(II) ion because it occurs in the same region for both
the geometries [32]. The experimental magnetic moment value for Cu(II) ion is 2.17
B.M. which is in the range for a square-planar geometry.
Table 3: Electronic spectral bands (cm–1) and magnetic moments of the H2L ligand and
its complexes
Compound
Magnetic Electronic spectral values/ (cm–1)
Proposed Geometry
moments/
µeff
H2L
-
33898, 31250, 28169, 23809
33898, 31250, 277777, 23256, 19608
33898, 31250, 25000, 20618
33898, 32258, 28571, 23809
33898, 30303, 25974, 22727, 19047
33898, 30303, 23529, 19230
-
[Mn(L)(NH3)]
[Co(L)(NH3)].H2O
[Ni(L)(NH3)]
[Cu(L)(NH3)].H2O
5.92
Tetrahedral
Tetrahedral
Tetrahedral
Square planar
Tetrahedral
4.06
3.52
2.17
Dia-
magnetic
[Zn(L)(NH3)].H2O
9

3-6- ESR spectra
The X-band of ESR spectrum of [Cu(L)(NH3)].H2O Schiff base complex was
shown in Fig. 4. The ESR spectrum of the Cu(II) complex was analyzed. The spin
Hamiltonian parameters (g11= 2.04 and g⊥= 2.02) and the G value (G= 2) of solid state
Cu(II) complex were calculated. Its ESR spectrum displayed axially symmetric g tensor
2
parameters with g11 > g⊥ > 2.0023 indicating that the dx −y2 orbital as a ground state [28].
In axial symmetry the g-values are related to the G-factor by the expression, G= (g11 -2) /
(g⊥- 2) = 4, which measures the exchange interaction between copper centers in the solid.
According to Hathaway [37], if the value of G is greater than 4, the exchange interaction
between copper(II) centers in the solid state is negligible, whereas when it is less than 4,
a considerable exchange interaction exists in the solid complex. The G value is less than
4, this supports the little presence of exchange coupling between copper(II) centers in the
solid state [38]. This hyperfine interaction observed for the complex is attributed to the
interaction with nitrogen and oxygen nuclei adjacent to copper ion. Kivelson and
Neiman, [39] have reported the g11 value < 2.3 for covalent character of the metal-ligand
bond and > 2.3 for ionic character. Applying this criterion the covalent character of the
metal-ligand bond in the complex under study can be predicated. The square-planar
geometry has a ground state configuration 2B1g ( unpaired electron in dX2-Y2 orbital) and
2A1 ( unpaired electron in dZ2 orbital), respectively. Molecular orbital coefficients, α 2 (A
measure of the covalence of the in-plane σ-bonding between a copper 3d orbital and the
2
ligand orbital) and β (covalent in-plane π-bonding), were calculated by using the
following equations [39-43], where α 2= 1 indicates complete ionic character, whereas
α 2 = 0.5 denotes 100% covalent bonding, with the assumption of negligibly small values
of the overlap integral.
α2 = ((A|| /0.036) + (g|| – 2.0023) + 3/7(g⊥ – 2.0023) + 0.04
β 2 = (g|| – 2.0023) E/ –8λα 2,
–1
Where λ = -828 cm for the free copper ion and E is the electronic transition energy.
2
The α2 (0.45) and β (0.24) values indicate that the in-plane σ-bonding and the in-plane
2
π-bonding are highly covalent. The lower value of β compared to α 2 indicates that the
in-plane π-bonding is more covalent than the in-plane σ-bonding. The α2 value for
copper(II) complex indicates a considerable covalency in the bonding between the Cu(II)
ion and the ligand.
0.8
0.6
0.4
0.2
0
0
1000
2000
3000
4000
5000
6000
-0.2
-0.4
Fig. 4: ESR spectrum of [Cu(L)(NH3)].H2O Schiff base complex
10

3-7- 1HNMR spectra
1
The HNMR spectrum of H2L Schiff base ligand was recorded to confirm the
structural. The spectrum of H2L ligand (Fig. 5) showed two weak broad peaks at δ =
13.42 and 15.14 ppm, that are assigned to –OH and –COOH protons. These peaks are
disappeared in the spectrum of zinc(II) complex (Fig. 5B). The singlet peak of –NH
(azomethine) in the H2L ligand (9.36 ppm) was shifted to lower value at 9.16 ppm in
zinc(II) complex, this confirm the participation of –NH group in the complexation. The
higher values of protons for the –OH, –COOH and –NH groups can be assigned to the
presence of intermolecular hydrogen bonding. The group of peaks (m, 10H) at δ = 6.79 –
8.40 ppm range are assigned to aromatic protons of the three aromatic rings and (s, 2H)
at δ = 2.50 and 3.30 ppm for DMSO and H2O/ DMSO, respectively.
Fig. 5A
11

Fig. 5B
Fig. 5: 1H-NMR spectra of A: H2L and [Zn(L)(NH3)].H2O Schiff base complex
3-8- Thermal analysis
The TG/DTG and DTA thermal curves of H2L, Mn(II), Co(II), Ni(II), Cu(II) and
o
Zn(II) Schiff base complexes in nitrogen environment with a heating rate 10 C/min were
given in Figs. 6&7 and the decomposition steps are assigned in Table 4. This table
illustrated to the behavior of the thermal degradation according to TG curves for each
step in the decomposition sequence of the H2L, Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)
Schiff base complexes. The mass losses obtained from TG curves are in a good
12

agreement with the calculated values. The pathway of these complexes is the same
sequences with overlapping steps vary from one complex to another as the following:
o
The H2L ligand melts at 256 C with simultaneous decomposition, (Fig. 6A).
From the TG curve, it appears that the sample decomposes in three main stages over the
o
temperature range 25-1000 C. The first step occurs at (25-271 C) with a mass loss of
o
o
(obs. = 11.91%, calc. = 11.68%). The second step falls in the range of 271-422 C with a
o
mass loss (obs. = 7.72%, calc. = 9.27%). The last one within the range 422-1000 C was
accompanied by mass loss (obs. = 67.44%, calc. = 66.68%). From the corresponding
o
DTA curve (Fig. 6B), two exothermic peaks are noted. The first maximum is at 183 C
and the second at 566 oC, respectively.
H
C
H
C
step 3
step 2
C14H10
O
step 1
N
N
C
C
OH HO
O
C
O
O
The thermal decomposition of Mn(II) complex occurs at strong DTGmax
decomposition steps (Fig. 7A). The first degradation step take place within the range of
o
21-300 C and it is corresponds to the decomposition of L Schiff base ligand and NH3
molecules due to a weight loss of (obs. = 61.83%, calc. = 62.05%). The second step falls
o
in the range of 300-1000 C which is assigned to loss of three carbon monoxide CO
molecules with a weight loss (obs = 22.24%, calc= 23.27%). The manganese pure metal
o
is the final product remains stable till 1000 C. The following is the mechanism of
achievement of Mn metal at the final decomposition products. MnO2 resulted from the
decomposition of manganese carbonate is conversed upon the carbothermal reduction to
manganese metal using coke (few carbon atoms produced from decomposition of H2L
moiety.
H
step 2
C
step 1
N
MnCO3 + 2C
Mn (metal)
Mn
C
- CO
O
O
O
NH3
Reduction
Mn (metal)
+2CO
MnO2 + 2C
From the corresponding DTA curve (Fig. 7B), two exothermic peaks are noted.
The first maximum is at 92 oC and the second at 243 oC, respectively.
o
The Co(II) complex decomposed in two steps. The first step ranged at 20-136 C
corresponding to the loss of H2O molecules representing a weight loss of (obs. = 4.64%,
calc. = 4.70%). The second step occurring at 136-800 corresponding to the loss of NH3
and Schiff base ligand molecules, the weight loss associated with this stage (obs. = 78.78
%, calc. = 79.89 %). The final residue at the end of this stage is cobalt metal residue.
From the corresponding DTA curve, one very strong exothermic peak is noted at 390 oC.
The CoO produced from the thermal decomposition of cobalt(II) carbonate is conversed
upon the carbothermal reduction to cobalt metal using coke (few carbon atoms produced
from decomposition of H2L moiety.
13

H
C
step 2
N
CoCO3
- CO2
Co
C
O
O
O
NH3
Reduction
Co (metal)
+CO
CoO + C
To make sure about the proposed formula and structure for the Ni(II) complex,
thermogravimetric and differential thermal analysis were carried out for this complex
under N2 flow. The thermal decomposition of the nickel(II) complex proceeds
approximately with main three degradation steps. The first stage occurs at maximum
o
o
temperature of DTGmax= 207 C (temperature range 22-272 C), the weight loss
associated with this stage (obs. = 61.71%, calc. = 60.82%) corresponding to the loss of
C15H14N2 (decomposition of L Schiff base ligand). The second step occurs at the
o
o
maximum temperature DTGmax= 316 and 480 C (temperature range 272-1000 C). The
weight loss at this step (obs. = 17.15%, calc. = 15.34%) associated with the loss of 2CO
gas molecules. The final residue at the end of this stage is NiO+ C (residual carbon).
H
C
step 1
step 2
N
NiCO3
NiO
- CO2
Ni
C
O
O
O
NH3
The thermal degradation of the Cu(II) complex take place in mainly five
degradation stages with DTGmax= 81 (20-92 oC), 207 (155-245 oC), 283 and 324 (245-372
o
oC), and 417 (372-800) C. The first stage of decomposition occurs at a temperature
o
maximum of DTGmax= 81 C, the found weight loss associated with this step is (obs. =
9.17%, calc. = 9.02%) and may be attributed to the loss of H2O and NH3 molecules. The
decomposition steps from second-to fifth were occurs at a temperature maximum of 207,
283, 324 and 417 oC. The weight loss found at these steps equals to (obs. = 69.70%, calc.
= 70.36%) corresponds to the loss of C18H11NO2 (decomposition L Schiff base ligand).
o
The final thermal product obtained at 800 C is CuO as a residue. The interesting point
for this system is the resulted of copper(II) oxide at low temperature 475 oC (calcinations
point).
H
C
step 1-5
N
CuO
Ni
C
O
O
O
NH3
From the corresponding DTA curve, four exothermic peaks are noted at 208, 291,
331 and 420 oC, respectively.
The thermal decomposition of the Zn(II) complex occurs in definite five
degradation stages with DTGmax= 130 (30-249 oC), 342 (249-356 oC), 389 and 445 (356-
o
465 oC), and 510 (465-800) C. The first stage of decomposition occurs at a temperature
14

o
maximum of DTGmax= 130 C, the found weight loss associated with this step is (obs. =
8.97%, calc. = 8.97%) and may be attributed to the loss of H2O and NH3 molecules. The
decomposition steps from second-to fifth were occurs at a temperature maximum of 342,
389, 445 and 510 oC. The weight loss found at these steps equals to (obs. = 74.26%, calc.
= 74.10%) corresponds to the loss of C18H11NO2 (decomposition L Schiff base ligand).
o
The final thermal product obtained at 800 C is zinc metal as a residue. From the
corresponding DTA curve, two exothermic peaks are noted at 457 and 511 oC,
respectively, and oly one endothermic peak at 131 oC.
H
step 2
C
step 1
N
Zn (metal)
ZnCO3
- CO2
Zn
C
O
O
O
NH3
Reduction
Zn (metal)
+CO
ZnO + C
Table 4: Thermogravimetric data of the H2L and its Schiff base complexes
Complex
H2L
Steps
Temp. range
(°C)
DTG peak DTA peak
(°C)
Decomposed
assignments
Weight loss
Found (Calcd.
%)
(°C)
1st
25 – 271
271– 422
422 – 1000
193
331
590
183
566
- H2O2
- HCN
11.91 (11.68)
7.72 (9.27)
67.44 (66.68)
2nd
3rd
- C14H10O
3C
residue
1st
2nd
Mn(II)
Co(II)
Ni(II)
Cu(II)
21 – 300
300 – 1000
222
364
92
243
-NH3+C15H11N
-3CO
61.83 (62.05)
22.24 (23.27)
residue
1st
2nd
Mn metal
- H2O
-C18H11NO3+ NH3
Co metal
- C15H14N2
- 2CO
NiO + C
- H2O + NH3
- C18H11NO2
20 – 136
136 – 800
261
384
390
4.64 (4.70)
78.78 (79.89)
residue
1st
2nd
residue
1st
2nd
22 – 272
272 – 1000
207
316, 480
74
219
61.71 (60.82)
17.15 (15.34)
507
-
20 – 92
155 – 800
81
207, 283
324, 417
9.17 (9.02)
69.70 (70.36)
208, 291
331,420
residue
1st
2nd
CuO
- H2O + NH3
- C18H11NO3
Zn(II)
30 – 249
249 – 800
130
342, 389
445, 510
131
-
457, 511
8.97 (8.97)
74.26 (74.10)
residue
Zn metal
15

Fig. 6A
16

Fig. 6B
Fig. 6: TG (A) and DTA (B) curves of H2L ligand
17

Fig. 7A
18

Fig. 7B
Fig. 7: TG (A) and DTA (B) curves of [Mn(L)(NH3)] Schiff base complex
19

Base on the spectroscopic and thermal analyses data of the Mn(II), Co(II), Ni(II), Cu(II)
and Zn(II) Schiff base complexes the suggested structure can be formulated as shown in
Fig. 8.
H
C
H
C
N
N
.H O
2
Co
C
Mn
C
C
C
O
O
O
O
O
O
O
O
NH
NH
3
3
3
3
H
C
H
C
N
N
.H O
2
Ni
Cu
C
O
O
O
O
O
NH
NH
3
H
C
N
.H O
2
Zn
O
O
NH
Fig. 8: Suggested structures of [M(L)(NH3)].nH2O Schiff base complexes (where M=
Mn(II), Co(II), Ni(II), Cu(II) and Zn(II); n= 0 or 1)
3-9- XRD and SEM studies
The main target of this paper beside the synthesis and characterization of the
novel Schiff base and its Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes is to study
of the final thermal decomposition products at calcinations temperatures. These residuals
were checked using scanning electron microscopy (SEM), and x- ray diffraction (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 and XRD, the diameters of the residual samples for Co(II) and Ni(II) are about 50
and 65 nm, respectively. Figure 9 show the scanning electron microscopy pictures of
[Co(L)(NH3)].H2O and [Ni(L)(NH3)] particles. By comparison between the residual
products in this study, the cobalt(II) and nickel(II) oxides nanoparticles in the literature
20

[44, 45], it is obvious that the particles (50 and 65 nm diameters) are smaller and the H2L
Schiff base ligand can be used as a good precursors with low calcinations temperatures.
The x-ray powder diffraction patterns in the range of 4o< 2θ < 70o for the Mn(II), Co(II),
o
Ni(II), Cu(II) and Zn(II) complexes and 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 products of cobalt and nickel H2L complexes
were recorded between 4o and 70o 2θ and are given in Fig. 10. The values of 2θ, full
width at half maximum (FWHM) of prominent intensity peak, relative intensity and
particle size of cobalt and nickel residual products were calculated. The crystallite size of
the cobalt and nickel residuals at 600 oC (Fig. 11) could be estimated from XRD patterns
by applying FWHM of the characteristic peaks using Deby-Scherrer equation 1 [46].
D= Kλ/βCosθ ……….. (equ. 1)
Where D is the particle size of the crystal gain, K is a constant (0.94 for Cu grid), λ is the
x-ray wavelength (1.5406 Ǻ), θ is the Bragg diffraction angle and β is the integral peak
width. The particle size was estimated according to the highest value of intensity
compared with the other peaks. The particle size for the cobalt and nickel thus obtained
were 50 and 65 nm, respectively. These data gave an impression that the particle size
located within nano scale range.
Fig. 9A
21

Fig. 9B
Fig. 9C
Fig. 9: SEM images of A-H2L, and its B-Co(II) and C-Ni(II) Schiff base complexes
22

Fig. 10A
23

Fig. 10B
24

Fig. 10C
25

Fig. 10D
26

Fig. 10E
27

Fig. 10F
Fig. 10: XRD spectra of A-H2L, and its B-Mn(II), C-Co(II), D-Ni(II), E-Cu(II) and F-
Zn(II) Schiff base complexes
28

8000
7000
6000
5000
4000
3000
2000
1000
0
NiO
CoO
600
500
400
300
200
100
0
20
40
60
80
2-Theta- Scale
Fig. 11: XRD spectra of cobalt and nickel oxides produced after thermal decomposition
of [Co(L)(NH3)].H2O and [Ni(L)(NH3)] Schiff base complexes at 600 oC
3-10- Kinetic thermodynamic parameters
The kinetic thermodynamic studies upon the thermal degradation processes are a
powerful indication to provide sufficient knowledge about Arrhenius parameters viz.
activation energy (E*), frequency factor (A), enthalpy of activation (H*), entropy of
activation (S*) and free energy of activation (G*). From TG/DTG curves, Coats-Redfern
and Horowitz-Metzger [47, 48] were employed to calculate mentioned kinetic
parameters. The data was summarized and tabulated in Table 5. In fact the increasing in
(A) value led to decreasing in (E*), so, when the activation energy has a higher value the
thermal stability increased. The higher values of (E*) and lower values of (A) are
supported the reaction to proceed slower than normal [49, 50]. This fact has been
applicable for the H2L complexes studied in the present paper. The negative values of
(S*) indicate that the activated complex has a more ordered [51] than that of either the
reactants. The values of both E* and H* are equivalent.
29