Synthesis, spectroscopy and thermal study of some nickel(II) complexes containing tridentate Schiff bases and substituted amine ligands, X-ray crystal structure of nickel(II) complex

Article abstract of DOI:10.1016/j.saa.2012.03.039

Some new tridentate ONO and ONS Schiff base complexes of [NiL(amine)] (L = Salicylidene2-aminophenol and Salicylidene2-aminothiophenol, amine = benzylamine, morpholine, pyrrolidine and piperidine) were synthesized and characterized by IR, UV-vis, ¹

Full text of DOI:10.1016/j.saa.2012.03.039

Spectrochimica Acta Part A 94 (2012) 302–307
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectroscopy and thermal study of some nickel(II) complexes
containing tridentate Schiff bases and substituted amine ligands, X-ray crystal
structure of nickel(II) complex
Ali Hossein Kianfara,∗, Masomeh Bahramianb, Hamid Reza Khavasic
a Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran
b Department of Chemistry, Yasouj University, Yasouj, Iran
c Department of Chemistry, Shahid Beheshti University, G. C., Evin, Tehran 1983963113, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Some new tridentate ONO and ONS Schiff base complexes of [NiL(amine)] (L = Salicylidene2-aminophenol
and Salicylidene2-aminothiophenol, amine = benzylamine, morpholine, pyrrolidine and piperidine) were
synthesized and characterized by IR, UV–vis, 1H NMR spectroscopy and elemental analysis. The geometry
of [NiL2(bzlan)] determined by X-ray crystallography indicates that the complex has planar structure and
has four coordinate in the solid state. The thermogravimmetry (TG) and differential thermoanalysis (DTA)
of the synthesized complexes were carried out in the range of 20–700 ◦C, leading to decomposition of
ONO type in two stages and of ONS type in three stages. The ONO and ONS complexes were decomposed
to NiO and NiS respectively. Thermal decomposition of the complexes is closely the depends upon nature
of the Schiff base ligands and proceeds via first order kinetics.
Received 26 December 2011
Received in revised form 29 February 2012
Accepted 9 March 2012
Keywords:
Schiff base complexes
Nickel complexes
Thermogrvimetry
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
of 20–700 ◦C. The thermal decomposition kinetic parameters were
also calculated and discussed using Coats and Redfern method [14].
Schiff bases have been used as ligands because of their ability
to create stable coordination compounds with different oxidation
states. Schiff base complexes have centered on the role of such com-
plexes in providing synthetic models for the metal containing sites
in metallo-proteins and -enzymes [1–5]. The tridentate Schiff bases
and their complexes were reported previously [6–8]. Recently, they
were reported as effective corrosion inhibitors for some metals in
acidic media [9]. Until now, the structure of some nickel [10–12]
and copper [13] complexes containing tridentate Schiff bases and
amine were studied and their coordination geometries were iden-
tified.
Herein we prepared tridentate Schiff bases by the condensation
of salicylaldehyde with 2-aminophenol and 2-aminothiophenol.
The [NiL(OH2)] complexes of synthesized ligands were pre-
pared in methanol and treated with different amines to prepare
[NiL(amine)] complexes [Fig. 1]. The synthesized complexes were
identified by IR, NMR, UV–vis spectroscopy and elemental analysis.
The structure of [NiL2(bzlan)] was determined by X-ray crystallog-
raphy. The thermogravimetry (TG) and differential thermoanalysis
(DTA) of the nickel(II) complexes were carried out in the range
2. Experimental
2.1. Chemicals and apparatus
All of the chemicals and solvents used were reagent quality
and used without further purification. Infrared spectra (KBr discs)
were recorded on a FT-IR JASCO-680 spectrophotometer in the
4000–400 cm−1. The elemental analyses were determined on a
CHN-O-Heraeus elemental analyzor. UV–vis spectra were recorded
on a JASCO V-570 spectrophotometer in the 190–900 nm. The 1H
NMR spectra were recorded in CDCl3 on DPX-400 MHz FT-NMR.
Thermogravimmetry (TG) and differential thermoanalysis (DTA)
were carried out on a PL-1500. The measurements were performed
in air atmosphere and the heating rate was kept at 10 ◦C min−1
.
2.2. Synthesis
The tridentate Schiff base ligands, L1(ONO donor) and L2(ONS
donor) and the NiL(OH2) complexes were prepared according to
the literature [15].
The NiL(amine) complexes were synthesized by refluxing
methanolic solutions of the NiL(OH2) complexes and amines. The
reaction was refluxed for 4 h. The resulting red color solution
was filtrated. After 24 h, the resulting pin shape crystals were
∗
Corresponding author. Tel.: +98 311 3913251; fax: +98 311 3912350.
E-mail addresses: akianfar@cc.iut.ac.ir, asarvestani@yahoo.com (A.H. Kianfar).
1386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2012.03.039

A.H. Kianfar et al. / Spectrochimica Acta Part A 94 (2012) 302–307
303
H
CH3OH
H
X
N
O
Ni(OAc)2.4H2O
+
N
XH
Ni
OH2
OH
H
X
N
O
H
CH3OH
X
N
O
amine
+
Ni
OH2
Ni
amine
X = O-, S-
amine = benzylamine, morpholine, pyrrolidine, piperidine
O
CH2NH2
N
N
H
N
H
H
Fig. 1. The structure of nickel complexes.
NiL1(pprdn): Yield (80%). Anal. calc. for C18H20N2O2Ni: C, 60.89;
H, 5.68; N, 7.89%. Found; C, 60.14; H, 5.84; N, 8.15%. FT-IR (KBr cm−1
filtered, washed with methanol and recrystalized from 2:1 ratio
of dichloromethane/ethanol and dried in vacuum.
)
H2L1: Yield (90%). (C13H11NO2), FT-IR (KBr cm−1
) ꢀmax
ꢀmax 3278 (N H), 1602 (C N), 1527 (C C). UV–vis, ꢁmax (nm)
(ε, L mol−1cm−1) (Ethanol): 419 (16,000), 249 (9000), ı (400 MHz,
CDCl3, Me4Si) 2.8 (s, H, NH), 1.6–3.7 (m, 10, CH2), 6.5–7.5 (m, 8H,
Aromatic), 8.1 (s, 1H, HC N).
3100–2400 (O H), 1631 (C N), 1529 (C C). UV–vis, ꢁmax (nm) (ε,
L mol−1 cm−1) (CHCl3): 354 (7000), 269 (6000).
H2L2: Yield (85%). (C13H11NOS), FT-IR (KBr cm−1) ꢀmax 3256
(S H), 1614 (C N), 1564 (C C). UV–vis, ꢁmax (nm) (ε, L mol−1cm−1
)
NiL2(pprdn): Yield (80%). Anal. calc. for C18H20N2OSNi: C, 58.25;
H, 5.43; N, 7.54%. Found; C, 58.01; H, 5.56; N, 7.88%. FT-IR (KBr cm−1
)
(CHCl3): 345 (6500), 276 (6000).
NiL1(H2O): Yield (80%). FT-IR (KBr cm−1) ꢀmax 3424 (O H), 1616
(C N), 1539 (C C). UV–vis, ꢁmax (nm) (ε, L mol−1cm−1) (Ethanol):
405 (6000), 298 (4700).
ꢀmax 3226 (N H), 1606 (C N), 1572 (C C). UV–vis, ꢁmax (nm)
(ε, L mol−1cm−1) (Ethanol): 425 (8800), 272 (22,000), ı (400 MHz,
CDCl3, Me4Si) 1.7 (s, H, NH), 1.4–3.6 (m, 10H, CH2), 6.6–7.4 (m, 8H,
Aromatic), 8.4 (s, 1H, HC N).
NiL2(H2O): Yield (80%). FT-IR (KBr cm−1) ꢀmax 3426 (O H), 1605
(C N), 1524 (C C). UV–vis, ꢁmax (nm) (ε, L mol−1cm−1) (Ethanol):
417 (9000), 272 (15,000).
NiL1(mrpln): Yield (80%). Anal. calc. for C17
H18N2O3Ni: C, 56.87;
H, 5.05; N, 7.80%. Found; C, 56.33; H, 5.29; N, 8.08%. FT-IR (KBr
cm−1) ꢀmax 3250 (N H), 1603(C N), 1528 (C C). UV–vis, ꢁmax (nm)
(ε, L mol−1cm−1) (Ethanol): 419 (13,000), 249 (3600), ı (400 MHz,
CDCl3, Me4Si) 2.1 (s, H, NH), 3.2–3.9 (s, 8H, CH2), 6.5–7.5 (m, 8H,
Aromatic), 8.1 (s, 1H, HC N).
NiL1(bzlan): Yield (85%). Anal. calc. for C20H18N2O2Ni: C, 63.37;
H, 4.78; N, 7.39%. Found; C, 62.27; H, 4.57; N, 7.81%. FT-IR (KBr
cm−1) ꢀmax 3295, 3186 (N H), 1605 (C N), 1530 (C C). UV–vis,
ꢁmax (nm) (ε, L mol−1cm−1) (Ethanol): 419 (16,000), 249 (16,000),
ı (400 MHz, CDCl3, Me4Si) 2.3 (s, 2H, NH2), 4.0 (s, 2H, CH2), 6.5–7.4
(m, 13H, Aromatic), 7.8 (s, 1H, HC N).
NiL2(mrpln): Yield (80%). Anal. calc. for C17H18N2O2SNi: C,
54.43; H, 4.83; N, 7.46%. Found; C, 53.95; H, 4.72; N, 7.93%. FT-
IR (KBr cm−1) ꢀmax 3263 (N H), 1603(C N), 1525 (C C). UV–vis,
ꢁmax (nm) (ε, L mol−1cm−1) (Ethanol): 424 (8000), 272 (22,000), ı
(400 MHz, CDCl3, Me4Si) 1.8 (s, H, NH), 1.6–3.3 (s, 8H, CH2), 6.6–7.4
(m, 8H, Aromatic), 8.4 (s, 1H, HC N).
NiL2(bzlan): Yield (85%). Anal. calc. for C20H18N2OSNi: C, 60.79;
H, 4.59; N, 7.09%. Found; C, 60.02; H, 4.73; N, 7.45%. FT-IR (KBr cm−1
)
ꢀmax 3291, 3182 (N–H), 1603 (C N), 1528 (C C). UV–vis, ꢁmax (nm)
(ε, L mol−1cm−1) (Ethanol): 424 (9000), 274 (76,000), ı (400 MHz,
CDCl3, Me4Si) 2.0 (s, 2H, NH2), 4.0 (s, 2H, CH2), 6.6–7.4 (m, 13H,
Aromatic), 8.3 (s, 1H, HC N).
NiL1(prldn): Yield (80%). Anal. calc. for C17H18N2O2Ni: C, 59.87;
2.3. Crystal data collection and processing of [NiL(bzlan)] (1)
H, 5.32; N, 8.21%. Found; C, 60.27; H, 5.04; N, 8.69%. FT-IR (KBr cm−1
)
ꢀmax 3287 (N H), 1604 (C N), 1539 (C C). UV–vis, ꢁmax (nm) (ε,
L mol−1cm−1) (Ethanol): 420 (22,000), 249 (22,700), ı (400 MHz,
CDCl3, Me4Si) 2.1 (s, H, NH), 1.7–3.4 (m, 8H, CH2), 6.5–7.5 (m, 8H,
Aromatic), 8.1 (s, 1H, HC N).
The X-ray diffraction measurements were made on a STOE
IPDS-2T diffractometer with graphite monochromated Mo-K␣ radi-
ation. For this complex a yellow plate crystal with a dimension
of 0.50 mm × 0.15 mm × 0.20 mm was chosen and mounted on a
glass fiber and used for data collection. Cell constants and an ori-
entation matrix for data collection were obtained by least-squares
refinement of diffraction data from 4497 unique reflections. Data
were collected at a temperature of 298(2) K to a maximum 2Â
value of 58.4◦ in a series of ␻ scans in 1◦ oscillations and inte-
grated using the Stoe X-AREA [16] software package. The numerical
NiL2(prldn): Yield (75%). Anal. calc. for C17H18N2OSNi: C, 57.17;
H, 5.08; N, 7.84%. Found; C, 56.54; H, 4.80; N, 8.17%. FT-IR (KBr cm−1
)
ꢀmax 3215 (N H), 1604 (C N), 1573 (C C). UV–vis, ꢁmax (nm) (ε,
L mol−1cm−1) (Ethanol): 426 (12,000), 271 (24,300), ı (400 MHz,
CDCl3, Me4Si) 1.8 (s, H, NH), 1.9–3.3 (s, 8H, CH2), 6.6–7.4 (m, 8H,
Aromatic), 8.4 (s, 1H, HC N).

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A.H. Kianfar et al. / Spectrochimica Acta Part A 94 (2012) 302–307
absorption coefficient, ꢂ, for Mo-K␣ radiation is 1.298 mm−1. A
numerical absorption correction was applied using X-RED [17] and
X-SHAPE [18] softwares. The data were corrected for Lorentz and
Polarizing effects. The structures were solved by direct methods
[19] and subsequent difference Fourier maps and then refined on
F2 by a full-matrix least-squares procedure using anisotropic dis-
placement parameters [20]. H atoms were positioned geometrically
and constrained to ride on their parent atoms. The NH2 hydrogen
atoms were located in a difference Fourier map and then refined
isotropically. Atomic factors are from International Tables for X-
ray Crystallography [21]. All refinements were performed using the
X-STEP32 crystallographic software package [22].
3. Results and discussion
3.1. IR characteristics
The IR spectra of the nickel(II) Schiff base complexes synthesized
here are given in Section 2.2. The phenolic OH stretching frequency
of the ligands was approved in the 3100–2500 cm−1 region due
to the internal hydrogen bonding vibration (O H· · ·N). This band
disappeared in the spectra of the complexes [23–25].
Fig. 2. Crystal structure of [Ni(ONS)(bzlan)] complex.
Table 1
Crystallographic and structure refinements data for complex [Ni(ONS)(bzlan)].
The C N bond stretching frequency of L1 and L2 were approved
in 1631 cm−1 and 1614 cm−1 region respectively [26,27]. In the
complexes the C N stretching shifted to a lower frequencies and
observed in 1616–1602 cm−1 region, indicating a decrease in the
Formula
C20H18N2NiOS
393.12
Formula weight
Temperature/K
298(2)
C
N bond order due to the coordinate bond formation between
Wavelength ꢁ/Å
0.71073
the metal and the imine nitrogen lone pair [26,27].
Crystal system
Triclinic
Space GROUP
P¯ı
The amine bands, ꢀ (NH), of [NiL(amine)] complexes were
Crystal size/mm3
0.50 × 0.20 × 0.15
5.6249(6)
11.3415(12)
14.0736(14)
69.417(8)
89.559(8)
83.506(8)
834.62(16)
2
appeared at about 3295–3113 cm−1
.
a/Å
b/Å
3.2. Electronic spectra
c/Å
˛/◦
ˇ/◦
The spectral data of the synthesized complexes are given in
Section 2.2. The electronic spectra of the Schiff bases consists of rel-
atively intense bands in the 250–350 nm region, involving ␲ → ␲*
transition [23,24]. The bands at higher energies correspond to
␲ → ␲* transitions of aromatic rings, while the band at lower ener-
gies is attributed to the ␲ → ␲* transition of azomethine group.
Some of the nickel complexes exhibit d–d transition, which over-
laps with the azomethine transition.
ꢃ/◦
Volume/Å3
Z
Density (calc.)/g cm−1
 ranges for data collection
F(0 0 0)
1.564
1.5–29.2
298
Absorption coefficient
Index ranges
1.298
−7 ≤ h ≤ 7
−14 ≤ k ≤ 15
−19 ≤ l ≤ 19
9437
4497, (0.083)
234, 0
0.0578, 0.1532
0.0700, 0.1669
0.90
Data collected
Unique data (Rint
Parameters, restrains
Final R1, wR2 (Obs. data)
3.3. 1H NMR spectra
)
The 1H NMR spectral data for [NiL(amine)] complexes are given
in Section 2.2. The CH2 and NH signals of amines appear in the
range of 1.4–4.0 and 1.7–2.8 ppm, respectively. The appearance of
the amine signals indicates the coordination of amine ligands in
the equatorial position. The signals of aromatic protons lie between
6.5 and 7.5 ppm. The azomethine hydrogen (HC N) of [NiL(amine)]
complexes appears in the range of 7.8–8.4 ppm. In the ONO com-
plexes the HC N and the NH protons are shifted up field and down
field, respectively, while ONS complexes show a reverse trend. The
down field chemical shift of the amine NH resonance in the ONO
complexes relative to ONS complexes indicates that the N· · ·H· · ·O
intramolcular hydrogen bonding is probably strong enough in solu-
tion [28].
a
a
Final R1, wR2 (All data)
Goodness of fit on F2 (S)
3
˚
Largest diff peak and hole/e A
0.97, −0.71
R1 = ꢄ||Fo| − |Fc||/ꢄ|Fo|, wR2 = [ꢄ(w(Fo − Fc2)2)/ꢄw(Fo2)2]1/2
.
a
2
Table 2
Selected bond distances (Å) and bond angles (◦) for [Ni(ONS)(bzlan)].
Bond distances
Bond angles
Ni1 O1
Ni1 N1
Ni1 S1
Ni1 N2
O1 C1
N1 C7
N1 C8
S1 C13
C6 C7
1.865(2)
1.882(2)
2.157(1)
1.944(3)
1.301(4)
1.318(4)
1.427(4)
1.746(3)
1.417(5)
1.485(4)
1.508(4)
O1 Ni1 N1
N1 Ni1 S1
S1 Ni1 N2
N2 Ni1 O1
N1 Ni1 N2
O1 Ni1 S1
Ni1 N2 C14
N2 C14 C15
C8 N1 C7 C6
N2 C14 C15 C16
96.61(11)
89.48(9)
91.90(10)
82.11(12)
177.75(12)
173.15(8)
123.8(2)
3.4. Description of the molecular structure of [NiL2(bzlan)] (1)
The complex [NiL2(bzlan)] was characterized by X-ray diffrac-
tion, and the ORTEP representation is shown in Fig. 2. Relevant
X-ray diffraction data and selected bond lengths and angles are
listed in Tables 1 and 2, respectively. This complex crystallizes in the
triclinic space group P¯ı. The crystal structure of [NiL2(bzlan)] shows
113.3(3)
−174.7(3)
N2 C14
C14 C15
47.9(4)

A.H. Kianfar et al. / Spectrochimica Acta Part A 94 (2012) 302–307
305
Fig. 4. The TG and DTA of NiL1(prldn) complex.
Fig. 3. Crystal packing diagram of [Ni(ONS)(bzlan)].
a tridentate ONS coordination of the Schiff base and a monoden-
tate benzylamine ligand. The angles O(1) Ni(1) N(1) = 96.61(11)◦,
N(1) Ni(1) S(1) = 89.48(9)◦, S(1) Ni(1) N(2) = 91.90(10)◦ and
N(2) Ni(1) O(1) = 82.11(12)◦ indicate that the coordination
geometry of the nickel atom is distorted square planar. The Ni
˚
ion is 0.13 A out of the best plane going through the atoms O1,
N1, S1 and N2. The Ni O, Ni N and Ni S distances of 1.865(2)
Å, 1.882(2) Å and 2.157(2) Å for Ni(1) O(1), Ni(1) N(1) and
Ni(1) S(1) respectively are in the ranges observed for analogous
compounds of Ni square planar complexes containing ONS Schiff
Fig. 5. The TG and DTA of NiL2(bzlan) complex.
˚
base ligand [10–12]. The Ni Namine distance (1.944(3) A) is longer
˚
than the Ni NONS distance (1.882(2) A). This is similar to what was
observed for [Ni(ONS)(amine)] complexes in which the Ni Namine
˚
˚
distances range from 1.950 A to 1.957 A and the Ni NOSN distances
H
H
˚
˚
S
range from 1.873 A to 1.890 A [10–12]. The structural data on
known nickel (II) square planar complexes having NOS coordina-
tion and different monodentate aliphatic N-donor ligands were
reported previously [26–28]. The coordination geometries in these
complexes are distorted square planar.
N
O
O
N
Ni
Ni
amine
amine
O
As can be seen from the packing diagram of complex 1 (Fig. 3),
step one
head-to-tail N(amine)-H· · ·S hydrogen bonds [H2C· · ·S1i = 2.71(6),
step one
i
i
◦
˚
N2· · ·S1 = 3.527(3) A and N2-H2C· · ·S1 = 162(5) , symmetry code(i)
1 − x, 1 − y, 2 − z] between adjacent molecules produce a dimer.
It seems that the weak intermolecular ␲· · ·␲ interactions
˚
[3.6537(19) A, symmetry code(ii) 1 + x, y, z] between six-membered
H
H
S
N
O
phenyl ring and five-membered Ni–S–C–C–N ring are effective in
the stabilization of the lattice.
O
N
O
Ni
Ni
3.5. Thermal analysis
The thermal decomposition of the [NiL(OH2)] and [NiL(amine)]
complexes presented characteristic pathways, depending on the
nature of the Schiff base ligands and amines, as can be seen from
the TG/DTA curves in Fig. 4. The absence of weight loss up to 80 ◦C
indicates that there is no water molecule in the crystallin solid. Also,
in [NiL(OH2)] complexes, the TG showed weight loss up to 100 ◦C
indicating the presence of water molecule coordinated to com-
plexes [23,29]. All the L1( ONO) and L2( ONS) complexes were
decomposed in two and three steps respectively (Figs. 4–6). The
temperature range and the percentage of loss weight for steps were
collected in Tables 3–4. Thermalgravimmetry clearly reveals that
all the L1(ONO) complexes obtained here, provide NiO as the final
species [25], whereas the L2(ONS) complexes provide NiS at final
stage.
step two
step two
NiO
H
H
S
N
Ni
step three
The complex, [NiL1(OH2)] decomposes in two steps. The first
step occurred up to about 142 ◦C and was attributed to the release of
water. The second mass loss between 410 and 473 ◦C was assigned
to the Schiff base ligand, with the formation of the NiO.
NiS
Fig. 6. The proposed decomposition pathway of the nickel complexes.

306
A.H. Kianfar et al. / Spectrochimica Acta Part A 94 (2012) 302–307
Table 3
Thermal and kinetics parameters for nickel complexes.
Compounds
NiL1(H2O)
T (◦C)a
Percent (%)b
E* (kJ mol−1
)
A* (s−1
)
S* (kJ mol−1 K−1
)
H* (kJ mol−1
)
G* (kJ mol−1
)
202–258
410–473
150–211
400–465
163–221
393–487
124–205
400–474
174–214
414–474
5(6)
26.8
396.9
148.9
141.2
169.9
165.2
184.3
212.2
284.9
202
2.5 × 10−1
7.5 × 1026
3.6 × 1014
6.8 × 107
1.5 × 1016
5.5 × 109
5.9 × 1018
1.8 × 1013
3.5 × 1029
3.4 × 1012
−250
266
37
24.8
393.2
147.3
137.4
168.2
161.6
182.7
208.5
283.3
198.4
86
273
140
180
154
189
159
206
220
202
66(67)
20(21)
58(57)
20(24)
52(54)
20(24)
55(55)
25(28)
51(48)
NiL1(prldn)
NiL1(mrpln)
NiL1(pprdn)
NiL1(bzlan)
−98
68
−61.7
118
5.5
320
−8.3
a
The temperature range of decomposition pathways.
Precent of weight lose found (calculated).
b
Table 4
Thermal and kinetics parameters for nickel complexes.
Compounds
NiL2(H2O)
T (◦C)a
Percent (%)b
E* (kJ mol−1
)
A* (s−1
)
S* (kJ mol−1 K−1
)
H* (kJ mol−1
)
G* (kJ mol−1
)
167–197
332–432
502–586
175–315
354–447
500–567
187–334
362–493
481–555
178–348
351–406
500–604
180–330
350–440
450–570
5(6)
175.03
127.76
106.25
39.8
58.2
84.7
44.3
24.7
70.8
30.2
81.7
91.2
50.2
65.31
40.9
3.9 × 1012
1.9 × 109
1.6 × 106
7.9
9.4 × 10−2
−6.9 × 101
−1.3 × 102
−225
173.5
124.7
101.8
38.1
54.6
80.2
42.4
21.1
66.5
28.7
78.8
86.8
48.6
62.2
36.5
1.7 × 102
1.5 × 102
1.7 × 102
85
147
184
90.5
137
153
73.6
31(31)
33(33)
22(20)
29(26)
24(28)
22(23)
29(25)
21(27)
27(27)
25(24)
22(25)
24(23)
26(25)
24(27)
NiL2(prldn)
NiL2(pprdn)
NiL2(bzlan)
NiL2(mrpln)
89.9
−211
1.1 × 103
−190
15.8
−219
0.1
−267
1.5 × 104
0.6
−169
−245
1.1 × 104
2.5 × 103
7.7 × 101
2.4 × 104
8.4 × 10−1
−169
139
185
−185
−2.1 × 102
−1.6 × 102
−2.5 × 102
8.9 × 101
1.2 × 102
1.7 × 102
a
The temperature range of decomposition pathways.
Precent of weight lose found (calculated).
b
The complexes, [NiL1(amine)] decompose in two steps. The first
by calculating the correlation coefficient. The other systems and
their steps show the same trend.
step occurred in the range 124–229 ◦C and was attributed to the
release of amine. The second mass loss between 393 and 487 ◦C
was assigned to the Schiff base ligand, with the formation of the
NiO.
The entropy of activation S =/ was calculated using the equation
kTs
h
#
/R
The complex, [NiL2(OH2)] decomposes in three steps. The first
step occurred up to about 167 ◦C and was attributed to the release
of water. The second thermal event that observes between 332 and
432 ◦C is related to release of phenoxy. The third mass loss between
502 and 586 ◦C was assigned to the rest of the ligand, with the
formation of the NiS.
A =
eS
(2)
6.4
6
The complexes, [NiL2(amine)] decomposes in three steps. The
first step occurs in the range of 175–348 ◦C and was attributed to
the release of amine. The phenoxy moiety of the Schiff base ligand
is released in the second thermal event between 350 and 493 ◦C.
The thrid mass loss between 450 and 604 ◦C was assigned to the
rest of the ligand, with the formation of the NiS.
R2 = 0.994
3.6. Kinetics aspects
5.6
5.2
All the well-defined stages were selected to study the kinetics of
decomposition of the complexes. The kinetics parameters (the acti-
vation energy E and the pre-exponential factor A) were calculated
using the Coats–Redfem equation [14],
ꢀ
ꢁ
ꢀ
ꢁ
g(˛)
T2
AR
ꢅE
2RT
Ea
Ea
log
= log
1 −
−
(1)
2.1
2.15
2.2
2.25
2.303 RT
1000/T
where g(˛) = [(Wf)/(Wf − W)]. In the present case, a plot of L.H.S (left
hand side) of this equation against 1/T gives straight line (Fig. 7)
whose slope and intercept are used to calculate the kinetics param-
eters by the least square method. The goodness of fit was checked
103.T-1(0C)
log(W )/(W −W)
f
f
Fig. 7. Coats–Redfern plots of NiL1(prldn) complex, step 1, A =
.
2
T

A.H. Kianfar et al. / Spectrochimica Acta Part A 94 (2012) 302–307
307
where k, h and Ts are the Boltsman constant, the Planck’s con-
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4. Conclusions
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Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2012.03.039.