Synthesis, characterization and thermal study of some tetradentate Schiff base transition metal complexes

Article abstract of DOI:10.1007/s10973-009-0205-2

Several mononuclear Co(II), Ni(II), Cu(II), and Fe(II) complexes of tetradentate salpren-type diimine, obtained from 3,5-di-tert-butyl-2- hydroxybenzaldehyde and 1,3-diaminopropane have been prepared and characterized by analytical, spectroscopic (FT-IR,

Full text of DOI:10.1007/s10973-009-0205-2

J Therm Anal Calorim (2009) 98:785–792
DOI 10.1007/s10973-009-0205-2
Synthesis, characterization and thermal study of some
tetradentate Schiff base transition metal complexes
¨
¨
Fatih Do g˘ an Æ Mahmut Ulusoy Æ Omer F. Ozt u¨ rk Æ
Ismet Kaya Æ Bekir Salih
_
Received: 19 March 2009 / Accepted: 5 June 2009 / Published online: 28 August 2009
Ó Akad e´ miai Kiad o´ , Budapest, Hungary 2009
Abstract Several mononuclear Co(II), Ni(II), Cu(II), and
Fe(II) complexes of tetradentate salpren-type diimine,
obtained from 3,5-di-tert-butyl-2-hydroxybenzaldehyde and
Introduction
Intermolecular electron transfer is a fundamental chemical
phenomenon and relates specifically to redox processes
which occur in both natural and synthetic electron-transfer
systems [1]. The ability of metal ions to control the oxi-
dation potentials of organic molecules by complexation has
a significant role in biological electron-transfer processes,
molecular electronics and also in catalysis [2]. The Ni(II)
ions play a central role in biological redox metalloenzymes
like plastocyanin, hemocyanin, azurin, galactose oxidase
and others [3]. It should be noted that while the chemistry
of metal complexes with salen-type and other polydentate
ligands bearing 2,4-t-butyl moieties has been extensively
studied because of their efficient catalytic activity and their
use as model complexes for metalloproteinase having
metal centers and proximal organic radicals in their active
site[4]. Tetradentate Schiff base complexes have been
extensively studied. Kumar [5] has investigated the thermal
stabilities of some new cobalt complexes. The decompo-
sition mechanism and kinetic parameters of a complex of
1
,3-diaminopropane have been prepared and characterized
by analytical, spectroscopic (FT-IR, UV–VIS) techniques,
magnetic susceptibility measurements and thermogravi-
metric analyses (TG). The thermodynamic and thermal
properties of complexes have been investigated. For further
characterization Direct Insertion Probe-Mass Spectrometry
(
DIP-MS) was used and the fragmentation pattern and also
stability of the ions were evaluated. The characterization
of the end products of the decomposition was achieved by
X-ray diffraction. The thermal stabilities of metal complexes
0
of N,N -bis(3,5-di-t-butylsalicylidene)-1,3-propanediamine
ligand (L) were found as Ni(II) [ Cu(II) [ Co(II) [ Fe(II).
Keywords Activation energy ꢀ Sterically hindered
diimine ꢀ Thermal decomposition ꢀ Transition
metal complexes
0
N,N -etylenebis(salicylideneiminato) diaquochromium(III)
nitrate, [Cr(salen)(H O)]NO was studied by Wang [6].
F. Do g˘ an (&)
Faculty of Education, Secondary Science and Mathematics
Education, C¸ anakkale Onsekiz Mart University,
17020 Canakkale, Turkey
e-mail: fatihdogan@comu.edu.tr
2
3
Also, Do g˘ an et.al. [7, 8] have investigated the thermal
behavior, kinetic and thermodynamic parameters of various
metal complexes and salts using TG/DTG, DTA.
M. Ulusoy
Department of Chemistry, Faculty of Science,
Ege University, 35100 Izmir, Turkey
In the present work, the synthesis, spectroscopic charac-
terization of the Cu(II), Ni(II), Co(II) and Fe(II) complexes
from Schiff base (L) formed from 3,5-di-tert–butyl-2-
hydroxybenzaldehyde and 1,3-diaminopropane are reported
except Cu(II) and Ni(II) complexes since they have been
published before [9] and we have also investigated thermal
behaviors and thermodynamic properties of synthesized
complexes to understand the mechanisms of decomposition
and thermodynamic parameters. In the decomposition
¨
¨
_
O. F. Ozt u¨ rk ꢀ I. Kaya
Department of Chemistry, C¸ anakkale Onsekiz Mart University,
1
7020 Canakkale, Turkey
B. Salih
Department of Chemistry, Faculty of Science,
Hacettepe University, Ankara, Turkey
123

7
86
F. Do g˘ an et al.
kinetic study, the integral methods employing the Coats–
Redfern [10], van Krevelen [11], MacCallum–Tanner [12],
Madhusudanan–Krishnan–Ninan equations [13] and the
approximation method Horowitz–Metzger equation [14]
were used for the calculation of kinetic and thermodynamic
parameters such as the reaction order n, the activation
energy E, the pre-exponential factor A, the entropy change
Initial temperature was set to 50 °C for 10 min and then
temperature was increased up to 420 °C with 10 °C min
temperature ramp. Finally temperature was hold at 420 °C
for 50 min.
-
1
Synthesis of Co(II) and Fe(II) complexes
#
#
0
DS , the enthalpy change DH , and the Gibbs free change
One mmole N,N -bis(3,5-di-t-butylsalicylidene)-1,3-pro-
panediamine was dissolved in 30 mL absolute methanol and
#
DG . Also the heat capacity is calculated from the results of
differential scanning calorimetry (DSC).
1 mmole Co(OAc) ꢀ 4H O or FeCl ꢀ 4H O in 10 mL
2
2
2
2
methanol were mixed. Desired products were precipitated
immediately. The stirred mixture was refluxed for 60 min.
The mixture was evaporated to 15–20 mL left to cool to room
temperature. The complexes were filtered off, washed with a
Experimental
Instrumental
small amount of methanol/H O (1:1) and filtered in vacuo
2
again. All complexes recrystallized in CH Cl /Ethanol(1/3).
2
2
3
,5-di-tert–butyl-2-hydroxybenzaldehyde (3,5-DTB) was
synthesized according to the literature procedure [15],
,3-diaminopropane is purchased from Aldrich (pure) and
used without purification. The elemental analyses were
1
Results and discussions
_
determined in the TUBITAK Laboratory (Turkish Scien-
Characterization of Co(II) and Fe(II) complexes
tific and Technological Research Council), IR spectra were
recorded on a Perkin Elmer Spectrum RXI FT-IR Spec-
trometer as KBr pellets, Magnetic Susceptibilities were
determined on a Sherwood Scientific Magnetic Suscepti-
bility Balance (Model MK1) at room temperature (20 °C)
The analytical data for all these were presented in Table 1. In
the spectrum of ligand, a strong band observed in the IR
-
1
spectra of the free ligand in 1,630 cm region which is
attributed to the C=N strech, showed a negative shift to
-
1
using Hg[Co(SCN) ] as a calibrant; diamagnetic correc-
ca. 1,615–1,623 cm in the spectra of all the complexes,
indicating coordination of the azomethine nitrogen atom to
metals [17]. The salpren ligand shows a strong and broad OH
4
tions were calculated from Pascal’s constants [16], UV
spectra were recorded on a Schimadzu 1601 PC. The
residual end products of heating were identified by X-ray
powder diffractometry using a Rigaku DMAX 2200 XRD
instrument (Cu lamp, kKa = 1,5418, Rigaku, Tokyo,
Japan). Thermogravimetric (DTG/TG) curves were per-
formed on a Seteram Labsys TG-16 thermobalance, oper-
ating in dynamic mode, with the following conditions;
sample mass *5 mg, heating rate = 10 °C/min, atmo-
-
1
band centered at 3,400 cm due to the phenolic O–H bonds.
The position and the broadness of the band are indicative of
hydrogen bonding between the phenolic protons and the
imine nitrogen atoms. This OH band disappeared while the
complexation of the ligand with Co(II) ion due to breaking
off the phenolic protons. On the other hand, Fe(II) (salpren)
-
1
complex shows a broad band at 3,446–3,346 cm indicat-
ing the coordination of water molecule to metal center. The
decomposition temperature and the mass losses of the
complexes were calculated from the TGA data. Observed
mass loss for the Fe(II) (salpren) complex from the TGA data
is 3.14%. This suggests that Fe(II) (salpren) complex has 1
mole water per complex molecule in the coordination sphere.
This is also supported by the elemental analysis data. The
structure recommended is shown in Scheme 1.
3
-1
sphere of nitrogen (10 cm min ), sealed platinum pan.
The DSC curves were obtained using DSC–60 Schimadzu
apparatus (heating rates of 10 °C/min, aluminum crucible,
mass *5 mg, in nitrogen atmosphere).
Ligand (L) and its metal ion complexes, such as Co(II),
Ni(II), Cu(II) and Fe(III)-complexes, were analyzed using
Agilent 5973 Inert Mass Selective Detector equipped with
Direct Insertion Probe (HPP7&ProbeDirect, Scientific
Instrument Services, Ringoes, NJ USA). About 1 mg of the
ligand and its complexes were weighted and then inserted
inside the quartz sample tube (Scientific Instrument Ser-
vices, Ringoes, NJ USA) that was used for inserting the
sample inside mass spectrometer. At the mass spectrometer
part, Electron Impact Ionization (EI) source was used, the
temperature of the source was set to 140 °C, vacuum was
The electronic spectral data of the synthesized ligand
was recorded in chloroform solutions. In the spectrum of
the Schiff base ligand, the aromatic bands at 220–265 nm
are attributed to a benzene p ? p* transition. The band at
425 nm is assigned to the imino p ? p* or n ? p* tran-
sition [18]. The electronic Spectra of the complexes were
examined in chloroform solvent. The bands below 420 nm
have very high extinction coefficients and are almost cer-
tainly associated with intraligand p ? p* and n ? p*
-
6
1
.5 9 10 Torr during the recording of mass spectra. The
Direct Insertion Probe program was set as given below:
1
23

Synthesis, characterization and thermal study of some tetradentate Schiff base transition metal complexes
787
Table 1 The colors, formulas, formula masses, melting points, magnetic susceptibilities, yields and elemental analyses results of the complexes
-
1
Compounds
F.W./g mol
Color
m.p./°C Yield/% leff [B.M] Elementel analyses/% calculated (found) C H N
Co(II) (salpren) C33
H
48
N
2
O
2
Co 563.68
Dark brown 153
73
68
1.8
70.32 (70.65)
68.50 (68.33)
8.58 (8.64)
8.71 (8.56)
4.97 (4.50)
4.84 (4.54)
Fe(II) (salpren) C33
H
50
N
2
O
3
Fe 78.61
Purple
158
5.35
Scheme 1 Synthetic route to
the metal complexes
Co(II) or Fe(II) salt
MeOH
N
N
N
N
M
O
OH HO
O
.
M = Co(II) and Fe(II) H O
2
Table 2 IR and electronic spectral data for salpren, Co(II) and Fe(II) (salpren) complexes
-
1
-1
Compounds
IR spectra/cm
Electronic spectra*/k nm
tO–H
tC = N
Salpren
3,410
–
1,630
1,623
1,615
230
266
274
263
356
330
332
406
533
425*
512*
605*
Co(II) (salpren)
Fe(II) (salpren)
644*
2
3,446 (H O)
*
Shoulder
transitions, and absorptions at 420–500 nm are assigned to
metal-to-ligand charge transfer (MLCT) transitions. The
weak shoulder bands over 500 nm is because of the d ? d
transitions. The colors, formulas, formula masses, melting
points, magnetic susceptibilities, yields, elemental analy-
ses, IR and electronic spectral data obtained for the com-
pounds described in this work are summarized in Tables 1
and 2. The magnetic behavior of the Fe(II) complex of
salpren is consistent with the fact that this complex has four
unpaired electrons and suggests that they have distorted
structures with considerable delocalization.
the main peak of the ligand obtained at 5.6 min retention
time, some other decomposition peaks were observed.
When the mass spectrum of the main peak on the total ion
chromatogram was evaluated, it was noticed that this
compound corresponded to the mass spectrum of L exactly.
In the mass spectrum given in Fig. 1b, the peaks appeared
at 506, 491, 260, 246, 219, 232, 57 and 238 atomic masses
?
?
?
characterized the M , [M-15] , [C H NO] , [C H
16 24
1
7
26
?
NO] , [C H NO-27] , [C H NO-28] , [(CH ) C]
?
?
?
1
6
24
17 26
3 3
2
?
and [M-15-15] . Especially, the peak with high intensity
at 238 nominal atomic mass is really interesting and rep-
resents a very stable doubly charged ion of the ligand in
EI-Mass spectrometry, which is unexpected. The doubly
charged ion’s stability is because of the high volume of
ligand and the charged locations are far enough away from
each other to eliminate charge repulsion.
Magnetic moments (4.09 BM) of the cobalt(II) complex
at room temperature, which suggests a spin quartet state
S = 3/2 in a tetrahedral geometry [19]. According to the
electronic spectrum and magnetic measurements the iron
atom is pentacoordinated in a square-pyramidal geometry,
with the tetradentate salpren ligand in a square planar
coordination, by two nitrogen and two oxygen atoms, with
the aqua ligand in an apical position [20].
When mass spectra of metal complexes of this ligand
were interpreted, similar fragmentations were observed but
doubly charged ion intensity of the complexes accompa-
nied by the elimination or two methyl groups from both
bulky sides of the complexes were found to be higher than
the intensity of the same peak of pure ligand. For the metal
complexes, the mass of the peaks observed on mass spectra
with their per cent intensities are given in Table 3.
GC-MS studies
Mass spectrum of L is given in Fig. 1 with the total ion
chromatogram of L. On the total ion chromatogram, beside
123

7
88
F. Do g˘ an et al.
A
A
25
20
15
10
5
15
10
5
0
0
0
20
40
60
80
2
4
6
8
10
Retention time/min
Rentention time/min
B 1.4
1.2
B 3.0
2
.5
1.0
0
0
0
.8
.6
.4
2
.0
1
1
0
0
.5
.0
.5
.0
5
55 560 565 570
0.2
.0
0
0
100
200
300
m/e
400
500
600
0
100
200
300
m/e
400
500
600
Fig. 2 Total ion chromatogram (a) and mass spectrum of L-Cu (II)
complex (b). Mass spectrum was obtained at 41.4 retention time
Fig. 1 Total ion chromatogram (a) and mass spectrum of L ligand
b). Mass spectrum was obtained at 5.6 retention time
(
69.17% and 30.83% naturally abundance. The doubly
charged ion of the complex formed upon the leaving of two
methyl groups from both bulky sides of the complex yielded
again two peaks appeared at 269 and 270 nominal masses
In order to evaluate the high intense doubly charged ion
which is overlapped with one intense fragment ion of the
pure ligand further, mass spectra of copper complex of L
with the total ion mass chromatogram of the complex is
given in Fig. 2. Following the isotopic peak masses and
intensities of copper in the complex, the stability of doubly
charged ion intensity yielded from metal complex of L could
be examined. Evaluating the isotopic peak masses and
intensities of copper in either single charge molecular ion or
doubly charged molecular ion form, the presence of doubly
charged ions in the spectrum could be examined clearly.
Single charged molecular ions at 567 and 569 nominal
13
again showing the copper isotope distribution with C.
These results clearly show that complex yields high intense
(very stable) double charged ion loosing two methyl groups.
Thermodynamic and thermal studies
The complexes exhibited an endothermic process. The area
of the endothermic peak corresponds to the heat of fusion
and the peak temperature corresponds to the melting point.
?
?
masses are the M and [M ? 2] characterizing the most
The melting (T
complexes are given in Table 4. The heat capacities C
p
) and transition temperatures (T
1
, T
2
) of the
of
6
3
65
abundant copper isotopes, which have Cu and Cu with
p
Table 3 Mass and intensity (%) of the peaks were evaluated from mass spectra of the studied complexes
Cobalt complex
Nickel complex
Iron complex
Copper complex
Nominal Intensity Type of ion Nominal Intensity Type of ion
mass
Nominal Intensity Type of ion
mass
Nominal Intensity Type of ion
mass
mass
?
?
?
?
5
63
67
100
77.9
M
562
266
100
79.8
M
560
265
100
[M ? 2]
567
269
97.8
100
M
2
?
2?
2?
2
[M-15-15]
[M-15-15]
50.4
[M-15-
1
[M-15-15]
2
?
5 ? 2]
?
?
?
5
48
62.5
[M-15]
547
564
56.3
[M-15]
545
34.5
[M-15]
270
56.9
[M-15-
1
2?
5 ? 2]
?
?
?
?
5
2
7
24.7
12.2
[(CH
3
)
3
C]
46.0
41.3
[M ? 2]
57
16.7
7.4
[(CH
?
3
)
3
C]
552
569
50.9
49.1
[M-15 ? 2]
?
[M ? 2]
?
26NO] 267
60
[C17
H
[M-15-
1
558
[M]
2?
5 ? 2]
2
?
?
2?
?
231
216
259
4.5
4.4
4.2
[L-15-15]
57
30.4
18.1
9.4
[(CH
3
)
3
C]
264
5.1
4.0
3.9
[M-15-15]
260
23.8
3.4
[C17
H
26NO]
25NO]
?
18NO] 260
?
?
[C14H
[C17H
26NO] 216
529
[C14H18NO] 250
?
?
238
[M-15-16]
247
9.6
[C16H
1
23

Synthesis, characterization and thermal study of some tetradentate Schiff base transition metal complexes
789
Table 4 The TG data for salpren, Co(II), Ni(II), Cu(II), and Fe(II) complexes
Complex
C
p
/
T
p
/°C First
DTGmax/ Mass loss, Dm Second DTGmax/ Mass loss, Dm Third
calc./found/% step/°C °C calc./found/% step/°C
Residue Calc./
found/%
1
-
kJ g °C
step/°C °C
1
Salpren
1.89
147.78 253–328 317
145.79 363–420 413
141.42 351–405 336
147.53 329–420 380
151.57 162–190 181
96.0 (–)
–
–
–
–
–
3.91 (–)
Ni(II) (salpren) 2.91
Cu(II) (salpren) 3.81
Co(II) (salpren) 2.35
Fe(II) (salpren) 2.50
88.3 (86.9)
86.2 (87.2)
85.2 (86.8)
3.6 (3.1)
420–570 –
405–600 –
420–610 –
346–375 361
–
–
NiO
CuO
CoO
FeO
11.7 (13.1)
13.8 (12.8)
14.8 (13.2)
15.3 (12.4)
–
–
–
–
81.1 (84.6)
375–
6
10
0
2
.00
0.0
mass loss in the temperature range 351–405 °C. The next
decomposition step occurs in the temperature 405–600 °C
and corresponds to the formation CuO (calc./found:
13.8/12.8%) (Table 4). Fe(II) complex is thermally stable
up to 162 °C and undergoes decomposition beyond this
temperature, as indicated by the first mass loss step in the
TG curve. The mass loss at this temperature corresponds
5
1
1
%
0 %
5 %
20 %
1
2
3
4
5
-salpren,L
-FeL.H O
1
234 5
2
-CoL
-CuL
-NiL
to elimination of H O (calc./found: 3.6/3.1%). The second
2
5
1
%
0 %
decomposition step starts to 346 °C and continues 375 °C.
After decomposition, the mass loss at 375–610 °C corre-
spond to the formation of FeO (calc./found: 15.3/12.4%).
The end products were conformed with the XRD data.
An as example the X-Ray pattern of the end product of
Ni(II) complexes can be shown in Fig. 4.
1
2
5 %
0 %
8
0.0
1
00.0
1
50 200 250 300 350 400 450 500 550 600
Temperature/°C
The kinetic of heterogeneous condensed phase reactions
that occur in nonisothermal conditions is usually described
by equation,
Fig. 3 The TG curves of ligand and its complexes
bðda=dTÞ ¼ A fðaÞ exp ðꢁE=RTÞ
ð1Þ
the complexes were calculated from DSC results and given
in Table 4. The TG curves of the complexes are shown in
Fig. 3 and were studied in greater detail. All complexes
were studied by thermogravimetric analysis from ambient
temperature to 700 °C in nitrogen atmosphere. The tem-
perature ranges and percentage mass losses are given in
Table 4, together with the temperatures of greatest rate of
decomposition (DTGmax) and the theoretical percentage
mass loss. Thermal curves obtained for most of the com-
pounds were very similar in character. All complexes show
two distinct steps mass loss except Fe(II) complex and
salpren ligand [L] in their TG/DTG curves. Salpren ligand
is one step and starts to decompose 253 °C and this step
continues up to 328 °C. The TG curve of Co(II) complex
indicates that the mass change begins at 329 °C and con-
tinuous up to 420 °C. The next decomposition step occurs
in the temperature range 420–610 °C and corresponds to
the formation of CoO (calc./found: 14.8/13.2%) (Table 4).
The Ni(II) complex was stable up to 363 °C. The first step
of thermal decomposition was completed at 420 °C. The
second decomposition step starts to 420 °C and continues
where a is the degree of conversion, b is the linear heating
rate, and A is pre-exponential factor, and f(a) is the dif-
ferential conversion function. For calculate kinetic
parameters, the different reaction models may be used. The
n
fraction mass loss, a and corresponding (1 - a) are cal-
culated from TG curves, where n depends upon the reaction
120
100
80
50
4
2
0
0
20
30
40
50
2θ/degree
5
70 °C. The solid residue was NiO (calc./found:
1
1.7/13.1%) (Table 3). The TG of Cu(II) complex reveal a
Fig. 4 X-Ray powder diffraction pattern of NiO
123

7
90
F. Do g˘ an et al.
model. In studying the decomposition kinetic, five methods
in the literature were chosen: Coats–Redfern (CR), Horo-
witz–Metzger (HM), van Krevelen (vK), MacCallum–
Tanner (MC) and Madhusudanan–Krishnan–Ninan meth-
ods(MKN) and the methods may be expressed by following
equations,
(Eqs 2, 4–6) against 1/T, for van Krevelen equation (Eq. 3)
the left-hand side is plotted against ln T. The values E and
A were calculated from the slope and intercept of the
straight lines, respectively.
According to Coats and Redfern method, the plot of ln
2
(g(a)/T ) versus 1/T gives straight line with slope equals to
-
E/R. The activation energies of complexes were calcu-
1
.
The Coats–Redfern method
lated from the slope of Arrhenius curves and given Table 5.
The second method of calculation of activation energy
E, was developed by Madhusudanan–Krishnan–Ninan.
According to this method, a relationship between ln
ꢀ
ꢁ
2
ln g(aÞ=T ¼ ln½ðAR=bEÞð1 ꢁ ð2RT=EÞÞꢂ ꢁ ðE=RTÞ
ð2Þ
1
,9206
(
g(a)/T
) versus 1/T in same conditions is constructed.
The other method used to calculate the activation energies
is that of MacCallum–Tanner. The activation energy of
decomposition can be thus determined by Eq. 4. From the
plot it is possible calculate the activation energies from the
slopes. The activation energies of the ligand and complexes
2
.
The van Krevelen method
h
i
Ea=RTm
ln gðaÞ ¼ Að0:368=TmÞ
=bðEa=RTm þ 1Þ
þ ððE =RT Þ þ 1Þ ln T
ð3Þ
ð4Þ
a
m
-
1
are between 114.3 and 276.1 kJ mol . The activation
energy was also determined by the method of van Krevelen
-
1
3
.
The MacCallum–Tanner method
in nitrogen for mass loss thermograms of 10 °C min and
can calculated from slopes of the log g(a) against ln T plot.
Finally, in case of Horowitz–Metzger method the activa-
tion energies were calculated from the slopes of the ln g(a)
versus O– plots as 245.36, 156.43, 145.33, 176.94 and
0
:4351
log gðaÞ ¼ logðAE=RTÞ ꢁ 0:4828 E
ꢁ ðð0:449
ꢁ
3
þ 0:217 EÞ=10 TÞ
-
1
168.32 kJ mol
.
For all methods, determination of the pre-exponential
4
.
The Madhusudanan–Krishnan–Ninan method
factor and reaction order is possible from the expression of
1
:9206
ln[gðaÞ=T
ꢂ ¼ lnðAE=RTÞ þ ð3:7678 ꢁ 1:9206 ln E
0:12040ðE=TÞÞ
g(a) in Eq. 3 and n = 1:
ꢁ
1ꢁn
gðaÞ ¼ 1 ꢁ ð1 ꢁ aÞ = 1 ꢁ n
ð5Þ
Moreover, Table 5 summarizes the reaction orders, pre-
exponential factors, correlation coefficients and the
activation energies obtained by the five different methods
examined in this study. The results are in good agreement
with the values obtained from all of them. The results
indicate that the values of all methods are comparable.
They are similar to the values given in the literature for
salpren ligand and metal complexes.
5
.
Horowitz–Metzger method
The Horowitz–Metzger method introduced a characteris-
tic temperature T and a parameter O– such that O– = T - T .
If the reaction order is 1, T is defined as the tempera-
m
m
m
ture at which (1 - a) = 1/e = 0.368 and the final
expression is:
m
As seen in Table 5, the value of correlation coefficients
of linearization curves of salpren ligand and metal com-
plexes are approximately 1.00 and values of reaction orders
are around 1.00 for complexes. The kinetic data obtained
by different methods agree with each other.
2
lnln gðaÞ ¼ Eh=RT
If the reaction order is unknown, Tm is defined for the
maximum heating rate.
m
When O– = 0, (1 - a) = (1 - a)m and (1 - a) =
and,
m
#
#
1
/1-n
The enthalpy DH , activation entropy DS , and the free
n
#
energy of activation DG , of the complexes and salpren
ligand were calculated using the following relations [21]:
2
2
m
ln gðaÞ ¼ lnðART =bEÞ ꢁ ðE=RTmÞ þ ðEh=RT Þ ð6Þ
m
A plot of ln g(a) versus O– can yield activation energy.
#
#
DS ¼ 2:303 log ðAh=kTÞR; DH ¼ E ꢁ RT; DG
In the equations above, g(a), T , E, R, are the integral
#
m
¼
DH ꢁ TDS
function of conversion, DTG peak temperature, activation
-1 -1
-
energy (kJ mol ), and gas constant (8.314 J mol
1
K
),
where h is the Planck constant and T is the temperature,
A is the pre-exponential factor. The thermodynamic
parameters calculated were reported in Table 5.
respectively. The kinetic parameters were calculated from
the linear plots of the left-hand side of kinetic equations
1
23

Synthesis, characterization and thermal study of some tetradentate Schiff base transition metal complexes
791
Table 5 The kinetic data on metal complexes of salpren
-
1
-1
#
-1 -1
K
#
-1 -1
K
#
-1 -1
K
Method Complexes
n
E/kJ mol
ln A/min
Correlation
coefficient, r
DS /J mol
DH /J mol
DG /J mol
CR
Salpren ligand
Ni(II) salpren
Cu(II) salpren
Co(II) salpren
0.7 111.8
1.1 170.3
0.7 207.6
0.8 147.9
22.79
28.79
47.00
24.65
50.35
39.67
20.63
27.63
46.97
26.16
52.23
39.73
29.14
78.38
56.33
32.98
58.70
48.76
12.15
12.71
12.74
11.78
12.15
12.51
0.99934
0.99818
0.99748
0.99643
0.99621
0.99790
0.99935
0.99838
0.99750
0.99787
0.99636
0.99791
0.99944
0.99476
0.99768
0.99821
0.99649
0.99809
0.99925
0.99848
0.99734
0.99665
0.99612
0.99812
-61.12
-12.45
139.2
106.89
164.60
202.04
142.47
193.53
214.33
107.19
171.11
266.54
159.47
207.33
214.53
109.39
167.71
270.54
142.27
192.63
217.43
144.49
214.00
296.74
178.47
211.93
248.83
142.95
173.13
108.90
172.81
116.22
164.44
153.86
186.27
173.62
181.63
122.96
164.34
114.33
-106.61
125.56
127.41
83.831
119.64
232.73
314.31
394.25
278.74
278.83
342.17
-46.45
170.2
Dehydradation 0.9 197.3
Fe(II) salpren
Salpren ligand
Ni(II) salpren
Cu(II) salpren
Co(II) salpren
Dehydradation
Fe(II) salpren
Salpren ligand
Ni(II) salpren
Cu(II) salpren
Co(II) salpren
0.7 219.6
0.7 112.1
78.68
MKN
MC
HM
-79.09
-22.12
138.8
1
176.8
0.7 272.1
1
1
164.9
211.1
-33.96
185.8
0.7 219.8
0.7 114.3
1.1 173.4
0.7 276.1
0.7 147.7
79.16
-8.357
399.9
216.7
22.75
Dehydradation 0.9 196.4
239.6
Fe(II) salpren
Salpren ligand
Ni(II) salpren
Cu(II) salpren
Co(II) salpren
Dehydradation
Fe(II) salpren
0.7 222.7
149.4
154.2
1
-149.6
-146.2
-145.8
-153.6
-147.4
-147.2
1.4 219.7
0.8 302.3
1.2 183.9
1
215.7
0.9 254.1
The activation energy and Gibbs free energy of the
complexes is expected to increase proportional to the
decrease in their radii. Complexes of Cu, Ni and Co have a
square-planar geometry and show similar decomposition
steps, the smaller size of Cu(II) as compared to Co(II) and
Ni(II) permits a closer approach of the ligand to Cu(II) ion.
Hence the E value for the Cu(II) complex is higher than
that of Co(II) and Ni(II). The E values for thermal
decomposition with respect to the above methods can be
put into a descending order as, ECu [ E [ E . The
leaving from both sides of the ligand and its metal ion
complexes was really high. This is the case of the location
of these two doubly positive charged ion enough far away
from each other due to the bulky structure of the species.
Isotopic distribution of the metal complexes of the ligand
was yielded new information to evaluate of the exact
fragmentation of the complex especially for the doubly
charged ion stability. The TGA curves of all the com-
pounds show almost a similar decomposition when heated
about 700 °C. The complexes prepared with different
metals decompose in two-step process. Using the CR, HM,
MT and MKN methods performed kinetic analysis of the
thermogravimetric data. The activation energies obtained
by non-isothermal conditions are compared. The thermal
stabilities of metal complexes of salpren ligand were found
as Ni(II) [ Cu(II) [ Co(II) [ Fe(II). These study show
that there is a relationship between the ionic radius of the
metal and the thermal stability of the complex [22, 23]. The
melting points of the complexes increase in order;
Fe(II) [ salpren [ Co(II) [ Ni(II) [ Cu(II) corresponding
the numerical values in Kelvin; 151.57, 147.78, 147.53,
145.79 and 141.42 in same order.
Ni
Co
activation energies corresponding decomposition steps are
-
1
in the range of 111.8–302.3 kJ mol which indicates in
this order: Ni(II) [ Cu(II) [ Co(II). The negative values of
#
DS in the studied complexes indicate that the reaction
rates are slower than normal.
Conclusions
DIP-MS was found to be very powerful technique to
characterize complex structure. It was noticed that doubly
charged ion stability occurred by two methyl groups
123

7
92
F. Do g˘ an et al.
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