Synthesis, characterization, and thermal decomposition of fluorinated salicylaldehyde Schiff base derivatives (salen) and their complexes with copper(II)

Article abstract of DOI:10.1007/s10973-009-0453-1

Trifluoromethoxy functionalized copper(II) Schiff base complexes N,N′-bis(5-trifluoromethoxysalicylaldehyde) cyclohexanediiminatodiaquacopper(II) and N,N′-bis(5- trifluoromethoxysalicylaldehyde)phenylenediiminatocopper(II) were synthesized and characteriz

Full text of DOI:10.1007/s10973-009-0453-1

J Therm Anal Calorim (2010) 101:199–203
DOI 10.1007/s10973-009-0453-1
Synthesis, characterization, and thermal decomposition
of fluorinated salicylaldehyde Schiff base derivatives (salen)
and their complexes with copper(II)
¨
¨
¨
Gokturk Avsar Æ Huseyin Altinel Æ
Mustafa Kemal Yilmaz Æ Bilgehan Guzel
Received: 30 June 2009 / Accepted: 27 August 2009 / Published online: 11 September 2009
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract Trifluoromethoxy functionalized copper(II)
Schiff base complexes N,N0-bis(5-trifluoromethoxysalicyl-
aldehyde)cyclohexanediiminatodiaquacopper(II) and N,N0-
bis(5-trifluoromethoxysalicylaldehyde)phenylenediimina-
tocopper(II) were synthesized and characterized. Thermal
decompositions of the synthesized complexes were studied
by thermogravimetry in order to evaluate their thermal
stability and thermal decomposition pathways. Three sim-
ilar decomposition steps occurred for the two copper
complexes. Mass losses and evolved gasses were charac-
terized by
studied in catalyzing several transformations of organic
molecules due to the versatility of their steric and elec-
tronic properties [2–4]. Copper(II) complexes of salen have
been used in the aziridination and cyclopropanation of
olefins and phenol oxidation [5].
Fluorinated derivatives of Schiff base ligands have
widely been studied in alternative solvent systems such as
bi-phasic reactions and supercritical carbon dioxide
(scCO2) due to the solubility properties. scCO2 is emerging
as an alternative solvent for various chemical transforma-
tions, because it is non-toxic and environmentally benign
[6]. Although the structure, scCO2 solubility, and catalytic
activity of fluorinated salen were studied previously [7, 8],
no thermal decomposition data have been reported in the
literatures. Differential thermal analysis (DTA) and ther-
mogravimetric (TG) are useful to study the modes of
thermal decompositions as well as the composition of some
metal complexes of Schiff bases [9]. This article reports the
synthesis, characterization, and detailed thermal decom-
positions of fluorinated salen copper(II) complexes. The
decomposition kinetic parameters such as reaction order, n,
the activation energy, E*, entropies, DS*, and the pre-
exponential factor, A, were calculated by using the equa-
tion Coats–Redfern of integral method and the equation
Horowitz–Metzger of approximation method.
TG/DTA-MS. Kinetic parameters were calculated and the
results showed that the values obtained are comparable.
Keywords Schiff base ꢀ Salen ꢀ Copper(II) complexes ꢀ
Thermal decomposition ꢀ Coupled TG/DTA-MS
Introduction
Over the past three decades, there have a number of
important advances in the development of general methods
for catalytic reactions. Schiff bases derived from salicyl-
aldehyde and diamines, as N,N0-bis(salicylaldehydo) ethy-
lenediamine (H2-salen), are one of the most important
synthetic ligands systems in asymmetric catalysis [1].
Transition metal complexes of salen have been extensively
Experimental
G. Avsar (&)
Reagent and physical measurements
Chemistry Department, Faculty of Science and Letters,
Mersin University, 33342 Mersin, Turkey
e-mail: gavsar@mersin.edu.tr; gokturkavsar@yahoo.com
All chemicals were of reagent grade quality and used as-
received. The DTA, TG curves, and mass spectra (MS) are
obtained with Perkin-Elmer model working simultaneously
with DTA and TG apparatus combined with Pfeifer model
H. Altinel ꢀ M. K. Yilmaz ꢀ B. Guzel
Chemistry Department, Faculty of Science and Letters,
C¸ ukurova University, 01330 Adana, Turkey
123

200
G. Avsar et al.
MS system. The heating rate and other characteristics are
given as follows: heating rate—10 K min-1, atmosphere—
Table 1 Analytical data for copper(II) complexes
Compound
Found (calc.)/%
nitrogen, flow rate of furnace atmosphere—100 mL min-1
,
C
H
N
Cu
crucible—Platinum, sample size—5–10 mg, reference
CuL1
CuL2
44.7 (44.9)
48.3 (48.4)
3.8 (3.7)
2.3 (2.2)
4.6 (4.7)
4.9 (5.1)
10.7 (10.8)
11.6 (11.7)
substance—a-Al2O3.
MS system, Pfeifer model, was used to identify pyro-
lysis products evolved during heating. IR spectra were
recorded on a Perkin-Elmer Mattson 1000 FT-IR spec-
trometer as KBr pellets in the range of 4000–400 cm-1
Table 2 Selected IR data for ligands and complexes (cm-1
)
.
Elemental analyses were recorded on a LECO CHNS-932
analyzer for C, H, and N, and Hitachi 180-80 polarized
Zeeman Atomic Absorption spectrometer for Cu.
Compound
t(–HC=N)
t(C–N)
t(C–O)
t(Cu–O)
L1
L2
CuL1
CuL2
1635(s)
1612(s)
1596(w)
1573(w)
1377(m)
1391(m)
1417(w)
1427(w)
1258(s)
1243(s)
1313(m)
1319(m)
–
–
Synthesis
981(w)
978(w)
Preparation of the Schiff bases
s strong, m medium, w weak
The fluorinated Schiff base was prepared essentially as
described in the literature [10]. For preparation of ligands, an
ethanol solution of 2-hydroxy-5-(trifluoromethoxy)benzal-
dehyde (3.15 mmol) was added dropwise, at room temper-
ature, to a solution of (1R,2R)-cyclohexane-1,2-diamine (for
L1) or 1,2-diaminobenzene (for L2) (1.55 mmol) in 30 mL
ethanol, yielding a large amount of yellow precipitate
[2-((E)-((1R,2R)-2-((E)-2-hydroxy-5-(trifluoromethoxy)benzyl
ideneamino)cyclohexylimino)methyl)-4-(trifluoromethoxy)-
phenol = L1 and 2-((E)-(2-((E)-2-hydroxy-5-(trifluoromethoxy)
benzylideneamino)phenylimino)methyl)-4-(trifluoromethoxy
phenol = L2]. The mixture was stirred for 30 min at room
temperature and filtered under vacuum. Crystallization
from dichloromethane gave the spectroscopically pure
product as yellow crystalline compound (yield: 89% for L1
and 91% for L2).
The analytical data for the investigated complexes are
summarized in Table 1. The calculated values were found
to be compatible with the theoretical values. According to
the recorded IR spectra, important bands for structural
assignments are given in Table 2.
Results and discussion
Characterization of the compounds
The IR spectra of the complexes were compared with salen
ligands to obtain the information about binding the ligands
to copper in the complexes. The characteristic strong band
of the azomethine (-HC=N) group were observed at 1635–
1612 cm-1 in the spectra for free ligands. This band is
shifted to the 1596–1573 cm-1 region in the copper com-
plexes, indicating the azomethine–copper coordination as
expected [12, 13]. The frequencies of the C–N stretching
bands were observed in the 1377 and 1391 cm-1 region for
ligands and in the region of 1417 and 1427 cm-1 for the
complexes. These results are in agreement with those of
reported values, in the region of 1350–1410 cm-1. The
spectra of free ligands show strong bands in the region of
1258–1243 cm-1, assigned to the C–O stretching of the
phenol group. However, after complexation of C–O group
via oxygen to Cu, these bands observed at the region of
1313–1319 cm-1, indicating the other coordination of the
Schiff bases through the phenolic oxygen atom. The band
in the 978 and 981 cm-1 region is related to the stretching
of M–O.
Preparation of copper(II) complexes
The copper(II) complexes of L1 and L2 were prepared
essentially as described in the literature [11]. A solution of
1.2 mmol of Cu(AcO)2ꢀ4H2O in 30 mL EtOH was added
to a solution of 1.2 mmol corresponding ligands in 40 mL
EtOH at room temperature. The reaction mixture was
stirred for 2 h at 80 °C. The mixture was concentrated to
20 mL to precipitate the complexes out of the solution
(Fig. 1a, b). The crude products were recrystallized from
warm dichloromethane (yield: 81% for CuL1 and 84% for
CuL2).
N
O
N
O
N
O
N
O
Cu
Cu
Thermal behavior of complexes
F3CO
OCF3
F3CO
OCF3
(b)
(a)
CuL1 and CuL2 were studied by thermogravimetric anal-
Fig. 1 Structural representations of the complexes: a CuL1, b CuL2
ysis from ambient temperature to 1200 °C under nitrogen
123

Synthesis, characterization, and thermal decomposition
201
Thermal decomposition of CuL1
atmosphere. The TG curves were redrawn as % mass loss
versus temperature, and DTG curves were redrawn as the
rate of loss of mass versus temperature. Typical TG, DTG,
and DTA curves of CuL1 and CuL2 are presented in Figs. 2
and 3, respectively, and the temperature ranges, percentage
mass losses of the decomposition reaction, and the MS
cycles are given in Table 3, together with evolved moiety
and the theoretical percentage mass losses. All decompo-
sition products were confirmed with simultaneous MS
spectra.
The DTA/TG/DTG curves of the compound are shown in
Fig. 2. From the TG curve, it appeared that the sample
decomposes in three stages over the temperature range
316–1200 °C. As it is seen from the DTA/TG/MS curves
that are shown in Fig. 2, the first decomposition occurs at a
temperature range between 316 and 353 °C with a mass
loss of 6.2% due to the loss of two moles of water, 18 m/z
that was confirmed with MS spectra curves corresponding
to cycle 14. The second decomposition can be divided into
two sub-stages, IIa and IIb, at a temperature range of (starts
at 353 °C, ends at 440 °C) 353–392 and 393–440 °C,
respectively, with a 68.6% mass loss due to the 2 moles of
C7H3F3O, 161 m/z (stage IIa) and C6H10, 82 m/z (stage IIb)
groups assigned to cycle 16 which is agreement with the
68.8% theoretical mass loss. From the DTG curve, there
There is no detectable change in TG curves up to 300 °C
for both CuL1 and CuL2 complexes. The overall losses of
mass from the TG curves are 89.97% for CuL1 and 88.59%
for CuL2. The complexes show a three-stage mass loss. All
decomposition stages were observed as nearly the same,
except the first stage mass loss for CuL1 which was
attributed to the release of water.
Cycle no
Cycle no
5
10
15
20
25
30
35
40
45
5
10
15
20
25
30
35
40
45
100
80
100
80
60
40
20
TG
TG
Endo down
Endo down
DTA
+
3
+
CF fragment of C H F O , m/z=161
DTA
7
3
3
DTG
60
DTG
40
335
76 m/z
161 m/z
18 m/z
82 m/z
509°C
600
20
69 m/z
42 m/z
161 m/z
0
200
400
600
800
1000
1200
0
200
400
800
1000
1200
Temperature/°C
Fig. 2 DTA/TG/DTG-MS curves of CuL1
Temperature/°C
Fig. 3 DTA/TG/DTG-MS curves of CuL2
Table 3 Thermoanalytical results for the investigation compounds
Sample Stage
Evolved
moietya
MS analysis/ MS cycle noa
Temperature range
DTG
T
DTA
T
Mass loss founda
(calc.)/%
m/za
(time)/min
max/°C
max/°C
DTG/°C
DTA/°C
CuL1
I
2H2O
18
14 (33.7)
16 (38.9)
316–353
353–392
393–440
320–331
353–436
335
376
335
376
6.22 (6.13)
IIa
IIb
III
2(C7H3F3O) 161
68.64 (68.84)
C6H10
82
42
2(OCN)
440–1200 440–1200
–
980, 1090
14.13 (14.21)
11.03 (10.83)
Residue Cu
CuL2
I
2(C7H3F3O) 161
14 (33.7)
19 (46.8)
328–411
412–598
328–410
411–604
369
509
–
310 melting 369 58.92 (59.09)
II
III
C6H6
76
42
–
14.31 (13.95)
15.38 (15.41)
11.41 (11.55)
2(OCN)
27–36 (67.4–90.8) 608–1200 605–1200
980, 1090
Residue Cu
According to the simultaneous MS spectra results
a
123

202
G. Avsar et al.
40
20
are two maxima observed at 335 and 376 °C corresponding
to the first and the second mass losses, respectively. And
the third stage of mass loss occurs at 440–1200 °C with a
mass loss of 14.1% corresponds to the two OCN group.
And at the end of decomposition stages, metallic Cu
formed as a residue. Three endothermic peaks were noted
from the corresponding DTA curve. The first and second
peaks were observed at 335 °C as very weak and at 376 °C
as sharp maxima, respectively. The third one was observed
as a broad peak at the temperature range of 440–1200 °C.
All the decomposition steps for the evolved moiety were
simultaneously confirmed by MS data shown in Fig. 2, and
given in Table 3.
1/T X 103/K–1
1,5
0
0
0,5
1
2
2,5
3
1
-20
-40
-60
-80
CuL
2
CuL
Fig. 4 The linearization curves of Coats–Redfern method of the
decomposition stage IIa for CuL1 and stage I for CuL2 complexes
80
Thermal decomposition of CuL2
CuL2
60
40
From Fig. 3, the TG of CuL2 reveals a mass loss in the
temperature range 328–1200 °C, corresponding to the
formation of Cu as a residue. From the DTA curve, the
complex melts at 310 °C, and the first decomposition step
starts occurring at the temperature range 328–411 °C, due
to the cycle 14. Decomposition product, two moles of
C7H3F3O, 161 m/z group with a mass loss of 58.8%, is
observed from TG analysis which supported by MS curves.
The second decomposition step occurs at the temperature
range 412–598 °C due to the formation of Cu(OCN)2. The
decomposition product C6H6, 76 m/z group, was confirmed
with MS that seen at cycle 19 shown in Fig. 3. And the
third mass loss of 15.4% corresponds to the two OCN
group, 42 m/z, and at the end of decomposition, metallic
Cu formed as a residue. Except the first endothermic peak
corresponding to the melting of the compound, one broad
endothermic and one exothermic peak were observed in the
DTA analysis. The exothermic peak maxima observed at
369 °C corresponding to the first decomposition product.
The other broad endothermic peak is in the temperature
range of 605–1200 °C. All the decomposition steps for the
evolved moiety have also simultaneously been confirmed
by MS data and given in Table 3. The increasing ionic
abundance at cycle 16 belongs to the curve of 69 m/z may
CuL1
20
θ
0
-200
-100
0
100
200
300
400
500
600
700
-20
Fig. 5 The linearization curves of Horowitz–Metzger method of the
decomposition stage IIa for CuL1 and stage I for CuL2 complexes
Table 4 Kinetic data on the investigated compounds for stage IIa for
CuL1 and for stage I for CuL2
Compounds Reaction Parameters From Coats– From Horowitz–
order, n
Redfern
equation
Metzger equation
CuL1
CuL2
0.815
E*
A
191.8
228.8
2.515 9 1013 2.546 9 1016
DS*
R
32.9
62.7
0.9928
0.9924
0.962
E*
A
379.4
392.6
7.02 9 1028 1.151 9 1030
DS*
R
328.6
324.2
0.9994
0.9986
Unit of parameters: E* in kJ mole-1, A in s-1, DS* in J mole-1 K-1
r correlation coefficient of the linear plot
,
?
be assigned as CF3 fragment, which appears after the
decomposition product C7H3F3O, 161 m/z.
Decomposition kinetics
respectively. Kinetic parameters for the same decomposi-
tion stage IIa for CuL1 and stage I for CuL2 calculated by
employing the Coats–Redfern and Horowitz–Metzger
equations are summarized in Table 4. The results show the
values obtained by two methods are comparable.
Coats–Redfern [14] and Horowitz–Metzger [15] methods
were used to calculate the decomposition kinetic parame-
ters. From the TG curves, the order, n, activation energy,
E*, entropies, DS*, and pre-exponential factor, A, of the
thermal decomposition have been elucidated by the well-
known methods [14–16].
Conclusions
The linearization curves of Coats–Redfern and Horo-
witz–Metzger methods are shown in Figs. 4 and 5,
As a conclusion, the complexes have similar decomposi-
tion steps and the kinetic data reached by both of the
123

Synthesis, characterization, and thermal decomposition
203
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