Polymeric and sandwich Schiff's bases complexes derived from 4,4'-methylenedianiline : CCCharacterization and thermal investigation

Article abstract of DOI:10.1007/s10973-006-8281-z

Cobalt(II), nickel(II) and copper(II) complexes of Schiff's bases derived from 4,4'-methylenedianiline and pyridine-2-carboxaldehyde(L¹), furan-2-carboxaldehyde(L²) or thiophene-2-carboxaldehyde(L ³), were prepared and characterized by different analytical and spectral methods. The Schiff bases behave as neutral tetradentate ligands. The chloro-complexes of (L²) with (2:3) mole ratio have a polymeric nature. However, that of L¹ and L³ with (1:1) mole ratio showed a sandwich structure. All complexes display an octahedral geometry, except complex (2) which has a tetrahedral one. O _h/T _d equilibrium for chloro-complexes of cobalt with ligand L¹ was established in the solid state. ESR spectra of solid copper(II) complexes showed isotropic and axial type with dx ²-y ² ground state. The thermal study showed that the complexes with different solvents of crystallization exercise different types of interaction. The observed thermochromic phenomenon for cobalt complex was explained along with its thermal behaviour.

Full text of DOI:10.1007/s10973-006-8281-z

Journal of Thermal Analysis and Calorimetry, Vol. 91 (2008) 3, 929–936
POLYMERIC AND SANDWICH SCHIFF’S BASES COMPLEXES
DERIVED FROM 4,4'-METHYLENEDIANILINE
Characterization and thermal investigation
S. A. AbouEl-Enein*
Chemistry Department, Faculty of Science, Menoufia University, Shebin El-Kom, Egypt
Cobalt(II), nickel(II) and copper(II) complexes of Schiff’s bases derived from 4,4'-methylenedianiline and pyridine-2-
carboxaldehyde(L1), furan-2-carboxaldehyde(L2) or thiophene-2-carboxaldehyde(L3), were prepared and characterized by different
analytical and spectral methods. The Schiff bases behave as neutral tetradentate ligands. The chloro-complexes of (L2) with (2:3)
mole ratio have a polymeric nature. However, that of L1 and L3 with (1:1) mole ratio showed a sandwich structure. All complexes
display an octahedral geometry, except complex (2) which has a tetrahedral one. Oh/Td equilibrium for chloro-complexes of cobalt
with ligand L1 was established in the solid state. ESR spectra of solid copper(II) complexes showed isotropic and axial type with
dx2–y2 ground state. The thermal study showed that the complexes with different solvents of crystallization exercise different types
of interaction. The observed thermochromic phenomenon for cobalt complex was explained along with its thermal behaviour.
Keywords: 4,4'-methylenedianiline (MDA), polymeric metal complexes, Schiff’s bases, thermal analysis, thermochromic
Introduction
Experimental
Materials
4,4'-methylenedianiline, known as diaminodiphenyl
methane (MDA), is used as intermediate in the manu-
facture of polyurethane foams. It is also used as a cur-
ing agent for epoxy resins, urethane elastomers, a cor-
rosion preventative for iron, antioxidant for
lubricating oils, rubber processing and preparation of
azo-dyes [1, 2]. MDA is a hazardous substance that
causes liver damage, skin and eye irritation [1–3]. On
the other hand, it was reported that some Schiff bases
of aniline derivatives display anti-inflammatory and
antipyretic properties. These properties increased
All the chemicals used were reagent grade (BDH or
Aldrich). Schiff’s bases were prepared by addition of
4,4'-methylenedianiline (MDA) to pyridine-2-
carboxaldehyde (L1) I, furan-2-carboxaldehyde (L2)
II or thiophene-2-carboxaldehyde (L3) III in (1:2) mo-
lar ratio in ethanol. The reaction mixture was stirred
in air at 50°C for 30 min. The formed precipitate was
I
H
H
N
N
with
copper(II)
complexes
[4].
C
N
C
N
Bis-(4-aminophenyl-methane) salicylaldehydeimine
ligand and its metal complexes were also synthesized
and characterized [5]. The complexes were found to
be active against some microorganisms.
CH
2
II
H
In the present work, metal complexes of differ-
ent Schiff’s bases of 4,4'-methylenedianiline with
pyridine-2-carboxaldehyde, furan-2-carboxaldehyde
or thiophene-2-carboxaldehyde were prepared and
characterized. This was carried out in an attempt to
investigate the effect of donor atoms (N,O,S) in het-
ero-rings on the coordination mode of the ligand. The
metal complexes obtained were characterized by dif-
ferent analytical and spectral methods. The thermal
behaviours of some metal complexes obtained were
also investigated.
H
O
O
C
C
CH
N
N
2
III
H
H
S
S
C
C
CH
N
N
2
Scheme 1 I – Bis-[4-benzylidene-pyridine-2'-yl] methane (L1),
II – Bis-[4-benzylidene-furan-2'-yl] methane (L2),
III – Bis-[4-benzylidene-thiophene-2'-yl] meth-
ane (L3)
*
dr.saeyda_elenein@yahoo.com
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2008 Akadémiai Kiadó, Budapest

ABOUEL-ENEIN
Table 1 Colors, elemental analysis results, magnetic moments (B.M.) and molar conductivities of the prepared metal
complexes
Color
FW
Found (Calc.)/%
a
LM
meff
No. Compound
(B.M.)
C
H
N
M
L1
Yellow
376.47
80.00
5.30
14.50
(14.9)
–
–
–
48
C25H20N4
(79.80)
(5.35)
1
[Co2L2Cl4]·6H2O·0.5EtOH
1
2
3
4
5
6
Brown
1143.8
53.76
4.92
9.80
10.30
4.60
4.33
3.11
3.2
C51H55Cl4Co2N8O6.5
(53.56)
(4.85)
(9.80)
(10.30)
1
[Co2L2]·Cl4·8H2O
Green
51.46
4.66
9.49
9.80
173
5.19
5.04
27.5
29.1
–
C50H56Cl4Co2N8O6
1156.8
(51.91)
(4.90)
(9.69)
(10.20)
1
[Ni2L2Cl4]·9H2O·EtOH
Dark brown
1220.34
51.77
5.29
9.00
9.50
C52H64Cl4Ni2N8O10
(51.18)
(5.29)
(9.18)
(9.62)
1
[Ni2L2Cl4]·10H2O
Reddish brown
1191.94
50.09
5.06
9.20
10.00
(9.82)
C50H60Cl4Ni2N8O10
(50.38)
(5.07)
(9.40)
1
[Cu2L2Cl4]·2H2O·2EtOH
Dark brown
1150.03
56.38
4.83
9.10
10. 90
1.75
2.12
C54H56Cl4Cu2N8O4
(56.40)
(4.90)
(9.70)
(11.04)
1
[Cu2L2Cl4]·7H2O
Yellowish green
1148.12
52.32
4.77
9.46
10.80
C50H54Cl4Cu2N8O7
(52.31)
(4.74)
(9.76)
(11.06)
L2
Yellow
354.41
77. 80
5.00
7.60
–
C23H18N2O2
(77. 90)
(5.00)
(7.90)
7
8
9
[Co2L23]n·(Cl4·H2O·EtOH)n
(C71H62Cl4Co2N6O8)n
Brown
61.60
4.9
6.30
8.30
–
4.90
3.28
1.02
1387.10
(61.48)
(4.50)
(6.00)
(8.50)
[Ni2L23]n·(Cl4·2EtOH)n
(C71H62Cl4Ni2N6O8)n
Brown
62.80
5.30
6.23
7.75
–
1414.20
(62.00)
(4.70)
(5.90)
(8.27)
[Cu2L23]n·(Cl4·6H2O·EtOH)n
(C71H72Cl4Cu2N6O13)n
Dark brown
1486.2
57.31
5.10
5.65
8.60
–
(57.38)
(4.88)
(5.70)
(8.55)
L3
Yellow
386.41
71.80
4.80
7.20
–
–
C23H18N2S2
(71.50)
(4.70)
(7.00)
10
11
[Ni2L32Cl4]·6H2O·EtOH
C48H54Cl4Ni2N4S4O7
Pale yellow
1185.8
48.62
4.50
4.28
9.40
39.9
50.1
3.05
0.99
(48.62)
(4.59)
(4.72)
(9.87)
[Cu2L32Cl4]·2EtOH
Dark brown
1133.92
53.30
4.40
4.80
11.30
C50H48Cl4Cu2N4S4O2
(53.00)
(4.30)
(4.90)
(11.21)
FW: Formula mass, M: Metal analysis, LM: Molar conductance in 10–3 M DMF, a: Ohm–1 mol–1 cm2, meff (B.M.) per metal ion
filtered off, washed with ethanol several times and
dried. The general structures of ligands obtained,
from elemental analyses and spectral methods, are
given in Scheme 1.
IR spectra were recorded using KBr discs on a
Perkin-Elmer 1430 spectrophotometer. Electronic ab-
sorption spectra were recorded as Nujol mulls using
Perkin-Elmer Lambda-4B spectrophotometer. Room
temperature magnetic susceptibility measurements
were carried out on a modified Gouy-type magnetic
balance, Herts SG8-5HJ. Diamagnetic correction was
done using Pascal constants [8]. The molar conduc-
tivity was measured for (10–3M) DMF solutions using
a Tacussel conductometer type CD6N.
Co(II), Ni(II) and Cu(II) complexes of all ligands
were prepared by the addition of 0.02 mole of the metal
chloride dissolved in ethanol to a hot ethanol solution of
0.01 mole of ligand. The reactants were stirred for 2 h at
70°C. The precipitates obtained were filtered off,
washed with ethanol and dried in vacuum and stored in
a desiccator over CaCl2/P4O10 for two weeks. The com-
plexes of pyridine derivative (L1) (1, 3, 5) were prepared
by the same method in (1:1) mole ratio.
Thermal analyses (DTA/TG) were measured in a
stream of nitrogen atmosphere within the temperature
range (25–1000°C) using a Shimadzu DTA/TG – 50
with a heating rate of 10°C min–1. The flow rate of N2
was 10 cm3 min–1. The mass of the investigated sam-
ples was 0.9718–5.6740 mg. ESR spectra were re-
corded at 100 kHz-modulation and 4G-modulation
amplitude on variation using ESR spectrophotometer
(Bruker Model EMX) at the National Center of
Researches and Radiation Technology, Egypt.
Methods
The elemental analyses were performed using a
Perkin-Elmer C H N 2400 elemental analyzer. Metal
analyses were carried out complexometrically [6, 7].
930
J. Therm. Anal. Cal., 91, 2008

POLYMERIC AND SANDWICH SCHIFF’S BASES COMPLEXES DERIVED FROM 4,4'-METHYLENEDIANILINE
Results and discussion
peared on complexation. This indicates the
participitation of sulphur atom in complexation [15].
All the complexes are stable and non-hygroscopic.
The metal complexes of the furan-derivative are in-
soluble in most organic solvents. This behaviour
could be attributed to the polymeric nature of the
complexes [9]. The metal complexes of pyridine and
thiophene derivatives are soluble in DMF. The molar
conductivity values of the soluble complexes in DMF
(Table 1) indicate nonelectrolytic nature [10, 11], ex-
cept for the green cobalt complex (2). The molar con-
ductivity value of that complex is 176 mol–1 cm2,
typified 1:2 electrolyte [12].
Electronic spectra
Electronic spectra and room temperature magnetic
moment are measured, from their values the follow-
ing can be pointed out.
Cobalt complexes
The green cobalt(II) complex (2) showed intense
multicomponent band with maxima at 620, 632, 668
and 704 nm. This band is assigned to tetrahedral con-
figuration around the metal ion [21]. This assignment
was also confirmed by the value of magnetic moment
(meff=4.33 B.M.). The spectra of complexes (1 and 7)
display a strong band at 416–422 nm and another
weak splitted band at 624–710 nm. These bands gath-
ered with the meff value (4.6–4.9 B.M) indicate an oc-
tahedral geometry [21, 22].
Infrared spectra
The spectra of the ligands show a band within the range
1598–1627 cm–1 which is assigned to u(C=N) of
azomethine group [10, 13]. The spectra also display
other bands near 1628, 1357–1282 and 717–700 cm–1
assigned to pyridine ring, furan ring stretching and
u(C–S–C), respectively [14, 15]. The pyridine, furan
and thiophene ring bending vibration appeared at (637,
582, 516, 483), (637, 582) and (566, 444, 430) cm–1, re-
spectively [14]. The spectra of all complexes display
bands in the range 3560–3342 cm–1 due to u(H2O)
[7, 16, 17]. The observed low frequency shift of u(C=N)
for all complexes relative to that of the corresponding
free ligand is due to the participitation of azomethine
group in coordination. The spectra are also character-
ized by a new band in range 408–527 cm–1 assigned to
u(M–N) [15, 18]. The spectrum of the pyridine
ligand (I) complexes showed changes in position and
shape of pyridine ring bending in/out of the plane at
637, 583 and 516, 483 cm–1 and pyridine ring at
1628 cm–1. This is attributed to the participitation of
pyridyl nitrogen atom in the coordination with metal
ion. For the furan ligand (II) complexes, the furan ring
bending band at 582 cm–1 was shifted to high frequency
by 5–10 cm–1 on complexation. Also, the strong furan
ring stretching bands at 1357 and 1280 cm–1 suffer from
changes (in both shape and position) on complexation.
The first peak shifted to lower frequency by 26 cm–1
whereas the second one weakened. This indicates the
participitation of oxygen atom of furan ring in coordina-
tion. The coordination through oxygen atom of furan
ring was also confirmed by the appearance of a medium
new band at 506–555 cm–1 which is assigned to u(M–O)
[15, 19, 20]. For thiophene ligand (III) complexes, the
spectrum showed that the thiophene ring stretching
bands at 1519 and 1500 cm–1 suffer from low frequency
shifts on complexation. The u(C–S–C) of free ligand
gave a low frequency shift by a value of 20 cm–1. Also,
thiophene ring bending vibration at 566 cm–1 displayed
a positive/negative shift whereas that at 440 cm–1 disap-
Nickel complexes
The spectra of nickel(II) complexes gave three bands
in the ranges 336–382, 404–488 and 698–716 nm, in-
dicating an octahedral geometry [4, 23]. The room
temperature magnetic moment values in the range
(meff =3.05–3.28 B.M.) are consistent with the octahe-
dral geometry [24, 25].
Copper complexes
The spectra of copper(II) complexes display bands at
338–356, 428–464, 524–584 and 680–712 nm. These
bands are assigned to tetragonally distorted octahedral
structure [26]. The geometry obtained was also con-
firmed by the values of meff. The observed lower mag-
netic moment values for complexes 9 and 11 (meff 0.996,
1.023 B.M) may be attributed to Cu–Cu interaction, due
to the crystal packing in the solid state [5, 26].
The room temperature solid powder (ESR) data
of copper(II) complexes showed that complexes (5, 6
and 11) are of isotropic behaviour with g=2.10, 2.07
and 2.08, respectively. These values confirm an octa-
hedral geometry with covalent bonding [27]. Cop-
per(II) complex (9) gave anisotropic symmetry with
two g-values, g11=2.2 and g^=2.06. The data show
g11>g^>ge confirming a dx2–y2 ground state in a dis-
torted octahedral geometry [26, 28]. The G value is a
measure of the exchange interaction between copper
centers in polycrystalline solid. If G>4 exchange in-
teraction is negligible and if G<4 considerable ex-
change interaction occurred in the solid complex.
Complex (9) gave G value=3.3, indicating the pres-
ence of exchange coupling [29].
J. Therm. Anal. Cal., 91, 2008
931

ABOUEL-ENEIN
- 1 0 0
- 8 0
- 6 0
- 4 0
- 2 0
- 0
T G
D T A
1 0
0
2 0 0
4 0 0 6 0 0
T e m p e r a t u r e /° C
8 0 0
Fig. 1 DTA/TG curves for metal complexes
932
J. Therm. Anal. Cal., 91, 2008

POLYMERIC AND SANDWICH SCHIFF’S BASES COMPLEXES DERIVED FROM 4, 4'-METHYLENEDIANILINE
Table 2 Thermal analysis (DTA/TG) data for the metal complexes
Temp. range/°C
DTA Peak/
°C
Mass loss
Ts/
No. Compound
Reaction
Assignment*
Found (Calc.)/ %
°C
DTA
TG
1
1 [Co2L2Cl4]·
endo (63.34) 29–169.2
29–169.2
9.71 (9.63)
1.98 (2.01)
6H2O
a
304
6H2O·0.5EtOH shoulder end 169.2–250 169.2–250
0.5EtOH
b+ green
form
o
endo (274)
250–304
850
250–304
–
phase change
Oh brown –
Td green
c
304–437
437–850
12.66 (12.41)
61.20 (61.63)
4Cl atoms
2MDA, 20C, 6H2,
2N2
c
remain
850
14.43 (14.50)
2Co+4C
1
2 [Co2L2]·Cl4·
endo (64.6)
endo (305)
29–157.1
29–157.1
9.5 (9.34)
–
6H2O
a
332
8H2O
157.1–332. 157.1–332.9
9
lattice rearrangement
332–462.2
15.62 (15.39)
65.09 (65.09)
(9.76) (10.18)
4Cl atoms, 2H2O
2 molecules of ligand
2 Co
c
322–462.2
endo
462–542.3,
c
(504.7),
462–542.3, 542–803
endo (690.6) 542.3–803 803
remain
1
3 [Ni2L2Cl4]·
endo (77.3)
endo (170)
25–130
25–130
12.50 (12.62)
10.36 (10.24)
6H2O, EtOH
a, b
345
9H2O·EtOH
130– 369
130–345,
345–369
369 –555
3H2O, 2Cl atoms
a and c
endo (470)
endo (600)
369–555
555–750
25.40 (25.24)
38.34 (38.25)
13.14 (13.55)
2Cl atoms,
c
c
3-pyridine rings
2 diphenylmethane,
5N, 5C, H
555–725
750°
2Ni+4C
remain
a
1
4 [Ni2L2Cl4]·
endo (98.2)
endo (334)
28–180
28–180
15.36 (15.10)
–
10H2O
364
177
212
10H2O
180–364
180–364
lattice rearrangement
shoulder
364–410
410–725
364–410
410–725
11.80 (11.90)
57.91 (58.12)
4Cl atoms
2N2, 2MDA, 19C,
6H2
c
c
endo (480)
725
14.85 (14.88)
2Ni+5C
remain
1
5 [Cu2L2Cl4]·
endo (67.14) 20–116
20–116
5.70 (5.57)
1.63 (1.57)
H2O, EtOH
H2O
a, b
a
2H2O·2EtOH
shoulder
(143.2)
116–177
116–177
177–390
390–650
650–820
177–390
390–772
16.35 (16.35)
60.61 (60.24)
EtOH, 4Cl atoms
2MDA, 19C, 6H2,
2N2
b, c
c
endo (532),
endo (752)
772
15.71 (16.27)
7.70 (7.80)
2Cu+5C
remain
a
1
6 [Cu2L2Cl4]·
endo (63.06) 23–120,
endo (187.5) 120–212
23–120,
120–212
212–350
5H2O
7H2O
shoulder
212–250,
250–350
350–544
544–650
650–855
12.25 (12.36)
65.78 (65.93)
4Cl atoms
2 ligand, 2H2
c
c
endo (463),
endo (633)
shoulder
350–814
818
13.37 (13.85)
3.46 (3.33)
2CuO
remain
7 [Co2L23]n·
endo (61.7)
27–146
27–146
EtOH
b
146
117
(Cl4·H2O·EtOH)n exo (379.4)
146–670
i) 146–365.7 11.27 (11.53)
ii) 365.7–470 51.0 (51.10)
iii) 470–611 23.54 (23.24)
H2O,4Cl atoms
2 ligand
a,c
c
MDA, 10C
2CoO
c
611
10.73 (10.80)
remain
8 [Ni2L23]n·
endo (56)
endo (256)
25–117
25–117
117–339
339–561
561
5.75 (5.67)
10.9 (10.85)
75.7 (75.10)
7.65 (8.27)
1.75 EtOH
4Cl atoms,0.25EtOH
3 ligands
b
c
(Cl4·2EtOH)n
117–339
2Ni
remain
J. Therm. Anal. Cal., 91, 2008
933

ABOUEL-ENEIN
Table 2 Continued
Temp. range/°C
Mass loss
Found (Calc.)/
DTA Peak/
°C
Ts/
No. Compound
9 [Cu2L23]n·
Reaction
Assignment
DTA
TG
°C
%
endo (61.88) 31–165
31–165
6.41 (6.42)
2.75H2O, EtOH
3.25H2O
4Cl atoms
3 ligands
2Cu
a, b
209
(Cl4·6H2O·EtOH)n endo (219)
165–309
i)165–209 3.92 (3.94)
ii) 209–309 9.24 (9.55)
a
c
endo (692)
309–1044 309–670
670
72.06 (71.54)
8.37 (8.55)
c
remain
10 [Ni2L32Cl4]·
6H2O·EtOH
endo (48.0), 28–74,
(115) 74–138
endo (288.4) 138–369
28–74,
1.96 (1.89)
1.25H2O
a
369
74–138
138–369
369–511
4.32 (4.26)
0.25H2O,EtOH
2MDA, 4.5H2O,
4Cl, 10C, 2H2
2NiS
a, b
c
endo (413)
369–469
77.95 (78.58)
511
15.77 (15.23)
8.60 (8.23)
remain
b
11 [Cu2L32Cl4]·
2EtOH
endo(50.5),
(127)
32–156
32–156
2EtOH
156
endo (209),
(245)
156–236
236–304
156–236
236–304
304–594
6.00 (6.20)
2Cl
c
c
c
10.38 (10.36)
60.50 (60.74)
3.16 (3.13)
Cl, 4C,2S
2DMA, 6C, 2 thiophene
exo 716
567.5–772 594–704
704
Cl
11.36 (11.50)
2Cu
remain
*a – dehydration, b – desolvation, c – decomposition, Ts – decomposition temperature
Thermal studies
was followed by another endothermic peak (shoulder) in
the temperature range 169–250°C corresponding to the
loss of 0.5 EtOH. DTA curve also display an endother-
mic peak near 250–304°C. This peak is assigned to
thermochromic phase change from brown into dark
green one [21, 32]. This assignment was confirmed by
TG data which show no mass loss in that temperature
range. This thermochromic phase change is reversible
through (1 h) in the solid state and may take place
through chloride ion exchange between ionisable and
coordination spheres, giving an octahedral (brown
form)/tetrahedral (green form) transformation [21]. This
type of transformation was derived from electronic
spectral measurements of both brown and green forms.
The green form displays a similar spectrum to that of
tetrahedral green complex (2). Complex (1) also shows
a similar thermochromic behaviour in hot DMF solution
where the brown octahedral form change into tetrahe-
dral green one. Such transformation is also reversible on
cooling as in the solid state. The observed lower mag-
netic moment value of both brown and green forms (4.6
and 4.33 B.M) may be attributed to some type of equi-
librium between both forms in the solid state. DTA
curve also displays a number of endothermic peaks in
the temperature range 304–850°C that may be assigned
to thermal decomposition of complex to give a mixture
of cobalt metal and carbon as a final product. This as-
signment was also confirmed by TG mass loss (Ta-
DTA and TG curves of the investigated metal com-
plexes (1–11) are given in Fig. 1. The results of thermal
analysis together with their assignments are also given
in (Table 2). It was found that all metal complexes are
thermally stable up to 48°C and the complexes lose their
solvents of crystallization in one or multi-steps. The en-
dothermic dehydration and/or desolvation process are
generally extended over a broad temperature range
25–369°C [30–32] and sometimes overlap with the de-
composition step for complexes (2, 3, 5, 7, 9 and 10).
The dehydration peak is followed by an endo- or exo-
thermic peak which is assigned to decomposition pro-
cess. As derived from TG mass loss (Table 2), the gen-
eral mechanism for decomposition of chloro-complexes
started with the elimination of chloride atoms [32, 33].
This may be attributed to the weak nature of metal chlo-
ride bond relative to other bonds in molecule. This step
was followed by the decomposition or removal of the
organic ligands. The solid residue of thermal decompo-
sition (Table 2) are metal [34, 35], metal oxide [36, 37],
metal sulphide [38] or a mixture of metal and carbon
[5, 21]. DTA curve of the brown cobalt(II) complex (1)
(Fig. 1) gave an endothermic peak in the temperature
range 29–169°C. This peak is assigned to loss of six
molecules of water of crystallization as derived from TG
mass loss (Table 2). This endothermic dehydration peak
1
[Co2L2Cl4 ]× 6H2O× 0.5EtOH¾¾¾®[Co2L2Cl4 ]× 0.5EtOH¾¾¾®[Co2L2Cl4 ]
1
1
29–169°C
169–250°C
brown O
loss6H
O
2
brown O
h
loss0.5 EtOH
h
1
[Co2L2Cl4 ]¾¾¾®[Co2L2 ]× Cl4 ¾¾¾®2Co+4C
1
250–304°C
304–850°C
phase change
dark green
decomposition
934
J. Therm. Anal. Cal., 91, 2008

POLYMERIC AND SANDWICH SCHIFF’S BASES COMPLEXES DERIVED FROM 4, 4'-METHYLENEDIANILINE
ble 2). The thermal behaviour of the complex can be
represented as follows:
EtOH molecule corresponding to mass loss of 3.33%.
The exothermic decomposition takes place through
dechlorination as well as loss of the two ligand mole-
cules in the temperature rang 146–611°C. The final
product of decomposition is CoO as derived from TG
mass loss.
DTA curve of green tetrahedral cobalt(II) com-
plex (2) (Fig. 1) gave two successive endothermic peaks
near 64 and 305°C. These peaks are assigned to dehy-
dration and lattice rearrangement [5, 32], respectively as
derived from TG mass loss (Table 2). TG curve displays
a mass loss (9.5%) in the temperature range 29–157°C
corresponding to six molecules of water. No mass loss
was observed in the temperature range 157–333°C, con-
firming the lattice rearrangement assignment [32].
Those two endothermic peaks were also followed by
other endothermic peaks in the temperature range
333–803°C, assigned to material decomposition to give
finally cobalt metal. The observed higher thermal stabil-
ity of the green form up to (333°C) than that of brown
form (304°C) may be attributed to the increased number
of water molecules of crystallization which play an ef-
fective role in the lattice forces [39].
The DTA curves of nickel and copper complexes
(10, 11) display endothermic peaks in the temperature
range 28–369°C, assigned to dehydration / or
desolvation as indicated from TG mass loss (Table 2).
The thermal decomposition of complexes takes place
through successive endothermic/exothermic pro-
cesses within the temperature range 156–772°C. As
derived from TG mass loss, the decomposition pro-
ceeds via dechlorination and ligand molecules loss in
accordance with the general behaviour of the other in-
vestigated complexes. The final products are NiS and
Cu metal for complex (10) and (11), respectively.
The observed lower thermal stability of copper
complexes of ligands I and III than those of cobalt and
nickel complexes may be attributed to the higher repul-
As shown in DTA/TG curves (Fig. 1) of reddish
brown and dark brown nickel(II) complexes, the com-
plexes loss their solvent of crystallization through endo-
thermic (one or two steps) process. The reddish brown
form (4) changes into a dark brown one in the tempera-
ture range 180–364°C through an endothermic lattice
rearrangement. This lattice rearrangement was derived
from TG measurements which show no mass loss in that
temperature range (Table 2). This thermal behaviour is
similar to a great extent to that of its room temperature
isostructural cobalt(II) complex (1).
H
H
C
C
X
X
CH2
N
N
.
.
nH2O mEtOH
Cl
M
Cl
Cl
M
Cl
N
N
X
CH2
X
C
C
H
H
TG and DTA curves of isostructural copper(II)
complexes of pyridine derivatives (5, 6) are given in
Fig. 1. Both complexes display a number of endother-
mic splitted DTA peaks in the temperature range
25–212°C. These peaks are assigned to loss of some sol-
vents of crystallization as derived from TG mass losses.
The endothermic desolvation peaks are followed by a
number of endothermic/exothermic events that are as-
signed to material decomposition to give finally (Cu+C)
and CuO for complexes (5) and (6), respectively. It is
noteworthy to mention that the yellowish green form of,
complex (6) changes to a dark brown one, (5) on heat
treatment in the solid state or dissolution in DMF.
The polymeric nickel(II) and copper(II) complexes
of ligand II (8, 9) largely exhibit similar thermal behav-
iours (Fig. 1). This is due to their isostructural character
at room temperature. The observed endothermic DTA
peaks together with the corresponding TG mass losses
(Table 2) are assigned to desolvation as well as material
decomposition. The decomposition proceeds via rupture
of coordinate bond by elimination of three ligand mole-
cules along with dechlorination to give nickel and cop-
per metals as final products. As shown in Table 2 and
Fig. 1, the DTA curve of complex (7) displays an endo-
thermic peak at 61.7°C which is assigned to loss of one
Complex
M
n
m
1
3
Co (II)
Ni (II)
Ni (II)
Cu (II)
Cu (II)
Ni (II)
Cu (II)
6
8
0.5
1
4
10
2
–
5
2
6
7
–
10
11
6
1
–
2
X: represents N or S atom of pyridine ring (1-6)
or thiophene ring (10, 11)
H
H
O
O
N
N
CH
CH
N
N
2
2
N
N
O
M
O
M
. .
Cl4 zH2O mEtOH
(
)
n
O
O
H
H
n
Complex
M
Z
m
7
8
9
Co (II)
Ni (II)
Cu (II)
1
–
6
1
2
1
Scheme 2
J. Therm. Anal. Cal., 91, 2008
935

ABOUEL-ENEIN
13 R. Olar, M. Badea, E. Cristurean, V. Lazar, R. Cernet and
sion between bonding pair of electrons in the valence
shell of copper ion relative to those of cobalt and nickel
[40]. Also, the complexes of ligand II generally display
lower thermal stability than those of ligands I and III.
This may be related to the steric hindrance around the
metal ion in the polymeric complexes of ligand II.
On basis of the above discussion together with
elemental analyses and TG measurements, the struc-
tures in Scheme 2 can be suggested, for the studied
metal complexes.
C. Balotescu, J. Therm. Anal. Cal., 80 (2005) 451.
14 J. B. Lambert, H. F. Shurvell, L. Verbit, R. G. Cooks and
G. H. Stout, Organic Structural Analysis, Macmillan Pub-
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15 G. G. Mohamed, M. M. Omar and A. M. M. Hindy,
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16 E. C. Rodrigues, A. B. Siqueira, E. Y. Ionashiro,
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17 B. K. Singh, R. K. Sharma and B. S. Garg, J. Therm. Anal.
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18 G. Singh and D. K. Pandey, J. Therm. Anal. Cal.,
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Conclusions
19 M. Tas and H. Bati, J. Therm. Anal. Cal., 85 (2006) 295.
20 W. Brzyska and W. Ozga, J. Therm. Anal. Cal.,
84 (2006) 385.
Metal complexes of Schiff’s base ligands derived
from 4,4’-methylenedianiline and pyridine, furan or
thiophene-2-carboxaldehyde were prepared and in-
vestigated. DTA and TG studies of complexes ob-
tained display the following points:
21 H. A. El-Boraey, J. Therm. Anal. Cal., 81 (2005) 339.
22 I. Labádi, L. Horváth, G. Kenessey and G. Liptay,
J. Therm. Anal. Cal., 83 (2006) 247.
23 A. B. P. Lever, Inorganic Electronic Spectroscopy, 2nd
.
Edn., Elsevier, Amsterdam 1984.
• The general mechanism for decomposition of
chloro-complexes started with the elimination of
chloride followed by the decomposition or removal
of organic ligands.
24 W. Ferenc, B. Bocian and J. Sarzynski, J. Therm. Anal.
Cal., 84 (2006) 377.
25 I. Labadi, G. Kenessey and G. Liptay, J. Therm. Anal.
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26 M. S. Masoud, S. A. AbouEl-Enein, M. E. Aayd and
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27 A. S. El-Tabl, Trans. Met. Chem., 27 (2002) 166.
28 K. Narang and V. P. Singh, Trans. Met. Chem.,
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• The thermal stability is controlled by the metal ion
type and steric effect of the ligands.
• Cobalt(II) complex, (1) displays a reversible
thermochromic phase change in the solid state and
in DMF solution.
29 A. S. El-Tabl, Bull. Korean Chem. Soc.,
25 (2004) 1757.
30 P. Masset, J. Y. Poinso and J. C. Poignet, J. Therm. Anal.
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DOI: 10.1007/s10973-006-8281-z
936
J. Therm. Anal. Cal., 91, 2008