Spectral studies of complexes of nickel(II) with tetradentate schiff bases having N2O2 donor groups

Article abstract of DOI:10.1016/S1386-1425(02)00142-7

Complexes of nickel(II) of N,N′-disalicylidene-1,2-phenylenediamine (H₂dsp), N,N′-disalicylidene-3,4-diaminotoluene (H₂dst), 4-nitro-N,N′-disalicylidene-1,2-phenylenediamine (H₂ndsp) and N,N′-disalicylidene ethylenediamine

Full text of DOI:10.1016/S1386-1425(02)00142-7

Spectrochimica Acta Part A 59 (2003) 229ꢁ234
/
www.elsevier.com/locate/saa
Spectral studies of complexes of nickel(II) with tetradentate
schiff bases having N O donor groups
2
2
B.S. Garg ꢀ, Deo Nandan Kumar
Department of Chemistry, University of Delhi, Delhi 110007, India
Received 19 February 2002; accepted 9 March 2002
Abstract
Complexes of nickel(II) of N,N’-disalicylidene-1,2-phenylenediamine (H
luene (H dst), 4-nitro-N,N’-disalicylidene-1,2-phenylenediamine (H ndsp) and N,N’-disalicylidene ethylenediamine
2
dsp), N,N’-disalicylidene-3,4-diaminoto-
2
2
2
(H salen) have been prepared and characterised by elemental analysis, electronic, IR, magnetic susceptibility
1
measurement, H NMR and thermal studies. TG studies show that the Ni(dsp) and Ni(salen) complex decomposed
in one step and Ni(dst) and Ni(ndsp) complex in two steps. Kinetic and thermodynamic parameters were computed
from the thermal decomposition data. The activation energy of either one step decomposition or two step
ꢂ1
decomposition of complexes lies 72ꢁ
#
/
95 kJ mol
2002 Elsevier Science B.V. All rights reserved.
range.
Keywords: Schiff base; Nickel(II); Thermal studies
1
. Introduction
Tetradentate schiff base complexes of nickel
compounds in catalytic reactions has been con-
sidered [3]. These studies dealing mainly with
synthesis, spectroscopic, structural, electrochemi-
cal and magnetic properties, photo and thermo-
afford two main differences relative to macrocyclic
ligands: easier access to mixed donor environments
and an open equatorial ring, the hole size of which
can in principle accommodate more easily the
expected changes in metal size upon oxidation/
reduction [1]. A considerable number of schiff base
complexes have potential biological interest, being
used as more or less successful models of biological
compounds [2]. On the other hand, the use of these
chroism have been extensively reviewed [4ꢁ7].
/
In view of recent interest in the energetics of
metal ligand binding in metal chelates involving N,
O donor ligands [8ꢁ10] we started to study schiff
/
base complexes derived from N,N’-bridged tetra-
dentate ligands involving an N O donor atoms.
2
2
However, very little work has been done on
thermal studies of tetradentate schiff base com-
plexes of Ni(II). Hence, this paper describes the
synthesis, spectral, and thermal studies of new
Ni(II) complexes derived from N,N’-disalicyli-
ꢀ
E-mail address:
Corresponding author. Tel./fax: ꢃ
/
91-11-7666250
deonandan2002@rediffmail.com (D.
Nandan Kumar).
dene-1,2-phenylenediamine (H dsp), N,N’-disali-
2
1386-1425/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 1 3 8 6 - 1 4 2 5 ( 0 2 ) 0 0 1 4 2 - 7

230
B.S. Garg, D. Nandan Kumar / Spectrochimica Acta Part A 59 (2003) 229ꢁ234
/
cylidene-3,4-diaminotoluene (H dst), 4-nitro-
2
microcrystalline solids were filtered off, washed
with ethanol and diethyl ether and dried under
vacuum over P O .
N,N’-disalicylidene-1,2-phenylenediamine
(
(
H ndsp) and N,N’-disalicylidene ethylenediamine
2
4
10
H salen). Kinetic and thermodynamic parameters
2
have been calculated using Coats and Redfern [20]
and Zsako [21] method.
2.3. Analysis and physical measurements
The metal content of each complex was deter-
mined by Atomic absorption spectroscopy techni-
que on AA-640-13, Shimadzu (Japan) machine.
Magnetic moments were measured at room tem-
perature by vibrating sample magnetometer
(VSM) model 155 (Princeton applied research) at
2
. Experimental
All the chemicals used were of A.R. grade and
were used as such. Solvents were dried before use
by conventional methods.
5500 Gauss field strength. UVꢁvisible spectra
/
were recorded in DMSO on Beckman DU-64
spectrophotometers. IR spectra was recorded on
Perkin-Elmer FT-IR spectrophotometers spec-
2
.1. Ligand syntheses
1
All the tetradentate schiff base ligands except
H dst were prepared by condensations between
trum 2000 in KBr and polyethylene pellets. H
NMR was recorded on a Bruker Advance 300
machine. TG and DTA were simultaneously
recorded on Rigaku 8150 thermoanalyser, in static
2
diamines and hydroxyaldehydes in ethanol or
methanol and were purified by recrystallization
from a dichloromethane/ hexane mixed solvent
through the partial evaporation of the more
volatile dichloromethane.
ꢂ1
air at the heating rate of 10deg min . A platinum
crucible was used with alumina as the reference
material. The number of decomposition steps were
identified using TG. The activation energy (E) and
frequency factor (ln A) of the degradation process
were obtained by Coats and Redfern method [20].
Apparent activation entropy was calculated by
Zsako [21] method.
H dst was prepared by dissolving 25 mmol
2
(
3.050 g) of 3,4-diaminotoluene in 100 ml of
ethanol and stirred for 3h. After that 50 mmol
6.106 ml) of salicylaldehyde was mixed in 150 ml
(
of ethanol. The 3,4-diaminotoluene solution was
added to the salicylaldehyde solution using an
overhead stirr for complete mixing. Some yellow
precipitate resulted. The crude product was re-
crystallised from dichloromethane/hexane (1:2)
3. Results and discussion
mixed solvent. Melting point: 1208 C, yield Â
/
All the complexes were brown or red and
microcrystalline, non-hygroscopic and insoluble
in water, methanol, ethanol, dichloromethane
and acetone but soluble in hot DMF and
DMSO. These were decomposed in the range of
1
8
0%, H NMR in CDCl , phenolic Oꢀ
/
H [13.14
s, 1), 13.08 (s, 1)], aldimine proton [8.58 (s, 1) 8.57
s, 1)], aromatic protons [7.26ꢁ7.36 (m, 4), 6.94ꢁ
6.9 (m, 2)], methyl proton [2.30 (s,
3
(
(
/
/
7
.11 (m, 5), 6.7ꢁ
/
3
)] (Fig. 2(a)).
217ꢁ2978 C. Possible compositions of the com-
/
plexes were calculated and compared with the
experimental values as presented in Table 1.
2
.2. Synthesis of complexes
One mmol of NiAc2×4H O was dissolved in
/
3.1. UVꢁvisible spectra
/
2
ethanol and stirred for 2 h and 1 mmol of requisite
ligand was suspended in hot ethanol and stirred
for 3 h. Ethanolic solutions of the schiff base were
added to ethanolic nickel(II) (Ni(II)) acetate
tetrahydrate solutions and the resulting mixtures
refluxed, after cooling, brown or red brown
The electronic spectral data are given in Table 1.
The very intense bands at low wavelengths have
been assigned to charge transfer transition [11,12],
for complexes with aromatic bridges these bands
occur at longer wavelengths, as expected from the

B.S. Garg, D. Nandan Kumar / Spectrochimica Acta Part A 59 (2003) 229ꢁ
/
234
231
Table 1
Analytical and electronic spectral data for Ni(II) complexes
S. no.
Complex
Composition
Found (calcd)%
dꢂ
/
d transition
Charge transfer
transition (nm)
(
nm)
C
H
N
M
1
2
3
4
Ni(dsp)
Ni(dst)
C
C
C
C
20
H
21
H
20
H
16
H
14
N
16
N
13
N
14
N
2
2
3
2
O
2
O
2
O
4
O
2
Ni
Ni
Ni
Ni
64.41
3.75
(3.76)
4.39
7.52
(7.51)
7.23
15.73
(15.74)
15.16
479, 450, 380
481, 450, 380, 354
486, 422, 386, 300
450, 404, 326
(
(
(
(
64.40)
65.15
65.17)
57.45
57.46)
59.13
59.13)
(4.14)
3.10
(7.24)
10.10
(10.05)
8.61
(15.17)
14.05
Ni(ndsp)
Ni(salen)
(3.11)
4.30
(4.31)
(14.05)
18.06
(18.07)
537
(8.62)
higher aromaticity of the ligands which eases
delocalisation of electron density.
ion [15]. Coordination of azomethine nitrogen is
confirmed with the presence of a new bands at
ꢂ1
The weaker band in the region 530ꢁ/600 nm in
430ꢁ
/
480 cm
region assignable to n(Niꢀ
/
N) for
the spectra of complexes with aliphatic imines is
assigned to unresolved transitions from the four
low-lying d-orbitals to the empty dxy orbital
these complexes [16,17]. The n(Cꢀ
/
O) frequency
shifts in the complexes towards lower or higher
values as a result of coordination of the oxygen to
[
11,12]. This band could not be observed for
the metal ion [18]. A new band in the 400ꢁ
/
450
ꢂ1
complexes with aromatic imine bridges since it is
masked by the high-intensity charge transfer
transitions.
cm
region in the spectra of the complexes is
assignable to n(Niꢀ
/O).
The energy of the band assigned to dꢁd transi-
tions can provide a rough estimate of the ligand
field strength, since one of the electronic transi-
/
1
.3. Magnetic susceptibility measurement and H
3
NMR spectroscopy
tions comprised in the band envelope is dxy
and the energy associated with this transition is
1
/
d
2
/
x ꢂ
All complexes are diamagnetic at RT revealing
1
the square planar geometry around Ni(II) ion. H
y2
1
0 DqꢁC [12]. No comparison is possible between
/
NMR spectra of all the complexes were recorded
in DMSO-d solution at 300 MHz (Fig. 2(b)). The
solvent impurity DMSO resonates near 2.0 ppm.
energies for d-d transitions for complexes with
aliphatic and aromatic imine bridges, as they are
not observed in the latter complexes (Fig. 1).
6
1
The H NMR spectra of all the schiff bases
indicate the presence of either one or two azo-
methine groups. Due to different chemical envir-
onments two signals are recorded for the
azomethine protons in the H dst and H ndsp.
3
.2. IR spectra
The spectra of the ligand exhibit broad medium
ꢂ1
2
2
intensity bands in the 2500ꢁ
/
2750 cm and 3338ꢁ
/
H dsp and H salen gives one signal. Intramolecu-
2 2
ꢂ1
3
353 cm
intramolecular H bonding vibration (Oꢀ
In the spectra of complexes these bands disappear
13,14].
The vibrations of the azomethine groups of the
range which are assigned to the
lar hydrogen bonding also accounts for the high
frequency of the signals for the orthophenolic
hydrogens in all the schiff bases.
/
H. . .N).
1
[
The H NMR spectra of all the schiff base Ni(II)
complexes, show a down-field shift in the fre-
quency of azomethine protons of aromatic bridge
and upfield shift in the aliphatic bridge confirming
coordination of the metal ion to both groups. In
all the complexes, no signals is recorded for a
ꢂ1
free ligands are observed at 1614ꢁ1635 cm . In
/
the complexes these bands are shifted to the lower
frequencies, indicating that the nitrogen atom of
the azomethine group is coordinated to the metal

232
B.S. Garg, D. Nandan Kumar / Spectrochimica Acta Part A 59 (2003) 229ꢁ234
/
1
Fig. 2. (a) H NMR (300 MHz) spectra of H
Ni(dst) in DMSO-d
2
dst and (b)
6
.
phenolic hydrogen in the 12ꢁ13.5 ppm region, as
/
in the case of the schiff base indicating deprotona-
tion of the orthohydroxyl group.
The coordination of all ligand is also affirmed
by the almost 1 ppm upfield change in chemical
shift for certain aromatic protons in its aldehydic
ring. But there is no upfield change in complex
Ni(salen). The imine proton signal is a doublet.
This is explained by the restricted freedom of
motion present in the complex, which do not
average the chemically inequivalent imine protons
and largely retain upon coordination and in
Ni(ndsp) complex not obscured by the nitro-
deshielded aromatic proton signals. For Ni(salen)
Fig. 1. (a) UV spectra of Ni(dsp) complex. (b) UV spectra of
Ni(dst) complex. (c) UV spectra of Ni(ndsp) complex and (d)
UV spectra of Ni(salen) complex. (e) Visible spectra of
Ni(salen) complex.

B.S. Garg, D. Nandan Kumar / Spectrochimica Acta Part A 59 (2003) 229ꢁ
/
234
233
Table 2
Thermal data and kinetic parameters for Ni(II) complexes
a
n
#
#
#
Complex
Step Order of rk
n)
E
ln A
(minꢂ1)
DH
(J mol
DS
(JK
DG
(
(kJ molꢂ1)
ꢂ1
ꢄ/
10ꢂ3
)
ꢂ1
molꢂ1
)
(kJ molꢂ1)
1
2
I
1
1
1
1
1
1
95.03
72.33
83.60
93.46
89.91
82.14
3.36
8.55
3.78
3.86
3.75
3.60
ꢂ
ꢂ
/
326.13
27.90
457.35
8.09
1597.33
1527.55
ꢂ
/
4.27
3.30
3.52
3.51
3.56
4.09
ꢃ
/
2.84
1.83
2.91
2.43
4.18
4.08
I
/
ꢂ
/
ꢃ
/
II
I
ꢃ
/
ꢂ
/
ꢃ
/
3
4
ꢂ
/
ꢂ
/
ꢃ
/
II
I
ꢃ
/
ꢂ
/
ꢃ
/
ꢃ/
ꢂ/
ꢃ/
complex the integrated intensities showed the
single resonance at 3.46 ppm (low field shifts)
which was derived from protons in the ethylene
linkage which are equivalent under the prevailing
conditions.
complex. The first step in the decomposition
sequence at 150ꢁ2508 C corresponds to the loss
/
of methyl and nitrogroup in complex 2 and 3
respectively. The inflexion of the TG curve at a
temperatures range above 3908 C indicates the
decomposition of the organic part of the chelate,
leaving metallic oxide at the final temperature [19].
The thermal degradation of the complex can be
depicted as follows:
3
.4. Thermal analyses
TG and DTA studies were carried out on the
ligand and its complexes in the temperature range
upto
0
C H N O Ni
NiO
of 20ꢁ7008 C. The thermal analyses show that
/
20 14
2
2
ꢀ
6
50
C
there are two endothermic peak in the DTA curve
of the ligand. The first is the melting point of the
ligand, because no loss of weight was observed in
the TG curve and second corresponds to decom-
position of the ligand. TG studies of all the
complexes showed no weight loss upto 1508 C,
indicating the absence of water molecule in the
*
CH3
H C*C H N O Ni
3
20 13
2
2
ꢀ
50ꢂ200 C
1
upto
0
C H N O Ni
NiO
2
0
13
2
2
ꢀ
650
C
*
NO2
O N*C H N O Ni
2
20 13
2
2
ꢀ
50ꢂ250 C
1
upto
0
C H N O Ni
NiO
2
0
13
2
2
ꢀ
50 C
6
upto
0
C H N O Ni
NiO
1
6
14
2
2
ꢀ
650 C
From the TG curves the order of reaction (n),
activation energy (E) and frequency factor (ln A)
of the reactions have been enumerated and are
given in Table 2. The weight change is plotted on
the ordinate with decreasing weights downwards
and temperature (T) on the abscissa increasing
from left to right. The methods of Coats and
Redfern [20] has been used for deriving kinetic
parameters (Fig. 3). The calculation of the heat of
#
the reaction (DH ) from the DTA curves was done
by using:
Fig. 3. Kinetic parameter of Ni(dsp) complex.

234
B.S. Garg, D. Nandan Kumar / Spectrochimica Acta Part A 59 (2003) 229ꢁ234
/
DH(muv) ꢄ 60 ꢄ 10ꢂ6 ꢄ M
[
[
[
3] M.M. Taqui Khan, D. Srinivas, R.I. Kureshi, N.H. Khan,
#
kJ molꢂ1
DH ꢅ
Inorg. Chem. 29 (1990) 2320.
4] M. Calligaris, G. Nardin, L. Randaccio, Coord. Chem.
Rev. 7 (1972) 385.
1000
where Mꢅ
/
molecular weight of the complex.
5] M. Calligaris, L. Randaccio, in: G. Wilkinson (Ed.),
Comprehensive Coordination Chemistry, vol. 2 (Chapter
#
Apparent activation entropy (DS ) is calculated
by Zsako [21] method and free energy of activation
is calculated by Gibb’s equation.
2
0.1), Pergamon, London, 1987, p. 715.
[6] J. Costamagna, J. Vargas, R. Latorre, A. Alvarado, G.
Mena, Coord. Chem. Rev. 119 (1992) 67.
#
The DS values were negative, which indicate a
[7] A.D. Garnovskii, A.L. Nivorozhkin, V.I. Minkin, Coord.
Chem. Rev. 126 (1993) 1.
more ordered activated state that may be possible
through the chemisorption of oxygen and other
decomposition products [22]. The enthalpies of
activation are negative for complex 1 and first step
decomposition of complexes 2 and 3 and is
positive for second step decomposition of com-
plexes 2 and 3 and for complex 4 also. However,
the negative values of the entropies of activation
are compensated by the values of the enthalpies of
[
8] M.A.V. Ribeiro da Silva, M.D.M.C. Ribeiro da Silva,
M.C.S.S. Rangel, G. Pilcher, M.J. Akello, A.S. Carson,
E.H. Jamea, Thermochim. Acta 160 (1990) 267.
[9] M.A.V. Ribeiro da Silva, M.D.M.C. Ribeiro da Silva,
M.M.C. Bernardo, L.M.N.B.F. Santos, Thermochim.
Acta 205 (1992) 99.
[
[
10] M.A.V. Ribeiro da Silva, M.D.M.C. Ribeiro da Silva,
J.A.B.A. Tuna, L.M.N.B.F. Santos, Thermochim. Acta
2
05 (1992) 115.
activation leading to almost the same values
ꢂ1
11] A.B.P. Lever, Inorganic Electronic Spectroscopy, 2nd edn,
Elsevier, New York, 1984.
[12] G. Maki, J. Chem. Phys. 28 (1958) 651.
(
activation. The order of activation energy (E) is
1.80ꢁ4.20 kJ mol ) for the free energies of
/
[
[
[
13] M. Tumer, H. Koksal, M.K. Sener, S. Serin, Trans. Met.
Chem. 24 (1999) 414.
Ni(dsp)ꢀNi(ndsp)ꢀNi(salen)ꢀNi(dst).
/
/
/
14] M. Tumer, H. Koksal, S. Serin, Synth. React. Inorg. Met.
Org. Chem. 26 (1996) 1589.
Acknowledgements
15] P. Sousa, J.A.G. Vazquez, J.A. Masaquer, Trans. Met.
Chem. 9 (1984) 318.
One of the authors, D.N.K. is thankful to the
Council of Scientific and Industrial Research,
India, for awarding a research fellowship.
[16] S.K. Agrawal, D.R. Tuflani, R. Gupta, S.K. Hajela, Inorg.
Chim. Acta 129 (1987) 257.
[
[
17] N. Saha, S. Sinha, Ind. J. Chem. 29A (1990) 292.
18] K. Nakamoto, Infrared and Raman Spectra of Inorganic
and Coordination Compounds, Wiley, New York, 1978.
19] A.A. El-Bindary, A.Z. El-Sonbati, Polish J. Chem. 74
(2000) 615.
[
References
[
[
[
20] A.W. Coats, J.P. Redfern, Nature 201 (1964) 68.
21] J. Zsako, J. Phys. Chem. 72 (1968) 2406.
22] P.M. Madusudanan, K.K.M. Yasuff, C.G.R. Nair, J.
Therm. Anal. 8 (1975) 31.
[
[
1] A.F. Cristin, B. de Castro, J. Chem. Soc. Dalton Trans.
1998) 1491.
2] K.S. Suslick, T.J. Reinert, J. Chem. Educ. 62 (1985) 974.
(