Transition metal(II) ions with dinegative tetradentate schiff base: Synthetic, thermal, spectroscopic and coordination aspects

Article abstract of DOI:10.1007/s10973-005-7284-5

Some new coordination polymers of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), obtained from the interaction of metal acetate with dipotassium salt of N,N'-di(carboxyethylidene)terephthalaldehydediimine (K₂SB) are described. The products, which have been characterized by elemental analyses, magnetic measurements, thermogravimetric analyses, electronic and infrared spectral studies, have composition, [M(SB)(H₂O)₂] _n. These colored coordination polymers are non-hygroscopic and quite stable at room temperature. On the basis of analytical data and IR studies, a 1:1 metal to ligand stoichiometry has been suggested to these coordination polymers. The IR studies have also revealed that ligands are coordinated to metal ion through carboxy oxygen and azomethine nitrogen. All the studies suggested tetradentate nature of the ligand with octahedral symmetry of the coordination polymers. All the coordination polymers are insoluble in acetone, ethanol, chloroform, methanol, benzene, DMF and DMSO. The thermal decomposition of the coordination polymers is studied and indicates that not only the coordinated water is lost but also that the decomposition of the ligand from the coordination polymers is necessary to interpret the successive mass loss. Springer-Verlag 2006.

Full text of DOI:10.1007/s10973-005-7284-5

Journal of Thermal Analysis and Calorimetry, Vol. 86 (2006) 3, 803–807
TRANSITION METAL(II) IONS WITH DINEGATIVE TETRADENTATE
SCHIFF BASE
Synthetic, thermal, spectroscopic and coordination aspects
*
H. M. Parekh, P. K. Panchal and M. N. Patel
Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar, 388 120 Gujarat, India
Some new coordination polymers of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), obtained from the interaction of metal acetate
with dipotassium salt of N,N’-di(carboxyethylidene)terephthalaldehydediimine (K
been characterized by elemental analyses, magnetic measurements, thermogravimetric analyses, electronic and infrared spectral
studies, have composition, [M(SB)(H O) . These colored coordination polymers are non-hygroscopic and quite stable at room
2
SB) are described. The products, which have
2
2 n
]
temperature. On the basis of analytical data and IR studies, a 1:1 metal to ligand stoichiometry has been suggested to these
coordination polymers. The IR studies have also revealed that ligands are coordinated to metal ion through carboxy oxygen and
azomethine nitrogen. All the studies suggested tetradentate nature of the ligand with octahedral symmetry of the coordination
polymers. All the coordination polymers are insoluble in acetone, ethanol, chloroform, methanol, benzene, DMF and DMSO. The
thermal decomposition of the coordination polymers is studied and indicates that not only the coordinated water is lost but also that
the decomposition of the ligand from the coordination polymers is necessary to interpret the successive mass loss.
Keywords: coordination polymers, spectroscopic analyses, tetradentate Schiff base, thermal analyses, transition metal
Introduction
Experimental
Reagent and solvents
The interest in the construction of coordination poly-
mers by linking transition metal ions with polydentate
ligands has been constantly growing over the past
years [1–7]. Coordination polymers (chelate polymers)
are defined as materials in which metal ions are linked
together with di- or polyfunctional ligands. Coordina-
tion polymers are usually known for their thermal sta-
bility [8, 9]. However, other equally important applica-
tions have been reported such as their use as solar
All the chemicals used were of analytical grade.
Terephthalaldehyde, DL-alanine, potassium hydroxide
and metal acetate were purchased from E. Merck (In-
dia) Ltd., Mumbai. The organic solvents were purified
by standard methods [14].
Synthesis of ligand
energy converters [10] and their ability to remove SO
x
A solution of potassium hydroxide (20 mmol, 1.12 g)
and NO from the environment [11]. The choice of the
x
in 50 mL absolute alcohol was added to DL-alanine
metal ions, the ligand design, the counter ions and the
solvents can have a considerable effect on the final ar-
chitecture of the coordination polymers and particu-
larly its dimensionality [12]. In continuation of earlier
work [13] herein we describe synthesis, characteriza-
tion and thermal studies of the coordination polymers
with Schiff base. The structure of the Schiff base is
shown in Scheme 1.
(
20 mmol, 1.78 g). The mixture was stirred until it dis-
solved in the ethanol–KOH solution. Then an ethanolic
solution (100 mL) of terephthalaldehyde (10 mmol,
.34 g) was added quickly. The mixture was heated on
1
a water bath for an hour. A yellow crystalline solid was
obtained on cooling at room temperature. The product
was filtered, washed with ethanol and dried in a vac-
uum desiccator. Yield: 56%; m.p.: >360°C.
Synthesis of the coordination polymers
The methanolic solution of 100 mL metal acetate
(
10 mmol) was added slowly to a methanolic solution
(100 mL) of dipotassium salt of N,N’-di(carboxy-
ethylidene)terephthalaldehydediimine (K SB)
2
Scheme 1 Structure of the Schiff base (K SB)
2
*
Author for correspondence: jeenenpatel@yahoo.co.in
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2006 Akadémiai Kiadó, Budapest

PAREKH et al.
a
Table 1 Analytical and physical data of Schiff base and its coordination polymers
Found (calcd.)/%
Empirical formula of
monomer unit
Colour
m.p./°C
(yield/%)
C
H
N
metal
–
2
K SB
yellow (56)
brown (47)
brown (53)
green (50)
green (52)
yellow (49)
yellow (46)
47.75 (47.72)
3.98 (3.97)
7.96 (7.94)
7.63 (7.67)
7.56 (7.58)
7.54 (7.59)
7.43 (7.49)
7.47 (7.45)
6.67 (6.62)
>360
>360
>360
>360
>360
>360
>360
14 14 2 2 4
C H K N O
2 2 n
[Mn(SB)(H O) ]
46.01 (46.05)
45.57 (45.55)
45.52 (45.58)
44.93 (44.99)
44.73 (44.77)
39.76 (39.79)
4.99 (4.93)
4.87 (4.83)
4.88 (4.84)
4.84 (4.81)
4.76 (4.79)
4.29 (4.26)
15.01 (15.04)
15.71 (15.96)
15.73 (15.91)
17.05 (17.00)
17.36 (17.41)
26.57 (26.60)
14 2 6
C H18MnN O
2 2 n
[Co(SB)(H O) ]
14 2 6
C H18CoN O
2 2 n
[Ni(SB)(H O) ]
14 2 6
C H18NiN O
2 2 n
[Cu(SB)(H O) ]
C
14
H18CuN
2
O
6
[Zn(SB)(H
2
2 n
O) ]
C
14
H18ZnN
2
O
6
[Cd(SB)(H
2
2 n
O) ]
14 2 6
C H18CdN O
a
2
K SB=dipotassium salt of N,N’-di(carboxyethylidene)terephthalaldehydediimine
(
10 mmol, 3.52 g) in 1:1 mole ratio. The mixture was
two potassium ions from Schiff base ligand. The poly-
meric compounds were insoluble in common organic
compounds and, therefore, precluded the determina-
tion of molecular mass. Elemental analyses, physical
properties and infrared data provide good evidence that
the chelates are polymeric in nature [15]. The sug-
gested structure of the coordination polymers is shown
in Scheme 2.
heated for 8 h at 80°C to ensure complete precipita-
tion and then allowed to cool overnight at room tem-
perature. The obtained coordination polymers were
filtered, washed with methanol and dried in air. The
coordination polymers are insoluble in all common
organic solvents like acetone, ethanol, methanol,
chloroform, benzene, dimethyl formamide and di-
methyl sulfoxide.
Infrared spectra
Results and discussion
In order to study the binding mode of Schiff base to the
metal ion in the coordination polymers, the IR spec-
trum of the free ligand was compared with the spectra
of the corresponding coordination polymers. The infra-
red spectra of the coordination polymers are shown in
Fig. 1. In the spectra of the Schiff base, a strong band
Table 1 lists the analytical data for the ligand
(
K SB) and their coordination polymers with metal
2
ions. The coordination polymers are of the general
formulae [M(SB)(H O) ] and were prepared by
2
2 n
–1
following reaction.
at 1635 cm is attributable to the –C=N group, indi-
cates the formation of the Schiff base. On coordination,
due to possible drift of the lone pair density towards
the metal ion, the azomethine –C=N bond is expected
to absorb at lower frequency in the coordination poly-
M(CH COO) +K SB→
M(SB)(H O) ] +2CH COOK
2 2 n 3
3
2
2
[
The formation of coordination polymers hav-
–
1
ing 1:1 metal–ligand mole ratio facilitated by loss of
mers. The band observed at ~1605–1615 cm indi-
cates the coordination of the azomethine nitrogen to
the metal ion [16]. In all the coordination polymers, a
–1
new band is seen in the 525–535 cm region, which is
probably due to the formation of M–N bonds [17]. The
infrared spectra of the coordination polymers exhibit a
–1
broad band in the region 3300–3500 cm is due to
–1
νO–H and other bands at ~850 and ~715 cm are due to
the rocking and wagging mode of the OH group [18].
The presence of later band indicates the coordination
nature of the water molecule [19]. The two absorption
Scheme 2 Structure of the coordination polymers;
–1
bands occurring near 1595 and 1400 cm in the Schiff
2 2 n
[M(SB)(H O) ] where M=Mn(II), Co(II), Ni(II),
base (K SB) corresponding to the asymmetric and
2
Cu(II), Zn(II) and Cd(II)
804
J. Therm. Anal. Cal., 86, 2006

TRANSITION METAL(II) IONS WITH DINEGATIVE TETRADENTATE SCHIFF BASE
tion polymer, the reflectance spectra exhibits the bands
of medium intensity at ~9200, ~18000
and ~19000 cm , which are assigned to the transitions
–1
4
4
4
4
T (F)→ T (F) (ν ), T (F)→ A (F) (ν ) and
1g
2g
1
1g
2g
2
4
4
T (F)→ T (P) (ν ), respectively, of an octahedral
1g
1g
3
cobalt(II) coordination polymer [22] and the magnetic
moment value is 4.19 B.M. The electronic spectra of
the Ni(II) coordination polymer exhibits absorption
–1
bands at ~10500, ~18165 and ~24100 cm attributed
3
3
3
3
to A (F)→ T (F) (ν ), A (F)→ T (F) (ν ) and
2g
2g
1
2g
1g
2
3
3
A (F)→ T (P) (ν ) transitions, respectively, in an
2g
1g
3
octahedral geometry [23]. The value of the magnetic
moment (2.92 B.M.) may be taken as additional evi-
dence for their octahedral structure. The ground state
6
of Mn(II) is A1g. The Mn(II) coordination polymer in
an octahedral field should have three transitions corre-
4
6
4
–1
6
sponding to A → T (ν ~15000 cm ), A → T
1
1
g
1g
6
1
1g
2g
–1
–
4
4
(
ν ~19600 cm ) and A → A , E (ν ~24500 cm )
2
1g
1g
g
3
in increasing order of energy. The magnetic moment
value of the Mn(II) coordination polymer is 6.18 B.M.,
suggesting an octahedral geometry [24]. The Cu(II) co-
ordination polymer display
2
a
broad band
–1
2
at ~15500 cm due to the E → T transition and the
g
2g
Fig. 1 Infrared spectra of the coordination polymers
magnetic moment value is 1.78 B.M., which are close
to spin-only value (1.73 B.M.) expected for an un-
paired electron, which offers the possibility of an octa-
hedral geometry [25]. Electronic spectral data and
magnetic moments of coordination polymers are sum-
marized in Table 2. The values of the electronic param-
eters such as the ligand field splitting energy (10 Dq),
Racah interelectronic repulsion parameter (B),
nephelauxetic ratio (β), and ratio ν /ν are presented in
symmetric stretching vibration bands of the ionic
carboxy group νCOO, in the coordination polymers are
shifted to lower frequencies ~1585 and 1390 cm , re-
–1
spectively [20]. The appearance of a new band
–1
at 415–420 cm due to νM–O [21] further confirms the
coordinated nature of the carboxylate groups. The co-
ordination polymers show sharp band in the
2
1
–1
range 750–780 and 1525–1535 cm are due to aro-
Table 3. The Zn(II) and Cd(II) coordination polymers
1
0
matic νC–H and νC=C–,1 respectively. The band in the
are diamagnetic as expected for d systems.
range 1370–1390 cm is due to ν C– CH 3
.
Thermogravimetric studies
Magnetic moments and electronic spectra
The thermogravimetric analysis for the coordination
polymers was carried out within a temperature range
The information regarding geometry of the coordina-
tion polymers is obtained from their electronic spectral
data and magnetic moments. For the Co(II) coordina-
from 50 to 800°C in N atmosphere to establish their
2
compositional differences as well as to ascertain the na-
a
Table 2 Electronic spectral data and magnetic moments of coordination polymers
–1
Coordination polymers
Absorption/cm
Transition
μeff/B.M. (calcd.)
6
6
6
4
1
5000
19600
4500
A
1g→4T1g
[
Mn(SB)(H
2
O)
2
]
n
A → T
6.18 (5.92)
1
g
2g
4
4
2
A
1g→ A1g, E
g
4
4
4
4
9
200
T
1g(F)→4T2g(F)
[
Co(SB)(H
2
O)
2
]
n
18000
T (F)→ A (F)
4.19 (3.87)
1g
2g
4
1
9000
0500
T
1g(F)→ T1g(p)
3
3
3
3
1
A
2g(F)→3T2g(F)
[
Ni(SB)(H
2
O)
2
]
n
18165
4100
A (F)→ T (F)
A
2.92 (2.83)
1.78 (1.73)
2g
1g
3
2
2g(F)→ T1g(p)
2
2
[
Cu(SB)(H
2
O)
2
]
n
15500
E
g
→ T2g
a
2
K SB=dipotassium salt of N,N’-di(carboxyethylidene)terephthalaldehydediimine
J. Therm. Anal. Cal., 86, 2006
805

PAREKH et al.
a
Table 3 Electronic parameters of the Co(II) and Ni(II) coordination polymers
–
1
Observed bands/cm
Coordination
polymers
ν
2
/ν
1
B
β
β°
10 Dq
ν
1
ν
2
ν
3
[
[
Co(SB)(H
2
O)
2
]
n
9200
18000
18165
19000
24100
1.95
1.73
728
717
0.75
0.69
25
31
10320
10500
Ni(SB)(H
2
O)
2
]
n
10500
a
K
2
SB=dipotassium salt of N,N’-di(carboxyethylidene)terephthalaldehydediimine
The ligand field splitting energy (10 Dq), interelectronic repulsion parameter (B) and covalency factor (nephelauxetic ratio) β for
the Co(II) and Ni(II) coordinating polymers have been calculated using the secular equations given by König [30]
for Co(II) complexes
0 Dq=1\2[(2ν –ν )+(ν +ν
+10 Dq
(free ion)=971]
for Ni(II) complexes
10 Dq=ν
15B=(ν +ν
β=B\B [B (free ion)=1030]
β°=(1–β)⋅100
2
2
1/2
1
1
3
1
ν
3
–ν1 )
]
1
3
1
5B=ν
3
0
–2ν
[B
1
2
3
)–3ν
1
β=B\B
0
0
0
β°=(1–β)⋅100
a
Table 4 Thermogravimetric data
Coordination
polymers
TG
range/°C
Mass loss estimated
(calcd.)/%
Activation energy,
–1
Assignment
E
a
/kcal mol
1
1
50–180
80–800
9.81 (9.86)
loss of two coordinated water molecules
[
[
[
[
[
[
2 2 n
Mn(SB)(H O) ]
4.12
80.53 (80.57)
decomp. of ligand and formation of metal oxide
1
1
50–180
80–800
9.74 (9.75)
loss of two coordinated water molecules
Co(SB)(H
2
O)
2
]
n
5.45
3.66
4.66
5.28
4.05
77.59 (77.53)
decomp. of ligand and formation of metal oxide
1
1
50–180
80–800
9.79 (9.76)
loss of two coordinated water molecules
2 2 n
Ni(SB)(H O) ]
79.76 (79.76)
decomp. of ligand and formation of metal oxide
1
1
50–180
80–800
9.67 (9.63)
loss of two coordinated water molecules
Cu(SB)(H
2
2 n
O) ]
78.74 (78.71)
decomp. of ligand and formation of metal oxide
1
1
50–180
80–800
9.53 (9.58)
loss of two coordinated water molecules
2 2 n
Zn(SB)(H O) ]
78.36 (78.32)
decomp. of ligand and formation of metal oxide
1
1
50–180
80–800
8.58 (8.51)
loss of two coordinated water molecules
2 2 n
Cd(SB)(H O) ]
69.69 (69.61)
decomp. of ligand and formation of metal oxide
a
2
K SB=dipotassium salt of N,N’-di(carboxyethylidene)terephthalaldehydediimine
The TG curves of the Mn(II), Co(II), Ni(II),
Cu(II), Zn(II) and Cd(II) coordination polymers show
a two-decomposition steps within the temperature
ranges of 150–180 and 180–800°C. The first estimated
mass losses (%) for [M(SB)(H
polymers are of 9.81 (9.86), 9.74 (9.75), 9.79 (9.76),
.67 (9.63), 9.53 (9.58) and 8.58 (8.51) within the tem-
2 2 n
O) ] coordination
9
perature range of 150–180°C may be attributed to the
loss of two coordinated water molecules [27] of the
Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) coordi-
nation polymers, respectively. The second estimated
mass losses (%) for [M(SB)(H
polymers are of 80.53 (80.57), 77.59 (77.53),
79.76 (79.74), 78.74 (78.71), 78.36 (78.32) and
9.69 (69.61) within the temperature range of
80–800°C may be attributed to the loss of ligand mol-
2 2 n
O) ] coordination
Fig. 2 Thermogravimetric curve of the [Ni(SB)H
nation polymer
2 2 n
O) ] coordi-
6
1
ture of associated water molecules [26]. The Thermo-
gravimetric curve of the coordination polymer is shown
in Fig. 2. The determined temperature ranges, percent
mass losses and thermal effects accompanying the
changes in the coordination polymers on heating are
given in Table 4, which revealed the following findings.
ecule and formation of metal oxide of the Mn(II),
Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) coordination
polymers, respectively.
The kinetic parameters, especially activation en-
ergy (E ) is helpful in assigning the strength of the
a
bonding of ligand moieties with the metal ion. The
806
J. Therm. Anal. Cal., 86, 2006

TRANSITION METAL(II) IONS WITH DINEGATIVE TETRADENTATE SCHIFF BASE
calculated E values of the investigated complexes i.e,
a
13 N. H. Patel, P. K. Panchal and M. N. Patel, Synth. React.
Inorg. Met.-Org. Nano-Met. Chem., 35 (2005) 109.
the stage of the formation of volatile gas products, are
–
1
14 A. I. Vogel, Textbook of Practical Organic Chemistry,
th
in the 3.66–5.45 kcal mol range. The relative high
Ea value indicates that the ligand is strongly bonded to
metal ion [28]. Based on the activation energy values,
the thermal stability of the coordination polymers in
the decreasing order is: Co>Zn>Cu>Mn>Cd>Ni [29].
5
Edn. Longman, London 1989.
5 V. V. Korshak, S. V. Vinogradova and Artemova,
Vysokomolekul Soidien, 2 (1960) 492; Chem. Abstr.,
5 (1961) 3404c.
1
5
1
1
1
1
2
2
2
2
2
2
2
6 R. K. Agarwal, H. Agarwal and I. Chakraborti,
Synth. React. Inorg. Met.-Org. Chem., 25 (1999) 679.
7 E. M. Jouad, A. Riou, M. Allain, M. A. Khan and
G. M. Bouet, Polyhedron, 20 (2001) 67.
Acknowledgements
8 M. Tümer, B. Erdogan, H. Köksal, S. Serin and M. Y. Nutka,
Synth. React. Inorg. Met.-Org. Chem., 28 (1998) 529.
9 M. A. Banares, M. Gonzalez and R. J. Ruano, Polyhedron,
5 (1986) 1371.
We wish to express our gratitude to the Head, Department of
Chemistry, Sardar Patel University, Vallabh Vidyanagar,
India, for providing the necessary laboratory facilities.
0 Y. T. Li, C. W. Yan, C. S. Xu and D. Z. Liao,
Synth. React. Inorg. Met.-Org. Chem., 30 (2000) 1069.
1 G. G. Mohamed, N. E. A. El-Gamed and E. A. Nour El-Dien,
Synth. React. Inorg. Met.-Org. Chem., 31 (2001) 347.
2 C. H. Krishna, C. M. Mahapatra and K. A. Dash,
J. Inorg. Nucl. Chem., 39 (1977) 1253.
References
1
2
3
4
5
S. R. Batten and R. Robson, Angew. Chem. Int. Ed.,
7 (1998) 1460.
3
3 M. M. Khalil, A. H. H. El-Ghandour, M. Mostafa and
M. M. Shoukry, Polyhedron, 13 (1994) 3295.
O. M. Yaghi, M. O’Keeffe, N. W. Ockwig, H. K. Chae,
M. Eddaoudi and J. Kim, Nature, 423 (2003) 705.
S. Kitagawa, R. Kitaura and S.-I. Noro, Angew. Chem.
Int. Ed., 43 (2004) 2334.
4 A. B. P. Lever, Electronic spectra of dn ions. In Inorganic
nd
Electronic Spectroscopy, 2 Ed., Elsevier, Amsterdam 1984.
5 A. L. Abuhijleh, C. Woods and I. Y. Ahmed,
Inorg. Chim. Acta, 190 (1991) 11.
S. Kitagawa and K. Uemura, Chem. Soc. Rev.,
3
4 (2005) 109.
H. W. Roesky and M. Andruh, Coord. Chem. Rev.,
1 (2003) 236.
6 N. Wasi and H. B. Singh, Synth. React. Inorg. Met.-Org.
Chem., 18 (1988) 473.
9
2
2
7 H. A. El-Boraey, J. Therm. Anal. Cal., 81 (2005) 339.
8 J. Garcice, M. C. Molla, J. Borras and E. Escriva,
Thermochim. Acta, 106 (1986) 155.
6
7
C. Janiak, J. Chem. Soc., Dalton Trans., 14 (2003) 2781.
N. H. Patel, K. N. Patel and M. N. Patel, Synth. React.
Inorg. Met.-Org. Chem., 32 (2002) 1879.
2
3
9 J. T. D’Sa, V. J. Rao, K. C. Patel and R. D. Patel,
Angew. Makromol. Chem., 79 (1979) 133.
0 E. König, The nephelauxetic effect. In Structure and
Bonding, Springer Verlag, New York 1971, p. 9, 175.
8
9
A. Bajpai, S. Rai and U. D. N. Bajpai, Polym. J.,
(
Tokyo) 29 (1997) 44; Chem. Abstr., 127 (1997) 126137.
K. Tokaji and I. Tomita, Endo T Macromolecules,
0 (1997) 7386.
0 D. H. Grayson and J. Kelly, M Sol. Energy R and D Eur. Com-
3
1
munity, Ser. D. (1983) (Photo Chem., Photo Electrochem.,
Photobiol. Processes) 51; Chem. Abstr., 99 (1983) 178958.
1 N. Toshima, Kogya Zairyo, 39 (1991) 45; Chem. Abstr.,
Received: August 5, 2005
Accepted: November 11, 2005
OnlineFirst: May 23, 2006
1
1
115 (1991) 238558F.
2 A. N. Khlobystov, A. J. Blake, N. R. Champness,
D. A. Lemenovskii, A. G. Majouga, N. V. Zyk and
M. Schröder, Coord. Chem. Rev., 222 (2001) 155.
DOI: 10.1007/s10973-005-7284-5
J. Therm. Anal. Cal., 86, 2006
807