Coordination chain polymers of some transition metals with Schiff base

Article abstract of DOI:10.1081/SIM-100105259

The Schiff base derived from terephthalaldehyde and o-aminophenol is known as N,N′-di(o-hydroxyphenyl)terephthalaldehydediimine and is termed here as H₂SB. The polychelates of this Schiff base having the general formula [M(SB)(H₂O)

Full text of DOI:10.1081/SIM-100105259

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COORDINATION CHAIN POLYMERS OF SOME TRANSITION
METALS WITH SCHIFF BASE
Nilesh H. Patel a , K. M. Patel a , K. N. Patel a & M. N. Patel b
a Department of Chemistry , Sardar Patel University , Vallabh Vidyanagar, Gujarat, 388 120,
India
b Department of Chemistry , Sardar Patel University , Vallabh Vidyanagar, Gujarat, 388 120,
India
Published online: 15 Feb 2007.
To cite this article: Nilesh H. Patel , K. M. Patel , K. N. Patel & M. N. Patel (2001) COORDINATION CHAIN POLYMERS OF SOME
TRANSITION METALS WITH SCHIFF BASE, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 31:6, 1031-1039,
DOI: 10.1081/SIM-100105259
To link to this article: http://dx.doi.org/10.1081/SIM-100105259
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(6), 1031±1039 (2001)
COORDINATION CHAIN POLYMERS
OF SOME TRANSITION METALS
WITH SCHIFF BASE
Nilesh H. Patel, K. M. Patel, K. N. Patel,
and M. N. Patel*
Department of Chemistry, Sardar Patel University,
Vallabh Vidyanagar-388 120, Gujarat, India
ABSTRACT
The Schi€ base derived from terephthalaldehyde and
o-aminophenol is known as N,N0-di(o-hydroxyphenyl)tere-
phthalaldehydediimine and is termed here as H2SB. The
polychelates of this Schi€ base having the general formula
[M(SB)(H2O)2]n [where M ˆ Mn(II), Co(II), Ni(II), Cu(II),
Zn(II) and Cd(II)] have been synthesized and characterized
on the basis of elemental analyses, infrared spectra, electronic
spectra, magnetic measurements and thermogravimetric ana-
lyses. The Schi€ base act as uninegative bidentate ligand and
bonding occurs through the hydroxyl oxygen and nitrogen
atoms. An octahedral geometry has been assigned to all of the
prepared polychelates.
*Corresponding author. E-mail: jeenen@redi€mail.com
1031
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

1032
PATEL ET AL.
INTRODUCTION
The study of polychelates or coordination polymers is of recent
interest. The coordination polymers of terephthalaldehyde containing
Schi€ bases have been prepared by Dey et al1. The present communica-
tion describes the synthesis of the Schi€ base of terephthalaldehyde and
o-aminophenol, which is capable of being bidentate and should form
linear polymers when allowed to react with suitable metal ions like
Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II). The structures of the
polymeric metal chelates were established on the basis of elemental ana-
lyses, infrared spectra, electronic spectra, magnetic and thermogravimetric
measurements.
The suggested structure of N,N0-di(o-hydroxyphenyl)terephthal-
aldehydediimine) (H2SB) is shown in Fig. 1.
EXPERIMENTAL
The chemicals employed were of analytical grade and were used
without further puri®cation.
Synthesis of the Ligand
An ethanolic solution (100 mL) of terephthalaldehyde (1.34 g, 1 mmol)
and an ethanolic solution (200 mL) of o-aminophenol (2.18 g, 2 mmol) were
mixed and a yellow crystalline solid was obtained immediately. The mixture
was heated on a water bath for one hour. The ligand was ®ltered, washed
successively with water and ethanol and dried in air. They are insoluble in
common organic solvents like benzene, chloroform, and acetone but soluble
in dimethylformamide.
Figure 1. Suggested structure of the ligand.

COORDINATION CHAIN POLYMERS
Synthesis of the Complexes
1033
The solution of metal acetate (2 mmol) in dimethyl formamide
(100 mL) was added slowly to a dimethyl formamide solution (100 mL) of
the ligand (0.6 g, 2 mmol) in 1:1 molar ratio. The mixture was heated for ten
hours at 120 ꢀC to ensure complete precipitation and then allowed to cool
overnight at room temperature. The obtained metal chelates were ®ltered,
washed with dimethyl formamide and dried in air. The polymeric chelates
are insoluble in all common organic solvents like acetone, ethanol, chloro-
form, methanol, benzene and dimethylformamide.
Analytical Procedures
The chelates were analyzed for the metal contents by the EDTA
titration technique2. The magnetic moment were obtained by Gouy's
method using mercury tetrathiocyanatocobaltate(II) as
a calibrant
(wg ˆ 6.44610À6 c.g.s. units at 20 ꢀC). Diamagnetic corrections were made
using Pascal's constant. The infrared spectra were recorded on a FT-IR
Nicolet 400 D spectrophotometer. The electronic spectra were measured on
a Beckman DK-2A spectrophotometer using MgO as reference. Nitrogen,
carbon and hydrogen were analysed with an Heraeus C, H, N analyzer
(Germany). A 951 Du Pont analyzer (Germany) was used for thermo-
gravimetric analyses. The experiment was started by heating the system at a
constant rate of 10 ꢀC per minute. Samples supplied by the Mettler company
were used for calibration of the thermobalance.
RESULTS AND DISCUSSION
The analytical data of the ligand and complexes and some physical
properties are listed in Table I. The reaction to form the complexes may be
represented as follows:
MꢁCH3COO† ‡ H2SB À! ‰ MSBꢁH2O† Š ‡ 2 CH3COOH
2
2 n
H2SB ˆ N; N0-diꢁo-hydroxyphenyl†terephthalaldehydediimine
M ˆ MnꢁII†; CoꢁII†; NiꢁII†; CuꢁII†; ZnꢁII†; and CdꢁII†:
The nature of the ligand, high thermal stability and metal-ligand ratio
(1:1) and insolubility of the complexes in common organic solvents suggest
their polymeric nature3. The insolubility of the complexes in common

1034
PATEL ET AL.

COORDINATION CHAIN POLYMERS
1035
organic solvents does not permit a determination of the molecular weights
but indicate a polymeric nature. It is suggested that the compounds are
coordination chain polymers4,5. Elemental analyses, physical properties and
infrared data provide good evidence that the compounds are polymeric. The
analytical data indicate that the polychelates have the general formula
[MSB(H2O)2]n.
The probable structure of the complexes shown in Fig. 2.
Magnetic Measurements
The magnetic measurement data are presented in Table I. The
magnetic moment value of the Cu(II) chelate (1.88 B.M.) is slightly higher
than the spin-only value (1.73 B.M.) expected for one unpaired electron,
which o€ers the possibility of an octahedral geometry6. The e€ective
magnetic moment of the Ni(II) chelate is (2.84 B.M.) indicating that this
chelate is also having an octahedral structure7. The observed magnetic
moment of the Co(II) chelate (4.38 B.M.) is in good agreement with high-
spin octahedral geometry8. The magnetic moment value for the Mn(II)
chelate is 6.1 B.M., which is slightly greater than spin-only value
5.92 B.M., but within the limits of spin-free values for ®ve unpaired
electrons, indicating that the chelates are high-spin six-coordinated9.
The magnetic moment determination shows that the Zn(II) and Cd(II)
chelates are diamagnetic.
Figure 2. Suggested structure of [MSB(H2O)2]n.

1036
PATEL ET AL.
Electronic Spectra
The electronic spectra of the chelates were recorded in the solid state.
The nickel(II) chelate gave three bands at 10,525, 16,970 and 25,000 cmÀ1
3
3
corresponding to the transitions A2g(F)?3T2g(F)(n1), A2g(F)?3T1g(F)(n2)
and 3A2g(F)?3T1g(P)(n3), respectively. The values of the ligand ®eld splitting
energy (10Dq), Racah interelectronic repulsion parameter (B), nephelauxetic
ratio (b) and ratio n2=n1 are presented in Table II and are consistent with the
values for an octahedral geometry. The electronic spectra of the mangane-
se(II) chelate show three weak bands at 14,600, 20,000 and 25,600 cmÀ1
which have been assigned to the transitions 6A1g?4T1g(4G), 6A1g?4T2g(4G)
6
and A1g(F)?4A1g, 4Eg (4G), respectively, in an octahedral ®eld of the
manganese(II) ion. The electronic spectra of the cobalt(II) chelate
show three bands at 9,090, 18,348 and 19,230 cmÀ1 which have been assigned
4
4
to the transitions T1g(F)?4T2g
,
4T1g(F)?4A2g and T1g(F)?4T1g(P),
respectively. The values of the ligand ®eld splitting energy (10Dq),
Racah interelectronic repulsion parameter (B), nephelauxetic ratio (b)
and ratio n2=n1 are presented in Table II and are consistent with the
values for an octahedral structure. The electronic spectra of the copper(II)
2
chelate10 exhibit a band at 16,500 cmÀ1 assigned to the Eg?2T2g transition
considering an octahedral geometry. A strong charge transfer band is
observed at 24,500 cmÀ1
.
Thermogravimetric Analyses
It has been observed that all the chelates show a loss in weight cor-
responding to two water molecules in the range 150to 180 ꢀC, indicating
that these water molecules are coordinated to the metal ion11. The TG
curves indicate that above 180 ꢀC the compounds start to loose mass with
partial evaporation of the Schi€ base. In the temperature range 180to
450 ꢀC the Schi€ base molecules are lost. In all of the cases the ®nal products
Table II. Re¯ectance Spectral Data of the Co(II) and Ni(II) Complexes
Observed Band (cmÀ1
)
Compound
n1
n2
n3
n2=n1
B
b
bꢀ
10Dq
[CoSB(H2O)2]n 9,090 18,348 19,230 2.01 751.45 0.773 22.7 10,221
[NiSB(H2O)2]n 10,525 16,970 25,000 1.61 693.00 0.672 32.7 10,525

COORDINATION CHAIN POLYMERS
Table III. Infrared Spectral Data of the Polychelates (cmÀ1 a
1037
)
Compound
n(O-H)
n(M-O)
n(C-O)
n(M-N)
n(CˆN)
H2SB
3375 s
3430b
3415 b
3420b
3425 b
3440 b
3425 b
7
1380s
1400s
7
440m
430 s
445 w
435 s
440 m
425 s
1625 s
1605 w
1600 w
1595 w
1595 w
1602 w
1605 w
[MnSB(H2O)2]n
[CoSB(H2O)2]n
[NiSB(H2O)2]n
[CuSB(H2O)2]n
[ZnSB(H2O)2]n
[CdSB(H2O)2]n
410m
405 m
405 m
415 m
410 m
420m
1390 s
1387 s
1384 s
1406 s
1391 s
ab ˆ broad, m ˆ medium, s ˆ strong, w ˆ weak.
are metal oxides. These results are in good accordance with the composition
of the complexes.
Infrared Spectra
The important infrared spectra of the chelates and their assignments
are presented in Table III. The spectra of H2SB show a medium intense
band at 2700 cmÀ1 due to intramolecularly hydrogen bonded n(OH)12. The
infrared spectra of the Schi€ base show a weak band at 320073600 cmÀ1
which is assigned to hydrogen bonded O-H stretching. This band becomes
broader on chelation. The spectra of the chelates exhibit a broad band in the
region of 330073400 cmÀ1 suggesting the presence of water molecule13,14
.
À1
The weak bands around 860and 700cm
are assigned as OH stretching,
rocking and wagging vibrations, respectively15. The presence of coordinated
water molecules is also con®rmed by elemental analyses and thermogravi-
metric analyses. The characteristic bands appearing at 159071630and
138071410cm À1 may be assigned to CˆN and phenolic C-O stretching
vibrations, respectively16,17. The ligand shows the CˆN stretching band
at 1625 cmÀ1 which shifts to 159571610cm À1 in the chelates indicating
the involvement of the azomethine nitrogen in coordination16. The band
appearing at about 410cm À1 is n(M-O)18. The band appearing at about
450cm À1 is n(M-N)19.
ACKNOWLEDGMENTS
The authors are thankful to the Head, Department of Chemistry,
Sardar Patel University, Vallabh Vidyanagar, India, for providing the
necessary laboratory facilities.

1038
PATEL ET AL.
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Received January 27, 1999
Accepted May 3, 2001
Referee I: K. P. Gable
Referee II: X. R. Bu