Syntheses, spectroscopic, and magnetic properties of polystyrene-anchored coordination compounds of tridentate ONO donor Schiff base

Article abstract of DOI:10.1080/00958972.2011.552108

The crosslinked chloromethylated polystyrene (PSCH₂-Cl) reacts with the Schiff base, derived from condensation of PSCH₂-Cl with 3-formylsalicylic acid and salicylhydrazide to form a polystyrene-anchored Schiff base, PSCH₂-LH₃ (1). Compound 1 reacts with a number of metal ions to form polystyrene-anchored coordination compounds, PSCH₂-LHM·DMF (where M = Cu, Zn, Cd, UO₂, and MoO₂), PSCH2-LHM′ = 3DMF (where M′ = Mn, Co, and Ni), PSCH₂-LHFeCl·2DMF, and PSCH₂-LHZr(OH) ₂·2DMF. The polystyrene-anchored coordination compounds have been characterized by elemental analyses, spectra (infrared, reflectance, and electron spin resonance) and magnetic susceptibility measurements. The polystyrene-anchored compounds are magnetically dilute. Shifts in band positions of the groups involved in coordination have been utilized to find tridentate ONO donor behavior of 1. The polystyrene-anchored Zn(II), Cd(II), Zr(IV), MoO₂(VI), and UO₂(VI) compounds are diamagnetic, while Mn(II), Co(II), Ni(II), Cu(II), and Fe(III) compounds are paramagnetic. The polystyrene-anchored Cu(II) compound is square planar; Zn(II) and Cd(II) compounds are tetrahedral; Co(II), Ni(II), Mn(II), Fe(III), MoO₂(VI), and UO₂(VI) compounds are octahedral; and Zr(IV) compound is pentagonal bipyramidal.

Full text of DOI:10.1080/00958972.2011.552108

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Syntheses, spectroscopic, and magnetic
properties of polystyrene-anchored
coordination compounds of tridentate
ONO donor Schiff base
Dinesh Kumar a , Praveen Kumar Gupta b , Amit Kumar b , Durga
Dass c & Arun Syamal d
a Department of Chemistry, National Institute of Technology,
Kurukshetra 136119, Haryana, India
b Department of Chemistry, Haryana College of Technology and
Management, Kaithal 136027, Haryana, India
c Department of Chemistry, Sri Krishna Institute of Engineering
and Technology, Kurukshetra 136119, Haryana, India
d School of Coordination Chemistry, D Wing, Ushanagar, Bhandup,
Mumbai 400 078, India
Version of record first published: 04 Feb 2011.
To cite this article: Dinesh Kumar, Praveen Kumar Gupta, Amit Kumar, Durga Dass & Arun Syamal
(2011): Syntheses, spectroscopic, and magnetic properties of polystyrene-anchored coordination
compounds of tridentate ONO donor Schiff base, Journal of Coordination Chemistry, 64:4, 590-599
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Journal of Coordination Chemistry
Vol. 64, No. 4, 20 February 2011, 590–599
Syntheses, spectroscopic, and magnetic properties of
polystyrene-anchored coordination compounds of tridentate
ONO donor Schiff base
DINESH KUMARy, PRAVEEN KUMAR GUPTA*z, AMIT KUMARz,
DURGA DASSx and ARUN SYAMAL{
yDepartment of Chemistry, National Institute of Technology,
Kurukshetra 136119, Haryana, India
zDepartment of Chemistry, Haryana College of Technology and Management,
Kaithal 136027, Haryana, India
xDepartment of Chemistry, Sri Krishna Institute of Engineering and Technology,
Kurukshetra 136119, Haryana, India
{School of Coordination Chemistry, D Wing, Ushanagar,
Bhandup, Mumbai 400 078, India
(Received 24 August 2010; in final form 18 November 2010)
The crosslinked chloromethylated polystyrene (PSCH2–Cl) reacts with the Schiff base, derived
from condensation of PSCH2–Cl with 3-formylsalicylic acid and salicylhydrazide to form a
polystyrene-anchored Schiff base, PSCH2–LH3 (1). Compound 1 reacts with a number of metal
ions to form polystyrene-anchored coordination compounds, PSCH2–LHM ꢀ DMF (where
M ¼ Cu, Zn, Cd, UO2, and MoO2), PSCH2–LHM0 ꢀ 3DMF (where M0 ¼ Mn, Co, and Ni),
PSCH2–LHFeCl ꢀ 2DMF, and PSCH2–LHZr(OH)2 ꢀ 2DMF. The polystyrene-anchored coor-
dination compounds have been characterized by elemental analyses, spectra (infrared,
reflectance, and electron spin resonance) and magnetic susceptibility measurements. The
polystyrene-anchored compounds are magnetically dilute. Shifts in band positions of the
groups involved in coordination have been utilized to find tridentate ONO donor behavior of 1.
The polystyrene-anchored Zn(II), Cd(II), Zr(IV), MoO2(VI), and UO2(VI) compounds are
diamagnetic, while Mn(II), Co(II), Ni(II), Cu(II), and Fe(III) compounds are paramagnetic.
The polystyrene-anchored Cu(II) compound is square planar; Zn(II) and Cd(II) compounds
are tetrahedral; Co(II), Ni(II), Mn(II), Fe(III), MoO2(VI), and UO2(VI) compounds are
octahedral; and Zr(IV) compound is pentagonal bipyramidal.
Keywords: Schiff base; Coordination compound; Paramagnetic; Magnetically dilute; ESR
1. Introduction
Anchoring chelating ligands to insoluble polymer matrices and their reaction with metal
ions provide a route for synthesis of immobilized transition metal compounds. Polymer-
anchored compounds have numerous applications in organic synthesis [1], immobili-
zation of enzymes [2], biological systems [3], water treatment [4], as catalysts [5], etc.
*Corresponding author. Email: praveen_gemini@yahoo.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2011.552108

Polystyrene-anchored coordination compounds
591
A perusal of the literature indicates that several polymer-anchored ligands containing
oxygen donors like crown ethers [6], ꢀ-diketone [7], iminodiacetic acid [8],
iminodipropionic acid [9], etc. have been reported. The coordination complexes of
aroyl hydrazones possess biological activity as inhibitors for enzymes [10]. Here, we
describe the syntheses and characterization of polystyrene-anchored coordination
compounds of 1 with Cd(II), Co(II), Cu(II), Mn(II), Ni(II), Zn(II), Fe(III), Zr(IV),
MoO2(VI), and UO2(VI) ions. The present compounds may act as catalysts for various
oxidation reactions.
O
O
CH PS
O
O
CH PS
2
2
C
C
HO
HO
OH
OH
O
HO
N
C
H
C
C
N
N
C
N
H
H
I
2. Experimental
2.1. Materials
Chloromethylated polystyrene (PSCH2–Cl) (0.94 mmol of Cl per gram of resin and 1%
crosslinked with divinylbenzene) was a product of Sigma Chemical Co. (USA). The
other chemicals and solvents were obtained from sources mentioned earlier [11].
3-Formylsalicylic acid, salicylhydrazide, and zirconium(IV) acetate were synthesized
by following reported procedures [12–14].
2.2. Analyses and physical measurements
Leaching of metal ions from the corresponding polystyrene-anchored coordination
compounds and estimation of the amount were carried out as reported [11]. The
coordinated DMF molecules were determined by heating the corresponding polystyr-
ene-anchored coordination compounds in an air oven at a definite temperature for 3 h.
IR spectra were recorded using KBr pellets (4000–400 cmꢁ1) on a Nicolet Fourier
transform infrared spectrophotometer calibrated with polystyrene. Reflectance spectra
were recorded on a Beckmann DU spectrophotometer attached with a reflectance
apparatus. Magnetic susceptibility measurements were carried out at room tempera-
ture, using double-ended, one-sided, sealed Gouy tubes and Hg[Co(NCS)4] as the
standard. The diamagnetic corrections were computed using the procedure developed
for polymer-supported coordination compounds [15]. Magnetic susceptibilities for
diamagnetism of ligand and metal ions were corrected for temperature-independent
paramagnetism (TIP) term. The TIP values were taken as 200 ꢂ 10ꢁ6 cgs units for
Co(II) and Ni(II) and 60 ꢂ 10ꢁ6 cgs units for Cu(II). The TIP value for Fe(III) was
6
taken as zero as the high-spin d5 system has a A1g ground state. Electron spin
resonance (ESR) spectra were recorded at liquid N2 temperature in polycrystalline
solids on a Varian V4502-12 X-band ESR spectrophotometer with 100-KHz

592
D. Kumar et al.
modulation using diphenylpicrylhydrazide as a g-marker and monitoring the frequency
with frequency meter.
2.3. Synthesis of 3-formylsalicylic acid–salicylhydrazide
An MeOH solution (25 mL) of salicylhydrazide (1.52 g, 10 mmol) was added slowly to
MeOH solution (30 mL) of 3-formylsalicylic acid (1.66 g, 10 mmol). The mixture was
refluxed on a water bath for 45 min. The light yellow precipitates obtained were
suction filtered, washed with MeOH, and finally dried; m.p. ¼ 250ꢃC. Anal.
Calcd for C15H12N2O5 (%): N, 9.33. Found: N, 9.29. Yield ¼ 65%. IR bands:
1670 cmꢁ1 [ꢁ(C¼O)(carboxylic)], 1610 cmꢁ1 [ꢁ(C¼N)(azomethine)], and 1545 cmꢁ1
[ꢁ(C–O)(phenolic)].
2.4. Synthesis of polystyrene-anchored Schiff base (PSCH2-LH3)
Chloromethylated polystyrene (PSCH2–Cl) (1.0 g) was suspended in DMF (20 mL) for
45 min. A DMF solution (40 mL) of 3-formylsalicylic acid–salicylhydrazide (0.85 g,
2.82 mmol) was added to the above suspension. Ethyl acetate (100 mL) and
triethylamine (5 mL) were then added to the above mixture. The mixture was refluxed
for 8 h while stirring magnetically and then cooled to room temperature. The pale
yellow product was suction filtered, washed thoroughly with DMF, ethyl acetate,
EtOH, MeOH, and petroleum ether, and dried as mentioned above. IR bands:
1740 cmꢁ1 [ꢁ(C¼O)(ester)], 1615 cmꢁ1 [ꢁ(C¼N)(azomethine)], and 1540 cmꢁ1 [ꢁ(C–O)
(phenolic)].
2.5. Syntheses of coordination compounds of PSCH2–LH3 (1)
0.5 g of 1 was suspended in DMF (20 mL) for 1 h and DMF solution of appropriate
metal salt (0.94 mmol) was added. The mixture was refluxed on a water bath for 5–10 h
and the products obtained were suction filtered, washed several times with ethyl acetate
and DMF, and then dried as mentioned above.
3. Results and discussion
For the synthesis of polystyrene-anchored compounds, chloromethylated polystyrene
containing 0.94 mmol of Cl per gram of resin and 1% crosslinked with divinylbenzene
was selected because a higher crosslinking may affect the metal binding power of
PSCH2–LH3. Polymer with low chlorine concentration was selected in order to avoid
formation of magnetically concentrated metal coordination compounds. The poly-
styrene-supported Schiff base used for the synthesis of polystyrene-bound coordination
compounds has the structure 1, synthesized by reacting chloromethylated polystyrene
and the Schiff base in 1 : 3 ratio in DMF, causing considerable swelling of PSCH2–Cl.
The chloromethylated polystyrene is white, while polystyrene-supported Schiff base is
yellow; the color remains unchanged even after repeated washings with DMF, ethyl

Polystyrene-anchored coordination compounds
593
acetate, ethanol, and petroleum ether. Since the coupled polymer is insoluble in
common organic solvents, a heterogeneous synthetic route was used for metal-bound
polymers. DMF was selected as a solvent because it has high dielectric constant and is
more effective in swelling PSCH2–Cl and PSCH2–LH3. The formation of the PSCH2–
LH3 and its coordination compounds are given below:
O
HO
C
HO
OH
C
O
DMF, ethyl acetate,
–
PSCH Cl +
2
C
I
triethylamine, reflux, -HCl
N
N
H
H
DMF
reflux
PSCH2–LH3 + M(CH3COO)2
PSCH2–LHM⋅DMF + 2CH3COOH
[M = Cd(II), Cu(II), Zn(II), UO2(VI)]
PSCH2–LHM⋅3DMF + 2CH3COOH
[M = Mn(II), Co(II), Ni(II)]
DMF
PSCH2–LH3 + FeCl3
PSCH2–LHFeCl⋅2DMF + 2HCl
reflux
DMF
4PSCH2–LH3 + [Zr4(OH)8(H2O)16](CH3COO)8
4PSCH2–LHZr(OH)2⋅2DMF
reflux
+ 8CH3COOH + 16H2O
DMF
PSCH2–LH3 + MoO2(acac)2
PSCH2–LHMoO2⋅DMF + 2acacH
reflux
In the synthesis of polystyrene-bound Schiff base, the percent reaction conversion
was found to be 100 and there was no chlorine present in the polymer-bound Schiff
base. This was possible by maintaining a very large excess of chloromethylated
polystyrenes (Schiff base ratio of 1 : 3). If the ratio was 1 :53, then the polystyrene-
bound Schiff base always contained some unreacted –CH2Cl group. In the synthesis of
the polystyrene-anchored metal compounds, the ligand : metal ratio was maintained at
1 : 2, giving percent conversion less than 100. The percent reaction conversion of
PSCH2–LH3 to produce the corresponding coordination compounds ranges from 35.4
to 93.3 (table 1). The metal binding capacities of the Schiff base are 0.22–0.58 mmol
of metal per gram (table 1). The coordinated DMF is lost completely on heating the
metal-bound polymers in air.
Infrared spectral data of polystyrene-supported Schiff base and its coordination
compounds are presented in table 2. The ꢁ(C¼O)(carboxylic) stretch in 3-formylsalicylic
acid occurs at 1660 cmꢁ1. The polystyrene-bound Schiff base shows a new band at
1740 cmꢁ1 due to the ꢁ(C¼O)(ester) [11]. The shift of ꢁ(C¼O) is indicative of covalent
bond formation between Schiff base with chloromethylated polystyrene through
carboxylic acid. Schiff base and 1 occur in keto form as shown by the presence of a
strong band at ꢄ1680 cmꢁ1. This band disappears in the polystyrene-anchored
coordination compounds, indicating destruction of carbonyl moiety due to enolization,

594
D. Kumar et al.
Table 1. Characterization data of the polystyrene-anchored coordination compounds.
Found (Calcd) (%)
Metal-binding
capacity
Percent
reaction
Polystyrene-anchored
coordination compounds
Color
Yellow
Brown
Dark brown
Dark brown
Green yellow
Light yellow
M
DMF
(mmol gꢁ1 of resin) conversion
PSCH2–LHCd ꢀ DMF
PSCH2–LHCo ꢀ 3DMF
PSCH2–LHCu ꢀ DMF
PSCH2–LHMn ꢀ 3DMF
PSCH2–LHNi ꢀ 3DMF
PSCH2–LHZn ꢀ DMF
PSCH2–LHFeCl ꢀ 2DMF
4.0 (7.44)
1.3 (3.67)
2.5 (4.34)
3.2 (3.43) 12.8 (13.69)
3.3 (3.66) 12.3 (13.66)
2.6 (4.83)
4.8 (13.66)
2.9 (4.99)
0.36
0.22
0.39
0.58
0.56
0.38
0.41
0.25
0.50
0.49
53.8
35.4
57.6
93.3
90.2
55.9
64.2
40.3
76.4
81.3
2.5 (4.47)
2.8 (4.99)
6.0 (9.33)
3.7 (9.14)
3.6 (4.78)
Reddish brown 2.3 (3.58)
2.3 (5.71)
4.8 (6.28)
PSCH2–LHZr(OH)2 ꢀ 2DMF Cream
PSCH2–LHMoO2 ꢀ DMF
PSCH2–LHUO2 ꢀ DMF
Light yellow
Orange
11.6 (14.27) 3.6 (4.38)
Table 2. Infrared spectral data (cmꢁ1
coordination compounds.
) of polystyrene-anchored Schiff base and the
Polystyrene-anchored
coordination compounds
ꢁ(C¼N)
ꢁ(C–O)
(phenolic)
ꢁ(C¼O)
(azomethine)
(DMF)
ꢁ(N–N)
PSCH2–LH3
1615
1595
1590
1590
1600
1595
1600
1605
1605
1600
1590
1540
1550
1545
1545
1550
1545
1550
1550
1545
1550
1545
–
1040
1055
1060
1055
1060
1055
1065
1065
1055
1060
1050
PSCH2–LHCd ꢀ DMF
PSCH2–LHCo ꢀ 3DMF
PSCH2–LHCu ꢀ DMF
PSCH2–LHMn ꢀ 3DMF
PSCH2–LHNi ꢀ 3DMF
PSCH2–LHZn ꢀ DMF
PSCH2–LHFeCl ꢀ 2DMF
PSCH2–LHZr(OH)2 ꢀ 2DMF
PSCH2–LHMoO2 ꢀ DMF
PSCH2–LHUO2 ꢀ DMF
1645
1660
1660
1650
1645
1660
1655
1650
1655
1640
leading to the formation of 4C¼N–N¼C5 group [16]. The polystyrene-anchored
coordination compounds exhibit a new strong band at 1225–1230 cmꢁ1 due to ꢁ(C–
O)(enolic) stretch [17]. Polystyrene-supported Schiff base exhibits ꢁ(N–N) at 1040 cmꢁ1
which undergoes shift by 10–25 cmꢁ1 to higher wavenumber indicating monodentate
linking [18] of4N–N5, as a shift450 cmꢁ1 is usually for bidentate linking of4N–N5.
Polystyrene-supported Schiff base exhibits a strong band at 1615 cmꢁ1 due to
ꢁ(C¼N)(azomethine). In polystyrene-anchored coordination compounds, this band
undergoes a shift to lower energy by 10–25 cmꢁ1 which indicates that the azomethine
nitrogen is coordinated to metal. Compound 1 exhibits a strong band at 1540 cmꢁ1 due
to the ꢁ(C–O)(È) stretch, which undergoes a shift by ꢅ10 cmꢁ1 in the polystyrene-
anchored compounds, indicating coordination of the phenol [11]. Thus the infrared data
indicate tridentate ONO donor behavior of 1. The ꢁ(C¼O) stretch of DMF occurs at
1680 cmꢁ1 and shifts [11] by 20–40 cmꢁ1 to lower wavenumber in the polystyrene-
anchored coordination compounds, indicating coordination of DMF through oxygen.
The absence of a band at 820–860 cmꢁ1 in polystyrene-anchored Fe(III) compound
precludes the presence of a (Fe–O–Fe) bridged structure [11]. In the Zr(IV) compound,

Polystyrene-anchored coordination compounds
595
the absence of a band at 850–950 cmꢁ1 characteristic of ꢁ(Zr¼O) suggests [19]
PS–LHZr(OH)2 ꢀ 2DMF and not PS–LHZrO(H2O) ꢀ 2DMF. The presence of a new
band at 1140 cmꢁ1 due to ꢂ(Zr–OH) [11] supports the suggested structure of the Zr(IV)
compound. A pentagonal bipyramidal structure is suggested for the Zr(IV) compound.
The polystyrene-anchored MoO2(VI) compound exhibits bands at 950 and 915 cmꢁ1 due
to the ꢁsy(O¼Mo¼O) and ꢁasy(O¼Mo¼O), respectively [11]. These band are in the usual
ranges, 892–964 and 840–925 cmꢁ1, respectively, reported for MoO2(VI) compounds.
The IR data indicate the presence of cis-MoO2 since a complex with a trans-MoO2
moiety is expected to show only the ꢁasy(O¼Mo¼O) band [20]. The absence of a band
around 770 cmꢁ1 in the present compound indicates the absence of an oligomeric chain
structure with ꢀ ꢀ ꢀMo¼Oꢀ ꢀ ꢀMo¼Oꢀ ꢀ ꢀ interaction [20]. The polystyrene-anchored
UO2(VI) compound exhibits a strong band at 915 cmꢁ1 due to ꢁasy(O¼U¼O) [11], in
the usual range (870–950 cmꢁ1) reported for UO2(VI) compounds [21]. The observation
of only one ꢁasy(O¼U¼O) band indicates trans-UO2 ꢁsi1nce the ꢁsy(O¼U¼O) is infrared
˚
inactive. The force constant ( fU–O) is 6.96 mdyn A which lies in the usual range
(6.58–7.03 mdyn Aꢁ1) observed for UO2(VI) compounds [21]. The U–O bond length
˚
˚
is 1.74 A in the range 1.60–1.92 A observed for octahedral UO2(VI) [21].
˚
The room temperature magnetic susceptibilities and the magnetic moments of the
compounds are given in table 3. The polystyrene-anchored Co(II), Mn(II), Ni(II), and
Fe(III) compounds exhibit magnetic moments 4.89, 5.99, 3.25, and 5.96 B.M.,
respectively, which lie in the normal ranges for magnetically dilute octahedral
compounds of these metal ions [22]. The polystyrene-supported Cu(II) compound
exhibits a magnetic moment of 2.18 B.M. in the range 1.7–2.2 B.M. expected for
magnetically dilute Cu(II) compounds [22] (S ¼ ½ system). The Zn(II), Cd(II),
MoO2(VI), UO2(VI), and Zr(IV) compounds are diamagnetic.
Electronic spectra of the compounds could not be recorded in nujol mull as the
polystyrene-anchored compounds do not form a good mull. Therefore, the reflectance
spectra of these compounds were recorded (table 3). The polystyrene-bound Co(II)
compound exhibits three bands at 9100, 13,000, and 18,800 cmꢁ1 due to the
4
4
4
4
4
4T1g(F) ! T2g(ꢁ1), T1g(F) ! A2g(ꢁ2), and T1g(F) ! T1g(ꢁ3) transitions in an
Table 3. Magnetic moment and reflectance spectral data of polystyrene-anchored coordination
compounds.
Magnetic
moment
(B.M.)
Polystyrene-anchored
coordination
compounds
ꢃdia
(10ꢁ6 cgs (10ꢁ6 cgs
ꢃcMorr
ꢁmax
Dq
ꢀ0
(%)
units)
units)
(Temperature (K)) (cmꢁ1
)
(cmꢁ1
)
B0
ꢀ
PSCH2–LHCo ꢀ 3DMF
ꢁ2554
10,121
4.89 [295]
9100
1021
721 0.74
26
13,000
18,800
16,800
16,000
22,500
9820
15,870
25,300
13,000
17,100
25,100
PSCH2–LHCu ꢀ DMF
PSCH2–LHMn ꢀ 3DMF
ꢁ1539
ꢁ1057
2046
15,238
2.18 [290]
5.99 [294]
PSCH2–LHNi ꢀ 3DMF
ꢁ1087
4501
3.25 [293]
5.96 [293]
982
766 0.74
26
PSCH2–LHFeCl ꢀ 2DMF
ꢁ1455
15,137

596
D. Kumar et al.
octahedral symmetry [23]. The ꢁ3 : ꢁ1 value of the present compound is 2.07, in the usual
range (2.0–2.80) [23]. The spectral parameters [23] of the compound are: Dq ¼ 1021 cmꢁ1
,
B0 ¼ 721 cmꢁ1, ꢀ ¼ 0.74, and ꢀ0 ¼ 26%. The lower values of B0 (721 cmꢁ1) in comparison
to the free ion value of 971 cmꢁ1 and ꢀ0 value of 26% suggest the covalent nature of the
complex. The Cu(II) compound exhibits a broad band at 16,800 cmꢁ1 due to
2B1g ! A1g, B2g, and Eg transitions characteristic of square-planar CuNO3 coordi-
nation sphere [23]. The absence of a band at 8000–10,000 cmꢁ1 precludes a tetrahedral
structure [24]. The metal-bound Mn(II) compound exhibits two bands at 16,000 and
2
2
2
6
4
6
4
22,500 cmꢁ1 due to the A1g ! T1g(G) and A1g ! T2g(G) transitions, respectively,
in an octahedral symmetry [23]. The polystyrene-bound Ni(II) compound exhibits bands
at 9820, 15,870, and 25,300 cmꢁ1 due to A2g ! T2g (ꢁ1), A2g ! T1g(P) (ꢁ2), and
3
3
3
3
3A2g ! T1g(F) (ꢁ3), respectively, in an octahedral symmetry [23]. The ꢁ2 : ꢁ1 value for the
3
Ni(II) compound is 1.62, in the usual range 1.6–1.82 reported for octahedral Ni(II)
compounds [23]. The spectral parameters [23] for the present compound are
Dq ¼ 982 cmꢁ1, B0 ¼ 766 cmꢁ1, ꢀ ¼ 0.74, and ꢀ0 ¼ 26%. The reduction in the Racah
parameter from the free ion value of 1056–982 cmꢁ1 and ꢀ0 value of 26% are indicative
of covalent compound [23]. The polystyrene-anchored Fe(III) compound exhibits bands
at 13,000, 17,100 and 25,100 cmꢁ1 due to the A1g ! T1g(G), A1g ! T2g, and
6
4
6
4
6A1g ! A1g(G) transitions, respectively, in octahedral symmetry [23].
4
The large size of the ligand framework keeps adjacent metal centers separated, and as
a result dipolar broadening is almost absent in these compounds. The polystyrene-
anchored Cu(II) compound exhibits a good ESR spectrum in polycrystalline solid in the
absence of the host diamagnetic diluent. The ESR spectrum shows four well-resolved
hyperfine lines with no super-hyperfine lines. However, the half-field signal (DMs ¼ ꢆ2)
corresponding to Cu–Cu interaction was not observed ruling out magnetic exchange,
indicating the magnetically dilute nature of PSCH2–LHCu ꢀ DMF. The spin-
Hamiltonian parameters of the Cu(II) compound (S ¼ ½, I ¼ 3/2) have been calculated
as: g ¼ 2.24 and g ¼ 2.07, A ¼ 1.64 ꢂ 10ꢁ2 cmꢁ1, and A ¼ 2.2 ꢂ 10ꢁ3 cmꢁ1. The
k
?
k
?
observed order of A and g values (A 4A ; g 4g 42.0023) indicates that Cu(II)
k
?
k
?
compound possesses a square-planar structure, and the ground state [25] of CuII is
predominantly dx2 ꢁ y2 (2B1). Here g and g denote the effective g-values when the
k
externally applied DC field is parallel (B ) and perpendicular (B ) to the symmetry axis
?
k
?
of the crystalline field around the paramagnetic center. The geometric parameter (G),
a measure of the exchange interaction is 3.5, consistent with dx2 ꢁ y2 ground state [26].
The value of g 52.3 indicates significant covalent character in the M–L bond [27]. The
k
covalent nature of the metal–ligand bond is indicated by g and ꢄ2Cu values. The
molecular orbital coefficient, i.e. covalency parameter ꢄ2Cu (a measure of covalency of
the in-plane ꢅ-bonding) has been calculated using the equation [28]: ꢄ2Cu ¼ ꢁ(A /
k
0.036) þ (g ꢁ 2.0023) þ 3/7(g ꢁ 2.0023) þ 0.04. A value of ꢄ2 ¼ 0.5 indicates the
k
?
Cu
complete covalent bonding, while the value of ꢄ2Cu ¼ 1.0 suggests complete ionic
bonding. The observed value (ꢄ2Cu ¼ 0.76) of the present Cu(II) coordination compound
indicates significant covalent character in the M–L bonding [29]. The symbol ꢆPd
represents the Fermi contact contribution (A) to the coupling, where Pd is the dipolar
contribution. The values of Pd and ꢆ were calculated using the relation [29]:
Pd ¼ ꢁ(A ꢁ A )/0.78 and ꢆ ¼ ꢁ0.48 ꢁ (A /Pd). Values of Pd and ꢆ for the polystyr-
k
?
k
ene-supported Cu(II) compound are 1.82 ꢂ 10ꢁ2 cmꢁ1 and 0.42, respectively. The lower
value of Pd of the Cu(II) compound in comparison to that of the free ion
(3.5 ꢂ 10ꢁ2 cmꢁ1) indicates covalent interaction in the metal ligand system. A positive

Polystyrene-anchored coordination compounds
597
value of ꢆ predicts that A should be greater than A and this too has been observed.
k
?
The absence of an ESR band at ꢄ1500 G due to DMs ¼ 2 transition in the polystyrene-
supported Cu(II) compound indicates the absence of Cu–Cu interaction in the
compound.
The Cu(II) ions situated on the phenyl rings of the polymer (which are 8–9 styrene
units apart in the polymer chain) represent an ideal magnetically dilute situation, since
the pathway for dimer formation with Cu–Cu interaction is blocked. Since the
polystyrene is 1% crosslinked with divinylbenzene, the polymer chains get twisted and
overlapped; some of the reactive centers come close to one another and as a result weak
Cu–Cu interaction may occur which could not be detected in the ESR measurements.
4. Conclusion
The data suggest a square-planar structure, 2 for PSCH2–LHCu ꢀ DMF; tetrahedral
structures, 3 for PSCH2–LHM ꢀ DMF (M ¼ Zn, Cd); octahedral structures, 4 for
PSCH2–LHM ꢀ 3DMF (M ¼ Mn, Co, Ni), 5 and 6, respectively, for PSCH2–
LHM0 ꢀ DMF (M0 ¼ UO2 and MoO2), 7 for PSCH2–LHFeCl ꢀ 2DMF and a pentagonal-
bipyramidal structure, and 8 for PSCH2–LHZr(OH)2 ꢀ 2DMF.
H
A
H
O
PS
O
C
H
C
O
PS
C
H
O
A
C
M
O
O
C
Cu
O
C
O
C
N
N
H
C
N
H
N
HO
HO
2 (A = DMF)
3 (M = Zn, Cd)
H
H
C
O
PS
C
H
O
O
PS
O
C
A
O
U
C
A
O
H
O
A
O
M
O
C
N
N
C
A
N
O
H
H
C
N
C
HO
HO
5
4 (M = Co, Mn and Ni)

598
D. Kumar et al.
H
H
C
H
O
PS
C
O
O
H
C
PS
O
A
H
O
C
Cl
O
O
N
O
O
O
N
Fe
Mo
C
C
A
H
A
C
N
C
N
HO
HO
7
6
H
O
C
H
C
PS
C
H
O
O
N
N
OH
HO
Zr
A
A
O
C
OH
8
Acknowledgments
The authors (P.K. Gupta, A. Kumar, and D. Dass) are grateful to the respective
Directors of their Institute for providing financial assistance for this study.
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