Electronic, cyclic voltammetry, IR and EPR spectral studies of copper(II) complexes with 12-membered N4, N2O2 and N 2S2 donor macrocyclic ligands

Article abstract of DOI:10.1016/j.saa.2004.04.018

A new series of copper(II) complexes have been synthesized with macrocyclic ligands having three different donating atoms in the macrocyclic ring. It has been shown that the stereochemistry of complexes is dependent on the coordinated anions. These complexes are characterized by various physicochemical techniques, viz. elemental analysis, molar conductance, magnetic susceptibility measurements, IR, electronic, ¹H NMR and EPR spectral studies. Cyclic voltammetric behavior of the complexes has also been discussed. The observed anisotropic g-values indicate that the chloro and acetate complexes are six-coordinate tetragonal. Whereas the sulfato and nitrato complexes are found to have five-coordinate square-pyramidal and four-coordinate square-planar geometry, respectively.

Full text of DOI:10.1016/j.saa.2004.04.018

Spectrochimica Acta Part A 61 (2005) 437–446
Electronic, cyclic voltammetry, IR and EPR spectral studies
of copper(II) complexes with 12-membered
N4, N2O2 and N2S2 donor macrocyclic ligands
Sulekh Chandra∗, Rajiv Kumar
Department of Chemistry, Zakir Husain College, University of Delhi, J. L. Nehru Marg, New Delhi 110002, India
Received 8 September 2003; accepted 9 April 2004
Abstract
A new series of copper(II) complexes have been synthesized with macrocyclic ligands having three different donating atoms in the
macrocyclic ring. It has been shown that the stereochemistry of complexes is dependent on the coordinated anions. These complexes are
characterized by various physicochemical techniques, viz. elemental analysis, molar conductance, magnetic susceptibility measurements,
1
IR, electronic, H NMR and EPR spectral studies. Cyclic voltammetric behavior of the complexes has also been discussed. The observed
anisotropic g-values indicate that the chloro and acetato complexes are six-coordinate tetragonal. Whereas the sulfato and nitrato complexes
are found to have five-coordinate square-pyramidal and four-coordinate square-planar geometry, respectively.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Macrocyclic ligand; Copper(II); Electronic; IR; EPR; Cyclic voltammetry
1. Introduction
complexes with N4, N2O2 and N2S2 donor 12-membered
macrocyclic ligands.
Nature prefers macrocyclic derivatives for many fun-
damental biological functions such as photosynthesis and
transport of oxygen in mammalian and other respiratory
systems [1]. Hence the synthesis and studies of model sys-
tems are important which show important properties such as
thermodynamic, kinetic stability [2], electron transfer and
magnetic interaction between metal centers [3]. These are
effected by the ring size, coordination sites and electronic
effect [4] at aromatic ring of the ligand system. Since the
late 1980s, the study of copper(II) complexes has attracted
considerable attention due to relevance of copper(II) in
biological systems [5]. There have been several attempts
to model the active center of biological molecules that in-
cludes copper atom on their structure such as haemocyanin
or other biological proteins [6]. In view of the above appli-
cations, it is highly desirable to synthesize and characterize
the copper(II) complexes with such ligands. In this paper
we report the synthesis and characterization of copper(II)
2. Experimental
All the chemicals used were of AnalaR grade, and pro-
cured from Fluka and Sigma Aldrich. Metal salts were pur-
chased from E. Merk and used as received. All solvents were
used of spectroscopic grade.
3. Synthesis of diamines
1,2-Di(o-aminophenoxy)ethane (Fig. 1a), 1,2-di(o-amin-
ophenylamino)ethane (Fig. 1b) and 1,2-di(o-aminophenyl-
thio)ethane (Fig. 1c) were prepared and characterized by the
procedure as reported earlier [7]. All these diamine are used
for the preparation of macrocyclic ligands.
3.1. Characterization of diamines
1,2-Di(o-aminophenoxy)ethane, mp 130–132 ◦C. 1H
NMR (CDCl3) δ 7.0 (2H, d), δ 6.6 (2H, m), δ 6.3 (2H, d),
(2H, m), δ 4.0 (4H, O–CH2). 1,2-Di(o-aminophenylamino)
∗
Corresponding author.
E-mail addresses: schandra 00@yahoo.com (S. Chandra),
chemistry rajiv@hotmail.com (R. Kumar).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.04.018

438
S. Chandra, R. Kumar / Spectrochimica Acta Part A 61 (2005) 437–446
Fig. 1. Structure of diamines.
1
ethane, mp 135–136 ◦C. H NMR (CDCl3) δ 7.1 (2H, m),
δ 6.7 (2H, d), δ 6.6 (2H, m), δ 6.3 (2H, d), δ 3.0 (4H,
NH–CH2). 1,2-Di(o-aminophenylthio)ethane, mp 75 ◦C. 1H
NMR (CDCl3) δ 7.2 (2H, d), δ 7.1 (2H, m), δ 6.6 (2H, m),
δ 6.3 (2H, d), δ 2.8 (4H, S–CH2).
diene[N2S2]ane [L3] (Fig. 2c) containing aromatic head,
and lateral units macrocyclic ligands were prepared by the
procedure as reported earlier [7].
To an ethanolic solution (25 ml) of benzil (0.005 mol,
1.05 g) an EtOH solution of (25 ml) of 1,2-di(o-aminophen-
oxy)ethane or 1,2-di(o-aminophenylamino)ethane or 1,2-
di(o-amino phenyl thio)ethane (0.005 mol) was added in
presence of few drops ∼1 ml of conc. HCl. The resulting
solution was refluxed for 5–7 h. The resulting solution was
concentrated to half of its volume under reduced pressure
and kept overnight. The white/white off crystals formed,
which were filtered, washed with EtOH and dried under
vacuum over P4O10.
3.2. Preparation of macrocyclic ligands
2,3-Diphenyl-1,4-diaza-7,10-dioxo-5,6:11,12-dibenzo[e,
k]-cyclododeca-1,3-diene[N2O2]ane (L1) (Fig. 2a), 2,3-
diphenyl-1,4,7,10-tetraaza-5,6:11,12-dibenzo[e,k]-cyclodo-
deca-1,3-diene[N4] ane (L2) (Fig. 2b) and 2,3-diphenyl-1,4-
diazo-7,10-dithia-5,6:11,12-dibenzo[e,k]-cyclododeca-1,3-
Fig. 2. Structure of macrocyclic ligands.

S. Chandra, R. Kumar / Spectrochimica Acta Part A 61 (2005) 437–446
439
3.3. Characterization of macrocyclic ligands
Leeds Northrup Conductivity Bridge 4995. IR spectra were
recorded on a Perkin Elmer 137 instrument as KBr pellets.
The electronic spectra of the complexes were recorded on
a Shimadzu UV mini-1240 spectrophotometer in DMF so-
lution. C, H and N analysis were carried out on a carl-Ebra
1106 elemental analyzer. Nitrogen contents was determined
These ligands are characterized on the basis of elemental
1
analysis, H NMR and infrared spectra.
• Yield 71%, mp 172 ◦C. Found: C, 80.0; H, 5.0; N, 6.2.
1
C28H22N2O2 calculated: C, 80.4; H, 5.3; N, 6.7%. H
1
by the Kjeldahl’s method. H NMR spectra were recorded
NMR: δ 7.2–7.3 (10H, m), δ 7.1 (2H, m), δ 7.0 (2H, d), δ
6.9 (2H, d), δ 6.6 (2H, m), δ 4.0 (4H, O–CH2) for ligand
L1.
on a Bruker Avance 300 spectrometer at 100 kHz modu-
lation at room temperature. EPR spectra were recorded at
room temperature on a varion E-4 EPR spectrometer at
∼9.1 GHz and 100 kHz field modulation and phase sensitive
detections by using DPPH as marker. The copper content in
the complexes was determined gravimetrically as CuSCN.
Cyclic voltammograms of the copper(II) complexes in
MeCN at 300 K were recorded by using a BAS electro-
chemical analyses. The electrolyte cell contains a reference
Ag/AgCl electrode, Pt wire as auxiliary electrode. Unless
otherwise stated all potentials were referred to Ag/AgCl.
• Yield 67%, mp 179 ◦C. Found: C, 80.1; H, 5.3; N, 13.1.
C28H24N4 calculated: C, 80.7; H, 5.8; N, 13.4%. 1H
NMR: δ 7.2–7.4 (10H, m), δ 7.1 (2H, m), δ 6.9 (2H, d), δ
6.7 (2H, d), δ 6.6 (2H, m), 3.0 (4H, NH–CH2) for ligand
2.
• Yield 70%, mp 182 ◦C. Found: C, 74; H, 4.3; N, 6.0.
C28H22N2S2 calculated: C, 76.6; H, 4.9; N, 6.2%. 1H
NMR: δ 7.2–7.24 (10H, m), δ 7.27(2H, d), δ 7.1 (2H, m),
δ 6.9 (2H, d), δ 6.6 (2H, m), δ 4.0 (4H, m, S–CH2) for
ligand 3.
5. Results and discussion
3.4. Preparation of the complexes
All the complexes are found to have the composition
A hot EtOH, solution (25 ml) of the corresponding
CuLX2·nH2O (where L = Ligand L1, L2, or L3, and X =
Cl−, CH3COO−, NO3 and (1/2)SO42−). Chloro, acetato
−
hydrated copper(II) salt CuX2·nH2O, 0.005 mol (where
X = Cl−, CH3COO−, NO3 and (1/2)SO42−) was added
−
and sulfato complexes of Cu(II) show molar conductances in
the range of 0–20 ꢀ−1 cm2 mol−1 (Table 1) corresponding to
non-electrolytes whereas, the nitrato complexes were found
to be 1:2 electrolytes. Therefore, these complexes may be
formulated as [Cu(L)X2], [Cu(L)SO4] and [Cu(L)](NO3)2,
respectively.
to a hot EtOH solution (25 ml) of the corresponding lig-
and (0.005 mol). The mixture was refluxed on water bath
at 80 ◦C for 5–7 h. On cooling, a colored precipitate was
formed. It was filtered, washed with EtOH and dried over
P4O10 under vacuum.
6. IR spectra
4. Physical measurements
There is no absorption bands at 3380–3400 and
1640–1720 cm−1 in the IR spectra of the ligands show
Magnetic susceptibility measurements were carried out
a CAHN 2000 Faraday balance using Hg[Co(CNS)4]
(χg = 16.44 × 10−6 g cm−3 at 28 ◦C) as the calibrant.
Molar conductance measurements were carried out on a
=
the absence of free amino (–NH2) and kenotic (>C O)
group. This indicates that complete condensation takes
Table 1
Analytical data of copper(II) complexes
Complexes
Yield mp
(%)
Molar
Color
Elemental analysis calculated (found) (%)
Cu
(◦C) conductance
(ꢀ−1 cm2 mol−1
)
C
H
N
[Cu(L1)(CH3COO)2], CuC32H28N2O6
[Cu(L1)(CI2)], CuC28H22N2O2Cl2
[Cu(L1)](NO3)2, CuC28H22N4O8
40
42
47
50
55
58
61
63
210 7.00
235 13.00
217 205
219 19
235 6.00
238 8.00
240 210
221 11.0
240 17
Dark blue
Blue
Blue
Light blue
Green
10.58 (10.25) 64.05 (63.75) 4.70 (4.35)
11.50 (11.26) 60.82 (60.61) 4.00 (3.75)
10.49 (10.21) 55.50 (55.21) 3.65 (3.26)
10.99 (10.71) 58.18 (57.71) 3.84 (3.51)
10.62 (10.52) 64.26 (63.99) 5.05 (4.91)
4.67 (4.52)
5.06 (4.82)
9.25 (8.72)
4.85 (4.35)
9.37 (9.17)
10.17 (9.88)
13.91(12.96)
9.73 (9.62)
4.43(4.10)
[Cu(L1)SO4], CuC28
H22N2O6S
[Cu(L2)(CH3COO)2], CuC32H30N4O4
[Cu(L2)(Cl2)], CuC28H24N4Cl2
[Cu(L2)](NO3)2, CuC28H24N6O6
[Cu(L2)(SO4)], CuC28H24N4O4S
Dark green 11.53 (11.21) 61.04 (60.96) 4.39 (4.21)
Light green 10.52 (10.26) 55.68 (55.28) 4.00 (3.72)
Green
11.03 (10.90) 58.38 (57.91) 4.20 (4.01)
60.79 (60.61) 4.46 (4.11)
10.86 (10.62) 57.48 (57.40) 3.78 (3.52)
9.95 (9.82)
10.41 (10.32) 55.12 (54.91) 3.63 (3.22)
[Cu(L3)(CH3COO)2], CuC32H28N2S2O4 52
Shiny blue 10.05 (9.75)
[Cu(L3)(Cl2)], CuC28H22N2S2Cl2
[Cu(L3)](NO3)2, CuC28H22N4S2O6
[Cu(L3)(SO4], CuC28H22N2S3O4a
57
68
61
219 11
241 215
250 16
Light blue
Sky blue
Blue
4.80 (4.53)
52.71 (52.30) 3.47 (31.16) 8.78 (8.52)
4.60 (4.31)

440
S. Chandra, R. Kumar / Spectrochimica Acta Part A 61 (2005) 437–446
=
place between the NH2 and >C O In the IR spectrum
of (L2) a sharp band is appeared at 3320 cm−1 corre-
sponding to ν(NH) group. New characteristic band due to
8.1. Acetato and chloro copper(II) complexes
All the complexes show two characteristic bands in range
of 13,899–15,600 and 16,722–18,860 cm−1. These may be
=
(>C N) in the ligands are appeared at 1627 (L1), 1628
(L2) and 1607 cm−1 (L3). The position of this band is
shifted to lower frequency in the complexes as com-
pared to free macrocyclic ligands, suggesting that the
assigned to B1g
→
2A1g and B1g
→
2Eg transitions,
2
2
respectively [13] according to tetragonal geometry.
=
coordination takes place through the nitrogen of ν(C N)
8.2. Nitrato complexes
group [8].
Nitrato complexes of all ligands display three elec-
tronic spectral bands in the range of 15,600–16,920,
18,832–18,867 and 31,526–33,783 cm−1 indicating four-
coordinated square-planar geometry [13] (Fig. 3).
6.1. Bands due to anions
IR spectra of nitrato complexes show sharp absorption
bands at 1382 (L1), 1380 (L2) and 1384 cm−1 (L3) corre-
sponding to free nitrate group [9]. The sulfato complexes
show bands at 1180–1120 (ν3) and 760–690 cm−1 (ν4) cor-
responding to unidentate nature [10]. Acetato complexes
exhibit bands at 1565–1557 (ν1) and 1410–1420 cm−1
(ν2). This indicates unidentate nature of acetate group
[11].
8.3. Sulfato complexes
Sulfato complexes all ligands show electronic bands at
8500 and 10,100 cm−1 corresponding to five-coordinate
square-pyramidal geometry.
9. EPR spectra
7. Magnetic moments
The EPR spectrum of copper(II) complexes provides in-
formation about hyperfine and super hyperfine structures. It
is very important to understand the metal ion environment
in the complexes, i.e. the geometry, nature of the donat-
ing atoms from the ligands and degree of covalency of the
copper(II)–ligands bonds.
All the complexes show magnetic moments in the range
of 1.90–2.00 B.M. indicating monomeric nature of the com-
plexes.
9.1. Chloro and acetato complexes
8. Electronic spectra
All the complexes show anisotropic EPR spectra
(Figs. 4–7) characteristic to a tetragonal geometry for cop-
per(II) complexes.
Electronic spectra of six coordinate copper(II) complexes
have either D4h or C4v symmetry, and the eg and t2g level
of the D free ion term will split in to B1g, A1g, B2g and
2
g-Tensor values have been calculated by Kneiibuhl’s
method and results are presented in Table 2.
Eg level, respectively Thus the three spin allowed transi-
tions are expected in the visible and IR region. But only few
complexes are known in which such bands are resolved ei-
ther by Gaussian analysis or single crystal polarization stud-
ies. These bands may be assigned to following transitions:
g-Tensor values of copper(II) complexes can be used to
derive the ground state. In an elongated octahedron the 3d
unpaired electrons for copper(II) ions lies in dx2−y2 orbital
2
2
2
2B1g → A1g (dx2−y2 → dz2 ), B1g → B2g (dx2−y2
→
(2B1 as ground state). The g-values were given by g
=
ꢀ
2
dxy) and B1g
→
2Eg (dx2−y2 → dxzdyz) in order of in-
2(1 − 4λ/∆1) and g = 2(1 − λ/∆2). In a compressed oc-
⊥
tahedron, on the other hand, the 3d unpaired electron lies in
the dz2 orbital (2A1g ground state). The g-values were given
by g = 2 and g = 2(1 − 3λ/∆3) where ∆1, ∆2 and ∆3
creasing energy. The energy level sequence will depend on
the amount of distortion due to ligand field and Jahn–Teller
effect [12].
ꢀ
⊥
Table 2
Ligand field (cm−1) parameters of acetate and chloro copper(II) complexes
Complex
g
g
giso
A
A
⊥
Aiso
G
α2
β2
ꢀ
⊥
ꢀ
[Cu(L1)(CH3COO)2]
[Cu(L1)(CI2)]
[Cu(L2)(CH3COO)2]
[Cu(L2)(Cl2)]
[Cu(L3)(CH3COO)2]
[Cu(L3)(Cl2)]
2.21
2.20
2.19
2.11
2.17
2.15
2.08
2.06
2.05
2.06
2.07
2.05
2.12
2.10
2.09
2.09
2.10
2.08
175
177
170
166
168
165
76
74
68
67
65
72
109
108
102
100
99.0
103
2.6
3.3
3.8
3.8
2.4
3.0
0.79
0.80
0.69
0.72
0.73
0.78
0.91
0.90
0.96
0.99
0.93
0.98

S. Chandra, R. Kumar / Spectrochimica Acta Part A 61 (2005) 437–446
441
Fig. 3. Suggested structure of copper(II) complexes.
ular orbital coefficients ␲ bonding (β2) and ␴ bonding (α2),
are calculated [16]. α2 and β2 values indicate that there is a
substantial interaction in-plane ␴ bonding whereas in-plane
␲ bonding is almost ionic.
are dx2−y2 → dxy, dx2−y2 → dxz, dyz and dx2−y2 → dz2
excitation energy, respectively, and λ is the spin orbit cou-
pling constant [14]. From the observed g-values it is evident
that the unpaired electron lies predominantly in dx2−y2 or-
bital. Different EPR parameters are calculated and given in
Table 2.
9.3. EPR spectra of sulfato complexes
9.2. Nitrato complexes
Since the IR spectra of these complexes show monoden-
tate behavior of sulfato group, a five coordinated geometry
may be assigned to these complexes. The two configurations
square-pyramidal and trigonal bipyramidal are characterized
by ground state dx2−y2 and dz2 , respectively [17]. EPR spec-
tra of copper(II) (Fig. 9) provide a very good basis for dis-
tinguish between these two general states. For systems with
g3 > g2 > g1 the ratio of (g2 − g1/g3 − g2) (here after
The EPR spectra of [Cu(L)](NO3)2 complexes (Fig. 8)
were also recorded as polycrystalline sample and in DMSO,
which suggests that the complexes have square-planar ge-
ometry. Related data are listed in Table 3.
The results also indicate that the exchange couplings are
not effective in nitrato complexes of all ligands [15]. Molec-

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S. Chandra, R. Kumar / Spectrochimica Acta Part A 61 (2005) 437–446
Fig. 4. (A) EPR spectrum of [Cu(L1)CI2], (B) [Cu(L2)CI2] and (C) [Cu(L3)CI2], ν = 9.38 GHz.
Fig. 5. EPR spectrum of copper(II) complexes in aqueous solution (A) [Cu(L1)CI2], (B) [Cu(L1)(CH3COO)2], (C) [Cu(L2)CI2], and (D)
[Cu(L2)(CH3COO)2].
Table 3
EPR spectra data copper(II) nitrato complexes
Complex
g
ꢀ
g
giso
A
A
⊥
Aiso
G
A
α2
β2
⊥
ꢀ
[Cu(L1)](NO)3
[Cu(L2)](NO)3
[Cu(L1)](NO)3
2.10
2.12
2.16
2.02
2.05
2.03
2.09
2.07
2.07
158
145
149
55
58
65
89.3
87.0
93.0
5.43
4.36
4.50
0.58
0.62
0.68
0.78
0.85
0.90
1.95
1.99
2.00

S. Chandra, R. Kumar / Spectrochimica Acta Part A 61 (2005) 437–446
443
Fig. 6. EPR spectrum of copper(II) complexes in forezen solution (77 K) (A) [Cu(L1)CI2], (B) [Cu(L1)(CH3COO)2], (C) [Cu(L2)CI2], (D)
[Cu(L2)(CH3COO)2], (E) [Cu(L3)CI2], (F), [Cu(L3)(CH3COO)2]. Scan mang. 150 mT, ν = 100 kHz, microwave frequency 9.51–9.54.
Fig. 7. (A) EPR spectrum of [Cu(L1)(CH3COO)2], and (B) [Cu(L2) (CH3COO)2]. ν = 9.49 GHz.
called the parameter R) is a very useful for this purpose. If
the ground state is dz2 the value of R is greater than 1. On the
other hand, for the ground state being predominantly dx2−y2
the value of R is less than 1. The complexes under study
show the value of R (Table 4) less than 1, thus indicating
five-coordinate trigonal bipyramidal geometry.
the reduction potential was observed with change in macro-
cyclic chelate ring size in the presence of unsaturated macro-
cyclic cavity. If we compare two macrocyclic rings one of
them was containing saturated ring and other has unsaturated
ring then the metal ion present in the saturated macrocyclic
ring is oxidized first. This may be influenced from the fact
that the change in ring size did not affect the first oxidation
10. Cyclic voltammetry
Table 4
EPR spectra data of copper(II) sulfato complexes
The synthesized macrocyclic ligands and their complexes
have two dissimilar saturated and unsaturated N4, N2O2 and
N2S2 macrocyclic cavity. The reduction of the metal ion was
effected in the presence of unsaturated macrocyclic cavity
and first its reduction start. It was observed that the change in
Complex
g3
g2
g1
R
[Cu(L1)SO4]
[Cu(L2) SO4]
[Cu(L3) SO4]
2.11
2.18
2.15
2.06
2.13
2.12
2.01
2.06
2.08
0.50
0.58
0.55

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S. Chandra, R. Kumar / Spectrochimica Acta Part A 61 (2005) 437–446
Fig. 8. (A) EPR spectrum of [Cu(L1)](NO3)2, DMSO solution 300 K. (B) EPR spectrum of [Cu(L2)](NO3)2, DMSO solution 17 K.
potential of the metal ion. This indicates that small changes
in the electronic and structural co-ordination environment,
affect the redox potential of the complexes.
This statement is also supported by the appearance of a
Cu(II)/Cu(I) stripping wave at −0.78 V to −0.65 Ag/AgCl
on the return oxidative sweep. For [Cu(L2)]2+, the Cu(I)
redox couple is anodic ally shifted by 0.35 V and appeared
at −1.10 V to 0.96 Ag/AgCl. The significantly greater case
of reduction can be attributed to the more Cu–N bonds of the
The redox of the metal complexes was studied in the
potential range +1.20 to −1.80. Cl− < MeCOO− complexes
of L1, L2 and L3 show a reversible Cu(II)/Cu(I) in the range
of −1.40 to −1.475 V versus Ag/AgCl during the reverse
sweep potential at −1.65 V.
complexes relative to those of [Cu(L1)]2+ and [Cu(L3)]2+
.
Most of the complexes have higher (ꢁEp = Epc − Epa)
values. It is due to the differences between the original
complex and the reduced species. After the second reduc-
tion the complexes may under go ligand replacement re-
action and form new species. Due to this the oxidation
peak is not related to the corresponding reduction peak of
the original complexes. Hence, these reduction processes
are not reversible. The same interpretation holds good for
the redox process of the complexes in the anodic potential
region.
This region shows oxidation waves of the complexes.
Coulometric studies confirmed that each reduction is as-
sociated with a single electron transfer process. When the
potential is swept below −1.65 V, an irreversible wave at
−1.790 V was found and the Cu(II)/Cu(I) couple also be-
come irreversible. This behavior, consistent with that of the
copper(II) complexes of all 12-membered different donating
macrocyclic complexes [18]. It is attributed to the electro-
chemical demetalation of the complexes.

S. Chandra, R. Kumar / Spectrochimica Acta Part A 61 (2005) 437–446
445
Fig. 9. (A) EPR spectrum of [Cu(L1)SO4], (B) [Cu(L2)SO4] and (C) [Cu(L3)SO4]. ν = 9.38 GHz.
Complexes [Cu(L2)]2+ give two distinct irreversible re-
dox couples in the oxidative sweep. The first, at +0.94 V
versus Ag/AgCl, was attributed to the oxidation involving
the >NH lone pairs. The second appears at +1.18 V ver-
sus Ag/AgCl. It may be assigned to the Cu(III)/Cu(II) redox
couple [19].
are also due to SSPL, New Delhi, for recording magnetic
moment and RSIC I.I.T. Bombay for recording EPR spectra.
References
We are studying here three different donating atoms
macrocyclic ligands. These have two unsaturated nitrogen
(azomethine) as a donating group and other groups are
oxygen, nitrogen and sulfur atoms. Mandal et al. [20] have
reported that the first one electron reduction potential is
shifted towards more cathodic waves with increase in the
saturation of the azomethine linkage in macrocyclic sys-
tems. Hence, it is reasonable to believe that in the macro-
cyclic complex the first one electron reduction occurs at
Cu(II) ion coordinated to unsaturated nitrogen atoms and
second at the ion coordinated to saturated nitrogen, oxygen
and sulfur atoms.
[1] H.R. Diril, X. Chang, S.K. Zhang, J.A. Larsen, C.G. Polenza, H.J.
Pierpont, S. Schugar, S. Isted, D.N. Hendrickson, J. Am. Chem. Soc.
109 (1987) 6207.
[2] L.F. Lindoy, The Chemistry of Macrocyclic Ligands, Cambridge
University Press, Cambridge, 1989.
[3] V.L. Pecoraro, M.J. Baldwin, A. Gelasco, Chem. Rev. 94 (1994)
807.
[4] M. Yonemura, Y. Matsumuro, H. Furutochi, M. Ohba, H. Okwa,
D.E. Fenton, Inorg. Chem. 36 (1997) 2711.
[5] Reinhammar, Copper Proteins and Copper Enzymes, vol. 3, CRC
Press, Boca Raton, FL, 1982, p. 1.
[6] C. Lodeuo, R. Bastida, E. Bertola, A. Macias, A. Rodriguez, Poly-
hedron 22 (2003) 1701.
[7] S. Chandra, R. Kumar, Trans. Met. Chem. 29 (3) (2004)
269.
[8] S.C. Cummings, D.H. Busch, J. Am. Chem. Soc. 92 (1970)
1924.
The oxidation potential of the metal center is influ-
−
enced by the axial anions, e.g. Cl−, CH3COO−, NO3 or
(1/2)SO42−. The axial chloro complexes are oxidized at
less positive potentials than those of other anion containing
complexes. This may be due to the higher basicity of the
chloride than the other anion [21].
[9] W. Radecka-Paryzek, Inorg. Chem. Acta L-21 (1985) 109.
[10] J.E. Finhalt, R.W. Anderson, J.A. Fyfe, K.G. Caulton, Inorg. Chem.
4 (1965) 43.
[11] H.B. Klevens, J.R. Platt, J. Chem. Phys. 17 (1949) 1714.
[12] A.B.P. Lever, Inorganic Electronic Spectroscopy, 2nd ed., Elsevier,
Amsterdam, 1984.
Acknowledgements
[13] B.J. Hathaway, J.N. Bradley, R.D. Gillard, Essays in Chemistry,
Academic Press, New York, 1971, p. 61.
[14] B.J. Hathaway, A.A.G. Tomlinson, Coord. Chem. Rev. 5 (1970) 1.
[15] A.M.F. Benial, V. Ramakrishnan, R. Murugesan, Spectrochim. Acta
153 (1990) 207.
[16] A. Veeraraj, P. Sami, N. Raman, Proc. Ind. Acad. Sci. 112 (5) (2000)
515.
One of the authors (Rajiv) is greatly thankful to his
younger brother Bitto for motivation. Thanks also due to the
Principal of Zakir Husain College for providing laboratory
facilities and the UGC, New Delhi for financial assistance
and USIC Delhi University for recording IR spectra. Thanks
[17] A. Bencini, D. Gatteschi, Inorg. Chem. 1977 (1994) 16.

446
S. Chandra, R. Kumar / Spectrochimica Acta Part A 61 (2005) 437–446
[18] P. Zanello, R. Seeber, A. Cinquantini, G. Mazzocchin, L. Fabbrizzi,
J. Chem. Soc., Dalton Trans. 893 (1949).
[20] S.K. Mandal, L.K. Thompson, K. Nag, J.P. Charland, E.J. Gabe,
Inorg. Chem. 26 (1987) 1391.
[19] P.V. Bernhardt, B.M. Flanagan, M.J. Riley, J. Chem. Soc., Dalton
Trans. 3579 (1999).
[21] S. Pal, M.M. Olmstead, W.H. Armstrong, Inorg. Chem. 34 (1995)
4708.