Synthesis, spectroscopic, and electrochemical characterization of a Schiff base: 4,4'-bis[(4-diethylaminosalicylaldehyde)diphenyl methane]diimine and its complexes with copper(II), cobalt(II), and cadmium(II)

Article abstract of DOI:10.1080/15533174.2011.614993

The synthesis of a new ligand tetradentate Schiff base: 4,4'-bis[(4-diethyl aminosalicylaldehyde) diphenyl methane] diimine (H₂L), obtained by condensation of 4,4'-diaminodiphenyl methane with 4-diethylaminosalicylaldehyde, and its complexes with copper(II), cobalt(II) and cadmium(II), is described. The metal complexes were characterized by elemental analysis, by UV-visible, infrared, and EPR spectroscopy, by cyclic voltammetry, and by thermal analysis (DTA-TG). The coordination of the metal ions to the ligand occurs through the N₂O₂ system. Thermal studies indicate that the ligand is more stable than the metal complexes (up to 310°C).

Full text of DOI:10.1080/15533174.2011.614993

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Synthesis, Spectroscopic, and Electrochemical
Characterization of a Schiff Base: 4,4′-bis[(4-
diethylaminosalicylaldehyde)diphenyl methane]diimine
and Its Complexes With Copper(II), Cobalt(II), and
Cadmium(II)
Sonia Benabid a , Tahar Douadi a , Houria Debab a , Marc De Backer b & François-Xavier
Sauvage b
a Laboratoire d’Electrochimie des Matériaux Moléculaires et Complexes. Département de
Génie des Procédés, Faculté des sciences de l’ingénieur , Université Ferhat Abbas , Sétif ,
Algérie
b LASIR , CNRS UMR 8516, USTL, Villeneuve d’Ascq , France
Published online: 31 Jan 2012.
To cite this article: Sonia Benabid , Tahar Douadi , Houria Debab , Marc De Backer & François-Xavier
Sauvage (2012) Synthesis, Spectroscopic, and Electrochemical Characterization of a Schiff Base: 4,4′-bis[(4-
diethylaminosalicylaldehyde)diphenyl methane]diimine and Its Complexes With Copper(II), Cobalt(II), and
Cadmium(II), Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:1, 1-8, DOI:
10.1080/15533174.2011.614993
To link to this article: http://dx.doi.org/10.1080/15533174.2011.614993
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:1–8, 2012
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.614993
Synthesis, Spectroscopic, and Electrochemical
Characterization of a Schiff Base: 4,4ꢀ-bis
[(4- diethylaminosalicylaldehyde)diphenyl methane]
diimine and Its Complexes With Copper(II), Cobalt(II),
and Cadmium(II)
Sonia Benabid,1 Tahar Douadi,1 Houria Debab,1 Marc De Backer,2
and Franc¸ois-Xavier Sauvage2
1
´
´
´
´
Laboratoire d’Electrochimie des Materiaux Moleculaires et Complexes. Departement de Genie des
´ ´
´
´
´
´
´
Procedes, Faculte des sciences de l’ingenieur, Universite Ferhat Abbas, Setif, Algerie
2LASIR, CNRS UMR 8516, USTL, Villeneuve d’Ascq, France
Anthonysamy et al.[13] In the corresponding nickel(II) com-
The synthesis of a new ligand tetradentate Schiff base: 4,4ꢀ-
bis[(4-diethyl aminosalicylaldehyde) diphenyl methane] diimine
(H2L), obtained by condensation of 4,4ꢀ-diaminodiphenyl methane
with 4-diethylaminosalicylaldehyde, and its complexes with cop-
per(II), cobalt(II) and cadmium(II), is described. The metal com-
plexes were characterized by elemental analysis, by UV-visible,
infrared, and EPR spectroscopy, by cyclic voltammetry, and by
thermal analysis (DTA-TG). The coordination of the metal ions to
the ligand occurs through the N2O2 system. Thermal studies indi-
cate that the ligand is more stable than the metal complexes (up to
310◦C).
plexes, the coordination occurs through the nitrogen and oxy-
gen atoms of the ligand. Cyclic voltammetry measurements
show for each complex two quasireversible one-electron waves.
Ramachandraiah et al.[14] described the synthesis of tetraden-
tate ligands from 4,4ꢁ-bis(salicylideneimino)diphenyl methane
(sal-dadpmX, with X H, Me, OMe and Cl). These ligands led
to [M2(sal-dadpm X)2] complexes, where M is Co(II), Ni(II),
Cu(II), or dioxouranium (IV). The copper complexes are pseu-
dotetrahedral binuclear species, whereas other complexes in this
series are polynuclear octahedral species. In this article, we
describe the synthesis of a new tetradentate Schiff base: 4,4ꢁ-
bis[(4-diethyl aminosalicylaldehyde)diphenyl methane]diimine
(H2L, Figure 1). This compound was reacted with Cu(II) and
Co(II) chlorides and Cd(II) perchlorates in order to prepare the
corresponding metal complexes. The structures of the products
are discussed on the basis of IR spectra and thermal analysis.
In addition, the electrochemical behavior of these complexes
in dimethylformamide (DMF) is described. Our results will be
compared to those obtained by Yoshida et al.[15] and Kruger
et al.,[16] who studied ligands and their metal complexes iden-
tical to ours, but that did not bear the N(Et)2 function, and
Averseng’s et al.,[17] who investigated compounds bearing the
N(Et)2 function with a different internal molecular structure.
Keywords cyclic voltammetry, metal complexes, Schiff base,
tetradentate
INTRODUCTION
Over the past two decades, considerable attention has been
paid to the chemistry of Schiff bases containing nitrogen and
other electron donors and their metal complexes.[1–6] This can
be attributed to their stability[7] and their potential applications
in many fields such as oxidation catalysis[1] and electrochem-
istry.[2] They also find applications in medicine as antibacte-
rial or anticancer agents, in the preventive treatment against
corrosion, nuclear wastes, and water treatment.[8–11] There-
fore, symmetrical as well as non-symmetrical Schiff bases
have also been extensively employed as ligands for complex-
ation of metal ions.[12] Recently, some symmetrical Schiff
bases with carbonyl functional groups have been described by
EXPERIMENTAL
General
All chemicals used, 4,4ꢁ-diaminodiphe´nyl methane, 4-
diethyl aminosalicylaldehyde, tetrabutylammonium perchlorate
(TBAP), spectral-grade organic solvents—ethanol, methanol,
dimethylformamide (DMF), dimethylsulfoxyde (DMSO),
toluene, chloroform(CDCl3)), metal salts (CuCl2.2H2O,
Received 28 March 2011; accepted 11 August 2011.
Address correspondence to Franc¸ois-Xavier Sauvage, LASIR,
CNRS UMR 8516, Baˆtiment C5, USTL, 59655 Villeneuve d’Ascq
Ce´dex, France. E-mail: fxsauvage@univ-lille1.fr
1

2
S. BENABID ET AL.
OH
HO
N
CH2
N
N
N
FIG. 1. Chemical structure of the ligand.
1
CoCl2.6H2O and Cd(ClO4)2.6H2O)—were purchased from Pro-
labo© and were used without further purification.
(76.61); H, 7.42 (7.35); N, 10.34 (10.21). H NMR: (CDCl3
as solvent, δ in ppm): 8.38 (s, CH N, 2H), 6.16–7.39 (m, Ar-H,
14H), 13.87 (s, Ar-OH-o, 2H), 1.189 (t, CH/CH3, 12H), 3.39
(q, CH/CH2, 8H), 3.97 (s, CH/CH2, 2H). UV-visible: λmax nm;
All elemental analysis were carried out at the Service
d’Analyse d’analyses du C.N.R.S., I.C.S.N. at Gif-sur-Yvette,
France. The melting points were determined with a Ko¨fler
bench. FTIR spectra were recorded as pressed KBr discs, us-
ing a Perkin-Elmer FTIR 1000 series spectrophotometer in the
range 4000–400 cm−1. The UV-visible spectra were recorded in
DMSO solutions with a Unicam UV300 spectrophotometer. The
1H NMR spectra were recorded in CDCl3 with TMS as internal
reference on a JEOL GSX WB spectrometers at 270 MHz. Elec-
trochemical measurements were carried out at 25◦C on a Volta-
lab 32 (DEA 332 type): the working electrode (2 mm diameter)
and the auxiliary electrode were Pt. The reference was a satu-
rated calomel electrode. DMF was used as solvent and the ionic
strength was maintained at 0.1 M, with TBAP as supporting
electrolyte. The concentration of all species was 2.5 × 10−3 M.
Thermal analyses were performed on TA instrument DTA/TG
2960. Samples were heated at a programmed rate of 5◦C.min−1
in a dynamic He atmosphere. The EPR spectra of the complexes
were recorded with a Bruker Elexys 580-FT, using continuous
wave in the X-band at room temperature and at 110 K.
(εmax
M
−1.cm−1, DMSO as solvent): 382 (176.8 103), 270 (44.1
103). FT-IR: (KBr, cm−1): 3454 ν(Ar-OH), 1629 ν(C N), 1422
ν (Ar-C C), 3022 ν(Ar-CH), 2969 ν (Alph-CH), 1246 ν(C-O),
1196 ν (C-N).
Synthesis of the Complexes
All metal complexes were prepared by mixing equimolar
amounts of ligand H2L (0.21 g, 10 mL) in toluene and hydrated
chlorides and perchlorates (15 mL) in EtOH. The mixture was
refluxed for 8 h. The complex was filtered, washed several times
with hot EtOH and dried under vacuum.
Copper complex (2): Yield: 54.7%, color: brown, m.p.: >260◦C.
Elemental analysis, found (calculated [the basis of the
calculated values will be discussed below]: C, 55.94
(53.84); H, 4.93 (5.42); N, 7.44 (7.18). UV-visible: λmax
nm (εmax
M
−1.cm−1, DMSO as solvent): 390 (170.103),
274 (52.103). FT-IR: (KBr, cm−1): 3478 ν(H2O), 1613
ν(C N), 1506 ν (Ar-C C), 2974 ν (Alph-CH), 1244
ν(C-O), 1193 ν (C-N), 614ν(Cu-O), 530 ν(Cu-N).
Synthesis of the Ligand (H2L)
The results of all elemental analyses are summarized in Cobalt complex (3): Yield: 88%, color: green, m.p.: >260◦C. El-
Table 1.
emental analysis, found (calculated): C, 60.83 (60.35);
Theligand4,4ꢁ-bis[(4-diethylaminosalicylaldehyde)diphenyl
methane]diimine was prepared by reacting 4,4ꢁ-
diaminodiphenyl methane and 4-diethylaminosalicylaldehyde
in MeOH (molar ratio 1:2) as previously described. [18–20] The
mixture was refluxed for 3 h. The yellow product obtained was
H, 5.74 (6.08); N, 8.13 (8.04). UV-visible λmax nm
(εmax
M
−1.cm−1, DMSO as solvent): 389 (251.103), 274
(39.5 103). FT-IR: (KBr, cm−1): 3476 ν(Ar-OH), 1604
ν(C N), 1506 ν (Ar-C C), 2976 ν (Alph-CH), 1245
ν(C-O), 1196 ν(C-N), 540ν(Co-O), 479 ν(Co-N).
filtered, washed twice with hot MeOH, and finally recrystallized Cadmium complex (4): Yield: 71.45%, color: yellow. m.p.:
from toluene and dried under vacuum.
>260◦C. Elemental analysis, found (calculated): C,
H2L (1): (C35H40N4O2). Yield: 84.5%, color: yellow, m.p:
62.97 (62.08); H, 5.89 (5.95); N, 8.26 (8.27). UV-visible:
λmax nm (εmax
205◦C. Elemental analysis, found (calculated%): C, 76.93
M
−1.cm−1 DMSO as solvent): 385
TABLE 1
Analytical data for the ligand and the complexes
Elemental analysis found (calculated)
Compound
color
yield%
m.p. (◦C)
C (%)
H (%)
N (%)
Ligand H2L (1)
yellow
brown
green
84.5
54.7
88.0
71.45
205
>260
>260
>260
76.93 (76.61)
55.94 (53.84)
60.83 (60.35)
62.97 (62.08)
7.42 (7.35)
4.93 (5.42)
5.74 (6.08)
5.89 (5.95)
10.34 (10.21)
7.44 (7.18)
8.13 (8.04)
8.26 (8.27)
Copper complex (2)
Cobalt complex (3)
Cadmium complex (4)
yellow

COMPLEXES OF A SCHIFF BASE WITH Cu(II), Co(II) AND Cd(II)
3
TABLE 2
IR spectral assignments for the ligand and its complexes (all wavenumbers in cm−1
)
Compound
ν(O-H)
ν(C N)
ν(C-O)
ν(M-O)
ν(M-N)
Ligand H2L (1)
3454 (br)
3478 (br)
3476 (br)
3444 (br)
1629 (sh)
1613 (sh)
1604 (sh)
1606 (s)
1246 (m)
1244 (m)
1245 (m)
1238 (m)
Copper complex (2)
Cobalt complex (3)
Cadmium complex (4)
614 (w)
540 (w)
622 (w)
530 (w)
479 (w)
494 (w)
br: broad; sh: sharp; m: medium; s: strong; w: weak.
(192.2 103), 277 (33.103). FT-IR: (KBr, cm−1): 3444
ν(H2O), 1606 ν(C N), 1516 ν(Ar-C C), 2978 ν(Alph-
CH), 1238 ν (C-O), 1192 ν (C-N), 622 ν(Cd-O), 494 ν
(Cd-N).
The IR spectra of the ligand and its complexes of Cu(II),
Co(II), and Cd(II) are characterized by the appearance of a broad
band in the 3500–3400 cm−1 region due to the O-H stretching vi-
brations in the case of the ligand and the complex of Co(II)[23–25]
and to hydration water molecules ν(H2O)[26] in the case of the
complex of Cu(II) and Cd(II).
The spectra of the ligand and its complexes are also dom-
inated by bands at 2978–2969 cm−1 due to ν(Alph-CH)
groups.[27] The band at 1246 cm−1 for the ligand H2L is as-
signed to the phenolic C-O stretching vibration that is shifted to
lower frequencies by 1–8 cm−1 due to O-metal coordination.[28]
Complementary evidence of the bonding is also shown by the
fact that new bands in the IR spectra of the complexes appear
at 530–479 and 622–540 cm−1 assigned to ν(M-N)[29–31] and
ν(M-O) stretching vibrations.[32]
RESULTS
The analytical and spectral data of the Schiff base ligand
and its complexes of Cu(II), Co(II), and Cd(II) are summarized
in Tables 1, 2, and 3. The isolated solids are stable in air
and are insoluble in common organic solvents, but fairly
soluble in CDCl3, DMF, and DMSO.
1H NMR Spectra
The ligand is symmetrical. Therefore, the hydrogen atoms
in the two benzene rings are equivalent. The azomethine group
is shown at δ = 8.38 ppm as a singlet, whereas the phenolic
proton is observed at δ = 13.87 ppm as a singlet.[21] The ligand
shows singlet signals for CH3, CH2 as singlet, and aromatic
protons in the ranges of 1.20 ppm, 3.97 ppm, and 6.17–7.39
ppm, respectively. No correct NMR spectra of the complexes
could be obtained; as it will be seen subsequently this can be
explained by their paramagnetic nature.
Electronic Spectra
The electronic spectra of the ligand and their complexes were
recorded in DMSO. The absorption bands below 300 nm are
almost identical and can be assigned to π–π∗ transitions in the
benzene ring and azomethine (C N) groups.[33] The absorption
bands observed in the 382–390 nm range are probably due to
the transitions of n–π∗ of imine groups.[34] There are changes
in the shape of the spectra of the complexes, which results in a
bathochromic shift assigned to an intramolecular charge transfer
interaction.[35] MLCT transitions cannot be detected, probably
Infrared Spectra
In the spectrum of the ligand, the ν(CH N) vibration of the
azomethine group occurs at 1629 cm−1. In the complexes, this
vibration is shifted to the lower regions by 16–25 cm−1. This
effect can be assigned to the complexation of the metal ion by
nitrogen atoms of the azomethine groups (Table 2).[22]
TABLE 3
Electronic spectral assignments, λmax (nm) for compounds 1–4
Compound
λmax (nm)
Assignment
H2L (1)
270
382
274
390
274
389
277
385
π–π∗
n–π∗
π–π∗
n–π∗
π–π∗
n–π∗
π–π∗
n–π∗
Copper complex (2)
Cobalt complex (3)
Cadmium complex (4)
FIG. 2. DTA-TG analyses curves of ligand (color figure available onlne).

4
S. BENABID ET AL.
TABLE 4
V (Figure 3a). The peak at –1.85 V is due to the reduction of the
imino moiety of the molecule.[36] When the sweep is performed
between 0.00 and +1.80 V, two anodic peaks are obtained at
+0.95 and +1.35V, the first one being assigned to the amine
moiety and the second one to the phenol group (Figure 3b).[36]
The cyclic voltammogram for the electro-oxidation of the
Cu(II) complex (2) in region from 0.00 to +1.80 V, shows three
anodic peaks at +0.60, +0.97, and +1.32V and one cathodic
peak observed at +0.20 V (Figure 3c). The quasireversible oxi-
dation peak at +0.60V is due to the oxidation of the complexed
Cu(II) to Cu(III) and the return peak at +0.20V corresponds to
the reduction of Cu(III) to Cu(II).[37,38] The peaks at +0.97 and
+1.32V are nearly at the same potential values as the corre-
sponding ligand. When sweeping from –1.50 to 1.00 V (Figure
3d) three cathodic peaks occur at +0.20, –0.75, and –1.48V and
two anodic peaks at –0.32 and +0.60 V. The first, second and
third reduction waves correspond to Cu(III) → Cu(II), Cu(II)
→ Cu(I) and Cu(I) → Cu(0), respectively.[39,40] Finally Cu(0)
is oxidized back to coordinated Cu(II) (anodic peak at –0.32
V) because this peak disappears when the sweep is limited to
–1.00V. When performing successive sweeps, the potential of
the peak at –0.32V is shifted to –0.16V. This displacement is
probably due to the deposition of copper.
Decomposition temperature of compounds 1–4
Compound
Td(◦C)
Ligand H2L (1)
310
235
250
220
Copper complex (2)
Cobalt complex (3)
Cadmium complex (4)
due to either their low extinction coefficients or the large width
of the bands (Table 3).
Thermal Analysis
In order to have more information about their thermal stabil-
ity, the ligand and its metal complexes were studied by thermo-
gravimetric (DTA-TG) techniques in the temperature range of
25–400◦C under a helium atmosphere. The thermogram of the
ligand exhibits a single endothermic peak at 205◦C, correspond-
ing to its melting point. The ligand is stable up to 310◦C, and
then decomposes (Figure 2). The TG curve of the copper com-
plex (2) show a loss of weight where the corresponding DTA
curve show an exothermic peak at 235◦C, which indicates de-
composition of the complex backbone. The complex of cobalt
(3) and cadmium (4) decomposes in one step at 250◦C and
220◦C, respectively, therefore showing that the thermal stability
of the compounds studied increases in the order H2L1 (1) > Co
complex (3) > Cu complex (2) > Cd complex (4) (Table 4).
The reduction voltammogram of the Co(II) complex,
recorded between 0.00 and –1.40 V vs. SCE (Figure 3e), dis-
plays two cathodic peaks located at –0.41 and –1.05 V vs. SCE.
They correspond to the reduction of Co(II) → Co(I) and Co(I)
→ Co(0), respectively. Additionally, there is one reoxidation
peak located at –0.18 V vs. SCE. This latter peak corresponds
to the reoxidation to Co(II) of the Co(0) deposited at –1.05 V
vs. SCE.[41,42]
The electrochemical oxidation of the Co(II) shows three an-
odic peaks when sweeping from –1.80 to +1.80 V (Figure 3f).
The first, quasireversible, one (Figure 3g) located at +0.52 V
vs. SCE corresponds to a one-electron transfer couple [Co(II)
→ Co(III)], the second and third irreversible peaks, located at
+0.88 V and +1.30 V vs. SCE are assigned to the oxidation of
the amine and phenol groups.
Electrochemical Behavior
The electrochemical profiles of the ligand H2L and its
complexes were studied in DMF by cyclic voltammetry on a
platinum working electrode and a saturated calomel reference
electrode, using TBAP as the supporting electrolyte. The main
electrochemical data are given in Table 5 and some typical
voltammograms are presented in Figure 3.
For the ligand, a cyclic sweep in the +0.00 to –2.00 V range
shows a cathodic peak at –1.85 V and an anodic peak at –0.84
TABLE 5
Cyclic voltammetry
Oxidation
Reduction
Ec (V)
Compound
sweep
1
E range (V)
Ea (V)
Ec (V)
Ea (V)
–0.84
Ligand H2L (1)
0.00/–2.00
0.00/+1.80
0.00/+1.80
–1.50/+1.00
0.00/–1.40
–1.85
+0.95 +1.35
+0.60 +0.97 +1.32
+0.60
Copper complex (2)
Cobalt complex (3)
Cadmium complex (4)
1
3
1
3
1
+0.20
+0.20
–0.32
–0.18
–0.18
–0.57
–0.75 –1.48
–0.41 –1.05
–0.93 –1.18 –1.70
–1.45
–1.80/+1.80
+0.52 +0.88 +1.30
+1.15 +1.43
+0.16
–1.80/+1.80
DMF, 25◦C, TBAP 0.1 M, V vs. SCE; Ea: anodic; Ec: cathodic.

COMPLEXES OF A SCHIFF BASE WITH Cu(II), Co(II) AND Cd(II)
5
(a)
(b)
70
60
50
40
30
20
10
0
20
0
-20
-40
-60
-80
-10
0
500
1000
1500
2000
-2000
-1500
-1000
-500
0
E (mV/ECS)
E(mV/ECS)
20
15
10
5
120
100
80
(c)
(d)
60
0
40
-5
20
-10
-15
0
-20
-200
0
200
400 600
800 1000 1200 1400 1600 1800 2000
E (mV/ECS)
-1500
-1000
-500
0
500
1000
E (mV/ECS)
300
250
200
150
100
50
8
(e)
(f)
6
4
2
0
-2
-4
-6
-8
-10
-12
0
-50
-100
-2000 -1500 -1000
-500
0
500
1000
1500
2000
-1600 -1400 -1200 -1000
-800
-600
-400
-200
0
200
E (mV/ECS)
E (mV/ECS)
80
(g)
60
40
20
0
-20
-40
-2000 -1500 -1000
-500
0
500
1000
1500
2000
E (mV/ECS)
FIG. 3. Cyclic voltammetry (DMF, 25◦C, ionic strength: 0.1 mol.L−1, TBAP 0.1 M, V vs. SCE, v = 100 mV s−1, I in µ µA). (3a): ligand (1) (0.00 to –2.00 V),
(3b): ligand (1) (0,00 to +1,80 V), (3c): Cu(II) complex (2) (0.00 to +1.80 V), (3d): Cu(II) complex(2) (–1.50 to +1.00V), (3e): Co(II) complex (3) (0.00 to –1.40
V), (3f): Co(II) complex (3) (–1.80 to +1.80 V), (3g): Cd(II) complex (4) (–1.80 to +1.80 V) (color figure available onlne).

6
S. BENABID ET AL.
FIG. 4. EPR spectra of (a) {Cu} (2), (b){Co} (3) and (c) {Cd} (4) at 110 K in the solid state.
For the Cd(II) compound (4), when sweeping from –1.80 to be assumed that the origin of this signal lies in the formation
+1.80 V, one cathodic wave at –1.45 V and three anodic waves of organic radical species formed during synthesis. In the case
at –0.57, +1.15, and +1.43 V are obtained (Figure 3g). In this of Cu complex, the EPR line shape is broad and slightly asym-
case, it can be noted that the oxidation of the phenolic part of the metric. Its g value is relatively close to that of the free electron.
Schiff base occurs at higher potential values than for the other There is no evidence of signal around g = 4 or traces of hyper-
compounds (+1.43 V instead of +1.38 V). The peak at –1.45 fine splitting. Examples of this are present in related systems
V correspond to the reduction of Cd(II) complex.
studied as powdered samples.[43] Complexes of cobalt show an
extremely broad and asymmetric signal indicating that the mag-
netic site is strongly distorted. This signal can be analyzed in
EPR Spectroscopy
The X-band EPR spectra of the Cu, Co and Cd complexes
(2–4) have been recorded as powdered samples at 110 K us-
ing DPPH as the g marker (Figure 4). The EPR spectral
parameters are presented in Table 6. Although a complete anal-
ysis of these complexes has not yet been completed, the spec-
tra show the presence of paramagnetic species, but they differ
markedly as a function of the cation involved. The Cd complex
shows a narrow signal. Because Cd++ is diamagnetic, it must
TABLE 6
EPR parameters of the complexes 2–4
Compound
g (110K)
ꢀHPP (G)
Copper complex (2)
Cobalt complex (3)
Cadmium complex (4)
2.024
2.273
2.009
200
—
15

COMPLEXES OF A SCHIFF BASE WITH Cu(II), Co(II) AND Cd(II)
7
terms of g// (1.52) and g⊥ (2.46) contributions that could be This point obviously necessitates further investigation that is
attributed to some symmetry of the paramagnetic site.
presently in progress.
DISCUSSION
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