Nickel (II) and copper (II) complexes derived from NNOS donor unsymmetrical tetradentate schiff base ligands: Synthesis, characterization, and thermodynamic studies

Article abstract of DOI:10.1080/10426500903074841

A set of eight unsymmetrical tetradentate Schiff bases (cdPhsalpd = Methyl-2-{[3-(2-hydroxyphenyl)phenylidynenitrilo]propyl}amino-1- cyclopentenedithiocarboxylate; cd3-, 4-, 5-OMesalpd = Methyl-2-{[3-(2-hydroxy 3-, 4-, 5-methoxyphenyl)methylidynenitrilo]propyl} amino-1- cyclopentenedithiocarboxylate; cd5Clsalen = Methyl-2-{[3-(2-hydroxy-5-chloro phenyl)methylidynenitrilo]propyl}amino-1-cyclopentenedithiocarboxylate; cd5Brsalen = Methyl-2-{[3-(2-hydroxy-5-bromophenyl)methylidynenitrilo]propyl} amino- 1-cyclopente- nedithiocarboxylate; cd5NO2salen = Methyl-2-{[3-(2-hydroxy- 5-nitrophenyl)methylidyne- nitrilo]propyl}amino-1-cyclopentenedithiocarboxylate; and cd5SO3Na = Methyl-2-{[3- (2-hydroxy-5-sodiumsulfitephenyl) methylidynenitrilo]propyl} amino-1-cyclopentenedithi- ocarboxylate, have been obtained by condensation of methyl-2-(3-aminopropylamino) cyclopentenedithiocarboxylate (Hcdpd) with some substituted salicylaldehydes, 2-hydroxy acetophenone, and 2-hydroxy benzophenone, which present a NNOS coordination spheres. Also, the metal complexes (M = Cu, Ni) of these ligands were prepared and characterized by elemental analysis, IR, 1H NMR, UV-Vis, and mass spectrometry.The formation constants and the thermodynamic free energies were measured using UV-Vis spectrophotometry titration for 1:1 complex formation at constant ionic strength 0.1 M (NaClO4) at 25°C in DMF. The trend of the complex formation of the nickel and copper complexes is as follows: [M(cdMesalpd)] > [(Mcdsalpd)] > [M(cdPhsalpd)] and [M(cd5OMesalpd)] > [M(cd3OMesalpd)] > [M(cd4OMesalpd)] and [M(cd5OMesalpd)] > [M(cdsalpd)] > [M(cd5Brsalpd)] > [M(cd5Clsalpd)] > [M(cd5SO3Nasalpd)] [M(cd5NO2salpd)]. Our results revealed the thermodynamic formation constant, Kf, and the free energy values for Cu(II) complexes are higher than the Ni(II) complexes. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. Copyright Taylor & Francis Group, LLC.

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Nickel (II) and Copper (II) Complexes
Derived from NNOS Donor
Unsymmetrical Tetradentate Schiff Base
Ligands: Synthesis, Characterization, and
Thermodynamic Studies
Mozaffar Asadi a , Sheida Esmaielzadeh a & Khosro Mohammadi b
a Chemistry Department, College of Sciences , Shiraz University ,
Shiraz, I. R. Iran
b Chemistry Department, Faculty of Sciences , Persian Gulf
University , Bushehr, I. R. Iran
Published online: 02 Jul 2010.
To cite this article: Mozaffar Asadi , Sheida Esmaielzadeh & Khosro Mohammadi (2010) Nickel (II) and
Copper (II) Complexes Derived from NNOS Donor Unsymmetrical Tetradentate Schiff Base Ligands:
Synthesis, Characterization, and Thermodynamic Studies, Phosphorus, Sulfur, and Silicon and the
Related Elements, 185:7, 1445-1454, DOI: 10.1080/10426500903074841
To link to this article: http://dx.doi.org/10.1080/10426500903074841
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Phosphorus, Sulfur, and Silicon, 185:1445–1454, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500903074841
NICKEL (II) AND COPPER (II) COMPLEXES DERIVED
FROM NNOS DONOR UNSYMMETRICAL TETRADENTATE
SCHIFF BASE LIGANDS: SYNTHESIS,
CHARACTERIZATION, AND THERMODYNAMIC STUDIES
Mozaffar Asadi,1 Sheida Esmaielzadeh,1
and Khosro Mohammadi2
1Chemistry Department, College of Sciences, Shiraz University, Shiraz, I. R. Iran
2Chemistry Department, Faculty of Sciences, Persian Gulf University,
Bushehr, I. R. Iran
A set of eight unsymmetrical tetradentate Schiff bases (cdPhsalpd = Methyl-2-{[3-(2-
hydroxyphenyl)phenylidynenitrilo]propyl}amino-1-cyclopentenedithiocarboxylate; cd3-, 4-,
5-OMesalpd = Methyl-2-{[3-(2-hydroxy 3-, 4-, 5-methoxyphenyl)methylidynenitrilo]propyl}
amino-1-cyclopentenedithiocarboxylate; cd5Clsalen = Methyl-2-{[3-(2-hydroxy-5-chloro
phenyl)methylidynenitrilo]propyl}amino-1-cyclopentenedithiocarboxylate; cd5Brsalen =
Methyl-2-{[3-(2-hydroxy-5-bromophenyl)methylidynenitrilo]propyl}amino- 1-cyclopente-
nedithiocarboxylate; cd5NO2salen = Methyl-2-{[3-(2-hydroxy-5-nitrophenyl)methylidyne-
nitrilo]propyl}amino-1-cyclopentenedithiocarboxylate; and cd5SO3Na = Methyl-2-{[3-
(2-hydroxy-5-sodiumsulfitephenyl)methylidynenitrilo]propyl} amino-1-cyclopentenedithi-
ocarboxylate, have been obtained by condensation of methyl-2-(3-aminopropylamino)
cyclopentenedithiocarboxylate (Hcdpd) with some substituted salicylaldehydes, 2-hydroxy
acetophenone, and 2-hydroxy benzophenone, which present a NNOS coordination spheres.
Also, the metal complexes (M = Cu, Ni) of these ligands were prepared and characterized
by elemental analysis, IR, 1H NMR, UV-Vis, and mass spectrometry.
The formation constants and the thermodynamic free energies were measured using
UV-Vis spectrophotometry titration for 1:1 complex formation at constant ionic strength
0.1 M (NaClO4) at 25◦C in DMF. The trend of the complex formation of the nickel and
copper complexes is as follows: [M(cdMesalpd)] > [(Mcdsalpd)] > [M(cdPhsalpd)] and
[M(cd5OMesalpd)] > [M(cd3OMesalpd)] > [M(cd4OMesalpd)] and [M(cd5OMesalpd)] >
[M(cdsalpd)]
> [M(cd5Brsalpd)] > [M(cd5Clsalpd)] > [M(cd5SO3Nasalpd)] >
[M(cd5NO2salpd)]. Our results revealed the thermodynamic formation constant, Kf, and
the free energy values for Cu(II) complexes are higher than the Ni(II) complexes.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords Coordination; metal complexes; Schiff base ligand; thermodynamic; unsymmetrical
Received 21 January 2009; accepted 28 May 2009.
We are grateful to Shiraz University Research Council for their financial support.
Address correspondence to Mozaffar Asadi, Chemistry Department, College of Sciences, Shiraz University,
Shiraz 71454, I. R. Iran. E-mail: asadi@susc.ac.ir, mozaffarasadi@yahoo.com
1445

1446
M. ASADI ET AL.
INTRODUCTION
Schiff base ligands are of significant interest not only for their pharmacological
properties as antibacterial, anticancer, and antifungal agents,1,2 but also for their capacity
for chemical recognition of anions and metals of biochemical and environmental impor-
tance.3–5 Schiff base complexes containing different central metal atoms have been studied
in great detail for their various crystallographic features, enzymatic reactions, steric effects,
structure-redox relationships, mesogenic characteristics, catalysis, magnetic properties, and
their important role in the understanding of the coordination chemistry of transition metal
ions.6
Symmetric tetradentate Schiff base complexes have been used extensively as macro-
cycle models,7 while unsymmetric complexes are very important in biological systems
and in industrial catalysis.8,9 One of the most important classes of unsymmetric com-
plexes mixed nitrogen–sulfur donor ligands with metal ions by bonding through sulfur and
azomethine nitrogen of ligands. Tetradentate ligands with N2OS10,11 and N2S2 coordi-
12
nation spheres were prepared. In recent years, complexes containing sulfur donors have
received considerable attention due to the identification of a sulfur-rich coordination en-
vironment in biological centers.13 When the ligands are complexed with metal ions, their
biological activities are increased.14 The first reports of the active site structure of type
I blue copper (II) containing protein were published in 1983.15,16 There has been great
interest in designing highly distorted MN2S2 systems that may serve as spectral models
of the active sites of the metalloenzymes.17,18 Nickel has been discovered of the active
site of several other classes of enzymes, including hydrogenases,19–22 methyl co-enzyme
reductases,23 and CO dehydrogenases.24
In this article, we report the synthesis and characterization of some unsymmetrical
Schiff base ligands and their Ni(II) and Cu(II) complexes (see Scheme 1). The compounds
were characterized by elemental analysis, IR, NMR, mass, and UV-Vis techniques. We
have also measured the thermodynamic formation constant, Kf, and the free energy, ꢀG◦, at
25◦C in DMF solvent for the complexes. By comparing the spectral and the thermodynamic
properties of Ni(II) and Cu(II) Schiff base complexes, we aimed to investigate the effects
of different electronic and steric behaviors.
RESULTS AND DISCUSSION
Synthesis of the Schiff base complexes may be represented by Equation (1):
M(OAc)2 · nH2O + H2LX → MLX + 2HOAc + (n-2)H2O(X = 1 − 8)
(1)
The analytical data of the ligands and their complexes together with physical properties
are summarized in Table I. All the ligands and their complexes gave satisfactory elemental
analysis.
Spectral Characterization
Electronic absorption spectra. The electronic spectra of the Schiff base ligands
in the DMF solvent show a low intensity band in the 295–314 nm region, which is assigned
to π–π∗ transition, and a relatively intense band in 395–398 nm region, which is due to n–π∗
excitation.25,26 Electronic spectra of M(cdRABsalpd) were recorded in the interval 300–700
nm in DMF solvent at room temperature. Spectra of Ni(II) and Cu(II) complexes are very

NICKEL (II) AND COPPER (II) COMPLEXES
1447
NH2
NH
+
O
NH
SNH4
SH
Me2(SO4)
below 20ºC
HCl
,
CS2 NH4OH
S
C
S
0ºC
ice cooling
8h
,
C S
SMe
NH
NH2(CH2)3NH2
24h
NH NH2
S
S
H
H
H2O
C SMe
MeS C
N(CH2)3N
S
C SH
SMe
MeS
Hcdpd
+
2"
2"
1"
3"
1"
5'
5'
3"
R
R C=O
OH
R
4'
3'
1'
4'
3'
1'
N
S
N
NH
S
N
1
3
6
5
1
6
M
M(OAc)2.nH2O
M = Ni, Cu
2'
2'
2
2
5
B
O
HO
B
MeS
MeS
3
4
B
A
4 A
A
Empirical
formula
Abbreviation
of compounds
No.
R
A
B
H2L1
H2L2
H2L3
H2L4
H2L5
H2L6
H2L7
H2L8
C23H26N2OS2
C18H24N2O2S2
C18H24N2O2S2
C17H22N2O2S2
C17H21N2ClOS2
C17H21N2BrOS2
C17H21N3O3S2
C17H21N2O4S3Na
Ph
H
H
H
H
H
H
H
H
OMe
H
OH
H
H
H
H
OMe
H
Cl
Br
NO2
SO3Na
H2cdPhsalpd
H2cd4OMesalpd
H2cd5OMesalpd
H2cd4OHsalpd
H2cd5Clsalpd
H2cd5Brsalpd
H2cd5NO2salpd
H
H
H2cd5SO3Nasalpd
Scheme 1
similar, where two or three intense bands in the region 320–448 nm are observed (see Table
S1, available online in the Supplemental Materials). In Ni(II) complexes, the observed
bands in the region 430–450 nm are probably due to S–M and O–M, LMCT transitions, and
occur at energies similar to those found for the corresponding symmetric metal complexes
[M(salen)]27 and [M(cd2en)].12 The low energy band is typical of d–d transitions in square
planar nickel (II) complexes with mixed coordination spheres containing nitrogen and sulfur
atoms, suggesting that all the nickel (II) complexes studied remain approximately square
1
planar, even in strong donor solvents.28 This is in accordance with the H NMR spectra
obtained in CDCl3, DMSO-d6, which show that the Ni(II) complexes are diamagnetic in
this solvent29 (see the Supplementary Materials). The d–d bands are not observed due to
the low concentration (∼10−4 M) of the complexes solution. These bands should be low in
intensity in the region of 600–700 nm.30
The electronic spectra of unsymmetrical Schiff base copper (II) complexes have
a band in the region of 320–336 nm attributed to the π–π∗ transition. The broad,
slightly intense, and poorly resolved bands between 390–398 nm may be assigned to
O(phenolat)↔CuII LMCT or MLCT.31 The d–d bands were not observed in these com-
plexes similar to Ni(II) complexes.

1448
M. ASADI ET AL.
Table I Analytical and physical data of the unsymmetrical Schiff bases complexes
Anal. Found (Calc.)(%)
Formula
No.
weight
410.59
364.52
364.52
350.49
368.93
413.39
379.49
436.53
421.20
407.17
425.62
470.07
436.17
493.21
472.12
426.05
426.05
421.03
439.40
474.92
441.02
498.06
Yield (%)
61
Mp (◦C)
182
117
126
197
112
120
128
238
204
248
240
233
226
265
216
219
208
221
217
205
214
265
C
H
N
S
H2L1
H2L2
H2L3
H2L4
H2L5
H2L6
H2L7
H2L8
NiL3
NiL4
NiL5
NiL6
NiL7
NiL8
CuL1
CuL2
CuL3
CuL4
CuL5
CuL6
CuL7
CuL8
67.04
(67.28)
59.34
(59.31)
58.96
(59.31)
58.04
(58.26)
55.12
(55.34)
49.12
(49.39)
53.64
(53.81)
46.51
(46.77)
51.15
(51.33)
50.04
(50.15)
47.61
(47.97)
43.15
(43.44)
46.83
(46.81)
41.68
(41.40)
58.85
(58.51)
50.68
(50.74)
51.04
6.74
(6.38)
6.87
(6.64)
6.83
(6.64)
6.60
(6.33)
5.43
(5.74)
5.40
(5.12)
5.89
(5.58)
5.11
(4.85)
5.55
(5.26)
5.27
(4.95)
4.67
(4.50)
4.25
(4.07)
4.47
(4.39)
4.24
(3.88)
5.32
(5.12)
5.04
(5.20)
5.29
7.03
(6.82)
8.04
(7.69)
7.89
(7.69)
7.68
(7.99)
7.61
(7.59)
6.53
(6.78)
11.32
(11.07)
6.71
(6.42)
6.72
(6.65)
6.75
(6.88)
6.32
(6.58)
6.05
(5.96)
9.70
(9.63)
5.47
(5.68)
5.78
(5.93)
6.77
(6.58)
6.83
(6.58)
7.05
15.40
(15.62)
17.28
(17.59)
17.45
(17.59)
18.40
(18.29)
17.18
(17.38)
15.78
(15.51)
16.58
(16.90)
21.98
(22.03)
15.34
(15.22)
15.78
(15.75)
14.90
(15.06)
13.75
(13.64)
14.45
(14.70)
19.63
(19.50)
13.68
(13.58)
14.83
(15.05)
14.77
73
80
77
70
70
92
54
80
74
67
68
95
51
61
74
83
(50.74)
49.64
(49.56)
47.79
(47.43)
43.24
(42.99)
46.57
(5.20)
4.67
(4.89)
4.21
(4.45)
4.11
(4.03)
4.12
(15.05)
15.32
(15.56)
14.65
(14.90)
13.24
(13.50)
14.32
74
(6.80)
6.22
(6.51)
5.68
(5.90)
9.77
(9.53)
5.35
71
68
92
(46.30)
41.04
(4.34)
4.18
(14.54)
19.40
52
(41.00)
(3.84)
(5.62)
(19.31)
Analysis of the results shows that the positions of the LMCT bands are not very
sensitive to different substitutions on salicylaldehyde and imine band, and may not be
directly related to the electron donor/acceptor ability of the substituents.32
Figure S1 (Supplemental Materials) shows the electronic spectral change observed in
DMF solution when Cu2+ ion was added to Schiff base ligand H2cd5Brsalpd. In the absence

NICKEL (II) AND COPPER (II) COMPLEXES
1449
Table II 1H NMR data of the unsymmetrical Schiff bases and their Ni(II) complexes (in ppm)
OH
proton
NH or SH
proton
Imine
proton
Phenyl
proton
1,3-Diaminopropan
proton
Substituted
(X,Y)
No.
SCH3
H2L1a
H2L2a
H2L3a
H2L4a
H2L5a
H2L6a
H2L7a
H2L8b
NiL1a
NiL2a
NiL3a
NiL4a
NiL5a
NiL6a
NiL7a
NiL8b
15.40
13.70
12.86
13.63
13.20
13.21
14.46
13.50
—
—
—
—
—
12.03
12.44
12.38
12.25
12.45
12.45
12.46
12.26
—
—
—
—
—
—
7.15–7.52
6.39–7.11
6.75–6.87
6.15–7.15
6.88–7.23
6.84–7.34
6.98–8.25
6.78–7.65
6.33–7.67
6.10–6.90
6.50–6.81
6.06–6.92
6.68–7.01
6.63–7.26
6.70–7.94
6.33–7.40
2.07, 3.41, 3.50
2.03, 3.44, 3.71
2.17, 3.69, 3.82
1.87, 3.44, 3.54
2.05, 3.44, 3.76
2.06, 3.44, 3.76
2.10, 3.47, 3.83
1.94, 3.30, 3.65
1.81, 3.44, 3.56
1.83, 3.49, 3.63
1.77, 3.60, 3.67
1.80, 3.48, 3.60
1.85, 3.60, 3.65
1.84, 3.62, 3.70
1.82, 3.62, 3.75
1.78, 3.52, 3.59
2.55
2.60
2.55
2.49
2.60
2.58
2.57
2.46
2.69
2.67
2.67
2.67
2.67
2.66
2.68
2.46
—
3.81
3.86
—
—
—
—
—
—
3.70
3.70
—
—
—
8.28
8.34
8.36
8.35
8.35
8.47
8.59
—
7.44
7.64
7.45
7.53
7.52
8.11
8.26
—
—
—
—
—
—
—
—
aSolvent is CDCl3.
bSolvent is DMSO-d6.
of a Cu2+ ion the yellow H2cd5Brsalpd solution showed the absorption bands at 313 and
395 nm. As the Cu2+ ion solution was added, the signal of H2cd5Brsalpd decreased, and
those of the new complex [Cu(cd5Brsalpd)] at 287, 336, and 390 increased in intensity with
the isobestic points at 305, 322, 373, 424 nm. The last spectrum of the titration was similar
to the spectrum of [Cu(cd5Brsalpd)] complex that has been synthesized and characterized
separately by different methods.
1H NMR spectra. The spectra of the complexes were recorded in CDCl3 and
DMSO-d6 solution at 250 MHz, and chemical shifts are in units of ppm relative to TMS
as internal standard on the delta (δ) scale. The 1H NMR spectra of the Schiff base ligands
and their complexes was collected in Table II. Five distinct peaks at 2.46–2.69 ppm,
6.06–8.25 ppm, 7.52–8.59 ppm, 12.03–12.46 ppm, and 13.20–15.40 ppm are assigned to
SCH3, phenyl, azomethine, amine or thio, and hydroxyl protons, respectively. The hydroxyl
proton and amine or thio (NH or SH) proton disappears in the complexes, indicating that the
OH and NH or SH groups have been deprotonated and bonded to metal ions.12 Comparing
1
the H NMR spectra of the free ligands and complexes shows that the azomethine and
aromatic protons resonance of the ligands are shifted to upfield in the Ni complexes.33 A
singlet signal at δ = 3.81, 3.86 ppm is assigned to those Schiff bases and their complexes
that have an OCH3 group. The signals due to OCH3 are also affirmed by an up-field change
in chemical shift for Ni(II) complexes.
IR spectra. Important IR bands of the ligands and complexes with their assignment
are presented in Table III. The absorption band around 1600 cm−1 is assigned to an
azomethine group,34 and the phenolic ν(C O) stretching band is observed at 1230–1296
cm .
−1 35 Strong bands at 1440–1490 cm−1 have been previously assigned to ν(C C) phenyl
ring stretching vibrations.36 Some of their sulfur addition products assigned the bands in the
range 700–800 cm−1 to C S, and the bands between 1100–1185 cm−1 are probably due to
the coupling ν(C S) ν(C N).37–39 Upon complexation, the positions of these bands are
+

1450
M. ASADI ET AL.
Table III Infrared data of the unsymmetrical Schiff bases and their complexes (in cm−1
)
Phenolic
(C O)
Substituted
(A,B)
Compounds
(C S)
(C S + C N)
(C C)
(C N)
H2L1
H2L2
H2L3
H2L4
H2L5
H2L6
H2L7
H2L8
NiL1
NiL2
NiL3
NiL4
NiL5
NiL6
NiL7
NiL8
CuL1
CuL2
CuL3
CuL4
CuL5
CuL6
CuL7
CuL8
756
790
779
786
761
763
740
732
748
786
748
784
723
732
736
720
748
786
767
784
717
725
726
732
1134
1140
1153
1164
1130
1181
1105
1118
1134
1126
1153
1134
1120
1172
1103
1110
1134
1118
1149
1134
1120
1180
1103
1110
1280
1272
1269
1234
1269
1280
1296
1272
1280
1268
1215
1234
1268
1280
1291
1244
1270
1271
1261
1226
1264
1275
1294
1265
1481
1488
1481
1458
1479
1481
1442
1481
1442
1458
1461
1450
1450
1458
1442
1458
1442
1450
1442
1450
1456
1458
1442
1465
1604
1635
1639
1643
1635
1635
1651
1635
1602
1614
1623
1620
1627
1620
1627
1620
1596
1625
1631
1630
1635
1627
1635
1627
3296
1353, 1550
650, 1200
3233
1356, 1550
650, 1200
3217
1351, 1548
650, 1190
shifted by ca. 2–25 cm−1 to lower frequency. This indicates that coordination takes place
through the azomethine nitrogen and sulfur of the ν(C S) group and oxygen atom of the
−1
phenolic group.33,39 Two sharp peaks at around 1300 cm−1 and 1550 cm
are typical
of nitro group in H2L7, NiL7, and CuL7 and two absorption bands in 650 and 1200 cm−1
are assigned to ν(S O) and ν(S O) stretching in H2L8, NiL8, and CuL8, which undergo
minor changes in their complexes. It may therefore be that the NO2 and SO3 groups are not
coordinated to the metal ions.40
Mass spectra. The mass spectra of the ligands show intense molecular ion peaks
m/z [M]+. The mass spectra of some compounds, also a show prominent peak corresponding
to m/z [M+1]+ (see Table S2 in the Supplemental Materials).
The Formation Constants and the Thermodynamic
Free Energy Calculations
Formation constants have been determined by UV-vis absorption spectroscopy
through titration of the ligands with various concentrations of the metal ions at constant
ionic strength 0.1 M (NaClO4) at 25◦C. The complex formation constants, Kf, were calcu-
lated using the SQUAD computer program,41 designed to calculate the best values for the
formation constants of proposed equation model [Equation (1)] by employing a nonlinear,
least-squares approach.

NICKEL (II) AND COPPER (II) COMPLEXES
1451
Also the free energy change, ꢀG◦, of the formed complexes was determined by
ꢀG◦ = −RT lnKf, where Kf is the complex formation constant, R is the gas constant, and T
is the temperature in Kelvin. The formation constants and the free energy data are collected
in Table S3 (Supplementary Materials). The results show that Cu(II) has a greater tendency
to bind with the ligands than Ni(II), which may be attributed to its higher positive charge
distribution and the ligand deformation geometry.
The electronic effect of para substituted Schiff base ligands. In this part
of the work, we studied the electronic effect of para substitutional groups bonded to
Schiff base ligands complexed to Ni(II) and Cu(II) ions. The formation constants and
the thermodynamic parameter are collected in Table S4 (Supplemental Materials). On the
basis of the thermodynamic results, the trend of the interaction between the unsymmetrical
ligands and Cu(II) and Ni (II) ions is as follows:
cd5OMesalp > cdsalpd > cd5Brsalpd > cd5Clsalpd > cd5SO3Nasalpd > cd5NO2salpd
In the para substituted Schiff base ligands, the formation constants varies as can be expected
from the electronic effects of the substituents at position 5. Thus, the formation constants
decrease according to the sequence OMe > H > Br > Cl > SO3 > NO2, i.e., in order of
an increase in both electron-withdrawing and π-acceptor qualities of the substituents and
the donor ability of the ligand groups (mainly the phenoxy groups). Similar results have
been reported previously for electrochemical properties of the analogous Cu(II), Ni(II), and
Co(III) systems.42–44 The acceptor functional groups make the Schiff base a poor donor
ligand and decrease the formation constants, while the donor groups increase the formation
constants because they leads to increased donor ability of Schiff base ligands; therefore
the ligands have NO2 and SO3 group, and H2cd5NO2salpd and H2cd5SO3Nasalpd have
the smallest formation constant, while the ligands that have OMe groups have the highest
formation constant because OMe is a donating group.45 Therefore, in the stabilization of the
tetra-coordinated complex, the donation power of the Schiff base is important, and hence
their formation constants, Kf, with donors are higher.
The effect of the position of substituents. In continuation of our studies
on formation constants of complexes, we have studied here the effect of the position of
substituents on the phenyl ring of Schiff base on the formation constant of the complexes of
H2cd3OMesalpd,11 H2cd4OMesalpd (H2L2), and H2cd5OMesalpd (H2L3) with Cu(II) and
Ni(II) ions. The results show the following trend of complex formation of a given cation
towards the Schiff bases:
cd5OMesalpd > cd3OMesalpd > cd4OMesalpd
In the case of H2L3, the methoxy group situated in the para position to the phenolic oxygen
donor atoms of N2OS backbone can release the electron directly and stabilize the tetra-
coordinate complex, so the formation constant is larger than that for meta position in the
H2L2, and H2cd3OMesalpd, which has the steric effect (see Table S4).43
The electronic effect of the equatorial Schiff base ligands. The substi-
tutional effects on the imine bond were studied by determining the formation constants
for [M(cdPhsalpd)] and [M(cdMesalpd)] where M
Ni, Cu. The results show the
following trend in the complexes formation between ligand Schiff bases H2cdPhsalpd,
H2cdMesalpd,11 with Ni(II) and Cu(II) ions (Table S5): M(cdMesalpd) > M(cdsalpd) >
M(cdPhsalpd).

1452
M. ASADI ET AL.
These values for electron-releasing methyl Schiff bases were more than those for
electron-withdrawing phenyl Schiff bases.46 The phenyl group makes the Schiff base a
poor donor ligand (and a good acceptor ligand) and decreases the formation constants,
while the methyl group is a donating group and increases the formation constant.
CONCLUSION
1. The formation constants, Kf, and the free energy values for Cu(II) complexes are higher
than the Ni(II) complexes, which may be attributed to its higher positive charge distri-
bution and the ligand deformation geometry.
2. The trend of the complex formation of the para substitutional groups bonded to Schiff
base ligands complexed to Ni(II) and Cu(II) ion decreases as follows: cd5OMesalpd >
cdsalpd > cd5Brsalpd > cd5Clsalpd > cd5SO3Nasalpd > cd5NO2salpd
3. The formation constants for M[(cd3-, 4-, 5-OMesalpd)] complexes has the following
trend: cd5OMesalpd > cd3OMesalpd > cd4OMesalpd
4. The trend of the complex formation of the substitutional on imine bond Schiff base
ligands complexed to Ni(II) and Cu(II) ion decreases as follow: cdMesalpd > cdsalpd >
cdPhsalpd
5. In the series [H2cdRABsalpd], it seems that the combination of strain, strength of the
ligand field, the electronic effect, the geometry of the ligand, the electron configuration,
and the ionic radii of the metal can affect the complex formation constants.
EXPERIMENTAL
Synthesis of Schiff Base Ligands
Methyl-2-(3-aminopropylamino)cyclopentenedithiocarboxylate (Hcdpd) was pre-
pared by published methods.11,47,48 The ligands were prepared by addition of the equimo-
lar amount of the appropriate salicylaldehyde derivatives to a methanolic solution of
Hcdpd. The yellow products were recrystallized from methanol/chloroform 1:1 (v:v) (see
Scheme 1).
Synthesis of the Complexes
A novel series of mononuclear tetradentate complexes M(cdRABsalpd), (M = Ni,
Cu) were synthesized as follows: To a solution of the appropriate ligand (1 mmol) in 10
mL of chloroform/methanol 2:1 (v:v), a solution of metal acetate (1 mmol) in 10 mL of
methanol was added. The solution was stirred for 15 min and then allowed to stand at room
temperature for 24 h. After filtering, the brown and the green powders were recrystallized
from acetonitrile/methanol 1:1 (v:v) (see Scheme 1).
Thermodynamic Studies
The formation constant measurements were carried out by spectrophotometric titra-
tion at constant ionic strength 0.1 M (NaClO4) at 2 5◦C ( 0.1◦C). In a typical measurement,
2.5 mL solution of ligands (10−5 M) in a DMF was titrated with various concentrations
of the metal acetate (10−5–10−4 M) in DMF. UV-vis spectra were recorded in the range

NICKEL (II) AND COPPER (II) COMPLEXES
1453
290–700 nm about 5 min after each addition. The formed product shows different ab-
sorption from the free ligand, while the metal ion solution shows no absorption at those
wavelengths. For example, the variation of the electronic spectra for H2cd5Brsalpd titrated
with various concentration of Cu(II) acetate at 25◦C in DMF is shown in Figures S1 and
S2. The same is valid for other systems.
REFERENCES
1. F. M. Morad, M. M. El, Ajaily, and S. Ben Gweirif, J. Scie. App., 1, 2 (2007).
2. V. P. Daniel, B. Murukan, B. S. Kumari, and K. Mohanan, Spectrochim. Acta Part A, 70, 403
(2008).
3. K. R. Surati and B. T. Thaker, Russ. J. Coord. Chem., 34, 25 (2008).
4. M. K. Srivastava, B. Mishra, and M. Nizamuddin, Ind. J. Chem., 40B, 342 (2001).
5. K. R. Surati, B. T. Thaker, and G. R. Shah, Synth. React. Inorg. Met-Org. Nano-Met. Chem., 38,
272 (2008).
6. E. Peker and S. Serin, Met. Org. Chem., 34, 859 (2004).
7. M. K. Taylor, K. D. Trotter, J. Reglinski, L. E. A. Beriouis, A. R. Kennedy, C. M. Spickett, and
R. J. Sowden, Inorg. Chim. Acta, 361, 2851 (2008).
8. M. Karatepe and F. Karatas, Cell. Biochem., 24, 547 (2006).
9. B. Sarkar, G. Bocelli, A. Cantoni, and A. Ghosh, Polyhedron, 27, 693 (2008).
10. L. Gomes, E. Pereira, and B. Castro, J. Chem. Soc., Dalton Trans., 1373 (2000).
11. E. Pereira, L. Gomes, and B. Castro, J. Chem. Soc., Dalton Trans., 629 (1998).
12. E. M. Martin and R. D. Bereman, Inorg. Chim. Acta, 188, 221 (1991).
13. J. C. Fontecilla, J. Biol. Inorg. Chem., 1, 91 (1996).
14. M. A. Ali, A. H. Mirza, A. Monsur, S. Hussain, and M. Nizamaddin, Polyhedron, 20, 1045
(2001).
15. E. I. Solomon, K. W. Penfild, and D. E. Wilcox, Struct. Bonding, 53, 1 (1983).
16. J. M. Guss and H. C. Freeman, J. Mol. Bio., 169, 521 (1983).
17. K. D. Kralin and J. Zubieta, Copper Coordination Chemistry: Biochemical and Bioinorganic
Perspective (Adenine, New York, 1982).
18. O. P. Anderson, J. Becher, H. Frydendahl, L. F. Taylor, and H. Toftlund, J. Chem. Soc., Chem.
Commun., 699 (1986).
19. J. J. G. Moura, M. Teixeira, I. Moura, A. V. Xavier, and J. LeGall, J. Mol. Catal., 23, 303 (1984).
20. R. D. Cammack, D. O. Hall, and K. K. Rao, Microbial Gas Metabolism: Mechanistic, Metabolic
and Biotechnological Aspects (Academic Press, New York, 1985).
21. H. Frydendahl, H. Toftlund, J. Becher, J. Dutton, K. S. Murray, L. F. Taylor, O. P. Anderson, and
E. R. T. Tiekink, Inorg. Chem., 34, 4467 (1995).
22. R. D. Cammaclc, D. Patil, R. Aguirre, and E. C. Hatchikian, FEBS Lett., 142, 289 (1982).
23. S. W. Ragsdale, L. G. Ljungdahl, and D. V. Dervartanian, Biochem. Biophys. Res. Commun.,
115, 658 (1983).
24. S. W. Ragsdale, H. G. Wood, and W. E. Antholine, Proc. Natl. Acad. Sci. U. S. A., 82, 6811
(1985).
25. S. M. Grawford, Spectrochim. Acta, Part A, 19, 255 (1963).
26. R. C. Felicio, E. T. G. Canalheiro, and E. R. Dockal, Polyhedron, 20, 261 (2001).
27. R. H. Holm, J. Am. Chem. Soc., 82, 5632 (1960).
28. A. B. P. Lever, Inorganic Electronic Spectroscopy (Elsevier, New York, 1984), 2nd ed.
29. B. Castro, E. Pereira, and L. Gomes, Inorg. Chim. Acta, 271, 83 (1998).
30. Y. Zhang, W. J. Ruan, X. J. Zhao, G. H. Wang, and A. Z. Zhu, Polyhedron, 22, 1535 (2003).
31. N. Daneshvar, A. A. Entezami, L. A. Khandar, and L. A. Saghatforoush, Polyhedron, 22, 1437
(2003).

1454
M. ASADI ET AL.
32. (a) B. J. Hathaway, G. Wilkinson, R. D. Gillard, and J. A. McCleverty, Comprehensive Co-
ordination Chemistry. The Synthesis, Reactions, Properties and Applications of Coordination
Compounds (Pergamon, Oxford, UK, 1987); (b) B. J. Hathaway and D. E. Billing, Coord. Chem.
Rev., 5, 1420 (1970).
33. A. Khandar, B. Shaabani, F. Belaj, and A. Bakhtiari, Polyhedron, 25, 1893 (2006).
34. H.Beraldo and D. X. West, Trans. Met. Chem., 22, 249 (1997).
35. A. D. Garnovskii, A. L. Nivorozhkin, and V. I. Minkin, Coord. Chem. Rev., 14, 126 (1993).
36. S. K. Mondal, P. Poul, R. Ray, and K. Nag, Trans. Met. Chem., 9, 247 (1984).
37. S. Chandra and A. Rathi, J. Saudi. Chem. Soc., 5, 175 (2001).
38. S. C. Cummings, P. R. Blum, and R. M. C. Wei, Inorg. Chem., 13, 450 (1974).
39. S. Chandra and U. Kumar, Spectrochim. Acta Part A, 61, 219 (2005).
40. D. Nandankumar and B. S. Gary, Spectrochim. Acta Part A, 64, 141 (2006).
41. D. L. Leggett, Computational Methods for the Determination of Formation Constant (Plenum
Press, New York 1985).
42. A. H. Sarvestani, and S. Mohebbi, J. Chem. Res., 4, 257 (2006).
43. M. Asadi, Kh. Aein Jamshid, and A. H. Kyanfar, Inorg. Chim. Acta, 360, 1725 (2007).
44. A. J. Gordon and R. A. Ford, The Chemist’s Companion: A Handbook of Practical Data,
Techniques (Wiley, New York, 1972).
45. M. Asadi, A. H. Saravestani, and M. Abbasi, J. Chem. Res., 1, 56 (2007).
46. M. Asadi and Z. Asadi, Trans. Met. Chem., 32, 387 (2007).
47. B. Bordas, P. Sohar, G. Matolcsy, and P. Berencsi, J. Org. Chem., 37, 1727 (1972).
48. K. Nag and D. S. Joardar, Inorg. Chim. Acta, 14, 133 (1975).