Spectroscopic, thermal and electrochemical studies on some nickel(II) thiosemicarbazone complexes

Article abstract of DOI:10.1016/j.saa.2004.02.035

Several complexes of thiosemicarbazone derivatives with Ni(II) have been prepared. Structural investigation of the ligands and their complexes has been made based on elemental analysis, magnetic moment, spectral (UV-Vis, i.r., ¹H NMR, ms), and

Full text of DOI:10.1016/j.saa.2004.02.035

Spectrochimica Acta Part A 61 (2005) 243–252
Spectroscopic, thermal and electrochemical studies on
some nickel(II) thiosemicarbazone complexes
R.M. El-Shazlya, G.A.A. Al-Hazmia,∗, S.E. Ghazya,
M.S. El-Shahawib, A.A. El-Asmya
a
Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt
Chemistry Department, Faculty of Science, Mansoura University, Damietta, Egypt
b
Received 24 November 2003; received in revised form 18 February 2004; accepted 18 February 2004
Abstract
Several complexes of thiosemicarbazone derivatives with Ni(II) have been prepared. Structural investigation of the ligands and their
complexes has been made based on elemental analysis, magnetic moment, spectral (UV–Vis, i.r., 1H NMR, ms), and thermal studies. The i.r.
spectra suggest the bidentate mononegative and tridentate (neutral, mono-, and binegative) behavior of the ligands. Different stereochemistries
were suggested for the isolated complexes. The thermogravimetry (TG) and derivative thermogravimetry (DTG) have been used to study the
thermal decomposition and kinetic parameters of some ligands and complexes using the Coats-Redfern and Horowitz-Metzger equations. The
redox properties and stability of the complexes toward oxidation waves explored by cyclic voltammetry are related to the electron withdrawing
or releasing ability of the substituent of thiosemicarbazone moiety. The samples displayed NiII/NiI couples irreversible waves associated with
NiIII/NiII process.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Nickel(II) complexes; Mass spectra; Thiosemicarbazone complexes; IR spectroscopy; Redox properties
the NiI/NiII and NiII/NiIII couples have been shown to be
markedly affected by the nature of the solvent, background
electrolyte, and the structure of the chelating ligand and the
complex [7].
1. Introduction
Macrocyclic Schiff bases of thiosemicarbazones and their
metal complexes are well known to be biologically impor-
tant and interesting because of their anticarcinogenic, an-
tibacterial, and antifungal properties [1,2]. Also, they have
been screened for their medicinal properties because they
posses some degree of cytotoxic activity [3].
The biological activity of certain thiosemicarbazones is
due to their ability to form chelates with transition metal ions
[4]. Crystal structures for salicylaldehyde thiosemicarbazone
and 2-hydroxyacetophenone-thiosemicarbazone have been
reported [5], and both mainly exist in the E-conformation
with respect to the thiosemicarbazone azomethine bond. Bi-
ological activities may also related to the redox properties of
the complexes [6]. The redox properties include oxidation
and reduction of the central metal ion and various oxidation
and reduction of the ligands, and the processes involve both
the central atom and the ligand [6]. The redox potential of
Ni(II) complexes of acetophenone, 4-aminoacetophenone,
and 4-acetylacetophenone thiosemicarbazones containing
the neutral or anionic forms of these ligands were prepared
and fully characterized [8]. As a part of our work involving
thiosemicarbazone derivatives and their complexes [9–11],
this paper gives an insight about the preparation, spectral,
characterization, and cyclic voltammetric studies of some
Ni(II) complexes. The kinetics and thermodynamic param-
eters for some thermal decomposition steps as well as the
mechanisms and kinetics of the electron transfer of the
observed electrode couples for some complexes have been
critically studied.
2. Experimental
∗
All chemicals used were of analytical reagent grade
(BDH) and used as supplied.
Corresponding author. Tel.: +22-50-2340100; fax: +22-50-2246781.
E-mail address: gamilalhazmi@hotmail.com (G.A.A. Al-Hazmi).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.02.035

244
R.M. El-Shazly et al. / Spectrochimica Acta Part A 61 (2005) 243–252
N4HR
S
R
were then refluxed on a water bath for 2–3 h. Few drops of
R
2
glacial acetic acid being added at the onset of the reflux.
The precipitates formed were separated out, filtered off,
recrystallized from ethanol, and dried in a desiccator over
anhydrous CaCl2. The proposed chemical structures of the
prepared thiosemicarbazone ligands are in good agreement
with the stoichiometries concluded from their analytical
data and mass spectra (Table 1) and confirmed from the IR
spectral data (Table 2). Most of these ligands are white or
pale yellow and have melting point below 245 ◦C (Table 1).
4
N
C
R
C
NH
C
N
NHR
2
NH
C
R
S
R = H or OH
R = H or OCH3
R = H, C6 H5 or p
R = H or CH3
H or OH
=
=
R
R
H, C H , C H or p-ClC H
6 4
-ClC H
2
5
6
5
6
4
Fig. 1. General formulas of the ligands.
1
The H NMR spectra of the reagents HAET, HAPT, and
2.1. Preparation of ligands
H2HyMPT in d6-DMSO show signals at δ = 12.08–11.40
and 9.92–8.51 ppm assigned to the N2H and N4H protons,
respectively [12]. The spectra of HAT and H2ST show sig-
nals at δ = 10.29, 10.07, and 8.09, 8.03 ppm safely assigned
to the NH2 and NH protons, respectively. Moreover, the
spectrum of H2ST shows the OH and NH2 proton signals at
10.17 and 10.07 ppm [9], respectively. The general structure
of the ligands is given in Fig. 1, where the abbreviations and
their names are listed in Table 1.
The thiosemcarbazone ligands (Fig. 1) were prepared
by mixing equimolar amounts of acetopenone (12 ml,
0.1 mol), salicylaldehyde (12.2 ml, 0.1 mol), benzophenone
(18.2 g, 0.1 mol), and/or o-hydroxymethoxybenzophenone
(22.8 g, 0.1 mol) in 30 ml ethanol, with an ethanolic solution
(20 ml) of thiosemicarbazide (9.1 g, 0.1 mol), ethyl- (11.9 g,
0.1 mol), phenyl- (16.7 g, 0.1 mol), and/or p-chlorophenyl
(20.1 g, 0.1 mol) thiosemicarbazides. The reaction mixture
Table 1
Abbreviation, name, melting point, elemental analysis and formula weight (F.W.) of the prepared ligands
Abbreviation
Name
m.p. (oC)
Found (Calcd. %)
C
F.W.
H
Founda
Calcd.
HAT
HAET
HAPT
HApClPT
H2ST
H2SET
H2SPT
H2SpClPT
H2HyMBPT
1-Acetophenonethiosemicarbazone
132
145
198
190
245
184
205
212
110
55.8 (55.9)
60.0 (59.7)
67.0 (66.9)
58.8 (59.3)
49.3 (49.2)
53.3 (53.8)
61.0 (61.9)
54.3 (54.9)
66.0 (66.8)
5.7 (5.7)
6.4 (6.8)
5.9 (5.6)
4.2 (4.6)
5.0 (4.6)
5.4 (5.9)
4.8 (4.8)
4.0 (3.9)
4.8 (5.1)
–
193.3
221.3
269.4
303.8
195.2
223.3
271.3
305.9
377.5
1-Acetophenone-4-ethylthiosemicarbazone
1-Actophenone-4-phenylthiosemicarbazone
1-Acetophenone-4-p-chlorophenylthiosemicarbazone
1-Salicylaldehydethiosemicarbazone
1-Salicylaldehyde-4-ethylthiosemicarbazone
1-Salicylaldehyde-4-phenylthiosemicarbazone
1-Salicylaldehyde-4-p-chlorophenylthiosemicarbazone
1-(2-Hydroxy-4-methoxybenzophenone)
4-phenylthio-semicarbazone
221.0
–
304.0
–
223.0
–
304.0
377.0
H2HyMBpClPT
1-(2-Hydroxy-4-methoxybenzophenone)
4-p-chloro-phenylthiosemicarbazone
1-Benzophenonethiosimecarbazone
135
191
61.2 (61.2)
66.6 (65.8)
4.3 (4.4)
4.6 (5.1)
412.0
255.9
411.9
255.3
HBT
a
Values obtained from mass spectra.
Table 2
Physical properties, analytical data and formula weight (F.W.) of the prepared nickel(II) complexes
No.
Complex
Color
m.p. (◦C)
Found (Calcd. %)
F.W.
C
H
Ni
Founda
Calcd.
1
2
3
4
5
6
7
8
9
[Ni(AT)2]H2O
[Ni(AET)2]
[Ni2(APT)3(OH)(H2O)]H2O
[Ni(ApClPT)2]
[Ni(HST)(OAc)]
[Ni(SET)(H2O)]1.5H2O · C2H5OH
[Ni(HSPT)(OAc)(H2O)2]
[Ni(H2SpClPT)(OAc)2(H2O)]
[Ni(HHyMBPT)(OH)(H2O)]
[Ni2(H2HyMBpClPT)(Oac)4(H2O)3]
[Ni(BT)(OAc)(H2O)2]H2O
Dark brown
Dark brown
Yellowish green
Yellowish brown
Pale brown
Reddish brown
Brown
Brown
Yellow
Reddish brown
Greenish brown
268
234
47.5 (46.8)
52.3 (52.9)
55.0 (55.4)
54.8 (54.2)
38.1 (38.5)
38.8 (38.8)
44.9 (45.3)
43.2 (43.0)
53.0 (53.6)
42.1 (42.5)
46.6 (47.1)
4.4 (4.7)
5.1 (5.6)
4.0 (4.8)
4.2 (3.9)
3.5 (3.5)
5.7 (5.9)
4.5 (4.5)
4.0 (4.3)
3.9 (4.5)
4.4 (4.4)
4.1 (4.7)
12.3 (12.7)
11.4 (11.7)
11.9 (12.0)
8.6 (8.8)
19.2 (18.8)
16.0 (15.8)
13.8 (13.8)
11.7 (11.3)
12.5 (12.5)
14.1 (14.3)
14.4 (14.4)
–
461.1
499.3
975.5
664.3
311.9
371.1
424.1
500.7
470.2
819.5
426.1
499.0
–
>300
>300
>300
>300
>300
>300
223
664.0
312.0
369.0
422.0
498.0
470.0
820.0
–
10
11
>300
>300
a
Values obtained from mass spectra.

R.M. El-Shazly et al. / Spectrochimica Acta Part A 61 (2005) 243–252
245
2.2. Preparation of complexes
The elemental analysis, color, and melting point together
with the formula weight obtained from the ms spectra for
the complexes are listed in Table 2. Attempts to propose the
structure of the isolated complexes come from full investi-
gation using the following studies.
All complexes were prepared by adding stoichiometric
quantities of the ligands (3 mmol) in ethanol and nickel ac-
etate (3 mmol) in bidistilled water. The reaction mixtures
were then refluxed on a water bath for 4–6 h. The precipi-
tates formed were filtered off, washed with hot water, hot
ethanol, and diethylether, and finally dried in a vacuum des-
iccator over anhydrous CaCl2.
3.1. IR spectral studies
The most characteristic bands of the ligands and their
complexes are summarized in Table 3. Representative ex-
ample for their spectra is given in Fig. 2.
2.3. Physical measurements
The coordination sites of ligands under investigation
with Ni(II) ions were elucidated using IR spectra. The
data obtained suggest that the ligands bind to the metal
ions by several manners. Firstly, HAT, HAET, HAPT,
HApClPT, and HBT behave as mononegative bidentate
C and H content was determined at the Microanalytical
Unit of Cairo University. The analysis of metal ions was
carried out according to the standard methods [13].
The infrared spectra, as KBr discs, were recorded on a
Mattson 5000 FTIR Spectrophotometer. The electronic and
1H NMR (200 MHz) spectra were recorded on UV2–100
Unicam UV–Vis and a Varian Gemini Spectrophotometers,
respectively. The mass spectra were recorded on a Var-
ian MAT 311 instrument. The thermal studies were carried
out on a Shimadzu thermogravimetric analyzer at a heating
rate of 10 ◦C min−1. The cyclic voltammetry measurements
were carried out with a Potentiostat wave generator (Oxford
Press) equipped with a Phillips PM 8043 X-Y recorder. The
electrode assembly consists of platinum wires of 0.5 diam-
eter as working and counter electrodes and Ag/AgCl as a
reference electrode. Tetrabutylammonium tetraflouroborate
(TBA+BF4−) was used as supporting electrolyte.
=
and coordinate through the C N and C–S groups with
displacement of one hydrogen atom upon enethiolization.
The mode of coordination was found in [Ni(AT)2]H2O,
[Ni(AET)2], [Ni2(APT)3(OH)(H2O)]H2O, [Ni(ApClPT)2],
and [Ni(BT)(OAc)(H2O)2]H2O, and was suggested by the
following evidence: (i) the disappearance of ν(N2H), (−ii1)
=
the shift of ν(C N) to lower frequency by 10–65 cm
[14], (∗iii) the appearance of a new band attributed to
=
=
ν(C N ) at the same spectral region for the ν(C N) of the
thiosemicarbazone moiety, (iv) coordination of the azome-
thine nitrogen is also consistent with the presence of a new
band at 440–460 cm−1 assignable to the ν(Ni–N) vibration
[15], and (v) the thioamide band (IV) is absent with the
simultaneous appearance of new bands in the 610–680 and
345–370 cm−1 regions due to the ν(C–S) [16] and ν(Ni–S)
vibrations [17], respectively.
3. Results and discussion
Secondly, H2SpClPT and H2HyMBpClPT appear to be
in the thioketo form, neutral, and tridentate, coordinating
The isolated complexes are stable in air, insoluble
in water and common organic solvents, but completely
soluble in DMF and DMSO except for [Ni(AT)2]H2O,
[Ni(HHyMBPT)(OH)(H2O)], [Ni(AET)2], and [Ni2(H2
HyMBpClPT)(OAc)4(H2O)3], which are partially soluble
in DMF and DMSO.
=
=
via the C S, C N, and phenolic oxygen groups. This be-
havior is observed in [Ni(H2SpClPT)(OAc)2(H2O)] and
[Ni2(H2HyMBpClPT)(OAc)4(H2O)3] and supported by
=
=
the following evidence: (i) the ν(C S) and ν(C N) bands
are shifted to lower frequency by 5–45 cm−1, and (ii) the
Table 3
Significant IR spectral bands (cm−1) of the nickel(II) complexes with relevant bands of the free ligand in parenthesis
ν(N4H)
ν(N2H)
ν(C N)
ν(C S)
ν(C–S) δ(OH)
ν(Ni–O) ν(Ni–N) ν(Ni–S)
=
=
Complex ν(NH2)
ν(OH)
1
3395 (3410)
–
–
(3220)
1620 (1630) (790)
645
–
–
454
355
3345 (3370)
2
3
4
5
–
–
–
–
3210(3320) (3225)
3290(3300) (3250)
3280(3290) (3240)
1565 (1630) (790)
1575 (1605) (795)
1590 (1635) (795)
1605 (1610) (780)
610
615
610
650
–
1340
–
–
–
–
445
460
450
425
365
345
370
350
3435
–
3325 (3370) 3405 (3440)
3260 (3315)
–
(3165)
1330 (1365) 505
6
7
8
9
10
11
–
–
–
–
(3405)
3330 (3355) (3250)
1595 (1605) (790)
1600 (1620) (835)
620
655
–
–
–
1330 (1375) 500
1375 (1389) 500
1305(1330) 505
1320(1327) 505
1310(1350) 505
440
450
420
440
410
440
340
350
345
–
385
355
3420 (3405) 3385 (3380) (3145)
3320 (3335) 3230 (3235) 3130 (3154) 1605 (1610) 820 (830)
3460 (3470) 3295 (3300) 3160 (3160) 1590 (1635) 810 (810)
3430 (3440) 3230 (3290) 3110 (3180) 1590(1635) 745 (790)
–
3365 (3365)
3280 (3260)
–
–
(3175)
1590 (1620) (800)
680
–
490

246
R.M. El-Shazly et al. / Spectrochimica Acta Part A 61 (2005) 243–252
(a
)
(b)
3500
3000
2500
2000
1500
1000
500
4000
wavenumbers
Fig. 2. IR spectra of: (a) [Ni2(H2HyMBpClPT)(OAc)4(H2O)3] and (b) [Ni(BT)(OAc)(H2O)2]H2O.
shift of ν(C N) band from 1605 to 1595 cm−1, and (iv) the
phenolic oxygen of these ligands occupy the third coordi-
nation site with the shift of ν(OH) band by 10–15 cm−1
to lower frequency. The band at 505 cm−1 is assignable
to ν(Ni–O) of the bridging phenolate oxygen, and (iii) the
appearance of new bands in the low frequency region at
345–385 and 410–420 cm−1, which are assigned to the
ν(Ni–S) and (Ni–N) [18] vibrations, respectively.
=
new bands observed at 440 and 500 cm−1 attributed to the
ν(Ni–N) and ν(Ni–O) vibrations, respectively, gave a good
evidence for the participation of N and O donors.
In [Ni(HHyMBPT)(OH)(H2O)], H2HyMBPT behaves as
a mononegative, bidentate ligand coordinating via the de-
protonated OH and C N groups as shown in Scheme 1. The
=
The third mode of chelathion was found through the
mode of complexation is suggested by the clear change in the
position of ν(C N) band by 44 cm−1, the shift of ν(OH) and
=
C N, C–S, and phenolic oxygen groups in which H2ST
=
and H2SPT act as mononegative tridentates. This behavior
is found in [Ni(HST)(OAc)] and [Ni(HSPT)(OAc)(H2O)2].
δ(OH) to lower frequency, the appearance of new bands at
440 and 505 cm−1 assigned to ν(Ni–N) and ν(Ni–O). Also,
2
Elucidation of this mode is proposed by: (i) the disappear-
=
the ν(C S) and ν(N H) bands remain unshifted, suggesting
2
=
ance of ν(N H), (ii) the shift of ν(C N) bands to lower
=
that the C S group is out of coordination.
frequency by 50–20 cm−1, (iii) the disappearance of ν(C S)
=
The acetate group coordinates in a monodentate or biden-
tate manner [19]. The monodentate in [Ni(HST)(OAc)], [Ni
(HSPT)(OAc)(H2O)2], and [Ni(H2SpClPT)(OAc)2(H2O)] is
with the appearance of a new band at 650–655 cm−1, (iv)
the shift (15–35 cm−1) of ν(OH) and (15–35 cm−1) of
δ(OH) to lower frequency, and (v) new bands −a1ppeared in
the low frequency region for ν(Ni–S) at 350 cm , ν(Ni–N)
at 425–450 cm−1, and ν(Ni-O) at 500–505 cm−1 gave a
good evidence for the participation of S, N, and O donors.
In [Ni(SET)(H2O)]1.5H2O·C2H5OH, the ligand releases
the hydrogen ions from both the thioketo, through thioeno-
lization, and the OH groups and behaves as a binegative
OH2
Ni
NH
CH3O
O
C
OH
NH
N
C
S
tridentate. This behavior was confirmed based on the follow-
2
=
ing evidence: (i) the disappearance of ν(N H) and ν(C S)
conjugated with the appearance of ν(C–S) at 620 cm−1 and
ν(Ni-S) at 340 cm−1, (ii) the deprotonated OH group occu-
pies the third (through bridging) coordination site, (iii) the
Scheme 1.

R.M. El-Shazly et al. / Spectrochimica Acta Part A 61 (2005) 243–252
247
deduced from the frequency difference (ꢀν) between νs and
H
C
νas (more than 185 cm−1) [20]. The bidentate behavior of the
acetate group in [Ni(BT)(OAc)(H2O)2]H2O is supported by
the appearance of two new bands at 1420 and 1525 cm−1 due
to symmetric and asymmetric stretching vibrations, respec-
tively. [Ni2(H2HyMBpClPT)(OAc)4(H2O)3] displays three
bands in its spectrum at 1525, 1395, and 1337 cm−1, which
are assigned to the existence of bidentate and monodentate
coordinations of the acetate group [21]. The monodentate
behavior is deduced from the frequency difference (ꢀν =
188 cm−1) between the 1525 and 1337 cm−1 bands, and
the difference between the 1525 and 1395 cm−1 (ꢀν =
88 cm−1) bands is correlated to the bidentate behavior.
H
N
NH2
N
N
C
C
N
S
C
N
O
S
H
OH2
H2O
Ni
Ni
O
H
O
O
OAc
C
O
H
CH3
H
H
(a)
(b)
CH3O
C
H
H
O
N
N
3.2. Magnetic and electronic spectral studies
Ni OAc
S
H2O
O
C
H3C
C
O
NH
Cl
The magnetic moments and electronic spectral bands of
the complexes are summarized in Table 4.
OH2
H2O
Ni
AcO
O
Ac
The magnetic moment values of [Ni(HSPT)(OAc)(H2
O)2], [Ni(H2SpClPT)(OAc)2(H2O)], [Ni2(H2HyMBpClPT)
(OAc)4(H2O)3], and [Ni(BT)(OAc)(H2O)2]H2O are found
within the range reported for the octahedral geometry around
the Ni(II) ion [22]. The value (1.8 B.M.) measured for
each nickel atom in [Ni2(H2HyMBpClPT)(OAc)4(H2O)3]
is less than that reported for systems containing two un-
paired electrons, which may be attributed to the existence
of nickel–nickel interaction [23].
(c)
Scheme 2.
parameters Dq, B, and β of some of the complexes are
given in Table 4. The Dq values are found in the range
(9.80–10.3) × 103 cm−1 close to that observed for NiO4N2
and reasonable for most complexes containing oxygen, ni-
trogen, and/or sulphur. The observed Dq values ordered the
ligands in the middle range of the spectrochemical series
and provides that the C N, OH, and C S of the ligands are
complexed to the Ni(II) ion in an octahedral geometry.
The B values of the prepared octahedral complexes
(Table 4) were found in the range 69.9–72.0% that of the
free ion (B◦ = 1030 cm−1) [25], indicating considerable
overlap with strongly covalent nickel-ligand bond character
[23]. The decrease in B values is most likely associated
with the reduction in the nuclear charge of the cation.
The electronic spectra of these complexes, recorded in
Nujol mull and DMF solutions, have a great similarity and
show two main broad bands centered at 16,665–18,050
=
=
and 23,255–24,510 cm−1 assigning to the A2g
→
3T1g
3
3
(F) and A2g
→
3T1g (P) transitions, respectively, in
an octahedral geometry [24]. The proposed structures
for [Ni(HSPT)(OAc)(H2O)2], [Ni(BT)(OAc)(H2O)2]H2O,
and [Ni2(H2HyMBpClPT)(OAc)4(H2O)3] are shown in
Scheme 2 (a, b, and c, respectively). The spectrochemical
Table 4
Magnetic moment, electronic spectral data in DMF and nujol (in parentheses) of the nickel(II) complexes with some ligand field parameters
Complex
µeff
(B.M.)
υmax (cm−1
)
Ligand field parameters
Supposed structure
B (cm−1
)
β
10Dq (cm−1
–
)
1
0.90
22575 (20875), 18380 (17575)
–
–
Tetrahedral + square
planar (nujol)
Tetrahedral
2
3
4
3.51
3.21
2.16
16865 (17300)
24690, 17950 (17390)
24570 (20705), 16665 (17855)
–
–
–
–
–
–
–
–
–
Tetrahedral
Tetrahedral + square
planar (nujol)
Tetrahedral + square
planar (nujol)
Tetrahedral + square
planar
5
6
0.95
1.26
24440 (20240), 17390 (17665)
20245 (20450), 16475 (17210)
–
–
–
–
–
–
7
8
9
10
11
3.05
2.80
3.80
1.80
2.90
23925 (23925), 17545 (18050)
23585 (23585), 16950 (17730)
17450 (17270)
23925 (23255), 17240 (17220)
23420 (24510), 17360 (16665)
750 (7640)
720 (750)
–
700 (730)
740 (710)
0.72 (0.74)
0.66 (0.72)
–
0.68 (0.71)
0.71(0.68)
100060 (10170)
9900 (10000)
–
10395 (9830)
9905 (10180)
Octahedral
Octahedral
Tetrahedral
Octahedral
Octahedral

248
R.M. El-Shazly et al. / Spectrochimica Acta Part A 61 (2005) 243–252
The nephelauxetic parameter, β is in the range 0.66–0.74,
91
indicating that these ligands are in the middle of the
nephelauxetic of other nitrogen, sulphur, and oxygen donor
series. The values are higher than that observed for NiN6
or NiO6, confirming the coordination via N, O, and/or
S. Thus, it seems reasonable to presume that most of the
chelates formed in this series involve NiO4NS or NiO4N2
chromophores.
52
The magnetic moment values (3.51, 3.21, and 3.80 B.M.)
measured for the complexes [Ni(AET)2], [Ni2(APT)3(OH)-
(H2O)]H2O, and [Ni(HHyMBPT)(OH)(H2O)] lie in the
range reported for a tetrahedral structure [26]. The lower
value measured per one nickel atom for the binuclear com-
plex may be due to nickel–nickel interaction [23]. This ge-
ometry is further evidenced by the electronic spectral data,
which show one d–d transition band at 16,865–17,950 cm−1
which is assigned to the T1 → T1 (P) transition.
,
3
3
The complexes [Ni(AT)2]H2O, [Ni(ApClPT)2], [Ni(HST)
(OAc)], and [Ni(SET)(H2O)]1.5H2O · C2H5OH have 0.90,
2.16, 0.95, and 1.26 B.M. magnetic moments, respectively,
which are less than that reported for the d8–octahedral
and/or tetrahedral complexes and higher than diamagnetic
square-planar complexes. The values may suggest the ex-
istence of the complexes in a mixed stereochemistry [27].
Such supposition is also confirmed from the analysis of
their electronic spectra, which show two bands. The band
observed at 16,475–18,380 cm−1 is in accordance with a
Fig. 3. Mass spectrum of the complex [Ni(HST)(OAc)].
tetrahedral configuration and assigned to the 3T1 → T1 (P)
3
3.3. Mass spectra
d–d transition. The other band at 20,240–22,575 cm−1 is
referring to a square-planar geometry [11]. The DMF has a
large effect in the spectra of [Ni(ApClPT)2], [Ni(AT)2]H2O,
and [Ni(HST)(OAc)] and no effect in the spectrum of
[Ni(SET)(H2O)]1.5H2O · C2H5OH, indicating that the
DMF acts as a ligand in such complexes. Scheme 3 (a–c)
represents the structure of [Ni(AT)2]H2O, [Ni(AET)2], and
[Ni(ApClPT)2], respectively.
The spectra and the position of the bands of some com-
plexes in DMF are found to be different from the correspond-
ing ones recorded in nujol (Table 4), showing that these
complexes are significantly unstable, commencement of
solvolysis or presence of low symmetry components of crys-
tal field [23]. These complexes could also undergo chemical
dissolution in DMF and hence the composition of the chro-
mophores may become different in solution than in solid.
The mass spectra of most complexes were recorded and
their molecular ion peaks confirm the suggested formula
of these complexes. The calculated and found values of
the molecular weights of some of the complexes are given
in Table 2. Representative mass spectrum of the complex
[Ni(HST)(OAc)] is shown in Fig. 3. The spectrum shows
numerous peaks representing successive degradation of the
molecule. The observed peak at m/e 312.0 (Calcd. 311.7)
represents the molecular ion peak of the complex with
30.19% abundance. Scheme 4 demonstrates the proposed
paths of the decomposition steps for the investigated com-
plex. One of the strongest peaks (base peak) at m/e 91.0
represents the stable species C2H5NOS.
3.4. Thermal studies
3.4.1. Kinetic analysis
Non-isothermal kinetic analyses for the decomposition of
HAET, HAPT, and H2HyMBPT and some Ni(II) complexes
were carried out by the application of two different proce-
dures: the Coats-Redfern [28] and the Horowitz-Metzger
[29] methods. The kinetic parameters (E and n) were calcu-
lated according to the above two methods, where the thermo-
dynamic parameters (ꢀH∗, ꢀS∗ and ꢀG∗) were calculated
according to the Coats-Redfern equation and their values
are tabulated in Table 5. The activation enthalpy (ꢀH∗), the
activation entropy (ꢀS∗), and the free energy of activation
NHR
C
N
H3C
S
C
N
S
Ni
C
N
CH3
N
C
RHN
R = H (a), C2H5 (b) or p-ClC6H4 (c)
Scheme 3.

R.M. El-Shazly et al. / Spectrochimica Acta Part A 61 (2005) 243–252
249
C10H11NiN3O3S
M+311.7 (312.0)(30.19%)
C22H28NiN6S2
-2(C10H13N)
o
220 - 312 C
58.9 (58.9%)
C2H2NiN4S2
-NH
7.0 (6.0%)
o
459 - 551 C
C3H5NO2S
m/e 119.0 (119.0)(58.48%) m/e 225.0 (225.0)(24.53%)
C9H11N3O2S
C2HNiN3S2
-CO
-C2H5N2OS
-105.0
-C2N2
o
553 - 660 C
-28.0
10.3 (10.4%)
C2H5NOS
m/e 91.0 (91.0)
base peak
C7H6NO
m/e 120.0(121.0)(47.17%)
Decomposition products
+
-CHN
-27.0
NiS
17.7 (18.1%)
-NH2
-16.0
C6H5O
Scheme 5. Proposed thermal decomposition pattern of [Ni(AET)2].
C2H3OS
m/e 75.0(75.0)(60.90%)
m/e 93.0(92.90)(37.74%)
-O
involved in the Horowitz-Metzger method. The activation
energies could not be calculated for the overlapping or
unsuitable steps. The relatively high E values indicate that
the ligand is strongly bonded to the Ni(II) ions. The nega-
tive ꢀS∗ values in [Ni2(APT)3(OH)(H2O)]H2O (third step)
and [Ni2(H2HyMBpClPT)–(OAc)4(H2O)3] (first and sec-
ond steps) indicate that the activated complexes have more
ordered structure than the reactants and the reactants are
slower than the normal [30,31].
-16.0
C6H5
m/e 77.0(77.0)(54.19%)
-C2H2
-26.0
C4H3
m/e 51.0(51.0)(75.47%)
Scheme 4. Proposed fragmentation pattern of [Ni(HST)(OAc)].
The thermal decomposition of some ligands and com-
plexes was recorded at temperature 30–1000 ◦C. The ther-
mograms exhibit several thermal events. The first step in
the TG thermogram of some complexes corresponds to the
expulsion of water of crystallization and/or coordination.
The end products for most complexes were NiS or NiO.
The activation energies calculated for the first step in the
TG thermograms of the ligands and complexes lie in the
ranges 83.9–127.7 and 164.0–304.0 kJ mol−1, respectively
(Coats-Redfern equation).
(ꢀG∗) were calculated using the following equations:
ꢀ
ꢁ
ꢂꢃ
Zh
ꢀS∗ = 2.303 log
R
KT
ꢀH∗ = E − RT
ꢀG∗ = ꢀH∗ − Ts ꢀS∗
The thermal decomposition of [Ni(AET)2] (Fig. 4) as
an example for the decomposition of these compounds
shows three steps at 220–312, 459–551, and 553–660 ◦C
(Scheme 5). The first step due to elimination of 2(C10H13N)
where Z, K, and h are the pre-exponential factor, Boltz-
man, and Plank constants, respectively [30]. Comparison
of the two sets of kinetic parameters shows no significant
difference between them considering the approximations
Table 5
Kinetic parameters of the thermal decomposition of some of ligands and their complexesa
Compound
Step
Coats-Redfern equation
Horowitz-Metzger equation
ꢀS∗
ꢀH∗
ꢀG∗
r
n
E
r
n
E
HAET
HAPT
H2HyMBPT
1st
1st
1st
2nd
1st
3rd
6th
1st
2nd
1st
2nd
0.9989
0.9999
0.9982
0.9987
1.0000
0.9922
0.9995
0.9707
0.9962
0.9993
0.9999
1.00
0.66
2.00
2.00
2.00
0.33
1.00
1.00
1.00
1.00
1.00
100.9
83.9
0.9980
0.9998
0.9973
0.9977
1.0000
0.9940
0.9995
0.9707
0.9958
0.9992
0.9985
1.00
0.66
2.00
2.00
2.00
0.33
1.00
1.00
1.00
1.00
1.00
107.1
89.6
−141.8
−164.1
−58.8
−88.4
119.6
−25.2
2.4
255.7
178.2
−25.1
−299.1
96.7
79.9
167.4
158.9
151.1
185.6
170.3
193.8
276.0
166.9
196.1
146.6
252.5
127.7
140.1
296.2
183.6
284.5
304.2
304.7
164.0
46.5
138.3
145.7
309.5
191.3
295.3
311.2
315.1
173.4
60.5
123.8
135.4
232.4
179.1
253.0
299.7
299.8
159.7
70.1
[Ni(AET)2]
[Ni2(APT)3(OH)(H2O)]H2O
[Ni(ApClPT)2]
[Ni(HhyMBPT)(OH)(H2O)]
[Ni2(H2HyMBpClPT)(Oac)4(H2O)3]
a
r = correlation coefficient, n = order of the decomposition reaction; E, ꢀH∗, and ꢀG∗ are in kJ mol−1, ꢀS∗ in J K mol−1
.

250
R.M. El-Shazly et al. / Spectrochimica Acta Part A 61 (2005) 243–252
(A)
(B)
Fig. 4. TG (A) and DTG (B) thermograms of the complex [Ni(AET)2].
Table 6
a
Electrochemical data of some of the prepared nickel(II) complexes in DMF–TBA+ BF−
4
Complex
First electrode couple
Second electrode couple
Ep,a
Ep,c
ꢀEp
E1/2
Ep,a
Ep,c
ꢀEp
E1/2
[Ni(AT)2]H2O
[Ni(AET)2]
[Ni2(APT)3(OH)(H2O)]H2O
[Ni(ApClPT)2]
−1.12
−0.80
−0.20
−0.72
−1.39
−1.20
−0.78
−1.08
0.27
0.40
0.58
0.36
−1.25
−1.00
−0.49
−0.90
1.28
1.19
0.86
1.20
0.94
1.14
0.78
0.98
0.34
0.05
0.08
0.22
1.11
1.16
0.82
1.09
a
Scan rate = 100 mV sec−1; E1/2 = (Ep,c + Ep,a)/2.
(Calcd. 58.9%, found 58.9%) has activation energy of
296.2 kJ mol−1 and second order reaction. Elimination of
2NH (Calcd. 6.0%, found 7.0%) takes place in the second
step. The second and third steps are not suitable for kinetic
analysis. The final stable residue as identified from the mass
loss consideration is NiS (Calcd. 18.1%, found 17.7%).
+1.5 V
1µA
3.5. Cyclic voltammetry
The cyclic voltammetric behavior of the complexes
[Ni(AT)2]H2O, [Ni(AET)2], [Ni2(APT)3(OH)(H2O)]H2O,
−
and [Ni(ApClPT)2] in DMF–TBA+BF4 are found similar
and displayed two well-defined electrode couples. The re-
sults are summarized in Table 6. Representative data are also
shown in Fig. 5. The complexes showed two successive one
electron processes. The first electrode couple of these com-
plexes is safely assigned to the irreversible couple NiII/NiI
with E1/2 of −0.49 to −1.25 V (∆Ep = 0.27–0.58 V) and
represented as follows:
-1.5 V
Fig. 5. Cyclic voltammogram of the complex [Ni(AT)2]H2O in
DMF–TBA+BF− vs. Ag/AgCl electrode.
4

R.M. El-Shazly et al. / Spectrochimica Acta Part A 61 (2005) 243–252
251
The dependence of the voltammetric responses of the
NiII/NiIII couple on the scan rate and on the depolarizer
concentration is that typical of an ECE (chemical reaction
coupled between two charge transfer processes) mechanism
in which an irreversible first order chemical reaction is
interposed between two successive one-electron transfers
[34]. For an ECE process with an irreversible chemical
reaction, ip,c/υ1/2 showed decrease with increasing scan
rate. The ratio ip,c/υ1/2 slowly decreases with scan rate
(20–200 mV/sec) for all complexes, confirming that the
observed behavior favors the ECE mechanism. The depen-
dence of the cathodic peak current ip.c of the electrode couple
NiII/NiIII on the square rate of the sweep rate (υ1/2) suggests
diffusion-controlled electrochemical process (Fig. 6B).
As may be observed in Table 6, substitution on thiosemi-
carbazone moiety has a significant effect on E1/2 for
the complexes; electron-withdrawing groups stabilize the
Ni(II) in the complexes [Ni2(APT)3(OH)(H2O)]H2O and
[Ni(ApClPT)2] while the electron-donating group fa-
vor oxidation to Ni(III). This is possibly because the
electron-withdrawing chlorine or phenyl ring makes the
complex more positively charged and hence causes it to
be more easily reduced. Similarly the electron-donating
groups make the complexes [Ni(AT)2]H2O and [Ni(AET)2]
less positively charged and hence less easily reduced. The
oxidation potential of this couple does not correlate lin-
early with the Hummett constant (␴), and the E◦ of the
couple is sensitive to the nature of the substituent in the
thiosemicarbazone moiety with NiII/NiIII.
-0.80
-0.85
-0.90
-0.95
-1.00
-1.05
-1.10
-1.15
-1.20
1.0
1.5
2.0
2.5
3.0
logυ
(A)
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
5
10
15
υ1/2
20
25
(B)
Fig. 6. The dependence of the cathodic peak potential Ep,c (A) and the
cathodic peak current ip,c (B) of the electrode couple NiII/NiI of the
complex [Ni(AT)2]H2O.
4. Conclusion
A series of Ni(II) complexes of some thiosemicarbzones
have been prepared and fully characterized. The kinetic and
thermodynamic characteristics of some of the prepared com-
plexes are discussed. Proposed fragmentation and thermal
decomposition patterns for some of the complexes are also
given. The cyclic voltammetric of the complexes showed
that the Ni(II) compounds undergo one-electron reduction
and oxidation to form the corresponding Ni(I) and Ni(III)
compounds. The Ni(I) and Ni(III) compounds may be found
being used as one-electron redox reagents since the former
is a strong reducing agent and the latter is strong oxidizing
agent.
NiIIL + e− ↔ NiIL
The second electrode couple wit E1/2 = 0.82–1.11 V is
assigned to the irreversible electrode couple NiII/NiIII by
comparison with analogous Ni(II) complexes [7]. The irre-
versible nature of the observed electrode couples has been
established by comparing its peak current height (Ip,c/Ip,a
>
1) with other similar complexes [7]. The irreversible nature
of this couple is also confirmed by the linear dependence of
the cathodic peak potential (Ep,c) with logaritm sweep rate
(log υ) as shown in Fig. 6A. From the slope of this line
and assuming the number of electrons (n) involved in the
oxidation step equals one, the value of the electron transfer
coefficient (α ) is 0.59. The peak-to-peak potential separa-
tion (ꢀEp) of the electrode couple NiII/NiIII increased with
increasing the scan rate confirming the occurrence of a slow
chemical reaction and a limited mass transfer following the
electrode process [32]. Thus, the electron transfer process is
irreversible and the species that initially formed in the elec-
trode process may also react further to give products that are
not reoxidezed at the same potintial as in the first formed
species [33].
References
[1] A.A. El-Asmy, T.Y. Al-Ansi, Y.M. Shaibi, Transition Met. Chem.
14 (1989) 446.
[2] P. Bindu, M.R.P. Kurup, T.R. Satyakeerty, Polyhedron 18 (1998) 321.
[3] E. Franco, E.P. Torres, M.A. Mendiola, M.T. Sevilla, Polyhedron 19
(2000) 441.
[4] R.P. John, A. Sreekanth, R. Maliyckal, P. Kurup, Chemica Acta Part
A 59 (2003) 1349.

252
R.M. El-Shazly et al. / Spectrochimica Acta Part A 61 (2005) 243–252
[5] D.X. West, Y-H. Yang, T.L. Klein, K.I. Goldbery, A.E. Liberta,
[19] K. Nakamoto, “Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds”, 3rd Edn., Wiley, New York, 305, 1978.
[20] A.H. Osman, A.A.M. Aly, N.A. El-Maali, G.A.A. Al-Hazmi, Synth.
React. Inorg. Met. Org. Chem. 32 (2002) 1293.
Polyhedron 14 (1995) 3051.
[6] J.A. Streeky, D.G. Pillsburg, D.H. Busch, Inorg. Chem. 19 (1984)
3148.
[7] M.S. El-Shahawi, W.E. Smith, Analyst 119 (1994) 327.
[8] A.A. El-Asmy, Y.M. Shaibi, I.M. Shedaiwa, M.A. Khattab, Synth.
Rect. Inorg. Met. Org. Chem. 20 (1990) 461.
[9] S.I. Mostafa, A.A. El-Asmy, M.S. El-Shahawi, Transition Met. Chem.
25 (2000) 470.
[10] J.P. Jasinski, J.R. Bianchani, J. Cueva, F.A. El-Saied, A.A. El-Asmy,
D.X. West, Z. Anorg. Allg. Chem. 629 (2003) 202.
[11] F.A. El-Saied, A.A. El-Asmy, W. Kaminstry, D.X. West, Transition
Met. Chem. 28 (2003) 954.
[12] D.X. West, Y-H. Yang, T.L. Klein, K.I. Goldberg, A.E. Liberta, J.
Valdes-Matinez, S. Hernandez-Ortega, Polyhedron 14 (1995) 1681.
[13] A.I. Vogel, “A Text Book of Quantitative Inorganic Analysis”, Long-
mans, London, 1961.
[21] A. El-Shekeil, A.Z. El-Sonbati, Transition Met. Chem. 17 (1992)
420.
[22] A.A. El-Asmy, Y.M. Shaibi, I.M. Shedaiwa, M.A. Khattab, Synth.
Rect, Inorg. Met. Org. Chem. 18 (1988) 331.
[23] A.B.P. Lever, “Inorganic Electronic Spectroscopy”, Elsevier, Ams-
terdam, 1986.
[24] A.A. El-Asmy, M. Mounir, Transition Met. Chem. 13 (1988) 143.
[25] J.E. Huhely “Inorganic Chemistry, Principles of Structure and
Reactivity” 3rd Edn., Haper Collins publishers, 1983.
[26] A.A. El-Asmy, K.M. Ibrahim, M.M. Bekheit, M.M. Mostafa, Synth.
React. Inorg. Met. Org. Chem. 15 (1985) 287.
[27] A.A. El-Asmy, T.Y. Al-Ansi, R.R. Amin, M. Mounir, Polyhedron 9
(1990) 2029.
[14] D.X. West, M.M. Salberg, G.A. Bain, A.E. Liberta, Transition Met.
Chem. 22 (1997) 180.
[15] D.X. West, A.K. El-Sawaf, G.A. Bain, Transition Met. Chem. 23
(1998) 1.
[16] A.A. El-Asmy, M.A. Morsi, A.A. El-Shafei, Transition Met. Chem.
11 (1986) 494.
[28] A.W. Coats, J.P. Redfern, Nature 20 (1964) 68.
[29] H.H. Horowitz, G. Metzger, Anal. Chem. 25 (1963) 1464.
[30] R.M. Mahfouz, M.A. Monshi, S.M. Alshehri, N.A. El-Salam, A.M.A.
Zaid, Synth. React. Inorg. Met. Org. Chem. 31 (2001) 1873.
[31] A.A. Aly, A.S.A. Zidan, A.I. El-Said, J. Thermal Anal. 37 (1991)
627.
[17] D.X. West, M.A. Lockwood, A.E. Liberta, X. Chen, R.D. Willett,
Transition Met. Chem. 18 (1993) 221.
[18] N.C. Saha, R.J. Butcer, S. Chaudhuri, N. Saha, Polyhedron 22 (2003)
383.
[32] N.C. Paramanik, S. Bhatacharya, Polyhedron 16 (1997) 1761.
[33] M.C. Huges, D.J. Macero, Inorg. Chem. 3 (1974) 2739.
[34] A.J. Bard, L.R. Faulkner, “Electrochemical Methods Fundamental
and Applications”, John Wiley, New York, 1980, p. 218.