Synthesis, characterization, thermal, and redox properties of a vic-dioxime and its metal complexes

Article abstract of DOI:10.1080/00958972.2010.504259

A new vic-dioxime ligand containing benzophenone hydrazone units, N'-(benzophenone hydrazone)glyoxime [LH₂] has been prepared from benzophenone hydrazone and anti-chloroglyoxime in absolute ethanol. Mononuclear nickel(II), cobalt(II), copper(II), zinc(II), and cadmium(II) complexes were also synthesized. Ligand and complexes were characterized by elemental analyses, FT-IR, ¹H NMR, and ¹³C NMR spectroscopy, magnetic moments, and DTA/TG techniques. On the basis of the magnetic and spectral evidences a square-planar geometry for Ni(II) and Cu(II) complexes, tetrahedral for Cd(II) and Zn(II) complexes, and octahedral for Co(II) complex were proposed. Redox behaviors of ligand and its complexes were also investigated by cyclic voltammetry at the glassy carbon electrode.

Full text of DOI:10.1080/00958972.2010.504259

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Synthesis, characterization, thermal,
and redox properties of a vic-dioxime
and its metal complexes
a
Asuman Uçar a , Pervın Devecı , Bılge Taner a , Mükerrem Findik
a , Soner Bereket a , Emıne Özcan a & Alı Osman Solak b
a Department of Chemistry, Faculty of Science , Selçuk
University , Konya, Turkey
b Department of Chemistry, Faculty of Science , Ankara
University , Ankara, Turkey
Published online: 17 Aug 2010.
To cite this article: Asuman Uçar , Pervın Devecı , Bılge Taner , Mükerrem Findik , Soner Bereket ,
Emıne Özcan & Alı Osman Solak (2010) Synthesis, characterization, thermal, and redox properties
of a vic-dioxime and its metal complexes, Journal of Coordination Chemistry, 63:17, 3083-3092,
DOI: 10.1080/00958972.2010.504259
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Journal of Coordination Chemistry
Vol. 63, No. 17, 10 September 2010, 3083–3092
Synthesis, characterization, thermal, and redox properties
of a vic-dioxime and its metal complexes
_
_
_
ASUMAN UC¸
¨
ARy, PERVIN DEVECI*y, BILGE TANERy,
MUKERREM FINDIKy, SONER BEREKETy,
_
_
¨
EMINE OZCANy and ALI OSMAN SOLAKz
yDepartment of Chemistry, Faculty of Science,
Selc¸ uk University, Konya, Turkey
zDepartment of Chemistry, Faculty of Science,
Ankara University, Ankara, Turkey
(Received 15 September 2009; in final form 5 May 2010)
A new vic-dioxime ligand containing benzophenone hydrazone units, N0-(benzophenone
hydrazone)glyoxime [LH2] has been prepared from benzophenone hydrazone and anti-
chloroglyoxime in absolute ethanol. Mononuclear nickel(II), cobalt(II), copper(II), zinc(II),
and cadmium(II) complexes were also synthesized. Ligand and complexes were characterized
by elemental analyses, FT-IR, 1H NMR, and 13C NMR spectroscopy, magnetic moments, and
DTA/TG techniques. On the basis of the magnetic and spectral evidences a square-planar
geometry for Ni(II) and Cu(II) complexes, tetrahedral for Cd(II) and Zn(II) complexes, and
octahedral for Co(II) complex were proposed. Redox behaviors of ligand and its complexes
were also investigated by cyclic voltammetry at the glassy carbon electrode.
Keywords: vic-Dioxime; Benzophenone hydrazone; Transition metal complexes; DTA/TG
techniques; Cyclic voltammetry
1. Introduction
Effort has been dedicated toward the design and synthesis of supramolecular
architectures of coordination complexes [1]. vic-Dioximes are ligands with excellent
coordination capability to generate mono-, bi- or trinuclear complexes, which are
commonly used as precursors for the formation of supramolecular architectures [2].
Because of the presence of mildly acidic hydroxyl and slightly basic azomethine groups,
vic-dioximes are amphoteric ligands that form corrin-type square planar, square
pyramidal, tetrahedral, and octahedral complexes with transition metal ions, such as
nickel(II), copper(II), palladium(II), cobalt(II), cobalt(III), zinc(II), and cadmium(II).
The primary reason for interest in these ions is their existence in biological systems.
In order to understand the role of these metal ions, it is necessary to study analogous
complexes, such as metal dimethyl–glyoxime chelates [3]. So the synthesis and
characterization of various vic-dioximes and their transition metal complexes [4]
*Corresponding author. Email: pervindeveci@gmail.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ꢀ 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.504259

3084
A. Uc¸ar et al.
induced steadily growing interest in oxime coordination compounds due to applications
in medicine [5], catalysis [6], electrooptical sensors [7], liquid crystals [8], and trace-metal
analysis [9].
Like vic-dioximes, hydrazones are a versatile class of compounds with several
applications. Due to their chelating behavior, hydrazones are used in analytical
chemistry as selective metal-extracting agents as well as in spectroscopic determination
of certain transition metals [10]. Hydrazone derivatives possess anti-microbial [11],
anti-tubercular [12], and anti-convulsant [13] properties. Moreover, the copper(II)
complex of salicylaldehyde benzoylhydrazone was shown to be a potent inhibitor of
DNA synthesis and cell growth [14]. Some hydrazone analogues have been investigated
as potential oral iron-chelating drugs for the treatment of genetic disorders, such as
thalassemia [15], and have also been suggested as possible metal-chelating agents for
treating neurodegenerative disorders, such as Alzheimer’s disease [16]. We assume that
due to fundamental significance of vic-dioximes and hydrazones in biochemistry and
their great potential for important applications, attachment of hydrazone moieties on a
vic-dioxime can lead to new vic-dioxime derivatives with unique properties. The present
study reports synthesis, characterization, and redox behavior of a new vic-dioxime and
its transition metal complexes bearing a hydrazone unit.
The structures of the ligand and its complexes have been identified by elemental
analyses, magnetic susceptibility measurements, 1H NMR, 13C NMR, and FT-IR
spectroscopy. Thermal behavior of Cu(II), Ni(II), Co(II), Zn(II), and Cd(II) complexes
of N0-(benzophenone hydrazone)glyoxime were studied by DTA and TG.
Electrochemical behaviors of the ligand and its complexes were investigated by cyclic
voltammetry (CV).
2. Experimental
2.1. Materials
Hydroxylamine hydrochloride, sodium carbonate, chloral hydrate, sodium hydroxide
(NaOH), sulfuric acid, hydrochloric acid, ethanol (EtOH), diethyl ether, n-hexane,
dimethyl sulfoxide (DMSO), NiCl2 ꢀ 6H2O, CoCl2 ꢀ 6H2O, CuCl2 ꢀ 2H2O, CdCl2 ꢀ H2O,
ZnCl2, tetrabutylamoniumtetrafluoroborate (TBATFB), benzophenone hydrazone,
and ethylacetate were received from Merck and used as supplied. Silica gel (70–230
mesh) was used for chromatographic separations. All organic solvents were dried and
purified by usual methods. anti-Chloroglyoxime was prepared according to the
literature procedure [17].
2.2. Measurements
Elemental analyses (C, H, N) were determined using a LECO-932 CHNSO model
1
analyzer. H NMR and 13C NMR spectra were recorded on a Bruker GmbH Dpx-
400 MHz High Performance Digital FT-NMR spectrometer with DMSO-d6 as the
solvent and Me4Si as internal reference. Infrared (IR) spectra of solid samples were
recorded from 600 to 4000 cmꢁ1 on a Perkin-Elmer Spectrum 100 FT-IR spectrometer
(Universal/ATR Sampling Accessary). Magnetic moments of the complexes were

vic-Dioxime and its metal complexes
3085
Scheme 1. Synthesis of vic-dioxime ligand [LH2] (1).
measured using a Sherwood Scientific Model MX1 Gouy magnetic susceptibility
balance at room temperature using Hg[Co(SCN)4] as calibrant; diamagnetic corrections
were calculated from Pascal’s constants. Melting points were determined using an
electrothermal apparatus and were uncorrected. Thermal measurements were carried
out on a Setaram Labsys TG-DTA Instrꢁu1ments thermal analysis system under
nitrogen, applying a heating rate of 10ꢂC min from 25ꢂC to 1073ꢂC. Electrochemical
experiments were performed using a CH Instruments electrochemical analyzer (model
600C series) equipped with BAS C3 cell stand. Working electrode was a bare glassy
carbon disc (BAS) with a geometric area of 0.027 cm2. The reference electrode was
a Ag/AgCl/KCl(sat.) and the counter electrode was a Pt wire.
2.3. Synthesis of [LH2] (1)
About 0.49 g (2.5 mmol) benzophenone hydrazone was dissolved in 10 mL absolute
EtOH. To the reaction mixture, 0.3 g (2.5 mmol) anti-chloroglyoxime in absolute EtOH
(10 mL) was added dropwise with continuous stirring. Addition was complete in 15 min
and the mixture was stirred at room temperature for 1.5 h. The pH of the solution was
3.5–4.0 and adjusted to 6.5–7.0 by addition of a 1% NaOH solution in EtOH. Then, the
product was precipitated by addition of 20 mL H2O, filtered, washed with H2O several
times, and purified by column chromatography on silica gel using ethyl acetate and
n-hexane (2 : 1) as eluent. A white crystalline solid was obtained (Scheme 1).
Yield: 0.45 g (64%). m.p.: 165ꢂC. Anal. Calcd C15H14N4O2 (282) (%): C, 63.83; H, 4.96;
N, 19.86. Found (%): C, 64.16; H, 5.05; N, 19.26. FT-IR (KBr): 3334 (N–H), 3283
(O–H), 3070–3000 (Ar–H), 1660 (C¼N), 961 (N–O) cmꢁ1
.
1H NMR (DMSO-d6):
ꢀ ¼ 7.70–7.40 (m, 6H, Ar–H), 8.08 (s, 1H, C–H), 8.42 (s, 1H, N–H), 10.51 (s, 1H, OHb),
11.66 (s, 1H, OHa); 13C NMR (DMSO-d6): ꢀ ¼ 127.10, 128.94, 130.66, 132.16 (Ar–C),
141.20 (C5), 145.67 (C6), 147.88 (C7).
2.4. Synthesis of [Ni(LH)2] (2), [Cu(LH)2] (3), and [Co(LH)2 ꢀ 2H2O] (4)
A solution of NiCl2 ꢀ 6H2O (0.29 g, 1.25 mmol), CuCl2 ꢀ 2H2O (0.21 g, 1.25 mmol), or
CoCl2 ꢀ 6H2O (0.29 g, 1.25 mmol) in water (10 mL) was added to a solution of [LH2] (1)
(0.70 g, 2.5 mmol) in 10 mL ethanol at room temperature. A distinct change in color
and decrease in pH (3.5–4.0) was observed. While stirring at the same temperature,
ethanolic NaOH (1%) was added to increase the pH to 5.0–5.5. After heating the

3086
A. Uc¸ar et al.
reaction mixture for 2 h in a water bath at 45–50ꢂC the precipitate was filtered off,
washed several times with water, ethanol, and diethyl ether, and then dried in vacuum.
2.4.1. Compound 2. Yield: 0.56 g (72%). m.p.: 4300ꢂC, Anal. Calcd C30H26N8O4Ni
(621) (%): C, 57.97; H, 4.19; N, 18.04. Found (%): C, 58.17; H, 5.98; N, 18.24. FT-IR
(KBr): 3322 (N–H), 1777 (O–H ꢀ ꢀ ꢀ O), 1588 (C¼N), 980 (N–O), 3060–3010 (Ar–H).
1H NMR (DMSO-d6): ꢀ ¼ 8.12–7.01 (m, 12H, Ar–H), 10.21 (s, 2H, C–H), 11.60 (s, 2H,
N-H), 15.03 (s, 2H, O–H ꢀ ꢀ ꢀ O). 13C NMR (DMSO-d6): ꢀ ¼ 126.50, 127.94, 130.86,
131.20 (Ar–C), 135.90 (C5), 138.20 (C6), 159.85 (C7).
2.4.2. Compound 3. Yield: 0.34 g (44%). m.p.: 4300ꢂC. Anal. Calcd C30H26N8O4Cu
(626) (%): C, 57.51; H, 4.15; N, 17.90. Found (%): C, 58.21; H, 4.76; N, 18.15. FT-IR
(KBr): 3373 (N–H), 1740 (O–H ꢀ ꢀ ꢀ O), 1613 (C¼N), 980 (N–O), 3065–3015 (Ar–H).
2.4.3. Compound 4. Yield: 0.53 g (65%). m.p.: 4300ꢂC. Anal. Calcd C30H30O6N8Co
(657) (%): C, 54.88; H, 4.56; N, 17.05. Found (%): C, 55.18; H, 4.33; N, 17.35. FT IR
(KBr): 3370 (N–H), 3414 (H2O), 1740 (O–H ꢀ ꢀ ꢀ O), 1607 (C¼N), 986 (N–O), 3067–3017
(Ar–H).
2.5. Synthesis of [Zn(LH)Cl] ꢀ H2O (5) and [Cd(LH)Cl] ꢀ H2O (6)
A solution of ZnCl2 (0.34 g, 2.5 mmol) or CdCl2 ꢀ 2H2O (0.54, 2.5 mmol) in water
(10 mL) was added to a solution of [LH2] (1) (0.7 g, 2.5 mmol) in 10 mL ethanol at room
temperature. A distinct change in color and a decrease in the pH of the solution
(3.5–4.0) were observed. While stirring at the same temperature, ethanolic NaOH (1%)
was added to increase the pH to 10.0–11.0 for Cd(II) and 7.0–7.5 for Zn(II).
2.5.1. Compound 5. Yield: 0.65 g (65%). m.p.: 4300ꢂC. Anal. Calcd
C15H15O3N4CIZn (399) (%): C, 45.06; H, 3.75; N, 14.02. Found (%): C, 45.23; H,
3.35; N, 14.32. FT-IR (KBr): 3415 (H2O) 3333 (N–H), 3331 (O–H), 1646 (C¼N),
973(N–O), 3060–3020 (Ar–H).
2.5.2. Compound 6. Yield: 0.59 g (53%). m.p.: 124ꢂC. Anal. Calcd C15H15O3N4CICd
(446) (%): C, 40.31; H, 3.36; N, 12.55%. Found (%): C, 41.13; H, 4.01; N, 11.86.
FT-IR (KBr): 3415 (H2O), 3365 (N–H), 3316 (O–H), 1620 (C¼N), 980 (N–O), 3062–
3020 (Ar–H).
3. Results and discussion
3.1. 1H and 13C NMR results
1
When the H NMR spectrum of the ligand in DMSO was examined (Supplementary
material) peaks corresponding to N–OH were observed at 11.66 (s, 1H) and 10.51 ppm

vic-Dioxime and its metal complexes
3087
(s, 1H). A single chemical shift for each OH (OHa, OHb) suggests that the oxime groups
are in the E,E form [18, 19]. The N–H protons give only one singlet at 8.42 ppm. The
C–H protons adjacent to the oxime groups were observed at 8.08 ppm. The spectrum
is in accord with the previously reported oxime derivatives [19, 20].
A 13C NMR spectrum is convenient to prove the structure of vic-dioximes. In the 13
C
NMR spectrum of 1 (Supplementary material) the carbon resonances of oxime were
observed at 147.88 (C7) and 145.67 (C6) ppm. Observation of dioxime carbons in
13C-NMR spectra at two different frequencies indicates that the vic-dioxime ligands
have the anti-structure [21, 22]. The values for 1 are in good agreement with those
of vic-dioximes [23, 24]. The peaks of (Ar)2C¼Nꢁ (C5) and Ar–C were at 141.20 and
127.10–132.16 ppm, respectively, as expected.
Although the solubility of the Ni(II) complex in organic solvents was limited, we were
able to obtain 1H NMR and 13C NMR spectra for this complex (Supplementary
1
material). H NMR spectra of 2 have intra-molecular D2O-exchangeable H-bridges
(O–H ꢀ ꢀ ꢀ O), which were observed by a new signal at low field, ꢀ ¼ 15.03 ppm. The
chemical shifts of –NH and –CH protons were observed at 11.60 and 10.21 ppm as
singlets for 2, respectively. Ar–H protons were observed at 8.12–7.01 ppm as multiplets.
In the 13C NMR spectrum of the Ni(II) complex, carbon resonances of the dioxime
groups were observed at 159.85 (C7) and 138.20 (C6) ppm. Two different frequencies
of the dioxime group in 13C NMR indicate that the vic-dioxime complex has an
anti-structure [21, 22]. The peaks of (Ar)2C¼N– (C5) and Ar–C were observed at 135.90
and at 126.50–131.20 ppm, respectively, which are in good agreement with those of
vic-dioxime complexes [23, 24].
3.2. IR results
IR data give further useful information on the structure of the [LH2] and its complexes.
Important IR spectral bands are summarized in table 1. For the ligand and some
complexes, bands at 3283–3415 cmꢁ1 may be assigned to ꢁ(O–H) [25] and strong bands
at 1588–1660 cmꢁ1 are assigned to azomethine group vibrations [26]. In IR spectra of
the Co(II), Ni(II), and Cu(II) complexes, the absorption assigned to (C¼N) in the free
ligand is shifted slightly to lower frequencies (1588–1613 cmꢁ1) after complexation,
owing to N,N-metal coordination [19, 27, 28]. The disappearance of absorptions at
3283 cmꢁ1 [ꢁ(O–H)] in the Ni(II), Co(II), and Cu(II) complexes along with the presence
of absorptions at 3322–3373 cmꢁ1 [ꢁ(N–H)], 1588–1613 cmꢁ1 [ꢁ(C¼N)], and 980–
986 cmꢁ1 [ꢁ(N–O)] are in agreement with the proposed structures. In IR spectra of the
cobalt complex a strong broad band at 3414 cmꢁ1 confirms the presence of coordinated
water [27]. As a distinct lowering in the pH of the solution was observed during complex
formation, deprotonation of the ligand with subsequent N,N-chelation of the vic-
dioximes probably occurs [28]. The usual intramolecular hydrogen-bonded bending
vibrations (O–H ꢀ ꢀ ꢀ O) associated with square-planar vic-dioxime complexes were
characterized by weak deformation bands at 1740–1777 cmꢁ1 in these complexes
[21, 29]. The values agree with previously reported diaminoglyoxime derivatives [30].
In the IR spectra of Zn(II) and Cd(II) complexes, the ꢁ(C¼N) around 1620–
1646 cmꢁ1 is shifted to 1660 cmꢁ1 in [LH2]. There is no (O–H ꢀ ꢀ ꢀ O) peak, as expected
for complexes with the formula shown in scheme 2. At the same time, the N–O band
around 961 cmꢁ1 in the free ligand moved to lower frequency by ca 20 cmꢁ1 after Zn(II)

3088
A. Uc¸ar et al.
Table 1. IR spectral data of the free ligand and its complexes.
Compound
N–H
O–H
O–H ꢀ ꢀ ꢀ O
C¼N
N–O
C–H(Ar)
1
2
3
4
5
6
3334
3322
3373
3370
3333
3365
3283
–
1660
1588
1613
1607
1646
1620
961
980
980
986
973
980
3070–3000
3060–3010
3065–3015
3067–3017
3060–3020
3062–3020
–
–
1777
1740
1740
–
3414 (H2O)
3331, 3415 (H2O)
3316, 3415 (H2O)
–
Scheme 2. Synthetic scheme for 2–6.
and Cd(II) complex formation. These results suggest that the ligand is coordinated
to each metal through nitrogen and oxygen donors. A chloride and water are also
coordinated to each metal ion as reported for Zn(II) and Cd(II) complexes of
vic-dioximes [31, 32].
The reaction of [LH2] with nickel(II), cobalt(II), and copper(II) gives products with
1 : 2 metal–ligand ratios (scheme 2). [LH2] reacts with zinc(II) and cadmium(II) in a 1 : 1
metal–ligand ratio to give complexes with two of the four metal coordination sites
occupied by nitrogen of each oxime and oxygen of the other group [33]. The analytical
data and other spectral analyses are in good agreement with the proposed stoichiometry
of the complexes in scheme 2.

vic-Dioxime and its metal complexes
Table 2. TG data for 2–6.
3089
Temperature
range (ꢂC)
Leaving
group
Weight loss
(Calcd/found), %
Residue
(Calcd/found), %
Compound
2
3
4
256–448
448–1083
149–413
413–1073
155–180
180–490
490–1073
140–145
145–480
480–1073
140–145
145–510
510–1073
2C13H11N2
C4H4N4O3
2C13H11N2
C4H4N4O3
2H2O
2C13H11N2
C4H4N4O3
H2O
C13H11N2CI
C2H2N2O
H2O
C13H11N2CI
C2H2N2O
62.81/62.80
25.12/24.85
62.30/63.10
24.92/24.74
5.48/6.02
59.36/60.01
23.74/23.01
4.51/4.33
57.70/58.04
17.52/18.98
4.03/4.36
51.62/52.02
15.68/15.67
NiO
12.03/12.35
CuO
12.71/13.02
CoO
11.40/11.87
5
6
ZnO
20.30/20.43
CdO
28.79/28.80
3.3. Absorption spectra
Absorption spectra of 1 and its mononuclear complexes in DMSO are provided in
Supplementary material. UV-Vis spectra of the Ni(II) complex showed absorption
peaks at 271 and 328 nm, due to ꢂ!ꢂ* and n!ꢂ* transitions of –C¼N and charge-
transfer arising from metal to ligand or ligand to metal [34, 35]. The absorption
spectrum of 4 has a band around 480 nm, possibly due to d–d transition from a
distorted octahedral stereochemistry. The expected weak dꢁd transitions in the visible
region for other complexes cannot be detected.
3.4. Magnetic moments
Magnetic moment measurements of all metal complexes carried out at 25ꢂC show that
Ni(II), Cd(II), and Zn(II) complexes are diamagnetic, whereas magnetic moments of
Cu(II) and Co(II) complexes are 1.52 and 3.90 B.M., respectively. According to the
results, square-planar geometry is expected for the Ni(II) and Cu(II) complexes, while
distorted octahedral high-spin geometry is expected for the Co(II) complex because the
coordinated ligands are different, and also ꢃeff is higher than the expected value for the
Co(II) complex [36].
3.5. TG/DTA results
Thermal properties of the transition metal derivatives with azomethines (oximes, Schiff
bases and hydrazones) have been investigated [37]. Thermal properties of the complexes
were investigated using TG/DTA with decomposition step, product loss, and found and
calculated weight loss percentages are depicted in table 2.
Co(II) complex is stable up to 155ꢂC, where dehydration begins. For Co(LH)2 ꢀ 2H2O,
loss of the axial water is overlapped in the first transition (temperature range: 155–180ꢂC,
weight loss exp.: 6.02%, Calcd: 5.48%). In the thermal decomposition of Co(II) complex,
at first the coordinated water, then the amine group and last the equatorial oxime is
lost [38].

3090
A. Uc¸ar et al.
The Ni(II) complex of vic-dioxime loses 87.65% of its original mass between 25ꢂC
and 1073ꢂC, with 12.35% greenish-black residue. Sample decomposes in two stages, the
first stage was between 256ꢂC and 448ꢂC with 62.80% mass loss, and the second stage
between 448ꢂC and 1083ꢂC with 24.85% mass loss. The theoretical mass of remaining
NiO is 12.03% which corresponds to 12.35% from TG studies.
TG studies on the Cu(II) complex showed initial mass loss at 149ꢂC losing 63.10 and
24.74% in each stage at 149–413 and 413–1073ꢂC, respectively. TG curves of the Zn(II)
and Cd(II) complexes (Calcd: 4.51%, exp: 4.33% for [Zn(LH)Cl] ꢀ H2O and Calcd:
4.03%, exp: 4.36% for [Cd(LH)Cl] ꢀ H2O) show weight loss at 140–145ꢂC, indicating
that Zn(II) and Cd(II) complexes contain one coordinated water [31]. Thermal analysis
curves are provided in Supplementary material.
3.6. Electrochemical measurements
Electrochemistry of 1 and its Ni(II), Cu(II), and Co(II) complexes (2–4) was studied
using CV in DMSO (0.1 mol Lꢁ1 TBATFB) at a glassy carbon electrode. Voltammetric
measurements of free ligand (1) were carried out to compare with its metal complexes
(2–4) (Supplementary material). Comparison of redox data of 1 with previously
reported oxime–metal complexes [39] imply that the first oxidation (Ia) and the first
reduction (Ic) correspond to the oxime moieties, while the second oxidation (IIa) and
reduction (IIc) belong to benzophenone hydrazone moieties.
Ni(II) complex (2) displays three reduction and one oxidation waves. The first
reduction wave at ꢁ1.7 V (IIIc) is a reversible one-electron process assigned to the
Ni(II)/Ni(I) redox couple. The peak separation is 90 mV for this reduction process at a
scan rate of 0.100 V sꢁ1. As the redox chemistry of a Ni(II) complex of a structurally
similar vic-dioxime has been reported in the literature [39], no coulometric experiments
have been performed for the determination of the number of electrons transferred
in 2. In addition, the reversibility of the CV for 2 indicates that the complex is stable
and robust during the redox process.
Cu(II) complex (3) also displays three reduction waves as for 2; the first wave is a
reversible one-electron process with a peak separation of 40 mV. Peak currents for 2
are in the same order as 3 indicating that both processes occur with one electron,
assuming that the diffusion coefficients are equal. Thus, the first reduction corresponds
to Cu(II)/Cu(I) redox couple [40].
Comparison of the voltammetric data of 3, 2, and 1 suggests that the second and the
third reductions (I and II) are oxime- and benzophenone hydrazone-based processes,
respectively, but occur at potentials less negative than those of 1, presumably due to
charge transfer from ligand to metal during the formation of metal complexes, as is
observed by C¸ amur et al. [39]. The wave at ꢁ0.6 V is not understood, but assigned to
reduction oxygen of peroxide [41].
Co(II) complex (4) displays a CV wave for Co(II)/Co(I), but cathodic peaks and
their corresponding anodic peaks which belong to the vic-dioxime groups and
benzophenone hydrazone moieties are not well-defined, probably due to the relative
stability of the Co(II) complex as compared to the Ni(II) and Cu(II) complexes.
Cd(II) and Zn(II) complexes had negligible change on the cyclic voltammogram
of 1.

vic-Dioxime and its metal complexes
3091
4. Conclusion
This work introduces preparation, characterization, thermal properties, and electro-
chemical behavior of a new vic-dioxime ligand and its metal complexes. We have
attempted to prepare single crystals of ligand and metal complexes in different solvents,
but could not prepare single crystals. On the basis of the magnetic and spectral evidence
a square-planar geometry for Ni(II) and Cu(II) complexes, tetrahedral for Cd(II) and
Zn(II) complexes, and octahedral for Co(II) complexes are proposed. Additionally, TG
studies show that all the metal complexes converted by pyrolysis to corresponding
oxides.
Acknowledgments
This work was supported by the Research Fund of Selcuk University Project Number:
09201023 and 08401056.
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