The first example of calix[4]pyrrole functionalized vic-dioxime ligand: Synthesis, characterization, spectroscopic studies and redox properties of the mononuclear transition metal complexes

Article abstract of DOI:10.1016/j.ica.2010.08.003

Novel calix[4]pyrrole bearing vic-dioxime ligand (LH₂) of the general formula, R₁R₂C₂N₂O ₂H₂ (where, R₁ = C₆H₅- and R₂ = C₃₉H₅₀N₅-) has been synthesized by the reaction of anti-chlorophenylglyoxime with 3-aminophenylcalix[4]pyrrole at room temperature. The mononuclear Cu(II), Ni(II) and Co(II)complexes of this vic-dioxime ligand were prepared and their structures were confirmed by elemental analysis, FT-IR, TGA and magnetic susceptibility measurements; the HMBC, DEPT, ¹H and ¹³C NMR spectra of the LH₂ ligand were also reported. The electrochemical property of the complexes was investigated in DMSO by cyclic voltammetry at 200 mV s^-1 scan rate. The cyclic voltammetric measurements clearly indicated that Co(LH)₂·2H₂O complex differs from the Ni(LH)₂ and Cu(LH)₂ complexes upon the exhibition of quasi-reversible one-electron transfer reduction process in the negative region instead of an irreversible process.

Full text of DOI:10.1016/j.ica.2010.08.003

Inorganica Chimica Acta 363 (2010) 4017–4023
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Inorganica Chimica Acta
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The first example of calix[4]pyrrole functionalized vic-dioxime ligand:
Synthesis, characterization, spectroscopic studies and redox properties
of the mononuclear transition metal complexes
Bilge Taner a, Pervin Deveci a, Soner Bereket a, Ali Osman Solak b, Emine Özcan a,
⇑
a Selçuk University, Faculty of Science, Department of Chemistry, Konya, Turkey
b Ankara University, Faculty of Science, Department of Chemistry, Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel calix[4]pyrrole bearing vic-dioxime ligand (LH2) of the general formula, R1R2C2N2O2H2 (where,
R1 = C6H5- and R2 = C39H50N5-) has been synthesized by the reaction of anti-chlorophenylglyoxime with
3-aminophenylcalix[4]pyrrole at room temperature. The mononuclear Cu(II), Ni(II) and Co(II)complexes
of this vic-dioxime ligand were prepared and their structures were confirmed by elemental analysis, FT-
IR, TGA and magnetic susceptibility measurements; the HMBC, DEPT, 1H and 13C NMR spectra of the LH2
ligand were also reported. The electrochemical property of the complexes was investigated in DMSO by
cyclic voltammetry at 200 mV sÀ1 scan rate. The cyclic voltammetric measurements clearly indicated that
Co(LH)2Á2H2O complex differs from the Ni(LH)2 and Cu(LH)2 complexes upon the exhibition of quasi-
reversible one-electron transfer reduction process in the negative region instead of an irreversible
process.
Received 9 February 2010
Received in revised form 20 July 2010
Accepted 2 August 2010
Available online 6 August 2010
Keywords:
vic-Dioximes
Transition metal complexes
Calix[4]pyrrole
3-Aminophenylcalix[4]pyrrole
Cyclic voltammetry
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
erties of calix[4]pyrrole derivatives, there are no reports cited in
the chemical literature including structural analyses of calix[4]pyr-
The coordination chemistry of vic-dioxime compounds has been
becoming increasingly interesting and has been studied from a
variety of perspectives by many different research groups [1–7].
Because of the potential applications of metal complexes of these
compounds, they have been shown to be useful in many research
areas such as medicine [8], catalysis [9], electrooptical sensors
[10] and trace metal analysis [11]. Calix[4]pyrroles and their deriv-
atives have recently become the subject of intensive research
aimed at the development of novel ligands [12], because, the com-
pounds are capable of selective binding of anionic [13], cationic
[14] and neutral moeities [15] both in the solution and the solid
states. In the research of second generation calixpyrrole [16], Sess-
ler and co-workers employed three fluorescent calix[4]pyrroles
prepared by attaching commercial dyes to 3-aminophenylca-
lix[4]pyrrole. The unique character of these compounds is that they
support additional binding sites that can dramatically increase the
binding capability to anions. Anion binding is a key process in
many chemical and biochemical phenomena, as evidenced by the
fact that many substrates of structurally characterized enzymes
are anionic in nature [17]. Even though a great number of
calix[4]pyrrole derivatives have been synthesized and reviews
have been published giving an overview of the synthesis and prop-
role functionalized vic-dioxime ligands and their transition metal
complexes. For that reason, we think that synthesis of vic-dioxime
compounds that functionalized with calix[4]pyrrole derivative can
generate new materials with interesting properties due to their
above mentioned specific complexation abilities with different an-
ions, metal cations, and neutral compounds.
The aim of the present study is to obtain and characterize
calix[4]pyrrole bearing vic-dioxime ligand and to prepare its nick-
el(II), cobalt(II) and copper(II) complexes. The newly prepared li-
gand was characterized fully in order to confirm the proposed
structure using NMR (1H, 13C, HMBC, DEPT), IR and elemental anal-
ysis. The composition of Co(II), Ni(II) and Cu(II) complexes have
been identified by elemental analysis, FT-IR and magnetic suscep-
tibility measurements. Thermal decomposition of related com-
plexes was investigated by thermogravimetric analysis (TGA) and
the cyclic voltammetric measurements of the complexes have also
been conducted to investigate electrochemical behavior of their re-
duced or oxidized species in nonaqueous solution.
2. Experimental
2.1. Materials and measurements
⇑
All chemicals were of reagent grade quality and were used
without purification; anti-chlorophenylglyoxime (1) [18] and
Corresponding author. Tel.: +90 332 2233859.
E-mail address: emineozcann@gmail.com (E. Özcan).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.08.003

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Scheme 1. Synthesis of 3 and its complexes (4–6); (i) Et2O, Et3N, RT, 3 h; (ii) NiCl2Á6H2O or CuCl2Á2H2O; (iii) CoCl2Á6H2O.

B. Taner et al. / Inorganica Chimica Acta 363 (2010) 4017–4023
4019
3-aminophenylcalix[4]pyrrole (2) [16] were prepared according to
a described procedures. All solvents were of reagent grade and
were purified according to standard procedures. Elemental analy-
ses (C, H, N) were determined using a LECO-932 CHNSO model ana-
lyzer. 1H NMR and 13C NMR spectra were recorded on a Bruker
GmbH Dpx-400 MHz High Performance Digital FT-NMR spectrom-
eter with DMSO-d6 as the solvent with Me4Si as internal reference.
The IR spectra of solid samples (KBr tablets) were recorded in the
range from 200 cmÀ1 to 4000 cmÀ1 on a Perkin–Elmer Model
1605 FT-IR spectrophotometer. Magnetic moments of the com-
plexes were measured using a Sherwood Scientific Model MX1
Gouy magnetic susceptibility balance at room temperature using
Hg[Co(SCN)4] as calibrant; diamagnetic corrections were calcu-
lated 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
Instruments thermal analysis system in dinitrogen atmospheres,
applying a heating rate of 10 °C minÀ1 in a temperature range of
25–1073 °C All the electrochemical experiments were performed
using a CH Instruments electrochemical analyzer (model 600C ser-
ies) equipped with BAS C3 cell stand. Working electrode was a bare
or modified glassy carbon disk (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.
2.2. Synthesis of the ligand [LH2] (3)
A mixture of amino-modified calixpyrrole (2) (0.1 mmol, 59
mg), anti-chlorophenylglyoxime (0.1 mmol, 19 mg), Et2O (15 mL)
and Et3N (0.1 mL) was stirred overnight at room temperature. Then
the solution was washed three times with saturated NaHCO3
(3 Â 15 mL). The organic phase was collected, dried with Na2SO4
and the solvent was removed under reduced pressure and recrys-
tallized from warm ethanol, giving bright yellow needles. Yield:
25%; m.p.: 168 °C, Elemental analysis Anal. Calc.: C, 75.10; H,
7.59; N, 13.05. Found: C, 74.95; H, 7.47; N, 12.96%. IR (KBr) mmax
/
cmÀ1: 3415 (N–H), 3368 (O–H), 3022–3059 (C–HAr), 1610 (C@N),
978 (N–O), 1H NMR (400 MHz, DMSO-d6, ppm): 0.45–0.56 (m,
18H, CH3), 1.31–1.69 (m, 15H, CH2), 2.01 (s, 3H, CH3), 5.63–6.09
(br m, 8H, pyr-CH), 6.80–7.80 (br m, 9H, Ar-CH), 8.24 (br s, 2H,
NH), 8.55 (br s, 2H, NH), 10.17 (s, 1H, N–OH), 11.05 (s, 1H, N–
OH), 13C NMR (400 MHz, DMSO-d6, ppm): 7.65, 8.32, 8.74, 8.89,
8.93, 9.35, 9.42, 27.30, 28.90, 29.20, 29.70, 30.66, 31.79, 42.59,
43.31, 43.38, 44.78, 103.11, 104.65, 104.72, 105.18, 112.13,
Fig. 1. (a) 13C NMR and (b) DEPT spectra of ligand.

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113.71, 115.54, 127.92, 128.96, 129.90, 130.42, 135.92, 136.39,
138.56, 147.78, 149.61.
then filtered and washed with water, ethanol and ether and dried
in vacuo.
2.3. Preparation of mononuclear complexes, [Ni(LH)2] (4),
[Cu(LH)2](5), [Co(LH)2Á2H2O](6)
2.3.1. Data for (4)
Yield: 58%, m.p.: >200 °C; Elemental analysis Anal. Calc.: C,
72.37; H, 7.19; N, 12.58. Found: C, 72.25; H, 7.08; N, 12.45%. IR
A solution of 0.05 mmol metal salt [NiCl2Á6H2O (0.0118 g),
CuCl2Á2H2O (0.0084 g) CoCl2Á6H2O (0.0116 g)] in 5 mL of hot etha-
nol, was added dropwise to a stirred solution of 3 (0.1 mmol,
75 mg) in 5 mL of ethanol. The pH of the reaction mixture was
around 3.5–4.0 and was then adjusted to 5.5–6.0 by adding 1%
NaOH solution. The mixture was stirred on a water bath at 60 °C
for 2 h in order to complete the precipitation. The precipitates were
(KBr)
m
max/cmÀ1: 3318 (N–H), 3060–3010 (C–HAr), 1725 (O–
HÁ Á ÁO), 1595 (C@N), 982 (N–O), 1H NMR (400 MHz, DMSO-d6,
ppm): 0.24–0.54 (m, 36H, CH3), 1.05–1.86 (m, 36H, CH2 + CH3),
5.44–5.88 (br m, 16H, pyr-CH), 6.04–7.35 (br m, 18H, Ar-CH),
8.80 (br s, 4 , NH), 9.22 (br s, 4H, NH), 15.93 (s, 2H, O–HÁ Á ÁO),
MS(ES-MS), m/z: 1559 [M+H]+,
leff: diamagnetic.
Fig. 2. HMBC spectrum of the ligand in DMSO.
Fig. 3. The 1H NMR spectrum of the nickel(II) complex (2) in DMSO-d6 at 25 °C (400 MHz).

B. Taner et al. / Inorganica Chimica Acta 363 (2010) 4017–4023
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2.3.2. Data for (5)
in which the ligands chelate via nitrogen and oxygen donor atoms.
In the IR spectrum of the Co(II) complex, coordinated H2O mole-
cules were identified by a strong broad OH absorption around
3435 cmÀ1 [19]. The FT-IR spectra of all of the compounds exhib-
ited two medium intensity absorption signals at between
3000 cmÀ1 and 3100 cmÀ1 result from phenyl group. Additionally,
the strong and very strong CH2 stretching bands were observed at
Yield: (52%); m.p.: >200 °C, Elemental analysis Anal. Calc.: C,
72.15; H, 7.16; N, 12.54. Found: C, 71.95; H, 7.07; N, 12.47%. IR
(KBr)
m
max/cmÀ1: 3373 (N–H), 3060–3010 (C–HAr), 1740 (O–
HÁ Á ÁO), 1580 (C@N), 985 (N–O).
leff: 1.59.
2.3.3. Data for (6)
2944 cmÀ1 and 2824 cmÀ1
.
Yield: (46%); m.p.: >200 °C, Elemental analysis Anal. Calc.: C,
According to magnetic susceptibility measurements, while
complex 5 and 6 were paramagnetic with a magnetic susceptibility
values 1.59 and 2.14 BM, respectively, complex 4 was diamagnetic,
consistent with the formation of a low spin d8 square planar geom-
etry. On the basis of the magnetic and spectral evidence an octahe-
dral geometry for Co(II) complex was proposed and it is consistent
with the formation of octahedral structure with water molecules
occupying axial positions. The suggested structures of the com-
plexes are shown in Scheme 1.
70.73; H, 7.27; N, 12.29. Found: C, 70.67; H, 7.20; N, 12.37%. IR
(KBr)
m
max/cmÀ1: 3435 (H2O), 3370 (N–H), 3067–3017 (C–HAr),
1740 (O–HÁ Á ÁO), 1587 (C@N), 983 (N–O).
leff: 2.14.
3. Results and discussion
3.1. Synthesis and characterization of LH2 ligand and its complexes
3-Aminophenylcalix[4]pyrrole was reacted with anti-chloro-
phenylglyoxime in diethyl ether to yield the desired vic-dioxime li-
gand and which crystallized in warm ethanol for further
purification. Mononuclear Ni(II), Cu(II) and Co(II) complexes (4–
6) were synthesized in ethanol by reacting NiCl2Á6H2O, CuCl2Á2H2O
and CoCl2Á6H2O with new ligand (3) in the presence of NaOH. The
routes employed in the synthesis of the vic-dioxime ligand and its
nickel(II), cobalt(II) and copper(II) complexes are outlined in
Scheme 1.
When the 1H NMR spectra of the ligand in DMSO was examined,
peaks corresponding to N–OH protons (11.46 ppm and 10.59 ppm
(s, 2H)) was observed downfield. This assignment was further sub-
stantiated by disappearance of the corresponding OH peaks when
ligand underwent deuterium exchange. These values are in accord
with the previously reported oxime derivatives [3,5,19,20]. This
compound showed various doublets and quartet (not resolvable)
at 6.80 and 7.80 ppm for aromatic protons. Two broad singlets
were observed one at 8.24 ppm and the other at 8.55 ppm for pyr-
role N–H groups. In addition, the two quaternary hydroxyimino
carbon atoms (C@N–O), appeared at 149.61 and 147.78 ppm,
which was confirmed by their disappearence in DEPT NMR spec-
trum (Fig. 1b). Observation of dioxime carbons in 13C NMR spectra
at two different frequencies indicates that the vic-dioxime ligands
have the anti-structure [19].
The structural formula of 3 was deduced from FT-IR, NMR (1H,
13C, HMBC, DEPT) and elemental analysis data. In the IR spectrum
of 3, the strong
m(NH), m(OH), m(C@N) and m(NO) characteristic
stretching vibrations bands were observed at 3415, 3368, 1610
and 978 cmÀ1, respectively. The IR spectra of complexes showed
a weak deformation band at 1725–1740 cmÀ1, indicative of intra-
molecular hydrogen bonded bending vibrations (O–HÁ Á ÁO) associ-
By HMBC spectrum, specific assignments of protons and car-
bons are made as follows. HMBC of the ligand shows correlations
that support the proposed structure. HMBC spectrum shows the
d 10.59 proton corresponds to d 147.78 carbon, and d 11.46 proton
corresponds to d 149.61 carbons (Fig. 2). Other correlations are also
in accordance with the expected structure.
ated with the square-planar vic-dioxime complexes. As
m(NO)
stretching vibrations of LH2 shift to slightly higher frequencies,
the (C@N) stretching vibrations shift to slightly lower frequencies,
m
and it indicates the coordination of the azomethine nitrogen to the
metal center [19]. Deveci et al. [3] and Yuksel et al. [5] showed that
vic-dioxime ligand form square-planar Ni(II) and Cu(II) complexes
Fig. 4. Mass spectrum of the nickel(II) complex (2).

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Although the solubility of the Ni(II) complex in organic solvents
The mass spectrum of this compound (Fig. 4) was measured
using the ES/MS technique and the Ni(II) complex (2) displayed a
significant peak corresponding to [M]+ at m/z = 1559.74. The ele-
mental analysis data of this compound were also in accordance
with the proposed formulation.
The thermal behaviour of Cu(II), Ni(II) and Co(II) complexes
have been studied by DTA and TG. Thermal curve of the complexes
are seen in Fig. 5. In the TG curve of the Ni(II), Cu(II) and Co(II)
complexes (calc: 95.21%, exp: 94.18% for [Ni(LH)2], calc: 94.91%,
exp: 94.01% for [Cu(LH)2] and (calc: 95.30%, exp: 95.04% for
[Co(LH)2Á2H2O]) weight loss was observed in the range 25–
1100 °C. It was concluded from TG studies that all the Ni(II), Cu(II)
and Co(II) complexes examined were converted to the correspond-
ing oxides [ref verelim]. The final decomposition products were
identified by IR spectroscopy with corresponding spectra obtained
was limited, we was able to obtain 1H NMR spectra for this com-
plex (Fig. 3). The 1H NMR spectra of the Ni(II) complex (2) was
characterized by the existence of intra-molecular D2O-exchange-
able H-bridge (O–HÁ Á ÁO) protons which were observed by a new
signal at low field, d = 15.93 ppm. The other protons observed for
complex are very similar to those which are found for ligand.
Fig. 6. Cyclic voltammograms of 1 mM (a) nickel(II) complex (4) (b) copper(II) (5)
complex (c) cobalt(II) complex (6) of 3 in DMSO containing 0.1 M TBATFB as
supporting electrolyte at the glassy carbon electrode versus Ag/AgCl/KCl(sat.). Scan
rate is 200 mV s.
Fig. 5. Thermal curves of the (a) Ni(LH)2 (b) Cu(LH)2 (c) Co(LH)2Á2H2O.

B. Taner et al. / Inorganica Chimica Acta 363 (2010) 4017–4023
4023
under the same conditions as the pure oxides. Its thermal decom-
4. Conclusions
position reveals that the Cu(II) and Ni(II) complexes do not contain
the adsorbed or coordinated water or solvent molecules, which are
consistent with the analytical and spectroscopic data. [19]. The
presence of coordinated water molecules in Co(II) complex further
corroborates the assumption made on the basis of the infrared
spectral studies [20].
In this work, we have synthesized and characterized a new vic-
dioxime ligand and three new Ni(II), Co(II) and Cu(II) complexes.
Also, we have investigated redox behaviors of Ni(II), Co(II) and
Cu(II) complexes of ligand by cyclic voltammetry at glassy carbon
electrode. Electrochemical data have shown that nickel and copper
complexes exhibit almost similar electrochemical behavior, with
the irreversible reduction processes based on metal cations, while
the Co(II) complex displays quasi-reversible one-electron transfer
reduction process in the cathodic region based on metal.
3.2. Electrochemical behavior of complexes of LH2 ligand
The ability of oxime-aminophenylcalix[4]pyrrole ligands to sta-
bilize reduced and oxidized forms of metal ions has sparked inter-
est in their role in bioinorganic systems [21]. Hence, for a better
understanding of their properties, the investigation of redox
behavior has a vital importance. Although various oximes and their
metal and non-metal compounds have been studied extensively
and practical applications in many important chemical processes
have been found, electrochemistry of vic-dioximes is scarce. There-
fore, the redox properties of the complexes were investigated in a
solution of 1 mM (4–6) in 0.1 M TBATFB in DMSO versus Ag/AgCl/
KCl(sat.) reference electrode using cyclic voltammetry (CV) with a
scan rate of 200 mV sÀ1 between 0 V and À1.6 V at the glassy car-
bon electrode. The cyclic voltammograms for 4 and 5 display al-
most similar redox potentials associated with M(II)/M(I) (M = Ni,
Cu). In both complexes irreversible reduction wave was observed
at Ec = À743 mV for 4 and Ec1 = À638 mV for 5 (Fig. 6). A second
reversible wave at Ec2 = À800 mV (with an anodic counterpart at
Ea2 = À640 mV) was also observed in the voltammogram which
may be ascribed to the Cu(I)/Cu(0) reduction due to the less stable
Cu(I) ions in solution. The cyclic voltammogram of Co(II) complex
is shown in Fig. 6c, the reduction process refers to the metal-based
CoII/CoI couples. The anodic, Epa and cathodic, Epc, potentials appear
at À570 and À750 mV, respectively, at a scan rate of 200 mV s. On
Acknowledgments
This work was supported by TUBITAK (Scientific and Techno-
logical Research Council of Turkey) with project numbers of
108T655.
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