Electrochemical and electrical properties of novel mono and ball-type phthalocyanines

Article abstract of DOI:10.1016/j.poly.2012.09.048

New mononuclear Co(II) phthalocyanine 3 and ball-type homobinuclear Cu(II)-Cu(II) and Zn(II)-Zn(II) phthalocyanines, 4 and 5 respectively, were synthesized using the corresponding metal salts and the 4,4′-(methane-5- methyl-3-(1-methylcyclohexyl)-2,2′-phenoxy)diphthalonitrile ligand 2, which was prepared from the reaction of 4-nitrophthalonitrile with bis[2-hydroxy-5-methyl-3-(1-methylcyclohexyl)phenyl]methane (1). The novel compounds 3-5 have been characterized using their elemental analysis data and UV-Vis, IR, ¹H NMR and MALDI-TOF mass spectra. The redox properties of the complexes were investigated by cyclic voltammetry in a non-aqueous medium. The electrochemical measurements showed that complex 5 forms a mixed-valence reduction species, due to the strong intramolecular interactions between the two phthalocyanine rings. Complex 4 displayed Pc ring-based redox signals with very high peak currents, which were attributed to the adsorption of the complex on the working electrode. Dc and ac electrical properties of films of 3, 4 and 5 were also investigated as a function of temperature (295-523 K) and frequency (40-10⁵ Hz). From the dc conductivity measurements, activation energy values of the films were found, being 0.70, 0.66 and 0.68 eV for films of 3, 4 and 5, respectively. From impedance spectroscopy measurements, it was observed that the bulk resistance decreases with increasing temperature, indicating semiconductor properties.

Full text of DOI:10.1016/j.poly.2012.09.048

Polyhedron 49 (2013) 129–137
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Electrochemical and electrical properties of novel mono and
ball-type phthalocyanines
Emel Ermißs a, Yasemin Çimen a, Fatih Dumludag˘ b, Ali Rıza Özkaya c, Bekir Salih d, Özer Bekarog˘lu e,
⇑
a Department of Chemistry, Anadolu University, 26470 Eskißsehir, Turkey
b Department of Physics, Marmara University, 34722 Göztepe, Istanbul, Turkey
c Department of Chemistry, Marmara University, 34722 Göztepe, Istanbul, Turkey
d Department of Chemistry, Hacettepe University, 06532 Beytepe, Ankara, Turkey
e Department of Chemistry, Technical University of Istanbul, 34469 Maslak, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
New mononuclear Co(II) phthalocyanine 3 and ball-type homobinuclear Cu(II)–Cu(II) and Zn(II)–Zn(II)
phthalocyanines, 4 and 5 respectively, were synthesized using the corresponding metal salts and the
4,40-(methane-5-methyl-3-(1-methylcyclohexyl)-2,20-phenoxy)diphthalonitrile ligand 2, which was
prepared from the reaction of 4-nitrophthalonitrile with bis[2-hydroxy-5-methyl-3-(1-meth-
ylcyclohexyl)phenyl]methane (1). The novel compounds 3–5 have been characterized using their ele-
mental analysis data and UV–Vis, IR, 1H NMR and MALDI-TOF mass spectra. The redox properties of
the complexes were investigated by cyclic voltammetry in a non-aqueous medium. The electrochemical
measurements showed that complex 5 forms a mixed-valence reduction species, due to the strong intra-
molecular interactions between the two phthalocyanine rings. Complex 4 displayed Pc ring-based redox
signals with very high peak currents, which were attributed to the adsorption of the complex on the
working electrode. Dc and ac electrical properties of films of 3, 4 and 5 were also investigated as a func-
tion of temperature (295–523 K) and frequency (40–105 Hz). From the dc conductivity measurements,
activation energy values of the films were found, being 0.70, 0.66 and 0.68 eV for films of 3, 4 and 5,
respectively. From impedance spectroscopy measurements, it was observed that the bulk resistance
decreases with increasing temperature, indicating semiconductor properties.
Received 21 June 2012
Accepted 22 September 2012
Available online 6 October 2012
Keywords:
Phthalocyanines
Ball-type
Conductance
Electrochemistry
Spectroelectrochemistry
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
types of structures. Our group has published a number of papers
on ball-type Pcs with different bridging units in recent years. These
The syntheses and studies of phthalocyanines (Pcs) are among
the priorities of modern Pc chemistry due to their various indus-
trial and technological applications, such as pigments and dyes,
chemical sensors, photodynamic therapy sensitizers, optical
recording and non-linear optical materials, photovoltaics, catalysts,
electrochromic materials and electronic device components [1–6].
Ball-type Pcs are a new class of compound, the first of which
was reported in 2002 [7,8]. These studies primarily focused on
their synthesis and did not make any attempt to investigate their
properties. Ball-type Pcs, metal free or containing two homo or
hetero-metal centers, have attracted much attention because of
their intrinsic properties. These Pcs have four bridged substituents
on the peripheral position of each benzene ring which connect two
face to face Pc molecules. The chemical and physical characteristic
of these compounds vary with the nature of bridging groups, which
also determine the distance between the face to face Pc molecules,
and the central metals. These Pcs can be tailored to form various
compounds showed intrinsic electrochemical, electrical, gas sens-
ing, non-linear optical and catalytic properties [9]. In one of the
previous studies [10], pentaerythritol was employed to obtain a
ball-type Pc, which allowed us to prepare various novel ball-type
Pcs with interesting physical properties [11]. In another study, a
compound with four free hydroxyl groups, 1,1,2,2-tetrakis(p-
hydroxy-phenyl)-ethane, was used to obtain a ball-type Pc, result-
ing in a completely different across adjacent ring formed mono Pc
[12]. Some advance reactions showed that the four hydroxyl
groups are very functional to obtain unprecedented Pcs. Our
continuing effort in the design of novel ball-type Pcs with potential
applicability in various technological uses encouraged us to syn-
thesize iron–iron and iron–cobalt centered ball-type Pcs. These
compounds showed gas sensing properties and a remarkable elec-
trocatalytic performance towards oxygen reduction [13,14].
In this study, the synthesis and characterization of new
mononuclear Co(II) 3 and ball-type homo-dinuclear Cu(II)–Cu(II)
4 and Zn(II)–Zn(II) 5 Pcs linked with four [2,20-methylenebis-[6-
(1-methylcyclohexy)-p-methyl-phenoxyphthalonitrile]
2
units
⇑
Corresponding author. Tel.: +90 216 359 01 30; fax: +90 216 386 08 24.
E-mail address: obek@itu.edu.tr (Ö. Bekarog˘lu).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.09.048

130
E. Ermißs et al. / Polyhedron 49 (2013) 129–137
have been achieved. Their electrochemical and electrical properties
were also examined.
0.155 mmol) was powdered in a quartz crucible, and then transferred
to a reaction tube. The mixture was heated for 10 min at 300 °C. After
cooling the tube contents to room temperature, the dark-green residue
was ground and washed with distilled water to remove excess of cobalt
chloride. Finally, the residue was washed repeatedly with hot water,
ethanol and acetone. This compound is soluble in DCM, THF, DMF,
DMSO and pyridine. Mp >300 °C. Yield: 28 mg (55%). UV–Vis (DCM)
2. Experimental
2.1. Synthesis and characterization
kmax (nm) (log
(4.153). IR (KBr pellet)
e
): 323 (4.503), 426.5 (4.373), 455.5 (4.464), 681.5
2.1.1. Materials and methods
m
/cmꢀ1: 3072 (aromatic CH), 2954, 2925 and
All reagents and solvents were used as received and were of re-
search grade. The starting material 2 was synthesized by the meth-
od described previously in the literature [9]. Melting points were
determined with a Sanyo Gallenkamp melting point apparatus
using a capillary tube. IR spectra were recorded on a Perkin-Elmer
Spectrum 100 spectrometer as KBr pellets. Electronic spectra were
recorded on a Shimadzu 2450 UV–Vis spectrophotometer. Elemen-
tal analyses were performed by the Elementar Vario EL III instru-
ment. 1H NMR and 13C NMR spectra were recorded on a Bruker
500 MHz Ultrashield spectrometer equipped with a 5 mm PABBO
BB-inverse gradient probe. The 1H and 13C chemical shifts are re-
ported in ppm relative to tetramethylsilane or the deuterated sol-
vent as an internal reference. Spectral splitting patterns are
designated as: s, singlet; d, doublet; t, triplet; q, quartet; m, multi-
plet; br, broad.
Mass spectra were acquired with the Voyager-DE™ PRO MALDI
matrix cyano-4-hydroxycinnamic acid (ACCA), prepared in an eth-
anol:water mixture, 1:1 v/v ratio at a concentration of 10 mg/mL.
MALDI samples were prepared by mixing sample solutions
(2 mg/mL in a tetrahydrofuran (THF):water mixture, 1:1 v/v ratio,
and in some cases, acetic acid was added to increase the solubility)
with the matrix solution (1:10 v/v) in a 0.5 mL EppendorfÒ micro
2862 (aliphatic CH), 2230 (C„N), 1719, 1615, 1606 (aromatic C@C),
1437, 1363, 1311, 1227 (Ar–O–Ar), 1201, 1161, 1120, 1055, 930, 883,
859, 768, 750. Anal. Calc. for C180H176CoN16O8: C, 78.61; H, 6.45; N,
8.15; O, 4.65. Found: C, 78.55; H, 6.50; N, 8.19; O, 4.60%. MALDI-TOF-
MS m/z: 2748 (M+H).
2.1.2.3. 20,100,160,240-Tetrakis[2,20-methylenebis-(6-(1-methylcyclohexyl-
p-cresoyl]phthalo-cyaninato Cu(II) (4). The synthesis of 4 was carried
out using the same procedure as in the synthesis of 3. CuCl2ꢁ2H2O
(0.027 g, 0.158 mmol) was used as the copper source. It is soluble
in DCM, THF, DMF, DMSO and pyridine. Mp >300 °C. Yield: 13 mg
(24%). UV–Vis (DCM) kmax (nm) (log
455.5 (4.826), 690.5 (3.877). IR (KBr pellet)
e
): 324 (4.336), 428 (4.693),
m
/cmꢀ1: 3073 (aromatic
CH), 2954, 2928 and 2864 (aliphatic CH), 1719, 1606 (aromatic
C@C), 1454, 1438, 1363, 1227 (Ar–O–Ar), 1200, 1120, 883. Anal. Calc.
for C180H176Cu2N16O8: C, 76.70; H, 6.29; N, 7.95; O, 4.54. Found: C,
76.66; H, 6.31; N, 7.98; O, 4.51%. MALDI-TOF-MS m/z: 2815 (M+H).
2.1.2.4. 20,100,160240-Tetrakis[2,20-methylenebis-(6-(1-methylcyclohexyl-
p-cresoyl ]phthalo-cyaninato Zn(II)] (5). The synthesis of 5 was carried
out using the same procedure as followed for 3. Zn(OAc)2ꢁ2H2O
(0.040 g, 0.182 mmol) was used as the zinc source. It is soluble in
DCM, THF, DMF, DMSO and pyridine. Mp >300 °C. Yield: 15 mg
tube. Finally 0.5 lL of this mixture was deposited on the sample
plate, dried at room temperature and then analyzed with the MAL-
DI-TOF mass spectrometer equipped with a nitrogen UV-laser
operating at 337 nm. Spectra were recorded in the reflectron mode
with an average of 100 shots.
(29%). UV–Vis (DCM) kmax (nm) (loge): 335 (4.418), 623.5 (3.872),
689.5 (4.239). 1H NMR (500 MHz, CDCl3) d (ppm): 7.28–6.60 (m br,
40H, aromatic), 3.90–0.90 (m br, 136H, aliphatic). IR (KBr pellet)
m
/cmꢀ1: 3070 (aromatic CH), 2924 and 2855 (aliphatic CH), 1771,
1718, 1614, 1445, 1362, 1311, 1274 (Ar–O–Ar), 1222, 1041, 926,
858, 747. Anal. Calc. for C180H176N16O8Zn2: C, 76.60; H, 6.29; N,
7.94; O, 4.54. Found: C, 76.57; H, 6.27; N, 7.91; O, 4.57%. MALDI-
TOF-MS m/z: 2817 (M+H).
2.1.2. Synthesis
2.1.2.1. 2,20-Methylenebis-[6-(1-methylcyclohexyl)-p-cresoylphthalo-
nitrile] (2). A mixture of bis[2-hydroxy-5-methyl-3-(1-methylcy
clohexyl)phenyl]methane (1) (1.80 g, 4.00 mmol), 4-nitrophthalo-
nitrile (1.40 g, 8.10 mmol) and anhydrous K2CO3 (3.50 g) in
25 mL dry dimethylformamide (DMF) was stirred at 70 °C for
70 h under a N2 atmosphere. The progress of the reaction was
monitored by TLC. After cooling the reaction mixture to room
temperature, it was poured into 150 mL cold water and a brown
precipitate was obtained. This was filtered off and the presence
of two substances in it was determined by TLC. The honey-colored
pure product 2 was isolated by column chromatography. Yield
0.75 g (26%). This compound is soluble in chloroform, dichloro-
methane (DCM), ethyl acetate and DMF. Mp: 117–120 °C. 1H
NMR (500 MHz, CDCl3) d (ppm): 7.63 (d, 2H, J = 8.66 Hz), 7.21 (s,
2H), 7.00 (s, 2H), 6.97 (s, 2H), 6.73 (s, 2H), 3.97 (s, 2H), 2.36 (s,
6H), 1.58–1.31 (m, 20H), 1.05 (s, 6H). 13C NMR (500 MHz, CDCl3)
d (ppm): 161.12, 150.88, 139.67, 137.49, 135.00, 132.78, 127.71,
127.63, 125.15, 122.83, 118.90, 117.10, 115.26, 109.60, 37.41,
33.92, 31.90, 27.80, 27.47, 22.74, 21.49. IR spectrum (KBr disk,
2.2. Electrochemical measurements
The electrochemical measurements were carried out with a
Princeton Applied Research Model VersoStat II potentiostat/galva-
nostat controlled by an external PC and utilizing a three electrode
configuration at 25 °C. A platinum disk, a platinum spiral wire and
a SCE served as the working, counter and reference electrodes for
the cyclic voltammetry measurements. The reference electrode
was separated from the bulk of the solution by a double bridge.
Electrochemical grade tetrabutylammonium perchlorate (TBAP)
in extra pure DMSO was employed as the supporting electrolyte
at a concentration of 0.10 M. High purity N2 was used for deoxy-
genating the solution for at least 20 min prior to each run and to
maintain a nitrogen blanket during the measurements. For con-
trolled potential coulometry (CPC) studies, a Pt gauze working
electrode (10.5 cm2 surface area), a Pt wire counter electrode sep-
arated by a glass bridge, and a saturated calomel electrode (SCE) as
a reference electrode were used. In situ spectroelectrochemical
measurements were carried out by an Agilent Model 8453 diode
array spectrophotometer equipped with a potentiostat/galvanostat
and utilizing an optically transparent thin layer (OTTLE) cell with a
three-electrode configuration at 25 °C. The working electrode was
transparent Pt gauze, a Pt wire counter electrode and a SCE refer-
ence electrode separated from the bulk of the solution by a double
bridge were used.
m
/cmꢀ1): 3075 (aromatic CH), 2926–2856 (aliphatic CH), 2232
(C„N), 1594 (aromatic C@C), 1487, 1247 (Ar–O–Ar), 1200, 1165,
837. Anal. Calc. for C45H44N4O2: C, 80.33; H, 6.59; N, 8.33; O,
4.76. Found: C, 80.37; H, 6.51; N, 8.37; O, 4.71%. MALDI-TOF-MS
m/z: 695 [M+Na]+.
2.1.2.2. 23,10,16,24-Tetrakis(2,20-methylenebis-[6-(1-methylcyclohexyl-5-
methyl-phenoxy-phthalonitrile]-p-cresoylphthalocyaninato Co(II) (3). A
mixture of
2
(0.050 g, 0.074 mmol) and CoCl2ꢁ6H2O (0.037 g,

E. Ermißs et al. / Polyhedron 49 (2013) 129–137
131
2.3. Electrical characterization
An interdigital transducer (IDT) was employed as transducer in
order to investigate the electrical properties of the compounds. The
interdigital transducers were fabricated onto a glass substrate. The
method for the fabrication of IDTs has been described previously in
the literature [15]. The transducer contains 10 finger pairs of gold
electrodes with a 100
lm width. The space between the electrodes
is also 100 m. In order to obtain thin films of the synthesized
l
compounds, the molecules were dissolved in THF using micro cen-
trifuge tubes. The homogenous solutions were coated onto the IDT
using the smearing method. The substrate temperature was kept
constant at 295 K during the deposition of the solution onto the
IDT. To reveal the electrical properties of the compounds, such as
the dc and ac charge transport mechanism and semiconducting
behavior, two types of measurements were performed. The first
one was the investigation of the dc electrical properties of the com-
pounds, and the second was of the ac properties. To do this, inter-
digitated gold electrodes coated with the compounds were placed
into a home-made temperature controlled aluminum chamber.
Electrical contacts between electrodes and measurement chamber
were achieved using silver paste. Dc current values were acquired
by applying dc voltages between ꢀ1 and +1 V with 50 mV steps to
the films of the compounds. The data for dc conductivity were ac-
quired using a Keithley model 617 programmable electrometer. Ac
conductivity and impedance spectra (IS) measurements were per-
formed using a Keithley model 3330 LCZ meter (40–105 Hz). All the
electrical measurements were done between the temperatures of
295 and 523 K, in an ambient vacuum (<10ꢀ3 mbar) in the dark.
The temperature was measured using a Chromel–Alumel thermo-
couple. Both the dc and ac conductivity data were recorded using
an IEEE-488 data acquisition system.
3. Results and discussion
3.1. Synthesis and characterization
The starting compound 2 for the syntheses of the targeted Pcs
was obtained by the reaction of bis[2-hydroxy-5-methyl-3-(1-
methylcyclohexyl)phenyl]methane (1) with 4-nitrophthalonitrile
in dry DMF in the presence of dry K2CO3 under a N2 atmosphere.
The 1H NMR, 13C NMR and IR spectra and elemental analysis were
used to characterize 2. Complexes 3–5 were synthesized by heat-
ing 2 with CoCl2, CuCl2 or Zn(OAc)2 (Scheme 1). The melting points
of compounds 3–5 were found to be higher than 300 °C. While the
zinc and copper salts yielded ball-type Pcs, the cobalt salt formed
only a mono Pc. Characterization of compounds 3–5 involving a
combination of methods, including elemental analysis, IR, MAL-
DI-TOF-MS and UV–Vis spectra, confirmed the proposed structures
for the compounds.
Scheme 1. Reagents and conditions: (i) K2CO3, DMF, N2, 70 h, 70 °C; (ii) CoCl2, N2,
10 min, 300 °C; and (iii) CuCl2 or Zn(OAc)2, N2, 10 min, 300 °C.
In the FTIR spectrum of 2, the presence of a C„N group was
indicated by the intense stretching band at 2232 cmꢀ1. The spec-
trum also showed an aromatic C–H peak at 3075 cmꢀ1, an aliphatic
C–H peak at 2926–2856 cmꢀ1, an aromatic C@C peak at 1594 cmꢀ1
2954–2855 cmꢀ1 indicated the presence of aliphatic CH groups
for Pcs 3–5.
and Ar–O–Ar stretching band at 1247 cmꢀ1
.
The 1H NMR spectra also correlated well with the structures of
the synthesized compounds. In the 1H NMR spectrum of 2, which
was taken in chloroform, the aromatic protons appeared at
7.63 ppm as a doublet (2H), 7.21 ppm as a singlet (2H), 7.00 ppm
as a singlet (2H), 6.97 ppm as a singlet (2H) and 6.73 ppm as a
singlet (2H). On the other hand, the aliphatic protons appeared at
3.97 ppm as a singlet (–CH2 bridge protons, 2H), 2.36 ppm as a
singlet (aromatic ring –CH3 protons, 6H), 1.05 ppm as a singlet
(aliphatic cyclohexane ring –CH3 protons, 6H) and as a multiplet
in the range of 1.58–1.31 ppm (20H in the cyclohexane rings).
For 3 and 4, 1H NMR measurements were precluded owing to their
A diagnostic feature of Pc formation is the disappearance of the
sharp C„N vibration at 2232 cmꢀ1. The IR spectra of 4 and 5
showed no C„N vibration band, whereas the IR spectra of 2 and
3 showed this vibration band at 2232 and 2230 cmꢀ1, respectively.
The rest of the spectra of 3–5 were closely similar to that of 2. The
absence of vibration bands for 4 and 5 is one of the indications for
ball-type Pc formation. The IR spectra of Pcs 3–5 showed aromatic
C@C (in phenyl rings) peaks at around 1605–1606 cmꢀ1, aromatic
CH peaks at around 3070–3075 cmꢀ1 and Ar–O–Ar peaks at around
1220–1275 cmꢀ1
. In addition, the stretching vibrations at

132
E. Ermißs et al. / Polyhedron 49 (2013) 129–137
Fig. 1. Positive ion and reflectron mode MALDI-TOF-MS spectrum of 3 (C180H176-
CoN16O8) in -cyano-4-hydroxycinnamic acid MALDI matrix using a nitrogen laser
(at 337 nm wavelength) accumulating 100 laser shots. Inset spectrum shows the
expanded molecular mass region of the complex.
Fig. 2. Positive ion and reflectron mode MALDI-TOF-MS spectrum of 4 (C180H176-
Cu2N16O8) in -cyano-4-hydroxycinnamic acid MALDI matrix using a nitrogen laser
(at 337 nm wavelength) accumulating 100 laser shots. Inset spectrum shows the
expanded molecular mass region of the complex.
a
a
paramagnetic nature. In the 1H NMR spectrum of 5 in CDCl3 the
peaks are broad when compared with those of 2. In the 1H NMR
spectrum of 5, the aromatic protons appeared at 7.28–6.60 ppm
(m, 40H, broad) and the aliphatic protons at 3.90–0.90 ppm (m,
136H, broad).
The UV–Vis spectra of 3–5 in DCM showed typical absorptions
for Pcs between 666 and 686 nm in the Q-band region. The Q-
band of each complex was attributed to the transition from the
highest occupied molecular orbital (HOMO) to the lowest unoccu-
pied molecular orbital (LUMO) of the Pc ring. The B-band absorp-
tions in the UV region of 320–340 nm were observed due to the
transitions from the deeper levels to the LUMO of all the com-
plexes. The strong absorptions between 425 and 460 nm in the
spectra of 3 and 4 arise from ligand metal charge transfer (LMCT)
transitions [3]. The spectra of 3–5 showed an additional weak
vibrational satellite band at ca. 600 nm, a blue shift from the nor-
mal Q-band, as a result of exciton coupling between the Pc units
[16]. Depending on the bridged compounds, metals and solvent,
the electronic and other properties of Pcs and ball-type Pcs
change dramatically. Also the bridged substituents and the dis-
tance between the two Pc molecules of the ball-type Pcs affect
considerably the degree of the interaction [17]. The intensities
of the Q-bands relative to B were low for 3–5, which indicated
very strong aggregation of the Pc molecules. It is also known that
aggregation is enhanced by the solvent polarity and the presence
of aliphatic side chains [3,18–20].
Fig. 3. MALDI-TOF-MS spectrum of 5 (C180H176Zn2N16O8) in
a-cyano-4-hydroxy-
cinnamic acid MALDI matrix using nitrogen laser (at 337 nm wavelength)
a
accumulating 100 laser shots. Inset spectrum shows the expanded molecular mass
region of the complex.
3.2. Electrochemistry
The redox properties of 3–5 were examined by cyclic voltam-
metry and CPC in DMSO/TBAP. A typical voltammogram of 3 is
shown in (Fig. 4). It displays an oxidation couple in addition to
three reduction processes. The first reduction and the first oxida-
tion couples are one-electron reversible and quasi-reversible pro-
cesses with half-peak potentials (E1/2) of ꢀ0.50 V versus SCE and
+0.36 V versus SCE and anodic to cathodic peak separations of
0.060 and 0.120 V, respectively. If the transition metal ion con-
cerned has no accessible d orbital levels between the HOMO and
the LUMO energies of a Pc species, then all its redox processes
are Pc ring-based. The nickel, copper, zinc and some other MPcs be-
have in this fashion, with the M(II) central ion being unchanged as
the MPc unit is either oxidized or reduced [21–24]. However, the
metal center in some MPcs, such as CoPc, FePc and MnPc, are re-
dox-active due to the presence of d orbital levels within the
HOMO–LUMO gap of the Pc species [21,23,24]. These species vary
their electrochemical behavior according to their environment in
solution and thus their electrochemistry is split into two sections,
that referring to donor solvents and that referring to non-donor
solvents. The main difference lies in whether the metal or the ring
is oxidized first. Donor solvents strongly favor Co(III)Pc(ꢀ2) by
coordinating along the axis to form six coordinate species. If such
donor solvents are absent, then oxidation to Co(III) is inhibited
MALDI-MS spectra of all the metal complexes were recorded in
a-cyano-4-hydroxycinnamic acid with better intensity than other
novel MALDI matrices (Figs. 1–3). For the high resolution spectra,
reflectron mode positive ion MALDI-MS spectra were recorded.
High values for the peak intensities could not be obtained in the
reflectron mode, but highly resolved MALDI-MS spectra were ob-
tained, which enabled comparisons between the experimental
and theoretical isotopic mass distributions, thus confirming the
metal complexes in detail. When the mass spectra were recorded
in the linear and positive ion mode, more intense signals were ob-
tained, but without resolution. For this reason, all mass spectra re-
ported were obtained in the reflectron and positive ion mode.
MALDI-MS spectra for all the complex compounds were evaluated
and it was concluded that the compounds were perfectly purified
and these metal complexes were more stable under the laser and
MALDI-MS conditions in the linear mode mass spectrometer. For
all the complexes, a few fragmentation peaks were observed and
no other intense ions from impurities were seen in the MALDI-
MS spectra. This showed that the complexes were synthesized by
the experimental route given.

E. Ermißs et al. / Polyhedron 49 (2013) 129–137
133
as stepwise one-electron redox couples of the two cofacial Pc units,
as a result of the interaction between them and thus, the splitting
of the molecular orbitals. It is clear from the previous studies that
the ZnII metal center is not redox-active in metallophthalocyanines
and thus all the redox processes of 5 are ligand-based [21,23,24].
These processes should be associated with the presence of
mixed-valence first- and second-reduced species, [ZnIIPc(ꢀ2)ꢁZnII-
Pc(ꢀ3)]ꢀ and [ZnIIPc(ꢀ3)ꢁZnIIPc(ꢀ4)]3ꢀ, respectively. The mixed-
valence splitting energy,
D
Es, values of the Pc(ꢀ2)/Pc(ꢀ3) and
Pc(ꢀ3)/Pc(ꢀ4) redox processes in 5 are 0.41 and 0.36 V respec-
tively, indicating remarkable stability of the mixed-valence
species. The splitting of a redox process, i.e., Pc(ꢀ2)/Pc(ꢀ3), for 5,
due to the formation of a stable mixed-valence intermediate,
[ZnIIPc(ꢀ2)ꢁZnIIPc(ꢀ3)]ꢀ, is a measure of the equilibrium (compro-
portionation) constant, Kc [21], for a reaction such as:
h
i
h
iꢀ
½ZnIIPcðꢀ3Þꢂ22ꢀ þ ZnIIPcðꢀ2Þ ¢ 2 ZnIIPcðꢀ2Þ ꢁ ZnIIPcðꢀ3Þ
2
where the mixed-valence splitting,
DEs is related to Kc, via:
Fig. 4. Cyclic voltammogram of 5 ꢃ 10ꢀ4 mol dmꢀ3 3 at 0.050 V sꢀ1 in DMSO/TBAP.
D
Es ¼ ðRT=nFÞ lnðKcÞ
ð1Þ
The values of Kc obtained for the mixed-valence species of
5, [ZnIIPc(ꢀ2)ꢁZnIIPc(ꢀ3)]ꢀ and [ZnIIPc(ꢀ3)ꢁZnIIPc(ꢀ4)]3ꢀ
, are
DEs values of 5 give
8.56 ꢃ 106 and 1.22 ꢃ 106. The high Kc and
evidence of the delocalization of charge among the cofacial Pc
units, and thus the formation of electrochemically reduced
mixed-valence species.
Fig. 6 shows the cyclic voltammograms of 4 at various scan
rates in DMSO/TBAP. Complex 4 displays two reduction and three
oxidation signals. However, the first and second oxidation couples
merge into one couple at high scan rates. The voltammetric behav-
ior of 4 is considerably different from that of 5. First of all, the peak
currents of all the redox signals are much higher than those of 5.
This implies that complex 4 is adsorbed on the surface of the work-
ing electrode. When the voltammograms at different scan rates
were recorded with a freshly cleaned electrode and immediately
after the freshly cleaned electrode had been immersed into the
solution for each scan rate, the peak currents were generally pro-
portional to the scan rate. In addition, when the voltammograms
for a given scan rate were recorded with different waiting times
after the freshly cleaned working electrode had been immersed
into the solution, the peak currents increased with increasing
waiting time and constant peak current values were reached in
approximately 15 min. These observations provide strong support
Fig. 5. Cyclic voltammogram of 5 ꢃ 10ꢀ4 mol dmꢀ3 5 at 0.050 V sꢀ1 in DMSO/TBAP.
and ring oxidation occurs first. Thus, the first oxidation and the
first reduction processes of 3 are probably metal-based and
correspond to Co(II)Pc(ꢀ2)/[Co(III)Pc(ꢀ2)]+ and Co(II)Pc(ꢀ2)/
[Co(I)Pc(ꢀ2)]ꢀ, respectively, since the voltammetric measurements
were carried out in DMSO/TBAP. In most cases, the potential differ-
ence between the metal-based first reduction and Pc ring-based
second reduction processes of a CoPc is approximately 1.00 V
[21]. Thus, the possibility of the correspondence of the R2 couple
to the reduction of the Pc ring is excluded, and it may be attributed
to the reduction of nitrile groups, while the hardly detected (due to
its occurrence at very negative potentials) ill-defined R3 couple
probably corresponds to the reduction of the Pc ring.
Compound 5 displayed four reductions at E1/2 = ꢀ0.37, ꢀ0.78,
ꢀ1.05 and ꢀ1.41 V versus a saturated calomel electrode (SCE) in
DMSO/TBAP. The CPC studies showed that each redox process in-
volves the transfer of one electron. A typical cyclic voltammogram
for 5 at 0.050 V sꢀ1 is shown in Fig. 5. The CPC studies of the vol-
tammetric couples showed that the number of electrons trans-
ferred for each redox process (p) is equal to unity. The transfer of
one electron in each of the broadly separated steps implies that
the reduction of each MPc ring of 5 occurs at different potentials
Fig. 6. Cyclic voltammogram of 5 ꢃ 10ꢀ4 mol dmꢀ3 4 in DMSO/TBAP.

134
E. Ermißs et al. / Polyhedron 49 (2013) 129–137
performed at different temperatures in the temperature range
295–523 K in an ambient vacuum (<10ꢀ3 mbar) in the dark. The
current values passing through the films were recorded versus
the applied voltages (I–V curves). The dc conductivity of the films
was determined using Eq. (2) and the slope of the I–V curves:
ꢀ ꢁꢀ
ꢁ
I
V
d
rdc
¼
ð2Þ
ð2n ꢀ 1Þlh
where (I/V) is slope of the I–V graph, d is the distance between the
finger pair, n is the number of the finger pair, l is the overlap length
and h is the thickness of the electrodes.
Fig. 8 shows the lnrdc ꢀ 1/T curves of films of 3, 4 and 5. The
conductivity of films of 3, 4 and 5 were found to be 3.4 ꢃ 10ꢀ10
,
9.8 ꢃ 10ꢀ10 and 3.7 ꢃ 10ꢀ10 S/cm at 295 K, respectively. The con-
ductivity values increased to 1.6 ꢃ 10ꢀ5, 8.3 ꢃ 10ꢀ6 and 1.2 ꢃ
10ꢀ5 S/cm at 523 K, respectively. As shown in Fig. 8, the lndc con-
ductivities of the films increase with increasing temperature in a
linear form. This behavior of lndc conductivity with temperature
indicates that the compounds 3, 4 and 5 are semiconductors.
Further, the linear relation also shows that the compounds behave
as intrinsic semiconductors in the temperature range 295–495 K.
After 495 K, the slope of the 4 begins to decrease. It is well known
that the structural/compositional lattice defects increases the
localized states and that affects the dc conductivity. The change
in behavior of the rdc ꢀ 1/T curve after 495 K for the film of 4
may be attributed to the occurrence of a phase transition or the
presence of different crystallographic phases [26,27]. The temper-
ature dependence of the dc conductivity can be expressed by the
Arrhenius equation (Eq. (3)) [28,29]:
ꢀ
ꢁ
ꢀEA
rdc
¼
r0 exp
ð3Þ
kT
where EA is the activation energy, T is the temperature, k is
Boltzmann’s constant and 0 is a pre-exponent factor of dc conduc-
r
tivity. From the slope of straight portions of the curves in Fig. 8, the
activation energies were calculated. The values were found as 0.70,
0.66 and 0.68 eV for the films of 3, 4 and 5, respectively. The calcu-
lated dc conductivity values of the films of 3, 4 and 5 exhibited the
same order of conductivity values as other reports on different Pc
films [14]. Our activation energy values were also of the same order
of magnitude as activation energy values in other reports on differ-
ent Pc films, namely 0.6–0.8 eV [14,30].
Ac conductivity studies were also carried out on the films of 3, 4
and 5 in a home-made aluminum chamber at different tempera-
tures in the temperatures range 295–523 K in an ambient vacuum
(<10ꢀ3 mbar) in dark, as for the dc conductivity measurements.
The ac conductivity measurements were performed in the
Fig. 7. In situ UV–Vis spectral changes monitored during (A) the first reduction (at
ꢀ0.90 V versus SCE) and (B) the second reduction (at ꢀ1.60 V versus SCE) processes
of 4 in DMSO/TBAP.
for the idea of adsorption. It is expected that all the redox processes
are Pc ring-based since Cu(II) is redox-inactive in metallophthalo-
cyanines. However, the oxidation processes of 4 occur at less
positive potentials than those of similar ball-type Pcs involving
redox-inactive metal centers [25]. This may be due to the adsorp-
tion of 4 on the working electrode since the oxidation potentials of
the adsorbed species are expected to be less positive than those of
the species in solution. Another possibility is that the irreversible
second reduction process R2 is due to demetallation of 4 and the
working electrode is plated with metallic copper. Fig. 7 shows
the in situ UV–Vis spectral changes observed during the first and
second reduction processes of 4. The decrease in the Q band
absorption without shift and the formation of a new band at
583 nm during the first reduction process (Fig. 7A), similar changes
in the Q band absorption and also the appearance of a new band at
608 nm during the second reduction process (Fig. 7B) confirm that
both the first and the second reduction processes are Pc ring-based.
Thus, the idea that the second reduction process is related to the
demetallation of 4 is excluded.
3.3. Electrical measurements
Dc conductivity studies were done on films of 3, 4 and 5 in a
home-made aluminum chamber. The measurements were
Fig. 8. The variation of dc conductivity with inverse of temperature for the films of
3, 4 and 5 between the temperatures of 295 and 523 K.

E. Ermißs et al. / Polyhedron 49 (2013) 129–137
135
Fig. 11. Temperature dependence of the exponent s of films of 3, 4 and 5 in the high
frequency (Pꢄ1 kHz) region.
Fig. 9. Frequency dependence of the ac conductivity of the film of 4 between the
temperatures of 295 and 523 K.
the variation of the exponent s with temperature was examined. s
values were calculated from the slope of the straight portions of
the rac versus
x plot.
Calculated values of s for the films of 3, 4 and 5 are around 0.9 at
295 K and decrease to 0.1 at 523 K, and the other s values at tem-
peratures between 295 and 523 K are between 0.1 and 0.9. The var-
iation of the s values of the films with temperature in the high
frequency region (Pꢄ1 kHz) is given in Fig. 11. As seen from this
figure, the s values decrease with increasing temperature. Accord-
ing to the band theory, the ac conductivity should be frequency
independent and it drops at a sufficiently high frequency. On the
contrary to the band model, in the hopping model the electrons
in charged defect states hop over the coulomb barrier. This model
predicts a frequency dependent ac conductivity, which increases
with increasing frequency under the condition that the frequency
exponent s 6 1 [32]. In the Correlated Barrier Hopping (CBH) model
[32], the ac conductivity (first order approximation) is given by:
Fig. 10. Frequency dependence of the ac conductivity of films of 3, 4 and 5 at 523 K.
frequency range 40–105 Hz. Fig. 9 shows the variation of the ac
conductivity of a film of 4 with frequency in the temperature range
1
24
rac
¼
np
3N2eeoxR6x
ð5Þ
295–523 K. The ac conductivity (rac) of the film increases with
where N is the spatial density of defect states,
e
and
e
o are dielectric
increasing temperature. The temperature dependence of the ac
conductivity of the film can be analyzed in two parts, (i) low tem-
perature region (T < ꢄ438 K) and (ii) high temperature region
(T > ꢄ438 K). In the low temperature region, the conductivity of
the film strongly depends on the frequency, with different slopes
in different frequency regions. The conductivity of the film in-
creases with increasing frequency in this temperature region. In
the high temperature region (T > ꢄ438 K) the frequency depen-
dence of the ac conductivity of the film decreases in the measured
frequency range for the film of 4. In this region, we observed differ-
ent a frequency dependence of the ac conductivity for films of 3
and 5 compared to that of film 4. Fig. 10 shows this difference at
constants of the materials and free space, respectively, n = 1 for a
single electron n = 2 for hopping of two electrons and R is the hop-
x
ping distance. The hopping distance at the frequency
x
is given by:
e2
Rx
¼
ð6Þ
p
eeo½WM ꢀ kT lnð1= soÞꢂ
x
The CBH model, which was developed by Elliot [32,33], predicts
a temperature-dependent s value which is given by:
6kBT
s ¼ 1 ꢀ b ¼ 1 ꢀ
Wm
ð7Þ
where kB is Boltzmann’s constant, Wm is the binding energy and T is
temperature. In this model the s values decrease with increasing
temperature. Our results show that s is a function of temperature
for all the films and shows a general tendency to decrease with
increasing temperature over the measured frequency range at
temperatures T < ꢄ438 K. The variation of s with temperature in
523 K. While the slope of the rac versus
x curves can be analyzed
in two different frequency regions (40–104 and 104–105 Hz) for the
film of 4, the slopes for the films of 3 and 5 can be analyzed in four
different frequency regions (10–102, 102–103, 103–104 and 104–
105 Hz). At temperatures T > 438 K, the slope of the curves
decreases with increasing temperature in all frequency range
measurements for the films of 3 and 5 (except the frequency range
of 40–103 Hz). However, at all temperatures the frequency
dependence of the measured ac conductivity of the films obeys
the universal power law. The universal power law is given by the
Eq. (4) [31]:
the high frequency region (
x
P ꢄ1 kHz) and the variation of ac
conductivity with frequency (Figs. 9 and 11) are in agreement with
the prediction of the hopping model. The same type of temperature
dependence for s was observed in other reports on different Pc films
[15,34]. The variation of s with temperature in the low frequency
region (
x
< ꢄ1 kHz) is given in Fig. 12. As can be seen clearly from
rac ¼ Axs
ð4Þ
Fig. 12, while the s values decrease with increasing temperature for
temperatures T < ꢄ438 K, the values increase with increasing
temperature for temperatures T > ꢄ438 K, except for the film of 4.
where
x
is the angular frequency, and A and s are material depen-
dant constants. To investigate the conduction mechanism involved,

136
E. Ermißs et al. / Polyhedron 49 (2013) 129–137
Fig. 12. Temperature dependence of the exponent s of films 3, 4 and 5 in the low
frequency (6ꢄ1 kHz) region between the temperatures of 348 and 523 K.
In the quantum–mechanical tunneling (QMT) model [35], the expo-
nent s is almost equal to 0.8 and increases slightly with temperature
or is independent of temperature. Because of this, the QMT model is
not applicable to our results. In the QMT model the s values can be
calculated using (Eq. (8)) [32]:
4
s ¼ 1 ꢀ
ð8Þ
lnð1=x
so
Þ
where
so is the characteristic relaxation time. According to the over-
lapping-large polaron tunneling (QLPT) model [33], the exponent s
is both frequency and temperature dependent and decreases with
increasing temperature to a minimum value at a certain tempera-
ture, then it increases with increasing temperature. This model is
also not applicable to our results. The small polaron quantum
mechanical tunneling (SP) model predicts an increase in s with an
increase in temperature [32,33]. It is also well known that the low
values of s indicate a multi-hopping process, while high values of
s indicate a single hopping process.
According to these models, we can conclude that the charge
transport mechanism of the film of 4 can be modeled by single
hopping over all the measured frequency and temperature ranges.
However, the charge transport mechanism for the films of 3 and 5
can be interpreted in two parts. In the low temperature region
(T < ꢄ438 K) the dominant conduction mechanism can be modeled
by single hopping over the measured frequency range. In the high
temperature region (T > ꢄ438 K) the conduction mechanism can be
modeled depending on frequency region, (i) high frequency region
Fig. 13. The cole–cole plot at temperatures (A) T 6 363 K for the film of 4 (B)
T P 458 K for the film of 4 and (C) T P 458 K for the film of 5.
(
x
> ꢄ1 kHz) and (ii) low frequency region (
high frequency region (
> ꢄ1 kHz), the s values are between
0.85 and 0.06, and decrease with increasing temperature, but in
the low frequency region
x
6 ꢄ1 kHz). In the
x
Fig. 13A, the impedance spectra are characterized by the appear-
ance of semicircular shaped arcs for the film of 4 at temperatures
T 6 363 K. The existence of a semicircular shaped curve in the
Nyquist plot means that the impedance becomes capacitive, even
at high frequencies. The curves can be modeled by a resistor paral-
lel with a capacitor in series with another resistor [34]. Films of 3
and 5 also showed the same behavior at those temperatures. At the
temperatures T P 458 K, films of 3, 4 and 5 showed different
behavior. Fig. 13B shows the impedance spectra for the film of 4
and Fig. 13C for the film of 5 at temperatures T P 458 K. By
examining Fig. 13A and B, we can say that the semicircular arcs
transform into full semicircles as the temperature rises for the film
of 4. With an examination of Fig. 13B, the effect of the temperature
on the impedance spectra can be seen clearly. The impedance spec-
tra consist of depressed semicircles with different radii, the radius
of a semicircle decreases with increasing temperature.
(
x
6 ꢄ1 kHz), they increase with
increasing temperature (for the films of 3 and 5). We can conclude
that in the high temperature region (T > ꢄ438 K) the dominant
conduction mechanism for the films of 3 and 5 can be modeled
by small polaron tunneling (SP) in the low frequency region and
by single hopping in the high frequency region.
To ensure the complete characterization of the electrical prop-
erties of the compounds, the impedance spectroscopy technique
was used in the frequency range 40–105 Hz. The impedance data
representation is obtained by plotting ꢀZ00(
x) (the imaginary com-
ponent of the impedance) against Z0(
x) (the real component of the
impedance) (Z(
x
) = Z0(
x
)
jZ00(
x)), commonly called the Nyquist
plot. Fig. 13A and B show the Z0(
x
) and ꢀZ00(
x) components of
the impedance data plotted in the complex impedance plane for
the film of 4 and Fig. 13C for the film of 5, recorded at the indicated
temperatures (in Fig. 13A the x-axis and y-axis are not drawn on
the same scale to show the behavior of the curves). As seen from
An ideal semicircle in the complex plane only appears in Debye
dispersion relations for a single-relaxation time process. Most of

E. Ermißs et al. / Polyhedron 49 (2013) 129–137
137
the materials show a pronounced deviation from the Debye treat-
ment, as in our case. In this case, the relaxation time is considered
as a distribution of values, rather than a single relaxation time [36].
The depressed semicircles with different radii indicate a deviation
from the Debye dispersion relation. Therefore, the equivalent cir-
cuit is modified to include a constant phase element (CPE). The ser-
ies resistance in the equivalent circuit represents ohmic losses in
the test fixture and electrode sheet resistance. The parallel resis-
tance is of the coating material in parallel with that of the sub-
strate. The intercepts of the semicircular arcs with the real axis
give us information on the bulk resistance of the compounds. From
the complex impedance spectra as a function of temperature, it is
observed that the bulk resistance decreases with increasing
temperature, indicating semiconductor properties. A monotonic
decrease in this resistance suggests that the increase of tempera-
ture lowers the barrier for charge transport. For the film of 5 at
temperatures T P 458 K, in addition to Fig. 13B, a straight line
was observed in the low frequency region (Fig. 13C). The straight
line in the low frequency region indicates the presence of a
Warburg component [37]. The complex impedance spectra
(Nyquist plots) of the film of 3 at temperatures T P 458 K were
similar to those in Fig. 13C.
BIBAM Research Center of Anadolu University for NMR spectra
and we also thank Dr. Z. Odabasß for drawing Scheme 1.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2012.09.048.
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We gratefully acknowledge the financial support in part from
the Turkish Academy of Sciences (TUBA). We thank the staff of