Synthesis and electrochemical behavior of novel peripherally and non-peripherally substituted ball-type cobalt phthalocyanine complexes

Article abstract of DOI:10.1016/j.poly.2010.11.028

The syntheses of new ball-type Co(II) phthalocyanines containing 4,4′-(9H-fluorene-9,9-diyl)diphenol substituents at non-peripheral (complex 6) and peripheral (complex 7) positions are presented. These complexes were characterized by UV-Vis, FT-IR, mass s

Full text of DOI:10.1016/j.poly.2010.11.028

Polyhedron 30 (2011) 522–528
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and electrochemical behavior of novel peripherally and
non-peripherally substituted ball-type cobalt phthalocyanine complexes
Mevlüde Canlıca a, Irvin Noel Booysen b, Tebello Nyokong b,
⇑
a Yildiz Technical University, Chemistry Department, Inorganic Chemistry Division, Davutpasa Campus, 34220 Esenler, Istanbul, Turkey
b Rhodes University, Chemistry Department, P.O. Box 6140, Grahamstown, South Africa
a r t i c l e i n f o
a b s t r a c t
The syntheses of new ball-type Co(II) phthalocyanines containing 4,40-(9H-fluorene-9,9-diyl)diphenol
substituents at non-peripheral (complex 6) and peripheral (complex 7) positions are presented. These
complexes were characterized by UV–Vis, FT-IR, mass spectroscopy and electrochemical methods. Both
complexes exhibit metal and ring based redox processes, typical of cobalt phthalocyanine complexes.
For 6, the metal based reduction was observed at ꢀ0.46 V followed by a ring based reduction at
ꢀ1.40 V. The metal oxidation for 6 was observed at +0.16 V and the ring based oxidation at +1.05 V.
For 7, reductions are easier but the oxidations are more difficult. The metal based reduction for 7 was
observed at ꢀ0.38 V followed by a ring based reduction at ꢀ1.03 V. The metal oxidation for 7 was
observed at +0.20 V and the ring based oxidation at +1.35 V.
Article history:
Received 28 July 2010
Accepted 16 November 2010
Available online 30 November 2010
Keywords:
Cobalt phthalocyanine
Ball-type phthalocyanines
Cyclic voltammetry
Spectroelectrochemistry
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
We also discuss the influence of a versus b substitution on the elec-
trochemical properties of these complexes.
Metallophthalocyanines (MPcs) have been extensively studied
due to their diversity of applications, which include molecular
electronics [1], non-linear optics [2], liquid crystals [3], photosen-
sitizers [4] and electrocatalysis [5,6]. Electrochemical studies of
MPc complexes are also important with regard to their potential
application as electrochromic materials where several colors are
displayed depending on the applied potential on the electrode sur-
face [7–9].
Cofacial or ball-type Pcs were published in the literature for the
first time in 2002 [10,11]. However, studies on non-peripherally
substituted CoPc ball-type derivatives containing bulky substitu-
ents (and hence less aggregated) are still limited. It has been re-
ported that ball-type Pcs show spectroscopic and electrochemical
properties which differ significantly from the parent monomer
[12–25]. Ball-type Pcs have four bridged substituents on the
peripheral positions of each benzene ring of the two Pc units, the
latter are arranged cofacially, resulting in a ball-type structure.
The electronic properties of ball-type Pcs can change dramatically
depending on the bridging compounds or the central metal. The
distance between the two Pc units affect the degree of interactions
between the rings [12].
2. Experimental
2.1. Materials
3-Nitrophthalonitrile
1 and 4-nitrophthalonitrile 2 were
synthesized as reported in the literature [26]. 4,40-(9H-fluorene-
9,9-diyl)diphenol 3 was obtained from commercial suppliers.
Anhydrous potassium carbonate, cobalt(II) chloride and tetrabutyl-
ammonium tetrafluoroborate (TBABF4) were purchased form Sig-
ma–Aldrich. Dimethylsulfoxide (DMSO), tetrahydrofuran (THF)
and chloroform were obtained from Saarchem. Silica gel 60 for col-
umn chromatography was purchased from MERCK. All solvents
were dried and purified as described by Perrin and Armarego
[27]. All other reagents were used as received.
2.2. Equipment
UV–Vis absorption spectra were obtained using a Varian 500
UV–Vis–NIR spectrophotometer. IR spectra were obtained using a
Perkin–Elmer 2000 FT-IR spectrometer. Elemental analysis was
done using a Vario-Elementar Microcube ELIII. Mass spectral anal-
ysis was done using a Thermo Finnigan MAT LCQ or an ABI Voyager
DE-STR MALDI-TOF instrument.
In this paper, we describe the syntheses, electrochemical and
spectroelectrochemical properties of new symmetrically (peripher-
ally and non-peripherally) substituted ball-type CoPcs (Scheme 1).
Cyclic voltammetry (CV) and square wave voltammetry (SWV)
data were obtained with an Autolab potentiostat PGSTAT 30 (Eco
Chemie, Ultretch, The Netherlands) driven by the General Purpose
⇑
Corresponding author. Tel.: +27 46 6038260; fax: +27 46 6225109.
E-mail address: t.nyokong@ru.ac.za (T. Nyokong).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.11.028

M. Canlıca et al. / Polyhedron 30 (2011) 522–528
523
O
O
NC
N
CN
NC
NC
O
O
NC
N
N
N
Co
O
N
N
N
O
N
i
ii
N
O
O
NO2
N
(2)
N
N
+
NC
N
Co
N
N
N
(5)
O
O
HO
HO
(7)
O
(3)
NC
O
CN
N
N
N
N
+
O
O
N
NC
CN
Co
N
N
O
O
i
ii
N
O2
N
O
O
N
(1)
N
N
N
NC
CN
N
Co
N
N
N
(4)
O
O
(6)
Scheme 1. Synthesis of complex 6 and 7. (i) K2CO3, DMSO, rt, 3 days. (ii) CoCl2, 320 °C, 5 min.
Electrochemical Systems data processing software (GPES, software
version 4.9, Eco Chemie) using a three electrode set-up that con-
sisted of a glassy carbon-working electrode (GCE, 3.0 mm diame-
ter), Ag|AgCl wire pseudo reference electrode and a platinum
wire counter electrode. The potential response of the Ag|AgCl pseu-
do reference under aqueous conditions was less than Ag|AgCl (3 M
KCl) by 0.015 0.003 V. The SWV settings were: step poten-
tial = 5 mV, pulse height = 25 mV, pulse frequency = 15 Hz. Prior
to use, the electrode surface was polished with alumina on a Bueh-
ler felt pad and rinsed with excess Millipore water. All electro-
chemical experiments were performed in freshly distilled dry
DMSO containing TBABF4 as a supporting electrolyte. Solutions
for the electrochemical studies were deaerated by bubbling argon
before use and the electrochemical set-up was kept under argon
atmosphere throughout the experiments. Spectroelectrochemical
experiments were conducted using a home-made optically trans-
parent thin-layer electrochemical (OTTLE) cell connected to a Bio
analytical system (BAS) CV 27 voltammogram.
and then the pure product was dried using phosphorous pentoxide.
Yield: 2.1 g. IR (KBr) (m
max/cmꢀ1): 3059 (ArACH), 2232 (C„N),
1573 (C@C), 1251 (CAOAC). 1H NMR (DMSO-d6) d, ppm: 7.97
(2H, d), 7.83 (2H, m), 7.51 (2H, d), 7.45 (2H, t) 7.38 (2H, t), 7.31
(2H, d), 7.26 (6H, d, Ar0AH), 7.16 (4H, d). Anal. Calc. for
C
41H22N4O2: C, 81.71; H, 3.68; N, 9.31. Found: C, 81.92; H, 3.79;
N, 9.96%. MS m/z: 602.64. Found [M]+: 602.18.
2.3.2. 4,40-(4,40-(9H-fluorene-9,9-diyl)bis(4,1-phenylene))bis(oxy)di-
phthalonitrile (5)
Complex 5 was synthesized as described for 4 except complex 2
instead of 1 was employed. The amounts of reagents were the
same. Yield: 2.1 g. IR (KBr) (m
max/cmꢀ1): 3059 (ArACH), 2233
(C„N), 1575 (C@C), 1253 (CAOAC). 1H NMR (DMSO-d6): d, ppm
8.08 (2H, d), 7.97 (2H, d), 7.79 (2H, s), 7.51 (2H, d), 7.45 (2H, t),
7.38 (2H, t), 7.36 (4H, d), 7.26 (2H, d), 7.14 (4H, d). Anal. Calc. for
C
41H22N4O2: C, 81.71; H, 3.68; N, 9.31. Found: C, 81.02; H, 3.56;
N, 9.06. MS m/z: 602.64. Found [M+H2O]+: 621.19.
2.3.3. 10,110,150,250-[Tetrakis(4,40-(1,10-binaphthyl-8,80-diyl(oxy))di-
phenyl)]bis-phthalocyaninato dicobalt(II) (6)
2.3. Syntheses
The target precursors were prepared by a nucleophilic aromatic
Complex 4 (0.100 g) and CoCl2 (0.100 g) were ground in a quartz
crucible and heated in a sealed glass tube for 5 min under an argon
atmosphere at 320 °C. After cooling to room temperature, the blue-
green reaction product was washed with hot methanol (MeOH)
and hot water. The product was separated by column chromatog-
raphy on silica gel with CHCl3 and a gradient of CHCl3–MeOH up
to 50%. Yield 0.015 g. Blue-green color. M.p. > 350 °C. UV–Vis
substitution reaction between 3-nitrophthalonitrile
1
or 4-
nitrophthalonitrile
Scheme 1.
2
and 4,40-(9H-fluorene-9,9-diyl)diphenol
3
2.3.1. 3,30-(4,40-(9H-fluorene-9,9-diyl)bis(4,1-phenylene))bis(oxy)di-
phthalonitrile (4)
(CHCl3) kmax/nm (log
e
/dmꢀ3 molꢀ1 cmꢀ1): 688 (4.86), 323 (4.73).
Compound 3 (2.22 g, 6.33 mmol) was dissolved in dry DMSO
(15 mL) and 1 (2.19, 12.66 mmol) was added under an inert atmo-
sphere. To this reaction mixture, finely ground anhydrous K2CO3
(3.50 g, 12.66 mmol) was added. After 4 h of stirring at room tem-
perature another batch of potassium carbonate (0.40 g, 2.88 mmol)
was added, and this same amount was added again after 24 h of
stirring. After a total of 72 h of stirring, the reaction mixture was
poured into water (50 mL), resulting in the formation of a yellow
precipitate. The crude product was centrifuged and was further
purified by chromatography over a silica gel column using CHCl3
as the eluent. The product was recrystallized from ethanol (EtOH)
IR (KBr) (
m
max/cmꢀ1): 3055 (ArACH), 1579 (C@C), 1251 (CAOAC).
Anal. Calc. for C164H88N16O8Co2: C, 77.90; H, 3.51; N, 8.86. Found:
C, 78.57; H, 3.55; N, 9.16%. MALDI-TOF-MS m/z Calc.: 2528.42.
Found [Mꢀ5H]+: 2523.0.
2.3.4. 20,100,160,240-[Tetrakis(4,40-(1,10-binaphthyl-8,80-diyl(oxy))di-
phenyl)]bis-phthalocyaninato dicobalt(II) (7)
Complex 7 was synthesized as described for 6, except complex 5
instead of 4 was employed. The amounts of reagents were the
same. Yield: 0.038 g. Blue-green color. M.p. > 350 °C. UV–Vis

524
M. Canlıca et al. / Polyhedron 30 (2011) 522–528
(CHCl3) kmax/nm (log
e
/dmꢀ3 molꢀ1 cmꢀ1): 664 (4.67), 325 (4.73).
and 325 nm for 6 and 7, respectively. Typical of ball-type phthalo-
cyanines, the intensity of the B-bands is high relative to the Q-band
when compared to the monomer, and this may be due to intramo-
lecular interactions between the Pc rings [30]. For example a CoPc
tetra substituted at the non-peripheral positions with 3,4-(methyl-
IR (KBr) (m
max/cmꢀ1): 3054 (ArACH), 1579 (C@C), 1245 (CAOAC).
Anal. Calc. for C164H88N16O8Co2: C, 77.90; H, 3.51; N, 8.86%. Found:
C, 78.57; H, 3.10; N, 9.03%. MALDI-TOF-MS m/z Calc.: 2528.42.
Found: [M+H2O]+: 2546.51, [Mꢀ11H]+: 2517.6.
endioxy)-phenoxy substituents gave a log
e value for the Q-band of
5.39 compared to 4.75 for the B-band [31], whereas complex 7
3. Results and discussion
shows a log
e value of 4.67 for the Q-band compared to 4.73 for
the B band.
3.1. Syntheses and characterization
The aggregation behavior of a Pc is depicted as a coplanar asso-
ciation of rings, progressing from the monomer to a dimer and to
higher order complexes, which are dependent on concentration,
the nature of the solvent and substituents, metal ions and temper-
ature [32]. Aggregation in MPcs is typified by broadened or split Q-
band, with the high energy band being due to the aggregate and
the low energy band due to the monomer. As expected for ball-
type structures, complexes 6 and 7 have broad spectra [12–
25,33]. A band near 620 nm in ball-type phthalocyanines has been
associated with exciton coupling between the two Pc rings [33]. A
strong intermolecular interaction between the Pc rings in ball-type
Pc complexes is expected to result in a splitting of the molecular
orbitals and hence a lowering of the symmetry, resulting in the
splitting of the Q-band. The spectra of complexes 6 and 7 in chlo-
roform shows bands in the 600 nm region, which could be a com-
bination of vibronic bands and the band due to exciton coupling
between the two rings. There is no clear splitting in the Q-band
of both complexes, suggesting that the interactions are not very
strong. The broadening is larger for 7, showing more intermolecu-
lar interactions and possibly aggregation. The peripherally substi-
tuted complex 7 is expected to show more aggregation than the
non-peripherally substituted complex 6 [28].
The substituted phthalonitriles were synthesized according to
the synthetic route shown in Scheme 1. New binuclear, ball-type
Co(II)Pcs (6 and 7) were prepared by the reaction of compound 4
or 5 with CoCl2. The structure and purity of the CoPc derivatives
were confirmed by UV–Vis, IR, mass spectroscopies and elemental
analyses. Complexes 6 and 7 are soluble in DMSO, THF and CHCl3,
and are partially soluble in most other organic solvents.
The IR spectra of 6 and 7 show no C„N vibrational peak (2233
or 2232 cmꢀ1) which was observed in the IR spectra of compounds
4 and 5. This confirms the formation of the desired CoPc deriva-
tives. The remaining IR spectra are very similar for compounds
4–7. The IR spectra of 4–7 showed ArAOAAr vibrational band
bands between 1235 and 1255 cmꢀ1. The 1H NMR spectrum of 5
shows a characteristic sharp singlet at 7.79 ppm, which is assigned
to the peripherally positioned proton on the CNAArAH moiety. In
both 1H NMR spectra of 4 and 5 the total number of protons inte-
grates to 22.
Elemental analysis results are also consistent with the proposed
structures of 4–7. The purified ball-type phthalocyanines were fur-
ther characterized by mass spectra. The deprotonated molecular
ion peaks were observed at m/z 2523.0 (for 6) and 2546.51 and
2517.6 (for 7), which concur with the theoretical calculated molec-
ular ions (See Supplementary materials, Fig. 1). These results con-
firm that the complexes have been synthesized successfully.
The UV–Vis spectra of 6 and 7 in CHCl3 are in accordance with
the trend found in the literature, Fig. 1. The phthalocyanines show
typical electronic spectra with two main absorption bands in the
UV region (320–350 nm, the B-bands) and the visible region
(600–700 nm, the Q-band). The characteristic Q-band transition
of metallophthalocyanines with D4h symmetry is observed as a sin-
gle band of high intensity in the visible region. Complexes 6 and 7
have Q-band absorption maxima at 688 and 664 nm in chloroform,
3.2. Voltammetric studies
The electrochemistry of ball-type phthalocyanine complexes
containing electroactive central metals is characterized by the for-
mation of mixed valance species [12]. Multi-electron processes are
known in the cyclic voltammetry of these complexes. The observa-
tion of one-electron processes in homo-dinuclear ball-type MPc
complexes is attributed to a strong interaction between the rings,
resulting in the splitting of the cyclic voltammetry peaks and the
formation of mixed redox processes. The transfer of two electrons
in each redox step suggests that there is no considerable interac-
tion between the two Pc rings, and that the two rings are reduced
and oxidized at the same potentials.
Complex 6 (Fig. 2) exhibited five redox processes, which are not
reversible in some cases. The lack of reversibility of redox couples
is typical behavior of ball-type MPc complexes and has been asso-
ciated with interactions between the Co2Pc2 units [12,34]. The
reported electrochemistry of ball-type phthalocyanines is charac-
terized by weak and often irreversible cyclic voltammograms
[12,25]. The cyclic voltammograms observed in Figs. 2 and 3 are
typical [12,25] of ball-type phthalocyanines.
respectively, as is shown in Fig. 1. It is well known that
a substitu-
tion results in red shifting of the spectra in MPcs [28,29], this is due
to the electron density enhancement caused by the substitution at
the non-peripheral position. The B-bands were observed at 323
5
4
Redox couple III in Fig. 2 is reversible, with a peak to peak sep-
aration (DE) of 80 mV (DE = 85 mV for ferrocene standard). Pro-
3
6
cesses I, I0, II and IV are not clearly reversible. The reversibility or
relative intensities of the peaks could not be improved by changing
the scanning direction or using a narrow potential window. Process
II is only clearly observed on the square wave voltammogram at
ꢀ0.46 V, Table 1, whereas process I is irreversible and is not ob-
served on the square wave voltammogram, Fig. 2b, this is due to
the extreme sensitivity of this technique to the reversibility of a
couple and the chemical stability of the redox products. Using
the known redox behavior of monomers and ball-type CoPc com-
plexes, where the first reduction occurs on the central metal, pro-
cess II is assigned to (CoIIPcꢀ2)2/[(CoIPcꢀ2)2]2ꢀ. The assignment is
2
1
0
7
320
420
520
620
720
Wavelength / nm
Fig. 1. Absorption spectra of complexes 6 and 7 (4 ꢁ 10ꢀ5 mol dmꢀ3) in CHCl3.

M. Canlıca et al. / Polyhedron 30 (2011) 522–528
525
Fig. 2. (A) Cyclic and (B) square wave voltammograms of 1 ꢁ 10ꢀ3 M complex 6 in
Fig. 3. (A) Cyclic and (B) square wave voltammograms of 1 ꢁ 10ꢀ3 M complex 7 in
freshly distilled DMSO containing 0.1 M TBABF4 supporting electrolyte. Insert to B:
SWV at a narrower potential window.
freshly distilled DMSO containing 0.1 M TBABF4 supporting electrolyte.
consistent with the UV–Vis spectrum (Fig. 1) which does not show
splitting, and hence shows that there are no strong interactions be-
tween the two rings, suggesting a two electron transfer process.
This assignment will be confirmed below using spectroelectro-
chemistry. The irreversible process I (at ꢀ0.9 V), is then assigned
to the subsequent ring reduction (CoIPcꢀ2)2]2ꢀ/[(CoIPcꢀ3)2]4ꢀ) for
complex 6, in comparison also with complex 7 below, which con-
firms a process in this potential range to be ring reduction, Table 1.
Process I0 is then assigned to further ring reduction and the forma-
tion of (CoIPcꢀ2)2]4ꢀ/[(CoIPcꢀ4)2]6ꢀ, Table 1. Process III shows a
much higher intensity compared to II. This process could reflect
on the overlap of two processes. Again using the literature [34],
we assigned couple III (at 0.16 V) to [(CoIIIPcꢀ2)2]2+/[CoIIPcꢀ2)2. Pro-
cess IV (at 1.05 V) is at the limit of solvent–electrolyte system, and
hence it is not well refined. However this process may be assigned
to a subsequent ring oxidation ([(CoIIIPcꢀ2)2]2+/[(CoIIIPcꢀ1)2]4+). Ta-
ble 1 compares the redox processes for the complexes reported
here with those of monomers peripherally and non-peripherally
substituted with substituents containing oxygen bridges. Oxida-
tion seems to occur more easily for the ball-type complexes com-
pared to monomers. However this is a tentative suggestion since
the substituents are not exactly the same in the two systems.
Complex 7 exhibited five redox processes (Fig. 3), more clearly
visible on the square wave voltammogram, especially process III.
Process II was reversible, but the remaining processes exhibited a
lack of reversibility, typical of ball-type MPc complexes [34]. An
additional process (compared to complex 6) at 0.44 V (labeled
III0) was observed for complex 7, which could be due to aggregated
species or the presence of mixed valance processes. The observa-
tion of process III having a higher intensity than the remaining
processes for 6 and the observation of an extra peak for 7 suggest
a separation of the redox peaks III and III0 for 7 which were
overlapped as III for 6. For complex 6, which is non-peripherally
substituted, there is less splitting of the orbitals hence less splitting
of the redox process compared to 7. Less splitting of the orbitals
suggests that there are lower interactions of the rings in 6, as also
observed in the UV–Vis spectra in Fig. 1, which shows more broad-
ening in 7 compared to 6. The assignments of the processes for 7
are similar to those of 6 (Table 1). Complex 6 is easier to oxidize
and more difficult to reduce compared to complex 7.
3.3. Spectroelectrochemical studies
The nature of the redox couples was probed via spectroelectro-
chemistry to confirm the above mentioned assignments. Fig. 4A
shows the application of potentials more negative than couple II
for complex 7. The starting spectrum in Fig. 4A is broader than ob-
served in Fig. 1 and shows a blue shifted band near 620 nm due to
aggregation at the concentrations used for the OTTLE cell. The
spectral changes in Fig. 4A shows a shift in the Q-band from 662
to 703 nm. This is accompanied by the formation of new peak cen-
tered at 469 nm, which is characteristic of CoIPc species [29]. Also
the shift in the Q-band to the red without a decrease in intensity is
typical of metal based processes in MPc complexes [29]. The spec-
tral changes in Fig. 4A show diffuse isosbestic points near 329, 380,
560 and 690 nm, suggesting more than two species in solution. The
spectral changes are attributed to central metal reduction in ball-
type complexes, where reduction occurs in both Pc units as fol-
lows: (CoIIPcꢀ2)2/[(CoIPcꢀ2)2]2ꢀ [34].
The number of electrons was calculated to be approximately
two, using Eq. (1)

526
M. Canlıca et al. / Polyhedron 30 (2011) 522–528
Table 1
Peak potentials (Ep or E ) for the redox processes of complexes 6 and 7 in DMSO containing 0.1 M TBABF4.
½
Complex 6
ꢀ1.40 (I0)
Complex 7
Complex 8a
Complex 9b
[(CoIPcꢀ3)2]4ꢀ/[(CoIPcꢀ4)2]6ꢀ
ꢀ0.90 (I)
[(CoIPcꢀ2)2]2ꢀ/(CoIPcꢀ3)2]4ꢀ
ꢀ0.46 (II)
(CoIIPcꢀ2)2/[(CoIPcꢀ2)2]2ꢀ
+0.16 (III)
[(CoIIIPcꢀ2)2]2+/(CoIIPcꢀ2
ꢀ1.03 (I)
ꢀ1.36
ꢀ1.45
2ꢀ
2ꢀ
[(CoIPcꢀ2)2]2ꢀ/[(CoIPcꢀ3)2]4ꢀ
ꢀ0.39 (II)
(CoIPcꢀ2)ꢀ/(CoIPcꢀ3
)
(CoIPcꢀ2)ꢀ/(CoIPcꢀ3
)
ꢀ0.27
ꢀ0.38
(CoIIPcꢀ2)2/[(CoIPcꢀ2)2]2ꢀ
+0.2 (III) and +0.44 (III0)
CoIIPcꢀ2/(CoIPcꢀ2
+0.56
)
CoIIPcꢀ2/(CoIPcꢀ2
+0.49
)
ꢀ
ꢀ
)
2
[(CoIIIPcꢀ2)2]2+/(CoIIPcꢀ2
)
2
(CoIIIPcꢀ2)+/CoIIPcꢀ2
+1.03
(CoIIIPcꢀ2)+/CoIIPcꢀ2
+0.92
+1.05 (IV)
+1.35 (IV)
[(CoIIIPcꢀ1)2]4+/[(CoIIIPcꢀ2)2]2+
[(CoIIIPcꢀ1)2]4+/[(CoIIIPcꢀ2)2]2+
(CoIIIPcꢀ1
)
2+/(CoIIIPcꢀ2
)
(CoIIIPcꢀ1 2+/(CoIIIPcꢀ2
) )
+
+
a
The data for non-peripheral tetra 3,4-(methylendioxy)-phenoxy substituted cobalt phthalocyanine monomer are from Ref. [31] and in DMF containing 0.1 M TBABF4.
The data for peripheral tetra 3,4-(methylendioxy)-phenoxy substituted cobalt phthalocyanine monomer are from Ref. [31] and in DMF containing 0.1 M TBABF4.
b
Fig. 4. UV-Vis spectral changes observed for the reduction of complex 7 at potentials of: (A) couple II (ꢀ0.40 V); (B) couple I (ꢀ1.1 V); (C) process III (0.50 V); (D) process IV
(1.4 V). The initial spectrum (dashed line) of B is the final spectrum of A. The initial spectrum (dashed line) of D is the final spectrum of C. The dotted line shows the first
spectrum in all figures. Solvent: DMSO containing 0.1 M TBABF4 supporting electrolyte.
Q ¼ nFVC
ð1Þ
rings, as evidenced also by the broadening of the UV–Vis spectra
in Fig. 1, for 7 in particular. Application of a zero potential regener-
ated 80% of the original complex, which emphasises the reversibil-
ity of this process.
where n, F, V and C are the number of electrons transferred, Fara-
day’s constant, volume and concentration of the electroactive spe-
cies respectively. For the calculation of the number of electrons,
three independent experiments were performed, giving an average
of two electrons. The observation of two-electron processes in the
homo-dinuclear ball-type CoPc complex 7 suggests that there is
no considerable interaction between the two Pc rings and that the
two rings are reduced and oxidized at the same potentials. How-
ever, the lack of clear isosbestic points suggests that there some
unresolved splitting of the redox processes, resulting in some mixed
valence complexes which absorb at slightly different wavelengths.
The unresolved splitting suggests some interaction between the
Application of more negative controlled potentials (ꢀ1.1 V, pro-
cess I) for 7, Fig. 4B, show a collapse in the Q-band with a shift in
the band at 469 to 491 nm and formation of new bands between
500 and 600 nm. The formation of new weak bands in the 500–
600 nm area is characteristic of ring based reduction and the for-
mation of Pcꢀ3 species [35]. There is a lack of clear isosbestic points
in Fig. 4B, showing the involvement of more than two species as
discussed for process II above. We suggest that the spectral
changes are due to the reduction of both rings, forming the
[(CoIPcꢀ3)2]4ꢀ species [34]. The number of electrons transferred

M. Canlıca et al. / Polyhedron 30 (2011) 522–528
527
the involvement of only two species. The total number of electrons
was calculated to be two at the end of the electrolysis. We assign
process III to [(CoIIIPcꢀ2)2]2+/[CoIIPcꢀ2)2.
A
Upon proceeding to more positive potentials (1.4 V), all the
bands decreased in intensity, with only a small increase in the
500 nm area, typical [35] of ring oxidation, Fig. 4D. It was not pos-
sible to calculate exactly the number of electrons involved. How-
ever the irreversible process IV may tentatively be assigned to
the redox couple [(CoIIIPcꢀ2)2]2+/[(CoIIIPcꢀ1)]4+, where both rings
are being oxidized.
Fig. 5A shows the spectral changes observed on application of
the potentials of couple II for complex 6. The Q-band shifts from
682 to 709 nm, but with diffuse isosbestic points. The lack of clear
isosbestic points suggest that there are more than two species in
solution, and hence imply the presence some unresolved splitting
of the redox processes and the possibility of some mixed valence
complexes which absorb at slightly different wavelengths, as ob-
served for complex 7. We assign process II to (CoIIPcꢀ2)2/
[(CoIPcꢀ2)2]2ꢀ. The subsequent reduction will be at the ring.
Fig. 5B shows the spectral changes observed on application of the
potentials of process III for complex 6. The spectral changes consist
of a shift in the Q-band from 684 to 693 nm, with an increase in
intensity. These spectral changes are typical of metal oxidation in
CoPc complexes [30]. There are clear isosbestic points at 684,
500 and 339 nm, showing that only two species are present in
solution. The number of electrons obtained following the oxidation
was still two, suggesting that the two rings are oxidized at exactly
the same potential for 6. Fig. 5C shows the spectral changes ob-
served on application of the potentials of process IV for 6. There
is a decrease in the Q-band and the formation of a weak band near
500 nm, confirming ring oxidation.
B
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
300
400
500
600
700
800
4. Conclusions
Wavelength/ nm
The syntheses and electrochemical properties of new symmet-
rically substituted (at non-peripheral (6) and peripheral (7) posi-
tions) ball-type CoPc derivatives are presented. The effects of the
position of the substituent on these properties were explored. Both
complexes exhibits ligand and metal based redox processes. Com-
plex 6, which is non-peripherally substituted, is easier to oxidize
and more difficult to reduce than 7. The interaction between the
two CoPc rings is less severe for 6 as compared to 7.
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
C
Acknowledgements
This work was supported by the Department of Science and
Technology (DST) and the National Research Foundation (NRF),
South Africa through DST/NRF South African Research Chairs Initiative
for the Professor of Medicinal Chemistry and Nanotechnology, as
well as Rhodes University.
300
400
500
600
700
800
Wavelength/nm
Fig. 5. UV/Vis spectral changes observed for the reduction of complex
6 at
Appendix A. Supplementary data
potentials of: (A) couple II (ꢀ0.50 V); (B) process III (0.30 V); (C) process IV (1.1 V).
The initial spectrum (dashed line) of C is the final spectrum of B. The dotted line
shows the first spectrum in all figures. Solvent: DMSO containing 0.1 M TBABF4
supporting electrolyte.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2010.11.028.
was found to be two using Eq. (1), and again using three indepen-
dent experiments.
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