Non-covalent associates of metal phthalocyanines: the role of axial ligand and catalytic activity

Article abstract of DOI:10.1007/s11172-016-1572-z

The problem about the role of the coordinated exobidentate ligand in the formation of dimeric structures of sulfonated cobalt phthalocyanine derivatives is considered. The size of the peripheral substituent of the macrocycle and remoteness of the ionogenic group from the macrocycle play the key role in the formation of dimers of a specified type. As the extension of the peripheral substituent of the macrocycle increases, the stability of dimeric associates of the Н-type decreases and that of the associates formed due to the donor—acceptor interaction (J- and Т-aggregates) increases. The latter can be stabilized by hydrogen bonds at the periphery of the macromolecule. A series of catalytic activity of the macrocycles under study is inverted compared to the series of stability of the H-dimers.

Full text of DOI:10.1007/s11172-016-1572-z

Russian Chemical Bulletin, International Edition, Vol. 65, No. 9, pp. 2220—2228, September, 2016
2220
Nonꢀcovalent associates of metal phthalocyanines:
the role of axial ligand and catalytic activity*
A. S. Vashurin
Ivanovo State University for Chemistry and Technology, Institute of Chemistry of Macroheterocyclic Compounds,
7 Sheremetevskii prosp., 153000 Ivanovo, Russian Federation.
Fax: +7 (493) 241 7995. Eꢀmail: asvashurin@mail.ru
The problem about the role of the coordinated exobidentate ligand in the formation of
dimeric structures of sulfonated cobalt phthalocyanine derivatives is considered. The size of the
peripheral substituent of the macrocycle and remoteness of the ionogenic group from the
macrocycle play the key role in the formation of dimers of a specified type. As the extension of
the peripheral substituent of the macrocycle increases, the stability of dimeric associates of the
Нꢀtype decreases and that of the associates formed due to the donor—acceptor interaction
(Jꢀ and Тꢀaggregates) increases. The latter can be stabilized by hydrogen bonds at the periphery
of the macromolecule. A series of catalytic activity of the macrocycles under study is inverted
compared to the series of stability of the Hꢀdimers.
Key words: CoII phthalocyanines, liquidꢀphase system, selfꢀassociation, ligand, molecular
complex, stability, mercaptane, oxidation.
Waterꢀsoluble derivatives of metal porphyrins and their
some ligands from the coordination mode of the macroꢀ
cycle and secondary interactions at the periphery.16 A comꢀ
bination of structural and coordination methods in the
variation of the associative equilibrium in liquidꢀphase
systems based on metallocomplex porphyrins and their
structural analogs seems to be most promising, since this
makes it possible to retain the properties of the macroꢀ
cycle upon the production of catalytically active matꢀ
erials.17,18
Sulfonic acids are of special interest among waterꢀsolꢀ
uble derivatives of metal phthalocyanines, which is priꢀ
marily caused by their solubility in a broader range of pH
compared to similar carboxylic acids that are soluble, as
a rule, only in strongly alkaline media.19
In solutions, metal phthalocyanines mainly form homoꢀ
aggregates due to column packing of macrocycles by overꢀ
lapping πꢀelectronic systems and highly ordered aggreꢀ
gates of the ladder type (Jꢀaggregates) because of the inꢀ
teraction of the coordination mode of one macromolecule
and peripheral substituent of another macromolecule.20—22
Chain Tꢀaggregates are formed in particular cases. The
influence of the association type of metal phthalocyanines
on their catalytic activity in the reactions was not exactly
established. In this case, the mechanism of the process
plays the determining role. For example, for the catalytic
oxidation of mercaptanes to disulfides, aggregation in
which the coordination mode of the macrocycle is inꢀ
volved decreases, as a rule, catalytic activity.23—25 Simulꢀ
taneously, an increase in the number of ionogenic groups
favors the dissociation of Hꢀaggregates,26 which does not
structural analogs, such as phthalocyanines and porphyrꢀ
azines, exhibit unique catalytic,1,2 photochemical,3,4 and
biological5,6 properties, determined by the ability of these
compounds to selfꢀorganization and nonꢀcovalent interꢀ
action with ligands7,8 in solutions. Processes of selfꢀaggreꢀ
gation of tetrapyrrole macroheterocyclic compounds are
used for the preparation of supramolecular nanostructures and
materials with specified properties for technology and medꢀ
icine and for modeling complicated natural processes.9—12
The processes of selfꢀassembling of metal phthaloꢀ
cyanines and metal porphyrins in solutions can be conꢀ
trolled and both due to a change in the structure of the
periphery of the macrocyclic complex and by the variation
of the parameters of the medium in which the complex
exists. The modern possibilities of synthetic chemistry
make it possible to prepare phthalocyanine macrocycles
with the almost inexhaustible variety of peripheral substitꢀ
uents.13—15 However, when preparing supramolecular porꢀ
phyrin systems, one should take into account that the
solubility of these compounds depends strongly on the
nature of substituents, because the solvation of the macroꢀ
cycle is restricted.15 The control of associative equilibria
of metal phthalocyanines in solutions only due to complex
formation with donor organic molecules also results in
additional restrictions, because it is difficult to remove
* Based on the materials of the International Congress on the
Heterocyclic Chemistry "KOSTꢀ2015" (October 17—23, 2015,
Moscow, Russia).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2220—2228, September, 2016.
1066ꢀ5285/16/6509ꢀ2220 © 2016 Springer Science+Business Media, Inc.

Associates of metal phthalocyanines
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 9, September, 2016 2221
Cobalt phthalocyaninate formed was extracted from the reaction
mixture with DMSO and precipitated from the extract with abꢀ
solute ethanol. The obtained precipitate was filtered off and
washed with ethanol in the Sohxlet apparatus. The final purificaꢀ
tion was conducted by chromatography on silica gel M 60
(DMF—H2O (1 : 1 vol/vol) mixture as an eluent). The yield was
0.39 g (54%). A blueꢀgreen powder was highly soluble in water,
a DMF—H2O mixture, DMSO, and an aqueous solution of alkali.
Found (%): С, 58.42; Н, 2.70; N, 7.62; S, 8.80. C72H40N8S8O16Со.
Calculated (%): С, 59.22; Н, 2.74; N, 7.68; S, 8.80. IR (KBr),
ν/cm–1: 1045 (—S=O), 1103 (—S=O), 1205 (Ar—O—Ar).
Cobalt tetraꢀ4ꢀ[(6,8ꢀdisulfoꢀ2ꢀnaphthyl)oxy]phthalocyanꢀ
inate (СоРсIII) was synthesized by the above presented proceꢀ
dure using 4ꢀ[(6´,8´ꢀdisulfoꢀ2´ꢀnaphthyl)oxy]phthalonitrile poꢀ
tassium salt (1.01 g). The yield was 0.53 g (59%). A blueꢀgreen
powder was highly soluble in water, a DMF—H2O mixture,
DMSO, and an aqueous solution of alkali. Found (%): С, 48.32;
Н, 2.20; N, 6.23; S, 14.43. C72H40N8S8O28Со. Calculated (%):
С, 48.57; Н, 2.25; N, 6.30; S, 14.39. IR (KBr), ν/cm–1: 1039
(—S=O), 1103 (—S=O), 1210 (Ar—O—Ar).
always lead to an increase in the catalytic activity because
of the formation of Тꢀ and Jꢀaggregates.
In this work, we attempted to establish a relationship
between the structure of the macroheterocyclic molecule,
the type of formed associates, and its catalytic activity
depending on the nature of the coordinated ligand using as
examples the sulfonated derivatives of cobalt phthaloꢀ
cyanine of a regularly changed structure.
Experimental
Cobalt 2,9,16,23ꢀtetrakis(1ꢀbenzotriazolyl)ꢀ3,10,17,24ꢀtetraꢀ
kis(4ꢀsulfoꢀ1ꢀnaphthoxy)phthalocyaninate (СоРсIV) was syntheꢀ
sized using an earlier described procedure30,31 by the sulfonation
of the starting phthalocyanine. A solution of cobalt 2,9,16,23ꢀ
tetrakis(1ꢀbenzotriazolyl)ꢀ3,10,17,24ꢀtetrakis(1ꢀnaphthoxy)ꢀ
phthalocyaninate (160 mg, 0.1 mmol) in a mixture of chlorosulꢀ
fonic acid (2 mL, 18 mmol) and thionyl chloride (2 mL, 18 mmol)
was stirred for 2 h at 20 °С. Then the reaction mixture was poured
on ice mixed with sodium chloride (0.1 weight fraction). The
obtained precipitate was collected on the Schott filter and dried
in a drying box over H2SO4 (conc.) for 72 h. Sulfochlorides were
extracted with acetone, and then the preparation was dried. Then
sulfochlorides were hydrolyzed by reflux in water. The yield of
the final product was 82—85%. An additional purification was
carried out by chromatography (silica gel M 60 as a sorbent,
DMF as an eluent). Found (%): С, 52.00; H, 4.05; N, 12.43;
S, 5.36. C98H52N20S4O16Со•16Н2О. Calculated (%): С, 52.01;
H, 3.82; N, 12.64; S, 5.78. IR (KBr), ν/cm–1: 745 (C—N);
1045 (N=N); 1230 (Ar—O—Ar); 1060 (С—S); 1150—1190
(S=O, SO3H). MS (MALDIꢀTOF) m/z: 1932.71 [M + 4 H]+.
1Н NMR (DMSOꢀd6), δ: 7.45 (Ar—H(5)), 7.94 (Ar—H(4)),
8.07 (Ar—H(6)), 8.29 (Ar—H(3)) all triazole groups;
7.64 (Ar—H(8)), 7.73 (Ar—H(7)), 7.85 (Ar—H(11)), 8.18
(Ar—H(10)), 8.53 (Ar—H(9)), 8.85 (Ar—H(12)) all naphthoxy
groups; 8.97 (SO3H).
Compound
CoPcI
R1
H
R
SO3H
CoPcII
H
H
CoPcIII
CoPcIV
CoPcV
Cobalt tetrasulfophthalocyaninate (СоРсI). A commercial
sample with 99.9% purity (Sigma Aldrich) was used. Two abꢀ
sorption maxima are detected in the electronic absorption specꢀ
trum of an aqueous solution of СоРсI (рН 7.2). UV (H2O),
Cobalt 2,9,16,23ꢀtetrakis(1ꢀbenzotriazolyl)ꢀ3,10,17,24ꢀtetraꢀ
kis(1,6ꢀdisulfoꢀ2ꢀnaphthoxy)phthalocyaninate (СоРсV) was synꢀ
thesized similarly to СоРсIV. Cobalt 2,9,16,23ꢀtetrakis(1ꢀbenzoꢀ
triazolyl)ꢀ3,10,17,24ꢀtetrakis(2ꢀnaphthoxy)phthalocyaninate
was taken as the starting compound for sulfonation. Found (%):
С, 42.29; H, 4.42; N, 9.73; S, 9.36. C96H52N20S8O28Со•32Н2О.
Calculated (%): С, 42.29; H, 4.14; N, 9.91; S, 9.08. IR (KBr),
ν/cm–1: 741 (C—N); 1049 (N=N); 1262 (Ar—O—Ar);
1091 (С—S); 1158 (S=O, SO3H). MS (MALDIꢀTOF), m/z:
λ
max/nm: 630 (dimer), 667 (monomer). IR (КBr), ν/cm–1: 1720,
1632, 1502, 1452, 1489, 1409, 1379, 1134, 1192—1197, 1049,
1032—1035, 935, 839—855, 770, 700, 618. The intense bands at
700, 1032—1035, and 1192—1197 cm–1 are caused by the
sulfo groups present in the molecule. The absorbance at 839—855
is due to the С—Н vibrations of the 1,2,4ꢀsubstituted benzene
cores added to the porphyrazine ring.27 1Н NMR (CDCl3), δ:
7.82 (Ar—H), 8.31 (Ar—H), 8.49 (Ar—H).
Cobalt tetraꢀ4ꢀ[(6ꢀsulfoꢀ2ꢀnaphthyl)oxy]phthalocyaninate
(СоРсII) was synthesized using a known procedure28,29 from the
corresponding nitrile. A mixture of 4ꢀ[(6´ꢀsulfoꢀ2´ꢀnaphthyl)ꢀ
oxy]phthalonitrile potassium salt (0.78 g) and anhydrous cobalt
chloride (0.065 g) was heated with stirring for 60 min to 190—195 °С.
1
2248.82 [M]+. Н NMR (DMSOꢀd6), δ: 7.48 (Ar—H(5)), 7.75
(Ar—H(4)), 7.94 (Ar—H(6), Ar—H(7)), 8.14 (Ar—H(3)) all benzoꢀ
triazole groups; 8.33 (Ar—H(2), macroring); 8.72 (Ar—H(8),
Ar—H(9), Ar—H(11), benzonaphthoxy groups); 8.83, 8.81 (SO3H).
Commercial reagents 1,4ꢀdiazabicyclo[2.2.2]octane (DABCO),
pyrazine (Pz), creatinine (Сrt), 2ꢀmercaptoethanol (Sigma Aldrich),
and sodium N,Nꢀdiethylcarbamodithiolate (DTC) (KhimMed,
Russia) with purity ≥99.9% were used as received.

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Vashurin
The stability constants (Ks) of the molecular complex were
calculated on the basis of a change in the absorbance of the
solution in the range of the Q band16,32
The procedure for the determination of the current concenꢀ
tration of the substrate, conversion, and yield of disulfide was
described in detail earlier.35,36
Electronic absorption spectra were recorded on a Unico 2800
spectrophotometer (USA) in a spectral range of 200—1000 nm.
Solutions for absorption spectra recording were placed in quartz
cells with a thickness of 2, 5, or 10 mm and maintained at
a constant temperature. Elemental analysis was carried out on
a Flash HCNSꢀOEA 1112 chromatographic analyzer (Germany).
The helium flow rate was 140 mL min–1, the temperature in the
reactor was 1173 K, the oxygen flow rate was 250 mL min–1, and
the storage time was 12 s. IR spectra were recorded in the FTꢀIR
mode on an Avatar 360 spectrometer (USA) in a frequency range
of 400—4000 cm–1. NMR spectra were obtained on a Bruker
Avanceꢀ500 spectrometer (Germany) at a working frequency of
500 MHz using TMS as an internal standard. When the NMR
spectra of metal phthalocyanines were recorded, the degree of
oxidation of the macrocycle was stabilized according to known
methods.37 The mass spectrum was obtained on an Axima
MALDIꢀTOF spectrometer (Shimadzu, Japan).
.
The equilibrium concentration of the molecular complex
was calculated by the equation
(1)
where cCoPс·L is the equilibrium concentration of the molecular
complex; c0
is the initial concentration of the macrocycle;
CoPс
and A0, Ap, and Ak are the absorbance of the Q band of the initial
solution, solution at the current concentration of the ligand, and
final solution, respectively. The concentration of the free ligand
was determined by the equation
(2)
Results and Discussion
Taking into account Eqs (1) and (2), the equation for the
calculation of the stability constant takes the form
Earlier, when studying the associative state СоРсI—
СоРсV in water, we established that the monomer—assoꢀ
ciate equilibrium was shifted toward the existence of the
macrocycle in solution in the form of dimers.32,38,39 The
dimerization of СоРсI—СоРсIV in aqueous solutions proꢀ
ceeds predominantly via the Нꢀtype.38 The introduction
of an additional sulfo group in the case of СоРсV results in
the equilibration in a solution between the Нꢀ and Jꢀagꢀ
gregates.31 The stability of the dimeric associates in water
decreases in the order СоРсV > СоРсI > СоРсII >
> СоРсIV > СоРсIII. This sequence shows the influence
of the nature of peripheral substituents on association proꢀ
cesses. The position of СоРсV in this order seems interestꢀ
ing. In spite of the presence of eight sulfo groups in the
composition of this macrocycle, the stability of its associꢀ
ates turned out to be the highest, confirming the assumpꢀ
tion about the ambiguous influence of the nature of peꢀ
ripheral substituents on the association processes of metal
phthalocyanines in solutions.
The study was carried out under the conditions of a ligand
excess over metal phthalocyanine and, therefore, the equilibriꢀ
um concentration of the ligand was assumed to be equal to its
initial concentration, which simplified the calculation procedure
The stability constant (β) of the sandwich associates was
determined from the data of electron absorption spectra at two
wavelengths (before and after the shift)33 and calculated by the
equation
For the coordination of monodentate molecular ligands,
such as pyridine and piperidine, the associative equilibriꢀ
um shifts toward monomerization to 90% due to the forꢀ
mation of 1 : 1 molecular complexes.38 High stability of
these complexes in solutions does not allow one to directly
form ordered phthalocyanine structures of a specified type.
However, changes appear in the associative state of the
macrocycle with an increase in the specific solvating abilꢀ
ity of the medium. Therefore, the replacement of pyridine
by pyrazine containing two nitrogen atoms accessible for
the coordination interaction with the Нꢀdimer is of cerꢀ
tain interest.
where λ is the initial wavelength, λ is the wavelength after the
1
2
shift of the absorption maximum, ΔА0 is the maximum change in
the absorbance of the solution at a given wavelength, and ΔАi is
the change in the absorbance at a given wavelength at a given
concentration.
The catalytic activity of the studied metal phthalocyanines
was tested in homogeneous catalysis of the oxidation of aqueꢀ
ous—alkaline solutions (рН 9—10) of 2ꢀmercaptoethanol and
DTC with air oxygen. The oxidation occurs with the formation
of the corresponding disulfide34,35 (Scheme 1).
Scheme 1
Evidently, the following equilibria can be observed in
the system upon the addition of pyrazine to an aqueous
solution of СоРсI—V:
2 RSH + 0.5 O2
RSSR + H2O.

Associates of metal phthalocyanines
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 9, September, 2016 2223
A
(CoPc)2 + L
(CoPc)2 + 2 L
(CoPc)2 + L
CoPc•L + CoPc,
2 CoPc•L,
(3)
(4)
(5)
1.8
1.5
1.2
0.9
0.6
0.3
673
2
CoPc•L•CoPc.
665
625
The electronic absorption spectrum of an aqueous soluꢀ
tion of СоРсI after titration with pyrazine (Fig. 1) exhibits
a consecutive decrease in the absorbance intensity and
a hypsochromic shift (by 20 nm) of the band of the dimeric
form of the macrocycle (625 nm) along with an increase
in the intensity and a bathochromic shift (to 10 nm) of the
absorption band of the monomer. Isosbestic points are
also detected in the spectra. The composition of the comꢀ
plex calculated by the semilogarithmic method40 gives the
СоРсI : Pz ratio equal to 1 : 1. In other words, in this
system the associative equilibrium is shifted due to the
existence of СоРсI monomers as molecular complexes
with pyrazine in the system, which corresponds to equilibꢀ
rium (4). The stability constant of the molecular complex
is presented in Table 1.
An increase in the size of the peripheral substituent in
the phthalocyanine macrocycle and the removal of the
sulfo group result in a change in the degree of association.
Two stages of the process occurred during the titration of
an aqueous solution of СоРсII by pyrazine can spectrally
be distinguished. At the first stage, the dimerization is
enhanced and a new type of associates is formed, which
appears in the absorption spectrum as an increase in the
intensity of the absorption band of the dimeric form of
СоРсII, a significant broadening of this band, and its baꢀ
thochromic shift of 15 nm (Fig. 2). These spectral changes
indicate a coordination interaction. The СоРсII : Pz ratio
obtained by the Bent—French method40 is 1 : 0.48 (or
∼2 : 1 based on the entire ligand molecule). In this case,
the transformation of the Нꢀaggregates of СоРсII into
sandwich type dimers is most probable, and equilibrium
(5) takes place in the system. At the second stage (when
pyrazine is accumulated in the system), the monomerizaꢀ
tion of СоРсII occurs, which is related to the coordinaꢀ
1
605
500 550 600 650 700 750 800 850 λ/nm
Fig. 1. Changes in the absorption spectra upon the titration of
an aqueous solution of СоРсI (5.26•10–5 mol L–1) with pyrꢀ
azine: 1, initial solution and 2, after titration with pyrazole
(сPz = 16.3•10–3 mol L–1). T = 298.15 K.
tion of the second ligand by the sandwich dimer to form
unstable complexes that give a 1 : 1 complex upon decomꢀ
position. The composition of the intermediate complexes
calculated from the spectral data by the semilogarithmic
method has the 2 : 2 ratio.
The modification of the periphery of the phthaloꢀ
cyanine macrocycle by an additional triazole fragment does
not induce substantial changes in the dimerization type.
The chemical shift of the protons of sulfo groups in СоРсIV
indicates that the macrocycle exists in the molecular form
in DMSO. The chemical shift of the protons of the sulfo
group is not detected in deuterated water, indicating the
ionized form of the macrocycle in the solution. In addiꢀ
tion, the position of the chemical shifts of the Ar—H proꢀ
tons exhibits an upfield shift. This indicates a strong assoꢀ
ciation due to π—πꢀoverlapping of two macrocycles, adꢀ
ditionally due to the interaction at the periphery of the
macromolecule. For an aqueous solution of СоРсIV, specꢀ
tral changes similar to those occurring for СоРсII are
observed upon the addition of pyrazine, and the final comꢀ
plex formation product is the 1 : 1 СоРсIV•Pz complex.
Table 1. Stability constants of the sandwich dimers (β) and molecular complexes (Ks) and the catalytic activity for
the oxidation of DTC (kapp) for СоРс in aqueous media at 298.15 K*
Macrocycle
Pz
Сrt
Ks/L mol–1
kapp•105/s–1
χ (%)
β/L mol–1
Ks/L mol–1
(2 : 1)
СоРсI
Does not form
21300 50
Does not form
71050 50
13800 50 (1 : 1)
11271 2 (2 : 2)
16700 (1 : 1)
11230 2 (2 : 2)
11127 50 (1 : 1)
97020 50 (2 : 5)
8700 50 (1 : 1)
2100 80 (1 : 1)
5500 20 (1 : 1)
2800 60 (1 : 2)
17.9 0.2
15.4 0.1
12.6 0.1
19.8 0.2
82
80
79
73
СоРсII
СоРсIII
СоРсIV
СоРсV
Does not form
Does not form
17.5 0.1
84
* The ratio of СоРс to Pz (or Сrt) in the complex composition is given in parentheses.

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Vashurin
A
which is caused by different electronꢀdonor abilities of
pyrazine and DABCO in the dimer composition. The staꢀ
bility of the monoligand axial complexes of the studied
СоРс correlates with the stability of dimers of the sandꢀ
wich type. It was experimentally found that for complex
formation with DABCO the shift of the monomer—dimer
equilibrium is achieved due to the primary formation of
1 : 1 axial complexes, whereas dimers of the sandwich type
are formed first in the case of pyrazine. In addition, the
geometric factor plays an important role in the formation
of dimers. The planar pyrazine molecule enters the coorꢀ
dination mode of the Нꢀdimer more easily coordinating
by two phthalocyanine molecules, whereas the bulky
DABCO molecule experience spatial hindrances.
An increase in the number of functional groups at the
periphery of the macromolecule should enhance the effect
of electrostatic repulsion of the peripheral substituents
upon the formation of stack dimers. The lowest stability of
the Нꢀassociates is observed for complex СоРсIII.41
Therefore, high stability of axial complexes with donor
ligands can be expected.
a
0.4
0.3
0.2
0.1
633
615
1
480 540 600 660 720 780 840 λ/nm
A
b
0.5
0.4
0.3
0.2
0.1
670
630
The titration of an aqueous solution of СоРсIII with
pyrazine induces changes in the absorption spectra that
characterize the shift of the associative equilibrium toꢀ
ward monomeric forms (Fig. 3). However, it should be
mentioned that the presence of families of isosbestic points
in the spectrum characterizes the parallel occurrence of
several processes. Obviously, no dimers of the sandwich
type are formed in the case. The stability of monoligand
complex СоРсIII•Pz coincides with the stability of similar
complex СоРсIII•DABCO in an aqueous solution, which
can be explained by the formation of a structural cavity
upon the displacement of water from the internal coordiꢀ
nation sphere of metal phthalocyanine for entering the
DABCO molecule. Evidently, this effect is less pronounced
in the case of planar pyrazine. This favors the incomplete
displacement of the water molecules solvating the macroꢀ
cycle, which results in the compensation of the electronꢀ
480 540 600 660
720 780
840 λ/nm
Fig. 2. Changes in the absorption spectra upon the titration of an
aqueous solution of СоРсII (5.91•10–5 mol L–1) with pyrazine:
(а) to the achievement of сPz = 2.3•10–4 mol L–1 and (b) сPz
= 2.3•10–4—2.3•10–2 mol L–1. T = 298.15 K.
=
An increase in the stability of the sandwich dimer of
СоРсIV compared to a similar dimer for СоРсII is due,
most probably, to the position of the functional group in
the peripheral substituent. The quantum chemical modelꢀ
ing of the sandwich dimer by the HF/6ꢀ31G method shows
that the macrocyclic molecules are arranged not in paralꢀ
lel but at an angle, the value of which ranges from 20° to
26° depending on the macrocycle. Evidently, in the case
of the location of the ionogenic groups at the ends of the
peripheral substituent (СоРсII), the effect of the electroꢀ
static repulsion will be more noticeable, which influences
the stability of the sandwich dimers. In the case of СоРсI,
this effect probably exceeds the force of the coordination
interaction of the axial complex СоРсI•Pz with the second
macrocycle molecule, resulting in the absence of this type
of associates in an aqueous solution.
A
0.4
0.3
0.2
0.1
The replacement of pyrazine by a DABCO molecule
results in a change in the stability of the sandwich type
associates. For example, dimer СоРсII•DABCO•СоРсII
(β = 52•103 L mol–1 41
)
is more stable than a similar assoꢀ
500
550
600
650
700
750 λ/nm
ciate for СоРсIV (β = 28.4•103 L mol–1).42 In the case of
complex formation with DABCO, СоРсI is capable of
forming dimers of the sandwich type (β = 8•103 L mol–1),41
Fig. 3. Changes in the absorption spectra upon the titration of an
aqueous solution of СоРсIII (4.92•10–5 mol L–1) with pyrazine
(сPz = 0—1.8•10–2 mol L–1). T = 298.15 K.

Associates of metal phthalocyanines
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 9, September, 2016 2225
donor properties of the ligand by the solvent. In addition,
the ability of DABCO to form intrinsic associates and
associates with the solvent43 also affects this process.
A more pronounced monomerization upon the coorꢀ
dination of the axial ligand was expected for СоРсV due to
the triazole fragment than that for СоРсIII. However,
other spectral changes are observed in the absorption specꢀ
trum (Fig. 4). The initial state of СоРсV in the form of
Jꢀaggregates favors the competition of the ligand for the
central metal cation in the phthalocyanine composition.
The existence of large spaces in the Jꢀaggregate compared
to those in the Hꢀdimer is convenient for the incorporaꢀ
tion of the ligand molecule into the associate cavity. The
changes observed in the absorption spectrum (see Fig. 4)
are related to the enhancement of association and transiꢀ
tion of one type of dimers to another. The appearance of a
small shoulder at 460 nm indicates the partial charge reꢀ
distribution on the central cation of the phthalocyanine
macrocycles in the dimer composition. Under these conꢀ
ditions, this corresponds to the transition from formal
СоIIРс to СоРсIII with an incomplete change in the residꢀ
ual positive charge on the central cation, which is an adꢀ
ditional confirmation of nonꢀadditivity of charges in
the associated structures of metal porphyrins and metal
phthalocyanines.44 Similar changes were also observed for
complex formation with DABCO, indicating similarity of
these processes. The composition of the СоРсV·Pz associꢀ
ate is 2 : 5. Such an unexpected composition of the comꢀ
plex cannot be explained so simply. In this case, two routes
can presumably take place. In the first case, the dimer
includes the solvent molecules that specifically bind (eviꢀ
dently, through a hydrogen bond) pyrazine molecules. In
the second case, the formation of an associate of this comꢀ
position can be related to the transition of cobalt to an
increased oxidation state. An insufficient compensation of
the residual positive charge of the metal cation in the agꢀ
gregate composition will result in the coordination of two
pyrazine molecules at one side of the phthalocyanine
macrocycle and in binding two such complexes into an
associate by the fifth (bridging) ligand molecule. The exꢀ
istence of extracomplexes of tetrapyrrole macroheteroꢀ
cycles with ligands coordinated at one side is well known.16,45
The value of stability constant of the obtained associate is
more characteristic of the second route of dimerization.
The interaction of СоРсV with DABCO in solution afꢀ
fords the structures (1 : 2) transformed into stable associꢀ
ates of the sandwich type (β = 34.2•103 L mol–1). No
principal changes are observed in weakly coordinating solꢀ
vents, such as ethanol, and only the stage related to the
process of solvent transliganding to pyrazine.42,46
In the case of the ligands with nonequivalent reaction
centers, the association can be controlled by the variation
of the coordination ability of the ligand. For proton miꢀ
gration in solution, a creatinine molecule can exist as a
mixture of three tautomeric forms (1—3, Scheme 2).
Scheme 2
Obviously, tautomeric form 2 acts as an intermediate
one between the acidic (1) and basic (3) forms. The quanꢀ
tum chemical modeling of the tautomeric forms of creatiꢀ
nine in the HF (3ꢀ21G and 6ꢀ31G basis sets), B3LYP,
and PBE0 (6ꢀ31G** basis set) approximations made it
possible to establish that aminic form 3 is predominantly
formed for creatinine. These results are consistent with
the known assumption about the degree of tautomerizaꢀ
tion of creatinine in solutions and in the crystalline state.47
The 1Н NMR spectrum (δ, ppm: 2.95 (CH3), 3.96 (CH2),
4.7 (NH2)) detected for a solution of creatinine in D2O
confirms the assumption about the predominant existence
of tautomeric form 3 in the solution, which agrees with
the known results.48—50
The changes corresponding to the dissociation of
Нꢀaggregates and formation of molecular complexes are
observed in the absorption spectrum (Fig. 5) upon the
complex formation of Нꢀdimers of СоРсI and СоРсIII
with creatinine. The spectrum contains two isosbestic
points. It was found for both cases that metal phthalocyaꢀ
nine additionally coordinated one creatinine molecule. The
1H NMR spectrum exhibits the splitting of the signal of
the protons of the amino group of the creatinine molecule,
which shows different effect of the circular current of the
macrocycle on these protons. The band of vibrations of
the imine group undergoes transformation in the IR specꢀ
trum of the molecular complex for СоРсI and СоРсIII.
An array of the obtained data suggests that the creatinine
A
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
400
500
600
700
800 λ/nm
Fig. 4. Changes in the absorption spectra upon the titration of an
aqueous solution of СоРсV (7.99•10–5 mol L–1) with pyrazine
(сPz = 0—7.9•10–3 mol L–1). T = 298.15 K.

2226
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 9, September, 2016
Vashurin
A
crease in the number of associated forms is related to the
rearrangement of the Нꢀaggregate into a dimer of the sandꢀ
wich type. The presence of a shoulder in the absorption
spectrum in a range of 680 nm characterizes phthalocyanine
in the partially monomerized form. Evidently, this is
a molecular complex with creatinine. The isolation of the
contributions of the monomeric and associated forms by the
mathematical decomposition of the absorption spectrum
made it possible to estimate the stability of complex
СоРсII•Crt (see Table 1), which turned out to be several
times lower than those of similar complexes СоРсI and
СоРсIII.
2.4
2.0
1.6
1.2
0.8
0.4
672
630
611
In the case of structural modification of the phthaloꢀ
cyanine macrocycle by the triazole fragment, the tendency
observed for complex formation with nitrogenꢀcontaining
ligands in aqueous media is retained. Several stages are
observed in the absorption spectrum (Fig. 7) for the comꢀ
plex formation of СоРсIV, indicating a complicated charꢀ
acter of this process. At the first stage, the Нꢀassociates
interact with creatinine, resulting in the decomposition of
these dimers. However, no significant increase in the abꢀ
sorption band of the monomeric forms is observed. Unstable
equilibria of the associates of different types are observed
550
600
650
700
750 λ/nm
Fig. 5. Changes in the absorption spectra upon the titration of an
aqueous solution of СоРсI (7.58•10–5 mol L–1) with creatinine
to the molar ratio nСоРсI : nCrt = 1 : 200 at 298.15 K.
molecule is coordinated by the iminic nitrogen atom parꢀ
allel to the macrocycle plane with the stabilization of the
complex by the hydrogen bond between the intracyclic
nitrogen atom of the phthalocyanine macrocycle and the
proton of the amino group of creatinine. It is noteworthy
that the Q band is rather broadened for the formation of
complex СоРсI, and the relaxation effect related to the
formation of adducts of the molecular complex with the
solvent and/or free ligands appears in the range of the band
of the dimer (630 nm), which is not observed for СоРсIII.
This fact is evidently related to size effects of peripheral
substituents of the phthalocyanine macrocycles.
As already mentioned earlier, the removal of the ionoꢀ
genic group from the conjugated system of the macrocycle
decreases the influence of electronic effects of the substitꢀ
uents on the state of the coordination mode. For СоРсII,
the introduction of creatinine into the system does not
result in the dissociation of the associate (Fig. 6). An inꢀ
A
a
1.0
0.8
0.6
0.4
0.2
500
600
700
800
900 λ/nm
A
b
A
0.8
625
0.7
1.0
0.8
0.6
0.4
0.2
689
0.6
0.5
615
0.4
0.3
0.2
0.1
500
600
700
800
900
λ/nm
525
600
675
750
825
λ/nm
Fig. 7. Changes in the absorption spectra upon the titration of an
aqueous solution (pH 7.9) of СоРсIV (7.1•10–5 mol L–1) with
creatinine to the molar ratio nСоРсI : nCrt = 1 : 200 (а) and at the
nСоРсI : nCrt molar ratios from 1 : 200 to 1 : 250 (b).
Fig. 6. Changes in the absorption spectra upon the titration of an
aqueous solution of СоРсII (1.21•10–4 mol L–1) with creatiꢀ
nine (сСrt = 0—5•10–3 mol L–1) at T = 298.15 K.

Associates of metal phthalocyanines
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 9, September, 2016 2227
for the titration of СоРсIV with creatinine until the
achievement of the ligand : macrocycle molar ratio equal
to 0.7. As this molar ratio increases, 1 : 2 СоРсIV•Crt
molecular complexes are formed. A new process accomꢀ
panied by a change in the state of the chromophoric system
of СоРсIV is observed in the absorption spectrum (see
Fig. 7, b) when a 200ꢀfold molar excess of creatinine over
the macrocycle is achieved in the solution. It can be assumed
that for a ligand excess in the solution, when the additional
coordination of creatinine on the central cation is possible
no more, its specific interaction occurs with the peripheral
substituents, which favors the formation of filament assoꢀ
ciates. The modification of the peripheral substituent by
an additional sulfo group (СоРсV) results in processes
similar to those occurred during complex formation with
pyrazine with the only distinction that the Q band in the
absorption spectrum is split before the achievement of the
molar ratio СоРсV : Сrt = 1 : 0.4, which characterizes the
formation of a new type of associates involving creatinine.
However, these associates decompose as the amount of
the ligand in the solution increases.
An array of the data obtained shows the influence of
the nature of peripheral substitution on processes of assoꢀ
ciation and complex formation with the ligands. This inꢀ
fluence is primarily caused by the electronic effects of the
substituents exerted on the conjugated πꢀsystem of the
macrocycle, which results, in turn, in different states of
the coordination mode. At the same time, the dimensionꢀ
al factor is also significant for the formation of the space
around the central cation of the phthalocyanine macroꢀ
cycle in the dimer composition. The obtained experimenꢀ
tal data on the stability of the molecular complexes with
the axial ligands and transformation of the dimeric associꢀ
ates are very useful for the investigation of mechanisms of
oxidation of various organic substrates in the presence of
the phthalocyanine catalysts.
exerts no significant effect and the associates already
formed in the solution participate in the process. The nonꢀ
linear character of changing kapp for СоPcII is observed in
the concentration range from 6•10–6 to 8•10–5 mol L–1
.
At a concentration of 3•10–5 mol L–1, the efficiency of
oxidation in the presence of СоPcII and СоPcV is someꢀ
what lower than that for СоPcI. The catalytic activity of the
studied macrocycles in the oxidation of DTC and 2ꢀmerꢀ
captoethanol decreases in the order СоРсIII > СоРсIV >
> СоРсI ≥ СоРсV > СоРсII and does not directly depend
on the stability of the dimeric associates in the solution,
which makes doubtful the thesis about an unambiguous
decrease in the catalytic activity in the association of metal
phthalocyanines. A tendency is observed for increasing
catalytic activity in the series of metal phthalocyanines
similar to the series of stability of 1 : 1 molecular comꢀ
plexes, which shows an important role of the stability of
the formed adduct upon the dimer—ligand (substrate),
which occurs during catalysis.
To conclude, the nature of the peripheral substitution
in the phthalocyanine macrocycle exerts a substantial efꢀ
fect on the processes of formation of associates of an asꢀ
signed type. The removal of the functional group from the
conjugated system decreases the substituent effect on the
coordination mode with the simultaneous enhancement
of the weak specific interaction at the periphery. The ligand
geometry is very significant for entering the cavity of the
Нꢀassociate and formation of dimers of the sandwich type.
The interrelation of association processes and catalytic
activity is complicated, but it can unambiguously be conꢀ
cluded that the association processes do not always subꢀ
stantially decrease the catalytic activity.
This work was financially supported by the Russian
Science Foundation (Project No. 14ꢀ23ꢀ00204, "Synthesis,
Isolation, Purification, and Structure Determination of
the Studied Compounds and Materials") and the Council
on Grants at the President of the Russian Federation
(Program for State Support of Young Russian Scientists
(Candidates of Science), Project No. MKꢀ2776.2015.3,
"Investigation of Physicochemical Properties").
The catalytic activity of metal phthalocyanines in the
liquidꢀphase oxidation of mercaptanes depends directly
on the state of the coordination site and, hence, on the
type and stability of the associate in water. In spite of
distinctions, the presently known mechanisms of the oxꢀ
idation process36,51 include the stage (or several stages)
related to the coordination of the substrate and/or oxidant
on the central metal cation.
References
When the concentrations of oxygen and catalyst and
the pH of the solution are constant, the oxidation of DTC
and 2ꢀmercaptoethanol occurs in the kinetic region. We
have earlier shown that the noncatalytic oxidation of DTC
is very slow (kapp = 1.7•10–5 s–1).52 The dependence of
kapp on the concentration for СоPcI is nonlinear and tends
to reach a plateau at a high content of the macrocycle,
which is caused by processes of selfꢀassociation of the
catalysts described above. The concentration of CoPcI
about 3•10–5 mol L–1 is optimum for catalysis. At this
concentration, the factor of dimerization enhancement
1. C. Colomban, E. V. Kudrik, P. Afanasiev, A. B. Sorokin,
Catalysis Today, 2014, 235, 14.
2. J. C. Bricker, L. Laricchia, Topics Catal., 2012, 55, 1315.
3. V. Çakir, D. Çakir, M. Pi kin, M. Durmu , Z. Biyiklio lu,
J. Luminescence, 2014, 154, 274.
4. A. Günsela, A. T. Bilgi lia, E. Kirba b, S. Güneyc, M. Kanꢀ
daza, J. Photochem. Photobiol. A: Chem., 2015, 310, 155.
5. H.ꢀN. Xu, H.ꢀJ. Chen, B.ꢀYu. Zheng, Yu.ꢀQ. Zheng, M.ꢀR.
Ke, J.ꢀD. Huang, Ultrasonics Sonochemistry, 2015, 22, 125.
6. S. Mori, H. Yoshiyama, E. Tokunaga, N. Iida, M. Hayashi,
T. Obata, M. Tanaka, N. Shibata, J. Fluor. Chem., 2015,
174, 137.

2228
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 9, September, 2016
Vashurin
7. Y. G. Gorbunova, A. G. Martynov, A. Yu. Tsivadze, in Handꢀ
book of Porphyrin Science, Eds K. M. Kadish, K. M. Smith,
R. Guilard, World Scientific, 2012.
8. T. Basova, A. Hassan, M. Durmu , A. G. Gürekd, V. Ahsen,
Coord. Chem. Rev., 2016, 310, 131.
9. C. J. Medforth, Zh. Wang, K. E. Martin, Yu. Song, J. L.
Jacobsen, J. A. Shelnutt, Chem. Commun., 2009, 7261.
10. M. A. Gradova, K. A. Zhdanova, N. A. Bragina, A. V. Loꢀ
banov, M. Ya. Mel´nikov, Russ. Chem. Bull. (Int. Ed.), 2015,
64, 806 [Izv. Akad. Nauk, Ser. Khim., 2015, 806].
11. M. Shaik, V. K. Rao, M. Gupta, P. Pandey, Thin Solid Films,
2012, 526, 256.
12. V. B. Sheinin, E. V. Bobritskaya, S. A. Shabunin, O. I. Koifꢀ
man, Macroheterocycles, 2014, 7, 209.
13. Yu. Bandera, M. K. Burdette, J. A. Shetzline, R. Jenkins,
S. E. Creager, S. H. Foulger, Dyes and Pigments, 2016,
125, 72.
32. A. Filippova, A. Voronina, A. Vashurin, N. Litova, M. Raꢀ
zumov, S. Pukhovskaya, Eur. Chem. Bull., 2014, 3, 1055.
33. H. L. Anderson, C. A. Hunter, M. N. Meah, J. K. M. Sandꢀ
ers, J. Am. Chem. Soc., 1990, 112, 5780.
34. J. K. Joseph, S. L. Jain, B. Sain, Ind. Eng. Chem. Res., 2010,
49, 6674.
35. A. Vashurin, V. Maizlish, S. Pukhovskaya, A. Voronina,
I. Kuzmin, N. Futerman, O. Golubchikov, O. Koifman,
J. Porphyrins and Phthalocyanines, 2015, 19, 573.
36. A. B. Sorokin, Chem. Rev., 2013, 113, 8152.
37. Handbook of Porphyrin Science, Vol. 6, NMR and EPR Techꢀ
niques, Eds K. M. Kadish, K. M. Smith, R. Guilard, World
Scientific, Singapore, 2010.
38. A. A. Voronina, I. A. Kuzmin, A. S. Vashurin, G. P. Shaposhꢀ
nikov, S. G. Pukhovskaya, O. A. Golubchikov, Russ. J. Gen.
Chem. (Engl. Transl.), 2014, 84, 1777 [Zh. Obshch. Khim.,
2014, 84, 1540].
14. V. Çakir, M. Göksel, M. Durmu , Z. Biyiklio lu, Dyes and
Pigments, 2016,125, 414.
15. S. Z. Yildiz, S. Colak, M. Tuna, J. Mol. Liq., 2014, 195, 22.
16. B. D. Berezin, O. I. Koifman, Russ. Chem. Rev., 1980,
49, 1188.
17. Yu. S. Marfin, A. S. Vashurin, E. V. Rumyantsev, S. G.
Puhovskaya, J. SolꢀGel Sci. Technol., 2013, 66, 306.
18. A. A. Voronina, I. A. Tarasyuk, Yu. S. Marfin, A. S. Vashuꢀ
rin, E. V. Rumyantsev, S. G. Pukhovskaya, J. NonꢀCrystal.
Solids, 2014, 406, 5.
19. G. P. Shaposhnikov, V. P. Kulinich, V. E. Maizlish, Modifiꢀ
tsirovannye ftalotsianiny i ikh strukturnye analogi [Modified
Phthalocyanines and Their Structural Analogs], KRASAND,
Moscow, 2012, 480 pp. (in Russian).
20. JꢀAggregates, Ed. T. Kobayashi, World Scientific, Singapore,
Vol. 2, 2012.
21. A. W. Snow, in The Porphyrin Handbook, Eds K. M. Kadish,
K. M. Smith, R. Guilard, Academic Press, New York, 2003,
Vol. 17, p. 129.
22. M. Sevim, M. N. Yarasir, A. Koca, M. Kandaz, Dyes and
Pigments, 2014, 111, 190.
23. V. Iliev, V. Alexiev, L. Bilyarska, J. Mol. Catal. A: Chem.,
1999, 137, 15.
39. A. Voronina, A. Vashurin, N. Litova, M. Shepelev,
S. Pukhovskaya, Izv. Vuz. Khim. Khim. Tekhnol. [Bulletin of
Higher Educational Institutions. Chemistry and Chemical Techꢀ
nology], 2014, 57, 51 (in Russian)].
40. I. Ya. Bernshtein, Yu. L. Kaminskii, Spektrofotometricheskii
analiz v organicheskoi khimii [Spectrophotometric Analysis
in Organic Chemistry], Moscow, Khimiya, 1986, 200 pp.
(in Russian).
41. A. A. Voronina, A. A. Filippova, A. S. Vashurin, S. G.
Pukhovskaya, O. A. Golubchikov, G. P. Shaposhnikov, Russ.
J. Gen. Chem. (Engl. Transl.), 2015, 85, 1195 [Zh. Obshch.
Khim., 2015, 85, 1713].
42. A. A. Voronina, A. A. Filippova, S. A. Znoiko, A. S. Vashuꢀ
rin, V. E. Maizlish, Russ. J. Inorg. Chem. (Engl. Transl.),
2015, 60, 1407 [Zh. Neorg. Khim., 2015, 60, 1537].
43. E. P. Zhiltsova, T. N. Pashirova, R. R. Kashapov, N. K.
Gaisin, O. I. Gnezdilov, S. S. Lukashenko, A. D. Voloshina,
N. V. Kulik, V. V. Zobov, L. Ya. Zakharova, A. I. Konovꢀ
alov, Russ. Chem. Bull. (Int. Ed.), 2012, 64, 113 [Izv. Akad.
Nauk, Ser. Khim., 2012, 110].
44. D. W. Dixon, V. Steullet, J. Inorg. Biochem., 1998, 69, 25.
45. E. N. Ovchenkova, T. N. Lomova, Russ. J. Org. Chem.
(Engl. Transl.), 2011, 47, 1581 [Zh. Org. Khim., 2011, 47, 1551].
46. A. Voronina, A. Filippova, M. Razumov, I. Kuzmin,
M. Shepelev, A. Vashurin, O. Golubchikov, Eur. Chem. Bull.,
2015, 4, 335.
47. J. S. Craw, S. P. Greatbanks, I. H. Hillier, Ma. J. Harrison,
N. A. Burton, J. Chem. Phys., 1997, 106, 6612.
48. H. Yamomoto, Ch. Ohira, T. Aso, W. Pfleiderer, Bull. Chem.
Soc. Jpn, 1987, 60, 4115.
24. M. Kobayashi, Yu. Kigawa, K. Satoh, K. Sawada, J. Porpꢀ
hyrins and Phthalocyanines, 2012, 16, 183.
25. A. L. Lyubimtsev, I. E. Nifant´ev, Russ. Chem. Bull. (Int. Ed.),
2004, 53, 346 [Izv. Akad. Nauk, Ser. Khim., 2004, 332].
26. M. Kimura, Y. Yamaguchi, T. Koyama, K. Hanabusa,
H. Shirai, J. Porphyrins and Phthalocyanines, 1997, 1, 309.
27. A. N. Sidorov, I. P. Kotlyar, Opt. Spektrosk. [Optics and
Spectroscopy], 1961, 11, 175 (in Russian).
49. H. Krawczyk, A. Pietras, J. Mol. Struct., 2008, 882, 116.
50. H. Krawczyk, A. Pietras, A. Kraska, Spectrochim. Acta, Part
A, 2007, 66, 9.
28. V. P. Kulinich, G. P. Shaposhnikov, R. A. Badaukaite,
Macroheterocycles, 2010, 3, 23.
29. S. A. Znoiko, A. S. Kambolova, V. E. Maizlish, G. P.
Shaposhnikov, I. G. Abramov, S. I. Filimonov, Russ. J. Gen.
Chem. (Engl. Transl.), 2009, 79, 1735 [Zh. Obshch. Khim.,
2009, 79, 1376].
51. E. M. Tyapochkin, E. I. Kozliak, J. Mol. Catal.A: Chem.,
2005, 242, 1.
52. A. S. Vashurin, S. G. Pukhovskaya, A. S. Semeikin, O. A.
Golubchikov, Macroheterocycles, 2012, 5, 72.
30. K. Sakamoto, E. OhnoꢀOkumura, Materials, 2009, 2, 1127.
31. A. Vashurin, A. Filippova, S. Znoyko, A. Voronina, O. Lefeꢀ
dova, I. Kuzmin, V. Maizlish, O. Koifman, J. Porphyrins and
Phthalocyanines, 2015, 19, 983.
Received January 21, 2016;
in revised form May 16, 2016