Coordination of pyridine and piperidine by cobalt complexes of water-soluble porphyrin and phthalocyanines

Article abstract of DOI:10.1134/S0036023610040108

The extracoordination reactions of nitrogen-containing bases pyridine and piperidine with cobalt complexes of water-soluble porphyrin and phthalocyanines were studied. The stability constants of the axial complexes of cobalt porphyrins and cobalt phthalocyanines with pyridine and piperidine were determined.

Full text of DOI:10.1134/S0036023610040108

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 4, pp. 552–555. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © L.Zh. Guseva, S.G. Pukhovskaya, O.A. Golubchikov, 2010, published in Zhurnal Neorganicheskoi Khimii, 2010, Vol. 55, No. 4, pp. 605–608.
COORDINATION COMPOUNDS
Coordination of Pyridine and Piperidine by Cobalt Complexes
of WaterꢀSoluble Porphyrin and Phthalocyanines
L. Zh. Gusevaa,b, S. G. Pukhovskayab, and O. A. Golubchikova
a Institute of Solution Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia
b Ivanovo State University of Chemical Technology, Ivanovo, Russia
Received April 21, 2008
Abstract—The extracoordination reactions of nitrogenꢀcontaining bases pyridine and piperidine with cobalt
complexes of waterꢀsoluble porphyrin and phthalocyanines were studied. The stability constants of the axial
complexes of cobalt porphyrins and cobalt phthalocyanines with pyridine and piperidine were determined.
DOI: 10.1134/S0036023610040108
Extracoordination directly defines the manifestaꢀ
(
log
417 (5.62).
Step 2. A solution of 5,10,15,20ꢀtetraꢀ4ꢀ
ε
)): 643 (3.43), 589 (3.82), 546 (3.79), 514 (4.30),
tion of catalytic or electrocatalytic activity by metal
porphyrins and metal phthalocyanines. In this conꢀ
tent, considerable recent attention has focused on
these extracoordination reactions in both experimenꢀ
tal and theoretical studies [1–3].
pyridylporphyrin (0.5 g, 0.808 mmol) and bromoaceꢀ
tic acid (3.0 g, 21.6 mmol) in DMF (30 mL) was
refluxed for 1 h. Then, the solution was cooled and
diluted with benzene (30 mL). The precipitate was filꢀ
tered off, washed with acetone, and dried at 75
air. The yield was 0.9 g (91%). UVꢀVis (water, λmax, nm
The purpose of the present work is to study the
equilibrium of the extracoordination of the nitrogenꢀ
containing bases pyridine (Py) and piperidine (Pip) by
cobalt complexes of waterꢀsoluble porphyrin and
phthalocyanines.
°С in
(
log )): 630 (3.49), 585 (3.91), 556 (3.86), 519 (4.23),
423 (5.41 (water). H NMR (
internal standard): 8.91 (d, = 6.6 Hz, pyridine
9.25 (d, = 6.6 Hz, pyridine ꢀН), 9.07 (s, pyrrole
ꢀH).
Stage 3. Freshly prepared poorly soluble cobalt
hydroxide (the solubility of Co(OH)2 in water is ~2
10–4 wt %) was added to an aqueous solution of porꢀ
phyrin H2P in a ratio of 1 : 100, and the mixture was
magnetically stirred for 8 h at 50 . The formation of
ε
1
δ, ppm, D2O, TMS as
J
αꢀН)
J
β
EXPERIMENTAL
β
The cobalt complex of waterꢀsoluble porphyrin
СоС48Н32N8O8 (I) was synthesized as described in [4]
through three stages: (1) the synthesis of 5,10,15,20ꢀ
tetraꢀ4ꢀpyridylporphyrin, (2) the synthesis of
5,10,15,20ꢀtetra(4Nꢀcarboxymethylenepyridyl)porꢀ
×
I
°С
phyrin tetrabromide (H2P
the cobalt complex of H2P
I
I
), and (3) the synthesis of
the metal porphyrin was monitored by spectrophoꢀ
tometry. The solution was purified by repeated filtraꢀ
tion, and the complex was reprecipitated from a benꢀ
zene solution. The resulting precipitate was washed
(СоРI)
.
Stage 1. A mixture of pyrrole (5 mL, 0.072 mol)
and pyridineꢀ4ꢀcarboxaldehyde (7.7 g, 0.072 mol) was
added dropwise to boiling propionic acid (200 mL).
The resulting mixture was refluxed for 45 min, and
propionic acid was distilled off in a vacuum of a waterꢀjet
pump. The residue was mixed with benzene (600 mL),
with acetone and dried at 75
°С. The yield was 96%.
UVꢀVis (water, λmax, nm
(5.00).
(
log
ε
)): 540 (3.78), 429
The cobalt complex of phthalocyanine
II) was obtained by the condensaꢀ
washed with an ammonia solution and water, and CoC36H20N4O12S4
(
dried over sodium sulfate. The benzene solution was
chromatographed on a column packed with alumina
(Brockmann activity grade III) and eluted with benꢀ
zene, and the red band of porphyrin was collected. The
eluate was evaporated, and the porphyrin was precipiꢀ
tated with methanol. The precipitate was filtered off,
washed with methanol, and dried in air at 75 С. The
yield was 0.85 g (7.6%), Rf = 0.71 (Silufol, chloroform–
methanol (5 : 1)). UVꢀVis (chloroform, λmax, nm
tion of sulfophthalic and phthalic acids with urea and
cobalt chloride in the presence of a catalyst as
1
described in [5]. Cobalt tetracarboxyphthalocyanine
III (CoC40H20N4O8) was synthesized by the Wyler
method, namely, by smelting hemimellitic acid (1,2,3ꢀ
°
1
Porphyrin
supplied by, respectively, Prof. A.S. Semeikin and Dr. V.E. Maiꢀ
zlish (Ivanovo State University of Chemical Technology).
I and cobalt phtalocyanines II and III were kindly
552

COORDINATION OF PYRIDINE AND PIPERIDINE
553
Table 1. Absorption spectra of aqueous solutions of cobalt
porphyrin and cobalt phthalocyanines II and III
tricarboxybenzene) with urea in the presence of
ammonium chloride and ammonium molybdate as a
catalyst at 200–210°С according to a known proceꢀ
dure [6].
I
λ
max, nm (logε)
Metal complex
pH
I
7.6 427 (5.02), 540 (4.06), 595 (sh)
7.6 338, 475, 664
7.6 617, 674
The cobalt phthalocyanine complexes were puriꢀ
fied by reprecipitation from concentrated sulfuric acid
followed by the extraction of admixtures soluble in
organic solvents with acetone and ethanol in a Soxhlet
extractor [5, 6].
II
III
III
9.2 620, 678
Pyridine (Py) and piperidine (Pip) were purified by
standard methods [7–9].
Table 2. Stability constants of the axial complexes of Co porꢀ
phyrins and Co phthalocyanines with piperidine and pyridine
The water content was determined by the Fischer
titration, and it did not exceed 0.01%.
Metal complex
Extraligand
pH
K
st, mol–1
Phosphate buffers were prepared as described
in [10].
I
Pip
Pip
Pip
Py
7.6
7.6
7.6
7.6
9.2
9.2
200 50
45 10
II
The extracoordination of Pip and Py by the cobalt
porphyrin and phthalocyanine complexes were studꢀ
ied by spectrophotometry on a Specord Mꢀ400 instruꢀ
ment in 50ꢀmL cells (the absorbing layer thickness was
100 mm) at 293.15 0.10 K. A specified volume of the
solution of the extraligand was added to a solution of
metal porphyrin, using a microsyringe (the dosage
III
II
300 110
14
2
III
III
Py
160 30
130 40
Pip
error was 0.05%). The increase in the solution volꢀ
≤
ume in the cell after the end of titration did not exceed
0.05%.
The electronic absorption spectra of for aqueous
solutions of the cobalt complexes of compounds
are given in Table 1.
I–III
The cobalt phthalocyanine complex containing
four carboxyl groups exists in aqueous solutions as an
equilibrium mixture of monomeric and associated
forms. The degree of dissociation of the carboxyl
groups increases with pH, favoring the equilibrium
shift to the monomeric form of the complex. Thereꢀ
fore, the absorption bands in the spectrum of comꢀ
pound III exhibit the bathochromic shift from 615 to
622 nm with increasing pH.
RESULTS AND DISCUSSION
The extracoordination processes of the nitrogenꢀ
containing ligands were studied for the cobalt comꢀ
plexes of waterꢀsoluble porphyrin
carboxyꢀsubstituted derivatives of phthalocyanines II
and III
I and the sulfoꢀ and
.
R
R
N
The stability constants (Kst) of the piperidine and
pyridine extracomplexes of compounds
ous solutions were determined to model the reactions
that occur in biological systems.
In organic solvents, extracoordination processes
can proceed via one and two steps, depending on the
nature of the complexing atom in the metal porphyrin
[1–3]. In our case, in aqueous buffer solutions, the
I
–
III in aqueꢀ
Co
N
N
N
R
R
CH2COO−
R
N+
I
: R =
spectral changes of cobalt complexes I–III (CoP)
upon the addition of Py and Pip occur with the retenꢀ
tion of distinct isosbestic points (the characteristic
spectrum is shown in Fig. 1). This asserts that only two
colored forms at equilibrium exist in the solution. The
analysis of the data given below suggests the following
equilibrium in the solution:
R
N
N
Co
СоР + L
where L is Py or Pip.
СоР(L)
(1)
N
N
The absorbances of the solutions at the analytical
wavelengths listed in Table 1 were used for the calculaꢀ
tion of the equilibrium constants (Table 2). Solutions
R
R
II: R = SO3H; III: R = COOH
with very low concentrations of the reactants (cСоP
<
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 4 2010

554
GUSEVA et al.
0.6
0.2
А
1.6
1.2
0.8
0.4
–0.2
–0.6
2.0
1.8
1.6
1.4 –logcPip
Fig. 2. Plot of log
[
(
A
–
A
)/(A
– A )] vs. logcL for the
f
0
i
i
extracoordination of piperidine by phthalocyanine comꢀ
plex II
.
corresponding decrease in the effective positive charge
on the cobalt cation.
600
620
640
660
680
λ
, nm
Piperidine is a substantially stronger donor of a
σ
Fig. 1. Changes in the electronic absorption spectra due to
the extracoordination of complex III with piperidine.
electron pair than Py, due to which st increases threeꢀ
K
fold on going from the pyridinate to piperidinate
extracomplex of tetrasulfonic acid of cobalt phthaloꢀ
cyanine. However, it should be kept in mind that,
unlike Pip, Py can participate in ꢀbonding with the
cobalt cation. This likely explains the fact that the
pyridinate and piperidinate extracomplexes of comꢀ
10–6, L < 10–4 mol/L) were used. Hence, the solutions
c
were considered ideal, and Kst were calculated by the
equation
π
Кst
=
сСоР(L)/[cСоP
cL].
(2)
pound III have equal Kst values at pH 9.2.
The equilibrium concentrations of the extracomplexes
were calculated using the equation
As compared to the porphyrinates, the phthalocyaꢀ
ninates are characterized by a decreased electron denꢀ
sity on the central nitrogen atoms and, accordingly,
the effective positive charge on the central metal catꢀ
ion in the phthalocyanine complexes is higher than
that in similar metal porphyrins. That is why the extraꢀ
complexes of metal phthalocyaninates are more stable
than the corresponding metal porphyrin derivatives.
cCoP(L) = cC0 oP(A0 − Ai)/(Ai − Af)
,
(3)
where сCoР(L) is the equilibrium concentration of
0
CoP(L);
Ai, and
is the starting concentration of CoP; A0,
cCoP
Af are the initial, equilibrium, and final absorꢀ
bance values in the solution, respectively. All studies
were carried out under the conditions of a considerꢀ
able (more than 50ꢀfold) excess of the extraligand over
the metal porphyrin, which made it possible to neglect
the decrease in the extraligand concentration due to its
coordination by the cobalt complexes. This allowed us
to calculate the equilibrium constants by the equation
In this context, it is important that
Kst of the piperidiꢀ
nate of porphyrin complex is 4.5ꢀfold higher than
I
that of phthalocyanine derivative II, although the
former is inferior in stability to the extracomplex
formed by compound III. It is most likely that four
mesoꢀpyridyl substituents of compound I substantially
increase the effective positive charge on the cobalt caꢀ
tion.
Кst
=
(A0
–
Ai)/[(Ai
–
Af)сL].
(4)
The number of ligands added to the metal porphyꢀ
rin can be monitored by the slope of the plots
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COORDINATION OF PYRIDINE AND PIPERIDINE
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