Russian Chemical Bulletin, International Edition, Vol. 50, No. 4, pp. 638640, April, 2001 638
1066-5285/01/5004-638 $25.00 ©2001 Plenum Publishing Corporation
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 613615, April, 2001.
Structural features of sublimed layers of
meso-mono-4-pyridyltriphenylporphyrinatocobalt(II)
and reversible binding of molecular oxygen
T. S. Kurtikyan,
a,b«
G. G. Martirosyan,
b
R. K. Kazaryan,
c
and V. N. Madakyan
c
a
Armenian Institute of Applied Chemistry,
70 prosp. Bagratunyats, 375005 Yerevan, Republic of Armenia.
Fax: +7 (885 2) 23 2145. E-mail: tkurt@msrc.am
b
Research Center of Molecular Structure of the National Academy of Sciences of the Republic of Armenia,
26 prosp. Azatutyana, 375014 Yerevan, Republic of Armenia
c
M. Geratsi Medical State University,
375025 Yerevan, Republic of Armenia
The interaction of oxygen with sublimed layers of meso-monopyridyltriphenylporphyrina-
tocobalt(II) (CoMPyTPP) was studied by electronic absorption and IR spectroscopy. The
reversible binding of O
2
to the axial 5-position was shown for the freshly sublimed layers: the
6-position can either be free, or occupied by the pyridyl group of the adjacent molecule in the
layer. The concentration of the complexes of the first type decreases to zero with time, whereas
that of the second type complexes increases. The binding of oxygen on the sublimed layers of
CoMPyTPP differs substantially from that on meso-tetraphenylporphyrinatocobalt(II) and meso-tet-
ra-3(4)-pyridylporphyrinatocobalt(II), which loose their capability of O
2
binding with time.
Key words: meso-monopyridyltriphenylporphyrinatocobalt(II), sublimed layers, oxygen
binding, IR spectroscopy, electronic absorption spectroscopy.
The capability of chelate Co
II
complexes of oxygen
binding evoked an interest to search for the systems, which
retain the capability of oxygen fixation for a long time.
1
Some metalloporphyrins are known as efficient oxygen
carriers and promising adsorbents of oxygen,
2
artificial
hemoglobin,
3
and oxygen-permselective membranes.
4
Thin porphyrin layers can be used in photovoltaic
cells,
5
gas sensors,
6
and heterogeneous catalytic systems.
7,8
The studies of sublimed layers of cobalt(II) meso-tetra-
phenylporphyrinate (CoTPP)
9
and structurally similar
cobalt(II) meso-tetra-4(3)-pyridylporphyrinates (CoT4PyP
and CoT3PyP)
10,11
showed that on storing at room
temperature the films loose the ability to bind Î
2
.
According to the spectral data, the CoT4PyP and
CoT3PyP layers slowly loose the ability to bind oxygen
because they form saturated complexes with coordina-
tion number 6 due to the interaction of the metal ions
with the pyridyl groups of adjacent molecules. It could
be expected that a decrease in the number of pyridyl
groups in the meso-positions of the porphyrin macrocycle
decreases the probability of formation of these structures
and improves the oxygen-binding affinity of the layer.
In this work, we synthesized cobalt(II) meso-mono-4-
pyridyltriphenylporphyrinate (CoMPyTPP) and studied
the ability of its sublimed layers obtained under different
conditions to bind oxygen.
Experimental
ÑîÌÐóÒÐÐ samples were synthesized using the method of
mixed aldehydes.
12
Sublimed layers were obtained on supports
of an optical cryostat, which were stored at either 77 K or room
temperature according to a published procedure.
9
To obtain the layers with a thickness convenient for IR
spectral studies, sublimation was performed for ∼3 h, and for
recording electronic absorption spectra (EAS), it took up to tens
of min. Thoroughly dried and pre-cooled oxygen was slowly fed
to a cryostat from a vessel attached to a mercury gauge for
measurements of the Î
2
pressure (∼60 Torr at temperatures of
the support near the temperature of liquid nitrogen). Then the
sublimed layer was stored for 30 min while the temperature was
alternated in the following sequence: 80 → 120 → 80 Ê, oxygen
was pumped out, and electronic or IR spectra were recorded.
IR spectra were recorded on a Specord M-80 spectropho-
tometer. The spectral width of the gaps was 4 cm
1
. Electronic
absorption spectra were measured on a Specord M-40 spectro-
photometer.
Results and Discussion
Figure 1 presents the IR spectra of the ÑîÌÐóÒÐÐ
layer recorded after this layer was first sublimed on a
support cooled with liquid nitrogen and then stored at
60 Torr Î
2
. As can be seen in Fig. 1, introduction of O
2
results in the appearance of two new absorption bands at
1250 and 1167 cm
1
. After the support was heated to
room temperature, both bands disappear and the initial
spectrum is restored. On admission of new portions of
Î
2
, these bands appear again, but the intensity of the
low-frequency band increases at the expence of the
high-frequency band. Introduction of O
2
on the layer
stored for 1 day at room temperature gives the spectrum
with the band at 1250 cm
1
decreased and with the band