Carbon monoxide coordination by iron(II) meso-mono-4-pyridyltriphenylporphyrinate (FeM4PyTPP) and its structure in sublimed layers

Article abstract of DOI:10.1023/A:1013009011699

Interaction of CO with sublimed layers of iron(II) meso-mono-4-pyridyltriphenylporphyrinate (FeM4PyTPP) resulting in the formation of known mono- and dicarbonyl complexes was studied using IR spectroscopy. The frequency of the stretching vibration of the coordinated CO in the monocarbonyl complex was found to be ～20 cm^-1 higher than in the complex with iron meso-tetraphenylporphyrinate (FeTPP), with the former complex being significantly more stable than the latter. The differences observed in CO coordination by porphyrins with close structures are explained by the formation, in the FeM4PyTPP sublimed layers, of oligomeric structures where the pyridyl group of one molecule is coordinated by the metal ion of the neighboring molecule. This conclusion is confirmed by a comparative analysis of IR spectra of FeM4PyTPP and FeTPP in the regions of structurally sensitive vibrations.

Full text of DOI:10.1023/A:1013009011699

Russian Journal of Coordination Chemistry, Vol. 27, No. 12, 2001, pp. 846–851. Translated from Koordinatsionnaya Khimiya, Vol. 27, No. 12, 2001, pp. 898–903.
Original Russian Text Copyright © 2001 by Kurtikyan, Martirosyan, Kazaryan, Madakyan.
Carbon Monoxide Coordination by Iron(II)
meso-Mono-4-Pyridyltriphenylporphyrinate (FeM4PyTPP)
and Its Structure in Sublimed Layers
T. S. Kurtikyan, G. G. Martirosyan, R. K. Kazaryan, and V. N. Madakyan
Armenian Institute of Applied Chemistry, Yerevan, Armenia
Molecular Stucture Research Center, National Academy of Sciences of Armenia, Yerevan, Armenia
Geratsi State Medical University, Yerevan, Armenia
Received February 5, 2001
Abstract—Interaction of CO with sublimed layers of iron(II) meso-mono-4-pyridyltriphenylporphyrinate
(FeM4PyTPP) resulting in the formation of known mono- and dicarbonyl complexes was studied using IR spec-
troscopy. The frequency of the stretching vibration of the coordinated CO in the monocarbonyl complex was
found to be ~20 cm–1 higher than in the complex with iron meso-tetraphenylporphyrinate (FeTPP), with the
former complex being significantly more stable than the latter. The differences observed in CO coordination by
porphyrins with close structures are explained by the formation, in the FeM4PyTPP sublimed layers, of oligo-
meric structures where the pyridyl group of one molecule is coordinated by the metal ion of the neighboring
molecule. This conclusion is confirmed by a comparative analysis of IR spectra of FeM4PyTPP and FeTPP in
the regions of structurally sensitive vibrations.
Metal complexes of meso-pyridyl-substituted por- make it possible to establish the structure of their sub-
phyrins are presently of interest to researchers [1] due limed layers, which is important to know for their use
to their capability of self-organizing through coordina- in optoelectronic devices.
tion of the pyridyl group of one molecule by the metal
This work deals with spectral studies of the interac-
ion of a neighboring molecule. A great number of
tion of carbon monoxide with sublimed layers of
supramolecular sets has been obtained from the Zn, Ru,
iron(II)
meso-mono-4-pyridyltriphenylporpyrinate
and Os metalloporphyrins.At the same time, the similar
properties of Co and Fe porphyrinates, which are
important due to their biological activity, remain poorly
studied.
(FeM4PyTPP) (Ä) compared to its structural analog
FeTPP (Ç), which is widely used in investigations.
The specific nature of reversible oxygen coordina-
tion by sublimed layers of meso-tetrapyridyl-substi-
tuted Co porphyrins (CoT4PyP and CoT3PyP) was pre-
viously reported in [2–4]. In this case, the frequency
ν(O2) of the coordinated oxygen was about 100 cm–1
lower, while the thermal stabilities of these complexes
were noticeably higher, than that in oxygen coordina-
tion by sublimed layers of the tetraphenyl derivative
CoTPP [5]. The differences observed were interpreted
as the formation of oligomers in the solid phase of
pyridyl-substituted derivatives as a result of coordina-
tion of the pyridyl group of one molecule by a cobalt
atom of the nearest molecule.
N
Fe
N
N
Fe
N
N
N
N
N
N
(A)
(B)
Since Fe(II) porphyrinates are easily oxidized in air
to form µ-oxodimers, in our work, we used a more sta-
ble hexacoordinated dipiperidine extracomplex,
FeM4PyTPP(Pip)2. H2M4PyTPP was obtained by the
mixed aldehyde method [7]. The compound purity was
confirmed by data from thin-layer chromatography and
NMR and UV spectroscopy, which coincided with the
data cited in [7]. FeM4PyTPP(Pip)2 and FeTPP(Pip)2
were prepared as described in [8].
It was recently discovered that the low-temperature
sublimed layers of cobalt meso-mono-4-pyridyltriphe-
nylporphyrinate (CoM4PyTPP) reversely bind oxygen
in two different ways [6], i.e., with the formation of
pentacoordinated complexes, such as CoTPP · O2 [5],
and with the formation of hexacoordinated complexes
with the pyridyl group in the trans-position to oxygen.
Therefore, studies of the interaction of the simplest
C18O (enriched to 81.4%) was purchased from the
ligands with metal complexes of pyridylporphyrins Institute of Isotpes (Georgia).
1070-3284/01/2712-0846$25.00 © 2001 åÄIä “Nauka /Interperiodica”

CARBON MONOXIDE COORDINATION
847
Frequencies of coordinated CO and of the structurally sensitive vibrations (cm–1) [11] in IR spectra of carbonyl FeTPP and
FeM4PyTPP extracomplexes in their sublimed layers
ν
FeTPP · 2CO FeM4PyTPP · 2CO FeTPP · CO FeM4PyTPP · CO FeM4PyTPP* FeM4PyTPP**
ν{CO(C18O)} 2032 (1982)
2031 (1981)
1352
1964 (1918)
1342
1985 (1940)
1350
I
1352
795
1349
1343, 1350
795, 802sh
435, 467vs
II
III
796
803
795, 803sh
463
802
462
462
436
467, 435svs
* Freshly sublimed layer at 80 K.
** At T = 293 K, after carbonyl complex decomposition through evacuation at increased tamperature for many hours.
FeM4PyTPP(Pip)2 (about 10 mg) was placed in a heated, the maximum of the combined band shifts
Knudsen cell and was kept under high vacuum (~10–5 torr) upfield and ν(CO) turns out to be ~20 cm–1 higher than
at T ≈ 250°C for several hours. This procedure resulted the respective band in the spectrum of the FeTPP · CO
in complete detachment of the axial ligands, which was extracomplex (Fig. 1, spectra b, c).
varified by vacuum measurements at the cryostat outlet.
The monocarbonyl complexes of the metallopor-
Then, the cell temperature was raised to 300–350°ë
phyrins under consideration also greatly differ in ther-
and sublimation of FeM4PyTPP was conducted for 2–
mal stability. In the case of FeM4PyTPP, evacuation at
~230 K results in complete decomposition of the dicar-
3 h onto a CsI plate located in the optical cryostat and
cooled with liquid nitrogen. CO (C18O) was thoroughly
bonyl complex. The intensity of the monocarbonyl
dried over P2O5 and supplied to the cryostat at a low
complex band (1985 cm–1) increases. For CO detach-
rate from a vessel equipped with a manometer to mea-
ment to be full, the evacuation should be conducted at
sure the equilibrium pressure in the cryostat.
353 K for several hours. With FeTPP, evacuation per-
IR spectra were recorded on a Specord M-80 spec- formed at a lower temperature (~230 K) and resulting
trophotometer. The spectral slit width was 4 cm–1 when in decomposition of the dicarbonyl complex is accom-
measuring outline spectra and 2 cm–1 when taking spec- panied by partial decomposition of the monocarbonyl
tra in the regions of structurally sensitive vibrations of compound with ν(CO) at 1964 cm–1. In this case, the
iron porphyriantes (see below). The electronic absorp- coordinated CO is completely eliminated during evac-
tion spectra were recorded on a Specord M-40 spectro- uation over several dozens of minutes even at room
photometer, and NMR spectra were measured using temperature. The increased thermal stability of the
Varian Mercury 300 spectrometer (solution in CDCl3). monocarbonyl complex FeM4PyTPP agrees with data
from [12] on the correlation between the stability of
The low-temperature sublimed layers of metal com-
carbonyl complexes of iron porphyrinates and the fre-
plexes of meso-tetraarylporphyrins have a microporous
quency ν(CO) of the extracomplex; i.e., more stable
complexes exhibit higher values of ν(CO).
structure [5] like that of their bulky samples [9]. There-
fore, potential ligands can easily diffuse into the bulk
layer. The obtained adducts can be characterized by
The investigated porphyrins also behave in different
spectral methods; solvent interference is absent in this ways when the layer heated to room temperature and
case.
containing monocarbonyl complexes is again cooled.
With the same equilibrium pressures of CO in the cry-
ostat, the concentration of a newly formed dicarbonyl
complex is sufficiently higher in the case of FeTPP
(Fig. 2, spectra a, b).
At liquid nitrogen temperature and at a CO equilib-
rium pressure of ~1 torr in the cryostat, the layers of the
studied metalloporphyrins consist mainly of dicarbonyl
complexes with a frequency of antiphase stretching
vibtations of νas{CO(C18O)} at 2030(1980) cm–1 [10].
Distinctions discovered in the behavior of two met-
The data in the table reveal that the frequencies ν(CO) alloporphyrins with close structures can be explained if
due to the dicarbonyl complexes of both metallopor- the coordination bond is suggested to form in the sub-
phyrins are very close. At the same time, the frequen- limed layer between the pyridyl group of one molecule
cies and shapes of the bands of the monocarbonyl com- and the iron ion of the neighbouring molecule in the
plexes are different. The singlet band ν(CO) in the case of the pyridyl-substituted derivative. With rapid
spectrum of the monocarbonyl complex FeTPP does freezing out of translational degrees of freedom of the
not show significant frequency shifts with temperature molecules in the course of porphyrin sublimation onto
growth; this is accompanied by decomposition of the a low-temperature surface, the concentration of such
thermally unstable dicarbonyl complex and by the for- structures in the layer is small. The layer mainly con-
mation of additional amounts of the monocarbonyl sists of tetracoordinated FeM4PyTPP molecules capa-
complex. In the case with FeM4PyTPP and at liquid ble of forming hexacoordinated dicarbonyl and penta-
nitrogen temperature, this band consists of two super- coordinated monocarbonyl complexes when CO is sup-
posed bands (Fig. 1, spectrum a). When the layer is plied. An increase in the temperature of the support is
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 12 2001

848
KURTIKYAN et al.
‡
‡
b
b
c
1968
1964
1985
2032
T, %
10
2032
2030
T, %
10
1985
0
0
ν, cm–1
1950
Fig. 2. Regions of stretching vibration of the coordinated
CO in IR spectra of sublimed layers of (a) FeM4PyTPP and
(b) FeTPP in the presence of CO (p = 1 torr) after heating
the low-temperature sublimate to room temperature and
subsequent cooling to 80 K.
1964
1980
2060
1900
ν, cm–1
this appears as a gradual shift of the combined band
toward high frequencies.
Fig. 1. IR spectra of a sublimed FeM4PyTPP layer in the
region of stretching vibrations of coordinated CO in the
presence of CO (p = 1 torr) at (a) 80 K; (b) at ~230 K, after
evacuation of the layer characterized by the spectrum a; and
(c) at ~230 K, after short-time evacuation of the FeTPP
layer containing carbonyl complexes.
The spectral changes due to the formation of two
types of monocarbonyl complexes are not as pro-
nounced here as in the case of the above-mentioned
CoM4PyTPP + O2 system [6], since for the latter sys-
tem, ∆ν(O2) in the penta- and hexacoordinated adduct
with the additional pyridyl group in the fifth position
amount to 80 cm–1, whereas in the system under study,
∆ν(CO) ≈ 20 cm–1 and they do not split due to the large
half-width of the bands.
accompanied not only by decomposition of the dicar-
bonyl complex but also by growth in the mobility of
molecules in the layer, which results in the formation of
hexacoordinated monocarbonyl complexes with a
pyridyl group of the neighboring molecule in the sixth
coordination position. When the layer is kept at
increased but still low temperatures (below room tem-
perature), the concentration of these extracomplexes
with ν(CO) = 1985 cm–1 increases, while the concentra-
tion of pentacoordinated monocarbonyl complexes
The layer produced by FeM4PyTPP sublimation on
the surface at room temperature and its subsequent
exposure to an atmosphere of CO with further cooling
to 77 K has ν(CO) = 1985 cm–1, while the band from the
dicarbonyl complex can barely be distinguished in the
spectrum. The same situation is observed in the case of
low-temperature sublimates kept under vacuum for
with ν(CO) ≈ 1964 cm–1 decreases. In the UR spectrum, several days at room temperature. The most reasonable
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 12 2001

CARBON MONOXIDE COORDINATION
849
interpretation of these data is the formation of oligo- gomer terminal molecules capable of forming dicarbo-
meric structures in the layer with a low content of oli- nyl complexes.
O
C
N
N
N
N
N
Fe
N
N
C O
Fe
N
N
C
O
N
N
N
N
N
Fe
N
C
O
n
The other possible reason for the observed differ- assigned to vibrations with a predominate contribution
ences between the monocarbonyl complexes FeTPP ν(CC) from the phenyl rings [15]. The pyridyl ring
and FeM4PyTPP associated with the intramolecular vibration with a similar shape also lies in this range,
effect of the pyridyl group on the electronic structure of while the additional asymmetry produced by the nitro-
Fe(II) and, thus, on the frequency of the coordinated gen atom favors an increase in the intensity of the
CO cannot explain any of the listed experimental data. respective band. Identical IR spectra suggest that
Moreover, this mechanism should also affect the fre- FeM4PyTPP will also exhibit the regularities we
quency νas(CO) of the dicarbonyl extracomplexes; this observed in the FeTPP extracomplexes.
is not actually observed.
A large number of IR spectra was examined in [11,
Unlike the CoTPP extracomplexes, in the case of 13] for penta- and hexacoordinated FeTPP complexes
FeTPP, the axial coordination has an effect on the vibra- with N, O, S, and C donor ligands to reveal three bands
tional spectrum of porphyrin itself [11, 13]. This occurs (I–III) assigned to standard vibrations of the macrocy-
due to the close values of the energies of the dπ-orbitals cle, which are sensitive to the nature and number of
of the metal and the π-orbitals of porphyrin in the Fe axial ligands present. The positions of these bands in
complexes. The interaction of the metal d-orbitals with the spectrum of the monocarbonyl complex of
the porphyrin π-orbitals, which is almost absent in the FeM4PyTPP coincides with their positions in the spec-
other transition-metal porphyrinates due to a great dif- tra of hexacoordinated complexes but differs from the
ference in the energies, leads, in the case of the Fe [11, positions of the respective bands in the spectrum of the
13] and Mn [14] porphyrinates, to a situation wherein pentacoordinated FeTPP · CO complex (table), which
the electronic effects caused by the axial coordination also supports the suggested mechanism. The structur-
can directly influence the electronic density distribution ally sensitive frequencies of FeM4PyTPPP itself,
in the macrocycle itself. As a result, certain standard which was produced after decomposition of the carbo-
vibrations of the macrocycle become sensitive to the nyl complex through evacuation at increased tempera-
nature of the extraligand and to the type of its coordina- tures, are very close to the frequencies of pentacoordi-
tion with the central metal ion.
nated high-spin FeTPP complexes [2].
As we expected, the IR spectra of FeM4PyTPP and
One more argument in favor of the main conclusion
FeTPP are very close. The main difference lies in the can be found when considering the band at 1600 cm–1,
higher intensity of the band at 1600 cm–1 in the which, in the case of FeM4PyTPP sublimed layers,
FeM4PyTPP spectrum; this band in the spectra of the unlike FeTPP layers, is sensitive to the availability of
metal complexes of the meso-tetraphenylporphyrin is the axial ligand. The high-frequency region of this band
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 12 2001

850
KURTIKYAN et al.
which is significant due to the very strong π-acceptor
properties of CO.
Thus, the conducted spectral measurements indicate
that in the FeM4PyTPP sublimed layers, the oligomeric
structures are realized due to intermolecular coordina-
tion bonds. As a result, the porosity of the layer with
such structures should change. Molecules in the metal
complexes of the meso-tetraphenylporphyrins are
arranged in layers with the porphyrin rings located in
parallel to one another. Pores in these compounds are
long narrow channels lying opposite to the axial posi-
tions of the metals and are usually filled with solvent or
ligand molecules. When these molecules are absent, the
structure becomes substantially thicker and the cross
section of the pores significantly decreases [9], prevent-
ing the reagents from diffusing into the bulk layer. This
is the reason for the less effective coordination of CO
by sublimed FeTPP layers kept under vacuum at room
temperature for several days.
‡
b
c
1596
When the metalloporphyrin molecules contain func-
tional substituents capable of specific intermolecular
interactions (hydrogen bonds, coordination, etc.), the
supramolecular organization of the system can notice-
ably change [18–20]. For 4-pyridyl-substituted deriva-
tives, such coordination will evidently make the neigh-
boring molecules orient themselves perpendicular to
one another and will result in the formation of substan-
tially larger pores [21] as compared to those formed in
thickened MTPP structures. Indeed, the sublimed
FeM4PyTPP layers also effectively bind CO when the
layer is stored for several weeks. Moreover, this capa-
bility also appears when the layer is exposed to a mix-
ture of atmospheric air and CO, with the content of the
latter component being less than 1%. The spectral mea-
surements show that, unlike FeTPP, the layers of
FeM4PyTPP are oxidized very slowly (the appearance
and growth in the intensity of the band νas(Fe–O–Fe) of
the µ-oxodimer in the range of 879 cm–1) even when
kept in air.
1600
T, %
10
1600
0
–1
1620
1580
ν, cm
Fig. 3. IR spectra of a sublimed FeM4PyTPP layer in the
region of ν(CC) of the aryl rings after deposition at (a) 80 K,
(b) after the layer is exposed to CO and heated to room tem-
perature, and (c) after evacuation at 353 K over several
hours.
The discovered features of CO coordination by the
sublimed FeM4PyTPP layers are expected to prove
useful in practice.
in the spectrum of the monocarbonyl FeM4PyTPP
complex contains a shoulder which disappears after
removal of CO through evacuation at increased temper-
atures (Fig. 3, spectrum c). The shape of this band also
differs from that of the band observed in the spectrum
of the FeM4PyTPP layer sublimed on a low-tempera-
ture surface (Fig. 3, spectrum a).
REFERENCES
1. Imamura, T. and Fukushima, K., Coord. Chem. Rev.,
2000, vol. 198, p. 133.
2. Kurtikyan, T.S. and Madakyan, V.N., Koord. Khim.,
1992, vol. 18, no. 2, p. 139.
3. Kurtikyan, T.S. and Madakyan, V.N., Koord. Khim.,
1992, vol. 18, no. 8, p. 869.
As we said above, this band is due to the standard
vibrations of the pyridyl ring. In the case of pyridine, it
is a combined vibration involving ν(CC) and β(CCH)
[16], which is mostly shifted upfield in the course of
coordination [17]. A similar situation is likely to occur
in our case as well. An additional high-frequency shift
of this band during coordination of CO in the sixth
position should be explained in terms of its trans-effect,
4. Kurtikyan, T.S., Martirosyan, G.G., and Madakyan, V.N.,
Spectroscopy of Biological Molecules: New Directions,
Greve, J., Puppels, G.J., and Otto, C., Eds., Dordrecht:
Kluwer, 1999, p. 79.
5. Kurtikyan, T.S., Gasparyan, A.V., Martirosyan, G.G.,
and Zhamkochyan, G.A., Zh. Prikl. Spektrosk., 1995,
vol. 62, no. 6, p. 62.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 12 2001

CARBON MONOXIDE COORDINATION
851
6. Kurtikyan, T.S., Martirosyan, G.G., Kazaryan, R.K., and 14. Kurtikyan, T.S., Stepanyan, T.G., Martirosyan, G.G.,
Madakyan, V.N., Izv. Ross. Akad. Nauk, Ser. Khim.,
2001, vol. 50, no. 4, p. 613.
et al., Izv. Ross. Akad. Nauk, Ser. Khim., 2000, no. 9,
p. 1551.
7. Williams, G.N., Williams, R.F.X., Lewis, A., and Ham-
bright, P., J. Inorg. Nucl. Chem., 1979, vol. 41, no. 1,
p. 41.
8. Epstein, L.M., Straub, D.D., and Maricondi, C., Inorg.
Chem., 1967, vol. 6, no. 6, p. 172.
9. Byrn, M.P., Curtis, C.J., Hsiou, Y., et al., J. Am. Chem.
Soc., 1993, vol. 115, no. 21, p. 9480.
10. Wayland, B.B., Mehne, L.F., and Swartz, J., J. Am.
Chem. Soc., 1978, vol. 100, no. 8, p. 2379.
11. Oshio, H., Ama, T., Watanabe, T., et al., Spectrochim.
Acta, A, 1984, vol. 40, no. 9, p. 863.
12. Collman, J.P., Brauman, J.I., Halbert, T.R., and Suslick, K.S.,
Proc. Natl. Acad. Sci. USA, 1976, vol. 73, no. 10,
p. 3333.
15. Li, X., Czernuszewicz, R., Kincaid, J., et al., J. Phys.
Chem., 1990, vol. 94, no. 1, p. 31.
16. Sverdlov, L.N., Kovner, M.A., and Krainov, E.P., Kole-
batel’nye spektry mnogoatomnykh molekul (Vibration
Spectra of Polyatomic Molecules), Moscow: Nauka,
1970, p. 464.
17. Gill, N.S., Nutal, R.H., Scaife, D.F., and Sharp, D.W.,
J. Inorg. Nucl. Chem., 1961, vol. 18, no. 1, p. 79.
18. Gardner, M., Guerin, A.J., Hunter, C.A., et al., New J.
Chem., 1999, p. 309.
19. Goldberg, I., Krupitsky, H., Stein, Z., and Hsiou, Y.,
Supramol. Chem., 1995, vol. 4, p. 203.
20. Kumar, R.K., Balasubramanian, S., and Goldberg, I.,
Inorg. Chem., 1998, vol. 37, no. 3, p. 541.
13. Kurtikyan, T.S., Gasparyan, A.V., Akopyan, M.E., and
Zhamkochyan, G.A., Khim. Zh. Arm., 1995, vol. 48, 21. Kropitsky, H., Stein, Z., Goldberg, I., and Strouse, C.E.,
nos. 1–3, p. 45.
J. Inclusion Phenom., 1994, vol. 18, p. 177.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 12 2001