Stereochemistry and properties of the M(II)-N(py) coordination bond in the low-spin dipyridinated iron(II) and cobalt(II) phthalocyanines

Article abstract of DOI:10.1016/S0020-1693(02)01060-5

A comparison between the coordination bond M(II)-N(py) and vibrational properties and stereochemistry of the dipyridinated iron(II) and cobalt(II) phthalocyaninato complexes, FePc(py)₂ and CoPc(py)₂ (Pc=C₃₂H₁₆N₈, py=C₅H₅N), is carried out using the single crystal X-ray diffraction and the vibrational spectroscopy. Both dipyridinated complexes have been synthesized in crystalline form by heating of the β-FePc or β-CoPc in pyridine at 160°C. The crystals are formed during the slowly cooling process. The crystal of FePc(py)₂ and CoPc(py)₂ are isostructural. They crystallize in the space group P2₁/c of the monoclinic system with two molecules per unit cell. The structural results and coordination bond properties are strictly related in these complexes. The Fe²⁺ and Co²⁺ cations are coordinated by four N-isoindole atoms of the phthalocyaninato(2-) macrocycle and axially by two nitrogen atoms of pyridine molecules to form a tetragonal bypyramid. The vibrational M-N_isoindole parameters are much more affected than the corresponding structural parameters by the difference in the electronic structure of the Co and Fe. The axial M(II)-N(py) bond length depends strongly on the electron configuration of the central metal. The value of the M(II)-N(py) bond length of 2.039(2) A? in FePc(py)₂ and 2.340(2) A? in CoPc(py)₂ clearly evidences on the localization of the unpaired electron on the d_z² orbital of the Co in the cobalt complex. The electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements have also detected the unpaired electron in the molecule of CoPc(py)₂. EPR and magnetic susceptibility measurements performed on a solid sample of FePc(py)₂ shown on its diamagnetic character. The importance of the d(π)→π*(Pc) back donation is manifested in the difference between the values of the C-N_isoindole and C-N_azamethine bond lengths of the Pc macrocycle.

Full text of DOI:10.1016/S0020-1693(02)01060-5

Inorganica Chimica Acta 342 (2003) 64Á76
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Stereochemistry and properties of the M(II)ꢀ
/
N(py) coordination
bond in the low-spin dipyridinated iron(II) and cobalt(II)
phthalocyanines
Jan Janczak ꢀ, Ryszard Kubiak
W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, PL-50-950 Wroclaw, Poland
Received 23 January 2002
Abstract
A comparison between the coordination bond M(II)ꢀ
/
N(py) and vibrational properties and stereochemistry of the dipyridinated
iron(II) and cobalt(II) phthalocyaninato complexes, FePc(py)2 and CoPc(py)2 (Pcꢁ
/
C32H16N8, pyꢁC5H5N), is carried out using
/
the single crystal X-ray diffraction and the vibrational spectroscopy. Both dipyridinated complexes have been synthesized in
crystalline form by heating of the b-FePc or b-CoPc in pyridine at 160 8C. The crystals are formed during the slowly cooling
process. The crystal of FePc(py)2 and CoPc(py)2 are isostructural. They crystallize in the space group P21/c of the monoclinic
system with two molecules per unit cell. The structural results and coordination bond properties are strictly related in these
complexes. The Fe2ꢂ and Co2ꢂ cations are coordinated by four N-isoindole atoms of the phthalocyaninato(2-) macrocycle and
axially by two nitrogen atoms of pyridine molecules to form a tetragonal bypyramid. The vibrational Mꢀ
much more affected than the corresponding structural parameters by the difference in the electronic structure of the Co and Fe. The
axial M(II)ꢀN(py) bond length depends strongly on the electron configuration of the central metal. The value of the M(II)ꢀN(py)
/Nisoindole parameters are
/
/
˚
˚
bond length of 2.039(2) A in FePc(py)2 and 2.340(2) A in CoPc(py)2 clearly evidences on the localization of the unpaired electron on
the d2z orbital of the Co in the cobalt complex. The electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility
measurements have also detected the unpaired electron in the molecule of CoPc(py)2. EPR and magnetic susceptibility
measurements performed on a solid sample of FePc(py)2 shown on its diamagnetic character. The importance of the d(p)0
/
pꢀ(Pc) back donation is manifested in the difference between the values of the Cꢀ
/
Nisoindole and Cꢀ/Nazamethine bond lengths of
the Pc macrocycle.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Metallophthalocyanines; Iron(II) and cobalt(II) complexes; Crystal structures; Low-spin complexes; Spectroscopy; EPR
1. Introduction
energy conversion [5] and even as photosensitizers for
photodynamic cancer therapy [6]. Many of these appli-
cations closely depend on the nature of the metal ion
incorporated at the center of the 18p-electron aromatic
phthalocyaninato(2-) macroring. The mobile p-electrons
of the phthalocyaninato(2-) macrocycle and the possi-
bility of the macrocycle to oxidation or reduction can
serve as current carriers and provide the basis for
semiconducting and conducting properties [7].
The solid state properties of the metal(II) phthalo-
cyanines depend on their crystalline modification. Most
of the metal(II) phthalocyanines crystallize in two, a and
b, crystalline modifications. However, up to now both
forms are structurally characterized by X-ray on single
crystal only for metal-free phthalocyanine [8,9]. In the
The stereochemistry and electronic properties of the
metal(II) phthalocyaninato(2-) complexes (M(II)Pc)
have been widely studied [1]. Metallophthalocyanines
have many unique properties that make them important
and useable in different fields. Especially, they are used
as colorants in the chemical industry [2], organic
semiconductors for gas-sensor [3], visual pigments in
display devices [4], photochemical redox agents in solar
ꢀ Corresponding author. Tel.: ꢂ
029
E-mail address: janczak@int.pan.wroc.pl (J. Janczak).
/
48-71-343 5021; fax: ꢂ48-71-441
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 0 6 0 - 5

J. Janczak, R. Kubiak / Inorganica Chimica Acta 342 (2003) 64Á
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65
course of our investigations of metallophthalocyanines
we have stated on the basis of X-ray single crystal
examination that magnesium phthalocyanine molecules
in the crystal form dimers of (MgPc)2 [10]. This is in
contrast to the metal(II) phthalocyaninato(2-) com-
plexes of the d-block metals (Mn, Fe, Co, Ni, Cu and
Zn), which b form crystal structures are stabilized by the
hexylamine has been characterized by single crystal X-
ray diffraction [22].
The goal of this study was to obtain the iron(II) and
cobalt(II) dipyridineted phthalocyaninato complexes in
the crystalline form and the information concerning
their stability. Subsequently, to extend the information
about the stereochemistry and the coordination bond
properties we compared the crystal structures of
FePc(py)2 and CoPc(py)2 with the previously described
structure of MgPc(py)2 complex [19]. In order to
4ꢂ
/
2 coordination of the central metal ion. The dimers
of (MgPc)2 are stabilized in the crystal by 4ꢂ
/1
coordination of the magnesium ion as a result of the
intermolecular Mgꢀ ꢀ ꢀNazamethine interaction. This inter-
action leads to the significantly great deviation of the
magnesium atom from the phthalocyaninato(2-) plane
and is undoubtedly the reason for the unusual solid-
state properties of magnesium phthalocyanine as well as
for the unstability of the crystals under ambient atmo-
sphere and/or under pure O2 or N2. The magnesium
phthalocyanine in this condition undergoes transforma-
tion to form some complexes with the compositions of
(MgPc)2O2 and (MgPc)2N2 [11].
rationalize, the dependence of the Mꢀ
/
N bonds strength
on their electronic configuration has been discussed.
2. Experimental
2.1. Syntheses of the complexes
The ability of the metal(II) phthalocyanines to
coordinate additional ligands or solvent molecules
containing N or O n-donor atoms is well known. Lever
[12] has mentioned the existence of pyridine complexes
in solution for FePc, MgPc and for MnPc. However,
later it has been stated that the MnPc is able to form a
stable pyridine complex only in an oxidative form; and
the m-oxo-bis(phthalocyaninato(2-)) manganese(III)
complex, (MnPc(py))2O, has been isolated and structu-
rally characterized [13,14]. An existence of the six-
coordinated complex between 4-methylpyridine and
FePc has also been reported [15]. Later this bis(4-
methylpyridine) phthalocyaninato(2-) iron(II) complex
and the corresponding cobalt phthalocyanine complex
have been structurally characterized [16]. Subsequently
for CoPc the five- and six-coordinated pyridine com-
plexes, CoPc(py) and CoPc(py)2, have been reported
[17,18], however, well-characterized solid compounds on
single crystal have never been described.
The FePc and CoPc were obtained from Aldrich.
Although, the bottles were labeled as iron and cobalt
phthalocyanines the analysis implies on the small
amount of impurity. Both metallophthalocyanines
were purified by heating under vacuum at about
210 8C. After 1 day the purity of both metallophthalo-
cyanines have been checked on an energy dispersive
spectrometer (the purity over 99.0%). The X-ray powder
diffraction patterns clearly shown that both M(II)Pc
after heating procedure exist in b-crystalline modifica-
tion. The single crystals of FePc(py)2 and CoPc(py)2
suitable for X-ray analysis have been obtained by
following procedure. A suspension of 0.2 g FePc or
CoPc (both in b-form) in 50 ml of twice distilled and dry
pyridine was heated in an evacuated glass ampoule at
160 8C for 5 h. Next the ampoule was slowly cooled to
the room temperature (r.t.) (3 8C hꢃ1). During the
cooling procedure the parallelepiped violet crystal of
FePc(py)2 or CoPc(py)2 in various size were formed.
Elemental analysis was carried out on an energy
dispersive spectrometer. Found for FePc(py)2: C,
69.49; H, 3.70; Fe, 7.47 and N, 19.34%, for CoPc(py)2:
C, 69.22; H, 3.51; Co, 8.12; and N, 19.15%. Calc. for
C32H16N8Fe(C5H5N)2: C, 69.43; H, 3.61; Fe, 7.69 and
N, 19.27% and for C32H16N8Co(C5H5N)2: C, 69.14; H,
3.58; Co, 8.08 and N, 19.20%.
In the course of our investigations, quite recently,
studying the magnesium phthalocyanine in pyridine
solution, we have obtained the dipyridinated magnesium
phthalocyanine MgPc(py)2 complex in crystalline form
[19]. Additionally we have stated that the crystals of
MgPc(py)2 are stable under dry atmosphere, and under
moist this complex interacts with the water molecules
and converts into the MgPcH2O×
scheme: MgPc(py)2ꢂH2O0MgPcH2O×
plex of MgPcH2O×2py has been previously structurally
/
2py according to the
/
/
/2py. The com-
/
2.2. Thermal measurements
characterized [20]. For the complex of MgPc axially
ligated by two pyridine molecules, we have not observed
any evidence for the existence of the 1:1 complex as was
mentioned for the complex of CoPc with pyridine [18].
In addition it has been shown that zinc phthalocyanine
forms some complexes with various amines [21,22], and
one of them, the zinc phthalocyanine complex with n-
Thermal analyses were carried out on a Lineis L81
thermobalance aparaturs with Pt crucibles. The pow-
dered Al2O3 has been used as a standard reference. The
measurements on the several samples have been per-
formed under static air atmosphere on heating from r.t.
to about 300 8C with the heating rate of 2 8C minꢃ1
.

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Table 1
Crystal data, data collection and refinement details for FePc(py)2 and CoPc(py)2
Formula
C32H16N8Fe(C5H5N)2
726.58
C32H16N8Co(C5H5N)2
729.66
Molecular weight
Crystal system
Space group
monoclinic
P21/c
monoclinic
P21/c
Unit cell dimensions
˚
a (A)
˚
9.576(2)
19.929(4)
9.179(2)
111.68(3)
1627.8(6)
2
9.865(2)
19.904(4)
9.142(2)
112.10(3)
1663.8(6)
2
b (A)
˚
b (A)
b (8)
Volume, V (A)
˚
Z
Dcalc. (g cmꢃ3
)
1.482
1.48
0.71073
1.457
1.45
0.71073
Dobs. (measured, floatation) (g cmꢃ3
)
˚
Radiation, Mo Ka (A)
Index ranges
h
ꢃ13012
ꢃ26027
ꢃ10012
15 338
ꢃ13013
ꢃ25027
ꢃ11012
13 345
k
l
Reflections collected
Independent reflections
Observed reflections
4236 (Rintꢁ0.0629)
1901 [I ꢀ2s(I)]
0.514
3934 (Rintꢁ0.0427)
2295 [I ꢀ2s(I)]
0.566
Absorption coefficient m (mmꢃ1
)
Correction: Lorentz polarization, face-indexed analytical absorption
Tminꢁ0.8527, Tmaxꢁ0.9456
Tminꢁ0.8053, Tmaxꢁ0.9352
Refinement on F2
R(F2ꢀs)
0.0548
0.0665
0.0417
0.0809
wR(F2 all reflections)
Goodness-of-fit, S
Largest D/s
0.996
0.000
1.015
0.000
ꢃ3
˚
Residual electron density e A
ꢂ0.380, ꢃ0.577
ꢂ0.312, ꢃ0.283
RꢁSjjFojꢃjFcjj/SFowR(F2)ꢁ{S(w(Fo2ꢃFc2)2]/SwFo
}
1/2; wꢃ1ꢁ[s2(Fo2)ꢂ(0.0143P)2] for Fe complex and wꢃ1ꢁ[s2(Fo2)ꢂ0.0312P] for Co
4
complex where Pꢁ(Fo2ꢂ2Fc2)/3.
2.3. X-ray single crystal measurements
were refined with anisotropic thermal parameters for all
non-hydrogen atoms by full-matrix least-squares meth-
ods using SHELXL-97 program [25]. More details on data
collection and refinement parameters are collected in
Table 1.
Data collection for both single crystals were carried
out on a four-circle KUMA KM-4 diffractometer
equipped with a two-dimensional area CCD detector.
The graphite monochromatized Mo Ka radiation (lꢁ
/
˚
0.71073 A) and v-scan technique with Dvꢁ
/
0.758 for
2.4. Electron paramagnetic resonance measurements
one image were used for data collection. The 960 images
for six-different runs covering over 90% of the Ewald
sphere were performed. One image as a standard was
used for monitoring the intensities after every 40 images.
Integration of the intensities, correction for Lorenz and
polarization effects were performed using a KUMA KM-4
CCD software [23]. The face-indexed analytical absorp-
tion was calculated using the SHELXTL program [24].
Almost 4236 for FePc(py)2 and 3934 for CoPc(py)2
Electron paramagnetic resonance (EPR) measure-
ments were carried out on SE-Radiopan and ESP 300
E-Bruker X-band spectrometers at r.t. The studies were
performed on solid samples of 2Á10 mg. The g-factors
/
and the line widths of the signals were determined. The
concentration of the free radicals in the CoPc(py)2
samples were calculated using standard integration of
the derivative signal and by comparing the area of the
free EPR signal with the area determined with the free
radical standard. DPPH, TEMPO, TEMPOL and
Rickitt’s ultramarine were used as standards [26].
independent reflections (total 15 338 and 13 345, Rint
ꢁ
/
0.0640 and 0.0427, for Fe and Co crystal, respectively)
were used for crystal structure solution and refinement.
Both structures were solved by the Patterson method.
The hydrogen atoms of the phenyl rings were located
from Dr maps, but in the final refinement their
positions were constrained using HFIX 43 with the
isotropic thermal parameters of 1.2Ueq of the carbon
atoms linked directly to the H atoms. Both structures
2.5. Magnetic susceptibility measurements
The temperature dependence of the magnetic suscept-
ibility were taken from 300 to 1.8 K with a Quantum
Design SQUID magnetometer (San Diego, CA). Data

J. Janczak, R. Kubiak / Inorganica Chimica Acta 342 (2003) 64Á
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67
were recorded at the magnetic field of 0.5 T on samples
of 30Á100 mg.
/
2.6. Spectroscopic measurements
Middle-IR spectra of the solid material (KBr pellets)
and Far-IR spectra (Nujol mulls, polyethylene disc)
were recorded at r.t. on a Bruker IFS 113 V FTIR
spectrometer. Measurements of the electronic spectra
were carried out at r.t. using a CARRY VARIAN/
5EUV-VIS-NIR spectrometer. The UVÁVis spectra
/
were recorded from solution in dichloromethane, pyri-
dine and DMSO in 0.5 cm quartz cell.
3. Results and discussion
3.1. Synthesis and characterization
Fig. 1. Thermograms of the solid state samples of the FePc(py)2 (a)
and CoPc(py)2 (b) complexes.
Our preparation method of the single crystals of the
dipyridinated iron and cobalt phthalocyaninato(2-)
complexes, FePc(py)2 and CoPc(py)2, is very fast and
simple. A suspension of b-FePc and b-CoPc in purified
pyridine was heated in an evacuated glass ampoule at
160 8C by 5 h. During the heating process the molecule
of FePc or CoPc interacts by its positively charged
central metal atom with the lone electron pair of
nitrogen atom of pyridine molecule. As a result of the
interaction the dipyridinated complexes are formed.
During a slowly cooling process (108 hꢃ1) the violet
crystals are appeared. The first crystals have been
observed at about 100 8C; from this temperature point
the cooling process was twice slower. The obtained
crystals of FePc(py)2 and CoPc(py)2 are well soluble in
pyridine, DMF, DMSO and other N- and O-donor
solvents as well as in an aromatic solvents like quinoline
or chloronaphthalene. The solubility in water is not
significant.
relation to the magnesium ion and, therefore, the
coordination Mꢀ
/
N(py) bonds (MꢁFe, Co) are much
/
stronger than in the magnesium analogue [15]. Contact
of the FePc(py)2 and CoPc(py)2 with dilute acid lead to
the demetallation, yielding metal-free phthalocyanine in
the a form, which was identified by X-ray powder
diffraction method [9].
As can be seen from the thermograms (Fig. 1(a) and
(b)), the FePc(py)2 complex is more stable than the
cobalt analogue. Thus, it should be stated that the axial
coordination Feꢀ
/
N(py) bonds in FePc(py)2 are stronger
than the CoꢀN(py) bonds in the CoPc(py)2 complex.
/
The CoPc(py)2 complex is stable up to about 140 8C,
while the FePc(py)2 complex is stable up to about
225 8C. Above these temperature points two axial
equivalent bonds in FePc(py)2 and in CoPc(py)2 break
simultaneously giving FePc and CoPc in powdered
form. Their X-ray powder diffraction patterns indicate
on the b modification. There was no evidence on the
formation of the 1:1 adducts (M(II)Pc:py) by the
thermal dissociation.
In contrast to the crystals of MgPc(py)2 which are
unstable under laboratory atmosphere, both dipyridi-
neated iron and cobalt phthalocyaninato(2-) complexes
are stable. The crystals of MgPc(py)2 under moist
atmosphere interact with water molecules and transform
into a hydrated complex with the composition of
(MgPcH2O)×
/
2py. In the crystal of (MgPcH2O)×
/
2py the
3.2. Description of the structures
water molecule is coordinated to the magnesium cation,
while the pyridine molecules as acceptors are joined to
The crystals of the two complexes are isostructural.
The molecular structure of the dipyridinated iron and
cobalt phthalocyaninato(2-) complexes is illustrated in
Fig. 2. The metal cations (Fe, Co) lie at the inversion
center, thus, the M(II)Pc(py)2 molecules are centrosym-
metric. The coordination polyhedron around Fe(II) and
Co(II) approximates to a tetragonal bypiramid. In both
complexes the central metal ion (Fe2ꢂ, Co2ꢂ) and the
four coordinated isoindole nitrogen atoms of the
phthalocyaninato(2-) macrocycle lie on a plane. The
the MgPcH2O by Oꢀ
water molecule [15]. Thus, the coordination Mgꢀ
bond is stronger than coordination MgꢀN(py) in
/
Hꢀ ꢀ ꢀN(py) hydrogen bonds with
/
O
/
magnesium phthalocyaninato complexes, while in both
Fe and Co complexes the coordination bonds with axial
pyridine molecules are stronger than the bonds with
ligands containing oxygen atom. This is probably due to
the dp(metal)0
/
pꢀ(Pc) back donation which make the
central metal ion (Fe, Co) much more positive in

68
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Table 2
Selected bond lengths (A) and angles (8) for FePc(py)2 and CoPc(py)2
˚
FePc(py)2
CoPc(py)2
Bond lengths
MꢀN1
MꢀN3
MꢀN5
N1ꢀC1
N1ꢀC8
N2ꢀC8
N2ꢀC9
N3ꢀC9
N3ꢀC16
N4ꢀC1i
N4ꢀC16
1.938(2)
1.939(2)
2.039(2)
1.366(3)
1.382(3)
1.333(3)
1.330(3)
1.381(3)
1.378(3)
1.335(3)
1.325(3)
1.930(2)
1.931(2)
2.340(2)
1.376(2)
1.376(2)
1.333(2)
1.329(2)
1.376(2)
1.377(2)
1.327(2)
1.327(2)
Bond angles
N1ꢀMꢀN3
N1ꢀMꢀN3i
N1ꢀMꢀN5
N1ꢀMꢀN5i
N3ꢀMꢀN5
N3ꢀMꢀN5i
90.19(8)
89.81(8)
90.47(8)
89.53(8)
90.00(8)
90.00(8)
90.01(7)
89.99(7)
91.28(6)
88.72(6)
89.33(6)
90.67(6)
458, makes the axial pyridine ligand plane parallel to the
MꢀN(azamethine) axis and reduces the non-bonding dis-
/
tances between hydrogen atoms of pyridine (H in orto
positions) and the azamethine nitrogen atoms of phtha-
locyaninato(2-) macrocycle. This conformation of
MPc(py)2 complexes is the most stable, and is preferable
in the solution, since the greatest interaction (attractive
forces) between the hydrogen atoms of pyridine mole-
cules in orto positions and the N-azamethine atoms. The
intermolecular interactions as well as the crystal packing
forces present in the crystal make the rotation angle of
the axial pyridine plane to the value of 28.6(2)8 in
CoPc(py)2 and 36.1(2)8 in FePc(py)2. These angles are
significantly different to that observed in the axially
ligated by 4-methylpyridine cobalt and iron phthalocya-
ninato(2-) complexes (see Table 3); this is likely due to
the additional interaction with the additional 4-methyl-
pyridine molecule, since they crystallizes with 4-methyl-
pyridine molecules as solvent [16]. In the isostructural
crystals of MgPc(py)2 the rotation angle of axial
pyridine molecule is much more similar to the cobalt
than to the iron complex, 26.6(2)8 [19].
Fig. 2. Molecular structure of the FePc(py)2 (a) and CoPc(py)2 (b)
with the labeling of the atoms. Displacement ellipsoids are drawn at
the 50% probability level. Hydrogen atoms are shown as spheres of an
arbitrary radius.
two axial pyridine molecules are coordinated by their
lone-electron pair at the nitrogen atom to the central
metal cation. The dihedral angle between the N4-
isoindole plane of phthalocyaninato macrocycle and
that containing the axially coordinated pyridine mole-
cules is only slightly different from 908 (89.37(8) and
89.04(8)8 in FePc(py)2 and in CoPc(py)2, respectively).
The orientation of the axial pyridine ligands relative to
the phthalocyaninato(2-) ring is well described by the
The main differences between FePc(py)2 and
torsion angle of N3ꢀ
/
Mꢀ
/
N5ꢀ
/
C17 (Mꢁ
/
Fe, Co). The
N5 axis
CoPc(py)2 structures are found in the axial Mꢀ
/N(py)
rotation of pyridine ligand around the Mꢀ
/
bond distances (Table 2), which are longer in the
˚
CoPc(py)2 [2.340(2) A] than in the FePc(py)2 [2.039(2)
would reduce the steric effect, i.e. the non-bonding
distances between the hydrogen atoms of the axial
pyridine ligand in orto positions and the atoms of the
phthalocyaninato(2-) macrocycle. In particular, if the
rotation angle is equal 0, the pyridine plane is parallel to
˚
A], and as mentioned above in the rotation angle of
axially coordinated pyridine ligands. The long Coꢀ
/
N(py) axial bond in CoPc(py)2 is likely due to the
unpaired electron which is essentially localized on the dz2
orbital of the Co2ꢂ. The unpaired electron has also been
detected by EPR measurement on a solid state sample.
the Mꢀ
/
N3 bond, or at equivalent position rotated by
N1 bond,
908, the pyridine molecule is parallel to the Mꢀ
/
making the non-bonding Cꢀ ꢀ ꢀH distances greater than
˚
2.5 A. The second orientation, with the rotation angle of
The values of the Mꢀ/N(py) coordination bond length in

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69
Table 3
Comparison of the coordination of the central metal ion in dipyridinated phthalocyaninato(2-) complexes
Compound
FePc(py)2
FePc(4-Mepy)2
FePc
CoPc(py)2
CoPc(4-Mepy)2
CoPc
MgPc(py)2
MgPc
˚
MꢀNiso (A)
1.938(2)
2.039(2)
36.1(2)
1.935(3)
2.040(3)
42.6(4)
1.373(7)
1.328(4)
[16]
1.926(2)
1.930(2)
2.340(2)
28.6(2)
1.930(4)
2.322(5)
35.7(5)
1.373(7)
1.334(7)
[16]
1.908(2)
2.006(2)
2.376(2)
26.6(2)
1.367(2)
1.343(2)
[19]
2.011(3)
˚
MꢀNaxial (A)
Rotation angle (8)
˚
CꢀNiso (A)
1.377(3)
1.331(3)
This work
1.378(3)
1.322(3)
[35]
1.376(2)
1.329(2)
This work
1.368(4)
1.318(4)
[33]
1.376(2)
1.334(2)
[10]
˚
CꢀNaza (A)
Reference
both complexes indicate on their strength and well
correlate with the stability of these complexes. The axial
pyridine molecules are stronger coordinated in Fe-
complex, and the FePc(py)2 complex is more stable
than the CoPc(py)2 complex, as shown the termogravi-
metric experiments. A similar correlation between the
short, in Pc-plane, and long, perpendicular to the Pc,
Mꢀ
/
N bond distances are observed in cobalt phthalo-
cyaninato(2-) complex with two axially coordinated 4-
methylpyridine molecules [16] and in the isostructural
crystal of MgPc(py)2 (Table 3) [19]. The long Mꢀ
/
N
coordinated bonds have also been observed in several
axially coordinated porphyrinato magnesium complexes
[27Á30], and in axially coordinated porphyrinato cobal-
/
t(II) complexes [31,32].
The coordination bond distance calculated by Little
2
N(sp ) is equal to 2.05 A (in the
˚
and Ibers Co(III)ꢀ
/
absence of electron localization on the d2z orbital) [32].
Therefore, the lengthening of the axial Co(II)ꢀN(py)
/
˚
bond by about 0.3 A in octaethyl-prophyrinato(2-)co-
balt(II) complex ligated axially by two molecule of 3-
methylpyridine is attributed to the occupancy of dz2
Fig. 3. Arrangement of the M(II)Pc(py)2 molecules (Mꢁ
the unit cell.
/
Fe,Co) in
orbital by a single unpaired electron. The value of 2.05
˚
A for the Co(III)ꢀ
/
N(sp2) bond in absence of electron on
˚
d2z orbital correlate well with the value of 2.039(2) A
observed in the low-spin FePc(py)2 complex for axially
coordinated pyridine molecules. This is in agreement
with the absence of the EPR signal for the solid state
sample of FePc(py)2 (the low-spin complexes of Fe(II)
are EPR inactive).
the metal d(p) orbitals to the ligand pꢀ(eg) antibonding
orbital, since the calculated maximum charge density is
mainly located on those atoms [37Á39]. The accumula-
/
tion of the charge density on the outer carbon atoms of
pyrrole rings and on the bridging azamethine nitrogen
atoms of the phthalocyaninato(2-) macrocycle has been
also evidenced in the experimental density maps derived
from the low temperature high resolution X-ray experi-
ments [40].
The arrangement of the FePc(py)2 and CoPc(py)2
molecules in the unit cell is illustrated in Fig. 3. Both
crystals are built up from isolated M(II)Pc(py)2 mole-
cules, which form alternating sheets, which molecules
related by a screw axis and glide plane. In one sheet the
planes of phthalocyaninato(2-) macrocycle are parallel
to each other, while between the sheets the phthalocya-
ninato(2-) planes are perpendicular. Within each sheet
the neighboring molecules are overlapped by their two
The Cꢀ
/
C and Cꢀ
/
N bond distances of the phthalo-
cyaninato(2-) macrocycle in both M(II)Pc(py)2 com-
plexes are normal, the values of the chemically
equivalent bond lengths are not different from the
corresponding values found in other metallophthalo-
cyaninato complexes [33Á36]. However, it should be
/
noted that the good accuracy of the present structure
determinations and relatively low standard deviations
indicate on the small differences between the average
values of Cꢀ
/
Niso and Cꢀ/Naza bond lengths (Table 3).
These differences indicate an accumulation of the charge
density on the outer carbon atoms of pyrrole rings as
well as on the bridging azamethine nitrogen atoms of the
phthalocyaninato(2-) macrocycle and can, therefore, be
explained by an important electron back donation from
˚
phenyl rings which are separated by about 3.3 A in
˚
FePc(py)2 and about 3.4 A in CoPc(py)2. These values

70
J. Janczak, R. Kubiak / Inorganica Chimica Acta 342 (2003) 64Á76
/
Mꢀ
/
N coordination bond strength. Therefore, this
method have also been used for characterization of the
dipyridineated iron and cobalt phthalocyaninato com-
plexes. The IR spectra of FePc(py)2 and CoPc(py)2
complexes in the low-frequency region (500Á )
100 cmꢃ1
/
are shown in Fig. 4(a) and (b). A comparison of the
frequencies of the dipyridinated iron and cobalt phtha-
locyaninato complexes with their non-ligated FePc and
CoPc are collected in Table 4. As can be seen from Table
4 all the bands related the vibration of the phthalocya-
ninato(2-) macrocyclic ligand are shifted to the higher
frequency compared with the metal-free phthalocyanine
[42Á
/
44]. However, the Mꢀ/N stretching assignments for
several metallophthalocyaninato complexes by Kobaya-
shi [43], which are widely cited, were done only on the
basis of the appearance of the bands in the spectra of
metallophthalocyanines, which did not appear in the
spectrum of metal-free phthalocyanine. Therefore, the
assignment of the Mꢀ/N stretching vibration band for
several metallophthalocyanines in the spectral region
from 185 to 98 cmꢃ1 presents some difficulties, since the
bands in this region could be attributed to the bending
Nꢀ
The assignments of the Mꢀ
the NꢀMꢀN angular deformation presented here are
/
Mꢀ
/
N motion.
/N stretching vibration and
/
/
empirical but supported by analogy to that carried out
for several isotope-substituted metallophthalocyanines
[44] and metalloporphirines [45Á50]. The normal co-
ordinate analyses for metallophthalocyanines [51] as
well as the semi-empirical calculated spectra predict one
/
Fig. 4. Fra-IR spectrum of FePc(py)2 (a) and CoPc(py)2 (b).
are comparable with the van der Waals distance (ꢁ
/
3.4
A) [41] for an aromatic carbon atoms and indicate on
the pÁp clouds interaction between the ring system.
IR-active Mꢀ
/
N stretching mode [52,53], however, since
˚
the conjugated ring system in this mode may be mixed
with the macrocyclic motions and distributed into more
than one absorption [45]. The comparison between FePc
and CoPc and their dipyridinated complexes are com-
prised in Table 4. In the non-ligated FePc and CoPc
/
3.3. Vibrational properties
complexes, the one Mꢀ
/
N stretching vibration band (Eu)
The vibrational properties, especially that in the low-
frequency spectroscopic region, can be easily related to
the stereochemical features, since they can serve to
provide information about the reflect changes in the
metal oxidation state and the symmetry surrounding the
central metal as well as giving direct information on the
has been observed in agreement with the D4h symmetry
of chromofore. The ligation of FePc and CoPc by two
pyridine molecules leads to the lowering of the com-
plexes to the D2h symmetry, and two IR-active bands
(B2uꢂB3u) should be expected. However, in both
/
Table 4
Comparison of the far-infrared spectral data of the FePc(py)2 and CoPc(py)2 and their non-ligated phthalocyanines: b-FePc and b-CoPc
Compound
n(MꢀN(py))
d(NꢀMꢀN)
Ring deformation bands
Reference
b-FePc
308s
331s
330s
314s
312s
312s
160vs, 154sh
165m
160s
515m, 435vs, 343w, 292m, 232w, 124s
519m, 443vs, 366w, 301m, 240w, 195w, 128m
520m, 444vs, 389w, 300s, 246m, 118m
519m, 435vs, 372w, 302s, 240w, 122s
516s, 435vs, 429w, 300m, 228w, 122w-
518s, 435vs, 298m, 228w, 124m
[42,43,45,63]
This work
[16]
FePc(py)2
FePc(4-Mepy)2
b-CoPc
172vs
173s
172vs, 166sh
[42,43,63]
this work
[16,54]
CoPc(py)2
CoPc(4-Mepy)2
b-H2Pc
498m, 435m, 342m, 282s, 238w, 140w, 127w
[42,43,63]
v, very; s, strong; m, medium; w, weak; sh, shoulder.

J. Janczak, R. Kubiak / Inorganica Chimica Acta 342 (2003) 64Á
/76
71
dipyridinated complexes only one stretching vibration
band is observed (Fig. 4(a) and (b)). This is probably
due to the long axial bond, especially observed in the
Co-complex, resulting in a reduction of the splitting of
the Eu stretching band; undoubtedly the difference
is in agreement with the EPR measurement (no EPR
signal for the FePc(py)2 complex was observed). The
occupation of the eg orbitals, to which back donation is
done, increases from b-FePc to FePc(py)2. This is in
agreement with the large shift of the n(Feꢀ
/
N(pc))
between the Mꢀ
/
N(py) bond length in Fe and Co
˚
stretching vibration in FePc(py)2 to a higher frequency.
This cannot be the case for the cobalt complexes, which
have the same ground-state configuration. The differ-
ence in the electronic configurations also explains the
complexes of 0.28 A is not effective in this context as
suggested Cariati et al. [16]. The splitting of the N(pc)ꢀ
N(pc) angular deformation observed in the spectrum
/
Mꢀ
/
of cobalt phthalocyanine ligated axially by two molecule
of 4-methylpyridine is in agreement with the observed
differences in the Mꢀ
/
N(pc) energy between the
FePc(py)2 and CoPc(py)2 complexes. The contribution
of the double excited configuration e3gb22a12g to the
ground state of the cobalt complex is certainly more
important than the triplet excited configuration e3gb22a1g
to the ground-state of FePc(py)2 complex, what explains
difference between the N1(pc)ꢀ
Coꢀ
N3i(pc) angles [16,54]. A similar splitting of the
N(pc)ꢀFeꢀN(pc) is observed in the spectrum of b-FePc.
/
Coꢀ
/
N3(pc) and N1(pc)ꢀ
/
/
/
/
The angular anisotropy of the b-FePc is in agreement
with the X-ray structural results [35], they have shown
the observed lower value of n(Coꢀ/N(pc)) vibrational
the difference between the N1ꢀ
/
Feꢀ
/
N3 and N1ꢀ
/
Feꢀ
/
N3i
frequency in the spectrum of the CoPc(py)2 complex.
The vibrational data clearly evidence that the electronic
ground-state configuration is mainly responsible for the
angles and confirm that the bending vibrational fre-
quencies are more sensitive to the structural changes
than the stretching vibration. In these dipyridinated iron
and cobalt phthalocyaninato complexes, the X-ray
change of the n(Coꢀ/N(pc)) vibrational frequencies
observed in the spectra of Fepc(py)2 and CoPc(py)2
complexes. The difference of the mass between the iron
and cobalt complexes play minor role, otherwise the
structural results have clearly shown that the N1ꢀ
N3 and N1ꢀMꢀ Fe, Co) are almost
N3i angles (Mꢁ
identical and almost equal to 908, therefore, a single
unsplitt N(pc)ꢀMꢀN(pc) angular deformation band has
been observed in both far-infrared spectra. Comparing
the far-infrared spectra of FePc(py)2 and CoPc(py)2
(presented here) with the spectra of their non-ligated
FePc and CoPc complexes [43,45] (Table 4), we were not
/
Mꢀ
/
/
/
/
difference in the stretching vibration n(Mꢀ
/
N(pc)) be-
/
/
tween these dipyridinated complexes would be compar-
able to assign any band to the Feꢀ
/
N(py) and Coꢀ
/
N(py)
vibration, which would be expected near 300 cmꢃ1. This
is probably due to their weak intensity or/and coupled.
The frequency of the n(Feꢀ
tion is strongly affected by the axial coordinated
pyridine molecules in FePc(py)2 (the shift ꢁ
23 cmꢃ1
in relation to b-FePc), while the frequencies of the
n(CoꢀN(pc)) stretching vibration in b-CoPc as well as in
/N(pc)) stretching vibra-
/
/
CoPc(py)2 are almost the same (see Table 4). This can be
explained by the change of the ground-state configura-
tions of the ligated iron phthalocyanine (FePc(py)2) in
relation to non-ligated iron phthalocyaninie (b-FePc)
and unchanged ground state configuration in ligated
and non-ligated cobalt phtalocyaninato complexes. In
accordance to the magnetic properties [55Á58] and EPR
/
measurements [59] performed on the b-CoPc the
ground-state configuration can be expressed: e4gb22ga1g.
The EPR and magnetic measurements performed on the
ligated dipyridinated cobalt phthalocyanine (presented
here) clearly show the unchanged ground-state config-
uration of the central cobalt ion. The ground-state
configuration of intermediate-spin complex of iron(II)
phthalocyanine (b-FePc) with the spin Sꢁ
/
1 [35] accord-
ing to the EPR, magnetic and Mossbauer measurements
¨
can be expressed as: e3gb22ga11g or eg2b22ga12g [60Á
62]. The
ligation of FePc by two pyridine molecules leads to the
/
change of the ground state configuration to e4gb22g, which
Fig. 5. Middle IR spectrum of FePc(py)2 (a) and CoPc(py)2 (b).

72
J. Janczak, R. Kubiak / Inorganica Chimica Acta 342 (2003) 64Á76
/
Table 5
Middle-IR spectral data for FePc(py)2 and CoPc(py)2 (in cmꢃ1
)
a
FePc(py)2
FePc [63]
CoPc(py)2
CoPc [63]
Assignment
571 (m)
641 (w)
574 (w)
642 (w)
572 (m)
641 (w)
574 (m)
642 (m)
f(CꢀC) macrocycle ring deformation
f(CꢀC) macrocycle ring deformation
g(CꢀH) in pyridine
g(CꢀH) out of plane deformation
g(CꢀH) in pyridine
g(CꢀH) out of plane deformation
n(CꢀN) stretching
698 (m)
727 (vs)
736 (m)
752 (m)
779 (w)
695 (m)
727 (vs)
737 (m)
754 (m)
775 (m)
868 (w)
732 (vs)
730 (vs)
755 (s)
755 (s)
780 (s)
865 (w)
911 (s)
781 (m)
875 (w)
909 (m)
869 (w)
915 (w)
931 (w)
g(CꢀH) out of plane deformation
g(CꢀH) out of plane deformation
n(CꢀN) in pyridine
913 (m)
935 (w)
1040 (w)
1069 (m)
1089 (m)
1096 (m)
1117 (s)
1160 (m)
1165 (m)
1216 (w)
1286 (m)
1327 (m)
1367 (m)
1377 (vs)
1421 (m)
1445 (m)
1465 (vs)
1482 (s)
1509 (w)
1034 (w)
1072 (m)
1091 (s)
1097 (m)
1120 (s)
1158 (m)
1165 (m)
1216 (w)
1286 (m)
1328 (m)
1368 (m)
1378 (vs)
1421 (m)
1446 (m)
1463 (vs)
1480 (m)
1519 (m)
b(CꢀH) in pyridine
1069 (m)
1084 (s)
1072 (s)
1086 (s)
b(CꢀH) in plane deformation
n(CꢀN) stretching in pyrrole
n(CꢀN) in pyridine
b(CꢀH) bending in plane
b(CꢀH) bending in pyridine
n(CꢀN) in plane
n(CꢀN) in pyridine
n(CꢀN) in isoindole
n(CꢀC) in isoindole
n(CꢀC) in pyridine
n(CꢀC) in pyridine
n(CꢀC) in isoindole
n(CꢀC) in pyridine
n(CꢀC) in pyridine
n(CꢀC) in pyridine
n(CꢀC) in pyrrole
1120 (vs)
1120 (vs)
1163 (s)
1162 (s)
1288 (m)
1332 (s)
1288 (s)
1333 (vs)
1420 (s)
1510 (s)
1426 (s)
1520 (s)
a
v, very; s, strong; m, medium; w, weak.
able with that between the b-FePc and b-CoPc. It can be
concluded that the vibrational data can be correlated
with the structural results only if the electronic config-
uration does not change.
The middle IR spectra of FePc(py)2 and CoPc(py)2
are shown in Fig. 5(a) and (b), respectively. Comparison
with their non-ligated b-FePc and b-CoPc complexes is
listed in Table 5. The spectroscopic characterization of
the FePc and CoPc assignment of the bands for b-FePc
and b-CoPc are widely described in the literature
[42,43,45,63]. As can be seen from Table 5 the most of
the IR bands present in the spectrum of b-FePc and b-
CoPc are also observed in the spectrum of dipyridinated
iron and cobalt phthalocyaninato complexes but with
slightly modified frequencies. The assignment of the
bands related to the axially coordinated pyridine
molecules is supported by correlation with the spectrum
of free pyridine and several metallodipyridinated com-
plexes M(py)2X2 [64]. The discussion of the spectro-
scopic properties in more details and assignments of the
vibrational bands in the middle IR spectrum have been
made in previous paper [19] which reported the spectro-
scopic properties and structure of dipyridinated magne-
sium phthalocyanine, MgPc(py)2.
3.4. Magnetic properties
A plot of the reciprocal molar susceptibility versus
temperature for the CoPc(py)2 complex is shown in Fig.
6. To the molar susceptibility the correction for dia-
magnetic susceptibility of the phthalocyanine molecule
has been included [58]. The experimental data are well
approximated by a CurieÁ/Weiss law with the value of
Fig. 6. Plot of the inverse molar susceptibility vs. temperature for the
CoPc(py)2 complex.
u $ 8.5 K for the Curie constant. The effective
/
ꢃ
/

J. Janczak, R. Kubiak / Inorganica Chimica Acta 342 (2003) 64Á
/76
73
Table 6
Effective magnetic moment for M(II)Pc and M(II)Pc(py)2 complexes
Compound
Coordination number of
the central metal
Number of unpaired
electrons
meff (mB)
Theoretical spin-only
(mB)
Theoretical L-S
(mB)
Reference
a-CoPc
b-CoPc
CoPc(py)2
b-FePc
4
4
6
4
6
4
6
1
1
1
2
0
4
2
2.14Á
2.66Á
1.82
/
2.38 1.73
3.00
3.00
3.00
4.47
0
[55,59,61]
[55,57,59]
this work
/2.73 1.73
1.73
3.71Á
/
3.85 2.83
0
[55,57,61,65]
this work
[55]
FePc(py)2
0
CrPc
CrPc(py)2
3.49
3.16
4.89
2.83
5.48
4.47
[55]
magnetic moment calculated for the CoPc(py)2 at room
temperature (298 K) is meff
1.82 mB, and indicates on
samples magnetically diluted by isomorphic crystal of
diamagnetic metal-free phthalocyanine, NiPc or ZnPc
[59]. The EPR spectra of both a- and b-CoPc complexes
exhibit, similarly to the CoPc(py)2 complex, an axial
symmetry (see Table 7). The resolving of the hyperfine
coupling is hindered in the polycrystalline solid sample,
but the shift of the gꢁ value towards higher fields is
observed, correlating to the greater strength of the axial
ligands.
The magnetic susceptibility of the iron phthalocya-
nine, FePc, has been performed several times
[55,57,61,65] and the effective magnetic moment (Table
6) is intermediate between theoretical spin-only values
ꢁ
/
the one unpaired electron per CoPc(py)2 molecule. For a
comparison, the effective magnetic moment measured
on the non-ligated cobalt(II) phthalocyanine depends on
the crystal modification of the CoPc complex. The
effective magnetic moment at room temperature re-
ported by several authors [55,57,59,61,65] for the a-
CoPc is about 15% lower than that observe for b-CoPc.
The comparison of magnetic properties for CoPc(py)2
and a-CoPc and b-CoPc is collected in Table 6, which
also comprise the properties of other ligated and non-
ligated phthalocyaninato complexes, M(II)Pc and
M(II)Pc(py)2. The effective magnetic moment of the
CoPc(py)2 is slightly greater than the spin-only value of
1.73 mB, but significantly smaller than those found in
both a-CoPc and b-CoPc. The greater values of the
magnetic moment in the a-CoPc and b-CoPc complexes
in relation to the dipyridinated complex can be ex-
plained by a greater contribution of the orbital moment
to the ground state. The value of the magnetic moment
of 1.82 mB indicates on the low-spin CoPc(py)2 complex.
The EPR measurement on a solid crystalline sample
of CoPc(py)2 shows axial magnetic symmetry with two
Sꢁ
FePc [60,66,67] indicate that the central ion in the FePc
molecule is in Sꢁ1 state with a large zero-field splitting
such that the level MSꢂ
O lies about 70 cmꢃ1 below the
/
1 and Sꢁ
/
2 state. The Mossbauer studies on the
¨
/
/
doublet MSꢁ
/
91[60]. The electronic configuration was
/
assumed to be (dxzdyz)3(dxy)2(d2z)1 giving na orbitally
3
non-degenerate ground term B2g with two unpaired
electrons. The EPR measurement performed on a solid
polycrystalline sample of FePc(py)2 showed no reso-
nance signal. The magnetic susceptibility experiment on
polycrystalline sample of FePc(py)2 shows its diamag-
netic character. Both EPR and magnetic susceptibility
principal g values: gꢁ ꢁ
calculation of the spin concentration yields 8.29ꢄ
spins per g, i.e. $1 unpaired electron per CoPc(py)2
/
2.2157 and g ꢁ
/
1.9987. The
jj
/
1020
/
molecule. The EPR measurements of a-CoPc and b-
CoPc modifications have been performed on a solid
Table 7
The EPR g parameters of cobalt(II) phthalocyaninato(2-) complexes
at room temperature (298 K)
Compound
gꢁ
g
jj
Reference
a
a
a-CoPc (solid state)
b-CoPc (solid state)
CoPc (in solution)
2.422
2.89
2.007
1.91
[65]
[65]
[17]
[18]
2.268
2.28
2.016
2.13
CoPc(py) (solid state)
CoPc(py)2 (solid state)
CoPc(4-Mepy) (solid state)
CoPc(4-Mepy)2 (solid state)
2.2157 1.9987 This work
2.27
2.21
2.11
2.02
[18]
[18]
Scheme 1. A s bonding diagram for Fe(II) in a strong-field tetragonal
environment.
a
Diluted in isomorphic crystals of a-ZnPc and b-ZnPc, respectively.

74
J. Janczak, R. Kubiak / Inorganica Chimica Acta 342 (2003) 64Á76
/
and cobalt complexes of the vapor phase. Several
theoretical calculations for the D4h symmetry of the
metallophthalocyanine molecules predict five distinct
bands (Q, B, N, L and C) in the spectral region between
200 and 800 nm [69,70]. The Q band corresponds to the
excitation between HOMO (a1u) to LUMO (ee), while B
band is mostly an a2u
0
/
eg transition. Both (Q and B)
bands are characteristic for the phthalocyaninato ligand.
As can be seen from Fig. 7 the Q band in both FePc(py)2
and CoPc(py)2 spectrum splits into two bands. The
splitting value of Q band is equal to :60 nm and is
/
likely due to the vibronic coupling in the excited state
[71]. The N, L and C bands resulting from a contribu-
tions of a2u
0
/
eg, b2u
0
/
eg and a1u
0/eg transitions [72].
As can be seen from Table 8 the spectra of CoPc and
CoPc(py)2 are similar, since they have the same ground
state configuration of the cobalt(II). However, one
additional band at ꢁ415 nm is observed in the
/
spectrum of FePc(py)2 in relation to the spectrum of
FePc. Several authors have assigned this band to the
electronic transition from a deeper level to the half-
occupied HOMO level. Thus, the band is an evidence for
the existence of the one-oxidized free radical phthalo-
cyaninato(1-) ring as observed in the spectrum of one-
oxidized metallophthalocyaninato complexes, such as
LiPc, LnPc2 or InPc2 [73]. However, the EPR measure-
ment on the solid sample of FePc(py)2 showed no signal,
therefore, the bands at 415 nm cannot be attributed to
the transition in the radical form, since the low-spin
(Sꢁ
0) dipyridinated iron(II) phthalocyanine (e4gb22g) do
/
Fig. 7. UV-Vis spectrum of FePc(py)2 (a) and CoPc(py)2 (b).
not posses a hole in their eg level. Further, as suggested
by Lever et al. [74] this band cannot be attributed to the
LMCT transition. Kobayashi and Yanagawa [75] stu-
died the dipyridinated iron(II) tetraphenyl porphrine
experiments clearly shown that ligation of the iron
phthalocyanine by pyridine molecules leads to the
change of the ground-state from Sꢁ
/
1 (for FePc,
e3gb22ga11g) to Sꢁ0 (FePc(py)2, eg4b22g). The FePc(py)2 is
assigned the band at 21 000 cmꢃ1 (ꢁ
415 nm) to the
/
/
charge transfer from iron to axially coordinated pyridine
ꢀ
b3u(2px ). This assignment seems
a low-spin complex, according to the molecular orbital
diagram (Scheme 1) of Fe(II) in a strong-field tetragonal
environment [68].
molecules, b2g(dp)0
/
entirely reasonable.
3.5. UVÁVis spectroscopy
/
4. Conclusions
The electronic absorption spectra of FePc(py)2 and
CoPc(py)2 in dichloromethane are shown in Fig. 7(a)
and (b), respectively. The observed bands are listed in
the Table 8, which also comprise the electronic absorp-
tion bands for the non-ligated phthalocyaninato iron
Our investigations showed that both axially dipyridi-
nated iron(II) and cobalt(II) phthalocyaninato(2-) com-
plexes are stable under normal conditions, in contrast to
the
dipyridinated
magnesium
phthalocyanine
Table 8
UVÁVis spectral bands [nm]
/
Compound
Q
B
N
L
C
Reference
FePc
676
650
657
670
610
594
600
605
340
322
315
344
300
282
280
282
242
240
240
238
212
210
210
212
[70]
FePc(py)2 in CH2Cl2
CoPc
CoPc(py)2 in CH2Cl2
415
This work
[70]
This work

J. Janczak, R. Kubiak / Inorganica Chimica Acta 342 (2003) 64Á
/76
75
(c) T.C. Oldham, D. Phillips, J. Photochem. Photobiol. B55
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(MgPc(py)2), which is unstable and interacts with water
molecule converts into 4ꢂ1 coordinated complex of
(MgPcH2O)×2py [19]. The stability of the FePc(py)2 and
CoPc(py)2 complexes correlate well with the strength of
the axial M(II)ꢀN(py) bonds. The CoꢀN(py) bond is
N(py) bond due to the unpaired
/
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longer than the Feꢀ
/
electron localized on d2z orbital of Co. Ligation of the
inermediate-spin iron(II) phthalocyanine by pyridine
molecules leads to the change of the ground state
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configuration of the central ion from Sꢁ
b22g a11g) to Sꢁ0 (FePc(py)2, eg4 b22g), while in the cobalt
phthalocyanine the ligation not change the ground state
configuration of the central Co ion (e4g b22g a11g, Sꢁ
1/2).
/
1 (FePc, e3g
/
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This is fully consistent with the EPR and magnetic
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5. Supplementary material
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 176533 and 176534 for
CoPc(py)2 and FePc(py)2, respectively. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
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Acknowledgements
This research was supported by a grant (No 3 T09A
180 19) from the Polish State Committee for Scientific
Research.
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