Comparative study of structure-properties relationship for novel β-halogenated lanthanide porphyrins and their nickel and free bases precursors, as a function of number and nature of halogens atoms

Article abstract of DOI:10.1021/ic000738h

The synthetic route of partially β-halogenated via a metal-assisted reaction and perhalogenated terbium complexes is described. This protocol allows the facile insertion of the halogens (bromines or chlorides) to the porphyrin peripheral positions. The electronic absorption spectra and the redox potentials of the free porphyrins as well as the terbium complexes are dramatically affected as the number of halogen atoms increase. In fact, two antagonistic effects are responsible for that, the inductive and the distortion effects on the porphyrin ring. They result in a red shift for the Soret band and a stabilization/destabilization of the HOMOs/LUMOs which in turn is manifested by variations on the redox potentials. The novel crystal structure of the Ni(Cl₈TPP) is discussed in great detail and compared with the previously reported structures of Tb(Cl₈TPP) (OAc)(DMSO)₂·3PhCH₃·MeOH and H₂(Br₈TPP), as well as with other perhalogenated nickel porphyrins available in the literature.

Full text of DOI:10.1021/ic000738h

Inorg. Chem. 2002, 41, 2648−2659
Comparative Study of Structure−Properties Relationship for Novel
â-Halogenated Lanthanide Porphyrins and Their Nickel and Free Bases
Precursors, as a Function of Number and Nature of Halogens Atoms
G. A. Spyroulias,†,‡ A. P. Despotopoulos,† C. P. Raptopoulou,§ A. Terzis,§ D. de Montauzon,|
,†
R. Poilblanc,| and A. G. Coutsolelos*
Department of Chemistry, Laboratory of Bioinorganic Coordination Chemistry, School of Science,
UniVersity of Crete, P.O. Box 1470, 714 09, Heraklion, Crete, Greece, Institute of Materials
Science, NCRS “Demokritos”, 15310 Agia ParaskeVi, Athens, Greece, and Laboratoire de Chimie
de Coordination, CNRS, UPR 8241 lie´e par conVention a` l’UniVersite´ Paul Sabatier et a` l’Institut
Polytechnique de Toulouse, 205 route de Narbonne, 31077-Toulouse Cedex, France
Received July 5, 2000
The synthetic route of partially â-halogenated via a “metal-assisted” reaction and perhalogenated terbium complexes
is described. This protocol allows the facile insertion of the halogens (bromines or chlorides) to the porphyrin
peripheral positions. The electronic absorption spectra and the redox potentials of the free porphyrins as well as
the terbium complexes are dramatically affected as the number of halogen atoms increase. In fact, two antagonistic
effects are responsible for that, the inductive and the distortion effects on the porphyrin ring. They result in a red
shift for the Soret band and a stabilization/destabilization of the HOMOs/LUMOs which in turn is manifested by
variations on the redox potentials. The novel crystal structure of the Ni(Cl8TPP) is discussed in great detail and
compared with the previously reported structures of Tb(Cl8TPP) (OAc)(DMSO)2‚3PhCH ‚MeOH and H (Br8TPP),
3
2
as well as with other perhalogenated nickel porphyrins available in the literature.
Introduction
later when they were successfully used for olefin epoxidation
and alkane hydroxylation reactions and were established as
remarkably active and robust catalysts.8-16 In â-halogenated
porphyrins possessing more than four halogens in the pyrrole
positions, nitrogen basicity is considerably decreased because
of the electron-withdrawing effect of the peripheral substit-
uents to the macrocycle. Introduction of halogens to the
â-pyrrole carbons results in the distortion of the macrocycle,
The first report of the meso-tetrakis-(2,6-dichloro-phenyl)-
porphyrin1 was followed by an increased development of
new synthetic routes toward the halogenation of the por-
phyrin ring as effective and robust catalysts.2-4
Although â-substituted, mainly halogenated, porphyrins
had appeared by the mid-1970s,5-7 it was almost 10 years
This contribution is dedicated to the memory of our colleague and
friend, Dominique de Montauzon.
(6) Callot, H. J. Bull. Soc. Chim. Fr. 1974, 7-8, 1492.
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* To whom correspondence should be addressed. E-mail: coutsole@
chemistry.uch.gr. Phone: ++30.810.393636. Fax: ++30.810.393601 or
++30.810.393671 PCmodem.
† University of Crete.
‡ Current address: Center of Magnetic Resonance-CERM, Department
of Chemistry, University of Florence, Polo Scientifico, Via L. Sacconi 6,
IT-50019 Sesto Fiorentino (FI), Italy.
§ Institute of Materials Science, NCRS “Demokritos”.
| L’Universite´ Paul Sabatier et a` l’Institut Polytechnique de Toulouse.
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2648 Inorganic Chemistry, Vol. 41, No. 10, 2002
10.1021/ic000738h CCC: $22.00 © 2002 American Chemical Society
Published on Web 04/25/2002

NoWel â-Halogenated Lanthanide Porphyrins
and this effect is pronounced when more than four halogens
replace the corresponding pyrrole hydrogens. Concequently,
a red shift of the Soret band transition energy and a decrease
in the HOMO-LUMO energy gap expressed via the large
shift of the redox potentials of the porphyrin ring have been
observed.17-29 The â-halogenated porphyrin derivatives with
iron or manganese are considered as mimetic models for
cytochrome P450s because of their similar catalytic activity.
Also, such perhalogenated derivatives have been studied in
suprabiotic catalysis30,31 while only recently D. Dolphin
communicated that the iron â-halogenated derivative of
5,10,15,20-tetrakis(2,6-dichlorophenyl)-porphyrin oxidizes
the analgesic lidocaine in a similar way to that of mammalian
livers.32
protocols for high yield, â-tetra- or octahalogenated por-
phyrins still remains a major challenge.
Metalation of porphyrins with lanthanides results in two
different classes of interesting complexes: the lanthanide
monoporphyrinates and the lanthanide “sandwich-like” bispor-
phyrinates. The former compounds were reported in the early
1970s52,53 and studied as photochemical probes,54-56 NMR
shift reagents,57,58 and contrast agents,59 while the latter
species appeared almost 10 years later60,61 and have been
extensively studied as models of the active center, the so-
called “special pair”, in the photosynthetic bacteria.62-66 The
axial ligation of the Ln metal center, for the Ln monopor-
phyrinates, was debated for a long time.67 Only recently
has the first X-ray crystal structure determination of a
lanthanide monoporphyrinate been reported by our group,29
several years after the crystal structure of the acetatolutetium
monophthalocyaninate, [Lu(OAc)(Pc)(H2O)2]‚H2O‚2MeOH.68
We report here the detailed synthetic procedures for the
synthesis of â-tetra- or octachlorinated and the corresponding
brominated 5,10,15,20-tetraphenylporphyrin derivatives, the
structural, optical and electrochemical properties of the parent
Ni halogenated porphyrins, their demetalation products (free
bases), and the corresponding Tb monoporphyrinic com-
plexes.
Although there are recent advances in the development
of the â-halogenated33-38 or other symmetrical or unsym-
metrical â-substituted porphyrins,39-47 as well as the ulti-
mately synthesized perfluorinated48,49 or pernitrated50,51 por-
phyrins, the development of new improved, simplified
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Inorganic Chemistry, Vol. 41, No. 10, 2002 2649

Spyroulias et al.
Aldrich, respectively, and used as received. Tetrahydrofuran, THF,
was purchased from Merck and distilled under argon and over a
mixture of sodium/benzophenone. Tetra- n-butylammonium per-
chlorate, TBAP, purchased from Fluka, was recrystallized from
absolute ethanol and then dried in a vacuum oven at 40 °C. N-
Bromo- and chlorosuccinimide were purchased from Fluka and were
either purified as reported in the literature69 or used as received.
All synthetic procedures were performed under an argon stream.
Instrumentation and Methods. Absorption spectra were col-
lected on a Perkin-Elmer Lambda 6 grating spectrophotometer.
Spectra for ꢀ measurements were recorded in CH2Cl2 or PhCH3
(solutions of 0.05 × 10-3 M). Electrochemistry experiments carried
out with a homemade potensiostat using interfacing hardware with
a PC-compatible microcomputer. The positive feedback (scan rate
> 1 V‚s-1) or interrupt (scan rate < 1 V‚s-1) methods were used
to compensate for uncompensated resistance (IR) drop. Electro-
chemical experiments were performed in an airtight three-electrode
cell connected to a vacuum/argon line. The cell was degassed and
filled according to standard vacuum techniques. The reference
electrode consisted of a saturated calomel electrode (SCE) separated
from the solution by a bridge-compartment filled with a solution
of the same supporting electrolyte in the same solvent as that used
in the cell. The counter-electrode was a spiral of ∼1 cm2 apparent
surface area, made of a 8 cm-long and 0.5 mm-diameter platinum
wire. The working electrode was a rotating disk electrode (RDE)
with a 2 mm-diameter Pt disk (Tacussel EDI) or an ultramicro-
electrode consisting of a 100 mm-diameter Pt disk.
characteristic Soret band. To minimize possible loss of the desired
product(s), the following chromatographic proceedure was applied.
Elution of the excess of the chlorinated agent is achieved by pure
MeOH. The first fraction, with dark brown color due to the large
amount of decomposed succinimide, is eluted rapidly together with
small amounts of partially halogenated porphyrins. The major part
of porphyrins eluted only when the CH2Cl2/MeOH mixture is
applied as eluant. Using a mixture of solvents, CH2Cl2/MeOH
(0.01-0.2:1 v/v), several chlorinated side products, as dark green
fractions, with Soret bands having λmax values smaller than 425
nm, were removed. This is indicative for the lower degree of
peripherally chlorinated porphyrins. No fraction with a λmax bigger
than 425 nm was obtained, or the concentration of such products
is so small that they could not be detected by UV-vis spectroscopy.
The gradual increase of CH2Cl2 in solvent mixtures facilitates the
elution of these partially chlorinated porphyrins as green fractions.
The desired product, Ni(Cl4TPP), was eluted with CH2Cl2, CHCl3,
or PhCH3. The solvents were evaporated under vacuum, the solid
was redissolved in CH2Cl2/MeOH (1:1, v/v), and the chromato-
graphic procedure was repeated using a column of 5 cm × 12 cm
with the same solvents, except methanol, in the same order as
described. The resulting product recrystallized from CH2Cl2/MeOH
(1:5, v/v). Yield: 31%. 1H NMR (CDCl3, 250 MHz): δ ) 8.65-
8.85 (multiplet, 4H, pyr), 8.05-8.20 (multiplet, 8H, o-Hphenyl),
7.75-8.00 (multiplet, 12H, m-Hphenyl and p-Hphenyl). MS (MALDI-
TOF): m/z 809 [M]+. Anal. Calcd for C44H24Cl4N4Ni: C, 65.31;
H, 2.99; Cl, 17.52; N, 6.92. Found: C, 65.05; H, 3.21; Cl, 16.97;
N, 6.45.
Porphyrins. H2(TPP) and Ni(TPP) were synthesized, accord-
ing to literature procedures [abbreviations: (OEP)2-
)
â-Octachloro-5,10,15,20-tetraphenylporphinato Nickel, 2. To
a solution of 1.0 g (1.50 mmol) of Ni(TPP) in 60 mL of 1,2-o-
dichlorobenzene was added 2.4 g (18.0 mmol) N-chlorosuccinimide.
The solution was brought to reflux for 2-3 h, and the reaction
was monitored using UV-vis spectroscopy (the Soret band shifted
from 411 to 439 nm). The purification/isolation procedure applied
for the octachlorinated and octabrominated derivatives is similar
to that described for the analogous tetrahalogenated porphyrins, but
usually, one column chromatography procedure carried out on a 5
cm × 12 cm column is adequate for the isolation of analytically
pure octachlorinated porphyrins. Column package has been per-
formed with CH2Cl2/MeOH (1:1, v/v) mixtures as in the case of
tetrahalogenated derivatives. The pure MeOH as eluant is followed
by CH2Cl2/MeOH mixtures with initial volume in CH2Cl2 higher
than that used in the case of tetrachlorinated derivatives. That
facilitates the elution of undesired partially halogenated porphyrins
(the octachlorinated product is rather difficult to elute from the top
of the column when the volume of CH2Cl2 is less than in 50%,
v/v, for the eluant). Thus, elution of porphyrins with less than eight
chlorines could start with CH2Cl2/MeOH (0.3:1, v/v), yielding green
fractions, and that holds even for solvent mixtures 50%-60% in
CH2Cl2. Under these conditions, only fractions with λmax smaller
than 439 nm were collected. Using pure CH2Cl2, CHCl3, or PhCH3
the desired octachlorinated compound is eluted. Purple crystals of
the Ni(Cl8TPP) suitable for X-ray structure analysis were obtained.
Yield: 70%. 1H NMR (CDCl3, 250 MHz): δ ) 7.90-8.00
(multiplet, 8H, o-Hphenyl), 7.65-7.80 (multiplet, 12H, m-Hphenyl and
p-Hphenyl). MS (MALDI-TOF): m/z 947 [M]+. Anal. Calcd for
C44H20Cl8N4Ni: C, 55.81; H, 2.13; Cl, 29.95; N, 5.92. Found: C,
55.65; H, 2.21; Cl, 29.97; N, 5.80.
2,3,7,8,12,13,17,18-octaethyl porphyrinate; (TPP)2- ) 5,10,15,20-
tetraphenyl porphyrinate; [Cl8TPP]2- ) 2,3,7,8,12,13,17,18-octa-
â-chloro-5,10,15,20-tetrakis(phenyl) porphyrinate; [Br8TPP]2-
)
2,3,7,8,12,13,17,18-octa-â-bromo-5,10,15,20-tetrakis(phenyl) por-
phyrinate; [Cl4TPP]2- ) tetra-â-chloro-5,10,15,20-tetrakis(phenyl);
and [Br4TPP]2- ) tetra-â-bromo-5,10,15,20-tetrakis(phenyl) por-
phyrinate dianions].70 The synthetic procedures described for all
the tetra- and octahalogenated porphyrins are modified protocols
reported only on the synthesis of octachloroporphyrin.17
â-Tetrachloro-5,10,15,20-tetraphenylporphinato Nickel, 1. To
a solution of 1.0 g (1.50 mmol) of Ni(TPP) in 60 mL of 1,2-o-
dichlorobenzene was added 800 mg (6.0 mmol) of N-chlorosuc-
cinimide. The solution was brought to reflux for 2 h. The reaction
was monitored by UV-vis spectroscopy (the Soret band shifted
from 411 to 425 nm). After the end of the reaction, the solvent
was distilled under reduced pressure and the crude residue redis-
solved in the minimum volume of a mixture of CH2Cl2/MeOH (1:
1, v/v) before being applied on a column for chromatography
(Al2O3, basic, grade I, 5 cm × 6 cm). Methanol is widely used for
the column chromatography procedure because it has a dual effect
on crude reaction mixtures: it solubilizes the succinimide and makes
its elution faster and easier while the halogenated product, which
is slightly soluble in that solvent, remains at the top of the column.
Note: An alternative method for succinimide removal from the
crude reaction mixture might be the treatment of the crude reaction
residue in methanol with a subsequent filtration. However, the
solution was found to contain minor amounts of the chlorinated
products together with the vast majority of succinimide. The
presence of the chlorinated porphyrins was manifested by the
â-Tetrabromo-5,10,15,20-tetraphenylporphinato Nickel, 3. To
a solution of 1.0 g (1.50 mmol) of Ni(TPP) in 60 mL of 1,2-o-
dichlorobenzene was added 1.067 g (6.0 mmol) of N-bromosuc-
cinimide. The solution was brought to reflux for 2 h, and the
reaction was followed by UV-vis spectroscopy. During the course
(69) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: New York, 1988; p 105.
(70) Fuhrhop, J. H.; Smith, K. M. Porphyrins and Metalloporphyrins;
Elsevier Scientific Publishing Co.: Amsterdam, 1975; Section H, p
757.
2650 Inorganic Chemistry, Vol. 41, No. 10, 2002

NoWel â-Halogenated Lanthanide Porphyrins
of the reaction, the Soret band was shifted from 411 to 430 nm.
The purification/isolation procedure followed was identical to that
described previously for the tetrachlorinated derivative. Yield: 35%.
1H NMR (CDCl3, 250 MHz): δ ) 8.75-9.0 (multiplet, 4H, pyr),
8.15-8.3 (multiplet, 8H, o-Hphenyl), 7.80-8.00 (multiplet, 12H,
m-Hphenyl and p-Hphenyl). MS (MALDI-TOF): m/z 987 [M]+. Anal.
Calcd for C44H24Br4N4Ni: C, 53.54; H, 2.45; Br, 32.38; N, 5.68.
Found: C, 53.05; H, 3.00; Br, 31.95; N, 6.05.
7.90-8.00 (multiplet, 12H, m-Hphenyl and p-Hphenyl), 1.25 (doublet,
2H, N-H). Anal. Calcd for C44H22Br8N4: C, 42.42; H, 1.78; Br,
51.31; N, 4.50. Found: C, 42.60; H, 1.70; Br, 51.37; N, 4.70.
Note: Addition of small amounts of D2O in the NMR tube of all
the porphyrin samples results in the disappearance of the exchange-
able N-H protons, thus verifying in the case of derivatives 6 and
8 the significant downfield shift of those protons with respect to
the tetrahalogenated porphyrins.
â-Octabromo-5,10,15,20-tetraphenylporphinato Nickel, 4. To
a solution of 1.0 g (1.50 mmol) of Ni(TPP) in 60 mL of 1,2-o-
dichlorobenzene was added 3.204 g (18.0 mmol) of N-bromosuc-
cinimide. The solution was brought to reflux for 2-3 h, and the
reaction was monitored by UV-vis spectroscopy. During the course
of the reaction, the Soret band was shifted from 411 to 449 nm
and the Ni(Br8TPP) purified as described previously. Yield: 85%.
1H NMR (CDCl3, 250 MHz): δ ) 8.00-8.10 (multiplet, 8H,
o-Hphenyl), 7.75-7.90 (multiplet, 12H, m-Hphenyl and p-Hphenyl). MS
(MALDI-TOF): m/z 1302.5 [M]+. Anal. Calcd for C44H20Br8N4-
Ni: C, 40.57; H, 1.55; Br, 49.07; N, 4.30. Found: C, 40.65; H,
1.70; Br, 49.00; N, 4.42.
Demetalation of â-Octahalogeno-5,10,15,20-tetraphenylpor-
phinato Nickel (X ) Cl, Br and n ) 4 or 8). A 400 mg portion
of any Ni(XnTPP) derivative was suspended in 100 mL of CH2-
Cl2, into a round-bottom flask, while 30 mL of H2SO4 (98%) was
added with great care. The mixture was rigorously stirred for 3-4
h at room temperature, and the progress of the demetalation was
followed by UV-vis spectroscopy and by TLC plates. After the
end of the reaction, the flask was transferred to an ice bath, and
NH3 solution (25%) was added dropwise, under great precaution,
to avoid overheating and violent boiling/evaporation of the organic
solvent. The mixture was extracted several times with H2O and
washed with a saturated solution of NaHCO3 until pH 7.0. The
organic phase dried for 45 min-1 h on MgSO4 and evaporated
under vacuum. The crude product was redissolved in minimum
volume of a mixture of CH2Cl2/MeOH (1:3, v/v) and applied on a
column for chromatography (Al2O3, basic, grade I, 5 cm × 10 cm)
using as eluant solvent mixtures such as CH2Cl2/MeOH (0.01-
0.5:1, v/v). Analytically pure tetra- and octahalogenated free bases
were obtained by using CH2Cl2 as eluant. The solvents were
evaporated and the products recrystallized from CH2Cl2/MeOH (1:
5, v/v). Dark green crystals of H2(X8TPP)‚2DMF suitable for X-ray
crystal structure analysis were obtained by slow diffusion of DMF
into a saturated solution of the porphyrin in PhCH3 and simultaneous
slow evaporation at room temperature.
â-Tetrachloro-5,10,15,20-tetraphenylporphyrin, 5. Yield: 78%.
1H NMR (CDCl3, 250 MHz): δ ) 8.65-8.75 (multiplet, 4H, pyr),
8.00-8.10 (multiplet, 8H, o-Hphenyl), 7.60-7.80 (multiplet, 12H,
m-Hphenyl and p-Hphenyl), -2.80 (doublet, 2H, N-H). Anal. Calcd
for C44H26Cl4N4: C, 70.23; H, 3.48; Cl, 18.84; N, 7.45. Found: C,
70.50; H, 3.71; Cl, 17.97; N, 7.85.
â-Octachloro-5,10,15,20-tetraphenylporphyrin, 6. Yield: 88%.
1H NMR (CDCl3, 250 MHz): δ ) 8.10-8.15 (multiplet, 8H,
o-Hphenyl), 7.70-7.80 (multiplet, 12H, m-Hphenyl and p-Hphenyl), 1.55
(broad, 2H, N-H). Anal. Calcd for C44H22Cl8N4: C, 59.36; H, 2.49;
Cl, 31.86; N, 6.29. Found: C, 59.50; H, 2.70; Cl, 31.97; N, 6.50.
â-Tetrabromo-5,10,15,20-tetraphenylporphyrin, 7. Yield: 71%.
1H NMR (CDCl3, 250 MHz): δ ) 8.70-8.85 (multiplet, 4H, pyr),
8.05-8.15 (multiplet, 8H, o-Hphenyl), 7.60-7.80 (multiplet, 12H,
m-Hphenyl and p-Hphenyl), -2.85 (doublet, 2H, N-H). Anal. Calcd
for C44H26Br4N4: C, 56.81; H, 2.82; Br, 34.36; N, 6.02. Found: C,
56.50; H, 2.51; Br, 34.52; N, 6.00.
â-Tetrahalogeno-5,10,15,20-tetraphenylporphinato Terbium
(Acetato) 9 and 11 (X ) Cl, Br). To a solution of 150 mg of
H2(X4TPP) (0.20 mmol for X ) Cl and 0.16 mmol for X ) Br)
was added 300 mg (0.6 mmol) of Tb(acac)3‚H2O in a round-bottom
flask containing 20 mL of 1,2,4-trichlorobenzene. The solution was
brought to reflux for 3-4 h. The reaction was monitored by UV-
vis spectroscopy, and the Soret band was red-shifted from 426-
430 to 431-432 nm. After the end of the reaction, the solvent was
distilled under reduced pressure and the crude residue redissolved
in the minimum volume of PhCH3 before the mixture was applied
on a column for chromatography (Al2O3, basic, grade I, 3 cm × 5
cm). The unreacted free base is eluted easily from the top of the
column while CH2Cl2 and CH2Cl2/MeOH (1:0.1-1, v/v) were used
as solvent mixtures. Thus, the complete elution of the free porphyrin
is achieved, and the elution of the terbium complexes started. Using
as eluant pure MeOH and MeOH/DMSO (2:1, v/v) mixtures, the
elution procedure is accelerated, and the complexes were recovered.
The solvents were removed under reduced pressure, and the solid
residue is recrystalized from PhCH3 or mixtures of PhCH3/
petroleum ether (1:5, v/v) yielding amorphous purple solid. After
filtration, the solid is washed with cold petroleum and diethyl ether
and dried for 2-3 days under vacuum at 40 °C. Total yields: 9,
48%; 11, 55%. Anal. Calcd for 9 (Me2SO)2 C50H39Cl4N4O4S2Tb:
C, 53.39; H, 3.50; Cl, 12.61; N, 4.98. Found: C, 52.90; H, 3.44;
Cl, 13.02; N, 5.10. Calcd for 11 (Me2SO)2 C50H39Br4N4O4S2Tb:
C, 46.11; H, 3.02; Br, 24.54; N, 4.30. Found: C, 46.03; H, 3.04;
Cl, 24.64; N, 4.34.
â-Octahalogeno-5,10,15,20-tetraphenylporphinato Terbium
(Acetato) 10 and 12 (X ) Cl, Br). To a solution of 300 mg of
H2(X8TPP) (0.33 mmol for X ) Cl and 0.24 mmol for X ) Br)
was added 300 mg (0.6 mmol) of Tb(acac)3‚H2O in a round- bottom
flask containing 20 mL of 1,2,4-trichlorobenzene. The solution was
brought to reflux for 3-4 h. The reaction was monitored by UV-
vis spectroscopy, and the Soret band was red-shifted from 453 or
469 nm (for X ) Cl and X ) Br, respectively) to 458-460 nm (X
) Cl) and 473-474 nm (X ) Br). After the end of the reaction,
the solvent was distilled under reduced pressure. The purification
and isolation of the complexes was carried out in an identical way
to that described for the â-tetrahalogenated derivatives. The
complexes are recrystalized either from saturated PhCH3 solutions
or from mixtures of PhCH3/petroleum ether (1:5, v/v) and dried
for 2-3 days under vacuum at 40 °C. Total yields: 10, 70%; 12,
66%. Green crystals suitable for X-ray crystal analysis, Tb(Cl8-
TPP)(OAc)(DMSO)2, were recovered after slow evaporation of
PhCH3 solution. Anal. Calcd for 10 (Me2SO)2 C50H35Cl8N4O4S2-
Tb: C, 47.57; H, 2.79; Cl, 22.46; N, 4.44. Found: C, 47.91; H,
2.90; Cl, 22.28; N, 4.45. Calcd for 12 (Me2SO)2 C50H35Br8N4O4S2-
Tb: C, 37.11; H, 2.18; Br, 39.50; N, 3.46. Found: C, 36.91; H,
2.22; Br, 39.40; N, 3.42.
X-ray Structure Determination. A green crystal of Ni(Cl8TPP)
(0.10 × 0.20 × 0.50 mm3) was mounted on a P21 Nicolet diffrac-
tometer upgraded by Crystal Logic and measured using Zr-filtered
Mo radiation. A flat octahedral dark green crystal of H2(Br8TPP)‚
2DMF (0.20 × 0.40 × 0.40 mm3) and a deep purple crystal of
Tb(Cl8TPP) (OAc)(DMSO)2‚3PhCH3‚MeOH (0.08 × 0.12 × 0.50
â-Octabromo-5,10,15,20-tetraphenylporphyrin, 8. Yield: 82%.
1H NMR (CDCl3, 250 MHz): δ ) 8.40-8.50 (multiplet, o-Hphenyl),
Inorganic Chemistry, Vol. 41, No. 10, 2002 2651

Spyroulias et al.
Table 1. Crystal Data for Ni(Cl8TPP), H2(Br8TPP)‚2DMF, and
Tb(Cl8TPP)(OAc)(DMSO)2‚3PhCH3‚MeOH
fixed to 0.50; the solvent methanol was refined with occupation
factor fixed to 0.25.
Ni(Cl8TPP) H2(Br8TPP)‚DMF
Tb complex
Results
formula
fw
temp, K
λ, Å
a, Å
C44H20Cl8N4Ni C50H36Br8N6O2
C72H63Cl8N4O5S2Tb
946.95
298
1392.16
298
1570.91
298
Modifying known protocols, we achieved the high-yield
synthesis of brominated and chlorinated Ni derivatives of
5,10,15,20-tetraphenylporphyrin, bearing four or eight halo-
gens at â-pyrolle positions. The demetalation of the Ni
compounds yielded the free porphyrins which are then
reacted with the acetylacetonato salt of Tb leading to the
first lanthanide complexes with polyhalogenated and distorted
porphyrins. The physicochemical properties of the haloge-
Mo KR, 0.71073 Mo KR, 0.71073 Mo KR, 0.71073
10.727(1)
27.014(4)
14.423(2)
111.168(3)
3897.6(9)
4
20.59(1)
19.776(5)
13.516(3)
30.015(6)
108.409(7)
7612(3)
4
P21/c
1.371
1.271
b, Å
c, Å
10.935(6)
â
V, Å3
Z
4637(4)
4
I41/a
1.994
6.965
1.049
0.0471b
0.1164b
space group
P21/a
D
calcd, Mg m-3 1.614
1
µ, mm-1
GOF
R1
1.074
nated compounds are studied by UV-vis and H NMR
1.110
1.126
spectroscopy and electrochemical methods. An attempt to
understand the consequences of the number and nature of
the halogen atoms, as well as to clarify the impact of presence
and the nature of the metal ion on the physicochemical
properties of the compounds, is presented in the following
section. The afforded X-ray structure of Ni(Cl8TPP) is
described, and the structural features are discussed and
compared with Ni complexes of other polyhalogenated
porphyrin macrocycles as well as with the Tb octachloro
complex. The structural characteristics of the previously
communicated X-ray structure of the octabrominated free
base29 are also presented and compared with the structures
of the other halogenated compounds described in this work.
0.0569a
0.0875a
0.0754c
0.2080c
wR2
a For 2493 reflections with I > 2σ(I). b For 1996 reflections with I >
2σ(I). c For 6363 reflections with I > 2σ(I).
mm3) were mounted in air and covered with epoxy glue. Diffraction
measurements were made on a Crystal Logic Dual Goniometer
diffractometer using graphite monochromated Mo radiation. Unit
cell dimensions for the three structures were determined and refined
by using the angular settings of 25 automatically centered reflections
in the range 11° < 2θ < 23°, and they appear in Table 1. Intensity
data were recorded using a θ-2θ scan. Three standard reflections
monitored every 97 reflections showed less than 3% variation and
no decay. Lorentz, polarization, and ψ-scan absorption corrections
were applied using Crystal Logic software. The structures were
solved by direct methods using SHELXS-8671 and refined by full-
matrix least-squares techniques on F2 with SHELXL-93.72 Supple-
mentary crystal data for Ni(Cl8TPP) are the following: 2θmax ) 47°,
scan speed 1.5°/min, scan range 2.4 + R1R2 separation, reflections
collected/unique/used ) 5733/5379(Rint ) 0.0649)/5368, 594
parameters refined, R1/wR2 (for all data) ) 0.0786/0.1375, [∆/σ]max
) 0.007, [∆F]max/[∆F]min ) 0.406/-0.371 ꢀ/Å3. All hydrogen atoms
were located by difference maps and their positions refined
isotropically. All nonhydrogen atoms were refined anisotropically.
For H2(Br8TPP)‚2DMF, the data are the following: 2θmax ) 50°,
scan speed 1.0°/min, scan range 2.5 + R1R2 separation, reflections
collected/unique/used ) 2114/1996(Rint ) 0.0495)/1991, 157
parameters refined, R1/wR2/GOF (for all data) ) 0.0864/0.1392,
[∆/σ]max ) 0.194, [∆F]max/[∆F]min ) 0.677/-0.476 ꢀ/Å3. All
hydrogen atoms (except those of N1 and C10 which were introduced
at calculated positions as riding on bonded atoms) were located
by difference maps and refined isotropically. All non-hydrogen
atoms refined anisotropically, but the atoms of the solvents refined
isotropically. For Tb(Cl8TPP)(OAc)(DMSO)2‚3PhCH3‚MeOH,
the data are the following: 2θmax ) 44.3°, scan speed 1.0°/min,
scan range 2.3 + R1R2 separation, reflections collected/unique/used
) 8864/8658(Rint ) 0.0192)/8641, 696 parameters refined,
R1/wR2/GOF (for all data) ) 0.1106/0.2630, [∆/σ]max ) 0.882,
[∆F]max/[∆F]min ) 2.498/-1.729 ꢀ/Å3 in the vicinity of the heavy
metal. All hydrogen atoms were introduced at calculated positions
as riding on bonded atoms. All non-hydrogen atoms were refined
anisotropically, except those of the solvent molecules which were
refined isotropically. The phenyl ring of one toluene solvent
molecule was fixed to a regular hexagon and its occupation factor
Discussion
Synthesis. Traylor and Tsuchiya8 reported for the first time
the bromination of Zn tetrakis(2,6-dichlorophenyl) porphyrin
by action with N-bromosuccinimide (NBS). All the haloge-
nated porphyrins reported herein were prepared according
to the experimental procedure reported by Dolphin and co-
workers17,37 for the synthesis of â-octachloro tetrakis(2,6-
dichlorophenyl) porphyrin. However, no attempts have been
reported, as far as we know, for the synthesis of â-tetra-
bromo-, â-tetrachloro-, or â-octabromo-tetraphenylporphyrins
via an NBS/NCS protocol. The only protocol still used for
the bromination of tetraphenylporphyrin is that reported
by Bhyrappa and Krishnan.33 Our attempts to achieve the
synthesis of hyperbrominated porphyrin rings led to a
synthetic protocol which is remarkably fast and simple
compared to that for the Cu derivative33,73 and exhibits the
advantage that gives the desired products in higher yields
(up to 85%). However, the reaction time required for the
demetalation of the nickel derivative is slightly longer.
For the synthesis of the nickel â-tetrahalogenated deriva-
tives (1 and 3, Chart 1), the same experimental conditions
were used (see also Experimental Section) and should yield
products with one halogen in each pyrrole ring,29 according
to extensive studies reported by Crossley et al.74 This lack
of stereospecificity is rationalized by the predominant
absence of localized double-bond character in the metal
derivatives, instead of the free base. This suggests the
introduction of one halogen atom in each pyrrolic/pyrrolenic
(71) Sheldrick, G. M. SHELXS-86: Structure SolVing Program; University
of Gottingen: Germany, 1986.
(72) Sheldrick, G. M. SHELXL-93: Crystal Structure Refinement; Uni-
versity of Gottingen: Germany, 1993.
(73) Spyroulias, G. A.; Coutsolelos, A. G. Polyhedron 1995, 14, 2483.
(74) Crossley, M. J.; Burn, P. L.; Chew, S. S.; Cuttance, F. B.; Newson, I.
A. J. Chem. Soc., Chem. Commun. 1991, 1564.
2652 Inorganic Chemistry, Vol. 41, No. 10, 2002

NoWel â-Halogenated Lanthanide Porphyrins
Chart 1
been performed as described elsewhere (see also Experi-
mental Section). All the compounds gave satisfactory
elemental analysis, and the nature of the axial ligand has
been identified by IR77 spectroscopy and X-ray crystal-
lographic studies. The pyrolysis of Tb(acac)3‚H2O during the
course of the high-temperature metalation reaction provides
a reasonable explanation for the presence of the acetato
ligand as axial ligand on the terbium ion.78-80
UV-Vis Spectroscopy. The number and the nature of the
â-pyrrole substituents on the porphyrin core affect the
structure and the spectroelectrochemical properties of the
macrocycle. Semiempirical AM1 electronic structure calcula-
tions indicate that HOMO and LUMO orbitals are destabi-
lized by the distortion of the ring when â-pyrrole hydrogens
are replaced by other bulky substituents.21,26,81-83 The
electronic properties of the substituent groups, electron
acceptors or electron donors, influence the properties of the
porphyrin to a different extent. The halogenation of the
porphyrin ring causes severe distortion to the ring, and as a
consequence, the Soret absorption band is considerably
shifted to lower energy while the Q bands are also shifted
to lower energy but to a smaller extent (Table 2). According
to the number of halogens inserted on the macrocyclic ring,
the Soret band is bathochromically shifted from 20 nm when
four halogens are inserted, 1 and 3, to up to 40 nm (for eight
halogens), 2 and 4, in the Ni porphyrin complexes (Soret
λmax ) 411 nm for Ni(TPP), CH2Cl2, 20 °C). The same
bathochromic shift, though of a higher magnitude, is
observed in the case of the free base porphyrins (Table 2).
While the TPP free base presents a Soret λmax at 417 nm
(CH2Cl2, 20 °C), the Soret absorption in â-tetrahalogenated
free porphyrins is bathochromically shifted to 426-430 nm
(5, 7) and to 453 and 469 nm for the â-octachloro- and
bromosubstituted porphyrins (6, 8), respectively. Finally,
comparable shifts experience the Soret absorption in the
case of Tb porphyrin complexes (Soret λmax ) 420 nm for
Tb(TPP)(acac), CH2Cl2, 20 °C) (Table 2). The number of
halogens in â pyrrole positions, in addition to the dramatic
effect on the transition energy of the Soret band, influences
the number and the nature of Q bands as well. In the case of
the Ni complexes, the spectra present the typical absorption
for the Ni complex in the region of Q bands (540 and 543
nm for the â-tetra and 553 and 561 nm for the â-octachloro
and -bromo derivatives, respectively (Table 2)). A weak
absorption band, rather a shoulder, is also observed at a lower
transition energy than the main Q band, around 580-600
nm. However, the spectral features observed for the free
ring instead of two halogens in the antipode pyrroles as has
been reported for the â-tetrahalogenated tetramesytilporphy-
rin.75
However, the fact that multiple ill-resolved peaks corre-
1
sponding to pyrrole proton resonances are observed by H
NMR spectroscopy data makes it unfeasible to determine
whether any of the pyrrole proton signals split because of
vicinal coupling, if there are any vicinal protons. This
indicates that the four remaining pyrrole protons are un-
equivalent, suggesting that the halogenation procedure yields
a mixture of isomers. Similar kinds of regioisomers are also
observed in the case of thallium complexes of tetrachlorinated
TPP and detected only through 205Tl NMR spectroscopy.76
Attempts to separate the mixture of compounds did not
succeed because of their identical behavior on different
chromatography material even when a variety of solvent
mixtures was used as eluant. Thus, the exact composition
of the mixture is rather difficult to detect. Nevertheless, no
noticeable difference in physical properties associated with
the magnitude of ring distortion should be anticipated because
â-tetrasubstituted porphyrin cores are nearly planar.75 This
aspect is also supported by the electrooxidation potentials
for â-tetrabromo- and chloro-TPP reported in this study (see
also the Electrochemistry section). Oxidation potentials,
which are rather sensitive to ring distortion,26 exhibit E1/2
values almost identical to those of antipodal tetrahalogenated
TMP,75 indicating that various distribution/substitution pat-
terns of four halogens on the pyrroles do not induce a
different degree of ring distortion and consequently do not
significantly influence the HOMO energy. Finally, it should
be noted that the possibility of an isomeric substitution
pattern was taken under consideration in the following
discussion and evaluation of the experimental results.
Insertion of the Tb ion from Tb(acac)3‚H2O into H2(XnTPP)
in 1,2,4-tcb yields purple Tb(X4TPP)(OAc), 9 and 11, (X )
Cl, Br and n ) 4) and deep purple Tb(X8TPP)(OAc), 10
and 12, (X ) Cl, Br and n ) 8) compounds after 2-4 h.
Purification and isolation of the lanthanide porphyrins have
(77) For all the Tb halogenated porphyrins characteristic bands observed
in the area of 1440-1446 and 1490-1496 cm-1 attributable to O2-
CMe, bidendate coordination of the acetato ligand is indicated.29
(78) Wong, C.-P.; Veintecher, R. F.; Horrocks, D. W., Jr. J. Am. Chem.
Soc. 1974, 96, 7149.
(79) Wong, C.-P.; Horrocks, D. W., Jr. Tetrahedron Lett. 1975, 2637.
(80) Buchler, J. W.; Eickelmann, G.; Puppe, L.; Rohbock, K.; Schneehage,
H. H.; Weck, D. Liebigs Ann. Chem. 1971, 745, 135.
(81) Barkigia, K. M.; Chantranupong, L.; Smith, K. M.; Fajer, J. J. Am.
Chem. Soc. 1988, 110, 7566.
(75) Ochsenbein, P.; Ayougou, K.; Mandon, D.; Fischer, J.; Weiss, R.;
Austin, R. N.; Jayaraj, K.; Gold, A.; Terner, J.; Fajer, J. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 348.
(82) Gassman, P. G.; Ghosh, A.; Almlof, J. J. Am. Chem. Soc. 1992, 114,
9990.
(83) Parusel, A. B. J.; Wondimagegn, T.; Ghosh, A. J. Am. Chem. Soc.
2000, 122, 6371-6374.
(76) Coutsolelos, A. G.; Daphnomili, D. Inorg. Chem. 1997, 36, 4614.
Inorganic Chemistry, Vol. 41, No. 10, 2002 2653

Spyroulias et al.
Table 2. UV-Vis Data for â-Tetra- and Octahalogenated Porphyrins
M(XnTPP) in CH2Cl2 Where M ) H2, Ni, or Tb(OAc), X ) Cl or Br,
and n ) 4 or 8 [λmax/nm, (log ꢀ dm-3 mol-1 cm-1)]
B bands
Q bands
Ni(XnTPP)
Ni(Cl4TPP)
Ni(Cl8TPP)
Ni(Br4TPP)
Ni(Br8TPP)
1
2
3
4
425
5.68
439
5.67
430
5.67
449
5.66
540
3.00
553
3.04
543
3.08
561
3.08
580(sh)
587(sh)
581(sh)
599(sh)
H2(XnTPP)
H2(Cl4TPP)
H2(Cl8TPP)
H2(Br4TPP)
H2(Br8TPP)
5
6
7
8
426
5.44
523
4.54
551
4.04
527
4.29
569
4.02
599
3.56
601
4.03
598
3.51
625
4.14
667
3.54
719
3.85
673
3.49
745
3.88
355
4.30
453
5.38
430
5.40
469
5.31
368
4.48
Tb(XnTPP)(OAc)
Tb(Cl4TPP)(OAc)
9
432
5.25
563
4.20
553
3.69
569
4.15
552
3.48
596
3.76
598
3.85
596
3.64
612
3.42
Tb(Cl8TPP)(OAc) 10 358
4.33
Tb(Br4TPP)(OAc) 11
460
4.77
432
5.20
474
4.65
652
3.69
Tb(Br8TPP)(OAc) 12 366
669
3.50
4.40
bases exhibit striking differences with the halogen-free H2-
(TPP) precursor, manifested in the area of the Q bands.
Specifically, both the tetrahalogenated derivatives present
three Q bands instead of the four in the case of H2(TPP)
(Figure 1). The two higher energy Q bands, slightly shifted
compared to the analogous band in H2(TPP),84 observed at
523, 599 nm (for Cl4TPP) and at 527, 598 nm (for Br4TPP),
could be compared with the Qy(1,0) and Qx(1,0), while the
higher energy Qy(1,0) seems to gain in intensity and the
Qy(0,0) band (which is observed in H2(TPP)) is probably
shifted to higher energy and could be observed as a shoulder
to the Qy(1,0) band (Figure 1). The lower energy Q band
observed for the X4TPP derivatives (where X ) Cl or Br)
presents an unusual large value at 667 nm (for Cl4TPP) and
673 nm (for Br4TPP) compared with similar data reported
in the case of the â-tetrahalogenated tetrakismesitylporphyrin
with two halogens on antipodal pyrroles.75 The two octa-
halogenated porphyrins present rather similar optical features
(Figure 1) that are (i) the high energy band at 355 and 368
nm (for Cl8TPP and Br8TPP respectively), (ii) the batho-
chromically shifted Soret absorption at 453 nm (Cl8TPP) and
469 nm (Br8TPP), and (iii) three Q bands, two at the area of
560-625 nm and the third at the area of 719-745 nm. The
only observed difference between them lies in the intensity
of the higher energy Q band, for which, in the case of the
â-octachloroporphyrin (at 561 nm), the intensity is almost
equal with the intensity of the Q band at 601 nm. In contrast,
Figure 1. UV-vis spectra of (a) H2(Cl8TPP) and (b) Tb(Cl8TPP)(OAc)
in CH2Cl2.
the intensity of the higher energy Q band of the â-octabromo
compound (at 569 nm) is of significantly lower intensity
compared with the Q band at 625 nm. The two tetrahalo-
genated Tb complexes exhibit rather similar spectral features
with the TPP complexes (Table 2). The Soret absorption is
red-shifted (432 nm), while three bands appeared at the area
550-600 nm with that at 569 nm exhibiting the higher
intensity. However, this is not the case in the spectra of
Tb(X8TPP) complexes. Three rather broad absorption bands
were observed between 550 and 670 nm. In both octahalo-
genated porphyrins, the higher energy Q band (at 553 nm in
both complexes) is of lower intensity while that of lower
energy at 652 nm (for Cl8TPP complex) and 669 nm (for
Br8TPP complex) exhibits the higher intensity among the
three (Figure 1).
Electrochemistry. Cyclic voltammetry experiments for all
the complexes were carried out in CH2Cl2, containing 0.1
M NBu4PF6. One reduction and one oxidation process was
observed for each H2(X4TPP) derivative, and two reduction
and two oxidation waves were observed for the H2(X8TPP)
analogues. Under the same conditions, all the Tb(XnTPP)-
(OAc) complexes manifest two reduction and three oxidation
processes. All of the described electrochemical reactions are
reversible and, in each case, correspond to one-electron
(84) H2(TPP) exhibits four Q bands where its origin lies in the vibronic
mixing resulting in the appearance of Qy(1,0), Qy(0,0), Qx(1,0), and
Qx(0,0) transitions in the order of decreasing energy and intensity.
Gouterman, M. The Porphyrins; Dolphin, D., Ed.; Academic Press:
New York, 1978; Vol. III, p 1. Those bands in CH2Cl2, 20 °C, appeared
at 517, 550, 592, and 650 nm, respectively.
2654 Inorganic Chemistry, Vol. 41, No. 10, 2002

NoWel â-Halogenated Lanthanide Porphyrins
Table 3. Half-Wave Potentials (V vs SCE) for Oxidation and Reduction of â-Tetra- and Octahalogenated Porphyrins M(XnTPP)X (where M ) H2 or
Tb(OAc), X ) Cl or Br and n ) 4 or 8) in THF/NBu4ClO4 0.1 M (V vs SCE)
porphyrin
E1/2 2nd red
E1/2 1st red
E1/2 1st ox
E1/2 2nd ox
E1/2 3rd ox
HOMO-LUMO
Soret λmax (nm)
H2(Cl4TPP)
H2(Cl8TPP)
H2(Br4TPP)
H2(Br8TPP)
1
2
3
4
a
-1.10
-0.83
-1.02
-0.77
1.12
1.04
1.05
0.93
a
1.26
a
a
a
a
a
2.22
1.87
2.07
1.70
426
456
430
462
-1.11
a
-1.18
1.17
Tb(Cl4TPP)(OAc)
Tb(Cl8TPP)(OAc)
Tb(Br4TPP)(OAc)
Tb(Br8TPP)(OAc)
9
10
11
12
-1.22
-1.17
-1.03
-1.04
-1.00
-0.87
-0.93
-0.86
0.98
1.03
0.81
0.86
1.19
1.26
1.10
b
1.57
1.63
1.49
b
1.98
1.90
1.74
1.72
430
460
432
474
a Not observed. b Not measured/ill-defined redox couple.
transfer. The electron withdrawing character of the bromine
and chlorine substituents is expected to influence significantly
the electrochemical properties of the porphyrinic derivatives.
Consequently, the presence of these groups at â-pyrrole
positions stabilizes both the HOMOs and the LUMOs with
respect to those of the unsubstituted derivatives. Thus, the
chloro- or bromosubstituted porphyrins would be easier to
reduce and harder to oxidize, and the ring-centered electro-
reductions should shift anodically with respect to their
precursors. So, the more substituted the pyrrole ring is with
halogen, the harder it would be to oxidize because of the
more electron deficient character of the halogenated por-
phyrin ring. Nevertheless, this is not the case (Table 3). As
has been theoretically83,85 and experimentally82 demonstrated,
one must also consider the steric constraints caused by
addition of up to eight bulky groups on â-pyrrolic positions,
like Cl and Br, which strongly modify the redox properties
due to the ring deformation.83 The observation is in agree-
ment with the reported systematic electrochemical study of
iron porphyrins Fe(BrnTPP)Cl (where n ) 0, 1, 2, ..., 8) by
Kadish and co-workers,26,86 where it has been proven that
for 1-3 bromine substituents the redox potentials are
governed by the induction effect. In contrast, for 4 up to 8
bromines, the reduction potential is still governed by the
inductive effects, while in the case of the oxidation potentials
the distortion dominates the inductive effect. Because macro-
cycle distortion destabilizes the HOMOs, leaving the LUMOs
relatively unchanged (slight stabilization), and the destabiliz-
ing effect on the HOMOs predominates in the severely
distorted octahalogenosubstituted porphyrins, they are not
only easier to oxidize than the tetrahalogeno compounds, but
they are also easier to reduce. However, at this point, it
should be noted that because the molecular structures of
tetrahalogenated tetraphenylporphyrins have not been deter-
mined, and isomers with unknown distribution of the four
halogens should be considered, a quantitative evaluation of
the distortion effect in the redox properties of the compounds
is rather difficult. Insights for the molecular structures of
tetrahalogenated compounds are provided and taken into
account in the discussion that follows, by the crystal struc-
tures of almost planar tetrabromo- and tetrachlorotetramesityl-
porphyrins with the two halogens sited in antipodal pyrroles.
Regarding the redox potentials, listed in Table 3, it is evident
that the H2(X4TPP) derivatives are more difficult to reduce
and oxidize, relative to the H2(X8TPP) analogues. This is in
good agreement with the reported data of Kadish mentioned
previously.26,86 Furthermore, in agreement with recently
published data, the E1/2(1st-ox)-E1/2(1st-red) or HOMO-
LUMO gaps of the H2(BrnTPP), derivatives are smaller than
those of the corresponding chlorinated compounds.75 The
Tb(X4TPP)(OAc) complexes are more readily reduced and
oxidized relative to the corresponding free bases, 5 and 7.
However, concerning the metalated derivatives of the octa-
halogenated species (10 and 12), these are slightly easier to
oxidize but considerably less easy to reduce, than their free
base precursors. This, as expected, results in a larger
HOMO-LUMO gap for the Tb(X8TPP)(OAc) complexes
relative to their free bases, 6 and 8. However, regarding the
Soret transition energies of Tb(X4TPP)(OAc) and Tb(X8TPP)-
(OAc), they are clearly red-shifted relative to those of the
free base analogues, as previously stated, in contrast to
predicted values.18,23,24 Interestingly, Tb(X8TPP)(OAc) 10 and
12 are somewhat less easily oxidized than the corresponding
Tb(X4TPP)(OAc) species, 9 and 11, despite their higher
number of halogen substituents, unlike the case of iron
â-octabromoporphyrins.26,86 However, these results suggest
that the bulky, electron-rich Tb ion either decreases the
degree of distortion of the porphyrin macrocycle or the
contribution of the metallic orbitals modulates the energies
of the redox-active orbitals of the ring.
Description of the Structures. An ORTEP diagram of
Ni(Cl8TPP) with an atomic labeling scheme is given in
Figure 2, and selected bond distances and angles are listed
in Table 4. The coordination geometry around Ni is square
tetragonal with bond lengths ranging from 1.899(6) to
1.911(6) Å (mean value Ni-N ) 1.909 Å). The metal lies
on the mean plane of the C20N4 core atoms (mean deviation
0.005 Å). The presence of nickel in the macrocyclic cavity
along with the substitution on the Câ and Cm atoms of the
porphyrin results in the saddle and ruffling of the ligand.
The mean absolute displacement of the nitrogen atoms from
the C20N4 mean plane is 0.14 Å. In the more substituted
porphyrinic Ni complexes19 H2(Br8TMP) (2,3,7,8,12,13,17,18-
octabromo-5,10,15,20-tetramesitylporphyrin) and H2(Br8Tp-
FPP) [2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(penta-
fluoprophenyl)porphyrin], the deviation of the four nitrogen
atoms from the C20N4 mean plane is 0.19 and 0.20 Å,
respectively. The presence of the chlorine atoms in Câ carbon
atoms of the porphyrin skeleton in Ni(Cl8TPP) results in the
(85) Barkigia, K. M.; Renner, M. W.; Furenlid, L. R.; Medforth, C. J.;
Smith, K. M.; Fajer, J. J. Am. Chem. Soc. 1993, 115, 3627.
(86) Kadish, K; Autret, M.; Ou, Z.; Tagliatesta, P.; Boschi, T.; Fares, V.
Inorg. Chem. 1997, 36, 204.
Inorganic Chemistry, Vol. 41, No. 10, 2002 2655

Spyroulias et al.
Table 4. Selected Bond Distances (Å), Angles (deg), and
Averages for Ni(Cl8TPP) H2(Br8TPP)‚2DMF and
Tb(Cl8TPP)(OAc)(DMSO)2‚3PhCH3‚MeOH
bonds
Ni(Cl8TPP) H2(Br8TPP)‚2DMF Tb(Cl8TPP)(OAc)
M-N(1)
M-N(2)
M-N(3)
M-N(4)
N-Ca
1.911(6)
1.899(6)
1.908(6)
1.900(6)
1.361
1.434
1.348
1.879
1.418
1.481
2.41(1)
2.431(9)
2.44(1)
2.43(1)
1.381
1.444
1.358
1.72
1.404
1.505
73.8
116.2
107.4
108.4
107.6
124
1.384
1.443
1.348
1.705
1.394
1.488
Ca-Cb
Cb-Cb
X-Cb
Ca-Cm
Cm-Cphenyl
(N-M-N)cis
(N-M-N)trans
Ca-N-Ca
N-C-Cb
Ca-Cb-Cb
N-Ca-Cm
90.3
171.6
107.3
108.3
107.7
123.9
109.3
107.5
107.7
123.5
Table 5. Structural Characteristics between Ni Perchlorinated and Ni
Perbrominated Porphyrins, Indicating the Distortion of Porphyrin Core
Average Displacement of Selected Atoms
of Porphyrin from C20N4 Mean Plane
atom(s)
Ni(Cl8TPP)
Ni(Br8TPP)
Ni(Br8TpFPP)
N
0.14
0.19
0.20
Cm
Cb
Cl1/Br1
Cl2/Br2
0.54
0.36
0.18
0.67a, 1.12b
0.93
1.20, 0.80c
2.16
1.24a, 1.08b
2.23
2.07
1.26
1.84
Dihedral Angles with the C20N4 Mean Plane
group
Ni(Cl8TPP)
Ni(Br8TPP)
36.00
Ni(Br8TpFPP)
36.40, 41.40
pyrrols
34.0, 32.9
28.3, 27.1
52.2, 54.3
59.4, 63.0
phenyls
58.30
39.80, 45.70
47.00, 48.10
a Average value of C2, C7, C12, C17 displacements. b Average value of
C3, C8, C13, C18 displacements. c Average value of C2, C3 displacements.
combination with the phenyl substituents on the Cm atoms
result in the twist distortion of the molecule. The average
deviation of the Cm atoms from the C20N4 mean plane is
0.54 Å, which is larger than the values of 0.36 and 0.18 Å
reported for Ni(Br8TMP) and Ni(Br8TpFPP), respectively.
The short nickel-nitrogen bond length (mean 1.904 Å) is
also responsible for the twist distortion observed in the
porphyrin skeleton. Because of the larger steric effects
observed in the phenyl substituted bromoporphyrins in Ni-
(Br8TMP) and Ni(Br8TpFPP), the phenyl rings rotate toward
the mean porphyrin plane by angles of 58.3(6)° and
39.8(6)°-48.1(5)°, respectively. In the case of Ni(Cl8TPP),
the steric effects between the chlorine substituents and the
phenyl rings are not so severe, and the phenyl rings are less
rotated with respect to the C20N4 mean plane (52.2°, 54.3°,
59.4°, and 63.0°). The substituted pyrrole rings are coplanar
within experimental error. The slightly increased distortion
caused by the nickel insertion is reflected in the different
displacements of the chlorine atoms from the mean pyrrole
plane (mean values: 0.05 Å for Cl1, Cl3, Cl5, Cl7 and 0.23
Å for Cl2, Cl4, Cl6, Cl8). In the case of Ni(Br8TMP) and Ni-
(Br8TpFPP), these values are 0.09 (Br1), 0.24 (Br2) and 0.15
(Br1), 0.27 Å (Br2), respectively. The substituted pyrrole rings
are tilted alternatively up and down with respect to the
Figure 2. ORTEP diagram of Ni(Cl8TPP) with 50% thermal probability
ellipsoids showing the atomic labeling scheme with the corresponding figure
showing the displacement of core atoms from the mean plane.
saddling distortion of the ligand, expressed by the mean
absolute displacement of the Câ atoms from the C20N4 mean
plane (0.67 Å for C2, C7, C12, C17 and 1.12 Å for C3, C8,
C13, C18). The average absolute displacement of the corre-
sponding chlorine atoms bonded to Câ atoms is 0.93 (for
Cl1, Cl3, Cl5, Cl7) and 2.07 Å (for Cl2, Cl4, Cl6, Cl8). A
comparison of these values with those reported for Ni(Br8-
TMP) and Ni(Br8TpFPP) (Table 5) indicates that Ni(Cl8TPP)
is somehow less saddle distorted. The Câ and Br displace-
ments from the C20N4 mean plane for Ni(Br8TMP) are 1.20/
0.80 and 2.16/1.26 Å, respectively, and for Ni(Br8TpFPP),
these values are 1.24/1.08 and 2.23/1.84 Å, respectively. The
presence of the metal ion in the porphyrin cavity in
2656 Inorganic Chemistry, Vol. 41, No. 10, 2002

NoWel â-Halogenated Lanthanide Porphyrins
Table 6. Intra- and Intermolecular H-bonds Observed in the X-ray
Crystal Structure of H2(Br8TPP)
Intramolecular
N-H‚‚‚N
N‚‚‚N
N-H‚‚‚N (angle (°))
2.510(6)
2.955(6)
113.3(4)
(0.25 + y, 0.75 - x, -0.25 - z)
2.617(6) 2.955(6)
(0.25 + y, 0.75 - x, -0.25 - z)
104.7(4)
Intermolecular
N‚‚‚O
3.01(1)
N-H‚‚‚O
N-H‚‚‚O (angle (°))
2.18(1)
162.6(6)
(0.25 + y, 0.75 - x, -0.25 - z)
porphyrin-core mean plane by 34.0°, 32.9°, 28.3°, and 27.1°,
while in Ni(Br8TMP) the tilting is 36.0(5)°, and in Ni(Br8-
TpFPP), it ranges from 36.4(8)° to 41.4(8)°. The compound
H2(Br8TPP) crystallizes in the tetragonal space group I41/a;
the origin was taken on the center of symmetry. The
asymmetric unit contains one quadrant of the H2(Br8TPP)
molecule and one-half of a DMF solvent molecule. The
oxygen and the nitrogen atoms of the DMF sit on a C2 axis;
therefore, the molecule is disordered. The structure consists
of chains directed parallel to the c-axis formed by alternating
porphyrin molecules and two DMF solvent molecules. An
ORTEP diagram of the molecule with the atomic labeling
is given in Figure 3, selected bond distances and angles are
presented in Table 4, while H-bonds are given in Table 6.
Two types of H-bonds are observed: (i) bifurcated H-bonds
inside the porphyrin core, also observed in other porphyrin
derivatives,87 and (ii) intermolecular H-bonds between the
N-H group and the oxygen atom of the DMF solvent
molecule. An ORTEP diagram of Tb(Cl8TPP)(OAc)(DMSO)2‚
3PhCH3‚MeOH with the atomic labeling scheme is given in
Figure 4, and selected bond distances are given in Table 4.
A detailed description of the structures of H2(Br8TPP)‚2DMF
and Tb(Cl8TPP)(OAc)(DMSO)2‚3PhCH3‚MeOH has been
given elsewhere.29 A comparison of the structural charac-
teristics of the three structures reported herein is given in
Tables 6 and 7. Considering the octachloro complexes of
Ni and Tb, great differences in the distortion of the porphyrin
are observed. The insertion of the relatively small nickel ion
into the cavity of the macrocycle results in its twisted
distortion expressed by the Cm displacement from the C20N4
mean plane (0.54 Å). On the contrary, the relatively larger
terbium ion lies 1.42 Å out of the C20N4 mean plane; thus,
no twisted distortion is observed (Cm displacement ) 0.025
Å). The saddle distortion, expressed by the Câ displacement
from the C20N4 mean plane, dominates in both structures.
As has been observed in a series of porphyrins and their
metal derivatives,88,89 there is a strong tendency that as the
Câ displacement increases the phenyl rings become much
more nearly coplanar with the porphine nucleus because of
the extreme tilting of the pyrrole rings. These trends are also
Figure 3. ORTEP diagram of H2(Br8TPP) with 50% thermal probability
ellipsoids showing the atomic labeling scheme with the corresponding figure
showing the displacement of core atoms from the mean plane.
observed in our complexes. In the case of the free base
H2(Br8TPP), the saddle distortion (Câ ) 1.382/1.145 Å) and
the tipping of the pyrrole rings (44.4°) results in particularly
acute dihedral angles for the phenyl rings relative to the
C20N4 mean plane (29.7°).
Concluding Remarks
For all the compounds studied, the presence of eight
halogens on the porphyrin â-pyrrole positions caused a larger
red shift of the Soret band than the presence of four halogens.
As expected, brominated derivatives present the larger shift
for the Soret band. Bromine is slightly less electronegative
than chlorine but causes larger distortions on the porphyrin,
and spectral red-shift has been found to be strongly coupled
to the degree of ring distortion.22 However, the absolute value
(87) Chan, K. S.; Zhou, X.; Luo, B. S.; Mak, T. C. W. J. Chem. Soc.,
Chem. Commun. 1994, 271.
(88) Silvers, S. J.; Tulinsky, A. J. Am. Chem. Soc. 1967, 89, 3331.
(89) Scheidt, W. R.; Lee, Y. J. In Metal Complexes with Tetrapyrrole
Ligands I; Buchler, J. W., Ed.; Springer-Verlag: New York, 1987; p
2.
Inorganic Chemistry, Vol. 41, No. 10, 2002 2657

Spyroulias et al.
Table 7. Structural Characteristics of H2(Br8TPP)‚2DMF and
Tb(Cl8TPP)(OAc)(DMSO)2‚3PhCH3‚MeOH, Indicating the Distortion
of Porphyrin Core
Average Displacement (Å) of Selected Atoms
of Porphyrin from C20N4 Mean Plane
atom(s)
Tb(Cl8TPP)(OAc)
H2(Br8TPP)a
N
0.134
0.033
Cm
Cb
Cl1/Br1
Cl2/Br2
0.025
0.317
0.90, 0.88a
1.67c
1.382, 1.145b
2.764e
1.63d
2.069e
Dihedral Angles with the C20N4 Mean Plane
group
Tb(Cl8TPP)(OAc)
H2(Br8TPP)
pyrrols
19.6, 33.4
21.7, 35.5
47.6, 49.6
50.9, 49.6
44.4
29.7
phenyls
a Average value of C2, C7, C12, C17 and C3, C8, C13, C18 displacements,
respectively. b Average value of C2, C3 (and their symmetrical atoms)
displacements. c Average value of Cl1, Cl3, Cl5, Cl7 displacements. d Average
value of Cl2, Cl4, Cl6, Cl8 displacements. e Average value of Br1 (and its
symmetrical atoms) and Br2 (and its symmetrical atoms) displacements.
of Cl8TPP complexes. The half-wave potentials measured
for all the free porphyrins are in good agreement with the
potentials measured for the tetra- and octahalogenated
derivatives of 5,10,15,20-tetramesitylporphyrins.75 All the Tb
complexes oxidized easier than the corresponding free bases,
while only Tb tetrahalogenated complexes reduced easier
with respect to their free bases. The HOMO-LUMO energy
gap for all the halogenated compounds studied varies from
2.22 to 1.70 V and is smaller than that of the free TPP which
measured 2.32 V.75 The HOMO-LUMO gap is found to be
considerably smaller in the case of tetrahalogenated Tb
complexes than the corresponding free bases, while for
octahalogenated Tb complexes it is somewhat larger when
compared with the corresponding free porphyrins. The
possibility that electron-transfer processes involve molecular
orbitals with major or minor metal character could not be
excluded, and studies on the whole series of lanthanide
perhalogenated complexes are under way.90 However, sys-
tematic studies of mono- or bisporphyrinates along the series
of lanthanide ions demonstrate that the electrode reactions
observed are porphyrin-centered. Because the crystal struc-
tures of the Ni and Tb complexes with the octachlorinated
porphyrin are available, a structure-properties correlation
could be attempted. Tb complexes exhibit Soret transitions
of lower energy than Ni complexes, and the effect is
particularly pronounced in the case of octahalogenated
compounds. In this case, the Soret absorption band was found
more than 20 nm bathochromically shifted for Tb complexes,
with respect to those of Ni. However, if the energy of
electronic transitions is governed by the distortion of the
porphyrin (either because of the peripheral substituents or
because of the metal ion), then the compound with the more
distorted macrocycle should exhibit the lowest energy Soret
band. According to the data acquired during the X-ray
diffraction studies of the Tb and Ni compounds, the more
Figure 4. ORTEP diagram of Tb(Cl8TPP)(OAc)(DMSO)2‚3PhCH3‚MeOH
with 50% thermal probability ellipsoids showing the atomic labeling scheme
with the corresponding figure showing the displacement of core atoms from
the mean plane.
of λmax is not the same for free porphyrin and its metalated
complexes. So, absorption bands in the electronic spectra of
the free bases are more shifted to the red than those of the
Ni complexes. The absorption bands of the terbium com-
plexes are the most red shifted in the series of the compounds
studied. The absolute value, λmax, of the Soret band in the
case of octahalogenated compounds follows the order Tb
complexes > free bases > Ni complexes. The same holds
for tetrahalogenated derivatives, though differences are less
pronounced. Although in the case of halogen-induced free-
porphyrin distortion the most deformed ring exhibits the most
red-shifted Soret absorption band (in case of Br8TPP deriva-
tives), this is not the case for the metal-induced distortion
(90) Spyroulias, G. A.; Coutsolelos, A. G. Work in progress.
2658 Inorganic Chemistry, Vol. 41, No. 10, 2002

NoWel â-Halogenated Lanthanide Porphyrins
distorted porphyrin is found to be Ni(Cl8TPP), manifested
by the Cm displacement. Consequently, the metal derivative
of the octachlorinated TPP with the most distorted ring
exhibits the higher Soret transition energy, and we can
deduce that the nature of the metal ion could strongly
influence the properties of the complexes in addition to the
already mentioned reasons. The X-ray data obtained indicate
that in the series of metal complexes of (Cl8TPP)2- the size
of the metal ion compensates to the ring distortion. The most
distorted porphyrin ring manifested by the displacements of
pyrrole nitrogens and Cm from planarity is found for the
complex with the smaller metal ion, the Ni. The terbium
ion lies 1.28 Å out of the N4 mean plane, while the Ni, with
considerably smaller ionic radius, is hosted in the macrocycle
cavity causing core contraction.19 However, the crystal
structure of the free H2(Cl8TPP) is not available, and thus,
the different effect of each metal ion could not be safely
concluded. One should mention that when free porphyrin
and the Ni complex of octabromo derivatives of tetramesityl-
porphyrin and tetra(pentafluorophenyl)porphyrin are com-
pared, the distortion of the Ni complex is found to be more
severe (on the basis of UV-vis data). The effect of metal
size on the distortion and consequently on the properties of
partially halogenated or perhalogenated porphyrin derivatives
is of particular interest. Studies including the rational
synthesis of new perhalogented metalloporphyrins or metal-
free porphyrins in order to monitor the conformational and
physicochemical changes of those compounds are currently
in progress.90
Acknowledgment. This research was supported by the
Greek General Secretariat of Research and Technology, the
Centre National de la Recherche Scientifique, and the Paul
Sabatier University of Toulouse and Elais corporation. We
are also grateful to Mr. John Boutaris and the Agricultural
Bank of Greece (A.T.E.) for financial support to C.P.R. as
well as the two reviewers for their insightful comments.
Supporting Information Available: Detailed experimental data
for X-ray structural analyses. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC000738H
Inorganic Chemistry, Vol. 41, No. 10, 2002 2659