Synthesis and characterization of (octaaryltetraazaporphyrinato)indium(III) complexes for optical limiting

Article abstract of DOI:10.1021/ic0205738

The preparation of (octaaryltetraazaporphyrinato)indium(III) chlorides [aryl = phenyl (5a), p-tert-butylphenyl (6a), p-(trifluommethyl)phenyl (7a), m-(trifluommethyl)phenyl (8a)] and their reactions with aryl Grignard reagents XMgBr to give 5b-8b [X = p-(

Full text of DOI:10.1021/ic0205738

Inorg. Chem. 2003, 42, 2683−2694
Synthesis and Characterization of
(Octaaryltetraazaporphyrinato)indium(III) Complexes for Optical Limiting
Sergej Vagin,† Markus Barthel, Danilo Dini, and Michael Hanack*
Lehrstuhl fu¨r Organische Chemie II, UniVersita¨t Tu¨bingen, Auf der Morgenstelle 18,
D-72076 Tu¨bingen, Germany
Received September 20, 2002
The preparation of (octaaryltetraazaporphyrinato)indium(III) chlorides [aryl ) phenyl (5a), p-tert-butylphenyl (6a),
p-(trifluoromethyl)phenyl (7a), m-(trifluoromethyl)phenyl (8a)] and their reactions with aryl Grignard reagents XMgBr
to give 5b−8b [X ) p-(trifluoromethyl)phenyl] and 5c (R ) 3,5-difluorophenyl) are described. The characterization
of all compounds by UV−vis, FT-IR, and 1H and 13C NMR spectroscopy was performed. The hypsochromic shift
of all bands in the absorption spectra of complexes 5a−8a is observed in the sequence 6a < 5a < 7a ≈ 8a. This
is associated with the increasing electron-withdrawing character of the aryl substituents in the periphery of the
tetraazaporphyrin macrocycle. Compounds 8a,b are very good soluble in organic solvents with 8a exhibiting the
higher photochemical stability among the various synthesized species. The optical limiting (OL) properties of the
complexes have been studied and correlated with the structure of the (tetraazaporphyrinato)indium(III) complexes
and the electronic nature of the different substituents. In particular, the OL effect at 532 nm increases on going
from the series of compounds 5 to the series 8.
Introduction
have to be found in the presence of an extended network of
π-electrons which infer a high electrical polarizability to the
Conjugated macrocycles such as metallophthalocyanines
(PcM’s), metallonaphthalocyanines (NcM’s) and metallotet-
raazaporphyrins (TAPM’s) have been extensively studied due
to their widespread usage in various important fields of
material science.1 The recognition of the importance of these
classes of materials as far as nonlinear optics is concerned
is relatively recent.2 In fact, PcM’s, NcM’s, TAPM’s, and
their derivatives are new functional compounds which
constitute the active materials in advanced devices based on
nonlinear optical properties.3 In particular, it has been proved
that PcM’s and analogous species produce strong optical
limiting (OL) effects,2a-e which can be profitably exploited
for the protection of light-sensitive elements against ac-
cidental or hostile intense radiations.2f,4 The reasons for that
(2) (a) Nalwa, H. S.; Shirk, J. S. In Phthalocyanines: Properties and
Applications; Leznoff, C. C., Lever, A. B. P., Eds.; VCH: Weinheim,
Germany, 1996; Vol. 4, p 79. (b) Perry, J. W.; Mansour, K.; Lee, I.
Y. S.; Wu, X. L.; Bedworth, P. V.; Chen, C. T.; Ng, D.; Marder, S.
R.; Miles, P.; Wada, T.; Tian, M.; Sasabe, H. Science 1996, 273, 1533.
(c) Shirk, J. S.; Pong, R. G. S.; Flom, S. R.; Heckmann, H.; Hanack,
M. J. Phys. Chem. A 2000, 104, 1438. (d) Dini, D.; Barthel, M.;
Hanack, M. Eur. J. Org. Chem. 2001, 3759. (e) Hanack, M.; Dini,
D.; Barthel, M.; Vagin, S. Chem. Rec. 2002, 2, 129. (f) Spangler, C.
J. Mater. Chem. 1999, 9, 2013. (g) Nalwa, H. S.; Hanack, M.;
Pawlowski, G.; Engel, M. K. Chem. Phys. 1999, 245, 17. (h) Zyss, J.
Molecular Nonlinear Optics, Academic Press: New York, 1993. (i)
Van Stryland, E. W.; Hagan, D. J.; Xia, T.; Said, A. A. In Nonlinear
Optics of Organic Compounds and Polymers; Nalwa, H. S., Miyata,
S., Eds.; CRC Press: Boca Raton, FL, 1997; p 841. (j) De la Torre,
G.; Vazquez, P.; Agullo-Lopez, F. Torres, T. J. Mater. Chem. 1998,
8, 1671.
(3) (a) Khoo, I. C.; Simoni, F.; Umeton, C. NoVel Optical Materials and
Applications; John Wiley and Sons: New York, 1996. (b) Dalton, L.
R.; Steier, W. H.; Robinson, B. H.; Zhang, C.; Ren, A.; Garner, S.;
Chen, A.; Londergan, T.; Irwin, L.; Carlson, B.; Fifield, L.; Phenlan,
G.; Kincaid, C.; Amend, J.; Jen, A. J. Mater. Chem. 1999, 9, 1905.
(c) Canva, M.; Stegeman, G. I. In Polymers for Photonics Applications
I, AdVances in Polymeric Science 158; Lee, K. S., Ed.; Springer:
Berlin, 2002; pp 87-121.
* To whom correspondence should be addressed. E-mail: hanack@
uni-tuebingen.de. Fax: +49+7071+295268.
† On leave from Ivanovo State University of Chemistry and Technology,
153460 F. Engels str., 7 Ivanovo, Russia.
(1) (a) Hanack, M.; Lang, M. AdV. Mater. 1994, 6, 819. (b) McKeown,
N. B. Phthalocyanine Materials- Synthesis, Structure and Function;
Cambridge University Press: Cambridge, U.K., 1998. (c) Gairns, R.
S. The Chemistry and Technology of Printing and Imaging Systems;
Blackie: London, 1996; p 76. (d) Phthalocyanines: Properties and
Applications; Leznoff, C. C., Lever, A. B. P., Eds.; VCH: Weinheim,
Germany, 1989-1996; Vols. 1-4. (e) Law, K. Y. Chem. ReV. 1993,
93, 449. (f) Bonnett, R. Chem. Soc. ReV. 1995, 24, 19.
(4) (a) Anderberg, B.; Wolbarsht, M. L. Laser Weapons: The Dawn of a
New Military Age; Plenum Press: New York, 1992. (b) Hollins, R.
C. Curr. Opin. Solid State Mater. Sci. 1999, 4, 189. (c) Robertson, J.;
Smith, A.; Duignan, J.; Milsom, P.; Bourhill, G. Appl. Phys. Lett. 2001,
78, 1183. (d) Van Stryland, E. W.; Sheik-Bahae, M.; Said, A. A.;
Hagan, D. J. Prog. Cryst. Growth Charact. 1993, 27, 279.
10.1021/ic0205738 CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/28/2003
Inorganic Chemistry, Vol. 42, No. 8, 2003 2683

Vagin et al.
Figure 1. Structure and designation of synthesized indium complexes.
molecule5 and, in addition, take part in a number of fast
transitions in the spectral regions of OL interest.6 Moreover,
the versatility of the synthetic methods offers the possibility
of modifying the skeleton of these conjugated macrocycles
in a plethora of ways by modulating all the various con-
stituents according to predefined molecular structures.7
Indium phthalo- and naphthalocyanines are well-known
as active materials for OL applications.2e,8 In these complexes
the trivalent nature of the coordinated central In atom requires
the presence of a monovalent axial ligand which is ap-
proximately oriented in a perpendicular direction with respect
to the plane defined by the coordinating macrocycle.9 The
nature of the peripheral substituents and axial ligands in these
indium-macrocycle complexes influences the stability and
the relative OL performance. The introduction of sterically
large axial substituents leads to a decrease of the aggregation
tendency of the complexes. Aggregates are mostly coplanar-
associated arrangements driven by enhanced van der Waals
attractive forces of the Pc rings. For an OL material this
aggregation must be avoided, since strong intermolecular
interactions open additional relaxation pathways and, thereby,
shorten the exited-state lifetime which reduces the effective
nonlinear absorption.8a The presence of peripheral substitu-
ents facilitates the solubilization of the substituted compounds
as well, but in some cases these can lead to a decrease of
the photochemical stability of the substituted compounds
under the conditions at which OL is required.10
Studies on the OL effect produced by indium tetraaza-
porphyrins have not been reported up to now, and only few
indium(III) complexes of octaphenyltetraazaporphyrin are
known.11
In this work we report on the synthesis and the OL prop-
erties of a series of new axially coordinated indium(III) octa-
aryltetraazaporphyrins (see Figure 1) of the general formula
[(Ar)8TAP]In(X), with Ar ) phenyl (Ph, series 5), p-tert-
butylphenyl (p-t-BuPh, series 6), p-(trifluoromethyl)phen-
yl, (p-CF3Ph, series 7), and m-(trifluoromethyl)phenyl (m-
CF3Ph, series 8) and X ) Cl (series a), p-(trifluoromethyl)-
phenyl (p-TMP, series b), and 3,5-difluorophenyl (DFP,
series c).
Experimental Section
Diphenylfumaronitrile (1) was prepared from benzyl cyanide
(purity 98%, Fluka) according to a reported procedure12 and purified
additionally by vacuum distillation. Bis(p-tert-butylphenyl)fuma-
ronitrile (2) was obtained from p-tert-butylbenzyl bromide (purity
90%, Fluka) by the combination of methods described in the
literature.13,14
Solvents for synthesis, chromatography, and spectroscopic char-
acterization of compounds were pure chemicals (Aldrich, Fluka).
(5) Drechsler, M.; Muller, E. W. Z. Phys. 1952, 132, 195.
(6) (a) Lee, L. K.; Sabelli, N. H.; Le Breton, P. R. J. Phys. Chem. 1982,
86, 3926. (b) Edwards, L.; Gouterman, M. J. Mol. Spectrosc. 1970,
33, 292.
(7) Hanack, M., Heckmann, H.; Polley, R. In Methods of Organic
Chemistry, 4th ed.; Houben-Weyl, Vol. E9d; Thieme Verlag: Stuttgart,
Germany, 1997; p 717.
(8) (a) Hanack, M.; Schneider, T.; Barthel, M.; Shirk, J. S.; Flom, S. R.;
Pong, R. G. S. Coord. Chem. ReV. 2001, 221, 235. (b) Krivokapic,
A.; Anderson, H. L.; Bourhill, G.; Ives, R.; Clark, S.; McEwan, K. J.;
Kenneth, AdV. Mater. 2001, 13, 652. (c) J. W. Perry, Mansour, K.;
Miles, P.;Chen, C. T.; Marder, S. R.; Kwag, G.; Kenney, M. Polym.
Mater. Sci. Eng. 1995, 72, 222.
The OL effect is a photoinduced change of light transmis-
sion through a material or a device, which consists of the
decrease of the transmittance when the light intensity exceeds
a system-dependent threshold value.4c An appropriate equa-
tion describing the OL effect is
2
-(dIin/dz) ) [R(Iin)]Iin ) R0Iin + â0Iin
(1)
(9) Schweiger, K.; Hueckstaedt, H.; Homborg, H. Z. Anorg. Allg. Chem.
1998, 624, 44.
(10) Winter, G.; Heckmann, H.; Haisch, P.; Eberhardt, W.; Hanack, M.;
Luer, L.; Egelhaaf, H. J.; Oelkrug, D. J. Am. Chem. Soc. 1998, 120,
11663.
(11) Stuzhin, P. A.; Migalova, I. S.; Homborg, H. Russ. J. Coord. Chem.
2000, 26, 6.
(12) Cook, A. H.; Linstead, R. P. J. Chem. Soc. 1937, 929.
(13) Marinina, L. E.; Mikhalenko, S. A.; Luk’yanets, E. A. Russ. J. Gen.
Chem. 1973, 43, 2010.
(14) Baumann, T. F.; Barrett, A. G. M.; Hoffman, B. M. Inorg. Chem.
1997, 36, 5661.
with Iin being the intensity of the incident light, z the direction
of light propagation, R(Iin) the general intensity-dependent
absorption coefficient, R0 the linear absorption coefficient,
and â0 the nonlinear absorption coefficient. In eq 1, the
effective intensity-dependent absorption coefficient R(Iin) is
expressed in the form R 0 + â0Iin, thus showing the nonlin-
earity of the optical properties of the irradiated material.4d
2684 Inorganic Chemistry, Vol. 42, No. 8, 2003

(Octaaryltetraazaporphyrinato)indium(III) Complexes
THF for Grignard reactions was thoroughly dried by refluxing with
sodium and distilled. All reactions with Grignard reagents were
carried out under nitrogen atmosphere. Quinoline was additionally
purified by vacuum distillation under nitrogen.
Bis(p-(trifluoromethyl)phenyl)fumaronitrile (4). p-(Trifluo-
romethyl)benzyl cyanide (4 g, 21.2 mmol; purity 98%, Aldrich),
I2 (5.4 g, 42.5 mmol), Na (0.97 g, 42.2 mmol), methanol (16 mL),
and diethyl ether (70 mL) were used by applying the similar method
of preparation as described for the meta-precursor 3. The formation
of precipitate was observed during the reaction. After the reaction
mixture was poured into 100 mL of cold water, the diethyl ether
was added until complete dissolution of the precipitate. The organic
phase was treated further as described above for the meta-derivative.
Yield: 2.7 g (7.4 mmol, 69%) of colorless crystals. Mp: 234-
236 °C. FT-IR (KBr) (ν, cm-1): 3111 vw; 2226 (νCN) w; 1929
vw; 1618 w; 1410 m; 1323 vs; 1234 w; 1202 m; 1188 m; 1165 s;
1130 vs; 1070 s; 1018 m; 860 m; 833 s; 764 m; 660 m; 638 w;
604 m; 492 w; 424 w. 1H NMR (CDCl3) (δ, ppm): 7.96 (d, 4H, 3J
≈ 8.0 Hz); 7.82 (d, 4H, 3J ≈ 8.0 Hz). 13C NMR (CDCl3) (δ, ppm):
The following equipment was used for characterization: UV-
1
vis, Shimadzu UV-365; FT-IR, Bruker IFS-48; H and 13C-NMR,
Bruker AC 250 (1H, 250.131 MHz; 13C, 62.902 MHz); mass, Varian
Mat 711; elemental analyses, Carlo-Erba elemental analyzer 1104,
1106.
Optical Limiting Measurements. The OL effect for the various
octaaryltetraazaporphyrins has been studied with the Z-scan tech-
nique in the open aperture and closed aperture configurations.15
The samples are solutions of octaaryltetraazaporphyrins in toluene
with concentrations (0.5-5) × 10-4 M. The optical cell was a quartz
cuvette with optical path thickness equal to 0.1 cm. The sample
irradiation was realized with a pulsed Nd:YAG laser (from
Continuum Minilite, Edinburgh, Scotland) emitting at the second
harmonic (λ ) 532 nm). Samples linear transmittance at the
wavelength of laser irradiation ranged in the interval 70-90%. The
maximum energy per laser pulse was 100 mJ. The pulse duration
ranged in the interval 3-7 ns. The frequency of sample irradiation
was 10 pulses/s. The Nd:YAG laser beam was focused with a
neutral lens having the focal distance equal to 10 cm. During the
Z-scan determinations the sample spanned a total length of 3.5 cm
centered at the beam focus. The displacement of the sample along
the Z-scan direction was controlled by means of a piezoelectric
driver. The laser beam radius was approximately 0.5 cm before
lens focusing. The recording of sample transmittance was taken
every 0.05 cm along the spanned length. The reported values of
transmittance were averaged on a basis of 20 determinations/
analyzed Z-position.
Bis(m-(trifluoromethyl)phenyl)fumaronitrile (3). m-(Trifluo-
romethyl)benzyl cyanide (10 g, 52.4 mmol; purity 97%, Aldrich)
and resublimed I2 (13.4 g, 0.105 mol) were dissolved in 130 mL
of diethyl ether and cooled to 0 °C. A cooled solution of Na (2.4
g, 0.104 mol) in 35 mL of methanol was added to this mixture
dropwise over 20-30 min, maintaining the temperature of reaction
mixture strictly in the range of 0 to -5 °C. After all of the sodium
methoxide solution had been added, the reaction mixture was stirred
at this temperature for 10 min and then poured into 200 mL of ice
water. The organic phase was separated and washed consecutively
with 100 mL of aqueous solution of sodium thiosulfate (3%) and
100 mL of distilled water. n-Hexane (50 mL) was added to the
obtained slightly yellowish diethyl ether phase, and the solvents
were removed under vacuum until 30 mL remained. The precipi-
tated colorless crystals were immediately filtered off, washed with
a small portion of n-hexane, and dried in vacuo (0.1 bar) at 80-90
°C. Yield: 5.7 g (15.6 mmol, 58%). Mp: 164-165 °C. FT-IR
(KBr) (ν, cm-1): 3090 w; 2228 (ν CN) m; 1614 w; 1489 w; 1443
m; 1333 vs; 1290 w; 1236 s; 1196 s; 1173 s; 1134 vs; 1103 m;
1076 s; 1040 w; 1001 w; 916 m; 881 m; 814 m; 802 s; 766 w; 698
s; 673 m; 656 m. 1H NMR (CDCl3) (δ, ppm): 8.02-8.07 (m, 4H);
5
2
134.7 (q, J ≈ 1.4 Hz); 133.8 (q, J ≈ 33.3 Hz); 129.2 (s); 126.5
3
1
(q, J ≈ 3.7 Hz); 125.8 (s); 123.2 (q, J ≈ 272.8 Hz); 115.6 (s).
Mass (FD): m/z ) 365.9 (M+). Anal. Calcd for C18H8F6N2, M )
366.3 g/mol: C, 59.03; H, 2.20; N, 7.65. Found: C, 59.00; H, 2.13;
N, 7.77.
(Octaphenyltetraazaporphyrinato)indium(III) chloride (5a).
InCl3 (1 g, 4.5 mmol) and 1 (4 g, 17.4 mmol) were heated in 20
mL of quinoline in the presence of 5 drops of 1,8-diazabicyclo-
[5.4.0]undec-7-ene (DBU, purity 99%, Fluka) at 230 °C for 6 h.
The quinoline was distilled off in a vacuum, and the crude product
was washed with methanol by Soxhlet extraction and finally dried
in a vacuum (0.1 bar, 60 °C, 24 h.). Yield: 2 g (1.87 mmol, 43%)
of dark greenish-brown crystalline powder. UV-vis (CH2Cl2) (λmax
,
nm/rel intens): 378/0.773; 475/0.227; 590/0.218; 642 /1.00.
FT-IR (KBr) (ν, cm-1): 3053 w; 1456 m; 1367 m; 1300 w; 1198
w; 1186 w; 1140 m; 1003 s; 986 vs; 920 w; 876 m; 822 w; 800 w;
787 w; 773 w; 756 m; 746 m; 729 m; 712 w; 692 s; 604 m; 534
m; 517 w. Anal. Calcd for C64H40N8ClIn, M ) 1071.4 g/mol: C,
71.75; H, 3.76; N, 10.46. Found: C, 71.95; H, 3.50; N, 10.74.
(Octakis(p-tert-butylphenyl)tetraazaporphyrinato)indium-
(III) chloride (6a). InCl3 (0.5 g, 2.26 mmol) and 2 (3 g, 8.77 mmol)
were heated (240 °C, 7 h) in 10 mL of 1-chloronaphthalene in the
presence of DBU (5 drops). The reaction mixture was cooled slowly
to induce crystallization and poured into 100 mL of methanol. The
precipitate was centrifuged and washed with methanol in a Soxhlet.
For further purification, the product was dissolved in CH2Cl2 and
filtered and an equal amount of methanol was added to the filtrate.
Dichloromethane was partially removed from the obtained solution
using a rotary evaporator, and the formed precipitate was filtered
off and dried in a vacuum (0.1 bar, 60 °C, 24 h). Yield: 1.3 g
(0.86 mmol, 39%) of red-brown powder. UV-vis (CH2Cl2) [λmax
,
nm /log(ꢀ)]: 383/4.94; 500/4.50; 602/4.42; 653/5.07. FT-IR (KBr)
(ν, cm-1): 3082 vw; 3038 vw; 2964 vs; 2905 m; 2868 w; 1610 w;
1493 w; 1460 m; 1425 vw; 1393 w; 1369 m; 1300 w; 1269 m;
1194 w; 1146 w; 1109 m; 1016 w; 989 vs; 881 w; 839 m; 806 w;
1
3
775 vw; 748 w. H NMR (CDCl3) (δ, ppm): 8.32 (d, 16H, J ≈
8.4 Hz); 7.61 (d, 16H, J ≈ 8.4 Hz); 1.51 (s, 72H). 13C NMR
3
3
3
7.84 (d, 2H, J ≈ 8.0 Hz); 7.71 (t, 2H, J ≈ 7.8 Hz). 13C NMR
(CDCl3) (δ, ppm): 156.8 (s); 151.3 (s); 142.6 (s); 132.7 (s); 130.5
(s); 125.3 (s); 34.9 (s); 31.6 (s). Mass (FD): m/z ) 1519.9 (M+).
Anal. Calcd for C96H104N8ClIn, M ) 1520.2 g/mol: C, 75.85; H,
6.90; N, 7.37. Found: C, 75.43; H, 7.13; N, 7.73.
2
4
(CDCl3) (δ, ppm): 132.2 (s); 132.1 (q, J ≈ 33 Hz); 131.8 (q, J
≈ 0.9 Hz); 130.2 (s); ≈130.2 (q, covered); 128.7 (q, 3J ≈ 3.5 Hz);
125.7 (q, 3J ≈ 3.8 Hz); 123.2 (q, 1J ≈ 272.8 Hz); 115.6 (s). Mass
(FD): m/z ) 366.1 (M+). Anal. Calcd for C18H8F6N2, M ) 366.3
g/mol: C, 59.03; H, 2.20; N, 7.65. Found: C, 58.90; H, 2.06; N,
7.69.
(Octakis(p-(trifluoromethyl)phenyl)tetraazaporphyrinato)-
indium(III) chloride (7a). InCl3 (0.3 g, 1.35 mmol), 4 (1.5 g,
4.10 mmol), and DBU (4 drops) were heated in 5 mL of quinoline
at 230 °C for 8 h. After cooling, to wash the product, methanol
(50 mL) was added to the reaction mixture. The mixture was
intensively stirred for 10 min, and water (5 mL) was added dropwise
to complete the precipitation of the product. The precipitate was
(15) (a) Sheik-Bahae, M.; Said, A. A.; Wei, T.; Hagan, D. J.; Van Stryland,
E. W. IEEE J. Quantum Electron. 1990, 26, 760. (b) Kandasamy, K.;
Divakar, K.; Deshpande, R. R.; Puntambekar, P. N.; Singh, B. P.;
Shetty, S. J.; Srivastava, T. S. Appl. Phys. B 1997, 64, 479.
Inorganic Chemistry, Vol. 42, No. 8, 2003 2685

Vagin et al.
centrifuged, the methanol solution was removed, and the same
washing procedure was repeated twice. The solid was dissolved in
CH2Cl2 and filtered through a glass filter G4. Methanol (50 mL)
was added to the obtained solution, and the solvents were partially
removed using a rotary evaporator. The precipitation of the product
was completed by addition of few drops of water, and the precipitate
was filtered off. After drying in a vacuum (0.1 bar) at 90 °C, the
product was continuously washed with hexane in a Soxhlet, dried
again, and chromatographed on silica gel (CH2Cl2, the green fraction
was collected). Yield: 0.50 g (0.31 mmol, 30%) of dark greenish
powder. UV-vis (CH2Cl2) [λmax, nm/log(ꢀ)]: 379/5.03; 457/4.30;
585/4.37; 638/5.16. FT-IR (KBr) (ν, cm-1): 1618 m; 1464 w; 1408
w; 1371 w; 1325 vs; 1175 s; 1134 s; 1069 s; 1018 m; 988 s; 881
w; 847 m; 810 vw; 777 w; 683 m; 623 w; 603 w; 432 w. 1H NMR
(CDCl3) (δ, ppm): 8.30 (d, 16H, 3J ≈ 8.2 Hz); 7.85 (d, 16H, 3J ≈
8.4 Hz). 13C NMR (THF-d8) (δ, ppm): 158.1 (s); 143.4 (s); 137.3
was added. The formed precipitate was centrifuged, dissolved in
50 mL of methanol, crystallized by dropwise addition of water,
and centrifuged again. After the sample was dried in a vacuum at
80 °C, 180 mg (0.112 mmol) of dark-green powder was obtained.
Yield: 82%. UV-vis (CH2Cl2) [λmax, nm /log(ꢀ)]: 378/5.05; 458/
4.31; 584/4.38; 636/5.15. FT-IR (KBr) (ν, cm-1): 1373 w; 1331
vs; 1312 s; 1279 m; 1198 m; 1169 s; 1128 s; 1097 m; 1076 m;
1009 m; 914 m; 808 m; 744 vw; 719 m; 698 m; 687 w; 654 vw.
3
1H NMR (CDCl3) (δ, ppm): 8.35 (d, 8H, J ≈ 8.1 Hz); 8.27 (s,
3
3
8H); 7.87 (d, 8H, J ≈ 8.1 Hz); 7.72 (t, 8H, J ≈ 7.9 Hz). 13C
NMR (CDCl3) (δ, ppm): 156.6 (s); 143.0 (s); 135.5 (s); 132.6 (s);
2
3
131.3 (q, J ≈ 32.8 Hz); 129.4 (q, J ≈ 4.1 Hz); 129.3 (s); 125.9
3
1
(q, J ≈ 3.7 Hz); 123.9 (q, J ≈ 272.8 Hz). Mass (FD): m/z )
1614.9 (M+). Anal. Calcd for C72H32N8F24ClIn, M ) 1615.3
g/mol: C, 53.54; H, 2.00; N, 6.94. Found: C, 52.73; H, 2.11; N,
6.87.
2
(s); 134.3 (s); 131.6 (q, J ≈ 32.4 Hz); 126.4 (q, nonresolved);
p-(Trifluoromethyl)phenylmagnesium bromide [(p-TMP)-
MgBr] in a THF solution was prepared by stirring magnesium
turnings (25 mg, 1.1 mmol) with p-(trifluoromethyl)phenyl bromide
(0.15 mL, 1.0 mmol) in 2 mL of dry THF at room temperature.
(p-(Trifluoromethyl)phenyl)(octaphenyltetraazaporphyrinato)-
indium(III) (5b). Compound 5a (150 mg, 0.14 mmol) was
suspended in dry THF (15 mL) at room temperature. The freshly
prepared THF solution of (p-TMP)MgBr was added dropwise to
this mixture using a syringe. The reaction mixture was stirred for
17 h and then poured into 100 mL of an ice-methanol mixture
(approximately 1:1) and centrifuged. The obtained precipitate was
washed with methanol, dried, and chromatographed (silica gel/
CH2Cl2, the first fraction was taken). Yield: 83 mg (0.070 mmol,
50%). UV-vis (CH2Cl2) [λmax, nm/log(ꢀ)]: 395/5.01; 483/4.16; 591/
4.39; 643/5.15. FT-IR (KBr) (ν, cm-1): 3055 w; 1599 vw; 1460
m; 1387 w; 1367 m; 1325 s; 1300 vw; 1200 vw; 1182 w; 1163 m;
1138 m; 1126 m; 1049 m; 1003 m; 984 vs; 914 w; 876 m; 822 m;
773 m; 744 m; 692 s; 604 m. 1H NMR (CDCl3) (δ, ppm): 8.28-
1
125.5 (q, J ≈ 271.9 Hz). Mass (FD): m/z ) 1614.5 (M+). Mass
-
(FAB): m/z ) 1578.8 (M+ Cl). Anal. Calcd for C72H32N8F24-
ClIn, M ) 1615.3 g/mol: C, 53.54; H, 2.00; N, 6.94. Found: C,
53.65; H, 2.05; N, 7.07.
Octakis(m-(trifluoromethyl)phenyl)tetraazaporphyrin (8). Na
(0.2 g, 8.70 mmol) was dissolved in methanol (20 mL), and the
solution was cooled in ice-water bath. Compound 3 (1.5 g, 4.17
mmol) was added to this solution with stirring. A stream of dry
ammonia was bubbled through the reaction mixture for 1 h at ice
bath temperature and then for 1 h at room temperature. Completion
of reaction was monitored by TLC, until no traces of starting
material were detected. The greenish-yellow reaction mixture was
poured into 50 mL of cold water, and the organic phase was
extracted with three 50 mL portions of chloroform. The chloroform
solution was washed with 100 mL of water, dried over anhydrous
Na2SO4, and filtered, and the solvent was evaporated. The residual
viscous material was dissolved in n-pentanol (7 mL) and heated at
140 °C for 16 h. The reaction mixture was slowly cooled and then
filtered. The precipitate was washed with small portions of hexane
or methanol and dried in a vacuum at 60 °C. Yield: 0.82 g (0.56
mmol, 54%) of crystalline powder with violet reflection. UV-vis
(CH2Cl2) [λmax, nm/log(ꢀ)]: 365/4.98; 422 sh; 552 sh; 590/4.78;
658/5.00. FT-IR (KBr) (ν, cm-1): 3300 vw; 1489 vw; 1435 vw;
1331 vs; 1313 s; 1279 w; 1184 s; 1167 s; 1126 s; 1097 m; 1076
m; 1036 vw; 988 w; 906 w; 885 w; 804 m; 758 w; 698 s; 654 w.
3
8.32 (m, 16H); 7.54-7.57 (m, 24H); 6.33 (d, 2H, J ≈ 8.0 Hz);
4.22 (d, 2H, 3J ≈ 8.0 Hz). 13C NMR (CDCl3) (δ, ppm): 157.5 (s);
142.4 (s); 134.5 (s); 133.4 (s); 133.0 (s); 128.4 (s); 128.2 (s). Anal.
Calcd for C71H44N8F3In, M ) 1181.0 g/mol: C, 72.21; H, 3.76; N,
9.49. Found: C, 71.89; H, 3.69; N, 9.43.
(p-(Trifluoromethyl)phenyl)[octakis(p-tert-butylphenyl)tet-
raazaporphyrinato]indium(III) (6b). Compound 6a (160 mg,
0.105 mmol) in 15 mL of THF was used for the reaction similar to
the preparation of 5b. After the addition of (p-TMP)MgBr the
reaction mixture was stirred for 1 h and treated further as described
for 5b. Yield: 125 mg (0.077 mmol, 73%) of a dark violet powder.
UV-vis (CH2Cl2) [λmax, nm/log(ꢀ)]: 402/4.98; 504/4.31; 600/4.41;
653/5.10. FT-IR (KBr) (ν, cm-1): 2964 vs; 2905 m; 2868 m; 1610
m; 1493 m; 1462 s; 1423 w; 1389 m; 1367 s; 1325 s; 1298 w;
1269 m; 1196 m; 1165 m; 1144 m; 1130 m; 1109 s; 1047 m; 1016
m; 988 vs; 881 m; 847 m; 839 s; 820 m; 806 m; 746 m; 679 w. 1H
NMR (CDCl3) (δ, ppm): 8.33 (d, 16H, 3J ≈ 8.4 Hz); 7.60 (d, 16H,
3J ≈ 8.4 Hz); 6.28 (d, 2H, 3J ≈ 7.5 Hz); 4.15 (d, 2H, 3J ≈ 7.5 Hz);
1.51 (s, 72H). 13C NMR (CDCl3) (δ, ppm): 157.5 (s); 151.0 (s);
3
1H NMR (CDCl3) (δ, ppm): 8.38 (d, 8H, J ≈ 7.7 Hz); 8.27 (s,
3
3
8H); 7.86 (d, 8H, J ≈ 8.1 Hz); 7.71 (t, 8H, J ≈ 7.7 Hz); -1.76
(s, 2H). 13C NMR (CDCl3) (δ, ppm): 153.6 (s); 141.4 (s); 135.6
2
3
(s); 133.0 (s); 131.2 (q, J ≈ 32.5 Hz); 129.3 (q, J ≈ 4.1 Hz);
3
1
129.2 (s); 125.6 (q, J ≈ 3.7 Hz); 123.4 (q, J ≈ 272.5). Mass
(FD): m/z ) 1467.1 (M+). Anal. Calcd for C72H34N8F24, M )
1467.1 g/mol: C, 58.95; H, 2.34; N, 7.64. Found: C, 58.88; H,
2.21; N, 7.73.
Octakis(p-(trifluoromethyl)phenyl)tetraazaporphyrin (7) was
prepared identically to 8. Yield: 53% of dark-green insoluble
powder. UV-vis [solid state, poly(chlorotrifluoroethylene)] [λmax
,
nm]: 376; 464; 610; 680. FT-IR (KBr) (ν, cm-1): 3296 vw; 1618
w; 1491 vw; 1412 vw; 1328 vs; 1169 s; 1132 s; 1114 m; 1070 s;
1034 w; 1019 m; 968 m; 849 m; 839 m; 778 w; 764 w; 725 vw;
677 w; 616 w; 431 w. Anal. Calcd for C72H34N8F24, M ) 1467.1
g/mol: C, 58.95; H, 2.34; N, 7.64. Found: C, 58.80; H, 2.05; N,
7.62.
3
142.2 (s); 134.6 (s); 132.7 (s); 130.7 (s); 125.3 (s); 122.6 (q, J ≈
3.7 Hz); 34.9 (s); 31.6 (s). Mass (FD): m/z ) 1629.6 (M+). Anal.
Calcd for C103H108N8F3In, M ) 1629.9 g/mol: C, 75.90; H, 6.68;
N, 6.87. Found: C, 76.22; H, 6.86; N, 6.89.
(p-(Trifluoromethyl)phenyl)[octakis(p-(trifluoromethyl)-
phenyl)tetraazaporphyrinato]indium(III) (7b). A freshly prepared
solution of (p-TMP)MgBr in THF was added dropwise to a solution
of 7a (100 mg, 0.062 mmol) in 10 mL of THF and stirred for 1 h
at room temperature. The reaction mixture was poured into 100
mL of ice-methanol mixture (1:1) and centrifuged. The precipitate
(Octakis(m-(trifluoromethyl)phenyl)tetraazaporphyrinato)-
indium(III) chloride (8a). InCl3 (0.2 g, 0.9 mmol) and 8 (0.2 g,
0.136 mmol) were refluxed in DMF (15 mL) for 2 h. After the
reaction mixture was cooled to room temperature, water (10 mL)
2686 Inorganic Chemistry, Vol. 42, No. 8, 2003

(Octaaryltetraazaporphyrinato)indium(III) Complexes
Scheme 1. Preparation of 5a-c, 6a,b, and 7a,b
was washed with aqueous methanol, dried, and chromatographed
(silica gel/CH2Cl2, the first fraction). Yield: 53 mg (0.031 mmol,
50%) of dark green powder. UV-vis (CH2Cl2) [λmax, nm/log(ꢀ)]:
393/4.96; 587/4.34; 639/5.12. FT-IR (KBr) (ν, cm-1): 1618 m;
1474 vw; 1410 vw; 1327 vs; 1169 s; 1128 s; 1069 s; 1018 m; 986
s; 881 w; 845 m; 820 vw; 777 vw; 729 vw; 683 w; 623 w; 602
Yield: 85 mg (0.074 mmol, 48%). UV-vis (CH2Cl2) [λmax,
nm/log(ꢀ)]: 392/5.00; 481/4.19; 591/4.38; 643/5.13. FT-IR (KBr)
(ν, cm-1): 3055 w; 1597 w; 1583 m; 1458 m; 1408 m; 1369 m;
1300 w; 1271 w; 1202 w; 1184 w; 1140 m; 1119 w; 1028 vw;
1003 m; 984 vs; 914 w; 876 m; 849 w; 822 m; 787 vw; 773 m;
744 m; 692 s; 604 m. 1H NMR (CDCl3) (δ, ppm): 8.28-8.32 (m,
16H); 7.54-7.57 (m, 24H); 5.71-5.80 (m, 1H); 3.59-3.63 (m,
2H). Anal. Calcd for C70H43N8F2In, M ) 1149.0 g/mol: C, 73.18;
H, 3.77; N, 9.75. Found: C, 73.30; H, 3.55; N, 9.59.
1
3
vw; 430 w. H NMR (CDCl3) (δ, ppm): 8.29 (d, 16H, J ≈ 8.2
3
3
Hz); 7.83 (d, 16H, J ≈ 8.4 Hz); 6.39 (d, 2H, J ≈ 7.5 Hz); 4.24
(d, 2H, J ≈ 7.7 Hz). 13C NMR (THF-d8) (δ, ppm): 158.6 (s);
3
2
143.1 (s); 137.5 (s); 135.3 (s); 134.3 (s); 131.4 (q, J ≈ 32.8 Hz);
1
3
Results and Discussion
126.3 (q, nonresolved); 125.5 (q, J ≈ 271.9 Hz); 123.6 (q, J ≈
3.7 Hz). Mass (FD): m/z ) 1723.9 (M+). Anal. Calcd for
C79H36N8F27In, M ) 1725.0 g/mol: C, 55.01; H, 2.10; N, 6.50.
Found: C, 55.23; H, 2.12; N, 6.37.
Synthesis. The cyclotetramerization of diaryl derivatives
of fumaronitrile in the presence of metal salts is a good
method for the preparation of (octaaryltetraazaporphyrinato)-
metal complexes. In particular, (octaphenyltetraazaporphy-
rinato)indium(III) chloride (5a) is formed in 37% yield by
refluxing diphenylfumaronitrile with anhydrous InCl3 in
freshly distilled 1-chloronaphthalene.11
The similar route (see Scheme 1) was chosen here for the
preparation of (octaphenyl-, (octakis(p-tert-butylphenyl)- and
(octakis(p-(trifluoromethyl)phenyl)tetraazaporphyrinato)-
indium(III) chlorides (5a, 6a, and 7a, respectively). [(Ph)8TAP]-
In(Cl) (5a) was synthesized by heating diphenylfumaronitrile
(1) with a slight excess of InCl3 in freshly distilled quinoline
in the presence of catalytic amounts of DBU. The poor
solubility of the product in common organic solvents, caused
by a strong aggregation of the macrocyclic molecules, sug-
gested a continuous extraction of impurities in a Soxhlet
apparatus.
The more soluble [(p-t-BuPh)8TAP]In(Cl) (6a), containing
eight tert-butyl groups in the periphery of the macrocycle,
was prepared by heating bis(tert-butylphenyl)fumaronitrile
(2) and InCl3 in 1-chloronaphthalene in the presence of DBU.
The product precipitated from the reaction mixture after
cooling as a crystalline powder and was purified by extraction
of impurities with methanol, followed by recrystallization
from CH2Cl2/CH3OH solution, in 40% overall yield.
To prepare [(p-CF3Ph)8TAP]In(Cl) (7a), quinoline was
found to be a convenient solvent. However, the yield of the
product appeared to be lower, compared to 5a or 6a, and
the purification of 7a requires column chromatography.
To use the similar route for the preparation of [(m-
CF3Ph)8TAP]In(Cl) (8a) is more complicated due to the high
(p-(Trifluoromethyl)phenyl)[octakis(m-(trifluoromethyl)-
phenyl)tetraazaporphyrinato]indium(III) (8b). A freshly prepared
solution of (p-TMP)MgBr in THF was added dropwise to a solution
of 8a (100 mg, 0.062 mmol) in 10 mL of THF and stirred for 1 h
at room temperature. The reaction mixture was poured into 100
mL of ice-methanol mixture (1:1) and centrifuged. The precipitate
was thoroughly washed with aqueous methanol to remove the violet
byproduct, dried, and chromatographed (silica gel/CH2Cl2, the first
fraction). Yield: 60 mg (0.035 mmol, 56%) of dark green powder.
UV-vis (CH2Cl2) [λmax, nm/log(ꢀ)]: 394/5.03; 585/4.38; 637/5.17.
FT-IR (KBr) (ν, cm-1): 1599 vw; 1466 vw; 1447 w; 1391 vw;
1371 w; 1331 vs; 1312 s; 1279 m; 1198 m; 1167 s; 1126 s; 1097
m; 1076 m; 1049 w; 1015 w; 1007 m; 914 m; 806 m; 764 w; 716
1
m; 698 m; 687 w; 654 w; 596 vw; 532 vw. H NMR (CDCl3) (δ,
3
3
ppm): 8.35 (d, 8H, J ≈ 7.7 Hz); 8.27 (s, 8H); 7.85 (d, 8H, J ≈
7.7 Hz); 7.69 (t, 8H, 3J ≈ 7.7 Hz); 6.42 (d, 2H, 3J ≈ 7.7 Hz); 4.25
(d, 2H, 3J ≈ 7.7 Hz). 13C NMR (CDCl3) (δ, ppm): 157.3 (s); 142.6
2
(s); 135.6 (s); 134.4 (s); 133.0 (s); 131.2 (q, J ≈ 32.8 Hz); 129.4
(q, 3J ≈ 3.7 Hz); 129.2 (s); 127.6 (s); 125.6 (q, 3J ≈ 3.7 Hz); 123.9
1
3
(q, J ≈ 272.4 Hz); 123.2 (q, J ≈ 3.7 Hz). Mass (FD): m/z )
1725.3 (M+). Anal. Calcd for C79H36N8F27In, M ) 1725.0 g/mol:
C, 55.01; H, 2.10; N, 6.50. Found: C, 54.73; H, 2.06; N, 6.32.
(3,5-Difluorophenyl)(octaphenyltetraazaporphyrinato)indium-
(III) (5c). Mg (50 mg, 2.1 mmol) and 3,5-difluorophenyl bromide
(0.23 mL, 2.0 mmol) in 3 mL of THF was stirred at room
temperature until most of the magnesium turnings were dissolved.
The obtained solution of (3,5-difluorophenyl)magnesium bromide
was added dropwise using a syringe to a suspension of 5a (165
mg, 0.154 mmol) in 30 mL of dry THF. The reaction mixture was
stirred at room temperature for 18 h, poured into 50 mL of ice
water, and centrifuged. The precipitate was washed with methanol,
dried, and chromatographed (silica gel/CH2Cl2, the first fraction).
Inorganic Chemistry, Vol. 42, No. 8, 2003 2687

Vagin et al.
Scheme 2. Preparation of [(p-CF3Ph)8TAP]H2 (7), [(m-CF3Ph)8TAP]H2 (8). and [(m-CF3Ph)8TAP]In(Cl) (8a)
solubility of this compound in organic solvents. Furthermore,
the usage of high-boiling solvents, such as quinoline or,
especially, 1-chloronaphthalene, for the reaction of bis(m-
(trifluoromethyl)phenyl)fumaronitrile (3) with InCl3 leads to
the formation of different byproducts, namely adducts with
a molecular mass higher than the desired indium chloride
complex, as well as the products of decomposition of the
solvents. The preparation of 8a was carried out according
to the route presented in Scheme 2. The reaction of dinitrile
3 with ammonia in methanol in the presence of sodium
methoxide gave most likely the diimino derivative, which
easily underwent cyclotetramerization upon refluxing in
1-pentanol. The octakis(m-(trifluoromethyl)phenyl)tetraaza-
porphyrin (8), formed in this reaction, was reacted with InCl3
in DMF to yield 8a. However, this approach was not suitable
for the preparation of 7a since the corresponding octakis-
(p-(trifluoromethyl)phenyl)tetraazaporphyrin (7) cannot be
dissolved even in boiling DMF. For this reason compound
7 was not characterized by NMR and MS, but EA, solid-
state UV-vis, and FT-IR were obtained to prove its
formation. The heterogeneous reaction of 7 with InCl3 in
refluxing DMF led only to a decomposition of 7, and no
formation of 7a was observed.
Substitution of the axial chlorine in 5a-8a by aryl groups
to form complexes with In-C bonds was carried out
according to the procedure which we have published for
indium phthalo- and naphthalocyanines:16 reaction of the
appropriate Grignard reagents with the corresponding in-
dium chloride complexes in THF. The yields obtained are
close to 50% and are similar to those found for the In-
phthalocyanines.16 Substitution of chlorine by the p-(trifluo-
romethyl)phenyl group (p-TMP) leads to a higher solubility
of [(Ph)8TAP]In(p-TMP) (5b) (≈3 × 10-3 M or 3.5 mg/
mL, saturated solution in CH2Cl2) compared to 5a (<10-3
M, CH2Cl2). Compounds 6a and 6b are highly soluble in
solvents with medium polarity such as chloroform and
dichloromethane (>8 × 10-2 M or 120 mg/mL, CH2Cl2),
as expected from their structure. The introduction of the
trifluoromethyl group into a meta-position of the peripheral
phenyl substituents leads to a remarkably high solubility of
8 (≈200 mg/mL, CH2Cl2) and 8a,b in most organic solvents
including methanol due to the steric hindrance of the m-CF3-
Ph groups, which are not coplanar with the tetraazaporphyrin
macrocycle, preventing aggregation of the molecules. In
contrast, a trifluoromethyl group in the para-position of
phenyl substituents leads to good solubility only in THF;
the solubility of 7a in dichloromethane is ca. 1.2 × 10-3
M
(2 mg/mL). The values of solubility were estimated only at
room temperature and are approximate, especially for highly
soluble compounds.
Characterization. Mass spectra were obtained for all
soluble complexes using field desorption technique. Only
M+ peaks were detected for all investigated compounds; no
fragmentation signals were observed. For 7a an additional
FAB-mass spectrum was recorded and an intense peak of
fragment M+ - Cl was detected. No peak of M+ was found
in this spectrum, indicating the splitting of the axial ligand
under the conditions of FAB technique. Moreover, in the
FAB-mass spectrum of 5b, no M+ peak nor its heavy
fragments peaks were found due to complete decomposition
under these conditions. The poor solubility of 5a-c did not
allow us to record their FD-mass spectra.
The UV-Vis data obtained for 5a-8a, 5b-8b, and 5c are
given in the Experimental Section. The spectra of all
compounds (see Figure 2) show two intense bands at 636-
653 (Q-band) and 379-402 (B-band) nm caused by π f
π* transitions typical for diamagnetic (tetraazaporphyrinato)-
metal complexes. The Q-band, observed in the visible region,
is due to the a1u f eg* transition, and the B-band in the
near-ultraviolet region is caused by an a2u f eg* transition.17
The bands of lower intensity, found in the spectral window
(16) (a) Hanack, M.; Heckmann, H. Eur. J. Inorg. Chem. 1998, 367. (b)
Schneider, T.; Heckmann, H.; Barthel, M.; Hanack, M. Eur. J. Org.
Chem. 2001, 3055.
2688 Inorganic Chemistry, Vol. 42, No. 8, 2003

(Octaaryltetraazaporphyrinato)indium(III) Complexes
Figure 2. UV-vis spectra of compounds 5a, 6a, and 7a,b in dichlo-
romethane.
between the Q- and B-bands, are vibronic satellites on the
blue side of the Q-band and charge transfer (CT) bands which
usually occur on the red side of the B-band in metal
octaphenyltetraazaporphyrins. Unlike the complexes of Fe,
Ru, or other metals with an open d-configuration,18a the CT
band in the gap between Q- and B-bands observed for the
complexes of (Ar)8TAP’s with metals with closed d0 or d10
configuration, e.g. In(III) or Mg(II), cannot be associated
with the transitions involving metal d-orbitals and is probably
an n f π* charge transfer localized on the macrocycle.
The log(ꢀ) values of the Q-bands of 5a-8a, 5b-8b, and
5c are in the range of 5.07-5.17 depending on the nature of
the peripheral substituents and axial ligands; they are slightly
higher than those found for axially coordinated (octaphen-
Figure 3. FT-IR spectra of compounds 5a,b, 6a, 7a, and 8a in KBr.
changing the electron-withdrawing to -donating substituents
in the order 7a ≈ 8a < 5a < 6a.
Substitution of axial chlorine by aryl results in a strong
bathochromic shift of the B-band (19 nm for 6b and 14 nm
for 7b) but has no noticeable influence on the position of
the Q-band. This fact indicates that the a2u orbital, which
has a significant electron density on coordinating N-atoms
of the macrocycle, is very sensitive to the nature of the axial
ligand and is destabilized by axial aryls because of their
electron-donating effect on indium. In contrast, the a1u orbital
has nodes on the internal N-atoms and may be considered
as not influenced by axial ligands. This approach was also
successfully used for describing qualitatively the spectra of
bis-axially coordinated complexes of (octaphenyltetraaza-
porphyrinato)ruthenium(II).18 Similar dependence of spectral
pattern on axial substitution was observed for indium phthalo-
and naphthalocyanines.8a,16
18b
19
yltetraazaporphyrinato)ruthenium(II)
complexes.
and -iron(II)
Introduction of electron-donating t-Bu groups at the para-
position of the peripheral phenyl rings leads to a red shift of
the Q- and B-bands (11 and 4 nm, respectively) in 6a and
to a slight decrease of their intensity. That is likely due to a
destabilization of occupied a1u and a2u orbitals, as compared
with nonsubstituted (octaphenyltetraazaporphyrinato)indium
chloride. The presence of electron-withdrawing CF3 groups
in meta- or para-positions in 7a and 8a results in an opposite
effect, however, less pronounced (see Figure 2). A red shift
and increasing intensity were observed for the CT band when
The IR spectra are rather specific for each of the prepared
(octaaryltetraazaporphyrinato)indium chlorides 5a-8a; the
substitution of axial chlorine by the p-TMP group results in
additional bands (see Figure 3). The most intense bands in
the spectra of 5a-c are observed in a region of 500-1600
cm-1 and are caused by combined vibrations of peripheral
phenyl rings and the macrocyclic skeleton. They are similar
(17) (a) Gouterman, M. J. Mol. Spectrosc. 1961, 6, 138. (b) Gouterman,
M.; Wagniere, G.; Snyder, L. C. J. Mol. Spectrosc. 1963, 11, 108.
(18) (a) Stuzhin, P. A.; Homborg, H. Russ. J. Coord. Chem. 1997, 23, 623.
(b) Stuzhin, P. A.; Vagin, S. I.; Hanack, M. Inorg. Chem. 1998, 37,
2655.
(19) Vagin, S. I.; Stuzhin. P. A.; Hanack, M. Russ. J. Gen. Chem. 1999,
69, 308.
Inorganic Chemistry, Vol. 42, No. 8, 2003 2689

Vagin et al.
to those observed for (octaphenyltetraazaporphyrinato)-
indium(III) complexes with other axial ligands such as F,
SCN, and OCN11 and for complexes of octaphenyltetraaza-
porphyrin with other metals.20 The stretching vibration of
the macrocycle skeleton, in which the inner N-atoms are
involved, appeared to be the most sensitive to the nature of
central metal and was observed at 1456 cm-1 for 5a in
contrast to 1495 and 1472 cm-1 for bis(tert-butyl isocyanide)-
(octaphenyltetraazaporphyrinato)iron(II) and -ruthenium(II)
complexes, respectively.20 Another intense vibration, sensi-
tive to the metal nature, is found at 1140 cm-1, which is
probably a deformation vibration of the macrocycle skeleton.
The IR spectra of 6a,b and 7a,b in the range of 600-900
cm-1 are different compared to 5a-c due to the para-
substitution in the peripheral phenyl rings. It results also in
an increasing intensity of CdC valence vibration of phenyl
rings at 1610 cm-1 for 6a,b and 1618 cm-1 for 7 and 7a,b.
In addition, the spectra of 6a,b show intense bands at 2964,
2905, and 2868 cm-1 due to the stretching vibrations of the
tert-butyl groups. The very intense asymmetrical and sym-
metrical stretching vibrations of CF3 groups in peripheral
aromatic rings, along with the mixed νC-F and deformation
aryl ring modes, are dominating in the spectra of 7, 7a,b
and 8, 8a,b. They were observed at approximately 1330,
1170, 1130, and 1070 cm-1; their positions slightly depend
on the location of CF3 groups in the aryl substituents.
Figure 4. Designation of protons and carbon atoms used in Tables 1
and 2.
signals was observed. The spin coupling constant are
approximately 271 Hz (1J), 33 Hz (2J), and 3.7 Hz (3J).
The assignment of 13C resonances, made for compounds
5-7, is obvious and was carried out according to the nuclear
Overhauser effect as well as splitting of signals (for 7a,b
due to the presence of fluorine atoms). However, in the case
of 8a,b the correct assignment of atoms C-4, C-4′, C-5′, and
C-6 required the additional exploration of one of the samples
by the HC-Cosy technique. The two-dimensional spectra,
recorded for 8b, is presented in Figure 5. It clearly indicates
that the signals of C-4, C-4′, C-5′, and C-6 atoms appear at
129.4, 135.6, 129.2, and 125.6 ppm, respectively.
The positions of C-1 and C-2 signals of the macrocycle
and C-R and C-â signals of the coordinated p-TMP group
are almost independent of the nature of substituents in the
peripheral aryls, showing no strong electron redistribution.
However, the positions of the peripheral aryl 13C resonances
are rather effected by substituents, as should be expected.
Substitution of axial chlorine by p-TMP results in a slight
deshielding of C-1 and shielding of C-2 atoms, which was
also observed for analogous complexes of phthalocyanines.21
EA data for the prepared compounds are in general in
satisfactory agreement with the calculated values. However,
the low conformity of data with the theoretical values for
several porphyrazine samples, e.g. 8a, can result from the
influence of the heavy metal and/or fluorine present in these
compounds. Similar difficulties in combustion analysis were
also observed in case of phthalo- and naphthalocyanines.16
The preliminary investigation of light stability of some of
the prepared compounds was carried out in chloroform
solution in a quartz cuvette, directly exposed to sunlight.
Under these conditions, compound 5b moderately decom-
poses to form 5a, followed by decomposition of the
macrocycle. Under the same conditions, no decomposition
was observed for compound 8a, which indicates the stabiliz-
ing effect of electron-withdrawing substituents.
The characteristic vibrations of axial p-TMP group were
observed at 1325 (strong band), 1165, 1129, and 1048
(medium bands) cm-1, and their frequencies are practically
independent of the nature of the macrocycle. Similar vibra-
tions at 1163, 1127, and 1047 were observed for (t-Bu)4PcIn-
(p-TMP).16 However, the vibration band of coordinated
p-TMP at 1325 cm-1 was not revealed in this case because
it was masked by the strong band of the phthalocyanine
marocycle at 1330 cm-1.
Due to the strong π-electron ring current of the macro-
1
cycle, the protons of axial p-TMP group in the H NMR
spectra of 5b-8b are shielded and their resonances are
significantly shifted to high field comparing to (trifluoro-
methyl)phenyl bromide. In contrast, the signals of peripheral
aryl protons appear at lower field than in the corresponding
dinitriles 1-4, in the range of 7.5-8.4 ppm. Especially strong
shifts, caused by the ring current effect, are observed for
ortho-protons (both of axial ligand and peripheral aryls),
which are the closest to the macrocycle center (see Figure 4
and Table 1). The small low-field shift of proton resonances
of axial ligand, observed for 7b or 8b compared to 6b, is
the result of decreased shielding by π-electron ring current
of the macrocycle due to the electron-withdrawing influence
of peripheral substituents.
The 13C NMR data of 5b, 6a,b, 7a,b, and 8a,b are given
in Table 2. Although all carbon atoms of the macrocycles
were observed, the intensity of signals of p-TMP carbons is
very low and only dCH- groups could be found (atoms
C-R and C-â).
Due to the presence of fluorine atoms in most of the
studied compounds, quadruplet splitting of some of 13C
(20) Vagin, S. I. Diss. Kand. Khim. Nauk, Ivanovo, Russia, 2000.
(21) Heckmann, H. Ph.D. Diss. Thesis, Tu¨bingen, Germany, 1999.
2690 Inorganic Chemistry, Vol. 42, No. 8, 2003

(Octaaryltetraazaporphyrinato)indium(III) Complexes
Table 1. Assignment of Proton Resonances (See Figure 4) of (Octaaryltetraazaporphyrinato) indium Complexes in CDCl3 (250 MHz)
posn and multiplicitya of proton signals, ppm
macrocycle
H-2
ax ligand
H-â
compd
H-1
H-1′
H-2′
H-3
H-4
H-R
H-γ
5b
5c
6a
6b
7a
7b
8a
8b
8.30, m
8.30, m
8.32, d
8.33, d
8.30, d
8.29, d
8.35, d
8.35, d
8.30, m
8.30, m
8.32, d
8.33, d
8.30, d
8.29, d
8.27, s
8.27, s
7.56, m
7.56, m
7.61, d
7.60, d
7.85, d
7.83, d
7.72, t
7.69, t
7.56, m
7.56, m
7.61, d
7.60, d
7.85, d
7.83, d
7.56, m
7.56, m
4.22, d
3.61, m
6.33, d
5.76, m
1.51, s
1.51, s
4.15, d
4.24, d
4.25, d
6.28, d
6.39, d
6.42, d
7.87, d
7.85, d
a The spin coupling constants are given in the Experimental Section. Key: s, singlet; d, doublet; t, triplet; m, multiplet.
Table 2. Assignment of 13C Resonances (See Figure 4) of (Octaaryltetraazaporphyrinato) indium Complexes in CDCl3 or THF-d8 (62.9 MHz)
posn and multiplicitya of 13C signals, ppm
macrocycle
ax ligand
compd
C-1
C-2
C-3
C-4
C-4′
C-5
C-5′
C-6
C-7
C-8
C-R
C-â
5b
6a
6b
7ab
7bb
8a
157.5, s
156.8, s
157.5, s
158.1, s
158.6, s
156.6, s
157.3, s
142.4, s
142.6, s
142.2, s
143.4, s
143.1, s
143.0, s
142.6, s
133.4, s
130.5, s
130.7, s
137.3, s
137.5, s
132.6, s
133.0, s
133.0, s
132.7, s
132.7, s
134.3, s
134.3, s
129.4, q
129.4, q
133.0, s
132.7, s
132.7, s
134.3, s
134.3, s
135.5, s
135.6, s
128.4, s
125.3, s
125.3, s
126.4, nr
126.3, nr
131.3, q
131.2, q
128.4, s
125.3, s
125.3, s
126.4, nr
126.3, nr
129.3, s
129.2, s
128.2, s
151.3, s
151.0, s
131.6, q
131.4, q
125.9, q
125.6, q
134.5, s
122.7, nr
34.9, s
34.9, s
125.5, q
125.5, q
123.9, q
123.9, q
31.6, s
31.6, s
134.6, s
135.3, s
134.4, s
122.6, q
123.6, q
123.2, q
8b
a The spin coupling constants are given in the Experimental Section. Key: s, singlet; q, quadruplet; nr, nonresolved multiplicity. b In THF-d8.
Previous studies on the nonlinear optical properties of
porphyrins have been carried out mostly on meso-substitut-
ed23 porphyrins whereas â-substituted systems have received
attention only recently.24 The reason for that has to be found
in the early discovery of the reverse saturable absorption
shown by solutions of meso-substituted porphyrins in high
boiling point solvents, e.g. toluene, under pulsed irradiation
with a Nd:YAG laser at 532 nm,23d which has stimulated
further research on the nonlinear optical properties of these
compounds. To our knowledge, studies on the nonlinear
optical properties of tetraazaporphyrins and their derivatives
with the structures analogous to those presented here have
not been reported in the literature so far.
The synthesized [(Ar)8TAP]In(X)’s have shown nonlinear
optical behavior for the change of their transmittance in so-
lution at different levels of irradiation.25 [(Ar)8TAP]In(X)’s
solutions behave like reverse saturable absorbers (RSA)22,26
which become more opaque with the augmentation of the
irradiation.23d The effect of reverse saturable absorption
Figure 5. HC-Cosy spectra of 8b in CDCl3.
(22) Hercher, M. Appl. Opt. 1967, 6, 947.
(23) (a) Venugopal Rao, S.; Naga Srinivas, N. K. M.; Narayana Rao, D.;
Giribabu, L.; Maiya, B. G.; Philip, R.; Kumar, G. R. Opt. Commun.
2000, 182, 255. (b) Venugopal Rao, S.; Naga Srinivas, N. K. M.;
Narayana Rao, D.; Giribabu, L.; Maiya, B. G.; Philip, R.; Kumar, G.
R. Opt. Commun. 2001, 192, 123. (c) Ono, N.; Ito, S.; Wu, C. H.;
Chen, C. H.; Wen, T. C. Chem. Phys. 2000, 262, 467. (d) Blau, W.;
Byrne, H.; Dennis, W. M.; Kelly, J. M. Opt. Commun. 1985, 56, 25.
(e) Chen, P.; Tomov, I. V.; Dvornikov, A. S.; Nakashima, M.; Roach,
J. F.; Alabran, D. M.; Rentzepis, P. M. J. Phys. Chem. 1996, 100,
17507.
(24) (a) O’Keefe, G. E.; Denton, G. J.; Harvey, E. J.; Philips, R. T.; Friend,
R. H.; Anderson, H. L. J. Chem. Phys. 1996, 104, 805. (b) Correa, D.
S.; De Boni, L.; Dos Santos, D. S.; Neto, N. M. B.; Oliveira, O. N.;
Misoguti, L.; Zilio, S. C.; Mendonca, C. R. Appl. Phys. B 2002, 74,
559.
Optical Limiting Measurements. Conjugated macro-
cycles such as phthalocyanines and porphyrins usually give
rise to the optical limiting effect by means of a mechanism
based mostly upon the reverse saturable absorption (ex-
cited-state absorption ESA).22 This could be verified in
phthalocyanines by determining the absorption spectrum of
optically pumped phthalocyanines2c which have an excited-
state absorption cross section much higher than the ground-
state absorption cross section at the wavelength of irradiation.2b
In these systems such an effect has been described by
considering the absorbing macrocycle as a four-level system
whose excited state gives rise to reverse saturable absorp-
tion.2b,c,22
(25) Sauter, E. G. Nonlinear Optics; Wiley: New York, 1996.
(26) (a) Gires, F. IEEE Trans. 1966, QE-2, 624. (b) Guiliano, C. R.; Hess,
L. D. IEEE J. Quantum Electron. 1967, 3, 358.
Inorganic Chemistry, Vol. 42, No. 8, 2003 2691

Vagin et al.
Figure 7. Electronic energy level diagram for a five-level system. The
electronic states associated with energy levels i ) 0, 1, and 2 are singlet
states. The electronic states associated with energy levels i ) 3 and 4 are
triplet states.The symbol σi represents the absorption cross section for the
electronic transition between the ith level (lower energy) and the i + 1th
level (upper energy). ISC represents the process of intersystem crossing
from singlet to triplet states. For sake of clarity the various relaxation
processes of fluorescence and phosphorescence are omitted.
the diminution of transmittance is gradual and NLO behavior
is observed already at fluence (F) values lower than 2 J cm-2
(this corresponds to |Z| > 170 × 10-4 m in the Z-scan
profile). The presence of two regimes of nonlinearity in the
profiles of Figures 6 can be observed. The change of
transmittance slope in the Z-scan profiles occurs approxi-
mately at Z ≈ (50 × 10-4 m (F ≈ 10 J cm-2) and Z ≈
(25 × 10-4 m (F ≈ 15 J cm-2) respectively for 8a,b (Fig-
ure 6). This is probably due to the onset of an additional
fluence-activated mechanism of absorption when high ir-
radiation occurs.22 The minimum transmittance of 8a,b in
correspondence of the focus (Z ) 0) is 65-70% of their
linear value. If a mechanism of excited-state absorption
(ESA)2,22,23d,27b,28 takes place in the occurrence of RSA
behavior for (trifluoromethyl)phenyl-substituted TAP’s, then
the observation of two possible regimes of nonlinearity could
be associated with the involvement of various excited states
with different absorption cross sections, whose absorption
occurs at different levels of dye solution irradiation.28b,29 For
a RSA based on an ESA mechanism involving a five-level
system (Figure 7) the relationship between light-intensity
variation through the optical medium and the optical medium
properties is28b
Figure 6. Z-scan profiles of 8a (a) and 8b (b).
consists of the reversible decrease of the system transmittance
with the increase of the incident light intensity.22 The
solutions of dyes showing such a phenomenon are generally
described as systems whose photogenerated excited states
are strongly light-absorbing.4d,27 Despite the nonlinearity of
the resulting optical effect, the fundamental processes at the
basis of the reverse saturable absorption are essentially two
consecutive linear absorptions.4d,22 Nonlinear transmission
of [(Ar)8TAP]In(X) solutions is in the range 60-80% of the
linear transmission value. The extent of the transmission
decrease depends on the chemical nature of the absorbing
[(Ar)8TAP]In(X). The lowest nonlinear transmission is
presented by the groups of species 7 and 8 which are
characterized by the presence of CF3 group in the para- or
meta-position of the phenyl substituent. In these cases the
minimum transmittance ranges in the interval 65-70% of
the linear value. The typical Z-scan profiles for the octakis-
((trifluoromethyl)phenyl)-substituted TAP’s are presented in
Figure 6. In particular, the open-aperture Z-scan patterns for
8a,b are shown.
-(dIin/dz) ) σ0(NT - N1 - N3)Iin + σ1N1Iin + σ3N3Iin
(2)
in which NT represents the total number of dye molecules/
volume unit, Ni defines the population of the ith level (see
Figure 7) expressed with the same units of NT, and σi is the
absorption cross section of the optical transition originated
from the ith level. Equation 2 is valid under the assumption
that N2 and N4 are approximately zero; i.e., the populations
of the excited states at the upper energy levels are negligible
(Figure 7).28b Equation 2 shows that the variation of light
intensity through a solution of a dye described as a five-
level system is a function of four variable parameters, i.e.,
N1, N3,σ1, and σ3, σ0 being known from the absorption
The linear transmission of 8a,b is 75% at 532 nm under
the experimental conditions of OL data acquisition. The
absorption cross sections σ0 for 8a,b in the ground state are
respectively 1.99 and 1.78 × 10-17 cm2. In these materials
(27) (a) Shirk, J. S.; Pong, R. G. S.; Bartoli, F. J.; Snow, A. W. Appl.
Phys. Lett. 1993, 63, 1880. (b) Xia, T.; Hagan, D. J.; Dogariu, A.;
Said, A. A.; Van Stryland, E. W. Appl. Opt. 1997, 36, 4110.
(28) (a) Miles, P. A. Appl. Opt. 1994, 33, 6965. (b) Tutt, L. W.; Boggess,
T. F. Prog. Quantum Electron. 1993, 17, 299.
(29) Sun, Y. P.; Riggs, J. E. Int. ReV. Phys. Chem. 1999, 18, 43.
2692 Inorganic Chemistry, Vol. 42, No. 8, 2003

(Octaaryltetraazaporphyrinato)indium(III) Complexes
characteristics of the dye in the linear regime and NT being
a fixed value in a sample. In the case of species 7 and 8 it
is believed that the two different regimes of nonlinearity
(Figure 6) are mostly due to different steady-state values of
N1 and N3 at the various levels of irradiation, σ1 and σ3 being
exclusively system-dependent and not intensity-dependent
parameters.28b,29 The sole recording of the Z-scan profile is
not sufficient for the univocal determination of all variable
parameters N1,N3,σ1, and σ3. If we assume that all the dye
molecules are present in the same absorbing state in cor-
respondence of the critical points of the Z-scan profiles (ap-
proximation of the saturation of the second-photon absorp-
tion from one type of excited state),28b in correspondence
with the focus and the slope change point, it is reasonable
to define an average absorption cross section σav in these
two points as
σav ) (N0σ0 + N1σ1 + N3σ3)/NT
(3)
In correspondence with the slope change in the Z-scan
profiles of Figure 6, it is expected that the main contribution
of the second-photon absorption arises from the singlet
excited state i ) 1 possessing probably the maximum value
of population N1 at that level of irradiation. In this case σavNT
is constituted mostly by the terms N0σ0 + N1σ1 and the
process of intersystem crossing (ISC) populating the level 3
(Figure 7) is supposed to be not very active at low levels of
irradiation. On the other hand, at the maximum levels of
irradiation the contribution in σavNT should be mostly due
to N0σ0 + N3σ3 because of the intervention of ISC which
populates the level 3 and decreases the population at i ) 1.
Figure 8. Z-scan profiles of 5b (a) and 5c (b).
In correspondence of the slope changes it is found σav
)
3.00 and 3.41 × 10-17 cm2 respectively for 8a,b when
|Z| ) 30 × 10-4 m (Figure 6a) and 25 × 10-4 m (Figure
6b), whereas the values of σav at the focus (Z ) 0) are
respectively 4.89 × 10-17 and 4.29 × 10-17 cm2 for 8a,b.
The present hypothesis of the intervention of different kinds
of excited states for the process of second photon absorption
involving the triplet excited state as most absorbing state in
the regime of maximum irradiation is partially substantiated
by the fact that triplet excited states have generally larger
absorption cross sections with respect to singlet excited states
in conjugated macromolcules.2b,c, 23e,30
Another type of Z-scan profile (Figure 8) is presented by
the series 5 of the described compounds (Figure 1).
Figure 9. Z-scan profile of 6b taken as an example of OL effect produced
by compounds of series 6.
The optical behavior of the compounds belonging to the
series 5 is characterized by constant transmission (70% at
532 nm in the linear regime) up to approximately Z ≈ (20
× 10-4 m, followed by an abrupt decrease of transmission
when the sample approaches the focus. At the focus (Z ) 0
cm) the incident intensity Iin is approximately 2 GW cm-2
and the system presents the minimum transmittance which
is not less than the 80% of the value presented in the linear
regime. This would correspond to an actual resulting
transmission of about 55% at the maximum level of
irradiation. The series 5 is photochemically stable when the
incident radiation intensity is not higher than 2 GW cm-2 at
532 nm. For the series 5 the ground-state absorption cross
sections σ0 at 532 nm ranges in the interval (1.0-1.5) ×
10-16 cm2, thus resulting relatively higher with respect to
compounds 7 and 8. The solutions of 5 showing the Z-scan
profiles of Figure 8 have a linear absorption coefficient R
equal to 1.55 cm-1. In correspondence to the focus, i.e., at
the maxium level of irradiation, the average absorption cross
sections σav are in the range (4.8-5.2) × 10-16 cm2 for the
species 5.
In Figure 9, the Z-scan profile of the sole species 6b is
presented as an example for the OL effect produced by the
group of compounds 6.
(30) Wei, T. H.; Hagan, D. J.; Sence, M. J.; Van Stryland, E. W.; Perry,
J. W.; Coulter, D. R. Appl. Phys. B 1992, 54, 46.
Inorganic Chemistry, Vol. 42, No. 8, 2003 2693

Vagin et al.
In the linear regime of transmission 6b has a value of σ0
equal to 2.48 × 10-18 cm2 whereas at the beam focus (Z )
0) with Iin ) 1.3 GW cm-2 σav reachs the value 3.20 × 10-18
cm2. At the beam focus the minimum transmittance of 6b
is approximately 90% of the linear transmittance value
()70%).
Conclusions
The synthesis of new octaaryl-substituted (tetraazapor-
phyrinato)indium(III) complexes with nonlinear optical prop-
erties is reported. (Octaaryltetraazaporphyrinato)indium(III)
chlorides with phenyl, p-tert-butylphenyl, p-(trifluoromethyl)-
phenyl, and m-(trifluoromethyl)phenyl as aryl substituents
have been prepared, and their structures have been character-
ized. Axial substitution at the central indium atom within
this series of compounds could be achieved via Grignard
reactions producing novel systems with p-(trifluoromethyl)-
phenyl and 3,5-difluorophenyl as new axial ligands. The
optical limiting effect of the synthesized aryl-substituted
(tetraazaporphyrinato)indium(III) complexes has been studied
with the Z-scan technique. It was found that the tetraaza-
porphyrins substituted with trifluoromethylphenyl groups
showed the better limiting performance and presented the
highest photochemical stability. Consequently, it was possible
to correlate the nonlinear optical behavior of these structurally
modulated compounds with the electronic nature of the
substituents at the periphery of the macroring and the axial
ligands.
From the compared analysis of the OL data presented in
Figures 6, 8, and 9, it is evident that [(Ar)8TAP]In(X)
complexes bearing the same type of substituents on the
peripheral phenyl rings have similar values of the minimum
transmittance at the maximum levels of irradation. This
would confirm unambiguously the determining role of the
nature of the peripheral substituents Ar in this class of
octaaryl-substituted (TAP)In(X) complexes. In terms of OL
performance, the group of compounds 7 and 8, i.e. those
possessing the electron-withdrawing group CF3 in Ar, present
the most convincing results in terms of low transmittance at
high levels of irradiation and a NLO behavior starting at
relatively low values of incident radiation fluence. The
absence of any group with strong electronic character in Ar
substituents (series 5) gives rise to an OL response character-
ized by a high threshold value for the occurrence of the
limiting effect and relatively small decreases of transmit-
tance. The OL effect presented by the series 6 of [(Ar)8TAP]-
In(X) whose structure contains an electron-releasing group
[-C(CH3)3] in the substituent Ar is characterized by the
lower variations of transmission with the increasing incident
intensity. Such a behavior would indicate the relatively scarce
polarizability of the conjugated π-electrons in these systems
under the action of the high-intensity radiation electric field.31
Acknowledgment. We express our gratitude to Dr. B.
Go¨rlach for recording the NMR spectra, Dr. L. Subramanian
for fruitful discussion, and Prof. W. Blau (Department of
Physics at Trinity College, Dublin, Ireland) for offering the
equipment for optical limiting experiments. Financial support
from the Deutsche Forschungsgemeinschaft (Phthalocyanine
und Naphthalocyanine des Indiums und Titans fu¨r Optical
Limiting-Experimente, Ha 280/65-1) and European Com-
munity (Contract HPRN-CT-2000-00020) is gratefully
acknowledged.
(31) (a) Orr, B. J.; Ward, J. F. Mol. Phys. 1971, 20, 513. (b) Truchado, D.;
Hierro, A.; Diaz-Garcia, M. A.; Agullo-Lopez, F. J. Mod. Opt. 1997,
44, 179.
IC0205738
2694 Inorganic Chemistry, Vol. 42, No. 8, 2003