Fig. 2 shows the Mössbauer spectrum of 4 taken for a
microcrystalline sample at 77 K. The IS and QS values are 0.42
and 3.05 mm s21, respectively. The large QS value indicates
that the complex is either in the pure S = 3/2 or in the admixed
S = 3/2, 5/2 spin state;12 the IS and QS values for the pure S =
3/2 complex [Fe(OETPP)(THF)2]ClO4 are 0.50 and 3.50 mm
s21, respectively, at 80 K.5 To further confirm the spin state of
4, the effective magnetic moments (meff) were measured in the
temperature range 2–300 K by SQUID magnetometry. As
shown in Fig. 3, the meff values are 3.8–3.9 mB in a wide range
of temperature, which are quite close to the spin-only value,
3.87 mB, expected for the S = 3/2 state. On the basis of the
spectroscopic and magnetic results, we have concluded that 4 is
an essentially pure intermediate spin complex.
macrocycle shift high spin complexes into the admixed
intermediate spin regime.2 In addition to the short Fe–Np bonds,
the S4 saddling of the core could further raise the energy levels
of the dp orbitals due to the strong iron (dp)–porphyrin (pp)
interactions caused by the effective overlap of these orbitals.18
2
Thus, the energy gap between the dz and dp orbitals decreases
as the porphyrin core deforms. Under this situation, if the
axially coordinated halide ligand changes from F2 and Cl2 to
2
2
2
Br , and then to I , the energy level of the dz orbital continues
to drop to form the pure S = 3/2 spin state in the iodide
complex. In conclusion, we have shown that even five-
coordinated (porphyrinato)iron(III) complexes carrying an io-
dide ligand can be in an essentially pure intermediate spin state
if the porphyrin cores are strongly S4 saddled.
Formation of the very pure intermediate spin complex 4
could be explained in terms of the short Fe–Np bond lengths
expected for the strongly S4 saddled OETPP core.4–9,13 The
This work was supported by the Grant in Aid for Scientific
Research on Priority Areas (A) (No 12020257 to M. N.) from
the Ministry of Education, Culture, Sports, Science and
Technology, Japan. T. I. is grateful to JSPS Research Fellow-
ship for young scientists. Thanks are due to the Research Center
for Molecular Materials, the Institute for Molecular Science
(IMS). The authors are grateful to Mr Masahiro Sakai of the
IMS for the assistance of EPR and SQUID measurements.
short Fe–Np bond length is the general condition for the iron(III
)
ions in porphyrins and porphyrin isomers to have an inter-
mediate spin state. In fact, we have reported that both
[Fe(TiPrP)(THF)2]+ and [Fe(TPrPc)(THF)2]+ have an essen-
tially pure S = 3/2 spin state;5,14 the former has short Fe–Np
bonds due to the strongly S4 ruffled porphyrin ring,15,16 and the
latter is supposed to have short Fe–Np bonds because of the
intrinsic nature of the porphycene core. Thus, even five-
coordinated Fe(etioPc)Cl is in the admixed S = 3/2, 5/2 spin
state as is revealed from the magnetic and structural measure-
ments.17 The results are consistent with the proposal given by
Reed and Guiset that the increased tetragonality of the
Notes and references
1 W. R. Scheidt, in The Porphyrin Handbook, ed. K. M. Kadishi, K. M.
Smith and R. Guilard, Academic Press, San Diego, 2000, vol. 3, pp.
49–112.
2 C. A. Reed and F. Guiset, J. Am. Chem. Soc., 1996, 118, 3281.
3 Abbreviations: OETPP, TPrPc, and etioPc; dianions of
2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin,
2,7,12,17-tetrapropylporphycene,
and
3,6,13,16,-tetraethyl-
2,7,12,17-tetramethylporphycene, respectively. 4-CNPy; 4-cyanopy-
ridine.
4 T. Ikeue, Y. Ohgo, T. Yamaguchi, M. Takahashi, M. Takeda and M.
Nakamura, Angew. Chem., Int. Ed., 2001, 40, 2617.
5 T. Ikeue, T. Saitoh, T. Yamaguchi, Y. Ohgo, M. Nakamura, M.
Takahashi and M. Takeda, Chem. Commun., 2000, 1989–1990.
6 K. M. Barkigia, M. W. Renner and J. Fajer, J. Porphyrins Phthalocya-
nins, 2001, 5, 415.
7 V. Schünemann, M. Gerdan, A. X. Trautwein, N. Haoudi, D. Mandon,
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8 K. M. Barkigia, M. D. Berber, J. Fajer, C. J. Medforth, M. W. Renner
and K. M. Smith, J. Am. Chem. Soc., 1990, 112, 8851.
9 R.-J. Cheng, P.-Y. Chen, P.-R. Gau, C.-C. Chen and S.-M. Peng, J. Am.
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10 Small peaks at the low field edge in the EPR spectrum of 3 are due to the
contamination of a trace amount of 2.
Fig. 2 Mössbauer spectrum of 4 taken at 77 K.
11 G. Palmer, in Iron Porphyrins, Part II, ed. A. B. Lever and H. B. Gray,
Addison-Wesley, Reading, 1983, pp. 43–88.
12 J. Sams and T. B. Tsin, in The Porphyrin, Vol. IV, ed. D. Dolphin,
Academic Press, New York, 1979, pp. 425–478.
13 Y. Ohgo, T. Ikeue and M. Nakamura, Inorg. Chem., 2002, 41, 1698.
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15 Y. Ohgo, T. Saitoh and M. Nakamura, Acta Crystallogr., Sect. C, 2001,
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16 J.-P. Simonato, J. Pecaut, L. Le Pape, J.-L. Oddou, C. Jeandey, M.
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17 Y. Ohgo, S. Neya, T. Ikeue, N. Funasaki and M. Nakamura, Acta
Crystallogr., Sect. C, 2001, 57, 1046.
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19 M. Nakamura, T. Yamaguchi and Y. Ohgo, Inorg. Chem., 1999, 38,
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Fig. 3 Temperature dependence of the effective magnetic moments of 4.
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