highly deformed porphyrin complexes.8,15 We have recently
determined the crystal structure of 1.16 As expected, 1 has a
strongly S4-ruffled porphyrin core with the meso-carbons
deviating above and below the average porphyrin plane by ca.
0.68 Å. The Fe–N(porphyrin) bond distances of 1, av.
1.967(12) Å, are significantly shorter than those of other
bis(THF) complexes such as [Fe(OEP)(THF)2]ClO4 (av.
1.994 Å),4 [Fe(TEtP)(THF)2]ClO4 (av. 2.006 Å)17 and
[Fe(TPP)(THF)2]ClO4 (av. 2.016 Å).18
In conclusion, we have shown that highly S4-ruffled 1 and S4-
saddled 2 are highly pure intermediate spin complexes on the
basis of the NMR, EPR, Mössbauer, and magnetic data.
This work was supported by a Grant-in-Aid for Scientific
Research (No. 10640551) from the Ministry of Education,
Science, Culture and Sports of Japan. Thanks are due to the
Research Center for Molecular Materials, the Institute for
Molecular Science, for assistance in obtaining the low-
temperature spectra. The authors are grateful to Dr Hiroshi
Fujii, Dr Yasuhiro Funahashi, and Mr Masahiro Sakai of the
Institute for Molecular Science for assistance with the SQUID
measurements.
Fig. 3 Mössbauer spectra of (a) 1 taken at 76 K and (b) 2 taken at 290 K.
estimated to be 3.99 and 1.97, suggesting that the spin state of
1 should be regarded as S = 3/2 at 4.2 K. Magnetic moments
taken for the solid sample by SQUID showed almost constant
values, 3.90 ± 0.10 mB at 50–300 K, which are quite close to the
spin only value m = 3.87 mB expected for S = 3/2 complexes.
Fig. 3a shows the Mössbauer spectrum measured on a
microcrystalline sample at 76 K. The isomer shift (d; relative to
a-iron foil) and quadrupole splitting (DEq) were determined to
be 0.34 and 3.71 mm s21, respectively. Large DEq values are
usually observed for complexes with S = 3/2 or S = 3/2,5/2.14
Taken together, it is concluded that 1 is a highly pure
intermediate spin complex.
2 was similarly prepared from [Fe(OETPP)Cl] and AgClO4
in THF solution. The coordination of the THF ligands was
confirmed by 1H NMR analysis. Fig. 1b shows the temperature
dependence of the chemical shifts of some protons. Fairly large
downfield shifts of the methylene signals, 51.0 and 17.5 ppm at
233 K, clearly indicate that the b-pyrrole carbons have a
considerable amount of p-spin density. Fig. 2b shows the EPR
spectrum taken in frozen CH2Cl2 solution at 4.2 K. The g values
were 4.01 and 2.00, suggesting that the spin state of 2 should
also be represented as S = 3/2 at 4.2 K. The spin state was
further confirmed by the magnetic moments determined by the
Evans method in CH2Cl2 solution as well as by SQUID
magnetometry in the solid; the former showed the magnetic
moment to be 4.0 ± 0.1 mB at 193–303 K, and the latter gave
values 3.85 ± 0.05 mB at 20–300 K. Fig. 3b shows the
Mössbauer spectrum measured on a microcrystalline sample at
290 K. The d and DEq values were determined to be 0.50 and
3.50 mm s21, respectively. Taken together, it is concluded that
2 is also a very pure intermediate spin complex.
Notes and references
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9 Abbreviations: OETPP, TiPrP, TEtP, and OEP are the dianions of
2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin,
5,10,15,20-tetraisopropylporphyrin,
5,10,15,20-tetraethylporphyrin,
and 2,3,7,8,12,13,17,18-octaethylporphyrin, respectively.
10 V. Schünemann, M. Gerdan, A. X. Trautwein, N. Haoudi, D. Mandon,
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16 Y. Ohgo, T. Saitoh and M. Nakamura, Acta Crystallogr., Sect. C,
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17 Y. Ohgo, T. Saitoh and M. Nakamura, Acta Crystallogr., Sect. C, 1999,
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Formation of the very pure intermediate spin complexes, 1
and 2, indicates that the S = 3/2 state is stabilized in both ruffled
and saddled porphyrin complexes. The major reason must be the
short Fe–N(porphyrin) bond lengths commonly observed in
18 L. Chen, G.-B. Yi, L.-S. Wang, U. R. Dharmwardana, A. C. Dart, M. A.
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1990
Chem. Commun., 2000, 1989–1990