Difference in spin crossover pathways among saddle-shaped six-coordinated iron(III) porphyrin complexes

Takahisa Ikeue, Yoshiki Ohgo, Owendi Ongayi, M. Graça H Vicente, Mikio Nakamura

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Abstract

The electronic states of a series of saddle-shaped porphyrin complexes [Fe(OMTPP)L2]+ and [Fe(TBTXP)L2]+ have been examined in solution by 1H NMR, 13C NMR, and EPR spectroscopy and by magnetic measurements. While [Fe(OMTPP)(DMAP) 2]+ and [Fe(TBTXP)(DMAP)2]+ maintain the low-spin (S = 1/2) state, [Fe(OMTPP)(THF)2]+ and [Fe(TBTXP)(THF)2]+ exhibit an essentially pure intermediate-spin (S = 3/2) state over a wide range of temperatures. In contrast, the Py and 4-CNPy complexes of OMTPP and TBTXP exhibit a spin transition from S = 3/2 to S = 1/2 as the temperature was decreased from 300 to 200 K. Thus, the magnetic behavior of these complexes is similar to that of [Fe(OETPP)PY2]+ reported in our previous paper (Ikeue, T. ; Ohgo, Y.; Yamaguchi, T.; Takahashi, M.; Takeda, M.; Nakamura, M. Angew. Chem., Int. Ed. 2001, 40, 2617-2620) in the context that all these complexes exhibit a novel spin crossover phenomenon in solution. Close examination of the NMR and EPR data of [Fe(OMTPP)L2]+ and [Fe(TBTXP)L 2]+ (L = Py, 4-CNPy) revealed, however, that these complexes adopt the less common (dxz, dyz) 4(dxy )1 electron configuration at low temperature in contrast to [Fe(OETPP)Py2]+ which shows the common (dxy)2(dxz, dyz) 3 electron configuration. These observations have been attributed to the flexible nature of the OMTPP and TBTXP cores as compared with that of OETPP; the relatively flexible OMTPP and TBTXP cores can ruffle the porphyrin ring and adopt the (dxz, dyz)4(d xy)1 electron configuration at low temperature. Therefore, this study reveals that the rigidity of porphyrin cores is an important factor in determining the spin crossover pathways.

Original languageEnglish
Pages (from-to)5560-5571
Number of pages12
JournalInorganic Chemistry
Volume42
Issue number18
DOIs
Publication statusPublished - 2003 Sep 8

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Porphyrins
saddles
porphyrins
crossovers
Iron
iron
Nuclear magnetic resonance
Paramagnetic resonance
Electrons
nuclear magnetic resonance
Temperature
configurations
Magnetic variables measurement
Electronic states
electrons
Rigidity
rigidity
magnetic measurement
Spectroscopy
examination

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Difference in spin crossover pathways among saddle-shaped six-coordinated iron(III) porphyrin complexes. / Ikeue, Takahisa; Ohgo, Yoshiki; Ongayi, Owendi; Vicente, M. Graça H; Nakamura, Mikio.

In: Inorganic Chemistry, Vol. 42, No. 18, 08.09.2003, p. 5560-5571.

Research output: Contribution to journalArticle

Ikeue, Takahisa ; Ohgo, Yoshiki ; Ongayi, Owendi ; Vicente, M. Graça H ; Nakamura, Mikio. / Difference in spin crossover pathways among saddle-shaped six-coordinated iron(III) porphyrin complexes. In: Inorganic Chemistry. 2003 ; Vol. 42, No. 18. pp. 5560-5571.
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abstract = "The electronic states of a series of saddle-shaped porphyrin complexes [Fe(OMTPP)L2]+ and [Fe(TBTXP)L2]+ have been examined in solution by 1H NMR, 13C NMR, and EPR spectroscopy and by magnetic measurements. While [Fe(OMTPP)(DMAP) 2]+ and [Fe(TBTXP)(DMAP)2]+ maintain the low-spin (S = 1/2) state, [Fe(OMTPP)(THF)2]+ and [Fe(TBTXP)(THF)2]+ exhibit an essentially pure intermediate-spin (S = 3/2) state over a wide range of temperatures. In contrast, the Py and 4-CNPy complexes of OMTPP and TBTXP exhibit a spin transition from S = 3/2 to S = 1/2 as the temperature was decreased from 300 to 200 K. Thus, the magnetic behavior of these complexes is similar to that of [Fe(OETPP)PY2]+ reported in our previous paper (Ikeue, T. ; Ohgo, Y.; Yamaguchi, T.; Takahashi, M.; Takeda, M.; Nakamura, M. Angew. Chem., Int. Ed. 2001, 40, 2617-2620) in the context that all these complexes exhibit a novel spin crossover phenomenon in solution. Close examination of the NMR and EPR data of [Fe(OMTPP)L2]+ and [Fe(TBTXP)L 2]+ (L = Py, 4-CNPy) revealed, however, that these complexes adopt the less common (dxz, dyz) 4(dxy )1 electron configuration at low temperature in contrast to [Fe(OETPP)Py2]+ which shows the common (dxy)2(dxz, dyz) 3 electron configuration. These observations have been attributed to the flexible nature of the OMTPP and TBTXP cores as compared with that of OETPP; the relatively flexible OMTPP and TBTXP cores can ruffle the porphyrin ring and adopt the (dxz, dyz)4(d xy)1 electron configuration at low temperature. Therefore, this study reveals that the rigidity of porphyrin cores is an important factor in determining the spin crossover pathways.",
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AU - Nakamura, Mikio

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