Electronic structure of six-coordinate iron(III) monoazaporphyrins

Kenichiro Nakamura, Akira Ikezaki, Yoshiki Ohgo, Takahisa Ikeue, Saburo Neya, Mikio Nakamura

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Abstract

The electronic structures of six-coordinate iron(III) octaethylmonoazaporphyrins, [Fe(MAzP)L2]± (1), have been examined by means of 1H NMR and EPR spectroscopy to reveal the effect of meso-nitrogen in the porphyrin ring. The complexes carrying axial ligands with strong field strengths such as 1-Melm, DMAP, CN-, and tBuNC adopt the low-spin state with the (dxy) 2(dxz, dyz)3 ground state in a wide temperature range where the 1H NMR and EPR spectra are taken. In contrast, the complexes with much weaker axial ligands, such as 4-CNPy and 3,5-Cl2Py, exhibit the spin transition from the mainly S = 3/2 at 298 K to the S = 1/2 with the (dxy)2(dxz, d yz)3 ground state at 4 K. Only the THF complex has maintained the S = 3/2 throughout the temperature range examined. Thus, the electronic structures of 1 resemble those of the corresponding iron(III) octaethylporphyrins, [Fe(OEP)L2] ± (2). A couple of differences have been observed, however, in the electronic structures of 1 and 2. One of the differences is the electronic ground state in low-spin bis( tBuNC) complexes. While [Fe(OEP)(tBuNC)2] + adopts the (dxz, dyz)4(d xy)1 ground state, like most of the bis(tBuNC) complexes reported previously, [Fe(MAzP)(tBuNC)2] + has shown the (dxy)2(dxz, d yz)3 ground state. Another difference is the spin state of the bis(3,5-Cl2Py) complexes. While [Fe(OEP)(3,5-Cl 2Py)2]+ has maintained the mixed S = 3/2 and 5/2 spin state from 298 to 4 K, [Fe(MAzP)(3,5-Cl2Py) 2]+ has shown the spin transition mentioned above. These differences have been ascribed to the narrower N4 cavity and the presence of lower-lying π* orbital in MAzP as compared with OEP.

Original languageEnglish
Pages (from-to)10299-10307
Number of pages9
JournalInorganic Chemistry
Volume47
Issue number22
DOIs
Publication statusPublished - 2008 Nov 17

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Ground state
Electronic structure
Iron
electronic structure
iron
ground state
Paramagnetic resonance
Nuclear magnetic resonance
Ligands
Porphyrins
nuclear magnetic resonance
ligands
porphyrins
Nitrogen
Spectroscopy
field strength
Temperature
octaethylporphyrin
nitrogen
orbitals

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Nakamura, K., Ikezaki, A., Ohgo, Y., Ikeue, T., Neya, S., & Nakamura, M. (2008). Electronic structure of six-coordinate iron(III) monoazaporphyrins. Inorganic Chemistry, 47(22), 10299-10307. https://doi.org/10.1021/ic800674d

Electronic structure of six-coordinate iron(III) monoazaporphyrins. / Nakamura, Kenichiro; Ikezaki, Akira; Ohgo, Yoshiki; Ikeue, Takahisa; Neya, Saburo; Nakamura, Mikio.

In: Inorganic Chemistry, Vol. 47, No. 22, 17.11.2008, p. 10299-10307.

Research output: Contribution to journalArticle

Nakamura, K, Ikezaki, A, Ohgo, Y, Ikeue, T, Neya, S & Nakamura, M 2008, 'Electronic structure of six-coordinate iron(III) monoazaporphyrins', Inorganic Chemistry, vol. 47, no. 22, pp. 10299-10307. https://doi.org/10.1021/ic800674d
Nakamura K, Ikezaki A, Ohgo Y, Ikeue T, Neya S, Nakamura M. Electronic structure of six-coordinate iron(III) monoazaporphyrins. Inorganic Chemistry. 2008 Nov 17;47(22):10299-10307. https://doi.org/10.1021/ic800674d
Nakamura, Kenichiro ; Ikezaki, Akira ; Ohgo, Yoshiki ; Ikeue, Takahisa ; Neya, Saburo ; Nakamura, Mikio. / Electronic structure of six-coordinate iron(III) monoazaporphyrins. In: Inorganic Chemistry. 2008 ; Vol. 47, No. 22. pp. 10299-10307.
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N2 - The electronic structures of six-coordinate iron(III) octaethylmonoazaporphyrins, [Fe(MAzP)L2]± (1), have been examined by means of 1H NMR and EPR spectroscopy to reveal the effect of meso-nitrogen in the porphyrin ring. The complexes carrying axial ligands with strong field strengths such as 1-Melm, DMAP, CN-, and tBuNC adopt the low-spin state with the (dxy) 2(dxz, dyz)3 ground state in a wide temperature range where the 1H NMR and EPR spectra are taken. In contrast, the complexes with much weaker axial ligands, such as 4-CNPy and 3,5-Cl2Py, exhibit the spin transition from the mainly S = 3/2 at 298 K to the S = 1/2 with the (dxy)2(dxz, d yz)3 ground state at 4 K. Only the THF complex has maintained the S = 3/2 throughout the temperature range examined. Thus, the electronic structures of 1 resemble those of the corresponding iron(III) octaethylporphyrins, [Fe(OEP)L2] ± (2). A couple of differences have been observed, however, in the electronic structures of 1 and 2. One of the differences is the electronic ground state in low-spin bis( tBuNC) complexes. While [Fe(OEP)(tBuNC)2] + adopts the (dxz, dyz)4(d xy)1 ground state, like most of the bis(tBuNC) complexes reported previously, [Fe(MAzP)(tBuNC)2] + has shown the (dxy)2(dxz, d yz)3 ground state. Another difference is the spin state of the bis(3,5-Cl2Py) complexes. While [Fe(OEP)(3,5-Cl 2Py)2]+ has maintained the mixed S = 3/2 and 5/2 spin state from 298 to 4 K, [Fe(MAzP)(3,5-Cl2Py) 2]+ has shown the spin transition mentioned above. These differences have been ascribed to the narrower N4 cavity and the presence of lower-lying π* orbital in MAzP as compared with OEP.

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