meso Substituent Effects on the Geometric and Electronic Structures of High-Spin and Low-Spin Iron(III) Complexes of Mono-meso-Substituted Octaethylporphyrins

Heather Kalish, Jason E. Camp, Marcin Stepien, Lechoslaw Latos-Grazynski, Marilyn M. Olmstead, Alan L. Balch

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Introduction of a single meso substituent into ClFeIII(OEP) or K[(NC)2Fe(OEP)] results in significant changes in the geometric and/or spectroscopic properties of these complexes. The mono-meso-substituted iron(III) complexes ClFeIII(meso-Ph-OEP), ClFeIII(meso-Bu-OEP), ClFeIII(meso-MeO-OEP), ClFeIII(meso-Cl-OEP), ClFeIII(meso-NC-OEP), ClFeIII(meso-HC(O)-OEP), and ClFeIII(meso-O2N-OEP) were isolated and characterized by their UV/visible and paramagnetically shifted 1H NMR spectra. The structures of both ClFeIII(meso-Ph-OEP) and ClFeIII(meso-NC-OEP) were detd. by x-ray crystallog. Both mols. have five-coordinate structures typical for high-spin (S = 5/2) iron(III) complexes. However, the porphyrins themselves no longer have the domed shape seen in ClFeIII(OEP), and the N4 coordination environment possesses a slight rectangular distortion. These high-spin, mono-meso-substituted iron(III) complexes display 1H NMR spectra in chloroform-d soln. which indicate that the conformational changes seen in the solid-state structures are altered by normal mol. motion to produce spectra consistent with Cs mol. symmetry. In pyridine soln. the high-spin six-coordinate complexes {(py)ClFeIII(meso-R-OEP)} form. In methanol soln. in the presence of excess potassium cyanide, the low-spin six-coordinate complexes K[(NC)2FeIII(meso-R-OEP)] form. The 1H NMR spectra of these show that electron-donating substituents produce an upfield relocation of the meso-proton chem. shifts. This relocation is interpreted in terms of increased contribution from the less common (dxz,dyz)4(dxy)1 ground electronic state as the meso substituent becomes more electron donating.
Original languageEnglish
Pages (from-to)989-997
Number of pages9
JournalInorganic Chemistry
Issue number4
Early online date31 Jan 2002
Publication statusPublished - 1 Feb 2002


  • iron porphyrin substituent effect structure electronic state
  • conformation iron porphyrin meso substituent effect
  • crystal structure iron chloro porphyrin

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