Effect of Meso Substituents on Exchange-Coupling Interactions in μ-Oxo Iron(III) Porphyrin Dimers

Jeffrey H. Helms, Leonard W. Ter Haar, David L. Harris, William E. Hatfield, K. Jayaraj, Glen E. Toney, A. Gold, Tabitha D. Mewborn, Jeanne R. Pemberton

Research output: Contribution to journalArticlepeer-review

35 Scopus citations

Abstract

The μ-Oxo iron(III) porphyrin dimers [(TPP)Fe]2O, [(TPP(4-OCH3))Fe]2O, [(TPP(4-CF3))Fe]2O, and [(TPP(F5))Fe]2O (where TPP is meso-tetraphenylporphyrin, TPP(4-OCH3) is meso-tetrakis(4-methoxyphenyl)porphyrin, TPP(4-CF3) is meso-tetrakis-(4-(trifluoromethyl)phenyl)porphyrin, and TPP(F5) is meso-tetrakis(pentafluorophenyl)porphyrin) have been studied to determine the effect of peripheral substituents on the porphyrin rings on properties of the molecules. Variable-temperature magnetic susceptibility studies on solid samples yielded the following exchange-coupling constants for the antiferromagnetically coupled iron(III) ions:-146.8 cm-1, [(TPP(4-OCH3))Fe]2O;-135.7 cm-1, [(TPP)Fe]2O;-136.4 cm-1, [(TPP(4-CF3))Fe]2O;-146.9 cm-1, [(TPP(F5))Fe]2O. Variable-temperature 13C NMR studies of dichloromethane solutions yield exchange-coupling constants of-150 cm-1for [(TPP(4-OCH3))Fe]2O, -145 cm-1for [(TPP)Fe]2O, and-129 cm-1 for [(TPP(F5))Fe]2O. Raman spectra were collected in the region of the energy of the outer-ring stretching modes found at approximately 1560 cm-1. The position of this band is empirically related to the porphyrin core size, and the data indicate that the porphyrin center-pyrrole nitrogen (Ct-N) distances increase in the order [(TPP(F5))Fe]2O < [(TPP(4-CF3))Fe]2O < [(TPP)Fe]2O < [(TPP(4-OCH3))Fe]2O. The data support the hypothesis that the porphyrin ring core size increases as the electron-releasing capability of the peripheral substituent increases. For the para-substituted complexes, increasing core size correlates with stronger axial binding, reflected in stronger antiferromagnetic coupling. The anomalous behavior of [(TPP(F5))Fe]2O may result from distortions caused by steric interactions of the o-fluorines.

Original languageEnglish (US)
Pages (from-to)2334-2337
Number of pages4
JournalInorganic Chemistry
Volume25
Issue number14
DOIs
StatePublished - Jul 1986

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Fingerprint Dive into the research topics of 'Effect of Meso Substituents on Exchange-Coupling Interactions in μ-Oxo Iron(III) Porphyrin Dimers'. Together they form a unique fingerprint.

Cite this