Crystal environments probed by EPR spectroscopy. Variations in the EPR spectra of CoII(octaethylporphyrin) doped in crystalline diamagnetic hosts and a reassessment of the electronic structure of four-coordinate cobalt(II)

Andrew Ozarowski, Hon Man Lee, Alan L. Balch

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53 Citations (Scopus)

Abstract

The powder and single-crystal EPR spectra of CoII(OEP) (OEP is the dianion of octaethylporphyrin) doped into a range of diamagnetic crystals including simple four-coordinate hosts, H2(OEP), the triclinic B form of NiII(OEP), the tetragonal form of NiII(OEP) and ZnII(OEP); five-coordinate hosts, (μ-dioxane)-{Zn II(OEP)}2 and (py)ZnII(OEP); six-coordinate hosts, (py)2ZnII(OEP) and (py)2Mg II(OEP); and hosts containing fullerenes, C60· 2ZnII(OEP)·CHCl3, C70·Ni II(OEP)·C6H6·CHCl3, and C60·NiII(OEP)·2C6H 6 have been obtained and analyzed. Spectra were simulated using a program that employed the exact diagonalization of the 16 × 16 complex spin Hamiltonian matrix. The EPR spectra of these doped samples are very sensitive to the environment within each crystal with the crystallographic site symmetry determining whether axial or rhombic resonance patterns are observed. For CII(OEP) doped into tetragonal NiII(OEP) (which displays a very large g⊥ of 3.405 and a very small gII of 1.544) and several other crystals containing four-coordinate metal sites, the g components could not be fit using existing theory with the assumption of the usual z2 ground state. However, reasonable agreement of the observed EPR parameters could be obtained by assuming that the unpaired electron resides in an xy orbital in the four-coordinate complexes.

Original languageEnglish
Pages (from-to)12606-12614
Number of pages9
JournalJournal of the American Chemical Society
Volume125
Issue number41
DOIs
Publication statusPublished - 2003 Oct 15

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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