High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in tetrapyrrole complexes

J. Krzystek, Luca A. Pardi, Louis Claude Brunel, Luca A. Pardi, David P. Goldberg, Brian M. Hoffman, Silvia Licoccia, Joshua Telser

Research output: Contribution to journalArticlepeer-review

32 Scopus citations

Abstract

High-field and -frequency electron paramagnetic resonance (HFEPR) spectroscopy has been used to study three complexes of high spin Manganese(III), 3d4, S=2. The complexes studied were tetraphenylporphyrinatomanganese(III) chloride (MnTPPCl), phthalocyanatomanganese(III) chloride (MnPcCl), and (8,12-diethyl-2,3,7,13,17,18-hexamethylcorrolato)manganese(III) (MnCor). We demonstrate the ability to obtain both field-oriented (single-crystal like) spectra and true powder pattern HFEPR spectra of solid samples. The latter are obtained by immobilizing the powder, either in an n-eicosane mull or KBr pellet. We can also obtain frozen solution HFEPR spectra with good signal-to-noise, and yielding the expected true powder pattern. Frozen solution spectra are described for MnTPPCl in 2:3 (v/v) toluene/CH2Cl2 solution and for MnCor in neat pyridine (py) solution. All of the HFEPR spectra have been fully analyzed using spectral simulation software and a complete set of spin Hamiltonian parameters has been determined for each complex in each medium. Both porphyrinic complexes (MnTPPCl and MnPcCl) are rigorously axial systems, with similar axial zero-field splitting (zfs): D≈-2.3 cm-1, and g values quite close to 2.00. In contrast, the corrole complex, MnCor, exhibits slightly larger magnitude, rhombic zfs: D≈-2.6 cm-1, |E|≈0.015 cm-1, also with g values quite close to 2.00. These results are discussed in terms of the molecular structures of these complexes and their electronic structure. We propose that there is a significant mixing of the triplet (S=1) excited state with the quintet (S=2) ground state in Mn(III) complexes with porphyrinic ligands, which is even more pronounced for corroles.

Original languageEnglish (US)
Pages (from-to)1113-1127
Number of pages15
JournalSpectrochimica Acta - Part A Molecular and Biomolecular Spectroscopy
Volume58
Issue number6
DOIs
StatePublished - 2002

Funding

This work was supported by the NHMFL (J.K., L.A.P., and L.-C.B.), CNR (S.L.), NSF (B.M.H.), and Roosevelt University (J.T.). We thank Dr. H. Weihe (Ørsted Institute, Copenhagen, Denmark) for providing us with the EPR simulation program and assistance with its use. We also thank Prof. B.R. McGarvey (University of Windsor, Ontario, Canada) for assistance with the ligand-field analysis. Ms. C. D'Ottavi (Tor Vergata, Rome) is thanked for technical assistance. Prof. D. Budil (Northeastern University, Boston, MA, USA) is acknowledged for the software routine which allowed elimination of dispersion components from HFEPR spectra.

Keywords

  • Corroles
  • Electron paramagnetic resonance
  • High-field electron paramagnetic resonance
  • Manganese(III)
  • Porphyrins
  • Tetrapyrroles

ASJC Scopus subject areas

  • Analytical Chemistry
  • Instrumentation
  • Atomic and Molecular Physics, and Optics
  • Spectroscopy

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