title: High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in tetrapyrrole complexes.
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 (MnTPPCI), 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 approximately -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 approximtely -2.6 cm(-1), absolute value(E) approximately 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.
authors: Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Florida State University, Tallahassee 32310, USA.
authors: J
authors: J
authors: Krzystek
authors: Luca A
authors: LA
authors: Pardi
authors: Louis-Claude
authors: LC
authors: Brunel
authors: David P
authors: DP
authors: Goldberg
authors: Brian M
authors: BM
authors: Hoffman
authors: Silvia
authors: S
authors: Licoccia
authors: Joshua
authors: J
authors: Telser
mesh_terms: D001965:Bromides / Q000032:analysis; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D004583:Electrons; D007477:Ions; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D008956:Models, Chemical; D009942:Organometallic Compounds / Q000032:analysis / Q000737:chemistry; D011166:Porphyrins / Q000032:analysis / Q000737:chemistry; D017680:Potassium Compounds / Q000032:analysis
chemical_list: C468626:(8,12-diethyl-2,3,7,13,17,18-hexamethylcorrolato)manganese(III); D001965:Bromides; D007477:Ions; D008024:Ligands; D009942:Organometallic Compounds; D011166:Porphyrins; D017680:Potassium Compounds; C101263:chloro(5,10,15,20-tetraphenylporphyrinato)manganese(III); D008345:Manganese; C039004:potassium bromide