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High frequency and field EPR spectroscopy of Mn(III) complexes in frozen solutions

Krzystek, J. ; Telser, Joshua

Journal of magnetic resonance (1997), 2003-06, Vol.162 (2), p.454-465 [Revista revisada por pares]

United States: Elsevier Inc

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  • Título:
    High frequency and field EPR spectroscopy of Mn(III) complexes in frozen solutions
  • Autor: Krzystek, J. ; Telser, Joshua
  • Materias: Electron Spin Resonance Spectroscopy - methods ; Ethylenediamines - chemistry ; manganese ; metalloporphyrins ; Models, Chemical ; Organometallic Compounds - chemistry ; Porphyrins - chemistry ; Software
  • Es parte de: Journal of magnetic resonance (1997), 2003-06, Vol.162 (2), p.454-465
  • Notas: ObjectType-Article-2
    SourceType-Scholarly Journals-1
    ObjectType-Feature-1
    content type line 23
    ObjectType-Article-1
    ObjectType-Feature-2
  • Descripción: We have performed high-frequency and -field electron paramagnetic resonance (HFEPR) experiments on two complexes of high-spin Mn(III) (3d 4, S=2): mesotetrasulfonato-porphyrinatomanganese(III) (Mn(TSP)) and [( R, R)-(−)- N, N ′-bis(3,5-di- tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III)] (Mn(salen)). The main aim of this work was to qualitatively and quantitatively characterize the conditions suitable for HFEPR of high-spin transition metal complexes in frozen solutions, and compare them with experiments performed on solid samples. Mn(TSP) is a porphyrin complex soluble in water, in contrast to most metalloporphyrins. Mn(salen), often referred to as Jacobsen’s catalyst, is a complex widely used in organic synthesis for alkene epoxidation, and is soluble in organic solvents. High-quality HFEPR signals were observed for solid state Mn(TSP), as has been previously shown for many Mn(III) complexes. The present study is, however, the first to report high-quality HFEPR spectra of a Mn(III) complex in frozen aqueous solution. Analysis of the data yielded the following spin Hamiltonian parameters: S=2; D=−3.16±0.02 cm −1 , E=0, and isotropic g=2.00(2). No X-band EPR signals were observed for Mn(TSP), which is a consequence of this being a rigorously axial spin system. Mn(salen), in contrast, did not give good quality HFEPR spectra in the solid state, but high-quality HFEPR spectra were recorded in frozen organic solutions. Analysis of the data yielded the following spin Hamiltonian parameters: S=2; D=−2.47±0.02 cm −1 , |E|=0.17±0.01 cm −1 , and isotropic g=2.00(2). These values differ from those reported using X-band parallel mode EPR [J. Am. Chem. Soc. 123 (2001) 5710], as discussed in the text. Therefore, a comparison between HFEPR and parallel-mode X-band spectroscopy is made. Finally, the concentration sensitivity aspect of HFEPR spectroscopy is also discussed.
  • Editor: United States: Elsevier Inc
  • Idioma: Inglés
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