Mn K-edge X-ray absorption studies of mononuclear Mn(III)–hydroxo complexes

Academic Article

Abstract

  • Abstract: Mn K-edge X-ray absorption spectroscopy experiments were performed on the solid- and solution-phase samples of [MnII(dpaqR)](OTf) (R=H, Me) and [MnIII(OH)(dpaqR)](OTf). The extended X-ray absorption fine structure (EXAFS) data show distinct differences between the MnII and MnIII–OH complexes, with fits providing metric parameters in excellent agreement with values from X-ray crystallography and density functional theory (DFT) computations. Evaluation of the EXAFS data for solid-phase [MnIII(OH)(dpaq)](OTf) resolved a short Mn–OH bond distance of 1.79 Å; however, the short trans-amide nitrogen bond of the supporting ligand precluded the resolution of the Mn–OH bond distance in the corresponding solution-phase sample and for both [MnIII(OH)(dpaqMe)](OTf) samples. The edge energy also increases by approximately 2 eV from the MnII to the MnIII–OH complexes. Experimental pre-edge analysis shows the MnII complexes to have pre-edge areas comparable to the MnIII–OH complexes, despite the presence of the relatively short Mn–OH distance. Time-dependent density functional theory (TD-DFT) computations illustrate that Mn 3d–4p mixing, a primary contributor to pre-edge intensities, decreases by ~ 0.3% from the MnII to MnIII–OH complexes, which accounts for the very similar pre-edge areas. Collectively, this work shows that combined EXAFS and XANES analysis has great potential for identification of reactive MnIII–OH intermediates, such as those proposed in enzyme active sites. Graphical Abstract: [Figure not available: see fulltext.].
  • Authors

    Digital Object Identifier (doi)

    Author List

  • Rice DB; Wijeratne GB; Jackson TA
  • Start Page

  • 1281
  • End Page

  • 1293
  • Volume

  • 22
  • Issue

  • 8