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Preparation and Properties of a Monomeric High-Spin MnV–Oxo Complex

Taguchi, Taketo, Gupta, Rupal, Lassalle-Kaiser, Benedikt, Boyce, David W., Yachandra, Vittal K., Tolman, William B., Yano, Junko, Hendrich, Michael P., Borovik, A. S.
Journal of the American Chemical Society 2012 v.134 no.4 pp. 1996-1999
Raman spectroscopy, X-radiation, electron paramagnetic resonance spectroscopy, ligands, manganese, oxidation, oxygen, oxygen evolving complex, stable isotopes
Oxomanganese(V) species have been implicated in a variety of biological and synthetic processes, including their role as a key reactive center within the oxygen-evolving complex in photosynthesis. Nearly all mononuclear Mnⱽ–oxo complexes have tetragonal symmetry, producing low-spin species. A new high-spin Mnⱽ–oxo complex that was prepared from a well-characterized oxomanganese(III) complex having trigonal symmetry is now reported. Oxidation experiments with [FeCp₂]⁺ were monitored with optical and electron paramagnetic resonance (EPR) spectroscopies and support a high-spin oxomanganese(V) complex formulation. The parallel-mode EPR spectrum has a distinctive S = 1 signal at g = 4.01 with a six-line hyperfine pattern having Az = 113 MHz. The presence of an oxo ligand was supported by resonance Raman spectroscopy, which revealed O-isotope-sensitive peaks at 737 and 754 cm–¹ assigned as a Fermi doublet centered at 746 cm–¹(Δ¹⁸O = 31 cm–¹). Mn Kβ X-ray emission spectra showed Kβ′ and Kβ₁,₃ bands at 6475.92 and 6490.50 eV, respectively, which are characteristic of a high-spin Mnⱽ center.