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 Mn V-oxo complexes have tetragonal symmetry, producing low-spin species. A new high-spin Mn V-oxo complex that was prepared from a well-characterized oxomanganese(III) complex having trigonal symmetry is now reported. Oxidation experiments with [FeCp 2] + 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 A z = 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(Δ 18O = 31 cm -1). Mn Kβ X-ray emission spectra showed Kβ' and Kβ 1,3 bands at 6475.92 and 6490.50 eV, respectively, which are characteristic of a high-spin Mn V center.