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

摘要

Oxomanganese(V) species have been implicated in a variety of biological and synthetic processes, including 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 Mn^V–oxo complex that is high-spin is now reported, which was prepared from a well-characterized oxomanganese(III) complex having trigonal symmetry. Titration 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 cm⁻¹ and 754 cm⁻¹ assigned as a Fermi doublet centered at 746 cm⁻¹(Δ¹⁸O = 31 cm⁻¹). Kβ Mn X-ray emission spectra showed Kβ' and Kβ1,3 bands at 6475.92 and 6490.50 eV, which are characteristic of a high-spin Mn^V center.