title: Geometric and electronic structure of a peroxomanganese(III) complex supported by a scorpionate ligand.
abstract: A monomeric Mn(II) complex has been prepared with the facially-coordinating Tp(Ph2) ligand, (Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate). The X-ray crystal structure shows three coordinating solvent molecules resulting in a six-coordinate complex with Mn-ligand bond lengths that are consistent with a high-spin Mn(II) ion. Treatment of this Mn(II) complex with excess KO2 at room temperature resulted in the formation of a Mn(III)-O2 complex that is stable for several days at ambient conditions, allowing for the determination of the X-ray crystal structure of this intermediate. The electronic structure of this peroxomanganese(III) adduct was examined by using electronic absorption, electron paramagnetic resonance (EPR), low-temperature magnetic circular dichroism (MCD), and variable-temperature variable-field (VTVH) MCD spectroscopies. Density functional theory (DFT), time-dependent (TD)-DFT, and multireference ab initio CASSCF/NEVPT2 calculations were used to assign the electronic transitions and further investigate the electronic structure of the peroxomanganese(III) species. The lowest ligand-field transition in the electronic absorption spectrum of the Mn(III)-O2 complex exhibits a blue shift in energy compared to other previously characterized peroxomanganese(III) complexes that results from a large axial bond elongation, reducing the metal-ligand covalency and stabilizing the σ-antibonding Mn dz(2) MO that is the donor MO for this transition.
authors.affiliation: Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, KS 66045, USA. taj@ku.edu.
authors.forename: Hannah E
authors.initials: HE
authors.lastname: Colmer
authors.forename: Robert A
authors.initials: RA
authors.lastname: Geiger
authors.forename: Domenick F
authors.initials: DF
authors.lastname: Leto
authors.forename: Gayan B
authors.initials: GB
authors.lastname: Wijeratne
authors.forename: Victor W
authors.initials: VW
authors.lastname: Day
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Jackson
mesh_terms: D002942:Circular Dichroism; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D008968:Molecular Conformation; D056928:X-Ray Absorption Spectroscopy
chemical_list: D056831:Coordination Complexes; D008024:Ligands; D008345:Manganese