title: Isolation of monomeric Mn(III/II)-H and Mn(III)-complexes from water: evaluation of O-H bond dissociation energies.
abstract: The syntheses and properties of the monomeric [MnIII/IIH31(OH)]-/2- and [MnIIIH31(O)]2- complexes are reported, where [H31]3- is the tripodal ligand tris[(N'-tert-butylureaylato)-N-ethyl)]aminato. Isotope-labeling studies with H218O confirmed that water is the source of the terminal oxo and oxygen in the hydroxo ligand. The molecular structures of the [MnIIH31(OH)]2- and [MnIIIH31(O)]2- complexes were determined by X-ray diffraction methods and show that each complex has trigonal bipyramidal coordination geometry. The MnIII-O distance in [MnIIIH31(O)]2- is 1.771(4) A, which is lengthened to 2.059(2) A in [MnIIH31(OH)]2-. Structural studies also show that [H31]3- provides a hydrogen-bond cavity that surrounds the MnIII-O(H) units. Using a thermodynamic approach, which requires pKa and redox potentials, bond dissociation energies of 77(4) and 110(4) kcal/mol were calculated for [MnIIH31(O-H)]2- and [MnIIIH31(O-H)]-, respectively. The calculated value of 77 kcal/mol for the [MnIIH31(O-H)]2- complex is supported by the ability of [MnIIIH31(O)]2- complex to cleave C-H bonds with bond energies of <80 kcal/mol.
authors.affiliation: Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, USA.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Gupta
authors.forename: Cora E
authors.initials: CE
authors.lastname: MacBeth
authors.forename: Victor G
authors.initials: VG
authors.lastname: Young
authors.forename: A S
authors.initials: AS
authors.lastname: Borovik
mesh_terms: D004563:Electrochemistry; D017895:Manganese Compounds / Q000737:chemistry* / Q000302:isolation & purification; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry* / Q000302:isolation & purification; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D017895:Manganese Compounds; D010087:Oxides; D014867:Water; C027424:manganese oxide