title: Structural investigation of high-valent manganese-salen complexes by UV/Vis, Raman, XANES, and EXAFS spectroscopy.
abstract: XANES and EXAFS spectroscopic studies at the Mn-K- and Br-K-edge of reaction products of (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride ([(salen)Mn(III)Cl], 1) and (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) bromide ([(salen)Mn(III)Br], 2) with 4-phenylpyridine N-oxide (4-PPNO) and 3-chloroperoxybenzoic acid (MCPBA) are reported. The reaction of the Mn(III) complexes with two equivalents of 4-PPNO leads to a hexacoordinated compound, in which the manganese atom is octahedrally coordinated by four oxygen/nitrogen atoms of the salen ligand at an average distance of approximately 1.90 A and two additional, axially bonded oxygen atoms of the 4-PPNO at 2.25 A. The oxidation state of this complex was determined as approximately +IV by a comparative study of Mn(III) and Mn(V) reference compounds. The green intermediate obtained in reactions of MCPBA and solutions of 1 or 2 in acetonitrile was investigated with XANES, EXAFS, UV/Vis, and Raman spectroscopy, and an increase of the coordination number of the manganese atoms from 4 to 5 and the complete abstraction of the halide was observed. A formal oxidation state of IV was deduced from the relative position of the pre-edge 1s-->3d feature of the X-ray absorption spectrum of the complex. The broad UV/Vis band of this complex in acetonitrile with lambda(max)=648 nm was consistent with a radical cation structure, in which a MCPBA molecule was bound to the Mn(IV) central atom. An oxomanganese(V) or a dimeric manganese(IV) species was not detected.
authors.affiliation: Universität Stuttgart, Institut für Physikalische Chemie, Pfaffenwaldring 55, 70569 Stuttgart, Germany. m.feth@ipc.uni-stuttgart.de
authors.forename: Martin P
authors.initials: MP
authors.lastname: Feth
authors.forename: Carsten
authors.initials: C
authors.lastname: Bolm
authors.forename: Jens P
authors.initials: JP
authors.lastname: Hildebrand
authors.forename: Manuela
authors.initials: M
authors.lastname: Köhler
authors.forename: Oliver
authors.initials: O
authors.lastname: Beckmann
authors.forename: Matthias
authors.initials: M
authors.lastname: Bauer
authors.forename: Rivo
authors.initials: R
authors.lastname: Ramamonjisoa
authors.forename: Helmut
authors.initials: H
authors.lastname: Bertagnolli