title: Electronic structure and spectroscopic properties of mononuclear manganese(III) Schiff base complexes: a systematic study on [Mn(acen)X] complexes by EPR, UV/vis, and MCD spectroscopy (X = Hal, NCS).
abstract: The manganese(III) Schiff base complexes [Mn(acen)X] (H2acen: N,N'-ethylenebis(acetylacetone)imine, X: I(-), Br(-), Cl(-), NCS(-)) are considered as model systems for a combined study of the electronic structure using vibrational, UV/vis absorption, parallel-mode electron paramagnetic resonance (EPR) and low-temperature magnetic circular dichroism (MCD) spectroscopy. By variation of the co-ligand X, the influence of the axial ligand field within a given square-pyramidal coordination geometry on the UV/vis, EPR, and MCD spectra of the title compounds is investigated. Between 25000 and 35000 cm(-1), the low-temperature MCD spectra are dominated by two very intense, oppositely signed pseudo-A terms, referred to as "double pseudo-A terms", which change their signs within the [Mn(acen)X] series dependent on the axial ligand X. Based on molecular orbital (MO) and symmetry considerations, these features are assigned to π(n.b.)(s, a) → yz, z(2) ligand-to-metal charge transfer transitions. The individual MCD signs are directly determined from the calculated MOs of the [Mn(acen)X] complexes. The observed sign change is explained by an inversion of symmetry among the π(n.b.)(s, a) donor orbitals which leads to an interchange of the positive and negative pseudo-A terms constituting the "double pseudo-A term".
authors: Institut für Anorganische Chemie, Christian-Albrechts-Universität zu Kiel, D-24118 Kiel, Germany.
authors: Anne
authors: A
authors: Westphal
authors: Arne
authors: A
authors: Klinkebiel
authors: Hans-Martin
authors: HM
authors: Berends
authors: Henning
authors: H
authors: Broda
authors: Philipp
authors: P
authors: Kurz
authors: Felix
authors: F
authors: Tuczek
mesh_terms: D002712:Chlorides; D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D006219:Halogens / Q000737:chemistry*; D007097:Imines / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010422:Pentanones / Q000737:chemistry*; D011789:Quantum Theory; D012545:Schiff Bases / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013861:Thiocyanates / Q000737:chemistry*
chemical_list: D002712:Chlorides; D006219:Halogens; D007097:Imines; C582862:N,N'-ethylenebis(acetylacetone)imine; D009942:Organometallic Compounds; D010422:Pentanones; D012545:Schiff Bases; D013861:Thiocyanates; D008345:Manganese