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)

Inorg Chem. 2013 Mar 4;52(5):2372-87. doi: 10.1021/ic301889e. Epub 2013 Feb 14.

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".

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chlorides
  • Circular Dichroism
  • Electron Spin Resonance Spectroscopy
  • Electrons
  • Halogens / chemistry*
  • Imines / chemistry*
  • Manganese / chemistry*
  • Molecular Structure
  • Organometallic Compounds / chemical synthesis
  • Organometallic Compounds / chemistry*
  • Pentanones / chemistry*
  • Quantum Theory
  • Schiff Bases / chemistry*
  • Spectrophotometry, Ultraviolet
  • Thiocyanates / chemistry*

Substances

  • Chlorides
  • Halogens
  • Imines
  • N,N'-ethylenebis(acetylacetone)imine
  • Organometallic Compounds
  • Pentanones
  • Schiff Bases
  • Thiocyanates
  • Manganese