X-ray magnetic circular dichroism investigation of magnetic contributions from Mn(III) and Mn(IV) ions in Mn12-ac

We present the results of an x-ray magnetic circular dichroism (XMCD) investigation of the molecular superparamagnet Mn12-ac. Thanks to an approach based on chemical synthesis of model compounds, the contributions of Mn(III) and Mn(IV) ions to the absorption spectrum and the dichroic signal of Mn12-ac have been separated. The two contributions have been analyzed by simulating the XMCD spectra of Mn12-ac by means of crystal-field multiplet calculations. The ferrimagnetic structure of Mn12-ac has been confirmed, and the individual magnetic moments of Mn(III) and Mn(IV) ions are in good agreement with the values obtained by means of first-principles calculations and polarized neutron diffraction experiments. The orbital and spin contributions to the magnetic moment have been evaluated for each manganese ion, providing the evidence of negligible orbital magnetic moments for both Mn(III) and Mn(IV) ions.