A density functional study on magnetic exchange interaction between Mn(II) ion and nitronyl nitroxide radical in trans- and cis-metal-radical complexes

摘要

The magneto-structural correlation between a Mn(II) ion, coordinated in an octahedral environment, and two nitronyl nitroxide radical ligands in trans- and cis-metal-radical complexes is investigated by the broken symmetry (BS) approach within density functional theory (DFT). The dependences of coupling constants J on three structural parameters: (i) bond angle(∈) (Mn-O-N (nitroxide)); (ii) rotating angle(∈), defined by the nitronyl nitroxide radical plane rotating around the axial Mn-O (nitroxide); (iii) bond distance R (Mn-O (nitroxide)) are directly calculated. Our calculations showed that both trans- and cis-Mn(II)-radical complexes behave a stronger antiferromagnetic interaction, consistent with experiments. In view of molecular orbital theory, the direct exchanges, including σ-type and π-type exchanges, are responsible for the magnetic exchange pathways. There is a preferable linear correlation between the calculated coupling constants J and the overlap integral squares between the local magnetic orbitals at the various rotating angle(∈) at the fixed bond angle(∈) and bond distance R, in both trans- and cis-Mn(II)- radical complexes.