Radical-substituted dihydrophenazine radical cation salts: Molecular packing structure and bulk magnetic property

Abstract

Radical-substituted radical cation salts are exotic species that are potentially applicable as spin building blocks for molecular magnets. We recently found that these species, which are derived from a diphenyldihydrophenazine ( DPP ) framework, are stable under aerated conditions at room temperature. Of these species, nitronyl nitroxide ( NN • )-substituted DPP •+ tetrachloroferrate ( NNDPP ••+ · FeCl 4 – ) showed antiferromagnetic interaction at low temperature (<150 K), whereas the tetrabromoferrate salt NNDPP ••+ · FeBr 4 – exhibited a magnetic phase transition at 6.7 K to produce a bulk ferrimagnet. Both salts had very similar molecular structures. The difference in the magnetic properties was ascribed to the difference in molecular packing structures. A significant difference in these two salts was observed at the ( NNDPP ••+ )–( NNDPP ••+ ) intermolecular contact, including the oxygen atom of the nitroxide moiety; NNDPP ••+ ·FeCl 4 – had a serious antiferromagnetic O–O (nitroxide oxygen, 3.02 Å) intermolecular contact, whereas NNDPP ••+ ·FeBr 4 – had a ferromagnetic O–HC (2.53 Å) intermolecular contact.