Coordination Complexes with <i>cis-</i>TCNE Radical Anion Ligands. Models of M[TCNE]₂ Magnets

The synthesis and characterization of two manganese(II) complexes formally each featuring two cis-tetracyanoethylenide radical anionic ligands (TCNE•/-) are reported. In each case, tris(pyrazol-1-ylmethyl)amine serves as a capping ligand, blocking three facial coordination sites. Crystal structures show that the two TCNE anions in each molecule exhibit an intramolecular stacking interaction that forms what can be considered a coordinated (TCNE2)2- moiety. These molecules are presumed to be structural models of some of the local bonding in the family of amorphous, ferrimagnetic, M[TCNE]2·y(solvent) coordination polymer magnets. Magnetic measurements indicate that the (TCNE2)2- bridge is diamagnetic and not a good mediator of magnetic exchange, a result that might explain the observed lower ordering temperatures in some of the polymer magnets.