Dialkyldicyanofumarate diesters: Tunable building blocks for molecule-based ferromagnets

Dicyanofumarate diesters have been discovered to be viable and versatile al ternatives to tetracyanoethylene as building blocks for the synthesis of mo lecule-based magnets. The reaction of decamethylmanganocene, Mn(Cp*)(2), an d dimethyldicyanofumarate, DMeDCF, in methylene chloride at -50 degrees C g ives a one-to-one charge-transfer salt ferromagnet, [Mn(Cp*)(2)][DMeDCF], t hat possesses one of the highest Curie temperatures, 10.6 +/- 0.1 K, ever o bserved in this class of compounds. At 1.8 K, this compound exhibits hyster esis with H-coer similar to 7 kG. Measurement of ac susceptibility suggests some glassiness in the ferromagnetic state, similar to that seen for the t etracyanoethylene analogue, [Mn(Cp*)(2)][TCNE]. Diethyldicyanofumarate, DEt DCF, reacts with decamethylmanganocene to give the homologous salt, [Mn(Cp* )(2)][DEtDCF]. In contrast to the dimethyl ester, the magnetic properties o f this compound are those of a glassy, hysteretic metamagnet that exhibits coercivity of around 10 kG at 1.8 K.