M[TCNQ]_y-Based Magnets (M = Mn, Fe, Co, Ni; TCNQ = 7,7,8,8-tetracyano-p-quinodimethane)

A family of molecule-based magnets of general formula M[TCNQ] y (M = Mn, Fe, Co, Ni; TCNQ = 7,7,8,8-tetracyano- p -quinodimethane) has been synthesized and characterized. The materials have been synthesized from both M a (CO) b and [M(NCMe) 6 ][SbF 6 ] 2 starting materials, complementing previous studies utilizing [M(NCMe) 6 ][BF 4 ] 2 . Magnetic ordering was observed for all materials with T c values between 8 K [M = Ni from Ni(CO) 4 ] and 60 K {M = Mn from [Mn(NCMe) 6 ][SbF 6 ] 2 }. The materials from [M(NCMe) 6 ][SbF 6 ] 2 displayed the highest critical temperatures, followed by those from M a (CO) b . With the exception of M = Ni, the lowest T c 's are obtained from the [M(NCMe) 6 ][BF 4 ] 2 route, which was previously reported. The materials from [M(NCMe) 6 ][SbF 6 ] 2 also exhibit the highest coercivity, followed by those from [M(NCMe) 6 ][BF 4 ] 2 . With the exception of M = Fe, the materials from M a (CO) b exhibit the lowest coercive fields. In general, magnets made from [M(NCMe) 6 ][SbF 6 ] 2 have a reduced χ‘ ‘( T ) frequency dependence with respect to materials from [M(NCMe) 6 ][BF 4 ] 2; thus, they exhibit less glassy magnetic behavior. Elemental analysis data indicate that small amounts of counterions and solvent are present in the products of these reactions, but less than better-coordinating [BF 4 ] - . Thus, the synthetic route has a significant effect on the magnetic properties of the materials, and enhanced T c 's are observed when less-coordinating anions are used. Although the structures of the materials are not known, it is proposed that the S = 1/2 [TCNQ] • - sp-hybridized Ns bond to multiple metal ions, thereby facilitating magnetic coupling and ordering.