M[TCNQ]γ-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)][SbF6](2) starting materials, complementing previous studies utilizing [M(NCMe)(6)][BF4](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)][SbF6](2)}. The materials from [M(NCMe)(6)][SbF6](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)][BF4](2) route, which was previously reported. The materials from [M(NCMe)(6)][SbF6](2) also exhibit the highest coercivity, followed by those from [M(NCMe)(6)][BF4](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)][SbF6](2) have a reduced chi(T) frequency dependence with respect to materials from [M(NCMe)(6)][BF4](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 [BF4](-). 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.