Assembled structures and magnetic properties of viologen–[M(mnt)2] charge-transfer salts (mnt = maleonitriledithiolate; M = Cu, Ni, Pt)

Ion-pair compounds of phenyl-substituted viologen dications with [M(mnt)2] dianions were prepared and characterized. (Benzyl viologen)[M(mnt)2] (M = Cu (1), Ni (2), Pt (3)) and (phenyl viologen)[Cu(mnt)2] (4) exhibited mixed-stack crystal structures, whereas (dinitrophenyl viologen)[Cu(mnt)2] (5) exhibited no π–π interactions. Magnetic susceptibility measurements revealed that 1 exhibits a ferromagnetic exchange interaction (Weiss constant θ = +0.9 K), possibly mediated by the diamagnetic cation. Antiferromagnetic interactions were observed for 4 (θ = −2.0 K) and 5 (θ = −2.9 K), whereas 2 and 3 were diamagnetic. Absorption bands assignable to charge transfer were observed in the mixed-stack salts in the visible to near-infrared region.