Intermolecular Magnetic Coupling Mechanism for a New Ionic Pair Salt [Ni(bpy)(3)][Ni(mnt)(2)](2)

A new ionic pair salt [Ni(bpy)(3)][Ni(mnt)(2)](2) (mnt = 1,2-dicyanoethane-1,2-dithiolate) has been prepared and its crystal structure was determined by X-ray crystallography at 293, 200 and 100 K. In the mononuclear radical anionic complex, the nickel ion assumes a slightly distorted square-planar geometry. There is a special kind of stacking interactions at each temperature (i.e., Model A at 293 K, Model B at 200 K and Model C at 100 K). The variable-temperature magnetic moments indicate that there is a strong anti-ferromagnetic interaction between the adjacent pi-pi stacking mononuclear mononuclear radical anionic complexes and especially the anti-ferromagnetic coupling strength is close to the diamagnetism at 100 K. The theoretical calculations reveal for the first time that the spin densities between the short contact atoms are beta state and the anti-ferromagnetic coupling property of this crystal may be related to the beta state spin densities between the short contact atoms. The theoretical calculations further confirm that the strong anti-ferromagnetic coupling strength should be relevant to the larger spin densities on the short contact atoms and the larger overlap integrals between the short contact atoms.