The pseudo-polyrotaxane structure of [(H-bpy + )- (DB-24-crown-8)] ∞ (H-bpy + = monoprotonated 4,4-bipyridinium; DB-24-crown-8 = dibenzo-24-crown-8) has been incorporated into the anion radical salt [Ni(dmit) 2 ] − (dmit 2− = 1,3-dithiole-2-thione-4,5-dithiolate). (H-bpy + )(DB-24-crown-8)[Ni(dmit) 2 ] − crystallized as two polymorphs, crystals 1 and 2. Crystal 1 was found to have a lower density and looser packing structure in which H-bpy + forms a one-dimensional hydrogen-bonding chain that passes though the crown ether ring of DB-24-crown-8. DB-24-crown-8 adopts a U-shaped conformation in which two phenylene rings sandwich one of the pyridyl rings of H-bpy + to stabilize the structure. The [Ni(dmit) 2 ] − anions are arranged in a layer parallel to the (10) plane with uniform side-by-side interactions. A structural phase transition was observed at 235 K, accompanied by ordering of the polyrotaxane structure. In crystal 1, at 173 K, H-bpy + is twisted around the central C−C bond, which perturbs the arrangement of [Ni(dmit) 2 ] − through short C−H⋅⋅⋅S contacts. As a result, the semiconducting behavior, with an activation energy of 0.21 eV, becomes insulating below 235 K. The crystal exhibits ferromagnetic interactions because of the weak side-by-side interactions between [Ni(dmit) 2 ] − anions. Crystal 2 has a similar pseudo-polyrotaxane structure but showed no phase transition. This suggests that the looser crystal packing in crystal 1 induces the structural change of the pseudo-polyrotaxane, perturbing the electron system of [Ni(dmit) 2 ] − .
ASJC Scopus subject areas
- Organic Chemistry