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Hydrogen-Bonded Polyrotaxane Cation Structure in Nickel Dithiolate Anion Radical Salts: Ferromagnetic and Semiconducting Behavior Associated with Structural Phase Transition |
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| Authors: | Yuki Shirakawa Dr. Kiyonori Takahashi Dr. Hiroyasu Sato Dr. Norihisa Hoshino Hayato Anetai Prof. Shin-ichiro Noro Prof. Tomoyuki Akutagawa Prof. Takayoshi Nakamura |
| Affiliation: | 1. Graduate School of Environmental Science, Hokkaido University, N10W5, Sapporo, 060-0810 Japan;2. Rigaku Corporation, Akishima, Tokyo, 196-8666 Japan;3. Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577 Japan Graduate School of Engineering, Tohoku University, 6-6-7, Aramaki Aza Aoba Aoba-ku, Sendai, 980-8579 Japan;4. Graduate School of Engineering, Tohoku University, 6-6-7, Aramaki Aza Aoba Aoba-ku, Sendai, 980-8579 Japan;5. Graduate School of Environmental Science, Hokkaido University, N10W5, Sapporo, 060-0810 Japan Faculty of Environmental Earth Science, Hokkaido University, N10W5, Sapporo, 060-0810 Japan |
| Abstract: | 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]− (dmit2− = 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]−. |
| Keywords: | insulators radical ion salts magnetic properties phase transitions rotaxanes semiconductors |