Hydrogen-Bonded Polyrotaxane Cation Structure in Nickel Dithiolate Anion Radical Salts: Ferromagnetic and Semiconducting Behavior Associated with Structural Phase Transition

Yuki Shirakawa, Kiyonori Takahashi, Hiroyasu Sato, Norihisa Hoshino, Hayato Anetai, Shin ichiro Noro, Tomoyuki Akutagawa, Takayoshi Nakamura

Research output: Contribution to journalArticle

2 Citations (Scopus)

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 ] (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 ] .

Original languageEnglish
Pages (from-to)6920-6927
Number of pages8
JournalChemistry - A European Journal
Volume25
Issue number28
DOIs
Publication statusPublished - 2019 May 17

Keywords

  • insulators
  • magnetic properties
  • phase transitions
  • radical ion salts
  • rotaxanes
  • semiconductors

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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