title: Charge-transfer solids using nucleobases: supramolecular architectures composed of cytosine and [Ni(dmit)2] assembled by multiple hydrogen bonds and heteroatomic contacts.
abstract: Protonated species of the nucleobase cytosine (C), namely the monoprotonated CH(+) and the hemiprotonated CHC(+), were used to obtain four charge-transfer complexes of [Ni(dmit)2] (dmit: 1,3-dithiole-2-thione-4,5-dithiolate). Diffusion methods afforded two semiconducting [Ni(dmit)2](-) salts; (CH)[Ni(dmit)2](CH3CN) (1) and (CHC)[Ni(dmit)2] (2). In salt 1, the [Ni(dmit)2](-) ions with a S = 1/2 spin construct a uniform one-dimensional array along the molecular long axis, and the significant intermolecular interaction along the face-to-face direction results in a spin-singlet ground state. In contrast, salt 2 exhibits the Mott insulating behavior associated with uniform 1D arrays of [Ni(dmit)2](-), which assemble a two-dimensional layer that is sandwiched between the layers of hydrogen-bonded CHC(+) ribbons. Multiple hydrogen bonds between CHC(+) and [Ni(dmit)2](-) seem to result in the absence of structural phase transition down to 0.5 K. Electrooxidation of [Ni(dmit)2](-) afforded the polymorphs of the [Ni(dmit)2](0.5-) salts, (CHC(+))[{Ni(dmit)2}(0.5-)]2 (3 and 4), which are the first mixed-valence salts of nucleobase cations with metal complex anions. Similar to 2, salt 3 contains CHC(+) ribbons that are sandwiched between the 2D [Ni(dmit)2](0.5-) layers. In the layer, the [Ni(dmit)2](0.5-) ions form dimers with a S = 1/2 spin and the narrow electronic bandwidth causes a semiconducting behavior. In salt 4, the CHC(+) units form an unprecedented corrugated 2D sheet, which is sandwiched between the 2D [Ni(dmit)2](0.5-) layers that involve ring-over-atom and spanning overlaps. In contrast to 3, salt 4 exhibits metallic behavior down to 1.8 K, associated with a wide bandwidth and a 2D Fermi surface. The ability of hydrogen-bonded CHC(+) sheets as a template for the anion radical arrangements is demonstrated.
authors.affiliation: Faculty of Agriculture, Meijo University, Shiogamaguchi 1-501 Tempaku-ku, Nagoya 468-8502 (Japan), Fax: (+81) 52-833-7200. yyoshida@meijo-u.ac.jp.
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Yoshida
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Maesato
authors.forename: Manabu
authors.initials: M
authors.lastname: Ishikawa
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Nakano
authors.forename: Takaaki
authors.initials: T
authors.lastname: Hiramatsu
authors.forename: Hideki
authors.initials: H
authors.lastname: Yamochi
authors.forename: Gunzi
authors.initials: G
authors.lastname: Saito
mesh_terms: D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000737:chemistry; D003596:Cytosine / Q000737:chemistry*; D006860:Hydrogen Bonding; D007477:Ions / Q000737:chemistry*; D060526:Magnetic Fields; D008958:Models, Molecular; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D014050:Toluene / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: C504559:1,3-dithiole-2-thione-4,5-dithiolate; D056831:Coordination Complexes; D007477:Ions; C586596:Ni(1,3-dithiole-2-thione-4,5-dithiolate)2; D009942:Organometallic Compounds; D014050:Toluene; D009532:Nickel; D003596:Cytosine
keywords: conducting materials; crystal engineering; hydrogen bonds; magnetic properties; nucleobases