Charge-Transfer Solids Using Nucleobases: Supramolecular Architectures Composed of Cytosine and [Ni(dmit)2] Assembled by Multiple Hydrogen Bonds and Heteroatomic Contacts

• Published in: Chemistry : a European journal 2013-09, Vol.19 (37), p.12325-12335
• Main Authors: Yoshida, Yukihiro, Maesato, Mitsuhiko, Ishikawa, Manabu, Nakano, Yoshiaki, Hiramatsu, Takaaki, Yamochi, Hideki, Saito, Gunzi
• Format: Article
• Language: English
• Subjects: Anions; Arrays; Cations; Chemistry; conducting materials; Coordination Complexes - chemical synthesis; Coordination Complexes - chemistry; Coordination compounds; Corrugated sheet; crystal engineering; Cytosine - chemistry; Hydrogen Bonding; Hydrogen bonds; Ions - chemistry; Magnetic Fields; magnetic properties; Models, Molecular; Nickel - chemistry; nucleobases; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Ribbons; Tapes (metallic); Toluene - analogs & derivatives; Toluene - chemistry; Two dimensional
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201300865

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. Nucleobase‐based conductors: Various combinations between the nucleobase cytosine (C) with different protonation states and [Ni(dmit)2] (dmit=1,3‐dithiole‐2‐thione‐4,5‐dithiolate) with different redox states afforded four salts with dissimilar supramolecular motifs and electronic properties. Especially, the unprecedented corrugated 2D sheet of hemiprotonated CHC+ units afforded the first metallic salt that contains a mixed‐valent metal complex anion combined with a nucleobase cation.