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

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 ](CH 3 CN) ( 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.