Quasi-three-dimensional network of molecular interactions and electronic structure of a new organic semiconductor, ET(NCS)0.77.

The radical cation salt ET(NCS)0.77 [bis(ethylenedithio)tetrathiafulvalene thiocyanate (1/0.77)] has been prepared for the first time by electrocrystallization and its crystal and electronic structure at 110 K was investigated. The unit-cell dimensions are orthorhombic, a = 6.638 (1), b = 8.309 (2), c = 28.776 (6) A, V = 1587.1 (6) A3, space group Pbcm, Z = 4. The compound has a layered structure. The ET radical cations of the conducting cationic layer build stacks. In the anionic layer the thiocyanate groups form polymeric chains where they are oriented in a 'head-to-tail' mode. The structure has short intermolecular contacts of the cation-cation, anion-anion and cation-anion types, which leads to the formation of a three-dimensional structure of intermolecular interactions. This phenomenon is very rare in molecular conductors. Tight binding band structure calculations suggest, however, that the interlayer interactions through the anions are weak and that the incomplete occupation of the anion sites is the reason for the activated conductivity of the salt.